U.S. patent application number 15/962657 was filed with the patent office on 2018-08-23 for cooling facility and method.
The applicant listed for this patent is Constellium Neuf-Brisach. Invention is credited to Pierre AUCOUTURIER, Daniel BELLOT, Vincent DUHOUX, Bruno MAGNIN, Jose ROCHE.
Application Number | 20180236514 15/962657 |
Document ID | / |
Family ID | 51610169 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180236514 |
Kind Code |
A1 |
DUHOUX; Vincent ; et
al. |
August 23, 2018 |
COOLING FACILITY AND METHOD
Abstract
A cooling method for a rolling ingot of aluminium alloy after
metallurgical homogenization heat treatment of said ingot and
before hot rolling, characterized in that cooling by 30 to
150.degree. C. is performed at a rate of 150 to 500.degree. C./h,
with a thermal differential of less than 40.degree. C. throughout
the treated portion of the ingot is disclosed. A facility allowing
use of said method and said implementation is also disclosed.
Inventors: |
DUHOUX; Vincent; (Coublevie,
FR) ; MAGNIN; Bruno; (Saint-Aupre, FR) ;
BELLOT; Daniel; (Izeaux, FR) ; ROCHE; Jose;
(Bowling Green, KY) ; AUCOUTURIER; Pierre;
(Sundhoffen, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Constellium Neuf-Brisach |
Biesheim |
|
FR |
|
|
Family ID: |
51610169 |
Appl. No.: |
15/962657 |
Filed: |
April 25, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15326753 |
Jan 17, 2017 |
|
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PCT/FR2015/051915 |
Jul 10, 2015 |
|
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15962657 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21B 2003/001 20130101;
C21D 1/667 20130101; B21B 45/004 20130101; B21B 2045/0212 20130101;
C21D 11/005 20130101; B21B 2261/04 20130101; B21B 2261/20 20130101;
C22F 1/04 20130101; B21B 37/74 20130101; B21B 2261/12 20130101;
C22F 1/002 20130101; B21B 2001/225 20130101; B21B 45/0218 20130101;
B21B 2261/06 20130101 |
International
Class: |
B21B 37/74 20060101
B21B037/74; B21B 45/02 20060101 B21B045/02; C22F 1/04 20060101
C22F001/04; C21D 1/667 20060101 C21D001/667; C22F 1/00 20060101
C22F001/00; C21D 11/00 20060101 C21D011/00; B21B 45/00 20060101
B21B045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2014 |
FR |
1401679 |
Claims
1. A method of cooling an aluminum alloy rolling ingot after a
metallurgical homogenization heat treatment of said ingot at a
homogenization temperature, optionally between 450 to 600.degree.
C., and prior to hot rolling, wherein the aluminum alloy rolling
ingot has a format of dimensions from 250 to 800 mm in thickness,
from 1000 to 2000 mm in width, and from 2000 to 8000 mm in length;
a top surface, a bottom surface, and four side surfaces, wherein
the top and bottom surfaces have a larger surface area than the
side surfaces; and a head and a foot corresponding to extremities
in a longitudinal direction, wherein cooling, by a cooling value of
30 to 150.degree. C., is performed at a rate of from 150 to
500.degree. C./h, with a thermal differential of less than
40.degree. C. over the entire ingot cooled from the homogenization
temperature thereof.
2. The method of claim 1, wherein cooling is carried out in at
least two phases: a first spraying phase in which the ingot is
cooled in a chamber equipped with a spray system comprising ramps
of nozzles for spraying cooling liquid or spray under pressure,
divided into upper and lower parts of said chamber, so as to spray
the larger top and bottom surfaces of said ingot, and a
complementary phase of thermal equalization in still air, in a
tunnel with interior reflective walls, lasting from about 2 to
about 30 minutes, depending on the fonnat of the ingot and the
cooling value.
3. The method of claim 2, wherein the spray system guides the
cooling liquid or spray under pressure to the ingot edges where the
cooling liquid or spray under pressure is discharged in form of a
cascade without touching the ingot's side surfaces.
4. The method according to claim 2, wherein the spraying and
thermal equalization phases are repeated and for an overall average
cooling of more than 80.degree. C.
5. The method according to claim 2, wherein the cooling liquid or
spray under pressure is water.
6. The method according to claim 2, wherein the head and the foot
of the ingot, corresponding to 300 to 600 mm at ends thereof, are
cooled less than the rest of the ingot.
7. The method according to claim 2, wherein cooling of the head and
foot is modulated by turning the ramps of nozzles on or off.
8. The method according to claim 2, wherein the spraying phases and
not therma equalization are repeated, and in that the head and foot
of the ingot are cooled differently from the rest of the ingot in
at least one of the spray phases.
9. The method according to claim 8, wherein a first spray phase is
performed with zero heel, or continuous spraying of the ingot
followed, without a first thermal equalization phase, by a second
spray phase with a heel of a pair of ramps, thereby allowing to
reduce the duration of a final equalization phase necessary for
thermal balancing of the ingot.
