Arc Blow in Welding
Arc blow in welding is a phenomenon that can occur while welding, in which the arc becomes unstable and wanders or oscillates away from the point of welding.
This can lead to poor weld quality (unsatisfactory welds) and increased risk of burn-through, especially in thin materials.
There are several causes of arc blow, including:
- Magnetic fields: Arc blow can be caused by external magnetic fields, such as those produced by nearby equipment or materials. This can be particularly problematic when welding in close proximity to other metal objects.
- Electrical current: Welding with alternating current (AC) can be more susceptible to arc blow than welding with direct current (DC).
- More as explained later in this post in depth.
It is not possible to eliminate the welding arc blow however it can be reduced or controlled to an acceptance level using various techniques as explained in this article.
Arc blow welding definition
Arc blow is a welding defect which is encountered during Stick Welding, also called shielded metal arc welding (SMAW), (manual metal arc welding –MMAW in UK).
It occurs when the arc becomes unstable and begins to wander or wander off the intended weld path, resulting in a poor-quality weld.
Arc blow in manual metal arc welding is caused by can be caused by a variety of factors, including the presence of a magnetic field, the proximity of ferromagnetic materials, and the orientation of the weld.
How to prevent arc blow in welding?
Unfortunately, Magnetic arc blow in welding can’t be completely eliminated. However, it can be reduced to controlled within an acceptable level during welding.
In electric welding arc blow can be avoided by several ways such as:
- Change Current type: Changing from DC to AC will remove the arc blow effect in Stick Welding, especially when welding with an amperage more than 240 amps.
- Using short arc length: It is proven that short arc length compared to longer arc length are less prone to arc blow effect in welding.
- Change the welding angle: Changing the electrode angle opposite to the arc blow direction will counter the arc blow as shown in figure 3-45.
- Increase the distance between the electrode and the workpiece: A larger distance between the electrode and the workpiece can help reduce the influence of a magnetic field on the arc.
- Change in welding position: Changing welding position to flat can help to minimize arc blow. Horizontal & vertical downhill are more prone to arc blow.
- Use a welding current with a lower frequency: A lower frequency current can help stabilize the arc and prevent arc blow.
- Use a shielded metal arc welding (SMAW) technique that is less prone to arc blow: There are several SMAW techniques that are less prone to arc blow, such as the weave bead technique in place of stringer bead technique.
- Use a non-conductive backing strip: A non-conductive backing strip can help reduce the influence of a magnetic field on the arc.
- Wrap your earthing wire around the work: Keeping your earthing wire cable in a circle around the workpiece will generates additional magnetic field that can neutral existing magnetic field to control arc blow.
What causes arc blow in stick welding
There are several factors that can cause arc blow in shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA):
- The presence of a magnetic field: A magnetic field can cause the arc to become unstable and wander, leading to arc blow.
- The proximity of ferromagnetic materials: The presence of ferromagnetic materials, such as iron or steel, can cause the arc to become unstable and wander, leading to arc blow.
- The orientation of the weld: Horizontal welding position & vertical-down position are more prone to arc blow.
- The welding current: A welding current with a high frequency can cause the arc to become unstable and wander, leading to arc blow.
- Residual magnetic field in material: Presence of residual magnetic field in a material will cause arc blow in welding.
Magnetic Flux Lines and Wire Behavior
When electrons flow through a wire, they generate magnetic flux lines that form circles around the path of flow. These flux lines distribute evenly along a current-carrying wire. However, if the wire is bent, the flux lines on one side become compressed while those on the other side stretch out.
This uneven spacing of flux lines exerts a force on the wire, attempting to straighten it and restore even spacing. Generally, this force is small and does not cause the wire to move. However, at very high welding amperages (600 amperes or more), the force can actually cause the wire to move.
Arc Blow and Uneven Flux Lines
Welding current flowing through a plate or residual magnetic fields within the plate can result in unevenly spaced flux lines. These uneven flux lines can, in turn, cause the welding arc to move during the welding process, a phenomenon known as arc blow.
Arc blow causes the arc to drift, similar to how a string would drift in the wind. Arc blow tends to be more problematic when the magnetic fields are highly uneven, such as in corners, at the ends of plates, or when the work lead is connected to only one side of a plate.
Managing Arc Blow
The complexity of a weldment increases the likelihood of experiencing arc blow. Complex weldments can distort the magnetic flux lines in unexpected ways. If severe arc blow occurs during welding, it is important to stop welding and take corrective measures to control or reduce it.
Several approaches can be employed to manage arc blow, including:
- Connecting the work lead to the end of the weld joint and welding away from it.
- Using two work leads, one on each side of the weld.
- Utilizing alternating current (AC) welding, as the changing direction of the current prevents the flux lines from exerting enough force to bend the arc before the current switches direction.
- Adjusting the arc length to be very short.
- Employing large tack welds or altering the electrode angle.
Considerations for Welding Practice Plates
Arc blow may not pose a significant problem when learning to weld in a shop setting, as most welding tables are made of steel. However, if a pipe stand is used to hold welding practice plates, arc blow can become an issue. In such cases, re-clamping the practice plates can help mitigate the effects of arc blow.
How Arc Blow affect welding Quality?
Arc Blow is an unpredictable phenomenon in welding, which can cause a variety of problems that impair the quality and strength of welds.
It occurs when an electrical current is carried away from the arc by magnetic forces rather than through the workpiece.
This causes welders to experience problems such as poor welds, excessive welding spatters, a lack of fusion between the two pieces being welded, undercut along the joint, porosity within the weld joints and even incomplete fusion.
It’s important for welders to understand what arc blow is and how it affects their work if they want to ensure they’re producing high-quality welds consistently.
Arc blow can be caused by many factors in a welding environment such as electrical fields originating from nearby power lines or large machinery, incorrect polarity settings on equipment or high levels of magnetic force present during welding operations.
What is arc blow in mma welding?
It can be identified by a visible displacement of the arc away from its intended direction, causing weld defects and poor weld quality.
Arc blow can even cause the electrode to stick or short-circuit, leading to further weld problems and possible safety hazards.