Low-emission cold-setting binder for the foundry industry

Abstract

The present invention relates primarily to a mixture that is suitable for use in the no-bake process for producing cores and molds for the foundry industry, and a reaction mixture comprising said mixture and an acid hardener (i.e. an acid catalyst). The present invention further relates to a method of producing a mixture according to the invention and a method of producing a mold or a core. The invention also relates to a mold or a core for producing metal objects and a kit comprising a mixture according to the invention and certain acid hardeners. The invention further relates to the use of a mixture according to the invention as cold-setting binder and the use of said mixtures or reaction mixtures in a no-bake process for producing metal objects.

Claims

1. A binder mixture for a no-bake process, comprising (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 25 wt. %, (b) 45 wt. % or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) reaction products of formaldehyde with furfuryl alcohol and optionally further constituents, and (b-2) optionally reaction products of formaldehyde with one or a plurality of other compounds, which is not or are not furfuryl alcohol, (c) water, wherein the amount of water is at most 20 wt. %, (d) one or a plurality of organic acids with a pKa value greater than or equal to 2.5 at 25 C. and/or salts thereof, wherein the mixture has a content of free formaldehyde of at most 0.5 wt. %, the percentages by weight being relative to the total weight of the mixture, and wherein the one or a plurality of organic acids and/or salts thereof is selected from the group consisting of benzoic acid, lactic acid, citric acid, phthalic acid, 2,4-dihydroxybenzoic acid, salicylic acid and salts thereof.

2. The binder mixture for a no-bake process according to claim 1, comprising (a) monomeric furfuryl alcohol, wherein the amount of furfuryl alcohol is at most 24.75 wt. %, and/or (c) water, wherein the amount of water is at most 15 wt. %, wherein the percentages by weight are relative to the total weight of the mixture.

3. The binder mixture for a no-bake process according to claim 1, wherein the amount of constituent (b) is 50 wt. % or more, wherein the percentages by weight are relative to the total weight of the mixture.

4. The binder mixture for a no-bake process according to claim 1, wherein constituent (b) comprises (b-1) 50 wt. % or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further constituents, (b-2) reaction products of formaldehyde with one or a plurality of other compounds, which is not or are not furfuryl alcohol, said reaction products being different from constituent (b-1), wherein the amount of these further reaction products is at most 15 wt. %, wherein the percentages by weight are relative to the total weight of the mixture.

5. The binder mixture for a no-bake process according to claim 1, wherein the content of free formaldehyde is at most 0.4 wt. %, wherein the percentages by weight are relative to the total weight of the mixture.

6. The binder mixture for a no-bake process according to claim 1, wherein the ammonia content is at most 1 wt. %, wherein the percentages by weight are relative to the total weight of the mixture.

7. The binder mixture for a no-bake process according to claim 1, wherein the total nitrogen content is at most 4 wt. %, wherein the percentages by weight are relative to the total weight of the mixture.

8. The binder mixture for a no-bake process according to claim 1, wherein constituent (b-1) comprises 2,5-bis(hydroxymethyl)furan (BHMF) in an amount of at least 1 wt. %, relative to the total weight of a mixture according to the invention.

9. The binder mixture for a no-bake process according to claim 8, wherein the weight ratio of constituent (a) and 2,5-bis(hydroxymethyl)furan (BHMF) of constituent (b-1) is in the range from 3:1 to 1:3.

10. The binder mixture for a no-bake process according to claim 1, wherein the total content of compounds with a molecular weight above 5000 dalton (g/mol) is at most 3 wt. %, determined by gel permeation chromatography according to DIN 55672-1 (February 1995), relative to the total weight of the mixture.

11. The binder mixture for a no-bake process according to claim 1, wherein the ratio of weight average molecular weight M.sub.w to number average molecular weight M.sub.n of constituent (b-1) is in the range from 5:1 to 9:8.

12. The binder mixture for a no-bake process according to claim 1, additionally comprising as further constituent (e) one or a plurality of adhesion promoters selected from the group of silanes, N-aminopropylmethyldiethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldiethoxysilane and/or N-aminopropyltriethoxysilane, in a total amount of up to 3 wt. %, wherein the percentages by weight are relative to the total weight of the mixture.

