GB1596373A - Manufacture of fibres from an attenuable material by means of gaseous currents - Google Patents

Abstract

The process consists in generating neighbouring gas jets (b, c, d, e, etc.) adjacent to a convex guiding surface (14), in diverting the jets and the streams which they induce by flow and adherence along the guiding surface and in bringing laces of ductile substance (s) into the streams induced by the jets in zones situated between the latter on the convex surface. In a second stage each jet enters a main gas stream (B) forming a zone of interaction and entraining the partially drawn fibre therein; the latter is then subjected to additional drawing in the interaction zone. The process is employed especially for making fibres from glass. <IMAGE>

Description

(54) MANUFACTURE OF FIBERS FROM AN ATTENUABLE MATERIAL BY MEANS OF GASEOUS CURRENTS (71) We, SAINT-GOBAIN INDUSTRIES, a French Company, of 62 Boulevard Victor Hugo, Neuilly-Sur-Seine, France, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process and an apparatus for the manufacture of fibres from an attenuable material and it concerns in particular the attenuation of thermoplastic materials, in particular mineral materials such as glass or similar compositions which are converted into the molten state by heating.The present invention also applies to the fibre formation of certain organic materials such as polystyrene, polypropylene, polycarbonates or polyamides but since the apparatus is more particularly of interest for the attenuation of glass and similar thermoplastic materials, the description will refer to the case of glass by way of example.

Certain techniques using whirling currents for the manufacture of fibres by the attenuation of molten glass are already known.

In particular, the publication of French Patent No. 2,223,318 describes the formation of pairs of counter-rotating tornadoes in a zone of interaction produced by direction of a gas jet known as secondary jet or carrier jet to a main gas current of larger dimensions and causing it to penetrate the said current, a stream of molten glass being delivered into the said zone to be attenuated there. Several jets may be associated with one and the same main current.

Furthermore, in our British Patent Specification No. 1513060, it is provided to carry out attenuation preferably in two stages, the first stage taking place in each secondary jet while the second occurs in the corresponding zones of interaction of the main current. In this application, secondary jets are emitted at a distance from the main current and from the source of supply of attenuable material and these jets are disturbed by a deflector system.

More precisely, the secondary jets, emitted from a series of orifices, are directed to the surface of a deflector which causes their deflection and the flowing of the deflected jets in the direction of the main current. On penetrating the main current, these deflected jets create therein zones of interaction with pairs of tornadoes, where attenuation takes place as indicated above. It is also provided to place the jets in relation to the deflector in such a manner that their impact with the surface of the deflector causes them to spread out sideways, the jets moreover being sufficiently close together so that adjacent jets impinge upon each other close to the free edge of the deflector.This deflection and this impingement of the jets causes the formation of pairs of tornadoes and zones of low pressure, which zones are situated just downstream of the edge of the deflector, and surrounding gas or air is carried into these zones.

The tornadoes form on the edges of each jet and therefore surround each zone of low pressure where the flow is virtually laminar. The streams of molten glass are introduced into these zones of laminar flow, whereby the delivery of streams of glass into the system is enabled to be stabilised. Each stream of glass is then carried along by the flow of each jet and brought to the corresponding zone of interaction formed by penetration of the jet into the main current and is attenuated in this zone.

The present invention, like Specification No. 1513060, provides the formation of zones of interaction by penetration of jets into a main current and the attenuation of streams of glass in these zones but the jets are produced differently and the delivery of streams of molten glass to these jets takes place in different positions.

