Want to stay up to date on all the latest and greatest purging techniques? Articles by Purgex staff are sometimes featured in Plastics Technology. The first article below was written by our very own David Denzel!
Dave Denzel is our resident processing guru here at Neutrex. His 30+ years’ experience in the plastics industry has made him an outstanding resource on plastics processing.
Having worked in the manufacturing plant as an injection molding manager and a senior process engineer, as well as in the classroom as a molding instructor, Dave brings a unique perspective to the plastics field. Dave will give some advice on purging, molding, or just share a handy trick he’s picked up along the way.
These tips are not meant to be all inclusive, but will be included here as a basic guideline to troubleshooting. Contact your material, machine, or mold supplier for additional information concerning your specific product.
Reasons for Screw Slippage and How to Solve It.
One problem for injection molders or extrusion molders is screw slippage. Screw slippage occurs when the screw has difficulty picking up material from the feed throat which causes increased cycle time and other molding issues. One situation that causes screw slippage is changing from a high temperature material, such as nylon and ABS, to a lower temperature material like TPO or PP. If you start lowering your temperatures too soon, the previous material won’t be removed completely and buildup will occur. Buildup continues to accumulate after each material change until slippage occurs.
I’ve seen all types of strange techniques to remove this buildup, such as dropping pallet wood, walnut shells, or hand soap into the feed throat. Aside from potentially being very damaging to your machine, these methods are time consuming since removing the nozzle or die head is still required. They also do nothing to clean internal components, such as the check ring, and can give off a very strong odor.
Solution: You can stop your machine and take it apart to manually remove the buildup. The major downside is that this will take considerable time away from production.
Another answer would be to use a Purgex™ purging compound as a maintenance purge. Purgex works to remove buildup in the feed zone, thus protecting against screw slippage. With consistent use of Purgex™ between material changes, buildup of materials on your barrel, screw, and hot runner systems will be greatly reduced or eliminated.
If you have any questions regarding screw slippage or Purgex, please feel free to email or call me at 1-800-803-6242.
Many of us in the molding industry have first-hand knowledge of the smoke and smell emitted from Acetal when purging. One trick I use is to submerge the purge pile into a bucket of water immediately after purging. This creates a barrier around the purge pile, trapping the gas and odor inside.
Note: Purgex is recommended for use on Acetal materials; the active ingredients in Purgex neutralize Acetal, resulting in a significant reduction of odor and gas when purging.
Purgex is safe and effective for hot runner systems with gates as small as 0.030-inch (0.75 mm). Purgex contains a lubricant for fluidity and ease of removal. Depending on resin type and gate size, it may be necessary to raise the hot runner temperatures 50˚F to enhance the flow. Call or email us and we will work with you to determine the best method to use.
Have your own question or problem you’d like some advice on? Fill out the form below and we’ll select questions for future installment to Dave’s Tip of the Month.