Operating a Gas Welding Torch


Summary:

The oxyfuel gas welding torch mixes the combustible and combustion-supporting gases. It provides the means for applying the flame at the desired location. A range of tip sizes is provided for obtaining the required volume or size of welding flame which may vary from a short, small diameter needle flame to a flare 3/16 in. (4.8 mm) or more in diameter and 2 in. (51 mm) or more in length.

The inner cone or vivid blue flare of the burning mixture of gases issuing from the tip is called the working flare. The closer the end of the inner cone is to the surface of the metal being heated or welded, the more effective is the heat transfer from flame to metal. The flame can be made soft or harsh by varying the gas flow. Too low a gas flow for a given tip size will result in a soft, ineffective flame sensitive to backfiring. Too high a gas flow will result in a harsh, high velocity flame that is hard to handle and will blow the molten metal from the puddle.

The chemical action of the flame on a molten pool of metal can be altered by changing the ratio of the volume of oxygen to acetylene issuing from the tip. Most oxyacetylene welding is done with a neutral flame having approximately a 1:1 gas ratio. An oxidizing action can be obtained by increasing the oxygen flow, and a reducing action will result from increasing the acetylene flow. Both adjustments are valuable aids in welding.

Working Pressures for Operating a Welding Torch

The required working pressure increases as the tip orifice increases. The relation between the tip number and the diameter of the orifice may vary with different manufacturers. However, the smaller number always indicates the smaller diameter. For the approximate relation between the tip number and the required oxygen and acetylene pressures, see tables 11-1 and 11-2.

Tip Size, Oxygen PSI and Acetylene PSI for Injector Type Torch

Low Pressure or Injector Type Torch Settings

Tip Size, Oxygen PSI and Acetylene PSI for Balanced Pressure Type Torch

Balanced Pressure Torch Settings

Note: Oxygen pressures are approximately the same as acetylene pressures in the balanced pressure type torch. Pressures for specific types of mixing heads and tips are specified by the manufacturer.

Gas Welding Torch Flame Adjustment and Types

The oxyfuel gas welding torch mixes the combustible and combustion-supporting gases. It provides the means for applying the flame at the desired location. A range of tip sizes is provided for obtaining the required volume or size of welding flame which may vary from a short, small diameter needle flame to a flare 3/16 in. (4.8 mm) or more in diameter and 2 in. (51 mm) or more in length.

The inner cone or vivid blue flare of the burning mixture of gases issuing from the tip is called the working flare. The closer the end of the inner cone is to the surface of the metal being heated or welded, the more effective is the heat transfer from flame to metal. The flame can be made soft or harsh by varying the gas flow. Too low a gas flow for a given tip size will result in a soft, ineffective flame sensitive to backfiring. Too high a gas flow will result in a harsh, high velocity flame that is hard to handle and will blow the molten metal from the puddle.

The chemical action of the flame on a molten pool of metal can be altered by changing the ratio of the volume of oxygen to acetylene issuing from the tip. Most oxyacetylene welding is done with a neutral flame having approximately a 1:1 gas ratio. An oxidizing action can be obtained by increasing the oxygen flow, and a reducing action will result from increasing the acetylene flow. Both adjustments are valuable aids in welding.

Flare Adjustment

Torches should be lighted with a friction lighter or a pilot flame. The instructions of the equipment manufacturer should be observed when adjusting operating pressures at the gas regulators and torch valves before the gases issuing from the tip are ignited.

The neutral flame is obtained most easily by adjustment from an excess-acetylene flame, which is recognized by the feather extension of the inner cone. The feather will diminish as the flow of acetylene is decreased or the flow of oxygen is increased. The flame is neutral just at the point of disappearance of the "feather" extension of the inner cone. This flame is actually reducing in nature but is neither carburizing or oxidizing.

A practical method of determining the amount of excess acetylene in a reducing flame is to compare the length of the feather with the length of the inner cone, measuring both from the torch tip. A 2X excess-acetylene flame has an acetylene feather that is twice the length of the inner cone. Starting with a neutral flame adjustment, the welder can produce the desired acetylene feather by increasing the acetylene flow (or by decreasing the oxygen flow). This flame also has a carburizing effect on steel.

The oxidizing flame adjustment is sometimes given as the amount by which the length of a neutral inner cone should be reduced, for example, one tenth. Starting with the neutral flare, the welder can increase the oxygen or decrease the acetylene until the length of the inner cone is decreased the desired amount. See figure 11-1.

Welding Torch Temperature

Welding Torch Flame Temperature Graph

Lighting the Welding Torch

To start the welding torch, hold it so as to direct the flame away from the operator, gas cylinders, hose, or any flammable material. Open the acetylene torch valve 1/4-turn and ignite the gas by striking the spark lighter in front of the tip.

Since the oxygen torch valve is closed, the acetylene is burned by the oxygen in the air. There is not sufficient oxygen to provide complete combustion, so the flame is smoky and produces a soot of fine unburned carbon. Continue to open the acetylene valve slowly until the flame burns clean. The acetylene flame is long, bushy, and has a yellowish color. This pure acetylene flame is unsuitable for welding.

Slowly open the oxygen valve. The flame changes to a bluish-white and forms a bright inner cone surrounded by an outer flame. The inner cone develops the high temperature required for welding.

The temperature of the oxyacetylene flame is not uniform throughout its length and the combustion is also different in different parts of the flame. It is so high (up to 6000ºF (3316ºC)) that products of complete combustion (carbon dioxide and water) are decomposed into their elements. The temperature is the highest just beyond the end of the inner cone and decreases gradually toward the end of the flame. Acetylene burning in the inner cone with oxygen supplied by the torch forms carbon monoxide and hydrogen. As these gases cool from the high temperatures of the inner cone, they burn completely with the oxygen supplied by the surrounding air and form the lower temperature sheath f1ame. The carbon monoxide burns to form carbon dioxide and hydrogen burns to form water vapor. Since the inner cone contains only carbon monoxide and hydrogen, which are reducing in character (i.e., able to combine with and remove oxygen), oxidation of the metal will not occur within this zone. The chemical reaction for a one-to-one ratio of acetylene and oxygen plus air is as follows:

C2H2 + O2 = 2CO + H2 + Heat

This is the primary reaction: however, both carbon monoxide and hydrogen are combustible and will react with oxygen from the air:

2CO + H2 + 1.502 = 2CO2 + H2O + Heat

This is the secondary reaction which produces carbon dioxide, heat, and water.

Welding Jobs in Your Area

Powered by ZipRecruiter

For Additional Reading on Buying a Gas Welding Torch

Ask a Welder Now
4 Welders are Online Now.
A Question is Answered Every 12 Seconds!
Ask A Welder >


Page Author:

Welding Jobs in Your Area