FR2468473A1 - IMPROVEMENT TO PNEUMATIC HEELS. - Google Patents

Abstract

Improvement brought to tire beads. This improvement consists in coating the outer surface of the bead wire with a mixture having a vulcanization rate lower than that of all the other mixtures included in the structure of the bead wire, so that at the end of a semi-treatment Appropriate vulcanization, the bead is compacted internally but its outer surface is still almost raw and therefore in possession of the chemical and physical characteristics necessary to achieve good adhesion on the elements which will then be assembled to the bead during the tire building process . The vulcanized bead according to the invention behaves like a single monolithic structure, which makes it possible to improve the duration and the behavior on the road of the tire.

Description

The present invention relates to pneumatic

  for motor vehicles and it concerns more

  particularly the heels of these tires, that is to say the two radially innermost annular portions of the carcass, which serve to establish the connection between the

  pneumatic tire and the corresponding mounting rim

  anchor this tire on this rim; the invention relates more particularly to the annular elements of

  reinforcements that stiffen these heels and make them inexistent

  tensile in the circumferential direction.

  The fundamental importance of these tire areas

  is well known to those skilled in the art. Indeed, the heels condition in a preponderant measure the duration

  and the on-road performance of the tire in service

  everything in the case of tires for heavy road transport. It is universally known that tire heels are reinforced by annular elements

  circumferentially inextensible metals, usually

  rods. A well-known example of a bead wire is

  the one consisting of several turns of

  choked, juxtaposed and parallel to each other, which are grouped together

  laid in several layers superimposed radially so

  to constitute a quadrangular section packet.

  More recently, there has been a major breakthrough of another type of rod which comprises a metal ring core, of hexagonal cross section, whose base is inclined 150 on the axis of the rim and which is composed of coils juxtaposed with round or flat wire, a type that is used in giant tires

of the type without room.

  In this case, the section of this soul is

  smoothly rounded with rubber tongues to facilitate the overturning of carcass plies around the bead during the making process and more

  precisely, during the conformation phase of the tire.

  Indeed, the web or plies of the carcass of the tire must have their ends turned around the rods so as to be firmly anchored to these inextensible elements. It is only on this condition that the carcass is able to withstand the tensile forces that are exerted on the reinforcing cords

  tablecloths by conformation and vulcanization pressure

  during the tire preparation procedure.

  Whatever the size and section of the rods has always been found, especially for

  the rods with polygonal section, that the efforts

  inside the heel structure during the vulcanization phase result in deforming the section of the bead wire, which then takes an irregular shape, to

  approximately in diamonds, this results in a modification

  of the global geometry of the section of the heel

  by the characteristics of the project.

  In the prior art a large number of different solutions have been tried to thwart this

  phenomenon by giving transversal rigidity to the

  rods. Among other things, a technology that has proved particularly effective is to subject the rod to a semivulcanization, possibly after

  wrapped the latter with a rubberized fabric, dis-

  placed in wrapping or helix on all its development

  circumferential, before using the rod during the pro-

  manufacture of the carcass of the tire.

  Unfortunately, this operation presents a

  serious inconvenience. More specifically, the semi-vulcanization process

  canisation deprives the exposed elastomeric portion of the bead wire, that is to say the outer surface of the bead wire, made of rubberized threads, or the outer surface of the eventual coating of the rod of its adhesiveness and certain

  chemical characteristics of raw rubber, which are necessary

  to ensure adhesion and weldability on the

  other components of the carcass, thus making it more

  and more difficult the establishment of a chemical or physical connection between the rubber of the rod and that of

  other constituents during the rest of the process of con-

perfection.

  It is therefore essential to submit the trin-

  thus semi-vulcanized gels to a subsequent solution wiping treatment in order to restore at least this semi-product the mechanical characteristics of adhesiveness required, since the chemical characteristics do not

can no longer be restored.

  This accessory operation, that is to say the painting rods dissolution is a delicate phase of the tire making process because of the consequences that a poor performance of this phase can have on the quality of the finished tire, without

  count the significant expense of time or the economic impact

  significant impact of this operation.

