GB1595830A - Of gaseous currents manufacture of fibres from an attenuable material by means - Google Patents

Abstract

The process consists in generating at least one pair of gas jets (a - a) with kinetic energies per unit volume and dimensions which are substantially equal, whose axes are situated practically in the same plane, the two jets converging to form a combined flow after their impact and in conveying the ductile substance (S) into a zone of gases induced by one of the two jets, which zone is situated outside the angle included between these jets. In a second stage the combined flow enters a main gas stream (10) to form a zone of interaction into which the partially drawn fibre is introduced in order to be subjected to additional drawing therein. 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 body corporate, 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:- The present 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. 2223 318 describes the formation of pairs of counter-rotating tornadoes in a zone of interaction produced by directing 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.

In the apparatus used for carrying out this process, the glass supply orifice which directs the stream of glass to the zone of interaction produced as described above is situated at or virtually at the boundary of the main current. It is also possible, however, as described in our British Patent No. 1 521 343, to place the glass supply orifice at some distance from the boundary of the main current and deliver the stream of glass to the said zone of interaction by gravity.

It has also been envisaged to place both the glass supply orifices and the emission orifices for the secondary jets at some distance from the boundary of the main current, the streams of glass being in that case introduced into the corresponding zone of interaction by the action of the said jets themselves, so that the streams are subjected to two stages of attenuation, one in the secondary jet and the other in the main current. This arrangement has been described in particular in our British Patent No. 1 513 060 and our Application No.

50314/77 (Serial No. 1 592 683).

Furthermore, according to this lastmentioned application, the formation of a stable zone of laminar flow situated between two counterrotating tornadoes is brought about in the secondary (or carrier) jet which delivers the glass into the zone of interaction with the main current. The stream of glass is conducted to this laminar zone and then enters the region of tornadoes which subsequently merge downstream of the carrier jet before the latter reaches the main current. The first stage of attenuation thus takes place while the stream of glass is carried in the pair of tornadoes of the carrier jet and subjected to their action whereas the second stage, which is advantageous but sometimes optional, takes place in the zone of interaction formed with the main current, after entry of the carrier jet and of the partially attenuated stream of glass.

In the application in question, the zone of laminar flow and the tornadoes of carrier jet associated with each fibre forming centre are produced by a disturbance of the jet, whereby the jet is deflected. This disturbance is produced by interposing, in the path of the jet emitted from each fibreforming centre, a deflector or guide device which modifies this path, the resulting deflection of the jet contributing to the stability and regularity of functioning in spite of the gap between the point at which the glass is delivered into the carrier jet and the main current.

One particularly important object of the present application is also the obtaining of satisfactory stability of the stream of glass or other attenuable material by the creation, in a gaseous flow. of a zone of laminar flow situated between the tornadoes. The gaseous flow produced according to the present invention, however, does not result from the disturbance of a carrier jet by a mechanical element or deflector device and furthermore it provides various quite specific and particularly interesting advantages which will be emphasised in the course of the description.

According to the present invention, there is used, for each fibre forming centre, a pair of carrier jets whose convergent axes are situated in the same plane so that the jets impinge on each other in this plane. At each fibre forming centre, the impact of the two jets causes the flow resulting from the pair of combined jets, termed as combined flow, to spread out on each side of the common plane. This spreading out in the lateral direction is limited, preferably by placing the pairs of jets sufficiently close together to enable each combined flow to produce an impact on the flow of the adjacent fibre forming centres, which are also in the process of spreading out. This limitation of the spreading out causes and promotes the development, in the flows, of pairs of separate tornadoes and zones of laminar flow situated each between the two tornadoes of one and the same pair.

The streams of glass or other attenuable material are delivered to the jets close to each zone of laminar flow, starting from a position situated in the common plane and d on one side of the pair of jets of a fibre forming centre. They are thus introduced into the zones of laminar flow and then enter the tornadoes. where they are attenuated.

Another characteristic of the invention consists of using two jets of approximately the same dimension for each fibre forming centre. The kinetic energies per unit volume of these two jets are substantially equal.

Although this system of double jet enables attenuation to be carried out in a single stage, solely in the tornadoes produced in the combined flow of the two jets, it is preferred to manufacture the fibres by a two-stage process in which the combined flow issuing from the pair of jets is also used as means for delivering the stream of glass into a zone of interaction with a main current whose path intercepts the combined flow, this method resulting in finer fibres due to the additional attenuation.

