ADDITIVE MIXTURE FOR MOULDING MATERIAL MIXTURES FOR THE PRODUCTION OF WATER-GLASS-BONDED CASTING MOULDS AND CASTING CORES

Abstract

A description is given of the use of an additive mixture (A) for combination with a solution or dispersion (B) comprising waterglass, for producing a moulding material mixture for producing articles from the group consisting of foundry moulds and foundry cores; a multi-component binder system comprising (A) an additive mixture and (B) a solution or dispersion comprising waterglass; a moulding material mixture comprising a mould base material (C) and also components (A) and (B) of such a multi-component binder system; a method for producing an article from the group consisting of foundry moulds and foundry cores; articles from the group consisting of foundry moulds and foundry cores; and the use of such an article for metal casting, preferably for light metal casting, more particularly for aluminium casting.

Claims

1. Multi-component binder system comprising (A) an additive mixture comprising (A-1) particulate, amorphous silicon dioxide, (A-2) a salt M.sub.5(PO.sub.4).sub.3OH, wherein M is an alkaline earth metal, the additive mixture being a solids mixture or a suspension, (B) a solution or dispersion comprising waterglass as components spatially separate from one another.

2. Multi-component binder system according to claim 1, wherein the salt (A-2) is Ca.sub.5(PO.sub.4).sub.3OH and/or the particulate, amorphous silicon dioxide (A-1) is selected from particulate synthetic amorphous silicon dioxide which comprises as a secondary constituent at least carbon, the fraction of silicon dioxide being 90% or more, based on the total mass of the particulate synthetic amorphous silicon dioxide and the secondary constituents, preferably producible by reduction of quartz in an arc furnace; particulate synthetic amorphous silicon dioxide which comprises as a secondary constituent oxides of zirconium, preferably producible by thermal decomposition of ZrSiO.sub.4; particulate synthetic amorphous silicon dioxide producible by oxidation of metallic silicon using an oxygen-containing gas; particulate synthetic amorphous silicon dioxide producible by quenching of a silicon dioxide melt; fumed silica, preferably producible by pyrolysis of silicon tetrachloride; and mixtures thereof.

3. Multi-component binder system according to claim 1, wherein, in the additive mixture (A), the ratio of the mass of particulate, amorphous silicon dioxide (A-1) to the mass of salt (A-2) is in the range from 1:3 to 40:1.

4. Multi-component binder system according to claim 1, wherein the waterglass in component (B) comprises cations of one or more alkali metals M from the group consisting of lithium, sodium and potassium, preferably cations of one or both alkali metals from the group consisting of sodium and potassium, and/or wherein component (B) has an alkali metal silicate content in the range from 20% to 60%, based on the total mass of component (B), and/or wherein the molar SiO.sub.2/M.sub.2O modulus of the waterglass is preferably in the range from 1.6 to 4.0, M.sub.2O denoting the total amount of oxides of alkali metals M.

5. Moulding material mixture comprising (C) a mould base material and also components (A) and (B) of a multi-component binder system as defined in claim 1, wherein the moulding material mixture comprises salts (A-2) in a concentration of 0.01% to 5%, based on the total mass of the mould base material.

6. Moulding material mixture according to claim 5, wherein the moulding material mixture comprises particulate, amorphous silicon dioxide (A-1) in a concentration of 0.05% to 3.0% Ca.sub.5(PO.sub.4).sub.3OH in a concentration of 0.01% to 5% waterglass in a concentration of 0.2% to 3%, based in each case on the total mass of the mould base material.

7. Method for producing an article from the group consisting of foundry moulds and foundry cores, wherein the article is formed by combining a mould base material (C) with the components (A) and (B) of a multi-component binder system as defined in claim 1 and thermally curing the binder.

8. Method according to claim 7, comprising the steps of producing a moulding material mixture, shaping the moulding material mixture, preferably by means of a moulding tool, and thermally curing the binder system in the shaped moulding material mixture, wherein the moulding material comprises component (C) a mould base material and also components (A) and (B), wherein the moulding material mixture comprises salts (A-2) in a concentration of 0.01% to 5%, based on the total mass of the mould base material.

