Following procedure given for
beginners to learn gas welding of plates.
1. Arrange a piece of sheet metal conveniently on
the welding table.Light the blow pipe (welding torch) and adjust the flame to
neutral.
2. Holding the blow pipe so that the nozzle makes
an angle of about 650 with the sheet, let the flame play on a point
just inside the right edge of the sheet and with the inner cone of flame about
3 mm away from the surface of the sheet, hold the blow pipe until a pool of
molten metal about 4 to 6 mm in diameter has been formed. Make this pool move
across the sheet in the desired direction. To do this the blow pipe should be
moved so as to make a series of overlapping ovals.
3. The next step is to deposit a fusion bead using
a filler metal rod. The material and size of filler rod will change depending
on the base metal and its thickness. (i.e. for welding plain carbon steel plate
of 16 gauge, a filler rod of low carbon steel with 3 mm diameter is used).The
welding blow pipe is held in the right hand (for right handed welder) and the
rod in the left hand. The angle of the welding rod with the line of weld should
be about 400.
4.
Place the end of the rod in the molten pool, and
make the pool travel across the sheet. The motion of the blow-pipe is such that
the flame will follow a series of overlapping ovals of molten metal.
5.
There are two types of welding methods.
a)
Leftward or forward methods and
b)
Rightward or backward method.
Fig.
Process Of Gas Welding
Leftward or forward method of welding:
It is done from right to left.
The blow pipe is held in the right hand and the welding rod in the left hand.
The head of the blow pipe is held at an angle of 600 – 700
to the plane of the weld, and the welding rod at 300 – 400.
The tip of the cone should
never touch the weld metal or the filler rod and, as the rod is melted, the
flame is fed forward to build up the molten pool of weld metal, and then held
back slightly to allow the heat to penetrate the weld.
The ‘leftward method’ is
suitable for sheet metal upto 3.0 mm and also for thicker plates, but in this
case the blow pipe moves from side to side, to fuse the sides of the ‘Vee’.
Rightward or backward method of
welding
It is carried out from left to
right, the rod following the blowpipe i.e. opposite to leftward welding.
The blow pipe should make an
angle of 400 – 500 with the plane of weld, and the
welding rod should be at angle of 300 – 400.
The cone of the flame in
rightward welding is deeper in the vee than in leftward welding, and the inner
cone is kept a short distance from the welding rod and deposited metal. The
welding rod is made to form a series of loops, in addition to its forward
movement to ensure that both sides of the weld are fused.
The advantages claimed for
‘rightward welding’ are a saving of time in welding thicker plates, economy in
gas, greater ductility of weld and lack of distortion and less likelihood of
annealing being required.
Filler rods and fluxes for gas welding:
Material used for gas welding
are bare wires or rods. They are usually slightly coated with copper, so that
they do not get rapidly rusted. Wires are supplied in the form of coils. Rods
are cut in general upto 1 meter long.
Wires and rods suitable for the
joint are used for joining the parts by welding and have same characteristic as
the base metal.
The material may be laid on the
surface of the work in order to build up a fresh surface during fabrication and
repair work. The weld metal has characteristics that are different from those
of the base metal of the work piece.
Since work pieces or parts of
different thicknesses are welded, the filler rod must also be of different
thickness. Filler rods of following sizes are available – 1, 2, 3, 4, 5, and 6
mm.
Flux is required for welding
many metals, except ordinary grades of wrought iron and mild steel. Its main
purpose is to dissolve the surface film of oxide on the metal and prevent
oxidation by the atmosphere. During welding the dissolved oxides float on the
top of the molten metal as slag and thus can be removed after cooling and
solidification of weld material.
For welding ‘ferrous metals’
following fluxes are found to be excellent – Borax, sodium, carbonate, sodium
bicarbonate and sodium silicate, with small additions of vigorous deoxidizing
substances.
For welding ‘ nonferrous metals
and alloys’, sodium and potassium borates, carbonates, chlorides, sulphates and
boric acid have been found suitable. Fluxes for aluminium consists of alkaline
fluorides, chlorides and bisulphates.
Advantages and uses of gas welding
Following are the advantages of
gas welding process –
- The equipment is comparatively inexpensive and require little maintenance.
- It is portable and can be easily used either in the factory or outside field.
- With proper technique, the process is applicable to all ferrous and non-ferrous metals and alloys.
- The equipment can be used for cutting also, usually called as ‘ gas cutting’.
- The process is especially adopted to the welding of sheet metals, to flame hardening and to the application of many hard facing materials.
- Due to above advantages the process is popularly used in several industries like sheet metal work, tubing, industrial piping, automotive, shipyards maintenance and repair works etc.
