Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENT:tON
This invention relates to a method of bonding
a tubular shaft to an end fitting to produce a joint
which assures axial alignment of the shaft and the end
fitting and is capable of transmitting a high torque.
One obvious method of bonding a tubular shaft
to an end fitting is to provide the end fitting with a
rod-shaped mating~section which fits into the shaft9
coat the mating section and/or the inner circumference
of the shaft with a suitable cement or bonding agent,
and then insert the mating section into the shaft.
However, this method suffers from the disadvantage that
the bonding agent employed tends to rub off the mating
section when it is inserted into the shat i too tight
a fit is provided, or~ alternatively, is accompanied by
leakage of the bonding agent from the annular space
between the mating section and the shaft if the fit is
too loose. In any event, tha end result is a loss of
bonding agent and~ a weakening of the joint, so that the
desired degree of bonding is not attained. Furthermore,
in certain instances, as in the case of the bonding of
a universal joint fitting in a drive shaft, it is essen- -
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; tial that the fitting be aligned concentrically in the
sh ft, and this method does not provide for obtaining ~ -
~- a secure joint having such concentric alignment
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An alternative method of bonding a tubular
shaft to an end fitting having a rod-shaped mating
section is to first insert the mating section into the
shaft, and then inject the bonding agent into the annular
space between the mating section and the shaft from a
hole in the side of the shaft. A second hole in the
side of the shaft is also necessary in such case, of
course, to allow for the release of air displaced by the
bonding agent. However, not only is this technique quite
slow, but oftentimes it fails to completely fill the annular
space between the mating section and the shaft with bonding
agent, resulting in voids between them and a poor bond.
Visual inspection of the joint, of course, is not possible,
so that the presence of such voids, and the r sulting poor
bond, goes undetected.
One very effective way of bonding a tubular
shaft to an end fitting having a rod-shaped mating sec-
tion is disclosed in United States Pat. No. 4,041,599.
Said method comprises: (1) fitting a pair of parallel
annular grooves positioned near the base and top of the
mating section of the end fitting with a pair of resil- `
ient sealing rings having inner diameters such that they
are retained in place by the grooves and outer diameters
greater than that of the mating section, said sealing
rings being designed to fit snugly into the tubular
shaft and form a tight fit between the mating section
and the shaft; ~2) inserting the base of the mating
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section containing the first of said resilient sealing
rings into one end of the tubular shaft so as to compress
said resilient sealing ring snugly between the mating
section and the inner circumference of that end of said
tubular shaft, said end of said tubular shaft having the
neck of a funnel tightly fitted about its outer circum-
ference; (3) filling the funnel with a suitable liquid
bonding agent; (4) further inserting the mating section
of the end fitting into the tubular shaft, thereby
creating a vacuum in the annular spacing between said
mating section and said tubular shaft so as to cause
the bonding agent in the funnel to flow into and fill
said annular spacing; ~5) continuing to insert the
mating section of the end fitting into the tubular shaft
until the annular space between said ma~ing section and
said tubular shaft has been completely illed with bond-
ing agent and the second resilient sealing ring at the
top of the mating,section has beenforced into the shaft
and snugly compressed between said mating section and
said tubular shaft, thereby entrapping and sealing said
bonding agent in said annular space, and (6) curing
said bonding agent to the thermoset state so as to bond
the sh~ft cmd the mating section of the end fitting
together. ~Not only does this method provide a secure
bond between the mating section of the end fitting and
the shaft, but it also assures accurate centering of
the mating section in the shaft. For this reason it
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is particularly suitable whenever concentric alignment
of the mating section of an end fi~ting in a sha~t is
necessary, such as when thP mating section of a universal
joint fitting is bonded to a clrive shaft. However, while
the joint produced in this marmer has bee.n found satis-
actory for most applications and capable of transmitting
relatively high torqu~ loads 9 it has not been found satis-
factory for transmitting extremely high torque loads.
Thus, although fully acceptable as a bond between a
universal joint fitting and a drive shaft when such
assembly is used in automobiles, the joint produced in
this manner has been found wanting when such assembly
is used in trucks.
SUMM~RY OF THE INVENTION
.
