Method and apparatus for cold rolling piping element connections having multiple outward steps

An apparatus for cold rolling a piping element connection with multiple outward steps has first and second rollers, a driver for the second roller, and a positioning roller. The first roller rotates about a first axis, with first and second upper surfaces of rotation centered thereabout, the first surface mean diameter being less than that of the second surface. The first roller has an upper leading edge between the first and second upper surfaces. The second roller is mounted for rotation about a second axis parallel to the first axis, with first and second lower surfaces of rotation centered thereabout, the first surface mean diameter being less than that of the second surface, and the second roller having a lower trailing edge between the first and second lower surfaces. The first and second rollers are mounted for movement together and apart in a plane of the first and second axes for engagement and cold rolling of multiple outward steps in the piping element connection placed therebetween which are essentially parallel to the centerline of the piping element connection that is positioned therebetween.

BACKGROUND OF THE INVENTION 
The invention relates to a method for joining tubing, fittings and valves 
of different standard diameter types. 
For the purposes of the invention description presented herein, "CT" will 
be used to represent "standard water tube" size copper and copper alloy 
tubing, and "IP" will be used to represent "standard outside diameter" 
size steel pipe. In addition, the terms "tubing" and "pipe" are considered 
to be interchangeable, and reference to "copper tubing" will also be taken 
as referring to "copper alloy tubing" as an alternative. 
A grooved end pipe coupling, e.g. of the type illustrated in FIGS. 1 and 
1A, is used for joining together piping elements, e.g. tubing, fittings, 
valves, etc., in a leak tight assembly by use of grooves that are cut, 
cast or formed in the ends of the piping elements. Referring to FIGS. 2 
and 3, critical parameters of a grooved end connection include: the gasket 
seat diameter, D.sub.s, groove diameter, D.sub.g, gasket seat width, 
W.sub.s, and groove width, W.sub.g. In the case of wrought metal piping 
elements, e.g., as above, tubing, fittings or valve bodies, the grooved 
end of the piping element, P, is conventionally produced by either a cut 
(machining) operation or a rolling (contour roll forming) operation as 
shown in piping element, P.sub.cut, of FIG. 2, and piping element 
P.sub.roll, of FIG. 3, respectively. In the case of a cast fitting or 
valve body, the grooved end connection is normally either cut in the 
configuration of a piping element, P.sub.cut shown in FIG. 2, or cast in 
the dual outward step configuration of a piping element, P.sub.cast, shown 
in FIG. 4. 
Cut grooves for use with grooved end pipe couplings are typically prepared 
by the use of a lathe and, heretofore, roll grooves for use with grooved 
end pipe couplings have been prepared by an apparatus similar in function 
to that described in Kunsman, U.S. Pat. No. 3,995,466 and Dole, U.S. Pat. 
No. 5,279,143. Both of these patents describe a means for contour roll 
forming a groove in the end of the pipe element by which a segment of the 
pipe is press formed or stretched into the desired configuration by 
forcing a shaped die roll located outside of the pipe against a form roll 
located inside of the pipe. 
Other examples of contour roll forming of pipes are presented in 
Constantine, Great Britain Patent 18201, Pritchett et al., U.S. Pat. No. 
3,191,416 and Vaill et al., U.S. Pat. No. 3,290,914. Although these letter 
three patent references describe devices which force a die roll located 
inside the pipe against a form located outside of the pipe, the contour 
roll forming principle is the same as for the previous two patent 
references. That is, the pipe is locally shaped by radial press forming or 
stretching, into the desired contour. 
Referring again to FIGS. 1 and 1A, a typical grooved end pipe coupling 10 
consists of two or more housing segments 12, 14, a gasket 16, and 
fastening means, e.g. nuts 18 and bolts 20 for securing the assembly 
together with the end connections to be joined. The housing segments have 
keys 22 around the inner periphery at both ends, a shoulder 24 also around 
and just inside of each key, and a gasket cavity 26. The keys fit into the 
grooves 30 to axially and transversely retain the end connections. The 
keys and shoulders are involved to varying degrees in maintaining the 
coupling assembly generally centered about the grooved end connection. The 
shoulder fits closely around the gasket seat diameter to prevent the 
gasket from extruding outwardly under the internal pressure of the piping 
system, the gasket being retained in the gasket cavity and producing a 
seal on the gasket seat surfaces to form a leak tight assembly. 
Traditionally, copper tubing has been joined by soldering or brazing. 
However, recent emphasis on use of lead free solder has considerably 
increased the difficulty of producing a soldered, leak free joint, 
especially in the 3 inch and above tubing diameter sizes. This has 
increased the potential cost effectiveness of using grooved end pipe 
couplings in copper tubing system construction. 
Until now, grooved end pipe couplings for joining copper piping elements 
(tubing, fittings, valves, etc.) have only been available in couplings 
specifically designed to accommodate roll grooved (contour roll formed) CT 
size wrought copper tubing, which has average outside diameters that are 
slightly less than those for the same nominal IP size steel pipe (as 
detailed, e.g., in the publication "The Copper Connection" by The 
Victaulic Company of America). By way of example only, a 4-inch nominal CT 
size copper tube has an average outside diameter ("OD") of 4.125 inches, 
while 4-inch nominal IP size steel pipe has an average outside diameter of 
4.500 inches. 
