Amino acid-containing moulding material mixture for production of mouldings for the foundry industry

Abstract

The present invention relates to a mold material mixture for producing moldings for the foundry industry, in particular for producing foundry molds, cores or feeders for the foundry industry, which comprises A) one or more pourable, refractory fillers, B) a binder system comprising i) formaldehyde, a formaldehyde donor and/or precondensates of formaldehyde and ii) an amino acid. The present invention additionally relates to the use of amino acids in a mold material mixture for producing moldings for the foundry industry or for producing moldings for the foundry industry, a process for producing a mold material mixture and a process for producing a molding for the foundry industry.

Claims

1. A mold material mixture for producing moldings for the foundry industry, which comprises A) one or more pourable, refractory fillers, B) a no-bake binder system comprising i) formaldehyde, a formaldehyde donor and/or precondensates of formaldehyde, and furan derivatives and/or furfuryl alcohol or precondensates of furan derivatives and/or furfuryl alcohol; and ii) an amino acid selected from the group consisting of glycine, glutamine, alanine, valine, and serine, wherein the molar ratio of amino acid to free formaldehyde is from 4:1 to 1:0.5.

2. The mold material mixture as claimed in claim 1, wherein the amino acid is glycine.

3. The mold material mixture as claimed in claim 1, wherein the one or more pourable, refractory fillers are selected from the group consisting of silica sand, fused silica sand, olivine sand, chrome-magnesite granules, aluminum silicates, heavy minerals, industrial ceramics, feldspar-containing sands, andalusite sands, hollow α-alumina spheres, spheres composed of fly ashes, rice hull ashes, expanded glasses, foamed glasses, expanded perlites, core-shell particles, and fly ashes.

4. The mold material mixture as claimed in claim 3, wherein the aluminum silicate is J-sand; the heavy minerals are selected from the group consisting of chromite, zircon sand, and R-sand; and the industrial ceramics are selected from the group consisting of chamotte, M-sand, bauxite sand and silicon carbide.

5. The mold material mixture as claimed in claim 1, wherein the one or more pourable, refractory fillers have an average particle diameter d50 in the range from 0.001 to 5 mm.

6. The mold material mixture as claimed in claim 5, wherein the one, at least one of the several or all pourable, refractory fillers have an average particle diameter d50 in the range from 0.01 to 3 mm.

7. The mold material mixture as claimed in claim 1, wherein the ratio of the total mass of the one or more pourable, refractory fillers to the total mass of constituents of the no-bake binder system of the mold material mixture is in the range from 100:5 to 100:0.1.

8. The mold material mixture as claimed in claim 7, wherein the ratio of the total mass of pourable, refractory fillers to the total mass of constituents of the binder system of the mold material mixture is in the range from 100:3 to 100:0.4.

9. The mold material mixture as claimed in claim 1, wherein the no-bake binder system is curable to give a i) phenol/furfuryl alcohol/formaldehyde resin, ii) furfuryl alcohol/formaldehyde resin, iii) urea/furfuryl alcohol/formaldehyde resin or iv) urea/furfuryl alcohol/phenol/formaldehyde resin.

10. The mold material mixture as claimed in claim 1, wherein the proportion of the amino acid in the mold material mixture is from 0.005 to 2% by weight based on the solids content of the total mold material mixture.

11. The mold material mixture as claimed in claim 10, wherein the proportion of the amino acid in the mold material mixture is from 0.01 to 1% by weight.

12. The mold material mixture as claimed in claim 1, wherein the molar ratio of amino acid to free formaldehyde is from 3:1 to 1:0.9.

13. A process for producing a mold material mixture as claimed in claim 1, which comprises the following steps: a) production or provision of one or more pourable, refractory fillers, b) production or provision of a no-bake binder system comprising i) formaldehyde, a formaldehyde donor and/or precondensates of formaldehyde, and furan derivatives and/or furfuryl alcohol or precondensates of furan derivatives and/or furfuryl alcohol; and ii) an amino acid selected from the group consisting of glycine, glutamine, alanine, valine, and serine, wherein the molar ratio of amino acid to free formaldehyde is from 4:1 to 1:0.5; and c) mixing of all components.

14. A molding for the foundry industry produced using a mold material mixture as defined in claim 1.

15. A process for producing a molding for the foundry industry, which comprises the following steps: i) production or provision of a mold material mixture as claimed in claim 1, ii) shaping of the mold material mixture to give an uncured molding and iii) curing the uncured molding or allowing the latter to cure, so that a molding for the foundry industry results, wherein the curing is effected without heating by addition of a hardener during production or provision of the mold material mixture, wherein the hardener is an organic or inorganic acid.

