What is the pressure holding function of the injection molding machine?

The holding pressure function of the injection molding machine:

The holding pressure is used to prevent the product from shrinking. For some products that require fast injection speed and long cooling time, holding pressure is required, and holding pressure is generally low speed and high pressure, otherwise it is ineffective.

The injection pressure has both pressure and speed. Holding pressure only works on pressure and not speed. Injection pressure is to put the molten material into the mold at the required speed. All injection cylinders move forward at the pressure and speed you set, and the oil continues to flow into the cylinder as the cylinder moves forward. Holding pressure is the oil giving the cylinder the pressure you set, but the oil no longer increases. As the piston in the cylinder moves forward, the pressure becomes smaller and smaller. Until the material cools and the pressure no longer drops. The pressure and speed of holding pressure are definitely less than the injection pressure and speed.

The role of the pressure-holding switch of the injection molding machine:

When the injection process is completed, the cavity is full of melt. At this point, the injection screw top position, due to the cooling effect of the mold at a lower temperature, the injection mold cavity of the molten material shrinks, for the density of the product quality, to prevent the melt from flowing over and shrinking in the cavity to compensate for the product, a certain pressure must be maintained in the hydraulic cylinder during injection, pushing the screw to continue to apply pressure to the molten material in the mold until the melt is cooled and sealed at the gate. At this time, the pressure exerted by the screw on the molten material is called the pressure-holding pressure, also known as the secondary pressure. During the pressure-holding process, the screw may move forward slightly due to feeding.

When the molten material in the mold cavity loses the possibility of flowing back from the gate, the internal pressure holding can be released (the high pressure in the mold closing hydraulic cylinder can also be released at this time) (that is, the gate is closed), and the hydraulic cylinder is injected to allow the product to cool and shape in the mold.