In addition to the use of specifically designed grooved end pipe couplings, 
however, within the present state of the art, other means have been 
employed to join tubing with an average outside diameter smaller than the 
actual diameter of an IP size steel pipe of the same nominal diameter. For 
example, a specially designed ring with an average outside diameter 
equivalent to that of IP size pipe may be secured in a sealed arrangement 
to the end of a tube having a smaller average outside diameter, or the 
average outside diameter of the pipe can be increased to that of IP size 
pipe through the use of a ring secured in a sealed arrangement around the 
ends of lower average diameter pipe. These approaches would be similar to 
the Type A through E pipe end ring concepts shown in AWWA Standard C-606 
for Grooved and Shouldered Joints. 
Also, within the grooved end pipe coupling industry, it has been known to 
expand the end of a pipe by contour roll forming although the published 
objectives of this concept have been to either expand the ends of IP size 
grooved end steel pipe to eliminate the reduced wall thickness of cut 
(machined) groove joints, or to eliminate the protrusion 32 inside the 
pipe which is associated with conventional roll grooving as shown in FIG. 
3, and described in Table A, below. 
TABLE A 
______________________________________ 
Roll Groove Dimensions for Steel Pipe (Inches) 
NOMINAL W.sub.S 
W.sub.g D.sub.g D.sub.s 
______________________________________ 
2 .625 .344 2.250-.015 
2.375 
21/2 .625 .344 2.720-.018 
2.875 
3 .625 .344 3.344-.018 
3.500 
4 .625 .344 4.344-.020 
4.500 
5 .625 .344 5.395-.022 
5.562 
6 .625 .344 6.455-.022 
6.625 
Tolerances: 
W.sub.s, W.sub.g = .+-..030 
D.sub.g = +.000 
D.sub.s = See IP size OD tolerances in TABLE I 
(below). 
______________________________________ 
Prior art concerning roll grooving (contour roll forming) of copper tubing 
is also described in the brochure "The Copper Connection", by Victaulic 
Company of America, with respect to their specially designed copper 
connections. These grooved end couplings are of the same basic concept or 
design as grooved end pipe couplings for roll grooved IP size steel pipe; 
however, the dimensions of the couplings have been dimensionally altered 
to accommodate the smaller average outside diameter dimensions for copper 
tubing. 
Standard roll grooving reduces the internal diameter of the tubing at the 
roll groove and thereby increases the restriction to the fluid flow 
stream. This somewhat impedes fluid flow through the pipe and also creates 
a more pronounced area for possible damage when used in abrasive media 
service. This factor is described in literature for the Victaulic Company 
of America Style 24 expanded pipe coupling, which is used to expand carbon 
steel pipe in abrasive service where the radially inward indentation 
created by standard roll grooving would be subject to excessive abrasion. 
This process, however, forms only the pipe end shoulder (gasket seating 
surface). 
SUMMARY OF THE INVENTION 
This invention describes an apparatus for cold rolling a piping element 
connection having multiple outward steps essentially parallel to the 
centerline of the piping element. The functioning principle or objective 
of this apparatus is distinguished from the prior art which utilizes 
contour roll forming to selectively stretch or press form areas adjacent 
to the end of the piping element connection in that, the apparatus of this 
invention utilizes cold rolling to selectively thin areas adjacent to the 
end of the piping element connection and, by so doing, cause the pipe to 
be locally expanded into multiple outward steps. The objection of the 
apparatus of this invention is further distinguished from the prior art by 
the fact that the cold rolling operation work-hardens the tubing which 
increases the ultimate tensile and yield strengths of the cold worked 
material which compensates for any loss in joint strength due to the 
slight thinning of the material making up the piping element connection. 
Contour roll forming does not do this. In addition, this cold rolling 
apparatus is distinguished from prior roll grooving art in that the 
rollers inside and outside the pipe of this invention both contact 
opposite wall surfaces of the piping element in the area of the groove 
parallel to the centerline of the piping element whereas, only the roller 
outside of the pipe is allowed to contact the groove wall surface in an 
area parallel to the centerline of the piping element, in the case of the 
prior art. 
Lastly, the cold rolling apparatus of this invention is distinct from prior 
contour roll forming art used to outwardly stretch selected areas adjacent 
to the end of the pipe in that, in the case of the prior art, continued 
forcing of the die roll located inside of the pipe does not expand the 
pipe beyond the dimensions established by the form located outside of the 
pipe, whereas, with the apparatus of this invention, continued application 
of force by the roller located outside of the pipe against the roller 
located inside of the pipe, with the pipe wall therebetween, will continue 
to thin the pipe wall and locally expand the pipe. 
