Metal deforming – With cleaning – descaling – or lubrication of work or product – Lubricating
Reexamination Certificate
2001-02-26
2004-04-20
Crane, Daniel C. (Department: 3725)
Metal deforming
With cleaning, descaling, or lubrication of work or product
Lubricating
C072S200000, C072S206000, C072S403000, C072S407000
Reexamination Certificate
active
06722174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a hot-rolled steel plate manufacturing apparatus and method for pressing a long material such as a continuously cast slab in a plate thickness direction, and to a plate thickness press apparatus and method used for the apparatus and the method.
2. Description of the Related Art
1. In hot rolling of a thin plate such as a hot-rolled steel plate, a slab
20
is typically rolled by a roughing mill
7
so as to obtain an intermediate thickness (a rolled material in this state is referred to as a sheet bar), and it is thereafter rolled by a finishing mill
3
so as to have a thickness of a final product. Here, as to the dimension of the slab
20
, the dimension of a heating furnace
13
for heating the slab
20
is an upper limit. As a result, the steel whose amount corresponds to one steel converter is usually divided into ten or more slabs
20
. It is to be noted that the slab is referred to as a hot slab or simply referred to as a material according to needs.
A sheet bar
20
A outputted from the roughing mill
7
has a defect of shape called a tongue or a fishtail necessarily produced at front and rear ends in greater or lesser degrees, similarly as in rolling of a regular plate. Incidentally, the “tongue” means a defect of shape that a central portion at the end in the plate width direction protrudes in the tongue-like form. The “fishtail” means a defect of shape that the both edges at the end in the plate width direction protrude in the fishtail-like form. Since both the tongue and the fishtail have the width narrower than that of a normal portion, they are apt to be easily deformed.
If these defects of shape are left as they stand, the deformation is further advanced by the finishing mill
3
in the next step, which may cause rolling trouble. The defects of shape are, therefore, cut and removed at the stage of the sheet bar
20
A. The product yield is reduced as the cut and removed portion (which will be referred to as a “crop” hereinafter) becomes longer.
The finishing mill
3
is a continuous rolling mill generally composed of several stands and performs rolling to a steel tape having a thin thickness with tensile force applied thereto. A portion distanced from a front end of the hot-rolled steel plate by approximately 100 meters which has been subjected to finishing rolling is, however, rolled with no tensile force acting thereon until the front end reaches coilers
5
a
and
5
b
. Further, in this period, since traveling of the front end becomes unstable due to lifting and the like caused by collision with a carrier roll or a wind blast, rolling must be carried out by reducing a rolling speed to approximately half of that in the steady state (after reaching the coilers) in general.
Further, a shape of a rear end is also degraded because the tensile force becomes zero after it moves out from a final stand of the finishing mill
3
. Such a non-steady portion is typically inferior to a steady portion in material and shape because cooling becomes uneven due to reduction in a temperature in conveyance or a defect of shape. Since rolling trouble caused due to such a defect of material and shape or meandering involved by the defect of shape lowers the capacity utilization ratio, this can be a serious adverse factor for reduction in the yield.
For improvement in the yield in finishing rolling, a method for connecting multiple sheet bars to each other to perform finishing rolling has been developed. For example, Japanese Patent Application Laid-open No. 84109-1992 proposes a method by which the front end of a sheet bar is sequentially coupled to the rear end of a preceding sheet bar so that finishing rolling is continuously performed to multiple sheet bars.
With this prior art technique, since rolling similar to that in the steady state is possible with respect to the coupled front and rear ends, the yield of the front and rear ends (non-steady portions) can be improved. Further, as to the front end portion, rolling can be performed at the same rolling speed as that in the steady state (after reaching the coilers), thereby improving the rolling efficiency. Furthermore, since a plurality of sheet bars are connected to each other to be rolled, the rolling efficiency can be more improved as compared with intermittent rolling.
Besides, there are also proposed other methods for manufacturing a long sheet bar such as a method for coupling multiple slabs or a method for directly rolling a continuously cast slab. As the method for coupling multiple slabs, Japanese Patent Application Laid-open No. 106403-1982 proposes a method by which a front end of a slab is sequentially coupled to a rear end of a preceding slab and the coupled multiple slabs are continuously rolled into a sheet bar by a planetary mill group.
Moreover, Japanese Patent Application Laid-open No. 92103-1984 proposes a method by which a slab whose amount corresponds to one steel converter is turned into a sheet bar by a rolling mill having a large thickness reduction amount to be wound around a coil as it is, and the coil of this sheet bar is then rewound to perform finishing rolling. Similarly, Japanese Patent Application Laid-open No. 85305-1984 proposes a method by which a slab cast by a special continuous casting machine (which is referred to as a rotary caster) at a high speed is turned into a sheet bar by rolling, it is once taken up to be wound in a rewinding machine and finishing rolling is thereafter carried out.
According to these conventional methods, crop cutting only at the front and rear ends of the long sheet bar can suffice, and the crop does not occur for each slab. The yield can be thus improved. Additionally, according to these methods, finishing rolling can obtain advantages similar to those in the method by which multiple sheet bars are connected to each other to perform finishing rolling.
These prior art techniques, however, have the following problems.
At first, in the method disclosed in Japanese Patent Application Laid-open No. 89109-1992, a part having a defective shape at the front and rear ends of the sheet bar must be cut off in order to connect the multiple sheet bars. The problem of reduction in the yield due to generation of the crop, therefore, remains. Further, a connected portion of the sheet bars has the strength lower than that of any other portion, and fracture at the connected portion in the middle of finishing rolling may force stoppage of the line. Furthermore, since the sheet bars are actually connected by welding, the structure of the connected portion becomes rough and large, which may possibly lead to generation of a defect of material or of a surface crack.
Moreover, in the method for coupling multiple slabs disclosed in Japanese Patent Application Laid-open No. 106403-1982, since the plate thickness of the slab to be coupled is large, it is difficult to completely couple the slabs in a short period of time. In addition, even if they are coupled in a short period of time, a hydrostatic pressure component as well as tensile stress may act on the coupled portion to cause peeling of the coupled surface when finishing rolling is conducted with a large thickness reduction amount. Therefore, the reduction amount must be decreased, and the efficiency of roughing rolling lowers.
Additionally, in the method for directly rolling a continuously cast slab disclosed in Japanese Patent Applications Laid-open Nos. 92103-1984 and 85305-1984, there is a problem that the efficiency of rolling is reduced due to limitation in a casting speed. According to the latter patent application, it is determined that the casting speed of 10 mpm is possible as the casting ability (weight per unit time), but there is actually no example reporting casting at such a high speed has achieved success in light of the operation and the quality.
As similar to the conventional techniques, in the method for directly rolling a continuously cast slab, a rolling speed of the roughing rolling mill at an initial stage is decrease
Ide Kenichi
Ishii Hajime
Iwanami Toshio
Masuda Sadakazu
Mikami Masao
Crane Daniel C.
Griffin & Szipl
NKK Corporation
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