EP2841220A1

EP2841220A1 - Method for producing moulds and cores for metal casting and moulds and cores produced according to this method

Info

Publication number: EP2841220A1
Application number: EP13726092.3A
Authority: EP
Inventors: Diether Koch; Oliver Schmidt
Original assignee: ASK Chemicals GmbH
Current assignee: ASK Chemicals GmbH
Priority date: 2012-04-26
Filing date: 2013-04-26
Publication date: 2015-03-04
Also published as: DE102012103705A1; KR20150006024A; JP2015514591A; RU2014146801A; BR112014026456A2; WO2013159762A1; US20150129155A1; CA2870115A1; CN104470652A

Abstract

The invention relates to a method for producing casting moulds and cores, in which a foundry base material comprising at least one refractory material and a binder curable by CO2, preferably based on water glass, is cured by gassing with CO2 and flushing with a second gas. The invention further relates to moulds and cores produced according to this method.

Description

Method for producing molds and cores for casting metal, and molds and cores produced by this method

The invention relates to a process for the production of molds and cores, wherein a molding material mixture of at least one refractory material and a CO2-curable binder, preferably containing or consisting of water glass, by gassing with CO ₂ or a C0 ₂ -containing gas and rinsing with a second gas containing no CO ₂ , but at least less CO ₂ , is cured. Furthermore, the invention relates to the forms and cores produced by this process.

State of the art

For the production of molds and cores i.A. a refractory molding base, e.g. Quartz sand, and a suitable binder. The refractory molding base material is preferably present in a free-flowing form, so that the mixture of mold base material and binder, the so-called molding material mixture, filled into a suitable mold, can be compacted and cured there. The binder produces a firm cohesion between the particles of the mold base, so that the molds and cores obtain the required mechanical stability.

Molds form the outer wall of the casting during casting, cores are used when cavities are required within the casting. It is not absolutely necessary that the forms and cores are made of the same material. Thus, e.g. In chill casting, the external shape of the castings with the help of metallic permanent molds. Also, a combination of shapes and cores produced by different methods is possible. What is explained below with reference to cores applies analogously to molds produced by the same process (casting molds) and vice versa.

For the production of cores it is possible to use both organic and inorganic binders, the hardening of which can be effected in each case by cold or hot processes. Cold processes are processes which are carried out essentially at room temperature without heating the mold used for core production.

CONFIRMATION COPY The curing is usually carried out by a chemical reaction, which is triggered for example by the fact that a gas is passed through the molding mixture to be cured. In hot processes, the molding material mixture is heated to a temperature sufficiently high after shaping by the heated mold to expel, for example, the solvent contained in the binder and / or to initiate a chemical reaction by which the binder is cured by, for example, crosslinking.

For example, it is known from GB 654817 to cure binders based on water glass by CO2. In the 50s and 60s of the 20th century, the water glass C0 ₂ method was widely used. One of the weak points of this process is that the cores made therefrom have relatively low strengths, especially immediately after their production. Although longer gassing times with CO2 lead to higher initial strengths, at the same time the strengths suffer from storage after 1 to 2 days. In addition to relatively low initial and final strengths, the water glass C02 process allows only low to medium production speeds.

It has therefore been proposed to combine the classical CCV curing with a subsequent so-called "hot air process", as described by YA Owusu (YA Owusu, Ph. D. Dissertation "Sodium Silicate Bonding in Foundry Sands", Pennsylvania State University, May 1, 1980, p. 88, 1 02-103 and AFS Transactions, Vol. 89, 1981, pp. 47-54). The Hot Air Process is a hardening of the oven after CO2 fumigation. This is also confirmed by the dissertation by YA Owusu. This method gives better strength than at least some water glass binders than with pure CO2 curing, but has the disadvantage that the production time for the cores expands from a few seconds to several minutes. DE 10201 1010548-A1 describes a method for curing water-glass-bonded molding mixtures, wherein a combination of air and carbon dioxide flow is used. It turned out that the molding material mixture must first be perfused with air and then with CO2 or with an air-carbon dioxide mixture. Furthermore, it is of great importance for this invention that the alkali metal silicate solutions used have a weight ratio of SiO 2 to metal oxide in the range from 1.5: 1 to 2.0: 1. Another patent which describes such a method is WO 80/01254 A1. This discloses a method for curing a water glass-containing molding material mixture, which is heated at a temperature of 1 10 to 180 ° C and at the same time CO2 or a CO2-air mixture is passed.

The PL 129359 B2 describes a binder for the production of molds for metal casting, which is composed of water glass and urea resin. The curing takes place by flushing the molding material mixture with a CO ₂ -air mixture. It is advantageous if the gases are heated to temperatures of 60-200 ° C. Another publication describing the use of a CO ₂ -air mixture is CN 941 1 1 187 A.

EP 2014392 B1 discloses the use of amorphous spherical SiO ₂ , which is present in more than two particle size classifications. However, EP 2014392 B1 does not disclose the use of a second gas stream and brings the SiO ₂ in aqueous suspension, which is disadvantageous because of the increased water input for the (early) strengths of molded articles produced by the present inventive method. Good strength even after short curing times are necessary to be able to safely handle the ever more complicated thin-walled casting molds, which are increasingly required today, and at the same time to ensure high productivity. It is therefore not surprising that the water glass CO ₂ process has rapidly lost importance with the advent of processes based on organic binders, in particular the so-called Ashland polyurethane cold box process.

However, all organic binders have the disadvantage that they thermally decompose during casting and pollutants such. As benzene, toluene or xylenes, can release. In addition, many organic binder systems release solvents to the environment during core production and storage, or unpleasant-smelling gases are used as curing catalysts. Although various measures have succeeded in reducing all these emissions, they can not be avoided with organic binders. For this reason, efforts have been increasing again for some years to develop binders which are completely based on inorganic materials or contain at most a small proportion of organic compounds. In order to achieve high strengths at short cycle times, for example, one went the way to make the curing in a hot tool and if necessary. In addition, hot air to pass through the molding material mixture to drive out the water present as a solvent as completely as possible. Such a system is described for example in EP 1802409 B1 (US 7770629). However, these methods have the disadvantage that the tools must be made heatable and the heating causes additional energy consumption, which represents a significant cost burden for the process.

OBJECT OF THE INVENTION The inventors have therefore set themselves the task of developing a process that allows molds and cores using a C0 ₂ -hardenable binder on an inorganic basis to produce in unheated tools, the strengths of the same binder and identical binder content Already without subsequent heat treatment should be much higher than in the previously known cure with CO ₂ , especially immediately after removal from the mold.

Summary of the Invention This object is achieved by a method having the features of claim 1. Advantageous developments of the method according to the invention are the subject of the dependent claims or described below.

Surprisingly, it has been found that cores having good strengths are obtained by the combination of C0 ₂ hardening by a first gas and flushing of the molding material mixture with a second gas, also referred to below as purge gas. In this case, first gas and second gas should not be interpreted as giving up the first gas before the second gas, on the contrary, the sequences can be any and also first and / or second gas can also be given up several times. However, it is preferred that the second gas be last and independently of this, the first gas first introduced into the mold. For the first gas, hereinafter also referred to C0 ₂ gas, gas temperatures in the fumigation between 15 ° C and 120 ° C, preferably 15 ° C and 100 ° C, and particularly preferably between 25 ° C and 80 ° C, are advantageous. The gas temperature refers here as well as in the further description of the method according to the invention to the temperature which has the gas entering the mold. The second gas also preferably has gas temperatures of 15 to 120 ° C, preferably between 15 ° C to 100 ° C, and more preferably between 25 ° C and 80 ° C, however, higher temperatures often allow shortening of the purge time. An upper limit due to the curing mechanism does not exist. In practice, depending on the shape and size of the core or mold, the temperatures will be between 40 ° C and 250 ° C, preferably between 50 ° C and 200 ° C. Economic reasons speak against the use of very high temperatures, since the prices of the heaters required for this increase sharply with increasing power and the cost for effective insulation of the lines is very high. For example, the temperature of the first gas is about the same as the temperature of the second gas. Preferably, however, the temperature of the second gas is higher than the temperature of the first gas.

