Hybrid lubricant composition for steelmaking

Abstract

Disclosed are a hybrid lubricant composition a hybrid lubricant composition for steelmaking process, which has improved durability, etc., so as to be suitable for a continuous casting machine operating at a high temperature under high load during a steelmaking process, and a method of preparing the same.

Description

BACKGROUND OF THE DISCLOSUREField of the Disclosure

[0001] The present disclosure relates to a hybrid lubricant composition for steelmaking. More specifically, the present disclosure relates to a hybrid lubricant composition for steelmaking process, which has improved durability, etc., so as to be suitable for a continuous casting machine operating at a high temperature under high load during a steelmaking process, and a method of preparing the same.Description of Related Art

[0002] In the ironmaking process, various foreign materials or contaminants are generated due not only to exposure to high temperature and corrosive environments, but also to wear on parts. As an example, continuous casting machines typically operate under conditions of high temperatures, low speeds, and frictional corrosion due to cooling water. In this way, as the machines are exposed to risk factors that affect mechanical structural stability, such as impact loads, high maintenance costs are required, and furthermore, efficient process operation is hindered by frequent replacement.

[0003] In the steelmaking process, large-sized bearings are mainly used, and various performance characteristics such as heat resistance, wear resistance, load carrying capacity, durability, and the like need to be satisfied owing to the severe operating environment. In particular, since the continuous casting machine is exposed to humid environments as well as high temperatures compared to bearing operating environments used in general industries, the use of polyurea-based grease, which has better performance than existing lithium-based bearing grease, is being considered.

[0004] Polyurea-based grease offers superior performance compared to lithium grease in view of heat resistance, load resistance, water resistance, durability, etc., and also has the advantage of reducing energy consumption. For this reason, polyurea-based grease is widely being applied to motor drive systems (e.g., Korean Patent No. 2312591). However, polyurea-based grease is hardened in harsh environments such as continuous casting lines in the steelmaking process, e.g., high-temperature environments of 150° C. or more, which causes grease transfer lines to become blocked, deteriorating grease pumpability.

[0005] In addition, durability has improved compared to lithium grease, extending relubrication interval, but it still does not meet user requirements, and hence, thorough research is being conducted to address this issue.SUMMARY OF THE DISCLOSURE

[0006] An embodiment of the present disclosure provides a hybrid lubricant composition capable of exhibiting improved durability under harsh environments of the steel industry, for example under high temperature, high load, and humidity environments applied to bearings in a continuous casting machine in a steelmaking process.

[0007] Another embodiment of the present disclosure provides a hybrid lubricant composition capable of significantly extending relubrication interval thanks to improved long-term durability even when applied to a continuous casting machine in a steelmaking process.

[0008] A first aspect of the present disclosure provides a hybrid lubricant composition for steelmaking, comprising, based on the total weight of the lubricant composition, (i) 14 to 37 wt % of a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener, (ii) 62 to 85 wt % of a base oil, and (iii) 0.3 to 2 wt % of a zinc-based compound as an additive,

[0009] wherein the weight ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener is adjusted in a range of greater than 1:1 to 3:1, and

[0010] the calcium sulfonate-based thickener comprises calcium sulfonate having a total base number (TBN) of 200 to 500, and further comprises 10 to 50 wt % of calcium carbonate in the form of calcite based on the weight of the calcium sulfonate-based thickener.

[0011] According to an embodiment, calcium carbonate in the calcium sulfonate-based thickener may have a particle diameter of 0.3 μm or less.

[0012] According to an embodiment, the calcium sulfonate-based thickener may further comprises at least one calcium salt selected from the group consisting of fatty acid calcium, calcium acetate, and calcium borate.

[0013] According to an embodiment, respective contents of fatty acid calcium, calcium acetate, and calcium borate contained in the calcium sulfonate-based thickener may be adjusted in ranges of up to 3 wt %, up to 2.5 wt %, and up to 2 wt %, based on the total weight of the lubricant composition.

[0014] According to an embodiment, the calcium sulfonate-based thickener may further include dodecylbenzenesulfonic acid in an amount of up to 1 wt % based on the total weight of the lubricant composition.

[0015] According to an embodiment, the polyurea-based thickener may comprises polyurea, which is a reaction product of a diisocyanate compound and an aliphatic monoamine compound.

[0016] According to an embodiment, the diisocyanate compound may be at least one selected from the group consisting of diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, and dimethyl diphenylene diisocyanate, and the aliphatic monoamine compound may be at least one selected from the group consisting of aniline, cyclohexylamine, octylamine, dodecylaniline, octadecylamine, hexylamine, heptylamine, nonylamine, ethylhexylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, pentadecylamine, nonadecylamine, eicodecylamine, oleylamine, linoleylamine, linolenylamine, methylcyclohexylamine, ethylcyclohexylamine, dimethylcyclohexylamine, diethylcyclohexylamine, butylcyclohexylamine, amylcyclohexylamine, propylcyclohexylamine, cyclooctylamine, benzylamine, phenethylamine, methylbenzylamine, biphenylamine, phenylisopropylamine, and phenylhexylamine.

[0017] According to an embodiment, the diisocyanate compound may be diphenylmethane diisocyanate, and the aliphatic monoamine compound may be cyclohexylamine and octylamine.

[0018] According to an embodiment, the polyurea may be diurea.

[0019] According to an embodiment, the base oil may be a Group I base oil and / or a Group II base oil.

[0020] According to an embodiment, the base oil may have a kinematic viscosity (ASTM D 445) at 40° C. of 200 to 700 cSt.

[0021] According to an embodiment, the zinc-based compound may be a zinc dithiophosphate-based compound and / or a zinc dithiocarbamate-based compound.

[0022] According to an embodiment, the zinc-based compound may be at least one selected from the group consisting of zinc dialkyl dithiophosphate and zinc dialkyl dithiocarbamate.

[0023] A second aspect of the present disclosure provides a method of preparing the hybrid lubricant composition described above, comprising:

[0024] a) preparing a reaction mixture by combining base oil, overbased calcium sulfonate, water, and at least one acid selected from the group consisting of boric acid and fatty acid;

[0025] b) forming a calcium sulfonate-based lubricant by adding acetic acid and alcohol to the reaction mixture, performing reaction under elevated temperature conditions to produce calcium carbonate in the form of calcite, and then removing impurities through additional heating;

[0026] c) forming a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener in the base oil by adding a diisocyanate compound and an aliphatic monoamine compound to the calcium sulfonate-based lubricant and performing reaction in-situ for forming a polyurea-based thickener under elevated temperature conditions of 130 to 200° C.; and

[0027] d) adding an additive ingredient comprising a zinc-based antioxidant to the product of step c).

[0028] According to an embodiment, the reaction mixture may be formed by further adding dodecylbenzenesulfonic acid in step a).

[0029] According to an embodiment, the reaction may be performed with the further addition of base oil in step c).

[0030] A third aspect of the present disclosure provides a lubrication method comprising:

[0031] applying the hybrid lubricant composition described above to a bearing of a continuous casting machine in a steelmaking process.

[0032] According to an embodiment, the continuous casting machine may be operated under conditions of temperature of at least 100° C. and relative humidity of at least 40%.

[0033] According to an embodiment, the continuous casting machine may be operated under conditions of relative humidity of 50 to 80%.DETAILED DESCRIPTION OF THE DISCLOSURE

[0034] The present disclosure may be realized in its entirety based on the following description. It should be understood that the following description is given of preferred embodiments of the present disclosure, and the present disclosure is not necessarily limited thereto. In addition, the accompanying drawings are provided to aid understanding of the present disclosure, and the present disclosure is not limited thereto, and details regarding individual components may be appropriately understood by the specific intent of the related description given below.

[0035] Terms used herein may be defined as follows.

[0036] “Grease” may refer to a solid or semi-solid material in which a thickener is dispersed in a liquid lubricating base oil, and may additionally contain other ingredients that impart specific properties thereto, and for example, grease may be a gel-type dispersion in which the continuous phase is formed of a lubricating base oil and the dispersed phase (e.g., thickener) is an anisotropic solid that penetrates the liquid phase.

[0037] “Flash Point” is a property that generally indicates how easily a material or composition, typically a fluid, may ignite or burn. Hydrocarbons having relatively high flash points are less likely to ignite than materials having relatively low flash points.

[0038] “Viscosity” is a physical property that describes the stickiness of a fluid, and “kinematic viscosity” is the value obtained by dividing the viscosity by the density of the fluid. Typically, kinematic viscosity tends to decrease with an increase in temperature.

[0039] “Worked penetration” is an indicator of the hardness of grease. Typically, high worked penetration means that the grease is soft, whereas low worked penetration means that the grease is hard. The worked penetration of grease may vary depending on the type and content of the thickener, the content of the lubricating base oil, and the viscosity.

[0040] “Total base number (TBN)” may mean a value indicating the amount (mg) of KOH equivalent to the amount of acid required to neutralize the alkali ingredient contained in 1 gram of lubricating oil, and may be measured by, for example, ASTM D2896.

[0041] “Continuous casting machine” refers to a machine used in the process of converting liquid iron into a solid. In this continuous casting machine, liquid molten steel is placed or injected in a mold and passes through a continuous caster, where it cools and solidifies to continuously form intermediate materials such as slabs, blooms, billets, etc.

[0042] Herein, when it is said that a composition “includes” a component, it means that it may further include other components, unless stated otherwise.

[0043] Terms such as “on” or “above” and “under” or “below” may be understood to describe the relative positional relationship between components or members, and the terms “located on” or “located under” may be understood to express the relative positional relationship not only in a state of contact with a specific object but also in a state of not contacting the same.Hybrid Lubricant Composition

[0044] A hybrid lubricant composition according to an embodiment of the present disclosure is a lubricant present in a gel state, which is a semi-solid state, and is equivalent to grease. Specifically, when applied onto machines requiring lubrication or parts thereof, the hybrid lubricant composition is converted into liquid in a state where lubrication is required (e.g., a state where the temperature rises due to friction), whereas it is maintained in a semi-solid state in case of deviating from the state where the temperature rises due to frictional heat, so that oil leakage may be suppressed.

[0045] In particular, in cases where large-sized bearings, etc. are used in a continuous casting machine in a steelmaking process and where they are exposed to severe (or harsh) operating environments, such as high temperature and humid environments compared to operating environments in other fields, a mixed thickener obtained by combining two types of thickeners (i.e., a polyurea-based thickener and a calcium sulfonate-based thickener) is applied. In this case, the composition and properties thereof are precisely controlled, such that improved durability and high-temperature pumpability as well as long-term durability may be achieved.

[0046] Lithium-based thickeners that have been conventionally widely used have no major problems when applied to grease for vehicles such as constant velocity joints, but under high temperature and high humidity environments such as in a continuous casting machine in a steelmaking process, the lifespan of bearings to which the lubricant is applied may be shortened due to grease oxidation resulting from lack of thermal stability. Furthermore, in case that moisture penetrates the grease, the lubricant may soften, deteriorating long-term durability. On the other hand, a polyurea-based thickener, which is another type of thickener, provides good properties such as heat resistance, water resistance, etc., but tends to harden at a high temperature.

[0047] Considering the characteristics of the conventional thickeners described above, in the present embodiment, a calcium sulfonate-based thickener and a polyurea-based thickener are each selected, and a mixed thickener thereof is used. In this embodiment, the ratio of the polyurea thickener to the calcium sulfonate-based thickener is adjusted to a level much higher than the generally recognized level, thereby realizing lubricant properties suitable for unique operating conditions encountered in the continuous casting machine during the steelmaking process.Mixed Thickener

[0048] The hybrid lubricant composition according to the present embodiment is grease, in which a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener is dispersed in a lubricating base oil (base oil).

[0049] The polyurea-based thickener may comprise polyurea produced by reacting a diisocyanate compound and an aliphatic monoamine compound. This urea formation reaction may be typically based on a mechanism in which 1 mole of diisocyanate compound and 2 moles of aliphatic monoamine compound react stoichiometrically.

[0050] In this regard, the diisocyanate compound may be at least one selected from among aryl diisocyanate, alkyl diisocyanate, and the like, for example, at least one selected from among diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, dimethyl diphenylene diisocyanate, and the like. In a certain embodiment, the diisocyanate compound may be diphenylmethane diisocyanate (for example, 4,4-diphenylmethane diisocyanate), which may be advantageous in that it enables the production of a thickener that provides excellent mechanical stability and grease fluidity.

[0051] Meanwhile, the monoamine may be at least one selected from among, for example, aniline, cyclohexylamine, octylamine, dodecylaniline, octadecylamine, hexylamine, heptylamine, nonylamine, ethylhexylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, pentadecylamine, nonadecylamine, eicodecylamine, oleylamine, linoleylamine, linolenylamine, methylcyclohexylamine, ethylcyclohexylamine, dimethylcyclohexylamine, diethylcyclohexylamine, butylcyclohexylamine, propylcyclohexylamine, amylcyclohexylamine, cyclooctylamine, benzylamine, phenethylamine, methylbenzylamine, biphenylamine, phenylisopropylamine, phenylhexylamine, and the like. In a certain embodiment, the monoamine may be at least one selected from among aniline, cyclohexylamine, octylamine, and the like. Also, in a certain embodiment, a combination of cyclohexylamine and octylamine may be used, which may be advantageous in obtaining heat resistance, durability, shear stability, etc.

[0052] In addition, examples of the polyurea may include diurea, triurea, tetraurea, and the like, among which diurea is preferable because it is able to minimize changes in grease penetration due to oxidation at room temperature and high temperature over time.

