U.S. patent application number 14/757818 was filed with the patent office on 2016-05-12 for coating compositions for casting moulds and cores for avoiding maculate surfaces.
This patent application is currently assigned to ASK Chemicals GmbH. The applicant listed for this patent is ASK Chemicals GmbH. Invention is credited to Michael Kloskowski, Matthias Schrod, Reinhard Stotzel.
Application Number | 20160129496 14/757818 |
Document ID | / |
Family ID | 40977587 |
Filed Date | 2016-05-12 |
United States Patent
Application |
20160129496 |
Kind Code |
A1 |
Stotzel; Reinhard ; et
al. |
May 12, 2016 |
Coating compositions for casting moulds and cores for avoiding
maculate surfaces
Abstract
The invention relates to a size composition (coating
composition) for casting moulds and cores, comprising at least one
metal additive which contains a metal or a compound of a metal,
wherein the metal is selected from one of groups 7 or 9 to 12 of
the Periodic Table of the Elements. The invention also relates to a
process for producing a casting mould, which comprises a mould
coating of the size (coating) according to the invention, and to
the use of said mould for the casting of metals.
Inventors: |
Stotzel; Reinhard;
(Solingen, DE) ; Schrod; Matthias; (Ergolding,
DE) ; Kloskowski; Michael; (Dusseldorf, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASK Chemicals GmbH |
Hilden |
|
DE |
|
|
Assignee: |
ASK Chemicals GmbH
Hilden
DE
|
Family ID: |
40977587 |
Appl. No.: |
14/757818 |
Filed: |
December 23, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12994578 |
Nov 24, 2010 |
|
|
|
PCT/EP2009/056434 |
May 27, 2009 |
|
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14757818 |
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Current U.S.
Class: |
164/14 ; 164/349;
164/369 |
Current CPC
Class: |
B22C 9/10 20130101; B22C
3/00 20130101; B22C 9/18 20130101; B22C 9/02 20130101 |
International
Class: |
B22C 3/00 20060101
B22C003/00; B22C 9/18 20060101 B22C009/18; B22C 9/02 20060101
B22C009/02; B22C 9/10 20060101 B22C009/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2008 |
DE |
DE 102008025460.6 |
Claims
1. A coated mould and/or coated core prepared by a process
comprising: curing a mixture of at least one refractory mould
material and at least one binder to form a mould and/or a core; and
applying a coating composition to the mould and/or the core to form
the coated mould or the coated core; wherein said coating
composition applied comprises at least one carrier liquid and a
metal additive that comprises a metal or a compound of a metal,
wherein the metal is manganese, and wherein the fraction of the
metal additive is less than 50 wt. % based on the solid content of
the coating composition, and wherein the metal additive is
contained in the coating composition in a fraction of at least 10
wt. % based on the solid content of the coating composition.
2. (canceled)
3. The coated mould and/or coated core according to claim 1,
wherein the metal is employed in pure form or in the form of an
alloy with other metals.
4. The coated mould and/or coated core according to claim 1,
wherein the metal or metal compound of a metal is contained in the
metal additive in a fraction of at least 10 wt. %, determined as
metal and based on the weight of the metal additive.
5. (canceled)
6. The coated mould and/or coated core according to claim 1,
wherein the metal is contained in the metal additive in the form of
an iron alloy.
7. The coated mould and/or coated core according to claim 1,
wherein the metal additive has a mean particle size (D50) in the
range from 0.5 to 5000 .mu.m.
8. The coated mould and/or coated core according to claim 1,
wherein the coating composition contains a solvent and the solvent
is formed, at least in part, of at least one alcohol.
9. The coated mould and/or coated core according to claim 8,
wherein the at least one alcohol forms a fraction of at least 50
wt. % in the solvent.
10. A method for producing a casting mould, wherein a mould
material mixture is provided that contains at least one refractory
mould material and a binder, the mould material mixture is shaped
to a basic mould comprising a mould cavity, and at least the faces
of the mould cavity of the basic mould are coated with a coating
composition, wherein said coating composition comprises at least
one carrier liquid and a metal additive that comprises a metal or a
compound of a metal, wherein the metal is manganese, and wherein
the fraction of the metal additive is less than 50 wt. % based on
the solid content of the coating composition, and wherein the metal
additive is contained in the coating composition in a fraction of
at least 10 wt. % based on the solid content of the coating
composition.
11. (canceled)
12. (canceled)
13. (canceled)
14. The coated mould and/or coated core according to claim 1,
wherein the fraction of the metal additive in the coating
composition is less than 40 wt. % based on the solid content of the
coating composition.
15. The coated mould and/or coated core according to claim 1,
wherein the composition further contains a binder.
16. The coated mould and/or coated core according to claim 1,
wherein the fraction of the metal additive in the coating
composition is less than 35 wt. % based on the solid content of the
coating composition.
17. The coated mould and/or coated core according to claim 1,
wherein the manganese is in the form of a manganese oxide or a
manganese salt.
18. The coated mould and/or coated core according to claim 1,
wherein the moulds and cores are dead moulds.
19. A coated mould and/or coated core prepared by a process
comprising: curing a mixture of at least one refractory mould
material and at least one binder to form a mould and/or a core; and
applying a coating composition to the mould and/or the core to form
the coated mould and/or the coated core; wherein said coating
composition applied comprises at least one carrier liquid and a
metal additive that comprises a metal or a compound of a metal;
wherein the metal is manganese, and wherein the fraction of the
metal additive is less than 50 wt. % based on the solid content of
the coating composition, and wherein the metal or compound of a
metal is contained in the metal additive in a fraction of at least
10 wt. %, determined as metal and based on the weight of the metal
additive.
20. A coated mould and/or coated core according to claim 19,
wherein the metal additive is contained in the coating composition
in a fraction of at least 10 wt. % based on the solid content of
the coating composition.
Description
[0001] The invention relates to a size (coating), which is
particularly adapted for mass casting, a method for producing a
cast part and a casting mould comprising a mould coating.
[0002] Most products of the iron and steel industry, as well as
those of the nonferrous metal industry undergo casting for the
first shaping. The molten materials, either ferrous metals or
nonferrous metals, are converted into geometrically defined objects
with defined workpiece properties. In order to shape the cast
parts, very complicated casting moulds must sometimes first be
produced to receive the melts. The casting moulds are divided into
dead moulds, which are destroyed after every casting process, and
permanent moulds, with each of which a large number of cast parts
can be produced.
[0003] The dead moulds usually consist of a mineral, refractory,
granular mould material that is often mixed with various further
additives, for example in order to achieve a good casting surface
that is solidified with the aid of a binder. Washed, graded silica
sand is usually used as a refractory, granular mould material.
Chromite, zircon and olivine sand are also employed for specific
applications in which particular requirements must be satisfied. In
addition, mould materials based on fireclay, as well as magnesite,
silimanite or corundum are still used. The binder with which the
mould materials are solidified can be of an inorganic or organic
nature. Smaller dead moulds are predominantly produced from mould
materials that are solidified by bentonite as a binder, whilst
organic polymers are usually used as a binder for larger moulds.
The production of casting moulds is usually carried out by first
mixing the mould material with the binder in such a way that the
particles of the mould material are coated with a thin film of the
binder. This mould material mixture is then introduced into a
suitable mould and optionally compressed to achieve sufficient
stability of the casting mould. The casting mould is then cured,
for example by being heated or by adding a catalyst. Once the
casting mould has reached at least a specific initial strength, it
can optionally be removed from the mould and for complete curing be
transferred to a kiln for example in order to be heated there for a
specific period of time to a specific temperature.
[0004] Permanent moulds are used for the production of a large
number of cast parts. They must therefore withstand the casting
process and the associated loads without becoming damaged.
Depending on the field of application, particular cast irons as
well as unalloyed and alloyed steels, and also copper, aluminium,
graphite, sintered metals and ceramic materials have proven to be
effective materials for permanent moulds. Gravity die casting,
high-pressure die casting, centrifugal casting and continuous
casting methods are examples of permanent mould casting.
[0005] Casting moulds are subjected to very high thermal and
mechanical loads during the casting process. Faults may therefore
be produced at the contact face between liquid metal and the
casting mould, for example where the casting mould cracks or liquid
metal penetrates into the structure of the casting mould. The faces
of the casting mould that come into contact with the liquid metal
are usually provided with a protective coating that is also
referred to as a size. A size of this type usually consists of an
inorganic refractory material and a binder that are dissolved or
suspended in a suitable solvent, for example water or alcohol.
[0006] The surface of the casting mould can thus be modified by
these coatings and adapted to the properties of the metal to be
processed. The appearance of the cast part can thus be improved by
the size by producing a smooth surface since irregularities caused
by the size of the particles of the mould material are compensated
for by the size. The size can furthermore influence the cast part
metallurgically, for example by selectively transferring additives
at the surface of the cast part into the cast part via the size,
these additives improving the surface properties of the cast part.
