U.S. patent application number 11/359032 was filed with the patent office on 2007-02-01 for direct casting utilizing stack filtration.
This patent application is currently assigned to Lectrotherm, Inc.. Invention is credited to Michael W. Kohler, David A. Lazor, Karl J. Schwenk, Thomas J. Todaro, David O. Warren.
Application Number | 20070022841 11/359032 |
Document ID | / |
Family ID | 37692843 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070022841 |
Kind Code |
A1 |
Todaro; Thomas J. ; et
al. |
February 1, 2007 |
Direct casting utilizing stack filtration
Abstract
A casting system includes a filtration assembly including a
filter vessel housing spaced filters pre-heated to a temperature
approximating a pouring temperature of molten material to be
filtered to prevent breakage of the filter due to thermal shock
from contact with the molten material. Preferably, an induction
coil is used to inductively heat a susceptor adjacent the filter
vessel or inductively heat filters which themselves serve as
susceptors. Typically, the filter vessel is disposed below a
pouring vessel and above a mold, pour cup and any sprue system used
and is heated independently from the same. The filters are heated
during pouring to facilitate flow of the molten material
therethrough whereby very fine filters may be used. Spacing of the
filters enhances flow control and allows a head of molten material
to form whereby dross floats to the top of the head to prevent its
entry into the mold.
Inventors: |
Todaro; Thomas J.;
(Branchville, NJ) ; Warren; David O.; (Cloverdale,
CA) ; Lazor; David A.; (Girard, OH) ; Schwenk;
Karl J.; (Canton, OH) ; Kohler; Michael W.;
(Canton, OH) |
Correspondence
Address: |
SAND & SEBOLT
AEGIS TOWER, SUITE 1100
4940 MUNSON STREET, NW
CANTON
OH
44718-3615
US
|
Assignee: |
Lectrotherm, Inc.
|
Family ID: |
37692843 |
Appl. No.: |
11/359032 |
Filed: |
February 21, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60703831 |
Jul 29, 2005 |
|
|
|
Current U.S.
Class: |
75/407 |
Current CPC
Class: |
B22D 43/004 20130101;
Y02P 10/234 20151101; Y02P 10/20 20151101; C22B 9/023 20130101 |
Class at
Publication: |
075/407 |
International
Class: |
C22B 9/02 20060101
C22B009/02 |
Claims
1. A method comprising the steps of: pre-heating at least one
filter to a filter temperature which will prevent breakage of the
filter due to thermal shock from contact with molten material; and
passing molten material through the at least one filter.
2. The method of claim 1 wherein the step of pre-heating includes
the step of pre-heating the at least one filter to a temperature
which is within 75 degrees Fahrenheit of a pouring temperature of
the molten material.
3. The method of claim 2 further including the steps of melting a
metal or metal alloy to form the molten material; and heating the
molten material to the pouring temperature.
4. The method of claim 1 further including the steps of heating a
mold; and transferring a portion of the filtered molten material
into the heated mold; and wherein the step of pre-heating includes
pre-heating the at least one filter independently of heating the
mold.
5. The method of claim 1 wherein the step of passing includes the
step of passing molten material through the at least one filter
which is disposed within a filter vessel and further including the
step of transferring molten material from the filter vessel into at
least one mold.
6. The method of claim 5 wherein the step of transferring includes
the step of transferring molten material from the filter vessel
into the at least one mold via a transferring assembly which is
free of a filter.
7. The method of claim 1 further including the steps of covering a
filter vessel which houses the at least one filter with a cover to
facilitate the pre-heating of the at least one filter; moving at
least a portion of the cover to create access to an entrance
opening into the filter vessel; and pouring molten material through
the entrance opening into the filter vessel.
8. The method of claim 1 wherein the step of pre-heating includes
the step of heating a susceptor inductively and transferring heat
from the susceptor to the at least one filter.
9. The method of claim 1 wherein the step of pre-heating includes
the step of coupling an induction coil electromagnetically to the
at least one filter to inductively heat the at least one filter
directly.
10. The method of claim 1 wherein the step of pre-heating includes
the step of pre-heating the at least one filter within a filter
vessel to the filter temperature while the filter vessel is
disposed in a pouring position for receiving the molten material
from a pouring vessel.
11. The method of claim 1 further including the step of heating the
at least one filter with a heat source other than the molten
material during the step of passing to facilitate flow of the
molten material through the at least one filter.
12. A method comprising the steps of: passing molten material
through at least one filter disposed within a filter vessel;
heating the at least one filter with a heat source other than the
molten material during the step of passing to facilitate flow of
the molten material through the at least one filter; and
transferring filtered molten material from the filter vessel into a
containing vessel.
13. The method of claim 12 further including the steps of melting a
metal or metal alloy to form the molten material.
14. The method of claim 12 wherein the step of transferring
includes the step of transferring molten material from the filter
vessel into at least one mold via a transferring assembly which is
free of a filter.
15. The method of claim 12 wherein the step of passing includes the
step of passing molten material through two filters which are
spaced from one another.
