Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1994-04-26
1995-10-10
Kastler, Scott
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
266252, C21D 900
Patent
active
054567734
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to heat treatment for metal articles in a roll type furnace, in particular for relatively thin steel parts which easily warp when exposed to heat, such as ball bearing raceways, sheet metal rounds, blades and the like.
A device for heat treatment for metal articles is known (DE-PS 31 50 576), in which annealing frames equipped with the metal parts in the single divisions are disposed upon a rolling track. The annealing frames equipped with the metal articles are run through a furnace. It is however difficult to prevent that metal parts with a lengthwise dimension of some centimeters and a small thickness of some millimeters are not warped permanently after the heat treatment.
Furthermore, in connection with the heat treatment of metal parts it is up to now usual to use furnaces comprising an atmosphere containing protective gas and with partially electrical heating in order to prevent that e.g. the carbon content of the metal parts changes during the heat treatment process or the metal parts oxidize. For most metal parts, neither recarburization nor decarburization nor oxidation is desired.
SUMMARY OF THE INVENTION
The invention deals with the problem to allow a heat treatment of metal parts in which the metal parts do not warp and in which only insignificant marginal re- or decarburizations as well as insignificant marginal oxidations or marginal scaling occur.
This is achieved by a process of the kind mentioned in the introduction, characterized by the fact that the metal articles are heated in stages up to 800.degree.-850.degree. C. in several pre-heating zones (I, II) with atmospheres containing free oxygen, then the metal articles are heated in a high temperature zone (II) in a reducing atmosphere containing no free oxygen and run through this zone relatively quickly, the burners of the high temperature zone (III) are timed with shorter or longer periods, depending on the quantity of metal articles supplied and the amount of heat to be transmitted, and that the rolls are set in the high temperature zone (III) at a short distance from each other and the baffle plates (S, US) between the zones (I, II, III) are set at smallest possible distance from the rolling track or the metal articles on the rolling track, with the burners being located above and below the rolling track.
During the process according to the invention, at the beginning the temperature gradient immediately above the rolling track is so small that the metal articles that are present there cannot warp. Such a temperature distribution can however be achieved only with a roll type furnace heated directly with high speed burners. In a roll type furnace with sole upper heating or with application of auxiliary annealing means or annealing frames, this cannot be achieved.
In connection with the annealing operation of steel parts, according to the invention, ceramic rolls or rolls free from carbon with an adequate heat solidity are preferably applied. Furthermore, phenomenons known as "pittings" can be prevented this way, since no contact of hot metal with hot metal occurs during the annealing process, but the steel parts rest on the ceramic rolls. In known roll type furnaces for the heat treating metal industry, mainly metal rolls are employed, requiring a relatively large effort for the air or water cooling of the rolls.
To keep the oxygen content in the furnace as low as possible, the burners are operated without excess air in the high temperature area, like in the heat-treatment for the tempering of steel, the so-called austenitization area. In a process according to the present invention, the burners are adjusted in a way that no protective gas is required. This is caused by the fact that such metal parts easily scale on the surface, with a thickness of the layer of 0.01-0.03 mm approximately. This marginal scaling does not influence the product quality, on the contrary the scaling prevents that the metal articles re- or decarbonate, so that a uniform structure after the heat-treatment i
REFERENCES:
patent: 5314170 (1994-05-01), Tada et al.
J. Wunning, "Die Warmebehandlung in der Fertigungslinie mit einem neuartigen Rollenherdofen", HTM Harterei-Technische Mittelungen, 45, No. 6, Dec. 1990, pp. 325-329.
Daido Tokushuko KK, Abstract of Japanese Application No. JP820224597, Publication No. JP59113117, Patent Abstracts of Japan, vol. 008, No. 232, Oct. 24, 1984.
Bittner Hans-Georg
Weber Hartmut
Heimsoth Verwaltungen GmbH & Co. KG
Kastler Scott
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