Steel cord

A steel cord for reinforcing rubber articles comprises one wave-form or helical core steel filament and a plurality of sheath steel filaments disposed around the core steel filament, the pitch Pc of the core steel filament is 3.0 dc/0.34.ltoreq.Pc.ltoreq.10.0 dc/0.34 (dc=diameter of steel core filament) and the core forming ratio Rc=Lc/dc (Lc is an amplitude of the wave or helix of the core steel filament) is within a particular range varying depending on the number of sheath steel filaments. The rubber articles containing the steel cord have an improved resistance to corrosion propagation and a high strength. A pneumatic tire is reinforced with the above-mentioned steel cord and contains a cross belt layer where PA1 (i) an angle .theta. formed by a reinforcing steel cord and the equatorial plane of the tire is: EQU 12.degree..ltoreq..theta..ltoreq.30.degree. PA1 (ii) a gap between adjacent two steel cords in the same layer, I, is: EQU 0.5 mm.ltoreq.I.ltoreq.2.0 mm PA1 (iii) a gauge of the gum between two facing cords, G, is: EQU 0.35 mm.ltoreq.G.ltoreq.2.0 mm The pneumatic tire exhibits suppression of development of crack at the belt end in addition to the advantages as above.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a steel cord for reinforcing rubber 
articles, and more particularly, to a steel cord-for reinforcing rubber 
articles capable of improving the resistance to corrosion propagation. 
2. Description of the Related Art 
Products reinforced with steel cords are liable to suffer from corrosion of 
steel filaments caused by water entering the products and thereby the 
durability and life of the products are lowered. 
For example, when steel cords used in a belt of a tire with a void and the 
tire tread is subjected to damage reaching the belt, water entering the 
belt spreads along the longitudinal direction of the cord through the 
voids in the steel cords. As a result, rust formed due to water also 
diffuses and the adhesion between rubber and steel cord is lowered at that 
portion. Finally, separation phenomena occur. 
In order to prevent such corrosion propagation, there is proposed a cord 
structure in which rubber can sufficiently penetrate into the inside of 
the cord through gaps between adjacent metal filaments by curing process. 
Japanese Patent Publication Nos. 21641/1987 and 49421/1985 disclose that 
gaps between filaments of a cord can be formed by excess shaping. However, 
retaining such gaps is difficult and moreover the advantageous effect 
varies undesirably depending on the manner of handling in the step of 
manufacturing tires. 
On the contrary, there are proposed techniques for assuring gaps between 
filaments by improving the cord structure without shaping filaments. 
Japanese Patent Application Laid-open Nos. 38208/ 1985 and 1790/1984 
disclose that one of the above-mentioned cord structure, so-called "(1+5) 
structure" cord composed of one core filament and five sheath filaments, 
has gaps between sheath filaments and rubber can easily penetrate the 
gaps, and further this cord can be produced by one-step twisting. As a 
result productivity is high. 
Indeed the average sheath gaps are sufficient in such a cord structure, but 
deviation occurs in the arrangement of sheath filaments and there are 
formed attaching portions of the filaments resulting in forming the 
portions where rubber does not penetrate due to fluctuation in the 
manufacturing procedure. 
Japanese Patent Application Laid-open No. 175503/ 1989 proposed a steel 
cord composed of one core filament and six sheath filaments, and Japanese 
Utility Model Application No. 178204/1985 and Japanese Patent Application 
Laid-open No. 154086/1990 disclose two-layer twisted steel cords composed 
of a core of two metal filaments and a sheath filament disposed around the 
core. 
In particular, the (1+6) structure cord of the above-mentioned Japanese 
Patent Application Laid-open No. 175503/ 1989 can be produced by one step 
twisting and therefore, is advantageous from the standpoint of 
productivity. The disclosed (1+6) cord has a structure such that the 
diameter of the core filament is larger than that of the sheath filament 
so as to ensure a gap larger than a predetermined size between adjacent 
sheath filaments for enabling rubber to penetrate the inside. However, 
since partly a deviation occurs in the arrangement of sheath cores, rubber 
does penetrates at the side where sheath filaments contact each other and 
therefore, a sufficient resistance to corrosion propagation can not be 
attained in the case of tires for trucks running a severely rough road 
with much water. Further, the weight of cord is large and the productivity 
is lowered. 
Japanese Patent Application Laid-open No. 131404/ 1981 discloses that a 
cord of (1+5) structure may be formed such that the core filament is 
lightly waved, but in this cord structure the diameter of the core 
filament is thinner than that of the sheath filament and therefore, the 
distance between sheath filaments is so narrow that rubber can not easily 
enter the gap, and further, since rigidity of core filament is so low that 
the wave shape of the core exhibits only a lowered effect. In addition, 
when the core shaping ratio (waving) is large, the strength is lowered. 
It may be thought that a diameter of the core filament is made larger than 
that the sheath filament to assure a gap larger than a predetermined size 
between adjacent filaments for purposes of making rubber penetrate the 
inside. However, such method increase the total weight of the cord, the 
productivity is deteriorated and deviation of the arrangement of sheath 
filament occurs partly to cause attachment between sheath filaments each 
other. As a result, rubber can not penetrate the cord resulting in less 
resistance to corrosion propagation, 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a steel cord capable of 
improving the life of rubber articles. 
Another object of the present invention is to provide a steel cord capable 
of improving the resistance to corrosion propagation of rubber articles. 
A further object of the present invention is to provide a steel cord 
capable of improving a resistance to corrosion propagation of and 
imparting a high strength to rubber articles. 
Still another object of the present invention is to provide a pneumatic 
tire reinforced with one of the above-mentioned steel cords. 
