We’re here to shed some light on the fascinating process of submerged arc welding. This method, which has been used for decades in various industries, offers numerous benefits and efficiencies when it comes to joining metal components. So, how exactly does submerged arc welding work? Well, let’s dive in and explore the inner workings of this innovative technique.
What is Submerged Arc Welding?
Submerged Arc Welding (SAW) is a welding process that utilizes an electric arc to join two pieces of metal together. This process involves the formation of a molten pool and the use of a flux to protect the weld from atmospheric contamination. SAW is particularly effective for welding thick materials and is commonly used in industries such as shipbuilding, pressure vessel fabrication, bridge construction, and heavy machinery manufacturing.
Definition of Submerged Arc Welding
Submerged Arc Welding, often abbreviated as SAW, is a welding process in which the welding arc is completely submerged under a granular flux. This flux serves multiple purposes, such as providing protection to the arc from the surrounding atmosphere, creating a protective slag layer over the weld, and facilitating the removal of impurities through chemical reactions. This process is typically used for joining thick materials and offers several advantages in terms of productivity, weld quality, and automatic operation.
Components of Submerged Arc Welding System
A typical submerged arc welding system comprises several essential components. These include the welding power source, the welding head, the flux, the wire electrode, and the electrode feed mechanism. The welding power source supplies the necessary electrical current for the welding arc, while the welding head directs and controls the movement of the arc and the electrode. The flux acts as a shielding medium and provides necessary elements for the welding process, while the wire electrode serves as the filler material. Finally, the electrode feed mechanism ensures a continuous supply of the wire electrode to the welding head.
Advantages of Submerged Arc Welding
Submerged Arc Welding is known for its high productivity. The process allows for continuous and efficient welding, minimizing the downtime between welds. With the ability to weld long, uninterrupted lengths, SAW is especially suitable for mass production and large-scale welding projects. This high productivity results in significant time and cost savings for industries that require efficient welding processes.
Another advantage of submerged arc welding is its ability to achieve deep penetration into the base material. The molten pool formed during the process has excellent heat transfer characteristics, allowing for efficient fusion between the base metal and the filler material. This deep penetration capability makes SAW particularly useful when welding thick materials, ensuring strong and reliable welds.
Submerged Arc Welding is an automatic process, which means that it can be easily mechanized and integrated into automated welding systems. This automation eliminates the need for manual intervention and reduces the reliance on skilled operators. By using automated equipment, companies can achieve consistent and reliable weld quality, improve productivity, and ensure worker safety.
High Weld Quality
SAW is renowned for its high weld quality. The submerged arc welding process creates a protective slag layer that shields the weld from atmospheric contamination, thus minimizing the risk of defects such as porosity or oxidation. The deep penetration also contributes to the quality of the welds by ensuring a strong fusion between base and filler materials. This high weld quality makes submerged arc welding a preferred choice for critical applications that demand superior strength and integrity.
Suitability for Thick Materials
Submerged Arc Welding is particularly well-suited for welding thick materials. The process’s ability to achieve deep penetration, coupled with the use of filler material, allows for efficient fusion and the creation of strong welds. As a result, SAW is commonly used in industries that work with thick plates, pipes, and structures, such as shipbuilding, pressure vessel fabrication, bridge construction, and heavy machinery manufacturing.
Disadvantages of Submerged Arc Welding
One of the main drawbacks of submerged arc welding is its limited portability. The setup and equipment required for SAW can be bulky and heavy, making it challenging to perform welding tasks in confined spaces or hard-to-reach areas. Additionally, the necessity for a constant supply of flux and wire electrode adds to the overall weight and complexity of the welding setup. Therefore, SAW is better suited for stationary applications or situations where portability is not a primary concern.
Need for Operator Skill
Although submerged arc welding is an automatic process, it still requires skilled operators to set up and control the welding parameters. Operators need to have a good understanding of the equipment, welding procedures, and safety precautions to ensure successful welds. Proper joint preparation, correct flux selection, and precise adjustment of parameters such as current, voltage, and travel speed are crucial for achieving optimal weld quality. Therefore, companies using submerged arc welding must invest in training their operators to ensure the best results.
