METHOD OF PREPARING A PARTICULATE REFRACTORY COMPOSITION FOR USE IN THE MANUFACTURE OF FOUNDRY MOULDS AND CORES, CORRESPONDING USES, AND RECLAMATION MIXTURE FOR THERMAL TREATMENT

Abstract

Described is a method of preparing a particulate refractory composition for use in the manufacture of foundry moulds and cores from spent foundry moulds or cores formed of refractory material and a binder containing water glass, the method comprising the following steps: providing broken material from spent foundry moulds or cores or preparing broken material from spent foundry moulds or cores, wherein the broken material comprises particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface, mixing the broken material with particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, to give a mixture and subjecting the mixture to a heat treatment at a temperature of 400° C. or higher. Also described are a corresponding use, a reclamation mixture, and a method of making a foundry mould or core.

Claims

1. A method of preparing a particulate refractory composition for use in the manufacture of foundry moulds and cores from spent foundry moulds or cores formed of refractory material and a binder containing water glass, the method comprising the following steps: providing broken material from spent foundry moulds or cores or preparing broken material from spent foundry moulds or cores, wherein the broken material comprises particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface, mixing the broken material with particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, to give a mixture and subjecting the mixture to a heat treatment at a temperature of 400° C. or higher.

2. The method according to claim 1, wherein the heat treatment is at a temperature in the range of from 400 to 750° C., preferably in the range of from 570 to 730° C., more preferably in the range of from 630 to 730° C., most preferably in the range of from 670 to 730° C. and/or is conducted in a fluidized bed or thermal sand reclamation unit, wherein simultaneous with or after the heat treatment in the fluidized bed or thermal sand reclamation unit dust and/or fines and/or solid matter comprising alkali ions are preferably removed.

3. The method according to claim 1, wherein the step of preparing broken material from spent foundry moulds or cores, wherein the broken material comprises particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface, comprises a mechanical treatment of material from spent foundry moulds or cores comprising refractory material and a binder containing water glass so that the material is broken, wherein preferably the broken material comprises particles of refractory material having hardened water glass binder on their surface and/or the mechanical treatment comprises two or more successive breaking steps in order to convert the material from spent foundry moulds or cores comprising refractory material and a binder containing water glass into particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface.

4. The method according to claim 1, wherein the step of mixing the broken material with the particulate amorphous oxide is conducted in the presence of a liquid phase, preferably in the presence of an aqueous liquid phase, more preferably in the presence of an aqueous liquid phase comprising water in an amount of 80% by weight or more, based on the total amount of the liquid phase, wherein the step of mixing is preferably conducted in the presence of one or more organic compounds as constituents of the aqueous liquid phase, and/or in the step of mixing the broken material with the particulate amorphous oxide the broken material is mixed with a suspension of the particulate amorphous oxide in a liquid phase, wherein preferably the liquid phase is an aqueous liquid phase, wherein more preferably the liquid phase is an aqueous liquid phase comprising water in an amount of 80% by weight or more, based on the total amount of the liquid phase, wherein preferably the aqueous liquid phase comprises one or more organic compounds.

5. The method according to claim 1, wherein the broken material is also mixed, simultaneously or successively, with one or more materials selected from the group consisting of phyllosilicates, preferably selected from the group consisting of kaolinite, metakaolin, montmorillonite, halloysite, hectorite, smectite, muscovite, pyrophyllite, synthetic phyllosilicates and mixtures thereof, wherein preferably the phyllosilicates are partially or completely calcined, preferably as a pre-mixture with the particulate amorphous oxide, more preferably as a pre-mixed suspension in a liquid phase also comprising the particulate amorphous oxide, wherein preferably the liquid phase is an aqueous liquid phase, wherein more preferably the liquid phase is an aqueous liquid phase comprising water in an amount of 80% by weight or more, based on the total amount of the liquid phase, wherein preferably the aqueous liquid phase comprises one or more organic compounds, suspending agents, preferably illite containing clay, smectite and/or attapulgite, wetting agents, dispersing agents, anti-settling agents, dyes, pigments, biocides, preferably fungicides, zeolites, and aluminium hydroxide.

6. The method according to claim 1, wherein the particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, comprises one more substances selected from the group consisting of silica fume, preferably selected from the group consisting of silica obtained by oxidation of metallic silicon with an oxygen containing gas, and silica obtained by thermal decomposition of ZrSiO.sub.4 to ZrO.sub.2 and SiO.sub.2, amorphous silica, precipitated silicic acid, pyrogenic silicic acid, and silica obtained by atomization of a silica melt and subsequent solidification.

