SIZED MOLDS OBTAINABLE FROM A MOLDING MATERIAL MIXTURE CONTAINING AN INORGANIC BONDING AGENT AND PHOSPHATIC COMPOUNDS AND OXIDIC BORON COMPOUNDS AND METHOD FOR PRODUCTION AND USE THEREOF

Abstract

Sized molds for metal casting are obtained from molding material mixtures on the basis of inorganic bonding agents containing at least one phosphatic compound and at least one oxidic boron compound, especially sized, water glass-bound forms and cores, having at least one refractory base molding material, water glass as inorganic bonding agent and amorphous particulate silicon dioxide and one or more powdery oxidic boron compounds and one or more phosphatic compounds. The invention furthermore relates to a method for producing sized foundry mold bodies and use thereof, in particular for producing cast parts from iron alloys. The sizing is a water-based sizing.

Claims

1. A mould or core having a coating obtained by moulding and hardening a moulding material mixture to obtain a mould or core and the mould or core, wherein the moulding material mixture at least comprises: a refractory mould base material; water glass; particulate amorphous silicon dioxide, in the range of 0.1 to 2% by weight, relative to the weight of the refractory mould base material; at least one oxidic boron compound, in the range of greater than 0.002 and less than 1% by weight, relative to the weight of the refractory mould base material; and at least one phosphate-containing compound, in the range of 0.05 to 1.0% by weight, relative to the weight of the refractory mould base material; and the coating is a water-containing coating.

2. The mould or core of claim 1, wherein the coating comprises: (A) at least the following clays: (A1) palygorskite, in the range of 1 to 10 parts by weight; (A2) hectorite, in the range of 1 to 10 parts by weight; and (A3) sodium bentonite, in the range of 1 to 20 parts by weight, relative to the ratio of components (A1), (A2) and (A3) relative to each other; and (B) a carrier liquid containing water which is completely vaporisable at up to 160° C. and 1013 mbar; and (C) a refractory base material, different from (A).

3. The mould or core of claim 2, wherein the coating has one or more of the following features: (i) a total clay content (A1), (A2) and (A3) of the coating amounting to 0.1% to 4.0% by weight, preferably 0.5 to 3.0% by weight and more preferably 1.0 to 2.0% by weight, relative to the solids content of the coating; (ii) the carrier liquid comprises more than 50% by weight of water and optionally further contains alcohols, including polyalcohols and polyether alcohols; (iii) the solids content of the coating composition is from 20% to 90% by weight, more preferably from 30% to 80% by weight; (iv) the coating composition contains 10 to 85% by weight of refractory base materials relative to the solids content of the coating composition.

4. The mould or core of claim 1, wherein the oxidic boron compound is selected from the group consisting of: borates, borophosphates, borophosphosilicates and mixtures thereof and the oxidic boron compound is in particular a borate, preferably an alkali borate and/or alkaline earth metal borate such as sodium borate and/or calcium borate.

5. The mould or core of claim 1, wherein the oxidic boron compound is built up from B—O—B structural elements and, irrespective thereof, does not contain organic groups.

6. The mould or core of claim 1, wherein the oxidic boron compound is added as a solid in powder form, in particular having an average particle size of greater than 0.1 μm and less than 1 mm, preferably greater than 1 μm and less than 0.5 mm, and more preferably greater than 5 μm and less than 0.25 mm.

7. The mould or core of claim 1, wherein the oxidic boron compound is added or contained in an amount of greater than 0.005% by weight and less than 0.4% by weight, more preferably greater than 0.01% by weight and less than 0.1% by weight, and most preferably greater than 0.02% by weight and less than 0.075% by weight, relative to the weight of the refractory mould base material.

8. The mould or core of claim 1, wherein the refractory mould base material is selected from the group consisting of: comprises silica sand, zircon sand, chrome ore sand, olivine, vermiculite, bauxite, fireclay, glass beads, glass granules, aluminium silicate hollow spheres and mixtures thereof and preferably consists of more than 50% by weight of silica sand relative to the weight of the refractory mould base material.

9. The mould or core of claim 1, wherein greater than 80% by weight, preferably greater than 90% by weight, and more preferably greater than 95% by weight, of the moulding material mixture is refractory mould base material.

10. The mould or core of claim 1, wherein the refractory mould base material has average particle diameters of 100 μm to 600 μm, preferably 120 μm to 550 μm.

