U.S. patent application number 10/511785 was filed with the patent office on 2006-03-09 for rapid cooling method for parts by convective and radiative transfer.
Invention is credited to Florent Chaffotte, Didier Domergue, Aymeric Goldsteinas, Linda Lefevre, Laurent Pelissier.
Application Number | 20060048868 10/511785 |
Document ID | / |
Family ID | 31970862 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060048868 |
Kind Code |
A1 |
Lefevre; Linda ; et
al. |
March 9, 2006 |
Rapid cooling method for parts by convective and radiative
transfer
Abstract
A rapid cooling method for metal parts, using a pressurized
cooling gas, characterized in that the cooling gas comprises one
(or several) principal gas(es) absorbing infra-red radiation,
selected in such a way as to improve thermal transfer to the part
by combining radiative and convective transfer pheonomena in order
to optimize the convective transfer coefficient.
Inventors: |
Lefevre; Linda; (Versailles,
FR) ; Domergue; Didier; (Palaiseau, FR) ;
Chaffotte; Florent; (Chatillon, FR) ; Goldsteinas;
Aymeric; (Le Fontanil, FR) ; Pelissier; Laurent;
(St Jean De Moirans, FR) |
Correspondence
Address: |
Linda K Russell;Air Liquide
Intellectual Property Department
Suite 1800 2700 Post Oak Boulevard
Houston
TX
77056
US
|
Family ID: |
31970862 |
Appl. No.: |
10/511785 |
Filed: |
January 9, 2003 |
PCT Filed: |
January 9, 2003 |
PCT NO: |
PCT/FR03/00053 |
371 Date: |
July 25, 2005 |
Current U.S.
Class: |
148/633 ;
148/660; 148/712 |
Current CPC
Class: |
C21D 1/767 20130101;
C21D 2241/01 20130101; C21D 1/613 20130101 |
Class at
Publication: |
148/633 ;
148/660; 148/712 |
International
Class: |
C21D 1/613 20060101
C21D001/613 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 20, 2002 |
FR |
02/11680 |
Claims
1-14. (canceled)
15. A method which may be used for rapidly cooling metal parts with
a pressurized cooling gas mixture, wherein: a) said mixture
comprises at least one infrared radiation absorbing gas; and b)
said mixture has convective heat transfer properties superior to
those of nitrogen in similar cooling conditions.
16. The method of claim 15, wherein said mixture further comprises
an additive gas, wherein said additive gas comprises at least one
member selected from the group consisting of: a) helium; b)
hydrogen; and c) mixtures thereof.
17. The method of claim 15, wherein said mixture further comprises
a supplementary gas.
18. The method of claim 16, further comprising adjusting the
composition of said mixture to obtain an average mixture density
substantially equal to that of nitrogen.
19. The method of claim 16, further comprising adjusting the
composition of said mixture to optimize said mixture's convective
heat transfer coefficient, as compared to the individual convective
heat transfer coefficients of each component of said mixture.
20. The method of claim 16, further comprising: a) cooling said
parts in a vessel, wherein said vessel comprises a gas stirring
system; and b) adjusting the composition of said mixture to obtain
an average density of said mixture which is capable of being
stirred by said stirring system, without having to make significant
changes to said vessel.
21. The method of claim 16, further comprising adjusting the
composition of said mixture so that endothermic chemical reactions
can occur between said absorbing gas and at least one other
component of said mixture.
22. The method of claim 16, wherein said absorbing gas comprises
CO.sub.2.
23. The method of claim 15, wherein said absorbing gas comprises at
least one member selected from the group consisting of: a)
saturated hydrocarbons; b) unsaturated hydrocarbons; c) CO; d)
H.sub.2O; e) NH.sub.3; f) NO; g) N.sub.2O; h) NO.sub.2; and i)
mixtures thereof.
24. The method of claim 15, wherein the content of said absorbing
gas in said mixture is between about 5% to about 100% of the total
mixture volume.
25. The method of claim 24, wherein said content is between about
20% to about 80%.
