U.S. patent number 3,688,540 [Application Number 05/052,838] was granted by the patent office on 1972-09-05 for tube rolling mill employing a tapered mandrel and a cluster of rolls that each have specially designed tube contacting grooves.
This patent grant is currently assigned to Superior Tube Company, Norristown, PA. Invention is credited to Richard E. Russel.
United States Patent |
3,688,540 |
|
September 5, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
TUBE ROLLING MILL EMPLOYING A TAPERED MANDREL AND A CLUSTER OF
ROLLS THAT EACH HAVE SPECIALLY DESIGNED TUBE CONTACTING GROOVES
Abstract
A tube rolling mill having two sets of three rolls each which
are reciprocatingly driven along a length of a tube supported by a
tapered mandrel. Each roll is forced against the tube by its
individual cams each having a surface with one or more tapers which
are related to multiple mandrel taper in a manner to provide
reduction in both wall thickness and inside diameter of the tube.
Each roll is provided with a tube contacting groove having in
cross-section a central arc with a radius of curvature
substantially equal to the smallest radius of that portion of the
tube contacted by the roll, with either side of the central arc
joined by lines tangent thereto with large radii of curvature
chosen so that each roll contacts a tube in two zones around its
circumference. The rolls are pressed against the tube upon the
urging of the tapered cam surface against a roll trunnion. The
radius of the trunnion is carefully chosen to control longitudinal
forces transferred to the tube by the roll.
Inventors: |
Richard E. Russel (Paoli,
PA) |
Assignee: |
Superior Tube Company, Norristown,
PA (N/A)
|
Family
ID: |
26731147 |
Appl.
No.: |
05/052,838 |
Filed: |
July 7, 1970 |
Current U.S.
Class: |
72/208;
72/214 |
Current CPC
Class: |
B21B
21/005 (20130101); B21B 23/00 (20130101) |
Current International
Class: |
B21B
21/00 (20060101); B21B 23/00 (20060101); B21b
017/06 () |
Field of
Search: |
;72/208,209,234,370,214 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Milton S. Mehr
Attorney, Agent or Firm: Woodcock, Washburn, Kurtz &
Mackiewicz
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of application Ser. No. 845,832,
filed July 29, 1969, now abandoned, and is related to application
Ser. No. 845,833, filed July 29, 1969, now U.S. Pat. No. 3,611,775.
Claims
What is claimed is:
1. In a tube rolling mill of the type wherein a plurality of
grooved rolls are reciprocated along a working length of a mandrel
in a manner that the grooves of each roll may contact and roll
along a tube carried by the mandrel, said rolls being constrained
to follow a predetermined path relative to the mandrel, the
improvement wherein the groove of each of said rolls is of uniform
radial cross-sectional shape around an entire circumferential
surface of the roll, said groove shaped in radial cross-section
having an arcuate line in a center portion thereof with a radius of
curvature equal to or a few percent less than the smallest tube
outside surface radius for which said predetermined roll path
provides, said groove additionally including in cross-section
symmetrical lines on either side of said arcuate line that are
shaped to provide two zones of contact around the tube
circumference along substantially the entire working mandrel length
for which the mandrel and roll paths are adapted to receive and
reduce the tube.
2. A tube rolling mill according to claim 1 wherein said mandrel is
tapered along its said working length in order to provide
significant tube inside diameter reduction as well as wall
thickness reduction.
3. A tube rolling mill according to claim 1 wherein said
symmetrical lines on either side of said arcuate line in groove
radial cross-section are substantially straight lines tangent to
said arcuate line.
4. In a tube rolling mill characterized by a tube supporting
mandrel, a roll housing surrounding said mandrel and adapted to
reciprocate over a defined stroke distance along the length of said
mandrel, a plurality of rolls journaled in said roll housing in a
manner to be free to rotate about their axes which lie in a common
plane of the housing that is substantially perpendicular to said
mandrel, said rolls arranged to contact said tube simultaneously,
each of said rolls having its largest radius circumferential
surface with a tube contacting groove of uniform shape around said
roll, a pair of cam surfaces associated with each of said rolls and
adapted to be reciprocated along the length of said mandrel a cam
working length distance that is a constant multiple of the roll
housing stroke distance, each of said rolls including a pair of
trunnions on opposite sides of its said largest radius
circumferential surface for bearing against its associated pair of
cams in a manner to be guided thereby so that each roll groove
follows a predetermined path relative to the mandrel, thereby to
control the portion of the roll housing stroke distance in which
the rolls will contact the tube and also to control the amount of
roll bite into the tube and thus tube wall thickness reduction
which results from reciprocating said rolls over the tube, the
improvement wherein each of said roll grooves is shaped to have two
zones of contact over substantially the entire portion of the roll
housing stroke distance in which the rolls will contact the tube,
thereby having a variable effective roll groove radius between a
minimum and a maximum along the tube length, thus causing torque
forces over at least a portion of the tube contacting length of the
rolls that impart longitudinal forces to the tube, the further
improvement wherein the radii of each pair of roll trunnion
surfaces are of a value to balance against each other the roll bite
and torque forces imparted to said tube, whereby the maximum
longitudinal forces of the tube caused by the rolling are
minimized.
5. A tube rolling mill according to claim 4 wherein the radii of
each pair of said roll trunnions is substantially equal to the
minimum effective roll groove radius divided by said constant
multiple relating the cam working length and roll housing
stroke.
6. A tube rolling mill according to claim 4 wherein said mandrel is
significantly tapered along a portion of its length where a tube
carried thereby is contacted by said rolls, thereby to provide
significant tube inside diameter reduction as well as wall
thickness reduction.