According to one aspect of the present invention, there is provided a steel 
cord for reinforcing rubber articles which comprises 
one wave-form core steel filament, and a plurality of sheath steel 
filaments disposed around the wave-form core steel filament, 
the pitch Pc of the crimped core steel filament being in the following 
range, 
EQU 3.0 dc/0.34.ltoreq.Pc.ltoreq.10.0 dc/0.34 
where dc is the diameter of the core steel filament, and the core forming 
ratio Rc (=Lc/dc) where dc is as defined above and Lc is an amplitude of 
the crimp of the core steel filament 
being selected from the group consisting of 
EQU 0.12.ltoreq.Rc.ltoreq.1.0 
in the case of five sheath steel filaments, 
EQU 0.12.ltoreq.Rc.ltoreq.1.5 
in the case of six sheath steel filaments, 
EQU 0.48.ltoreq.Rc.ltoreq.1.86 
in the case of seven sheath steel filaments, and 
EQU 0.98.ltoreq.Rc.ltoreq.2.36 
in the case of eight sheath steel filaments. 
According to another aspect of the present invention, there is provided a 
steel cord for reinforcing rubber articles which comprises 
one helical core steel filament, and a plurality of sheath steel filaments 
disposed around the helical core steel filament, 
the pitch Pc of the helical core steel filament being in the following 
range, 
EQU 3.0 dc/0.34.ltoreq.Pc.ltoreq.10.0 dc/0.34 
where dc is the diameter of the core steel filament, the core forming ratio 
Rc(=Lc/dc) where dc is as defined above and Lc is an amplitude of the 
helix of the core steel filament 
being selected from the group consisting of 
EQU 0.12.ltoreq.Rc.ltoreq.1.0 
in the case of five sheath steel filaments, 
EQU 0.12.ltoreq.Rc.ltoreq.1.5 
in the case of six sheath steel filaments, 
EQU 0.42.ltoreq.Rc.ltoreq.1.8 
in the case of seven sheath steel filaments, and 
EQU 0.74.ltoreq.Rc.ltoreq.2.12 
in the case of eight sheath steel filaments, and the helical direction 
being opposite to the direction of twisting the sheath steel filaments. 
According to a further aspect of the present invention, there is provided a 
pneumatic tire reinforced with one kind of the above-mentioned steel cords 
which comprises a cross belt layer where 
(i) an angle .theta. formed by a reinforcing steel cord and the equatorial 
plane of the tire is: 
EQU 12.degree..ltoreq..theta..ltoreq.30.degree. 
(ii) a gap between adjacent two steel cords in the same layer, I, is: 
EQU 0.5 mm.ltoreq.I.ltoreq.2.0 mm 
(iii) a gauge of the gum between two facing cords, G, is: 
EQU 0.35 mm.ltoreq.G.ltoreq.2.0 mm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to one aspect of the present invention, there is used a wavy core 
steel filament. The shape of wave is within a range determined by a 
particular range of amplitude and a particular range of pitch depending on 
the number of sheath steel filaments disposed around one wavy core steel 
filament. Thus, a gap between sheath steel filaments into which rubber 
penetrates can be assured. The wavy core serves to attain the following 
advantages. 
The wavy shape can be formed in a high productivity at a low cost. Sheath 
filaments do not substantially contact one another. Further, the cord 
itself can be a flat cord since it has a flat core. Therefore, the 
increase in cord thickness due to forming of core can be prevented, the 
increase of the rubber layer gauge can be prevented. Moreover, the rubber 
permeability can be improved resulting in increasing the resistance to 
corrosion propagation. 
As to the shape of wave, a wave similar to a triangle which has a sharp 
apex is not preferable while a wave having a mild curve such as a sine 
wave is preferable since concentration of a stress to the apex can be 
avoided. As used herein the terms "wavy" and "wave-form" are 
interchangeable. 
The core shaping ratio Rc(=Lc/dc) of the "one wave-form core steel 
filament" is in the following range: 
EQU 0.12.ltoreq.Rc.ltoreq.1.0 
for (1+5) structure 
EQU 0.12.ltoreq.Rc.ltoreq.1.5 
for (1+6) structure 
EQU 0.48.ltoreq.Rc.ltoreq.1.86 
for (1+7) structure 
EQU 0.98.ltoreq.Rc.ltoreq.2.36 
for (1+8) structure. 
In the partentheses above, 1 stands for "one wave-form core steel filament" 
and 5, 6, 7 and 8 stand for the numbers of sheath steel filaments. 
When the Rc is lower than the above-mentioned range, a sufficient effect of 
dispersing the arrangement of sheath steel filaments, assuring properly 
the sheath gap and making rubber penetrate into the inside of cord is not 
obtained. On the contrary, Rc is higher than the above-mentioned range, 
the configuration of the filaments becomes uneven, and in the case where a 
tensile load is put on the cord, the stress is not uniformly applied and 
thereby, the strength of cord is lowered. 
The pitch Pc of the wavy core steel filament is in the following range: 
EQU 3.0 dc/0.34.ltoreq.Pc.ltoreq.10.0 dc/0.34 
When Pc is larger than this range, a sufficient effect of dispersing the 
arrangement of sheath steel filaments, assuring properly the sheath gap 
and making rubber into the inside of cord is not obtained. On the 
contrary, when Pc is smaller than this range, the strength of core steel 
filament is lowered due to the load put on the core steel filament upon 
forming, and a load is not uniformly applied to core steel filaments and 
sheath steel filaments and the cord strength becomes insufficient in the 
case where a tensile load is applied to the cord. 
When the steel cord is used as a reinforcing material so as to assure the 
strength of the rubber composite and make the rubber composite lighter, it 
is preferable to use a steel cord composed of a high tensile strength 
steel containing 0.80-0.85% by weight of carbon. 