26. The method of claim 15, wherein said gas mixture comprises a
binary CO.sub.2/He mixture, wherein the CO.sub.2 content of said
mixture is between about 20% to about 80% of the total mixture
volume.
27. The method of claim 15, wherein said gas mixture comprises a
binary CO.sub.2/H.sub.2 mixture, wherein the CO.sub.2 content of
said mixture is between about 20% to about 80% of the total mixture
volume.
28. The method of claim 15, further comprising recycling said
mixture wherein said recycling comprises: a) recompressing said
mixture prior to a subsequent use; and b) processing said mixture
to recover at least one component of said mixture, wherein said
processing comprises at least one process selected from the group
consisting of: 1) separating; and 2) purifying.
29. A method which may be used for rapidly cooling metal parts with
a pressurized cooling gas in an apparatus, said method comprising:
a) cooling said parts with said cooling gas, wherein said cooling
gas comprises: 1) about 20% to about 80%, of the total cooling gas
volume, of an infrared absorbing gas; and 2) about 80% to about
20%, of the total cooling gas volume, of a second gas, wherein said
second gas comprises at least one member selected from the group
consisting of: i) hydrogen; ii) helium; and iii) mixtures thereof;
and b) adjusting the composition of said cooling gas so that
significant later changes to said apparatus are unnecessary.
Description
[0001] The present invention relates in general to the heat
treatment of metals and more particularly to the operation of gas
hardening of steel parts having previously undergone heat treatment
(such as heating before quench, annealing, tempering) or
thermochemical treatment (such as case hardening, carbonitriding).
Such gas hardening operations are generally carried out by
circulating a pressurized gas in a closed circuit between a charge
and a cooling circuit. For practical reasons, gas quench hardening
installations generally operate under pressures between 4 and 20
times the atmospheric pressure (4 to 20 bar or 4 000 to 20 000
hectopascals). In the present description, the pressure is
designated by the bar, with the understanding that 1 bar is equal
to 1 000 hPa.
[0002] FIG. 1 very schematically shows an example of a gas quench
hardening installation. This installation 1 contains a charge 2 to
be cooled disposed in a sealed vessel 3. The charge is typically
surrounded by baffle plates 4 to guide the gas flow. A desired gas
mixture is introduced under pressure at a gas inlet 5, with the
understanding that the cooling gases can, for example, be
introduced in the form of a preformed mixture or that a plurality
of distinct gas inlets can be provided for introducing various
cooling gases separately. A connection for placing the vessel under
vacuum (not shown) is routinely provided. A turbine 6 driven by a
motor 7 is used to circulate the gases, for example by passing from
a cooling circuit 9 to the charge to be cooled 2. The cooling
circuit 9 routinely consists of pipes conveying a cooling
fluid.
[0003] The installation in FIG. 1 is only shown by way of example
of one of the numerous possible and existing structures for
circulating a cooling gas in a vessel. Conventionally, the pressure
is about 4 to 20 bar during the cooling phase. Numerous variants
are possible, as regards the disposition of the charge, the gas
flow direction, and the method for circulating these gases.
[0004] For practical reasons, the gas most commonly used for
cooling is nitrogen, because it is an inert and inexpensive gas.
Furthermore, its density is ideal for simple installations with
blowers or turbines, and its heat transfer coefficient is
sufficiently satisfactory. In fact, it is known, in gas hardening
systems, that the temperature must be lowered as rapidly as
possible for the steel transformation to occur satisfactorily, from
the austenitic phase to the martensitic phase without passing
through the pearlitic and/or bainitic phases.
[0005] However, it has been observed that in certain critical
cases, nitrogen quench hardening installations are not suitable for
obtaining a sufficient temperature lowering rate. Hydrogen and
helium quench hardening have therefore been tested. A drawback of
the use of these gases is that existing installations, dimensioned
for nitrogen quench hardening, particularly as regards ventilation
capacity, are not optimized for the use of a gas of substantially
different density. Furthermore, helium is a substantially more
costly gas than nitrogen, while hydrogen incurs risks of
inflammability and its use requires special precautions.
