U.S. patent application number 16/623044 was filed with the patent office on 2020-05-28 for steel cord and single steel wire having excellent straightness quality for reinforcing tire and manufacturing method thereof.
This patent application is currently assigned to Hongduk Industrial Co., Ltd.. The applicant listed for this patent is Hongduk Industrial Co., Ltd.. Invention is credited to Do Hun Kim, Pyeong Yeol Park.
Application Number | 20200165695 16/623044 |
Document ID | / |
Family ID | 65016639 |
Filed Date | 2020-05-28 |
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United States Patent
Application |
20200165695 |
Kind Code |
A1 |
Park; Pyeong Yeol ; et
al. |
May 28, 2020 |
Steel Cord and Single Steel Wire Having Excellent Straightness
Quality for Reinforcing Tire and Manufacturing Method Thereof
Abstract
Provided are a steel cord and a single steel wire having
excellent straightness quality for reinforcing tire and a method of
manufacturing the steel cord and single steel wire. The steel cord
and the single steel wire include a wire undergoing through a
drawing process, a heating process performed in a state in which
tension is applied to the wire, and a cooling process; and a
winding portion on which the wire is wound, the winding portion
having a diameter greater than a diameter of the wire, wherein,
when an end of the wire that has been wound on the winding portion
for six months to one year is fixed on a point and the wire is
pulled down vertically to 400 mm, a distance between a first axis
that is perpendicular to the point and an opposite end of the wire
is 30 mm or less. The method of manufacturing the steel cord and
single steel wire having excellent straightness quality for
reinforcing tire includes: a wire preparing process, a heating
process, a cooling process, and a winding process.
Inventors: |
Park; Pyeong Yeol;
(Pohang-si, Gyeongsangbuk-do, KR) ; Kim; Do Hun;
(Yangsan-si, Gyeongsangnam-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hongduk Industrial Co., Ltd. |
Pohang-si, Gyeongsangbuk-do |
|
KR |
|
|
Assignee: |
Hongduk Industrial Co.,
Ltd.
Pohang-si, Gyeongsangbuk-do
KR
|
Family ID: |
65016639 |
Appl. No.: |
16/623044 |
Filed: |
March 20, 2018 |
PCT Filed: |
March 20, 2018 |
PCT NO: |
PCT/KR2018/003217 |
371 Date: |
December 16, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 9/52 20130101; B60C
9/0007 20130101; B60C 9/00 20130101; B21F 9/00 20130101; B29D 30/38
20130101 |
International
Class: |
C21D 9/52 20060101
C21D009/52; B21F 9/00 20060101 B21F009/00; B60C 9/00 20060101
B60C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2017 |
KR |
1020170090378 |
Claims
1. A steel cord and a single steel wire having excellent
straightness quality for reinforcing tire, the steel cord and the
single steel wire comprising: a wire undergoing through a drawing
process, a heating process performed in a state in which tension is
applied to the wire, and a cooling process; and a winding portion
on which the wire is wound, the winding portion having a diameter
greater than a diameter of the wire, wherein, when an end of the
wire that has been wound on the winding portion for six months to
one year is fixed on a point and the wire is pulled down vertically
to 400 mm, a distance between a first axis that is perpendicular to
the point and an opposite end of the wire is 30 mm or less.
2. The steel cord and the single steel wire of claim 1, wherein a
heating temperature in the heating process is 200.degree. C. or
less, and a cooling temperature in the cooling process is
40.degree. C. or less.
3. The steel cord and the single steel wire of claim 2, wherein the
heating temperature, a heating time, and the tension applied to the
wire during the heating process satisfy condition A below,
condition (A): T+13.67 In(t)+2.7 .tau..gtoreq.425 (In condition
(A), T is an absolute temperature K of the heating temperature, t
denotes the heating time s, and .tau. is the tension (kgf) applied
to the wire).
4. A method of manufacturing a steel cord and a single steel wire
having excellent straightness quality for reinforcing tire, the
method comprising: preparing a wire that has been drawn; heating
the wire in a state in which tension is applied to the wire;
cooling down the wire; and winding the wire on a winding portion
having a diameter that is greater than a diameter of the wire.
