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Sticking – undesired adhesion of powders to metal surfaces during compaction

Adhesion of powders to metal surfaces during compaction (referred to as “sticking”) is a significant problem in powder pressing sectors including pharmaceuticals, food, detergents, batteries etc. Sticking is difficult to predict in early stage of product formulation and process development and usually manifests during full production scale where high productivity machines such as rotary tablet presses are used. The remedy consists of stopping production, remove, clean, reassemble tooling and continue processing until the material builds up on the tooling surfaces again.

We will use COMSOL finite element software in order to carry out a thermo-mechanical analysis of the powder-tool interface in order to provide insight into sticking mechanisms and help identifying material characterisation requirements. Sticking is a problem inherent to compaction, thus detailed knowledge of stress and deformation is necessary between tooling and particles as well as bulk level. This is a 100% numerical modelling project.

Sticking can also be understood as a balance between material deposition on the surface and material removal (similar to wear as the powder itself continues to slide along the surface during compaction). The formulation can include abrasive components. You will develop rate equations to describe this process;

Experimental evidence is provided by: Tsosie et al. (2017) used electron microscopy observations and identified that material not only sticks to tool surfaces but can also be removed during compaction. They proposed a mechanism for sticking which includes fragmentation at the interface of the tooling.

Key reading: Tsosie H., Thomas J., Strong J. et al. 2017. Scanning Electron Microscope Observations of Powder Sticking on Punches during a Limited Number (N