According to the invention, an apparatus for cold rolling a piping element 
connection having multiple outward steps essentially parallel to the 
centerline of the piping element comprises a first roller mounted for 
rotation about a first axis, the first roller defining at least a first 
upper surface of rotation extending axially and centered about the first 
axis, and a second upper surface of rotation extending axially and 
centered about the first axis, the first upper surface having a mean 
diameter and the second upper surface having a mean diameter, the mean 
diameter of the first upper surface being less than the mean diameter of 
the second upper surface, and the first roller further defining an upper 
leading edge between the first upper surface and the second upper surface, 
a second roller mounted for rotation about a second axis parallel to the 
first axis, the second roller defining at least a first lower surface of 
rotation extending axially and centered about the second axis, and a 
second lower surface of rotation extending axially and centered about the 
second axis, the first lower surface having a mean diameter and the second 
lower surface having a mean diameter, the mean diameter of the first lower 
surface being greater than the mean diameter of the second lower surface, 
and the second roller further defining a lower trailing edge between the 
first lower surface and the second lower surface, means for driving the 
second roller to rotate about the second axis, and the first roller and 
the second roller mounted for relative movement together and apart in a 
plane of the first axis and the second axis for engagement and forming of 
multiple outward steps in a piping element connection placed therebetween, 
the first upper surface being disposed in substantial axial registration 
with the first lower surface, the second upper surface being disposed in 
substantial axial registration with the second lower surface, and the 
upper leading edge being offset axially from the lower trailing edge to 
provide a predetermined spacing dependent upon the wall thickness of the 
piping element in which multiple outward steps essentially parallel to the 
centerline of the pipe element are to be formed, and a means for 
offsetting the centerline of the piping element at a slight angle to the 
right of the plane formed by the first and second roller axes when viewing 
the second roller as rotating counterclockwise. 
Preferred embodiments of this aspect of the invention may include one or 
more of the following additional features. The first lower surface has a 
taper extending axially and inwardly from a region of the lower trailing 
edge, toward the second axis. Preferably, the taper has an angle of 
approximately 1.degree. to 3.degree.. The second roller further defines an 
end surface adjacent the first lower surface and spaced from the lower 
trailing edge, the end surface extending radially outward and generally 
perpendicular to the second axis. The apparatus further comprises a means 
for offsetting the centerline of the piping element at an angle of 
0.5.degree. to 2.degree. to the right of the plane formed by the first and 
second roller axes, when viewing the second roller as rotating clockwise, 
the means consisting of a first positioning roller mounted for rotation 
about a third axis parallel to the first axis and offset to a first side 
of the plane of the first and second axes, and a second positioning roller 
mounted for rotation about a fourth axis parallel to the first axis and 
offset to a second side, opposite the first side, from the plane of the 
first and second axes and having a surface positioned for engagement with 
an outside surface of the piping element. Preferably, the third axis is 
spaced from the plane by a first positioning distance and the fourth axis 
is spaced from the plane by a second positioning distance greater than the 
first positioning distance; the third axis being to the left of the plane 
and the fourth axis being to the right of the plane, when viewing the 
second roller as rotating counterclockwise. 
According to another aspect of the invention, a method for cold rolling 
multiple outward steps in a piping element connection essentially parallel 
to the centerline of the piping element comprises the steps of: (a) 
providing a cold rolling apparatus as described above; (b) positioning an 
end of a piping element connection to be cold rolled with multiple outward 
steps between the first roller and the second roller, with the end of the 
piping element connection engaged with the end surface of the second 
roller, the piping element connection axis being angularly offset downward 
from the second axis when viewing the second roller as rotating clockwise; 
(c) engaging opposite inner and outer surfaces at an end region of the 
piping element connection between the first roller and second roller while 
providing support for the piping element connection at a point spaced from 
the end to be cold rolled, the second roller being driven; (d) causing the 
upper leading edge of the first roller to engage the outer surface of the 
piping element connection in a manner to produce a torque to draw the 
piping element connection toward the end surface of the second roller; (e) 
applying force to urge the first roller and the second roller together 
with the first upper surface disposed in substantial axial registration 
with the first lower surface, the second upper surface disposed in 
substantial axial registration with the second lower surface, and the 
upper leading edge offset axially from the lower leading edge to provide a 
predetermined spacing to accommodate the wall thickness of the piping 
element connection; (f) continuing application of force until the second 
upper surface of the first roller and the first lower surface of the 
second roller contact opposite wall surfaces of the piping element 
connection; (g) further continuance of the application of force to 
selectively thin areas adjacent to the end of the piping element 
connection until the pipe is locally expanded to within the desired range 
of diameters, and the angular offset of the axis of the piping element 
connection from the second axis is reduced to approximately zero; (h) 
stopping the apparatus or moving apart of the first roller and the second 
roller to prevent further thinning of the pipe wall and expansion of the 
pipe; and, (i) removing the piping element connection in which multiple 
outward steps have been formed. 
According to still other aspects of the invention, a wrought metal piping 
element connection having multiple outward steps essentially parallel to 
the centerline of the piping element in at least one end is formed by the 
described method, and a copper piping connection has multiple outward 
steps essentially parallel to the centerline of the piping element, e.g. 
cold rolled, in at least one end. 