  The object of the invention is to create a new type of tire carcass heel rod that can be semi-vulcanized without losing its external surface.

  its weldability and stickiness characteristics,

  that the rod can be used immediately after

  semi-vulcanization without requiring intermediate operations.

  The subject of the invention is therefore a tire for vehicle wheels comprising a tread, flanks and heels for anchoring the tire to the corresponding rim, these beads being reinforced with an annular reinforcing structure, this tire characterized in that said annular reinforcement structure comprises

  a metal ring core, circumferentially inex-

  tensible, a first layer or layer of compaction, made

  of a first mixture and placed in contact with said soul

  and a second layer, or coating layer, which completely encloses the first layer and said core and which is made of a second mixture, the vulcanization rate of this second mixture being lower than that of the first mixture. It should be indicated now that the term "vulcanization speed" refers to the speed with which a mixture changes from the uncured or uncured state, which is distinguished by the predominance of the plasticity characteristics, to the vulcanized state, which is distinguished by the

  predominance of elasticity characteristics.

  This passage can be highlighted and

  detected by the gradual change in the value of cer-

  some parameters, for example the modulus of elasticity of the

  mixed; in this particular case, the speed of vulcanization

  can then be defined by increasing the

  value of the modulus of elasticity per unit of time.

  Anyway, this argument will be taken again

  in more detail in the following description.

  To return to the subject of the invention, a first preferred embodiment, especially designed to be applied to tires of the type without

  chamber, comprises a soul composed of several

  juxtaposed and which has in cross-section a

  substantially hexagonal shape, the radially

  the interior of this section being inclined about 15 on the axis of said annular reinforcing structure, this

  soul being entirely wrapped in said first layer.

  This embodiment is still perfected

  the second layer or coating layer, which is constituted by a fabric of cords, reinforced with cords made of a material which is shortened by the effect of the

  heat, and which is rubberized using said second material

  lange, this second layer being wound on the first layer and on the soul in the form of a strip whose cords

  are arranged longitudinally and wound helically

  this along the entire length of the circumferential development of

  said annular reinforcement structure.

  In a very advantageous form, provision is made between said cord fabric and said first layer, in a radially outer position with respect to the core, a

  lenticular filling, made of a third metal

  while said cord fabric is coated, on its outer surface with respect to the core, with a sheet, preferably between 0.5 and 0.8 mm thick,

  third mixture which has a vulcanization speed indi

  than the second mixture.

  The third mixture, that of the filling,

  on the contrary, preferably has a vulcaniza-

  substantially equal to that of the first mixture.

  In all cases, said first layer, which is preferably between 1.5 and

  2 mm, is made of a mixture which, subjected to a heat treatment,

  at a temperature of not more than 1200 ° C., reaches a degree of vulcanization, defined by the variation curve of its elastic modulus, not less than 20% and preferably

  not less than 30%, with a duration of treatment not greater than

than 15 minutes.

  In accordance with what has been stated above,

  said fourth mixture, which has a vulcanization speed

  less than that of each of the other mixtures

  in the rod according to the invention, in particular

  when subjected to heat treatment at a temperature of

  of not less than 1200, reaches a degree of vulcanization, defined by the curve of variation of its elastic modulus, not more than 15% and preferably not more than 10% with a

  treatment time not less than 15 minutes.

  The figures of the annexed drawing, given as

  non-limiting example, will make clear how

vention can be realized.

  FIG. 1 is a diagram composed of vulcanization curves which serve for the definition of the speed

and the degree of vulcanization.

  FIG. 2 illustrates in detail a particular embodiment of the annular element according to the invention in its version for pneumatic type

without a room.

24684'73

  Figure 3 illustrates in detail

  cut of a tubeless tire bead, armed with

  annular reinforcing member of FIG.

  First, the quantitative significance of the vulcanization, semivulcanization, velocity and

  degree of vulcanization that have been used so far.

