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EP 1 530 651 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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24.11.2010 Bulletin 2010/47 |
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Date of filing: 14.12.2000 |
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International Patent Classification (IPC):
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International application number: |
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PCT/IB2000/001993 |
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International publication number: |
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WO 2002/048419 (20.06.2002 Gazette 2002/25) |
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METHOD AND APPARATUS FOR SIMPLIFIED PRODUCTION OF HEAT TREATABLE ALUMINUM ALLOY CASTINGS
WITH ARTIFICIAL SELF-AGING
VERFAHREN UND VORRICHTUNG ZUR VEREINFACHTEN HERSTELLUNG VON WÄRMEBEHANDELBAREN ALUMINIUMLEGIERUNGSGUSSTEILEN
MIT KÜNSTLICHER SELBSTALTERUNG
PROCEDE ET APPAREIL DE FABRICATION SIMPLIFIEE DE PIECES MOULEES EN ALLIAGE D'ALUMINIUM
APTES AU TRAITEMENT THERMIQUE A AUTOVIEILLISSEMENT ARTIFICIEL
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Designated Contracting States: |
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DE FR GB IT |
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Date of publication of application: |
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18.05.2005 Bulletin 2005/20 |
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Proprietor: Tenedora Nemak, S.A. de C.V. |
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Garcia, Nuevo Léon, D.F. 66000 (MX) |
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Inventors: |
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- GARZA-ONDARZA, Oscar
Adolfo Lopez Mateos 402
Nuevo Leon
Mexico, D.F. 66250 (MX)
- VALTIERRA-GALLARDO, Salvador
Satillo
Coahuila
Mexico, D.F. 25290 (MX)
- MOJICA-BRISENO, Juan Francisco
Monterrey
Nuevo Leon
Mexico, D.F. 64860 (MX)
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Representative: HOFFMANN EITLE |
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Patent- und Rechtsanwälte
Arabellastrasse 4 81925 München 81925 München (DE) |
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References cited: :
EP-A- 0 743 372 US-A- 5 112 412 US-A- 5 788 784 US-A- 5 922 147
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US-A- 1 852 621 US-A- 5 536 337 US-A- 5 788 784 US-A- 5 922 147
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for making aluminum alloy
castings, wherein the heat-treatment processes of the prior art are simplified, by
actually eliminating some traditional steps and equipment. The invention is applicable
for example in the production of cylinder heads, motor blocks and the like, for automotive
engines. The invention provides many advantages over the prior art heat-treatments,
with an increased productivity of the casting plants, and lower capital and operation
costs as well. The invention is particularly useful for producing aluminum alloys
of the 3xx. x series of the classification of the Aluminum Association (AA), especially
for T6 and T7 properties.
[0002] This invention is broadly applicable to the production of any aluminum alloy casting
which in the past has derived meaningful benefit from quenching and artificial aging
in an aging furnace. The invention eliminates the need for an aging furnace, while
retaining the benefits thereof. This improvement has been styled herein as artificial
self-aging (to distinguish from natural aging at ambient temperatures and from prior
art artificial aging, which requires an aging furnace).
[0003] This invention is broadly-applicable to the production of any aluminium alloy casting
of the type having significant precipitation hardening with meaningful benefit from
"solution" heat treating and aging.
BACKGROUND ART
[0004] For a good background discussion and definitions of "heat treatable aluminum alloy
castings", "artificial aging" (see also "precipitation hardening"), "quenching", "solution
heat treatment", "casting series 3xx. x", and "T6 & T7 tempers" see the ASM Handbook
series; particularly
Volume 4 (1991), entitled "Heat Treating" (especially pages 841-879; see
p. 841 for "heat treatable",
p. 851 et seq. for "quenching" and
p. 859 for "age hardening") and
Volume 2 (1990), entitled "Properties and Selection: Nonferrous Alloys and Special
Purpose Materials", (especially pages 15-41; see
p. 39 for "heat treatable",
p. 40 for "artificial aging") both being tenth editions, and also
Volume 15 (1988), entitled "Casting" ninth edition (specially pages 757-761, see
pp. 760-1 for "quenching" and "aging"); all published by ASM International.
[0005] In the production of cast parts made of aluminum alloys it has always been thought
in the past to be necessary for many such castings (especially with a T6 or T7 temper)
to undergo an elaborate heat-treating process in order to impart to the cast parts
the necessary mechanical properties (like hardness and tensile strength required for
the demanding working uses of said parts).
[0006] It is known that the degree of hardness and other mechanical properties of the cast
parts depend on the thermal history of the cast parts after having been cast in the
mold. The Aluminum Association (AA) has classified the most used aluminum alloys and
the several standard heat treatments used in the industry. Examples of such standard
heat-treatments those denominated T6 and T7, which designate a standard set of mechanical
properties developed by certain castings of primarily silicon-copper-aluminum alloys.
[0007] The automotive industry throughout the world demands very strict quality standards.
Casting plants making aluminum motor parts must therefore be able to produce cast
parts which consistently comply with the minimum levels of mechanical properties specified
for each part Since quality is a must, the casting plants follow those procedures
and processes which are well tested and have proven reliable for many years. The production
process currently followed in the industry comprises filling a mold with liquid aluminum
alloy, cooling the cast part in the mold in order to obtain a solidified casting,
extracting the casting from the mold, and allowing the cast part to cool-down naturally
to ambient temperatures, and then subjecting batches of such cooled castings to the
aforementioned "solution" heat-treating process. One way to reduce the heat load in
the solution heat treatment furnace, has been to remove the sand cores and riser portions
of the castings after natural cooling and before the "solution" heat treatment. The
heat treating of the prior art comprises heating the preferably trimmed castings in
a furnace to temperatures above about 470°C (typically in the range between 480°C
and 495°C) for a certain period of time, usually in the range between at least 2 to
7 hours. This treatment is performed in order to bring back into solid solution the
copper and/or other alloying elements that give the castings their hardness. It is
known that, while the casting metal is in the molten state, the alloying elements
are in solution in the aluminum substrate. During the cooling process, particularly
if the cooling is carried out at a slow rate, there is a tendency for the different
elements to become segregated. Therefore, traditionally the casting is re-heated in
a "solution" heat treatment furnace for several hours, and only then is quenched,
i.e. rapidly cooled down by a fluid quench from a temperature for example about 480°C
to around 85°C, so that the solid solution is preserved (before segregation can occur).
