Thermal radiation temperature response to rotomolding mold of a polyethylene fertilizer tank

A rotomolding process (rational molding) has widely been used to make the seamless hollow parts of complex shapes in plastic manufacturing. The steady-state temperature of the heating chamber is very essential to the rotomolding process. This study aims to obtain the uniform distribution of temperature field on the inner wall surface of the mold during the heating stage of the polyethylene fertilizer storage tank. The numerical simulation and experiment were also investigated to determine the temperature response of the rotomolding mold under the action of heat radiation in the heating chamber. A combustion and thermal radiation model was established using the fire dynamics simulator (FDS) software. A heating chamber (including 10 m3 rotomolding mold) was used to simulate the heating and the temperature change during the process. The temperature was obtained at each collection point on the sidewall surface of the mold during simulation. An optimal temperature measurement was then determined using the heat map of the temperature field distribution on the sidewall surface of the heating chamber at 60 s. The temperature-time variation curve of the measurement point was plotted, where the steady-state time of the heating chamber temperature was obtained as 40 s, and the variation range was 174 -186 ℃. Taking the linear low-density polyethylene (LLDPE) as a research material, a 3D simulation model of the 10 m3 rotomolding mold was constructed using the ANSYS Workbench platform. The transient thermal module was used to simulate the temperature distribution on the inner surface of the model in the heating stage of the rotomolding mold. As such, the temperature change range of the inner wall surface of the mold was determined to be 237-278 ℃ during the heating stage, according to the temperature-time change curve of the heating area of the heating gun. Furthermore, a rotomolding testing platform was built with the dimension of 4 m×2.4 m×2.8 m in a factory in Shihezi, Liaoning Province, China. The validation test was designed to be repeated four times independently, with each heating time of 75 min and cooling time of 30 min. The time interval between the two experiments was 30 min to allow the heating chamber and the mold for cooling down to the ambient temperature. Thermocouples were arranged to collect the temperature data at the best measurement point on the side wall of the heating chamber. Four experiments were carried out, where the steady-state temperature variation of the heating chamber was 175-200 ℃. Consequently, the FDS+ANSYS approach was verified to compare the accuracy of the simulation model and experimental measurement.