EP1567576A1

EP1567576A1 - Method for producing shaped bodies, particularly cores, molds and feeders for use in foundry practice

Info

Publication number: EP1567576A1
Application number: EP03785750A
Authority: EP
Inventors: Antoni Gieniec; Henning Rehse; Dieter Koch; Günter Weicker; Dietmar Chmielewski
Original assignee: Ashland Suedchemie Kernfest GmbH
Current assignee: Ashland Suedchemie Kernfest GmbH
Priority date: 2002-12-05
Filing date: 2003-12-05
Publication date: 2005-08-31
Also published as: KR20050084181A; DE10256953A1; JP2006518667A; WO2004050738A1; CN1732195A; US20060151575A1; CA2508723A1; WO2004050738A8; MXPA05005934A; AU2003294795A1; BR0317066A

Abstract

The invention relates to a method for producing shaped bodies, particularly cores, molds and feeders for use in foundry practice, comprising the following the steps: a) producing a composition containing: i) at least one phenol resin in solid form; ii) at least one polyisocyanate, and; iii) at least one refractory material, whereby the composition is produced at a temperature that is lower than the melting temperature of the at least one phenol resin; b) shaping the composition to form a shaped body; c) increasing the temperature of the composition above the melting point of the at least one phenol resin in order to harden the mixture. The invention also relates to shaped bodies, particularly cores, molds and feeders for use in foundry practice, which can be obtained by said method, and to a composition such as one used in this method.

Description

PATENT APPLICATION

Process for the production of moldings, in particular cores, molds and feeders for foundry technology

DESCRIPTION

The present invention relates to a process for the production of moldings, in particular cores, molds and feeders in foundry technology, moldings which have been obtained by this process, and a composition as used in this process.

Such moldings are required in two versions: as so-called cores or molds for the production of castings, and as hollow bodies (so-called feeders) for holding liquid metal as a compensation reservoir to prevent shrinkage-related casting defects during metal solidification. The mixtures for the production of such moldings contain a refractory material, for example quartz sand, the grains of which the molding of the molded body can be connected by a suitable binder in order to achieve sufficient mechanical strength of the mold.

The moldings have to meet various requirements. During the casting process itself, they must first have sufficient stability and temperature resistance in order to absorb the liquid metal into the hollow mold formed from one or more shaped bodies. After the solidification process begins, the mechanical stability of the mold is ensured by the solidified metal layer that has formed along the walls of the hollow mold. The material of the shaped bodies must then decompose under the influence of the heat given off by the metal in such a way that it loses its mechanical strength, that is to say the cohesion between individual grains of refractory material is broken. This is achieved, for example, by the binder decomposing under the influence of heat. After cooling, the solidified casting is shaken, and ideally the material of the shaped pieces disintegrates into fine sand, which can be poured out of the cavities of the metal mold.

A distinction is made between cold and hot processes in the processes for producing the moldings mentioned.

Gas hardening has assumed a dominant position in cold processes.

A two-component system is used for gas curing in the polyurethane cold box process. The first component consists of the solution of a polyol, usually a phenolic resin. The second component is the solution of a polyisocyanate.

According to US 3,409,579 A, the two components of the Reacted polyurethane binder by passing a gaseous tertiary amine after molding through the molding material / binder mixture.

The curing reaction of polyurethane binders is a polyaddition, i.e. a reaction without elimination of by-products such as Water. Other advantages of this cold box process include good productivity, dimensional accuracy of the moldings and good technical properties (strengths, processing time of the molding material / binder mixture, etc.).

However, the advantages mentioned are also offset by certain weaknesses of the polyurethane cold box process, for example emissions from the amine used as a catalyst, which has to be extracted with great effort and separated in an acid scrubber, and emissions from evaporating solvents and residual monomers during core production or especially when it comes to core storage.

The thermosetting (hot) processes include the hot box process based on phenol or furan resins, the warm box process based on furan resins, and the croning process based on phenol novolak resins.

The thermosetting processes have stabilized their position in core production for foundry technology for years. In the first two technologies - hot box and warm box - liquid resins are processed into a molding material mixture with a latent hardener that is only effective at elevated temperatures.

In the croning process, molding materials such as quartz, chrome ore, zircon sands etc. are encased at a temperature of approx. 100-160 ° C with a phenol novolak resin that is liquid at this temperature. As a reaction partner for later curing, hexamethyl O 2004/050738 lentetramine added.

Shaping and curing take place at the above thermosetting technologies in heated tools that are heated to a temperature of up to 300 ° C.

Binders suitable for hot curing generally contain water that has to be expelled during curing. Since the hardening is a polycondensation from a chemical point of view, this creates additional water, which must also be removed.

Another disadvantage is the elimination of formaldehyde during curing, especially with so-called croning sands, so that these processes cannot be said to be emission-free.