According to the present invention, a plurality of successive jets which are spaced apart from each other and adjacent to a convex guide surface is produced and these jets and the gas which they induce are caused to deflect by means of a convex guide element, to the surface of which each flow adheres. The cross-section of each jet is larger along the convex surface than in a direction at right angles thereto so that the jets flow over the said surface, following its curvature. This deflection of a jet which is produced by adherence to a curved surface is known as the Coanda effect. The deflection along the convex surface causes a pair of counterrotating tornadoes to develop in the flow of each jet.The sense of rotation of the tornadoes and the distance between consecutive jets are such that at the point of contact with the surface of the guide element, the induced gas is driven into predetermined spaces between the jets. The flow of surrounding air or gas induced between each jet is quasilaminar on the guide surface and the streams of molten glass are introduced into each laminar flow situated between two adjacent jets. This delivery of glass into the zones of laminar flow enables the streams of glass to be more perfectly stabilised. From these zones, each stream of glass is then carried into the flow of one of the jets and is thus subjected to a primary attenuation.According to the preferred embodiment of the invention, however, and in order to obtain finer fibres, it is provided that the main gas current already mentioned be used in combination with the secondary jets and their associated guide element. Each stream of glass driven into the flow of a jet is partially attentuated and then carried into the zone of interaction which is produced with the main current, in order to be attenuated there in a second stage, as will be explained later.

Although the system consists of first directing the streams of glass between the jets in order subsequently to bring them into these jets, it enables the supply of glass to be very effectively stabilised due to the fact that the zones of laminar flow are situated on a fixed mechanical structure, namely the surface of the guide element The following description given with reference to the drawings shows clearly the advantages and various objects of the invention and describes in particular the attenuation in two stages without intermediate fragmentation of the streams of attenuable material.

Figure 1 represents schematically in elevational view the main elements of an apparatus for fibre formation and collection of the fibres according to the invention, certain parts treing shown in section.

Figure 2 is a schematic view in perspective and on a larger scale of the main elements of the fibre forming apparatus, comprising several fibre-forming centres, certain parts being in section and others torn out to show certain characteristics of the system.

Figure 3 is a vertical section on an enlarged scale taken in a plane passing through a jet emission orifice and showing the various elements of a fibre forming centre.

Figure 4 is a vertical section similar to Figure 3 but in the plane passing through a glass supply tip, that is to say a plane between two adjacent jet emission orifices.

Figure 5 represents more particularly certain dimensions which must be taken into consideration to establish the operating conditions for carrying out a preferred embodiment of the invention, for one fibre forming centre.

Figure 6 is a schematic view in elevation taken on the line VI-VI of Figure 5 and Figure 7 is a horizontal section on the line 7-7 of Figure 5 also indicating certain dimensions to be considered.

Referring first to Figure 1, the reference numeral 10 indicates a generator such as a burner having a nozzle 11 emitting a main current B. This main current generator is supplied with air and fuel through the connection 12.

In Figure 2 may be seen jet emission orifices 22a, 22b, 22c, 22d, 22e and 22f emitting the jets from the manifold box 13. These successive orifices are spaced apart from each other and arranged along a convex guide element 14. They are larger in a direction along the leading edge of the guide element than in a direction at right angles thereto. Moreover, they can be divided by planes of symmetry at right angles to the guide element and advantageously parallel to each other.

According to a preferred embodiment of this invention, the jet emission orifices are virtually rectangular; the ratio of the two dimensions of the orifices to each other will be indicated later with reference to Figures 5 and 6.

Figures 1 to 4 show that the jets b, c, d and e are initially emitted adjacent to the leading edge of the curved guide element 14 and in a direction virtually tangential to its surface, the core of each jet exactly following the curved surface, as indicated by the core bc of the jet b in Figure 3. Due to the position and form of the emission orifice such that the larger side of each jet is in contact with the curved guide surface, the jets are subjected to a Coanda effect, that is to say they are adhere to the convex surface of element 14 as they flow and are hence subjected to a deflection along a path which substantially follows the curvature of the said surface.The flow of each jet, for example that of the jet emitted by orifice 22b, at the same time causes an induction of surrounding air or gas, the combined actions of deflection and induction of air giving rise to a pair of tornadoes indicated schematically by 23b-23b in the case of jet b in Figure 2, in the region where this jet is shown in its exploded view. The currents of induced air are represented by arrows in Figures 2, 3 and 4.

