EP0111865A2

EP0111865A2 - A different circumferential speed rolling mill

Info

Publication number: EP0111865A2
Application number: EP83112482A
Authority: EP
Inventors: Toshiyuki Kajiwara
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1982-12-13
Filing date: 1983-12-12
Publication date: 1984-06-27
Also published as: JPS59107703A; EP0111865A3; JPH0510161B2

Abstract

A different circumferential speed continuous rolling mill including a plurality of rolls (1,2,3,4;5,6,) including one roll cooperating with other rolls to roll a trip simultaneously at a plurality of rolling points to continuously roll the strip by rotating the one roll at a circumferential speed distinct from the circumferential speed of other rolls is equipped with a tension difference applying device (7,11,12;8) located in a path of travel of the strip between a first rolling point at which the strip is brought into contact with the one roll and rolled thereby and a second rolling point at which the strip is brought into contact with the one roll again and rolled thereby after clearing the first rolling point, so as to thereby create a difference in the tension applied to the strip between a portion of the strip located at an delivery end of the first rolling point and a portion of the strip located at an delivery end of the second rolling point. The tension difference applying device is operative to increase the tension applied to a portion of the strip located between the first rolling point of the one roll and the tension difference applying device and decrease the tension applied to a portion of the strip located between the tension difference applying device and the second rolling point of the one roll. Thus rolling energy can be fed to the strip not only from the rolls but also from the tension difference applying device to enable continuous rolling with a high degree of efficiency.

Description

FIELD OF THE INVENTION

This invention relates to different circumferential speed continuous rolling mill capable of increasing the rolling reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view of a four-high rolling mill of the prior art;
Fig. 2 is a schematic view of a different circumferential speed five-high rolling mill of the prior art;
Fig. 3a is a view in explanation of a rolling performed at a constant rolling speed referred to as an NR rolling;
Fig. 3b is a view in explanation of a rolling performed at a different rolling speed referred to as a PV rolling;
Fig. 3c is a view in explanation of a rolling performed at intermediate between those of the NR rolling and PV rolling which is referred to as an NPV rolling;
Fig. 4 is a schematic view of a continuous rolling system of the prior art;
Fig. 5 is a schematic view of an embodiment of the different circumferential speed continuous rolling mill according to the invention;
Fig. 6 is a schematic view of another embodiment of the different circumferential speed continuous rolling mill according to the invention;
Fig. 7 is a diagrammatic representation of the relation between the rolling speed and the coefficient of friction with reference to coolant oils;
Fig. 8 is a view in explanation of balancing of forces exerted in strip material being rolled by the rolling mill according to the invention;
Fig. 9 is a characteristic view showing allowable maximum rolling reductions in relation to rolling roll diameters;
Fig. 10 is a schematic view of a further embodiment of the different circumferential speed continuous rolling mill according to the invention; and
Fig. 11 is a schematic view of a still further embodiment of the different circumferential speed continuous rolling mill according to the invention.

