阅读说明：本技术 涂料组合物、涂覆铸模的方法、涂料组合物用于涂覆铸模的用途以及铸模 (Coating composition, method for coating a casting mould, use of a coating composition for coating a casting mould and a casting mould ) 是由 R·斯托泽尔 J·克罗克 于 2020-04-15 设计创作，主要内容包括：本发明涉及一种涂料组合物,其包含固体组分,所述固体组分包含能够在约150-约1000℃的温度范围内分解出CO-(2)并且D50值为至多约10μm的第一固体。此外,本发明涉及一种涂覆铸模的方法、所述涂料组合物用于涂覆铸模的用途以及经涂覆的铸模。(The present invention relates to a coating composition comprising a solid component comprising a polymer capable of decomposing to CO in the temperature range of about 150 to about 1000 ℃ 2 And a D50 value of at most about 10 μm. Furthermore, the invention relates to a method for coating a casting mould, to the use of the coating composition for coating a casting mould and to the coated casting mould.)

1. A coating composition comprising:

a solid component comprising a solid component capable of decomposing CO at a temperature in the range of about 150 to about 1000 ℃₂And a first solid having a D50 value of at most about 10 μm.

2. The coating composition of claim 1, wherein the first solid has a D99 value of at most about 30 μ ι η and a D90 value of at most about 20 μ ι η.

3. The coating composition according to claim 1 or 2, wherein the first solid is selected from carbonates of elements of groups 2, 7, 8, 9, 10, 11 and 12 of the periodic table of the elements.

4. A 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 or 2, wherein the first solid is selected from starch, in particular rice or oat starch.

6. The coating composition of any one of claims 1-5, wherein the coating composition further comprises a carrier liquid, and wherein the carrier liquid preferably comprises water.

7. The coating composition of claim 6, wherein the solubility product of the first component in the carrier liquid is pK_LAnd at least about 4 at 25 ℃.

8. A method of coating a casting mold, wherein the method comprises the steps of:

(a) providing a casting mould, optionally provided with one or more cores, comprising surfaces defining a casting cavity,

(b) providing a coating composition according to any one of claims 1-7; and

(c) the coating composition is applied to at least a portion of the surfaces defining the casting cavity.

9. The method of claim 8, wherein the coating composition further comprises a carrier liquid and the coating composition is dried after step (c).

10. The method of claim 8 or 9, wherein the coating penetrates at least 2mm into the coated surface and the layer thickness of the coating after drying the coating is at most about 100 μ ι η.

11. Use of a coating composition according to any one of claims 1-7 for coating a casting mould, wherein the casting mould, optionally provided with one or more cores, comprises a surface defining a casting cavity, and the coating composition is applied to at least a part of the surface defining the casting cavity.

12. Use according to claim 11, wherein the coating penetrates at least 2mm into the coated surface and the layer thickness of the coating after drying of the coating is at most about 100 μm.

13. A coated casting mould, optionally provided with one or more casting cores, obtainable by the method of any one of claims 8-10.

Technical Field

The present invention relates to a coating composition capable of suppressing the pulse marks in iron and heavy metal castings. The invention further relates to a method for coating a casting mould, to the use of the coating composition for coating a casting mould, and to a corresponding casting mould.

Prior Art

Most products in the iron, steel and non-ferrous metal industries undergo a casting process for their initial forming. During these processes, molten material, ferrous or non-ferrous metals are transformed into shaped objects with certain workpiece properties. To form a casting, a potentially quite delicate mold must first be prepared to receive the molten metal. Casting molds are classified as either lost foam, which breaks after each casting, or permanent mold, which can be used to produce large quantities of castings. The lost foam is usually composed of a refractory granular mold base material, which is cured by a curable binder.

The mold is concave; they comprise a cavity into which material is poured to obtain the casting to be formed. The internal profile of future castings is formed by cores. In the manufacture of the mold, a cavity is formed in a mold base material using a mold of a casting to be produced. The internal profile is formed by cores formed in a separate core box.

For the preparation of the moulds, organic and inorganic binders can be used, the curing of which can be carried out by cold or hot methods. Cold processes are processes in which the curing is carried out substantially at room temperature without heating the mold base material mixture. Curing is typically carried out by a chemical reaction, which may be initiated, for example, by passing a gaseous catalyst through the mold base material mixture to be cured, or by adding a liquid catalyst to the mold base material mixture. In the thermal method, the mold base material mixture is heated to a sufficiently high temperature after molding, for example, to remove a solvent contained in the binder, or to initiate a chemical reaction by which the binder is cured due to crosslinking.

The preparation of the mould can be carried out by first mixing the mould base material with the binder so that the particles of the mould base material are coated with a film of the binder. The mold base material mixture obtained from the mold base material and the binder can then be introduced into the respective mold and optionally compacted in order to obtain a sufficiently stable mold. Subsequently, the mold is cured, for example by heating the mold or by adding a catalyst that causes the curing reaction. When the mold reaches at least a certain initial strength, it can be removed from the mold.

As already mentioned, the casting moulds for producing metal bodies usually consist of so-called cores and moulds. The core and the mould must meet different requirements. The mold provides a relatively large surface area to release gases formed during casting due to the influence of the hot metal. Typically, the insert provides only a very small area through which gas can escape. Thus, if too much gas is formed, there is a risk that gas will enter the liquid metal from the core and cause casting defects to form. Thus, the internal cavity is typically provided in the form of a sand core that is cured by a cold box binder, i.e., a polyurethane-based binder, while the external contour of the casting is formed by a more cost-effective mold, such as a green sand mold, a mold bonded by furan or phenolic resin, or by a steel mold.

For larger moulds, organic polymers are mainly used as binders for the refractory granular mould base material. Washed and graded quartz sand is commonly used as the refractory granular mold base material, but other mold base materials such as zircon sand, chromite sand, chamotte, olivine sand, feldspar sand and andalusite sand may 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.

At present, organic binders such as polyurethane, furan resin or epoxy acrylate binders are often used for the manufacture of casting moulds, wherein the curing of the binder is carried out by adding a catalyst.

The selection of a 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 example, polyurethane adhesives are often used to produce small castings, which are produced in large quantities because they allow for fast cycle times and therefore also allow for a series production.