Such post solution-treatment quench cooling may commonly be continued in a manner
sufficient to bring the castings down to any of a number of different temperatures
and at different rates according to the final properties of the alloy to be emphasized.
[0008] This quenching step produces a supersaturated solid solution that causes the alloy
to harden naturally as time passes. Finally, in order to accelerate and improve this
age hardening, the quenched castings are maintained at temperatures of about 200°C
in an "aging" furnace for about 2 or more hours. The time spent in the "aging" furnace
at elevated artificial aging temperatures brings the alloy to at least a partial coherency
in its structure giving the required hardness and strength properties.
[0009] U.S. patent No. 5,788,784 to Koppenhoefer et al. discloses a process for heat-treating light metal castings that requires "a solution
heat treatment furnace 2, an adjoining quenching device 3, as well as an aging furnace
4", all particularly for cylinder heads of piston engines. In the 5,788,784 process,
after solidifying and removing the casting from the mold, said castings unconventionally
are not naturally cooled, yet are still solution heat treated (claiming the advantage
of using the residual heat of the casting present at the approximate 530°C temperature
of such treatment). Thereafter, the castings are quenched with an air/water mixture
down to 130°C to 160°C, and then aged in a furnace at approximately 170°C to 210°C
(thus taking advantage of some relatively minor residual heat carryover into the aging
furnace), and are then finally cooled to room temperature after, for example, four
hours of furnace aging. The castings are individually quenched with a mist-type fine
mixture of air and water, which is "nozzle sprayed on all sides" of the casting.
[0010] Koppenhoefer asserts a number of advantages by reason of quenching the castings with
an air-water spray, for example that a uniform and low-distortion cooling is achieved,
that the adhering core sand is not wetted at the elevated quenching temperatures and
can be collected clean and reused after regeneration, and that the residual heat of
the casting remaining at 130° to 160°C can be used to aid in the subsequent furnace
aging step (by not cooling down the casting too much and leaving some heat in said
casting). Quenching the casting by directing the sprayed water on all sides of the
casting suggests that most of the residual heat is lost, with that amount retained
being mainly in the inner portion of the casting. This also suggests that a large
temperature gradient would have to be maintained between the interior and the surface
of the casting in order for the amount of retained residual heat carried over into
the aging step to be meaningful. Such large differentials in temperature across the
casting (particularly the end product portion thereof) is one of the problems to be
avoided while quenching a piece in order to avoid stresses and achieve the T6 or T7
properties and also to avoid spheroidization of the alloying elements.
[0011] U.S. patent No. 5,112,412 to Plata et al. teaches a process for cooling large cast billets of aluminum after a temperature
homogenization (re-heat) annealing step. Annealing is a softening process for aluminum
(just the opposite of the strengthening and hardening heat treatment of the present
invention), and this Plata patent is silent on how the cooling is to be done to accomplish
a particular result (mainly mentioning only that it be "in accordance with the alloy
composition" and describing how the "automated and controlled manner of spraying can
be adjusted to different shaped billets, as they may differ from the usual round shape").
This patent first describes cooling the annealed billet with a spray on all sides.
This decreases the temperature at the surface of said billet, while the center portion
(inaccessible to the spray) necessarily cools more slowly and thus initially remains
at a relatively higher temperature. The billet leaves the spray and is allowed to
equalize its internal and external temperatures in an insulated chamber. In another
embodiment, Plata et al describes a process modification in the case of a so-called
(but otherwise unidentified) "hard" alloy to continue spraying until the billet has
achieved an equalized temperature. An example of this temperature is given as "310
C.-350 C. in AlMgSi alloys" (a range above most age hardening but typical of softening
annealing). The teaching includes the possibility of varying the intensity of the
continuous spray, but only for the purpose of achieving a "better balanced heat flow"
and a temperature zone "preferably distributed homogeneously during cooling so that
no or only minimal deformations, stresses or cracks form". For example, the patent
states that circular billets are sprayed evenly, but a rectangular billet may be sprayed
with different intensity along it periphery. This difference in spray intensity is
to achieve uniformity of cooling during the quench (just the opposite of subjecting
the casting to a significant differential or complete absence of quench cooling of
a specific waste portion of the casting in order to maintain such portion at a significantly
higher temperature during the quench of the work portion (and much less to identify
such a waste portion which is accessible to the spray, but is not to be so spray cooled).
Thus, even though one of the embodiments discloses a spray process involving a difference
in the temperature between certain portions of the billet which later reach an equalized
temperature, there is no disclosure of differential quenching of selected portions
of the casting to promote rather than minimize an initial significant heat differential
between selected different portions of the casting (particularly with the division
being between equally exposed waste and workpiece portions). Furthermore, Plata et
al. teaches a process of cooling the surfaces of the workpiece (billet) on all sides,
while the inner portion of the workpiece remains hot. If this process is applied to
the workpiece portion of the castings for cylinder heads or blocks for engines, it
will cause a different distribution of the alloying elements and thus it will fail
to achieve the objects of the present invention (which provides a quenching step to
produce uniform properties such as those obtained with a T6 treatment, all with accelerated
aging but without the need for an aging furnace). In applicant' casting, the unquenched
portion is an existing waste portion that is put to a useful interim purpose but whose
ultimate alloy and physical properties are irrelevant Engine castings, if made by
the Plata process would be rejected.
