U.S. patent application number 14/414066 was filed with the patent office on 2015-07-23 for method for treating elongated metal product by heating and oxidizing the surface in a controlled environment.
The applicant listed for this patent is AIR PRODUCTS GMBH, KTS WIRE LTD.. Invention is credited to Maximus Akuh, Brian Cashmore, Guido Plicht, Kris Wiloch.
Application Number | 20150203950 14/414066 |
Document ID | / |
Family ID | 46766420 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203950 |
Kind Code |
A1 |
Akuh; Maximus ; et
al. |
July 23, 2015 |
Method for Treating Elongated Metal Product by Heating and
Oxidizing the Surface in a Controlled Environment
Abstract
A method and apparatus are provided for making a metal product
with improved surface characteristics. The method provides for
treating the metal product through a method including: heating the
metal product; exposing the outer surface of the metal product to a
controlled environment; and oxidising the outer surface of the
metal product. The heating may take the metal product to an
elevated temperature, the elevated temperature of the metal product
being at least 725.degree. C. The method further includes a
controlled environment around the metal product which is controlled
with respect to the atmosphere around the metal product, and in
particular the nitrogen and/or oxygen and/or hydrogen content
thereof. The result is a more consistent surface for elongate metal
products, having a more consistent colour to the surface, a more
durable and hard wearing surface and/or a surface which is not
prone to flaking.
Inventors: |
Akuh; Maximus; (Hattingen,
DE) ; Plicht; Guido; (Hattingen, DE) ; Wiloch;
Kris; (Leeds, GB) ; Cashmore; Brian; (Leeds,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KTS WIRE LTD.
AIR PRODUCTS GMBH |
Leeds
Hattingen |
|
GB
DE |
|
|
Family ID: |
46766420 |
Appl. No.: |
14/414066 |
Filed: |
July 10, 2013 |
PCT Filed: |
July 10, 2013 |
PCT NO: |
PCT/GB2013/051835 |
371 Date: |
January 9, 2015 |
Current U.S.
Class: |
148/240 ;
118/725 |
Current CPC
Class: |
C23C 8/02 20130101; C21D
9/54 20130101; C21D 9/562 20130101; Y02P 10/253 20151101; C21D 9/60
20130101; C21D 9/52 20130101; C21D 9/561 20130101; C23C 8/10
20130101; C21D 9/525 20130101; C21D 1/76 20130101; C23F 17/00
20130101; Y02P 10/25 20151101; C23C 8/12 20130101; C23C 8/14
20130101; C21D 9/56 20130101; C21D 1/74 20130101 |
International
Class: |
C23C 8/12 20060101
C23C008/12; C21D 1/76 20060101 C21D001/76; C23F 17/00 20060101
C23F017/00; C21D 9/52 20060101 C21D009/52 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2012 |
GB |
1212251.1 |
Claims
1. A method for treating a metal product, the method comprising:
heating the metal product; exposing the outer surface of the metal
product to a controlled environment; and oxidising the outer
surface of the metal product.
2. The method according to claim 1, the method further comprising
heating the metal product to an elevated temperature, the elevated
temperature of the metal product being at least 725.degree. C.
3. The method according to claim 1, the method further comprising
the controlled environment being controlled with respect to the
atmosphere around the metal product.
4. The method according to claim 3, the method further comprising
the nitrogen and/or oxygen and/or hydrogen content being
controlled.
5. The method according to claim 1, the method further comprising
the controlled environment being provided within a container
provided in a first process stage, the container being a tube or
other elongate container, and the metal product passing through the
container.
6. The method according to claim 1, in which a gas mixture is fed
to the controlled environment and in which the H.sub.2 to O.sub.2
ratio in the total gas mixture is between 1.5:1 and 4:1.
7. The method according to claim 1, in which a gas mixture is fed
to the controlled environment and in which the H.sub.2 to O.sub.2
ratio in the total gas mixture is between 1.65:1 and 3.5:1.
8. The method according to claim 1, in which a gas mixture is fed
to the controlled environment and in which the H.sub.2 to O.sub.2
ratio in the total gas mixture is between 1.5:1 and 2:1
9. The method according to claim 1, in which a gas mixture is fed
to the controlled environment and in which the H.sub.2 to O.sub.2
ratio in the total gas mixture is between 3.2:1 and 3.7:1.
10. The method according to claim 1, the method further comprising
that the surface of the metal product oxidises in a first process
stage.
11. The method according to claim 10, in which the oxidation is
substantially completed in the controlled environment.
12. The method according to claim 1, the method further comprising
that the surface of the metal product is reduced in a first process
stage.
13. The method according to claim 12, in which the reduction is
substantially completed in the controlled environment.