Furthermore, the sizes form a layer that chemically insulates the
casting mould from liquid metal during casting. Any adhesion
between the cast part and the casting mould is thus prevented in
such a way that the cast part can be removed from the casting mould
without difficulty. In addition, the size ensures a thermal
separation between the casting mould and the cast part. This is
particularly important in the case of permanent moulds. If this
function is not fulfilled, a metal mould for example will be
subjected to such high thermal loads during the successive casting
processes that it will be destroyed prematurely. However, the size
can also be used to selectively control the heat transfer between
the liquid metal and casting mould, for example in order to form a
specific metal structure as a result of the cooling rate.
[0007] The sizes used conventionally contain, for example, clays,
quartz, diatomaceous earth, cristobalite, tridymite, aluminium
silicate, zirconium silicate, mica, fireclay or else coke or
graphite as raw materials. These raw materials cover the surface of
the casting mould and seal the pores against penetration of the
liquid metal into the casting mould. As a result of their high
insulating capability, sizes that contain silicon dioxide or
diatomaceous earth as raw materials are often used since these
sizes can be produced at low cost and are available in large
volumes.
[0008] It has already been attempted to selectively introduce alloy
constituents into the surface of a cast part via a size layer, for
example in order to improve the hardness of the surface. K.
Herfurth and S. Pinkert, Technische Zeitschrift fur das
Gie.beta.ereiwesen, 19, 1973, 365-400, as well as K. Herfurth, S.
Pinkert, K. Nowak, "Oberflachenlegierungen von Stahlguss in der
Gie.beta.form", Freiberger Forschungsbericht, B 184 1975, 203-215
thus describe pastes that contain large amounts of transition
metals such as chromium, nickel or manganese in the form, for
example, of ferrochromium or ferromanganese. The fraction of these
metals or alloys in the paste is considerably more than 50 wt. %.
In addition, a binder is also contained in the paste, normally
water glass. These pastes are applied to faces of the casting mould
that come into contact with the liquid metal material, normally
steel, during casting. During casting the metals contained in the
paste are melted by the heat of the liquid metal material and form
an alloy therewith locally at the surface of the cast part, this
alloy then setting as a peripheral shell. Depending on the way in
which the process is carried out, peripheral shells with a
thickness of up to 10 mm may be produced. These peripheral shells
may thus be very hard. In order to produce a casting mould, for
example a dredging shovel, it would no longer be necessary with
this method to produce the entire cast part from the corresponding
alloy. Instead it would be sufficient to selectively produce merely
the portions of the casting mould that are particularly loaded, for
example the teeth of the dredging shovel, with the aid of the alloy
constituents contained in the paste during the casting process from
an alloy that makes it possible to achieve particularly high
surface hardness. However, what is problematic in this method is
the different shrinkage coefficient of the various materials. The
cured surface layer does not therefore have the same thickness
throughout or else irregularities in the surface are observed, such
as cracks, chips or recesses.
[0009] In iron and steel casting, faults sometimes form at the
surface of the cast part, such as a maculate, uneven or burnt-in
surface, chips, pitting, holes or pinholes or white or black
coatings are formed. The causes of these faults are not yet fully
understood. It has been attempted to combat them, for example by
changing the casting parameters, modifying the binder system of the
casting mould or else adding various additives to the sizes.
However the success of these measures has generally been
unsatisfactory. The fault does initially disappear. However it
reappears after some time, although it is impossible to predict the
timing, intensity and size of the fault.
[0010] If the aforementioned faults do occur, complex reworking of
the surface of the cast part is necessary in order to achieve the
desired surface properties. This requires addition process steps
and therefore a reduction in productivity or an increase in costs.
If the faults occur at faces of the cast part that are not easily
accessible or are inaccessible, this can also lead to wastage of
the cast part.
[0011] The object of the invention is therefore to propose measures
that can be used in metal casting to improve the surface of the
cast part in such a way that the extent of surface treatment of the
cast part after casting can be reduced.
[0012] This object is achieved with a size composition having the
features of claim 1. Advantageous developments of the size
composition according to the invention are the subject of the
dependent claims.
[0013] It has surprisingly been found that adding a specific metal
additive, to a size composition can lastingly improve the quality
of the surface of the cast part, and for example the formation of
graining at the surface of the cast part is largely or completely
suppressed. It is not observed that larger amounts of the metal
additive or its constituents pass into the cast part. There are
therefore no difficulties caused by different expansion or
shrinkage coefficients between the cast part and peripheral
shell.
[0014] In accordance with the invention the metal additive
contained in the size composition contains at least one metal or a
compound of a metal, the metal being selected from one of groups 7
or 9 to 12 of the Periodic Table of the Elements.
[0015] The groups are numbered based on the currently applicable
rules of the IUPAC. In accordance with the old rules of the IUPAC,
group 7 corresponds to group VIIA. Groups 9 and 10 correspond to
the elements Co, Rh, Ir as well as Ni, Pd and Pt of the old group
VIIIA and groups 11 and 12 correspond to groups IB or IIB of the
old notation.
[0016] The metal additive can contain a metal, i.e. the metal in
the oxidation state zero, the metal possibly being employed both in
pure form and in the form of an alloy with other metals. However,
the metal additive can also be present in the form of an oxidised
metal, i.e. in the form of an oxide or a salt, such as a carbonate,
a nitrate or chloride, the oxide being preferred.
[0017] The metal is preferably employed in reduced form, i.e. in
the oxidation state zero.
[0018] A plurality of the named metals or compounds of these metals
can be contained in the metal additive. However, only one of the
metals is preferably contained in the metal additive in reduced or
oxidised from.
[0019] Metals or their compounds selected from groups 7, 10 or 11
of the Periodic Table of the Elements are preferably used in the
metal additive, manganese, nickel and copper being particularly
preferred.
[0020] The metal additive may be formed merely of the named metals
or their compounds. However it is also possible that further metals
or compounds are contained in the metal additive in addition to
these metals or their compounds.
[0021] In accordance with a preferred embodiment the metal or metal
compound, calculated as metal and based on the weight of the metal
additive, is contained in the metal additive in an amount of at
least 10 wt. %, especially in an amount of at least 20 wt. %,
preferably in an amount of at least 30 wt. %, particularly
preferably in an amount of at least 40 wt. % and more particularly
preferably in an amount of at least 50 wt. %.
[0022] In accordance with one embodiment the metal additive is only
formed of at least one of the named metals, particularly manganese,
nickel or copper. However, in accordance with one embodiment it is
sufficient for the metal or its compound to be contained in the
metal additive in an amount of less than 90 wt. %, in accordance
with a further embodiment in an amount of less than 80 wt. % and in
accordance with yet a further embodiment in an amount of less than
70 wt. %.
[0023] In addition to the metal additive, the size composition can
also contain further constituents that are conventional for sizes.
In accordance with a preferred embodiment the metal additive is
contained in the size composition in an amount, based on the solid
fraction of the size composition, of at least 10 wt. %, preferably
at least 15 wt. % and particularly preferably at least 20 wt. % in
order to achieve a lasting influence on the surface of the cast
part.
[0024] As already explained, the size is not preferably used to
achieve an alloy of a surface layer of a cast part, but instead so
the surface or a peripheral shell has substantially the same
composition as portions of the cast part that are arranged spaced
from the surface of the cast part, i.e. in its volume.
[0025] It is therefore preferably provided for the fraction of
metal additive in the size composition to be selected as less than
50 wt. %, especially less than 40 wt. % and particularly preferably
less than 35 wt. % based on the solid content of the size
composition.
[0026] As already explained, the metal additive may contain merely
at least one of the above-mentioned metals, preferably at least one
metal of manganese, nickel and copper. However, in accordance with
one embodiment it is also possible for the at least one metal to be
contained in the metal additive in the form of an alloy. In
accordance with one embodiment the metal is contained in the metal
additive in the form of an iron alloy. The fraction of iron in the
metal additive, expressed as elemental iron, is preferably selected
in the range from 20 to 80 wt. %, especially 30 to 70 wt. %.
[0027] In addition to the metal and the iron, the alloy may also
contain further constituents.
[0028] In accordance with a further embodiment the metal additive
contains aluminium as a constituent, the fraction of aluminium in
the metal additive, determined as elemental aluminium, is selected
as especially less than 10 wt. % and preferably less than 8 wt. %.
In accordance with one embodiment the metal additive contains
aluminium in a fraction of more than 2 wt. %. In accordance with
one embodiment of the size according to the invention the metal
additive comprises a fraction of aluminium in the range from 2 to 8
wt. %, preferably 3 to 6 wt. %, particularly preferably 3 to 5 wt.
%.
[0029] In accordance with one embodiment the metal additive can
also be used in a silicon alloy. The silicon fraction of a silicon
alloy of this type is preferably selected in a range from 20 to 80
wt. %, particularly preferably 50 to 70 wt. %.
[0030] The metal additive may comprise yet further constituents, in
particular metals, the fraction thereof especially being selected
as less than 2 wt. %, preferably less than 1 wt. %.
[0031] These further constituents are preferably selected from the
group of cerium, magnesium, chromium and molybdenum.
[0032] The fractions of these alloy constituents are preferably
between 0.01 and 2 wt. %, preferably 0.1 to 1 wt. % based on the
metal additive. The metal additive may also contain calcium as a
further alloy constituent. The content of calcium is preferably in
the range from 0.2 to 2 wt. %, particularly preferably 0.5 to 1.5
wt. %.
