Plastic Injection Molding Defects: Splay

Welcome to our Plastic Injection Molding Defects series, where we will explain some common defects seen by injection molders and offer ways of fixing or preventing them.

What is Splay?

Splay is a cosmetic defect that occurs in plastic injection molding, when silver or white streaks appear on the surface of the part.

It can be difficult to determine what is truly splay, as its appearance is very similar to other defects. Lookalikes include surface scratches, scuffs, flow lines, delamination from contamination, and flaking (also known as cold slugs).

What Causes Splay?

There are many possible culprits for the appearance of splay. Chapter 42 of Injection Molding Advanced Troubleshooting Guide: The 4M Approach outlines a specific troubleshooting method for determining the source and correcting it. The defect could be due to any number of issues with the molding process, the mold itself, the machine, or the material.

Table 42.1 Splay Troubleshooting Chart, found in Injection Molding Advanced Troubleshooting Guide: The 4M Approach (p. 414)

Molding Process Mold Machine Material
drying venting screw design contamination
high melt temperature hot runner temperatures temperature control excessively wet
decompression cold slug wells damaged components wrong material
back pressure sprue and nozzle tip orifice cracked feed throat blowing agent
screw recovery rate sharp corners lack of process control
residence time gate flaking
screw recovery lubricants
feed throat temperature cracked mold
inconsistent material feed leaking air
Venturi effect


To begin, determine how the defect appears on the parts. If the marks appear consistently in the same location on parts, the problem is likely stemming from the mold itself. If the defect is all over the part and/or appears in random places, that usually means the issue comes from the molding material or process.

We recommend referencing the Troubleshooting Guide to help you fully understand which of the above may be causing the defect and how to best fix it. At Nanoplas, we are particularly familiar with lubricants’ contribution to splay through our discussions with molding professionals over the years, so we’ll explore ways to address this possible culprit in the rest of this post.

Over-Lubricated Molds Can Cause Splay

If the defect appears immediately after the mold has come back from the toolroom, it may be due to too much grease or lubricant being applied to the mold. In this case, grease from the lifters or ejector pins can bleed onto the core surface, get pulled onto the surface, and leave splay marks or streaks.

Similarly, lubricants and metal protectants can become trapped in mold inserts and bleed out, getting pulled onto the mold surface and causing splay.

“Less is more” when it comes to applying mold maintenance products in a way that won’t cause problems. You may need to wipe out the excess lubricant, even disassembling the mold as necessary to get all the excess. For more information related to mold maintenance, read: How to Properly Apply Injection Mold Coating.

If decreasing the amount of grease or lubricant causes wear or other issues, you may want to try higher performing mold maintenance products that can do the job with less volume per application.

How to Fix Splay

Again, be sure to fully troubleshoot each key area of injection molding—the molding process, mold, machine, and material—to find the true source and determine the best course for addressing your unique situation.

If you suspect the mold grease is causing the issue, it may be time to try something new.

Switch Mold Maintenance Products

Nanoplas has several products that can eliminate splay caused by over-lubrication.

Some rust preventatives can use a heavy wax or too much solvent, making it necessary to clean the mold before use to prevent splay caused by the bleeding or breakdown of grease. The Nanoplas family of rust preventatives are truly “dry” and leave a light film that will not bleed or break down grease. On a typical startup, the Nanoplas rust preventatives will be gone in 2-4 shots.

If grease is getting into the molding area, that means it is breaking down from a rust preventative, cleaner, or heat. Nanoplas greases do not break down and will not bleed into the molding area like other greases. This eliminates grease from the splay equation.

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

Want to learn more? Check out these other great articles that solve common injection mold issues:

Source: Injection Molding Advanced Troubleshooting Guide: The 4M Approach by Randy Kerkstra and Steve Brammer.