EP2451596B1 - Mold wash for manufacturing mold coatings - Google Patents

Description

The present invention relates to a size for the production of mold coatings by application to inorganic or organic bonded moldings in lost molds or on cores for iron and steel casting.

Casting in a lost form is a common process for producing near-net shape components. After casting, the mold is destroyed and the casting is removed.

Shapes are negatives, they contain the emptying cavity, which results in the casting to be produced. The inner contours of the future casting are formed by cores. In the manufacture of the mold, the cavity is shaped into the molding material by means of a model of the casting to be manufactured. Inner contours are represented by cores formed in a separate core box. For lost molds and cores predominantly refractory granular materials such as washed, classified quartz sand are used as molding materials. Other materials include zirconium, chromite sands, chamottes, olivine sands, feldspathic sands and andalusite sands. To produce the casting molds, the molding materials are bound with inorganic or organic binders. In many cases, bentonites or other clays are used as inorganic binders. The molded materials are compacted to increase the strength. Frequently, in particular for the production of cores, are hardening, with used inorganic or organic resin binders bonded molding materials. Curing is due to a chemical reaction in a hot or cold process. Frequently, corresponding molding materials are also gassed for curing. Also, the curing of the binder can be done by heating the molding material and expelling a solvent, which then causes hardening.

Usually, the surfaces of the molds and cores are coated with a size. Ready-to-use sizes for coating molds and cores are suspensions of fine-grained, refractory to highly refractory inorganic materials in a carrier liquid, e.g. Water or a solvent. The size is applied by a suitable application method, for example spraying, dipping, flooding or brushing on the inner contour of the mold or on the core and dried there, so that a size coat (size film) is formed. The drying of the size coat may be accomplished by the application of heat or radiant energy, e.g. by microwave radiation, or by drying in the room air done. In the case of solvent-containing sizing, the drying can also be carried out by burning off the solvent.

1. 1. Verbesserung der Gussoberfläche bezüglich ihrer Glätte
2. 2. Saubere Trennung zwischen flüssigem Metall und Form
3. 3. Vermeidung von chemischen Reaktionen zwischen Formstoff und Schmelze, dadurch Erleichterung der Trennung zwischen Formstoff und Gussstück
4. 4. Vermeidung von Oberflächenfehlern am Gussstück wie z.B. Gasblasen, Penetrationen, Blattrippen und Schülpen.

The sizing coatings should, inter alia, fulfill the following functions:

1. 1. Improvement of the casting surface with regard to its smoothness
2. 2. Clean separation between liquid metal and mold
3. 3. Prevention of chemical reactions between molding material and melt, thereby facilitating the separation between molding material and casting
4. 4. Prevention of surface defects on the casting such as gas bubbles, penetrations, leaf ribs and slugs.

The aforementioned functions 1 to 3 are usually fulfilled by combinations of various suitable refractory materials. As fireproof materials and minerals are referred to here, which can withstand the temperature load during casting by a molten iron, as high refractory materials and minerals that can withstand the casting heat of a molten steel in the short term. As refractory material, for example, mineral oxides such as corundum, magnesite, quartz, chromite and olivine, furthermore silicates such as zirconium silicate, chamotte, andalusites, pyrophyllite, kaolinite, mica and other clay minerals are used individually or in combination. Graphite and coke are also used. The refractories are in a carrier liquid suspended. Solvents such as ethanol or isopropanol can serve as the carrier liquid, but today water is usually preferred as the carrier liquid.

Further bases for sizes are suspending agents, e.g. water swellable clays such as smectites, attapulgites or sepiolites or swellable organic thickeners such as e.g. Cellulose derivatives or polysaccharide. Further, a size includes a binder to fix the refractories on the molding material. As a rule, synthetic resins or synthetic resin dispersions are used here, e.g. Polyvinyl alcohol, polyacrylates, polyvinyl acetates and corresponding copolymers. Natural resins, dextrins, starches and peptides can also be used as binders. The aforementioned swellable clays can also take over the functions of the binder.

