A Short Note On Welding
Presently, many process of welding have been developed and there is probably no industry which is not using welding in any form for the fabrication of their products. Researches have led to join dissimilar metals also by the mean of welding. The beauty of welding is that welded joint can have more than 100 percent strength than the single unit. Welding is easier to joint different parts of the products compared to others.
Welding nowadays is extensively used in the fields like:
- Automobile industry
- Aircraft machine frames
- Structural work
- Machine repair work
- Ship building
- Pipe line fabrication
- In thermal power plants
- Fabrication of metal structures and refineries, etc.
Welding are basically classified as solid phase welding and fusion welding:
Fusion welding: is the coalescence of two materials by the application of heat. The two joining parts are paced together; a filler material is melt by the introduction of heat and solidifies upon cooling thus joining the part. The heat can be produced by myriad number of ways.
Solid phase welding: are produced by bringing the clean faces of component into intimate contact to produce metallic bond with or without the application of heat but the application of pressure is very essential to induce plastic flow.
Advantages of welding over other type of joints:
- Buildings , bridges and structures can be built lighter and thus higher due to reduction in weight
- These are cheap also due to reduction in weight and material cost. Additional joints strength can be obtained by using considerably smaller structural members. Joints are compact and do not require additional plates as in case of riveted joints.
- Welded joints have high corrosion resistance compared to bolted and riveted joints.
- Welded joints are fluid tight for tanks and vessels.
- Welded structures can be altered easily and economically
- Many different types of joints are possible in welded joints.
Additional Points Worth Pondering:
Welding process produces rays of longer wavelengths compared to X –rays or gamma rays. These can be broken into visible light rays, infra rays, ultraviolet rays. Visible light can induce eye strain and general discomfort. Ultraviolet rays are invisible and can cause burns on unprotected skin. Infra-red rays have longer wavelength and these produce heat when they strike and absorbed by the surface. Prolonged exposure can cause skin burns.
Protection of the welder from the process
Welders have to protect themselves while welding. They have to prevent them from sparks and hot molten metal, UV rays, infra-red rays, visible light rays, welding fumes and other hazards.
A welder should wear welding jacket or sleeves made of leather or denim. Leather sleeves, high top boots. Clothes should be fit tight enough so that no bare skin is exposed to sparks or ultra violet rays. Safety glasses or glasses fitted with side shields must be worn.
Welded joints remain in tension
The weld filler material is in liquid state and it undergoes both solidification shrinkage and contraction during cooling. Parent metal being colder and larger in mass inhibits the contraction of the weld material putting weld in tension.
Relieving the tension by hammering
The welder peen the weld joint with the hammer while doing so introduces the stress and thus build up tension in the weld is relieved. Surface oxides and residual flux present on weld surface also get removed. For uniform cleaning and stress removal, shot blasting is preferred.