Page 100 - CITS - Welder - Trade Theory

WELDER - CITS

Type of flame : Neutral flame to be used. Application of flux: No flux is required
After treatment : Most of them do not respond to any heat treatment process. Therefore except cleaning no
post-heat treatment is required.
Medium carbon steel : These steel have a carbon range from 0.30 to 0.6 percent. They are strong and hard but
can not be welded as easily a slow carbon steels due to the higher carbon content. They can be heat treated. It
needs greater care to prevent formation of crack around the weld area, or gas pockets in the bead, all of which
weaken the weld.

Welding procedure : Most medium carbon steels can be welded in the same way as mild steel successfully
without too much difficulty but the metal should be preheated slightly to160°C to320°C (to dull red hot).
After completion of welding, the metal requires post-heating to the same preheating temperature, and allowed to
cool slowly.
After cooling, the weld is to be cleaned and inspected for surface defects and alignment.
Plate edge preparation: the plate edge preparation depending on the thickness of the material to be welded.
High carbon steel: High carbon steels contain 0.6%to1.2% carbon. This type of steel is not wieldable by gas
welding process because it is difficult to avoid cracking of base metal and the weld.
Welding procedure:
The type of edge preparation, nozzle size, filler rod size, pitch of tack for different thickness of sheets to be
welded.
Start welding from the right hand edge of the joint and proceed in the left ward direction.

Thickness Preparation Assembly Pitch of tacks Nozzle size Filler rod
(mm)

1mm Square edge No gap 20 1 1.2mm
1.2mm Square edge No gap 20 2 1.2mm
1.5mm Square edge No gap 25 2 1.6mm

3mm No gap 45 5 3mm

Keep the tip of the inner cone of the flame within 1 to1.5 mm of the molten puddle, and hold the blowpipe at an
angle of 80-90° to the work.

In this way the filler rod which melts at a lower temperature than steel can flow forward and fill up the groove of
the metal as it fuses. Shows the type of edge preparation used for 3mm thick metal.

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