7. In a tube rolling mill characterized by a tube supporting
mandrel a roll housing surrounding said mandrel and adapted to
reciprocate over a defined stroke distance along the length of said
mandrel, a plurality of rolls in two clusters journaled in said
roll housing in a manner to be free to rotate about their axes, the
axes of a first cluster of rolls lying in a first plane of the
housing, the axes of a second cluster of rolls lying in a second
plane of the housing, said first and second planes being
substantially perpendicular to said mandrel and separated a fixed
distance in said roll housing, each of said rolls having its
largest radius circumferential surface provided with a tube
contacting groove of uniform shape around said roll, a pair of cam
surfaces associated with each of said rolls and adapted to be
reciprocated along the length of said mandrel a cam working length
that is a constant multiple of the roll housing stroke distance,
each of said rolls including a pair of trunnions on opposite sides
of its said largest radius circumferential surface for bearing
against its associated pair of cams in a manner to be guided
thereby so that each roll groove follows a predetermined path
relative to the mandrel, thereby to control the portion of the roll
housing stroke distance over which the rolls will contact the tube
and also to control the amount of roll bite into the tube and thus
tube reduction which results from reciprocating said rolls over the
tube, said rolling mill additionally characterized by means for
advancing tubing along the mandrel an increment of feed each roll
housing stroke, the improvements comprising, a taper on said
mandrel such that its largest diameter end in oriented for only the
first cluster of rolls to contact at the larger end a tube carried
by the mandrel and its smaller diameter end is oriented only for
the second cluster of rolls to contact at the smaller end a tube
carried by the mandrel, said smaller diameter being substantially
equal to the desired inside diameter of a finished tube, each of
said roll grooves shaped to have two zones of contact over
substantially the entire portion of the roll housing stroke
distance in which the roll will contact the tube, thereby having a
variable effective roll groove between a minimum and a maximum
during its contact along the length of the tube, thus causing
torque forces over at least a portion of a length of the tube for
which each roll is adapted to contact which impart longitudinal
forces to the tube, and the radii of each pair of trunnion surfaces
of each roll in said second cluster being of a value to drive the
tube in a direction opposite to the direction of rolling for
substantially the entire length of the tube that the roll is
adapted to contact, whereby the maximum longitudinal forces
transferred from the second cluster of rolls to said tube are
minimized.
8. A tube rolling mill according to claim 7 with the further
improvement wherein the radii of each pair of trunnion surfaces of
each roll in said first cluster is of a magnitude so that the two
clusters of rolls when both are in contact with a tube would tend
to elongate the tube between them if there were no slippage of the
rolls on the tube, said elongating capability of the rolls equal to
or slightly less than the actual elongation of the tube due to its
reduction.
9. A tube rolling mill according to claim 8 wherein the radii of
each pair of trunnion surfaces of each roll in said first cluster
is such that the actual tube elongation for said increment of feed
is equal to or greater than the elongation capability of the two
clusters of rolls but less than twice said elongation
capability.
10. A tube rolling mill according to claim 9 wherein the radii of
each pair of trunnion surfaces of each roll in said second cluster
is substantially equal to the minimum effective tube contacting
groove radius of the roll divided by said constant multiple between
the cam working length and roll housing stroke distance.
11. A tube rolling mill characterized by a plurality of rolls
pivotally mounted in a roll housing which is reciprocated along a
length of a tube, and further characterized by cam surfaces for
rotatably guiding each roll against said tube with predetermined
displacements, said cam surfaces being reciprocated in a direction
along the length of said tube with a cam working length that bears
a constant relationship to the roll housing stroke, the improvement
comprising: a tube contacting groove in an outer circumferential
surface of each of said rolls, said groove having a uniform
cross-section therearound, and a trunnion surface on each roll for
contacting said cam surface, the radius of said trunnion surface
adjusted to minimize longitudinal forces along said tube.
12. A tube rolling mill according to claim 11 wherein the groove of
each of said rolls is shaped in cross-section in a manner to
contact said tube at two zones therearound throughout most of said
length of tube.
13. A tube rolling mill according to claim 11 wherein said uniform
groove includes in cross-section an arcuate line in the center
thereof bounded on either side by substantially straight lines
tangent to said arcuate surface, said arcuate line having a radius
of curvature substantially equal to the smallest tube outer surface
radius which said roll is designed to contact.
14. In the art of reducing metal tubing by use of an internal
mandrel and external rolls, a method of reducing the internal
diameter and wall thickness of a tube, comprising the steps of:
contacting the outside surface of the tube at two areas thereof
with each of said rolls for substantially the entire time each of
said rolls is biting into said tube, and applying torque to each of
said rolls in an amount to minimize maximum longitudinal forces
imparted to said tube as a result of said torque and said each of
said rolls biting into said tube so as to balance the tube thrust
caused by the roll bite against the tube thrust imparted by rolling
torque.
15. In the art of reducing metal tubing by use of an internal
mandrel and at least two sets of external rolls separated a fixed
amount along the length of the mandrel, comprising the steps of:
reciprocating the sets of rolls relative to the mandrel, moving one
of said sets of rolls against the tube on the mandrel in a manner
to effect primarily inside diameter reduction of the tube, and
concurrently moving the other of said sets of rolls against said
tube in a manner to effect primarily wall thickness reduction.
Description
This invention relates generally to a method and apparatus for
reducing and elongating metal tubing and more particularly to
improvements in a method and apparatus for reducing and elongating
metal tubing with the use of rolls.
Metal tubing is used in a wide variety of environments and for many
different applications. This requires that the tubing be available
with a wide variety of inside and outside diameters and wall
thicknesses. In order to effectively utilize the economies of mass
production, metal tubing is initially manufactured in only a few
standard sizes. This makes it necessary to modify tubing of a
standard manufactured size to obtain a size needed for a particular
application involving smaller quantities of tubing than can be
economically manufactured directly.
A machine for reducing tubing of a standard manufactured size is
described by Krause in the Iron and Steel Engineer, Aug. 1938,
pages 16-29, and in several patent publications such as U.S. Pat.
Nos. 2,161,064, 2,161,065, and 2,223,039. The machines described
therein utilize a single set of two rolls operating against a
mandrel supported tube to effect the tube's reduction. Each roll is
rolled along a working length of the tube in response to the
movement of a cam for controlling the pressures exerted by the roll
against the tube. These machines provide for only a limited
reduction in wall thickness without significant reduction of the
inside diameter of the tube.
