WO2011077068A1

WO2011077068A1 - Method and apparatus for forming glass flakes and fibres

Info

Publication number: WO2011077068A1
Application number: PCT/GB2010/002130
Authority: WO
Inventors: Charles Watkinson
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-12-23
Filing date: 2010-11-18
Publication date: 2011-06-30
Anticipated expiration: 2012-06-23
Also published as: GB0922514D0

Abstract

Apparatus for forming fibres or flakes of material includes means (1) for producing a heated stream of molten material and means (3, 5) for feeding the stream in a substantially vertically downward direction. The apparatus further includes means (7) for receiving the downwardly directed stream and forming fibres or flakes therefrom. Means (11, 13, 15, 17) are provided to effect a change in the temperature of the stream and heat transferring means (25) are mounted at least partially in the stream during operation of the apparatus. The heat transferring means are positioned so as to receive RF radiation or electric current whereby energy is transferred to the molten material stream.

Description

METHOD AND APPARATUS FOR FORMING GLASS FLAKES AND FIBRES Field of the Invention

The invention relates to methods and apparatus for forming flakes or fibres of glass or of other similar materials, including ceramic material.

The present invention is applicable to any material which melts when heated and is capable of being formed into flakes and fibres. Such entities are increasingly being used for the reinforcement of plastics or other composite materials.

Background to the Invention

In our European patent specification No 0 289 240 there is disclosed apparatus for forming flakes of material from a heated stream of molten material. The apparatus comprises means for feeding the stream in a downwards direction into a rotating cup, the cup being arranged with its open mouth facing upwardly such that molten material within the cup is caused to flow over the upper edges of the cup and flow outwards in a radial direction due to centrifugal force. The apparatus also includes a pair of spaced apart substantially parallel plates arranged about the cup such that the material leaving the cup by centrifugal force passes through a gap defined between the plates. The plates are mounted within a vacuum chamber arranged such that a vacuum is applied to the space between the plates to draw air from outside the chamber between the plates in a radial direction to prevent the molten material from touching the sides of the plates and to cool material until it reaches a solid state pulling the material in a radial direction thereby keeping the material in the form of a flat film and breaking it into small platelets.

In the production of glass or ceramic fibre or flake the thickness is determined in part by the temperature and volume of the flow stream entering the spinning device producing the product. As the flow stream is necessarily open to atmosphere between an outlet from which the stream emerges and the spinning device, it is subject to heat loss and variation in temperature. The loss of heat is detrimental to the production of thin fibres or flake, particularly in the sub-micron range and changes in temperature as small as one degree cause variation in thickness. The viscosity of the glass mass within a source tank or reservoir is determined by temperature variations which in turn cause changes in mass flow through the outlet from which the stream emerges. Additional mass flow changes are caused by head variations within the tank.

Furthermore, in order to compensate for the heat loss outside the source tank, the temperature within the tank may need to be higher than the stream temperature by some hundreds of degrees. This is not only energy wasteful but may cause severe erosion and corrosion of the refractory lining within the tank.

WO2004/056716 describes apparatus, and a corresponding method, for forming fibres or flakes of material comprising means for producing a heated stream of molton material, means for feeding the stream in a substantially vertically downward direction, means for receiving the downwardly directed stream and for forming fibres or flakes therefrom, and means for effecting a change in the temperature of the stream subsequent to the production thereof whereby fibres or flakes of a desired thickness are obtained.

The apparatus may include means for applying a high frequency (RF) current or an electric current to the vertically downwardly travelling stream.

In order to advance the technology beyond that described in WO2004/056716, more efficient methods of heating the glass stream, once it has left the glass tank, are required.

Statements of the Invention

According to the present invention there is provided apparatus for forming fibres or flakes of material comprising means for producing a heated stream of molten material, means for feeding the stream in a substantially vertically downward direction, means for receiving the downwardly directed stream and for forming fibres or flakes therefrom, and means for effecting a change in the temperature of the stream subsequent to the production thereof, whereby fibres or flakes of a desired thickness are obtained, wherein heat transferring means are mounted at least partially in the molton material stream, during operation of the apparatus, said heat transferring means being positioned so as to receive RF radiation or electric current whereby energy is transferred from the RF radiation or the electric current to the molton material stream. Preferably, the heat transferring means is located entirely within the glass stream.

