GB2203392A

GB2203392A - Radial tire reinforcement

Info

Publication number: GB2203392A
Application number: GB08808470A
Authority: GB
Inventors: Koji Takahira
Original assignee: Toyo Tire and Rubber Co Ltd
Current assignee: Toyo Tire Corp
Priority date: 1987-04-10
Filing date: 1988-04-11
Publication date: 1988-10-19
Anticipated expiration: 2008-04-11
Also published as: JPS63256782A; JPH044163B2; DE3811850A1; GB8808470D0; GB2203392B

Description

e X 241n23392 i "RADIAL TIRE m The present invention relates to a radial

tire reinforced with steel cords which are used for carcass plies, chafers; belts etc. and more particularly to an improvement in the construction of the steel cords.

Heretofore, there have been used the steel cords having the structure of 2 + 7 as shown in Fig. 3, 3 + 9 in Fig. 4 or 1 x 12 in Fig. 5.

Steel cords 3 of 2 + 7 in Fig. 3, however, having a core 6 composed of two filaments 4 twisted together as shown in the figures, the alignment of the filaments becomes vertical at one position in the lengthwise direction of the cords as shown in Fig. 3(A), while the alignment becomes lateral at another position as shown in Fig. 3(B). These alignments every 1/4 pitch. It results in that said composed of different portions having a flexural rigidity in the lengthwise of the cords." When said cords are applied the portions in a lateral alignment having a lower flexural rigidity are subjected to a concentrated fatigue breakage. Furthermore, outer filaments 5 which form an outer layer 7 are apt to close to a center over a circumscribed circle of the appear at cords are different direction to a tire 2 1k core 6 as shown in the figures by a solid line compared with a dotted line which illustrates an expected position. Accordingly, the difference of the flexural rigidity between the vertical alignment portions and the lateral alignment portions becomes larger, so there is a serious problem in the fatigue resistance. In. addition, all filaments of said cords being covered by rubber, residual air which is caught during tire formation is hardly passed away to the outside through the inside of the cords. Then a tire is manufactured with remaining air in the cords, so that the tire manufactured is subjected to an early failure due to the residual air.

Steel cords 3 of 3 + 9 as shown in Fig. 4 having a narrow space between adjacent outer filaments 5, the penetration of rubber into the cords is insufficient, so that the outer -filaments 5 contact with each other and wear out. It results in the deterioration of fatigue resistance.

Steel cords 3 of 1 x 12 as shown in Fig. 5 are composed of 12 filaments having a same diameter which are twisted in the same direction with the same pitch, so the outer filaments 5 -fit in surface depressions of a core strand 6 and thereby the penetration of rubber is hindered. Consequently, core filaments 4 are apt to be drawn out during a tire service.

As mentioned above, prior art steel cords have not been provided with balanced properties between the -2- uniform flexural rigidity and the rubber penetration property.

it is therefore an object of the present invention to provide a radial tire -reinforced with steel cords which have uniform flexural rigidity throughout the lengthwise direction of the cords and have a good rubber penetration property and further have a structure to eliminate the contact of outer filaments.

In accordance with the present invention, a sectional construction, twisting direction and twisting pitch of a steel cord are specified as set forth hereinafter to solve the problems in prior arts.

Excessive penetration of rubber into a cord causes the retention of air which is caught during tire formation. A tire produced with such steel cords causes an early separation failure. On the contrary, less penetration of rubber into a cord has filaments worn out due to the contact of filaments with each other, so the cord is likely fatigued and rusted. Therefore, it Is important to construct a steel cord so that the penetration of rubber may be well controlled by a preferable air permeability of steel cord whereby the retention of air is eliminated and an early separation failure is prevented.

In accordance with the above, a steel cord to be -3- used for a radial tire of the present invention is constructed as follows.

All filaments used in a cord are advantageously substantially equal in diameter. The core and alter layer are advantageously twisted in the same direction but with a different pitch. The core is composed of 3 to 4 filaments and the outer layer is composed of a number of filaments which is equal to or less than the number which is 5 greater than the number of core filaments.

Twisting both the core and the outer layer in the same direction can make a cross angle of the filaments small between the core and the outer layer, so contact pressure between the core and outer filaments is eliminated and thereby fatigue resistance is improved.

Twisting with a different pitch prevents the insufficiency of rubber penetration due to a structural defect caused by twisting them in the same direction with a same pitch as shown in Fig. 5. It is preferable that the outer -layer has- a -twisting- pitch larger that of the core. The m.st preferred ratio of the pitch of the outer layer to that of the core is 2:1 but a modified ratio of 3:2 may also be used. A modification of the pitch in the range of 50% is employable.

