COLD-PILGER ROLLING MILL

Abstract

Pilger rolling mill for working a hollow into a tube has a first roll stand mounted linearly moveable in a direction of motion. Translational motion of the roll stand causes rotational motion of the drive gear due to the cogging of the drive gear with the gear rack and, hence, also rotational motion of the roller arranged on the shaft of the drive gear and rotational motion of the other one of the two rollers in the opposite direction. Roll stand is connected with a crank drive and rotational motion of a motor drive is transformed into an oscillating translational motion of the roll stand by a connecting rod. Gear rack holder allows adjustment of the pilger rolling mill with respect to tube diameters of finished rolled tubes by arranging the first roll stand exchangeable by a second roll stand with a second dimension being different from the first dimension.

Claims

1. A pilger rolling mill for working a hollow into a tube comprising: a first roll stand mounted linearly movable in a direction of motion, wherein two rollers are pivotably mounted on shafts on the roll stand for working the hollow into the tube, wherein one of the rollers is arranged on a shaft with a drive gear and wherein the drive gear cogs with a fixed gear rack, and wherein the gear rack is attached to a gear rack holder such that a translational motion of the roll stand causes a rotational motion of the drive gear and the roller; and a crank drive connected to the roll stand, wherein the crank drive transforms a rotational motion of the motor drive by a connecting rod into an oscillating translational motion of the roll stand during operation of the pilger rolling mill, and wherein the gear rack holder is arranged in a way that the first roll stand with a first dimension is exchangeable by a second roll stand with a second dimension being different from the first dimension.

2. The pilger rolling mill according to claim 1, wherein the gear rack holder is arranged in a way that the gear rack is attachable at the gear rack holder at at least two positions being separated from each other in a direction parallel to the shafts of the rollers.

3. The pilger rolling mill according to claim 1, wherein the gear rack holder is arranged in a way that the gear rack is attachable at the gear rack holder at least at two positions being separated from each other in a direction perpendicular to the shafts of the rollers and perpendicular to the direction of motion of the roll stand, and wherein a distance between these positions measured in a direction perpendicular to the shafts of the rollers and perpendicular to the direction of motion of roll stand is at least 10 mm.

4. The pilger rolling mill according to claim 1, wherein the pilger rolling mill comprises two gear rack holders with gear racks mounted on these gear rack holders arranged mirror symmetrically with respect to a reference plane being perpendicular to the shafts of the rollers, wherein the shaft of one of the two rollers, preferably the lower roller, carries a drive gear on each side of the reference plane, wherein both drive gears cog with one of the gear racks each, and wherein a cylindrical axis of the hollow receivable between the rollers, lies within the reference plane.

5. The pilger rolling mill according to claim 1, wherein the gear rack holder is mounted pivotably away from the roll stand with respect to an axis being parallel to the direction of motion of the roll stand, such that a fast exchange of the roll stand is enabled.

6. The pilger rolling mill according to claim 1, wherein the gear rack holder is pivotably mounted with respect to an axis being parallel to the direction of motion of the roll stand, and wherein the gear rack holder is hydraulically bracable in a direction perpendicular to the shafts of the rollers, such that the gear rack holder absorbs forces acting in a direction parallel to the reference plane during operation of the pilger rolling mill.

7. The pilger rolling mill according to claim 1, wherein the gear rack holder or parts thereof are exchangeable by a gear rack holder or parts thereof, such that the gear rack is attachable to the gear rack holder at least at two positions being separated from each other in a direction parallel to the shafts of the rollers.

8. The pilger rolling mill according to claim 1, wherein the roll stand is movably mounted in a floating bearing, preferably in a hydraulically liftable slide, and wherein the floating bearing is arranged in a way that it facilitates an adjustment of the clearance between the drive gear and the gear rack in a direction perpendicular to the shafts of the rollers and perpendicular to the direction of motion of the roll stand.

9. The pilger rolling mill according to claim 1, wherein the rollers (2, 3) are arranged one above the other, and wherein the shafts of both rollers are connected by two gear wheels cogging with each other in a way that a rotational motion of one of the two rollers (2, 3) leads to a rotational motion of the other one of the rollers (2, 3) in the opposite direction.

10. The pilger rolling mill according to claim 1, wherein the shafts of the rollers comprise at least one bearing each, and wherein at least one bearing of one of the two rollers and one bearing of the other one of the two rollers are hydraulically braced against each other.