5. The method of claim 4, further comprising measuring straightness
by fixing an end of the wire that has been wound on the winding
portion for six months to one year at a point and pulling down the
wire vertically to 400 mm, wherein, in the measuring of the
straightness, a distance between a first axis that is perpendicular
to the point and an opposite end of the wire is 30 mm or less.
6. The method of claim 4, wherein a heating temperature in the
heating of the wire is 200.degree. C. or less, and a cooling
temperature in the cooling of the wire is 40.degree. C. or
less.
7. The method of claim 6, wherein the heating temperature, a
heating time, and the tension applied to the wire during the
heating of the wire satisfy condition A below, condition (A):
T+13.67 In(t)+2.7 .tau..gtoreq.425 (In condition (A), T is an
absolute temperature K of the heating temperature, t denotes the
heating time s, and .tau. is the tension (kgf) applied to the
wire).
Description
TECHNICAL FIELD
[0001] One or more embodiments of the disclosure relate to a steel
cord and a single steel wire having excellent straightness quality
for reinforcing tire and a method of manufacturing the same, and
more particularly, to a steel cord and a single steel wire having
excellent straightness quality for reinforcing tire, which are
capable of accelerating strain aging of the steel cord and the
single steel wire and improving straightness quality after aging by
heating and cooling down the steel cord and the single steel wire
to remove stress remaining in the steel cord and the single steel
wire, and a method of manufacturing the steel cord and the single
steel wire.
BACKGROUND ART
[0002] In general, a steel cord and a single steel wire are used to
reinforce elastomers such as tires for vehicles, industrial belts,
etc. In particular, a steel cord and a single steel wire used to
reinforce tire are demanded to meet various quality criteria in
order to function as a reinforcing material in rubber.
[0003] It takes a few months to use a steel cord and a single steel
wire as a tire reinforcing material. That is, the steel cord and
the single steel wire are wound on a spool having a certain inner
diameter and used a few months later. Based on the characteristics
of the steel cord and the single steel wire, that is, using the
steel cord and the single steel wire a few months after the
winding, the straightness of the steel cord and the single steel
wire is a significant characteristic of the steel cord and the
single steel wire for reinforcing tire. That is, inferior
straightness affects work processability during manufacturing of
the tire and generates a buckling effect and a tip rising effect,
and thus, there may be an issue during rolling and cutting
processes of a tire manufacturer.
[0004] The straightness of the steel cord and the single steel wire
may be changed due to following causes. The steel cord and the
single steel wire include carbon steel of 0.5 to 1.1C wt %. In the
carbon steel, interstitial solid atoms C and N are diffused over
time and moved and fixed to adjacent dislocations. Therefore, when
the steel cord and the single steel wire are manufactured and wound
on a spool having a certain inner diameter, the straightness of the
steel cord and the single steel wire changes due to the diffusion
and fixation of the C and N atoms and the straightness quality
degrades.
[0005] According to the steel cord and the single steel wire of the
related art, the steel cord and the single steel wire having
excellent straightness quality after aging may not be provided.
That is, even though the steel cord and the single steel wire
according to the related art have excellent straightness at an
initial stage of manufacturing, when a long period of time passes
in a state in which the steel cord and the single steel wire are
wound on the spool having a certain inner diameter, the
straightness changes due to the strain aging under the stress
within an elastic region and it is difficult to satisfy the
straightness quality.
DESCRIPTION OF EMBODIMENTS
Technical Problem
[0006] One or more embodiments of the disclosure relate to a steel
cord and a single steel wire having an excellent straightness
quality for reinforcing tire, the steel cord and the single steel
wire may have an improved straightness quality after being aged by
heating and cooling down the steel cord and the single steel wire
in order to remove stress remaining in the steel cord and the
single steel wire and to promote strain aging of the steel cord and
the single steel wire, and a method of manufacturing the steel cord
and the single steel wire.
Solution to Problem
[0007] According to an aspect of the disclosure, a steel cord and a
single steel wire having excellent straightness quality for
reinforcing tire, the steel cord and the single steel wire
includes: a wire undergoing through a drawing process, a heating
process performed in a state in which tension is applied to the
wire, and a cooling process; and a winding portion on which the
wire is wound, the winding portion having a diameter greater than a
diameter of the wire, wherein, when an end of the wire that has
been wound on the winding portion for six months to one year is
fixed on a point and the wire is pulled down vertically to 400 mm,
and a distance between a first axis that is perpendicular to the
point and an opposite end of the wire is 30 mm or less.