9. Method according to claim 7, wherein the thermal curing takes place at a temperature in the range from 100° C. to 300° C., more preferably 100° C. to 250° C.

10. Method according to claim 7, wherein the article is formed through layer-by-layer build-up.

11. Article from the group consisting of foundry moulds and foundry cores, producible by a method as defined in claim 7, and/or comprising a mould base material (C) which is bound by the curing product of a binder, and salts (A-2) in a concentration of 0.01% to 5%, based on the total mass of the mould base material, wherein the binder comprises: (A) an additive mixture comprising (A-1) particulate, amorphous silicon dioxide, (A-2) a salt M.sub.5(PO.sub.4).sub.3OH, wherein M is an alkaline earth metal, the additive mixture being a solids mixture or a suspension, (B) a solution or dispersion comprising waterglass as components spatially separate from one another.

12. Article according to claim 11, wherein the article comprises Ca.sub.5(PO.sub.4).sub.3OH in a concentration of 0.01% to 5%, based on the total mass of the mould base material.

13. A method of light metal casting, comprising: providing an article according to claim 11 for metal casting.

14. A method of producing a foundry mould or a foundry core, comprising: providing an additive mixture (A) as a component of a multi-component binder system or of a moulding material mixture, wherein the additive mixture (A) is a solids mixture or suspension comprising (A-1) particulate, amorphous silicon dioxide, and (A-2) a salt M.sub.5(PO.sub.4).sub.3OH, wherein M is an alkaline earth metal, wherein the multi-component binder system further comprises (B) a solution of dispersion comprising waterglass and (A) and (B) are components spatially separate from one another, wherein the moulding material mixture comprises the multicomponent binder system and (C) a mould base material, wherein the moulding material mixture comprises salts (A-2) in a concentration of 0.01% to 5%, based on the total mass fo the mould base material.

15. A method of producing a multi-component binder system as defined in claim 1, comprising: adding (A-2) a salt M.sub.5(PO.sub.4).sub.3OH, wherein M is an alkaline earth metal, as part of component (A) of a multi-component binder system as defined in claim 1.

Description

[0164] The invention is elucidated further below with reference to non-limiting working examples and comparative examples.

1. Production of Test Specimens

[0165] In order to produce moulding material mixtures, an additive mixture (A) comprising [0166] (A-1) particulate amorphous silicon dioxide (product “RW-Fuller Q1 Plus” RW Silicium GmbH Rottwerk Pocking, obtained by thermal decomposition of ZrSiO.sub.4, [0167] (A-2) Ca.sub.5(PO.sub.4).sub.3OH (inventive; supplier: Budenheim, see Table 1 below) [0168] or a non-inventive additive (for details see Table 1 below)
was stirred by hand into the pre-introduced mould base material (C) (H31 sand), to give a premix comprising the mould base material (C) and the additive mixture (A).

[0169] Subsequently [0170] (B) an aqueous solution comprising [0171] 36.2 wt % of sodium potassium waterglass with a molar modulus of 2.1 and an Na.sub.2O/K.sub.2O ratio (molar) of around 7.7; and [0172] 2.0 wt % of surface-active substance, e.g. wetting agent, e.g. sodium 2-ethylhexylsulfate EHS 40 (supplier: Hoesch) [0173] (based in each case on the total mass of component (B))
was added to the premix, and the components of the moulding material mixture were mixed for 120 s in a Bull mixer (from Morek Multiserw) at 220 rpm.

[0174] In order to produce a non-inventive reference mixture, [0175] (A-1) particulate amorphous silicon dioxide (for product details see above)
was stirred by hand into the pre-introduced mould base material (C) (H31 sand), to give a premix comprising the mould base material (C) and particulate, amorphous silicon dioxide (A-1).

[0176] Subsequently [0177] (B) an aqueous solution comprising waterglass (concentration and composition as indicated above)
was added to the premix, and the components of the moulding material mixture were mixed for 120 s in the Bull mixer (from Morek Multiserw) at 220 rpm.

