NEWS & EVENTS

Solution for burning defect of plastic product on molding

01/04/2020
Burning defects of plastic products form during the injection molding process but the main cause is from the plastic injection molding 

In the mass plastic molding process, defects can occur. There are slight defects which can still be accepted through customs. On the contrary, there are defects that will cause the product to be completely eliminated, such as a burning defect.
Solutions to fix mold burning defects

Burning is a phenomenon in which black burnt material appears on the surface of injection molding products. At the time of molding, injecting hot plastic into the cavity, any remaining air inside the cavity will be compressed and heated. Therefore, the plastic flow in the mold cavity is in a state of melting and having high temperatures, the situation of overheating breaks the physical properties of the plastic leading to burning.

The effect of surface flammability is not good in terms of the quality of the product's appearance, lack of or deformation of the parts according to the prototype of the product, reducing or destroying the physical properties of plastic, etc.
Plastic Injection Molding Burn Marks


To overcome the problem of evaporation on plastic injection molds, we can do the following:

Provide vents by adding exhaust at the burnt position.
Make the vents deep, providing enough exhaust path to be removed in the mold cavity. A common practice is to divide the component at that location into two or more parts so that the air can escape through the component assembly opening.
Separating the mold and maintaining clean vents.
Increasing the surface air release of the mold
Use vacuum equipment
Change port position and port size: changing gate position will push the defect position to a new position. And if the new location has a better chance of air release, the problem will be solved.
Implementing the change solution on the mold is not as easy as what we mentioned. Therefore, these solutions should be implemented by a professional mold designer & manufacturer to avoid overcoming the burning problem and other defects will occur.

Remedy solutions for burning associated with injection molding conditions
Slow down the injection speed: then the pressure rises slowly enough time for air to escape.
Make cylinder temperature lower
Prevent the stagnation of plastic inside the cylinder
Try reducing the clamping force. When the clamping force is set too high, it compresses the mold to the point where the vent is pinched.
The remedy related to the design of injection molding products

Designing of plastic injection molding products will also become a major cause of the burning of the surface of plastic products during injection molding. The proposed disability-related options for specific product design are as follows:

A blueprint should be used to avoid thin wall parts in the product. That is, the design of the injection molding product must ensure that the finished product is not too thin, the wall thickness is in the appropriate condition without causing errors when casting.
Change the product wall thickness and change the flow pattern of molten plastic. The thin product will make it difficult for the injection molding process to create the perfect product. Therefore, for thin-walled products or calculating the increase in wall thickness of the product at the allowable standard.
If necessary, the shape of the product part may need to be changed to allow blocked air to escape.
In summary, the above measures are for reference only. To know the specific cause of the burning phenomenon on plastic products and have a thorough solution, you need professional advice, the help of a unit specializing in molds and plastic injection molding.




 

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