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Graphite powder has a flaky crystal structure and excellent lubricity. And also has good electrical conductivity, thermal conductivity, anti-wear, extreme pressure, temperature resistance (temperature up to 450 ℃) and chemical stability, and other characteristics, so graphite powder is widely used in the machinery industry to make a variety of lubricants.
As lubricant, the graphite powder fine particles are evenly distributed in water, oil, or other media to form a stable gel. It can be directly applied to the parts that need lubrication by rubbing, dipping, or spraying. It can be added to various lubricant and used in combination. It is in contact with the metal surface, not only can form a robust lubricating film, but also improve the wetting performance of the metal surface to other lubricant oil, thereby maintaining long-term lubrication. Besides, because graphite powder exists as pleasant particles, it is easy to penetrate closely matching sliding or rotating parts and play a functional role in lubrication.
Graphite has a hexagonal crystal structure. Because the bonding force between the planes parallel to the base plane is weak, these crystals are natural to shear between the aircraft, that is, the friction is small, and they can support the load perpendicular to the base plane. It has the best properties as a dry lubricant.
Graphite powder, as dry lubricant, can be splash-lubricated in the form of dry powder. It can be used as an additive to make water and oil agents. It can also be combined with other materials to form a composite material for lubrication in transmission — wear-resistant parts.
Graphite powder lubricant can be divided into three types: water agent, colloidal graphite and micronized graphite powder, and its usage is as follows:
(1) Particle graphite powder
Apply directly to the rotating or sliding part, or mix it into the medium, such as kerosene, gasoline or light mineral oil, and phenolic resin or water glass, and spray or dip the part to be lubricated or covered. It depends on needs, generally 10% ~ 20%.
The graphite powder is put into the gearbox, and the powder flies up due to the stirring action of the gear and enters into various friction parts to form dust lubrication. Dust-type lubrication has been applied in the transmission and rear axle differential gearboxes of automobile chassis and has achieved absolute results.
Dust-type lubrication is relatively simple, as long as the solid lubricant powder is poured into the gearbox. During use, the solid lubricant film can be replenished continuously and automatically. And it can run for a long time without manual film protection, and maintenance is relatively simple.
(2) Oil lubricant
It can be directly added to the lubricating oil used in the original lubricating system and used in combination. The amount of use depends on the needs, generally about 2 ~ 10%.
When graphite powder is dispersed in lubricating oil, its lubricity depends not only on the lubricating properties of graphite but also on the performance of the lubricating oil. The test proves that the lubricating film composed of stone tools has the best lubricating performance if it contains 7 to 8 times the amount of lubricating oil of the stone tools. The particle size of graphite dispersed in lubricating oil should be comprehensively considered according to the requirements of use. Generally, 4 to 10 μm particles are often used, because the abrasive wear of 4 to 5 μm is the smallest, and the abrasive wear of 1 μm or less and 150 μm or more is the largest.
(3) Water agent
Graphite powder is directly added to water or emulsified, cutting fluid for use. The amount used depends on the needs, generally about 5-10%.
A suspension of graphite powder dispersed in water, oil, or solvents, commonly used as a lubricant release agent for metal thermoplastic pressure processing. As a friction modifier, graphite can increase the bearing capacity, wear resistance and heat resistance, etc., and has excellent high-temperature adhesion. Graphite milk made of graphite with an average particle size of 10 μm is applied to hot forging, which can be used above 500℃and can be used for forging to 800 ℃ for a short time.
For example, graphite milk is essential in the drawing of tungsten wires. The quality of graphite milk directly affects the quality of tungsten wire (consistent wire diameter and surface defects, etc.) and the wear of drawn diamond die holes. Before pulling, the graphite emulsion is coated on the surface of the drawn tungsten wire in advance and then passed through a heating furnace (the furnace temperature is between 500 and 850 ° C) at a speed of 30 to 70 μm/min. Then the drawing process is completed through a diamond die hole.