16. A kit for producing a mold material mixture and/or for producing a molding, the kit comprising: I) a no bake binder system comprising, i) formaldehyde, a formaldehyde donor and/or precondensates of formaldehyde, and furan derivatives and/or furfuryl alcohol or precondensates of furan derivatives and/or furfuryl alcohol; and ii) an amino acid selected from the group consisting of glycine, glutamine, alanine, valine, and serine, wherein the molar ratio of amino acid to free formaldehyde is from 4:1 to 1:0.5; and II) a hardener, wherein the hardener is selected from the group consisting of a sulfonic acid, phosphoric acid, carboxylic acid, methanesulfonic acid and sulfuric acid and mixtures thereof and III) optionally one or more pourable, refractory fillers.

17. The kit as claimed in claim 16, wherein the hardener is a sulfonic acid, wherein the sulfonic acid is para-toluenesulfonic acid.

Description

EXAMPLES

Example 1 (According to the Invention)

(1) Production of a Binder System:

(2) 0.43 g of glycine (5.7 mmol) was added to 100 g of a commercial phenol-furan cold-cure resin from Hüttenes-Albertus with the designation XA20 (furfuryl alcohol: 78%, free phenol: 4.5%, water content: 2%, free formaldehyde content: 0.171% (corresponding to 5.7 mmol); obtainable from Hüttenes-Albertus Chemische Werke GmbH) at a temperature of 40° C. and the mixture was stirred for 60 minutes. After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.09%.

(3) Production of a Mold Material Mixture:

(4) At room temperature (18-22° C.) and a relative atmospheric humidity (RAH) of 40-55%, 100 parts by weight of silica sand H32 (Quarzwerke Frechen) were placed in a laboratory mixer (BOSCH), admixed with 0.5 part by weight of hardener (Aktivator 100 SR; para-toluenesulfonic acid 65%, <0.5% of H.sub.2SO.sub.4) and mixed for 30 seconds. 1.0 part by weight of the binder system produced was subsequently added and the mixture was mixed for a further 45 seconds. The temperature of the mold material mixture produced was 18-22° C.

(5) Production of (Test) Moldings:

(6) The mold material mixture was subsequently introduced manually into a test bar mold and compacted by means of a hand plate. Cuboidal test bars having the dimensions 220 mm×22.36 mm×22.36 mm, known as Georg-Fischer test bars, were produced as test specimens.

(7) Determination of the Processing Time (PT) and Curing Time (CT):

(8) To determine the processing time (PT) and curing time (CT) of the mold material mixture, the setting behavior was observed on a Georg-Fischer test bar using the testing pin in accordance with the VDG leaflet P 72.

(9) Determination of the Bending Strength Value:

(10) The respective bending strength values were determined in accordance with the VDG leaflet P 72. To determine the bending strengths, the test bars were placed in a Georg-Fischer strength testing apparatus equipped with a three-point bending device (DISA-Industrie AG, Schaffhausen, CH) and the force which led to fracture of the test bars was measured.

(11) The bending strengths were measured after one hour, after two hours, after four hours and after 24 hours after production of the (test) moldings to be tested (storage of the cores after demolding in each case at room temperature 18-22° C., relative atmospheric humidity (20-55%)).

(12) The values determined are summarized in table 1.

(13) The (test) moldings according to the invention produced from the mold material mixture according to the invention display an improved bending strength compared to the (test) moldings produced in comparative examples 1 and 2 after 24 hours without the setting behavior being adversely affected. In addition, the content of free formaldehyde in the binder system according to the invention is lower than the content of free formaldehyde in the binder systems as per comparative examples 1 and 2.

Example 2 (According to the Invention)

(14) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 5.7 mmol of alanine were used instead of glycine.

(15) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.08%.

Example 3 (According to the Invention)

(16) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 5.7 mmol of serine were used instead of glycine.

(17) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.09%.

Example 4 (According to the Invention)

(18) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 5.7 mmol of valine were used instead of glycine.

(19) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.09%.

Comparative Example 1 (not According to the Invention)

(20) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 5.7 mmol of urea were used instead of the glycine.

(21) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.13%.

Comparative Example 2 (not According to the Invention)

(22) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, no glycine was added.

(23) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.15%.

