Thermit Welding History, Definition and Principle of Operation

Thermo Chemical Welding Processes
Thermit Welding History, Definition and Principle of Operation
Thermit Welding Mixtures
Various Methods of Thermit Welding
Procedure for Thermit Welding
Advantages and Disadvantages of Thermit Welding
Uses and Applications of Thermit Welding
Atomic Hydrogen Welding Defintion and Principle of Operation
Atomic Hydrogen Welding Equipment
Parameters for Manual Atomic hydrogen Welding of Butt Joints
Advantages and Disadvantages of Atomic Hydrogen Welding
Applications of Atomic Hydrogen Welding

Thermit Welding History, Definition and Principle of Operation

Thermit Welding History,Definition and Principle of Operation - THERMIT WELDING HISTORY Goldschmidt discovered them, it welding in the year 1896. He was of the opinion that a cold mixture of metallic oxide and finely divided aluminium could be ignited in one spot and that the reaction of this spot would furnish sufficient heat to propage reaction throughout the entire mass.
DEFINITION Thermit welding comprises a group of welding processes where in coalesence is produced by heating with superheated liquid metal and slag resulting from chemical reaction between a metal oxide and, aluminium, with or without the application of pressure. The liquid metal acts as filler metal too. PRINCIPLE OF OPERATION Thermit welding is based on casting and foundry practice, and consists essentially of providing, by means of a chemical (thermit) reaction, a volume of molten weld metal which is poured into the joint to be welded.
	The chemical or thermit reaction takes place between a metal oxide (usually iron oxide) and a metal reducing agent (usually aluminium but sometimes magnesium also). The chemical affinity of aluminium for oxygen is the basis for the thermit process. Thermit reaction is an exothermic one. A few typical thermit reactions are given below: (i) 3Fe₃O₄ + 8Al--> 9Fe + 4Al₂O₃203 (3088°C) 719.3 kcal (ii) Fe₂O₃ + 2Al--> 2Fe + Al₂O₃ (29600C) 181.5 kcal (iii) 3CuO + 2Al -->3Cu + Al₂O₃ (4865°C) 275.3 kcal
(iv) Cr2O3 + 2Al--> 2Cr + Al₂O₃ (2977°C) 546.5 kcal The reaction listed as (i) above is the one most commonly used in thermit welding. The theoretical temperature resulting from this reaction is 3088°C, but radiant heat losses and losses to the reaction vessel however reduce this temperature to about 2538°C. Other additions to adjust the chemical composition of the metal and the slag for fluidity ultimately reduce the filler weld metal temperature to about 21000C. The thermit reaction is nonexplosive. The thermit mixture is ignited with the help of a special low ignitiontemperaturepowder which in turn is lighted by a burning magnesium ribbon, by a spark or with a match.

Home | Site map | Submit Article | Directory | Search