Metal working – Method of mechanical manufacture – Combined manufacture including applying or shaping of fluent...
Patent
1996-01-25
1998-03-03
Arbes, Carl J.
Metal working
Method of mechanical manufacture
Combined manufacture including applying or shaping of fluent...
118 68, 118620, 427432, 266112, F16J 1512
Patent
active
057221510
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and a device for making semi-finished products in the form of thin metal bars in which, an uncooled, cleaned metal profile having a low heat content is run continuously from the bottom to the top through a melt pool of material of the same composition.
2. Description of the Prior Art
A process and a device for producing thin metal bars are disclosed in EP 0 311 602 B1. A metal profile, for example, in the form of a strip-type steel sheet (blank) having a clean surface and a thickness of 0.1 to 1.4 mm, is run continuously through the bottom of a melt pool container filled with a steel melt of the same composition. For this purpose, there is a slot-type opening in the bottom of the melt container that is equipped with a sealing device for preventing the melt from flowing out. The temperature of the melt lies in the vicinity of the liquidus temperature T.sub.liq. The steel strip moves through the melt at a constant speed and passes out of the melt upwardly. Because of the low heat content of the steel strip (strip temperature is approximately equal to room temperature), an adherent layer of crystallized and still molten melt develops on its surface. The thickness of this layer may be several times the thickness of the original blank. The thickness of the layer depends, on retention time in the melt (speed of blank), the melt temperature (temperature difference relative to the solidus temperature T.sub.sol), the melt heat and the specific heat of the material used, and the thickness of the blank. The operation must be conducted in such a manner as to avoid remelting the already adherent crystalline like structure. Under these conditions, a temperature gradient is induced across the thickness of the strip. As the strip moves through the melt pool, the temperature is lowest in the interior of the blank and rises toward the edge. A qualitatively similar temperature curve is also present in the adherent layer. The temperature in the outermost region of the layer, is the liquidus temperature, T.sub.liq.
Initially, the adherent layer consists of a mixture of crystalline like structure and molten melt (mushy zone). The portion of the molten phases in the layer increases in a direction toward the melt. After leaving the melt pool, blank and the adherent layer cool, whereby the temperature gradient that has existed until now is reversed. The adherent layer then solidifies completely.
From EP 0 311 602 B1 also discloses that the semi-finished product produced as described above, after it leaves the melt pool and until it cools or enters a forming machine to undergo a hot or cold forming process, is to be kept in an atmosphere for protection against oxidation. A portion of the total amount of finished product produced in this manner is then fed back to the start of the process as blank and run through the melt pool once again.
Until now, a crucial obstacle has hindered the practical application of this process in making steel strip material. Consumers of high-quality cold or hot strip demand among other things, that the range of deviation in sheet metal thickness be no greater than 2% of the nominal thickness. A tight tolerance of this kind cannot be reliably maintained using the aforementioned process. Irregularities in strip thickness which exist after the strip left the melt pool and which exceed the prescribed maximum limit are practically impossible to eliminate by means of subsequent forming procedures. This is because, given the extreme flatness of the semi-finished product used in the rolling process (width-gauge ratio of at least 60), the subsequent forming (with decreasing thickness) takes place, essentially in the longitudinal direction only; no further significant undoing occurs. Existing differences in thickness, along a line at a right angle to the longitudinal direction of the strip, therefore remain, relatively unchanged.
EP 0 311 602 B1 also describes another embodiment of the process wherein, in a reverse fashion,
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El Gammal Tarek
Hamacher Peter Lorenz
Menne Ulrich
Parschat Lothar
Pleschiutschnigg Fritz P.
Arbes Carl J.
Mannesmann Aktiengesellschaft
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