The use of two-component polyurethane adhesives in the production of cores has gained significant importance in the foundry industry. One component comprises a polyol having at least two OH groups per molecule and the other component comprises a polyisocyanate having 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, either simultaneously or sequentially, with a suitable mold base material, such as quartz sand. This mixture, called the mold base material mixture, is then transferred to the reservoir of the core blowing machine, then conveyed by compressed air into the forming tool and finally solidified therein by passing gaseous low-boiling tertiary amines as catalysts, thus producing solid self-supporting cores (US 3,409,579). As further components, the mould base material may also comprise additives, as described for example in EP0795366a 1.

For example, quartz sand, zircon sand or chrome sand, olivine, chamotte and bauxite can be used as the refractory material. Furthermore, synthetically produced mould base materials may also be used, for example hollow aluminium silicate spheres (so-called microspheres), glass beads, glass granules or spherical ceramic mould base materials known as "ceramic beads" or "carboaccumacast". Mixtures of the mold base materials are also possible.

To improve the surface finish of the casting, the cores and molds may be coated with a coating known as a finish prior to use.

Conventional coating compositions comprise at least one fire resistant material as the intended part. The purpose of such refractory materials is primarily to influence the surface of the casting to be coated in order to meet the above-mentioned requirements with regard to avoiding sand defects leading to defects and impurities in the casting.

For example, in the casting art, the refractory material may close the sand holes of the core or molded part to prevent sand staining of the cast metal.

Examples of refractory substances are pyrophyllite, zirconium silicate, andalusite, chamotte, iron oxide, kyanite, bauxite, olivine, alumina, quartz, talc, calcined kaolin (metakaolin) and/or graphite alone or in mixtures thereof.

For example, WO 2004/083321a1 and EP 2364795a1 describe the use of fine-grained materials, such as metakaolin, which can impregnate the sand pores, and flaked pyrophyllite which covers the sand surface and thus provides good resistance to the formation of veining marks and staining.

Typically, the coating composition comprises a carrier liquid. The solid components of the coating composition may form a suspension with the carrier liquid, whereby the solid components become processable and are applied to the object to be coated by a suitable method, such as dipping.

Generally, when coating porous materials, the application behavior of the coating is determined not only by the rheology of the coating, but also by the absorption behavior of the porous body and the retention capacity of the coating material to the carrier liquid. In terms of the absorption behavior of the porous bodies, it should be noted that substrates with hydraulic binders, such as clays, cements and water glasses, generally absorb the carrier liquid to a particularly high degree.

In the case of coatings based on aqueous systems, the use of suspending agents, such as natural mucilages or cellulose derivatives, is known. Although they lead to a high water retention capacity of the coating substance material, the rheology of the system is negatively affected, since the coatings exhibit unfavorable, lower intrinsic viscosity properties and they will run off more viscous. This can lead to undesirable application characteristics, such as droplet formation and sagging, and uneven layer thicknesses. Especially in dip coating, it is important to optimize the flow behavior of the coating to achieve profile formation, uniform layer thickness and low droplet formation.

Essentially, any coating should remain homogeneous during processing to avoid precipitation of solids in suspension. In combination with the desired application behavior, the rheological properties and the degree of thixotropy of the composite suspension should meet the desired requirements.

For example, swellable activated layered silicates are used in many technical fields as thickeners for aqueous systems. By using shear forces, the layer silicate is dispersed in the system in the form of a finely divided distribution, in which the individual layer flakes are substantially or completely separated from one another and form a colloidal dispersion or suspension in the system, which results in a gel structure.

A method of making foundry moulds and cores from resin-bonded foundry sand comprises making a base mould or base core, for example from foundry sand, and applying a coating comprising a refractory inorganic component to at least those surfaces of the base mould/base core which are in contact with the foundry metal. In one aspect, the purpose of the mold coating is to affect the surface of the molded part, improve the appearance of the casting, metallurgically affect the casting and/or prevent casting defects. In addition, these coatings or paints serve to chemically insulate the mold from the liquid metal during casting, thereby preventing any adhesion and allowing subsequent separation of the mold and casting. In addition, the coating provides a thermal barrier between the mold and the casting. The heat transfer can be used in particular to influence the cooling of the casting. In practice, the problem of expansion errors of the sand recurs in the production of cold box cores, due to the so-called reversion of the quartz from α -quartz to β -quartz, and the expansion of about 1% of its length at about 580 ℃, which leads to the generation of stresses in the sand core surface. This leads to so-called veining (broken cores with sand-stained metal) or sand inclusion (loose sand layers), which leads to a raised casting surface and, in other areas, to sand inclusions.

Another problem is the increasing demand by manufacturers of automotive castings for thinner wall castings of 3-5mm with a high dimensional accuracy of 0.2-0.3 mm. Since commercially available coatings are usually applied in automotive castings with a dry layer thickness of 0.2-0.4mm to avoid casting defects, the high layer thickness constitutes a limitation for improving dimensional tolerances. So-called bead formation or sagging during the application of the coating also causes problems with dimensional accuracy and non-staining of thin-walled castings.

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 d >38 μm and a second relatively fine fraction having a particle size d <38 μm, wherein no more than 10% of the total particulate refractory filler has a particle size of 38 μm < d <53 μm and 0-50% of the second relatively fine fraction consists of calcined kaolin.

DE 102009032668a1 describes a ready-to-use washing liquid for producing a mold coating on a lost foam or core for iron and steel casting, wherein the washing liquid contains inorganic hollow bodies in a proportion of 0.001 wt.% or more and 1 wt.% or less, characterized in that the inorganic hollow bodies consist partly or completely of crystalline material.

WO 2006/063696a1 describes a sizing composition for foundry moulds comprising a solvent component and a solid component, characterized in that the solid component comprises as main component a mixture of metakaolin and pyrophyllite.

EP 2176018A1 describes a process for preparing a compound in SO₂A method for casting vermicular and nodular cast iron in sand combined with epoxy resin, wherein carbonate prevents sulfur from causing graphite deterioration at the metal edges. Alkaline earth metal carbonates are mentioned in particular.

DE 102016211930a1 describes the use of carbonates and/or phosphates in combination with refractory fillers, preferably on acid-bonded sand moulds to avoid so-called white films.

WO 2011/075220a1 describes the use of carbonates as additives in sand mixtures to prevent the formation of veining marks; although particle size distribution is not shown, particle sizes greater than 50 μm are typically used to reduce strength loss.

It is an object of the present invention to provide a coating composition which allows the production of thin-walled castings with high dimensional tolerances and ensures good protection against veining and sand.

Brief description of the invention

Accordingly, the present invention relates to the following points.

