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Doing some plumbing work tonight, I discovered deficient workmanship involving
a welded PVC connection. I believe some people misunderstand the dissolving
mechanism of PVC cement and treat it like glue. Proposed is a non-chemical
replacement for PVC solvent work.
In the proposed replacement
for the prior art, the plumbing technician first wraps
a thin resistive wire several times around the male fitting to be joined. The
technician then joins the two pieces together, leaving the coiled wire between the
pieces to be joined. An electric current is then applied to the wire, melting the
two pieces together for a positive connection. The excess wire is then clipped off.
The wire would be lightly insulated (like magnet wire) and consist of a metal with
a fair amount of electrical resistance and heat tolerance (like steel). A handheld
device could perhaps deliver the right amount of current over the right amount of
time to a coil of wire with a prescribed number of turns with published presets.
Ultrasonic welding
http://www.emersoni...son/Pages/home.aspx
Works on many ductile materials, including plastic. Extremely expensive. [Alterother, Mar 05 2012]
Sharkbite couplings
http://www.sharkbiteplumbing.com/
Quick, easy, and expensive. [Alterother, Mar 05 2012]
[link]
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Not in Canada. Well, maybe since the government would get to tax three separate trades.
As a tile setter I am already no longer allowed to install toilets or drains anymore, and as soon as wiring is involved the plumber will no longer be allowed to install the product without voiding all said partys' ass-coverings. |
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Good home owner DIY product though. |
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Polyethylene piping (at least for industrial applications) has pre-made joints very much like this. One example is the vinidex electrofusion joint, basically it's a socket (with heating element inside) that the two pipe lengths are butted together inside. Electrical power is applied and the components fuse together, socket included. |
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I think they're available for ABS as well. |
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Is PVC suitable for thermal joining? |
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I don't think that pvc can be fused by melting and considering how well solvent welding works I just can't see the merit in this. |
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I misread the title of this idea (several times, actually - I blame my new varifocals) as "Olympic PVC Welding". I thought "There's another idea, jumping on the Olympics bandwagon - on the other hand, why shouldn't welding be an Olympic sport?". |
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"Flashdance Triathlon" just sounds so good you should post that as a separate idea. |
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PVC is so easy to stick together that I'm not sure what value the electric welding angle brings, other than perhaps eliminating the horrid solvent smell. |
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An obligatory misread of the title might lead one to imagine New Age priests sitting around in chanting meditation trying to weld PVC with their mind. |
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PVC can be heat-joined, but only fresh out of the extruder
and only if it's treated to a cryo-bath directly afterward.
My paternal grandfather developed this technique while
working for Baxter-Travenol during the 1960s. |
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Heating PVC to melting point after the material has been
set results in a brittle compound unless it is cooled at a
specific rate with specific setting intervals, much like the
process for tempering certain alloys. I don't know
the figures. Also, all of the existing resistance-welding
elements I know of (though I'm hardly the be-all end-all of
welding knowledge) run far too hot for this application. |
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It's a neat idea, but I don't see how it would be an
improvement over PVC cement. If it worked, which it
might, it would accomplish exactly the same thing in
roughly the same time, it would stink like a garbage
fire, and people who don't understand how the 2-part
cement works would be completely baffled by the
resistance-welding process. |
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[bigsleep], thanks for the call-out, but I prefer surgical
staples. My Dad's the suture artist in the family. |
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It shouldn't be too hard to develop an ultrasonic joint welder. |
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An ultrasonic welder wouldn't be accurate enough, I think, unless you worked out some really good focussing and a program for each shape of joint. |
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As for the original idea, I've seldom seen a PVC joint that could accommodate wires, or wires that could stand being shoved into a tight fitting. You'd need to wrap the wires onto the tube, melt them in, scrape off the excess PVC, insert and melt again, then you'd find the wires had sunk further into the tubing. |
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I make didgeridoos out of 1 1/4 inch PVC (schedule 40, four feet long, round the inside of the mouth end), and shape them by gentle heating and bending. PVC that has melted is nasty, brutish and sharp. |
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// An ultrasonic welder wouldn't be accurate enough, I
think, unless you worked out some really good focussing
and a program for each shape of joint. // |
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Somebody did just that. Saw one at a trade show 2 years
ago. <link> |
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Crack another joke like that and we'll lock you in the
broom cupboard with [beanangel]. |
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I agree - no advantage over solvent welding
(except that nobody has yet seen a failed joint
using this heat-element idea). |
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Apart from the brittleness of the plastic if wrongly
heat-treated, there's also the problem of flow and
gap-filling. In a solvent joint, the solvent flows
readily and is usually taken into all areas of the
joint by capillarity, unless there's a big gap or too
little solvent. In contrast, hot PVC is quite
viscous, so any areas which were under-heated
wouldn't get filled by inflow of molten PVC from
nearby. |
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Solvent welding fails if there's a big gap, but I
suspect heat welding wouldn't fare much better in
these cases. |
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Instead of resistive wire, the pipes could have an embedded injection conduit . PVC cement would be injected through the conduit and exit through apertures at the joint. |
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...thereby combining the drawbacks of both
methods? |
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Regular solvent joints are about as simple and
reliable as it can get, yet there's always one schmoe
who can make a complete gewermlich of it. |
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Actually, if you did want to do this, you might be
better off with some sort of induction coil
embedded in the joint, with a clamp-around
transformer. No wires sticking out. |
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If you're looking for a mess-free, odor-free, leak-free, and
nearly-idiot-proof method of joining PVC home-plumbing
pipe, check out sharkbites <link>. If you're working with
bigger pipe... well, there's a reason PVC cement is the
prevalent method. |
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//why shouldn't welding be an Olympic sport?// |
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There are international welding competitions of various
types. A disproportionate number of world champion
welders come from South Africa and the state of Maine.
[The Alterother] is not one of them. |
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//A disproportionate number of world champion
welders come from South Africa and the state of
Maine// and who can blame them? |
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finally my degree in welding engineering has paid off!!!!! |
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As mentioned thermal welding has similar limitations to chemical bonding. namely that poor fitup, poor material cleanliness and poor procedure control are the most common culprits. I'm not a plastics guy I don't know if PVC is fit for thermal welding. Also most thermal welding processes need some type of atmospheric control and cleanliness control (good luck bonding to an old fiting full of sludge. |
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Also by putting wire in there you have this nast mixed metallic--> plastic joint and the viscosity of plastic is high so basically it won't flow or wet around the wire. You'll have all the same problems of glue at twice the cost. I wouldn't look to welding as an easy low skill solution. |
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//There are international welding competitions of various types. A disproportionate number of world champion welders come from South Africa and the state of Maine. [The Alterother] is not one of them. |
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Funny you mention that, I was a competitive welder in a previous life at one of the best schools in the country (didn't end up being one of the best welders though). The skills USA and international skills trade competition carry the motto " the olympics of skilled trades" |
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//I was a competitive welder in a previous life at one of the best schools in the country// - yes but how good are you at the other events in [bigsleep]'s "Flashdance Triathlon", pole dancing and stitching up a bite-wound on a dog? |
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