As mentioned in Description of the Related Art above, when the diameter of 
the core filament is much thinner or thicker than that of the sheath 
filament, there are various disadvantages. 
Therefore, for purposes of eliminating such disadvantages and further 
enhancing the productivity of the manufacturing step, it is preferable 
that the diameter of the core steel filament dc is substantially the same 
as the diameter of the sheath steel filament ds. 
That is, when dc is much smaller than ds, the distance between sheath steel 
filaments becomes so narrow that the penetration of rubber is adversely 
affected and the rigidity of the core steel filament is so low that the 
advantages due to the wave-form are lowered. 
On the contrary, when dc is much larger than ds, the weight of the cord 
increases and productivity becomes low. Further, deviation of the 
arrangement of sheath filaments occurs partly to cause attachment between 
sheath filaments, resulting in less penetration of rubber and insufficient 
resistance to corrosion proparation. 
According to another aspect of the present invention, there is used one 
helical core steel filament. When a plurality of core filaments are used, 
voids are formed in the core portion and rubber can not penetrate 
thereinto. On the contrary, when one helical core steel filament is used, 
the disadvantage of a plurality of core filaments can be eliminated and 
further, concentration of a stress can be avoided due to the helical shape 
resulting in good fatigue resistance and excellent strength. 
The core shaping ratio Rc(=Lc/dc)of the "one helical core steel filament" 
is in the following range: 
EQU 0.12.ltoreq.Rc.ltoreq.1.0 
for (1+5) structure 
EQU 0.12.ltoreq.Rc.ltoreq.1.5 
for (1+6) structure 
EQU 0.42.ltoreq.Rc.ltoreq.1.8 
for (1+7) structure 
EQU 0.74.ltoreq.Rc.ltoreq.2.12 
for (1+8) structure 
In the parentheses above, 1 stands for "one helical core steel filament" 
and 5, 6, 7 and 8 stand for the numbers sheath steel filaments. 
When the Rc is lower than the above-mentioned range, a sufficient effect of 
dispersing the arrangement of sheath steel filaments, assuring properly 
the sheath gap and making rubber penetrate into the inside of cord is not 
obtained. On the contrary, Rc is higher than the above-mentioned range, 
the configuration of the filaments becomes uneven, and in the case where a 
tensile load is put on the cord, the stress is not uniformly applied and 
thereby, the strength of cord is lowered. 
The pitch Pc of the helical core steel filament is in the following range: 
EQU 3.0 dc/0.34.ltoreq.Pc.ltoreq.10.0 dc/0.34 
When Pc is larger than this range, a sufficient effect of dispersing the 
arrangement of sheath steel filaments, assuring properly the sheath gap 
and making rubber into the inside of cord is not obtained. On the 
contrary, when Pc is smaller than this range, the strength of core steel 
filament is lowered due to the load put on the core steel filament upon 
shaping, and a load is not uniformly applied to core steel filaments and 
sheath steel filaments and the cord strength becomes insufficient in the 
case where a tensile load is applied to the cord. 
The core forming ratio Rc and the pitch of helical core steel filament Pc 
are determined by measuring a steel core taken out from a rubber article 
without causing plastic deformation. 
The helical direction of the core steel filament is opposite to the 
direction of twisting the sheath steel filaments according to the present 
invention. When both directions are the same, the length of the helical 
core steel filament contacting the same sheath filament becomes long and 
therefore, the helical core steel filament contacts two sheath filaments 
and portions into which rubber can not penetrate (cf. FIG. 10, the right 
upper part where a helical core steel filament 5 contacts two sheath steel 
filaments) are connected in the longitudinal direction resulting in a low 
resistance to corrosion propagation. 
When the steel cord is used as a reinforcing material to assure the 
strength of the rubber composite and make the rubber composite lighter, it 
is preferable to use a steel cord composed of a high tensile strength 
steel containing 0.80-0.85% by weight of carbon. 
In this aspect of the present invention, it is also preferable that the 
diameter of the helical core steel filament dc is substantially the same 
as the diameter of the sheath steel filament ds. The reason is the same as 
that in the previous aspect of the present invention relating to the wavy 
core steel filament and sheath steel filaments. 
The steel cord for reinforcing rubber articles of the present invention is 
useful as a reinforcing material for various rubber articles, for example, 
rubber composites such as pneumatic tires, belts for industry and the 
like. 
The steel cord according to the present invention can suppress the 
propagation of corrosion due to water and the like, that is, the 
resistance to corrosion propagation is improved, and therefore, the 
separation phenomenon can be prevented while the strength of cord can be 
retained. 
Rubber can sufficiently penetrate into the steel cord of the present 
invention, that is, a sufficient amount of rubber after curing can stably 
penetrate into the steel cord having the particular structure according to 
the present invention. 
According to the present invention, using a helical core steel filament, 
sheath filaments can be brought into a state that they do not 
substantially contact one another, by making the helical direction of the 
helical core steel filament opposite to the direction of twisting the 
sheath steel filaments. 
The steel cord of the present invention can be manufactured having a good 
productivity and is not adversely affected by the fluctuation in the 
manufacturing step. 
According to the present invention, durability of rubber articles, for 
example, rubber composites, can be improved and the life can be extended 
while the mechanical strength of the rubber articles is retained. 
FIG. 1 shows schematically a cross sectional view of a (1+5) steel cord 
composed of one wavy core filament 1 and five sheath filaments 2 twisted 
around the wave-form core filament 1 according to the present invention. 
The wavy core filament 1 extends in the space shown by the closed dotted 
line. 
FIG. 2 shows schematically cross sectional view of a conventional (1+5) 
steel cord. Around a core filament (not formed) 3 are twisted five sheath 
filaments 4, and three of the sheath filaments are contacted with each 
other. 