Finishes may contain further additives, in the case of aqueous sizes in particular preservatives and rheologically active additives and adjusters. Rheologically active additives and / or adjusting agents are used to adjust the flowability of the size desired for processing. In the case of aqueous sizes wetting agents can also be used to achieve a better wetting of the molding material. The person skilled in the art is familiar with ionic and nonionic wetting agents. For example, dioctylsulfosuccinates are used as ionic wetting agents and alkynediols or ethoxylated alkynediols are used as nonionic wetting agents.

Due to the complexity of today's castings, in particular, the function of sizing coatings to avoid surface defects on the casting is gaining in importance. Because the core geometries are becoming ever more filigree and the shapes more and more complex, the demands on the molded materials and especially the sizes are increasing. Due to the thermal expansion of the sand contained in the molding material through the casting heat can break inorganic and in particular resin-bonded molds and cores, so that the liquid metal penetrates into the mold or the core. The resulting surface defects, e.g. Leaf ribs are difficult to remove.

The pyrolysis of resin-bonded molded materials by the casting heat produces gases. These can lead to casting defects. In this connection, various causes leading to the formation of these casting defects called gas defects can be distinguished.

On the one hand, gas errors, such as from HG Levelink, FPMA Julien and HCJ de Man in Foundry 67 (1980) 109 described. caused by "exogenous" gases. These "exogenous gases" arise mainly during the pyrolysis of organic binders on contact with the molten metal in the mold or the core. These gases generate a gas pressure in the molding material, which, if it exceeds the metallostatic back pressure, can lead to gas defects in the casting, usually in its upper region. These gas bubbles usually have a smooth inner surface.

Another type of gas error is eg of Gy. Nandori and J.Pal. Miskoloc and K. Peukert in Foundry 83 (1996) 16 describe. These are gas bubbles that occur associated with slag jobs. The cause of such gas slag faults are "exogenous", ie coming from the molding material and mold cavity, and "endogenous", ie to view from the melt gases. These gases partially react with the melt, resulting in oxide-rich slags. These slags together with the remaining gases form gas faults. An influencing factor for the formation of these gas defects is the gas permeability of the molding material coated with the size coat.

In places where the surface of a core or mold is not sufficiently protected against melt penetration, penetration often occurs. These errors must be removed from the casting consuming.

During the casting process, the sizing coating may peel off the core or mold if a high gas pressure due to pyrolysis of the molding material binder builds up in the core and the sizing presents high resistance to this pressure due to low gas permeability. If the gas pressure exceeds the adhesive forces of the sizing coating on the core or the mold, the sizing will be abated. Casting errors caused by melting in the melt size particles are the result.

It has already been tried to develop sizing that counteract these casting defects. For example, by addition of platelet-shaped phyllosilicates such as calcined kaolins, pyrophyllites, talc and mica or other clay minerals to the size arise on the molds or cores sizing coatings that can be well deformed under the action of tensile forces. The individual platelets overlap one another and can cover the cracks caused by the thermal expansion of the sand in the molding material. Because of their dense Texture are sizing coatings containing platy phyllosilicates, but only slightly permeable to gas. In the thermal decomposition of the binder of the molding material resulting gases so difficult to pass through these layers, it form high gas pressures, which can lead to the above-mentioned gas and flaw defects.

In the patent application WO 2007/025769 Sizing (there also known as molding compositions with molding material mixtures) described which contain an addition of borosilicate glass in a proportion of at least 0.001%, preferably at least 0.005% by weight, in particular at least 0.01% by weight based on the solids content of the sizing. The proportion of borosilicate glass is preferably less than 5% by weight, more preferably less than 2% by weight and most preferably within a range of 0.01 to 1% by weight, in each case based on the solids content of the size. According to a particularly preferred embodiment, borosilicate glass in the form of hollow microspheres, ie hollow beads having a diameter in the order of preferably 5 to 500 .mu.m, more preferably 10 to 250 .mu.m, whose shell is constructed of borosilicate glass, is used. It is believed that the borosilicate glass melts under the influence of the temperature of the liquid metal and thereby cavities are released, which can compensate for the volume expansion of the molding material caused by the casting heat. Preferably, the softening point of the borosilicate glass is set in the range of less than 1500 ° C, particularly preferably in the range of 500 to 1000 ° C. When using these sizes, flaking off of the size coat under the influence of the liquid metal is unlikely to occur. In addition, it was found that no leaf ribs form and a smooth casting surface is obtained.

