Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
  • B22C1/183—Sols, colloids or hydroxide gels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
  • B22C1/186—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents contaming ammonium or metal silicates, silica sols
  • B22C1/188—Alkali metal silicates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/12—Treating moulds or cores, e.g. drying, hardening
  • B22C9/123—Gas-hardening

Definitions

• the invention relates to a process for the preparation of molding compositions based on inorganic binders for the production of molds and cores for metal casting, comprising at least one refractory molding material, one or more lithium compounds, at least water glass as an inorganic binder and amorphous silica as an additive. Furthermore, the invention relates to a lithium-containing inorganic binder and a method for producing molds and cores using the molding material mixtures prepared by the above method.
• 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 present 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 must meet different requirements. In the casting process itself, they must first have sufficient strength and temperature resistance in order to be able to absorb the liquid metal in the cavity formed from one or more casting molds. After the start of the solidification process, the mechanical stability of the casting is ensured by a solidified metal layer which forms along the walls of the casting mold.
• the material of the casting mold must now decompose under the influence of the heat given off by the metal in such a way that it loses its mechanical strength, that is to say the cohesion between individual particles of the refractory material is removed. Ideally, the mold decays back to a fine sand that can be easily removed from the casting.
• the surface of the casting mold can be modified and matched to the properties of the metal to be processed.
• the size can be used to improve the appearance of the casting by creating a smooth surface because the size compensates for irregularities caused by the size of the grains of the molding material.
• defects develop on the surface of the casting, such as a scarred, rough or mineralized surface, chipping, pits, holes or pinholes, or white or black deposits are formed.
• the sizing may metallurgically affect the casting by, for example, selectively transferring additives to the casting at the surface of the casting via the sizing, which enhance the surface properties of the casting.
• the sizings form a layer which chemically isolates the casting mold from the liquid metal during casting. This prevents any adhesion between the casting and the casting mold so that the casting can be easily removed from the casting mold.
• the sizing can also be used to selectively control the heat transfer between the liquid metal and the casting mold in order, for example, to effect the formation of a specific metal structure by the cooling rate.
• a size usually consists of an inorganic refractory and a binder which are dissolved or slurried in a suitable solvent, for example water or alcohol. If possible, one would dispense with the use of alcohol-containing sizes and instead use aqueous systems, since in the course of the drying process, the organic solvents cause emissions.
• a suitable solvent for example water or alcohol.
• 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, i.d.R. at room temperature or at a temperature caused by any 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.
• hot processes the molding material mixture after shaping is e.g. heated by the heated mold to a sufficiently high temperature to expel the solvent contained in the binder and / or to initiate a chemical reaction by which the binder is cured.
• organic binders Due to their technical properties, organic binders have currently been economically viable. the greater importance in the market. Regardless of their composition, however, they have the disadvantage that they decompose during casting and thereby sometimes emit considerable amounts of pollutants such as benzene, toluene and xylene. In addition, the casting of organic binder usually leads to odor and smoke pollution. In some systems, undesirable emissions even occur during the production and / or storage of the molds. Although emissions could be reduced over the years due to binder development, they can not be completely avoided with organic binders.
• the thermal curing of water glass deals with the US 5,474,606 in which a binder system consisting of alkali water glass and aluminum silicate is described.
• inorganic binders have relatively low strengths. This is especially evident immediately after the removal of the mold from the tool.
• the strengths at this time which are also referred to as hot strengths, but are particularly important for the production of complicated and / or thin-walled moldings and their safe handling.
• the cold strength which is the strength after complete curing of the mold, is an important criterion, so that the desired casting can be produced with the required dimensional accuracy.
• filigree hollow molds as described, for example, in US Pat. are required for the production of complicated and / or thin-walled moldings, not sufficiently compacted.
• inorganic binders Another significant disadvantage of inorganic binders is their comparatively low storage stability at elevated air humidity.
• the moisture content of the air is given as a percentage for a specific temperature by the relative humidity or in g / m 3 by the absolute humidity.
• the storage stability of molds, which were prepared by hot curing and using inorganic binder decreases significantly, especially at an absolute humidity of 10 g / m 3 , which is characterized by an increased decrease in the strengths of, in particular produced by hot curing, casting molds during storage makes noticeable.
