Working with gas, welders gain deeper insight into the process

February 2014 - Companies today typically employ the latest technology in welding engineering and manufacturing processes to maximize efficiency and quality while minimizing cost. Of course, this has both pros and cons.

In earlier times, the pace of change in metal joining technologies was slower. From forging and forge welding emerged gas and stick welding, MIG, MAG and TIG welding, submerged arc and laser welding. The process of developing better and faster technology has itself gotten faster in the last 40 years. Yet, much can be learned from studying the role of gas welding in metal forming and fabrication.

With gas welding equipment one can do soft soldering, brazing and coating, as well as weld sheet metal and solid steel up to 3⁄4 in. (19 mm) thick. The technology also supports aluminum welding and using the cutting torch to separate steel.

For training purposes, gas welding is inexpensive and provides a slower and more intense learning experience through which welders learn necessary skills in terms of the correct fusion process.

In learning to form the puddle between the base metal and filler rod, welders develop their future “signature” welds with good continuity and even penetration.

Let’s look at some of the fundamentals underlying the process of welding with gas.

Workpiece preparation. Joint edges must be given the correct form and shape before welding. Material surfaces must be free of rust, oil, scale, grease and paint.

The welding rod. Also known as filler rod, this provides the extra material required for the fusion process and closing the weld gap. Its properties must match the material being welded. Frequently it is copper coated to protect it from corrosion.

Types of welding seams. The parts to be welded are joined into a weldment by the welding seam at the joint. Common joint types are the butt joint, corner joint and the T-joint. In butt welding the parts lie on a plane surface. The usual type of welding seams are the I-seam, typical of an open square butt weld, and the V-seam, which is used for materials that are 1⁄4 in. (6 mm) or thicker. Furthermore there is in-corner-joint welding. In this position,  the parts are placed with their edges together at any desired  angle toward each other. For the T-joint welding, the end face of one part rests at a right angle on the surface of the other. Other common welding seam types are the edge filled seam and the throat seam.

Setting the welding flame. When igniting the flame, the oxygen valve is opened first, then the fuel gas valve. At that point striking a spark completes the ignition. Both gases are mixed in the welding torch, and if the mixing ratio is correct, a bright, sharply bounded cone is produced. In creating a neutral flame, oxygen and acetylene are mixed in the ratio 1:1:1.

The white cone portion of the flame indicates incomplete combustion of the gases (forming carbon monoxide and hydrogen) because there is a shortage of oxygen. The flame beyond this area has a reducing effect. For example, it removes oxygen from the surrounding air or from the workpiece being welded. This effect prevents the formation of oxides on the workpiece during the welding process.

When extinguishing the flame the gas valve must be closed first, then the oxygen valve. The remaining oxygen pressure purges any remaining acetylene.

Variants of the gas welding process

Leftward welding, also called forehand welding. This method is used on sheet metal up to 1⁄8 in. (2.5 mm) thick, and the welding rod is advanced before the flame. The flame creates a weld puddle in front of it, resulting in a loss of heat, rapid cooling, and produces a welding seam structure that is not very homogeneous.

Rightward welding, also called backhand welding. This method is used for material thicker than 1⁄8 in. and the rod follows the flame. The weld puddle created with this method does not spread. The heat of the flame is blown back and preheats the material well.

A tack weld at the beginning and end of a butt seam joint will prevent a wide V-spread of the parts during the process of welding the length of the seam. FFJ

Udo O. J. Huff is an independent consultant with project experience in machine building, welding engineering, training and development. He holds Master of Education and Bachelor of Science in Technology degrees from Bowling Green State University. Questions or comments? E-mail uhuff@sbcglobal.net.