U.S. patent application number 12/097416 was filed with the patent office on 2009-08-06 for thermal isolation screen for isolating an electromagnetic inductor, and heat treatment installation comprising such a screen.
This patent application is currently assigned to FIVES CELES. Invention is credited to Jean-Louis Bigan, Jean Hellegouarc'h, Jean-Yves Ren, Philippe Roehr.
Application Number | 20090194258 12/097416 |
Document ID | / |
Family ID | 37081459 |
Filed Date | 2009-08-06 |
United States Patent
Application |
20090194258 |
Kind Code |
A1 |
Roehr; Philippe ; et
al. |
August 6, 2009 |
THERMAL ISOLATION SCREEN FOR ISOLATING AN ELECTROMAGNETIC INDUCTOR,
AND HEAT TREATMENT INSTALLATION COMPRISING SUCH A SCREEN
Abstract
Thermal insulation screen transparent to magnetic flux, intended
to isolate an electromagnetic inductor with a transverse or
pseudo-transverse field, from the radiation of a heated product
(1), the thermal screen being made up of a matrix of blocks (7)
made of a thermally insulating material and of a plurality of tubes
(8) cooled by the circulation of a fluid, these tubes being
imprisoned in said matrix of blocks and the tubes and the blocks
being held in place by a support. The screen includes, behind the
blocks, heat-conducting means (10) placed so as to intercept the
heat flux passing through the blocks, these conducting means being
thermally coupled to the cooled tubes (8) for discharging the heat
flux into the tubes.
Inventors: |
Roehr; Philippe;
(Lautenbach-zell, FR) ; Ren; Jean-Yves;
(Guebwiller, FR) ; Hellegouarc'h; Jean; (Le
Perreux Sur Marne, FR) ; Bigan; Jean-Louis; (Evry,
FR) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W., SUITE 1100
WASHINGTON
DC
20006
US
|
Assignee: |
FIVES CELES
Lautenbach-zell
FR
|
Family ID: |
37081459 |
Appl. No.: |
12/097416 |
Filed: |
December 26, 2006 |
PCT Filed: |
December 26, 2006 |
PCT NO: |
PCT/FR2006/002879 |
371 Date: |
September 25, 2008 |
Current U.S.
Class: |
165/104.19 |
Current CPC
Class: |
H05B 6/365 20130101;
F27B 9/36 20130101; C21D 9/561 20130101; C21D 1/42 20130101; F27D
99/0006 20130101; C21D 9/60 20130101; Y02P 10/25 20151101; H05B
6/36 20130101; C21D 9/56 20130101 |
Class at
Publication: |
165/104.19 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 2006 |
FR |
0600053 |
Claims
1. Thermal insulation screen transparent to magnetic flux, intended
to isolate an electromagnetic inductor with a transverse or
pseudo-transverse field from the radiation of a heated product, the
thermal screen being made up of a matrix of blocks made of a
thermally insulating material and of a plurality of tubes cooled by
the circulation of a fluid, these tubes being imprisoned in said
matrix of blocks, the tubes and the blocks being held in place by a
support, characterized in that it includes, behind the blocks,
heat-conducting means placed so as to intercept the heat flux
passing through the blocks, these conducting means being thermally
coupled to the cooled tubes for discharging the heat flux into the
tubes.
2. Thermal insulation screen according to claim 1, wherein the
heat-conducting means are equipped with means for preventing, or
reducing, the formation of currents induced by the magnetic
flux.
3. Thermal insulation screen according to claim 1, wherein the
heat-conducting means are formed by a metal screen thermally
coupled to the cooled tubes.
4. Thermal insulation screen according to claim 3, wherein the
metal screen is formed by metal fins that extend to the rear of the
blocks, each fin being in thermal contact with a cooled tube.
5. Thermal insulation screen according to claim 4, wherein the fins
are produced by lengths of metal wire that are fixed to the cooling
tubes.
6. Thermal insulation screen according to claim 1, wherein the
means for preventing, or reducing, the formation of induced
currents generated by the magnetic flux comprise slots made in the
conducting means.
7. Thermal insulation screen according to claim 6, wherein the
slots are oriented transversely to the longitudinal direction of
the tubes.