16. The method of claim 15 wherein the step of passing includes the
step of passing molten material through two filters which are
spaced from one another by a spacer disposed within the filter
vessel between the two filters.
17. The method of claim 12 wherein the step of passing includes the
step of passing molten material through at least one filter in such
a manner to allow a head of molten material to form whereby dross
floats to the top of the head of molten material.
18. The method of claim 17 wherein the step of transferring
includes the step of transferring molten material and the dross out
of the filter vessel so that molten material enters a mold and the
dross remains in a structure intermediate the filter vessel and the
mold.
19. The method of claim 12 wherein the step of passing includes the
step of passing molten material through at least one preheated
filter having at least twenty pores per inch.
20. The method of claim 12 further including the step of
pre-heating the at least one filter to a filter temperature which
will prevent breakage of the filter due to thermal shock from
contact with the molten material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 60/703,831 filed Jul. 29, 2005; the disclosure
of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The invention relates generally to the casting of molten
metals or other molten/liquid materials. More particularly, the
invention relates to a filtration system used for such melting and
casting. Specifically, the invention relates to a filtration system
wherein the filters are preheated to a temperature similar to a
pouring temperature of the molten material to prevent breakage of
the filters due to thermal shock and frozen metal clogging
associated with temperature filtration.
[0004] 2. Background Information
[0005] In the melting, casting and/or other processing of metals or
other materials, there is often a substantial amount of impurities
within the metal or other materials to be melted. Separating these
impurities from the desired material which is ultimately to be used
in a finished product presents a host of problems. While filtering
methods known in the art have addressed these issues to a certain
degree, there remains a great deal of room for improvement. While
the following background information pertains primarily to the
melting and casting of metals and most particularly of super
alloys, the filtration issues remain for other molten materials and
the present invention is related to the filtering of essentially
any type of molten material.
[0006] It has long been understood that the direct casting of super
alloys and other metals for precision casting components has
suffered from impurities entrapped in the master melt alloy. Most
master alloys contain impurities such as dross, cut off and
cleaning fragments, pipe scale, condensate and melting vessel
fragments. Upon re-melting of the master alloy, crucible fragments,
oxidized metal and condensate particles can enter the melt. The
impurities become entrapped within the casting or on the surface
thereof and often cause the casting to be reworked or scrapped.
These impurities are identified as casting inclusions. Filtering is
often used to help remove these impurities; however, conventional
filtration techniques often cause more inclusions than they
prevent.
[0007] Generally, in the casting of large equiaxed cast components,
master melt alloy is re-melted in a melting vessel and poured
directly into an invested shell. Often a filter is placed in the
pour cup or mold cup of the invested shell to help reduce the
amount of resultant inclusions in the cast component. In this
system and method, the filter is maintained at or close to the
shell temperature, which is significantly lower than the alloy pour
temperature and thus can negatively effect the pour temperature and
if the alloy freezes, the filters can become clogged. Because of
the difference in temperatures, thermal shock can occur and cause
fragments of the filter to break off and enter the shell of the
mold. In addition, because pouring speed or fill rate is critical
to the metallurgical properties of the castings, filter pore size
must be relatively large so as not to impede the flow of metal into
the shell. Often ceramic fiber gaskets are used to seal the filter
within the pour cup. The fibrous nature of these gaskets can also
contribute to inclusions within the cast component. Such problems
greatly reduce the overall effectiveness of pour cup filtering.
Alternatively, in-line gate filtering can be employed in the
casting of equiaxed components. In this method, ceramic filters are
placed in the metal feed runners of the mold. This type of system
requires that the mold be configured so that a filter can be placed
in the gating either during wax set up or after wax removal. In
both techniques, the filters are held at shell temperatures and can
be thermally shocked when the molten alloy is poured through them.
The filters at these shell temperatures can negatively effect the
pour temperature and clog the filters if the alloy freezes. Again
the filter pore size needs to be large so as not to effect the fill
rate. In addition, the material used to affix the filter in place
may be a contaminant as well.
[0008] In the casting of directionally solidified castings, master
melt alloy is re-melted in a melting vessel and poured directly
into an invested shell. Filters are often placed in the bottom feed
runners of the wax trees prior to investment. Viscous wax is
injected through the filter so that the filters can be attached to
the wax tree. This puts considerable stress on the ceramic filters
leading to loose fragments that can enter the mold. Because the
filter is located in the metal feed runner, alloy loss is a
consideration. After solidification, metal is imbedded in the
filter and cannot be readily reverted. Thus, bottom feeding is
effective, but comes at a significant alloy cost. In addition, the
bottom feed filter system may prevent tight baffling of the
components and affect grain quality.
[0009] Often in the manufacturing of master alloys, molten metal is
poured from a melting vessel into a tundish that filters and
funnels the alloy into a fixed solidification mold, tube or pig.