[0178] The compositions of all moulding material mixtures produced are reported in Table 1. In Table 1, “pbw” stands for “parts by weight”.

[0179] The moulding material mixtures obtained in this way were each introduced using compressed air (4 bar=400 kPa) into the moulding tool, whose core box temperature was 180° C. The shooting time was 3 s, followed by a curing time of 30 s (delay time 3 s). Throughout the curing time, the cores were additionally gassed with hot air (180° C., 2 bar=200 kPa). Each shot produced three flexural bars with dimensions of 22.4 mm×22.4 mm×186 mm.

TABLE-US-00001 TABLE 1 H31 sand Component Component Mixture (C) (B) (A-1) Additive Note A 100 pbw 2.2 pbw 0.5 pbw — non-inventive B 100 pbw 2.2 pbw 0.5 pbw 0.3 pbw inventive Ca.sub.5(PO.sub.4).sub.3OH (A-2) (Budenheim Product No. C23-02) C 100 pbw 2.2 pbw 0.5 pbw 0.3 pbw inventive Ca.sub.5(PO.sub.4).sub.3OH (A-2) (Budenheim Product No. C13-08) D 100 pbw 2.2 pbw 0.5 pbw 0.3 pbw inventive Ca.sub.5(PO.sub.4).sub.3OH (A-2) (Budenheim Product No. C13-09) E 100 pbw 2.2 pbw 0.5 pbw 0.3 pbw non-inventive β-tricalcium phosphate Ca.sub.3(PO.sub.4).sub.2 (Budenheim Product No. C13-13) F 100 pbw 2.2 pbw 0.5 pbw 0.3 pbw Alodur ZK SF non-inventive (by-product from zircon corundum production, in dust form, from Treibacher Schleifmittel, cf. DE102012113073A1)

[0180] The various kinds of the inventive Ca.sub.5(PO.sub.4).sub.3OH (A-2) (each identified by a separate product number) differ in their particle size. The medians (d.sub.50) in the particle size distribution, determined by laser scattering, for the additives of mixtures B and D-F are reported in Table 1a.

TABLE-US-00002 TABLE 1a Duration of Manufacturer- ultrasound Refractive Median specified treatment index d.sub.50 Additive fineness [min] (R) [μm] Ca.sub.5(PO.sub.4).sub.3OH (A-2) fine 15 1.45-0.01 1.6 (Budenheim Product No. C23-02) powder (used in mixture B) Ca.sub.5(PO.sub.4).sub.3OH (A-2) extra-fine 15 1.45-0.01 1.3 (Budenheim Product No. C13-08) powder (used in mixture C) Ca.sub.5(PO.sub.4).sub.3OH (A-2) micro-fine 18 1.45-0.01 0.9 (Budenheim Product No. C13-09) powder (used in mixture D) β-Tricalcium phosphate Ca.sub.3(PO.sub.4).sub.2 powder 12 1.40-0.01 1.9 (Budenheim Product No. C13-13) Non-inventive (used in mixture E)

2. Test Methods

2.1 Determination of Particle Size Distribution

[0181] Approximately 1 teaspoon each of the particulate amorphous silicon dioxide (A-1) “RW-Fuller Q1 Plus” and of the phosphate additive (see Table 1a) were admixed with about 100 ml of fully demineralized (FD) water and the resulting batch was stirred with a magnetic stirrer (IKAMAG RET) for 30 seconds at a stirring speed of 500 revolutions per minute. Subsequently, an ultrasound probe (Hielscher; model UP200HT), pre-set to 100% amplitude and equipped with the S26d7 sonotrode (Hielscher), was immersed into the sample and used to sonicate the sample. The ultrasound treatment here was continuous (not pulsed). Stirring continued during the ultrasound treatment for the phosphate samples.