As according to WO2007 / 025769 a melting of the hollow spheres of borosilicate glass is intended, the sizing coating after the melting of the hollow spheres on holes through which the liquid metal can penetrate to the surface of the core or the mold. So there is a risk of penetration errors. This problem can not be solved by the use of Borosilikatglaskugeln higher melting point, because glasses contain in addition to the network former boron oxide and so-called network converter such as sodium oxide and potassium oxide, all three compounds with virtually all of the above ingredients of sizing (except carbon or graphite) , especially all platelet-shaped clay minerals and silicates low form melting compounds. In addition, hollow spheres made of borosilicate glass are not very stable mechanically. Therefore, they are very easily broken under the pressure load inevitably involved in the preparation of sizing. Another disadvantage of using hollow spheres made of borosilicate glass is their strong alkalinity. This leads to an unfavorable change in the pH of the sizings. Therefore, according to a variant of the molding composition WO2007 / 025769 the addition of an acid or an acid source provided.

From the WO 94/26440 Sizing agents are known which have a content of inorganic hollow spheres of 1 to 40%, preferably of at least 4%, or even at least 10%, based on the weight of the ready-to-use sizing. The hollow spheres consist, for example, of silicates, in particular of aluminum, calcium, magnesium and / or zirconium, of oxides such as aluminum oxide, quartz, magnesite, mullite, chromite, zirconium oxide and / or titanium oxide, of borides, carbides and nitrides such as silicon carbide, titanium carbide, titanium boride, Boron nitride and / or boron carbide, or carbon. However, hollow spheres made of metal or glass can also be used. These hollow spheres are effective in several ways. Thus, the dense packing of the base particles in the sizing, which may be considered to be the main cause of the low gas permeability, is lightened by the beads and made more gas permeable. It is also believed that at the beginning of the casting process, the insulating properties of the hollow spheres and the gas-permeable size coatings cause a delayed heat transfer through the size in the molding material. Later, the hollow spheres melt in the casting heat and / or break under the casting pressure, causing numerous micro-defects in the size coat, thus increasing the gas permeability of the size coat.

Again, due to the large amount of melting hollow spheres, the possibility that can form holes in unfavorable overlap of individual hollow spheres in the size coat, so that the casting may have penetration errors.

Due to the problems outlined above, it appears advantageous, instead of hollow spheres made of glass, to use inorganic hollow bodies of materials which have a similar or similar composition to the above-mentioned refractories, in particular the platelet-shaped refractory materials, and / or which react very slowly with the refractories contained in the sizing. For this purpose, the inorganic hollow body should have a high softening temperature, so that they do not melt during the casting process, and a higher mechanical stability than hollow spheres made of glass. Furthermore, it is desirable to reduce the need for hollow spheres without having to accept an increased incidence of casting defects.

These objects are achieved by a ready-to-use size for the production of moldings by application to inorganic or organic bonded moldings in lost molds or on cores for iron and cast steel, which contains a weight-based proportion of 0.001% to 0.99% of inorganic hollow bodies , wherein the inorganic hollow body partially or completely made of crystalline material.

Surprisingly, it has been found that, based on the total weight of the ready-to-use sizing, an addition of less than 1% of inorganic hollow bodies, which consist partially or completely of crystalline material, is sufficient to reduce the formation of gas defects, penetrations and leaf ribs. In particular, those gas defects that occur in connection with oxide-rich slags are reduced. This was due to the revelation in WO 94/26440 not to be expected. In the exemplary embodiments specified there, only sizes having a content by weight of hollow spheres of aluminum silicate of at least 4% of the ready-to-use size, ie four times the lower limit value of 1% specified there, were tested. From the comparison of the embodiments of WO 94/26440 with proportions of 0 and 4, 5 and 10% hollow spheres of aluminum silicate in the ready-made size is also clear that the gas permeability increases with the proportion of hollow spheres, ie, the advantageous effect of the hollow spheres seems higher, the greater the proportion of hollow spheres in the ready-made sizing is.

