US3638468A

US3638468A - Roll-changing means for four-high rolling mill

Info

Publication number: US3638468A
Application number: US862331A
Authority: US
Inventors: Kakichi Fukui; Shiro Imai
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1968-10-02
Filing date: 1969-09-30
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01
Also published as: DE1949602A1; GB1273016A; DE1949602C3; DE1949602B2

Abstract

Roll changing means for a four-high rolling mill for automatically and rapidly changing top and bottom working rolls and top and bottom backup rolls without necessitating the use of a crane by combining a working roll changing truck and a backup roll changing truck in a double-sled shifted sidewise manner.

Description

O United States Patent [151 3,638,468

Fukui et al. Feb. I, 1972 [54] ROLL-CHANGING MEANS FOR FOUR- [56] References Cited HIGH ROLLING MILL UNITED STATES PATENTS [72] Inventors: Eukui; Shiro lmai, both of 3,221,530 12/ 1965 Swallow et al ..72/239 Japan 3,312,096 4/1967 Stubbs et a1. ..72/23s Assignee: Hitachi Ltd Tokyo Japan Beard 3,518,862 7/1970 Dehaine et al ..72/238 [22] Filed: Sept. 30, 1969 21 A L N 862,331 Primary Examiner-Charles W. Lanham 1 pp 0 Assistant Examiner-B. J. Ollila Attorney-Craig, Antonelli and Hill [30] Foreign Application Priority Data Oct. 2, 1968 Japan ..43/71 121 [57] ABSTRACT Roll changing means for a four-high rolling mill for automati- {521 US. Cl ..72/238, 72/239 ally an rapidly changing t p n bottom w rking r ll n [5 l Int. Cl ..B2lb 31/10 p and bottom backup rolls Without necessitating the use Of a [58] 72/237, 233, 239 crane by combining a working roll changing truck and a Field of Search backup r011 changing truck in a double-sled shifted sidewise manner.

17 Claims, 4 Drawing Figures I. n II I; 42

VI 3} I] I E" 3 35 39 7 26 PATENTED FEB 7 i972 SHEU 2 0F 4 ROLL-CHANGING MEANS FOR FOUR-HIGH ROLLING MILL y matically change a top and a bottom working roll and a top and a bottom backup roll of a four-high rolling mill, the changing operation being performed rapidly and efficiently without necessitating the use of a crane.

Hithertofore, since the operation for changing working rolls of a rolling mill has been performed by using a roll-changing jig, such as a porter bar, a C-hook and the like to remove and replace one or more working rolls, it has been always necessary to use a crane, and increased labor hours and highly skilled workmen were required.

In order to solve the above mentioned problems, there have been proposed a turntable-type roll changing means as disclosed in the US. Pat. No. 3,208,260 and a double-sled-type roll-changing means as disclosed in the US. Pat. No. 3,3l2,096. However, the turntable type is complicated in its mechanism and requires an increased space, so that it cannot be practically employed in a continuous rolling mill in which the distance between each roll stand unit is small. Further, in a four-high rolling mill, even when the turntable-type is used for changing working rolls, C-hook and the like is used for changing backup rolls.

Further, in applying the double-sled type in a four-high rolling mill, when it is desired to change backup rolls, working roll-changing trucks should necessarily be transferred transversely in order to provide spaces for performing the operation for changing the backup rolls. Particularly, in a continuous rolling mill, since the spaces for transversely transferring the trucks are limited, it was only possible to employ, as far as the backup rolls are concerned, an essentially single sled type in which the rolls are withdrawn from rolling mill stand and thereafter hoisted by an overhead travelling crane to be replaced by new backup rolls.

Thus, in a four-high rolling mill, in order to remove and replace top and bottom working rolls and top and bottom backup rolls by either of the conventional changing means, a crane operation using a C-hook and the like is required and it is difficult to decrease the time required for the changing "operation and thus to increase the operational efficiency of the rolling mill.

f The primary object of the present invention is to provide roll changing means for a four-high rolling mill in which top and bottom working rolls and top and bottom backup rolls can be automatically, rapidly and efficiently removed and replaced in a double-sled manner without necessitating the use of any crane operation during changing operation.

Another object of the present invention is to provide roll changing means in which a working roll-changing truck and a backup roll-changing truck are so combined that the space occupied by the means, particularly the distance through which the rolls are transversely transferred, is substantially decreased and that the means can be employed in a continuous rolling mill.