13. The binder mixture for a no-bake process according to claim 1, additionally comprising one or a plurality of further constituents, selected from the group of (f) organic curing moderators, selected from the group of glycols with 2 to 12 carbon atoms, in an amount of up to 10 wt. %, relative to the total weight of the mixture, (g) inert organic solubilisers, selected from the group of alcohols ROH, wherein R denotes a C1-C4 alkyl residue, (h) reaction products of furfuryl alcohol and one or a plurality of aldehydes with 2 or more carbon atoms, (j) organic compounds that have one or a plurality of H.sub.2N groups and/or one or a plurality of HN groups, (k) phenolic compounds, with 6 to 25 carbon atoms and/or one, two, three or four hydroxyl groups bound directly to an aromatic ring, (m) benzyl alcohol, (n) aldehydes with 2 or more carbon atoms selected from the group consisting of acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes.

14. The binder mixture for a no-bake process according to claim 1, wherein the pH of the mixture at 25 C. is in the range from 5 to 9.5.

15. The binder mixture for a no-bake process according to claim 1, wherein the mixture is a mixture that is stable in storage, which has a storage stability of at least 3 months at 20 C., wherein during the storage period the viscosity value of the mixture at 20 C., measured according to DIN 53019-1: 2008-09, increases by at most 80%, and the proportion by weight of constituent (a) decreases by at most 10% relative to the initial amount of monomeric furfuryl alcohol at the start of the storage period.

16. The binder mixture for a no-bake process according to claim 1, further comprising methanol as an inert organic solubiliser.

17. The binder mixture for a no-bake process according to claim 1, that is produced by a method including the following step: (S-1) reacting a furfuryl alcohol with formaldehyde and optionally further constituents in the presence of one or a plurality of organic acids with a pKa value greater than or equal to 2.5 at 25 C. and/or salts thereof, wherein the molar ratio of the total amount of furfuryl alcohol used to the total amount of formaldehyde used is greater than or equal to 1.

18. Reaction mixture, comprising (i) a mixture according to claim 1; (ii) an acid, wherein the acid has a pKa value of less than 2 at 25 C., wherein the reaction mixture comprises a content of free formaldehyde of max. 0.4 wt. %, and wherein the percentages by weight are relative to the total weight of the reaction mixture.

19. Reaction mixture according to claim 18, wherein the reaction mixture comprises no sulphuric acid or comprises sulphuric acid in an amount of max. 1 wt. %, wherein the percentages by weight are relative to the total weight of the reaction mixture minus the total weight of refractory granular materials in the reaction mixture.

20. Reaction mixture according to claim 18, wherein the acid of component (ii) is selected from the group of organic acids.

21. Reaction mixture according to claim 1, additionally comprising (iii) one or a plurality of refractory granular materials in an amount of 80 wt. % or more relative to the total weight of the reaction mixture.

22. Reaction mixture according to claim 1, wherein the mixture does not contain sulphur dioxide, a peroxide, or both sulphur dioxide and a peroxide.

23. Method of preparing a mixture according to claim 1, with the following step: (S-1) reaction of furfuryl alcohol with formaldehyde and optionally further constituents in the presence of one or a plurality of organic acids with a pKa value greater than or equal to 2.5 at 25 C. and/or salts thereof wherein the molar ratio of the total amount of furfuryl alcohol used to the total amount of formaldehyde used is greater than or equal to 1.

24. Method according to claim 23, wherein step (S-1) takes place at a temperature in the range from 90 to 160 C.

25. Method according to claim 23, with the following further steps: (S-2) preheating of the reaction mixture resulting from step (S-I) to a temperature in the range from 40 to 90 C. (S-3) optionally adjustment of the desired pH value with an inorganic base, (S-4) addition of one or a plurality of compounds that can react with any formaldehyde still present (S-5) preheating of the reaction mixture resulting from the preceding steps to a temperature in the range from 10 to 50 C. (S-6) optionally addition of further constituents.

