JP2851990B2 - Hot finish rolling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling order planning method for improving a sectional profile in hot rolling of a steel strip.

[0002]

2. Description of the Related Art In hot rolling of a steel strip, a work roll of a rolling mill wears only in a portion where the steel strip passes as the rolling progresses, and the surface profile of the roll becomes concave, and subsequently, the width becomes wide. When the steel strip is rolled, there is a problem that a normal sectional profile cannot be obtained. FIG. 1 shows a conceptual diagram of a roll profile after a certain amount of rolling, and an abnormal cross-sectional profile (b) obtained when a wide steel strip is rolled using the roll.

[0003] Under the above-described conditions, a so-called coffin schedule method has long been adopted as a rolling sequence plan for hot rolling. FIG. 2 shows an example of the coffin schedule. In the coffin schedule, after the rolls are changed, the steel strips with several widths are sequentially expanded from the narrow one to the maximum width (a in the figure), and then the whole is sequentially shifted from wide to narrow (b in the figure). The rolling order is determined so as to avoid the influence of wear caused by the preceding steel strip.

According to this method, the influence of the concave profile due to the abrasion of the roll is avoided, but since the rolling order is strictly controlled by the width, recent energy-saving techniques such as hot charging and direct roll combined with the previous process are adopted. In this case, the scale of one schedule was reduced, and the frequency of changing rolls was increased.

[0005] In response to this problem, in recent years, an online roll polishing apparatus for continuously polishing a roll in a rolling mill and maintaining an initial profile of the roll has been put into practical use. The online roll polishing aims to prevent a concave roll profile due to the progress of roll wear, and to enable a wide steel strip to be rolled after a narrow steel strip is rolled. An example of roll profile control will be described.

In the figure, A is an example in which no online roll polishing is applied, and the roll is worn in a concave shape according to the width of the rolled steel strip, and B is a portion through which material does not pass due to online roll polishing. This is an example in which the initial roll profile is maintained by polishing the substrate.

FIG. 4 shows an example of an on-line roll polishing apparatus, wherein 1 is a cup-shaped grindstone, 2 is a grindstone pressing cylinder, and a polishing apparatus comprising a grindstone 1 and a cylinder 2 is oscillated in the roll axis direction by a grindstone rocking apparatus (not shown). Move. FIG. 5 shows an example in which the on-line roll polishing apparatus of FIG. 4 is installed in the three subsequent stands of the hot finishing mill group.

As described above, by applying the online roll polishing, it is not necessary to consider the influence of the wear profile of the roll when the width of the rolling schedule is shifted, and the rolling order of the steel strip does not need to be greatly restricted by the width. The scale of the rolling schedule can be increased three to five times as much as before while hot-charging the raw material supplied from the process.

FIG. 6 shows an example of the configuration of a rolling schedule after such an online roll polishing is applied, and Table 1 shows its effects. On average, the scale of the rolling schedule is 4.2 times larger than that of the conventional rolling schedule.
° C.

[0010]

[Table 1]

[0011]

However, as shown in Table 1, the occurrence rate of abnormalities in the cross-sectional profile of the steel strip is 0.1%.
From 0.6% to 0.6%. The cause is described below. FIG.
In the schedule shown in FIG. 5, there is a case where a large number of the same widths are continuously rolled as shown by A or B in the figure. As a result of the increase in the schedule size, the number of continuous lines reaches 30 to 90 lines. FIG. 7 shows a change in the profile of the roll and the profile of the steel strip to be rolled at that time, starting from the first roll.

After the start of the rolling of the steel strip, the width of the steel strip is gradually affected by the heat, and a difference in expansion between the roll and the part having less heat influence in the body length direction appears. As the same width rolling increases, the convex thermal crown becomes remarkable, and as a result, the profile of the steel strip gradually changes from a normal convex shape to a concave shape, and the edge of the plate becomes thicker at around the 20th line. This makes the profile unsuitable for the next step, cold rolling.

In order to solve this profile failure,
For example, in the example of FIG. 7, a method of replacing the roll at the fifteenth roll and rolling the roll with a new roll having no thermal expansion, or performing rolling by 5
A method of cooling the entire roll after stopping for 10 minutes can be considered, but it is not preferable in terms of rolling efficiency, roll cost, and the like. The present invention provides a method of reducing the occurrence rate of abnormalities in the profile of a steel strip cross section by preventing a reduction in rolling efficiency and an increase in roll cost when 30 to 90 steel strips having the same rolling width are continuously rolled. Is what you do.

[0014]

The gist of the present invention is as follows. When using a hot finish rolling mill installed with an online roll polishing device to prevent changes in the roll profile due to abrasion of the material passing through the rolled material, when continuously rolling many steel strips of the same rolling width A hot finish rolling method comprising rolling at least one steel strip 150 mm or more wider than the width of the steel strip so that the steel strip is not rolled more than 20 consecutively.

Hereinafter, the present invention will be described in detail. As a result of analyzing many changes in the roll profile as shown in FIG. 7 occurring during rolling, the inventors mixed a steel strip wider than the width while the same steel strip was continuous, and rolled the steel strip. It has been found that the thermal crown as shown in the typical fifteenth to twentieth lines of FIG.

