Generally, in mold processing, if the surface of the product that needs to be processed by injection molding equipment will be large and small defects, generally these defects will appear in the gate position, and the gate position belongs to the starting position of mold processing. Therefore, these two positions are prone to problems, then we need to find ways to eliminate these defects, so that the display effect can be improved.
Dark spot defects and subtle defects can appear near the gate, and feel when producing high viscosity, low mobility materials such as PC, PMMA, or ABS in particular. When the surface layer of the resin cooled by the resin flows away, the visible surface of such defects of the product may occur.
It is often found that the technical defects often occur in the filling and pressure maintaining stage. In fact, dark spots appear near the gate, usually at the beginning of the injection time cycle. The experimental results show that the problem of surface slip is actually due to injection velocity, more precisely the velocity of the current assets at the front of the melt flow.
Even if the injection velocity of melt is constant when it enters the mold, the flow velocity will change. When entering the gate area of the mold, the melt speed is very high, but after entering the mold cavity, the melt speed begins to decline. This change in the flow velocity at the front end of the melt flow can lead to surface defects.
One way to solve this problem is to reduce the injection rate. In order to reduce the velocity of the melt flow front at the gate, injection can be divided into several stages and the injection speed can be gradually increased.
Another reason is that the low melting temperature of the product is the dark point, and the increase of the barrel temperature can reduce the back pressure of the screw to improve the possibility of this phenomenon. In addition, the surface defects will be produced when the temperature of the die is too low, and the mold temperature is a feasible choice to overcome the surface defects of the product.