Shielded Metal Arc Welding (SMAW) is a commonly used welding method across various industries. This method involves using a coated electrode that melts to permanently join metals.

The working principle of SMAW includes creating an electric arc between the electrode and the work metal, generating high heat to melt the electrode and partially the work metal.

The welding electrode plays a crucial role, with different types and specifications designed to meet various welding needs. 

Electrode specifications encompass factors like coating type, diameter, and material composition. Additionally, SMAW welding variables, such as current, voltage, and welding speed, also influence the final outcome of the welding process.

In this article, we will delve into the definition of SMAW, how it works, the role of welding electrodes, diverse electrode specifications, and critical variables in SMAW welding.

Definition of SMAW

Shielded Metal Arc Welding (SMAW), also known as "stick welding," is an electric arc welding technique. In this process, welding heat is generated by an electric arc between a covered metal electrode and the workpiece. The electrode contains a filler metal surrounded by slag, acting as a protective shield during welding.

The term SMAW implies joining or adding metal to surfaces. "Shielded" signifies the elimination of air around the weld to ensure quality. In another sense, it relates to the electrode core wrapped with flux.

"Metal" refers to the electrode core, a conductor rod melting to fill the weld pool. "Arc" denotes the plasma release transforming electrical energy into heat, and "welding" indicates metal joining by fusion.

The protective measures in SMAW involve displacing air through electrode combustion gases and shielding molten metal with flux or slag. These actions prevent harmful effects on the weld pool caused by air constituents.

Related article: GTAW (TIG) Welding Shielding Gas: Various Types and Characteristics

SMAW Welding Process

Illustration: smaw welding process

The principle of operation for Shielded Metal Arc Welding (SMAW) involves the transformation of electrical power into heat energy to create a welding arc. The intense heat from this arc melts a portion of both the workpiece and the electrode tip. The welder maintains the arc length by adjusting the gap between the electrode and the weld pool. When the arc is extinguished, the molten material solidifies into a continuous metal solid.

In the SMAW process, the power source is connected in a series circuit with the electrode and workpiece. The power source has two output terminals, with one linked to the workpiece and the other to the electrode. As long as the electrode is away from the workpiece, an open circuit exists, creating a voltage difference.

When the welder brings the electrode tip closer to the workpiece, an electric arc is formed upon contact. The contact allows current to flow, and maintaining a specific distance between the electrode tip and the workpiece induces a voltage drop, creating the arc. The arc's current is carried by plasma, the ionized state of a gas.

The direction of current flow depends on the welding machine setting. If set to direct current electrode positive (DCEP), the cathode is on the workpiece, and the anode is at the electrode tip. The energy converted into heat by the arc is influenced by gas ionization ease and transmitted current. Temperature distribution depends on generated heat, lost heat, and arc dimensions.

The arc's intense heat melts the electrode core and burns the covering flux. Some covering materials vaporize, producing gas, while others form a protective cone around the core wire. Simultaneously, molten metal forms a pool on the workpiece surface near the arc.

During the initial welding stages, a quasi-steady state forms, and the welder can manipulate the electrode. Porosity is a concern at this point due to the incomplete shield development and remaining air in the welding location.

Related article: Welding Energy: Powering the Fusion of Precision and Efficiency

SMAW Electrodes

SMAW electrodes play a crucial role in the welding process, featuring a covering with a specific composition that enhances the welding and imparts valuable properties to the weld. The covering is vital, as it facilitates arc stability; without it, welding could lead to issues like brittle deposits, dissolved oxygen and nitrogen, irregular weld beads, and undercut in the workpiece.

These electrodes, with their wrapped covering, not only supply filler metal but also protect the welding process. Covered electrodes have a diverse core wire composition and various flux coverings, each serving distinct functions:

• Covering the Molten Metal and Weld Pool: The covering envelops the molten metal and weld pool, promoting proper solidification.
• Shielding Gas: It acts as a shielding gas, preventing atmospheric contamination during the arc and weld metal flow.
• Ionizing Elements: The covering provides ionizing elements, ensuring a smoother arc operation.
• Deoxidizers and Scavengers: It contains deoxidizers and scavengers, refining the grain structure of the weld metal.
• Alloying Elements: Certain electrodes introduce alloying elements like nickel and chromium, especially in stainless steel welding.
• Additional Metals: Some electrodes include metals like iron powder to boost deposition rates, enhancing efficiency.

Understanding the multifaceted functions of the electrode covering is essential for achieving high-quality welds and preventing defects in the workpiece.