10. The method according to claim 2, wherein transverse thermal
uniformity of the ingot is ensured by modulating spraying in the
ingot width by switching the nozzles or spray nozzles on or off, or
screening said spraying.
11. The method according to claim 1, wherein the nozzles produce
full cone jets with an angle of between 45 and 60.degree., and
lower nozzle axes are oriented normally to the bottom surface of
the ingot.
12. A facility for cooling an aluminum alloy rolling ingot after a
metallurgical homogenization heat treatment of said ingot at a
homogenization temperature, comprising: a spray chamber comprising
ramps of nozzles for spraying cooling liquid or spray under
pressure, arranged in upper and lower parts of said chamber, so as
to spray two large surfaces, top and bottom, of said ingot, wherein
upper nozzle ramps are paired in the direction of movement of the
ingot; in any given pair, the upper ramps are inclined such that:
jets of the two paired nozzle ramps are oriented in opposition to
one another; the jets have a normal edge to the upper surface of
the ingot; an equalization tunnel in still air on leaving the spray
chamber, in a tunnel whose internal walls and roof are made of an
internally reflective material, allowing equalization of the ingot
by heat diffusion in said ingot, the core warming the surfaces.
13. The facility according to claim 12, wherein: the cooling liquid
or spray nozzles of the cell produce full cone jets with an angle
of between 45 and 60.degree..
14. The facility according to claim 12, wherein: lower nozzle axes
are oriented normally to the lower surface of the ingot.
15. The facility according to claim 12, wherein: an overlap of jets
of the two paired ramps is between 1/3 and 2/3 of the width of each
jet, and optionally substantially half.
16. The facility according to claim 12, wherein an envelope of the
two paired nozzle ramps so formed has an M profile.
17. The facility according to claim 12, wherein: pairs of upper and
lower nozzle ramps are placed substantially face-to-face, so that
upper and lower spray lengths are substantially equal and opposite
each other.
18. The facility according to claim 12, wherein the entire
facility, spray chamber and equalization tunnel are controlled by a
thermal model encoded on a PLC, the thermal model determining the
settings of the facility according to the temperature estimated by
thermal measurement at the start of the spray chamber and according
to the target output temperature, optionally at a start temperature
for hot rolling.
19. The facility according to claim 12, wherein: wherein the
aluminum alloy rolling ingot has a format of dimensions from 250 to
800 mm in thickness, from 1000 to 2000 mm in width, and from 2000
to 8000 mm in length; a top surface, a bottom surface, and four
side surfaces, wherein the top and bottom surfaces have a larger
surface area than the side surfaces; and a head and a foot
corresponding to extremities in a longitudinal direction, and
wherein the spray system guides the cooling liquid or spray under
pressure to the ingot edges where the cooling liquid or spray under
pressure is discharged in form of a cascade without touching the
ingot's side surfaces.
20. A method for treating an ingot in a facility according to claim
12, comprising: centering the ingot at an entrance to the facility;
measuring upper surface temperature of the ingot; calculation by
the PLC, using the thermal model, of the spray chamber settings
depending on the input temperature and the target output
temperature, optionally target cooling of the ingot, including
determining the number of ramps activated, the number of nozzles
activated at the ingot edges, speed of movement of the ingot within
the spray chamber, starting and stopping the spraying ramps, and
the holding time in the equalization tunnel; moving the ingot
continuously through the spray chamber, with upper and lower
spraying according to the PLC calculations; transfer of the ingot
from the spray chamber to the equalization tunnel; and holding the
ingot in the equalization tunnel for a period determined by the
PLC.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation application of U.S.
patent application Ser. No. 15/326,753, filed Jan, 17, 2017, which
is a .sctn. 371 National Stage Application of PCT/FR2015/051915,
filed Jul. 10, 2015, which claims priority to application no.
1401679 (France), filed Jul. 23, 2014. Each of these applications
is incorporated by reference in its entirety
FIELD OF THE INVENTION
[0002] The invention relates to the field of rolling aluminium
alloy ingots or slabs.
[0003] More specifically, the invention relates to a particularly
rapid, homogeneous and reproducible method for cooling the ingot
between homogenization and hot rolling operations.
[0004] The invention also relates to the facility or equipment used
to implement the method.
DESCRIPTION OF RELATED ART
[0005] Transformation of aluminium alloy rolling ingots from
casting requires metallurgical homogenization heat treatment before
hot rolling. This heat treatment is carried out at a temperature
near the soleus of the alloy, higher than the hot rolling
temperature. The difference between the homogenization temperature
and the hot rolling temperature is between 30 and 150.degree. C.
depending on the alloys. The ingot must therefore be cooled between
leaving the homogenization furnace and being hot rolled. For
reasons of either productivity or metallurgical structure, notably
preventing certain surface defects on the finished sheet, it is
highly desirable to cool the ingot quickly between leaving the
homogenization furnace and the hot-rolling mill.
