U.S. patent application number 14/350210 was filed with the patent office on 2014-08-28 for coating compositions for inorganic casting molds and cores, comprising formic acid esters, and use thereof.
The applicant listed for this patent is ASK Chemicals GmbH. Invention is credited to Michael Kloskowski, Peter Wachtarczyk, Carolin Wallenhorst.
Application Number | 20140242269 14/350210 |
Document ID | / |
Family ID | 47115089 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140242269 |
Kind Code |
A1 |
Kloskowski; Michael ; et
al. |
August 28, 2014 |
COATING COMPOSITIONS FOR INORGANIC CASTING MOLDS AND CORES,
COMPRISING FORMIC ACID ESTERS, AND USE THEREOF
Abstract
The subject matter of the invention relates to coating
compositions comprising formic acid esters, an aqueous carrier
liquid and pulverulent refractory material, and to the use thereof
for casting molds, in particular those produced using water glass
as a binder.
Inventors: |
Kloskowski; Michael;
(Duesseldorf, DE) ; Wachtarczyk; Peter; (Solingen,
DE) ; Wallenhorst; Carolin; (Duesseldorf,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASK Chemicals GmbH |
Hilden |
|
DE |
|
|
Family ID: |
47115089 |
Appl. No.: |
14/350210 |
Filed: |
October 5, 2012 |
PCT Filed: |
October 5, 2012 |
PCT NO: |
PCT/DE2012/000973 |
371 Date: |
April 7, 2014 |
Current U.S.
Class: |
427/134 ;
106/38.2; 106/38.22; 523/139 |
Current CPC
Class: |
B22C 9/12 20130101; B22C
1/04 20130101; B22C 1/188 20130101; B22C 3/00 20130101 |
Class at
Publication: |
427/134 ;
106/38.22; 523/139; 106/38.2 |
International
Class: |
B22C 1/04 20060101
B22C001/04; B22C 3/00 20060101 B22C003/00; B22C 1/18 20060101
B22C001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 2011 |
DE |
102011115024.6 |
Claims
1. A sizing composition comprising: (A) esters of formic acid; (B)
a carrier fluid comprising or consisting of water, and (C)
refractory materials.
2. The sizing composition according to claim 1, wherein the alcohol
group(s) of the formic acid ester(s) in each case contain fewer
than 10 carbon atoms.
3. The sizing composition according to claim 2, wherein the
concentration of the formic acid esters in the sizing composition
amounts to 1 to 8% by weight.
4. The sizing composition according to claim 1, wherein the carrier
fluid comprises of more than 50% by weight of water.
5. The sizing composition according to claim 1, wherein the solids
content of the sizing composition amounts to 30 to 70% by
weight.
6. The sizing Sizing composition according to claim 1, wherein the
sizing composition comprises 10 to 85% by weight of refractory
material, based on the solids content of the sizing
composition.
7. The sizing composition according to claim 1, wherein the
refractory materials are selected from the group consisting of:
quartz, aluminum oxide, zirconium dioxide, aluminum silicates,
zirconium sands, zirconium silicates, olivine, talc, mica, coke,
feldspar, diatomite, kaolins, calcined kaolins, kaolinite,
metakaolinite, iron oxide, bauxite and mixtures thereof.
8. The sizing composition according to claim 1, in which the
refractory materials have particle sizes of 0.1 to 500 .mu.m,
measured by light scattering according to DIN/ISO 13320.
9. The sizing composition according to claim 1, wherein the sizing
composition comprises 0.1 to 20% by weight, of at least one binder,
based on the solids content of the sizing composition.
10. The sizing composition according to claim 1, wherein the sizing
composition comprises a lustrous coal forming agent or
graphite.
11-14. (canceled)
15. The sizing composition according to claim 1, wherein the
alcohol group(s) of the formic acid ester(s) in each case contain
fewer than 6 carbon atoms.
16. The sizing composition according to claim 1, wherein the
alcohol group(s) of the formic acid ester(s) in each case contain
fewer than 3 carbon atoms.
17. The sizing composition according to claim 2, wherein the
concentration of the formic acid esters in the sizing composition
amounts to 2 to 8% by weight.
18. The sizing composition according to claim 2, wherein the
concentration of the formic acid esters in the sizing composition
amounts to 3 to 6% by weight.
19. The sizing composition according to claim 4, wherein the
carrier fluid further comprises alcohols, including polyalcohols
and polyether alcohols.
20. The sizing composition according to claim 19, wherein the
carrier fluid can be fully evaporated at up to 160.degree. C. and
1013 mbar.
21. The sizing composition according to claim 1, in which the
refractory materials have particle sizes of 1 to 200 .mu.m,
measured by light scattering according to DIN/ISO 13320.
22. The sizing composition according to claim 1, wherein the sizing
composition comprises 0.5 to 5-% by weight of at least one binder,
based on the solids content of the sizing composition.