Lack of Versatility for Thin Materials
While submerged arc welding excels in welding thick materials, it is less versatile when it comes to thin materials. The high heat input and deep penetration characteristic of SAW can lead to distortion, warping, or burn-through in thin metal sheets. Moreover, the large flux layer required for reliable shielding may interfere with the visibility of the weld puddle. In such cases, other welding processes, such as gas metal arc welding or tungsten inert gas welding, may be more suitable for joining thin materials.
Special Equipment Requirement
Submerged arc welding requires specific equipment and consumables that may not be readily available or compatible with other welding processes. The need for a welding power source capable of delivering high currents, a dedicated welding head to direct the arc and wire electrode, and a suitable flux formulation adds to the initial setup cost. Moreover, the continuous replenishment of flux and wire electrode also incurs ongoing consumable expenses. Therefore, companies considering submerged arc welding must weigh the initial investment and maintenance costs against the benefits it offers.
Submerged Arc Welding Process
Preparation of Welding Joint
Before the actual welding process, proper preparation of the welding joint is critical for achieving a sound and strong weld. This includes cleaning the joint surfaces to remove any dirt, oil, rust, or other contaminants that can hinder the welding process. Joint preparation also involves chamfering or beveling the edges of the base metal to facilitate better penetration and a larger welding area.
Preparation of Submerged Arc Welding System
The next step in the submerged arc welding process is preparing the welding system. This includes setting up the welding power source and connecting it to the welding head. The appropriate wire electrode and flux must be selected based on the material being welded and the desired weld characteristics. The flux is typically granular and needs to be loaded into a hopper or flux recovery system. The wire electrode is fed from a spool or drum into the electrode feed mechanism, which controls its speed and position.
Setting the correct welding parameters is crucial for achieving optimal weld quality in submerged arc welding. These parameters include the welding current, arc voltage, travel speed, wire feed speed, and electrode stick-out. The welding current determines the amount of heat input, while the arc voltage affects the stability and quality of the arc. The travel speed determines the weld’s width and penetration, and the wire feed speed controls the deposition rate. The electrode stick-out ensures the correct positioning of the wire electrode in relation to the joint.
Once the welding system and parameters are set, the actual welding process can begin. The welding head is positioned and guided along the joint, maintaining the desired arc length and travel speed. The electrical current passes through the wire electrode, creating an electric arc that melts both the wire and the base metal. The flux, dispensed from the hopper, melts and forms a protective slag layer that shields the weld from the surrounding atmosphere. This slag layer also helps to remove impurities and solidify the molten pool. As the weld cools down, the molten metal solidifies, forming a strong and durable joint.
Equipment and Consumables for Submerged Arc Welding
Welding Power Source
The welding power source is an essential component of the submerged arc welding system. It supplies the electrical current (typically DC or AC) required to create and maintain the welding arc. The power source must be able to provide high currents, as submerged arc welding typically demands currents in the range of 200 to 2000 amperes. The power source should also have features like adjustable voltage and current controls to allow operators to set the desired welding parameters.
The welding head, or the torch, is responsible for directing and controlling the movement of the welding arc and electrode. It ensures the correct position of the wire electrode in relation to the joint, maintains the desired arc length, and controls the wire feed speed. The welding head may have additional features such as wire straighteners, motorized torch positioning systems, and oscillators for weld bead shaping.
Flux is a crucial component in submerged arc welding as it serves multiple purposes. The flux granules are selected based on the welding application and the desired weld characteristics. The flux provides the necessary shielding to protect the arc from the surrounding atmosphere, preventing oxidation and contamination. It also acts as a medium for deoxidation and removal of impurities from the weld pool. Additionally, the flux forms a slag layer over the weld, which protects it from atmospheric corrosion during the cooling process.
The wire electrode is the filler material used in submerged arc welding. It can be solid or tubular, depending on the application requirements. The wire electrode should have good weldability, high deposition rates, and mechanical properties compatible with the base metal. Copper-coated wire electrodes are commonly used, as the copper coating helps improve electrical conductivity and minimizes interactions with the molten pool.
Electrode Feed Mechanism
The electrode feed mechanism controls the speed and positioning of the wire electrode. It ensures a continuous supply of the wire and allows for precise wire feed speed adjustments. The mechanism can be either manual or motorized, depending on the welding setup and the desired level of automation. Proper adjustment of the electrode feed mechanism is essential for maintaining a stable arc and achieving consistent weld quality.
