Mill housings for cluster mills

A two-part housing assembly for a cluster mill. The housing assembly has substantially the same size, form and structure as a monobloc housing, but is divided along a horizontal plane located at or close to its horizontal center line into upper and lower mill housings each provided with a roll cavity and a roll cluster therein. The gap between the work rolls of the roll clusters is adjusted by symmetrical equal and opposite movement of the upper and lower mill housings achieved by four identical screws, one located in each corner of the mill housing assembly. Each screw has two threaded portions of opposite hand, one threaded portion engaging a threaded nut of opposite hand non-rotatively mounted in a recess in the upper mill housing and the other threaded screw portion engaging a threaded nut of appropriate hand non-rotatively mounted in a recess in the lower mill housing. Each screw supports the upper and lower mill housings. A jack for each screw is provided in the mill base to support and rotate that screw. The upper and lower mill housings are adjustably prestressed together, at a spacing determined by the screws, by a pair of tie rods affixed to the piston of a hydraulic cylinder located at each corner of the mill housing assembly.

TECHNICAL FIELD 
This invention relates to a housing for cluster mills used for the cold 
rolling of metal strip, and more particularly to such a housing having the 
advantages of a two part structure and the rigidity of a monobloc 
structure. 
BACKGROUND ART 
The majority of cluster mills for cold rolling metal strip have been 
provided with monobloc housings of the type shown in U.S. Pat. Nos. 
2,169,711; 2,187,250; and 2,776,586, or of the improved type taught in 
U.S. Pat. No. 3,815,401, and also illustrated in FIGS. 1a and 1b herein. 
The advantage of the monobloc housing over any other housing type is great 
rigidity which is required in order to roll strip having the greatest 
uniformity in thickness. It will be noted by one skilled in the art that, 
as time progresses, requirements for gauge accuracy (i.e. thickness 
uniformity) are becoming increasingly stringent. 
However, there are some disadvantages with respect to the monobloc housing, 
which, for some applications, can cause serious difficulties. These 
disadvantages can be summarized as follows: 
Firstly, if a mill wreck occurs, i.e. the strip breaks and then accumulates 
in a tangled mass of scrap inside the housing, it sometimes takes several 
hours to remove the tangled strip, to enable rolling to recommence, and so 
significant lost production occurs. It would be advantageous in such cases 
to be able to separate upper and lower halves of the housing to provide 
more room for removal of scrap strip. This is particularly important for 
high speed mills. 
Secondly, for some applications, it would be advantageous to be able to 
roll with a larger range of work roll diameters than can be achieved with 
a monobloc housing. 
Thirdly, the ability to separate upper and lower halves of the housing 
would facilitate threading of the strip. 
Fourthly, the ability to mount force measuring devices between upper and 
lower halves of the housing would enable more accurate measurement of roll 
separating force, which could be useful for purposes of data logging and 
improving accuracy of automatic gauge control systems. 
Prior art alternative housing designs have overcome some of these 
difficulties in some cases and, in other cases, have overcome all of the 
difficulties, but paid the penalty of a great reduction in mill rigidity. 
Some examples of such prior art are shown in FIGS. 2, 3a and 3b. 
In FIG. 2, the housing is made in two halves, an upper half 112 and a lower 
half 113 which are clamped together using four hydraulic cylinders 115 
(one at each corner) and fixed spacers 116 to separate upper and lower 
halves at a predetermined spacing. This design gives a rigidity close to 
that of the monobloc housing, but permits the upper and lower housing 
halves to be separated by operating the hydraulic cylinders in the 
appropriate direction. With this design, all four difficulties can be 
overcome, but two disadvantages remain. One is that it is necessary to 
change spacers 116 to permit a substantial change in work roll diameter. 
This is an inconvenience in applications where such diameter changes are 
frequent. Secondly, if there is a substantial change in work roll 
diameter, and spacers 116 are changed to suit, then the pass line height 
changes, because the lower housing is fixed. This can cause difficulties 
because other devices such as work roll thrust bearings, strip wipers, 
thickness gauges, mill drive spindles all operate best at a fixed pass 
line level. 