However, the tundishes are typically equipped with coarse filters,
in conjunction with alternating dams and weirs, over and under
which the molten material respectively flows. In many cases, the
tundish assembly is radiantly preheated off-line from the melt
system and often to a temperature lower than the alloy pour
temperature, and then moved into a pouring position where the
tundish assembly is not further heated. Because the temperature of
the tundish is lower than the alloy pour temperature, filtration
needs to be coarse. Also, since the temperature is lower than the
solidification point of the alloy, any interruption in pouring may
cause the system to freeze prematurely, resulting in the need to
replace the tundish or eliminate its use for the remainder of the
pour. In addition, because the tundish assembly is preheated
offline and then moved into the pouring position without additional
heating, this configuration and method would not allow for the use
of fine filters.
[0010] Thus, there remains a need for a method and system for
eliminating impurities prior to molten metal entering a mold. The
present system and method addresses this problem and is
particularly useful for large equiaxed castings. However, the
present invention may be employed on directionally solidified
castings and master melt production as well as with essentially any
type of molten material.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention provides a method comprising the steps
of pre-heating at least one filter to a filter temperature which
will prevent breakage of the filter due to thermal shock from
contact with molten material; and passing molten material through
the at least one filter.
[0012] The present invention further provides a method comprising
the steps of passing molten material through at least one filter
disposed within a filter vessel; heating the at least one filter
with a heat source other than the molten material during the step
of passing to facilitate flow of the molten material through the at
least one filter; and transferring filtered molten material from
the filter vessel into a containing vessel.
[0013] In general, the present invention provides a filtration
system which prevent thermal shock of the filters, prevents the
freezing of the molten material within the filters to prevent
clogging thereof, minimizes or eliminates negative effects to the
pourtemperature to thus maintain a desired pourtemperature, and
removes impurities ranging even to extremely small sizes.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0014] FIG. 1 is a sectional view of a first embodiment of the
casting and filtration system of the present invention as viewed
from the side.
[0015] FIG. 2 is similar to FIG. 1 and shows molten material being
poured into the filter vessel, moving through the filters therein
and pouring into the pour cup and sprue system into a pair of
molds.
[0016] FIG. 3 is a view similar to FIG. 1 of a second embodiment of
the casting and filtration system of the present invention.
[0017] FIG. 4 is a view similar to FIG. 1 of a third embodiment of
the casting and filtration system of the present invention.
[0018] Similar numbers refer to similar parts throughout the
specification.
DETAILED DESCRIPTION OF THE INVENTION
[0019] A first embodiment of the casting system of the present
invention is indicated generally at 100 in FIGS. 1-2; a second
embodiment is indicated generally at 300 in FIG. 3; and a third
embodiment is indicated generally at 400 in FIG. 4.
[0020] Casting system 100 includes a pouring vessel 102 which is
often a melting crucible, a filtration system or assembly 104
disposed below vessel 102, a transferring system or shell or
assembly 106 disposed below assembly 104 and first and second
containing vessels in the form of molds 108 and 110 disposed below
transferring assembly 106. Typically, assembly 106 and molds 108
and 110 are a single assembly.
[0021] Pouring vessel 102 defines a cavity 112 for containing
molten material. Vessel 102 is typically either a main melt furnace
in which material is melted or a refining hearth which receives
molten material from the main melt furnace. Pouring vessel 102 is
disposed above filtration assembly 104 for pouring molten material
into assembly 104 via any manner known in the art, such as bottom
pouring, overflow pouring or tilting. A heat source 113 is
positioned for melting material within cavity 112 of vessel 102 or
within a melting furnace which pours molten material into cavity
112. Heat source 113 may be any suitable heating mechanism to
include, for example, a plasma torch, an arc electrode, an electron
beam apparatus, an inductive heating assembly, a resistance heating
assembly and so forth.
[0022] In accordance with a feature of the invention and with
continued reference to FIG. 1, filtration assembly 104 is located
outside of assembly 106 and includes first, second and third
filters 114, 116 and 118 which are spaced from one another and are
heatable to a temperature which will prevent them from breaking due
to thermal shock when molten material is poured therethrough.
Filters 114, 116 and 118 may be formed of any suitable material
which is appropriate to the temperature at which they will be used
and the type of molten material which will be poured therethrough,
along with other pertinent environmental factors. The material of
which the filters are made is typically based on compatibility with
the molten material, affinity for the capturing of dross and
potentially for chemical cleaning and stabilization. Filters 114,
116 and 118 may, for example, be formed of ceramic materials such
as alumina, mullite, silica, zirconia, calcia, titania and yittria.
They may also be formed of various metals, graphite, carbon
composites, resins, oxides, nitrides and so forth. Where
appropriate, the filters may be used as a susceptor, as later
explained, in which case the filters may be formed of such
materials as graphite, an alumina-graphite mix, a silica-graphite
mix, a clay-graphite, a silicon-carbide or other materials suitable
to the purpose.
[0023] More particularly and with continued reference to FIG. 1,
first filter 114 has an upper surface 140 and a lower surface 142
defining therebetween a first constant thickness T1. Filter 114
also has an outer perimeter 144. Similarly, second filter 116 has
an upper surface 146 and a lower surface 148 defining therebetween
a constant thickness T2. Filter 116 also has an outer perimeter
150. Likewise, third filter 118 has an upper surface 152 and a
lower surface 154 defining therebetween a constant thickness T3.
