Plastic mold opening, the plastic mold opening structure can be confirmed after each part of the mold detailed planning, that is, to confirm the size of each template and parts, cavity and core size. Primary planning parameters such as shrinkage of relevant data will be involved. Therefore, only by grasping the shrinkage ratio of forming plastics can we confirm the size of each part of cavity. Even if the selected mold structure is correct, but the parameters are not appropriate, it is not possible to produce qualified plastic parts.
The properties of thermoplastics are that they swell when heated and shrink when cooled, and of course shrink when pressurized. In the process of injection molding, the molten plastic is first injected into the mold opening cavity of the plastic parts. After the filling, the molten material cools and solidifies. When the plastic parts are taken out from the mold opening, the shortening will appear, which is called forming shortening. Plastic pieces from the mold out to secure this period of time, the scale will still show a small change, a change is to continue to shorten, this shorten called after the shorten.
Another change is that some hygroscopic plastics swell with moisture absorption. For example, when the water content of nylon 610 is 3%, its scale increase is 2%. When the water content of glass fiber reinforced nylon 66 was 40%, the scale increment was 0.3%. But the primary effect is to shorten the shape. Now confirm all sorts of plastic shrinkage rate (form shortens + after shortens) method, introduce the DIN16901 rule in German national norm commonly. In other words, the difference between the mold cavity size of plastic parts at 23℃±0.1℃ and the size of plastic parts after forming for 24 hours was calculated at the temperature of 23℃ and the relative humidity of 50±5%.