U.S. patent application number 11/854324 was filed with the patent office on 2008-03-13 for method and apparatus for heat treatment of steel rail.
This patent application is currently assigned to Panzhihua Iron and Steel (Group) Corporation. Invention is credited to Jinlong Zhan.
Application Number | 20080060726 11/854324 |
Document ID | / |
Family ID | 37777909 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080060726 |
Kind Code |
A1 |
Zhan; Jinlong |
March 13, 2008 |
METHOD AND APPARATUS FOR HEAT TREATMENT OF STEEL RAIL
Abstract
The present invention discloses a heat treatment method of steel
rail, comprising the steps of: (1) keeping the rolled hot steel
rail running continuously, and performing hot straightening process
for it; (2) performing first heat treatment process for the rolled
hot steel rail after the hot straightening process, i.e., forced
cooling the rail head and the rail base of the steel rail in a
jetting air cooling manner, and (3) performing second heat
treatment process for the steel rail after the first heat treatment
process, i.e., heating the rail head of the steel rail to a
temperature of 850.about.950.degree. C., and then forced cooling
the rail head of the steel rail in a jetting air cooling manner to
a temperature that is close to the temperature of the rail base of
the steel rail. Since the steel rail experiences second heat
treatment process by reheating after it is heat treated using the
residual heat of rolling, phase transition occurs in the steel rail
in the two rapid cooling processes, and finer metallographic
structure is obtained in the steel rail. When the steel rail
experiences the second heat treatment process, the rail web and the
middle part of the rail head have already been at high temperature,
therefore the energy consumption in reheating is reduced. The
present invention also discloses a heat treatment apparatus of
steel rail using the above method.
Inventors: |
Zhan; Jinlong; (Panzhihua,
CN) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Assignee: |
Panzhihua Iron and Steel (Group)
Corporation
Panzhihua
CN
|
Family ID: |
37777909 |
Appl. No.: |
11/854324 |
Filed: |
September 12, 2007 |
Current U.S.
Class: |
148/581 ;
266/252 |
Current CPC
Class: |
C21D 1/42 20130101; C21D
2211/009 20130101; Y02P 10/253 20151101; C21D 9/04 20130101; Y02P
10/25 20151101; C21D 2221/00 20130101 |
Class at
Publication: |
148/581 ;
266/252 |
International
Class: |
C21D 9/04 20060101
C21D009/04; C21D 1/74 20060101 C21D001/74 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2006 |
CN |
200610021821.9 |
Claims
1. A heat treatment method of steel rail, comprising: (1) keeping
the rolled hot steel rail running continuously, and performing hot
straightening process for it; (2) performing first heat treatment
process for the rolled hot steel rail after the hot straightening
process, i.e., forced cooling the rail head and the rail base of
the steel rail in a jetting air cooling manner; and (3) performing
second heat treatment process for the steel rail after the first
heat treatment process, i.e., heating the rail head of the steel
rail to a temperature of 850.about.950.degree. C., and then forced
cooling the rail head of the steel rail in a jetting air cooling
manner to a temperature that is close to the temperature of the
rail base of the steel rail.
2. The method of claim 1, wherein, in the first heat treatment
process at step (2), the rail head and the rail base of the steel
rail are cooled at a rate of 1.about.5.degree. C./s for
90.about.130 s to a temperature of 500.about.600.degree. C.
3. The method of claim 1, wherein, in the second heat treatment
process at step (3), the rail head of the steel rail is cooled at a
rate of 1.about.5.degree. C./s for 90.about.130 s to a temperature
of 450.about.600.degree. C.
4. The method of claim 1, wherein, in the second heat treatment
process at step (3), an intermediate frequency induction heater is
used to heat the rail head of the steel rail.
5. The method of claim 1, wherein, after the second heat treatment
process at said step (3), subsequent finishing works are performed
for the steel rail after the steel rail is cooled to the normal
temperature.
6. A heat treatment apparatus of steel rail, which is arranged
following the steel rail rolling production line, comprising a
front supporting unit (10), a hot straightening unit (20), a first
air cooling unit (30), a heating unit (50), and a second air
cooling unit (60) that are arranged in the order of the heat
treatment processes of the steel rail.
7. The apparatus of claim 6, wherein: the front supporting unit
(10), the hot straightening unit (20), the first air cooling unit
(30), the heating unit (50), and the second air cooling unit (60)
are arranged orderly and linearly in the direction of the steel
rail rolling production line.
