WO2014059969A2

WO2014059969A2 - Mould material mixtures on the basis of inorganic binders, and method for producing moulds and cores for metal casting

Info

Publication number: WO2014059969A2
Application number: PCT/DE2013/000612
Authority: WO
Inventors: Dennis BARTELS; Heinz DETERS; Antoni Gieniec; Diether Koch; Hannes LINCKE; Martin Oberleiter; Oliver Schmidt; Carolin WALLENHORST
Original assignee: Ask Chemicals Gmbh
Priority date: 2012-10-19
Filing date: 2013-10-18
Publication date: 2014-04-24
Also published as: DE102012020511A1; WO2014059969A3

Abstract

The invention relates to mould material mixtures on the basis of inorganic binders, for producing moulds and cores for metal casting. Said mixtures consist of at least one refractory mould base material, an inorganic binder and particulate amorphous silicon dioxide as an additive. The invention also relates to a method for producing moulds and cores using said mould material mixtures.

Description

Forming substance mixtures based on inorganic binders and process for producing molds and cores for metal casting

The invention relates to molding compositions based on inorganic binders for the production of molds and cores for metal casting consisting of at least one refractory molding material, an inorganic binder and particulate amorphous silica as an additive. Furthermore, the invention relates to a process for the production of molds and cores using the molding material mixtures.

State of the art

Casting molds are essentially composed of molds and molds and cores which represent the negative molds of the casting to be produced. These cores and forms consist of a refractory material, such as quartz sand, and a suitable binder, which gives the mold after removal from the mold sufficient mechanical strength. The refractory molding base material is preferably in a free-flowing form, so that it can be filled into a suitable mold and compacted there. The binder produces a firm cohesion between the particles of the molding base material, so that the casting mold obtains the required mechanical stability. Molds form the outer wall of the casting during casting, cores are used to form cavities within the casting. It is not absolutely necessary that the forms and cores are made of the same material. Thus, for example, the external shape of the castings with the help of permanent metal molds done with chill casting. Also possible is a combination of molds and cores made from differently blended molding compounds and by different processes. If, in simplification, only forms are mentioned below, the statements apply to the same extent to cores based on the same molding material mixture and produced by the same process. For the production of molds both organic and inorganic binders can be used, the curing of which can be effected in each case by cold or hot processes. Cold processes are those processes which are carried out essentially without heating the mold used for core production, generally at room temperature or at a temperature caused by a possible reaction. The curing takes place, for example, in that a gas is passed through the molding mixture to be cured and thereby initiates a chemical reaction. In hot processes, the molding material mixture is heated to a sufficiently high temperature after molding, for example by the heated mold, to expel the solvent contained in the binder and / or to initiate a chemical reaction by which the binder is cured.

Due to their technical properties, organic binders have currently been used in economic terms. the greater importance in the market. Regardless of their composition, however, they have the disadvantage that they decompose during the casting and thereby z. significant amounts of pollutants, e.g. Benzene, toluene and xylenes emit. In addition, the casting of organic binder usually leads to odor and smoke pollution. In some systems, undesirable emissions even occur during core production and / or storage. Although binder emissions have reduced emissions over the years, they can not be completely avoided with organic binders. For this reason, in recent years, the research and development work has again turned to the inorganic binder to further improve these and the product properties of the molds and cores thus produced.

Inorganic binders have been known for a long time, especially those based on water glasses. They were widely used in the 1950s and 60s, but with the advent of modern organic binders, they quickly lost their importance. There are three different methods of curing the water glasses:

Passing a gas, eg CO ₂ , air or a combination of both,

- Addition of liquid or solid hardeners, e.g. ester

- Thermal curing, eg in a hot box process or by microwave treatment. C0 ₂ curing is described, for example, in GB 634817, hardening by means of hot air without C0 ₂ addition, for example in H. Polzin, W. Tilch and T. Kooyers, Foundry Practice 6/2006, p. 171. A further development of C0 ₂ -curing by a subsequent flushing with air is disclosed in DE 102012103705.1.

The ester cure is e.g. from GB 1029057 known (so-called no-bake method).

With the thermal curing of water glass are concerned, for example, US 4226227 and EP 1802409, wherein in the latter case of the molding material mixture of synthetic amorphous Si0 _{2 is added} to increase the strength.

Other known inorganic binders are based on phosphates and / or a combination of silicates and phosphates, wherein the curing also takes place according to the abovementioned methods. These include, for example, US Pat. No. 5,644,015 (phosphate binder, thermal curing), US Pat. No. 6,139,619 (silicate / phosphate binder, thermal curing), US Pat. No. 2,895,838 (silicate / phosphate binder, CO ₂ curing) and US Pat. No. 6,299,677 (Silicate / phosphate binder, ester hardening). In the cited patents or applications EP 1802409 and DE

102012103705.1 it is proposed to add in each case amorphous silicon dioxide to the molding material mixtures. The task of Si0 ₂ is to improve the disintegration of the cores after a thermal load, eg after casting. In EP 1802409 and DE 102012103705.1 it is stated in detail that the addition of synthetic amorphous Si0 ₂ causes a significant increase in strength.