1. A coating composition comprising:

a solid component comprising a catalyst capable of decomposing CO at a temperature of about 150 to about 1000 ℃₂And which has a D50 value of at most about 10 μm.

2. The coating composition of point 1, wherein the first solid has a D99 value of at most about 30 μm and a D90 value of at most about 20 μm.

3. The coating composition according to point 1 or 2, wherein the first solid is selected from carbonates of elements of groups 2, 7, 8, 9, 10, 11 and 12 of the periodic table of the elements.

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.

5. The coating composition according to point 1 or 2, wherein the first solid is selected from starch, in particular rice or oat starch.

6. The coating composition according to any of points 1-5, wherein the coating composition further comprises a carrier liquid, and wherein the carrier liquid preferably comprises water.

7. The coating composition according to point 6, wherein the solubility product of the first component in the carrier liquid is pK_LAnd at least about 4 at 25 ℃.

8. A method of coating a casting mold, wherein the method comprises the steps of:

(a) providing a casting mould, optionally provided with one or more cores, comprising surfaces defining a casting cavity,

(b) providing a coating composition according to any one of points 1-7; and

(c) applying the coating composition to at least a portion of the surfaces defining the casting cavity.

9. The method according to point 8, wherein the coating composition further comprises a carrier liquid and the coating composition is dried after step (c).

10. The method according to point 8 or 9, wherein the coating penetrates at least 2mm into the coated surface and the layer thickness of the coating after drying of the coating is at most about 100 μm.

11. Use of a coating composition according to any one of points 1 to 7 for coating a casting mould, wherein the casting mould, optionally provided with one or more cores, comprises a surface defining a casting cavity, and the coating composition is applied to at least a part of the surface defining the casting cavity.

12. The use according to point 11, wherein the coating penetrates at least 2mm into the coated surface and the layer thickness of the coating after drying of the coating is at most about 100 μm.

13. A coated casting mould, optionally provided with one or more casting cores, obtainable by the method according to any one of points 8-10.

Drawings

FIG. 1: schematic side view of a step core

FIG. 2: schematic top view of a step core

FIG. 3: schematic side view of a dome core

Detailed Description

The present invention relates to a coating composition comprising:

a solid component comprising a catalyst capable of decomposing CO at a temperature of about 150 to about 1000 ℃₂And which has a D50 value of at most about 10 μm.

Solid component

The solid components are all components that are present as solids after drying the ready-to-use coating composition. In this context, the drying temperature may be, for example, 120 ℃.

First solid

The particle size distribution of the components of the coating composition, in particular the first solid, may be determined on the basis of the pass ratios D99, D90, D50 and D10. They are measures of the particle size distribution. Thus, the passage ratios D99, D90, D50 and D10 indicate that a proportion of 99%, 90%, 50% or 10% of the particles pass through a sieve whose mesh width corresponds to the specified size fraction. For example, at a D50 value of 10 μm, 50% of the particles have a size of less than 10 μm. The particle size and the pass ratio D99, D90, D50 and D10 can be determined by laser diffraction granulometry according to ISO 13320. The proportions are given on a volume basis. In the case of non-spherical particles, the assumed spherical particle size is calculated and used as a basis.

In a preferred embodiment, the first solid has a D10 value of no more than about 3 μm, more preferably from about 0.1 to about 2 μm, and especially preferably from about 0.1 to about 1 μm.

The first solid has a D50 value of no more than about 10 μm, preferably from about 0.5 to about 10 μm, more preferably from about 0.5 to about 7 μm, and especially preferably from about 0.5 to about 6 μm.

In a preferred embodiment, the first solid has a D90 value of no more than about 20 μm, more preferably from about 5 to about 15 μm, and especially preferably from about 5 to about 10 μm.

In a preferred embodiment, the first solid has a D99 value of no more than about 30 μm, more preferably from about 5 to about 20 μm, and especially preferably from about 5 to about 15 μm.

In preferred embodiments, one or more of the above D10, D50, D99, and D90 values are simultaneously met. In a particularly preferred embodiment, the aforementioned values of D50, D99, D90 and optionally D10 are simultaneously met.

The desired particle size may be adjusted by comminuting the first solid until the desired particle size is obtained. Alternatively or additionally, the desired particle size may be provided by screening. In the case of the synthesized first solid, the process parameters can also be adjusted during the preparation in such a way that the desired particle size is obtained.

The first solid decomposes to CO at a temperature of about 150 to about 1000 deg.C, preferably about 300 to about 1000 deg.C₂. This can be done by heating the first solid in a tube furnace under a nitrogen atmosphere and then measuring whether or not CO is evolved at least one temperature in the range by absorption with milk of lime in a wash bottle and subsequent filtration, drying and gravimetric determination₂To be measured. CO 2₂The partial pressure should be less than 0.01 bar to avoid errors due to effects on chemical equilibrium. Thus, the CO of the present invention₂Comprises only the decomposition of the first solid, wherein CO is produced₂Rather than its combustion.

The chemical composition of the first solid is not particularly limited, provided that the first solid can decompose CO as desired₂。

In one embodiment, the first solid is selected from carbonates of elements of groups 2, 7, 8, 9, 10, 11 and 12 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 carbonates of Mg, Ca, Mn, Fe, Cu and Zn, especially preferably carbonates of Mg, Ca, Mn and Fe, even more preferably carbonates of Mg, Ca and Fe.

Mixed carbonates of the above elements, such as calcium magnesium carbonate, may also be used as carbonates. Mixtures of the above carbonates are also possible.

Furthermore, it goes without saying that 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 elements of groups 2, 7, 8, 9, 10, 11 and 12 of the periodic table of the elements is preferably greater than about 50% by weight, more preferably greater than about 70% by weight, and particularly preferably greater than 90% by weight.

Calcium carbonate

Calcium carbonate CaCO₃It can be used in its pure form or in the form of natural minerals such as calcite (calcspar, double spar), aragonite and vaterite. Known natural minerals comprising calcite, aragonite or vaterite are chalk, limestone and marble.

The calcium carbonate may be synthetically prepared according to methods known in the art. Among other processes, known are precipitation with carbon dioxide, lime-soda and the Solvay process in which calcium carbonate is a by-product of ammonia production.

