Note: Descriptions are shown in the official language in which they were submitted.
26;~
This invention relates to apparatus and methods
for bonding precured rubber tread strips to tire casings.
In the known technique of bonding a precured
rubber tread strip to a tire casing, the bonding opera-
tion is carried out by interposing a self-vulcanizing
bonding material between the tire casing and the tread
strip and by pressing the tire casing and tread strip to-
gether while applying sufficient heat to cause vulcaniza-
tion of the bonding material. The pressing operation is
generally carried out by means of a differential fluid
pressure applied between the inside of the tire casing
and the outside of the tread strip, and means are provid-
ed for venting air from between the cover and the strip.
One difficulty which sometimes arises is that the bond
between tire casing and tread strip is not uniformly strong
at all point~ with the result that the bond may fail dur-
ing subsequent use of the tire. Another difficulty which
may arise is that the tread strip may become distorted or
slightly displaced during the pressing and heating opera-
tion with the result that the vulcanized assembly is un-
satisfactory. One cause of a poor bond is the presence
of air between the tire casing and tread strip during
vulcanization. Distortion or displacement of the tread
strip generally results from non-uniformity of pressure
during vulcanization. When the vulcanizing operation is
carried out in a pressure chamber large enough to receive
a plurality of tires, a further problem is that each tire
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1(J93263
may not receive the same heat and differential pressure
treatment.
Distortion during vulcanization may also result
from the inherent flexibility of the tread strip, and
this problem is more likely to occur when the outer sur-
face of the tread strip has been previously slitted with
a large number of parallel slits for the purpose of in-
creasing traction and wear life. The slitting operation
itself may introduce a separate problem in that the slits
form the tread ribs into a large number of tread lugs
which may be torn away from the undertread portion during
use of the tire, unless the slitting operation has been
performed properly.
Removal of air is most readily effected by cov-
ering the tread strip and at least the adjacent side walls
of the tire casing with a flexible impervious cover or
envelope, sealing the cover to the tire and effecting a
differential pressure between the interior and exterior
of the cover as by applying fluid pressure to the exter-
ior of the cover or applying a vacuum to the space betweenthe cover and the assembly of tire casing and tread strip
or a combination of both fluid pressure and vacuum applied
sequentially or simultaneously. In either case the air
is exhausted through a suitable conduit which is in com-
munication at one end with the space. The pressing and
vulcanizing operation may be carried out using the same
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1~93263
fluid pressure differential technique or by means of me-
chanical pressure. Examples of different air explusion
and/or pressing operations are more fully described in
United States patents 2,976,910 (Nowak), 3,236,709 (Carver),
3,325,326 (Schelkmann), 3,752,726 (Barefoot), and
3,745,084 (Schelkmann).
It has been recognized, for example, in the
aforenoted United States patents 3,325,326 and 3,745,084
that the pressing together of the tread strip and tire
casing may sometimes produce variations in the pressure
being applied at different locations, with the result that
the bonding medium and/or the tread are distorted or shift-
ed during bonding. The resulting product may be unsatis-
factory in having a nonuniform bond between tread and
tire casing or in having other defects. The problem is
thought to arise because pressure is exerted by whatever
pressing element is used only on the outer surfaces of
the tread profilesO In spite of the air removal opera-
tion some air may remain in the tread profiles with a re-
sulting reduction in the pressure transmitted to thoseportions of the tread strip and those portions of bonding
material lying directly ~elow the circumferential tread
grooves. The solution proposed by United States patent
3,325,326 is to first apply a vacuum inside the envelope
and fluid pressure to the exterior of the envelope and
then increase the pressure inside the envelope. The sol-
- - \
1~193263
ution proposed by United States patent 3,745,084 is to
assure that the envelope penetrates to the bottom of the
groOveR .
