To elaborate on the additives of gear oil in detail is too lengthy, we will discuss it separately in the future. In this series, a brief overview of additives for gear oil will be provided.

Extreme pressure and anti-wear agents: It is unrealistic to completely distinguish between these two concepts, as there is no clear boundary between them. They can even be collectively referred to as load additives along with friction improvers. However, extreme pressure and anti-wear agents are easier to understand in English. In boundary lubrication, when the metal surface is only subjected to moderate loads, if there is an additive that can be adsorbed on the metal surface or wear violently with the metal surface, this additive is called an anti-wear additive. When the metal surface is subjected to high loads, a large amount of metal surface comes into direct contact, generating a large amount of heat, and the film formed by the anti-wear agent is also destroyed, no longer protecting the metal surface. If there is an additive that can react chemically with the metal surface to form a chemical reaction film, it can lubricate the metal surface, prevent scratches and even welding. This most demanding boundary lubrication is usually called extreme pressure lubrication, and this additive is called extreme pressure additive.

Its varieties cover a wide range, including typical sulfur-containing compounds, phosphorus containing compounds, chlorinated compounds, and metal containing compounds. Here we will focus on chlorine containing extreme pressure agents, including chlorinated paraffin, chlorinated fatty acid esters, cyclic chlorides, etc.:

Chlorine containing extreme pressure agents generate metal chlorides such as FeCl2 and FeCl3 on the contact surface with metals. Iron chlorides have a layered structure, low critical shear strength, and low friction coefficient, but their heat resistance is low. They fail at 300 ℃ -400 ℃ and decompose into HCl and Fe (OH) 2 when in contact with water, losing their lubricating effect and causing chemical wear and corrosion. In addition, chlorides are toxic and their use is restricted. Currently, gear oils containing chlorides have been phased out, except for metalworking oils that are still used.

In vehicle gear oil, CRC L-37 is a low-speed high torque gear bench test, and its tooth surface damage is mainly surface fatigue pitting and peeling. Preventing metal surface fatigue is the main function of phosphorus containing extreme pressure agents. For example, dibutyl phosphate (T304) is very effective in preventing surface fatigue of metals. However, it also has the disadvantage of easy rusting. Therefore, how to use T304 well in the formula is a very artistic thing.

We can think of phosphating treatment on metal surfaces in the materials industry, which aims to improve the corrosion resistance of metals. Although the phosphating film is thin, it is a non-metallic non-conductive isolation layer that can transform excellent conductors on the surface of metal workpieces into poor conductors, suppress the formation of micro batteries on the surface of metal workpieces, and effectively prevent metal corrosion. ② Improve the adhesion between the metal substrate and the coating. On the one hand, the phosphating film is a tightly integrated structure with the metal workpiece. On the other hand, the phosphating film has porosity, allowing other coatings to penetrate into these pores and tightly bond with the phosphating film, improving adhesion. ③ Provide clean surfaces. Phosphating film can only grow on the surface of metal workpieces without rust layers. Therefore, metal workpieces treated with phosphating can provide a clean, uniform, and rust free surface. ④ Improve surface friction performance.

In fact, phosphorus containing compounds form phosphate films with metal surfaces at certain temperatures and pressures, so conversely, phosphate is a corrosion inhibitor. The antagonistic effects of extreme pressure anti-wear and corrosion inhibition are fully demonstrated in phosphorus containing compounds, and solving such contradictions is the success of formula development. Ha, philosophy is the summary and generalization of natural sciences, so what seems like a simple lubricant is endless fun!