U.S. patent application number 10/975875 was filed with the patent office on 2006-05-04 for filters made from chemical binders and microspheres.
Invention is credited to Ronald C. Aufderheide, Ralph E. Showman.
Application Number | 20060091070 10/975875 |
Document ID | / |
Family ID | 36260578 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060091070 |
Kind Code |
A1 |
Aufderheide; Ronald C. ; et
al. |
May 4, 2006 |
Filters made from chemical binders and microspheres
Abstract
This invention relates to filters made from a refractory
material, preferably an insulating material, and chemical binder.
The filters are used in the foundry industry to filter molten
metal. The invention also relates to a process for preparing the
filters.
Inventors: |
Aufderheide; Ronald C.;
(Dublin, OH) ; Showman; Ralph E.; (Galloway,
OH) |
Correspondence
Address: |
David L. Hedden;ASHLAND INC.
P. O. Box 2219
Columbus
OH
43216
US
|
Family ID: |
36260578 |
Appl. No.: |
10/975875 |
Filed: |
October 28, 2004 |
Current U.S.
Class: |
210/510.1 ;
164/134; 164/358; 210/435 |
Current CPC
Class: |
B22C 9/086 20130101;
B01D 39/2079 20130101 |
Class at
Publication: |
210/510.1 ;
164/134; 164/358; 210/435 |
International
Class: |
B22C 9/08 20060101
B22C009/08; B01D 24/00 20060101 B01D024/00 |
Claims
1. A filter comprising a refractory material bonded together with
an effective bonding amount of a foundry binder.
2. The filter of claim 1 wherein the refractory material is an
insulating material that comprises ceramic microspheres.
3. The filter of claim 2 which is shaped such that it has an
entrance means and exit means.
4. The filter of claim 3 wherein the exit means is flat.
5. The filter of claim 4 wherein the exit means is concave.
6. The filter of claim 5 wherein the exit means is convex.
7. A process for preparing a filter comprising: (a) forming a mix
comprising a refractory material and an effective bonding amount of
a foundry binder, (b) shaping said mix to form a shape, such that
shape contains openings through which molten metal can pass; and
(c) curing said shape.
8. The process of claim 7 wherein the process is a cold-box process
comprising: (a) forming a mix comprising a refractory material and
an effective bonding amount of a foundry binder, (b) shaping said
mix to form a shape, such that shape contains openings through
which molten metal can pass; and (c) curing said shape with a
gaseous curing catalyst.
9. The process of claim 8 wherein the refractory is an insulating
material comprises ceramic microspheres.
10. The process of claim 9 wherein the binder is a phenolic
urethane binder and the catalyst is triethylamine.
11. A no-bake process for preparing a filter comprising: (a)
forming a mix comprising a refractory material, an effective
bonding amount of a foundry binder, and a liquid curing catalyst;
and (b) shaping said mix to form a shape, such that shape contains
openings through which molten metal can pass.
12. The process of claim 11 wherein the refractory material is an
insulating material comprising ceramic microspheres.
13. The process of claim 12 wherein the binder is a phenolic
urethane binder and the catalyst is a liquid tertiary amine.
14. A filter prepared by the process of claim 6, 7, 8, 9, 10, 11,
12, or 13.
15. A process for casting a metal part which comprises: (a)
inserting the filter of claim 1, 2, 3, 4, 5, or 6 into a pouring
cup or directly in a sprue of a mold assembly; (b) manufacturing
the filter as an integral part of the pouring cup or mold assembly
(b) pouring metal, while in the liquid state, through said filter;
(c) allowing said metal to cool and solidify; and (d) then
separating the cast metal part from the casting assembly.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to filters made from a refractory
material, preferably an insulating material, and chemical binder.
The filters are used in the foundry industry to filter molten
metal. The invention also relates to a process for preparing the
filters.
