GB2081247A - Vitreous Melt for Spun Fibres - Google Patents

Abstract

A melt of igneous aluminosilicate rock, such as an olivine basalt, is made suitable for the production of fibre substantially free from non-fibrous (granular) material by incorporating in it an alkaline-reacting sodium compound, preferably sodium carbonate (Na2CO3), to depress the temperature at which the melt has a viscosity suitable for spinning.

Description

SPECIFICATION Vitreous Melt for Production of Vitreous Fibres This invention relates to vitreous melts suitable for the production of vitreous fibres, such for example as are used for heat insulation.

Vitreous fibres can be made from a melt of cheap raw material, namely, a melt of igneous aluminosilicate rock, usually a basalt. In the method usually adopted, a stream of the melt is converted to fibres by blowing it with high pressure steam or air or by projecting it from the surface of a rapidly rotating wheel. This method leads to the formation of a product contaminated with a high proportion of granular (non-fibrous) material known as 'shot', which often forms as much as 40% by weight of the product.

We have been concerned to obtain from rock melts a product containing practically no shot, and have investigated the possibility of applying to rock melts the kind of procedure common in the preparation of glass fibres, in whicha glass melt is made to flow through small holes in a rotor, and the individual extremely fine streams issuing from the holes are then solidified into fibres. In such a process, which for convenience we refer to as 'spinning', the temperature of the melt has to be carefully controlled; it must not be too low, for otherwise crystallisation of the melt may lead to blocking of the holes in the rotor; and if it is too high, excessive corrosion of the rotor may occur.However, it is characteristic of igneous alumino-silicate rocks that, at temperatures below 1 250C which are most practicable for the operation of conventional rotors, either they do not form a melt or, if they do, the melt has too high a viscosity.

We have now found that a melt of igneous alumino-silicate rock can be made suitable for the production of spun fibres usable as heat insulation by incorporating in it an alkaline-reacting sodium compound. This has the effect of depressing the temperature at which the melt is of a viscosity suitable for spinning. Of course, the proportion of sodium compound that is included is kept below that at which crystallisation of the melt occurs to any substantial extent. Ordinarily, the proportion of sodium compound employed will form from 5 to 25% (calculated as equivalent Na2O) by weight of the whole (or "modified melt").

The sodium compound preferably employed is sodium carbonate (Na2CO3; 106 g of which are equivalent to 62 g Na2O) though the more expensive bicarbonate (168 g equivalent to 62 g Na2O) or the less convenient hydroxide (NaOH, 80 g equivalent to 62 g Na2O) can be used if desired.

The preferred proportion of alkaline-reacting sodium compound used is 10 to 20% (calculated as equivalent Na2O) by weight of the whole.

In general, it is desirable to aim at formation of a modified melt which at temperatures below 1 2500C will have a viscosity of 400 poise, so as to enable use of spinners constructed from such available alloys as nickel-chrome superaloys.

The invention which is specially applicable to the preparation of spinnable melts from the basalts, particularly the olivine basalts and additionally the quartz-dolerite basalts, is further illustrated by the following example.

Example This example illustrates the preparation and use of modified melts based on an olivine basalt of composition: SiO2, 50.39/0; TiO2, 2.6%; Awl 0 16.4%, Fe203 +FeO, 11.3%; CaO, 8.5% MgO, 4.9%; K20, 1.8%; Na 0 4.0%; P205, 0.5%; Mn304, 0.2%. The raw basalt formed a melt which at 1 2500C had a viscosity too high for it to be spinnable at that temperature.

Modified melts, as set out below, were made, based on the above basalt, by melting the broken rock with the stated proportions of anhydrous sodium carbonate, and refining each melt by holding it at 1 4000C for 1 6 hours to allow escape of carbon dioxide and formation of a homogeneous melt.

Modified Melt 1 Made with the use of an amount of Na2CO3 equivalent to 15% Na2O by weight of whole. Melt 1 was spinnable at about 1 2000C (viscosity 400 poise) to form 5,um diameter fibres which were entirely acceptable as heat insulation material.

Modified Melt 2 A second modified melt, made with use of an amount of Na2CO3 equivalent to 20% Na2O by weight, was spinnable (viscosity of 400 poise) at about 1 1300C.

Claims

1. A melt of igneous aluminosilicate rock suitable for the production of spun vitreous fibres, said melt incorporating an added alkaline-reacting sodium compound.

