USE OF CLOSED-PORE MICROSPHERES OF EXPANDED PEARLITE AS A FILLER FOR THE PRODUCTION OF MOULDINGS FOR THE FOUNDRY INDUSTRY

Abstract

The present invention relates to the use of closed-pore microspheres of expanded perlite as a filler for producing moldings for the foundry industry, to a composition for producing moldings for the foundry industry, comprising closed-pore microspheres of expanded perlite as a filler, and a binder, the binder being selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch, and also to moldings for the foundry industry and to a process for producing a molding for the foundry industry.

Claims

1. A method of producing moldings for the foundry industry comprising using closed-pore microspheres of expanded perlite as a filler for moldings for the foundry industry, wherein the closed-pore microspheres have a closed foam structure with pores separated from one another, and a virtually smooth surface.

2. The molding as claimed in claim 15, wherein the microspheres are obtainable by a process in which a perlite sand is expanded in a trickle channel having multistage temperature zones.

3. The molding as claimed in claim 15, wherein the microspheres have a particle size d50 of 100 to 400 m.

4. The molding as claimed in claim 15, wherein the microspheres are closed on their surface.

5. The molding as claimed in claim 15, wherein the microspheres have a ratio of pure density to apparent density of greater than 1.8, the apparent density and the pure density being determined with the helium pyknometer.

6. The molding as claimed in claim 15, wherein the microspheres have a particle strength of above 1.3 N/mm.sup.2.

7. The molding as claimed in claim 15, wherein the microspheres have a bulk density of below 500 kg/m.sup.3.

8. The molding as claimed in claim 15, wherein the molding further comprises additional constituents selected from the group consisting of spheres of flyash, foamed glass, quartz sand, calcined kieselguhr, schamotte, cordierite, mullite, and mixtures thereof.

9. The molding as claimed in claim 15, wherein the molding further comprises an organic or inorganic binder or a mixture of organic and inorganic binder and the binder is selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch.

10. The molding as claimed in claim 15, wherein the moldings for the foundry industry are selected from the group consisting of insulating or exothermic feeders, feeder surrounds, feeder sleeves, feeder caps, filling funnels, supply elements, and heating pads.

11. The molding as claimed in claim 15, for producing insulating or exothermic feeders for nonferrous casting.

12. A composition for producing moldings for the foundry industry, comprising closed-pore microspheres of expanded perlite as a filler, and a binder; wherein the closed-pore microspheres have a closed foam structure with pores separated from one another; wherein the binder is selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch.

13. The composition as claimed in claim 12, wherein the microspheres are obtainable by a process in which perlite sand is expanded in a trickle channel having multistage temperature zones.

14. The composition as claimed in claim 12, further comprising constituents selected from the group consisting of spheres of flyash, foamed glass, quartz sand, calcined kieselguhr, schamotte, cordierite, mullite, and mixtures thereof.

15. A molding for the foundry industry, produced using closed-pore microspheres of expanded perlite, having a closed foam structure with pores separated from one another, and a virtually smooth surface; and a binder, the binder optionally being selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch.

16. A process for producing a molding for the foundry industry, having the following steps: (a) producing or providing closed-pore microspheres of expanded perlite as defined in claim 1, (b) mixing the closed-pore microspheres of expanded perlite, produced or provided in step (a), with a binder and also optionally further constituents to give a composition, and (c) molding and curing the composition from step (b) to give a molding or (i) producing or providing a composition comprising closed-pore microspheres of expanded perlite as a filler, and a binder, the binder being selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch, and (ii) molding and curing the composition from step (i) to give a molding.

17. The method according to claim 1, wherein the closed-pore microspheres have a virtually smooth surface.

18. The composition according to claim 12, wherein the closed-pore microspheres have a virtually smooth surface.

Description

[0121] FIG. 1 shows a temperature/time plot of inventive example 2 (identified as inventive 3; bold dashed line) and of comparative examples 2 (identified as standard formula 1; continuous line) and 3 (identified as standard formula 2; gray dashed line). It shows that the temperature of the aluminum melt is maintained for longer in the closed feeder produced, in other words that the aluminum melt cools more slowly.

[0122] The present invention is elucidated in more detail below by means of examples.

EXAMPLES

[0123] Measurement Methods:

[0124] 1. Particle Size Determination: [0125] The particle sizes of closed-pore microspheres are determined by sieving in accordance with DIN 66165-2 (4.1987), employing method F therein (mechanical sieving with agitated individual sieve or sieve set in gaseous fluid at rest). A vibrational sieving machine of type RETSCH AS 200 control is used; the amplitude is set at level 1.8; there is no interval sieving at 10 seconds; the sieving time is minutes.

[0126] 2. Determination of Bulk Density: [0127] The bulk density was determined according to DIN EN ISO 60 2000-1.

