What is Shielded Metal Arc Welding (SMAW)

How Does Shielded Metal Arc Welding Work?

Before welding with the SMAW method, turn on an SMAW welding power source. This power source supplies the energy required to generate an electric arc. An electrode holder and a work clamp are attached to the power source. The work clamp can be connected to a conductive surface or the workpiece itself. The holder is subsequently put with a stick electrode.

If you want to strike the electric arc, you can bring the electrode into contact with the workpiece with a light touch. Then, you can pull the electrode back slightly. This action develops the arc and leads to the melting of the workpiece and the consumable electrode while facilitating the passage of electrode droplets from the electrode to the weld pool. 

It should be noted that the orientation of the electrode to the workpiece while striking the electric arc. The tip will likely adhere to the metal if the electrode is perpendicular to the workpiece. This fuses the electrode to the workpiece and causes it to heat up extremely quickly. Hence, the electrode tip must be at a lower angle to the workpiece to permit the weld pool to flow out of the arc. 

The flux coating disintegrates when the electrode melts, releasing shielding gases that shelter the weld region from oxygen and other atmospheric gases. Furthermore, the flux creates molten slag that covers the filler as it moves from the electrode to the weld pool. Slag floats to the surface of the weld pool and then prevents the weld from contamination when it solidifies. Once hardened, it must be gradually removed by chipping to expose the final weld. 

SMAW Equipment and Setup for Shielded Metal Arc Welding

The equipment required for stick welding comprises the following:

Power Source (Welding Machine)

The power source provides constant current output. Depending on the application, stick welding can be used in alternating (AC) or direct (DC) power sources. Note that the formation of the arc needs a current of enough amperage. The amperage must be set correctly since the arc will not form if it is set too low. The arc will be inconsistent, the weld puddle will be overly fluid, and there will be a lot of spatter if the amperage is too high. As for voltage, it can be regulated by moving the electrode closer or farther from the workpiece.

The power source of the stick welding process comes from the welding machine. The SMAW welding machine provides the electric current for welding. It generates a constant amperage in alternating current (AC) or direct current (DC). This current flows from the machine to the electrode, across the welding arc, and back to the machine through the work clamp. When buying a SMAW machine, you should ensure its capabilities meet the size and type of electrodes you use.

Electrode Holder 

Electrode holders come in different sizes and can carry different current capacities. An electrode holder can be used to hold the SMAW electrode and connect it to the welding machine. It is also responsible for delivering the welding current to the electrode and precisely feeding the electrode to the weld joint. In addition, it protects the hand of the welder from arc and electrical current damage. Some electrode holders feature detachable clamp plates, so you can replace them instead of the entire holder when worn.

Work Clamp 

The work clamp is an important part of the welding machine because it completes the electrical circuit between the welding machine and the workpiece, making welding possible. Often, it attaches to return leads and clamps onto your workpiece and is used to prevent electrical shock. Note that the ground clamp must carry the electric current without overheating to prevent risks when using it. Once the work clamp starts to wear, you replace it. 

Welding Cables 

Remember that a successful shielded metal arc welding process requires a complete electrical circuit. Welding cables carry electrical current between your workpiece and electrodes. The welding cables utilized in SMAW are characterized by their flexibility and insulation. They must have enough cross-sectional area and length to conduct the welding current with low voltage drop. A stick welding machine has two welding cables. One connects the electrode holder to the welding machine, and another connects the work clamp to the welding machine.

SMAW Electrodes

SMAW electrodes are consumable electrodes coated in flux and add the metal into the weld puddle to form the weld bead. It protects the weld area from the atmosphere as the arc melts it. You can choose different electrode types based on the metal being welded. Different SMAW electrodes come in different chemical compositions that can influence the arc stability, deposition rate, depth of penetration, and other factors. 

Functions of Stick Welding Electrodes

The SMAW electrode has several purposes:

• It carries electric current from the machine to the workpiece.
• It acts as the filler material melts at the arc to form the weld. 
• A flux coating shields the weld from the atmosphere.
• The core of the SMAW electrode is a bare metal rod designed to match the base metals of the weld joint. The numbers on this rod represent a categorization of the electrode’s properties.

Types of Stick Welding Electrodes

Stick welding electrodes are divided into three main categories:

Cellulosic Electrodes

Cellulosic electrodes have a high cellulose content in the coating and are distinguished by a deeply penetrating arc and a quick burn-off rate, resulting in high welding rates. These electrodes are simple to utilize in any position and are well-known for their application in the ‘ stovepipe’ welding method. Cellulosic electrodes offer suitability for vertical down welding and reasonably good mechanical properties. However, the high level of hydrogen generated by them would increase the risk of cracking in the heat-affected zone (HAZ).

