CORES FOR DIE CASTING

Abstract

What are described are the use of a refractory coating composition for production of cores for diecasting, a kit for production of cores for use in diecasting, a method of producing cores for use in diecasting, cores for use in diecasting, and the use of such cores in diecasting, especially of lightweight metals

Claims

1. A kit for production of cores for use in diecasting, comprising, as separate components, (A) a mold base material selected from the group consisting of quartz sand, chromium ore sand, olivine sand, aluminum silicate sands and mixtures thereof; (B) particulate amorphous silicon dioxide or an additive mixture comprising particulate amorphous silicon dioxide; (C) a solution or dispersion comprising waterglass or a kit comprising raw materials for production of a solution or dispersion comprising waterglass; (D) a composition for production of a coating, said composition comprising (D1) a carrier liquid selected from the group consisting of water and mixtures of water with one or more alcohols; (D2) a constituent from the group consisting of (D2a) dissolved in the carrier liquid, one or more acids, where the aqueous phase formed by the carrier liquid with the acids dissolved therein has a pH of 5 or less, (D2b) one or more organic compounds of the formula (I) ##STR00004## where R1 and R2 are each monovalent groups independently containing 1 to 26 carbon atoms, where the R1 group is attached via a carbon atom present in the R1 group or via an oxygen atom present in the R1 group, and where the R2 group is attached via a carbon atom present in the R2 group, or are joined to one another to form a ring structure, such that the ring structure comprises a total of 4 to 7 ring atoms and the R1 and R2 groups comprise a total of 2 to 26 carbon atoms, where the R1 group is attached via a carbon atom present in the group or via an oxygen atom present in the R1 group, and where R2 is attached via a carbon atom present in the group; (D3) one or more refractories in the form of platelet-shaped particles (D4) one or more refractories in the form of grainy particles wherein the proportion of the refractories (D3) is in the range from 15% to 80, based on the total mass of refractories (D3) and refractories (D4) in component (D).

2. The kit as claimed in claim 1, wherein constituents (D1), (D2a) or (D2b), (D3) and (D4) are present in component (D), based in each case on the total mass of component (D), in the following concentration: (D1) 20% to 75% (D2a) 0.1% to 10% or (D2b)0.1% to 10% (D3) 10% to 58% (D4) 14% to 64%.

3. The kit as claimed in claim 1, wherein, in component (D), (D2a) the acids are selected from the group consisting of organic acids selected from the group consisting of mono-, di- and tricarboxylic acids, and inorganic acids selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid and acidic phosphates; and/or (D2b) the organic compounds of the formula (I) are selected from the group consisting of esters, lactones and acid anhydrides; and/or (D3) the refractories in the form of platelet-shaped particles are selected from the group consisting of macrocrystalline graphites, α-boron nitride and sheet silicates; and/or (D4) the refractories in the form of grainy particles are selected from the group consisting of microcrystalline graphites, carbon black, coke, zirconium silicate, andalusite, sillimanite, kyanite, quartz, quartz glass, mullite, fireclay, aluminum oxides, bauxite, wollastonite, titanium dioxides, olivine, alkaline earth metal phosphates of the composition M.sub.5(PO.sub.4).sub.3OH where M is an alkaline earth metal, silicon nitride and rutile.

4. The kit as claimed in claim 3, wherein, in component (D), the refractories (D4) further comprise: (D4a) amorphous particulate silicon dioxide.

5. The kit as claimed in claim 1, wherein the amorphous particulate silicon dioxide in component (B) and in constituent (D4) of component (D) is independently selected from the group consisting of particulate synthetic amorphous silicon dioxide containing at least carbon as a secondary constituent, where the proportion of silicon dioxide is 90% or more, based on the total mass of the particulate synthetic amorphous silicon dioxide and of the secondary constituents; particulate synthetic amorphous silicon dioxide comprising oxides of zirconium as secondary constituent; particulate synthetic amorphous silicon dioxide producible by oxidizing metallic silicon by means of an oxygenous gas; particulate synthetic amorphous silicon dioxide producible by quenching a silicon dioxide melt; fumed silica; and mixtures thereof.

6. The kit as claimed in claim 1, wherein component (B) is a pulverulent additive mixture comprising particulate amorphous silicon dioxide, and one or more oxidic boron compounds, preferably selected from the group consisting of borates, boric acids, boric anhydrides, borosilicates, borophosphates and borophosphosilicates.

