U.S. patent application number 09/769955 was filed with the patent office on 2002-09-19 for pressurized molten metal holder furnace.
Invention is credited to Kinosz, Michael J., Kuhns, F. Donald JR., Mbaye, Moustapha, Meyer, Thomas N., Righi, Jamal.
Application Number | 20020130450 09/769955 |
Document ID | / |
Family ID | 25087026 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020130450 |
Kind Code |
A1 |
Kinosz, Michael J. ; et
al. |
September 19, 2002 |
PRESSURIZED MOLTEN METAL HOLDER FURNACE
Abstract
A bottom heated holder furnace (10) for containing a supply of
molten metal includes a storage vessel (20) having sidewalls (22)
and a bottom wall (24) defining a molten metal receiving chamber
(26). A furnace insulating layer (32) lines the molten metal
receiving chamber (26). A thermally conductive heat exchanger block
(50) is located at the bottom of the molten metal receiving chamber
(26) for heating the supply of molten metal. The heat exchanger
block (50) includes a bottom face (55), side faces (56), and a top
face (57). The heat exchanger block (50) includes a plurality of
electrical heaters (70) extending therein and projecting outward
from at least one of the faces of the heat exchanger block (50),
and further extending through the furnace insulating layer (32) and
one of the sidewalls (22) of the storage vessel (20) for connection
to a source of electrical power. A sealing layer (60) covers the
bottom face (55) and side faces (56) of the heat exchanger block
(50) such that the heat exchanger block (50) is substantially
separated from contact with the furnace insulating layer (32). A
gas pressurization valve (118) is in fluid communication with the
molten metal receiving chamber (26) and the interior of the heat
exchanger block (50) for pressurizing the interior of the holder
furnace (10).
Inventors: |
Kinosz, Michael J.; (Apollo,
PA) ; Meyer, Thomas N.; (Murrysville, PA) ;
Kuhns, F. Donald JR.; (Medina, OH) ; Mbaye,
Moustapha; (Owensboro, KY) ; Righi, Jamal;
(Monroeville, PA) |
Correspondence
Address: |
Webb, Ziesenheim, Logsdon,
Orkin & Hanson, P.C.
700 Koppers Building
436 Seventh Avenue
Pittsburgh
PA
15219-1818
US
|
Family ID: |
25087026 |
Appl. No.: |
09/769955 |
Filed: |
January 25, 2001 |
Current U.S.
Class: |
266/242 |
Current CPC
Class: |
C22B 9/006 20130101;
F27D 3/1536 20130101; F27B 3/04 20130101; F27B 3/08 20130101; F27B
3/20 20130101; F27D 1/0006 20130101; F27D 3/1518 20130101; F27D
2099/0011 20130101; F27D 99/0006 20130101; F27D 1/0009
20130101 |
Class at
Publication: |
266/242 |
International
Class: |
C22B 007/00 |
Claims
We claim:
1. A holder furnace, comprising: a storage vessel having sidewalls
and a bottom wall defining a molten metal receiving chamber for
containing a supply of molten metal; at least one furnace
insulating layer lining the molten metal receiving chamber of the
storage vessel; a thermally conductive heat exchanger block located
at the bottom of the molten metal receiving chamber for heating the
supply of molten metal, with the heat exchanger block having a top
face, a bottom face, and side faces, and with the heat exchanger
block having a plurality of electrical heaters extending therein
and projecting outward from at least one of the faces of the heat
exchanger block and further extending through the furnace
insulating layer and at least one of the sidewalls of the storage
vessel for connection to a source of electrical power; a sealing
layer covering the bottom face and side faces of the heat exchanger
block such that the heat exchanger block is substantially separated
from contact with the furnace insulating layer; and a gas
pressurization valve in fluid communication with the molten metal
receiving chamber, and in fluid communication with the interior of
the heat exchanger block through the electrical heaters, with the
gas pressurization valve configured for connection to a gas
pressurization source and further configured to pressurize the
molten metal receiving chamber and the heat exchanger block upon
connection to the gas pressurization source and activation of the
gas pressurization valve.
2. The holder furnace of claim 1, further comprising a cover
positioned on top of the storage vessel and enclosing the molten
metal receiving chamber, with the cover including a first conduit
extending therethrough and in fluid communication with the gas
pressurization valve for pressurizing the molten metal receiving
chamber, and with the cover further including a second conduit
extending therethrough for removing molten metal from the molten
metal receiving chamber upon pressurization.
3. The holder furnace of claim 1, wherein the portion of the
electrical heaters extending outward from the sidewall of the
storage vessel is enclosed in a common chamber connected to the gas
pressurization valve and configured for pressurization upon
activation of the gas pressurization valve.
4. The holder furnace of claim 1, wherein the sealing layer
comprises an alumina fiber mat.
5. The holder furnace of claim 1, wherein the heat exchanger block
is made of one of graphite and silicon carbide.
6. The holder furnace of claim 1, wherein the electrical heaters
extend between opposite sidewalls of the storage vessel and through
the heat exchanger block, wherein the electrical heaters each
include a continuous heating element extending through at least one
of the opposite sidewalls, the at least one furnace insulating
layer, and extending at least partially through the heat exchanger
block, and wherein the electrical heaters each further include
respective tubes extending through the opposite sidewalls, the at
least one furnace insulating layer, and extending at least
partially into opposite faces of the heat exchanger block, with the
heating element for the electrical heaters extending at least
partially through each of the respective tubes.
