U.S. patent application number 17/603828 was filed with the patent office on 2022-07-07 for coating composition, method for coating a casting mold, use of the coating composition for coating a casting mold, and casting mold.
The applicant listed for this patent is ASK CHEMICALS GMBH. Invention is credited to Jorg KROKER, Reinhard STOTZEL.
Application Number | 20220212246 17/603828 |
Document ID | / |
Family ID | |
Filed Date | 2022-07-07 |
United States Patent
Application |
20220212246 |
Kind Code |
A1 |
STOTZEL; Reinhard ; et
al. |
July 7, 2022 |
COATING COMPOSITION, METHOD FOR COATING A CASTING MOLD, USE OF THE
COATING COMPOSITION FOR COATING A CASTING MOLD, AND CASTING
MOLD
Abstract
The present invention relates to a coating composition,
comprising a solids component which comprises a first solid that is
able to cleave CO2 in a temperature range from about 150 to about
1000.degree. C., and that has a D50 value of at most about 10 pm.
It is furthermore directed to a method for coating a casting mold,
the use of the coating composition for coating a casting mold, and
the coated casting mold.
Inventors: |
STOTZEL; Reinhard;
(Solingen, DE) ; KROKER; Jorg; (Fountain Hills,
AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASK CHEMICALS GMBH |
Hilden |
|
DE |
|
|
Appl. No.: |
17/603828 |
Filed: |
April 15, 2020 |
PCT Filed: |
April 15, 2020 |
PCT NO: |
PCT/EP2020/060607 |
371 Date: |
October 14, 2021 |
International
Class: |
B22C 3/00 20060101
B22C003/00; C09D 1/00 20060101 C09D001/00; C09D 103/02 20060101
C09D103/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2019 |
DE |
10 2019 002 802.3 |
Claims
1. A coating composition, comprising: a solids component which
comprises a first solid that is able to cleave CO.sub.2 in a
temperature range from about 150 to about 1000.degree. C., and that
has a D50 value of at most about 10 .mu.m.
2. The coating composition according to claim 1, wherein the first
solid has a D99 value of at most about 30 .mu.m and a D90 value of
at most about 20 .mu.m.
3. The coating composition according to claim 1, wherein the first
solid is selected from carbonates of the elements of the 2.sup.nd,
7.sup.th, 8.sup.th, 9.sup.th, 10.sup.th, 11.sup.th and 12.sup.th
groups of the periodic table of elements.
4. The coating composition according to claim 3, wherein the first
solid is selected from calcium carbonate, magnesium carbonate,
dolomite or iron carbonate, or mixtures thereof.
5. The coating composition according to claim 1, wherein the first
solid is selected from starch.
6. The coating composition according to claim 1, wherein the
coating composition further comprises a carrier liquid.
7. The coating composition according to claim 6, wherein the
solubility product of the first component in the carrier liquid, in
terms of K.sub.sp, at 25.degree. C., is at least about 4.
8. A method for coating a casting mold, wherein the method
comprises the steps of: (a) providing a casting mold comprising a
surface which defines a casting cavity, (b) providing a coating
composition according to claim 1; and (c) applying the coating
composition to at least one part of the surface which defines the
casting cavity.
9. The method according to claim 8, wherein the coating composition
further comprises a carrier liquid and the coating composition is
dried after step (c).
10. The method according to claim 8, wherein the coating penetrates
at least 2 mm into the coated surface, and the layer thickness of
the coating after drying the coating is at most about 100
.mu.m.
11-12. (canceled)
13. A coated casting mold prepared by the method according to claim
8.
14. The coating composition according to claim 5, wherein the first
solid is selected from rice or oat starch.
15. The coating composition according to claim 6, wherein the
carrier liquid comprises water.
16. The method according to claim 8, wherein the casting mold is
equipped with one or more casting cores.
17. A coated casting mold comprising a surface which defines a
casting cavity having a coating layer on at least one part of the
surface which defines the casting cavity, wherein the coating layer
comprises a solids component which comprises a first solid that is
able to cleave CO.sub.2 in a temperature range from about 150 to
about 1000.degree. C., and that has a D50 value of at most about 10
.mu.m.
18. The coated casting mold of claim 17, wherein the casting mold
is equipped with one or more casting cores.
19. The coated casting mold of claim 17, wherein the coating
penetrates at least 2 mm into the coated surface, and the layer
thickness of the coating after drying the coating is at most about
100 .mu.m.
20. The coated casting mold of claim 17, wherein the first solid
has a D99 value of at most about 30 .mu.m and a D90 value of at
most about 20 .mu.m.
21. The coated casting mold of claim 17, wherein the first solid is
selected from carbonates of the elements of the 2.sup.nd, 7.sup.th,
8.sup.th, 9.sup.th, 10.sup.th, 11.sup.th and 12.sup.th groups of
the periodic table of elements.
22. The coated casting mold of claim 17, wherein the first solid is
selected from calcium carbonate, magnesium carbonate, dolomite or
iron carbonate, or mixtures thereof.
Description
TECHNICAL FIELD
[0001] The present invention is directed to a coating composition
capable of suppressing veining in iron and heavy metal casting. The
present invention is furthermore directed to a method for coating a
casting mold, the use of the coating composition for coating a
casting mold, and the corresponding casting mold.
STATE OF THE ART
[0002] Most products in the iron, steel and non-ferrous metal
industries undergo casting processes for their initial forming.
During these processes, molten materials, ferrous metals or
non-ferrous metals, are turned into shaped objects with certain
workpiece properties. For forming the castings, casting molds,
which can be quite intricate, must first be prepared to receive the
molten metal. The casting molds are classified as lost molds, which
are destroyed after each casting, or permanent molds, which can be
used to produce a large number of castings. The lost molds usually
consist of a refractory, granular mold base material, which is
solidified by means of a curable binder.
[0003] Molds are negatives; they comprise the cavity into which the
material is cast to obtain the casting to be formed. The inner
contours of the future casting are formed by cores. In the
manufacture of the mold, the cavity is formed in the mold base
material using a model of the casting to be produced. Inner
contours are shaped by cores which are formed in a separate core
box.
[0004] For the preparation of the molds, both organic and inorganic
binders can be used, the curing of which can be carried out by cold
or hot processes. A cold process is a process in which the curing
is essentially carried out at room temperature without heating the
mold base material mixture. The curing is usually carried out by a
chemical reaction, which can be triggered, for example, by having a
gaseous catalyst pass through the mold base material mixture to be
cured, or by adding a liquid catalyst to the mold base material
mixture. In hot processes, the mold base material mixture is heated
to a sufficiently high temperature after forming, for example to
remove the solvent contained in the binder, or to initiate a
chemical reaction by which the binder is cured due to
crosslinking.
[0005] The preparation of the molds can proceed such that the mold
base material is first mixed with the binder so that the grains of
the mold base material are coated with a thin film of the binder.
The mold base material mixture obtained from the mold base material
and the binder can then be introduced into a corresponding form and
optionally compacted in order to obtain a sufficiently stable mold.
Subsequently, the mold is cured, for example by heating it or by
adding a catalyst that causes a curing reaction. When the mold has
reached at least a certain initial strength, it can be removed from
the form.
[0006] As was already mentioned, casting molds for the production
of metal bodies often consist of so-called cores and molds. The
cores and molds have to meet different requirements. Molds provide
a relatively large surface area to release gases that are formed
due to the effect of the hot metal during casting. Cores usually
only provide a very small area through which the gases can be
discharged. Thus, if too much gas is formed, there is a risk that
gas from the core enters the liquid metal and leads to the
formation of casting defects. The inner cavities are therefore
often provided as sand cores which have been solidified by cold box
binders, i.e. a binder based on polyurethanes, while the outer
contour of the casting is formed by more cost-effective molds, such
as a green sand mold, a mold bound by a furan resin or a phenolic
resin, or by a steel mold.
