SMAW: Shielded metal arc welding
SMAW is a metal joining process in which welding is performed in an inert gaseous environment, produced by burning a coated flux on a stick electrode.
In this process, coalescence is produced by heating the workpiece with an electric arc established between the flux-coated electrode and the workpiece.
SMAW welding process
SMAW stands for shielded metal arc welding process, also known as manual metal arc welding or stick welding. Welding by this method is comparatively easier than other processes. But in some welding positions, welding by this method also demands skill.
The desired heat to melt the metal is obtained from the welding arc using an electric power source. AC transformers, DC generators, or inverters are mainly used in the SMAW welding process.
The heat required for welding is obtained from an arc between a coated electrode and the workpiece. First, the electrode is scratched and pulled on the base metal.
With a minimum distance, a spark(arc) jumps, which remains between the electrode and the workpiece. The spark produces heat which is used to melt the electrode so that the joint can be welded.
Heat can be increased or decreased by applying high or low arc current. A high current with a short arc length produces a lot of intense heat.
SMAW stands for shielded metal arc welding process,wherein coalescence is produced by heating the workpiece with an electric arc established between the flux-coated electrode and the job.Weldworld
Use of flux in smaw
The flux covering decomposes due to arc heat and performs several functions, mainly including stability of the welding arc, and weld metal protection.
Shielded metal arc welding (SMAW) is a welding process in which coalescence of metals is produced by heat from an electric arc maintained between the tip of a consumable electrode and the surface of the base material in the joint being welded.Encyclopedia of Materials: Metals and Alloys, 2022
Working principle of SMAW
In the smaw welding method, the arc melts the electrode end and molten droplets of material are transferred through an arc from the electrode to the joint and deposited.
The flux coating burns and melts to form a gaseous shield and slag to prevent further atmospheric contamination of the molten weld metal.
Once the arc is established and the arc length adjusted, the electrode is inclined at an angle of approximately 20 degrees with the vertical. In order to obtain a comparatively deeper penetration, the electrode angle is further reduced with the vertical which is necessary to maintain a constant arc interval.
Welding characteristics of smaw arc welding
The factor affecting welding characteristics in smaw welding are as follows:
- Weld bead and penetration size of the weld
- Electrode size and type
- Electrode polarity and current
- Arc length and arc trevel
By employing higher arc currents, lower arc travel speeds, and weaving the electrodes appropriately, the bead width can be increased, If the bead width is greater, it is a weak point for the welded structure.
According to most general welding standards, the width of the weld bead is only allowed up to 3 times the electrode thickness.
Weaving factors in smaw arc welding
Weaving refers to the simultaneous movement of the welding arc during welding. Weaving helps to give better fusion ‘on the sides of the welds.
As we discuss weaving is only allowed 2.5 to 3 times the electrode dia.
Further details >>> WEAVING IN WELDING OPERATION
Welding equipment of smaw process
The equipment used in smaw welding is cheap and portable as compared to other processes. Some of the Essential tools and equipment for smaw welding are as follows:
Welding supply(Power source)
Although AC transformers and DC generators or rectifiers can be employed for inductive welding, it becomes necessary to select a good machine to get good quality welding. such as:
AC power source
At high arc currents, AC gives a smooth arc, there is no chance to arc blow, once the arc is established,easily maintained and controlled,and suitable for welding thicker pieces of metals.
Provides high efficiency, consumes less energy per unit weight of the deposited metal, and has high no-load voltage.
the melting rate of the electrode cannot be controlled by using an AC power source due to equal heat generated at the electrode and workpiece.
DC power source
DC arc is more stable than AC, here the arc heat can be regulated by changing the electrode polarity. It is preferred for welding some non-ferrous metals and alloy,
Welding machine for smaw
The primary function of a welding power source is to provide sufficient power to get the desired heat for melting the joint and the most commonly used power source for AC welding is a transformer.
A Transformer may be a single-phase, two phases, or three phases. For thinner sections with small diameter electrodes, welding machines with Single-phase transformers are quite enough because they supply lower currents.
Two-phase and three-phase supply transformers operate at higher currents and are used for the welding of thicker jobs.
Further details >>> POWER SOURCE IN ARC WELDING
Electrode holder and welding cables
An electrode holder is an important tool in the smaw welding process wherein the electrode holder clamps the end of the electrode with copper contact shoes built into its head.
Welding cables for smaw arc welding
Insulated welding cables are used in smaw welding wherein cables are covered in a smooth and hard-wearing protective rubberized flexible sheath. These cables are capable to resist water, oil, etc.
Advantages & Limitations of Arc Welding
As discussed earlier, SMAW or stick welding is simpler and cheaper than other welding processes. Due to its portability, it is able to work anywhere.
it is a popular welding process due to its lightweight and universal availability. Welding can be performed in any position with the highest weld quality.
The process can be very well employed for hard-facing and metal deposition to recover parts or develop other characteristics such as wear resistance, etc.
Apart from having many benefits, there are also some limitations like,
- Due to the limited length of each electrode and the brittle flux, The coating on it is difficult to mechanize.
- Due to the use of flux-coated electrodes, there is a chance of slag entrapment and other associated defects.
- Comparatively a slower process because of using a stick electrode, which need to be changed after finished.