In addition, there have been several disclosures by Argonne
National Laboratories resulting to similar machines. In an Argonne
paper ANL-MS-990, dated Mar., 1968, entitled "Fabrication of
Vanadium Alloy Tubing" by Mayfield and Karasak, a rolling mill is
disclosed which is capable of limited inside diameter tube
reduction. In an Argonne print MY-B-2700-A-19D, part 33D, a roll
groove design is described wherein the roll groove has a center
arcuate surface terminating in two tangent straight surfaces at its
edge. The radius of the arcuate surface matches the largest radius
of a tube length to be worked by the roll, whereby the tangent flat
surfaces serve only as side relief for non-uniform deformation of
the tube. Such single point contact of the roll groove with a tube
is not an efficient working arrangement.
Several publications by Russian authors have described similar tube
rolling mills. These disclosures, however, tend to show that three
or six roll tube rolling machines now in existence have merit in
reducing wall thickness while possessing only limited capability
for reducing the inside diameter. Such machines do not enjoy a wide
application to the tube industry since the majority of such
applications require substantial reduction in diameter.
Therefore, it is a primary object of this invention to provide a
tube rolling mill capable of making large reductions in both wall
thickness and inside diameter.
It is also an object of this invention to provide a tube rolling
mill with a high efficiency and feed rate.
It is a further object of this invention to provide a tube rolling
mill with a high degree of reliability and additionally with a
capability of producing reduced tubes with a wide variety of wall
thicknesses and inside diameters.
It is yet another object of this invention to provide a tube
rolling process that produces a reduced tube of improved
quality.
These and additional objects are accomplished by a machine
according to this invention in which a number of elements are
combined to reduce tube wall thickness and additionally reduce the
tube inside diameter without a machine complexity any greater than
exists in other tube reducing machines. Two sets of three rolls
each are provided for contacting a tube with grooves provided
around the circumferential edges of each roll. Each roll is
rotatably attached to a roll housing and is reciprocated thereby
along a working length of a mandrel which is designed to fit within
a tube to be reduced. Each set of three rolls is clustered around
the tube with their axes of rotation located in a plane
substantially perpendicular to the length of the mandrel and
displaced 120.degree. from each other. Two sets of rolls are
spatially fixed relative to one another in a direction along the
length of the mandrel by the roll housing. One set of rolls reduces
the tube an intermediate amount and the second set of rolls
completes the reduction to the dimensions desired. The axes of
rotation of the rolls of one set are displaced 60.degree. from the
axes of rotation of the rolls of the other set. The mandrel is
tapered along at least a portion of its working length over which
the roll housing reciprocates the tube contacting rolls. The rolls
are urged toward the mandrel by an individual cam surface for each
roll, said cam making a contact with a roll along its surface
substantially opposite the tube contacting surface. The cam and
mandrel are shaped so that each roll contacts a tube to be reduced
during at least a portion of each reciprocating stroke of the roll
housing.
The tube contacting groove around the outer edge of each roll has a
uniform shape in cross-section at any point around the
circumference of the roll. As each roll is pressed against a tube
and rolled therealong, the outside diameter of the tube becomes
smaller. The cross-sectional shape of the groove includes an
arcuate portion in the middle thereof having a radius of curvature
substantially equal to or slightly less than the smallest radius of
the outside surface of a tube portion contacted by that particular
roll. On either side of this arcuate portion of the groove is in
cross-section a substantially flat portion extending on either side
to the edge of the groove, the flat portions joining the arcuate
portion as a tangent thereto. The advantage of this arrangement is
that at the beginning of the working stroke, a tube contacts the
roll groove at two portions (zones) therealong and does so
throughout the working stroke. This two-zone contact of each roll
groove makes more efficient use of the working stroke. With a six
roll machine, a tube is contacted at twelve zones therearound,
thereby providing considerably more surface area contact between
the rolls and the tube than in other machines. This results in a
greater effective volume of metal reduction per rolling stroke and
a better quality reduced tube.
The cams and the mandrel are cooperatively shaped in a manner to
provide a maximum bite of each roll at its contact zones into the
tube to be reduced. A maximum bite is provided throughout wall
reduction portions of the working stroke and is slightly less than
the bite which will strain any portion of the tube to its point of
rupture. At the beginning of the working stroke, this bite is much
larger than at the end of the working stroke. This maximum bite at
points along the tube is dependent upon, among other things, the
material of the tube being reduced. Such a maximization of the roll
bite additionally improves the reduction possible in a given
working length of the machine.
The cams are attached to a cam housing which is reciprocated along
the length of the mandrel in order to contact the rolls and guide
them against the tube without significant slippage between each
roll and its cams. Instead of contacting the outer circumference of
the roll, the cams are designed to contact trunnions provided on
either side of each roll. This has the advantage that a larger
bearing surface may be provided to prolong the life of the rolls
and the cams, as well as to allow an adjustment which is beneficial
to the tube rolling process. The roll housing and cam housing are
driven from a common motor source with a constant ratio of
velocities therebetween. This velocity ratio and the relationship
between the radius of the roll's trunnions and the radius of that
portion of the roll groove contacting a tube at a specific point
thereof determines the degree to which the roll will tend to apply
torque to the tube and cams, and thereby determines the tendency of
the groove to slip against the surface of the tube when the tube is
adequately held against lateral movement.
For a given configuration, the torque forces causing such slippage
vary along the working length of the tube since the effective
radius of the roll varies therealong. It has been found desirable
to control the torque forces tending to slip the roll against the
tube in a manner to compensate for the horizontal forces applied to
the tube by a roll biting into the tube wall. Such compensation
allows mandrel and tube gripping devices to more accurately
position the tube. The compensation also allows larger roll bites
without creating forces of a magnitude that cause machine elements
to fail, thereby accomplishing more tube reduction in a given
working length and amount of time.
When a rolling mill employing two sets (stages) of rolls that
simultaneously contact a tube is used, it has been found desirable
to balance the torque forces between rolls of each set to
compensate for tube elongation.
For a more detailed understanding of the invention and for further
objects and advantages thereof, reference is made to the following
description of its preferred embodiments taken in conjunction with
the accompanying drawings.
FIG. 1 illustrates in a partially exploded view a rolling mill
according to the present invention;
FIG. 2 is a cross-sectional view of FIG. 1 taken through the first
stage (set) of rolls at 2--2;
FIG. 3 is a cross-sectional view of FIG. 1 taken through the second
stage (set) of rolls at 3--3;
FIG. 4 schematically illustrates the operation of the primary
operating components of the rolling mill illustrated in FIGS. 1, 2
and 3;
FIG. 5 shows the shape of a preferred tube contacting groove of a
roll for use in the rolling mill shown in FIGS. 1--3; and
FIG. 6 shows a side view of a preferred roll illustrating an
optimum trunnion radius for use in the rolling mill shown in FIGS.
