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  • plastic "welding"

    In most cases I can use chemical bonds for plastics when I am building them up for machining. Recently I was asked if I could weld them instead. This is for the food industry and to meet there standards in some areas. I have the use of a hand held welding unit for testing but it has no controles other than a regulater for the air. I am getting more and more into machining plastics today and I would like to get seriouse and try to find out as much about it as possible. Especialy the area of the more preferred type of welders and also in the tips and tricks department. Is any body familiar with the plastic "welding" process? I have some basics and it appears pretty simple and thats what is scarry.

  • #2
    Check out the current issue of HSM pretty well covers it, for an intro.

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    • #3
      are you aware the last HSM covers some of this?

      -just wondering, not everybody got theirs yet.

      you beat me Rustybolt

      [This message has been edited by dsergison (edited 04-28-2004).]

      [This message has been edited by dsergison (edited 04-28-2004).]

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      • #4
        In my case the lady in the post office gets to read it first and then her husband. When there done there is the town council. After that it is put in my mail box. Should have it soon. In some ways this is good because it save me disposing of the wrapper and other loose paper.

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        • #5
          I've done a little plastic welding before, pretty neat.

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          • #6
            I used one that sounds similar to your unit. The air controls the temp of the tip; more air = less heat.
            Had to monkey around with it to get the plastic "welding rod" to come out hot enough to wet to the parent material without burning.

            There's also ultrasonic units available; they work pretty slick, kind of like a spot welder.

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            • #7
              The plastic likes to be clean before welding. I've had my fun trying to weld old and sometimes discolored plastic. I've used brake cleaner to prepare the surfaces with good results. I'm sure it depends on the plastic, though. Find out if there's a surface prep recommended for the plastic you're using.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #8
                I have made a few tanks of plastic. First time I used a commercial rig- it consisted of a small air compressor, some air hose and what looked like a soldering iron, all in a briefcase size container. The power was 700 watts. Rental was high and long trip to rent. The plastic company gave me several articles that were re-prints from "Plant Engineering magazine". The Info was useful. I checked and can not find the articles now- I would offer to mail to you. The process is more like brazing than welding. The three plastics must be very similar in melting etc to weld. I had much trouble finding rods that would weld neatly. Finally, just cut rod from the parent sheets.

                The real trick is that you want all three pieces (two parts and rod) at same temp. When the rod can be forced deep into the joint you just keep pressing it in. You "push" the rod instead of dragging it.

                After couple tanks were fabricated, I took a 1500 watt heat gun (made of metal not plastic) made a shroud to go over the heating element, with a 1/4 inch tube about 6" inches long to carry the hot air to the job. I used a heavy duty variac to adjust the heat, the valve on the heat gun let me adjust air flow.

                I later put the heating element on a separate cord from the blower. Then I could better control the heat and still keep air flow high. It was a waste of time though. The first set up worked as well as the rented rig or my "improved " version, The plastic company made up some like the first version and last time I was there they preferred it to the "professional job" (more heat, faster welding)>

                Harbor freight sells rig for less then 50 dollars that probably works well. It has adequate heat power so it should be fast enough. Just keep temps low as you can and still get a good bead. The tanks are in use over 15 years now, now problems. I made the holding tanks in my motor home well over ten years ago. Over 100,000 miles, some rough roads (Hovenweep for example) and never a leak. I avoid butt joints where possible, plastic "angle iron" around the corner seams, and with 4 by 8 foot sheets of plastic I needed no butt joints. Be glad to discuss by email or phone if you have questions. but the best thing is to ask you plastics company for info, and practice.

                It is an easy skill to acquire and hands don't need to be a steady as for welding or even brazing.

                EDIT COMMENT: THe unit you use sounds very much like the one I rented. But what you NEED is low pressure air at just enough volume to heat the joint. trying to keep the temp low by increasing the air flow was the short coming in the rented rig. avoid "cooking" the plastic.

                [This message has been edited by docsteve66 (edited 05-04-2004).]