Binders are also used in other systems in which particles made of different materials are combined in order to obtain moldings with certain properties. However, these binder systems are generally not suitable for use in the production of moldings for foundry technology, since these do not have the required properties, high thermal and mechanical stability at the start of the casting process and easy disintegration with the progressive solidification of the molten metal.

EP 0 022 215 A1 describes a process for the production of moldings based on polyurethane. First, in a first reaction step, polyisocyanates with polyhydroxyl compounds, for example novolaks, are converted in an NCO / OH equivalent ratio of 0.8: 1 to 1.2: 1 to a solid, pulverizable and meltable product that is still free isocyanate - And has hydroxyl groups. This product will then cured in a second reaction stage after or with simultaneous shaping by heating to 100 to 250 ° C. to form a cross-linked, no longer meltable molded body. The process is particularly suitable for the production of moldings for the electrical industry, such as insulators, switch parts, casings for electronic components, transformers, instrument transformers or also binders for heat-crosslinkable powder coatings or solvent-based coatings for the production of coatings of any kind. The process is suitable not for the production of moldings for foundry technology, since the moldings do not have the required properties when decomposing under the influence of heat.

WO 00/36019 describes a binder composition for the production of wood composite materials. The wood chips are mixed with a binder composition, which essentially consists of a polyphenyl isocyanate and a solid resole resin, and shaped into the desired shaped body. In the examples, the polymerization of the binder is carried out without the addition of a solvent. Due to the use of wood chips, the temperature stability required for moldings for foundry technology is not ensured.

DE 21 43 247 A describes thermosetting molding compositions for the production of friction bodies. The polymeric binder is made from phenoplasts which contain prepolymerized isocyanate compounds. A trimerization catalyst is additionally added to the isocyanate compounds for prepolymerization. For example, asbestos or metal oxides are mentioned as fillers. This document, too, cannot provide any suggestions for improvements in the field of moldings for foundry technology, since the friction bodies should not disintegrate under the action of high heat, but on the contrary, a possible should have high resistance.

EP 0 362 486 A2 describes molding materials which comprise a granular material and a binder. The molding materials are used for the production of moldings for foundry technology, for example for the production of cores and feeders. The binder comprises a phenonovolac whose molar ratio of phenol to formaldehyde is 1: 0.25 to 1: 0.5. The phenolic novolak is dissolved in a suitable solvent and mixed with the granular material and a polyisocyanate to produce the molding material. After shaping, the moldings are cured by adding a gaseous catalyst. This document describes a modification of the cold box process, in which a certain type of phenolic resin is used. However, this process leads to the same disadvantages as described above, namely an emission of catalyst and solvents during storage and a strong development of smoke during casting.

The problems of emissions in the manufacture, storage and use of feeders in particular, and the poor decomposition of the food residues after the casting, have been known for some time.

None of the conventional methods: green stand method, C0 ₂ - gassing method, filter silt method or cold box method has so far been able to exclude the aforementioned problem areas.

The present invention was therefore based on the object of providing a process for the production of moldings, in particular cores, molds and feeders in foundry technology, in which the disadvantages of the prior art are avoided. In particular, the molded articles produced by the process according to the invention should have minimal emissions and a show low gas release and condensate formation (formation of crack products) during casting as well as very good dimensional stability.

It has now surprisingly been found by the inventors that the emissions, vapors and fumes which have hitherto been produced during the production, storage and use of moldings, in particular feeders, can be reduced or avoided altogether and at the same time an optimal disintegration of the feed residue after the casting can be ensured by curing a composition based on solid phenolic resin, polyisocyanate and a refractory by heating. The polyurethane reaction, which is a polyaddition, is carried out by heat curing at least one phenolic resin in solid form, preferably as a powder, with at least one liquid or solid polyisocyanate.

In detail, the method proceeds in such a way that a composition is first produced which comprises at least the following components.

i. at least one phenolic resin in solid form; ii. at least one polyisocyanate; and iii. at least one refractory.

Phenolic resin and polyisocyanate form the binding agent for binding the refractory grains. The composition is made at a temperature that is below the melting temperature of the at least one phenolic resin.

The constituents of the composition mentioned are used in customary proportions. Based on the total mass of the composition, the binder formed from phenolic resin and polyisocyanate forms a proportion of less than 10% by weight. preferably less than 8% by weight, particularly preferably less than 4% by weight. In the production of cores and molds in particular, the proportion of the binder is preferably selected in the range from less than 2% by weight, particularly preferably in the range from 0.5 to 1.6% by weight. When using solid refractories such as quartz sand or chamotte, the amounts of binding agent used in the manufacture of feeders can be used in similar or the same amounts as mentioned above. If refractories with low density are used, in particular hollow microspheres, the proportion of the binder increases based on the weight. Due to the low density of these hollow microspheres, proportions of the binder in the range of preferably less than 10% by weight, particularly preferably in the range of 6 to 8% by weight, are used.

