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Subject: Re: reworking polypropylene

Date: 01/29/02 at 10:38 PM
Posted by: Carl Howarth
E-mail: howarthc@mediaone.net
Message Posted:

In Reply to: reworking polypropylene posted by Leo on 01/29/02 at 9:32 PM:

Leo,

Tough call. Likely, the PP sheet in that thickness had a LOT of stresses on the surface due to the extrusion process. Even molded parts have the same problem. When you machined it, you relieved the stresses on 1 side, allowing it to warp.

2 choices.

1. 'Anneal' the material before you start by heating in an oven for a few hours, and letting it very slowly cool. This should relieve some of the stresses. For PP, something like 150 F should be OK, but higher temps might be needed.
2. Fixture the existing part and heat it to bring back the shape.

Good luck,
Carl


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