JPH0534083B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention is directed to a cast iron with a thickness of 20 to 50 mm manufactured by a continuous casting method.
This invention relates to a heavy reduction rolling mill for producing a hot rolled steel strip by strongly reducing a thin cast slab of 1 mm in diameter.

(b) Prior Art In recent years, due to technological improvements in continuous casting, thin slabs with a thickness (20 to 50 mm) that is a fraction of the conventional thickness have been manufactured. There is a desire to develop a compact rolling mill that can roll this thin slab into hot rolled steel strips at low equipment costs.

As an alternative to the usual hot strip mill, there are rolling mills consisting of planetary mills and planishing mills. Although this rolling mill is cheaper than a hot strip mill and suitable for small-scale production, planetary mills are mechanically dependent on forging using rolls, which generates extremely loud noise, and the edge of the rolled material Since it is V-shaped, it has to be trimmed, which has the disadvantage of lowering yield.

In the conventional four-layer inter-rolling mill shown in Fig. 1,
When strong reduction rolling with a reduction ratio of 70 to 90% is performed in one pass, the rolling load and rolling torque become extremely large, resulting in insufficient power and strength of the rolling mill, making rolling impossible. Therefore, work roll 1a,
If the diameter of 1b is made small, the rolling load and rolling torque are significantly reduced, but two new problems arise when the work roll is made small in diameter.

First, the first problem is that the biting angle α of the tip of the rolled material 2 increases, making biting impossible. The second problem is that when using a work roll driven rolling mill like a normal rolling mill, it is impossible to transmit the required rolling torque with the roll shaft diameter of the small diameter work roll. . This is because the effect of reducing the rolling torque by reducing the diameter of the work roll is approximately inversely proportional to the diameter of the roll barrel portion, while the transmittable torque is approximately inversely proportional to the cube of the roll shaft diameter. and,
Normally, the diameter of the roll shaft is approximately proportional to the diameter of the roll barrel, making it impossible to drive small-diameter work rolls.

As a solution to these problems, there is a method of applying indentation stress on the entry side of the rolled material. Generally, as a measure to improve the biting property, the indentation stress σ is 1Kg/
It has been found that a dose of less than mm ² is sufficiently effective.
On the other hand, the effect of the indentation stress as a countermeasure to the second problem described above is that the rolling torque is reduced by applying the indentation stress at the entrance side of the rolling mill.

For example, we investigated the case where a thin slab of 1250 mm wide, 30 mm thick, and heated at 1000°C was rolled with a work roll of 300 mm in diameter at a reduction rate of 73%. As a result, as in normal rolling, when the indentation stress σ = 0, the required rolling torque G ₀ for the two upper and lower rolls is 115 tons・
It was m. On the other hand, the required rolling torque for two upper and lower rolls when indentation stress σ = 6Kg/mm ² is applied.
G ₁ is 100ton°m. Therefore, σ=6Kg/
In the case of mm ² , there is a rolling torque reduction effect of 13% compared to the case of σ=0.

However, in this case, it is impossible to apply these rolling torques from the work roll shaft, and backup roll drive has to be used. In this case, slippage between the work roll and the backup roll becomes a practical problem.

The minimum friction coefficient μmin required to transmit this rolling torque from the back-up roll to the work roll is given by the following formula.

μmin=G/PD……(1) Where, G: Required rolling torque (for 2 rolls) P: Rolling load D: Work roll diameter In this case, as mentioned above, indentation stress is applied on the entry side. Then, as described above, the rolling torque G decreases and the rolling load P increases. Therefore, (1)
μmin in the equation decreases considerably with the addition of indentation stress.
Actually, when the μmin value of equation (1) was examined under the above rolling conditions, the results were as follows: σ=0, μmin=0.13 σ=6Kg/mm ² , μmin 0.10. The fact that μmin is small means that slips between rolls will not occur if the friction coefficient μ between the rolls that can actually be expected is larger than the above μmin value, and the improvement effect from μmin = 0.13 to 0.10 is actually quite large. .

Further, other effects when applying indentation stress on the entry side include the following. Normally, when heavy reduction rolling is performed, an unstable rolling phenomenon called a slip phenomenon occurs. This slip phenomenon means that the advance ratio of the material to be rolled relative to the work roll becomes smaller, and eventually the exit speed of the material to be rolled becomes smaller than the circumferential speed of the roll (in this case, the advance ratio becomes negative).
It is a phenomenon. Although this slip does not occur, in heavy reduction rolling, the material to be rolled becomes unstable in the roll axis direction, meandering occurs, and there is a strong tendency for camber (sideways curved shape) to occur on the exit side. It is possible to exert a stabilizing effect on the unstable phenomenon of the rolled material including slips by adding the application of entry side pushing. That is,
When an indentation stress is applied to the slip on the entry side, the neutral point (the point where the speed of the rolled material and the roll speed match) shifts to the entry side, and the advance rate becomes positive and stabilized. Moreover, the meandering and camber of the rolled material are prevented by the effect of restraining the rolled material from moving in the roll axis direction due to the application of the pushing force on the entry side.

