U.S. patent application number 09/761543 was filed with the patent office on 2001-09-20 for exothermic sleeve mixes containing fine aluminum.
Invention is credited to Aufderheide, Ronald C., Showman, Ralph E., Twardowska, Helena.
Application Number | 20010022999 09/761543 |
Document ID | / |
Family ID | 23527472 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022999 |
Kind Code |
A1 |
Twardowska, Helena ; et
al. |
September 20, 2001 |
Exothermic sleeve mixes containing fine aluminum
Abstract
The invention relates to an exothermic sleeve composition
comprising (a) an oxidizable metal where the oxidizable metal
comprises fine aluminum as the major component, and (b) an
oxidizing agent capable of generating an exothermic reaction. The
invention also relates to the use of the sleeve composition to
prepare sleeves, the sleeves prepared with the sleeve compositions,
and the use of the sleeves to prepare metal castings.
Inventors: |
Twardowska, Helena; (Dublin,
OH) ; 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: |
23527472 |
Appl. No.: |
09/761543 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09761543 |
Jan 16, 2001 |
|
|
|
09386884 |
Aug 31, 1999 |
|
|
|
Current U.S.
Class: |
428/34.6 ;
164/131; 164/6; 75/314 |
Current CPC
Class: |
B22C 1/00 20130101; Y10T
428/1317 20150115; B22D 7/104 20130101 |
Class at
Publication: |
428/34.6 ; 164/6;
164/131; 75/314 |
International
Class: |
C21B 003/02 |
Claims
1. An exothermic sleeve composition comprising: (a) an oxidizable
metal where the oxidizable metal comprises fine aluminum as the
major component, and (b) an effective amount of an oxidizing agent
capable of generating an exothermic reaction.
2. The composition of claim 1 wherein the fine aluminum comprises a
particle distribution such that 95 weight percent of the aluminum
passes through a 100 mesh as determined by the US Standard Screen
Test.
3. The sleeve composition of claim 2 wherein the fine aluminum
comprises a particle distribution such that 95 weight percent
passes through a 140 mesh as determined by the US Standard Screen
Test.
4. The composition of claim 3 wherein the fine aluminum comprises
at least 5 to 45 weight percent of the sleeve composition.
5. The sleeve composition of claim 4 wherein the sleeve composition
contains from 30 weight percent to 80 weight percent of hollow
alumina microspheres, where said weight is based upon the total
weight of the sleeve composition.
6. The sleeve composition of claim 4 wherein the sleeve composition
contains sand as a refractory in an amount of 30 weight percent to
70 weight percent based upon the total weight of the sleeve
composition.
7. A sleeve mix comprising the sleeve composition of claim 1, 2, 3,
4, 5, or 6 and an effective binding amount of an organic foundry
binder.
8. A cold-box process for making an exothermic sleeve comprising:
(A) introducing the sleeve mix of claim 7 into a sleeve pattern to
prepare an uncured sleeve; (B) contacting said uncured sleeve
prepared by (A) with a vaporous curing catalyst; (C) allowing said
sleeve resulting from (B) to cure until said sleeve becomes
handleable; and (E) removing said sleeve from the pattern.
9. The process of claim 8 wherein the binder is selected from the
group consisting of phenolic urethane binders and epoxy-acrylic
binders.
10. The process of claim 9 wherein the binder level is from about 4
weight percent to about 12 weight percent based upon the weight of
the sleeve composition.
11. A sleeve prepared by the process of claim 10.
12. A process for casting a metal part which comprises: (1) using
an exothermic sleeve of claim 11 in a mold assembly of a casting
assembly; (2) pouring metal, while in the liquid state, into said
casting assembly; (3) allowing said metal to cool and solidify; and
(4) then separating the cast metal part from the casting
assembly.
13. A metal part prepared in accordance with claim 12.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an exothermic sleeve composition
comprising (a) an oxidizable metal where the oxidizable metal
comprises fine aluminum as the major component, and (b) an
oxidizing agent capable of generating an exothermic reaction. The
invention also relates to the use of the sleeve composition to
prepare sleeves, the sleeves prepared with the sleeve compositions,
and the use of the sleeves to prepare metal castings.