DESCRIPTION OF THE PRIOR ART

In recent years, there has been a strong desire to convert production system from that of independent stands to that of a plurality of stands integrated into a single production line, to save power and labor. In this regard, installations have already been realized which are designed to provide facilities in a single production line for performing cold rolling, cleaning, annealing and temper rolling. In this case, the speed of the production line would largely be governed by the speed at which continuous annealing is performed. Generally, the rolling speed of a cold rolling mill is 3-5 times as high the speed at which annealing is performed from the point of view of economy. Thus, integration of cold rolling and annealing into a single line of production would rise to the problem that the speed at which rolling is effected would have to be reduced to an economically unacceptable level. To obviate this problem, it would be necessary to meet the economic requirement by reducing the number of groups of rolling mills or the number of stands of a standem mill.
_Fig. 1 shows a four-high rolling mill (hereinafter 4H mill) typical of rolling mills of the prior art. The 4H mill comprises upper and lower working rolls 1 and 2 supported by backing-up rolls 4 and 5 respectively to perform rolling between the upper and lower working rolls .1 and 2. Although not shown, the 4H mill further comprises other expensive equipment, including a roll stand, a screw-down device, a roll drive, etc. Thus, if an additional working roll were used with a 4H mill to enable rolling simultaneously at two rolling points as shown in Fig. 2, excellent economic effects could be achieved. However, there is some snag which stands in the way of realizing benefits from use of an additional roll for the aforesaid purpose. In performing rolling in a usual manner, the working rolls 1 and 2 or 2 and 3 which form a set have the same circumfernetial speed which is substantially equal to the delivery speed of a rolled strip and the entering speed of the roller strip is lower than the circumferential speed of the rolls by a magnitude substantially corresponding to the rolling reduction rate y. When rolling is performed by the rolling mill shown in Fig. 2, circumferential speeds v₁, v₂ and v₃ of the upper and lower working rolls 1, 2 and 3 respectively are equal to one another. Thus, the following relation holds:
Accordingly, v₁ = v₂ ⁼ v₃, and a strip to be rolled 10 by the working rolls 1 and 2 has a speed v_s2 which has the following relation:
The rolled strip 10 introduced to between the working rolls 2 and 3 has a speed v_s2' which has the following relation:
Thus, v_s2' ^< v_s2 and the rolled strip 10 will have a loop at the delivery end of the working rolls 1 and 2. This makes it necessary to use a loop car 6 for accommodating the loop of the rolled strip 10.
Assume that the rolled strip 10 delivered from the working rolls 2 and 3 has a speed v_s3 = 500 m/min, and a rolling reduction rate y of the working rolls 2 and 3 is y = 30%. Then, the speed V at which the loop car 6 should move while rolling is being performed can be expressed as follows:
Thus, the loop car should be moved at the speed of 75 m/min during rolling, making it impossible to use the loop car 6 with a production line for performing continuous rolling.
To eliminate this condition, the requirement vs2 = vs2' should be met. To this end, it is necessary that at least the relation v₃> v₂ or v₂ > v₁ should hold. This is already known as different circumferential speed rolling (PV).
To enable the invention to be better understood, the different circumferential speed rolling will be outlined. Fig. 3a shows constant circumferential speed rolling (NR) of the prior art in which the circumferential speed of the roll becomes equal to the speed of the rolled strip at a neutral angle ϕ in both the upper and lower working rolls. Let the neutral angles of the upper and lower working rolls be denoted by φ₁ and φ₂ respectively. Then the following relation holds:
In this case, a drive torque of the roll gives a tangential force F to a rolled strip by the friction between the rolls and the rolled strip. The force F is maximized as designated by F when φ₁ = φ₂ = 0. Assume that, when φ₁ = φ₂ > 0, a rolling pressure P and a coefficient of friction p between the rolls and the rolled strip are approximately constant during the time they are in contact with each other. Then, the following relation holds:
If φ₁ ⁼ φ₂ ⁼ φ, then the following relation holds:
In the PV rolling shown in Fig. 3b, the following equation can be obtained by substituting φ₁ = 6 and φ₂ = 0 equation (1):
Thus, it is not possible for the upper and lower rolls to conjointly give a tangential force to the rolled strip. That is, the rolls are incapable of supplying energy necessary for effecting rolling to the rolled strip, and instead the difference in the tension of the rolled strip between the entering and delivery ends of the nip of the rolls is utilized. This relation is expressed by the following equation:

where a_d, σ_e: tension (kg/mm²) of the rolled strip at delivery and entering end.
S : means deformation resistance (1 g/mm²) of the rolled strip.
y : rolling reduction rate

