Capillary rheology studies of INVAR 36 feedstocks for powder injection moulding

• We studied the rheology of feedstocks based on INVAR 36 and CAB and PEG binders.
• We measured the viscosity at different conditions by capillary rheometer.
• The behaviour of the feedstocks was discussed and adjusted to viscosity models.
• We propose a model that describes the viscous behaviour of the studied feedstocks.

Capillary rheology was used to determine the shear viscosities of low expansion alloy INVAR 36 feedstocks for powder injection moulding (PIM) based on gas atomized powders and cellulose acetate butyrate (CAB) and poly-ethylene glycol (PEG) binders. Different variables that describe the flow behaviour were analysed, in particular, the relationships between viscosity of the melted feedstock with different conditions, such as shear rate (γ˙), temperature (T), solid loading (Φ) and particle size (PS). The viscous behaviour was physically interpreted and discussed, and a generalised rheological model was proposed that involves all of the dependant parameters: γ˙, T, Φ and PS. The particular rheological behaviour of the feedstocks, which deviates from typical pseudoplastic behaviour, has a relevant correlation with the proposed model. Moreover, the model can be used when similar behaviours are observed in other systems.

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