[0182] The optimum duration of ultrasound treatment, which is dependent on the type of particle, was ascertained by carrying out a measurement series with multiple samples for each species, and varying the duration of ultrasound treatment in each series. The duration of ultrasound treatment, starting from 10 seconds, was extended for each additional sample, and, immediately after the end of the ultrasound treatment, the particle size distribution was determined by laser scattering (LA-960) in each case, as described below. With increasing duration of ultrasound treatment, the median particle size distribution determined initially dropped, until finally, as the duration of ultrasound treatment was increased further, it climbed again. The duration of ultrasound treatment after which the lowest median particle size distribution was obtained is the optimum duration of ultrasound treatment. For “RW-Fuller Q1 Plus”, the optimum duration of ultrasound treatment is 240 seconds. For the individual phosphate additives, the respective optimum duration of ultrasound treatment is reported in Table 1a.

[0183] The particle size distribution was determined using a Horiba LA-960 instrument (hereinafter LA-960). For the measurements, the circulation rate was set at 6, the stirring speed at 8, the data recording of the sample to 30 000, the convergence factor to 15, the type of distribution to volume, and the refractive index (R) for particulate amorphous silicon dioxide to 1.50-0.01i (1.33 for FD water as dispersing medium) and the refractive index (B) to 1.50-0.1i (1.33 for FD water as dispersing medium). The setting of the refractive index (R) and (B) (both identical) for the phosphate additives is reported in Table 1a. The laser scattering measurements were carried out at room temperature (20° C. to 25° C.).

[0184] The measuring chamber of the LA-960 was filled three-quarters full with fully demineralized water (FD water) (maximum filling level). The stirrer with the specified setting was then started, the circulation was switched on, and the water was degassed. After that a blank measurement was carried out with the specified parameters.

[0185] Then, immediately after the ultrasound treatment, a volume of 0.5-3.0 ml was withdrawn centrally, using a disposable pipette, from the samples prepared as described above. The entire contents of the pipette were then introduced into the measuring chamber, so that the transmission of the red laser was between 80% and 90% and the transmission of the blue laser was between 70% and 90%. Measurement was then commenced. The measurements were evaluated automatically on the basis of the specified parameters.

[0186] For the particulate amorphous silicon dioxide (A-1) “RW-Fuller Q1 Plus”, the method described above (with the duration of the ultrasound treatment corresponding to the optimum value indicated above) gave a median (d.sub.50) particle size distribution of 0.84 μm. For the phosphate additives, the medians (d.sub.50) of the particle size distribution, determined by means of the above-described method (with the duration of the ultrasound treatment corresponding in each case to the optimum value specified in Table 1a) are reported in Table 1a.

2.2 Determination of Flexural Strength

[0187] To determine the flexural strengths, the test bars produced were inserted into a Georg-Fischer strength testing instrument, equipped with a 3-point bending device (from Multiserw), and the measurement was made of the force which caused the test bars to break. The flexural strengths were measured 15 s (hot strengths) or 1 hour (cold strengths) after removal from the shaping tool. The measurement values obtained are reported hereinafter as the median of 3 measurements, rounded to a whole number divisible by 10.

2.3 Determination of Core Weight

[0188] The core weight was determined using a standard commercial laboratory balance, and is reported as the median of 9 measurements.

2.4 Assessment of Casting Quality

[0189] In order to assess the effect of the composition of the moulding material mixture on the cast surface and on the amount of sand adhesions on the castings, casting experiments from an aluminium alloy were carried out. For these experiments, one core per moulding material mixture (moulding material mixtures A, B, C, D, E and F; see Table 1 above), thus 6 cores in all, were installed in an outer mould of sand in such a way that three of the four long sides of the core in each case come into contact with the melt during the casting operation. Three sand moulds were prepared in this way, with the cores of moulding material mixture A, B, C, D, E and F being located at a different position in each mould, and were cast with an aluminium alloy (EN AC-43000) at a casting temperature of about 745° C. After the cooling of the melt in the sand mould, the castings were unpacked from the sand mould, the cores were removed by hammer strike, and the casting surface which was in contact with the core was blown with a compressed-air gun.

