PIERCING MILL

Abstract

 A piercing mill, which can manufacture thin-wall tubes, can secure a sufficient support rigidity of disk roller, and can improve the ease of work for adjusting the position of the disk rollers. The piercing mill compresses a mill housing, a pair of disk frames 6 which can be opened sideward in a pivoting manner with reference to a pass line, and a pair of sliding frames 8 which are vertically arranged within each of the disk frames so as to be slidable. A skew angle of the disk roller 4 is set by sliding the sliding frames in opposite directions. The piercing mill improve the ease of work for positional adjustment required when the disk rollers are exchanged. In addition, since the skew angle of the disk roller can be set easily and reliably, the range of thin-wall tube rolling can be expanded.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a piercing mill for use with a seamless steel tube and, more particularly, to a piercing mill which enables thin-wall piercing without impairing the ease of work for adjusting position of disk rollers.

BACKGROUND ART OF THE INVENTION

[0002] As a method of manufacturing seamless steel tubes under hot working conditions, the Mannesmann tube-making process is widely employed. In this tube-making process, a round billet heated to a high temperature is fed as a material to be rolled into a piercing mill (a so-called "piercer"), which pierces the axial center portion of the round billet to obtain a hollow shell. The thus-obtained hollow shell is fed, directly or as needed after undergoing an expansion or wall-thinning process in an elongator having the same structure as that of the piercing mill, into a subsequent elongating mill such as a plug mill, a mandrel mill, or the like so as to be elongated. Subsequently, the thus-elongated tube undergoes a finishing process provided by a stretch reducer for shape correction, a reeler for polishing, and a sizer for sizing, thereby becoming a seamless steel tube product.

[0003] The piercing mill is comprised of a pair of piercing rollers disposed in a vertical direction with respect to a pass line of a material to be rolled, and a pair of disk rollers disposed in a direction perpendicular to the direction of layout of the piercing rollers. The piercing mill is arranged so as to pierce and roll the material while supporting and rotating it by use of the piercing rollers and the disk rollers. The piercing rollers and the disk rollers are integrally retained and fixedly positioned with respect to each other within a mill housing during at least the rolling operation.

[0004] As described above, the piercing mill processes the material while pressing the piercing rollers down on the material remained at a high temperature, and therefore working surfaces of the piercing rollers are damaged with a lapse of roll time. The disk rollers are also abraded when they come into contact with the material. For these reasons, the piercing rollers and the disk rollers must be periodically exchanged. Particularly, the disk rollers must be exchanged by lifting them one at a time by use of an overhead traveling crane while the mill housing is in an open state. Use of such an overhead traveling crane in the exchange the pair of disk rollers consumes much time, inevitably resulting in a reduction in the availability of the piercing mill.

[0005] Various measures have already been proposed to solve this problem associated with the exchange of the disk rollers of the piercing mill. One example is disclosed in Japanese Patent Publication (Kokoku) No. 63-64248; namely, the structure of a piercing mill capable of exchanging disk rollers without use of an overhead traveling crane. In this structure, the disk rollers are supported by drive shafts in a cantilever fashion and, therefore, have insufficient rigidity when they are positioned during operation. More specifically, if the disk rollers possess low support rigidity, they may rotate in an eccentric manner while in contact with the material, thereby generating surface flaws in the material.

[0006] If a thin-wall hollow shell is manufactured by piercing and rolling, a bulge in the outer circumference increases as the degree of draft in the wall thickness of the hollow shell increases, in turn making the hollow shell susceptible to guide flaws.