[0033] The particle size of the metal additive should preferably
not be selected to be too small, particularly if the metals,
preferably manganese, nickel and copper, are contained in the metal
additive in elemental form since there is then an increased risk
that the metal additive will react with further constituents of the
size composition and, for example, become oxidised. On the other
hand, the particle size should preferably not be selected to be too
large, since otherwise the metal additive may, for example, sink in
the size composition and therefore the metal additive will be
applied unhomogeneously over the face of a casting mould.
[0034] The metal additive preferably has a mean particle size
(D.sub.50) of less than 0.5 mm, preferably less than 0.4 mm,
particularly preferably less than 0.3 mm. The mean particle size
(D.sub.50) can be ascertained, for example, by screen analysis or
by laser granulometry. The metal additive contained in the size
according to the invention usually has a relatively high density
and thus sinks quickly in the size. However, this sinking can be
decelerated by adding a floating agent. The sinking of the inoculum
can also be reduced further by decreasing the particle size, in
such a way that the inoculum remains suspended homogeneously in the
size. As a further advantage, when using a spraying device to apply
the size, the nozzle of the spraying device is less easily blocked
when using a metal additive with a fine particle size. The inoculum
particularly preferably has a mean particle size of less than 0.3
mm. With decreasing particle size however, the specific surface of
the metal additive increases and therefore reactivity with the
liquid contained in the size, for example water, also increases. In
the case of a reaction of the metal additive with water for
example, gas formation is observed that leads to foam formation.
The size can no longer be reliably pumped or sprayed. The mean
particle size is therefore preferably selected to be greater than
50 .mu.m, particularly preferably greater than 80 .mu.m. The metal
additive is preferably used with a particle size in the range from
20 to 1000 .mu.m, more preferably from 80 to 300 .mu.m.
[0035] The size composition according to the invention is
preferably provided in the form of a paste or a suspension. In this
embodiment the size composition contains a carrier liquid. This
carrier liquid is suitably selected in such a way that it can be
completely evaporated in the conditions that prevail conventionally
during metal casting. The carrier liquid should therefore
preferably have a boiling point at normal pressure of less than
approximately 130.degree. C., preferably less than 110.degree.
C.
[0036] The carrier liquid may be formed in part or completely of
water. However, oxidation of the metal additive may be observed,
particularly if the metal additive is present in the form of
elemental metals or an alloy of elemental metals. In accordance
with a preferred embodiment the size composition thus contains a
solvent that is formed at least in part of an organic solvent.
[0037] The oxidation of the metal additive is repressed by a high
fraction of organic solvent, for example an alcohol. As a further
advantage the size can be dried very easily after application by
burning off the solvent.
[0038] If an organic solvent is contained in the size composition,
the fraction thereof in the carrier liquid is especially selected
to be greater than 20 wt. %, preferably greater than 30 wt. % and
particularly preferably greater than 40 wt. %.
[0039] The carrier liquid may be formed completely of the organic
solvent. However, in accordance with one embodiment the fraction of
organic solvent in the carrier liquid may also be selected to be
lower. In accordance with one embodiment the fraction of organic
solvent in the carrier liquid is less than 90 wt. %, in accordance
with a further embodiment less than 80 wt. % and in accordance with
a further embodiment less than 70 wt. %.
[0040] Examples of suitable solvents include aliphatic,
cycloaliphatic or aromatic hydrocarbons that preferably comprise 5
to 15 carbons, or esters of aliphatic carboxylic acids in which the
carboxylic acids preferably comprise 2 to 20 carbon atoms and the
alcohol constituent of the ester preferably comprises 1 to 4 carbon
atoms. Examples of further preferred organic solvents include
ketones with preferably 4 to 20 carbon atoms. Ethers are also
suitable as a solvent, in this instance it also being possible to
use polyglycols.
[0041] In accordance with a preferred embodiment the solvent is at
least partly formed of at least one alcohol that preferably
comprises 1 to 10 carbon atoms. Exemplary alcohols are ethanol,
n-propanol, isopropanol and butanol.
[0042] If an alcohol is used as a constituent of the carrier
liquid, the fraction thereof based on the weight of the carrier
liquid is preferably selected to be greater than 50 wt. % and
preferably greater than 60 wt. %.
[0043] In addition to the constituents already named, the size
composition according to the invention may also contain further
constituents that are conventional for sizes.
[0044] In accordance with a preferred embodiment the size
composition according to the invention thus comprises at least one
pulverulent refractory material. This refractory material seals the
pores in a casting mould against the penetration of the liquid
metal. Thermal insulation between the casting mould and liquid
metal is further achieved by the refractory material. Refractory
materials that are conventional in metal casting can be used as a
refractory material. Examples of suitable refractory materials
include quartz, aluminium oxide, zirconium oxide, aluminium
silicates such as pyrophyllite, kyanite, andalusite or fireclay,
zircon sand, zircon silicates, olivine, talc, mica, graphite, coke,
feldspar, diatomaceous earth, kaolin, calcined kaolin, kaolinite,
metakaolinite, iron oxide and bauxite.
[0045] The refractory material is provided in powder form. The
particle size is selected in such a way that a stable structure is
produced in the coating and the size can preferably be distributed
over the wall of the casting mould with a spray device in a
trouble-free manner. The refractory material suitably has a mean
particle size in the range from 0.1 to 500 .mu.m, particularly
preferably in the range from 1 to 200 .mu.m. In particular,
materials that have a melting point at least 200.degree. C. above
the temperature of the liquid metal and that do not react with the
metal are suitable as a refractory material.
[0046] The fraction of refractory material based on the solid
fraction of the size composition is especially selected to be
greater than 10 wt. %, preferably greater than 20 wt. % and
particularly preferably greater than 30 wt. %. In accordance with
one embodiment the fraction of refractory material is selected to
be less than 80 wt. %, in accordance with a further embodiment less
than 70 wt. % and in accordance with a further embodiment less than
60 wt. %.
[0047] In accordance with one embodiment the size according to the
invention may comprise at least one floating agent. The floating
agent increases the viscosity of the size in such a way that the
solid constituents of the size do not sink in the suspension or
only sink to a slight extent. Both organic and inorganic material,
or else mixtures of these materials can be employed to increase
viscosity. Examples of suitable inorganic floating agents include
highly swellable clays.
[0048] In order to prevent sinking of the solid constituents and to
simultaneously achieve uniform application over the casting mould,
the viscosity is especially selected in a range from 1000 to 3000
mPas, particularly preferably 1200 to 2000 mPas.
[0049] The metal additive can then be distributed approximately
homogeneously in the size and therefore also applied uniformly to a
wall of a casting mould. The amount of metal additive applied to
the surface of the casting mould can thus be controlled very
precisely.
[0050] Both two-layer silicates and three-layer silicates can be
used as highly swellable layer-lattice silicates, for example
attapulgite, serpentines, kaolins, bentonites such as saponite,
montmorillonite, beidellite and nontronite, vermiculite, illite,
hectorite and mica. Hectorite also affords the size thixotropic
properties, facilitating the formation of the protective layer on
the casting mould since the size no longer flows after application.
Since lattice-layer silicates contain water in the intermediate
layers and this does not evaporate during application of the size
to the hot casting mould having a temperature in the range from
approximately 250 to 350.degree. C., the amount of clay is
preferably selected to be minimal. The amount of highly swellable
lattice-layer silicate is preferably selected to be in the range
from 0.01 to 5.0 wt. %, particularly preferably in the range from
0.1 to 1.0 wt. % based on the solid content of the size.
[0051] Organic thickening agents are preferably selected as the
floating agent since they can be dried after application of the
protective coating to such an extent that they hardly still release
water upon contact with the liquid metal. Considered examples of
organic floating agents include swellable polymers, such as
caboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl
celluloses, mucilages, polyvinyl alcohols, polyvinyl pyrrolidone,
pectin, gelatin, agar agar and polypeptides, and alginates.
[0052] In accordance with a preferred embodiment the size according
to the invention comprises at least one binder as a further
constituent. The binder makes it possible to achieve better fixing
of the size or, of the protective coating produced from the size to
the wall of the casting mould. In addition, the mechanical
stability of the protective coating is increased by the binder in
such a way that low erosion under the influence of the liquid metal
is observed. The binder preferably cures irreversibly in such a way
that an abrasion-proof coating is obtained. Binders that do not
resoften upon contact with ambient moisture are particularly
preferred. All binders that are used in sizes may be contained.
Both inorganic and organic binders can be used. For example clays,
in particular bentonite can be used as a binder.
[0053] Curable binders are particularly used. For example, in the
case of acrylate systems, curing can be achieved by radical formers
that decompose when irradiated with high-energy radiation, for
example ultraviolet radiation, with the formation of radicals.
[0054] Other exemplary binders include starches, dextrin, peptides,
polyvinyl alcohol, polyvinyl acetate copolymers, polyacrylic acid,
polystyrene and/or polyvinyl acetate polyacrylate dispersions.
Binder systems are generally preferably used that can be introduced
into aqueous, alcohol or aqueous-alcohol systems and do not
resoften after curing under the effect of ambient moisture.
