Bearing lubricating grease and preparation method thereof

Abstract

The invention discloses bearing lubricating grease and a preparation method thereof. The lubricating grease comprises the following components: 60-90% of base oil, 5-20% of a thickening agent, 1-30% of a solid additive (containing components A and B) and 1-1.2% of an auxiliary additive. Wherein the component A is a surface-modified molybdenum disulfide nanosheet (the average particle size is 0.1-5 microns), the component B is polytetrafluoroethylene micro powder (the average particle size D50 is 0.5-10 microns), and the weight ratio of the component A to the component B is 1: 1-1: 3. The preparation method comprises the following steps: heating part of base oil, and adding a thickening agent raw material to react to form a lubricating grease base; pre-dispersing the component A and part of the base oil or the dispersion medium into slurry; adding the slurry A and the slurry B into a lubricating grease base at 70-100 DEG C, and performing high-shear dispersion; and optionally adding auxiliary additives, mixing, grinding, homogenizing, and degassing to obtain a finished product. The lubricating grease has excellent dispersion stability and good comprehensive performance, ensures uniform and stable dispersion of the solid additive, and has a good use effect.

Description

TECHNICAL FIELD

[0001] The present application relates to a bearing grease and a preparation method thereof. BACKGROUND

[0002] Bearing is a key component in mechanical equipment, and its lubrication state directly affects the reliability, efficiency and service life of the equipment. Grease is widely used in bearing lubrication due to its good adhesion, sealing and long-acting. Traditional bearing grease is mainly based on mineral oil, synthetic oil (such as PAO, ester oil, silicon oil, etc.) and thickening agent (such as lithium base, composite lithium base, polyurea, bentonite, etc.). However, under harsh working conditions such as high load, impact load, extreme temperature (high temperature or low temperature), high speed, vacuum or extremely low noise / vibration requirement, the traditional grease may face the following problems: the oil film strength is insufficient, leading to boundary lubrication, aggravating wear, the base oil volatilizes and oxidizes at high temperature, the structure of the thickening agent is destroyed, leading to lubrication failure, the thickening agent becomes hard at low temperature, the starting torque is large, and even cannot be lubricated, the oil separation is serious after long-term operation, the effective lubricating components are reduced, and the noise and vibration levels cannot meet the requirements of high-precision equipment; in order to improve the lubrication performance under extreme conditions, solid lubricants such as molybdenum disulfide (MoS2), graphite, polytetrafluoroethylene (PTFE) and boron nitride (BN) are often added to the grease. However, the existing grease with solid lubricant additive has the following disadvantages: the dispersion stability of the solid additive is poor, which is easy to settle and agglomerate, resulting in uneven performance of the grease and shortening the service life; the oxidation resistance / anti-corrosion performance of some additives (such as MoS2) decreases in humid environment; high content of additives may cause large change in grease consistency (too soft or too hard) and poor colloidal stability (serious oil separation). Some additives (such as graphite) may increase the electrical conductivity, which is not suitable for occasions requiring insulation; for extremely low noise / vibration requirements, some solid particles may become a source of vibration. The prior art fails to synergistically optimize the type, particle size, morphology, surface treatment and ratio of base oil, thickening agent and solid additive to meet multiple harsh performance requirements at the same time. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a bearing grease and a preparation method thereof, which provides a bearing grease with excellent dispersion stability and good comprehensive performance. The method can also ensure that the solid additive is uniformly and stably dispersed in the grease system, and has good use effect.

[0004] To achieve the above object, the application provides a bearing lubricating grease, which comprises the following components in percentage by weight: base oil: 60-90%; thickening agent: 5-20%; solid additive: 1-30%, wherein the solid additive comprises component A and component B; the component A is surface-modified molybdenum disulfide nanosheet with an average particle size of 0.1-5 μm, and the component B is polytetrafluoroethylene micro powder with an average particle size D50 of 0.5-10 μm; the weight ratio of the component A to the component B is 1:1 to 1:3; auxiliary additive: 1-1.2%.

[0005] As a further setting of the application, the component A is surface-modified by one or more of silane coupling agent, titanate coupling agent or fluorine-containing surfactant.

[0006] As a further setting of the application, the component B is polytetrafluoroethylene micro particle with a specific morphology of spherical or fibrous.