[0012] One or more of the present inventors' recent
U.S. patent, No. 5,922,147 (to Valtierra et al.), mentioned above, discloses an improved heat-treating method whereby the castings
are quenched immediately after having been extracted from the mold, thus eliminating
"solution" heat treatment and avoiding the need for a solution heat treatment furnace;
while nevertheless producing castings with similar properties to those that undergo
the traditional solution heating step. The 5,922,147 patent process provides a casting
plant with greatly improved productivity and significant savings in capital and operational
costs. This patent, however, does not teach or suggest a method capable of eliminating
also the aging furnace.
SUMMARY OF THE INVENTION
[0013] According to a first aspect of the invention, there is provided a method of quenching
and artificially aging an aluminum alloy casting having a riser portion and a workpiece
portion, said method comprising: selectively quench cooling the workpiece portion
of the casting while maintaining the riser portion at a relatively higher temperature;
initiating the quench when the casting is at elevated temperatures with its alloying
elements in solid solution; proceeding with the quench to cool the workpiece portion
sufficiently rapidly to inhibit precipitation of the alloy elements and thereby to
maintain such elements in supersaturated solution within the aluminum matrix, discontinuing
the quench when the workpiece portion is cooled to a temperature which is at or below
the range for artificial aging; artificially aging said workpiece portion within a
range of temperatures and over an effective time period appropriate for such aging
of the aluminium alloy casting workpiece primarily by means of residual heat flowing
from the relatively hotter riser portion.
[0014] According to a second aspect of the invention, there is provided the use of an apparatus
for quenching and artificially aging a hot aluminum alloy casting (20) having a riser
portion (24) and a workpiece portion (22), the apparatus comprising:
- a quench unit (10);
- an aging unit;
- transfer means (16), arranged to move at least one casting (20) successively through
said units, the transfer means arranged to position such casting (20) in said quench
unit (10) in an oriented position; and
- cooling means (30) for quenching the casting,
wherein the use of the apparatus comprises rapidly and selectively quenching the workpiece
portion (22) of the casting (20) in said oriented position, largely to the exclusion
of the riser portion (24), which riser portion (24) will thus initially remain at
a relatively higher temperature.
[0015] Embodiments of the present invention can improve one or more of the present inventors'
aforementioned 5,922,147 patent by simplifying even further the overall heat-treatment
of the castings, although broadly it can be applied separately. These embodiments
of the invention can dispense with the aging furnace, in addition to preferably also
dispensing with the solution furnace. Therefore, the invention is able to provide
a method and apparatus for producing the casting in a considerably shorter time, with
less capital, and lower production costs, while maintaining and even improving on
required mechanical properties of the castings.
[0016] Preferred embodiments of the present invention use a selectively directed spray quench
in a manner which can eliminate expensive equipment and reduce significantly the overall
production time. The castings are preferably so quenched promptly after demolding
in accordance with one or more of the present inventors' own recent patent (
US Patent No. 5,922,147) to obtain the properties of a conventional "solution" heat treatment (such as the
properties required by a T6 temper) but without the usual "solution" heat treatment
in a furnace.
[0017] Furthermore,
Koppenhoefer (US Patent No. 5,788,784) discussed above, does not teach or suggest the present inventors' invention of selectively
quenching only the end product portion of the casting in order to use eventually the
unquenched retained residual heat from the sprue and from any other temporarily retained
waste portion of the casting (including sand cores) in order to enable aging of said
casting without need for an aging furnace. In contrast, the Koppenhoefer teaches decoring
the resin bonded sand cores from the castings by being "pyrolytically destroyed" during
solution heat treatment and further removed during quenching, all prior to aging.
[0018] It is another advantage obtainable with embodiments of the present invention to provide
method and use of apparatus for producing aluminium alloy castings having similar
mechanical properties as those produced by the prior art methods while avoiding the
necessity of an aging furnace, and preferably also of a solution heat furnace.
[0019] It is a further advantage obtainable with embodiments of the invention to increase
the productivity of a casting plant and to reduce its capital costs and its operating
costs significantly.
[0020] Other advantages obtainable with embodiments of the invention will be evident to
those skilled in the art or will be pointed out hereafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] To enable a better understanding of the present invention, and to show how the same
may be carried into effect, reference will now be made, by way of example only, to
the accompanying drawings, in which:-
Figure 1 is a graph showing the different casting temperature paths followed over
time during the heat treatment according to the conventional prior art, according
to one or more of the present inventors' most recent prior art process (shown in U.S. Patent 5,922,147 to Valtierra et al.); and in one embodiment according to the method of the present invention with respect
to the workpiece portion and also to the riser portion;
Figure 2 is a schematic side elevational view of a preferred embodiment according
to the method of the present invention illustrating a series of stations making up
the quench portion of a casting production line, showing some castings (each comprised
of both the workpiece portion and the riser portion) and spray nozzles used for quenching
only the workpiece portion oriented uppermost; and
Figure 3 is a schematic frontal view of the embodiment shown in Figure 2, showing
the nozzles directing the spray or mist selectively onto the workpiece portion of
the casting.