According to another aspect of the invention, an apparatus for cold roll 
forming multiple, generally coaxial steps in a circumferential wall of a 
piping element having a base circumference and a base wall thickness 
comprises an outside roller die mounted for rotation about a first axis 
and an inside roller die mounted for rotation about a second axis, 
parallel to the first axis, at least one of the outside roller die and the 
inside roller die being mounted for pivoting movement about a pivot point 
on its respective axis, the outside roller die defines a first outside 
roller surface of rotation extending axially and centered about the first 
axis, a second outside roller surface of rotation extending axially and 
centered about the first axis, and a third outside roller surface of 
rotation extending axially and centered about the first axis, the first 
outside roller surface has a mean diameter, the second outside roller 
surface has a mean diameter, and the third outside roller surface has a 
mean diameter, the mean diameter of the third outside roller surface being 
less than the mean diameter of the second outside roller surface and 
greater than the mean diameter of the first outside roller surface. The 
inside roller die defines a first inside roller surface of rotation 
corresponding and opposed to the first outside roller surface, and 
extending axially and centered about the second axis, a second inside 
roller surface of rotation corresponding and opposed to the second outside 
roller surface and extending axially and centered about the second axis, 
and a third inside roller surface of rotation corresponding and opposed to 
the third outside roller surface and extending axially and centered about 
the second axis, the first inside roller surface having a mean diameter, 
the second inside roller surface having a mean diameter, and the third 
inside roller surface having a mean diameter, the mean diameter of the 
third inside roller surface being greater than the mean diameter of the 
second inside roller surface and less than the mean diameter of the first 
inside roller surface. The first, second and third outside roller surfaces 
are positioned for engagement with an outside surface of the wall of the 
piping element, and the first, second and third inside roller surfaces are 
positioned for engagement with an inside surface of the wall of the piping 
element. The first, second and third outside roller surfaces together with 
the first, second and third inside roller surfaces define a nip, the first 
axis, the second axis and the nip are disposed in a common plane. Means 
for driving at least the outside roller die or the inside roller die to 
rotate about its respective axis, and means for urging together the 
outside roller die and the inside roller die, each being mounted for 
relative movement together and apart, in the plane of the first axis, the 
second axis and the nip, in a manner to engage the wall of a piping 
element disposed in the nip therebetween and applying sufficient 
compressive force for forming by cold rolling of multiple steps by 
reducing the thickness of the wall of the piping element connection 
disposed therebetween in the nip. The first outside roller surface being 
disposed in substantial axial registration with the first inside roller 
surface, the second outside roller surface being disposed in substantial 
axial registration with the second inside roller surface, and the third 
outside roller surface being disposed in substantial axial registration 
with the third inside roller surface, and the second outside roller 
surface having an axial length and the second inside roller having an 
axial length, the axial length of the second outside roller surface being 
less than the axial length of the second inside roller surface to provide 
a predetermined spacing dependent upon the base wall thickness of the 
piping element in which multiple steps are to be formed. Whereby, during 
rotation of the outside roller die and the inside roller die, the wall 
thickness of the piping element is reduced about a first circumferential 
region of limited axial extent, a second region of limited axial extent, 
and a third region of limited axial extent, to increase the circumference 
of the piping element in the first, second and third circumferential 
regions by conservation of wall material, the degree of reduction of wall 
thickness, and the resulting circumference, in the third region being 
greater than the degree of reduction of wall thickness, and resulting 
circumference in the second region, and less than the degree of reduction 
of wall thickness, and resulting circumference in the first region, 
thereby to form by cold rolling multiple steps in a piping element 
connection placed in the nip between the outside and inside roller dies, 
the resulting circumference in the first, second and third regions being 
greater than the base circumference and the resulting wall thickness in 
the first, second and third regions being less than the base wall 
thickness. The bearing allowing equalization of the forces on the first, 
second and third regions as the outside roller die and the inside roller 
die are brought together. This equalization of forces provides for a high 
degree of uniformity in the thickness of each of the first, second and 
third regions. 
In preferred embodiments of this aspect of the invention, the outside 
roller die mounted for rotation about the first axis is mounted on a 
spherical bearing for pivoting movement about a pivot point on the first 
axis. 
Objectives of this invention include providing a convenient, low cost means 
for joining "standard water tube" size wrought copper and copper alloy 
tubing, fittings and valve connections to any combination of each other 
through use of conventional grooved end pipe couplings sized for use with 
"standard outside diameter" size steel pipe; as well as providing for 
joining "standard water tube" size wrought copper and copper alloy tubing, 
fittings and valve connections with end connections of steel, or any other 
suitable strength material, manufactured in accordance with the outside 
diameter dimensions of "standard outside diameter" size steel pipe. 
The objectives also include providing a process for expansion of a tube end 
in a manner that does not create a restriction in the tube which can 
impede the flow in any way, and which also does not produce an area for 
potential accelerated abrasive damage. 