7. The method according to claim 3, with the following steps in the process of preparing broken material from spent foundry moulds or cores: producing a moulding mixture comprising refractory material and a binder containing water glass and a particulate amorphous silicon dioxide, moulding of the moulding mixture, curing of the moulding mixture to give a cured foundry mould or core, using the cured foundry mould or core in a metal casting process to give a spent foundry mould or core.

8. The method according to claim 7, wherein the binder additionally comprises one or more compounds selected from the group consisting of phosphorus-containing compounds, preferably selected from the group consisting of sodium metaphosphate, sodium polyphosphate and mixtures thereof, carbohydrates, surfactants, preferably an anionic surfactant, more preferably carrying a sulfate, sulfonate, or phosphate group, barium sulfate, and oxidic boron compounds, preferably selected from the group consisting of borates, borophosphates, borophosphosilicates and mixtures thereof.

9. The method according to claim 1, wherein the total amount of particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, is in the range of from 0.01 to 3.0% by weight, preferably in the range of from 0.03 to 0.9% by weight, more preferably in the range of from 0.04 to 0.8% by weight, most preferably in the range of from 0.06 to 0.4% by weight, based on the total weight of broken material, and/or in the range of from 10 to 60% by weight, preferably in the range of from 13 to 50% by weight, more preferably in the range of from 20 to 40% by weight, most preferably in the range of from 25 to 35% by weight, based on the total weight of hardened water glass binder on the surface of the particles and/or the aggregates of particles of refractory material in the broken material.

10. The method according to claim 1, wherein the particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, has a D.sub.90 of less than 100 μm, preferably less than 45 μm, more preferably less than 25 μm, most preferably less than 5 μm, and/or the particle size of the broken material is in the range of from 100 to 600 μm, preferably in the range of from 120 to 550 μm, more preferably in the range of from 150 to 500 μm, and/or the ratio of the D.sub.90 of the particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, to the size of the particles and/or aggregates of particles of refractory material in the broken material is less than 1:1, preferably less than 1:10, more preferably less than 1:20, most preferably less than 1:120.

11. The method preferably according to claim 1, of preparing a particulate refractory composition for use in the manufacture of foundry moulds and cores from spent foundry moulds or cores formed of refractory material and a binder containing water glass, the method comprising the following steps: providing broken material from spent foundry moulds or cores or preparing broken material from spent foundry moulds or cores, wherein the broken material comprises particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface, mixing the broken material with particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, in the presence of an aqueous liquid phase, to give a mixture and subjecting the mixture to a heat treatment at a temperature in the range of from 400 to 750° C., preferably in the range of from 570 to 730° C., more preferably in the range of from 630 to 730° C., most preferably in the range of from 670 to 730° C., wherein the heat treatment is conducted in a fluidized bed.

12. A method of reclamation, comprising: providing an aqueous suspension comprising an aqueous liquid phase comprising water in an amount of 80% by weight or more, based on the total amount of the liquid phase, and particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide, wherein the aqueous suspension is a constituent of a reclamation mixture comprising broken material from spent foundry moulds or cores, wherein the broken material comprises particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface.

13. A reclamation mixture for thermal treatment, comprising: (i) broken material from spent foundry moulds or cores, wherein the broken material comprises particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface, and (ii) an aqueous suspension comprising an aqueous liquid phase comprising water in an amount of 80% by weight or more, based on the total amount of the liquid phase, and particulate amorphous oxide comprising silicon dioxide in an amount of 85% by weight or more, based on the total amount of the particulate amorphous oxide.

14. The method of making a foundry mould or core comprising the following steps: preparing a particulate refractory composition according to a method as defined in claim 1, mixing the particulate refractory composition with a binder, preferably a water glass binder, shaping the resulting mixture, and curing the binder in said shaped mixture.

Description

EXAMPLES

Example 1: Preparation and Composition of an Aqueous Suspension for Use as Constituent of Reclamation Mixtures for Thermal Treatment

[0185] An aqueous suspension (“Suspension A”) was prepared.