Ready-to-use sizing is understood to mean that the base mass of the sizing has been diluted with a carrier liquid, for example water, such that one for coating molds or cores by means of one of the abovementioned techniques in the desired suspension is present in the desired layer thickness. For this purpose, the sizes are diluted with a carrier liquid, for example water to a suitable viscosity. In the case of the dipping application, the sizes to achieve the desired coating thickness of the size coat, for example from 0.1 to 0.6 mm, are typically at viscosities of 11.5 seconds. to 16 sec. measured in a 4 mm immersion discharge cup diluted in accordance with DIN 23211. For other application methods, other viscosities must be chosen accordingly. The determination of suitable viscosities and layer thicknesses is one of the skills of the skilled person.

The inorganic materials of which the inorganic hollow bodies are formed are distinguished by the presence of X-ray diffraction analysis of detectable crystalline structures. That is, in the materials of the hollow body there are regions with three-dimensional periodic order, the extent of which is greater than the coherence length of the X-radiation (about 10 nm), so that in the X-ray diffraction analysis sharp reflections are observed. The crystalline fraction is preferably 5% by weight or more, more preferably 20% by weight or more. In contrast, the material is the off WO 2007/025769 known hollow spheres of borosilicate glass non-crystalline, because glass is a supercooled melt, ie it is in the amorphous state.

The inorganic hollow bodies preferably have a softening point of 1000 ° C. or higher, preferably 1100 ° C. or higher, determined by means of a heating microscope. Particular preference is given to inorganic hollow bodies having a softening point between 1200 ° C. and 1450 ° C., determined by means of a heating microscope. The determination of the softening point and the melting point of ceramics in a heating microscope is based on the measurement of the projection area of a cylindrical sample and its change with temperature. The softening point is the temperature at which the first detectable melt phenomena occur, which are manifested by smoothing of rough surfaces and the beginning of edge rounding. The hemisphere or melting point is the temperature at which the sample is deformed to a hemisphere by the formation of melt phases.

The inorganic hollow bodies of the size according to the invention, which consist partially or completely of crystalline material, contain no boron oxides, which act as network formers for glasses, and thus also no borosilicate glass. As a network converter acting compounds such as sodium and potassium oxide, which also as Flux act and reduce the melting temperature, are at best contained as impurities. Therefore, in the sizings of the invention, the formation of low-melting compounds by reaction of the network converters and fluxes sodium oxide and potassium oxide and the network former boron oxide with platelet-shaped clay minerals and silicates usually contained in the sizing is suppressed. Preferably, in the inorganic hollow bodies to be used according to the invention, the content of the compounds acting as fluxes and network converters is preferably less than 4% by weight of sodium oxide and / or potassium oxide.

The inorganic hollow bodies consist for example of silicates, preferably of aluminum, calcium, magnesium or zirconium, or of oxides, preferably aluminum oxide, quartz, mullite, chromite, zirconium oxide and titanium oxide, or of carbides, preferably silicon carbide or boron carbide or of nitrides, preferably boron nitride or mixtures of these materials, or mixtures of inorganic hollow bodies of these materials are used.

By hollow bodies are meant, without limitation to the spherical shape arbitrarily shaped three-dimensional structures having a cavity inside which occupies 15% or more, preferably 40% or more, more preferably 70% or more of the volume of the three-dimensional structure. This cavity can be completely enclosed by a shell of inorganic material, as in the case of hollow spheres, or incompletely enclosed, as in the case of a tube open at the ends, for example.

These inorganic hollow bodies are preferably hollow spheres having a diameter of less than 400 μm, preferably 10 to 300 μm, particularly preferably 10 to 150 μm.

The inorganic hollow bodies are characterized by a high mechanical stability, so that they can withstand the pressure load, which inevitably occurs in the production of sizes. For this purpose, the inorganic hollow bodies to be used according to the invention preferably have compressive strengths of 10 MPa or higher, preferably of 25 MPa or higher. The compressive strength of hollow bodies made of glass is generally lower than 10 MPa. So have in the embodiments of the WO2007 / 025769 used hollow microspheres a compressive strength of only 4 MPa. The compressive strengths can be determined in an isostatic pressure test based on ASTM D3102-72.

Preference is furthermore given to inorganic hollow bodies, in particular hollow spheres, having an outer diameter of from 10 to 150 μm.