BACKGROUND OF THE INVENTION
[0002] A casting assembly typically consists of a pouring cup, a
gating system (including downsprue, choke, and runner), riser,
sleeve, mold, core, and other components. To produce a metal
casting, metal is poured into the pouring cup of the casting
assembly and passes through the gating system to the mold and/or
core assembly where it cools and solidifies. The metal part is then
removed by separating it from the core and/or mold assembly.
[0003] Risers or feeders are reservoirs that contain excess molten
metal. The excess molten metal is needed to compensate for
contractions or voids of metal that occur during the casting
process. Metal from the riser fills such voids in the casting when
the casting metal contracts. Thus the metal from the riser needs to
remain in a liquid state for a longer period of time, so it can
provide metal to the casting as it cools and solidifies. Sleeves
are used to surround or encapsulate the riser and other parts of
the casting assembly in order to keep the molten metal in the riser
hot and maintain it in the liquid state for a longer time.
[0004] In order to serve their function, sleeves have exothermic
and/or insulating properties. Exothermic sleeves function by
liberating heat. This liberated heat satisfies some or all of the
specific heat requirements of the riser and limits the temperature
loss of the molten metal in the riser, thereby keeping the metal
hotter and liquid longer. Insulating sleeves, on the other hand,
maintain the heat of the molten metal in the riser by insulating it
from the surrounding mold assembly.
[0005] For years sleeves were produced by "ramming", "vacuuming",
and "blowing or shooting", methods well known in the art. More
recently, it was discovered that sleeves could be made by
chemically curing a shaped sleeve mix with a curing catalyst by the
no-bake and cold-box process. See published application WO
97/35677, which hereby incorporated by reference. These processes
provide sleeves with improved dimensional accuracy.
[0006] Typical exothermic sleeve formulations contain aluminum as a
fuel, metal oxides and nitrates as oxidizers, and fluoride
containing compounds as fluxing agents. The aluminum is typically
used is granular and/or a powder, having a broad particle size
distribution, and is considered "coarse" in nature. The exothermic
sleeves prepared with this coarse aluminum produce an acceptable
exothermic reaction in most cases, but the surface finish of the
casting metal against the sleeve material is often "rough" because
the massive heat produced by the exotherm of the sleeve. This is a
concern to foundries because a rough casting surface finish
requires extra cleaning time and machining before the casting can
be used effectively. In some cases the surface finish is so rough
that the casting is defective and scrapped.
[0007] One method used to prevent the exotherm from the sleeve from
causing a poor surface finish is to move the riser sleeve away from
the casting assembly. By doing this, the casting is exposed to less
heat, and the risk of a poor surface finish is decreased. The
disadvantage of this remedy is that it increases the amount of
riser metal used, which lowers the casting yield.
[0008] An example of a method used to move the sleeve away from the
riser sleeve is the so-called "spring thorn". The spring thorn is a
"spring-loaded locator" that creates a gap between the riser sleeve
and the casting that allows sand to build-up between the riser
sleeve and the surface of the casting. This molding sand acts as a
barrier between the sleeve and the surface casting and keeps the
exotherm created by the riser away from the casting surface. The
spring thorn is particularly useful for mounting riser sleeves used
with high pressure, green sand molding equipment to cast metals.
Another way to reduce the negative impact of the sleeve's exotherm
on the surface finish of the casting is by adding a protective
layer of metal (a riser "pad") between the riser sleeve and the
casting assembly. After the casting is made and the riser is
removed from the casting, this additional pad of metal must be
removed from the casting. The disadvantage of this technique is
that it adds processing steps, which increases the cost of the
casting.
SUMMARY OF THE INVENTION
[0009] The invention relates to an exothermic sleeve mix
comprising:
[0010] (a) an oxidizable metal where the oxidizable metal comprises
fine aluminum as the major component, and
[0011] (b) an oxidizing agent capable of generating an exothermic
reaction.