1--3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a cam housing 11 is reciprocated relative to a
machine frame 13 along a slide 15 in substantially a straight line.
An electric motor 17, also attached to the frame 13, drives a
flywheel 19. A rod 21 (partially broken away) is connected between
the flywheel 19 at a crank pin 20 and the cam housing 11 to convert
rotary motion of the flywheel to reciprocable motion of the cam
housing. Within the cam housing 11 is a reciprocatable roll housing
23, shown removed from the cam housing for clarity of illustration.
A pinion gear 25 engages a rack 27 that is rigidly attached to the
frame 13. A second pinion gear 26 engages a rack 29 that is rigidly
attached to the cam housing 11. The pinion gears 25 and 26 are
concentric about a common axis of rotation 30 and are nonrotatable
relative to each other. The reciprocable motion of the axis of
rotation 30 of the pinion gear 25 is communicated to the roll
housing 23 by means of a connecting rod 31 (shown herein as two
sections since the roll housing 23 is shown removed from the cam
housing 11). The cam housing 11 has a maximum reciprocation stroke
distance that is equal to the diameter of the circular path taken
by the crank pin 20. From the geometry of the driving arrangement
of FIG. 1, the roll housing 23 has a maximum reciprocation stroke
distance that is equal to the maximum stroke of the cam housing 11
multiplied by the diameter of the pinion gear 25 and then divided
by the sum of the diameters of the pinion gears 25 and 26. The use
of two pinion gears having different radii as herein has the effect
of increasing the length of the working zone along the tube without
increasing the stroke length of the cam housing. It should be noted
that although the double pinion gear arrangement herein is very
convenient for controlling the maximum relative cam housing and
roll housing stroke distances, and thereby their relative
velocities, other specific mechanical arrangements, such as one
employing levers, may also be employed for the same purpose.
Another aspect of the geometry of the arrangement in FIG. 1 is that
the cam housing stroke distance is equal to the sum of the roll
housing stroke and the working stroke length of the cams (the
distance along each cam that contacts a roll trunnion) within the
cam housing. It follows, then, that the cam length contacted by
each roll bears the same relationship to the roll housing stroke as
a ratio of the diameter of the cam housing pinion gear 26 to the
diameter of the roll housing pinion gear 25.
A tube 33 to be reduced is inserted through an opening 35 of the
roll housing 23, and is carried by a mandrel 37. The mandrel 37 is
rigidly held fixed relative to the machine frame 13 by an
appropriate gripping device 36, which also provides for removing
the mandrel. An appropriate apparatus 38 is provided for positively
gripping the tube 33 linearly over a working length of the mandrel
37, and further to incrementally rotate the tube. The apparatus 38
causes such feeding and rotation of the tube being reduced at
specific portions of the reciprocating cycle, as is hereinafter
discussed.
FIGS. 2 and 3 better show the relationship of tube deforming rolls
and the cam housing as sectional views of FIG. 1. A first set of
rolls 39, 41 and 43, shown in FIG. 2, are held in the roll housing
23 with their axes of rotation lying substantially in a plane
perpendicular to the mandrel 37 and making an angle of 120.degree.
with each other. Similarly, a second set of rolls 45, 47 and 49,
shown in FIG. 3, are held by the roll housing 23 in the position
that their axes of rotation lie substantially in a plane
perpendicular to the mandrel 37 and at a spatially fixed distance
along the length of the mandrel from the plane in which the axes of
rotation of the first set of rolls 39, 41 and 43 lie. Furthermore,
the axes of rotation of the two sets of rolls are angularly
displaced from each other by 60.degree..
Although held by the roll housing 23 against movement relative
thereto in the direction of its reciprocation, each roll is free to
move in a direction normal to the mandrel. Each roll is resiliently
urged by a set of springs (such as springs 49 and 50, each held
within a roll guide) out of the roll housing 23 and against its
associated cam surfaces. Alternatively, the rolls may be
hydraulically urged against their associated cams. Each roll has a
trunnion formed on either side thereof, such as trunnions 51 and 53
on either side of the roll 45. Each roll is associated with a pair
of cam tracks upon which its pair of trunnions ride. The two cams
associated with each roll are designated herein with the same
number as the roll but with an asterisk placed after the reference
number of one of the cam tracks and a double asterisk placed after
the number referring to the other of the cam tracks. The cams are
long metal bars shaped in a manner discussed hereinafter and
rigidly attached to the cam housing 11. This attachment is
accomplished through a recessed member for each pair of cams, such
as a recessed member 55 which is shaped to support the cams 45* and
45**. Notice that the cams 45* and 45** each have a sloped side
surface which allows fastening them to the recessed member 55 by a
wedge 57 which is attached to the recessed member by a threaded
fastener 58.
It should be noted with reference to FIGS. 1, 2 and 3, the ease
with which the cam surfaces may be replaced in the cam housing 11
and also the ease with which the rolls may be replaced in the roll
housing 23. A given pair of cams are removed by removing their
associated wedge. The rolls are merely lifted out of the roll
housing 23 when the roll housing is removed to a position as
illustrated which is out of the cam housing 11. The mandrel 37 is
also easily removed. These features allow quick conversion of the
tube rolling mill to receive raw tubes of various sizes and also to
produce finished tubes with various wall thicknesses and inside
diameters.
The schematic diagram of FIG. 4 illustrates operation of the
rolling mill illustrated in FIGS. 1, 2 and 3. The mandrel 37 is
shown in cross-section along its length which includes a tube
working zone B-J wherein at all points therealong the tube 33 is
contacted by one or both sets of rolls to accomplish reduction
either in wall thickness or inside diameter or both. The mandrel
has a diameter d.sub.1 at its large end which is something slightly
less than the inside diameter of the starting tube 33, thereby
allowing the tube to be slid easily over the mandrel. The small end
of the mandrel has a diameter d.sub.2 which is substantially equal
to the desired inside diameter of the reduced tube. The mandrel 37
is gradually tapered within the tube working zone from one of these
diameters to the other. This taper is significantly in excess of
that required for tube relief. The diameters d.sub.1 and d.sub.2
may differ by 20 or 30 percent or more, depending on the tube
inside diameter reduction desired.
