Black Spots Of Common Problems In Injection Molding

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What is a black spot? Black spot refers to the black spots or stripes on the molded products.
Causes of black spots on injection molded parts:
1. Resin decomposition
As plastic is a chemical, it will decompose gradually when it is heated above the melting point. The higher the temperature, the longer the time and the faster the decomposition. In addition, there are some areas in the barrel that are easy to retain resin, such as check check valve and thread.china mold maker The resin remaining in these parts will be scorched or carbonized and then dropped into the molded product, causing black spots.
2. Insufficient cleaning
The reason for the black spots is that the previously used resin remains in the injection molding machine due to insufficient cleaning. As mentioned above, due to the presence of areas that are easy to hold the resin, such as stop rings and threads, the corresponding strength and cleaning time must be applied to these areas during material change. In addition, cleaning methods suitable for each material must be used. It is ...
... relatively easy to clean similar resins, but if different types of materials are cleaned, due to the different melting point or decomposition temperature, there is compatibility between the resins. Despite cleaning, in many cases, it can not be completely removed.
3. Foreign matter mixing (pollution)
Pollution is also one of the causes of black spots. If some particles in the feed hopper are mixed with other resins with lower decomposition temperature, black spots may be easily caused due to resin decomposition. In addition, attention should be paid to recycling plastics. This is because recycled plastics are easier to decompose after multiple heats. In addition, it may be contaminated by metals in the recycling process.
Injection parts black spot solution:
1. Clean thoroughly until no black spots appear.
Black dots tend to stay in the stop ring and screw into the barrel. If there is a black spot, it is estimated that the cause of the black spot is likely to remain in the barrel. Therefore, after the appearance of black spots, it is necessary to thoroughly clean the lens barrel, and then take countermeasures (otherwise, the black spots will never disappear).
2. Try to reduce the resin temperature
Recommended temperature for all resins (also included in product catalog or product packaging). Check whether the setting temperature of the molding machine is out of the range. If so, lower the temperature. In addition, the temperature displayed on the molding machine is the temperature of the sensor area, which is different from the actual resin temperature. If possible, it is recommended to use a resin thermometer, etc., to measure the actual temperature. In particular, areas prone to resin retention (such as check rings) may cause black spots, so pay special attention to the temperature nearby.
3. Reduce residence time
Even if the setting temperature of the molding machine is within the recommended temperature range of various resins, long-term retention may lead to resin deterioration and black spots. If the molding machine provides delay setting function, please make full use of it and select the injection molding machine suitable for the mold size.
4. Is it polluted?
Occasionally mixing other resins or metals can also cause black spots.
Surprisingly, the main reason is inadequate cleaning. Please thoroughly clean and remove the resin used in the last injection process before carrying out the work. When using recycled plastics, check for foreign material in the particles.
 
 
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