7. The holder furnace of claim 6, further including sealing gaskets
positioned within the heat exchanger block, and wherein the sealing
gaskets cooperate, respectively, with ends of the tubes extending
into the opposite faces of the heat exchanger block for preventing
molten metal from leaking into the tubes and contacting the heating
element of the electrical heaters.
8. The holder furnace of claim 7, wherein the tubes are ceramic
insulating tubes and are each surrounded by a layer of ceramic
fiber rope for preventing molten metal from the supply of molten
metal from leaking into the ceramic insulating tubes and contacting
the heating element of the electrical heaters.
9. The holder furnace of claim 8, further including flange plates
attached, respectively, to the ceramic insulating tubes at the
opposite sidewalls of the storage vessel, and wherein the ceramic
insulating tubes are held in compression against the opposite
sidewalls of the storage vessel by the flange plates and mechanical
fasteners.
10. A heat exchanger block for heating molten metal in a holder
furnace, comprising: a thermally conductive block having a top
face, bottom face, and side faces; a plurality of continuous
heating elements extending into the thermally conductive block and
including a portion projecting outward from one of the side faces
of the thermally conductive block; a first plurality of tubes
positioned, respectively, about the portion of the heating elements
projecting outward from the thermally conductive block, with the
first plurality of tubes extending at least partially into the
thermally conductive block; and a first plurality of sealing
gaskets located within the thermally conductive block and
positioned, respectively, adjacent ends of the first plurality of
tubes extending into the thermally conductive block, with the
sealing gaskets cooperating with the ends of the first plurality of
tubes for preventing molten metal from contacting the heating
elements when the heat exchanger block is used in the holder
furnace.
11. The heat exchanger block of claim 10, wherein the heating
elements extend through the thermally conductive block
substantially to an opposite side face of the thermally conductive
block, with the heating elements each having an end terminating
within the thermally conductive block, and with the heat exchanger
block further including: a second plurality of tubes extending at
least partially into the opposite side face of the thermally
conductive block and cooperating, respectively, with the ends of
the heating elements located within the thermally conductive block;
and a second plurality of sealing gaskets located within the
thermally conductive block and positioned, respectively, adjacent
ends of the second plurality of tubes extending into the thermally
conductive block at the opposite side face, with the sealing
gaskets cooperating with the ends of the second plurality of tubes
extending into the thermally conductive block at the opposite side
face for preventing molten metal from contacting the heating
elements when the heat exchanger block is used in the holder
furnace.
12. The heat exchanger block of claim 11, wherein the first and
second plurality of tubes are ceramic insulating tubes, and wherein
exposed portions of the first and second plurality of ceramic
insulating tubes extending outward from the side faces of the
thermally conductive block are surrounded by a layer of ceramic
fiber rope for preventing molten metal from the holder furnace from
leaking into the first and second plurality of ceramic insulating
tubes and contacting the heating elements when the heat exchanger
block is used in the holder furnace.
13. The heat exchanger block of claim 10, further including a
sealing layer covering the bottom face and side faces of the
thermally conductive block, with the sealing layer comprising an
alumina fiber mat.
14. The heat exchanger block of claim 10, wherein the thermally
conductive block is made of one of graphite and silicon
carbide.
15. A holder furnace, comprising: a storage vessel having sidewalls
and a bottom wall defining a molten metal receiving chamber for
containing a supply of molten metal; at least one furnace
insulating layer lining the molten metal receiving chamber of the
storage vessel; a thermally conductive heat exchanger block located
at the bottom of the molten metal receiving chamber for heating the
supply of molten metal, with the heat exchanger block having a top
face, a bottom face, and side faces, and with the heat exchanger
block having a plurality of electrical heaters extending therein
and projecting outward from at least one of the faces of the heat
exchanger block and further extending through the furnace
insulating layer and at least one of the sidewalls of the storage
vessel for connection to a source of electrical power; a sealing
layer covering the bottom face and side faces of the heat exchanger
block such that the heat exchanger block is substantially separated
from contact with the furnace insulating layer, with the sealing
layer further extending along a portion of the top face of the heat
exchanger block, and with the furnace insulating layer overlapping
the sealing layer extending along the portion of the top face of
the heat exchanger block; and a gas pressurization valve in fluid
communication with the molten metal receiving chamber, and in fluid
communication with the interior of the heat exchanger block through
the electrical heaters, with the gas pressurization valve
configured for connection to a gas pressurization source and
further configured to pressurize the molten metal receiving chamber
and the heat exchanger block upon connection to the gas
pressurization source and activation of the gas pressurization
valve.
16. The holder furnace of claim 15, further comprising a cover
positioned on top of the storage vessel and enclosing the molten
metal receiving chamber, with the cover including a first conduit
extending therethrough and in fluid communication with the gas
pressurization valve for pressurizing the molten metal receiving
chamber, and with the cover further including a second conduit
extending therethrough for removing molten metal from the molten
metal receiving chamber upon pressurization.