It is advantageous by the above measures to counteract the cooling of the molding material mixtures to be observed during the gasification by tempering the two gas streams. The use of existing heatable molds is by no means excluded in the described method, it opens up the possibility of the tools for cost reduction either cold, ie at ambient or room temperature of 15 to 30 ° C, or at lower than that operate at normal temperatures, ie lower than 200 ° C, or lower than 120 ° C or even lower than 100 ° C, in particular cheaper non-heated tools can be used. Such tools are not heatable, ie they have no heating device itself such as an electric heater, but can be heated by the introduced tempered gas. The inventive method also does not exclude, then subject the cores or molds to an additional heat treatment. The method according to the invention comprises the steps:

Preparation of a molding material mixture of at least one refractory molding material and a C0 ₂ -hardenable binder, preferably based on water glass

· Forming the molding material mixture

• Flow through the molding material mixture with the C0 ₂ gas

• if necessary, flowing through the molding material mixture with the C0 ₂ gas and the purge gas in alternation and

Flowing through the molding material mixture with a second gas (purge gas)

Detailed description of the invention

In the preparation of the molding material i.A. The procedure is such that the refractory molding base material is initially charged and the binder is added with stirring. It is stirred further until a uniform distribution of the binder is ensured on the molding material.

The molding material mixture is then brought into the desired shape. In this case, customary methods are used for the shaping. For example, the molding material mixture can be shot by means of a core shooting machine with the aid of compressed air into the mold. Curing then takes place by first passing (in particular) the CO ₂ gas through the tool filled with the molding material mixture, followed by a post-rinse with the second gas. It is immediately clear to the person skilled in the art that there are various design possibilities for this process.

For example, it is by no means compulsory (but often advantageous) to use pure CO ₂ (for example technical grade) as C0 ₂ gas for precuring. To achieve the shortest possible cure times, however, it is advantageous that the CO ₂ - gas contains at least 50% by volume C0 _2, preferably at least 80% by volume of C0. ₂

Conversely, it is not necessary for the second gas to be completely CO ₂ -free, such as synthetic air or nitrogen. For cost reasons, air is preferred. The purge gas may even be mixed with CO ₂ , but not more than 10% by volume, more preferably not more than 5% by volume, in particular not more than 2% by volume or even not more than 1% by volume. The transition from C0 ₂ gas to the second gas need not be done in one step, gradual or fluid transitions are also possible. In addition, both gases or just one of them can be pulsed through the molding material mixture.

A further variant consists of first removing a portion of the water present in the molding material mixture by a short gassing with the C0 ₂ -pure gas as purge gas, then curing the binder with the C0 ₂ gas and optionally again the core for further drying to treat with the C0 ₂ low-gas.

The dosage of CO ₂ can be done either by setting a specific C0 ₂ flow for the C0 ₂ gas or a certain gassing pressure. For which of the two options one chooses in practice, depends on many factors, such as the geometry and size of the core, the tightness of the mold, the ratio of gas inlet to gas outlet, the gas permeability of the molding material, the diameter of the Gas line, binder content, desired gassing time, etc. To optimize the properties, the gassing parameters may be adjusted depending on the requirements of the selected core or mold geometry within the scope of the present disclosure and those of ordinary skill in the art. As a rule, a CO ₂ -FIUSS between 0.5 L / min. and 600 L / min. choose, preferably between 0.5 L / min. and 300 L / min. and more preferably between 0.5 L / min. and 100 L / min (each standard liters). According to another embodiment, the CO ₂ -FIUSS is between 0.5 L / min. and 30 L / min. choose, preferably between 0.5 L / min. and 25 L / min. and more preferably between 0.5 L / min. and 20 L / min. This embodiment is particularly advantageous at low gas temperatures for the CO ₂ or the CO ₂ -containing gas of 15 to 40 ° C.

In the case of a pressure control, the pressures of the CO ₂ gas usually move between 0.5 bar and 10 bar, preferably between 0.5 bar and 8 bar and more preferably between 0.5 bar and 6 bar. In the case of air as a purge gas, this can be taken from the compressed air network usually found in foundries, so that the pressure prevailing therein represents the upper limit for gassing for purely practical reasons. The lower limit for effective fumigation with air is about 0.5 bar. At a lower pressure, the fumigation time would be greatly prolonged, which would be associated with a loss of productivity.

All pressures, unless otherwise specified, are all based on overpressure, i. a pressure above the ambient pressure.

For the ratio of the gassing of the first (CO ₂ gas) and second gas (purge gas) to one another, for example between 2:98 to 90:10, preferably between 2:98 to 20:80 and particularly preferably between 5:95 to 30: 70 vary. However, since it is also an objective of this application, in addition to the improvement of the strengths, to keep the consumption of CO ₂ as low as possible, the fumigation time with the CO ₂ gas should preferably not exceed 60% of the total gasification time, particularly preferably not more than 50%.

By suitably selecting the gassing parameters and the layout of the tools, it is possible to ensure that, even with larger cores, production times corresponding to those of organic binders, e.g. less than 3 minutes, preferably less than 2.5 minutes, and more preferably less than 2 minutes. If necessary, such an optimization can also be carried out with the aid of a computer simulation.

It is readily possible to modify the curing of the molding material according to the invention by known methods, e.g. by applying a vacuum. In addition, further known steps can be added to the actual curing process, for example a treatment with microwaves or heating in the oven.

As a refractory molding base material can be used for the production of molds usual materials. Suitable examples are quartz, zircon or chrome ore sand, olivine, vermiculite, bauxite and chamotte. It is not necessary to use only new sands. In terms of resource conservation and to avoid landfill costs, it is even advantageous to use the highest possible proportion of regenerated used sand. A suitable sand is described, for example, in WO 2008/101668 (= US 2010/173767 A1). Also suitable are regenerates, which are obtained by washing and subsequent drying. Applicable but less preferred are regenerates obtained by purely mechanical treatment. As a rule, the regenerates can replace at least about 70% by weight of the new sand, preferably at least about 80% by weight and more preferably at least about 90% by weight.

Further, as refractory mold raw materials and artificial molding materials may be used such. Glass beads, glass granules, the known under the name "Cerabeads" or "Carboaccucast" spherical ceramic mold base materials or Aluminiumiumsilikatmikrohohlkugeln (so-called Microspheres). Such aluminosilicate hollow microspheres are marketed, for example, by Omega Minerals Germany GmbH, Norderstedt, in various qualities with different contents of aluminum oxide under the name "Omega-Spheres." Corresponding products are available from PQ Corporation (USA) under the name "Extendospheres". available.

The average diameter of the molding base materials is generally between 100 and 600 μm, preferably between 120 μm and 550 μm, and particularly preferably between 150 μm and 500 μm. determined by sieving according to DIN ISO 3310.