7. The kit as claimed in claim 1, wherein component (C) one or more oxidic boron compounds, where the total concentration of oxidic boron compounds calculated as B.sub.2O.sub.3 is 0.4% to 1.0%.

8. The kit as claimed in claim 1, wherein component (C) is a solution or dispersion comprising lithium-containing waterglass, or a kit containing raw materials for production of a solution or dispersion comprising lithium-containing waterglass.

9. A method of producing cores for use in diecasting, comprising the steps of (a) producing a molding material mixture by mixing components (A), (B) and (C) (b) shaping the molding material mixture (c) thermally curing the shaped molding material mixture to form a main body of the core to be produced (d) applying a composition (D) or a coating composition formed by diluting a composition (D) with carrier liquid (D1) to the main body and then drying, such that a coating is produced on the main body, forming a core comprising the main body and a coating disposed atop the main body, which extends at least over the entire surface of the core that comes into contact with a metal melt in the casting operation, wherein components (A), (B), and (C), and composition (D) are defined as follows: A) a mold base material selected from the group consisting of quartz sand, chromium ore sand, olivine sand, aluminum silicate sands and mixtures thereof; (B) particulate amorphous silicon dioxide or an additive mixture comprising particulate amorphous silicon dioxide; (C) a solution or dispersion comprising waterglass or a kit comprising raw materials for production of a solution or dispersion comprising waterglass; (D) a composition for production of a coating, said composition comprising (D1) a carrier liquid selected from the group consisting of water and mixtures of water with one or more alcohols; (D2) a constituent from the group consisting of (D2a) dissolved in the carrier liquid, one or more acids, where the aqueous phase formed by the carrier liquid with the acids dissolved therein has a pH of 5 or less, (D2b) one or more organic compounds of the formula (I) ##STR00005## where R1 and R2 are each monovalent groups independently containing 1 to 26 carbon atoms, where the R1 group is attached via a carbon atom present in the R1 group or via an oxygen atom present in the R1 group, and where the R2 group is attached via a carbon atom present in the R2 group, or are joined to one another to form a ring structure, such that the ring structure comprises a total of 4 to 7 ring atoms and the R1 and R2 groups comprise a total of 2 to 26 carbon atoms, where the R1 group is attached via a carbon atom present in the group or via an oxygen atom present in the R1 group, and where R2 is attached via a carbon atom present in the group; (D3) one or more refractories in the form of platelet-shaped particles (D4) one or more refractories in the form of grainy particles wherein the proportion of the refractories (D3) is in the range from 15% to 80, based on the total mass of refractories (D3) and refractories (D4) in component (D).

10. The method as claimed in claim 9, wherein, in step (c), the thermal curing is effected at temperatures in the range from 100° C. to 300° C.

11. The method as claimed in claim 9, wherein, in step (d), the main body on application of the composition (D) or of the coating composition is at a temperature of less than 80° C.; and/or the composition (D) or coating composition is applied to the surface of the main body by a method selected from the group consisting of spraying, dipping, flow coating and painting, preferably dipping; and/or the drying is effected at temperatures in the range from 80° C. to 220° C.

12. A core comprising (i) a main body comprising (A) a mold base material selected from the group consisting of quartz sand, chromium ore sand, olivine sand, aluminum silicate sands and mixtures thereof and (B) particulate amorphous silicon dioxide bound by waterglass (ii) and a coating disposed atop the main body, which extends at least over the entire surface of the core that comes into contact with a metal melt in the casting operation, where the coating comprises: (D3) one or more refractories in the form of platelet-shaped particles (D4) one or more refractories in the form of grainy particles wherein the proportion of the refractories (D3) is in the range from 15% to 80, based on the total mass of refractories (D3) and refractories (D4).

13-14. (canceled)

15. A method of using a core in diecasting, comprising producing a core by a method as claimed in claim 9, inserting the core into a casting mold, producing a casting by pouring a metal melt under a pressure of up to 200 MPa into the casting mold and allowing the metal melt to solidify, removing the core from the casting.

16. The method of claim 15, wherein the metal melt comprises aluminum or an aluminum alloy.

17. A method of using a core in diecasting, comprising providing a core as claimed in claim 12, inserting the core into a casting mold, producing a casting by pouring a metal melt under a pressure of up to 200 MPa into the casting mold and allowing the metal melt to solidify, removing the core from the casting.