Third filter 118 also has an outer perimeter 156. In the embodiment
shown, each of filters 114, 116 and 118 have constant thicknesses
T1, T2 and T3 which are the same as one another. However, this may
vary as desired for the purposes for which the filters are used. In
addition, the thicknesses T1, T2 and T3 are not necessarily
constant, but may vary across the respective filters.
[0024] The filtration capability of the filters grows increasingly
finer from top to bottom so that second filter 116 is finer than
first filter 114 and third filter 118 is finer than second filter
116. The size of the pores used with such filters may vary greatly.
For example, for rather coarse filtering, pores which are
approximately one inch across may be used while on the other end of
the scale, filters having pores similar to that of tissue paper may
be used. The filtration capacity of a given filter is commonly
measured in pores per inch (ppi), which means pores per linear
inch. Filters ranging from 5 ppi to 70 ppi are reasonably common.
However, use of filters which are finer than 45 ppi in the melting
of metals and other materials with relatively high melting points
is not as common generally. Filters ranging from 10 to 30 ppi are
fairly common in the art. Thus, by way of example and especially
for use with the melting of metals or various alloys, first filter
114 may be approximately 10 ppi, second filter 116 may be
approximately 20 ppi and third filter 118 may range from 30 to 45
ppi. However, it is noted that with the use of the present
invention, filters which are extremely fine may be used.
[0025] With continued reference to FIG. 1, filters 114, 116 and 118
are disposed within a passage 120 formed in a filter vessel 122.
Passage 120 has an entrance opening 124 adjacent an upper end 126
of filter vessel 122 and an exit opening 128 adjacent a lower end
130 of vessel 122. Passage 120 of filter vessel 122 includes an
upper reservoir 121 disposed above first filter 114. Filter vessel
122 includes a sidewall 132 having an inner surface 134 and an
outer surface 136. Commonly, sidewall 132 is substantially
cylindrical but may have any shape which is suitable to the
purpose. Adjacent lower end 130, a shelf 138 is disposed adjacent
sidewall 132 inwardly thereof. Shelf 138 may be formed integrally
with sidewall 132 and preferably extends in a continuous manner all
the way around and in abutment with inner surface 134 of sidewall
132.
[0026] The respective outer perimeters 144, 150 and 156 of filters
114, 116 and 118 are all of a mating configuration with inner
surface 134 of sidewall 132. Third filter 118 is seated on shelf
138 with lower surface 154 of filter 118 contacting shelf 138
adjacent outer perimeter 156 of filter 118. Second filter 116 is
spaced upwardly from third filter 118 by a distance D1, which is
more particularly defined between upper surface 152 of third filter
118 and lower surface 148 of second filter 116. Likewise, first
filter 114 is spaced upwardly from second filter 116 by a distance
D2, which is more particularly defined between upper surface 146 of
second filter 116 and lower surface 142 of first filter 114.
[0027] More particularly, filtration assembly 104 includes first
and second spacers 158 and 160 disposed within passage 120 of
filter vessel 122 so that first spacer 158 spaces second and third
filters 116 and 118 from one another and second spacer 160 spaces
first and second filters 114 and 116 from one another. More
particularly, first spacer 158 has a sidewall 162 having an outer
surface 164 and an inner surface 166 defining a passage 168
extending from a top 170 to a bottom 172 of first spacer 158.
Preferably, outer surface 164 of first spacer 158 is of a mating
configuration with inner surface 134 of sidewall 132 of filter
vessel 122. First spacer 158 at bottom 172 thereof is seated atop
third filter 118 along upper surface 152 adjacent outer perimeter
156. Second filter 116 is seated along lower surface 148 adjacent
outer perimeter 150 atop first spacer 158 at top 170 thereof.
[0028] Similarly, second spacer 160 has a sidewall 174 having an
outer surface 176 and an inner surface 178 defining a passage 180
extending from a top 182 to a bottom 184 of second spacer 160.
Second spacer 160 at bottom 184 thereof is seated atop second
filter 116 along upper surface 146 adjacent outer perimeter 150.
First filter 114 along lower surface 142 adjacent outer perimeter
144 is seated atop second spacer 160 at top 182 thereof. Thus,
first spacer 158 has a height equal to distance D1 and second
spacer 160 has a height equal to distance D2. Distances D1 and D2
may or may not be the same as one another depending on the desired
spacing to be set between the various filters, as will be detailed
further below.
[0029] Filtration assembly 104 further includes a host vessel 186
within which filter vessel 122 is disposed. More particularly, host
vessel 186 includes a sidewall 188 having an outer surface 190 and
an inner surface 192 defining a passage 194 extending from a top
196 to a bottom 198 of host vessel 186. Inner surface 192 of
sidewall 188 of host vessel 186 is of mating configuration with
outer surface 136 of sidewall 132 of filter vessel 122 so that
filter vessel 122 is disposed within passage 194 of host vessel 186
with said outer surface 136 in abutment with said inner surface
192.