According to one aspect of the present invention, there is provided roll-changing means for a four-high rolling mill comprising means provided in a rolling mill stand in parallel relation with a roll axis for supporting the roll for axial movement when it is removed and replaced, lifting means for placing said roll on said support means when the roll is being removed and replaced, transfer means for axially transferring the roll from and into the rolling mill stand, a working roll-changing truck provided outside the rolling mill stand for carrying used and new working rolls, a backup roll-changing truck for carrying said working roll-changing truck and used and new backup rolls, transverse transfer means for transferring said backup roll-changing truck in the direction perpendicular to the m ll axis so as to change the relative position of the used and backup rolls, means for enabling the transverse transfer means to he used for transversely transferring the working roilchanging truck, and retracting means for retracting said working roll-changing truck when the backup roll is being changed.

The present invention will now bedesc'ribed with respect to an embodiment thereof taking reference to the accompanying drawings, in which:

FIG. I is a front view of a four-high rolling mill embodying the roll-changing means'of the present invention;

FIG. 2 is a side view thereof;

FIG. 3 is a plan view of FIG. 2;

FIG. 4 is a sectional view taken along the line lV-IV of FIG. 3; and, 3 FIG. 5 is a sectional view taken along the line V-V of FIG.

Referring to the drawings, the numeral I shows a rolling mill stand, and 2 and 3 show a top and a bottom backup rolls respectively which are assembled in a window 1 formed in the rolling mill stand I. The backup rolls 2 and 3 can be moved axially through said window I when it is desired to replace them by another pair of rolls. The numerals 2' and 3"show another pair of backup rolls which are to be assembled in the place of the

backup rolls

2 and 3, and 4 and 5 show top and bottom working rolls which can be moved axially through the window I. The numerals 4' and 5' are another pair of top and bottom working rolls which are placed on a working roll-changing truck which will be described later. The numerals 6 and 7 show bearing chocks provided at the journal of the top and

bottom backup rolls

2 and 3, and 8 and 9 show bearing chocks at the ends of the top and bottom working rolls 4 and 5. The numeral 10 is a carrier which is connected with a balance cylinder (not shown) of said top backup rolls 2 and adapted to the top backup roll 2 so that a space is provided for facilitating the roll changing operation, 11 a screwed member of screwdown mechanism, and 12 a protecting cover. The numeral 13 shows balance cylinders provided between the Bizaring chocks 8 and 9 of the top and bottom working rolls respectively, and 14 shows roll changing rails for the top and bottom working rolls 4 and 5. The rails 14 are disposed at the opposite sides of the window I of the rolling mill stand 1 in parallel relation with roll axis and held during rolling operation by the bearing chock 7 of the bottom backup roll 3. The rails 14 are so arranged that they are pushed upwardly to a predetermined position by hydraulic cylinders 16 when it is desired to replace the top and bottom working rolls 4 and 5. The hydraulic cylinders 16 are provided at the opposite sides of the rolling mill stand I. The numeral 15 shows positioning stoppers for the roll-changing rails I4 which are lifted by the hydraulic cylinder I6, and 17 shows wheels mounted on the bearing chock 9 of the bottom working roll 5. The wheels I7 rotate along the roll changing rails 14 when the top and bottom working rolls 4 and 5 are being replaced. The numeral I8 shows a traction car which is integrally connected with the bearing chocks 8 and 9 and adapted to carry the top and bottom working rolls 4 and 5 into and from the rolling mill stand I. The traction car 18 is disposed along a line parallel to the roll axis. The numeral 19 is a working roll-changing truck for carrying new working rolls which are to be moved into the rolling mill stand I, used working rolls which are to be moved out of the rolling mill stand I, and a stool 45 which is to be inserted between the bearing chocks 6 and 7 of the top and bottom backup rolls 2 and 3 respectively. The truck I9 is so arranged adjacent to the operating side of the rolling mill stand I that its upper surface forms an aligned continuous plane with the upper surface of the rails 14 when the rolls are being removed and replaced. The numeral 20 shows a vertically movable floor plate carrying

traction car

18, and 22 shows rails provided on the floor plate 20. The car 18 is movable along the rails 22. The car I8 is driven along the

rails

21 and 22 provided on the working roll changing truck 19 and the floor plate 20 respectively by the rotation of an electric motor 1 23 which is transmitted through worm gear means (not shown), a pinion shaft 24 and racks 25 and 25' provided on the working roll-changing truck 19 and the floor plate 20 respectively. The numeral 26 shows a backup roll changing truck for carrying the working roll changing truck 19 and the unused backup rolls 2' and 3'. The truck 26 is transversely movable sidewise to the roll axis. The truck 26 is provided with