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                • #9
                  gunsmith,

                  I've done a fair amount of ABS plastic welding repairing motorcycle bodywork. I've used both http://www.usplastic.com/catalog/default.asp
                  and http://www.urethanesupply.com/
                  for information, supplies and welders. You may have already seen these but just in case....

                  Allen

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                  • #10
                    Doc: That's a good idea of using some of the same material to make the rods from. Ensures the best bond to I suppose. I am about to try this and will let you know how it works out. Lots of sites on the net to get info and equipment from as well. My plan is to expand to some commercial equipment for what I will be doing but first I'll try with the free stuff.

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                    • #11
                      I regularly weld plastic agruclutural feed, water, spray tanks. The best rod is a piece of the base material, but often the lid from a coffee can or equvalent will work great cut in strips. I use a Milwalkee heat gun with home made tips to concentrate heat. I just hold it further from tank to reduce heat.

                      The one plastic, I have never had success with is the black Rubbermaid brand water troughs. Even a piece of the parent material does not work. It seals and looks good, but cracks back out the minute some weight in the form of water is applied. A neighbor who is a good customer feeds cattle and runs a stocker steer operation and he probably has 50 of these cracked troughs. He was a dealer for them at his feed store, but now will not use or sell any more. They seem to crack from the weight of the water pushing out on the sides. We have been successful in saving the non cracked ones by making a spreader bar out of tubing and bolting the endplates to keep all expansion away. Igf you have a rod that works on Rubbermaid, let me know. I recently welded two 6" cracks in a 750 gallon molassas tank and it made this old diabetic boy hungry for something sweet.

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                      • #12
                        the harbor freight one works well with the router speed controll, and regulating the input down to 35-40. then using the built in regulator to tune to about 1.5 - 2 psi for use.

                        the built in reg has a bleed orfice which prevents it from running low enough to cook the iron. but it's like a wind tunnel with 100 psi supply air. so cranking the air compressor down to 40 or so lets you have a much more usable range.

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                        • #13
                          The unit I have for testing has a good regulator but I wasn't sure of what pressure I should be using for the air. Is there a need for any inline equipment or will it function just on the airline air? Also I heard that the better guns have digital temperature controles? Getting complicated but like anything else cost will play a part in the unit I get.

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                          • #14
                            The heat gun i mentioned was an OLD Milwaukee. Nozzle pressure with the damper wide open was excessive. I don't think the gun had as much as two psi at the nozzle.

                            Never tried welding rubber maid stuff, but I did some repair work on old plastic. even a rod made from the original material would just pull out after welding. the solution was a through cleaning (MEK or acetone probably). The trick to plastic welding is getting it all to same temp and ,just like any other welding, get it clean. I suspect rubber maid has lots of "plasticizer" and it might boil out and make a bad joint. on old stuff, a pocket knife to make a "vee" for welding helps when repairing cracks. Grinders leave too much debris behind and tends to melt the work edges and even "burn " the plastic. Keep in mind that I have NOT done this for a full time job. A good professional would probably have done it faster and better (probably) if they been available.

                            Speaking of melting by the tools- use lots of plain water for cooling when machining. Again I am not a professional so maybe there is a better coolant than water, but water works for me.

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                            • #15
                              Hey gunsmith, have you looked into injection welders. I was just at a plastics show earlier this week and I got to check out the who range of them. Personally from what I saw, the hot air welders weren't too impressive. If you can justify the expense, and I really wish I could myself, get yourself an injection welder. they work just like an injection molder and you get a nice very professional looking bead. the joints are also incredibly strong. There was one company that stood out as having the best system for injection welding. Go to www.drader.com and look at the injectiweld. the guy let me demo his machine and it was rediculously easy to use. The welders from other companies apparently have a bit of a learning curve, but the drader is as easy as using a hot glue gun. They're about $4 000 canadian, so they're not cheap by any means but if you can justify it, I'd say go for it. BTW I don't have any affiliation with this company what so ever, I was just very impressed with their stuff.
                              hope this helps
                              Andrew

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