[0053] Meanwhile, the calcium sulfonate-based thickener may be in the form of calcium sulfonate and / or a calcium sulfonate complex. Here, calcium sulfonate may be overbased calcium sulfonate. The total base number (TBN) of the overbased calcium sulfonate may be adjusted in the range of, for example, about 200 to 500, for example about 250 to 450, for example about 300 to 400. Within this range, the calcium sulfonate-based thickener (particularly, calcium carbonate therein) may be uniformly dispersed in the base oil, and a robust lubricating film may be formed, thereby improving wear resistance and load carrying capacity. Furthermore, since stable micelles are formed even upon contact or mixing with a large amount of moisture during operation in the continuous casting machine, rust formation and deterioration of the lubricant composition due to moisture may be suppressed. However, if the total base number of calcium sulfonate is too low, it may affect the thickener formation, producing soft grease, whereas if it is too high, the content of the calcium sulfonate thickener is low, which may have an influence on extreme pressure resistance, durability, shear stability, mechanical stability, etc., which are affected by the content of the thickener. Therefore, it may be advantageous to have the TBN adjusted within the aforementioned range.

[0054] According to an embodiment, the calcium sulfonate-based thickener may contain calcium carbonate, which may be calcium carbonate in the form of calcite. As an example, calcium carbonate in the form of calcite may be formed when amorphous calcium carbonate is converted into crystalline calcium carbonate during conversion of the overbased calcium sulfonate. For example, the content of calcium carbonate in the form of calcite in the calcium sulfonate-based thickener may be adjusted in the range of, for example, about 10 to 50 wt %, for example about 15 to 45 wt %, for example about 20 to 43 wt %. According to a certain embodiment, the content of calcium carbonate in the form of calcite in the calcium sulfonate-based thickener may be adjusted in the range of, for example, about 25 to 40 wt %, for example about 28 to 37 wt %, for example about 30 to 35 wt %. If the content of calcium carbonate in the form of calcite in the calcium sulfonate-based thickener is too low, durability may deteriorate, and in particular, load carrying capacity (or load resistance) may significantly decrease. On the other hand, if it is too high, extreme pressure resistance may be improved, but wear resistance may significantly decrease. Hence, it may be advantageous to appropriately adjust the content thereof within the aforementioned range.

[0055] In addition, calcium carbonate contained in the calcium sulfonate-based thickener may be provided in the form of particles. As such, the particle diameter (size) of calcium carbonate may be in the range of, for example, about 0.3 μm or less, for example about 0.01 to 0.25 μm, for example about 0.05 to 0.2 μm, for example about 0.08 to 0.15 μm.

[0056] According to an embodiment, the calcium sulfonate-based thickener may further contain other calcium salts (e.g., fatty acid calcium, calcium acetate, calcium borate, etc.) in addition to calcium carbonate. According to an embodiment, the fatty acid used to form fatty acid calcium may be a fatty acid having 10 to 30 carbon atoms, and an example thereof may include at least one selected from among stearic acid, dodecanoic acid, palmitic acid, oleic acid, ricinoleic acid, decanoic acid, tetradecanoic acid, hydroxystearic acid, and the like. In a certain embodiment, it may be advantageous to use hydroxystearic acid, which affects not only lubricity but also long-term stability and durability.

[0057] According to an embodiment, the content of fatty acid calcium that may be contained in the calcium sulfonate-based thickener may be adjusted in the range of, for example, up to about 3 wt %, for example about 0.5 to 2.5 wt %, for example about 0.8 to 2 wt %, for example about 1 to 1.7 wt %, based on the total weight of the lubricant composition.

[0058] In addition, the content of calcium acetate that may be contained in the calcium sulfonate-based thickener may be adjusted in the range of, for example, up to about 2.5 wt %, for example about 0.1 to 2 wt %, for example about 0.3 to 1.5 wt %, for example about 0.5 to 1 wt %, based on the total weight of the lubricant composition.

[0059] In addition, the content of calcium borate that may be contained in the calcium sulfonate-based thickener may be adjusted in the range of, for example, up to about 2 wt %, for example about 0.1 to 1.5 wt %, for example about 0.2 to 1 wt %, for example about 0.3 to 0.6 wt %, based on the total weight of the lubricant composition.

[0060] According to an embodiment, the calcium sulfonate-based thickener may further contain dodecylbenzenesulfonic acid, which may function to effectively disperse calcium carbonate in the lubricant. As such, the content of dodecylbenzenesulfonic acid may be adjusted in the range of, for example, up to about 1 wt %, for example about 0.1 to 0.9 wt %, for example about 0.3 to 0.8 wt %, for example about 0.4 to 0.7 wt, based on the total weight of the lubricant.

[0061] According to an embodiment, the calcium sulfonate-based thickener may have viscosity (100° C.) as measured by ASTM D 445 in the range of, for example, about 40 to 100 cSt, for example about 50 to 90 cSt, for example about 60 to 80 cst. If the viscosity of the calcium sulfonate-based thickener is too low, it is difficult to form the minimum oil film required for lubrication, which may cause long-term lubricity problems and increase the likelihood of part breakage. On the other hand, if the viscosity of the calcium sulfonate-based thickener is excessively high, a large amount of heat may be generated due to viscosity resistance during lubrication inside the bearing, which may cause part breakage during long-term lubrication. In consideration thereof, it may be advantageous to appropriately adjust the viscosity thereof within the aforementioned range.

[0062] In an embodiment, it is noteworthy that the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener is adjusted to exceed the level recognized in the art so as to improve pumpability at a high temperature while maintaining good lubrication performance over a long period of time in the severe environment unique to a steelmaking process, for example a continuous casting machine.

[0063] In this regard, the weight ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener may be adjusted in the range of greater than about 1:1 to about 3:1, for example about 1.2 to about 2.8:1, for example about 1.4 to about 2.5:1, for example about 1.5 to about 2.2:1. If the content of the polyurea-based thickener is excessively high compared to the content of the calcium sulfonate-based thickener, problems such as blockage of transfer lines due to reduced pumpability caused by the high-temperature operating environment in the continuous casting machine may occur. On the other hand, if the content of the polyurea-based thickener is too low, water resistance, long-term durability, etc. in high humidity environments to which the continuous casting machine is continuously exposed may deteriorate.

[0064] In addition, according to an embodiment, the content of the mixed thickener based on the total weight of the lubricant composition may be adjusted in the range of, for example, about 14 to 37 wt %, for example about 15 to 32 wt %, for example about 16 to 30 wt %, for example about 17 to 28 wt %. If the content of the mixed thickener in the total lubricant composition (hybrid lubricant) is too low, a phenomenon in which long-term durability deteriorates due to reduction of shear stability, mechanical stability, etc. may occur, whereas if it is too high, a change in grease penetration may occur even with a small amount of oil leakage at a high temperature, and the hardened grease eventually has reduced lubricity, causing part breakage. Hence, it may be advantageous to adjust the content thereof within the aforementioned range.

[0065] In consideration thereof, in the present embodiment, when the mixed thickener in which two types of thickeners are combined in the ratio described above is used in a predetermined amount based on the total lubricant, problems resulting from existing lubricants applied in steelmaking processes may be alleviated.Base Oil

[0066] In the present embodiment, the base oil is a medium in which various additive ingredients including a thickener are dispersed, and is generally a liquid ingredient that may exhibit non-volatility at room temperature. Base oil is the main ingredient of grease and has a significant impact on the lubricating function of grease. Mineral oil-type base oil, synthetic base oil, etc. may be used. In this regard, the mineral oil-type base oil may be at least one selected from among paraffinic oil and naphthenic oil. In paraffinic base oil, when the content of straight-chain paraffin is high, there is a tendency to form large crystals, and when the content of branched-chain paraffin is high, there is a tendency to form smaller crystals. Also, naphthenic base oil tends to solidify and form an opaque solid phase, and exhibits a relatively low pour point.

[0067] According to an embodiment, the base oil may be derived from mineral oil or biomass, and may be further refined as necessary. Also, in some cases, two or more among the types of base oil described above may be used in combination.

[0068] In an embodiment, the kinematic viscosity of the base oil may be one of the factors that affect the film thickness of the oil at the lubricating interface and thereby exhibit efficient anti-wear performance. The kinematic viscosity thereof at 40° C. (ASTM D 445) may be adjusted in the range of, for example, about 200 to 700 cSt, for example about 300 to 600 cSt, for example about 350 to 550 cSt. In addition, the kinematic viscosity of the lubricating base oil at 100° C. may be adjusted in the range of, for example, about 15 to 60 cSt, for example about 20 to 55 cSt, for example about 25 to 45 cSt.

[0069] According to an embodiment, the density (ASTM D 1298; 15° C.) of the base oil may be in the range of, for example, about 0.82 to 0.92 g / cm3, for example about 0.85 to 0.91 g / cm3, for example about 0.88 to 0.9 g / cm3.

[0070] Also, the flash point (ASTM D92) of the base oil may be in the range of, for example, at least about 200° C., for example at least about 230° C., for example at least about 260° C., for example about 280 to 330° C.

[0071] In addition, according to an embodiment, the pour point (ASTM D97) of the base oil may be, for example, about −5° C. or less, for example about −7° C. or less, for example about-10° C. or less.

[0072] According to an embodiment, the base oil may include Group I base oil, Group II base oil, Group III base oil, Group IV base oil, etc. known in the art. For example, Group I base oil (saturates <90, sulfur >0.03%, and viscosity index of 80 to less than 120), and / or Group II base oil (saturates ≥90, sulfur≤0.03%, and viscosity index of 80 to less than 120) may be used, which may be advantageous in view of excellent thickener forming ability, hydrolytic stability, additive solubility, etc.

[0073] According to an embodiment, the content of the base oil in the hybrid lubricant composition may be adjusted in the range of about 62 to 85 wt %, for example about 64 to 83 wt %, for example about 68 to 80 wt %, for example about 70 to 78 wt&, based on the total weight of the lubricant composition. In this regard, if the content of the base oil is too low, hard grease may be formed, which reduces grease fluidity and lubricity, whereas if it is too high, soft grease may be formed, which may cause problems such as grease dripping and oil leakage. Hence, it may be advantageous to adjust the content thereof within the aforementioned range.Additive

[0074] According to an embodiment of the present disclosure, the hybrid lubricant composition contains a zinc-based compound as an additive.

[0075] A zinc-based compound primarily functions as an antioxidant, and may additionally function as an anti-wear agent. Such a zinc-based compound exhibits stable properties at a high temperature, rendering the lubricant composition suitable for the high-temperature operating environment of a continuous casting machine in a steelmaking process.

[0076] According to an embodiment, the zinc-based compound may be a zinc dithiophosphate-based compound and / or a zinc dithiocarbamate-based compound. As such, the alkyl group may indicate a linear, branched, or cyclic moiety of 1 to about 20 carbon atoms, for example 1 to 10 carbon atoms, for example 1 to 5 carbon atoms. In this regard, for example, the zinc dithiophosphate-based compound may be zinc dialkyl dithiophosphate. Also, the zinc dithiocarbamate-based compound may be zinc dialkyl dithiocarbamate.

[0077] According to a certain embodiment, the alkyl group of the zinc dialkyl dithiophosphate salt may be derived from a primary alcohol and a secondary alcohol, and the molar ratio of the secondary alcohol relative to the primary alcohol may be adjusted in the range of, for example, about 0.2 to 1.5, for example about 0.4 to 1.2, for example about 0.6 to 1.1, for example about 0.7 to 1.

[0078] According to an embodiment, the content of the zinc-based compound, based on the weight of the hybrid lubricant composition, may be adjusted in the range of, for example, about 0.3 to 2 wt %, for example about 0.5 to 1.8 wt %, for example about 0.7 to 1.5 wt %, for example about 0.9 to 1.2 wt %. In this regard, if the content of the zinc-based compound is too low, grease oxidation stability and wear resistance may deteriorate, causing a shortened grease lifespan, whereas if it is too high, it may act as an obstacle in the formation of a thickener, causing a problem in which the grease becomes soft. Hence, it may be advantageous to adjust the content thereof within the aforementioned range.

[0079] Meanwhile, the lubricant composition according to the present embodiment may further contain at least one selected from among additive components known in the art in addition to the zinc-based compound described above. Examples of the optional additive ingredient or ingredients may include a pour point depressant, an antioxidant other than the zinc-based compound, an anti-wear agent, an anti-corrosion agent, a surfactant, a lubricity enhancer, a friction reducer, and the like.

[0080] In this regard, the pour point depressant may include any one or a mixture of two or more selected from among, for example, alkyl methacrylate, polyacrylate, polyarylamide, condensation products of haloparaffin wax and aromatic compounds, vinyl carboxylate polymers, vinyl esters of fatty acids, allyl vinyl ether, and the like.

[0081] Examples of the antioxidant other than the zinc-based compound may include an amine compound (e.g., alkyl amine or 1-phenylaminonaphthalene), phenylnaphthylamine or aromatic amine (e.g., diphenylamine), a phenol compound (e.g., 2,6-di-t-butyl-4-methylphenol), a sulfur antioxidant, etc., which may be used alone or in combination of two or more thereof.

[0082] The anti-wear agent may include, for example, a phosphorus-based anti-wear agent, and examples thereof include a phosphite compound (tributyl phosphite, trioleyl phosphite, etc.), a phosphate compound (e.g., tricresyl phosphate, dilauryl phosphate, etc.), an amine phosphate compound (e.g., dibutyloctylamine phosphate, dilauryl octylamine phosphate, etc.), and a phosphorothioate compound (e.g., triphenylphosphorothioate, etc.), which may be used alone or in combination of two or more thereof.

