Railway track switch lubricating grease and preparation method thereof

Abstract

The invention discloses lubricating grease for a railway track switch and a preparation method of the lubricating grease, relates to the technical field of lubricating grease, and aims to solve the problem of developing special lubricating grease which is high in dropping point, resistant to vibration, wide in temperature range, free of heavy metal, long-acting and stable for the switch. Lithium 12-hydroxystearate and a rapid cooling process are utilized to form a crystal soap fiber network, so that the problems of failure of high-temperature melt flow and breakage of a vibration oil film are thoroughly solved; a PAO and naphthenic oil compound system is used for cooperating with composite nanoparticles, namely calcium carbonate is used for filling micro pits, sulfide generates a FeS chemical film, the fretting wear resistance and the self-cleaning performance of a switch rail and slide plate friction pair are remarkably improved, and wide-temperature-range adaptation is achieved; inactive thioester is introduced to be matched with the alkyl diphenylamine antioxidant and the succinic acid half ester antirust agent, so that the stability and the water spraying resistance of the colloid are synchronously improved on the basis of meeting the heavy metal-free environment-friendly standard, and the service life is prolonged.

Description

Technical Field

[0001] This invention relates to the technical field of lubricating grease, specifically a railway track switch lubricating grease and its preparation method. Background Technology

[0002] As a crucial turning mechanism in railway tracks, the reliable operation of turnouts directly impacts train safety. The slide plate plays a dual core role: supporting the movable switch rail and securing the stock rail. When the switch rail changes position, the sliding friction between the switch rail and the slide plate accounts for a significant portion of the turnout's switching resistance. To reduce this switching force, a common practice both domestically and internationally is to apply lubricant to the switch rail-slide plate friction pair.

[0003] However, the railway track switches served by this lubricant are exposed to extremely harsh operating conditions for extended periods, facing multiple failure challenges: First, the coupling effect of high temperature and vibration is significant. In summer, the rail temperature often rises above 70°C, coupled with more than 2,000 high-frequency mechanical vibrations per day. This causes traditional calcium / sodium-based greases, due to their low dropping point, to easily melt and flow away. Furthermore, the vibration shearing action exacerbates oil film rupture, resulting in significant fluctuations in frictional resistance. Second, fretting wear and environmental pollution are prominent issues. Small displacements between sliding pairs can easily trigger abrasive wear, and sand and dust intrusion in open-air environments further worsen the wear condition. Existing grease films are also insufficient in strength. Furthermore, its self-cleaning ability is weak, making it difficult to effectively address various issues. Thirdly, its operating temperature range is extremely wide; in frigid regions, the starting temperature can drop as low as -60℃, while the instantaneous temperature of friction hotspots exceeds 100℃. Conventional greases' viscosity-temperature properties are insufficient to meet such a broad temperature requirement. Fourthly, environmental protection and long-term performance bottlenecks are prominent. Extreme pressure agents containing heavy metals face strict environmental regulations, and active sulfur components easily corrode copper components. Simultaneously, the grease's colloidal stability is poor, leading to rapid oil separation and short service life. Fifthly, the risk of water erosion cannot be ignored; rainwater erosion can damage the grease's structural integrity, causing metal surface corrosion and accelerating wear. Therefore, there is an urgent need to develop a high-dropping-point, vibration-resistant, wide-temperature-range, heavy metal-free, and long-lasting stable grease specifically for switchgear. Summary of the Invention

[0004] To address the aforementioned problems, specifically those raised in the background section, this invention provides a railway track switch grease comprising at least the following mass percentages: 5%-10% lithium-based thickener; 30%-40% PAO; 30%-40% naphthenic oil; 0.1%-0.5% alkyl diphenylamine antioxidant; 2%-5% inorganic salt nanoparticles; 2%-5% sulfide nanoparticles; 0.5%-2% inorganic zinc salt rust inhibitor; 1%-5% sulfurized fatty acid esters and sulfurized fatty acid methyl esters; and 0.1%-1% corrosion inhibitor.