[0012] The surface finish of the casting that is in contact with
the heat produced by the burning of the exothermic sleeve is
improved, if fine aluminum is used in the exothermic sleeve mix.
Smoother castings are made, similar to or better than that of cores
and molds made with sand. The sleeve compositions are used to make
castings from metals, e.g iron, duticle iron, steel, aluminum,
etc.
[0013] A smoother finish reduces the need for cleaning and
machining the casting. As a result, the exothermic riser sleeve can
be placed directly in contact with the surface of the casting.
Special mounting techniques, such as the so-called "spring thorn
locator" that increase the cost of making the casting, are not
required.
DEFINITIONS AND ABBREVIATIONS
[0014] The following definitions and abbreviations are
stipulated:
[0015] .mu.m - microns.
[0016] Casting assembly - assembly of casting components such as
pouring cup, gating system (downsprue, runner, choke), molds, core,
riser, sleeve, etc., which are used to make a metal casting.
[0017] ISOCURE.RTM. cold-box binder - a two part
polyurethane-forming cold-box binder where the Part I is a phenolic
resin similar to that described in U.S. Pat. No. 3,485,797. The
resin is dissolved in a blend of aromatic, ester, and aliphatic
solvents, and a silane. Part II is the polyisocyanate component,
and comprises a polymethylene polyphenyl isocyanate, a solvent
blend consisting primarily of aromatic solvents and a minor amount
of aliphatic solvents, and a benchlife extender. The weight ratio
of Part I to Part II is about 55:45.
[0018] Exothermic sleeve - a sleeve that has exothermic properties
compared to the mold/core assembly in which it is used.
[0019] Gating system - system through which metal is directed from
the pouring cup to the mold and/or core assembly. Components of the
gating system include the downsprue, runners, choke, etc.
[0020] Handleable - the ability of a sleeve to be transported from
one place to another without sagging or breaking.
[0021] Microspheres - alumino-silicate hollow spheres such as those
described in WO 97/35677.
[0022] Mold assembly - an assembly of molds and/or cores made from
a foundry aggregate (typically sand) and a foundry binder, which is
placed in a casting assembly to provide a shape for the
casting.
[0023] Riser - cavity connected to a mold or casting cavity of the
casting assembly which acts as a reservoir for excess molten metal
to prevent cavities in the casting as it contracts on
solidification.
[0024] Sleeve - any moldable shape having exothermic and/or
insulating properties made from a sleeve composition that covers,
in whole or part, any component of the casting assembly.
[0025] US Standard Screen Test 8"- test to determine particle size
distribution using set of sieves diameter and aperture sizes from 4
inches to 500 mesh.
BEST MODE AND OTHER MODES
[0026] The exothermic sleeve composition comprises (a) fine
aluminum and (b) an oxidizing agent. The sleeve compositions are
used to make sleeve mixes that contain (1) an exothermic sleeve
composition, and (2) an effective amount of a chemically reactive
inorganic or organic binder. The sleeve mix is shaped and cured by
contacting the sleeve with an effective amount of a curing
catalyst.
[0027] The fine aluminum, typically a powder, is defined as
aluminum having a particle distribution such that 95 weight percent
of the aluminum passes through 1 00 mesh as determined by the US
Standard Screen Test, preferably a particle distribution such that
more than 95 percent of the aluminum passes through the 140
mesh.
[0028] Aluminum can be used as a pure metal, as an alloy with
magnesium, silicon, copper, or possibly a component of a waste
material. Although not preferred for achieving the best surface
finish, minor amounts of coarse aluminum can be mixed with the fine
aluminum to reduce the cost of the sleeve composition.sup.1, for
instance up to 15 weight percent based on the amount of aluminum,
preferably less than 5 weight percent. Coarse aluminum is aluminum
having a particle distribution outside the definition stipulated
for fine aluminum. .sup.1Existing commercial formulations contain
large amount of coarse Al, up to 100 weight %, where the weight
percent is based upon the total weight of aluminum used. But the
surface finish of casting is usually very poor, resulting in
extensive machining.
