Stretch reducing mill

The disclosure is directed to improvement in stretch reducing mills utilized in the manufacture of seamless and welded tubing. The stretch reducing mill is well known in its generalities, and the disclosure is directed to improvements in the construction of such mills in the interest of increasing the efficiency of operation and performance of the mill. The disclosure is directed in part to the construction of a multi-stand stretch reducing mill with improved arrangements for removably securing the individual mill stands in position. This includes a heavy, massive structural beam from which all of the individual mill stands are suspended and which additionally serves, when the mill is ready for operation, as a means for holding the mill stands in position. In the latter capacity, the beam contributes both in terms of its great weight and in terms of distributing clamping forces to the individual mill stands from a limited number of clamps. The mill also includes an improved arrangement for longitudinally clamping together a series of consecutive mill stands, using a combination of hydraulic clamping cylinders and a mechanical fail-safe system, enabling the advantages of hydraulic clamping to be enjoyed while avoiding any serious consequences from untimely failure of hydraulic pressure. An additional feature of advantage included in the disclosure is an improved mechanism for effecting simultaneous coupling and decoupling of the individual mill stands to their respective individual drive motors.

BACKGROUND AND SUMMARY OF THE INVENTION 
In the manufacture of seamless and welded tubing, it is a conventional 
practice to initially form the tubing to a larger diameter and with a 
greater wall thickness than is generally desired. Among the finishing 
operations to which this tubing is subjected frequently is reduction in 
size in a stretch reducing mill. The stretch reducing mill typically 
consists of a series of consecutive mill stands of progressively 
decreasing diameter, arranged with individual drives, such that each stand 
is operated at a higher speed than the previous stand. The arrangement is 
such that, not only is the diameter of the tubing progressively reduced 
from stand to stand, but the tubing is also placed under controlled 
tension between stands, resulting in a controlled elongation of the tubing 
over and above that which would normally result from the fact of the tube 
being reduced in diameter. By properly relating the reduction in diameter 
to the elongation, the finished tubing may be controlled both as to its 
outside diameter and as to its wall thickness. 
Since a standard size of incoming tubular stock is customarily processed 
into finished tubing of various sizes and wall thicknesses, it is 
generally necessary to set up the stretch reducing mill so as to 
accommodate relatively frequent reorganization. Typically, this is 
accomplished by removably mounting the individual mill stands in a base or 
foundation structure. When it is desired to change over the mill from one 
size of finished tubing to another, the existing combination of mill 
stands is removed and replaced by another combination, which is 
appropriate to the intended new production. Pursuant to the present 
invention, improvements are provided in the construction of a stretch 
reducing mill, which greatly facilitate the changeover of the mill from 
one mill stand combination to another. Thus, providing improved 
flexibility in production scheduling, while at the same time providing for 
down time of the mill to be kept at a practical minimum. 
According to one of the more specific aspects of the invention, a 
multi-stand stretch reducing mill is provided in which a series of 
adjacent mill stands are secured at the top to a massive, retaining beam, 
which extends the full length of the mill, over the tops of the individual 
mill stands. The retaining beam is connected or arranged to be connected 
to each of the mill stands and thus can serve as a means for 
simultaneously lifting all of the mill stands out of the foundation and 
conveying them to the preparation floor. This retaining beam, because of 
its inherent massive weight, serves, when the mills are in working 
position, to assist in holding the mill stands in place on the mill 
foundation. In addition, the retaining beam serves as a medium to which 
vertically downward clamping force may be applied to the individual mill 
stands, through a relatively limited number of high power clamping 
devices. By serving in a dual capacity of a hold-down means and also a 
lifting and carrying means, the massive retaining beam enables the 
changeover of the mill to be accomplished quickly and with great 
efficiency. 
