Process for producing a metallic casting or a cured shaped part using aliphatic polymers comprising hydroxy groups

Abstract

A process (i) for producing a metal casting or (ii) for producing a cured shaped part for use in the casting of metallic castings is described. Furthermore, the use of an aliphatic polymer which comprises structural units containing hydroxy groups and has been crosslinked by etherification as binder of a shaped part for use in the casting of metallic castings is described. A shaped part for use in the casting of metallic castings, comprising at least one base mould material and a cured binder comprising or consisting of an aliphatic polymer which comprises structural units containing hydroxy groups and has been crosslinked by etherification, is likewise described. In addition, a cured shaped part which is producible by a process according to the invention and also a mould material mixture for use in the process of the invention are described.

Claims

1. A process (i) for producing a metallic casting or (ii) for producing a cured shaped part selected from the group consisting of casting mould, core and feeder for use in the casting of metallic castings, comprising: provision or production of a base mould material, provision or production of (a) an aqueous mixture comprising one or more aliphatic polymers in each case comprising structural units containing hydroxy groups and having the formula (I)
—CH.sub.2—CH(OH)—  (I), provision or production of (b) an aqueous mixture comprising one or more acids and/or one or more heat-labile acid precursors as catalyst for etherification of the hydroxy groups of the aliphatic polymer or polymers, combining of the base mould material with (a) the aqueous mixture comprising one or more aliphatic polymers and (b) with the aqueous mixture comprising one or more acids and/or one or more heat-labile acid precursors to give a mould material mixture, wherein the mould material mixture is free of aromatics and free of phenolic resins, shaping of the mould material mixture and to effect curing of the shaped mould material mixture to give the cured shaped part, heating of the shaped mould material mixture so that heat-labile acid precursors present in the mould material mixture decompose with liberation of acid and/or hydroxy groups of the aliphatic polymer or polymers crosslink with one another in the presence of the acid or acids with etherification of the hydroxy groups, and removal of water from the heated shaped mould material mixture, wherein the one or more acids and/or the one or more heat-labile acid precursors are selected from the group consisting of: inorganic prone acids which have a pKa of ≤7, monoprotic organic protic acids, which have a pKa of ≤7, Lewis acids, selected from the group consisting of boron trifluoride and the chlorides and bromides of boron, aluminium, phosphorus, antimony, arsenic, iron, zinc, and tin, and salts which can be thermally decomposed to acids, selected from the group consisting of: ammonium salts of mineral acids, and sulphuric acid salts of alkanolamines.

2. The process according to claim 1, wherein the total moisture content of the mould material mixture is set before or during shaping of the mould material mixture so that a mould material mixture which is able to be shot to give a shaped part, and/or is able to be stamped to give a shaped part, results; and/or the step of curing of the shaped mould material mixture by heating of the shaped mould material mixture and removal of water from the heated shaped mould material mixture is carried out at least until a water-resistant cured shaped part results, and/or the shaping of the mould material mixture is carried out by shooting, or by introduction into a moulding box, and/or the mould material mixture comprises a sand, and has a proportion of solids of more than 95% by weight, based on the total mass of the mould material mixture, and/or foam formation or bubble formation in the mould material mixture is minimised or avoided when carrying out the process in one or both steps selected from combining of the base mould material with (a) the aqueous mixture comprising one or more aliphatic polymers and (b) with the aqueous mixture comprising one or more acids and/or one or more heat-labile acid precursors to give a mould material mixture and shaping of the mould material mixture.

3. The process according to claim 1, wherein the heating of the shaped mould material mixture is carried out to a temperature in the range from 100° C. to 300° C., and/or the removal of water from the heated shaped mould material mixture is carried out by means of one or more measures selected from the group consisting of passage of a heated gas, evacuation and drying in a drying apparatus.

4. The process according to claim 1, wherein the aliphatic polymers used can be produced by at least partial hydrolysis of polyvinyl acetate, and/or are dissolved in the aqueous mixture in which they are present in an amount of at least 90% by weight, based on the total mass of aliphatic polymers used.

5. The process according to claim 1, wherein the one or more aliphatic polymers comprise one or more polyvinyl alcohols, where the totality of the polyvinyl alcohols used has a degree of hydrolysis of >50 mol %, and/or has a dynamic viscosity in the range from 0.1 to 30 mPa.Math.s determined on a 4% strength (w/w) aqueous solution of the totality of the polyvinyl alcohols used at 20° C.

6. The process according to claim 1, wherein the base mould material comprises: one or more particulate refractory solids selected from the group consisting of oxides, silicates and carbides, in each case comprising one or more elements from the group consisting of Mg, Al, Si, Ca, Ti, Fe and Zr; mixed oxides, mixed carbides and mixed nitrides, in each case comprising one or more elements from the group consisting of Mg, Al, Si, Ca, Ti, Fe and Zr; and graphite and/or one or more particulate lightweight fillers selected from the preferred group consisting of core-shell particles, having a glass core and a refractory shell; spheres composed of fly ash; composite particles; perlite; rice hull ash; expanded glass, hollow glass spheres, and hollow ceramic spheres.

7. The process according to claim 1, wherein the ratio of the total mass of aliphatic polymers used to the total mass of base mould material used is in the range from 0.2:100 to 13:100, and/or the ratio of the sum of the total mass of the aqueous mixture comprising one or more aliphatic polymers (a) which is used and the total mass of the aqueous mixture comprising ono or more acids and/or one or more heat-labile acid precursors (b) which is used to the total mass of base mould material used is in the range from 1:100 to 50:100; and/or the ratio of the total mass of acids and/or heat-labile acid precursors used to the total mass of aliphatic polymers used is in the range from 1:5 to 1:50.

8. The process according to claim 1 wherein the one or more acids and/or the one or more heat-labile acid precursors, are selected: from the group consisting of inorganic protic acids which have a pKa of ≤3 and/or from the group consisting of phosphoric acid and sulfuric acid.

9. The process (i) according to claim 1 comprising: contacting of the cured shaped part with a casting metal to produce a metallic casting, with the casting metal solidifying in contact with the cured shaped part.

10. The process (i) according to claim 1, wherein the casting metal is selected from the group consisting of aluminium, magnesium, tin, zinc and alloys thereof and/or the temperature of the casting metal during casting is not higher than 900° C.