Solid refractories, such as quartz sand, have a bulk density in the range of approximately 120 to 200 g / 100 ml. Based on the mixture as a whole, the binder is then preferably in amounts of less than 4 g / 100 ml, particularly preferably less than 3 g / 100 ml, and particularly preferably in amounts in the range of 1 to 2.8 g / 100 ml.

If hollow microspheres are used, they have a bulk density in the range of approximately 30 to 50 g / 100 ml. Appropriate amounts of binder are then used there, which are preferably in the range of less than 6 g / 100 ml, particularly preferably less than 4 g / 100 ml, and in particular in the range of 1 to 3.5 g / 100 ml. The reference value of 100 ml given here refers to the bulk volume.

The bulk density or the bulk volume is determined by first weighing a 100 ml cylinder which was cut off at the 100 ml mark. A powder funnel is then placed on this measuring cylinder and the one to be measured Material, for example the refractory or the composition filled in one go. The powder funnel is then removed so that a cone of the material to be measured forms above the opening of the measuring cylinder. The excess material is wiped off with the help of a spatula so that the measuring cylinder is filled flush to its upper edge. After material on the outside of the measuring cylinder has been removed, the measuring cylinder is weighed again. After subtracting the weight of the measuring cylinder, the bulk density per 100 ml is obtained. From this, the amount of binder contained in the composition per 100 ml can also be calculated.

The higher amount of binder required when using hollow microspheres is further explained by their higher specific surface area. For example, solid refractory materials, such as quartz sand, preferably have an average grain diameter in the range from approximately 0.2 to 0.4, while the diameter of the hollow microspheres is usually a power of ten lower, that is to say in the range from approximately 0.02 to 0, 04 mm.

The remaining proportion of the composition to 100% by weight is made up of the refractory. If the composition contains other components, their share will be charged to the refractory.

A solid phenolic resin or a mixture of two or more phenolic resins is thus used as the first component of the binder. For the definition of phenolic resins in the context of the present invention, reference can be made, for example, to the Römpp Lexikon Chemie, 10th edition (1998), pages 3251-3253. In particular, phenolic resins are formed in a condensation reaction in acidic and alkaline solution from phenols and aldehydes, especially formaldehyde. In addition to phenol itself, homologs or derivatives of phenol, in particular its alkyl (cresols, xyleno- le, butyl, nonyl, octylphenol) and aryl derivatives (phenylphenol), dihydric phenols (resorcinol, bisphenol A) and naphthols.

The phenolic resins resulting from the condensation reactions of phenols with aldehydes can be divided into the so-called novolaks and the so-called resols. Solid novolaks as well as solid resols can be used in the context of the present invention. Novolaks are preferred, however. It was found within the scope of the present invention that particularly advantageous shaped bodies are obtained when solid novolaks are used in the composition. In part, but not limited to this mechanism, this can be attributed to the fact that a part of the methyl groups present in resoles can split off again under the action of the heat required for curing, with the emission of formaldehyde. The most important aldehyde component for the production of phenolic resins is formaldehyde in various forms (aqueous solution, paraformaldehyde, formaldehyde-releasing compounds, etc.). Other aldehydes, e.g. Acetaldehyde, benzaldehyde or acrolein) are only used to a minor extent for the production of phenolic resins. However, the use of ketones as carbonyl compound is also conceivable.

By "solid phenolic resin" or "phenolic resin in solid form" is meant according to the invention any phenolic resin which, at the temperatures used during the preparation of the composition with the phenolic resin and the polyisocyanate, i.e. is present in solid form before curing at elevated temperatures. It is preferably a phenolic resin whose melting point is below approximately 120 ° C., in particular between approximately 60 and 110 ° C., particularly preferably between approximately 60 and 100 ° C.

The second component of the composition is at least one Polyisocyanate. All compounds with at least two isocyanate groups (functionality> 2) can be used. This includes the aliphatic, cycloaliphatic or aromatic polyisocyanates. Because of their reactivity, aromatic polyisocyanates such as diphenylmethane diisocyanate in a mixture with its higher homologs (so-called polymeric MDI) are preferred. Functionalities between 2 and 4, in particular between 2 and 3, are particularly preferred.

Phenolic resin and polyisocyanate are preferably used in an equivalent ratio, based on their reactive hydroxyl or isocyanate groups. The ratio of the reactive hydroxyl groups of the phenolic resin to the isocyanate groups of the polyisocyanate is preferably selected in the range from 0.8: 1 to 1.2: 1.

All refractories which are customary in the production of moldings for the foundry technology can be used as refractories. Suitable refractories are e.g. Quartz sand, olivine, chrome ore sand, zircon sand, vermiculite and artificial molding materials such as Cerabeads or aluminum silicate hollow spheres (so-called microspheres) that can be solidified with the binders described above. These and other additional components can be added or mixed in a customary manner before, during or after the preparation of the composition, but before the composition has cured.

