[Ti] Re: cracked edge

[Dan K]

I wrote:
>>The plastic edging is almost certainly a form of polycarbonate and 
>>therefore cracks can be 'welded' using a solvent-type welder.

To which "Dr. Trevor J. Hutley" <hutley at geneva-link.ch> replied:
>As a polymer technologist, I think you may becorrect that the 
>case/edge may be made from polycarbonate.  I do not know for sure.
>
>Whilst polycarbonate is a tough polymer, it is rapidly destroyed by 
>many solvents.  So I would urge caution.  Xylene is a good solvent, 
>but will destroy it.  I am pretty sure that amyl acetate is a 
>practical solvent for welding polycarbonate.  There may be others. 
>Anyone thinking of solvent-welding ought to be careful that the 
>solvent they use is not just a solvent for polycarbonate but a 
>non-destructive one.
>
>All that said, solvent welding is a good repair technique, if it is 
>appropriate for the damage.
Hey, you're just the sort of expert we need for this topic!

AFAIK, we've only guessed at the TiBook edge's plastic type, well, at 
least that's my case. I had originally assumed it to be ABS, but in 
previous conversations here on the Ti-list the consensus was some sort of 
polycarb the most likely.

How can we tell its exact composition? And if it is polycarb, are there 
different polycarb 'flavors' that might dictate a best-choice specific 
solvent welder to use? Apple's TiBook patent (number 6,574,096):
<http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p
=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6,574,096.WKU.&OS=PN/6,574,096&R
S=PN/6,574,096>

. . . repeatedly mentions polycarb, for example:
". . . polycarbonate, carbon-fiber filled polycarbonate, or other 
materials suitable for injection molding."

The welder I've been using is Ambroid ProWeld. Here's an apparently 
knowledgable description from the PB mail-list, by <ACFX44501 at aol.com>:
>Pro-Weld is a proprietary combination of M-E-K, methylene chloride, and a 
>bunch of other stuff which makes it particularly good for ABS parts of all 
>kind, but Mac parts in particular.
>
>I've repaired entire Apple Color LaserWriter housings with Pro-Weld, and 
>never had a re-break, even on this exceptionally heavy machine.

I've had mixed results using ProWeld on TiBook edgeing cracks. ProWeld 
does solve the edging, but the repairs usually aren't very strong, at 
least in comparison to similar repairs I've done on ABS PowerBook 
plastics. It may be the lack of strength in my TiBook edge repairs is 
related to the very small contact area of the thin-profile part. Or it 
may be that ProWeld isn't a very good choice for this repair.

I (and others too, I'm sure!) would be much obliged for some expert 
advice on this topic. I'd really like to pin this one down, especially 
with so many TiBooks afflicted with cracked edges, it'd be very nice to 
have a correct repair procedure.

dan k

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