JPS59185502A - Continuous rolling method - Google Patents

Abstract

PURPOSE:To improve rolling efficiency and to prevent breakage trouble in the inside of a mill by heating, before rolling, a joining part of strips of different thicknesses and reducing the variation of rolling load at the joining part at the time of rolling while changing the thickness of strip. CONSTITUTION:A hot rolled strip S to be cold rolled is unwound from a coiler 1 placed at the inlet side to cut its front and rear ends by a shear 2. The strips are butt welded together by a welder 3, and the joined strip is sent to the inlet side of a cold tandem mill 5 through a loop car 4. A welded point detector 6 and a heating device 7 are arranged at the inlet side of the mill 5, and a detecting signal is sent to the device 7 when the welded point is detected by the detector 6. The device 7 decides the passing time of the welded point basing on the line speed and the distance from the detector 6 to heat only the welded point. The strip having the deformation resistance reduced by heating the welded point is rolled by the mill 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining and continuously rolling a plurality of strips having different thicknesses.

More specifically, the present invention relates to a continuous rolling method in which a plurality of steel strips having different thicknesses are joined and continuously rolled, and the rolling load at the joint is reduced to smoothly change the thickness during running.

Conventionally, in the rolling of cold-rolled steel sheets, a method has been adopted in which strips of different thicknesses are joined together and continuously rolled to improve rolling efficiency.

Figure 1 (A) shows strip knobs S1 and S with different plate thicknesses.
2 are butt welded together. Generally, weld beads B1 and B2 are cut using a bead trimmer as shown by dotted lines in the figure to form the shape shown in FIG. 1(B). Methods of smoothing this stepped portion with a roll or the like, cutting it with a cutting tool, or melting it are disclosed in Japanese Patent Application Laid-Open No. 49-35247, Japanese Patent Application Laid-Open No. 57-'79089, and the like. However, the following inconvenience occurs.

(1) In butt welding of strips with different thicknesses, there is a large difference in the melting state due to the difference in heat capacity at the ends of both strips.

(2) Even if the known technology is used to reduce the appearance to flat scraps, a slight step remains, which tends to cause fractures in the mill during cold rolling.

(3) Even if the weld bead is removed and smoothed using a bead trimmer, a step still remains. Furthermore, if the difference in plate thickness is too large, it becomes impossible to remove the step with a bead trimmer.

(4) Furthermore, if cold rolling is performed continuously without completely removing the step weld, there will be large load fluctuations and mass flow fluctuations when the welding point passes through the rolls, so it is recommended to reduce the rolling speed extremely. There is a risk that the rolling stock may be forced to roll or squeezed. If a problem such as a strip breakage occurs in the mill during continuous rolling, the line must be stopped, resulting in a large loss.

(5) Furthermore, due to changes in load balance due to line deceleration at the welding point and switching from automatic to manual operation, it is necessary to cut off long sections at off-gauge sections before and after the welding point, which reduces yield. do.

As described above, in the conventional technology, in order to avoid problems caused by the difference in thickness of these strips, it is necessary to limit continuous rolling to combinations of strips with a narrow range of difference in thickness, and the continuous rolling is There has been a problem in that rolling efficiency and roll unit consumption are reduced due to difficulty in scheduling rolling or consolidating lots.

The present invention aims to solve the problems of the prior art as described above, and more specifically, by expanding the range of difference in thickness of the strip that can be continuously rolled by welding, it enables smooth continuous rolling. The purpose is to improve rolling efficiency and roll consumption.

According to the present invention, in a method of joining a plurality of strips having different thicknesses and continuously rolling the strips while changing the thickness at the joining point, the joining portion is heated before rolling and the rolling distance along the joining point is changed. The continuous rolling method described above is provided, which is characterized in that rolling load fluctuations at the joint portion are reduced during plate thickness change rolling.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 is a schematic diagram of a cold rolling line implementing the present invention. A hot rolled strip S to be cold rolled is unwound from an entry coiler 1, and a shear 2 is used to unwind the leading and trailing ends of the continuous strip. The part is cut off. The welding machine 3 then butt-welds the strips, and the joined strips are sent to the inlet of a cold tandem mill 5 via a loop car 4.