Rutile Electrodes

The coating on rutile electrodes has a high proportion of titanium oxide (rutile). Titanium oxide enhances smooth arc operation, simple arc ignition, and reduced spatter. They may be utilized in all positions and with AC and DC power sources. The electrodes are well suited for welding fillet joints in the horizontal/vertical (H/V). Rutile electrodes produce viscous slag and fluid slag, which is easily removable.

Basic Electrodes

The coating of basic electrodes possesses a significant amount of calcium carbonate (limestone) and calcium fluoride (fluorspar). As a result, their slag coating is more fluid than rutile coatings. In addition, it freezes quickly, which aids welding in the vertical and overhead positions. Basic electrodes can be employed for welding medium and heavy section fabrications that demand improved weld quality, excellent mechanical properties, and fracture resistance. However, these electrodes result in poor bead profile and difficult slag removal.

Personal Protective Equipment 

Apart from the equipment mentioned earlier, other essential items include a welding helmet, gloves, protective clothing, and safety glasses. These tools ensure your safety and enable you to carry out the welding process effectively.

• Welding Helmet – A welding hood can protect your eyes and face from harmful UV rays of electric arcs.
• Safety Glasses – Without safety glasses, it is also easy for sparks and debris to enter your eyes.
• Welding Gloves – Welding gloves protect your hands and keep them safe as they move closer to the arc.
• Protective Clothing – Your arms or legs would come into contact with something hot enough to burn you, such as sparks flying. Wearing protective clothing defends against welding-related burns.
• Chipping Hammer and Wire Brush – Apart from the safe equipment mentioned before, a chipping hammer and wire brush are required to remove slag after welding. This is because SMAW would leave a layer of hard slag on the weld; these two tools can chip away and then clear away this hard coating so you can see the underlying weld.

What Metals Can Be Welded with SMAW?

The metals that can be welded using shielded metal arc welding (SMAW) include:

Carbon Steel 

The ease of welding carbon steel with SMAW is largely impacted by its carbon content. Higher carbon content makes welding more difficult and increases the possibility of cracking, whereas low carbon content simplifies welding. Also, considering the amount of carbon and the desired weld properties, pre-weld and post-weld heat treatments may be necessary. You should choose proper electrode selection and welding methods to achieve successful welds without flaws such as porosity, cracking, or severe distortion. 

Tool Steel

If you use the proper filler metal and execute the required preheat and post-weld treatments, SMAW may be used to weld tool steel while maintaining its high hardness, resistance to wear, and toughness. The utilization of this welding technique facilitates the job of repairing or altering tools, dies, and molds fabricated from tool steel. Note that some tool steels contain alloying elements such as chromium that might affect weldability.  As a result, preheating and post-weld heat treatment are often required to minimize the occurrence of cracking and maintain the proper hardness of the material.

Stainless Steel

Stainless steel is noted for its non-hardenability upon cooling and its exceptional toughness, which typically removes the need for pre- or post-weld heat treatment. Chromium carbide precipitation could occur during stainless steel welding, possibly affecting corrosion resistance. Nevertheless, the prevention of chromium carbide precipitation during stainless steel welding can be achieved by employing filler electrodes that have a low carbon content and carefully controlling the heat input. In addition, using suitable passivation and post-weld cleaning procedures aids in preserving the corrosion resistance of stainless steel.

Cast Iron

SMAW allows you to repair cast iron workpieces or fuse cast iron with other metals. While SMAW offers localized heating, it is crucial to remember that cast iron welding has unique requirements. These include careful preheating, electrode compatibility testing, and post-weld heat treatment to decrease stress, avoid cracking, and produce optimal outcomes.

Nickel

Nickel is SMAW weldable and has good corrosion resistance, high-temperature strength, and thermal expansion qualities. Proper joint preparation and heat input control is necessary to minimize cracking and generate stable welds. Nickel welding is widely employed in various sectors, including chemical processing, aerospace, and power generation.

Copper

Welders frequently avoid using the SMAW process for aluminum and copper. Compared to steel, copper possesses the properties of high thermal conductivity and lower point. This makes welding copper become a challenge. Yet, oxygen-free and phosphorus-deoxidized copper is considered to be more readily weldable. It has several applications, including plumbing, heat exchangers, and electrical wiring. 

What are the Advantages and Disadvantages of SMAW (Stick Welding)?

SMAW is a versatile, portable, and inexpensive welding process. It is well-suited for many applications, such as construction, maintenance, and fieldwork. The following talks about the advantages and disadvantages of stick welding:

Advantages of Shielded Metal Arc Welding

Several key advantages make SMAW a cost-effective general-purpose welding technique. Let us take a closer look at them.

