Thermit Welding

THERMIT WELDING:
          Thermit welding is an effective, highly mobile, method of joining heavy section steel structures such as rails. Essentially a casting process, the high heat input and metallurgical properties of the Thermit steel make the process ideal for welding high strength, high hardness steels such as those used for modern rails.
          Thermit Welding is a skilled welding process and must not be undertaken by anyone who has not been trained and certificated to use it.
Detailed operating instructions are provided for each of our processes, but the welding methods all comprise of 6 main elements:
  1. A carefully prepared gap must be produced between the two rails, which must then be accurately aligned by means of straightedges to ensure the finished joint is perfectly straight and flat.
  2. Pre-formed refractory moulds which are manufactured to accurately fit around the specific rail profile are clamped around the rail gap, and then sealed in position. Equipment for locating the preheating burner and the Thermitt container is then assembled.
  3. The weld cavity formed inside the mould is preheated using an oxy fuel gas burner with accurately set gas pressures for a prescribed time. The quality of the finished weld will depend upon the precision of this preheating process.
  4. The Thermit® Portion is manufactured to produce steel with metallurgy compatible with the specific type of rail to be welded. On completion of the preheating, the container is fitted to the top of the moulds, the portion is ignited and the subsequent exothermic reaction produces the molten Thermitt Steel. The container incorporates an automatic tapping system enabling the liquid steel – which is at a temperature in excess of 2,500°C – to discharge directly into the weld cavity.
  5. The welded joint is allowed to cool for a predetermined time before the excess steel and the mould material is removed from around the top of the rail with the aid of a hydraulic trimming device.
  6. When cold the joint is cleaned of all debris, and the rail running surfaces are precision ground the profile. The finished weld must then be inspected before it is passed as ready for service.

ADVANTAGES:
1.The heat necessary for welding is obtained  from a chemical reaction and thus no costly power supply is required. Therefore broken parts (rails etc.) can be welded on the site itself.
2.For welding large fractured crankshafts.
3.For welding broken frames of machines.
4.For building up worn wobblers.
5.For welding sections of castings where size prevents there being cast in one piece.
6.For replacing broken teeth on large gears.
7.Forgings and flame cut sections may be welded  together to make huge parts.
8.For welding new necks to rolling mill rolls and pinions.
9.For welding cables for electrical conductors.
10.For end welding of reinforcing bars to be used in concrete (building) construction.
LIMITATIONS:
1.Thermit welding is applicable only to ferrous metal parts of heavy sections, i.e., mill housings and heavy rail sections.
2.The process is uneconomical if used to weld cheap metals or light parts.

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