11. The mould or core of claim 1, wherein the particulate amorphous silicon dioxide has a surface area determined according to BET of between 1 and 200 m.sup.2/g, preferably greater than or equal to 1 m.sup.2/g and less than or equal to 30 m.sup.2/g, more preferably from 1 to less than or equal to 19 m.sup.2/g.

12. The mould or core of claim 1, wherein the moulding material mixture comprises a binder, wherein the binder comprises the water glass, the particulate amorphous silicon dioxide, the oxidic boron compound and the phosphate-containing compound, such that the particulate amorphous silicon dioxide is used in an amount of 1 to 80% by weight, preferably between 2 and 60% by weight, relative to the total weight of the binder.

13. The mould or core of claim 1, wherein the particulate amorphous silicon dioxide has an average primary particle diameter determined by dynamic light scattering of between 0.05 μm and 10 μm, preferably between 0.1 μm and 5 μm, and more preferably between 0.1 μm and 2 μm.

14. The mould or core of claim 1, wherein the particulate amorphous silicon dioxide is selected from the group consisting of: precipitated silicon dioxide, flame-hydrolytically or arc-produced pyrogenic silicon dioxide, amorphous silicon dioxide produced by thermal decomposition of ZrSiO.sub.4, silicon dioxide produced by oxidation of metallic silicon by means of an oxygen-containing gas, spherical particle quartz powder produced by melting and rapid re-cooling of crystalline quartz, and mixtures thereof.

15. The mould or core of claim 1, wherein the moulding material mixture contains the particulate amorphous silicon dioxide in amounts of 0.1 to 1.5% by weight, relative to the mould base material, and, irrespective thereof, the moulding mixture comprises a binder and the particulate amorphous silicon dioxide, wherein the binder comprises the water glass, the particulate amorphous silicon dioxide, the oxidic boron compound and the phosphate-containing compound and the particulate amorphous silicon dioxide is contained in the binder in amounts of 2 to 60% by weight, more preferably 4 to 50% by weight, relative to the weight of the binder including water, wherein the solids content of the binder is from 20 to 55% by weight, preferably from 25 to 50% by weight.

16. The mould or core of claim 1, wherein the particulate amorphous silicon dioxide has a water content of less than 5% by weight and more preferably less than 1% by weight.

17. The mould or core of claim 1, wherein the water glass including the water is present in the moulding material mixture in an amount of 0.75% to 4% by weight, more preferably between 1% and 3.5%, relative to the weight of the refractory mould base material, and wherein, also irrespective thereof, but preferably in combination with the above values, the solids content of water glass further preferentially is from 0.2625 to 1.4% by weight, preferably 0.35 to 1.225% by weight, relative to the weight of the refractory mould base material in the moulding material mixture.

18. The mould or core of claim 1, wherein the water glass has a molar modulus SiO.sub.2/M.sub.2O in the range from 1.6 to 4.0, more preferably 2.0 to less than 3.5, with M=lithium, sodium and potassium or M=sodium and potassium.

19. The mould or core of claim 1, wherein the phosphate-containing compound is an inorganic phosphate compound with phosphorus in the +5 oxidation state, wherein metaphosphates and/or polyphosphates are preferred, in particular each as alkali phosphate or as alkaline earth metal phosphate, wherein more preferably the alkaline earth metal is sodium.

20. The mould or core of claim 1, wherein the moulding material mixture contains the phosphate-containing compound in an amount of 0.1 and 0.5% by weight, relative to the weight of the refractory mould base material.

21. A method of producing a coated mould or core, comprising the steps of: providing a moulding material mixture as defined in claim 1 by combining and mixing the substances or components recited therein; introducing the moulding material mixture into a mould; and obtaining a mould or core by hardening the moulding material mixture in a heat hardening step in which water is heated and removed, preferably by exposing the moulding material mixture to a temperature of 100° C. to 300° C.; and coating the obtained mould or core with a water-containing coating.

22. The method of claim 21, wherein: the moulding material mixture is introduced into the mould by means of a core shooter with the aid of compressed air; and the mould is a moulding tool through which one or more gases flow, wherein the one or more gases includes carbon dioxide, and preferably wherein the carbon dioxide and/or air is heated to above 60° C.