In FIGS. 3a and 3b the mill housing is split into two halves and reduced in 
width so that the two halves can fit in the windows of two four-high type 
mill housings, utilizing the standard screwdown and pass line height 
adjusting mechanisms built-in to the four-high housings. FIGS. 3a and 3b 
show a hydraulic screwdown cylinder 109 at the bottom of each housing 
window and a screw 108 and nut for pass line height adjustment at the top 
of each housing window. This design overcomes all four of the above 
difficulties, but gives a much less rigid (and much more expensive) 
structure than the monobloc housing. 
The present invention is based upon the discovery that a mill housing 
assembly for a cluster mill can be provided having substantially the same 
size, form and structure as a conventional monobloc mill housing. The mill 
housing assembly of the present invention is divided along a horizontal 
plane close to or at its horizontal center line into an upper mill housing 
and a lower mill housing. By provision of jack and screw assemblies at the 
four corners of the mill housing assembly, and by provision of adjustable 
tie rod means at the four corners of the mill housing assembly, a 
structure can be provided which compares favorably with a monobloc mill 
housing from the standpoint of rigidity, while possessing all of the 
advantages of a two-piece mill housing including the ability to separate 
the upper and lower mill housings to clear wrecks, a wide range of roll 
gap settings, and the operation of a fixed pass line level. 
DISCLOSURE OF THE INVENTION 
According to the invention there is provided a two-part housing assembly 
for a cluster mill. The housing assembly has substantially the same size, 
form and structure as a monobloc housing. The housing assembly is divided 
along a horizontal plane close to or at its horizontal center line into an 
upper mill housing and a lower mill housing. Each mill housing is provided 
with a roll cavity and a roll cluster in the roll cavity. Each roll 
cluster comprises a work roll, intermediate rolls and backing assemblies. 
The gap between the work rolls of the roll clusters is adjusted by 
symmetrical equal and opposite movement of the upper and lower mill 
housings. To accomplish this, four identical screws are provided, one 
located in each corner of the mill housing assembly. Each screw has two 
threaded portions of opposite hand. One threaded portion of each screw 
engages an appropriately threaded nut non-rotatively mounted in a corner 
recess of the upper mill housing. Similarly, the other threaded portion of 
each screw engages an appropriately threaded nut non-rotatively mounted in 
a corner recess in the lower mill housing. As a consequence, rotation of 
all of the screws in one direction will cause the upper and lower mill 
housings to separate vertically. Similarly, rotation of all of the screws 
in the opposite direction will cause the upper and lower mill housings to 
shift vertically toward each other. Since both mill housings move equally 
in opposite directions, the pass line is fixed. 
Both the upper mill housing and the lower mill housing are supported by the 
four screws. The four screws, in turn, are supported by and rotated by 
four jacks mounted in the mill base. Each of the jacks has an input shaft 
connected to a motor. The input shafts of the jacks located at the forward 
corners of the mill housing assembly are connected together. Similarly, 
the input shafts of the jacks located at the rearward corners of the mill 
housing are also connected together. 
At each comer of the mill housing assembly, a hydraulic cylinder is mounted 
at the top of the upper mill housing. Each cylinder has a piston. Each 
piston is connected to a pair of tie rods which pass with clearance 
through bores in the upper mill housing and are threadedly engaged in 
bores in the lower mill housing. The four hydraulic cylinder/tie rod 
assemblies adjustably prestress the upper and lower mill housings 
together, at a spacing determined by the screws.

DETAILED DESCRIPTION OF THE INVENTION 
For all of the cluster mill housing types shown in the drawings, the 
housings or housing elements are provided with four upper partial bores 
110 and four lower partial bores 111. These upper and lower partial bores 
define the periphery of the upper and lower portions of the roll cavity of 
the housing. In a monobloc housing such as that of FIG. 1, the roll cavity 
constitutes a single cavity. In a two part mill housing, the upper portion 
of the roll cavity is formed in the upper housing part and the lower 
portion of the roll cavity is formed in the lower housing part, as shown 
in FIGS. 2, 3a, 3b, 4 and 5. As is best shown in FIG. 1a, work rolls 104, 
between which the roll gap is formed and between which the strip 105 
passes and is rolled, are each supported by two first intermediate rolls 
103. The two first intermediate rolls 103 are supported by three second 
intermediate rolls 102 which, in turn, are supported by four sets of 
caster bearings 101. As is well known in the art, each set of caster 
bearings is mounted on a common shaft 106, and this shaft is supported 
against the adjacent one of the mill housing partial bores 110 or 111 by a 
set of saddles 1.07, such saddles being located at each end of the shaft, 
and between each caster bearing and its neighbor on the shaft. Each 
assembly of caster bearings, shaft and saddles is known as a backing 
assembly, there being 8 backing assemblies in all. Conventionally, the 8 
backing assemblies are designated A through H as shown in FIG. 1. Each set 
of one work roll, two first intermediate rolls, three second intermediate 
rolls and four backing assemblies is known as a roll cluster. There are 
two roll clusters, an upper one and a lower one. Such clusters are known 
in the art as 1-2-3-4 or 20-high clusters. This invention applies to mills 
having this cluster type and also to mills having the cluster type known 
in the art as 1-2-3 or 12-high clusters. 