  It is known that elastomeric materials subjected to

  heat treatment, undergo an irreversible change

  certain of their physical and chemical characteristics

  nomic. For example, a typical characteristic is the passage of a mixture of the plastic state (raw mixture) to

  the elastic state (optimally vulcanized mixture).

  The change of certain characteristics

  can be related to variations in a given parameter when

  from a minimum value (taken for zero) to a value

  their maximum, which in some cases may be constant, that is to say, which no longer changes when the

heat treatment applied.

  It is thus possible to call the state reached by an elastomer composition during processing its degree of vulcanization and this degree can be indicated by relating it to the corresponding value of the chosen parameter.

  for guide, a value that is expressed as a percentage of

  range between the minimum and maximum values.

  So we say that a mixture is raw, half

  vulcanized or vulcanized depending on the degree of vulcanization achieved.

  The values that this parameter takes successively

  With the progress of the vulcanization, shown in a time-value diagram, it is possible to draw a curved line which graphically represents the appearance of the vulcanization of the elastomer composition as a function of time. The tangent, point by point, to this curve

  represents the rate of vulcanization of the elastic composition

  tomère at this point and can be expressed mathematically by the ratio of the increase in value of the guide parameter to the time interval on either side of the point

  considered, during which this increase takes place.

  As a first approximation, this speed

  depends on the temperature applied but, at the same time,

  temperature and other conditions of the heat treatment, it depends on the formula of the elastomeric composition,

  that is, the type and quantity of certain ingredients

  known as accelerators.

  FIG. 1 shows the qualitative diagram of one of these parameters and, more precisely of the elastic modulus, for three different mixtures A, B, C. The above diagram is established in the manner

  following: after setting two coordinate axes

  its rectangular dimensions, the abscissa

  the ordinates the absolute values of the elastic modulus, expri-

  eg, in mecapascals; these values can be

  easily determined by procedures and with the help of

  truments well known to those skilled in the art.

  After having fixed the conditions of

  temperature (and temperature of the applied pressure, eg constant temperature and atmospheric pressure),

  elastic modulus curve measured on the elastic composition

  mother at predetermined intervals of heat treatment.

  In fact, FIG. 1 is a consequential modification of the diagram just described in which, for the sake of convenience, values have been indicated instead.

  absolute, percentage values (which are more significant) than

  than the absolute values for the needs of the pre-

  description) using this way a single

  reading scale for the three mixtures, which facilitates

  the comparison between the three curves.

  This diagram is called a curve of vul-

  and represents the appearance of the variation of the vulcanization of the elastomer composition considered according to the conditions set: the material in question is called "vulcanized" when its degree of vulcanization has exceeded 90%; it is described as "raw" for a degree of vulcanization of less than 15% and is described as "half

  vulcanized "in the intermediate stages.

  In particular, in FIG. 1, at time t1 of the same heat treatment, the three mixtures A, B and C respectively reached vulcanization degrees of 5%,

15%, 37%.

  The slope of the vulcanization curve,

  its derivative, defines, as indicated above, the speed of vulcanization of a mixture in that, with a low slope (low speed), the time necessary to obtain complete vulcanization ( 100%) of the material

  elastomer with a given heat treatment is longer.

  By acting on the formula of the composition

  elastomer, it is possible to obtain mixtures which have differ-

  different speeds of vulcanization, naturally equal heat treatment; the solution of this problem, after fixing the desired behavioral characteristics, is within the reach of those skilled in the art and, in any case, leaves the

field of the invention.

  It is now possible to understand the meaning of previously fixed conditions

  the invention with regard to the degree of vulcaniza-

  (20%) and maximum (15%) respectively

  by the first mixture and the fourth mixture after a heat treatment whose conditions have been set (time

and temperature).

  Moreover, the thermal treatment men-

  tion, which serves to define the. boundaries of the area of protection

  of the invention, is not necessarily the semivulcanization treatment to which the raw rod will be subjected

  but it may be a different treatment related to

  effectively prepared, especially for the purpose of

  in the laboratory the response of mixtures to conditions

required.