The present invention provides a method for
securely bonding a tubular shaft to an end fitting to
produce an assembly wherein the shaft and end fitting
are in axial alignment and which is capable of trans-
mitting high torque, which method makes use of an end
fitting provided with a mating section having two con-
centric cylindrical walls which describe an annular
cavity or socket adapted to receive the tubular shaft
therein. Said process comprises: (1) fitting an annular
groove positioned near the top of the inner cylindrical
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resilient sealing ring having an inner diameter such ~hat
it is retained in place by the groove and an outer diameter
greater than that of the oute:r diameter of said inner
cylindrical wall, said sealing ring being designed to
fit snugly into the tubular shaft and form a tight fi
between said inner cylindrical wall and thP shat; (2)
filling the annular cavity between the inner and outer
cylindrical walls of the mating section of the end fitting
with a suitable liquid bonding agent; (3) inserting one
end of the tubular shaft into the annular cavity between
the inner and outer cylindrical walls of the mating section
of the end fitting so as to compress the resilient sealin~
ring at the top of the inner cylindrical wall snugly be- .
tween said inner cylindrical wall and the inner circum- . :
ference of the tubular shaft and effect a seal therebe-
tween; ~4) further inserting the tubular shaft into the
annular cavity between the inner and outer cylindrical
walls of the mating section of the end fitting, thereby
displacing excess bonding ag~nt present in the annular
: 20 cavity and causing said excess bonding agent to 10w out
of said annular cavity via the space between the outer
~ circum~erence of the tubular shaft and the inner circum- -
: ference o the outer cylindrical wall o the mating sec-
tion; (5) continuing to insert the tubular shaft into
the annular cavity between the inner and outer cylindrical
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walls of the mating section of the end fitting until said
tubular shaft has been forced into place over an annular
shoulder positioned near the base of the inner cylindrical
wall, said annular shoulder having an outer diametPr greater
than that of the outer diameter of said inner cylindrical
wall and being designed to it snugly into the tubular
shaft and form a tight fit between said inner cylindrical
wall and the inner circumference of said tubular shaft;
and (6) curing said bonding agent to the thermoset state
so as to bond the shaft and the mating section of the
end fitting together in axial alignment.
BRIEF DESCRIPTION OF THE INVENTION
Figure la is a partial cutaway elevation view
showing a universal joint having a mating section pro-
vided with a bonding socket adapted to receive a tubular
drive shaft as such a shaft is being inserted into the
bonding socket.
Figure lb is a partial cutaway elevation view
; showing the universal joint and tubular drive ~haft of
Figure la after the tubular shaft has been fully inserted
: ~ into the bonding socket and bonded to the mating section
of the universal joint,
: D AILED DESCRIPTION OF THE INVENTION
While the~invention is generally useful whenever
secure boncling of a tubular shaft to an end fitting is
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desired, it is particularly applicable whenever the assembly
is required to carry a very high torque load, such as when
a universal joint fittin~ is bonded to a drive shaft and
the assembly is employed a~ part of the drive train
system of a truck. The high torque carrying capacity
of the joint produced in accordance with the invention
results from the fact that the shaft is bonded to the
mating section of the end fitting on both its interior
and exterior surfaces and is in axial alignment with
the end itting. Such axial alignment of the shaft
and the end fitting results from the presence of the
resilient sealing ring positioned near the top of the
inner cylindrical wall of the mating section, and the
annular shoulder positioned near the base of said inner
cylindrical wall, which contact the inner surface of
the ~ubular shaft and center the shaft around said wall
when the shaft is inserted into the bonding socket of
the end fitting. I In addition to centering the shaft
and retaining itin proper geome~ric relationship to
the inner cylindrical wall, the resilient sealing ring
and annular shoulder serve to retain and prevent leakage
of bonding agent present in the space between said wall
and the inner surface of the shaft.
E'eierring now to the drawings, universal joint
.
10 is provided with a mating section 11 having sn inner
cylindrica:L wali 12 and a concentric outer cylindrical
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wall 13 which together describe an annular cavity or
socket 14. Positioned around the outer circumference
of the inner cylindrical wall near its top is a rubber
sealing ring 15. Ring 15 has an inner diameter such
that it is retained in place by means of an annular
groove (not shown) in inner cylindrical wall 12 and an
outer diameter slightly greater than that of the outer
diameter of said inner cylindrical wall. Preferably,
annular shoulder 16 is positioned around the outer
circumference of the inner cylindrical wall adjacent
to and above ring 15 and serves as a backing or said
ring. Positioned around the outer circumerence of the
inner cylindrical wall near its base and parallel to
rubber sealing ring 15 is annular shoulder 17. Annular
shoulder 17 has an outer diameter slightly greater than
that of the outer diameter of inner cylindrical wall 12
and may either be an integral part of the inner cylindri-
cal wall or a second sealing ring held in place on the
innex cylindrical wall in the same manner as sealing
ring 15. Both ring 15 and shoulder 17 have outer diame-
ters such that they will fit snugly and orm a tight
fit between the outer circumference of inner cylindrical
wall 12 and the inner circumference of tubular carbon
fiber-reinforced epoxy drive shaft 18 when tubular shaft
18 is inserted into the annular space between inner
cylindrical wall 12 and outer cylindrical wall 13. Inner
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cylindrical wall 12 has an uuter diameter of 4.534 inches.
