Common Causes of Injection Molding Defects and Some Preventive Measures

Plastic Injection Molding Machine

When it comes to injection blow molding, you may inadvertently make one of several expensive errors. For example, injected-molded products may have quality issues. In serious cases, these issues may negatively affect the function, safety, and performance of the end-product. There might be a problem with your injection blow molding process or tooling design.

Getting Flow Lines

One issue is to find flow lines on your product. These are lines in a different color than the rest of the product. It often shows up on narrow sections of your component. You may also see a band shaped like a ring on the surface. For certain products, such as sunglasses, these errors are not acceptable.

The problem often results from variations in how fast the material cools down. Another cause is differences in the thickness of the wall, which causes the plastic to cool at different speeds. What you can do to fix it is to increase the pressure, injection speed, and temperature. You can also try rounding the corner of the mold in the injection blow molding machinery, so the flow rate will be more consistent.


A burn mark might appear on your product as either a rusty or black discoloration on the edge of your surface. While this does not affect the integrity of your part, it is unsightly, and customers may reject the piece.

Usually, the reason for a burn mark is the air that has become trapped. That causes overheating in your mold during the injection process. If you inject your material too quickly or overheat it, you may notice burns, as well. Many injection blow molding machine manufacturers recommend lowering the mold and melting temperature to avoid overheating. You can also enlarge the gas vents, so any trapped air can easily escape. 


This is a deformity that can happen if your components shrink unevenly. If the cooling process does not allow for uniformity, then it can stretch as some parts shrink faster than others. You can allow it to cool down slowly, so everything will be a bit more level.

You can prevent this issue by making sure that the material is not too hot in the beginning. You can also try using different materials, as some of them do not shrink as much during cooling.

Injection Blow Molding Machine Manufacturers

There is a fine balance you have to achieve when you want to do injection blow molding right. For example, you do not want to overheat the material and cause burns, but underheating can result in uneven marks on the product. Choosing the right injection blow molding machinery can go a long way toward helping you strike that balance. Pet All Manufacturing Inc. is a supplier of quality equipment. To discuss your project requirements, give us a call today.

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