[0029] The oxidizing agent used for the exothermic sleeve includes
iron oxide, manganese oxide, nitrates, potassium permanganate, etc.
Oxides do not need to be present at stoichiometric levels to
satisfy the metal aluminum fuel component since the riser sleeves
and molds in which they are contained are permeable. Thus oxygen
from the oxidizing agents is supplemented by atmospheric oxygen
when the aluminum fuel is burned. Typically the weight ratio of
aluminum to oxidizing agent is from about 10:1 to about 1:1,
preferably about 5:1 to about 1.5:1.
[0030] Depending upon the degree of exothermic properties wanted in
the sleeve, the amount of fine aluminum in the sleeve composition
will range from 5 weight percent to 45 weight percent, typically 20
weight percent to 35 weight percent, based upon the weight of the
sleeve composition.
[0031] Insulating materials can be added to the sleeve composition.
Such materials include refractory materials (e.g. magnesia,
alumina, sand, and aluminosilicate), hollow microspheres, and
fibers. The amount of insulating material in the sleeve composition
ranges from 30 weight percent to 85 weight percent, typically 30
weight percent to 70 weight percent, where the weight percent is
based upon the weight of the sleeve composition. Preferably used as
the insulating material are hollow aluminosilicate microspheres
such as those described in WO 97/35677, which is hereby
incorporated by reference.
[0032] The sleeve mixes can also contain refractories such as
silica, sand, magnesia, alumina, olivine, chromite,
aluminosilicate, and silicon carbide among others. These
refractories are preferably used in amounts less than 60 weight
percent based upon the weight of the sleeve composition, more
preferably less than 25 weight percent based upon the weight of the
sleeve composition.
[0033] In addition, the sleeve composition may contain fillers,
additives, and fluxes, such as cryolite (Na.sub.3AlF.sub.6),
potassium aluminum tetrafluoride, potassium aluminum
hexafluoride.
[0034] The sleeve compositions are mixed with chemical binders to
form a sleeve mix. Any inorganic or organic foundry binder, that
sufficiently holds the sleeve mix together in the shape of a sleeve
and polymerizes in the presence of a curing catalyst, will work.
Examples of such binders include inorganic binders such as sodium
silicate binders cured with carbon dioxide (see U.S. Pat. No.
4,985,489 which is hereby incorporated into this disclosure by
reference), and organic binders such as phenolic resins, phenolic
urethane binders, furan binders, alkaline phenolic resole binders
(see U.S. Pat. No. 4,750,716 which is hereby incorporated by
reference), and epoxy-acrylic binders among others. Preferred
binders include epoxy-acrylic binders sold by Ashland Inc. under
the ISOSET.RTM. trademark. 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. Most preferred as the binder are amine
curable phenolic urethane binders, are described in U.S. Pat. No.
3,485,497, U.S. Pat. Nos. 3,409,579, and 3,676,3923, 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.
[0035] The amount of binder needed is an effective amount to
maintain the shape of the sleeve and allow for effective curing,
i.e. which will produce a sleeve which can be handled or
self-supported after curing. An effective amount of binder is
greater than about 4 weight percent, based upon the weight of the
sleeve composition. Preferably the amount of binder ranges from
about 5 weight percent to about 15 weight percent, more preferably
from about 6 weight percent to about 12 weight percent.
[0036] Curing the sleeve by the no-bake process takes place by
mixing a liquid curing catalyst with the sleeve mix, shaping the
sleeve mix containing the catalyst, and allowing the sleeve 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.
[0037] Curing the sleeve by the cold-box process takes place by
blowing or ramming the sleeve mix into a pattern and contacting the
sleeve 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 resin. Carbon dioxide (see U.S. Pat. No.
4,985,489, which is hereby incorporated 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.
