Sprue sticking mould (appearance)
Sprue residue refers to a phenomenon in which the sprue of the molded product fails to leave the mold.
If the size of the sprue increases due to the application of holding pressure for a long time, or the sprue part of the mold is injured, resistance will be generated, so that the sprue cannot fall off when the mold is opened.

The cause of sprue sticking molding

1. The sprue curing is not sufficient
When the sprue is not completely cured, because the shrinkage at the moment is very small, the sprue is close to the mold, and the strength is also low, so if the sprue is to be withdrawn at this time, it will be very easy to break. In this way, the sprue remains. Resin temperature, mold temperature, and cycle time (cooling time) all have an impact on sprue curing.

2. Excessive pressure holding
The sprue section is closest to the barrel nozzle and is therefore easy to hold pressure. Therefore, when high holding pressure is applied, the size of the sprue will increase, and the resistance during demoulding will also increase accordingly, so that the sprue is prone to mold sticking.

3. Problems in mold construction
The slope of the sprue part is small, and the resistance of the fixed side to demould increases. Although the sprue lock is set up to pull out the sprue from the fixed side, if it is fragile, the lock can be damaged, causing the sprue to fall off the moving side. Also, if a shunt lockout is used, sprues and splitters sometimes stick to the fixed side because it is too secure.

4. Problems inherent in hierarchies
Impact resistance grades, or alloy materials, shrink less, adhere more easily to molds than standard grades, and are also less strong. In this way, sprue sticking is more likely to occur.

Countermeasures for sprue sticking molds

1. Make the sprue fully cool and solidify before opening the mold
Reduce mold temperature and extend cooling time. Especially for materials with low strength and slow curing, reducing the mold temperature will be an effective method.

2. Reduce the holding pressure
Reducing holding pressure is also effective. The packing pressure applied to the product cavity becomes 0 after the gate is closed, so if the packing pressure is not applied thereafter, the sprue will not be subjected to useless holding pressure. However, if it is too low, it is easy to cause the injection volume to be unstable, so it is necessary to be careful.

3. Improve the mold
The angles necessary for the slope of the sprue have not been specifically specified. However, if sprue sticking is possible, increasing the angle is also effective. Reinforced sprue locking (increased size and increased incline) is also effective. On the contrary, since it may become difficult to fall off due to ejection, it is necessary to adjust it at the same time as the actual molding.

If the runner locks too firmly, change the size of the section slightly to a smaller size.