Example 5 (According to the Invention)

(24) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 100 g of a commercial phenol-furan cold-cure resin from Hüttenes-Albertus having the designation Kaltharz 7864 (furfuryl alcohol: 40%, free phenol: 4%, water content: 2%, free formaldehyde content: 0.125% (corresponding to 4.2 mmol); obtainable from Hüttenes-Albertus Chemische Werke GmbH) were used instead of the phenol-furan cold-cure resin having the designation XA20 used in example 1. However, 4.2 mmol of glycine were used.

(25) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.04%.

(26) The values determined are summarized in table 1.

(27) The (test) moldings according to the invention produced from the mold material mixture according to the invention display an improved bending strength compared to the (test) moldings produced in comparative examples 3 and 4 after four hours without the setting behavior being adversely affected. In addition, the content of free formaldehyde in the binder system according to the invention is lower than the content of free formaldehyde in the binder systems as per comparative examples 3 and 4.

Example 6 (According to the Invention)

(28) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 5. However, 4.2 mmol of alanine were used instead of glycine.

(29) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.05%.

Example 7 (According to the Invention)

(30) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 5. However, 4.2 mmol of serine were used instead of glycine.

(31) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.06%.

Example 8 (According to the Invention)

(32) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 5. However, 4.2 mmol of valine were used instead of glycine.

(33) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.05%.

Example 9 (According to the Invention)

(34) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 5. However, 4.2 mmol of glutamine were used instead of glycine.

(35) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.03%.

Comparative Example 3 (not According to the Invention)

(36) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 5. However, 4.2 mmol of urea were used instead of the glycine.

(37) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.12%.

Comparative Example 4 (not According to the Invention)

(38) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 5. However, no glycine was added.

(39) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.17%.

Example 10 (According to the Invention)

(40) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 100 g of a commercial phenol-furan cold-cure resin from Hüttenes-Albertus having the designation Kaltharz 8117 (furfuryl alcohol: 50%, free phenol: 3-4%, water content: 2%, free formaldehyde content: 0.120% (corresponding to 4 mmol); obtainable from Hüttenes-Albertus Chemische Werke GmbH) were used instead of the phenol-furan cold-cure resin having the designation XA20 used in example 1. However, 4.0 mmol of glycine were used.

(41) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.05%.

(42) The values determined are summarized in table 1.

(43) The (test) moldings according to the invention produced from the mold material mixture according to the invention display an improved bending strength compared to the (test) moldings produced in comparative examples 5 and 6 after 24 hours without the setting behavior being adversely affected. In addition, the content of free formaldehyde in the binder system according to the invention is lower than the content of free formaldehyde in the binder systems as per comparative examples 6 and 5.

Example 11 (According to the Invention)

(44) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 10. However, 4.0 mmol of alanine were used instead of glycine.

(45) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.05%.

Example 12 (According to the Invention)

(46) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 10. However, 4.0 mmol of serine were used instead of glycine.

(47) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.08%.

Example 13 (According to the Invention)

(48) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 10. However, 4.0 mmol of valine were used instead of glycine.

(49) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.07%.

Example 14 (According to the Invention)

(50) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 10. However, 4.0 mmol of glutamine were used instead of glycine.

(51) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.03%.

Comparative Example 5 (not According to the Invention)

(52) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 10. However, 4.0 mmol of urea were used instead of the glycine.

(53) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.05%.

Comparative Example 6 (not According to the Invention)

(54) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 10. However, no glycine was added.

(55) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.15%.

Example 15 (According to the Invention)

(56) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 100 g of a commercial phenol-furan cold-cure resin from Hüttenes-Albertus having the designation Kaltharz 8500 (furfuryl alcohol: 57%, free phenol: 1.1-1.8%, water content: 8-10%, free formaldehyde content: 0.25% (corresponding to 8.3 mmol); obtainable from Hüttenes-Albertus Chemische Werke GmbH) were used instead of the phenol-furan cold-cure resin having the designation XA20 used in example 1. However, 8.3 mmol of glycine were used.

(57) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.04%.

(58) The values determined are summarized in table 1.

(59) The (test) moldings according to the invention produced from the mold material mixture according to the invention display an improved bending strength compared to the (test) moldings produced in comparative examples 7 and 8 after 24 hours without the setting behavior being adversely affected. In addition, the content of free formaldehyde in the binder system according to the invention is lower than the content of free formaldehyde in the binder systems as per comparative examples 7 and 8.

Example 16 (According to the Invention)

(60) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 15. However, 8.3 mmol of alanine were used instead of glycine.

(61) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.04%.