8. The apparatus of claim 6, wherein: the front supporting unit
(10), the hot straightening unit (20) and the first air cooling
unit (30) are arranged orderly and linearly in the direction of the
steel rail rolling production line; the heating unit (50) and the
second air cooling unit (60) are arranged orderly and linearly
opposite to the direction of the steel rail rolling production
line; and a translating unit (40) is provided between the outlet of
the first air cooling unit (30) and the inlet of the heating unit
(50).
9. The apparatus of claim 6, wherein: said front supporting unit
(10) comprises a steel rail tilter (11) provided to turn the steel
rail (1) to the state where the rail head of the steel rail faces
upwards, a steel rail lifter (13) provided to lift the steel rail
(1) onto the front roller track (12), and the front roller track
(12) provided to convey the steel rail (1) to the hot straightening
unit (20); said hot straightening unit (20) comprises at least
three pairs of active straightening rollers (21) and passive
straightening rollers (22) arranged spacing apart each other in the
convey direction of the steel rail; said first air cooling unit
(30) and said second air cooling unit (60) each comprises an upper
guide mechanism (34) and a lower guide mechanism (35) provided to
constrain the movement tract of the steel rail (1), a first jetting
air cooler (31) disposed above the rail head of the steel rail (1)
to jet air towards and cool the top surface of the rail head, a
second jetting air cooler (32) disposed at both sides of the rail
head of the steel rail (1) to jet air towards and cool both sides
of the rail head, and a third jetting air cooler (33) disposed
below the rail base of the steel rail (1) to jet air towards and
cool the rail base; and said heating unit (50) comprises an upper
guide mechanism (52) and a lower guide mechanism (53) provided to
constrain the movement trace of the steel rail (1), and a heater
(51) provided to heat the rail head of the steel rail (1).
10. The apparatus of claim 9, wherein, said heater (51) is an
intermediate frequency induction heater (51).
11. The apparatus of claim 8, wherein, said translating unit (40)
comprises a quick steel raising and shifting machine (41).
12. The apparatus of claim 6, wherein, a collection rack (70) is
provided after said second air cooling unit (60).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn. 119
from Chinese Patent Application No. 200610021821.9 filed on Sep.
12, 2006, the disclosure of which is incorporated herein by
reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to a heat treatment method of
steel rail and a heat treatment apparatus of steel rail using the
method.
BACKGROUND
[0003] There have been increasing requirements for steel rails as
the railway transportation tends to high speed and heavy load.
Years of study and application practice have shown: the heat
treatment can produce fine pearlite metallographic structure of
steel rails and afford desired mechanical properties to steel
rails; it is a powerful means for improving service life of steel
rails. In the prior art, there are mainly two ways for heat
treatment of steel rails: one way is to reheat the rolled steel
rail finished product having normal temperature (also referred to
as "off-line heat treatment process"); Another way is to utilize
the residual heat of rolling process to heat the steel rails on the
steel rolling production line (also referred to as "on-line heat
treatment process"). These techniques can be seen from the content
disclosed in CN 1083013C and the References cited in the Background
Part of CN 1083013C, which are incorporated herein by
reference.
[0004] The off-line heat treatment process can afford fine
pearlitic microstructure and therefore the hardened layer may have
higher strength, toughness and hardness because the rolled steel
rail experiences two phase transition processes. However, the
off-line heat treatment process has the following inherent
drawbacks: high energy consumption, shallow hardened layer,
existence of a softened belt in the transitional zone between the
hardened layer and the non-hardened layer, and low steel rail
straightness since the steel rail straightness is ensured by roller
straightening which can only be carried out once for the same steel
rail; the steel rail has been roller straightened before heat
treatment, and therefore it can't be roller straightened again
after heat treatment.
[0005] The on-line heat treatment process is featured with low
energy consumption, deep hardened layer, smooth transition of
structure and hardness of the rail head of steel rail, free of
hardness caving and softened belt, and high straightness. However,
the on-line heat treatment process has the following inherent
drawbacks: the rolled steel rail experiences only one phase
transition process, and therefore the obtained metallographic
structure is not so fine as that of the steel rails treated through
off-line heat treatment process.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a heat
treatment method of steel rail, which can not only make the
metallographic structure of the produced steel rails more fine to
improve service life of the steel rails, but also reduce energy
consumption and steel rail heat treatment cost.
