Method and Device for Producing Hollow Microglass Beads

Abstract

The invention relates to a method and a device for producing hollow microglass beads (3.4) from molten glass (3), wherein the hollow microglass beads (3.4) are manufactured in a diameter range from 0.01 mm to 0.1 mm in a continuously operating process while avoiding glass filament formation. Molten glass strands (3.1) exiting a melting device (1) are atomized by means of hot gas (14) to form glass particles (3.2). Subsequently, during passage through a rounding/expansion duct (6), the glass particles (3.2) are rounded to form solid microglass beads (3.3) and expanded to form hollow microglass beads (3.4). The hollow microglass beads (3.4) can advantageously be used as a filler for lightweight building materials or as a constituent part of coatings, paints and plasters/renders.

Claims

1. Method for producing hollow microglass beads, wherein a glass melt, which contains at least one substance in dissolved form which is gaseous in the range from 1100 C. to 1500 C., is produced in a melting device and the glass melt in the form of one or more molten glass strands exits from the melting device through a discharge opening, characterised in that (a) the glass strands are produced with a diameter from 0.5 mm to 0.8 mm, (b) by control of the temperature of the glass melt, the viscosity thereof as it exits as a glass strand is set to 0.5 dPa s to 1.5 dPa s; (c) by means of a hot gas flowing out of a high-pressure hot gas nozzle, the molten glass strand or strands is or are atomised to form glass particles after the exit from the melting device, (d) the glass particles are blown by the flowing hot gas directly into an immediately adjoining, heated, rounding/expansion duct oriented in the flow direction, wherein during the passage through the rounding/expansion duct the glass particles are transformed into solid microglass beads as a result of the surface tension during the heating, and the solid microglass beads then expand to form hollow microglass beads as a result of the degassing of the dissolved gaseous substances, and (e) after the exit from the rounding/expansion duct the hollow microglass beads are cooled by means of cooling air and collected in solid form.

2. Method for producing hollow microglass beads according to claim 1, characterised in that a plurality of glass strands which are spaced apart from one another are produced, and a nozzle plate comprising a plurality of nozzles formed as conical through openings is used, in each case with a circular cross-section and with a diameter in the range from 1 mm to 3 mm, on or inside the discharge opening.

3. Method for producing hollow microglass beads according to claim 1, characterised in that the gas velocity of the hot gas as it impinges on the glass strand or strands is 300 m s.sup.1 to 1500 m s.sup.1.

4. Method for producing hollow microglass beads according to claim 1, characterised in that the temperature of the hot gas is 1500 C. to 2000 C.

5. Method for producing hollow microglass beads according to claim 1, characterised in that the glass melt used contains sulfur trioxide, oxygen, nitrogen, sulfur dioxide, carbon dioxide, arsenic oxide, antimony oxide or mixtures thereon in dissolved form.

6. Method for producing hollow microglass beads according to claim 5, characterised in that the glass melt used contains sulfur trioxide in a proportion by mass in the range from 0.6% to 0.8%.

7. Method for producing hollow microglass beads according to claim 5, characterised in that the glass melt used contains arsenic oxide or antimony oxide in a proportion by mass in the range from 0.1% to 0.5%.

8. Method for producing hollow microglass beads according to claim 1, characterised in that a transport gas is blown in axially by means of a transport gas nozzle into the rounding/expansion duct, in order to keep the glass particles, the solid microglass beads as well as the hollow microglass beads suspended and to assist the transport thereof through the rounding/expansion duct.

9. Device for carrying out the method according to claim 2, characterised in that the discharge opening is arranged in the bottom region of the melting device, wherein the nozzle plate is mounted on or inside the discharge opening in such a way that the glass melt exclusively exit from the conically formed nozzles, the nozzle plate has nozzles each having a circular cross-section and having a diameter in the range from 1 mm to 1.6 mm, wherein the nozzle plate can be heated electrically; the high-pressure hot gas nozzle is positioned immediately below and alongside the discharge opening, wherein the high-pressure gas nozzle is oriented so that when the method is being carried out the hot gas flowing out of the high-pressure hot gas nozzle impinges on the glass strands exiting from the nozzles, the rounding/expansion duct is arranged in the flow direction of the hot gas which, when the method is being carried out, flows out of the high-pressure hot gas nozzle after the discharge opening, a cooling air funnel for delivery of the cooling air is positioned in the flow direction of the hot gas after the rounding/expansion duct, wherein the funnel opening is facing the rounding/expansion duct, and the funnel neck of the cooling air funnel forms a discharge duct for collecting the cooled hollow microglass beads.

