Stand change carriage comprising hydraulic motor

Abstract

To provide a stand change carriage having a drive concept, which can be used more flexibly than in the prior art.SOLUTION: The invention relates to a stand change carriage (10) for simultaneously receiving and transporting a plurality of stands of a rolling mill for rolling metal rods, wires or pipes. The stand change carriage comprises: a plurality of stand places (16), one stand being receivable individually in each of the stand places (16). The stand change carriage (10) comprises: a plurality of steerable wheels (20), in order to transport the stands on rails or along a rail-less mill floor; and at least one hydraulic motor (21) which is operatively connected to at least one of the wheels (20) in order to drive it.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a stand exchange carriage for simultaneously receiving and transporting multiple stands of a rolling mill for rolling metal bars, wire rods, or tubes. [Background technology]

[0002] For rolling metal bars, wires or tubes, rolling mills are usually used which comprise a number of stands arranged one behind the other in the rolling direction, said stands comprising the rollers themselves which apply the rolling force to the material being rolled to produce the metal bars, wires or tubes.

[0003] During operation, the rollers wear and, as a result, they must be periodically re-ground. Therefore, the stand with the rollers to be re-ground must be removed from the rolling mill and transported to a stand workshop. After the rollers have been re-ground, each stand must be transported from the stand workshop back to the rolling mill and inserted into the rolling mill. Furthermore, different stands must be used for different thicknesses of rolled products, and the calibers of the stands are preset in advance for the desired thickness of each rolled product.

[0004] To change the stands of a rolling mill, stand exchange carriages are used in a known manner, which can simultaneously receive several stands and transport them reliably between the rolling mill and the stand workshop. As described, for example, in DE 10 20 05 14 52 A1, in principle, a distinction can be made between two different types of stand exchange systems in which different stand exchange carriages are used.

[0005] In a first known stand exchange system, the stand exchange carriages do not have their own drive source but are instead moved using one or more external control cable systems. For this purpose, control cables and a transport sled attached to the control cables are installed under the factory floor, forming a base on which the wheels of the stand exchange carriage run. The exchange carriage can be attached to the transport sled using connecting rods and can be moved by the control cables. In this system, the stand exchange carriage is mounted on rails and has a first section of rails extending parallel to the rolling mill, as well as a second section of rails arranged perpendicular to the first section of rails. At the switching point connecting the two sections, the stand exchange carriage can switch between the two sections by pivoting its wheels by approximately 90°. This allows, for example, for a stand exchange carriage to be temporarily parked on a transverse track in order to change the arrangement of the stand exchange carriages in front of the rolling mill. This system allows for a relatively flexible selection of which stand exchange carriage to return to the stand workshop or to move to the rolling mill.

[0006] In this type, the stand change carriage has no driven axles at all, and the control cable system, recessed into the factory floor, allows the stand change carriage to be installed at a lower height. In particular, wheels that can pivot approximately 90° can also be easily realized. However, this comes at the expense of increasing the space required under the factory floor, since multiple components required for the control cable system, such as the coupling and uncoupling stations, cable tensioning devices, and switching actuators, must be accommodated under the factory floor. This is particularly disadvantageous when the rolling mill is located on the upper floors of the rolling mill, because the ceiling height of the lower floors must be significantly reduced in the area of ​​the control cable system, which complicates the building construction technology. Furthermore, with this concept, the complexity of the control cable system increases very rapidly with the number of stand change carriages and rail sections to be moved, making it difficult to flexibly adapt to structural changes in the rolling mill or stand workshop.

[0007] In the second type of stand exchange system, the stand exchange carriage has a direct electric drive for one or more wheels. Stand exchange systems with such stand exchange carriages are, in principle, more suitable because they eliminate the need for a control cable system within the rolling mill. However, power lines are still connected to these "self-propelled" units with cable carriers to ensure the necessary control signals and power for the electric motors. The cable carriers also ensure that such stand exchange carriages are only used when equipped with cables, and only one cable carrier, and therefore only one carriage with its own drive, is used per track section. Furthermore, the need for very long lines makes it practically difficult to transport the stand exchange carriage directly to a remote stand workshop. As a result, the removed stands must be carefully and time-consumingly transferred by crane from the stand exchange carriage to another transport means previously placed near the rolling mill, where there is often little room for other structures.

