Retrofit Method and Apparatus for Rolling Mills

The present invention provides an apparatus and method for retrofitting a hydraulic roll actuating mechanism in a screw down rolling mill. In accordance with the present invention, an exterior housing element of the frame of the screw down mill is replaced by a hydraulic cylinder adapted to use the housing mounts, and to be positioned over the vertical opening in the frame which originally accommodated the actuating screw member. A piston rod sleeve extending from the hydraulic cylinder and enclosing the piston rod is fitted within the original screw member opening and threadedly engaged with the existing screw nut for transmitting reaction forces to the frame.

The provision of hydraulic roll actuation is frequently desired in existing screw down rolling mills to eliminate the inefficiencies of the mechanical screw arrangement and to provide the control advantages associated with the fast response to hydraulic systems. Presently, the conversion of a screw down mill to hydraulic actuation is a time consuming and expensive process. For example, the known conversion techniques and apparatus typically necessitate a month of mill down time which results not only in the direct conversion expenses but also the loss of significant production time.

In the conversion of rolling mills, it is desirable to avoid alteration of the frame since this not only generates significant expenses but also tends to reduce the frame structure and the capacity of the mill. Accordingly, conversion procedures have heretofore favored techniques wherein the hydraulic system is essentially fitted within the mill window either above the top backup chock or below the bottom backup chock. The fitting of the hydraulic system within the mill window imposes severe design restraints upon the hydraulic unit and, in many instances, the desired hydraulic unit still cannot be fitted within the mill window without significant reworking of the mill frame or backup chocks.

When a mill is originally designed for hydraulic actuation, it is desirable to locate the hydraulic unit clear of the mill window as illustrated in U.S. Pat. Nos. 3,242,711 and 3,435,649. In original designs, the remote disposition of the hydraulic cylinder allows sufficient space for preferred cylinder designs and removes the cylinder from the unfavorable environment of the rolling process. In addition, the unobstructed positioning of the hydraulic cylinder facilitates subsequent maintenance and enables certain control advantages.

In accordance with the present invention, an apparatus and method for retrofitting a hydraulic roll actuating mechanism in a screw down rolling mill are provided. A hydraulic cylinder is fitted to the frame of the mill in an orientation corresponding to the original screw drive mechanism with or without limited reworking of the frame of the mill. The hydraulic cylinder is fitted adjacent the opening in the frame which originally accommodated the screw member, and a piston rod sleeve is mounted within the opening for receiving a piston rod. The piston rod sleeve has external threads which threadedly engage the original screw nut of the mill. In this manner, the existing screw down mill structure is efficiently fitted with the hydraulic roll actuating mechanism, and the original load capacity of the mill is not reduced since the existing load carrying, frame structure is essentially maintained.

In the illustrated embodiment, the cross sectional area of the original screw member opening is approximately equally divided between the cross sectional areas of the piston rod sleeve and piston rod. Accordingly, the hydraulic actuation forces and the resulting reaction forces imposed upon the mill frame are carried by structurally comparable members so as to maximize the capacity of the retrofitted system. In view of the inefficiencies of screw actuation wherein high torsional stresses are generated in order to provide useful compressive stresses, the substantially complete use of the existing space originally allocated to the actuation means by the hydraulic mechanism of the subject invention actually results in a more efficient mill.

As indicated above, the hydraulic cylinder is fitted to the frame in an orientation corresponding to that of the original screw drive mechanism. Generally, the screw drive mechanism is enclosed by an exterior housing element, and the original frame structure is provided with suitable mounts for securing the housing element thereto. The hydraulic cylinder can be designed or adapted to use the existing frame mounts, even though the mounts are not structurally designed to carry actuation forces or reaction forces, since the reaction forces are carried by the piston rod sleeve and directly transmitted to the frame through the existing screw nut.

FIG. 1 is a cross-sectional end view of the upper portion of a conventional screw down rolling mill with certain elements shown in elevation for purposes of clarity; and

FIG. 2 is a cross-sectional end view of the rolling mill of FIG. 1 retrofitted in accordance with the present invention to provide hydraulic roll actuation.

Referring to FIG. 1, a conventional, screw down rolling mill 10 having a frame 12 is shown. The mill 10 is provided with a screw down actuation mechanism generally indicated at 14 for operation of the rolls of the mill. The mill 10 is of the four-high type wherein large backup rolls are employed to reinforce smaller working rolls. However, the present invention is applicable to the conversion of all of the various types of mills including two-high, three-high and the illustrated four-high mill.

