IE43347B1 - Process and apparatus for making fibres from attenuable material, for example, glass - Google Patents

Abstract

1521343 Glass fibres SAINT-GOBAIN INDUSTRIES 5 Feb 1976 [18 Feb 1975] 04585/76 Heading C1M Fibres of an attenuable material (e.g. glass) are made by forming a stream of the material, directing a main gaseous blast transverse to the stream and spaced from the delivery means, directing at least one secondary gaseous jet of smaller cross-section than the blast towards the latter, the jet having a kinetic energy per unit volume sufficient to cause it to penetrate the blast and form a zone of interaction, the stream meeting the blast adjacent the interaction zone. The size of the space may be increased by deflecting the blast away from the delivery means and the stream entering the interaction zone may be stabilized by an additional gaseous jet downstream of the stream with respect to the blast flow directed towards the zone.

Description

This invention relates to a process and apparatus for making fibres from attenuable material, for example glass, according to which a main gaseous blast and at least one secondary gaseous jet,are generated, the jet being directed so that it encounters the main blast, and its kinetic energy being sufficient for it to enter the main blast, to create • a zone of interaction adjacent the penetration path of the jet in the main blast; the attenuable- material, softened by heat, is supplied to the boundary of the main blast, into which it is caused to be introduced so as to reach the zone of interaction, which causes attenuation of the material into fibres.

An object of this invention is to provide improvements in such process and in apparatus for carrying it out, with particular reference to the introduction of the attenuable material into the zone of interaction.

According to this invention a process for making fibres from attenuable material comprises;- forming at least one stream of attenuable material and feeding it from delivery means; directing a main gaseous blast in a path transverse to the stream and spaced from the delivery means; directing at least one secondary gaseous jet of smaller cross section than that of the blast towards the latter, the secondary jet having a kinetic energy per unit of volume sufficient to cause.it to penetrate the blast so as to form a zone of interaction, the stream of attenuable material being caused to pass across the space between the delivery means and the main blast so as to meet the blast at a point adjacent the zone of interaction.

Also according to this invention a process for the production of glass fibres comprises:- supplying by gravity a stream of molten glass from a supply orifice;directing a main gaseous blast transverse to the stream at a distance below the supply orifice; and directing a gaseous secondary jet of smaller cross-section than that of the main blast and having a kinetic energy per unit of volume sufficient to cause it to penetrate the blast so as to form a zone of interaction, the secondary jet being directed from a point above the main blast obliquely downwards to create the zone of interaction in the area in which the stream of molten glass encounters the main blast. The distance between the supply orifice and the main blast makes it possible to keep the path of the fibres clear from all components of apparatus downstream of the zone of interaction and to reduce the influence of heat emanating from components from which the softened, attenuable material and the main blast are supplied.

The invention also includes apparatus which comprises:first means to propagate a main gaseous blast; second means to propagate at least one secondary gaseous jet of smaller cross-section than that of the blast, which jet is directed so as to enter transversely into the main blast to form a zone of interaction, the kinetic energy per unit of volume of the jet being greater than that of the main blast; and delivery means including a supply orifice for delivering a stream of attenuable material and so positioned that there is a space between the blast and the delivery means, the supply orifice causing the stream to pass across the space to meet the blast at a point adjacent the zone of interaction. 3 3 4 7 The invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which :Figure 1 is a section through one embodiment of 5 apparatus for making glass fibres: Figure 2 is a section through a second embodiment; Figure 3 is a partial underneath plan showing the layout of glass, supply orifices and secondary jet nozzles of the embodiment of Figure 2; Figure 4 is a section through another embodiment as seen on the line 4-4 of Figure 6; .

Figure 5 is like Figure 4 but as seen on the plane 5-5 of Figure 6; Figure 6 is a partial underneath plan of the apparatus 15 of Figures 4 and 5; Figure 7 is a section of a third embodiment; Figure 8 is a schematic isometric view of a fourth embodiment; Figure 9 is a schematic partial section of a fifth 20 embodiment: Figure 10 is an elevation of the embodiment of Figure ϋ as seen from the right-hand side of Figure 9; and Figure 11 is a section of a sixth embodiment.

Referring to the drawings the main gaseous current or 25 blast is always indicated by 12A and the orifices for the carrier or secondary jet and for the glass are indicated respectively by 36 and 37. - 4 Figure 1 shows the first embodiment which has a crucible 200 combined with a hopper 201 for introducing molten glass, .which is the attenuable material. The main gaseous current or blast is ejected from a generator 202 horizontally and at a level below the crucible 200. The orifice for the carrier jet 36 forms the lower, open end of a jet pipe 203 which is fed by a duct 204 connected to a burner or other source of gaseous carrier jet by a pipe 205. The jet pipe 203 is situated at an angle in relation to the axis of the main current 12A, and the jet orifice 36 is at a distance above the boundary of the main current leaving the structure 202. The carrier jet and the main current interact to create an interaction zone in knovm manner, the said zone being located below the orifice 37· The glass is introduced in the form of a fine stream or · · filament S which falls from the orifice 37, enters the interaction zone, where it is attenuated to fibre in known manner.