18. The method of claim 17, wherein the metal melt comprises aluminum or an aluminum alloy.

19. A method of using a core in diecasting, especially in the diecasting of lightweight metals, comprising providing a core produced by a method as claimed in claim 9, inserting the core into a casting mold, producing a casting by pouring a metal melt under a pressure of up to 200 MPa into the casting mold and allowing the metal melt to solidify, removing the core from the casting.

20. The method of claim 19, wherein the metal melt comprises aluminum or an aluminum alloy.

Description

WORKING EXAMPLES

[0274] 1. Production of Cores

[0275] Components (A)-(D) of a kit of the invention were provided for production of cores for use in diecasting. The composition of components (A)-(D) is described below. For the production of comparative cores, the same components (A)-(C) were provided, as was a noninventive coating composition, the composition of which is specified below.

[0276] Step (a): Production of a Molding Material Mixture

[0277] A molding material mixture was produced by mixing [0278] (A) H32 quartz sand as mold base material with [0279] (B) particulate amorphous silicon dioxide (0.3% to 1.5%, based on the total mass of the mold base material (A)),
and [0280] (C) a solution of waterglass (alkali metal silicate) containing lithium, sodium and potassium ions (0.3% to 3% solution (C), based on the total mass of the mold base material)

[0281] Steps (b) and (c): Production of the Main Bodies for Cores

[0282] This molding material mixture was used, in a customary manner, by [0283] (b) shaping the molding material mixture by means of a core shooting machine
and [0284] (c) thermally curing the shaped molding material mixture in the core box heated to a temperature in the range from 100° C. to 250° C., assisted by aeration with air heated to a temperature in the range from 100° C. to 250° C.,
to form the main bodies for the cores to be produced.

[0285] Step d): Application of the Coating Composition

[0286] A coating composition was applied to the main bodies that had been cooled down to a temperature of less than 80° C., preferably 15° C. to 35° C.

[0287] Cores of the invention were produced using coating compositions (refractory coating) that were formed by diluting the concentrates (D) (see tables 1 and 2 below) with water as carrier liquid (D1). The coating composition was applied in each case to the surface of the main body by dipping the main bodies into a bath containing the respective coating composition. Comparative cores were produced using a coating composition that was formed by diluting the concentrate (V) (see table 1 below) with isopropanol as carrier liquid. The noninventive coating composition corresponds to customary commercially available refractory coating compositions. Refractory coatings customarily used in the prior art for waterglass-bound cores are those wherein the carrier liquid contains alcohols as main constituent, and little or no water, since water attacks the alkali metal silicate skeleton of waterglass-bound cores.

[0288] The viscosities of the inventive and noninventive coating composition are virtually identical. “Other constituents” (see table 1) are constituents that are customary in the prior art from the group consisting of wetting agents, rheological additives, binders, suspension aids and biocides.

[0289] Subsequently, the cores of the invention obtained in this way were subjected to a temperature in the range from 80° C. to 220° C., and the comparative cores to a temperature in the range from 15° C. to 30° C., such that the carrier liquid evaporates, and a coating of the nonvolatile constituents of the respective coating composition is formed on the main body.

TABLE-US-00001 TABLE 1 Composition of the coating compositions Concentrate (D) Concentrate (V) for for inventive noninventive coating coating composition 1 composition V Constituent % by wt. % by wt. Carrier liquid (D1) Water 38.5 Isopropanol 34 Water 4 Constituent (D2) Acid (D2a) 0.5 — 0 Refractories (D3) Sheet silicates 31 — 0 (pyrophyllites, powdered clay) Refractories (D4) Zirconium 8 Zirconium 40 silicate silicate Microcrystalline 8 Aluminum oxide 14.5 graphite Particulate 10 amorphous silicon dioxide (D4a) Other constituents 4 7.5 Inventive coating Noninventive coating composition composition Concentrate 100 parts by weight 100 parts by weight concentrate (D) concentrate (V) Dilution by 40 parts by weight 5 parts by weight carrier liquid of water of isopropanol

