THE INFLUENCE OF THE TIME OF APPLICATION OF CONTACT PRESSURE ON PARTICLE ADHESION TO A SUBSTRATE SURFACE

A centrifuge method has been employed to investigate the effect of the time of application of the preliminary pressing force on particle adh esion to a steel surface. The geometric median adhesion forces obtaine d for four powders (i.e. polyethyleneglycol (PEG) 4000, pregelatinised starch (Starch 1500), spray-dried lactose and calcium carbonate) incr eased with the length of time the adhering particles were subjected to the applied load before detachment was assessed. A more substantial i ncrease in the median adhesion force was observed for the harder spray -dried lactose than for the softer PEG 4000 and for Starch 1500. This may be due to the inherent brittle structure of the lactose particles, rendering the solids more susceptible to the applied pressure at prol onged durations, which consequently gave rise to greater change in adh esion. On the assumption that the deformation occurring in the adhesio n was predominantly plastic, the phenomenon of strain hardening was fo und to take effect sooner in a harder solid than in a softer material.