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More Than You Need To Know About Welding Magnets

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  • More Than You Need To Know About Welding Magnets

    In another thread, I was involved with an off-topic discussion of the strength of cheap permanent magnets and how they might affect the weld plasma , if left in place while welding operations took place. Another poster tried to claim that such magnets had little or no effect on a weld, and that such magnets were too weak to have any effect on weld plasma, in spite of evidence from TWI and Lincoln proving him wrong.
    Here is the weldment and magnets that were under discussion.

    Click image for larger version  Name:	Magnets and Plug Weld .png Views:	0 Size:	448.2 KB ID:	709818

    This denial of the effect of one of the forces of nature aroused a bit of curiosity about the actual magnetic field of some cheap permanent magnets that I had used for more than half a century, for tacking operations only. To check on this, I used the magnets on hand, and a compass in place of a gauss meter:

    Click image for larger version  Name:	Magnets used.JPG Views:	0 Size:	813.8 KB ID:	709819

    In the pic above, the letter size sheet of paper gives some idea of scale, and also shows the repulsive force of like poles, since the small magnets were held against the large magnet and, when released, were repelled about 3”, a rough indication of field strength. About the same distance was reached when like poles of the 2 smaller magnets were pressed together and released, showing that the close field of these magnets is quite strong.

    The real surprise was the outer limit of the field. The small magnets had the ability to move a compass needle at approximately 3’, while the large magnet had the same ability at about 6’. This means that every thing within a 6 ft dia. circle of the smaller magnets or, a 12’ dia. circle of the larger magnet was being subjected to some magnetic force, which would increase as they moved closer.

    As the magnets were moved closer to the compass, the increased field strength was powerful enough to completely reverse the compass needle at about 16” for the smaller magnets, and, about 3’ for the larger. When all three magnets are placed around the compass about 3-4” away, and one is moved or rotated, the compass needle flicks wildly to unpredictable locations as it is affected by the changing magnetic fields (this would be the condition in the plug-weld pic above).

    Coupled with the fact that the magnetic field is also redirected by the shape of the magnets, shape of the weldment, polarity of welding, pole location, and location of the magnet attachments, it is obvious that the any arc plasma in the plug weldment above is going to be strongly affected, in complex and unpredictable ways, and, removal of all magnets would allow the precise placing of the arc demanded by a successful small bore plug-weld. Also, the assertion that the magnetic field of the magnets is too weak to affect the positive or negative ions of the arc plasma is silly, since these are sub-atomic particle-sized, and compass needles and heavy magnets, massive in comparison, ARE affected by the fields, as shown above.

    Finally as noted in the Lincoln article I cited earlier, magnetic fields created by welding actions are strong enough to create arc plasma affects, without assistance from welding magnets. As the illustration from the TWI job-knowledge article cited below shows, simply welding close past your work cable can create a field with enough magnetism to affect a weld, let alone just arc plasma.

    Click image for larger version  Name:	Ground placement and arc blow  TWI .png Views:	0 Size:	126.8 KB ID:	709820
    All of the above can be checked at home with your own magnets, if you doubt anything said, with one condition. If you are in the habit of welding up fit-ups with magnets in place, they may have lost much of their magnetism due to heat-exposure. (see “Curie point”). Most of us avoid this by tacking and replacing magnets with clamps where restraint is necessary.








    Last edited by Northweldor; 06-23-2020, 06:48 AM.

  • #2
    Interesting read Northweldor...

    Never heard of this before. I have questions if you have a few minutes....

    1. If it does cause an arc deflection what will that do? I see the picture and the weld looks crooked and I assume the magnet caused this. Will this effect the strength of the weld or just make it not "pretty"??

    2. When this occurs will the magnet attract or repel the arc? Would it matter if a MIG polarity was set for + or - ? (for example using flux core wire vs. solid).

    3. Could a magnetic field be used to deliberately guide the arc?

    Polyoxybenzylmethylenglycolanhydride

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    • #3
      Originally posted by Nipper View Post
      Interesting read Northweldor...

      Never heard of this before. I have questions if you have a few minutes....

      1. If it does cause an arc deflection what will that do? I see the picture and the weld looks crooked and I assume the magnet caused this. Will this effect the strength of the weld or just make it not "pretty"??

      2. When this occurs will the magnet attract or repel the arc? Would it matter if a MIG polarity was set for + or - ? (for example using flux core wire vs. solid).

      3. Could a magnetic field be used to deliberately guide the arc?
      1) No magnet was involved in the TWI job information: that deflection was caused by the magnetic field generated by placing the work connection in the middle of the weld, and welding past it. It could affect the strength of the weld, but a skilled weldor would notice the arc blow and would use skill to correct it.

      2) If the process is AC, magnetism will have little effect. However, with DC, the arc plasma will be deflected by like poles, and attracted by unlike poles. If the north pole of a magnet (+) is placed close to a weld and the positive electrode approaches it, the arc plasma will be deflected. If the electrode is negative the arc plasma will be attracted. If the south pole of the magnet (-) is used, the opposite will occur.

