METHOD FOR PRODUCING REFRACTORY COMPOSITE PARTICLES AND FEEDER ELEMENTS FOR THE FOUNDRY INDUSTRY, CORRESPONDING FEEDER ELEMENTS AND USES

Abstract

A method for producing a feeder element is described. The method includes (a) producing composite particles having a particle size of less than 2 mm in a matrix encapsulation method with the following steps: (a1) producing droplets of a suspension from at least (i) one or more refractory substances, (ii) one or more of fillers having a bulk density in the range from 10 to 350 g/L, expandants, and pyrolysable fillers, (iii) as continuous phase, a solidifiable liquid, (a2) solidifying the droplets with the refractory substance(s) and density-reducing substance(s) are encapsulated therein, (a3) treating the hardened droplets to form composite particles, (b) mixing the composite particles with a binder and, optionally, further constituents to give a feeder composition, (c) shaping and curing the feeder composition to give a feeder element. Also described are a method for producing refractory composite particles and the use of the composite particles.

Claims

1. A method for producing a feeder element for the foundry industry, comprising the following steps: (a) producing composite particles having a particle size of less than 2 mm, determined by sieving, in a matrix encapsulation method with the following steps: (a1) producing droplets of a suspension from at least the following starting materials: (i) one or more refractory substances selected from the group consisting of refractory solids and precursors of refractory solids, (ii) one or more density-reducing substances selected from the group consisting of lightweight fillers having a respective bulk density in the range from 10 to 350 g/L, expandants and pyrolysable fillers, (iii) as continuous phase, a solidifiable liquid, (a2) solidifying the solidifiable liquid, so that the droplets harden to hardened droplets and the refractory substance or substances and also the density-reducing substance or substances are encapsulated in the solidifying continuous phase, (a3) treating the hardened droplets, so that the said composite particles result, (b) mixing the composite particles produced in step (a) or a fraction of these composite particles with a binder and also, optionally, further constituents to give a feeder composition, (c) shaping and curing the feeder composition to give a feeder element.

2. The method as claimed in claim 1, wherein in step (a1) droplets are produced by means of one or more nozzles, preferably vibrational nozzles, and/or in step (a2) the solidifying of the solidifiable liquid is induced by cooling, drying or chemical reaction.

3. The method as claimed in claim 1, wherein the solidifiable liquid used in step (a1) is a liquid which is solidifiable by chemical reaction and in step (a2) the solidifying of the solidifiable liquid is induced by chemical reaction.

4. The method as claimed in claim 1, wherein the solidifiable liquid is a liquid solidifiable by cation exchange reaction, preferably a liquid solidifiable by reaction with calcium ions and/or barium ions and/or manganese ions, more preferably by reaction with calcium ions.

5. The method as claimed in claim 1, wherein the solidifiable liquid is a liquid solidifiable by reaction with calcium ions, which comprises one or more binders selected from the group consisting of alginate, PVA, chitosan and sulphoxyethylcellulose, and/or is an aqueous solution, in which case the solidifiable liquid is preferably an aqueous alginate solution.

6. The method as claimed in claim 1, wherein the lightweight filler or at least one of the lightweight fillers used in step (a) as density-reducing substance of component (ii), preferably having a particle size of less than 0.8 mm, more preferably less than 0.5 mm, very preferably less than 0.3 mm, determined by sieving, is selected from the group consisting of: inorganic hollow beads, organic hollow beads, particles of porous and/or foamed material, rice husk ash, core-shell particles and calcined kieselguhr and/or wherein the expandant or at least one of the expandants used in step (a) as component (ii) is selected from the group consisting of: carbonates, hydrogencarbonates and oxalates, coconut shell flour, walnut shell flour, grape kernel flour, olive stone flour, starch, wheat flour, maize flour, potato dextrin, sugars, plant seeds, wood flour, and rice husk ash, and/or wherein the pyrolysable filler or at least one of the pyrolysable fillers used in step (a) as component (ii) is selected from the group consisting of: plastics beads and Styropor beads.