As can be seen in Figure 2, the sense of rotation of the tornadoes 23b is directed downwards at the lateral edges, in particular of jet b and of each jet in general. Due to the fact that the jet emission orifices are spaced apart from each other in the lateral direction, the surrounding gas or air is induced between two adjacent jets and flows over the surface of the guide element 14 in a quasilaminar fashion and in the same general direction as the flow of the jets. These regions of laminar flow are represented in Figure 2 by dotted lines on the surface of the guide element and they are characterised by a relatively low pressure and a certain stability or more exactly an absence of turbulence. The tips 16 which supply the molten glass are placed between the jets, in positions such that the streams of glass are introduced into the zones of laminar flow between the jets.The glass is supplied from a source indicated schematically at 15, comprising a bushing 17 which has a series of delivery tips spaced apart from each other. The molten glass flows through the feed tips 16 ending in orifices 25 which advantageously enable bulbs or tapering cones of glass T to be obtained, which are transformed into streams of glass S.

Figure 2 shows a series of such cones Tb, Tc, Td and Te, each situated in a plane between two adjacent jets, and it will be noted that the cone Tb gives rise to a stream of glass which subsequently enters the jet b while the cones Tc and Td give rise to streams of glass entering the respective flows of the jets c and d. In order to obtain this distribution of streams of glass among the respective jets, it is preferable to stagger the glass delivery tips 16 and consequently the cones T towards one of the adjacent jets while leaving them in planes situated between these jets, as mentioned above. This asymmetric positioning of the feed tips will be explained in more detail later with reference to Figure 6. This asymmetry is highly desirable for the purpose of ensuring that each stream of glass will enter a given jet.

Figure 3 is a schematic view through the plane of symmetry of the emission orifice 22b and of the corresponding jet b. The feed tip 16, the cone of glass Tb and the stream S which enters the jet b are therefore seen in elevational view in this case. The section of Figure 4, on the other hand, is taken through the plane of the feed tip 16 forming the cone of glass Tb, and the aforesaid parts are therefore shown in section.

The lower part S' of the stream of glass is represented in dotted lines in Figure 4 to indicate that it is in the plane of jet b and that this jet therefore carries the stream into the zone of interaction with the main current B.

The representation of the flow of each jet in Figure 2 should be interpreted as follows: In the region adjacent to the downstream edge of the guide element 14, the tornadoes are particularly well formed and attain their maximum power, as indicated at 23b. Their intensity subsequently diminishes progressively as the jets move downwards, this reduction in intensity being indicated by the vaguely defined lines 23c which appear where the jet is shown in exploded view, about midway between the downstream edge of the guide element 14 and the region where the jet penetrates the main current.

On approaching the main current, although the intensity of the whirling movements diminishes in each jet and the tornadoes intermingle with other parts of the flow and merge, each jet still possesses sufficient kinetic energy on the whole to penetrate the main current and form the pairs of tornadoes 24b, 24c, 24d. In other words, the merged flow still has a higher kinetic energy per unit volume than the main current. The mode of formation of these tornadoes in the zone of interaction has already been explained in detail in the Patent Specification and Publication mentioned above and it therefore suffices to recall here that apart from the condition relating to the respective kinetic energies, a secondary jet which is smaller in section in a direction transverse to the main current than the said main current is used for forming the zone of interaction.The secondary jet is preferably smaller in cross-section than the main current.

One of the characteristics of the system of emission of jets described above relates to the dimensions of the jets and of the corresponding orifices. It is advised to use emission orifices which are larger in the direction of the guide element than at rihtangles thereto and preferably rectangular. This shape favours the adherence of the jets along the guide surface and the development of the desired pairs of tornadoes in each jet. It should be noted, however, that square orifices could also be used, although this departs from the optimum operating conditions.