The composition is made at a temperature that is below the melting temperature of the at least one phenolic resin. Common mixing processes are used. For example, phenolic resin and refractory can first be intimately mixed in a mixer and then the polyisocyanate can be added. However, the order in which the individual components of the composition are mixed can also be changed. In one embodiment, components i to iii described above can therefore each be added separately to a mixer in order to obtain the composition. However, it is also possible to first mix the at least one refractory with the phenolic resin, in particular to coat the at least one refractory with the phenolic resin, so that a mixture of solid refractory and phenolic resin is obtained, from which the addition of at least one polyisocyanate then results the composition is made.

It can be done in such a way that the phenolic resin is melted and then mixed with the at least one refractory, which is in granular or powdery form. The particles of the at least one refractory are coated with the phenolic resin. The mixture is then cooled again below the solidification point of the phenolic resin, so that the particles of the refractory are surrounded by a shell made of solid phenolic resin. Further processing then takes place as described above. The polyisocyanate is added, the temperature being below the melting temperature of the at least one phenolic resin in order to obtain the composition.

The composition is then brought into the desired shape. Here, too, customary shaping methods are used. The molded body now has a relatively low mechanical stability. For curing, the temperature of the composition is raised above the melting point of the at least one phenolic resin.

The curing of the composition or of the moldings produced therewith can take place at a temperature of approximately 150-300 ° C., in particular approximately 170-270 ° C., particularly preferably approximately 180-250 ° C. be performed. At a temperature which is above the melting point of the at least one phenolic resin, the solid resin melts and, as a liquid component, undergoes an addition reaction with the polyisocyanate present. The reaction between the two liquid components now proceeds very quickly and, as in the known heat-curing processes, leads to the hardening of the shaped bodies.

At temperatures below the melting point of the at least one phenolic resin, between the binder components, i.e. little reaction takes place between the phenolic resin and the isocyanate, i.e. the processing time of the molding material / binder mixture is sufficiently long, preferably at least a few hours after the preparation of the composition, in order to be able to process it into shaped articles with excellent results after its production.

The method according to the invention is particularly suitable in the field of foundry technology both for producing so-called cores or molds and for producing hollow bodies, so-called feeders.

Cores and shapes are bodies that are used to form the inner and outer contours of castings. They consist of molding materials (molding raw materials) or refractories that can be solidified with a binder.

The moldings can also be designed as feeders. In principle, feeders are cavities that are connected to the mold cavity of the casting, are filled with liquid metal by the casting flow and are dimensioned and designed such that the solidification module of the feeder is greater than that of the casting. In foundry technology, the shaping and curing, in particular of the molds, cores and feeders that contain the composition, can be carried out in heated tools. These are familiar to the person skilled in the art.

It is possible to manufacture the feeders from a heat-insulating and / or heat-emitting (exothermic) mass. The insulating effect is obtained through the use of refractories, some of which can also be in the form of fibers and which are characterized by a very low thermal conductivity. In recent developments, hollow microspheres based on aluminum silicate have also proven to be very effective. Examples of such hollow microspheres are Extendospheres SG (PQ Corporation) and U-Spheres (Omega Minerals Germany GmbH) with an aluminum oxide content of approx. 28 to 33%, as well as Extendospheres SLG (PQ Corporation) and E-Spheres (Omega Minerals Germany GmbH) with one Alumina content of more than 40%. In addition to the refractories, exothermic masses also contain oxidizable metals such as Aluminum and / or magnesium, oxidizing agents such as e.g. Sodium or potassium nitrate and optionally fluorine carriers such as Cryolite. Both insulating and exothermic mixtures are known and e.g. in EP 0 934 785 AI, EP 0 695 229 Bl and EP 0 888 199 Bl.

The oxidizable metals and the oxidizing agents are added in customary amounts, as are described, for example, in the patent publications mentioned. Based on the total mass of the composition, the metals preferably form a proportion of 15 to 35% by weight. The oxidizing agent preferably forms a proportion of 20 to 30% by weight. The proportions also depend on the molecular weight of the oxidizing agent or the oxidizable metal.

The polyisocyanates used according to the invention can also if necessary, be dissolved in solvents. Non-polar or weakly polar substances such as aromatic solvents or fatty acid esters are used as solvents. Strongly polar solvents, such as esters or ketones, dissolve the solid novolak and lead to an undesirable, drastic reduction in the processing time of the molding material / binder mixture, even at room temperature. However, the absence of solvents in the compositions and the moldings produced from them is particularly preferred, in particular the absence of solvents for the at least one phenolic resin and the absence of solvents for the at least one polyisocyanate, since this gives surprisingly good results with regard to the properties of the cured moldings were achieved.