[0007] For larger molds, organic polymers are mostly used as
binders for the refractory, granular mold base material. Washed and
classified quartz sand is often used as a refractory, granular mold
base material, but other mold base materials such as zircon sands,
chromite sands, chamotte, olivine sands, feldspathic sands, and
andalusite sands can also be used. The mold base material mixture
obtained from the mold base material and the binder is preferably
present in a free-flowing form.
[0008] Currently, organic binders such as polyurethane, furan resin
or epoxy acrylate binders, are often used for the production of
casting molds, in which the curing of the binder is carried out by
the addition of a catalyst.
[0009] The choice of the suitable binder depends on the shape and
size of the casting to be produced, the production conditions, and
the material used for the casting. For instance, polyurethane
binders are often used in the production of small castings, which
are produced in large numbers, as they allow fast cycle times and
thus also series production.
[0010] The use of two-component polyurethane binders for the
production of cores has gained significant importance in the
foundry industry. One component contains a polyol with at least two
OH groups per molecule, and the other one a polyisocyanate with at
least two NCO groups per molecule. In one type of core production,
the so-called cold box process, the two components are first mixed
simultaneously or consecutively with a suitable mold base material,
e.g. quartz sand. This mixture, which is referred to as mold base
material mixture, is then transferred to the reservoir of a core
shooter, then transported into a forming tool by means of
compressed air and is finally cured therein by passing through a
gaseous low-boiling tertiary amine as a catalyst, thus yielding a
solid, self-supporting core (U.S. Pat. No. 3,409,579). As further
components, the mold base material may also contain additives, as
for example described in EP 0 795 366 A1.
[0011] Quartz, zircon, or chrome ore sand, olivine, chamotte, and
bauxite can for example be used as refractory materials.
Furthermore, synthetically produced mold base materials can be used
as well, such as hollow aluminum silicate balls (so-called
microspheres), glass beads, glass granules or the spherical ceramic
mold base materials known as "cerabeads" or "carboaccucast".
Mixtures of the said mold base materials are also possible.
[0012] In order to improve the surface finish of the castings, the
cores and molds can be coated with a coating referred to as finish
before use.
[0013] Conventional coating compositions comprise at least one
refractory substance as a purposive portion. The purpose of this
refractory material is mainly to influence the surface of the
casting to be coated in order to comply with the above-mentioned
requirements with regard to the avoidance of sand defects which
lead to defects and impurity in the casting.
[0014] For example, in foundry technology, the refractory material
can close the sand pores of a core or molded part to prevent a
penetration of the casting metal.
[0015] Examples of refractory substances are pyrophyllite,
zirconium silicate, andalusite, chamotte, iron oxide, kyanite,
bauxite, olivine, alumina, quartz, talc, calcined kaolins
(metakaolin) and/or graphite alone or mixtures thereof.
[0016] For example, WO 2004/083321 A1 and EP 2 364 795 A1 describe
the use of a fine-grained material, such as metakaolin, which can
impregnate the sand pores, and a platelet-shaped coarse
pyrophyllite, which covers the surface of the sand and thus
provides good protection against both veining and penetration.
[0017] Conventionally, a coating composition comprises a carrier
liquid. The solid components of the coating composition can form a
suspension with the carrier liquid, whereby the solid components
become processible and are applied to the body to be coated by a
suitable method, such as e.g. immersion.
[0018] In general, when coating porous substances, the application
behavior of the coating material is not only determined by the
rheology of the coating material, but also by the absorption
behavior of the porous body as well as the retention capacity of
the carrier liquid by the coating substance. With regard to the
absorption behavior of porous bodies, it should be noted that
substrates with hydraulic binders such as clay, cement and water
glass usually absorb the carrier liquid to a particularly high
degree.
[0019] In the case of coating materials based on an aqueous system,
the use of suspending agents, such as natural slimes or cellulose
derivatives, is known. Although they result in a high water
retention capacity of the coating substance material, the rheology
of the system is negatively impacted in that the coating materials
exhibit unfavorable, lower intrinsically viscous properties, and
that they will flow off more viscously. This can lead to
undesirable application features such as drop formation and
sagging, as well as uneven layer thicknesses. In particular in
immersion coating, the optimization of the flow behavior of the
coating material for achieving contour formation, a uniform layer
thickness and a low drop formation is important.
[0020] Basically, any coating material should be kept in a
homogeneous state during processing in order to avoid precipitation
of the solids in the suspension. In combination with the required
application behavior, the rheological character as well as the
degree of thixotropy of the complex suspensions should meet the
desired requirements.
[0021] For example, swellable activated layered silicates are used
in numerous technical fields as thickeners for aqueous systems. By
using shear forces, the layered silicates are dispersed in the
system in a finely distributed form, wherein the individual layered
platelets largely or completely detach from each other and form a
colloidal dispersion or suspension in the system, which leads to a
gel structure.
[0022] A method for the preparation of casting molds and cores from
resin-bound molding sand comprises, for example, the manufacture of
a basic mold or a base core from the molding sand and the
application of a coating containing refractory inorganic components
at least on those surfaces of the basic mold/base core that come
into contact with the cast metal. On the one hand, the purpose of
the mold coatings is to influence the surface of the molded part,
to improve the appearance of the casting, to influence the casting
metallurgically and/or to prevent casting defects. Furthermore,
these coats or coatings serve to chemically insulate the mold from
the liquid metal during casting, thereby preventing any adhesion
and allowing the subsequent separation of mold and casting. In
addition, the coating provides a thermal barrier between the mold
and the casting. The heat transfer can be used specifically to
influence the cooling of the casting. In the production of cold box
cores, problems with expansion errors of the sand occur time and
again in practice, which lead to stresses in the core surface due
to the so-called quartz inversion from .alpha.-quartz to
.beta.-quartz, and a length expansion of about 1% at approx.
580.degree. C. This results in so-called veining (cracked cores
with penetrated metal) or scabbing (loosened sand layer), which
lead to a raised casting surface and, in other areas, to sand
inclusions.
[0023] Another issue is the increasing demand of automotive casting
manufacturers for ever thinner-walled castings from 3 to 5 mm with
a high dimensional accuracy of 0.2 to 0.3 mm. Since commercially
available coatings are typically applied with a dry layer thickness
of 0.2 to 0.4 mm in automotive casting to avoid casting defects,
the high layer thickness constitutes a limitation for improving
dimensional tolerance. So-called fat edge formation or sagging
during the application of the coating also lead to problems with
the dimensional accuracy and impermeability of thin-walled
castings.
[0024] WO 2011/110798 describes a foundry coating composition
comprising a liquid carrier, a binder, and a particulate refractory
filler, wherein the particulate refractory filler comprises a first
relatively coarse fraction having a particle size of d>38 .mu.m
and a second relatively fine fraction having a particle size of
d<38 .mu.m, wherein no more than 10% of the total particulate
refractory filler has a particle size of 38 .mu.m<d<53 .mu.m
and 0 to 50% of the second relatively fine fraction consists of
calcined kaolin.
[0025] DE 10 2009 032 668 A1 describes a ready-to-use wash for
producing mold coatings on lost molds or on cores for iron and
steel casting, wherein the wash contains a proportion by weight of
0.001% or more, and 1% or less of inorganic hollow bodies,
characterized in that the inorganic hollow bodies consist partly or
completely of crystalline material.
[0026] WO 2006/063696 A1 describes a sizing composition for casting
molds, comprising a solvent component and a solid component,
characterized in that the solid component comprises a mixture of
metakaolinite and pyrophyllite as a main component.
[0027] EP 2 176 018 A1 describes a method for casting vermicular
and spheroidal graphite cast iron in a SO.sub.2 epoxy bound sand,
wherein carbonates prevent the sulfur from causing a graphite
degeneration at the edge of the metal. Inter alia, an earth alkali
carbonate is mentioned.
[0028] DE 10 2016 211 930 A1 describes the use of carbonates and/or
phosphates in combination with refractory fillers, preferably on
acid-bound sand molds to avoid the so-called white film.
[0029] WO 2011/075220 A1 describes the use of carbonates as an
additive against veining formation in the sand mixture; while there
is no indication of the particle size distribution, usually, grain
sizes of more than 50 pm are used in order to reduce the loss of
strength.
