Description

Technical Field

[1 ] The invention relates to a steel bead core for pneumatic tyres, more

particularly, a steel bead core with stable profile, and limit the fretting between carcass ply and bead.

Background Art

[2] A pneumatic tire generally comprises a crown that comes into contact with the ground and, on either side of the crown, a sidewall the inner edge of which, intended to be supported by the rim of a wheel, is formed by the bead. The bead has among its components at least one bead core. The latter fulfils various functions. It serves in particular as anchorage for the ply or plies forming the carcass of the tire and withstands the forces exerted on it by the carcass under the effect of the inflation pressure and the deformations resulting from the travel of the tire. The bead core also serves to ensure the transmission of longitudinal forces and, in the case of tubeless tire, to ensure a seal between the tire and the wheel rim.

[3] Prior art US3949800 discloses a tire having beads provided with package cores around which the carcass reinforcement ply or plies are wound. The bead comprises at least one package bead core of one or more wires having a quadrilateral section with at least two parallel opposite sides to improve the stability of shape. The category of quadrilaterals having at least two parallel opposite sides comprises rectangles, squares, diamonds, parallelograms, trapezoids and isosceles trapezoids.

[4] Prior art US4166492 further discloses a bead core having a substantially parallelogram-shaped cross section, in which the individual wires in the wound wire ply are juxtaposed in the same plane extending substantially axially of the bead core, and the planes of the individual wire piles which are closely superposed are mutually radially displaced with respect to one another. The stability of the cross-sectional shape of a bead core formed of individual wires of rectangular cross-section is improved.

[5] Although the beads possibly comprise an insert of stuffing rubber, and the bead cores possibly have a sheathing or covering of rubber, fretting happens between the carcass ply and bead under the complex transverse and longitudinal forces during utilization of the tire. The sharp edges of the bead core may cut through the sheathing rubber, and metal to metal fretting occurs between carcass ply reinforcement and bead core.

[6] Prior art DE8033602U discloses a bead core wherein the two edges at the two corners connecting the inner surface of the bead core are round.

Although the two round edges reduce the fretting between carcass ply reinforcement and bead core, the fretting at the corners connecting the outer surface of the bead core still occurs under the complex transverse and longitudinal forces during utilization of the tire.

Disclosure of Invention

[7] The primary object of the invention is to provide a steel bead core with

stable profile and limit the fretting between carcass ply and bead.

[8] The second object of the invention is to provide a steel bead core with

simple structure and easy to make.

[9] According to present invention, a bead core comprises at least one metal wire having a cross section of a quadrilateral with two parallel opposite faces, the at least one wire forming adjoining multiple windings through the bead core, the adjoining windings making metal-to metal contact with each other along their facing surfaces, wherein the edges at the four corners of the bead core are round to decrease fretting. The round edge means on the cross-sectional view of the bead core the profile of the corner is a curve without sharp angle. The radius of the round edges of the bead core is between 0.3mm and 1 .6mm. Here a winding means a loop of metal wire, and multiple windings are radially superposed loops of metal wire.

[10] According to present invention, a bead core has a substantially

parallelogram-shaped cross section, the individual wires in the wound wire ply are juxtaposed on the same line extending substantially axially of the bead core on the cross sectional view, the individual wire plies which are closely radially superposed are mutually axially displaced with respect to one another. The edges at the four corners of the bead core are round to decrease fretting, and the radius of the round edges of the bead core is between 0.3mm and 1.6mm. Here a ply means a layer of individual wires which are juxtaposed on the same line extending substantially axially of the core on the cross sectional view. Mutally axially displaced means in the cross sectional view of the bead core, the plies of the individual wires are shifted over a step in the axial direction of the bead core to form a substantially parallelogram-shaped cross section.

[1 1 ] According to one embodiment, the wire forming the bead core has a

rectangular cross section with four round edges along the entire length of the wire, in order to form the four round edges of the bead core.

Alternatively, the wire has only round edges at the level of the four corners of the bead core. In the cross sectional view, the width of the wire is between 1 .5mm and 2.5mm. The thickness of the wire is between 1 .0mm and 1 .6mm. The radius of the round edges of the wire is between 0.3mm and 0.8mm.

[12] According to another embodiment, the edges at the two ends of the wound wire plies are round, wherein the juxtaposed multiple wires form a ply extending substantially axially of the bead core. The wire may be a flat wire with naturally rounded surfaces as a result of rolling by means of two rollers. Further more, the surfaces at the two ends of the wound wire plies are round, while the wires in between have rectangular cross section.

Brief Description of Figures in the Drawings

[13] Figure 1 illustrates a cross sectional view of a bead core according to

present invention.

[14] Figure 2 illustrates a cross sectional view of a bead core according to

present invention.

[15] Figure 3 illustrates the cross-sectional changes at different positions on the same wire.

[16] Figure 4 illustrates a cross sectional view of a wire having rectangular cross section with four round edges.

[17] Figure 5 illustrates a cross sectional view of a wound wire ply, wherein the edges at the two ends of the ply are round.

[18] Figure 6 illustrates a cross sectional view of a flat wire with naturally

rounded surfaces.

[19] Figure 7 illustrates a cross sectional view of a wound wire ply, wherein the surfaces at the two ends of the ply are round. Mode(s) for Carrying Out the Invention

[20] Figure 1 illustrates a cross sectional view of a bead core according to

present invention. The bead core 2 comprises nine metal wires 6 having a cross section of a quadrilateral with two parallel opposite faces. Each wire 6 forms adjoining eight windings through the bead core 2, the adjoining eight windings make metal-to-metal contact with each other along their facing surfaces. The edges 10 at the four corners of the bead core 2 are round.