In EP 2014392 B1, it is proposed to add a suspension of amorphous, spherical SiO ₂ to the molding material mixture consisting of molding material, sodium hydroxide solution, alkali silicate binder and additives, the SiO _{2 being} to be present in two particle size classifications. With this measure, a good flowability, high bending strength and a high curing rate should be obtained. Task

The object of the present invention is to further improve the properties of inorganic binders, in order to make them even more universally applicable and to make them an even better alternative to the currently dominant organic binders. In particular, it is desirable to provide molding material mixtures which, because of further improved strength and / or improved densification, make it possible to produce cores of complex geometry or, in the case of simpler core geometries, to reduce the amount of binder and / or shorten the curing times.

Summary of the invention

This object is achieved by molding mixtures with the features of the independent claims. Advantageous developments are the subject of the dependent claims and are described below.

Surprisingly, it has been found that there are certain types of amorphous silicas which differ significantly in their action as additive of the binder from the others.

If crystalline quartz (quartz glass) is melted and cooled rapidly, suitable synthetic amorphous SiO _{2 is obtained} and it is found that, given identical amounts added and under identical reaction conditions, significantly improved strengths are obtained and / or the core weight is higher than at the use of the synthetic amorphous SiO ₂ mentioned in EP 1802409 from other production processes. Increasing the core weight with the same outer dimensions of the core leads to a reduction in gas permeability, which indicates a denser packing of the shaped particles.

Preference is given to a preparation of quartz glass, after which the quartz glass is not subjected to grinding after cooling. For this reason, the particles are spherical and not splintered. The particles have the desired size due to their production. The particulate amorphous Si0 ₂ prepared by the above method is also characterized by the term "artificially produced (particulate) amorphous S1O2." The particulate S1O2 can also be described cumulatively or alternatively to the preparation by the following parameters.

The molding material mixture according to the invention comprises at least:

a refractory base molding material,

an inorganic binder, preferably based on water glass, phosphate or a mixture of both,

- An additive consisting of particulate amorphous S1O2, by

Melting and rapid re-cooling of crystalline quartz was made.

Detailed description of the invention

In the preparation of a molding material i.A. The procedure is such that the refractory molding base material is initially charged and then the binder and the additive are added together or successively with stirring. Of course, it is also possible first to add the components in whole or in part and then to stir and / or during this. Preferably, the binder is charged before the additive. It is stirred until a uniform distribution of the binder and the additive is ensured in 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. Another possibility is to let the molding material mixture free-flowing trickle from the mixer in the mold tool and compress them there by shaking, stamping or pressing.

The hardening of the molding material mixture takes place according to an embodiment of the invention after the hot-box process, ie it is hardened with the aid of hot tools. The hot tools preferably have a temperature of 100 to 300 ° C, more preferably of 120 ° C to 250 ° C. A gas (eg CO ₂ or CO ₂ enriched air) is preferably passed through the molding material mixture, this gas preferably having a temperature of from 100 to 180 ° C., particularly preferably from 120 to 150 ° C., as described in EP 1802409B1. The above process (hot-box process) is preferably carried out in a core shooter.

Regardless of this, the curing can also take place in that CO ₂ , a CO ₂ / gas mixture (eg with air) or CO ₂ and a gas / gas mixture (eg air) successively (as described in detail in DE 102012103705.1) by the cold mold The term "cold" means temperatures below 100 ° C., preferably below 50 ° C. and in particular at room temperature (eg 23 ° C.) Guided gas or gas mixture may preferably be slightly heated, ie, up to a temperature of 120 ° C, preferably up to 100 ° C, particularly preferably up to 80 ° C.

Last but not least, it is also possible, as an alternative to the above two methods, to add a liquid or solid hardener to the molding material mixture before shaping, which then effects the curing reaction.

As refractory molding base material (hereinafter abbreviated to molding base material (s)), materials customary for the production of casting molds can be used. 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 have the highest possible proportion of regenerated

To use old 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. It is also possible to use regenerates obtained by purely mechanical treatment. In general, the regenerates can make up at least about 70% by weight of the molding base material, preferably at least about 80% by weight and more preferably at least about 90% by weight. The average diameter of the molding materials is usually between 100 μιτι and 600 μητι, preferably between 120 μιτι and 550 μιτι and more preferably between 150 μιτι and 500 μιτι. The particle size can be determined, for example, by sieving according to DIN ISO 3310.

