U.S. patent application number 13/319252 was filed with the patent office on 2012-03-15 for tyre bead wire and process for production thereof.
This patent application is currently assigned to FUJI SHOJI CO., LTD.. Invention is credited to Masatomo Kawashima, Hidetoshi Shibuya.
Application Number | 20120064357 13/319252 |
Document ID | / |
Family ID | 43297657 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120064357 |
Kind Code |
A1 |
Kawashima; Masatomo ; et
al. |
March 15, 2012 |
TYRE BEAD WIRE AND PROCESS FOR PRODUCTION THEREOF
Abstract
A tire bead wire and a process for producing a tire bead where a
carbon steel wire rod containing carbon in a range of 0.61% or more
to 0.65% or less in weight percent and having a diameter in a range
of 5.5 mm to 6.5 mm is wiredrawn through a single wiredrawing
process to a predetermined final wiredrawing diameter having a true
strain in a range of 2.0 to 4.0 and is turned to a pearlite
structure in which ferrite and cementite are drawn in parallel with
a narrow interval therebetween.
Inventors: |
Kawashima; Masatomo;
(Gifu-ken, JP) ; Shibuya; Hidetoshi; (Gifu-ken,
JP) |
Assignee: |
FUJI SHOJI CO., LTD.
HASHIMA-SHI
JP
|
Family ID: |
43297657 |
Appl. No.: |
13/319252 |
Filed: |
May 26, 2010 |
PCT Filed: |
May 26, 2010 |
PCT NO: |
PCT/JP10/58916 |
371 Date: |
November 7, 2011 |
Current U.S.
Class: |
428/544 ;
140/71R; 420/8; 428/378 |
Current CPC
Class: |
Y10T 428/12 20150115;
C21D 2211/009 20130101; C22C 38/02 20130101; C23C 2/38 20130101;
C21D 7/02 20130101; B21C 1/003 20130101; C22C 38/04 20130101; Y10T
428/2938 20150115; C21D 8/065 20130101; C21D 9/34 20130101; B60C
15/04 20130101; C23C 2/02 20130101 |
Class at
Publication: |
428/544 ;
140/71.R; 420/8; 428/378 |
International
Class: |
D02G 3/12 20060101
D02G003/12; C22C 38/00 20060101 C22C038/00; D02G 3/36 20060101
D02G003/36; B21F 45/00 20060101 B21F045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 5, 2009 |
JP |
2009-136252 |
Claims
1-5. (canceled)
6. A tire bead wire, comprising: carbon in a range of 0.61% or more
to 0.65% or less in weight percent; and a pearlite structure
comprising ferrite and cementite, wherein the bead wire has a final
diameter, wherein the bead wire has a true strain in a range of 2.0
to 4.0, wherein the ferrite and cementite have a narrow interval
therebetween.
7. The bead wire of claim 6, wherein the bead wire has a final
diameter in a range of 0.94 to 2.20 mm.
8. The bead wire of claim 6, wherein the bead wire has a final
diameter in a range of 0.94 to 1.30 mm.
9. The bead wire of claim 6, wherein the bead wire has a final
diameter in a range of 1.5 to 2.20 mm.
10. The bead wire of claim 6, further comprising Si.
11. The bead wire of claim 6, further comprising Mn.
12. The bead wire of claim 6, further comprising Si and Mn.
13. The bead wire of claim 6, wherein the bead wire comprises
carbon in a range of 0.61% or more to 0.63% or less in weight
percent.
14. The bead wire of claim 6, wherein the bead wire comprises
carbon in a range of 0.63% or more to 0.65% or less in weight
percent.
15. A process for producing a tire bead wire, the process
comprising: (a) wiredrawing, only once, a carbon steel wire rod
comprising carbon in a range of 0.61% or more to 0.65% or less in
weight percent and having an initial diameter in a range of 5.5 mm
to 6.5 mm, to obtain a tire bead wire having a final diameter less
than the initial diameter and a true strain in a range of 2.0 to
4.0; then (b) bluing the tire bead wire; and, after the bluing, (c)
plating the tire bead wire.
16. The process of claim 15, wherein, after the wiredrawing (a),
the bead wire has a final diameter in a range of 0.94 to 2.20
mm.
