JPH01258802A - Method for hot finish rolling - Google Patents

Abstract

PURPOSE:To perform strong draft rolling with a high yield by continuously performing finish rolling by joining the rear end of a preceding rough bar and the top end of a succeeding rough bar and bringing a friction coefficient between a work roll and a rolled stock not to be larger than a specific value at down stream side stands in a finish rolling mill line. CONSTITUTION:A rough bar 11 rolled by a rough rolling final stand 1 is wound on a winder 2 into a coil, is rewound by a rewinder 3, and is joined with the rear end of a precedently finish rolled rough bar 12 by a joiner 4. A looper 5 for rough bars is installed and the rear end of the preceding bar 12 is temporarily stopped. A finish rolling mill line 6 is composed of seven mill stands and lubricating devices 7 are installed in the inlet side of the last two stands respectively to supply a lubricant to work rolls. Hot highly lubricated rolling is performed with a friction coefficient between work rolls and a rolled stock is <=0.2. A strip rolled to have a prescribed sheet thickness is wound on a down coiler 10 after cooling in a coolzone 8. Thus, a rolling limit of downstream side stands of a hot finish rolling mill line is improved and strong draft rolling is performable.

Description

DETAILED DESCRIPTION OF THE INVENTION B) Industrial Field of Application The present invention relates to a hot finish rolling method for obtaining a hot rolled copper strip by finish rolling a rough bar rolled by a row of rough rolling mills. It is.

(B) Prior art Usually, when producing hot rolled steel strip with a thickness of 1.2 to 5 m, continuous casting equipment is used to produce a hot rolled steel strip with a thickness of 200 to 300 am and a width of 1000 to 2.0 m.
A slab of approximately 0001 in length is produced, and this slab is cut into a length of approximately 101 in a continuous casting line. The cut slab is
The hot rolling process is still being transported and heated to a predetermined temperature (1050°C) in a heating furnace.
~1200°C), then continuous rolling or reverse rolling is performed using several rough rolling mills to obtain a thickness of 30°C.
It is rolled to about ~50w, and then finished into a hot-rolled steel strip with a thickness of 1.2 to 5 mm in a finishing mill line of 6 to 7 stands.

In particular, the rolling reduction rate is 30 to 50 at the stand upstream of the finishing mill row.
%, and is usually rolled at a reduction rate of 15 to 30% at the downstream stand. However, in recent years, there has been an increase in the demand for thinner ordinary steel (thickness 1.2 mm or less), and low-temperature rolling is required to improve the mechanical properties (e.g. elongation, γ value, etc.) of hot-rolled steel strips even at ordinary thickness. In addition, there is an increasing need for strong reduction rolling that performs rolling at a reduction rate higher than that of conventional methods, and there is a need to increase the capacity of hot rolling finishing mills, especially the strong reduction capacity of downstream stands.

The rolling limit of normal hot plate rolling is determined by rolling load/rolling torque limitations and motor power limitations due to strength constraints of a rolling mill such as the strength of rolling rolls. therefore,
As the deformation resistance of the rolled material increases, the wider the width, or the faster the rolling speed, the lower the rolling limit becomes.

Further, as the rolled material becomes thinner, the flattening deformation of the work rolls in contact with the rolled material becomes larger, and the rolling load increases, so that the reduction limit for thin material rolling decreases.

A method of reducing the diameter of work rolls to reduce rolling load and rolling torque in order to increase the intensity of rolling in a finishing rolling mill, and using indirect drive to ensure rolling torque when rolling small diameter work rolls, or There is a method of increasing the rolling load limit by increasing the strength of the rolling mill including the rolls, and increasing the rolling torque limit by improving the strength of the drive system and motor/plow. However, in either case, major equipment modification is required and it is not possible to improve the width of the rolling limit.

In addition to the above-mentioned method, as a method for achieving strong rolling reduction in a hot rolling mill, there is a method of using a hot lubricant, reducing rolling load and rolling torque, and improving the rolling reduction limit.

This method requires few equipment modifications and is very inexpensive. However, in order to significantly reduce the rolling load and rolling torque, it is necessary to use a lubricant with high lubricity (that is, the coefficient of friction between the work roll and the rolled material is very small). , rolling instability phenomena such as poor biting of the tip of the rolled material and occurrence of slip between the rolled material and the work rolls become a problem.

As a countermeasure to this problem, as shown in Japanese Patent Application No. 62-73831, a rolling material buckling prevention guide is installed at the entrance side of the rolling mill.
There is a method of applying pushing force when biting. However, in the finishing rolling mill feed downstream stand, buckling occurs even with a small pushing force because the plate thickness is thin, and the rolling is unsteady at the time of biting, making it difficult to control the pushing force with high precision. It turned out to be very difficult to carry out indentation rolling in the downstream stand.

(c) Problems to be Solved by the Invention The problems to be solved by the present invention are to significantly reduce the load and torque, and to reduce the heavy rolling force even when the plate thickness is thin, such as when rolling in a stand downstream of the finish rolling mill. In order to realize rolling,
To obtain a hot finish rolling method that enables stable operation without causing sheet threading problems such as poor biting or rolling instability phenomena such as slip between rolls even when a highly lubricating lubricant is used. .

(d) Means for Solving the Problems The hot finish rolling method of the present invention is a method for obtaining a hot rolled steel strip by hot finish rolling a rough bar rolled by a row of rough rolling mills in a row of finishing mills. , the trailing end of the leading rough bar and the tip of the succeeding rough bar are sequentially joined, and the hot height is set such that the coefficient of friction between the work roll and the rolled material is 0.2 or less in the downstream stand of the finishing rolling mill row. The above problem is solved by means of lubricated rolling.

