Magnetism in the weld process and its effects.

[bear4]

We have a special automated welding process for welding up and making long tubes. We are trying to get a full penetration weld, and are currently at approximately 60 to 70%. These auto welders are custom made machines that compress the tube together and weld at the same time. We are experencing a tremendous amount of magnetism at the machine and repair of the tube after auto welding is excessive. Repair welders are trying to weld and magnetism is causing through back. If we eliminate the magnetism at the autowelders can we obtain 100% penetration.

 

[deanc]

1.Change your ground location.
2.Do you have any coils of lead in the near location?
3.Could you use AC?
4.Can you wrap your electrode lead around your product?
5.You may be able to place magnets in areas that will help.
6.Can you relocate your process in regards to earth poles?

Do a web search for "arc blow". You will find other tips.

 

[metengr]

bear4;
Could you please describe your process in greater detail? This might help to pinpoint solution(s), as mentioned by deanc.

Is this automated process for making seam welded tubing?
What is the welding process, is filler metal used?
What is the tube material?

 

[bear4]

Thankyou deanc & metengr for your input. Now let me be more descriptive of the process. First of all yes it is a seam welded tube process. The material is a 1020 grade low carbon steel,and the weld process is currently DC submerged arc welding. We are currently grounded thru the machine not the work peice and we are using L60 & L61 Lincoln Wire & 760 flux. I have checked the material for magnetism before we autoweld and there is no magnetism in the part prior to the weldment of the tube. The material is consistant in thickness and is a medium grade material. I have taken gauss readings at the autoweld machines themselves and the magnetism in the machines are off the scale. These are very old specialized weld processing seam welders. The material is compressed by the machine and they have a guide roller that tracks the seam. The tube is hooked up to a transfer buggy that actually pulls the tube thru the machine. The weld machine its self does not move, the tube is pulled thru the machine and the top and side guides that compress the tube are metal, so they aplly a lubricant to the tube so it can be pulled thru the machine. Question is if I eliminate the magnetic field at the machine itself will this help us get to a full pen weld.

 

[deanc]

Give you some ideas.

http://www.ap-automation.com/downloads/ma_brochure.pdf

http://www.millerwelds.com/education/tech_articles/articles33.php

 

[metengr]

I am not an expert in SAW but I do know that the typical setting is DC current with reverse polarity for weld joint penetration. If you are having problems with magnetism affecting the welding arc, as deanc mentioned above, you cold switch to an AC current setting.

I have heard that using an AC setting for SAW will reduce magnetic arc blow affects. To answer your question - eliminating magnetism should enable you to achieve full penetration weld joints.

 

[Carburize]

Is this a new problem that has just appeared on the particular machine?

 

[stanweld]

Please note that magnetic effects are inherrent in the arc welding process. You cannot eliminate magnetic fields in the leads and in the transformers. The strength of the magnetic field is directly proportional to the current. Ground locations need to checked and reviwed. Also take a good look at welding with AC as metengr and deanc have proposed.

 

[amorrison]

Shots in the dark.
Steel mesh shielding(4x8 ft sheets) to contain magnetic field.
Consider how at what part of the welding frequency cycle the arc quits. The work is magnetized twice(+ and -)for each sinewave? frequency cycle. What the last current>magnetic field is - produces the permanent magnet in the steel. If the welder stops the current when the current is not zero(ie. crossover point in the frequency cycle a permanent magnet (steel) can result.
Answer? 1. Adjust welder to shut off at crossover point in cycle.
Answer? 2. Pull arc away as weld ends

Investigate how demagnetizers work - usually AC magnetic saturation followed by decreased current until no magnetic field is left.

 

[sayee1]

What is the travel speeds you are using? Since this is automated tube welding using 760 flux, I would assume you are using higher travel speeds then normally used with SAW. What is the thickness of the tube(s) being welded and what is the groove detail? Is it square butt or is it vee?

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!