14. The method according to claim 1, in which the method further
comprises a quenching stage, the quenching stage being provided
after the first process stage, the quench stage hardening the metal
product.
15. The method according to claim 1, in which the method further
comprises a further immersion stage, the further immersion stage
being provided after the first process stage and/or after the
quenching stage, the further immersion stage tempering the metal
product.
16. The method according to claim 1, in which the method further
comprises a further quenching stage, the further quenching stage
being provided after the first process stage and/or after the
quenching stage and/or after the further immersion stage, the
further quenching stage hardening the metal product.
17. The method according to claim 1, in which the method of
treating provides that the characteristics and/or properties of the
surface do not alter after the quenching stage, particularly with
respect to the oxidisation of the surface.
18. The method according to claim 17 in which the method provides
that less than 1% of the oxidation of the surface of the metal
product occurs after the further quenching stage, preferably after
the tempering stage and most preferably after the quenching
stage.
19. Apparatus for treating a metal product, the apparatus
comprising: a heating stage for heating the metal product; a
controlled environment, to which the outer surface of the metal
product is exposed; an oxidising stage for oxidising the outer
surface of the metal product.
20. A method for treating a metal product, the method comprising:
heating the metal product; exposing the outer surface of the metal
product to a controlled environment; oxidising the outer surface of
the metal product; quenching the metal product; and tempering the
metal product.
21. Apparatus for treating a metal product, the apparatus
comprising: a heating stage for heating the metal product; a
controlled environment, to which the outer surface of the metal
product is exposed; an oxidising stage for oxidising the outer
surface of the metal product; a quenching stage for quenching the
metal product; and an tempering stage for tempering the metal
product.
Description
[0001] This invention concerns improvements in and relating to
products and methods for making them, particularly with reference
to the surface properties thereof. Elongate products, such as wire
products, are of particular interest.
[0002] In existing techniques for the production and treatment of
extremely elongate metal products, such as wire products, there are
problems with the colour and consistency of the surface
produced.
[0003] Attempts have been made to improve the position through the
use of chemical treatments and the additional of salts and the
like. However, such approaches have either been unsuccessful, for
instance due to the resultant surface flaking off) or undesirable
for other reasons (for instance because of the cost of the
extensive modifications to the conventional process that they
require to implement).
[0004] The present invention has amongst its possible aims to
address such shortcomings. The present invention has amongst its
possible aims to provide benefits to the products without expensive
or extensive alteration to the conventional processes.
[0005] According to a first aspect of the invention we provide a
method for treating a metal product, the method comprising:
[0006] a) heating the metal product;
[0007] b) exposing the outer surface of the metal product to a
controlled environment; and
[0008] c) oxidising the outer surface of the metal product.
[0009] The method of treating may include a first process stage.
The first process stage may provide the heating for the metal
product.
[0010] The heating may be provided in one or more furnaces. One or
more or all of the furnaces may be induction furnaces. The heating
may be provided by the temperature profile within the furnace. The
heating may take the metal product from an ambient temperature to
an elevated temperature. The elevated temperature of the metal
product may be at least 725.degree. C., possibly at least
750.degree. C., preferably at least 850.degree. C., more preferably
at least 875.degree. C., ideally at least 890.degree. C. The
elevated temperature may be at most 1400.degree. C., preferably at
most 1380.degree. C. The elevated temperature of the metal product
may be in the range 700.degree. C. to 1400.degree. C., preferably
the range 725.degree. C. to 950.degree. C., more preferably
820.degree. C. to 900.degree. C. or still more preferably
825.degree. C. to 855.degree. C.
[0011] The controlled environment may be controlled with respect to
temperature, for instance such that a temperature range is
maintained.
[0012] The controlled environment may be controlled with respect to
the atmosphere around the metal product, for instance the nitrogen
and/or oxygen and/or hydrogen content may be controlled.
[0013] The controlled environment may provide one form of
controlled environmental conditions provided in it. Preferably the
controlled environment provides a consistent temperature ranges
and/or mixtures of gases within it.
[0014] The controlled environment may be provided within a
container provided in the first process stage. The container may be
a tube or other elongate container. The wire may pass through the
container, for instance from a container entrance to a container
exit. The container entrance and/or exit may be profiled to
correspond to the metal products profile, for instance with a small
tolerance, for instance so as to minimise gas leakage from the
controlled environment.
[0015] Separate controlled environments may be provided for
separate strands of the metal product or a common controlled
environment may be provided for multiple strands of the metal
product.