DETAILED DESCRIPTION
[0022] In order to better describe the invention, the present inventors specifically identify
the two major parts of the casting as a riser portion (the riser portion being that
portion which is subsequently removed and discarded) and a workpiece portion (the
workpiece portion being the portion used for the end product). A "riser" is a reservoir
of liquid metal used to largely compensate for shrinkage of a casting as it cools
in its mold. The term "riser" also commonly has the meaning used in this application,
namely the solidified metal portion of the casting remaining in the reservoir after
the casting is cooled. "Riser portion" is intended to include at least the riser and
additionally in its broader sense can include other similar waste attachments such
as sprue, runners, gates, etc. formed as part of the original casting. When the casting
is demolded from the typical water-cooled mold, the workpiece commonly has a temperature
of about 400°C and the riser one of about 500°C. The invention achieves its advantages
by a selective quench of only the workpiece portion to surface temperatures preferably
in the range from above about 100°C to about 130°C, at a rate sufficient to achieve
a supersaturated solution of the hardening element (typically copper) in the aluminum
alloy of the workpiece at the atomic level. Preferably, to perform this selective
quench, spray nozzles are set to direct the water spray or mist on the workpiece and
minimize any impingement on the riser. This workpiece-directed quench permits the
riser (subjected only to natural or at most a minimized indirect cooling) to maintain
a significantly higher temperature typically above about at least 300°C to 350°C during
the workpiece quenching step. Thereafter, when the quenching is finished, the residual
heat in the sprue portion is used as a heat reservoir to slightly re-heat the workpiece
and maintain it (by conductive phenomena) in the artificial aging temperature range
of between 140°C and 250°C, and preferably about 180°C to about 220°C, for an adequate
time period, to thus achieve the desired properties for the workpiece. The invention
dispenses with the need to supply furnace heat for re-heating and maintaining the
whole casting in the artificial aging temperature range and simplifies the casting
plant by thus rendering the aging furnace unnecessary. The final quench temperature
should not be so low that the residual heat from the riser is too little to maintain
the workpiece in the required aging temperature range for the necessary length of
time. Also, if the workpiece surface temperature is maintained high enough above the
boiling point of the spray liquid (typically water) throughout the quench, then liquid
overflow onto the riser can be more easily minimized or avoided altogether and the
latent heat of can be utilized and concentrated on the workpiece. A copious flow of
a fine water mist is especially effective, since the mist particles evaporate immediately
and there is no liquid wetting of the hot workpiece surface that can flow over onto
the riser .
[0023] It has been found that the existing riser mass as dictated by ordinary foundry practice
is sufficient to achieve this result (i.e. provides an adequate heat reservoir for
the artificial age hardening without need for an aging furnace); however, it would
be within the scope of this invention to increase the mass as needed for the desired
inventive result.
[0024] Even though the temperature of the workpiece and the riser greatly depends on the
mass and the surface area of both portions, the quenching temperature can be regulated
to achieve the advantages of the invention at different temperature paths. Also the
aging position of the casting plant can be insulated to prolong the artificial aging
step at elevated temperatures for a more extended time period as may be needed (or
even make use of a heat exchanger to take advantage of other residual or excess heat
sources that may be available elsewhere in the casting plant system), all as an aid
to avoid the need for the added expense of an aging furnace.
[0025] The invention is herein described as applied to the production of cylinder heads
for automotive motors using generally silicon-based aluminum alloys of the AA 3xx.x
series, having T6 and T7 properties (such as particularly A319), but it will be evident
to those skilled in the art, that the invention can in its broader aspects be also
applied to other metal alloys and to the heat-treating of other castings.
[0026] Figure 1 is a graph showing the different temperature paths vs. time of various castings;
with the prior art processes in dotted lines and embodiments of the present invention
in continuous lines. Nowadays, the most common practice of the prior art (shown in
the graph by the thinner dotted line) includes, after demolding, the steps of subjecting
the casting to: natural cooling, reheating and maintaining in a solution heat furnace,
quenching, and reheating and maintaining in an aging furnace. Another illustrated
prior art temperature path (shown by the bold dotted line) is the heat treatment disclosed
in one or more of the present inventors' very recent
U.S. Patent 5,922,147 (wherein the solution treatment is omitted entirely, with the quenching of the casting
occurring without natural cooling after demolding, and preferably immediately).
[0027] Also shown in the graph in Figure 1, are the casting temperature paths of the workpiece
portion and of the riser portion according to the method of the present invention
(shown in respective continuous lines). As it can be seen, there is a selective quenching
of the workpiece portion of the casting. At the same time, the riser remains essentially
unquenched, with any cooling typically occurring only naturally and at a much lower
rate; so that when the quenched workpiece has a temperature of about 120°C, the riser
still has a temperature about 350°C. At about that point, before the quench reaches
ambient temperature, the quenching step is stopped and the casting (riser and workpiece
together) is allowed to homogenize its temperature with the workpiece being mainly
in the range of from about 160°C to about 220°C (initially towards the high end of
the range, preferably). This essentially duplicates the conventional temperature profile
of a casting maintained in an aging furnace after the quenching step, while surprisingly
eliminating the need for any aging furnace. This is possible, because there is sufficient
mass in the riser to function as an adequate reservoir of heat available for a sufficient
duration to achieve complete aging.
[0028] Figure 2 schematically shows a preferred embodiment of the apparatus used for the
quenching step in accordance with the invention. Immediately after demolding, the
casting 20, broadly comprising riser 24 and the workpiece 22, is placed on a conveyor
16 by means of a feeding robot 12. The conveyor 16 has structural supports 18 (such
as rollers)located through the quenching unit 10. Also provided in the quenching unit
10 are an air header 26 and a water header 28, both being connected to spray nozzles
30. Spray nozzle 30 projects a water spray or an air driven mist 32 that is directed
to impinge mainly on the workpiece portion 22 of the casting 29 positioned on the
conveyor 16. Since rapid cooling rates are quite important to achieve the desired
properties in the workpieces 22, and the nozzles 30 in this embodiment are in a fixed
position within the quenching unit 10, the conveyor 16 is operated discontinuously
in order to transport castings 20 from one quenching station 33 to the next in a step-wise
mode (over a distance 34). After the castings 20 have traveled along the length of
the conveyor 16 within the quenching unit 10, the residence time needed for quenching
the workpieces 22 to the desired temperatures is completed. Finally, a withdrawing
robot 14 transports the quenched castings to a place to be aged artificially at still
elevated temperatures over an extended time utilizing the reservoir of heat remaining
in the riser 24. In order to improve the quenching operation of the quenching unit
10, a fan 13 can be supplied to extract the vapor produced by the evaporation of the
sprayed water while quenching the workpieces 22 of castings 20.
[0029] Figure 3 shows an end view of the quenching unit 10. The same elements bear the same
reference numerals of Figure 2. Additionally shown is an air supply 25 for air header
26, preferably at high pressure in order to achieve a better water spray or mist.