17. The process of claim 15, wherein the carbon steel wire rod has
an initial diameter of 5.5 mm and, after the wiredrawing (a), the
bead wire has a final diameter in a range of 0.94 to 1.30 mm.
18. The process of claim 15, wherein the carbon steel wire rod has
an initial diameter of 6.5 mm and, after the wiredrawing (a), the
bead wire has a final diameter in a range of 1.5 to 2.20 mm.
19. The process of claim 15, wherein the carbon steel wire rod
further comprises Si.
20. The process of claim 15, wherein the carbon steel wire rod
further comprises Mn.
21. The process of claim 15, wherein the carbon steel wire rod
further comprises Si and Mn.
22. The process of claim 15, wherein the carbon steel wire rod
comprises carbon in a range of 0.61% or more to 0.63% or less in
weight percent.
23. The process of claim 15, wherein the carbon steel wire rod
comprises carbon in a range of 0.63% or more to 0.65% or less in
weight percent.
24. A tire bead wire obtained by the process of claim 15.
Description
TECHNOLOGICAL FIELD
[0001] The present invention relates to a tyre bead wire and a
production process therefor used in producing bead cores made of
carbon steel wires being reinforcements of automotive tyres.
BACKGROUND ART
[0002] Tyre bead wires are required to be tough and high in
durability. In general, as the tyre bead wires, there have been
used those which are 1.55 mm in diameter and equal to 1880
N/mm.sup.2 or higher in tensile strength or those which are 0.94 mm
in diameter and equal to 1840 N/mm.sup.2 or higher in tensile
strength. Like this, the bead wires require a high tensile
strength. Thus, as material wires of hard steel wires, there has
been used a high-carbon steel wire rod which is primarily 5.5 mm in
diameter and has a carbon content in a range of 0.69-0.86 weight
percents, and the bead wire rod is manufactured by being subjected
to a wiredrawing process in which a total area-reduction rate is in
a range of 92-97 percents or so.
[0003] The high-carbon steel wire rod is regulatively cooled after
being hot-rolled if need be, and the resultant wire rod of pearlite
structures having a diameter in a range of 5.5-6.5 mm is
repetitively subjected to wiredrawing processes and patenting
treatments to become a diameter in a range of 3.0-2.0 mm for a
final wiredrawing. The wire rod of this diameter, after being
subjected to the final wiredrawing, is then subjected to a bluing
treatment and a plating treatment and is coiled, whereby there can
be manufactured a steel cord that is usable as reinforcement in
radial tyres, conveyor belts or the like. For example, Patent
Document 1 describes a process for producing steel cords of this
kind.
[0004] Further, for example, Patent Document 2 describes a process
for performing a second wiredrawing process without performing an
intermediate patenting treatment. In the process described in
Patent Document 2, by exerting a mechanical external force on a
steel material to deform the same, the temperature of the steel
material is raised to sufficiently dry borax in the second
wiredrawing process, so that the second wiredrawing process can be
realized without suffering seizure and wire breaking.
PRIOR ART DOCUMENTS
[0005] Patent Document 1: JP7-3338 A [0006] Patent Document 2:
JP2008-284581 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0007] In order to manufacture a wire of a predetermined diameter
through a first wiredrawing process only (omission of the second
wiredrawing process) by omitting the intermediate patenting
treatment, it is necessary to use a material wire rod of a special
diameter which is thinner than 5.5 mm for general purpose in terms
of preventing wire breaking due to a high-stress processing as well
as of maintaining the post-wiredrawing strength at a predetermined
strength. However, unlike the case of using a wire rod of 5.5 mm
diameter for general purpose, the wire rod of the special wire
diameter (e.g., 5.0 mm or less in diameter) which is small in
production volume is required to be repetitively subjected to
wiredrawing processes and patenting treatments, and this gives rise
to problems that increase the cost for the material wire rod and
thus, the production cost for bead wires and hence, for tyres.
[0008] Further, in recent years, in an aspect of environment, tyres
are increased in a rate to be used twice with treads repaired after
a first long-term use, and thus, requirements for adhesive strength
and durability after the long-term use have been increasing in a
respect of adhesion of bead wires to surrounding rubber.
