This invention applies to 20-high cluster mills used for the cold rolling of metal strip, and having a 1-2-3-4 roll arrangement as shown in U.S. Pat. Nos. 2,169,711; 2,187,250; 2,479,974; 2,776,586 and 4,289,013, such mills being commonly known as "Sendzimir" mills, "Z" mills or "Sendzimirs".
It is particularly concerned with improved means for shaping the profile of the rolling mill to the profile of the strip, in order to achieve uniform elongation at every point across the width of the strip, thus enabling uniform tension distribution, and strip of good flatness.
In cluster mills of the type to which the present invention is directed, as shown in FIGS. 1-5, a pair of work rolls 12, between which the strip 8 passes during the rolling process, is supported by a set of four first intermediate rolls 13, which are in turn supported by a set of six second intermediate rolls consisting of four driven rolls 15 and two non-driven idler rolls 14. The second intermediate rolls are supported in their turn by eight backing assemblies, each consisting of a plurality of roller bearings 30 mounted upon a shaft 18. The shaft 18 is supported at intervals along its length by saddles, each saddle consisting of a ring 31 and a shoe 29 (these parts being bolted together). The saddle shoes 29 rest in a series of partial bores in a mill housing 10, of the type generally described in U.S. Pat. No. 3,815,401.
It is normal practice to label the backing assemblies and their components as shown in FIG. 5, where, in this view of the operator's side or front of the mill, the leftmost upper assembly is labelled "A", and working clockwise around the mill, the remaining assemblies are labelled "B" through "H". This labelling convention will be followed in this specification, such labels being applied to both assemblies and constituent parts.
In general, all of the saddles on all eight backing assemblies include eccentrics 23, which are keyed to the respective shafts, (similar to what is shown at 24 in FIG. 3) and provided with bearing surfaces on their outside diameters, which engage with bores in saddle rings 31, such that rotation of the respective shafts will cause radial motion of shafts and of bearings mounted thereon.
In the case of assemblies A,D,E,F,G and H, the saddles are known as "plain saddles" and eccentrics 23 mount directly within saddle rings 31, and slide within these rings as the respective shafts are rotated. In such cases, because the friction between the sliding surfaces is high, shafts will not be adjusted under load (i.e. during rolling). A,D,E and H shafts eccentrics are known as the "side eccentrics". Rotating these shafts is used to adjust the radial position of their bearings to take up wear on rolls 12 through 15.
F and G shaft eccentrics are known as the "lower screwdown eccentrics". Rotation of F and G shafts and their eccentrics can be used to take up for roll wear also, but is more frequently used to adjust the level of the top surface of lower work roll 12. This is known as "adjusting the pass line height" or "pass line adjustment".
In the case of assemblies B and C, the saddles are known as "roller saddles". For small mills (which have no crown adjustment) the construction is the same as for the plain saddles, with the exception that a single row of rollers (similar to those shown at 37 in FIG. 3) is interposed between the outside of each eccentric 23 and the inside of the mating saddle ring 31. This enables the shafts and eccentrics (which are keyed together similarly to what is shown in FIG. 3) to roll within saddle rings 31. The friction is then sufficiently low for adjustment to be made under load. This adjustment is known as the "upper screwdown" or "screwdown" and is used to adjust the roll gap (gap between work rolls 12) under load. The method adopted, as is well known in the art, is to use two double racks (not shown), one engaging gears 22 on shafts B and C at the operator's side, and one engaging gears 22 on shafts B and C at the drive side (see FIG. 4). Each double rack is actuated by a direct acting hydraulic cylinder, and a position servo is used to control the position of the hydraulic pistons, and so control the roll gap.
For larger mills (and for some newer small mills) provision is made for individual adjustment of the radial position of shaft, bearings and eccentric rings at each saddle position. This adjustment is known as "crown adjustment" and the prior art construction used to achieve it is shown generally in FIGS. 1 through 4.
On the B and C saddles, the saddle rings 31 are provided with a larger diameter bore 32, so that a second set of rollers 33 and a ring 34 (the outside diameter of which is eccentric relative to its inside diameter) can be interposed between saddle ring 31 and rollers 37. Rings 34 are known as "eccentric rings". A gear ring 38, having gear teeth 40, is mounted on each side of each eccentric ring 34, and rivets 39 are used to retain gear rings 38, eccentric 23, eccentric ring 34, saddle ring 31 and shoe 29, with two sets of rollers 33 and 37, together as one assembly, known as the saddle assembly.
As shown in FIGS. 1 and 2, a double rack 41 is used at each saddle location, to engage with both sets of gear teeth 40 on each gear ring 38 on both B and C saddle assemblies. A hydraulic cylinder, or motor driven jack (not shown), is used at each saddle location in order to translate the rack. In the example of FIG. 4, seven individual drives would be provided, one at each saddle location. These are known as "crown adjustment" drives. If one drive is operated, its respective double rack 41 moves in a vertical direction, rotating the associated gear rings 38 and eccentric rings 34. This causes radial movement of eccentrics 23 on shafts B and C at the saddle location on which the eccentric rings rotate, and a corresponding change in the roll gap at that location, shafts 18 bending to permit this local adjustment.
Although independent drives are provided at each saddle location, the adjustment is not truly independent, due to the transverse rigidity (i.e. resistance to bending) of each shaft 18. This rigidity is augmented by the practice of clamping all the eccentrics 23 and inner rings of bearings 30 axially along the length of the shaft between screwdown gears 22, thus effectively forming a tube along the outside of each shaft 18, which stiffens the shaft and makes bending of the shaft even more difficult. This stiffness is sufficiently high to cause stalling of any drive which is driven to a position too far away from the position of the neighboring drives.
Furthermore, any profile of the backing assembly achieved by operation of the crown adjustment drives is not fully effective at the roll gap, because of the transverse rigidity of intermediate rolls between assemblies B and C and the work roll. Since work rolls 12 and first intermediate rolls 13 are relatively small in diameter, they are flexible and so create no problems. The drive rolls 15 primarily transfer forces between first intermediate rolls 13 and backing assemblies A and D (or E and H), and are only obliquely supported by backing assemblies B and C (or F and G). The primary path of the support forces provided by backing assemblies B and C is through the upper idler roll 14, and it is the rigidity of this roll which can attenuate the effect of profile adjustments on B and C assemblies, particularly if profiles having double or triple curvature, rather than simple crowned (i.e. single curvature) forms, are attempted.
In fact, the prior art teaches us that the means shown in FIGS. 1 through 4 is a means of crown adjustment, although it is well known in the art that the means can be used to "tilt" the mill, i.e. to provide a roll gap which is tapered in form, being larger at one end of the work rolls than the other end. It should be noted that such "tilting" does not require bending of backing shafts 18.
It is the object of this invention to provide means to enable more complex roll gap profiles to be achieved on such mills, by providing new forms of backing shafts and idler rolls, which have much smaller transverse rigidity than prior art forms, and to provide new mountings for bearings and eccentrics on backing shafts which will not cause augmentation of transverse rigidity.