The monobloc housing of FIGS. 1a and 1b can be described as consisting of a 
roof portion 120, in which partial bores 110 are formed, a floor portion 
121 in which partial bores 111 are formed, and two side frame portions 122 
(left side) and 123 (right side) which connect the roof and floor 
portions. Each side frame portion consists of an upper beam portion 124 
and a lower beam portion 125, these beam portions being connected together 
at their ends by the column portions 126. During rolling, the action of 
the roll separating force tends to force the roof portion 120 up and the 
floor portion 121 down. This force is transmitted by shear through roof 
and floor portions to beam portions 124 and 125 respectively of the side 
frame portions 122 and 123, and the separating force is reacted by tension 
in column portions 126. 
In the case of the monobloc housing of FIGS. 1a and 1b and the prestressed 
housing of FIG. 2, an eccentric is mounted between each saddle and its 
shaft on at least some of the backing assemblies. The eccentrics are keyed 
to their respective shaft, such that rotation of the shaft causes movement 
of shaft axis (and hence of caster bearings mounted on that shaft). 
Backing assemblies B and C, which are so equipped, are used as screwdown 
means to directly adjust roll gap. Similarly equipped backing assemblies F 
and G are used for pass line adjustment and thus affect roll gap. 
Similarly equipped backing assemblies A, H, D and E make adjustment for 
roll wear and have some affect on roll gap. Of course, the range of 
adjustment of roll gap achieved by the use of eccentrics on the backing 
assemblies is limited, even if eccentrics are provided on all eight 
backing assemblies A-H. Typically, for a 50 inch wide mill, screwdown and 
pass line adjustment are limited to about 3/8 inch each, and adjustment 
for roll wear is limited to about 1/2 inch. 
In the case of the housing design of FIGS. 3a and 3b, the roll gap is 
adjusted by means of hydraulic screwdown cylinders 109 and/or rotation of 
pass line height adjustment screws 108 so it is not necessary to provide 
eccentrics on the backing assemblies. In this case total adjustment of 
roll gap of 5 or 6 inches, or even more, is easily obtainable. 
A preferred embodiment of the present invention is shown in FIGS. 4 and 5. 
The objective of this invention is to combine the rigidity of the prior 
art monobloc housing of FIG. 1 with the adjustability and wide range of 
roll gap setting of the prior art arrangement of FIG. 3. 
The mill housing, which is similar in form, structure, and size to that of 
FIG. 1, is split along a horizontal plane close to or at its horizontal 
center line into an upper housing 11 and a lower housing 12, columns 126 
each being split into an upper portion 126A (part of the upper housing) 
and a lower portion 126B, (part of the lower housing). The upper and lower 
housings are mounted on, and spaced apart by four screws 13, one at each 
corner, located substantially at the centers of the column portions 126A 
and 126B. Each screw 13 is provided with a right hand thread 15, engaging 
an upper nut 17, and a left hand thread 14, engaging a lower nut 16 (See 
FIG. 4). Each upper nut 17 is located in a recess 46 in its respective 
housing corner, and is provided with a commercially available ring-shaped 
load cell 18 (such as the "Pressductor".RTM. type manufactured by ABB Inc. 
of Milwaukee, Wis.) mounted concentrically on its upper surface. Top 
housing 11 rests upon the four load cells 18, and its weight is 
transmitted through these load cells, and through nuts 17 to screws 13. 