11. The process according to claim 1, wherein the one or more aliphatic polymers comprise one or more polyvinyl alcohols, where the totality of the polyvinyl alcohols used has a degree of hydrolysis of in the range from 70 mol % to 100 mol %, and/or has a dynamic viscosity in the range from 1.0 to 15 mPa.Math.s determined on a 4% strength (w/w) aqueous solution of the totality of the polyvinyl alcohols used at 20° C.

12. The process according to claim 1, wherein the base mould material comprises: one or more particulate lightweight tillers selected from the preferred group consisting of core-shell particles, having a glass core and a refractory shell and a bulk density in the range from 470 to 500 g/l; spheres composed of fly ash; composite particles; closed-pored microspheres composed of expanded perlite; rice hull ash; expanded glass, hollow glass spheres, and hollow α-alumina spheres.

13. The process according to claim 1, wherein the ratio of the total mass of aliphatic polymers used to the total mass of base mould material used is in the range from 0.3:100 to 10:100 and/or the ratio of the sum of the total mass of the aqueous mixture comprising one or more aliphatic polymers (a) which is used and the total mass of the aqueous mixture comprising one or more acids and/or one or more heat-labile acid precursors (b) which is used to the total mass of base mould material used is in the range from 1.5:100 to 40:100; and/or the ratio of the total mass of acids and/or heat-labile acid precursors used to the total mass of aliphatic polymers used is in the range from 1:10 to 1:50.

14. The process according to claim 1, wherein the one or more acids and/or the one or more heat-labile acid precursors are selected from the group consisting of: inorganic protic acids which have a pKa of ≤5, monoprotic organic protic acids which have a pKa of ≤7, water-soluble Lewis acids.

15. The process according to claim 1, wherein the ratio of the total mass of aliphatic polymers used to the total mass of base mould material used is in the range from 0.5:100 to 9:100, and/or the ratio of the sum of the total mass of the aqueous mixture comprising one or more aliphatic polymers (a) which is used and the total mass of the aqueous mixture comprising one or lore acids and/or one or more heat-labile acid precursors (b) which is used to the total mass of base mould material used is in the range from 2:100 to 35:100; and/or the ratio of the total mass of acids and/or heat-labile acid precursors used to the total mass of aliphatic polymers used is in the range from 1:20 to 1:40.

Description

FIGURES

(1) FIG. 1 shows the left-over pieces of a comparative standard bending test bar “B cold box” in an iron casting after casting. It can be seen that the left-over pieces of the cold box-bound standard bending test bar remain virtually completely in the iron casting and were very difficult to remove (poor ability to remove the core, cf. Example 7).

(2) FIG. 2 shows the left-over pieces of a comparative standard bending test bar “B-V38” in an iron casting after casting. It can be seen that the left-over pieces of the standard bending test bar “B-V38” were able to be removed readily and virtually completely from the iron casting (good core removal capability, cf. Example 7).

(3) FIG. 3 shows the left-over pieces of a standard bending test bar “B-E61.3V1” produced by the process of the invention in an iron casting after casting. It can be seen that the left-over pieces of the standard bending test bar “B-E61.3V1” were able to be removed very readily and virtually completely from the iron casting (very good core removal capability, cf. Example 7).

(4) The FIGS. 4 to 9 described below show cross sections of a cut-open iron casting which is sawn open in the middle (along the support surfaces of the standard bending test bar), so that the hollow spaces produced by standard bending test bars in the iron casting (after removal thereof from the iron casting) are divided into two halves in the middle of the length in the iron casting (for more details see Example 7). The cross sections of the hollow spaces produced by the standard bending test bars (casting negative) are as a result half in the upper half of the sawn-open metal casting (produced by the part of the standard bending test bar located at the top during the casting of iron, “upper mould half”) and half in the lower half of the sawn-open metal casting (produced by the part of the standard bending test bar located at the bottom during the casting of iron, “lower mould half”).

(5) FIG. 4 shows, in cross section, the upper mould half of the iron casting. It is possible to see here the upper half of the hollow space (casting negative) formed by the standard bending test bar B-V38 (comparison) after removal thereof from the metal casting. It is possible to see with the aid of the straight wooden spatula laid on this upper side of the casting negative that the casting negative has a significant concave (away from the wooden spatula) deformation in the middle, which has arisen as a result of the deformation of the standard bending test bar B-V38 during casting with iron. Cores which are not dimensionally stable during casting cannot be used for manufacture of metal castings.

(6) FIG. 5 shows, in cross section, the lower mould half of the iron casting. It is possible to see here the lower half of the hollow space (casting negative) formed by the standard bending test bar B-V38 (comparison) after removal thereof from the metal casting. It is possible to see with the aid of the straight wooden spatula laid on this underside of the casting negative that the casting negative has readily visible concave (away from the wooden spatula) deformations on each of the sides, which have arisen as a result of the deformation of the standard bending test bar B-V38 during casting with iron.

(7) FIG. 6 shows, in cross section, the upper mould half of the iron casting. It is possible to see here the upper half of the hollow space (casting negative) formed by the standard bending test bar B-cold box (comparison) after the removal thereof from the metal casting. With the aid of the straight wooden spatula laid on this upper side of the casting negative, it is possible to see that the casting negative has no visible deformations and accordingly the standard bending test bar B-cold box (comparison) has not become visibly deformed during casting with iron. In addition, strong distortions in the region of the sand core can be seen. These have an adverse effect on the casting.

(8) FIG. 7 shows, in cross section, the lower mould half of the iron casting. It is possible to see here the lower half of the hollow space (casting negative) formed by the standard bending test bar B-cold box (comparative) after the removal thereof from the metal casting. With the aid of the straight wooden spatula laid on this underside of the casting negative, it is possible to see that the casting negative has no visible deformations and accordingly the standard bending test bar B-cold box (comparison) has not become visibly deformed during casting with iron. In addition, severe distortions in the region of the sand core can be seen. These have an adverse effect on the casting.

(9) FIG. 8 shows, in cross section, the upper mould half of the iron casting. It is possible to see here the upper half of the hollow space (casting negative) formed by the standard bending test bar B-E61.3V1 (produced by the process of the invention) after removal thereof from the metal casting. With the aid of the straight wooden spatula laid on this upper side of the casting negative, it is possible to see that the casting negative has no visible deformations and accordingly the standard bending test bar B-E61.3V1 has not become visibly deformed during casting with iron. In comparison with FIG. 6 and FIG. 7, significantly lower distortion can also be seen.