In casting experiments with aluminum, it was found that, when using mold-like raw materials, especially glass beads, glass granules or microspheres, less molding sand adheres to the metal surface after casting than when using pure quartz sand. The use of artificial mold base materials therefore makes it possible to produce smoother cast surfaces, wherein a complex after-treatment by blasting is not required or at least to a significantly lesser extent.

It is not necessary to form the entire molding base material from the artificial molding base materials. The preferred proportion of the artificial molding base materials is at least about 3% by weight, particularly preferably at least 5% by weight, particularly preferably at least 10% by weight, preferably at least about 15% by weight, particularly preferably at least about 20% by weight. , based on the total amount of refractory molding material. The refractory molding base material preferably has a free-flowing state, so that the molding material mixture according to the invention can be processed in conventional core shooting machines.

As a further component, the molding material mixture according to the invention comprises a water glass-based binder. As a water glass while standard water glasses can be used, as they are already used as binders in molding material mixtures.

Water glasses are aqueous solutions of alkali silicates, especially lithium, sodium and potassium silicates and are also found in other fields such as e.g. in construction application as a binder. The production of water glass z. B. large industrial by melting of quartz sand and alkali metal carbonates at temperatures of 1350 ° C to 1500 ° C. The glass of water is initially in the form of a piece of solid glass, which is dissolved in water using temperature and pressure. Another method for the production of water glasses is the direct dissolution of quartz sand with caustic soda.

The alkali silicate solution obtained can then be adjusted to the desired molar ratio SiO ₂ / M ₂ O by addition of alkali hydroxides and / or alkali oxides and their hydrates. Furthermore, the composition of the alkali silicate solution can be adjusted by dissolving alkali silicates having a different composition. In addition to alkali metal silicate solutions, hydrous alkali metal silicates present in solid form, such as, for example, the product groups Kasolv, Britesil or Pyramid from PQ Corporation, are also suitable.

The binders can also be based on water glasses which contain more than one of the abovementioned alkali ions, for example the lithium-modified water glasses known from DE 2652421 A1 (= GB 1532847). Furthermore, the water glasses may also contain multivalent ions, such as, for example, boron or aluminum (corresponding examples are described in EP 2305603 A1 (= WO201 1/042132 A1)). The water glass preferably has a molar modulus S1O2 / M2O in the range from 1.6 to 4.0, in particular 2.0 to less than 3.5, where M is lithium, sodium or potassium.

The water glasses preferably have a solids content greater than or equal to 30% by weight, more preferably greater than or equal to 33% by weight, and particularly preferably greater than or equal to 36% by weight. The upper limits for the solids content of the preferred water glasses are less than or equal to 65% by weight, more preferably less than or equal to 60% by weight and particularly preferably less than or equal to 55% by weight. The solid content is determined on a Satorius MA30 Moisture Analyzer, with about 3-4 g of the binder on an aluminum pan (diameter = 10 cm, height = 0.7 cm) at a temperature of 140 ° C to constant mass become.

In addition, the water glasses have a solids content, calculated as M ₂ O and S1O 2, in the range from 25 to 65% by weight, preferably from 30 to 60% by weight. The solids content refers to the amount of alkali silicates contained in the water glass, calculated as S1O2 and M2O.

Depending on the application and the desired strength level, between 0.5% by weight and 5% by weight of the water glass-based binder are used, preferably between 0.75% by weight and 4% by weight, particularly preferably between 1% by weight and 3, 5 wt.%, Each based on the molding material. The term refers to water glasses with a solids content as indicated above and includes the diluent water.

Based on the amount of alkali metal silicates, calculated as M ₂ O and SiO ₂ , which are added to the mold base with the inorganic binder according to the invention, without consideration of the diluent, the amount of binder used is 0.2 to 2.5% by weight. , preferably 0.3 to 2 wt.% Relative to the molding material, wherein M ₂ 0 has the meaning given above. Preferably, the molding material mixture further contains a proportion of a particulate metal oxide which is selected from the group of silica, alumina, titania and zinc oxide and mixtures thereof or mixed oxides, in particular silica, alumina and / or aluminosilicates. The particle size of these metal oxides is preferably less than 300 μηι, preferably less than 200 μηι, more preferably less than 100 μηι and has, for example, an average primary particle size between 0.05 μηι and 10 μηι.

The particle size can be determined by sieve analysis. More preferably, the sieve residue on a sieve with a mesh size of 63 μηι less than 10 wt .-%, preferably less than 8 wt .-%. Particularly preferred as the particulate metal oxide silica is used, in which case synthetically produced amorphous silica is particularly preferred. As the particulate silica, precipitated silica and / or fumed silica is preferably used.

Optionally, the molding material mixture may contain amorphous S1O2. It has surprisingly been found that the addition of amorphous S1O2 to the molding material mixture has a positive effect not only on the hot curing described in EP 1802409 B1 (= US Pat. No. 7,770,629), but also on the inventive hardening by means of CO2 gas and purge gas. At the initial strengths, the increase in strength is significantly higher than when the binder content is increased by the same amount, while at the final strengths the higher binder content has a more favorable effect, so that alternatives are available depending on the desired effect.

The amorphous SiO 2 preferably used according to the present invention has a water content of less than 15% by weight, in particular less than 5% by weight, and particularly preferably less than 1% by weight. In particular, the amorphous S1O2 is used as a powder.

As amorphous S1O2 both synthetically produced and naturally occurring silicas can be used. However, the latter, known for example from DE 102007045649, are not preferred because they usually contain not inconsiderable crystalline fractions and are therefore classified as carcinogenic. Synthetically, non-naturally occurring amorphous S1O2 is understood, ie the production thereof comprises a chemical reaction, for example the preparation of silica sols by ion exchange processes from alkali silicate solutions, the precipitation from alkali silicate solutions, the flame hydrolysis of silicon tetrachloride or the reduction of quartz sand with coke in the electric arc furnace during the production of Ferrosilicon and silicon. The amorphous SiO ₂ produced by the latter two processes is also referred to as pyrogenic SiO ₂ .

Occasionally, synthetic amorphous S1O2 is understood as meaning only precipitated silica (CAS No. 1 12926-00-8) and SiO ₂ produced by flame hydrolysis (Pyrogenic Silica, Fumed Silica, CAS No. 1 12945-52-5), while in the case of ferrosilicon or silicon-produced product only as amorphous Si0 ₂ (Silica Fume, Microsilica, CAS No. 69012-64-12) is called. For the purposes of the present invention, the product formed in the production of ferrosilicon or silicon is also understood as a synthetic amorphous S1O2.

Preference is given to using precipitated silicas and pyrogenic, ie flame-hydrolysed or arc-produced S1O2. Particular preference is given to using amorphous SiO ₂ produced by thermal decomposition of ZrSiO ₄ (see DE 102012020509) and SiO ₂ produced by oxidation of metallic Si by means of an oxygen-containing gas (see DE 102012020510). Also preferred is quartz glass powder (mainly amorphous SiO 2) which has been produced by melting and rapid re-cooling of crystalline quartz, so that the particles are spherical and not splintered (see DE 10201202051 1). The average primary particle size of the synthetic amorphous silicon dioxide can be between 0.05 μm and 10 μm, in particular between 0.1 μm and 5 μm, more preferably between 0.1 μm and 2 μm. The primary particle size was determined by means of dynamic light scattering on a Horiba LA 950 and checked by scanning electron micrographs (SEM images) on a Nova NanoSEM 230 from FEI. Furthermore, details of the primary particle shape up to the order of 0.01 μητι could be made visible with the aid of SEM images. The SiO2 samples were dispersed in distilled water for SEM measurements and then coated on a copper banded aluminum holder before the water was evaporated. Furthermore, the specific surface area of the synthetic amorphous silicon dioxide was determined by means of gas adsorption measurements (BET method) according to DIN 66131. The specific surface area of the synthetic amorphous SiO ₂ is between 1 and 200 m ² / g, in particular between 1 and 50 m ² / g, more preferably between 1 and 30 m ² / g. If necessary. The products can also be mixed, for example to obtain specific mixtures with certain particle size distributions.