It should also be noted that according to the present invention, the tornadoes form without the need for adjacent jets to impinge upon each other and without the need for the presence of mechanical structures placed along the lateral surfaces of each jet in order to channel or confine them. By virtue of this characteristic, it becomes possible to choose any distance between the jet emission orifices, provided the distance is sufficient to leave spaces on the surface of the deflector 14 and between successive jets where the surrounding induced gas creates zones of laminar flow into which the streams of glass will be delivered.

The mode of embodiment of the invention described above, which is characterised by the formation of zones of laminar flow on the surface of an element forming an integral part of the apparatus, namely the convexly curved guide element 14, enables very high stability to be obtained not only in these zones but also in adjacent parts of the jets, which helps to stabilise the introduction of streams of glass into the system.

The kinetic energies of the jet and of the main current are influenced by various factors, in particular the velocities and temperatures of the jet and current.

Since the density of gas varies with its temperature, these temperatures are a determining parameter. In certain Patent publications, such as publication No.

2,223,318 mentioned above, the jet and the main current are both at temperatures very much higher than room temperature, for example, at temperatures of the order of 800"C and 15800C, respectively, although in numerous cases it is preferred to use a jet at a much lower temperature, for example close to room temperature.

For supplying gas for the jet it then becomes possible to use any source of air instead of a burner or some other heating device. Moreover, the velocity of the jet may be reduced until it is below that of the main current and the jet may then still have sufficient kinetic energy to enable it to penetrate the main current and form the zone of interaction cdntaining the tornadoes used for attenuating the stream of glass in the main current.

It will also be recalled that the jets associated with the curved guide element and the particular position described above for supplying the glass may be used on their own to effect attenuation but it is preferred to add the main current and combine it with the jets to subject each stream of glass to two stages of attenuation, one in the flow of each jet and the second in the zone of interaction of a jet with the main current.

Reference will now be made to Figures 5, 6 and 7 to explain various parameters. Figure 5 represents schematically the main elements of the fibre forming system according to the invention, namely the device for generating the main current, the jet emitter, the convex guide element deflecting the flow and forming the tornadoes in the jet, and the source of supply of attenuable material. In this figure and in Figures 6 and 7 are given symbols identifying various parameters such as dimensions and angles to which references are made in the Tables below which show both the suitable ranges of variation of the dimensions and angles and their preferred values.

TABLE I Bushing and Delivery Tip for Attenuable Material Preferred value Symbol (mm) Range dT 2 1-5 IT 1 1-5 lR 5 (#10 2 2 1-5 DR 5 1-10 TABLE II Jet Emitter and Convexly Curved Guide Element Preferred value Symbol (mm, degrees) Range dj 2 0.5 D 3 Yjj 2 1-10 YJF 2 DJ~DJ+YJJ 222 RD 2.5 dj aD 45 30--90 aJB 45 2W90 As shown in Figure 6, the distance between the glass supply orifices is substantially the same as that between successive planes of symmetry of the jet emission orifices. Furthermore, each glass supply tip is so arranged that a stream of glass S is delivered between two adjacentjets into the zone of laminar flow covering the curved guide element 14 but preferably in a position which is offset from the midline. That tip which is placed closer to one jet than to the adjacent jet delivers a stream of glass which consequently will always enter the flow of the closer jet and in a very stable manner.

TABLE III Main Current Preferred value Symbol (mm) Range dB 10 5-20 TABLE IV Relative Position of the Various Elements Preferred value Symbol (mm) Range ZJF 5 1-15 ZJB 20 12-30 XBF -5 0--20 XJF 5 0--10 The number of fibre forming centres may amount to 150 but in a normal fibre forming installation for glass or a similar thermoplastic material, a suitable bushing would have about 70 supply tips.

The expression "supply orifice" for attenuable material used in the description should be interpreted in a very general sense. It may denote either a single orifice or a series of orifices or a supply slot associated with a row of jets flowing over the curved guide element. In the case where supply orifices are replaced by one slot, this is placed transversely to the main current and preferably downstream of a row of jets associated with the guide element, the attenuable material delivered from the slot being then subdivided into a series of cones and streams under the influence of the jets and of the currents induced by the jets.