(10) FIG. 9 shows, in cross section, the lower mould half of the iron casting. It is possible to see here the lower half of the hollow space (casting negative) formed by the standard bending test bar B-E61.3V1 (produced by the process of the invention) after removal thereof from the metal casting. With the aid of the straight wooden spatula laid on this underside of the casting negative, it can be seen that the casting negative has no visible deformations and accordingly the standard bending test bar B-E61.3V1 (produced by the process of the invention) has not become visibly deformed during casting with iron.

(11) FIG. 10 shows, in cross section, an iron cube (modulus 1.68 cm) obtained in test casting using a cold box-bound feeder produced by a method which is not according to the invention, with the connection of the residual feeder composed of iron discernible at the top. Significant sink hole formation in the residual feeder, which extends into the metallic casting (iron cube), can be seen. For further explanations in respect of FIG. 10, see Example 13.

(12) FIG. 11 shows, in cross section, an iron cube (modulus 1.68 cm) obtained in test casting using a water glass-bound feeder produced by a method which is not according to the invention, with connection of the residual feeder composed of iron discernible at the top. Significant sink hole formation in the residual feeder, which extends far into the metallic casting (iron cube), can be seen. For further explanations in respect of FIG. 11, see Example 13.

(13) FIG. 12 shows, in cross section, an iron cube (modulus 1.68 cm) obtained in test casting using a feeder produced according to the invention (“feeder B-E68.4”), with connection of the residual feeder composed of iron discernible at the top. No sink hole formation in the metal casting (iron cube) can be seen; sink holes appear only in the residual feeder. For further explanations in respect of FIG. 12, see Example 13.

EXAMPLES

(14) The following examples are intended to illustrate and explain the invention, without restricting its scope.

(15) Unless indicated otherwise, the experiments were each carried out under laboratory conditions (atmospheric pressure, temperature 20° C., atmospheric humidity 50%).

Example 1

Production of Mould Material Mixtures

(16) The constituents indicated in Table 1 below were used to produce mould material mixtures.

(17) TABLE-US-00001 TABLE 1 Constituents of mould material mixtures Mould material mixture Constituent F-cold box F-V38 F-E61.3V1 F-E68.4 Silica sand BO42 100 100 100 100 [parts by weight] Aqueous PVAL mixture 0 4.0 3.918 3.890 [parts by weight] Aqueous sulfuric acid 0 0 0.082 0.110 mixture [parts by weight] Cold box activator 6324 1.2 0 0 0 [parts by weight] Cold box gas resin 7241 1.2 0 0 0 [parts by weight]

(18) Silica sand BO 42 (CAS No. 014808-60-7) from Bodensteiner Sandwerk GmbH & Co. KG was used as base mould material in each case.

(19) A 25% strength by weight solution of polyvinyl alcohol (>93% of polyvinyl alcohol) having a degree of hydrolysis of about 88 mol % and a dynamic viscosity in the range from 3.5 to 4.5 mPa.Math.s (measured as 4% strength by weight aqueous solution at 20° C. in accordance with DIN 53015), methanol content <3% by weight; CAS RN 25213-24-5, from Kuraray, was used as aqueous PVAL mixture.

(20) A 36.5% strength by weight aqueous solution of sulfuric acid, CAS RN 7664-93-9, was used as aqueous sulfuric acid mixture.

(21) A polyisocyanate customary for producing cold box binders (polyurethane resin based on benzyl ether) (activator 6324 from Hüttenes-Albertus Chemische Werke GmbH) was used as cold box activator 6324.

(22) A phenolic resin customary for producing cold box binders (polyurethane resin based on benzyl ether) (gas resin 7241 from Hüttenes-Albertus Chemische Werke GmbH) was used as cold box gas resin 7241.

(23) The mould material mixtures were produced as indicated below:

(24) Mould material mixture F-cold box: the constituents indicated in Table 1 were mixed with one another in an electric mixer (Bosch Profi 67), forming a mould material mixture which could be shot or stamped to give a shaped part. The mould material mixture cold box is a mould material mixture for comparative purposes produced by a process which is not according to the invention.

(25) Mould material mixture F-V38: the constituents indicated in Table 1 were mixed with one another in an electric mixer (Bosch Profi 67), forming a mould material mixture which could be shot or stamped to give a shaped part. The mould material mixture V38 is a mould material mixture for comparative purposes which has not been produced by the process of the invention or is not used in such a process.

(26) Mould material mixture F-E61.3V: the constituents indicated in Table 1 were combined with one another in an electric mixer (Bosch Profi 67). For this purpose, the aqueous PVAL mixture and the aqueous sulfuric acid mixture were firstly combined with one another by means of mixing in a manner known per se to give a premix (or to give a binder system) and this premix was then combined with the initial charge of silica sand (base mould material) by mixing in the electric mixer. A mould material mixture which could be shot or stamped to give a shaped part was formed. The mould material mixture F-E61.3V is a mould material mixture produced by the process of the invention or used in such a process.

(27) Mould material mixture F-E68.4: the constituents indicated in Table 1 were combined with one another in an electric mixer (Bosch Profi 67). For this purpose, the aqueous PVAL mixture and the aqueous sulfuric acid mixture were firstly combined with one another by mixing in a manner known per se to give a premix (or to give a binder system) and this premix was then combined with the initial charge of silica sand (base mould material) by mixing in the electric mixer. This formed a mould material mixture which could be shot or stamped to give a shaped part. The mould material mixture F-E61.3V is a mould material mixture produced by the process of the invention or used in such a process.

Example 2

Production of Standard Bending Test Bars

(28) Standard bending test bars (representing a cured shaped part for use in the casting of metallic castings) for test purposes were produced in a manner known to a person skilled in the art from the mould material mixtures indicated in Example 1 by ramming (dimensions: 172×23×23 mm) in accordance with the method in the information sheet P73 (February 1996 issue) of the Verein Deutscher Gießereifachleute (hereinafter cited as “VDG information sheet P73”), No. 4.1.