23. The sizing composition according to claim 10, wherein the
lustrous coal forming agent or graphite is present in the amount of
0.1 to 10% by weight.
24. The sizing composition according to claim 10, wherein the
lustrous coal forming agent or graphite is present in the amount of
0.5 to 3% by weight.
25. A mold or core for casting, comprising: a molding material
mixture, coated with a sizing composition according to claim 1; and
a binder comprising water glass.
26. The mold or core of claim 25, wherein: the molding material
mixture comprises at least one member selected from the group
consisting of: silicon dioxide, aluminum oxide, titanium oxide and
zinc oxide.
27. The mold or core of claim 25, wherein: the sizing composition
is diluted with at least water before coating the molding material
mixture.
28. A method for sizing a mold or core for casting, comprising the
steps of: providing a mold or core for casting, the mold or core
comprising a molding material mixture and a binder comprising water
glass; and coating the mold or core with a sizing composition
comprising: esters of formic acid; a carrier fluid comprising
water, and refractory materials.
29. The method of claim 29, wherein: the molding material mixture
comprises at least one member selected from the group consisting
of: silicon dioxide, aluminum oxide, titanium oxide and zinc
oxide.
30. The method of claim 29, wherein: the sizing composition is
diluted with at least water before the coating step.
Description
[0001] The invention relates to a sizing composition comprising
formic acid esters as a coating composition for casting molds. The
sizing composition is suitable for cores and molds producing water
glass as the binder.
PRIOR ART
[0002] Casting molds can be produced from a refractory material,
for example quartz sand, by shaping into a casting mold and binding
using a suitable binder to guarantee adequate mechanical strength.
Thus casting molds are produced using a refractory basic material
and a suitable binder. The refractory basic mold material is
preferably present in free-flowing form, so that it can be packed
into a suitable hollow mold and compacted there. The binder
produces firm cohesion between the particles of the basic mold
material, so that the mold form achieves the necessary mechanical
stability.
[0003] Both organic and inorganic binders can be used for producing
casting molds, and they can be cured by cold or hot processes. Cold
processes are those that are essentially performed at room
temperature without heating the casting molds. In these cases the
curing is usually performed by a chemical reaction, initiated, for
example, by passing a gas as a catalyst through the mold to be
cured. In hot processes, the molding mixture, after forming, can be
heated to a temperature high enough, for example, to expel the
solvent present in the binder or to initiate a chemical reaction by
which the binder is cured, for example by cross-linking.
[0004] Regardless of the curing mechanism, all organic systems
share the fact that they undergo thermal decomposition when the
liquid metal is filled into the casting mold and in this process
may release toxic materials, such as benzene, toluene, xylene,
phenol, formaldehyde and other cracking products, some of which
have not been identified.
[0005] It has become possible to minimize these emissions by
various measures, but they cannot be avoided altogether in the case
of organic binders. To minimize or prevent the emission of
decomposition products during the casting process, binders may be
used which are based on inorganic materials or which contain a very
small fraction of organic compounds. Such binder systems have long
been known.
[0006] Binder systems have been developed which can be cured by
passing gases into them. A system of this type is described, for
example, in GB 782205, in which an alkali water glass is used as
the binder and can be cured by passing in CO.sub.2. In U.S. Pat.
No. 6,972,059 B1 an exothermic feeder mass containing an alkali
silicate as binder is described. In addition, binder systems that
are self-curing at room temperature have been developed. One such
system, based on phosphoric acid and metal oxides, is described for
example in U.S. Pat. No. 5,582,232. Finally, inorganic binder
systems that are cured at higher temperatures, for example in a hot
tool, are also known. Such hot-curing binder systems are known, for
example, from U.S. Pat. No. 5,474,606, in which a binder system
consisting of alkali water glass and aluminum silicate is
described.
[0007] In U.S. Pat. No. 7,022,178 B1 a binder system for molding
sands for producing cores is described. The binder system, based on
water glass, consists of an aqueous alkali silicate solution and a
hygroscopic base, for example sodium hydroxide, which is added in a
ratio of 1:4 to 1:6. The water glass has a SiO.sub.2/M.sub.2O
modulus of 2.5 to 3.5 and a solids fraction of 20 to 40%. To obtain
a free-flowing molding material mixture that can also be packed
into core molds with complicated shapes, and to control the
hygroscopicity, the binder system also contains a surface-active
material, such as silicone oil, which has a boiling point
.gtoreq.250.degree. C. The binder system is mixed with a suitable
refractory material, such as quartz sand, and can then be shot into
a core box using a core shooting machine. The curing of the molding
material mixture is accomplished by withdrawing the remaining
water. The drying or curing of the casting mold can also take place
with the aid of microwaves.
[0008] The use of organic acids such as formic acid in sizes for
the formation of metal salts with these acids is known, for example
from GB 2294040 A and DE 2129479 A. Formic acid esters and their
influence on the stability of the molds and cores are not disclose
in GB 2294040 A and DE 2129479 A.