Calcium carbonate exists in several anhydrous forms as well as two hydrate crystal forms and other amorphous forms. Starting at a temperature of about 600 ℃, they decompose into calcium oxide and carbon dioxide:

CaCO₃→CaO+CO₂

according to the present invention, the type of calcium carbonate is not particularly limited. Any known calcium carbonate may be used. The calcium carbonate may preferably be selected from calcite and aragonite, more preferably the calcium carbonate is calcite.

Magnesium carbonate

Magnesium carbonate MgCO₃It can be used in its pure form or in the form of natural minerals such as magnesite (magnesite), brucite, nesquehonite and pentanesquehonite.

Magnesium carbonate may be synthetically prepared according to methods known in the art. Among other methods, precipitation with carbon dioxide is known.

According to the present invention, the type of magnesium carbonate is not particularly limited. Any known magnesium carbonate may be used. The magnesium carbonate may preferably be selected from magnesite, white magnesite and supersalite; especially preferred is magnesite.

Calcium magnesium carbonate

Calcium carbonate and magnesium carbonate can be used as mixed carbonic acidAnd (3) salt. A known calcium magnesium carbonate is dolomite CaMg (CO)₃)₂It is also found as dolomite, corundum and pearl dolomite.

According to the present invention, the type of calcium carbonate and magnesium carbonate is not particularly limited; preferably, dolomite can be used.

Iron carbonate

Iron carbonate FeCO₃Can be used in its pure form or in the form of natural minerals such as siderite, ironlime (ironlime), feldspars (ironspar), spades (spar iron stone), chalcopyrite (chalybeate), and steryl stone (steelstone); siderite is preferably used. Alternatively, the iron carbonate may be synthetically prepared according to methods known in the art.

Manganese carbonate

Manganese carbonate MnCO₃It can be used in its pure form or in the form of a natural mineral such as rhodochrosite. Alternatively, the manganese carbonate may be synthetically prepared according to methods known in the art.

Zinc carbonate

Zinc carbonate ZnCO₃Can be used in its pure form or in the form of natural minerals such as calamine. Alternatively, the zinc carbonate may be synthetically prepared according to methods known in the art.

Copper carbonate

Copper carbonate CuCO₃It can be used in the form of a basic compound or in the form of natural minerals such as malachite and celestite. Alternatively, copper carbonate may be synthetically prepared according to methods known in the art.

The following table provides a summary of the properties of the preferred carbonate compounds.

As CuCO₃ Cu(OH)₂

In a preferred embodiment, the first solid is selected from calcium carbonate, magnesium carbonate, dolomite or iron carbonate or mixtures thereof.

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.

In its ready-to-use form, the coating composition preferably comprises a carrier liquid. Preferably, the first solid is 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 pK at 25 ℃ of at least about 4, preferably at least about 6_LThe product of solubility is indicated. The solubility product can be measured by mixing a quantity of the substance to be measured (e.g. 100g) into a quantity of solvent (e.g. 1 litre) at a temperature of 25 ℃, filtering the liquid and determining the dissolved content by evaporation of the solvent or by chemical analysis of the dissolved substance.

The amount of the first solid in the solid component is not particularly limited, and may be about 65 to about 99% by weight, preferably about 80 to about 99% by weight, more preferably about 90 to about 99% by weight. The upper limit of the amount of the first solid in the solid component may be 90% by weight, preferably 95% by weight. Natural minerals generally contain a mixture of various compounds. If natural minerals are used, the amount of the first solid means that CO is decomposed at a temperature in the range of about 150 to about 1000 deg.C₂The amount of the compound of (1). CO is not decomposed from, for example, 90% by weight of calcium magnesium carbonate and 10% by weight₂In the case of dolomite rock composed of other components, only 90% by weight of calcium magnesium carbonate will be considered for the above amount calculation. Therefore, CO cannot be decomposed₂Will be part of the solid components provided that they remain as solid residues during the defined drying period.

Second solid

The solid component may comprise a second solid in addition to the first solid. The second solid is understood to be incapable of decomposing CO at a temperature in the range of about 150 to about 1000 deg.C₂Any solid of (a).

Examples of the second solid include graphite, mica, non-swellable aluminum silicate and swellable layered silicate.

The graphite may be present in an amount of from 0 to about 20 wt%, preferably from 0 to about 10 wt%, based on the solid components.

One or more types of mica may be used. Examples include muscovite or phlogopite. Mica may be present in an amount of from 0 to about 10 weight percent, preferably from 0 to about 5 weight percent, more preferably from 0 to about 2 weight percent, based on the solid component.

The second solid may comprise one or more non-swellable aluminium silicates. Examples include pyrophyllite, metakaolin, mullite, kyanite or sillimanite. Preferred are pyrophyllite and metakaolin. The non-swellable aluminum silicate may be present in an amount of from 0 to about 10% by weight, preferably from 0 to about 5% by weight, based on the solid components.

In a preferred embodiment, the second solid (other than the swellable layered silicate) has a D10 value of no more than about 15 μm, preferably from about 0.1 to about 10 μm, more preferably from about 0.1 to about 8 μm, and especially preferably from about 0.1 to about 7 μm.

In preferred embodiments, the second solid (other than the swellable layered silicate) has a D50 value of no more than about 50 μm, more preferably from about 0.5 to about 30 μm, more preferably from about 0.5 to about 25 μm, and even more preferably from about 0.5 to about 20 μm.

In a preferred embodiment, the second solid (other than the swellable layered silicate) has a D90 value of no more than about 100 μm, more preferably from about 5 to about 90 μm, more preferably from about 5 to about 80 μm, and especially preferably from about 5 to about 75 μm.

In a preferred embodiment, the second solid (other than the swellable layered silicate) has a D99 value of no more than about 250 μm, more preferably from about 5 to about 200 μm, more preferably from about 5 to about 150 μm, and especially preferably from about 5 to about 100 μm.

In preferred embodiments, one or more of the above D50, D99, and D90 values are simultaneously met. In a particularly preferred embodiment, the above-mentioned values of D10, D50, D99 and D90 are simultaneously satisfied.

The term "swellability" refers to the property that a solid dispersed in a solvent is incorporated into the solvent and thus becomes more bulky. This generally increases the viscosity greatly.