Liquid supply 27 feeds header 28, which can handle water or any other suitable liquid
cooling medium.
[0030] Even though the process described on figures 2 and 3 teaches a quenching unit for
processing castings 20 in a step-wise mode and with the riser 24 oriented as the base
of the casting 20, it will be evident to those skilled in the art that the quenching
unit 10 of the invention could be operated continuously preferably with moving headers
and spray nozzles or in a batch processing system as well. Another change that can
be performed to the embodiments of the invention without departing from its scope
comprises locating the spray nozzles below the castings thus directing the spray 32
upwardly. In this case, the sprue portion 24 of the castings 20 would be positioned
above the workpiece 22.
[0031] As previously indicated, the invention in its broader aspects can be applicable to
other aluminum alloys and heat treating processes wherein the aging furnace step is
normally used, including those prior art systems still using a conventional solution
heat treatment with a subsequent quenching step.
1. A method of quenching and artificially aging an aluminum alloy casting (20) having
a riser portion (24) and a workpiece portion (22), said method comprising:
selectively quench cooling the workpiece portion (22) of the casting while maintaining
the riser portion (24) at a relatively higher temperature;
initiating the quench when the casting (20) is at elevated temperatures with its alloying
elements in solid solution;
proceeding with the quench to cool the workpiece portion (22) sufficiently rapidly
to inhibit precipitation of the alloy elements and thereby to maintain such elements
in supersaturated solution within the aluminum matrix,
discontinuing the quench when the workpiece portion (22) is cooled to a temperature
which is at or below the range for artificial aging;
artificially aging said workpiece portion (22) within a range of temperatures and
over an effective time period appropriate for such aging of the aluminum alloy casting
workpiece primarily by means of residual heat flowing from the relatively hotter riser
portion (24).
2. A method according to claim 1, wherein the artificial aging of said workpiece portion
is carried out without actively heating the overall casting (20).
3. A method according to claims 1 or 2, wherein the mass, shape and the cross-sectional
area of attachment of the riser portion (24) relative to the workpiece portion (22)
and the temperature differential therebetween are chosen to be sufficient to maintain
the workpiece portion (22) within the temperature and time period ranges required
for the artificial aging.
4. A method according to any one of the preceding claims, wherein said selective quench
cooling is performed by spraying a quenching fluid (32) on the surfaces of said workpiece
portion (22).
5. A method according to any one of the preceding claims, wherein said quenching fluid
(32) is water.
6. A method according to any one of the preceding claims, wherein said quench is by a
water mist.
7. A method according to any one of the preceding claims, wherein said quench is initiated
when the casting (22) is at a temperature above about 350°C.
8. A method according to any one of the preceding claims, wherein said quench is less
than five minutes in duration.
9. A method according to any one of the preceding claims, wherein said quench is discontinued
when the workpiece portion (22) reaches a temperature on the order of 100°C to 130°C,
while the riser portion (24) remains above 300°C.
10. A method according to any one of the preceding claims, wherein said quench is discontinued
when the workpiece portion (22) reaches about 130°C.
11. A method according to any one of claims 1 to 9, wherein said quench is discontinued
when the workpiece portion (22) reaches about 120°C.
12. A method according to any one of the preceding claims, wherein said artificial aging
of the workpiece portion (22) is at a temperature between 140°C and 250°C.
13. A method according to any one of the preceding claims, wherein said artificial aging
of the workpiece portion (22) is at a temperature between 180°C to 220°C.
14. A method according to any one of the preceding claims, wherein said artificial aging
is for a period of time from two to five hours.
15. A method according to any one of the preceding claims, wherein said workpiece portion
(22) is decored after the artificial aging.
16. A method according to any one of the preceding claims, wherein said casting (20) is
insulated during artificial aging to prolong the duration of the artificial aging
process without adding heat to the casting (20).
17. A method according to any one of the preceding claims, wherein a heat treatable aluminum
alloy having properties, including hardness and strength, which are improved by precipitation
hardening through aging.
18. A method according to any one of the preceding claims, wherein said casting (20) is
formed from an aluminum alloy of the 3xx.x series according to the Aluminum Association
(AA) classification having Al, Si, & Cu or Mg as the principal casting constituents,
with properties at least equal to a T6 or T7 temper.
19. A method according to claim 18, wherein said casting (20) is made from an A319 aluminum
alloy with up to a 5% copper content.
20. A method according to any one of the preceding claims, further comprising:
solidifying and extracting the casting (20) from its mold while said casting is at
a temperature above 400°C;
heating said castings (20) in a solution furnace to solution heat treating temperatures
for a time period from about 2 to 7 hours.
21. A method according to claim 20, wherein said heating of said castings (20) in a solution
furnace is to a range of solution heat treatment temperatures from about between 480°C
and 495°C.
22. A method according to claim 20 or 21, further comprising naturally cooling the casting
(20) after extraction from its mold and before solution heat treating said castings.
23. A method of producing a workpiece, comprising the steps of:
performing the method of any of claims 1 to 22; and
removing the riser portion from the casting, to produce said workpiece.
24. A method according to claim 23, wherein the workpiece is a cylinder head for an automotive
engine.
25. Use of an apparatus for quenching and artificially aging a hot aluminum alloy casting
(20) having a riser portion (24) and a workpiece portion (22), the apparatus comprising:
- a quench unit (10);
- an aging unit;
- transfer means (16), arranged to move at least one casting (20) successively through
said units, the transfer means arranged to position such casting (20) in said quench
unit (10) in an oriented position; and
- cooling means (30) for quenching the casting,
wherein the use of the apparatus comprises rapidly and selectively quenching the workpiece
portion (22) of the casting (20) in said oriented position, largely to the exclusion
of the riser portion (24), which riser portion (24) will thus initially remain at
a relatively higher temperature.