Also preferred are inorganic hollow bodies, in particular hollow spheres, having a Mohs hardness of 5 to 6.

Also preferred are hollow bodies, in particular hollow spheres with a compressive strength of 25 MPa or more.

Also preferred are inorganic hollow body, in particular hollow balls, with a cavity which occupies 70% or more of the total volume of the hollow body or the hollow sphere.

Individual or all of the preferred properties of the inorganic hollow bodies are preferably realized in combination with each other.

• einem Außendurchmesser im Bereich von 10 bis 150 µm,
• einem Hohlraum, der 70 % oder mehr des Gesamtvolumens der Hohlkugel einnimmt;
• einem Erweichungspunkt von 1200 °C bis 1450 °C eine Mohs-Härte von 5 bis 6 und
• eine Druckfestigkeit von 25 MPa oder höher.

Particular preference is given in the sizes according to the invention to individual, the majority or all of the inorganic hollow bodies used which are inorganic hollow spheres which form during the combustion of coal in power plants as part of the fly ash. These hollow spheres are deposited from the flue gas stream and are described under the name cenospheres (Cenospheres CAS No .: 93924-19-7). These inorganic hollow spheres preferably have the following properties:

• an outer diameter in the range of 10 to 150 μm,
• a cavity occupying 70% or more of the total volume of the hollow sphere;
• a softening point of 1200 ° C to 1450 ° C a Mohs hardness of 5 to 6 and
• a compressive strength of 25 MPa or higher.

However, since such hollow spheres are available only to a limited extent, the low content of the sizes according to the invention of such inorganic hollow bodies has an advantage over the prior art WO 94/26440 represents.

In a further preferred variant of the size according to the invention inorganic hollow body made of carbon, preferably nano-hollow body made of carbon, for example carbon nanotubes (carbon nanotubes) and / or fullerenes. It is also possible to use mixtures of inorganic hollow bodies of carbon and inorganic hollow bodies of one or more of the other materials mentioned above.

1. (a) anorganische Hohlkörper, die teilweise oder vollständig aus kristallinem Material bestehen,
   sowie vorzugsweise
2. (b) ein oder mehrere feuerfeste oder hochfeuerfeste Materialien, die keine Hohlkörper sind wie unter (a) definiert,
3. (c) eine oder mehrere Trägerflüssigkeiten wie z.B. Wasser,
4. (d) ein oder mehrere Suspensionsmittel wie z.B. in Wasser quellbare Tonminerale,
5. (e) ein oder mehrere Biozide,
6. (f) gegebenenfalls ein oder mehrere Netzmittel,
7. (g) gegebenenfalls ein oder mehrere Stellmittel oder/und rheologische Additive,
8. (h) gegebenenfalls ein oder mehrere Bindemittel.

Contains a ready-to-use size according to the invention

1. (a) inorganic hollow bodies which consist partly or completely of crystalline material,
   and preferably
2. (b) one or more refractory or high refractory materials which are not hollow bodies as defined under (a),
3. (c) one or more carrier liquids, such as water,
4. (d) one or more suspending agents, such as water-swellable clay minerals,
5. (e) one or more biocides,
6. (f) optionally one or more wetting agents,
7. (g) optionally one or more adjusting agents and / or rheological additives,
8. (h) optionally one or more binders.

For the purpose of calculating the composition of the size, those substances which can be assigned to more than one of components (a) to (h) are to be assigned to the former of these components.

The present invention also provides the use of a size according to the invention for the production of a coating on a mold or a core for use in the foundry.

The present invention also relates to a mold or a core for iron and steel casting, wherein the mold or the core on the casting metal surface facing a size coat comprising the drying product of a size according to the invention, wherein the thickness of the size coat 0.05 mm or more, preferably 0.15 mm or more and more preferably 0.25 to 0.6 mm, and the use of such a mold or such a core for producing an iron or cast steel piece.

