Friction is the process in which the sliding motion of the interacting surface is subject to several influencing parameters to produce resistance. Most people think that surface roughness is the main factor in friction. However, when considering that the actual contact area may be less than 1% of the surface contact area, the actual roughness becomes less important. The cause of friction should be the result of bonding at the molecular level of rough contact.
In the case of insufficient lubricating film thickness on the metal surface, rough contact points may cause cold welding, which is a prerequisite for adhesive wear. The adhesion on these rough spots undergoes a reinforcement hardening process. Therefore, the shear point generally occurs at the level below the rough contact point where the metal is not strengthened. As metal shears, the rough tip is either transferred to another surface or broken down into an abrasive particle.
Adhesion is generally considered the initial form of mechanical wear. In addition to the wear of the abrasive particles, there are external sources of wear, causing the abrasive wear to become more destructive. This form of wear is called three-body wear. The two-body wear is caused by sharp surface contact points produced by cutting or planing.
Surface fatigue occurs during rolling contact. The fatigue mechanism comes from the formation of cracks and growth inside the working surface or surface layer. High stress under surface rolling conditions will cause fatigue wear.
2. How to control friction and wear?
The friction and wear control additive is mixed with a small amount of base oil, which has the polarity to promote the adsorption of the metal surface. Due to the conditions of interaction, these adsorption forces chemically react with the surface, which is inversely proportional to the conditions that produce sufficient oil film thickness: higher pressure and higher temperature.
When the machine surface interacts with higher pressure and temperature, the additive will reduce the impact of metal-to-metal contact (wear) by creating a more ductile initial molecular layer on the machine surface. These friction control layers directly reduce the contact process The shear strength becomes a "victim". The initial layer can release the force of the weaker molecular bond of the lubricant and the rough boundary conditions between the metal and the metal to produce a strong bond, thereby reducing friction. The formation of low-shear-strength films is also affected by the type of basic raw materials and mechanical surface metallurgy.
There are three types of lubricant additives that help reduce friction and control wear. They are friction modifiers, anti-wear additives, and extreme pressure additives.
When poorly lubricated or poorly lubricated machine surfaces are in sliding contact, the physical molecular interaction at the actual contact pressure point needs attention. Under the action of such molecules on the surface of the machine, the boundary conditions will be constrained by many physical and chemical principles. When additive compounds are selected for oil film strength protection, attention must be paid to the balance of machine surface oxidation, corrosion, chemical absorption, and other chemical reactions.