[0083] Examples of the anti-corrosion agent may include dinonylnaphthalene sulfonate, sorbitan ester, sarcosine, succinimide, fatty acid derivatives, imidazoline, etc., which may be used alone or in combination of two or more thereof.

[0084] Examples of the friction reducer may include oleyl amide, alkyl and / or aryl phosphate esters, phosphonic esters, thiophosphate esters, etc., which may be used alone or in combination of two or more thereof.

[0085] The content of the optional additive ingredient described above may be adjusted in the range of, for example, up to about 3 wt %, for example up to about 2.5 wt %, for example up to about 2 wt %, for example about 0.2 to 1.5 wt %, based on the weight of the hybrid lubricant composition.Properties of Lubricant Composition

[0086] The hybrid lubricant composition according to the present embodiment properties such as heat resistance, extreme pressure resistance, long-term lubricity, durability, water resistance, high-temperature pumpability, etc. in a balanced manner under harsh operating environments in a steelmaking process, for example in a continuous casting machine.

[0087] According to an embodiment, the worked penetration (25° C., 60 W; ASTM D 217) of the lubricant composition is a property indicating the extent of thinness of the grease-type lubricant, and a higher value indicates a thinner state. The worked penetration of the lubricant composition according to the present embodiment may be in the range of, for example, about 220 to 350, for example about 280 to 345, for example about 310 to 340.

[0088] According to an embodiment, the worked stability (105 W; ASTM D 217) of the lubricant composition is a property indicating the mechanical stability of grease, and the smaller the difference from the worked penetration, the better the mechanical stability. Therefore, the worked stability may be evaluated by the difference from the worked penetration value, and may be higher, in the range of, for example, about 50 or less, for example about 45 or less, for example about 30 to 40.

[0089] According to an embodiment, the roll stability (mechanical stability) of the lubricant composition is a property indicating the shear stability of grease, and the smaller the change in worked penetration, the better the shear stability. In this regard, the roll stability of the lubricant composition may be evaluated by the difference from the worked penetration value as measured by ASTM D 1831, and may be higher, in the range of, for example, about 20 or less, for example about 15 or less, for example about 3 to 10.

[0090] According to an embodiment, the dropping point of the lubricant composition is a property indicating the heat resistance of grease, for example an indicator of durability under elevated temperature conditions. In this regard, the dropping point may be in the range of, for example, about 255° C. or more, for example about 259° C. or more, for example about 262 to 270° C., as measured by ASTM D 566.

[0091] According to an embodiment, the oil separation of the lubricant composition is an indicator of storage stability (e.g., storage stability under elevated temperature conditions), and may be in the range of, for example, about 5 or less, for example about 4 or less, for example about 3.5 or less, for example about 2 to 3, for example about 2.2 to 2.6, as measured by ASTM D 6184.

[0092] According to an embodiment, the 4-ball wear resistance (ASTM D 2266) of the lubricant composition is a property indicating the wear resistance or lubricating ability of grease, and may be, for example, about 0.7 mm or less, for example about 0.65 mm or less, for example about 0.6 mm or less, for example about 0.59 mm or less.

[0093] In addition, the load carrying capacity or load resistance (ASTM D 2596) of the lubricant composition is a property indicating the load carrying capacity of grease, and may be, for example, about 160 to 340 kgf, for example about 200 to 330 kgf, for example about 230 to about 320 kgf, for example about 250 to 315 kgf.

[0094] Furthermore, the SRV rolling test (cylinder on disk; ASTM D 5707) of the lubricant composition is a property indicating the frictional characteristics of grease, and the depth of the measured wear scar may be in the range of, for example, about 25 μm2 or less, for example about 20 μm2 or less, for example about 8 to 15 μm2, for example about 9 to 13 μm2.

[0095] In addition, the lubricant composition according to the present embodiment may exhibit good pumpability (or flowability) even under high temperature conditions such as in a continuous casting machine in a steelmaking process. In order to evaluate pumpability, the apparent viscosity (DIN 51810) at each of room temperature and high temperature is measured, confirming the properties related to high-temperature stability and high-temperature hardening, and pumpability at a high temperature may be confirmed depending on the extent of hardening. In this regard, if the apparent viscosity at a high temperature increases in a positive direction compared to the apparent viscosity at room temperature, this may indicate that the grease is hardening compared to the penetration at room temperature, which may cause problems with pumpability. From this point of view, the lubricant composition according to the present embodiment may exhibit a property in which the apparent viscosity value at a high temperature decreases compared to the apparent viscosity value at room temperature.

[0096] Also, water resistance of the lubricant composition (ASTM D 1264) may be evaluated by expressing the amount of grease loss, which is a criterion for judging resistance to water, as a weight proportion. In this regard, in the lubricant composition according to the present embodiment, the amount of grease loss may be, for example, 1.9 wt % or less, for example 1 wt % or less, for example about 0.9 wt % or less, for example about 0.8 wt % or less.Preparation of Hybrid Lubricant Composition

[0097] According to an embodiment of the present disclosure, the hybrid lubricant composition described above may be prepared by various methods.

[0098] As an example, a polyurea-based lubricant (grease) and a calcium sulfonate-based lubricant (grease) are each prepared, and then combined with an additive component at a predetermined ratio to prepare a hybrid lubricant composition. As such, the mixing conditions of two types of lubricants are not particularly limited, but the mixing temperature may be adjusted in the range of, for example, about 10 to 150° C., for example about 20 to 80° C., for example about 30 to 70° C. Also, the mixing may be performed under stirring conditions, in which case the mixing time may be adjusted in the range of, for example, about 0.1 to 48 hours, for example about 1 to 24 hours, for example about 3 to 15 hours.

[0099] According to an alternative embodiment, the hybrid lubricant composition may be obtained by preparing a sulfonate-based lubricant (for example, a calcium sulfonate-based lubricant), forming a polyurea-based thickener in-situ, and introducing an additive ingredient according to the following steps a) to d).Preparing Reaction Mixture (Step a)

[0100] According to an embodiment, first, a reaction mixture for preparing a sulfonate-based lubricant is prepared. To this end, overbased calcium sulfonate (having a TBN of, for example, 200 to 500), water, and at least one acid selected from the group consisting of boric acid and fatty acid are added to the base oil. As such, boric acid may function as a complexing agent and may react with calcium to form calcium borate as described below. In addition, the fatty acid is an ingredient that may react with calcium to form soap, namely fatty acid calcium, and as described above, the fatty acid may be a fatty acid having 10 to 30 carbon atoms, for example, at least one selected from among stearic acid, dodecanoic acid, palmitic acid, oleic acid, ricinoleic acid, decanoic acid, tetradecanoic acid, hydroxystearic acid, etc.

[0101] Also, according to an embodiment, when preparing the reaction mixture, dodecylbenzenesulfonic acid may be further added to promote dispersion of calcium carbonate in the subsequent step, as described above.

[0102] According to an embodiment, when mixing the components described above, the mixing temperature may be adjusted in the range of, for example, about 30 to 60° C., for example about 35 to 55° C., for example about 38 to 52° C., for example about 40 to 50° C.Forming Calcium Sulfonate-Based Lubricant (Step b)

[0103] According to an embodiment, a calcium sulfonate-based lubricant is formed using the reaction mixture prepared in the previous step.

[0104] To this end, acetic acid and alcohol may be added to the reaction mixture and reacted. As such, reaction may be performed under elevated temperature conditions. As an example, the reaction temperature may be adjusted in the range of, for example, about 60 to 100° C., for example about 70 to 90° C., for example about 75 to 85° C. Here, water, acetic acid, and alcohol may function to rapidly convert some of calcium in the amorphous overbased calcium sulfonate material in the reaction mixture into calcium carbonate having a calcite crystal structure. By way of example, the alcohol may typically be an aliphatic alcohol, for example, an aliphatic alcohol having 1 to 5 carbon atoms, for example an aliphatic alcohol having 1 to 3 carbon atoms. Examples of the alcohol may include methanol, ethanol, isopropanol, n-propanol, iso-butanol, t-butanol, n-pentanol, and the like, and for example methanol may be used.

[0105] For example, the weight ratio of acetic acid to water may be adjusted in the range of, for example, about 0.2 to 0.6:1, for example about 0.25 to 0.5:1, for example about 0.3 to 0.4:1. Also, the weight ratio of alcohol to water may be adjusted in the range of, for example, about 0.05 to 0.3:1, for example about 0.07 to 0.25:1, for example about 0.1 to 0.2:1. Since the formation of calcium carbonate particles having a calcite structure may be effectively promoted in the ratios described above, it may be advantageous to adjust the ratios thereof within the aforementioned ranges.

[0106] According to an embodiment, the time involved in the conversion reaction is not particularly limited, but may be adjusted in the range of, for example, about 0.1 to 10 hours, for example about 0.2 to 5 hours, for example about 0.4 to 1 hours.

[0107] After performing the conversion reaction described above, a process of removing impurities generated during the reaction, such as byproducts such as moisture, may be performed. To this end, additional heating may be conducted. As such, the additional heating temperature is not particularly limited, but may be adjusted in the range of a temperature higher than the preceding reaction temperature, for example, above about 100° C., for example about 103 to 120° C., for example about 105 to 115° C. This additional heating time is not particularly limited, and may be set in the range of, for example, about 0.5 to 5 hours, for example about 1 to 3 hours, for example about 1.5 to 2.5 hours.

[0108] In this way, heating is performed as a post-treatment process for removing impurities, thereby forming a calcium sulfonate-based lubricant in which the calcium sulfonate-based thickener is dispersed or contained in the base oil.Forming Polyurea-Based Thickener (Step c)

[0109] According to an embodiment, forming a polyurea-based thickener in-situ is performed by adding a reactant for polyurea formation to the calcium sulfonate-based lubricant. To this end, a diisocyanate (isocyanate) compound and an aliphatic monoamine compound are added to the calcium sulfonate-based lubricant to perform polyurea formation reaction. As such, when the calcium sulfonate-based lubricant contains base oil in the amount described above, the need to add base oil is reduced, but typically, base oil is added together with the polyurea reactant to sufficiently dissolve the reactant.

[0110] When the reactant is sufficiently dissolved, urea formation reaction is performed under elevated temperature conditions. In this regard, the temperature during reaction may be adjusted in the range of, for example, about 130 to 200° C., for example about 150 to 190° C., for example about 160 to 180° C. In addition, the reaction time is not particularly limited, but may be adjusted in the range of, for example, about 0.1 to 1 hours, for example about 0.15 to 0.5 hours, for example about 0.18 to 0.3 hours.

[0111] According to the reaction described above, a mixed thickener is formed in which the calcium sulfonate-based thickener and the polyurea-based thickener are sequentially formed in the base oil. In contrast to an embodiment in which individual thickeners are simply prepared separately and then mixed, this mixed thickener is present in a form in which two types of thickeners are in close contact through in-situ synthesis, and the synergistic effect due to interaction therebetween may be maximized.Mixing Additive (Step d)

[0112] As described above, after synthesis of the polyurea thickener in situ, mixing the additive ingredient is performed. As such, the additive essentially includes a zinc-based compound as an antioxidant, and optionally, at least one among various additive ingredients may be further added.

[0113] In an embodiment, in order to suppress phenomena such as deterioration of the lubricant composition, it is preferable to introduce and disperse the additive at a temperature lower than the polyurea thickener forming reaction temperature but at which the additive may be sufficiently dispersed. Taking this into consideration, the temperature for additive introduction and dispersion may be adjusted in the range of, for example, about 100° C. or less, for example about 60 to 95° C., for example about 70 to 90° C., which may be understood as illustrative.

[0114] In addition, a mixing or dispersing device known in the art may be used to disperse the formed mixed thickener, including the additive ingredient, with a uniform particle size. As an example, the mixing or dispersing device may be at least one selected from among a static mixer, a Mantin Gaulin homogenizer, a microfluidizer, a colloid mill, a homogenizer, a top roll, a Henschel mixer, and the like, and for example a homogenizer, for example a high-pressure homogenizer (e.g., operated under a pressure of about 300 to 400 bar) may be used.

[0115] Also, the mixing time may be adjusted in the range of, for example, about 0.5 to 5 hours, for example about 0.6 to 3 hours, for example about 0.7 to 2 hours, for example about 0.8 to 1 hour, but is not limited thereto.Use of Hybrid Lubricant Composition

[0116] According to another embodiment of the present disclosure, the hybrid lubricant composition described above may be applied to various machines, vehicle parts (e.g., gears, belts, chains, wire ropes, mechanical continuously variable transmissions, etc.), and the like, and specifically, when the hybrid lubricant composition is applied to a continuous casting machine in a steelmaking process, for example to a bearing in a continuous casting machine, the advantage as a lubricant may be more prominent. The continuous casting machine is typically driven or operated under high temperature and high humidity conditions (or contact with moisture).

[0117] As an example, the continuous casting machine includes a ladle configured to hold molten steel refined in the steelmaking process, a tundish configured to supply molten steel through an injection nozzle connected to the ladle and temporarily store the same, a mold configured to receive the molten steel temporarily stored in the tundish and initially solidify the same into a certain shape, and a cooling line provided under the mold and having a number of segments arranged to cool the unsolidified cast piece and perform a series of forming operations.

[0118] In the machine described above, molten steel drawn from the ladle and the tundish is placed in a mold and cast into a cast piece such as a slab, bloom, or billet having a predetermined shape at a predetermined width and thickness by a cutting process. As such, cooling water is continuously sprayed onto the surface of the cast piece manufactured using the continuous casting machine during the continuous casting process, and the cast piece is cooled by cooling water spray, manufacturing a final cast piece.