sliding surfaces

27 and 28 for carrying the backup roll for sliding movement in the direction of roll axis, and with a plurality of rails 29 for carrying the working roll changing truck 19 for movement in the direction of roll axis. The backup rollchanging truck 26 is further slidably mounted on supporting pedestals 31 and 31' and can be transversely moved in the direction perpendicular to the roll axis by hydraulic cylinder 30. The numerals 32 and 32' show stoppers for the trucks 26 provided at the opposite ends of the supporting

pedestals

31 and 31 and 33 and 33' show intermediate stoppers which can be adjusted in position by a hydraulic cylinder 34 and is adapted to limit the transverse travel of the backup roll changing truck 26. The numeral 35 shows a changing sled for carry ing the bearing chock 7 of the bottom backup roll 3, 36 a frame for connecting the operating side sled 35 and a sled on the drive side (not shown), and 37 an intermediate supporting pedestal for guiding the top and bottom backup rolls 2 and 3 from the rolling mill stand 1 to the backup roll changing truck 26 when the rolls are being changed. The pedestal 37 is so arranged that its upper surface aligns with the lower surface of said sled 35 and the upper surface of the truck 26. The numeral 38 shows a hydraulic cylinder for moving the top and bottom backup rolls 2 and 4 from and into the rolling mill stand 1, 39 a hook for connecting the hydraulic cylinder 38 and the sled 35, 40 an arm extending from the lower side of the working roll changing truck 19, and 41 a hook rotatably mounted on said arm 40 for connecting the working rollchanging truck 19 with the sled 35. By this hook 41, the working rollchanging truck 19 can be moved rearwardly simultaneously when the top and bottom backup rolls 2 and 3 are moved outwardly from the rolling mill stand 1. The numeral 42 shows a hydraulic cylinder for effecting the vertical movement of the

floor plate

20, and 43 shows shunt rails provided on the base below the floor plate 20 at a lever the same as the rails 29 for carrying the truck 19. The shunt rails are provided for retracting the working roll-changing truck 19 from the backup roll-changing truck 26 when the backup rolls 2 and 3 are being changed. The numeral 44 shows shunt rails provided at a level same as the rails 22 for carrying the traction car 18. The shunt rails 44 are provided for retracting the car 18 and the working rolls 4 and rearwardly. The numeral 45 shows a stool adapted to be inserted between the backup rolls 2 and 3 after the working rolls 4 and 5 are retracted from the rolling mill stand I, 46 a stool inserted between the top and bottom backup rolls 2' and 3', and 47 a hook for connecting the traction car 18 and the bottom working roll 5.

When it is desired to remove and replace the working rolls 4 and 5, the top backup roll 2 is upwardly moved by the balance cylinder (not shown) through the carrier beam to provide a space required to change the rolls. Then, the rails 14 are moved upwardly by the hydraulic cylinders 16 until they engage with the stoppers l5, and the top and bottom working rolls 4 and 5 are placed on the rails 14. In this position, the upper surface of the rails 14 and the upper surface of the rails 21 of the truck 19 align with each other. Thereafter, the top and bottom working rolls 4 and 5 with the bearing chocks 8 and 9 are slidably moved by the traction car 18 along the rails 14 onto the rails 21 from the rolling mill stand 1. Prior to this step, a new set of top and bottom working rolls are placed on the rail 21' of the working roll changing truck 19. (The drawings show a position in which the backup rolls are being changed, so that the stool 45 is disposed on the rail 21'. Further, a new pair of backup rolls 2' and 3' are disposed on the sliding surface 27 of the truck 26. However, when only the working rolls are to be changed, they may be omitted and the sliding surface 27 may be left free of rolls). Thus, when the top and bottom working rolls 4 and 5 are completely transferred on the truck 19, the hydraulic cylinder 30 is actuated to move the working roll changing truck 19 together with the truck 26 in the direction perpendicular to the roll axis until the axes of the new working rolls align with the center of the rolling mill.

Inthis case, in order to determine the transversely transferred position of the trucks, the intermediate stoppers 33 are used.