In accordance with another aspect of the invention, an improved arrangement 
is provided for longitudinally clamping into the mill foundation a series 
of individual mill stands. The improved arrangement comprises a series of 
hydraulic cylinders, arranged in a configuration to correspond to the 
alignment of spacing bosses provided on each of the mill stands. In 
conjunction with the several hydraulic cylinders, there is provided a 
heavy-duty mechanical locking mechanism, which is activated after the mill 
stands have been hydraulically clamped. In normal operations, the 
mechanical locking system functions only in a standby capacity. However, 
should there be a failure or reduction in the hydraulic clamping pressure 
during operation of the mill, the standby mechanical locking system will 
prevent any significant displacement of the mill stands, which might 
otherwise result in serious damage to the mill. 
In accordance with a further specific aspect of the invention, an improved 
and simplified arrangement is provided for effecting the coupling and 
decoupling of the individual mill stands to their respective drive motors 
when changing over the mill. The improved arrangement is in the form of a 
common clutch beam, which extends along the full length of the mill and is 
carried by a series of crank levers. The series of levers is actuated 
simultaneously, by actuation of a longitudinally extending tension bar, so 
that the clutch beam is caused to move transversely with respect to the 
mill axis to effect declutching. Since a mill of typical construction 
utilizes alternate high and low drive inputs, the clutch beam assembly of 
the invention is arranged to extend along the mill between the levels of 
the upper and lower drives and is provided with alternately upwardly and 
downwardly extending clutching yokes for engagement with the alternate 
high and low mill drives. 
The prior art considered to be of interest includes the William R. Scheib 
U.S. Pat. No. 3,328,973, assigned to Aetna-Standard Engineering Co., a 
subsidiary of White Consolidated Industries, Inc. General features of the 
mill arrangement are also shown in the Gillet U.S. Pat. No. 3,355,923, the 
Chang U.S. Pat. No. 3,221,529, and the Kocks U.S. Pat. No. 2,214,279. 
For a better understanding of the above and other features and advantages 
of the invention, reference should be made to the following detailed 
description of a preferred embodiment, and to the accompanying drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the drawings, and initially to FIGS. 1 and 2 and 8 
thereof, the stretch reducing mill of the invention includes a foundation 
structure 10, which includes a pair of elongated, longitudinally extending 
foundation beams 11, 12 connected together and supported at appropriate 
places by plates 13-16, forming a rigid weldment structure. Along the tops 
of the foundation beams 11, 12 extend foundation rails 17, 18, on which 
are received and supported a plurality of mill stands 19. In the 
representative mill disclosed herein, provision is made for up to 
twenty-four active mill stands, although in many cases less than 
twenty-four active stands are required, in which case some of the stands 
at the exit end of the series may be dummies. 
At each end of the foundation 10 there is provided an end frame structure 
20, 21 (at the entry and exit ends respectively). The end frames are 
secured to the foundation beams 11, 12, and also are connected 
longitudinally by a plate structure 22 (FIG. 8) which extends the full 
length of the foundation along the back or drive side. Thus, the end 
frames 20, 21 form part of a rigid foundation and frame structure for the 
several mill stands 19. 
The individual mill stands 19, one of which is evident in FIG. 8, include 
mill housings 23, which may either be roll housings, or dummies. In the 
illustration of FIG. 8, the housing 23 supports three working rolls 24 
arranged in a "Y" configuration. These rolls are geared together and are 
arranged to be driven through an input shaft 25 connected to a drive 
system in a manner to be described. Typically, the next successive mill 
housing will be inverted, so that the next set of working rolls has a 
configuration of an inverted "Y". To this end, in accordance with known 
general principles, the mill housings 23 are designed to be generally 
symmetrical about the central axis 26, so that any mill housing may be 
installed "right side up" or "upside down". The drive shaft 25 for each 
mill housing is offset somewhat from the central axis 26 of the mill pass 
such that, with the housing in one orientation, the drive shaft is below 
the pass line and, with the housing in the reverse orientation, the drive 
is above the pass line. By this means, alternate housings may be arranged 
with high and low drive inputs. 