7. The method as claimed in claim 1, wherein the refractory solid or at least one of the refractory solids used in step (a1) as refractory substance of component (i) is selected from the group consisting of: oxides, nitrides and carbides, each comprising one or more elements from the group consisting of Si, Al, Zr, Ti, Mg and Ca, mixed oxides, mixed carbides and mixed nitrides, each comprising one or more elements from the group consisting of Si, Al, Zr, Ti, Mg and Ca, and graphite, wherein preferably the refractory solid or at least one of the refractory solids used in step (a1) as refractory substance of component (i) is selected from the group consisting of: aluminium oxide, zirconium oxide, titanium dioxide, graphite, silicon dioxide, magnesium oxide, calcium oxide, calcium silicate, phyllosilicates, preferably mica, aluminium silicates, magnesium aluminium silicate, preferably cordierite, silicon carbide, and boron nitride and/or the precursor or at least one of the precursors of refractory solids that is used in step (a1) as refractory substance of component (i) is selected from the group consisting of aluminium hydroxide, magnesium hydroxide, phyllosilicates, preferably kaolinite, montmorillonite and illite, clays, preferably kaolin and bentonite, phosphates and carbonates.

8. The method as claimed claim 1, wherein the treating as per step (a3) is carried out such that the bulk density of the resultant composite particles is lower than the bulk density of the hardened droplets in the dried state and/or the said composite particles possess a bulk density <700 g/L, preferably <400 g/L, more preferably <300 g/L.

9. The method as claimed in claim 1, wherein the composite particles resulting in step (a3) and/or the composite particles used in step (b) at least partly possess a particle size in the range from 0.125 mm to 0.5 mm, determined by sieving.

10. The method as claimed in claim 1, wherein component (ii) comprises, as density-reducing substance or substances, one or more expandants and the treating as per step (a3) is carried out such that the expandant or the two or more expandants expand and so form cavities in the resultant composite particle and/or comprises one or more pyrolysable fillers and the treating as per step (a3) is carried out such that the pyrolysable filler or the two or more pyrolysable fillers pyrolyse and so form cavities in the resultant composite particle.

11. The method as claimed in claim 1, wherein component (i) comprises, as refractory substances, one or more precursors of refractory solids and the treating as per step (a3) comprises a thermal treatment in which the precursors are converted into a refractory solid, wherein preferably the precursor or at least one of the precursors of refractory solids is a clay and the treating as per step (a3) comprises a thermal treatment at a temperature in the range from 900 to 980? C., so that the clay is converted into a refractory solid, in which case the clay preferably comprises kaolinite and/or illite.

12. The method as claimed in claim 11, wherein preferably a temperature of 1000? C. is not exceeded during the thermal treatment.

13. The method as claimed in claim 11, wherein in step (a3) the hardened droplets are treated so that, as an intermediate, solid particles result, and wherein subsequently the surface of these solid particles is sealed, preferably by means of an organic coating material, so that the said composite particles result.

14. The method as claimed in claim 13, wherein in step (b) an organic binder is used as binder, preferably a cold-box binder, and wherein in step (c) the curing takes place by the cold-box method by gassing with an organic amine.

15. The method as claimed in claim 13, wherein in step (b) one or more further constituents are used which are selected from the group consisting of spheres of fly ash, rice husk ash, core-shell particles, calcined kieselguhr, aluminium, magnesium, silicon, iron oxide, manganese oxide, silicon dioxide, chamotte, mullite, potassium nitrate and sodium nitrate.

16. A feeder element producible by a method as claimed in claim 13.

17. A matrix encapsulation process, preferably using a nozzle, more preferably using a vibrating nozzle, for producing composite particles having a bulk density <700 g/L, preferably <400 g/L, more preferably <300 g/L, comprising producing feeder elements for the foundry industry.

18. A method of producing a feeder element, comprising providing sealed composite particles consisting of a composite particle, which can be produced by means of a matrix encapsulation process, and of a shell, which surrounds and seals the composite particle and consists of an organic coating material, as a filler in a feeder element, preferably in a feeder element produced by means of the cold-box process.

19. A method for producing refractory composite particles having a particle size of less than 2 mm, determined by sieving, comprising the following steps: (a1) producing droplets of a suspension from at least the following starting materials: (i) one or more refractory substances selected from the group consisting of refractory solids and precursors of refractory solids, (ii) one or more density-reducing substances selected from the group consisting of lightweight fillers having a respective bulk density in the range from 10 to 350 g/L, expandants and pyrolysable (iii) as continuous phase, a solidifiable liquid, (a3) treating the hardened droplets, so that the said refractory composite particles result.

20. The use of refractory composite particles producible by the method as claimed in claim 19 as constituent of a feeder element.

Description

FIGURES

[0285] FIG. 1: FIG. 1 shows the residue in the crucible after the sintering test at 1600? C. of the inventive composite particles B36.

[0286] As can be seen in FIG. 1, a small proportion of the inventive composite particles has sintered together, but at the same time there is still a considerable proportion present in a free-flowable form.