[0009] However, inorganic binders also have drawbacks compared with
organic binders; for example, the known inorganic binders result in
low stability of the casting molds produced by using them toward
high atmospheric humidity and toward water. Thus storage of the
moldings over a long period of time, as is customary with organic
binders, is not definitely possible. To achieve higher initial
strengths, better resistance of the casting molds toward
atmospheric moisture and better results on the surface of the
casting, in U.S. Pat. No. 7,770,629 B2 a molding mixture is
suggested which in addition to a refractory basic mold material
contains a water glass-based binder. A fraction of a particulate
metal oxide is added to the mold material mixture. Preferably,
precipitated silica or pyrogenic silica is used as the particulate
metal oxide.
[0010] The methods described for producing casting molds and cores
generally also include the application of a refractory mold
coating, also known as sizing agent, at least to the surfaces of
the basic mold that come into contact with the cast metal. The mold
coatings are primarily intended to influence the surface of the
molded parts, to improve the appearance of the casting, to
influence the casting metallurgically, and/or to prevent casting
defects.
[0011] The sizing agents generally used contain as their basic
materials, for example, clays, quartz, diatomaceous earth,
crystobalite, tridymite, aluminum silicate, zirconium silicate,
mica and/or fireclay and also coke and graphite. These basic
materials are the defining parts of the sizing agent, which cover
the mold surface and close the pores against the penetration of the
casting metal.
[0012] With the aid of these coatings, therefore, the surface of
the casting mold can be modified and tailored to the properties of
the metal being processed. For example, the sizing agent can
improve the appearance of the casting by producing a smooth
surface, since the sizing agent smooths out irregularities caused
by the [different] sizes of the granules of the molding material.
In addition, the sizing agent can metallurgically influence the
casting in that, for example, through the sizing agent, additives
at the surface of the casting are selectively transferred into the
casting, improving the surface properties of the casting.
[0013] In addition, the sizing agents form a layer that chemically
isolates the casting mold during the casting of liquid metal. In
this way, any adhesion between the casting and the casting mold is
prevented, so that the casting can be removed from the casting mold
without problems. However, the sizing agent can also be used to
control the heat transfer between liquid metal and casting mold, in
order for example to accomplish the formation of a certain metal
microstructure via the cooling rate.
[0014] Today, the curing of the inorganic binders used takes place
increasingly via a condensation reaction initiated by elevated
temperatures, in which the formation of the binder bridges occurs
through splitting off of water. Like many chemical reactions, this
is a reversible reaction, i.e., the bonds can be broken by contact
and reaction with water, wherein the extent of this reaction
depends heavily on the process parameters for core production.
Under the process parameters typically used in mass production
(rapid cycling, high temperatures), the casting molds lose their
strength due to contact with water and to some extent also, to
contact with alcohol; the surface softens and the casting mold
loses its shape.
STATEMENT OF THE PROBLEM
[0015] The invention was based on the task of suggesting a sizing
agent through which the most defect-free possible coating,
especially of inorganic cores and molds, can be assured, without
negatively impacting the stability of the cores or molds and thus
their processing and storage.
SUMMARY OF THE INVENTION
[0016] This task is accomplished with the features of claim 1;
advantageous embodiments form the subject matter of the dependent
claims or are described in the following.
[0017] In a preferred embodiment, the sizing composition according
to the invention is prepared in the form of a paste or a
suspension. In this embodiment, the sizing composition contains a
carrier fluid.
[0018] Surprisingly it was found that when certain additives are
added to an aqueous sizing composition, the quality of the dressed
inorganic cores and molds can be lastingly improved, and for
example, a shelf life of several days for the cores and molds can
be achieved without difficulty.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Esters of formic acid (methanoic acid) are used as an
additive component of the sizing composition, wherein the mean
chain length of the alcohol or alcohol mixture used in the
esterification is especially less than 6 carbon atoms and
particularly preferably less than 3 carbon atoms. Formic acid
methyl ester (methyl formate) and formic acid ethyl ester (ethyl
formate) are particularly preferably used. It is also possible for
the alcohol group(s) or some of the alcohol groups to bear one or
two additional groups such as ether groups, hydroxy groups, ester
groups or carboxyl groups, or for the formic acid to be
cross-linked through the second or third hydroxy group, e.g., by
condensation.
[0020] The total quantity of the above additives, based on the
sizing composition, amounts to 1 to 8%, preferably 2 to 8%, and
particularly preferably 3 to 6%. For example, "methyl formate pure"
from BASF may be used as the additive. It has the CAS number
107-31-3.
[0021] Depending on the desired use of the sizing composition,
e.g., as a base coat or top coat, and the desired layer thickness
of the coating produced from the sizing composition, additional
characteristic parameters of the sizing composition can be set.