Related article: FCAW Welding: Choosing Gas-Shielded Wires Guide

Classification of SMAW Electrodes.

The American Welding Society (AWS) establishes a classification system for coated electrodes in the United States, denoted by the letter "E" (for electrode) followed by four (or five) digits for carbon and low-alloy steel coated electrodes, with optional suffixes. Here's what these digits signify:

• First Digits (Tensile Strength): Indicates the minimum tensile strength of the deposited weld metal in 1,000 psi.
• Third (or Fourth) Digit (Welding Position): Indicates the welding position the electrode is suitable for.
• Fourth (or Fifth) Digit (Current Characteristics and Coating Type): Describes the current characteristics and electrode coating type.
• Suffixes: Optionally added to the classification and reveal the chemical composition of the deposited weld metal.

Electrode size is determined by core wire diameter and length, with standard diameters ranging from 1/16 inch (1.6 mm) to 5/16 inches (7.9 mm). Lengths vary from 9 inches (229 mm) to 18 inches (457 mm), with specialty electrodes extending up to 36 inches (914 mm). The standard electrode length is 14 inches (346 mm). Uncoated electrode tips, crucial for electrical contact, have lengths from 3/4 in. (19 mm) to 1-1/2 in. (38 mm).

Understanding these classifications and dimensions is vital for selecting the appropriate electrode for specific welding requirements.

Equipment Required

In the world of welding, mastering the process goes hand in hand with understanding the essential equipment needed to achieve optimal results.

Shielded Metal Arc Welding (SMAW), also known as stick welding, relies on a carefully selected set of tools to create strong and reliable welds.

From power sources to protective gear, each component plays a crucial role in ensuring the success and safety of the welding process. In this section, we will explore the key equipment required for SMAW:

1. Power Source: SMAW requires a welding power source that provides the necessary current to maintain the arc. Common power sources include constant current (CC) and constant voltage (CV) machines.
2. Electrodes: Electrodes are available in various sizes and types, each designed for specific applications. The coating on the electrode determines the characteristics of the arc, the weld bead, and the overall quality of the weld.
3. Welding Cables and Clamps: These are essential for connecting the power source to the electrode holder and workpiece, completing the electrical circuit.
4. Electrode Holder: Also known as a stinger, this is used to hold and control the electrode during welding.
5. Protective Gear: Welders must wear appropriate personal protective equipment, including helmets, gloves, and clothing, to ensure safety during the welding process.

SMAW Welding Variables.

In metal arc welding, understanding welding variables is crucial for achieving desired results. These variables fall into three categories: fixed/preselected, primary, and secondary.

• Fixed/Preselected Variables: Set before welding and include electrode type, size, and current type. These cannot be changed during welding.
• Primary Variables: Mainly adjustable and control the welding process after fixed variables. Key ones are welding current, arc voltage, and travel speed, influencing bead width, height, penetration, arc stability, and soundness.
• Secondary Variables: Smaller and adjustable, challenging to measure. Examples include work angle and electrode travel angle.

Key Aspects:

• Weld Penetration: Deepest point reached by weld metal.
• Bead Height (Capping): Height of weld metal above the base metal.
• Deposition Rate: Weight of metal deposited per unit of time.

Achieving Quality:

• Focus on three main characteristics: penetration, deposition rate, and bead shape.
• Influence of welding variables on these characteristics is illustrated in the chart.

Understanding and effectively managing these variables are essential for controlling welding processes and ensuring high-quality welds. The effects of primary variables on weld bead production are summarized in the provided illustration.

Advantages of SMAW

In the realm of welding techniques, Shielded Metal Arc Welding (SMAW), also known as stick welding, stands out for its unique array of advantages. This tried-and-true welding method offers a host of benefits that make it a preferred choice for various applications.

From its simplicity and versatility to its ability to excel in challenging environments, SMAW holds a special place in the welding toolkit. In this section, we'll explore the distinct advantages that set SMAW apart from other welding processes:

• Portability: SMAW is a versatile process that can be used in various locations, including outdoor and remote sites, where other methods might be impractical.

• Simple Setup: The equipment required for SMAW is relatively straightforward, making it accessible for welders of all skill levels.

• Versatility: SMAW can be used on a wide range of materials, including carbon steel, stainless steel, and various alloys.

• No Gas Required: Unlike some other welding methods, SMAW doesn't require an external shielding gas, which can be beneficial in certain environments.

Applications of SMAW