• This effect is attributable, in particular in the case of hot curing, to a reverse reaction of the polycondensation with the water of the air, which leads to a softening of the binder bridges.
• the decrease in strength under such storage conditions is sometimes associated with the occurrence of so-called storage cracks. Due to the decrease in strength, the structure of the casting mold is weakened, which in places can lead to slight tearing of the casting mold in areas of high mechanical stress.
• cores which have been hot-cured using an inorganic binder have low resistance to water-based resin coatings, e.g., as compared to organic binders. Simple. That is, their strengths are enhanced by the coating e.g. fall sharply with an aqueous sizing and this method is difficult to implement in practice.
• the EP 1802409 B1 discloses that higher strengths and improved storage stability can be realized through the use of a refractory mold base, a water glass based binder and a proportion of particulate amorphous silica. As a curing method, in particular the hot curing is described in detail. Another possibility for increasing the storage stability is the use of organosilicon compounds, such as in US 6017978 is set forth.
• the improvement in the moisture resistance of water glass binders is described in the DE 2652421 A1 and the US 4347890 described.
• the DE 2652421 A1 deals in particular with various processes for the preparation of lithium-containing binders based on aqueous alkali silicate solutions.
• the in the DE 2652421 A1 Binders described are characterized by a weight ratio Na 2 O and / or K 2 O: Li 2 O: SiO 2 in the range of 0.80 - 0.99: 0.01 - 0.20: 2.5 - 4.5, which corresponds to a molar ratio of Li 2 O / M 2 O of 0.02-0.44 and a molar ratio SiO 2 / M 2 O of 1.8-8.5.
• [M 2 O] denotes the sum of the amounts of alkali metal oxides.
• the binders described therein have improved water resistance, that is, they are less prone to absorbing water from the atmosphere, as demonstrated by gravimetric studies. Although the production of foundry molds is given as a possible application, no information is given on the strength of the molds produced, let alone their storage stability.
• the US 4347890 describes a method for producing an inorganic binder, consisting of an aqueous sodium silicate solution and a solution of a lithium compound, in which case in particular lithium hydroxide and lithium silicate are preferred.
• the lithium compound is added to increase the moisture stability of the binder.
• the invention therefore an object of the invention to provide a molding material mixture or a binder for the production of molds for metal processing available, which meet the requirements described above (a) to (e).
• the molding material mixture is characterized by the fact that the casting molds produced from it have an increased storage stability with a simultaneously high level of strength.
• the casting molds produced with the molding material mixture are more stable than water-based molding coatings, ie molding coatings with a water content of at least 50% by weight of the carrier liquid.
• the molding mixtures allow the foundries to produce casting molds with a sufficient storage stability and increased stability to water-based molding coatings, without compromising their strength or the flowability of the molding material mixture.
• the molar ratio [Li 2 O active ] / [M 2 O] in the molding material mixture is 0.030 to 0.17, preferably 0.035 to 0.16 and particularly preferably 0.040 to 0.14, and the molar ratio [SiO 2 ] / [ M 2 O] is 1.9 to 2.47, preferably 1.95 to 2.40 and more preferably 2 to 2.30.
• Component (A) is called additive.
• component (B) including component (A) has a molar ratio [Li 2 O active ] / [M 2 O] of 0.030 to 0.17, preferably 0.035 to 0.16 and more preferably 0.040 to 0.14 and a molar ratio [SiO 2 ] / [M 2 O] of 1.9 to 2.47, preferably 1.95 to 2.40 and more preferably from 2 to 2.30.
• the component additive consists of one or more solids, in particular in the form of a free-flowing powder.
• all lithium compounds contributing to the [Li 2 O active ] content are present in component B.
• molding material As a refractory molding material (hereinafter abbreviated molding material (s)), the usual materials for the production of 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 use the highest possible proportion of regenerated used sand.
• molding material 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.
• the average diameter of the molding base materials is generally between 100 ⁇ m and 600 ⁇ m, preferably between 120 ⁇ m and 550 ⁇ m, and particularly preferably between 150 ⁇ m and 500 ⁇ m
• the particle size can be determined, for example, by screening according to DIN 66165 (Part 2).
• 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 Aluminiumiumsilikatmikrohohlkugeln (so-called Microspheres).
• Such aluminosilicate hollow microspheres 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”.