FIG. 3 schematically shows a cross sectional view of a core filament 1 cut 
parallel to the wave plane of the present invention, dc stands for the 
diameter of core filament 1, Lc the amplitude of the wavy core filament 
and Pc the pitch of the wavy core filament. 
Core forming ratio Rc is defined as follows: 
EQU Rc=Lc/dc 
FIG. 4 shows schematically a cross sectional view of a (1+6) steel cord 
composed of one wavy core filament 1 and six sheath filaments 2 twisted 
around the wave-form core filament 1 according to the present invention. 
The wavy core filament 1 extends in the space shown by the closed dotted 
line. 
FIG. 5 shows schematically a cross sectional view of a conventional (1+6) 
steel cord composed of one core filament 3 not formed and six sheath 
filaments 4 twisted around the core filament 3. The diameter of core 
filament 3 is larger than that of sheath filament 4. Two sheath filaments 
and three sheath filaments are contacted one another. 
FIG. 6 shows schematically a cross sectional view of a (1+7) steel cord 
composed of one wavy core filament 1 and seven sheath filaments 2 twisted 
around the wave-form core filament 1 according to the present invention. 
The wavy core filament 1 extends in the space shown by the closed dotted 
line. 
FIG. 7 shows schematically a cross sectional view of a (1+8) steel cord 
composed of one wavy core filament 1 and eight sheath filaments 2 twisted 
around the wavy core filament 1 according to the present invention. 
The wavy core filament 1 extends in the space shown by the closed dotted 
line. 
FIG. 8 shows schematically a cross sectional view of a (1+5) steel cord 
composed of one helical core filament 1 and five sheath filaments 2 
twisted around the helical core filament 1 in which the helical direction 
of the helical core filament 1 is opposite to the direction of twisting 
the sheath filaments 2 according to the present invention. 
The helical core filament 1 extends in the space shown by the closed dotted 
line. 
FIG. 9 is a schematical side view of a helical core filament 1 viewed from 
the direction perpendicular to the axis of the helical core filament. 
dc stands for the diameter of the helical core filament, Lc is the 
amplitude of the helical core filament and Pc the pitch of the helical 
core filament. 
FIG. 10 shows schematically a cross sectional view of a (1+5) steel cord 
composed of one helical core filament 5 and five sheath filaments 6 
twisted around the helical core filament 5 in which the helical direction 
of the helical core filament 5 is the same as the direction of twisting 
the sheath filaments 6. The helical core filament 5 extends in the space 
shown by the closed dotted line. 
The three sheath filaments 6 at the right hand side of the cord are in 
contact with each other. 
FIG. 11 shows schematically a cross sectional view of a (1+6) steel cord 
composed of one helical core filament 5 and six sheath filaments 6 twisted 
around the helical core filament 5 in which the helical direction of the 
helical core filament 5 is opposite to the direction of twisting the 
sheath filaments according to the present invention. 
The helical core filament 5 extends in the space shown by the closed dotted 
line. 
FIG. 12 shows schematically a cross sectional view of a (1+7) steel cord 
composed of one helical core filament 5 and seven sheath filaments 6 
twisted around the helical core filament 5 in which the helical direction 
of the helical core filament 5 is opposite to the direction of twisting 
the sheath filaments 6 according to the present invention. 
The helical core filament 5 extends in the space shown by the closed dotted 
line. 
FIG. 13 shows schematically a cross sectional view of a (1+8) steel cord 
composed of one helical core filament 5 and eight sheath filaments 6 
twisted around the helical core filament 5 in which the helical direction 
of the helical core filament 5 is opposite to the direction of twisting 
the sheath filaments 6 according to the present invention. 
The helical core filament 5 extends in the space shown by the closed dotted 
line. 
According to a further aspect of the present invention, there is proposed a 
pneumatic tire in which one of the above-mentioned steel cords is used as 
a reinforcing steel cord and the angle .theta. formed by a reinforcing 
steel cord and the equatorial plane of the tire, the gap between adjacent 
two steel cords in the same layer, I, and the gauge of the gum between two 
facing cords, G, are within the respective numerical ranges as mentioned 
above. 
The angle .theta. is 12.degree..ltoreq..theta..ltoreq.30.degree.. When 
.theta. is less than 12.degree., the shearing strain between layers during 
tire running increases and the separation is liable to occur. 
The gap, I, is 0.5 mm.ltoreq.I.ltoreq.2.0 mm. When I is less than 0.5 mm, 
adjacent cracks formed at the end of belt are connected with one another 
and extend to the direction of the equatorial plane. As a result, 
separation is liable to occur. 
The gauge of the gum, G, is 0.35 mm.ltoreq.G.ltoreq.2.0 mm. When G is less 
than 0.35 mm, the shearing strain between rubber layers of the cross belt 
layer during tire running increases and the separation is liable to occur. 
On the contrary, when .theta., I or G is larger than the upper limit, 
30.degree., 2.0 mm or 2.0 mm, the stiffness of the cross belt layer in the 
direction of the equatorial plane is lowered, and the diameter of tire 
increases upon elevating the inner pressure and running. Therefore, strain 
occurs in the rubber around the steel cords, As a result, the separation 
is liable to occur. 
A spiral filament may be added to the reinforcing steel cord. By adding a 
spiral filament, the shape at the cord cut end can be controlled, and 
therefore, the productivity is improved and development of crack formed at 
the belt end can be suppressed. 
Even when the spiral filament is added, the diameter of the cord is not 
markedly affected, but the above-mentioned advantage can be obtained which 
is a far better advantage though adding the spiral filament is not 
essentional. 
The reinforcing steel cord is preferably made of a steel containing 
0.80-0.85% by weight of carbon. Further, the diameter of the core steel 
filament dc is preferably substantially the same as the diameter of the 
sheath steel filament ds. The advantages resulting from the 
above-mentioned carbon content and the filament diameters dc and ds are 
similar to those with respect of the steel cord itself as mentioned above. 