Thus, the truck 26 can only be moved to the position in which 5 it engages with the stoppers 33. Thereafter, the traction car 18 is operated and the new working rolls are moved into the rolling mill stand 1. Then, the changing rails I4 are lowered by the hydraulic cylinder 16 and the backup rolls 2 are returned to its initial position by the balance cylinder (not shown) which acts through the carrier beam 10. Finally, the screw II is adjusted and thus the rolling mill becomes ready for operation. The removed working rolls 4' and 5' are transferred by the traction car 18 to a suitable position and from there they are carried by a crane.

The operation in which the backup rolls are removed and replaced will now be described. The stool 45 is placed on the rails 21' of the working roll-changing truck 19 and a pair of new backup rolls 2' and 3 with metal chocks are mounted on the sliding surface 27 of the backup roll-changing truck 26. The stool 46 is interposed between the said bearing chocks. When the upper and lower working rolls 4 and 5 are transferred to the working roll changing truck 19 as shown by 4' and 5' in the drawings through the steps of the abovedescribed working roll-changing operation, the hook 47 is disconnected with the traction car 18 placed on the rails 22 and thereafter the hydraulic cylinder 30 is actuated to move the backup roll-changing truck 26 and the working roll-changing truck 19 in the direction perpendicular to the rollaxis until the center of the stool 45 aligns with the center'of the rolling mill or until the trucks are stopped by the intermediate stopper 33. In this position, the traction car 18 is again operated so as to move the spacer 45 into the rolling mill stand 1 through the intervention of the hook 47. Thereafter, the car lowered by the hydraulic cylinder 16 until the stool 45 is placed on the bearing chocks 7 of the bottom backup roll 3. The top backup roll 2 is further lowered through the carrier beam 10 until its metal chocks 6 rides on said stool 45.

The removed working rolls 4' and 5' are placed on the working roll changing truck 19 when the stool 45 is being moved into the rolling mill stand 1, and when the backup rollchanging truck 26 is moved with the working roll-changing truck 19 to the position shown in FIG. 3 in which the truck 26 is stopped by the stoppers 32, the rolls 4' and 5' are transferred along the rails 21 of the working roll changing truck I9 and the rails 22 of the floor plate 20 onto the shunt rails 44. Thereafter, the floor plate 20 is lifted by the hydraulic cylinder 42 to provide a space for receiving the truck 19. Then, the top and bottom backup rolls 2 and 3 with bearing chocks are removed as a unit from the rolling mill stand 1 by the hydraulic cylinder 38 which acts through the hook 39 and the sled 35, and are transferred through the intermediate supporting pedestal 37 to the sliding surface 28 of the backup roll-changing truck 26. In this instance, since the work roll changing truck 19 is connected with the sled 35 by the hook 41, the truck 19 is moved on the shunt rails 43 provided below the floor plate 20 simultaneously as the backup rolls 2 and 3 are removed from the rolling mill stand. Therefore, the working roll-changing truck 19 does not interfere with the backup rolls when the rolls are moved onto the truck 26. Thereafter, the hooks 39 and 41 are opened to disconnect the sled 35.

Then, the intermediate stopper 33 is moved away from the operative position by the hydraulic cylinder 34, and the hydraulic cylinder 30 is actuated to move the backup rollchanging truck 26 until it engages with the stoppers 32'. Thus, the center of the new backup rolls 2 and 3' comes into alignment with the center of the rolling mill. Thereafter, the hook 39 is connected with the changing sled 35' of the new backup rolls 2' and 3', and the hydraulic cylinder 38 is actuated to move the rolls 2 and 3' into the rolling mill stand 1. After the backup rolls are moved into the rolling mill stand, said top and bottom backup rolls 2 and 3 are carried out by a crane, and the backup roll-chaning truck 26 is transversely moved until it 18 is again returned on the rails 22. Then, the rails 14 are engages with the intermediate stopper 32. Thereafter, the hook 39 and the arm 40 are connected with each other, and the hydraulic cylinder 38 is actuated to move the working changing truck 19 onto the backup roll-changing truck 26. The floor plate 20 is then lowered to the original position by the hydraulic cylinder 42. From this position, the removed working rolls 4' and 5' are transferred by the traction car 18 from the shunt rail 43 through the rail 22 to the rail 21 of the working roll-changing truck 19. As the next step, the upper backup roll in the rolling mill stand 1 is lifted by the balance cylinder (not shown) through the carrier beam 10, and the rail 14 is lifted to a predetermined position by the hydraulic cylinder 16. Thereafter, as in the working roll-changing operation, the stool 46 which has been moved into the rolling mill stand is replaced by the top and bottom working rolls 4 and 5' by using the traction car 18. Then, the balance cylinder for the backup roll (not shown) and the balance cylinder 13 for the working roll are actuated, and the screw 11 of the screwdown mechanism is adjusted as required. Thus, the rolling mill becomes ready for operation.