[0007] As a further setting of the application, the base oil is one or more of mineral oil, poly-alpha-olefin synthetic oil, ester oil, alkyl naphthalene oil, silicone oil or polyether oil; the base oil has a kinematic viscosity at 40℃ of 30-500 cSt.

[0008] As a further setting of the application, the thickening agent is one or more of lithium-based thickening agent, composite lithium-based thickening agent, polyurea thickening agent, composite calcium sulfonate thickening agent, bentonite or organic bentonite.

[0009] As a further setting of the application, the lubricating grease has a cone penetration at 25℃ of 220-350, unit: 0.1 mm, and a dropping point higher than 200℃.

[0010] As a further setting of the application, the solid additive further comprises component C, which is selected from one or more of boron nitride, graphene and soft metal powder.

[0011] The beneficial effects of such arrangement are: the grease has excellent dispersion stability: through surface modification technology and high shear dispersion process, the dispersion uniformity and long-term storage stability of solid additives in the grease system are significantly improved, effectively preventing sedimentation and caking, and ensuring uniform and long-lasting performance of the grease; it also has excellent extreme pressure and wear resistance: through the synergistic effect of modified MoS2 and PTFE, a firm protective film is formed on the friction surface, significantly improving the load capacity of the grease, significantly improving the PB value and PD value of the four-ball test and FZG passing grade, effectively reducing the wear of the bearing under high load and impact load, and prolonging the service life of the bearing. At the same time, it has good antifriction and noise reduction performance, the addition of PTFE and BN effectively reduces the friction coefficient, and the good dispersion makes the grease have very low running noise and vibration, especially suitable for precision machine tools, motors, household appliances and other bearings with strict noise requirements; it also has wide temperature adaptability, thanks to the high-drop-point thickening agent (composite lithium, polyurea), high-viscosity-index synthetic base oil, antioxidant additive, and the thermal stability of the solid additive itself, the grease can maintain good consistency and lubrication performance at high temperatures, even at temperatures higher than 180℃ or even higher than 200℃, the base oil has low volatilization loss and excellent oxidation stability; and it has good low-temperature starting performance, the low-temperature antifriction effect of low-freezing-point synthetic oil and PTFE makes the grease have small starting torque at minus 40℃, which can ensure normal starting and running of the bearing; the grease also has good colloidal stability The application further discloses a preparation method of the bearing grease, which comprises the following steps: (a) heating part of base oil, adding thickening agent raw materials to react, and forming a grease base; (b) pre-dispersing the component A with part of the base oil or a dispersion medium to form a component A slurry; (c) adding the component A slurry and the component B into the grease base obtained in step (a) at 70-100 DEG C; (d) dispersing the mixture by using a high-shear dispersion device; (e) optionally adding auxiliary additives and uniformly mixing; (f) grinding, homogenizing, degassing and obtaining a finished product.

[0012] As a further arrangement of the method, the pre-dispersing in step (b) is performed by using a high-speed shearing machine or a ball mill; the high-shear dispersion device in step (d) is a homogenizer, a colloid mill or a three-roll mill, and the dispersion treatment time is 20-120 minutes.

[0013] The beneficial effects of such an arrangement are: in this way, the base oil is selected from 60-90% mineral oil or synthetic oil (40℃ viscosity 30-500cSt), matched with 5-20% lithium-based, polyurea and other thickening agents, and the base structure formed by reaction can be stably maintained at a cone penetration of 220-350 and a dropping point of 200℃ or higher, ensuring the structural stability and lubrication persistence in a wide temperature range. The surface-modified (silane, titanate, etc.) molybdenum disulfide nanosheet (0.1-5μm) improves the compatibility with the oil phase, and its layered structure can enhance the anti-wear and friction-reducing effect; polytetrafluoroethylene micro powder (0.5-10μm, spherical or fibrous) is compounded at a ratio of 1:(1-3), and the low surface energy characteristics are further used to reduce the friction coefficient; the two kinds of solid particles are uniformly distributed at the micro-nano level in the pre-dispersion and high shear process, avoiding the lubrication failure caused by agglomeration. The combination of such component matching and preparation process makes the lubricating grease have excellent high and low temperature adaptability, wear resistance and structural stability, which can meet the bearing working condition requirements of high load and wide temperature range, and significantly prolong the service life of the equipment. DETAILED DESCRIPTION

