Thermal expansion of high-density polyethylene in hot plate welding applications

This research studies high-density polyethylene (HDPE) behavior that is not easily identifiable in a production setting, but is, nevertheless, necessary for consideration when specifying equipment performance for hot plate welding (HPW) applications. Thermal expansion in polymers can depend on several factors, such as the specific type of polymer, its degree of cross-linking, and the temperature range over which the expansion occurs. This physical behavior can affect the process by prolonging the cycle time if the equipment is not sized correctly for the application. This research uses HDPE samples with different surface areas and varying process parameters (force and temperature) to collect data on the sample size change. Experimental results are compared with a recommended industrial guideline of 0.2 to 0.5 MPa of pressure for the Matching stage (stage for surface conformation). Obtained findings indicate that this industrial guideline is very temperature dependent. Data collected in the experiment were used to develop a mathematical model for thermal expansion under different parameters. This study also presents a visual interpretation of HDPE behavior on the effect of temperature if the pressure is increased or decreased.