Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-02-26
2001-04-24
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S570000, C148S639000, C148S643000, C148S695000
Reexamination Certificate
active
06221185
ABSTRACT:
This application is a 371 of PCT/DE96/01602 Aug. 26, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for manufacturing components from light metal strip.
2. Description of the Prior Art
In a light metal strips of naturally hard Al alloys, in particular of the AlMg or AlMg—Mn types, problems occur during cold forming at the cut edges from slitting, attributable not only to the microcracks caused by the slitting but also in particular to the cold hardening brought about as a result. To ensure greatest possible plasticity, the entire sheet bars are soft-annealed in the stack or the entire coil is soft-annealed in a so-called bell-type furnace. During drawing off of the strip from the soft-annealed coil, the coil curvature is straightened until flat. This straightening produces a certain additional cold hardening, which leads to a further increase in the yield strength and reduction in stress. What is disadvantageous in the known methods is the amount of energy and time expended for the soft-annealing of the entire material.
DE 3247698 C2 discloses an intermediate annealing of strip of an AlMgMn alloy. This intermediate annealing, which takes place between two successive cold rolling passes, is carried out as coil annealing at a temperature of 300 to 410° C. during a period of ½ to 8 hours. Alternatively, the annealing may also take place at 300 to 400° C. as continuous strip annealing for a period of 2 seconds to 2 minutes. Both annealing methods expend considerable amounts of energy (time, temperature) and the handling effort is also considerable. The last-mentioned annealing method for continuous strip annealing also requires enormous expenditure on equipment.
DE 4313543 C1 discloses a method for the heat treatment of continuous light-metal strips. For thin-walled strips with a thickness of 0.02 to 1.5 mm in particular, problems occur in the edge region in cases of high through-running speeds and/or great strip widths. The edge regions often become wavy, which may disrupt later processing. This edge region effect can be avoided if more heat is supplied per unit area to the edge regions of the strip than to the central region of the strip, at least over part of the treatment zone. This type of annealing corresponds in principle to continuous strip annealing with a steeper temperature gradient in the edge region to avoid wave formation. The already known disadvantages of continuous strip annealing likewise apply here.
SUMMARY OF THE INVENTION
The object of the invention is to specify a method for manufacturing components from critical formation light metal strip which is less costly than the known method with regard to energy consumption, cycle time and expenditure on equipment.
This object is achieved according to the invention by briefly heating only the region of the longitudinal edges of the cold-slit hot-rolled strip in such a way that a temperature-time range customary for soft annealing is passed through. This is the case if the heat in the longitudinal edge region penetrates to a depth in the strip width of at least 1 mm to a maximum of 10 mm and the supply of heat is adjusted in such a way that a temperature of over 150° C. is reached over a time span of more than 0.1 seconds to a maximum of 10 seconds. Investigations in this connection have shown that the cut edges of the slit strip are to be regarded as critical for the subsequent cold forming operations. It has been established that microcracks form in this region during slitting and can lead to inadmissible incipient cracks during cold forming. It is already known to mill off these cut edges in order to eliminate the critical region in this way. This prior art method of milling is very time-consuming and removal of the chips gives rise to considerable problems. Furthermore, it is uneconomical, since the slit strips have to be cut wider, according to the machining depth, in order to achieve the desired normal size.
The required heat input for the soft annealing of the regions of the longitudinal edges may take place by means of radiation, convection or conduction, as options or in combination. Inductive heating has been found to be particularly favorable, since in these methods considerable amounts of heat can be introduced in a relatively short time, so that this operation does not become the cycle-determining working step. Alternatively, it is also possible to introduce the heat by means of lasers or conventional gas burners.
REFERENCES:
patent: 4405386 (1983-09-01), Mravic et al.
patent: 4959107 (1990-09-01), Wallick et al.
patent: 3247698A (1984-07-01), None
patent: 3318861 (1984-11-01), None
patent: 3405478A (1985-08-01), None
patent: 3903726A (1990-08-01), None
patent: 4313543 (1994-04-01), None
patent: 196 19 034 U (1997-01-01), None
patent: 699775A (1996-03-01), None
Japan Patent Abstract, vol. 009, No. 268 (M-424) JP 60 11 4412-A (Nitsushin Seikou KK), Jun. 20, 1985, Oct. 25, 1985.
Duning Ralf
Gohrbandt Uwe
Sollner Gerhardt
Tanzmann Wolfgang
Tummler Helmut
Cohen & Pontani, Lieberman & Pavane
Michelin Kronprinz Werke GmbH
Yee Deborah
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