The effect of dosator nozzle wall texture on capsule filling with the mG2 simulator

The effect on capsule filling, using an mG2 simulator, of the surface texture of the bore of the dosator nozzle has been investigated for size fractions of lactose. Since the angle of powder-wall friction between the powder and the nozzle cannot be readily measured insitu, this was determined using flat plates with similar surface textures fitted into a Jenike shear cell apparatus. The problems of reproducing surface textures on both types of surface are discussed and a lapping process employed as the most suitable method. Angles of wall friction for the nozzle surfaces were extrapolated from the values obtained from flat plates of similar roughness. Capsule filling experiments, using the mG2 simulator, showed the three resurfaced nozzles produced more uniform fill weights with smaller measured compression and ejection stresses than an untreated nozzle surface. One lapped nozzle surface produced a slightly greater improvement than the others. This supports the concept of an optimum angle of wall friction for powder retention (and hence uniformity of fill) with a minimum of applied compression stress.