Referring to FIG. 14, a schematical cross sectional view is illustrated 
perpendicular to cords of layer A of a cross belt layer 10 composed of 
layer A and layer B, at the crown center portion of a tire of the present 
invention. 
The letter i denotes a gap between adjacent two steel cords in the same 
layer, and G a gauge of the gum between two facing cords. 
The pneumatic tire according to the present invention exhibits a good 
suppression to the propagation of corrosion due to water and the like 
while the strength of cord can be retained, and the tire structure is 
suitable for suppressing development of cracks at the belt end. Therefore, 
the durability of the tire is improved and the life of tire can be 
improved to a great extent. 
The present invention is now more particularly described with reference to 
the following examples which are for the purpose of illustration only and 
are intended to imply no limitation thereon. 
EXAMPLES 1-16, COMATIVE EXAMPLES 1-14 
There were prepared thirty radial tires for truck and bus of size of 10.00 
R20 having a belt in which steel cords were buried, the steel cords having 
core forming ratio Rc, core wavy pitch Pc, cord structure, core filament 
diameter dc, sheath filament diameter ds, and sheath twisting pitch Ps as 
shown in Tables 1-6. 
The resulting thirty radial tires were evaluated for resistance to 
corrosion propagation (separation resistance) and cord strength. The 
results are shown in Tables 1-6. 
The resistance to corrosion propagation was measured as follows. 
A belt cord (100 mm) covered with rubber was taken out from a tire and the 
side surface was covered with a silicone sealant. Then, one end of the 
cord was soaked in a 10% aqueous solution of NaOH and the aqueous solution 
was allowed to enter the cord from the cut surface only. After 24 hours of 
the soaking, the rubber was peeled off by means of pinchers, and the 
length (mm) of the cord where the metal was exposed was regarded as a 
corrosion propagation portion. 
TABLE 1 
__________________________________________________________________________ 
Example 
1 2 3 4 5 6 
__________________________________________________________________________ 
Core forming ratio Rc 
0.15 
0.47 
0.47 
0.62 
1.0 0.47 
Core wave-form pitch Pc 
3.3 3.3 4.4 5.5 9.0 3.0 
(mm) 
Cord structure 1 + 5 
1 + 5 
1 + 5 
1 + 5 
1 + 5 
1 + 5 
Core filament diameter dc 
0.34 
0.34 
0.34 
0.34 
0.34 
0.23 
(mm) 
Sheath filament diameter ds 
0.34 
0.34 
0.34 
0.34 
0.34 
0.23 
(mm) 
Sheath twisting pitch Ps 
17 17 17 17 17 11.5 
(mm) 
Resistance to corrosion 
20 10 10 10 15 10 
propagation (mm) 
Cord strength (kgf) 
171 170 171 170 169 77 
__________________________________________________________________________ 
TABLE 2 
______________________________________ 
Comparative Example 
1 2 3 4 5 
______________________________________ 
Core forming ratio Rc 
0.10 0.47 1.2 0.47 1.2 
Core wave-form pitch 
4.4 2.8 5.5 11.0 3.0 
Pc (mm) 
Cord structure 
1 + 5 1 + 5 1 + 5 1 + 5 1 + 5 
Core filament 
0.34 0.34 0.34 0.34 0.23 
diameter dc (mm) 
Sheath filament 
0.34 0.34 0.34 0.34 0.23 
diameter ds (mm) 
Sheath twisting pitch 
17 17 17 17 11.5 
Ps (mm) 
Resistance to 
85 10 10 100 10 
corrosion propagation 
(mm) 
Cord strength (kgf) 
171 155 153 170 69 
______________________________________ 
TABLE 3 
______________________________________ 
Example 
7 8 9 10 11 
______________________________________ 
Core forming ratio Rc 
0.15 0.47 0.32 0.47 0.47 
Core wave-form pitch 
3.3 3.3 4.4 4.4 5.5 
Pc (mm) 
Cord structure 
1 + 6 1 + 6 1 + 6 1 + 6 1 + 6 
Core filament 
0.34 0.34 0.34 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.34 0.34 0.34 0.34 0.34 
diameter ds (mm) 
Sheath twisting pitch 
17 17 17 17 17 
Ps (mm) 
Resistance to 
30 10 15 10 17 
corrosion propagation 
(mm) 
Cord strength (kgf) 
201 199 200 200 200 
______________________________________ 
TABLE 4 
______________________________________ 
Example 
12 13 14 15 16 
______________________________________ 
Core forming ratio Rc 
0.62 1.5 0.47 1.2 1.0 
Core wave-form pitch 
5.5 9.0 3.0 6.5 6.0 
Pc (mm) 
Cord structure 
1 + 6 1 + 6 1 + 6 1 + 8 1 + 7 
Core filament 
0.34 0.34 0.23 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.34 0.34 0.23 0.34 0.34 
diameter ds (mm) 
Stheath twisting pitch 
17 17 11.5 17 17 
Ps (mm) 
Resistance to 
10 20 10 20 20 
corrosion propagation 
(mm) 
Cord strength (kgf) 
199 197 90 253 225 
______________________________________ 
TABLE 5 
______________________________________ 
Comparative Example 
6 7 8 9 10 
______________________________________ 
Core forming ratio Rc 
0.10 0.47 1.6 0.47 0 
Core wave-form pitch 
4.4 2.8 6.0 11.0 -- 
Pc (mm) 
Cord structure 
1 + 6 1 + 6 1 + 6 1 + 6 1 + 6 
Core filament 
0.34 0.34 0.34 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.34 0.34 0.34 0.34 0.28 
diameter ds (mm) 
Sheath twisting pitch 
17 17 17 17 14 
Ps (mm) 
Resistance to 
100 10 10 100 60 
corrosion propagation 
(mm) 
Cord strength (kgf) 
200 182 180 200 150 
______________________________________ 
TABLE 6 
______________________________________ 
Comparative Example 
11 12 13 14 
______________________________________ 
Core forming ratio Rc 
0 1.6 0.4 0.90 
Core wave-form pitch Pc 
-- 3.0 6.0 6.5 
(mm) 
Cord structure 1 + 6 1 + 6 1 + 7 1 + 8 
Core filament diameter dc 
0.40 0.23 0.34 0.34 
(mm) 
Sheath filament diameter ds 
0.34 0.23 0.34 0.34 
(mm) 
Sheath twisting pitch Ps 
17 11.5 17 17 
(mm) 
Resistance to corrosion 
55 10 80 80 
propagation (mm) 
Cord strength (kgf) 
202 80 225 253 
______________________________________ 
Comparative Example 1 shows that the resistance to corrosion propagation 
was as poor as 85 mm when the core forming ratio was less than 0.12. 
