Page 102 - CITS - Welder - Trade Theory

WELDER - CITS

For welding heavy aluminum plates, 4 mm or more in thickness, the edges should be beveled to form 90°
Included angle with
a root gap of 1.6mm to 3mm.
Preparation, pitch of tack, nozzle, size, filler rod etc. are given in Table1 for butt joints.
Importance of flux:

Since aluminum oxidizes very rapidly, a layer of flux must be used to ensure a sound weld. Aluminum flux powder
I strobe mixed with water (two parts of flux to one part of water).
The flux is applied to the joint by mean so f a brush. When a filler rod is used, the rod is also coated with flux.
On heavy sections, it is advisable to coat the metal as well as the rod for greater ease in securing better fusion.
Necessity of preheat:
Aluminum and its alloys possessing thermal conductivity and high specific and latent heat. For this reason, a
large amount of heat is required for fusion welding.
To ensure fusion and complete penetration to avoid cracking, and to reduce gas consumption, aluminum casting
sand assemblies in wrought alloys of above 0.8mmaretobepreheated.
Preheating temperature varies from 250°C to 400°Caccording to the size of the work, and can be done by using
a torch or by keeping the job in the furnace where preheating is done.

Welding procedure: Various processes of welding of aluminium-Oxy-acetylene welding
Thickness Preparation Assembly Pitch of tacks Nozzle size Filler rod
(mm)
1 Square No gap 25 1 2.5 mm

1.2 Square No gap 40 2 2.5 mm
1.5 Square No gap 40 2 2.5 mm
3 1.5-3 mm gap 75 5 3. 15 mm

a) Manual metal arc welding, b) TIG welding, c) MIG welding, d) Resistance welding, e) Carbon arc welding,
f) Solid state welding, g) Cold welding, h) Diffusion welding, i) Explosive welding, j) Ultrasonic welding.
Advantages of adopting oxy-acetylene process for welding of aluminum
i Simple and low cost equipment
ii For welding thinner sheets, gas welding may prove to be economical.
Disadvantages

i The flux residue, if not properly removed, may result in corrosion.
ii Distortion is greater than in arc welding.
iii Heat-affected zone is wider than in arc welding. Welding speed is lower

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CITS : C G & M - Welder - Lesson 14-26 CITS : C G & M - Welder - Lesson 14-26