[0119] In this way, a series of procedures in the continuous casting machine for the steelmaking process is exposed to high temperatures compared to typical mechanical devices, and the transfer lines that supply a lubricant to the bearings in the machine are also exposed to high temperatures, and moisture continuously comes into contact with or penetrates the lubricant film due to cooling water spray.

[0120] According to an embodiment, the internal temperature of the continuous casting machine may be in the range of, for example, at least about 100° C., for example about 120 to 250° C., for example about 130 to 200° C., for example about 150 to 180° C. Also, the internal relative humidity of the continuous casting machine may be in the range of, for example, at least about 40%, for example about 50 to 80%, for example about 60 to 70%.

[0121] When applying a lubricant for bearings operated under harsh conditions in the continuous casting machine, such as a lubricant for bearings in a general machine or a lubricant for vehicles (e.g., constant velocity joints), there are significant problems such as poor water resistance and reduced pumpability, but such problems may be effectively alleviated by applying the hybrid lubricant composition according to the present embodiment. For example, the hybrid lubricant composition may be applied to bearings in a continuous casting machine by automatic injection through a transfer line.

[0122] A better understanding of the present disclosure may be obtained through the following examples. However, these examples are merely set forth to illustrate the present disclosure and are not to be construed as limiting the present disclosure.EXAMPLES

[0123] Base oil used in Example and Comparative Examples is a 150 BS base oil, and properties thereof are shown in Table 1 below.TABLE 1ClassificationPropertiesSpecific gravity (4° C.)0.9Kinematic viscosity (40° C.)460cStKinematic viscosity (100° C.)30cStFlash point328°C.Pour point−12°C.Viscosity index95Min.Carbon residue0.10wt %Acid number (TAN)0.01

[0124] The properties of the grease composition manufactured according to the present example were measured as follows.

[0125] Worked penetration was measured according to ASTM D 217. After 60 mixing cycles in a mixer maintained at 25° C., a cone weighing 102.5±0.05 g was freely dropped onto the sample surface for 5 seconds. The penetration depth of the cone was measured in 1 / 10 mm increments.

[0126] Worked stability was measured according to ASTM D 217. After 100,000 mixing cycles in a mixer, a cone weighing 102.5+0.05 g was freely dropped onto the sample surface for 5 seconds. The penetration depth of the cone was measured in 1 / 10 mm increments, and the difference thereof from the worked penetration was calculated.

[0127] Roll stability was evaluated according to ASTM D1831. 50 g of grease with the measured worked penetration was evenly applied inside the cylinder, and the roll was installed inside the cylinder. Next, the cylinder was rotated at 165 rpm for 2 hours at a constant temperature, and the worked penetration of the grease was measured and changes thereof were recorded.

[0128] Dropping point was measured according to ASTM D 566. Specifically, grease was applied to a specified cup with a diameter of 10 mm, and the temperature at which the base oil was separated and first fell with an increase in temperature was measured.

[0129] Oil separation was evaluated according to ASTM D 6184. 10 g of the sample was placed on a 250 μm nickel mesh cone, and the weight of the separated oil was represented as wt % after a predetermined time (24 h) at a set temperature (100° C.).

[0130] Wear resistance was evaluated according to the 4-ball wear test (ASTM D 2266). Specifically, three fixed balls and one rotary ball were in point contact and operated under certain conditions, and the average wear surface of the three fixed balls was checked in mm (test conditions: rotation speed of 1200±60 rpm, load of 40±0.2 kgf, duration of 60±1 minutes, and temperature of 75±2° C.).

[0131] Load carrying capacity (load resistance) was evaluated according to ASTM D 2596, for example a shell-type 4-ball test was used, where three fixed balls and one rotary ball were in point contact and operated under certain conditions, and the load was measured when the four balls stuck to each other or wore by 4 mm or more (test conditions: rotation speed of 1770±60 rpm, duration of 10 seconds, and temperature of 27±8° C.).

[0132] SRV test was performed as a rolling test to evaluate bearing simulation. Specifically, the lower specimen disk and the upper specimen cylinder (2 pieces) were brought into contact with each other, and rolling lubrication was performed under programmed conditions (frequency, stroke, load, time, and temperature). After evaluating the coefficient of friction, the depth of the wear scar on the lower specimen was measured. The SRV test conditions are shown in Table 2 below.TABLE 2ClassificationTest conditionsPretestLoad: 500N, Stroke Amplitude: 1 mm, Temperature:100° C., Frequency: 20 Hz, Duration: 1 hrMain testLoad: 2000N, Stroke Amplitude: 1 mm, Temperature:100° C., Frequency: 20 Hz, Duration: 18 hrApparent viscosity was measured using an Anton Paar rheometer (MCR 302) according to DIN 51810. The measurement conditions were gap=0.5 mm, shear rate: 1 1 / s, and measuring system: PP25.

[0134] Water wash-out was measured according to ASTM D 1264. A 6204 ball bearing was attached to the housing and rotated at 600 rpm, and distilled water was sprayed at a rate of 5 ml / sec for 1 hour at 38° C. The weight loss of the sample was represented as wt %.Example 1

[0135] A hybrid lubricant composition was prepared according to the reactant composition shown in Table 3 below.

[0136] Overbased calcium sulfonate, dodecylbenzenesulfonic acid, 12-hydroxystearic acid, water, boric acid, and base oil were placed in a 3 L pilot reactor and heated to 40° C. After checking the temperature, acetic acid and methanol were added, the temperature was raised to 80° C., and reaction was carried out for 30 minutes. Thereafter, the temperature was raised to 110° C. and maintained for 2 hours to evaporate moisture.

[0137] Next, cooling was performed using cooling oil, and methylene diphenyl diisocyanate and base oil were added to the calcium sulfonate lubricant (grease) in which reaction was completed, and dissolution of methylene diphenyl diisocyanate was confirmed. Subsequently, cyclohexylamine and octylamine were added, the temperature was raised to 170° C. and maintained for 10 minutes, and then reaction was terminated.

[0138] Next, zinc dialkyl dithiophosphate was added as an additive at a temperature of 100° C. or less and passed through a high-pressure homogenizer, thereby preparing a final hybrid lubricant composition.Comparative Example 1

[0139] A hybrid lubricant composition was prepared according to the reactant composition shown in Table 3 below.

[0140] Methylene diphenyl diisocyanate was placed in a 3 L pilot reactor and base oil was added thereto. The reaction mixture was heated to 70° C. and stirred. After confirming dissolution of methylene diphenyl diisocyanate, a solution containing cyclohexylamine amine and octylamine dissolved in base oil was placed in the reactor. Thereafter, the temperature of the internal reactant was raised to 170° C. and maintained for 10 minutes, and then reaction was terminated, and stirring was performed at a rotation speed of 50 to 100 rpm.

[0141] Next, zinc dialkyl dithiophosphate was added as an additive at a temperature of 100° C. or less and passed through a high-pressure homogenizer, thereby preparing a final hybrid lubricant composition.Comparative Examples 2 and 3

[0142] Respective hybrid lubricant compositions were prepared in the same manner as in Example 1, with the exception that the mixing ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener was changed as shown in Table 3 below.TABLE 3ComparativeComparativeComparativeClassificationExample 1Example 1Example 2Example 3ThickenerPolyurea-based601005040mixingthickenerratioCalcium sulfonate-40—5060based thickenerReactantOverbased calcium9.90—12.3814.85compositionsulfonate(wt %)(TBN 400)Dodecylbenzenesulfonic0.59—0.740.89acid12-hydroxystearic1.19—1.491.78acidWater2.38—2.973.56Base oil (150BS)72.4184.1670.3968.41Acetic acid0.79—0.991.19Methanol0.40—0.500.59Boric acid0.20—0.250.304,4-6.128.175.084.09diphenylmethanediisocyanateCyclohexylamine4.385.833.472.92Octylamine0.640.840.740.42Zinc dialkyl1.001.001.001.00dithiophosphateTotal100.00100.00100.00100.00

[0143] The properties of the lubricant compositions manufactured according to Example 1 and Comparative Examples 1 to 3 were tested, and the results thereof are shown in 5 Table 4 below.TABLE 4TestComparativeComparativeComparativePropertiesstandardExample 1Example 1Example 2Example 3Penetration (60 W)ASTM D326320334357Worked stability (105 W)217362(+36)360(+40)386(+52)408(+51)Mechanical stabilityASTM D333(+7)343(+18)367(+33)390(+33)1831Dropping point (° C.)ASTM D264253255258566Oil separation (wt %)ASTM D2.53.12.72.861844-Ball wear (mm)ASTM D0.570.520.60.5222664-Ball load (kgf)ASTM D2501602503152596Apparent 25° C.DIN413385429340viscosity, Pa · s150° C.51810243(−170)583(+198)236(−193)134(−206)Water wash-out, wt %ASTM D0.71.90.80.81264SRVSRVCOF—0.0050.0080.0050.005simulationrollingAveragetesttestDepth11.636.736.629.6(Cylinder(μm2)ondisk)

[0144] As described above, a significant improvement effect was achieved using a mixed thickener obtained by combining a polyurea-based thickener and a calcium sulfonate-based thickener, in which the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener was set to be high, compared to when using the polyurea-based thickener alone (Comparative Example 1) and using mixed thickeners in which the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener was 5:5 (Comparative Example 2) and 4:6 (Comparative Example 3).

[0145] Moreover, it is noteworthy that the two types of thickeners with different properties may be closely mixed together as a result of containing the mixed thickener in a manner that forms a polyurea-based lubricant in-situ in a calcium sulfonate-based lubricant rather than simply mixing the two types of thickeners, so that not only the individual advantages of each thickener but also a synergistic effect through interaction therebetween may be effectively obtained.

[0146] In addition, it can be confirmed through the results of apparent viscosity and water wash-out that high-temperature stability and water resistance are clearly improved.

[0147] As is apparent from the foregoing, a hybrid lubricant composition for steelmaking according to an embodiment of the present disclosure contains a mixed thickener of a polyurea-based thickener and a calcium sulfonate-based thickener, in which the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener is increased to a high level, thereby making it possible to achieve lubricant properties suitable for steel, for example for bearings in a continuous casting machine in a steelmaking process. In addition, by forming two types of thickeners in situ, the combined effect can be maximized along with the advantages of each thickener. Furthermore, excellent long-term durability can be exhibited, heat resistance and extreme pressure resistance can be ensured, and good long-term lubricity can be obtained due to the clean dispersion effect of calcium sulfonate. Moreover, a zinc compound serving as an additive provides the advantage of improved relubrication interval compared to conventional greases by virtue of good stability under high-temperature operating conditions unique to the steelmaking process. Therefore, widespread commercialization thereof is expected in the future.

[0148] All simple modifications or changes of the present disclosure fall within the scope of the present disclosure, and the specific protection scope of the present disclosure will be made clear by the appended claims.

Examples

example 1

[0135]A hybrid lubricant composition was prepared according to the reactant composition shown in Table 3 below.

[0136]Overbased calcium sulfonate, dodecylbenzenesulfonic acid, 12-hydroxystearic acid, water, boric acid, and base oil were placed in a 3 L pilot reactor and heated to 40° C. After checking the temperature, acetic acid and methanol were added, the temperature was raised to 80° C., and reaction was carried out for 30 minutes. Thereafter, the temperature was raised to 110° C. and maintained for 2 hours to evaporate moisture.

[0137]Next, cooling was performed using cooling oil, and methylene diphenyl diisocyanate and base oil were added to the calcium sulfonate lubricant (grease) in which reaction was completed, and dissolution of methylene diphenyl diisocyanate was confirmed. Subsequently, cyclohexylamine and octylamine were added, the temperature was raised to 170° C. and maintained for 10 minutes, and then reaction was terminated.

[0138]Next, zinc dialkyl dithiophosphate was...

BACKGROUND OF THE DISCLOSUREField of the Disclosure

[0001] The present disclosure relates to a hybrid lubricant composition for steelmaking. More specifically, the present disclosure relates to a hybrid lubricant composition for steelmaking process, which has improved durability, etc., so as to be suitable for a continuous casting machine operating at a high temperature under high load during a steelmaking process, and a method of preparing the same.Description of Related Art

[0002] In the ironmaking process, various foreign materials or contaminants are generated due not only to exposure to high temperature and corrosive environments, but also to wear on parts. As an example, continuous casting machines typically operate under conditions of high temperatures, low speeds, and frictional corrosion due to cooling water. In this way, as the machines are exposed to risk factors that affect mechanical structural stability, such as impact loads, high maintenance costs are required, and furthermore, efficient process operation is hindered by frequent replacement.

[0003] In the steelmaking process, large-sized bearings are mainly used, and various performance characteristics such as heat resistance, wear resistance, load carrying capacity, durability, and the like need to be satisfied owing to the severe operating environment. In particular, since the continuous casting machine is exposed to humid environments as well as high temperatures compared to bearing operating environments used in general industries, the use of polyurea-based grease, which has better performance than existing lithium-based bearing grease, is being considered.

[0004] Polyurea-based grease offers superior performance compared to lithium grease in view of heat resistance, load resistance, water resistance, durability, etc., and also has the advantage of reducing energy consumption. For this reason, polyurea-based grease is widely being applied to motor drive systems (e.g., Korean Patent No. 2312591). However, polyurea-based grease is hardened in harsh environments such as continuous casting lines in the steelmaking process, e.g., high-temperature environments of 150° C. or more, which causes grease transfer lines to become blocked, deteriorating grease pumpability.

