THERMIT WELDING
Welding the parts by using liquid Thermit
steel around the portion to be welded is called Thermit welding. this is
a type of fusion welding process. In this process, neither arc is
produced to heat parts nor flames are used. high temperature is being
obtained by the usage of the exothermic reaction. Welding principle is
the heat of the Thermit reaction used for welding in plastic state and
mechanical pressure is applied for the joint.
It
depends on the chemical reaction between iron oxide and aluminium. The
reaction in thermit welding is that the reaction takes place about 30sec
only and the heat liberation temperature is about 2800°C. It is twice
the melting temperature of steel.
Working
Thermit
is a mixture of aluminium and iron Oxide in the ratio of 1:3. This is
placed in a furnace and it is ignited. On heating the chemical reaction
takes place. Due to this, liquid and slag are formed which are used for
welding.
The Thermit welding process is classified into two types.
1. Pressure welding process
During the pressure welding process, the following steps are adopted.
· The parts to be welded are butted and enclosed in a mould. The mould can be easily removed after the welding of metals.
· The heated iron stag is poured to the mould.
· Then the aluminium oxide is poured on the parts to be welded.
· This will create the heating of parts and then the pressure is applied on the workpiece to join.
2. Non-pressure welding
In this process, the following steps are adopted.
· The parts to be welded are lined up in parallel and a groove is taken in the parts.
· The wax pattern is formed in and around the welding parts.
· Then sand is rammed around he wax pattern and mould is completed with gate, runner and riser around the joint area.
· Then the mould is heated and wax is melted, it will give a space between the joint.
·
Finally, the heated iron slag and aluminium are poured into the mould
after solidification of liquid metal. Thus, the joint is made.
LASER BEAM WELDING
The word laser sands for light Amplification by the stimulated emission of radiation.
Principle
Light
energy is converted into heat energy. Here, the light energy is
produced from the laser source like ruby rod in the form of
monochromatic light.
Working
Electrical
discharge from the capacitors makes the flash tube converts the
electrical energy into light flashes. Then ruby rod is exposed to the
intense light flash. This helps the chromium atoms of the crystal
excited and pumped to a high energy level beam. This high energy level
is immediately reduced to intermediate and drop to original state with
the evolution of red fluorescent light.
This
laser light is intense and can be readily focused without loss of
intensity. The laser light is focused by the focusing lens to the work
piece in the form of coherent monochromatic light.
The
light energy is impacted to the work piece. This light energy gets
converted into heat energy. This heat energy is sufficient to melt the
materials to be welded. The various laser forms that are generally used
are Liquid laser, Gas laser, Ruby laser, Semi-conductor laser.
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