Liquid isocyanates, especially polymeric MDI, are preferred. In principle, however, the reaction is also possible with solid isocyanates, e.g. 1,5-naphthalene diisocyanate or the likewise solid so-called blocked isocyanates, e.g. Desmodur AP stable (Bayer AG), possible. However, curing with these isocyanates is significantly slower. Liquid polyisocyanates are understood to be those which, at the temperatures used during the preparation of the composition with the phenolic resin and the polyisocyanate (in particular at room temperature), i.e. before curing at elevated temperatures, in liquid form.

The at least one phenolic resin preferably comprises a novolak, the melting point of the phenolic resin or novolak being below approximately 120 ° C., in particular between approximately 60 and 110 ° C., particularly preferably between approximately 60 and 100 ° C.

The curing is preferably carried out at a temperature from 150 ° C. to 300 ° C., in particular from 170 ° C. to 270 ° C., particularly preferably from 180 ° C. to 250 ° C. The curing preferably takes place without the addition of a catalyst. Already by heating the composition described above, a sufficiently high crosslinking rate is achieved to enable the molded articles to be manufactured industrially.

In order to further increase the speed at which the shaped bodies are cured, however, catalysts in liquid or solid form can also be added to the composition. These can be, for example, amines and metal compounds as are known as catalysts from polyurethane chemistry. Examples of suitable amino compounds are tetraethylbutane diamine (TMBDA), 1,4-diaza (2,2,2) bicyclooctane (DABCO) or dimethylcyclohexylamine. The amine compounds used as catalysts are preferably low-volatility and, under normal conditions, have a boiling point which is higher than 150 ° C., preferably higher than 200 ° C. In contrast to catalysts which are used in the cold box process and which have a low boiling point of usually well below 100 ° C, these high-boiling amines cause no or only extremely low emissions in the fully cured molded articles. According to one embodiment of the invention, a solid catalyst can also be added to the composition to accelerate curing. A solid catalyst is understood to mean a catalyst which is in solid form at room temperature. Compounds of tin, in particular organic compounds of tin, such as e.g. Dibutyltin dilaurate (DBTL), dibutyltin oxide (DBTO), tin dioctoate or diethyltin chloride. Among them, DBTL is particularly preferred.

The solid and liquid catalysts are preferably added in an amount of 0.01-10% by weight, preferably 0.1-8% by weight, particularly preferably 0.2-6% by weight, of the composition. give, the percentages each refer to the amount of binder, that is, to the sum of the phenolic resin and the polyisocyanate used. The liquid catalysts are used in smaller amounts compared to the solid catalysts. An amount in the range of 0.01-1% by weight, preferably 0.1-0.5% by weight, is usually sufficient here.

These solid and liquid catalysts are very effective. To facilitate dosing, these solid and liquid catalysts can therefore be diluted with an inert solvent. An inert solvent is understood to mean solvents which do not react with the catalyst, the polyisocyanate and the phenolic resin and which do not dissolve the phenolic resin or in the smallest possible amount. Suitable solvents are aromatic solvents, such as toluene or xylene. The amount of the solvent is chosen to be as small as possible, on the one hand to enable precise metering of the catalyst and, on the other hand, to introduce the smallest possible amount of residual solvent into the moldings. The solutions preferably have a concentration of the catalyst in the range from 1 to 50% by weight, preferably 2 to 10% by weight.

The composition can also contain a carboxylic acid, for example salicylic acid or oxalic acid. Surprisingly, although acids per se act as inhibitors in the manufacture of polyurethanes, it has been found that the addition of carboxylic acids does not affect the reaction, i.e. curing accelerates. Without being bound by this theory, the inventors assume that the carboxylic acids lower the melting point or the melt viscosity of the phenolic resin. The carboxylic acids are added in amounts as indicated for the catalysts.

In addition to the components already mentioned, the composition tion also contain other usual ingredients in usual amounts. The use of internal release agents such as calcium stearate, silicone oils, fatty acid esters, waxes, natural resins or special alkyd resins simplifies the detachment of the cores from the mold. The storage of the hardened moldings and their resistance to high atmospheric humidity can be improved by adding silanes.

The moldings for the foundry technology produced by the process according to the invention are distinguished by a low emission of pollutants. Since no solvent and no gaseous catalyst are preferably used for the production of the shaped bodies, no amines, for example, escape during storage, so that no corresponding odor nuisance has to be accepted. In addition, the casting process itself has a significantly lower smoke development compared to moldings obtained by the cold box process. The invention therefore also relates to moldings, in particular cores, molds and feeders for foundry technology, which have been obtained by the process described above.

These moldings are preferably free from solvents and / or gaseous catalysts.