[0022] The carrier fluid may be partially or completely composed of
water. The carrier fluid is the component that can be evaporated at
160.degree. C. and normal pressure and in this sense, by
definition, is primarily the component that is not the solids
content. The carrier fluid contains water to the extent of more
than 50% by weight, preferably 75% by weight, especially more than
80% by weight, and optionally greater than 95% by weight of
water.
[0023] The additional constituents in the carrier fluid may be
organic solvents. Suitable solvents are alcohols, including
polyalcohols and polyether alcohols. Examples of alcohols are
ethanol, n-propanol, isopropanol, butanol and glycol.
[0024] The solids content of the ready-to-use sizing composition is
preferably adjusted in the range of 10 to 85-% by weight, or in the
sale-ready form (before dilution), especially 30 to 70-% by
weight.
[0025] For example, the sizing agent can comprise the combination
of certain clays as constituents of the sizing agents. The clay
material used was a combination of [0026] a) 1 to 10 parts by
weight, especially 1 to 5 parts by weight, of palygorskite, [0027]
b) 1 to 10 parts by weight, especially 1 to 5 parts by weight, of
hectorite and [0028] c) 1 to 20 parts by weight, especially 1 to 5
parts by weight, of sodium bentonite (in each case relative to one
another), especially in a weight ratio of palygorskite to hectorite
of 1 to 0.8 through 1.2 and a ratio of palygorskite to hectorite
together to sodium bentonite of 1 to 0.8 through 1.2. The total
clay content of the above clays in the sizing agents is 0.1 to 4.0%
by weight, preferably 0.5 to 3.0% by weight and particularly
preferably 1.0 to 2.0% by weight, based on the solids content of
the sizing composition. The shelf life of the cores and molds can
be further increased using these clays.
[0029] In addition, the sizing composition can contain salts of the
metals magnesium and/or manganese in a concentration of, optionally
in combination, greater than 1% by weight, based on the sizing
composition. Particularly suitable for use as anions of the salts
are sulfate ion{s} and or chloride ions, wherein the magnesium is
especially used in the +2 or +4 oxidation state and/or manganese in
the +2 oxidation state and the concentration of the salts in
particular amounts to more than 3-% by weight and especially
greater than 5-% by weight, based on the sizing composition.
According to one embodiment, the concentration of the salts amounts
to maximally the saturation concentration of the carrier fluid used
or the concentration amounts to less than 10-%, but in that case
based on the sizing composition.
[0030] Thus the sizing composition according to the invention
contains at least one powdered refractory material. This refractory
material serves to block the pores in a casting mold against the
penetration of the liquid metal. In addition, the refractory
material achieves thermal insulation between the casting mold and
the liquid metal. Examples of suitable refractory materials are
quartz, aluminum oxide, zirconium oxide, aluminum silicates such as
pyropillite, kyanite, andalusite or fireclay, zirconium sands,
zirconium silicates, olivine, talc, mica, coke, feldspar,
diatomite, kaolins, calcined kaolins, kaolinite, metakaolinite,
iron oxide and/or bauxite.
[0031] The refractory material is prepared in powdered form. The
particle size is selected such that a stable structure is formed in
the coating and that the sizing agent preferably can be distributed
without problems on the wall of the casting mold using a spray
device. Suitably, the refractory material has a mean particle size
(measured by light scattering according to DIN/ISO 13320) in the
range of 0.1 to 500 .mu.m, particularly preferably in the range of
1 to 200 .mu.m. Particularly suitable as refractory materials are
those that have a melting point that is at least 200.degree. C.
above the temperature of the liquid metal and independently of
this, do not react with the metal.
[0032] The fraction of the refractory material (in each case
contributing only to the solids content), e.g., in the commercial
form of a paste, relative to the solids fraction of the sizing
material composition, is advantageously more than 70% by weight,
preferably more than 80% by weight, and particularly preferably
more than 85% by weight.
[0033] According to one embodiment (in each case contributing only
to the solids content), the fraction of the refractory material is
selected to be less than 70-% by weight, according to another
embodiment less than 60-% by weight and according to another
embodiment less than 50-% by weight.
[0034] In another embodiment the sizing material according to the
invention may contain at least one suspending agent. The suspending
agent brings about an increase in the viscosity of the sizing
agent, so that the solid constituents of the sizing agent do not
drop to the bottom in the suspension, or do so to only a slight
degree. Organic or inorganic materials or mixtures thereof can be
used to increase the viscosity. Suitable inorganic suspending
agents are, for example, strongly swelling clays, such as sodium
bentonite.
[0035] Alternatively or additionally, the suspending agent may also
include organic thickeners, since after application of the
protective coating, these can be dried to such an extent that they
scarcely release any water after application of the protective
coating. Possible organic suspending agents are, for example,
swellable polymers such as carboxymethyl-, methyl-, ethyl-,
hydroxyethyl- and hydroxypropylcelluloses, plant mucilages,
polyvinyl alcohols, polyvinylpyrrolidone, pectin, gelatin,
agar-agar, polypeptides and/or alginates.
