The plastic injection molding factory BOOLING is not always smooth sailing in the production and manufacturing process. Various problems may appear on the surface of the products, which requires rich production experience to analyze and solve the problems.

1. Shrinkage Marks

The uneven shrinkage marks caused by large differences in wall thickness in plastic products are called shrinkage marks. If the molding process is not properly controlled, the injection pressure and injection speed should be appropriately increased, the pressure of compressed melt should be increased, and the injection and holding time should be extended to compensate for the shrinkage of the melt and increase the injection buffer. But if the holding pressure is too high, it can cause protrusions. If there are depressions and shrinkage marks near the gate, the pressure holding time can be extended accordingly; When the depression occurs at the wall thickness of the plastic part, the cooling time of the plastic part in the mold cavity can be appropriately extended; If the depression and shrinkage marks around the insert are caused by local shrinkage of the melt, it may be due to the low temperature of the insert. In this case, the plastic injection molding factory should try to increase the temperature of the insert; If the depression on the surface of the plastic part is caused by insufficient feeding, it should be considered to increase the feeding amount. In addition, the plastic parts must have sufficient cooling time inside the mold. To avoid defects, the gate or runner section should be appropriately enlarged based on the actual processing situation. The gate position should be designed as symmetrical as possible, and the feeding port should be set in the part with a larger wall thickness than the plastic part. If dents and shrinkage marks occur at a location far from the gate, it is generally due to poor flow of molten material in a certain part of the mold structure, which hinders the transmission of pressure. Defects caused by this reason should be appropriately enlarged in the structural dimensions of the mold pouring system, and it is best that the flow channel can extend to the area where the dents occur. For plastic parts with high requirements for smoothness, plastics with lower shrinkage rates should be used as much as possible, and the amount of lubricant can be appropriately increased in the raw materials. When the shape and structure design of the plastic part is unreasonable, it should be redesigned to ensure even wall thickness as much as possible. Adjusting the structural parameters of the pouring system or changing the wall thickness distribution can also effectively solve the problem of significant differences in plastic wall thickness.

2. Water Ripple

Water ripple generally appears near the gate and is a mark that appears when the melt flows, which cannot be eliminated after the product is formed. Water ripple is formed by the rapid cooling of the first batch of molten material entering the mold cavity, and the subsequent injection of hot molten material pushing the first batch of cooled molten material to slip, forming a water ripple-like pattern. The main methods to improve this problem include increasing the melt temperature and mold temperature, accelerating injection speed, and increasing the holding pressure. The cooled plastic remaining at the front end of the nozzle, which directly enters the molding cavity, will also produce water ripples. Therefore, to prevent the generation of water ripples, a plastic injection molding factory can open a cold material well at the end of the main channel.

3. Airlines

During the injection molding process, if the injection speed is too fast but the gate is too small, it is easy to cause drastic changes in the flow of the melt and air inclusion. Clear shadows will appear at the gate position, turning position, and step position of the plastic part, which are called air marks. It is possible to slow down the injection speed or increase the size of the gate appropriately.

4. Black Stripes

Black stripes are black stripes that appear on the surface of plastic parts, also known as black stripes. The thermal decomposition of formed materials is the main reason for the occurrence of black stripes, which is particularly common in plastics with poor thermal stability (such as PVC). Preventing the melt temperature inside the barrel from being too high and slowing down the injection speed can effectively prevent the occurrence of black stripes. If there are scratches or notches on the barrel or screw, the material in this part is prone to thermal decomposition due to overheating. In addition, another important reason for thermal decomposition caused by melt retention is the cracking of the check ring. For plastics with high viscosity or easy decomposition, special attention should be paid to preventing the occurrence of black stripes.