METHOD FOR PRODUCING CASTING MOLDS, CORES AND BASIC MOLD MATERIALS REGENERATED THEREFROM

Abstract

What are described is a process for producing casting molds, cores and mold base materials regenerated therefrom, a mixture for combination with a solution or dispersion comprising waterglass for production of casting molds and/or cores, a molding material mixture, a mold base material mixture, and a casting mold or a core. What is also described is the corresponding use of an amount of particulate sheet silicates having a d.sub.90 of less than 45 μm or a corresponding mixture as additive for production of a molding material mixture comprising waterglass and particulate amorphous silicon dioxide, which is cured by chemical reaction of constituents of the molding material mixture with one another, in the production of a casting mold or a core, to facilitate the breakdown and/or to increase the regeneratability of the casting mold or core.

Claims

1. A process for producing casting molds, cores and mold base materials regenerated therefrom, comprising the following steps for production of a casting mold or a core: providing or producing a molding material mixture comprising a mold base material a solution or dispersion comprising waterglass 0.1% to 3% by weight of particulate amorphous silicon dioxide and, to facilitate the breakdown and/or to increase the regeneratability of the casting mold or the core, one or more particulate sheet silicates in a total amount of 0.05% to 1.5% by weight, where the d.sub.90 of the total amount of the sheet silicates is less than 45 μm, where the percentages are each based on the total mass of the molding material mixture, shaping the molding material mixture, curing the molding material mixture by chemical reaction of constituents of the molding material mixture with one another, so as to result in the casting mold or the core.

2. The process as claimed in claim 1, wherein the waterglass in the molding material mixture has a modular SiO.sub.2/M.sub.2O modulus in the range from 1.6 to 4.0, preferably in the range from 1.8 to 2.5, where M.sub.2O denotes the total amount of lithium oxide, sodium oxide and potassium oxide.

3. The process as claimed in claim 1, wherein the average diameter of the mold base material particles is in the range from 100 μm to 600 μm.

4. The process as claimed in claim 1, wherein the molding material mixture comprises fumed particulate amorphous silicon dioxide and/or the particulate amorphous silicon dioxide is a fumed particulate amorphous silicon dioxide.

5. The process as claimed in claim 1, wherein the one or more particulate sheet silicates are present in the molding material mixture in a total amount of 0.1% to 0.4% by weight, preferably of 0.1% to 0.3% by weight, where the d.sub.90 of the total amount of the sheet silicates is less than 45 μm.

6. The process as claimed in claim 1, comprising the providing or producing of a molding material mixture comprising a mold base material, a solution or dispersion comprising waterglass, one or more particulate sheet silicates in a total amount of 0.1% to 0.4% by weight, preferably 0.1% to 0.3% by weight, where the d.sub.90 of the total amount of the sheet silicates is less than 45 μm, 0.3% to 3% by weight, preferably 0.57% to 0.77% by weight, of particulate amorphous silicon dioxide, preferably fumed particulate amorphous silicon dioxide, and 0.01% to 1% by weight of graphite, where the percentages are each based on the total mass of the molding material mixture.

7. The process as claimed in claim 1, wherein the mold base material comprises quartz sand, preferably at least 50% by weight, more preferably at least 80% by weight, of quartz sand, based on the total mass of the mold base material, and/or wherein the curing of the molding material mixture is assisted or brought about by heating the shaped molding material mixture, preferably by heating in a heated shaping mold, preferably in a heated shaping mold with a temperature in the range from 100 to 300° C., and/or by gassing with hot air, where the heating and/or the gassing preferably establishes a temperature in the range from 120 to 180° C. at least in regions of the shaped molding material mixture, is assisted or brought about by the hydrolysis of an ester, where at least one of the esters is preferably selected from the group consisting of the intramolecular or intermolecular reaction products of an alcohol and an acid, where the alcohol is selected from the group consisting of C1-C8 monoalcohols, C1-C8 dialcohols, preferably C2-C8 dialcohols, and C1-C8 trialcohols, preferably C3-C8 trialcohols, preferably selected from the group consisting of ethylene glycol, propane-1,2-diol and glycerol, and the acid is selected from the group consisting of organic C2-C8 monocarboxylic acids, organic C2-C8 dicarboxylic acids, organic C2-C8 tricarboxylic acids, preferably organic C4-C8 tricarboxylic acids, and inorganic acids, preferably selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, succinic acid, malonic acid, phosphoric acid, sulfuric acid, boric acid and carbonic acid, where at least one of the esters is preferably propylene carbonate or y-butyrolactone, or is assisted or brought about by gassing of the shaped molding material mixture with a gas or gas mixture containing less than 1 mol % of CO.sub.2.