      3) Magnetic force is used most often in plasma cutting to produce more desirable cut profiles, but could have been used in the plug weld in discussion above. If one magnet was placed with the correct pole directly under the weld, the arc plasma would be drawn into the hole, increasing penetration.
      Last edited by Northweldor; 06-24-2020, 12:08 PM.

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      • #4
        Originally posted by Nipper View Post
        Interesting read Northweldor...

        Never heard of this before. I have questions if you have a few minutes....

        1. If it does cause an arc deflection what will that do? I see the picture and the weld looks crooked and I assume the magnet caused this. Will this effect the strength of the weld or just make it not "pretty"??

        2. When this occurs will the magnet attract or repel the arc? Would it matter if a MIG polarity was set for + or - ? (for example using flux core wire vs. solid).

        3. Could a magnetic field be used to deliberately guide the arc?
        I answered your questions, but, for some reason, my post was flagged. Likely, it will soon be available.

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        • #5
          All I know is I made a heavy duty welding table out of an 1 1/4" plate of left over Hardox 400 that is magnetic and affects the welding of solid mig and dual shield so much an aluminum plate has to be laid on the top.

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          • #6
            Originally posted by Northweldor View Post

            I answered your questions, but, for some reason, my post was flagged. Likely, it will soon be available.
            Thanks North, I will check back. I understand how it might do it but I never gave it any thought before.
            Last edited by Nipper; 06-24-2020, 10:41 AM.
            Polyoxybenzylmethylenglycolanhydride

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            • #7
              Originally posted by lars66 View Post
              All I know is I made a heavy duty welding table out of an 1 1/4" plate of left over Hardox 400 that is magnetic and affects the welding of solid mig and dual shield so much an aluminum plate has to be laid on the top.
              Interesting. Have you tried de-gaussing with AC or wrapped cables?

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              • #8
                Originally posted by Northweldor View Post

                Interesting. Have you tried de-gaussing with AC or wrapped cables?
                Nope never tried that trick. I use the table for heavy work clamping and beating which will shift the strongest part of the magnetism around some .

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                • #9
                  Originally posted by Northweldor View Post

                  1) No magnet was involved in the TWI job information: that deflection was caused by the magnetic field generated by placing the work connection in the middle of the weld, and welding past it. It could affect the strength of the weld, but a skilled weldor would notice the arc blow and would use skill to correct it.
                  Help me out with this part....
                  Just to be clear. When you say "work connection", are you referring to the ground clamp?

                  Polyoxybenzylmethylenglycolanhydride

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                  • #10
                    Originally posted by Nipper View Post

                    Help me out with this part....
                    Just to be clear. When you say "work connection", are you referring to the ground clamp?
                    Correct. It's not really a ground, so the term is adapting. It can be any polarity, and is a conducting part. I learned it as the "ground," too, but as an electrician see the issue.

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                    • #11
                      Originally posted by lars66 View Post

                      Nope never tried that trick. I use the table for heavy work clamping and beating which will shift the strongest part of the magnetism around some .
                      If you take any AC machine you have around, and set it at where ever it has 100% duty cycle, and short it out for a 5 min. period of time with a big electrode, then switch locations of your stinger and work connection, and repeat 4 or 5 times, it should get rid of the residual magnetism. I have a friend who owns a high amperage SAW, and he uses this method, and swears by it. I think his AC machine puts out 200 A at 100%, so a smaller machine might take longer, depending on the area of the table.

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                      • #12
                        This is actually great information. Whenever I have a lousy weld I can add this to my list of excuses.....

                        "Magnets did this."
                        Polyoxybenzylmethylenglycolanhydride

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                        • #13
                          After trying the on/off, the regulars sucks lol. Easier to position it without the attraction and just turn it on when you’re ready to go.

                          Also, the cleaning. Turn it off and wipe clean. I hated the regulars because they would attract metal shavings, washers, bits of wire, all kinds of **** and are a pain to clean off.

                          Looks like the Strong Hands one is the same price on Amazon but there’s an HF almost everywhere now, might be easier than ordering online if you have one around you.

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                          • #14
                            Originally posted by viewcart View Post
                            After trying the on/off, the regulars sucks lol. Easier to position it without the attraction and just turn it on when you’re ready to go.

                            Also, the cleaning. Turn it off and wipe clean. I hated the regulars because they would attract metal shavings, washers, bits of wire, all kinds of **** and are a pain to clean off.

                            Looks like the Strong Hands one is the same price on Amazon but there’s an HF almost everywhere now, might be easier than ordering online if you have one around you.
                            If you read the rest of the thread, you would notice that your comment has very little to do with the topic under discussion, which is how cheap permanent magnets can have adverse effects on weld plasma.

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