Wednesday, April 20, 2011

What did you use last time?

Plastics News has a thought provoking article raising this question. The article largely features a talk given by a PP supplier, Perrite, who as you would expect, is trying to get designers to look at using PP in settings that it has not be previously considered. Before I get into it, let me be clear: I am not picking on this speaker or the company or its products. I'm just using it to point out that resin decisions can be complicated by non-scientific reasons.

The article cites one example of resin replacement that is quite catching and well argued:
"(The speaker Mark) Lewis cites the example of the humble electrical socket back plate, which is typically molded from polyamide, PBT or PC. The back plate needs to be physically tough for installation, but just once, notes Lewis. And while thermal resilience is also required, "two hours at 100 deg C is not particularly demanding," he adds. In terms of flame retardance, V2 or V-0 materials are typically used in the back socket but in actual fact, this level is not demanded. "The BS1363 glow wire flammability index is sufficient," says Lewis.

The material must be injection moldable, but tight tolerances are not required and while back plates are typically colored black, "there is no need for any particular coloration because the component is not visible," according to Lewis. Perrite has shown that impact copolymer PP filled with a 10% loading of talc is more than capable of meeting system requirements, meeting glow wire tests and also being RoHS and Reach-compliant."
As I said, the argument is compelling to make the change. But at the same time, I can imagine some years down the road sitting in a witness stand being asked questions by a lawyer who is giving me the impression that he had absolutely nothing more to do all day and possibly all week then ask me more questions. Consider this:

"Dr. Spevacek, given that our investigator's report showed the jury overwhelming and incontravertible evidence that the fire that destroyed my client's house leaving her a poor, penniless widow started in the electrical box, could you please tell the jury why you thought saving a few pennies by switching to this new, ahem POLLY-PROP, excuse me POLLY-PRO-PILL-ENE chemical would be a good idea?"

Let's just say that "well the supplier said it was o.k." would not be a good answer.

Again, let me be clear: I am not picking on this speaker or the company or its products. It's just that sometimes there are strong reasons for doing what you've always done and doing what your competitors are doing. Sadly, courts of law do not rely on scientific truth, common sense or reason. With two adversarial parties, there is no effort made to decide what is right, only who wins, and that decision can be made on emotional issues such as I tried to pose in my imaginary cross-examination.

I do very much support the actions and questioning that the speaker proposes. It is important to keep considering new options, but as we all quickly learn after a few years on the job, making a decision on scientific and engineering principles alone never happens.

1 comment:

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