According to one important aspect of the pres-
ent invention a special liner is inserted between the
tread strip and the flexible cover. The liner in the
form of a thin flexible perforated film of stretchable,
non-stick material, provides lubrication between the cover
and the tread strip, and due to its stretch properties it
allows the liner and the cover to conform to the tread
pattern during the pressing and bonding operation. This
penetration of the liner and cover to the bottom of the
tread grooves aids in exhausting all air from the space
between the cover and the assembly of tire and tread strip
because the air in the tread grooves passes outwardly
through the perforations in the liner and is then exhaust-
ed through the conduit provided for this purpose. In ad-
dition penetration of the liner and cover into the tread
pattern tends to stabilize the shape and position of the
tread strip, thereby avoiding bond discontinuities which
would result from deformation of the tread strip during
bonding. The liner can be made of a variety of natural
or synthetic materials such as natural or synthetic rub-
ber, polyesters, or polyolefins such as polyethylene,
polypropylene, polybutenes, polyisoprene and their co-
polymers. Polypropylene film has been found superior to
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films of rubber, polyethylene, mylar and other materials
because even when it is perforated with many small holes
it provides good lubrication without tearing or breaking
during entry into the tread pattern and during subsequent
removal. That is, it permits the cover to slip easily
into the tread grooves without tending to hang up on and
distort the tread when the pressing operation causes the
cover to press against the tread. This in turn aids in
obtaining uniform pressure on the tread strip. The film
also retains its non-stick properties so that it can be
removed as one-piece after the bonding operation. A par-
ticularly useful liner is polypropylene film of about
0.00125 inch thickness provided with spaced apart rows of
1/16 inch fine perforations or score marks. The rows may
be spaced apart about 1-3/16 inches, and the fine perfor-
ations or score marks in each row may be spaced apart
about 3/16 inch. The spacings may be less or more by
about 25%. During use the stresses on the film cause the
fine perforations or score marks to open up in a direction
transverse to the rows so as to form larger perforations
of perhaps 3/16 inch diameter.
According to another important aspect of the
invention strips or pads of special stretchable wick ma-
terial is placed between the flexible cover and the tire
and tread assembl~ at the location of the air exhaust
connection to aid in the release of entrapped air. The
*
Trademark
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~93263
strips or pads of about 4 inches in width are placed
transversely of the tire so as to extend from below the
bond line on one side of the tire, over the tread strip
to a location below the bond line on the other side of
the tire. If necessary a similar strip may be placed
circumferentially around the tread strip~ this is often
de~irable if the tread strip is "slick", that is, having
no tread grooves. The preferred wick material is a por-
OU8 flexible fabric having stretch properties in two di-
rections which are at a right angle to each other. The
fabric is preferably woven fabric of 70,denier nylon fill-
ing yarn and 280 denier spandex warp yarn or equivalent
structure having 16~ stretch in the warp direction and
7~ stretch in the width direction. The fabric may be
.020 inch thick with a yarn count of about 20 warp yarns
per inch and about 60 filling yarns per inch. A pad for
use as described above may consist of 4 to 6 layers of
the fabric treated with bag coat lubricant. The function
of the pad cooperates with the function of the perforated
polypropylene film, if the latter is present, to release
entrapped air and to achieve equal curing pressure on the
tread ribs. The pads must be of sufficient width to ex-
tend beyond the base dimensions of the exhaust valves on
the envelope. The pads are particularly useful in re-
treading large tires such as are employed on heavy-duty
earth moving vehicles (off-the-road vehicles); this type
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l(~g32fi3
of tire does not have small tread grooves, and normally
a perforated lubricating liner is not used in the retread-
ing operation.
Another important aspect of the invention is
the structure and operation of an improved pressure cham-
ber which controls the application and removal of pres-
sure and heat during the bonding operation, Heretofore
the retreading of a plurality of tires simultaneously in
a single pressure chamber relied on the manipulation of
hand-operated valves to control differential pressure dur-
ing inflation and deflation of the tires. This sometimes
resulted in a wide variation in inflation rates for dif-
ferent tires in the pressure chamber and in slow reduc-
tion of the pressure differential after bonding. These
procedures required considerable personnel time, and in
addition the variables introduced into the bonding oper-
ation sometimes led to tread and tire distortions and
poor air exhaustion. For example, if tire pressure was
too low a poor bond might result along the center of the
periphery of the tire. If insufficient air was removed
a poor bond along the shoulder might result.
The present invention provides a pressure cham-
ber which operates automatically to apply a uniform heat
and pressure treatment to all tires in the chamber. In
order to pressurize the chamber and simultaneously inflate
the tires while maintaining inflation pressure higher than
1093Z63
chamber pressure, the system provides a common fluid pres-
sure manifold connected to each tire individually and to
the chamber, together with a pressure differential check-
valve and pressure-regulating devices arranged to assure
that the tires are always pressurized to a higher pres-
sure than the chamber. The chamber temperature is con-
trolled and recorded automatically throughout the process.