Composing the core with 3 to 4 filaments retains a proper air permeability. In case of two filaments, the difference of flexural rigidity occurs in the lengthwise direction and besides air is likely to remain due to the insufficiency of air permeability.

Z 1 1 1 In case of 5 f i laments, the center space of the core becomes too large, as shown in Fig. 6, to be filled with rubber, so it shows excessive air permeability and easily rusts.

Composing the outer layer with the number of f ilaments which is equal to or less than 5 greater than the number of the core filaments is based on the following reasons.

Gener41ly, the number of the outer filaments has previously been one greater than the number of the core f ilaments. The cord structure of 3 + 9 as shown in Fig. 4 is proper in this sense. But, as mentioned before, the penetration of rubber is insufficient. Accordingly, the present Invention employs the cord structure wherein the upper limit of the additional number is 5 in order to promote the rubber penetration.Consequently the cord structure in accordance with the present invention is 3 + 1, 3 + 2, 3 + 3, 3 + 4, 3 + 5, 3 + 6, 3 + 7. 3 + 8, 4 + 1, 4 + 2, 4 + 3, 4 + 4, 4 + 5, 4 + 6, 4 + 7, 4 + 8 and 4 +9.

By employing such a construction, penetration sufficient the rubber into the, steel cords is aade just to - eliminate - the. ret- ention of residual air caused by the insufficiency of air permeability due to excessive rubber penetration as well as an early separation failure caused by said residual air. On the other hand, the defects caused -5- 1 by the insufficiency of rubber penetration such as fretting wear between filaments, fatigue and occurrence of rust due to excessive air permeability are eliminated. Contact pressure between the core filaments and the outer filaments is diminished by twisting in the same direction, so contact fatigue is also eliminated. Uniform flexural rigidity in the lengthwise direction of the cords eliminates the occurrence of partial fatigue.

Accordingly a radial tire produced with the steel cords in accordance with the present invention is free from the residual air defects, fatigue and rust and consequently enjoy high durability and a long life.

in the accoinpanying drawings, - Fig. 1 is a cross-sectional view of one embodiment of the steel cords to be used for a radial tire in accordance With the present invention; Fig. 2 is a cross-sectional view of another embodiment of the steel cords for a radial tire in accordance with the present invention; Fig. 3 to Fig. 5 are cross-sectional views showing examples of prior art steel cords;

Fig. 6 is a cross-sectional view showing a comparative structure of a steel cord for comparison with the cord of the present invention.

The following embodiitents i.1lustrate the invention: Embodiment 1 Four types of steel cords are prepared. One is -6- 1 the steel cord in accordance with the present invention which have the cord structure shown in Fig. 1. Other three are prior art steel cords and comparative cords. Each structure is shown in Table

Cord mark A is a steel cord in accordance with the present invention which is composed of a core 1 of 3 filaments and an outer layer of 8 filaments, that is, 3 + 8 structure as shown in Fig. 1. Cord marks B and C are prior art steel cords of 3 + 9 and 2 + 7 as shown in Fig. 4 and Fig. 3 respectively. Cord mark D is a comparative cord of 5 + 6 illustrated in Fig. 6.

Table 1 cord mark A B C D structure 3+8xO.22mm 3+9x0.22mm 2+7x0.22am, 5+6xO.22mm direction of twist S S S S (core) direction of twist S S S S (outer) pitch of twist (MM) 6.0 6.0 6.0 7.0 (core) pitch of twist (MM) 12.0 12.0 12.0 14.0 (outer) 1 strength(kg) 110 120 90 110 rubber penetration 12 55 0 1260 (cc/min) fatigue resistance 156 100 129 76 rubber penetration:

In the center portion of a rubber piece of 50mm length a test cord is embedded. Compressed air of 2kgf /cm is introduced from one end and the flow of air is measured.

Smaller value indicates that a larger amount of rubber penetrates into the cords.

Fatigue resistance is indicated in the form of an index by setting the value of cord mark B to be 100.

Then radial tires of 11R 22.5 were prepared using the above steel cords for carcass plies. Comparative tests were conducted upon radial tires TA of the embodiment of the present invention and tires TB, TC, TD for comparison. Test results are shown in Table 2 wherein the value is indicated in the form of an index by setting the value of a comparison TB to be 100.

