Plastic Corner Molding in China – Molding the Edges

May 09, 2021

Your Comprehensive Guide on Plastic Corner Molding in China

Sharp edges no doubt look great. But, they can be huge trouble when molding plastic parts. They increase stress concentration which can lead to part failure. These sharp edges most commonly occur in non-obvious places such as a strengthening rib. For this reason, plastic corner molding in China tries to avoid it at all costs. Want to learn more about the design considerations for injection molding? This guide will tell you everything that you need to know. Keep reading!

plastic corner molding in China

Design Considerations for Plastic Corner Molding in China

There is a huge risk of error while designing corners for plastic corner molding in China. These issues can range from small surface faults to some grave problems that can impact the performance and the functionality of the product. These errors can occur due to many problems such as the process of the molding, the material used, and the tooling design.

We have listed some obvious mistakes that make occur while molding the edges of a plastic product below. Let’s take a look at them.

1.      Flow Lines

Flow lines look like a curvy pattern and are of a different color than the rest of the area. These lines occur due to difference in the cooling speed of the material when it flows in multiple directions in the mold. They most commonly appear on the narrower sections of the molded component.

Sometimes, they are even visible as ring-shaped bands on the surface of the product near the entry points. Although these lines do not impact the integrity of the product, they can be unpleasing to the eyes. Moreover, the consumer may even reject the product if they found flow lines on it.

2.      Warping

Warping is another common defect that occurs during plastic corner molding in China. It is a sort of deformation that appears when different parts of molded products are shrunk unevenly. When the shrinkage is uneven, it puts stress on different parts of the product. As a result, bending of the finished part takes place.

It occurs when the cooling process takes place too quickly. Furthermore, the excessive temperature can sometimes make the problem worse. Another reason for warping can be the mold design. When the walls of the design are of uneven thickness, this may also result in warping.

3.      Burn Marks

These marks look like rust-colored or black discoloration and may appear on the corner or the surface of the molded plastic part. Generally, these marks do not affect the integrity of the product unless the product burns so much that it is degraded.

So, why do these marks occur on plastic products? Well, the most common reason that they appear is because of the trapped air, overheating, and resin during the mold cavity. So, if you want to avoid these burn marks, you must lower the melting temperature and reduce the injection speed.

4.      Sink Marks

For those of you who don’t know, sink marks are depressions that appear on the surface of the product that is extremely flat and smooth. These marks appear in the plastic product when its inner molded part shrinks.

When the inner part shrinks, it pulls the material from the edges inward. So, what causes the depression in the surface that was smooth and flat before? The sink marks appear when the molded material takes a lot of time to cool down.

This results in shrinkage which then pulls the material from the edges inwards before it has the chance of cooling down. As a result, depressions in the form of sink marks occur.

5.      Air Pockets

Air pockets are air bubbles that are trapped in a finished product that is molded. Although it is considered a small defect by the quality control professionals, the large and numerous voids have the power of weakening the plastic product.

That’s because the air is below the surface of the product where the molded material should have been. Unsuitable molding pressure is one of the most common causes of air pockets or vacuum voids. The inadequate molding pressure forces the air that is trapped in the product from the mold cavity. As a result, air pockets may occur in the edges of the plastic molded product.

6.      Jetting

Jetting is a kind of a corner molding defect that appears when a jet of molten material is injected into the mold cavity. The major cause of jetting is all the extra injection pressure.

When the material solidifies before the cavity is filled, it results in jetting. It does not only look unpleasing to the eyes but it can result in the weakness of the product as well. Therefore, it should be avoided at all costs. You can reduce the injection pressure and increase the mold and material temperature to avoid jetting.

7.      Weld Lines

Weld lines are another common molding mistake that appears in the products of plastic corner molding in China. These lines appear on the surface of the edges where the molten material has converged after splitting into different directions in the mold.

This results in hair-like weld lines. These lines have the capability of weakening the strength of the product. Therefore, they must not be taken lightly and should be avoided at all costs.

So, how can you avoid weld lines in your plastic molded products? Well, the answer is extremely simple. All you need to do is increase the temperature of the material during molding and raise the speed and the pressure of the injection.

plastic corner molding in China

Final Words

Although sharp edges look pleasing to the eyes, they are not suitable for plastic corner molding. They can result in the weakening of the product. For this reason, they must be avoided at all costs.

We hope the above mentioned defects will help you identifying the molding defects when you see one so that you can avoid them later. For more information, reach out to us and we will be happy to assist you.