[0287] FIG. 2: FIG. 2 shows the crucible residue after the sintering test at 1600? C. of the non-inventive composite particles W250-6.

[0288] As is seen in FIG. 2, the crucible residue has sintered together, forming a coherent crucible cake.

[0289] FIG. 3: FIG. 3 shows a photograph of the crucible contents after the sintering test at 1600? C. of the non-inventive composite particles KHP 108.

[0290] As can clearly be seen, the contents of the crucible have fused to give a continuous mass.

[0291] FIG. 4: FIG. 4 shows a micrograph of the inventive composite particles B36 after the sintering test at 1600? C.

[0292] As can be seen very well, the inventive composite particles after the sintering test have not as yet formed sinter necks.

[0293] FIG. 5: FIG. 5 shows a micrograph of the non-inventive composite particles W250-6 after the sintering test at 1600? C.

[0294] As can clearly be seen, sinter necks have formed between the non-inventive composite particles and the entire non-inventive composite particles have therefore joined together is to form a coherent crucible cake.

[0295] FIG. 6: FIG. 6 shows the residue in the crucible after the sintering test at 1700? C. of the inventive composite particles B36.

[0296] A small proportion of the inventive composite particles have sintered together. However, a considerable proportion is still in a free-flowable form.

[0297] FIG. 7: FIG. 7 shows the crucible residue after the sintering test at 1700? C. of the non-inventive Hargreaves hollow-bead corundum composite particles.

[0298] It can be seen that the entire non-inventive composite particles have joined together to form a coherent crucible cake.

[0299] FIG. 8: FIG. 8 shows the crucible residue after the sintering test at 1700? C. of the non-inventive KKW hollow-bead corundum composite particles.

[0300] As can clearly be seen, the entire non-inventive composite particles have joined together to form a coherent crucible cake.

[0301] FIG. 9: FIG. 9 shows a scanning electron micrograph of the inventive composite particles B36 after the sintering test at 1700? C.

[0302] As can be seen very well, the inventive composite particles after the sintering test have not as yet formed sinter necks.

[0303] FIG. 10: FIG. 10 shows a micrograph of the non-inventive Hargreaves hollow-bead corundum composite particles after the sintering test at 1700? C.

[0304] The particles have undergone superficial melting during the sintering test, causing all of the non-inventive composite particles to join together during solidification to form a coherent crucible cake.

[0305] FIG. 11: FIG. 11 shows an enlarged micrograph of FIG. 10 of the non-inventive KKW hollow-bead corundum composite particles after the sintering test at 1700? C.

[0306] The particles have undergone superficial melting during the sintering test, causing all of the non-inventive composite particles to join together during solidification to form a coherent crucible cake.

[0307] FIG. 12: FIG. 12 shows an inventive test bar produced with composite particles B36-albumen whose surface has been sealed.

[0308] FIG. 13: FIG. 13 shows inventive test bars produced by means of composite particles B36 (no surface sealing).

[0309] FIG. 14: FIG. 14 shows two half-sections of an iron casting produced in a cube test with non-inventive feeder elements.

[0310] FIG. 15: FIG. 15 shows two half-sections of an iron casting produced in a cube test with inventive feeder elements.

[0311] FIG. 16: FIG. 16 shows an XRD of a kaolin. The Y-axis shows the counts of the measurement (corresponding to the intensity of the reflections) and the X-axis shows the angle in the 2-THETA scale.

[0312] The major reflections of kaolinite are easily visible at an angle of around 12? 2-theta, 20? 2-theta and 25? 2-theta.

[0313] FIG. 17: FIG. 17 shows an XRD of the hardened droplets produced in step (a2) after they have dried. Visible on the Y-axis are the counts of the measurement (corresponding to the intensity of the reflections) and on the X-axis the angle in the 2-THETA scale.

[0314] Here again, the principal reflections of the kaolinite are readily visible at an angle of around 12? 2-theta, 20? 2-theta and 25? 2-theta. Additionally, corundum, added as refractory filler, is detected.

[0315] FIG. 18: FIG. 18 shows an XRD of the inventively produced composite particles after sintering at 900? C. Visible on the Y-axis are the counts of the measurement (corresponding to the intensity of the reflections) and on the X-axis the angle in the 2-THETA scale.

[0316] It can easily be seen that after sintering at 900? C., the reflections of the kaolinite are no longer visible. The main phase detected is corundum, which was added as a refractory filler.

[0317] FIG. 19: FIG. 19 shows an XRD of the inventively produced composite particles after sintering at 980? C. Visible on the Y-axis are the counts of the measurement (corresponding to the intensity of the reflections) and on the X-axis the angle in the 2-THETA scale.