[0006] The desired cooling rate for the ingot is between 150 and
500.degree. C/h.
[0007] Given the great thickness of aluminium alloy rolling ingots,
which is between 250 and 800 mm, air cooling is particularly slow:
the rate of air cooling for an ingot 600 mm thick is between
40.degree. C./h in still air or with natural convection, and
100.degree. C./h in vented air or with forced convection.
[0008] Air cooling does therefore not make it possible to achieve
the desired cooling rates.
[0009] Cooling by means of a liquid or spray (a mixture of air and
liquid) is much faster because the value of the exchange ratio,
known to experts in the field by the name HTC (Heat Transfer
Coefficient) between a liquid or a spray and the hot surface of the
metal ingot is significantly higher than the value of the same
coefficient between air and the ingot.
[0010] The liquid chosen, alone or in a spray, is for example,
water, and in this case, ideally deionized water. Therefore, the
HTC coefficient is between 2000 and 20000 W/(m.sup.2K) between
water and the hot ingot, while it is between 10 and 30 W/(m.sup.2K)
between air and the hot ingot.
[0011] However, cooling by means of a liquid or spray usually
generates naturally high thermal gradients in the ingot: [0012] The
dimensionless Biot number illustrates the thermal homogeneity of
cooling. It is the ratio of the internal thermal resistance of a
body (internal heat transfer by conduction) to its surface thermal
resistance (heat transfer by convection and radiation).
[0012] Bi=HTCD/.lamda.
[0013] HTC being the exchange coefficient between the fluid and the
ingot,
[0014] D, the characteristic dimension of the system, here the
half-thickness of the ingot,
[0015] .lamda., the thermal conductivity of the metal, for example,
for an aluminium alloy, 160 W/(m.sup.2K).
[0016] If Bi<<1, the system is practically isothermal, and
cooling is uniform.
[0017] If Bi>>1, the system is thermally very heterogeneous
and the ingot is the site of high thermal gradients.
[0018] For an ingot of thickness of 600 mm, the Biot number is:
[0019] Between 0.02 and 0.06 for cooling in still or ventilated
air. The Biot number is small in relation to 1: the ingot is cooled
isothermally. [0020] Between 4 and 40 for water cooling. The Biot
number is high in relation to 1: the ingot is cooled very
heterogeneously throughout its thickness.
[0021] This heterogeneity is also reflected in the width of the
ingot, due to the effects of rims and edges, which are naturally
more cooled than the large surfaces of the ingot.
[0022] It is also reflected in the length of the ingot, by corner
effect, naturally cooled along the three faces that make it up.
[0023] Thermal heterogeneity is a major handicap for cooling using
a liquid or a spray. It is a problem not only for the following
method, i.e. hot rolling but it is also potentially detrimental to
the quality of the final product, namely aluminium alloy sold in
coils or plates with high mechanical properties.
[0024] Systems known from prior art do not seek to limit the
heterogeneity of cooling.
[0025] Cooling methods using a cooling liquid known from prior art,
especially for heavy sheets, operate either by immersion in a tank,
or by passing through a spray box but without any particular
attention paid to controlling the heat balance of the product. So
these methods: [0026] do not make it possible to obtain a uniform
thermal field in the cooled ingot [0027] cannot guarantee the
reproducibility of the cooling from one ingot to another.
SUMMARY
[0028] The invention aims to correct all of the major defects
related to cooling processes for thick ingots from prior art and to
ensure: [0029] Rapid cooling, at a rate of at least 150.degree.
C./h, and by a significant amount, i.e. 30 to 150.degree. C.
cooling from a temperature of the order of 450 to 600.degree. C.
[0030] A homogeneous and controlled thermal field across the ingot
[0031] The assurance of perfect reproducibility from one thick
ingot to another.
SUBJECT OF THE INVENTION
[0032] The invention relates to a cooling method for a typical
aluminium alloy rolling ingot of dimensions 250 to 800 mm in
thickness, from 1000 to 2000 mm in width and 2000 to 8000 mm in
length after metallurgical homogenization heat treatment of said
ingot at a temperature typically between 450 to 600.degree. C.
depending on the alloys and prior to hot rolling, characterized in
that the cooling, by a value of 30 to 150.degree. C., is performed
at a rate of from 150 to 500.degree. C./h, with a thermal
differential of less than 40.degree. C. over the entire ingot
cooled from its homogenization temperature.
[0033] Thermal differential is taken to mean the maximum difference
between temperature readings taken throughout the volume of the
ingot, or DTmax.
[0034] Advantageously, cooling is carried out in at least two
phases:
[0035] A first spraying phrase in which the ingot is cooled in a
chamber comprising ramps of nozzles or tuyers for spraying cooling
liquid or spray under pressure, divided into upper and lower parts
of said cell, so as to spray the two large top and bottom surfaces
of said ingot,
[0036] A complementary phase of thermal equalization in still air,
in a tunnel with interior reflective walls, lasting from 2 to 30
minutes depending on the ingot format and the cooling value.