Working Principles of Submerged Arc Welding
Electrical Circuit in Submerged Arc Welding
In submerged arc welding, a closed electrical circuit is formed. The welding power source generates an electrical current that passes through the wire electrode, creating an arc between the electrode and the base material. The arc serves as a heat source, melting both the wire electrode and the base metal. The molten metal then solidifies, forming a solid weld joint.
Formation of Molten Pool and Protective Slag
As the wire electrode melts, it generates an arc that heats the surrounding base metal. The arc’s heat, combined with the electrical resistance between the wire and the base metal, creates a molten pool. The molten pool is protected from atmospheric contamination by the flux, which forms a granular blanket around the arc. This protective slag layer shields the weld from oxidation, prevents impurities from entering the weld pool, and assists in the solidification process.
Solidification and Final Weld Formation
As the welding arc is moved along the joint, the molten metal in the weld pool cools down and solidifies. The molten metal from the wire electrode fuses with the molten base metal, forming a metallurgical bond. The solidification process typically starts from the bottom of the weld pool and progresses upwards. As the weld cools, the slag layer solidifies on top of the weld, creating a protective coating. The final result is a sound and durable weld joint with the desired mechanical properties.
Factors Affecting Submerged Arc Welding
The electrical parameters, such as welding current and arc voltage, play a crucial role in determining the weld quality and characteristics. Higher currents result in increased heat input, deeper penetration, and higher deposition rates. The arc voltage affects the stability of the arc and the size of the molten pool. Proper adjustment of these parameters is essential to achieve the desired weld appearance, penetration depth, and mechanical properties.
The welding speed determines the width and length of the weld bead and influences the overall heat input into the joint. High welding speeds can lead to insufficient heat input, resulting in poor fusion and inadequate penetration. On the other hand, slow welding speeds may cause excessive heat input, leading to distortion, burn-through, and increased welding time. Optimizing the welding speed is crucial for achieving sound and efficient welds.
Arc voltage, or arc length, affects the stability and quality of the welding arc. An optimal arc voltage ensures a stable and consistent arc, preventing arc wandering and erratic weld bead formation. Too high an arc voltage may cause excessive spatter and an unstable arc, while too low an arc voltage can cause the arc to extinguish. Proper control of the arc voltage is necessary to achieve a smooth and controlled welding process.
The choice of flux is vital in submerged arc welding as it influences the characteristics and properties of the weld. Different flux formulations offer varying levels of deoxidation, slagging, and arc stability. The flux should be selected based on factors such as the base metal composition, joint design, welding position, and desired weld quality. Using the correct flux ensures proper protection of the arc, effective removal of impurities, and desirable metallurgical properties in the final weld.
Proper joint design is essential in submerged arc welding to ensure a strong and reliable weld. Factors such as joint geometry, gap width, and bevel angle impact the weld strength, penetration, and appearance. The joint design should provide good access for the welding head and allow for efficient heat transfer. Adequate reinforcement and appropriate chamfering or beveling help promote proper fusion between the base metal and the filler material.
The thickness of the base material influences the welding parameters and techniques used in submerged arc welding. Thicker materials require higher currents, longer arc times, and slower travel speeds to achieve proper penetration and fusion. For thin materials, lower currents and faster travel speeds are preferred to prevent burn-through or excessive heat input. Understanding the relationship between material thickness and welding parameters is crucial for producing sound welds.
Applications of Submerged Arc Welding
Submerged arc welding is extensively used in shipbuilding due to its efficiency and ability to weld thick steel plates. Ship hulls, decks, and other structural components are commonly joined using SAW. The deep penetration capability of SAW ensures strong and reliable welds, essential for the structural integrity and safety of marine vessels. The high productivity of SAW is also advantageous for meeting tight production schedules in shipyards.
Pressure Vessel Fabrication
Pressure vessels, such as tanks, boilers, and pipelines, often require welding processes that can handle high temperatures and pressures. Submerged arc welding is well-suited for pressure vessel fabrication due to its ability to produce strong and defect-free welds in thick materials. The automatic nature of SAW allows for efficient welding of circumferential and longitudinal welds, ensuring the structural integrity and leak-free operation of the pressure vessels.
Bridges, especially those made of steel, require robust and durable welds to withstand heavy loads and harsh environmental conditions. Submerged arc welding is commonly used in bridge construction due to its ability to produce high-quality welds in thick materials. The high productivity of SAW is advantageous for constructing long-span bridges, where efficient welding processes are necessary to meet project deadlines.
