Advanced Welding Technology

Topic: Atomic Hydrogen Arc Welding

Ilyas HussainP2MFG15006

definition

Atomic hydrogen welding (AHW) is an arc welding process that makes use of an arc between two tungsten metal electrodes within an atmosphere composed of hydrogen. Shielding is obtained from the hydrogen.

The electric arc produced in the process efficiently breaks up the molecules of hydrogen that later recombine through an extreme release of heat.

Equipments and Parameters required in AHW

2 tungsten electrode.Hydrogen gas cylinder with regulator and hose.Electrode holder or torch.300 V AC power supply machine with controller.Filler rod if needed.

Operation Of AHW

The equipment consists of a welding torch with two tungsten electrodes inclined and adjusted to maintain a stable arc.

Annular nozzles around the tungsten electrodes carry the hydrogen gas supplied from the gas cylinders.

AC power source is suitable compared to DC, because equal amount of heat will be available at both the electrodes.

A transformer with an open circuit voltage of 300 volts is required to strike and maintain the arc.

The work pieces are cleaned to remove dirt, oxides and other impurities to obtain a sound weld. Hydrogen gas supply and welding current are switched ON.

An arc is stuck by bringing the two tungsten electrodes in contact with each other and instantaneously separated by a small distance, say 1.5 mm, such that the arc still remains between the two electrodes.

As the jet of hydrogen gas passes through the electric arc, it disassociates into atomic hydrogen by absorbing large amounts of heat supplied by the electric arc.

H2 = H + H – 422KJ (endothermic reaction) Recombination takes place as the atomic hydrogen

touches the cold work piece liberating a large amount of heat.

H + H = H2 + 422 KJ (Exothermic reaction)

What to avoid in AHW Too little heat or too much heat according to material to

be weld. Too little heat is indicated if too much time required for fusion.

Arc gap should not be too small or large otherwise very less heat will be released.

Less heat causes small pool, difficult to maintain, surface porosity and it solidify fast and uneven.

Too much heat should be avoided otherwise wide pool and hole will form in weld material.

If heat and arc is correct then also proper fusion doesn’t occur then reduce the welding speed or the current setting should be increased.

To weld delicate metals, arc distance should be less so to weld with less heat.

Distance between weld metal and arc should be avoided. Arc should touch the weld metal.

Successful welding in AHW depends on

Size of the arc. Contact of the arc with the work. Speed of travel. Current setting.

Advantages of AHW Intense flame is obtained which can be concentrated at

the joint. Hence, less distortion. Work piece do not form a part of the electric circuit.

Hence, problems like striking the arc and maintaining the arc column are eliminated.

Separate flux / shielding gas is not required. The hydrogen envelop itself prevents oxidation of the metal and the tungsten electrode.

Welding is faster.

The average temperature of the flame is approximately 4000 deg. C., This is the third hottest flame after dicyanoacetylene at 4987 °C and cyanogen at 4525 °C.

Hydrogen gas flows by the tungsten electrodes in the holder, keeping them cooler and lengthening the electrode life.

An automatic atomic - hydrogen welding process has also been developed in which, instead of using hydrogen from high-pressure cylinders, the hydrogen is obtained by cracking anhydrous ammonia.“

The heat produced by this torch is sufficient to weld tungsten (3422 °C), the most refractory metal.

Filler material is not used. In fillet weld only, filler is used. Or in other material if to have any change in composition of weld.

Hydrogen supply and arc can be easily controlled by welder so because of that heat is controlled to weld different metals.

Because of the powerful reducing action of the atomic hydrogen, alloys can be melted without fluxes and without surface oxidation.

limitations Cost of welding by this process is slightly higher than

with the other process. Welding is limited to flat positions only. Because of the high levels of heat produced in this

welding process, welders need to be even more aware of the dangers they are exposed to.

Skilled welder is required. Due to advances in inert gases AHW may be limited. Hydrogen is highly inflammable gas so it should be

taken care.

Applications of AHWAtomic hydrogen welding is used in those

applications where rapid welding is necessary, as for stainless steels and other special alloys.

For most of the ferrous and non ferrous metals.

For thick as well as thin sheets or small diameter wires (2-10mm).

Can be applied almost to any metal, specially in light gauge metal, special ferrous alloys, and most non ferrous metals and alloys.

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