[0006] It should also be emphasized that all these prior approaches
(like those recommending the use of hydrogen or helium) were based
on an attempt to improve only the convective heat transfer in the
treatment chamber.
[0007] The prior art can be illustrated by citing the specific
approach of patent EP-1 050 592, which provides for the presence of
gases such as CO.sub.2 and NH.sub.3 in the quenching gas, but
without any additional improvement in the quenching efficiency in
comparison with the inert mixtures already employed, the usefulness
of their presence deriving chiefly, according to the patent, from
two factors, on the one hand, the simultaneous achievement of
thermochemical effects (oxidation, nitriding, etc.) which can be
expected, and, on the other, the easier physical integration in a
comprehensive heat treatment method (e.g. in a case hardening
method) because the downstream hardening can then use the same
gases as the actual treatment located upstream.
[0008] Still in connection with CO.sub.2, reference can be made to
the following two patents in which, when CO.sub.2 is mentioned in
hardening operations, this occurs in a completely different
application (for example, in plastics technology as in patent WO
00/07790 or in liquid form as in patent WO 97/15420).
[0009] In this context, one of the objects of the present invention
is to provide a quench hardening installation using a cooling gas
that is thermally more efficient than nitrogen but is inexpensive
and simple to use, allowing the cooling of the most demanding
materials.
[0010] A further object of the present invention is to provide a
cooling method using a gas compatible with existing installations
currently functioning with nitrogen (and hence not requiring any
significant change to the installation).
[0011] To achieve these objectives, the present invention, in a
method for rapidly cooling metal parts using a pressurized cooling
gas, provides for the use of a cooling gas which comprises one or a
plurality of gases absorbing infrared radiation, selected so as to
improve the heat transfer to the part by combining radiative and
convective heat transfer phenomena, and so as to improve the
convective heat transfer coefficient in comparison with
conventional conditions of cooling with nitrogen.
[0012] The concept of "improvement in comparison with conventional
conditions of cooling with nitrogen" should be understood according
to the invention as comparing identical pressure, temperature or
quenching installation conditions.
[0013] The method according to the invention can further adopt one
or a plurality of the following technical features: [0014] the
cooling gas also comprises an additive gas selected from helium,
hydrogen or mixtures thereof; [0015] the cooling gas further
comprises a supplementary gas; [0016] the composition of the
cooling gas is also adjusted so as to obtain an average density of
the cooling gas thus produced which is approximately the same as
that of nitrogen; [0017] the composition of the cooling gas is also
adjusted so as to optimize the convective heat transfer coefficient
in comparison with the convective heat transfer coefficients of
each of the components of the cooling gas considered individually;
[0018] the cooling operation is carried out in a vessel in which
the parts to be treated are disposed, the vessel being equipped
with a gas stirring system, and the composition of the cooling gas
is also adjusted so as to obtain an average density of the cooling
gas thus produced which is adapted to said stirring system of the
vessel, without the need to make significant changes to said
vessel; [0019] the composition of the cooling gas is also adjusted
so that, during the parts cooling phase, endothermic chemical
reactions can occur between the absorbent gas or one of the
absorbent gases and another of the components of the cooling gas;
[0020] said infrared absorbing gas is CO.sub.2; [0021] said
infrared absorbing gas is selected from the group formed of
saturated or unsaturated hydrocarbons, CO, H.sub.2O, NH.sub.3, NO,
N.sub.2O, NO.sub.2, and mixtures thereof; [0022] the proportion of
absorbent gas in the cooling gas is between 5 and 100%, and
preferably between 20 and 80%; [0023] the cooling gas is a binary
CO.sub.2/He mixture, of which the CO.sub.2 content is between 30
and 80%; [0024] the cooling gas is a binary CO.sub.2/H.sub.2
mixture, of which the CO.sub.2 content is between 30 and 60%;
[0025] an operation of recycling of the cooling gas is carried out
after use, suitable for recompressing the gas before a subsequent
use, and, as required, also for separating and/or purifying it,
thereby to recover all or part of the components of the cooling
gas.
