Stefan Trethan wrote:
>>Some good information on hot air plastic welding can be
>>found here;
>>http://www.tempatron.co.uk/pdf_files/Principles.pdf
>>
>
>
>
> I trust this is already in the links section under tank costruction?
> if not it would be good if it gets there.
I just checked, and the link is indeed listed under "Acid Etching
and Electroplating Tank Construction"
>
> I agree that welding is superior, however it is also harder to master,
> and expensive if you have to buy the gun. So if your application does allow
> gluing i would not dismiss it completely as an option.
Welding is a skill that's takes a fair amount of practice to
learn. But it is often that welding is the only method suitable
to joining plastic. You are correct saying that if something can
be glued then its should be glued and not welded because its
simpler. PVC pipe fittings is an example of glued plastic.
Sometimes a the flat face of a PVC block or sheet can be glued to
another.
>
> Do you all weld with a special welding shoe or someone with a round
> nozzle only? i really expected slow speed welding to work (As described in
> the
> pdf, but i couldn't get anything useful so far (i admit i have no tried
> enough maybe).
>
> What are the ideal plastics to try with?
> i only know ABS was a complete failure, it got charred and blistery and
> still
> did not really fuse.
> PVC did work a bit better, but still not perfect.
I only have experience with PVC. But I've heard polypropylene
(PP) is only slightly more difficult to weld. Each plastic
required a different welding technique. I believe ABS is similar
to PVC.
PVC and PP are the two most common tank building materials. PP
can have a tendency to warp after welding and folding, especially
if thin sheets are used (< 4 mm).
With regards to PVC welding, If you are experiencing burned
surfaces then you have the temperature too high or you are moving
the air nozzle two slow, which is allowing the plastic too much
time to heat up. There is a fine balance between nozzle moving
speed and temperature.
I have only ever welded with the round nozzle ("slow speed
welding" as described in the PDF) , since I often welding inside
tanks and around tight corners which cannot be done with a speed
nozzle. Welding with a plain round nozzle will take more practice
but has advantage of being more flexible in application.
> i expect polypropylene to work well, it is shaped nicely by heat.
> What about polyethylene, the PE shrinks under heat strong, or is this
> only true for the bottles and stuff? i would expect it to be problematic
> to weld?
>
> Is there any surface preparation to do?
> i have this acryl/plexiglas here that gets really soft (like soft rubber),
> but it does not fuse with the welding rod of the same material,
> if i heat more it charrs.
>
Surface prep is important to get good contact area for fusing
between the rod and plastic. Just as metal welding a V grove is
often made in the location to be welded.
Some plastics, such as acrylic and polycarbonate will burn in air
before reaching melting temperature. I don't know if they can be
welded with hot air, but rather nitrogen might be needed.
Nitrogen gas welding is not practical the hobbyist so I would
stay with PVC. You can try hot air welding on some scrap PP to
get familiar with, but I don't know how difficult PP is to work
with. It took me many number of hours of practicing on scrap
pieces before I could weld up tank.