The compaction of some solid lubricant materials

Samples of −100 mesh powders of stearic acid, palmitic acid, sodium stearate, potassium stearate, lithium stearate, calcium stearate, magnesium stearate, zinc stearate, zinc oleate, boric acid and a synthetic wax, were compacted and the die reaction determined using a “moving-die” technique. The shear strength of the compacts measured in a punch penetration test, with the exception of boric acid and zinc stearate, was independent of the compaction pressure above 500 kg/cm2. Solid discs of stearic acid and palmitic acid possessed the same shear strength as the powder compacts; discs of synthetic wax and zinc stearate gave higher values than the corresponding powder compacts. Values of shear strength calculated from measurements of die reaction were higher than values obtained in the shear strength test, but show good agreement with the results calculated by other workers from sliding friction experiments. Shear strength values for compacts of boric acid and discs of synthetic wax, talc crystal, and graphite, indicate that these materials are unlikely to be such good lubricants as stearic acid or its salts.