_d

_e

Fig. 3c shows NPV rolling which is intermediate between the NR rolling and PV rolling and intended to obviate the defects of the PV rolling while sacrificing its merits to a certain extent.
In this case, the tangential force F can be expressed, from equation (1), as follows because φ₂ = 0:
Since 8 ^> φ₁, F ^> 0.
When this process is used, it is possible to obtain a reduction in rolling load and perform different circumferential speed rolling without excessively increasing the tension of the strip.
Thus, if it is possible to perform different circumferential speed rolling, it is possible to perform continuous rolling in which the same roll simultaneously performs rolling at two rolling points without the risk of developing a loop. Fig. 4 shows the manner in which continuous rolling is performed by the NPV rolling process, in which the strip 10 to be rolled is successively rolled by the rolls 1, 2, 3 and 4 and, following completion of rolling, the strip 10 is wound on the rolls 2 and 3 to be rolled again. In this case, the PV rolling process and NPV rolling process may be used. It is not possible to use the NR process, as aforesaid. Table 1 summarized the characteristics of continuous rolling performed by the PV and NPV rolling processes.
In the rolling mill shown in Fig. 4 in which the PV continuous rolling process is used, the circumferential speeds v₁, v₂, v₃ and v₄ of the rolling rolls and the speeds v_s1. v_s2' ^v _s3 and ^v _s4 of the strip have the following relation:
Thus, in Fig. 4, when one considers the rolling torque, it will be seen that the roll 4 designated by #4 roll in Table 1 has a torque of plus 100 and the roll 3 designated by #3 roll in Table 1 has a torque of minus 100 at the rolling point R₃₄ and a torque of plus 100 at the rolling point R₂₃ with the effects of winding the strip on the roll 3 omitted. The results obtained with the rolls 2 and 1 are as shown in Table 1 by referring to #2 and #1 rolls respectively. Thus, the total torque of the four rolls becomes zero, and the energy necessary for performing rolling should be obtained by the difference in the tension given to the strip between the enternance and the delivery of the rolling point as shown by equation (4).
In normal rolling of the prior art, the rolling reduction rate is about 30 - 50%. If it is desired to perform three pass rolling simultaneously, then a rolling reduction of 66 - 87% corresponding to three pass rolling performed at the rate of 30 - 50% is desirable. If this rolling reduction is to be achieved only by the difference in tension applied to the strip, then the following relation is obtained from equation (4) and rupture of the strip might result:
Also, to keep the tension a_d at the level of 0.1S ~ 0.38S for normal stable rolling, the rolling reduction should be kept at a low level which would defeat the aforesaid purpose.
From the consideration set forth hereinabove, it will be seen that the PV continuous rolling process has little practical value. Then, let us consider the NPV continuous rolling process. This rolling process enables the intermediate rolls or #2 roll and #4 roll to supply positive energy to the rolling mill because these rolls have a torque of not +100 - 100 = 0 but a torque of over unity. It is necessary that a suitable value be selected for this torque or a circumferential speed in such a manner that no loop is formed by the strip on the delivery end of the rolling point or excessive slip of the rolls with respect to the strip is availed. Experiments were conducted on single pass different circumferential speed rolling. The results show that the rolling can be performed stably when the rolling torque on the low speed side is up to minus 50 while the rolling torque on the high speed side is kept at plus 100. Thus, if the torque on the minus side is kept at 50, then it is possible to obtain a rolling torque distribution shown in Table 2 in which it will be seen that the total torque is plus 150 and a critical slip force approximate to that of normal rolling is obtained in spite of the rolling being performed by varying the roll speed.
In Fig. 4 is shown a rolling mill in which the NPV continuous rolling process is incorporated. In this rolling mill, the following relation holds:
However, the following problem should be obviated to enable the NPV continuous rolling process to be put to practical use and achieved the desired results.
The problem is that, since the rolling is not performed by the NR rolling process, the rolling energy supplied to the rolls is below that corresponding to one pass of the rolling process of the prior art in spite of the fact that three pass rolling is performed. Thus, it is necessary to provide means for supplying additional rolling energy to the rolls to enable the desired results to be achieved by the NPV continuous rolling process.
Japanese Patent Laid-Open No. 39104/81 and Japanese Patent Laid-Open No. 111504/81 disclose a continuous rolling mill of the different circumferential speed type equipped with tension adjusting means for adjusting the magnitude of tension applied to the strip to be rolled between the rolling passes, to enable rolling to be performed at a high rolling reduction rate.
However, some disadvantages are associated with the tension adjusting means of the prior art. In the tension adjusting means described in the aforesaid documents, tension is successively given to the strip between the rolling passes. Thus, the larger the number of passes, the higher becomes the value of the tension because it is obtained by integration, thereby causing rupture of the strip. This defect makes it impossible to carry out continuous rolling of a large number of passes.