By agglomeration, the amorphous SiO ₂ types mentioned form slightly larger aggregates. For a uniform distribution of the amorphous SiO ₂ in the molding material mixture, it is important that the aggregates partially break up again during mixing in smaller units or not exceed a certain size from the outset. Preferably, to describe the extent of agglomeration, the residue when passing through a 45 mesh sieve (325 mesh) is not more than about 10 weight percent, more preferably not more than about 5 weight percent. and most preferably not more than about 2% by weight.

Depending on the production method and producer, the purity of the amorphous SiO _{2 can} vary greatly. Types having a content of at least 85% by weight of SiO ₂ , preferably of at least 90% by weight and more preferably of at least 95% by weight, have proven to be suitable.

Depending on the application and desired strength level, between 0.1% by weight and 2% by weight of the particulate amorphous SiO ₂ are used, preferably between 0.1% by weight and 1.8% by weight, more preferably between 0.1% % By weight and 1.5% by weight, based in each case on the basic molding material.

The ratio of water glass binder to amorphous SiO ₂ can be varied within wide limits. This offers the advantage of greatly improving the initial strengths of the cores, ie, the strength immediately after removal from the tool, without significantly affecting the ultimate strengths. This is of great interest especially in light metal casting. On the one hand, high initial strengths are desired in order to be able to easily transport the cores after their production or to assemble them into whole core packages, on the other hand, the final strengths should not be too high to avoid difficulties in core decay after casting. Based on the weight of the binder, the amorphous SiO 2 is preferably present in a proportion of from 2 to 60% by weight, more preferably from 3 to 55% by weight, and especially preferably from 4 to 50% by weight or particularly preferably based on the ratio Solids content of water glass to amorphous Si0 ₂ from 10: 1 to 1: 1, 2 (parts by weight).

The addition of the amorphous Si0 ₂ can be carried out according to EP 1802409 B1 both before and after the binder addition directly to the refractory material, but it can also, as described in EP 1884300 A1 (= US 2008/029240 A1), first a premix of S1O2 with at least a part of the binder or sodium hydroxide solution are prepared and then added to the refractory material. Any binder or binder portion still present which is not used for the premix may be added to the refractory material before or after the addition of the premix or together with it. Preferably, the amorphous S1O2 is added directly to the refractory prior to binder addition.

Without wishing to be bound by this, the inventors believe that the strongly alkaline water glass can react with the silanol groups located on the surface of the amorphous silica and that upon evaporation of the water, an intense bond between the silica and the then solid water glass is produced ,

In a further embodiment, barium sulfate may be added to the molding material mixture in order to further improve the surface of the casting, in particular in light metal casting, such as aluminum casting. The barium sulfate may be synthetically produced as well as natural barium sulfate, i. be added in the form of minerals containing barium sulfate, such as barite or barite. This and other features of the suitable barium sulfate and of the molding material mixture produced therewith are described in more detail in DE 102012104934 and the disclosure content thereof is also made by reference to the disclosure of the present patent.

The barium sulfate is preferably used in an amount of 0.02 to 5.0% by weight, more preferably 0.05 to 3.0% by weight, particularly preferably 0.1 to 2.0% by weight, or 0.3 to 0 , 99% by weight, in each case based on the entire molding material mixture added. According to a further embodiment, other substances which are distinguished by a low wetting with molten aluminum, for example boron nitride, can also be added to the molding material mixture according to the invention. Such a mixture of low-wetting substances, which contains, inter alia, barium sulfate as a low-wetting agent, can likewise lead to a smooth, sand-bond-free casting surface. Based on the total amount of non / low wetting substances, the proportion of barium sulfate should be greater than 5% by weight, preferably greater than 10% by weight, particularly preferably greater than 20% by weight or greater than 60% by weight.

The upper limit is pure barium sulfate - the proportion of barium sulfate in non-wetting agents in this case is 100% by weight. The mixture of non-wetting / low-wetting substances, in particular barium sulfate, is preferably used in an amount of 0.02 to 5.0% by weight, more preferably 0.05 to 3.0% by weight, particularly preferably 0.1 to 2.0 % By weight or 0.3 to 0.99% by weight, based in each case on the molding material mixture.

In a further embodiment, the additive component of the molding material mixture according to the invention may further comprise at least one particulate or a particulate mixed metal oxide of aluminum or of aluminum and zirconium, as described in DE 1020121 13073 and DE 1020121 13074, respectively , By means of such additives, castings, in particular made of iron or steel, with very high surface quality can be obtained after the casting of metal, so that only little or even no reworking of the surface of the casting is required after removal of the casting mold.

The particulate or mixed metal oxide shows no or at least a very low reactivity with the inorganic binder, in particular the alkaline water glass, at room temperature. The particulate metal oxide comprises or consists in particular of at least one aluminum oxide in the alpha phase and / or at least one aluminum / silicon mixed oxide, with the exception of aluminum / silicon mixed oxides having a phyllosilicate structure. Particulate metal oxides containing at least one alpha-phase aluminum oxide and / or at least one aluminum / silicon mixed oxide, with the exception of aluminum / silicon mixed oxides having a phyllosilicate structure, are understood to be not only particulate metal oxides which are pure alumina or pure aluminosilicates or aluminosilicates exist but also mixtures of the above metal oxides with other oxides such as zirconium, zirconium incorporated into the aluminum / silicon mixed oxides or heterogeneous, ie consisting of several phases mixtures which consist inter alia of at least two of the following solids or phases: alumina-containing and / or aluminum / silicon oxide-containing solids or phases.

Preference is given to particulate metal oxide selected from the group of corundum plus zirconium dioxide, zirconium mullite, zirconium corundum and aluminum silicates (with the exception of those having a layered silicate structure) plus zirconium dioxide and, if appropriate, optionally containing further metal oxides.

Not suitable as additives for the binder are aluminum / silicon mixed oxides with layer structure, such as metakaolines, kaolins, kaolinite. Also not suitable is pyrogenic, amorphous alumina. The particulate mixed metal oxide is at least one particulate compound oxide or particulate mixture of at least two oxides or is present at least as a particulate composite oxide adjacent at least one further particulate oxide, wherein the particulate mixed metal oxide comprises at least one oxide of aluminum and at least one oxide of zirconium.

Under particulate mixed metal oxides containing in addition to an oxide of aluminum additionally an oxide of zirconium are understood not only pure aluminum oxides and zirconium oxides, but also mixed oxides such as aluminum silicates and zirconium oxide or heterogeneous, ie consisting of several phases mixtures of substances including a or several alumina-containing and zirconium oxide-containing solids or phases. Preferably, the particulate mixed metal oxide according to the invention is selected from one or more members of the group of a) corundum plus zirconium dioxide, b) zirconium mullite, c) zirconium corundum and d) aluminum silicates plus zirconium dioxide and can optionally additionally contain further metal oxides.