Heavy Machinery Manufacturing
Submerged arc welding finds extensive use in the manufacturing of heavy machinery, such as construction equipment, mining machinery, and agricultural machinery. SAW’s deep penetration capability and high productivity make it an ideal choice for welding thick materials commonly found in heavy machinery. The automatic nature of SAW also allows for the efficient production of large quantities of welds, contributing to the timely delivery of machinery to customers.
Safety Considerations in Submerged Arc Welding
Welding Fumes and Ventilation
One of the primary safety concerns in submerged arc welding is the generation of welding fumes. The flux used in SAW can emit highly hazardous fumes and particles when exposed to high temperatures. Proper ventilation systems, including local exhaust ventilation, should be installed in the welding area to remove and control the fumes. Personal protective equipment, such as respirators, should also be used to protect welders from inhaling the harmful fumes.
Protective Clothing and Equipment
Welders involved in submerged arc welding must wear appropriate protective clothing and equipment to ensure their safety. This includes fire-resistant clothing, gloves, welding helmets with suitable lenses, and protective footwear. The clothing should cover the whole body to protect against sparks, molten metal splatter, and ultraviolet radiation emitted during the welding process. Welders should also use welding curtains or screens to shield nearby workers from the welding arc.
Electrical Safety Measures
As with any welding process, electrical safety is crucial in submerged arc welding. Welders must follow proper grounding and electrical connection procedures to prevent electric shocks. The welding power source should be inspected regularly for any faults or defects. Operators should also ensure that welding cables and connections are in good condition and correctly rated for the welding current. Adhering to electrical safety measures minimizes the risk of electrical accidents and ensures a safe working environment.
Common Defects in Submerged Arc Welding
Incomplete fusion is a defect where the weld metal does not fully fuse with the base metal or previously deposited weld metal. This defect weakens the weld joint and reduces its load-carrying capacity. It may occur due to inadequate heat input, improper joint preparation, or improper welding technique. Proper adjustment of welding parameters, good joint fit-up, and effective flux selection can help prevent incomplete fusion.
Porosity is the presence of gas pockets or voids within the weld metal. It can result from the entrapment of atmospheric gases, moisture, or contaminants during the welding process. Porosity weakens the weld and reduces its resistance to corrosion and fatigue. Proper flux selection, adequate shielding gas, and clean base material are essential in minimizing the risk of porosity.
Cracking refers to the formation of cracks in the weld metal or heat-affected zone. Cracks can occur due to excessive stress, insufficient fill of the joint, or improper cooling rates. The presence of hydrogen or brittle phases in the weld metal can also contribute to cracking. Proper joint design, preheating of the base material, and post-weld heat treatment can help reduce the occurrence of cracking.
Undercut is a groove or depression along the edges of the weld bead. It occurs when the base metal melts and flows away from the weld, leaving a groove. Undercut weakens the joint and decreases its fatigue strength. It can be caused by excessive heat input, excessive travel speed, or improper torch manipulation. Maintaining suitable travel speed, controlling heat input, and proper torch manipulation can help prevent undercut.
Underfill refers to an insufficient weld fill, where the weld metal does not completely fill the joint. It can occur due to inadequate welding current, insufficient travel speed, or improper torch manipulation. Underfill weakens the joint and reduces its load-carrying capacity. Proper adjustment of welding parameters, maintaining suitable travel speed, and proper torch manipulation can help ensure adequate weld fill.
Spatter refers to the ejection of small droplets of molten metal that can adhere to surrounding surfaces during the welding process. It can be caused by excessive heat input, improper wire stick-out, or improper shielding gas flow. Spatter affects the weld appearance and cleanliness and can lead to unnecessary cleaning and rework. Proper adjustment of welding parameters, maintaining suitable wire stick-out, and optimizing shielding gas flow can help minimize spatter.
In conclusion, Submerged Arc Welding is a versatile welding process that offers numerous advantages for joining thick materials. Its high productivity, deep penetration capability, and automatic operation make it a popular choice in various industries. While there are limitations and considerations, such as limited portability and the need for operator skill, submerged arc welding remains a reliable method for achieving strong and durable welds. Proper equipment selection, adherence to safety guidelines, and awareness of potential defects are crucial for successfully implementing submerged arc welding in various applications.