Upon completior. of the bonding operation a timer and spe-
cial exhaust valve arrangement permit the tires to exhaust
more rapidly than the c~am~er pressure so that the chamber
pressure causes partial collapse of the tires thereby
rendering them loose on their rims~ Alternatively a de-
gree of tire pressure may be maintained so that the tires
are still partially inflated when they are removed from
the chamber. This is desirable when the tires are to be
allowed to cure for an additional period of time, in an
inflated condition while cooling.
According to another aspect of the present in-
vention the problem of unequal pressure distribution in
and on the tread strip and bonding medium is at least par-
tially solved by inserting temporary pressure transmitting
members, or support members into the circumferential tread
grooves during the pressing and bonding operation. The
support members are preferably in the form of elastic
rings or endless ribs each of which engages the bottom
and sides of its respective grooves so as to substantial-
_g_
1C19326;~
ly fill the groove. It has been found that the resilientmaterial of the support members positively transmits the
pre9sure of the pressing element to the bottom and sides
of the groove to distribute the pressure evenly. This
technique is very useful in retreading tires which have
relatively narrow tread grooves, such as passenger car
tires and airplane tiresO ~t may also be useful at the
tread splice area when retreading truck tires. The tech-
nique is generally unnecessary when the tread voids are
sufficiently wide to permit the flexible cover to pene-
trate to the bottoms of the voids.
Specifically it has been found that the presence
of the rings during pressing and bonding are very effec-
tive to transmit the radial pressure of the pressing ele-
ment evenly to the tread and bonding medium, to avoid the
formation of thic~ and thin areas of bonding medium, to
stabilize the tread strip against distortion of the tread
ribs and the undertread portions under the grooves, and
to prevent lateral displacement of the tread strip itself.
A further advantage of the rings relates to the splice
which is normally present between the two ends of the
tread strip. The splice is usually made by placing bond-
ing medium between the two ends of the tread strip as it
is wrapped around the tire casing. During the pressing
operation thls bonding medium is compressed between the
two ends of the tread strip, and when the envelope does
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1~93263
not extend to the bottom of the tread groove some of this
bonding medium may be forced radially outward into the
groove where it cures and forms a dam which may complete- !
ly fill the cross section of the groove at the location
of the splice. The rings, in transmitting pressure to
the splice area~ prevents the formation of dams by forc-
ing any displaced bonding medium against the bottom of
the grooves so as to form thin layers.
The rings are particularly useful during bond-
ing of tread strips which have been slit with a large num-
ber of closely spaced parallel cuts extending across the
tread at an angle to the tread grooves. These slits or
cuts penetrate radially into the tread ribs whereby each
rib is divided into a large number of small separate tread
elements which enhance the gripping power of the tread
during road use. These tread elements, and consequently,
the undertread portion of the tread strip are rather eas-
ily deflected or distorted during the pressing and bonding
operation, but it has been found that the rings of this
invention are very effective in supporting or stabilizing
the elements. The slitting of tire treads to improve per-
formance is, broadly, a well-known technique as disclosed,
for example in United States Patent 3,683,728 (Meserve).
The rings may be inserted into the tread grooves
prior to or after the conventional stitching operation.
Stitching is the term applied to the step of applying a
_ 1 1 _
10~3263
roller or rollers to the circumference of the assembly of
tire casing, bonding medium and tread strip while rotating
the assembly in order to provide initial adhesion of the
tread strip to the tire caslng prior to applying an en-
velope to the assembly. ~y inserting the rings prior to
the stitching operation the rings become firmly seated in
the tread grooves by the action of the stitching roller,
inasmuch as the latter presses against the outer surface
of the tread strip with sufficient force to temporarily
deflect the tire casing radially inwardly.
The support members may be employed in any type
of bonding operation involving the pressing of a tread
strip against the tire casing by a flexible pressing ele-
ment such as an envelope or by a solid pressing element
such as smooth rigid mold members or a flexible metal
band. The support members have particular advantage in
the envelope type of operationt because it has been found
that it is very seldom possible to force the envelope com-
pletely nto the tread grooves due to the thic~ness of
the envelope which is required for strength and durabil-
ity. The envelope may penetrate part way into the grooves,
and, therefore, the suppcrt members need not always com-
pletely fill the grooves. The members need only substan-
tially fîll the grooves and by this is meant that the en-
velope will tightly engage the outwardly facing surfaces
of the members so that the pressure exerted by the envel-
ope will be transmitted to the bottom of the grooves.
