Cold Slug Injection Molding

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What is Cold Slug in Injection Molding?

Injection molding cold slug refers to a phenomenon where plastic material solidifies in the spruce within the tooling system after every material processing cycle. Of course, this may affect the normal injection molding material through the spruce all to the mold cavity.

Ideally, in your next material injection molding cycle, it will be impossible for the material that remains to melt completely. A reason an injection molding tooling should be configured to deal with the problem.

Effects of Cold Slug on Injection Molded Parts

Remember, the cold slug will interfere with the normal injection molding process in many ways. For instance:

Reduce Mold Size – Clogging mold which will eventually change the intended part design.

Restricted Material Flow – Restrict material flow which can also affect the molding process since this may cause partial filling of the mold. That is if it restricts flow in the mold runner and cavity.

Compromise Part Quality – This can cause marks or scars on the injection molded part. This will compromise the quality of the final part design.

Importance of Cold Slug Well in Injection Molding

As the name suggests, this system acts as a “trap” or “well” that collects cold slugs from injection molded material. Usually, it acts as an important quality control measure during the injection molding process.

During any injection molding cycle, there is always some material that may solidify within the nozzle tip. At the same time, it is important to note that the slug that forms at the tip of the nozzle is not always bad. In most cases, during plastic part ejection, it will prevent drool.

However, during the next cycle of your plastic injection molding, it can be a problem. It is for this reason that injection mold tooling systems feature cold slug well as part of the design. This is quite critical during the cold runner injection molding process.

Causes of Cold Slug Injection Molding

During any material injection molding cycle, many factors may interfere with the optimal material processing.

Possible Cause of Cold Slug Injection Molding Possible Ways to Solve the Problem
Low injection molding temperature ·         Usually, this may cause premature solidification during the injection molding process
Low pressure ·         You must subject plastic material to sufficient pressure that will ensure material flows into the mold cavity before the solidification begins
Low dwell time ·         Dwell time should be reasonable to ensure the material solidifies at the right time and filling the mold appropriately
When the material injection speed is insufficient ·         Injection speed varies with the material type. The speed should be reasonable enough to allow material to fill the mold before solidification starts.
Mold gate design ·         Usually, two variables may cause cold slug in injection molding – the location of the gate and size. Both the size and location of the gate should be such that it allows the material to flow freely thereby filling the mold


In most cases, cold slug in injection molding can be frustrating. Therefore, adopting mechanisms to solve this injection molding defect will help improve material processing quality and part consistency.

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