In each fibre forming centre, the tornadoes produced in the flow of each pair of jets converge downstream of the zone of laminar flow. and the combined flow progresses in the direction of the main current to penetrate the latter and thus produce a zone of interaction also comprising a pair of tornadoes, the characteristics of which are described in the publication of French Patent No. 2223 318.

Each stream of glass is thus subjected to a primary attenuation in a gaseous flow, and more precisely between two tornadoes produced by each pair of carrier jets, and the partially attenuated stream is then subjected to a second attenuation in the zone of interaction produced by penetration of the flow of the combined carrier jets into the main current. This process of attenuation into a single fibre by two stages enables long fibres to be obtained without fragmentation.

The advantages and the concrete embodiments of the invention will emerge more clearly from the description given below with reference to the Figures.

Figure 1 is a schematic elevational view of the main elements of a fibre forming and collecting apparatus according to the invention, showing certain parts in section; Figure 2 is a schematic perspective view on a larger scale, showing the mode of operation of the fibre forming apparatus of Figure 1; Figure 3 is a vertical section on an even larger scale of the elements forming a fibre forming centre, taken through the plane of the jet emission orifice; Figure 4 is a transverse section taken on the line 4-4 of Figure 3; Figure 5 is a section of the main elements of the fibre forming apparatus, representing in particular certain dimensions which must be taken into account to establish the operating conditions for the preferred method of carrying out the invention; Figure 6 is a detailed view in section, showing the dimensions between the orifices for adjacent jets; ; Figure 7 is a transverse section through a tip of a bushing for supplying an attenuable material, also indicating certain dimensions which are to be taken into account.

Referring first to Figure 1 which represents schematically at 8 a device for generating the main current, such as a burner, having a nozzle 9 which emits a main current 10 in an approximately horizontal direction although this current may, of course, be given other directions.

A collector 13 connected by way of a connection 12 to a jet manifold box 11 supplies the latter with compressed gas, for example compressed air.

Figures 2 and 3 also show that the jet manifold box 11 comprises pairs of orifices 14 and 15 for the emission of jets, successive pairs of orifices having the references 14a-15a; 14b-15b; 14c-15c; 14d-15d. The jets emitted from these pairs of orifices are indicated by the corresponding letters.

Figure 2 shows three pairs of jets in perspective view whereas only a single pair of jets a-a is shown in Figures 1 and 3. To each pair of jets corresponds a fibre forming centre.

At each fibre forming centre, the jets of one pair, for example the jets a-a, impinge against each other in their common plane to produce a combined flow, indicated by A in Figure 1, in which a stream of attenuable material is subjected to a first stage of attenuation or primary attenuation. The combined flow or combined carrier jet travels downwards and penetrates the main current 10, creating with it a zone of interaction which is used for a second stage of attenuation.

In these Figures, a source of glass supply is indicated schematically at 16. It comprises a bushing 17 having a series of tips 18 for supplying glass spaced apart from each other, each comprising a supply orifice 18a and, upstream thereof, a metering orifice 19. The glass is thus delivered in a bulbous form G from which the streams of glass S flow downwards, each fibre forming centre comprising one bulb and one stream. The fibres formed from a series of fibre forming centres distributed transversely across the width of the main current 10 are then deposited on a perforated conveyor or belt 20 in the form of a sheet of fibres B.The distribution of the fibres over this conveyor takes place inside a chamber which is bounded, for example, by a wall 21, the distribution being effected by the action of suction chambers 22 preferably situated below the conveyor 20 and connected by pipes 23 to one or more suction fans represented schematically at 24.

The formation of fibres by means of the apparatus described above is explained and analysed in more detail with reference to Figures 2, 3 and 4.

As already mentioned above, the process proper to each fibre forming centre is preferably connected with the action of the jets of adjacent centres. In Figure 2, the complete process of fibre formation is shown for the fibre forming centre corresponding to the jets b-b and only part of the process is shown for the fibre forming centres relating to the jets a-a and c-c.