[0009] Further, in an aspect of production, it is conventional that
for a continuous production, a material wire rod as material is
subjected to a wiredrawing process as a wire rod in use is welded
to a wire rod to be used next. However, with an increase in carbon
content, such welding causes a remarkable change in structure at a
portion that was heated at a high temperature, and this gives rise
to a problem that a large influence is given on strength and
toughness.
[0010] The present invention has been made in order to solve the
foregoing problems in the prior art, and an object thereof is to
provide a tyre bead wire and a production process for the same
which are capable of employing a carbon steel wire rod having a
general-purpose wire diameter whose carbon content in weight
percent is in a range of 0.61% or more to 0.65% or less, and of
wiredrawing the rod to a predetermined final wiredrawing diameter
suitable for bead wires through one process without performing a
patenting treatment.
Measures for Solving the Problem
[0011] The feature of the invention in a tyre bead wire according
to Claim 1 resides in that a carbon steel wire rod containing
carbon in a range of 0.61% or more to 0.65% or less in weight
percent and having a diameter in a range of 5.5 mm to 6.5 mm is
wiredrawn through one wiredrawing process to a predetermined final
wiredrawing diameter with a true strain in a range of 2.0 to 4.0
and is turned to pearlite structures in which ferrite and cementite
are drawn in parallel with an interval therebetween made to be
narrow.
[0012] The feature of the invention in the tyre bead wire according
to Claim 2 resides in that in Claim 1, the one wiredrawing process
results in wiredrawing to a diameter in a range of 0.94 mm to 1.30
mm.
[0013] The feature of the invention in a tyre bead wire production
process according to Claim 3 resides in that a carbon steel wire
rod containing carbon in a range of 0.61% or more to 0.65% or less
in weight percent and having a diameter in a range of 5.5 mm to 6.5
mm is wiredrawn through one process to a predetermined final
wiredrawing diameter with a true strain in a range of 2.0 to 4.0
and that the wire rod after the wiredrawing is blued and then, is
plated.
[0014] The feature of the invention in the tyre bead wire
production process according to Claim 4 resides in that in Claim 3,
the carbon steel wire rod being 5.5 mm in diameter is wiredrawn to
a final wiredrawing diameter in a range of 0.94 to 1.30 mm.
[0015] The feature of the invention in the tyre bead wire
production process according to Claim 5 resides in that in Claim 3,
the carbon steel wire rod being 6.5 mm in diameter is wiredrawn to
a final wiredrawing diameter in a range of 1.5 to 2.20 mm.
Effects of the Invention
[0016] In the invention of the tyre bead wire according to Claim 1,
the carbon steel wire rod containing carbon in the range of 0.61%
or more to 0.65% or less in weight percent and having the diameter
in the range of 5.5 mm to 6.5 mm is wiredrawn through one
wiredrawing process to the predetermined final wiredrawing diameter
with the true strain in the range of 2.0 to 4.0 and is turned to
the pearlite structures in which ferrite and cementite are drawn in
parallel with the interval therebetween made to be narrow.
Therefore, although the carbon steel wire rod of a general-purpose
diameter is employed, it can be realized to obtain a useful tyre
bead wire which is superior in tensile strength, is excellent in
adhesion of the bead wire to surrounding rubber, and does not bring
about the breaking of wire during the wiredrawing and the breaking
of wire at welded parts thereof.
[0017] In the invention of the tyre bead wire according to Claim 2,
since the one wiredrawing process results in wiredrawing to the
diameter in the range of 0.94 mm to 1.30 mm, it can be realized to
obtain the bead core of the diameter suitable for production of
bead cores easily and efficiently.
[0018] In the invention of the tyre bead wire production process
according to Claim 3, the carbon steel wire rod containing carbon
in the range of 0.61% or more to 0.65% or less in weight percent
and having the diameter in the range of 5.5 mm to 6.5 mm is
wiredrawn through one process to the predetermined final
wiredrawing diameter with the true strain in the range of 2.0 to
4.0. Therefore, it becomes possible to wiredraw the carbon steel
wire rod of the relatively low carbon content at the high
area-reduction rate without a patenting treatment and to wiredraw
the carbon wire rod of the general-purpose wire diameter (5.5-6.5
mm diameter) through the one process to the final wiredrawing
diameter suitable for bead wire without bringing about the breaking
of the wire but with a required tensile strength secured.