[0008] A heating temperature in the heating process is 200.degree.
C. or less, and a cooling temperature in the cooling process is
40.degree. C. or less. The heating temperature, a heating time, and
the tension applied to the wire during the heating process satisfy
condition A below: condition (A): T+13.67 In(t)+2.7
.tau..gtoreq.425 (In condition (A), T is an absolute temperature K
of the heating temperature, t denotes the heating time s, and .tau.
is the tension (kgf) applied to the wire).
[0009] According to another aspect of the disclosure, a method of
manufacturing a steel cord and a single steel wire having excellent
straightness quality for reinforcing tire includes: preparing a
wire that has been drawn; heating the wire in a state in which
tension is applied to the wire; cooling down the wire; and winding
the wire on a winding portion having a diameter that is greater
than a diameter of the wire.
[0010] The method may further include measuring straightness by
fixing an end of the wire that has been wound on the winding
portion for six months to one year at a point and pulling down the
wire vertically to 400 mm, wherein, in the measuring of the
straightness, a distance between a first axis that is perpendicular
to the point and an opposite end of the wire is 30 mm or less.
[0011] A heating temperature in the heating of the wire is
200.degree. C. or less, and a cooling temperature in the cooling of
the wire is 40.degree. C. or less. The heating temperature, a
heating time, and the tension applied to the wire during the
heating of the wire may satisfy condition A below: condition (A):
T+13.67 In(t)+2.7 .tau..gtoreq.425 (In condition (A), T is an
absolute temperature K of the heating temperature, t denotes the
heating time s, and .tau. is the tension (kgf) applied to the
wire).
Advantageous Effects of Disclosure
[0012] According to the disclosure, stress remaining in a steel
cord and single steel wire is removed by heating and cooling down
the steel cord and single steel wire, and thus the steel cord and
single steel wire for reinforcing tire, wherein the steel cord and
single steel wire have excellent straightness quality, that is, the
straightness does not change even when the steel cord and the
single steel wire are wound on a winding portion having a certain
inner diameter for a long period of time, may be provided.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a graph of an influence of a drawing strain on
cementite volume fraction and lamellar spacing.
[0014] FIG. 2 is a diagram showing measurement of straightness of a
wire according to an embodiment.
[0015] FIG. 3 is a processing diagram illustrating a method of
manufacturing a steel cord and a single steel wire having an
excellent straightness quality for reinforcing tire, according to
an embodiment.
[0016] FIG. 4 is a diagram showing a variation in a tensile
strength of a wire according to a heating temperature.
[0017] FIGS. 5A to 5D is pictures showing a variation in a
microstructure of a wire according to a heating temperature.
[0018] FIGS. 6A to 9 are diagrams showing carbon distribution for
each microstructure position according to the heating temperature
by using a field ion microscopy (FIM) and an atom probe tomography
(APT).
[0019] FIG. 10 is a diagram of a heating unit, a cooling unit, and
a winding unit used in a method of manufacturing a steel cord and a
single steel wire having an excellent straightness quality for
reinforcing tire, according to an embodiment.
[0020] FIGS. 11 and 12 are tables showing a variation in a
straightness according to a heating temperature, a heating time,
and tension applied to a wire.
[0021] FIG. 13 is a table showing a straightness of a steel cord
according to an embodiment as compared with that of a steel cord
according to the related art.
MODE OF DISCLOSURE
[0022] One or more embodiments of the disclosure relate to a steel
cord and a single steel wire having excellent straightness quality
for reinforcing tire and a method of manufacturing the same, and
more particularly, to a steel cord and a single steel wire having
excellent straightness quality for reinforcing tire, which are
capable of promoting strain aging of the steel cord and the single
steel wire and improving straightness quality after aging by
heating and cooling down the steel cord and the single steel wire
to remove stress remaining in the steel cord and the single steel
wire, and a method of manufacturing the steel cord and the single
steel wire. One or more embodiments of the disclosure will be
described in detail with reference to accompanying drawings.
[0023] The steel cord and single steel wire having excellent
straightness quality for reinforcing tire according to the
embodiment may include a wire 110 and a winding portion 120 on
which the wire 110 may be wound.
