Page 58 - CITS - Welder - Trade Theory

WELDER - CITS

Lesson 12&13 : Arc blow and method to control arc blow

Objectives

At the end of this lesson you shall be able to
• explain the arc blow in DC welding
• explain the effects of arc blow on welds
• describe the various methods used to control the arc blow.

Arc blow in dc welding: When the arc deviates from its regular path due to the magnetic disturbances it is called
‘Arc blow’. (Fig 1)

Fig 1

Causes and effects of arc blow: Whenever a current flows in the electrode a magnetic field is formed around the
electrode and the arc F1 and F3 (Fig 2). Likewise a similar magnetic field is also formed around the base metal F2
(Fig 2). Due to the interaction of these two magnetic fields, the arc is blown to one side of the joint. At the starting
of the weld there will be forward blow and at the end backward blow. (Fig 3)

Fig 2

Due to this the following effects occur
- More spatters with less deposition of weld metal.

- Poor fusion/penetration.
- Weak welds.
- Difficulty in depositing weld metal at the required place in the joint.
- The bead appearance will be poor and slag inclusion defect will also take place.

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CITS : C G & M - Welder - Lesson 10&11