26. Method according to claim 23, wherein the total amount of furfuryl alcohol used is at least 50 wt. % wherein the percentages by weight are relative to the total weight of the resultant mixture.

27. Method of producing a mould or a core comprising the steps: Curing of a mixture according to claim 1, or a reaction mixture comprising the mixture according to claim 1 and an acid, wherein the acid has a pKa value of less than 2 at 25 C., wherein the reaction mixture comprises a content of free formaldehyde of max. 0.4 wt. %, and wherein the percentages by weight are relative to the total weight of the reaction mixture; wherein curing preferably takes place at a temperature below 60 C.

28. Kit, comprising as a first component, a mixture according to claim 1, as a second component, an aqueous solution of an acid, wherein the acid has a pKa value of less than 2 at 25 C.

Description

EXAMPLES

(1) Unless stated otherwise, all figures given refer to weight. Abbreviations used: FA=furfuryl alcohol, AI=assessment index.

(2) The chemical and physical parameters of the resins are compared in Table 1 below. The values given correspond to average values, which are typical for the respective binder.

(3) The no-bake binders not according to the invention, with the designations KH-Ref1 and KH-Ref2, are commercially available products.

(4) TABLE-US-00001 TABLE 1 KH-Ref1 KH-Y KH-Ref2 (not according to the (according to the (not according to the invention) invention) invention) Total amount of FA 87 wt. % 67 wt. % 75 wt. % used Content of monomeric 87 wt. % 24.5 wt. % 63 wt. % FA Total nitrogen content 1.05 wt. % 2.85 wt. % 3.5 wt. % Water content 10 wt. % 11 wt. % 10 wt. % Free formaldehyde 0.15 wt. % 0.15 wt. % 0.06 wt. % Density at 20 C. 1.130 g/cm.sup.3 1.185 g/cm.sup.3 1.160 g/cm.sup.3 Dyn. viscosity at 20 C. 10 mPa * s 65 mPa * s 20 mPa * s Appearance light brown, cloudy dark brown, clear dark brown, clear

(5) The no-bake binder KH-Ref2, not according to the invention, also investigated here for comparative purposes, had the following composition:

(6) TABLE-US-00002 Cold resin TN-X 56.0 wt. % Content of monomeric FA 41.3 wt. % Water 2.5 wt. % N- 0.2 wt. % aminopropylmethyldiethoxysilane

(7) These constituents of the no-bake binder KH-Ref2 were introduced into a reactor with stirring, and the constituents were mixed for 15 minutes.

(8) Production of the Cold Resin TN-X:

(9) Furfuryl alcohol (60.30 wt. %), paraformaldehyde 91% (15.88 wt. %), formic acid 85% (0.60 wt. %), urea (12.59 wt. %), water (3.56 wt. %), ethanol (4.95 wt. %), ammonia 25% in water (2.12 wt. %).

(10) The reactor content is stirred throughout the process. A reactor is loaded with 489.9 kg furfuryl alcohol, 63.0 kg urea, 158.8 kg paraformaldehyde 91%, 35.6 kg water and 49.5 kg ethanol and they are mixed thoroughly. Then 4.8 kg formic acid 85% is added and the resultant mixture is heated to 90 C. At time intervals of about 30 minutes, a further 62.9 kg urea is added gradually at 90 C. Then this reaction mixture is cooled a little and 113.1 kg furfuryl alcohol is added. After further cooling to 50 C., finally a pH in the range from 8.1 to 8.8 is established by adding 25% ammonia in water. The resultant product is designated here as mixture TN-X, not according to the invention.

(11) Data for the cold resin TN-X: water content: 13.5 wt. %, total nitrogen content: 6.2 wt. %, formaldehyde content: 0.1 wt. %, viscosity at 20 C.: 95 mPas.

