Even when the melt enters the Dustbin Mould, the injection speed is constant and its flow rate changes. The melt flow rate is high when entering the gutter box gate area, but the melt flow rate begins to decrease after entering the mold cavity, ie, the dustbin mould filling stage. Variations in the flow rate at the front end of the melt stream can cause surface defects in the product.
Reducing the speed of injection is one way to solve this problem. In order to reduce the velocity of the melt flow front at the gate, the injection can be divided into several steps and the injection speed is gradually increased with the aim of obtaining a uniform melt flow rate throughout the filling phase.
Low melting temperatures are another cause of dark spots on the product. Increasing the barrel temperature and increasing the back pressure of the screw can reduce the likelihood of this happening. In addition, the low temperature of the dustbin mould can also cause surface defects, so increasing the temperature of the dustbin mould is another feasible way to overcome the surface defects of the product.
Defects in the dustbin mould design can also create dark spots near the gate. By changing the radius you can avoid sharp corners at the door. Care should be taken to check that the gate design is appropriate when designing the location and diameter of the gate.