[0008] Furthermore, in practice, only the second type of stand change carriage is used, which can only move forward and backward, but not laterally. Therefore, the arrangement of the second type of stand change carriage along the rolling mill cannot be changed, and this type of stand change carriage cannot be kept waiting in the second row in front of the rolling mill until it is used. The reason why there are no electrically driven stand change carriages that can change the direction of movement is due to the available installation space. Due to the size of the sufficiently dimensioned electric motor and its drive unit, the wheel pivot area of ​​the second type of stand change carriage requires more space than the first type. Nevertheless, in order to design the stand change carriage as compact as possible overall, the wheels are arranged in an intermediate space provided between the stand storage areas. However, it is no longer possible to arrange an electric drive source with an angle gear that can pivot together with the wheels to enable an instant change of direction of movement within this limited space. In other words, the space required for the wheel pivot area of ​​the stand change carriage is too large. A lateral clearance around the stand exchange carriage must also be provided, into which the drive unit consisting of an electric motor and a gearbox may extend when the wheels are pivoted. However, too large a distance between the stand exchange carriage and the rolling mill is disadvantageous when inserting the stand into the rolling mill. Another reason is the need for power lines. As in a control cable system, when transitioning to another track section, the stand exchange carriage must be connected to another cable carrier, which entails further technical complications. Furthermore, it must be ensured that the cable carriers of the individual track sections are not damaged when the stand exchange carriage crosses. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] German Patent Application Publication No. 102014015963 Summary of the Invention [Problem to be solved by the invention]

[0010] Against this background, it is an object of the present invention to provide a stand exchange cart from the above-mentioned technical field, which has a drive concept that can be used more flexibly than in the prior art. In particular, it is an object of the present invention to provide a stand exchange cart in which the direction of movement can be changed. In particular, it is an object of the present invention to provide a stand exchange cart that can be used as universally as possible in as many different factories as possible. In particular, it is an object of the present invention to provide a stand exchange cart that can be used as autonomously as possible. [Means for solving the problem]

[0011] This object is achieved by a stand exchange carriage according to claim 1. Advantageous embodiments of the invention emerge from the dependent claims.

[0012] A stand exchange carriage for simultaneously receiving and transporting a plurality of stands of a rolling mill for rolling metal bars, wire rods, or tubes includes a plurality of stand storage spaces, each of which can receive one stand individually, and a plurality of steerable wheels for transporting the stands along rails or along a factory floor without rails.

[0013] The stand exchange truck includes at least one hydraulic motor operatively coupled to the at least one wheel for driving the wheel.

[0014] Hydraulic motors are characterized by a high driving torque. Therefore, they are particularly well suited to moving heavy stand exchange carriages. Furthermore, hydraulic motors can be designed more compactly compared to electric motors with similar torque. Therefore, the use of hydraulic motors makes it possible to keep the size of the wheel pivot area relatively small. For example, if the wheel pivoting is enabled by angle gears attached to the wheel, the space required for the wheel pivot area does not increase significantly, despite the additional components, compared to non-pivoting wheels driven by an electric motor.

[0015] Furthermore, the small space required for the hydraulic motor allows the installation height of the stand exchange cart according to the invention above the factory floor to be comparable to that of known stand exchange carts driven by control cables. The invention thus makes it possible to provide a steerable and self-propelled stand exchange cart, i.e., the stand exchange cart does not rely on an external drive or on a rail system, which makes it more versatile in use than the stand exchange carts known from the prior art.

[0016] In an advantageous embodiment, the hydraulic motor is a radial piston motor or an axial piston motor. These motor types, and in particular the radial piston motor of the two, are particularly compact in design and allow for a steerable stand exchange carriage with a particularly low installation height. Low-speed radial piston motors in particular are very compact in design and, in particular, have a very small longitudinal length, which is preferably less than 0.2 m. In this respect, longitudinal means the direction extending along the rotation axis of the radial piston motor. When such motors are used, the pivoting drive unit can be realized by a hydraulic motor and wheels, which require a small wheel pivot range and a small clearance around the stand carriage for pivoting.

[0017] Preferably, each wheel is associated with and operatively connected to its own one of at least one hydraulic motor. The compact design allows for a separate hydraulic motor for each wheel, which increases the drive force of the stand exchange carriage. It is also conceivable to replace a single large motor, which requires a relatively large amount of space and a minimum installation height of the stand exchange carriage, with several smaller hydraulic motors having the same total drive force, each of which requires less space. The minimum installation height can therefore be reduced. Due to the small dimensions of the hydraulic motors, particularly radial piston motors, this preferred embodiment allows each driven wheel to be steerable without significant space requirements. However, it is also possible for each wheel not to have its own hydraulic motor.

