Note: Descriptions are shown in the official language in which they were submitted.
10~
This invention relates to applying a tread to a tyre,
for example a pneumatic tyre, either for retreading used
tyres or for applying the treads of new tyres.
The terms tread and tyre are used generically herein
to mean the wearing surface and the body or carcass of a
natural or synthetic rubber tyre assembly, respectively.
It is known to make or retread a tyre assembly by
preparing a tread band in a mould to give the desired tread
pattern and then to apply the tread band onto a prepared
(e.g. buffed and trued) tyre carcass. The tread band may
be vulcanised before being applied to the carcass. A
bonding material, such as unvulcanized rubber, may be
interposed between the carcass and the tread band, and
pressure and/or heat may be applied to set the bonding
material and unite the tread band with the tyre carcass.
The pressure may be applied in various ways; for example an
air bag may be placed with the tyre carcass and may be
inflated to press the carcass outwardly against the tread
~and while the latter is held in a mould. It is also known
~20~ to sandwich the tyre carcass and tread band assembly between
two air bags in a relatively large mould and then inflate -
these bags to press the tread band and tyre carcass against
each other (this method is particularly applicable to radial
ply tyres). British Patent specifications 1379253 and
1389421 both in the name of Kentredder Ltd. and sealed on
April 30, 1975 and July 30, 1975 respectively, describe such
prior methods.
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1060614
According to the present invention there is provided amethod of applying a tread to a tyre carcass by compressing at
least the wearing surface of a precured tread in strip form in
a direction parallel to the longitudinal axis of the strip and
bonding the tread to a carcass whilst maintaining the compres-
sion of the tread whereby the wearing surface of the final
assembly remains under compression.
The compression is preferably such that the periphery of
the wearing surface is shortened by at least 0.5~, and prefer-
ably by 1~ to 10%, more preferably by l~ to 6~.
The tread band may be formed of any conventional materialused for making t~res, such as natural or synethetic rubber
;~ (including plastics material such as polyurethane~ When it is
of rubber, it is desirable that it should be vulcanized before ~-
being applied to the carcass, as this provides the optimum im-
provements in the wearing properties of the products of the
present invention.
The tread strip may for example be prepared as an annular
band made in a mould whose radius is such that the annular band
is slightly too big for the carcass. In accordance with the
present invention, the annular band is then compressed and is
bonded onto the carcass while being maintained in its compress-
ed state. In one preferred embodiment, the annular band is
coated on its inner surface with a solution of bonding agent
, (for example an uncured rubber) and a thin layer of cushion
rub~er is interposed between it and the carcass to which has
been applied an appropriate bonding agent; pressure is then ap-
plied to force the annular band against the carcass while
reducing the radius of the annular band, resulting in compres-
sion of the tread band.
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~0~ 614
A form of fluid pressure may be used to appl~ the
tread band to the carcass; for example the assembled tread
and carcass may be surrounded by an inflatable vessel (such
as an air bag) itself surrounded by a rigid frame, so that
the pressure applied to the assembly may be controlled by
controlling the degree of inflation. Alternatively, a clip
of the "Jubilee" type may be used to compress the tread
band onto the carcass.
It is also possible for the tread band, along with the
cushion rubber strip if desired, to be bonded (while under
compression~ to an inextensible breaker strip so that the
tread is maintained in compression; the combined tread/breaker ~-
strip is then applied to the carcass.
In another preferred method, where a preformed annular
tread band is used, it may be formed in the usual manner in
a mould, and it may then be compressed into another mould
having a smaller diameter than the first mould, being held
in the other mould while the carcass is applied to it and
while bonding is effected. This method is for example
particularly suitable for retreading radial ply or bias-
belted tyres, as it does not require extension of the tyre
carcass, which extension is difficult or impossible to effect
with such tyres. Again, it is possible to use an adjustable
mould whose radius may be decreased, for example by
mechanical means.
In an alternative method, a strip of tread band
material may be used instead of a preformed annular band.
The strip is moulded as a curved strip having a radius
of curvature less than that of the carcass. As a result,
when the strip is fitted onto the carcass, its outer or
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1061)~
wearing surface is compressed relative to the inner or
bonding surface. In this case, it is desirable to form the
strip so that it includes an inextensible reinforcing strip
along or near its inner surface so that, when the strip is
fitted onto the carcass, the bonding surface of the strip
is not under tension.