[0186] Suspension A is an aqueous suspension of 25% by weight of the silica fume SIF-A-T (Yingkou Imerys Astron Chemicals Co., Ltd; CAS-number: 69012-64-2; SiO.sub.2-content=95% by weight) and 25% by weight of the phyllosilicate Satintone® W/Whitetex® (calcined kaolinite from BASF Catalysts LLC, screen residue by 325 Mesh=0.02%; avg. Stokes equivalent particle diameter=1.4 μm) in water. Both, the % by weight of silica fume as well as the % by weight of phyllosilicate, are based on the total amount of the suspension. The D.sub.50 of the silica fume used is between 1 and 2 μm. The D.sub.90 of the silica fume used is 4.485 μm.

[0187] Suspension A was prepared with procedures known in the art. This included mixing of the respective constituents (water, silica fume, phyllosilicate). Significant characteristics of Suspension A are summarized in Table 1.

TABLE-US-00001 TABLE 1 Suspension A Water (liquid phase) [% by weight] 50 Satintone W (phyllosilicate) [% by weight] 25 Silica fume SIF-A-T (particulate amor- 25 phous oxide) [% by weight] pH 4.6 Color white

Example 2: Pilot Plant Trials

[0188] Pilot plant trials were carried out in a “Single Axis Attrition Flasher” (Chin Ying Foundry Material co. LTD) mechanical treatment machinery as well as in a “Energy-Saving Counter Flow Furnace “SX2-5-12 (Chin Ying Foundry Material co. LTD) fluidized bed. Both of the facilities were built by CHIN YING FOUNDRY MATERIAL (TIANJIN) CO., LTD and placed in its Tianjin plant, China. The pilot trials were carried out as follows:

Example 2.1: Preparation of Broken Material from Spent Foundry Cores, Preparation of a Reclamation Mixture, and Preparation of Particulate Refractory Compositions

[0189] I) Spent foundry cores (previously used for aluminium casting) formed of refractory material (calcined quartz sand from the LIANXIN SAND GROUP; AFS value between 50 and 55; clay content less than 0.1%) and a binder system containing water glass (Cordis® 8593 from the company Huttenes-Albertus Chemische Werke GmbH) as well as particulate amorphous silica (Anorgit®8610 from the company Huttenes-Albertus Chemische Werke GmbH, comprising an amount of particulate amorphous silica of between 65 to 70% by weight, based on the total amount of Anorgit® 8610) were mechanically treated (i.e., broken) by conducting a single or two successive breaking steps. Herein, the material from the spent foundry cores is converted into broken material comprising particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface. [0190] a. In a first breaking step, a total amount of 1000 kg of spent foundry sand from said spent foundry cores was broken by an ordinary foundry crusher. The resulting broken material is subsequently labelled “Sample A”. [0191] b. In a second successive breaking step, a total amount of 750 kg of “Sample A” was further mechanically treated (broken) with a “Single Axis Attrition Flasher” mechanical facility. The Single Axis Attrition Flasher is a discontinuous facility. The second successive breaking step was carried out in three batches of 250 kg per batch. All three batches were treated by applying a power of 15 kW, a rotation speed of 1800 r/min and a treatment duration of 20 min. The resulting broken material is subsequently labelled “Sample B”. [0192] c. The resulting Sample A and Sample B, both comprising particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface, were collected for further application. [0193] II) Aqueous Suspension A was prepared according to “Example 1: Preparation and composition of an aqueous suspension for use as constituent of reclamation mixtures for thermal treatment”. [0194] III) The broken material of Sample B was treated in two different ways, (a) without and (b) with employment of Suspension A: [0195] a. 300 kg of Sample B were fed to an “Energy-Saving Counter Flow Furnace SX2-5-12” fluidized bed, which was preheated to 730° C. There, sample B was subjected to a heat treatment for 1 hour at 730° C., subsequently smoldered for 4 hours without heating and subsequently cooled down. The resulting particulate refractory composition is subsequently labelled “Sample C”. [0196] b. Another 300 kg of Sample B were mixed with 3 kg of Suspension A, to give a homogeneous mixture of Sample B and Suspension A, i.e. a reclamation mixture for thermal treatment according to the invention. Afterwards, the resulting reclamation mixture for thermal treatment was subjected to the same (heat) treatment as described in step III) a. The resulting particulate refractory composition prepared by the method according to the invention is subsequently labelled “Sample D”.