[0030] It was an object of the present invention to provide a
coating composition which allows the production of thin-walled
castings with a high dimensional tolerance and which ensures a good
protection against veining and penetration.
DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1: Schematic side view of a step core
[0032] FIG. 2: Schematic top view of a step core
[0033] FIG. 3: Schematic side view of a dome core
SUMMARY OF THE INVENTION
[0034] Accordingly, the present invention is directed to the
following points. [0035] 1. A coating composition, comprising:
[0036] a solids component which comprises a first solid that is
able to cleave CO.sub.2 in a temperature range from about 150 to
about 1000.degree. C., and that has a D50 value of at most about 10
.mu.m. [0037] 2. The coating composition according to point 1,
wherein the first solid has a D99 value of at most about 30 .mu.m
and a D90 value of at most about 20 .mu.m. [0038] 3. The coating
composition according to point 1 or 2, wherein the first solid is
selected from carbonates of the elements of the 2.sup.nd, 7.sup.th,
8.sup.th, 9.sup.th, 10.sup.th, 11.sup.th and 12.sup.th groups of
the periodic table of elements. [0039] 4. The coating composition
according to point 3, wherein the first solid is selected from
calcium carbonate, magnesium carbonate, dolomite or iron carbonate,
or mixtures thereof. [0040] 5. The coating composition according to
point 1 or 2, wherein the first solid is selected from starch, in
particular rice or oat starch. [0041] 6. The coating composition
according to any of points 1 to 5, wherein the coating composition
further comprises a carrier liquid, and wherein the carrier liquid
preferably comprises water. [0042] 7. The coating composition
according to point 6, wherein the solubility product of the first
component in the carrier liquid, in terms of pK.sub.L, at
25.degree. C., is at least about 4. [0043] 8. A method for coating
a casting mold, wherein the method comprises the steps of: [0044]
(a) providing a casting mold, optionally equipped with one or more
casting cores, comprising a surface which defines a casting cavity,
[0045] (b) providing a coating composition according to one of
points 1 to 7; and [0046] (c) applying the coating composition to
at least one part of the surface which defines the casting cavity.
[0047] 9. Method according to point 8, wherein the coating
composition further comprises a carrier liquid and the coating
composition is dried after step (c). [0048] 10. Method according to
point 8 or 9, wherein the coating penetrates at least 2 mm into the
coated surface, and the layer thickness of the coating after drying
the coating is at most about 100 .mu.m. [0049] 11. Use of a coating
composition according to any of points 1 to 7 for coating a casting
mold, wherein the casting mold, optionally equipped with one or
more casting cores, comprises a surface which defines a casting
cavity, and the coating composition is applied to at least one part
of the surface which defines the casting cavity. [0050] 12. Use
according to point 11, wherein the coating penetrates at least 2 mm
into the coated surface, and the layer thickness of the coating
after drying the coating is at most about 100 .mu.m. [0051] 13. A
coated casting mold, optionally equipped with one or more casting
cores, obtainable by the method according to one of points 8 to
10.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The present invention is directed to a coating composition,
comprising:
[0053] a solids component which comprises a first solid that is
able to cleave CO.sub.2 in a temperature range from about 150 to
about 1000.degree. C., and that has a D50 value of at most about 10
.mu.m.
[0054] Solids Component
[0055] Solids components are all components that are present as
solids after the drying of the ready-to-use coating composition. In
this context, the drying temperature can, for example, be
120.degree. C.
[0056] First Solid
[0057] The particle size distribution of the individual components
of the coating composition, and in particular of the first solid,
can be determined on the basis of the passage proportions D99, D90,
D50 and D10. They are measures for the particle size distribution.
Accordingly, the passage proportions D99, D90, D50 and D10 denote
the proportions in 99%, 90%, 50% or 10% of the particles which pass
through a sieve with a mesh width corresponding to the designated
grain size fraction. For example, at a D50 value of 10 pm, 50% of
the particles have a size of less than 10 pm. The grain size and
the passage proportions D99, D90, D50 and D10 can be determined by
laser diffraction granulometry according to ISO13320. The passage
proportions are given on a volume basis. In the case of
non-spherical particles, a hypothetical spherical grain size is
calculated and used as a basis.
[0058] In a preferred embodiment, the D10 value of the first solid
is no more than about 3 .mu.m, more preferably from about 0.1 .mu.m
to about 3 .mu.m, more preferably from about 0.1 .mu.m to about 2
.mu.m, especially preferred from about 0.1 .mu.m to about 1
.mu.m.
[0059] The D50 value of the first solid is no more than about 10
.mu.m, preferably from about 0.5 .mu.m to about 10 .mu.m, more
preferably from about 0.5 .mu.m to about 7 .mu.m, especially
preferred from about 0.5 .mu.m to about 6 .mu.m.
[0060] In a preferred embodiment, the D90 value of the first solid
is no more than about 20 .mu.m, more preferably from about 5 .mu.m
to about 20 .mu.m, more preferably from about 5 .mu.m to about 15
.mu.m, especially preferred from about 5 .mu.m to about 10
.mu.m.
[0061] In a preferred embodiment, the D99 value of the first solid
is no more than about 30 .mu.m, more preferably from about 5 .mu.m
to about 30 .mu.m, more preferably from about 5 .mu.m to about 20
.mu.m, especially preferred from about 5 .mu.m to about 15
.mu.m.
[0062] In a preferred embodiment, one or more of the
above-mentioned D10, D50, D99, and D90 values are fulfilled
simultaneously. In a particularly preferred embodiment, the
above-mentioned D50, D99, D90 values, and optionally the D10 value,
are fulfilled simultaneously.
[0063] The desired grain size can be adjusted by crushing the first
solid until the desired grain size is obtained. Alternatively, or
additionally, the desired grain size can be provided by screening.
In the case of synthetic first solids, it is also possible to
adjust the process parameters during production in such a way that
the desired grain size is achieved. The first solid cleaves
CO.sub.2 in the temperature range from about 150 to about
1000.degree. C., preferably about 300 to about 1000.degree. C. This
can be determined by heating the first solid in a tube furnace
under a nitrogen atmosphere, and then, by absorption in a wash
bottle with milk of lime and subsequent filtration, drying and
gravimetric determination, measuring whether CO.sub.2 is emitted at
at least one temperature in the mentioned range. The CO.sub.2
partial pressure should be less than 0.01 bar to avoid errors due
to an influence on the chemical equilibrium. Thus, the cleaving of
CO.sub.2 according to the present invention only encompasses the
decomposition of the first solid, wherein CO.sub.2 is produced, and
not a combustion of the same.
[0064] The chemical composition of the first solid is not
particularly limited, provided that the first solid is able to
cleave CO.sub.2 as required.
[0065] In one embodiment, the first solid is selected from
carbonates of the elements of the 2.sup.nd, 7.sup.th 8.sup.th,
9.sup.th, 10.sup.th, 11.sup.th, and 12.sup.th groups of the
periodic table. Preferably, the first solid is selected from
carbonates of Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, and Zn,
preferably Mg, Ca, Mn, Fe, Cu, and Zn, especially preferred Mg, Ca,
Mn, and Fe, even more preferred Mg, Ca, and Fe.
[0066] Mixed carbonates of the above elements, such as
calcium-magnesium carbonate, can also be used as carbonates.
Mixtures of the carbonates mentioned above are also possible.
[0067] Furthermore, it goes without saying that the carbonates can
be used not only in their pure form but also in the form of natural
minerals. In the case of natural minerals, the content of
carbonates of the elements of 2.sup.nd, 7.sup.th, 8.sup.th,
9.sup.th, 10.sup.th, 11.sup.th, and 12.sup.th groups of the
periodic table is preferably more than about 50 wt.-%, more
preferably more than about 70 wt.-% and especially preferred more
than 90 wt.-%.
[0068] Calcium Carbonate
[0069] Calcium carbonate CaCO.sub.3 can be used in its pure form or
in the form of a natural mineral such as calcite (calcspar, double
spar), aragonite and vaterite. Known natural minerals containing
calcite, aragonite or vaterite are chalk, limestone and marble.
