How to fix Splay mark on PP plastic injection molded part

Splay mark, is also called as Splash Mark or Silver Streak.It is a cosmetic defect that occurs in plastic injection molding process, when silver or white streaks appear on the surface of the molded part.

Sometimes Splay can be quite difficult to determine, as the appearance is very similar to other injection molding defects, such as surface scratches, scuffs, flow lines, delamination from contamination, and flaking (also known as cold slugs).

Why there is Splay?

There are many possible reasons for the appearance of splay mark, molding process, the mold itself, the machine, or the material.   Material

The most common cause of splay is material moisture. It is easy to identify that.  The moisture splay does not occur in the same place every time, or in some cases the splay is all over the part.

In this case, use dry material, review material drying process, review material storage for contamination issues

Molding process

Too much heat can have an appearance similar to moisture splay. The splay condition can completely cover a part, or it can appear inconsistently in various areas on the part. Look for signs of stickiness or burning. Another sign can be the smell of overheated material.

Once overheat is identified, check barrel temperatures, back pressure and barrel residence time being too long

  Generally,shear during injection molding process is another cause of splay mark.It repeatedly occurs in the same location on a part. The best method for determining root cause is to note where within the flow front the shear is occurring.


If the marks appear consistently in the same location on parts, the problem is likely stemming from the mold itself.

We recommend contacting us for Troubleshooting Guide to help you fully understand which of the above may be causing the defect and how to best fix it. At Hsmolds,   we are particularly familiar with possible causes contributing to splay through our rich experience over the years and how to address the defect,  below is only one sample of it.

Part Name Auto Bumper
material PP
color black
die temperature 55℃
gate Edge gate

The material splay doesn’t appearing on the bumper doesn’t only affect the cosmetic look, but also the mechanical property. How to fix it?

Splay mark on the PP plastic bump

1) Possible causes and remedies

1.Plastic injection mold : it is a plastic injection mold with hot and cold runner system. However, there is no cold slug well.

2.Molding process:it is found that the sealing of valve gate is not tight enough and cold plastic remains on the injection gate. The pressure that closes the valve gate is pretty low and works poorly.

Correction:in this case, we increase the pressure of sealing valve by pneumatic booster pump. Splay mark is gone when no material leaks through the hot runner tip. Look at pictures as shown.

Feel free to contact us if you have questions about our products and how they might solve your injection molding problems.

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