[0005] A further provision of the present invention is that the lithium-based thickener is prepared by adding 12-hydroxystearic acid to an aqueous solution of lithium hydroxide and then dehydrating and saponifying it.

[0006] A further provision of the present invention is that the inorganic salt nanoparticles are specifically calcium carbonate.

[0007] A further feature of the present invention is that the corrosion inhibitor is selected as a succinic acid half-ester type corrosion inhibitor.

[0008] A method for preparing a railway track switch grease includes at least the following steps: S1. Premix PAO and naphthenic oil to form a homogeneous saponified oil; S2. Take 60%-70% of the saponified oil, heat it to 80℃, and add 12-hydroxystearic acid to dissolve it; S3. Slowly add lithium hydroxide aqueous solution to carry out saponification reaction at 100-105℃ for 1.0-1.5h; S4. After the saponification reaction is complete, raise the temperature to 205-208℃ and keep it warm for 20-30 minutes. S5. Add the remaining 30%-40% of saponified oil as cooling oil for rapid cooling; S6. Cool to 90℃, add additives, stir, and roll through a three-roll mill three times to obtain the finished grease.

[0009] A further provision of the present invention is that the additive is composed of alkyl diphenylamine antioxidant, calcium carbonate, sulfide nanoparticles, inorganic zinc salt rust inhibitor, sulfurized fatty acid ester, sulfurized fatty acid methyl ester, and succinic acid half ester type corrosion inhibitor.

[0010] The beneficial technical effects of this invention are as follows: This grease is modified with a lithium-based thickener, namely lithium 12-hydroxystearate, which forms a crystalline soap fiber network through a rapid cooling process, completely solving the problems of high-temperature melting failure and vibration oil film rupture; it adopts a PAO and naphthenic oil compound system to synergistically composite nanoparticles, namely calcium carbonate filling micro-pits and sulfides generating FeS chemical film, which significantly improves the anti-fretting wear ability and self-cleaning ability of the friction pair between the tip rail and the slide plate, and achieves wide temperature range adaptability (-60℃~150℃); it introduces non-active sulfur esters combined with alkyl diphenylamine antioxidants and succinic acid half ester rust inhibitors, which simultaneously improve the stability and water resistance of the colloid while meeting the heavy metal-free environmental protection standards, thus extending its service life. Attached Figure Description

[0011] Figure 1 A schematic diagram of the power monitoring curve after using this grease is shown. Detailed Implementation

[0012] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0013] This invention proposes a railway track switch grease, comprising at least the following mass percentages: A 5%-10% lithium-based thickener is prepared by dehydrating and saponifying 12-hydroxystearic acid with an aqueous lithium hydroxide solution. Existing greases may experience melting failure due to their low dropping point in the high-temperature environment of railway turnouts during summer (70°C), leading to grease loss. During frequent switching operations at railway turnouts, vibration can also cause the oil film of existing greases to rupture, resulting in lubrication failure. Vibration-induced oil film rupture can cause unstable resistance during turnout switching, i.e., fluctuations in the power curve.

[0014] To address the aforementioned issues, this application employs a lithium-based thickener with a high dropping point (≥180℃). This characteristic ensures that the grease does not melt and fail in the high-temperature environment of railway turnouts at 70℃ in summer, thereby significantly extending the lubrication cycle and avoiding the inconvenience of frequent recoating due to high-temperature loss.

[0015] Meanwhile, the ribbon-like double-strand soap fiber structure formed by the lithium-based thickener can effectively absorb mechanical shear forces through elastic deformation during high-frequency switching of railway turnouts, ensuring the stability of the grease consistency. This directly solves the problem of oil film rupture caused by vibration and eliminates resistance fluctuations during turnout switching. As shown in the attached figure, the measured power curve is stable.

