Gas burn" in injection molding refers to a specific defect that occurs on the surface of plastic products. Injection molding is a process in which molten plastic material is injected under high pressure into the mold of an injection molding machine and cooled to form a product. During this process, flammable gases (low molecular weight components, moisture, flame retardants, etc.) generated from the plastic material and air are rapidly adiabatically compressed inside the mold, causing the gases to burn, which can result in a burnt plastic molded product.
When gas burning occurs, discoloration and short shots in the burned areas result in defective products. In addition, if burning occurs in the weld area, the strength of the product is extremely reduced, so care must be taken.
The main causes of gas burns are the following factors
(1) Plastic materials
Plastic materials used in injection molding may contain volatile components such as plasticizers, solvents, demolding
agents, and stabilizers added by the manufacturing process or raw materials.
Plastic materials used in injection molding may contain volatile components such as plasticizers, solvents, demolding
agents, and stabilizers added by the manufacturing process or raw materials.
In the injection molding process, these components can vaporize at high temperatures and be released as flammable
gases.
If these components vaporize under high temperatures and are released as flammable gases, they may cause gas burns.
PPS, ABS, PPO, PA, and PBT are materials that often generate gas.
(2) Molding
When plastic materials are injected at high speed in injection molding, if the mold is not equipped with sufficient gas
venting, gas can be released from the plastic material.
If the mold is not equipped with sufficient gas ventilation, flammable gases generated from the plastic material may
escape from the mold
The gas is rapidly adiabatic compressed together with air without enough time to escape from the mold, resulting in high
temperatures and oxidative combustion, which can cause burning.
This can result in high temperatures and oxidative combustion, which can cause burning.
(3) Product and mold design
If the design specifications of the product or mold do not provide sufficient gas venting in spite of the shape of the
product or mold that easily accumulates gas, the gas will be trapped and burnt by oxidation combustion.
If the design specifications of the product or mold do not allow for sufficient gas venting despite the shape of the product
or mold that easily accumulates gas, the gas may become trapped and gas burning may occur.
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