[0026] The invention further relates to the use, in an installation
for rapidly cooling metal parts using a pressurized cooling gas,
which installation is optimized for operation with nitrogen, of a
cooling gas comprising from 20 to 80% of an infrared absorbing gas
and from 80 to 20% of hydrogen or helium or mixtures thereof, the
composition of the cooling gas being adjusted so as to make
significant changes to the installation unnecessary.
[0027] As will have been understood, the concepts according to the
invention of "choice" of the absorbent gas or gases, or of
"adjustment" to obtain the desired properties of heat transfer
coefficient, or of density or of endothermic character, must be
understood as pertaining to the nature of the components of the
mixture and/or their content in this mixture.
[0028] The merit of the present invention is accordingly to stand
apart from the conventional approach of the prior art of simply
improving the convective heat transfer conditions, by demonstrating
that the proportion of radiative heat transfer in the total heat
transfer is between about 7 and 10% (in the range from 400 to
1050.degree. C.), hence very significant, and that it is therefore
extremely advantageous to address this aspect of the heat transfer
to account for it and to exploit it.
[0029] These objects, features and advantages, and others of the
present invention, are described in detail in the following
non-limiting description of particular embodiments, provided with
reference to the figures appended hereto among which:
[0030] FIG. 1, previously described, shows an example of a gas
quench hardening installation;
[0031] FIGS. 2A and 2B show the convective heat transfer
coefficient of various gas mixtures at various pressures, in the
case of a fluid in parallel flow between cylinders; and
[0032] FIG. 3 shows the variation in temperature as a function of
time for various quenching gases used in the same conditions.
[0033] According to the present invention, it is proposed to use,
as a quenching gas, a gas absorbing infrared radiation or a mixture
based on such infrared absorbing gases (designated below by
absorbent gas), such as carbon dioxide (CO.sub.2) and, if required,
containing one of more gases having a good convective heat transfer
capability (designated below by additive gas) added to it, such as
helium or hydrogen.
[0034] Such a mixture offers the advantage, in comparison with
conventional quenching gases or gas mixtures using gases
transparent to infrared radiation, such as nitrogen, hydrogen and
helium, of absorbing heat both by convective and radiative
phenomena, thereby increasing the total heat flux extracted from a
charge to be cooled.
[0035] It is possible to add, to this mixture, other gases,
designated herein after by supplementary gas, such as nitrogen,
considered both as a simple carrier gas and in a more active role
making it possible, as shown below, to optimize the properties of
the gas mixture, such as density, thermal conductivity, viscosity,
etc.
[0036] According to an embodiment of the present invention, as
shown in FIGS. 2A and 2B, it is proposed to use certain gas
mixtures as defined above, which further present better convective
heat transfer coefficients (kH) in watts per square meter and per
Kelvin than each of the gases considered individually. As shown
above in fact, according to one advantageous embodiment of the
invention, the composition of the cooling gas is adjusted so as to
"optimize" the convective heat transfer coefficient in comparison
with the convective heat transfer coefficients of each of the
components of the cooling gas considered individually. The term
"optimization" used here should be understood accordingly as taking
place at the peak of the curve concerned, or much lower (for
example, for economic reasons) but in any case so as to have a
convective heat transfer coefficient that is better than each of
the convective heat transfer coefficients of each of the components
of the cooling gas considered individually.
[0037] According to a further advantageous embodiment of the
present invention, it is proposed to use an absorbent gas mixture
(and if applicable an additive gas) possibly with the addition of
supplementary gases, in density conditions optimized so that
hardening can be carried out in quench hardening installations
normally designed and optimized to operate in the presence of
nitrogen. For this purpose, carbon dioxide is mixed, for example,
with helium, used as an additive gas, so as to combine an
optimization of the convective heat transfer coefficient with an
average mixture density that is approximately the same as that of
nitrogen. Existing installations can accordingly be used with
comparable ventilation rates and capacities and existing gas
ventilation and deflection structures, without having to make
significant changes to the installation.
[0038] This offers the advantage that, in a given installation,
optimized for nitrogen hardening, the user can, in normal
conditions, when appropriate to the materials concerned, use
nitrogen as a quenching gas and, only in the specific cases of more
demanding materials, i.e. when the specific conditions of the parts
or the steels to be treated demand specific treatments, use for
example the mixture of carbon dioxide and helium given as an
example, or the mixture of carbon dioxide and hydrogen also
exemplified herein.