• the preferred proportion of artificial molding bases is at least about 3% by weight, more preferably at least about 5% by weight, more preferably at least about 10% by weight, preferably at least about 15% by weight, most preferably at least about 20% % By weight, in each case based on the total amount of the refractory molding material.
• the molding material mixture comprises an inorganic binder based on alkali silicate solutions.
• alkali metal silicates in particular lithium, sodium and potassium silicates, which are also referred to as water glass, find application as binders in other fields, such as in construction.
• the preparation of water glass is e.g. large-scale by melting quartz sand and alkali carbonates at temperatures of 1350 ° C to 1500 ° C.
• the water glass is initially in the form of a piece of solid glass, which is dissolved by the application of temperature and pressure in water.
• Another method for the production of water glasses is the direct dissolution of quartz sand with caustic soda.
• the resulting alkali metal silicate solution can then be adjusted to the desired molar ratio [SiO 2] / [M 2 O] by addition of alkali metal 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.
• 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 may also be based on water glasses containing more than one of said alkali ions.
• the lithium-containing binder or the lithium-containing molding material mixture is prepared by adding a lithium compound, namely amorphous lithium silicate, Li 2 O and / or LiOH to an inorganic binder.
• a lithium compound namely amorphous lithium silicate, Li 2 O and / or LiOH
• Amorphous lithium silicate, Li 2 O and LiOH also include their hydrates.
• the lithium compound can be added both in powder form and in an aqueous solution or suspension.
• the lithium-containing binder is a homogeneous solution of the lithium compounds described above in the binder according to the invention.
• the addition of the lithium compound can also take place exclusively via the component (A), additive, to the molding material mixture, but it is preferred to add the lithium compound at least partially, preferably exclusively, via the component (B), inorganic binder.
• the component (B) of inorganic binder according to the invention is distinguished from the prior art by a low viscosity and thus high flowability of the molding material mixture produced therewith.
• the composition of the inorganic binder component according to the invention is given by the proportion of SiO 2 , K 2 O, Na 2 O, Li 2 O and H 2 O.
• the molar ratio [Li 2 O active ] / [M 2 O] of the molding material mixture, the inorganic binder component and the additive or the inorganic binder alone is greater than or equal to 0.030, preferably greater than or equal to 0.035 and particularly preferably greater than or equal to 0.040.
• the upper limits are less than or equal to 0.17, preferably less than or equal to 0.16, and most preferably less than or equal to 0.14. The aforementioned upper and lower limits can be combined as desired.
• the molar ratio [SiO 2 ] / [M 2 O] of the molding material mixture, the components inorganic binder and additive or the inorganic binder alone is greater than or equal to 1.9, preferably greater than or equal to 1.95, and particularly preferably greater than or equal to 2.
• the upper limit for the molar ratio [SiO 2 ] / [M 2 O] is less than or equal to 2.47, preferably less than or equal to 2.40, and particularly preferably less than or equal to 2.30.
• the aforementioned upper and lower limits can be combined as desired.
• the inorganic binders preferably have a solids content of greater than or equal to 20% by weight, preferably greater than or equal to 25% by weight, more preferably greater than or equal to 30% by weight and particularly preferably greater than or equal to 33% by weight.
• the upper limits for the solids content of the preferred water glasses are less than or equal to 55% by weight, preferably less than or equal to 50% by weight, more preferably less than or equal to 45% by weight and particularly preferably less than or equal to 42% by weight.
• the solids content is defined as the weight fraction of M 2 O and SiO 2 .
• the inorganic binder according to the invention contains both amorphous lithium and sodium and potassium silicates.
• Potassium-containing water glasses have compared to pure sodium or.
• mixed lithium sodium water glasses have a lower viscosity.
• the mixed according to the invention particularly preferred, mixed lithium-sodium-potassium water glasses thus combine the advantage of increased moisture stability at the same time a high level of strength and a further reduction in viscosity.
• Low viscosity values are indispensable for automated mass production in order to ensure a good flowability of the molding material mixture, thus enabling complex core geometries.
• the potassium content of the inorganic binder according to the invention must not be too high, since an excessively high potassium content has a negative effect on the storage stability of the casting molds produced.
• the molar [K 2 O] / [M 2 O] ratio in the inorganic binder, in particular in component B, is preferably greater than 0.03, particularly preferably greater than 0.06 and particularly preferably greater than 0.1.
