Several additives to improve the extreme pressure capacity of grease

2020-06-08 22:36:25 0


This is a class of widely used additives. Commonly used additives are divided into compounds containing S, P, Cl and other elements according to the composition; various heavy metal chalcogenide compounds and other inorganic and organic solid lubricants; various metal fillers and so on. According to its mechanism of action, it can be divided into reactive type and layered crystal lubrication type. The reactive type includes two types of reaction between the additive and the metal surface to form a protective film and the additive itself decomposing to form a protective film. Generally, the reactive additives should be added after the fat is cooled to avoid the decomposition and failure of the additives at high temperature, and can also reduce the influence of the additives on the structure and performance of the fat. Most fillers are layered solid lubricants, such as graphite, MoS2, etc.

  Anti-wear extreme pressure additives can be divided into anti-wear agents, extreme pressure agents and anti-friction wear agents according to their functions. Anti-wear agents mainly play a role in reducing friction and wear. The extreme pressure agent is mainly to prevent the metal from sintering or to improve the bearing capacity of the grease. The anti-friction wear agent mainly inhibits the occurrence of oxidation, vibration wear and friction rust on the fretting wear surface. Phosphorus compounds are generally wear-resistant, while sulfur and chlorine compounds are not effective for reducing wear, but are effective for improving extreme pressure and improving load resistance. The combined chlorine and phosphorus compounds or phosphorus and sulfur compounds are both wear-resistant and Extreme pressure. In order to improve the antiwear and extreme pressure properties of the grease, two or more additives may be used in combination. However, attention should be paid to the problems of polar compounds softening grease and corroding copper.

  According to the solubility in the base oil, extreme pressure antiwear agents are divided into oil-soluble and non-oil-soluble types. Sulfur, phosphorus, chlorine, molybdenum and other organic compounds are oil-soluble extreme-pressure anti-wear additives, such as polysulfide isobutylene, zinc dialkyl dithiophosphate, dialkyl dithiocarbamate, dialkyl disulfide Molybdenum oxysulfide ([(RO)2PS2]2MoOxSy), dialkyl disulfide carbamate sulfide molybdenum ([R2NCS2]2Mo2OxSy), etc.

A few non-oil-soluble anti-wear extreme pressure agents are organic solid lubricants, most are inorganic solid lubricants, such as polyaryl sulfide and dicalcium phosphate compound additives, Cu[(C6H11NO)n](OH)2, MCA( Melamine), MoS2, CeF3, SbSbS4, Cu, etc.

  Dialkyl dithiocarbamate is a one-dose, two-purpose additive. It has both anti-oxidation, anti-wear and extreme pressure resistance, and is a general-purpose multi-effect additive. Such additives have been successfully used in many greases, engine oils and industrial lubricants. Its bivalent and trivalent metal salts, such as zinc and cadmium salts, are mainly used as antioxidants, and also have anti-wear extreme pressure properties. Zinc salt can also act as a metal deactivator. Molybdenum, lead and antimony salts are mainly used as anti-wear extreme pressure agents and also as antioxidants. Trioctylmethyl thiomolybdate quaternary ammonium salt extreme pressure agent increases the Timken OK load of polyurea fat (136 ~ 276kg), but it is not effective when used in soap grease. The reaction product of alkenyl succinic anhydride and ethanolamine can improve the fretting wear resistance of polyurea or lithium grease. In lithium-based greases, lanthanum oxide has good abrasion resistance extreme pressure, and has a good synergy with molybdenum alkyl dithiocarbamate. The polycondensation product of fatty dibasic acid and fatty dihydric alcohol (relative molecular weight 500-5000) is an excellent anti-wear extreme pressure agent.

  Borate or borate is a new type of anti-wear extreme pressure agent. Dispersing agent (such as anionic surfactant petroleum sulfonate) is used to disperse very fine borate in mineral oil. The borate is non-crystalline small balls with an average diameter of 01μm. It forms a microsphere film on the metal surface. The microsphere film has one to several layers, which can play a good lubricating role and improve the anti-wear extreme pressure performance.


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