8. Thermal insulation screen according to the claim 4, wherein the
slots open onto the longitudinal edges of the metal screen and are
closed near the central portion.
9. Thermal insulation screen according to claim 4, wherein each fin
extends on either side of a tube.
10. Thermal insulation screen according to claim 9, wherein each
fin extends, on each side of a tube, over substantially half the
gap between two adjacent tubes.
11. Thermal insulation screen according to claim 4, wherein each
fin is welded to a tube.
12. Thermal insulation screen according to claim 4, wherein the
fins are formed by slots made in an extruded or drawn metal
screen/tube assembly made as a single part.
13. Thermal insulation screen according to claim 4, wherein the
region of the fin adjacent to the tube has the form of a cradle
that follows a portion of the contour of the tube.
14. Thermal insulation screen according to claim 4, wherein the
fins are provided over the entire length of the tubes, in the
region of the inductor to be protected from the heat flux.
15. Heat treatment installation, especially a furnace, which
includes an electromagnetic inductor having a transverse or
pseudo-transverse field, for heating a product, characterized in
that it includes, for protecting the inductor against the thermal
radiation of the heated product, at least one thermal screen
according to claim 1.
Description
[0001] The invention relates to a cooled thermal insulation screen
transparent to magnetic flux, intended to isolate an
electromagnetic inductor having a transverse or pseudo-transverse
field from the radiation of a heated product. The thermal screen is
made up of a matrix of blocks made of a thermally insulating
material and of a plurality of metal tubes cooled by the
circulation of a fluid, these tubes being imprisoned in said matrix
of blocks, and the tubes and the matrix of blocks being held in
place on a support, which is located on the opposite side from the
product to be heated.
[0002] The invention relates more particularly, but not
exclusively, to a thermal insulation screen for an electromagnetic
induction device for heating a continuously running metal
strip.
[0003] EP 1 349 431 discloses a chamber with a thermal insulation
screen and a support consisting of a sheath.
[0004] The materials of the support are electrically insulating and
consist, for example, of a composite, glass fibres plus epoxy or
other resin, glass or ceramic. The support for the thermal screen
must not be exposed to excessively high temperatures, typically
below 120.degree. C. and preferably below 90.degree. C., depending
on the materials used for this support.
[0005] The electromagnetic coils for the induction heating are
located on the opposite side of the screen from the product to be
heated. To obtain good energy efficiency, it is necessary for these
coils to be as close as possible to the product to be heated. It is
therefore desirable for the thickness of the various walls of the
screen to be as small as possible, while still ensuring sufficient
thermal protection.
[0006] The tendency is to increase the temperature of the heated
product, especially for metallurgical reasons, such that the risks
of raising the temperature of the support for the screen above the
acceptable limit increase substantially.
[0007] For better protection of the screen support, it may be
conceivable to reduce the separation between the tubes cooled by
the circulation of a fluid. However, these tubes are preferably
formed by straight segments of coils obtained by bending several
times, in opposite directions, a length of tube. The diameter of
the tubes used imposes a minimum radius of curvature for bending
them, so that it is not possible to reduce the separation between
the tubes below a value imposed by acceptable bending of the
tubes.
[0008] The drawbacks of the prior techniques for a thermal screen
stem not only from the technological problems of manufacturing
hairpins from tubes bent through 180.degree. with smaller bending
radii, but also thermal problems induced by the reduction in the
centre-to-centre spacing of the tubes. Such a reduction in
centre-to-centre spacing of the tubes results in: [0009] increased
thermal losses, as additional losses occur in the magnetic field
since the length of tubes lying in the field is increased; and
[0010] lower surface temperature of the blocks, which may affect
the heating of the product.
[0011] The object of the invention is, above all, to provide a
cooled thermal insulation screen that allows better thermal
protection of the support for the screen without substantially
increasing the thickness of the layer of insulating material, and
without having to modify the spacing between the tubes cooled by
the circulation of a fluid.
