Welding

There are different ways to connect the parts together. The most usual are fastening by bolts or rivets, soldering and welding. If you want to do the continuous joint on long parts of joining surfaces you need welding. This is the main feature of welding, especially for enclosed containers such as boilers, etc.

Welding is a fabrication that joins materials by causing fusion, which usually melts the base material. Usually, there are fillers that added to joining base materials. The joint is created in the process of cooling the pool of those molten materials. Joint is usually stronger than a base material. In addition, welded parts can be pressurized.

The original fusion technique is known from the earliest uses of iron. The process of joining small pieces of iron to larger ones was through heating to welding temperature and hammering or pressing together. The most common today's welding techniques are arc welding, oxyacetylene welding, resistance, electron-beam, friction, laser welding and other. The shielded metal-arc welding is the most used technique. An electric arc is created between materials leading to electrode's metal melting and transferring it to the joint in this process. Another technique is gas (usually oxyacetylene) welding. The source of heat in this process is acetylene burned in the atmosphere of oxygen. For the resistance welding, the main source of heat is the electrical resistance of the joint. Such welds are made using low-voltage and high current power source with pressure applied. A dense stream of high-velocity electrons bombarding the joint is a source of heat for electron-beam welding. The friction welding is based on heating joining parts by friction. Laser welding is accomplished when materials are fused together by heat generated from a laser source.

A proper weld joint can be prevented by dirt, rust, grease, and oxidation. To protect hot metal from these there are two protection methods used in all weld processes: flux or shielding gas. Welding flux is used in solid, paste or liquid form. When evaporated, it creates a small pocket of gas. This is how the oxidation process prevented. But solid flux must be removed after completing the welding. To protect welding shielding gas surrounds point of welding.

Carbon and low-alloy steels are the most frequently used materials in welded constructions. The weldability of steels varies depending on a carbon content and total alloying content. Aluminium alloys are also generally weldable. Copper and its alloys are also weldable, but the high thermal conductivity makes welding difficult. As a rule, you can easily weld plastic or glass. The most common technique to weld them is heating to melting range and adding pressure on surfaces.

The quality of weld depends on the base material, filler and flux material, energy and design. The strength of material and weld depends on the welding method and concentration of energy input, type of the flux and filler, and weldability of the base material. The weld quality also much depends on the heat-affected zone. Usually, one of the destructive or nondestructive methods is used to test the quality of the weld. Possible defects of welds are cracks, gas, and non-metallic inclusions, distortions, incomplete penetration, lack of fusion and lamellar tearing.

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