[0318] After sintering at 980? C., it is not possible to detect any reflections of the kaolinite; instead, the newly formed mullite phase (peaks at 16.5? 2-theta; 26? 2-theta and 41? 2-theta) is detected by x-ray diffraction. Also detected is corundum, which was added as a refractory filler.

[0319] FIG. 20: FIG. 20 shows a scanning electron micrograph of the inventively produced composite particles with the designation B36 (see examples further on below in the text).

[0320] FIG. 21: FIG. 21 shows an enlarged scanning electron micrograph of the inventively produced composite particles with the designation B36 (see examples further on below in the text).

[0321] It is very readily apparent that the various refractory fillers are surrounded individually by the continuous phase and are therefore held together more firmly, giving the inventively produced composite particles the desired dimensional stability and desired thermal stability.

[0322] FIG. 22: FIG. 22 shows a greatly enlarged scanning electron micrograph of the inventively produced composite particles B36.

[0323] FIG. 23: FIG. 23 shows a light micrograph of the inventively produced composite particles with the designation F3 (see Table 1 further on below in the text) immediately prior to treatment in a muffle furnace.

[0324] It can be seen very well that the particles immediately prior to treatment in the muffle furnace are very compact and have only sporadic cavities.

[0325] FIG. 24: FIG. 24 shows a light micrograph of the inventively produced composite particles with the designation F3 (see Table 1 further on below in the text) after treatment in a muffle furnace.

[0326] It can be seen very well that the particles after treatment in the muffle furnace have a considerable number of cavities, formed by the expanding of the utilized expandant during the thermal treatment.

[0327] In the text below, the present invention is elucidated in more detail with examples:

[0328] Measurement Methods:

[0329] 1. Particle Size Determination: [0330] The determination of the particle sizes of composite particles by sieving takes place in accordance with DIN 66165-2 (4.1987) using method F identified therein (machine sieving with agitated individual sieve or sieve set in gaseous fluid at rest). [0331] A Retsch AS 200 control vibrational sieving machine is used; the amplitude is set to level 2, there is no interval sieving, and the sieving time is 1 minute. [0332] The determination of particle sizes of lightweight fillers used in step (a) as density-reducing substance of component (ii) takes place likewise in accordance with DIN 66165-2 (4.1987) using method F identified therein (machine sieving with agitated individual sieve or sieve set in gaseous fluid at rest). Again, a Retsch AS 200 control vibrational sieving machine is used; the amplitude is set to level 2, there is no interval sieving, and the sieving time is 1 minute. [0333] The determination of the particle sizes of refractory solids having a particle size of less than 0.1 mm takes place by means of sieving in accordance with DIN 66165-2 (4.1987) using method D specified therein (machine sieving with resting individual sieve in agitated gaseous fluid, with air jet sieve).

[0334] 2. Determination of Bulk Density: [0335] The bulk density was determined according to DIN EN ISO 60 2000-1.

[0336] 3. Determination of Water Absorptiveness: [0337] The determination of the water absorption was carried out using an Enslin instrument. Evaluation took place in accordance with DIN 18132.

[0338] 4. Determination of Phase Composition: [0339] The powder diffractograms were recorded using a Siemens D 5005 powder diffractometer with a copper anode. The measurements took place in the diffraction angle range 3-70? 2-theta; step width 0.020?; counting time 4 steps/sec. Evaluation was made using the EVA standard software and ICDD PC-PDF database.

[0340] 5. Determination of Chemical Composition and Morphology: [0341] The morphology of the samples was carried out by means of a JSM 6510 SEM from Jeol. The chemical composition was carried out by means of EDX analysis using an EDX from Oxford INCA. [0342] Additionally, for the determination of the morphology, a VisiScope ZTL 350 light microscope with Visicam 3.0 camera was utilized.