Example 2.2: Consumption of Acid, Electrical Conductivity and Optical Analysis of the Sand Grain Surfaces of the Broken Material from Spent Foundry Cores and of the Particulate Refractory Compositions Prepared According to Example 2.1

[0197] The consumption of acid (COA) and the electrical conductivity were measured and determined for Sample A, Sample B, Sample C, Sample D as well as for a new particulate refractory composition (i.e. calcined quartz sand from the LIANXIN SAND GROUP). The COA is a value used in inorganic, analytical chemistry (involving acid-base titration of a sample) to determine the alkali-content of a sample. The electrical conductivity value is measured to determine the content of conductive substances in a sample. Both values are directly related to the “cleanliness” of a sample. Low values of both COA and electrical conductivity indicate a high degree of sample cleanliness. A high cleanliness of particulate refractory compositions is preferred as clean materials generally show better properties when used in the manufacture of foundry moulds and cores. The cleanliness of the samples was furthermore evaluated by an analysis of the sand grain surfaces of the respective samples, by means of an optical microscope.

Determination of the Consumption of Acid (COA):

Devices Used for the Determination of the COA:

[0198] analytical balance (accuracy: ±0.01 g); [0199] 250 mL laboratory bottle with cap; [0200] magnetic stirrer; [0201] PTFE cylindrical magnetic stirrer bar (ca. 50×8 mm); [0202] burette; [0203] 50 mL pipettes; [0204] 300 mL Erlenmeyer flasks (wide neck); [0205] filter funnel; [0206] filter paper; [0207] filter holder.

Reagents Used for the Determination of the COA:

[0208] hydrochloric acid (0.1 mol/L); [0209] sodium hydroxide solution (0.1 mol/L); [0210] bromothymol blue (0.1% by weight in ethanol); [0211] ultra-pure water.

[0212] For the determination of the consumption of acid, 50 g±0.01 of sample (Sample A, Sample B, Sample C, Sample D, and new particulate refractory composition) were weighed into a 250 mL laboratory bottle containing a magnetic stirrer bar. Subsequently, 50 mL of ultra-pure water and 50 mL of 0.1 mol/L hydrochloric acid were given into the laboratory bottle by using 50 mL pipettes. After closing the laboratory bottle with the cap, the resulting suspension was firstly stirred with a magnetic stirrer for 5 minutes was left afterwards for 1 hour. A blind suspension (i.e. without 50 g±0.01 of sample) was prepared in the same way.

[0213] Next, the suspensions obtained were filtered into an Erlenmeyer flask by using a filter system. The solid residue (filter cake) was then washed five times with 10 approximately millilitres of ultra-pure water each, whereby the washing water was added to the filtrate. After adding 4 to 5 drops of bromothymol blue indicator the filtrate (together with the washing water) was titrated from yellow to blue with 0.1 mol/L sodium hydroxide solution.

[0214] The COA was the calculated as follows:

[00001]$\mathrm{COA}\left[g\mathrm{HCL}\text{/}\mathrm{kg}\mathrm{sample}\right]=\left(V_{\mathrm{blind}}\left(\mathrm{mL}\right)-V_{\mathrm{sample}}\left(\mathrm{mL}\right)\right)\times \frac{100}{\mathrm{weight}\mathrm{of}\mathrm{sample}\left(g\right)}\times 36.46\times 0.001\times 10$

wherein,
V.sub.blind is the consumed volume (mL) of 0.1 mol/L sodium hydroxide solution for the blind suspension, and
V.sub.sample is the consumed volume (mL) of 0.1 mol/L sodium hydroxide solution for the corresponding suspension of Sample A, Sample B, Sample C, Sample D or new particulate refractory composition.

Determination of the Electrical Conductivity:

Devices Used for the Determination of the Electrical Conductivity:

[0215] Laboratory balance (accuracy=±0.01 g); [0216] 250 mL beaker; [0217] PTFE cylindrical magnetic stirrer bar (ca. 50×8 mm); [0218] Conductivity meter; [0219] Measuring cylinder; [0220] Heating plate.

Reagents Used for the Determination of the Electrical Conductivity:

[0221] Ultra-Pure water.

[0222] For the determination of the electrical conductivity 50±0.01 g of sample (Sample A, Sample B, Sample C, Sample D, and new particulate refractory composition) and approximately 100 mL ultra-pure water were given into the beaker. The resulting suspension was placed on a heating plate and was brought to boil. After 5 min of boiling, the suspension was cooled down to room temperature and subsequently the electrical conductivity was measured by using the conductivity meter.