In addition, artificial molding materials can also be used as mold base materials, in particular as an additive to the above molding base materials but also as an exclusive molding base material, such as Glass beads, glass granules, the known under the name "Cerabeads" or "Carboaccucast" spherical ceramic mold base materials or Aluminiumilmilikmikrohohlkugeln (so-called.

Microspheres). Such aluminum silicate microbubbles are marketed, for example, by Omega Minerals Germany GmbH, Norderstedt, under the name "Omega-Spheres." Corresponding products are also available from PQ Corporation (USA) under the name "Extendospheres".

In casting experiments with aluminum, it has been found that, when using artificial mold 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 wt.%, Particularly preferably at least about 5 wt.%, Particularly preferably at least about 10 wt.%, Preferably at least about 15 wt.%, Particularly preferably at least about 20% by weight, in each case based on the total amount of the refractory molding base material.

As a further component, the molding material mixture of the invention comprises an inorganic binder, for example based on water glass. Conventional water glasses can be used as the water glass, as they have hitherto been used as binders in molding material mixtures. These water glasses contain dissolved alkali silicates and can be prepared by dissolving glassy lithium, sodium and potassium silicates in water. The water glasses preferably have a molar modulus Si0 ₂ / M ₂ O in the range from 1.6 to 4.0, in particular from 2.0 to less than 3.5, where M is lithium, sodium or potassium. 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 polyvalent ions such as, for example, boron or aluminum (corresponding examples are described in EP 2305603 A1 (= WO2011 / 042132 A1)).

The water glasses have a solids content in the range of 25 to 65 wt.%, Preferably from 30 to 60 wt.%. The solids content refers to the amount of Si0 ₂ and M ₂ 0 contained in the water glass.

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% by weight refers to water glasses with a solids content as indicated above, i. includes the diluent.

Instead of water glass binders, it is also possible to use those based on water-soluble phosphate glasses and / or borates, as described, for example, in US Pat. in US 5,641,015.

The preferred phosphate glasses have a solubility in water of at least 200 g / L, preferably at least 800 g / L and contain between 30 and 80 mol% P ₂ 0 ₅ , between 20 and 70 mol% Li ₂ 0, Na ₂ 0 or K ₂ 0, between 0 and 30 mol% CaO, MgO or ZnO and between 0 and 15 mol% Al ₂ 0 ₃ , Fe ₂ 0 ₃ or B ₂ 0 ₃ . The particularly preferred composition is 58 to 72% by weight of P ₂ O ₅ , 28 to 42% by weight of Na ₂ O and 0 to 16% by weight of CaO. The phosphate anions are preferably present in the phosphate glasses as chains. The phosphate glasses are usually used as about 15 to 65% strength by weight, preferably as about 25 to 60% strength by weight aqueous solutions. However, it is also possible to add the phosphate glass and the water separately to the molding base material, with at least part of the phosphate glass dissolving in the water during the preparation of the molding material mixture.

Typical addition amounts of the phosphate glass solutions are from 0.5% by weight to 15% by weight, preferably from 0.75% by weight to 12% by weight, more preferably from 1% by weight to 10% by weight, based in each case on the molding base material , The term refers to phosphate glass solutions having a solids content as indicated above, i. includes the diluent.

In the case of curing according to the so-called no-bake method, the molding material mixtures preferably further contain hardeners which bring about the solidification of the mixtures without the need for heat supply or for a gas to be passed through the mixture. These hardeners may be liquid or solid, organic or inorganic in nature. Suitable organic hardeners are e.g. Esters of carbonic acid such as propylene carbonate, esters of monocarboxylic acids having 1 to 8 carbon atoms with mono-, di- or trifunctional alcohols such as ethylene glycol diacetate, glycerol mono-, di- and - triacetic acid esters, and cyclic esters of hydroxycarboxylic acids such as γ- butyrolactone. The esters can also be mixed with one another. Suitable inorganic hardeners for waterglass-based binders are e.g. Phosphates such as Lithopix P26 (an aluminum phosphate of Fa.

Zschimmer and Schwarz GmbH & Co KG Chemical Factories) or Fabutit 748 (an aluminum phosphate from the company Chemische Fabrik Budenheim KG). The ratio of hardener to binder can vary depending on the desired property, eg processing time and / or breaking time of the molding material mixtures. Advantageously, the proportion of hardener (weight ratio of hardener to binder and, in the case of water glass, the total mass of the silicate solution or other binders incorporated in the solvent) is greater than or equal to 5% by weight, preferably greater than or equal to 8% by weight, particularly preferably greater than or equal to 0% by weight, in each case based on the binder. The upper limits are less than or equal to 25% by weight, based on the binder, preferably less than or equal to 20% by weight, more preferably less than or equal to 15% by weight. Furthermore, the molding material mixtures contain a proportion of above artificially produced particulate amorphous SiO 2, which was prepared by melting and cooling of crystalline quartz. Corresponding products are marketed, for example, by Denkikagaku Kougyo KK.

