Development and application of graphite materials as lubricants

With the development of science and technology and the deepening of research work, graphite has appeared in the form of various derivatives, such as graphite fluoride, intercalated graphite of metal compounds, expanded graphite, etc., and has been well applied in lubrication practice.
1、Dry powder graphite lubricant
The production of graphite powder can be divided into mechanical pulverization and airflow pulverization. Airflow pulverization can obtain fine graphite powder (such as 1μm size). Further, the particle size is uniform and the product purity is high, but it is difficult to obtain flaky graphite particles. Mechanical pulverization, particularly wet mechanical pulverization, or use of a dispersant can obtain a flaky graphite powder, but the production efficiency is low.
With the good film-forming property of graphite powder, people have used direct rubbing, roller coating and other methods to make the graphite powder form a dry powder film on the surface of the lubricated workpiece to achieve lubrication of low-speed light-load operation equipment. The flying powder of graphite powder can also be used. Achieve powder splash lubrication of enclosed gear reducers.
The mixing of graphite powder with gasoline or alcohol can be applied to the lubrication of the fire wire roller of bridge crane, which not only ensures the electric conductivity of the roller, but also improves the lubrication conditions between the wheels and shafts, thus increasing the service life of the fire wire roller by three times. A series of SS film-forming lubricating pastes developed in our country have been successfully applied to vacuum bearings and gears by making dry lubricating film from graphite and other multicomponent powders with binder.
In the manufacture of seamless steel tubes and the lubrication of steel wire dry drawing production, the multi-component compound composed of graphite prevents the sintering under severe conditions such as high temperature and heavy load of 1000 °C, ensuring the normal production. . In the high-alloy steel and nickel alloy steel plastic processing lubrication, if the low melting point metal Pb, Zn, Sn, etc. are used as the lubricant, the boundary infiltration of the soft metal abrasive grains can occur, which leads to the stress damage of the Taijin products; S, CI, F elements and H2O lubricants will cause corrosion of the alloy. The high-temperature lubricant based on graphite is free of soft metals, sulfur and halogen, and can withstand high temperatures of 1100 °C. At the same time, the shortage of the above-mentioned lubricants is avoided, and the harm to the working environment is alleviated.
Fluorinated graphite powders are also used as solid lubricants in many applications. Japan Carbon Corporation is the first manufacturer to develop fluorinated graphite. It used fluorinated graphite to improve the sliding properties of the company’s mechanical carbon. Sumitomo Co. of Japan used graphite fluoride as a solid lubricant to coat the surface of molten iron cooling equipment coated with copper or nickel, greatly reduces the friction coefficient and greatly reduces the traction power.
2、Water-based graphite lubricant
The water-based graphite lubricant is a water-based graphite colloidal dispersion system composed of graphite fine powder, binder, diffusing agent, coating film reinforcing agent and the like. In water-based graphite lubricants, the content of graphite particles is generally 20 to 40%; the binder is 4 to 15%, and the stabilizer is 0.5 to 1.0%. The test results of friction coefficient of several water-based graphite lubricants show that the friction coefficient of water-based graphite lubricants is maintained between 0.02 and 0.20 at high temperatures from room temperature to 700 °C. Therefore, water-based graphite lubricants are widely used in the lubrication of high temperature processing such as die forging, drawing and hot rolling of metals.
In the die forging processing lubrication of vehicle steel, the water-based graphite lubricant can increase the life of the mold by more than one time and increase the demolding efficiency by more than twice as compared with the heavy oil lubricant. Extrusion of 6063 aluminum alloy; using LWH-series water-based graphite lubricant to solve the problem of bonding between extrusion pad and pressure residue generated by hydrocarbon oil lubricant, and avoiding the disadvantages of excessive smoke and polluting labor environment . In the multi-mode drawing lubrication process of fine tungsten wire, the application of the fine water-based graphite lubricant developed improves the graphite emulsion on the surface of the tungsten wire and the surface of the mold compared with the water-based graphite emulsion of S-0. Adhesion makes the utilization rate of multi-mode brushed diamond die holes increase by 4 to 5 times, reaching the advanced level of similar products.
In the plastic working of the metal, the water-based graphite lubricant is uniformly sprayed on the surface of the mold cavity to thereby lubricate the workpiece. In general, this uniform water-based graphite film is suitable for high or low deformation speed, so it is beneficial to promote the flow of metal, reduce the tendency of sticking the mold, and has the resistance to withstand large temperature gradients and reduce the generation of flames and smoke during processing, extending mold life and increasing production efficiency. Therefore, water-based graphite lubricants are worthy of further development and application.
3、Oil-based graphite lubricant
The addition of a solid lubricant to the grease is an important means to improve the antifriction and antiwear properties of the grease. As a filler for grease, graphite effectively improves the pressure and wear resistance of the grease film, and is especially suitable for high-load mechanical equipment and lubrication of railway wheel and rail. Therefore, graphite is often combined with high-viscosity mineral oil to form a fat, which has a wide variety and a wide range of applications.
As an additive to lubricating oil, graphite is often compounded with engine oils and organic additives to prepare oil-based graphite lubricants suitable for various working conditions. In the processing of deep drawing parts of stainless steel, due to the large degree of deformation, it is decided to use oil-based graphite lubricant: soap emulsion + oil oleic acid + graphite powder composite formula for drawing martensite stainless steel Products. The oil-based graphite moisturizer formed by graphite or combined molybdenum disulfide is also used for lubrication and cooling of warm die forging of light alloys (aluminum alloy, magnesium alloy).
Gear lubrication of bridge cranes and hot strip mills, when using graphite and organic additives, not only reduces friction, but also increases load. Compared with SP gear oil, it can save energy for bridge cranes 3%~9%, so that the strip hot rolling mill energy saving 3.1 ~ 4.18.
Graphite has been used in vehicle engine oil, and many kinds of oil-based graphite additives have been developed, which can save about 5% of fuel oil. At the same time, graphite has played an obvious role in reducing exhaust emissions, reducing oil consumption, prolonging oil change cycle and improving engine life.
The key to the application of oil-based graphite lubricants is the dispersion stability of graphite particles in lubricating oil. Therefore, the ultrafine graphite particles and the use of dispersants are very important, especially for vehicle engine oil.
Author: Zhou Qiang, Xu Ruiqing