[0036] The fraction of the suspending agent, based on the total
sizing composition, is advantageously selected as 0.1 to 5% by
weight, preferably 0.5 to 3% by weight, particularly preferably 1
to 2% by weight.
[0037] According to a preferred embodiment, the sizing agent
according to the invention contains at least one binder as an
additional component. The binder makes possible better fixation of
the sizing agent or the protective coating made from the sizing
agent onto the wall of the casting mold. In addition, the binder
increases the mechanical stability of the protective coating, so
that less erosion is observed under the influence of the liquid
metal. Preferably the binder cures irreversibly, so that an
abrasion-resistant coating is obtained. Particularly preferred are
binders that do not soften again under contact with atmospheric
humidity. Fundamentally any binder used in sizing agents may be
present. Both inorganic and organic binders may be used. Suitable
binders for use include, for example, clays, especially bentonite
and/or kaolin.
[0038] The fraction of the binder is preferably selected in the
range of 0.1 to 20% by weight, particularly preferably 0.5 to 5% by
weight, based on the solids content of the sizing composition.
[0039] According to an additional, preferred embodiment, the sizing
agent contains a graphite fraction. This supports the formation of
lamellar carbon at the interface between casting and casting mold.
The fraction of the graphite is preferably selected in the range of
1 to 30% by weight, especially preferably 5 to 15% by weight, based
on the solids content of the sizing composition. In iron casting,
graphite has a beneficial effect on the surface quality of the
casting.
[0040] Optionally, the sizing composition according to the
invention may contain other constituents customary in sizing
agents, for example wetting agents, defoamers, pigments, colorants
or biocides. The fraction of these additional constituents in the
ready-to-use coating composition is advantageously less than 10% by
weight, preferably less than 5% by weight and particularly
preferably less than 1% by weight.
[0041] For example, wetting agents may include anionic and
non-anionic surfactants, especially those with an HSB value of at
least 7. One example of such a wetting agent is disodium
dioctylsulfosuccinate. The wetting agent is preferably used in a
quantity of 0.01 to 1% by weight, preferably 0.05 to 0.3% by
weight, based on the ready-to-use sizing composition.
[0042] Defoamers, also known as antifoamers, can be used to prevent
foam formation during the production or application of the sizing
composition. Foam formation during application of the sizing
composition can lead to lack of uniformity in the layer thickness
and to holes in the coating. For example, silicone oil or mineral
oil may be used as defoamers. The defoamer is advantageously
present in a quantity of 0.01 to 1% by weight, preferably of 0.05
to 3% by weight, based on the ready-to-use sizing composition.
[0043] In the sizing composition according to the invention, the
usual pigments and colorants may be used if desired. These are
added to achieve contrast, e.g., between different sizing agents,
or to create a stronger separating effect of the sizing agent from
the casting.
[0044] Examples of pigments are red and yellow iron oxide and
graphite. Examples of colorants are commercial colorants such as
the Luconyl.RTM. colorant series from BASF AG, Ludwigshafen, DE.
The colorants and pigments are preferably present in a quantity of
0.01 to 10% by weight, preferably of 0.1 to 5% by weight, based on
the solids content of the sizing composition.
[0045] According to an additional embodiment, the sizing
composition contains a biocide to prevent bacterial attack and thus
avoid a negative effect on the rheology and the binding strength of
the binder.
[0046] This is especially preferred when the carrier fluid
contained in the sizing composition is made up essentially (on a
weight basis) of water, and thus the sizing agent according to the
invention is supplied in the form of a so-called aqueous sizing
agent. Examples of suitable biocides are formaldehyde,
2-ethyl-4-isothiazolin-3-one (MIT),
5-chloro-2-methyl-4-isothiazolin-3-one (CIT) and
1,2-benzisothiazolin-3-one (BIT). Preferably, MIT, BIT or a mixture
thereof is used. The biocides are usually used in a quantity of 10
to 1000 ppm, preferably of 50 to 500 ppm, based on the weight of
the ready-to-use sizing composition.
[0047] In addition to the constituents mentioned in the preceding,
the sizing composition according to the invention may contain
additional constituents customary for sizing agents.
[0048] The sizing composition according to the invention may be
made by the usual methods. For example, a sizing composition
according to the invention can be prepared by initially taking
water and then dispersing clay, acting as a suspension agent, in it
using a high-shear agitator. Then the refractory components,
pigments and colorants, as well as the metal additive are mixed in
until a homogeneous mixture forms. Finally, wetting agents,
antifoamers, biocides and binders are mixed in.
[0049] The sizing composition according to the invention can be
prepared and sold as a ready-to-use formulated sizing agent.