These and other features of the invention will be apparent from the 
following description of a presently preferred embodiment, and from the 
claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention provides a convenient, low cost method and apparatus for 
utilizing grooved end pipe couplings designed and used for many years with 
IP size steel pipe for the joining of CT size wrought copper piping 
elements, or with any other wrought metal piping elements having a 
connection with an average outside diameter equal to or less than the 
average groove diameter commonly used for IP size steel pipe. 
Briefly, according to the method of the invention, the end of a piping 
element connection is expanded in two or more steps by cold rolling the 
gasket seat diameter (D.sub.s), groove diameter (D.sub.g) and gasket seat 
width (W.sub.s) to predetermined dimensions equivalent to those commonly 
used for grooved end IP size steel pipe connections. 
The grooved piping industry has traditionally used the terms "groove width" 
and "groove diameter" and for the purpose of this describing this 
invention, these terms will be maintained, with "groove diameter" 
(D.sub.g) representing the same surface as with conventional roll grooving 
and "groove width" (W.sub.g) representing the width of the groove surface. 
A comparison of average outside diameters for IP size steel pipe and CT 
size copper tubing for the 2 through 6 inch sizes are shown in Tables I, 
II and III. The average outside diameter specifications for CT size tubing 
are given in ASTM B88, while the average outside diameters for IP size 
pipe are specified in ASTM A53, although other standards address these 
parameters as well. 
Although the end connections of copper fittings and valve bodies can be 
formed in a manufacturing facility, it is important, in particular from a 
cost effective installation viewpoint, to be able to form the end 
connections of the copper tubing at an installation site. 
TABLE I 
______________________________________ 
Comparison of Average Outside Diameters 
For CT Size Tubing and IP Size Pipe 
in the 2-6 Inches Nominal Size Range 
Nominal 
Size Average Outside Diameters (Inches) 
(Inches) 
IP Size Tolerance CT Size 
Tolerance 
______________________________________ 
2 2.375 .+-..024 2.125 .+-..002 
21/2 2.875 .+-..029 2.625 .+-..002 
3 3.500 +.035/-.031 3.125 .+-..002 
4 4.500 +.045/-.031 4.125 .+-..002 
5 5.562 +.056/-.031 5.125 .+-..002 
6 6.625 +.063/-.031 6.125 .+-..002 
______________________________________ 
TABLE II 
______________________________________ 
Tubes To Be Joined 
(Tube Wall Thickness (Inches)) 
TYPE K TYPE L TYPE M TYPE DMV 
ASTM ASTM ASTM ASTM 
NOMINAL B-88 B-88 B-88 B-306 
______________________________________ 
2 .083 .070 .058 -- 
21/2 .095 .080 .065 -- 
3 .109 .090 .072 .045 
4 .134 .110 .095 .058 
5 .160 .125 .109 .072 
6 .192 .140 .122 .083 
______________________________________ 
TABLE III 
______________________________________ 
Pipe Schedules Commonly Joined 
(Tube Wall Thickness (Inches)) 
NOMINAL SCH. 40 SCH. 10 SCH. 5 
______________________________________ 
2 .154 .109 .065 
21/2 .203 .120 .083 
3 .216 .120 .083 
4 .237 .120 .083 
5 .258 .134 .109 
6 .280 .134 .109 
______________________________________ 
According to the method of the invention, the multiple step expansion or 
cold rolling of the copper tubing end at the installation site is 
accomplished by use of a rolling operation which actually expands the end 
of the tube. The cold rolling operation can be performed at the 
installation site using roll grooving equipment that is generally used for 
the roll grooving of IP size steel pipe, where the roll grooving equipment 
is modified according to the invention. 
Referring to FIGS. 5, 5A and 5B, in the case of dual outward step expanded 
piping element connections, an apparatus 40 of the invention requires 
modification to the steel pipe roll grooving equipment to include 
specially designed, corresponding top (driven) roller 42 and bottom 
(driving) roller 44, and an additional bracket 46 (FIG. 7B) for securing 
two positioning rollers 48, 50. 
The top and bottom rollers 42, 44 are made of a hardened steel and the 
rollers are designed to expand the end of the tube, T, through a cold 
rolling operation, rather than to contour roll form a groove or channel in 
the end of the pipe as generally done for IP size steel pipe. The 
positioning rollers 48, 50 hold the tube in position during the tube end 
expansion operation, and, furthermore, provide downward and lateral forces 
to the tube, T, to prevent it from spiraling out from between the top and 
bottom rollers 42, 44 during the cold rolling operation. The components 
required for the dual outward step expansion, and the process for 
expansion, are described more fully below. 
Referring now to FIG. 6, in the expansion of the tube end, T.sub.e, to form 
the groove diameter (D.sub.g) and gasket seat diameter (D.sub.s) according 
to the invention, the tubing end is radially outwardly expanded in two 
areas, which is referred to as a dual step expansion. The first step in 
the expansion establishes the gasket seat diameter (surface 52) and the 
second step establishes the groove diameter (surface 54). The critical 
dimensions for roll grooving of IP size steel pipe are shown in FIG. 3, 
and the critical dimensions associated with the dual step cold rolling 
expansion of CT size tubing are shown in FIG. 6. 