(29) To cure the bending test bars, the procedure indicated below was used in each case:

(30) Bending test bar B-cold box: The mould material mixture cold box (see Example 1) was shaped as described above by ramming in a bending bar ramming box. The shaped mould material mixture was subsequently cured by means of the cold box process by passing gaseous (under the process conditions) N,N-dimethylpropylamine (about 1 ml liquid, 15 s) through it in accordance with the method in VDG information sheet P73, No. 4.3, method A.

(31) Bending test bars B-V38, B-E61.3V1, B-E68.4: In all three cases, the mould material mixtures (for production, see Example 1) were shaped as described above by ramming in a bending bar ramming box. The shaped mould material mixtures were subsequently in each case cured by heating of the shaped mould material mixture in a drying oven for 25 minutes at 210° C. and removal of water from the shaped mould material mixture by ambient air deaeration of the drying oven to give the cured shaped part (standard bending test bar).

(32) As an alternative method of curing to give the cured shaped part, bending test bars (dimensions: 187×22×22 mm) B-E68.4 were shaped using the mould material mixture F-E68.4 by shooting in a conventional core shooting machine as is also used for inorganic binders to give a shaped mould material mixture and cured by means of a tool having a temperature of 200° C. and blowing hot air (200° C., pressure: 6 bar) through it to give a cured shaped part. The shooting and passage of hot air were carried out under the length of the bending test bars.

Example 3

Determination of the Strength of Standard Bending Test Bars

(33) The final strengths of the standard bending test bars produced in Example 2 above were in each case tested: the final strengths of the standard bending test bars B-cold box were for this purpose tested 24 hours after they had been produced. The final strengths of the standard bending test bars B-V38, B-E613V1 and B-68.4 were for this purpose in each case tested 30 minutes after they had been produced (drying). All standard bending test bars were stored under laboratory conditions. A triplicate determination of the final strengths, as described in the VDG information sheet P73, No. 5.2, using a Georg Fischer strength testing apparatus type PFG with low-pressure pressure gauge (with motor drive), was carried out in each case.

(34) The bending strengths of the standard bending test bars reported below in Table 2 were determined in this way:

(35) TABLE-US-00002 TABLE 2 Final strengths of standard bending test bars Bending test bar: B-cold box B-V38 B-E61.3V1 B-E68.4 Bending strengths 720 670 780 795 (production by ramming) [N/cm.sup.2] Bending strengths n.d. n.d. n.d. 650 (production by shooting) [N/cm.sup.2] n.d.: values not determined.

(36) It can be seen from the values reported in Table 2 that the shaped parts (standard bending test bars) B-E61.3V1 and B-E68.4 produced by the process of the invention have at least comparable and even better values for the final strengths than a corresponding shaped part produced by a customary cold box process. The shaped part B-V38 produced by a process which is not according to the invention (without catalytically active acid) displayed by comparison the lowest bending strength (final strength) under the experimental conditions.

Example 4

Production of Comparative Mould Material Mixtures

(37) The constituents indicated in Table 3 below were used to produce further comparative mould material mixtures which were not produced by the process of the invention but instead by a process based on the process described in the document EP 1 721 689 A1.

(38) TABLE-US-00003 TABLE 3 Constituents of comparative mould material mixtures Comparative mould material mixture Constituent F-V01 F-V02 F-V03 Silica sand BO42 100 100 100 [parts by weight] Polyvinyl alcohol 0.2 0.2 1.2 [parts by weight] Starch (dextrin) 1.0 1.0 0 [parts by weight] Citric acid monohydrate 0.4 0.4 0.4 [parts by weight] Water 6.0 3.0 6.0 [parts by weight]

(39) Polyvinyl alcohol (>93%, granular) having a degree of hydrolysis of about 88 mol % and a dynamic viscosity in the range from 3.5 to 4.5 mPa.Math.s (measured as 4% strength by weight aqueous solution at 20° C. in accordance with DIN 53015), methanol content: <3% by weight; CAS RN 25213-24-5 was used as polyvinyl alcohol.

(40) Comparative mould material mixture F-V01: the constituents indicated in Table 3 were mixed with one another in an electric mixer (Bosch Profi 67) and stirred until foamy. A fluid, castable mould material mixture which could, however, not be shot or stamped to give a shaped part was formed.

(41) Comparative mould material mixture F-V02: the constituents indicated in Table 3 were mixed with one another in an electric mixer (Bosch Profi 67) and stirred until foamy. A mould material mixture which could be shot or stamped to give a shaped part was formed.

(42) Comparative mould material mixture F-V03: the constituents indicated in Table 3 were mixed with one another in an electric mixer (Bosch Profi 67) and stirred until foamy. A fluid, castable mould material mixture which could, however, not be shot or stamped to give a shaped part was formed.

(43) The three comparative mould material mixtures F-V01, F-V02 and F-V03 were subsequently, where possible, in each case shaped by ramming as described above (see Example 2) in a bending bar ramming box to give a shaped mould material mixture. Where possible, the shaped mould material mixture was then cured to give a cured shaped part:

(44) Comparative mould material mixture F-V01: it was not possible to produce a dimensionally stable shaped mould material mixture under the standard conditions indicated (ramming), so that no cured shaped part could be produced.

(45) Comparative mould material mixture F-V02: a mould material mixture shaped to give a bending test bar was obtained. This was cured as indicated below (see Example 5) to give a shaped part (bending test bar B-V02) and the result was compared with the result of a process according to the invention (see below, B-E61.3V1).

(46) Comparative mould material mixture F-V03: it was not possible to produce a dimensionally stable shaped mould material mixture under the standard conditions indicated (ramming). The mould material mixture was then heated in the bending test bar mould for 1 minute at 250° C. in a drying oven and evaluated after cooling to room temperature: a cured shaped part had not been formed; the mould material mixture was still soft. A further mould material mixture produced in the same way was heated in the bending test bar mould in the convection drying oven for 5 minutes at 250° C. This resulted in formation of a hard outer shell on the shaped mould material mixture, but the interior of the mixture still remained soft.

(47) It can be seen from the above observations that the comparative mould material mixtures F-V01 and F-V03 (corresponding to the process as indicated in the document EP 1 721 689 A1) could not be shot to give a shaped part or stamped to give a shaped part.

(48) Furthermore, it can be seen from the above observations that it was not possible to obtain shaped parts cured so as to be water-resistant when using the comparative mould material mixtures F-V02 and F-V03 under the experimental conditions.

