GB1587575A

GB1587575A - Bead wire for tyre covers

Info

Publication number: GB1587575A
Application number: GB4770677A
Authority: GB
Original assignee: Euteco SpA
Current assignee: Euteco SpA
Priority date: 1976-11-19
Filing date: 1977-11-16
Publication date: 1981-04-08
Also published as: IT1123937B

Description

(54) BEAD WIRES FOR TYRE COVERS (71) We, EUTECO S.p.A., an Italian Joint Stock Company, of 11, Via Galiani, Milan, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment The present invention relates to bead wires for pneumatic tyre covers.

Tyres currently known and used include a reinforcement called a carcase formed by plies whose cords are arranged in parallel in each ply. The carcases, which confer strength to the covering are generally either of crossply or radial type. Crossply tyres comprise a number (usually, but not necessarily, an even number) of plies in which the direction of the cords is alternately crossed when passing from one ply to the next. Radial tyres comprise one or more radial plies, arranged that is, in such a way that the cords of each individual ply lie in planes passing through the tyre's axis of rotation or at a small angle thereto.

There are also reinforcements in which the cords of the plies, extending from bead wire to bead wire, have an arrangement which is in part typical of a crossply carcase and in part typical of a radial carcase.

In the case of all carcases described, the plies are anchored to the beads, which are in contact with the rim of the wheel, to resist the internal inflation pressure. Thus the plies are folded over metal rings (called bead wires) which are inextensible, or nearly inextensible, and which themselves comprise an independent reinforcement, incorporated in the beads of the tyres. In summary the bead wires have the function of anchoring the carcase plies and of rendering the beads sufficiently inextensible to hold the covering onto the wheel rim.

Various types of bead wires are currently known and used, which may be grouped into the following three categories: braided type bead wires; single wire pack bead wires; -wire belt pack bead wires.

Braided bead wires are generally constituted by a circular core formed by a ring of steel wire, or cord of other metallic material, with welded ends and by one or more steel wires wound helically onto said core, to form a number of helices lying adjacent to one another covering the core itself. Such bead wires have a substantially circular section.

Single wire pack bead wires are obtained commencing with a steel cord, as such, or previously rubberized by drawing through an appropriate composition comprising elastomers, filler and vulcanizing agents.

The wire, rubberized or not, is turned round a pulley template so as to form a predetermined number of circular, or substantially circular, turns, lying adjacent one another such as to give a bead wire of the desired section such as for example a rectangular, hexagonal or parallelogram form, with parallel or sloping base in regard to the rotation axis.

Wire belt pack bead wires are formed commencing with a flat belt of two or more wires lying side by side, usually each rubberized by drawing. The bead wire is obtained from this belt by spiral turning to produce a plurality of turns, until the final desired section is attained. In this way a predetermined number of wires is used depending on the strength it is intended to confer on the bead wire. The resulting bead wire section may be square, rectangular or of parallelogram form.

This last type of bead wire is that used today in the majority of cases especially because of its simple and rapid manufacture and it also offers the advantages relating to low cost.

In these known methods generally wires of solid circular section having a diameter of from 0.8 to 4 mm are used.

The single wire pack bead wires or wire belt pack bead wires provide the advantage of low cost, but also present a number of disadvantages. In fact, the bead wires tend to have an excessive rigidity against transverse bending, that is when they are flexed relative to the plane in which the ring formed by the bead wire lies. This gives rise to disadvantages at the time of mounting the covering onto the rim when the beads of the covering and thus the bead wires are subjected to a transverse flexing to pass over the edge of the mounting rim.

The rigidity on the one hand makes the mounting operation laborious, and on the other than can cause permanent deformities in the bead wire and thus in the bead. It is not uncommon for breakage of the bead wire to occur.

Moreover the bead wires have a tensile strength which, in relation to the steel section contained in the bead wire, is only partially used and its value increases relatively little over a certain number of turns of the single wire or of the belt of wires.

In other words the tensile force exercised on the carcase plies placed in tension by the internal pressure of inflation, is normally borne by the turns placed in radially innermost position and to a far lesser degree by the outer turns. As a consequence the layers of wire turns forming the bead wire hardly cooperate with one another on account of the low extensibility of the steel wire at the working loads per unit area to which it is subjected.

Such disadvantages are absent, or substantially absent, in the braided type bead wires owing to their elastic characteristics.

Braided type bead wires in fact render easier the assembly of the covering onto the rim, permanent deformities do not arise and better advantage may be taken of the strength of the wires contained in the bead wire section. However braided type bead wires have not as yet had a wide application in the art; this is in view of their high costs.

