Welding knowledge of electrode arc welding

Welding, particularly Electrode Arc Welding, is a skill that demands both technical knowledge and practical understanding to ensure high-quality and durable welds. The welding rod, which serves as a core component in this process, is classified into various types based on the materials they are designed to weld. These include carbon steel welding rods, low alloy steel welding rods, stainless steel welding rods, cladding welding rods, cast iron welding rods, nickel and nickel alloy welding rods, copper and copper alloy welding rods, aluminum and aluminum alloy welding rods, low temperature welding rods, structural steel welding rods, molybdenum chromium molybdenum heat-resistant steel welding rods, and special purpose welding rods. Each type is tailored to provide optimal performance with specific materials, showcasing the versatility and indispensability of welding rods in creating strong, lasting joints. However, electrode arc welding is not suitable for certain applications, such as welding active metals like titanium, niobium, and zirconium, or welding very thin weldments less than 1mm thick, as well as for mass production scenarios.

The power supply for electrode arc welding typically adopts a steep drop external characteristic. The most effective supply is one characterized by constant current plus "external resistance" to ensure the arc remains stable. Using a constant voltage external characteristic power supply is generally not recommended because fluctuations in welding current and unstable arc lengths can lead to quality issues. Welding in various positions – overhead, horizontal, vertical, and fillet – presents unique challenges and requires specific techniques and adjustments to ensure optimal results. Overhead welding, for instance, is considered the most difficult. Success in this position demands the use of the shortest arc length, smaller diameter welding rods, faster welding speeds, and appropriate welding current. Multi-layer welding in overhead positions can benefit from techniques such as crescent or zigzag strip welding, with a controlled swing amplitude to prevent defects. Conversely, long arc, high current, and slow welding procedures are to be avoided given their potential to compromise weld integrity.

Horizontal welding also requires precise technique, especially the use of smaller diameter welding rods, appropriate rod angles, and welding methods. Here, the arc thrust must sufficiently support the molten metal droplets to prevent defects such as upper side bite edge and lower side weld bead, as well as incomplete penetration. Vertical welding follows similar stringent requirements. Typically, electrode arc welding in vertical combinations is conducted from the bottom up, but special electrodes are available for downward welding. Uniform speed and controlled angle adjustments are essential to ensure consistent weld quality. Short arc techniques with smaller currents are also preferred for vertical welds, ensuring even penetration and minimizing risks of defects.

Welding fillet joints involves specific electrode angles, generally within a 65-80° range in the welding direction. The arc should be directed towards the thicker plate to equalize heating temperatures across both plates. Multi-layered welding in fillet joints necessitates consistent angle adjustments based on the weld’s position and thickness, ensuring well-formed welds. If the workpiece is manageable, transitioning it to a boat-shaped welding position can enhance weld quality. For varying plate thicknesses, proper electrode position is crucial to avoid significant temperature differences, which can lead to weld defects like single-sided welds, undercuts, and impermeable fillet welds.

When initiating the arc, a slight extension of the arc or preheating the starting weld point is advised. Once the molten pool forms, shortening the arc to 2-4 mm facilitates normal welding. Particularly for critical structures, starting (and returning) plates should be utilized to ensure uniform penetration and width of the welds. Immediate transitioning from arc ignition to normal welding can result in defects such as pores, incomplete penetration, and slag inclusions. Therefore, adherence to these procedural nuances is vital for ensuring the reliability and strength of the welds.

In summary, understanding the common sense and technical nuances of electrode arc welding is crucial for achieving high-quality results. Each variation in welding rod types caters to specific materials, and the power supply characteristics, welding techniques, and positional adjustments all play significant roles in determining weld quality. Proper preheating, angle adjustments, and controlled welding parameters not only prevent defects but also ensure the durability and integrity of the welds, underscoring the need for a detailed and informed approach to this intricate process.