[0024] The wire 110 undergoes through a drawing process, a heating
process performed in a state in which tension is applied to the
wire, and a cooling process. In detail, the wire 110 is a steel
cord and single steel wire that may be used to reinforce tire, and
may include 0.5 to 1.1 wt % of carbon steel.
[0025] Undergoing through the drawing process denotes that the wire
110 undergoes through a process including the drawing process. In
detail, the wire 110 may be patented in order to ensure excellent
strength and processability. When the wire 110 is patented, a
pearlite microstructure that is an aggregate of cementite including
a carbon component and ferrite including Fe may be obtained. A
material that has been patented may undergo through a plating
process for plating brass, a drawing process for drawing to 0.15 mm
to 0.4 mm, and a stranding process for forming a steel cord by
twisting one to several tens of wires. (When the wire 110 is a
single steel wire, the stranding process may not be performed.) The
drawing process through which the wire 110 undergoes may denote any
type of process provided that the process includes the drawing
process.
[0026] The drawing process causes large deformation in a material
and deforms a pearlite structure of high-carbon steel and
accelerates decomposition of cementite in a lamellar layer. FIG. 1
is a graph of an influence of a drawing strain on cementite volume
fraction and lamellar spacing. As the drawing strain increases, the
lamellar spacing is linearly reduced and the cementite volume
fraction decreases. This denotes that the cementite is decomposed
while drawing the wire. Therefore, the cementite is decomposed due
to the deformation generated during the drawing process and a
fraction of C and N, that is, interstitial solid atoms, increases
in a ferrite matrix phase.
[0027] Here, strain aging is shown when the interstitial solid
atoms such as C, N, etc. are fixed at dislocations according to
time, and factors thereof may include time, temperature, a density
of dislocations, etc. as well as a density of the solid atoms.
Moreover, dislocations of high density are in the material having a
large plastic deformation through the drawing process, which
further accelerates the aging.
[0028] That is, when the steel wire that has undergone the drawing
process is wound on a spool having a certain inner diameter, the
cementite is decomposed and strain aging occurs, and there is a
change in the straightness and the target straightness may not be
obtained.
[0029] The wire 110 undergoes through a drawing process, a heating
process performed in a state in which tension is applied to the
wire 110, and a cooling process, in order to artificially
accelerate and finish diffusion of the solid atoms. As such, even
after the wire 110 is wound on the winding portion 120 having a
certain inner diameter, the aging may not occur. Here, the winding
portion 120 may have a diameter that is greater than 300 times a
diameter of the wire 110, and the wire 110 is wound thereon.
[0030] Preventing of the aging will be described in detail with
reference to FIG. 2. That is, an end 111 of the wire 110 that has
been wound on the winding portion 120 for six months to one year is
fixed at a point 150, and then the wire 110 is pulled down
vertically. Here, the wire 110 is pulled down to 400 mm. That is, a
distance between the end 111 of the wire and an opposite end 112 of
the wire 110 is 400 mm.
[0031] Whether the aging does not occur in the wire 110 may be
determined based on a distance between a first axis 151 that is
perpendicular to the point 150 and the opposite end 112 of the wire
110. In the steel cord and single steel wire for reinforcing tire
according to the disclosure, the wire 110 that has undergone
through the drawing process undergoes through the heating process
and the cooling process, and thus the distance between the first
axis 151 that is perpendicular to the point 150 and the opposite
end 112 of the wire 110 is equal to or less than 30 mm.
[0032] A heating temperature is 200.degree. C. or less in the
heating process, in which the wire 110 is heated in a state where
the tension is applied to the wire 110, and a cooling temperature
after the heating of the wire 110 may be 40.degree. C. or less,
that is, room temperature. Here, the heating temperature may range
from 50.degree. C. to 200.degree. C. and the cooling temperature
may range from 10.degree. C. to 40.degree. C.
[0033] The heating temperature, the heating time, and the tension
applied to the wire 110 during the heating process in which the
wire 110 is heated may satisfy the following condition (A).
[0034] Condition (A): T+13.67 In(t)+2.7 .tau..gtoreq.425 (In
condition (A), T is an absolute temperature K of the heating
temperature, t denotes the heating time s, and .tau. is the tension
(kgf) applied to the wire)
[0035] The heating process for heating the wire 110 and the cooling
process for cooling down the heated wire 110 will be described in
more detail in the method of manufacturing of the steel cord and
the single steel wire having excellent straightness quality for
reinforcing tire, which will be described later.
