U.S. patent application number 10/293920 was filed with the patent office on 2003-08-21 for sand casting foundry composition and method using thermally collapsible clay minerals as an anti-veining agent.
Invention is credited to Brown, Richard K., Lafay, Victor S..
Application Number | 20030155098 10/293920 |
Document ID | / |
Family ID | 47019203 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155098 |
Kind Code |
A1 |
Brown, Richard K. ; et
al. |
August 21, 2003 |
Sand casting foundry composition and method using thermally
collapsible clay minerals as an anti-veining agent
Abstract
A sand casting foundry composition reduces thermal defects that
cause veining in metal parts cast from sand casting foundry shapes
formed from the foundry composition. Foundry sand grains are mixed
substantially uniformly with thermally collapsible clay mineral
particles, and a curable binder coats the sand grains and the
thermally collapsible clay mineral particles to establish core and
mold foundry shapes used to cast the metal part. Anti-veining
capability occurs because the thermally collapsible clay mineral
particles exhibit an inherent characteristic of crystal structure
collapse upon exposure to temperatures encountered in casting the
metal part. The crystal structure collapse yields space which is
consumed by thermal expansion of the sand grains in the foundry
composition. This compensatory effect avoids the creation of
mechanical forces and stresses within the foundry shape that cause
the cracks and fissures in the foundry shape that lead to
veining.
Inventors: |
Brown, Richard K.;
(Billings, MT) ; Lafay, Victor S.; (Cincinnati,
OH) |
Correspondence
Address: |
John R. Ley
Suite 610
5299 DTC Boulevard
Greenwood Village
CO
80111
US
|
Family ID: |
47019203 |
Appl. No.: |
10/293920 |
Filed: |
November 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60332679 |
Nov 14, 2001 |
|
|
|
Current U.S.
Class: |
164/529 |
Current CPC
Class: |
C04B 2111/0087 20130101;
C04B 14/108 20130101; B22C 1/02 20130101; C04B 26/16 20130101; C04B
14/06 20130101; C04B 2111/00939 20130101; C04B 26/16 20130101 |
Class at
Publication: |
164/529 |
International
Class: |
B22C 001/04 |
Claims
I claim:
1. A foundry composition which reduces thermal defects that cause
veining in metal parts cast from sand casting foundry shapes formed
from the foundry composition, comprising: a plurality of foundry
sand grains; a plurality of thermally collapsible clay mineral
particles substantially uniformly distributed throughout the sand
grains to form a matrix of sand grains and thermally collapsible
clay mineral particles; and a curable binder coating the sand
grains and the thermally collapsible clay mineral particles to hold
the sand grains and thermally collapsible clay mineral particles
within the matrix in a predetermined position upon curing.
2. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles have an inherent
characteristic of crystal structure collapse upon exposure to a
temperature to which the foundry shapes are subjected from molten
metal when casting the metal part; and the thermally collapsible
clay mineral particles are weakened by the crystal structure
collapse to achieve at least one of a reduction in physical size of
the thermally collapsible clay mineral particles, disintegration of
the thermally collapsible clay mineral particles into smaller
physical sizes or a reduced capacity to resist compression and
deformation from external forces.
3. A foundry composition as defined in claim 2, wherein: the
thermally collapsible clay mineral particles undergo crystal
structure collapse at peak endothermic temperatures in the range of
about 600.degree. C. to about 700.degree. C.
4. A foundry composition as defined in claim 2, wherein: the sand
grains have an inherent characteristic of expansion in physical
size upon exposure to a temperature to which the foundry shapes are
subjected from molten metal when casting the part; and at least one
of the reduction in physical size of the thermally collapsible clay
mineral particles, the disintegration of the thermally collapsible
clay mineral particles into smaller physical sizes or the
compression and deformation of the thermally collapsible clay
mineral particles occurs from expansion in physical size of the
sand grains.
5. A foundry composition as defined in claim 4, wherein: the
temperature at which the thermally collapsible clay mineral
particles experience crystal structure collapse is within a range
of temperatures similar to those at which the sand grains will have
achieved their maximum rate of thermal expansion and most of their
physical thermal expansion.
6. A foundry composition as defined in claim 5, wherein: the
temperature at which the sand grains experience their maximum rate
of thermal expansion and most of their physical thermal expansion
is approximately 650.degree. C.
7. A foundry composition as defined in claim 2, wherein: the
thermally collapsible clay mineral particles undergo crystal
structure collapse at peak endothermic temperatures in the range of
about 600.degree. C. to about 700.degree. C.
8. A foundry composition as defined in claim 1, wherein. the sand
grains have an inherent characteristic of expansion in physical
size upon exposure to a temperature to which the foundry shapes are
subjected from molten metal when casting the metal part; the
thermally collapsible clay mineral particles have an inherent
characteristic of crystal structure collapse upon exposure to a
temperature to which the foundry shapes are subjected from molten
metal when casting the metal part; and the crystal structure
collapse of the thermally collapsible clay mineral particles yields
sufficient volumetric space within the matrix to compensate for an
increase in volume created by the thermal expansion of the sand
grains at the temperature to which the foundry shapes are subjected
from the molten metal when casting the metal part.
9. A foundry composition as defined in claim 8, wherein: a
volumetric quantity of the thermally collapsible clay mineral
particles and a distribution of thermally collapsible clay mineral
particles within the matrix yield volumetric space distributed
within the matrix resulting from the crystal structure collapse
which is sufficient to accept an increase in physical dimension of
the sand grains from thermal expansion at the temperature to which
the foundry shapes are subjected from molten metal when casting the
metal part.
10. A foundry composition as defined in claim 8, wherein: a
volumetric quantity of the thermally collapsible clay mineral
particles and a distribution of the thermally collapsible clay
mineral particles within the matrix and a size of the thermally
collapsible clay mineral particles yield volumetric space
throughout the matrix which approximately counterbalances an amount
of expansion in physical dimension of the sand grains throughout
the matrix at the temperature to which the foundry shapes are
subjected from molten metal when casting the metal part.
11. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles have an inherent
characteristic of crystal structure collapse upon exposure to a
temperature to which the foundry shapes are subjected from molten
metal when casting the metal part; and a volumetric quantity of the
thermally collapsible clay mineral particles and a size of the
thermally collapsible clay mineral particles within the matrix
separate a sufficient number of the sand grains from adjoining sand
grains within the matrix to yield sufficient volumetric space
within the matrix at the temperature at which crystal structure
collapse occurs to compensate for an increase in volume created by
thermal expansion of the sand grains upon exposure to the
temperature to which the foundry shapes are subjected from the
molten metal when casting the metal part.
12. A foundry composition as defined in claim 11, wherein: the
thermally collapsible clay mineral particles are particles of clay
selected from the group consisting of bentonite, kaolin and
attapulgite.
13. A foundry composition as defined in claim 11, wherein: the
thermally collapsible clay mineral particles are particles of
bentonite clay.
14. A foundry composition as defined in claim 11, wherein: the
thermally collapsible clay mineral particles include clay minerals
selected from the group consisting of illite, illite-smectite mixed
layer clay minerals, chlorite, halloysite, kaolinite, sepiolite,
palygorskite, montmorillonite, beidelite, nontronite, saponite and
hectorite.
15. A foundry composition as defined in claim 11, wherein: the
thermally collapsible clay mineral particles are particles of clay
minerals selected from the group consisting of sodium bentonite,
calcium bentonite, a mixture of sodium and calcium bentonite, or a
bentonite with any exchangeable cation.
16. A foundry composition as defined in claim 1, wherein: the sand
grains are foundry sand grains.
17. A foundry composition as defined in claim 16, wherein: the
foundry sand grains are substantially silica sand grains.
18. A foundry composition as defined in claim 1, wherein: the
binder is a resin-type chemical binder.
19. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles are in a free flowing
particulate form prior to distribution within the sand grains and
have a particle size in the range of about 75 micrometers to 3.4
millimeters.
20. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles are in a free flowing
particulate form prior to distribution within the sand grains and
have a particle size in the range of about 425 micrometers to 2.0
millimeters.
21. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles have a moisture
content of from 0.1% to about 12% prior to distribution within the
sand grains.
22. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles have a moisture
content of from 3% to about 5% prior to distribution within the
sand grains.
23. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles form about 1% to 15%
of the dry weight of the foundry composition.
24. A foundry composition as defined in claim 1, wherein: the
thermally collapsible clay mineral particles form about 1% to 7% of
the dry weight of the foundry composition.
25. A method of making a foundry composition which reduces thermal
defects that cause veining in metal parts cast from sand casting
foundry shapes formed from the foundry composition, comprising:
mixing a plurality of foundry sand grains and a plurality of
thermally collapsible clay mineral particles to form a mixture in
which the thermally collapsible clay mineral particles are
substantially uniformly distributed among the sand grains in the
mixture; and coating the mixture of sand grains and thermally
collapsible clay mineral particles with a binder sufficient to hold
the mixture of sand grains and thermally collapsible clay mineral
particles in the foundry shapes after the binder is cured.
26. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles with an inherent
characteristic of crystal structure collapse upon exposure to a
temperature to which the foundry shapes are subjected from molten
metal when casting the metal part.
27. A method as defined in claim 26, further comprising: selecting
the thermally collapsible clay mineral particles to weaken by
crystal structure collapse upon exposure to the temperature to
which the foundry shapes are subjected from molten metal when
casting the metal part to achieve at least one of a reduction in
physical size of the thermally collapsible clay mineral particles,
disintegration of the thermally collapsible clay mineral particles
into smaller physical sizes or a reduced capacity to resist
compression and deformation from external forces.
28. A method as defined in claim 27, further comprising:
distributing the thermally collapsible clay mineral particles
within the mixture by mixing the thermally collapsible clay mineral
particles and the sand grains; selecting thermally collapsible clay
mineral particles of a predetermined size for distribution within
the mixture; selecting a predetermined volumetric quantity of
thermally collapsible clay mineral particles at the predetermined
sizes for distribution within the mixture; and selecting the
predetermined sizes and volumetric quantities and distributing the
thermally collapsible clay mineral particles to yield volumetric
space within the foundry shape resulting from crystal structure
collapse which is sufficient to accept an increase in physical
dimension of the sand grains from thermal expansion at the
temperature to which the foundry shapes are subjected from molten
metal when casting the metal part.
29. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles to undergo crystal
structure collapse when subjected to peak endothermic temperatures
in a range of about 600.degree. C. to about 700.degree. C.
30. A method as defined in claim 29, further comprising: selecting
the sand grains with a characteristic of achieving their maximum
rate of thermal expansion and most of their physical thermal
expansion at temperatures of about 650.degree. C.
31. A method as defined in claim 25, further comprising: selecting
the sand grains with a characteristic of having achieved their
maximum rate of thermal expansion and most of their physical
thermal expansion at approximately a peak endothermic temperature
at which the mineral components of the thermally collapsible clay
mineral particles undergo crystal structure collapse.
32. A method as defined in claim 25, further comprising: selecting
thermally collapsible clay mineral particles of a volumetric
quantity and with a predetermined size to separate a sufficient
number of the sand grains from adjoining sand grains within the
matrix to yield sufficient volumetric space within the foundry
shapes at the temperature at which crystal structure collapse
occurs to compensate for an increase in volume created by thermal
expansion of the sand grains upon exposure to the temperature to
which the foundry shapes are subjected from the molten metal when
casting the metal part.
33. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles as particles of
clay selected from a group consisting of bentonite, kaolin and
attapulgite.
34. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles from the group
consisting of sodium bentonite, calcium bentonite, a mixture of
sodium and calcium bentonite, or a bentonite with any exchangeable
cation.
35. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles to include clay
minerals selected from the group consisting of illite,
illite-smectite mixed layer clay minerals, chlorite, halloysite,
kaolinite, sepiolite, palygorskite, montmorillonite, beidelite,
nontronite, saponite and hectorite.
36. A method as defined in claim 25, further comprising: using a
resin-type chemical binder to coat the mixture.
37. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles to have a
free-flowing particulate form prior to inclusion in the mixture and
with a particle size in the range of about 75 micrometers to 3.4
millimeters.
38. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles to have a free
flowing particulate form prior to inclusion in the mixture and with
a particle size in the range of about 425 micrometers to 2.0
millimeters.
39. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles to have a moisture
content of from 0.1% to about 12% prior to mixing with the sand
grains.
40. A method as defined in claim 25, further comprising: selecting
the thermally collapsible clay mineral particles to have a moisture
content of from 3% to about 5% prior to mixing with the sand
grains.
41. A method as defined in claim 25, further comprising: adding the
binder to the mixture after the sand grains and thermally
collapsible clay mineral particles have been mixed to form the
mixture; and coating the mixture with the binder added to the
mixture.
42. A method as defined in claim 25, further comprising: using
thermally collapsible clay mineral particles in the mixture in an
amount of about 1% to 15% of the dry weight of the mixture.
43. A method as defined in claim 25, further comprising: using
thermally collapsible clay mineral particles in the mixture in an
amount of about 1% to 7% of the dry weight of the mixture.
44. A method of making a foundry shape which reduces thermal
defects that cause veining in metal parts cast from the foundry
shapes, comprising: mixing a plurality of foundry sand grains with
a plurality of thermally collapsible clay mineral particles to form
a mixture in which the thermally collapsible clay mineral particles
are substantially uniformly distributed among the sand grains in
the mixture; coating the mixture of sand grains and the thermally
collapsible clay mineral particles with a binder sufficient to hold
the sand grains and thermally collapsible clay mineral particles in
position relative to one another after the binder has cured;
shaping the binder-coated mixture into a predetermined
configuration defining the foundry shape; and curing the binder
while maintaining the predetermined configuration to establish the
foundry shape.
45. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles with an inherent
characteristic of crystal structure collapse upon exposure to a
temperature to which the foundry shape is subjected from molten
metal when casting the metal part.
46. A method as defined in claim 45, further comprising: selecting
the thermally collapsible clay mineral particles to weaken by the
crystal structure collapse upon exposure to the temperature to
which the foundry shapes are subjected from molten metal when
casting the metal part to achieve at least one of a reduction in
physical size of the thermally collapsible clay mineral particles,
disintegration of the thermally collapsible clay mineral particles
into smaller physical sizes or a reduced capacity to resist
compression and deformation from external forces.
47. A method as defined in claim 46, further comprising:
distributing the thermally collapsible clay mineral particles
within the mixture by mixing the thermally collapsible clay mineral
particles with the sand grains; selecting thermally collapsible
clay mineral particles of a predetermined size for distribution
within the mixture; selecting a predetermined volumetric quantity
of thermally collapsible clay mineral particles at the
predetermined sizes for distribution within the mixture; and
selecting the predetermined sizes and volumetric quantities and
distributing the thermally collapsible clay mineral particles to
yield volumetric space within the foundry shapes resulting from
crystal structure collapse which is sufficient to accept an
increase in physical dimension of the sand grains from thermal
expansion at the temperature to which the foundry shapes are
subjected from molten metal when casting the metal part.
48. A method as defined in claim 46, further comprising: selecting
the predetermined sizes of the thermally collapsible clay mineral
particles to separate a sufficient number of the sand grains from
adjoining sand grains within the foundry shapes to yield sufficient
volumetric space within the foundry shapes at the temperature at
which crystal structure collapse occurs to compensate for an
increase in volume created by thermal expansion of the sand grains
upon exposure to the temperature to which the foundry shapes are
subjected from the molten metal when casting the metal part.
49. A method as defined in claim 44, further comprising: selecting
a resin-type chemical binder to coat the mixture.
50. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles as particles of
clay selected from a group consisting of bentonite, kaolin and
attapulgite.
51. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles from the group
consisting of sodium bentonite, calcium bentonite, a mixture of
sodium and calcium bentonite, or a bentonite with any exchangeable
cation.
52. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles to include clay
minerals selected from the group consisting of illite,
illite-smectite mixed layer clay minerals, chlorite, halloysite,
kaolinite, sepiolite, palygorskite, montmorillonite, beidelite,
nontronite, saponite and hectorite.
53. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles to have a
free-flowing particulate form prior to inclusion in the mixture and
with a particle size in the range of about 75 micrometers to 3.4
millimeters.
54. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles to have a free
flowing particulate form prior to inclusion in the mixture and with
a particle size in the range of about 425 micrometers to 2.0
millimeters.
55. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles to have a moisture
content of from 0.1% to about 12% prior to mixing with the sand
grains.
56. A method as defined in claim 44, further comprising: selecting
the thermally collapsible clay mineral particles to have a moisture
content of from 3% to about 5% prior to mixing with the sand
grains.
57. A method as defined in claim 44, further comprising: adding the
binder to the mixture after the sand grains and thermally
collapsible clay mineral particles have been mixed to form the
mixture; and coating the mixture with the binder added to the
mixture.
58. A method as defined in claim 44, further comprising: using
thermally collapsible clay mineral particles in the mixture in an
amount of about 1% to 15% of the dry weight of the mixture.
59. A method as defined in claim 44, further comprising: using
thermally collapsible clay mineral particles in the mixture in an
amount of about 1% to 7% of the dry weight of the mixture.
60. A method of casting a metal part using core and mold foundry
shapes formed by the method defined in claim 44, comprising:
positioning the core and mold foundry shapes relative to one
another to define the metal part to be cast; pouring molten metal
between the core and mold foundry shapes; and solidifying the
molten metal while confined between the core and mold foundry
shapes.
61. A method as defined in claim 60, further comprising: removing
the cast part from the core and mold foundry shapes after the metal
has solidified.
62. A metal part cast by using the method defined in claim 61.
Description
CROSS-REFERENCE TO RELATED U.S. APPLICATION
[0001] This invention and application is related to and claims the
benefit of U.S. Provisional application titled "Method for
Producing Foundry Shapes," Serial No. 60/332,679, filed Nov. 14,
2001, of which the present applicants are inventors. The subject
matter of this provisional patent application is incorporated
herein by this reference.
FIELD OF THE INVENTION
[0002] This invention relates to foundry techniques used to create
sand cast metal parts. More particularly, the present invention
relates to a new and improved sand casting foundry composition and
method using thermally collapsible clay minerals as an anti-veining
agent to prevent veining defects in the cast metal parts.
BACKGROUND OF THE INVENTION
[0003] Sand casting is a process used in the foundry industry to
produce cast parts. In sand casting, disposable foundry shapes are
made by forming a sand-based foundry composition into predetermined
configurations and curing the composition to preserve those foundry
shapes. A binder in the foundry composition maintains the
predetermined configuration of the foundry shape. The foundry shape
which defines the exterior of the resulting cast part, known as a
mold, is positioned relative to the foundry shape which defines the
interior of the cast part, known as a core. With the mold and the
core foundry shapes oriented as desired, molten metal is poured
between them. The foundry shapes confine the molten metal while it
cools and solidifies into the resulting cast part.
[0004] The binder must have the capability to preserve the
predetermined configurations of the mold and core foundry shapes
while those foundry shapes are oriented in the appropriate
relationship to create the cast parts and during the time while the
molten metal solidifies into the cast part. The typical type of
foundry sand used for this purpose is silica sand, although other
useful foundry sands include chromite, zircon and olivine sands.
Two basic types of binders are commonly employed: inorganic
binders, such as clay, and chemical binders, such as phenolic resin
binders.
[0005] The most widely used inorganic binder for a sand-based
foundry composition is bentonite clay. The foundry composition of
the sand and bentonite clay binder is referred to as green sand.
Green sand is a water tempered sand mixture having plasticity. A
green sand foundry composition is typically formed by mulling
silica sand, bentonite and a small amount of tempering water. The
tempering water allows the bentonite to become sufficiently plastic
so that it may be smeared relatively uniformly and thinly over the
sand grains during the mulling process. The thin coating of the
bentonite on each sand grain interacts with the thin coating on the
adjacent sand grains causing the sand grains to be held in place in
the mold and core foundry shapes. Green sand molding is economical
and is widely used to cast ferrous as well as non-ferrous metal
parts. Green sand molding permits high quantity, high quality
foundry production, particularly for smaller cast parts.
[0006] Chemically-bonded, sand-based foundry compositions use a
variety of polymerizable or curable organic and inorganic resin
binders to hold the sand grains together in the desired mold or
core shape. Chemical bonding involves mixing the sand and a
polymerizable or curable binder. Once the mixture of the sand
grains and the uncured binder have been shaped into the desired
configuration, the chemical binder is polymerized or cured by the
addition of a catalyst and/or heat, resulting in converting the
shaped configuration into hard, solid, cured mold or core foundry
shapes. Examples of curable resin binders include phenolic and
furan resins. In a typical no-bake process, i.e. one which does not
involve the addition of heat for curing, the sand, binder, and a
liquid curing catalyst are mixed and compacted to produce the
desired configurations of the mold or core foundry shapes. A
commonly used no-bake binder is a polyurethane binder, derived by
curing a polyurethane forming binder material with a liquid
tertiary amine catalyst.
[0007] When subjected to the heat of the molten metal, the sand
grains in mold and core foundry shapes expand. If the sand grains
in the molds and cores are too close together, the sand grains
expand in size and push on the adjacent sand grains. The thermal
expansion opens up small cracks and fissures in the molds and
cores, and the molten metal penetrates into those cracks and
fissures. When the molten metal solidifies, raised, narrow ridges
on the surfaces of the cast part result at those locations where
the molten metal penetrated into the small cracks and fissures. The
resulting narrow ridges are referred to as "veins" or "veining".
The veining may make it necessary to surface grind or machine away
the projecting veins. Of course, such surface grinding or machining
increases the cost of producing the cast part.
[0008] Another type of foundry shape defect is caused by gas
formation, particularly within core foundry shapes. Water in green
sand casting foundry compositions will volatilize into steam in the
presence of the hot molten metal. Trapped steam may cause pin holes
or cracks in the foundry shape, resulting in the metal penetration
into the foundry shape. The gas may also create an uneven or
discontinuous surface in the cast part. Gas pressure also results
from the volatilization of certain chemical constituents in foundry
compositions. It is desirable to use chemical binders which are not
susceptible to excessive volatilization, particularly in core
foundry shapes.
[0009] Expansion and cracking from gas pressure is more of a
problem in core foundry shapes, because core foundry shapes are
typically surrounded by the molten metal due to their internal
position. Those binders which produce significant amounts of gas
when exposed to metallurgical temperatures may only be used in
foundry shapes where the confined gas has an avenue to escape,
otherwise the gas itself may induce cracks, fissures and pin holes.
Mold foundry shapes are exposed to the ambient atmosphere and
therefore provide avenues for the gas pressure to escape, although
the gas pressure may nevertheless create defects in mold foundry
shapes. To avoid excessive gas creation where a clay binder is
used, the amount of tempering water used to activate the clay
binders and allow it to be smeared over the sand grains is
limited.
[0010] A wide variety of different agents have been added to sand
casting foundry compositions in an attempt to improve the
properties of core and mold foundry shapes to avoid veining and
other casting defects. These additives, known generically as
anti-veining agents, include starch based products, dextrin, fine
ground glass particles, red talc and wood flour, i.e. particles of
wood coated with a resin, granular slag, pulverized sea-coal,
alkaline earth or alkaline metal fluoride, and lithia-containing
materials, among many other things. Several types of iron oxide are
also used as anti-veining agents. These include red iron oxide,
also known as hematite (Fe.sub.2O.sub.3), black iron oxide, also
known as magnetite (Fe.sub.3O.sub.4), yellow ochre, and a black
hematite known as Sierra Leone concentrate.
[0011] Each of these anti-veining agents are theorized to function
in a different way to avoid or reduce the incidence of cracks,
fissures and the other defects in the foundry shapes which cause
veining. It is generally believed that the iron oxides increase the
hot plasticity of the sand mixture by the formation of a glassy
layer between the sand grains. The glassy layer deforms without
fracturing at metallurgical temperatures, to prevent fissures in
the foundry shapes. Grains of slag are thought to become soft at
metallurgical temperatures permitting the sand grains to expand.
Sea-coal and other combustible anti-veining agents are believed to
form volatile gas at metallurgical temperatures leaving void space
into which the sand grains expand.
