Note: Descriptions are shown in the official language in which they were submitted.
CA 02354284 2001-07-27
TECHNIQUE FOR THE PARTIAL SUBSTITUTION OF DAMAGED METAL CORDS IN THE
SIDEWALLS OF MEDIUM AND LARGE RADIAL TIRES AND TI-II: MEANS TO PERMIT
THEIR SUBSTITUTION.
The invention concerns a technique to carry out repairs on the sidewalls of
medium and large size
radial tires, such as those used for lorries, very large dumpers and diggers
and, for example, those
used in the lift trucks of contaiiiers, heavy duty cranes which travel over
land, operating machinery
for shifting materials and very large dumpers etc., which have incurred damage
to and/or breakage
of the metal cords especially in the case of larger tire damage which, though
repairable,
compromises the rigidity of the tire sidewalls.
Moreover, the invention also concerns the specific materials used in carrying
out the technique,
which consist in layers of rubber containing radially arranged metal cords,
layers of rubberised
fabric, layers of unvulcanised rubber and so on.
In order to carry out the aforementioned repairs on medium-sized tires, as for
example those of
lorries and medium-sized dumpers, special techniques and patches are used,
these being the subject
matter of Italian and foreign patents by the same owner N.EP 0353313,
designating Italy too; US
Patent N. 5,139,840; Patent N. 196 3887 in Japan; Patent N. 1334375 in Canada.
Said patches, trapezoidal in shape, are vulcanised so as to maintain an arched
curved shape and are
made up of two layers of only rubber, one layer of rubber containing radially
arranged rectilinear
metal cords, a layer of rubberised fabric positioned over this last mentioned
layer and by a rubber
dowel which is inserted into the cut-out window opening in the sidewall of the
tire in order to
remove the damaged cords.
Concerning much larger tires, having a belt diameter of some metres for which
it is necessary to cut
out large openings to substitute the damaged radial metal cords and to restore
the rigidity of the
damaged sidewalls, the current state-of-the-art offers no such technique,
suitable means or relative
know-how.
On the other hand, for the inevitable manufacturing drawbacks which are also
present in medium-
sized tires, in some cases the trapezoidal patches cannot be as perfectly
applied as they should, since
the radial metal cords of the tire walls often do not have a perfectly
rectilinear disposition, since
they may be more or less waved transversal to the radial cords and remain
positioned on the metal
cords of the patches thus causing an increase in the rigidity of the tire
sidewalls.
This makes it difficult to obtain a perfectly trapezoidal window opening with
a radial axis in which
to insert the rubber dowel part of the patch, and the realisation of two co-
axial trapezoidal slots
along the longitudinal length of the window opening into which are inserted
the two ends of the
metal cord layer not positioned over the dowel.
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Moreover, the application of the trapezoidal patches requires a vast array of
different sized patches
for each type of tire and relative to each damaged area in order to exactly
substitute the number of
damaged radial cords.
The invention as claimed intends to supply the techniques and means both for
the repair and
substitution of the radial cords of tires of medium siz-e without causing
superimposition of the
substituted cords onto the undamaged ones, and to regain the necessary
rigidity of the damaged
sidewalls of very large tires whose cords must be replaced.
The advantages of the invention, apart from the functional ones, lie, in
particular, in the economic
aspect, when considering the high costs of medium and large size tires and
given that repairs carried
out using the technique according to the invention allow for the complete
restoration of the function
of the tires in question.
Accordingly, in one aspect, the invention provides a method for the partial
substitution of
damaged metal cords in sidewalls of medium and large sized radial tires and of
means to
permit their substitution, the method comprising the step of removal of the
damaged areas from
the sidewall of the tire in order to form a trapezoidal opening the height of
which corresponds
to the length of the removed cords, the transversal bases of said opening
being transversal to
the radial cords of the tire and the sides being parallel to the undamaged
cords which delimit
said opening, the greater base of this opening being located in the area of
the edge of the tire
belt.