11. The pilger rolling mill according to claim 1, wherein a stroke length of the roll stand, which is determined by the eccentricity of a crankshaft pin being attached at the connecting rod, is set for the largest processable tube diameter and remains the same for all processable tube diameters.

12. The pilger rolling mill according to claim 1, wherein a stroke length of the roll stand, which is determined by the eccentricity of a crankshaft pin being attached to the connecting rod, is adjustable for different processable tube diameters.

13. The pilger rolling mill according to claim 1, wherein the crank shaft of the crank drive comprises a co-rotating balance mass, wherein the balance mass is arranged in a way that it compensates or almost compensates first order moments conducted by the first roll stand, which is placed in the pilger rolling mill, and wherein the mass of the first roll stand is smaller than the mass of the second roll stand.

14. The pilger rolling mill according to claim 1, wherein the pilger rolling mill comprises a compensation shaft with a second co-rotating balance mass, wherein the crank shaft and the compensation shaft are effectively connected in a way that the compensation shaft rotates at double angular velocity of the crank shaft during operation of the cold pilger rolling mill, wherein the second balance mass is arranged in a way that it compensates or almost compensates first order moments conducted by the first roll stand, which is placed in the pilger rolling mill, and wherein the mass of the first roll stand is smaller than the mass of the second roll stand.

Description

[0058] Further advantages, features and applications of the present invention become apparent from the following description of a preferred embodiment and from the accompanying figures.

[0059] FIG. 1 shows a schematic cross-sectional side view of a layout of a pilger rolling mill according to an embodiment of the present invention.

[0060] FIG. 2a shows a front view of a first roll stand of the pilger rolling mill of FIG. 1.

[0061] FIG. 2b shows a diagonal view from above onto the roll stand of FIG. 2a with the gear rack holder in an open position.

[0062] FIG. 3a shows a front view of a second roll stand of the pilger rolling mill of FIG. 1.

[0063] FIG. 3b shows a diagonal view from above onto the roll stand of FIG. 3a with the gear rack holder in an open position.

[0064] In FIG. 1, the layout of a pilger rolling mill according to the invention is shown in a schematic cross-sectional side view, wherein features not essential for the understanding have been omitted. The shown pilger rolling mill comprises a roll stand 1 with rollers 2, 3, two drive gears 6 arranged on the shaft of the lower roller 3, two gear racks 5 each attached to a gear rack holder 4, a calibrated mandrel 7 as well as a feed clamping carriage 8. Here, the drive gears 6 are not visible, since one is hidden by the lower roller 3 and the other has been omitted in this illustration for the sake of clarity. The gear racks 5 as well as the gear rack holders 4 are not shown in FIG. 1 either.

[0065] In the shown embodiment, even though not visible in FIG. 1, the pilger rolling mill comprises two gear rack holders 4 being arranged mirror symmetrically with respect to a reference plane, which is perpendicular to the shafts of the rollers. Fixed gear racks 5 are attached to these gear rack holders 4. Here, the gear rack holders 4 are pivotably mounted away from the roll stand 1 with respect to a pivoting axis 13 extending parallel to the direction of motion of the roll stand.

[0066] During pilgering at the rolling mill shown in FIG. 1, the hollow 9 is fed stepwise in a direction towards the mandrel 7 or over the mandrel 7, respectively. At the same time, the rotating rollers 2, 3 are moved back and forth horizontally over the mandrel 7 and, hence, over the hollow 9. In this process, the horizontal motion of the rollers 2 and 3 is determined by the roll stand 1, at which the rollers 2, 3 are pivotably mounted. The roll stand 1 is moved back and forth with the crank drive in the direction parallel to the mandrel, while the rollers 2, 3 themselves maintain their rotation due to the gear racks 5 which are fixed relative to the roll stand 1. Drive gears 6, which are rigidly corrected to the lower roller axis, cog with the gear racks 5. In this process, firstly a translational motion of the roll stand 1 is transformed into a rotational motion of the drive gears 6. At the shaft of the lower roller 3, the drive gears 6 are arranged right and left to each gear wheel 14 not shown in FIG. 1, such that the rotational motion of the drive gears 6 causes a rotational motion of the lower gear wheels 14. The lower gear wheels 14 cog with one upper gear wheel 15 of the same diameter each, which are arranged vertically one above the other and are not shown in FIG. 1, wherein the upper gear wheel 15 is arranged on the shaft of the upper roller 2. Due to this, the upper gear wheels 15 are rotated with the same angular velocity as the lower gear wheels 14, but with the opposite direction of rotation when compared with the lower gear wheels 14. Hence, by the gear wheels 14, arranged on the shaft of the lower roll 3, cogging with the gear wheels 15, arranged on the shaft of the upper roller 2, a rotational motion of the rollers 2 and 3 is caused in opposite directions with respect to each other.