Surprisingly, it has been shown that artificially produced particulate amorphous Si0 ₂ with identical amounts added and reaction conditions the nuclei higher strengths and / or a higher core weight gives as a result of this process than amorphous Si0 ₂ from other manufacturing processes, such as silicon or Ferrosiliciumproduktion, the flame hydrolysis of SiCl ₄ or a precipitation reaction. The molding material mixtures according to the invention thus have an improved flowability and can therefore be more compacted at the same pressure.

Both have a positive effect on the performance properties of the molding material mixtures, since in this way cores with more complex geometries and / or thinner wall thicknesses can be produced than hitherto. For simple cores without great demands on the strengths, it is conversely possible to lower the binder content and thus increase the efficiency of the process. The improved compaction of the molding mixture brings with it yet another advantage that the particles of the molding material mixture are in a closer bond than in the prior art, so that the core surface is pore-free, resulting in a reduced roughness depth of the casting.

Without wishing to be bound by this theory, the inventors assume that the improved flowability is due to the fact that the particulate amorphous SiO ₂ used according to the invention is less prone to agglomeration than the amorphous SiO ₂ from the other production processes and therefore already without the action of strong shear forces more primary particles are present. It can be seen that there are more isolated particles in the SiO ₂ according to the invention than in the case of an amorphous non-inventive SiO ₂ produced in the production of silicon / ferrosilicon. There, one recognizes a stronger adhesion of individual spheres into larger associations, which can no longer be broken up into the primary particles. The particle size was determined by means of dynamic light scattering on a

Horiba LA 950 determines the scanning electron micrographs using a Nova NanoSem 230 ultrahigh-resolution scanning electron microscope from FEI equipped with a Through The Lens Detector (TLD). For the SEM measurements, the samples were dispersed in distilled water and then applied to a copper tape-covered aluminum holder before the water was evaporated. In this way, details of the

Primary particle shape to the order of 0.01 μητι be made visible.

The amorphous S1O2 produced by melting and rapid cooling is also available in a very pure form. The SiO ₂ content can be more than 99.5% by weight, the amorphous fraction usually making up more than 90% by weight, preferably more than 93% by weight and particularly preferably more than 95% by weight.

The water content of the particulate amorphous SiO 2 used according to the invention is less than 10% by weight, preferably less than 5% by weight, and more preferably less than 2% by weight. In particular, the particulate amorphous SiO _{2 is used} as a dry powder. The powder is trickling and free-flowing under its own weight.

The average particle size of the particulate amorphous S1O2 preferably moves between 0.05 μm and 10 μm, in particular between 0.1 μm and 5 μm, and particularly preferably between 0.1 μm and 2 μm, whereby primary particles with diameters between approx 0.01 μιη and about 5 μιη were found. The determination was carried out with the aid of dynamic light scattering on a Horiba LA 950.

The particulate amorphous silica preferably has an average particle size of preferably less than 300 μητι, preferably less than 200 μιη, more preferably less than 100 μιη. The particle size can be determined by sieve analysis. The sieve residue of the particulate amorphous SiO ₂ in a passage through a sieve with 125 μm mesh size (120 mesh) is preferably not more than 10% by weight, more preferably not more than 5% by weight and most preferably not more than 2% by weight. %. The sieve residue is determined according to the machine screen method described in DIN 66165 (Part 2), wherein additionally a chain ring is used as screen aid. It has furthermore proven to be advantageous if the residue of particulate amorphous SiO ₂ used according to the invention, when passing through a sieve having a mesh size of 45 μm (325 mesh), does not exceed about 10% by weight, particularly preferably not more than approx 5% by weight and most preferably not more than about 2% by weight (sieving according to DIN ISO 3310).

By means of scanning electron micrographs, the ratio of primary particles (non-agglomerated, non-fused and unmelted particles) to the secondary particles (agglomerated, intergrown and / or fused particles including particles which are (clearly) not spherical)

Have to be determined) of the particulate amorphous SiO ₂ . These images were taken using a Nova NanoSem 230 ultra-high resolution scanning electron microscope from FEI equipped with a Through The Lens Detector (TLD).

The samples were then dispersed in distilled water and then applied to a copper tape-bonded aluminum holder before the water was evaporated. In this way, details of the primary particle shape could be visualized up to 0.01 pm.