[0070] Calcium carbonate can be produced synthetically according to
the methods known in the art. Among other methods, precipitation
with carbon dioxide, the lime-soda process, and the Solvay process,
in which calcium carbonate is a by-product of ammonia production,
are known.
[0071] Calcium carbonate occurs in several anhydrous forms as well
as in two hydrate modifications and other amorphous forms. Starting
at a temperature of about 600.degree. C., they decompose into
calcium oxide and carbon dioxide:
CaCO.sub.3.fwdarw.CaO+CO.sub.2
[0072] According to the present invention, the type of calcium
carbonate is not particularly limited. Any known calcium carbonate
can be used. The calcium carbonate can preferably be selected from
calcite and aragonite, more preferably, the calcium carbonate is
calcite.
[0073] Magnesium Carbonate
[0074] Magnesium carbonate MgCO.sub.3 can be used in its pure form
or in the form of a natural mineral such as magnesite (bitter
spar), barringtonite, nesquehonite and lansfordite.
[0075] Magnesium carbonate can be produced synthetically according
to the methods known in the art. Among other methods, a
precipitation with carbon dioxide is known.
[0076] According to the present invention, the type of magnesium
carbonate is not particularly limited. Any known magnesium
carbonate can be used. The magnesium carbonate can preferably be
selected from magnesite, magnesia alba, and upsalite; magnesite is
especially preferred.
[0077] Calcium-Magnesium Carbonate
[0078] Calcium carbonates and magnesium carbonate can be used as
mixed carbonates. A known calcium-magnesium carbonate is dolomite
CaMg(CO.sub.3).sub.2, which can also be found as dolomite spar,
diamond spar and pearl spar.
[0079] According to the present invention, the type of
calcium-magnesium carbonate is not particularly limited;
preferably, dolomite can be used.
[0080] Iron Carbonate
[0081] Iron carbonate FeCO.sub.3 can be used in its pure form or in
the form of a natural mineral such as siderite, iron lime, iron
spar, spade iron stone, chalybeate, and steel stone; preferably
siderite is used. Alternatively, iron carbonate can be produced
synthetically according to the methods known in the art.
[0082] Manganese Carbonate
[0083] Manganese carbonate MnCO.sub.3 can be used in its pure form
or in the form of a natural mineral such as rhodochrosite.
Alternatively, manganese carbonate can be produced synthetically
according to the methods known in the art.
[0084] Zinc Carbonate
[0085] Zinc carbonate ZnCO.sub.3 can be used in its pure form or in
the form of a natural mineral such as smithsonite. Alternatively,
zinc carbonate can be produced synthetically according to the
methods known in the art.
[0086] Copper Carbonate
[0087] Copper carbonate CuCO.sub.3 can be used in the form of basic
compounds or in the form of a natural mineral such as malachite and
azurite. Alternatively, copper carbonate can be produced
synthetically according to the methods known in the art.
[0088] The following table provides an overview of the properties
of preferred carbonate compounds.
TABLE-US-00001 CO.sub.2 Cleaving Solubility Product Compound
[.degree. C.] pK.sub.L Calcite 898 8.48 Magnesite 650 8.03 Dolomite
800 17.09 Siderite 200 10.89 Zinc carbonate 180 10.00 Copper
carbonate 280 9.63 Malachite* 350-384 33.16 Rhodochrosite 350 10.39
*as CuCO.sub.3 Cu(OH).sub.2
[0089] In a preferred embodiment, the first solid is selected from
calcium carbonate, magnesium carbonate, dolomite, or iron
carbonate, or mixtures thereof.
[0090] In a second embodiment, the first solid is selected from
starch, in particular rice or oat starch. Preferably, the starch
should be insoluble in the carrier liquid as described below.
[0091] In its ready-to-use form, the coating composition preferably
comprises a carrier liquid. It is preferred that the first solid be
insoluble in the carrier liquid. In the context of the present
invention, the term "insoluble in the carrier liquid" means that
the first solid has a solubility product, expressed as pK.sub.L, of
at least about 4, preferably at least about 6, at 25.degree. C. The
solubility product can be measured by mixing a certain amount of
substance to be measured (e.g. 100 g) into a certain amount of
solvent (e.g. 1 liter) at a temperature of 25.degree. C., filtering
the liquid, and determining the dissolved content either by
evaporation of the solvent or by chemical analysis of the dissolved
substance.
[0092] The amount of the first solid in the solids component is not
particularly limited and can be from about 65 to about 99 wt.-%,
preferably about 80 to about 99 wt.-%, more preferably about 90 to
about 99 wt.-%. The upper limit of the amount of the first solid in
the solids component can be 90 wt.-%, preferably 95 wt.-%. Natural
minerals often contain mixtures of various chemical compounds. If a
natural mineral is used, the amount of the first solid specified
above refers to the amount of chemical compound(s) which can cleave
CO.sub.2 in the temperature range of about 150 to about
1000.degree. C. In the case of dolomite rock consisting, for
example, of 90 wt.-% calcium-magnesium carbonate and 10 wt.-% of
other components that cannot cleave CO.sub.2, only the 90 wt.-% of
calcium-magnesion carbonate would be taken into account for the
calculation of the above-mentioned amount. The 10 wt.-% of other
components which cannot cleave CO.sub.2 would thus be part of the
solids component, provided that they remain as a solid residue
during the defined drying.
[0093] Second Solid
[0094] In addition to the first solid, the solids component may
also contain a second solid. The second solid is understood to be
any solid that is unable to cleave CO.sub.2 in the temperature
range of about 150 to about 1000.degree. C.
[0095] Examples of the second solid include graphite, mica,
non-swellable aluminium silicates and swellable layered
silicates.
[0096] Graphite can be present in an amount from 0 to about 20
wt.-%, preferably from 0 to about 10 wt.-%, based on the solids
component.
[0097] One or more types of mica can be used. Examples include
muscuvite or phlogopite mica. Mica can be present in an amount from
0 to about 10 wt. %, preferably from 0 to about 5 wt.-%, more
preferably from 0 to about 2 wt.-%, based on the solids
component.
[0098] The second solid can contain one or more non-swellable
aluminium silicates. Examples include pyrophyllite, metakaolinite,
mullite, kyanite or sillimanite. Pyrophyllite and metakaolinite are
preferred. Non-swellable aluminum silicates can be present in an
amount from 0 to about 10 wt.-%, preferably from 0 to about 5
wt.-%, based on the solids component.
[0099] In a preferred embodiment, the D10 value of the second solid
(except the swellable layered silicates) is no more than about 15
.mu.m, preferably from about 0.1 .mu.m to about 10 .mu.m, more
preferably from about 0.1 .mu.m to about 8 .mu.m, especially
preferred about 0.1 .mu.m to about 7 .mu.m.
[0100] In a preferred embodiment, the D50 value of the second solid
(except the swellable layered silicates) is no more than about 50
.mu.m, more preferably from about 0.5 .mu.m to about 30 .mu.m, more
preferably from about 0.5 .mu.m to about 25 .mu.m, even more
preferably from about 0.5 .mu.m to about 20 .mu.m.
[0101] In a preferred embodiment, the D90 value of the second solid
(except the swellable layered silicates) is no more than about 100
.mu.m, more preferably from about 5 .mu.m to about 90 .mu.m, more
preferably from about 5 .mu.m to about 80 .mu.m, especially
preferred from about 5 .mu.m to about 75 .mu.m.
[0102] In a preferred embodiment, the D99 value of the second solid
(except the swellable layered silicates) is no more than about 250
.mu.m, more preferably from about 5 .mu.m to about 200 .mu.m, more
preferably from about 5 .mu.m to about 150 .mu.m, especially
preferred from about 5 .mu.m to about 100 .mu.m.
[0103] In a preferred embodiment, one or more of the
above-mentioned D50, D99, and D90 values are fulfilled
simultaneously. In a particularly preferred embodiment, the
above-mentioned D10, D50, D99, and D90 values are fulfilled
simultaneously.