1. (a) 0,0011 bis 3,5 % an anorganischen Hohlkörpern, die teilweise oder vollständig aus kristallinem Material bestehen,
2. (b) 20 bis 75 % an einem oder mehreren feuerfesten oder hochfeuerfesten Materialien, die keine Hohlkörper sind wie unter (a) definiert,
3. (c) 15 bis 80 % an einer oder mehreren Trägerflüssigkeiten, z.B. Wasser,
4. (d) 0,1 bis 10 % an einem oder mehreren Suspensionsmitteln wie z.B. in Wasser quellbare Tonminerale,
5. (e) 0,01 bis 0,6 % an einem oder mehreren Bioziden,
6. (f) 0 bis 4 % an einem oder mehreren Netzmitteln,
7. (g) 0 bis 2 % an einem oder mehreren Stellmitteln und/oder rheologische Additiven,
8. (h) 0 bis 2 % an einem oder mehreren Bindemitteln.

The present invention also encompasses a concentrate for the preparation of a ready-to-use size according to the invention, the concentrate having the following composition, based on its total weight:

1. (a) from 0.0011 to 3.5% of inorganic hollow bodies consisting partly or wholly of crystalline material,
2. (b) 20 to 75% of one or more refractory or refractory materials other than hollow bodies as defined in (a),
3. (c) 15 to 80% of one or more carrier liquids, eg water,
4. (d) 0.1 to 10% of one or more suspending agents, such as water-swellable clay minerals,
5. (e) 0.01 to 0.6% of one or more biocides,
6. (f) 0 to 4% of one or more wetting agents,
7. (g) 0 to 2% of one or more adjusting agents and / or rheological additives,
8. (h) 0 to 2% of one or more binders.

For the purpose of calculating the composition of the concentrate, those substances which can be assigned to more than one of the components (a) to (h) are to be assigned to the former of these components.

• Her- oder Bereitstellen eines Konzentrates wie oben beschrieben,
• Mischen des Konzentrates mit Wasser oder einer anderen Trägerflüssigkeit in einem solchen Mischungsverhältnis, dass eine gebrauchsfertige erfindungsgemäße Schlichte erhalten wird.

The present invention also provides a process for the preparation of a size from a concentrate according to the invention described above, the process comprising the following steps:

• Preparing or providing a concentrate as described above
• Mixing the concentrate with water or other carrier liquid in such a mixing ratio that a ready-to-use size according to the invention is obtained.

• Her- oder Bereitstellen eines zu beschichtenden Formkörpers oder Kerns,
• Bereitstellen einer gebrauchsfertigen erfindungsgemäßen Schlichte oder Herstellen einer solchen Schlichte nach dem oben beschriebenen erfindungsgemäßen Verfahren,
• Auftragen der gebrauchsfertigen Schlichte auf den Kern oder den Formkörper, so dass ein Schlichteüberzug entsteht mit einer Dicke von 0,05 mm oder mehr, vorzugsweise von 0,15 mm oder mehr und besonders bevorzugt von 0,25 mm bis 0,6 mm.

The present invention furthermore relates to a process for producing a size coat on a shaped body or core, comprising the steps:

• Providing or providing a shaped body or core to be coated,
• Providing a ready-to-use size according to the invention or producing such a size according to the inventive method described above,
• Applying the ready-to-use size to the core or the molding so that a size coat is formed having a thickness of 0.05 mm or more, preferably 0.15 mm or more, and more preferably 0.25 mm to 0.6 mm.

The sizings according to the invention are applied to the lost molds or cores, for example by dipping, flooding, spraying or brushing, and then dried, preferably by the application of heat or microwave radiation, so that sizing coatings are formed on the molds or cores.

embodiments

A size having the composition shown in Table 1 is prepared by mixing the components with a stirrer and then breaking up by shearing for 10 minutes with a high speed spinning dissolver. Corresponding production methods are known to the person skilled in the art and, for example, in the patent application WO 94/26440 described. Table 1 material Simple basic approach
[Share in weight%] water 53 Aluminum silicate refractory 15 clay mineral 5.8 mica 18 iron oxide 1 graphite 5 dextrin 0.5 actuating means 0.5 preservative 0.3 defoamers 0.5 wetting agent 0.4 total 100

From this basic formulation, sizes A, B, C, D and E, the compositions of which are given in Table 2 below, were prepared by mixing with a dissolver disk and diluted with water as indicated to give ready-to-use sizes.

