Comparison of available techniques for characterising the air induced segregation tendencies of powders

This paper considers two techniques that can be applied to undertaking evaluations of the segregation behaviour of predominantly fine powders that are subject to interaction with counter directional air flows. The current provision of test equipment is limited to two main approaches to the establishment of powder sensitivity to interaction with air. The first technique involves the controlled introduction of air through a test sample of powder in order to purge fines, whilst the second technique generates conditions within the test equipment that permit the momentary passage of a controlled volume of air through a bed of descending powder. The former test approach has been found to have its application limited to the testing of non-cohesive powders (i.e. powder through which the introduced air can pass) - the testing of cohesive powders being ineffective due to the tendency of the powder bed to generate fissures through which the air flows or to move upwards as a continuous plug. The latter test overcomes this test limitation through the use of a larger diameter test section and powder insensitive method of powder introduction into the test section. The results presented demonstrate the fundamental differences in the outputs of the respective testers, in terms of the range of powders that can be accommodated and the potential application for test data derived.