BACKGROUND OF THE INVENTION
[0002] Metal castings are made by pouring molten metal through a
gating system into a casting assembly made of molds and cores. The
molds and cores are typically made by shaping a mixture of a
foundry aggregate, e.g. sand, and a foundry binder. When the molten
metal is cooled, the metal casting is separated from the molds and
cores and any excess aggregate and binder are removed from the
casting.
[0003] Molten metal used to produce metal castings typically
contains contaminants, e.g. metal oxides. Filters are used
extensively in the foundry industry to filter contaminants found in
molten metal. Typically the filter is made from ceramic materials
that are formed by extrusion, pressing, or by impregnating a
ceramic slurry into a foam. The shape is dried in an oven and fired
in a kiln oven to cure the filter.
[0004] Patents describing various filters used in the foundry
industry include U.S. Pat. No. 6,468,325 (making and firing in a
kiln to for a filter), U.S. Pat. No. 6,296,794 (pressed porous
filter bodies), U.S. Pat. No. 5,961,918 (honeycomb extruded
filter), U.S. Pat. No. 5,190,897 (ceramic foam filter), U.S. Pat.
No. 5,104,540 (filter with a carbon coating to minimize thermal
shock to the filter), and U.S. Pat. No. 4,921,616 (alveolar ceramic
filters for high melting metals).
[0005] Most of the filters described in these patents describe
design changes to improve the filtering of tramp particles out of
the liquid metal. The focus of the design is on the ability of the
filter to trap small particles in the metal that could become a
defect in the casting. Manufacturing costs, removal from the gating
system, metal contamination by the filter itself, and design
flexibility are not significantly addressed.
[0006] Furthermore, filters typically used in the foundry industry
are hard to prime because of their mass and the relatively short
time required to pour a casting. This is because filters require a
large amount of heat to bring them up to the temperature of the
metal. The heat needed to prime the filter comes from the molten
metal, which in turn also cools the metal at a rapid rate.
[0007] There is also a problem with pieces of the filter getting
back into the furnace when the metal from the gating system is
re-melted. The filters become impregnated with metal and remain in
the gating. When the gating system is returned to the furnace for
re-melting small pieces of the filter can get trapped in the
furnace and stay in the metal when it is poured potentially causing
casting defects. Therefore, it is customary to remove the pieces of
the filter from the molten metal in the furnace.
[0008] All citations referred to in this application are expressly
incorporated by reference.
DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1. Photocopy of a picture of convex shaped filter used
in a pouring cup.
[0010] FIG. 2. Photocopy of a picture of concave shaped filter exit
(right picture).
[0011] FIG. 3. Photocopy of a picture of traditional ceramic
cellular filter in a pouring cup.
[0012] FIG. 4. Photocopy of a picture of pressed traditional
ceramic cellular filter.
[0013] FIG. 5. Photocopy of a picture of a cellular filter
integrated in the bottom of a pouring cup.
[0014] FIG. 6. Photocopy of a picture of a slotted filter
integrated in a pouring cup by machining slots in a solid bottom
cup.
[0015] FIG. 7. Photocopy of a picture of test of convex exit
surface filter showing separating streams.
[0016] FIG. 8. Photocopy of a picture of test of concave exit
surface filter showing individual streams being forced back
together.
BRIEF SUMMARY OF THE INVENTION
[0017] This invention relates to the manufacture, design and use of
filters made from a refractory material, preferably an insulating
material comprising ceramic microspheres, and a chemical binder.
The filters are used in the foundry industry to filter molten metal
during the casting of metal parts. The invention also relates to a
process for making the filters, the unique designs that can be
developed, and the use of the filters to make metal castings.
[0018] The filters utilize an insulating refractory that reduces
the rate at which it heat is absorbed. The low density of the
filters means they do not require as much heat to bring them to the
temperature of the metal. Together, the insulation properties and
low absorption rate of heat from the metal results in a filter that
is easier to prime.
[0019] The filters can also contain minor amounts of exothermic
materials that will provide some of the heat required to heat up
the filter and further reduce the amount of heat absorbed from the
metal. This will further improve the priming of the filter.