As is shown best in FIGS. 8 and 9, the mill housings 23 advantageously 
consist of two symmetrical housing halves 27, 28 which, together, contain 
the various support bearings and drive gears for the mill rolls 24. The 
housing halves 27, 28 are connected together by a plurality of through 
bolts 29. On the front and back faces of the assembled housing, there are 
provided four bosses 30. These are machined to considerable accuracy to 
define the front and back planes of the housing 23 and to establish the 
overall thickness of the housing to very close tolerances. In some cases, 
it may be desired to utilize special machined inserts 31 (FIG. 9) to form 
the bosses 30. In other cases, the bosses may be an integral part of the 
housing halves 27, 28. In either case, it may be desirable to recess the 
center area of the bosses to receive the heads and nuts of the clamping 
bolts 29. 
Each of the mill housings 23 is precision machined to form upper and lower 
support surfaces 32, 33 and adjacent lateral guide surfaces 34, 35. These 
support and guide surfaces are accurately located with respect to the pass 
line 26 of the mill such that, when the mill housing is supported on the 
foundation rails 17, 18, in either orientation of the housing, the axis of 
the housing is precisely located on the mill pass line, both vertically 
and transversely. Desirably, the upper and lower extremities of the mill 
housings are tapered at 36, to assist in guiding of the housing into 
position of the foundation rails 17, 18 during the make-up of a mill 
assembly. 
In accordance with one aspect of the invention, each of the mill housings 
23 is provided on its upper and lower ends with spaced front and back 
flanges 40, 41 defining a space for the reception of a U-shaped hold-down 
block 42, to be further described. A combined lifting and hold-down pin 43 
extends between each of the flanges 40, 41, the pin being aligned with the 
central vertical axis through the mill housing. 
Engaging each of the several mill housings 24, by means of their respective 
lifting and hold-down pins 43, is an elongated retaining beam 44. The beam 
extends the full length of the foundation frame and has keys 45, 46 at 
each end (see FIGS. 5, 11) slideably engagable with vertical guides 47, 48 
in the respective entry and exit end frames 20, 21. As reflected in FIGS. 
8 and 9, the retaining beam 44 is provided with a hold-down block 42 for 
each location of mill stand, properly aligned to be received between the 
spaced housing flanges 40, 41. 
In the illustrated arrangement, the retaining beam 44 advantageously is in 
a form of a rather massive H-beam having heavy upper and lower flanges 49, 
50 and a central vertical web 51. At each mill housing location, a pair of 
elongated bolts 52, 53 extend slidingly through the flanges 49, 50, on 
opposite sides of the central web 51, each pair of bolts engaging a 
hold-down block 42 at their lower ends. Flanged bushings 54 surround the 
lower portions of the bolts 52, 53 and engage the upper surface of the 
hold-down block. Heavy compression springs 55 are provided about the upper 
portions of the bolts 52, 53, maintained in compression between the upper 
beam flange 49 and the flanged bushings 54. The springs 55 serve normally 
to urge the bushings 54, bolts 52, 53 and hold-down blocks 42 downwardly, 
to positions limited by the bolt heads 56. However, when the retaining 
beam 44 is lowered down onto a series of assembled mill housings, the 
lifting and hold-down pins 43 are received in the downwardly opening bight 
areas 57 of the hold-down blocks 42, eventually becoming seated in the 
closed ends of the bight areas, and displacing the hold-down blocks 
relative to the retaining beam 44, against the compression springs as the 
latter continues to be lowered. Accordingly, when the retaining beam 44 is 
in position, the series of mill housings is pressed downward by the 
massive weight of the beam acting through the several pins 43. 
Although the retaining beam 44 in the illustrated mill structure 
contributes significantly to the necessary hold-down force for the mill 
housings, the structure of the invention further includes a limited number 
of hold-down clamps, which are arranged to engage and forceably press 
downward on the upper flange 49 of the retaining beam to augment the 
downward acting weight of the beam. Because of the inherent strength and 
relative rigidity of the massive retaining beam 44, a limited number of 
hold-down clamps may be utilized, with the clamping force being 
distributed effectively through the heavy beam. In a representative mill, 
the springs 55 may be pre-loaded to an initial compression force of about, 
say, 750 pounds each. When clamping force is applied, this may be 
increased to, say, 1,250 pounds per spring. 