[0018] Preferably, all wheels are designed to be steerable, allowing for a change in direction of travel of at least 30°, more preferably 90° or more. A stand change carriage with such wheels can not only move forward and backward, but can also instantly assume a different direction, particularly a direction perpendicular to the original direction of travel. As a result, the stand change carriage can be maneuvered particularly easily and space-savingly, even in extremely narrow surroundings. Thus, multiple stand change carriages can be arranged in any desired arrangement in front of a rolling mill, even in extremely narrow spaces. However, it is also possible, as an alternative, for only some wheels to be steerable, or to be steerable around a smaller steering angle. In this way, the arrangement of stand change carriages can be configured based on the rolling mill.

[0019] In this case, the contact surface of the stand storage area on which the stand rests after being received by the stand exchange cart is spaced from the factory floor by no more than 50 cm, preferably no more than 40 cm, more preferably no more than 30 cm, and more preferably no more than 20 cm. In this way, for normal stands, it is possible to ensure that the lowest point of the stand moves just above the factory floor. However, instead, a recess can be provided in the factory floor to allow the stand to be moved at a lower height, or a crane or the like can be used to lift the stand to a higher contact surface and move it at that height.

[0020] In a typical bar mill, the rolling line extends approximately 0.9 m to approximately 1.1 m above the factory floor, and in some cases even lower. Therefore, the underside of the stand is usually located only approximately 0.2 m to approximately 0.3 m above the factory floor. Therefore, it is desirable that the installation height of the stand exchanger should not be higher in the area of ​​the stand receiving area. According to this preferred configuration, the contact surface of the stand storage area on which the stand rests after being received by the stand exchanger is spaced 40 cm or less from the factory floor, so that the stand exchanger can be advantageously used on existing rolling mills without the need for complicated adjustments to the mill or factory floor. In some cases, the lowest point of the stand is a downwardly protruding joint. This determines the lowest point. According to the above advantageous configuration, the stand exchanger is simply designed so that the joint is a safe small distance from the ground. However, not all stand designs have joints that protrude downward from the stand, and therefore for these stands a lower contact surface is possible than for stands with such downwardly protruding joints. A lower contact surface is particularly advantageous when replacing stand exchange systems based on control cables, where the height of the rolling mill above the factory floor is low due to constructional conditions. Alternatively, the stand area can be designed with a higher contact surface.

[0021] Preferably, the stand exchange carriage is equipped with a steering drive for steering at least two, preferably all, of the wheels. This type of stand exchange carriage can be operated in a rail-mounted or rail-free manner. In other words, in the case of rail-free operation, steering of the stand exchange carriage and setting of the direction of movement are possible by corresponding setting of the steering drive. In the case of a rail-mounted stand exchange carriage, a steering drive is advantageous because it is no longer necessary to provide a switching actuator at the switching point itself for steering the wheels at the switching point between two sections of track. However, the wheels of the stand exchange carriage can also be automatically steerable without a steering drive, for example by means of a rail.

[0022] Preferably, the steering drive comprises a chain drive, so that a central input to the steering drive can be easily distributed to each steerable wheel of the stand exchange carriage. Alternatively, the steering drive can also be designed differently, in particular by providing several drives, each steering one wheel.

[0023] More preferably, the steering drive comprises a spindle, which can be integrated into the chain drive, and which makes it possible to ensure that the steering drive is self-locking.

[0024] In an advantageous embodiment, at least one hydraulic motor, together with its associated wheels, can be turned around the steering axis. The motor and wheels thus form, so to speak, a steerable drive unit. A ring gear is non-rotatably attached to the drive unit, with which, for example, a gear of a steering drive can engage, thereby forming a gearbox. In this way, the wheels can be steered instantly without the application of significant force.

[0025] Preferably, during operation of the stand exchange carriage, one stand location is arranged, as viewed from above, between at least two wheels. As a result, the installation height of the stand exchange carriage in the area of ​​the stand location can be kept particularly low, since it is not restricted by the space required for the wheel pivot area. This makes it possible to push the stand from a very low stand base of the rolling mill onto the stand location of the stand exchange carriage without overcoming a significant height difference.

[0026] Preferably, the stand change carriage is equipped with an energy source, in particular a battery, for supplying energy to the at least one hydraulic motor. This type of configuration makes the stand change carriage independent of external energy sources. This makes it possible to completely dispense with the provision of supply lines, in particular cable carriers for cables, etc. to the stand change carriage, so that the stand change carriage is not limited in terms of its travel radius. However, an external energy supply is also possible in principle.

