Flame or Gas(Oxyacetylene) Welding

The fusion of the base metal and filler is achieved by employing a blowtorch as shown in below figure. The torch utilizes a flammable gas (acetylene generally,  hydrogen,  propane etc.) along with oxygen to produce the required amount of heat.

The flame comprises of following two zones

1. Cone  : It is at the immediate exit of blow torch. In case of acetylene gas being used, this zone releases hydrogen and carbon monoxide. Temperature at cone tip is about 3000C in case of oxyacetylene flame and the atmosphere is reducing.
2. Plume: It is the zone where combustion is completed. This zone can be oxidizing, neutral or reducing based on the oxygen to acetylene ratio with neutral ration lying somewhere in 1 to 1.2.

Flow of gases can be regulated. The range of flow possible depends upon the size of nozzle.

Classification of Industrial Welding Processes

Classification of Welding Processes

Industrial  welding  processes  are  set  out  here  according  to  the  criteria  defined

above, namely: 

• Processes utilizing the fusion without mechanical action
• Processes utilizing the fusion combined with mechanical action
• Processes utilizing heating without fusion but with a mechanical action
• Processes utilizing a mechanical action without heating

Details of each are covered below.

It is also a common practice to classify welding processes according to

• Modes of action :  flame,  electric  arc,  plasma,  Joule  effect,  spark, induction, friction, explosion, etc.
• Means of protection against atmosphere: shielding gas or slag

Processes utilizing the fusion without mechanical action

For welding processes operating without voluntary mechanical action, welding can be described by distinguishing the modes of heating used and protecting the molten metal against the chemical action of surroundings. Following are the types

• Flame or gas welding
• Plasma welding
• Arc welding
• Vertical electroslag welding
• Aluminothermic welding

Obstacles in welding and solution

Obstacles to welding

Such obstructions can be of various kinds: 
– geometrical surface irregularities,
– pollution of the surface (oxides, grease, moisture, etc.),
– chemical elements brought in by the surrounding air.

Mitigation of welding obstructions

To mitigate them, surface preparation(grinding, machining etc.) is to be done before welding.
All pollutants present on the surfaces to be welded are eliminated by

• Mechanical Actions (sanding, grinding etc.)
• Chemical Means (solvents, scouring, drying)

Harmful affects of atmosphere on weld

Welding carried in atmosphere is susceptible to contamination by oxygen, nitrogen, hydrogen (H2 formed by dissociation of water vapors). These are elaborated below.

What is Welding?

In general, welding is the process of joining, together pieces of metals or metallic parts by bringing them into intimate proximity and heating the places of contact to a state of fusion or plasticity.
Welding makes it possible to reconstitute  metallic  continuity  between  the  components  to  be  assembled. 
Theoretically,  it involves  bringing  the  surfaces  to  be linked closer so that the surface atoms are at a distance of the order of the inter-nodal distances of their own crystalline system. This is practically impossible to achieve due to obstructions and practical constraints. Hence artificial activation of mating surfaces is required.
Welding may be done with or without direct application of heat and/or application of mechanical force as per combinations listed below

• processes utilizing the fusion without mechanical action;
• processes utilizing the fusion combined with mechanical action; 
• processes utilizing heating without fusion but with a mechanical action; 
• processes utilizing a mechanical action without heating.