Anyone know what chemicals do they use to clean the screws on injection molding machines? Something that oxidizes plastic? The handles look like they were made in a 2-shot mold, hard plastic frame with soft plastic touch surfaces. If some cleaning chemicals got stuck between the shots they could eventually leak out and somehow start the exothermic reaction upon contact with air.

I have been to an injection molding shop a few times and it always seemed like a lot of labor was going in to cleaning the molds and the injection screws. Maybe a worker found a shortcut.