TABLE-US-00002 TABLE 2 Composition of further coating compositions for the production of cores of the invention Concentrate (D) for inventive coating composition No. 2 3 4 5 % by % by % by % by Constituent wt. wt. wt. wt. Carrier liquid Water 49.5 Water 49.5 Water 44.5 Water 36 (D1) Constituent Acid (D2a) 0.5 Acid (D2a) 0.5 Acid (D2a) 0.5 Acid (D2a) 0.5 (D2) Refractories Sheet silicates 26 Sheet silicates 26 Sheet silicates 23 Sheet silicates 31 (D3) (mica, powdered (pyrophyllites, (pyrophyllites, (mica, powdered clay) mica, powdered mica, powdered clay) clay) clay) Refractories Microcrystalline 12 Microcrystalline 12 Microcrystalline 8 Microcrystalline 8 (D4) graphite graphite graphite graphite Zirconium 10 Zirconium 9 silicate silicate Particulate 8 Particulate 8 Particulate 10 Particulate 8 amorphous amorphous amorphous amorphous silicon dioxide silicon dioxide silicon dioxide silicon dioxide (D4a) (D4a) (D4a) (D4a) Other 4 4 4 7.5 constituents Concentrate 100 parts by weight 100 parts by weight 100 parts by weight 100 parts by weight concentrate (D) concentrate (D) concentrate (D) concentrate (D) Dilution by 40 parts by weight of 25 parts by weight of 40 parts by weight of 40 parts by weight of carrier liquid water water water water

[0290] 2. Light Microscopy Analysis

[0291] Pieces were sawn out of an inventive core (production and composition as described in point 1, coating composition as specified in table 1 above) and a noninventive core (production and composition as described in point 1, coating composition as specified in table 1 above) and embedded by means of a two-component epoxy resin under reduced pressure. This was followed by preparation by means of a Struers Tegramin 20 grinding and polishing machine. This involved first grinding the samples by means of diamond disks and subsequently polishing with diamond suspensions until the final stage, resulting in what is called a polished section. Thereafter, the polished sections produced were microscopically examined by means of a Zeiss Axioscope 5 light microscope with Axiocam 305 color (D) microscopy camera.

[0292] On comparison of the dried cores (inventive vs. noninventive), a distinct difference in surface characteristics was apparent. In the case of noninventive cores, the refractory coating has penetrated very deep into the main body and has barely any surface-sealing action, such that the mold base material (A) is clearly apparent through the coating by the naked eye. Inventive cores, by contrast, feature a smooth surface seal, meaning that a coherent top layer virtually free of macroscopic pores has been deposited above the main body such that it is not apparent which mold base material (A) is present beneath the coating.

[0293] FIG. 1 shows a polished section of the noninventive core; FIG. 2 shows a polished section of the inventive core. The section in each case extends over a near-surface region of the main body and the coating disposed on the surface thereof. In the main body, the relatively large particles of the mold base material (H32 quartz sand, see above) are clearly apparent (at the lower edge of the image in FIG. 1, at the upper edge of the image in FIG. 2). The coating adjoins the surfaces of the outer particles of the main body.

[0294] FIG. 1 shows that the grainy particles of the noninventive coating composition have been deposited entirely randomly, i.e. without any particular alignment, on the surface of the core. Although the grainy particles penetrate into pores between the particles of the mold base material, these are not covered and sealed. Therefore, the surface formed by the coating is not smooth and flat, but at least partly reproduces the contours of the surface of the main body, meaning that the coating has unevenness and depressions that to a certain degree reflect the irregularities of the surface of the main body.

[0295] FIG. 2 shows that the platelet-shaped particles of the coating composition of the invention are aligned with their longest dimension parallel to the core surface, and hence bridge and cover the unevenness and depressions filled by the grainy particles on the surface of the main body, such that the irregularities of the surface of the main body barely affect the surface of the coating. Therefore, the coating has a relatively flat and smooth surface.

[0296] 3. Casting Tests

[0297] Casting tests with aluminum were conducted in a cold-chamber diecasting machine. It was possible here with cores of the invention to successfully produce castings with a gate speed of 15 m/s to 20 m/s without penetration defects (penetration of the melt into the core) or core fracture. In the case of casting with noninventive cores under the same conditions, by contrast, penetration defects were always found. After casting, the cast parts are quenched in a water bath. The core can be leached out of the casting, for example, by gradual dissolution of the alkali metal silicate binder in water or removed by means of water jetting.