The sizings were applied by dipping onto cores made by cold box. The achieved coating thicknesses of the size coatings were 0.5 mm in the wet, matted state. Subsequently, the cores were dried in a drying oven at 150 ° C for 30 minutes. All further investigations were carried out with the sized cores thus prepared (see Table 2). It turns out that when using the sizes according to the invention on the castings fewer leaf ribs and distortions are formed than when using a size according to the prior art with a higher proportion of inorganic hollow bodies. Table 2 material Simple A (comparison) Simple B Simple C Simple D (comparison) Simple E (comparison) Proportion [wt. %] Proportion [wt. %] Proportion [wt. %] Proportion [wt. %] Proportion [wt. %] basic approach 99.5 99.5 99.5 97.0 97.0 water 0.5 0.4 - 1.7 - Ceramic hollow spheres - 0.1 0.5 1.3 3.0 (Cenospheres CAS No. 93924-19-7) total 100 100 100 100 100 Thinner for setting the ready-to-use processing state 1000g sizing + 370ml water 1000g sizing + 380ml water 1000g sizing + 380ml water 1000g sizing + 340ml water 1000g sizing + 360ml water Achieved layer thickness on the core * (in the matted state) 0,5mm 0,5mm 0,5mm 0,5mm 0,5mm Leaf rib training casting test 1 No leaf ribs No leaf ribs No leaf ribs No leaf ribs Penetrations casting test 2 No penetration No penetration Light penetrations Light penetrations * Core made by the cold box polyurethane process: 70 parts by weight quartz sand, 30 parts by weight chromite sand, 1.8 parts by weight resin components, tertiary amine catalyst.

• 50 Gewichtsteile feldspathaltiger Sand
• 50 Gewichtsteile Quarzsand
• 1,8 Gewichtsteile Harzkomponenten

FIG. 1 shows the results of measurements of the gas pressure as a function of time in each one coated with the above sizing A, B, C, D, and E core. The measuring method for determining the gas pressure in cores has been described by HG Levelink, FPMA Julien and HCJ de Man in Foundry 67 (1980) 109. The test temperature is 1445 ° C. The composition of the cores is as follows:

• 50 parts by weight feldspathic sand
• 50 parts by weight of quartz sand
• 1.8 parts by weight of resin components

Surprisingly, it has been shown that with the sizes B and C according to the invention, final coatings on cores and molds are obtained after drying, which reduce the formation of gas defects despite a higher gas pressure in the molding material than in the comparative experiment with size E.

How out FIG. 1 it can be seen, in the absence of the inorganic hollow body in the sizing (comparative experiment with size A), the gas pressure in the molding material is significantly higher. It follows that even in comparison to the prior art (Comparative Example E) small proportion of inorganic hollow bodies in the sizes according to the invention sufficient to reduce the gas pressure so far that hardly any gas defects are observed on the castings. In particular, it is found in practice that such gas defects that occur associated with oxide-rich slags greatly reduced occurrence. However, sizing with higher levels of hollow spheres, due to their high gas permeability, act primarily against exogenous gas bubbles.

The tests with the sizes of Examples B and C show that at least comparable advantages with the sizes according to the invention as with the sizes according to WO 2007/025769 were achieved, ie the formation of leaf ribs was reduced and prevents chipping of the size coat. In addition, the formation of penetrations was reduced or prevented.

With a size according to Example C cores for the production of engine parts, which were manufactured by the cold box process, coated. For a batch of 500 pieces, no exogenous gas faults and, in particular, gas faults associated with slag were observed.

Claims (15)

1. Ready-to-use wash for producing mould coatings on lost moulds or on cores for iron and steel casting, wherein the wash contains a proportion by weight of 0.001 % to 0.99 % of inorganic hollow bodies, characterised in that the inorganic hollow bodies consist partly or completely of crystalline material.
2. Wash according to claim 1, characterised in that said inorganic hollow bodies have a softening point of 1,000 °C or higher, preferably 1,100 °C or higher, particularly preferably a softening point between 1,200 °C and 1,450 °C.
3. Wash according to claim 1 or 2, characterised in that said inorganic hollow bodies consist of

