The wear appears to be either a chemical reaction to the screw surface, or severe abrasion.
The "yellow" material I assume is one of the additives in your master batch. That said, it appears that it is a powder of some sort and not part of a color concentrate or master batch in the typical sense of the word. The first photo shows a close up of the second turn of the screw and it too exhibits the same pitting as that seen in what appears to be the transition section of the screw, although not nearly as bad as evidenced by the second photo, which shows the transition and first few turn in the same view. This leads me to lean towards abrasion as the material is more tightly packed in this area than the first few turns at the feed.
I am betting that the metering section shows little or no signs of wear as the ingredients are well mixed and lubricated by the time it reaches that section.
To help define the problem, can you tell us if the same material has ever run on this machine with a different screw or on another machine without experiencing a similar issue.
As to the different melt temperatures of the various ingredients, I doubt that has nothing to do with the wear. It looks more to be a mechanical issue as the leading or pushing edge of the flight appears to be worn down thinner in the one photo indicating abrasion, whereas a chemical reaction might affect the complete screw in a uniform pattern
As to the screw “breaking”, that is another story and would require more details such as screw speed at break, motor amps, and barrel temperatures at a minimum. Not knowing those details makes it difficult to put the blame on the manufacturer.
Hope that helps
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