[0027] Advantageously, at least one hydraulic motor is part of a closed hydraulic circuit with a pump, which is preferably designed without a tank. If the hydraulic motor is in a closed circuit with a pump, pressure can be applied to the hydraulic fluid circulating in the closed system, the hydraulic circuit, in order to operate the hydraulic motor. In this case, for example, there is no need to provide the stand exchange cart with a pressure accumulator that needs to be constantly filled from the outside. In this way, an autonomously functioning stand exchange cart can be realized. The omission of a tank allows for a particularly compact design. On the other hand, providing a tank can also have advantages.

[0028] Preferably, a battery-operated electric motor is mounted on the stand exchange carriage to supply hydraulic pressure to, and thereby drive, at least one hydraulic motor. This particularly preferred embodiment constitutes a powerful, pollution-free, autonomously functioning variant of the stand exchange carriage. In this case, the electric motor can be mounted at a point on the stand exchange carriage that does not impair the installation height of the stand storage area. The same applies to the battery.

[0029] Preferably, the stand change carriage is equipped with an inductive charging mechanism. If a rechargeable battery is used as an energy carrier for supplying the electrical components of the stand change carriage, the battery can be charged in a contactless manner. For example, when charging the stand change carriage, it is conceivable to move the stand change carriage equipped in this way in a charging compartment of a rolling mill or stand workshop, where the mating part of the inductive charging mechanism is located underground or above ground. In order to use areas with particularly high energy demands and at the same time take advantage of relatively long dwell times, this charging compartment can also be installed directly in the rolling mill. As a result, the battery can be of small dimensions.

[0030] The stand change car preferably includes a wireless data gearbox device that controls the stand change car, so that commands and parameters for the stand change car can be transmitted to the stand change car from an external control system. For example, it is conceivable that the stand change car can be moved remotely between different locations within the rolling mill, stand workshop, and / or between the rolling mill and stand workshop as required. In this case, control can be fully or partially autonomous. For example, in an automated process, it is conceivable that a monitoring system recognizes a stand change or finds that one is necessary and then prepares the stand change car at the stand workshop or rolling mill.

[0031] Further preferably, the data gearbox device is configured to transmit one or more operating states of the stand exchange cart, preferably to the control system and / or other stand exchange carts. The operating states may include, but are not limited to, the battery charge state, the load state by the stand, and the position of the stand exchange cart. This enables fully autonomous operation of the stand exchange cart as an "autonomous guided vehicle" or "autonomous mobile robot". Multiple stand exchange carts can thus exchange their operating states with each other directly and / or indirectly via the control system, so that these states can also be taken into account in their control.

[0032] Preferably, the stand exchange cart comprises at least four stand storage locations.

[0033] Many rolling mills are designed with four stands arranged one behind the other in the rolling direction, and in such a stand base it is particularly advantageous to also provide four stand spaces for the stand exchange carriage, so that all the stands can be exchanged simultaneously using the stand exchange carriage.

[0034] Preferably, the stand holder is designed to receive a stand having a hexagonal outer shape when viewed along the rolling direction of the stand, but alternatively, the stand holder can be designed to receive a stand of a different shape, for example a regular stand having a square outer shape.

[0035] In particular in the case of hexagonal stands, but in principle also in the case of square stands, the joints of the roller shafts, by means of which the rolling torque is introduced onto the roller shafts, may extend obliquely downwards and to the side from which the stand is changed. In this configuration, the stand changing carriages described above can make an additional contribution to the safety of the machine, since they cover these joints when the rolling mill is in operation, provided that they remain on the stand base during operation of the rolling mill.

[0036] Further advantages and developments of the invention will become apparent from the following description of the drawings and from all claims. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a side perspective view of a preferred stand exchange dolly. [Figure 2] 2 is a view of the preferred stand exchange carriage of FIG. 1 from the opposite side. [Figure 3] FIG. 1 is a top view of a preferred stand exchange dolly. [Figure 4] FIG. 1 is a bottom view of a preferred stand exchange dolly. [Figure 5] 1 is a side view of a preferred stand exchange trolley with one stand location occupied by a stand; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0038] FIG. 1 shows a preferred stand exchange carriage 10 that receives four stands. To this end, the stand exchange carriage 10 is provided with four stand storage spaces 16, all designed to receive individual stands. FIG. 1 shows the side of the stand exchange carriage that faces the rolling mill during stand exchange. Each stand storage space 16 includes a recess 18 in the body 11 of the stand exchange carriage 10 and a pair of sliding rails 17 on either side of the recess 18. Each stand can be pushed onto the stand exchange carriage 10 on the sliding rails 17, or lifted onto the stand exchange carriage 10. In this way, the pair of sliding rails 17 forms a contact surface for the stand housing of the received stand, and the recesses 18 form spaces for stand parts that protrude from the stand housing, such as a coupling for the rotating shaft. The stand exchange carriage 10 includes three intermediate spaces 28, one for each stand storage space 16. As will also be seen below, further components, in particular wheels 20, are arranged below the stand exchange carriage 10 in said intermediate space 28. On the upper side, the outer intermediate space 28 accommodates further components of the steering drive under a cover 27, as will be explained in more detail below.