[0019] In addition, because the carbon wire rod is low in carbon
content to be softened, the workability in wiredrawing the carbon
steel wire rod can be improved, and the productivity can be
enhanced. Further, in continuously wiredrawing the wire rod, it
becomes easier to perform a welding at the time of welding material
wires which welding is required in a continuous production by using
a material wire in use and another material wire to be used next,
and the breaking of wire at the welded portion is made to be hard
to occur.
[0020] In the invention of the tyre bead wire production process
according to Claim 4, since the carbon steel wire rod being 5.5 mm
in diameter is wiredrawn to the final wiredrawing diameter in the
range of 0.94 to 1.30 mm, it is possible to employ the carbon steel
wire rod of 5.5 mm diameter for general purpose, and an equipment
for the patenting treatment can be made to be unnecessary, so that
the bead wire can be manufactured at a low cost.
[0021] In the invention of the tyre bead wire production process
according to Claim 5, since the carbon steel wire rod being 6.5 mm
in diameter is wiredrawn to the final wiredrawing diameter in the
range of 1.5 to 2.20 mm, it is possible to employ the carbon steel
wire rod of 6.5 mm diameter for general purpose, and an equipment
for the patenting treatment can be made to be unnecessary, so that
the bead wire can be manufactured at a low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] [FIG. 1] is a view illustrating the layers of ferrite and
cementite having been drawn in parallel by wiredrawing.
[0023] [FIG. 2] is a chart of an embodiment showing production
processes in a tyre bead wire production process of the present
invention.
[0024] [FIG. 3] is photos of the surfaces of bead wires in the
state that plated surface layers are removed from the bead wires
which are manufactured as shown in FIG. 2.
FORM FOR IMPLEMENTING THE INVENTION
[0025] Hereinafter, description will be made regarding a tyre bead
wire production process in an implementation form of the present
invention.
[0026] Bead wires for vehicle tyres are required to be tough and
high in durability. The strength of a bead wire can be intensified
by wiredrawing and thinning in wire diameter a wire rod which has
fine pearlite structures (2-phase structure of ferrite (Fe) and
cementite (Fe.sub.3C)) and which has been subjected to a patenting
treatment. Tyres which employ bead cores produced by using the bead
wire made of such a wire rod can contribute to requirements for
high strength, high toughness and light weight. This is because, as
shown in FIG. 1, the wiredrawing process causes the crystals of
high strength cementite (Fe.sub.3C) and ferrite (Fe) to be drawn
and to be oriented in parallel in the wiredrawing direction, so
that the width of ferrite phases is narrowed to increase the
strength. And, the thinner the wiredrawing process makes the wire
diameter, the higher the strength becomes.
[0027] However, the thinner the wire diameter is made, the harder
the wire rod becomes, and the flexibility is lost. Thus, the wire
diameter to which the wire rod can be fined by one wiredrawing
process is restrained as a matter of course. For this reason, in
order to attain a desired wire diameter, it is required to carry
out, after a wiredrawing process to a predetermined wire diameter,
a patenting treatment to return the wire rod again to fine pearlite
structures suitable for wiredrawing, and then to carry out another
wiredrawing process again. By the repetition of these processes,
for instance, the wire rod of 5.5 mm in wire diameter is wiredrawn
to 1.20 mm diameter, and then, a bluing treatment is carried out at
a temperature in a range of 380 to 480.degree. C. to give a stretch
necessary for steel wire. And, a plating treatment is carried out
to enhance the adhesibility of the bead wire to surrounding rubber,
and then, the bead wire is coiled by a coiler in the form of a
coil. However, the process like that is required to install an
equipment for the patenting treatment in the production
facility.
[0028] A small-diameter material wire of, for example, 4.0 mm or
4.5 mm in wire diameter can be used in order to make the equipment
for the patenting treatment unnecessary and in order to wiredraw a
wire rod through one wiredrawing process to a desired wire diameter
(2.20-0.94 in diameter) suitable for bead wire. However, in order
to realize this, material wires of the special diameter must be
obtained from steel manufacturers.