According to the present invention there is provided a bead wire for reinforcement of a bead of a pneumatic tyre cover which bead wire is in the form of a ring comprising at least two turns of one or more metal reinforcement cords, the or each metal reinforcement cord consisting of a plurality of wires wound together and about each other.

The bead wire of the present invention is of the pack type but may be endowed with characteristics of high flexibility and strength compared with conventional pack type bead wires. in particular the bead wire according to the present invention can have mechanical characteristics equal to or superior to those of braided type bead wires and can be constructed in a simple and rapid manner similar to the pack type bead wires.

The bead wire according to the present invention can thus be obtained by turning a single metal reinforcement cord as defined or a plurality of parallel metal reinforcement cords (a belt of two or more cords) at least twice around a pulley template in the same way and on the same apparatus as for conventional type bead wires. The pulley template can have a cylindrical or frusto conical outer surface possibly fitted with a groove of required section. Thus there can be obtained a ring containing in its overall section a total number of cords depending on the strength of the cords themselves and on the total tensile strength desired for the bead wire.

The metal reinforcement cords may be of steel or other metallic material. Each cord comprises at least two wires of appropriate diameter wound together with a pitch, the value of which will be discussed later.

The wires forming each cord may have the same diameter or at least one may have a different diameter from the others.

Whether a single cord or a belt of two or more cords is being used the cord or cords may be coated with a non-vulcanised elastomer compound joining adjacent turns as in conventional rubberising systems.

The base of the bead wire, that is the innermost layer of turns (in the case of a construction with a single cord) or the innermost belt turn may be of cylindrical configuration to give an inner cylindrical surface coaxial with the axis of rotation, or may be of frusto conical configurtion such that the inner bead wire surface is inclined with respect to the axis of rotation.

The bead wires of the present invention may be used to anchor cross, radial or mixed type carcase plies.

The invention accordingly also provides a pneumatic tyre cover wherein both beads comprise a bead wire according to the present invention.

Suitably the metal reinforcement cord used is formed by two or more wires of from 0.15 to 1.5 mm, in diameter, wound together with a pitch of from 2 to 60 times the diameter of the wire.

According to a preferred embodiment of the present invention steel cords are used formed by from two to four wires wound together, each wire having a diameter of from 0.3 to 0.6 mm and the pitch being of from 20 to 50 times the diameter of the wires themselves.

The bead wire according to the present invention offers unexpectedly high qualities of flexibility and confers on a covering containing it, better characteristics of uniformity in the sense that a motor vehicle on which are mounted coverings having bead wires according to the present invention offers fewer vibrations and in consequence fewer geometric imperfections in the coverings themselves.

The fewer geometric imperfections prob- ably derive from the fact that the flexibility qualities of the bead wires of the present invention enable, during the moulding of the tyre, better uniformity to be achieved in the arrangement and tension of the wires forming the body.

It is also noted that in coverings of the "tubeless" type fitted with bead wires according to the invention, displacement of the bead is minimised in its correct mounting seating on the rim, even with very reduced pressures of inflation in relation to the normal value. This increases the safety of such coverings in the case of slow and progressive deflation owing to small perforations or air losses.

The coverings may contain two or more bead wires in each bead and said bead wires may have a cylindrical or frusto conical base and have an internal diameter equal to or different from one another.

According to one embodiment of the same covering there are used at least one bead wire with a cylindrical base and at least one bead wire with a frusto conical base, the internal diameter of the bead wire with cylindrical base being less than that of the bead wire with the conical base, the internal diameter of the latter being the smaller of the diameters that may be measured at its ends widthwise.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section showing a bead wire of the braided type known in the art; Figure 2 is a partial cross-section showing the manufacture of a single wire pack bead wire by turning a single steel wire onto pulley; Figure 3 is a cross-section through a known belt pack bead wire; and Figure 4 is a cross section through a bead wire according to the present invention.

The bead wire of the braided type known in the art shown in Figure 1, comprises a core 1 composed of a wire having a diameter of, for example 1.55 mm, and of outer wires 2 having a diameter of 1 mm. Each of the outer wires 2 is wound helically around the core until to cover the core itself with helices lying side by side. In this manner a layer or crown is formed which in the example shown has seven wires.

The known pack bead wire shown in Figure 2 is obtained by starting from a single steel wire 3, of solid circular section, turned in a number of turns of as many times as there are intended to have wire sections in the overall section of the bead wire.