This method may also be used when a tyre, e.g. an
agricultural tyre is treaded with lugs. In this case, a lug
to be applied to a particular part of a tyre carcass surface
is formed with a radius o~ curvature less than that of the
surface to which it is to be applied. Again, it is desirable
to incorporate a reinforcing strip adjacent the bonding
surface of the lug.
When an annular tread band is to be fitted to a tyre
carcass in accordance with the present invention, the tread
band can be inserted into an annular mould of smaller radius ~ -
(as mentioned above) and the tyre carcass is then inserted
within the tread band. ~his can be done by spreading apart
the beads of the tyre carcass so that its circumference is reduc-
ed. However, it has been found in practice, especially with rad-
ial tyres, that the spreading apart of the beads has a tendency
to cause the formation of a single large inward fold or
crinkle in the carcass, and this is difficult to remove once
the tyre is in the mould and it may lead to a defective final
product if allowed to persist throughout the curing operation.
A similar problem can occur, although to a lesser extent,
when the tread band is compressed into the mould of smaller
diameter; in this case, if an inward crinkle or fold occurs,
then it is difficult to achieve an even compression.
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10ti06~4
The present invention provides an apparatus which avoids
this tendency to ~orm an inward deformation and which can be
adapted to give even compression of a tread band in a mould.
According also to the present invention there is provided
apparatus comprising a tyre mould having an inner annular surface
for holding a tread band, in which means are provided at spaced
intervals around the circumference of the mould for preventing a
tyre carcass or a tread band inserted into the mould from touching
the said inner surface at the places where such means are located,
the said means being removable after the tyre carcass or tread
band has been placed in the mould so that the tyre carcass or
tread band can then accurately bear against the whole of the
inner annular surface of the mould.
The said means may comprise a series of pairs (for exam-
ple, six pairs) of holes at equal intervals through the side walls
of the mould and corresponding rods slidable through each pair of
holes so that the rods are spaced from the inner annular surface
of the mould. With the rods in place in the corresponding pairs
of holes, the tread band is placed in the mould and is induced to
form small inward crinkels ~for example, six) rather than a single
large crinkle; the rods are then withdrawn and the small crinkles
are readily accommodated by even compression of the tread band.
More important, after the tread band has thus ~een
placed in the mould, the rods may again be inserted through
the corresponding pairs of holes and the tyre carcass may
then be introduced into the mould where it also forms a
corresponding number (for example six) of small inward
crinkles, which, after withdrawal of the rods, are readily
accommodated. By this, a complete contact of the ~onding
surfaces of the tread band and the tyre carcass may be achieved.
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10~
In the method of the invention (whether or n~t the
special apparatus just described is used), the bonding of a
tyre tread to a wheel or carcass may be effected with the
application of heat. The pressure assembly, including the
tread and the carcass, may be placed in a heated chamber.
If a metal mould is being used, heat may be applied directly
to it so as to be conducted to the bonding surface.
Generally in the present invention, the periphery of
the tread band is reduced by at least 0.5~, preferably
1 - 10~, by the compression applied to it in accordance
with the invention.
The important thing in the present invention is for the
wearing surface~of the tread band to be under compression.
This is usually most easily achieved by placing the whole
thickness of the tread band under compression, but this is
not essential, especially if the tread band is of substantial
thickness. It is the wearing surface ~the surface which
meets the road surface) which must be under the specified
compression.
The invention will now be described with reference to
the accompanying schematic drawings, in which
Figuxe 1 is a section of a mould with a compressed,
pre-vulcanised tread band in position, :
Figure 2 is a section of a mould with a tread band
and a breaker strip in place ready to receive a tyre
carcass: -
Figure 3 is a section of a conventional mould -
containing a tread band and a radial-ply tyre,
Figure 4 i9 a cross-section of a mould provided with
means for facilitating the insertion of a radial ply tyre,
.
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Figures S and 6 are sections of the mould of Figure
4 showing a radial-ply tyre being inserted,
Figure 7 is a part cross~section of a tyre carcass
suitable for a tyre of an agricultural vehicle,
Figure 8 is a cross-section of a lug for application
to the carcass of Figure 7, and
Figure 9 is an ele~ation o~ a tyre having tread applied
in segments. - -
Referring to Figure 1, a tyre carcass which is to be
treaded is buffed down to the correct size for a plain ring
mould 1. A pre~vulcanised tread band 2 is then prepared whose
periphery is about 2~ longer than the periphery of the mould 1.