[0029] Therefore, in the present implementation form, as the
material wire for bead wire, a wire rod being a carbon steel whose
carbon content is in a range of 0.61-0.65 in weight percent and is
lower than the carbon content of the prior at wire rod, and having
a wire diameter in a range of 5.5-6.5 mm is wiredrawn through one
process to a predetermined final wiredrawing diameter (2.20-0.94 mm
diameter) suitable for bead wire without being subjected to a
patenting treatment. Although the area reduction rate becomes
larger in comparison with the area reduction rate in the prior art,
the wire rod is lower in carbon content than that in the prior art
and is a softer material than that in the prior art. Therefore,
wiredrawing at a high area-reduction rate can be done. Moreover, as
a result of wiredrawing the carbon steel of the low carbon content
at the high area-reduction rate, there can be obtained a bead wire
that is turned to pearlite structures in which, as shown in FIG. 1,
ferrite (Fe) and cementite (Fe.sub.3C) are narrowed in the interval
therebetween and are drawn in parallel with fine and smooth
structures, that can secure a tensile strength and a toughness
required for bead wire, that is excellent in the adhesion to
surrounding rubber, and that can prevent the breaking of wire
during the wiredrawing and the breaking of wire at welded
portions.
[0030] FIG. 2 shows a production process for bead wire. A carbon
steel (wire rod) having a wire diameter in a range of 5.5-6.5 mm
and a carbon content in a range of 0.61-0.65 in weight percent is
uncoiled from a coiler (10) and has an oxide film on the surface
removed by a descaling device (11). Then, the carbon steel is made
to pass through a coating liquid adhesion device to adhere a
coating liquid on the surface of the wire rod (12) and is dried.
Thereafter, the wire rod is wiredrawn by serially arranged dry
wiredrawing devices 30 through one process to a predetermined final
wiredrawing diameter (2.20-0.94 mm diameter) with a true strain in
a range of 2.0-4.0 (13) and is coiled by a coiler (14).
[0031] At this time, in the case of the wire diameter being 5.5 mm,
the final wiredrawing diameter which is to be obtained by the
wiredrawing through one process is preferably in a range of
0.94-1.30 mm diameter or so, and in the case of the wire diameter
being 6.5 mm, the final wiredrawing diameter which is to be
obtained by the wiredrawing through one process is preferably in a
range of 1.5-2.20 mm diameter or so.
[0032] Subsequently, the wire rod which has been wiredrawn to the
final wiredrawing diameter is uncoiled from the coiler (20) and
then, is subjected to a bluing treatment by a bluing treatment
device (21). And, the wire rod is plated by a plating treatment
device (22) and is coiled by a coiler (23), whereby a tyre bead
wire is produced.
[0033] In continuously producing wire rods, in order to perform the
continuous production by using a material in use and a material to
be used next without discontinuing the production, it is required
to join the terminal end of the material in use and the starting
end of the material to be used next by welding. The productivity is
largely influenced in dependence on an occurrence rate of wire
breakings at welded portions where a tensile load and a bending are
weaker than other portions. However, welding causes each welded
portion and portions close thereto having been exposed to a high
temperature to be remarkably changed in structure as the carbon
content in the material increases, and requires carrying out
tempering. Nevertheless, the influence goes to remain and provides
a large influence on tensile strength and toughness. On the other
hand, in the case that the carbon content in the material is low,
the occurrence rate of wire breakings caused by welding decreases,
and the productivity increases.
[0034] Further, the adhesion force between a bead wire and rubber
is determined in dependence on a chemical bonding force brought
about by a chemical reaction between the rubber and the plated
layer on the surface of the bead wire and a physical bonding force
of an anchor effect to wrinkles (unevenness) on the surface of the
bead wire. Therefore, although being limitative, the anchor effect,
when increased, makes it possible to go up the adhesion force.
Particularly, the physical bonding force by the anchor effect is
effective where a tyre is subjected to a high temperature, a high
moisture and repetitive strains due to a hard travelling which
causes the adhesive interface between the rubber and the surface of
the bead wire to deteriorate and raises the rate at which the
boundary surface is exposed.
Embodiment
[0035] Next, the construction and operation effects of the present
invention will be described in detail based on an embodiment.