Aluminum silicates are here understood as meaning both aluminosilicates and aluminosilicates. Both the aluminum / silicon mixed oxides and the aluminum silicates, if they are not amorphous (ie, there is crystallinity or partial crystallinity here), are preferably island silicates. In isolated silicates, the Si0 ₄ units (tetrahedral) contained in the structure are not directly linked to each other (no Si-O-Si linkages), instead, there are links of the tetrahedral Si0 ₄ units to one or more Al atoms (Si-O Al). The Al atoms are coordinated by 4, 5, and / or 6 oxygen atoms.

Typical representatives of these island silicates are (according to the classification of minerals according to Strunz, 9th edition), for example, mullite (melt and sintered mullite are meant here as well as Zr0 ₂ -containing mullite) and sillimanite and other members of the sillimanite group (for example kyanite or andalusite ), wherein from the sillimanite group particularly preferably kyanite is used. Particularly preferred is an amorphous aluminum silicate (except those with phyllosilicate structure) with greater than 50 atomic% of aluminum atoms based on the sum of all silicon and aluminum atoms, possibly also containing zirconium / zirconium oxide, or an alumina-containing dust, which as by-product produced in zirconium corundum production and therefore may contain zirconium oxide in finely divided form. These as well as further features of the suitable particulate or particulate mixed metal oxides of aluminum or of aluminum and of zirconium are described in greater detail in DE 1020121 13073 and DE 1020121 13074, respectively, and these are also claimed for the disclosure of the present industrial property right ,

The particulate amorphous silica added to the molding compound mixture to increase the strengths may be added as part of the particulate mixed metal oxide or separately. In any event, the statements made herein on the concentration of the particulate mixed metal oxide and the particulate amorphous silica are each without the other component (s). In case of doubt the component has to be calculated out.

In a further embodiment, the additive component of the molding material mixture according to the invention may comprise a phosphorus-containing compound. Such an addition is preferred in very thin-walled sections of a casting mold and in particular in cores, since in this way the thermal stability of the cores or of the thin-walled section of the casting mold can be increased. This is of particular importance when the liquid metal encounters an inclined surface during casting and exerts a strong erosive effect there due to the high metallostatic pressure or can lead to deformations of thin-walled sections of the casting mold in particular. Suitable phosphorus compounds do not or not significantly affect the processing time of the novel molding material mixtures. Suitable representatives and their added amounts are described in detail in WO 2008/046653 A1 and this is also claimed to the extent of the disclosure of the present patent.

Binders containing water have a poorer flowability compared to organic solvent-based binders. This means that molds with narrow passages and multiple deflections can be filled less well. As a result, the cores may have portions with insufficient compaction, which in turn may lead to casting defects during casting. According to an advantageous embodiment, the molding material mixture according to the invention contains a proportion of platelet-shaped lubricants, in particular graphite or M0S2. Surprisingly, it has been found that with the addition of such lubricants, in particular graphite, even complex shapes can be produced with thin-walled sections, wherein the casting molds consistently have a uniformly high density and strength, so that substantially no casting defects were observed during casting. The amount of added platelet-shaped lubricant, in particular graphite, is preferably 0.05 wt.% To 1 wt.%, Based on the molding material. In place of the platelet-shaped lubricants, it is also possible to use surface-active substances, in particular surfactants, which improve the flowability of the molding material mixture. Suitable representatives of these compounds are described, for example, in WO 2009/056320 (= US 2010/0326620 A1). Mentioned here are in particular surfactants with sulfuric acid or sulfonic acid groups.

In addition to the constituents mentioned, the molding material mixture according to the invention may also comprise further additives. For example, internal release agents can be added which facilitate the detachment of the molds from the mold. Suitable internal release agents are e.g. Calcium stearate, fatty acid esters, waxes, natural resins or special alkyd resins.

Surprisingly, it has been found that the addition of an organic additive leads to an improvement in the surface quality of a casting, in particular in aluminum casting. The mechanism of action of the organic additives has not been clarified. Without wishing to be bound by this theory, the inventors assume that at least part of the organic additives burns during the casting process and thereby creates a thin gas cushion between liquid metal and the molding material forming the wall of the casting mold and thus a reaction between liquid metal and molding material is prevented. Further, the inventors believe that some of the organic additives under the reducing atmosphere of the casting form a thin layer of so-called lustrous carbon, which also prevents reaction between metal and molding material. As a further advantageous effect, an increase in the strength of the casting mold after curing can be achieved by adding the organic additives.

It was surprising that the improvement of the surface of the casting with very different organic additives can be achieved. Suitable organic additives are, for example, phenol-formaldehyde resins, such as novolaks, epoxy resins, such as bisphenol A epoxy resins, bisphenol F epoxy resins or epoxidized novolacs, polyols, such as polyethylene glycols or polypropylene glycols, glycerol or polyglycerol, polyolefins, such as Polyethylene or polypropylene, copolymers of olefins, such as ethylene or propylene, and further comonomers, such as vinyl acetate or styrene and / or diene monomers, Polyamides such as polyamide-6, polyamide-12 or polyamide-6,6, natural resins such as gum rosin, fatty acid esters such as cetyl palmitate, fatty acid amides such as ethylenediamine bisstearamide, carbohydrates such as dextrins and metal soaps such as Stearates or oleates of divalent or trivalent metals. The organic additives can be contained both as a pure substance, as well as a mixture of different organic compounds.

The organic additives are preferably in an amount of 0.01 to 1 wt.%, Or 0, 1 -1, 0 wt.%, Particularly preferably 0.05 to 0.5 wt.%, Particularly preferably 0, 1 -0 , 2% by weight, in each case based on the molding material added.

Furthermore, silanes can also be added to the molding material mixture according to the invention in order to increase the resistance of the molds and cores to high air humidity and / or water-based molding coatings. According to a further preferred embodiment, the molding material mixture according to the invention contains a proportion of at least one silane. Suitable silanes are, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes. Examples of suitable silanes are γ-aminopropyltrimethoxysilane, γ-hydroxypropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, γ-

Mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane and N-β (aminoethyl) -y-aminopropyltrimethoxysilane. Based on the binder, typically 0.1 to 2% by weight of silane is used, preferably 0.1 to 1% by weight.

Further suitable additives are alkali metal siliconates, for example potassium methyl siliconate, of which 0.5 to 15% by weight, preferably 1 to 10% by weight and more preferably 1 to 5% by weight, based on the binder, can be used. If the molding material mixture comprises an organic additive, then it can be added per se at any point in time during the preparation of the molding material mixture. The addition of the organic additive can be carried out in bulk or in the form of a solution. Water-soluble organic additives can be used in the form of an aqueous solution. If the organic additives are soluble in the binder and are stable in storage over several months in the binder, they can also be dissolved in the binder and thus added together with this the molding material. Water-insoluble additives may be used in the form of a dispersion or a paste. The dispersions or pastes preferably contain water as the liquid medium. Contains the molding material silanes and / or Alkalimethylsilikonate, they are usually added in the form that they are incorporated in advance in the binder. However, they can also be added to the molding material as a separate component.

Inorganic additives can also positively influence the properties of the cores produced by the process according to the invention. Thus, e.g. the carbonates mentioned in AFS Transactions, Vol. 88, pp 601-608 (1980), or Vol. 89, pp 47-54 (1981), the moisture resistance of the cores during storage, whereas those of WO 2008/046653 (= CA 2666760 A1) known phosphorus compounds increase the thermal stability of the cores.

