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Old 31st July 2010, 09:00 PM   #1
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Default Heat setting PVC ?

Hello,
I am currently re-furbishing some ESL57. I have gathered all needed equipement: PVC 12um, Mylar 6um, Elvamide, ...
I will heat set mylar once put under tension, because it's recommended to do so. For the mylar itself but for the coating as well.
But what about PVC ? Mylar will be warmed up to 150C but PVC cannot stand upper than 80C (glass transition temperature): is it still worth it for PVC ?
Of course I can do it in doubt but my current bench is adapted to higher temperatures.
Thank you.
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Old 31st July 2010, 10:26 PM   #2
SY is offline SY  United States
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Why do you need the PVC under tension?

Also, glass transition is NOT the melting point, just the point at which it goes rubbery.
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Old 1st August 2010, 07:35 AM   #3
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Quote:
Originally Posted by SY View Post
Why do you need the PVC under tension?

Also, glass transition is NOT the melting point, just the point at which it goes rubbery.
Heat-setting is done under tension when using hanging weights, as Quad used to do it in factory (see photos from Quad factory: there is an oven on one end of the stretching jig). This releases residual stress.
Mylar shrinks slightly with heat which is not a problem but PVC which goes rubbery cannot be heated above 80C under tension. Well I did not try it myself but that's what I was told by someone who made the experiment.
Maybe the answer is to warm it higher (lower than melting point but higher than glass point) before tensioning just for fixing Elvamide then put it under tension. In that case this means that PVC will not be heat-set, and maybe does not need to.
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Old 1st August 2010, 11:55 AM   #4
SY is offline SY  United States
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Oh, so you were trying to use PVC as the diaphragm? Not a great choice- high creep for plasticized films.

Now, PVDC film makes a great diaphragm, but it's getting hard to find.
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Old 1st August 2010, 12:17 PM   #5
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Quote:
Originally Posted by SY View Post
Oh, so you were trying to use PVC as the diaphragm? Not a great choice- high creep for plasticized films.

Now, PVDC film makes a great diaphragm, but it's getting hard to find.
Indeed. I understand that mylar is a better choice.
Yet I will use PVC for bass panel just to re-build as close as possible as the original.
The tweeter will be re-build using mylar.
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Old 1st August 2010, 01:49 PM   #6
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Quote:
Originally Posted by SY View Post
Oh, so you were trying to use PVC as the diaphragm? Not a great choice- high creep for plasticized films.

Now, PVDC film makes a great diaphragm, but it's getting hard to find.
Saran is a copolymer of PVDC and PVC, about 15 to 25 % of the latter.
It seems though the Window Insulator Kit contains either PV(D)C
or Saran kinda film, on avail from 3M, Henkel(Duck) and others.
It shrinks nicely, better say a lot (40%) using hair dryer.
Sincerely,
Alex
P.S. What exactly is the problem with PVC shrinking process?
I used exactly hair dryer for it.
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