According to the invention, a welding point detector 6 is installed on the entry side of the tandem mill 5.
and a heating device 7 are arranged. The welding point detector 6 is a plate thickness detector of a known type (when a welding point is detected, a detection signal is sent to the heating device 7, and the heating device 7 determines whether the welding point has passed based on the line speed and the distance from the detector 6). It is configured to determine the time and heat only the welding point.

FIG. 3 shows an embodiment of the heating device 7, consisting of induction heating coils 7a, 7b, 7C, through which the strip S passes. These induction coils 7a, 7b, 7C are sequentially energized in synchronization with the line speed so as to heat only the welding point.

As described above, the strip whose deformation resistance is reduced by induction heating at the welding point is rolled in the cold tandem mill 5.
The stepped portion as shown in FIG. 1(B) is deformed gently as shown in FIG. 1(C) by the reduction by the first stage mill, and does not cause large load fluctuations during passage.

The heating device 7 for locally heating the strip may be constructed by an appropriate means such as laser heating in addition to induction heating.

Example A hot-rolled strip of low carbon steel 5S41 with a thickness of 3fi and a width of 1000m was butt welded with a strip of 2.3cm thick and 1000m wide, and 25 induction coils with a width of 40ON were connected to this joint as shown in Fig. 3. It was passed through the coil and heated.

Each coil was energized in synchronization with the passing speed of the joint so that only the joint was always heated, and the coils were heated from room temperature to 400°C. The frequency of use of the induction coil was 5 KHz, and the power used was 2000 KW (for heating section weight 3.14+r).

2. After finishing the cold rolling of the 31111 strip,
The 3.0 Tsuru strip was finished into a cold-rolled strip with a thickness of 0.79 m and a width of 1000 m. As a result of reducing the line speed to 100 mpm when passing the joint, the rolling load was gently reduced by about 30% when passing the joint, and there was no large load fluctuation.

As in the above embodiments, according to the method of the present invention, strips having different thicknesses can be continuously rolled without large load fluctuations. Normally, the range of plate thickness difference that allows continuous cold rolling is approximately 1 (i.e. 3.1 mm) for the preceding material with a thickness of 2,31,111 mm.
However, the method of the present invention has made it possible to perform continuous rolling without the restriction of the difference in plate thickness.

Normally, in cold rolling, continuous rolling of wide to narrow strips is desirable in terms of sheet quality (dimensions, flatness) and roll unit consumption, but conventional continuous rolling has a narrow tolerance range for sheet thickness differences. Therefore, it is difficult to follow this principle,
There was also the possibility of a decline in quality. However, the method of the present invention expands the allowable range of plate thickness differences, making it easier to set up a rolling schedule, and also makes it possible to sequentially roll from wide to narrow width materials, ensuring quality.

According to experiments conducted by the present inventors, it has become possible to continuously roll strips with different thicknesses as shown in Table 1 below.

Table 1 (Combinations of strips that can be continuously rolled) ○: Combinations that are possible even with conventional methods ◎ 2 Combinations made possible by the method of the present invention As described above, the present invention improves rolling efficiency and reduces problems such as breakage in the mill. This greatly contributes to avoiding accidents and improving quality.

[Brief explanation of drawings]

Figures 1 (A), (B), and (C) show the state in which strips of different thickness are joined by butt welding, the weld bead removed, and cold rolled in the first stand after processing according to the present invention. Indicates the status of each. FIG. 2 is a schematic diagram of a cold rolling line modified to carry out the method of the invention. FIG. 3 is a schematic diagram of a heating device used in one embodiment of the present invention. (Reference number) S, Sl, 32 Ni lip, B1, B2: /8 contact bead, d: Step at joint, 1: Entrance coiler, 2: Shear, 3: Welding machine, 4: Loop car, 5: Cold Tandem mill, 6: Welding point detector, 7:
Heating device, 7a, '7b, 7c: induction carp/l/. Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Masahiko Arai

Claims (1)

[Claims] In the method of joining multiple strips of different thickness and continuous rolling while changing the thickness during running at the joining point,
A continuous rolling method characterized in that the joint portion is heated before rolling to reduce rolling load fluctuations at the joint portion during rolling to change plate thickness during running.