The present invention has been described and illustrated with reference to a preferred embodiment, however, it should of course be understood that the embodiment is merely an example and various changes and modifications may be made without departing from the spirit and scope of the present invention.

We claim:

1. Roll-changing means for a four-high rolling mill comprising means provided in a rolling mill stand in parallel relation with a roll axis for supporting the roll for axial movement when it is removed and replaced, lifting means for placing said roll on said support means when the roll is being removed and replaced, transfer means for axially transferring the roll from and'into the rolling mill stand, a working roll-changing truck provided outside the rolling mill stand for carrying used and new working rolls, a backup roll-changing truck for carrying said working roll-changing truck and used and new backup rolls, transverse transfer means for transferring said backup roll-changing truck in the direction perpendicular to the roll axis so as to change the relative position of the used and new backup rolls, means for enabling the transverse transfer means to be used for transversely transferring the working rollchanging truck, and retracting means for retracting said working roll-changing truck in a direction substantially parallel to said roll axis when the backup roll is being changed.

2. Roll-changing means for a four-high rolling mill in accordance with claim I, in which said lifting means comprises hydraulic cylinders and linkages provided at the opposite sides of the rolling mill stand for vertically moving said support means.

3. Roll-changing means for a four-high rolling mill in accordance with claim 2, in which the transfer means for axially moving the top and bottom work rolls includes a traction car which is arranged so as to move along rails which are provided outside the rolling mill stand and in alignment with roll-changing rails in the rolling mill stand.

4. Roll-changing means for a four-high rolling mill in accordance with claim 3, in which said traction car includes an electric motor and a mechanism for transferring the rotation of the motor, a pinion shaft in the mechanism being arranged to engage with racks provided on the working roll-changing truck and a floor plate.

5. Roll-changing means for a four-high rolling mill in accordance with claim 3, in which the rails along which the traction car moves comprises rails provided on the working rollchanging truck outside the rolling mill stand, rails provided on a floor plate which is behind the working roll-changing truck, and shunt rails provided further rearwardly of said floor plate.

6. Roll-changing means for a four-high rolling mill according to claim 5, in which the transfer means for axially moving the top and bottom backup rolls comprises a hydraulic cylinder, a sled for carrying bearing chocks of the bottom backup roll and a hook for connecting the hydraulic cylinder and the sled.

7. Roll-changing means for a four-high rolling mill accord ing to claim 6, in which said working roll-changing truck is mounted for movement in the direction of roll axis on the backup roll-changing truck and has on its upper surface two sets of rails for supporting the used and new working rolls and a stool inserted between the top and bottom backup rolls.

8. Roll-changing means for a four-high rolling mill according to claim 7, in which the backup roll-changing truck is slidably mounted on pedestals on the base so as to be transversely moved by the hydraulic cylinder in the direction perpen dicular to the roll axis.

9. Roll-changing means for a four-high rolling mill in accordance with claim 8, in which said backup roll-changing truck is provided with a sliding surface for carrying the backup rolls for sliding movement in the direction of roll axis and a plurality of rails for carrying the working roll-changing truck for movement in the direction of roll axis.

10. Roll-changing means for a four-high rolling mill in accordance with claim 8, in which the pedestal is provided with a pair of stoppers provided at the opposite sides thereof for limiting the transverse transfer distance of the backup rollchanging truck and a pair of intermediate stoppers which can be selectively moved into and out of the operative position.

11. Roll-changing means for a four-high rolling mill in accordance with claim 1, in which an intermediate pedestal is provided between the rolling mill stand and the backup rollchanging truck for guiding the backup rolls, the intermediate pedestal being so arranged that its upper surface aligns with the lower surface of the sled for the backup roll and the sliding surface on the backup roll-changing truck.

12. Roll-changing means for a four-high rolling mill in accordance with claim 11, in which the sled for the backup roll can be connected with the working roll-changing truck by means of a rotatable hook whereby the working roll-changing truck is rearwardly moved simultaneously when the backup rolls are moved from the rolling mill stand to the backup rollchanging truck.

13. Roll-changing means for a four-high rolling mill in accordance with claim 5, in which the floor plate located rearwardly of the working roll-changing truck is vertically movable, the floor plate being moved upwardly to provide a space for receiving the working roll-changing truck.