[0016] The controlled environment may be provided with a gas inlet
and/or gas outlet. The controlled environment may be provided with
a gas inlet proximal to the inlet for the metal product to the
controlled environment. The gas inlet and the inlet for the metal
product may be separate from one another. The controlled
environment may be provided with a gas outlet proximal to the
outlet for the metal product from the controlled environment.
Preferably a common outlet is provided.
[0017] The gas inlet may feed a gas mixture to the controlled
environment from a gas feed system. The gas feed system may be
provided with a nitrogen supply and/or oxygen supply and/or
hydrogen supply. Preferably one or more or all of the gases are
provided in single element form. Preferably separate supplies of
nitrogen and oxygen are provided, but a common supply, for instance
an air supply could be used. The supplies may be provided by
pressurised storage tanks.
[0018] The nitrogen supply may be provided at a pressure of at
least 10 BAR in the store, for instance gas cylinders.
[0019] The oxygen supply may be provided at a pressure of at least
10 BAR in the store, for instance gas cylinders.
[0020] The hydrogen supply may be provided at a pressure of at
least 10 BAR in the store, for instance gas cylinders.
[0021] The gas supplies may connected to a mixer. The mixer may
control the proportions of the oxygen and/or nitrogen and/or
hydrogen in the gas mixture.
[0022] The H.sub.2 to O.sub.2 ratio in the total gas mixture may be
between 1.5:1 and 4:1, preferably between 1.6:1 and 3.7:1, more
preferably between 1.65:1 and 3.5:1. The H.sub.2 to O.sub.2 ratio
in the total gas mixture may be at least 1.5:1, preferably at least
1.6:1, more preferably at least 1.65:1. The H.sub.2 to O.sub.2
ratio in the total gas mixture may be at most 4:1, preferably at
most 3.7:1, more preferably at most 3.5:1.
[0023] According to one preferred form, for instance producing a
black surface finish, the H.sub.2 to O.sub.2 ratio in the total gas
mixture may be between 1.5:1 and 2:1, preferably between 1.6:1 and
1.85:1, more preferably between 1.65:1 and 1.8:1. The H.sub.2 to
O.sub.2 ratio in the total gas mixture may be at least 1.5:1,
preferably at least 1.6:1, more preferably at least 1.65:1. The
H.sub.2 to O.sub.2 ratio in the total gas mixture may be at most
2:1, preferably at most 1.85:1, more preferably at most 1.8:1.
[0024] According to another preferred form, for instance producing
a blue surface finish, the H.sub.2 to O.sub.2 ratio in the total
gas mixture may be between 3.2:1 and 3.7:1, preferably between
3.3:1 and 3.6:1, more preferably between 3.35:1 and 3.5:1. The
H.sub.2 to O.sub.2 ratio in the total gas mixture may be at least
3.2:1, preferably at least 3.3:1, more preferably at least 3.35:1.
The H.sub.2 to O.sub.2 ratio in the total gas mixture may be at
most 3.7:1, preferably at most 3.6:1, more preferably at most
3.5:1.
[0025] The oxygen proportion may be between 0.7% and 2.3% of the
total gas mixture, preferably between 0.8% and 2.2%, more
preferably between 0.9% and 2.1%.
[0026] The hydrogen proportion may be between 3% and 3.9% of the
total gas mixture, preferably between 3.2% and 3.7%, more
preferably between 3.3% and 3.6%.
[0027] According to one preferred form, for instance producing a
black surface finish, the oxygen proportion may be between 1.7% and
2.3% of the total gas mixture, preferably between 1.8% and 2.2%,
more preferably between 1.9% and 2.1%. The hydrogen proportion may
be between 3% and 3.9% of the total gas mixture, preferably between
3.2% and 3.7%, more preferably between 3.3% and 3.6%.
[0028] According to another preferred form, for instance producing
a blue surface finish, the oxygen proportion may be between 0.7%
and 1.3% of the total gas mixture, preferably between 0.8% and
1.2%, more preferably between 0.9% and 1.1%. The hydrogen
proportion may be between 3% and 3.9% of the total gas mixture,
preferably between 3.2% and 3.7%, more preferably between 3.3% and
3.6%.
[0029] The nitrogen proportion may represent the balance after the
oxygen proportion and hydrogen proportion.
[0030] The pressure in the gas mixer may be under 10 BAR, for
instance under 5 BAR.
[0031] The gas mixture may be fed from the gas mixer to a reactor.
The gas mixture may be fed to the reactor directly or more
preferably via a buffer tank. A catalytic reactor may be provided.
The reactor may cause the oxygen and hydrogen to at least partially
react. The reactor may cause the production of water. The reaction
may consume all of the oxygen.
[0032] After the reaction and/or after exiting the reactor, the gas
mixture may have a temperature of between 100.degree. C. and
280.degree. C., preferably between 150.degree. C. and 230.degree.
