Gels come from many different sources such as suppliers, processes, and contamination. But one thing for sure is that gels are a quality nightmare.
While recently working with some folks who blow film for a living, I learned of a problem that has been going on for some time and continuing to build. Gels have been becoming a big issue. These Gels cause rejects in the final product, which results in loss of money due to scrapped product and lost time.
This company has many machines processing PP, HDPE, LDPE, and LLDPE resins into mono and multi-layered films using spiral dies. Over the years these dies have been taken apart hundreds and hundreds of times to clean. I have recently learned that low-flow areas in dies can and will cause gels to occur due to the “low flow” or worn areas not shearing the material as needed. This can be diagnosed by noticing if the gels tend to line up in a line coming out of the die. Gels do not know how to line up unless they are mechanically driven to do so.
Here is a tip on how to know whether your die is worn and creating gels. At the end of the production run, drop in a hand full of colored pellets into the production resin. It does not matter which color, but darker is better than lighter colors. Allow this material to flow through the system. Once the color has stopped coming out of the die and it is just natural resin, run the material all the way out and stop the machine and disconnect the die. At this point, we need to tear the die apart. As you start to peel the layers down, look for any color left in the die. If there is colorant left in the die, this is where the worn area is located inside the die. This die should be taken offline and repaired.
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