[0343] 6. Method for Determining the Thermal Stability (Sintering Test): [0344] The sintering test in the present invention was carried out for determining the thermal stability of various raw materials along the lines of the VDG datasheet P26 Testing of moulding base materials. A quantity of particles of the same composition, for analysis, was subjected to defined thermal treatment (for example 1600? C. or 1700? C. for half an hour in each case) in a Carbolite HTF 1800 oven with a type E 3216 temperature control, and then evaluated by way of defined mechanical loading, by means of sieving. [0345] First of all, the quantity of particles under investigation was sieved using a sieve of mesh size 0.5 mmsee Table 2 belowor of 0.71 mmsee Table 3 belowin order to ensure the reproducibility and comparability of the various experiments. [0346] The sieved particles were subsequently subjected to defined thermal treatment in an aluminium oxide crucible, with the following steps: [0347] preliminary sintering of the samples, 30 min at 900? C. in the preheated oven, to ensure identical thermal loading for the comparative samples as for the inventive composite particles, [0348] heating of the samples with defined oven transit (Carbolite HTF 1800 oven with type E3216 temperature control): from 25? C. to 200? C. at 1 K/min, subsequently at 3 K/min until the end temperature (1600? C. for half an hoursee Table 2 belowor 1700? C. for half an hoursee Table 3 below) and subsequent cooling to room temperature at 3 K/min. [0349] Thereafter the cooled particles were photographed with aluminium oxide crucible (see FIG. 3 (particles fused), FIG. 6 and FIG. 7) or without aluminium oxide crucible (see FIG. 1, FIG. 2 and FIG. 8) and, where the particles under investigation have not melted during the defined thermal treatment, the aluminium oxide crucible in which the particles under investigation were heated was clamped into a sieving tower and subjected to mechanical stress by defined sieving with a control sieve on a Retsch AS 200 for 1 minute in each case at an amplitude of 2 without interval sieving, i.e. with permanent sieving. The mesh size of the control sieve was set at the maximum anticipated particle size of the particles under investigation (either 0.5 mmsee Table 2 belowor 0.71 mmsee Table 3 below). The ratio of sieve residue to sieve undersize is employed as an evaluation criterion (cf. VDG datasheet P26 Testing of moulding base materials, October 1999). At a factor of sieve residue/sieve undersize of greater than 1, the sample is considered to have undergone sintering and therefore not to have thermal stability. [0350] Sample-specific parameters such as the particle size of the respective sample, for example, were taken into account in the evaluation.

[0351] Experimental Section (Parts 1 to 3):

[0352] Experimental Part 1Production According to Step (a) of the Method of the Invention of Composite Particles (B36, B37, B31) Having a Particle Size of Less than 2 mm (Also Referred to Below as Inventive Composite Particles):

[0353] (a1) Production of Droplets of a Suspension from Starting Materials:

[0354] A 1% strength aqueous sodium alginate solution was prepared (1 wt % sodium alginate from Alpichem with CAS No. 9005-38-3, based on the total mass of the aqueous solution).

[0355] The dispersant Sokalan? FTCP 5 from BASF was diluted with water to produce a corresponding dispersing solution; the ratio by mass of Sokalan? FTCP 5 to water was 1:2.

[0356] The 1% strength aqueous sodium alginate solution prepared and the dispersing solution prepared were subsequently mixed in a mixing ratio as per Table 1, to give a solidifiable liquid (solidifiable liquid for use as continuous phase as constituent (iii) as per step (a1)).

[0357] Then, with stirring, precursors of refractory solids and refractory solids selected in accordance with Table 1 below (constituent (i) according to step (a1)) were added to the solidifiable liquid until a creamy suspension was formed.

[0358] Subsequently, with stirring, borosilicate beads were added to the creamy suspension, in a quantity according to Table 1 below as an example of a lightweight filler (constituent (ii) as per step (a1)), followed subsequently by an amount of water as per Table 1. This resulted in a dilute suspension.

TABLE-US-00002 TABLE 1 Ingredients for producing composite particles of the invention and resultant bulk density thereof. Starting Ingredients Composition of the suspension material Constituent Manufacturer (weight fractions) Precursor of (i) Kaolin TEC Amberger 11.00 10.0 11.0 10.0 15.0 refractory Kaolinwerke solids [wt %] (i) K?rlicher Blauton K?rlicher 5.00 5.00 5.00 5.00 5.00 Tonund Schamottewerke Mannheim & Co. KG (i) Kaolin BASF 10.85 10.0 (Satintone?W(Whitetex)) Refractory (i) Nabalox? NO315 Nabaltec AG 10.85 10.0 substance [wt %] Light-weight (ii) Borosilicate glass beads 3M 3.15 5.00 3.15 filler [wt %] (product name: 3M Glass Deutschland Bubbles K1) with a bulk GmbH density of 60 g/L Light-weight (ii) Expanded perlite (product RS Rohstoff- 8.00 filler [wt %] name: Eurocell 140) with a Sourcing bulk density of 120 g/L GmbH Expandant (ii) Wood flour Ligno-Tech Brandenburg 10.0 [wt %] 120 mesh TR with a Holzm?hle bulk density of 110 g/L Expandant (ii) Coconut shell flour Mahlwerk 5.00 [wt %] Coconit 300 Neubauer- Friedrich with a bulk density of Geffers GmbH 500 g/L Expandant (ii) Sugar having a bulk S?dzucker AG 5.00 [wt %] density of 850 g/L 1% sodium Sodium alginate; Applichem 65.0 65.0 65.00 60.0 57.0 alginate CAS: 9005-38-3 solution [wt %] Dispersing Sokalan? FT CP5 in BASF 5.00 5.00 5.00 5.00 5.00 solution water (1.2) [wt %] Water 20.0 20.0 25.0 45.0 25.0 [wt %] Resultant inventive composite particles B36 B37 B31 F3 E6 Bulk density immediately before treatment 350 260 320 390 300 in the muffle furnace [g/L] Bulk density after treatment in the muffle 340 250 305 300 250 furnace (inventive composite particles) [g/L]