[0036] Referring to FIG. 3, the method of manufacturing the steel
cord and single steel wire having excellent straightness quality
for reinforcing tire may include preparing wire (S100), a heating
process (S200), a cooling process (S300), a winding process (S400),
and a measuring process of straightness (S500). (Here, the heating
process S200 and the cooling process S300 correspond to the
above-described process for heating the wire 100 and the process
for cooling down the heated wire 110.) The process of preparing
wire (S100) includes preparing a drawn wire.
[0037] The process of preparing wire (S100) may include various
processes, provided that the process of drawing the wire 110 is
included. The heating process S200 is a process for heating the
drawn wire 110 in a state in which the tension is applied to the
wire 110.
[0038] FIG. 4 shows a variation in a tensile strength according to
a heating temperature of the wire 110 that is drawn. Referring to
FIG. 4, the tensile strength of the wire 110 is the maximum between
a temperature range of 100.degree. C. to 150.degree. C. and is
reduced at a temperature 200.degree. C. or greater. The variation
in the strength within the above temperature range is caused by a
dislocation lock effect due to carbon atoms. Also, the reduction in
the strength at the temperature of 200.degree. C. or greater is
caused due to recovery and recrystallization effects. FIG. 5A shows
a change in a microstructure of the wire 110 that is not heated,
and FIGS. 5B, 5C, and 5D respectively show changes in the
microstructure of the wire 110 at the temperature of 150.degree.
C., 200.degree. C., and 350.degree. C., respectively.
[0039] In FIGS. 5A to 5D, a bright portion denotes a ferrite layer
including Fe and a dark portion denotes a cementite layer including
Fe.sub.3C. Pearlite has a structure, in which the ferrite layer
including Fe and the cementite layer including Fe.sub.3C are
alternately stacked as layers. Referring to FIGS. 5A to 5D, the
microstructure of a drawn wire (FIG. 5A) shows the pearlite
arranged in the drawing direction and is not noticeably different
from the microstructures at the temperature of 200.degree. C. or
less (FIGS. 5B and 5C).
[0040] However, in the microstructure at the temperature of
350.degree. C. (FIG. 5D), a lamellar layer of a round shape is
observed, that is, a microstructure in recovery process is
observed. The changes in the tensile strength and the
microstructure shown in FIGS. 4 and 5A to 5B are exhibited due to
the movement of carbon, and movement of the carbon and the
dislocation fixing may be accelerated through the heating
process.
[0041] In detail, when the wire 110 is heated at the temperature of
200.degree. C. or less, the tensile strength may be increased
without changing the microstructure largely. However, when the
heating temperature is excessively higher than 200.degree. C., a
physical aspect of the wire deteriorates so that the change in the
microstructure may be observed and the tensile strength decreases.
That is, it may be understood that the temperature at which the
heating effect may be sufficiently exhibited while showing a
similar structure as that of not being heated may be 200.degree. C.
or less. FIGS. 6A to 9B are diagrams showing carbon distribution
for each microstructure position according to the heating
temperature by using a field ion microscopy (FIM) and an atom probe
tomography (APT).
[0042] FIGS. 6A, 7A, 8A, and 9A show FIM images according to the
temperature, and FIGS. 6B, 7B, 8B, and 9B show distribution of
carbons according to the temperature. In FIGS. 6A to 9B, a bright
portion denotes ferrite and a dark portion denotes cementite. FIGS.
6A and 6B shows a state in which the drawing process is performed
and the heating process is not performed, and the lamellar
structure in which the ferrite and the cementite are clearly
distinguished from each other is observed.
[0043] That is, right after the drawing, decomposition of the
cementite is restricted. Here, restriction on the decomposition of
the cementite denotes that the cementite is not decomposed in the
wire that has undergone through the drawing process, and thus the
cementite is decomposed when the wire is wound on the winding
portion and accordingly the strain aging may occur. FIGS. 7A and 7B
shows a state in which the drawing process is performed and then
the heating process is performed at a temperature of 150.degree.
C.