[0037] Typically, this time is approximately 30 min for total
cooling of the order of 150.degree. C. to from substantially
500.degree. C. and a few minutes for cooling by about 30.degree.
C.
[0038] According to a variant of the invention, the spraying and
thermal equalization phases are repeated in the case of very thick
ingots and for an overall average cooling of more than 80.degree.
C.
[0039] Most commonly, the coolant, including that in a spray, is
water, and preferably deionized water.
[0040] According to a particular embodiment, the head and the foot
of the ingot, or typically the 300 to 600 mm at the ends, are less
cooled than the rest of the ingot, so as to maintain a hot head and
foot, a favourable configuration for engaging the ingot during
reversible hot rolling.
[0041] To this end, the cooling of the head and foot may be
modulated either by turning the ramps of spray nozzles or tuyers on
or off, or by the use of screens preventing or reducing spraying by
said spray nozzles. Furthermore, the spraying phases, and not
thermal equalization, can be repeated, and the head and foot of the
ingot, or typically the 300 to 600 mm at the ends, cooled
differently from the rest of the ingot in at least one of the spray
chambers.
[0042] According to a version that complies with the latter option,
the first spray pass is performed with zero heel, or continuous
spraying of the ingot such as is shown in FIG. 14, followed,
without a first thermal equalization phase, by a second spray pass
with a heel of a pair of ramps such as is shown in FIG. 12, thereby
making it possible to significantly reduce the duration of the
final equalization phase necessary for thermal balancing of the
ingot.
[0043] In a preferred variant of the invention, the longitudinal
thermal uniformity of the ingot is improved by relative movement of
the ingot in relation to the spray system: the ingot passes or
moves with a reciprocating movement facing a fixed spray system or
vice versa, nozzles or spray nozzles moving relative to the
ingot.
[0044] Typically, the ingot moves horizontally in the spray chamber
and its speed is greater than or equal to 20 mm/s, or 1.2
m/min.
[0045] Also preferably, the transverse thermal uniformity of the
ingot is ensured by modulating spraying in the ingot width by
switching of the nozzles or tuyers on or off, or screening said
spraying.
[0046] The invention also relates to a facility for using the
method as above, comprising a spray chamber provided with ramps of
nozzles or tuyers for spraying cooling liquid or spray under
pressure, arranged in the upper and lower parts of said cell, so as
to spray the two large top and bottom surfaces of said ingot,
[0047] An equalization tunnel in still air on leaving the spray
chamber, in a tunnel whose internal walls and roof are made of an
internally reflective material, allowing equalization of the ingot
by heat diffusion in said ingot, the core warming the surfaces.
[0048] According to a preferred embodiment:
[0049] The cooling liquid or spray nozzles produce full cone sprays
or jets with an angle of between 45 and 60.degree.
[0050] The lower nozzle axes are oriented normally to the lower
surface.
[0051] Preferably, the upper nozzle ramps are paired in the
direction of movement of the ingot.
[0052] In any given pair, the upper ramps are inclined such that:
[0053] The jets of the two paired upper nozzle ramps are oriented
in opposition to one another [0054] The jets have a normal edge to
the upper surface of the ingot [0055] The overlap of two jets is
between 1/3 and 2/3 of the width of each jet, and preferably
substantially half [0056] The envelope of the two jets so formed
has an M profile.
[0057] The pairs of upper and lower nozzle ramps are placed
substantially face-to-face, so that the upper and lower spray
lengths are substantially equal and opposite each other.
[0058] Because of the pairing of the upper nozzles in opposition
and the M profile of the jets, the spray length is controlled to
promote lateral discharge of the liquid or spray sprayed on the
upper surface, guiding it to the ingot edges where it is discharged
in the form of a cascade without touching the ingot small surfaces
thereby permitting uniform cooling in the longitudinal and
transverse directions of the ingot.
[0059] As for the liquid, whether alone or in the cooling spray,
this can be recovered, typically in a container located under the
facility, recycled and thermally controlled.
[0060] In an improved means of implementation, the entire facility,
spray chamber and equalization tunnel is controlled by a thermal
model encoded on a programmable logic controller (PLC), the thermal
model determining the settings of the facility according to the
temperature estimated by thermal measurement at the start of the
spray chamber and according to the target output temperature,
typically the start temperature for hot rolling.
[0061] According to an advantageous embodiment, operation of the
facility comprises the following steps: [0062] Centring the ingot,
at the entrance to the facility [0063] Measuring the upper surface
temperature of the ingot [0064] Calculation by the PLC, using the
thermal model, of the spray chamber settings depending on the
target input temperature and the target output temperature, i.e.
target cooling of the ingot, including determining the number of
ramps activated, the number of nozzles open at the ingot edges,
speed of movement of the ingot within the spray chamber, starting
and stopping the spraying ramps, and the holding time in the
equalization tunnel [0065] Moving the ingot continuously through
the spray chamber, with upper and lower spraying according to the
PLC calculations [0066] Transfer of the ingot from the spray
chamber to the equalization tunnel [0067] Holding the ingot in the
equalization tunnel for a period determined by the PLC.
