Terms of Use - Contact Us - Make a Donation

Oxygas Welding Techniques

Oxygas welding maybe done using either the forehand or the backhand method. Each of these techniques has special advantages and you should become skillful with both. The deciding factor that determines whether a technique is considered forehand or backhand is the relative position of the torch and rod during welding, not the direction of welding. The best method to use depends upon the type of joint, joint position, and the need for heat control on the parts to be welded.

FOREHAND WELDING

Forehand welding (fig. 5-8) is often called PUDDLE or RIPPLE WELDING. In this method of welding, the rod is kept ahead of the flame in the direction in which the weld is being made. You point the flame in the direction of travel and hold the tip at an angle of about 45 degrees to the working surfaces. This flame position preheats the edges you are welding just ahead of the molten puddle. Move the rod in the same direction as the tip, and by moving the torch tip and the welding rod back and forth in opposite, semicircular paths, you can distribute the heat evenly. As the flame passes the welding rod, it melts a short length of the rod and adds it to the puddle. The motion of the torch distributes the molten metal evenly to both edges of the joint and to the molten puddle.

The forehand method is used in all positions for welding sheet and light plate up to 1/8 of an inch thick. This method is ideal because it permits better control of a small puddle and results in a smoother weld. The forehand technique is not recommended for welding heavy plate due to its lack of base metal penetration.

BACKHAND WELDING

In backhand welding (fig. 5-9), the torch tip precedes the rod in the direction of welding and the flame points back at the molten puddle and completed weld. The welding tip should make an angle of about 60 degrees with the plates or joint being welded. The end of the welding rod is placed between the torch tip and the molten puddle.

Less motion is used in the backhand method than in the forehand method. If you use a straight welding rod, you should rotate it so the end rolls from side to side and melts off evenly. You might have to bend the rod when working in confined spaces. If you do, it becomes difficult to roll a bent rod, and to compensate, you have to move the rod and torch back and forth at a rather rapid rate. When making a large weld, you should move the rod so it makes complete circles in the molten puddle. The torch is moved back and forth across the weld while it is advanced slowly and uniformly in the direction of the welding.

The backhand method is best for welding material more than 1/8 of an inch thick. You can use a narrower vee at the joint than is possible in forehand welding. An included angle of 60 degrees is a sufficient angle of bevel to get a good joint. The backhand method requires less welding rod or puddling as the forehand method.

By using the backhand technique on heavier material, you can increase your welding speed, better your control of the larger puddle, and have more complete fusion at the weld root. If you use a slightly reducing flame with the backhand technique, a smaller amount of base metal is melted while welding the joint. When you are welding steel with a backhand technique and a slightly reducing flame, the absorption of carbon by a thin surface layer of metal reduces the melting point of the steel. This speeds up the welding operation, This technique is also used in surfacing with chromium-cobalt alloys.

MULTILAYER WELDING
Multilayer welding  is used in order to avoid carrying too large a puddle of molten metal when welding thick plate and pipe. Large puddles are difficult to control. Concentrate on getting a good weld at the bottom of the vee in the first passe Then, in the next layers, concentrate on getting good fusion with the sides of the vee and the previous layer. The final layer is easily controlled to get a smooth surface. This method of welding has an added advantage in that it refines the previous layer as the succeeding layer is made. In effect, it heat-treats the weld metal by allowing one layer to cool to a black heat before it is reheated This improves the ductility of the weld metal. If this added quality is desired in the last layer, an additional or succeeding layer is deposited and then machined off.

JOINT EDGE PREPARATION

Sheet metal is easily melted and does not require special edge preparation. In welding operations involving plate, joint edge preparation and proper spacing between edges are important factors. The thickness of the plates determines the amount of edge preparation required. The faces of square edges can be butted together and welded You can use this type of joint on plate up to 3/16 of an inch thick. For plate 3/16 to 1/4 of an inch thick, a slight root opening between the parts is necessary to get complete penetration. Plate more than 1/4 of an inch thick requires beveled edges and a root opening of 1/16 of an inch. For oxygas welding on plate more than 1/4 of an inch thick, bevel the edges at an angle of 30 degrees to 45 degrees, making the groove included angle from 60 degrees to 90 degrees. You can prepare the edges by flame cutting, shearing, flame grooving, machining, chipping, or grinding. In any case, the edge surfaces should be free of oxides, scale, dirt, grease, or other foreign matter.

Plate from 3/8 to 1/2 of an inch thick can be welded from one side only, but thicker sections should be welded by preparing the edges on both sides. Generally, butt joints prepared on both sides permit easier welding, produce less distortion, and ensure better weld qualities.

Heavy steel plate is rarely welded with oxygas unless other types of welding equipment are not available. The welding of heavy plate is just not cost effective because of the amount of gas consumed and time used to complete a weld. If at all possible, use a form of electric arc welding because the joint can be welded faster, cheaper, and there is less heat distortion.

Copyright © 2001-2006 SweetHaven Publishing Services
All rights reserved