The pre-vulcanised tread band 2 is then placed in the mould as
seen in Figure 1 so that it is in e~en compression throughout.
The oversize tread band 2 may be more easily compressed into
the mould 1 if a silicone rubber lubricant is spread around the
surface of the mould 1.
In the remainder of the procedure (not illustrated) a
layer of bonding material, with or without cement, is applied to
the buffed surface of the carcass or to the inside of the tread
band 2 (preferably the former) and the beads of the tyre are - -
spread apart in order to reduce its diameter and allow its -
insertion into the mould inside the tread band 2. On release of
the beads, the prepared bonding surfaces are brought into contact
and heat and pressure are applied to secure the bond. This method
is applicable to cross ply, radial or bias-belted tyres. ~ -
: .
A very similar method may be employed when it is desired to
incorporate a breaker strip. Referring to Figure 2, the tread
band 2 is similarly compressed into a mould 1, and then an in-
extensible breaker strip 3 is bonded to the tread band. The
breaker strip 3 will ensure that the tread band 2 will be
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10~i0~i14
maintained ~nder compression. A layer of bonding material
4 is then applied to the breaker strip 3, and a tyre carcass
is then inserted into the mould 1. In this case, the buffed
tyre carcass has the same diameter as the breaker strip 3.
If this method used with a cross-ply tyre, the tyre is
converted into a bias-belted tyre.
In the methods of both Figuxes 1 and 2, pressure may
for example be applied to assist bonding by means of an air-
bag inflated within the tyre carcass in the mould, and heat
may be applied by placing the entire mould in an oven or by
using a mould having internal heating elements.
When superimposing the prepared tyre on to the compressed
tread band, there may be a risk of trapping air between the
two. This can be guarded against by providing blow holes
through the thinner parts of the vulcanised tread through -
which air can escape.
Referring to ~igure 4, an annular mould 21 is channel-
shaped to recei~e a tread band 22. The side walls of the
mould project beyond the tread band 22 and include a series
of pairs of holes 7, 7' spaced around the circumference. A ~ -
rod 8 is received in each pair of holes 7, 7' and extends
through the mould at a spaced distance from the inner (tread-
receiving) wall of the mould.
Referring to Figure 3, the mould 21 carrying a tread band
22, but nct having the rods 8 in place, has received a radial-
ply tyre carcass 5. A large inward crinkle 6 has formed in
the tyre carcass 5; this crink~e is very difficult to remove,
and will cause an area of weakness in the f;nished tyre.
Referring to ~igures 5 and 6, a generally similar mould ;
21 carries a tread band 22 but with six rods 8 in place!The
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iOf~)614
tyre carcass 5, which has been placed in the mould 21 with
the rods 8 in place, has been induced to form six small --
crinkles 9 instead of a single large crinkle. When the rods
8 are removed (Figure 6) the small crinkles are easily
accommodated in the mould and disappear, and a good seal of
tread band 22 to carcass 5 is now possible.
Referring now to Figure 7, there is shown a section of
a tyre carcass 10 suitable for an agricultural vehicle. The
radius of curvature of the outer surface of this section of
carcass is r. Figure 8 shown a lug 12 to be fitted to this
section of tyre. The lug comprises a pre-vulcanised rubber
strip having a radius of curvature rl, where rl is less than r.
The wearing surface of the lug is indicated at 11 and adjacent
the other surface 13 there is provided reinforcement 14 le.g. -
a wire mesh) in the rubber which makes the lug inextensible at
that point.
The lug 12 is fitted over the tyre section 10 and as its
radius of curvature is increased, the wearing surface of the
lug is brought under compression.
Figure 9 shows a tyre carcass 5 being treaded in a seg-
mental fashion, for example as described in British Patent spec-
ification 1471535 in the name of Kentredder sealed on April 29,
1977~ A number of strips, for example four, are prepared for
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; appllcation to the crown of the carcass so that together they
form a complete tread which may, for certain purposes have a
smooth wearing surface. A strip 23 (Figure 9) is moulded with
: :
a radius of cuxvature less than that of the tyre so that the
strip, strip 24 in the Figure, has a compressed wearing surface. ~ -
It has subsequently been found that by means of the pre-
sent invention the life of a tyre is made much greater than
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if the treading were carried out in the convention~.l way.
Thus, pneumatic tyres retreaded in accordance with the
present invention have given much longer services than tyres
similarly retreaded without compression of the tread surface
and have even given longer service than new tyres made in the
conventional way.
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