Example 17 (According to the Invention)

(62) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 15. However, 8.3 mmol of serine were used instead of glycine.

(63) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.05%.

Example 18 (According to the Invention)

(64) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 15. However, 8.3 mmol of valine were used instead of glycine.

(65) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.07%.

Example 19 (According to the Invention)

(66) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 15. However, 8.3 mmol of glutamine were used instead of glycine.

(67) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.06%.

Comparative Example 7 (not According to the Invention)

(68) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 15. However, 8.3 mmol of urea were used instead of the glycine.

(69) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.19%.

Comparative Example 8 (not According to the Invention)

(70) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 15. However, no glycine was added.

(71) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.27%.

Example 20 (According to the Invention)

(72) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 1. However, 100 g of a commercial furan cold-cure resin from Hüttenes-Albertus having the designation Kaltharz TDE 20 (furfuryl alcohol: 70%, water content: 5-7%, free formaldehyde content: 0.23% (corresponding to 7.7 mmol); obtainable from Hüttenes-Albertus Chemische Werke GmbH) were used instead of the phenol-furan cold-cure resin having the designation XA20 used in example 1. However, 7.7 mmol of glycine were used.

(73) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.09%.

(74) The values determined are summarized in table 1.

(75) The (test) moldings according to the invention produced from the mold material mixture according to the invention display an improved bending strength compared to the (test) moldings produced in comparative example 9 after 24 hours without the setting behavior being adversely affected. In addition, the content of free formaldehyde in the binder system according to the invention is lower than the content of free formaldehyde in the binder systems as per comparative example 9.

Example 21 (According to the Invention)

(76) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 20. However, 7.7 mmol of alanine were used instead of glycine.

(77) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.08%.

Example 22 (According to the Invention)

(78) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 20. However, 7.7 mmol of serine were used instead of glycine.

(79) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.09%.

Example 23 (According to the Invention)

(80) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 20. However, 7.7 mmol of valine were used instead of glycine.

(81) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.07%.

Comparative Example 9 (not According to the Invention)

(82) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 20. However, no glycine was added.

(83) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.23%.

Example 24 (According to the Invention)

(84) Production of a Binder System:

(85) 0.62 g of glycine (8.3 mmol) was added to 100 g of a commercial phenol-furan warm box resin from Hüttenes-Albertus having the designation “Furesan 7682” (furfuryl alcohol: 57%, free phenol: 1.0-1.6%, water content: 8-10%, free formaldehyde content: 0.25% (corresponding to 8.3 mmol); obtainable from Hüttenes-Albertus Chemische Werke GmbH) at a temperature of 40° C. and stirred for 60 minutes. After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.07%.

(86) Production of a Mold Material Mixture:

(87) At room temperature (18-22° C.) and a relative atmospheric humidity (40-55%), 100 parts by weight of silica sand H32 are placed in a laboratory mixer (BOSCH), admixed with 0.3% of hardener (Furedur 2) and the mixture is mixed for 15 seconds. The sand/hardener mixture is subsequently provided with 1.5 parts by weight of resin and mixed for a further 150 seconds. The temperature of the mold material mixture produced is 18-22° C.

(88) Production of (Test) Moldings:

(89) The mold material mixture was subsequently introduced by hand into a test bar mold, compacted using a hand plate and cured at 220° C. Cuboidal test bars having the dimensions 220 mm×22.36 mm×22.36 mm, known as Georg-Fischer test bars, were produced as test specimens.

(90) Various test moldings were produced and these were cured for 15, 30, 60 or 120 seconds at 220° C.

(91) The hot bending strength (bending strength immediately after demolding of the hot (test) molding) and the cold bending strength (bending strength of the cooled (test) molding after 24 hours) were determined on the (test) moldings produced in accordance with the method of determination described in example 1.

(92) The results are summarized in table 2.

(93) The cold bending strength of the (test) molding produced is higher than in the case of comparative example 11 in which no amino acid was added. In the case of the specimens having a short baking time (15 and 30 seconds), the cold bending strength is particularly high. The hot bending strengths are not adversely affected.

(94) These results are particularly surprising since it has hitherto been assumed in the case of phenol-furan warm box resins that high bending strengths (in particular at short baking times) can be achieved only when there is a high content of free formaldehyde.

Example 25 (According to the Invention)

(95) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 24. However, 8.3 mmol of alanine were used instead of glycine.

(96) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of below 0.08%.

(97) The results are summarized in table 2.