• the upper limit of the molar ratio [K 2 O] / [M 2 O] results in a value of less than or equal to 0.25, preferably less than or equal to 0.2, and particularly preferably less than or equal to 0.15.
• the aforementioned upper and lower limits can be combined as desired.
• [K 2 O] the following compounds are finally included: amorphous potassium silicates, potassium oxides and potassium hydroxides, including their hydrates.
• greater than 0.5% by weight, preferably greater than 0.75% by weight and particularly preferably greater than 1% by weight, of the binder according to the invention are used.
• the upper limits here are less than 5% by weight, preferably less than 4% by weight and particularly preferably less than 3.5% by weight.
• The% by weight refers to the inorganic binders with a solids content as indicated above, i. the% by weight includes 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 O has the meaning given above.
• the binder according to the invention may additionally contain alkali borates.
• Alkaline borates as constituents of water glass binders are used, for example, in GB 1566417 discloses where they serve to complex carbohydrates.
• Typical addition levels of the alkali borates are from 0.5% to 5% by weight, preferably from 1% to 4% by weight and more preferably from 1% to 3% by weight, based on the weight of the binder.
• a proportion of a particulate amorphous SiO 2 in the form of the additive component is added to the molding material mixture in order to increase the strength level of the casting molds produced with such molding material mixtures.
• An increase in the strengths of the casting molds, in particular the increase in hot strengths, can be advantageous in the automated production process.
• the particulate amorphous silica has a particle size of preferably less than 300 microns, preferably less than 200 microns, more preferably less than 100 microns. The particle size can be determined by sieve analysis.
• the sieve residue of the particulate amorphous SiO 2 when passing through a 125 ⁇ m mesh (120 mesh) sieve is preferably not more than 10% by weight, more preferably not more than 5% by weight, and most preferably not more than 2%. %.
• 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.
• 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.
• the amorphous SiO 2 is used as a pourable powder.
• amorphous SiO 2 both synthetically produced and naturally occurring silicas can be used.
• the latter known for example from DE 102007045649 , but are not preferred because they usually contain not inconsiderable crystalline components and are therefore classified as carcinogenic.
• amorphous SiO 2 Synthetically , non-naturally occurring amorphous SiO 2 is understood, but the preparation comprises a (man-induced) chemical reaction, for example the production of silica sols by ion exchange processes from alkali silicate solutions, the precipitation of alkali metal silicate solutions, the flame hydrolysis of silicon tetrachloride or the reduction of silica sand with coke in the electric arc furnace in the production of ferrosilicon and silicon.
• the amorphous SiO 2 produced by the latter two methods is also referred to as pyrogenic SiO 2 .
• synthetic amorphous SiO 2 is only precipitated silica ( CAS-No. 112926-00-8 ) and flame-hydrolysed SiO 2 (pyrogenic silica, fumed silica, CAS-No. 112945-52-5 ), while the product resulting from the production of ferrosilicon or silicon is merely understood as amorphous SiO 2 (silica fume, microsilica, CAS-No. 69012-64-12 ) referred to as.
• the product formed in the production of ferrosilicon or silicon is also understood as a synthetic amorphous SiO 2 .
• fused quartz powder (mainly amorphous SiO 2 ), which has been prepared by melting and rapid re-cooling from crystalline quartz, so that the particles are spherical and not splintered (see DE 102012020511 ).
• the average primary particle size of the synthetic amorphous silicon dioxide may be between 0.05 ⁇ m and 10 ⁇ m, in particular between 0.1 ⁇ m and 5 ⁇ m and particularly preferably between 0.1 ⁇ m and 2 ⁇ m.
• the primary particle size can be determined, for example, by means of dynamic light scattering (eg Horiba LA 950) and checked by scanning electron microscope images (SEM images with, for example, Nova NanoSEM 230 from FEI).
• SEM images with, for example, Nova NanoSEM 230 from FEI.
• the samples are dispersed in water in an ultrasonic bath prior to particle size measurements.
• details of the primary particle shape up to the order of 0.01 ⁇ m could be visualized with the aid of SEM images.
• the SiO 2 samples were dispersed in distilled water for SEM measurements and then coated on a copper tape-covered aluminum holder before the water was evaporated.
• the mean primary particle size is preferably between 0.05 ⁇ m and 10 ⁇ m, measured with dynamic light scattering (for example Horiba LA 950) and, if necessary, checked by scanning electron microscope images.