10. Device according to claim 9, characterised in that the end region of the discharge duct arranged in the flow direction terminates with a rotary feeder or a cyclone precipitator.

11. Device according to claim 9, characterised in that the nozzles of the nozzle plate are arranged in a line.

12. Device according to claim 11, characterised in that the nozzle plate has two symmetrically curved reinforcing beads ) which extend along the nozzle in mirror image to one another.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The invention is explained in greater detail below on the basis of embodiments and with reference to the schematic drawings. In the drawings:

[0044] FIG. 1 shows the device for carrying out the method for producing hollow microglass beads, and

[0045] FIG. 2 shows the nozzle plate with five nozzles in top view and in cross-section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] According to a first exemplary embodiment according to FIG. 1, soda-lime glass is melted with a proportion by mass of 0.8% of sulfur trioxide in the melting device 1, an electrically heated platinum melting vessel, at 1450 C. By means of the discharge opening 1.2 in the bottom of the melting device 1, molten glass 3 enters through the electrically heated nozzle plate 2 made of platinum with 20 linearly arranged nozzles 2.1 with a respective diameter of 1.5 mm out of the melting device 1. The viscosity of the glass melt 3 is 0.5 dPa s. The exiting molten glass strands 3.1 with a diameter of 0.7 mm are atomised immediately after the exit from the nozzle 2.1 by the hot gas 14 from the high-pressure hot gas nozzle 4 of an oxygen/natural gas high-pressure burner to form glass particles 3.2. In this case the hot gas flows at right angles against the glass strands 3.1 with a gas velocity of 600 m/s. Then the glass particles 3.2 enter the immediately adjoining rounding/expansion duct 6 which is made from refractory material and is longitudinally heated by means of the transport gas 15 from the transport gas nozzle 5 of a transport gas burner.

[0047] The temperature in the rounding/expansion duct 6 is 1500 C. The solid microglass beads 3.2 initially formed from the glass particles 3.2 in the rounding/expansion duct 6 then expand to form hollow microglass beads 3.4 and ultimately enter the discharge duct 9 made from stainless steel. Cooling air 7 is blown into this duct via cooling air funnels 8 for cooling the exhaust gases, and then exits again at the end of the discharge duct 9 as exhaust air 11 through the sieve 10. The sieve 10 prevents the exit of the hollow microglass beads 3.4. These are conveyed out of the discharge duct 9 through the rotary feeder 12. The hollow microglass beads 3.4 have a diameter from 0.02 mm to 0.05 mm.

[0048] In a second exemplary embodiment borosilicate glass with a proportion by mass of 0.5% antimony oxide in einem conventional melter at a melting temperature of 1600 C. The molten glass 3 enters the feeder at a temperature of 1450 C. through an electrically heated discharge opening 1.2 with a sieve insert to keep refractory particles away from the electrically heated nozzle plate 2 with 22 linearly arranged nozzles 2.1 having a diameter in each case of 1.5 mm. The atomisation of the molten glass, the transport through the rounding/expansion duct 6 and the discharge correspond to those in the first exemplary embodiment. The diameter of the hollow microglass beads 3.4 is in the range from 0.02 mm to 0.04 mm.

[0049] The nozzles 2.1 of the nozzle plate 2 according to FIG. 2 exhibit above and below the row of nozzles in each case a symmetrically curved reinforcing bead 2.2. The reinforcing beads 2.2 are formed in the sheet metal components of the nozzle plate 2.

LIST OF REFERENCE NUMERALS

[0050] 1 melting device/crucible [0051] 1.1 insulation [0052] 1.2 discharge opening [0053] 2 nozzle plate [0054] 2.1 nozzle [0055] 2.2 reinforcing bead [0056] 3 glass melt [0057] 3.1 glass strand, molten [0058] 3.2 glass particle [0059] 3.3 solid microglass bead [0060] 3.4 hollow microglass bead [0061] 4 high-pressure hot gas nozzle [0062] 5 transport gas nozzle [0063] 6 rounding/expansion duct [0064] 7 cooling air [0065] 8 cooling air funnel [0066] 9 discharge duct [0067] 10 sieve [0068] 11 exhaust air [0069] 12 rotary feeder [0070] 13 discharge of the hollow microglass beads [0071] 14 hot gas [0072] 15 transport gas