[0007] FIG. 1 is a schematic representation of the anomalous shape of a thin-wall hollow shell formed when the hollow shell is rolled by piercing rollers through use of disk rollers. In FIG. 1, material 1 to be rolled is helically traveling in a direction perpendicular to the plane of the drawing while being pierced by a plug 3 and rolled by piercing rollers 2, and disk rollers 4. At this time, if the bulge in the circumference of the material 1 becomes large as a result of a decrease in the degree of draft, the material 1 is partially drawn into the clearance between the edge of a material-receiving side of each disk roller 4 and the outgoing side of the corresponding piercing roller 2, thereby generating guide flaws in the outer surface of the material. If the amount of the drawn portion of the hollow shell is considerably large, the material stops rotating, thereby interrupting the rolling operation. As illustrated in FIG. 2, the disk rollers 4 are arranged so as to cross each other at a predetermined skew angle α (alpha) with respect to a pass line X-X along which the material travels while being rolled, such that the edges of the disk rollers 4 become parallel to outgoing sides of the piercing rollers 2 with a small clearance between them. In this case, if the support rigidity of the disk rollers 4 is insufficient, the disk rollers 4 rotate in an eccentric manner, thereby promoting generation of guide flaws.

SUMMARY OF THE INVENTION

[0008] The conventionally-proposed piercing mill is likely to generate flaws in the surface of a material to be rolled because of low support rigidity of disk rollers. Further, in the case where the disk rollers are arranged at a skew angle α, eccentric rotations of the disk rollers cannot be prevented, thereby promoting generation of the guide flaws.

[0009] In contrast, if an attempt is made to ensure sufficient support rigidity of the disk rollers, the structure of the piercing mill becomes complicated and attended by a further reduction in the ease of work for setting the skew angle α of the disk rollers and for adjusting the position thereof. The decrease in the ease of exchange of the disk rollers results not only in the reduced availability of the piercing mill but also in a reduction in the overall efficiency of manufacture of seamless steel tubes, particularly in the case of recent continuous Mannesmann tube manufacturing facilities aimed at highly efficient production of seamless steel tubes.

[0010] The object of the present invention is to solve the drawbacks in the conventional piercing mill and to provide a piercing mill which enables flexible manufacture of a variety of differently-sized seamless steel tubes in small quantities by improving the ease of work such as setting of the skew angle α of the disk rollers, while ensuring sufficient support rigidity of the disk rollers and expanding the range of thin-wall tube rolling, to thereby improve the performance of the piercing mill.

[0011] The gist of the present invention resides in a piercing mill for use in manufacturing seamless steel tubes as defined by the following (1) through (4). Part number used therein are described in FIG. 4 and 5, which will be described later.

(1) A piercing mill for use with a seamless steel tube manufacturing system having an integral type mill housing which houses a pair of piercing rollers 2 disposed so as to be opposite to each other with respect to a pass line, and a pair of disk rollers 4 disposed so as to be opposite to and to cross each other such that a clearance between the surface of a material-receiving side of each disk roller 4 and the surface of an outgoing-side of each piercing roller 2 becomes small. The piercing mill further comprises a pair of disk frames 6 which are attached to the respective lateral sides of the mill housing 5 and which can be opened sideward in a pivoting manner; and a pair of sliding frames 8 slidably arranged within each of the disk frames 6 and adapted to hold the disk roller 4 integrally formed with a shaft. The skew angle of each of the disk roller 4 is set by sliding the sliding frames 8 in opposite directions.

(2) The piercing mill described in (1) further comprises an upper chock frame 11 which is fitted to an upper portion of a shaft 4s of the disk roller 4 and which supports and incorporates a chock 13 while permitting pivoting of the chock 13; a lower chock frame 12 which is fitted around a lower portion of the shaft 4s of the disk roller 4 and which supports and incorporates the chock 13 while permitting pivoting of the chock 13; an upper opening control frame 10a which is attached to the upper sliding frame 8a of the pair of sliding frames and controls the opening of the upper chock frame 11; and a lower opening control frame 10b which is attached to the lower sliding frame 8b and controls the opening of the lower chock frame 12. The disk roller 4 integrally formed with the shaft 4s can be supported at both of its ends by respectively fitting the chock frames 11 and 12 into the upper and lower opening control frames 10a and 10b. In this case, a pin is preferably used to support the chock while permitting pivoting motion.

(3) The piercing mill as defined in (1) or (2) is characterized in that the height of the disk roller is controlled by a balancing device provided on the upper sliding frame 8a, and the opening of the disk roller is adjusted by screw-down mechanisms provided on the pair of sliding frames 8a and 8b.