Figure 3 shows on a larger scale what takes place at the fibre forming centre comprising the jets a-a. To analyse the process or operation, it must first be remembered that every gaseous jet induces a movement of surrounding air when it is emitted from an orifice. Each of the jets a therefore has a central partj or core surrounded by an envelope of gas containing induced air, which envelope is indicated by the letter i.

This envelope rapidly grows in size as the flow of jet progresses while the core of the jet remains a relatively short central part having the form of a cone. The velocity of the gas forming the core of the jet is equal to that of the jet at the moment when it leaves the orifice but the velocity of the gas of the envelope diminishes as the flow progresses. The arrows in Figures 2 and 3 indicate the induction of air by the flow of the jets as well as by the flow of the main current.

If one uses a pair of jets having approximately the same kinetic energy per unit volume and preferably also approximately the same dimensions, and these two jets have their axes situated in the same plane and converging so that they meet preferably at an acute angle, the combined flow will spread out laterally downstream of the region of impact of the two jets, that is to say it will spread out in directions transverse to the plane of the axes of the jets. According to the present invention, the pairs of jets, or the planes containing their axes, are sufficiently close together to ensure that at each fibre forming centre the lateral spreading out of the combined flow from a pair of jets will be inhibited or limited by impact against the flow of pairs of adjacent jets which are also in the process of spreading out.This impact between adjacent combined flows produces two pairs of tornadoes of small dimensions in each flow, the apices of the tornadoes of one pair being situated at some distance apart on each side of the plane containing the axes of the jets.

Upper and lower pairs of tornadoes are shown schematically in Figures 2, 3 and 4.

The tornadoes of the upper pair, indicated by the reference tu-tu, are formed by currents rotating towards each other in the upper part of the tornadoes and away from each other in the lower part, as indicated by the arrows in Figure 4, while the tornadoes of the lower pair, indicated by the letters tl-tl, turn in the opposite sense.

Between the two pairs of tornadoes, in the region of mutual impact of the jets, there is formed a zone L of laminar flow associated with these tornadoes, at the level of which zone the induction of air is very intense, and it is precisely in this zone L, beside the upper tornadoes, that the stream of glass S is introduced. This stream is formed from the bulb or cone of glass G, the position of which is staggered in relation to the jet emitter. However, since the bulb of glass G is in an attenuable or fluid state when it leaves the tip of the bushing, the stream of attenuable glass S is deflected from the initial position of the bulb towards the zone of laminar flow L due to the intense intake of induced air, and this in effect ensures that the stream of attenuable material will be delivered into the laminar zone.Consequently, even if the tip 18 which supplies the glass is slightly out of alignment with the pair of jets, the intake of induced air will automatically compensate for this fault and will lead the stream of glass into the correct position.

It will thus be understood that the formation, at each fibre forming centre, of at least one pair of tornadoes bordering on a zone of laminar flow and the delivery of the material in an attenuable state into a region close to the said zone cause the stream of material to be automatically carried into this zone by the currents of induced air which, as explained above, automatically compensate for any faults in alignment, thereby stabilizing the introduction of the attenuable material into the system. This stability is achieved even if the tips from which the glass is supplied are considerably spaced apart from the jet emitters, this spacing apart being desirable in that it facilitates control and maintenance of the required temperature both for the glass supply tips and for the jet emitters.

Downstream of the laminar zone L, the two tornadoes tu-tu, as also tl-tl, tend to merge, and as the flow progresses downstream they tend to lose their identity, as represented in Figure 2, in the section showing the two pairs of tornadoes originating in the jets c-c. The combined flow of each pair of jets then progresses downwards to penetrate the main current 10, as illustrated for the flow issuing from the pair of jets b-b. The combined jet then forms, with the main current and inside it, the zone of interaction which has been completely analysed in the Patent publication mentioned above. This zone comprises a supplementary pair of tornadoes T.

It will be noted that each plane containing the axes of jets of one pair intersects the main current, preferably along a straight line substantially parallel to the direction of propagation of said current.

Each stream of glass S is thus subjected to a primary attenuation in the flow of combined jets, between the zone of laminar flow or point of introduction of the glass and the point of penetration of the jet into the main current, the partially attenuated stream being then subjected to an additional attenuation in the zone of interaction of the said flow with the main current. It will be seen from the figures that these two stages of attenuation are effected without fragmentation of the stream of glass, so that each stream gives rise to a single fibre.