It should also be noted that the operating conditions of the system according to the present invention will vary according to various factors, for example the characteristics of the material to be converted into fibres.

As indicated earlier, the invention is applicable to the attenuation of a wide range of attenuable materials. The temperature of the bushing or of the source of supply will, of course, vary according to the particular material to be converted into fibres, and in the case of the attenuation of glass or other inorganic thermoplastic materials, it will generally vary within a range of 1400 to 1800"C. For a conventional glass composition, the temperature of the bushing is about 1480"C.

The unit pull rate may vary from 20 to 150 kg per aperture per 24 hours, 50 to 80 kg per aperture per 24 hours being typical values.

Certain values relating to the jet and the main current are also important, as indicated in the Tables below, in which the following symbols have been used: p=pressure T=temperature V=velocity p=mass per unit volume TABLE V Emission of Jet Symbol Preferred value Range Pj (bars) 2.5 1-50 Tj(0C) 20 upto 1860 Vj (m/sec) 300 200-900 pjVj2 (bars) 2.1 0.8A0 TABLE VI Main Current Symbol Preferred value Range PB (mbars) 95 30--250 TB(0C) 1450 1300--1800 v, (m/s) 320 200-550 PBVB (bars) 0.2 0.06-0.5 If both the gas jets and the main current are employed, each gas jet has a higher kinetic energy per unit volume than the main current, as already explained above. There may be used, for example, a jet having a kinetic energy per unit volume equal to about 10 times that of the main current.

WHAT WE CLAIM IS: 1. Process for the manufacture of fibres from an attenuable material by means of gaseous currents, characterised in that a plurality of successive jets spaced apart from each other and adjacent to a convex guide surface is produced, the jets and the currents which they induce are deflected by flowing along and adhering to the said convex guide surface, the induced currents forming zones of laminar flow on this convex guide surface between adjacent jets, and the streams of attenuable material are delivered between the jets into the zones of laminar flow, the said streams being thereby carried by and attenuated in the flow of the jets.

2. Process according to claim 1, characterised in that the section of each jet is larger in the direction along the guide surface than in a direction perpendicular thereto.

3. Process according to one of the claims 1 and 2, characterised in that a pair of counterrotating tornadoes is formed on the lateral edges of each jet by deflection of the jets along the convexly curved guide surface, the zones of laminar flow formed on the said guide surface by induced currents being situated between the pairs of adjacent tornadoes.

4. Process according to one of the claims 1 to 3, characterised in that the jets have planes of symmetry perpendicular to the convex guide surface.

5. Process according to claim 4 characterised in that the streams of attenuable material are delivered to the zones of laminar flow in positions which are staggered laterally with respect to the planes which are equidistant from two consecutive jets.

6. Process according to one of the claims 1 to 5, characterised in that a main gaseous current having a larger section than the jets is produced and directed transversely to the deflected jets, the latter having each a kinetic energy per unit volume greater than that of the main current in order to penetrate the latter and create zones of interaction into which the streams of partially attenuated material are introduced to be subjected to an additional attenuation.

7. Process according to one of the preceding claims, characterised in that the path of the deflected jets is directed downwards in the direction of the main current.

8. Process according to one of the preceding claims, characterised in that the temperature of the gaseous jets is substantially equal to room temperature.