[0039] 2 shows the stand exchange carriage 10 from the opposite side. The recess 18 is closed on this side, so that the stand exchange carriage has a substantially uniform installation height, except for structures above the intermediate space 28 and in the rear and front regions of the carriage. In this embodiment, a hydraulic pump 32 is mounted on its side, which is driven by an electric motor 33. In principle, the hydraulic pump 32 and / or the electric motor 33 could be accommodated elsewhere on the stand exchange carriage 10. However, the illustrated side mounting is advantageous, since these components are not in the way when approaching the rolling mill. The hydraulic pump 32 supplies pressurized hydraulic oil to the hydraulic system of the stand exchange carriage 10.

[0040] Additionally, a chain drive 22 is provided on the side thereof. The chain drive 22 is part of a steering system described in more detail below and serves to distribute the central input of the steering drive to all steerable wheels of the stand exchange carriage.

[0041] Figure 3 shows the stand exchange carriage 10 from above. In this view, the cover 27 covering the two outer intermediate spaces 28 has been removed, thereby revealing the spindle rods 25, each of which is located in one of the intermediate spaces 28. The spindle rods 25 comprise spindles 26 in two parts. A sprocket 34 is non-rotatably mounted on the spindle rod 25 on the side of the chain drive 22, with which the chain drive 22 engages. The spindles 26 each mesh with an upper gear 29, which in turn drives a shaft 31 arranged perpendicular to the drawing.

[0042] FIG. 4 shows the stand exchange carriage 10 from below. In this view, the recess 18 is here a raised portion of the body 11 of the stand exchange carriage 10. There is sufficient space in the intermediate space 28 to accommodate the drive units 24, each consisting of a wheel 20 and a hydraulic motor 21. The hydraulic motor 21 is integrated into the hydraulic system of the stand exchange carriage 10 in a manner conventional in the art. To improve clarity, the necessary hydraulic lines are not shown. Overall, the stand exchange carriage 10 comprises four structurally identical drive units 24, two of which share one of the intermediate spaces 28. In this embodiment, the hydraulic motors 21 of the drive units 24 are designed as radial piston motors, the longitudinal dimension of which is less than 20 cm. Therefore, the drive units 24 are extremely compact overall. Furthermore, a ring gear 23 is attached to the drive units 24. Each drive unit 24 can rotate together with the ring gear 23 around a steering axis perpendicular to the drawing. Due to its compact design, the drive units 24 can rotate approximately 360° around the steering axis without interfering with the body 11 of the stand exchange cart 10, despite the narrow intermediate space 28. The direction of movement of each wheel 20 can thus be set as desired, so that the stand exchange cart 10 can instantly make any desired changes in its direction of movement. In the position shown in FIG. 3, all wheels 20 are oriented perpendicular to the longitudinal direction of the stand exchange cart, along which the stands are aligned in a row. In this position, the stand exchange cart can be moved sideways toward the rolling mill. A lower gear 30 meshes with the ring gear 23 of each drive unit, so that the respective drive unit 24 is rotated around the steering axis by rotation of the lower gear 30. Thus, four such lower gears 30 are provided in total, which are part of the steering drive system of the stand exchange cart 10. Each lower gear 30 is connected via a shaft 31 to an associated upper gear 29, and thereby to the chain drive 22. The mechanism is adapted to steer the wheels 20 in unison and in synchronization when the chain drive 22 is in operation.However, in addition or instead, embodiments are also conceivable in which only two wheels 20, in either case sharing an intermediate space 28 or arranged on one side of the stand exchange cart 10, can be steered independently of the other two wheels 20. This makes it possible, for example, to efficiently turn the stand exchange cart 10. Preferably, for this purpose, the rotation directions of the individual hydraulic motors can also be set separately from one another. The chain drive 22 can be driven hydraulically, for which reason it is integrated into a hydraulic system, although drive using an electric motor is also possible.

