A new environmental bulk powder caking tester

Bulk powder transformations, such as caking, can lead to numerous problems within industry when storing or processing materials. The extent of bulk powder caking may vary significantly due to a number of factors, such as time, environment and mechanical conditions. However, there are few caking testers available for rapidly conditioning a sample and monitoring time-dependent consolidation behaviour whilst providing a final measure of caking. In this paper a new bulk powder tester is introduced. The tester is placed within a temperature controlled chamber and has conditioning air at a desired relative humidity percolating through a powder bed to rapidly expose a sample to desired equilibrium moisture content. The temperature and relative humidity at the inlet and exit of the powder bed are recorded. The height of the sample is logged as a function of time during consolidation in order to analyse powder bed response to environmental conditions. Finally, the caking tester has been developed to easily open to expose the caked sample without causing significant disturbance. A sensitivity study with a hygroscopic powder has been performed to evaluate the ability of the caking tester to differentiate caking propensity of the material exposed to various conditions. It is shown that at different environmental and mechanical conditions the caking tester can differentiate caking behaviour with both the in-situ creep measurement and cake strength, which is measured at the end of the trial. Using this approach, the cake strength is shown to depend on sample consolidation, while the extent of consolidation is related to the environmental and mechanical conditions to which the sample is exposed. (C) 2013 Elsevier B.V. All rights reserved.