[0020] The filters address most of the issues that are currently
not being addressed in the current filter designs, e.g. reducing
manufacturing costs, ease of removal from the gating system,
reduced metal contamination, and improved design flexibility.
[0021] Traditional filters are formed into a flat shape so the
filters can be dried and fired in a high temperature furnace. The
shapes need to be of a design that can be easily handled and loaded
into a furnace without breaking or distorting. Therefore, the
traditional shapes include flat surfaces (so they can be fully
supported on boards or trays while the filters are being dried and
fired) on the top and bottom of the filter. Only the sides have
different shapes.
[0022] The process used to prepare the filters described herein
allows for much more design flexibility since the filter is cured
against the tooling and can be handled immediately upon removal
from the tooling. The filter can even be machined if desired to
create undercuts and back-drafts to provide more efficient
filtration of the molten metal.
[0023] The process for making the filters has the following
advantages:
[0024] 1. No heat is required to cure the filter.
[0025] 2. The refractory used to make the filter can be bonded with
a wide variety of conventional foundry binders.
[0026] 3. When cold box, hot-box, shell resins, and no-bake binders
are used, the filter is cured against the tool. This allows for
more design flexibility compared to the current filters that need
to be placed on a plate and then fired in a kiln at extremely high
temperatures.
[0027] 4. There are potentially lower capital costs required to
enter into the business and the manufacturing costs of the filters
is potentially lower.
[0028] 5. The filter can be incorporated as an integral part of a
pouring cup, thus eliminating the need for assembly.
[0029] 6. After the filter is exposed to the molten metal that is
poured through it, the strength of the filter is very low and can
be blasted off of the gating system, thus minimizing the amount of
filter material that would get back into the furnace. This is a
concern and a nuisance with the current ceramic fired filters.
[0030] 7. Special prototype designs can be machined and/or cut from
blanks of bonded and cured microspheres thus allowing for more
design flexibility, including convex and concave surfaces, slots
versus holes, and angled holes to name a few.
[0031] 8. Special additives can be added to the filter formulation
that can provide various benefits to the metal, such as but not
limited to, iron oxide to reduce the carbon decomposition of the
binder, and exothermic materials to provide heat to the filter,
etc. When making traditional ceramic filters, the firing process in
the kiln ovens would burn off or neutralize the effects on most
additives.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The detailed description and examples will illustrate
specific embodiments of the invention and will enable one skilled
in the art to practice the invention, including the best mode. It
is contemplated that many equivalent embodiments of the invention
will be operable besides these specifically disclosed.
[0033] For purposes of defining this invention, a "filter" is
defined as a foundry shape having openings, e.g. holes, pores,
channels, etc. through which molten metal flows, and which contains
a surface that traps and removes contaminants in from the molten
metal, e.g. metal oxides, etc. Openings in the filter can be
obtained, for example, by drilling holes, cutting slotted vents in
the bottom of a pouring cup, using pins in a pattern to make holes
in the filter, and any other effective means.
[0034] The filter can be used in the mold, by itself to clean the
molten metal, as part of a pouring cup and filter assembly,
integrated into the pouring cup, integrated into the mold itself,
or any other design that uses the teachings of this invention to
filter molten metal when making a casting.
[0035] The filter may have traditional flat surfaces, a concave
surface on the exit side of the filter which causes the metal to
spread out into individual streams, which is bad for oxidizing the
surface of the metal, but preferably has a convex surface on the
exit side of the filter, which brings the individual streams back
together helping to minimize the surface available for
oxidation.
[0036] The refractory material used to make the filter comprises an
insulating material. The insulating material will primarily depend
upon the mold material. Examples of insulating materials include
sand, pearlite, alumina, hollow glass spheres, etc. Blends of these
materials may also be used. Preferably used as the insulating
material are microspheres, most preferably ceramic microspheres.
