Solid Lubricants as Friction Modifi ers 175
- Plastic fl ow. The lubricant should not undergo plastic deformation when loads are applied
directly perpendicular to the direction of motion. The solid should be able to withstand
the intimate contact between the mating surfaces so that a continuous fi lm of lubrication is
maintained.
This chapter attempts to guide the formulator toward making successful choices in solid lubricants.
It briefl y summarizes the physical and chemical properties of the solid lubricant and discusses the
merits of each type of major lubricant as well as the recommended application. The information will
assist in understanding the chemistry of the lubricant and its general mechanism of lubrication.
6.2 SOLID LUBRICANT PROPERTIES
6.2.1 GRAPHITE
Graphite is most effective for applications involving high-temperature and high load-carrying
situations. These capabilities make graphite the solid lubricant of choice for forging processes. Solid
lubricants such as MoS 2 will oxidize too rapidly to be of any value at the typical hot-forging tem-
perature range of 760–1200°C, although MoS 2 has a greater lubrication capability than graphite.
FIGURE 6.2 Surface asperities.
FIGURE 6.3 Burnished lubricant.