Messages Archive

Re: Adhesives and polycarbonate

Larry Clinton At Frankfort, (Central) Indiana
You are correct! Several years ago when I was an Engineer over several assembly lines, I had an issue with some acrylic clear shields used on pneumatic assembly machines cracking fairly often and having to be replaced. I had researched polycarbonate (Lexan) and decided to fabricate some and install them on the more troublesome machines. They were easier to fabricate as the material bent 90 deg in a brake and drilled / tapped easily.

After a few weeks usage the shields cracked around every screw mounting and anywhere else where they were stressed. I found the cause was that we had a "lube station" about 50 ~ 75 foot away where we dipped lubricated small parts in a screened bucket and allowed to drain by hanging the bucket above the tank. The lubricant was Aeroshell 7, thinned with 1,1,1-trichloroethane.

I found the Lexan was ultra sensitive to any chlorinated solvent
and would literally disintegrate when stressed and exposed to these. Had some egg on my face when I had to have all new acrylic shields made and the Lexan ones replaced!

We also had a major customer that required we ultrasonic stake a Lexan shaft extension to a TV control we produced. (They made the Lexan material). We recommended using Nylon as it was easier to mold and assemble but they insisted. A few months after the units were installed and in the field, they had a major issue and recall due to the extensions failing and the knobs falling off.

It was determined the issue was that the TV's owners were using a household cleaner to clean the sets which contained a chlorinated solvent. The company immediately (and quietly) switched to a nylon part!

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