Arc Length
Definition :— The straight distance between the arcing end of the electrode and the job surface where molten metal globules are deposited during welding is called are length .
The length of arc is an important variable in arc welding . The connect arc length is that which maintains a smooth arc . An experienced welder recognises the correct arc length by it's crackling sound .
Types of Arc Length :–
There are three types of Arc length.
1. Normal Arc Length .
2. Long Arc Length .
3. Short Arc Length .
(i) Normal Arc Length :—
When the arc length is approximately equal to the diameter of the core wire of the electrode which is used , then this type of arc length is called normal arc length .
Effects :–
Normal arc is a stable arc producing steady sherp crackling sound and it has the following efforts :
(1) Stable Arc
(2) Smooch or uniform bead appearance
(3) Proper fusion and proper penetration
(4) Reduction in spatters
(5) Correct metal deposition
(6) Less chance of atmospheric contamination
(ii) Long Arc Length :—
If the arc length is more than the diameter of the core wire of the electrode which is used , then it is called long arc length .
Effects :–
Long arc length makes humming sound and it has the following effects :
(1) Unstable arc .
(2) A good part of heat will be lost to the atmosphere
(3) Poor fusion and poor penetration .
(4) Oxidation of weld metal .
(5) More spatters , indicating more wastage of electrode metal .
(6) Poor control of molten metal .
(7) The metal will drop off the electrode in large globules which on hiting the cold base metal with poor fusion.
(iii) Short Arc Length :—
If the arc length is less than the dia-meter of the core wire of the electrode which is used , is called short arc length .
Effects :–
Shout arc length makes a popping sound and it has the following effects :
(1) Electrode will stick to the metal feequently .
(2) More fusion and more penetration with less spatters .
(3) Manipulation of the electonde will be difficult .
(4) Irregular bead .
(5) Higher metal with narrow bead .
ARC BLOW IN DC ARC WELDING
Definition :– When the welding arc deviates from its regular path due to magnetic disturbances , it is called arc blow .
Arc blow is a disturbing factor in DC arc welding . It is the unwanted wandering of the welding arc from its intended path . The arc thus nolonger remains stable in arc blow . It occurs only when DC is used .
Causes of Arc Blow :–
When ever a current flows in the electrode a magnetic field is formed around the electrode , like wise a similar magnetic field is also formed around the base metal . Due to the interaction of these two magnetic fields , the arc is blown to one side forward or backward of the joint .
Effects of Arc Blow :–
Due to arc blow the following effects occur .
(1) Difficulty in depositing weld metal at the required place in the joint .
(2) More spatters with less deposition of weld metal .
(3) Poor fusion and penetration .
(4) Weak Welds .
Remedies / Methods Used To Control The Arc Blow :–
The arc blow can be controlled by :
(1) Welding away from the earth connection .
(2) Changing the position of the earth connection on the work .
(3) Changing the position of the work on the welding table .
(4) Wrapping the Welding cable fewer times around the work .
(5) Welding towards a heavy welding tack or a weld already made .
(6) Keeping a magnetic bridge on the top of the groove joint .
(7) Holding the correct electrode angle with a short arc.
(8) Using 'run on' and 'run off' plates .
WELDING POSITION
Some difference of opinion exists in various shops regarding the exact method of designating the various welding positions , also the scheme adopted in this country differs solightly from that used in other countries .
As the welding position of a weld is defined by its slope and rotation , so it is necessary to know what is :
(i) Weld slope .
(ii) Weld rotation .
Axis of Weld :– The imaginary line paasing through the weld centre lengthwise is known as axis of the weld .
Face of Weld :– Face of weld is the exposed surface of a weld made in a welding process on the side from which the welding is done .
Weld Slope :– Weld slope is the angle formed between the line of weld root and the horizontal reference plane .
Weld Rotation :– Weld Rotation is the angle formed between the upper portion of the vertical reference plane which passing through the line of the weld poot , and the line drawn from the line of weld root which intersects the weld surface at night angles and at a point equidistant from both edges of the weld .
DEFINITIONS OF WELDING POSITION
| Position | Symbol | Slope | Rotation |
|---|---|---|---|
| Flat or Downhand |
F | Not exceeding 10⁰ |
Nor exceeding 10⁰ |
| Inclined | I | Exceeding 10⁰ but beyond 45⁰ |
Not exceeding 90⁰ |
| Horizontal | H | Not exceeding 10⁰ |
Exceeding 10⁰ but beyond 90⁰ |
| Vertical | V | Exceeding 45⁰ | Any |
| Overhead | O | Not exceeding 45⁰ |
Exceeding 90⁰ |