C., more preferably between 165.degree. C. and 210.degree. C. The
temperature and/or other conditions are preferably such that no
liquid water is present.
[0033] The gas mixture may pass through a heat exchanger before
reaching the controlled environment. The heat exchanger may be used
to control the temperature of the gas mixture, for instance to
maintain the gas mixture below a temperature limit.
[0034] The gas mixture may have a pressure of less than 1 BAR when
entering the controlled environment, for instance between 0.3 and
0.6 BAR.
[0035] The method of treating may provide that the surface of the
metal product oxidises in the first process stage, for instance in
a first reaction, preferably within the controlled environment. The
oxidation may be to the form Fe.sub.3O.sub.4 and/or according to
the reaction form 3Fe+4H.sub.2O->Fe.sub.3O.sub.4+4H.sub.2. This
oxidation may be completed in the controlled environment.
[0036] The method of treating may provide that the surface of the
metal product is reduced in the first process stage, for instance
in a second reaction, preferably with the second reaction occurring
after the first reaction, preferably within the controlled
environment. The reduction may be to the form FeO and/or according
to the reaction of form Fe.sub.3O.sub.4+H.sub.2->3FeO+H.sub.2O.
This reduction may be completed in the controlled environment.
[0037] The metal product may be pre-formed before the use of the
method of treating. The method of treating may alter one or more
surface properties and/or characteristics of the pre-formed metal
product. The method of treating may alter one or more internal
properties and/or characteristics of the pre-formed metal product.
The method of treating may alter one or more properties and/or
characteristics for the whole of the pre-formed metal product.
[0038] The metal product may be fed to the method of treating from
a storage location. The storage location may be one or more
coils.
[0039] Preferably multiple strands of the metal product are fed
through the method of treating in parallel with one another.
[0040] The method of treating may include a quenching stage. The
quenching stage may be provided after the first process stage. The
quenching stage may be provided immediately after the first process
stage. The quenching stage may harden the metal product. The
quenching stage may increase or provide Martensite content for the
metal product. The quenching stage may be provided with oil. The
oil may be circulated and/or may be cooled. The metal product may
be immersed in the oil as it passes through the quenching
stage.
[0041] The temperature of the metal product on entering the
quenching stage may be at an exit elevated temperature. The exit
elevated temperature of the metal product may be at least
725.degree. C., possibly at least 750.degree. C., preferably at
least 850.degree. C., more preferably at least 875.degree. C.,
ideally at least 890.degree. C. The exit elevated temperature may
be at most 1400.degree. C., preferably at most 1380.degree. C. The
exit elevated temperature of the metal product may be in the range
700.degree. C. to 1400.degree. C., preferably the range 725.degree.
C. to 950.degree. C., more preferably 820.degree. C. to 900.degree.
C. or still more preferably 825.degree. C. to 855.degree. C. The
temperature of the metal product on leaving the quenching stage may
be less than 50.degree. C., more preferably less than 35.degree.
C.
[0042] The method of treating may include a further immersion
stage. The further immersion stage may be provided after the first
process stage and/or after the quenching stage. The further
immersion stage may be provided immediately after the quenching
stage. The further immersion stage may treat the metal product, for
instance to temper the metal product. The further immersion may
increase the ductility and/or remove internal stresses in the metal
product. The further immersion stage may be provided with molten
lead. The molten lead may be circulated and/or may be heated. The
metal product may be immersed in the molten lead as it passes
through the further immersion stage.
[0043] The temperature of the metal product on entering the further
immersion stage may be less than 50.degree. C., more preferably
less than 35.degree. C. The temperature of the metal product on
leaving the further immersion stage may be in the range 370.degree.
C. to 650.degree. C., more preferably in the range 390.degree. C.
to 610.degree. C.
[0044] The method of treating may include a further quenching
stage. The further quenching stage may be provided after the first
process stage and/or after the quenching stage and/or after the
further immersion stage. The further quenching stage may be
provided immediately after the further immersion stage. The further
quenching stage may harden the metal product. The further quenching
stage may be provided with water and/or oil, for instance as oil
dissolved in water. The oil may be circulated and/or may be cooled.
The metal product may be immersed in the oil as it passes through
the further quenching stage.
[0045] The temperature of the metal product on entering the further
quenching stage may be in the range 350.degree. C. to 650.degree.
C. or more preferably 390.degree. C. to 610.degree. C. The
temperature of the metal product on leaving the further quenching
stage may be less than 80.degree. C., more preferably less than
65.degree. C.
[0046] The method of treating may provide a metal product cleaning
stage, for instance after the further quenching stage and/or before
a product storage stage. The metal product cleaning stage may
remove material from the metal product. The metal product cleaning
stage may be provide an air wipe.