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1093Z63
The preferred form of support members are re-
silient ru~ber rings capable of substantial elastic ex-
tension~ each ring being formed from a length of rubber
stock by stapling or splicing or otherwise securing the
ends of the length together. Preferably the rings have
circumferences less than the circumference of the tire
and tread assembly so that they may be inserted into the
tread grooves by stretching them over the circumference
of the assembly and then allowing them to contract so as
to fit snugly in~o the tread grooves, or at least to lie
in the upper portion of the grooves so that they can then
be pressed completely into the grooves. The flexibility
of the rings is such that they follow the normal serpen-
tine or zig-zag shape of the grooves.
The cross-sectional shape of a ring may be cir-
cular or other shape, it being only necessary that the
flexibility and resilience of the material of the ring
being 3uch that the ring generally conforms to the shape
of the groove when pressure is applied to the outer sur-
face of the ring. It is important, however, that the ringhave a width dimensior. which will permit easy insertion
of the ring into the groove and subsequently provide sup-
port for the tread profiles when pressure is being ap-
plied. In the relaxed condition the ring may have a width
dimension of 80% ~ lO0/o of the groove width~ The height
dimension of the rir.g may be S~/O - 100% of the groove
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1~93263
depth. As an example, a 0.250 inch diameter ring is
appropriate for a passenger tread having a groove width of
0.250 inch to 0.300 inch and a groove depth of 0.4375 inch.
The rings may be of solid or tubular cross section,
and if tubular they may be inflatable so that upon
introduction of fluid pressure they expand into even tighter
engagement with the sides and bottom of the tread grooves.
The rings may also take the form of spaced apart ribs
projecting from a common thin web which in the operative
position of the rings will overlie the outermost surfaces
of the tread ribs.
In accordance with one broad aspect, the invention
relates to a method of bonding precured tread strips to a
plurality of inflatable tires simultaneously by means of a
self-vulcanizing bonding material interposed between the tire
and the tread strip, said method comprising: applying to each
assembly of tire and tread strip a flexible impervious cover
which forms a sealed space between the cover and the assembly,
placing a plurality of the assemblies in a vessel, connecting
all said spaces with the atmosphere, connecting the interior
of each tire to a common fluid pressure manifold, connecting
the interior of the vessel to said manifold, supplying fluid
pressure of a preselected magnitude to said manifold,
controlling the pressure delivered to the interior of the
tixes and to the interior of the vessel so that tire inflation
pressure is always greater than vessel pressure, effecting
vulcanization of said bonding material, and reducing the
fluid pressure in said tires and in said vessel.
In accordance with another aspect, the invention
relates to apparatus for bonding precured tread strips to
tires by means of self-vulcanizing bonding material interposed
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between the tread strips and the tires, said apparatus
comprising a vessel having releasable closure means for
permitting entry and xemoval of tire and tread assemblies
and for sealing the vessel to permit its interior to be
pressurized with fluid pressure, a fluid pressure manifold,
a plurality of inflating conduits each connected at one end
to said manifold and connectable at the other end to the
interior of a tire for inflating the tire, and means
connecting manifold with the interior of the vessel, said
means including a conduit and a pressure differential check
valve which maintains the pressure to the vessel at a lower
value than the pressure in the inflating conduits when
pressurized fluid is supplied to the manifold, said means
further including a pressure regulator which maintains the
pressure in the vessel at a lower value than the pressure in
the inflating conduits after the tires have been pressurized
to the pressure existing in the manifold.
In accordance with a further aspect, the invention
relates to the method of bonding a precured tread strip to a
tire by means of a vulcanizable bonding material interposed
between the tire and the tread strip, placing the assembly
of tire and tread strip in a vessel and pressurizing the
interior of the tire to inflate the same and pressurizing the
interior of the vessel in a manner to press the tread strip
and the tire together, the improvement comprising: supplying
a pressure fluid through a first pressure regulator to a
conduit into a manifold, passing a portion of the pressure
fluid in the manifold to the interior of the tire, and
simultaneously passing another portion of the pressure fluid
in the manifold through a pressure differential check valve
and a second pressure regulator to the interior of the vessel
at a predetermined lower pressure than the pressure being
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, :
~(J93263
supplied to the interior of the tire.