In one embodiment, the second solid comprises one or more swellable layered silicates to reduce the settling behavior of the coating composition and control rheology. The swellable layered silicate is not particularly limited. Any swellable layered silicate known to those skilled in the art that is capable of storing water between its layers may be used. Preferably, the swellable layered silicate may be selected from the group consisting of attapulgite (palygorskite), ball clay, serpentine, kaolin, smectite (e.g. saponite, montmorillonite, beidellite and nontronite), vermiculite, illite, sepiolite, synthetic lithium-magnesium layered silicate RD and mixtures thereof, particularly preferably from the group consisting of attapulgite (palygorskite), serpentine, smectite (e.g. saponite, beidellite and nontronite), vermiculite, illite, sepiolite, synthetic lithium-magnesium layered silicate RD and mixtures thereof, particularly preferably the swellable layered silicate is attapulgite. Attapulgite is preferred because of its increased flow limit.

Further, the particle size of the swellable layered silicate is not particularly limited, and any usual particle size may be used. The values given for D10, D50, D90 and D99 for the second solid also apply to the swellable layered silicate.

In a preferred embodiment, the swellable layered silicate has a D10 value of no more than about 5 μm, preferably from about 0.1 to about 5 μm, more preferably from about 0.1 to about 4 μm, and especially preferably from about 0.1 to about 3 μm.

In a preferred embodiment, the swellable layered silicate has a D50 value of no more than about 30 μm, preferably from about 0.5 to about 25 μm, more preferably from about 0.5 to about 20 μm, and especially preferably from about 0.5 to about 15 μm.

Preferably, the swellable layered silicate may have a D90 value of no greater than about 50 μm, more preferably from about 5 to about 40 μm, even more preferably from about 5 to about 30 μm, and most preferably from about 5 to about 25 μm.

In a preferred embodiment, the swellable layered silicate has a D99 value of no more than about 100 μm, preferably from about 5 to about 90 μm, more preferably from about 5 to about 80 μm, and especially preferably from about 5 to about 75 μm.

In preferred embodiments, one or more of the above D50, D99, and D90 values are simultaneously met. In a particularly preferred embodiment, the above-mentioned values of D50, D99 and D90 are simultaneously met.

The amount of swellable layered silicate (especially attapulgite) in the coating composition is not particularly limited; it may preferably be about 0 to about 5 parts by weight, more preferably about 0.1 to about 5 parts by weight, especially preferably about 0.1 to about 4 parts by weight, most preferably about 0.1 to about 2 parts by weight, based on the solid component.

Carrier liquid

The coating composition may include a carrier liquid to facilitate application. The carrier liquid is any component that evaporates when the ready-to-use coating composition is dried and is not present in the dried coating.

The coating composition may be provided as a dry powder, as a concentrate containing a portion of the desired amount of carrier liquid and which must be diluted with additional carrier liquid prior to use, or as a ready-to-use coating composition already containing the desired amount of carrier liquid.

The carrier liquid may be selected by one skilled in the art depending on the intended application. Preferably, the carrier liquid may be selected from water, alcohols such as aliphatic C₁-C₅An alcohol, or a mixture 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 preferably water.

Coating compositions whose carrier liquid consists essentially of water are commonly referred to as water coatings. Coating compositions whose carrier liquid consists essentially of an alcohol or alcohol mixture are referred to as alcohol coatings. In one embodiment of the present invention, the carrier liquid comprises from about 0 to about 100% by weight, preferably from about 30 to about 100% by weight, more preferably from about 60 to about 100% by weight, of water, based on the carrier liquid, and as further components from about 100 to about 0% by weight, preferably from about 70 to about 0% by weight, more preferably from about 40 to about 0% by weight, of one or more alcohols as defined above. According to the invention, pure water coatings as well as pure alcohol coatings and water/alcohol mixtures can be used. In a particularly preferred embodiment, water is the only carrier liquid. Alternatively, it is also possible to prepare coating compositions whose solvent component consists of an alcohol, or, in the case of so-called hybrid coatings, initially only of water. These coatings can be used as alcohol coatings by dilution with an alcohol or alcohol mixture. Preference is given to using ethanol, propanol, isopropanol and mixtures thereof.

Other organic solvents may be used if desired. Examples include alkyl acetates such as ethyl acetate and butyl acetate, and ketones such as acetone and methyl ethyl ketone. The amount of the other organic solvents is not particularly limited, and preferably they are present in an amount of about 0 to about 10 weight percent, more preferably about 0 to about 5 weight percent, and especially preferably about 0 to about 1 weight percent, based on the carrier liquid.

The amount of carrier liquid in the coating composition is not particularly limited, and it is preferably present in an amount of 80% by weight or less, more preferably 75% by weight or less, and particularly preferably 70% by weight or less.

Accordingly, the amount of the solid component in the coating composition is preferably about 20% by weight or more, more preferably about 25% by weight or more, and particularly preferably about 30% by weight or more.

In a ready-to-use coating composition, the carrier liquid is preferably present in an amount of about 40 to about 85 wt.%, more preferably about 45 to about 85 wt.%, and especially preferably about 50 to about 85 wt.%.

Thus, the amount of solid components 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 preferably from about 15 to about 50 wt.%.

Optional additives

In addition to the above-mentioned components, the coating composition may comprise conventional additives, such as binders, wetting agents, defoamers, pigments, dyes and biocidal active ingredients.

Adhesive agent

The function of the binder is primarily to bind the solid components. Preferably, the adhesive is characterized by irreversible bonding, thus producing a wear resistant coating on the mold. The wear resistance is very important for the final coating, since if the coating lacks wear resistance, thenThe coating may be damaged. In particular, the adhesive should not soften due to humidity. According to the invention, all binders which are customarily used, for example, in aqueous and/or hydro-alcoholic systems can be used. As binders, for example, water-soluble starches or dextrins having D50 values greater than about 10 μm (preferably at least about 15 μm) and being soluble in the carrier liquid; a peptide; polyvinyl alcohol; polyvinyl acetate copolymers; polyacrylic acid; polystyrene; polyvinyl acetate; a polyacrylate dispersion; and mixtures thereof. In a preferred embodiment of the invention, the binder comprises a dispersion of an alkyd resin, which is soluble in water and lower (e.g. C)_1-4) Alcohols such as ethanol, propanol and isopropanol. Examples of alkyd resins include unmodified water-dispersible alkyd resins based on natural oils or their fatty acids and polyols, as described for example in US 3,442,835, or isocyanate-modified alkyd resins, as described for example in US 3,639,315, preferably epoxy urethane-modified alkyd resins according to DE 4308188. For example, products from the NECOWEL series available from ASK Chemicals GmbH, 40721 Hilden, Germany may be used. Other preferred binders are polyvinyl alcohol and polyvinyl acetate copolymers, in particular polyvinyl alcohol.