  In any case, the respect of the conditions

  by this description for mixing the second

  layer guarantees the possibility of obtaining the results

  that is, at the end of the semi-vulcanization treatment

  the mixture constituting the outer surface of the rod is still substantially raw and therefore in possession of all the features necessary to achieve

  first of all a good adhesion (during the operation of con-

  fection) and then a solid chemical bond (during the

  carcass in the mold) together with the other

  Although this mixture is already chemically bonded to the inner part of the rod which is made compact and dimensionally stable by the semi-vulcanization treatment. We will now move to Figure 2 which shows

  in detail with an overview in perspective and with

  a hexagonal rod according to the invention in its

  pneumatic version of the type without chamber.

  If we first consider the essential elements

  of the structure, the annular reinforcing element,

  peeled higher rod, is constituted by a metal ring core C, circumferentially inextensible, composed

  several turns of wire suitably

  so that the soul has in cross section a hexagonal form

  gonale, the radially innermost side of the hexagon

  being inclined at an angle y of about 150 on the axis of the trin-

  and, therefore, on the axis of the tire (Figure 3).

  As is well known, in the technical art of

  it has been advantageously realized the soul, not in round wire

  circular section) but in flat wire with rectangular section

or polygonal.

  In contact with this soul, is planned a first

  layer 1 of compaction, made of a first mixture, and la-

  so-called soul as well as the first layer 1 are entirely

  enclosed in a second layer 2 made of a second

lange different from the first.

  We will now turn to the examination of the accessory elements of the structure. Between the compacting layer 1 and the coating layer 2 is interposed a profile 3, of lenticular section, made of a mixture different from that

  layers 1 and 2 and whose function is to increase the

  Another advantage of this invention is that the outer surface of the coating layer 2 is advantageously covered by a sheet 4 made of a mixture which in turn is different from the previous mixtures. In the rod just described, the compacting layer I fully encapsulates the metal core while the coating layer 2 is composed of a rubberized cord fabric reinforced with textile cords.

  which are preferably composed of a material which retracts

  under the effect of heat, for example, nylon. This weave

  su is used in the form of a strip 6 whose cords are arranged in the longitudinal direction, and which is wound helically, turns against turn, over the entire length

  circumferential development of the bead wire.

  According to the conditions laid down by the

  the minimum thickness of layer 1 is between 1.5 and 2 mm while the thickness of sheet 4 may vary

between 0.5 and 0.8 mm.

  Finally, with regard to the vulcanization rates, the mixing of the layer 2 is slower than that of the layer 1; the mixture 3 preferably has the same speed as that of the layer 1 while the mixture

  sheet 4 is slower than that of layer 2.

  The behavior of the rod according to the invention

  is now clearly understandable. Having agreed

  the correlations linking the velocities of vulva

  mixtures (ie the formulas of these

  langes) to the applied heat treatment (time-temperature), a semi-vulcanization process is carried out in which the layer 1 first reaches a non-negligible degree of vulcanization, at least greater than 20% (expressed by reference to the modulus elastic mixture of the mixture), this fluid layer first along the surface of the metal core, to round the corners and form around the core a substantially rounded section core and then tightening or compaction the soul in its shape of hexagonal section thus rendered indeformable. At the same time, the profile 3 also takes a

  degree of vulcanization no different from that of layer 1.

  The mixture of the layer 2, on the other hand being slower than the mixture of the previous layer 1, has

  every moment of the semi-vulcanization cycle a degree of vulca-

  lowering, so that the cords of heat-shrinkable material can take their state of tension around a

  already consolidated core, which has far-reaching consequences

  on the compactness and outer surface of the rod.

  This surface actually acquires a light form-

  wavy, helically shaped, similar to the threads of a

  as a result of the slight depression that the cords suffered

  radially towards. inside, with penetration into the

layer of the underlying nucleus.

  The Applicant has found that this aspect of the outer surface of the rod substantially promotes anchoring

  from the rod to the elements that come together, such as

  the carcass and the filling, which determines a

  improved heel quality.