17. The holder furnace of claim 15, wherein the portion of the
electrical heaters extending outward from the sidewall of the
storage vessel is enclosed in a chamber connected to the gas
pressurization valve and configured for pressurization upon
activation of the gas pressurization valve.
18. The holder furnace of claim 15, wherein the sealing layer
comprises an alumina fiber mat.
19. The holder furnace of claim 15, wherein the heat exchanger
block is made of one of graphite and silicon carbide.
20. The holder furnace of claim 15, wherein the electrical heaters
extend between opposite sidewalls of the storage vessel and through
the heat exchanger block, wherein the electrical heaters each
include a continuous heating element extending through at least one
of the opposite sidewalls, the at least one furnace insulating
layer, and extending at least partially through the heat exchanger
block, and wherein the electrical heaters each further include
respective tubes extending through the opposite sidewalls, the at
least one furnace insulating layer, and extending at least
partially into opposite faces of the heat exchanger block, with the
heating element for the electrical heaters extending at least
partially through each of the respective tubes.
21. The holder furnace of claim 20, further including sealing
gaskets positioned within the heat exchanger block, and wherein the
sealing gaskets cooperate, respectively, with ends of the tubes
extending into the opposite faces of the heat exchanger block for
preventing molten metal from leaking into the tubes and contacting
the heating element of the electrical heaters.
22. The holder furnace of claim 21, wherein the tubes are ceramic
insulating tubes and are each surrounded by a layer of ceramic
fiber rope for preventing molten metal from the supply of molten
metal from leaking into the ceramic insulating tubes and contacting
the heating element of the electrical heaters.
23. The holder furnace of claim 22, further including flange plates
attached, respectively, to the ceramic insulating tubes at the
opposite sidewalls of the storage vessel, and wherein the ceramic
insulating tubes are held in compression against the opposite
sidewalls of the storage vessel by the flange plates and mechanical
fasteners.
24. The holder furnace of claim 15, wherein the portion of the top
face of the heat exchanger block having the sealing layer thereon
defines a non-linear path such that any molten metal leakage into
the furnace insulating layer follows a torturous path along the
sealing layer.
25. The holder furnace of claim 15, wherein the portion of the top
face of the heat exchanger block having the sealing layer thereon
defines a plurality of ribs such that any molten metal leakage into
the furnace insulating layer follows a torturous path along the
sealing layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a holder furnace for
containing a supply of molten metal and, more particularly, to a
pressurized and bottom heated holder furnace for containing a
supply of molten metal.
[0003] 2. Description of the Prior Art
[0004] Molten metal holding furnaces, or holder furnaces, are used
in the art for holding and/or melting molten metal. Holding
furnaces are often used to contain a supply of molten metal for
injection into a casting machine. For example, U.S. Pat. No.
4,753,283 to Nakano discloses a horizontal injection casting
machine in which molten metal is maintained in a holding furnace
which periodically provides molten metal to the casting machine.
Molten metal from a larger smelting furnace is supplied
periodically to the holding furnace to maintain a set amount of
molten metal in the holding furnace. The holding furnace is heated
by a burner located adjacent a sidewall of the holding furnace.
[0005] In addition to the burner arrangement disclosed by the
Nakano patent, several other methods are known in the art for
heating molten metal contained in a holding furnace. Several common
methods include induction heating, radiant heating, and immersion
heating. For example, U.S. Pat. No. 4,299,268 to Lavanchy et al.
discloses a molten metal casting arrangement in which molten metal
is contained in a large capacity pressure ladle (i.e., holding
furnace) that is heated by a heating inductor located at the bottom
of the pressure ladle. The pressure ladle periodically supplies
molten metal to a smaller capacity tilting ladle, which supplies
molten metal to a casting apparatus. U.S. Pat. No. 3,991,263 to
Folgero et al. discloses a similar molten metal holding system to
that disclosed by the Lavanchy et al. patent, but the system
disclosed by the Folgero et al. patent is pressurized.
[0006] U.S Pat. No. 4,967,827 to Campbell discloses a melting and
casting apparatus in which electric radiant heating elements are
used to heat molten metal passing from a holding furnace to a
casting vessel. U.S. Pat. No. 5,398,750 to Crepeau et al. discloses
a molten metal supply vessel in which a plurality of electric
immersion heaters is used to heat molten metal in a holding
furnace. The immersion heaters extend downward from the holding
furnace cover and are partially submerged in the molten metal
contained in the holding furnace. U.S. Pat. No. 5,567,378 to
Mochizuki et al. discloses a similar immersion heater arrangement
to that found in the Crepeau et al. patent.
[0007] The above-discussed radiant heating and immersion heating
elements for heating molten metal in a holding furnace are located
above the surface of the molten metal and are "top" heating
arrangements. The "top" heating arrangements known in the art
require a significant amount of space above the holding furnace for
the individual heating elements. For example, the immersion heaters
and electric radiant heaters discussed previously in connection
with the Crepeau et al. and Campbell patents require a significant
amount of space above the surface of the molten metal in the
holding furnace, as well as a support structure above the holding
furnace for supporting the heating elements above the surface of
the molten metal. External heating arrangements, such as the burner
arrangement disclosed by the Nakano patent, heat the holding
furnace along a bottom wall or sidewall of the holding furnace, and
typically require space along the sides or bottom of the holding
furnace for the heating elements. With such top/external heating
arrangements, it is difficult to maintain a constant molten metal
temperature in the holding furnace.