(12) Production of the No-Bake Binder KHY According to the Invention:

(13) Furfuryl alcohol (66.98 wt. %), paraformaldehyde 91% (12.38 wt. %), benzoic acid (1.56 wt. %), urea (6.07 wt. %), water (6.94 wt. %), ethanol (2.98 wt. %), monoethylene glycol (1.99 wt. %), N-aminopropyltriethoxysilane (Dynasilane 1506) (0.40 wt. %), sodium hydroxide solution 33% in water (0.70 wt. %).

(14) The reactor content is stirred throughout the process. A reactor is loaded with 223.2 kg furfuryl alcohol and 5.2 kg benzoic acid and they are mixed thoroughly (pH: 3.7-4.2) and then 123.8 kg paraformaldehyde is added. Then it is heated within 30-60 minutes to 100 to 110 C. and this temperature is maintained for 60 minutes. At this temperature, two further portions of furfuryl alcohol and benzoic acid are added to the reaction mixture with a time interval. Then the temperature is raised to about 135 C. and the reaction mixture is heated under reflux (duration: 3 to 5 hours, the reflux temperature decreases slowly and continuously to approx. 125 C.). Then the resultant reaction mixture is cooled quickly, 60.7 kg urea is added and it is cooled further. At a temperature of 60 C., 4.0 kg of sodium hydroxide solution (33% in water) is added, establishing a pH value in the range from 5.5-6.0 (measured at 20 C.). After the reaction mixture has cooled further to about 30 C., 69.4 kg water, 29.8 kg ethanol and 19.9 kg monoethylene glycol and 4.0 kg Dynasilane 1506 are added and mixed. Optionally, finally the pH value of the reaction mixture is adjusted to 5.5-6.5 with max. 3.0 kg sodium hydroxide solution (33% in water). The resultant product is designated herein as mixture KH-Y according to the invention.

(15) Bending Strengths and Setting Behaviour

(16) The respective bending strength values were determined according to VDG Code of Practice P 72 (October 1999) (Testing of cold-setting, synthetic resin-bonded moist moulding materials with hardener added).

(17) The moulding mixture was produced in a laboratory mixer (BOSCH). For this, first the parts by weight of acid hardener given in Table 2 were added in each case to 100 parts by weight of quartz sand H32 (Frechen Quartz Works) and mixed for 30 seconds. Then the parts by weight of binder shown in Table 2 were added and mixed for a further 45 seconds. The resultant mixture was produced at room temperature (18-22 C.) and a relative humidity (RH) of the air of 20-55%. The temperature of the sand was 18-22 C.

(18) Then the moulding mixture was placed by hand in the test bar mould and was compacted with a hand rammer.

(19) Test bars of rectangular parallelepiped shape with the dimensions 220 mm22.36 mm22.36 mm, so-called Georg-Fischer test bars, were produced as test specimens.

(20) For determination of the through-curing time, the moulding mixture is compacted with a hand rammer in a mould (beaker), height 80 mm and diameter 80 mm. The surface is checked at specified time intervals with a test nail. When the test nail no longer penetrates into the core surface, this represents the through-curing time.

(21) For determining the processing and curing time of the moulding mixture, the setting behaviour was observed with a Georg-Fischer test bar, with the test pin according to VDG P 72.

(22) The respective bending strength values were determined according to the aforementioned VDG-Code of Practice P 72. For determination of the bending strengths, the test bars were placed in a Georg-Fischer strength tester, equipped with a three-point bending device (DISA-Industrie AG, Schaffhausen, C H) and the force causing breakage of the test bar was measured.

(23) The bending strengths were after one hour, after two hours, after four hours and after 24 h after producing the moulding mixture to be tested (storage of the cores after removal from the mould, in each case at room temperature 18-22 C., RH 20-55%).

(24) Test series were conducted with the no-bake binder KH-Ref2 (not according to the invention) and two test series with the no-bake binder KHY (according to the invention), in each case with two different parts by weight of.

(25) The results of the respective strength tests are presented in Table 2 (Table 2a and 2b) as the mean value of two measurements.