Table 2

Embodiment Comparison tire mark TA TB TC TD ply cord A B c D end counts (number/5cm) 28.4 26 34.6 28.4 defects of residual air 4 100 162 3 separation resistance 261 100 72 68 retention of strength 162 100 114 89 Defects of residual air were tested for 1000 tires respectively.

separation resistance:

Each tire was inflated with 7.5kg/cmpressure and a drum test was conducted at 10Okm/h speed with a load of JIS 100%. Running period of times was indicated in the form of an index.

-:8_ a retention of strength:

Each tire was mounted on a truck. After running of 100,00Okm, each tire was detached from the truck and disassembled to take out ply cords. Then strength was measured and compared with the strength before running.

As apparent from Table 1 and Table 2, the steel cords of this. embodiment(cord mark A) being preferable both in air permeability and rubber penetration, the radial tire of this embodiment(tire mark TA) causes less defects of residual air and also shows better results both in the separation resistance and in the retention of strength. Thus a highly durable tire is obtained by the present invention. On the contrary, comparison tires using the steel cords which are excessive or insufficient in the air permeability and the rubber penetration are inferior in durability.

Embodiment 2 Radial tires of 11R22.5 were prepared using the same steel cords as in Embodiment 1 for chafer cords. Durability of bead portions was tested and the results are shown in Table 3.

Table 3 tire mark CA CB cc CD cord mark A B c D end counts (number/5cm) 28.4 26 34-6 28.4 durability of beads 318 100 55 70 -g- durability of beads:

Each tire was inflated with 6.Okg/ca pressure and a drum test was conducted with a load of JIS 260%. The values are indicated in the form of an index by setting the running period of times of CB to be 100.

As apparent from the table. the comparison tire CC which used steel cords C having an excellent amount of rubber penetration inbluded the residual air during vulcanization of the tire and the durability is inferior. The comparison tire CD using steel cords D which permit excessive air permeability shows inferior results.

On the contrary, the radial tire CA in accordance with the present invention shows excellent durability.

Embodiment 3 Different steel cords were prepared as shown in Table 4.

Table 4 cord mark E F G structure 3+8xO.35mm 1x12x0.35am 2+7x0.35mm, direction of -S S twist (core) direction of S S S twist (outer) pitch of twist 10/20 20 10/20 core/outer (mm) strength (kg) 300 330 250 rubber 15 600 0 penetration(cc/min) fatigue resistance 216 79 100 a Radial tires of 120OR24 were prepared using the above steel cords for belt reinforcement. Test results are shown in Table 5.

Table 5 tire mark TE TF TG end counts (number/5cm) 24 22 29 durability of belts 328 35 100 reason for puncture slipping-off belt interruption of tube of core filaments separation of test Durability of belts was measured by a drum test with a load of JIS 200%. The values are indicated in the form of an index by setting the running distance of the comparison tire TG to-be 100.

Comparison tire TF using the steel cords P which are inferior in'. the rubber. penetration. caused slipping-off of a core filament. Another comparison tire TG using the steel cords G which are inferior in the air permeability caused belt separation which originated f rom initial separation at a portion containing a residual air. Besides in some cords, core filaments were broken at every Smm length which seems to be caused by thenonuniformity of the flexural rigidity in the lengthwise direction.

On the contrary, the radial tire TE in accordance with the present invention' improved durability while the drum interrupted by the puncture of tube. - 11- shows an test was t -1

Claims

we claim:

1. A radial tire reinforced with steel cords comprising a core and an outer layer, the core comprising 3 to 4 filaments and the outer layer comprising a number of filaments equal to or less than the number 5 greater than the number of the core filaments, the filaments being substantially equal in diameter and the core filaments and the outer filaments having a twist of the same hand but different pitch.

2. A tire reinforced with steel cords as claimed in claim 1, wherein the cord structure is 3 + 8 comprising 3 core filaments and 8 outer filaments.

3. A tire as claimed in claim 1 or claim 2, wherein the pitch of the outer layer is longer than that of the core.

4. A tire as claimed in any one of claims 1 to 3, wherein the ratio of the pitches of the two layers is 2:1.

5. A tire cord as specified in any one of claims 1 to 4.

6. A tire or tire cord substantially as hereinbefore described with reference to and as illustrated by Fig. 4 or Fig. 5 of the drawings.

7. A tire or tire cord substantially as described in Embodiments 1A, 2A, and 3E.

8. Any new feature hereindescribed or any new combination of hereindescribed features.

Published 1988 at The Patent Office, State House, 6"1 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Mce, Sales Branch, St Mary Cray, Orpington, Kent BR.5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.

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