(98) The cold bending strength of the (test) molding produced is higher than in the case of comparative example 11 in which no amino acid was added. In the case of the specimens having a short baking time (15 and 30 seconds), the cold bending strength is particularly high. The hot bending strengths are not adversely affected.

(99) These results are particularly surprising since it has hitherto been assumed in the case of phenol-furan warm box resins that high bending strengths (in particular at short baking times) can be achieved only when there is a high content of free formaldehyde.

Example 26 (According to the Invention)

(100) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 24. However, 8.3 mmol of glutamine were used instead of glycine.

(101) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of below 0.08%.

(102) The results are summarized in table 2.

(103) The cold bending strength of the (test) molding produced is higher than in the case of comparative example 11 in which no amino acid was added. In the case of the specimens having a short baking time (15 and 30 seconds), the cold bending strength is particularly high. The hot bending strengths are not adversely affected.

(104) These results are particularly surprising since it has hitherto been assumed in the case of phenol-furan warm box resins that high bending strengths (in particular at short baking times) can be achieved only when there is a high content of free formaldehyde.

Example 27 (According to the Invention)

(105) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 24. However, 8.3 mmol of serine were used instead of glycine.

(106) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of below 0.08%.

Comparative Example 10 (not According to the Invention)

(107) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 24. However, 8.3 mmol of urea were used instead of the glycine.

(108) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.07%.

Comparative Example 11 (not According to the Invention)

(109) The production of the binder system, the mold material mixture and the (test) moldings was carried out in a manner analogous to example 24. However, no glycine was added.

(110) After cooling the binder system to room temperature (18-22° C.), the binder system had a content of free formaldehyde of 0.18%.

(111) Results:

(112) TABLE-US-00001 TABLE 1 Comparison of the processing time (PT) and curing time (CT) and also the bending strengths of the (test) moldings produced in examples 1 to 23 and comparative examples 1 to 9. Bending strengths after PT CT xx hours in [N/cm.sup.2] Example Additive [min] [min] 1 h 2 h 4 h 24 h Example 1 Glycine 7 11 250 300 380 460 Example 2 Alanine 9 12 220 300 360 430 Example 3 Serine 6 9 210 270 370 430 Example 4 Valine 7 10 230 300 370 440 Comparative Urea 17 27 55 165 185 200 example 1 Comparative No additive 9 12 260 310 350 390 example 2 Example 5 Glycine 14 20 140 240 360 380 Example 6 Alanine 13 20 110 210 300 370 Example 7 Serine 11 18 170 250 320 380 Example 8 Valine 14 22 130 220 350 360 Example 9 Glutamine 14 19 80 200 330 350 Comparative Urea 20 32 60 140 230 290 example 3 Comparative No additive 12 17 150 240 290 340 example 4 Example 10 Glycine 13 19 170 310 370 390 Example 11 Alanine 11 17 170 300 360 390 Example 12 Serine 10 17 190 310 370 380 Example 13 Valine 9 16 220 330 360 400 Example 14 Glutamine 11 16 160 390 360 390 Comparative Urea 18 28 45 175 205 256 example 5 Comparative No additive 11 18 130 240 340 350 example 6 Example 15 Glycine 7 10 210 320 400 480 Example 16 Alanine 9 13 180 310 390 450 Example 17 Serine 6 9 180 310 390 430 Example 18 Valine 6 10 200 320 400 440 Example 19 Glutamine 6 9 190 310 360 450 Comparative Urea 9 14 125 295 340 370 example 7 Comparative No additive 5 9 230 280 350 400 example 8 Example 20 Glycine 15 19 160 260 370 440 Example 21 Alanine 14 18 140 210 360 440 Example 22 Serine 12 18 170 220 400 430 Example 23 Valine 12 18 120 250 360 420 Comparative No additive 12 18 120 250 340 400 example 9

(113) TABLE-US-00002 TABLE 2 Comparison of the hot bending strengths and cold bending strengths of the (test) moldings produced in examples 24 to 26 and in comparative example 11. Hot bending strengths in [N/cm.sup.2]- Cold bending strengths [N/cm.sup.2]- tested immediately after production tested after cooling of the cores after . . . seconds baking time at after . . . seconds baking time at 220° C. 220° C. 15″ 30″ 60″ 120″ 15″ 30″ 60″ 120″ Comparative example 11 210 225 235 220 680 660 600 530 Example 24 215 220 240 230 740 710 630 580 Example 25 230 240 280 220 770 760 610 570 Example 26 200 220 270 220 780 740 610 550