In the preparation of the molding material mixture, the refractory molding base material is placed in a mixer and then preferably first added the liquid component and mixed with the refractory molding material until a uniform layer of the binder has formed on the grains of the refractory molding material. The mixing time is chosen so that an intimate mixing of refractory base molding material and liquid component takes place. The mixing time depends on the quantity of the molding material mixture to be produced and on the mixing unit used. Preferably, the mixing time is selected between 1 and 5 minutes. With preferred further agitation of the mixture, the solid component (s) in the form of the particulate mixed metal oxides, and optionally of the amorphous silicon dioxide, barium sulfate or other powdered solids is then added and then the mixture further mixed. Again, the mixing time depends on the amount of the molding mixture to be produced and on the mixing unit used. Preferably, the mixing time is selected between 1 and 5 minutes. A liquid component is understood to mean both a mixture of different liquid components and the totality of all liquid individual components, the latter being able to be added to the molding material mixture together or else successively. According to another embodiment, the solid components may first be added to the refractory base molding material and only then the liquid component of the mixture to be supplied. The molding material mixture is then brought into the desired shape. In this case, customary methods are used for the shaping. For example, the molding material mixture can be shot by means of a core shooting machine with the aid of compressed air into the mold. Another possibility is to trickle the molding material mixture free-flowing from the mixer into the mold and to compact them there by shaking, stamping or pressing. The processes according to the invention are in themselves suitable for the production of all casting molds customary for metal casting, that is to say, for example, of cores and molds.

Despite the high strengths which can be achieved with the method according to the invention, the cores produced with the molding material mixture according to the invention show a good disintegration after the casting, in particular during aluminum casting. However, the use of the moldings produced from the molding material mixture according to the invention is not limited to light metal casting. The molds are generally suitable for casting metals. Such metals include, for example, non-ferrous metals, such as brass or bronze, and ferrous metals.

Reference to the following non-limiting examples, the invention will be explained in more detail.

Examples

1 . Production of the molding material mixtures

1 .1. without addition of amorphous S1O2

5 kg of quartz sand H 32 from Quarzwerke Frechen GmbH were placed in the bowl of a mixer from Hobart (model HSM 10). With stirring, the binder was then added and mixed intensively with the sand for one minute. The respective addition amounts are listed in the individual experiments.

1 .2. with addition of amorphous S1O2

The procedure was as described under 1 .1 with the difference that before the binder addition 0.5 GT amorphous S1O2 calculated on the sand was added and mixed for one minute with this. The form of addition is listed in the individual experiments. 2. Preparation and testing of the test bodies

A portion of the molding material mixtures prepared according to 1 .1 or 1 .2 were transferred to the storage chamber of a core shooter H 1 Fa. Röperwerke AG. The remainder of the molding mixtures were stored in a carefully sealed vessel until replenishment of the core shooter to prevent dehydration and premature reaction with the CO2 present in the air. From the storage chamber, the molding material mixtures were shot by means of compressed air (4 bar) into a non-tempered mold provided with two engravings for round cores of 50 mm diameter and 50 mm height. Subsequently, the test cores were cured. Details about it are listed in the respective experiments. After curing, the test specimens were removed from the mold and their compressive strengths were determined immediately using a Zwick Universal Testing Machine (Model Z 010), ie a maximum of 15 seconds after removal, and after storage for 24 hours. The values listed in the tables are averages of 8 cores each. In order to largely eliminate the influence of climatic fluctuations, all test specimens used to determine the 24 hourly strengths were stored in a climatic chamber at 23 ° C and 50% humidity. In the case of Examples 4.01 to 4.07, the experiments were carried out on a core shooter L 1 from. Laempe & Mössner GmbH, which was equipped with a heating hose (type HT42-13) from. Hillesheim GmbH. For the testing of the molding material mixtures cuboidal test bars with dimensions of 150 mm x 22.36 mm x 22.36 mm were prepared (so-called Georg-Fischer-Riegel). The three-part mold used to produce four cuboid test bars simultaneously. Part of the molding material mixture prepared according to 1 .2 was transferred to the storage container of the core shooter, the mold was not electrically heated. The remainder of the respective molding mix was stored in a carefully sealed vessel until the core shooter was refilled to prevent it from drying out and to avoid premature reaction with the CO2 present in the air. The molding material mixtures were introduced by means of compressed air (4 bar) from the storage vessel into the mold and rinsed with hot CO2 or hot air. Further information on the flushing time of the compressed air or CO2 and the gas temperature are given in 6.. After curing, the mold was opened and the test bars removed. To determine the flexural strengths, the test bars were placed in a Georg Fischer Strength Tester equipped with a 3-point bender, and the force was measured which resulted in the breakage of the test bars. The flexural strengths were determined both immediately, ie not more than 15 seconds after removal (initial strengths) and also approx. 24 hours after production (final strengths).

The results of the strength tests are shown in Table 4. The values given here are averages of multiple determinations on at least 4 cores.

3. Curing with CO2

3.1. For the preparation of the test specimens were molding material mixtures consisting of quartz sand H 32 and 2.0 GT (GT = parts by weight), 2.5 GT or 3.25 GT of a sodium water glass with a molar modulus of about 2.33 and a solid of about 40 wt.% Used. For curing, CO2 (manufacturer and purity in each case: Linde AG, at least 99.5 vol.% CO2). passed through the molding material mixture. The temperature of the gas was between 22 and 25 ° C when it entered the mold. Table 1 lists the gassing times, the C0 ₂ flow and the compressive strengths found under these conditions (see Examples 1 .01 to 1 .21 and 1 .29 to 1 .42).

3.2. Part of the experiments according to 3.1. was repeated with the difference that 0.5 parts of amorphous silica in powder form were admixed with the molding material mixtures before the binder addition. The results are also shown in Table 1 (Examples 1 .22 to 1.28).

Table 1 (see appendix) shows: Without the addition of amorphous S1O2:

The strengths are dependent on the quantity of CU2 used for curing, the initial strengths increasing with increasing amount of CO2, the strengths falling after 24 hours of storage due to the known Überbegasungseffektes contrast (see Examples 1 .01 to 1 .21), the Überbegasungseffekt expected to occur later at higher binder levels. With the same absolute amount of CO 2, a low CO 2 FIUSS has a predominantly positive effect on the initial strengths, whereas a high CO 2 FIUSS has a positive effect on the final strengths (see Examples 1 .03 / 1 .08, 1 .04 / 1 .09 / 1 .15, 1 .05 / 1 .16, 1 .06 / 1 .1 1/1 .17, 1 .07 / 1 .12 / 1 .18, 1 .14 / 1 .20).

With addition of amorphous S1O2:

The addition of amorphous S1O2 causes an increase in strength over cores cured with the same fumigation parameters but not containing amorphous S1O2 (see Examples 1 .22 - 1 .28 compared to 1 .08 - 1 .14).

The loss of strength after 24 hours of storage due to the overgassing is reduced by the amorphous S1O2 (see Examples 1 .22 - 1 .28 compared to 1 .08 - 1 .14).

Except for long fumigation times, the addition of amorphous S1O2 causes a greater increase in the initial strengths than the increase in binder content by the same amount. On the other hand, the ultimate strengths increase much more when the binder content is high, but they also decrease more strongly with long fumigation times because of the overgassing effect (see Examples 1 .22 - 1 .28 in comparison to 1 .29 - 1 .35).