Comparative Example 2 shows that the cord strength was lowered to 155 kgf 
when the core wavy pitch was less than 3.00 mm. 
Comparative Example 3 shows that the cord strength was lowered to 153 kgf 
when the core forming ratio is larger than 1.0. 
Comparative Example 4 shows that the resistance to corrosion propagation 
was as poor as 100 mm when the core wavy pitch was larger than 10.0 mm. 
Comparative Example 5 shows that the cord strength was lowered to 69 kgf as 
compared with Example 6 when the core forming ratio was larger than 1.0 
though the core filament diameter and the sheath filament diameter were 
small. 
Comparative Example 6 shows that the resistance to corrosion propagation 
was as poor as 100 mm when the core forming ratio was smaller than 6.12. 
Comparative Example 7 shows that the cord strength was as poor as 182 kgf 
when the core wavy pitch Pc smaller then 3.0 dc/0.34. 
Comparative Example 8 shows that the cord strength was as poor as 180 kgf 
when the core forming ratio was larger than 1.5. 
Comparative Example 9 shows that the resistance to corrosion propagation 
was as poor as 100 mm when the core wavy pitch Pc was larger than 10.0 
dc/0.34. 
Comparative Examples 10 and 11 show that the resistance to corrosion 
propagation was poor in each case where the core filament was not formed 
into crimp. 
Comparative Examples 12 shows that the cord strength was as poor as 80 kgf 
when the core forming ratio was larger than 1.5 and each of the core 
filament and the sheath filament was 0.23 mm in diameter. 
Comparative Example 13 shows that the resistance to corrosion propagation 
was poor when a (1+7) structure was used and the core forming ratio was 
smaller than 0.48. 
Comparative Example 14 shows that the resistance to corrosion propagation 
was poor when a (1+8) structure was used and the core forming ratio was 
smaller than 0.98. 
EXAMPLES 17-32, COMATIVE EXAMPLES 15-30 
There were prepared thirty two radial tires for truck and bus of a size of 
10.00 R20 having a belt in which steel cords were buried, the steel cords 
having core forming ratio Rc, core helical pitch Pc, cord structure, core 
filament diameter dc, sheath filament diameter ds, sheath twisting pitch 
Ps, core shaping helical direction and sheath twisting direction as shown 
in Tables 7-12. 
The resulting 32 radial tires were evaluated for resistance to corrosion 
propagation (separation resistance) and cord strength. The results are 
shown in Tables 7-12. 
The resistance to corrosion propagation was measured as mentioned above. 
The helical direction and sheath twisting direction (Z and S) are difined 
by JIS G 3510. 
Separation resistance is measured by disintegrating a pneumatic tire fitted 
to a car and worn completely as a result of having run over a bad road and 
observing whether a separation at the end of belt occurred. 
TABLE 7 
______________________________________ 
Example 
17 18 19 20 21 
______________________________________ 
Core forming ratio Rc 
0.15 0.47 0.47 0.62 1.0 
Core helical pitch 
3.3 3.3 4.4 5.5 9.0 
(mm) 
Cord structure 
1 + 5 1 + 5 1 + 5 1 + 5 1 + 5 
Core filament 
0.34 0.34 0.34 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.34 0.34 0.34 0.34 0.34 
diameter ds (mm) 
Sheath twisting pitch 
17 17 17 17 17 
Ps (mm) 
Core forming helical 
Z Z Z Z Z 
direction 
Sheath twisting 
S S S S S 
direction 
Resistance to 
20 10 10 10 15 
corrosion propagation 
(mm) 
Cord strength (kgf) 
171 170 171 170 169 
______________________________________ 
TABLE 8 
______________________________________ 
Example 
22 23 24 25 26 
______________________________________ 
Core forming ratio Rc 
0.47 0.15 0.47 0.32 0.47 
Core helical pitch 
3.0 3.3 3.3 4.4 4.4 
(mm) 
Cord structure 
1 + 5 1 + 6 1 + 6 1 + 6 1 + 6 
Core filament 
0.23 0.34 0.34 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.23 0.34 0.34 0.34 0.34 
diameter ds (mm) 
Sheath twisting pitch 
11.5 17 17 17 17 
Ps (mm) 
Core forming helical 
Z Z Z Z Z 
direction 
Sheath twisting 
S S S S S 
direction 
Resistance to 
10 30 10 15 10 
corrosion propagation 
(mm) 
Cord strength (kgf) 
77 201 199 200 200 
______________________________________ 
TABLE 9 
__________________________________________________________________________ 
Example 
27 28 29 30 31 32 
__________________________________________________________________________ 
Core forming ratio Rc 
0.47 
0.62 
1.5 0.47 
1.2 1.0 
Core helical pitch (mm) 
5.5 5.5 9.0 3.0 6.5 6.0 
Cord structure 1 + 6 
1 + 6 
1 + 6 
1 + 6 
1 + 8 
1 + 7 
Core filament diameter dc 
0.34 
0.34 
0.34 
0.23 
0.34 
