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Cause analysis and solution of the overflow and burn phenomenon of plastic mold products

Update:07-04-2021
Summary:

The treatment of overflow should focus on the improveme […]

The treatment of overflow should focus on the improvement of the mold. In terms of molding conditions, you can start to reduce fluidity. Specifically, the following methods can be used:
1. Reduce injection pressure;
2. Lower the resin temperature;
3. Use high-viscosity grade materials;
4. Lower the mold temperature;
5. Grind the mold surface where the overflow occurs;
6. Use harder mold steel;
7. Improve the clamping force;
8. Adjust the bonding surface and other parts of the accurate mold;
9. Increase mold support column to increase rigidity;
10. Determine the size of different exhaust grooves according to different materials.

Analysis of the causes of burns in Automotive Moulds products and solutions:

Scorching, also known as scorching, dark spots, black streaks, etc., refers to the dark spots or dark streaks that appear on the surface of the product. Black spots and black streaks are the same type of flaws, and the severity of scorching is different, which is the main cause. The plastic is contaminated by impurities, improperly dried, or the plastic is carbonized due to overheating under high temperature and high pressure conditions, and the carbonized coke is mixed in the melt to form scorching.

According to the burn caused by different reasons such as machinery, mold or molding conditions, the solutions adopted are also different:

1. Mechanical reasons:
For example, due to abnormal conditions, the barrel is overheated, and the resin is injected into the product after high-temperature decomposition and burns, or due to the nozzle and screw threads in the barrel, the check valve and other parts of the barrel causing the resin to stagnate, which is decomposed and discolored. The product has dark brown burn marks in the product. At this time, the lock nozzle, screw and barrel should be cleaned;

2. The reason for the mold:
Mainly due to poor exhaust. This kind of burn usually occurs in a fixed place, which is easy to distinguish from the first situation. At this time, attention should be paid to measures such as adding exhaust grooves and anti exhaust rods;

3. In terms of molding conditions:
When the back pressure is above 300MPa, the barrel will overheat and cause burns. When the screw speed is too high, overheating will also occur, generally within the range of 40~90r/min. When there is no exhaust groove or the exhaust groove is small, the injection speed is too high and it will cause burns from the overheated gas.

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