Cracked Plastic Side Molding On Ti'books: Material and Repair

[Dan K]

I wrote:
>> Just an FYI for anyone interested, the 'trim' ring around the edge of
>> TiBooks is made of ABS plastic, not carbon fiber. It _is_ black ABS
>> however. :-)

to which Jerry Krinock <jerry at ieee.org> replied:
>I'm not sure I agree that this is ABS.  I agree it looks like ABS, but:

>1.  I tried to weld a crack yesterday using Oatey ABS drain pipe cement and
>clamping it together.  It did not work at all and showed no sign of
>dissolving the plastic.  If it was ABS, it would have worked.

I cannot explain why an ABS drain-pipe cement failed to solve it as I'm 
not familiar with the product  used. However, I'm not sure if drain-pipe 
is the same sort of thing as PowerBook plastic, even though both may be 
ABS . . . BTW, is this cement you used sort of the thicker gooey stuff? 
The product I've used (ProWeld) is extremely thin and can be wicked into 
the smallest crack.

Well, OK, perhaps it ain't ABS, it could be polycarbonate which material 
is mentioned several times in the best description of TiBook construction 
available, Apple's TiBook patent:
<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>

ProWeld's label doesn't mention polycarbonate, but grabbing an old 
beat-up B+W G3 side panel (marked >PC< polycarbonate) and dropping a spot 
of ProWeld onto it I see it does indeed solve.

>2.  ABS can have color molded in:
>
>http://www.dow.com/automotive/materials/products/magnum/product.htm
>
>We all know that painting this molding was one of the worst decisions Apple
>engineers ever made, but why would they have specified painting if the color
>could have been molded in?  (Possible bad answer: Metal in paint provides
>electromagnetic shielding needed for product to pass FCC and ETSI testing).

The plastic is _plated_ and then painted, so the paint itself doesn't 
need to provide any EMI shielding. I reckon since it was getting plated 
anyway, Apple figured they might as well try to co-ordinate the colors 
with matching paints. The (poorly done?) plating is what causes the 
bubbling problems when it begins to corrode under the paint.

>3.  I read somewhere else that it was carbon fiber.

What you refer to as carbon fiber I assume you mean carbon fiber 
reinforced plastic? I haven't read this, but that seems unlikely based on 
my own observations. I had to grind off some of the old adhesive (used to 
attach the 'trim ring' to the Ti top-plate) as part of my 'restoration' 
of a beatup 550 and can see no evidence of fibers in the plastic I ground 
off along with the old glue.

>4.  Ambroid Proweld (near the bottom of the following link) is listed as
>dissolving other types of plastic other than ABS:
>
>http://www.ambroid.com/Ambroid.html

I'm _NOT_ a plastics expert by any means. :-) As I say, it looks an awful 
lot like the PowerBook ABS plastics with which I'm previously familar and 
ProWeld was able to solve and fix it. 

Heck if I know. :-)

Dan K

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