26. Use of an apparatus according to claim 25, wherein said units are part of a continuous
processing line; said quench unit (10) is a spray containment housing; said cooling
means (30) is at least one liquid quench sprayer directed to impinge directly on essentially
only the workpiece portion (22) of the casting presented to it by the transfer means
(16) in the oriented position.
27. Use of an apparatus according to claims 25 or 26, wherein said aging unit is an insulated
tunnel housing.
28. Use of an apparatus according to any one of claims 25 to 27, wherein said aging unit
is not re-heated by means of a furnace.
29. Use of an apparatus according to any one of claims 25 to 28, wherein said cooling
means (30) has a plurality of liquid quench sprayers spaced apart along the processing
line, each impinging directly on essentially only the workpiece portion (22) of the
castings (20) successively presented to it by the transfer means (16) in the oriented
position so as to achieve quench cooling of the workpiece portion (22).
30. Use of an apparatus according to any one of claims 25 to 29, wherein said aging unit
is heated only by residual heat including from a heat exchanger.
1. Ein Verfahren zum Abschrecken und Warmauslagern eines Aluminiumlegierungsgusses (20),
der einen erhöhten Abschnitt (24) und einen Werkstückabschnitt (22) aufweist, wobei
das Verfahren umfasst:
selektives Abschrecken des Werkstückabschnitts (22) des Gusses unter Beibehaltung
einer relativ höheren Temperatur des erhöhten Abschnitts (24);
Einleiten des Abschreckens, wenn der Guss (20) eine erhöhte Temperatur hat, mit seinen
Legierungselementen als Mischkristalle vorliegend;
Fortsetzen des Abschreckens, um den Werkstückabschnitt (22) ausreichend schnell zur
Unterdrückung der Ausscheidung von Legierungselementen abzukühlen und dadurch diese Elemente in übersättigter Lösung in der Aluminiummatrix zu halten;
Abbrechen des Abschreckens wenn der Werkstückabschnitt (22) auf eine Temperatur heruntergekühlt
ist, die im oder unter dem Bereich zum Warmauslagern liegt;
Warmauslagern des Werkstücks (22) in einem Bereich von Temperaturen und über eine
effektive Zeitspanne, so bemessen, dass das Warmauslagern des Aluminiumlegierungsgusswerkstücks
vorwiegend durch Abfließen von Restwärme des relativ heißeren erhöhten Abschnitts
(24) stattfindet.
2. Verfahren nach Anspruch 1, wobei das Warmauslagern des Werkstückabschnitts ohne aktives
Erhitzen des gesamten Gusses (20) ausgeführt wird.
3. Verfahren nach Anspruch 1 oder 2, wobei die Masse, Form und die Querschnittsfläche
der Anbindung des erhöhten Abschnitts (24) relativ zum Werkstückabschnitt (22) und
die dazwischen liegende Temperaturdifferenz ausreichend gewählt sind, um den Werkstückabschnitt
(22) in den Bereichen von Temperaturen und Zeitspannen zu halten, die zum Warmauslagern
notwendig sind.
4. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abkühlen durch selektives
Abschrecken über das Ansprühen der Oberfläche des Werkstückabschnitts (22) mit einem
Abschreckfluid (32) erfolgt.
5. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abschreckfluid (32) Wasser
ist.
6. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abschrecken über Wassernebel
stattfindet.
7. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abschrecken eingeleitet
wird, wenn der Guss (22) ungefähr eine Temperatur über 350°C aufweist.
8. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abschrecken eine Dauer
von unter 5 Minuten beträgt.
9. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abschrecken abgebrochen
wird, wenn der Werkstückabschnitt (22) eine Temperatur im Bereich von 100°C bis 130°C
erreicht, während der erhöhte Abschnitt weiterhin über 300°C aufweist.
10. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Abschrecken abgebrochen
wird, wenn der Werkstückabschnitt (22) ungefähr 130°C erreicht.
11. Verfahren nach einem der Ansprüche 1 bis 9, wobei das Abschrecken abgebrochen wird,
wenn der Werkstückabschnitt (22) in etwa 120°C erreicht.
12. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Warmauslagern des Werkstückabschnitts
(22) bei einer Temperatur zwischen 140°C und 250°C stattfindet.
13. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Warmauslagern des Werkstückabschnitts
(22) bei einer Temperatur zwischen 180°C und 220°C stattfindet.
14. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Warmauslagern in einer
Zeitspanne zwischen zwei und fünf Stunden stattfindet.
15. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Werkstückabschnitt (22)
nach dem Warmauslagern entkernt wird.
16. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Guss (20) während des
Warmauslagerns isoliert ist, um die Dauer des Warmauslagerns ohne Zuführen von Wärme
zum Guss (20) zu verlängern.
17. Verfahren nach einem der vorhergehenden Ansprüche, wobei eine mit Wärme behandelbare
Aluminiumlegierung Eigenschaften besitzt, einschließlich Härte und Festigkeit, die
durch Ausscheidungshärten verbessert werden.
18. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Guss (20) aus einer Aluminiumlegierung
der 3xx.x Reihe nach der Klassifizierung der Aluminum Association (AA) erstellt wird,
der Al, Si, & Cu oder Mg als Gusshauptbestandteile aufweist, mit den Härtegraden T6
oder T7 entsprechenden Eigenschaften.
19. Verfahren nach Anspruch 18, wobei der Guss (20) aus einer A319 Aluminiumlegierung
mit bis zu 5% Kupfergehalt hergestellt wird.
20. Verfahren nach einem der vorhergehenden Ansprüche, weiterhin umfassend:
Erstarren und Herausnahme des Gusses (20) aus seiner Form während die Temperatur des
Gusses über 400°C beträgt; Aufheizen der Güsse (20) in einem Lösungsglühofen auf eine
Lösungswärmebehandlungstemperatur über eine Zeitspanne von ungefähr 2 bis 7 Stunden.
21. Verfahren nach Anspruch 20, wobei das Aufheizen der Güsse (20) in einem Lösungsglühofen
auf einen Bereich von Lösungswärmebehandlungstemperaturen zwischen ungefähr 480°C
bis 495°C erfolgt.