In order to demonstrate the cooperation between the cams and the
mandrel, one roll from each of the two sets of rolls is shown in
FIG. 4 as if they operated in the same plane so that the
relationship between them and their cooperation in reducing the
tube are illustrated. Rolls 39 and 45 are illustrated in FIG. 4
along with their associated cams 39* and 45*, respectively. The
axis of the roll 39 reciprocates along the tube between positions A
and I with a distance therebetween equal to the stroke distance of
the roll housing 23 (not shown in FIG. 4) in which the roll 39 is
journaled. Similarly, the axis of the roll 45 reciprocates along
the tube between positions D and K. The cams 39* and 45* are
attached to the cam housing 11 (not shown in FIG. 4) and thereby
are reciprocatably driven at a greater velocity than the axis of
the rolls, as described hereinabove. The cam 39* contacts a
trunnion 40 attached to the roll 39 and the cam 45* contacts the
trunnion 51 of the roll 45. The shape of the cams and of the
mandrel determine the displacements of rolls downward against the
tube to bring about a desired deformation of the tube.
Consider a single working stroke wherein the rolls and cams of FIG.
4 move from their far left hand position to the far right and back
again. This represents the extent of movement brought about by a
single revolution of the flywheel 19 of FIG. 1. The roll 39 begins
at the position A and the roll 45 begins at the position D. As
shown by the dashed lines, the roll 39 contacts the tube 33 for the
first time at about the position B and the roll 45 contacts the
tube 33 for the first time at approximately the position F.
Proceeding further to the right, the cooperative shapes of the cams
and the mandrel allow the roll 39 to be lifted from the tube 33 at
about the position F, as shown by the path [39] of the roll, away
from the tube. Similarly, the roll 45 is caused to be lifted from
the tube 33 at about the position J, as shown by the path [45] of
the roll, away from the tube. The roll 39 arrives at the position I
at the same time the roll 45 arrives at the position K to complete
the first one-half of the working stroke. The rolls 39 and 45 then
move back to their beginning positions A and D, respectively, to
complete one working stroke cycle. It may be noted that the "cam
working length" as used herein is a horizontal projection of the
length of a cam surface contacted by the trunnion. With reference
to the cam 39*, the cam working length thereof is the horizontal
distance between points A.sub.1 and I.sub.1.
The tube 33 is advanced (fed) by the apparatus 38 an increment to
the right while the rolls are drawn away from contact with the
tube, either at one or both ends of the working stroke. Similarly,
the apparatus 38 rotates the tube 33 either at one or both ends of
the working stroke. It is preferred to rotate the tube through a
small angle at each end of the working stroke because a smoother
finished tube is the result. The shape of the tube 33 shown in FIG.
4 within the working zone represents the finished shape thereof
after a working stroke and before the tube is fed an increment in
preparation for the next working stroke.
There are many specific cam and mandrel shapes that may be utilized
depending upon the specific tube reduction desired. FIG. 4
illustrates a preferred arrangement for major inside diameter
reduction. The following tabulation describes the work done by the
roll 39 within the working zone between lettered positions along
the length of the tube: Between B-C: The tube is reduced to
intimate contact with the mandrel. Between C-E: Primarily tube
diameter reduction is accomplished by the roll 39. Between E-F:
Primarily wall reduction is accomplished by the roll 39.
The following tabulation describes the work concurrently performed
by the roll 45 within the working zone between lettered positions
along the length of the tube: Between F-G: Primarily wall reduction
performed by the roll 45. Between G-H: Primarily wall reduction
performed by the roll 45 but with a lesser bite into the tube than
between F-G. Between H-J: This is a finishing zone where there is
substantially no taper to the mandrel 37 and with very little bite
of the roll into the tube.
To accomplish the above-noted specific tube reductions at various
points within the tube working zone, the mandrel has one or more
straight line tapers. The cams are shaped cooperatively therewith,
each having a plurality of straight line tapers. The cams of FIG. 4
have their roll contacting surfaces marked with subscripted letters
corresponding to the lettered positions along the tube. For
example, when the roll 39 is positioned at E along the tube, the
cam 39* is contacting the trunnion at position E.sub.1. Straight
line tapers are preferred for the cams and the mandrel since they
are easy to machine, although continuous curves may also be
employed.
The description herein with respect to FIG. 4 is exemplary only
with various changes in the specifics thereof being possible. For
example, if major inside tube diameter reduction is not required,
the portion B.sub.1 -F.sub.1 of the cam 39* may be shaped
differently relative to the portion B-F of the mandrel than as
shown to effect tube wall reduction between B-F instead of tube
diameter reduction. Also, the elements may be designed so that the
rolls 39 and 45 overlap in their work zones along a portion of the
tube, preferably with dissimilar cam tapers acting on the two rolls
in this common length of the tube. Also, certain applications may
require only a single taper along a working length of each of one
set of cams. Furthermore, in those cases where little inside
diameter reduction is desired, the cams and rolls described herein
may be used with a mandrel having little or no taper.
Along any of the portions of tube length wherein substantial wall
thickness reduction is desired, the controlling cam and mandrel
tapers are designed for a bite of the rolls into the tube at each
point within this portion that is approximately the same percentage
of the wall thickness at that point before the roll. This maximizes
the efficiency of the wall thickness reduction, thereby allowing
more reduction to be accomplished in a shorter portion of the
working stroke. Multiple straight line tapers on the cams may be
employed to approximate this constant percentage although
continuous curved cam surfaces are more exact. The amount of tube
feed for each stroke is then adjusted to a maximum for a given tube
material just short of that which ruptures the tube, thereby
maximizing productivity of the machine.