[0359] (a2) Solidification of the Solidifiable Liquid

[0360] The dilute suspension was introduced into plastic syringes and clamped into an LA-30 syringe pump. The delivery rate was 12 to 15 ml/min. The dilute suspension in the syringes was then pressed through a vibrational nozzle, causing the dilute suspension to emerge from the vibrational nozzle in uniform droplets. The droplets falling from the vibrational nozzle fell into a 2% strength aqueous calcium chloride solution (CaCl.sub.2), to product name Calcium Chloride 2-hydrate powder for analysis ACS from Applichem, CAS No. 10035-04-8, 2 wt % based on the total mass of the calcium chloride solution) and solidified, so that they hardened into hardened droplets and at the same time the refractory substances and also the borosilicate glass beads were encapsulated in the solidifying mixture (consisting of the 1% strength sodium alginate solution and the dispersing solution).

[0361] Note: The size of the hardened droplets was dependent on the composition of the dilute suspension, the conveying capacity of the pump and the vibrational frequency of the nozzle.

[0362] (a3) Treatment of the Hardened Droplets

[0363] The hardened droplets were subsequently scraped off and washed in water.

[0364] Thereafter the washed and hardened droplets were dried in a drying oven at 180? C. for 40 minutes. After drying, the resulting hardened droplets were pourable, and their bulk density immediately before treatment in the muffle furnace is reported in Table 1.

[0365] The pourable hardened droplets were subsequently heated in a preheated muffle furnace at 900? C. for 30 minutes. Cooling resulted in inventive composite particles.

[0366] As is evident from the last line of Table 1, the bulk densities measured for the inventive composite particles produced are below 350 g/L. Through a suitable choice of the refractory substances or of the precursors of refractory substances, and the lightweight fillers, the bulk density of resultant inventive composite particles can in fact be reduced to 250 g/L (cf. composite particles B37 and E6 in Table 1).

[0367] Sintering Test at 1600? C. for Comparing the Thermal Stability of Inventive and Non-Inventive Composite Particles

[0368] In accordance with the sintering test described earlier on above, inventive composite particles were tested in comparison to non-inventive composite particles KHP 108 (core-shell particles from Chemex) and non-inventive particles W 205-6 (WeiRe Spheres W250-6 product from Omega Minerals). The inventive and non-inventive particles had a particle size in the range from 0.25 to 0.5 mm. The sintering temperature was 1600? C. The control sieve for determining the sieve residue and the sieve undersize had a mesh size of 0.5 mm.

[0369] The results of the sintering tests are set out in Table 2.

TABLE-US-00003 TABLE 2 Results of sintering test at 1600? C. (preliminary sintering of the samples, 30 min at 900? C. in the preheated oven, then sintering temperature at 1600? C. for 30 min) inventive non-inventive non-inventive composite composite composite particles particles particles Designation of B36 W250-6 KHP 108 particles tested Particle size 0.25-0.5 0.25-0.5 0.25-0.5 [mm] Bulk density 340 390 540 [g/L] Result of sieve residue/ sieve residue/ completely sieving with sieve sieve melted, 0.5 mm control undersize = 0.4 undersize = 28.4 sieving not sieve possible Macroscopic see FIG. 1 see FIG. 2 see FIG. 3 appearance after sintering Microscopic see FIG. 4 see FIG. 5 appearance after sintering Result not sintered sintered fused

[0370] As is evident from Table 2, the ratio of sieve residue to sieve undersize for the inventive composite particles B36 after sintering is below 1, while this ratio is more than 1 for the non-inventive composite particles after sintering. Accordingly, the thermal stability of the inventive composite particles B36 at 1600? C. is better than that of the non-inventive composite particles.