[0043] A battery 35 or battery pack is located in the central intermediate space 28, which battery or battery pack powers the electric motor 33 and other electrical components. In this way, the illustrated stand exchange cart 10 can move completely autonomously.

[0044] 5 shows the preferred stand exchange carriage 10 from the side facing the rolling mill in the case of a stand exchange, with the stand 13 received in the stand storage 16 on the left side of the line of sight. It is clear that the joints 15 of the stand 13, which protrude from the stand housing 14, fit into the spaces of the recesses 18 in the stand storage 16. This figure also shows that the factory floor H is provided with rails S embedded in it, on which the wheels 20 of the stand exchange carriage roll. In this embodiment, the installation height B of the stand storage 16, i.e. the distance between the contact surface of the stand storage 16 and the factory floor H, is 39 cm. [Explanation of symbols]

[0045] 10 Stand exchange cart 11 Main unit 13 Stand 14 Stand housing 15 Joint 16 Stand space 17 Sliding rail 18 Depression 20 wheels 21 Hydraulic motor 22 Chain drive unit 23 Ring Gear 24 Drive unit 25 Spindle rod 26 Spindle 27 Cover 28 Intermediate Space 29 Upper Gear 30 Lower gear 31 Shaft 32 Hydraulic pump 33 Electric Motor 34 sprocket 35 Battery H Factory Floor S-rail B Installation height

Claims

1. A stand exchange carriage (10) for simultaneously receiving and transferring a plurality of stands (13) of a rolling mill for rolling metal bars, wire rods, or tubes, comprising: a plurality of stand locations (16), each of which can receive one of the stands (13) individually; a plurality of steerable wheels (20) for transporting said stand (13) on rails (S) or along a railless factory floor (H); at least one hydraulic motor (21) operatively connected to at least one of said wheels (20) for driving said wheels; A stand exchange cart equipped with:

2. 2. The stand exchange carriage according to claim 1, wherein the hydraulic motor (21) is a radial piston motor or an axial piston motor.

3. 3. A stand exchange trolley according to claim 1 or 2, wherein each wheel (20) is associated with, i.e. operatively connected to, its own at least one hydraulic motor (21).

4. 4. A stand exchange trolley according to any one of claims 1 to 3, wherein at least two, preferably all, of the wheels (20) are steerable to effect a change in direction of movement of at least 30° or more, preferably 90° or more.

5. 5. A stand exchange trolley according to any one of claims 1 to 4, wherein the contact surface of the stand storage area (16) has an installation height (B) of 50 cm or less, preferably 40 cm or less above the factory floor (H).

6. a steering drive for steering at least two, and preferably all, of said wheels (20); the steering drive preferably comprises a chain drive (22); The stand exchange cart according to any one of claims 1 to 5.

7. 7. The stand exchange trolley according to claim 6, wherein at least one hydraulic motor (21) and the associated wheels (20) form a drive unit (24) on which a ring gear (23) is non-rotatably mounted and which is pivotable about a steering axis.

8. A stand exchange cart according to any one of claims 1 to 7, wherein, during operation of the stand exchange cart (10), at least one stand storage space (16) is positioned between at least two of the wheels (20) when viewed from above.

9. 9. A stand exchange trolley according to any one of the preceding claims, comprising an energy source, in particular a battery (35), for supplying energy to said at least one hydraulic motor (21).

10. the at least one hydraulic motor (21) being part of a closed hydraulic circuit comprising a pump (32); The closed hydraulic circuit is preferably designed without a tank. A stand exchange cart according to any one of claims 1 to 9.

11. 11. The stand exchange trolley according to any one of claims 1 to 10, wherein a battery-operated electric motor (33) is mounted to supply hydraulic pressure to at least one of the hydraulic motors (21) and thereby drive the hydraulic motors.

12. A stand exchange trolley according to any one of claims 1 to 11, provided with an inductive charging mechanism.

13. 13. A stand exchange cart according to any one of claims 1 to 12, comprising a wireless data gearbox device for controlling the stand exchange cart (10), said wireless data gearbox device preferably further configured to transmit an operating status of the stand exchange cart (10).

14. A stand exchange trolley according to any one of claims 1 to 13, comprising at least four stand storage locations (16).

15. 15. A stand exchange trolley according to any one of claims 1 to 14, wherein the stand storage (16) is designed to receive a stand (13) having a hexagonal outer shape when viewed along the rolling direction of the stand (13).

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