Welding is a method used to join, reinforce or extend 2 or more structural steel members. Welded connections use a metal rod or electrode heated to 6500 degrees F to fuse the component pieces at the weld. First create the arc and then apply the weld along the seam. A brief description of the electric arc welding procedure is given below for the beginner. Make sure you are properly prepared to take on welding projects because the job can be dangerous.
Step - 1 Generate the Arc
The arc is generated when one terminal of a motor-generator is attached to the structural member, and the other terminal is connected to the electrode with a cable. The electrode contains a coating that creates a gaseous shield that protects the weld from impurities in the atmosphere as it vaporizes. The electrode material is chosen to have properties similar to that of the base metal, particularly its minimum tensile strength. The various types of weld include the slot weld, the plug weld and the groove weld.
You will need to wear a welder’s helmet with a filter lens for eye protection and heat resistant clothing and gloves. To strike the arc, bring the electrode in contact with the base metal and withdraw it slightly. Hold the electrode close enough to the steel member to establish a continuous arc between the base metal and the electrode. A pool of molten metal on the surface of the steel member fuses with the melting electrode.
Step 2 - Apply the Weld along the Seam
Groove welds are typically used to join adjacent plates along a beveled edge. The most common type of weld - the fillet weld - has a roughly triangular cross-section and is generally used to join steel plates in a lap, butt, corner or tee joint. The cross-section of a fillet weld can be likened to a right triangle. The equal sides are referred to as “legs” and the hypotenuse is called the “face” of the weld. The vertex of the triangle is considered the “root” and a line from the root perpendicular to the face is called the “throat”. The throat size is important because its area within the projected triangle is multiplied by the allowable shear stress to determine the strength of the weld. The strength of fillet welds are expressed in kips (1000 lbs) per linear inch based on either leg size or throat size.
Maintain the same distance as you draw the electrode slowly forward, so that a bead of molten metal is left along the seam. As the temperature of the weld quickly drops below the melting point of the steel, the bead cools and solidifies to form a joint that is stronger than the material itself. It is sometimes necessary to make a number of passes with the electrode to create a weld of sufficient depth.
Step 3 - Remove the Slag
As the coated electrode is fed into the seam, it produces a flux that forms a protective slag coating over the weld. After the weld is completed the slag coating can be broken off the weld by gently tapping with a hammer. The weld can then be ground to a smooth finish.