[0190] For the relative comparison of casting quality, the cast surfaces which were in contact with the cores were evaluated in terms of sand adhesions from 1 to 6 (1 is the best quality, i.e. very few sand adhesions, and 6 the lowest quality, i.e. copious sand adhesion), and the sum total over all three moulds was formed. The evaluation was carried out independently by 2 persons (1) and (2), after which the mean of the sum totals was formed. In addition, specifically, the amount of sand adhesions in comparison to the castings produced with cores from mixture A (without additive) was assessed.

3. Experimental Results

3.1 Core Weights and Flexural Strengths

[0191] The core weights and flexural strengths ascertained can be taken from Table 2.

[0192] Serving as a reference is mixture A (without additive). The results show that the core weight decreases slightly by the addition both of the additive for use in the invention (A-2) and also of the non-inventive additives ß-tricalcium phosphate (mixture E) and Alodur ZK SF (by-product of zircon corundum production, in dust form, from Treibacher Schleifmittel, mixture F). The hot strength, which is important for practical use, is unaffected (the fluctuations of ±10 N/cm.sup.2 are within the bounds of measurement accuracy). Only the cold strength decreases by around 100 N/cm.sup.2. Nevertheless, the cold strengths achieved are straight away sufficient for the use of cores in mass fabrication.

TABLE-US-00003 TABLE 2 Core weight and flexural strengths Core Hot Cold weight strength strength Mixture Additive [g] [N/cm.sup.2] [N/cm.sup.2] Note A — 152.5 190 560 non- inventive B Ca.sub.5(PO.sub.4).sub.3OH (A-2) 151.2 190 450 inventive (Budenheim Product No. C23-02) C Ca.sub.5(PO.sub.4).sub.3OH (A-2) 151.7 180 440 (Budenheim Product No. C13-08) D Ca.sub.5(PO.sub.4).sub.3OH (A-2) 151.6 200 430 (Budenheim Product No. C13-09) E β-Tricalcium phosphate 149.3 180 480 non- Ca.sub.3(PO.sub.4).sub.2 inventive (Budenheim Product No. C13-13) F AlodurZK SF 151.7 200 540

3.2 Casting Quality

[0193] The evaluation of the cast surface and the amount of sand adhesions in comparison to the castings produced with cores from mixture A (without additive) can be taken from Table 3.

[0194] Serving as a reference are the castings produced with cores from mixture A (without additive). These cores had numerous sand adhesions.

[0195] With the cores of inventive moulding material mixtures, a distinct reduction in the sand adhesions was achieved, in comparison to the cores of all the non-inventive mixtures, especially with respect to those made from the reference mixture A.

[0196] Surprisingly, indeed, with cores of the inventive moulding material mixtures B, C and D, substantially better results were achieved than with the cores made from the non-inventive moulding material mixture F, which contains the additive Alodur ZK SF (by-product of zircon corundum production, in dust form, from Treibacher Schleifmittel), which according to DE 10 2012 113 073 A1 improves cast surface quality in the case of grey cast iron.

[0197] With the additive ß-tricalcium phosphate (mixture E), tested for purposes of comparison, no marked improvement was achieved relative to the additive-free reference mixture A.

TABLE-US-00004 TABLE 3 Evaluation of the casting experiments Evaluation of sand adhesions Evaluation Evaluation Mean of Mixture Additive (1) (2) (1) and (2) Note A 18.0 16.0 17.0 non- inventive B Ca.sub.5(PO.sub.4).sub.3OH 6.0 7.0 6.5 inventive (Budenheim Product No. C23-02) C Ca.sub.5(PO.sub.4).sub.3OH 8.0 6.0 7.0 (Budenheim Product No. C13-08) D Ca.sub.5(PO.sub.4).sub.3OH 4.0 5.0 4.5 (Budenheim Product No. C13-09) E Ca.sub.3(PO.sub.4).sub.2 15.0 17.0 16.0 non- (Budenheim inventive Product No. C13-13) F AlodurZKSF 12.0 12.0 12.0