[0016] Lithium-based greases exhibit strong bonding strength to the liquid phase on the soap fiber surface and to the liquid phase within the crystal lattice, thus demonstrating excellent colloidal stability. Lithium, an alkali metal, has low water solubility, contributing to the strong water resistance of lithium-based greases. Lithium 12-hydroxystearate soap exhibits significant thickening ability for both mineral and synthetic oils. Compared to other calcium- and sodium-based greases, lithium-based greases require one-third less thickener and have a service life that is doubled or several times longer. Furthermore, lithium-based greases possess a low coefficient of friction.

[0017] The mixture comprises 30%-40% PAO and 30%-40% naphthenic oil. PAO is known for its excellent viscosity-temperature properties and shear stability, enabling it to form a stable lubricating film. Naphthenic oil, with its polarity, exhibits better adhesion to metal surfaces and dissolves additives more effectively. When mixed, the naphthenic oil helps PAO adhere better to the metal surface, forming a stronger and more continuous lubricating film. During frequent switching operations in switches, the metal at the joint experiences minute relative slippage, easily leading to fretting wear. The mixture of PAO and naphthenic oil may effectively suppress this wear through stronger adsorption and higher film strength.

[0018] During switch operation, dust, sand, or metal shavings may accumulate. This blended base oil has a stronger cleaning ability than ordinary base oil, helping to keep the inside of the switch relatively clean while lubricating, reducing the risk of jamming caused by foreign objects.

[0019] PAO has an extremely low viscosity-temperature coefficient, while naphthenic oils have a relatively high viscosity-temperature coefficient. The resulting mixture has a viscosity-temperature coefficient between the two. This allows the product of this application to exhibit excellent low-temperature performance over a wide temperature range of -60°C to 150°C, meeting the start-up and operation requirements of mechanical equipment in winter outdoor or specific environments. This is crucial for the stable operation of switches under complex temperature variation conditions.

[0020] 0.1%-0.5% alkyl diphenylamine antioxidant; the antioxidant mechanism of alkyl diphenylamine antioxidant is due to the conjugation system formed by the lone pair of electrons on the amino nitrogen atom and the π orbital of the benzene ring, and the inductive effect of the electron-donating group, which makes alkyl diphenylamine easy to lose hydrogen atoms on the amino group, forming nitrogen-containing free radicals that combine with peroxide free radicals to generate stable substances, thus achieving good antioxidant effect and reducing the oxidation of oils and fats.

[0021] The grease contains 2%-5% inorganic salt nanoparticles, specifically calcium carbonate. When these nano-calcium carbonate particles are added to the grease, they deform under the pressure of friction between the friction pairs during the friction process, forming a lubricating film in the contact area to achieve friction reduction and anti-wear effects. Furthermore, the inorganic salt nanoparticles are chemically stable and unaffected by indoor or outdoor temperatures, acids, alkalis, and other factors. They also isolate the friction pairs from direct contact, providing anti-wear and extreme pressure effects.

[0022] The use of 2%-5% sulfide nanoparticles is crucial in this application. Light-colored, nearly odorless sulfur-containing extreme pressure agents (such as lead sulfide, molybdenum disulfide, tungsten disulfide, zinc sulfide, and copper sulfide nano-sulfides) are essential. These nano-sulfides not only inherit the excellent extreme pressure properties of traditional sulfur-containing compounds but also exhibit significant friction-reducing effects due to their nanoscale structure, while possessing excellent thermal stability and wear resistance. Their core value lies in their ability to chemically react with the metal surfaces of the switch friction pairs (especially iron-based materials), generating an in-situ protective film of iron sulfide or ferrous sulfide. This effectively prevents critical components from scratching, sticking, or sintering under extreme loads, ensuring reliable equipment operation. Furthermore, they exhibit good extreme pressure properties and low chemical activity towards non-ferrous metals, perfectly meeting the environmental requirements of heavy metal-free greases. The mechanism of action of nano-sulfides is comprehensively reflected in three aspects: First, the "micro-bearing" effect generated by their spherical metal particles helps to reduce frictional resistance; second, under heavy load and high temperature conditions, these particles are flattened and form a protective physical film at the friction interface, significantly reducing friction and wear; and finally, the nanoparticles can effectively fill the micro-pits and damaged areas on the surface of the friction pair, playing a repair role. To comprehensively improve the overall performance of the grease, it is necessary to combine it with alkyl diphenylamine antioxidants and corrosion inhibitors. More importantly, the combined use of sulfur-containing extreme pressure agents and inorganic salt nanoparticles can produce a significant synergistic enhancement effect. This combination not only further optimizes anti-wear performance but also significantly improves extreme pressure bearing capacity, providing indispensable and powerful lubrication protection for railway track switches that withstand high loads and frequent operations.