However, the sizing agent can also be prepared and sold in
concentrated form. In this case, to produce a ready-to-use sizing
agent, the quantity of the carrier fluid needed to establish the
desired viscosity and density of the sizing agent is added. In
addition, the sizing agent according to the invention can also be
prepared and sold in the form of a kit, wherein for example the
solid component(s) and the solvent component(s) are present side by
side in separate containers. The solid component(s) can be supplied
as a powdered solids mixture in a separate container. Additional
liquid component(s) optionally to be used, for example binders,
surfactants, wetting agents/defoamers, pigments, colorants and
biocides, can also be present in this kit, once again in a separate
container. The solvent component(s) can either include the optional
additional components for use, e.g., in a single container, or they
can be present separate from other optional components in a
separate container.
[0050] To produce a ready-to-use sizing agent, the suitable
quantities of the solids components, the optional additional
components and the solvent components are mixed together.
[0051] The sizing compositions according to the invention are
suitable for coating casting molds. The term "casting mold" used
here includes all types of solid bodies needed for producing a
casting, e.g., cores, molds and dies. The use of the sizing agent
according to the invention also includes partial coating of casting
molds. The sizing agents are used for casting molds for metal
processing, obtainable from inorganic molding material mixtures
containing at least one refractory basic mold material, a water
glass-based binder and preferably a fraction of a metal oxide
selected from the group of silicon dioxide, especially amorphous
silicon dioxide, aluminum oxide, titanium oxide or zinc oxide and
mixtures thereof, wherein this is preferably present in particulate
form and especially has particle sizes of less than 300 .mu.m
(screen analysis). For example, amorphous silicon dioxide can be
obtained through precipitation processes starting from water glass,
which can be obtained by solubilizing quartz said with sodium
carbonate or potassium carbonate. Depending on the process
conditions, SiO.sub.2 obtained in this way is called precipitated
silica. Another important manufacturing variant is the production
of so-called pyrogenic SiO.sub.2 in an oxyhydrogen gas flame,
starting from liquid chlorosilanes such as silicon
tetrachloride.
[0052] The molding material mixtures and a method for producing
casting molds for metal processing using the cured molding material
mixtures are described in WO 2006/024540 (+U.S. Pat. No. 7,770,629
B2), and this publication is incorporated in the content of this
application to this extent. Preferred molding material mixtures are
the subject matter of the claims of WO 2006/024540. Thus the
casting molds to be coated typically comprise [0053] a) More than
80% by weight of a refractory basic mold material (including
additives that behave like refractory basic mold materials). [0054]
b) 0.01 to 5% by weight of cured water glass as a binder, [0055] c)
optionally 0 to 5% by weight of the above-named metal oxide or
metal oxides.
[0056] In addition, the invention relates to a method for producing
sized casting molds for metal processing with application of sizing
agents to the above-mentioned, partially or completely cured
inorganic molding material mixtures. The application or preparation
of the sizing agents can take place as follows:
[0057] In the case of dipping as an application method, the casting
mold, in the mold cavity of which a base coat of sizing agent has
been applied, is dipped for about 2 seconds to 2 minutes in a
container that is filled with a ready-to-use sizing composition
according to the invention.
[0058] The casting mold is then removed from the sizing composition
and excess sizing composition is allowed to run out of the casting
mold. The time taken for the excess sizing composition to run out
after dipping depends on the run-off behavior of the sizing
composition used.
[0059] In the case of spraying as the application method,
commercial pressure tank spraying devices are used. In this process
the sizing composition, in a diluted state, is filled into a spray
tank. Through the positive pressure to be applied, the sizing agent
can be forced into a spray gun, where it is sprayed with the aid of
separately controllable atomizing air. During spraying, the
conditions are advantageously selected such that the pressure for
the sizing composition and atomizing air are selected on the spray
gun is set so that the sizing composition that is sprayed atomizing
air strikes the mold or the core while said sizing composition is
still wet, but results in a uniform application.
[0060] In the case of flow coating as the application method, the
casting mold, optionally with a base coat applied in the mold
cavity, is covered with a ready-to-use sizing composition with the
aid of a tube, a lance or similar instruments.
[0061] In this process, the casting mold is covered completely with
the sizing composition and the excess sizing composition runs out
of the casting mold. The time taken for the excess sizing
composition to run off after flow coating depends on the flow
behavior of the sizing composition used.
[0062] In addition, the sizing agent can also be applied by
painting.
[0063] The carrier fluid contained in the sizing agent is then
evaporated, so that a dry sizing agent layer is obtained. Drying
methods used may include all conventional drying methods, for
example allowing to dry in air, drying with dehumidified air,
drying with microwave or infrared radiation, drying in a convection
oven and comparable methods.
[0064] In a preferred embodiment of the invention, the coated
casting mold is dried in a convection oven at 20 to 250.degree. C.,
preferably 50 to 180.degree. C.