[0005] In addition, durability has improved compared to lithium grease, extending relubrication interval, but it still does not meet user requirements, and hence, thorough research is being conducted to address this issue.SUMMARY OF THE DISCLOSURE

[0006] An embodiment of the present disclosure provides a hybrid lubricant composition capable of exhibiting improved durability under harsh environments of the steel industry, for example under high temperature, high load, and humidity environments applied to bearings in a continuous casting machine in a steelmaking process.

[0007] Another embodiment of the present disclosure provides a hybrid lubricant composition capable of significantly extending relubrication interval thanks to improved long-term durability even when applied to a continuous casting machine in a steelmaking process.

[0008] A first aspect of the present disclosure provides a hybrid lubricant composition for steelmaking, comprising, based on the total weight of the lubricant composition, (i) 14 to 37 wt % of a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener, (ii) 62 to 85 wt % of a base oil, and (iii) 0.3 to 2 wt % of a zinc-based compound as an additive,

[0009] wherein the weight ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener is adjusted in a range of greater than 1:1 to 3:1, and

[0010] the calcium sulfonate-based thickener comprises calcium sulfonate having a total base number (TBN) of 200 to 500, and further comprises 10 to 50 wt % of calcium carbonate in the form of calcite based on the weight of the calcium sulfonate-based thickener.

[0011] According to an embodiment, calcium carbonate in the calcium sulfonate-based thickener may have a particle diameter of 0.3 μm or less.

[0012] According to an embodiment, the calcium sulfonate-based thickener may further comprises at least one calcium salt selected from the group consisting of fatty acid calcium, calcium acetate, and calcium borate.

[0013] According to an embodiment, respective contents of fatty acid calcium, calcium acetate, and calcium borate contained in the calcium sulfonate-based thickener may be adjusted in ranges of up to 3 wt %, up to 2.5 wt %, and up to 2 wt %, based on the total weight of the lubricant composition.

[0014] According to an embodiment, the calcium sulfonate-based thickener may further include dodecylbenzenesulfonic acid in an amount of up to 1 wt % based on the total weight of the lubricant composition.

[0015] According to an embodiment, the polyurea-based thickener may comprises polyurea, which is a reaction product of a diisocyanate compound and an aliphatic monoamine compound.

[0016] According to an embodiment, the diisocyanate compound may be at least one selected from the group consisting of diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, and dimethyl diphenylene diisocyanate, and the aliphatic monoamine compound may be at least one selected from the group consisting of aniline, cyclohexylamine, octylamine, dodecylaniline, octadecylamine, hexylamine, heptylamine, nonylamine, ethylhexylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, pentadecylamine, nonadecylamine, eicodecylamine, oleylamine, linoleylamine, linolenylamine, methylcyclohexylamine, ethylcyclohexylamine, dimethylcyclohexylamine, diethylcyclohexylamine, butylcyclohexylamine, amylcyclohexylamine, propylcyclohexylamine, cyclooctylamine, benzylamine, phenethylamine, methylbenzylamine, biphenylamine, phenylisopropylamine, and phenylhexylamine.

[0017] According to an embodiment, the diisocyanate compound may be diphenylmethane diisocyanate, and the aliphatic monoamine compound may be cyclohexylamine and octylamine.

[0018] According to an embodiment, the polyurea may be diurea.

[0019] According to an embodiment, the base oil may be a Group I base oil and / or a Group II base oil.

[0020] According to an embodiment, the base oil may have a kinematic viscosity (ASTM D 445) at 40° C. of 200 to 700 cSt.

[0021] According to an embodiment, the zinc-based compound may be a zinc dithiophosphate-based compound and / or a zinc dithiocarbamate-based compound.

[0022] According to an embodiment, the zinc-based compound may be at least one selected from the group consisting of zinc dialkyl dithiophosphate and zinc dialkyl dithiocarbamate.

[0023] A second aspect of the present disclosure provides a method of preparing the hybrid lubricant composition described above, comprising:

[0024] a) preparing a reaction mixture by combining base oil, overbased calcium sulfonate, water, and at least one acid selected from the group consisting of boric acid and fatty acid;

[0025] b) forming a calcium sulfonate-based lubricant by adding acetic acid and alcohol to the reaction mixture, performing reaction under elevated temperature conditions to produce calcium carbonate in the form of calcite, and then removing impurities through additional heating;

[0026] c) forming a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener in the base oil by adding a diisocyanate compound and an aliphatic monoamine compound to the calcium sulfonate-based lubricant and performing reaction in-situ for forming a polyurea-based thickener under elevated temperature conditions of 130 to 200° C.; and

[0027] d) adding an additive ingredient comprising a zinc-based antioxidant to the product of step c).

[0028] According to an embodiment, the reaction mixture may be formed by further adding dodecylbenzenesulfonic acid in step a).

[0029] According to an embodiment, the reaction may be performed with the further addition of base oil in step c).

[0030] A third aspect of the present disclosure provides a lubrication method comprising:

[0031] applying the hybrid lubricant composition described above to a bearing of a continuous casting machine in a steelmaking process.

[0032] According to an embodiment, the continuous casting machine may be operated under conditions of temperature of at least 100° C. and relative humidity of at least 40%.

[0033] According to an embodiment, the continuous casting machine may be operated under conditions of relative humidity of 50 to 80%.DETAILED DESCRIPTION OF THE DISCLOSURE

[0034] The present disclosure may be realized in its entirety based on the following description. It should be understood that the following description is given of preferred embodiments of the present disclosure, and the present disclosure is not necessarily limited thereto. In addition, the accompanying drawings are provided to aid understanding of the present disclosure, and the present disclosure is not limited thereto, and details regarding individual components may be appropriately understood by the specific intent of the related description given below.

[0035] Terms used herein may be defined as follows.

[0036] “Grease” may refer to a solid or semi-solid material in which a thickener is dispersed in a liquid lubricating base oil, and may additionally contain other ingredients that impart specific properties thereto, and for example, grease may be a gel-type dispersion in which the continuous phase is formed of a lubricating base oil and the dispersed phase (e.g., thickener) is an anisotropic solid that penetrates the liquid phase.

[0037] “Flash Point” is a property that generally indicates how easily a material or composition, typically a fluid, may ignite or burn. Hydrocarbons having relatively high flash points are less likely to ignite than materials having relatively low flash points.

[0038] “Viscosity” is a physical property that describes the stickiness of a fluid, and “kinematic viscosity” is the value obtained by dividing the viscosity by the density of the fluid. Typically, kinematic viscosity tends to decrease with an increase in temperature.

[0039] “Worked penetration” is an indicator of the hardness of grease. Typically, high worked penetration means that the grease is soft, whereas low worked penetration means that the grease is hard. The worked penetration of grease may vary depending on the type and content of the thickener, the content of the lubricating base oil, and the viscosity.

[0040] “Total base number (TBN)” may mean a value indicating the amount (mg) of KOH equivalent to the amount of acid required to neutralize the alkali ingredient contained in 1 gram of lubricating oil, and may be measured by, for example, ASTM D2896.

[0041] “Continuous casting machine” refers to a machine used in the process of converting liquid iron into a solid. In this continuous casting machine, liquid molten steel is placed or injected in a mold and passes through a continuous caster, where it cools and solidifies to continuously form intermediate materials such as slabs, blooms, billets, etc.

[0042] Herein, when it is said that a composition “includes” a component, it means that it may further include other components, unless stated otherwise.

[0043] Terms such as “on” or “above” and “under” or “below” may be understood to describe the relative positional relationship between components or members, and the terms “located on” or “located under” may be understood to express the relative positional relationship not only in a state of contact with a specific object but also in a state of not contacting the same.Hybrid Lubricant Composition

[0044] A hybrid lubricant composition according to an embodiment of the present disclosure is a lubricant present in a gel state, which is a semi-solid state, and is equivalent to grease. Specifically, when applied onto machines requiring lubrication or parts thereof, the hybrid lubricant composition is converted into liquid in a state where lubrication is required (e.g., a state where the temperature rises due to friction), whereas it is maintained in a semi-solid state in case of deviating from the state where the temperature rises due to frictional heat, so that oil leakage may be suppressed.

[0045] In particular, in cases where large-sized bearings, etc. are used in a continuous casting machine in a steelmaking process and where they are exposed to severe (or harsh) operating environments, such as high temperature and humid environments compared to operating environments in other fields, a mixed thickener obtained by combining two types of thickeners (i.e., a polyurea-based thickener and a calcium sulfonate-based thickener) is applied. In this case, the composition and properties thereof are precisely controlled, such that improved durability and high-temperature pumpability as well as long-term durability may be achieved.

[0046] Lithium-based thickeners that have been conventionally widely used have no major problems when applied to grease for vehicles such as constant velocity joints, but under high temperature and high humidity environments such as in a continuous casting machine in a steelmaking process, the lifespan of bearings to which the lubricant is applied may be shortened due to grease oxidation resulting from lack of thermal stability. Furthermore, in case that moisture penetrates the grease, the lubricant may soften, deteriorating long-term durability. On the other hand, a polyurea-based thickener, which is another type of thickener, provides good properties such as heat resistance, water resistance, etc., but tends to harden at a high temperature.

[0047] Considering the characteristics of the conventional thickeners described above, in the present embodiment, a calcium sulfonate-based thickener and a polyurea-based thickener are each selected, and a mixed thickener thereof is used. In this embodiment, the ratio of the polyurea thickener to the calcium sulfonate-based thickener is adjusted to a level much higher than the generally recognized level, thereby realizing lubricant properties suitable for unique operating conditions encountered in the continuous casting machine during the steelmaking process.Mixed Thickener

[0048] The hybrid lubricant composition according to the present embodiment is grease, in which a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener is dispersed in a lubricating base oil (base oil).

[0049] The polyurea-based thickener may comprise polyurea produced by reacting a diisocyanate compound and an aliphatic monoamine compound. This urea formation reaction may be typically based on a mechanism in which 1 mole of diisocyanate compound and 2 moles of aliphatic monoamine compound react stoichiometrically.

[0050] In this regard, the diisocyanate compound may be at least one selected from among aryl diisocyanate, alkyl diisocyanate, and the like, for example, at least one selected from among diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, dimethyl diphenylene diisocyanate, and the like. In a certain embodiment, the diisocyanate compound may be diphenylmethane diisocyanate (for example, 4,4-diphenylmethane diisocyanate), which may be advantageous in that it enables the production of a thickener that provides excellent mechanical stability and grease fluidity.

[0051] Meanwhile, the monoamine may be at least one selected from among, for example, aniline, cyclohexylamine, octylamine, dodecylaniline, octadecylamine, hexylamine, heptylamine, nonylamine, ethylhexylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, pentadecylamine, nonadecylamine, eicodecylamine, oleylamine, linoleylamine, linolenylamine, methylcyclohexylamine, ethylcyclohexylamine, dimethylcyclohexylamine, diethylcyclohexylamine, butylcyclohexylamine, propylcyclohexylamine, amylcyclohexylamine, cyclooctylamine, benzylamine, phenethylamine, methylbenzylamine, biphenylamine, phenylisopropylamine, phenylhexylamine, and the like. In a certain embodiment, the monoamine may be at least one selected from among aniline, cyclohexylamine, octylamine, and the like. Also, in a certain embodiment, a combination of cyclohexylamine and octylamine may be used, which may be advantageous in obtaining heat resistance, durability, shear stability, etc.

[0052] In addition, examples of the polyurea may include diurea, triurea, tetraurea, and the like, among which diurea is preferable because it is able to minimize changes in grease penetration due to oxidation at room temperature and high temperature over time.

[0053] Meanwhile, the calcium sulfonate-based thickener may be in the form of calcium sulfonate and / or a calcium sulfonate complex. Here, calcium sulfonate may be overbased calcium sulfonate. The total base number (TBN) of the overbased calcium sulfonate may be adjusted in the range of, for example, about 200 to 500, for example about 250 to 450, for example about 300 to 400. Within this range, the calcium sulfonate-based thickener (particularly, calcium carbonate therein) may be uniformly dispersed in the base oil, and a robust lubricating film may be formed, thereby improving wear resistance and load carrying capacity. Furthermore, since stable micelles are formed even upon contact or mixing with a large amount of moisture during operation in the continuous casting machine, rust formation and deterioration of the lubricant composition due to moisture may be suppressed. However, if the total base number of calcium sulfonate is too low, it may affect the thickener formation, producing soft grease, whereas if it is too high, the content of the calcium sulfonate thickener is low, which may have an influence on extreme pressure resistance, durability, shear stability, mechanical stability, etc., which are affected by the content of the thickener. Therefore, it may be advantageous to have the TBN adjusted within the aforementioned range.

[0054] According to an embodiment, the calcium sulfonate-based thickener may contain calcium carbonate, which may be calcium carbonate in the form of calcite. As an example, calcium carbonate in the form of calcite may be formed when amorphous calcium carbonate is converted into crystalline calcium carbonate during conversion of the overbased calcium sulfonate. For example, the content of calcium carbonate in the form of calcite in the calcium sulfonate-based thickener may be adjusted in the range of, for example, about 10 to 50 wt %, for example about 15 to 45 wt %, for example about 20 to 43 wt %. According to a certain embodiment, the content of calcium carbonate in the form of calcite in the calcium sulfonate-based thickener may be adjusted in the range of, for example, about 25 to 40 wt %, for example about 28 to 37 wt %, for example about 30 to 35 wt %. If the content of calcium carbonate in the form of calcite in the calcium sulfonate-based thickener is too low, durability may deteriorate, and in particular, load carrying capacity (or load resistance) may significantly decrease. On the other hand, if it is too high, extreme pressure resistance may be improved, but wear resistance may significantly decrease. Hence, it may be advantageous to appropriately adjust the content thereof within the aforementioned range.