[0039] Obviously, as it will appear clearly to a person skilled in
the art, if the invention has been particularly illustrated above
using CO.sub.2, other gases absorbing IR radiation are also usable
here without departing at any time from the framework of the
present invention, such as saturated or unsaturated hydrocarbons,
CO, H.sub.2O, NH.sub.3, NO, N.sub.2O, NO.sub.2, and mixtures
thereof.
[0040] Similarly, if particular emphasis has been laid above on an
advantageous embodiment of the invention, in which the
concentrations of the various gases are adjusted to obtain both
good heat transfer efficiency and density conditions approaching
nitrogen, in order to avoid having to make any significant changes
to the installation, it is possible, without departing from the
framework of the present invention, to privilege the optimal heat
transfer conditions, even if it means using mixtures of density
more distant from that of nitrogen, and accordingly having to make
changes to the installation, particularly to the stirring motor
(adoption of a motor with a different power rating, or of a speed
variator system). This could, for example, be the case for a gas
mixture comprising 90% CO.sub.2 and 10% hydrogen, with a density
about 40% higher than that of nitrogen.
[0041] FIG. 2A shows, for pressures 5, 10 and 20 bar, the
convective heat transfer coefficient kH of a mixture of CO.sub.2
and helium, for various proportions of CO.sub.2 in the mixture.
Thus, the x-axis shows the ratio of the CO.sub.2 concentration,
c(CO.sub.2), to the total concentration of CO.sub.2 and He,
c(CO.sub.2/He). It may be observed that the convective heat
transfer coefficient reaches a peak at CO.sub.2 concentrations
between about 40 and 70%, in this case about 650 W/m.sup.2/K at 20
bar for a concentration of about 60%. Thus, the mixture not only
offers the advantage of having a density close to that of nitrogen,
but in addition, of having a higher convective heat transfer
coefficient than that of pure CO.sub.2.
[0042] FIG. 2B shows similar curves for mixtures of carbon dioxide
(CO.sub.2) and hydrogen (H.sub.2). It may be observed that the
convective heat transfer coefficient kH reaches a peak at CO.sub.2
concentrations between about 30 to 50%, in this case about 850
W/m.sup.2/K at 20 bar for a concentration of about 40%.
Furthermore, it shows that the convective heat transfer coefficient
kH is better for a mixture of carbon dioxide and hydrogen than for
a mixture of CO.sub.2 and helium.
[0043] A further advantage of the use of such a mixture of carbon
dioxide and hydrogen is that, under the usual conditions for
quench-hardening steel parts, endothermic chemical reactions occur
between the CO.sub.2 and the hydrogen, thereby further accelerating
the cooling. Moreover, it is observed that in the presence of
CO.sub.2, the explosion hazard associated with hydrogen is
substantially reduced, even if oxygen is inadvertently
introduced.
[0044] FIG. 3 shows the result of calculations simulating the
cooling of a steel cylinder by convective heat transfer with
various cooling gases in the case of a mixture flowing in parallel
to the length of the cylinders (cylinders simulating the case of
long parts). Curves are shown for pure nitrogen (N.sub.2), for a
mixture containing 60% CO.sub.2 and 40% helium, for pure hydrogen,
and for a mixture containing 40% CO.sub.2 and 60% hydrogen. This
latter mixture is observed to yield the best results, that is, the
highest cooling rate between 850 and 500.degree. C. For this latter
mixture, the hardening rate is improved by about 20% over pure
hydrogen and by about 100% over pure nitrogen.
[0045] Obviously, as already pointed out above, the present
invention is susceptible to a number of variants and modifications
which will appear to a person skilled in the art, particularly as
regards the choice of the gases, the optimization of the
proportions of each gas, with the understanding that, if desired,
ternary mixtures such as CO.sub.2/He/H.sub.2 can be used, and that
other gases could be added, called supplementary gases above.
* * * * *