BRIEF DESCRIPTION OF THE DRAWINGS
[0068] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0069] FIG. 1 shows a schematic diagram of the method according to
the invention in one pass. The ingot is removed from the
homogenization furnace 1 at its homogenization temperature. It is
transferred to the cooling machine, laterally centred and its
surface temperature is measured (2) by surface thermocouple, by
contact or with an infrared pyrometer, which will be less accurate.
The thermal model determines the spray chamber setting 3 (number of
pairs of activated ramps and ingot speed). Then the ingot is
treated in the spray chamber. When it leaves, it is dry and is
transferred (4) to an equalization tunnel 5 for a period determined
by the thermal model or depending on the amplitude of cooling
undergone. At the end, it is transferred to the hot rolling mill
6.
[0070] FIG. 2 shows a schematic diagram of the method according to
the invention in two passes or more. When the cooling target
amplitude is greater than 100.degree. C., a single pass through the
cooling machine may be insufficient. In this case, the ingot is
cooled for the first time in the first spray chamber 3. Then, with
or without passing through the intermediate equalization tunnel 5,
the ingot is transferred to the second cooling machine composed of
elements 6, 7 and 8, where it undergoes a complete cycle: spray
chamber and then, obligatorily, the equalization tunnel 8. The
duration of the final phase of equalization depends on the thermal
diffusivity of the material, and therefore the alloy, the target
cooling amplitude, and the severity of the target thermal before
hot rolling 9.
Multi-pass cooling can also be performed with a single machine, by
means of successive passages.
[0071] FIG. 3 is a schematic side view drawing of the spray
machine, the ingot running from left to right. It illustrates the
arrangement of the jets of liquid or spray sprayed on the ingot,
seen from the side, on the upper side and the lower side. The upper
and lower spray ramps are paired and opposite each other in pairs,
to ensure proper cooling uniformity in the thickness of the ingot.
The paired upper ramps are oppositely directed, which ensures that
the liquid or mist sprayed will be discharged transversely to the
ingot. The lower nozzle axes are oriented normally to the lower
surface of the ingot, the liquid running off by gravity. Compressed
air ramps (1-4) frame the ends of the spray chamber to prevent any
residual liquid runoff onto the ingot outside said cell.
[0072] FIG. 4 illustrates the effect of upper jets of liquid or
spray, seen from above the ingot. The concentration of the surface
flow rate of liquid or spray will be noted at the intersection of
opposing jets. This spraying layout helps removal of the liquid
along this transverse line with a high surface flow rate.
[0073] FIG. 5 shows the thermal kinetics of a 600 mm ingot,
calculated for average cooling of 40.degree. C., in one pass in the
spray machine, for an AA3104 type alloy according to designations
defined by the "Aluminum Association" in the "Registration Record
Series" that it publishes regularly. This shows changes in minimum
Tmin, maximum Tmax and average Tmoy temperatures in the ingot, and
the maximum temperature differential throughout the whole volume of
the ingot, over time (DT max).
[0074] FIG. 6 shows the thermal kinetics of a 600 mm ingot,
calculated for average cooling of 130.degree. C., in two passes in
the spray machine, for an AA6016 type alloy according to
designations defined by the "Aluminum Association" in the
"Registration Record Series" that it publishes regularly. This
shows, in the same way changes in minimum Tmin, maximum Tmax and
average Tmoy temperatures in the ingot, and the maximum temperature
differential throughout the whole volume of the ingot, over time
(DT max).
[0075] FIGS. 7 to 9 illustrate three spraying modes or strategies
transverse to the spray machine showing the position of the nozzles
on the spray ramps, the spraying machine being shown from the front
in all cases:
[0076] FIG. 7: Uniform temperature profile in the width of the
ingot
[0077] FIG. 8: Temperature profile with cold ingot edges, created
by surplus spraying on the ingot edges of the ingot
[0078] FIG. 9: Temperature profile with hot ingot edges, created by
insufficient spraying on the ingot edges of the ingot
[0079] FIG. 10 shows two spray width modes or strategies for a 600
mm thick and 1700 mm wide aluminium alloy ingot; on the left a
thermal profile in the transverse direction with cold ingot edges
and with 11 nozzles in action; on the right a thermal profile with
hot ingot edges with 9 nozzles in action.
[0080] FIG. 11 is the effect on the thermal profile (temperature in
.degree. C. as a function of position in the transverse direction,
from the axis of the ingot in m) of these two spray modes.
[0081] FIGS. 12 to 14 illustrate three examples of modes or
strategies for triggering spraying.
The thermal profile in the longitudinal direction of the ingot is
controlled by: Absence of, or very low runoff in the longitudinal
direction of the ingot, by mounting the upper ramps in opposition
Starting and stopping spraying of each pair of ramps at a specific
position of the ingot: this is the concept of a spraying heel.