[0023] 0.5%-2% inorganic zinc salt rust inhibitor; as zinc-containing compounds, inorganic zinc salts allow zinc to participate in the formation of a protective film with a certain hardness and toughness, acting as an isolation agent on the surface of friction pairs, reducing direct contact between metals, thereby reducing wear, extending the service life of mechanical equipment, and providing rust prevention. In addition, zinc salts also have thickening properties, helping grease to form a solid or semi-solid structure, thus improving its stability under high temperature and high pressure conditions. This maintains the stable performance of the grease during storage and use.

[0024] Inorganic salt nanoparticles, sulfide nanoparticles, and inorganic zinc salt rust inhibitors are selected to jointly achieve friction reduction and anti-wear effects. In the sulfide nanoparticles, metal ions are located at the center of the cubic crystal system, while sulfur ions occupy the corner positions of the cubic lattice. This structure gives it high stability, resulting in excellent lubrication performance and a low coefficient of friction. During friction, the nanoparticles adsorb and deposit on the surface of the friction pair, and may decompose under high temperature and high load conditions, releasing sulfur and metal elements. This generates a chemical reaction film containing Fe2O3, FeSO4, ZnO, and Fe3O4, thereby jointly producing a lubricating effect.

[0025] 1%-5% sulfurized fatty acid esters and sulfurized fatty acid methyl esters; primarily composed of inactive sulfur to avoid low-temperature corrosion (especially for copper parts), providing both oiliness and improved extreme pressure performance through the formation of a sulfurized film. Specifically, at high-temperature and high-pressure contact points (such as slide plates and switch rails), decomposition releases inactive sulfur, which reacts with the metal surface to form an iron sulfide chemical film, preventing scratches and sintering caused by direct metal contact. The polar ester groups in the molecule adsorb onto the metal surface to form a physical adsorption layer, reducing the starting friction coefficient and improving low-temperature lubrication. It also enhances the adhesion and dispersion of other solid additives (such as sulfide nanoparticles) on the friction surface.

[0026] 0.1%-1% Corrosion Inhibitor. A succinate half-ester type corrosion inhibitor is selected. Its unique chemical structure makes it a special corrosion inhibitor with excellent anti-emulsification properties, and its corrosion prevention performance is superior to standard calcium sulfonate and barium sulfonate. A crucial prerequisite for a rust inhibitor to exert good rust prevention performance is strong adsorption on the metal surface, especially the strong chemical adsorption of its polar groups. Therefore, its excellent rust prevention performance is mainly due to the presence of two carboxyl groups, providing numerous sites for chemical adsorption on the metal surface, resulting in strong chemical adsorption and easier formation of an adsorption film. Simultaneously, some carboxyl groups can form intermolecular hydrogen bonds. Under the combined effect of these two aspects, the rust inhibitor molecules can form a relatively dense adsorption film on the metal surface. Furthermore, the oil-soluble long carbon chain allows the rust inhibitor molecules to fully wet the base oil environment, resulting in a good effect of isolating the metal surface from H2O and O2.

[0027] A method for preparing a railway track switch grease includes at least the following steps: S1. Premix PAO and naphthenic oil to form a homogeneous saponified oil, providing a uniform dispersion environment for 12-hydroxystearic acid; S2. Take 60%-70% of the saponified oil and heat it to 80℃. Add 12-hydroxystearic acid to dissolve it. 80℃ is the suitable dissolution temperature for 12-hydroxystearic acid, ensuring that it melts completely and disperses evenly in most of the base oil, forming a homogeneous reaction precursor. This creates the necessary conditions for the next step of adding lithium hydroxide to carry out a uniform and thorough saponification reaction.