The ability to produce acceptable outward steps at the end of the tube 
requires control of the gasket seat diameter (D.sub.s), gasket seat width 
(W.sub.s), groove diameter (D.sub.g), groove width (W.sub.g) and the cross 
sectional profile of the tube end. 
In the establishment of the gasket seat diameter (D.sub.s), a feature 
commonly referred to as "flare" must be controlled. Flare is the outward 
expansion of the gasket seat diameter outside of parallel with the 
centerline of the tubing (.centerline..sub.T). It is measured as the 
maximum gasket seat diameter at the end of the tube. Excessive flare in CT 
size tubing can be more critical than in IP size pipe because the smaller 
wall thicknesses commonly associated with CT size tubing can allow one 
tube end to telescope into the other where there is excessive flare. The 
amount of flare can be controlled, and preferably eliminated altogether, 
by use of a suitable design for the bottom roller. As shown in FIG. 7, the 
surface 56 of the bottom roller 44 which forces the expansion of the 
gasket seat diameter is tapered slightly radially inwardly at angle, S 
(e.g., for practical purposes, approximately 1.degree. to 3.degree.) to 
distribute the tube forming load towards the back of the gasket seat. This 
slight inward taper is critical in the control of the amount of the tube 
end flare. 
Cold rolling of the gasket seat width (W.sub.s), groove width (W.sub.g) and 
cross-sectional profile of the dual outward step tube end are dependent 
upon the geometric relationship between the top and bottom rollers 42, 44, 
the dimensional configurations of the top and bottom rollers and the 
thickness, t, of the tube. The top and bottom rollers must be positioned 
to provide a predetermined spacing, S.sub.r, between the upper leading 
edge of the top roller 64 and the lower trailing edge of the bottom roller 
70, thereby allowing displacement of the tubing into this area during the 
tube end thinning and, therefore, expansion operation. The spacing between 
the upper leading and lower trailing edges of the first and second 
rollers, respectively, is selected to be large enough to prevent the 
material of the wall from becoming too thin, or pinching, as the wall 
material is displaced between the rollers. A difference in the thickness 
of the tubing material will effect the amount of thinning and pinching 
that will occur. The top and bottom rollers are also dimensioned to 
provide the desired gasket seat width and groove width. 
Referring again to FIG. 6, the shape of the tube end or connection profile 
is critical in maximizing the pressure retention capabilities of the 
coupling/connection joint. While the highest pressure retention 
capabilities can be achieved when the leading edge, E.sub.1, of the gasket 
seat portion of expanded tube end is at perpendicular to both the groove 
diameter and to the seat diameter, this relationship is not advisable from 
a roll forming operation standpoint, as creation of a right angle can 
result in excessive pinching, especially with thinner tube walls. It has 
been determined that a more realistic leading edge angle, L, i.e. one 
providing adequate pressure retention capabilities in combination with 
minimal thinning of the tubing wall, will generally range from 50 to 85 
degrees relative to the centerline of the tube (.centerline..sub.T) and 
gasket seat diameter, however, leading edge angles down to about 
30.degree. are acceptable for use with copper tubing. 
The dual outward step expansion roll forming process will now be described 
with reference to the FIGS. 8-11. 
Phase 1 
Referring first to FIG. 8 (and also with reference to FIGS. 7 and 7A), 
tube, T.sub.e, is positioned by the operator against the end surface 58 of 
the bottom roller 44 and rested on inwardly tapered surface 56. The top 
roller 42 is brought down by a force (pressure) actuated hydraulic 
actuator (not shown) and surface 60 of the top roller 42 is brought into 
contact with the outside surface 62 of the tube. At this point, the 
centerline of the tube (.centerline..sub.T) is angularly offset vertically 
downward from the centerline (.centerline..sub.D) of the driving or bottom 
roller 44 by the angle, .THETA. (approximately 1.degree. to 2.5.degree.). 
The tube has a tendency to drop, making angle .THETA. greater, unless an 
upward force is applied to support the tube. This support force can be 
provided by a pipe stand used to support longer tubes, or the operator can 
provide the required lifting force for shorter tube lengths. In FIG. 5A, 
the offset angle .alpha. is shown. This is the horizontal angle, between 
the centerline of the tube (.centerline..sub.T) and the plane formed by 
the centerline of the bottom roller (.centerline..sub.D) and the 
centerline of the top roller (.centerline..sub.R), and is approximately 
0.5.degree. to 2.degree. to the right when viewed with the driving roller 
44 rotating counterclockwise (indicated by arrow, R, in FIG. 5B). Still 
referring to FIG. 5B, the centerline of each of the positioning rollers 
48, 50 is located at unequal distances (X.sub.1 and X.sub.2) from the 
vertical centerline of the bottom roller (.centerline..sub.V). The values 
of these dimensions will vary with the distance between the positioning 
rollers 48, 50 and the driving roller 44; however, typically the 
difference will be maintained in the range of 0.050 inch to 0.250 inch, 
and typically at about 0.125 inch. The placement of the tube, T, between 
the positioning rollers orients the centerline of the tube 
(.centerline..sub.T) at an offset angle .alpha.. The tube positioning with 
the offset angle .alpha. causes the upper leading edge 64 of the top or 
driven roller 42 to produce a torque which tends to draw the tube, T, 
inward between the top and bottom rollers 42, 44, preventing the tube from 
spiraling out. This technique is also applicable to the conventional roll 
grooving of IP size steel pipe. 
