Monday, 7 April 2014

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MOVING CONTACT SHIELDED METAL ARC WELDING(a variant of SMAW)

                           

Before introducing you to this new process. I want to tell you some limitations of SMAW.
These are:-
1. Melting Rate/Productivity is low
2. Length of the Electrode is fixed.
3. Wastage of electrode in form of stubs.
4. Possibility of defects with every Stop & Start of Arc.

we use a variant of SMAW known as moving contact SMAW to overcome the problems of smaw.
First question is “why melting rate is low in SMAW”. Answer is we can not increase the current beyond a limit. Because welding electrode has resistance that is directly proportional to its length. 

Due to that resistance Electrode get heated during operation. Due to that pre heating of electrode its flux coating become use less. So to avoid the pre heating of flux we can not increase the welding current beyond a limit say 350 A. Due to same reason, we can not increase the length of the electrode(beyond 450 mm). We can not increase the length of the electrode due to some ergonomic reason also.
WHAT IS MOVING CONTACT SMAW:-
In this process power source remains same. This process is applied to V groove only. In the v groove we lay down the halph bared electrode one by one horizontally. Such that end of one electrode will touch the start of another electrode. There is a moving contact made of a conductor(you can use Copper or Iron bar). One terminal of power source connected to this moving contact & another terminal of it is connected to the workpiece that has V groove. Moving contact touches the bare side of the electrode. It can also slide over it.

Arc is started by touching the tip of the lying electrode with a bare electrode. Once the Arc is made. Arc started moving towards the moving contact. Now you move that contact with approximately same speed as of the arc. In this way you can make a joint that may be a Km long.
It is very easy process. Even a Child can make a joint with this process.

ADVANTAGE OF MOVING CONTACT SMAW:-
1. You can increase the current as much as you want. Because the distance between the arc and the moving contact is few cm. So pre heating of flux is also limited to that area only.
Due to use of very high current in this process, Melting rate increased thus productivity of the system increased. For higher current, We can use power source of our own choice.

2.Arc gap is fixed in this process so there is no need to try to maintain the constant arc gap. Here the arc gap is the thickness of the flux covering.

3. There is no need to change the electrode time to time. So there is no idle time. Also there is no stop & start of arc.
This is one of the intresting welding process. I hope you enjoy it.
If you have any doubt,ask me. Soon I will upload its video.



4 comments:

  1. Is making a moving joint difficult or we can use a simple roller for making a weld

    ReplyDelete
  2. You can make moving contact just by bending a rectangular steel bar. You may use roller. Roller is good option because rolling friction is less than sliding.

    ReplyDelete
  3. It would be pleasurable to know that the MIG welder can be easily operated by the user to join the metal parts, without having any prior experience of working with it.

    ReplyDelete
    Replies
    1. Nice to listen you. But in this article, I was talking about a variant of SMAW known as Moving contact SMAW. Do you know, It is easier to operate it when compared to MIG. Even a child can make a joint.

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