As mentioned above, in the case of heavy reduction rolling, it is effective to apply indentation stress on the entry side. However, as mentioned above, a relatively small indentation stress of less than σ = 1 Kg/mm ² is sufficient for the purpose of simply improving the biting property of the tip of the rolled material, but for reducing the rolling torque, σ = It is necessary to add a high indentation application of about 6 kg/mm ² .

As a method of applying such indentation stress, for example, as shown in Japanese Patent Publication No. 53-24172,
A method has been proposed in which compressive force is applied between two rolling mills (FIG. 2A). However, this method is completely unsuitable for the purpose of strongly reducing thin slabs as in the case of the present invention, and for cases where a high value of indentation stress is required as described above. That is, in such a method, the distance between the work rolls 3a, 3b of the rolling mill 3 and the work rolls 4a, 4b of the indentation rolling mill 4 becomes long, and as shown in FIG. Even when an indentation force of (for example, σ<1 Kg/mm ² ) is applied, buckling occurs in the rolled material 2, and a sufficient indentation force cannot be applied.

(c) Purpose of the invention The purpose of the present invention is to
The object of the present invention is to provide a high reduction rolling mill that can finish thin slabs of 20 to 50 mm into hot rolled steel strips using inexpensive equipment.

(D) Structure of the Invention The strong reduction rolling mill for thin slabs of the present invention comprises a pair of feed rolls and a multiple roll installed on the exit side of the rolls and having a pair of small diameter work rolls. , a common housing that supports the feed roll and the multiple rolls, and a roller guide that is installed between the feed roll and the multiple rolls and curves the material along the traveling direction of the material to be rolled. It is made up of

In the hard reduction rolling mill of the present invention, high indentation stress is applied to the rolled material at the entrance side of the multiple rolls without causing buckling in the rolled material between the feed roll and the multiple rolls. This makes it possible to bite the tip of the rolled material, and
The rolling torque of the multiple rolls is reduced to prevent slips between the rolls of the multiple rolls.

Next, the structure of the high reduction rolling mill of the present invention will be explained with reference to FIG. The multiple roll 10 is made up of a pair of small diameter work rolls 11a, 11b and a pair of backup rolls 12a, 12b. A pair of feed rolls 13a and 13b are installed on the inlet side of the multiplex roll 10. multiple rolls 10 and feed rolls 13a;
13b is installed in the housing 14 of the rolling mill. Multiple roll 10 and feed roll 13
a, 13b, there are roller guides 9, 23,
26 and 27 are provided. Upper backup
Roll 12a and upper feed roll 13
The reduction amount of a is adjusted by reduction screws 18 and 19, respectively.

The material to be rolled 2 is fed by feed rolls 13a, 13.
After being rolled at a reduction rate of 10 to 50% at step b, it is bent downward by the roller guide 23 closest to the roll exit side.
The course is corrected by the roller guides 26, 27 and the roller guide 9 installed on the entry side of the work rolls 11a, and the work rolls 11a, 11b
Embarrassed. The material to be rolled 2 is placed between the feed rolls 13a, 13b and the work rolls 11a, 11b to reduce the yield stress of the material to be rolled by appropriately adjusting the speed of drive motors (not shown) for both rolls. Apply a small compressive force (indentation stress). In addition, in this case, as for the curved shape of the rolled material 2 between both rolls, the maximum curve amount Δl (Fig. 3) is 200 mm.
The following shall apply.

The purpose of providing such a curved shape is to prevent buckling of the rolled material. Regarding this point, the effects of experimental studies are shown below.

Figure 4 shows an outline of this experimental apparatus. Roll diameter
A hydraulic jack 29 is installed as a pushing device on the entry side of the 130 mm double roll 28, and this roll 28
and the pushing device 29 from the center of the roll to the entry side 70
Five roller guides 30 with a diameter of 30 mm were used and arranged at a pitch of 45 mm starting at a position of mm. The experiment was conducted with a roll gap of 5 mm, a plate thickness of 8 mm, and a plate width of 80 mm.
mm, roll 2 only the tip of hot steel plate 31 at 900℃
After rolling at 8, the rolls 28 were stopped, the hot steel plate 31 was curved downward as in the roller guide 30, and compressive force was applied until buckling occurred.

