Page 96 - CITS - Welder - Trade Theory

WELDER - CITS

Removal of flux residues: After welding or brazing is over, it is essential to remove the flux residues. Fluxes in
general are chemically active. Therefore, flux residues, if not properly removed, may lead to corrosion of parent
metal and weld deposit.
Some hints for removal of flux residues are given below:
- Aluminium and aluminium alloys - As soon as possible after welding, wash the joints in warm water and brush
vigorously. When conditions allow, follow up by a rapid dip in a 5 percent solution of nitric acid; wash again,
using hot water to assist drying.
When containers, such as fuel tanks, have been welded and parts are inaccessible for the hot water scrubbing
method, use a solution of nitric and hydrofluoric acids. To each 5.0 liters of water add 400 ml of nitric acid(specific
gravity 1.42) followed by 33 ml of hydro fluoric acid (40 percent strength). The solution used at room

Fig 2

Gas welding Defects, Causes and remedies

Objectives : At the end of this lesson you shall be able to
• explain flux and its function in gas welding
• describe the types of welding fluxes and their storage.

Introduction A fault is an imperfection in the weld which may result in failure of the welded joint while in service.
The following defect occur commonly in gas welding.

1 Undercut - A groove formed along the toe of the weld on one side or both sides
Causes - Incorrect angle of tilt used in blow pipe manipulation.
Incorrect distance from plate surface. Use of too large a nozzle, Use of flame density high of oxidizing flame.
Remedies of undercut - maintain blowpipe at the correct angle, Use correct nozzle, speed of travel blow pipe
manipulation to semi circular.
2 Excessive convexity- Too much weld metal added to the joint so that there is excessive weld reinforcement.
Causes - weld speed very slow, Filler rod use more thickness, Excess heat build - up , use to large a nozzle.

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