[0044] Referring to FIGS. 7A and 7B, the bright portion and the
dark portion are evenly arranged, and thus, carbon atoms are evenly
distributed throughout the entire portions. Also, a concentration
of the carbon is 4 to 5 at % which is identical with an average
carbon content in the wire. (As described above, the wire may
include 0.5 to 1.1 wt % of carbon steel, and FIGS. 6A to 9B shows
that the wire includes 0.92 wt % of carbon steel. at %, that is,
atomic %, denotes an atomic ratio for a certain element, 0.92 wt %
may be converted into 4.5 at %, and thus the atomic ratio of the
carbon in a base material (wire) of Fe on average is 4.5 at %.
Referring to FIG. 7B, the atomic ratio of carbon is shown as 4 to 5
at % throughout the entire period, which denotes that the carbon
atoms are evenly distributed in the base material (wire). That is,
the wire is heated at the temperature of 150.degree. C. after the
drawing process, and then carbon atoms are moved and the aging
effect may be accelerated by the heating process. Acceleration of
the aging effect allows the wire to be aged through the heating
process before being wound on the winding portion so that the aging
may not occur later.
[0045] FIGS. 8A and 8B shows a state in which the heating process
is performed at the temperature of 200.degree. C. after the drawing
process and shows uneven carbon distribution as compared with FIGS.
7A and 7B. A region with high carbon concentration has a carbon
concentration lower than that of the cementite, that is, 25 at %,
and a region with low carbon concentration has a carbon
concentration, that is, 2 to 3 at %, which is lower than an average
carbon concentration of a wire heated at the temperature of
150.degree. C.
[0046] (Here, cementite denotes Fe.sub.3C that includes 6.67 wt %
of C (carbon) in Fe matrix phase.) Fe.sub.3C may be converted as
about 25 at %, and that the carbon concentration is lower than the
carbon concentrate of the cementite, that is, 25 at %, denotes that
the cementite region is decomposed and the carbon atoms are
decomposed into the matrix phase, or C is integrated on
dislocations or grain boundaries and a region having a high carbon
concentration is shown.) That is, as the heating temperature
increases from 150.degree. C. to 200.degree. C., carbon atoms are
continuously diffused, and the region with high carbon
concentration is regarded as a previous cementite region or a
ferrite lamellar region with integrated dislocations. FIGS. 9A and
9B shows a state in which the heating process is performed at the
temperature of 350.degree. C. after the drawing process, and a
noticeable difference is observed in FIGS. 9A and 9B as compared
with the microstructure shown in FIGS. 8A and 8B. In the FIM image
of FIG. 9A, bright and dark regions are clearly contrasted
similarly to the FIM image of the wire that has undergone the
drawing process but not the heating process as shown in FIG. 6A,
but a dark lamellar region that is spheroidized is observed.
[0047] A small cementite or spheroidized carbon is generated along
the grain boundary, and the carbon concentration in the ferrite is
lower than that of the wire that is heated at a lower
temperature.
[0048] That is, according to the result of observing the tensile
strength and the microstructure according to the heating process at
each temperature after the drawing process, at the heating
temperature of 150.degree. C. or less, interstitial solid atoms
such as C and N are diffused and fixed at the dislocations under a
cottrell effect, and thus, the tensile strength is increased and
the wire that is hard to be plastic deformed after being wound on
the winding portion may be obtained. However, when the heating
temperature is 200.degree. C. or greater, the tensile strength
decreases due to the recovery of the microstructure and
spheroidization of the cementite, which causes decrease in the
cutting force that is a quality criteria of the wire, and thus, it
is difficult to apply the heating process to the wire. Also, the
heating process at the high temperature accompanies increase in
manufacturing costs, and thus, the heating temperature may be at
150.degree. C. or less.
[0049] As described above, the heating temperature during the
heating process S200 is 200.degree. C. or less, for example,
150.degree. C. or less. (The heating temperature may range from
50.degree. C. to 200.degree. C.) Also, referring to FIG. 4, the
heating temperature in the heating process S200 may range from
80.degree. C. to 150.degree. C. in order to increase the tensile
strength. In the cooling process S300, the wire 110 that has
undergone through the heating process S200 is cooled down.