Example 5

Determination of the Water Resistances of Standard Bending Test Bars

(49) Shaped mould material mixtures F-V02 (comparison, see Example 4) and F-E61.3V1 (produced according to the invention, see Example 2) were produced and cured under the conditions indicated in Table 4 below, in each case in a convection drying oven, to give the cured shaped part (standard bending test bar).

(50) After curing was complete in each case, the bending strengths were determined in each case (as per Example 3) on the shaped parts which had been cooled for 30 minutes under laboratory conditions and cured and these bending strengths are likewise reported in Table 4.

(51) The cured shaped parts were subsequently tested to determine their water resistances by the method indicated below:

(52) Firstly, the intact standard bending test bars were dipped independently of one another into deionized water at 20° C. and atmospheric pressure for 30 minutes (stopwatch) in such a way that they were just completely covered with water. After the 30 minutes had expired, the standard bending test bars were promptly taken from the water and (if possible) tested to determine their consistency.

(53) The remaining hardness of the standard bending test bars was subsequently tested, if possible, using a core hardness tester GM-578 (from Simpson Technologies GmbH, Switzerland). For this purpose, the corresponding standard bending test bar was in each case placed on a solid support and the penetration depth of the core hardness tester (according to handling instructions for the core hardness tester) was in each case measured once at a point on the outer surface (which had been in contact with the water). The measurement was carried out a total of three times at various points on the outer surface and the average of the three measurements has in each case been reported in Table 4 (“penetration depth on outer surface”).

(54) In order to test the water resistance in the interior of the shaped part (here: the standard bending test bar) as well, bending test bars produced in the same way as indicated above using the mould material mixtures F-V02 (comparison, see Example 4) and F-E61.3V1 (produced according to the invention, see Example 2) were then each sawn through in the middle of the height and just fully immersed in water for 30 minutes as indicated above, with the sawn-open interior cross-sectional area of the standard bending test bars being fully in contact with the water. After the bending test bar had been taken from the water, the remaining hardness of the bending test bar was measured again, this time in the middle of the interior cross-sectional areas, using the core hardness tester as indicated above. The measurement was again carried out a total of three times at different points on the interior cross-sectional areas and the average of the three measurements has in each case been reported in Table 4 (“penetration depth at interior cross-sectional area”).

(55) TABLE-US-00004 TABLE 4 Water resistance of standard bending test bars Bending test bar B-E61.3V1-(2) B-V02 Curing conditions 20 min 30 min 20 min 30 min 210° C. 210° C. 210° C. 210° C. Bending strengths 870 750 240 330 (final strengths) [N/cm.sup.2] Penetration depth at 6.4 0.7 Not 2.4 outer surface [mm] measurable Penetration depth at 6.7 1.8 Not 7.6 interior cross-sectional measurable area [mm]

(56) The comment “not measurable” in Table 4 means that it was not possible to measure any penetration depth on the corresponding bending test bar using the core hardness tester because the bar had disintegrated during storage in water for 30 minutes.

(57) It can be seen from the measured values or comments in Table 4 that a cured shaped part produced by a process which is not according to the invention is not water-resistant (after 20 minutes at 210° C.) or not cured so as to be water-resistant all through (after 30 minutes at 210° C.) under the experimental conditions. In contrast, a cured shaped part produced by the process of the invention was, under the same experimental conditions, cured so as to be water-resistant after only 20 minutes (standard bending test bar does not disintegrate after being taken from the water) and was cured all through after 30 minutes (penetration depth of the core hardness tester on the interior cross-sectional area <4 mm).

Example 6

Determination of the Water Resistance of Standard Bending Test Bars

(58) Standard bending test bars produced as in Example 2 above were placed on shelves in such a way that only their ends rested on the shelf (support area about 1/10 of the total area of the underside of the standard bending test bars, see below, Table 5). The shelves with the standard bending test bars thereon were introduced into a container filled with water so that the undersides of the standard bending test bars rested completely against the surface of the water and could absorb water by capillary forces. The water resistance of the standard test bars was then assessed visually over a period of 10 days.

(59) The results of this experiment are indicated below in Table 5.

(60) TABLE-US-00005 TABLE 5 Water resistance of standard bending test bars Time of Bending test bar (observation) experiment B-cold box B-V38 B-E61.3V1 0 intact intact intact 3 s intact upper side intact displays moisture 37 s intact breakdown on intact support surface on one side 41 s intact breakdown on intact support surfaces both sides 351 s intact dissolution upper side displays moisture 10 d intact dissolved upper side displays moisture

(61) It can be seen from the observations reported in Table 5 that the standard bending test bar bound by means of cold box binders was still completely water-resistant after 10 days. The bending test bar B-E61.3V1 produced by the process of the invention absorbs water after some time, but does not visibly lose water resistance. The comparative bending test bar B-V38 produced by a process which is not according to the invention (no acid-catalyzed etherifying crosslinking of a polymer comprising hydroxy groups), in contrast, completely lost its water resistance and began to dissolve after only a very short time.

Example 7

Behaviour of Standard Bending Test Bars During Casting of Iron

(62) Standard bending test bars B-cold box (comparison), B-V38 (comparison) and B-E61.3V1 (produced by the process of the invention) produced as in Example 2 above were coated with a conventional alcohol wash (Koalid 4087 from Hüttenes-Albertus GmbH) in a manner known to those skilled in the art (conditions: running-out time 17.3 s; dipping time 7 s; drying at 110° C. for 40 minutes; wall thickness 325 μm in the wet state).

(63) The standard bending test bars coated with the alcohol wash were then placed in a furan resin mould (dimensions 280×200×130 mm) which had been coated with an undiluted conventional, zircon-containing wash (Zirkofluid 1219 from Hüttenes-Albertus GmbH) and in this mould horizontally cast with iron (casting temperature about 1440° C.; about 3.09% by weight carbon content, about 1.89% by weight silicon content, in each case based on the total mass of the iron which was cast), so that the standard bending test bars were in each case completely enclosed by the iron casting and experienced maximum stress in terms of the applied load (by the iron as casting metal) during casting.