Embodiment 1
[0036] As shown in Table 1, a hard steel wire rod of 5.5 mm in wire
diameter prescribed by JIS (Japanese Industrial Standards) G3506
SWRH62A was used as a material wire rod. The chemical components
were C: 0.63%, Si: 0.21% and Mn: 0.52%, and the remainder thereof
was Fe and inevitable impurities. An oxide film on the surface of
the material rod was removed by a descaling device, and then, the
material rod was made to pass through a coating liquid adhesion
device, whereby a coating liquid was adhered to the surface of the
wire rod and was dried. Thereafter, by dry wiredrawing devices
arranged in series, the wire rod was reduced in area through one
wiredrawing process to a predetermined wire diameter being 1.20 mm
diameter with a true strain in a range of 2.0-4.0. The drawn wire
rod was coiled by a coiler in the form of a coil, and the coiled
wire rod was uncoiled to be subjected to a bluing by being made to
pass through a bath held at a temperature of 430.degree. C. and
then, to a plating treatment, whereby a bead wire was produced.
COMPARED EXAMPLE 1
[0037] As shown in Table 1, a hard steel wire rod of 5.5 mm in wire
diameter prescribed by JIS G3506 SWRH72A was used as a material
wire rod. The chemical components were C: 0.71%, Si: 0.22% and Mn:
0.49%, and the remainder thereof was Fe and inevitable impurities.
An oxide film on the surface of the material rod were removed by
the descaling device, and then, the material rod was made to pass
through the coating liquid adhesion device, whereby the coating
liquid was adhered to the surface of the wire rod. Thereafter, by
the dry wiredrawing devices arranged in series, the wire rod was
reduced in area through one wiredrawing process to the
predetermined wire diameter being 1.20 mm diameter. The drawn wire
rod was coiled by the coiler in the form of a coil, and the coiled
wire rod was uncoiled to be subjected to the bluing by being made
to pass through the bath held at the temperature of 430.degree. C.
and then, to the plating treatment, whereby a bead wire was
produced.
COMPARED EXAMPLE 2
[0038] As shown in Table 1, a hard steel wire rod of 4.5 mm in wire
diameter prescribed by JIS G3506 SWRH72A was used as a material
wire rod. The chemical components were C: 0.72%, Si: 0.21% and Mn:
0.51%, and the remainder thereof was Fe and inevitable impurities.
An oxide film on the surface of the material rod was removed by the
descaling device, and then, the material rod was made to pass
through the coating liquid adhesion device, whereby the coating
liquid was adhered to the surface of the wire rod. Thereafter, by
the dry wiredrawing devices arranged in series, the wire rod was
reduced in area through one wiredrawing process to the
predetermined wire diameter being 1.20 mm diameter. The drawn wire
rod was coiled by the coiler in the form of a coil, and the coiled
wire rod was uncoiled to be subjected to the bluing by being made
to pass through the bath held at the temperature of 430.degree. C.
and then, to the plating treatment, whereby a bead wire was
produced.
TABLE-US-00001 TABLE 1 Mechanical Properties Chemical Number of
Adhesion Force (N) - Rubber Adhesion Rate (%) Kind of Steel
Components Tensile Breaking Breakings Initial Waterproof (Diameter
of (Weight %) Strength at Wire- at Welded Adhesion Adhesion
Material Wire) C Si Mn (N/mm.sup.2) drawing Portions Property
Property 1 Embodiment 1 0.63 0.21 0.52 2000 Nil 0 1320 - 95 1180 -
80 (5.5 mm) 2 Compared 0.71 0.22 0.49 2200 Many 2 1310 - 95 1135 -
80 Example 1 (5.5 mm) 3 Compared 0.72 0.21 0.51 1950 Nil 1 1275 -
90 1010 - 40 Example 2 (4.5 mm)
[0039] Tensile tests were carried out on the bead wires produced in
the aforementioned embodiment 1 and compared examples 1 and 2 to
test the tensile strengths (N/mm.sup.2), the situations of
wire-breaking at the time of wiredrawing, and the states of
wire-breaking at welded portions. The results are as described in
the aforementioned Table 1.