[0050] Since the wire 110 that has undergone through the heating
process S200 is exposed under an environment, in which C and N in
the wire 110 are likely to be diffused, the strain aging may not be
prevented when the wire 110 is wound without being sufficiently
cooled down. Therefore, the cooling process S300 is performed to
cool down the wire 110 that has undergone through the heating
process 8200.
[0051] A cooling temperature in the cooling process S300 may be
40.degree. C. or less, that is, may range from 10.degree. C. to
40.degree. C. In more detail, the cooling process S300 may be
performed at room temperature. The cooling process S300 may be
performed by various methods, e.g., an air cooling type method, a
water cooling type method, etc.
[0052] The winding process S400 is a process for winding the wire
110 that has undergone through the heating process S200 and the
cooling process S300 on the winding portion 120 having a diameter
that is greater than that of the wire 110. The diameter of the
winding portion 120 is greater than 300 times the diameter of the
wire 110, and when the diameter of the winding portion 120 is less
than 300 times the diameter of the wire 110, there may be an issue
when winding the wire 110. Therefore, the diameter of the winding
portion 120 may be greater than 300 times the diameter of the wire
110.
[0053] Referring to FIG. 10, the wire 110 undergoes through the
heating process S200 in a heater 130 and the cooling process S300
in a cooler 140, and then is wound on the winding portion 120.
Here, the heater 130 includes a first temperature sensor 131 in
order to sense and adjust the temperature applied to the wire 110
in the heating process S200, and the cooler 140 includes a second
temperature sensor 141 in order to sense and adjust the temperature
applied to the wire 110 in the cooling process S300. The method of
manufacturing the steel cord and single steel wire having excellent
straightness quality for reinforcing tire according to the
embodiment may further include the measuring process of the
straightness (8500).
[0054] Referring to FIG. 2, in the measuring process of the
straightness (S500), the end 111 of the wire 110 that has been
wound on the winding portion 120 for six months to one year is
fixed at the point 150, and then the wire 110 is pulled down
vertically to 400 mm. The wire 110 that is wound on the winding
portion 120 after undergoing through the heating process S200 and
the cooling process S300 has been already strain aged in the
heating process S200, and thus the strain aging no longer occurs
even when the wire 110 is wound on the winding portion 120.
[0055] This may be identified in the measuring process of
straightness (S500). In detail, in the measuring process of
straightness (S500), a distance between the first axis 151 that is
perpendicular to the point 150 and the opposite end 112 of the wire
110 may be 30 mm or less.
[0056] Since the wire 110 is heated in a state of being applied the
tension in the heating process S200, the tension applied to the
wire 110, the heating temperature of the wire 110, and a time taken
to heat the wire 110 may vary. In order to accelerate the strain
aging through the heating process S200, the heating temperature,
the heating time, and the tension applied to the wire 110 in the
heating process S200 may satisfy the condition A below.
[0057] Condition (A): T+13.67 In(t)+2.7 .tau..gtoreq.425 (In
condition (A), T is an absolute temperature K of the heating
temperature, t denotes the heating time s, and .tau. is the tension
(kgf) applied to the wire)
[0058] When an upper limit of the condition A exceeds 600, it is
inefficient in an economic aspect and a processability aspect, and
thus the condition A may be 600.gtoreq.T+13.67 In(t)+2.7
.tau..gtoreq.425. When the heating process is performed with the
heating temperature and the heating time satisfying the condition A
above, the interstitial solid atoms, e.g., C and N, are
sufficiently diffused and fixed at the dislocation, and thus, the
strain aging is accelerated and deformation may not occur even when
a long period time passes after winding the wire 110 on the winding
portion 120.
[0059] When the heating process is performed for a time period that
does not satisfy the condition A above at a predetermined
temperature, a bend radius of the straightness of the wire 110 is
less than that of right after the manufacturing, and when a tire
manufacturing process is performed to use the wire 110 as a tire, a
buckling or tip rising effect may occur.
[0060] Also, the tension applied to the wire 110 in the heating
process S200 affects the heating temperature and the heating
time.
[0061] As described above, the heating process S200 accelerates the
strain aging by diffusing the interstitial solid atoms. When the
tension applied to the wire 110 increases, the straightness of the
wire 110 also increases and an excellent effect of improving
straightness may be shown under the same heating condition.