A preferred tube contacting groove is illustrated in FIG. 5 for the
rolls of a rolling mill illustrated with respect to FIGS. 1-3. The
groove shape is uniform in cross-section at any radial plane
thereof. The groove cross-section is shown on a roll 79 which
represents relative roll groove dimensions for any roll shown in
FIGS. 1-3 for the purpose of describing roll groove design. In the
center of the groove is an arcuate portion 81 having a center of
curvature at a point 83. Joining either side of the arcuate center
portion 81 as tangents thereto at its end points 85 and 87 are
straight line segments 89 and 91 which extend to the groove outside
edges 97 and 99, respectively. The arcuate portion 81 extends for
an angular distance .phi. on either side of a center line.
The radius of curvature of the arcuate portion 81 is made
substantially equal to or slightly less than the smallest outside
tube radius the roll is designed to contact, such outside tube
radius being represented by a solid circle 93. This represents the
radius of the finished tube for the roll 45 shown in FIG. 4 and the
radius of the tube at location F for the roll 39. A circle 95 (FIG.
5) represents the largest outside tube radius which the roll groove
is designed to contact, that of the beginning tube for the roll 39
of FIG. 4 and that of the tube at position F for the roll 45.
This roll groove design provides two zones of contact for each roll
against the outside of the tube between the tube's larger portion
(95) and substantially until its smallest portion (93). Such
"two-zone rolling" accomplishes more reduction in a given working
zone of a tube when compared to a roll groove providing only one
zone of contact with the tube. Non-uniform tube wall strain is
reduced as well as resulting degradation of tube quality. Also,
required rolling forces, and thus machine wear, are reduced. To
optimize these advantages, the radius of the arcuate center portion
81 of the roll groove may be made 1 or 2 percent less than the
smallest outside tube radius to be contacted by the roll groove,
thereby extending two zone rolling over the entire length of the
tube contacted by the roll whereby roll life is extended. FIG. 5
illustrates such a preferred roll that is designed to contact the
tube at two zones throughout the stroke. A rolling radius r of the
roll 79 along the tube varies between R.sub.max (contacting tube
portion 95) and R.sub.min (contacting tube portion 93) during each
tube reducing stroke. An arcuate center portion 81 with a radius
significantly smaller than the finished tube outside radius (in the
extreme the groove becomes V-shaped) results in a finished reduced
tube surface that is irregular and rough.
When the roll 79 of FIG. 5 is pressed against a tube during the
rolling thereof, it bites into the tube at its zones of contact
with the roll groove. This results in the extreme edges 97 and 99
becoming closer to the tube. It is desirable to maintain a
clearance between the outside edges 97 and 99 and the tube outside
wall to prevent scoring or grooving of the tube. Therefore, a roll
having a given groove is limited to a maximum tube bite of
something less than the distance between the groove edges 97 and 99
and the largest tube portion to be contacted by the roll, a
distance "g" shown in FIG. 5. This clearance of the edges 97 and 99
is increased by decreasing the angle .phi.. However, as .phi. is
reduced to small values, the two zones of tube contact become
closer together thereby increasing wall strain and the possibility
of localized tube failure. Therefore, there is a trade-off between
the desire to maximize the bite of the roll into the tube and the
desire to maintain the advantage of two zone rolling. For a given
tube material, there is an optimum angle .phi. which allows the
roll to take the most efficient maximum bite into the tube, thereby
resulting in the most rapid feed rate of the tube through the
machine. An angle .phi. of from 30.degree. to 38.degree. is
satisfactory for most common tube materials and specific types of
reduction.
The tangential portions 89 and 91 of the roll groove are shown in
FIG. 5 as straight lines. However, these portions of the groove
may, alternatively, be given a curvature with one or more finite
radii of curvature. The edges 97 and 99 of the roll groove may be
curved to eliminate the sharp corner which can damage the tube
surface. The remaining segments of the tangential portions 89 and
91 may then remain straight or may be curved slightly, either
concave or convex. If part of the tangential portions is made
concave, tube wall shear decreases further since the total area of
tube contact becomes larger. However, the edges of the groove are
then brought closer to the tube outside wall by such a concave
shape which places limits on the maximum tube bite that may be
taken by such a roll groove. If part of the tangential groove is
made convex, the groove edges are removed further from the tube
wall thereby allowing an increased tube bite without the edges of
the groove scoring the tube surface.
Referring to FIG. 6, the various forces operating on a roll having
groove characteristics of roll 79 (FIG. 5) when operating in a
rolling mill described with respect to FIGS. 1-4, are shown. The
roll has a center of rotation 107 and contacts a tube 100 with a
rolling radius r that varies between R.sub.min and R.sub.max. A
roll trunnion 101 is contacted by its associated cam at a point 103
and the cam imparts a downward force thereon plus a horizontal
frictional force, as shown by the arrows in FIG. 6 at the point
103. The roll trunnion 101 is subjected to restraining forces
indicated by arrow 104 by the roll housing in which the roll is
journaled. The trunnion forces 104 may be in the direction shown or
may be in an opposite direction. The roll of FIG. 6 is illustrated
as biting into the wall of the tube 100 an amount B by contact
along the line 105 of the roll groove. The tube reacts against the
roll with a force indicated at 105 by its horizontal component h
and its vertical component v. The tube 100 is held by a mandrel
within the tube. The reactive horizontal force component h is a
result of the tube 100 being thrust by the roll bite B in the same
direction in which the roll is traveling. If the roll reciprocates
back and forth over the tube, the reversal of the horizontal force
h tends to cause oscillatory motion in the tube 100 and the mandrel
along their length. Such oscillatory motion is undesirable because
of added tool stresses created thereby. Such tool stresses limit
the amount of bite that can be taken by the rolls and thus limit
the amount of tube reducing that can be accomplished in a given
amount of time. Therefore, it is desirable to minimize the
oscillatory thrust of the rolls against a tube being reduced in
order to increase production of a tube reducing mill.
A technique for minimizing such forces on the tube and various
machine parts is to adjust the trunnion radius R.sub.J to provide a
reactive torque force .tau. by the tube in a direction opposite to
that of the reactive force h caused by the bite B. The torque force
.tau. (FIG. 6) is a frictional force between the tube and the roll.
It will be noted that although the tube contacting roll radius r of
FIG. 6 varies between R.sub.min and R.sub.max during the tube
reducing stroke, the trunnion radius remains a constant. Therefore,
there will be some torque (tangential) force applied by the roll to
the tube for at least a portion of each rolling stroke since the
torque force can be zero only when there is a proper match between
r and the trunnion radius R.sub.J. That is, the roll will tend to
slip against the tube 100 at any point thereof an amount dependent
on the rolling radius r at that tube point.
