METHOD FOR THE LAYER-WISE BUILDING OF BODIES COMPRISING REFRACTORY MOLD BASE MATERIAL AND RESOLES, AND MOLDS OR CORES MANUFACTURED ACCORDING TO SAID METHOD

Abstract

The invention relates to a method for the layer-wise building of bodies comprising a refractory mold base material and resoles, to three-dimensional bodies manufactured according to said method, and to the use thereof in metal casting. According to the method, the refractory mold base material is contacted with at least one ester to obtain an ester-impregnated mold material mixture.

Claims

1. A method for the layer-wise building of a body, comprising the steps of: combining at least one refractory mold base material and at least one ester, obtaining an ester-impregnated mold material mixture, spreading the ester-impregnated mold material mixture into of a thin layer having a layer thickness in the range of 1 to 6 grains, preferably 1 to 5 grains, and particularly preferably 1 to 3 grains, printing selected areas of the thin layer with a binder comprising at least resoles for curing the selected areas, and repeating the spreading and printing steps to produce an at least partially cured three-dimensional body.

2. The method according to claim 1, additionally comprising the step of: removing any unbound molding material mixture from the at least partially cured three-dimensional body; wherein an optional step of secondary curing of the partially cured three-dimensional body, in a furnace or by microwaves, may precede the removing step.

3. The method according to claim 1, wherein the refractory mold base material is selected from the group consisting of: quartz sand, zirconium sand, chromium ore sand, olivine, vermiculite, bauxite, fire clay, glass beads, glass granulate, aluminum silicate hollow microspheres and mixtures thereof, having, in particular, predominantly a round particle shape, and preferably consists of more than 50% by weight of quartz sand, with respect to the refractory mold base material.

4. The method according to claim 1, wherein more than 80% by weight, preferably more than 90% by weight, and particularly preferably more than 95% by weight of the mold material mixture is refractory mold base material.

5. The method according to claim 1, wherein the refractory mold base material has a mean particle diameter of 100 m to 600 m, preferably between 120 m and 550 m, determined by sieve analysis.

6. The method according to claim 1, wherein the mold material mixture comprises amorphous silicon dioxide, preferably with a surface area, determined according to BET, 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, and particularly preferably less than or equal to 15 m.sup.2/g.

7. The method according to claim 6, wherein the amorphous silicon dioxide is selected from the group consisting of: precipitation silica, pyrogenic silicon dioxide produced by flame hydrolysis or in the electric arc furnace, 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, quartz glass powder with spherical particles, which was prepared by melting and rapid re-cooling from crystalline quartz, and mixtures thereof, and preferably contains or consists of amorphous silicon dioxide prepared by thermal decomposition of ZrSiO.sub.4.

8. The method according to claim 6, wherein the amorphous silicon dioxide is used in quantities from 0.1 to 2% by weight, preferably 0.1 to 1.5% by weight, in each case with respect to the refractory mold base material.

9. The method according to claim 6, wherein the amorphous silicon dioxide has a water content of less than 5% by weight and particularly preferably less than 1% by weight.

10. The method according to claim 6, wherein the amorphous silicon dioxide is particulate amorphous silicon dioxide, preferably with a mean primary particle diameter, determined by dynamic light scattering, 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.

11. The method according to claim 1, wherein the resoles are added in a quantity from 0.8 to 5% by weight, preferably from 1 to 4% by weight, in each case with respect to the weight of the refractory mold base material.

12. The method according to claim 1, further comprising the step of: curing the body with CO.sub.2.

13. The method according to claim 1, wherein the mold material mixture contains at least one base, preferably an alkali hydroxide.

14. The method according to claim 1, wherein the resoles used in the printing step are in the form of an aqueous alkaline solution, preferably with a solid content from 30 to 75% by weight and a pH above 12.

15. The method according to claim 1, wherein the ester is an ester compound or a phosphate ester compound that can undergo alkaline hydrolysis.

16. The method according to claim 1, wherein the body is a mold or a core for metal casting.

17. The method according to claim 1, wherein the printing step is practiced using a printing head comprising a plurality of nozzles, wherein the nozzles are preferably selectively controllable individually.

18. The method according to claim 17, wherein the printing head can be moved in a controlled manner by a computer at least in one plane, and the nozzles apply the liquid binder layer-wise.

19. The method according to claim 17, wherein the printing head is a drop-on-demand printing head with bubble jet or piezo technology.

20. A mold or a core obtainable according to claim 1 for metal casting, in particular for iron or aluminum casting.

Description

EXAMPLES

[0078] The influence of the mold base material and of the microsilicas on the strengths was tested first using conventional test specimens, the so-called Georg-Fischer test bars.

[0079] The manufacturing of the casting molds by the 3-D printing technology, which was carried out later, confirmed the findings obtained in the process.

1. Manufacturing of the Specimens

1.1. Without Addition of SiO.SUB.2

[0080] The mold material was introduced into the bowl of a mixer from the company Hobart (model HSM 10). Subsequently, under stirring, first the curing agent and then the binder were added, and mixed in each case for 1 minute intensively with the mold base material. The type of the mold base material, of the curing agent and of the binder, as well as the respective added quantities are listed in Tab. 1.