[0012] According to the invention, a thermal insulation screen
transparent to magnetic flux, intended to isolate an
electromagnetic inductor with a transverse or pseudo-transverse
field from the radiation of a heated product, the thermal screen
being made up of a matrix of blocks made of a thermally insulating
material and of a plurality of metal tubes cooled by the
circulation of a fluid, these tubes being imprisoned in said matrix
of blocks, the tubes and the blocks being held in place by a
support, is characterized in that heat-conducting means are
provided to the rear of the blocks, these conducting means being
thermally coupled to the cooled tubes, said heat-conducting means
intercepting the heat flux that passes through the blocks and
discharging it into the cooled tubes.
[0013] The thermal screen according to the invention protects the
support by reducing the operating temperature thereof.
[0014] Preferably, the heat-conducting means are also equipped with
means for preventing, or reducing, the thermal losses resulting
from the induced currents generated by the magnetic flux.
[0015] The heat-conducting means may be made of stainless steel,
bronze, copper or another suitable material.
[0016] The heat-conducting means may be formed by a screen made of
a heat-conducting material, especially a metallic material,
thermally coupled to the cooled tubes. Advantageously, the screen
is formed by metal fins that extend behind the blocks, each fin
being in thermal contact with a cooled tube.
[0017] The means for preventing, or reducing, the formation of
induced currents may comprise slots made in the conducting means.
The slots are mainly oriented transversely to the longitudinal
direction of the tubes, but they may also be inclined thereto.
[0018] Advantageously, the slots open onto the longitudinal edges
of the metal screen and stop near the central portion.
[0019] The thermal screen is optimized when the induced currents
are extremely small. To do this, fins having a sufficiently small
area perpendicular to the magnetic field are provided. A good
result is obtained by reducing the pitch of the slots, by varying
the width of the slot and/or by varying the width of the fin and
its thickness.
[0020] According to one embodiment, the fins may be produced by
lengths of wire that are oriented radially and fixed to the cooled
tubes.
[0021] Each fin may extend, on each side of a tube, over
substantially half the gap between two adjacent tubes.
[0022] Each fin may be welded to a corresponding tube. The region
of the fin in contact with the tube may have the form of a cradle
that follows a portion of the contour of the tube.
[0023] The fins may be formed by slots made in an extruded or drawn
metal screen/tube assembly made as a single part.
[0024] Preferably, the fins extend over the entire length of the
tubes in the region of the inductor to be protected from the heat
flux.
[0025] The invention also relates to a heat treatment installation,
especially a furnace, which includes an electromagnetic inductor
having a transverse or pseudo-transverse field, for heating a
product, characterized in that it includes, for protecting the
inductor against the thermal radiation of the heated product, at
least one thermal screen as defined above.
[0026] The invention consists, apart from the arrangements
presented above, of a number of other arrangements that will be
explained in greater detail later with regard to exemplary
embodiments described with reference to the appended drawings,
which are in no way limiting. In these drawings:
[0027] FIG. 1 is a diagram of a metal strip heat treatment
installation with a thermal insulation screen transparent to
magnetic flux according to the invention;
[0028] FIG. 2 is a cross section on a larger scale of the thermal
insulation screen, with cut-away portions;
[0029] FIG. 3 is a plan view with cut-away portions of the thermal
insulation screen;
[0030] FIG. 4 is a cross section on a larger scale of detail IV of
FIG. 1 showing the heat-conducting means according to the
invention;
[0031] FIG. 5 is an end view of a heat-conducting means;
[0032] FIG. 6 is a partial plan view relating to FIG. 5; and
[0033] FIG. 7 illustrates, in vertical section, an alternative
embodiment of a heat-conducting means.
[0034] FIG. 1 of the drawings shows schematically a vertical
furnace H of a line for the heat treatment of a metal strip 1,
especially a steel strip, which runs continuously at a constant or
variable speed. In the example shown, the strip 1 runs vertically
between two rollers, a lower roller 2 and an upper roller 3
respectively. This example is not limiting--the strip 1 could run
horizontally in a horizontal furnace.
[0035] The furnace has generally a prismatic shape of rectangular
cross section and its internal volume is isolated from the external
atmosphere. The composition of the gas mixture inside the furnace
may vary depending on the zones in question. This gas mixture
comprises a relatively high proportion of hydrogen, favourable for
heat exchange.
[0036] The furnace H includes at least one heating section 4
equipped, on each side of the strip 1, with a half-inductor having
a transverse or pseudo-transverse flux 5a, 5b. A pair of
half-inductors constitutes a heating inductor.