8. The process as claimed in claim 1, wherein the casting mold produced or the core produced is heated temporarily at least in regions to a temperature of >900° C. such that the breakdown is subsequently facilitated, preferably with heating to a temperature of <1600° C., more preferably to a temperature in the range between 900° C. and 1600° C., and/or wherein the casting mold produced or the core produced is heated temporarily at least in regions, by contacting with a metal melt in the casting operation, to a temperature of >900° C. such that the breakdown is subsequently facilitated, preferably with heating to a temperature of <1600° C., more preferably to a temperature in the range between 900° C. and 1600° C., preferably using a metal melt consisting of iron, iron alloys, steel, steel alloys, brass or brass alloys.

9. The process as claimed in claim 8 for production of a regenerated mold base material from the casting mold produced or the core produced after the heating, comprising the following additional steps: acting mechanically on the casting mold produced or the core produced, such that the casting mold or core breaks down, producing the regenerated mold base material from the broken-down casting mold or the broken-down core, preferably comprising the separating-off and removing of dust, wherein the separating-off preferably comprises a physical separation.

10. The process as claimed in claim 1, wherein the molding material mixture provided or produced contains a proportion of regenerated mold base material produced from a casting mold produced or a core produced after a heating, comprising the following additional steps: acting mechanically on the casting mold produced or the core produced, such that the casting mold or core breaks down, producing the regenerated mold base material from the broken-down casting mold or the broken-down core, preferably comprising the separating-off and removing of dust, wherein the separating-off preferably comprises a physical separation and/or wherein the shaping of the molding material mixture and/or the curing of the molding material mixture is effected by means of a 3D printer and/or wherein the shaping of the molding material mixture is effected in a 3D printing method and the curing of the molding material mixture is effected during the 3D printing operation and/or after the 3D printing operation.

11. A mixture for combination with a solution or dispersion comprising waterglass for production of casting molds and/or cores, comprising 10% to 98% by weight of particulate amorphous silicon dioxide, preferably fumed particulate amorphous silicon dioxide, 0% to 15% by weight of graphite, one or more particulate mixed metal oxides, each comprising at least one oxide of aluminum and/or at least one oxide of zirconium, in a total amount of 0% to 80% by weight, and, to facilitate the breakdown and/or to increase the regeneratability of the casting mold or the core, one or more particulate sheet silicates in a total amount of 2% to 80% by weight, where the d.sub.90 of the total amount of sheet silicates is less than 45 m, where the percentages are based on the total mass of the mixture, preferably comprising 25% to 95% by weight, preferably 40% to 95% by weight, of particulate amorphous silicon dioxide, preferably fumed particulate amorphous silicon dioxide, 1.5% to 12.5% by weight, preferably 1.5% to 6% by weight, of graphite, one or more particulate mixed metal oxides, each comprising at least one oxide of aluminum and/or at least one oxide of zirconium, in a total amount of 0% to 65.5% by weight, preferably 0% to 45% by weight, one or more particulate sheet silicates in a total amount of 5% to 50% by weight, preferably 15% to 50% by weight, where the d.sub.90 of the total amount of sheet silicates is less than 45 μm, where the percentages are based on the total mass of the mixture, where the mixture is more preferably a solid-state mixture or a dispersion composed of two or more phases.

12. A multicomponent binder system comprising, as spatially separate or mutually mixed components, (A) mixture as claimed in claim 11, (B) a solution or dispersion comprising waterglass, preferably a waterglass having a modular SiO.sub.2/M.sub.2O modulus in the range from 1.6 to 4.0, preferably 1.8 to 2.5, where M.sub.2O denotes the total amount of lithium oxide, sodium oxide and potassium oxide.

13. A molding material mixture comprising (A) mixture as claimed in claim 11, (B) a solution or dispersion comprising waterglass, preferably a waterglass having a modular SiO.sub.2/M.sub.2O modulus in the range from 1.6 to 4.0, preferably 1.8 to 2.5, where M.sub.2O denotes the total amount of lithium oxide, sodium oxide and potassium oxide and as component (D) a refractory mold base material, preferably comprising, as refractory mold base material or as constituent of the refractory mold base material, a regenerated mold base material.

14. The method of an amount of particulate sheet silicates having a d.sub.90 of less than 45 μm or of a mixture as claimed in claim 11 as additive for production of a molding material mixture comprising waterglass and particulate amorphous silicon dioxide, preferably fumed particulate amorphous silicon dioxide, which is cured by chemical reaction of constituents of the molding material mixture with one another, in the production of a casting mold or a core, to facilitate the breakdown and/or to increase the regeneratability of the casting mold or core.