Analysis of the Sand Grain Surfaces by Means of an Optical Microscope

[0223] The analysis of the sand grain surfaces of the samples (Sample A, Sample B, Sample C, Sample D, and new particulate refractory composition) was carried out by taking pictures of the sand grain surfaces using an optical microscope (VHX550/1000D, Keyence). The assessment of cleanliness analyzed by means of an optical microscope was conducted on the basis of a scale from “1” to “5”, wherein 1 stands for “very clean” (no or almost no impurities—such as remaining hardened water glass—are visible on the surface of the particles examined) and 5 stands for “very dirty” (i.e. large amounts of impurities—such as remaining hardened water glass—are visible on the surface of the particles examined).

[0224] The results regarding the determination of the consumption of acid (COA), the determination of the electrical conductivity and the analysis of the sand grain surfaces by means of an optical microscope are summarized in Table 2.

TABLE-US-00002 TABLE 2 Assessment of cleanliness analyzed by COA Electrical means of an [g HCl/kg conductivity optical Sample sample] [μS/cm] microscope Reference samples A 24.1 1876 5 B 17.7 1294 4 C 5.2 128 3 Particulate refractory D 5.0 87 2 composition prepared by the method according to the invention (using suspension A) Reference sample New 4.5 30 1 particulate refractory composition

[0225] As can be seen from Table 2, the values for the consumption of acid (COA), the electrical conductivity and the cleanliness analyzed by means of an optical microscope for “Sample D” (i.e. the reclaimed particulate refractory composition prepared by the method according to the invention) are close to the ideal values represented by the reference sample of “New particulate refractory composition”. When comparing “Sample D” with “Samples A” and “Sample B” (i.e. broken material from spent foundry cores prepared by mechanical treatment, without additional heat treatment in fluidized bed), it should be noted that the values for COA, electrical conductivity and cleanliness analyzed by means of an optical microscope are significantly improved by the method according to the invention (Sample D). In addition, a direct comparison of “Sample D” with “Sample C” (i.e. a reclaimed particulate refractory composition, wherein the broken material used for preparing the particulate refractory composition was not mixed with particulate amorphous oxide and phyllosilicate prior to the heat treatment) demonstrates that “Sample D” shows better values in terms of COA, electrical conductivity and cleanliness analyzed by means of an optical microscope.

[0226] In summary, the results listed in Table 2 above show that the method according to the invention results in the preparation of particulate refractory compositions (from spent foundry cores) with extraordinary properties, which is not feasible with methods typically used in the art.

[0227] Additional investigations have also shown that a method according to the invention using an aqueous suspension of 50% by weight of the silica fume SIF-A-T in water, based on the total amount of the suspension (i.e. using a suspension not comprising phyllosilicate), leads to a particulate refractory composition with outstanding properties as well, wherein the measured values regarding COA, electrical conductivity and cleanliness analyzed by means of an optical microscope for the (reclaimed) particulate refractory composition prepared by the said suspension are almost as good as those of “Sample D”, and better than those of “Sample A”, “Sample B” or “Sample C”.

Example 3: Making of Foundry Cores for Casting Trials

Example 3.1: Making of Foundry Cores by Use of the Materials According to “Sample A”, “Sample B”, “Sample C” (not in Accordance with the Invention) and “Sample D” (in Accordance with the Invention) Prepared According to Example 2.1

[0228] “Sample A”, “Sample B”, “Sample C”, “Sample D” as well as a new particulate refractory composition ((i.e. calcined quartz sand from the LIANXIN SAND GROUP) were used to make specimen representing foundry cores (bending bars, dimensions: 22.4 mm×22.4 mm×178.0 mm).

[0229] Before foundry cores were made, the AFS values of the materials according to “Sample A”, “Sample B”, “Sample C” and “Sample D” as well as the “AFS value” of a new particulate refractory composition were determined based on the determination method described in the “VDG Merkblatt P 27”. According to the “VDG Merblatt R 202”, the AFS value is a parameter defined by the American Foundrymen's Society (AFS) to characterize the grain size. In this respect, the AFS value indicates the mesh count per inch of the sieve through which the material inspected would pass if it had a uniform grain size. To determine the AFS values, 100 g±0.01 g of each sample were weighted on a sieve tower (including a sieve set with sieves of the following meshes: 1.000 mm, 0.710 mm, 0.500 mm, 0.355 mm, 0.250 mm, 0.180 mm, 0.125 mm, 0.090 mm, 0.063 mm). The sieve tower was operated with an amplitude of 1.0 mm for 5 min, while the interval was set to 0 s. After completion of sieving the content of each sieve was weighted and the AFS value was calculated by using following equation:

[00002]$\mathrm{AFS}=\frac{\Sigma g_i.Math.M{3}_i}{g}$

wherein g is the total mass, g.sub.i is the mass of the individual grain classes (e.g. 1.000 mm to 0.710 mm) and M3.sub.i is the multiplication factor of the individual grain classes (as listed in “VDG Merkblatt P 27”).

