Fundamentals of Professional Welding

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5.1 Oxygas Welding Equipment

Oxygas Welding Equipment

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An oxygas welding outfit is basically the same as an oxygas cutting outfit with the exception of the torch. The welding outfit usually consists of a cylinder of acetylene or MAPP gas, a cylinder of oxygen, two regulators, two lengths of hose with fittings, and a welding torch with tips (fig. 5-1). An oxygas welding outfit also is called a welding rig.

In addition to the basic equipment mentioned, you also use the same auxiliary equipment that was discussed in and earlier lesson. This equipment consists of tip cleaners, cylinder trucks, clamps, and holding jigs. Safety apparel, which includes goggles, hand shields, gloves, leather aprons, sleeves and leggings, is essential and should be worn as required.

Oxygas welding equipment, like cutting equipment, may be stationary or portable. A portable oxygas outfit, as shown in figure 5-2, is an advantage when it becomes necessary to move the equipment.

To perform your welding duties, you must be able to set up the welding equipment and make the adjust-ments required to perform the welding operation. Thus it is important that you understand the purpose and function of the basic pieces of equipment that makeup the welding outfit.

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WELDING TORCHES

The oxygas welding torch mixes oxygen and fuel gas in the proper proportions and controls the amount of the mixture burned at the welding tip. Torches have two needle valves: one for adjusting the oxygen flow and the other for adjusting the fuel gas flow. Other basic parts include a handle (body), two tubes (one for oxygen and another for fuel), a mixing head, and a tip. On some models the tubes are silver-brazed to the head and the rear end forgings, which are, in turn, fitted into the handle. Welding tips are made from a special copper alloy and are available indifferent sizes to handle a wide range of uses and plate thicknesses.

Two general types of welding torches are used:

Low pressure
Medium pressure

The low-pressure torch is also known as an injector torch. The fuel-gas pressure is 1 psi (pound per square inch) or less. The oxygen pressure ranges between 10 to 40 pounds, depending on the size of the torch tip. A jet of relatively high-pressure oxygen produces the suction necessary to draw the fuel gas into the mixing head. The welding tips may or may not have separate injectors in the tip. Atypical mixing head for the low-pressure (or injector) torch is shown in figure 5-3.

Medium-pressure torches are often called balanced-pressure or equal-pressure torches because the fuel gas and the oxygen pressure are kept equal. Operating pressures vary, depending on the type of tip used.

DANGER

If acetylene is used as the fuel gas, the pressure must never be allowed to exceed 15 psi because acetylene becomes very dangerous at 15 psi and self-explosive at 29.4 psi.

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A typical equal-pressure welding torch, also called a general-purpose torch, is shown in figure 5-4. The medium pressure torch is easier to adjust than the low-pressure torch and, since equal gas pressures are used, you are less likely to get a flashback.

Welding TIPS and MIXERS are designed in several ways, depending on the manufacturer. Some torch designs have a separate mixing head or mixer for each tip size. Other designs have only one mixer for several tip sizes. Tips come in various types; some are one-piece hard-copper tips and others are two-piece tips that include an extension tube to make the connection be-tween the tip and the mixing head. When used with an extension tube, removable tips are made of hard copper, brass, or bronze. Tip sizes are designated by numbers, and each manufacturer has his own arrangement for classifying them. Tip sizes differ in the diameter of the hole.

FILLER RODS

The term filler rod refers to a filler metal used in gas welding, brazing, and certain electric welding processes in which the filler metal is not a part of the electrical circuit. The only function of the filler rod is to supply filler metal to the joint. Filler rod comes in wire or rod form that is often referred to as “welding rod.”

As a rule, filler rods are uncoated except for a thin film resulting from the manufacturing process. Filler rods for welding steel are often copper-coated to protect them from corrosion during storage. Most rods are furnished in 36-inch lengths and a wide variety of di-meters, ranging from 1/32 to 3/8 inch. Rods for weld-ing cast iron vary from 12 to 24 inches in length and are frequently square, rather than round. You determine the rod diameter for a given job by the thickness of the metal you are joining. Except for rod diameter, you select the filler rod based on the specifications of the metals being joined.

Many different types of rods are manufactured for welding ferrous and nonferrous metals. In general, welding shops stock only a few basic types that are suitable for use in all welding positions. These basic types are known as general-purpose rods.

Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy