Grading electrostatically charged powders esp. of plastics - using controlled humidity in carrier gas stream conveying powder through sieve

摘要

An improved method of grading electrostatically charged powdered material, esp. plastics powders, in the presence of a moving gas stream consists of subjecting the powders to an alternating voltage corona and simultaneously maintaining in the gas phase a humidity below the saturation level, more specifically a relative humidity of 20-80%. Used esp. for the grading of PVC or polyamide powders for use in melt coating processes, such as fluidised bed sintering, flame application or electrostatic coating procedures. The method results in a reduction of the very fine dust component entrained with the powder and also in considerably reduced tendency to adhere to the container walls and/or to form agglomerates.