[0030] Filtration assembly 104 further includes a susceptor 200
including a sidewall 201 having an inner surface 202 which defines
a passage 204 extending from a top 206 to a bottom 208 of susceptor
200. Host vessel 186 is disposed within passage 204 of susceptor
200 with outer surface 190 of sidewall 188 in abutment with inner
surface 202 of sidewall 201 of susceptor 200. In one preferred
embodiment, host vessel 186, filter vessel 122, filters 114, 116
and 118 and spacers 158 and 160 form a removable cartridge. The
cartridge may be quickly removed or changed out for several
purposes, to include a change in the material being melted within
system 100, in order to change the flow control of a given set of
filters, or when the filters have met their intended service
life.
[0031] Filtration assembly 104 further includes an induction coil
210 surrounding susceptor 200 and a power source 212 in electrical
communication with induction coil 210 for powering induction coil
210. Alternately, element 210 may represent a resistive heating
element which is powered by power source 212. Alternately, a heat
source 214 may be used in place of element 210 and power source 212
depending on the environment in which system 100 is used. Heat
source 214 may, for example, be a gas-burning heat source.
[0032] Filtration assembly 104 further includes a cover 216 at
least a portion of which is moveable in order to provide access to
entrance opening 124 of filter vessel 122 so that molten material
may be poured from pouring vessel 102 into passage 120 of filter
vessel 122. Thus, cover 216 may have a door which is moveable to an
open position to allow access to the entrance opening. Alternately,
cover 216 may be moveable between closed and open positions or may
be removable entirely in order to provide such access to entrance
opening 124.
[0033] Transferring assembly 106 includes a pour cup or mold cup
218 and a sprue system 220 disposed below pour cup 218. Pour cup
218 defines a cavity 222 which is in fluid communication with
passage 120 of filter vessel 122. Pour cup 218 defines a lower exit
opening 224 in fluid communication with cavity 222. Sprue system
220 defines a main channel or passage 226 in fluid communication
with exit opening 224 of pour cup 218, with main passage 226
dividing into first and second branch passages 228 and 230 having
respective exit openings 232 and 234. Containing vessels or molds
108 and 110 define respective cavities 236 and 238 which are
respectively disposed below and in fluid communication with exit
openings 232 and 234. Where the heating of molds 108 and 110 is
desirable, system 100 may include a heat source 239 for that
purpose. Heat source 239 may be any heating mechanism known in the
art, to include an inductive or resistance heating assembly or a
gas burning source. While containing vessels 108 and 110 are shown
as molds, they may also be other types of vessels for containing
molten material, such as a tundish/vessel from which semi-conductor
crystals may be pulled.
[0034] In accordance with the invention and with reference to FIG.
2, the operation of system 100 is now described. Heat source 113 is
operated to melt material to form molten material 240 and to heat
molten material 240 to a pouring temperature. Generally, molten
material 240 is poured or otherwise transferred through preheated
filters 114, 116 and 118 in order to filter molten material 240 to
whatever degree is suitable for the particular purpose. More
particularly, cover 216 is moved or removed from above filter
vessel 122 and molten material 240 is poured from pouring vessel
102 into passage 120 of filter vessel 122 via entrance opening
124.
[0035] More particularly, molten material 240, such as molten metal
or a metal alloy, is poured into upper reservoir 121 and then
passes from reservoir 121 through first filter 114 into passage 180
of second spacer 160 as indicated by Arrows A. Molten material 240
then flows from passage 180 through second filter 116 and into
passage 168 of first spacer 158 as indicated by Arrows B. Molten
material 240 then flows from passage 168 through third filter 118
and out of passage 120 via exit opening 128 into cavity 222 of pour
cup 218 as indicated at Arrows C. Molten material then flows from
cavity 222 into main passage 226 and branch passages 228 and 230 of
sprue system 220 and into respective molds 108 and 110 as indicated
by Arrows D and E.
[0036] More particularly, power source 212 is operated to pass an
electrical current through induction coil 210 which then
electromagnetically couples with susceptor 206 to inductively heat
susceptor 206. Heat created within susceptor 206 is then
transferred via host vessel 186 and filter vessel 122 to filters
114, 116 and 118. This is most preferably done while cover 216 is
in the closed position covering filter vessel 122, as shown in FIG.
1. Alternately, where filters 114, 116 and 118 are of a suitable
material to act as susceptors themselves, induction coil 210 may
electromagnetically couple directly with the filters in order to
heat them inductively in a direct manner. As previously noted,
element 210 may also be a resistive heating element so that power
source 212 may send an electrical current through the resistive
heating element 210 in order to produce heat which may be
transferred to filters 114, 116 and 118. In this alternative
embodiment, susceptor 206 would not be needed. Likewise, alternate
heat source 214 may be used in order to heat filters 114, 116 and
118.
