Characterization of Expanded Polypropylene Bead Foams with Modified Steam-Chest Molding

Steam is commonly used in polymer bead foam sintering due to its high heat transfer capacity. However, the pressure loss unavoidable during flow through the beads causes a temperature decrease and thereby negatively affects the sintering behavior. In order to reduce the sensitivity of the temperature to the pressure variation, hot air was added to the steam line. The effects of the flow rate, the pressure, and the temperature of the hot air on the surface roughness, thermal properties, and mechanical properties of the molded products were studied. The results showed that the introduction of hot air at a flow rate of 120 L/min decreased the total steaming time by about 32%. Further, a decrease of 16 °C in the processing temperature was observed, which decreased the surface roughness by 50%. Hot air improved the heat flow and thereby enhanced the uniformity of the tensile properties across the molded part.