The ratio of the primary particles to the secondary particles of the artificially produced particulate amorphous SiO ₂ is advantageously and independently characterized as follows: a) The particles are more than 20%, preferably more than 40%, more preferably more than 60% and very particularly preferably more than 80%, based on the total number of particles, in the form of essentially spherical primary particles, in each case in particular with the above limit values in the form of spherical primary particles with diameters of less than 4 μm, and particularly preferably less than 2 μm. b) The particles are more than 20% by volume, preferably more than 40% by volume, more preferably more than 60% by volume and most preferably more than 80% by volume, based on the cumulative volume of the particles, in the form of substantially spherical primary particles, in each case in particular with the above limit values in the form of spherical primary particles with diameters of less than 4 gm, and particularly preferably less than 2 [im. The calculation of the respective volumes of the individual particles as well as the cumulative volume of all particles was carried out under the assumption of a spherical symmetry present in each case for individual particles and with the aid of the diameter determined for each particle by means of SEM images. c) the particles are more than 20 area%, preferably more than 40 area ⁰ /), more preferably more than 60 area% and most preferably more than 80 area%, based on the cumulative area of the particles, in Form of substantially spherical primary particles before, in each case in particular with the above limits in the form of spherical primary particles with diameters smaller than 4 μιτι, and more preferably less than 2 gm.

The percentage detection is based on a statistical analysis of a variety of SEM images, agglomeration / adhesion / fusion is / are classified as such only if the respective contours of individual adjacent spherical (one inside the other) primary particles are no longer recognizable. In the case of superimposed particles, in which the respective contours of the spherical geometries (otherwise) can be seen, the classification is done as a primary particle, even if the view does not allow an actual classification due to the two-dimensionality of the images. When determining the area, only the visible particle areas are evaluated and contribute to the total.

Furthermore, the specific surface area of the particulate amorphous SiO _{2 used} according to the invention was determined by means of gas adsorption measurements (BET method, nitrogen) according to DIN 66131. It was found that there seems to be a relationship between BET and compressibility. Suitable particulate amorphous SiO ² used according to the invention has a BET of less than or equal to 35 m ² / g, preferably less than or equal to 20 m ² / g, particularly preferably less than or equal to 17 m ² / g and particularly preferably less than or equal to 15 m ² / g. The lower limits are greater than or equal to 1 m ² / g, preferably greater than or equal to 2 m ² / g, particularly preferably greater than or equal to 3 m ² / g and particularly preferably greater than or equal to 4 m ² / g.

If necessary. For example, the products may also be mixed, e.g. to selectively mixtures with certain compositions, average particle sizes and / or specific see surfaces.

Depending on the application and the desired strength level, between 0.1% by weight and 2% by weight of the artificially produced particulate amorphous SiO 2 are used, preferably between 0.1% by weight and 1.8% by weight and more preferably between 0.1% by weight ,% and 1, 5 wt.%, Each based on the molding material.

The ratio of inorganic binder to particulate amorphous SiO ₂ used according to the invention can be varied within wide limits. This offers the possibility of greatly varying the initial strengths of the cores, ie the strength immediately after removal from the mold, 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 complete 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 (including any diluents or solvents), the artificially produced particulate amorphous S1O2 is preferably present in a proportion of from 2% to 60% by weight, more preferably from 3% to 55% by weight and most preferably from 4% by weight to 50% by weight. The artificially produced particulate amorphous SiO ₂ corresponds to the particulate amorphous SiO ₂ according to the terminology of the claims and is used in particular as a powder, in particular with a water content of less than 5 wt.%, Preferably less than 3 wt.%, In particular less than 2 wt.%, (Water content determined by Karl Fischer). Irrespective of this, the ignition loss (at 400 ° C.) is preferably less than 6, less than 5 or even less than 4% by weight. The addition of the particulate amorphous Si0 ₂ used according to the invention can be carried out both before and after or mixed together with the binder addition directly to the refractory material. Preferably, the particulate amorphous S1O2 used according to the invention is added to the refractory dry and in powder form directly after the binder addition.

According to a further embodiment of the invention, a premix of Si0 ₂ is first prepared with an aqueous alkali solution, such as sodium hydroxide, and optionally the binder or a part of the binder and then added to the refractory molding material. The binder or binder fraction which may still be present and which is not used for the premix can be added to the molding base material before or after the addition of the premix or together with it.

According to a further embodiment, in addition to the particulate amorphous S1O2, a non-inventive synthetic amorphous S1O2 according to EP 1802409 B1, e.g. in the ratio of 1 to less than 1 are used.