[0128] 3. Determination of Chemical Composition and Morphology: [0129] The morphology of the samples was carried out by means of an SEM from Jeol, JSM 6510. The chemical composition was carried out by means of an EDX analysis using an EDX from Oxford INCA. [0130] To determine the morphology, furthermore, a VisiScope ZTL 350 light microscope with Visicam 3.0 camera was employed.

[0131] 4. Particle Strength: [0132] The particle strength was determined in a method based on DIN EN 13055-1 Annex A, method 1 (2*30 sec shaking with 0.5 mm amplitude).

Inventive Example 1 and Comparative Example 1

[0133] Using the constituents specified in the table below, test bars were then produced by the cold box process (catalyst N,N-dimethylpropylamine) and their flexural strength was determined in a method based on VDG standard P 73, method A (BOSCH Profi 67 mixer used, processing at ambient 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).

[0134] In inventive example 1, closed-pore microspheres of expanded perlite having a particle size d50 of 0.25 mm (d10=0.14 mm, d90=0.40 mm) and a bulk density of 300 g/l are used, with a particle strength of 2.0 N/mm.sup.2.

TABLE-US-00001 Inventive Comparative example 1 example 1 Expanded glass 0.1-0.3 mm 30.00 30.00 Expanded glass 0.25-0.50 mm 30.00 30.00 Closed-pore microspheres of 40.00 expanded perlite Cenolite P55120 (open-pore, 40.00 expanded perlite) Polyisocyanate component (Aktivator 8.00 8.00 6324, Httenes-Albertus) Benzyl ether resin component 8.00 8.00 (Gasharz 7241, Httenes-Albertus) Mass of cylinder [g] 41.5 39 Gas permeability 95 105 Flexural strength 1 h [N/cm.sup.2] 260 120 270 120 270 110 Mean flexural strength 1 h [N/cm.sup.2] 267 117 Flexural strength 24 h [N/cm.sup.2] 280 140 270 120 270 130 Mean flexural strength 24 h [N/cm.sup.2] 273 130

[0135] The mixture from inventive example 1 is suitable for use in feeders. The mixture from comparative example 1 is not suitable for use in feeders, owing to inadequate strengths.

Inventive Example 2 and Comparative Examples 2 and 3

[0136] Using the constituents indicated in the table below, feeder caps closed at the bottom were produced from each of the compositions by the cold box process (catalyst N,N-dimethylpropylamine), with the feeder caps produced from the different compositions having identical geometries.

[0137] The feeder caps produced are molded centrally into a loose quartz sand bed and provided in each case centrally with a coated Pt/Rh.Math.Pt thermocouple. The feeder caps were subsequently filled with an aluminum melt (Al 226), the bath temperature of the aluminum melt being 800 C. After the aluminum melt has been poured into the feeder caps, the temperature profile is recorded.

[0138] In inventive example 2, closed-pore microspheres of expanded perlite having a particle size d50 of 0.25 mm (d10=0.14 mm, d90=0.40 mm) and a bulk density of 300 g/l are used, with a particle strength of 2.0 N/mm.sup.2.

TABLE-US-00002 Inventive Comparative Comparative example 2 example 2 example 3 Spheres 100.0 18.0 Expanded glass 0.25-0.5 mm 30.0 30.0 Expanded glass 0.1-0.3 mm 30.0 52.0 Closed-pore microspheres of 40.0 expanded perlite Total dry mixture [% by mass] 100.0 100.0 100.0 Polyisocyanate component 8.0 8.0 7.5 (Aktivator 6324, Httenes- Albertus) Benzyl ether resin component 8.0 8.0 7.5 (Gasharz 7241, Httenes- Albertus)

[0139] FIG. 1 shows a temperature/time plot of example 2 (identified as inventive 3) and of comparative examples 2 (identified as standard formula 1) and 3 (identified as standard formula 2). Each casting took place at identical temperatures. It can be seen that the inventive composition from inventive example 2 exhibits a better insulating effect than the compositions from comparative examples 2 and 3.

Example 3: Determination of the Enslin Water Absorption of Perlites

[0140] The water absorption of open-pore, expanded perlite (Cenolite P55120) and of closed-pore microspheres of expanded perlite with a closed surface was determined by the method of Enslin. The determination was made under 0.5 g of the respective bulk product, using an Enslin apparatus. The results are summarized in the table below.

TABLE-US-00003 Water absorption Water absorption [ml/g] for closed-pore [ml/g] for open-pore, Time microspheres of expanded perlite elapsed [s] expanded perlite (Cenolite P55120) 30 1.1 1.6 40 1.1 2.0 60 1.1 2.1 120 1.1 2.1 180 1.1 2.1 300 1.1 2.1

[0141] The measurement results show clearly that the water absorption of closed-pore microspheres of expanded perlite is only around half as great as the water absorption of the open-pore, expanded perlite. As expected, substantially more water is able to penetrate the open pores of the open-pore, expanded perlite than in the case of closed-pore microspheres of expanded perlite.