[0007] Accordingly, the present invention provides a heat treatment
method of steel rail, comprising the following steps: (1) keeping
the rolled hot steel rail running continuously, and performing hot
straightening process for it; (2) performing the first heat
treatment process for the rolled hot steel rail after the hot
straightening process, i.e., forced cooling the rail head and the
rail base of the steel rail in a jetting air cooling manner; and
(3) performing second heat treatment process for the steel rail
after the first heat treatment process, i.e., heating the rail head
of the steel rail to a temperature of 850.about.950.degree. C., and
then forced cooling the rail head of the steel rail in a jetting
air cooling manner to a temperature that is close to the
temperature of the rail base of the steel rail.
[0008] The present invention also provides a heat treatment
apparatus of steel rail, which is arranged following the steel rail
rolling production line, comprising a front supporting unit, a hot
straightening unit, a first air cooling unit, a heating unit, and a
second air cooling unit that are arranged in the order of the heat
treatment processes of the steel rail.
[0009] The present invention has the following benefits: since the
steel rail experiences the second heat treatment process by
reheating just after it is heat treated using the residual heat of
rolling, phase transition occurs in the steel rail in the two rapid
cooling processes, and finer metallographic structure is obtained
in the steel rail, and thereby the wear resistant property, contact
fatigue resistant property, and service life of the steel rail are
improved and are higher than those of the heat-treated steel rails
produced through the prior on-line heat treatment process or
off-line heat treatment process. When the steel rail experiences
the second heat treatment process, the rail web and the middle part
of the rail head have already been at high temperature, therefore
the energy consumption in reheating can be reduced by 70% compared
with the off-line heat treatment process; therefore, the steel rail
production cost can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic plan layout of a heat treatment
apparatus of steel rail provided in the present invention;
[0011] FIG. 2 is a schematic plan layout of another heat treatment
apparatus of steel rail provided in the present invention;
[0012] FIG. 3 is a schematic cross-sectional view of the front
supporting unit in the heat treatment apparatus of steel rail in
the present invention;
[0013] FIG. 4 is a schematic top view of the hot straightening unit
in the heat treatment apparatus of steel rail in the present
invention;
[0014] FIG. 5 is a schematic cross-sectional view of the first air
cooling unit (second air cooling unit) in the heat treatment
apparatus of steel rail in the present invention,
[0015] FIG. 6 is a schematic cross-sectional view of the
translating unit in the heat treatment apparatus of steel rail in
the present invention; and
[0016] FIG. 7 is a schematic cross-sectional view of the heating
unit in the heat treatment apparatus of steel rail in the present
invention.
LIST OF REFERENCE NUMBERS
[0017] 1. steel rail; 2. extended roller track of the rolling
production line; 10. front supporting unit; 11. steel rail tilter;
12. front roller track; 13. steel rail lifter; 20. hot
straightening unit; 21. active straightening roller; 22. passive
straightening roller; 30. first air cooling unit; 31. first jetting
air cooler; 32. second jetting air cooler, 33. third jetting air
cooler; 34. upper guide mechanism; 35. lower guide mechanism; 40.
translating unit; 41. quick steel raising and shifting machine; 50.
heating unit; 51. intermediate frequency induction heater; 52.
upper guide mechanism; 53. lower guide mechanism; 60. second air
cooling unit; 70. collection rack.
DETAILED DESCRIPTION OF EMBODIMENTS
[0018] Hereunder, the present invention will be described in detail
according to the embodiments with reference to the accompanying
drawings.
[0019] The heat treatment method of steel rail provided in the
present invention comprises the following steps:
[0020] (1) keeping the rolled hot steel rail running continuously,
and performing hot straightening process for it;
[0021] (2) performing the first heat treatment process for the
rolled hot steel rail after the hot straightening process, i.e.,
forced cooling the rail head and the rail base of the steel rail in
a jetting air cooling manner; and
[0022] (3) performing second heat treatment process for the steel
rail after the first heat treatment process, i.e., heating the rail
head of the steel rail to a temperature of 850.about.950.degree.
C., and then forced cooling the rail head of the steel rail in a
jetting air cooling manner to a temperature that is close to the
temperature of the rail base of the steel rail.
[0023] Generally speaking, a steel rail comprises the rail head,
the rail web and the rail base along the cross section; wherein,
the rail head refers to the head part facing upwards when the steel
rail is mounted; the rail base refers to the bottom part that is
connected to the ground base; the rail web refers to the middle
part between the rail head and the rail base.