[0055] In accordance with a preferred embodiment an alkyd resin is
used as a binder, preferably selected in such a way that it is
soluble both in water and in low alcohols that preferably comprise
2 to 4 carbon atoms, such as ethanol, n-propanol and
isopropanol.
[0056] In accordance with a further embodiment the coating mass
according to the invention contains silica sol as a binder. The
silica sol is preferably produced by neutralizing water glass. The
amorphous silica sol contained preferably has a specific surface in
the range from 10 to 1000 m.sup.2/g, particularly preferably in the
range from 30 to 300 m.sup.2/g.
[0057] The fraction of the binder is preferably in the range from
0.1 to 20 wt. %, particularly preferably 0.5 to 5 wt. % based on
the solid weight of the size composition.
[0058] In accordance with a further preferred embodiment the size
contains a graphite fraction. This assists the formation of
lamellar carbon at the interface between the cast part and the
casting mould. The graphite fraction is preferably in the range
from 1 to 30 wt. %, particularly preferably 5 to 15 wt. % based on
the weight of the size.
[0059] The size composition according to the invention can
optionally also contain yet further components that are
conventional for sizes, for example wetting agents, antifoamers,
pigments, colorants or biocides. The fraction of these further
constituents in the ready-to-use coating mass is preferably
selected to be less than 1 wt. %.
[0060] For example anionic and non-anionic surfactants of medium
and high polarity that have a HSB value of at least 7 can be used
as wetting agents. An example of a wetting agent of this type is
disodium dioctyl sulphosuccinate. The wetting agent is especially
employed in an amount from 0.01 to 1 wt. %, preferably 0.05 to 0.3
wt. % based on the ready-to-use size composition.
[0061] Antifoamers or antifoaming agents can be used to prevent
foam formation during production of the size composition or during
application thereof. Foam formation during application of the size
composition may lead to an uneven layer thickness and to holes in
the coating. For example silicon or mineral oil can be used as
antifoamers. The antifoamer is especially contained in an amount
from 0.01 to 1 wt., preferably from 0.05 to 0.3 wt. % based on the
ready-to-use size composition.
[0062] Pigments and colorants used conventionally may optionally be
used in the size composition according to the invention. These are
added in order to achieve a contrast, for example between different
layers, or to produce a stronger separation effect of the size from
the cast. Examples of pigments include red and yellow iron oxide as
well as graphite. Examples of colorants include commercially
available colorants, such as the Luconyl.RTM. colour range from
BASF AG, Ludwigshafen, Germany. The colorants and pigments are
especially contained in an amount from 0.01 to 10 wt. %, especially
from 0.1 to 5 wt. % based on the solid content of the size
composition.
[0063] In accordance with a further embodiment the size composition
contains a biocide in order to prevent bacterial infection and
therefore to avoid a negative effect on the rheology and binding
force of the binder. This is particularly preferred if the carrier
liquid contained in the size composition is formed substantially of
water, i.e. the size composition according to the invention is
provided in the form of a `water size`. Examples of suitable
biocides include formaldehyde, 2-methyl-4-isothiazolin-3-one (MIT),
5-chloro-2-methyl-4-isothiazolin-3-one (CIT) and
1,2-benzisothiazolin-3-one (BIT). MIT, BIT or a mixture thereof are
preferably employed. The biocides are normally used in an amount of
10 to 1000 ppm, especially from 50 to 500 ppm based on the weight
of the ready-to-use size composition.
[0064] The solid content of the ready-to-use size composition is
especially selected to be in the range from 10 to 60 wt. %,
preferably 20 to 50 wt. %.
[0065] The size composition according to the invention can be
produced in accordance with conventional methods. For example a
size composition according to the invention can be produced by
providing water and decomposing in it a clay acting as a floating
agent with the use of a high-shear stirrer. The solid components,
pigments and colorants as well as the metal additive are then
stirred in until, a homogeneous mixture is produced. Lastly,
wetting agents, antifoaming agents, biocides and binders are
stirred in.
[0066] The size composition according to the invention can be
produced and distributed as a ready-to-use size. However, the size
according to the invention can also be produced and distributed in
concentrated from. In this instance the amount of carrier liquid
necessary to provide the desired viscosity and density of the size
is added to give a ready-to-use size. In addition, the size
composition according to the invention can also be provided and
distributed in the form of a kit, for example the solid components
and the solvent components being present beside one another in
separate containers. The solid components can be provided in a
separate container as a pulverulent solid mixture. Further liquid
components that may optionally be used, for example binders,
wetting agents, wetters/antifoamers, pigments, colorants and
biocides may also be present in this kit in a separate container.
The solvent components may either comprise the components that are
optionally to be used in addition, for example in a common
container, or they can be provided separately from further optional
constituents in a separate container. The suitable amounts of solid
components, the optional further components and the solvent
components are mixed together to produce a ready-to-use size. In
the ready-to-use state a size according to the invention especially
comprises a solid content of 20 to 80 wt. %, especially 30 to 70
wt. % based on the ready-to-use size composition. It is also
possible to provide a size composition according to the invention
in which the solvent components initially consist merely of water.
A ready-to-use alcohol size can be provided from this water size,
for example by adding a volatile alcohol or alcohol mixture,
preferably ethanol, propanol, isopropanol and mixtures thereof,
preferably in amounts from 40 to 200 wt. % based on the water size.
The solid content of an alcohol size of this type is preferably 20
to 60 wt. %, preferably 30 to 40 wt. %.
[0067] Further characteristic parameters of the size composition
can be adjusted depending on both the desired use of the size
composition, for example as a base coating or as a top coating, and
the desired layer thickness of the coating produced from the size
composition. In a preferred embodiment size compositions according
to the invention that are used to coat moulds and cores in foundry
engineering thus have a viscosity from 11 to 25 s, more preferably
12 to 15 s (determined in accordance with DIN 53211; 4 mm flow cup,
Ford Cup). Preferred densities of a ready-to-use size composition
lie in the range from 0 to 120.degree. Be, more preferably from 30
to 50.degree. Be (determined in accordance with the Baume buoyancy
method; DIN 12791).
[0068] The size compositions according to the invention are adapted
for coating casting moulds. The term `casting mould` used here
includes all types of bodies required to produce a cast part; such
as cores, moulds and metal moulds. The use of size compositions
according to the invention also includes a partial coating of
casting moulds.
[0069] The invention also therefore relates to a method for
producing a casting mould, in which at least one mould cavity
provided in the casting mould is coated with the size composition
according to the invention.
[0070] In the method: [0071] a mould material mixture is provided
that contains at least one refractory mould material and a binder,
[0072] the mould material mixture is shaped to a basic mould
comprising a mould cavity; and [0073] at least the faces of the
mould cavity of the basic mould are coated with a size composition
as described above.
[0074] A basic mould is first produced in a known manner from a
mould material mixture. In order to produce the mould mixture a
refractory mould material is mixed with a binder and then shaped to
a basic mould or part of a basic mould. The shape of the basic
mould corresponds substantially to the casting mould or part of the
casting mould. However, it does not comprise any coating with a
size.
[0075] All refractory materials that are conventional for the
production of moulds for the foundry industry can be used as a
refractory mould material. Examples of suitable refractory mould
materials include silica sand, zircon sand, olivine sand, aluminium
silicate sand and chromite sand or mixtures thereof. Silica sand is
preferably used. The refractory mould material should have a
sufficient particle size so the mould produced from the mould
material mixture exhibits sufficiently high porosity to make it
possible for volatile compounds to escape during the casting
process. At least 70 wt. %, particularly preferably at least 80 wt.
% of the refractory mould material preferably has a particle size
.ltoreq.290 .mu.m. The mean particle size of the refractory mould
material is preferably between 100 and 350 .mu.m. For example the
particle size can be ascertained by screen analysis. The refractory
mould material is present in pourable form in such a way that a
binder or liquid catalyst can be effectively applied to the
particles of the refractory mould material, for example in a
mixer.
[0076] In accordance with one embodiment regenerated used sands can
be used as a refractory mould material. Larger aggregates are
removed from the used sand and the grains of the used sand are
optionally isolated. After mechanical or thermal treatment the used
sands are dedusted and can then be used again. The acid balance of
the regenerated used sand is preferably checked before it is used
again. By-products contained in the sand, such as carbonates, may
be converted into the corresponding oxides particularly during
thermal regeneration and these oxides then react in an alkaline
manner. If binders are used that are cured with catalysis by an
acid, the acid added as a catalyst can, in this instance, be
neutralised by the alkaline components of the regenerated used
sand. For example in the case of mechanical regeneration of a used
sand, acid may remain in the used sand and this must be taken into
consideration when producing the binder since otherwise, for
example, the processing time of the mould material mixture may be
reduced.
[0077] The refractory mould material should be dry. The refractory
mould material especially contains less than 1 wt. % water. The
refractory mould material should not be too warm in order to
prevent premature curing of the binder under the influence of heat.
The refractory mould material should preferably be of a temperature
in the range from 20 to 35.degree. C. The refractory mould material
can optionally be cooled or heated.
[0078] All binders that are conventional for the production of
casting moulds for metal casting can be used as a binder. Both
inorganic and organic binders can be used. For example water glass,
which can be cured thermally or by the introduction of carbon
dioxide, may be used as an inorganic binder. Exemplary organic
binders include polyurethane no-bake and cold-box binders, binders
based on furan resins or phenol resins, or else epoxy acrylate
binders.