[0047] The method of treating may provide a rust preventer
application stage, for instance after the further quenching and/or
metal product cleaning stage and/or before a product storage stage.
The rust preventer may be applied by spraying and/or wetting and/or
immersion in the rust preventer.
[0048] The method of treating may fed the metal product, after one
or more treatments, to a metal product storage stage, such as one
or more coils.
[0049] The method of treating may provide that the characteristics
and/or properties of the surface do not alter after the quenching
stage, particularly with respect to the oxidisation of the surface.
The method of treating may provide that no or substantially no, for
instance less than 1%, of the oxidation of the surface of the metal
product occurs after the further quenching stage, preferably after
the tempering stage and most preferably after the quenching
stage.
[0050] The first aspect of the invention may include any of the
features, options and possibilities set out elsewhere in this
document, including in the other aspects of the invention.
[0051] According to a second aspect of the invention we provide
apparatus for treating a metal product, the apparatus including
[0052] a) a heating stage for heating the metal product; [0053] b)
a controlled environment, to which the outer surface of the metal
product is exposed; [0054] c) an oxidising stage for oxidising the
outer surface of the metal product.
[0055] The second aspect of the invention may include any of the
features, options and possibilities set out elsewhere in this
document, including in the other aspects of the invention.
[0056] According to a third aspect of the invention we provide a
method for treating a metal product, the method comprising: [0057]
a) heating the metal product; [0058] b) exposing the outer surface
of the metal product to a controlled environment; [0059] c)
oxidising the outer surface of the metal product; [0060] d)
quenching the metal product; and [0061] e) tempering the metal
product.
[0062] The third aspect of the invention may include any of the
features, options and possibilities set out elsewhere in this
document, including in the other aspects of the invention.
[0063] According to a fourth aspect of the invention we provide
apparatus for treating a metal product, the apparatus including
[0064] a) a heating stage for heating the metal product; [0065] b)
a controlled environment, to which the outer surface of the metal
product is exposed; [0066] c) an oxidising stage for oxidising the
outer surface of the metal product; [0067] d) a quenching stage for
quenching the metal product; and [0068] e) an tempering stage for
tempering the metal product.
[0069] The fourth aspect of the invention may include any of the
features, options and possibilities set out elsewhere in this
document, including in the other aspects of the invention.
[0070] According to a fifth aspect of the invention we provide a
metal product, the metal product being a heated, quenched and
tempered metal product.
[0071] The metal product may be formed of plain carbon steel and/or
steel alloy.
[0072] The metal product may be a wire. The metal product may be a
rolled wire. The metal product may be a shaped wire. The metal
product may be a flat wire. The metal product may have a width of
between 0.2 mm and 50 mm, more preferably between 1.5 mm and 22 mm.
The metal product may have a thickness of between 0.2 mm and 10 mm,
more preferably between 0.4 mm and 8 mm.
[0073] The metal product may have round edges or square edges. The
metal product may have a Hardness Rockwell C Scale RC of 20 to 60,
preferably 35 to 60, more preferably 40 to 55, for instance with a
5 point range. The metal product may have a tensile strength of
1000 to 2000 N/mm.sup.2, more preferably 1250 to 1750
N/mm.sup.2.
[0074] The surface of the metal product may not form any flakes,
for instance when scratched with a knife.
[0075] The surface of the metal product may be free from scales,
for instance when visually inspected.
[0076] The surface of the metal product may be consistent in
colour, for instance greater than 90% of the surface being of the
same colour, preferably greater than 98%, more preferably greater
than 99% and ideally greater than 99.9%. The colour may be black.
The colour may be dark blue. The colour may be brown or straw.
[0077] The metal product, particularly the surface of the metal
product may have a shelf life of at least 5 days, preferably at
least 8 days, more preferably at least 12 days and ideally at least
20 days, before visible rust forms on the surface, for instance
when stored at 15.degree. C. and 80% humidity.
[0078] The fifth aspect of the invention may include any of the
features, options and possibilities set out elsewhere in this
document, including in the other aspects of the invention.
[0079] Various embodiments of the invention will now be described,
by way of example only, and with reference to the accompanying
figures in which:
[0080] FIG. 1 is a schematic illustration of the process stages in
a conventional wire treatment process;
[0081] FIG. 2 is a schematic illustration of the process stages of
a wire treatment process according to an embodiment of the
invention;
[0082] FIG. 3 is a schematic detailed illustration of the
controlled environment of an embodiment of the invention;
[0083] FIG. 4 is a schematic illustration of a gas feed system;
and
[0084] FIG. 5 is a schematic illustration of an alternative gas
feed system.
