注射模脱出螺纹塑料制品脱模力矩的研究

建立了螺纹制品成型时的受力模型,指出由于收缩制件对型芯的正压力主要作用在型芯牙尖顶部及牙尖的一个侧面上,在型芯表面的其余部位压力基本为零,甚至在制品和型芯间存在有间隙。实验证实了上述假设的正确性。在此基础上推导出了新的脱模扭矩计算公式,公式表明,脱模扭矩的大小与塑料的弹性模量、泊松比、脱模时的收缩率、摩擦系数、塑件平均壁厚、螺纹牙尖角、螺牙高、扭径等因素有关。 用螺纹型芯可更换的试验模具,用多种塑料模制螺纹制品,实测其脱模扭矩证明了该公式的正确性

A STUDY ON UNSCREWING TORQUE FOR PLASTICS THREAD MOULDINGS

This paper dears with the study on unscrewing torque for plastics thread part. A new mechanical model of the pan and thread-forming core pin was established during the moulding. The auther suppose that the top and one side of each screw flight is compressed by the shrinkage pressure of the injection moulded part and the rest surface of the thread-forming core pin is free from pressure. And then a formula for calculating unscrewing torque was deduced. It depends on the elastic module, the Poison ratio, the shrinkage factor, the friction coefficient, the average thick of the wall of the moulded part, the angle of tooth point, the height of tooth and the diameter of heel. By using a mould which has a exchangeable thread-forming core pin to mould a plastics part with different plastics, the value of the measured unscrewing torque are identical with the theoretical value.