Sub Arc Welding: A Common Yet Highly Recommended Method in Fabrication

Submerged or Sub Arc Welding is a common arc welding process. It is considered as an ideal welding method to weld metal pieces especially during fabrication of street poles. The process involves heating the area by using metal electrode(s) and the work by using an arc or arcs. The solid or tubular (with a core made of metal) electrode or filler metal is constantly fed to produce a stream of molten metal which joins the weld. Molten granulated flux materials such as lime, magnesium oxide, silica, calcium fluoride and others protect the molten metal from the atmosphere. Thus, the arc zone and molten metal are “submerged” below the flux and hence the name. 

Sub Arc Welding

Equipment that is required for this welding: 

• Welding Head: This part of the machine holds and feeds the flux and feeding metal to the arc welding zone. The metal is electrified here to produce the arc.

• Flux: Granulated flux is an essential component of this process. The molten flux forms a barrier between the atmospheric elements and the molten metal and thus allows the weld to form properly. It is usually made up of silica, magnesium, aluminum, manganese, calcium oxide, calcium fluorides etc. Substances which too much of volatile gases are avoided in the composition of the flux material.

• Electrode: Sub arc welding filler metal is usually a common metal wire or made especially for the purpose. The thickness of the wire varies between 1.6-6mm. They are also used in twisted forms which help give an oscillation movement. The filler wires are also usually coated with copper to prevent rusting and increase electrical conductivity.

• Power Source: The power source for the sub arc welding must be rated to 100% duty cycle. A reason attributed to the fact that arc welding process is continuous and last up to 10 minutes at a time. If a lower e.g.60% duty cycle is used it is derated based on the duty cycle curve to up-regulated to provide for 100% performance. The equipment set usually ranges in strength from 300- 1500 Amperes. 

Advantages of Arc welding for fabrication of street poles: 

Sub Arc Welding

• Speed and deposition rates: Speeds over 5m/min 16ft/min can be achieved for thin sheets of metal and deposition of 45kg/h has been performed. Thus, this process of fabrication takes a short amount of time compared to other methods of welding.

• The quality of weld: Very high-quality welds can be achieved as the welds made by this process are strong, ductile, uniform and corrosion resistant. 

How do you ensure the safety and flux recovery during sub arc welding?

• Safety: Compared to the other methods of welding, sub arc welding process is a much safer form of welding. This is predominately due to the fact that very little arc fumes or arc light are produced. Weld splatter is much reduced as it is submerged under a layer of molten flux.

• Flux recovery: 50-90% of the flux can easily be produced and put back into the hopper. This not also reduces consumables and costs but also reduces the environmental impact.

• Preparation time on the work: Little or almost no edge preparation is required on most kinds of welds done by this method.

• High Operating factors: Easily automated for high operating factors.

• Interoperability of machines for different works: The same equipment can be used to perform welds of varying levels of thickness and types of works materials with very little change. 

Sub arc welding is a simple yet very useful welding process and an ideal process for the fabrication of street poles.