Coefficient of static and dynamic friction measurements for plastics against thermoforming plug materials at elevated temperatures
The gas assisted injection moulding (GAIM) process has benefits realised through material saving, improved product performance and lower capital cost of machinery. This important process is similar to conventional injection moulding in so far as polymer melt enters a cavity under pressure. However, before the melt completely fills the cavity, nitrogen gas is introduced into the melt at high pressure to complete the filling stage. Gas pressure is maintained to replace the packing pressure during cooling, normally supplied by the melt injection unit. Modelling of the GAIM cavity filling stage has used a variety of methods adapted from the widely used 2-D approach used for conventional injection moulding. Although these methods have been useful for rough predictions in mould filling without requiring excessive computational power, crucial information is missing regarding the final distribution of polymer and gas in any given cross section. Only true 3-D modelling techniques can provide the necessary information regarding the cross sectional form in a gas channel to determine residual wall thickness and bubble penetration. Presented here is a 3-D finite element implementation of a pseudo-concentration method. A fixed finite element grid is used to mesh the cavity. After each time step calculations of velocities in the x, y and z directions (u, v, w), pressure (p) and concentration (c) are made. The pseudo-concentration method uses a material label, or concentration (c), to distinguish between the polymer and gas; gas is cgas=0 and polymer is cpolymer=1. The concentration value at each node is rounded to cgas or cpolymer after each time step, except at the nodes bordering an element where the concentration contour of c=0.5 passes; this represents the polymer/gas interface. The exact location of the polymer/gas interface can therefore be interpolated and the residual wall thickness predicted from these modelling results. A typical simulation result is shown in figures 1 and 2, which only show the concentration contours representing the polymer and clearly show the formation of the gas bubble inside the specimen. Figure 1 shows a cross-section of our test specimen near the beginning of the 200mm uniform gauge length. Figure 2 shows contours along the centreline (lengthways) of the specimen. Reference Haagh G.A.A.V. and Van de Vosse F. N. Simulation of three dimensional polymer mould filling processes using a pseudo-concentration method. International Journal for Numerical Methods in Fluids, 28:1355-1369, 1998. Figure 1 Figure 2
Die design improvements through numerical simulation for the extrusion of EPDM compounds
In a joint project, a study was launched between our two groups to provide a reliable die design for an EPDM profile used in a pneumatic flexible mobile system patented by Conti-Tech. While the geometry of the profile does not appear at first sight to be overly complex, the presence of details of small dimensions and the tolerances required complicate the task of the designers. Concurrent experimental and numerical trials were thus conducted to provide a die which performed the task, while also satisfying additional requirements: reproducibility, limited disturbance to the flow pattern, short times to reach production conditions. Several approaches are tried to meet those criteria, from the application of the automatic die design capability of the software, to the numerical trial of modified dies, and finally to the evaluation and testing of a completely original die design.
Effect of temperature on the solvated electron in 1-propanol
Abstract The technique of pulse radiolysis has been used to study the effect of temperature on the solvated electron in 1-propanol. The spectrum of the solvated electron has been measured in the range 140–298 K. The wavelength at maximum absorption, λ max , decreases with decreasing temperature (corresponding to an increase in the energy, E max ) but the spectral width at half height, ΔE 1 2 , changes little with temperature. At temperatures above ≈180 K, the formation of the solvated electron is complete at the end of the pulse and its spectrum shows no change in shape with time. Below ≈170 K, the absorption spectrum is time-dependent in both liquid and glassy phases, the changes being attributed to the solvation process. The reaction(s) leading to solvated electron formation following the pulse show an activation energy of 22±2 kJ mol − and the solvated electron decays with an activation energy of 20±2 kJ mol −1 . The yield of solvated electrons decreases continuously with decreasing temperature in the range 298-77 K and, at all temperatures studied, is less than the total ionization yield measured by scavenging techniques.