The moldings according to the invention are suitable for light metal casting, in particular aluminum casting. State-of-the-art gas-forming binding systems often result in gas porosities. The organic binder system contained in the composition according to the invention shows only a slight formation of gas and condensate during casting, with very good disintegration at the same time. The difficulties described above due to gas porosity can therefore be avoided or at least significantly reduced. Because of their good properties during decay, the moldings are particularly suitable as cores and shapes for light metal casting, especially aluminum casting. However, the use of the moldings according to the invention is not restricted to light metal casting. They are generally suitable for casting metals. Such metals are, for example, non-ferrous metals, such as brass or bronzes, and iron metals.

The invention further relates to a composition for the production of moldings, in particular cores, molds and feeders, comprising at least a. a solid phenolic resin, b. at least one polyisocyanate, and c. at least one refractory.

The individual components correspond to the components as explained in the description of the method according to the invention.

In a particularly preferred embodiment, the refractory contains hollow microspheres, preferably based on aluminum silicate, in particular with a high aluminum oxide content of more than approximately 40% by weight, or a lower aluminum oxide content of approximately 28 to 33% by weight.

The composition preferably contains no solvent for the at least one phenolic resin and / or no solvent for the at least one polyisocyanate, and in particular there is no solvent.

The at least one phenolic resin preferably comprises a novolak, the melting point of the phenolic resin or novolak preferably being between about 60 and 120 ° C., in particular between about 60 and 110 ° C., particularly preferably between about 60 and 100 ° C.

In addition to the ingredients mentioned, the composition, such as already described in the process according to the invention, contain customary constituents. The composition can also contain oxidizable metals and suitable oxidizing agents for the production of exothermic feeders. In addition, the composition can also contain internal release agents, solid and / or liquid catalysts or also carboxylic acids or agents for lowering the melting point of the phenolic resin.

The binder mixture contained in the composition according to the invention for the production of moldings, in particular cores, molds and feeders, is generally suitable for improving the strength of the moldings, for reducing the hot deformation of the moldings, the development of smoke, the formation of gas and condensate, and the smell during storage Improvement of the casting properties, in particular the tendency of the leaf ribs and erosion during casting, or any combination of the above properties. In particular, this binder composition can improve the decay both of the cores and molds and of the food residues after the casting.

The invention is illustrated by the following non-limiting examples:

Examples:

1. Production and testing of the molding material / binder mixtures

1.1. Manufacture of cores with quartz sand

Quartz sand H 32 (Quarzwerke GmbH, Frechen) was used as the molding material for the production of the cores for laboratory testing of the sand technology and casting properties. .1.1. Cold box (comparative example)

100 GT quartz sand H 32 0.8 GT Isocure ^® 366 ^x 0.8 GT Isocure ^® 666 ^x ¹ Sales products from ASK, Hilden Isocure ^® 366: Benzyl ether resin dissolved in a mixture of esters, ketones and aromatics;

Isocure ^® 666: Technical diphenylmethane diisocyanate, dissolved in aromatics.

0.8 GT Isocure ^® 366 and 0.8 GT Isocure ^® 666 are successively added to 100 pbw (parts by weight) of H 32 quartz sand and mixed intensively in a laboratory mixer with a useful content of 5 kg from Vogel & Schemmann. With this mixture, test specimens (so-called Georg Fischer bars with the dimensions 150 mm x 22.36 mm x 22.36 mm) are produced, which are gassed with triethylamine (0.5 ml per test bar, 2 bar gassing pressure, 10 seconds. Fumigation time) are cured.

1.1.2. Warm box (comparative example)

100 GT quartz sand H 32 0.30 GT Hotfix ^® WB 220 ² 1.30 GT Kernfix ^® WB 185 ²

² sales products from ASK, Hilden; Hotfix ^® WB 220: aqueous solution of a sulfonic acid; Kernfix ^® WB 185: phenol / urea / formaldehyde cocondensate, dissolved in furfuryl alcohol. 0.30 GT Hotfix ^® WB 220 and 1.30 GT Kernfix ^® WB 185 are successively added to 100 GT quartz sand H 32 and mixed intensively in a laboratory mixer (see above). With this mixture, test specimens (Georg Fischer bars, see above) are produced, which are cured in heated molds of a H2 core shooter from Röper, Dülken, at a temperature of 220 ° C for 30 seconds.

1.1.3 Polyurethane hot curing (according to the invention)

The solid phenolic resins listed in Table I were used as the resin component.

Diphenylmethane diisocyanate (technical MDI) with the functionality of approx. 2.7 from Bayer AG was used as component 2.

100 GT quartz sand H 32 0.8 GT solid phenolic resin 0.8 GT techn. MDI

For 100 GT quartz sand H 32, 0.8 GT solid phenolic resin and 0.8 GT techn. MDI added and mixed intensively in a laboratory mixer (see above). This mixture is used to produce test specimens (see above) which are cured in heated molds at a temperature of 250 ° C for 30 seconds.