[0082] FIG. 12 corresponds to management of the thermal profile in
the longitudinal direction with hot ends, FIG. 13 with warm ends
and FIG. 14 with cold ends (with runoff at 1).
[0083] FIG. 15 illustrates the longitudinal thermal profile
(temperature in .degree. C. as a function of the position in length
L of the ingot in m) for the three aforementioned ingot end thermal
management strategies. In this example, the ingot is made from
AA6016 type alloy. 600 mm thick, average cooling is 100.degree. C.
in two passes, and the time spent in the thermal equalization
chamber is 10 min.
[0084] FIGS. 16 to 18 illustrate the thermal field, as a 3D
display, of the same example, entering the hot rolling stage for
the three aforementioned ingot end thermal management strategies,
FIG. 16 with hot ends, FIG. 17 with warm ends and FIG. 18 with cold
ends.
It can be seen that the spray triggering strategy clearly makes it
possible to control the longitudinal thermal profile of the
ingot.
[0085] FIG. 19 shows the thermal field of an ingot made of AA6016
type alloy, 600 mm thick, cooled to about 50.degree. C. in one pass
in the spray machine set with a spraying heel of a single ramp at
the ends of the ingot, as shown in FIG. 13. This setting gives a
very uniform thermal field with slightly warmer ends, which is
conducive to rolling.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0086] The invention essentially consists of a cooling process
using a cooling liquid or spray for a slab or a rolling ingot made
of aluminium alloy, of 30 to 150.degree. C. in a few minutes, i.e.
at an average cooling rate of between 150 and 500.degree.
C./hour.
[0087] It is principally made up of two phases:
[0088] A first phase in which the ingot is sprayed with a cooling
liquid or spray, typically using continuous spraying
[0089] A second phase of thermal equalization of the ingot.
[0090] During the first spraying phase, the ingot is cooled in a
chamber having nozzles spraying cooling liquid or spray under
pressure, typically water and preferably deionized.
[0091] The nozzles or tuyers are divided up in the upper and lower
parts of said chamber, so as to spray the two large upper and lower
surface of the ingot.
[0092] The option of a continuous spraying process can limit the
risk of hot spots related to contacts between the ingot and its
support, which generally consists of cylindrical or conical
rollers.
[0093] The average cooling of the ingot (.DELTA.Tmoy ingot) is
controlled by the spraying time for each section of the ingot.
[0094] During this phase, the ingot is thermally very heterogeneous
in its thickness, because of the high Biot number.
[0095] The cooling homogeneity in the width of the ingot is
controlled by: [0096] a) Controlling the spray width in the
transverse direction of the ingot, by the number of active nozzles
or the use of screens [0097] b) A spray method promoting lateral
discharge of the water sprayed on the upper surface. The cooling
liquid is guided to the ingot edges of the ingot and is discharged
in the form of a cascade without touching the small surfaces of
said ingot. Because of this, ingot cooling is very homogeneous.
This method in fact consists of pairing two ramps of nozzles,
arranged in opposition, as shown in FIGS. 3 and 4.
[0098] The cooling homogeneity in the length of the ingot is
controlled by: [0099] c) Controlling the beginning and the end of
spraying by triggering spraying ramps at the desired position on
the ingot or, again, by the use of screens. In this way, it is
possible for the head and the foot of the ingot not to be sprayed.
An ingot is then obtained with a hot head and foot, which helps it
to engage during reversible hot rolling [0100] d) Greatly reducing
runoff in the longitudinal direction of the ingot. This very low
runoff is achieved through characteristic b) above of the
invention, favouring lateral discharge of the cooling liquid
sprayed on top of the ingot.
[0101] The spray phase is therefore designed to reduce thermal
heterogeneity in the three directions of the ingot. The invention
particularly makes it possible to control the temperature profiles
in the transverse direction and in the longitudinal direction of
the ingot, which is very significant because possible thermal
gradients along the two large dimensions would be difficult to
reverse in a short time.
[0102] Then follows the phase of thermal equalization of the
ingot:
[0103] After spraying, the ingot is kept for a few minutes in a
configuration of low heat exchange with its environment. These
thermal conditions allow thermal equalization of the ingot, in a
few minutes for cooling by less than 30.degree. C. and in about 30
minutes maximum for cooling by 150.degree. C. This phase is
essential to achieve the required thermal uniformity
specifications. It enables a thermal differential of DTmax of less
than 40.degree. C. to be achieved on a large ingot.
[0104] The invention can also be adapted to high absolute cooling
values. When the required mean cooling of the ingot is greater than
typically 80.degree. C., it is possible to cycle all the "spray"
and "equalization" phases, reducing the average temperature of a
very thick ingot at each "spray-equalization" cycle.
[0105] The method described ensures rapid and controlled cooling of
a thick slab, in particular a rolling ingot, made of aluminium
alloy. It is also robust and prevents the known risks of local
excess cooling.