[0079] Binders based on polyurethanes are generally formed of two
components, a first component containing a phenol resin and a
second component containing a polyisocyanate. These two components
are mixed with the refractory mould material and the mould material
mixture is introduced into a mould by ramming, blowing, spraying or
another method, compressed and then cured. Depending on the method
used to introduce the catalyst into the mould material mixture, a
distinction is made between the `polyurethane no-bake method` and
the `polyurethane cold-box method`.
[0080] In the no-bake method a liquid catalyst, generally a liquid
tertiary amine is introduced into the mould material mixture before
this mixture is introduced into a mould and cured. Phenol resin,
polyisocyanate and a curing catalyst are mixed with the refractory
mould material in order to produce the mould material mixture. For
example it is possible to proceed in a manner in which the
refractory mould material is initially enveloped by a component of
the binder and for other components to then be added. The curing
catalyst is added to one of the components. The finished, prepared
mould material mixture must have a sufficiently long processing
time so the mould material mixture can be plastically deformed for
a sufficiently long period of time and processed to form a
mould.
[0081] Polymerisation must occur slowly in accordance with this so
the mould material mixture does not cure in the storage containers
or feed lines. On the other hand, curing must not occur too slowly
so it is possible to achieve a sufficiently high throughput during
the production of casting moulds. For example the processing time
can be influenced by the addition of retarders, which slow down the
curing process of the mould material mixture. For example a
suitable retarder is phosphorous oxychloride.
[0082] In the cold-box method the mould material mixture is
initially introduced into a mould without a catalyst. A gaseous
tertiary amine is then guided through the mould material mixture
and may optionally be mixed with an inert carrier gas. The binder
binds very quickly upon contact with the gaseous catalyst in such a
way that a high throughput is achieved during the production of
casting moulds.
[0083] The binder systems based cm polyurethanes contain a polyol
component as well as a polyisocyanate component, in this instance
it being possible to revert back to known components.
[0084] The polyisocyanate component of the binder may comprise an
aliphatic, cycloaliphatic or aromatic isocyanate. The
polyisocyanate especially contains at least 2 isocyanate groups,
especially 2 to 5 isocyanate groups per molecule. Depending on the
desired properties, mixtures of isocyanates can also be employed.
The isocyanates used may consist of mixtures of monomers, oligomers
and polymers and are therefore referred to hereinafter as
polyisocyanates.
[0085] Any polyisocyanate that is conventional in polyurethane
binders for mould material mixtures for the foundry industry can be
employed as a polyisocyanate component. Suitable polyisocyanates
include aliphatic polyisocyanates for example hexamethylene
diisocyanate, alicyclic polyisocyanates such as
4,4'-dicyclohexylmethane diisocyanate, and dimethyl derivatives
thereof. Examples of suitable aromatic polyisocyanates include
toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 1,5-naphthaline
diisocyanate, xylene diisocyanate and methyl derivatives thereof,
diphenylmethane-4,4'-diisocyanate and polymethylene polyphenol
polyisocyanate.
[0086] Although in principle all conventional polyisocyanates react
with the phenol resin with formation of a cross-linked polymer
structure, aromatic polyisocyanates are preferably employed,
particularly preferably polymethylene polyphenol polyisocyanate,
such as commercially available mixtures of
diphenylmethane-4,4'-diisocyanate, its isomers and higher
homologues.
[0087] The polyisocyanates can be employed both in a substance and
dissolved in an inert or reactive solvent. A reactive solvent is
understood to be a solvent that comprises a reactive group in such
a way that it is integrated into the skeleton of the binder during
setting of the binder. The polyisocyanates are preferably employed
in diluted form in order to better envelope the particles of the
refractory mould material with a thin film of the binder owing to
the lower viscosity of the solution.
[0088] The polyisocyanates or their solutions in organic solvents
are employed in sufficient concentrations to cure the polyol
components, normally in a range from 10 to 500 wt. % based on the
weight of the polyol components. 20 to 300 wt. % based on the same
principle are preferably employed. Liquid polyisocyanates can be
employed in undiluted form, whilst solid or viscous polyisocyanates
are dissolved in organic solvents. Up to 80 wt. %, especially up to
0.60 wt. % and particularly preferably up to 40 wt. % of the
isocyanate component may consist of solvents.
[0089] The polyisocyanate is preferably employed in such an amount
that the number of isocyanate groups is 80 to 120% based on the
number of free hydroxyl groups of the polyol component.
[0090] All polyols used in polyurethane binders can be employed as
a polyol component. The polyol component contains at least 2
hydroxyl groups that can react with the isocyanate groups of the
polyisocyanate component in order to cross-link the binder during
curing and thus achieve greater strength of the cured mould.
[0091] Phenol resins that are obtained by condensation of phenols
with aldehydes, preferably formaldehyde in liquid phase at
temperatures up to 180.degree. C. in the presence of a catalytic
amount of metal are preferably used as polyols. The methods for
producing phenol resins of this type are known per se.
[0092] The polyol component is preferably employed in a liquid
state or dissolved in organic solvents so as to make it possible to
achieve a homogeneous distribution of the binder over the
refractory mould material. The polyol component is preferably
employed in anhydrous form since the reaction of the isocyanate
component with water is an undesired side reaction. In this context
non-aqueous or anhydrous means a water content of the polyol
component of preferably less than 5 wt. %, preferably less than 2
wt. %.
[0093] `Phenol resin` is understood to be the reaction product of
phenol, phenol derivatives, bisphenols and higher phenol
condensation products with an aldehyde. The composition of the
phenol resin is dependent on the specifically selected starting
materials, the ratio of the starting material and the reaction
conditions. For example the type of catalyst, reaction time and
reaction temperature thus play an important role as well as the
presence of solvents and other substances.
[0094] The phenol resin is typically present as a mixture of
different compounds and may contain addition products, condensation
products and unreacted starting compounds, such as phenols,
bisphenol and/or aldehyde in very different ratios.
[0095] An `addition product` is understood to mean reaction
products in which an organic component substitutes at least one
hydrogen on a previously unsubstituted phenol or a condensation
product. `Condensation product` is understood to mean reaction
products with two or more phenol rings.
[0096] Phenol resins are produced as condensation reactions of
phenols with aldehydes and, depending on the quantitative
proportions of educts, the reaction conditions and catalysts used,
can be divided into two product classes: novolacs and resols:
[0097] Novolacs are soluble, meltable, non-self-curing and
storage-stable oligomers with a molecular weight in the range of
approximately 500 to 5,000 g/mol. They are formed during the
condensation of aldehydes and phenols in a molar ration of 1:>1
in the presence of acidic catalysts. Novolacs are
methylol-group-free phenol resins in which the phenyl cores are
linked via methylene bridges. They can be cured at increased
temperatures with cross-linking after the addition of curing
agents, such as formaldehyde-releasing agents, preferably
hexamethylenetetramine.
[0098] Resols are mixtures of hydroxymethyl phenols that are linked
via methylene and methylene ether bridges and are obtainable by
reacting aldehydes and phenols in a molar ratio of 1:1<0.1,
optionally in the presence of a catalyst, for example an alkaline
catalyst. They have a molecular weight M.sub.w of S 10,000
g/mol.
[0099] The phenol resins that are particularly suitable as the
polyol component are known under the name "o-o'" or "high-ortho"
novolacs or benzyl ether resins. They are obtainable by
condensation of phenols with aldehydes in a weak acidic medium with
the use of suitable catalysts.
[0100] Suitable catalysts for producing benzyl ether resins include
salts of divalent ions of metals, such as Mn, Zn, Cd, Mg, Co, Ni,
Fe, Pb, Ca and Ba. Zinc acetate is preferably used. The amount used
is not critical. Typical amounts of metal catalyst are 0.02 to 0.3
wt. %, preferably 0.02 to 0.15 wt. % based on the total amount of
phenol and aldehyde.
[0101] All phenols used conventionally are suitable for the
production of phenol resins. Substituted phenols or mixtures
thereof are employed in addition to unsubstituted phenols. The
phenol compounds are either not substituted in both ortho positions
or are not substituted in one ortho position and in the para
position in order to enable polymerisation. The remaining ring
carbon atoms can be substituted. The selection of the substituents
is not particularly limited provided the substituent does not
affect polymerisation of the phenol or aldehyde in a detrimental
manner. Examples of substituted phenols include alkyl-substituted
phenols, alkoxy-substituted phenols and aryloxy-substituted
phenols.
[0102] For example the above-mentioned substituents have 1 to 26,
preferably 1 to 15 carbon atoms. Examples of suitable phenols
include o-cresol, m-cresol, p-cresol, 3,5-xylene, 3,4-xylene,
3,4,5-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol,
p-butylphenol, 3,5-dibutylphenol, p-amylphenol, cyclohexylphenol,
p-octylphenol, p-nonylphenol, 3,5-dicyclohexylphenol,
p-crotylphenol, p-phenylphenol, 3,5-dimethoxyphenol and
p-phenoxyphenol.