In accordance with yet another aspect, the invention
relates to apparatus for bonding a precured tread strip to a
tire by means of a vulcanizable bonding material interposed
between the tread strip and the tire, said apparatus
comprising: a vessel for receiving a tire and tread assembly;
pressure fluid conduit means having an inlet for receiving
pressure fluid from a source thereof, said conduit means
including a first pressure regulator and a manifold connected
to said first pressure regulator to receive pressure fluid
therefrom; means for passing pressure fluid from said
manifold to the interior of said vessel, said means including
in flow sequence a differential pressure check valve and
a second pressure regulator; and a tire-inflating conduit
connected to said manifold, said inflating conduit having an
end located in said vessel and connectable to the interior of
a tire in said vessel, the arrangement of said pressure
regulators and said pressure differential check valve being
such that during pressurization of said manifold by way of
said first pressure regulator, the pressure fluid flows
simultaneously from said manifold to said inflating conduit
and to said vessel and such that thereafter the pressure in
said vessel is maintained at a lower value than the pressure
in said inflating conduit.
In the drawings:
Figure 1 is a schematic side view of a pressure
chamber for carrying out a bonding operation on a plurality
of tires;
Figure 2 is a schematic end view of the pressure
chamber of Figure l;
Figure 3 is a schematic sectional view of a tire
-15a-
~0~3Zfi3
and tread assembly being bonded together by a prior art
method and illustrating in exaggerated form some of the
distortion problems which may arise;
Figure 4 is a schematic fragmentary view of a
tire and tread assembly being bonded together using one
embodiment of the method and apparatus of the present
invention, in which support rings are provided in the tread
grooves;
Figure 5 is a view similar to Figure 4 illustrating
the use of a porous wick at the location of the air exhaust
conduit;
Figure 6 is a view similar to Figure 4 illustrating
the use of a perforated lubricating film between the tread
and the cover.
Figures 1 and 2 illustrate a cylindrical pressure
vessel 10 of sufficient size to receive a plurality of
assemblies 12 of tire casing and tread strips. One
~- -15b-
- 1093263
end of the vessel 10 is provided with a door 14 so that
each assembly 12 mounted on a rack 16, which is movable
along a track 18, may be placed in and withdrawn from
the vessel 10.
A typical assembly 12 is illustrated in Figure
2. For each assembly 12 the pressure vessel 10 is pro-
vided with a flexible vent line 20 having an inner end
22 adapted to be releasably connected to a vent element
24 of the respective assembly 12. The outer end 26 of
the vent line 20 communicates with the atmosphere by way
of a shut-off valve 28. For inflating the tire of each
assembly 12 the vessel 10 is provided with a flexible
line 30 having an inner end 32 fitting adapted to be con-
nected to the tire inflating element 34 of the respective
assembly 120 The fitting 32 includes a check valve which
prevents flow of pressure fluid from the line 30 when the
line 30 is not connected to the as embly 12.
The system for supplying fluid pressure to the
interior of the vessel 10 and for inflating the tire of
each assembly 12 includes a manifold 44 which receives
fluid pressure from an assembly provided with an inlet
fitting 43 adapted to be connected to a pressure source
such as compressed air~ From the fitting 43 the fluid
passes through a filter 52, a check valve 50, a solenoid
valve 48 and a pressure regulator 46 into the manifold
44. Each of the several tire-inflation lines 30 is con-
nected to the manifold 44 by a line 41 which includes a
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~3Z63
solenoid valve 62 and a manual shut-off valve 56~ The
assembly which transmits fluid from the manifold 44 and
the interior of the vessel includes a differential check
valve 42 ~ a pressure regulator 40 and a pipe 38 connected
to the vessel 10 by a fitting 36~ With appropriate valv-
ing changes pressure fluids other than air can be used.
The manifold 44 and the vessel 10 are provided
with pressure relief valves 58 and with solenoid-operated
exhaust valves 59 which exhaust to atmosphere.
Resistance heating elements 65 are located with-
in the vessel 10 for heating the interior of the vessel
10 to appropriate vulcanizing temperatures of 190F to
212Fo The heating elements 65 are protected from dam-
age by perforated metal grids 66~
; operation of the vessel 10 is as follows: Sev-
eral tire assemblies 12 are moved through the door 14
into the vessel 10 by sliding the respective supporting
rack 16 along the fixed track 18~ The vent conduits 20
and the pressure conduits 30 are connected to fittings
24 and 34 ~ respectively. The valves 48 and 62 are open.