• Stick welding has all-position welding capability. It can be performed at varying angles, including flat, horizontal, vertical, and overhead welding.
• The welder is portable and versatile. And compact, lightweight equipment can weld anywhere with access to power. It can weld a variety of metals and alloys.
• This process eliminates the need for external shielding gas. This is because consuming the flux coating releases a shielding gas that protects the weld pool from atmospheric contamination. 
• There are several welding techniques, such as whipping the electrode,  circle technique, and weaving. 
• The equipment is relatively simple to learn and inexpensive compared to other welding processes. It has lower startup costs.
• Metal surfaces do not need to be cleaned as thoroughly as they need in TIG welding.
• SMAW is good for the outdoors. The covered electrode works well outdoors, even in windy conditions.
• Deep weld penetration is achievable.
• Stick welding is usually the best choice when welding thicker metals.

Disadvantages of the Stick Welding

SMAW also comes with some limitations:

• The welding speed of SMAW is slower than other welding methods like MIG or flux core. This is because it has low weld deposition rates.
• It produces spatter, sparks, and slag. The slag needs to be chipped off post-weld.
• It requires coordination and skill of the welder.
• It generates fumes and gases, so ventilation is required. Ozone gas can be hazardous.
• Frequent stops to change electrodes reduce productivity.
• Welding thin materials is a challenge.
• Relatively slow process due to manual operation.
• Not suitable for reactive metals.

Applications and Industries of SMAW

Shielded metal arc welding is applied extensively in many industries due to its versatility:

Construction and Infrastructure – erecting steel buildings, bridges, pipelines, offshore platforms, and railway tracks.

Manufacturing – welding automotive parts, machinery, pressure vessels, storage tanks, pipes, boilers, and tools.

Maritime – shipbuilding and repair.

Energy – power plants, oil and gas, wind turbines, nuclear, hydroelectric.

Transportation – vehicles, aircraft, railcars.

Mining and Resources – equipment, machinery, infrastructure.

Maintenance and Repair – general fabrication, equipment upkeep across all sectors.

What is the Difference Between SMAW and GMAW?

SMAW and GMAW differ in terms of many aspects.

1. Process 

SMAW is a manual welding process using a coated electrode, whereas GMAW is a semi-automated or automated process that uses a continuous wire electrode.

2. Types of Gas Used for Shielding 

SMAW does not rely on external shielding gas and uses a flux-coated electrode that releases a protective gas to safeguard the weld area against contamination. However, GMAW still relies on an external shielding gas (such as argon or a mixture of argon and carbon dioxide) to protect the weld area.

3. Material to Weld 

GMAW can weld diverse materials, including steel, stainless steel, aluminum, and non-ferrous metals. Conversely, SMAW mainly weld ferrous metals, specifically steel, iron, and cast iron.

4. Equipment Cost 

Generally, GMAW needs a welding power source, shielding gas supply, and wire feeder. On the other hand, SMAW only requires a power source, electrode holder, ground clamp, and SMAW electrodes. Because the additional components are required for the GMAW, its equipment costs more than the SMAW equipment.

5. Ease of Operation 

SMAW is not inherently easier to use than GMAW. SMAW needs a higher level of skill and technique because of the difficulties in regulating slag, maintaining arc length, and operating electrodes. GMAW, on the other hand, provides greater automation and control, making it easier to use and grasp.

Tips for Successful Shielded Metal Arc Welding

To achieve successful Shielded Metal Arc Welding results, consider the following tips:

• Choose the right electrode for the material and application. 
• Control proper arc length that never surpasses the diameter of the core wire.
• Maintain proper electrode angle and travel speed to ensure a stable arc and consistent weld bead.
• Control the heat input by adjusting the amperage settings to prevent overheating or underheating. Higher amps increase deposition rate and penetration but can cause burn-through.
• Practice proper electrode manipulation techniques to achieve desired weld characteristics.
• Monitor the weld pool and adjust the electrode position to maintain a consistent bead shape and size.
• Conduct post-weld inspections to ensure the quality and integrity of the weld.

Summary

Shielded Metal Arc Welding involves using a consumable electrode coated in flux to join metal together. The electrode provides shielding gas and slag to protect the weld pool. Stick welding is a versatile and widely used welding process that offers numerous applications across almost any industry, environment, position, and metal. Although it is a relatively straightforward process and can produce high-quality welds, it still needs to be performed by experienced individuals. This is because it might still be challenging to regulate slag, maintain arc length, and operate electrodes.

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References

Shielded metal arc welding – From Wikipedia

MANUAL METAL ARC WELDING (MMA, SMAW, OR STICK WELDING) – From TWI Ltd