• 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 preferably between 1 and 35 m 2 / g, preferably between 1 and 17 m 2 / g and particularly preferably between 1 and 15 m 2 / g. If necessary.
• the products can also be mixed, for example to obtain specific mixtures with certain particle size distributions.
• 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.
• the particulate amorphous SiO 2 are used, preferably between 0.1% by weight and 1.8% by weight, particularly preferably between 0.1% by weight. % and 1.5 wt.%, in each case based on the molding material.
• the ratio of water glass to particulate metal oxide, and particularly 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.
• 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, ie the molding base should be easily removed after casting from cavities of the mold.
• the particulate amorphous SiO 2 in the molding material mixture is preferably in a proportion of 2 to 60 wt.%, Particularly preferably 3 to 55 wt.% And particularly preferably 4 to 50% by weight.
• the additive component barium sulfate may be added to further improve the surface of the casting, especially in light metal casting, such as aluminum casting.
• the barium sulfate can be synthetically produced as well as natural barium sulfate, ie added in the form of minerals containing barium sulfate, such as barite or barite.
• the additive component of the molding material mixture may further comprise at least aluminum oxides and / or aluminum / silicon mixed oxides in particulate form or metal oxides of aluminum and zirconium in particulate form, as described in US Pat DE 102012113073 or the DE 102012113074 to that extent, the additives disclosed therein are also considered part of the disclosure of the present patent.
• the additive component of the molding material mixture may comprise a phosphorus-containing compound.
• 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 addition levels are in the WO 2008/046653 A1 described in detail and this is so far as the disclosure of the present protective right asserted.
• the preferred proportion of the phosphorus-containing compound, based on the mold base, is between 0.05 and 1.0 wt .-%, and preferably between 0.1 and 0.5 wt .-%.
• the molding material mixture with the additive component organic compounds may be added.
• organic compounds may be advantageous for specific applications - for example, to regulate the thermal expansion of the cured molding material mixture. However, such is not preferred, as this in turn is associated with emissions of CO 2 and other pyrolysis products.
• the additive component of the molding material mixture contains a proportion of platelet-shaped lubricants, in particular graphite or MoS 2 .
• platelet-shaped lubricants in particular graphite or MoS 2 .
• the amount of added platelet-shaped lubricant, in particular graphite is preferably 0.05 to 1 wt.%, Particularly preferably 0.05 to 0.5 wt.%, Based on the molding material.
• the molding material mixture may also comprise further additives.
• release agents can be added which facilitate the detachment of the cores from the mold. Suitable release agents are e.g. 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.
• silanes can also be added to the molding material mixture, for example in order to further increase the storage stability of the cores and / or their resistance to water-based molding coatings.
• the molding material mixture therefore contains a proportion of at least one silane.
• silanes for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes can be used.
• silanes examples include ⁇ -aminopropyltrimethoxysilane, ⁇ -hydroxypropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, ⁇ -mercaptopropyltrimethoxysilane, ⁇ -glycidoxypropyltrimethoxysilane, ⁇ - (3,4-epoxycycloherxyl) trimethoxysilane, N- ⁇ - ( Aminoethyl) - ⁇ -aminopropyltrimethoxysilane and their triethoxyanalogous compounds.
• 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.
• the refractory molding base material is placed in a mixer and then 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 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.
• 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 entirety of all individual liquid components, the latter being able to be added to the molding material mixture jointly or else successively. In practice, it has proven useful to first add the (other) solid components to the refractory base molding material, to mix and only then to supply the liquid component (s) of the mixture, and then to mix again.
• the molding material mixture is then brought into the desired shape.
• customary methods are used for the shaping.
• 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 free-flow the molding material mixture from the mixer into the mold and to compact it there by shaking, stamping or pressing.
• the molding material mixture can in principle be cured by all curing methods known for water glasses, such as hot curing or by the CO 2 process.
• a further development of the CO 2 process, which involves a combination of CO 2 and air fumigation, is described in the DE 102012103705.1 described and also represents a suitable method for curing the molding material mixture.
• the CO 2 or the air or both gases can also be heated in this process, for example, to temperatures of up to 100 ° C.
• Another method for curing the molding material mixture is curing by means of liquid (e.g., organic esters, triacetin, etc.) or solid catalysts (e.g., suitable aluminum phosphates).