[21] Figure 2 illustrates a cross sectional view of a bead core according to

present invention. The bead core 2 has a cross-section which is in the general form of a parallelogram. The bead core 2 consists of eight radially superposed, and mutually axially displaced wire plies 4. Each ply 4, in turn, is formed of nine laterally adjacent individual wires 6 of substantially rectangular cross-section on the same line extending substantially axially of the bead core on the cross sectional view. The radially inner surface 8 of the bead core 2 is smooth and inclined at an angle a relative to the horizontal, wherein the angle corresponds to the angle of inclination of the inclined shoulder of the wheel rim. The individual wire plies 4 which are closely radially superposed are mutually axially displaced with respect to one another. The edges 10 at the four corners of the bead core 2 are round.

[22] The round edges 10 at the corners of the bead core 2 avoid the tension concentration at the corner and reduce the pressure on the sheathing rubber to maintain the cushion between carcass ply and bead to limit the fretting between carcass ply and bead. The four round edges 10 can be made by Turks head as disclosed in DE8033602U.

[23] Figure 3 illustrates the cross-sectional changes at different positions on the same wire 6 which is located at one end of the bead core. 3a shows the cross sectional view of the wire 6 at the first winding wherein the left- low edge is round. 3b shows the cross sectional view of the wire 6 at the intermediate windings, 2 ^nd to 7 ^th turns in Figure 1 and Figure 2, wherein the wire 6 has rectangular cross section. 3c shows the cross sectional view of wire 6 at the last winding wherein the left-up edge is round. If wire 6 is located at the other end of the bead core, the right-low edge of the first winding and the right-up edge of the last winding are round, while the other portion of wire 6 at the intermediate windings remains the

rectangular cross section. Under the control of PLC (program logic control), a series of Turks heads for different cross section profiles, can work systematically to produce a wire as illustrated in Figure 3.

[24] Figure 4 illustrates a cross sectional view of a wire 6 having a rectangular cross section with four round edges 12. W is the width of wire 6, T the thickness, and R the radius of the round edge 12. If wire 6 is used to make a bead core 2, the Turks head disclosed above to make the round edges 10 at the four corners of the bead core can be eliminated, because the wires 6 at the four corners of the bead core 2 already have round edges 12. Therefore, using pre-made wire 6 having a rectangular cross section with four round edges 12 may simplify the bead making process.

[25] Figure 5 illustrates a cross sectional view of a wound wire ply 4 comprising multiple wires 6, wherein the edges 10 at the two ends of the ply 4 are round. Compared with the bead core disclosed in prior art DE8033602U, bead core according to present invention not only has two round edges 10 at the two corners connecting the inner surface of the bead core, but also has two round edges 10 at the two corners connecting the outer surface of the bead core, which reduces the fretting between carcass ply and bead. The edges 10 can either be made by Turks head, or the wires 6 at the two ends of the ply 4 can be replaced with profiled wire 6 with round edges 12. Since the profiled wire 6 can be pre-made, the bead core making process can be simplified.

[26] Figure 6 illustrates a cross sectional view of a flat wire 6 with naturally

rounded surfaces. The flat wire 6 is also disclosed in WO90/12696A1 . If a flat wire 6 with naturally rounded surfaces is used to make a bead core 2, the Turks head mentioned above can also be eliminated, because each flat wire 6 at the four corners of the bead core 2 already has round surfaces 14 to avoid the tension concentration at the corner and reduce the pressure on the sheathing rubber to maintain the cushion between carcass ply and bead to limit the fretting between carcass ply and bead. Since the flat wire 6 can be pre-made by rolling process, the bead core making process can be simplified.

[27] Figure 7 illustrates a cross sectional view of a wound wire ply 4, wherein the surfaces 14 at the two ends of the ply are round while the wires 6 in between have rectangular cross section. The bead core according to figure 7 is more stable than that of figure 6, because the wires 6 in between have rectangular cross section to have more metal-to-metal surface contact to maintain the geometry of the bead core, while the two round surfaces 14 at the two ends of the ply can avoid the tension concentration and reduce the pressure on the sheathing rubber to maintain the cushion between carcass ply and bead to limit the fretting between carcass ply and bead. The round surface 14 can either be made by Turks head, or the wires 6 at the two ends of the ply 4 can be replaced with profiled wire 6 with round surface 14. Since the profiled wire 6 can be pre-made, the bead core making process can be simplified.

[28] The carbon content of the metal wire 6 is at least 0.70% by weight, e.g. at least 0.80% or at least 0.85%. The tensile strength of these metal wire 6 is at least 1800N/mm2, e.g. at least 2200N/mm2. Other contents of metal wire 6 for bead core 2 may be a manganese content between 0.40% and 0.70%, a silicon content between 0.10% and 0.35% and maximum sulphur and maximum phosphorus content of 0.04%, all percentages being percentages by weight. However, the presence of other element is not excluded.

[29] Usually the metal wire 6 is copper alloy, brass or bronze, coated to make a bead core 2. On one hand, the copper alloy coating on metal wire 6 can act as a lubricant to facilitate the wire drawing process or the profile deformation at Turks head. On the other hand, the copper alloy coating on metal wire 6 can promote the adhesion between bead core and adjacent rubber. Besides, the metal wire 6 can be coated with zinc. The zinc coating can be applied onto the wire by means of an electrolytic process or by means of a hot dip process, followed or not followed by a wiping operation in order to reduce the total weight of the zinc. Because of the presence of an iron zinc alloy layer that forms during the hot dip operation, the adhesion between the zinc coating and the wire is improved. Since zinc coating provides good corrosion resistance, zinc coating is preferred for bead wire rather than copper alloy coating.