With reference to FIGS. 2, 3 and 8, for example, the clamping means of the 
representative mill includes three sets of clamps 60, each consisting of a 
heavy clamping lever 61 pivoted at 62 on the structural weldment which 
forms the mill foundation and pivotable between clamping and release 
positions by means of heavy fluid cylinders 63 connected to the clamping 
levers by elongated operating rods 64. As shown in FIG. 3, for example, 
the clamping levers 61 are generally horizontal, when pressing downward on 
the retaining beam 44, and are pivoted to a generally vertical position, 
as shown in phantom lines, in order to release the retaining beam for 
removal of the mill housings. As reflected particularly in FIG. 2, a 
representative mill is provided with clamping assemblies adjacent each end 
and in the center of the mill. This, in conjunction with the relatively 
massive weight of the beam, serves to provide highly reliable and 
effective vertical clamping of the several mill housings. 
In accordance with a significant aspect of the invention, the several mill 
housings are arranged to be both lifted and held down, as desired, by 
means of the retaining beam 44. To enable the mill housings to be lifted, 
each of the hold-down blocks 42 is provided with a lifting pin 70, 
arranged to be received transversely in the downwardly projecting legs of 
the holding block 42. The lifting pins 70, which are advantageously 
provided with curved recesses to receive the housing pins 43, are 
slidingly received in the hold-down blocks 42, and are advantageously 
permanently connected to the retaining beam 44 by a chain 72. When the 
beam 44 is lowered into position on a preassembled group of mill housings 
23, the respective lifting pins 70 are inserted in place such that, when 
the beam is thereafter lifted, the entire group of mill housings is lifted 
by engagement of the pins 70 and 43. The arcuate recesses 71 in the 
lifting pins become engaged with the housing pins 43 during lifting, to 
effectively lock the lifting pins in position. In order to release a 
housing from the retaining beam 44, it is merely necessary to withdraw the 
appropriate lifting pin or pins and lift the beam. To facilitate lifting 
of the beam, it may be provided with appropriately located U-shaped bolts 
73 (FIG. 2) engagable by suitable crane and sling. 
As will be readily appreciated, while a given mill setup is in operation on 
the production line, an appropriate mill combination for the next 
production sequence may be preassembled on the preparation floor and, if 
two or more retention beams 44 are provided, the new mill combination may 
be set up, with its retaining beam in position and all of its lifting pins 
70 secured. To change over the mill to a new production requirement, all 
that is required is to unclamp and uncouple (by means still to be 
described) the mill stands from the foundation structure, release the 
vertical hold-down clamp 60 and lift off the retaining beam 44 with a 
suitable crane and sling, as reflected in phantom lines in FIG. 2. This 
assembly may be carried over to and deposited on the preparation floor, 
where the crane can be connected to the pre-prepared new mill combination, 
which is quickly carried over into position and lowered into the 
foundation structure, clamped and coupled. The entire sequence can be 
accomplished in a practical minimum of time. 
In some cases, it may not be necessary to remove all of the mill stands 19 
during a mill changeover. In such cases, selected ones of the lifting pins 
70 are simply pulled out of the hold-down blocks 42 before the retaining 
beam 44 is lifted. The disconnected mill stands simply remain in position, 
while those whose lifting pins 70 are connected are lifted away. 
In accordance with known principles, it is desired to longitudinally clamp 
the entire series of mill stands, so that they are packed tightly and 
solidly from one end to the other of the mill. To this end, the upstream 
or entry end of the mill (see FIG. 5) is provided with a plurality of 
compression pads 80, which are mounted on the end frame plate 81 and are 
accurately aligned with the machined bosses 30 of the mill stands 19. The 
entire stack of twenty-four mill housings is placed in compression by 
means of four hydraulic cylinders 82 mounted on the end frame plate 83 at 
the exit end (FIG. 11). The base ends of the cylinders 82 are mounted on 
the inside face of the plate 83, and the rod ends of the cylinders extend 
upstream and are provided with pads 84 arranged to engage the bosses 30 of 
the mill housing 19 at the exit end. After all of the mill housings have 
been lowered to place by the retaining beam 44, the four hydraulic 
cylinders 82 are actuated to extend, pressing on the four bosses 30 of the 
last mill stand and thereby placing all of the mill stands under 
compression through the aligned series of bosses 30. Desirably, the bosses 
are machined to predetermined narrow mill housing thickness tolerances 
(e.g., plus zero to minus six mils), so that the maximum tolerance range 
for the entire series of twenty-four mill stands is very small (e.g., 
around an eighth of an inch). The longitudinal compression of the 
cylinders 82, in conjunction with the vertical clamping afforded by the 
beam 44 and clamping assemblies 60 serves to solidly hold the several mill 
stands in position in the foundation structure 10. 
