Injection molding process, shrinkage Depression is relatively common phenomenon. The main reason for this situation are:
1. Machine aspects:
(1) the nozzle hole caused by too much financial and material reflux contraction, the resistance is too small when a large quantity insufficient contraction.
(2) insufficient clamping force will cause flash contraction, clamping system should check whether there is a problem.
(3) should be used in plastics plastics lack large amount of the machine, check the screw and barrel wear.
(1) design parts to make uniform thickness to ensure consistent shrink.
(2) mold cooling, heating system to ensure a consistent temperature of various parts.
(3) To ensure the smooth gating system, the resistance can not be too large, such as sprue, runner, gate size should be appropriate, the finish should be enough, the transition zone to transition circle.
(4) thin pieces should increase temperature to ensure smooth flowing material, for thick parts mold temperature should be lowered.
(5) to open the gate to be symmetrical, try to set up in parts walled parts, should increase the volume of cold slug well.
3. Plastic: the crystalline plastic than non-crystalline plastic shrink calendar harm, to appropriately increase the processing quantity, or addition change agents in plastics, to accelerate crystallization, reduce shrinkage depression.
(1) barrel temperature, volume changes, especially in the first furnace temperature of illiquid plastic should increase the temperature to ensure smooth.
(2) injection pressure, speed, back pressure is too low, injection time is too short, so that the quantity or insufficient density and shrinkage pressure, speed, back pressure is too big, too long and contraction caused by flash.
(3) feeding quantity that is consumed cushion injection pressure is too large, too small, insufficient quantity.
(4) that do not require precision parts, injection dwell in is completed, the outer part of the basic condensation hardening sandwich still soft and can top out of the workpiece, as soon as possible out of the mold and allowed to cool slowly in air or hot water You can make depression gentle contraction without affecting the use and less conspicuous.