Mixtures of inventive and non-inventive S1O2 can be advantageous if the effect of the particulate amorphous SiO 2 used according to the invention is to be "weakened." Additions of inventive and non-inventive amorphous SiO ₂ to the molding material mixture allow the strengths and / or In the case of an inorganic binder based on water glass, the molding material mixture according to the invention may comprise a phosphorus-containing compound in a further embodiment, such an additive being preferred for very thin-walled sections of a casting mold and in particular for cores The thermal stability of the cores or of the thin-walled section of the casting mold can be increased, which is particularly important when the liquid metal encounters an inclined surface during casting and there due to the high metallostati pressure exerts a strong erosive effect or can lead to deformations in particular thin-walled sections of the mold. Suitable phosphorus compounds do not or not significantly affect the processing time of the novel molding material mixtures. An example of this is sodium hexametaphosphate. Further suitable representatives as well as their added amounts are described in detail in WO 2008/046653 and this is to that extent also made a disclosure of the present property rights.

Although the molding material mixtures according to the invention already have an improved flowability compared to the prior art, if desired, these can be increased even further by the addition

platelet-shaped lubricant about to completely fill molds with particularly narrow passages. According to an advantageous embodiment, the molding material mixture according to the invention contains a proportion of platelet-shaped lubricants, in particular graphite or MoS ₂ . The amount of added platelet-shaped lubricant, in particular graphite, is preferably 0.05 wt.% To 1 wt.% Based on the molding material.

Instead of the platelet-shaped lubricant it is also possible to use surface-active substances, in particular surfactants, which likewise further improve the flowability of the molding material mixture according to the invention.

Suitable representatives of these compounds are e.g. in WO 2009/056320 (= US 2010/0326620 A1). Mentioned here are in particular surfactants with sulfuric acid or sulfonic acid groups. Other suitable representatives and the respective amounts added are described in detail in WO 2009/056320 and this is to that extent also made a disclosure of the present property rights.

In addition to the constituents mentioned, the molding material mixture according to the invention may also comprise further additives. For example, release agents can be added which facilitate the detachment of the cores from the mold. Suitable release agents are, for example, calcium stearate, fatty acid esters, waxes, natural resins or special alkyd resins. If these release agents are soluble in the binder and do not separate from it even after prolonged storage, especially at low temperatures, they may already be present in the binder component, but they may also form part of the additive or as a separate component of the molding material mixture be added. To improve the casting surface, organic additives may be added. Suitable organic additives are for example phenol-formaldehyde resins such as novolacs, epoxy resins such as

Bisphenol A epoxy resins, bisphenol F epoxy resins or epoxidized novolacs, polyols such as polyethylene or polypropylene glycols, glycerol or polyglycerol, polyolefins such as polyethylene or polypropylene, copolymers of olefins such as ethylene and / or propylene with others

Comonomers such as vinyl acetate or styrene and / or diene monomers such as butadiene, 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

Ethylenediaminebisstearamide, metal soaps such as stearates or oleates of divalent or trivalent metals and carbohydrates such as dextrins. Carbohydrates, especially dextrins are particularly suitable. Suitable carbohydrates are described in WO 2008/046651 A1. The organic additives can be used both as a pure substance, as well as in admixture with various other organic and / or inorganic compounds.

The organic additives are preferably used in an amount of from 0.01% by weight to 1.5% by weight, more preferably from 0.05% by weight to 1.3% by weight and most preferably from 0.1% by weight to 1 % By weight added, in each case based on the molding material.

Furthermore, it is also possible to add silanes to the molding material mixture according to the invention in order to increase the resistance of the cores to high humidity and / or to water-based molding coatings. According to a further preferred embodiment, the molding material mixture according to the invention therefore 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-ureidopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycycloherxyl) trimethoxysilane, N-β- (aminoethyl) -Y- aminopropyltrimethoxysilane and their triethoxyanaloge connections. The silanes mentioned, in particular the aminosilanes, can also

be prehydrolyzed. About 0.1% by weight to 2% by weight of silane, based on the binder, is typically used, preferably about 0.1% by weight to 1% by weight. Further suitable additives are alkali metal siliconates, for example potassium methyl siliconate, of which about 0.5% by weight to about 15% by weight, preferably about 1% by weight to about 10% by weight and particularly preferably about 1% by weight. can be used up to about 5 wt.% Based on the binder.

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 may take place in bulk or else 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 for several months without decomposition, they can also be dissolved in the binder and thus added together with 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.

If the molding material mixture contains silanes and / or alkali metal siliconates, they are usually added in the form that they are incorporated into the binder in advance. However, they can also be added to the molding material as a separate component.

Inorganic additives can also have a positive influence on the properties of the molding material mixtures 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 the WO 2008/046653 (= CA 2666760 A1) increase the thermal stability of the cores, as long as they are based on water glass.

Alkali borates as components of waterglass binders are described e.g. in EP 011 1398.