[0103] Phenol itself is particularly preferred. Higher condensed
phenols, such as bisphenol A are also suitable. In addition,
multivalent phenols that have more than one phenol hydroxyl group
are also suitable. Preferred multivalent phenols include 2 to 4
phenol hydroxyl groups. Special examples of suitable multivalent
phenols include catechol, resorcin, hydroquinone, pyrogallol,
fluoroglycine, 2,5-dimethyl resorcin, 4,5-dimethyl resorcin,
5-methyl resorcin or 5-ethyl resorcin.
[0104] Mixtures of different monovalent and multivalent and/or
substituted and/or condensed phenol components can also be used for
the production of the polyol component.
[0105] In one embodiment phenols of the general formula I:
##STR00001##
are used to produce the phenol resin component, in which A, B and
C, independently of one another, are selected from a hydrogen atom,
a branched or linear alkyl radical that, for example, may contain 1
to 26, preferably 1 to 15 carbon atoms, a branched or linear alkoxy
radical that, for example, may contain 1 to 26, preferably 1 to 15
carbon atoms, a branched or linear alkenoxy radical that, for
example, may contain 1 to 26, preferably 1 to 15 carbon atoms, or
an aryl or alkylaryl radical, for example bisphenyls.
[0106] Aldehydes of the formula:
R--CHO,
in which R is a hydrogen atom or a carbon atom radical with
preferably 1 to 8, particularly preferably 1 to 3 carbon atoms, are
suitable for the production of the phenol resin component. Special
examples include formaldehyde, acetaldehyde, propionaldehyde,
furfurylaldehyde and benzaldehyde. Formaldehyde is particularly
preferably used, either in its aqueous form, as para-formaldehyde
or trioxane.
[0107] An at least equivalent molar number of aldehyde based on the
molar number of the phenol component should be used in order to
obtain the phenol resins. The molar ratio of aldehyde to phenol is
preferably 1:1.0 to 2.5:1, particularly preferably 1.1:1 to 2.2:1,
particularly preferably 1.2:1 to 2.0:1.
[0108] The phenol component is produced by methods known to the
person skilled in the art. The phenol and the aldehyde are
converted in substantially anhydrous conditions in the presence of
a divalent metal ion at temperatures of preferably less than
130.degree. C. The water produced is distilled off. A suitable
entrainer, for example toluene or xylene, can be added to the
reaction mixture or distillation is carried out at reduced
pressure.
[0109] The phenol component is reacted with an aldehyde, preferably
to form benzyl ether resins for the binder of the mould material
mixture. Reaction with a primary or secondary aliphatic alcohol to
form an alkoxy-modified phenol resin is also possible in
single-step or two-step methods (EP-B-0 177 871 and EP 1 137 500).
In single-step methods the phenol, aldehyde and alcohol are reacted
in the presence of a suitable catalyst. In two-step methods an
unmodified resin is first produced that is then reacted with an
alcohol. When using alkoxy-modified phenol resins there is no
restriction on the molar ratio, but the alcohol component is
preferably used in a molar ration of alcohol:phenol of less than
0.25 in such a way that less than 25% of the hydroxymethyl groups
are etherified. Suitable alcohols include primary and secondary
aliphatic alcohols with a hydroxyl group and 1 to 10 carbon atoms.
Examples of suitable primary and secondary alcohols include
methanol, ethanol, propanol, n-butanol and n-hexanol. Methanol and
n-butanol are particularly preferred.
[0110] The phenol resin is preferably selected in such a way that
cross-linking with the polyisocyanate component is possible. Phenol
resins that comprise molecules with at least two hydroxyl groups
are particularly suitable for construction of a network. The phenol
resin component or isocyanate component of the binder system is
preferably employed as a solution in an organic solvent or a
combination of organic solvents. Solvents may be necessary in order
to keep the components of the binder in a sufficiently poorly
viscous state. This is necessary, inter alia, in order to obtain
uniform cross-linking of the refractory mould material and
pourability thereof.
[0111] All solvents that are conventionally used in binder systems
of this type for foundry engineering can be employed as solvents
for the polyisocyanate or polyol components of the binder system
based on polyurethanes. For example oxygen-rich, polar organic
solvents are suitable as solvents. Above all, dicarboxylic acid
ester, glycol ether ester, glycol diester, glycol diether, cyclic
ketones, cyclic esters or cyclic carbonates are suitable.
Dicarboxylic acid esters, cyclic ketones and cyclic carbonates are
preferably used. Dicarboxylic acid esters have the formula
R.sup.aOOC--R.sup.b--COOR.sup.a in which the radicals R.sup.a each
represent, independently of one another, an alkyl group with 1 to
12, preferably 1 to 6 carbon atoms, and R.sup.b is an alkylene
group, i.e. a divalent alkyl group with 1 to 12, preferably 1 to 6
carbon atoms. R.sup.b may also comprise one or more carbon-carbon
double bonds. Examples include dimethyl esters of carboxylic acids
with 4 to 10 carbon atoms that are obtainable, for example, under
the name "dibasic ester" (DBE) from Invista International S.a.r.l.,
Genf, Switzerland. Glycol ether esters are compounds of the formula
R.sup.c--O--R.sup.d--OOCR.sup.e, in which R.sup.c is an alkyl group
with 1 to 4 carbon atoms, R.sup.d is an ethylene group, a propylene
group or an oligomer ethylene oxide or propylene oxide and R.sup.e
is an alkyl group with 1 to 3 carbon atoms. Gycol ether acetates,
for example butylgycol acetate are preferred. Gycol diesters
correspondingly have the general formula
R.sup.eCOO--R.sup.dOOCR.sup.e, in which R.sup.d and R.sup.e are as
defined above and the radicals R.sup.e are each selected
independently of one another. Gycol diacetates, for example
propylene glycol diacetate are preferred. Gycol diethers can be
characterised by the formula R.sup.c--O--R.sup.d--O--R.sup.c, in
which R.sup.c and R.sup.d are as defined above and the radicals
R.sup.c are each selected independently of one another. A suitable
glycol diether is, for example, dipropylene glycol dimethylether.
Cyclic ketones, cyclic esters and cyclic carbonates with 4 to 5
carbon atoms are also suitable. For example a suitable cyclic
carbonate is propylene carbonate. The alkyl and alkylene groups may
each be branched or linear.
[0112] The fraction of the solvent in the binder system is
preferably selected to be not too high since the solvent evaporates
during the production and application of the mould produced from
the mould material mixture, and can therefore lead for example to
an annoying bad odour or to smoke formation during casting. The
fraction of the solvent in the binder system is preferably selected
to be less than 50 wt. %, particularly preferably less than 40 wt.
%, in particular preferably less than 35 wt. %.
[0113] As described above, the binder is first mixed with the
refractory mould material to form a mould material mixture in order
to produce the mould. If the mould is produced by the PU no-bake
method, a suitable catalyst may already be added to the mould
material mixture. Liquid amines are preferably added to the mould
material mixture. These amines preferably have a pK.sub.b value of
4 to 11. Examples of suitable catalysts include 4-alkyl pyridine,
in which the alkyl group comprises 1 to 4 carbon atoms,
isoquinoline, acrylpyridine such as phenylpyridine, pyridine,
acryline, 2-methoxypyridine, pyridazine, 3-chloropyridine,
quinoline, n-methylimidazole, 4,4'-dipyridine, phenylpropyl
pyridine, 1-methylbenzimidazole, 1,4-thiazine,
N,N-dimethylbenzylamine, triethylamine, tribenzylamine,
N,N-dimethyl-1,3-propanediamine, N,N-dimethylethanolamine and
triethanolamine. The catalyst may optionally be diluted with an
inert solvent, for example
2,2,4-trimethyl-1,3-pentadiol-diisobutyrate, or a fatty acid ester.
The amount of catalyst added is selected to be in the range of 0.1
to 15 wt. % based on the weight of the polyol component.
[0114] The mould material mixture is then introduced into a mould
using conventional means and compressed there. The mould material
mixture is then cured to form a mould. The mould should preferably
maintain its outer shape during curing.
[0115] If the curing process takes place by the PU cold-box method,
a gaseous catalyst is guided through the shaped mould material
mixture. Conventional catalysts in the field of the cold-box method
can be used as a catalyst. Amines are particularly preferably used
as catalysts, in particular preferably dimethylethylamine,
dimethyl-n-propylamine, dimethylisopropylamine,
dimethyl-n-butylamine, triethylamine and trimethylamine in their
gaseous form or as an aerosol.
[0116] In accordance with a further preferred embodiment a furan
resin or a phenol resin is employed as a binder, the mould material
mixture being cured in accordance with the "furan no-bake" method
with catalysis by a strong acid.
[0117] Furan and phenol resins exhibit very good decomposition
properties during casting. The furan or phenol resin decomposes
under the influence of the heat of the liquid metal and the
strength of the casting mould is lost. After the casting process,
cores can therefore be very easily emptied from cavities,
optionally after prior vibration of the cast part.