SUMMARY OF THE INVENTION

Accordingly, the object of this invention is to provide a different circumferential speed continuous rolling mill capable of supplying rolling energy of high magnitude to a strip between rolling passes, to enable continuous rolling with a high degree of efficiency.
According to the invention, there is provided a different circumferential speed continuous rolling mill comprising a plurality of rolls including one roll cooperating with other rolls to roll a strip simultaneously at a plurality of rolling points so as to continuously roll the strip by rotating the one roll at a circumferential speed distinct from the circumferential speed of other rolls, and tension difference applying means located in a path of travel of the strip between a first rolling point at which the strip is brought into contact with the one roll and rolled thereby and a second rolling point at which the strip is brought into contact with the one roll again and rolled thereby after clearing the first rolling point, to produce a difference the temperature of the strip between an delivery end of the first rolling point and an entering end of the second rolling point.
In the different circumferential speed continuous rolling mill of the aforesaid construction, it is possible to supply rolling energy to the strip not only from the rolls but also from the tension difference applying means, to enable continuous rolling with a high degree of efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the different circumferential speed continuous rolling mill in conformity with the invention will be described by referring to the accompanying drawings.
Fig. 5 shows one embodiment in which the different circumferential speed continuous rolling mill comprises working rolls 1, 2, 3 and 4 similar to the #1, #2, #3 and #4 rolls respectively shown in Table 2, backing-up rolls 5 and 6, rollers (which may be bridle rollers) 7 and 8 for avoiding winding of a strip 10 on the rolls, and roll coolant spray means 9 for spraying the rolls with a coolant to cool and lubricate the rolls. The numeral 11 is a support lever for supporting the bridle roller 7 which also supports a load cell 12 for measuring a tension T₂ of the strip 10. Drives 15 and 16 are provided to the bridle rollers 7 and 8 respectively for increasing the tension applied to the strip 10 by actuating the drives 15 and 16, as shown in Table 3. The working rolls 1, 2, ₃ and 4 have circumferential speeds v₁, v₂, v₃ and v₄ respectively which are set at values distinct from one another. The working rolls 2 and 3 each serves as one roll cooperating with other working rolls to continuously perform rolling on the strip 10 at two rolling points at the same time. The function of the bridle rollers 7 and 8 as tension applying means will be described.
It will be seen that, when the bridle rollers 7 and 8 serving as tension applying means are used for applying an equivalent torque by +100, it is possible to raise the total equivalent torque to +350, thereby enabling the rolling capacity to be greatly improved.
By increasing the tension applied to the strip 10 by using the bridle rollers 7 and 8, it is possible to increase the tension T₂ which helps the working rolls 1 and 2 (#1 and #2 rolls) and decrease a tension T_2' which applies the brake to the working rolls 2 and 3 (#2 and #3 rolls). Thus, by increasing the tension applied to a portion of the strip 10 on the entering end of a rolling point and decreasing the tension applied to a portion of the strip 10 on the delivery end of the rolling point, the ease with which different circumferential speed rolling is performed can be increased.
The mechanism whereby rolling can be performed at high rolling reduction with increased efficiency as a result of application of the difference in tension to the strip will be discussed.
Generally, when a coefficient of friction p between a strip to be rolled and rolling rolls is sufficiently high value to perform rolling, the rolling rolls can exert a sufficiently high tangential force F to the strip to impart rolling energy sufficiently high. Thus, the value of F shown in equation (1) is sufficiently even if the value of F is reduced by, for example, making the value of φ₁ large in comparison with the maximum tangential force F obtained by NR rolling. However, if the coefficient of friction p becomes smaller in value, then a slip occurs between the rolls and the strip, making, it impossible to continue a rolling operation. Generally, the higher the rolling speed becomes, the lower the coefficient of friction becomes. This relationship is shown in Fig. 7, in which curves A and B represent rolling operations using as a roll coolant a mineral oil base soluble oil and a beef tallow base soluble oil, respectively, which are usually used when a steel strip is subjected to cold rolling. The curves A and B indicate that coefficient of friction p is greatly changed in compliance with the rolling speed. The idea of using a roll coolant of high coefficient of friction to avoid the occurrence of a slip might come to mind. However, when such idea is put into practice, galling would occur between the rolls and the strip and it would be impossible to continue the rolling operation. To obviate this problem, the invention imparts rolling energy to a strip in the form of a difference in tension between one rolling point and another. In the system of the prior art shown in Fig. 4, the strip to be rolled wound on the rolling rolls has rolling energy imparted thereto by the frictional force exerted by the rolling rolls. However, since a slip occurs in this system, there is a care of causing the roll marks. Moreover, owing to the rolling rolls, there are the limitations which are to increase the coefficient of the surface of the rolling rolls and the angle at which the strip is wound on the rolls. The invention aims at imparting a difference in tension to the strip without relying on the rolling rolls as has been the case with the prior art. The end is attained by increasing tension at the delivery end of one rolling point and decreasing the tension at the entering end of the next following rolling point. Operation of the system of the invention with a marked increase in rolling reduction and a greatly improved efficiency of multiple pass rolling will now be described.