Suitable inorganic additives for improving the casting surface on the basis of BaSO ₄ are described in DE 102012104934.3 and can

Formstoffmischung be added as a complete or at least partial replacement of the above-mentioned organic additives. Further details such as the respective amounts added are described in detail in DE 102012104934.3 and this is also made to the extent of disclosure of the present property rights. Despite the high strengths which can be achieved with the novel molding material mixtures, the cores produced from these molding material mixtures show good disintegration after the casting, in particular in aluminum casting. However, the use of the cores produced from the molding mixtures 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 examples, the invention will be explained in more detail without being limited to these.

Examples:

1. Hot curing 1.1. Strengths and core weights depending on the type of added artificially produced particulate amorphous S1O2

1.1.1. Preparation of the molding material mixtures 1.1.1.1 Without addition of SiO ₂

Quartz sand was poured into the bowl of a mixer from Hobart (model HSM 10). With stirring, the binder was then added and each intensively mixed with the sand for 1 minute. The sand used, the type of binder and the respective amounts added are listed in Table 1.

1.1.1.2. With addition of SiO ₂

It became as under 1.1.1.1. method with the difference that after the binder addition of the molding material nor artificially produced particulate amorphous S1O2 was added and this was also mixed for 1 minute. The type of synthetic amorphous S1O2 and the amounts added are listed in Tab. 1.1.2. Production of the test specimens

For the testing of the molding material mixtures cuboid test bars with the dimensions 150 mm x 22.36 mm x 22.36 mm were prepared (so-called Georg Fischer bolt). Part of a 1.1.1. The mixture of molding materials produced in the storage bunker of an H 2.5 hot box core shooting machine of the

Röperwerk-Gießereimaschinen GmbH, Viersen, DE, whose mold was heated to 180 ° C. The remainder of the respective molding material mixture 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 CO _{2 present} in the air.

Table 1

Composition of the molding material mixtures

a) alkali water glass; Molar modulus about 2.1; Solid about 35% by weight

b) sodium polyphosphate solution; 52% by weight (NaPO ₃ ) n with n = approx. 25; 48% by weight of water c) Mixture of 83% by weight of a) and 17% by weight of b)

d) Microsilica 971 U (Eikern AS, production process: production of silicon / ferrosilicon) e) Microsilica white GHL DL 971 W (RW silicon GmbH, production process: see d) f) fused silica FB-3SDC (Denki Kagaku KK; Treatment of Natural Crystalline Si0 ₂ The molding compound blends were introduced into the mold from the storage bin using compressed air (5 bar), the residence time in the hot mold to cure the blends was 35 seconds, to accelerate the curing process, hot air was added during the last 20 seconds. 2 bar, 100 ° C when entering the tool) passed through the mold. The mold was opened and the test bars removed. According to this method, the test specimens are prepared to determine the core weights.

1 .1 .3. Examination of the test body

1 .1.3.1. strength test

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 breakage of the test bars.

The flexural strengths were determined according to the following scheme:

10 seconds after removal (hot strength)

approx. 1 hour after removal (cold strength)

The results are listed in Tab

1.1 .3.2. Determination of the core weight

Before the determination of the cold strengths, the Georg Fischer bars were weighed on a laboratory balance to an accuracy of 0.1 g. The results are listed in Tab.

Table 2

Bending strengths and core weights

Result:

From Table 2 it can be seen that the mode of production of the artificially produced amorphous Si0 ₂ exerts a significant influence on the properties of the cores. The cores produced with an inorganic binder and the SiO ₂ according to the invention have higher strengths and higher core weights than the cores which contain the SiO ₂ not according to the invention.

Claims

claims

1. molding material mixture for the production of molds and cores for metal processing, comprising at least

· A refractory base molding material;

• an inorganic binder and

• Particulate amorphous Si0 ₂ preparable by melting crystalline

Quartz and rapid re-cooling.

2. Molding material mixture according to claim 1, wherein the particulate amorphous Si0 _{2 has} a BET of greater than or equal to 1 m ² / g and less than or equal to 35 m ² / g, preferably less than or equal to 17 m ² / g and particularly preferably less than or equal to 15 m ² / G. having.

3. Molding material mixture according to one of the preceding claims, wherein the average determined by dynamic light scattering particle size (diameter) of the particulate amorphous Si0 ₂ in the molding material mixture between 0.05 μηι and 10 μηι, in particular between 0.1 m and 5 μηι and more preferably between 0.1 m and 2 m.

4. Molding material mixture according to one of the preceding claims, wherein the molding material mixture contains the particulate amorphous Si0 ₂ in amounts of 0.1 to 2 wt.%, Preferably 0.1 to 1, 5 wt.%, Each based on the mold base material, and independently of this 2 to 60% by weight, particularly preferably 4 to 50% by weight, based on the weight of the binder, wherein the solids content of the binding agent is from 25 to 65% by weight, preferably from 30 to 60% by weight.