SUMMARY OF THE INVENTION
[0012] The present invention relates to the use of thermally
collapsible clay mineral particles as an anti-veining agent in a
sand casting foundry composition used to create foundry shapes for
casting metal parts. The thermally collapsible clay mineral
particles include clay minerals that undergo crystal structure
collapse when the foundry shape is heated by the molten metal
during casting. With a sufficient concentration or volumetric
quantity of thermally collapsible clay mineral particles
distributed within the foundry shape, and with sufficient sizes of
the thermally collapsible clay mineral particles, the collapse of
the crystal structure will cause the thermally collapsible clay
mineral particles to yield space within the foundry shape
sufficient to compensate for the thermally-induced physical
expansion of the sand grains. The net result is a negligible change
in volume of the foundry shape during heating, thereby avoiding the
mechanical forces which cause cracks and fissures in the foundry
shape that result in veining.
[0013] The volumetric quantity of the thermally collapsible clay
mineral particles necessary to yield the physical volume sufficient
to compensate for the physical expansion of the sand grains may be
achieved by using a relatively larger number of relatively smaller
physically-sized particles or a relatively smaller number of
relatively larger physically-sized particles in the foundry
composition. An advantage of using a relatively smaller number of
relatively larger sized particles is that less resin binder is
consumed by the thermally collapsible clay mineral particles. Resin
binder is added to and mixed with the mixture of the sand grains
and thermally collapsible clay mineral particles to form the
foundry composition. Since resin binder is expensive, it is
important to limit the quantity used to the smallest amount
necessary to achieve adequate tensile strength of the foundry
shapes to resist breakage or deformation when the foundry shapes
are positioned to cast the metal part and while confining the
molten metal as its solidifies into the cast part. More surface
area is exhibited by a larger number of smaller sized particles as
compared to a smaller number of larger sized particles which occupy
the same volumetric space. The amount of resin binder consumed is
directly related to the surface area of the particles which must be
coated with that resin binder, and it is for this reason that a
relatively fewer number of relatively larger sized thermally
collapsible clay mineral particles is preferred.
[0014] These and other improvements are obtained in a number of
different forms of the present invention. A sand casting foundry
composition reduces thermal defects that cause veining in metal
parts cast from sand casting foundry shapes formed from the foundry
composition. Such a foundry composition comprises a plurality of
foundry sand grains, a plurality of thermally collapsible clay
mineral particles substantially uniformly distributed among the
sand grains to form a matrix of sand grains and thermally
collapsible clay mineral particles, and a curable binder coating
the sand grains and the thermally collapsible clay mineral
particles to hold sand grains and the thermally collapsible clay
mineral particles in position within the matrix upon curing. A
method of making the foundry composition involves mixing a
plurality of foundry sand grains with a plurality of thermally
collapsible clay mineral particles to form a mixture in which the
thermally collapsible clay mineral particles are substantially
uniformly distributed within the sand grains in the mixture, and
coating the mixture of sand grains and the thermally collapsible
clay mineral particles with a binder sufficient to hold sand grains
and thermally collapsible clay mineral particles in position
relative to one another after curing of the binder. A method of
making a foundry shape from the foundry composition involves mixing
a plurality of foundry sand grains with a plurality of thermally
collapsible clay mineral particles to form a mixture in which the
thermally collapsible clay mineral particles are substantially
uniformly distributed among the sand grains in the mixture, coating
the mixture of sand grains and thermally collapsible clay mineral
particles with a binder sufficient to hold the sand grains and clay
particles in place relative to one another after curing of the
binder, shaping the binder-coated mixture into a predetermined
configuration of the foundry shape, and curing the binder while
maintaining the predetermined configuration. A method of casting a
metal part using core and mold foundry shapes formed in this manner
involves positioning the core and mold foundry shapes relative to
one another to define the metal part to be cast, pouring molten
metal in the space between the core and mold foundry shapes, and
solidifying the molten metal while confined between the core and
mold foundry shapes.
[0015] These aspects of the invention may also be supplemented by
further preferable improvements. The thermally collapsible clay
mineral particles are selected to have a clay mineral with a
crystal structure that collapses upon exposure to the temperature
created by molten metal used in casting the metal part. Upon
collapse of the crystal structure, the thermally collapsible clay
mineral particles yield sufficient volumetric space to compensate
for and counterbalance the additional volumetric space consumed by
the thermal expansion of the sand grains, thereby avoiding the
creation of mechanical forces and stresses within the foundry shape
that lead to veining. The volumetric concentration and size of
thermally collapsible clay mineral particles determines the desired
yield volume to compensate for the thermal expansion of the sand.
The binder is preferably added after the sand grains and thermally
collapsible clay mineral particles have been mixed, thereby
facilitating the homogenous distribution of the thermally
collapsible clay mineral particles among the sand grains while
evenly coating the sand grains and thermally collapsible clay
mineral particles sufficiently to hold them together in the
predetermined desired foundry shape. This sequence of addition will
lead to less use of binder than if the binder is added before the
sand grains and the thermally collapsible clay mineral particles
have been mixed together. There are many other desirable
improvements described herein which may be practiced with the
different aspects of the present invention.
[0016] A more complete appreciation of the scope of the present
invention and the manner in which it achieves the above-noted and
other improvements can be obtained by reference to the following
detailed description of the presently preferred embodiments taken
in connection with the accompanying drawings, which are briefly
summarized below, and by reference to the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a combined diagrammatic illustration of the
components of a sand casting foundry composition and a flow chart
of the steps of making the sand casting foundry composition and of
the steps of using the sand casting foundry composition to produce
core and mold foundry shapes, according to the present
invention.
[0018] FIG. 2 is a flow chart illustrating the use of the foundry
shapes formed as shown in FIG. 1 to produce a cast part.
[0019] FIG. 3 is an idealized structural illustration of a few
randomly oriented sand grains which are separated by a thermally
collapsible clay mineral particle in the sand casting foundry
composition and foundry shape described in FIG. 1.
[0020] FIG. 4 is an enlarged partial view of FIG. 3, showing in an
idealized, magnified manner a compensatory effect of the thermally
collapsible clay mineral particle as the sand grains expand from
the effects of the temperatures to which the foundry shapes are
subjected during the casting process shown in FIG. 2.
[0021] FIG. 5 is an enlarged illustration similar to a portion of
FIG. 4 illustrating a negligible anti-veining effect created by a
sand casting foundry composition which utilizes thermally
collapsible clay mineral particles of insufficient volumetric
concentration and size.
DETAILED DESCRIPTION
[0022] A sand casting foundry composition 10 of the present
invention, illustrated in FIG. 1, comprises sand grains 12 and
thermally collapsible clay mineral particles 14 which are mixed
together relatively uniformly at 16 to form a mixture 18. The
mixture 18 is then coated at 20 with a binder 22. The resulting
sand casting foundry composition 10 is thereafter shaped into mold
and core foundry shapes at 24, after which the binder 22 is allowed
or caused to cure (set up) at 26 to hold the uniformly mixed sand
grains 12 and thermally collapsible clay mineral particles 14 into
integral, structurally-sound foundry shapes 28.
[0023] The foundry shapes 28 formed from the sand casting foundry
composition 10 are then used to produce cast metallic parts as
shown in FIG. 2. The cured core and mold foundry shapes 28 (FIG. 1)
are placed in a desired relationship with respect to one another to
define the cast part which will ultimately be produced, as shown at
30. With the foundry shapes in the desired orientation at 30, the
molten metal is poured at 32 into the spaces defined by and
existing between the positioned foundry shapes. The molten metal is
allowed to cool and solidify into the desired shape of the cast
part at 34. Once the molten metal has solidified sufficiently, the
cast part is removed from the foundry shapes as shown at 36. The
thermally collapsible clay mineral particles 14 act as an
anti-veining agent in the foundry shapes 28 (FIG. 1) to reduce
thermal expansion defects, such as veining, in ferrous and
non-ferrous cast metal parts produced.
[0024] The thermally collapsible clay mineral particles 14 (FIG. 1)
useful as anti-veining agents in the present invention must be
composed of a clay mineral with a crystal structure that has an
inherent characteristic and capability to collapse, contract,
compress and/or weaken physically and structurally, under the
influence of the typical temperatures to which the mold and core
foundry shapes are subjected by the hot molten metal when the metal
part is cast (FIG. 2). Upon collapse of the crystal structure, the
thermally collapsible clay mineral particles also collapse,
contract, compress and/or weaken physically and structurally to
yield volumetric space within the foundry shape sufficient to
accept and compensate for the physical expansion of the sand grains
in response to the elevated temperature from the molten metal. The
net result is a negligible change in volume of the foundry shape,
thereby avoiding the mechanical forces which cause the cracks and
fissures that result in veining. Although the characteristic of
crystal structure collapse in some clay minerals is known, the
advantageous use of such characteristics for anti-veining agents in
foundry compositions and foundry shapes is not known to have been
previously recognized or used.