[0024] Generally, the rolled hot steel rail is at 800.degree. C.
temperature or above, for example, 860.about.1200.degree. C. During
hot straightening process, the steel rail temperature can be equal
to or slightly lower than the temperature after rolling process,
for example, 750.about.850.degree. C. In the first heat treatment
process at said step (2), the rail head and rail base may be cooled
at a rate of 1.about.5.degree. C./s for 90.about.130 s preferably;
and the temperature after cooling is 450.about.600.degree. C.
preferably. In the second heat treatment process at said step (3),
the rail head is cooled at a rate of 1.about.5.degree. C./s for
90.about.130 s preferably; and the temperature after cooling is
450.about.600.degree. C. preferably. In said second heat treatment
process, preferably an intermediate frequency induction heater can
be used to heat the rail head.
[0025] After the second heat treatment process at said step (3),
subsequent finishing works can be performed for the steel rail
after the steel rail is cooled to the normal temperature.
[0026] In the heat treatment method of steel rail provided in the
present invention, since the steel rail experiences the second heat
treatment process by reheating just after it is heat treated using
the residual heat of rolling, phase transition occurs in the steel
rail in the two rapid cooling processes, and finer metallographic
structure is obtained in the steel rail, and thereby the wear
resistant property, contact fatigue resistant property, and service
life of the steel rail are improved and are higher than those of
the heat-treated steel rails produced through the prior on-line
heat treatment process or off-line heat treatment process. When the
steel rail experiences the second heat treatment process, the rail
web and the middle part of the rail head have already been at high
temperature, therefore the energy consumption in reheating can be
reduced by 70% compared with the off-line heat treatment process;
therefore, the steel rail production cost can be reduced.
EXAMPLE 1
[0027] Chemical composition of steel rail: C: 0.71.about.0.80%; Si:
0.50.about.0.80%; Mn: 0.75.about.1.05%; P: .ltoreq.0.030%; S:
.ltoreq.0.030%; V: 0.04.about.0.12%, the rest: iron and trace
impurities. The steel rail heat treatment processes are: when the
rolled hot steel rail is cooled to a temperature of 810.degree.
C..about.790.degree. C., perform hot straightening on the steel
rail; perform first heat treatment process, i.e., forced cooling
the rail head and the rail base of the steel rail in a jetting air
cooling manner at a rate of about 3.degree. C./s to a temperature
of about 550.degree. C.; perform the second heat treatment process,
i.e., heat the rail head to a temperature of 870.degree. C., and
then forced cooling the rail head in a jetting air cooling manner
at a rate of about 3.degree. C./s to the temperature close to the
rail base temperature (about 450.degree. C.); after the steel rail
is cooled to the normal temperature, perform subsequent finishing
works for the steel rail. After the two heat treatment processes,
the mechanical properties of the steel rail are: yield strength
Rp0.2.gtoreq.900 MPa, tensile strength Rm.gtoreq.1300 MPa, and
elongation A.gtoreq.12%.
EXAMPLE 2
[0028] Chemical composition of steel rail: C: 0.65.about.0.77%; Si:
0.15.about.0.35%; Mn: 1.10.about.1.50%; P: .ltoreq.0.035%; S:
.ltoreq.0.035%; the rest: iron and trace impurities. The steel rail
heat treatment processes are: when the rolled hot steel rail is
cooled to a temperature of 810.degree. C..about.790.degree. C.,
perform hot straightening to the steel rail; perform first heat
treatment process, i.e., forced cooling the rail head and the rail
base in a jetting air cooling manner at a rate of about 3.degree.
C./s to a temperature of about 550.degree. C.; perform second heat
treatment process, i.e., heat the rail head to a temperature of
870.degree. C., and then forced cooling the rail head in a jetting
air cooling manner at a rate of about 3.degree. C./s to the
temperature close to the rail base temperature (about 450.degree.
C.); after the steel rail is cooled to the normal temperature,
perform subsequent finishing works for the steel rail. The
mechanical properties of the steel rail are: Rp0.2.gtoreq.800 MPa,
Rm.gtoreq.1200 MPa, and A.gtoreq.10%.
[0029] Hereunder, the present heat treatment apparatus of steel
rail will be described in the embodiments, with reference to the
accompanying drawings.
[0030] As shown in FIG. 1 and FIG. 2, the heat treatment apparatus
of steel rail provided in the present invention is arranged
following the steel rail rolling production line, comprising a
front supporting unit 10, a hot straightening unit 20, a first air
cooling unit 30, a heating unit 50, and a second air cooling unit
60 that are arranged in the order of the heat treatment processes
of the steel rail. In addition, a collection rack 70 can be
arranged after the second air cooling unit 60 as required.