Each lower nut 16 is located in a recess 47 in its respective housing 
corner and rests upon spherical thrust washer pair 19/20 which, in turn, 
rests in the bottom of its recess 47. 
Each lower nut 16 is keyed to lower housing 12 by keys 21, which are bolted 
to the housing. When the mill is not loaded, lower housing 12 hangs on the 
four nuts 16 by means of keys 21, and its weight is thereby transferred 
to, and is supported by the four screws 13. Keys 21 also prevent rotation 
of nuts 16. 
Each upper nut 17 is keyed to upper housing 11 by keys 22. These keys 
prevent rotation of nuts 17, but do not support any load. 
Each screw 13 is supported by a jack 31. Jack 31 is a commercial unit 
having an output shaft 51 which rotates but does not move axially (such as 
rotating screw type jacks made by Duff-Norton Co. of Charlotte, N.C.). 
Such jacks incorporate a heavy thrust bearing to support high axial loads 
on their output shaft 51. The output shaft 51 of each jack 31 is bolted 
and keyed to its respective screw 13. 
Thus, them are four jacks 31, one at each corner of lower housing 12, two 
being at the front, as shown in FIG. 4, and appearing to the left in FIG. 
5, and two being at the back, as shown to the right in FIG. 5. 
As is best illustrated in FIG. 4, the input shaft 39 of each front jack 31, 
is double ended and is coupled to the input shaft of the other front jack 
31 via couplings 32 and cross shaft 35. The other end of each input shaft 
39 is driven by a hydraulic or electric motor 33 via a coupling 32. 
Encoder 34 is connected to one of the motors 33, and is used to sense 
angular position of input shafts 39. An identical arrangement is used for 
the two back jacks. 
By operating both pairs of motors (front pair and back pair) together, the 
four screws 13 rotate, and raise top housing 11 and lower bottom housing 
12, or raise bottom housing 12 and lower top housing 11, according to the 
direction of rotation of the motors 33. 
Since the pitches of the left and right hand threads 14 and 15 in screws 13 
are equal, the movements of top housing 11 and bottom housing 12 are 
always equal and opposite i.e. the plane of symmetry of the two housings 
always remains fixed. The plane of symmetry of the pinion stand (not 
shown) is made the same as that of the housings, the level of this plane 
being known as the pass line level. This feature is of great value in 
ensuring that the misalignment angles of upper and lower pairs of drive 
spindles (not shown) will always be substantially equal. As a consequence, 
the drive spindle strength is not compromised. 
By operating the front pair of motors 33 alone, or the back pair of motors 
33 alone, or driving front and back pairs in opposite directions, it is 
possible to tilt the upper housing 11 and lower housing 12 in opposite 
directions, thus forming a tapered form of roll gap, (where the roll gap 
is different at front and back of the mill) or, in the case of an 
initially tapered roll gap, correcting the roll gap to a parallel form in 
order to "level" the mill, as is known in the art. Such adjustments can be 
useful when rolling strip of non-uniform thickness, such as "wedge shaped" 
strip. Spherical washers 19 and 20 permit this tilt to take place without 
bending screws 13. 
During the rolling process, which reduces the thickness of the strip being 
rolled, a roll separating force (RSF) is developed, which acts, 
substantially vertically upwards on the upper roll cluster, and reacts 
substantially vertically downwards on the lower roll cluster. 
Since the magnitude of this force will usually be considerably higher than 
the weight of the upper roll cluster and upper housing 11, it is necessary 
to apply a prestressing force which preloads upper and lower housings 11 
and 12 together, this force being greater than the maximum RSF developed 
during rolling. 
The force is applied by four hydraulic cylinders acting through tie rods 
23, which clamp the upper and lower housings 11 and 12 together against 
the spacing structure formed by load cells 18, nuts 17, threaded portions 
15 and 14 of screws 13, nuts 16 and spherical washers 19 and 20. 
Because nuts 17 are each mounted at the inner faces of upper and lower 
housings, i.e. the faces which are closest to the pass line the portion of 
each screw 13 which is under load, i.e. that portion between threaded 
portions 14 and 15, is as short and therefore as rigid as it could 
possibly be. Thus, the rigidity of the spacing structure is extremely high 
and the rigidity of the total structure consisting of upper and lower 
housings, and the spacing structure is only slightly less than that of a 
monobloc housing. 