1.1.4. Polyurethane hot curing with the addition of reaction accelerators

1.1.4.1. Add a liquid catalyst

Example 1.1.3.1 was repeated, an additional 0.08 part by weight of a 5% strength solution of dibutyltin dilaurate (DBTL) in an aromatic solvent being added to the sand / binder mixture. As a result, the curing time could be reduced by approx. 50% at the same curing temperature as in 1.1.3.1.

1.1.4.2. Add salicylic acid

Example 1.1.3.1 was repeated, with an additional 0.08 part by weight of salicylic acid being added to the sand / binder mixture. As a result, the curing time could be reduced by approx. 50% at the same curing temperature as in 1.1.3.1.

1.1.4.3. Combination of reaction accelerators

Example 1.1.3.1 was repeated, with an additional 0.08 part by weight of salicylic acid and 0.08 part by weight of a 5% strength solution of dibutyltin dilaurate (DBTL) in an aromatic solvent being added to the sand / binder mixture. This allowed the curing time to be the same The curing temperature can be reduced by approx. 70% as in 1.1.3.1.

1.2. strength comparison

Table II shows the bending strengths of the cores from Examples 1.1.1, 1.1.2 and 1.1.3, specimens with the dimensions 150 mm × 22.36 mm × 22.36 mm (so-called Georg Fischer bars) are used ,

1.3. Comparison of hot deformation

24 hour old cores with the dimensions 150 x 22.36 x 11.18 mm were loaded at a temperature of 150 ° C for 30 minutes with a weight of 200 g, 400 g or 600 g in the middle of the core. After the cores had cooled, the deformation of the cores was measured.

The surprisingly low hot deformation of the cores produced with the binder mixture according to the invention compared to the cores produced by known cold box or warm box processes is evident.

1.4. Comparison of smoke development

The smoke intensity was determined photometrically using an ASK method. For this purpose, 24-hour-old cores measuring 30 mm × 22.36 mm × 22.36 mm were stored in a closed crucible for 3 minutes at a temperature of 650 ° C. The smoke produced during the thermal decomposition of the binder was then drawn through a flow-through cell with the aid of a vacuum pump and its intensity was measured using a DR / 2000 spectrophotometer from Hach.

1.5

Kernels manufactured according to 1.1 were subjected to an independent odor evaluation by three people after specified times. The result is shown in Table V.

1.6. Comparison of the tendency of the binder to form ribs and erosion during casting

For the technical casting assessment, the binding means from examples 1.1.1 and 1.1.3.1. The test was carried out with the so-called dome core test (foundry center of the TNO, Holland, publication 77, August 1960). Gray cast iron GG 25 was used at a casting temperature of 1390-1410 ° C.

The evaluation was between 1 (no casting error) and 10 (severe casting error)

The result is shown in Table VI.

Tables II - VI show that the new development meets the desired requirements:

high strength (Table II)

Reduction of hot deformation (Table III)

Reduction of smoke development compared to cold box cores (Table IV)

Odor reduction in core storage (Table V)

Improvement of the casting properties compared to cold box with regard to the tendency of the leaf ribs compared to cold box with regard to the tendency to leaf ribs (Table VI)

1.7. Manufacture of cores with hollow ceramic microspheres and exothermic mass

Ceramic microspheres with an Al ₂ 0 ₃ content of approximately 30%, so-called U-spheres from Omega Minerals Germany GmbH (Norderstedt), were used as the molding material for the insulating feeders.

The following composition was used as the exothermic mass:

Aluminum (0.063 - 0.5 mm grain) 25%

Potassium nitrate 22% hollow microspheres (U-Spheres der

Omega Minerals Germany GmbH) 44%

Refractory surcharge (chamotte) 9%

Alternatively, other conventional exothermic compositions can also be used, reference being made, for example, to the publications specified in the above description and to the compositions specified in the examples in WO 00/73236.

1.7.1. Shaped body with hollow micro spheres - insulating feeders

The following mixture was used to produce the tubular shaped bodies with the dimensions 0 60 mm (wall thickness 10 mm) x 150 mm: 100 GT hollow microspheres

4 pbw solid phenolic resin - Alnovol PN 332

4 GT techn. MDI (see above)

Mixing, shaping and curing were carried out analogously to 1.1.3

1.7.2. Comparison of smoke intensity and smoke duration

The above Moldings (1.7.1) were embedded in furan resin molds and filled with liquid aluminum (750 ° C). After the casting, the smoke development was observed and rated from 1 (hardly noticeable) to 10 (very strong). At the same time, the smoke duration was measured.