[0037] A thermal insulation screen E transparent to the magnetic
flux is provided, at the half-inductors 5a, 5b, so as to thermally
protect the inductors facing the heated product formed by the strip
1.
[0038] As may be seen in FIG. 2, the screen E comprises a support 6
formed from an electrically insulating and especially
gas-impermeable material. Advantageously, the support 6 is made of
a composite with an epoxy or similar resin.
[0039] The minimum dimension k (FIG. 2) of the space between
opposed faces of the screen E, along the direction orthogonal to
the strip 1, is imposed by considerations for the purpose of
avoiding any contact between the strip and the internal surface of
the screen. This dimension k may be around twenty centimetres.
[0040] The internal faces of the support 6 support and hold in
place, by fastening means (not shown), a matrix B of blocks 7 made
of thermally insulating material, especially ceramic, and a
plurality of tubes 8 cooled by the circulation of a fluid,
generally water. The tubes 8 are generally made of metal, but they
could be made of another material, for example glass completely
transparent to the magnetic field. The tubes 8 are imprisoned in
the matrix of blocks 7 and protected against the direct radiation
from the strip 1.
[0041] The tubes 8 preferably consist of straight segments.
According to the example shown in FIG. 3, the tubes 8 are segments
of a continuous coil obtained by successively bending a tube
through 180.degree. in opposite directions. An inlet and an outlet
for the cooling fluid are provided for each coil. Several coils
constituting successive panels may be juxtaposed against the
internal wall of the support 6. The internal diameter of the tubes
8 is about eight to ten millimetres.
[0042] The blocks 7, as may be seen in FIG. 2 and 4, are formed by
substantially rectangular parallelepipedal blocks, the two
longitudinal faces of which include recesses 7a, 7b in the form of
cylindrical portions suitable for following the contour of two
successive tubes 8. The blocks 7 may thus be engaged between two
straight tubes 8. The blocks 7 bear against one another along the
longitudinal direction of the tubes 8. A small transverse space 9
(FIG. 4) may be left between two adjacent blocks 7.
[0043] The front face 7c of the blocks 7 is the one directly
exposed to the thermal radiation from the strip 1. The rear face 7d
of the blocks, which is the face furthest from the strip 1, is at a
temperature considerably below that of the face 7c because of the
thermal resistance presented by the block 7 and because of the heat
extracted by the tubes 8 and the cooling fluid.
[0044] In order for the strip 1 to be heated with maximum energy
efficiency by electromagnetic induction with a transverse or
pseudo-transverse flux, it is desirable to place the inductors as
close as possible to the strip 1. When the treatment temperature of
the strip 1 increases, there is a risk of the support 6 being
exposed to too high a temperature.
[0045] To ensure effective thermal protection of the support 6,
without the thickness of the insulating blocks 7 being increased
and without reducing the distance between successive tubes 8, the
invention provides, at the rear face 7d of the blocks,
heat-conducting means 10 placed so as to intercept the heat flux Q
passing through the blocks 7. These conducting means 10 are
thermally coupled to the cooled tubes 8 in order to discharge the
heat flux Q into the tubes and into the cooling liquid circulating
in the tubes. Furthermore, the conducting means 10 are equipped, as
illustrated in FIG. 6, with means 11 for preventing or reducing the
formation of induced currents generated by the transverse
alternating electromagnetic flux.
[0046] Preferably, the conducting means 10 consist of a metal
screen S (FIG. 4) of small thickness j especially less than five
millimetres. The screen S covers most of the rear faces 7d of the
blocks.
[0047] The metal screen S is formed by a set of metal fins 12
separated from one another. Associated with each tube 8 are metal
fins 12 covering the rear face 7d of the blocks, each fin being in
thermal contact with the associated cooled tube 8. The terms "heat
sink" or "heat extractor" could be used as synonyms for the term
"fin".
