Rubber Chunking

What it is

Rubber chunking occurs when rubber erroneously adheres to the mold as it is being extracted from the mold. This leaves a void in the product being made as well as leaving residue in the mold, affecting both part and process.

What causes it

In a rubber-bonding environment, adhesives give off gasses onto the mold surface, causing the rubber to adhere (bond) to the mold. Chunking typically happens when the rubber-to-rubber bond is weaker than the rubber-to-mold surface bond, which the release agent is there to prevent. Adhesive off-gassing occurs in the closed mold when adhesive on a substrate is heated to the point of becoming a gas. If there is no rubber present in the cavity during this time, the adhesive will then transfer and bond to the mold. This most often happens in an injection molding or transfer molding environment.

Solutions

A good release agent will help prevent adhesive transfer to the mold (staining), eliminating chunking issues.

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