FIG. 5 shows the results when a pushing force was applied with the distance l between the roll 28 and the tip of the pushing device 29 being 370 mm. The horizontal axis in Figure 5 represents the maximum curvature Δl shown in Figure 4, and the vertical axis represents buckling.
Indicates the critical stress σ. The x mark in the diagram is the roller guide 3
This shows the buckling limit stress when an indentation force is applied to a hot steel plate without using 0.

The bending moment of each part between the roll 28 and the pushing device 29 is proportional to the product of the amount of curvature and the pushing force at each position, so if the maximum amount of curvature Δl is too large, buckling is likely to occur. The critical stress σ decreases.

As is clear from this experimental result, in Fig. 3, a roller guide is installed only in the lower part, and the material to be rolled 2 is given an appropriate downward convex curvature, and the material to be rolled is rolled with these roller guides 26 and 27. If material 2 is held, feed rolls 13a, 13b and workpiece
A considerably large indentation stress can be applied without buckling the rolled material between the rolls 11a and 11b. When applying a larger pushing force,
As the indentation stress increases, the bending moment gradually increases near the roll bite where the curvature is large. Therefore, if we assume that there is no roller guide 23, the feed roll 13 will eventually
Buckling occurs in the rolled material between a, 13b and the roller guide 26 or between the work rolls 11a, 11b and the roller guide 27. That is, Laura
The guide 23 not only gives the rolled material 2 a curved shape, but also has the effect of preventing buckling between the feed rolls 13a, 13b and the roller guide 26. Similarly, in order to prevent buckling of the rolled material between the work rolls 11a, 11b and the roller guide 27, the work rolls 11a,
It is also effective to install a roller guide 9 on the entrance side of 11b.

Taking this point into consideration, we also conducted various experiments regarding plate thickness and indentation length. As a result, the thickness
When rolling a hot thin slab of 20 to 50 mm with the high reduction rolling mill of the present invention, the distance between the feed roll and the multiple rolls (1 to 2 m) and the thickness (10 to 30 mm)
mm), it was found that the maximum amount of curvature ∆l is appropriate to be 200 mm or less. When Δl exceeds 200 mm, the change in curvature of the rolled material near the roll bite becomes excessive, and the bending moment becomes large in this area, causing buckling of the rolled material.

By the way, when giving a downwardly convex curved shape to a rolled material, as shown in FIG.
It is preferable that the guide 23 is installed below the upper feed roll 13a (ΔB=0 to 600 mm). The method of installing the roller guide 23 is as follows.
As shown in FIG. 6, it is preferable to install the non-driving roll 23 on a stripper guide 24 installed on the exit side of the feed roll 13a.
51-149152).

So far, we have talked about the structure of a rolling mill, focusing on the case where roller guides are installed at the top and bottom (Figure 3), and in particular how to prevent buckling by giving the rolled material a downwardly convex curved shape. The same buckling prevention effect can be obtained even if a convex curved shape is given in the same way.Also, when the pushing force is small, rollers are applied only in the direction that gives the curved shape, that is, the upper or lower part.
Experiments have shown that simply installing a guide can provide a sufficient buckling prevention effect.

(e) Example This is the same mechanism as the rolling mill shown in FIG. Work rolls 11a, 11b with roll diameter 300mm, roll body length 1700mm, roll diameter 1200mm, roll body length
A four-layer roll 21 consisting of 1700 mm back-up rolls 12a and 12b, and a roll diameter
Feed roll 1 with 1000mm and roll body length 1700mm
3a and 13b are built into the same housing. Work rolls 11a, 11b
and the feed rolls 13a, 13b.
A thin slab having a thickness of 40 mm and a width of 1250 mm was hot rolled using a rolling mill equipped with roller guides 23, 26, 27 of 200 mm and a roller guide 9 of 100 mm in diameter.

As a result, a maximum rolling reduction of 80% was obtained without buckling, and it was possible to roll the steel to a thickness of 8 mm. Feed rolls 13a and 13b at that time
The reduction amount of feed roll 13 is 15 mm.
The circumferential speeds of a, 13b and work rolls 11a, 11b are 8.8 m/min and 26 m/min, respectively.
Further, the indentation stress α was 5 Kg/mm ² .

FIG. 7 shows another embodiment of the invention. In this embodiment, the roll for heavy pressure is a 6-layer roll. In this case, the intermediate rolls 14a, 14b are
As shown in the figure, by forming a pair of rolls with a smaller diameter at one end of the rolls and shifting them in the roll axial direction according to the width of the rolled material 2,
Work roll 11 due to rolling load and compressive force
The deflection of a and 11b can be reduced.