[0055] In addition, calcium carbonate contained in the calcium sulfonate-based thickener may be provided in the form of particles. As such, the particle diameter (size) of calcium carbonate may be in the range of, for example, about 0.3 μm or less, for example about 0.01 to 0.25 μm, for example about 0.05 to 0.2 μm, for example about 0.08 to 0.15 μm.

[0056] According to an embodiment, the calcium sulfonate-based thickener may further contain other calcium salts (e.g., fatty acid calcium, calcium acetate, calcium borate, etc.) in addition to calcium carbonate. According to an embodiment, the fatty acid used to form fatty acid calcium may be a fatty acid having 10 to 30 carbon atoms, and an example thereof may include at least one selected from among stearic acid, dodecanoic acid, palmitic acid, oleic acid, ricinoleic acid, decanoic acid, tetradecanoic acid, hydroxystearic acid, and the like. In a certain embodiment, it may be advantageous to use hydroxystearic acid, which affects not only lubricity but also long-term stability and durability.

[0057] According to an embodiment, the content of fatty acid calcium that may be contained in the calcium sulfonate-based thickener may be adjusted in the range of, for example, up to about 3 wt %, for example about 0.5 to 2.5 wt %, for example about 0.8 to 2 wt %, for example about 1 to 1.7 wt %, based on the total weight of the lubricant composition.

[0058] In addition, the content of calcium acetate that may be contained in the calcium sulfonate-based thickener may be adjusted in the range of, for example, up to about 2.5 wt %, for example about 0.1 to 2 wt %, for example about 0.3 to 1.5 wt %, for example about 0.5 to 1 wt %, based on the total weight of the lubricant composition.

[0059] In addition, the content of calcium borate that may be contained in the calcium sulfonate-based thickener may be adjusted in the range of, for example, up to about 2 wt %, for example about 0.1 to 1.5 wt %, for example about 0.2 to 1 wt %, for example about 0.3 to 0.6 wt %, based on the total weight of the lubricant composition.

[0060] According to an embodiment, the calcium sulfonate-based thickener may further contain dodecylbenzenesulfonic acid, which may function to effectively disperse calcium carbonate in the lubricant. As such, the content of dodecylbenzenesulfonic acid may be adjusted in the range of, for example, up to about 1 wt %, for example about 0.1 to 0.9 wt %, for example about 0.3 to 0.8 wt %, for example about 0.4 to 0.7 wt, based on the total weight of the lubricant.

[0061] According to an embodiment, the calcium sulfonate-based thickener may have viscosity (100° C.) as measured by ASTM D 445 in the range of, for example, about 40 to 100 cSt, for example about 50 to 90 cSt, for example about 60 to 80 cst. If the viscosity of the calcium sulfonate-based thickener is too low, it is difficult to form the minimum oil film required for lubrication, which may cause long-term lubricity problems and increase the likelihood of part breakage. On the other hand, if the viscosity of the calcium sulfonate-based thickener is excessively high, a large amount of heat may be generated due to viscosity resistance during lubrication inside the bearing, which may cause part breakage during long-term lubrication. In consideration thereof, it may be advantageous to appropriately adjust the viscosity thereof within the aforementioned range.

[0062] In an embodiment, it is noteworthy that the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener is adjusted to exceed the level recognized in the art so as to improve pumpability at a high temperature while maintaining good lubrication performance over a long period of time in the severe environment unique to a steelmaking process, for example a continuous casting machine.

[0063] In this regard, the weight ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener may be adjusted in the range of greater than about 1:1 to about 3:1, for example about 1.2 to about 2.8:1, for example about 1.4 to about 2.5:1, for example about 1.5 to about 2.2:1. If the content of the polyurea-based thickener is excessively high compared to the content of the calcium sulfonate-based thickener, problems such as blockage of transfer lines due to reduced pumpability caused by the high-temperature operating environment in the continuous casting machine may occur. On the other hand, if the content of the polyurea-based thickener is too low, water resistance, long-term durability, etc. in high humidity environments to which the continuous casting machine is continuously exposed may deteriorate.

[0064] In addition, according to an embodiment, the content of the mixed thickener based on the total weight of the lubricant composition may be adjusted in the range of, for example, about 14 to 37 wt %, for example about 15 to 32 wt %, for example about 16 to 30 wt %, for example about 17 to 28 wt %. If the content of the mixed thickener in the total lubricant composition (hybrid lubricant) is too low, a phenomenon in which long-term durability deteriorates due to reduction of shear stability, mechanical stability, etc. may occur, whereas if it is too high, a change in grease penetration may occur even with a small amount of oil leakage at a high temperature, and the hardened grease eventually has reduced lubricity, causing part breakage. Hence, it may be advantageous to adjust the content thereof within the aforementioned range.

[0065] In consideration thereof, in the present embodiment, when the mixed thickener in which two types of thickeners are combined in the ratio described above is used in a predetermined amount based on the total lubricant, problems resulting from existing lubricants applied in steelmaking processes may be alleviated.Base Oil

[0066] In the present embodiment, the base oil is a medium in which various additive ingredients including a thickener are dispersed, and is generally a liquid ingredient that may exhibit non-volatility at room temperature. Base oil is the main ingredient of grease and has a significant impact on the lubricating function of grease. Mineral oil-type base oil, synthetic base oil, etc. may be used. In this regard, the mineral oil-type base oil may be at least one selected from among paraffinic oil and naphthenic oil. In paraffinic base oil, when the content of straight-chain paraffin is high, there is a tendency to form large crystals, and when the content of branched-chain paraffin is high, there is a tendency to form smaller crystals. Also, naphthenic base oil tends to solidify and form an opaque solid phase, and exhibits a relatively low pour point.

[0067] According to an embodiment, the base oil may be derived from mineral oil or biomass, and may be further refined as necessary. Also, in some cases, two or more among the types of base oil described above may be used in combination.

[0068] In an embodiment, the kinematic viscosity of the base oil may be one of the factors that affect the film thickness of the oil at the lubricating interface and thereby exhibit efficient anti-wear performance. The kinematic viscosity thereof at 40° C. (ASTM D 445) may be adjusted in the range of, for example, about 200 to 700 cSt, for example about 300 to 600 cSt, for example about 350 to 550 cSt. In addition, the kinematic viscosity of the lubricating base oil at 100° C. may be adjusted in the range of, for example, about 15 to 60 cSt, for example about 20 to 55 cSt, for example about 25 to 45 cSt.

[0069] According to an embodiment, the density (ASTM D 1298; 15° C.) of the base oil may be in the range of, for example, about 0.82 to 0.92 g / cm3, for example about 0.85 to 0.91 g / cm3, for example about 0.88 to 0.9 g / cm3.

[0070] Also, the flash point (ASTM D92) of the base oil may be in the range of, for example, at least about 200° C., for example at least about 230° C., for example at least about 260° C., for example about 280 to 330° C.

[0071] In addition, according to an embodiment, the pour point (ASTM D97) of the base oil may be, for example, about −5° C. or less, for example about −7° C. or less, for example about-10° C. or less.

[0072] According to an embodiment, the base oil may include Group I base oil, Group II base oil, Group III base oil, Group IV base oil, etc. known in the art. For example, Group I base oil (saturates <90, sulfur >0.03%, and viscosity index of 80 to less than 120), and / or Group II base oil (saturates ≥90, sulfur≤0.03%, and viscosity index of 80 to less than 120) may be used, which may be advantageous in view of excellent thickener forming ability, hydrolytic stability, additive solubility, etc.

[0073] According to an embodiment, the content of the base oil in the hybrid lubricant composition may be adjusted in the range of about 62 to 85 wt %, for example about 64 to 83 wt %, for example about 68 to 80 wt %, for example about 70 to 78 wt&, based on the total weight of the lubricant composition. In this regard, if the content of the base oil is too low, hard grease may be formed, which reduces grease fluidity and lubricity, whereas if it is too high, soft grease may be formed, which may cause problems such as grease dripping and oil leakage. Hence, it may be advantageous to adjust the content thereof within the aforementioned range.Additive

[0074] According to an embodiment of the present disclosure, the hybrid lubricant composition contains a zinc-based compound as an additive.

[0075] A zinc-based compound primarily functions as an antioxidant, and may additionally function as an anti-wear agent. Such a zinc-based compound exhibits stable properties at a high temperature, rendering the lubricant composition suitable for the high-temperature operating environment of a continuous casting machine in a steelmaking process.

[0076] According to an embodiment, the zinc-based compound may be a zinc dithiophosphate-based compound and / or a zinc dithiocarbamate-based compound. As such, the alkyl group may indicate a linear, branched, or cyclic moiety of 1 to about 20 carbon atoms, for example 1 to 10 carbon atoms, for example 1 to 5 carbon atoms. In this regard, for example, the zinc dithiophosphate-based compound may be zinc dialkyl dithiophosphate. Also, the zinc dithiocarbamate-based compound may be zinc dialkyl dithiocarbamate.

[0077] According to a certain embodiment, the alkyl group of the zinc dialkyl dithiophosphate salt may be derived from a primary alcohol and a secondary alcohol, and the molar ratio of the secondary alcohol relative to the primary alcohol may be adjusted in the range of, for example, about 0.2 to 1.5, for example about 0.4 to 1.2, for example about 0.6 to 1.1, for example about 0.7 to 1.

[0078] According to an embodiment, the content of the zinc-based compound, based on the weight of the hybrid lubricant composition, may be adjusted in the range of, for example, about 0.3 to 2 wt %, for example about 0.5 to 1.8 wt %, for example about 0.7 to 1.5 wt %, for example about 0.9 to 1.2 wt %. In this regard, if the content of the zinc-based compound is too low, grease oxidation stability and wear resistance may deteriorate, causing a shortened grease lifespan, whereas if it is too high, it may act as an obstacle in the formation of a thickener, causing a problem in which the grease becomes soft. Hence, it may be advantageous to adjust the content thereof within the aforementioned range.

[0079] Meanwhile, the lubricant composition according to the present embodiment may further contain at least one selected from among additive components known in the art in addition to the zinc-based compound described above. Examples of the optional additive ingredient or ingredients may include a pour point depressant, an antioxidant other than the zinc-based compound, an anti-wear agent, an anti-corrosion agent, a surfactant, a lubricity enhancer, a friction reducer, and the like.

[0080] In this regard, the pour point depressant may include any one or a mixture of two or more selected from among, for example, alkyl methacrylate, polyacrylate, polyarylamide, condensation products of haloparaffin wax and aromatic compounds, vinyl carboxylate polymers, vinyl esters of fatty acids, allyl vinyl ether, and the like.

[0081] Examples of the antioxidant other than the zinc-based compound may include an amine compound (e.g., alkyl amine or 1-phenylaminonaphthalene), phenylnaphthylamine or aromatic amine (e.g., diphenylamine), a phenol compound (e.g., 2,6-di-t-butyl-4-methylphenol), a sulfur antioxidant, etc., which may be used alone or in combination of two or more thereof.

[0082] The anti-wear agent may include, for example, a phosphorus-based anti-wear agent, and examples thereof include a phosphite compound (tributyl phosphite, trioleyl phosphite, etc.), a phosphate compound (e.g., tricresyl phosphate, dilauryl phosphate, etc.), an amine phosphate compound (e.g., dibutyloctylamine phosphate, dilauryl octylamine phosphate, etc.), and a phosphorothioate compound (e.g., triphenylphosphorothioate, etc.), which may be used alone or in combination of two or more thereof.

[0083] Examples of the anti-corrosion agent may include dinonylnaphthalene sulfonate, sorbitan ester, sarcosine, succinimide, fatty acid derivatives, imidazoline, etc., which may be used alone or in combination of two or more thereof.

[0084] Examples of the friction reducer may include oleyl amide, alkyl and / or aryl phosphate esters, phosphonic esters, thiophosphate esters, etc., which may be used alone or in combination of two or more thereof.

[0085] The content of the optional additive ingredient described above may be adjusted in the range of, for example, up to about 3 wt %, for example up to about 2.5 wt %, for example up to about 2 wt %, for example about 0.2 to 1.5 wt %, based on the weight of the hybrid lubricant composition.Properties of Lubricant Composition

[0086] The hybrid lubricant composition according to the present embodiment properties such as heat resistance, extreme pressure resistance, long-term lubricity, durability, water resistance, high-temperature pumpability, etc. in a balanced manner under harsh operating environments in a steelmaking process, for example in a continuous casting machine.

[0087] According to an embodiment, the worked penetration (25° C., 60 W; ASTM D 217) of the lubricant composition is a property indicating the extent of thinness of the grease-type lubricant, and a higher value indicates a thinner state. The worked penetration of the lubricant composition according to the present embodiment may be in the range of, for example, about 220 to 350, for example about 280 to 345, for example about 310 to 340.

[0088] According to an embodiment, the worked stability (105 W; ASTM D 217) of the lubricant composition is a property indicating the mechanical stability of grease, and the smaller the difference from the worked penetration, the better the mechanical stability. Therefore, the worked stability may be evaluated by the difference from the worked penetration value, and may be higher, in the range of, for example, about 50 or less, for example about 45 or less, for example about 30 to 40.

[0089] According to an embodiment, the roll stability (mechanical stability) of the lubricant composition is a property indicating the shear stability of grease, and the smaller the change in worked penetration, the better the shear stability. In this regard, the roll stability of the lubricant composition may be evaluated by the difference from the worked penetration value as measured by ASTM D 1831, and may be higher, in the range of, for example, about 20 or less, for example about 15 or less, for example about 3 to 10.