[0065] When alcohol-based sizing agents are used, the sizing
composition according to the invention is preferably dried by
burning off the alcohol or the alcohol mixture. In this case the
coated casting mold is additionally heated by the heat of
combustion. In an additional preferred embodiment, the coated
casting mold is dried in air without further treatment or using
microwaves.
[0066] The sizing agent can be applied in the form of a single
layer or in the form of several layers arranged one on top of the
other. In this process the individual layers may be the same or
different in terms of their composition. For example, first a base
coat can be produced from a conventional commercial sizing agent
that contains no metal additive according to the invention. For
example, water-based sizing agents or alcohol-based sixing agents
may be used. It is also possible to prepare all layers from the
sizing composition according to the invention. The layer that will
later come into contact with the liquid metal, however, is always
produced from the sizing agent according to the invention. When
several layers are applied, each individual layer may be dried
completely or partially after application.
[0067] The coating prepared from the sizing composition
advantageously has a dry layer thickness of at least 0.1 mm,
preferably at least 0.2 mm, particularly preferably at least 0.45
mm, especially preferably at least 0.55 mm. According to one
embodiment, the thickness of the coating is selected to be less
than 1.5 mm. The thickness of the dry layer in this case is the
layer thickness of the dried coating obtained by essentially
completely removing the solvent component and optionally curing
subsequently. The dry layer thickness of the base coat and the top
coat are preferably determined by measuring with the wet layer
thickness comb. The casting mold can then be assembled completely
if desired. The casing is advantageously performed to make iron and
steel castings.
Example
[0068] In this example the effects of additional various types of
waterglass hardeners in sizing agents on the strengths of the sized
cores were examined. Core layers 1 to 3 have the compositions
indicated in Tables 1 to 3.
TABLE-US-00001 TABLE 1 Composition of the sizing agents Sizing
Sizing Sizing agent 1 agent 2 agent 3 % by % by % by Component
weight weight weight Water 28.5 28.5 32.5 Methyl formate 4 -- --
Ethyl formate -- 4 -- Zircon flour 45 .mu.m 22.5 22.5 22.5 Attagel
(attapulgite) 40 1.5 1.5 1.5 PVA solution (25%) 1.5 1.5 1.5
Satintone W .RTM. 17 17 17 Surfynol .RTM. SEF (wetting agent 1) 0.2
0.2 0.2 Dynol .RTM. (wetting agent 2) 0.05 0.05 0.05 Foamstar .RTM.
MF342 (defoamer) 0.2 0.2 0.2 Pyrax RG 140 12 12 12 Gloss graphite
powder 85% C 12 12 12 Acticide .RTM. F(N) (preservative 1) 0.4 0.4
0.4 Acticide .RTM. MBS (preservative 2) 0.15 0.15 0.15
[0069] The mold casting sizing agent was produced as follows: water
is placed in a vessel and the clay(s) were broken up using a
high-shear unit and a chopper disk for at least 15 minutes. Then
the refractory components, pigments and colorants are mixed in for
at least 15 minutes until a homogeneous mixture forms. Together
with the solids described the additives methyl formate and ethyl
formate were added to sizing agent 1 and sizing agent 2. Finally,
additives such as wetting agents, defoamers and preservatives as
well as the binder are mixed in for 5 minutes.
[0070] For the experiments that follow, the sizing agents were
adjusted to a viscosity in the range of 0.6 Pas, suitable for
application. The adjustment was done by adding appropriate amounts
of water to the original composition and then homogenizing. The
main characteristic in this case is the viscosity, measured at
20.degree. C. with a Brookfield viscometer (DIN EN ISO 2555) and
with a DIN 4 mm viscosity flow cup (DIN EN ISO 2431).
TABLE-US-00002 TABLE 2 Application parameters Sizing Sizing Sizing
agent 1 agent 2 agent 3 Brookfield [Pas] 0.6 0.6 0.6 Flow time [s]
15.5 15.5 15.5 Solids content [%] 66.9 66.9 66.9 Penetration depth
2 2 2 [mm] according according not to patent to patent according to
patent
[0071] The methyl formate contained in sizing agent 1, along with
other characteristics, is able to undergo reaction with the
inorganic binder that is partially dissolved during the sizing
process. It produces complete curing of the dissolved inorganic
binder and thus greater stability of the sized cores. Conversely,
reducing the content in the layer leads to a loss of strength in
the core. The same is true for the ethyl formate used in sizing
agent 2. In the following, the performance of the corresponding
series of experiments, which served as the basis for the
observations described, will be described in detail.
[0072] Comparable behavior can likewise be achieved with chemically
related esters.
Producing and Testing the Molding Materials Test Pieces
[0073] Two different core geometries were investigated for
experimental purposes. One geometry, the so-called Georg Fischer
test bar, illustrates the behavior of the sized test pieces on
thicker core geometries, while the other geometry, so-called long
cores, illustrates the behavior of the sized test pieces on thin
geometries. Georg Fischer test bars are defined as rectangular test
bars with dimensions of 150 mm.times.22.36 mm.times.22.36 mm. The
long cores have dimensions of 13 mm.times.20 mm.times.235 mm.