• liquid e.g., organic esters, triacetin, etc.
• solid catalysts e.g., suitable aluminum phosphates
• rapid prototyping Another method for producing the casting molds is the so-called rapid prototyping.
• This technology differs in particular in that the molding material mixture is not compacted by pressure into the desired shape, but first the solid components such as the mold base material and possible additives are applied in layers. In the next step, the liquid component of the molding material mixture is specifically printed on the sand / additive mixture. The mold is then made by curing the "printed" areas.
• hardening in the area of rapid prototyping technology takes place, inter alia, by microwave curing, by hardening by means of a liquid or solid catalyst or by drying in an oven or in air. Further details on rapid prototyping technology can be found in the EP 0431924 B1 and US 6610429 B2 ,
• water is removed.
• condensation reactions between silanol groups are presumably also initiated so that crosslinking of the water glass occurs.
• the heating can be carried out, for example, in a mold, which preferably has a temperature of 100 to 300 ° C, particularly preferably from 120 ° C to 250 ° C.
• a gas for example air
• this gas preferably having a temperature of from 100 to 180.degree. C., particularly preferably from 120 to 150.degree.
• Further details of the curing of the mold are in the EP 1802409 B1 described in detail and this is also considered as part of the disclosure of the present patent.
• the removal of the water from the molding material mixture can also be carried out in such a way that the heating of the molding material mixture is effected by irradiation of microwaves.
• the irradiation of the microwaves can be made after the mold has been removed from the mold.
• the casting mold must already have sufficient strength.
• this can be achieved, for example, by curing at least one outer shell of the casting mold already in the molding tool.
• the removal of the water from the molding material mixture can also be carried out in such a way that the heating of the molding material mixture is effected by irradiation of microwaves. It is e.g.
• the molding base material with the solid, powdery component (s)
• this mixture in layers on a surface and print the individual layers using a liquid binder component, in particular with the aid of a waterglass, wherein the layered application of the solid mixture in each case one Printing process using the liquid binder follows.
• the entire mixture can be heated in a microwave oven
• 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.
• the cores produced from these molding material mixtures show good disintegration after casting, so that the molding material mixture can be removed again after casting, even from narrow and angular sections of the casting.
• the moldings produced from the molding material mixtures are generally suitable for casting metals, such as light metals, non-ferrous metals or ferrous metals.
• the casting mold has a very high stability under mechanical stress, so that even thin-walled sections of the casting mold can be realized without these being deformed by the metallostatic pressure during the casting process.
• Another object of the invention is therefore a mold, which was obtained by the inventive method described above.
• Tables 1, 2, 3 and 4 give an overview of the composition of the different inventive or non-inventive waterglass binders, which were tested in the present study.
• the preparation of the waterglass binder is carried out by mixing the chemicals indicated in Table 1 or 2, so that a homogeneous solution is present. Their use was only one day after their preparation to ensure their homogeneity.
• the concentration of the alkali oxides and of [SiO 2 ] in the waterglass binder used and their molar ratio and molar ratio [Li 2 O active ] / [M 2 O] are summarized in Tables 4 and 5.
• Table 3 gives an overview of the molding mixtures in which the lithium compound was added via the additive component. The addition of the solid lithium compound was carried out together with the amorphous SiO 2 (see 2.1).
• 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 prevent premature reaction with the CO 2 present in the air.
• the molding material mixtures were introduced from the storage bunker into the mold by means of compressed air (5 bar).
• the residence time in the hot mold for curing the mixtures was 35 seconds.
• hot air (2 bar, 100 ° C on entering the tool) was passed through the mold during the last 20 seconds. The mold was opened and the test bars removed.
• the test bars were placed in a Georg Fischer Strength Tester equipped with a 3-point flexure, 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 10 seconds after removal (hot strengths) and also approx. 24 hours after preparation (cold strengths).
• the storage stability was investigated by the cores then for a further 24 hours in a climatic chamber (Rubarth Apparate GmbH) at 30 ° C and a relative humidity of 60%, which corresponds to an absolute humidity of 18.2 g / m 3 , were stored and again their flexural strength was measured.
• the accuracy with which the predefined values for temperature and humidity were generated by the climate chamber was checked regularly with a calibrated testo 635 humidity / temperature / pressure dew point measuring instrument from testo.