(4) The piercing mill as defined in any one of (1) through (3) further comprises a rotary shaft 7 for supporting the shaft of the disk frame 6; clamping means 18 provided in the disk frame 6; and a clamping device 19 provided in the mill housing, whereby the disk frame 6 is fixedly supported in a heightwise direction thereof by means of the rotary shaft and the clamping device, as well as in the direction of pivotal movement of the disk frame 6 by the clamping device when it is closed and fixed to the mill housing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 

FIG. 1 is a view showing the anomalous shape of a thin-wall hollow shell when it is rolled by a piercing mill through use of disk rollers, and FIG. 2 is a schematic presentation of the setting the skew angle α of the disk rollers during rolling operation.

FIG. 3 is a view showing an example of the structure of a mill housing of a piercing mill according to the present invention.

FIG. 4 is a perspective view showing the overall structure by which a disk frame is supported when the disk frame is pivoted.

FIG. 5 is an illustrative perspective view of a main structure of the disk frame for supporting a disk roller integrally formed with a shaft.

FIG. 6 is a schematic illustration of an operation required to set the skew angle α of the disk roller.

FIG. 7 is a vertical cross-sectional view showing an example of the structure of the pair of disk rollers disposed so as to be opposite to each other within a mill housing.

FIG. 8 is a view showing an example of the structure of a clamping device disposed at a disk frame closure position in order to fix the disk frame to the mill housing.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] A piercing mill of the present invention is chiefly characterized by a pair of disk frames which are attached to the respective lateral sides of the mill housing and which can be opened sideward in a pivoting way; and a pair of sliding frames which are vertically arranged within each of the disk frames so as to be slidable and to hold the disk roller integrally formed with a shaft; wherein a skew angle of each of the disk roller is set by sliding the corresponding sliding frames in opposite directions.

[0014] Through adoption of the above-described configuration, it become possible to easily and reliably set the skew angle of the disk roller, while improving the ease of work for adjusting the height and opening of the disk rollers. More specifically, the disk rollers can be exchanged without use of an overhead traveling crane.

[0015] Further, the piercing mill comprises upper and lower chock frames which are provided at either end of the shaft of the disk roller and which support and incorporate chocks while permitting pivoting motion; and upper and lower opening control frames which are respectively attached to the upper and lower sliding frames and control the respective positions of the chock frames. The disk roller integrally formed with the shaft can be supported at both of its ends by respectively fitting the chock frames into the opening control frames.

[0016] As a result, in the piercing mill of the present invention, the clearance between the exit-side rollers and the disk rollers can be minimized, so that the range of thin-wall tube rolling can be expanded. Further, since sufficient support rigidity can be secured, it is possible to prevent the generation of surface flaws in the material which would otherwise result from eccentric rotation of the disk rollers when they come into contact with the material during piercing and rolling operation. Further, an example of the scheme for supporting the chock while permitting pivoting motion is a pin support.

[0017] The piercing mill further comprises a screw-down mechanism provided on each of the upper and lower sliding frames and a balancing device provided on the upper sliding frame or on each of the upper sliding frame and the upper opening control frame. The opening of the disk roller is adjusted by the screw-down mechanism, and the height of the disk roller is adjusted by the balancing device. As a result, it become possible to expand the range of thin-wall tube rolling by the piercing mill, while maintaining the ease of work for position adjustment and setting accuracy, and to facilitate the work for exchanging the disk rollers.

[0018] To ensure better accuracy of setting of the disk rollers, the piercing mill further comprises a rotary shaft for supporting the shaft of the disk frame, clamping means provided on the disk frame, and a clamping device disposed on the mill housing. The disk frame is fixedly supported in a heightwise direction thereof by means of the rotary shaft and the clamping means, as well as in the direction of pivotal movement of the disk frame by the clamping device when it is closed and fixed to the mill housing.

[0019] Accordingly, in the piercing mill of the present invention, it become possible to secure the support rigidity of the disk rollers and enable the production of tubes having a thinner wall, to thereby improve the performance of the piercing mill, while improving the ease of work for adjusting the position of disk rollers. Further, as described above, it is possible to achieve a reduction in the time required to exchange the disk rollers, as well as to save significantly labor in the operations themselves.