Preferably, the heat transferring means is an elongate element.

Preferably, the heat transferring means is a solid metal or alloy.

Preferably, the heat transferring means is made of platinum.

Preferably, the heat transferring means is positioned in the region where the glass stream is in downward free fall.

Preferably, the heat transferring means is located at least partially within the coil for the RF radiation.

Preferably, electric current is applied to the molton material stream and the heat transfer means includes two bars mounted in longitudinally aligned and spaced relationship.

Accordingly, the present invention improves the induction heating of the molton material stream. A receptor rod, made of platinum or other suitable high temperature material is located in the stream. This improves the permeability of the stream resulting in a better coupling of the coil.

As the molton stream increases temperature through heating of the receptor rod, the molton material became more receptive to RF. This method improves RF induction efficiency into the molton stream and is less susceptible to the change in stream formulation and variations in stream thickness. Within the introduction of the receptor rod it is possible to monitor and control the molton stream temperature more accurately using IR. Without the rod, the monitoring equipment gives inaccurate readings due to the thinness of the stream. Furthermore, the present invention provides a method for forming fibres or flakes of material, the method comprising producing a heated stream of molton material, feeding the stream in a substantially vertically downward direction, receiving the downwardly directed stream and forming fibres or flakes therefrom, and effecting a change in the temperature of the stream subsequent to the production thereof, wherein fibres or flakes of a desired thickness are obtained, and wherein the heat transferring means are mounted at least partially in the molton material stream, and applying RF radiation or electric current to the heat transferring means to transfer energy from the RF radiation or the electric current to the molton material stream B rief Description of the Drawin gs

The accompanying drawings are as follows:

Figure 1 is a schematic section through apparatus in accordance with the present invention, and

Figure 2 shows another embodiment of apparatus in accordance with the present invention.

Detailed Description of the Invention

Referring to the accompanying drawing, Figure 1 shows apparatus including a tank 1 for holding molten glass. Extending from tank 1 is an outlet conduit or bushing 3 which terminates in an outlet orifice 5. A glass stream is formed in conduit 3 from material fed from tank 1 and the internal diameter of orifice 5 defines the diameter of the stream of liquid glass at the point where it leaves conduit 3 and descends vertically from the orifice As indicated in the drawing, the stream extending from orifice 5 descends in a free fall vertically downwards towards a spinning device 7 which may be substantially as described in EP 0 289 240. The apparatus includes further components for producing the flake or fibres from the liquid stream 9, these components not being shown in Figure 1. However they may be substantially as shown and described in EP 0 289 240.

The apparatus includes a coil 11 which surrounds the stream 9 around about half its length in a central section of the vertically downward path. This coil is suitable for passing a high frequency (RF) current therethrough. The coil is connected by connections 13 and 15 to an RF heater 17 which generates the desired current level. The passage of the high frequency current through coil 11 causes the excitement of the molecules in the glass stream by microwave transmission. An infrared receptor (not shown) is located at the base of the glass stream and is connected to suitable control circuitry for regulating the coil output and thereby the amount of heat transmitted into the glass stream. A large amount of heat can be instantaneously created within the flow stream thereby allowing close temperature regulation.

Also shown in Figure 1 are components for another method of directly heating the glass stream. This method involves the passing of an electric current through the stream between upper and lower connections 19 and 21.

Upper connection 19 is in the form of an electrode connected to bushing 5. Such a connection can be achieved by using a bushing made of an electrically conductive material so that the bushing is itself the electrode or, alternatively, positioning an electrode either immediately in front of the bushing within the tank or immediately after it and in contact with the flow stream.

Lower connection 21 is made by means of a slip ring attached to the shaft of the spinning device and includes static brushes 22 through which the electrical connection is made. Control of the current is by way of a transformer (not shown) with suitable voltage and current output. Current variation may be achieved by, for instance, thyristor control and an infrared receptor as described above.