[0028] S3. Slowly add lithium hydroxide aqueous solution to carry out the saponification reaction at 100-105℃ for 1.0-1.5h. This step is the core chemical reaction, forming the grease skeleton structure. Because this saponification process is a dehydration reaction, the actual measured complete saponification reaction takes about 1.0h. S4. After the saponification reaction, raise the temperature to 205-208℃ and hold for 20-30 minutes. Holding at 205-208℃ drives a crucial crystal transformation of the 12-hydroxystearate lithium soap, growing it from a primary disordered state into long-chain, tough, and highly cross-linked β-crystalline fibers, forming a strong and stable three-dimensional network framework structure. This process significantly increases the dropping point of the finished grease, ensuring it does not soften or leak under harsh operating conditions such as high summer temperatures faced by railway equipment. Simultaneously, the well-developed soap fiber network greatly enhances colloidal stability and water resistance, effectively "locking in" the base oil and resisting rain and humid environments. Furthermore, this structure provides the grease with excellent mechanical stability, enabling it to withstand the vibrations and impacts from frequent switch operations and maintain stable consistency. Finally, this step also optimizes the consistency and appearance of the grease and completely removes residual moisture, laying a crucial structural foundation for the finished grease to achieve high reliability, long service life, and low maintenance in harsh railway application environments.

[0029] S5. Add the remaining 30%-40% of saponified oil as cooling oil for rapid cooling. During the high-temperature refining stage, lithium soap molecules are in a molten and disordered state. If cooled slowly, the soap molecules will rearrange sufficiently to form a coarse, low-crosslinking soap fiber structure with a diameter greater than 1μm. This structural characteristic will lead to two problems: first, the strength of the thickener skeleton will decrease, resulting in a decrease in the mechanical stability of the grease, manifested as a significant increase in the cone penetration after shearing; second, the adsorption capacity of the base oil will weaken, directly causing an increase in the oil separation rate.

[0030] In this application, a rapid cooling process is used, which instantly freezes the movement of soap molecules, thereby forming a dense, interwoven nanoscale soap fiber network. This microstructure can significantly improve the performance of lubricating grease: by increasing the specific surface area of ​​the soap fibers, it enhances the adsorption capacity of the base oil, thereby improving structural stability; at the same time, the dense fiber network can effectively improve shear resistance.

[0031] S6. Cool to 90℃, add additives, stir, and roll three times using a three-roll mill to obtain the finished grease. To effectively protect the activity of heat-sensitive components, precise control of the addition temperature is necessary: ​​the decomposition rate of antioxidants (alkyl diphenylamine) increases significantly above 100℃; sulfide nanoparticles are prone to oxidation and failure above 120℃, and adding them at 90℃ effectively avoids surface passivation; sulfide fatty acid esters should be added at low temperatures to prevent off-odors and discoloration caused by sulfur bond breakage. Simultaneously, at 90℃, the viscosity of the saponified oil (a mixture of PAO and naphthenic oils) decreases, providing a low-resistance dispersion environment for calcium carbonate, sulfide, and other nanoparticles, thereby optimizing dispersion kinetics and inhibiting particle aggregation.

[0032] The additive consists of alkyl diphenylamine antioxidant, calcium carbonate, sulfide nanoparticles, inorganic zinc salt rust inhibitor, sulfurized fatty acid ester, sulfurized fatty acid methyl ester, and succinic acid half-ester type corrosion inhibitor.

[0033] Appendix Figure 1 The curve showing the relationship between the total power of the turnout and the turnout current versus time shows that the stability of the curve of the switch rail-slide plate friction pair treated with this grease is effectively improved, and the fluctuation phenomenon of the turnout switching resistance is eliminated.