[0025] The thermally collapsible clay mineral particles are
obtained as particles of naturally occurring clays. Naturally
occurring clays are composed predominantly of one or more clay
minerals which were formed from the in situ chemical alteration of
parent rocks or sedimentary materials as part of a process of
dissolution and reprecipitation. Such clay minerals will form the
predominant proportion of commercially mined naturally occurring
clays from which the thermally collapsible clay mineral particles
are obtained for use as anti-veining agents in accordance the
present invention.
[0026] In addition to the clay minerals, the thermally collapsible
clay mineral particles will also include a considerably smaller
amount of other non-clay minerals. The non-clay minerals are
residuals which resulted from the natural clay formation process
when relatively insoluble minerals present in the parent material
survived the dissolution process intact or when non-clay minerals
were co-precipitated along with the clay minerals. For this reason
the mineral composition of naturally occurring clays may vary
considerably between deposits. The non-clay minerals are inherently
a part of commercially mined clay minerals, because the non-clay
minerals cannot be readily separated on a commercial basis from the
clay minerals. The non-clay minerals present in the thermally
collapsible clay mineral particles used as anti-veining agents in
the present invention will be a small fractional component of clay
minerals and will be insufficient to prevent the thermally
collapsible clay mineral particles from contracting or reducing in
physical size or diminishing in strength to facilitate crushing or
breaking, to yield sufficient volume to compensate for the expanded
sand grains at the elevated temperatures which result from casting
the part.
[0027] The clay minerals with a collapsible crystal structure
useful in the present invention include, but are not limited to:
illite, illite-smectite mixed layer clay minerals, chlorite,
halloysite, kaolinite, sepiolite, palygorskite, and clays from the
group of smectite minerals consisting of montmorillonite,
beidelite, nontronite, saponite and hectorite. A few
commercially-available natural clays containing one or more of
these clay minerals include bentonite, kaolin and attapulgite. Many
clay minerals have exchangeable cations associated with them. Where
cations are present, such as with clays of the smectite group, they
may be of any type, although sodium or calcium cations, or mixtures
of both, are most frequently found. Thermally collapsible clay
mineral particles are characteristically non-fissile, instead
forming angular-spherical particles of a variety of shapes.
[0028] Examples of non-clay minerals found in the thermally
collapsible clay mineral particles used as anti-veining agents in
the present invention include calcite, dolomite, muscovite and
biotite mica, pyrite, feldspar, gibbsite, quartz and opal
(amorphous silica). The quartz may be present as single, larger,
discrete crystals (sand) or as small agglomerations of very fine
grains (chert). The non-clay mineral component of the thermally
collapsible clay mineral particles does not contribute
significantly to particle durability or to significantly reduce
porosity. The non-clay mineral component plays no significant role
in the present invention and is present only because of the
practical impossibility of mining the thermally collapsible clay
mineral particles on an economic basis without also including
relatively small portions of the inseparable non-clay mineral
components.
[0029] The crystal structure collapse in the thermally collapsible
clay mineral particles is preferred to occur under the influence of
temperatures in a preferred range of about 600.degree. C. to about
700.degree. C., although some crystal structure collapse may occur
under the influence of temperatures as low as about 450.degree. C.
to as high as about 1,000.degree. C. The temperatures noted are the
peak endothermic temperatures, as defined by differential thermal
analysis, which are the temperatures at which the crystal structure
collapse is complete or maximized. In most cases, the crystal
structure collapse will start at lower temperatures and progress as
the temperature increases to the peak endothermic temperature. The
progressive nature of the crystal structure collapse coordinates
with the gradual expansion in size of the sand grains with
increasing temperature, so that the collapse of the crystal
structure and the expansion of the sand grains generally occur on a
coincident and counterbalancing basis.
[0030] Anti-veining agents which react to heating at too low a
temperature may weaken the foundry shape or evolve void space
between the sand grains prematurely before the sand grains are able
to swell in response to heating from the molten metal. This
premature reaction can create flaws in the surface of the foundry
shape resulting in metal penetration into the foundry shape.
Similarly, anti-veining agents which react to heating at
temperatures above the point at which most swelling of the sand
grains takes place may allow stresses to develop in the foundry
shape which cause it to fracture before the anti-veining agent can
function to relieve these stresses. This may allow the molten metal
to penetrate the foundry shape causing surface defects in the
casting. For this reason it is an important aspect of the present
invention that the crystal structure collapse in the thermally
collapsible clay mineral particles occur at temperatures that are
generally coincident with temperatures at which the sand grains
undergo thermally induced expansion.
[0031] The collapse of the crystal structure at elevated
temperatures deprives the particles of adequate strength to
maintain their physical size and shape, in which case the thermally
collapsible clay mineral particles may contract or reduce in
physical volumetric size to yield additional space into which the
sand grains can expand. In other cases, the crystal structure
collapse will diminish the strength of the particle itself
sufficiently so that it is crushed, compacted or deformed with
considerably less external force than would otherwise be required
if the crystal structure collapse had not occurred. The weakened
thermally collapsible clay mineral particles are more easily broken
or reduced in physical size and shape by the application of
external forces from the expanding sand grains. These
thermally-induced crystal structure collapse effects may occur
coincidentally and to various degrees in the thermally collapsible
clay mineral particles which are useful as anti-veining agents in
the present invention.
[0032] The manner in which the thermally collapsible clay mineral
particles are believed to act as an anti-veining agent may be
understood by reference to the idealized and generalized
illustrations of FIGS. 3 and 4. A single thermally collapsible clay
mineral particle 14a is used for illustration purposes in FIGS. 3
and 4 to represent the effect of the present invention. A
multiplicity of smaller thermally collapsible clay mineral
particles which occupy approximately the same volumetric space as a
single larger thermally collapsible clay mineral particle 14a would
also have essentially the same effect as is described with respect
to the single thermally collapsible clay mineral particle 14a. An
angular spherical shape of the thermally collapsible clay mineral
particle 14a has been shown for illustration purposes in FIGS. 3
and 4, but other shape or shapes of the thermally collapsible clay
mineral particle or particles would also have essentially the same
effect under the influence of crystal'structure collapse. FIG. 3 is
also intended to represent characteristics and results achieved by
the mixing step 16 and coating step 20 illustrated in FIG. 1, again
on an idealized and illustrative basis.
[0033] Three sand grains 12a, 12b and 12c and a single thermally
collapsible clay mineral particle 14a are shown in FIG. 3 in one of
many different possible types of random orientations in a much
larger matrix 40 of the sand grains 12 and thermally collapsible
clay mineral particles 14 which are held together by the binder 22
(not shown) in the foundry shapes 28 (FIG. 1). The size of a single
thermally collapsible clay mineral particle 14a is significant
relative to the size of the sand grains 12a, 12b and 12c such that
the single thermally collapsible clay mineral particle 14a
separates the sand grains 12a, 12b and 12c from one another and
props the sand grains apart. The cured binder (not shown), which
coats the sand grains 12a, 12b and 12c and the thermally
collapsible clay mineral particle 14a, maintains the orientation of
the sand grains relative to the clay particles to separate the sand
grains from one another. It is not necessary that all the sand
grains within the foundry shapes 28 (FIG. 1) be separated from one
another, but it is important that the volumetric concentration of
the thermally collapsible clay mineral particles and the size of
the thermally collapsible clay mineral particles be sufficient to
provide spaces between a sufficient number of the adjacent sand
grains throughout the matrix 40 so that the crystal structure
collapse of thermally collapsible clay mineral particles will
prevent cracks and fissures in the foundry shapes and thereby
obtain the desired anti-veining effect.