[0090] According to an embodiment, the dropping point of the lubricant composition is a property indicating the heat resistance of grease, for example an indicator of durability under elevated temperature conditions. In this regard, the dropping point may be in the range of, for example, about 255° C. or more, for example about 259° C. or more, for example about 262 to 270° C., as measured by ASTM D 566.

[0091] According to an embodiment, the oil separation of the lubricant composition is an indicator of storage stability (e.g., storage stability under elevated temperature conditions), and may be in the range of, for example, about 5 or less, for example about 4 or less, for example about 3.5 or less, for example about 2 to 3, for example about 2.2 to 2.6, as measured by ASTM D 6184.

[0092] According to an embodiment, the 4-ball wear resistance (ASTM D 2266) of the lubricant composition is a property indicating the wear resistance or lubricating ability of grease, and may be, for example, about 0.7 mm or less, for example about 0.65 mm or less, for example about 0.6 mm or less, for example about 0.59 mm or less.

[0093] In addition, the load carrying capacity or load resistance (ASTM D 2596) of the lubricant composition is a property indicating the load carrying capacity of grease, and may be, for example, about 160 to 340 kgf, for example about 200 to 330 kgf, for example about 230 to about 320 kgf, for example about 250 to 315 kgf.

[0094] Furthermore, the SRV rolling test (cylinder on disk; ASTM D 5707) of the lubricant composition is a property indicating the frictional characteristics of grease, and the depth of the measured wear scar may be in the range of, for example, about 25 μm2 or less, for example about 20 μm2 or less, for example about 8 to 15 μm2, for example about 9 to 13 μm2.

[0095] In addition, the lubricant composition according to the present embodiment may exhibit good pumpability (or flowability) even under high temperature conditions such as in a continuous casting machine in a steelmaking process. In order to evaluate pumpability, the apparent viscosity (DIN 51810) at each of room temperature and high temperature is measured, confirming the properties related to high-temperature stability and high-temperature hardening, and pumpability at a high temperature may be confirmed depending on the extent of hardening. In this regard, if the apparent viscosity at a high temperature increases in a positive direction compared to the apparent viscosity at room temperature, this may indicate that the grease is hardening compared to the penetration at room temperature, which may cause problems with pumpability. From this point of view, the lubricant composition according to the present embodiment may exhibit a property in which the apparent viscosity value at a high temperature decreases compared to the apparent viscosity value at room temperature.

[0096] Also, water resistance of the lubricant composition (ASTM D 1264) may be evaluated by expressing the amount of grease loss, which is a criterion for judging resistance to water, as a weight proportion. In this regard, in the lubricant composition according to the present embodiment, the amount of grease loss may be, for example, 1.9 wt % or less, for example 1 wt % or less, for example about 0.9 wt % or less, for example about 0.8 wt % or less.Preparation of Hybrid Lubricant Composition

[0097] According to an embodiment of the present disclosure, the hybrid lubricant composition described above may be prepared by various methods.

[0098] As an example, a polyurea-based lubricant (grease) and a calcium sulfonate-based lubricant (grease) are each prepared, and then combined with an additive component at a predetermined ratio to prepare a hybrid lubricant composition. As such, the mixing conditions of two types of lubricants are not particularly limited, but the mixing temperature may be adjusted in the range of, for example, about 10 to 150° C., for example about 20 to 80° C., for example about 30 to 70° C. Also, the mixing may be performed under stirring conditions, in which case the mixing time may be adjusted in the range of, for example, about 0.1 to 48 hours, for example about 1 to 24 hours, for example about 3 to 15 hours.

[0099] According to an alternative embodiment, the hybrid lubricant composition may be obtained by preparing a sulfonate-based lubricant (for example, a calcium sulfonate-based lubricant), forming a polyurea-based thickener in-situ, and introducing an additive ingredient according to the following steps a) to d).Preparing Reaction Mixture (Step a)

[0100] According to an embodiment, first, a reaction mixture for preparing a sulfonate-based lubricant is prepared. To this end, overbased calcium sulfonate (having a TBN of, for example, 200 to 500), water, and at least one acid selected from the group consisting of boric acid and fatty acid are added to the base oil. As such, boric acid may function as a complexing agent and may react with calcium to form calcium borate as described below. In addition, the fatty acid is an ingredient that may react with calcium to form soap, namely fatty acid calcium, and as described above, the fatty acid may be a fatty acid having 10 to 30 carbon atoms, for example, at least one selected from among stearic acid, dodecanoic acid, palmitic acid, oleic acid, ricinoleic acid, decanoic acid, tetradecanoic acid, hydroxystearic acid, etc.

[0101] Also, according to an embodiment, when preparing the reaction mixture, dodecylbenzenesulfonic acid may be further added to promote dispersion of calcium carbonate in the subsequent step, as described above.

[0102] According to an embodiment, when mixing the components described above, the mixing temperature may be adjusted in the range of, for example, about 30 to 60° C., for example about 35 to 55° C., for example about 38 to 52° C., for example about 40 to 50° C.Forming Calcium Sulfonate-Based Lubricant (Step b)

[0103] According to an embodiment, a calcium sulfonate-based lubricant is formed using the reaction mixture prepared in the previous step.

[0104] To this end, acetic acid and alcohol may be added to the reaction mixture and reacted. As such, reaction may be performed under elevated temperature conditions. As an example, the reaction temperature may be adjusted in the range of, for example, about 60 to 100° C., for example about 70 to 90° C., for example about 75 to 85° C. Here, water, acetic acid, and alcohol may function to rapidly convert some of calcium in the amorphous overbased calcium sulfonate material in the reaction mixture into calcium carbonate having a calcite crystal structure. By way of example, the alcohol may typically be an aliphatic alcohol, for example, an aliphatic alcohol having 1 to 5 carbon atoms, for example an aliphatic alcohol having 1 to 3 carbon atoms. Examples of the alcohol may include methanol, ethanol, isopropanol, n-propanol, iso-butanol, t-butanol, n-pentanol, and the like, and for example methanol may be used.

[0105] For example, the weight ratio of acetic acid to water may be adjusted in the range of, for example, about 0.2 to 0.6:1, for example about 0.25 to 0.5:1, for example about 0.3 to 0.4:1. Also, the weight ratio of alcohol to water may be adjusted in the range of, for example, about 0.05 to 0.3:1, for example about 0.07 to 0.25:1, for example about 0.1 to 0.2:1. Since the formation of calcium carbonate particles having a calcite structure may be effectively promoted in the ratios described above, it may be advantageous to adjust the ratios thereof within the aforementioned ranges.

[0106] According to an embodiment, the time involved in the conversion reaction is not particularly limited, but may be adjusted in the range of, for example, about 0.1 to 10 hours, for example about 0.2 to 5 hours, for example about 0.4 to 1 hours.

[0107] After performing the conversion reaction described above, a process of removing impurities generated during the reaction, such as byproducts such as moisture, may be performed. To this end, additional heating may be conducted. As such, the additional heating temperature is not particularly limited, but may be adjusted in the range of a temperature higher than the preceding reaction temperature, for example, above about 100° C., for example about 103 to 120° C., for example about 105 to 115° C. This additional heating time is not particularly limited, and may be set in the range of, for example, about 0.5 to 5 hours, for example about 1 to 3 hours, for example about 1.5 to 2.5 hours.

[0108] In this way, heating is performed as a post-treatment process for removing impurities, thereby forming a calcium sulfonate-based lubricant in which the calcium sulfonate-based thickener is dispersed or contained in the base oil.Forming Polyurea-Based Thickener (Step c)

[0109] According to an embodiment, forming a polyurea-based thickener in-situ is performed by adding a reactant for polyurea formation to the calcium sulfonate-based lubricant. To this end, a diisocyanate (isocyanate) compound and an aliphatic monoamine compound are added to the calcium sulfonate-based lubricant to perform polyurea formation reaction. As such, when the calcium sulfonate-based lubricant contains base oil in the amount described above, the need to add base oil is reduced, but typically, base oil is added together with the polyurea reactant to sufficiently dissolve the reactant.

[0110] When the reactant is sufficiently dissolved, urea formation reaction is performed under elevated temperature conditions. In this regard, the temperature during reaction may be adjusted in the range of, for example, about 130 to 200° C., for example about 150 to 190° C., for example about 160 to 180° C. In addition, the reaction time is not particularly limited, but may be adjusted in the range of, for example, about 0.1 to 1 hours, for example about 0.15 to 0.5 hours, for example about 0.18 to 0.3 hours.

[0111] According to the reaction described above, a mixed thickener is formed in which the calcium sulfonate-based thickener and the polyurea-based thickener are sequentially formed in the base oil. In contrast to an embodiment in which individual thickeners are simply prepared separately and then mixed, this mixed thickener is present in a form in which two types of thickeners are in close contact through in-situ synthesis, and the synergistic effect due to interaction therebetween may be maximized.Mixing Additive (Step d)

[0112] As described above, after synthesis of the polyurea thickener in situ, mixing the additive ingredient is performed. As such, the additive essentially includes a zinc-based compound as an antioxidant, and optionally, at least one among various additive ingredients may be further added.

[0113] In an embodiment, in order to suppress phenomena such as deterioration of the lubricant composition, it is preferable to introduce and disperse the additive at a temperature lower than the polyurea thickener forming reaction temperature but at which the additive may be sufficiently dispersed. Taking this into consideration, the temperature for additive introduction and dispersion may be adjusted in the range of, for example, about 100° C. or less, for example about 60 to 95° C., for example about 70 to 90° C., which may be understood as illustrative.

[0114] In addition, a mixing or dispersing device known in the art may be used to disperse the formed mixed thickener, including the additive ingredient, with a uniform particle size. As an example, the mixing or dispersing device may be at least one selected from among a static mixer, a Mantin Gaulin homogenizer, a microfluidizer, a colloid mill, a homogenizer, a top roll, a Henschel mixer, and the like, and for example a homogenizer, for example a high-pressure homogenizer (e.g., operated under a pressure of about 300 to 400 bar) may be used.

[0115] Also, the mixing time may be adjusted in the range of, for example, about 0.5 to 5 hours, for example about 0.6 to 3 hours, for example about 0.7 to 2 hours, for example about 0.8 to 1 hour, but is not limited thereto.Use of Hybrid Lubricant Composition

[0116] According to another embodiment of the present disclosure, the hybrid lubricant composition described above may be applied to various machines, vehicle parts (e.g., gears, belts, chains, wire ropes, mechanical continuously variable transmissions, etc.), and the like, and specifically, when the hybrid lubricant composition is applied to a continuous casting machine in a steelmaking process, for example to a bearing in a continuous casting machine, the advantage as a lubricant may be more prominent. The continuous casting machine is typically driven or operated under high temperature and high humidity conditions (or contact with moisture).

[0117] As an example, the continuous casting machine includes a ladle configured to hold molten steel refined in the steelmaking process, a tundish configured to supply molten steel through an injection nozzle connected to the ladle and temporarily store the same, a mold configured to receive the molten steel temporarily stored in the tundish and initially solidify the same into a certain shape, and a cooling line provided under the mold and having a number of segments arranged to cool the unsolidified cast piece and perform a series of forming operations.

[0118] In the machine described above, molten steel drawn from the ladle and the tundish is placed in a mold and cast into a cast piece such as a slab, bloom, or billet having a predetermined shape at a predetermined width and thickness by a cutting process. As such, cooling water is continuously sprayed onto the surface of the cast piece manufactured using the continuous casting machine during the continuous casting process, and the cast piece is cooled by cooling water spray, manufacturing a final cast piece.

[0119] In this way, a series of procedures in the continuous casting machine for the steelmaking process is exposed to high temperatures compared to typical mechanical devices, and the transfer lines that supply a lubricant to the bearings in the machine are also exposed to high temperatures, and moisture continuously comes into contact with or penetrates the lubricant film due to cooling water spray.

[0120] According to an embodiment, the internal temperature of the continuous casting machine may be in the range of, for example, at least about 100° C., for example about 120 to 250° C., for example about 130 to 200° C., for example about 150 to 180° C. Also, the internal relative humidity of the continuous casting machine may be in the range of, for example, at least about 40%, for example about 50 to 80%, for example about 60 to 70%.

[0121] When applying a lubricant for bearings operated under harsh conditions in the continuous casting machine, such as a lubricant for bearings in a general machine or a lubricant for vehicles (e.g., constant velocity joints), there are significant problems such as poor water resistance and reduced pumpability, but such problems may be effectively alleviated by applying the hybrid lubricant composition according to the present embodiment. For example, the hybrid lubricant composition may be applied to bearings in a continuous casting machine by automatic injection through a transfer line.

[0122] A better understanding of the present disclosure may be obtained through the following examples. However, these examples are merely set forth to illustrate the present disclosure and are not to be construed as limiting the present disclosure.EXAMPLES

[0123] Base oil used in Example and Comparative Examples is a 150 BS base oil, and properties thereof are shown in Table 1 below.TABLE 1ClassificationPropertiesSpecific gravity (4° C.)0.9Kinematic viscosity (40° C.)460cStKinematic viscosity (100° C.)30cStFlash point328°C.Pour point−12°C.Viscosity index95Min.Carbon residue0.10wt %Acid number (TAN)0.01

[0124] The properties of the grease composition manufactured according to the present example were measured as follows.

[0125] Worked penetration was measured according to ASTM D 217. After 60 mixing cycles in a mixer maintained at 25° C., a cone weighing 102.5±0.05 g was freely dropped onto the sample surface for 5 seconds. The penetration depth of the cone was measured in 1 / 10 mm increments.

[0126] Worked stability was measured according to ASTM D 217. After 100,000 mixing cycles in a mixer, a cone weighing 102.5+0.05 g was freely dropped onto the sample surface for 5 seconds. The penetration depth of the cone was measured in 1 / 10 mm increments, and the difference thereof from the worked penetration was calculated.