Even with the same solids content, the mixture of water glass binder and amorphous S1O2 offers advantages in terms of initial strengths compared to the increased binder quantity without amorphous S1O2, except for long gassing times. On the other hand, the increased binder content has a stronger effect on the final strengths, with the decrease in strength again being pronounced for long fumigation times as a result of overgassing (see Examples 1 .22 - 1 .28 in comparison to 1 .36 - 1 .42). 4. curing with air

4.1. To prepare the test specimens, molding material mixtures consisting of quartz sand H 32 and 2.0 GT, 2.5 GT and 3.25 GT of a sodium water glass with a molar modulus of about 2.33 and a solids content of about 40% by weight were used , For curing, compressed air was passed through the molding material mixture. The temperature of the compressed air was between 22 and 25 ° C when entering the mold. Table 2 shows the gassing times, the gassing pressure and the compressive strengths found under these conditions (see Examples 2.01 - 2.03 and 2.07 - 2.12).

4.2. Part of the experiments according to 4.1. was repeated with the difference that 0.5 parts of amorphous silica in powder form were admixed with the molding material mixtures before the binder addition. The results are also shown in Table 2 (see Examples 2.04 - 2.06). From Table 2 it can be seen:

Without addition of amorphous SiO ₂ :

The strengths depend on the amount of air passed through, with the initial strengths increasing more with increasing air volume than the final strengths (see Examples 2.01 - 2.03 and 2.07 - 2.12).

A higher binder content does not necessarily result in better strengths. This can probably be explained by the poorer compressibility and the increased water content in the molding compound mixture (see examples 2.01 - 2.03 compared to 2.07 - 2.12).

With addition of amorphous SiO ₂ :

The addition of amorphous SiO ₂ provides an increase in strength over cores cured with the same fumigation parameters but containing no amorphous SiO ₂ , with the initial strengths being more affected than the final strengths (see Examples 2.04 - 2.06 compared to 2.01 - 2.03).

The increase in strength by the amorphous SiO ₂ is greater than by an increase in the binder content by the same amount (see Examples 2.07 - 2.09 compared to 2.04 - 2.06).

The increase in strength through the amorphous SiO ₂ is greater than when the binder content is increased to the same solids content (see Examples 2.10 - 2.12 compared to 2.04 - 2.06). 5. Curing by a combination of CO2 and air

5.1. To prepare the test specimens, molding material mixtures consisting of quartz sand H 32 and 2.0 GT, 2.5 GT and 3.25 GT of a water glass with a molar modulus of about 2.33 and a solids content of about 40% by weight were used , For curing, first CO2 and then compressed air was passed through the molding material mixture. The temperatures of both gases were between 22 and 25 ° C when entering the mold.

Table 3 shows the gassing times of C0 ₂ and air, the C0 ₂ flow, the gas pressure (air) and the compressive strengths found under these conditions (see Examples 3.01 - 3.09, 3.19 - 3.27, 3.37 - 3.45).

5.2. Part of the experiments according to 5.1. was repeated with the difference that 0.5 parts of amorphous silica in powder form were admixed with the molding material mixtures before the binder addition. The results are also shown in Table 3 (see Examples 3.10 - 3.18, 3.28 - 3.36 and 3.46 - 3.48).

5.3. Part of the experiments according to 5.1. was repeated with the difference that the compressed air passed through the molding material mixtures was heated to approximately 100 ° C., measured on entry into the molding tool. The results are also shown in Table 3 (see Examples 3.49 - 3.51).

5.4. Part of the tests according to 5.2. was repeated with the difference that the compressed air passed through the molding material mixtures was heated to approximately 100 ° C., measured on entry into the molding tool. The results are also shown in Table 3 (see Examples 3.52 - 3.54). From Table 3 it can be seen:

Without addition of amorphous S1O2:

Combined COV air fumigation gives significantly better strengths than fumigation with CO2 or air alone (see Examples 3.01 -3.09 and 3.1 9-3.27 compared to 1 .01 -1 .21 and 2.01 -2.03, respectively).

An increase in the pressure during the fumigation with air causes a further increase in strength (see Examples 3.43-3.45 compared to 3.04-3.06). Warming of the gassing air causes an increase in the ultimate strengths (see Examples 3.49-3.51 in comparison to 3.04-3.06). That the initial strengths do not show the same effect can probably be explained by the fact that they were still warm at the time of the strength test.

Prolonging the fumigation time with CO2 does not in all cases have a positive effect on the strengths due to the overgassing effect (see Examples 3.01 -3.09 and 3.19-3.27). Increasing the CO 2 flow increases the initial strengths, but at the expense of the ultimate strengths (see examples 3.01 -3.09 compared to 3.19-3.27)

A higher binder content causes higher final strengths but not necessarily higher initial strengths. The latter can probably be explained by the increased proportion of water in the molding material mixture (see Examples 3.37-3.42 in comparison to 3.04-3.06)

With addition of amorphous S1O2:

The addition of amorphous S1O2 causes an increase in strength over cores cured with the same parameters but not containing amorphous S1O2, with the initial strengths being more affected than the final strengths. At higher CO2-FIUSS u / o. As a result of the overgassing effect, the final strengths of some of the longer C02 gassing times are partially reduced (see examples 3.10-3.18 compared to 3.01 -3.09 and examples 3.28-3.36 compared to 3.19-3.27).

The addition of amorphous S1O2 causes a greater increase in initial strengths than the same amount of binder content. On the contrary, the increased binder content has a stronger effect on the final strengths (see Examples 3.13-3.15 compared to 3.37-3.39)

Even with the same solids content, the mixture of waterglass binder and amorphous S1O2 offers advantages in the initial strengths compared to the correspondingly increased binder quantity without amorphous S1O2. On the other hand, the higher binder content has a stronger effect on the ultimate strengths (see Examples 3.13-3.15 compared to 3.40-3.42) An increase in the pressure during the fumigation with air causes a further increase in strength (see Examples 3.46-3.48 compared to 3.13-3.15) 6. Curing with C0 ₂ , air or by a combination of C0 ₂ and air with a gas temperature of 1 15 up to 90 ° C

6.1. To produce the test specimens, molding material mixtures consisting of quartz sand H 32 and 2.0 GT of a water glass with a molar modulus of about 2.33 and a solids content of about 40% by weight were used. Furthermore, 0.5 g of amorphous silica in powder form was admixed with the molding material mixtures before the binder addition. For curing C0 ₂ and then compressed air was passed through the molding material mixture. Both gases were heated by means of a heating hose to temperatures of up to 120 ° C. The temperatures of both gases when entering the mold were initially 15 ° C and many at 90 ° C during the 35 second fumigation. This temperature drop is due to the fact that the heating hose is unable to keep the gas temperature constant during the gassing. Immediately prior to the start of the experiment, the 4.04 test was repeated approximately 80 times over a period of 50 minutes, so that the mold reached the required operating temperature of about 60 ° C.

Table 4 shows the gassing times of C0 ₂ and air, the C0 ₂ flow, the gas pressure (air) and the flexural strengths found under these conditions (see Examples 4.01 - 3.07).