In the case in question a wire of 1.42 mm diameter is used, turned 19 times onto a pulley having a conical based groove 4 at its edge tilted at an angle equal to 15", in relation to the rotation axis XX' and having two walls 5 and 5' which contain the wire and confer the desired section to the bead wire.

The known pack bead wire shown in Figure 3 is obtained by starting from a belt of four wires each indicated by 6, having solid circular section, in which the wires forming the belt have been rubberized by drawing through an appropriate nonvulcanized elastomer composition, by means of a drawing head of rectangular form, being of such width as to allow a certain spacing between the wires and of slightly greater height than the diameter of the wires themselves.

According to what is shown in the Figure 3 the belt is formed into four turns to give sixteen wires in the overall section of the bead wire. In the case in question the individual wires have a diameter of 0.94 mm.

In the embodiment of the bead wire according to the present invention, shown in Figure 4, the arrangement is similar to that in Figure 3, that is of the wire belt pack type, and is formed by a belt of four cords, shown as 7, of three turns, to give twelve sections of cord in the overall section of the bead wire.

In the bead wire of Figure 4 each cord 7 is itself formed by four wires which in the specific case are wound together with an 18 mm pitch, each individual wire having a diameter of 0.45 mm.

In this case also the belt of cords is rubberized, by drawing, with a rectangular overall section and such as to leave a certain spacing between the cords along the greater side, the height also being slightly greater than the diameter of the cord itself.

In like manner it is possible according to the invention to obtain a bead wire similar to that of Figure 2 but using, in place of the circular section steel wire, a cord composed of two or more wires, of equal or different diameter to one another, wound together.

The advantages of the invention will now be further explained with reference to the following examples.

Example I A typical bead wire of the prior art of the solid circular section wire belt pack type for 165 SR 13 coverings was formed from belts of 4 wires by 4 spiral turns of said belt.

Said 4 x 4 formation, section of the bead wire comprised 16 wires in all.

Diameter of the elementary wires: 0.94 mm Section of the elementary wire: 0.693 mm2 Tensile strength of the wire: approxi mately 138 Kg.

Strength per unit area of the wire: approximately 200 Kg/mm2 Theoretical strength of the bead wire: 138 x 16 = 2210 Kg Practical strength of the bead wire with breaking point when applying a uniform force in radial direction on the base coil: approximately 1750 Kg.

Coefficient of use in the total steel section present in the bead wire: approximately 0.8.

Weight of wire: 5.44 gr/metre.

Weight index number of the steel in the bead wire: 5.44 x 16 = 87.04.

Example 2 A bead wire acording to the invention of the wire belt pack type for the 165 SR 13 coverings mentioned above was formed from a belt of 4 cords with 3 spiral turns of said belt. Every cord was formed of 4 wires with a diameter of 0.45 mm and wound with an 18 mm pitch. The 4 x 3 formation give a section of the bead wire containing 12 cords in all.

Section of the elementary wires of the bead wire: 0.158 mm2 Section of the cord: 0.158 x 4 = 0.632 mm Tensile strength of the cord: 158 Kg.

Strength per unit area of the section: 158/0.632 = 250 Kg/mm2 Theoretical strength of the bead wire: 158 x 12 = 1896 Kg Practical strength of the bead wire (calculated as in Example 1): approximately 1765 Kg Use coefficient of the total steel section in the bead wire: approximately 0.93 Weight of the cord: 5.20 gr/metre.

Weight index number of the steel in the bead wire: 5.20 x 12 = 62.4.

By comparing the data it is seen that the use of the cord in Example 2 of elementary wires with a diameter less than that of the single wires in Example 1, enables one to obtain in Example 2 a higher strength per unit area, that is 250 Kg/mm2 or more in comparison with a maximum of 200 Kg/mm2 obtainable with single wires normally adopted for bead wires. Moreover, in the case of Example 2 the use coefficient of the steel section of the bead wire is much better; this is attributable to the relatively high elasticity of the cord in relation to the single wire, a fact which enables the various layers of the bead wire to cooperate better together.

To summarise, by operating according to the present invention a saving is made in the weight of the steel used and in particular the index number 62.4 in Example 2, when compared with the value of 87.04 in Example 1, shows a saving of approximately 28%. Finally a bead wire configuration with three turns, rather than four, makes for more speed in the preparation of the bead wire itself.

All these factors added together compensate for the higher cost of the bead wire which derives from the use of a cord rather than a simple drawn wire. In each case the attendant advantages described above render the bead wire of the present invention far more preferable.