[0104] The term swellability refers to the property of solids
dispersed in solvents to incorporate the solvent and thus become
more voluminous. This usually greatly increases viscosity.
[0105] In one embodiment, the second solid comprises one or more
swellable layered silicates to reduce the settling behavior of the
coating composition and to control the rheology. The swellable
layered silicates are not particularly limited. Any swellable
layered silicate known to the person skilled in the art which is
capable of storing water between its layers can be used.
Preferably, the swellable layer silicate can be selected from
attapulgite (palygorskite), ball clay, serpentines, kaolins,
smectites (such as saponite, montmorillonite, beidellite and
nontronite), vermiculite, illite, sepiolite, synthetic
lithium-magnesium layered silicate LAPONITE RD and mixtures
thereof, especially preferred from attapulgit (palygorskite),
serpentine, smectites (such as saponite, beidellite and
nontronite), vermiculite, illite, sepiolite, synthetic
lithium-magnesium layered silicate LAPONITE RD and mixtures
thereof, and in particular it is preferred that the swellable
layered silicate be attapulgite. Attapulgite is preferred because
of the increase in the flow limit.
[0106] Furthermore, the grain size of the swellable layered
silicates is not particularly limited, any usual grain size can be
used. The D10, D50, D90, and D99 values given for the second solid
also apply to the swellable layered silicates.
[0107] In a preferred embodiment, the D10 value of the swellable
layered silicates is no more than about 5 .mu.m, preferably from
about 0.1 .mu.m to about 5 .mu.m, more preferably from about 0.1
.mu.m to about 4 .mu.m, especially preferred about 0.1 .mu.m to
about 3 .mu.m.
[0108] In a preferred embodiment, the D50 value of the swellable
layered silicates is no more than about 30 .mu.m, preferably from
about 0.5 .mu.m to about 25 .mu.m, more preferably from about 0.5
.mu.m to about 20 .mu.m, especially preferred from about 0.5 .mu.m
to about 15 .mu.m.
[0109] Preferably, the D90 value of the swellable layered silicates
can be no more than about 50 .mu.m, more preferably from about 5
.mu.m to about 40 .mu.m, especially preferred from about 5 .mu.m to
about 30 .mu.m, and most preferred from about 5 .mu.m to about 25
.mu.m.
[0110] In a preferred embodiment, the D99 value of the swellable
layered silicates is no more than about 100 .mu.m, preferably from
about 5 .mu.m to about 90 .mu.m, more preferably from about 5 .mu.m
to about 80 .mu.m, especially preferred from about 5 .mu.m to about
75 .mu.m.
[0111] In a preferred embodiment, one or more of the
above-mentioned D50, D99, and D90 values are fulfilled
simultaneously. In a particularly preferred embodiment, the
above-mentioned D50, D99, and D90 values are fulfilled
simultaneously.
[0112] The amount of the swellable layered silicates (in particular
attapulgite) in the coating composition is not particularly
limited; it can preferably be from about 0 to about 5 parts by
weight, more preferably from about 0.1 to about 5 parts by weight,
especially preferred about 0.1 to about 4 parts by weight, and most
preferred from about 0.1 to about 2 parts by weight, based on the
solids component.
[0113] Carrier Liquid
[0114] The coating composition may contain a carrier liquid to
facilitate application. A carrier liquid is any component which
evaporates when the ready-to-use coating composition is dried, and
which is not present in the dried coating.
[0115] The coating composition can be provided as a dry powder, as
a concentrate which contains a portion of the required amount of
carrier liquid and has to be diluted with additional carrier liquid
before use, or as a ready-to-use coating composition which already
contains the desired amount of carrier liquid.
[0116] The carrier liquid can be selected by a person skilled in
the art according to the intended application. Preferably, the
carrier liquid may be selected from water, alcohols such as
aliphatic C.sub.1-C.sub.5 alcohols, or mixtures thereof. In a
preferred embodiment, the carrier liquid is water, methanol,
ethanol, n-propanol, isopropanol, n-butanol, or mixtures thereof,
more preferably water, ethanol, isopropanol or mixtures thereof,
and especially preferred water.
[0117] Coating compositions whose carrier liquid consists mainly of
water are usually called water coatings. Coating compositions whose
carrier liquid consists mainly of alcohol or alcohol mixtures are
called alcohol coatings. In one embodiment of the present
invention, the carrier liquid comprises about 0 to about 100 wt.-%,
preferably approximately about 30 to about 100 wt.-%, more
preferably about 60 to about 100 wt.-%, water, and as a further
component, about 100 to about 0 wt.-%, preferably about 70 to about
0 wt.-%, more preferably about 40 to about 0 wt.-%, one or more
alcohols as defined above, based on the carrier liquid. According
to the present invention, pure water coatings as well as pure
alcohol coatings as well as water/alcohol mixtures can be used. In
a particularly preferred embodiment, water is the sole carrier
liquid. Alternatively, it is also possible to produce coating
compositions whose solvent component consists of alcohol or, in the
case of so-called hybrid coatings, initially consists only of
water. By diluting with an alcohol or an alcohol mixture, these
coatings can be used as alcohol coatings. Preferably, ethanol,
propanol, isopropanol and mixtures thereof are used.
[0118] If necessary, other organic solvents can be used. Examples
include acetic acid alkyl esters such as acetic acid ethyl ester
and acetic acid butyl ester, and ketones such as acetone and methyl
ethyl ketone. The amount of the other organic solvents is not
particularly limited, preferably, they are present in an amount of
from about 0 to about 10 wt.-%, more preferably from about 0 to
about 5 wt.-%, and especially preferred from about 0 to about 1
wt.-%, based on the carrier liquid.
[0119] The amount of the carrier liquid in the coating composition
is not particularly limited, preferably, it is present in an amount
of 80 wt.-% or less, more preferably 75 wt.-% or less, and
especially preferred 70 wt.-% or less.
[0120] Accordingly, the amount of the solids component in the
coating composition is preferably about 20 wt.-% or more, more
preferably about 25 wt.-% or more, and especially preferred about
30 wt.-% or more.
[0121] In the ready-to-use coating composition, carrier liquid is
preferably present in an amount of from about 40 to about 85 wt.-%,
more preferably from about 45 to about 85 wt.-%, and especially
preferred from about 50 to about 85 wt.-%.
[0122] Accordingly, the amount of the solids component in the
ready-to-use coating composition is preferably from about 15 to
about 60 wt.-%, more preferably from about 15 to about 55 wt.-%,
and especially preferred from about 15 to about 50 wt.-%.
[0123] Optional Additives
[0124] In addition to the above components, the coating composition
may contain common additives such as binders, wetting agents,
defoamers, pigments, dyes, and biocidal active ingredients.
[0125] Binder
[0126] The function of a binder is primarily to bind the solids
component. Preferably, the binder is characterized by an
irreversible bond and thus results in an abrasion-resistant coating
on the mold. Abrasion resistance is of great importance for the
finished coating, as the coating can be damaged if it lacks
abrasion resistance. In particular, the binder should not soften
due to humidity. According to the present invention, all binders
can be used which are conventionally used in, for example, aqueous
and/or water-alcohol systems. As a binder, water-soluble starches
or dextrins whose D50 value is more than about 10 .mu.m (preferably
at least about 15 .mu.m) and which are soluble in the carrier
liquid, peptides, polyvinyl alcohol, polyvinyl acetate copolymers,
polyacrylic acid, polystyrene, polyvinyl acetate polyacrylate
dispersions and mixtures thereof can for example be used. In a
preferred embodiment of the present invention, the binder comprises
a dispersion of an alkyd resin, which is soluble both in water and
in low (e.g. C.sub.1-4) alcohols, such as ethanol, propanol and
isopropanol. Examples of alkyd resins include unmodified
water-dispersible alkyd resins, based on a natural oil or the fatty
acids thereof with polyalcohols, as described for example in U.S.