~luid under pressure, for example air at 110 psi (pounds
per square inch), is then supplied to the fitting 43 so
as to pressurize the manifold 44 and to begin inflating
the tires and pressuring the vessel 10. The pressure in
the vessel 10~ and hence the pressure on the exterior of
the assemblies 12, is maintained 15 to 20 psi less than
the inflation pressure of the assemblies by means of the
1(;~93Z63
differential check valve 42. ThiS valve 42 remains clos-
ed if the pressure differential across its valve seat is
less than about 15-20 psi, and it opens if the differen-
tial is greater than about 15-20 psi. Thus, this valve
opens and allows air to enter the vessel 10 after a pre-
set pressure has been obtained in the manifold 44. If
the pressure in the vessel 10 increases over the preset
differential pressure, the valve 42 closes by spring pres-
sure and the tire assemblies 12 continue to inflate until
the differential pressure is again below that at which
the valve 42 is set to open. The valve 42 then opens and
again allows air to pass into the vessel 10.
At the same time the interior of the chamber 10
is heated to 190F to 212F by the electric resistance
elements 65 which are automatically controlled by a ther-
mostat (not shown).
This differential pressure is maintained through-
out the bonding process by the pressure regulators 40 and
46. The pressure differential is necessary to maintain
the correct tire configuration and to effect a seal of
the cover 122 (Figures 3-6) to the tire 110. The greater
pressure on the cover 122 forces all the air out from be-
tween the cover 122 and the tire 110 and this air flows
to the atmosphere through the conduit 20. Simul-
taneously, the tread strip 116 is pressed against the
tire 110 and the bonding medium 118 vulcanizes.
~t the completion of the bonding operation a
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1093263
timer 60 is energized and allows the vessel 10 and the
manifold 44 to exhaust. Each assembly 12 also exhausts
through the conduit 30 and the respective valve 56 to the
manifold 44~ Due to the relative size of the exhaust
ports t~e assemblies 12 become exhausted before the ves-
sel 10. This allows the pressure in the vessel 10 to
collapse the tire 110 of each assembly and to thereby aid
in unseating the tire from its rim 112.
Alternatively, by providing a solenoid valve 62
the tires 110 may be re-inflated automatically at the end
of the bonding process to a preset pressure and allowed
to cool. Another alternative is to stop the exhausting
of the tires at a preset pressure.
Yet another alternative is to reinflate the
collapsed tires 110 outside the vessel 10 to a desired
pressure and allow them to cool.
The reason for these alternatives is to provide
inflation after bonding (post cure inflation) in order to
reduce or eliminate shrinkage during the time the tire
110 is cooling. This is a particularly useful technique
for passenger car tires and light truck tires.
Figure 3 illustrates in schematic form a bond-
ing operation being carried out by the technique disclos-
ed in the aforenoted United States Patent 3,236,709 and
showing in exaggerated form some of the problems which
can arise as a result of non-unifQrm distribution of pres-
sure on the tread strip. There is shown a tire casing
--19--
1~3Zfi3
110 mounted on a rim 112 so as to be inflatable with air
or other fluid through a suitable valve 114. A prevul-
canized tread strip 116 has been wrapped around the cir-
cumference of the tire casing 110 with a bonding medium
118 interposed between the two. The bonding medium 118
may be any suitable rubber base composition which is cap-
able of self-vulcanization at elevated temperature and
capable of forming a bond between the tread strip 116
and the tire casing 110. Preferably the bonding medium
118 is vulcanizable at temperatures between about 190F.
and 250F, The tread strip 116 has been prevulcanized
under high pressure and as shown includes conventional
grooves 120 and ribs 121 each of which extends continu-
ously around the circumference.
Overlying the tread strip 116 and the side walls
of the tire casing 110 is a pressing element in the form
of a flexible rubber annular envelope 122 which extends
around the circumference of the tire and tread assembly.
The edges of the envelope 122 are temporarily sealed to
the side walls of the tire casing 110, as by being clamp-
ed at 124 between the side walls and the rim 112. The
entire assembly of rim 112, tire casing 110, tread strip
116, bonding medium 118 and envelope 122 is disposed in
a vessel 126 such as an autoclave. In order to press the
tread strip 116 against the circumferential of the tire
casing 110 and vulcanize the bonding medium 118, heated
-~n-
3263
fluid such as a mixture of steam and air is injected into
the vessel 126, a suitable connection 128 being provided
in the wall of the vessel 126 for this purpose. Alterna-
tively, the pressurizing fluid may be air and heat may be
supplied by other means such as the resistance heating
elements of Figure 2. The pressure should be no greater
than the inflating pressure in the tire casing so that
the latter will not be deformed. The tire casing will
always be inflated above the autoclave pressure.
lo The space between the inside surface of the en-
velope 122 and the asse~ly of tire and tread strip is
in communication with the atmosphere outside the vessel
126 as by means of a conduit 130 connected to the envel-
ope 122. The fluid pressure in the autoclave thereby
presses the envelope 122 into tight contact with the as-
sembly and forces the tread strip 116 against the circum-
ference of the tire casing 110, the air in the envelope
122 being forced out through the conduit 130.