[0008] An alternative to top/external heating arrangements is to
provide bottom heating devices in holding furnaces. Such bottom
heating devices are typically embedded within the bottom wall of
the holding furnace. One known bottom heating arrangement in a
molten metal holding furnace is disclosed by U.S. Pat. No.
5,411,240 to Rapp et al. The heating cycle of such bottom heating
arrangements places significant stress on the bottom wall of the
holding furnace. Such bottom heating arrangements are also
generally unsuitable for use with containment difficult metals such
as molten aluminum alloys. Any leakage of molten aluminum alloy
into the bottom wall of the holding furnace will cause failure of
the heating elements.
[0009] In view of the foregoing, an object of the present invention
is to provide a bottom heated holder furnace having improved molten
metal containment characteristics. In addition, it is an object of
the present invention to provide a bottom heated holder furnace
that is suitable for use with molten aluminum alloys. It is a
further object of the present invention to provide a holder furnace
that may be cyclically pressurized without large pressure drops
occurring within the holder furnace.
SUMMARY OF THE INVENTION
[0010] The above objects are accomplished with a pressurized molten
metal holder furnace in accordance with the present invention. The
holder firnace includes a storage vessel having sidewalls and a
bottom wall defining a molten metal receiving chamber for
containing the supply of molten metal. At least one furnace
insulating layer lines the molten metal receiving chamber of the
storage vessel. A thermally conducted heat exchanger block is
located at the bottom of the molten metal receiving chamber for
heating the supply of molten metal. The heat exchanger block has a
top face, a bottom face, and side faces. The heat exchanger block
includes a plurality of electrical heaters extending therein and
projecting outward from at least one of the faces of the heat
exchanger block, and further extending through the furnace
insulating layer and at least one of the sidewalls of the storage
vessel for connection to a source of electrical power. A sealing
layer at least partially covers the bottom face and side faces of
the heat exchanger block such that the heat exchanger block is
substantially separated from contact with the furnace insulating
layer. A gas pressurization valve is in fluid communication with
the molten metal receiving chamber and the interior of the heat
exchanger block through the electrical heaters. The gas
pressurization valve is configured for connection to a gas
pressurization source, and further configured to pressurize the
molten metal receiving chamber and the heat exchanger block upon
connection to the gas pressurization source and activation of the
gas pressurization valve.
[0011] The holder furnace may include a cover positioned on top of
the storage vessel and enclosing the molten metal receiving
chamber. The cover may include a first conduit extending
therethrough and in fluid communication with the gas pressurization
valve for pressurizing the molten metal receiving chamber. The
cover may further include a second conduit extending therethrough
for removing molten metal from the molten metal receiving chamber
upon pressurization.
[0012] The portion of the electrical heaters extending outward from
the sidewall of the storage vessel may be enclosed in a chamber
connected to the gas pressurization valve and configured for
pressurization upon activation of the gas pressurization valve. The
sealing layer may be an alumina fiber mat. The heat exchanger block
may be made of graphite, silicone carbide, or another substantially
equivalent material.
[0013] The electrical heaters may extend between opposite sidewalls
of the storage vessel and through the heat exchanger block. The
electrical heaters may each include a continuous heating element
extending through at least one of the opposite sidewalls, the at
least one furnace insulating layer, and extending at least
partially through the heat exchanger block. The electrical heaters
may each further include respective tubes extending through the
opposite sidewalls, the at least one furnace insulating layer, and
extending at least partially into opposite faces of the heat
exchanger block. The heating element for the electrical heaters may
extend at least partially through each of the respective tubes.
Sealing gaskets may be positioned within the heat exchanger block.
The sealing gaskets may cooperate, respectively, with ends of the
tubes extending into the opposite faces of the heat exchanger block
for preventing molten metal from leaking into the tubes and
contacting the heating element of the electrical heaters. The tubes
may be ceramic insulating tubes that are substantially surrounded
by a layer of ceramic fiber rope for preventing molten metal from
the supply of molten metal from leaking into the ceramic insulating
tubes and contacting the heating elements of the electrical
heaters.
[0014] Flange plates may be attached, respectively, to the ceramic
insulating tubes at the opposite sidewalls of the storage vessel.
The ceramic insulating tubes may be held into compression against
the opposite sidewalls of the storage vessel via the flange plates,
bolts, and a plurality of Belleville washers act to yield about 170
pounds of torque on each of the ceramic insulating tubes.
[0015] The sealing layer may further extend along a portion of the
top face of the heat exchanger block. The furnace insulating layer
may overlap the sealing layer extending along the top face of the
heat exchanger block. The portion of the top face of the heat
exchanger block having the sealing layer thereon may define a
non-linear path such that any molten metal leakage into the furnace
insulating layer follows a torturous path along the sealing layer.
A portion of the top face of the heat exchanger block having the
sealing layer thereon may also define a plurality of ribs such that
any molten metal leakage into the furnace insulating layer follows
a torturous path along the sealing layer.