(64) After the casting operation, the left-over residues of the standard bending test bars were removed from the iron casting by rotating the casting (so that the left-over residues of the standard bending test bars could fall out from the downwards-directed openings of the hollow spaces in the iron casting produced by the standard bending test bars) and the unpacking behaviour (core removal behaviour) of the standard bending test bars was evaluated visually. The following observations were made:

(65) The left-over residues of the standard bending test bar B-cold box (comparison) were virtually impossible to remove from the iron casting mould in the manner indicated above; they remained virtually completely in the iron casting (cf. FIG. 1).

(66) The left-over residues of the standard bending test bar B-V38 (comparison) could be removed readily and virtually completely from the iron casting in the manner indicated above (cf. FIG. 2).

(67) The left-over residues of the standard bending test bar B-E61.3V1 (produced by the process of the invention) could be removed very readily and virtually completely from the iron casting in the manner indicated above (cf. FIG. 3).

(68) The iron casting was subsequently sawn open in the middle (along the support surfaces of the standard bending test bars) so that the hollow spaces produced by the standard bending test bars were (after removal from the iron casting) divided into two halves right in the middle of the length in the iron casting. The cross sections of the hollow spaces produced by the standard bending test bars were as a result half in the upper half of the sawn-open metal casting (produced by the part of the standard bending test bar which was located at the top during the casting of iron, “upper mould half”) and half in the lower half of the sawn-open metal casting (produced by the part of the standard bending test bar located at the bottom during the casting of iron, “lower mould half”).

(69) The upper and lower mould halves which had been exposed in this way were subsequently assessed visually to determine the casting resistance of the standard bending test bars used in the casting of iron and the removal thereof from the mould by buoyancy in liquid iron (recognizable by the deformations in the iron casting caused thereby). For this purpose, a straight wooden spatula was laid along the cross sections of the hollow spaces on the upper and lower mould halves produced by the standard bending test bars and the deviations from the casting negative of the upper side (in the upper mould half) and underside (in the lower mould half) of the said hollow spaces from the straight shape of the wooden spatula were in each case assessed.

(70) The following observations were made here:

(71) Standard bending test bar B-cold box (comparison): The casting negatives of the upper side (in the upper mould half) and underside (in the lower mould half) of the standard bending test bar (B-cold box) displayed no significant deviation from the straight line of the wooden spatula. The standard bending test bar B-cold box accordingly had barely deformed on casting with iron and displayed a high casting resistance (cf. FIG. 6 and FIG. 7).

(72) Standard bending test bar B-V38 (comparison): The casting negative of the upper side (in the upper mould half) of the standard bending test bar B-V38 displayed a significant concave (away from the wooden spatula) deformation in the middle (max. height of the deviation: about 5 mm). The casting negative of the underside (in the lower mould half) of the standard bending test bar B-V38 displayed significant concave (away from the wooden spatula) deformations at the margins (max. height of the deviation: about 7 mm. The standard bending test bar B-V38 had accordingly become significantly deformed during casting with iron and displayed only a low casting resistance (cf. FIG. 4 and FIG. 5).

(73) Standard bending test bar B-E61.3V1 (produced by the process of the invention): The casting negatives of the upper side (in the upper mould half) and underside (in the lower mould half) of the standard bending test bar B-E61.3V1 displayed no significant deviation from the straight line of the wooden spatula. The standard bending test bar B-E61.3V1 had accordingly barely deformed during casting with iron and displayed a high casting resistance (cf. FIG. 8 and FIG. 9).

(74) It can be seen from the abovementioned observations that a shaped part produced by the process of the invention (here: standard bending test bar representing a core, feeder or mould) displayed very good removability of a core and also a high casting resistance during casting of metal and in the totality of its properties was significantly superior to the comparative shaped parts.

Example 8

Production of Standard Test Specimens (Standard Bending Test Bar and Standard Test Cylinder) from Insulating Feeder Composition as Mould Material Mixture

(75) The constituents indicated in Table 6 below were used to produce mould material mixtures for insulating feeders. The production of the mould material mixtures was carried out in a manner analogous to that indicated above in Example 1.

(76) Standard bending test bars were subsequently shaped from the resulting mould material mixtures and cured in a manner analogous to that in Example 2 above to give standard bending test bars as cured shaped parts. Furthermore, standard test cylinders (height: 50 mm, diameter: 50 mm) were produced by ramming in accordance with the VDG standard P38 from the mould material mixtures obtained and were cured in a manner analogous to Example 2 above to give cured shaped parts (25 minutes at 210° C. in a convection drying oven for standard bending test bars and standard test cylinders using mould material mixture F-E68.4 (2)).

(77) The 24 hour bending strengths (final strengths) of the standard bending test bars “B-cold box” (comparison) obtained were then determined in a manner analogous to that indicated above in Example 3. The bending strength of the standard bending test bars B-E68.4 obtained was determined after storage for 30 minutes under laboratory conditions (room temperature and room humidity) after completion of the drying procedure (final strengths). The results of all abovementioned measurements are reported below in Table 6 (in each case averages of 3 measurements).

(78) The values of the gas permeabilities of the standard bending test bars and standard test cylinders and also their weight determined in each case are likewise reported in Table 6. The gas permeability is a test parameter which gives information about the densification of the microstructure. In the case of a feeder in particular, this is a characteristic value which can give information about satisfactory removal of casting gases during the casting operation.

(79) TABLE-US-00006 TABLE 6 Constituents of mould material mixtures for insulating feeders Mould material mixture Constituent F-cold box (2) F-E68.4 (2) Expanded perlite 100 100 [parts by weight] Aqueous PVAL mixture 0 29.175 [parts by weight] Aqueous sulfuric acid mixture 0 0.825 [parts by weight] Cold box activator 6324 9.0 0 [parts by weight] Cold box gas resin 7241 9.0 0 [parts by weight] Mass of standard test cylinder [g] 47 42 Gas permeability of standard test 45 50 cylinder Bending strength [N/cm.sup.2] of bending 350 360 test bar (final strengths)

(80) The constituents “aqueous PVAL mixture”, “aqueous sulfuric acid mixture”, “cold box activator 6324” and “cold box gas resin 7241” indicated in Table 6 correspond to the constituents indicated in Example 1.

(81) It can be seen from the results reported above in Table 6 that an insulating feeder composition produced by the process of the invention has comparable properties, in particular a comparable bending strength (i.e. final strength), as an insulating feeder composition which has been produced by a known cold box process.

