Injection molding machines are divided into vertical, horizontal, and all-electric types, which can heat the plastic and apply high pressure to the molten plastic, so that it can be injected and fill the mold cavity. Recently, many friends have asked what is the function of holding pressure in the injection molding machine?
The role of holding pressure in injection molding machines:
Packing pressure is used to prevent product shrinkage, for some products that need fast injection speed and long cooling time, they need to use holding pressure, and holding pressure is generally low speed and high pressure, otherwise it is ineffective.
Injection pressure is both pressure and speed; And the pressure holding is only to give pressure, not speed. Injection pressure is to inject the melt 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 advances. And the holding pressure is the oil that gives the cylinder the pressure you set, but the oil no longer increases, and as the piston in the cylinder advances, the pressure becomes smaller and smaller. Until the handle cools down and the pressure does not decrease. The pressure and speed of holding pressure are definitely less than the pressure and speed of injection.
The function of pressure holding switch of injection molding machine:
When the injection process is completed, the whole mold cavity is filled with melt, at this time, the injection screw has traveled to the front position, due to the cooling effect of the low-temperature mold, the melt injected into the mold cavity produces shrinkage, in order to prepare a product with dense quality, prevent the melt in the mold cavity from backflow and compensate for the shrinkage of the product, a certain pressure must be maintained in the injection hydraulic cylinder, and the screw is pushed to continuously apply pressure to the melt in the mold until the melt is cooled and sealed at the gate, and the pressure of the screw acting on the melt at this time is called the pressure holding pressure, also known as the secondary pressure. During packing, the screw will move forward a little due to shrinkage.
When the pressure holding is carried out to the melt in the mold cavity and loses the possibility of reflux from the gate, the internal pressure holding pressure can be removed (at this time, the high pressure in the mold clamping hydraulic cylinder can also be removed) (that is, the gate is closed), and the hydraulic cylinder is injected to cool and shape the product in the mold.