In another aspect, the invention provides a method for partial substitution of
damaged metal
cords in the sidewalls of medium and large sized radial tires and the means to
permit their
substitution, medium-sized tires having diameters ranging from I000mm to
2000mm, and large
tires being those with a diameter greater than 2000mm, the method comprising:
removing a damaged area from the sidewall of the tire forming a trapezoidal
opening, the
height of which corresponds to the length of the removed cords, the
transversal bases of said
opening being transversal to the radial cords of the tire and the sides being
parallel to the
undamaged cords which delimit said opening, the greater base of the opening
being located in
the area of the edge of the tire belt;
realisation in the proximity to the basis of the trapezoidal opening of two
slots and whose axes
of symmetry are co-axial to the radial axis of symmetry of said opening, said
slots being
realised along the virtual extension of the radial sides of the same opening
and being delimited
above and below by two sides transversal to the radial
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cords of the tire, the depth of these slots being such that it uncovers the
original cords of the tire,
in order to obtain the smaller distance between the metal cords embedded in
the layer and said
uncovered metal cords of the tire once the layer has been positioned;
grinding and brushing of the inner surface of the tire along the outer
perimeter of the
trapezoidal shaped opening and the edges of the slots, so to obtain a
perimetral groove to the
opening and the relative slots being delimited by a width and showing a
texture type RMA 2-3;
insertion of a trapezoidal layer of unvulcanised rubber having a maximum width
equal to the
width of the slots, said .trapezoidal layer embedding a number of metal cords
equal to those
removed when the metal cords have the same diameter, or greater to those
removed when the
diameter of the metal cords of the layer is smaller;
application of one or more covering air-tight layers also containing a layer
of butyl rubber, on
the layer of metal cords, by means of a layer of adhesive unvulcanised rubber
so as to cover the
perimetral groove, the area of each covering layer being equal to the
delimited area of the outer
perimeter of the same perimetral groove;
filling, with unvulcanised rubber having suitable characteristics for sidewall
tires, of the outer
trapezoidal cavities formed by the opening and the outer surface of the layer
of metal cords; and
vulcanisation, using appropriate means, of the repaired area.
The invention is described in detail as follows with reference made to the
enclosed drawings which
illustrate respectively:
Fig. 1: the layers which allow for repair of a medium-sized tire;
Fig. 2: the layers which form the protective and finishing layer to be
positioned over the layer of
metal cords;
Fig. 3: Section AA of fig. 1;
Fig. 4. an example of the application of the layers as in fig. 1, to the
sidewalls of a medium-sized
radial tire, with parts of unvulcanised rubber filling partially removed fi-om
the window opening
Gom which the damaged metal cords have been removed;
Fig. 5. a layer of unvulcanised rubber with radial metal cords;
Fig. 6: the technique of application of the layers.as in fig. I to a mediuni-
sized tire;
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Fig. 7: the three layers which allow to carry out the repairing technique on
large tires;
Fig. 8: the composition of layers 9 and 10 of fig. 7;
Fig. 9: the technique of application of the layers of fig. 7 on a large size
tire;
Fig. 10: a dimensional comparison between a large tire with lateral
reinforcements and a medium-
sized tire without lateral reinforcements;
Fig. 11. an example of medium and large size tires compared to the average
human height;
Fig. 12. adaptability of the layer containing the radial metal cords on the
irregular edges of the
window opening realised to remove the damaged metal cords of medium and large
sized tires;
Background of the invention
The invention is based on the fact that the materials which permit the
carrying out of the technique
have neither been previously and reciprocally made solid nor vulcanised at the
same time so as to
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assume a stable single body, but rather are made up of single components and
vulcanised afler their
application to the zone to be repaired.
TECHNIQUE OF REPAIRING A MEDIUM-SIZED T'IRE
With regard to medium-sized tires having a diameter of less than 2000mm, the
single components
are a layer I of unvulcanised rubber containing metal cords and a multiple
layer 2 of only rubber,
which are applied immediately one after the other to the inner surface of the
tire P (fig. 1).
The distortion of unvulcanised rubber fig. 5, of the layer I allows for
adaptation of the lateral radial
cords 1.2 parallel to the radial cords of the tire, even wlien distorted, as
illustrated in fig. 12.
This avoids superimposing the lateral metal cords 1.2 of layer 1 on to the
undamaged radial cords
CR protruding from the edges of the window opening 5, if they are waved
instead of rectilinear.
The metal cords 1.2 of the layer 1 are radially arranged as the radial cords
CR in the sidewalls of the
tire: the number of cords contained in such a layer, partially trapezoidal in
shape, must be the same
as, or greater than, the number of the cords removed.
The aim of the second set of layers 2, also trapezoidal in shape, is to
protect layer I from oxidation,
to create a sufficient air-tight condition, indispensable to tubeless tires,
and to fmish off the
repaired area.
Said set, see figs. 2 and 4, is made up of a unit of superimposed rubber
layers, trapezoidal or
rectangular in shape, that is, of an outer layer 12 of anti-oxidant rubber,
such as butyl mixture, and
of a layer 2.1 of only rubber, consisting in a homogeneous mix, both
vulcanised simultaneously so
as to form a single unit.
Lastly, on the free side of layer 2.1, a thin sheet of adhesive unvulcanised
rubber is applied to be
attached to the surface of the layer 1 of metal cords, and to the surface of
the perimetral grooves 6,
D3 in width, which laterally delimit both the window opening 5 and the slots 4
into which the ends
of layer I are inserted; the grooves 6 being realised by grinding and brushing
the intact surface
surrounding the window opening 5.
Moreover, the second set of layers 2, has a greater area than the layers of
metal cords 1, the said
greater area being equal in area to that of the grooves 6.
The technique of substituting the damaged cords in a medium-sized tire is
based on the following
steps:
a) carrying out, on the sidewall two transversal cuts in the direction of the
radial cords to be
removed and two cuts parallel to the undamaged cords, so as to isolate and
remove only the
layers of damaged cords and to form a trapezoidal window opening 5.
