Generally, there are many kinds of ejection mechanism, which can be divided into ejection of ejector rod, pipe jacking, pushing plate, using or type parts according to different structures. For plastic with complex shape, mixed ejection may be adopted.
According to the power source, ejection and demoulding mechanisms can be divided into three categories:
(Manual pushing mechanism refers to the manual manipulation of the demoulding mechanism to pull the plastic parts out after the die is separated. It can be divided into two types: manual pushing in the die and manual pushing out outside the die. This kind of structure is mostly used in the case that the shape of the die or plastic parts is complex and the pushing mechanism can not be set, and the structure is simple and the output is small. At present, it is seldom used.
(2) The mobile pushing mechanism drives the pushing mechanism on the mould by the opening action of the injection machine to realize the automatic demoulding of the plastic parts. This kind of die structure is complex, mostly used in the production of large batches, is currently the most widely used kind of launch mechanism, but also the focus of this chapter. It includes ejection pin, push plate, pneumatic, internal thread and compound.
(3) Hydraulic and pneumatic push-out mechanisms generally refer to special hydraulic or pneumatic devices installed on injection machines or moulds to push plastic parts.
Simple demoulding mechanism refers to the demoulding mechanism which can directly remove the plastic parts after one push after opening the mould. This mechanism is also the most widely used structural form. It includes push rod, push tube and push plate demoulding mechanism, movable insert and die demoulding mechanism, multiple synthesis (combination) demoulding mechanism and hydraulic and pneumatic demoulding mechanism.
Push rod (ejector) demoulding mechanism
The ejection mechanism of the ejector rod is located on the side of the dynamic die of the die. The ejector rod generally ejects the inside, end and reinforcement of the plastic part. When the die opens to a certain stroke, the ejector rod ejects to push the ejector pad in the die and drive the ejector rod forward to eject the plastic parts from the cavity or core. The ejection rod is suitable for ejection of various plastic parts. The cross-section shape of the head of the common ejector rod is different, which is generally divided into circular or abnormal shapes. Round head top rod is easy to process and widely used, while special-shaped head top rod is suitable for special-shaped products.
Therefore, it is the simplest and most widely used demoulding mechanism to use push (top) rod plastic parts. It consists of push rod, reset rod, pull (hook) rod and other parts. In this mechanism, because the position of the push rod has a greater degree of freedom, it is used for special-shaped products such as push-up box and occasions where a larger demoulding force is needed locally. However, due to the small area of the push rod, there will be dents and other marks on the surface of the plastic parts. If improperly used, there will also be defects such as whitening and cracking at the push-up place. In addition, due to the long-term excessive wear of the push rod and hole, spills can also be caused.