Example 9

Casting of Shaped Parts with Aluminium or Iron

(82) Insulating (closed at the bottom by a plate) feeders were produced in a manner known to a person skilled in the art (treatment with catalyst gas N,N-dimethylpropylamine) from the insulating feeder compositions produced in Example 8 above using mould material mixture “F-cold box (2)” by shooting in a core shooting machine.

(83) Insulating feeders made from the insulating feeder compositions produced above in Example 8 using mould material mixture “F-E68.4 (2)” were shot in the same mould on the core shooting machine. Curing was carried out for 25 minutes at 210° C. in a drying oven (convection).

(84) Insulating feeders produced in this way were set into a cold box-bound mould sand mould and cast with aluminium to test their behaviour under metal casting conditions. Further insulating feeders produced in this way were likewise set in loose mould sand and cast with iron instead of aluminium.

(85) The following observations were made:

(86) When the insulating feeder produced using the comparative mould material mixture F-cold box (2) (not according to the process of the invention) was cast with aluminium, strong fume formation was observed and this continued even after removal of the cast feeder from the mould sand.

(87) When the insulating feeders produced using the mould material mixture F-E68.4 (2) (according to the process of the invention) were cast with aluminium, no fume formation was found. After the casting operation, the insulating feeder produced according to the invention displayed significantly better unpacking behaviour than the insulating feeder produced using the comparative mould material mixture F-cold box (2), i.e. the insulating feeder produced according to the invention could be separated significantly more readily from the aluminium. The aluminium castings formed displayed a significantly cleaner surface (i.e. without condensate deposits) than the aluminium castings which had been produced using the insulating feeder produced using the comparative mould material mixture F-cold box (2).

(88) When the insulating feeders produced using the comparative mould material mixture F-cold box (2) (not according to the process of the invention) were cast with iron (at a temperature of 1410° C.), fume formation and emission of odours was found.

(89) When the insulating feeder produced using the mould mixture F-E68.4 (2) (according to the process of the invention) was cast with iron (at a temperature of 1410° C.), no fume formation or emission of odours was found, even after the cast feeder had been taken from the mould sand. After the casting operation, the insulating feeder produced according to the invention displayed significantly better unpacking behaviour than the insulating feeder produced using the comparative mould material mixture F-cold box (2): when the casting specimen was mechanically pulled, the feeder cast with iron disintegrated virtually completely. In addition, the iron casting formed displayed a significantly cleaner surface, with more readily mechanically removable sand and a smoother surface structure than the iron casting which had been produced using the insulating feeder produced using the comparative mould material mixture F-cold box (2).

Example 10

Production of Standard Test Specimens from Exothermic Feeder Composition as Mould Material Mixture

(90) The constituents indicated in Table 7 below were used to produce mould material mixtures for exothermic feeders. The production of the mould material mixtures was carried out in a manner analogous to that indicated above in Example 1.

(91) Test specimens (standard bending test bars and standard test cylinders) were subsequently shaped from the mould material mixtures obtained and were cured in a manner analogous to Example 2 above to give cured standard bending test bars and standard test cylinders as (representative or model) cured shaped parts. The curing of the test specimens made using the mould material mixture F-E68.4 (3) was carried out by heating and removal of water for 25 minutes at 210° C. in a drying oven (convection).

(92) The bending strengths of the standard bending test bars obtained were then determined in a manner analogous to that indicated above in Example 3. The results of these measurements are reported below in Table 7 (averages of 3 measurements).

(93) The values of the gas permeabilities of the standard test cylinders and also their weight which were determined in each case are likewise reported in Table 7.

(94) TABLE-US-00007 TABLE 7 Constituents of mould material mixtures for exothermic feeders Mould material mixture Constituent F-cold box (3) F-E68.4 (3) Silica sand BO42 32.00 32.00 [parts by weight] Spheres composed of fly ash 25.00 25.00 [parts by weight] Aluminium 23.00 23.00 [parts by weight] Iron oxide 5.00 5.00 [parts by weight] Oxidant (KNO.sub.3) 12.00 12.00 [parts by weight] Igniter (cordierite) 3.00 3.00 [parts by weight] Aqueous PVAL mixture 0 14.588 [parts by weight] Aqueous sulfuric acid mixture 0 0.413 [parts by weight] Cold box activator 6324 4.50 0 [parts by weight] Cold box gas resin 7241 4.50 0 [parts by weight] Mass of standard test 98 92 cylinder [g] Gas permeability of standard 90 135 test cylinder Bending strength of standard 450 460 bending test bar (final strengths) [N/cm.sup.2]

(95) The constituents “aqueous PVAL mixture”, “aqueous sulfuric acid mixture”, “cold box activator 6324” and “cold box gas resin 7241” indicated in Table 7 correspond to the constituents indicated in Example 1.

(96) It can be seen from the results reported above in Table 7 that an exothermic feeder composition produced by the process of the invention has comparable properties, in particular a comparable bending strength (final strength), to an exothermic feeder composition produced by a known cold box process.

Example 11

Burning of Exothermic Feeders

(97) Standard test cylinders were produced by ramming in accordance with the VDG standard P38 from the exothermic feeder compositions produced above in Example 10. In the case of the exothermic feeder composition using mould material mixture “F-cold box (3)”, curing was carried out in a manner known to a person skilled in the art by treatment with the catalyst gas N,N-dimethylpropylamine. In the case of the exothermic feeder composition “F-E68.4 (3)”, curing to give the cured shaped part (exothermic feeder) was carried out by heating and removal of water for 25 minutes at 210° C. in a drying oven (convection).

(98) Exothermic feeders produced in this way were burnt in a manner known to a person skilled in the art in accordance with the VDG standard P81 (here without temperature-time measurement). The parameters reported below in Table 8 were determined here.

(99) TABLE-US-00008 TABLE 8 Parameters in the burning of exothermic feeders Exothermic feeder from mould material mixture Parameter F-cold box (3) F-E68.4 (3) Ignition time [s] 8 8 Burning time [s] 179 178

(100) In addition, the following observations were made:

(101) Significant fume formation was observed in the burning of the exothermic feeder which had been produced using the comparative mould material mixture F-cold box (3) (not according to the process of the invention) (conventional cold box binder).