Pat. No. 3,442,835, or isocyanate-modified alkyd resins, as
described for example in U.S. Pat. No. 3,639,315--which are
preferred--or epoxy urethane-modified alkyd resins according to DE
43 08 188. For example, products from the NECOWEL series from ASK
Chemicals GmbH, 40721 Hilden, Germany, can be used. Other preferred
binders are polyvinyl alcohols and polyvinyl acetate copolymers, in
particular polyvinyl alcohols.
[0127] The term "binder" refers to the effective binding component
which can also be present as a solution or dispersion in diluted
form.
[0128] The binders are preferably used in an amount of about 0.1 to
about 5 parts by weight, more preferably about 0.2 to about 2 parts
by weight, based on all components of the coating composition.
[0129] Wetting Agents
[0130] Anionic and non-anionic surfactants of medium and high
polarity (HLB value of 7 and higher) known to the person skilled in
the art can preferably be used as wetting agents. Examples of
wetting agents that can be used in the present invention include
disodium dioctylsulfosuccinate, ethoxylated
2,5,8,11-tetramethyl-6-dodecyn-5,8-diol, ethoxylated
2,4,7,9-tetramethyl-5-decyn-4,7-diol or combinations thereof; more
preferably, ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol can be
used.
[0131] The wetting agents are preferably used in an amount of from
about 0.01 to about 1 parts by weight, more preferably from about
0.05 to about 0.3 parts by weight, and even more preferably from
about 0.1 to about 0.3 parts by weight, based on all the components
of the coating composition.
[0132] Defoamers
[0133] Defoamers or antifoaming agents are used to prevent foaming
during the preparation of the coating composition according to the
present invention and during its application. Foaming during the
application of the coating composition can lead to an uneven layer
thickness and to holes in the coating. Silicone or mineral oil can
for example be used as defoamers.
[0134] Preferably, the defoamer can be selected from the FINASOL
product line, commercially available from Total Deutschland
GmbH.
[0135] In the coating composition according to the present
invention, defoamers are used in an amount of from about 0.01 to
about 1 parts by weight, more preferably from about 0.05 to about
0.3 parts by weight, and especially preferred from about 0.1 to
about 0.2 parts by weight, based on all the components of the
coating composition.
[0136] Pigments and Dyes
[0137] In the coating composition according to the present
invention, common pigments and dyes can optionally be used. They
are added if necessary, in order to achieve a visible contrast,
e.g. between different layers, or to create a stronger separation
between the coating and the casting. Examples of pigments include
red and yellow iron oxide. Examples of dyes are commercially
available dyes such as the LUCONYL products from BASF SE.
[0138] The dyes and pigments are usually used in an amount of from
about 0.01 to about 10 parts by weight, preferably from about 0.05
to about 5 parts by weight, based on all the components of the
coating composition.
[0139] Biocidal Active Ingredients
[0140] The coating composition can optionally contain one or more
biocidal active ingredients (especially if the carrier liquid
includes water) in order to prevent a bacterial infestation and
thus avoid a negative influence on the rheology and the bonding
strength of the binding agents. The biocidal active ingredients are
not particularly limited; preferably they can be selected from the
group consisting of formaldehyde, glutaraldehyde, tetramethylol
acetylene diurea, 2-methyl-4-isothiazoline-3-one (MIT),
5-chloro-2-methyl-4-isothiazoline-3-one (CIT),
1,2-benzisothiazolin-3-one (BIT), or mixtures thereof, more
preferably from 2-methyl-4-isothiazoline-3-one (MIT),
1,2-benzisothiazoline-3-on (BIT), or mixtures thereof.
[0141] The amount of biocidal active ingredients in the coating
composition is not particularly limited and depends on the selected
biocidal active ingredient. The amount can, for example, range from
about 0.001 to about 1.0 parts by weight, preferably from about
0.005 to about 1.0 parts by weight, more preferably from about
0.007 to about 1.0 parts by weight, even more preferably from about
0.007 to about 0.9 parts by weight, and especially preferred from
about 0.007 to about 0.8 parts by weight, based on all the
components of the coating composition.
[0142] In a preferred embodiment, a coating composition according
to the invention comprises about 10 to about 60 parts by weight
calcium carbonate, and about 0.1 to about 2 parts by weight
attapulgit, based on the solids component. Furthermore, the coating
composition comprises about 0.2 to about 2 parts by weight binder,
about 0.1 to about 0.3 parts by weight wetting agents, about 0.1 to
about 0.2 parts by weight defoamers, about 0.005 to about 0.3 parts
by weight biocidal active ingredient, as well as carrier liquid,
preferably water, to make up the difference to 100 parts by
weight.
[0143] Preparation of the coating composition The coating
compositions according to the present invention are prepared using
common methods. For example, a coating composition according to the
present invention is prepared by taking a large part of the carrier
liquid (preferably the entire amount of the carrier liquid) and
adding swellable layered silicates (if they are used) using a high
shear mixer (e.g. about 400 to about 2000 rpm) (premixture B in the
examples). Then, additional solids components are stirred in, for
example the first solid as well as pigments and dyes (if they are
used) until a homogenous mixture is obtained. The order in which
the components are added is of little or no relevance and can
easily be determined by the person skilled in the art. Finally, the
wetting agents, defoamers, biocidal active ingredients, and binders
are stirred in, if they are used. The coating composition is for
example prepared at a temperature of preferably about 5 to about
50.degree. C., more preferably about 10 to about 30.degree. C.,
with a stirrer speed of preferably about 400 to about 2000 rpm,
more preferably about 1000 to about 1500 rpm, and with a tooth disc
with preferably d/D=about 0.3 to about 0.7, more preferably
d/D=about 0.4 to about 0.6 (d is the diameter of the tooth disc of
the mixer, D is the diameter of the mixing vessel).
[0144] The properties of the coating composition are preferably
adjusted to an impregnating coating so that the first solid can
penetrate into the surface of the casting mold. In particular, it
is preferred that the impregnating depth of the coating composition
be at least about 2 mm, preferably from about 2 mm to about 20 mm,
more preferably from about 2 mm to about 6 mm. The impregnation
depth can be measured by cutting.
[0145] The dry layer thickness of the dried coating resulting from
the coating composition described above is the thickness of the
layer of the dried coating composition ("coating"), which is
determined by drying the coating composition by substantially
completely removing the carrier liquid. Preferably, the dry layer
thickness of the coating can be no more than about 100 .mu.m, more
preferably from about 10 .mu.m to about 100 .mu.m, and still more
preferably from about 10 .mu.m to about 50 .mu.m. The dry layer
thickness of the coating is determined either preferably by
measuring 3-point bending bars before and after finishing (dried)
with a micrometer screw or by measuring with a wet film thickness
comb gauge. For example, the dry layer thickness can be determined
with the comb gauge by scraping away the coating on the end marks
of the comb until the substrate appears. The dry layer thickness
can then be read from the markings of the teeth. Or, it is also
possible to measure the wet layer thickness in the matted state
(hereinafter referred to as the matte layer thickness) according to
DIN EN ISO 2808, wherein the dry layer thickness amounts to 70 to
80% of the thickness of the matted layer. A "matted" layer is a
layer that is no longer flowable, in which the solvent content is
reduced so much that the surface no longer has a gloss.
[0146] Preferably, the impregnating depth of the coating
composition is at least about 2 mm and the dry layer thickness is
no more than about 100 .mu.m. More preferably, the impregnating
depth of the coating composition is from about 2 mm to about 20 mm
(more preferably from about 2 mm to about 6 mm) and the dry layer
thickness from about 10 .mu.m to about 50 .mu.m.
[0147] The viscosity of the ready-to-use coating composition can be
adjusted from about 10 sec to about 16 sec, preferably from about
10 sec to about 13 sec, determined according to DIN 53211; flow cup
4 mm, Ford Cup.
[0148] The density of the ready-to-use finishing composition can,
for example, be from about 20 .degree.Be to about 50 .degree.Be,
preferably from about 25 .degree.Be to about 35 .degree.Be,
determined according to the Baume buoyancy method; DIN 12791.