[0085] Various techniques are known for the production and
treatment of extremely elongate metal products, such as wire
products. A consistent property of these production and treatment
techniques is that the surface which forms on the metal product is
inconsistent. This can manifest itself in terms of the colour of
the surface in particular. The surface is frequently uneven in
colour and with a sheen similar to that seen when oil spreads on
water. The inconsistency of the surface can also manifest itself in
terms of the surface being a heavy scale which has a tendency to
flake off with use and/or time.
[0086] The uneven properties of the surface are undesirable in a
number of respects. The uneven colour impairs the visibility of any
markings applied to the metal product, such as the distance
markings on a tape measure. The uneven properties can also shorten
the shelf life of the product before visible weathering or even
rusting has occurred. This is an issue with respect to the storage
of such metal products between production and subsequent use in a
further stage.
[0087] The present invention has amongst its possible aims to
provide a more consistent surface for elongate metal products. The
present invention has amongst its possible aims to provide a more
consistent colour to the surface of elongate metal products. The
present invention has amongst its aims to provide a more durable
and hard wearing surface and/or a surface which is not prone to
flaking. The present invention has amongst its possible aims to
provide a surface which is more resistant to oxidation and/or
rusting and/or weathering.
[0088] In a conventional wire treatment process, FIG. 1, a series
of parallel wires 1 are feed through the same treatment stages to
give maximum wire throughput for the process stages provided.
[0089] The pre-produced wire 1 is received coiled. The coiled wire
1 is fed from the coil 3 into the first process stage 5 and carries
on through all the stages and then on to a coil 27 after the last
process stage. Periodically new coils 3 are spliced to or otherwise
fed to form the wire strand going to the first process stage 5.
Periodically full coils are cut from the wire strand after the last
process stage and new coils of finished product started.
[0090] The first process stage 5 is an induction heated furnace 7.
This is used to raise the temperature of the wire strand to the
desired level. The temperature profile within the furnace may be
used to raise the temperature to the ultimate level needed. The
temperature within the first process stage 5 prevents oxidation of
the wire 1.
[0091] Upon leaving the first process stage 5, the hot wire 1 is
quickly quenched in a quenching stage 9. This is done by immersing
the wire 1 in a bath 11 of cooled oil 13. The oil 13 prevents
oxidation of the wire 1 and the exposure of the wire 1 between
leaving the furnace 7 and entering the oil 13 of the oil bath 11 is
short enough for there to be no material oxidation of the wire
1.
[0092] The combination of heating and quenching is used to give the
desired internal structure for the wire 1, namely a martensite.
[0093] From the quenching stage 9, the wire 1 proceeds into a
further immersion stage 15 in the form of a lead bath 17. The
molten lead 19 in this bath 17 is used to heat the wire 1 and cause
tempering. This prevents the brittleness which would otherwise be
present. The heat applied to the wire 1 in the bath 17 together
with moisture cause the oxidation of the surface of the wire 1
before it reaches the next stage.
[0094] From the further immersion stage 15, the wire 1 proceeds
into a final quench stage 21. The final quench stage 21 uses water
and a soluble oil in combination to reduce the wire temperature
quickly.
[0095] The cooled wire 1 then passes to an air wipe cleaning stage
23, a rust preventer application stage 25 and then onto the final
coil 27.
[0096] Oxidation for the wire occurs primarily after the further
immersion stage 15 and before the final quench stage 21.
[0097] In the wire production process of the present invention, the
minimal changes possible are made to the overall process, so as to
minimise the capital and operating costs for the revised process.
As a result, many of the stages are the same as in the conventional
method and the sequence in which they are provided is the same.
However, the environment provided and materials added to certain of
the stages is greatly changed and with very significant
results.
[0098] Once again, the pre-produced wire 1 is received coiled and
is fed to the first process stage 5. The first process stage 5 is
again an induction heated furnace 7.
[0099] In the furnace 7 the wire is heated according to the
temperature profile provided.
[0100] Unlike in the previous approach, as shown in FIG. 3, the
wire 1 enters a tube 53 whose axis 55 is aligned with the direction
of movement arrow A of the wire 1. Only one tube 53 is shown in
FIG. 2 for clarity reasons. The tube 53 is provided with an inlet
57 profiled to receive the wire 1 and minimise gas mixture 59 loss
from inside the tube 53. A similar structure is provided for the
outlet 61 at the end of the first process stage. The wire 1 is
inside the tube 53 throughout its time in the furnace 7.
[0101] On entry into the furnace 7, the temperature of the wire 1
is quickly raised from an ambient temperature, for instance
20.degree. C., to the controlled treatment temperature of between
725.degree. C. and 1450.degree. C.