The term "adhesive" refers to an effective adhesive component, which may also be present as a solution or dispersion in diluted form.

The binder is 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.

Wetting agent

Anionic and non-anionic surfactants of medium and high polarity (HLB value of 7 or higher) known to those skilled in the art may be preferably used as wetting agents. Examples of wetting agents useful in the present invention include disodium dioctyl sulfosuccinate, ethoxylated 2,5,8, 11-tetramethyl-6-dodecyne-5, 8-diol, ethoxylated 2,4,7, 9-tetramethyl-5-decyne-4, 7-diol, or combinations thereof; more preferably, ethoxylated 2,4,7, 9-tetramethyl-5-decyne-4, 7-diol may be used.

The wetting agent is preferably used in an amount of about 0.01 to about 1 part by weight, more preferably about 0.05 to about 0.3 part by weight, even more preferably about 0.1 to about 0.3 part by weight, based on all components of the coating composition.

Defoaming agent

Defoamers or antifoamers are used to prevent foaming during the preparation of the coating compositions of the present invention and during their application. Foaming during application of the coating composition can lead to uneven layer thicknesses and to the generation of holes in the coating. For example, silicone or mineral oil can be used as the defoaming agent. Preferably, the defoamer is selected from the FINASOL product line, commercially available from Total Deutschland GmbH.

In the coating composition of the present invention, the defoamer is used in an amount of about 0.01 to about 1 part by weight, more preferably about 0.05 to about 0.3 part by weight, and particularly preferably about 0.1 to about 0.2 part by weight, based on all components of the coating composition.

Pigments and dyes

In the coating composition of the present invention, conventional pigments and dyes may optionally be used. They can be added if desired, for example to obtain a visible contrast between the different layers, or to create a stronger separation between the coating and the casting. Examples of pigments include red iron oxide and yellow iron oxide. Examples of dyes are commercially available dyes, such as the LUCONYL product from BASF SE.

Dyes and pigments are generally used in amounts of about 0.01 to about 10 parts by weight, preferably about 0.05 to about 5 parts by weight, based on all components of the coating composition.

Biocide active ingredients

The coating composition may optionally comprise one or more biocidal active ingredients (especially if the carrier liquid comprises water) in order to prevent bacterial attack and thus avoid adverse effects on the rheology and bond strength of the binder. The biocidal active ingredient is not particularly limited; preferably, they may be selected from formaldehyde, glutaraldehyde, tetramethylol acetylene diurea, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-isothiazolin-3-one (CIT), 1, 2-benzisothiazolin-3-one (BIT), or a mixture thereof, more preferably from 2-methyl-4-isothiazolin-3-one (MIT), 1, 2-benzisothiazolin-3-one (BIT), or a mixture thereof.

The amount of the biocidally active ingredient in the coating composition is not particularly limited and depends on the selected biocidally active ingredient. For example, the amount can be 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 preferably from about 0.007 to about 0.8 parts by weight, based on all components of the coating composition.

In a preferred embodiment, the coating composition of the present invention comprises from about 10 to about 60 parts by weight calcium carbonate and from about 0.1 to about 2 parts by weight attapulgite, based on the solid component. In addition, the coating composition comprises from about 0.2 to about 2 parts by weight of a binder, from about 0.1 to about 0.3 parts by weight of a wetting agent, from about 0.1 to about 0.2 parts by weight of a defoamer, from about 0.005 to about 0.3 parts by weight of a biocidally active ingredient, and a carrier liquid, preferably water, to make up the difference to 100 parts by weight.

Preparation of the coating composition

The coating compositions of the present invention are prepared using conventional methods. For example, the coating composition of the invention is prepared by taking the majority of the carrier liquid (preferably the entire amount of carrier liquid) and adding the swellable layered silicate (if they are used) (premix B in the examples) using a high shear mixer (e.g. about 400 to about 2000 rpm). Then, the other solid components, such as the first solid and the pigment and dye (if they are used), are stirred in until a homogeneous mixture is obtained. The order of addition of the components has little or no relevance and can be readily determined by one skilled in the art. Finally, the wetting agent, the defoamer, the biocidally active ingredient and the binder, if they are used, are stirred in. For example, the coating composition is prepared at a temperature of preferably about 5 to about 50 ℃, more preferably about 10 to about 30 ℃, at a stirrer speed of preferably about 400 to about 2000rpm, more preferably about 1000 to about 1500rpm, and under a toothed disc of 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 toothed disc of the mixer and D is the diameter of the mixing vessel).

The properties of the coating composition are preferably adjusted to impregnate the coating so that the first solid can penetrate into the surface of the mold. In particular, it is preferred that the coating composition be impregnated to a depth of at least about 2mm, preferably from about 2 to about 20mm, more preferably from about 2 to about 6 mm. The depth of impregnation can be measured by cutting.

The dry layer thickness of the dried coating resulting from the above-described coating composition is the thickness of the layer of dried coating composition ("coating") which is determined by drying the coating composition by substantially complete removal of the carrier liquid. Preferably, the dry layer thickness of the coating may be no more than about 100 μm, more preferably from about 10 to about 100 μm, still more preferably from about 10 to about 50 μm. The dry layer thickness of the coating is preferably determined by measuring the 3-point bent bar with a micrometer screw before and after the dressing (drying) or by measuring with a wet film thickness comb gauge. For example, the dry layer thickness can be determined with a comb gauge by scraping off the coating on the end marks of the comb until the substrate appears. The dry layer thickness can then be read from the indicia of the teeth. Alternatively, the wet layer thickness in the matte state (hereinafter referred to as matte layer thickness) can also be measured according to DIN EN ISO 2808, wherein the dry layer thickness is 70-80% of the matte layer thickness. A "matte" layer is a layer that is no longer flowable, with the solvent content reduced to the point that the surface is no longer glossy.

Preferably, the coating composition has a depth of immersion of at least about 2mm and a dry layer thickness of no more than about 100 μm. More preferably, the coating composition has a depth of immersion of from about 2 to about 20mm (more preferably from about 2 to about 6mm) and a dry layer thickness of from about 10 to about 50 μm.

The viscosity of the ready-to-use coating composition can be adjusted to about 10 to about 16 seconds, preferably about 10 to about 13 seconds, as determined according to DIN 53211, flow cup 4mm, Ford cup.

