聚乙烯储肥罐滚塑成型模具热辐射温度响应

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

现有天然气加热型滚塑成型成品聚乙烯储肥罐存在壁面加热不均的问题,难以满足储肥罐壁厚均匀性要求。针对以上问题,该研究对滚塑模具在加热室内热辐射作用下的温度响应进行研究,提出基于数值模拟的分析方法。利用FDS(Fire Dynamics Simulator)软件构建加热室(含10 m^(3)滚塑模具)加热模型,模拟得到模具侧壁温度场分布热力图,获得加热室稳态温度变化范围为174~186℃;运用ANSYS软件建立容积10 m^(3)滚塑模具热响应模型,结合模具结构、钢材和线型低密度聚乙烯(Linear Low Density Polyethylene)的热物理特性,获得加热阶段模具内壁面温度场分布情况,确定加热阶段模具内壁面温度变化范围为237~278℃。搭建试验平台并设置验证性试验,通过对4次试验数据的分析及处理,得到加热室温度变化曲线。对比分析仿真及试验结果,得到稳态温度误差小于4%,确定了FDS+ANSYS方法的可行性、仿真模型及结果的正确性和准确性。该研究可为聚乙烯储肥罐壁面厚度均匀性及加热室性能研究提供参考。

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 m^(3)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 m^(3)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.