0.34 
(mm) 
Sheath filament diameter ds 
0.34 
0.34 
0.34 
0.23 
0.34 
0.34 
(mm) 
Sheath twisting pitch Ps 
17 17 17 11.5 
17 17 
(mm) 
Core forming helical direction 
Z Z Z Z Z Z 
Sheath twisting direction 
S S S S S S 
Resistance to corrosion 
17 10 20 10 20 20 
propagation (mm) 
Cord strength (kgf) 
200 199 197 90 253 225 
__________________________________________________________________________ 
TABLE 10 
______________________________________ 
Comparative Example 
15 16 17 18 19 
______________________________________ 
Core forming ratio Rc 
0.10 0.47 1.2 0.47 0.47 
Core helical pitch 
4.4 2.8 5.5 11.0 4.4 
(mm) 
Cord structure 
1 + 5 1 + 5 1 + 5 1 + 5 1 + 5 
Core filament 
0.34 0.34 0.34 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.34 0.34 0.34 0.34 0.34 
diameter ds (mm) 
Sheath twisting pitch 
17 17 17 17 17 
Ps (mm) 
Core forming helical 
Z Z Z Z S 
direction 
Sheath twisting 
S S S S S 
direction 
Resistance to 
85 10 10 100 55 
corrosion propagation 
(mm) 
Cord strength (kgf) 
171 155 153 170 171 
______________________________________ 
TABLE 11 
______________________________________ 
Comparative Example 
20 21 22 23 24 
______________________________________ 
Core forming ratio Rc 
1.2 0.10 0.47 1.6 0.47 
Core helical pitch 
3.0 4.4 2.8 6.0 11.0 
(mm) 
Cord structure 
1 + 5 1 + 6 1 + 6 1 + 6 1 + 6 
Core filament 
0.23 0.34 0.34 0.34 0.34 
diameter dc (mm) 
Sheath filament 
0.23 0.34 0.34 0.34 0.34 
diameter ds (mm) 
Sheath twisting pitch 
11.5 17 17 17 17 
Ps (mm) 
Core forming helical 
Z Z Z Z Z 
direction 
Sheath twisting 
S S S S S 
direction 
Resistance to 
10 100 10 10 100 
corrosion propagation 
(mm) 
Cord strength (kgf) 
69 200 182 180 200 
______________________________________ 
TABLE 12 
__________________________________________________________________________ 
Comparative Example 
25 26 27 28 29 30 
__________________________________________________________________________ 
Core forming ratio Rc 
0 0 0.47 
1.6 0.35 
0.65 
Core helical pitch (mm) 
-- -- 4.4 3.0 6.0 6.5 
Cord structure 1 + 6 
1 + 6 
1 + 6 
1 + 6 
1 + 7 
1 + 8 
Core filament diameter dc 
0.34 
0.40 
0.34 
0.23 
0.34 
0.34 
(mm) 
Sheath filament diameter ds 
0.28 
0.34 
0.34 
0.23 
0.34 
0.34 
(mm) 
Sheath twisting pitch Ps 
14 17 17 11.5 
17 17 
(mm) 
Core forming helical direction 
Z Z S Z Z Z 
Sheath twisting direction 
S S S S S S 
Resistance to corrosion 
60 55 55 10 90 90 
propagation (mm) 
Cord strength (kgf) 
150 202 202 80 225 253 
__________________________________________________________________________ 
In Tables 10 and 11, Comparative Examples 15-20 are concerned with (1+5) 
structure. 
Comparative Example 15 shows that the resistance to corrosion propagation 
was as poor as 85 mm when the core forming ratio Rc was less than 0.12. 
Comparative Example 16 shows that the cord strength was deteriorated when 
the core helical pitch Pc was less than 3.0 dc/0.34. 
Comparative Example 17 shows that the cord strength was deteriorated when 
the core forming ratio Rc was 1.0. 
Comparative Example 18 shows that the resistance to corrosion propagation 
was as poor as 100 mm when the core helical pitch Pc was larger than 10.0 
dc/0.34. 
Comparative Example 19 shows that the resistance to corrosion propagation 
was as poor as 55 mm when the helical direction was the same as the sheath 
twisting direction. 
In Table 11, Comparative Example 20 shows that the cord strength was 
deteriorated when the core forming ratio Rc was larger than 1.0. 
Comparative Examples 21-28 are concerned with (1+6) structure. 
Comparative Example 21 shows that the resistance to corrosion propagation 
was as poor as 100 mm when the core forming ratio Rc was less than 0.12. 
Comparative Example 22 shows that the cord strength was deteriorated when 
the core helical pitch Pc was smaller than 3.0 dc/0.34. 
Comparative Example 23 shows that the cord strength was deteriorated when 
the core shaping ratio Rc was larger than 1.5. 
Comparative Example 24 shows that the resistance to corrosion propagation 
was as poor as 100 mm when the core helical pitch Pc was larger than 10.0 
dc/0.34. 
In Table 12, Comparative Examples 25 and 26 are concerned with cases where 
no core forming was effected, and show that the resistance to corrosion 
resistance was deteriorated in both cases and when the sheath filament 
diameter was thinner, the cord strength was also lowered. 
Comparative Example 27 shows that the resistance to corrosion propagation 
was poor when the core forming helical direction was the same as the 
sheath twisting direction. 