In order to achieve the process described above at each fibre forming centre, in particular the formation of pairs of tornadoes each bordering on a zone of laminar flow, there is used a pair of jets having substantially the same kinetic energy per unit volume. The cross-sections of these two jets preferably also have identical surfaces although a slight difference between these surfaces may be allowed, particularly if the kinetic energies per unit volume of the two jets are virtually identical. Furthermore, the cross-sections of the two jets of one fibre forming centre advantageously have the same form.

The cross-section of a jet need not necessarily have exactly the same dimensions in the directions parallel to and transverse to the plane containing their axes, and furthermore these two dimensions are not necessarily equal to the corresponding dimensions of the second jet of the same pair. However, it is preferable and advantageous that these dimensions be identical or very similar both within one jet and as between two jets of one fibre forming centre. Furthermore, it is desirable that the pairs of adjacent jets have substantially the same dimensions in order to enable uniform formation of the pairs of tornadoes bordering on the zones of laminar flow to be effected when each combined flow impinges on the adjacent flow as they spread out laterally.This identity between the jets of successive fibre forming centres enables uniform and homogeneous conditions of fibre formation to be obtained in the various zones of interaction created by penetration of the jets into the main current.

The flow from each pair of jets may be utilised for the formation of fibres without the aid of the main current. However, in most cases, and particularly for the manufacture of relatively fine fibres, it is preferable to employ not only the primary attenuation carried out in the flow of a pair of jets but also the additional attenuation carried out in the zone of interaction resulting from the penetration of this flow into the main current.

In order that penetration may take place, the combined flow should have a greater kinetic energy per unit volume than the main current at the time of reaching this current.

It will also be noted that the jets grouped in pairs should have certain specific characteristics for forming the zone of laminar flow if the stream of glass is to be introduced into this zone without fragmentation. It is important that their axes should by virtually in the same plane and should meet preferably at an acute angle, advantageously between the limits indicated below. Other parameters mentioned with reference to Figures 5, 6 and 7 should also be taken into consideration.

Figure 5 represents, in a cross-sectional view similar to that of Figure 3, three main elements of the apparatus used to form at least one fibre forming centre. These elements are: the device for generating the main current, the jet emitter and the source of supplying an attenuable material. On these figures, as well as on Figures 6 and 7, are entered symbols identifying the various parameters as well as dimensions and angles referred to in the following Tables which give the most suitable ranges of variation of the dimensions and angles and their preferred values.

TABLE I Bushing and supply tips for supplying attenuable material Preferred Symbol value (mm) Range dT 2 1- 5 1T 1 1- 5 1R 5 0-10 dR 2 1- 5 DR 5 1 - 10 The expression "supply orifice" for attenuable material used in the description should be understood in a very general sense. It may denote either an isolated orifice associated with a single pair of jets or a series of orifices situated, for example, each at the end of a supply tip, or a supply slot common to a plurality of fibre forming centres, as explained in French Patent publication No. 2 223 318.

When a row of orifices is replaced by a slot associated with a row of pairs of jets and arranged transversely to the main current, the attenuable material delivered from the slot is divided into a series of cones and streams under the influence of pairs of jets and of air currents which they induce at the various fibre forming centres. Each stream of glass which has been formed is carried by the induced currents into the corresponding zone of laminar flow. In that case, the axis of each cone of glass is automatically situated in the plane containing the axes of the corresponding pair of jets.

TABLE 11 Emission of Pairs of Jets Preferred value Symbol (mm,degrees) Range dJ1 2 0.5- 4 dJ2 2 0.5 - 4 1J 3 at least 1 LJS 5 2 - 10 ajj 45 10 - 90 a JB 45 20 - 90 It will be noted that the device for emitting the pairs of jets may also consist of two jet manifold boxes superimposed on each other, each carrying on its front wall a single row of orifices arranged so that the grouping of the two manifold boxes forms pairs of orifices which have the characteristics mentioned above.

TABLE III Main current Preferred value Symbol (mm) Range 1B 10 5-20 TABLE IV Relative position of the various elements Preferred value Symbol (mm) Range ZJF 8 1 - 15 ZJB 17 12 - 30 XBJ 0 -20 - +5 XJF 5 0- 8 The negative values for the symbol XBJ apply to the case represented in Figure 5, in which the point of intersection of the paths or of the axes of the two jets emitted at each fibre forming centre is situated downstream of the outlet of the nozzle which emits the main current, viewed in the direction of propagation of this current.

