Pressure build-up during melt impregnation

Pultrusion compounding is a commonly used technique for mixing polymer with continuous reinforcement. It often involves pulling glass roving over staggered cylindrical pins immersed in a pool of liquid polymer. This causes polymer pressure to build-up in a wedge-shaped region located between the roving and pin. This pressure drives polymer into the roving. To study this pressure build-up, roving was pulled over an instrumented pin placed in a pool of silicone oil. A hole in the pin allowed pressure to be measured at various locations in the wedge as a function of pulling speed, oil viscosity, and inlet tension. These parameters were lumped together with the roving width to form a dimensionless group called the lubrication number. Studies using impermeable tape showed that, for lubrication values above 0.0001, the maximum pressure was equal to its theoretical value of tension divided by the product of tape width and pin radius. For permeable roving, the maximum pressure was significantly less than that value. Previously developed models for pulling force as a function of process parameters have also been validated. The implications of these findings with respect to abrasion are also discussed.