Comparative Example 28 shows that the cord strength was deteriorated when 
the core forming ratio was larger 1.5 (the filament diameter was as small 
as 0.23 mm in both core and sheath). 
Comparative Example 29 shows that the resistance to corrosion propagation 
was poor when the structure was (1+7) and the core forming ratio Rc was 
smaller than 0.42. 
Comparative Example 30 shows that the resistance to corrosion propagation 
was poor when the structure was (1+8) and the core forming ratio Rc was 
smaller than 0.74. 
COMATIVE EXAMPLES 31-42 
Following the procedures of Examples 1-16 under the conditions as shown in 
Tables 13-14, tires were prepared and the properties were tested. The 
results are shown in Tables 13 and 14. 
In Comparative Examples 31, 32, 37 and 38, .theta. was outside of the 
numerical range of the present invention. 
In Comparative Examples 33, 34, 39 and 40, I was outside of the numerical 
range of the present invention. 
In Comparative Examples 35, 36, 41, and 42, G was outside of the numerical 
range of the present invention. 
In the above cases, separation occurred as a result of the tire running. 
When the tires of Examples 1-5 were made under the conditions of 
.theta.=16.degree., I=0.8 mm, G=0.6 mm and those of Examples 7-16 under 
.theta.=16.degree., I=0.85 mm and G=0.6 mm, no separation occurred. 
COMATIVE EXAMPLES 43-48 
Following the procedures of Examples 17-32 under the conditions in Table 
15, tires were prepared and tested. The results are shown in Table 15. 
.theta. in Comparative Examples 43 and 44, I in Comparative Examples 45 and 
46, and G in Comparative Examples 47 and 48 were outside of the respective 
numerical conditions of the present invention, and separation occurred as 
a result of the tire running. 
When the tires of Examples 17-32 were made under .theta.=16.degree., I=0.85 
mm and G=0.6 mm, no separation occurred. 
TABLE 13 
__________________________________________________________________________ 
Comparative Example 
31 32 33 34 35 36 
__________________________________________________________________________ 
Core forming ratio Rc 
0.62 
0.62 
0.62 
0.62 
0.62 
0.62 
Core wave-form pitch Pc 
5.5 5.5 5.5 5.5 5.5 5.5 
(mm) 
Cord structure 1 + 5 
1 + 5 
1 + 5 
1 + 5 
1 + 5 
1 + 5 
Core filament diameter dc 
0.34 
0.34 
0.34 
0.34 
0.34 
0.34 
(mm) 
Sheath filament diameter ds 
0.34 
0.34 
0.34 
0.34 
0.34 
0.34 
(mm) 
Sheath twisting pitch Ps 
17 17 17 17 17 17 
(mm) 
.theta. (degree) 
11 31 16 16 16 16 
I (mm) 0.8 0.8 0.4 2.2 0.8 0.8 
G (mm) 0.6 0.6 0.6 0.6 0.03 
2.5 
Resistance to corrosion 
10 10 10 10 10 10 
propagation (mm) 
Cord strength (kgf) 
170 170 170 170 170 170 
Occurrence of separation 
Yes Yes Yes Yes Yes Yes 
__________________________________________________________________________ 
TABLE 14 
__________________________________________________________________________ 
Comparative Examples 
37 38 39 40 41 42 
__________________________________________________________________________ 
Core forming ratio Rc 
0.62 
0.62 
0.62 
0.62 
0.62 
0.62 
Core wave-form pitch Pc 
5.5 5.5 5.5 5.5 5.5 5.5 
(mm) 
Cord structure 1 + 6 
1 + 6 
1 + 6 
1 + 6 
1 + 6 
1 + 6 
Core filament diameter dc 
0.34 
0.34 
0.34 
0.34 
0.34 
0.34 
(mm) 
Sheath filament diameter ds 
0.34 
0.34 
0.34 
0.34 
0.34 
0.34 
(mm) 
Sheath twisting pitch Ps 
17 17 17 17 17 17 
(mm) 
Resistance to corrosion 
10 10 10 10 10 10 
propagation (mm) 
Cord strength (kgf) 
199 199 199 199 199 199 
.theta. (degree) 
11 31 16 16 16 16 
I (mm) 0.85 
0.85 
0.4 2.2 0.85 
0.85 
G (mm) 0.6 0.6 0.6 0.6 0.30 
2.5 
Occurrence of separation 
Yes Yes Yes Yes Yes Yes 
__________________________________________________________________________ 
TABLE 15 
__________________________________________________________________________ 
Comparative Example 
43 44 45 46 47 48 
__________________________________________________________________________ 
Core forming ratio Rc 
0.62 
0.62 
0.62 
0.62 
0.62 
0.62 
Core helical pitch Pc 
5.5 5.5 5.5 5.5 5.5 5.5 
(mm) 
Cord structure 1 + 6 
1 + 6 
1 + 6 
1 + 6 
1 + 6 
1 + 6 
Core filament diameter dc 
0.34 
0.34 
0.34 
0.34 
0.34 
0.34 
(mm) 
Sheath filament diameter ds 
0.34 
0.34 
0.34 
0.34 
0.34 
0.34 
Sheath twisting pitch Ps 
17 17 17 17 17 17 
(mm) 
Core forming helical direction 
Z Z Z Z Z Z 
Sheath twisting direction 
S S S S S S 
Resistance to corrosion 
10 10 10 10 10 10 
propagation (mm) 
Cord strength (kgf) 
199 199 199 199 199 199 
.theta. (degree) 
11 31 16 16 16 16 
I (mm) 0.85 
0.85 
0.4 2.2 0.85 
0.85 
G (mm) 0.6 0.6 0.6 0.6 0.30 
2.1 
Occurrence of separation 
Yes Yes Yes Yes Yes Yes 
__________________________________________________________________________