(150a) A New Measurement System to Evaluate Powder Flowability Based on Vibrating Capillary Method

The flowability of powders is of great industrial interest in particle design and quality control as well as in various bulk handling processes such as feeding, transportation, storage, mixing, and many others. For evaluating the flowability of powders, several common methods have been used, e.g. Carr's flowability index, flow factor measured with a Jenike shear tester, and flowability determined with a Hall-flowmeter. The Hall-flowmeter has an advantage of evaluating the actual flow; however, the method is restricted to powders flowing by gravity, and the evaluation factor is only the time required for a certain quantity of powder to flow through the funnel. Therefore, the development of a new method for evaluating the flowability of powders that do not flow easily by gravity is expected. From the viewpoint of highly-sensitive measurement, a small testing device is required and external forces overcoming the adhesive forces have to be continuously applied so as to make flow possible. Furthermore, well-defined evaluation factors are needed. A method using a vibrating capillary tube was developed to feed a small amount of fine powder and to control the mass flow rate. In general, fine powders cannot through the capillary tube because of the adhesiveness of the surface; however, applying vibration to the tube can make to reduce the particle-wall interaction forces and make flow possible. Recently, it was found that the vibrating capillary technique is applicable to characterize the flowability of fine powders. This paper presents a study on the performance of a newly developed measurement system based on the vibrating capillary method. The amplitude and frequency of vibration can be controlled by a computer and the mass of powder discharged from the vibrating capillary tube is measured by an electric balance. These data are continuously recorded into the computer. The powder flow characteristics, i.e., the mass flow rate depending on the condition of the vibration can be obtained by digital processing. The operation of the measurement system is simple and easy; each measurement time is only a few minutes. In this work, micrometer-sized particles were used and two factors, i.e. the critical amplitude to start flowing and the mass flow rate as a function of the amplitude of vibration were evaluated. Also, the performance of the measurement system in various conditions was discussed.