[0040] As clear from Table 1, according to the production process
in compared example 1, the wire rod with a sufficient tensile
strength (2200 N/mm.sup.2) was able to be obtained, but the wire
rod could not be drawn smoothly as a result that the high carbon
steel of the wire diameter 5.5 mm having a large carbon content was
reduced in surface to the 1.2 mm wire diameter through one process
being a heavy process. As a consequence, the breaking of the wire
took place at many portions thereon during the wiredrawing.
Further, because of being high in carbon content, the wire rod had
considerable changes in structure at the portions which were heated
at a high temperature during the welding, whereby the breaking of
the wire also took place at many welded portions.
[0041] Further, according to the production process in compared
example 2, since the area reduction rate (the quantity in process)
in the wiredrawing was smaller than that in compared example 1, the
breaking of wire did not occur during the wiredrawing. The tensile
strength was 1950 N/mm.sup.2 in a level that did not raise any
problem. However, because of being high in carbon content, as is
the case of compared example 1, the wire rod had considerable
changes in structure at the portions which were heated at the high
temperature during the welding, whereby the breaking of the wire
took place at a welded portion.
[0042] Furthermore, the carbon steel wire rod of the special wire
diameter (4.5 mm) is required, and in order to obtain the carbon
steel wire rod of the 4.5 mm wire diameter by the bead wire
manufacture itself, an equipment is required that carries out a
patenting treatment on a carbon steel wire rod for general purpose
(5.5-6.5 mm diameter) purchased from a steel manufacturer. Where
the bead wire manufacturer does not have the equipment, there is a
constraint that the manufacturer has to obtain expensive material
wires from a steel manufacturer.
[0043] On the contrary, in the aforementioned embodiment 1, because
of using the hard steel wire rod having 0.63 weight percents in
carbon content, the processing quantity was increased in comparison
with, for example, the wiredrawing in compared example 2 that was
carried out to make the wire rod from the 4.5 mm wire diameter to
the 1.20 mm wire diameter. However, because the carbon content was
low and the material was soft, the wire rod after the wiredrawing
was turned to pearlite structures in which ferrite and cementite
were drawn in parallel with a narrow interval therebetween and with
fine and smooth structures. Therefore, it became possible to easily
obtain a wire rod of a desired wire diameter through one
wiredrawing process without bringing about the breaking of wire and
the breaking of wire at welded portions during the wiredrawing, and
the tensile strength (2000 N/mm.sup.2) was also equal to that in
compared example 2 and became as designed.
[0044] In carrying out breaking tests at welded portions of the
material wires, eleven (11) material wires each being approximately
1 meter long were prepared for each of embodiment 1 and compared
examples 1 and 2 and were joined by welding to make one wire by
being repetitively subjected to welding, annealing and deburring in
accordance with the welding procedure in each of embodiment 1 and
compared examples 1 and 2. Thereafter, the wires each welded at 10
portions were wiredrawn to 1.20 mm diameter in a conventional
method, and the number of breakings of wire was counted. The
results were as described above (in Table 1).
[0045] Photos in FIG. 3 show in an enlarged scale the surfaces of
the bead wires in the state that plated layers were removed from
the surfaces of the bead wires each produced as shown in FIG. 2. In
the bead wire, the anchor effect of its adhesion to rubber is
influenced by groove intervals of wrinkles (unevenness) which are
generated with an increase in surface area resulting from a
decrease in diameter brought about by the wiredrawing. In FIG. 3,
(A) shows the surface of the bead wire produced in the
aforementioned embodiment 1, (B) shows the surface of the bead wire
produced in the aforementioned compared example 1, and (C) shows
the surface of the bead wire produced in the aforementioned
compared example 2. Adhesion tests before and after the aging were
carried out on these bead wires. Embodiment 1 had results that were
better than those of compared examples 1 and 2 in both of an
initial adhesion property before the aging and a waterproof
adhesion property representing tyres that had traveled after the
aging. On the other hand, in particular, compared example 2 had an
inferior result in the waterproof adhesion property. From this, it
was backed up that those in embodiment 1 and compared example 1 had
the groove intervals being excellent in anchor effect in comparison
with that in compared example 2.
[0046] The tests for adhesive forces were carried out based on the
rubber adhesion testing method prescribed in JIS G3510. Embedded
rubber of a conventional composition noted below was used as bead
insulation. The numerals show ratios in mass. The ratios are
natural rubber 50, SBR 50, carbon black 100 (SEAST.RTM. SO,
manufactured by TOKAI CARBON CO., LTD.), softening agent 25,
calcium carbonate 25, talc 10, stearic acid 2, zinc oxide 5, sulfur
8, and vulcanization accelerator 1.