[0034] Based on the test data and observed phenomena in the table below, the condition of this lubrication system is assessed as follows: 1. Visual inspection: The oil film is evenly and completely distributed, the surface is smooth and free of impurities, no resinous hardening or rust marks are found, and the lubrication coverage is good. 2. Physical properties: The oil film thickness meets the technical specifications, and the touch test shows clear fingerprint residue, indicating that the adhesion performance meets the standards; 3. Protective performance: After water spray test, obvious bead-like condensation forms on the surface of the slide plate, which has excellent hydrophobic properties and good waterproof effect; 4. Long-term effectiveness verification: After 7 days of aging testing, the system reached optimal lubrication conditions, maintaining a clear and stable oil film with a thickness sufficient for dynamic lubrication. Turnout operation parameter monitoring showed a smooth operating curve and a significant reduction in drive power compared to the initial state, eliminating the need for supplementary lubrication. The effective lubrication cycle is expected to be extended by more than 7 days.

[0035] project Experimental group (this product) Control group (commercially available common lithium-based ester) Infrared Lithium-based thickener, calcium-containing additive lithium-based thickener Drip 190 182 Working cone penetration 447 286 Flow pressure 1200mba 2300mba SRV friction coefficient 0.14 0.26 Waterproof Level 0 Level 1 Salt spray test Non-corrosive Corrosion Level 1 Rain test (Housing Law) The grease was retained well in the mold, and the layer thickness was good. A small amount of grease remaining in the mold is good, reducing the layer thickness. Weather resistance test A thick, viscous oil film was formed, and no corrosion was observed in the lubricated area. Reduced oil film, corrosion in lubricated areas Therefore, this grease is significantly superior to commercially available ordinary lithium-based grease in terms of high-temperature stability, low-temperature pumpability, and friction reduction performance, completely solving problems such as high-temperature melting flow and frictional resistance fluctuations in switchgear.

[0036] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to those processes, articles, or apparatus / devices.

[0038] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A railway track switch grease, comprising at least the following percentages by mass: 5%-10% lithium-based thickener; 30%-40% PAO; 30%-40% naphthenic oil; 0.1%-0.5% alkyl diphenylamine antioxidant; 2%-5% inorganic salt nanoparticles; 2%-5% sulfide nanoparticles; 0.5%-2% inorganic zinc salt rust inhibitor; 1%-5% of sulfurized fatty acid esters and sulfurized fatty acid methyl esters; 0.1%-1% corrosion inhibitor.

2. The railway track switch lubricant according to claim 1, characterized in that: The lithium-based thickener is prepared by dehydration and saponification of 12-hydroxystearic acid with an aqueous solution of lithium hydroxide.

3. The railway track switch lubricant according to claim 1, characterized in that: The inorganic salt nanoparticles are specifically calcium carbonate.

4. The railway track switch lubricant according to claim 1, characterized in that: The corrosion inhibitor is selected from succinic acid half-ester type corrosion inhibitors.

5. The method for preparing a railway track switch grease according to claim 1, characterized in that: It should include at least the following steps: S1. Premix PAO and naphthenic oil to form a homogeneous saponified oil; S2. Take 60%-70% of the saponified oil, heat it to 80℃, and add 12-hydroxystearic acid to dissolve it; S3. Slowly add lithium hydroxide aqueous solution to carry out saponification reaction at 100-105℃ for 1.0-1.5h; S4. After the saponification reaction is complete, raise the temperature to 205-208℃ and keep it warm for 20-30 minutes. S5. Add the remaining 30%-40% of saponified oil as cooling oil for rapid cooling; S6. Cool to 90℃, add additives, stir, and roll through a three-roll mill three times to obtain the finished grease.

6. The method for preparing a railway track switch grease according to claim 5, characterized in that: The additive consists of alkyl diphenylamine antioxidant, calcium carbonate, sulfide nanoparticles, inorganic zinc salt rust inhibitor, sulfurized fatty acid ester, sulfurized fatty acid methyl ester, and succinic acid half-ester type corrosion inhibitor.

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