One of the two transversal cuts is carried out near the edge of the tire belt
far enough from the
edge of the rim zone 7 in order to realise, on the intact undamaged part of
the tire, the slot 4.1
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into which the upper end 1.3 of the layer I of metal cords is to be inserted
and the other cut in
the lower end of the wider slot 4.2 into which the lower end of the same layer
I is to be inserted:
the trapezoidal slots 4, are obtained by scraping the rubber which covers the
two opposite ends
of the radial cords CR of the tire from which the damaged parts have been
removed, until the
cords are conipletely bare.
The depth S 1 of the slots 4 must be such that it can completely contain layer
1 of the metal
cords having a thickness S2 < S 1 and confer a sufficiently high resistance to
the radial shifting
determined by the tight contact between layer 1 and the bare cords.
b) Grinding and brushing of the inner surface of the tire so as to create the
grooves 6, width
D3, parallel to the sides of the window opening 5 and to the trapezoidal slots
4.1 and 4.2, to
delimit a trapezoidal surface having the same area as that of layer 2 in the
inner part of the
same grooves.
c) Application of layer 1 of unvulcanised rubber containing the metal cords
which will
substitute those removed;
d) Application of layer 2 within which layers 2.1 and 12 are vulcanised
together so as to form a
single unit by means of a thin sheet of adhesive unvulcanised rubber 11 to
permit attachment
to the opposite surface of the layer of metal cords 1;
e) Filling with unvulcanised rubber 3 the cavity 5.1 of the window opening 5
situated between
the outer surface of the tire and the convex surface of the layer 1;
fj Vulcanisation of the repaired area.
TECHNIQUE OF REPAIRING A LARGE TIRE
In the case of very large tires, having a diameter greater than 2000mm, or
even larger diameters,
see figs. 10 and 11, into which a reinforced and stiffening patch 15 is
inserted, such as those
used for lift trucks for containers, heavy duty cranes, dumpers etc., the
problem to solve is
trying to regain the rigidity compromised when the metal cords are
substituted, which is the
opposite case for medium-sized tires where flexibility is a functional
characteristic.
This is solved by using a double protection of the unvulcanised rubber layer 1
containing metal
cords made up of two sets of layers, 9 and 10 respectively, instead of only
one layer 2 as used
when repairing medium-sized tires.
The first protective set 9 is made up of two layers of rubberised fabric 9.1
in which the
reinforcing fibre cords which form the fabric are, compared to the axes of the
layers 9, angled in
a suitable way and conform to the teachings shown in other patents by the
sanie owner; a layer
of adhesive unvulcanised rubber 11 is placed over the above mentioned layers
in order to attach
the layer of metal cords to the surface of the layer 1.
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Tlie second protective sct 10 is made up of another two layers of rubberised
fabric 10.1 having
the same characteristics of rubberised fabric layers 9.1, upon which, on the
part which remains
inside the tire, a layer of butyl rubber 12 is placed to ensure further
necessary air-tightness, and
on the opposite part, a layer of adhesive unvulcanised rubber 11.
The sets of layers 9 and 10 have an area equal to that delimited by the outer
perimeter of the
grooves realised by grinding and brushing the zones adjacent to the perimeter
of the opening 5.
The layers of the set 9 formed by the rubberised fabrics 9.1 and the layers of
sets 10 formed by
the layers of rubberised fabric 10.1 and by the layer of butyl rubber 12 are
vulcanised
separately.
Therefore, the repairing technique for a large tire differs only in that there
is the application of
two protective groups instead of only one, as in the technique relative to the
repairing of
medium-size tires and the steps of such an application are the following:
1) carrying out of steps a), b) and c) as in the case of medium-sized tires;
2) Separate vulcanisation of the layers 9.1 of the set 9 and 10.1 and 12 of
set 10;
3) Superimposition with the vulcanised set on the metal cords I and attachment
thereof by
means of a layer of adhesive unvulcanised rubber 11;
4) Superimposition of the vulcanised set 10 to the layer formed by set 9 and
attachment thereof
by means of a layer of adhesive unvulcanised rubber 11;
5) Filling the cavity 5.1 of the outer surface with unvulcanised rubber 3
which has the features
of hardness and elasticity similar to those of the rubber of the sidewalls;
6) Vulcanisation of the repaired area.
The advantages of the technique lie above all in the manageability which
simplifies application
of the protective layers of the layer of the metal cords on large and
extensive areas.
Due to the limited thickness of the protective layers, the rolling necessary
for expelling air
trapped between the superimposed layers may be easily carried out manually.
This is facilitated by the presence of the adhesive layers of unvulcanised
rubber 11, not
vulcanised together with the components of the sets 9 and 10.
The pre-vulcanisation of the sets 9 and 10, in the subsequent vulcanisation of
the repaired area,
avoids the onset of anomalous forces on the layer of metal cords I due to the
greater
adaptability of the reinforcement, and also avoids any possible shifting of
the layer of metal
cords I from its manufacturing position.
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