[0106] The cooling machine or facility, which itself comprises,
firstly, at least one spray chamber, typically horizontal and
spraying continuously, and, secondly, at least one thermal
equalization tunnel.
[0107] The spray chamber allows phase 1 of the process described
above to be implemented.
[0108] The steps involved in processing the ingot in this machine
or facility are: [0109] 1) Centring the ingot, at the entrance to
the machine [0110] 2) Measuring the upper surface temperature of
the ingot [0111] 3) Calculation by the PLC, using the thermal
model, of the spray chamber settings depending on the input
temperature and the target output temperature, i.e. target cooling
of the ingot, including determining the number of ramps of nozzles
activated, the number of nozzles open at the ingot edges, speed of
movement of the ingot within the spray chamber, starting and
stopping the spraying ramps, the holding time in the equalization
tunnel [0112] 4) Moving the ingot through the spray chamber, with
upper and lower spraying according to the PLC calculations.
[0113] The spray chamber is provided with ramps of nozzles or
tuyers for spraying cooling liquid or spray under pressure.
[0114] If the latter is water, it should ideally be deionized or at
least very clean and with a very low mineral content, to prevent
clogging the nozzles and to ensure stability of heat transfer
between the water and the ingot. The spraying machine can
advantageously, particularly for reasons of economy, operate in a
closed cycle, for example with a catch basin under the spraying
machine.
[0115] The cooling liquid or spray nozzles produce full cone sprays
or jets with an angle of between 45 and 60.degree. (in the example:
60.degree. angle full cone nozzles of the Lechler brand). The
nozzle axes of the lower ramps are oriented normally to the lower
surface. The upper ramps are paired. In any given pair of upper
ramps, the ramps are inclined such that: [0116] The jets of the two
ramps are oriented in opposition to one another [0117] The jets
have a normal edge to the upper surface of the ingot [0118] The
overlap of two jets is between 1/3 and 2/3 of the width of the jet,
and preferably substantially half [0119] The envelope of the two
jets so formed has an M profile. [0120] The pairs of upper and
lower nozzle ramps are placed substantially face-to-face, so that
the upper and lower spray lengths are substantially equal and
opposite each other.
[0121] In the case of continuous spraying, the ingot travel speed
is greater than, or equal to 20 mm/s, or 1.2 m/min.
[0122] On leaving the spray chamber, the ingot is transferred, for
example using automated carriages, into one or more equalization
tunnel(s). The purpose of the tunnel is to minimize heat transfer
between the ingot and air, which helps to achieve better thermal
equalization of the ingot. This thermal equalization occurs by
diffusion of heat in the ingot, the core warming the surfaces of
the ingot.
[0123] The equalization tunnel consists of vertical walls and a
roof made from a materially that is ideally reflective on the inner
side of the tunnel.
[0124] It prevents air currents around the ingot, ensuring the
absence of heat transfer by forced convection. It also reduces heat
transfer by natural convection and limits radiative transfer if the
walls are reflective.
[0125] Finally, the cooling machine or facility comprising the
spray chamber and the equalization tunnel is controlled by a
thermal model encoded in the PLC of the machine. The thermal model
determines the settings of the machine depending on the temperature
at the start of the spray chamber, or input temperature, and
depending on the target output temperature, usually the rolling
temperature.
Examples
Example 1: Uniform Cooling by 40.degree. C. of an AA3104 Type Alloy
Ingot
[0126] FIG. 5 shows cooling by 40.degree. C. of an AA3104 type
alloy according to designations defined by the "Aluminum
Association" in the "Registration Record Series" that it publishes
regularly. The ingot is 600 mm thick, 1850 mm wide and 4100 mm
long.
[0127] The ingot leaves the homogenizing furnace at 600.degree.
C.
[0128] The ingot cooling method is the single-pass method described
in FIG. 1.
[0129] The ingot is transferred to the cooling machine in 180 s.
This transfer time includes: [0130] moving the ingot between the
furnace outlet and the inlet of the cooling machine [0131] lateral
centring of the ingot [0132] measuring the upper surface
temperature of the ingot [0133] The calculation time of the cooling
machine settings by the PLC (spray chamber and tunnel).
[0134] Then the ingot moves through the spray chamber, each point
of the ingot except the ends (head and foot) undergoing spraying
for 46 seconds. The surface flow rate of the spray is 500
l/(minm.sup.2) on the two large surfaces of the ingot. The spray
heel is set to a pair of ramps, as described in FIG. 12. On leaving
the spray chamber, the ingot is dry and is transferred in 30 s to
an equalization tunnel for a period determined by the thermal model
encoded in the PLC, here 300 s, or 5 minutes. At the end, the ingot
is transferred to the hot rolling mill with a temperature
uniformity better than 40.degree. C. over the complete ingot.
[0135] The ingot surface temperature drops to about 320.degree. C.,
while the core of the ingot remains almost isothermal during the
spraying phase. Then, by heat diffusion between the core and the
surface, the core gives up heat to the surface, and the ingot
becomes thermally uniform.