The number of fibre forming centres may amount to 150 but in a normal installation for producing fibres of glass or a similar thermoplastic material, a suitable bushing would contain, for example, 70 supply tips.

It should also be mentioned that the operating conditions of the system according to the present invention will vary as a function of various factors, for example according to the characteristics of the material which is to be converted into fibres.

As indicated earlier on, the present invention may be applied to a wide range of attenuable materials. When attenuating glass or other inorganic thermoplastic 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, generally within a temperature range of 1400 to 18000C. In the case of a conventional glass composition, the temperature of the bushing is in the region of 1480cm.

The unit pull rate may vary from 20 to 150 kg per aperture per 24 hours, typical values being between 40 and 60 kg per aperture per 24 hours.

Certain values relating to the jet and to 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 =specific gravity When attenuation is carried out in two stages, using both the double jet system and the main current, the flow of combined jets TABLE V Emission of Each Jet Symbol Preferred value Range PJ (bars) 2.5 1 - 15 TJ( C) 20 0-1500 VJ (m/sec) 330 330 - 900 PJV2J(bars) 2.1 0.8 - 40 TABLE VI Main Current Symbol Preferred value Range PB (mbars) 95 30 - 250 TB( C) 1450 1350 - 1800 VB (mlsec) 320 200 - 550 PBV2B(bars) 0.2 0.06 - 0.5 is narrower and preferably of smaller crosssection than that of the main current and it penetrates the latter to produce a zone of interaction in which the second stage of attenuation takes place For this purpose, this flow of combined jets should have a higher kinetic energy per unit volume than the main current in the region where the two cooperate.On reaching the main current, the flow may have, for example, a kinetic energy per unit volume equal to about 10 times that of the main current, as represented by the following equation: PJV2J = 10 PBV2B When attenuation is carried out in two stages, the two jets of a pair should preferably have the same dimension, as already noted above, and preferably also the same velocity and kinetic energy. A certain difference may, however, be allowed, at least for certain of these parameters.

The invention has a large number of advantages, in particular for the formation of fibres from various materials and particularly from mineral thermoplastic compositions such as glass.

Among the main advantages and characteristics, the following should be particularly noted: In the preferred embodiment of the invention, in which the pair of jets of each fibre forming centre also serves to carry the attenuable material into the zone of interaction produced by penetration of the combined flow into a main current, the employment of such a pair of jets stabilises the introduction of the stream of attenuable material both into the flow issuing from the jets and into the zone of interaction with the main current. Moreover, this stability of supply is achieved even where there is a considerable spacing apart or separation between the main elements of each fibre forming centre, that is to say the source of supply of attenuable material, the jet emission device and the device for generating the main current.Such a separation is very important for various reasons, in particular the desirability of preventing excessive transfer of heat between the various elements of the fibre forming system; in particular, it enables the desired temperature conditions for each of these elements to be established and maintained, this precise control of the temperatures being desirable for obtaining regular fibre formation and consequently fibres of high quality.

With regard to these temperatures, it will also be noted that for the jet it is advantageous to use a fluid such as compressed air at a temperature close to room temperature whereas the source of supply of attenuable material, for example glass, and the device for generating the main current are both maintained at relatively high temperatures. These temperature differences may effectively be maintained in the system according to the invention by virtue of this possibility of considerably separating the various elements.

Furthermore, the apparatus according to the present invention enables the advantages mentioned above to be obtained without the necessity of introducing a mechanical element along the path of the individual jet or of the pair of combined jets flowing to each fibre forming centre and hence without having to regulate its precise position. It will be remembered that the spreading out of the flow in a lateral direction is due to the mutual impact of the jets of each pair and that this spreading out is limited or inhibited by adjusting the distance between adjacent pairs of jets so that the flow of one fibre forming centre impinges on the adjacent flows.This particular arrangement enables the lateral spreading out of the combined jets to be limited and hence makes it possible to develop pairs of tornadoes bordering on the zones of laminar flow without placing any mechanical element in the path of the jets and consequently without having to encounter the problems of wear and tear, deterioration by heat or precise positioning of these elements, all problems which inevitably occur when the development of tornadoes in the jets is associated with the use of such mechanical elements. This particularly advantageous possibility of employing a minimum of mechanical structures in the region of the supply of attenuable material also reduces the risk of adherence or ac cumulation on these structures of material which is not drawn into fibres.