For the particular roll housing and cam housing driving arrangement
shown in FIG. 1,
roll housing stroke/cam working length = diameter of pinion gear
25/diameter of pinion gear 26 = N (1) The quantity N is defined in
equation 1 as a convenience so the relationship between a trunnion
radius R.sub.J and the rolling radius r as it affects a torque
force applied to the tube may be determined. A quantity NR.sub.J is
defined for convience as the "effective" roll trunnion radius. If
the effective trunnion radius is less than the rolling radius r at
some point along the tube during the reducing stroke, the tube is
driven by a torque force in a direction opposite to that being
traveled by the roll. Conversely, if the effective trunnion radius
is greater than r at some point along the tube, it is driven by a
torque force in the same direction in which the roll is traveling.
Finally, when the effective trunnion radius is equal to r there is
no thrust applied to the tube due to torque forces. A significant
part of the present invention is to balance tube thrust caused by
the roll bite against tube thrust imparted by rolling torque.
For each of the second stage rolls the rolling mill of FIGS. 1-4,
including roll 45, the effective trunion radius, NR.sub.J45, is
preferably made substantially equal to the minimum rolling radius,
R.sub.min. The torque force works to balance the thrust given the
tube by the roll bite. Referring to FIG. 4, the roll 45 first
contacts the tube at about location F. At this location, the
rolling radius r is substantially R.sub.max and, therefore, the
magnitude of the torque force is a maximum and in a direction
opposite to the direction in which the roll is traveling. As the
roll proceeds to location J, the rolling radius r becomes
substantially R.sub.min and the magnitude of the torque force will
be about zero. For most applications, the effective trunnion radius
NR.sub.J45 is preferably made a few percent (0-3%) less than
R.sub.min in order to provide a slight torque force at position J
in a direction opposite to the direction in which the roll is
traveling. Since the tube is elongating, the effective trunnion
radius NR.sub.J45 may even be slightly greater than R.sub.min in
certain cases so long as roll groove surface displacement at
position J relative to the tube surface is in a direction to the
left in FIG. 4 while the roll is proceeding to the right. These
considerations apply to a single stage rolling mill or to the
second stage of a two stage rolling mill.
It has already been pointed out that the torque forces applied to
the tube by a roll vary over the rolling stroke as the rolling
radius r varies. It may be noted that the forces applied to the
tube by a roll bite also vary somewhat in magnitude over a rolling
stroke as the roll bite B varies. Therefore, the two forces do not
necessarily cancel each other completely but the criteria for
trunnion radius design described herein can minimize the resultant
thrust on a tube by application of such forces. By minimizing the
resultant longitudinal force on the tube, the tube is more easily
held in place against oscillatory movement along its length. This
has an advantage that the tube is reduced in a more controlled
manner, resulting in a better quality reduced tube.
The discussion hereinbefore with respect to FIG. 6 has not
considered the fact that the tube material is flowing or elongating
with respect to the mandrel under the influence of the rolls
working to produce either a wall thickness reduction or a
significant means diameter reduction, or both. The degree of metal
flow or elongation can be seen to cumulatively increase along the
mandrel or stroke length during the progressive wall and/or
diameter reductions. If two sets of rolls, as described herein with
respect to FIGS. 1-4, are utilized, then while the centers of each
of the rolls are driven at the same velocity relative to the
mandrel by a journaled connection with a common roll housing, the
tube portions independently contacted by each of the two sets of
rolls must be moving at different velocities relative to the tube
mandrel. The portion of the tube contacted by the second stage
rolls (45, 47, 49) moves faster (more elongation) than the portion
of the tube contacted by the first stage rolls (39, 41, 43).
Therefore, the effective roll trunnion radius of each roll of one
set is also chosen relative to the effective trunnion radius of
each roll of the other set in order to take into account the
different flow velocity of the tube surface areas contacted
simultaneously by rolls of each of the roll sets.
A specific technique will now be described for designing the roll
trunnion radii for each of the rolls of the rolling mill described
with respect to FIGS. 1-4. The second stage rolls 45, 47 and 49
each have an effective roll trunnion radius as described
hereinabove. A procedure for determining an optimum trunnion radius
for each of the first stage rolls 39, 31, and 43 will be described
which results in minimizing longitudinal forces on the tube being
reduced.
Referring to FIG. 4, roll 39 is at position B1 when the roll 45
first contacts the tube at position F. Similarly, when the roll 39
is at position F and leaving contact with the tube, the roll 45 is
at the position G1. The section B1-G1 of the tube is of concern
since this section may be placed in tension or compression between
the rolls 39 and 45. The rolls 39 and 45 are separated at their
centers by a constant distance L.sub.O since they are both held by
the roll housing 23. Therefore,
L.sub.O = B1-F = F-G1 (2) At positions B, B1, F and G1, the tube
being reduced has cross-sectional areas A.sub.B, A.sub.B1, A.sub.F
and A.sub.G1, respectively. These areas are determined by the
specific shape of the mandrel and the cams associated with the
rolls.
At the end of each rolling stroke, the tube 33 is fed to the right
in FIG. 4 over the mandrel 37 in preparation for a new rolling
stroke. The amount of feed may be denoted as f.sub.B which
indicates the amount of tube movement due to feed at position B.
The material of the tube 33 at other positions along the tube 33 is
caused to move to the right during each stroke of the roll an
amount of the feed f.sub.B plus additional elongation due to the
fact that the tube material is caused to flow to the right as the
tube wall thickness and inside diameter are reduced. The total
elongation at various positions along the tube may be denoted as
f.sub.B1, f.sub.F and f.sub.G1, for instance. Each of these
elongation quantities is related to a corresponding cross-sectional
area of the tube in terms of tube volume as follows:
f.sub.B A.sub.B = f.sub.B1 A.sub.B1 = f.sub.F A.sub.F = f.sub.G1
A.sub.G1 (3) This relationship follows since tube material is not
lost during the rolling process. The volume of metal does not
change during the process but is merely redistributed into a
different shape.