Examples of ceramic microspheres include hollow aluminosilicate
microspheres, including aluminosilicate Extendospheres SG grades
available from Potters Beads a division of the PQ Corporation and
Envirospheres SLG available from Envirospheres Pty Ltd. The grade
of refractory chosen will depend upon the performance requirements
placed on the filter as well as the temperature of the metal
itself.
[0037] The thermal conductivity of the hollow aluminosilicate
microspheres ranges from about 0.15 W/m.K to about 0.25 W/m.K at
room temperature. The hollow aluminosilicate microspheres typically
have a particle size distribution of about 10 microns to about 350
microns. Preferred are hollow aluminosilicate microspheres having
an average diameter of about 120 microns to 130 microns and a wall
thickness of approximately 10% of the particle size. It is believed
that hollow microspheres made of material other than
aluminosilicate, having insulating properties, can also be used to
replace or used in combination with the hollow aluminosilicate
microspheres.
[0038] The weight percent of alumina to silica (as SiO.sub.2) in
the hollow aluminosilicate microspheres can vary over wide ranges
depending on the application, for instance from 25:75 to 75:25,
typically 33:67 to 50:50, where said weight percent is based upon
the total weight of the hollow microspheres. Hollow aluminosilicate
microspheres having a higher alumina content are better for making
filters used in pouring metals such as iron and steel which have
casting temperatures of 1300.degree. C. to 1700.degree. C. because
hollow aluminosilicate microspheres having more alumina have higher
melting points. Thus filters made with these hollow aluminosilicate
microspheres will not degrade as easily at higher temperatures.
[0039] Other refractories, because of their higher densities and
high thermal conductivities, may be used in the filter composition
to impart higher melting points to the filter so the filter will
not degrade when it comes into contact with larger volumes of the
molten metal during the casting process. Examples of such
refractories include silica, magnesia, alumina, olivine, chromite,
aluminosilicate, and silicon carbide among others. These
refractories are preferably used in amounts less than 94 weight
percent based upon the weight of the filter composition, more
preferably less than 50 weight percent based upon the weight of the
total refractory used to make the filter.
[0040] The filters made with hollow aluminosilicate microspheres
have low densities, low thermal conductivities, and excellent
insulating properties. The density of the filter composition
typically ranges from about 0.35 g/cc to about 0.45 g/cc,
preferably about 0.4 g/cc.
[0041] In addition, the filter composition may contain exothermic
materials (e.g. aluminum, iron oxide, manganese oxide, nitrate,
potassium permanganate, etc), fillers, and additives.
[0042] The amount of insulating material in the refractory material
can vary over wide ranges, but it typically ranges from 6 to 100
weight percent, preferably 50 to 100 weight percent, where the
weight percent is based upon the total weight of the refractory
material.
[0043] The binders that can be used to prepare the filter includes
any inorganic (e.g. sodium silicate binders cured with carbon
dioxide) or organic binder used in the foundry industry to bind an
aggregate into a foundry shape, e.g. a mold or core. For example,
any no-bake, cold-box, shell sand resin or hot-box binder, which
will sufficiently hold the mixture together in the shape of a
filter and polymerize in the presence of a curing catalyst, will
work. Examples of such binders include phenolic resins, phenolic
urethane binders, furan binders, alkaline phenolic resole binders,
and epoxy-acrylic binders among others. Particularly preferred are
epoxy-acrylic and phenolic urethane binders known as ISOSET.RTM.
ISOCURE and EXACTCAST.RTM. cold-box binders sold by Ashland
Chemical Company. The phenolic urethane binders are described in
U.S. Pat. Nos. 3,485,497 and 3,409,579, which are hereby
incorporated into this disclosure by reference. These binders are
based on a two part system, one part being a phenolic resin
component and the other part being a polyisocyanate component.
Phenolic urethane binders can be cured with both liquid no-bake
catalysts or vaporized liquids such as triethylamine in the
cold-box process. The epoxy-acrylic binders cured with sulfur
dioxide in the presence of an oxidizing agent are described in U.S.