[0067] Furthermore, each of the shafts of the upper and lower rollers 2, 3 comprises a left and right bearing, wherein the left bearing of the upper roller is hydraulically braced against the left bearing of the lower roller 3 as well as the right bearing of the upper roller 2 is hydraulically braced against the right bearing of the lower roller 3. The hydraulic bracing of the left and right bearings of both rollers 2, 3 against each other facilitates a precise adjustment of the roller slit. As a result, a very uniform shape of the tubes is obtained during rolling.

[0068] The feed of the hollow 9 over the mandrel 7 is carried out by the feed clamping carriage 8, which enables a translational motion in a direction parallel to the axis of the mandrel 7. The conically calibrated rollers 2, 3, arranged vertically one above the other in the roll stand 1, roll opposite to the feed direction of the feed clamping carriage 8 on the shell surface of the tube to be processed in a direction parallel to the cylindrical axis of the tube. The so-called pilgrim jaw created by the rollers grips the hollow 9. And the rollers 2, 3 push away a small material wave from the outside, which is stretched to the desired wall thickness by a smoothing caliber of the rollers 2, 3 and of the mandrel 7 until an idling caliber of the rollers 2, 3 releases the finished tube. During rolling, the roll stand 1 with the rollers 2, 3 fixed thereon moves opposite to the feed direction of the hollow 9. By the feed clamping carriage 8, the hollow 9 is pushed forward another step towards the mandrel after reaching the idling caliber of the rollers 2, 3, while the rollers 2, 3 together with the roll stand 1 move back to their horizontal starting position. At the same time, the hollow 9 is rotated with respect to its own axis in order to achieve a uniform shape of the finished tube. By rolling each tube section multiple times, a uniform wall thickness and circularity of the tube as well as uniform inner and outer diameters are achieved.

[0069] For a precise adjustment of the clearance between the drive gear 6 and the gear rack 5 in a direction perpendicular to the shafts of the rollers 2, 3 and perpendicular to the roll stand's direction of motion, the roll stand in FIG. 1, even though not noticeable, is mounted movable in a floating bearing, which here is formed a hydraulically liftable slide. The hydraulic bearing, besides the possibility of precise adjustments between drive gear 6 and gear rack 5, is distinguished by the possibility of easy assembly, which particularly simplifies and speeds-up the exchange of the roll stand 1. As a consequence, the downtimes related to an exchange of a roll stand can be reduced considerably. Furthermore such a bearing of the rollers 2, 3 does not require wear intensive seals and pistons. That means that the hydraulic bearing is essentially maintenance free and free of wear.

[0070] The stroke length of the pilger rolling mill shown in FIG. 1 is uniform for all processable tube diameters and is determined by the largest tube diameter to be processed in the pilger rolling mill.

[0071] This facilitates a simplified operating procedure, since no elaborated change of the crank pin 21 is required. Rather, the crank pin 21 stays the same for all processing steps.

[0072] In an alternative embodiment, it would be possible to design the stroke length of a pilger rolling mill adjustable for different processable tube diameters. For this, the distance between the rotation axis of the fly wheel of the crank drive and the fixing point of the connecting rod on the fly wheel is adjusted accordingly. This means that the crank pin 21 is modified. Consequently, the stroke length can be adjusted optimally with respect to the tube diameter to be processed, such that the different processable tube diameters can be manufactured with a better precision when compared to a stroke length staying the same for different processable tube diameters. For this, however, the elaborate change of the crank pin 21 has to be accepted.

[0073] In the shown embodiment, further, a central controller 20 is provided, which is connected to the drive of the compensation shaft 17 as well as to the drive of the crank shaft. The controller 20 controls the drives in a way that their drive shafts rotate in the same direction, wherein the rotational frequency of the compensation shaft 17 is double the rotational frequency of the crank shaft.

