The basic knowledge of thermal expansion of plastic mold parts is explained.
In order to maintain the proper surface temperature of the mold core, plastic molds are generally insulated at a temperature of 30 to 150°C.
Other parts, such as sprue bushes, runners, and the parts where the molten resin flows in, will receive the heat transferred from the resin at about 180 to 330°C.
Metal generally expands due to heat when the temperature rises, so the parts composed of plastic molds will also expand due to heat.
Thermal expansion will hinder the fitting gap of the guide-guide post/guide sleeve, affect the movement of the slider, change the size of the mold core, etc., and bring various adverse effects to the forming.
The basic thermal expansion size change is calculated using the following calculation formula.
λ: Dimensional extension due to thermal expansion (mm)
α: Linear expansion coefficient of metal (mm/mm)
L0: Initial length (mm)
t: initial temperature (℃)
t0: temperature after heating
The linear expansion coefficients of representative mold steels are shown in the table below.