(102) Virtually no fume formation was found in the burning of the exothermic feeder produced using the mould material mixture F-E68.4 (3) according to the process of the invention.

(103) It can be seen from the results reported above that cured shaped parts (here: exothermic feeders) produced by the process of the invention displayed significantly reduced emissions under practical conditions compared to shaped parts produced by the conventional cold box process.

Example 12

Production of Aqueous Binder Systems

(104) The constituents indicated in Table 9 below were used to produce aqueous binder systems.

(105) TABLE-US-00009 TABLE 9 Constituents of aqueous binder systems Aqueous binder system Constituent WB-V38 WB-E61.3V1 WB-E68.4 Aqueous PVAL mixture 100 97.94 97.26 [parts by weight] Aqueous sulfuric acid mixture 0 2.06 2.74 [parts by weight]

(106) The constituents “aqueous PVAL mixture” and “aqueous sulfuric acid mixture” indicated in Table 9 correspond to the constituents indicated in Example 1.

(107) The aqueous binder systems WB-E61.3V1 and WB-E68.4 are aqueous binder systems to be used according to the invention. The aqueous binder system WB-V38 is an aqueous binder system which is for comparison and is not to be used according to the invention.

Example 13

Test Casting of Iron Cubes

(108) The mould material mixtures indicated below in Table 10 were each shaped in a core shooting machine to give feeders.

(109) In the case of the feeder mixture “F-cold box (4)”, curing was carried out in a manner known to a person skilled in the art by treatment with the catalyst gas N,N-dimethylpropylamine. In the case of the “F-water glass” feeder mixture, curing was carried out for 25 minutes at 210° C. in a drying oven (convection). In the case of the feeder composition “F-E68.4 (4)”, curing to give the cured shaped part was carried out by heating and removal of water for 25 minutes at 210° C. in a drying oven (convection). This resulted in the feeders “feeder cold box” and “feeder water glass” produced by a method which was not according to the invention and in the feeders “feeder B-E68.4” produced according to the invention.

(110) TABLE-US-00010 TABLE 10 Compositions of mould material mixtures for feeders Mould material mixture Constituent F-cold box (4) F-water glass F-E68.4 (4) Silica sand 100 100 100 [parts by weight] Aqueous PVAL mixture 0 0 3.890 [parts by weight] Aqueous sulfuric acid 0 0 0.110 mixture [parts by weight] Cold box activator 6324 1.2 0 0 [parts by weight] Cold box gas resin 7241 1.2 0 0 [parts by weight] Sodium water glass binder 0 1.5 0 48/50 [parts by weight]

(111) The constituents indicated in Table 10 in each case correspond to the constituents indicated in Example 1 and the meanings thereof.

(112) As sodium water glass binder 48/50, use was made of an aqueous solution of a standard water glass binder having a water glass content (sodium silicate content) in the range from 25% by weight to 35% by weight and a pH at 20° C. in the range from 11 to 12 (CAS RN 1344-09-8).

(113) The abovementioned feeders were in each case checked for industrial usability, in particular the quality of their feeder action, by use in the test casting of an iron cube (model of a metallic casting). For this purpose, the feeders of the same size (i.e. in each case the same modulus) were each used in the test casting of cubes having a modulus of (i.e. having a ratio of volume to surface area of) 1.68 cm by means of iron (GGG40) at a casting temperature of 1400° C. A person skilled in the field of foundry technology will frequently utilize cubes which have a significantly greater modulus than the feeders for the quality evaluation in order to be able to obtain the best possible information on the solidification from the experiment. The quality of the feeding action is assessed from the depth of the sink hole extending into the cube: sink holes extending deeper into the cube (the metal casting) indicate a poorer feeding action.

(114) The test cubes produced as indicated above were sawn in the middle (halved) after casting and cooling to room temperature in order to expose their cross section and to assess the quality of casting, and also the quality of the feeder action of the feeders used in each case. The cross sections obtained by sawing-open of the test cubes with the visible feeder residue composed of iron attached at the top are depicted in FIG. 10 (casting of iron using the feeder “feeder cold box” which had been produced by a method which is not according to the invention), in FIG. 11 (casting of iron using the feeder “feeder water glass” produced by a method which is not according to the invention) and in FIG. 12 (casting of iron using the feeder “feeder B-E68.4” produced according to the invention).

(115) It can be seen in FIG. 10 that when using a cold box-bound feeder under the experimental conditions, significant sink hole formation which extends into the metallic casting takes place. The annotation “−15 mm” (left-hand half of the cross section) or “−16 mm” (right-hand half of the cross section) indicates in each case the distance between the line visible at the top in the image (at the feeder residue connection, i.e. the boundary between metallic feeder residue and the metallic casting) and the line visible at the bottom in the image (marking for the deepest point of the metallic casting or of the sink hole in the metallic casting).

(116) It can be seen in FIG. 11 that when using a water glass-bound feeder produced by a method which is not according to the invention under the experimental conditions, pronounced sink hole formation which extends far into the metallic casting takes place. The annotation “−33” (mm) (left-hand half of the cross section) or “−31” (mm) (right-hand half of the cross section) in each case indicates the distance between the line visible at the top in the image (at the feeder residue connection, i.e. the boundary between metallic feeder residue and the metallic casting) and the line visible at the bottom in the image (marking for the deepest point of the metallic casting or of the sink hole in the metallic casting). The poor quality of the feeder action of the water glass-bound feeder under the experimental conditions is presumably attributable to the comparatively high heat energy uptake of the water glass binder (known as its disadvantageous “quenching behaviour”) and the resulting comparatively early solidification of the cast metal.

(117) It can be seen in FIG. 12 that when using the feeder “feeder B-E68.4” produced according to the invention, the sink hole formed extends significantly less deeply into the iron casting (test cube) than when using known water glass-bound or cold box-bound feeders. The annotation “−3” (mm) (left-hand half of the cross section) or “−1” (mm) (right-hand half of the cross section) in each case indicates the distance between the line visible at the top in the image (at the feeder residue connection, i.e. the boundary between metallic feeder residue and the metallic casting) and the line visible at the bottom in the image.

(118) From the FIGS. 10 to 12 indicated above, it is therefore possible to see that a feeder produced according to the invention has a significantly improved feeding capability than the known cold box-bound or water glass-bound feeders employed for comparison.