Pat. No. 4,526,219, which is hereby incorporated into this
disclosure by reference.
[0044] The mixture of the ceramic microspheres and binder (filter
mix) can be shaped by using a pattern and then cured with a curing
catalyst. Curing the filter by the no-bake process takes place by
mixing a liquid curing catalyst with the filter mix, shaping the
filter mix containing the catalyst, and allowing the filter shape
to cure, typically at ambient temperature without the addition of
heat. The preferred liquid curing catalyst is a tertiary amine and
the preferred no-bake curing process is described in U.S. Pat. No.
3,485,797 which is hereby incorporated by reference into this
disclosure. Specific examples of such liquid curing catalysts
include 4-alkyl pyridines wherein the alkyl group has from one to
four carbon atoms, isoquinoline, arylpyridines such as phenyl
pyridine, pyridine, acridine, 2-methoxypyridine, pyridazine,
3-chloro pyridine, quinoline, N-methyl imidazole, N-ethyl
imidazole, 4,4'-dipyridine, 4-phenylpropylpyridine,
1-methylbenzimidazole, and 1,4-thiazine.
[0045] Curing the filter mix by the cold-box process takes place by
blowing or ramming the filter mix into a pattern and contacting the
filter with a vaporous or gaseous catalyst. Various vapor or
vapor/gas mixtures or gases such as tertiary amines, carbon
dioxide, methyl formate, and sulfur dioxide can be used depending
on the chemical binder chosen. Those skilled in the art will know
which gaseous curing agent is appropriate for the binder used. For
example, an amine vapor/gas mixture is used with phenolic-urethane
resins. Sulfur dioxide (in conjunction with an oxidizing agent) is
used with an epoxy-acrylic resins. See U.S. Pat. No. 4,526,219
which is hereby incorporated into this disclosure by reference.
Carbon dioxide (see U.S. Pat. No. 4,985,489 which is hereby
incorporated into this disclosure by reference) or methyl esters
(see U.S. Pat. No. 4,750,716 which is hereby incorporated into this
disclosure by reference) are used with alkaline phenolic resole
resins. Carbon dioxide is also used with binders based on
silicates. See U.S. Pat. No. 4,391,642 which is hereby incorporated
into this disclosure by reference.
[0046] Preferably the binder is an EXACTCAST.RTM. cold-box phenolic
urethane binder cured by passing a tertiary amine gas, such a
triethylamine, through the molded filter mix in the manner as
described in U.S. Pat. No. 3,409,579, or the epoxy-acrylic binder
cured with sulfur dioxide in the presence of an oxidizing agent as
described in U.S. Pat. No. 4,526,219. Typical gassing times are
from 0.5 to 3.0 seconds, preferably from 0.5 to 1.0 seconds. Purge
times are from 1.0 to 30 seconds, preferably from 1.0 to 10
seconds.
[0047] The amount of binder needed is an effective amount to hold
the filter together in the
[0048] desired shape. The amount can vary over wide ranges, but it
typically from 3.0 to 12.0 weight percent, preferably 6.0 to 10.0
weight percent, where the weight percent is based upon the total
weight of the refractory material.
[0049] In addition to making the filters with a pattern, the filter
could be made by other methods typically employed in the foundry
industry to make filters, e.g. extrusion, or pressed.
Alternatively, the filter could be molded onto the bottom of a
pouring cup or integrally in the gating system within the mold
itself, such that it would be an integral part of the pouring cup
and/or gating system within the mold assembly. This design
eliminates the need to assemble two parts (the pouring cup and the
filter) and would lower the cost of manufacturing.
[0050] Although the filters can be used to filter any molten metal,
they are particularly useful for filtering molten aluminum, because
aluminum is poured at a lower temperature and, as such, is less
likely to burn up the binder used to make the filter before the
mold is completely poured.
[0051] Ferrous metals with higher pouring temperatures will require
a stronger binder that contains a higher degree of hot strength,
possibly an inorganic binder, to hold the refractory together.
