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.
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.
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.
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.