Metal working – Method of mechanical manufacture – Combined manufacture including applying or shaping of fluent...
Reexamination Certificate
2000-07-20
2002-10-01
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Combined manufacture including applying or shaping of fluent...
C029S03300H, C029S03300H, C228S005700
Reexamination Certificate
active
06457227
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device for producing a thin steel strip, comprising at least one or more continuous-casting machines for casting thin steel slabs, a furnace device which is suitable for heating and/or homogenizing a slab, and at least one rolling device for reducing the thickness of a slab which is conveyed out of the furnace device.
The invention also relates to a process for producing a steel strip, in which liquid steel is cast in at least one continuous-casting machine to form a slab and, utilizing the casting heat, is conveyed through a furnace device and, in a rolling device, is rolled to form the strip with a desired final thickness.
BACKGROUND OF THE INVENTION
A device of this nature is described in application WO-A-97/46332. By this reference, the contents of this application are deemed to be incorporated into the present application. The said application proposes, inter alia, to use a device of this nature for an endless rolling process. In the said application, an endless rolling process is understood to mean a rolling process in which slabs or, following passage through a preliminary rolling device, strips are coupled together so that an endless rolling process can be carried out in a finishing mill.
In the past, it has been proposed to couple slabs together by providing the end of one slab with a shape which is such that it can be coupled to the front edge of a following slab which is also provided with a suitable, often complementary, shape. The devices which are required to do this are highly complicated and take up considerable amounts of space. In addition, the slabs which are to be coupled together are exposed to the atmosphere for a considerable length of time, with the result that the slabs cool down and a layer of oxide is formed on the slabs.
An endless rolling process, in particular when applied to thin-cast slabs, i.e. slabs with a thickness of 100 mm or less, preferably 80 mm or less, provides the possibility of achieving a very high level of temperature homogeneity during rolling. This advantage is to a considerable extent negated by a complicated coupling method as described above.
SUMMARY OF THE INVENTION
The object of the invention is to provide a device which makes it possible to couple together thin-cast slabs, which have optionally been reduced preliminary, quickly and easily. This object is achieved by means of a device which is characterized in that a welding machine is arranged between the continuous-casting machine or continuous-casting machines and the rolling device, for joining slabs together.
With a welding machine, it is possible to quickly join together end faces, which are straight or have some other simple shape, of two slabs which are to be coupled to one another. A welding machine does not take up much space, so that the slabs which are to be joined together are only exposed to the atmosphere for a short time and therefore also only emit heat to the environment during a short time. Consequently, the use of a welding machine also contributes to reducing the amount of oxide which is formed on the surface of the slabs which are welded together.
In order to avoid interim stores, for example in the form of a coil box, a preferred embodiment of the device according to the invention is characterized in that the welding machine is displaceable along a welding length in the standard passage direction of the slabs through the device towards the rolling device. By allowing the welding machine to move along with the slabs which are to be welded together, the slab, whether or not it has been reduced in size, and the strip can run at the same speed throughout the device, taking into account the reduction in thickness.
A further embodiment of the device according to the invention is characterized in that the welding machine is displaceable in the standard passage direction of the slabs through the device towards the rolling device at a speed of between 4 and 20 m/min, preferably at a speed of between 10 and 17 m/min. In an endless rolling process, the speed at which the slab enters the rolling device is, depending on the final strip thickness which is to be achieved and on whether this final thickness is reached in the austenitic, ferritic or austenitic-ferritic mixed field, in the range between 4 and 20 m/min, more preferably in the range between 10 and 17 m/min. For the process to operate efficiently, the speed at which the welding machine is displaced is preferably equal to the speed, if appropriate taking into account a reduction in thickness, at which the slab is introduced into the rolling device.
A further embodiment is characterized in that the welding machine is an induction-welding machine. This prevents the need to introduce into the weld a welding material with a chemical composition which differs from the chemical composition of the slabs which are to be welded together. This is particularly important for low-alloyed steel grades, in particular IF steel grades. In addition, the output of an induction-welding machine is easy to control.
The transfer of heat from the slabs which have been welded together to the atmosphere is limited further by an embodiment of the device according to the invention which is characterized in that the welding machine is provided with means for limiting the transfer of heat from the slabs to the environment.
It has been found that, using slab thicknesses and rolling speeds which occur in practice, the process can be operated with success, even using multi-strand continuous-casting machines, with a furnace device which is characterized in that the total length of the furnace device is between 250 and 330 m.
The slabs which are to be welded together are moved into a desired position with respect to one another using positioning means, after which the slabs are welded together by means of the welding machine, because the positioning means and the movable welding machine cannot be fully accommodated in a furnace and it is inevitable that during welding the slabs which are to be welded together will cool down in the area of the weld. In order to produce the desired temperature homogeneity of the slabs, a further embodiment of the device according to the invention is characterized in that the furnace device comprises a first zone and a second zone which, as seen in the standard passage direction, are positioned one behind the other, and the welding machine is arranged between the first and the second zones. The furnace device preferably has means for conveying through slabs at an accelerated speed in order to be able to empty the furnace device quickly following an interruption to the process, whether planned or not, and before another interruption occurs.
It has been found that a good weld, with little cooling of the slabs, can be obtained in an embodiment of the device according to the invention which is characterized in that the first zone and the second zone are positioned at a distance apart which, measured in the standard passage direction, is 4-25 m, preferably 5-17 m. In order to return the slabs which have cooled down during the welding to the correct temperature, a second zone is positioned downstream of the welding machine, as seen in the standard passage direction, which second zone, according to the invention, is characterized in that it has a length of between 25 and 100 m. It has been found that, depending on the rate at which welding can be carried out and the welding length, sufficient temperature homogenization can be achieved with such a length.
In the second zone, the welded slab is to reach a temperature homogeneity which is desired for the subsequent rolling process. It has been found that a good level of homogeneity is achieved within the available time and length of the second zone in an embodiment of the device according to the invention which is characterized in that the second zone comprises a reheat-up section and a heat-through section. In order to minimize cooling during the welding process in which the slabs which are to be welded together are exp
Nijveld Erik Marco
Zuurbier Simon Petrus Anthonium
Corus Staal BV
Echols P. W.
Stevens Davis Miller & Mosher LLP
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