Phase 2 
Referring now to FIG. 9, as the top roller 42 is displaced downward towards 
the bottom roller 44, the gasket seat surface 52 starts to be established 
through deformation of the tube wall material. The forces involved on the 
tube at this point are the vertical downward force (F.sub.T) induced by 
surface 60 of the top roller 42, the vertical upward reaction force 
(F.sub.B) maintained by surface 56 of the bottom roller 44, the two 
positioning forces (F.sub.P) induced by the positioning rollers 48, 50, 
and the forces created by the dynamics of the rolling action of the top 
roller, bottom roller and the tube (see FIGS. 5, 5A and 5B for force 
locations). Since the vertical forces (F.sub.T) and (F.sub.B) are applied 
at offset locations along the longitudinal axis of the tube, a moment is 
created which tends to lift the tube off the support. In order to resist 
this tendency, it is necessary that a position roller 48 also be used on 
the right side of the driving roller 44 (when viewing the driving roller 
as rotating counterclockwise), in order to impose a resisting force to 
help keep the tube in proper orientation. As the end of the tube becomes 
deformed, the offset angle .THETA. is reduced. As described above, the 
surface 56 of the bottom roller 44 is tapered inwardly to distribute the 
reaction force (F.sub.B) imposed by the bottom roller away from the end 
(tip) of the tube. As mentioned above, this taper is critical in 
controlling the amount of tube end flare. 
Phase 3 
Referring next to FIG. 10, the top roller 42 is further displaced by the 
force induced by the hydraulic actuator until the inside diameter of the 
tube comes in contact with surface 66 of the bottom roller 44 and surface 
61 of the top roller 42 comes in contact with the outside diameter surface 
62 of the tube T. It is desirable to have these two contacts occur almost 
simultaneously, in order to maintain their radial dimensional 
relationship, as the top roller is displaced downward, and there should be 
no further increase in the application of force to the top roller as soon 
as the contacts are made. At this point, the gasket seat width (W.sub.s) 
and the depth of the groove (i.e. the difference between the diameter of 
the seat (D.sub.s) and the diameter of the groove (D.sub.g)) have been 
defined and the vertical offset angle .THETA. has been further reduced. 
However, also at this point, .THETA. is approximately 0.4.degree. to 
1.6.degree.. The forces imposed by the top and bottom rollers 42, 44 on 
the tube T are acting in the same direction as in Phase 2 (FIG. 9), 
although the forces are now distributed across the two additional 
surfaces, i.e. surface 66 of the bottom roller 44 and surface 61 of the 
top roller 42. 
Phase 4 
Referring to FIG. 11, at the beginning of this phase, no additional force 
is required to create further downward movement of the top roller 42; 
however, the existing force induced by the hydraulic actuator is 
sufficient to cause a small amount of vertical downward movement of this 
top roller in order to reduce the tube wall thickness. This thinning of 
the tube wall by the cold rolling operation causes the tube to be locally 
expanded. The trailing edge, E.sub.t, is formed by a combination of the 
forces which are trying to thin the tube wall and expand the tube diameter 
along with the forces which are resisting the tube expansion. These forces 
act in opposite directions to each other and form a transition area in the 
tube which is being referred to as the trailing edge. The trailing edge is 
fully formed when the offset angle .THETA. is reduced to zero. However, 
the rotation and cold rolling (thinning) operation must be continued until 
the desired groove diameter is established at which point the cold rolling 
operation is complete. The apparatus must be shut off or the top roller 42 
raised for removing the tube in order to prevent further thinning and 
expansion of the pipe. The piping element connection is then removed from 
the apparatus. 
EXAMPLE 
For the purpose of example only, the typical groove dimensions for a dual 
step, expanded end copper tube formed according to the method of the 
instant invention, are provided in Table B, shown below. 
According to one preferred embodiment, the bottom roller 44 (FIG. 7) has an 
outer diameter of about 2.625 inches and an axial width of about 2.000 
inches. The axial width of surface 59 is about 0.500 inch and the axial 
width of tapered surface 56 is about 0.563 inch. The maximum diameter of 
surface 56 is about 1.865 inches. The inner surface tapers at about 
15.degree., from a diameter of 1.771 inches to 0.812 inch. 
Referring to FIG. 7A, the top roller 42 has a maximum outer diameter (at 
surface 60) of about 5.218 inches and an axial width of about 2.779 
inches. The axial width of surface 60 is about 1.028 inches. The outer 
diameter of surface 61 is about 5.064 inches and the axial width is about 
0.625 inch. The outer diameter of surface 63 is about 4.121 inches and the 
axial width is about 0.535 inch. The outer diameter of surface 65 is about 
4.877 inches and the axial width is about 0.250 inch. The inner bore 67 
has a diameter of about 1.382 inches. 