[0016] Further details and advantages of the present invention will
become apparent from the following detailed description in
conjunction with the drawings wherein like parts are designated
with like reference numerals throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional end view of a holder furnace
made in accordance with the present invention;
[0018] FIG. 2 is a cross-sectional end view of the holder furnace
of FIG. 1 viewed from an opposite end of the holder furnace from
the cross-sectional view shown in FIG. 1;
[0019] FIG. 3 is a cross-sectional top view of the holder furnace
of FIGS. 1 and 2 taken along lines III-III in FIG. 2;
[0020] FIG. 4 is a cross-sectional side view of the holder furnace
of the present invention;
[0021] FIG. 5 is an end view of the holder furnace of FIG. 2
showing hidden lines;
[0022] FIG. 6 is a cross-sectional side view of the holder furnace
of FIG. 4 taken along lines VI-VI in FIG. 4; and
[0023] FIG. 7 is a partial cross-sectional side view of an
alternative molten metal sealing arrangement for the holder furnace
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring to FIGS. 1-5 a molten metal holder furnace 10 made
in accordance with the present invention is shown. The holder
furnace 10 may be used as part of a molten metal casting system, a
degassing furnace, as part of a molten metal filtration system, or
in other ways customary in the art. The holder furnace 10 is
generally defined by a storage vessel 20 having sidewalls 22 and a
bottom wall 24, which generally enclose a molten metal receiving
chamber 26 of the holder furnace 10. The molten metal receiving
chamber 26 is configured to contain a supply of molten metal 27.
The storage vessel 20 may be made of metal and, preferably, steel.
The storage vessel 20 includes a base support structure 28 for
supporting the holder furnace 10.
[0025] The holder furnace 10 includes a plurality of furnace lining
layers 32 lining the molten metal receiving chamber 26. In a
preferred embodiment of the holder furnace 10, three furnace lining
layers 32 line the molten metal receiving chamber 26. The furnace
layers 32 may be cast as individual blocks within the molten metal
receiving chamber 26. A first layer 34 of the furnace lining layers
32 lies immediately adjacent and in contact with the sidewalls 22
and bottom wall 24 of the storage vessel 20. The first layer 34 is
preferably a thermal insulation layer and may have a thickness of
about one inch. The first layer 34 is preferably a microporous,
primarily pressed silica powder (50-90%) material that is
encapsulated in a woven fiberglass cloth. A suitable thermal
insulating material for the first layer 34 includes Microtherm
manufactured by Microtherm Inc., Maryville, Tenn.
[0026] A second layer 36 is positioned radially inward from the
first layer 34 and is in contact therewith. The second layer 36 is
preferably an aluminum-resistant, insulating and castable material.
The second layer 36 may be comprised of primarily silica and
alumina, and is preferably light in weight and possesses low
thermal conductivity properties. A suitable aluminum-resistant,
lightweight, insulating, and castable material for the second layer
36 may include approximately 35% silica and 45% alumina by weight.
A suitable aluminum-resistant, lightweight, insulating, and
castable material for the second layer 36 includes ALSTOP.TM.
Lightweight Castable manufactured by A. P. Green, Minerva,
Ohio.
[0027] A third layer 38 of the furnace lining layers 32 lies
radially inward from the second layer 36 and is in contact
therewith. The third layer 38 is preferably a high alumina content
castable layer. For example, the third layer 38 may include about
70-90% alumina by weight. A suitable material for the third layer
38 includes Grefcon.TM. 80A manufactured by RHI Refractories
America and having an alumina content of about 80% by weight. The
furnace lining layers 32 generally separate the sidewalls 22 and
bottom wall 24 of the storage vessel 20 from the molten metal 27
contained in the molten metal receiving chamber 26.
[0028] A furnace cover 40 is positioned on top of the storage
vessel 20 to substantially enclose the molten metal receiving
chamber 26, and preferably provides a substantially air tight seal
for the molten metal receiving chamber 26. The furnace cover 40 may
be made of metal, such as steel, and preferably includes an
insulating layer 42 facing the molten metal receiving chamber 26 to
protect the furnace cover 40 from contact with the molten metal 27
contained in the molten metal receiving chamber 26. The insulating
layer 42 is preferably an insulating blanket material. The
insulating blanket material protects the furnace cover 40 from
warping because of the high heat of the molten metal 27 in the
molten metal receiving chamber 26. Suitable materials for the
insulating material include any of the materials discussed
previously in connection with the furnace lining layers 32, such as
Microtherm, ALSTOP.TM. Lightweight Castable, and includes
Grefcon.TM. 80A, or substantially equivalent materials. Another
suitable material for the insulating layer 42 includes Maftec.TM.
manufactured by Thermal Ceramics Inc., Augusta, Ga. This material
is a heat storage multi-fiber blanket material that is heat
resistant to about 2900.degree. F. The furnace cover 40 may be held
in place by a plurality of clamps 43 and bolts.
[0029] The holder furnace 10 of the present invention is a "batch"
type holder furnace which requires that the furnace cover 40 be
removed periodically to replenish the supply of molten metal 27 in
the molten metal receiving chamber 26. The furnace cover 40
includes a first conduit 44 extending therethrough and which use is
described further hereinafter. The furnace cover 40 further
includes a second conduit, or pressure tube 46, also extending
through the furnace cover 40, and which is used to extract the
molten metal 27 from the holder furnace 10 during its operation.
