Dose uniformity of fine powders in ultrasonic microfeeding

Ultrasonic microfeeding can be used in solid freeforming and pharmaceutical dosing. In this work, dose uniformity was studied because it is one of the important factors in evaluation of microfeeding. The experiments were carried out in a computer-controlled microfeeding system. The powders used were H13 tool steel, tungsten carbide (WC) and glass beads. The experimental results show that the minimum dose mass for these powders in a 0.2 mm diameter nozzle is close to 0.1 mg, 14 mu g and 16 mu g respectively. The probability distributions of relative mean dose mass deviation can be divided into four categories: single symmetrical peak, single positive skewed peak, single negative skewed peak or double peaks. Because the signal amplitude voltage and oscillation period are the two important factors influencing dose mass, the effects of these two factors on standard deviation, relative standard deviation and probability distribution were studied and discussed. (c) 2007 Elsevier B.V. All rights reserved.