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Preventative Maintenance Purge Program to Avoid Pulling the Screw in Injection Molding

Written by: Purge Technical Manager, Dave Denzel

Recently I received a call from a Process Engineer where we had worked together in the past at a different company. He has now been working at this company that runs IM elastomers and learned I worked with purge compounds. He was experiencing contamination from degradation and asked if I could come by and help out. The last thing he wanted to do was pull the screw. I brought a mechanical purge and a chemical purge to evaluate. He was concerned with the properties of the mechanical purge so we tried the chemical purge first. It seemed to work pretty well, but after about a half hour of running production the contamination started to come back so I suggested to try the mechanical purge. The mechanical purge seemed to work really well, but he noticed a different color was now coming out. We decided to perform another mechanical purge in which another color came out. We decided to do one more purge before he would decide if pulling the screw was needed. This time a color came out that they had not run for 10 months, but the purge at the end seemed to be clean so after rinsing out the purge with the next production resin he started the press with no contamination after a two hour run. Needless to say the PE implemented a purge program to eliminate layering of the screw and then trained his process group to execute the program.

As a Best Practice, implementing iD Purge Compounds into a Preventative Maintenance Purge Program is essential to increasing efficiencies and profitability in any plastic processing facility. Whether experiencing black specks caused from resin degradation or color contamination from a previous production run, most part aesthetic issues are related to the lack of a better purging program.

The following Preventative Maintenance Program is recommended by iD Additives, Inc. for the Injection Molding Process and includes the following Steps:

Step 1: Purging the Screw and Barrel with a Mechanical Purge Compound this is the first step in removing the contamination and build up on the screw and in the barrel. Tougher Purging Applications may require Additional Purging Cycles.

Suggested Product: iD Purge MP / iD Purge MP/PE

Step 2: Intermittent Purging before/during and after production runs. This process varies depending upon the resin and colors being run - however, purging every two to three days would be a good place to start. Evaluation will determine whether longer periods may be introduced.

Suggested Product: iD QuickShots / iD Purge SP/PP / iD Purge SP/PE

Step 3: Shutdown and Start-Ups- Sealing the barrel with iD Purge for weekend or holiday shutdowns is great for removing oxygen from the barrel (eliminating any oxidation), as well as preventing any build up from carbon that may be in the initial stages.

Suggested Product: iD QuickShots / iD Purge SP/PP / iD Purge SP/PE

Step 4: Purging the Hot Runner/Manifold Systems- After the Screw and Barrel have been systematically purged clean, the final stage is designed to insure the mold and its components have been purged clean and are free of contamination.

Suggested Product: iD QuickShots / iD Purge SP/PP / iD Purge SP/PE

Incorporating different Typed of Purging Compound into a Preventive Maintenance Purge Program can substantially reduce layers of carbon build up, eliminate the potential of cross-contamination of resins and/or colors, and lessen the need for screw pulls.

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