In addition or as an alternative to the above described means for heating the glass stream, the apparatus may be provided with means for controlling the mass flow. These means are provided at the conduit 3 and involve cooling the glass stream emerging from the tank 1. The conduit is provided with an oversized aperture and is externally clad with a cooling jacket 23 through which may be fed cooling liquid. The jacket may be a simple coil wrapped round the bushing and fed with water or it may be an external annular ring through which compressed air is passed. As the molten glass passes through the bushing, the bushing is cooled and a layer of molten material is solidified within the bushing orifice. This has the effect of reducing the aperture size and thereby reducing the mass flow. Although there is a loss of heat from the flow stream, this is relatively small because the melt steam material is a poor thermal conductor when solidified.

Mounted within the glass stream 9 is a receptor rod 25 which is held in place by a receptor mount 27. Mount 27 enables the rod to be positioned accurately in the centre of the glass stream. The induction coil is designed to allow the receptor rod support to pass through without touching.

Referring to Figure 2 of the accompanying drawings, another way of heating the stream is to remove the induction coil, receptor bar and current flow from the spinning device to an outlet and introduce two stream electrode bars 27 and 29. These electrode bars are made from platinum but other suitable metals may be used.

The electrode bars are mounted on an X-Y-Z holder 31 which enables the electrode bars to be moved accurately in any plain independently. The stream electrode bars can be moved closer or further apart depending on glass formulation and thickness of the stream. Both electrode bars 27,29 can be moved closer to the tank outlet 5 or the spinner device The two electrode bars are electrically isolated from each other and from the X-Y-Z adjuster, the only electrical path being through the glass stream.

The 3 phase source of power can be AC or DC and fully variable to allow for complete control over the stream temperature. A 3 phase supply is connected between zones 1, 2 and 3. These zones are fully independently controlled from each other. Zone 1 is connected to connections 1 and 6 and is used to increase the temperature of glass to the outlet. Zone 2 is connected to connections 2 and 4 and is used to increase the temperature of the glass between the outlet and the first electrode bar. Zone 3 is connected to connections 4 and 5 and sets the main temperature of the glass stream.

The above described apparatus allows accurate control of current. This is necessary due to the change in resistivity of the glass.

Claims

1. Apparatus for forming fibres or flakes of material comprising means for producing a heated stream of molten material, means for feeding the stream in a substantially vertically downward direction, means for receiving the downwardly directed stream and for forming fibres or flakes therefrom, and means for effecting a change in the temperature of the stream subsequent to the production thereof, whereby fibres or flakes of a desired thickness are obtained, wherein heat transferring means are mounted at least partially in the molton material stream, during operation of the apparatus, said heat transferring means being positioned so as to receive RF radiation or electric current whereby energy is transferred from the RF radiation or the electric current to the molton material stream.

2. Apparatus according to Claim 1, wherein the heat transferring means is located entirely within the glass stream.

3. Apparatus according to Claim 1 or Claim 2, wherein the heat transferring means is an elongate element.

4. Apparatus according to any of the preceding Claims, wherein the heat transferring means is a solid metal or alloy.

5. Apparatus according to any of the preceding Claims, wherein the heat transferring means is made of platinum.

6. Apparatus according to any of the preceding Claims, wherein the heat transferring means is positioned in the region where the glass stream is in downward free fall.

7. Apparatus according to any of the preceding Claims, wherein the heat transferring means is located at least partially within the coil for the RF radiation.

8. Apparatus according to any of Claims 1 to 6, wherein an electric current is applied to the molton material stream and the heat transfer means includes two bars mounted in longitudinally aligned and spaced relationship.

9. Apparatus according to Claim 1 and substantially as herein described.

10. Apparatus according to Claim for forming fibres or flakes of material, substantially as described herein with reference to either Figure 1 or Figure 2 of the accompanying drawings.

11. A method for forming fibres or flakes of material, the method comprising producing a heated stream of molton material, feeding the stream in a substantially vertically downward direction, receiving the downwardly directed stream and forming fibres or flakes therefrom, and effecting a change in the temperature of the stream subsequent to the production thereof, wherein fibres or flakes of a desired thickness are obtained, and wherein the heat transferring means are mounted at least partially in the molton material stream, and applying RF radiation or electric current to the heat transferring means to transfer energy from the RF radiation or the electric current to the molton material stream.

12. A method according to Claim 1 1 and substantially as herein described.

13. A method for forming fibres or flakes of material substantially as described herein with reference to either Figure 1 or Figure 2 of the accompanying drawings.