[0127] Roll stability was evaluated according to ASTM D1831. 50 g of grease with the measured worked penetration was evenly applied inside the cylinder, and the roll was installed inside the cylinder. Next, the cylinder was rotated at 165 rpm for 2 hours at a constant temperature, and the worked penetration of the grease was measured and changes thereof were recorded.

[0128] Dropping point was measured according to ASTM D 566. Specifically, grease was applied to a specified cup with a diameter of 10 mm, and the temperature at which the base oil was separated and first fell with an increase in temperature was measured.

[0129] Oil separation was evaluated according to ASTM D 6184. 10 g of the sample was placed on a 250 μm nickel mesh cone, and the weight of the separated oil was represented as wt % after a predetermined time (24 h) at a set temperature (100° C.).

[0130] Wear resistance was evaluated according to the 4-ball wear test (ASTM D 2266). Specifically, three fixed balls and one rotary ball were in point contact and operated under certain conditions, and the average wear surface of the three fixed balls was checked in mm (test conditions: rotation speed of 1200±60 rpm, load of 40±0.2 kgf, duration of 60±1 minutes, and temperature of 75±2° C.).

[0131] Load carrying capacity (load resistance) was evaluated according to ASTM D 2596, for example a shell-type 4-ball test was used, where three fixed balls and one rotary ball were in point contact and operated under certain conditions, and the load was measured when the four balls stuck to each other or wore by 4 mm or more (test conditions: rotation speed of 1770±60 rpm, duration of 10 seconds, and temperature of 27±8° C.).

[0132] SRV test was performed as a rolling test to evaluate bearing simulation. Specifically, the lower specimen disk and the upper specimen cylinder (2 pieces) were brought into contact with each other, and rolling lubrication was performed under programmed conditions (frequency, stroke, load, time, and temperature). After evaluating the coefficient of friction, the depth of the wear scar on the lower specimen was measured. The SRV test conditions are shown in Table 2 below.TABLE 2ClassificationTest conditionsPretestLoad: 500N, Stroke Amplitude: 1 mm, Temperature:100° C., Frequency: 20 Hz, Duration: 1 hrMain testLoad: 2000N, Stroke Amplitude: 1 mm, Temperature:100° C., Frequency: 20 Hz, Duration: 18 hrApparent viscosity was measured using an Anton Paar rheometer (MCR 302) according to DIN 51810. The measurement conditions were gap=0.5 mm, shear rate: 1 1 / s, and measuring system: PP25.

[0134] Water wash-out was measured according to ASTM D 1264. A 6204 ball bearing was attached to the housing and rotated at 600 rpm, and distilled water was sprayed at a rate of 5 ml / sec for 1 hour at 38° C. The weight loss of the sample was represented as wt %.Example 1

[0135] A hybrid lubricant composition was prepared according to the reactant composition shown in Table 3 below.

[0136] Overbased calcium sulfonate, dodecylbenzenesulfonic acid, 12-hydroxystearic acid, water, boric acid, and base oil were placed in a 3 L pilot reactor and heated to 40° C. After checking the temperature, acetic acid and methanol were added, the temperature was raised to 80° C., and reaction was carried out for 30 minutes. Thereafter, the temperature was raised to 110° C. and maintained for 2 hours to evaporate moisture.

[0137] Next, cooling was performed using cooling oil, and methylene diphenyl diisocyanate and base oil were added to the calcium sulfonate lubricant (grease) in which reaction was completed, and dissolution of methylene diphenyl diisocyanate was confirmed. Subsequently, cyclohexylamine and octylamine were added, the temperature was raised to 170° C. and maintained for 10 minutes, and then reaction was terminated.

[0138] Next, zinc dialkyl dithiophosphate was added as an additive at a temperature of 100° C. or less and passed through a high-pressure homogenizer, thereby preparing a final hybrid lubricant composition.Comparative Example 1

[0139] A hybrid lubricant composition was prepared according to the reactant composition shown in Table 3 below.

[0140] Methylene diphenyl diisocyanate was placed in a 3 L pilot reactor and base oil was added thereto. The reaction mixture was heated to 70° C. and stirred. After confirming dissolution of methylene diphenyl diisocyanate, a solution containing cyclohexylamine amine and octylamine dissolved in base oil was placed in the reactor. Thereafter, the temperature of the internal reactant was raised to 170° C. and maintained for 10 minutes, and then reaction was terminated, and stirring was performed at a rotation speed of 50 to 100 rpm.

[0141] Next, zinc dialkyl dithiophosphate was added as an additive at a temperature of 100° C. or less and passed through a high-pressure homogenizer, thereby preparing a final hybrid lubricant composition.Comparative Examples 2 and 3

[0142] Respective hybrid lubricant compositions were prepared in the same manner as in Example 1, with the exception that the mixing ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener was changed as shown in Table 3 below.TABLE 3ComparativeComparativeComparativeClassificationExample 1Example 1Example 2Example 3ThickenerPolyurea-based601005040mixingthickenerratioCalcium sulfonate-40—5060based thickenerReactantOverbased calcium9.90—12.3814.85compositionsulfonate(wt %)(TBN 400)Dodecylbenzenesulfonic0.59—0.740.89acid12-hydroxystearic1.19—1.491.78acidWater2.38—2.973.56Base oil (150BS)72.4184.1670.3968.41Acetic acid0.79—0.991.19Methanol0.40—0.500.59Boric acid0.20—0.250.304,4-6.128.175.084.09diphenylmethanediisocyanateCyclohexylamine4.385.833.472.92Octylamine0.640.840.740.42Zinc dialkyl1.001.001.001.00dithiophosphateTotal100.00100.00100.00100.00

[0143] The properties of the lubricant compositions manufactured according to Example 1 and Comparative Examples 1 to 3 were tested, and the results thereof are shown in 5 Table 4 below.TABLE 4TestComparativeComparativeComparativePropertiesstandardExample 1Example 1Example 2Example 3Penetration (60 W)ASTM D326320334357Worked stability (105 W)217362(+36)360(+40)386(+52)408(+51)Mechanical stabilityASTM D333(+7)343(+18)367(+33)390(+33)1831Dropping point (° C.)ASTM D264253255258566Oil separation (wt %)ASTM D2.53.12.72.861844-Ball wear (mm)ASTM D0.570.520.60.5222664-Ball load (kgf)ASTM D2501602503152596Apparent 25° C.DIN413385429340viscosity, Pa · s150° C.51810243(−170)583(+198)236(−193)134(−206)Water wash-out, wt %ASTM D0.71.90.80.81264SRVSRVCOF—0.0050.0080.0050.005simulationrollingAveragetesttestDepth11.636.736.629.6(Cylinder(μm2)ondisk)

[0144] As described above, a significant improvement effect was achieved using a mixed thickener obtained by combining a polyurea-based thickener and a calcium sulfonate-based thickener, in which the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener was set to be high, compared to when using the polyurea-based thickener alone (Comparative Example 1) and using mixed thickeners in which the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener was 5:5 (Comparative Example 2) and 4:6 (Comparative Example 3).

[0145] Moreover, it is noteworthy that the two types of thickeners with different properties may be closely mixed together as a result of containing the mixed thickener in a manner that forms a polyurea-based lubricant in-situ in a calcium sulfonate-based lubricant rather than simply mixing the two types of thickeners, so that not only the individual advantages of each thickener but also a synergistic effect through interaction therebetween may be effectively obtained.

[0146] In addition, it can be confirmed through the results of apparent viscosity and water wash-out that high-temperature stability and water resistance are clearly improved.

[0147] As is apparent from the foregoing, a hybrid lubricant composition for steelmaking according to an embodiment of the present disclosure contains a mixed thickener of a polyurea-based thickener and a calcium sulfonate-based thickener, in which the ratio of the polyurea-based thickener to the calcium sulfonate-based thickener is increased to a high level, thereby making it possible to achieve lubricant properties suitable for steel, for example for bearings in a continuous casting machine in a steelmaking process. In addition, by forming two types of thickeners in situ, the combined effect can be maximized along with the advantages of each thickener. Furthermore, excellent long-term durability can be exhibited, heat resistance and extreme pressure resistance can be ensured, and good long-term lubricity can be obtained due to the clean dispersion effect of calcium sulfonate. Moreover, a zinc compound serving as an additive provides the advantage of improved relubrication interval compared to conventional greases by virtue of good stability under high-temperature operating conditions unique to the steelmaking process. Therefore, widespread commercialization thereof is expected in the future.

[0148] All simple modifications or changes of the present disclosure fall within the scope of the present disclosure, and the specific protection scope of the present disclosure will be made clear by the appended claims.

Examples

example 1

[0135]A hybrid lubricant composition was prepared according to the reactant composition shown in Table 3 below.

[0136]Overbased calcium sulfonate, dodecylbenzenesulfonic acid, 12-hydroxystearic acid, water, boric acid, and base oil were placed in a 3 L pilot reactor and heated to 40° C. After checking the temperature, acetic acid and methanol were added, the temperature was raised to 80° C., and reaction was carried out for 30 minutes. Thereafter, the temperature was raised to 110° C. and maintained for 2 hours to evaporate moisture.

[0137]Next, cooling was performed using cooling oil, and methylene diphenyl diisocyanate and base oil were added to the calcium sulfonate lubricant (grease) in which reaction was completed, and dissolution of methylene diphenyl diisocyanate was confirmed. Subsequently, cyclohexylamine and octylamine were added, the temperature was raised to 170° C. and maintained for 10 minutes, and then reaction was terminated.

[0138]Next, zinc dialkyl dithiophosphate was...

Claims

1. A hybrid lubricant composition for steelmaking, comprising, based on a total weight of the lubricant composition, (i) 14 to 37 wt % of a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener; (ii) 62 to 85 wt % of a base oil; and (iii) 0.3 to 2 wt % of a zinc-based compound as an additive,wherein a weight ratio of the polyurea-based thickener to the calcium sulfonate-based thickener in the mixed thickener is adjusted in a range of greater than 1:1 to 3:1, andthe calcium sulfonate-based thickener comprises calcium sulfonate having a total base number (TBN) of 200 to 500, and further comprises 10 to 50 wt % of calcium carbonate in form of calcite based on a weight of the calcium sulfonate-based thickener.

2. The hybrid lubricant composition of claim 1, wherein calcium carbonate in the calcium sulfonate-based thickener has a particle diameter of 0.3 μm or less.

3. The hybrid lubricant composition of claim 1, wherein the calcium sulfonate-based thickener further comprises at least one calcium salt selected from the group consisting of fatty acid calcium, calcium acetate, and calcium borate.

4. The hybrid lubricant composition of claim 3, wherein respective contents of fatty acid calcium, calcium acetate, and calcium borate contained in the calcium sulfonate-based thickener are adjusted in ranges of up to 3 wt %, up to 2.5 wt %, and up to 2 wt %, based on the total weight of the lubricant composition.

5. The hybrid lubricant composition of claim 1, wherein the calcium sulfonate-based thickener further comprises dodecylbenzenesulfonic acid in an amount of up to wt % based on the total weight of the lubricant composition.

6. The hybrid lubricant composition of claim 1, wherein the polyurea-based thickener comprises a polyurea, which is a reaction product of a diisocyanate compound and an aliphatic monoamine compound.

7. The hybrid lubricant composition of claim 6, wherein:the diisocyanate compound is at least one selected from the group consisting of diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, and dimethyl diphenylene diisocyanate, andthe aliphatic monoamine compound is at least one selected from the group consisting of aniline, cyclohexylamine, octylamine, dodecylaniline, octadecylamine, hexylamine, heptylamine, nonylamine, ethylhexylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, pentadecylamine, nonadecylamine, eicodecylamine, oleylamine, linoleylamine, linolenylamine, methylcyclohexylamine, ethylcyclohexylamine, dimethylcyclohexylamine, diethylcyclohexylamine, butylcyclohexylamine, propylcyclohexylamine, amylcyclohexylamine, cyclooctylamine, benzylamine, phenethylamine, methylbenzylamine, biphenylamine, phenylisopropylamine, and phenylhexylamine.

8. The hybrid lubricant composition of claim 1, wherein the base oil has a kinematic viscosity (ASTM D 445) at 40° C. of 200 to 700 cSt.

9. The hybrid lubricant composition of claim 1, wherein the zinc-based compound is at least one selected from the group consisting of zinc dialkyl dithiophosphate and zinc dialkyl dithiocarbamate.

10. A method of preparing the hybrid lubricant composition of claim 1, comprising:a) preparing a reaction mixture by combining base oil, overbased calcium sulfonate, water, and at least one acid selected from the group consisting of boric acid and fatty acid;b) forming a calcium sulfonate-based lubricant by adding acetic acid and alcohol to the reaction mixture, performing reaction under elevated temperature conditions to produce calcium carbonate in form of calcite, and then removing impurities through additional heating;c) forming a mixed thickener comprising a polyurea-based thickener and a calcium sulfonate-based thickener in the base oil by adding a diisocyanate compound and an aliphatic monoamine compound to the calcium sulfonate-based lubricant and performing reaction in-situ for forming a polyurea-based thickener under elevated temperature conditions of 130 to 200° C.; andd) adding an additive ingredient comprising a zinc-based antioxidant to a product of step c).

11. A lubrication method comprising applying the hybrid lubricant composition of claim 1 to a bearing of a continuous casting machine in a steelmaking process.

12. The lubrication method of claim 11, wherein the continuous casting machine is operated under conditions of temperature of at least 100° C. and relative humidity of at least 40%.