Pursuant to one of the more specific aspects of the invention, a simplified 
yet reliable arrangement is provided for mechanically locking the several 
hydraulic cylinders 82 against the eventuality of a loss of substantial 
reduction or hydraulic pressure. To this end, a heavy locking plate 90 
(FIGS. 11-14) is mounted for vertically guided sliding movement in the 
frame structure. To advantage, the front or downstream face 91 of the 
locking plate 90 may be slideably supported against bearing plates 92 
mounted on the front faces of the several longitudinal clamping cylinders 
82. The bearing plates 92, being solid with the cylinders, are in turn 
solid with the exit end frame structure 21, to which the hydraulic 
actuators 92 are directly mounted. Along the outside faces of the bearing 
blocks 82 are secured side bearings 93, which slideably engage the side 
and front edges 94, 95 of the locking plate 90, limiting the plate to 
vertical movement. 
As shown best in FIG. 12, the locking plate 90 is provided with a large 
central opening 96 arranged to receive an exit guide sleeve 97. The plate 
90 normally rests upon supporting surfaces 98 of the foundation beams 11, 
12, but it is capable of being raised by a lever 99 (FIG. 13) keyed to a 
shaft 100 and operated by a manual lever 101. The locking plate 90 is 
provided with four keyhole-shaped openings 102, the upper or narrow 
portions 103 of which are large enough to receive the rod portions 104 of 
the hydraulic actuators 82, while being substantially smaller than the 
enlarged compression pads 84 provided at the end extremities of the 
actuator rods. The lower portions 105 of the keyhole openings are large 
enough to accommodate the compression pads 84. When the locking plate 90 
is raised, by drawing back of the manual lever 101, the enlarged portions 
of the keyhole-shaped openings are aligned with the compression pads 84, 
and the actuating cylinders 82 may be retracted to unclamp the stack of 
mill stands. Thereafter, when a new stack of stands is in place, and the 
actuators 82 are energized to extend and apply clamping force, the 
compression pads 84 will be extended beyond the upstream face of the 
locking plate 90 (see FIG. 13). Desirably, the clearance between the back 
face 106 of the compression pads and the front face 107 of the locking 
plate will be very small, sufficient only to accommodate manufacturing 
tolerances in the thickness of the mill stands. After the mill stands are 
clamped, the manual lever 101 may be returned to an upright position, 
lowering the locking plate, until the narrow portion of the keyhole 
openings lie behind the compression pads. Thereafter, if there is any loss 
of fluid pressure in the actuators 82, the clamped mill stands will not be 
completely released, but will be released only to the extent of the slight 
clearance between the compression pads and the upstream face of the 
locking plate. This enables the mill to be brought to a stop without 
serious damage to its components. 
In the mill structure of the invention, a somewhat simplified and improved 
arrangement is provided for effecting simultaneous coupling and decoupling 
of the plurality of mill stands, to permit removal and replacement 
thereof. In this respect, the coupling and decoupling mechanism of the 
invention is intended to be a specific improvement upon the type of 
arrangement shown in, for example, the Gillet U.S. Pat. No. 3,355,923. 
Each of the mill stands, of course, has its own motor 108 and motor drive 
shaft 109. The drive shaft 25 of the mill is coupled with a retractable 
drive shaft 110 connected to a gear reducer 112 by means of a sliding, 
splined coupling 113 and shaft 111. At the forward end of each of the 
drive shafts 110 is a splined clutch coupling 114 which engages with the 
splined end of the housing drive shaft 25. Springs 115, within the splined 
drive coupling 113 serve to urge the clutch couplings 114 into driving 
engagement with the housing shafts 25, in a known manner. 