[0047] The tests were done with an embedded length of each bead
wire in the rubber set to 50 mm and a drawing velocity set to 150
mm/min, and visual evaluations were made regarding the drawing
force, i.e., an adhesion force (N)--rubber adhesion rate (%)
remaining on the bead wire. Those each with a plated layer of
Cu/Sn=93/7 on the surface were used as the bead wires.
[0048] The vulcanization condition for the initial adhesion
properties was for 40 minutes at 150.degree. C., and the waterproof
adhesion properties were evaluated by the aforementioned drawing
adhesion tests after leaving the vulcanized samples in an
atmosphere of 70.degree. C. and 95% RH for one week. A condition in
which tyres deteriorate due to heat after traveling was assumed for
the waterproof adhesion properties.
[0049] The foregoing embodiment has been described taking the
example that the hard steel wire rod of 5.5 mm in wire diameter
having the chemical components of C: 0.63%, Si: 0.21%, Mn: 0.52%,
and the remainder containing Fe and inevitable impurities was
reduced in area through one wiredrawing process to the 1.20 mm wire
diameter with the true strain in the range of 2.0.about.4.0. And,
almost the same effects as the forgoing embodiment 1 can be
obtained in the case that a hard steel wire rod of 6.5 mm in wire
diameter having the chemical components of C: 0.63%, Si: 0.21%, Mn:
0.52%, and the remainder containing Fe and inevitable impurities is
reduced in area through one wiredrawing process to 1.55 mm wire
diameter.
[0050] According to the bead wire in the foregoing implementation
form, the carbon steel wire rod containing carbon in the range of
0.61% or more to 0.65% or less in weight percent and having the
diameter in the range of 5.5mm to 6.5 mm is wiredrawn through one
wiredrawing process to the predetermined final wiredrawing diameter
with the true strain in the range of 2.0.about.4.0, so that the
wire rod is turned to pearlite structures in which ferrite and
cementite have been drawn in parallel with a narrow interval
therebetween. Therefore, although the carbon steel wire of the
diameter for general purpose is used, it is possible to obtain a
useful tyre bead wire which is superior in tensile strength, is
excellent in adhesion force of the bead wire to surrounding rubber,
and does not bring about the breaking of wire during the
wiredrawing and the breaking of wire at welded portions. In
particular, as a result of wiredrawing the carbon steel of the low
carbon content at the high area-reduction rate, it is possible to
realize the bead wire of the pearlite structures in which ferrite
(Fe) and cementite (Fe.sub.3C) are drawn in parallel with the
narrow interval therebetween and with the structures being fine and
smooth.
[0051] Further, according to the bead wire production process in
the foregoing implementation form, since the carbon steel wire rod
containing carbon in the range of 0.61 or more to 0.65 or less in
weight percent and having the diameter in the range of 5.5 mm to
6.5 mm is wiredrawn through one process to the predetermined final
wiredrawing diameter with the true stress in the range of 2.0-4.0,
it can be realized to wiredraw the carbon steel wire rod of the
relatively low carbon content at the high area-reduction rate
without a patenting treatment. Thus, it can be done to wiredraw the
carbon steel wire rod of the general-purpose wire diameter (5.5-6.5
mm diameter) through one process to the final wiredrawing diameter
suitable for bead wire without bringing about the breaking of wire
but with the required tensile strength secured.
[0052] Although the present invention has been described based on
the implementation form, the present invention is not limited to
the construction described in the implementation form and may take
various forms without departing from the gist of the present
invention described in the scope of the patent claims.
INDUSTRIAL APPLICABILITY
[0053] The tyre bead wire and the production process therefor
according to the present invention are suitable to obtain bead
wires used in producing bead cores which are reinforcement of
automotive tyres.
DESCRIPTION OF SYMBOLS
[0054] 11 . . . descaling treatment, 12 . . . coating fluid
adhesion treatment, 13 . . . wiredrawing process, 21 . . . bluing
treatment, 22 . . . plating treatment.
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