Gas Welding

Gas welding is used to heat the metal high-temperature flame, formed by the combustion of acetylene gas in a mixture with oxygen. In some cases, instead of acetylene can be used Substitutes: propane, butane, methane, gasoline fumes, or kerosene, IAF (methylacetylene-allene fraction). Recently, increases the amount of use as a fuel gas hydrogen produced by electrolysis of water.

Gas welding process

Combustible gas from a cylinder or a special gas generator enters the welding torch. From the tank to the burner receives oxygen. In the burner, they are mixed in certain proportions, and at the exit of the nozzle set on fire. The flame melts the edge of the workpiece, filler flow, and also serves as protection of molten metal from the atmosphere. Adjusting the flow of oxygen and fuel gas by the respective valves.

The structure of the flame for gas welding
In his section of the flame consists of three zones (see figure below):

• the core of the flame (A)
• reducing zone (B),
• flame (B).

The structure of the gas flame and the temperature distribution over its cross section

The maximum flame temperature is when the kernel in the recovery area. In this regard, it is in this area should be filler rod is melted and edges of the metal. When used instead of acetylene, other fuel gas flame temperature is reduced. Flame temperature is also dependent on the proportion in which the mixed oxygen and combustible gas.

Gas Welding Technology
The main parameters are the mode of gas welding power of the flame, torch angle and diameter of the filler rod. Power of the flame depends on the thickness of the metal and its thermal properties. The greater the thickness of the metal above the melting point and thermal conductivity, the greater must be the power of the flame. Power consumption is set flame fuel gas and oxygen. When welding steel and iron consumption of acetylene V a thickness δ is associated with the following equation:

V a = (100-150) δ l / h

When welding copper, due to its higher thermal conductivity:

V a = (150-200) δ l / h

The angle of the mouthpiece burner with respect to the plane of the products also depends on the thickness and thermophysical properties of the metal. With the change in thickness of the steel from 1 to 15 mm angle of the mouthpiece varies from 10-80 °.

TABLE. Changing the angle of the mouthpiece for gas welding, depending on the thickness of steel

δ, мм	to 1	1-3	3-5	5-7	7-10	10-12	12-15	> 15
α, °	10	20	30	40	50	60	70	80

At the initial weld metal for better heating and rapid formation of the weld pool angle of the largest set (80-90 °). It then decreases.

The diameter of filler rod is selected depending on the thickness of the metal, using the relation:

d = δ / 2 ÷ δ / 2 + 1 mm

Depending on the technique of welding distinguish left and right ways.

Right (A) and left (B) methods of gas welding

In the right way to gas welding torch flame is directed at the seam and the welding process is carried out from left to right. The burner is moved ahead of filler rod.

If left the way gas welding flame is directed away from the seam and the welding process is carried out from right to left. The burner is moved for the filler rod.

In the right way to gas welding is ensured the best protection the weld pool, the following gas flow rate, lower rate of cooling of the joint. At left is a better way the formation of a seam, since the welder can clearly see the welding process. When the thickness of the metal up to 3 mm more productive way to the left, at large thicknesses - right.

Advantages of Gas Welding
The main advantage of gas welding is its independence from the electric power sources. This makes it convenient to its use in the construction and installation conditions where there is always a power electric network. When gas welding heat input is easily changed into the metal by changing the angle of the burner and its distance to the product, thus avoiding even the burn-through when welding thin metal. A typical example is the welding of small diameter water pipes when there is no access to the back of the seam to place pads or jelly root. Gas welding equipment sufficiently mobile and transportable.

Disadvantages of Gas Welding
Disadvantages of Gas Welding is its low productivity, a large zone of thermal influence, the high skill requirements welder. In this regard, the machine-building enterprises with a stable program output gas welding can not compete with the arc and almost never used.

See also:
gas cutting
acetylene
gas welding of aluminum and other welding methods

Welding technology:

manual arc welding semi-automatic welding argon arc welding machine welding electroslag welding plasma welding laser welding electron beam welding

gas welding resistance welding spot welding seam welding projection welding butt welding welding underwater welding in space