[0074] Furthermore, the controller 20 guarantees an angularly synchronous rotation of both balance masses 16, 18 of crank shaft and compensation shaft 17. This means that both balance masses 16, 18 are positioned at the same angle after one revolution of the crank drive, wherein the balance mass 18 of the compensation shaft 17 performs two revolutions within the time interval in which the crank shaft performs a single revolution.

[0075] In FIG. 2a, a front view of the roll stand of the pilger rolling mill of FIG. 1 is shown. The roll stand 1 with a mass M.sub.1 is arranged for the processing of hollows with a diameter between 30 mm and 60 mm. The maximum stroke number of the roll stand, i.e. the maximum number of forth and back motions of the roll stand per time unit, is 200 per minute for the present embodiment shown in FIG. 2a. Since the productivity of a cold pilger rolling mill directly depends on the stroke number of the roll stand, a number of strokes per minute as large as possible is desired due to economic reasons.

[0076] The roll stand 1 in FIG. 2 comprises an arrangement of rollers 2, 3 and drive gears 6 being mirror symmetrically with respect to a reference plane 11, which is perpendicular to the shafts of the rollers 2, 3, wherein a cylindrical axis of the hollow 9, to be received between the rollers 2, 3, lies within the reference plane 11. Here, the drive gears 6 are rigidly connected with the shaft of the lower roller 3 and cog with the gear racks 5, which are also arranged mirror symmetrically at the gear rack holders 4. The gear racks 5 are not shown in FIG. 2a, since they are hidden by the gear rack holder 4.

[0077] In order to absorb the forces acting in a direction parallel to the reference plane 11 during operation of the pilger rolling mill, the gear rack holders 4 are hydraulically braced in a direction perpendicular to the shafts of the rollers. The hydraulic braising is conducted by a system of hydraulic nuts 12, which essentially consist of a ring piston and a cylinder. By a temporary pressure impact, a force is set up in a direction perpendicular to the shafts of the rollers. Due to this, temporary clamping and sliding forces can be set up, such that the roll stand 1 is held in a fixed position during the rolling process in a direction parallel to the shafts of the rollers 2, 3. Hence, the roll stand is prevented from sliding away due to torsional forces occurring.

[0078] Furthermore, the gear rack holder 4 shown in FIG. 2a is mounted pivotably away from the roll stand with respect to a pivot-axis 13 extending parallel to the gear rack 5. The pivot-axis is not shown in FIG. 2a due to its orientation into the image plane. By an easy raising of the gear rack holder 4 away from the roll stand, the drive gears 6 lose their contact to the gear racks 5, such that the roll stand 1 is not blocked by the gear rack holder 4 during lifting by a crane. Therefore, the roll stand 1 can be exchanged freely and in an easy and quick manner. This goes along with a larger flexibility of the processing steps with respect to the expandable range of processable tube diameters.

[0079] FIG. 2b shows a diagonal view from above onto the roll stand of FIG. 2a but with the gear rack holder 4 in an open position, wherein that the gear rack holder 4 has been pivoted with respect to its pivot-axis 13 away from the roll stand in the direction denoted by the arrow. As a result, the gear rack 5, which is attached to the gear rack holder 4, has no contact with the drive gear 6 any longer. Hence, the roll stand 1 is not blocked by the gear rack holder 4 any longer and can be removed from the pilger rolling mill by lifting in an easy and quick manner and can be exchanged by a second roll stand 1 with different dimensions.

[0080] FIG. 3a shows a front view of a second roll stand 1 of the pilger rolling mill of FIG. 1. In contrast to FIG. 2a, the roll stand 1 has larger dimensions with respect to the three spatial dimensions as well as with respect to the diameter of the rollers 2, 3 and drive gears 6, but the roll stand 1 can be installed into the same pilger rolling mill as shown in FIG. 1. The larger dimensions of the roll stand 1 shown in FIG. 3a are reflected in an increased mass when compared to the roll stand 1 of FIGS. 2a and 2b. In the present embodiment, the mass of the second roll stand is 2.5 times the mass M.sub.1 of the roll stand 1 of FIGS. 2a and 2b. Furthermore, the roll stand 1 shown in FIG. 3a is arranged for the processing of hollows with a diameter between 40 mm and 88 mm and, hence, for lager diameters when compared to the roll stand 1 of FIGS. 2a and 2b. The maximum stroke number of the roll stand 1 is 150 per minute, which is a correspondingly lower value in this regard.

