Analysis of the causes and countermeasures of mold sticking in the main flow channel

What is the main flow channel sticking to the mold (appearance)

Main runner residue is a phenomenon that the main runner of molded products fails to break away from the mold.

If the main runner size increases due to long-time pressure-holding, or if the main runner part of the mold is injured, resistance will be generated so that the main runner cannot come off when the mold is opened.
 

Main flow channel sticky mold generation causes

1、Mainstream channel curing is not sufficient

When the main channel has not been fully cured, due to the shrinkage at this moment being very small, the main channel close to the mold, the strength is also low, so if at this time to make the main channel out, it will be very easy to break. In this way, the main flow channel will be left behind. Resin temperature, mold temperature, and cycle (cooling time) on the mainstream channel curing have an impact.
 

2、Over-application of holding pressure

The main runner section is closest to the barrel nozzle, so it is easy to apply to hold pressure. Therefore, after applying high holding pressure, the size of the main flow channel will increase, and the resistance of the mold release will also increase accordingly so that the main flow channel is prone to sticky mold.
 

3、The problem of the mold structure

When the slope of the main flow channel is small, the resistance of the fixed side will increase. Although the main runner is locked to pull out the main runner from the fixed side, if it is weak, the lock will be damaged and the main runner will fall off from the mobile side. Also, if a manifold lock is used, because it is too strong, the main flow channel and manifold sometimes adhere to the fixed side.
 

4. Problems inherent in the grade

Compared with the standard grade, the impact resistance grade or alloy material shrinks less and adheres to the mold more easily and with lower strength. This makes it easier for the mainstream channel to stick to the mold.
 

Countermeasures for mold sticking in the main channel

1. Allow the main channel to cool and cure sufficiently before opening the mold

Reduce the mold temperature and extend the cooling time. Especially for the material with low strength and slow curing, lowering the mold temperature will be an effective method.

2、Lower the holding pressure

Reducing the holding pressure is also effective. The holding pressure applied to the product cavity will become zero after the gate is closed, so if no holding pressure is applied thereafter, the main flow path will not be subjected to useless holding pressure. However, the excessive reduction will easily lead to unstable injection volume, so care is needed.

3、 Improve the mold

The angle necessary for the slope of the main flow channel has not yet been specifically defined. However, if there is a possibility of mold sticking in the main channel, increasing the angle can be effective. Strengthening the main runner lock (increasing the size and enhancing the slope) is also effective. On the contrary, since it may become difficult to come off due to ejection, it needs to be adjusted while molding.

If the manifold lock is too strong, change the size of this part slightly.