GB2081763A

GB2081763A - Reinforcement cord for elastomers

Info

Publication number: GB2081763A
Application number: GB8113498A
Authority: GB
Original assignee: Trefilarbed SA
Current assignee: Trefilarbed SA
Priority date: 1980-08-12
Filing date: 1981-05-01
Publication date: 1982-02-24
Also published as: FR2488626A1; AU7043581A; LU82707A1; FR2488626B1; DE8029762U1; DE3042031A1; BE886238A; CA1146839A

Abstract

A wrap wire 4 is wound around a substantially flat bundle of three main wires 1-3 which may cross one another at points spaced along the bundles. <IMAGE>

Description

SPECIFICATION Reinforcement cord for elastomers The present invention relates to a cord which is to be embedded in an elastomer in order to reinforce the elastomer. Such cord is most often referred to as tyre cord and is used in tyres, inner tubes, and conveyor belts, for example.

Tyre is normally formed of three to five separate wires that are helically twisted together. It is standard practice to use brass-plated steel wire in order to increase the bond between the wire and the elastomer in which it will be embedded.

Normally very fine steel wires are used, having diameters between 0.1 mm and 0.40 mm. These wires are wound together like standard cable and then embedded in the elastomer which they are to reinforce. Such cord is subjected to considerable tension, bending stress, and axial compression as well as inner wear, corrosion, and metal fatigue. In fact the environment in which such cord is used is normally very hostile.

It has been suggested that the best way of decreasing the deleterious effects on the reinforcing cord is to embed it as thoroughly as possible in the elastomer. Thus it has been suggested in U.S. patents 4,022,009 and 4,030,248 to make the cord as open as possible so that the elastomer in which it is embedded will be able to directly contact as much of the surface of the wire as possible. In accordance with these patents several main wires are wound together in parallel line contact with each other in a helix, without twisting one wire about another, and another wrap wire is wound around these main wires in a helix of identical hand, but lying on the inside of the helix formed by the main wires.

Such a solution has given some advantages over the normal relatively solid wire. Nonetheless the centre wires of the main helix of such a cord are frequently almost completely out of contact with the elastomer in which the bord is embedded.

As a result some of the above-described problems of such cords are encountered by this improved cord.

What is desired is a tyre cord, whose use is of course not exclusively limited to tyres, which allows each and every wire of the cord to be embedded in an elastomer with virtually no surfaces of the wires out of contact with the elastomer.

The present invention provides a reinforcement cord having three generally parallel and coplanar main wires which extend longitudinally as a group in merely linear contact with one another, and a wrap wire similar to the main wires and wound around the group of main wires.

With this arrangement, therefore, the wires will have virtually all of their surfaces exposed for direct contact with the elastomer in which they are to be embedded. Thus transmission of tension between the wires and the elastomer is maximized, while protection of the wires both from corrosion and from rubbing on one another is minimized. At the same time the full tensile strength of the wires will be fully effective when the cord is embedded in an elastomer.

Preferably, in a given length of the cord, the wrap wire has a length which is at most 3% more than that of the main wires, i.e. the wire is wound at a very steep pitch. Two of the main wires may cross each other periodically. Thus the cord is a relatively loose bundle which, nonetheless, has all of the longitudinal tensile strength of the prior-art cords of more compact construction. Such cord is normally supplied ready-made on spools to the manufacturer of tyres, conveyor belts, and other reinforced elastomeric articles. The individual wires are also normally of the prestretched steel type of great tensile strength.

Preferably, all four wires of the cord are of identical material and diameter. The diameters preferably lie in the range of 0.10 to 0.40 mm.

The cord is normally straight and free of internal tension in unstressed condition. Thus the production of calandered inserts for radial tires is a relatively easy procedure with the cord according to the invention.

If one of the main wires is periodically crossed over one or both of the other main wires, any minor differences in length or composition of the main wires can be compensated out. During construction the wrap wire is normally pressed into tight permanent contact with the main wires, so as to be somewhat plastically deformed in its wound condition therearound. As a result the cord is mechanically extremely stable both when longitudinally stressed or unstressed.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figures 1, 2, and 3 are cross-sections through conventional cords; Figure 4 is a side view of the cord shown in Figure 2, on a reduced scale; Figure 5 is a cross-section through a cord according to the invention; and Figure 6 is a perspective view of the cord of Figure 5, on a reduced scale.

As shown in Figures 1, 2, 3, respectively, it is standard practice to form a wire cord of 3, 4, or 5 wires twisted in a tight helix as shown in Figure 4 for the four-wire cord. With such cord constructions it is obvious that the elastomer in which such a cord is to be embedded will hardly be able to contact all of the surface of the wires.

Figures 5 and 6 show how a cord according to the present invention is formed of three identical steel wires 1 , 2, and 3 arranged side-by-side substantially in a common plane so that the middle wire makes straight-line contact with each of the outer wires. A fourth such wire 4 is wound with around the flat bundle formed by the main wires 1 to 3, at a pitch that is large compared with its diameter.

Figure 6 aiso shows how the wire 1 is crossed over the wires 2 and 3. The crossing of an outer wire over at least one of the other two main wires is repeated at intervals so that any variations between the main wires will be compensated for.

The crossing points are spaced apart by a distarice less than or equal to 15 cm. The wrap wire 4 has a pitch which is shorter than the distance between the crossing points of the main wires 1 to 3, so that the wrap wire 4 is twisted around the bundle of main wires at least once between each pair of adjacent crossing points.

The cord shown in Figures 5 and 6 is ideally suited for use in a calandered body such as an insert for a radial tyre. During such calandering the elastomerforming the insert will contact and bond to virtually all of the surfaces of all the wires 1 to 4. No central hollow space as is obvious in Figures 1 to 3 is formed by these wires 1 to 4, so that extremely good force transmission between the wires 1 to 4 and the body in which they are embedded is ensured. Furthermore, since the amount of contact between the wires 1 to 4 is minimai, the emount of wear resulting from the wires rubbing on each other is reduced to an absolute minimum.

Normally such cord is supplied to the tyre or other manufacturer in the form seen in Figures 5 and 6, but wound up on spools. Once the cord has been assembled on a standard cabling machine which can easily be adapted to produce the cord according to this invention, it is passed through rollers so as permanently to deform the wrap wire 4 into contact with the main wires 1 to 3.

Claims

1. A reinforcement cord for elastomers, the cord comprising a substantially flat bundle of three main wires, and a wrap wire wound around the bundle.

2. A cord as claimed in claim 1, in which the wrap wire has a length which is at most 3% more than that of the bundle.

5. A cord as claimed in claim 1 or 2, in which, at crossing points spaced along the bundle, one of, the main wires crosses at least one of the others.

4. A cord as claimed in claim 3, in which the distance between adjacent crossing points is at + most 1 5 cm.

5. A cord as claimed in claim 3 or 4, in which the wrap wire is twisted about the bundle at least once between each pair of adjacent crossing points.

6. A cord as claimed in any of claims 3 to 5, in which the axes of the main wires are coplanar between the crossing points.

7. A cord as claimed in any of claims 1 to 6, in which the wires are 0.1-to 0.4 rnm in diameters

8. A cord as claimed in any of claims 1 to 7, in which the wires are identical in diameter.

9. A cord as claimed in any of claims 1 to 8, in which the wires are of steel.

10. A reinforcement cord substantially as described with reference to, and as shown in, Figures 5 and 6 of the accompanying drawings.

11. An elastomeric body reinforced by a cord according to any preceding claim.