Shielded metal arc welding (SMAW) is a manual arc welding process known as manual metal arc welding or stick welding. It uses a consumable and protected electrode.
During the operation, the electrode melts, and a cover from the electrode protects the weld area from oxygen and other atmospheric gases.
The primary purpose of shielded arc welding is to perform arc welding using a covered metal electrode to protect the weld. Requirements like a welding machine or power source provide an electric current for the welding.
Furthermore, an electrode holder will be needed to hold the SMAW electrode and connect it to the welding machine.
We often use SMAW techniques on carbon steel, low- and high-alloy steel, stainless steel, cast iron, and ductile iron. However, they are not suitable for non-ferrous metals. In this reading, we’ll explore SMAW: its applications, components, equipment setup, schematic representation, benefits and drawbacks, and operational principles.
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What is Shielded Metal Arc Welding (SMAW)?
Shielded metal arc welding is another type of arc welding process, which is also known as stick welding or manual arc welding. It utilizes a metallic consumable electrode with a specific composition to generate an arc on the workpiece.
This arc welding process is known as the simplest, least expensive, and most used type of arc welding process.
The SMAW process works with electrodes coated with a shielding flux; this flux melts together with the electrode’s metallic core, which forms gas and slag. This gas and slag shield the arc and the weld pool, and the flux cleans the metal surface.
This flux supplies some alloying elements to the weld, stabilizes the arc, and protects the molten metal from oxidation.
In other words, the main function of the shielding is to protect the arc and the hot metal from a chemical reaction with constituents of the atmosphere.
The SMAW process does not need filler metals, as the electrode is already coated with fluxing agents, scavengers, and slag formers. The filler is obtained from the electrode.
Applications of SMAW
The applications of shielded metal arc welding are so broad and it is one of the most widely used arc welding techniques. SMAW is often used on carbon steel, low- and high-alloy steel, stainless steel, cast iron, and ductile iron.
It can be used on copper, nickel, and their alloys, but not on aluminum.
When deep penetration is required, we use SMAW for welding pipelines, tanks, pressure vessels, structural elements, and fieldwork. It is ideal for pressure pipelines that cannot be welded from the inside.
Storage tanks, gear blanks, machinery, steel furniture, truck bodies, foundry equipment, shaft build-up, etc.
Structures, building construction, tanks, pipelines, machinery parts, automobile bodies, steel window frames, farm machinery, etc. vessels, tanks and boilers, pipelines, bridges, railway wagons, ships, and trailers.
Pressure pipelines that cannot be welded from the inside, oil storage tanks, and railway coach panels are examples of structures that require special construction techniques. Locomotive fireboxes, scooter frames.
The above-listed applications can be welded using shielded metal arc welding.
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SMAW Parts & Equipment
Shielded metal arc welding equipment typically consists of a constant current welding power supply and an electrode, with an electrode holder, a work clamp, and welding cables (also known as welding leads) connecting the two.
The welding machine or power source provides an electric current for welding, and the electrode holder holds the SMAW electrode and connects it to the welding machine.
Cables help to power the welding machine and connect the electrode holder to the welding machine. The ground clamp maintains the electric current between the welding machine and the workpiece.
Protective items like helmets, overalls, safety boots, and goggles are parts of shielded metal arc welding.
Welding Machine
A welding machine is essential for ensuring the safety of the workpiece and preventing electrical shock. It connects to the workpiece or fixture and needs a ground clamp to prevent overheating.
The welding cables used in SMAW are flexible and insulated, with two cables for the electrode holder and the ground clamp.
The arc length is a crucial factor in stick welding, as it determines the optimal arc length for the project. Stick welder manuals and guides provide recommendations based on the electrode selection, welding angle, and finish, which influence the amperage.
Travel speed is also influenced by the electrode angle and type, with fast-filling electrodes allowing higher travel speeds.
Welding techniques are crucial in determining the quality of the weld. Whipping the electrode works best on low-flux electrodes like E6010, E6011, and E6013, while the circle technique is commonly used by beginners for consistent travel speed.
When wider welds are required, weaving typically performs side-to-side motions after striking the arc.
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Diagram of SMAW
How Does SMAW Work?
Shielded metal arc welding (SMAW) is a welding process that uses heat from an electric arc to create coalescence of metals between the tip of a consumable electrode and the surface of the base material in the joint being welded.
This process involves an electric circuit including the power source, welding cables, electrode holder, and ground clamp.
The electrode and base metal are part of this circuit, and the welding begins when an arc forms between the base metal and electrode tip. Metal forms on the end of the electrode, transferring from the arc into a pool, and filler is deposited when the electrode is consumed.
Voltage is a key variable in stick welding, and it is regulated manually by moving the stick closer or farther from the work. Constant current power sources are used for most stick welding and other manual welding processes.
Reverse polarity is almost always used in SMAW welding processes to provide the best bead profile and penetration while reducing excessive spatter.
Some basic tools used in SMAW include an arc welding power source, electrode lead cable, electrode holder, leads, cables, cable connectors, ground clamp, and a cutting hammer.
Safety equipment, such as helmets, gloves, and protective clothing, is also essential for the welder’s safety.
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Stick Welding Electrode
Electrode type plays a crucial role in determining weld quality, as its chemical composition influences arc stability, deposition rate, and depth of penetration.
Stick welding electrodes are classified into three main categories: cellulosic electrodes, rutile electrodes, and basic electrodes. Cellulosic electrodes have a high cellulosic proportion, suitable for deep arc penetration and high weld speeds.
Rutile electrodes have a lot of titanium oxide, which helps reduce spatter, create a better bead shape, and keep the arc working steadily.
Basic electrodes have high quantities of calcium chloride and calcium carbonate, suitable for welds requiring excellent mechanical properties and resistance to cracking.
They are suitable for high weld speeds, but slag freezing is difficult to remove, leading to poor bead profiles.
Metal powder electrodes have a flux coating with iron powder, promoting higher welding current and higher deposition rates and efficiency compared to electrodes without iron powder. These electrodes are suitable for various welding positions and power sources.
Advantages and Disadvantages of SMAW
Shielded Metal Arc Welding (SMAW) offers numerous advantages, including easy and reliable operation results, the provision of shielding material on the electrode, and its affordability, simplicity, and portability.
It can weld various metals, including carbon, low-alloy steel, high-alloy steel, coated steel, tool and die steel, stainless steel, cast iron, copper and copper alloys, and nickel and cobalt alloys, and is flexible in application to various joint configurations and welding positions.
Stick welding is a versatile welding technique that can be performed at various angles, including flat, horizontal, vertical, and overhead positions. By understanding these factors, the welder can create a strong and efficient welding process.
However, SMAW has limitations, such as not being able to weld metals with low melting temperatures, affecting the deposition rate due to stub loss, generating excessive heat within the electrode, and not being stable for welding reactive metals like titanium, zirconium, tantalum, and niobium due to insufficient shielding.
Additionally, stick welding yields lower deposition rates than other welding processes like gas metal arc welding (GMAW) and flux core arc welding (FCAW) due to limited maximum useful current.