[0034] The anti-veining effect achieved by the thermally
collapsible clay mineral particles may be understood from FIG. 4,
by viewing the impact of the thermally collapsible clay mineral
particle 14a on the three sand grains 12a, 12b and 12c within the
matrix 40 when the foundry shape 28 (FIG. 1) is subjected to the
elevated temperature caused by the heat of the molten metal poured
between the foundry shapes (32, FIG. 2). The relatively high
temperature of the molten metal, for example at least about
1,540.degree. C. for iron, causes the crystal structure collapse in
the particle 14a, thereby diminishing the exterior physical size of
the thermally collapsible clay mineral particle 14a or permitting
the forces from the thermally-expanded sand grains 12a, 12b and 12c
to readily crush, compress, deform or break the particle 14a. The
diminished size or crushed shape of the particle 14a is illustrated
in idealized form by the dashed lines, while the solid outline
represents the previous dimension of the particle 14a prior to
thermal collapse or compression. The reduction in physical size,
which weakens the particle 14a as a result of the crystal structure
collapse, yields or creates additional volumetric space within the
matrix 40 as represented by the difference between the dashed lines
and the solid outlines of the particle 14a.
[0035] The relatively high temperature of the molten metal (34,
FIG. 2) causes the sand grains 12a, 12b and 12c to expand to an
increased physical size illustrated by the dashed lines compared to
the solid outline of the sand grains which represent their previous
dimension prior to thermal expansion. The sand grains 12a, 12b and
12c expand into the added volumetric space yielded by the thermal
collapse of the crystal structure of the clay mineral component of
the particle 14a. Thus, the collapsed or more readily compressible
particle 14a within the matrix 40 of the foundry shape 28 (FIG. 1)
yields enough space so that the sand grains 12a, 12b and 12c can
expand into that added space. The mechanical forces induced by
thermal expansion of each sand grain on the sand grains adjacent to
it within the foundry shape is thereby avoided, and as a result,
the cracks and fissures in the foundry shapes that allow metal
penetration and cause veining in the cast part are avoided.
[0036] The rate and amount of expansion of the sand grains is
dependent on the amount and type of natural impurities contained
within the sand grains. For quartz sand grains, the rate of thermal
expansion increases substantially with increases in temperature
until temperatures of about 650.degree. C. are reached, and then
after about 650.degree. C., further expansion almost levels off
with either a slight reduction in physical size or a further
increase in expansion of about 10% occurring over the temperature
range of from about 650.degree. C. to about 1,000.degree. C. The
temperature (650.degree. C.) correlates very closely with the
preferred peak endothermic temperature range (about 600.degree. C.
to about 700.degree. C.) at which crystal structure collapse occurs
in the thermally collapsible clay mineral particles, particularly
in comparison to the much higher temperatures to which the foundry
composition and foundry shapes are subject from the much hotter
molten metal when a metal part is cast. Accordingly, the yielding
effect achieved by the thermally collapsible clay mineral particles
occurs on a generally coincident and coordinated temperature basis
with the expansion of the sand grains to avoid inducing the
mechanical stresses that cause cracks and fissures in the foundry
shapes. The degree of thermal expansion for the typical silica sand
used in the North American foundry industry is typically in the
range of about 1.3 to 1.6% of the original sand volume, with
approximately 90% of that increase having occurred upon reaching
temperatures of about 650.degree. C.
[0037] The thermally collapsible clay mineral particles 14 are
distributed throughout the resulting foundry shape 28 in such a
manner that the idealized response described in connection with
FIGS. 3 and 4 is generally achieved throughout the foundry shape
28. While the orientation of the sand grains and the thermally
collapsible clay mineral particles within the matrix 40 will not
usually take the idealized form shown in FIGS. 3 and 4, but instead
will be a variety of different random orientations, the results are
substantially similar if the quantity of the thermally collapsible
clay mineral particles and the size of the thermally collapsible
clay mineral particles are sufficient to separate a significant
number of sand grains so that the collapse, contraction,
compression or breakage of the thermally collapsible clay mineral
particles yields adequate space to accept and compensate for the
thermal expansion of the sand grains.
[0038] In the present invention, thermally collapsible clay mineral
particles of adequate size and sufficient volumetric quantity yield
a sufficient amount of volume within the foundry shape to accept
and compensate for the thermally-induced expansion of the sand
grains. The size and quantity of the thermally collapsible clay
mineral particles required is related in significant part to the
amount of void volume or space between the sand grains. A larger
amount of void volume between the sand grains will require more and
larger thermally collapsible clay mineral particles in the mixture
18 (FIG. 1) to obtain the desired anti-veining effect. Although the
thermally collapsible clay mineral particle size and the amount of
thermally collapsible clay mineral particles used are interrelated,
the effective range of sizes of these particles in the mixture 18
(FIG. 1) relates to the size of the average void space or volume
between adjacent sand grains. A thermally collapsible clay mineral
particle which occupies somewhat more than the average void space
between adjacent sand grains will separate those adjacent sand
grains sufficiently so that their thermal expansion will be
counterbalanced by the thermal collapse of the thermally
collapsible clay mineral particle. On the other hand, the
anti-veining effect of a larger size thermally collapsible clay
mineral particle can also be achieved by a multiplicity of smaller
sized thermally collapsible clay mineral particles which provide
the same volumetric separation and collapse capability as a single
larger sized particle.
[0039] When the thermally collapsible clay mineral particles are
too small and when there is an insufficient volumetric quantity of
particles mixed with the sand grains, very little or no significant
anti-veining effect will be achieved. FIG. 5 illustrates the lack
of significant anti-veining effect created by thermally collapsible
clay mineral particles which are too small in physical size and of
insufficient volumetric quantity. In the idealized illustration of
FIG. 5, a single thermally collapsible clay mineral particle 14b is
again used for illustration purposes, but this single particle 14b
could also be replaced by a larger number of relatively smaller
thermally collapsible clay mineral particles having approximately
the same volumetric size as the single particle 14b. Again, like
FIGS. 3 and 4, an angular spherical shape of the thermally
collapsible clay mineral particle 14b has been illustrated, but
other shapes of the thermally collapsible clay mineral particle or
particles would also have essentially the same effect under the
influence of thermally-induced crystal structure collapse and
expansion pressure from the sand grains at the elevated
temperatures from the molten metal.
[0040] The situation illustrated in FIG. 5 is similar to that
illustrated in FIG. 3 except that the thermally collapsible clay
mineral particle 14b is not sufficiently large to prevent the sand
grains 12d, 12e and 12f from touching one another when thermally
expanded. The influence of the elevated temperature causes the
particle 14b to collapse, contract, compress or break, but this
reduction in size is of no significant benefit because it does not
yield sufficient space into which the sand grains 12d, 12e and 12f
can expand. Consequently the thermal expansion of the sand grains
causes them to contact, one another and to induce the mechanical
stress on the foundry shape which causes it to crack or fissure,
allowing the molten metal to invade the cracks and fissures to
cause the undesirable veining.
[0041] Taking into account the size of the thermally collapsible
clay mineral particles, a volumetric quantity of particles which is
too small within the foundry composition and the foundry shape is
one which does not yield enough space due to thermal crystal
structure collapse to accept the thermal expansion of the sand
grains. Although thermally collapsible clay mineral particles which
are too small and of insufficient quantity might nevertheless have
some capability to separate the sand grains, the degree of
separation is insufficient if the amount of space they yield is
insufficient to compensate for the greater amount of thermal
expansion of the sand grains. Under such circumstances the quantity
and size of the thermally collapsible clay mineral particles is
insufficient to prevent the sand grains from contacting one another
and inducing the mechanical stress in the foundry shape that opens
the cracks and fissures which lead to veining in the cast part.
[0042] Thermally collapsible clay mineral particles that are too
large are more difficult to mix and distribute evenly throughout
the sand grains in the mixture. Thermally collapsible clay mineral
particles which are not sufficiently evenly mixed with the sand
grains are not effective in preventing the cracks and fissures
uniformly throughout the foundry shape. Large numbers of relatively
small thermally collapsible clay mineral particles negatively
impact the tensile strength of the foundry shape. Large numbers of
smaller thermally collapsible clay mineral particles also consume
more binder. The effectiveness of the thermally collapsible clay
mineral particles as an anti-veining agent also depends on the
amount of collapse achieved by those particles. Having regard for
all of these factors, an acceptable size and volume of thermally
collapsible clay mineral particles must be generally be determined
experimentally and in relation to the type of foundry sand and the
degree of collapse of the thermally collapsible clay mineral
particles used.