• Examples 1.1 to 1.6 differ only in terms of their molar ratio [Li 2 O active ] / [M 2 O]
• the binders of Examples 1.7 to 1.12 have a different molar ratio at a constant value for the molar ratio [Li 2 O active ] / [M 2 O].
• the comparison of Examples 1.1 to 1.6 thus clarifies the influence of the molar ratio [Li 2 O active ] / [M 2 O] on the strength values, while Examples 1.7 to 1.12 illustrate the influence of the molar ratio [SiO 2 ] / [M 2 O] reflect.
• Examples 1.1 to 1.6 show no difference, while the cold strengths with increasing molar ratio [Li 2 O active ] / [M 2 O] a significant deterioration of the values by up to 40 N / cm 2 is recorded.
• Examples 1.1 to 1.6 illustrate that the sand cores produced with these binders have a high storage stability with a simultaneously high cold strength. A further increase in the molar ratio does not lead to a significant improvement in storage stability, while the cold strengths decrease.
• Example 3.3 illustrates the effect of the invention for molding material mixtures in which the lithium compound was added as an additive. Compared with the non-inventive examples 3.1 and 3.2, which contain no lithium, the storage stability of the cores produced with these binders is significantly increased, while the cold strengths are still at a good level.
• the increasing molar ratio of the binders has a clearly positive effect on the storage stability of the sand cores produced. While for examples 1.11 to 1.13, the strength of the cores after storage in the climatic chamber increase with increasing molar ratio, but due to the opposite trend of decreasing cold strengths no absolute improvement can be found. Thus, for the molar ratio [SiO 2 ] / [M 2 O], there is an optimum that the binders of composition 1.9 to 1.12 have. A lower molar ratio leads to a significantly reduced storage stability, while a further increase in the molar ratio has a negative influence on the cold strengths.
• the viscosity was measured on a Brookfield viscometer equipped with a small sample adapter. In each case about 15 g of the binder to be tested were transferred to the viscometer and measured their viscosity with the spindle 21 at a temperature of 25 ° C and a speed of 100 revolutions per minute. The results of the measurements are summarized in Table 7.
• Examples 1.1 to 1.6 differ only in terms of their molar ratio [Li 2 O active] / [M 2 O]
• the binders of Examples 1.7 to 1.12 have a different molar ratio [SiO 2 ] / [M 2 O] a constant value for the molar ratio [Li 2 O active ] / [M 2 O].
• the comparison of Examples 1.1 to 1.6 thus illustrates the influence of the molar ratio [Li 2 O active ] / [M 2 O] on the viscosity, while Examples 1.7 to 1.12 reflect the influence of the molar ratio.
• the binders according to the invention of Examples 1.2 to 1.6, 1.9 to 1.12 and 2.2 to 2.3 represent an improvement over the prior art, since the sand cores produced with them have good storage stability with simultaneously high cold strengths.
• the binders according to the invention are distinguished by low viscosity values and, owing to their comparatively low lithium content, by low production costs.
• the waterglass binders 2.1. and 1.3 the preparation of which was described in 1. used.
• the preparation of the molding material mixture or the test bars used is under 2.1. and 2.2. described.
• the addition amounts are identical to those in 2.2. and particulate amorphous silica POS BW 90 LD (supplier: Possehl Erz sparkler GmbH) was also used.
• the cores were stored at room temperature for 24 hours for complete cure and then immersed in a sizing for 1 to 4 seconds.
• the sized, ie coated with a thin film of size, cores were immediately dried in a drying oven (Model FED 115, Binder) at 100 ° C.
• An air change of 10 m 3 / h was achieved via an air supply pipe.
• the flexural strengths of the sized test bars were determined after 2, 6, 12 and 24 minutes, respectively, after the start of the drying process. Table 8 summarizes the results of the strength tests. The values given here are averages of 10 cores each. For comparison, the flexural strength of untreated test bars was determined. ⁇ b> Table 8 ⁇ / b> Bending strengths [N / cm 2 ] of the test bars produced Dwell time [min] in a drying oven at 100 ° C / after removal from the sizing bath Water glass binder 2.1 not according to the invention Water glass binder 1.3 according to the invention 0 / unsatisfactory 415 385 2 / finished 280 260 6 / settled 90 230 12 / settled 150 235 24 / finished 255 250

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