Outer cylindrical wall 13 has an inner diameter of 5.234
inches. Together the two walls describe an annular cavity
or bonding socket 0.350 inches wide and 4.500 inches long.
Tubular shaft 18 has an inner diameter of 4.574 inches, an
outer diameter of 5.074 inches, and is 0.250 inches wide.
Ring 15 and shoulder 17 are spaced 4.200 inches apart.
After annular cavity 14 between the outer c;r-
cumference of inner cylindrical wall 12 and the inner
circumference of outer cylindrical wall 13 is filled
with a suitable liquid bonding agent, tubular shaft 18
is inserted into the annular cavity and fitted snugly
over rubber sealing ring 15 positioned near the top of
cylindrical wall 12. Rubber sealing ring 15 is thereby
compressed so that it fits snugly between the outer
circumference of inner cylindrical wall 12 and the
inner circumference of tubular shaft 18 and bonding
agent present in annular cavity 14 is precluded from
escaping between said sha~t and said inner cylindrical ..
wali, As a result, as tubular shaft 18 is further in-
serted into annular cav~ty 14, any bonding agent displaced
from the annular cavity is forced to flow out via the
space between the outer circumference of tubular shaft
18 and the inner circumference of outer cylindrical
wall 13 (annular space 14a). At the same time, ,he
vacuum seal created by sealing ring 15 ensures that the
space between the shaft and the inner cylindrical wall
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(annular space 14b) remains filled with bonding agent as
the shaft is inserted into the annular cavity. Finally
tubular shat 18 is forced into place over annular shoulder
17 which, like sealing ring 15, fits tightly between the
outer circumference of inner cylindrical wall 12 and the
inner circumference of tubular shaft 18. As a result,
the bonding agent present between thP shaft and the inner
cylindrical wall is now permanently entrapped therebetween.
In addition to preventing escape or leakage o bonding
agent present between the shaft and the inner cylindrical
wall, ring 15 and annular shoulder 17 ensure'that the shaft
is in axial alig~ment with the inner cylindrical wall.
In order to facilitate insertion of tubular
shaft 18 into annular cavity 14, the inner and outer '~
sur~aces of the end of the tubular shaft to be inserted
into the annular cavity are preferably coated with the
bonding agant before the shaft is inserted into the
cavity. To secure,a better bond between the tubular
shaft and the walls of the cavity, it is also preferred
that the surfaces of the tubular shaft which are ~o be
inserted into the cavity be abraded, and that the walls
of the cavity be etched with acid. '
Aft:er tubular shat 18 has been fully inserted
into annular cavity 14 and forced into place over annular
shoulder 17, any excess bonding agent on the exterior
of sha~t 18 may be wipPd away,. The bonding agent in
annular space 14 is then cured, tbereby completing the
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process. If desired, a similar a~tachment may be made
at the other end of the shaft. In such case, a hole
should first be made in the mating section of said
attachment to allow for the escape of air when the
shaft is inserted into said mating section.
In order to ensure c~ial alignment and proper
bonding of the shaft and ~he end fitting, the radial space
b~tween the two concentric cylindrical walls of the mating
section of the end~fitting is preferably between 0.260
inches and 0.360 inchesg and the wall of the shaft is
between 0.240 inches and 0.300 inches thick. Most prefer-
ably, a spacing of 0.350 inches is provided between the
two concentric cylindrical walls, the wall of the shaft
is 0.250 inches thick, and the outer diameters of the
sealing ring and annular shoulder about the top and bottom
inner cylindrical wall are such that when the shaft is
positioned on the sealing ring and annular shoulder, and
thereby concentrically aligned between the two walls~ -
there is a spacing of from 0.010 and 0.030 inches between
the shaft and the inner cylindrical wall, most preferably
O.020 inches. The annular cavity between the two concen;
tri~ w~lls is suitably 4.500 inches long.
AI1Y low viscosity liquid bonding agent capable
Df adhering to both the mating section of the end fitting
and the tubular shaft can be employed in the process of
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the present invention, provided that such bonding agent
does not give of~ volatiles on curing. An epoxy resin
binder system is preferred because of its abili~y to
adhere to a widespread number of materials and its good
bonding characteristîcs. Such system comprises an epoxy
resin together with a reactive resin hardener and/or an
epoxy polymerization catalyst in an amount conventionally
used in the art to cure epoxy resins.