  The semi-vulcanization treatment, applied to the rod described above, is continued until

  the mixture of layer 2 has also reached a level

* Semi-vulcanization enough to tighten against each other the cords of the fabric, which is precisely in a state of tension, taking care however to interrupt this treatment

  before the mixture of sheet 4 exceeds a degree of vulnerability

canalisation equal to 15%.

  It is therefore obvious that the next rod

  the invention made compact enough to easily resist

  the deformation efforts resulting from the following phases:

  of the treatment, however, has an outer surface in a still raw mixture (this mixture will subsequently vulcanize in the vulcanization mold of the tire) and which is

  consequently possessing all the Chinese characteristics

  the physical and physical properties required to have good adhesion and weldability on the other elements of

  carcass of the tire which will then be assembled with the trin-

  gle, that is to say (see Figure 3) the layers 7 of the car-

breakage and heel filling 8.

  Figure 3 also shows one of the

  usual reinforcement strips 9, placed outside-

  the returned part of the carcass ply.

  Although the invention has been described in

  detail above about a particular form of reali-

  of the rod, one can easily find various

  very different versions depending on the type of ring reinforcement precisely required by the type of tire (pneumatic tires for private or giant pneumatic vehicles, with a textile or metal casing, for road transport,

and for special uses).

  For example, in the usual rods of rubberized wire with quadrangular section, the

  layer 1 can be replaced by the actual scrubbing of the wire

  and layer 2 by a rubber sheet or tissue.

  which can be wrapped in wrapping as well as in

propeller around the rod.

  Similarly, in the rods having a non-rubberized wire core and coated with a laminated rubberized fabric, the layer 1 may be formed by

  the rubber of the fabric and the layer 2 by the ex-

TER AL.

  Furthermore, if, in certain types of rods, there is a filling between the metal core and the rubberized fabric, the layer 1 may be that of the

  filling and layer 2 that of the coating fabric.

  It is therefore obvious that, on the basis of the explanations which have been provided so far, the person skilled in the art will have no difficulty, from the point of view

  design, to develop the most cost-effective solution

geuse for him.

  As already indicated, the rods according to the invention have proved to be capable of effectively solving the problem proposed, while also bringing about new and significant improvements in the quality of the tires. Indeed, in the first place, the invention has remedied the intrinsic weakness of the connection between the surface of the semi-vulcanized bead and the surface of the filling of the carcass ply, which surfaces are

mutual contact between them.

  In tires of the known art,

  this connection is entrusted solely to the painting of dissolu-

  since semi-vulcanization has deprived the mixture of

  coating of the rod its ability to bind chemical-

  at the molecular level in combination with the other elements mentioned above, thus creating a zone of separation, almost a

  fracture between the rod and the adjacent elements, the trin-

  gle and these elements being glued to each other by the liquid

of dissolution.

  In the tire according to the invention, this

  chemical bond can be established on the contrary (during the

  of the tire) thanks to the presence on the

  the rod of a mixture which is still believed after the

  semi-vulcanization treatment, which is therefore sensi-

  in the same state as the filling mixtures

  and the carcass plies, which are not yet semi-

  vulcanized. A gradual variation in the degree of vulcanization (in the semi-vulcanized bead wire) is thus observed through the coating, from the outside of the bead wire inwards, this degree varying between a minimum value and

  maximum value, probably due to the fact that,

  In the semi-vulcanization treatment, there is a migration of the ingredients of the elastomeric compositions in contact, especially those which act most on the vulcanization rate, from one mixture to another through

  the contact surface and therefore a variation

  the characteristics of the mixtures in contact.

  In conclusion, in the tire according to the invention, the vulcanized heel behaves as a monolithic structure, unique and continuous and not as two structures (naturally exaggerated) which are stuck at the level of the mutual contact surface between the coating

  of the rod and the adjacent elements, which are the

wise and the ply of the carcass.