[0118] The reactive furan resins contained as a first component in
"furan-no-bake binders" comprise furfuryl alcohol as a main
component. Furfuryl alcohol can react with itself under acidic
catalysis and form a polymer. Pure furfuryl alcohol is not
generally used for the production of furan no-bake binders, but
instead further compounds that are polymerised in the resin are
added to the furfuryl alcohol. Examples of compounds of this type
include aldehydes, such as formaldehyde or furfural, ketones such
as acetone, phenols, urea or else polyols such as sugar alcohols or
ethylene glycol. Yet further components that influence the
properties of the resin, for example the elasticity thereof, can be
added to the resins, For example melamine can be added to bind free
formaldehyde.
[0119] Furan no-bake binders are usually formed by first producing
furfuryl-containing precondensates from, for example, urea,
formaldehyde and furfuryl alcohol in acidic conditions. The
reaction conditions are selected in such a way that only slight
polymerisation of the furfuryl alcohol occurs. These precondensates
are then diluted with furfuryl alcohol. Resols can also be used to
produce furan no-bake binders. Resols are produced by
polymerisation of mixtures of phenol and formaldehyde. These resols
are then diluted with furfuryl alcohol.
[0120] The second component of the furan no-bake binder forms an
acid. On the one hand this acid neutralizes alkaline components
that are contained in the refractory mould material and, on the
other hand, catalyses the cross-linking of the reactive furan
resin.
[0121] Aromatic sulphonic acids and, in some special cases, also
phosphoric acid or sulphuric acid are usually used as acids.
Phosphoric acid is used in concentrated form, i.e. in
concentrations of more than 75%. However, it is only adapted for
the catalytic curing of furan resins with a relatively high
fraction of urea. The nitrogen content of resins of this type is
more than 2.0 wt. %. Sulphuric acid can be added to the furan
resins of weaker acids as a relatively strong acid as a starter for
the curing process. However, a smell that is typical of sulphur
compounds develops during casting. In addition there is the risk
that sulphur will be absorbed by the casting material and will
influence the properties thereof. Aromatic sulphonic acids are
usually employed as catalysts. Above all toluene sulphonic acid,
xylene sulphonic acid and benzene sulphonic acid are used owing to
their good availability and their high acid strength.
[0122] As the second largest group of acid-catalysed curable
no-bake binders, phenol resins contain resols, i.e. phenol resins
produced with an excess of formaldehyde, as a reactive resin
component. Phenol resins exhibit considerably lower reactivity
compared to furan resins and require strong sulphonic acids as
catalysts. Phenol resins exhibit relatively high viscosity that
increases during longer periods of storage of the resin. The
viscosity increases rapidly particularly at temperatures below
20.degree. C. in such a way that the sand must be heated in order
to be able to apply the binder uniformly to the surface of the sand
grains. Once the phenol no-bake binder has been applied to the
refractory mould material, the mould material mixture should be
processed as thoroughly as possible so as to not have to deal with
deterioration of the quality of the mould material mixture caused
by premature curing, which may lead to a deterioration in the
strength of the casting moulds produced from the mould material
mixture. When using phenol no-bake binders, the flowability of the
mould material mixture is generally poor. When producing the
casting mould, the mould material mixture must therefore be
compressed carefully in order to achieve a high level of strength
of the casting mould.
[0123] The mould material mixture should be produced and processed
at temperatures in the range from 15 to 35.degree. C. At
excessively low temperatures the mould material mixture cannot be
processed easily owing to the high viscosity of the phenol no-bake
resin. At temperatures above 35.degree. C. the processing time is
shortened by premature curing of the binder.
[0124] After casting, mould material mixtures based on phenol
no-bake binders, can also be reprocessed, mechanical or thermal or
combined mechanical/thermal methods possibly being used in this
instance also.
[0125] An acid is applied to the pourable refractory material, an
acid-coated refractory mould material being obtained. The acid is
applied to the refractory mould material using conventional
methods, for example by spraying the acid onto the refractory mould
material. The amount of acid is preferably selected to be in the
range from 5 to 45 wt. %, particularly preferably in the range from
20 to 30 wt. % based on the weight of the binder and determined as
pure acid, i.e. with no consideration of a solvent that may have
been used. If the acid is not already present in liquid form and
has a sufficiently low viscosity to be distributed over the
particles of the refractory mould material in the form of a thin
film, the acid is dissolved in a suitable solvent. Exemplary
solvents include water or alcohols or mixtures of water and
alcohol. However, particularly when using water, the solution is
produced as concentrated as possible so as to keep the amount of
water introduced into the binder or mould material mixture to a
minimum. The mixture is thoroughly homogenised from the refractory
mould material and acid to provide uniform distribution of the acid
over the particles.
[0126] A binder that is curable by acid is then applied to the
refractory mould material coated with acid. The amount of binder is
preferably selected to be in the range from 0.25 to 5 wt. %,
particularly preferably in the range from 1 to 3 wt. % based on the
refractory mould material and determined as resin component. All
binders that are curable by acid, in particular those binders
curable by acid that are already conventional for the production of
mould material mixtures for the foundry industry can be used as a
binder curable by acid. In addition to a cross-linkable resin, the
binder may also contain further conventional components, for
example solvents for adjusting the viscosity or extenders that
replace part of the cross-linkable resin.
[0127] The binder is applied to the refractory mould material
coated with acid and by moving the mixture is distributed over the
particles of the refractory mould material in the form of a thin
film.
[0128] The amounts of binder and acid are selected in such a way
that, on the one hand, a sufficient strength of the casting mould
is achieved and, on the other hand, a sufficient processing time of
the mould material mixture is achieved. For example a processing
time in the range from 5 to 45 minutes is suitable.
[0129] The refractory mould material coated with the binder is then
shaped by conventional methods to form a mould. For this purpose
the mould material mixture can be introduced into a suitable mould
and compressed there. The mould obtained is then left to cure.
[0130] All furan resins as already used in furan no-bake binder
systems can be used as furan no-bake binders.
[0131] The furan resins employed in technical furan no-bake binders
are usually precondensates or mixtures of furan resins with further
monomers or precondensates. The precondensates contained in furan
no-bake binders are produced in a manner known per se.
[0132] In accordance with a preferred embodiment furfuryl alcohol
is employed in combination with urea and/or formaldehyde or
urea/formaldehyde precondensates. Formaldehyde can be employed both
in monomeric form, for example in the form of a formalin solution,
and in the form of its polymers, such as trioxane or
paraformaldehyde. Other aldehydes or else ketones can also be used
in addition to or instead of formaldehyde. Examples of suitable
aldehydes include acetaldehyde, propionaldehyde, butyraldehyde,
acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde,
cinnamaldehyde, glyoxal and mixtures of these aldehydes.
Formaldehyde is preferred and is preferably employed in the form of
paraformaldehyde.
[0133] All ketones that exhibit sufficiently high reactivity can be
used as ketone components. Exemplary ketones include methyl ethyl
ketone, methyl propyl ketone and acetone, acetone being preferably
used.
[0134] The aldehydes and ketones named can be employed as
individual compounds or else mixed together.
[0135] The molar ratio of aldehyde, particularly formaldehyde, or
ketone to furfuryl alcohol may be selected within wide ranges. When
producing the furan resins especially 0.4 to 4 mol of furfuryl
alcohol, preferably 0.5 to 2 mol furfuryl alcohol can be used per
mol of aldehyde.
[0136] Furfuryl alcohol, formaldehyde and urea can be heated to
boiling point to produce the precondensates, for example after
adjustment of a pH value of more than 4.5, water being continuously
distilled off from the reaction mixture. The reaction time can be a
number of hours, for example 2 hours. In these reaction conditions
there is practically no polymerisation of the furfuryl alcohol.
However, the furfuryl alcohol is condensed in a resin together with
the formaldehyde and the urea.
[0137] In accordance with an alternative method furfuryl alcohol,
formaldehyde and urea are reacted under heat at a pH value of
considerably less than 4.5, for example at a pH of 2.0, the water
produced during the condensation process possibly being distilled
off at reduced pressure. The reaction product exhibits relatively
high viscosity and is diluted with furfuryl alcohol for production
of the binder until the desired viscosity is reached.
[0138] Combinations of these production methods can also be
implemented.
[0139] It is also possible to introduce phenol into the
precondensate. For this purpose the phenol may first be reacted
with formaldehyde in alkaline conditions to form a resol resin.
This resol can then be reacted or mixed with furfuryl alcohol or a
furan-group-containing resin. For example furan-group-containing
resins of this type can be obtained by the above-described methods.
Higher phenols can also be used for the production of the
precondensate, for example resorcin, cresol or else bisphenol A.
The fraction of the phenol or higher phenols in the binder is
especially selected to be in the range of up to 45 wt. %,
preferably up to 20 wt. % and particularly preferably up to 10 wt.
%. In accordance with one embodiment the fraction of the phenol or
higher phenols can be selected to be greater than 2 wt. %, in
accordance with a further embodiment greater than 4 wt. %.
[0140] Furthermore it is also possible to use condensates of
aldehydes and ketones that are mixed with furfuryl alcohol for
production of the binder. Condensates of this type can be produced
by reacting aldehydes and ketones in alkaline conditions.
Formaldehyde, particularly in the form of paraformaldehyde is
preferably used as aldehyde. Acetone is preferably employed as
ketone. Other aldehydes or ketones can also be used however. The
relative molar ratio of aldehyde to ketone is preferably selected
to be in the range from 7:1 to 1:1, preferably 1.2:1 to 3.0:1.