[0043] The sand grains 12 used in the foundry composition 10 (FIG.
1) are conventional foundry sands, typically silica sand, although
other useful foundry sands include chromite, zircon and olivine
sands. An example of commercially available foundry sand is Wedron
520 available from Fairmount Minerals. Sand grains of Wedron 520
have an American Foundry Society (AFS) size or grains fineness
number (GFN) of 59-65, which range corresponds to about the range
between U.S. standard (ASTM) No. 30 and No. 140 mesh sizes.
[0044] The thermally collapsible clay mineral particles which have
proved useful with the Wedron 520 sand have a granular or
particulate form having an average particle size of from about 74
micrometers to about 3.4 millimeters. More particularly, the
thermally collapsible clay mineral particles may range in size from
about 105 micrometers to about 2.0 millimeters. The most effective
particle size of the thermally collapsible clay mineral particles
is from about 425 micrometers to about 2.0 millimeters. Other sizes
of thermally collapsible clay mineral particles may be optimal for
other sizes of foundry sand, for the reasons noted above. Particles
having an average size of about 74 micrometers or greater are those
which are generally retained on the surface of a U.S. standard
(ASTM) No. 200 mesh sieve screen. Particles having an average
particle size of 105 micrometers or greater are those which are
generally retained on a surface of a U.S. standard No. 140 mesh
sieve screen. Particles having an average particle size of 425
micrometers or greater are those which are generally retained on a
surface of a U.S. standard No. 40 mesh sieve screen. Particles
having a nominal size of less than about 2.0 millimeters are those
which generally pass through a U.S. standard No. 10 mesh sieve
screen. Particles having an average size of less than about 3.4
millimeters are those which generally pass through a U.S. standard
No. 6 mesh sieve screen.
[0045] In general, to establish and control the anti-veining effect
achieved by the thermally collapsible clay mineral particles, it is
desirable to use predetermined desired sizes of the particles so
that the desired degree of volumetric space achieved by the
physical yielding of the thermally collapsible clay mineral
particles is controlled by the quantity or weight of the particles
added to the mixture 18 (FIG. 1). It is therefore preferable to
avoid substantial disintegration of the thermally collapsible clay
mineral particles 14 originally added for mixing at 16 (FIG. 1)
into smaller sizes.
[0046] The binder used in the present invention is preferably a
conventional chemical resin used in conventional foundry processes,
such as phenolic hot box, phenolic urethane, furan, sodium silicate
including ester and carbon dioxide system, polyester binders,
acrylic binders, alkaline binders, epoxy binders, and furan warm
box systems. A particularly useful binder is a no-bake resin binder
system available from Ashland Chemical Company of Covington, Ky.
This resin binder system comprises a three part phenolic urethane
system which includes a series of binders and a liquid
catalyst.
[0047] The moisture content of the thermally collapsible clay
mineral particles can also affect the anti-veining capability. If
the moisture content of the thermally collapsible clay mineral
particles is too high, the foundry shape can potentially crack or
fissure because of the excessive amount of steam created by
vaporization of the moisture by the heat of the molten metal. It is
therefore believed that the incidence of veining decreases with
decreasing moisture levels. Further, many of the chemical binders
used to produce this type of foundry shape are not compatible with
water. When using these binders the moisture content of the foundry
composition is inversely related to the tensile strength of the
cured foundry shape. Therefore, it is necessary to keep the
moisture level of the thermally collapsible clay mineral suitably
low in order to maximize the tensile strength of the cured foundry
shape of the present invention. From a practical standpoint, the
thermally collapsible clay mineral particles will typically have a
moisture level of from 0.1% to about 12%. Preferably the moisture
content of the thermally collapsible clay mineral particles used in
present invention should be within the range of about 3 to 5% on a
weight basis, with an optimal target moisture level of about
4%.
[0048] A method of making the sand casting foundry composition 10
is illustrated by FIG. 1. The method of making the foundry
composition comprises the step 16 of mixing the sand grains 12 and
the thermally collapsible clay mineral particles 14 into the
mixture 18. The mixture 18 contains a relatively uniform
distribution of the thermally collapsible clay mineral particles 14
throughout the mass or matrix of sand grains 12. The mixing step 16
may be accomplished by using any conventional mixing process.
Thereafter, at step 20, the binder is added to the mixture 18. The
binder is added to uniformly coat the sand grains and the thermally
collapsible clay mineral particles while maintaining their uniform
distribution within the mixture 18. The coating step 20 is
preferably executed by employing the conventional techniques used
for mixing conventional foundry resin-type binders with foundry
sand.
[0049] The order of addition of the thermally collapsible clay
mineral particles to the foundry composition is important in
securing the anti-veining function of the thermally collapsible
clay mineral particles within the foundry shape. The sand grains
are preferably mixed with the thermally collapsible clay mineral
particles first and then the foundry resin binder is added so that
the resin coats the surface of the sand grains and the thermally
collapsible clay mineral particles and provides a sand casting
foundry composition with the thermally collapsible clay mineral
particles dispersed throughout. Adding the binder to the mixture of
uniformly distributed thermally collapsible clay mineral particles
and sand grains does not disturb the uniformity. Adding the binder
to the existing mixture of sand grains and thermally collapsible
clay mineral particles also reduces consumption of the binder
because more binder is distributed uniformly over the sand grains
and less binder is available to be sorbed by the thermally
collapsible clay mineral particles within the mixture, compared to
the case where the binder is added to the thermally collapsible
clay mineral particles first and then the binder-coated thermally
collapsible clay mineral particles are attempted to be mixed with
the sand grains. Adding the binder to the thermally collapsible
clay mineral particles first would provide more of an opportunity
for the binder to be sorbed by the thermally collapsible clay
mineral particles rather than to be distributed over the sand
grains. Coating the sand grains with the binder first and then
attempting to uniformly mix in the thermally collapsible clay
mineral particles would inhibit the uniform distribution of the
thermally collapsible clay mineral particle and would require an
excessive amount of mixing to obtain the uniform mixture.
[0050] The sand grains 12 typically constitute about 85% to about
98.5% of the foundry composition 10 by weight. The thermally
collapsible clay mineral particles 14 typically constitute from
about 1% to about 10% of the foundry composition 10 by weight. More
preferably, the thermally collapsible clay mineral particles may be
present in an amount from about 1% to 7% by weight. Conventional
foundry resin-type binder 22 will be added in an amount from about
0.5 percent to about 5.0 percent by weight.
[0051] The sand casting foundry composition 10 is formed at step 24
into the foundry shapes 28 as shown in FIG. 1. Depending upon the
type of binder 22 added to the foundry composition 10, curing may
start to proceed immediately with the coating step 20, in which
case, it is necessary to shape the foundry composition 10 into the
core foundry shapes and mold foundry shapes on a relatively
immediate basis. In other cases, the addition of a physical
property or a chemical constituent of binder may be required after
the foundry composition 10 has been formed to cause the binder 22
coated at step 20 to set up or cure as shown at step 26. In any
event, the desired number and type of core and mold foundry shapes
are created by forming the foundry composition 10 into those
desired shapes before the foundry composition cures, as shown at
24. Thereafter, once the foundry composition 10 is in the desired
shape, the binder 22 is set up or cured as shown at step 26.
[0052] The curing which occurs at step 24 (FIG. 1) is achieved by
causing or allowing the binder 22 coated at step 20 (FIG. 1) to set
up to hold the sand grains and thermally collapsible clay mineral
particles in the desired foundry shapes. In this sense, curing
includes permitting the binder 22 to become effective for setting
up without further influence after the foundry composition has been
shaped into the foundry shapes at step 24, and also includes adding
physical properties or chemical constituents to the foundry
composition before or after shaping the foundry composition into
the foundry shapes to cause the binder 22 added to the foundry
composition 10 at step 20 to set up. If the type of binder 22 added
at step 20 is one which will commence curing only in response to
the addition of another chemical constituent, e.g. a catalyst, or
in response to the addition of a physical property, e.g. the
application of heat or pressure, and that chemical constituent or
physical property can be added at a later time so that it permeates
the complete shape of the mold or core foundry shape, the step 26
will involve adding the additional chemical constituent or physical
property which causes the binder to set up. If the type of binder
22 is one which commences curing once coated at step 20, the cure
step 26 will progress without further action as an inherent result
of the coating step 20.