From Table 4 it can be seen:

The values for the strengths clearly show that a combination of C0 ₂ and air fumigation is clearly superior to the sole fumigation with air or C0 ₂ . In particular, Examples 4.01 -4.03, in which the curing was carried out exclusively with C0 ₂ , have compared to Examples 4.05-4.07 of the process according to the invention significantly lower initial and, apart from Example 4.01, also final strengths. The strengths of Example 4.04, which shows the values for air alone fumigation, are also significantly lower than the strengths for the combined C02 air fumigation according to the invention. While the final strengths for Examples 4.05-4.07 are 10-60 N / cm ² above the values for Example 4.04, their initial strengths are 50-60 N / cm ² higher. Thus, the significantly higher initial strengths of Examples 4.05 to 4.07 make the effect according to the invention clear even at the here increased gas temperature of 15 to 90 ° C for the C0 ₂ and the air. Examples 4.05 to 4.07 show only minor differences, but these are not significant.

Table 1

(not according to the invention)

(a) sodium water glass, molar modulus about 2.33 (molar), solid about 40%

(b) Elkem 971 U, added as a dry powder

(c) Addition corresponds to the amount of binder + amorphous. S1O2 of experiments 1 .22 - 1.28

(d) Solid (1, 3 GT = 2 GT x 40% + 0.5) corresponds to Experiments 1.22 - 1.28 calculated from binder + amorphous. S1O2

h = hours, s = seconds

Table 2

(not according to the invention)

(a) sodium water glass, molar modulus about 2.33 (molar), solid about 40%

(b) Elkem 971 U, added as a dry powder

(c) Addition corresponds to the amount of binder + amorphous. Si0 _{2 of} the experiments 2.04 - 2.06

(d) Solid (1, 3 GT) corresponds to that of experiments 2.4 - 2.6 calculated from binder + amorphous. Si02

h = hours, s = seconds

Table 3

(Continuation)

(a) sodium water glass, molar modulus about 2.33 (molar), solid about 40%

(b) Eikern 971 U, added as a dry powder

(c) Addition corresponds to the amount of binder + amorphous. S1O ₂ of experiments 1.22 - 1 .28

(d) Solid (1, 3 GT = 2 GT ^* 40% +0.5) corresponds to that of experiments 1.22 - 1.28 calculated from binder + amorphous. S1O ₂

(e) air preheated to 100 ° C (measured at the entrance to the mold) (i) no complete cure

h = hours, s = seconds Table 4

(a) sodium water glass, molar modulus about 2.33 (molar), solid about 40%

(b) Microsilica POS B-W 90 LD from Possehl Erzkontor GmbH, added as a dry powder

Claims

claims

1. A method of making molds or cores comprising:

Providing a molding material mixture comprising at least one refractory molding material and an inorganic binder,

• introducing the molding material mixture into a mold, and

• curing of the molding material mixture in the mold while flowing through the molding material mixture

a) with gaseous C0 ₂ or a gas containing C0 ₂ as a first gas and

b) a second gas, wherein the second gas contains less carbon dioxide than the first gas.

2. The method of claim 1 wherein the molding material mixture is introduced by means of a core-shooting machine with the aid of compressed air into the mold and the mold is a mold and the mold is flowed through with the first and second gas.

3. The method according to at least one of the preceding claims, wherein the mold is either not heatable or heated to temperatures of less than 70 ° C, preferably less than 60 ° C and more preferably less than 40 ° C.

4. The method according to at least one of the preceding claims, wherein the binder is water glass, in particular water glass with a molar modulus Si0 ₂ / M ₂ 0 from 1, 6 to 4.0, preferably 2.0 to less than 3.5 with M equal to lithium , Sodium and / or potassium.

5. The method according to at least one of the preceding claims, wherein the molding material mixture contains at most 1% by weight, preferably at most 0.5% by weight, and particularly preferably at most 0.2% by weight, of organic compounds.

6. The method according to at least one of the preceding claims, wherein the second gas contains less than 10 vol.% C0 ₂ , in particular less than 2 vol.% C0 ₂ , and in particular air or nitrogen or a mixture thereof.

7. The method according to at least one of the preceding claims, wherein the first gas at least 25 mol% CO2, in particular at least 50 mol% CO2 and preferably at least 80 mol% CO2.

8. The method according to at least one of the preceding claims, wherein the gas flow of the first and / or the second gas 0.5 to 600 L / min. (Standard liters), preferably 0.5 to 300 L / min. and more preferably 0.5 L / min. up to 100 L / min. is.

9. The method according to at least one of the preceding claims, wherein the gas flow of the first and / or the second gas 0.5 to 30 L / min. (Standard liters), preferably 0.5 to 25 L / min. and more preferably 0.5 L / min. up to 20 L / min. is, preferably, when the first gas and / or the second gas at a temperature of 15 to 40 ° C are used.

10. The method according to at least one of the preceding claims, wherein the task pressure with respect to the shape of the first and / or the second gas between 0.5 and 10 bar, preferably between 0.5 bar and 8 bar, and more preferably between 0.5 and 6 bar.

1 1. Method according to at least one of the preceding claims, wherein the ratio of the gassing time with the first gas relative to the gassing time with the second gas 2: 98 to 90: 10, preferably 2:98 to 20:80 and particularly preferably 5:95 to 30:70 and, in particular with the first gas, is at most 60% of the sum of the fumigation time with the first and second gas.

12. The method according to at least one of the preceding claims, wherein the refractory base molding material quartz, zirconium or chrome ore, olivine, vermiculite, bauxite and / or chamotte comprises, in particular with average particle diameters of 100 to 600 [im, preferably from 150 to 500 [im.

1 3. The method according to at least one of the preceding claims, wherein the binder, in particular water glass, to 0.5 to 5 wt.%, Preferably 1 to 3.5 wt.%, Based on the molding material, in water glass based on a solids content of From 25 to 65% by weight, preferably from 30 to 60% by weight.

14. The method according to at least one of the preceding claims, wherein further amorphous S1O2 is used, in particular synthetic amorphous S1O2, and preferably with a mean primary particle sizes between 0.05 μηι and 10 μηι, in particular between 0, 1 μηι and 5 μηι, more preferably between 0, 1 μηι and 2 μηι, and independently thereof the BET surface area 1 to 200 m ² / g, in particular 1 to 50 m ² / g and particularly preferably 1 to 30 m ² / g.

15. The method according to at least one of the preceding claims, wherein the amorphous Si0 ₂ in amounts of 0, 1 to 2 wt.%, Preferably 0, 1 to 1, 5 wt.%, In each case based on the molding material is used and independently related thereto on the weight of the binder with 2 to 60 wt.%, Particularly preferably 4 to 50 wt.%.

16. The method according to at least one of the preceding claims, wherein the first gas at a temperature of 15 to 120 ° C, preferably from 15 to 100 ° C and particularly preferably from 25 to 80 ° C, is introduced into the mold and independently thereof second gas having a temperature in the same temperature interval or a temperature of 40 to 250 ° C is introduced into the mold, and preferably the temperature of the second gas when introduced into the mold is greater than that of the first gas.

17. The method according to at least one of the preceding claims, wherein the used amorphous S1O2 has a water content of less than 15 wt.%, In particular less than 5 wt.% And particularly preferably less than 1 wt.% And is used independently, in particular as a powder.

18. The method according to at least one of the preceding claims, wherein the first gas and second gas in any order and number of introduction operations, but at least temporarily separated from each other, are passed into the mold, wherein preferably the second gas is passed through the last mold and in particular first and only once the first gas and then the second gas is passed through the mold.

19. mold or core producible according to at least one of claims 1 to 18.