The pressure tube 46 may, for example, be used to place the holder
furnace 10 in fluid communication with a casting machine (not
shown). The holder furnace 10 would thus supply the molten metal 27
to the casting machine through the pressure tube 46 during
operation of the holder furnace 10.
[0030] The holder furnace 10 further includes a drain conduit 48
for draining the molten metal 27 from the molten metal receiving
chamber 26. The drain conduit 48 extends through the furnace lining
layers 32 and is in fluid communication with the molten metal
receiving chamber 26. Often, it may become necessary to entirely
replace the molten metal 27 in the molten metal receiving chamber
26 with a different molten metal alloy, or move the holder furnace
10 to a different location. The drain conduit 48 enables removal of
the molten metal 27 from the molten receiving chamber 26. A drain
plug 49 is used to seal the drain conduit 48 when the holder
furnace 10 is in operation.
[0031] The first conduit 44, second conduit or pressure tube 46,
and drain conduit 48 are each preferably lined with a refractory
material that is suitable for use with molten aluminum alloys.
Suitable refractory materials include Permatech.TM. Sigma or Beta
II castable refractory materials manufactured by Permatech, Inc.,
Graham, N.C. Permatech.TM. Sigma refractory material is mainly
comprised of about 64% silica, 30% calcium aluminate cement, and 6%
chemical frits by weight, and Permatech.TM. Beta II refractory
material is mainly comprised of about 62% alumina and 29% silica by
weight.
[0032] The holder furnace 10 includes a rectangular-shaped heat
exchanger block 50 located at the bottom of the molten metal
receiving chamber 26 defined by the storage vessel 20. The heat
exchanger block 50 is used to heat the molten metal 27 received in
the molten metal receiving chamber 26. Thus, the holder furnace 10
is generally heated from the bottom. The heat exchanger block 50 is
thermally conductive, and is preferably made of graphite, silicon
carbide or another material having similar thermally conductive
properties. The heat exchanger block 50 may be provided as a
single, large heat exchanger block having dimensions conforming to
the size of the molten metal receiving chamber 26, or as several
individual blocks (not shown) connected together along longitudinal
side or end edges by a tongue-in-groove connection. A preferred
tapered angle for such tongue-in-groove connection may be about
5.degree.. The heat exchanger block 50 generally has a bottom face
55, side faces 56, and a top face 57.
[0033] The heat exchanger block 50 is partially covered or enclosed
by a sealing layer 60. In particular, the sealing layer 60
preferably covers the heat exchanger block 50 on the bottom face 55
and side faces 56 of the heat exchanger block 50. The exposed top
face 57 of the heat exchanger block 50 defines a heat transfer
surface of the heat exchanger block 50. The top face 57, or heat
transfer surface, is intended for direct contact with the molten
metal 27 contained within the molten metal receiving chamber 26. In
summary, the sealing layer 60 generally separates the bottom face
55 and side faces 56 of the heat exchanger block 50 from contact
with the furnace lining layers 42. The sealing layer 60 is
preferably an alumina fiber mat material. A suitable material for
the sealing layer 60 is sold under the trademark SAFIL.TM. Alumina
LD Mat, and manufactured by Thermal Ceramics, Augusta, Ga. The
sealing layer 60, for example, may include about 90-96% alumina
fibers by weight.
[0034] The heat exchanger block 50 further includes a plurality of
electrical heaters 70 which are used to heat the heat exchanger
block 50 and, further, the molten metal 27 received in the molten
metal receiving chamber 26. The embodiment of the holder furnace 10
shown in FIGS. 1-5 includes a total of four electrical heaters 70.
However, it will be appreciated by those skilled in the art that
the heat exchanger block 50 may include any number of electrical
heaters 70. The electrical heaters 70 may, for example, be
resistive type electrical heating heaters that extend completely or
partially through the heat exchanger block 50.
[0035] The details of the heat exchanger block 50 and plurality of
electrical heaters 70 shown in FIGS. 1-5 will now be discussed in
detail with reference to FIGS. 3-6. It will be apparent that the
electrical heaters 70 shown in FIGS. 3-6 are identical, and a
discussion of the details of one of the electrical heaters 70 will
be illustrative of all of the electrical heaters 70 shown in FIGS.
3-6.
[0036] The electrical heater 70, in a preferred embodiment, extends
between opposite sidewalls of the storage vessel 20. The opposite
sidewalls of the storage vessel 20 are designated with reference
numerals 22A, 22B, respectively, and will be referred to as first
sidewall 22A and second sidewall 22B hereinafter for clarity. The
electrical heater 70 preferably extends through the first sidewall
22A, the furnace insulating layers 32, the heat exchanger block 50,
and the second sidewall 22B of the storage vessel 20. In FIGS. 3
and 4, the electrical heater 70 extends substantially parallel to a
longitudinal axis of the holder furnace 10. However, the present
invention envisions that the electrical heater 70 may be oriented
transverse to the longitudinal axis of the holder furnace 10, or at
any other orientation as long as the electrical heater 70 extends
substantially through the heat exchanger block 50.