WHAT WE CLAIM IS:- 1. A bead wire for reinforcement of a bead of a pneumatic tyre cover which bead wire is in the form of a ring comprising at least two turns of one or more metal reinforcement cords, the or each metal reinforcement cord consisting of a plurality of wires wound together and about each other.

2. A bead wire according to claim 1 wherein the ring is formed of a plurality of turns of a single metal reinforcement cord.

3. A bead wire according to claim 1 wherein the ring is formed of a plurality of turns of a belt of two or more metal reinforcement cords.

4. A bead wire according to any one of the preceding claims wherein each metal reinforcement wire has a diameter of from 0.15 to 1.5 mm.

5. A bead wire according to any one of the preceding claims wherein all the metal reinforcement wires are of the same diameter.

6. A bead wire according to any one of claims 1 to 4 wherein at least one of the wires of the or each metal reinforcement cord has a different diameter from the others.

7. A bead wire according to any one of the preceding claims wherein the wires forming the metal reinforcement cord are wound together with a pitch of from 2 to 60 times the diameter of the wires themselves.

8. A bead wire according to any one of the preceding claims wherein the metal reinforcement cord or cords are coated with a non-vulcanised elastomer composition which joins adjacent turns.

9. A bead wire constructed and arranged substantially as herein described with reference to Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mately 138 Kg. Strength per unit area of the wire: approximately 200 Kg/mm2 Theoretical strength of the bead wire: 138 x 16 = 2210 Kg Practical strength of the bead wire with breaking point when applying a uniform force in radial direction on the base coil: approximately 1750 Kg. Coefficient of use in the total steel section present in the bead wire: approximately 0.8. Weight of wire: 5.44 gr/metre. Weight index number of the steel in the bead wire: 5.44 x 16 = 87.04. Example 2 A bead wire acording to the invention of the wire belt pack type for the 165 SR 13 coverings mentioned above was formed from a belt of 4 cords with 3 spiral turns of said belt. Every cord was formed of 4 wires with a diameter of 0.45 mm and wound with an 18 mm pitch. The 4 x 3 formation give a section of the bead wire containing 12 cords in all. Section of the elementary wires of the bead wire: 0.158 mm2 Section of the cord: 0.158 x 4 = 0.632 mm Tensile strength of the cord: 158 Kg. Strength per unit area of the section: 158/0.632 = 250 Kg/mm2 Theoretical strength of the bead wire: 158 x 12 = 1896 Kg Practical strength of the bead wire (calculated as in Example 1): approximately 1765 Kg Use coefficient of the total steel section in the bead wire: approximately 0.93 Weight of the cord: 5.20 gr/metre. Weight index number of the steel in the bead wire: 5.20 x 12 = 62.4. By comparing the data it is seen that the use of the cord in Example 2 of elementary wires with a diameter less than that of the single wires in Example 1, enables one to obtain in Example 2 a higher strength per unit area, that is 250 Kg/mm2 or more in comparison with a maximum of 200 Kg/mm2 obtainable with single wires normally adopted for bead wires. Moreover, in the case of Example 2 the use coefficient of the steel section of the bead wire is much better; this is attributable to the relatively high elasticity of the cord in relation to the single wire, a fact which enables the various layers of the bead wire to cooperate better together. To summarise, by operating according to the present invention a saving is made in the weight of the steel used and in particular the index number 62.4 in Example 2, when compared with the value of 87.04 in Example 1, shows a saving of approximately 28%. Finally a bead wire configuration with three turns, rather than four, makes for more speed in the preparation of the bead wire itself. All these factors added together compensate for the higher cost of the bead wire which derives from the use of a cord rather than a simple drawn wire. In each case the attendant advantages described above render the bead wire of the present invention far more preferable. WHAT WE CLAIM IS:-

1. A bead wire for reinforcement of a bead of a pneumatic tyre cover which bead wire is in the form of a ring comprising at least two turns of one or more metal reinforcement cords, the or each metal reinforcement cord consisting of a plurality of wires wound together and about each other.

10. A pneumatic tyre cover wherein both

beads comprise a bead wire as claimed in any one of the preceding claims.

11. A pneumatic tyre according to claim 10 wherein each bead comprises at least two bead wires whose inner surface is cylindrical, the bead wires having the same or different diameters.

12. A pneumatic tyre according to claim 10 wherein each bead comprises at least two bead wires, one bead wire having a cylindrical inner surface and the other bead wire having a frusto conical inner surface.