Plastics processors neglect finer points of resin drying at their peril

Mark Haynie, Novatec
Mark Haynie, Dryer Product Manager at Novatec.

Perhaps this has happened to you. You go to change the bulb in your car’s headlights by pulling back the plastic clip that holds it in place. The clip breaks. Now, instead of replacing a $10 bulb, you’re looking at replacing a mounting system that will set you back several hundred dollars. It happened to Mark Haynie, Dryer Product Manager at auxiliary equipment supplier Novatec (Baltimore, MD), and he told me the anecdote to make a point about resin drying.

“Most of these clips are made of nylon, and I have had resin companies tell me, ‘you can’t over dry nylon.’ That’s interesting, I respond, because I’ve seen the results of that. ‘No, no, no—all you have to do is recondition the part,’ they will tell me,” said Haynie.

Reconditioning in this context means spraying the parts with water. “The nylon absorbs the water and suddenly the parts pass quality control (QC),” explained Haynie. “The part itself hasn’t really changed, but now you can ship it to your customer because it passed QC. When you take that part and put it under the hood of a car, where it’s a couple hundred degrees and it’s the middle of winter when things are at their most brittle, that reconditioned part all of a sudden fails. The objective for the plastics processor should not be passing a test, but making a good part that doesn’t fail,” stressed Haynie. Which brings us back to the topic of resin drying.

Mark Haynie will explain how to prevent polymer degradation during a presentation, Drying Specialty Plastics for Medical Molders and Extruders, on Feb. 5 at 4:45 PM during the Technical Solutions conference track at the co-located MD&M West and PLASTEC West trade show and conference. The event comes to Anaheim, CA, on Feb. 5 to 7, 2019. For more information and to register to attend, go to the PLASTEC West website.

Drying is a necessary evil for most plastics processors, acknowledged Haynie. “No one wants to do it,” he said, but doing a slapdash job of it will come back to bite you down the road, as the headlight anecdote illustrates. That applies equally to extrusion: Consider a catheter made of polyurethane. The material was selected partly because of its flexibility, but it has become brittle because of over drying. The result can be catastrophic, said Haynie, who has been designing and building dryer systems for nearly 40 years. He has a degree in chemical engineering and a post-graduate degree in mechanical engineering from John Hopkins University. 

Temperature setback and dew point measurement

The cost of resin can be the most expensive item in a plastic processor’s operation, noted Haynie, and that is especially true in medical applications. “If you buy the resin for specific properties that are not coming through in what you are producing, you are at a competitive disadvantage,” he said. So, resin drying is an important step in the production process, but processors would rather not think about it. That’s why Novatec and other suppliers of auxiliary equipment “spend a lot of time automating operations to dehumidify resins,” said Haynie.

One such operation is temperature setback. “When the resin has very little moisture, or if the throughput is less than what is rated for that equipment—I have a 400 pound/hour dryer but I’m only drying 200 pounds of resin, for example—theoretically I should be using about half the amount of energy,” explained Haynie. “In many cases, temperature setback typically asks, at what temperature would you like the setback and what would you like to set it to? Sometimes, people within my own organization don’t know the answers. So, we have built in algorithms that adjust the amount of energy used in relation to the amount of moisture and throughput at any given time.”

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