As roll 39 moves from position B1 to position F, the tube surface
over which it travels moves in a direction of rolling an amount
equal to f.sub.F -f.sub.B1. Also, as roll 45 moves from position F
to position G1, the tube surface over which it travels moves in the
direction of rolling an amount f.sub.G1 -f.sub.F plus an amount
f.sub.F -f.sub.B1. Therefore, the total elongation E.sub.LT between
the sets of rolls is as follows:
E.sub.LT = (f.sub.G1 -f.sub.F) + (f.sub.F -f.sub.B1) (4) = f.sub.B
A.sub.B (A.sub.B1 -A.sub.G1)/A.s ub.B1 A.sub.G1 (5) Equation 5
results from combining equations 3 and 4.
The distance between the sets of rolls, L.sub.O, may be expressed
in terms of each roll's effective trunnion radius and the number of
revolutions taken to travel a given linear distance along the cams.
This may be expressed as follows:
L.sub.O = .omega..sub.39 NR.sub.J39 (6) L.sub.O = .omega..sub.45
(7) sub.J45 where .omega. represents in radians the angular
displacement of the respective rolls against their driving cams
without slipping in traveling a distance L.sub.O.
Simultaneously, the roll 39 must travel a distance L.sub.39 along
the tube during the same angular displacement .omega..sub.39.
Similarly, the roll 45 must travel a distance L.sub.45 along the
tube during the same angular displacement of the roll 45 of
.omega..sub.45 radians. These conditions may be expressed as
follows:
L.sub.39 = .omega..sub.39 r.sub.39 (8) L.sub.45 = .omega..sub.4 5
r.sub.45 (9) where r.sub.39 and r.sub.45 represent average rolling
radii of the rolls 39 and 45 against the tube, respectively. The
average rolling radius is calculated as an arithmetical average
between R.sub.min and R.sub.max of each roll.
It is helpful to define a quantity E.sub.LR as the elongation
capability of the two sets of rolls. That is, E.sub.LR is that
elongation that may take place in the tube during the rolling
process which will not result in any slippage of the rolls against
the tube relative to one another. To express it another way,
E.sub.LR is that elongation of the tube which will result in the
rolls placing a tube section between the rolls neither in
compression nor tension. The elongation capability that the rolls
must have can be shown to be the following:
E.sub.LR = L.sub.39 -L.sub.45 (10)
If equations 6 and 8 are combined in a manner to eliminate their
common term .omega..sub.39, and if equations 7 and 9 are combined
in a manner to eliminate their common term .omega..sub.45, and,
further, if each of these resulting equations is solved for
L.sub.39 and L.sub.45, the resulting equations may be substituted
into equation 10 which will result in the following expression:
Therefore, equation 11 defines in terms of fixed parameters of the
tube rolling machine a capability of the rolls of that machine to
operate without slipping against the tube and thus without the
undesirable forces of compression or tension to which the tube may
be subjected. In order that the slippage and thus these forces are
made zero, the actual elongation of the tube E.sub.LT, as defined
in terms of other parameters of the machine according to equation
5, must be equal to the elongation capability of the rolling mill
as defined by equation 11. The following equation combining
equations 5 and 11 sets forth this condition: Equation 12 is solved
for the single unknown R.sub.J39. It will be noted that the
quantity R.sub.J45 has been determined in a manner outlined
hereinbefore for the second stage rolls in order to minimize thrust
upon the tube. A desired feed f.sub.B is assumed for the purpose of
solving equation 12 for R.sub.J39. The remainder of the quantities
of equation 12 are physical factors of the rolling mill. Therefore,
the trunnion radius R.sub.J39 of each roll of the first set of
rolls may be determined for a given feed f.sub.B to bring about the
desirable condition that the elongation capability of the two sets
of rolls E.sub.LR is equal to the actual elongation of the tube
E.sub.LT.
Due to a variety of conditions, the feed rate f.sub.B is not
conveniently maintained at the assumed value, especially during
start-up operations of the machine. Obviously, it is inconvenient
to change the trunnion radius of the first stage rolls 39, 41 and
43 each time the feed rate f.sub.B is changed somewhat. It has been
found as part of the present invention that the rolling mill may be
operated with the actual elongation of the tube E.sub.LT being
greater than the elongation capability of the rolls E.sub.LR. Under
such conditions, the two sets of rolls place the tube section
therebetween under longitudinal compression. This causes the tube
to become loose on the mandrel. The rolls are reactively thrust
against their cams and supports until resistance to rotation
develops at which point the rolls skid in relation to their cams
with resultant harm to the various working surfaces. However, these
undesirable results for a condition of E.sub.LT .noteq. E.sub.LR
are tolerable when the following conditions are met:
E.sub.LR .ltoreq. E.sub.LT < 2E.sub.LR (13) To state the
permissible variation another way, the feed rate can be increased
by up to a factor of 2 from the assumed f.sub.B for which the
trunnion radius R.sub.J45 was calculated according to equation
12.
It has been found that the converse situation of E.sub.LT less than
E.sub.LR is highly undesirable. When this occurs, the tube section
between the rolls is in longitudinal tension and the tube contracts
with resultant tightening on the mandrel. The resistance to
rotation of the rolls which develops under these conditions causes
a high reactive force 104 (FIG. 6) which results in early failure
of the roll trunnion journals. The reason for this appears to be
that the resistance to roll rotation causes the trunnion thrust
(force 104) to be in the same direction as the driving torque
applied by the cam to the roll through its trunnion (forces at
103). As the rolling stroke progresses, a mismatch between
roll/tube elongation occurs, the trunnion force 104 increases, the
horizontal cam driving torque force at 103 decreases and finally
reverses in direction to cause slippage between the roll and cam or
trunnion failure will occur. In the more permissible case of
E.sub.LT being greater than E.sub.LR, as noted with reference to
equation 13, the resistance on a roll causes trunnion thrust to be
in an opposite direction as the driving torque applied by the cam
to the roll through its trunnion so that as trunnion thrust (force
104) increases, the roll merely slips against the cam without major
harm.
It shall be understood that the invention is not limited to the
specific arrangements shown, and that changes and modifications may
be made within the scope of the appended claims.
* * * * *