[0074] The composition of the molding material mixture is shown in
Table 3. The following procedure was used for producing the Georg
Fischer test bar: the components listed in Table 3 were mixed in a
laboratory paddle vane type mixer (from Vogel & Schemmann AG,
Hagen DE).
[0075] For this purpose, first the quartz sand was placed in a
vessel and the water glass was added while stirring. A sodium water
glass containing some potassium was used as the water glass. The
SiO.sub.2:M.sub.2O modulus of the water glass was about 2.2,
wherein M is the sum of sodium and potassium. After the mixture was
agitated for one minute, amorphous silicon dioxide was optionally
added under further agitation. The amorphous silicon dioxide is
pyrogenic silica from the RW Silicium company. Then the mixture was
agitated for an additional minute.
[0076] The molding composition mixture was transferred to the
storage bunker, an H 2.5 Hot Box core shooting machine from the
Roperwerk-Giessereimaschinen GmbH, Viersen, DE, the molding tool of
which was heated to 180.degree. C. The molding composition mixture
was introduced into the molding tool using compressed air (5 bar)
and remained in the molding tool for an additional 35 seconds. To
accelerate the curing of the mixture, hot air (2 bar, 150.degree.
C. upon entry into the tool) was passed through the molding tool
for the last 20 seconds. The molding tool was opened and the test
bar removed.
[0077] The coating compositions were applied to the test bar by
dipping; the application parameters are listed in Table 2. The test
bars were coated either immediately after removal from the molding
tool or after a 30 min cooling time. After application of the
coating, the coated test bars were held in a drying oven for 30 min
at 150.degree. C.
[0078] To determine the bending strengths, the test bars were
placed in a Georg Fischer strength testing apparatus equipped with
a 3-point bending device (DISA Industrie AG, Schaffhausen, CH) and
the force resulting in breakage of the test bar was measured.
[0079] The bending strengths of the uncoated test bars were
measured according to the following plan: [0080] 10 seconds after
removal (hot strength) [0081] 1 hour after removal (cold strength).
[0082] The test bars were coated according to the following scheme:
[0083] coated 1 minute after removal (hot coating) [0084] coated 30
minutes after removal (cold coating) [0085] The coated bending
strengths of the coated test bars were measured according to the
following plan: [0086] 10 seconds after removal from the drying
oven [0087] (hot strengths, hot-coated) [0088] coated 30 minutes
after removal [0089] (cold strengths, hot-coated, immediately after
removal from oven) [0090] 10 seconds after removal from the drying
oven [0091] (hot strengths, cold-coated, room temperature
20.degree. C. [0092] coated 30 minutes after removal [0093] (cold
strengths, cold-coated)
TABLE-US-00003 [0093] TABLE 3 Composition of molding composition
mixtures Quartz Alkali sand water Amorphous H32 glass silica
Coating 1 100 GT 2.0 0.5 -- Comparison, not according to invention
2 100 GT 2.0 0.5 Sizing According to agent 1 invention 3 100 GT 2.0
0.5 Sizing According to agent 2 invention 4 100 GT 2.0 0.5 Sizing
Not according agent 3 to invention
TABLE-US-00004 TABLE 4 Strengths in Georg Fischer test bars Hot
Cold Hot Cold strength, strength, strength, strength, hot hot cold
cold coated coated coated coated [N/cm2] [N/cm2] [N/cm2] [N/cm2] 1
400 450 400 450 Comparison, not according to invention 2 300 400
320 470 According to invention 3 300 380 320 450 According to
invention 4 250 -- -- 340 Not according (broken) (broken) to
invention
TABLE-US-00005 TABLE 5 Strengths on long cores Hot Cold Hot Cold
strength, strength, strength, strength, hot hot cold cold coated
coated coated coated [N/cm2] [N/cm2] [N/cm2] [N/cm2] 1 250 280 250
280 Comparison, not according to invention 2 200 230 240 260
According to invention 3 180 210 200 230 According to invention 4
-- -- -- -- Not according (broken) (broken) (broken) (broken) to
invention
Results
[0094] The use of an alcohol-containing coating is undesirable
because of the drawback presented by the release of emissions
during the casting process. Using standardized water-based coating
agents, the test pieces made of water glass-containing molding
material agents lose considerable strength (sizing agent 4).
[0095] Surprisingly it was found, while seeking possibilities for
suppressing the reaction between the water from the coating and the
binder of the molding material, that the addition of formic acid
esters to the coating distinctly suppresses the effect. The
strengths are maintained. Esters with different chain lengths and
structures can be used, as is done for example in sizing agents 1
and 2 in Example 1. The high strengths compared to those with cores
sized with sizing agent 3 provide evidence for the positive
effect.
* * * * *