SHIELDED METAL ARC WELDING & GAS TUNGSTEN ARC WELDING

Shielded Metal Arc Welding and Gas Tungsten Arc Welding

Shielded Metal Arc Welding & Gas Tungsten Arc Welding

Shielded Metal Arc Welding

Introduction

Shielded Metal Arc Welding (SMAW) is defined as "an arc welding process in which coalescence of metals is produced by heat from an electric arc that is maintained between the tip of a flux covered electrode and the surface of the base metal in the joint being welded." This process is commonly referred to as stick welding.

The electrode consists of a solid metal core, which is covered by a metallic coating. The coatings composition is dependent on the type of electrode and welding polarity. It serves various functions during the welding process. These include; provide a shielding agent from the atmosphere which protects the molten pool; act as fluxing agents to cleanse the weld metal deposit, establish electrical characteristics of the electrode, provide a slag covering during cooling which can improve weld properties, enhance the ability to weld out of position, improve bead profile and appearance, and can add alloying elements to the weld to affect mechanical properties.

SMAW is the most widely used welding process in the US and the world. The equipment cost is low and can be portable, it can be done in areas of limited access, it can be done in all positions and it is a viable process for joining most metals and alloys. The low hydrogen (LH) mild steel electrodes are the most commonly used and represent up to 90% of the total market. All stick electrode readily absorb moisture which will detrimentally effect weld quality. The LH being the most affected and should be stored in an electrode oven before use.

SMAW is typically done with DC current, either electrode positive or negative, but can also be used with AC current. Electrode positive produces higher penetration patterns and typically operates better, but electrode negative results in the highest melting rate. Electrodes with high magnetic properties can experience arc blow with DC current and may be welded with AC setting. These include iron and nickel alloy rods. Also the AC power sources are less expensive. The process limitations include relatively low deposition rates and duty cycles, low efficiency, high spatter and fume generation and slag removal is often required upon weld completion.

Uses and operation

Shielded Metal Arc welding employs the heat of the arc to melt the base metal and the tip of a consumable covered electrode. The electrode and the work are part of an electric circuit. This circuit begins with the electric power source and includes the welding cables, an electrode holder, a workpiece connection, the workpiece (weldment), and an arc welding electrode. One of the two cables from the power source is attached to the work. The other is attached to the electrode holder.

Direct Current

Direct current is the most common current choice for stick welding. The current flows in one direction only and has many advantages over alternating current for the stick ...