[0136] The thermal differential in the ingot (dt max) is maximal at
the end of the spray phase; its value is approximately 280.degree.
C. for this configuration. It drops quickly once spraying of the
ingot stops: after a 6 minute wait (transfer and equalization in
the tunnel), the thermal differential DTmax is reduced to less than
40.degree. C.
Example 2: Uniform Cooling by 135.degree. C. of an AA6016 Type
Alloy Ingot
[0137] FIG. 6 shows uniform cooling by 135.degree. C. of an AA6016
type alloy ingot. The ingot is 600 mm thick, 1850 mm wide and 4100
mm long. The ingot leaves the homogenizing furnace at 530.degree.
C.
[0138] The ingot cooling method is the two-pass method described in
FIG. 2.
[0139] The ingot is transferred to the cooling machine in 100 s.
This transfer time includes: [0140] moving the ingot between the
furnace outlet and the inlet of the cooling machine [0141] lateral
centring of the ingot [0142] measuring the upper surface
temperature of the ingot [0143] the calculation time of the cooling
machine settings by the PLC. Then the ingot moves through the spray
chamber, each point of the ingot except the ends (head and foot)
undergoing spraying for 51 seconds. The surface flow rate of the
spray is 800 l/(minm.sup.2) on the two large surfaces of the ingot.
The spray heel is set to one ramp, as described in FIG. 13. On
leaving the spray chamber, the ingot is transferred in 60 seconds
to the second spray chamber without, in this example, passing
through the optional intermediate equalization tunnel. The ingot
then undergoes a second spraying, identical to the first: each
point of the ingot except for the ends undergoes spraying for 51
seconds, at a surface flow rate of 800 l/(minm.sup.2). On leaving
the second spray chamber, the ingot is transferred to the
equalization tunnel in 30 seconds. The ingot waits for several
minutes in the equalization tunnel. At the end, the ingot is
transferred to the hot rolling mill with a temperature uniformity
better than 40.degree. C. over the complete ingot.
[0144] The ingot surface temperature drops to about 60.degree. C.
The core of the ingot remains almost isothermal during the first
spray phase and then cools during the second spray phase. Then, by
heat diffusion between the core and the surface, the core gives up
heat to the surface, and the ingot becomes thermally uniform.
[0145] The thermal differential in the ingot (th max) is maximal at
the end of each of the spray phases, its value is approximately
470.degree. C. for this configuration. It drops quickly once
spraying of the ingot stops: the thermal differential DTmax of the
ingot is 55.degree. C. after a 13 minute wait in the tunnel and
falls to below 40.degree. C. after 23 minutes in the tunnel.
Example 3: Uniform Cooling by 125.degree. C. of an AA6016 Type
Alloy Ingot
[0146] The ingot is 600 mm thick, 1850 mm wide and 4100 mm long.
The ingot leaves the homogenizing furnace at 530.degree. C.
[0147] The ingot cooling method is the two-pass method described in
FIG. 2.
[0148] The ingot is transferred to the cooling machine in 100 s.
This transfer time includes: [0149] moving the ingot between the
furnace outlet and the inlet of the cooling machine [0150] lateral
centring of the ingot [0151] measuring the upper surface
temperature of the ingot [0152] the calculation time of the cooling
machine settings by the PLC. Then the ingot moves through the spray
chamber, each point of the ingot undergoing spraying for 51
seconds. The surface flow rate of the spray is 500 l/(minm.sup.2)
on the two large surfaces of the ingot. The spray heel is zero, as
described in FIG. 14. The ingot is therefore completely sprayed in
an identical manner, which generates a longitudinal thermal profile
with cold ends. On leaving the spray chamber, the ingot is
transferred in 60 seconds to the second spray chamber without, in
this example, passing through the optional intermediate
equalization tunnel. The ingot then undergoes a second spraying,
different from the first. The ingot, but this time not including
the ends, undergoes a second spraying for 51 seconds at a surface
flow rate of 500 l/(minm.sup.2). The spray heel is a pair of ramps,
as described in FIG. 12. This setting tends to straighten the cold
end thermal profile, generating an almost flat longitudinal thermal
profile on leaving the second spray chamber. On leaving the second
spray chamber, the ingot is transferred to the equalization tunnel
in 30 seconds. The ingot waits for only 10 minutes in the
equalization tunnel. At the end, the ingot is transferred to the
hot rolling mill with a temperature uniformity better than
40.degree. C. over the complete ingot.
[0153] Example 3 shows that a judicious choice of spraying heels
can significantly reduce equalization time after spraying. For a
cooling method in several passes, the choice of heels may differ
from one pass to another. For a cooling method in 2 passes, the
heel chosen for the first pass gains from being contrary to the
heel chosen for the second pass. In an optimized manner, and for a
cooling method in 2 passes, a first pass with zero heel (continuous
spraying of the ingot) followed by a second pass with a heel of a
pair of ramps can significantly reduce the equalization time
required for thermal balancing of the ingot.
* * * * *