Stable micro-feeding of fine powders using a capillary with ultrasonic vibration

Stable micro-feeding of fine powder based on the ultrasonic vibration feeding system is studied in this paper. The excitation source was directly contacted with the capillary in the ultrasonic powder-feeding device, which can transmit mechanical energy to the capillary directly. The capillaries with different structures were tested to determine the proper structure for stable feeding. The capillaries are suitable for stable feeding when the cone angle θ was in the range of 30°–60°. The powders in the pipe may exhibit three different types of structures: blocking, plugging and arching. The arching formed near the nozzle of the pipe was necessary for a stable feeding process. Amplitude of the pipe was another factor which influenced the stable feeding. The powder flowing out the capillary may undergo a process of slightly unstable flow, stable flow and super unstable flow as the amplitudes of the pipe gradually increased. The amplitudes of the pipe can be calculated after the amplitudes of the transformer have been measured. The proper amplitudes of pipe nozzle for stable feeding are in the range of 9.6 to 18 μm in the experiments. Some desired patterns were deposited, indicating the ultrasonic vibration feeder system could satisfy the requirement of stable feeding.