Some studies of friction and lubrication using an instrumented tablet machine†

Abstract

Samples of crystalline aspirin, hexamine, and sodium chloride, and a granulation of hexamine were compressed on an instrumented tablet machine. Further samples of these materials, together with samples of sucrose and sucrose granulation, were lubricated with 2% magnesium stearate −100 mesh powder and compacted under similar conditions. The effect of magnesium stearate on die wall friction depends on the ease of deformation of the base particles. For the materials used there is a linear relationship of the form Fa = kd(Pm.A) and a linear relationship exists between Fe and Fd up to the point where Fe becomes constant. Granulations required larger ejection forces at a given pressure than the corresponding crystalline material, particularly when the materials were lubricated; constant values of Fe were associated with compaction pressures at which the density of the ejected tablets became maximal. Values of Fe for tablets of unlubricated sodium chloride and hexamine granulation depend on particle size; the size of other materials used caused no such effect. Lubrication eliminated this size effect.