WHAT WE CLAIM IS: 1. Process for the manufacture of fibres from an attenuable material by attenuation by means of gaseous currents, characterised in that there is produced at least one pair of gas jets having substantially equal kinetic

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

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE V Emission of Each Jet Symbol Preferred value Range PJ (bars) 2.5 1 - 15 TJ( C) 20 0-1500 VJ (m/sec) 330 330 - 900 PJV2J(bars) 2.1 0.8 - 40 TABLE VI Main Current Symbol Preferred value Range PB (mbars) 95 30 - 250 TB( C) 1450 1350 - 1800 VB (mlsec) 320 200 - 550 PBV2B(bars) 0.2 0.06 - 0.5 is narrower and preferably of smaller crosssection than that of the main current and it penetrates the latter to produce a zone of interaction in which the second stage of attenuation takes place For this purpose, this flow of combined jets should have a higher kinetic energy per unit volume than the main current in the region where the two cooperate.On reaching the main current, the flow may have, for example, a kinetic energy per unit volume equal to about 10 times that of the main current, as represented by the following equation: PJV2J = 10 PBV2B When attenuation is carried out in two stages, the two jets of a pair should preferably have the same dimension, as already noted above, and preferably also the same velocity and kinetic energy. A certain difference may, however, be allowed, at least for certain of these parameters. The invention has a large number of advantages, in particular for the formation of fibres from various materials and particularly from mineral thermoplastic compositions such as glass. Among the main advantages and characteristics, the following should be particularly noted: In the preferred embodiment of the invention, in which the pair of jets of each fibre forming centre also serves to carry the attenuable material into the zone of interaction produced by penetration of the combined flow into a main current, the employment of such a pair of jets stabilises the introduction of the stream of attenuable material both into the flow issuing from the jets and into the zone of interaction with the main current. Moreover, this stability of supply is achieved even where there is a considerable spacing apart or separation between the main elements of each fibre forming centre, that is to say the source of supply of attenuable material, the jet emission device and the device for generating the main current.Such a separation is very important for various reasons, in particular the desirability of preventing excessive transfer of heat between the various elements of the fibre forming system; in particular, it enables the desired temperature conditions for each of these elements to be established and maintained, this precise control of the temperatures being desirable for obtaining regular fibre formation and consequently fibres of high quality. With regard to these temperatures, it will also be noted that for the jet it is advantageous to use a fluid such as compressed air at a temperature close to room temperature whereas the source of supply of attenuable material, for example glass, and the device for generating the main current are both maintained at relatively high temperatures. These temperature differences may effectively be maintained in the system according to the invention by virtue of this possibility of considerably separating the various elements. Furthermore, the apparatus according to the present invention enables the advantages mentioned above to be obtained without the necessity of introducing a mechanical element along the path of the individual jet or of the pair of combined jets flowing to each fibre forming centre and hence without having to regulate its precise position. It will be remembered that the spreading out of the flow in a lateral direction is due to the mutual impact of the jets of each pair and that this spreading out is limited or inhibited by adjusting the distance between adjacent pairs of jets so that the flow of one fibre forming centre impinges on the adjacent flows.This particular arrangement enables the lateral spreading out of the combined jets to be limited and hence makes it possible to develop pairs of tornadoes bordering on the zones of laminar flow without placing any mechanical element in the path of the jets and consequently without having to encounter the problems of wear and tear, deterioration by heat or precise positioning of these elements, all problems which inevitably occur when the development of tornadoes in the jets is associated with the use of such mechanical elements. This particularly advantageous possibility of employing a minimum of mechanical structures in the region of the supply of attenuable material also reduces the risk of adherence or ac cumulation on these structures of material which is not drawn into fibres. WHAT WE CLAIM IS:

1. Process for the manufacture of fibres from an attenuable material by attenuation by means of gaseous currents, characterised in that there is produced at least one pair of gas jets having substantially equal kinetic

energies per unit volume, the axes of which jets are situated virtually in the same plane, the two jets converging to impinge upon each other so that the flow formed by the two combined jets spreads out laterally, and in that the material is delivered in the form of a stream in an attenuable state into a zone of gas induced by one of the two jets, which zone is situated outside the angle between the two jets.