22. Verfahren nach Anspruch 20 oder 21, das weiterhin ein natürliches Abkühlen des Gusses
(20) nach der Entnahme aus seiner Form und vor der Lösungswärmebehandlung der Güsse
umfasst.
23. Verfahren zum Herstellen eines Werkstücks, die Schritte umfassend:
Durchführen des Verfahrens nach einem der Ansprüche 1 bis 22;
und
Entfernen des erhöhten Abschnitts des Gusses, um das Werkstück herzustellen.
24. Verfahren nach Anspruch 23, wobei das Werkstück ein Zylinderkopf für einen Automobilmotor
ist.
25. Verwendung einer Vorrichtung zum Abschrecken und Warmauslagern eines erhitzten Aluminiumlegierungsgusses
(20), der einen erhöhten Abschnitt (24) und einen Werkstückabschnitt (22) aufweist,
die Vorrichtung umfassend:
- eine Abschreckeinheit (10);
- eine Auslagerungseinheit;
- Transportmittel (16), angeordnet, um zumindest einen Guss (20) nacheinander durch
die Einheiten zu bewegen, wobei die Transportmittel derart angeordnet sind, um den
Guss (20) in der Abschreckeinheit (10) in einer ausgerichteten Lage zu positionieren;
und
- Mittel zum Kühlen (30) zum Abschrecken des Gusses,
wobei die Verwendung der Vorrichtung das schnelle und selektive Abschrecken des Werkstückabschnitts
(22) des Gusses (20) in der ausgerichteten Lage umfasst, hauptsächlich unter Ausschluss
des erhöhten Abschnitts (24), dessen erhöhter Abschnitt (24) deswegen ursprünglich
eine relativ höhere Temperatur beibehalten wird.
26. Verwendung einer Vorrichtung nach Anspruch 25, wobei die Einheiten Teil einer kontinuierlichen
Fertigungslinie sind; die Abschreckeinheit (10) eine abgeschlossene Sprühkammer ist;
die Mittel zum Kühlen (30) mindestens einen Abschreckungs-Flüssigkeits-Sprüher aufweisen,
der ausgerichtet ist, um im Wesentlichen direkt auf den Werkstückabschnitt (22) des
Gusses einzuwirken, der durch die Transportmittel (16) in der ausgerichteten Lage
zugeführt wird.
27. Verwendung einer Vorrichtung nach Anspruch 25 oder 26, wobei die Auslagerungseinheit
eine isolierte Tunnelkammer ist.
28. Verwendung einer Vorrichtung nach einem der Ansprüche 25 bis 27, wobei die Auslagerungseinheit
nicht erneut über einen Ofen erhitzt wird.
29. Verwendung einer Vorrichtung nach einem der Ansprüche 25 bis 28, wobei die Mittel
zur Kühlung (30) eine Mehrzahl von in Abständen entlang der Fertigungslinie angeordneten
Abschreck-Flüssigkeits-Sprühern aufweisen, wobei jeder im Wesentlichen direkt auf
den Werkstückabschnitt (22) der Güsse (20) einwirkt, die nacheinander durch die Transportmittel
(16) in der ausgerichteten Lage zugeführt werden, um das Abschrecken des Werkstückabschnitts
(22) zu erreichen.
30. Verwendung einer Vorrichtung nach einem der Ansprüche 25 bis 29, wobei die Auslagerungseinheit
nur über Restwärme, einschließlich der eines Wärmetauschers, erhitzt wird.
1. Procédé de trempe et de vieillissement artificiel d'une pièce (20) en alliage d'aluminium
ayant une partie de masselotte (24) et une partie de pièce d'usinage (22), ledit procédé
comprenant :
le refroidissement sélectif par trempage de la partie de pièce d'usinage (22) de la
pièce tout en maintenant la partie de masselotte (24) à une température relativement
plus élevée ;
l'initiation du trempage lorsque la pièce (20) est à des températures élevées avec
ses éléments d'alliage en solution solide ;
la poursuite du trempage pour refroidir la partie de pièce d'usinage (22) suffisamment
rapidement pour inhiber une précipitation des éléments d'alliage et pour ainsi maintenir
de tels éléments en solution supersaturée au sein de la matrice d'aluminium ;
l'interruption du trempage lorsque la partie de pièce d'usinage (22) est refroidie
à une température qui est dans ou en-dessous de la plage pour un vieillissement artificiel
;
le vieillissement artificiel de ladite partie de pièce d'usinage (22) dans une plage
de températures et sur une période de temps effective appropriée pour un tel vieillissement
de la pièce d'usinage de la pièce en alliage d'aluminium essentiellement au moyen
d'une chaleur résiduelle provenant de la partie de masselotte (24) relativement plus
chaude.
2. Procédé selon la revendication 1, dans lequel le vieillissement artificiel de ladite
partie de pièce d'usinage est effectué sans chauffage actif de la pièce (20) en général.
3. Procédé selon la revendication 1 ou 2, dans lequel la masse, la forme et la superficie
de la section transversale de fixation de la partie de masselotte (24) par rapport
à la partie de pièce d'usinage (22) et le différentiel de température entre celles-ci
sont choisis de façon à être suffisants pour maintenir la partie de pièce d'usinage
(22) dans les plages de température et de période de temps requises pour le vieillissement
artificiel.
4. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit refroidissement
sélectif par trempage est effectué par pulvérisation d'un fluide de trempage (32)
sur les surfaces de ladite partie de pièce d'usinage (22).
5. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit fluide
de trempage (32) est l'eau.
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit trempage
est effectué par un brouillard d'eau.
7. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit trempage
est initié lorsque la pièce (22) est à une température supérieure à environ 350°C.
8. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit trempage
est inférieur à cinq minutes en durée.
9. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit trempage
est interrompu lorsque la partie de pièce d'usinage (22) atteint une température de
l'ordre de 100°C à 130°C, tandis que la partie de masselotte (24) reste au-dessus
de 300°C.
10. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit trempage
est interrompu lorsque la partie de pièce d'usinage (22) atteint environ 130°C.
11. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel ledit trempage
est interrompu lorsque la partie de pièce d'usinage (22) atteint environ 120°C.
12. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit vieillissement
artificiel de la partie de pièce d'usinage (22) est effectué à une température entre
140°C et 250°C.
13. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit vieillissement
artificiel de la partie de pièce d'usinage (22) est effectué à une température entre
180°C et 220°C.
14. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit vieillissement
artificiel est effectué sur une période de temps de deux à cinq heures.
15. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite
partie de pièce d'usinage (22) est débourrée après le vieillissement artificiel.
16. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite
pièce (20) est isolée pendant le vieillissement artificiel pour prolonger la durée
du processus de vieillissement artificiel sans ajouter de chaleur à la pièce (20).
17. Procédé selon l'une quelconque des revendications précédentes, dans lequel un alliage
d'aluminium traitable à la chaleur ayant des propriétés, incluant une dureté et une
résistance, qui sont améliorées par un durcissement par précipitation par l'intermédiaire
d'un vieillissement.
18. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite
pièce (20) est formée à partir d'un alliage d'aluminium de la série 3xx.x selon la
classification de l'Aluminum Association (AA) ayant Al, Si, & Cu ou Mg comme les constituants
principaux de la pièce, avec des propriétés au moins égales à une trempe T6 ou T7.
19. Procédé selon la revendication 18, dans lequel ladite pièce (20) est fabriquée à partir
d'un alliage d'aluminium A319 avec une teneur en cuivre de jusqu'à 5%.
20. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre
:
la solidification et l'extraction de la pièce (20) de son moule tandis que ladite
pièce est à une température supérieure à 400°C ;
le chauffage desdites pièces (20) dans un four de traitement en solution à des températures
de traitement thermique en solution pendant une période de temps d'environ 2 à 7 heures.
21. Procédé selon la revendication 20, dans lequel ledit chauffage desdites pièces (20)
dans un four de traitement en solution est effectué dans une plage de températures
de traitement thermique en solution d'environ entre 480°C et 495°C.
22. Procédé selon la revendication 20 ou 21, comprenant en outre le refroidissement naturel
de la pièce (20) après extraction de son moule et avant le traitement thermique en
solution desdites pièces.
23. Procédé de production d'une pièce d'usinage, comprenant les étapes de :
mise en oeuvre du procédé selon l'une quelconque des revendications 1 à 22 ; et
enlèvement de la partie de masselotte de la pièce, pour produire ladite pièce d'usinage.
24. Procédé selon la revendication 23, dans lequel la pièce d'usinage est une culasse
pour un moteur d'automobile.
25. Utilisation d'un appareil pour tremper et vieillir artificiellement une pièce (20)
chaude en alliage d'aluminium ayant une partie de masselotte (24) et une partie de
pièce d'usinage (22), l'appareil comprenant :
- une unité de trempage (10) ;
- une unité de vieillissement ;
- un moyen de transfert (16), agencé de façon à déplacer au moins une pièce (20) successivement
à travers lesdites unités, le moyen de transfert agencé pour positionner une telle
pièce (20) dans ladite unité de trempage (10) dans une position orientée ; et
- un moyen de refroidissement (30) pour tremper la pièce,
dans laquelle l'utilisation de l'appareil comprend le trempage rapide et sélectif
de la partie de pièce d'usinage (22) de la pièce (20) dans ladite position orientée,
largement à l'exclusion de la partie de masselotte (24), laquelle partie de masselotte
(24) restera ainsi initialement à une température relativement plus élevée.
26. Utilisation d'un appareil selon la revendication 25, dans laquelle lesdites unités
font partie d'une ligne de traitement continu ; ladite unité de trempage (10) est
un logement de confinement pour pulvérisation ; ledit moyen de refroidissement (30)
est au moins un pulvérisateur de liquide de trempe dirigé de façon à venir frapper
directement essentiellement uniquement la partie de pièce d'usinage (22) de la pièce
qui lui est présentée par le moyen de transfert (16) dans la position orientée.
27. Utilisation d'un appareil selon la revendication 25 ou 26, dans laquelle ladite unité
de vieillissement est un logement en tunnel isolé.
28. Utilisation d'un appareil selon l'une quelconque des revendications 25 à 27, dans
laquelle ladite unité de vieillissement n'est pas réchauffée au moyen d'un four.
29. Utilisation d'un appareil selon l'une quelconque des revendications 25 à 28, dans
laquelle ledit moyen de refroidissement (30) a une pluralité de pulvérisateurs de
liquide de trempe espacés le long de la ligne de traitement, chacun venant frapper
directement essentiellement uniquement la partie de pièce d'usinage (22) de la pièce
(20) qui lui est successivement présentée par le moyen de transfert (16) dans la position
orientée de façon à réaliser le refroidissement par trempage de la partie de pièce
d'usinage (22).
30. Utilisation d'un appareil selon l'une quelconque des revendications 25 à 29, dans
laquelle ladite unité de vieillissement n'est chauffée que par une chaleur résiduelle,
incluant celle provenant d'un échangeur de chaleur.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only.
It does not form part of the European patent document. Even though great care has
been taken in compiling the references, errors or omissions cannot be excluded and
the EPO disclaims all liability in this regard.
Patent documents cited in the description
Non-patent literature cited in the description
- Heat Treating19910000vol. 4, 841-879 [0004]
- heat treatable841- [0004]
- quenching851- [0004]
- age hardening859- [0004]
- Properties and Selection: Nonferrous Alloys and Special Purpose Materials19900000vol.
2, 15-41 [0004]
- heat treatable39- [0004]
- artificial aging40- [0004]
- Casting19880000vol. 15, 757-761 [0004]
- ''quenching'' and ''aging''ASM International760-1 [0004]