[0038] Preferably sleeves are prepared by a cold-box process with a
phenolic urethane binder by passing a tertiary amine gas, such a
triethylamine, through the molded sleeve mix in the manner as
described in U.S. Pat. No. 3,409,579; or with an 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 2.0
seconds. Purge times are from 1.0 to 60 seconds, preferably from
1.0 to 10 seconds.
EXAMPLES
(General Procedure)
[0039] The exothermic sleeves were prepared with phenolic-urethane
binder using cold-box technology. The exothermic composition
contained aluminosilicate microspheres, aluminum powder, iron
oxide, manganese dioxide, potassium nitrate and cryolite. Those
components were mixed with an ISOCURE.RTM. Part I and Part II
binder and then cured with an amine catalyst using conventional
cold box technology. The sleeves were then tested for casting
performance in a ductile iron test casting. Evaluation of the
resulting castings included the safety margin of the riser and an
analysis of the surface finish of casting. All parts are by weight
and all percentages are weight percentages based upon the weight of
the sleeve composition unless otherwise specified.
Example A, B, 1, and 2
(Preparation of sleeve compositions)
[0040] Sleeve compositions were prepared by mixing the following
components with the aluminum powder described in Table I. The "fine
aluminum" and "coarse aluminum" used in the examples are described
in Table II.
1TABLE I (Exothermic sleeve composition) Component Amount
(pbw).sup.2 Microspheres 51 Potassium nitrate 8 Cryolite 3
MnO.sub.2 5 Fe.sub.3O.sub.4 5 Aluminum powder (Table II) 28
[0041]
2TABLE II PARTICLE SIZE DISTRIBUTION OF THE COARSE AND FINE
ALUMINUM USED IN THE SLEEVE COMPOSITION Weight % particle retained
on Mesh Aluminum Composition A 1 2 B.sup.3 Mesh no. .mu.m Coarse
Fine Fine Mixture 40 425 0 0 0 0 70 212 26 0 0 13 100 150 34 0 0 17
140 106 33 0 2 16.5 200 75 6 7 7 6.5 325 45 1 20 21 10.5 Pan <45
0 73 70 36.5 .sup.2Where pbw is based upon the total parts of
components used in the sleeve mix. .sup.3Sleeve composition B was a
50/50 weight percent mixture of mix A (coarse aluminum) and B (fine
aluminum).
Examples C, D, and 3, and 4
(Preparation of sleeves and sleeve mixes from aluminum compositions
A, B, 1, and 2)
[0042] Sleeves (C, D, 3, and 4) were prepared by mixing the
aluminum compositions (A, B, 1, and 2) with 8.8 parts of
ISOCURE.RTM. cold-box binder. Test sleeves (2".times.3") were
prepared by the ISOCURE.RTM. cold-box process along the lines
described in WO 97/35677, which is hereby incorporated by
reference.
Example E, F, and 5, and 6
(Preparation of castings from the sleeves C, D, 3, and 4)
[0043] Ductile iron castings were prepared from casting assemblies
where sleeves C, D, 3, and 4 were used to surround the top riser of
the casting assembly respectively. The test casting made is an
impeller casting having a weight of about 5.5 kg. and uses a
2".times.3" riser to feed the casting. The metal is poured down the
sprue from the side, filling the casting cavity first and then the
riser. The pouring temperature was 1400.degree. C. The surface
finish of the castings in contact with the sleeve was compared. The
results of the casting experiments are summarized in Table III
below. The safety margin of all the sleeved risers was measured and
was more than adequate.
3TABLE III (CASTING RESULTS) CASTING EXAMPLE SLEEVE Al
RESULTS/SURFACE FINISH G C Coarse (A) Poor H D Mix (B) Poor 6 3
Fine (1) Excellent 7 4 Fine (2) Excellent
[0044] The observations recorded in Table III indicate that the
ductile iron castings made with the sleeves that contained the fine
aluminum had excellent surface finish, while the castings prepared
with the sleeves that contained the coarse aluminum had poor
surface finish.
* * * * *