The density of the ready-to-use coating composition may, for example, be from about 20 to about 50 ° Be, preferably from about 25 to about 35 ° Be, determined according to the Baum buoyancy method, DIN 12791.

Use of coating compositions

The coating composition of the present invention can be used to coat a casting mold. One possible method comprises the steps of:

(a) providing a casting mold comprising surfaces defining a casting cavity,

(b) providing a coating composition of the present invention;

(c) applying the coating composition to at least a portion of a surface defining a casting cavity; and

(d) drying the coating composition.

All types of bodies necessary for producing the mould are called casting moulds. The casting mold is not particularly limited, and all casting molds commonly used in the iron, steel and non-metal industries, such as cores, molds or dies, may be used. The casting mold may be composed of a refractory granular mold base material which is cured by means of a curable binder. The refractory granular mold base material is not particularly limited, and any conventional mold base material can be used. Preferably, the refractory particulate mold base material may include quartz sand, zircon sand, chromite sand, chamotte, bauxite, olivine sand, feldspar sand, andalusite sand, aluminum silicate hollow spheres (also referred to as "microspheres"), glass beads, glass particles, ceramic spherical mold base materials known as "ceramic beads" or "carboaccess" or mixtures thereof. In particular, the coating composition of the invention is used for casting molds, wherein quartz sand or a proportion of quartz sand is used as mold base material.

The grit should have a particle size of about 100 to about 600 μm, preferably about 100 to about 500 μm, and most preferably about 200 to about 400 μm.

The curable adhesive is not particularly limited. Any curable adhesive known to those skilled in the art may be used. Preferably, an organic binder such as polyurethane, furan resin or epoxy acrylate binder, an inorganic binder such as water glass, or a mixture thereof; it is particularly preferred that the binder is based on a PUR cold box, water glass CO₂Methyl Formate (MF) as resole, CO as resole₂Furan resin, phenolic resin or water glass ester binders. Polyurethane adhesives are particularly preferred. The amount of the curable binder in the casting mold is not particularly limited; the binder may be present in any conventional amount. Preferably, the binder is present in an amount of about 0.2 to about 5 parts by weight, more preferably about 0.3 to about 4 parts by weight, and even more preferably about 0.4 to about 3 parts by weightBased on 100 parts by weight of the refractory particulate mold base material. The coating composition is suitable for all conceivable applications in which a casting mould is to be coated with a coating. Examples of casting moulds, i.e. cores and moulds for foundry applications include those made with a PUR cold box, water glass CO₂A resol MF and a resol CO₂Furan resin, phenolic resin or water glass ester bonded sand cores. Further examples of preferred casting moulds which can be coated with the coating composition according to the invention are described, for example, in "Formstoffe und Formverfahren" [ moulding materials and moulding methods]Eckart Fleming and Werner Tilch, Wiley-VCH, 1993, ISBN 3-527-.

The surface of the casting mould, optionally equipped with one or more cores, defines a casting cavity into which the liquid metal is introduced. The surface of the casting mold may be the surface of a core or the surface of a hollow mold. According to the invention, the casting mould and the core may be completely or partially coated. Preferably, the surfaces of the casting mould and core that are in contact with the cast metal are coated.

The coating composition is initially provided in a ready-to-use form. If present as a dry powder or concentrate, a carrier liquid is added to achieve the consistency desired for application.

In one embodiment, for example, the coating composition may be provided in the form of a kit (multi-component package comprising two or more containers for different components). The solid component and the carrier liquid may be present side-by-side in separate containers. All of the solid components may be present in one container as a powdered solid mixture. Alternatively, the components of the solid component may be provided as several separate components. If appropriate, further components to be used, such as binders, wetting agents, antifoams, pigments, dyes and biocidally active ingredients, can be present in the kit together with the abovementioned components or in one or more separate containers. The carrier liquid may include optional components to be used, if desired, e.g., in the same container, or it may be present in a separate container from the other optional components. To prepare a ready-to-use coating composition, the appropriate amounts of the components are mixed together.

Typically, the coating composition may be present as a water coating. Alternatively, a ready-to-use alcohol coating can be provided from the water coating by adding an alcohol.

There is no particular limitation in applying and drying at least one layer of the coating composition to at least a portion of the surfaces defining the casting cavity. All conventional application methods described in the art can be used for this purpose. Examples of preferred application methods are dip coating, flow coating, spray coating and painting. Conventional application methods are discussed, for example, in "Formstoff und Formverfahren" [ Molding materials and Molding methods ], Eckart Flemming and Werner Tilch, Wiley-VCH, 1993, ISBN 3-527-.

During the dip coating process, the casting mold is immersed, for example, in a container with the ready-to-use coating composition for about 1 second to about 2 minutes. The time required for the excess coating composition to run off after impregnation depends on the flow behaviour of the coating composition used. After a sufficient run-off time, the coated casting mold is dried.

As the drying method, all conventional drying methods known in the art may be used, such as air drying, drying in dehumidified air, drying with microwave or infrared radiation, drying in a convection oven, and the like. In a preferred embodiment of the invention, the coated molds are dried in a convection oven at a temperature of from about 100 to about 250 deg.C, more preferably from about 120 to about 180 deg.C. When an alcohol coating is used, the coating composition is preferably dried by burning off the alcohol or alcohol mixture. In this case, the coated casting mold is additionally heated by the heat of combustion. In another preferred embodiment, the coated casting mold is air dried without any further treatment.

The coating composition of the present invention can be used as a base layer. The dry layer thickness of the base layer is, for example, up to about 100 μm, more preferably from about 10 to about 80 μm, still more preferably from about 10 to 50 μm.

The casting mould coated according to the invention is preferably used for producing metal bodies. They are particularly useful in the manufacture of engines and engine components, brake disks, turbochargers, exhaust manifolds and general machine components.

In the casting process, a casting mould coated according to the invention is provided, liquid metal is filled into the mould, and after hardening of the metal, the casting mould is removed.

The present invention will be explained in the following examples; however, they should not limit the invention in any way.

