(335f) Tribocharging Quantification to Enhance Processability

Powder flowability is an important parameter to control in most manufacturing processes. Powder conveying is a common step to transport the material from a process step to another. During this transport, the powder must exhibit good flow properties. However, particle to particle and particle to pipe rubbing can build up charge in the powder. Therefore, a powder that has a good flowability at the beginning can become cohesive due to the charge buildup and shows a lower flowability as the interactions between particles increase due to the Coulomb force. This charge buildup depends on the nature of the powder as well as the material of the pipes. Thus, it is important to be able to predict and to measure the chargeability of a powder for process improvement, by selecting the adequate powder or pipe material.

While the mechanisms controlling triboelectric charging are still poorly understood, it remains possible to evaluate the ability of a powder to gain charge by measuring its charge density after a flow. We present here results on the chargeability of hypromellose powders with different grades. The electrostatic charging has been investigated with the GranuCharge. It consists of a steel bend pipe, which reproduces most of possible charging ways, i.e. rubbing between grains or with the tube and collisions. The powder flows in the tube and falls in a faraday cup which measures the total electric charge of the powder. Knowing the mass of powder, one defines the charge density of the powder.

One can build a classification of the different powders according to their chargeability. This classification is then correlated to what can be observed for the flowability of the different powders with a loss-in-weight compact feeder. Moreover, we show the effect of the pipe material on the chargeability by using different tubes (Stainless Steel, PVC, Aluminium, ....) to highlight the importance of selecting the good material for conveying. These results highlight the impact of charge buildup during powder flow and the importance to characterize it for process improvement.