I Need a Plastic Welding Lesson

[Dallas]

Hey all,
A few days ago, I went to Harbor Freight and purchased a Plastic Welder.
Today is the first time I've tried using it.
All I seem to be doing is burning the plastic I'm trying to practice on.

I have been practicing on a piece of Sched 40 PVC to see if I can make a decent bead on it.

The worthless little manual that came with it said to use 3-4 pounds of air, so that's where I started. The piece immediately started turning brown. I turned up the air pressure, and eventually got it up to about 10 pounds but then it was blowing the plastic away as it melted.

What am I doing wrong?
I will try welding some ABS tomorrow, so that I get some practice with all of the different kinds it does.

Dallas

[Melbo]

I wish I had known you wanted one of those welders.

I would have given you mine.

I tried on some poly eythelene ( is that the right spelling??) but it didn't work well enough that I thought I could do a seam that would not leak.

So I had some one custom build my tanks.

I never got mine to work well ( can you say impatience??)

Melbo

[FloridaCliff]

Dallas,

I believe you need a speed tip.

Check Gumpys site for the details.


Cliff

[Jerry Liebler]

Dallas,
    I'll start out by saying I have never used the Harbor Frieght plastic welder, but I've,pretty well, mastered welding polyethylene with a Steinel heat gun (thermistor temperature controlled) and several tips that probably would work on your welder.  I got 6 different tips off of Ebay for $10 and made an adapter to use them on the heat gun.  I think you'll need to reduce the power into the heater on your welder and use the lower air flow.  One fairly cheap way to reduce the power is to route it through a lamp dimmer, the kind that replace a wall switch and can handle the wattage of your heater.  You could place the lamp dimmer in a 2x4 box installed in an extension cord.  Dial the power down to where the plastic melts readily but doesn't smoke.  Heat the part to be welded first then put the rod into the puddle and play the air onto the rod and joint as you push the rod into the joint and as you move along the joint keep feeding rod into the joint with constant pressure on the rod. 
Regards
Jerry 4107 1120

[Dallas]

Thanks guys!
I believe I'll start looking for the tips for it.

Jerry,
I already have the dimmer setup you describe that I use for my soldering iron. I hadn't thought of using that. thanks!
And thanks for the primer!

Dallas

[Jerry Liebler]

Dallas,
    A soldering iron is an excellent tool for tack welding plastic, I tacked all my joints first with a temperature controlled soldering iron, then welded them normally.
Regards
Jerry 4107 1120

[Dallas]

Thanks Jerry!

Dallas

[Ednj]

Bring it all to Bruce's party, that way we can all play.
If I can make it I'll bring mine?

[youngone]

Hi i have never done any plastic welding but i had a guy come in to weld a 42 inch HDPE (high density ployethelen ) water pipe that had broken. He said the most important thing for welding any type of plastic is to get rid of the oxidation.What he used was a scraper. The kind with a removable blade. Also was a good practice to grind the edges beak kind to a 45 degrees. Then when you weld you get better penetration....Pat.

[muddog16]

Dallas, The low air settings of around 4 psi is probably the max pressure on air.  A couple of pointers always have the air on first before plugging the unit in and unplug it before you shut the air off, I always let the gun cool down to touch before shutting the air off, this is the most important thing to keep your plastic welder alive!  Second, as in any welding use the right rods for the correct material.  Gumpy talked about using a speed tip and highly recommended it, and I found this tip to be the secret of good plastic welding, feeding the rods and pulling the welder towards you worked the best for me, you could actually watch the plastic melt, take your time, and prep your area before welding.  When welding my water tanks i used bar clamps and beveled the joints, (gumpys' site is excellant for these pointers).  Not knowing what material you are going to weld on, I can say this about poly pro, its simple again take your time and don't rush it as the plastic melts you pull the gun towards yourself, and it fills in the bevel nicely as you go along all the time pushing gently with the rod into the speed tip.  Speaking of speed tip this single item made the difference. Yes I repeated that about the speed tip, its that important!  At Gumpy's site he has the address of where to find the speed tip, it will cost more than the gun, around 80 bucks but its worth every penny of that!  Good luck!                        Pat

[gumpy]

Well, I don't have much to add that isn't already on my web site. I have found that trying to weld PVC with the HF gun is a bit difficult. PVC melts at a much lower temp than polypro. ABS is a bit easier, but not much. I haven't tried putting a rheostat on my gun for PVC, but next time I need to weld PVC will try that. I think it would be the key. As you said, too much air causes other problems.

I'd suggest you get some polypro scraps and rod. You'll have better luck with that.

