From: Richard (metal@fullwave.com)
Date: Sat Aug 16 2003 - 11:49:24 PDT
Alan,
There's plastic...and then there's plastic.
They aren't all the same.
There are also two major types of glues:
1) Solvent glues: These actually -dissolve-
the plastic; and when the solvents evaporate,
the 2 pieces are now literally 1 piece.
PVC and ABS are almost always solvent-glued.
Polycarbonate (Lexan) can be, if you have the
right goo. Regular PVC pipe glue won't cut it.
2) Adhesive glues: These do NOT dissolve
the plastic, but bond with the molecules on
each surface. The two pieces glued together
are still two pieces.
Epoxies and silicones are the prime example of
adhesive glues.
Now, your fuel-tank is almost certainly made
from polyethylene or polypropylene; which
is a whole different kind of cat. As a general
rule, polyolefins like PE or PP just don't glue.
They -are- very resistant to petroleum stuff, and
real cheap; so that's why they're used for fuel tanks.
Note: most 12v battery cases are PP (the whitish
semi-translucent ones).
You will find that virtually no adhesive will either
dissolve or stick to PE or PP.
Having said that, I -did- see a glue hanging on
the rack in Ace hardware a couple years back;
who's package claimed it would glue "those hard
to glue" plastics...and I -think- they meant PE
and PP....but they were pretty vague about it;
and it was 10 bucks; so I never bought any.
PE and PP are generally welded...i.e. with a
plastic welder; which is kind of like a big soldering
iron (iron, not gun) with a hole through it, and
a spool of plastic 'wire', and a passage for compressed
air or nitrogen to be forced through. The hot gas
is used to melt the 'wire' and the pieces.
Imagine something like a big high-powered hot-glue gun
and a roll of weed-whacker line; and you've got the idea.
Plastic welding is also used a lot on solventable-plastics
like PVC as well; because it leaves a 'fillet' which vastly
strengthens the joint. Plating tanks are almost always
'heat welded' like this.
The bottom of the coolant tank on my TIG welder
cracked some years back; and I 'heat welded' it
with a big ol' 150-watt soldering iron with a standard
wedge tip. No 'wire'...I just ran the tip through the crack,
and mushed the plastic together as best I could.
It worked for 2 years; but is now leaking again.
If you have some ABS-pipe solvent cement around,
you could test a little of it on a non-critical place on
the tank, and if it immediately softens it; then you
got lucky, your tank is ABS or similar; and you can
glue it.
But if the tank is whitish semi-translucent plastic though,
then it's almost certainly PE or PP, and I don't think
there's any quick/easy/cheap answer; except for heat
welding it or replacing it (with a metal tank? <g>)
Richard
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