[0149] Use of the Coating Composition
[0150] The coating composition according to the present invention
can be used for coating a casting mold. One possible method
comprises the steps of: [0151] (a) providing a casting mold
comprising a surface which defines a casting cavity, [0152] (b)
providing a coating composition according to the present invention;
[0153] (c) applying the coating composition to at least one part of
the surface which defines the casting cavity; and [0154] (d) drying
the coating composition.
[0155] All types of bodies that are necessary for the production of
molds are referred to as casting molds. The casting molds are not
particularly limited, all casting molds commonly used in the iron,
steel and non-metal industries can be used, for example cores,
molds or dies. The casting molds can consist of a refractory,
granular mold base material, which is solidified by means of a
curable binder. The refractory, granular mold base material is not
particularly limited, any common mold base material can be used.
Preferably, the refractory, granular mold base material can
comprise quartz sand, zircon sand, chromite sand, chamotte,
bauxite, olivine sand, feldspathic sand, andalusite sand, aluminum
silicate hollow balls (also referred to as "microspheres"), glass
beads, glass granules, the ceramic spherical mold base material
known under the designation "cerabeads" or "carboaccucast", or
mixtures thereof. In particular, the inventive coating composition
is used for casting molds wherein quartz sand or proportions of
quartz sand were used as a mold base material.
[0156] The grain size of the sand should be from about 100 to about
600 .mu.m, preferably from about 100 to about 500 .mu.m and most
preferably from about 200 to about 400 .mu.m.
[0157] The curable binder is not particularly limited. Any curable
binder known to the person skilled in the art can be used.
Preferably, organic binders such as polyurethane, furan resin or
epoxy acrylate binders, inorganic binders, such as water glass, or
mixtures thereof can be used; it is especially preferred that the
binders are based on PUR cold box, water glass CO.sub.2, resol
methyl formate (MF), resol CO.sub.2, furan resin, phenolic resin,
or water glass ester binders. Polyurethane binders are particularly
preferred. The amount of curable binder in the casting mold is not
particularly limited; the binder may be present in any common
amount. Preferably, the binder is present in an amount of about 0.2
to about 5 parts by weight, further preferably of about 0.3 to
about 4 parts by weight, more preferably of about 0.4 to about 3
parts by weight, based on 100 parts by weight of the refractory,
granular mold base material. The coating compositions are suitable
for all conceivable applications where a casting mold is to be
coated with a coating. Examples of casting molds, i.e. cores and
molds used in foundry applications, include sand cores which are
bonded with PUR cold box, water glass CO.sub.2, resol MF, resol
CO.sub.2, furan resin, phenolic resin or water glass esters. Other
examples of preferred casting molds, which can be coated with the
coating compositions according to the present invention, are for
example described in "Formstoffe und Formverfahren" [Engl. molding
materials and molding methods], Eckart Flemming and Werner Tilch,
Wiley-VCH, 1993, ISBN 3-527-30920-9.
[0158] The surfaces of the casting mold, optionally equipped with
one or more casting cores, define a casting cavity into which the
liquid metal is introduced. The surfaces of a casting mold can be
the surfaces of a core or of a hollow mold. According to the
present invention, the casting molds and cores can be completely or
partially coated. Preferably, the surfaces of the casting mold and
cores that come into contact with the casting metal are coated.
[0159] The coating composition is initially provided in a
ready-to-use form. If it is present as a dry powder or as a
concentrate, carrier liquid is added to achieve the consistency
necessary for application.
[0160] In one embodiment, for example, the coating composition may
be provided in the form of a kit (multi-component pack containing
two or more containers for different components). The solids
component and the carrier liquid may be present side by side in
separate containers. All components of the solids component may be
present as a powdered solids mixture in one container. The
components of the solids component can alternatively be provided as
several separate components. Where applicable, other components to
be used, such as binders, wetting agents, defoamers, pigments,
dyes, and biocidal active ingredients, may be present in this kit
together with the above-mentioned components or in one or more
separate containers. The carrier liquid may either include the
optional components to be used if necessary, for example in the
same container, or it may be present separately from other optional
components in a separate container. In order to prepare a
ready-to-use coating composition, the appropriate quantities of the
components are mixed together.
[0161] Typically, the coating composition can be present as a water
coating. Alternatively, a ready-to-use alcohol coating can be
provided from this water coating by adding an alcohol.
[0162] The application and drying of at least one layer of a
coating composition to at least one part of the surface defining
the casting cavity is not particularly limited. All conventional
application methods described in the art can be used for this
purpose. Examples of preferred application methods are immersion
coating, flow coating, spray coating, and painting. Conventional
application methods are for example discussed in "Formstoffe und
Formverfahren" [Engl. molding materials and molding methods],
Eckart Flemming and Werner Tilch, Wiley-VCH, 1993, ISBN
3-527-30920-9.
[0163] During an immersion coating process, the casting mold is
immersed, for example, in a container with a ready-to-use coating
composition for about 1 second to about 2 minutes. The time it
takes for the excess coating composition to flow off after
immersion depends on the flow behavior of the coating composition
used. After a sufficient flow off period, the coated casting mold
is subjected to drying.
[0164] As a drying process, all conventional drying methods known
in the art can be used, such as air drying, drying in dehumidified
air, drying with microwave or infrared radiation, drying in a
convection furnace, and the like. In a preferred embodiment of the
present invention, the coated casting mold is dried at about 100 to
about 250.degree. C., more preferably at about 120 to about
180.degree. C., in a convection furnace. When alcohol coatings are
used, the coating composition is preferably dried by burning off
the alcohol or alcohol mixture. In that case, the coated casting
mold is additionally heated by the combustion heat. In a further
preferred embodiment, the coated casting mold is air-dried without
any further treatment.
[0165] The coating composition according to the present invention
can be used as a base layer. The dry layer thickness of the base
layer is, for example, at most about 100 .mu.m, more preferably
from about 10 .mu.m to about 80 .mu.m, and still more preferably
from about 10 .mu.m to 50 .mu.m.
[0166] Casting molds coated according to the present invention are
preferably used for the production of metal bodies. They are
particularly suitable for the manufacture of engine and engine
components, brake discs, turbochargers, exhaust manifolds, and
general machine components.
[0167] In a casting process, a casting mold coated according to the
invention is provided, liquid metal is filled into the mold, and
after the metal has hardened, the casting mold is removed.
[0168] The invention will be explained in the following examples;
however, they shall not restrict the invention in any way.
Examples
[0169] The following components were used:
TABLE-US-00002 Attapulgite ATTAGEL 40 from BASF, 67063
Ludwigshafen, Germany D99 appr. 50 .mu.m, D90 appr. 20 .mu.m, D50
appr. 9 .mu.m, D10 appr. 2 .mu.m Biocide ACTICIDE F (N) (70 wt.-%
tetramethylol acetylene diurea) from Thor GmbH, 67346 Speyer,
Germany Defoamer FINASOL, Total Deutschland GmbH, 10117 Berlin,
Germany Wetting agent SURFYNOL 440, Evonik Corporation, Allentown,
PA 18195, USA Binder POLYVIOL (25 wt.-% polyvinyl alcohol), Wacker
AG, 81737 Munich, Germany Amorphous graphite Georg H. Luh, 65396
Walluf, Deutschland D 99 appr. 90 .mu.m, D90 appr. 60 .mu.m, D50
appr. 18 .mu.m, D10 appr. 7 .mu.m Glossy powdered graphite Fa.