[0037] The electrical heater 70 includes a continuous heating
element 76 that extends through the first sidewall 22A, the furnace
insulating layers 32, and extends substantially through the heat
exchanger block 50. A portion 78 of the continuous heating element
76 projects outward from one of the side faces 56 of the heat
exchanger block 50. The opposite side faces of the heat exchanger
block 50 are designated with reference numerals 56A, 56B,
respectively, and will be referred to hereinafter as first side
face 56A and second side face 56B for clarity. The continuous
heating element 76 is preferably a resistive type electrical
heating element. For aluminum alloy applications, the heating
element 76 is preferably sized to maintain a system temperature of
between about 1300-1500.degree. F. and preferably about
1400.degree. F.
[0038] The heating element 76 includes an end 80, or "cold toe",
which terminates within the heat exchanger block 50. The portion 78
of the heating element 76 that projects outward from the first side
face 56A of the heat exchanger block 50 is preferably enclosed by a
first insulating tube 82. The first insulating tube 82 extends
through the first sidewall 22A, the furnace lining layers 32, and
extends partially into the first side face 56A of the heat
exchanger block 50. A second insulating tube 84 preferably extends
through the second sidewall 22B, the furnace insulating layers 32,
and extends partially into the second side face 56B of the heat
exchanger block 50. A first sealing gasket 92 is located within the
heat exchanger block 50 adjacent the end of the first insulating
tube 82 extending into the heat exchanger block 50 at the first
side face 56A. The first sealing gasket 92 cooperates with the end
of the first insulating tube 82 for preventing the molten metal 27
from contacting the continuous heating element 76. A second sealing
gasket 94 is located within the heat exchanger block 50 adjacent
the end of the second insulating tube 84 extending into the heat
exchanger block 50 at the second side face 56B. The second sealing
gasket 94 cooperates with the end of the second insulating tube 84
extending into the heat exchanger block 50 at the second side face
56B for preventing the molten metal 27 from contacting the
continuous heating element 76.
[0039] The first and second insulating tubes 82, 84 are preferably
ceramic insulating tubes. The first and second sealing gaskets 92,
94 are preferably made of an alumina fiber mat material having a
high alumina fiber content similar to the material used for the
sealing layer 50. A suitable material for the first and second
sealing gaskets 92, 94 is sold under the trademark SAFIL.TM.
Alumina LD Mat and manufactured by Thermal Ceramics, Augusta, Ga.,
as discussed previously in connection with the sealing layer
60.
[0040] The first and second insulating tubes 82, 84 are preferably
each surrounded by a layer of ceramic fiber rope 100 for preventing
the molten metal 27 from leaking into the first and second
insulating tubes 82, 84 and contacting the continuous heating
elements 76. A suitable ceramic fiber rope material includes
Fiberfrax high density rope manufactured by the Carborundum
Company, Niagara Falls, N.Y. Fiberfrax is comprised mainly of
aluminia-silica. Flange plates 102 are attached, respectively, to
the first and second insulating tubes 82, 84 at the first and
second sidewalls 22A, 22B of the storage vessel 20. The first and
second insulating tubes 82, 84 are preferably held in compression
against the first and second sidewalls 22A, 22B of the storage
vessel 20 by the flange plates 102, bolts 104, and a plurality of
washers 106. The washers 106 are preferably Belleville spring
washers, which are stacked on the bolts 104 to yield about 175
pounds of torque on the first and second insulating tubes 82, 84.
Thus, the first and second insulating tubes 82, 84 are held in
compression against the first and second sidewalls, or opposite
sidewalls 22A, 22B of the storage vessel 20 to counteract the
thermal expansion of the heat exchanger block 50 under heating
conditions.
[0041] The electrical heater 70 and, more particularly, the
continuous heating element 76 are connected to a source of
electrical power 112, which provides electrical power to the
continuous heating element 76. As stated previously, the
construction of the electrical heater 70 discussed hereinabove is
identical for each of the electrical heaters 70 used in the heat
exchanger block 50. A preferred embodiment of the holder furnace 10
includes a set of four electrical heaters 70.
[0042] Referring, in particular, to FIGS. 3, 4, and 6, the holder
furnace 10, in operation, is preferably pressurized by an external
gas pressurization source 114. To accomplish this, the holder
furnace 10 preferably includes a plurality of chambers 116 that
respectively enclose the drain conduit 48 and the first and second
insulating tubes 82, 84 extending outward from the opposite
sidewalls 22A, 22B of the storage vessel 20. Each of the chambers
116 is connected to a gas pressurization valve 118, which in turn
is connected to the gas pressurization source 114. The gas
pressurization valve 118 is also connected to the first conduit 44
passing through the furnace cover 40 for pressurizing the molten
metal receiving chamber 26. The chambers 116 enclosing the first
and second insulating tubes 82, 84 may be pressurized to pressurize
the interior of the heat exchanger block 50. The gas pressurization
valve 118 may be a three-way solenoid valve, another type of
control valve, or a simple hand operated valve. A suitable valve
includes ASCO 110 volt three-way solenoid valve manufactured by
Automatic Switch Co., Florham, N.J.
