Understanding powder caking: Predicting caking strength from individual particle contacts

The chemical, pharmaceutical and food industries generate an average output of 300,000 tonnes of solid products per company per year. Caking of these products is therefore a major concern to the industry. This paper concentrates on caking due to crystal bridges formed under the influence of humidity. Using the micro–macro approach, it is shown how the bulk strength of caked solids can be predicted from individual particle contacts. The individual particle contact measurements are performed in a new test device, the DAPP system, built for particles in the half-millimetre size range. For the modelling, a contact-dynamics model was adapted to caked systems. It proved important to use the complete crystal bridge strength distribution in the simulation. Under these conditions modelling and validation experiment coincided to a factor of two.