The thickness and flexibility of the envelope
122 and the width of the tread grooves 120 are such that
normally the envelope 122 cannot penetrate to the bottom
of the grooves, as shown in Figure 3, even though this
would be desirable. Instead~ the envelope 122 will nor-
mally penetrate only part way into the grooves 120 with
the results that air will be trapped in the grooves and
that there is less force at the bottoms of the grooves 120
and less pressing of those portions of the tread strip 116
--21--
1(~93Z63
against the tire casing. This alone may produce a weaker
bond under the grooves 120. At the same time, there is
maximum force being applied on the outer surfaces of the
tread ribs 121 without there being any support for the
sides of the ribs 121. The overall result of this state -
of non-uniform pressure being exerted on the tread strip
116 is that several forms of distortion of the latter and
of the bonding medium 118 may occur. One form of distor-
tion is that the undertread portions of the tread strip
may become humped, as shown at 132 in exaggerated form.
Also, the individual tread ribs 121 may pitch or tilt as
shown at 134. Further, the bonding medium 118 may become
distorted into thick and thin portions 136 and 138 from
movement of the individual ribs 121 or from lateral move-
ment of the entire tread strip 116. Still further, as
explained above but not shown in the drawing, bonding ma-
terial from the spliced ends of the tread strip 116 may
form a dam across one or more of the grooves 120.
Figure 4 illustrates how these defects are
avoided by the presence of support or stabilizing members
in the grooves 120 during the pressing and bonding opera-
tion. In the illustrated embodiment, the support members
are resilient flexible elastic O-rings 140 which have been
inserted into the grooves 120~ The material of the rings
140 may be neoprene or other age resisting rubber having
as original properties a tensile strength of at least 100
~22-
~093ZF~3
psi, 270 elongation and 60 f 3 Shore A Durometer and
having aged properties after 8 days at 230F. of 70 psi
tensile strength, 7~6 elongation and 72 f Shore A Duro-
meter. In a relaxed condition, the rings 140 should have
a circumference of about 75% of the circumference of the
assembly of tire casing and tread strip.
The rings 140 are inserted in the grooves 120
by stretching them over the circumference of the tire and
tread assembly and pressing them into the grooves 120
prior to enclosing the asse~bly in the envelope 122. It
is preferred that the insertion step be carried out simul-
taneously with stitching the tread strip 116 to the tire
casing 110 because this assures that each ring 140 will
be properly seated in the bottom of its groove before the
envelope 122 is applied.
As shown in Figure 4, each ring 140 should fit
snugly in its groove 120 so as to be in contact with the
bottom and at least a substantial portion of the side wall
of the groove 120. The envelope 122 contacts the outer
surface of the rings 140, so that autoclave pressure is
transmitted to the undertread portions of the tread 116
directly below the grooves 120. At the same time, the
tread ribs are supported against lateral distortion. The
result is that all portions of tread strip are pressed
against the circumference of tire casing 110 at essential-
ly the same pressure, and there is no distortion of the
bonding medium 118, the undertread, or the tread ribs
121.
Z63
Figure 5 illustrates the use of a pad 150 of
porous flexible wick material, as described previously,
disposed between the cover 122 and the tread strip 116.
In this embodiment the tread grooves 120 are rather wide.
The pad 150 and the cover 122 penetrate to the bottoms
of grooves 120 and therefore there is no need to provide
supporting rings in the grooves 120.
Figure 6 illustrates the use of a stretchable
lubricating film 152 of perforated polypropylene between
the cover 122 and the tread strip 116. The flexibility
and lubricating properties of the film 152 permit the
cover 122 to penetrate to the bottom of the grooves 120
to thereby press out all air and achieve uniform pressure
on the tread strip 116 without deformation of the latter.
Without the presence of the film 152 the conditions il-
lustrated in Figure 3 may occur.
-2~-