23. The method of claim 21, wherein, for hardening purposes, the moulding material mixture is subjected to a temperature of 100 to 300° C., preferably 120 to 250° C., preferably for less than 5 min, wherein the temperature is further preferably at least partially established by blowing heated air into a moulding tool.

24. A method for metal casting, comprising the step of: pouring a molten metal, particularly iron, into the mould or core of claim 1.

Description

EXAMPLES

[0174] The following example is intended to describe and explain the invention without limiting its scope.

Example: Influence of Powdered Oxidic Boron Compounds and/or Phosphate-Containing Compounds on the Bending Strengths in the Coating-Drying Process

[0175] So-called Georg Fischer test bars were produced for testing a moulding material mixture. Georg Fischer test bars are cuboid test bars with the dimensions 180 mm×22.36 mm×22.36 mm. The compositions of the moulding material mixtures are given in Table 1. The following steps were taken to produce the Georg Fischer test bars: [0176] The components listed in Table 1 were mixed in a laboratory paddle mixer HSM10 (HOBART GmbH, Hürth, DE). For this purpose, the silica sand was first introduced and then particulate amorphous SiO.sub.2 and, if necessary, powdery oxidic boron compounds and/or powdered phosphate-containing compounds were added. The mixture was mixed for one minute. The water glass used was sodium water glass, which had contents of potassium. In the following tables, the modulus is therefore given as SiO.sub.2:M.sub.2O, wherein M is the sum of sodium and potassium. In a second step, the water glass was added to the mixture of sand and the aforementioned powdery components, and the mixture was then stirred for another minute. [0177] The moulding material mixtures were transferred into the storage hopper of an L1 Labor Hot-Box core shooter from Lämpe & Mösner GmbH (Schopfheim, DE), whose moulding tool was heated to 180° C. [0178] The moulding material mixtures were introduced into the moulding tool by means of compressed air (3 bar) and remained in the moulding tool for another 35 seconds. [0179] To accelerate the hardening of the compounds, hot air (2 bar, 100° C. when entering the tool) was passed through the moulding tool during the last 25 seconds. [0180] The moulding tool was opened and the test bars removed.

[0181] To determine the bending strengths, the test bars (180 mm×22.36 mm×22.36 mm) were measured in a standard bending bar device of the type “Multiserw-Morek LRu-2e”, each with a standard measuring programme “Rg1v_B 870 N/cm.sup.2” (3-point bending device) from Multiserw-Morek (Bresnitz, PL). The bending strengths were measured according to the following scheme: [0182] 10 seconds after removal (heat strengths); [0183] 1 hour after removal (cold strengths); [0184] After storage for 24 hours at room temperature, followed by another 24 hours at 30° C. and 60% relative humidity in a climatic cabinet.

[0185] As shown in Table 3, the parameters of the coating composition used were adjusted for the purpose intended here, i.e. application to test cores by means of an immersion application or bath.

[0186] The density of the ready-to-use coating composition given in Table 3 was measured according to the standard test method DIN EN ISO 2811-2:2011.

[0187] The flow time of the ready-to-use coating composition given in Table 3 was measured according to the standard test method DIN 53211 (1974) using a DIN cup 4.

TABLE-US-00001 TABLE 1 Composition of the moulding material mixture. Silica Alkaline Amorphous sand H 32 water glass .sup.a) SiO.sub.2 .sup.b) Phosphate .sup.c) Borate .sup.d) [PW] [PW] [PW] [PW] [PW] 1.1 100 2.2 0.5 — — Not according to the invention 1.2 100 2.2 0.5 0.15 — Not according to the invention 1.3 100 2.2 0.5 — 0.05 Not according to the invention 1.4 100 2.2 0.5 0.15 0.05 According to the invention .sup.a) Alkali water glass with a SiO.sub.2:M.sub.2O modulus of approx. 2.2 .sup.b) Microsilica POS B-W 90 LD (amorphous SiO.sub.2, from Possehl Erzkontor; formed during thermal decomposition of ZrSiO.sub.2) .sup.c) Sodium hexametaphosphate (ICL BK Giulini GmbH) added as a solid .sup.d) Calcium metaborate (Carl Jäger GmbH) PW = parts by weight

TABLE-US-00002 TABLE 2 Strengths of the moulding material mixtures Relative Strength after retention of Heat Cold climatic strength after strength strength storage climatic [N/cm.sup.2] [N/cm.sup.2] [N/cm.sup.2] storage [%] 1.1 166 478 215 45 Not according to the invention 1.2 165 490 215 44 Not according to the invention 1.3 156 409 345 84 Not according to the invention 1.4 172 416 344 83 According to the invention