TABLE B 
______________________________________ 
Groove Dimensions for Dual Step 
Flared Copper Tube (Inches) 
NOMINAL W.sub.s 
W.sub.g D.sub.g D.sub.s 
______________________________________ 
2 .625 .344 2.250-.015 
2.375-.015 
21/2 .625 .344 2.720-.018 
2.875-.018 
3 .625 .344 3.344-.018 
3.500-.018 
4 .625 .344 4.334-.020 
4.500-.020 
5 .625 .344 5.395-.022 
5.562-.022 
6 .625 .344 6.455-.022 
6.625-.022 
Tolerances: W.sub.s, W.sub.g = .+-..030 
______________________________________ 
Referring to FIG. 7B, the positioning roller mounting bracket 46 defines 
sets of holes 47, 47' for fixing the positioning rollers 48, 50 with the 
desired spacing from the vertical centerline of the bottom roller (X.sub.1 
and X.sub.2) and spacing below the center line, M, of the bracket mounting 
hole (Y), as described in Table C, below. 
TABLE C 
______________________________________ 
Positioning Roller Spacing (Inches) 
NOMINAL X.sub.1 X.sub.2 
Y 
______________________________________ 
2 2.018 2.142 1.479 
21/2 2.546 2.670 1.918 
3 2.990 3.114 2.433 
4 3.520 3.644 2.849 
5 4.042 4.166 3.302 
6 4.592 4.716 3.667 
______________________________________ 
It has been found that if there is severe misalignment between the top and 
bottom rollers, a squeezing effect upon the tubing can occur, which can 
lead to material being forced from between the rollers along the axial 
direction. Even in the case of perfectly aligned rollers, the end of the 
tubing tends to expand more than the other areas, because there is less 
force resisting the expansion process there. This leads to a condition 
called "bell-mouthing" in which the outer diameter of the end of the 
tubing is slightly greater than the rest of the tubing and there is a 
slight taper to the exterior of the tubing which decreases as one proceeds 
further along the tubing from the end. 
Another embodiment of the invention, shown in FIG. 12 et seq., addresses 
these issues. Here, the top roller 102 is mounted to allow it to pivot 
about a center pivot point, P, to change alignment of its axis of 
revolution relative to the axis of revolution of bottom roller 104. This 
results in more equal expansion of the tubing for superior dimensional 
control. Even the bell-mouthing effect is minimized or avoided, because as 
the tubing end starts to grow relative to the other surfaces of the tube, 
its force against top roller 102 increases and top roller 102 adjusts 
pivotally so that there is a greater gap at the tube end than at other 
surfaces along the tube. Thus, the other surfaces will experience a 
relatively greater degree of thinning and will expand relatively faster. 
Once those surfaces are re-adjusted to match the tube end, top roller 102 
pivots in the opposite direction, returning toward a more neutral 
position. Thus, by slight pivoting adjustment of top roller 102, all the 
surfaces see more equal thinning and expansion rates. This can lead to 
even better dimensional control between the surfaces than in the case of 
using perfectly aligned, but non-adjusting rollers. 
Referring to FIG. 12, top roller 102 is mounted on a bearing 106, e.g. a 
spherical roller bearing or a spherical plain bearing. Bearing 106, held 
in place by an end cap 108, allows top roller 102 to pivot about point, P, 
in response to changes in tube alignment and tube wall thickness. Bottom 
roller 104 defines a back step 110 which permits an equalization of the 
forces over a gasket seat region 112 and back step 110 as top roller 102 
pivots. 
Referring to FIGS. 13 and 14, the expansion roll forming process is similar 
to that described above with reference to the FIGS. 8-11, although, in 
this case, when the top roller 102 is brought into contact with the 
outside surface of the tube, top roller 102 pivots to align its centerline 
with the centerline of the tubing. This distributes the forces placed upon 
back step 110 and seat region 112. During deformation of the tube wall 
material, top roller 102 pivots in response to changes in tube alignment 
and wall thickness resulting in more equal thinning and expansion of the 
tubing, as shown in FIG. 14. 
These and other embodiments of the invention are within the following 
claims. For example, while there is shown and described herein certain 
specific characteristics embodying the invention, it will be apparent to 
those skilled in the art that various modifications and rearrangements of 
the components may be made without departing from the spirit and scope of 
the fundamental inventive concept and that this inventive concept is not 
limited to the particular forms shown and described herein. As an example, 
it would be desirable to apply the dual outward step cold rolled expansion 
technique to any type of wrought metal tubing, fitting or valve body 
connection having an average outside diameter which is equal to or less 
than the average groove diameter commonly specified for IP size steel 
pipe, so that it could be joined to the latter using a grooved end pipe 
coupling designed for use with the particular IP size steel pipe of 
interest. In addition, the end connection of wrought metal tubing, 
fittings or valve bodies having an average outside diameter significantly 
smaller than the average groove diameter commonly specified for IP size 
steel pipe could be expanded in three or more steps. The first roller may 
be the driving roller with the second roller being the driven roller.