1.7.3. Shaped body with exothermic mixture - exothermic feeders

The following mixture was used to produce the tubular shaped bodies with the dimensions 0 60 mm (wall thickness 10 mm) x 150 mm. 100 GT exothermic mixture

4 pbw solid phenolic resin - Alnovol PN 332

4 GT techn. MDI

Mixing and shaping were carried out analogously to 1.1.3

1.7.4. Comparison of ignition time, smoke intensity and smoke duration

The above Shaped bodies (1.7.3) were placed on a hot plate at 1000 ° C, the ignition timing was measured and the smoke development (intensity and duration) was observed. The smoke intensity was rated from 1 (barely noticeable) to 10 (very strong).

Tables VII and VIII show that the new development offers advantages in terms of both the intensity and duration of the smoke compared to feeders on the market.

Claims

1. A process for the production of moldings, in particular cores, molds and feeders in foundry technology, comprising the following steps:

a. Preparation of a composition containing i. at least one phenolic resin in solid form ii. at least one polyisocyanate, and iii. at least one refractory, the composition being made at a temperature below the melting temperature of the at least one phenolic resin; b. Shaping the composition into a shaped body; c. Raising the temperature of the composition above the melting point of the at least one phenolic resin to cure the mixture.

2. The method according to claim 1, wherein the at least one refractory is mixed with the phenolic resin, in particular the at least one refractory is coated with the phenolic resin, so that a mixture of solid refractory and phenolic resin is obtained, from which subsequently by adding the at least one polyisocyanate the composition is made.

3. The method according to claim 1 or 2, wherein the shaping into a shaped body is carried out in a heated tool.

4. The method according to any one of the preceding claims, wherein the at least one refractory material is selected from the group of quartz sand, olivine, chrome ore sand, zircon sand, vermiculite, artificial molding materials such as Cerabeads or Mic- rospheres.

5. The method of claim 4, wherein the microspheres are designed as hollow microspheres, preferably based on aluminum silicate, in particular with a high alumina content of more than about 40 wt .-%, or a lower alumina content of less than about 40 wt .-%.

6. The method according to any one of the preceding claims, wherein the composition comprises exothermic components, in particular at least one oxidizable metal and an oxidizing agent.

7. The method according to any one of the preceding claims, wherein the production of the shaped body is carried out without the addition of a solvent.

8. The method according to any one of claims 1 to 6, wherein the at least one polyisocyanate is dissolved in a solvent, in particular an aromatic solvent or a fatty acid ester, in which the phenolic resin is preferably not or poorly soluble.

9. The method according to any one of the preceding claims, wherein the at least one polyisocyanate comprises an isocyanate with at least 2, in particular 2 to 4, particularly preferably 2 to 3 isocyanate groups per molecule.

10.The method according to any one of the preceding claims, characterized in that the at least one polyisocyanate is an aliphatic, cycloaliphatic and / or aromatic polyisocyanate, which is preferably in liquid form at room temperature.

11. The method according to any one of the preceding claims, characterized in that the at least one polyisocyanate comprises or represents an aromatic polyisocyanate, in particular diphenylmethane diisocyanate, in a mixture with its higher homologs (polymeric MDI), in particular with a functionality between 2 and 4.

12.The method according to any one of the preceding claims, characterized in that the at least one phenolic resin comprises or represents a novolak, preferably the melting point of the phenolic resin or novolak between about 60 and 120 ° C, in particular between about 60 and 110 ° C, particularly is preferably between about 60 and 100 ° C.

13. The method according to any one of the preceding claims, wherein the curing is carried out at a temperature of 150 ° C to 300 ° C, in particular from 170 ° C to 270 ° C, particularly preferably from 180 ° C to 250 ° C.

14.The method according to any one of the preceding claims, wherein the curing takes place without the addition of a catalyst.

15.The method according to any one of claims 1 to 13, wherein a solid and / or liquid catalyst is added to the mixture to accelerate the curing.

16.The method according to any one of the preceding claims, wherein a compound for lowering the melting point of the phenolic resin is added to the mixture.

17. Moldings, in particular cores, molds and feeders for foundry technology, obtainable by a process according to one of claims 1 to 16.

18. Shaped body according to claim 17, wherein these are free from solvents and / or gaseous catalysts.

19. Composition for the production of moldings, in particular cores, molds and feeders, containing at least a. a solid phenolic resin, b. at least one polyisocyanate, and c. at least one refractory.

20. The composition according to claim 19, characterized in that the refractory contains hollow microspheres, preferably based on aluminum silicate, in particular with a high alumina content of more than about 40 wt .-%, or a lower alumina content of about 28 to 33 wt .-% ,

21. The composition of claim 19 or 20, wherein no solvent for the at least one phenolic resin and / or no solvent for the at least one polyisocyanate is present, and in particular any solvent is missing.

22. The composition according to any one of claims 19 to 21, wherein the at least one phenolic resin comprises or represents a novolak, preferably the melting point of the phenolic resin or novolak between about 60 and 120 ° C, in particular between about 60 and 110 ° C, is particularly preferably between about 60 and 100 ° C.