TABLE-US-00001 TABLE 1 Molding material SiO.sub.2 .sup.(a) Curing agent .sup.(b) Binder .sup.(c) Mixture [100 GT] [GT] [GT] [GT] 1 H 32 .sup.(d) 0.3 1.5 2 H 32 .sup.(d) 0.3 0.3 1.5 3 Spherichrome .sup.(e) 0.3 1.5 4 Spherichrome .sup.(e) 0.3 0.3 1.5 5 Chromite .sup.(f) 0.3 1.5 6 Chromite .sup.(f) 0.3 0.3 1.5 7 Bauxite .sup.(g) 0.3 1.5 8 Bauxite .sup.(g) 0.3 0.3 1.5 9 Zirconium .sup.(h) 0.3 1.5 10 Zirconium .sup.(h) 0.3 0.3 1.5 11 Cerabeads .sup.(i) 0.3 1.5 12 Cerabeads .sup.(i) 0.3 0.3 1.5 .sup.(a) Possehl Mikrosilica POS B-W 90 LD (Possehl Erzkontor GmbH; manufacturing process: Production of ZrO.sub.2 and SiO.sub.2 from ZrSiO4 .sup.(b) Catalyst 5090 (ASK Chemicals GmbH) Triacetin .sup.(c) NOVASET 700 RPT .sup.(d) Quartz sand holders (MK 032) Quarzwerk .sup.(e) Chromite sand (Oregon Resources Corporationin Europecompany Possehl Erzkontor GmbH) .sup.(f) Chromium ore sand 0.1-0.4 MM .sup.(g) Bauxite Sand H 27 .sup.(h) Zirconium sand (East) .sup.(i) Cerabeads 650

1.2. With Addition of SiO.SUB.2

[0081] The procedure used was as in 1.1., except that, after the addition of curing agent, the synthetic amorphous SiO.sub.2 was also added and also mixed in for 1 minute. The type of the mold base material, of the curing agent and of the binder as well as the respective quantities added are listed in Table 1.

2. Manufacture of Test Bars

[0082] For the testing of the specimens, rectangular block test bars with the dimensions 220 mm22.36 mm22.36 mm were produced (so-called Georg-Fischer bars).

[0083] A portion of the mixtures prepared according to 1. was introduced into a molding tool with 8 engravings, compacted by compression with a hand plate, and, after the expiration of the stripping time, removed from the molding tool.

[0084] The processing time (PT), i.e., the time within which a mixture can be compacted without problem, was determined visually. The fact that the processing time has been exceeded can be seen if a mixture no longer flows freely but rolls off in slabs. The processing times of the individual mixtures are indicated in Table 2.

[0085] For the determination of the stripping time (ST), i.e., the time after which a mixture has solidified sufficiently so that it can be removed from the molding tool, a second portion of the respective mixture was introduced by hand into a round mold having a height of 100 mm and a diameter of 100 mm, and also compacted with a hand plate.

[0086] Subsequently, the surface hardness of the compacted mixture was tested at certain time intervals using the Georg-Fischer surface hardness tester. As soon as a mixture is sufficiently hard so that the test ball no longer penetrates into the core surface, the stripping time has been reached. The stripping times of the individual mixtures are indicated in Table 2.

3. Testing of the Bending Strengths

[0087] For the determination of the bending strengths, the test bars were inserted into a Georg-Fischer strength testing apparatus equipped with a 3-point bending device, and the force that led to the rupturing of the test bars was measured. The bending strengths were determined according to the following scheme: [0088] 4 hours after the molding [0089] 24 hours after the molding [0090] 24 hours after the molding plus 30 min post tempering at 120 C.

[0091] The results are listed in Tab. 2

TABLE-US-00002 TABLE 2 Bending strengths [N/cm.sup.2] 24 hours .sup.(c) PT .sup.(a)/ST .sup.(b) 120 C./30 Mixture [min] 4 hours 24 hours min/cold 1 5 22 155 210 250 2 5 25 160 220 310 3 4 35 190 295 435 4 4 30 310 420 895 5 2 13 195 200 140 6 2 12 240 230 145 7 1 16 205 285 300 8 1 17 245 310 360 9 2 15 210 275 320 10 2 15 255 300 360 11 1 20 165 270 320 12 1 18 240 265 410 .sup.(a) Processing time .sup.(b) Stripping time .sup.(c) 24 h old cores/tempered for 30 min at 120 C./strengthsmeasured after cooling

[0092] From Table 2 one sees that [0093] Spherichrome is superior to the South African chromium ore sand used to date in the foundries for all the strengths. [0094] In the case of secondary tempering, Spherichrome exhibits a strength increase that largely exceeds that of the other mold base materials tested. [0095] The addition of microsilica improves the strengths for all the mold base materials.

4. Casting Tests

[0096] In the case of the uncoated casting with iron at 1400 C., casting molds that were manufactured according to the 3-D printing technique using an ester-cured phenol resole exhibited a smoother cast surface and fewer gas inclusions than casting molds that were manufactured by means of the 3-D printing technology using an acid-curing furan resin.