  Obtaining this excellent connection between the constituent elements of the heel which have been listed above has thus made it possible to optimize both the shape of the bead wire, giving it a greater section, its degree of compactness and the stability of the form conferred on it, by pushing the semi-vulcanization to a very high degree, unknown in the tires of the prior art. Indeed, the increase in the surface resulting from the increase in the volume of the bead wire no longer affects the quality of the bead in the negative sense, thanks to the optimum fixing between the constituent elements while

  that the greater indeformability of the semi-vulcanic rod

  (which manifests itself during the process of vulcaniza-

  tion of the tire, joined to the larger volume of this bead wire, has allowed the profile of the carcass plies and reinforcement strips to be changed around said bead, thereby relieving the tissue cords of the stress concentrations which are on the contrary present in the tires of the prior art, in particular at the edges of the annular metal core, concentrations which very frequently resulted in the ripment of said cords

  or the tearing of the mixtures surrounding the bead wire, with

consecutive truction of the heel.

  It goes without saying that modifications can be made to the embodiments which have just been described, in particular by substitution of technical means

  equivalent, without departing from the scope of the invention.

Claims (12)

R E V E N D I C A T IO N S   1.- tire for vehicle wheels comprising a tread, flanks and heels for anchoring the tire to the corresponding rim, these beads being reinforced with an annular reinforcing structure, this tire being characterized in that said structure   annular reinforcement comprises a metal annular core (C), cir-   conferringly inextensible, a first layer or compacting layer (1) made of a first mixture and placed in contact with said metal core and a second layer, or coating layer (2), which completely encloses the first layer and said core and which is made of a second mixture, the vulcanization speed of this second mixture being   less than that of the first mixture.   2. A tire according to claim 1, characterized in that said core (C) is composed of several metal turns juxtaposed and that it has in section   right a substantially hexagonal shape, the radial side-   the innermost part of the hexagon being inclined about 150 on the axis of the annular reinforcing structure and   the core being entirely embedded in said first layer (1).   3. A tire according to claim 1, characterized in that said second layer (2) or layer of   coating, comprises a woven fabric (5) reinforced with   wheats made of a material which is shortened by the effect of   heat, and which is rubberized with the aid of said second   ge, this second layer being wound on the first cou-   in the form of a strip (6) whose cords are available   longitudinally and which is helically wound on all   the length of the circumferential development of said structure annular reinforcement.   4.- tire according to claims 2   and 3, characterized in that it comprises a lenticular-shaped filling made of a third mixture, interposed between the first layer and the second layer, in a   radially outer position relative to said core.   5.- tire according to claim 4,   characterized in that the vulcanization speed of the third   second mixture is substantially equal to that of the first   lange. 6. Pneumatic tire according to claim 3,   characterized in that the second layer or coating layer   ment is provided, on the surface e: dull with respect to the donkey,   of a leaflet made of a fourth mixture, the speed of vul-   of the fourth mixture being lower than that of the second mixture.   7. A tire according to claim 6, characterized in that said fourth mixture, when subjected to a heat treatment at a temperature below 120, reaches a degree of vulcanization, defined by means of   of the variation curve of its elastic modulus, not greater than   less than 15% for a duration of the said non-inferior at 15 minutes.   8. Pneumatic tire according to claim 7, characterized in that the degree of vulcanization is not greater than 10%.   9.- Pneumatic tire according to any one of   Claims 1 to 8, characterized in that the first   ge, subjected to heat treatment at a temperature not higher than 1200, reaches a degree of vulcanization, defined   by the variation curve of its elastic modulus, not less than   less than 20% for a duration of treatment not exceeding 15 minutes.   10. A tire according to claim 9, characterized in that said degree of vulcanization is not less than 30%.   11.- Pneumatic according to any one of   preceding claims, characterized in that the thickness   minimum of the first layer is between 1.5 and 2 mm.   12.- Pneumatic tire according to any one of   Claims 6 to 11, characterized in that the thickness of the   sheet of fourth mixture is between 0.5 and 0.8 mm.