The screw down actuation mechanism 14 includes as its principal parts a worm gear 16 connected to a drive motor (not shown), a worm wheel 18 which is splined to an actuating screw member 20 and a rotationally fixed screw nut 22 which is threadedly engaged with the screw member 20. The worm gear 16 and the worm wheel 18 are disposed within a cavity 23 defined by the frame 12 and a housing member 24. The housing member 24 includes a peripheral flange 26 which is configured to engage a mounting skirt 28 provided by the frame 12. The housing member 24 is secured to the frame 12 by means of studs 30 which are threadedly engaged with the mounting skirt 28 and extend through the flange 26 for engagement with nuts 32.

The worm wheel 18 is supported within the cavity 23 by means of an annular support skirt 34 provided by the frame 12 and an oppositely disposed support skirt 36 extending from the housing 24 with the interposition of suitable bearings 38. As indicated above, the worm wheel 18 is splined to the screw member 20 and, more particularly, an upper portion 20a of the screw member which comprises a spline shaft.

The screw member 20 extends through a vertical opening 40 in the frame 12, and it is threadedly engaged with the screw nut 22 which is disposed adjacent the lower end of the opening 40. The screw nut 22 is retained in position by a retainer plate 42 which is secured to the frame 12 by bolts 44. The screw member 20 extends through the opening 40 and into a mill window 46 for purposes of actuating the rolls of the mill.

The screw member 20 engages a pressure block 48 for purposes of operating a top backup chock 50 which is mounted within the mill window 46. The backup chock 50 engages a backup roll 52 which cooperates with a top work roll (not shown) and conventional bottom work and backup rolls (not shown).

Referring to FIG. 2, the rolling mill 10 is shown retrofitted for hydraulic roll actuation in accordance with the present invention. More particularly, the housing member 24 and the screw down actuation mechanism 14 except for the screw nut 22 have been removed, and the hydraulic retrofit apparatus generally indicated at 52 has been mounted to the frame 12. The principal parts of the hydraulic retrofit apparatus 52 comprises a hydraulic cylinder 54 including a removable end wall or closure 56, a piston 58, and a piston rod 60 which is received within a piston rod sleeve 62 extending from the hydraulic cylinder 54.

The hydraulic cylinder 54 is mounted to the frame 12 in substantially the same position as the housing member 24. The hydraulic cylinder 54 has a substantially circular cross section, and it is mounted above the opening 40 so that the piston 58, piston rod 60 and piston rod sleeve 62 are coaxial with the opening. To that end, the hydraulic cylinder 54 is provided with a peripheral flange 64 which is configured to fit the mounting skirt 28 of the frame 12. To accommodate the non-symmetrical configuration of the mounting skirt 28 with respect to the axis of the opening 40, the peripheral flange 64 is provided with a radially extending ear 64a. In the retrofitting operation, the studs 30 and nuts 32 shown in FIG. 1 have simply been replaced by bolts 66.

The hydraulic cylinder 54 includes a bottom wall 54a which is supported on the annular support skirt 34 and substantially disposed within the lowermost portion of the original cavity 23 (FIG. 1). Accordingly, the hydraulic retrofit apparatus efficiently utilizes the space rendered available by removal of the screw down actuation mechanism 14 and maximizes support by use of the skirts 28, 34.

The hydraulic cylinder 54 also includes an axially extending, cylindrically shaped sidewall 54b which is integrally formed with the bottom wall 54a. As indicated above, the hydraulic cylinder 54 is provided with a removable end closure 56 which is fitted adjacent the upper end of the cylinder. The fixing of the end closure 56 to the cylinder 54 is particularly advantageous since it enables the retrofit apparatus 54 to directly transmit reaction forces to the frame 12 by means of the piston rod sleeve 62 and screw nut 22 as indicated below in greater detail.

The end closure 56 is secured to the sidewall 54b of the cylinder 54 by a bayonet connection. To that end, the end closure 56 is provided with a bayonet rib 56a which is rotationally locked within a bayonet channel 54c provided in the sidewall 54b. The end closure 56 is provided with an O-ring 68 for purposes of forming a hydraulic seal.

As shown in FIG. 2, the piston 58 is in a fully retracted position with its upper surface disposed adjacent the lower surface of the end closure 56. The piston 58 is provided with an O-ring seal 70 for purposes of forming a hydraulic seal. The piston rod 60 is fitted within a recess in the lower surface of the piston 58, and it is secured to the piston for following movement by suitable means such as weld 72. The piston rod 60 extends downwardly from the piston 58 through the sleeve 62 and into engagement with the pressure block 48.