Description

EXAMPLES

[0295] There follows a detailed description of the invention by examples.

Examples C1-C5 and I1-I5

[0296] 1. Compositions and Sample Production: [0297] Firstly, a total of 5 cores of the invention that had been produced by a process of the invention from a molding material mixture of the invention (I1 to I5) were examined, as were five noninventive comparative examples (C1 to C5). The compositions of the respective molding material mixtures from which the corresponding cores were produced are summarized in table 1.

TABLE-US-00001 TABLE 1 Composition of the molding material mixtures used. All values are reported in parts by weight. Example Mold base material.sup.a) Binder.sup.b) Additive.sup.c) Silicate.sup.d) C1 100 2.2 — — C2 100 2.2 1.0 — C3 100 2.2 — 0.3 (silicate-1) C4 100 2.2 1.0 0.3 (silicate-X) C5 100 2.2 1.0 0.3 (silicate-Y) I1 100 2.2 1.0 0.3 (silicate-2) I2 100 2.2 1.0 0.3 (silicate-3) I3 100 2.2 1.0 0.3 (silicate-4) I4 100 2.2 1.0 0.3 (silicate-5) I5 100 2.2 1.0 0.3 (silicate-1) .sup.a)The mold base material used in each case was quartz sand (coarse foundry silica sand 1K 0.20/0.315/0.40) from Grudzen Las. .sup.b)The binder used in each case was an alkali waterglass having a molar SiO.sub.2:M.sub.2O modulus (M.sub.2O = total amount of Na.sub.2O and Li.sub.2O) of 1.95 and a solids content of 35% by weight. .sup.c)The additive used in each case was a mixture consisting of 95.625 parts by weight of fumed particulate amorphous silicon dioxide (CAS RN 69012-64-2) and 4.375 parts by weight of graphite. .sup.d)The silicates used in the examples according to table 1 were: Silicate-1: A calcined particulate sheet silicate having a d.sub.90 < 45 μm (sourced from Werba-Chem GmbH under the Werbalink ® MK-I trade name); Silicate-2: A natural particulate sheet silicate (halloysite) having a d.sub.90 < 45 μm (sourced from Osthoff Omega Group under the Halloysite JM1 mineral pigments trade name); Silicate-3: A synthetic particulate sheet silicate having a d.sub.90 < 45 μm (sourced from BYK Additives & Instruments GmbH under the Laponite ® RDS trade name); Silicate-4: A thermally activated particulate sheet silicate (metakaolin) having a d.sub.90 < 45 μm (sourced from BASF SE under the MetaMax ® trade name); Silicate-5: A natural particulate sheet silicate (montmorillonite) having a d.sub.90 < 45 μm (sourced from Alfa Aesar/Thermo Fischer (Kandel) GmbH under the Montmorillonite K10 trade name). Silicate-X: A natural island silicate (andalusite) having a d.sub.90 < 45 μm (sourced from Eggerding B.V. Industrial Minerals under the Andalusite 200 mesh trade name); (N.B.: not a particulate sheet silicate) Silicate-Y: A natural sheet silicate (montmorillonite) having a d.sub.90 > 45 μm (sourced from Damolin GmbH under the SorbixUS Premium (0.3-0.7 mm) trade name). (N.B.: d.sub.90 not less than 45 μm) [0298] The molding material mixtures specified in Table 1 were used, with the aid of a heatable mold for the production of flexural specimens as disclosed in VDG-Merkblatt M11 of March 1974, to produce test specimens by injection. Firstly flexural specimens of dimensions 22.4 mm×22.4 mm×165 mm were produced, which formed the basis for the subsequent studies of flexural strength, and secondly cylindrical test specimens having a height of 50 mm and a diameter of 50 mm, which were used in the determination of the breakdown properties. [0299] For this purpose, the components listed in table 1 were each mixed in a laboratory paddle mixer (from Multiserw). Forthis purpose, the quartz sand was initially charged and the pulverulent additive and any silicate were mixed in. Then the binder was added. The mixture was subsequently stirred for a total of two minutes. The molding material mixtures were each introduced by means of compressed air (4 bar) into the mold, the core box temperature of which was 180° C. The injection time was 3 s, which was followed by a hardening time of 30 s (delay time 3 s). The curing of the mixtures was accelerated by passing hot air (gassing pressure 2 bar, gassing and gassing hose temperature 150° C.) through the mold for a curing time of 30 s.