[0053] Once the binder has cured at step 26, the shapes of the
molds and cores established at 24 is fixed, and the foundry shapes
28 are completed. The completed foundry shapes 28 have sufficient
tensile strength and integrity so that they may be moved and
positioned for use in casting the metal part as has previously been
described in connection with FIG. 2. Of course, sometimes casting
the metal parts may require only a mold foundry shape and not a
core foundry shape, or vice versa.
EXAMPLES
[0054] Different silica sand-based sand casting foundry
compositions were prepared for the purpose of evaluating thermally
collapsible clay mineral particles as anti-veining agents and
comparing the anti-veining effects of thermally collapsible clay
mineral particles to other well-known anti-veining agents.
Effectiveness in preventing veining and strength of tensile
properties in the resulting foundry shapes were evaluated. The
thermally collapsible clay mineral particles used in these tests
were bentonite, which is composed primarily of the thermally
collapsible clay mineral montmorillonite. A widely used
anti-veining agent used for comparison to the thermally collapsible
clay mineral particles was "Veinseal" (trademark), a lithia and
iron oxide based anti-veining agent which is a widely used and
generally accepted as a leading anti-veining agent in the sand
casting foundry industry at the present time. The "Veinseal"
product is manufactured by Ashland Chemical Company.
[0055] Identical silica sand-based compositions were prepared
utilizing the anti-veining agents noted in the following Tables.
Test samples were prepared by blending Wedron 520 silica sand
grains and the anti-veining agent in a mixer for 30 seconds. The
addition of the three part Ashland binder system was completed
according to the manufacturers recommendations.
[0056] Tables 1 and 2 summarize the effectiveness of thermally
collapsible clay mineral particles and "Veinseal" anti-veining
additives. Table 1 is directed to test results for sand cores
coated with EZ Kote Graphite Coating.
1TABLE 1 Comparison Of Anti-Veining Agents Coated Sand Cores
Formula(wt)(g) Example Example Example Example Example Material
Control 1 2 3 4 5 Ashland (Part 1) 10 10 10 10 10 10 Pepset XI 1000
Ashland (Part 2) 8 8 8 8 8 8 Pepset XII 2000 Ashland Catalyst 3502
0.5 0.5 0.5 0.5 0.5 0.5 Sand 2000 1900 1900 1900 1940 1860 Sodium
Bentonite -- 100 -- 100 60 140 (#40 mesh) Veinseal -- -- 100 -- --
-- -- Veining (Number Observed) Horizontal 1 None None None 1 None
Vertical 2 None None None 2 None
[0057] Examples 1 and 2 illustrate the effectiveness of thermally
collapsible clay mineral particles as anti-veining agents, as
compared to the commercially available "Veinseal" anti-veining
agent. Examples 3-5 illustrate the effect of thermally collapsible
clay mineral particle concentration on veining.
[0058] Graphite coatings, such as EZ Kote, are known to reduce the
number and severity of veins and other surface defects in castings
by providing a more uniform core surface. In order to create a
worst-case condition a series of uncoated cores was also prepared
and tested. Table 2 is directed to test results for uncoated sand
cores.
2TABLE 2 Comparison Of Anti-Veining Agents Uncoated Sand Cores
Formula (wt)(g) Material Control Example 6 Ashland (Part 1) Pepset
XI 1000 10 10 Ashland (Part 2) Pepset XII 2000 8 8 Ashland Catalyst
3502 0.5 0.5 Sand 2000 1900 Sodium Bentonite -- 100 Veining (Number
Observed) Horizontal 2 None Vertical 4 1 (minor)
[0059] The tensile properties of various sand casting foundry
compositions were calculated based on retained tensile strength in
reference to the control material as indicated in Table 3 below.
Tensile strength is important to maintain the desired shape of the
mold or core before and during casting.
3TABLE 3 Comparison Of Anti-Veining Agents Uncoated Sand Cores
Retained Tensile Properties of Anti-Veining Foundry Compositions
Formulation of Prepared Mixtures (wt)(g) Example Example Example
Example Example Example Example Material Control 7 8 9 10 11 12 13
Ashland (Part 1) 10 10 10 10 10 10 10 10 Pepset XI 1000 Ashland
(Part 2) 8 8 8 8 8 10 8 8 Pepset XII 2000 Catalyst 0.5 0.5 0.5 0.5
0.5 0.5 0.5 0.5 Sand 2000 1970 1970 1970 1900 1970 1879 1900
Dextrin 30 20 10 -- -- -- -- Sodium Bentonite -- -- 0 0 0 0 9 100
(#40 mesh) Sodium Bentonite -- -- 10 20 7.5 15 22.5 0 (#200 mesh)
Iron Oxide -- -- -- -- 22.5 15 7.5 0 Relative Tensile 100% 34% 7%
1% 39% 7% 4% 47% Strength Veining (# Observed) Horizontal 3 2 2 2 1
1 1 1 (minor) (minor) Vertical 4 2 2 0 3 2 1 0
[0060] Table 4 illustrates additional examples of the present
invention.
4TABLE 4 Comparison Of Anti-Veining Agents Uncoated Sand Cores
Formula (wt) (g) Example Example Example 16 Material Control 14 15
(Comparative) Ashland (Part 1) 10 10 10 10 Pepset XI 1000 Ashland
(Part 2) 8 8 8 8 Pepset XII 2000 Ashland Catalyst 3502 0.5 0.5 0.5
0.5 Sand 2000 1900 1900 1900 Sodium Bentonite -- 100 -- -- (#40
mesh) Calcium Bentonite -- -- 100 -- (#40 mesh) Veinseal -- -- --
100 Veining (Number Observed) Horizontal 3 None None None Vertical
4 None None None
[0061] Other anti-veining agents may also be incorporated along
with the anti-veining thermally collapsible clay mineral particles
in the sand casting foundry composition of the present invention.
Such additional anti-veining agents may provide further and
additional benefits particular to those types of anti-veining
agents which, in combination with the thermally collapsible clay
mineral particles, result in better resistance to veining or
improved foundry shape tensile strength when forming the cast part.
For example, lithia and iron oxide anti-veining agents may be
particularly useful in conjunction with the anti-veining effect
obtained from the thermally collapsible clay mineral particles. The
addition rate of other anti-veining agent or agents used in
conjunction with the thermally collapsible clay mineral particles
of the present invention will be determined by the specific effect
that is desired for a particular foundry application, although it
generally will fall in the range of about 3 to 1 to 1 to 3,
thermally collapsible clay mineral to other anti-veining agent.
5TABLE 5 Comparison Of Anti-Veining Additives Uncoated Sand Cores
Formula (wt) (g) Example Example 15 Example Example Example
Material Control 14 (Comparative) 17 18 19 Ashland (Part 1) 10 10
10 10 10 10 Pepset XI 1000 Ashland (Part 2) 8 8 8 8 8 8 Pepset XII
2000 Ashland Catalyst 0.5 0.5 0.5 0.5 0.5 0.5 3502 Sand 2000 1900
1900 1900 1900 1900 Bentonite (#40) -- 100 -- 25 50 75 Veinseal --
-- 100 75 50 25 Veining (# observed) Horizontal 3 None None None 1
minor 1 Vertical 4 None None None 1 minor none
[0062] Mixing the thermally collapsible clay mineral particles with
the sand grains in a sand casting foundry composition substantially
improves the performance of the foundry shapes in producing the
cast part. The anti-veining effect of the thermally collapsible
clay mineral particles in the foundry shape can eliminate or
substantially reduce the extent and incidence of veining in the
cast part, while correspondingly eliminating or reducing the need
for surface grinding to remove undesirable veins projecting from
the cast part. Eliminating veining by use of the thermally
collapsible clay mineral particles in the foundry composition and
foundry shapes can significantly reduce the cost of producing the
cast part. Furthermore, because thermally collapsible clay mineral
particles are considerably less expensive than some other
anti-veining additives, like lithia-containing anti-veining agents,
the cost of producing the cast part may actually be diminished.
[0063] A presently preferred embodiment of the present invention
and many of its improvements have been described with a degree of
particularity. This description is a preferred example of
implementing the invention, and is not necessarily intended to
limit the scope of the invention. The scope of the invention is
defined by the following claims.
* * * * *