In order to decouple the drive shafts 110 from the mill stands 19, the 
drive shafts 110 are retracted away from the mill stands, against the 
action of the springs 115, until the coupling sleeve 114 is completely 
separated from the splined end of the mill drive shaft 25. Suitable 
openings 116 are provided in the foundation back wall 22 to receive the 
coupling sleeve 114 and permit full retraction thereof to disengage the 
mill stands. 
To effect the desired retracting movement of the shafts 110, each is 
provided with a collar or shoulder 117 engagable by yokes 118, 119 which 
extend respectively downward and upward from a clutch bar 120. According 
to one aspect of the invention, the clutch bar arrangement, although 
effectively extending the full length of the mill, need not and 
advantageously does not constitute a single uninterrupted bar. Rather, the 
bar is advantageously divided into a plurality of segments (typically 
three) with each segment being supported at its ends by suitable bearings 
122 (see FIGS. 6, 14) for transverse sliding movement relative to the 
foundation structure. To this end, each of a plurality of transversely 
disposed structural plates 123, forming part of the foundation weldment 
structure, is provided with a suitable opening 124 for the reception and 
horizontal transverse movement of the clutch bar 120. Some, but typically 
less than all of these plate openings will be provided with slide support 
bearings 122. 
The yoke members 118, 119 conveniently may be short sections of angle, one 
flange of which is bolted to the clutch bar 120 and the other flange of 
which is appropriately recessed to embrace the forward portions of the 
drive shafts 110, in front of the collars 117. Accordingly, when the 
clutch bar segments 120 are moved transversely, in a direction away from 
the mill stands 19, the collars 117 will be engaged by the respective 
clutch yokes 118, 119. This will effect the desired retraction of the 
drive shafts and disengagement of the mill stand drive shaft 25. For 
temporary support of the disengaged drive shaft, a pair of adjustable 
bolts 125 is positioned underneath each drive shaft. As the drive shafts 
are retracted, the clutch sleeves 114 are brought into a position above 
the supporting bolts 125. When the sleeves 114 are fully disengaged, they 
will drop down slightly on to the heads of the bolts 125, in an 
appropriate position to be reengaged with the next batch of mill stands. 
It will be understood, of course, that the mill drives are stationary at 
this time. 
In order to effect actuation of the clutch bar sections 120, each is 
engaged near each end by a crank lever arm 130 secured to a vertical shaft 
131 mounted by a bracket 132 on the foundation structure. At the opposite 
end of the shaft 131, is a second crank lever 133 pivotally connected to a 
pull rod 134. The pull rod, which may consist of a plurality of 
connected-together segments, is connected at the exit end of the 
foundation with an actuating cylinder 135. 
As is reflected in FIG. 7, the upper crank levers 133 are arranged 
substantially at right angles to the lower crank levers 130. The 
arrangement of these levers and of the pull rod 134 and actuator 135 is 
such that, when the actuator 135 is energized to retract, the pull rod 134 
is drawn to the left in FIG. 7 a distance sufficient to pivot the upper 
crank lever 133 through about 30.degree. of arc, passing through a 
position at right angles to the pull rod to a position as shown in phantom 
lines in FIG. 7. During this movement, the pull rod 134 is displaced 
slightly in a transverse direction. However, the limited transverse 
movement is accommodated easily by pivotable mounting of the actuator 135, 
at 136, and pivotable connection of the cylinder rod 137 to the pull rod 
at 138 (see FIG. 15). 
Movement of the clutch bar segments 120 is substantially confined to 
movement parallel to the axes of the drive shafts 110. Accordingly, the 
crank levers 130 are connected to the clutch bars 120 by means of rollers 
140, which are received in longitudinally elongated slots 141. The 
elongation of the slots 141 accommodates the slight longitudinal component 
of motion of the rollers 140, as the levers 130 are pivoted through their 
normal working arcs. 
