An understanding of the fluid motion and pressure build-up in a non-isothermal injection mold packing stage

Recently, experimental data on the gapwise-density variation across a mold thickness have shown that most of the previous mathematic models have severe deficiencies and limitations. The purpose of this work is to re-examine the non-isothermal fluid motion within a mold cavity during the packing stage. A non-isothermal fluid motion within a mold cavity during the packing stage. A non-isothermal governing equation was derived, and a flow mechanism was proposed for the pressure and density built-up within a cavity for a generalized Newtonian fluid flowing into a rectangular mold. The equation of state for polymeric melts was assumed to obey the Spencer-Gilmore equation. The pressure profile in a cavity was controlled by two opposite factors; namely, solidification and flow. The former tends to reduce local pressure because a cooled material occupies less space, while the latter tries to increase the pressure within a cavity and make it more uniform. Calculated results indicate that the pressure built up during the packing stage is strongly dependent on the melt viscosity, compressibility, and the boundary conditions of the cavity. Gapwise-density variations have been mathematically simulated and determined and they are qualitatively consistent with the previous data.