(26) In the first test series, in each case separately, 1 part by weight (corresponding to 1 wt. %, relative to the amount of sand used) of no-bake binder KH-Ref2 (not according to the invention) and KHY (according to the invention) was processed with 0.5 part by weight of a 65 wt. % solution of p-toluenesulphonic acid in water (corresponding to 0.325 part by weight of p-toluenesulphonic acid) into a moulding mixture.

(27) In the second test series, in each case separately, 1 part by weight (corresponding to 1 wt. %, relative to the amount of sand used) of no-bake binder KH-Ref2 (not according to the invention) and KHY (according to the invention) was processed with 0.4 part by weight of a 65 wt. % solution of p-toluenesulphonic acid in water (corresponding to 0.26 part by weight of p-toluenesulphonic acid) into a moulding mixture.

(28) Abbreviations Used:

(29) PT=processing time in minutes CT=curing time in minutes (100 g) TC=through-curing time in minutes VISC=viscosity in mPas at 20 C. BS1, BS2, BS4, BS24=bending strength after 1, 2, 4 or 24 hours (stated in each case in N/cm.sup.2)

(30) TABLE-US-00003 TABLE 2a Setting behaviour and bending strengths when using 0.325 part by weight of the acid hardener p-toluenesulphonic acid Binder PT CT TC BS1 BS2 BS4 BS24 KH-Ref2 16 24 42 180 400 430 500 KH-Y 15 23 41 160 350 450 570

(31) TABLE-US-00004 TABLE 2b Setting behaviour and bending strengths when using 0.26 part by weight of the acid hardener p-toluenesulphonic acid Binder PT CT TC BS1 BS2 BS4 BS24 KH-Ref2 25 35 63 140 335 360 460 KH-Y 24 33 68 85 310 335 435
Emission Measurements in Mixing, Filling, and Compacting, and Result of Casting

(32) The moulding mixtures described in Table 3 were processed into moulds and iron or steel casting was performed with both moulds. The measured harmful emissions in mixing, filling, and compacting are shown in Table 4. The result of casting was defect-free in both cases.

(33) TABLE-US-00005 TABLE 3 Composition of moulding mixtures Moulding mixture 1 Moulding mixture 2 (not according to the (according to the invention) invention) No-bake regenerated 100 parts by weight 100 parts by weight material p-Toluenesulphonic acid 0.3 part by weight 0.3 part by weight (65% in water) KH-Y (according to the 1.0 part by weight invention) KH-Ref1 1.0 part by weight (not according to the invention)

(34) TABLE-US-00006 TABLE 4 Results of measurement of harmful emissions in mixing, filling, and compacting Moulding mixture 1 (not according Moulding mixture 2 to the invention) (according to the invention) Furfuryl alcohol 33.00 mg/m.sup.3 10.77 mg/m.sup.3 Formaldehyde 0.222 mg/m.sup.3 0.049 mg/m.sup.3 AI TLV 0.822 0.325 AI Others 0.628 0.160 AI total 1.450 0.485

(35) The TLV values taken as a basis were the threshold limit values according to Technical Rules for Hazardous Substances (Technische Regel fr Gefahrstoffe, TRGS) 900 Edition January 2006 as amended June 2010 and TRGS 402, Edition January 2010, if no corresponding limits are published in TRGS 900.

(36) The assessment indices AI TLV were determined according to TRGS 402 clause 5.2. The assessment indices AI Others were determined according to TRGS 402 clause 5.3. TRGS 402 in the edition of January 2010 was taken as the basis.

(37) AI total=AI TLV+AI Others. This index should not exceed the limit of 1.

(38) The mixtures according to the invention permit compliance with the limit AI total.

(39) Investigations of Storage Stability

(40) The storage stability involved storage for a period of 6 months at a constant temperature of 20-22 C. and investigation at monthly intervals. For this, the viscosity of the cold resin KHY according to the invention was measured and the application properties of a corresponding moulding mixture were determined (as described above).