When the clutch actuator 135 is energized to extend, and permit return of 
the clutch bar 120 to its forward position, all of the drive shafts 110 
are urged to extend by means of the spring urged couplings 113. This 
permits the splined coupling 114 to become engaged with the drive shafts 
25, as soon as the splines are properly aligned. 
When changing a mill stand combination, it may also be appropriate to 
change the entrance and exit guide bushings. To this end, entrance and 
exit guide bushings 150, 97 respectively are removably received in collars 
151, 152 mounted on the end frame structures 20, 21. These bushings are 
held in place by gates 153, 154, which are pivoted in the end frames and 
are removably locked in operating position by swing bolts 155, 156. To 
change the guide bushings, the swing bolts are released and swung out of 
the way, permitting the gates 153, 154 to be pivoted downward out of the 
way and enabling the guide bushings to be withdrawn axially from the end 
frame. 
SUMMARY OF OPERATION 
In order to set up the stretch reduction mill for a given production run, a 
series of mill stands 19 is assembled on the preparation floor in the 
proper sequence. In general, an entire mill sequence is set up, including 
dummy stands at the downstream end, in cases where the full compliment of 
working mill stands is not required for the particular production 
scheduling. The preassembled mill stands are then individually engaged by 
the lifting pins 70 and U-shaped hold-down brackets 42 of a retaining beam 
44, which extends over the full length of the mill stand assembly. 
At the appropriate time, the retaining beam 44 is simply lifted bodily, 
along with all of the attached mill stands, and carried over to the 
foundation structure of the mill, where it is lowered carefully into 
place. In this connection, the slightly tapered end extremities of the 
mill stands will assist in guiding the individual stands into position on 
the foundation rails 17, 18. When the mill stands are finally at rest on 
the rails, they are accurately located vertically and transversely by 
reason of the precision machining of the surfaces 33, 35 in relation to 
the rails 17, 18. 
As the beam is lowered, its end extremities are guided into slots in the 
end frame structures 20, 21, which confine but do not support the ends of 
the beam. 
With the assembly of mill stands now loosely positioned on the foundation 
rails 17, 18, the entire stack of mill stands is locked together as a 
solid structure, and placed under compression, by energizing the four 
actuators 82, carried by the exit end frame 21. As these actuators are 
extended, the locking plate 90 is lowered into locking position, behind 
the compression pads 84, to prevent unintentional release of the several 
mill stands. 
After the mill stands have been longitudinally compressed, the vertical 
clamping actuators 63 are energized, displacing the retaining beam 44 
downward against the compressed springs 55. With the clamping levers 61 in 
their downward limit positions, the retaining beam 44 is held in a 
position spaced slightly above the tops of the hold-down blocks 42. 
Accordingly, all of the mill stands are urged downwardly under 
substantially equal forces determined by the compression of the heavy 
springs 55. 
With the mill stands now clamped in place, the clutch bar 120 can be 
released, permitting the splined couplings 114 to move forwardly, engaging 
the various drive shafts 25. The mill is then ready for normal operations. 
Since the retaining beam 44 remains in position above the mill stands, and 
indeed serves as the means for holding them in place, subsequent removal 
of an entire mill stand assembly is effected quickly and efficiently by 
simply releasing the vertical and longitudinal clamping forces on the mill 
stands, uncoupling the drives and lifting the retaining beam 44 bodily 
from the mill foundation, by means of a crane. The just removed assembly 
is carried by the crane to the preparation floor, where a new prepared 
assembly is picked up and carried back to the mill. The entire changeover 
sequence can be carried out with a minimum of interruption of the 
production of the tube mill, as will be appreciated. This is of particular 
importance, of course, where the tube is formed on a continuous basis, as 
in a continuous buttweld or continuous electric weld mill. 
It should be understood, of course, that the specific forms of the 
invention herein illustrated and described are intended to be 
representative only, as certain changes may be made therein without 
departing from the clear teachings of the disclosure. Accordingly, 
reference should be made to the following appended claims in determining 
the full scope of the invention.