2. A melt according to Claim 1, in which said sodium compound forms from 5 to 25% by weight of the whole.

3. A melt according to Claim 2, in which said sodium compound forms 10-20% by weight of the whole.

4. A melt according to Claim 1, 2 or 3, in which said sodium compound is sodium carbonate.

5. A melt according to any one of Ciaims 1 to 4, in which the rock is basalt.

6. A melt according to Claim 5, in which the rock is an olivine basalt.

7. A method of making vitreous fibre, which comprises spinning a melt as set forth in any preceding claim.

8. Spum vitreous fibres when obtained by the method of Claim 7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Vitreous Melt for Production of Vitreous Fibres This invention relates to vitreous melts suitable for the production of vitreous fibres, such for example as are used for heat insulation. Vitreous fibres can be made from a melt of cheap raw material, namely, a melt of igneous aluminosilicate rock, usually a basalt. In the method usually adopted, a stream of the melt is converted to fibres by blowing it with high pressure steam or air or by projecting it from the surface of a rapidly rotating wheel. This method leads to the formation of a product contaminated with a high proportion of granular (non-fibrous) material known as 'shot', which often forms as much as 40% by weight of the product. We have been concerned to obtain from rock melts a product containing practically no shot, and have investigated the possibility of applying to rock melts the kind of procedure common in the preparation of glass fibres, in whicha glass melt is made to flow through small holes in a rotor, and the individual extremely fine streams issuing from the holes are then solidified into fibres. In such a process, which for convenience we refer to as 'spinning', the temperature of the melt has to be carefully controlled; it must not be too low, for otherwise crystallisation of the melt may lead to blocking of the holes in the rotor; and if it is too high, excessive corrosion of the rotor may occur.However, it is characteristic of igneous alumino-silicate rocks that, at temperatures below 1 250C which are most practicable for the operation of conventional rotors, either they do not form a melt or, if they do, the melt has too high a viscosity. We have now found that a melt of igneous alumino-silicate rock can be made suitable for the production of spun fibres usable as heat insulation by incorporating in it an alkaline-reacting sodium compound. This has the effect of depressing the temperature at which the melt is of a viscosity suitable for spinning. Of course, the proportion of sodium compound that is included is kept below that at which crystallisation of the melt occurs to any substantial extent. Ordinarily, the proportion of sodium compound employed will form from 5 to 25% (calculated as equivalent Na2O) by weight of the whole (or "modified melt"). The sodium compound preferably employed is sodium carbonate (Na2CO3; 106 g of which are equivalent to 62 g Na2O) though the more expensive bicarbonate (168 g equivalent to 62 g Na2O) or the less convenient hydroxide (NaOH, 80 g equivalent to 62 g Na2O) can be used if desired. The preferred proportion of alkaline-reacting sodium compound used is 10 to 20% (calculated as equivalent Na2O) by weight of the whole. In general, it is desirable to aim at formation of a modified melt which at temperatures below 1 2500C will have a viscosity of 400 poise, so as to enable use of spinners constructed from such available alloys as nickel-chrome superaloys. The invention which is specially applicable to the preparation of spinnable melts from the basalts, particularly the olivine basalts and additionally the quartz-dolerite basalts, is further illustrated by the following example. Example This example illustrates the preparation and use of modified melts based on an olivine basalt of composition: SiO2, 50.39/0; TiO2, 2.6%; Awl 0 16.4%, Fe203 +FeO, 11.3%; CaO, 8.5% MgO, 4.9%; K20, 1.8%; Na 0 4.0%; P205, 0.5%; Mn304, 0.2%. The raw basalt formed a melt which at 1 2500C had a viscosity too high for it to be spinnable at that temperature. Modified melts, as set out below, were made, based on the above basalt, by melting the broken rock with the stated proportions of anhydrous sodium carbonate, and refining each melt by holding it at 1 4000C for 1 6 hours to allow escape of carbon dioxide and formation of a homogeneous melt. Modified Melt 1 Made with the use of an amount of Na2CO3 equivalent to 15% Na2O by weight of whole. Melt 1 was spinnable at about 1 2000C (viscosity 400 poise) to form 5,um diameter fibres which were entirely acceptable as heat insulation material. Modified Melt 2 A second modified melt, made with use of an amount of Na2CO3 equivalent to 20% Na2O by weight, was spinnable (viscosity of 400 poise) at about 1 1300C. Claims

1. A melt of igneous aluminosilicate rock suitable for the production of spun vitreous fibres, said melt incorporating an added alkaline-reacting sodium compound.

2. A melt according to Claim 1, in which said sodium compound forms from 5 to 25% by weight of the whole.

3. A melt according to Claim 2, in which said sodium compound forms 10-20% by weight of the whole.

4. A melt according to Claim 1, 2 or 3, in which said sodium compound is sodium carbonate.

5. A melt according to any one of Ciaims 1 to 4, in which the rock is basalt.

6. A melt according to Claim 5, in which the rock is an olivine basalt.

7. A method of making vitreous fibre, which comprises spinning a melt as set forth in any preceding claim.

8. Spum vitreous fibres when obtained by the method of Claim 7.