Note that the rolls having the shape shown in FIG. 8 are used as work rolls 11a and 11b of the four-layer type roll shown in FIG.
If the roll is used for rolling and shifted in the axial direction of the roll, it is effective to reduce the amount of plate crown and edge drop, which represent non-uniform thickness distribution in the width direction after rolling.

Furthermore, in Fig. 9, the feed roll is a four-layer roll with a relatively large work roll diameter, and the work rolls 25a and 25b are offset in the direction of the exit side, so that the direction of the resultant force of the rolling load and the compression force is changed. ,
By directing the back up rolls 13a and 13b in the direction of the line connecting the axes of the work rolls 25a and 25b, effective indentation rolling can be achieved. work rolls 11a, 11 of rolls for
b, and the distance between the axes of 25a and 25b can be shortened.

Next, an embodiment in which the high reduction rolling mill of the present invention is installed on the outlet side of a continuous casting apparatus for thin slabs will be described below.

In FIG. 10, a hot thin slab 33 cast from a continuous thin slab casting machine 32 (for example, the continuous casting machine disclosed in Japanese Patent Application No. 57-30931) is in a state where it can be rolled in a high frequency heating furnace 34. Heat to . When the temperature of the thin slab 33 is high and the casting speed is high, the high frequency heating furnace 34 is not necessarily required, and a heat insulating cover may be sufficient. Next, the thin slab 33 is reduced to a predetermined width using a width reduction device 35, and then subjected to strong reduction using a strong reduction rolling mill 36 of the present invention shown in FIG. After being strongly rolled, the material to be rolled is cooled to a target coiling temperature in a cooling zone 37, and then coiled in a coiler 38.
Immediately before the coiler 38, there is a running cutting machine 39.
A running cutting machine 39 cuts continuously rolled strips.
It is cut to a predetermined length and wound alternately around two coilers.

At the line shown in Figure 10, the thickness is 40 mm and the width is 40 mm.
It was possible to stably roll a 1250 mm thin slab to a thickness of 7 mm at the exit side using a high reduction rolling mill. Also, thickness 20
A thin slab with a width of 1250 mm could be stably rolled to an exit thickness of 3 mm.

(f) Effect As is clear from the above examples, the rolling mill according to the present invention can perform heavy reduction rolling with one stand, so the rolling line can be simplified and the rolling mill can be manufactured using the continuous casting method. Thin slabs with a thickness of 20 to 50 mm can be rolled into hot strips with low investment costs.
In addition, structurally, there are no problems such as noise or lower yields as with planetary mills. Furthermore, the temperature drop of the rolled material can be minimized, and heating energy can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional four-layer rolling mill. FIG. 2 is an explanatory diagram when indentation rolling is performed using a conventional rolling mill. FIG. 3 is a side view of the high reduction rolling mill of the present invention. FIG. 4 is an explanatory diagram of the experimental equipment used to study buckling of rolled materials. FIG. 5 is a graph showing experimental results obtained with the apparatus shown in FIG. 4. FIG. 6 is a partially enlarged view showing an example of installing a roller guide. FIG. 7 is an explanatory diagram showing another embodiment of the present invention. FIG. 8 is a schematic diagram showing the shape of the intermediate roll of the six-layer roll shown in FIG. 7. FIG. 9 is an explanatory diagram showing another embodiment of the present invention. FIG. 10 is an explanatory diagram showing an embodiment in which a high reduction rolling mill of the present invention is installed on the outlet side of a continuous thin slab caster. 2: Rolled material, 11a, 11b: Work roll, 10: Multiple rolls, 12a, 12b: Backup roll, 13a, 13b: Feed roll.
Roll, 14a, 14b: Intermediate roll, 18,1
9: Press down screw, 9, 23, 26, 27, 3
0: Roller guide, 24: Stripper guide, 25a, 25b, 28: Work roll, 2
9: Hydraulic jack, 32: Thin slab continuous casting machine, 3
3: hot thin slab, 34: high frequency heating furnace, 35: width reduction device, 36: strong reduction rolling mill, 37: cooling zone,
38: Coiler, 39: Running cutting machine.

Claims (1)

[Claims] 1. A pair of feed rolls, a multiple roll installed on the outlet side of the rolls and having a pair of small diameter work rolls, a common housing supporting the feed roll and the multiple roll, and a common housing for supporting the feed roll and the multiple roll. - A strong reduction rolling mill for thin slabs comprising a roller guide installed between rolls and multiple rolls to curve the material to be rolled along the traveling direction of the material.