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

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. The unit pull rate may vary from 20 to 150 kg per aperture per 24 hours, 50 to 80 kg per aperture per 24 hours being typical values. Certain values relating to the jet and the main current are also important, as indicated in the Tables below, in which the following symbols have been used: p=pressure T=temperature V=velocity p=mass per unit volume TABLE V Emission of Jet Symbol Preferred value Range Pj (bars) 2.5 1-50 Tj(0C) 20 upto 1860 Vj (m/sec) 300 200-900 pjVj2 (bars) 2.1 0.8A0 TABLE VI Main Current Symbol Preferred value Range PB (mbars) 95 30--250 TB(0C) 1450 1300--1800 v, (m/s) 320 200-550 PBVB (bars) 0.2 0.06-0.5 If both the gas jets and the main current are employed, each gas jet has a higher kinetic energy per unit volume than the main current, as already explained above. There may be used, for example, a jet having a kinetic energy per unit volume equal to about 10 times that of the main current. WHAT WE CLAIM IS:

1. Process for the manufacture of fibres from an attenuable material by means of gaseous currents, characterised in that a plurality of successive jets spaced apart from each other and adjacent to a convex guide surface is produced, the jets and the currents which they induce are deflected by flowing along and adhering to the said convex guide surface, the induced currents forming zones of laminar flow on this convex guide surface between adjacent jets, and the streams of attenuable material are delivered between the jets into the zones of laminar flow, the said streams being thereby carried by and attenuated in the flow of the jets.

2. Process according to claim 1, characterised in that the section of each jet is larger in the direction along the guide surface than in a direction perpendicular thereto.

3. Process according to one of the claims 1 and 2, characterised in that a pair of counterrotating tornadoes is formed on the lateral edges of each jet by deflection of the jets along the convexly curved guide surface, the zones of laminar flow formed on the said guide surface by induced currents being situated between the pairs of adjacent tornadoes.

4. Process according to one of the claims 1 to 3, characterised in that the jets have planes of symmetry perpendicular to the convex guide surface.

5. Process according to claim 4 characterised in that the streams of attenuable material are delivered to the zones of laminar flow in positions which are staggered laterally with respect to the planes which are equidistant from two consecutive jets.

6. Process according to one of the claims 1 to 5, characterised in that a main gaseous current having a larger section than the jets is produced and directed transversely to the deflected jets, the latter having each a kinetic energy per unit volume greater than that of the main current in order to penetrate the latter and create zones of interaction into which the streams of partially attenuated material are introduced to be subjected to an additional attenuation.

7. Process according to one of the preceding claims, characterised in that the path of the deflected jets is directed downwards in the direction of the main current.

8. Process according to one of the preceding claims, characterised in that the temperature of the gaseous jets is substantially equal to room temperature.

9. Apparatus for the manufacture of fibres from an attenuable material,

comprising at least one emitter of gaseous jets having emission orifices, and a source of supply of attenuable material provided with at least one supply orifice, characterised in that the emission orifices (22) for the gaseous jets are spaced apart from each other in the lateral direction and placed along a guide element (14) adjacent to the jets and having a convex surface which deflects their paths, and in that the supply source (16, 17) of attenuable material is placed opposite the convex surface of the guide element in order to direct the streams of material towards the currents induced by the jets in zones situated between the latter on the curved surface of the said element.

10. Apparatus according to claim 9, characterised in that each jet emission orifice is larger in the direction along the guide element than in a direction perpendicular thereto.

11. Apparatus according to one of the claims 9 and 10, characterised in that the leading edge of the guide element is adjacent to the jets flowing on the convex surface, and in that the orifices (25) for supplying material, which are situated between the jets, are staggered in relation to the mid-position.

12. Apparatus according to one of the claims 9 to 11, characterised in that the jet emission orifices have planes of symmetry perpendicular to the convex guide element.

13. Apparatus according to one of the claims 9 to 12, characterised in that each jet emission orifice is substantially rectangular.

14. Apparatus according to one of the claims 9 to 13, characterised in that the jet emission orifices are so arranged that one of the surfaces bordering the jets is substantially tangential to the part of the curved surface adjacent to the leading edge.

15. Apparatus according to one of the claims 9 to 14, characterised in that it comprises a generator (10, 11) producing a main current (B) of greater crosssection than the jets directed transversely to the deflected jets and intercepting them.