[0037] In any case and in accordance with a feature of the
invention, the filters 114, 116 and 118 are heated to a temperature
which will prevent them from breaking due to thermal shock when
molten material 240 is poured onto and through said filters. Molten
material 240 is melted and heated to its pouring temperature via
heat source 113 independently of the preheating of filters 114, 116
and 118. Once the filters are preheated to the desired temperature
and molten material 240 is ready to pour at its pouring
temperature, cover 216 is moved to its open position to allow the
pouring of molten material 240. The temperature to which filters
114, 116 and 118 are heated is approximately the same as the
pouring temperature of molten material 240. However, it will be
understood that the preheated temperatures of said filters may vary
to some degree while allowing them to avoid breakage due to thermal
shock. Depending on the composition of the filters and the pouring
temperature of the molten material, the range of the preheated
temperature of the filters may be fairly narrow or somewhat
broader. Typically, the filters will be heated to within 75.degree.
F. above or below the pouring temperature of molten material 240.
More preferably, the preheated temperature will be within
50.degree. F. of the pouring temperature and even more preferably
within 25.degree. F. of the pouring temperature of the molten
material. However, any suitable temperature above the pouring
temperature may be used, especially with regard to maintaining
fluidity of molten material 240.
[0038] Importantly, system 100 is configured so that filters 114,
116 and 118 may be heated independently of the temperature of the
molds 108 and 110, which are typically heated via heat source 239
to desired temperatures as well. Depending on the application, the
preheated temperature of molds 108 and 110 will vary, as previously
discussed in part in the Background section of the present
application.
[0039] In addition to the preheating of filters 114, 116 and 118 to
prevent their breakage due to thermal shock, said filters are also
heated throughout the melting process in order to maintain fluidity
of molten material 240 through the filters. This is especially
important to allow for the use of finer filters. Unless the
temperature of the filters is maintained sufficiently near and
preferably somewhat higher than the pouring temperature of molten
material 240, this fluidity is reduced enough to substantially
affect the flow rate of molten material 240 or even stop the flow
thereof altogether if the molten material 240 is allowed to freeze
up within the filters. It will be understood that the finer the
filter (i.e., the smaller the pore size), the more critical it is
to maintain the temperature of the filters sufficiently close to
the pouring temperature of the molten material in order to maintain
a desired flow or pour rate. System 100 is thus configured for
maximum filtration and sized to allow for an optimum pour rate.
[0040] Another advantage of filtration assembly 104 is the ability
to produce a head 242 of molten material 240 within filter vessel
122. In the process shown, head 242 of molten material 240 is
disposed within reservoir 121 of passage 120 of filter vessel 122.
Head 242 may be formed using a single filter by selecting a filter
having a suitable pore size to appropriately control the flow rate.
Alternately, as here, filters 114, 116 and 118 are spaced at
suitable distances D1 and D2 from one another and specific pore
sizes are chosen for each of said filters in order to control the
flow rate in a desired manner. Thus, as represented in FIG. 2, the
molten material 240 which is disposed between first and second
filters 114 and 116 and between second and third filters 116 and
118 it will preferably fill the respective spaces between said
filters. That is, passage 168 of first spacer 158 and passage 180
of second spacer 160 is preferably completely filled with molten
material 240 during the pouring process. However, heads of molten
material 240 similar to head 242 may also be formed between first
and second filters 114 and 116 and/or between second and third
filters 116 and 118 so that multiple heads may be formed. Head 242
is disposed above first filter 114 so as to allow dross 244 and
other like contaminants to flow out of the alloy or other molten
material atop head 242. Maintaining head 242 throughout the melting
process thus allows the dross to remain on the top and then at the
end of the pour to be captured before it enters molds 108 and 110.
More particularly, dross 244 will ultimately remain in structure
above said molds, more particularly within pour cup 218 or sprue
system 220. Thus, dross 244 does not contaminate the molded bodies
produced by molds 108 and 110.
[0041] Filters 114, 116 and 118 may be used with a pressurized
system if desired. As is well known, filtering surface area,
pressure and degree of filtration determine flow rate and these may
be tailored to a particular application of system 100. A variety of
advantages are readily noted with the use of system 100. It reduces
the number of inclusions and castings as compared to conventional
systems. It eliminates the need for fixing agents such as glues in
order to hold filters in place, and thus eliminates contamination
from such fixing agents. The use of filtration assembly 104 allows
pour cup 218 and sprue system 220 to be free of filters and
eliminates the need for filters elsewhere within system 100.
[0042] It is noted that filtration assembly 104 may be used with
another such filtration assembly or a plurality of other such
filtration assemblies wherein each assembly 104 may be stacked on
top of another in order to provide additional filtration during the
pouring process. In addition, filtration assembly 104 may be
adapted for use with a centrifugal apparatus so that the molten
material is not necessarily gravity fed nor fed by a pressurized
atmosphere. Thus, the molten material does not necessarily flow
downwardly through the filters although this would be the case in
the embodiments as shown. In addition, filters may be chosen which
are suited to the removal of microscopic particles. For instance,
filters having a high surface area and a high affinity for gases or
other constituents may be used to remove said gases or other
constituents from the molten material as it flows through the
filters.