Condensation is preferably carried out in alkaline conditions at pH
values in the range from 8 to 11.5, preferably 9 to 11. For example
a suitable base is sodium carbonate.
[0141] The amount of furfuryl alcohol contained in the furan
no-bake binder is, on the one hand, determined by the effort to
keep the fraction to a minimum for cost reasons. On the other hand,
the strength of the casting mould is improved by a high fraction of
furfuryl alcohol. However, very brittle casting moulds that are
difficult to work with are produced with a very high fraction of
furfuryl alcohol in the binder. The fraction of furfuryl alcohol in
the binder is especially selected to be in the range from 30 to 95
wt. %, preferably 50 to 90 wt. % and particularly preferably 60 to
85 wt. %. The fraction of urea and/or formaldehyde in the binder is
especially selected to be in the range from 2 to 70 wt. %,
preferably 5 to 45 wt. % and particularly preferably 15 to 30 wt.
%. The fraction includes both the unbound fractions of these
compounds contained in the binder and the fractions that are bound
in the resin.
[0142] Further additives can be added to the furan resins, such as
ethylene glycol or similar aliphatic polyols, for example sugar
alcohols such as sorbitol that act as extenders and replace some of
the furfuryl alcohol. If too much of these extenders are added this
may lead, in the worst case scenario, to a reduction in the
strength of the casting mould and to a reduction in reactivity. The
fraction of this extender in the binder is thus especially selected
to be less than 25 wt. %, preferably less than 15 wt. % and
particularly preferably less than 10 wt. %. In order to save costs
without having to deal with a considerable influence on the
strength of the casting mould, the fraction of the extender is
selected to be greater than 5 wt. % in accordance with one
embodiment.
[0143] The furan no-bake binder can also contain water. However
since water slows down the curing process of the mould material
mixture and is produced as a reaction product during curing, the
fraction of water is preferably selected to be minimal. The
fraction of water in the binder is especially less than 20 wt. %,
preferably less than 15 wt. %. From an economical point of view, an
amount of water of more than 5 wt. % can be tolerated in the
binder.
[0144] In the method according to the invention resols are used as
phenol resins. Resols are mixtures of hydroxymethyl phenols that
are linked via methylene and methylene ether bridges and are
obtainable by reacting aldehydes and phenols in a molar ratio of
1:<1, optionally in the presence of a catalyst, for example an
alkaline catalyst. They have a molecular weight M.sub.w of
.ltoreq.10,000 g/mol.
[0145] All phenols used conventionally are suitable for the
production of the phenol resins, phenol being particularly
preferred. Formaldehyde is preferably employed as an aldehyde
component, particularly in the form of paraformaldehyde.
Alternative phenols and aldehydes have already been described in
conjunction with the polyurethane binders. Reference is made to the
relevant passages.
[0146] The binders may contain further conventional additives, for
example silanes as coupling agents. Examples of suitable silanes
include aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes
and ureido silanes such as .gamma.-hydroxy propyl trimethoxysilane,
.gamma.-aminopropyltrimethoxysilane, 3-ureido propyl
triethoxysilane, .gamma.-mercaptopropyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane,
.beta.-(3,4-epoxycyclohexyl)trimethoxysilane, and
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane.
[0147] If a silane of this type is used, it is added to the binder
in an amount of 0.1 to 3 wt. %, preferably 0.1 to 1 wt. %.
[0148] The binders can also contain yet further conventional
components, for example activators or plasticiser.
[0149] The mould material mixture can also contain yet further
conventional constituents in addition to the refractory mould
material, the binder and optionally the catalyst. Exemplary further
constituents include iron oxide, ground flax fibres, wood dust
granules, ground coal or clay.
[0150] The mould material mixture is then shaped to form a basic
mould or part of a basic mould using conventional methods and is
optionally cured. The basic mould can then be assembled completely
or in part and the mould cavity provided in the basic mould can be
coated with the above-described size composition, either completely
or over portions. Conventional methods can be used for this. For
example the size composition can be applied by a dipping method,
flow coating, painting on or by spraying.
[0151] If the dipping method is used as the application method then
the casting mould of which the mould cavity has optionally been
covered with a basic coating is dipped in a container filled with a
ready-to-use size composition according to the invention for
approximately 2 seconds to 2 minutes. The casting mould is then
removed from the size composition and excess size composition is
drained off from the casting mould. The time taken for the excess
size composition to drain off after dipping depends on the runoff
behaviour of the size composition used.
[0152] If the spraying method is used as the application method
then commercially available pressure vessel spraying devices are
used, In this instance a pressure vessel is filled with the size
composition in the diluted state. The size can be pressed into a
spraying gun via the overpressure to be set and is then sprayed
with the aid of an atomiser that can be adjusted separately. The
conditions during spraying are preferably selected in such a way
that the pressure for the size composition and atomiser is adjusted
at the gun in such a way that the sprayed size composition is still
wet when it contacts the mould or core, but is applied
uniformly.
[0153] The carrier liquid contained in the size is then evaporated
in such a way that a dry size layer is obtained. All conventional
drying methods can be used as a drying method, for example open-air
drying, drying with dehumidified air, drying with microwave or
infrared radiation, drying in convection ovens and comparable
methods.
[0154] In a preferred embodiment of the invention the coated
casting mould is dried at 100 to 250.degree. C., preferably at 120
to 180.degree. C. in a convection oven. When using alcohol sizes,
the size composition according to the invention is preferably dried
by burning off the alcohol or alcohol mixture. In this instance the
coated casting mould is additionally heated by the combustion heat.
In a further preferred embodiment the coated casting mould is dried
in the open air with no further treatment.
[0155] The size layer can then optionally be cured, for example by
irradiation with UV radiation, if an appropriate curable binder is
contained in the size composition.
[0156] The size may be applied in the form of an individual layer
or else in the form of a plurality of superposed layers. The
individual layers may be of identical or different composition. For
example a base coating may first be produced from a commercially
available size that contains no metal additive according to the
invention. For example water sizes or else alcohol sizes may be
used as a base coating. However, it is also possible for all layers
to be produced from the size composition according to the
invention. The layer that will later come into contact with the
liquid metal is, however, always produced from the size according
to the invention. If a plurality of layers are applied, each
individual layer can be dried either completely or in part after
application.
[0157] The coating produced from the size composition especially
comprises a dry layer thickness of at least 0.1 mm, preferably at
least 0.2 mm, particularly preferably at least 0.55 mm. In
accordance with one embodiment the thickness of the coating is
selected to be less than 1.5 mm. In this instance the dry layer
thickness is the layer thickness of the dried coating obtained by
drying the size composition by substantially completely removing
the solvent components and optionally subsequent curing. The dry
layer thickness of the base coating and of the top coating are
especially ascertained by measurement with the wet-film thickness
comb.
[0158] The casting mould can then optionally be assembled
completely.
[0159] The invention further relates to the use of the
above-described casting mould to produce a cast part.
[0160] For this purpose a casting mould is first provided. This may
be a dead mould produced from a refractory material, for example
silica sand, and a binder, as described above, or else a permanent
mould as is used conventionally to produce pipes, bearings or
sleeves, the mould cavity being lined with the above-described size
composition. The casting mould comprises a protective coating, at
least on those faces that come into contact with the liquid metal,
which coating insulates the liquid metal from the casting mould and
can positively influence the nature of the surface of the cast
part. Liquid metal, especially iron or an iron alloy is now
introduced into the prepared casting mould. The liquid metal is
then left to set to form a cast part and then the cast part is
separated from the casting mould. Conventional methods are
implemented for this purpose. With dead moulds the casting mould is
mechanically destroyed, for example by vibration. With permanent
moulds the cast part is removed from the casting mould using
conventional methods.
[0161] The invention further relates to a casting mould that has a
mould coating produced from the above-described size. A casting
mould of this type advantageously comprises insulation between the
liquid metal and the casting mould, whereby the thermal load of the
casting mould during the casting process is reduced. As a further
advantage the mould coating comprises a metal additive that can
positively influence the surface properties of the cast part and,
in particular, represses the formation of a maculate surface on the
cast part.
[0162] Casting moulds that comprise a top coating produced from the
size composition according to the invention are used, inter alia,
to produce wind turbine hubs, grinding bowls, engines and engine
components, machine beds and turbines, general machine components
or pressing tools.
[0163] The invention will now be explained in greater detail with
reference to examples.
EXAMPLE 1
[0164] The core size used in the examples below had the composition
given in Table 1.
TABLE-US-00001 TABLE 1 Composition of the size Component Wt. %
zircon silicate 75 .mu.m 50.00 manganese (325 mesh) 20.00 clay
mineral 03.00 synthetic resins 02.00 rheological additives 00.50
ethanol 14.50 isopropanol 10.00
[0165] The mould casting size was produced as follows: isopropanol
is provided and the clay is decomposed therein by use of a
high-shear stirrer for at least 15 minutes. The refractory
components, pigments, manganese and colorants are then stirred in
for at least 15 minutes until a homogeneous mixture is produced.
Lastly, ethanol, rheological additives and binders are stirred
in.
* * * * *