Burns are a phenomenon in which black burnt material appears on the surface of the molded product. At the time of packing molten plastic into the cavity, any air remaining inside the cavity gets compressed and generated heat thereby burning the plastic causing these burns.
Burns cause defects such as defects in the external appearance quality of the product, missing parts in the shape of the product, reduction in the physical characteristics, etc.
The following methods can be thought of as the countermeasures for solving the problem of burns.
(1) Countermeasures related to molds1. Providing air vents.
2. Making air vents deep, providing sufficient air exhaust path.
3. Taking apart the mold and cleaning and maintaining the air vents.
4. Using a divided structure or nested structure for the mold and letting the air escape from the parting surface.
5. Using a vacuum suction apparatus.
6. Changing the gate position.
(2) Countermeasures related to the injection molding conditions1. Making slower the injection speed.
2. Making the cylinder temperature lower.
3. Making the charge quantity smaller.
4. Preventing stagnation of the plastic inside the cylinder.
(3) Countermeasures related to the molded product design1. Using a design that avoids thin walled parts in the product.
2. Changing the wall thickness of the product, and changing the flow pattern of the molten plastic.
3. Changing the shape in which air gets trapped.
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