[0062] Therefore, when the tension is applied to the wire 110 in
the heating process S200, the heating temperature and the heating
time may be reduced. FIGS. 11 and 12 are tables showing variations
in straightness according to time after the heating and cooling
processes are performed under the heating temperature, the heating
time, and the tension applied to the wire 110 according to the
condition A above. The wire 110 used in FIGS. 11 and 12 has a
structure of 2.times.0.30. (The structure of 2.times.0.30 denotes a
structure in which two wires each having a 0.3 mm diameter are
combined.)
[0063] FIG. 11 shows the change in straightness according to the
heating temperature and the heating time respectively when the
tension is 0.5 kgf, 1 kgf, 2 kgf, and 4 kgf, and FIG. 12 shows the
change in straightness according to the heating temperature and the
heating time respectively when the tension is 6 kgf, 8 kgf, and 10
kgf. Here, the straightness (mm) is measured in the measuring
process of straightness (8500). That is, the end 111 of the wire
110 is fixed at the point 150 and the wire 110 is vertically pulled
down to 400 mm, and then a distance between the first axis 151 that
is perpendicular to the point 150 and the opposite end 112 of the
wire 110 is measured. Also, the change in the straightness denotes
a difference between the straightness right after the manufacturing
of the wire and the straightness seven months later. Referring to
FIGS. 11 and 12, it may be understood that the straightness less
changes as the tension, the heating temperature, and the heating
time increase, and in a state in which the tension is 4 kgf or
greater, the straightness less changes according to fixed
conditions of the heating temperature and the heating time.
[0064] FIG. 13 shows changes in straightness in the steel cord
according to the embodiment and a steel cord of the related art,
which undergo through the heating process under the tension of 4
kgf and at the heating temperature 1500.degree. C. for two seconds.
Referring to FIG. 13, change in the straightness in the steel cord
according to the disclosure is greatly reduced as compared with the
steel cord according to the related art, and this denotes that the
straightness quality is improved. That is, when sufficiently high
heating temperature and long heating time are applied, the
interstitial solid atoms are actively diffused and strain aging is
accelerated. Thus, even when the wire 110 is wound on the winding
portion 120, the steel cord and single steel wire having less
change in the straightness may be manufactured, and the
straightness may be improved as the tension is high.
[0065] In detail, when the tension, the heating temperature, and
the heating time satisfying the condition A above are applied, the
steel cord and single steel wire having a straightness of 30 mm may
be manufactured.
[0066] The steel cord and single steel wire having excellent
straightness quality for reinforcing tire and the method of
manufacturing the steel cord and single steel wire according to the
disclosure may have the following effects. The stress remaining in
the steel cord and single steel wire is removed by heating and
cooling down the steel cord and single steel wire, and thus, the
steel cord and single steel wire for reinforcing tire, wherein the
steel cord and single steel wire have excellent straightness
quality, that is, the straightness does not change even when the
steel cord and the single steel wire are wound on the winding
portion having a certain inner diameter for a long period of time,
may be provided.
[0067] In detail, according to the disclosure, the strain aging of
the steel cord and single steel wire may be accelerated by
performing the heating process. It takes a few months to use the
steel cord and single steel wire according to the related art as
the tire reinforcing material, and to do this, the steel cord and
single steel wire are wound on a spool having a certain inner
diameter.
[0068] Then, strain aging may occur while the steel cord and the
single steel wire according to the related art are being wound on
the spool, which may cause straightness issue.
[0069] However, according to the disclosure, the strain aging that
may occur while the steel cord and single steel wire are wound on
the winding portion may be accelerated in advance through the
heating process and the cooling process, and then the strain aging
does not occur after winding the steel cord and single steel wire
and the steel cord and single steel wire may have excellent
straightness.
[0070] In addition, conditions of the heating process (heating
temperature, heating time, and tension applied to the wire) in
order not to change the straightness even when the wire is wound on
the winding portion for a long period of time are obtained through
the condition A above, and thus, the steel cord and single steel
wire having excellent straightness quality for reinforcing tire may
be provided. While the preferred embodiments of the present
invention have been described in detail, it will be apparent to
those skilled in the art that various modifications can be made to
the above-described exemplary embodiments of the present invention
without departing from the scope of the invention. Therefore, the
scope sought to be protected of the disclosure shall be defined by
the appended claims.
* * * * *