I remember one particular visit I had at a plant in Arizona. I was invited to a molding trial for Celcon M90. We were to mold wheels for VHS cassette tapes. I was brought out to the machine and I noticed it was running a lower temperature grade of Acetal. The operator ran off to get a purge compound that he would use to clean the screw and barrel before getting into the material we were going to run.
As the purge was introduced to the machine something troubling happened--the screw completely stopped!
The operator was not sure what was going on.
After further investigation, we learned that he used the wrong grade of purge compound.
The grade he selected was designed for higher temp resins.
The only way to resolve this dilemma was to increase the temperature of the barrel to exceed the limit of the Acetal that was still inside the barrel.
As you may know, Acetal is a temperature sensitive resin and as the heats came up, we developed a flamethrower at the nozzle of the machine and cleared the plant of all production personnel due to the degrading Acetal turning to a toxic gas.
We were very lucky not to have blown the hopper off the machine and through the roof.
The point is, make sure to grab the right grade of purge for the right job and always follow the suppliers recommended directions.
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