[0300] 2. Determination of Flexural Strength: [0301] Flexural strengths were determined by placing the test bars produced into a Georg Fischer strength tester, equipped with a 3-point bending apparatus (from Multiserw), and the force that led to fracture of the test bars was measured. The flexural strengths were measured 1 hour after removal from the mold (called “cold strength”). The measurements obtained are reported in table 2 under the “Bending resistance” entry as the median from 3 measurements.

[0302] 3. Examination of Breakdown Properties: [0303] To examine the breakdown properties, the cylindrical test specimens produced with a height of 50 mm and a diameter of 50 mm were subjected to thermal stress in a muffle furnace (from Nabertherm) at a temperature of 900° C. for 10 minutes. After the samples had been removed from the muffle furnace and cooled to room temperature, the test specimens were placed onto an agitated sieve (sieve placed on a vibration shaker, LPzE-3e, from Multiserw) having a mesh size of 1.40 mm and then agitated at the greatest possible amplitude (100% of the maximum possible apparatus setting) for 60 s. In each case, the mass both of the residue on the sieve and of the amount comminuted in the collection tray (broken-down fraction) were determined with a balance. The quotient of the weight of the broken-down fraction to the total mass of the two fractions is referred to as sieve passage and is reported in table 2 under the “Sieve passage” entry as an average from 4 measurements in each case. Improved breakdown properties are especially manifested in high values for sieve passage.

[0304] 4. Determination of the quality of the regenerated mold base material: [0305] The quality of a regenerated mold base material and its suitability for use in the production of waterglass-bound casting molds and cores having good breakdown properties can be described as good especially when the concentration of water-soluble salts and oxides, especially of water-soluble alkali metal salts and alkali metal oxides, in the regenerated mold base material is particularly low. This property can be examined with the aid of conductivity measurements. [0306] 4.1 For each measurement, first of all, a starting solution was produced by introducing 100 mL of ultrapure water into a beaker and adding 0.05 mL of a 1 M KCl solution. The conductivity of the resultant starting solution was determined with a SevenMulti pH/conductivity meter from Mettler Toledo; it corresponds to a blank value. [0307] 4.2 The regenerated mold base material was produced in each case by subjecting corresponding flexural specimens of dimensions 22.4 mm×22.4 mm×165 mm to thermal stress in a muffle furnace (from Nabertherm) at a temperature of 900° C. for 5 minutes. After the test specimens had been removed from the muffle furnace and cooled to room temperature, the test specimens were converted to a free-flowing state by manual mechanical action. 50 g of the regenerated mold base material produced in each case, without further processing, were introduced into the beaker containing the starting solution (see 4.1 above), which was then covered with a watchglass. The resultant suspension was heated to 100° C. on a hot plate, left at that temperature for 5 minutes and then cooled down to room temperature. The solids fraction of the suspension was separated off by filtration and the conductivity of the resultant filtrate was determined as described above under 4.1. In table 2, under the “Conductivity” entry, the value found as the average from 4 measurements in each case for the difference between the conductivity determined and the blank value determined beforehand in each case is reported. [0308] 4.3 The quality of a regenerated mold base material can also be assessed by the determination of the acid demand (in this regard see the VDG-Merkblatt P26 of October 1999). According to the VDG-Merkblatt P26 of October 1999, the acid demand was determined for selected samples, with production of the regenerated mold base material used as elucidated in 4.2. In table 2, under the “Acid demand” entry, the value found as the average from 4 measurements in each case is reported. [0309] 4.4 Measurements and conclusions:

TABLE-US-00002 TABLE 2 Measurements Flexural Sieve strength/ passage/ Conductivity/ Acid demand/ Example (N/cm.sup.2) (%) (μS/cm) (mg HCl/100 g) C1 300 8 2730 — C2 470 52 3340 213 C3 340 25 1870 — C4 460 76 2830 176 C5 440 73 2100 — I1 520 95 1130 75 I2 450 100 1370 — I3 390 100 790 — I4 400 99 1070 — I5 450 99 1420 — [0310] 4.4.1 It is apparent from table 2 that the process of the invention can give casting molds and cores having good flexural strengths. [0311] 4.4.2 Table 2 shows clearly that, for all the examples produced by the process of the invention, outstanding sieve passages (as a measure of the breakdown properties) of 95% to 100% were measured, all of which are significantly above the sieve passages of 8% to 76% that were ascertained for the comparative examples. [0312] It is found here more particularly that neither the exclusive use of a particulate sheet silicate (example C3, absence of (fumed) amorphous particulate silicon dioxide) nor that of (fumed) particulate amorphous silicon dioxide (example C2, absence of particulate sheet silicate) leads to such a marked increase in the sieve passage as the combinations of the invention (examples I1 to I5). There is a synergistic effect in the inventive examples which becomes particularly clear in that even the combined sieve passage of examples C2 and C3 is only 77% and hence well below the lowest value that was determined for examples I1 to I5. [0313] Furthermore, the comparison of examples I1 to I5 with example C4 shows clearly that an advantageous technical effect results only for particulate sheet silicates, and that, for example, the use of an island silicate such as andalusite (silicate X) leads to considerably poorer sieve passage. [0314] Moreover, the specific comparison of example I4 with example C5 shows that the technical effect results only for particulate sheet silicates having a d90 of the invention, whereas coarser-grain versions of the chemically identical sheet silicate (silicate Y in example C5) result in much poorer sieve passage. [0315] Furthermore, it is clearly apparent that the technical effect of the improved sieve passage is manifested for all the particulate sheet silicates examined (examples 11 to 15), regardless of chemical differences that exist between the particulate sheet silicates used. [0316] 4.4.3 The quality of the regenerated mold base materials obtained can additionally be assessed with the aid of the conductivity values, low conductivities being advantageous. [0317] Table 2 shows clearly that low conductivities of 790 to 1420 μS/cm have been measured for all the examples produced by the process of the invention, all of which are significantly below the high conductivities of 1870 to 3340 μS/cm that were ascertained for the comparative examples. [0318] It is found here that neither the exclusive use of a particulate sheet silicate (example C3, absence of (fumed) amorphous particulate silicon dioxide) nor that of (fumed) particulate amorphous silicon dioxide (example C2, absence of particulate sheet silicate) leads to such a marked decrease in conductivity as the combination of the invention (examples I1 to I5). More particularly, the exclusive use of (fumed) particulate amorphous silicon dioxide (example C2), as compared with example C1 (no amorphous silicon dioxide; no silicate), actually results in a rise in conductivity, which makes the synergistic effect of the combination of the invention (examples I1-I5) particularly clear. [0319] Moreover, the comparison of examples I1 to I5 with examples C4 and C5 shows clearly that this advantageous technical effect also results only for particulate sheet silicates, especially particulate sheet silicates that have a d90 of the invention, whereas the use of an island silicate (C4; silicate-X), just like the use of a coarser-grain version of a sheet silicate (C5, silicate-Y), leads to an unfavorably high conductivity value. [0320] Furthermore, it is clearly apparent that the technical effect of the improved screen passage is manifested for all the particulate sheet silicates examined (11 to 15), regardless of the chemical differences that exist between the compounds used. [0321] 4.4.4 Consideration of the measurements of acid demand that are compiled in table 2 makes it clear that the acid demand can be correlated directly with the conductivities discussed above under 4.4.3, and that the conductivity also decreases with the acid demand. [0322] 4.4.5 Beyond the measurements compiled in table 2, it has been found in in-house studies that a physical removal (sieving) of the dust fraction <125 μm of the regenerated mold base materials, in the case of molding material mixtures of the invention (examples I2 and I3), leads to a further decrease in conductivity by 10% to more than 20%. In the case of a noninventive mixture (example C2), by contrast, only a decrease in conductivity by about 5% was found after the removal. [0323] 5. Further studies: [0324] Studies were additionally conducted on cores that were produced using molding material mixtures of the invention or comparative molding material mixtures. The constituents of the molding material mixtures are first assigned abbreviations in table 3. According to table 4, the cores examined are classified into groups according to their constituents and assessed qualitatively with regard to their strength, breakdown properties and regeneratability.

TABLE-US-00003 TABLE 3 Constituents of the molding material mixtures used in the process. Abbreviation Constituent A Mold base material B Solution or dispersion comprising waterglass C 0.1% to 3% by weight of (fumed) particulate amorphous silicon dioxide D 0.05 to 1.5% by weight of island silicate E 0.05 to 1.5% by weight of sheet silicates, d.sub.90 > 45 μm F 0.05 to 1.5% by weight of particulate sheet silicates, d.sub.90 < 45 μm

TABLE-US-00004 TABLE 4 Qualitative assessment of the cores produced from the molding material mixtures used with regard to strength, breakdown properties and regeneratability. Constituents of the molding material No. mixture Strength Breakdown Regeneratability 1 A + B − − − − − − 2 A + B + C + + − − − 3 A + B + F − − − + 4 A + B + C + D + + + − − 5 A + B + C + E + + − 6 A + B + C + F + + + + + The symbols here have the following meanings: (− −) = very poor, (−) = comparatively poor, (+) = good and (+ +) = very good. [0325] The qualitative assessment in table 4 demonstrates that very good breakdown properties and very good regeneratability are observed only for molding material mixtures or cores of the invention (No. F) and that good strength is simultaneously observed for these.