Secondary ejection should be forced ejection, which is mainly used when hook cannot use lifter and slider is detached. Two-stage ejection is not necessarily only used for forced demoulding. Sometimes, in order to make product deeper or to avoid gate strain, two-stage ejection is a commonly used method.
Under normal circumstances, when removing finished product from mold, whether a single or multi-component ejection mechanism is used, ejection action is completed at one time. However, due to special shape of finished product or requirements for mass production, if finished product is still in mold cavity after one ejection or cannot fall off automatically, another ejection action is required. This kind of ejection action design is called secondary ejection.

 

Or in order to obtain a reliable demoulding effect, demoulding resistance of plastic part is decomposed, and mechanism to complete demoulding of plastic part through secondary demoulding action is called secondary demoulding mechanism, as shown in Figure 8.5.1.

 

Secondary demoulding mechanism example:

(1) As shown in Figure 8.5.2, plastic part has a semicircular depression between two bones, which is tightly wrapped by rear mold cavity. Demoulding mechanism is shown in Figure 8.5.3. The first demoulding makes plastic part come out of rear mold cavity, providing space for strong demoulding and deformation; second demoulding is done by ejector pins, and semicircular concave part of plastic part is forced out of core push block. Movement process of this mechanism: In the first demoulding, all four ejector plates move, ejector and core push block move at the same time. Demoulding distance ≥h makes plastic part come out of rear mold cavity, and demoulding is completed in one time. When swing block continues to move until it touches upper limit surface, swing block swings to make upper two needle plates move quickly, driving ejector to eject plastic part, completing secondary demoulding. This mechanism should pay attention to: h1>h, H>10mm+h1+(secondary demoulding movement distance).

 

 

 

Since submersible runner must be set on lifter block and glue is injected through lifter block, mold must ensure that runner is first separated from lifter block. Mold adopts a secondary ejection mechanism as shown in Figure 8.5.6. When this mechanism is demolded for the first time, pull rod keeps runner stationary, ejector and lifter are separated from plastic part by a distance M, so that plastic part is disconnected from submersible runner. Submersible runner is deformed and then separated from lifter block, and the first demolding is completed. In second demolding, all four ejector plates move to eject plastic part and runner from rear mold cavity. It should be noted that in order to ensure that runner is separated from lifter block, M>S (submersible runner length).

 

 

(2) Gate and runner parting line on plastic part are shown in Figure 8.5.5.

 

Because finished product is very deep, a ejector block is used for ejection. Since ejector block is equipped with a molding core insert, a special ejection method is used.

 

Delayed ejection is to solve problem that product cannot be automatically disconnected from gate (gate form. Overlap type or side gate). Delayed ejection only pushes on runner.
Delayed ejection can be accomplished by changing ejector pin.

 

As for two-section ejector pin, it is just to increase strength of ejector pin and avoid deflection deformation during ejection.
Using this kind of ejector pin to complete two-stage ejection is the simplest in terms of mold structure, and only requires tampering with ejector plate. Example given here is to use this mechanism to cut off latent gate.

 

During ejection, ejector on the left will move first, and ejector on the right will not start to move until lower fixed plate pushes against ejector head circled by a red line under ejector on the right. This secondary ejection structure can prevent latent gate from pulling finished product away from finished product during ejection.
Side gates can also be ejected in a similar way to avoid pulling finished product at gate position.
Of course, this ejection method is not only used for ejection near gate. Since starting position of second ejection stroke only needs to change columnar length under ejector to achieve it, and cost of mold making is relatively low, this ejection method is also very suitable for ejection of deeper box-shaped objects mentioned earlier.