[0371] Sintering Test at 1700? C. of Inventive Composite Particles and Non-Inventive Composite Particles

[0372] In accordance with the sintering test described earlier on above, inventive composite particles B36 were tested in comparison to non-inventive composite particles Hargreaves (hollow-bead corundum with >98.8% Al.sub.2O.sub.3 from Hargreaves raw material services GmbH) and non-inventive composite particles KKW (hollow-bead corundum with >98.8% Al.sub.2O.sub.3 from Imerys Fused Minerals Zschornewitz GmbH). The particle sizes of the composite particles were always in the specified range from 0.18 to 0.71 mm. The sintering temperature was 1700? C. The control sieve for determining the sieve residue and the sieve undersize had a mesh size of 0.71 mm.

[0373] The results of the test are set out in Table 3:

TABLE-US-00004 TABLE 3 Results of sintering test at 1700? C. (preliminary sintering of the samples, 30 min at 900? C. in the preheated oven, then sintering temperature at 1700? C. for 30 min) inventive non-inventive non-inventive composite composite composite particles particles particles Designation of B36 Hargreaves KKW particles tested Particle size [mm] 0.18-0.71 0.18-0.71 0.18-0.71 Bulk density [g/L] 340 980 770 Result of sieving sieve residue/ sieve residue/ sieve residue/ with 0.71 mm sieve sieve sieve control sieve undersize = 0.7 undersize > 1 * undersize > 1 * Macroscopic see FIG. 6 see FIG. 7 see FIG. 8 appearance after sintering Microscopic see FIG. 9 see FIG. 10 see FIG. 11 appearance after sintering Result not sintered sintered sintered * break-up of the sinter cake by sieving not possible

[0374] As is evident from Table 3, the ratio of sieve residue to sieve undersize for the inventive composite particles B36 after sintering is below 1, while this ratio is more than 1 for the non-inventive composite particles after sintering. Accordingly, the thermal stability of the inventive composite particles B36 at 1700? C. is better than that of the non-inventive composite particles.

[0375] Experimental Part 2Surface Sealing

[0376] The inventive composite particles B36 (cf. Table 1), after having been heated in a preheated oven at 900? C. for 30 minutes, were surface-sealed as follows.

[0377] The surface sealing took place with an aqueous albumen solution containing 6 wt % of High Gel egg white powder (product number 150063) from NOVENTUM Foods, based on the total weight of the aqueous solution formed.

[0378] The inventive composite particles B36 were subsequently mixed with the prepared albumen solution in a weight ratio of composite particles to albumen solution of 2:1 and were stirred in the resulting mixture until the albumen solution was completely absorbed. Thereafter the composite particles treated with the albumen solution were dried in a drying oven at 110? C. for 40 minutes. The resulting composite particles are referred to as B36-albumen.

[0379] Detection of the water absorption capacity of inventive composite particles B36 (without albumen cladding) and B36-albumen (with albumen cladding) using an Enslin instrument showed that the water absorption of the inventive composite particles is reduced by an albumen cladding from 1.6 ml/g (B36) to 0.1 ml/g (B36-albumen).

[0380] Using the constituents indicated in Table 4, the cold-box process (N,N-dimethylpropylamine catalyst) was then used to produce test bars, whose flexural strength was determined in a method based on VDG standard P 73, method A (BOSCH Profi 67 mixer used, processing at room temperature and ambient humidity, production by ramming, test values captured after 1 h and after 24 h, triplicate determination in each case) using the PFG strength testing apparatus with low-pressure manometer N (with motor drive).

TABLE-US-00005 TABLE 4 Use of inventive composite particles with and without albumen cladding (i.e. surface sealing). The figures for the weight percentages of the individual constituents are based on the total mass of the respective constitution of the feeder compositions (with composite particles B36-albumen or with composite particles B36). Constitution of the Constitution of the feeder composition feeder composition with surface- with non-surface- sealed composite sealed composite particles particles Constituents B36-albumen B36 KHP 108 0.25-0.5 mm 17.1 17.1 (Chemex raw material) [wt %] KHP 69 0.1-0.3 mm 42.74 42.74 (Chemex raw material) [wt %] Inventive composite 25.64 particles B36 [wt %] Inventive composite 25.64 particles B36-albumen [wt %] Polyisocyanate 7.26 7.26 component (Aktivator 6324, H?ttenes- Albertus) [wt %] Benzyl ether resin 7.26 7.26 component (Gasharz 7241, H?ttenes- Albertus) [wt %] Resultant Inventive V 1 KS 7 feeder element (cf. FIG. 12) (cf. FIG. 13) 24 h flexural strengths 170 70 of a test bar made from feeder composition (VDG standard P 73) [N/mm.sup.2] (average from three measurements)

[0381] Table 4 shows that when albumen is used as an agent for sealing the surface of composite particles produced inventively, test bars are obtained that have increased flexural strength. Corresponding feeder elements are therefore likewise particularly mechanically stable.