[0043] System 300 (FIG. 3) is similar to system 100 except for the
configuration of the filter vessel and the filters and the
elimination of spacers between filters. The pouring vessel and heat
sources for the pouring vessel and molds are also not shown for
simplicity. More particularly, system 300 includes a filtration
assembly 304 which includes first, second and third filters 314,
316 and 318 and a filter vessel 322. First filter 314 has an upper
surface 340, a lower surface 342 and an outer perimeter 344. First
filter 314 has a width W1 which is equivalent to a diameter thereof
when first filter 314 is circular when viewed from above.
Similarly, second filter 316 has an upper surface 346, a lower
surface 348 and an outer perimeter 350. Second filter 316 also has
a width W2 which is smaller than width W1 of first filter 314 and
corresponds to a diameter when second filter 316 is circular when
viewed from above. Third filter 318 has an upper surface 352, a
lower surface 354 and an outer perimeter 356 and a width W3 which
is smaller than width W2. Width W3 also corresponds to a diameter
when third filter 318 is circular when viewed from above.
[0044] Filter vessel 322 defines a passage 320 analogous to passage
120 of filter vessel 122 except that it is a stepped passage. More
particularly, filter vessel 322 defines a passage 320 having an
entrance opening 324 at an upper end 326 of filter vessel 322 and
an exit opening 328 at a lower end 330 of vessel 322. Filter vessel
322 has a stepped sidewall 332 having a stepped inner surface 334
and an outer surface 336 which is substantially the same as outer
surface 136 of filter vessel 122 and bears the same relation with
respect to host vessel 186. Sidewall 332 has an upper first section
358 and a second section 360 disposed therebelow with an inwardly
extending first shelf 362 therebetween whereby inner surface 334 of
sidewall 332 is stepped inwardly. Second section 360 is thicker
than first section 358. Sidewall 332 further includes a third
section 364 disposed below second section 360 with an inwardly
extending second shelf 366 therebetween whereby inner surface 334
is further stepped inwardly. Third section 364 is thicker than
second section 360. Sidewall 332 further includes a lower fourth
section 368 disposed below third section 364 with an inwardly
extending third shelf 370 disposed therebetween whereby inner
surface 334 is stepped further inwardly.
[0045] Thus, passage 320 of filter vessel 322 includes an upper
first section 372 disposed above first shelf 362 which has a width
which is substantially the same as or slightly larger than width W1
of first filter 314. Passage 320 further includes a second section
374 below first section 372 which is disposed between first shelf
362 and second shelf 366 and has a width which is substantially the
same as or slightly larger than width W2 of second filter 316.
Passage 320 further includes a third section 376 below second
section 374 which is disposed between second shelf 366 and third
shelf 370. Third section 376 has a width which is substantially the
same as or slightly larger than width W3 of third filter 318.
Passage 320 further includes a fourth section 378 disposed below
third section 376 or in other words disposed below third shelf 370.
Fourth section 378 has a width W4 which is smaller than width W3 of
third filter 318.
[0046] Thus, first filter 314 is disposed within first section 372
of passage 320 with lower surface 342 seated atop first shelf 362
of sidewall 332. Outer perimeter 344 of first filter 314 is
disposed closely adjacent or in abutment with inner surface 334
just above first shelf 362. Width W1 may be selected so that first
shelf 314 may be placed atop first shelf 362 without force or shelf
314 may be press fit into first section 372 of passage 320 so that
it is held snugly in place with outer perimeter 344 frictionally
engaging inner surface 334 of sidewall 332. Likewise, second filter
316 is disposed within second section 374 of passage 320 with lower
surface 348 thereof seated atop second shelf 366 of sidewall 322.
Like first filter 314, second filter 316 may be placed with or
without frictional engagement between outer perimeter 350 thereof
and inner surface 344. Similarly, third filter 318 is disposed in
third section 376 of passage 320 with lower surface 354 thereof
seated atop third shelf 370 of sidewall 332. Like the other
filters, third filter 318 may be seated with or without frictional
engagement between outer perimeter 356 of third filter 318 and
inner surface 334 of sidewall 332. The operation of system 300 is
essentially the same as system 100 and is therefore described only
with regard to distinctions from system 100. It is noted, however,
that the stepped passage 320 and differing widths of filters 314,
316 and 318 will require different calculations for controlling the
flow rate of molten material through filter vessel 322. It is
further noted that the elimination of spacers within the filter
vessel for spacing the filters from one another of course means
that molten material would not be flowing through passages and
spacers, but rather will flow from first section 372 through first
filter 314 and into second section 374, then through second filter
316 and into third section 376 and then through third filter 318
and into fourth section 378 before entering transferring assembly
106 as previously described with regard to system 100.