[0102] As the wire 1 is passing along the axis of a tube, as shown
in FIG. 3, the wire 1 is surrounded by the gas mixture 59 fed to
the tube through a gas inlet 65. The gas inlet 65 is connected to
the gas feed 67 system described in more detail below. The role of
the gas mixture 59 is also described in detail below.
[0103] The tube 53 and wire 1 pass through the furnace and are
maintained at the desired temperature there and prior to reaching
the bath 11. As an option, it would be possible to provide the
controlled conditions within a tube 53 provided after the furnace 7
and prior to reaching the bath 11, or combinations thereto.
[0104] The controlled conditions within the tube 53 mean that
oxidation occurs here. The temperature and the controlled
conditions control the oxidation. This is a fundamental difference
compared with the conventional approach where oxidation occurs in
the much later stages and the furnace is just used for heating.
[0105] Upon leaving the first process stage, and the tube 53, the
hot wire 1 is quickly quenched. This is done by immersing the wire
1 in a bath 11 of cooled oil 13. The oil 13 and temperature
reduction prevent further oxidation. During the short exposure
between leaving the furnace 7 and entering the oil 13 some further
oxidation may occur due to the conditions the wire 1 has already
been exposed to and/or the reactions already underway.
[0106] The combination of heating and quenching is used to give the
desired internal structure for the wire 1, namely a martensite, as
in the conventional process. However, the surface has been
materially altered relative to the surface at this stage in the
conventional process.
[0107] From the quenching stage 9, the wire proceeds into a further
immersion stage 15 in a lead bath. The molten lead 19 in this bath
17 is used to heat the wire 1 and cause tempering. This prevents
the brittleness which would otherwise be present.
[0108] From the further immersion stage 15, the wire proceeds into
a final quench stage 21. The final quench stage 21 uses water and a
soluble oil in combination to reduce the wire temperature
quickly.
[0109] The cooled wire 1 then passes to an air wipe cleaning stage
23, a rust preventer application stage 25 and then onto one of the
final coils 27.
[0110] Unlike in the conventional process, the oxidation for the
wire occurs primarily in the earlier stages of the process and no,
or substantially no, oxidation occurs after the final quench stage
21.
[0111] As mentioned above, the gas inlet 65 receives a gas mixture
59 from a gas feed system 67, as shown in FIG. 4. The gas feed
system 67 is provided with a nitrogen storage tank 69, a hydrogen
storage tank 71 and an oxygen storage tank 73. The three storage
tanks 69, 71, 73 are connected to a gas mixer 75. The nitrogen fed
to the gas mixer 75 from the compressed gas cylinders, reduces in
pressure from around 300 BAR (from a full cylinder) to 9.5 BAR in
the gas mixer 75. The hydrogen fed to the gas mixer 75 from the
compress gas cylinders, reduces in pressure from 172 BAR to 9.0
BAR.
[0112] The gases are mixed in the gas mixer 75 to give the gas
mixture 59 in the form of 2.7% H.sub.2+1.2% O.sub.2+96.1% N.sub.2.
The gas flow is reduced to 10-20 m.sup.3/h and introduced, via a
buffer tank 77, to a catalytic reactor 79. The gas mixer 75 is
connected to the buffer tank 77 to ensure a steady supply of the
gas mixture 59 to the controlled environment in the tube 53.
[0113] In the catalytic reactor 79, the oxygen is reacted with the
hydrogen. As a result of this reaction, H.sub.20+H.sub.2+N.sub.2
forms the gas stream and the temperature average of 204.degree. C.
is produced.
[0114] If higher temperatures for the gas stream are desired, then
a heat exchanger (not shown) can be used. The gas valves and gas
regulators are unable to handle the gas stream as hot as
230.degree. C. and so the heat would be introduced after it had
passed through those pieces of equipment, but before entering the
tubes 53.
[0115] When the gas mixture 59 is introduced to the tubes 53 which
define the controlled environment in the furnace, the gas mixture
59 is at 80.degree. C. to 230.degree. C. and the gas mixture 59 has
a dew point of around 20.degree. C. The combination of the gas
temperature and the dew point means that the H.sub.20 is maintained
as steam within the tubes 53.
[0116] All the oxygen from the water is used in the first oxidation
reaction. This reaction starts once the necessary temperature
threshold is reached and given the presence of the gas mixture.
This part of the process also provides some initial hardening. The
reaction can take place in temperature range of 575.degree. C. to
1377.degree. C. and is of the form
3Fe+4H.sub.2O->Fe.sub.3O.sub.4+4H.sub.2. A temperature of
900.degree. C. may be used.