(E) Effect The present inventors investigated highly lubricated rolling at the downstream stand of the finishing rolling mill, and found that in rolling at the downstream stand where the plate thickness is approximately 10 W or less, the rolled material on the entrance side of the stand is normally Even when such a low tension is applied, no slip occurs between the rolls and the rolled material, and in order to achieve highly lubricated rolling, it has been found that resolving the biting defects is the biggest issue. .

In order to solve the problem of biting, it is possible to pass the tip of the rolled material without applying lubricant. However, in this case, due to load and torque constraints, it is necessary to reduce the rolling of the tip lightly, that is, to thicken the thick plate at the tip. Therefore, the yield is significantly reduced in the conventional hot rolled steel strip manufacturing method. As a countermeasure for this, if the rough bars before finish rolling are connected and the finish rolling is made continuous, only the leading rough bar is threaded at the leading end, and a decrease in yield can be prevented.

Figures 2 and 3 show the relationship between the friction coefficient between the work roll and the rolled material, the rolling load of the finishing downstream stand, and the motor power.The rolling conditions were as follows: work roll diameter 750
m, rolling reduction rate 50%, plate width 1250 mm, finishing temperature 900℃
It is. The finishing speed for 3.2 m thick finished material is 460 r
e /1n, finishing speed of 1.2B thick finishing material is 600 m
/win As shown in Figure 6, in the case of 3.2 thick finished material, the friction coefficient between the rolled material and work roll is set to 0.2 or less due to motor power constraints, and 1.2 e
For UA thick finished materials, the friction coefficient is set to 0 due to rolling load constraints.
．． Must be 15 or less.

As a result of further various studies, we found that in order to achieve a 40-50% reduction in normal material at the downstream stand of the finishing mill,
It has been found that the coefficient of friction between the work roll and the rolled material needs to be 0.2 or less.

When highly lubricated rolling is carried out where the friction coefficient between the work roll and the rolled material is 0.2 or less, as mentioned above, the downstream stand will suffer from poor biting, and when the tip of the rolled material passes through. must be rolled without lubricant. In this case, it is necessary to increase the plate thickness due to load torque or motor power constraints, and in normal rolling,
Yield is significantly reduced due to poor tip plate thickness. For this reason, by connecting the rough bars before finish rolling and making the finish rolling continuous, the occurrence of sheet thickness defects is limited to only during rolling of the first rough bar, thereby achieving a significant improvement in yield.

(f) Example An embodiment of the present invention will be described with reference to FIG.

The rough bar 11 rolled by the final stand 1 of the rough rolling mill is wound into a coil shape by the winder 2. The rough bar 11 that has been wound is unwound by the unwinder 3 and joined 814.
As a result, it is joined to the rear end of the rough bar 12 which is finish-rolled in advance. In order to stop the rear end of the preceding rough bar 12 during joining, a rough bar looper 5 is installed on the entry side of the finishing rolling mill row 6.

The finishing rolling mill row 6 of this embodiment is composed of seven rolling stands, and the last two stands carry out lubricated rolling. The lubricating device 7 is installed on the entrance side of each of the final two stands, and supplies lubricant during rolling by applying it to the work rolls.

The copper strip that has been finish rolled to a predetermined thickness passes through a cooling zone 8 and is cooled to a predetermined winding temperature, and then is wound up by a down coiler 10. After the coil reaches a predetermined weight, it is cut by the copper band cutting machine 9, and winding is started again by another down coiler.

In order to clarify the effects of the present invention, the results of a comparative study of the rolling limits of the final two finishing stands during normal rolling and lubricated rolling according to the present invention are shown in Table 1, with a work roll diameter of 750 W.
The F6 and F7 stands are made of low carbon steel with a thickness of 3.2m.
6 In normal rolling, the reduction rate is 40% and the rolling load is 250°C.
When the lubricated rolling of the present invention is carried out, the rolling load is about 2000 tons even with a rolling reduction of 50%, and the total motor power of the F6 stand and F7 stand is about 2000 tons, which is the rolling limit. It is slightly smaller than when the pressure is reduced by 40%.

Table 1 (G) Effects According to the present invention, the rolling limit of the downstream stand of the hot rolling finishing mill row is improved and heavy reduction rolling becomes possible, so that the hot rolled steel strip can be made thinner or the mechanical properties can be improved. is realized. Also,
There are few thickness defects at the tip of the rolled material, and heavy reduction rolling with a high yield is possible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention, and FIGS. 2 and 3 are graphs showing the effects of lubricated rolling. 1: Rough rolling mill 2: Rough bar winder 3: Rough bar unwinder 4: Rough bar joining machine 5: Rough bar/louver 6
: Finishing mill row 7: Lubricant supply device 8: Cooling device 9: Steel strip cutting machine 10: Down coiler patent applicant
Sumitomo Metal Industries, Ltd. (4 others)

Claims (1)

[Claims] In a method for obtaining a hot-rolled steel strip by subjecting a rough bar rolled by a rough rolling mill row to hot finishing rolling in a finishing rolling mill row,
Finish rolling is made continuous by sequentially joining the rear end of the leading rough bar and the tip of the following rough bar, and the coefficient of friction between the work roll and the rolled material is 0.2 or less in the downstream stand of the finishing rolling mill row. A hot finishing rolling method comprising performing hot highly lubricated rolling to achieve a high lubricity.