What is the main runner stick mold (appearance)?
The main runner residue is a phenomenon in which the runner of the molded product fails to leave the mold.
If the holding pressure is applied for a long time to increase the size of the sprue, or the sprue part of the mold is damaged, resistance will be generated, so that the sprue cannot fall off when the mold is opened.
Causes of sticky mold in the runner
Insufficient curing of the runner
When the runner is not fully cured, the shrinkage at the moment is very small, and the runner is close to the mold, and the strength is also low.
Therefore, if the runner is pulled out at this time, it will be very easy to break. In this way, the runner remains. Resin temperature, mold temperature, and cycle time (cooling time) all affect the solidification of the runner.
The nozzle of the runner is separated from the barrel, so it is easy to apply holding pressure.
Therefore, after applying high holding pressure, the size of the sprue will increase, and the resistance during demolding will also increase correspondingly so that the sprue sticking easily occurs.
Problems with mold structure
If the slope of the runner part is too small, the resistance of the fixed side demolding will increase. Although the sprue lock is provided to pull out the sprue from the fixed side, if it is fragile, the lock will be damaged and the sprue will fall off the moving side.
In addition, if the runner lock is used, since it is too strong, the runner will sometimes stick to the fixed side.
The inherent problems of the grade
Compared with the standard grade, the impact resistance grade or alloy material shrinks less, it is easier to adhere to the mold, and the strength is lower. In this way, the main duct sticking is more likely to occur.
Countermeasures for mold sticking in the runner
- Let the runner fully cool and
solidify before opening the mold
Lower the mold temperature and extend the cooling time. Especially for materials with low strength and slow curing, lowering the mold temperature will be an effective method.
Lower the holding pressure
It is also effective to reduce the holding pressure. The holding pressure applied to the product cavity will become 0 after the gate is closed.
Therefore, if no holding pressure is applied afterward, the main runner will not withstand useless holding pressure. However, excessive reduction can easily lead to unstable injection volume, so attention should be paid.
Improve the mold
The angle necessary for the inclination of the runner has not yet been specifically specified. But if the sticking of the main runner is possible, increasing the angle is also effective.
It is also effective to strengthen the runner lock (enlarge the size and increase the slope). On the contrary, because it may become difficult to fall off due to ejection, it is necessary to adjust while actually forming.
If the shunt is locked too firmly, please slightly reduce the size of the part.