一种用于设计电加热滚塑工艺的传热计算方法

A computational method of heat transfer for design of electric⁃heating rotational molding process

首先针对一个空模具以及生产4种不同厚度的氢气瓶内胆的电加热滚塑工艺,通过实验分别测量了模具表面和模内的温度、加热时间和耗电量,并据此计算了在这5种情形下的加热效率和放大系数。然后提出了一种用于设计电加热滚塑工艺的计算方法。即在模具的材料和质量、模内粉料的物性和质量、工艺参数确定后,先计算出有效热能,接着根据放大系数初步估算出在加热阶段电热丝需发出的热能,并由此得出满负荷的加热功率和电热丝的长度。然后利用static bed模型通过FLUENT软件仿真计算出加热时间和电热丝实际需发出的热能。以一个中空立方形的塑料制品的电加热滚塑工艺为例说明了该方法的应用步骤,并研究了满负荷的加热功率和模具材料对加热效率、加热时间和电热丝实际需发出的热能的影响。结果表明,加热效率随氢气瓶内胆厚度的增加而下降,加热时间随着满负荷功率的增大而减少的速率变得越来越慢。采用钢制模具的加热时间比采用铝制模具更长,电热丝也需发出更多的热能。

First,temperatures at mold surface and inside mold,and heating time and consumed electricity were measured by means of experiments for electric⁃heating empty mold and rotational molding process to make liner of hydrogen cylin⁃der with four different thicknesses,and the heating efficiency and magnification factor were calculated in the five cases based on these measurements.Then,a computational method for the design of electric⁃heating rotational molding pro⁃cess was proposed.After the material and mass of mold,physical properties and mass of the powders inside the mold,and process parameters were defined,the effective thermal energy was calculated at first,and then the thermal energy from heating wire required in heating phase was estimated according to the magnification factor.As a result,the full load heating power and length of heating wire were obtained.The model of static bed was applied to simulate the heating time and thermal energy actually required from heating wire with the aid of the FLUENT software.The application steps of the method were illustrated through an electric⁃heating rotational molding process to make a hollow plastic cube.The in⁃fluence of the full load heating power and mold material on the heating efficiency and the heating time and thermal energy actually required from heating wire was investigated.The results indicated that the heating efficiency decreased with an increase in the thickness of the liner of hydrogen cylinders.The heating time decreased slowly with an increase in the full load power.In the application of the steel mold,the heating time became longer,and more thermal energy from heating wire was required compared to the application of an aluminum mold.