In Pursuit Of The Perfect Injection Moulded Part 2 – Burn Marks

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, tooling design or a combination of all three.

This is the second on our series of posts where we look at a number of issues that can affect the quality of the end product and some of the common remedies. This post is about Burn Marks.

Burn marks

Injection Moulded Part - Burn MarksBurn marks typically appear as black or rust-coloured discoloration on an edge or surface of a moulded plastic part.  Burn marks generally don’t affect part integrity, unless the plastic is burned to the extent of degradation.

Causes and prevention of burn marks

The usual cause for burn marks in injection-moulded parts is trapped air, or the resin itself, overheating in the mould cavity during the injection process. Excessive injection speeds or heating of the material often lead to overheating that causes burns. Consider the following preventative measures to avoid burn marks in moulded components:

  • Lower the melt and mould temperature to prevent overheating
  • Reduce the injection speed to limit the risk of trapping air inside the mould
  • Enlarge gas vents and gates to allow trapped air to escape the mould
  • Shorten the mould cycle time so that any trapped air and resin don’t have a chance to overheat

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.