[0117] The H.sub.2 in the gas mixture is used for the second
reaction. This second reaction starts once the first reaction
occurs and increases as the amount of the surface for which the
first reaction has occurred increases. This part of the process
also provides some further hardening and there is reduction of
Fe.sub.3O.sub.4 to FeO.
[0118] A gas removal hood may be provided over the bath 11 of
cooled oil 13 to capture the gaseous reaction products and
unreacted part of the gas mixture. This can assist in drawing off
the gas mixture and stopping any further reactions.
[0119] In an alternative form, the hydrogen storage tank can be
used with an air storage tank to provide the gas feed. The gases
when supplied in this form are less easily varied to provide some
of the process control characteristics, however, and so the three
separate gas stores are preferred. For instance, the dew point is
materially different in air when compared with that for oxygen. In
such a case, the compressed air (which is 20% O.sub.2+80% N.sub.2)
is fed to the gas mixer from the compress gas cylinders and the
pressure reduces from 200 BAR to 9.0 BAR.
[0120] In the alternative gas feed system shown in FIG. 5, the
operation is provided for in a similar manner to FIG. 4, but with
the oxygen or compressed air being fed direct from the storage tank
73 to the reactor 79.
[0121] In terms of the process conditions applying during these
stages: [0122] a) The wire 1 is uncoiled at 20.degree. C. or the
ambient temperature in the process plant. [0123] b) The induction
furnace is used in the first furnace stage to heat the wire from to
20.degree. C. up to 550.degree. C. [0124] c) In the tubes, the wire
is isolated from the ambient atmosphere and subjected to the
controlled atmosphere. The tubes are also insulated to maintain the
wire temperature at the desired level of 550.degree. C. [0125] d)
The controlled gas mixture is introduced to the tubes with the gas
at a temperature of between 20.degree. C. to 204.degree. C. [0126]
e) In the second furnace stage, the wire and controlled environment
is heated to 575.degree. C. This provides the first oxidation phase
and generates a consistent oxidation layer on the surface which is
blue in colour. The surface is oxidised to Fe.sub.3O.sub.4. [0127]
f) In the third furnace stage, additional heat is used to raise the
temperature to 900.degree. C. This provides a reduction phase and
generates a consistent oxidation layer on the surface which is
black in colour. The surface is reduced from Fe.sub.3O.sub.4 to FeO
by the H.sub.2 reduction. [0128] g) In the quench stage the wire
temperature drops from above 725.degree. C. (typically 840 to
900.degree. C.) to 30-35.degree. C. and the quench oil causes the
formation of the desired uniform martensite structure. [0129] h)
The lead bath stage is then used to temper the wire by heating the
wire again to 400 to 600.degree. C. [0130] i) The second quench
stage uses a water and soluble oil quench to take the wire
temperature back down to 30 to 60.degree. C. [0131] j) The air wipe
stage is used to clean the wire and to cool it further to 20 to
25.degree. C., or ambient conditions. [0132] k) The rust
preventative is applied at 20.degree. C., or ambient conditions.
[0133] l) The finished wire in the coiling stage is at 20.degree.
C., or ambient conditions.
[0134] In the above method, the temperature and gases in the
controlled environment are controlled so as to provide a uniform
black surface for the wire product. Other surface colours are
possible through alternative conditions.
[0135] The black colour is caused by the formation of FeO as the
surface material. This is based upon the proportion of H.sub.2
converted to H.sub.2O being correct for the oxidation to black FeO
as the oxide form.
[0136] If the level of H.sub.2 is lower, then the second phase will
not occur and the oxide will be in the form after the first
oxidising phase, namely Fe.sub.3O.sub.4.
[0137] If the level of H.sub.2O supplied to the first oxidation
phase is not high enough then a brown or straw colour oxide will
form. This is a result of the reaction
2Fe+3H.sub.2O->Fe.sub.2O.sub.3+3H.sub.2 (instead of
3Fe+4H.sub.2O->Fe.sub.3O.sub.4+4H.sub.2).
[0138] Hence, control of the hydrogen level and control of the
oxygen level can be used to control the colour of the product
formed. Other variations are anticipated to provide further colours
or shades of colour.
[0139] In addition to the surface colour control, the position at
which oxidation occurs in the overall process is changed. This
means that whilst in the conventional process the wire can be
exposed to air in two places late in the process sequence, in the
new process all the wire surface is fully oxidised prior to
reaching these locations and it is not possible for another
oxidation to occur as all Fe is protected with by the FeO surface
layer which has already fully formed.
[0140] Detection of any problems with the black oxide layer is
apparent from the blue or straw colour forming should there be any
surface damage in the lead tank, for instance, causing later air
oxidation.
* * * * *