[0020] An example of a specific structure of the piercing mill of the present invention is shown in FIG. 3 through 8, with reference to which the effects will be described in detail. Throughout the drawings, elements common to the drawings are assigned the same reference numerals.

[0021] FIG. 3 is a view showing an example of the structure of a mill housing of a piercing mill according to the present invention. Of the surfaces of a mill housing 5 which constitutes the main body of the piercing mill, the surfaces in a direction perpendicular to a pass line X-X are opened. In the mill housing 5 are housed a pair of piercing rollers 2 which are disposed so as to be opposite to each other with respect to the pass line X-X, and a pair of disk rollers 4 which are disposed so as to be opposite to each other and orthogonal to the piercing rollers 2. A pair of disk frames 6 are supported by rotary shafts 7 on the respective lateral surfaces of the mill housing 5 and can be opened sideward in a pivoting manner. A disk roller 4 integrally formed with a shaft is supported on the internal surface of each disk frame 6.

[0022] FIG. 4 is a perspective view showing the overall structure by which a disk frame is supported when the disk frame is pivoted. The disk frame 6 is supported by the rotary shaft 7 and is pivoted by the action of an unillustrated pivot cylinder. Exchange of the disk roller is performed in a state in which the disk frame 6 is swung. Inside the disk frame 6, upper and lower sliding frames 8 and upper and lower opening control frames 10 attached thereto are provided in order to vertically support the disk roller 4.

[0023] FIG. 5 is a perspective view illustrating a main structure of the disk frame supporting the disk roller integrally formed with the shaft. As shown in FIG. 7 in an enlarged manner, the sliding frame pair 8 consisting of the pair of an upper sliding frame 8a and a lower sliding frame 8b is provided within the disk frame 6. The upper and lower sliding frames 8a and 8b can slide in the direction indicated by arrow by the operation of a hydraulic cylinder 9 and a screw-down jack 9a (a hydraulic cylinder for use with the upper sliding frame 8a is not shown in the drawing). The upper opening control frame 10a is provided at the front end of the center of the upper sliding frame 8a, and the lower opening control frame 10a is provided at the front end of the center of the lower sliding frame 8b.

[0024] In contrast, the disk roller 4 is integrally formed with a shaft 4s. In FIG. 5, an upper chock 13 is fitted to an upper part of the shaft 4s of the disk roller 4, and this upper chock 13 is connected to a chock frame 11 via pin support. Since the chock 13 is retained by and incorporated in the upper chock frame 11 through support by a pin 13p, it can be pivoted in the direction of a skew line with skewing operations, which will be described later. A lower chock frame 12 which incorporates and supports the chock 13 via a pin, as is the case with the upper chock frame 11, is fitted around a lower part of the shaft 4s.

[0025] A screw-down screw support groove 11c for receiving a screw-down screw of a balancing device, which will be described later, is formed in the upper chock frame 11, and the upper chock frame 11 is fitted into the upper opening control frame 10a provided in the upper sliding frame 8a. The lower chock frame 12 is fitted into the lower opening control frame 10b provided in the lower sliding frame 8b.

[0026] As a result of fitting of the chock frames 11 and 12 pin-supported at the opposite ends of shaft 4s of the disk roller 4 into the upper and lower opening control frames 10, the disk roller 4 are vertically supported through its the opposite ends such that the upper chock 13 and the lower chock 13 are aligned vertically. Subsequently, the chocks 13 incorporated in the respective chock frames 11 and 12 are tilted around the pin 13b as a result of sliding of the upper and lower sliding frames 8a and 8b in opposite directions, setting the skew angle α of the disk roller 4 to a predetermined angle.

[0027] FIG. 6 is a schematic illustration of an operation required to set the skew angle α of the disk roller. In the setting operation, the upper chock frame 11 is fitted into the upper opening control frame 10a, and the lower chock frame 12 is fitted into the lower opening control frame 10b, so that the disk roller 4 is at both of its ends supported and is positioned in axis Y1-Y1 perpendicular to the pass line X-X. When the sliding frames 8a and 8b are slid in opposite directions, the chock frames 11 and 12 cause parallel movement. With this movement, the chocks 13 having the pins 13p supported by the chock frames 11 and 12 are tilted about the pins 13p along Y2-Y2 axis, so that the disk rollers 4 is located on Y2-Y2 axis. Through these operations, the disk roller 4 is tilted at a predetermined skew angle α with respect to the pass line X-X.