For example, FIG. 8 shows the relaxation state of the thermal crown when 10 pieces of the same width are rolled and 3 pieces of the wider width are rolled. The crown is almost near the initial state.

As described above, by appropriately inserting and rolling a steel strip having a wider width during the same width rolling, the steel strip having the same width can be continuously rolled without any profile abnormality. In this case, the effect can be obtained if the wide material inserted is 150 mm or more wider than the width of the continuous steel strip.

The reason why the strip profile is improved by rolling a wide material having a width of 150 mm or more is as follows. FIG. 9 shows a model of the heat balance of the roll during rolling.
As shown in the figure, there are a part that absorbs heat from the steel strip and a part that is water-cooled as a whole. A, B, in the roll body length direction
When divided into zones C, part A is cooled by the heating and cooling water from the steel strip, but there is almost no heat flow in the width direction, and part B has a large temperature gradient in the width direction and has a large temperature gradient in the width direction. This is a portion where heat flows, and is generally in the range of the steel strip edge position ± 150 mm. The portion C is a portion where cooling is dominant and the temperature is low and there is no flow of heat in the width direction. As a result, the temperature distribution in the roll body length direction (width direction) is as shown in FIG. Will be similar to

Therefore, for a steel strip having the same rolling width W, 150
By rolling a steel strip having a width of mm, the temperature distribution in zones A, B, and C in FIG. 10 shifts toward a temperature distribution shifted by 75 mm to the left and right, respectively. Thermal crown is reduced. For this reason, when W steel strip is rolled, its cross-sectional profile is improved.

[0020]

FIG. 5 shows an on-line roll polishing apparatus arranged on upper and lower work rolls of the latter three stands as shown in FIG. 5 to check the change of the roll profile due to the abrasion of the material passing portion as shown in FIG. In a rolling schedule of FIG. 6, 80 steel strips having the same width of 900 mm are continuously rolled at the A section of FIG. When 80 steel strips of the same width of 750 mm were continuously rolled at the part B, the abnormal rate of the steel strip cross-sectional profile was 0.6%.

On the other hand, in the part A of FIG.
Every 15 rolls of 0 mm of the same width are rolled, three rolls of 150 mm wider 1050 mm are rolled, and 80 rolls of the same width of 750 mm are continuously rolled.
Each time 15 steel strips of the same width of 50 mm were rolled, three steel strips of 150 mm wide and 900 mm wide were rolled. In the example of the rolling schedule configuration shown in FIG. 6, the abnormal rate of the steel strip cross-sectional profile was 0.1%. became.

In section A of FIG. 6, in which 80 steel strips having the same width of 900 mm are continuously rolled, every time 20 steel strips having the same width of 900 mm are rolled, 1050 mm is widened by 150 mm.
In section B, in which one steel strip of the same width of 750 mm is continuously rolled and 80 steel strips of the same width of 750 mm are continuously rolled, each time 20 steel strips of the same width of 750 mm are rolled, 900 mm is widened by 150 mm.
When one steel strip having a width was rolled, in the example of the rolling schedule configuration shown in FIG. 6, the abnormal rate of the steel strip cross-sectional profile was 0.3%.

[0023]

As described above, according to the hot finish rolling method of the present invention, the occurrence rate of abnormal profile of the steel strip cross section can be greatly reduced.

[Brief description of the drawings]

FIG. 1 shows a conceptual diagram of a roll profile after a certain amount of rolling and an abnormal cross-sectional profile obtained when a wide steel strip is rolled using the roll.

FIG. 2 is an explanatory diagram of a coffin schedule.

FIG. 3 is an explanatory diagram of a roll profile by applying an online roll.

FIG. 4 is an explanatory diagram of an example of an online roll polishing apparatus.

FIG. 5 is an explanatory diagram of an example of the arrangement of an online roll polishing apparatus in a continuous hot finishing mill.

FIG. 6 is an explanatory diagram of a configuration example of a rolling schedule after application of online roll polishing.

FIG. 7 is an explanatory diagram of a change state of a roll profile and a cross-sectional profile of a steel strip when a large number of steel strips having the same width are continuously rolled.

FIG. 8 is an explanatory view of the state of relaxation of the thermal crown when 10 pieces of 930 mm width are rolled and 3 pieces of 1200 mm width 270 mm wider than the width are rolled.

FIG. 9 is a heat balance model diagram of a roll during rolling.

FIG. 10 is an explanatory diagram of a temperature distribution in a roll body length direction after rolling.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-120266 (JP, A) JP-A-62-64406 (JP, A) JP-A-61-219211 (JP, A) 5370 (JP, B2) JP-B 60-5371 (JP, B2) JP-B 5-57043 (JP, B2) JP-B 56-17161 (JP, B2) (58) Fields surveyed (Int. Cl. ⁶ , DB name) B21B 1/00

Claims (1)

(57) [Claims] 1. A hot finishing mill in which an on-line roll polishing device is installed to prevent a change in roll profile due to abrasion of a material to be rolled, so that steel strips having the same rolling width are continuously formed. Hot rolling, wherein at least one steel strip having a width of 150 mm or more than its width is rolled in the middle so that the steel strip is not rolled more than 20 consecutively when performing multiple rolling. Rolling method.