[0081] The gear rack holder 4 according to the invention is located at a position further away from the reference plane 11 in a direction perpendicular to the reference plane 11 when compared with the gear rack holder 4 shown in FIG. 2a. In the embodiments shown in FIGS. 2a and 3a, this is enabled by a two-part design of the gear rack holders 4, 4. On the one hand, the gear rack holder comprises a basic carrier, and on the other hand, an adapter plate, which is attachable to the basic carrier in a way that the respective drive gear 6, 6 of the roll stand 1, 1 can cog with the gear rack 5, 5 attached to the respective gear rack holder 4, 4 at least at two positions separated from each other in a direction perpendicular to the reference plane 11. In case of FIG. 2a, this adapter plate is constructed larger in a direction parallel to the shafts of the rollers 2, 3 than in case of FIG. 3a, such that the gear rack 5 comprises a smaller distance from the reference plane 11 in the direction of the normal of the reference plane 11.

[0082] Besides the position parallel to the shafts of the rollers 2, 3, however, also an adjustment of the gear rack holder 4 is necessary in the direction perpendicular to the shafts of the rollers 2, 3 and perpendicular to the roll stand's 1 direction of motion. The required adjustment is caused by the larger diameter of the drive gear 6 when compared to the drive gear 6 shown in FIG. 2a. Such an adjustment is realized by the two-part gear rack holder 4 in terms of a basic carrier with adapter plates attached thereon and designed accordingly, such that the drive gear 6 of the roll stand 1 can cog with the gear rack 5, which is attached to the gear rack holder 4.

[0083] FIG. 3b shows a diagonal view from above onto the roll stand 1 of FIG. 3a. In this case, the gear rack holder 4 is pivoted away from the roll stand 1 with respect to the pivot-axis 13 extending parallel to the roll stand's direction of motion. The gear rack holder 4 is arranged in an open position like in FIG. 2b in such a way that the gear rack 5 attached to the gear rack holder 4 does not have any contact to the drive gear 6 of the roll stand 1. Even for an embodiment of a roll stand 1 with larger dimensions compared to the dimensions shown in FIGS. 2a and 2b, the roll stand 1 can be removed from the pilger rolling mill in an easy and quick manner with the pivot-mechanism exposing the roll stand 1.

[0084] For the purpose of original disclosure it is noted that all features, which a person skilled in the art derives from the present description, the figures and the claims, even though they are not concretely described in connection with certain further features, can be combined both as individual features as well as in arbitrary combinations with other features of the here disclosed features and groups of features as far as this is not explicitly ruled out or there are technical reasons that such combinations are not possible or nonsense. Only for the sake of the description's shortness and readability, an explicit and comprehensively description of all possible feature combinations has been omitted.

[0085] While the invention has been illustrated and described in detail in the figures and in the above description, this illustration and description is only by way of an example and is not meant to be a limitation of the scope of protection, which is defined by the claims. The invention is not limited to the disclosed embodiments.

[0086] Changes of the disclosed embodiments are obvious to a person skilled in the art on the basis of the figures and description and the attached claims. In the claims, the word comprise does not exclude other elements or steps, and the definite article a or an does not exclude a plural. The pure fact that certain features are claimed by separate claims does not exclude their combination. Reference numbers in the claims are not meant to be limiting to the scope of protection.

LIST OF REFERENCE NUMERALS

[0087] 1, 1 roll stand

[0088] 2, 2, upper roller

[0089] 3, 3 lower roller

[0090] 4, 4 gear rack holder

[0091] 5, 5 gear rack

[0092] 6, 6 drive gear

[0093] 7 calibrated mandrel

[0094] 8 feed clamping carriage

[0095] 9, 9 hollow

[0096] 10 cylinder axis of the hollow

[0097] 11, 11 reference plane

[0098] 12, 12 hydraulic nut

[0099] 13, 13 pivot-axis of the gear rack holder

[0100] 14, 14 lower gear wheel

[0101] 15, 15 upper gear wheel

[0102] 16 balance mass

[0103] 17 compensation shaft

[0104] 18 second balance mass

[0105] 19 connecting rod

[0106] 20 central controller

[0107] 21 crank pin