[0048] Each fin 12 is formed by a metal strip preferably extending
over the entire length of the tube 8. The strip has a projecting
central longitudinal portion 12a engaged in a free space 13 between
the rear edges of two successive blocks 7. The central portion 12a
comes into contact with the wall of the tube 8 to which it is
preferably welded. The metal strip extends on either side of the
central portion 12a, symmetrically or asymmetrically, with blades
12b, 12c meeting substantially at mid-width of each block 7. Such
an arrangement makes it possible to limit the length of the path
for discharging the heat into the tube 8 to substantially one half
of the width of a block 7. The ends of the blades 12b, 12c of two
successive fins are separated by a gap of small width m (FIG. 4),
especially less than five millimetres, and preferably less than two
millimetres. The rear face 7d of each block is thus practically
entirely covered by fins 12.
[0049] In the example shown in FIG. 2, the cross section of the
thermal screen has a substantially rectangular closed outline. This
example is not limiting. The thermal screen may consist, on each
side of the strip, of a plate having several layers (insulating
blocks, cooled tubes, conducting means). In this case, the cross
section of the screen would be a straight segment, as shown in FIG.
4. A plate-shaped heat screen according to the invention is
particularly suitable for installations such as those intended in
Patent Applications FR 05/06462 and FR 05/06463 filed on 24 Jun.
2005 by the same filing company CELES.
[0050] According to the exemplary embodiment shown in FIG. 4, the
central portion 12a of the fin has the shape of a dome with its
convex side turned towards the tube 8, said dome having oblong
openings 14 for welding it.
[0051] As a variant, as illustrated in FIG. 7, the projecting
central portion 12a has a concavity forming a cradle for following
the facing portion of the tube 8 and providing a larger contact
area for heat transfer.
[0052] According to another embodiment, the fins may be produced by
slots made in a tube 8/metal screen S assembly extruded or drawn as
a single part.
[0053] The means 11 for preventing, or reducing, the formation of
induced currents generated by the magnetic flux preferably comprise
slots 15 made in the fins 12. The slots are oriented mainly
transversely to the longitudinal direction of the fins, as
illustrated in FIG. 6, but they may also be inclined thereto. The
slots 15, which are parallel to one another, open onto the
longitudinal edges of the metal screen S and are closed near the
central portion 12a.
[0054] The thermal screen is optimized when the induced currents
are extremely small. To do this, fins having a sufficiently small
area perpendicular to the magnetic field are provided. A good
result is obtained by reducing the pitch of the slots, by varying
the width of the slot, especially by varying the thickness of a saw
cut constituting the slot, and/or by varying the width of the fin
and the thickness. According to one example, the slot width is 0.5
mm and the fin width between two slots is adapted to the electrical
loss of the currents induced in this fin.
[0055] As a variant, the fins may be produced by lengths of wire.
The lengths of wire are oriented transversely, radially or
obliquely to the cooling tubes 8 and are fixed, especially welded,
to the tubes 8, the assembly resembling a comb, the teeth of which
would be formed by the lengths of wire. The diameter of the wire
may be 1 mm with a gap between each wire of 0.3 mm, this gap
constituting the slot 15.
[0056] The fin 12, seen from above as illustrated in FIG. 6, has a
shape that resembles that of a fishbone.
[0057] The presence of the slots 15, which greatly reduce the
induced currents generated by the magnetic flux, reduces parasitic
heating that would lower the energy efficiency.
[0058] Advantageously, the tubes 8 and/or the fins 12 are made of
stainless steel. As a variant, the tubes 8 and/or the fins 12 are
made of bronze or copper, while other metals may also be
envisaged.
[0059] The operation results from the foregoing explanations.
[0060] The transverse alternating magnetic field heats the strip 1,
which radiates heat towards the surfaces that surround this strip.
The heat flux Q that passes through the blocks 7 to reach the rear
face 7d is predominantly intercepted by the fins 12 and discharged
into the tubes 8 and into the cooling fluid. The support 6 is
better protected against the heating that would be due to this flux
Q.
[0061] The invention makes it possible, without the thickness of
the heat screen E being substantially increased and without the
spacing of the tubes 8 being modified, to provide effective thermal
protection of the support 6 for high temperatures of the strip 1,
for example 1150.degree. C.
[0062] Although the description has been given with regard to a
strip 1, the invention applies to other types of metal products,
especially steel, copper or aluminium wires or plates. The product
may or may not be a running product.
* * * * *