Additionally, because of the lower melting point of the ceramic
microspheres, blends of microspheres and various metal oxide
ceramics may be needed for pouring larger volumes of metal at
higher pouring temperatures. These metal oxides could include
silica oxides, aluminum oxides, etc.
EXAMPLES
[0052] While the invention has been described with reference to a
preferred embodiment, those skilled in the art will understand that
various changes may be made and equivalents may be substituted for
elements thereof without departing from the scope of the invention.
In addition, many modifications may be made to adapt a particular
situation or material to the teachings of the invention without
departing from the essential scope thereof. Therefore, it is
intended that the invention not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this invention, but that the invention will include all embodiments
falling within the scope of the appended claims. In this
application all units are in the metric system and all amounts and
percentages are by weight, unless otherwise expressly
indicated.
Examples 1-2
Filters Integrally Formed in Pouring Cup
[0053] Insulating slotted and round hole filters were integrated
with a pouring cup. Samples were made by blowing a blend of 100% SG
grade microspheres bonded with 10% EXACTCAST.RTM. 101/201 cold box
resin. This mix was used to make a filter integrated into a pouring
cup. The filter mix was blown into the pouring cup pattern that had
been modified with pins on the bottom that would make the filter
openings. See FIG. 5. The mix was then gassed with triethylamine in
nitrogen at 20 psi according to known methods described in U.S.
Pat. No. 3,409,579. Gas time is 0.5 seconds second, followed by
purging with air at 20 psi for about 15 seconds. The slotted filter
was made by cutting slots in the bottom of a solid bottom cup. See
FIG. 6. These designs created a one piece pouring cup with an
integrated filter on the bottom of the cup. The holes were
distributed across the entire surface of the filter. A traditional
pressed ceramic filter was also tested as a basis for comparison.
See FIGS. 3 and 4.
Examples 3-4
Preparation of the Insulating Formula for Making Filters
[0054] Insulating round hole filters were prepared by drilling and
machining the forms from a slab of insulating material. The slab
was made by mixing 100% SG grade microspheres with 10% PEP SET.RTM.
X1000/X2000 no-bake binder sold by Ashland Casting Solutions, a
division of Ashland Inc. The resin was used at a at a 55/45 ratio
of part I to part II and was catalyzed with 3% PEP SET Catalyst
3501. These samples were subsequently machined into cellular
filters that contained a series of round holes and a 2'' diameter
filtering area with a convex and concave shaped exit surface as
shown in FIGS. 1 and 2 respectively.
[0055] Molten aluminum metal having a temperature of 760.degree. C.
was poured through the traditional pressed ceramic filter and the
filters made from microspheres in open air (no downsprue was
present) so the stream that exited the filter could be monitored.
The test was videotaped and the videotape was reviewed after the
test. In the initial test comparing fired ceramic pressed filters
to the filter made with the microspheres of the same design, the
aluminum exited both filters in individual streams. This can be
extremely detrimental to the aluminum casting because it exposes
more surface area to oxidation, which can lead to oxide defects in
the casting. In production practices the filter is incorporated in
a gating system which would eventually coalesce the individual
streams back together based on the gating design. However, the
faster the streams coalesce, the less exposure the surfaces of the
individual streams have to oxidation. If a filter could create the
streams to coalesce by the design of the filter working with the
surface tension of the metal, this would be the best option.
[0056] In an attempt to bring the individual stream exiting the
filter back together the exit side of the filter was made into a
convex in shape. This resulted in the individual metal streams
spreading out and separating even more, which would add to the
oxidation of the metal. See FIG. 7.
[0057] The next test was with a filter whose exit surface was
concaved. The results of this test showed a tendency for the
streams to come back together and recombine upon exiting the
filter. When used as part of a total gating system, this faster
means of recombining the metal helps eliminate metal oxides forming
at the exit face of the filter. See FIG. 8.
* * * * *