It should be understood that this rigidity is only maintained under the 
condition that the loaded portions of screws 13 are under compression. 
Thus, the prestressing force must be higher than the maximum roll 
separating force developed during rolling, to achieve this high rigidity. 
The design principle used here is known as the "short stress path" 
principle. Thus, the item which is subjected to the highest stress (the 
portion of screws 13 between threaded portions 14 and 15) is kept as short 
as possible in order to achieve maximum rigidity. 
Each hydraulic cylinder comprises a cylinder body 24, attached to upper 
mill housing 11 by bolts 44, a piston 25 which slides within the cylinder 
body 24, piston rods 23, which also fulfill the function of tie rods, and 
nuts 29 which secure piston 25 on the piston rods 23. Seals 26, 27 and 28 
are provided to prevent leakage of hydraulic fluid from the cylinder 24. 
Keys 30, bolted to piston 25, are used to lock nuts 29 against rotation 
and also to secure nuts 29 to piston 25, so that the weight of the piston 
is supported by rods 23. Piston 25 is connected to lower housing 12 by the 
two piston rods (tie rods) 23 which are screwed into threaded bores in the 
lower housing 12. 
This design of the hydraulic cylinder 24 is unique in that each cylinder 24 
has two parallel non co-axial piston rods 23 rather than the usual one. 
The purpose of this is to enable each cylinder 24 to be mounted co-axially 
with its respective screw 13, giving uniform stress in its respective 
screw 13 when the prestressing force is applied by supplying pressurized 
hydraulic fluid to the cylinder 24. To achieve this, the two tie rods 23 
straddle their respective screwdown nuts 16 and 17, and the axes of the 
two rods 23 and their respective nuts 16 and 17 all lie in one vertical 
plane. 
Although it is envisaged that this construction will provide many years of 
service with no maintenance other than lubrication, the invention provides 
for easy replacement of all parts. Each hydraulic cylinder 24 can be 
removed by removing its four bolts 44, one hydraulic hose (not shown), its 
two keys 30 and two nuts 29, and lifting the cylinder away. The rods 23 
can then be unscrewed and lifted out. 
Load cells 18 can be removed by operating motors 33 to separate upper and 
lower housings as far as possible. Thereafter a hydraulic jack can be 
placed between upper and lower housings 11 and 12 adjacent to the load 
cell 18 in question to take the weight of the upper housing 11 off the 
load cell 18. Then the load cell can be slid out horizontally to the front 
(front load cells) or to the back (back load cells) through the slot or 
recess 46 provided for the purpose in the upper housing, after first 
removing cover/retainer 43 (see FIG. 4) which serves to cover and retain 
load cell 18 and upper nut 17. This is accomplished by removing the screws 
which attach cover/retainer 43 to the upper housing. 
A similar cover 42 is provided in lower housing 12 for recess 47, and a 
long narrow cover 41 is provided for recess 48 (see FIG. 4). If these 
covers are removed, as well as cover 43, it is possible to slide out the 
entire assembly of screw 13, nuts 16 and 17, load cell 18 and washers 19 
and 20, from recesses 46, 47 and 48 for examination, replacement or 
repair. In such a case, the corner of lower housing 12 in question would 
be blocked, and the bolts and keys attaching screw 13 to output shaft 51 
of that jack 31 supporting the screw 13 in question would be removed, 
before the assembly could be slid out. It will be understood that a set of 
covers 41, 42 and 43 will be provided for the recesses 46, 47 and 47 for 
each screw assembly (13, 16, 17, 18, 19 and 20). 
It is envisaged that, with a mill according to this invention, the standard 
screwdown system operating via eccentrics on B and C backing assemblies 
would be retained. Furthermore, the pass line height adjusting system 
operating via eccentrics on F and G backing assemblies would be retained 
to provide for differences in roll sizes between upper and lower clusters. 
However, it would not be necessary to provide eccentrics on A, D, E and H 
backing assemblies, since the symmetrical housing separation adjustment 
achieved by rotation of screws 13 would provide for roll wear. 
Modifications may be made in the invention without departing from the 
spirit of it.