Hereunder, a heat treatment apparatus of steel rail with a
collection rack 70 will be described; however, it shall not be
understood that the collection rack 70 is a necessary component of
the present invention.
[0031] The front supporting unit 10, the hot straightening unit 20,
the first air cooling unit 30, the heating unit 50, the second air
cooling unit 60, and the collection rack 70 can be arranged in
different layout schemes, depending on the condition in the
production workshop.
[0032] As shown in FIG. 1, the front supporting unit 10, the hot
straightening unit 20, the first air cooling unit 30, the heating
unit 50, the second air cooling unit 60 and the collection rack 70
are arranged orderly and linearly in the direction of the steel
rail rolling production line. Such an arrangement is suitable for
the case that the longitudinal length of the production shop is
enough.
[0033] Alternatively, as shown in FIG. 2, the front supporting unit
10, the hot straightening unit 20 and the first air cooling unit 30
are arranged orderly and linearly in the direction of the steel
rail rolling production line; the heating unit 50, the second air
cooling unit 60 and the collection rack 70 are arranged orderly and
linearly opposite to the direction of the steel rail rolling
production line. In such a case, a translating unit 40 can be
provided between the outlet of the first air cooling unit 30 and
the inlet of the heating unit 50, to translate conveniently and
quickly the steel rail 1 from the first air cooling unit 30 to the
heating unit 50. Such an arrangement is suitable for the case that
the longitudinal length of the production workshop is not enough,
and it is helpful to utilize the width of the production workshop
reasonably and effectively.
[0034] Hereunder, the units of the heat treatment apparatus of
steel rail will be described in the embodiments, with reference to
the accompanying drawings.
[0035] FIG. 3 is a schematic cross-sectional view of the front
supporting unit 10. As shown in FIG. 3, the front supporting unit
10 mainly comprises a steel rail tilter 11, a steel rail lifter 13,
and a front roller track 12. The steel rail tilter 11 is provided
to turn the steel rail 1 to the state in which the rail head points
upwards; then, the steel rail lifter 13 lifts the steel rail 1 onto
the front roller track 12; next, the front roller track 12 conveys
the steel rail 1 to the hot straightening unit 20. The steel rail
tilter 11, the steel rail lifter 13, and the front roller track 12
are known to those skilled in the art, and thereby will not be
further described here.
[0036] FIG. 4 is a schematic top view of the hot straightening unit
20. As shown in FIG. 4, the hot straightening unit 20 mainly
comprises at least three pairs of active straightening rollers 21
and passive straightening rollers 22 arranged spacing apart each
other in the convey direction of the steel rail 1. The steel rail 1
conveyed from the front supporting unit 10 can be kept in straight
and level state by the active straightening rollers 21 and the
passive straightening rollers 22 when it is hot straightened. The
active straightening rollers 21 and the passive straightening
rollers 22 are known to those skilled in the art, and thereby will
not be further described here.
[0037] FIG. 5 is a schematic cross-sectional view of the first air
cooling unit 30. As shown in FIG. 5, the first air cooling unit 30
mainly comprises an upper guide mechanism 34, a lower guide
mechanism 35, a first jetting air cooler 31, a second jetting air
cooler 32, and a third jetting air cooler 33. The upper guide
mechanism 34 and the lower guide mechanism 35 are provided to keep
the steel rail 1 in straight and level state as required when the
steel rail 1 runs through the first air cooling unit 30. The first
jetting air cooler 31 is disposed above the rail head and jets air
towards and cools the top surface of the rail head. The second
jetting air cooler 32 is arranged on both sides of the rail head to
jet air towards and cool both sides of the rail head. The third
jetting air cooler 33 is disposed below the rail base and jets air
towards and cools the rail base. The rail head and the rail base
are cooled by force with the first jetting air cooler 31, the
second jetting air cooler 32, and the third jetting air cooler
33.
[0038] The second air cooling unit 60 can be in the same structure
as the first air cooling unit 30; therefore, the drawing and
description thereof is omitted here. In addition, the guide
mechanisms and the jetting air coolers are known to those skilled
in the art, and therefore will not be described further here.
[0039] FIG. 6 is a schematic cross-sectional view of the
translating unit 40. As shown in FIG. 6, the translating unit 40
mainly comprises a quick steel raising and shifting machine 41,
which is provided to translate the steel rail 1 quickly. The quick
steel raising and shifting machine 41 is known to those skilled in
the art, such as the one disclosed by CN 1847115A, and thereby will
not be described further here.