The piston rod sleeve 62 is disposed in a shouldered opening 74 in the bottom wall 54a, and it is secured to the hydraulic cylinder 54 in a convenient manner such as by weld 76. Accordingly, the piston sleeve 62 is provided with a radial flange 62a which is received in the shouldered opening 74. The flange 62a is hydraulically sealed by means of an O-ring and retainer plate assembly 78 disposed about the piston rod 60.

The piston rod sleeve 62 has a cylindrical configuration, and its outside diameter is sized to substantially almost fill the smallest diameter of the vertical opening 40. The lower portion of the sleeve 62 adjacent the mill window 46 is provided with external threads 62b for engaging the internal threads 22a of the screw nut 22. In this manner, the existing screw nut 22 is advantageously used to transmit the hydraulic reaction forces to the frame 12 of the mill.

The cross sectional area of the piston rod sleeve 62, aside from the flange 62a, is selected to be approximately equal to one-half of the cross-sectional area defined by the smallest diameter of the opening 40. Further, the cross-sectional area of the piston rod 60 is also approximately equal to one-half of the area of the opening 40 and equal to the cross-sectional area of the sleeve 62. In this manner, the load bearing capacity of each of the elements as well as the hydraulic system is maximized.

The hydraulic retrofit apparatus 52 includes a first hydraulic port 80 extending through the removable end closure 56 to the upper surface of the piston 58 and a second hydraulic port 82 extending through the sidewall 54b to the bottom surface of the piston 58. The ports are connected in a conventional manner to a source of hydraulic pressure (not shown), and they are arranged for both pressurizing and venting the respective operating portions of the hydraulic cylinder 54.

The hydraulic retrofit apparatus 52 can be used in both pressure rolling mill applications wherein a constant pressure is applied to the material to be rolled and automatic gauge control mills wherein the material to be rolled is provided at a substantially constant gauge by varying the applied pressure. The rolling mill 10, as shown in FIG. 2, is arranged for automatic gauge control, and a linear variable differential transformer 84 is carried by the end closure 56 for providing a hydraulic, position feedback signal. A servo valve 86 is also conveniently carried on the end closure 56. The transformer 84 and the servo valve 86 are arranged in a control system in a conventional manner to provide controlled hydraulic actuation in response to variations from a preselected control point.

As indicated above, the retrofitting of the mill 10 requires only limited reworking, if any, of the frame 12. For example, the flange 64 and the bottom wall 54a of the cylinder 54 as well as the piston rod sleeve 62 may be initially designed to fit the existing frame structure with or without limited reworking of the mounting skirt 28, the support skirt 34 and the opening 40 of the frame 12. The retrofit apparatus 52 can be fully assembled and fitted as a unit to the mill 10, and it can be threadedly engaged with the screw nut 22 as it is lowered into position by means of eyebolts 88 (only one of which is shown) symmetrically secured to the cylinder 54. Of course, the cylinder 54 and sleeve 62 can be initially fitted to the mill, and the remaining components of the retrofit apparatus 52 can be subsequently assembled.

The retrofitting apparatus and method of the present invention are particularly advantageous since they achieve in a retrofit situation many of the design benefits which are imparted to a mill in an original design application wherein hydraulic actuation is to be employed. As indicated above, the retrofitted hydraulic mechanism is disposed in an unobstructed position to provide adequate space for preferred cylinder design and to subsequently facilitate maintenance. The remote location of the hydraulic cylinder from the immediate environment of the rolling process is itself desirable, and it also enables the incorporation of control elements such as position feedback devices, servo valves and pressure transducers as a designed part of the hydraulic cylinder. As described in detail above with respect to the illustrated embodiment, the apparatus and method of the present invention may be readily employed to convert a screw down mill to hydraulic actuation with a minimum of effort and substantially no significant amount of frame modification. Moreover, the piston and sleeve arrangement maximize the load bearing capacity of the retrofitted mill with efficient use of the structural mill characteristics originally provided in the screw down mill design. In fact, the inefficiency of a screw mechanism as compared with hydraulic actuation and the over design of the original mill due to such inefficiency is advantageously employed in accordance with the present invention with respect to both the sizing of the hydraulic system and the use of the existing screw nut as a part thereof.