Georg H. Luh GmbH, 65396 Walluf, Deutschland; C content at least 85
wt.-%, ash at most 15 wt.-% Particle size distribution determined
with laser diffraction granulometry: D10 15 to 30 .mu.m, D50 80 to
120 .mu.m, D90 190 to 250 .mu.m Clay Karlicher Blauton
yellow-burning T7001 KTS, Karlicher Ton und Schamottewerke Mannheim
GmbH & Co. KG, 56218 Mulheim- Karlich, Germany; chemical
analysis, in wt.-% annealed: SiO.sub.2 53.66, Al.sub.2O.sub.3 37,
TiO.sub.2 3.75, Fe.sub.2O.sub.3 2.98, CaO 0.73, MgO 0.63, K.sub.2O
0.75, Na.sub.2O 0.07; sedimentation analysis by means of sedigraph
measurement in mass-%: <2.0 .mu.m 95.7, mineral analysis in
mass-%: kaolinite 70 to 75, illite 7.0, montmorillonite 15 to 20,
quartz 2.0, Fe--Ti minerals 3.0 Mica Fa. Georg H. Luh GmbH, 65396
Walluf, Deutschland; chemical analysis in wt.-%: SiO.sub.2 43 to
46, Al.sub.2O.sub.3 33 to 37, Fe.sub.2O.sub.3 2 to 5, K.sub.2O 9 to
11; screen analysis, passage through 60 .mu.m screen: 25 to 64
wt.-% Calcined kaolin Satintone W, BASF Corporation, Charlotte, NC,
USA D99 appr. 65.5 .mu.m, D90 8.53 .mu.m, D50 2.4 .mu.m, D10 appr.
0.4 .mu.m
[0170] The following components were examined as first solid:
TABLE-US-00003 Calcium carbonate ETIQUETTE VIOLETTE from Omya GmbH,
50679 Cologne, Germany D99 appr. 15 .mu.m, D90 appr. 8 .mu.m, D50
appr. 3 .mu.m, D10 appr. 1 .mu.m Dolomite HELADOL10, Helawit GmbH,
D-23829 Wittenborn, Germany D99 appr. 15 .mu.m, D90 appr. 8 .mu.m,
D50 appr. 3 .mu.m, D10 appr. 1 .mu.m Iron carbonate Cofermin
Chemicals GmbH & Co. KG, D-45130 Essen, Germany as obtained 100
mesh = 150 .mu.m micronized by grinding to D99 about 5 .mu.m, D90
about 1.4 .mu.m, D50 about 0.5 .mu.m, D10 about 0.2 .mu.m Rice
starch Hermann Kroner GmbH, D-49479 Ibbenburen, Germany D50 = about
5 .mu.m
[0171] A coating composition for coating a casting mold was
obtained as follows:
[0172] The first solid was combined with premixtures A and B, and
the coating composition was adjusted with additional water to a
flow viscosity of about 13 sec, determined with an immersion flow
cup according to DIN 53211 with a 4 mm nozzle.
TABLE-US-00004 Wt.-% Premixture A Premixture B Water 99.4 85.1
Wetting agent 0.6 Biocide 1.0 Binder 9.0 Attapulgite 4.0 Defoamer
0.9
[0173] All values are given in wt.-%.
[0174] Dome core molded bodies with the dimensions diameter 50 mm
and height 50 mm with an upper radius of 25 mm, and step cores with
the dimensions R.sub.1=63 mm/H.sub.1=25 mm, R.sub.2=54
mm/H.sub.2=25 mm, R.sub.3=45 mm/H.sub.3=25 mm, R.sub.4=37
mm/H.sub.4=25 mm, R.sub.5=28 mm/H.sub.5=25 mm, R.sub.6=21
mm/H.sub.6=25 mm, and R.sub.7=12 mm/H.sub.7=43 mm (wherein R; is
the radius and H.sub.i is the height of the i-th stage) were
prepared from Sand H32 from the Quarzwerke Group with 0.8 wt.-%
ASKOCURE 388 (available from ASK Chemicals, Hilden, Germany) and
0.8 wt.-% ASKOCURE 666, each based on the sand, using a
polyurethane cold box process by amine gassing with
dimethylethylamine. The level 0 of the dome core shown in FIG. 1 is
glued in and therefore does not come into contact with the
metal.
[0175] Subsequently, the dome cores or step cores were manually
immersed in the stirred coating composition and then dried in the
drying furnace at 120.degree. C.
[0176] The dried cores were freed from the coating by rubbing at
the core marks and the mirror surface, so that no compressive
stress is generated, and glued into the casting mold of sand H32
hardened by water glass/ester by means of ASKOBOND RAPID A
(available from ASK Chemicals, Hilden, Germany). After closing and
clamping the mold package by means of screw clamps, the castings
were performed at 1420.degree. C. with gray cast iron GJL 200.
[0177] After cooling and unpacking the castings, the cavity of the
core was sandblasted (2 bar pressure) and evaluated.
[0178] The veining was evaluated as follows:
[0179] Step core: The table below shows the number of veins on the
respective steps
[0180] Dome core: In the table below, the veining was rated with
school grades 1 to 6.
Examples According to the Present Invention: Dome Core
TABLE-US-00005 [0181] Iron Calcium carbonate DIN 4 mm Matte layer
Impregnation Premixture A carbonate Dolomite micronized Rice starch
Premixture B flow time thickness depth Evaluation Example (wt.-%)
(wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) (s) (.mu.m) (mm) veining* 1
34 46 20 13.0 50 4 1 2 34 46 20 12.5 75 4 1 3 34 46 20 11.5 25 4 2
4 34 46 20 14.0 100 4 2-3 *Grades: 1 = very good; 2 = good; 3 =
satisfactory; 4 = adequate; 5 = poor; 6 = insufficient
Examples According to the Present Invention: Step Core
TABLE-US-00006 [0182] Calcium Graphite DIN 4 mm Premixture A
carbonate Dolomite amorphous Premixture B flow time Examples
(wt.-%) (wt.-%) (wt.-%) (wt.-%) (parts by wt.) (s) 5 39 39 22 12.4
6 39 35 4 22 12.2 7 39 39 22 11.5 Matte layer Impregnation Number
of Number of Number of Number of thickness depth veins veins veins
veins Examples (.mu.m) (mm) Step 2 Step 3 Step 4 Step 5 5 75 4 0 0
0 2 6 50 5 0 0 0 3 7 50 4 0 0 0 3
[0183] When using the step core, which is glued into a cylindrical
sand mold with a cavity having a diameter of 150 mm and a height of
200 mm, so that the "foot" is at the top, the volume ratio of metal
to sand core gradually increases from the 1st step (the "foot",
R=63 mm). The casting mold is filled from the bottom. The "number
of veins step n" indicates the number of veins that are present on
the step core casting at the nth level.
[0184] Furthermore, as a comparative example, a dome core and a
step core were coated as described in the patent application DE 10
2018 004 234.1 according to manufacturer's specifications.
Non-Inventive Example: Dome Core
TABLE-US-00007 [0185] Glossy powdered Calc. DIN 4 mm Matte layer
Impregnation Premixture A Mica Clay graphite kaolin Premixture B
Water flow time thickness depth Evaluation Example (wt.-%) (wt.-%)
(wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) (s) (.mu.m) (mm) veining* 8
39 20 9 5 5 22 30 12.8 450 1 4
Non-Inventive Example: Step Core
TABLE-US-00008 [0186] Glossy powdered Calc. DIN 4 mm Premixture A
Mica Clay graphite kaolin Premixture B Water flow time Example
(wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) (s) 8 39 20
9 5 5 22 30.0 12.8 Matte layer Impregnation Number of Number of
Number of Number of thickness depth veins veins veins veins Example
(.mu.m) (mm) Step 2 Step 3 Step 4 Step 5 8 450 1 1 1 1 3
[0187] The results show that at a very low matte layer thickness of
only 25 to 100 .mu.m, the coating composition according to the
present invention shows a sufficiently high protection against
veining formation both in the dome core test and in the step core
test. For the evaluation, steps 1 to 5 were evaluated during the
step test, as this corresponds to the most common and demanding
applications in foundries for automotive parts in terms of the wall
thickness ratio of metal to sand. In this respect, the effect of
the coating composition according to the present invention exceeds
the effect of conventional coating compositions against veining
defects, which are applied with high layer thicknesses of 300 to
500 .mu.m.
[0188] It is apparent that the coating composition according to the
present invention saves the process step of adding a sand additive
and provides a much higher active ingredient concentration in the
zone where this concentration is needed. In particular, the gas
formation provides a very good protection against so-called
veining, which is often found in quartz sand due to the thermal
expansion of the quartz sand (quartz inversion) and the
insufficient thermal strength, observed especially in polyurethane
cold box cores.
* * * * *