[0014] The first embodiment of the bearing lubricating grease provided by the application has the following formula: 78% base oil, the base oil is selected from PAO100, which has a viscosity of about 100 cSt at 40℃; 11% thickening agent, the thickening agent is selected from lithium 12-hydroxystearate; in the solid additive, 5% A component and 5% B component, the A component is selected from MoS2 nanosheet (D50≈1μm) modified by silane coupling agent KH-550; the B component is selected from spherical PTFE micro powder (D50≈5μm); the additives are selected from 0.5% diphenylamine (antioxidant) and 0.5% barium petroleum sulfonate (antirust agent) based on the total mass fraction.

[0015] The preparation method of the first embodiment is as follows, including the following steps: adding 60% PAO 100 into a reaction kettle and heating to 95℃. Add 12-hydroxystearic acid and stir to dissolve. Slowly add the previously prepared lithium hydroxide aqueous solution (stoichiometric ratio), and saponify at 100℃ for 2 hours; increase the temperature to 200℃ for high temperature refining for 15 minutes; cool to 130℃, add the remaining 18% PAO 100 for rapid cooling; cool to 90℃. Then, pre-treat the modified MoS2 nanosheet and a small amount of PAO100 taken from the total amount of the formula in a high-speed shear machine at a speed of 5000 rpm for 30 minutes to form a slurry; at 90℃, add the MoS2 slurry and PTFE micro powder into the kettle; use a homogenizer (pressure 50 MPa) to perform cycle homogenization treatment on the mixture for 60 minutes; cool to below 70℃, add diphenylamine and barium petroleum sulfonate, and stir for 30 minutes; pass through a three-roll mill for 3 times, degas, and obtain the finished lubricating grease with a cone penetration of 280 and a dropping point of >250℃.

[0016] The present application provides a second embodiment of bearing grease, the formula is 70% base oil, the base oil is selected from pentaerythritol ester, which has a viscosity of about 46 cSt at 40°C; 13.8% thickener, the thickener is selected from tetrameric urea; among the solid additives, 8% of component A and 7% of component B, component A is selected from BN nanosheets treated with fluorine-containing surfactant (D50≈0.5 μm); component B is selected from fibrous PTFE (average length≈10 μm); the additives are selected from 1% of alkylated diphenylamine (antioxidant) and 0.2% of benzotriazole (metal passivator) based on the total mass fraction.

[0017] The preparation method of the second embodiment is as follows, including the following steps: 56% of pentaerythritol ester is added to a reaction kettle and heated to 95°C. Tetrameric urea is added and stirred to dissolve. A previously prepared aqueous lithium hydroxide solution (stoichiometric ratio) is slowly added, and the saponification reaction is carried out at 100°C for 2 hours; the temperature is raised to 200°C for high-temperature refining for 15 minutes; the temperature is lowered to 130°C, and the remaining 14% of pentaerythritol ester is added for rapid cooling; and the temperature is lowered to 90°C. After pretreatment, BN nanosheets treated with fluorine-containing surfactant and a small amount of pentaerythritol ester taken from the total amount of the formula are pre-dispersed in a high-speed shearing machine at 5000 rpm for 30 minutes to form a slurry; at 90°C, MoS2 slurry and fibrous PTFE are added to the kettle; the mixture is subjected to cyclic homogenization treatment using a homogenizer (pressure 50 MPa) for 60 minutes; the temperature is lowered to below 70°C, and alkylated diphenylamine and benzotriazole are added and stirred for 30 minutes; the mixture is ground for 3 passes by a three-roll mill, degassed, and the finished grease with a cone penetration of 280 and a dropping point > 250°C is obtained.

[0018] Comparative Example 1 uses the same base oil, thickener and additives as Example 1, but does not add any solid additives.

[0019] Comparative Example 2 uses the same base oil, thickener and additives as Example 1, but only adds 10% of unmodified ordinary MoS2 powder (D50≈10 μm) and only uses conventional stirring dispersion.