14. Roll-changing means according to claim 9, in which said transfer means comprises means for axially moving the top and bottom working rolls and means for axially moving the top and the bottom backup rolls and wherein said traction car includes an electric motor and a mechanism for transferring the rotation of the motor, a pinion shaft in the mechanism being arranged to engage with racks provided on the working rollchanging truck and a floor plate.

15. Roll-changing means according to claim 14, in which the pedestal is provided with a pair of stoppers provided at the opposite sides thereof while limiting the transverse transfer distance of the backup roll-changing truck and a pair of intermediate stoppers which can be selectively moved into and out of the operative position, and in which the floor plate located rearwardly of the working roll-changing trunk is vertically movable the floor plate being moved upwardly to provide a space for receiving the working roll-changing truck.

16. Roll-changing means according to claim 15, in which an intermediate pedestal is provided between the roll mill stand and the backup roll-changing truck for guiding the backup rolls, the intermediate pedestal being so arranged that its upper surface aligns with the lower surface of the sled for the backup roll and the sliding surface on the backup roll-changing truck.

17. Roll-changing means according to claim 16, in which the sled for the backup roll is connectable with the working roll-changing truck by means of a rotatable hook, whereby the working roll-changing truck is rearwardly moved simultaneously when the backup rolls are moved from the rolling mill stand to the backup roll-changing truck.

Claims

1. Roll-changing means for a four-high rolling mill comprising means provided in a rolling mill stand in parallel relation with a roll axis for supporting the roll for axial moveMent when it is removed and replaced, lifting means for placing said roll on said support means when the roll is being removed and replaced, transfer means for axially transferring the roll from and into the rolling mill stand, a working roll-changing truck provided outside the rolling mill stand for carrying used and new working rolls, a backup roll-changing truck for carrying said working roll-changing truck and used and new backup rolls, transverse transfer means for transferring said backup roll-changing truck in the direction perpendicular to the roll axis so as to change the relative position of the used and new backup rolls, means for enabling the transverse transfer means to be used for transversely transferring the working roll-changing truck, and retracting means for retracting said working roll-changing truck in a direction substantially parallel to said roll axis when the backup roll is being changed.

2. Roll-changing means for a four-high rolling mill in accordance with claim 1, in which said lifting means comprises hydraulic cylinders and linkages provided at the opposite sides of the rolling mill stand for vertically moving said support means.

5. Roll-changing means for a four-high rolling mill in accordance with claim 3, in which the rails along which the traction car moves comprises rails provided on the working roll-changing truck outside the rolling mill stand, rails provided on a floor plate which is behind the working roll-changing truck, and shunt rails provided further rearwardly of said floor plate.

7. Roll-changing means for a four-high rolling mill according to claim 6, in which said working roll-changing truck is mounted for movement in the direction of roll axis on the backup roll-changing truck and has on its upper surface two sets of rails for supporting the used and new working rolls and a stool inserted between the top and bottom backup rolls.

8. Roll-changing means for a four-high rolling mill according to claim 7, in which the backup roll-changing truck is slidably mounted on pedestals on the base so as to be transversely moved by the hydraulic cylinder in the direction perpendicular to the roll axis.

10. Roll-changing means for a four-high rolling mill in accordance with claim 8, in which the pedestal is provided with a pair of stoppers provided at the opposite sides thereof for limiting the transverse transfer distance of the backup roll-changing truck and a pair of intermediate stoppers which can be selectively moved into and out of the operative position.

11. Roll-changing means for a four-high rolling mill in accordance with claim 1, in which an intermediate pedestal is provided between the rolling mill Stand and the backup roll-changing truck for guiding the backup rolls, the intermediate pedestal being so arranged that its upper surface aligns with the lower surface of the sled for the backup roll and the sliding surface on the backup roll-changing truck.

12. Roll-changing means for a four-high rolling mill in accordance with claim 11, in which the sled for the backup roll can be connected with the working roll-changing truck by means of a rotatable hook whereby the working roll-changing truck is rearwardly moved simultaneously when the backup rolls are moved from the rolling mill stand to the backup roll-changing truck.

14. Roll-changing means according to claim 9, in which said transfer means comprises means for axially moving the top and bottom working rolls and means for axially moving the top and the bottom backup rolls and wherein said traction car includes an electric motor and a mechanism for transferring the rotation of the motor, a pinion shaft in the mechanism being arranged to engage with racks provided on the working roll-changing truck and a floor plate.