[0230] For making of the foundry cores (bending bars) 2.2 parts by weight of a binder containing water glass (Cordis® 8593 from the company Hüttenes-Albertus Chemische Werke GmbH, i.e. a water glass binder) and 1.3 parts by weight of an additive (Anorgit® 8610 from the company Hüttenes-Albertus Chemische Werke GmbH having an amount of particulate amorphous silica of between 65 to 70% by weight, based on the total amount of Anorgit® 8610) were homogenized (mixed) with 100 parts by weight (3500 g) of “Sample A”, “Sample B”, “Sample C”, “Sample D” or a new particulate refractory composition. Subsequently, foundry cores were made from the resulting mixtures by shooting using a “Universal Core Shooter (LUT)” from the company Morek Multiserw. The shooting of the foundry cores includes a shaping of the corresponding mixtures as well as curing of the binder in said shaped mixtures. The parameters for shooting of the foundry cores are listed Table 3.

TABLE-US-00003 TABLE 3 Shooting pressure 4.5 bar Duration of shooting 3 s Curing time 30 s Core box temperature 180° C. Gas air Gassing time 30 s Gas temperature 180° C.

[0231] Ten foundry cores (bending bars) for each sample (“Sample A”, “Sample B”, “Sample C”, “Sample D” and new particulate refractory composition) were made by the method stated above. The resulting foundry cores (bending bars) were used for core strength tests as well as for casting trials.

[0232] The core strength of foundry cores (bending bars) was tested in warm status (i.e. 15 s after shooting) as well as in cold status (i.e. 1 h after shooting). Each test regarding the core strength was repeated three times for each foundry core composition. The mean value was then calculated from each of the three measured values. The laboratory (in which the core strength tests were conducted) was air-conditioned with temperatures between 21 and 22° C. and a relative humidity between 44 and 45%. A sufficiently high core strength is one prerequisite for the use of a foundry mould or core for the purpose of casting.

[0233] Besides, seven bending bars per foundry core composition were weighed in cold status to obtain mean weights of the foundry cores. The mean weights of the foundry cores indicate how easy or difficult it is to compact the respective cores. The lower the mean weight of the foundry cores, the easier it is to compact the foundry cores. A high mean weight of a foundry core corresponds to a high compaction and usually means that the respective foundry core also shows improved values regarding strength and humidity resistance.

[0234] The results regarding the core strengths and the core weights of the foundry cores as well as the AFS values of the materials, used for making the foundry cores, are summarized in Table 4. The core strength values listed in Table 4 represent average values of the triple measurements carried out.

TABLE-US-00004 TABLE 4 Core strength Core strength Mean tested in warm tested in cold core status status weight AFS Sample [N/cm.sup.2] [N/cm.sup.2] [g] value A 160 350 149.7 40 B 210 430 158.0 50 C 200 430 159.3 46 D 200 430 158.8 46 New particulate 180 370 157.1 52 refractory composition

[0235] As can be seen from Table 4, the core strengths of foundry cores made by using “Sample A”, “Sample B”, “Sample C” or “Sample D” are close to (or even higher than) the core strengths of the foundry cores made by using a new particulate refractory composition. Furthermore, with exception of “Sample A”, the mean core weights of said samples are higher than the mean core weight of the foundry cores made by using a new particulate refractory composition. The AFS values of the broken materials from “Sample A”, “Sample B”, “Sample C”, and “Sample D” are in general smaller than (but in the same region as) the AFS value of the new particulate refractory composition.

Example 3.2: Casting Trials by Use of the Foundry Cores Made According to Example 3.1

[0236] Three foundry cores (bending bars) of each foundry core composition (A, B, C, D, new) were casted with an aluminum alloy. Details regarding the casting conditions are listed in Table 5.

TABLE-US-00005 TABLE 5 Casting temperature 710° C. Pouring time 13-15 s Name of foundry Daihatsu Tianjin Plant

[0237] Details regarding the composition of the aluminum alloy used are listed in Table 6.