[0028] The position of the disk roller 4; i.e., its height and opening is adjusted by the balancing device provided on the upper sliding frame, as well as by a screw-down mechanism provided on the sliding frame pair 8. The relationship between the arrangement of the disk rollers and the height and opening adjustment is shown in FIG. 7, which will be described next. As described above, the sliding of the disk roller in the front/back direction is performed by the operation of the hydraulic cylinder and the screw-down jack provided on each of the upper and lower sliding frames.

[0029] FIG. 7 is a vertical cross-sectional view showing an example of the structure of the pair of disk rollers disposed so as to be opposite to each other within a mill housing. In FIG. 7, the material 1 to be rolled is helically traveling in a direction perpendicular to the plane of the drawing, and a pair of disk rollers 4, 4' are disposed so as to support this material 1. Associated with piercing of the material 1, a thrusting force F1 and a rolling force F2 act on the disk rollers 4, 4'. The pair of disk rollers 4, 4' are identical to each other regarding construction exclusive of the degree of exertion of the thrusting force F1. Therefore, an explanation will be hereinbelow given to solely the construction and operation of the disk roller 4 of the disk roller pair provided on the lift side of the drawing.

[0030] As previously described, the chock frames 11 and 12 fitted around the shaft 4s of the disk roller 4 through chock 13 by means of pin 13p, are supported by the pair of upper and lower sliding frames 8a and 8b via the opening control frames 10a and 10b. As a result, the disk roller 4 is at both of its ends supported reliably, thereby providing sufficient support rigidity.

[0031] The balancing device 14 for controlling the height of the disk roller 4 is comprised of a screw-down (screw-up) screw 15 and a pull-back rod 16. The screw-down screw 15 is disposed on the upper opening control frame 10a, and the pull-back rod 16 is disposed on the upper sliding frame 8a. Although the screw-down screw 15 is disposed on the upper opening control frame 10a in FIG. 7, it may be provided on the upper sliding frame 8a.

[0032] The height of the disk roller 4 is set according to the amount of movement of the screw-down screw 15. That is, the screw-down screw 15 is inserted into the screw-down screw support groove 11c provided in the upper chock frame 11 and adapted to adjust the height of the disk roller 4. At this time, a pre-load is exerted on the disk roller 4. More specifically, as indicated by an arrow in the drawing, the pull-back rod 16 is inserted into the support groove 13c formed in the upper chock 13 and provides upward pressure in the direction opposite to the direction of screw-down action of the screw-down screw 15. This operation is called a "backlash elimination." Since the height of the disk roller 4 is controlled after the backlash has been absorbed, the accuracy of adjustment of the disk roller 4 is improved. As previously described, the disk roller 4' provided on the right side of FIG. 7 receives the thrusting force F1 from the material 1 in the opposite direction, and therefore the pre-load is exerted on the disk roller 4' in the direction opposite to the direction in which the disk roller 4 receives the pre-load. In other respects regarding construction and operation, the disk rollers 4, 4' on both sides of mill housing 5 are identical to each other.

[0033] Screw-down mechanisms 17 for controlling the opening of the disk roller 4 are each made up of the screw-down (screw-up) screw 15 and a pull-back rod (not shown), as is the case with the balancing device 14. The screw-down mechanisms 17 are provided to the respective upper and lower sliding frames 8a and 8b. As a result, the opening on the upper or lower side of the disk roller 4 is independently controlled according to the movement amount of the corresponding screw-down screw 15. The positions of the disk roller 4 are controlled while the backlash of the screw-down mechanism 17 by virtue of the pulling back action of the pull-back rod, and therefore the accuracy of adjustment of the disk roller can be considerably improved.