Examples

The following components were used:

AttaGel 40D 99 of about 50 μm, D90 of about 20 μm, D50 of about 9 μm, D10 of about 2 μm from BASF, 67063Ludwigshafen, Germany

Biocide obtained from Thor GmbH, 67346Speyer, Germany ACTICIDE F (N) (70% by weight tetrahydroxymethyl acetylene diurea)

Antifoam agent FINASOL, Total Deutschland GmbH, 10117Berlin, Germany

The wetting agent SURFYNOL 440, Evonik Corporation, Allentown, PA 18195, USA

Binders POLYVIOL (25% by weight polyvinyl alcohol), Wacker AG, 81737 Munich, Germany

Amorphous graphite Georg H.Luh, 65396Walluf, Germany D99 about 90 μm, D90 about 60 μm, D50 about 18 μm, D10 about 7 μm

Glossy powdered graphite fa.georg h.luh GmbH, 65396Walluf, germany; c content of at least 85 wt%, ash content of at most 15 wt%, particle size distribution determined using laser diffraction granulometry: d101-30 μm, D5080-120 μm, D90190-250 μm

Clay clayBlauton yellow-burning T7001KTS，Ton und Schamottewerke Mannheim GmbH&Co.KG，56218Germany; chemical analysis, expressed as% by weight of annealing: SiO 2₂ 53.66，Al₂O₃ 37，TiO₂ 3.75，Fe₂O₃ 2.98，CaO 0.73，MgO 0.63，K₂O 0.75，Na₂O0.07; sedimentation analysis was performed by sedimentation map measurement, in mass%:<2.0 μm 95.7, mineral analysis, in mass%: 70-75 parts of kaolin, 7.0 parts of illite, 15-20 parts of montmorillonite, 2.0 parts of quartz and 3.0 parts of Fe-Ti mineral

Mica fa.georg h.luh GmbH, 65396Walluf, germany; chemical analysis, in weight%: SiO 2₂43-46，Al₂O₃ 33-37，Fe₂O₃ 2-5，K₂O9-11; screening assay, screening by 60 μm: 25-64% by weight

Calcined kaolin Satintone W, BASF Corporation, Charlotte, NC, USA D99 about 65.5 μm, D908.53 μm, D502.4 μm, D10 about 0.4 μm

The following components were studied as first solids:

calcium carbonate is available from Omya GmbH, 50679Cologne, ETIQETTE VIOLETTE 99 about 15 μm, D90 about 8 μm, D50 about 3 μm, D10 about 1 μm in Germany

Dolomite HELADOL10, Helawit GmbH, D-23829Wittenborn, Germany D99 about 15 μm, D90 about 8 μm, D50 about 3 μm, D10 about 1 μm

Iron carbonate cofermemin Chemicals GmbH & co. kg, D-45130Essen, germany, obtained with a particle size of 100 mesh to 150 μm, micronized by milling to D99 of about 5 μm, D90 of about 1.4 μm, D50 of about 0.5 μm, D10 of about 0.2 μm

Rice starch HermannGmbH, D-49479 Ibbenbueren, Germany D50 ═ 5 μm

The coating composition for coating the casting mold is obtained as follows:

the first solid was mixed with premixes a and B and the coating composition was adjusted to a flow viscosity of about 13 seconds with additional water, as determined according to DIN 53211 with a 4mm nozzle using an immersion flow cup.

By weight%	Premix A	Premix B
			Water (W)	99.4	85.1
Wetting agent	0.6
			Biocide		1.0
Adhesive agent		9.0
			Attapulgite stone		4.0
Defoaming agent		0.9

All values are given in weight%.

Sand H32 from Quarzwerke Group and 0.8 wt.% ASKOCU by the polyurethane Cold Box method with Amines aerated with DimethylethylamineRE 388 (from ASK Chemicals, Hilden, Germany) and 0.8% by weight of ASKOCURE 666 (each based on sand) prepare domed core mouldings of dimensions 50mm diameter and 50mm height with an upper radius of 25mm, and of dimension R₁＝63mm/H₁＝25mm、R₂＝54mm/H₂＝25mm、R₃＝45mm/H₃＝25mm、R₄＝37mm/H₄＝25mm、R₅＝28mm/H₅＝25mm、R₆＝21mm/H₆25mm and R₇＝12mm/H₇43mm (wherein R_iIs the radius of the ith order and H_iHeight of the ith stage). The 0-stage of the dome core shown in fig. 1 is glued and therefore does not contact the metal.

Subsequently, the dome core or the step core was manually dipped in the stirred coating composition, and then dried in a drying oven at 120 ℃.

The dried cores were de-coated by rubbing at the core marks and mirror surfaces so that no compressive stress was generated and glued by ASKOBOND RAPID a (available from ASK Chemicals, Hilden, germany) into a casting mould with water glass/ester hardened sand H32. After closing and clamping the mold assembly by the screw clamp, casting was performed at 1420 ℃ with gray cast iron GJL 200.

After cooling and dismantling of the casting, the cavity of the core was sandblasted (2 bar pressure) and evaluated.

The pulse marks were evaluated as follows:

step core: the following table shows the number of pulse marks in each step

Dome core: in the following table, the pulse marks are rated with school grades 1-6.

The embodiment of the invention comprises the following steps: dome core

Grade: 1 is very good; 2 is good; 3 ═ satisfactory; 4 is sufficient; 5 is poor; 6 ═ deficiency

The embodiment of the invention comprises the following steps: step core

When a step core is used, it is glued into a cylindrical sand mould with a cavity of 150mm diameter, 200mm height, with the "foot" on top, and the volume ratio of metal to sand core increases from the 1 st step ("foot", R ═ 63 mm). The mold is filled from the bottom. The "number of vein marks of step n" indicates the number of vein marks existing on the nth step of the step core casting.

Furthermore, as a comparative example, the dome and step cores were coated as described in patent application DE 102018004234.1 according to the manufacturer's instructions.

The embodiment of the invention is as follows: dome core

The embodiment of the invention is as follows: step core

The results show that at very low matte layer thicknesses of only 25 to 100 μm, the coating compositions of the invention exhibit a sufficiently high protection against the formation of veils both in the dome core test and in the step core test. For the evaluation, the steps 1 to 5 were evaluated during the step test, since this corresponds to the most common and demanding applications in the automotive parts foundry in terms of metal to sand wall thickness ratio. In this regard, the effect of the coating composition of the present invention exceeds the effect of conventional coating compositions applied at high layer thicknesses of 300-500 μm against pulse mark defects.

Clearly, the coating composition of the present invention saves the process step of adding sand additives and provides a much higher concentration of active ingredients in the area where this concentration is needed. In particular, the gas formation provides very good protection against so-called veining which is often found in quartz sand, due to its thermal expansion (quartz reversal) and insufficient thermal strength, especially observed in polyurethane cold box cores.