TABLE-US-00006 TABLE 6 Components which (in addition to aluminium), are contained in the Amount [% by weight, based on the aluminium alloy used total amount of the aluminum alloy] Cu 2.56 Si 8.71 Mg 0.33 Zn 0.82 Fe 0.81 Mn 0.29 Na 0.003811

[0238] After the casting, the grade of casting surface quality for the castings obtained was assessed. The grade of casting surface quality was assessed on the basis of a scale from “1” to “4”, wherein “1” stands for a very good and “4” for a very poor surface quality of the castings obtained.

[0239] The results regarding the grades of casting surface quality for the castings obtained are summarized in Table 7. The given grades of casting surface quality represent in each case an overall assessment of all foundry cores of the same composition.

TABLE-US-00007 TABLE 7 Sample Grade of casting surface quality * A 4 B 4 C 2 D 1 New particulate 3 refractory composition

[0240] Regarding the grade of casting surface quality, castings produced by the use of foundry cores made of “Sample D” (i.e. made of the particulate refractory composition prepared by the method according to the invention) show the best results. The grade of casting surface quality of such castings is significantly better compared to the grade of casting surface quality of castings produced by the use of foundry cores made of “Sample A” and “Sample B” (i.e. made of broken material) and also better compared to the grade of casting surface quality for castings made of “Sample C” (i.e. made of a reclaimed particulate refractory composition, wherein the broken material used for preparing the particulate refractory composition was not mixed with particulate amorphous oxide and phyllosilicate prior to the heat treatment) or made of a new particulate refractory composition.

[0241] Castings with a superior grade of casting surface quality were also obtained by foundry cores made of a reclamation mixture which was prepared by a method according to the invention, wherein the broken material used was mixed with an aqueous suspension of 50% by weight of the silica fume SIF-A-T in water, based on the total amount of the suspension, prior to the heat treatment.

Example 4: Repetition of Examples 2.1 to 3.2 by Using a Different Spent Foundry Core Composition as Starting Material

[0242] The above Examples 2.1 to 3.2 were generally repeated. However, the spent foundry cores (which were used for preparing broken material, comprising particles and/or aggregates of particles of refractory material having hardened water glass binder on their surface) were formed of a refractory material different from those used in Example 2.1 (in particular, Mongolia quartz sand from the Ma'anshan Shenzhou Sand Corporation was used in Example 4), a binder containing water glass (Cordis®8593 from the company Huttenes-Albertus Chemische Werke GmbH) and an additive (Anorgit® 8610 from the company Huttenes-Albertus Chemische Werke GmbH).

[0243] The determination of COA, electrical conductivity, core strengths, mean core weight and AFS value as well as the assessment of cleanliness analyzed by means of an optical microscope and the assessment of the grade of casting surface quality were conducted in the same manner as described above. The corresponding results are summarized in Table 8. “Sample A.2”, “Sample B.2”, “Sample C.2” and “Sample D.2” were obtained in analogy to “Sample A”, “Sample B”, “Sample C” and “Sample D”, respectively. The reference sample “New particulate refractory composition” of Table 8 corresponds to a sample made by using new refractory material (i.e. Mongolia quartz sand from the Ma′anshan Shenzhou Sand Corporation).

TABLE-US-00008 TABLE 8 Assessment of Core Core cleanliness strength strength COA analyzed by tested in tested Mean Grade of [g HCl/ Electrical means of warm in cold core casting kg conductivity an optical status status weight AFS surface Sample sample] [μS/cm] microscope [N/cm.sup.2] [N/cm.sup.2] [g] value quality * A.2 28.8 1510 5 89 180 138.4 44 4 B.2 22 1370 5 140 300 153.5 54 3 C.2 12.6 200 3 140 280 150.4 45 2 D.2 10 90 2 130 280 150.4 43 1 New 7 40 1 130 230 154.0 52 1 particulate refractory composition

[0244] As can be seen from Table 8, the refractory composition prepared by the method according to the invention (“Sample D.2”) shows also in this case the best values with regard to COA, electrical conductivity, assessment of cleanliness analyzed by means of an optical microscope, and grade of casting compared to the according reference samples (“Sample A.2”, “Sample B.2” and “Sample C.2”). Thus, the method according to the invention offers particularly advantageous properties (regardless of the composition of the spent foundry mould or core used) in comparison with methods known from the state of the art.