Metal treatment – Compositions – Heat treating
Patent
1981-07-30
1983-02-15
Stallard, W.
Metal treatment
Compositions
Heat treating
266 51, B23K 706
Patent
active
043739695
DESCRIPTION:
BRIEF SUMMARY
The constant improvement in quality required for steel products together with the economies which have to be made in production costs lead to a continuous search for improvement in the quality and particularly the surface condition of semimanufactured products (ingots, blooms, slabs, billets, etc.) at an early stage of steel manufacture.
Crack removal by torch is a known method of burning the imperfect metal with a jet of pure oxygen, ie, eliminating surface defects: cracks, faults, burns and inclusions.
These torches may be manual or supported by machines. With torches used on machines, it is known to work by two very different methods: (1) high speed method known as washing or "scarfing". The method comprises burning the whole surface of the semimanufactured product to a constant, statistically defined depth, with a view to removing a large proportion of the surface defect, the work admittedly being completed by subsequent checking and additional repair of the product.
For this purpose it is known to use machines supporting a bank of oxygen torches, arranged in parallel to form a straight combustion bath, the combustion bath being displaced transversely to the semimanufactured product, sweeping over the whole of its surface. Even if the strength, ie the output, of the torches is programed as a function of the defects observed, the metal is burnt over the whole metallic surface of the product. This method has the serious disadvantage of wasting a large amount of metal.
(2) Selective method: so-called selective machines are used, with large torches of cylindrical cross section mounted on them and guided visually by the operator. This method is less rapid and removes only the imperfect parts of the metal.
The advantage of these machines lies in the improvement in the material yield because the removal of metal is controlled by the operator, who remains responsible for it and does not burn any good metal.
On the other hand, the performance of these machines, expressed as area treated per unit of time, depends directly on the strength of the torch.
Present solutions are thus based on torches of a strength which is a compromise between the selectivity requirements and productivity over a large area.
Furthermore, it is known: zones and thus enabling different quantities of metal to be removed at constant speed by lesser and greater displacement of the combustion bath; burn more or less metal with the same torch according to the speed of displacement; on the treated article after burning; which solidify instantaneously away from the action of the combustion zone; little carbon, the portion of metal under the combustion zone becomes fused without oxidation; that the kinetic energy of the oxygen projects the fused metal outside the combustion zone together with the slags; and that its abrupt solidification causes adhering burrs to form; combustion zone to be varied, thereby varying the profile left on the treated article; brush gives a rectangular combustion zone of which the short side can be cut back, causing a thin layer of metal to be removed over a large area; to obtain any of the results enumerated in the seven above points.
The object of the invention is to define a method of crack removal which is selective, ie which burns only the minimum of metal on the surface of the semimanufactured product, and yet with good productivity, with the maximum of imperfect metal being burnt very rapidly where such burning is necessary.
The method comprises removing cracks selectively with a multiple shape jet of oxygen, that is to say, removing cracks with a jet of oxygen of adjustable strength surrounded by heating flames, as in the prior art, but also of variable transverse cross section which is varied both in area and in shape from the outlet of the nozzle. The jet of oxygen varying both in strength, ie output, and in cross section, is formed by using a group of component jets arranged in a compact cluster and controlled individually or sector by sector, their orientation being adjustable as a unit, in place of a singl
REFERENCES:
patent: 3411466 (1968-11-01), Pfeuffer
patent: 3455747 (1969-07-01), Lytle
patent: 4013486 (1977-03-01), Engel
Etablissements Somalor-Ferrari "Somafer"
Stallard W.
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