[0034] The disk frames are closed and fixedly attached to the mill housing during the piercing and rolling operation. To this end, as illustrated in FIG. 4, the disk frames 6 are each fixedly maintained in a heightwise direction thereof by a combination of the rotary shaft 7 pivotally supporting the disk frame 6 and clamping means 18 provided on the disk frame 6. In contrast, the disk frames 6 are fixed in a pivoting direction thereof by a clamping device 19 disposed on the mill housing 5 at a disk frame closure position.

[0035] FIG. 8 is a schematic representation showing an example of the structure of a clamping device disposed at a disk frame closure position in order to fix the disk frame to the mill housing. A clamping device 19 is made up of a hydraulic cylinder 19a, a clamp lever 19b, a clamp 19c, and a clamp block 19d. The disk frame 6 is fixed in its pivoting direction by the clamp lever 19b and the clamp 19c as a result of actuation of the hydraulic cylinder 19a via the clamp block 19d attached to the disk frames. In this case, it is desirable to provide a level liner 20 to prevent the deflection of the disk frame 6 under its own weight.

INDUSTRIAL APPLICABILITY

[0036] According to the piercing mill of the present invention, it become possible to improve the ease of work for positional adjustment required upon exchange of disk rollers without use of an overhead traveling crane, while enabling easy and reliable setting of a skew angle of the disk roller, whereby production of tubes having thinner wall is enabled. Further, the piercing mill is arranged so as to be able to support both ends of a shaft integrally formed with the disk roller, which allows ensure of sufficient support rigidity. As a result, the disk rollers are prevented from rotating in an eccentric manner during the piercing and rolling operations, in turn preventing generation of surface flaws in the material to be rolled.

[0037] Moreover, since the piercing mill of the present invention is equipped with superior position adjustment and clamping mechanisms, the ease of work for position adjustment and setting accuracy are maintained, and the ease of the work for exchanging disk rollers can be improved without impairment of its function.

[0038] Therefore, the piercing mill of the present invention can be widely utilized in the field of seamless tube production so as to improve the production efficiency.

Claims

1. A piercing mill for use with a seamless steel tube manufacturing system having an integral type mill housing which houses a pair of piercing rollers disposed so as to be opposite to each other with respect to a pass line, and a pair of disk rollers disposed so as to be opposite to and to cross each other such that a clearance between the surface of a material-receiving side of each disk roller and the surface of an outgoing-side of each piercing roller becomes small, characterized by comprising: a pair of disk frames which are attached to the respective lateral sides of the mill housing and which can be opened sideward in a pivoting manner; and a pair of sliding frames which are vertically arranged within each of the disk frames so as to be slidable and to hold the disk roller integrally formed with a shaft, wherein a skew angle of each of the disk roller is set by sliding the corresponding sliding frames in opposite directions.

2. The piercing mill as defined in claim 1, characterized by further comprising an upper chock frame which is fitted to an upper portion of a shaft of the disk roller and which supports and incorporates a chock while permitting pivoting motion; a lower chock frame which is fitted around a lower portion of the shaft of the disk roller and which supports and incorporates the chock while permitting pivoting motion; an upper opening control frame which is attached to the upper sliding frame of the pair of sliding frames and controls the opening of the upper chock frame; and a lower opening control frame which is attached to the lower sliding frame and controls the opening of the lower chock frame, wherein the disk roller integrally formed with the shaft is supported at both of its ends by respectively fitting the chock frames into the opening control frames.

3. The piercing mill as defined in claim 2, characterized in that the chock is pivotably supported via a pin.

4. The piercing mill as defined in any one of claim 1 -3, characterized in that the height of the disk roller is adjusted by a balancing device provided on the upper sliding frame; and the opening of the disk roller is adjusted by screw-down mechanisms provided on the upper and lower sliding frames.

5. The piercing mill as defined in any one of claims 1 through 4, characterized by further comprising: a rotary shaft for supporting the shaft of the disk frame; clamping means provided on disk frame; and a clamping device disposed on the mill housing, whereby the disk frame is fixedly supported in a heightwise direction thereof by means of the rotary shaft and the clamping means, as well as in the direction of pivotal movement of the disk frame by the clamping means when it is closed and fixed to the mill housing.

Drawing