2. Process according to Claim 1, characterised in that the attenuable material is delivered into the zone of induced gas from a position situated on one side of the pair of jets, in the plane containing the axes of these jets.

3. Process according to Claim 1 or Claim 2, characterised in that the crosssections of the two gas jets of a pair have equal surfaces.

4. Process according to one of the Claims 1 to 3, characterised in that the lateral spreading out of the flow of combined jets is limited so as to develop on to the edges of the said flow a pair of tornadoes which are spaced apart and situated on either side of the common plane and between which extends a zone of laminar flow, the material being delivered into the zone of laminar flow in the form of a stream in an attenuable state.

5. Process according to one of the preceding claims, characterised in that a main gas current is produced in a direction which intersects the flow of combined jets, this combined flow having a higher kinetic energy per unit volume and smaller dimension than the main current in order that it penetrates the latter to produce a zone of interaction and deliver the stream of material into the said zone of interaction created with the main current.

6. Process according to any one of the preceding claims, characterised in that several pairs of gas jets spaced apart laterally are associated with a main gas current, the distance between successive pairs of jets being such that a combined flow encounters the adjacent combined flow, this lateral impact thus developing in each flow (of two combined jets) pairs of tornadoes between which extends a zone of laminar flow, and in that the material is conducted in the form of streams in the attenuable state into each zone of laminar flow, the streams of material being then carried into the various zone of interaction formed by the combined flows in the main current.

7. Process according to one of the preceding claims, characterised in that in the plane of the axes of the pair of jets and transversely thereto, the dimensions of the cross-section of one jet are substantially equal to the corresponding dimensions of the second jet of the same pair.

8. Process according to one of the preceding claims, characterised in that the angle between the axes of the gas jets of each pair is between 10 and 90 .

9. Process according to one of the preceding claims, characterised in that the plane containing the axes of the pair of jets intersects the main current along a straight line virtually parallel to the direction of propagation of the main current.

10. Apparatus for the manufacture of fibres from an attenuable material by means of gas currents, comprising at least one device for emitting gas jets and a source of supply of attenuable material equipped with at least one supply orifice, characterised in that the device for emitting gas jets has the orifices for emitting the jets grouped in pairs (14-15, 14a-15a; 14b-15b; 14c-15c), the jets issuing from the two orifices of a pair having substantially the same kinetic energy per unit volume and the axes of these two orifices being situated virtually in the same plane, where they converge to enable the two jets to impinge on each other and form a combined flow, and in that the supply orifice for the attenuable material is situated outside the angle formed by the axes of the emission orifices of a pair of jets so that the material is conducted in the form of a stream in an attenuable state into the zone of gas induced by one of the two jets.

11. Apparatus according to Claim 10, characterised in that the axis of the orifice supplying attenuable material is situated in the plane containing the axes of the orifices of the said pair of jets.

12. Apparatus according to Claim 10 or Claim 11, characterised in that the two orifices of one and the same pair have substantially identical surfaces.

13. Apparatus according to one of the Claims 10 to 12, characterised in that it comprises a generator producing a main gas current in a direction which intersects the path of the combined flows, the main current having a greater width than the combined flows which penetrate it.

14. Apparatus according to one of the Claims 10 to 13, characterised in that the successive pairs of jet emission orifices are spaced apart laterally by a distance such that each combined flow encounters the adjacent combined flow so that in each of these is developed a zone of laminar flow bordered by pairs of tornadoes, each supply orifice of attenuable material being placed opposite each zone of laminar flow.

15. Apparatus according to one of the Claims 10 to 14, characterised in that the two emission orifices of a pair of jets have the same form.

16. Apparatus according to one of the Claims 10 to 15, characterised in that the angle between the axes of the two jets of a pair is between 10 and 90 .

17. Apparatus according to one of the Claims 10 to 16, characterised in that the pairs of jet emission orifices are situated on the front wall of the same jet manifold box (11).

18. Apparatus according to one of the Claims 13 to 17, characterised in that each plane common to the axes of the two emission orifices of a pair of jets contains the outlet direction of the orifice of the main current generator.