   - silicates, preferably of aluminium, calcium, magnesium or zirconium, or of

   - oxides, preferably aluminium oxide, quartz, mullite, chromite, zirconium oxide or titanium oxide, or of

   - carbides, preferably silicon carbide or boron carbide, or of

   - nitrides, preferably boron nitride, or of

   - mixtures of these materials
   or
   are mixtures of inorganic hollow bodies made of these materials.
4. Wash according to any one of the preceding claims, characterised in that said inorganic hollow bodies are hollow balls with a diameter of less than 400 µm, preferably 10 to 300 µm, particularly preferably 10 to 150 µm, preferably hollow balls with an external diameter of 10 to 150 µm.
5. Wash according to any one of the preceding claims, characterised in that said inorganic hollow bodies are three-dimensional structures, preferably hollow balls, which have a cavity, which takes up 15 % or more, preferably 40 % or more, particularly preferably 70 % or more of the volume of the three-dimensional structure.
6. Wash according to any one of the preceding claims, characterised in that said inorganic hollow bodies have compressive strengths of 10 MPa or higher, preferably of 25 MPa or higher and/or have a hardness of 5 to 6 on the Mohs scale.
7. Wash according to any one of the preceding claims, characterised in that individual hollow bodies, the majority thereof or all said inorganic hollow bodies are hollow balls with

   - an external diameter in the range from 10 to 150 µm,

   - a cavity, which takes up 70 or more % of the total volume of the hollow balls,

   - a softening point of 1,200 °C to 1,450 °C

   - a hardness of 5 to 6 on the Mohs scale and

   - a compressive strength of 25 MPa or higher.
8. Wash according to any one of the preceding claims, characterised in that said inorganic hollow bodies are hollow balls corresponding to CAS-No. 93924-19-7 (cenospheres), which form during the combustion of coal at power stations as part of the fly ash and are separated from the exhaust gas flow.
9. Wash according to claim 1, characterised in that said inorganic hollow bodies consist of carbon or are mixtures of inorganic hollow bodies made of carbon and inorganic hollow bodies made of one or more of the materials according to claim 2, wherein said inorganic hollow bodies made of carbon preferably comprising nano hollow bodies made of carbon, for example carbon nanotubes or/and fullerenes.
10. Use of a wash according to any one of claims 1 to 9 for producing a coating on a mould or a core for use in casting.
11. Mould or core for iron and steel casting, characterised in that the mould or core on the surface facing the casting metal has a wash coating comprising the drying product of a wash as defined in claims 1 to 9, wherein the thickness of the wash coating is 0.05 mm or more, preferably 0.15 mm or more and particularly preferably 0.25 to 0.6 mm.
12. Use of a mould or a core according to claim 11 for producing an iron or steel casting.
13. Concentrate for producing a ready-to-use wash according to claims 1 to 9, wherein the concentrate based on its total weight has the following composition:

    (a) 0.0011 to 3.5 % of inorganic hollow bodies, which partially or completely consist of crystalline material

    (b) 20 to 75 % of one or more refractory or highly refractory materials, which are not hollow bodies as defined under (a)

    (c) 15 to 80 % of one or more carrier liquids, for example water

    (d) 0.1 to 10 % of one or more suspension agents such as, for example, clay minerals that are swellable in water

    (e) 0.01 to 0.6 % of one or more biocides

    (f) 0 to 4 % of one or more wetting agents

    (g) 0 to 2 % of one or more floating agents and/or rheological additives

    (h) 0 to 2 % of one or more binding agents
14. Method for producing a wash from the concentrate according to claim 13 comprising the steps:

    - producing or providing a concentrate as defined in claim 13,

    - mixing the concentrate with water or another carrier liquid in a mixing ratio such that a ready-to-use wash according to any one of claims 1 to 9 is obtained.
15. Method for producing a wash coating on a moulded body or core, comprising the steps:

    - producing or providing a moulded body or core to be coated,

    - providing a ready-to-use wash as defined in claims 1 to 9 or producing such wash by the method according to claim 14,

    - applying the ready-to-use wash to the core or the moulded body, so that a wash coating is produced with a thickness of 0.05 mm or higher, preferably of 0.15 mm or higher and particularly preferably of 0.25 mm to 0.6 mm.

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