[0020] The following performance tests were conducted on the greases obtained in Examples 1-2 and Comparative Examples 1-2: Cone penetration (ASTM D217): to test the consistency of the grease; Drop point (ASTM D2265): to test the high temperature resistance; Drop point (ASTM D2265): to test the high temperature resistance; Four-ball test (ASTM D2596, D4172): to test the maximum non-seizure load (PB value), to test the seizure load (PD value), and to test the wear scar diameter (WSD); FZG gear test (DIN 51354): to test the load-carrying capacity (failure stage); Friction coefficient test (SRV or high frequency reciprocating tester): to test the friction-reducing performance; Noise / vibration test: to test the running noise (dB value) and vibration speed (mm / s) on a standard bearing test rig; High temperature life test (ASTM D3336 or similar): to test the bearing running life at high temperature (e.g. 150℃, 180℃); Low temperature torque test (ASTM D1478): to test the low temperature starting and running performance; Dispersion stability observation / test: to observe the sedimentation, delamination, and to test the sedimentation amount after long-term storage (e.g. 3 months, 6 months).

[0021] The test results show that the solid additive enhanced bearing grease (Example 1-2) provided by the present application has significantly better comprehensive performance than the conventional greases without solid additives or containing only single / unoptimized solid additives, by using a specific proportion of modified MoS2 and PTFE combination and an optimized pretreatment and high-efficiency dispersion process. The grease of the present application performs outstandingly in high load-carrying capacity, low friction and wear, low noise / vibration, excellent high temperature stability and good dispersion stability, fully achieving the purpose of the present application, and is particularly suitable for harsh lubrication requirements.

[0022] The above examples are only one of the preferred specific examples of the present application, and the usual changes and substitutions made by those skilled in the art within the scope of the technical solutions of the present application are all included in the protection scope of the present application.

Claims

1. A bearing grease, characterized in that: By weight percentage, it includes the following components: base oil: 60%-90%; Thickener: 5%-20%; Solid additive: 1%-30%, wherein the solid additive comprises component A and component B; component A is surface-modified molybdenum disulfide nanosheets with an average particle size of 0.1-5 μm, and component B is polytetrafluoroethylene micropowder with an average particle size D50 of 0.5-10 μm; the weight ratio of component A to component B is 1:1 to 1:3; Auxiliary additives: 1~1.2%.

2. The bearing grease according to claim 1, characterized in that: Component A is surface modified by one or more of silane coupling agents, titanate coupling agents, or fluorinated surfactants.

3. The bearing grease according to claim 1, characterized in that: The specific morphology of the polytetrafluoroethylene particles, component B, is spherical or fibrous.

4. The bearing grease according to claim 1, characterized in that: The base oil is one or more of mineral oil, polyalphaolefin synthetic oil, ester oil, alkyl naphthalene oil, silicone oil or polyether oil; the kinematic viscosity of the base oil at 40°C is 30-500 cSt.

5. The bearing grease according to claim 1, characterized in that: The thickener is one or more of the following: lithium-based thickener, composite lithium-based thickener, polyurea thickener, composite calcium sulfonate thickener, bentonite, or organic bentonite.

6. The bearing grease according to claim 1, characterized in that: The grease has a cone penetration of 220-350 at 25°C (in 0.1 mm) and a dropping point above 200°C.

7. The bearing grease according to claim 1, characterized in that: The solid additive further includes component C, which is selected from one or more of boron nitride, graphene, and soft metal powder.

8. A method for preparing bearing grease according to any one of claims 1 to 7, characterized in that, Includes the following steps: A portion of the base oil is heated, and thickener raw materials are added to react and form a grease base. The component A is pre-dispersed with a portion of base oil or dispersion medium to form a slurry of component A; At 70-100°C, the slurry of component A and component B are added to the grease base obtained in step (a); The mixture is dispersed using a high-shear dispersion device; Optional additives may be added, and the mixture should be thoroughly mixed. The mixture is ground and homogenized, then degassed to obtain the final product.

9. The method for preparing bearing grease according to claim 8, characterized in that, In step (b), the pre-dispersion treatment is carried out using a high-speed shear mill or a ball mill; in step (d), the high-shear dispersion equipment is a homogenizer, a colloid mill, or a three-roll mill, and the dispersion treatment time is 20-120 minutes.