[0188] The strength tests of mixtures 1.1 to 1.4 show that the climatic stability of inorganically bound cores is not improved by the addition of a phosphate-containing component alone; the retention of strength in percent after climatic storage is almost identical for mixtures 1.1 (45%) and 1.2 (44%). However, a positive effect is achieved by adding an oxidic boron compound, in this case calcium metaborate. After climatic storage, 84% (mixture 1.3) or 83% (mixture 1.4) of the cold strength is obtained by the addition, while the phosphate-containing component again shows no additional influence in the comparison of mixtures 1.3 and 1.4.

TABLE-US-00003 TABLE 3 Parameters of the ready-to-use coating KERNTOP ® V 302/88. KERNTOP ® V 302/88 is a water-based coating based on aluminium silicate and graphite, solids approx. 49% by weight. Viscosity 12 Pa-s (at 25° C.). Matt layer Solids content Density (BV) Flow time for thickness [% by weight] [Pas] 4 mm [s] [μm] 33.8 0.6 13.0 325

[0189] To determine the softening of foundry cores (i.e. the maximum drop in bending strength), the test cores were coated (sized) one hour after core production with the coating composition according to Table 3 at room temperature (25° C.) by dipping (1 s dipping, 3 s holding time in the coating composition, 1 s removal). The wet film thickness of the coating was set to about 250 μm.

[0190] Subsequently, the coated test cores were dried under the conditions specified below (20 min, 140° C.) in a fan oven and the changes in each of their bending strengths examined under the drying conditions.

[0191] The coated test cores were each dried for a period of 20 minutes, and their bending strengths (in N/cm.sup.2, according to the definition given in leaflet R202 of the Verein Deutscher Gießereifachleute (Association of German Foundry Experts), October 1987 edition) were measured at various times during drying, and then again one hour after the end of the drying process, using a standard bending bar device type “Multiserw-Morek LRu-2e”, evaluated in each case according to the standard measuring programme “Rg1v_B 870.0 N/cm.sup.2” (3-point bending strength).

[0192] Table 4 shows the strength values for the examined coated test cores, produced with the moulding material mixtures 1.1 to and the coating according to Table 3. Therein, the cold strength of the uncoated cores, the minimum strength during the coating-drying process (absolute value), and the relatively largest drop in strength during the coating-drying process are compared. In addition, the cold strengths of the coated test cores are listed.

TABLE-US-00004 TABLE 4 Absolute bending strengths before and after the coating-drying process as well as the minimum bending strengths (related to the cold strengths, uncoated) during the coating-drying process (20 min, 140° C.). Minimum Maximum bending relative Cold strength drop in Cold strength, during the bending strengths, uncoated coating-drying strength coated [N/cm.sup.2] process [N/cm.sup.2] [%] [N/cm.sup.2] 1.1 478 56 88 319 Not according to the invention 1.2 490 115 77 329 Not according to the invention 1.3 409 154 62 344 Not according to the invention 1.4 416 256 38 315 According to the invention

[0193] The comparison of the minimum strengths during drying of the coating shows first of all a strong drop in strength for mixture 1.1; here up to 88% is lost compared to the cold strength of the uncoated cores.

[0194] For mixtures 1.2 to 1.4, this maximum loss in strength is reduced to 77-38%.

[0195] The application of a water-containing coating to an inorganic core suggests a collapse in strengths, as water is introduced into a moisture-sensitive system. The experiments described in this application show that the addition of an oxidic boron compound has a positive effect on maintaining the strength of a coated inorganic core (cf. Table 4, mixture 1.3).

[0196] For mixtures 1.2 and 1.4, no effect on the climatic stability by adding a phosphate-containing component is evident from the results in Table 2. In contrast, a positive effect is evident from the results in Table 4 when comparing mixtures 1.1 and 1.2, wherein the phosphate-containing component increases the retention of strength during the coating-drying process.

[0197] Likewise, when comparing mixtures 1.2, 1.3 and 1.4, it can be seen from Table 4 that the combined addition of a phosphate-containing component and an oxidic boron compound produces a stronger effect than the single addition of both components, and surprisingly the highest strength retention during the coating-drying process is achieved with the combined addition.