Fig. 8 shows the balancing of forces. When a strip is rolled at a constant rolling speed, a force urging the strip to move rearwardly is obtained by T₂' - T₃ + 2 x P sin
because there is no acceleration. The force with which the rolling rolls urge the strip to move forwardly is expressed by F shown by equation (1). Thus, the following relation holdes because these two forces are equal to each other:
By definition, F is 2µ P, and 6 is small in value. Thus,
or
In this case, an allowable maximum rolling reduction Δh_max can be obtained from the following equation (6) where R is the radius of the rolling rolls:
Let us consider the case in which T₃- T₂' = 0 in equation (6). In this case, the following relation holds:
Thus, in the NR rolling process, φ_{1 =} φ₂ = ₀ would be possible, and Δh_max could be maximized at 4_µ2_R. However, in the NPV process, φ₂ could be made substantially zero but a loop would be produced in the strip between the adjacent rolling points unless φ₁ has a large value. Assume that φ₂ ≒ 0. Then, the relation of the following equation (7) holds:
Fig. 9 shows the characteristics of Ah _max when the rolling rolls have a diameter of 500 mm (R = 250 mm). It will be seen that, when the value of µ becomes smaller and the ratio φ₁/θ becomes close to unity, the allowable rolling reduction becomes extremely small, rendering the rolling process unfit for practical use.
To perform multiple pass simultaneous rolling of a strip without developing a loop in the strip, it is necessary that rolling be performed with the ratio φ₁/θ having a value substantially close to unity. This is a decisively important problem, and the invention provides a solution to this problem by applying a difference in tension T₃- T₂ ¹ to the strip between the two rolling points. The effects achieved by the process according to the invention will be described.
In equation (6), when a strip of a thickness of 2.5 mm is rolled three times at a rolling reduction rate of 40%, the thickness of the strip will be successively reduced from 2.5 mm to 1.5 mm, 0.9 mm and 0.54 mm and the rolling reduction for each pass will be 1.0 mm, 0.6 mm and 0.36 mm respectively.
The second pass will be considered. Let the value of φ₁ be varied by using the values of µ = 0.05 and 0.025, R = 250 mm and φ₂ ≒ 0 in equation (6). Here, the tension will be considered per 1 mm of the strip. When the unit tension of the strip is denoted by σ_e, Q_d, the following relation holds;
The rolling load P is about 800 kg per 1 mm of the width of the strip when the rolling rolls have a diameter of 500 mm and the strip to be rolled is low-carbon steel, so that (T₃- T₂')/P = 19.5/800 = 0.0244.
Then, the following relation holds:
The results obtained are shown by broken line curves in Fig. 9.
From the foregoing, it will be seen that, by providing a difference in tension to the strip before and after a rolling point, it is possible to greatly increase the allowable rolling reduction. In Fig. 5, when the tension T₂ at the delivery end of the first rolling point is increased, it is possible to increase the allowable rolling reduction at the first rolling point. However, this will cause an increased in the tension of the strip at the entering end of the second rolling point and a reduction in the allowable rolling reduction at the second rolling point. According to the invention, means is provided for varying the tension applied to the strip so as to effect a rolling reduction of large magnitude at each of the first, second and third rolling points as described hereinabove and perform three pass rolling with a high degree of efficiency at a single stand rolling mill by increasing the delivery side tension T₂ at the first rolling point and decreasing the entering side tension T₂' at the second rolling point.
In the embodiment shown and described hereinabove, when the bridle rollers 7 and 8 are driven by the drives 15 and 16 respectively to increase the tension, for example, the tensions at the delivery end and the entering end of the bridle roller 7 are distinct from each other as designated by T₂ and T₂'. In this case, the accurate values of the tensions T₂ and T₂' can be obtained by calculation at a calculating unit 20 by sensing the total value T = T₂ + T₂' by means of the load cell 12 and obtaining the difference between them by means of a torque detector 19 attached to the bridle roller 7. More specifically, the torque detector 19 detects a torque Q which can be expressed as Q = (T₂' - T₂) R where R is the radius of the roller 7. Thus, by supplying the detected values of T and Q to the calculating unit 20 and doing calculation on them, it is possible to obtain the values of T₂ and T₂'. The values of T₂ and T2' thus obtained are compared with set values 21 to see whether they are optimum values, and a command signal is issued based on the result of comparison and fed into the drive 15 for the bridle roller 7, to positively control the tension of the strip 10. The speed of the strip 10 can be sensed by speed sensors 17 and 18 attached to the bridle rollers 7 and 8 respectively. Thus it is possible to control the speeds of rotation of the drives 15 and 16 by means of a control device 25 based on speed signals produced by the speed sensors 17 and 18 or to monitor the speed of the strip 10 by inputting the speed signals into a monitoring device 26. The embodiment of the invention shown and described hereinabove can achieve the following effects:

(1) Rolling energy of sufficiently high level to perform rolling of a strip-through a plurality of passes on a single stand rolling mill can be provided to the strip between the passes, so that different circumferential speed continuous rolling of the strip can be performed with a high degree of efficiency and a high degree of rolling reduction.
(2) The tension of the strip between the rolling points can be sensed with a high degree of precision and the control can be effected to keep the tension of the strip at an optimum value, thereby eliminating the risk of the strip being ruptured.
(3) The speed of the strip between the rolling points can be sensed and speeds or torques of the rolls can be controlled based on the values of the strip speed between the rolling points, thereby enabling different circumferential speed continuous rolling to be performed with a high degree of precision.

In the continuous rolling described hereinabove, the ability to apply tension to the strip can be increased by increasing the coefficient of friction of the surfaces of the bridle rollers and increasing the angle at which the strip is wound on each roller. An increase in the coefficient of friction of the surfaces of the bridle rollers can be achieved by coarsening the surfaces of the bridle rollers by applying a shot blast thereto or by applying to the surfaces of the bridle rollers a material tending to increase the coefficient of friction. An increase in the strip winding angle may be achieved by using a plurality of sets of bridle rollers 37, 38 and 39 and 32, 33 and 34 as shown in Fig. 6 which shows another embodiment of the invention.
In Fig. 6, the numerals 46, 47 and 48 designate guide rollers. However, these are not restrictive and tension gauges may be used in place of the guide rollers. Also, a drive may be connected to each of the bridle rollers 32 - 39.
In the embodiments shown and described hereinabove, the one rolling roll of the plurality of rolling rolls cooperating with other rolls to roll a strip simultaneously at a plurality of rolling points is two in number. However, the invention is not limited to this specific number of the one rolling roll and the number of the one rolling roll may be one as shown in Fig. 10 which shows still another embodiment in which rolling is performed simultaneously at two rolling points, in this case, the number of the rolling rolls performing rolling of the strip 10 includes three working rolls 1, 2 and 3. Thus, tension difference applying means is one in number which creates a difference in tension in a portion of the strop 10 disposed between a rolling point at which rolling is effected by the working rolls 1 and 2 of different circumferential speeds and the other rolling point at which rolling is effected by the working rolls 2 and 3 of different circumferential speed. It will be seen that the construction of the different circumferential speed continuous rolling mill shown in Fig. 10 having tension difference applying means attached to the bridle roller 7 is basically the same as the construction of the different circumferential speed continuous rolling mill shown in Fig. 5, so that the description of the construction shown in Fig. 10 will be omitted.
In the embodiments shown in Figs. 5, 6 and 10, the rolling points at which rolling is simultaneously effected by the one roll in cooperation with other rolling rolls are two in number. However, this is not restrictive and the invention may bave application in a continuous rolling system in which rolling is performed simultaneously at three or four rolling points by the one rolling roll cooperating with other rolling rolls.
Fig. 11 shows a further embodiment in which an internal working roll 40 is surrounded by external working rolls 50a, 50b and 50c supported by respective backing-up rolls 60 and rotating at circumferential speeds v₂, v3 and v₄ respectively which are distinct from the circumferential speed v_Iof the internal working roll 40, so that the strip 10 can be rolled simultaneously at three rolling points. In this embodiment, a bridle roller 70a is located in a path of travel of the strip 10 between a first rolling point between the internal working roll 40 and first external working roll 50a and a second rolling point between the internal working roll 40 and second external working roll 50b. The bridle roll 70a is provided with a drive 15 and supplies rolling energy to the strip 10. Another bridle roll 70 provided with a drive 16 is located in a path of travel of the strip 10 between the second rolling point and a third rolling point between the internal working roll 40 and third external working roll 50c to supply rolling energy to the strip 10. By providing the two bridle rolls, it is possible to produce a difference in the tension applied to the strips 10. The numerals 80 and 9 designate guide rollers for the strip 10 and fluid spray means for effecting cooling and lubrication of the strip 10, respectively. In the embodiment shown in Fig. 11, rolling energy of sufficiently high magnitude can be supplied to the strip between the rolling passes to enable the continuous rolling with a high degree of efficiency in the same way other embodiments of the invention.
From the foregoing description, it will be appreciated that according to the invention, there is provided a different circumferential speed continuous rolling mill capable of supplying rolling energy to the strip between the rolling passes from means other than the rolling rolls, to thereby enable continuous rolling to be effected with a high degree of efficiency.