When I started into plastic welding, some people (I think Ednj was one) told me I should use nitrogen instead of air on polypro. Having now done my tanks and the tanks for my Father-in-law's trailer, I can say that it is possible to weld polypro with air, but I do believe that using nitrogen would make welding easier, and produce a better quality and stronger weld. I couldn't justify the cost as I was only planning on doing one set of tanks, initially, but had I known up front how much I would actually be using the plastic welder, I'd have invested in a large tank of Nitrogen. I did try it on one small battery box I made, and felt it gave me better results, but the tank I borrowed was very small, and didn't even last to completion of the small box. That small bottle was very expensive to fill. A large tank would have been a better choice, as it didn't cost any more to fill than the small one, but I really never thought I'd be welding as much as I have. IF I were to do another set of tanks, I'd either rent or buy a large bottle on nitrogen.

While in Canada last year, I blew out a top seam on my large water tank (due to the way the upper tanks were plumbed). I recently removed the tank, and using a laminate cutting bit in my router I removed the old weld along the entire side, flush with the side. It worked great! I then used a V bit to cut the remaining old weld out and cut a new V channel deep enough to reach virgin plastic in the side and top, and then rewelded the entire seam. Turned out to be an easy repair. The hardest part was getting the tank out of the bay. I've also changed the plumbing so it won't happen again.

Maybe one day I'll make it to a rally and I can offer a demo. I did one in my garage a couple years ago for some local busnuts. Brian Diehl then successfully built his own tanks. I know a couple others have followed the info on my webpage and are happy with their results. Maybe Ednj or one of the others who have built their own tanks can do a demo for you at Bruce's party.

[Dallas]

Thanks Gumpy!
I read and reread your website with great admiration. I'll look around a see what I can find in the way of a speed tip for my HF welder, it looks as if that might be the way to go.
One problem I'm having is getting the air pressure down low enough. I thought it might be the redulator so I switched it out with a WATT regulator but it didn't make any difference. I now have the main regulator on the compressor shut almost all the way down and that has helped immensely.
Today I'm going to take an old cutting board out and cut it up and weld it back together to see if that works any better than the PVC.
The biggest problem I had with the PVC was that it would burn almost as soon as I put the air to it. I wonder if it's inherent in the type of PVC I was using.
I kind of figure that like with any other type of welding, the only way to get good is:
Practise... Practise... Practise!!!

And everyone else, Thanks for all of the great advice and input.
That's what makes this new board work so well!

Dallas

[gumpy]

Dallas,

Your cutting board is probably HDPE, which you will find is (almost) impossible to weld with the air gun. Don't waste your time, or the cutting board. It'll only frustrate you and will ruin a perfectly good cutting board.

Your description of the PVC burning is what I was seeing, too. I also had to put a regulator on my compressor, and then use the HF regulator to get the pressure down to about 4 psi. I set the compressor regulator to about 15 psi.  I forgot to include that in my page.

Go find some polypro. It'll make your learning so much easier. If you can't find any, let me know.

craig

[Dallas]

Dallas,

Your cutting board is probably HDPE, which you will find is (almost) impossible to weld with the air gun. Don't waste your time, or the cutting board. It'll only frustrate you and will ruin a perfectly good cutting board.

Your description of the PVC burning is what I was seeing, too. I also had to put a regulator on my compressor, and then use the HF regulator to get the pressure down to about 4 psi. I set the compressor regulator to about 15 psi.  I forgot to include that in my page.

Go find some polypro. It'll make your learning so much easier. If you can't find any, let me know.

craig

Thank Craig, I will get some tomorrow when I have a car.

Dallas

[Ednj]

Gumpy I have a question you said (due to the way the upper tanks were plumbed).
They broke.
What happened? Because rigid piping?
Do you need a flex joint? Expansion joint ECT?
Just curious.
>
As for the welding, Back then I had a unit that required being hooked to an air supply. Be it a compressor or Nitrogen bottle, or argon bottle or heileum, well I think you get the picture?
The Nitrogen worked the best for ploypro, Teflon, PVC, cpvc, kevlar again you get the picture.
Over the years I have built, Fume hood's, drip pans, holding tanks, piping systems, and just about anything plastic, you can think of for the use in a Chemical industry environment.
This burning of the material to be welded just don't happen with Nitrogen.
You can make it as hot as you want and it will only melt (no browning) there for you can run the bead of filler material as fast or as slow as you like.
When working for one of the largest specialty chemical companies in the world, nitrogen is no problem.
Yes now you can weld mostly all the above with only air, but I feel it is important to have the right equipment.
The newest unit that I have, has it's own compressor, no regulator or pressure gauge just a high and low setting. (Witch is really just more or less air)
I did attend a school for ploy vinyl chloride welding and obtained a diploma, I wouldn't say that means I know what I'm doing. But I got the sheepskin.
I am no longer welding plastic (for lack of a better word) for the industries. And I do have all the "RIGHT equipment" just sitting here in my garage (except the nitrogen) and I'm willing to help anyone anyway I can.
If I showed any of  you a 10-minute demo on welding plastic, you would not believe how easy it is to learn.
Much like metal welding it's all about heating the 2 surfaces to melting point and using filler of the same material to bond together keeping out as much oxygen as possible.
On another note I almost always use a router to cut, clean, chamfer the edges etc.
I hope this helps Ed-9-Nj