5. Molding material mixture according to one of the preceding claims, wherein the particulate amorphous Si0 _{2 used has} a water content of less than 10 wt.%, In particular less than 5 wt.% And particularly preferably less than 2 wt.% And is used independently in particular as a powder.

6. Molding material mixture according to one of the preceding claims, wherein the molding material mixture contains at most 1% by weight, preferably at most 0.2% by weight, of organic compounds.

7. Molding material mixture according to at least one of the preceding claims, wherein the inorganic binder is at least one water-soluble phosphate glass, a water-soluble borate and / or water glass and in particular a water glass with a molar modulus S1O2 / M2O of 1, 6 to 4.0, preferably 2, 0 to less than 3.5, with M being lithium, sodium and / or potassium.

8. Molding material mixture according to at least one of the preceding claims, wherein the molding material mixture contains 0.5 to 5 wt.% Water glass, preferably 1 to 3.5 wt.% Water glass, based on the molding material, wherein the solids content of the water glass 25 to 65 % By weight, preferably from 30 to 60% by weight.

9. Molding material mixture according to at least one of the preceding claims, wherein the molding material mixture further comprises surfactants, preferably selected from one or more members of the group of anionic surfactants, especially those having a sulfonic acid or sulfonate group, or in particular comprising oleyl sulfate, stearyl sulfate, palmitylsulfate , Myristylsulfate, laurylsulfate, decylsulfate, octylsulfate, 2-ethylhexylsulfate, 2-ethyloctylsulfate, 2-ethyldecylsulfate, palmitoleylsulfate, linolylsulfate, laurylsulfonate, 2-ethyldecylsulfonate, palmitylsulfonate, stearylsulfonate, 2-ethylstearylsulfonate, linolylsulfonate, hexylphosphate, 2-ethylhexylphosphate,

Capryl phosphate, lauryl phosphate, myristyl phosphate, palmityl phosphate,

Palmitoleyl phosphate, oleyl phosphate, stearyl phosphate, poly (1, 2-ethanediyl) phenol hydroxyphosphate, poly (1,2-ethanediyl) stearyl phosphate, and poly (1,2-ethanediyl) oleyl phosphate.

10. Molding material mixture according to claim 9, wherein the surfactant based on the weight of the refractory molding material in a proportion of 0.001 to 1 wt.%, Particularly preferably 0.01 to 0.2 wt.% Is contained in the molding material mixture.

1 1. molding material mixture according to at least one of the preceding claims, wherein the molding material mixture further contains graphite, preferably from 0.05 to 1 wt.%, In particular 0.05 to 0.5 wt.%, Based on the weight of the refractory mold base material.

12. Molding material mixture according to at least one of the preceding claims, wherein the molding material mixture further contains at least one phosphorus-containing compound, preferably from 0.05 and 1, 0 wt.%, Particularly preferably 0.1 and 0.5 wt.%, Based on the weight of the refractory base molding material.

13. Molding material mixture according to at least one of the preceding claims, wherein the particulate amorphous S1O2 is used as a powder, preferably anhydrous, apart from any of a possible moisture caused by room air.

14. Molding material mixture according to at least one of the preceding claims, wherein the molding material mixture is added to a curing agent, in particular at least one ester or phosphate compound.

15. A method of making molds or cores comprising:

Providing the molding material mixture according to at least one of claims 1 to 14 or providing the molding material mixture by combining the components of claims 1 to 14,

• introducing the molding material mixture into a mold, and

• curing of the molding material mixture.

16. The method according to claim 15, wherein the molding material mixture is introduced by means of a core shooter with the aid of compressed air into the mold and the mold is a mold and the mold with one or more gases is flowed through, in particular CO2.

17. The method of claim 15 or 16, wherein the molding material mixture is exposed to cure a temperature of at least 100 ° C for less than 5 min.

18. The method according to at least one of claims 15 to 17, wherein the hot-cured molding material mixture, in particular at 180 ° C, in the form of a shot at 5 bar Georg Fischer test bar of 220 mm x 22.36 x 22.36 mm, the under Use of the particulate amorphous S1O2, one by 1%, preferably 1, 5%, more preferably 2.0%, more preferably 2.5% and most preferably 3.0% increased core weight relative to a Georg Fischer test bars also 220 mm x 22.36 x 22.36 mm, prepared under the same conditions and with the same molding material mixture, but using Microsilica 971 U from Eikern instead of the particulate amorphous S1O2 according to one of claims 1 to 14.

19 .. Shape or core to produce according to at least one of claims 15 to 18.

20. Use of the molding material mixture according to at least one of claims 1 to 4 for the casting of aluminum, preferably also containing hollow microspheres in particular aluminosilicate hollow microspheres and / or

Borsilikatmikrohohlkugeln.