Claims

1. A different circumferential speed continuous rolling mill comprising:

a plurality of rolls (1,2,3,4; 5,6) including one roll cooperating with other rolls to roll a strip simultaneously at a plurality of rolling points to continuously roll the strip by rotating the one roll at a circumferential speed distinct from the circumferential speeds of other rolls; and

tension difference applying means (7,11,12,15; 8,16) located in a path of travel of the strip between a first rolling point at which the strip is brought into contact with the one roll and rolled thereby and a second rolling point at which the strip is brought into contact with the one roll again and rolled thereby after clearing the first rolling point, to produce a difference in the tension of the strip between delivery end of the first rolling point and an entering end of the second rolling point.

2. A different circumferential speed continuous rolling mill as claimed in claim 1, wherein said tension difference applying means is operative to increase the tension of a portion of the strip located between the delivery end of the first rolling point and the tension difference applying means and to decrease the tension of a portion of the strip located between the tension applying means and the second rolling point, to thereby apply a tension difference to the strip.

3. A different circumferential speed continuous rolling mill as claimed in claim 1, wherein said tension difference applying means comprises a roller (7;8), and a drive (15;16) for driving said roller for rotation.

4. A different circumferential speed continuous rolling mill as claimed in claim 1, wherein said tension applying means has a tension sensor means (12) for sensing the tension of the strip, said tension sensor means feeding a signal corresponding to the value of the tension of the strip to the tension difference applying means to control the operation of the tension difference applying means.

5. A different circumferential speed continuous rolling mill as claimed in claim 3, wherein the roller of said tension difference applying means has a speed sensor means for sensing the speed of the strip, said speed sensor means producing a signal based on the value of the speed of the strip to control said roll.

6. A different circumferential speed continuous rolling mill as claimed in claim 1, wherein said one roll and said tension difference applying means are plural in number and said tension difference applying means are each located in a path of travel of the strip between a first rolling point and a second rolling pint of each of said plurality of one rolls.

7. A different circumferential speed continuous rolling mill as claimed in claim 6, wherein each of said tension difference applying means increases the tension applied to a portion of the strip located between the first rolling point of each said plurality of one rolls and the tension difference applying means and decreases the tension applied to a portion of the strip located between the tension applying means and the second rolling point of each said one rolls, to thereby apply a tension difference to the strip.

8. A different circumferential speed continuous rolling mill as claimed in claim 6, wherein each said tension difference applying means comprises a roller, and a drive for driving said roller for rotation.