The following example is set forth for purposes
of illustration so that those skilled in the art may
better understand this invention. It should be under-
stood that it is exemplary only, and should not be con-
strued as limiting this invention in any manner.
. . .
EXAMPLE
The process of the invention was employed to
axially align and bond a tubular shaft to an end ~itting
to produce an assembly capable of transmitting high
torque. The tubular shaft selected was a carbon fiber-
reinforced epoxy drive shaft, and the end fitting employed
was a universal joint which was provided with a mating
~ection having two concentric cylindrical walls which
together described an annular cavity or socket adapted
to receive the tubular shaft, The inner cylindrical
wall had an outer diameter of 4c534 inches, the outer
cylindrical wall had an inner diameter of 5.234 inches,
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and the annular cavity or socket between the two walls
was 0.350 inches wide and 4.500 inches long. A rubber
"0" ring was fitted around the outer circumference of
the inner cylindrical wall near the top of said wall.
The "0" ring had an inner diarneter such that it was
retained in place by means of an annular groove in the
inner cylindrical wall and an outer diameter slightly
greater than that of the outer diameter of said inner
cylindrical wall. 'Positioned around the outer circum-
ference of the inner cylindrical wall, adjacent to and
above the "0" ring, was an annular shoulder which formed
an integral part of the wall and served as a backing for
said ring. Positioned around the outer circumference
of the inner cylindrical wall near its baseg parallel
to the rubber "0" ring near the top of said wall and
4,200 inches apart from it, was a second annular shoulder
which also formed an integral part of the wall and which,
like the "0" ring, had an outer diameter slightly greater
than that of the inner cylindrical wall.
The universal joint was placed vertically with
the mating section at the top and the annular cavity
between the inner and outer cylindrical walls of the
mating section was filled with an epoxy resin binder
system composed of one hundred (100) parts by weight
of a commercially available liquid epoxy resin produced
by the reaclion of epichlorohydrin and 2,2-bis(hydroxy-
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phenyl)propane (Epikote 828, manufactured by Shell
Chemicals UK Ltd.) and twenty-seven (27) parts by weight
of a diaminodiphenylmethane (DDM epoxy resin hardener,
manufactured by Anchor Chemical Co. UK Ltd.). This
binder system was also used to coat the inner and outer
surfaces o~ one end of a tubular carbon fiber-reinforced
epoxy drive shaft which had an inner diameter of 4.574
inches, an outer diameter of 5.074 inches, and ~as designed
to fit into the annular cavity betwesn the inner and
outer cylindrical walls of the mating section of the
universal joint (the coating was applied only to the
portion o the drive shaft which was to be inserted into
the annular space). The coated end of the drive sha~t
was then inserted into the annular cavity and fitted
snugly over the "O" ring at the top of the inner cylin-
drical wall of the m~ting section of the universal joint.
The shaft ~as then slowly pushed further into the annular
cavity, thereby causing excess bonding agent present :in
the annular cavity to flow out via the space between the
outer circumference of the tubular shat and the inner
circumference of the outer cylindrical wall. Finally,
the shaft was pressed snugly into place over the annular
shoulder near the base o~ the inner cylindrical wall o
the mating section of the universal joint, thereby
effec~ing a second seal between the inner circumference
o~ the shaft and the outer circumference o the inner
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cylindrical wall which, together with the seal effected
by the "0" ring at the top of the inner cylindrical
wall, permanently entrapped the bonding agent which
filled the annular space between the two walls so as to
prevent escape or leakage of the bonding agent. In
addition to prev~nting escape or leakage of bonding
agent present between the shaft and the inner cylindrical
wall, the "0" ring and annular shoulder ensure that ~he
shaft is in axial alignment with the inner cylindrical
wall.
The exterior of the drive shaft was then wiped
free of bonding agent which had exuded rom the space
between the outer circumference of the tubular shaft and
the inner circumference of the outer cylindrical wall
of the bonding socket of the mating section of the uni-
versal joint when the shaft was inserted into the bonding
socket. The bonding agent remaining in the bonding socket
was then allowed to stand at room temperature for 15 hours
to cause it to solidify. During this time, the universal
joint and the attached tubular shaft were keptin a verti-
cal position ~o prevent the bonding agent from flowing
out o the space between the outer circumference of the
tubular shaft and the inner circumference of the outer
cylindrical wall. After the bonding agent had cured to
the solid state, it was post cured by heating at a temper-
ature of 180C. for 1 hour.
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A like universal joint was then attached to
the..other end of the tubular shaft in like manner. The
mating section of the second universal joint contained
an air bleed hole positioned in its axis to allow air
to escape when the sha~t was pushed into it.
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