(41) For further investigation of the application properties, first a moulding mixture was produced. First, 0.5 part by weight of a 65 wt. % solution of p-toluenesulphonic acid in water was added to 100 parts by weight of quartz sand H32 (Frechen Quartz Works) and mixed for 30 seconds. Then 1 part by weight of binder KHY was added and mixed for a further 45 seconds. The resultant moulding mixture was produced at room temperature (20-22 C.) and relative humidity (RH) of 40-55%. The temperature of the sand was 20-22 C.

(42) TABLE-US-00007 TABLE 5 Measurements for the storage stability of the cold resin KH-Y according to the invention Storage time VISC PT CT BS1 BS2 BS4 BS24 0 month 52 15 22 105 345 435 460 1 month 60 10 14 210 420 540 495 2 months 67 12 16 140 325 460 550 3 months 69 14 19 125 295 490 500 4 months 71 13 18 120 380 480 520 5 months 99 11 16 100 290 430 430 6 months 109 13 18 150 255 410 435

(43) TABLE-US-00008 TABLE 6 Chemical and physical parameters of the no-bake binder KH-Y2 according to the invention KH-Y2 (according to the invention) Total amount of FA 70.18 wt. % used Content of monomeric 24.1 wt. % FA Total nitrogen content 0.75 wt. % Water content 10.5 wt. % Free formaldehyde 0.2 wt. % Density at 20 C. 1.185 g/cm.sup.3 Dyn. viscosity at 20 C. 70 mPa * s Appearance dark brown, clear

(44) Mixture KHY2 according to the invention has a very low total nitrogen content, so that this no-bake binder according to the invention is particularly suitable for iron and steel casting, in particular for the casting of stainless steel.

(45) Production of the No-Bake Binder KHY2 According to the Invention:

(46) Furfuryl alcohol (70.18 wt. %), paraformaldehyde 91% (12.03 wt. %), benzoic acid (1.64 wt. %), bisphenol A (2.75 wt. %), urea (1.72 wt. %), water (5.14 wt. %), ethanol (3.12 wt. %), monoethylene glycol (1.00 wt. %), N-aminopropyltriethoxysilane (Dynasilane 1505) (0.40 wt. %) potassium hydroxide solution 45% in water (2.02 wt. %).

(47) The reactor contents are stirred throughout the process. In a reactor, 234.0 kg furfuryl alcohol and 5.5 kg benzoic acid are mixed thoroughly (pH value: 3.7-4.2) and then 120.3 kg paraformaldehyde is added. It is then heated within 30-60 minutes to 100-110 C. and this temperature is maintained for 60 minutes. At this temperature, two further portions of furfuryl alcohol and benzoic acid are added to the reaction mixture with a time interval. Then the temperature is raised to about 135 C. and the reaction mixture is heated under reflux (duration: 3 to 5 hours, during which the reflux temperature decreases slowly and continuously to approx. 125 C.). Then the resultant reaction mixture is cooled a little, 27.50 kg bisphenol A is added and it is cooled further. At a temperature of 80 C., 20.2 kg potassium hydroxide solution (45% in water) is added and it is stirred for about one more hour. After the reaction mixture has cooled further to about 60 C., 31.2 kg ethanol and 17.2 kg urea are added. After the reaction mixture has cooled further to about 35 C., finally 51.4 kg water, 10.0 kg monoethylene glycol and 4.0 kg Dynasilane 1505 are added and mixed. The resultant product is designated herein as mixture KHY2 according to the invention.

(48) As in the first test series described above, correspondingly 1 part by weight (corresponding to 1 wt. %, relative to the amount of sand used) of no-bake binder KHY2 according to the invention was processed with 0.5 part by weight of a 65 wt. % solution of p-toluenesulphonic acid in water (corresponding to 0.325 part by weight of p-toluenesulphonic acid) into a moulding mixture.

(49) With this moulding mixture, the bending strengths and the setting behaviour were determined, according to the test conditions described above and according to the details given above.

(50) TABLE-US-00009 TABLE 6a Setting behaviour and bending strengths of the mixture KH-Y2 according to the invention, using 0.325 part by weight of the acid hardener p-toluenesulphonic acid Binder PT CT TC BS1 BS2 BS4 BS24 KH-Y2 9 15 41 165 320 380 525