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Causes of discoloration during injection molding


Discoloration during injection molding can be a frustrating obstacle in the production of plastic parts.  Apart from diminishing the aesthetic quality of parts, it can also indicate underlying issues that affect the structural integrity of the parts.  In this article, we will explore the common causes of discoloration during injection molding and how they can be prevented.

1.  Inadequate Temperature Control

One of the major causes of discoloration during injection molding is improper temperature control of the plastic material.  If the temperature of the plastic material is too high, it can result in thermal degradation which causes yellowing or browning of the part's surface.  On the other hand, if the temperature is too low, it can cause the material to have a bluish or whitish appearance, which is also unappealing.  

2.  Contamination

Contamination of plastic material with different colors or metallic impurities can cause discoloration during injection molding.  It's vital to ensure the raw materials used in the injection molding process are free from contamination.  For instance, the presence of a small quantity of PVC in polypropylene material will lead to significant discoloration, which is not easy to correct.

3.  Poor Venting and Drying

The injection molding process requires the material to be dry and free from moisture to prevent discoloration.  When moisture is present, a chemical reaction occurs during the heating process that leads to discoloration.  Poor venting during the injection molding process can also lead to trapped air in the parts, which can cause discoloration as well.

4.  Overheated Mold

The mold should be maintained at an optimal temperature to avoid discoloration during injection molding.  An overheated mold leads to poor material flow and high shear, which causes discoloration.  It's essential to use coatings on the molds to maintain the right temperature and avoid overheating during the injection molding process.

5.  Poor Injection Molding Machine Settings

Inadequate machine settings can also lead to discoloration during injection molding.  For example, excessive injection speed can cause surface scarring, leading to discoloration.  It's essential to optimize machine settings and run trials to ensure the right settings are used to produce high-quality finished products.

Preventing discoloration during injection molding requires an understanding of the underlying causes and investing in the right equipment and processes.  Avoiding contamination of the raw materials, maintaining the optimum temperature of the material and mold, drying the material,

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