Page 127 - CITS - Welder - Trade Theory

WELDER - CITS

Method of cleaning
There are two methods used for cleaning cast iron jobs.
a) Mechanical cleaning

b) Chemical cleaning
Mechanical cleaning is mostly used to clean the surface of the cast iron jobs.
In this method grinding, filing and wire brushing tec. are done.
The chemical cleaning process is applied to remove oil, grease and any other substances which cannot be
removed by mechanical cleaning.
Welding methods of cast iron
Flame (strict neutral flame): Nozzle no. 10 is used in the blow pipe and a strict neutral flame should be adjusted.
Care should be taken that there is not even the slightest trace of oxygen which would cause a weak weld through
oxidation.

Filler rod: A 5mm size round or square high (super) silicon cast iron filler rods containing 2.8 - 3.5 percentage
silicon are used for cast iron welding. The weld metal by this rod is easily machinable. (The S-CI 1 as per IS
1278 - 1972).

Flux: The flux should be of good quality to dissolve the oxides and prevent oxidation.
Cast iron flux is composed of borax, sodium carbonate, potassium carbonate, sodium nitrate and sodium
bicarbonate. This is in a powder form.

Technique of cast iron welding: The welding operations should be performed on the preheated, dull red hot,
cast iron piece. The preheating temperature for C.I welding varies from 200°C to 310°C.
The blowpipe angle should be 60° to 70° and the filler rod angle 40° to 50° to the line of weld. (Fig 2)

Fig 1 Fig 2

Table 1

Thickness mm Edge preparation mm Root gap Dia. of filler rod mm
0.8 Square - 1.6
1.6 Square 2.4 1.6
2.4 Square 3.2 1.6
3.2 80° Vee 3.2 2.4
4.0 80° Vee 3.2 3.2
5.0 80° Vee 3.2 4.0

Using the leftward or forehead technique, the first layer should be complete by giving a slight weaving motion to
the blowpipe but not to the filler rod. The hot rod end should be dipped into the powdered flux at intervals.
After the completion of the first layer, play the flame on the job so as to heat evenly and then deposit the second
layer with a slight reinforcement of weld metal from the surface of the job. (Fig 3)

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CITS : CG & M - Welder - Lesson 44 & 45