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Date: | Fri, 26 May 2006 18:35:15 +0300 |
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Werner
Tg is not a fixed value, even for a single given sheet of laminate. It
can drop by 30°C or possibly more depending on the history of the resin,
for example, if it has been subjected to a humid atmosphere or to the
vapours of certain chemicals. If you extend it to multiple sheets, those
sheets nearest the platens in the laminating press will have a different
Tg to those in the centre of the pile, because the temp profile is not
the same. Then, when it's a matter of different batches of resin mix...,
treater drying cycle..., prepreg age before pressing... etc., the
tolerance becomes very significant, even at the laminator's goods-out
door. By the time it reaches the assembler, a ± 25-30°C tolerance could
be normal.
This does not take into account the tolerance of measurement of a
physical phenomenon which is gradual in its application (the Tg depends
on the polymer MW, which is quite variable); there is no sharply defined
transition from a conchoidal fracture to a fluage.
Brian
Werner Engelmaier wrote:
> Hi Doug,
> Of course I do not suggest Tg 178 instead of 175; but the slash sheets give
> ranges on the same sheet thast include Tg's with 50 degree differences--they
> should perhaps be no ore than about 20.
>
>
>
> Werner
>
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