[0043] Alternatively to the configuration described hereinabove,
the chambers 116 around the first and second insulating tubes 82,
84 may be dispensed with entirely with suitable piping arrangements
substituted in their place. In such an arrangement, the gas
pressurization valve 118 would be in fluid communication with each
of the first and second insulating tubes 82, 84 individually, as
will be appreciated by those skilled in the art. Likewise, the
chamber 116 around the drain conduit 48 may be dispensed with and a
conduit (i.e., pipe, not shown) placed in direct fluid
communication with the gas pressurization valve 118. The gas
pressurization valve 118 is preferably configured to pressurize the
entire interior of the holder furnace 10. In particular, when the
gas pressurization valve 118 is open, gas from the gas
pressurization source 114 will simultaneously pressurize the molten
metal receiving chamber 26 and the interior of the heat exchanger
block 50 such that a uniform pressure exists within the holder
furnace 10. The gas pressurization valve 118 arrangement described
hereinabove will substantially prevent pressure differences from
occurring within the holder furnace 10 interior. The holder furnace
10, when pressurized, will be of increased pressure relative to
atmospheric pressure outside the holder furnace 10, but there will
be no substantial pressure gradients within the holder furnace
10.
[0044] A test unit, i.e., holder furnace, was designed and built
incorporating the pressurizing features described hereinabove. The
test unit was pressurized and depressurized without experiencing
any problems. The data from the test pressurization is shown in
Table 1 hereafter:
1TABLE I Cycling Pressure (psig) 4.2 6.4 8.0 10.3 Number of Cycles
935 631 935 2043 Pressurization/Release Time (sec) 100/100 110/115
130/135 155/155
[0045] In view of the foregoing, when electrical power is supplied
to the electrical heaters 70 and, in particular, the continuous
heating elements 76, the heat exchanger block 50 is heated. The
exposed heat transfer surface along the top face 57 of the heat
exchanger block 50, which is in contact with the molten metal 27 in
the molten metal receiving chamber 26, heats the molten metal 27.
The molten metal 27 in the molten metal receiving chamber 26 may,
therefore, be kept at a substantially uniform temperature. When the
desired molten metal temperature is established, the holder furnace
10 may be pressurized to force the molten metal 27 contained in the
molten metal receiving chamber 26 out of the holder furnace 10 via
the pressure tube 46. When the gas pressurization valve 118 is
open, the chambers 116 enclosing the drain conduit 48 and the first
and second insulating tubes 82, 84 are pressurized, which
pressurizes the interior of the heat exchanger block 50. Further,
opening gas pressurization valve 118 also pressurizes the molten
metal receiving chamber 26 through the first conduit 44 extending
through the furnace cover 40. As an example, the holder furnace 10
may be pressurized to 10-15 psig. The gas pressurization source 114
may be a source of inert gas, such as nitrogen or argon, or simply
compressed air. The pressure drop throughout the holder furnace 10
interior remains small at all times and on the order of less than
0.1 psig with the pressurizing arrangement discussed
hereinabove.
[0046] Referring now to FIG. 7, an alternative sealing arrangement
between the heat exchanger block 50 and the furnace insulating
layers 32 is shown. In the alternative arrangement, a portion 120
of the top face 57 of the heat exchanger block 50 defines a
"torturous" path to the third insulating layer 38, which generally
means that the path is non-linear. The torturous, non-linear path
shown in FIG. 7 is formed by a plurality of ribs 122 formed on the
top face 57 of the heat exchanger block 50. The sealing layer 60,
discussed previously, preferably covers the portion 120 of the top
face 57 of the heat exchanger block 50 defining the torturous,
non-linear path. The torturous, non-linear path is used to increase
the distance that any leaking molten metal must travel. Although
ribs 122 are shown in FIG. 7, the configuration may take on many
geometries as long as the length of the travel path for the molten
metal 27 is increased. The innermost furnace insulating layer 32,
the third layer 38, preferably overlaps the sealing layer 60
extending along the top face 57 of the heat exchanger block 50. The
third layer 38 may be widened to partially overlap the edges of the
top face 57. The weight of the third layer 38 compresses the
sealing layer 60, and further enhances the sealing characteristics
of the sealing layer 60. The alternative sealing arrangement
discussed hereinabove advantageously increases the length leaking
molten metal 27 must travel, and the molten metal 27 will generally
freeze before reaching the sidewalls 22 of the storage vessel 20.
This arrangement is particularly well-suited for metals having a
low melting point such as molten aluminum alloys.
[0047] The present invention provides a bottom heated holder
furnace having improved molten metal containment characteristics.
The bottom heated holder furnace of the present invention is
particularly well-suited for use with molten aluminum alloys and
the like because the electrical heaters used to heat the holder
furnace are isolated from contact with the molten metal.
Furthermore, the holder furnace interior of the present invention
may be pressurized without large pressure drops occurring within
the holder furnace, thus increasing the pressures at which the
holder furnace may operate. The holder furnace of the present
invention may be used as part of a molten metal casting system, a
degassing furnace, a molten metal filtration system, or in other
ways customary in the art.
[0048] While preferred embodiments of the present invention were
described herein, various modifications and alterations of the
present invention may be made without departing from the spirit and
scope of the present invention. The scope of the present invention
is defined in the appended claims and equivalents thereto.
* * * * *