Page 104 - CITS - Welder - Trade Theory

WELDER - CITS

b Too much acetylene will cause steam to form a porous weld.

Setting:
1.6 mm root gap between the sheets with a divergence allowance at the rate of 3-4mm per 300mm run.
Use wedge for welding longs e a min copper. No tacking is done.

Preheat: Surface of the base metal is raised to a fairly high temperature 750°C (peacock neck blue colour) before
the actual welding is started.
Welding technique:
Adopt leftward technique up to 3.5 mm thickness and rightward technique for 4 mm thickness and above. Usually
the welding starts from a point 40 to 50mm away from the right end of the job and after welding till the left end
turn the job by 180° and weld the balance non welded portion. Always welding is done towards the open end of
the joint

Control Distortion:
Divergence allowance (as already stated in job setting) acts as an effective controlling distortion. Chill plates or
backing bar also prevents distortion.
After treatment:
Penning is done in order to reduce the grain size and the locked up stresses. This is done when the metal is in
hot condition
Brass - Types - Properties and welding weldability

Objectives : At the end of this lesson you shall be able to
• state the composition of brass
• state the selection of nozzle, flame and flux
• explain the necessity of oxidising flame and welding technique.

Composition of brass: Brass is an alloy of copper and zinc in various proportions, possibly with the addition of
other elements in very less percentage.
The percentage of zinc various from 1 to 50% which makes available 15 individual commercial brasses. These
brasses containing 20 to 40% zinc have a variety of uses.
Melting temperature of brass: The melting point of copper is 1083°C and that of zinc is 419°C. Brass melts at
intermediate temperatures. The greater the amount of copper the higher the melting point. The melting point of
brass is generally around 950°C.

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