[0382] It is assumed that the composite particles B36 (without albumen) absorb a comparatively large amount of binder, which is then no longer available to form a flexurally strong binding of the test bars; the same is true, analogously, of corresponding feeder elements.

[0383] Experimental Part 3Production of a Feeder Element (Hereinafter: Inventive Feeder Element) Inventively

[0384] An inventive feeder element and a non-inventive feeder element were produced, in order to compare them in terms of their insulating properties, thermal stability and practical usefulness, as follows: [0385] inventive feeder element KS 611 with inventive composite particles B36-albumen with sealed surface (see above), [0386] and [0387] non-inventive feeder element STANDARD with non-inventive particles KHP 108 (see above) instead of the inventive composite particles B36-albumen. [0388] (a) Production or provision of inventive composite particles and non-inventive core-shell particles, respectively: [0389] The composite particles B36-albumen with sealed surface were produced as described above; the composite particles KHP 108 were provided. [0390] (b) Mixing of the inventive composite particles with sealed surface produced and of the non-inventive core-shell particles with a cold-box binder to give a feeder composition [0391] The precise constitutions of the feeder compositions for the non-inventive feeder element STANDARD and the inventive feeder element KS 611 are shown in Table 5 below. They were each mixed to give a homogeneous feeder composition. [0392] (c) Shaping and curing of the feeder composition to give a feeder element. [0393] The feeder compositions for the non-inventive feeder element STANDARD and the inventive feeder element KS 611 were subsequently each shaped in a core-shooting machine and gassed in accordance with the cold-box process (N,N-dimethylpropylamine catalyst). This gave the non-inventive feeder element STANDARD and the inventive feeder element KS 611.

TABLE-US-00006 TABLE 5 Constituents of the feeders used for casting (cube test). The figures for the weight percentages of the individual constituents are based on the total mass of the respective constitution of the feeder compositions (for the feeder element STANDARD and the feeder element KS 6II respectively). Constitution of the Constitution of the feeder composition feeder composition for the feeder element for the feeder element STANDARD KS 6II Constituents (not Inventive) (Inventive) KHP 69 [wt %] 59.83 59.83 Non-inventive and non- 25.65 surface sealed composite particles KHP 108 [wt %] Inventive composite 25.65 particles B36-albumen [wt %] Polyisocyanate 7.26 7.26 component (Aktivator 6324, H?ttenes-Albertus) [wt %] Benzyl ether resin 7.26 7.26 component (Gasharz 7241, H?ttenes-Albertus) [wt %] [0394] (d) Casting of a cube of iron using an inventive feeder KS 611 and a non-inventive feeder STANDARD [0395] The inventive feeder KS 611 and the non-inventive feeder STANDARD (as described above) were tested for their performance utility using so-called cube tests. These tests investigate in particular which feeder element exhibits the better feeding capacity when producing a casting in the form of a cube. [0396] The feeders produced according to the constitutions from Table 5 were each cast to the 1.2 cm modulus at 1400? C. with iron (GGG40) in the cube test.

[0397] The cuboid iron castings thus produced, with residual iron feeders, are shown in the halved condition (by sawing) in FIG. 14 (result when using a non-inventive feeder) and in FIG. 15 (result when using an inventive feeder).

[0398] FIG. 14 shows side cavities which extend down to a depth of 4 mm in the cast cube (cf. inscription ?4 in FIG. 14; distance between upper drawn line and lower drawn line=4 mm, upper line marks boundary between casting and the residual metallic feeder, lower line marks lowest penetration point of the side cavity).

[0399] FIG. 15 shows cavities only in the residual metallic feeder; no cavities extend into the cast cube (cf. inscription 7 and 13 in FIG. 15; distance between upper drawn line and lower to drawn line=7 and 13 mm, respectively, lower line marks boundary between casting and residual metallic feeder, upper line marks lowest point of the cavity in the residual metallic feeder; different values 7 mm and 13 mm result from the width of the sawblade).

[0400] From FIGS. 14 and 15 it is evident that the inventive feeder element KS 611 possesses improved feeding capacity in comparison to the non-inventive feeder element STANDARD.