[0047] Casting system 400 (FIG. 4) is similar to system 300 except
for the configurations of the filters, the filter vessel and the
host vessel, and the elimination of the sprue system whereby the
pour cup is seated atop a single cavity. More particularly, system
400 includes a filtration assembly 404 which includes first, second
and third filters 414, 416 and 418 each disposed in a passage 420
of a filter vessel 422. Passage 420 includes an entrance opening
424 adjacent an upper end 426 of vessel 422 and an exit opening 428
adjacent a lower end 430 of vessel 422. Vessel 422 includes a
frustoconical sidewall 432 having a frustoconical inner surface 434
defining passage 420 and a frustoconical outer surface 436.
Sidewall 432 tapers inwardly and downwardly, as do inner and outer
surfaces 434 and 436.
[0048] First filter 414 has an upper surface 440, a lower surface
442 and an outer perimeter 444 which tapers inwardly and downwardly
in mating relation to tapered inner surface 434 of sidewall 432.
Likewise, second filter 436 has an upper surface 446, a lower
surface 448 and an outer perimeter 450 which tapers inwardly and
downwardly in mating configuration with inner surface 434 of
sidewall 432. Second filter 416 is spaced downwardly from first
filter 414. Similarly, third filter 418 has an upper surface 452, a
lower surface 454 and an outer perimeter 456 which tapers inwardly
and downwardly in mating relation to inner surface 434 of sidewall
432. Third filter 418 is spaced downwardly from second filter 416.
Like systems 100 and 300, system 400 thus provides a plurality of
filters which are seated on a sidewall of or otherwise disposed
within a passage of a filter vessel without the need of any glue or
fixing agents to secure the filters therein. While systems 100, 300
and 400 may use glues or other such materials, it is preferred not
to do so in order to eliminate any additional contaminants to the
molten material.
[0049] Filtration assembly 404 further includes a host vessel 486
having a inwardly and downwardly tapering frustoconical inner
surface 488 and an outer surface 490 which is substantially the
same as the outer surface of host vessel 186 and has the same
relation with regard to susceptor 206. Inner surface 488 of host
vessel 486 is in mating relation with outer surface 436 of sidewall
432 of filter vessel 422. As previously noted, system 400 includes
a single mold 402 defining a cavity 404. Pour cup 218 is seated
atop mold 402 with cavity 222 thereof in fluid communication with
cavity 404 of mold 402.
[0050] In operation, system 400 works in substantially the same
manner as described with regard to systems 100 and 300. However,
system 400 shows the use of filtration assembly 404 with a single
mold 402, thereby eliminating the use of the sprue system. Thus,
molten material is poured directly from pour cup 218 into cavity
404 of mold 402. As with systems 100 and 300, system 400 provides a
filtration system in which pour cup 218 is free of filters as is
the remainder of the system aside from the filters within assembly
404.
[0051] Thus, systems 100, 300 and 400 provide a filtration system
for molten material wherein the filters are preheated to prevent
breakage thereof due to thermal shock upon contact by molten
material being poured through the filters. In addition, these
systems provide assemblies which allow for the continued heating of
the filters throughout the pouring process in order to maintain the
fluidity of the molten material as it passes through the filters to
provide a desirable flow rate and to prevent the clogging of the
filters. The use of the filtration assemblies disclosed herein are
useful in directional solidification and single crystal casting
because it allows for the elimination of bottom feed runners and
filters therein, which permits the use of tighter baffles and
internal chill systems while maintaining good filtration of the
re-melt alloy.
[0052] It will be appreciated that a number of variations may be
made which are within the scope of the invention. It has already
been noted that alternate heat sources may be used to heat the
filters of the present invention. As also suggested by the various
embodiments, the filters and filter vessels can be of a variety of
shapes, including those shown as well as cubic, hourglass-shaped,
torroidal, oval and so forth. Similarly, the shapes of the host
vessel, the susceptor and the induction coil may vary as well. For
instance, with system 400, each of the host, susceptor and
induction coil could be configured in a substantially frustoconical
shape or the like which more closely mimic the shape of the filter
vessel and thus reduce the thickness of the host vessel walls
adjacent the lower end thereof to allow for more efficient transfer
of heat from the susceptor to the filters. It is also noted that
the overall size of the filtration assembly can easily be as small
as one foot in width and one foot in height, thus illustrating the
adaptability of the invention for small spaces and the ease with
which such assemblies may be stacked as previously discussed.
Obviously, however, the size of the filtration assembly varies with
the application.
[0053] The present invention is useful over a very wide range of
melting temperatures and pouring temperatures. For instance, the
melting temperatures of various materials which can be used with
the present invention range anywhere from room temperature to
upward of 4000.degree. F. Typically in the case of super alloys,
the temperature range is roughly 2400.degree. F. to 3200.degree. F.
But of course, the pouring temperature is established by the
melting temperature of the given material.
[0054] In the foregoing description, certain terms have been used
for brevity, clearness, and understanding. No unnecessary
limitations are to be implied therefrom beyond the requirement of
the prior art because such terms are used for descriptive purposes
and are intended to be broadly construed.
[0055] Moreover, the description and illustration of the invention
is an example and the invention is not limited to the exact details
shown or described.
* * * * *