[0040] FIG. 7 is a schematic cross-sectional view of the heating
unit 50. As shown in FIG. 7, the heating unit 50 mainly comprises a
heater 51, an upper guide mechanism 52, and a lower guide mechanism
53. Preferably, the heater 51 is an intermediate frequency
induction heater 51 provided to heat the rail head of the steel
rail. The upper guide mechanism 52 and the lower guide mechanism 53
are provided to keep the steel rail 1 in straight and level state
as required when the steel rail 1 runs through the heater unit
50.
[0041] The collection rack 70 is provided to receive the steel rail
1 after heat treatment, so that the steel rail 1 is cooled to the
normal temperature on the collection rack 70 and then treated
through subsequent straightening, rail end machining, inspection,
and finishing works; finally, heat-treated steel rails with long
service life will be provided for the railway use.
[0042] Hereunder, the application of the heat treatment apparatus
of steel rail in the present invention will be further
described.
[0043] As shown in FIGS. 1, 2, and 3, during the steel rail heat
treatment process, the hot steel rail 1 is conveyed through the
extended roller track 2 of the rolling production line to the front
supporting unit 10 of the heat treatment apparatus. When the steel
rail 1 reaches the front supporting unit 10, it is turned by the
steel rail tilter 11 to the state in which the rail head faces
upwards; then, the steel rail 1 is lifted by the steel rail lifter
13 onto the front roller track 12.
[0044] When the steel rail 1 is cooled to the temperature of about
810.degree. C..about.790.degree. C., it is conveyed through the
front roller track 12 to the hot straightening unit in the
direction indicated by the arrow in FIG. 4; here, the steel rail 1
is hot straightened by the active straightening rollers 21 and the
passive straightening rollers 22 to be straight and level.
[0045] As shown in FIG. 5, the hot straightened steel rail 1 is
conveyed to the first air cooling unit 30; under control of the
upper guide mechanism 34 and the lower guide mechanism 35, the
steel rail 1 is kept in straight and level state and runs through
the first air cooling unit 30. Meanwhile, under the control of the
first, second and third jetting air coolers 31, 32 and 33, the rail
head and the rail base are cooled by force at a rate of
1.about.5.degree. C./s for the first heat treatment process; the
steel rail 1 is cooled to the temperature of about
500.about.600.degree. C. preferably.
[0046] As shown in FIG. 6, when the steel rail 1 leaves the first
air cooling unit 30 and arrives at the translating unit 40, the
first phase transition process is accomplished in the rail head and
the rail base of the steel rail 1; the quick steel raising and
shifting machine 41 of the translating unit 40 translates the steel
rail 1 quickly to the downstream heating unit 50.
[0047] As shown in FIG. 7, after the steel rail 1 is fed into the
heating unit 50, it is kept in straight and level state under
control of the upper guide mechanism 52 and the lower guide
mechanism 53. Meanwhile, the rail head of the steel rail 1 is
heated by the intermediate frequency induction heater 51 to the
temperature of about 870.degree. C.
[0048] As shown in FIG. 5, after the steel rail 1 leaves the
heating unit 50 and enters into the second air cooling unit 60, it
is kept in straight and level state and runs through the second air
cooling unit 60 under control of the upper guide mechanism 34 and
the lower guide mechanism 35. Meanwhile, under the control of the
jetting air coolers 31 and 32, the rail head of the steel rail 1 is
cooled by force at a rate of 1.about.5.degree. C./s for the second
heat treatment process; the steel rail is cooled to the temperature
of about 450.about.600.degree. C. preferably. At that time, the
jetting air cooler 33 below the steel rail 1 can jet air towards
the rail base of the steel rail 1 appropriately, so that the
temperature of the rail head is close to the temperature of the
rail base when the steel rail 1 leaves the second air cooling unit
60, and the steel rail 1 can enter into the collection rack 70
straightly.
[0049] After the steel rail 1 is cooled to the normal temperature
on the collection rack 70, it can be treated through straightening,
rail end machining, inspection, and finishing processes; therefore,
heat-treated steel rails with long service life can be provided for
railway use.
[0050] Although the invention has been described with respect to
specific embodiments, the details are not to be construed as
limitations, for it will become apparent that various embodiments,
changes and modifications may be resorted to without departing from
the spirit and scope thereof, and it is understood that such
equivalent embodiments are intended to be included within the scope
of this invention.
* * * * *