Charge is one of the important movment of the injection molding machine. It is for feeding in the new plastic material and plasticizing it. Suitable back pressure for charge is good for plasticizing.
How the charge action and back pressure work?
Please see above picture.
When the injection molding machine start charging. the hydraulic motor driving the screw to rotate.The new material feed inside the barrel of machine and then heated inside the barrel. the melt material move forward under the rotatation of the screw. The material mix in the thread position of screw, and heated by the heater and shear heat caused by the rotation of screw,which is called the plasticizing.
More and more melt material store in the front of the screw, then it will generate a force pushing the screw back moving. At this time, the hydraulic oil of the injection cylinder exhaust out slowly, by controlling the exhaust oil flow, we can control the resistance and speed of the screw returning in order to make sure the material are enough mixed and plasticizing. it is called back pressure.
by the way,since more and more melt material store in front of the screw,there will be little material leak out from the nozzle, the machine can give a force from the opposite direction to the injection cylinder. it will push the screw backward forcely while rotating,which is named suck-back.
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