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Ohmic PVC Welding

Sacrificial heating elements to weld PVC
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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.

kevinthenerd, Mar 05 2012

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]






       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.
  

       Good home owner DIY product though.   

       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.   

       I think they're available for ABS as well.   

       Is PVC suitable for thermal joining?
Custardguts, Mar 05 2012
  

       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.
WcW, Mar 05 2012
  

       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?".
hippo, Mar 05 2012
  

       "Flashdance Triathlon" just sounds so good you should post that as a separate idea.
hippo, Mar 05 2012
  

       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.   

       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.
RayfordSteele, Mar 05 2012
  

       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.   

       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.   

       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.   

       [bigsleep], thanks for the call-out, but I prefer surgical staples. My Dad's the suture artist in the family.
Alterother, Mar 05 2012
  

       It shouldn't be too hard to develop an ultrasonic joint welder.
mitxela, Mar 05 2012
  

       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.   

       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.   

       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.
baconbrain, Mar 05 2012
  

       // 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. //   

       Somebody did just that. Saw one at a trade show 2 years ago. <link>
Alterother, Mar 05 2012
  

       Crack another joke like that and we'll lock you in the broom cupboard with [beanangel].
Alterother, Mar 05 2012
  

       I agree - no advantage over solvent welding (except that nobody has yet seen a failed joint using this heat-element idea).   

       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.   

       Solvent welding fails if there's a big gap, but I suspect heat welding wouldn't fare much better in these cases.
MaxwellBuchanan, Mar 05 2012
  

       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.
xaviergisz, Mar 05 2012
  

       ...thereby combining the drawbacks of both methods?   

       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.
MaxwellBuchanan, Mar 05 2012
  

       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.
MaxwellBuchanan, Mar 05 2012
  

       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.
Alterother, Mar 05 2012
  

              //why shouldn't welding be an Olympic sport?//      

       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.
Alterother, Mar 05 2012
  

       //A disproportionate number of world champion welders come from South Africa and the state of Maine// and who can blame them?
MaxwellBuchanan, Mar 05 2012
  

       finally my degree in welding engineering has paid off!!!!!   

       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.   

       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.
metarinka, Mar 06 2012
  

       //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.   

       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"
metarinka, Mar 06 2012
  

       //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?
hippo, Mar 06 2012
  
      
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