In the embodiment of Figure 1 the vertical distance between the orifice 37 and the upper boundary of the main current 12A is from 10 to 100 mm. The distance between the orifice 36 and the produced axis of the orifice 37 measured in the direction of the main current 12A may be from 4 to 10 mm. Further, due to the positioning and spacing of the various parts of the apparatus, it is preferable that the jet pipe 203 and consequently the jet should be at an angle to the axis of the main current 12A. This angle should be less than 90°, and may be in the range of from 45° to 85°. Preferably, the range is from 75° to 85°. The relationship of angle and spacing should be appropriate for - 5 347 the creation of an interaction zone at a point substantially vertically below tlie orifice 37. It is also preferable to locate the jet pipe 203 and consequently the orifice 36 in such a way that, viewed in relation to the direction of the main current 12A, the orifice 36 is upstream of the stream S. The angle of the jet pipe 203 should produce emission of the carrier jet in a direction generally transverse to the main current, but which exerts a component of force in the downstream direction of the main current, thus promoting formation of fibre and movement of attenuated fibre downstream ’in the main current. , The apparatus will preferably have a number of glass fibre attenuating assemblies or stations as described above. The parameters, including the kinetic energy of the main current and of the carrier jet in their effective area, and their temperature and the speed as well as the glass temperature, and the relationship between the sizes of the orifices for the glass and for the carrier jet, may conform in general to the parameters of previously known apparatus, although it should be noted that in some instances parameters may vary from those previously known. Thus the present invention provides for the orifice for introduction of glass to be spaced from the nearest boundary of the main current. Other modifications may be incorporated, some of which will be described below.

With the apparatus of the present invention it is possible to use less restricted limits for the ratios of the kinetic energy of the carrier jet to that of the main current in their - 6 •5 3 3 47 effective area, in comparison with the known apparatus, and effective results may he achieved whilst remaining within a ratio range of from 4:1 and 35:1 for the kinetic energy of the carrier jet to that of the main current.

The size of the orifice for the carrier jet may he smaller than that used in the known apparatus. For example, the orifice of the carrier jet may he smaller than the orifice for the glass, that is, it may he from approximately l/6 of the diameter of the orifice for the glass to approximately the same diameter. The orifice diameter of the carrier jet may vary from approximately 0.3 to 2.5 mm. The use of a small orifice for the carrier jet necessitates at the same time tho use of a high carrier jet pressure, hut the other operating conditions remain substantially the same. It is possible to use carrier jet pressures from 2 bars to 25 bars.

In the embodiments of the invention which include carrier jets of small diameter, the distance between the axes of the orifices for the carrier jet and the glass, measured in the direction of the main current, may he 3 to 4 times the diameter of the orifice of the carrier jet, or from 1 mm to 10 mm.

In operation of the apparatus of Figure 1, currents of air are induced hy the carrier jet as indicated hy the arrows 206, and these induced currents flow over the glass filament S, tending more and more to draw the filament towards the carrier jet as it approaches the boundary of the main current. This action has a stabilising influence, that is, it tends to ensure constant and stable entry of the glass filament into - 7 433 47 the interaction zone.

Figure 1 shows that there is a considerable space between and around all the main components oi the glass attenuating assembly, which comprise the crucible 200, the duet 204, and the generator 202. Due to this increased spacing between the main components, transfer of heat fromihe crucible 200 to the other components is reduced. As a result it is possible to control more easily and accurately the temperature of the glass. The apparatus also allows the use of molten glass or other attenuable material at a higher temperature, or to obtain a higher output.

Although Figure 1 shows a single fibre producing Station, it is possible to have a number of such stations disposed transverse to the direction of the main current.

The orifice 37 may be a simple oi'ifiee or may be as described below with reference to Figures 2 and 3.

Referring now to Figures 2 and 3, It will be seen that the general arrangement of the main components is similar to that of Figure 1, but the vertical distance between the orifice 37 and the upper; boundary of the main current 12A is less.

The sides of the crucible 200 are protected with fibrous insulation 207 containing for example 60% Al^Og and 40% silica,to reduce heat loss from the crucible and also to protect the jet pipes 203 from the great heat of the crucible. To withstand the heat of the molten glass, the crucible 200 is normally made of a platinum alloy and the thermal insulation 207 makes it possible to construct the other components, such as the jet pipe 203, from a less expensive metal, for example, stainless steel. - 8 With the insulation 207, it is possible to maintain a greater temperature difference between the glass on one hand and the gas forming the carrier jet on the other. In this way, even when the carrier jet has a relatively low temperature, the insulation 207 makes it possible to keep a relatively high glass temperature without excessive heat loss. This arrangement facilitates high production.

The passage for glass at the bottom of the crucible has a calibrating aperture 37£ and the passage widens out both above and below this aperture. The widening above the aperture 37c is in the shape of a funnel, to facilitate flow of glass through the calibration aperture towards the lower wider section which provides a small reservoir or pocket from which the filament or fine stream S of glass flows. The circumference of the supply orifice 37 may be 2 to 3 times that of tho aperture 37c., and all the periphery of this supply reservoir is wetted by the glass, which contributes to the stability of the bulb of glass at the orifice, particularly at high temperature. Due to the supply reservoir or pocket, the base of the bulb or cone of glass formed is larger, and consequently gives rise to a longer bulb, thus forming a greater distance between the point of supply of the glass and the point where the stream S is formed from the bulb. This increase in the distance from the base to the point where the stream originates reduces the tendency of fibres to accumulate on the components of the attenuating station.

Although the pocket or reservoir which terminates the orifice 37 may be circular, it is advantageous for it to he - 9 33 1V oval in shape, with the longer axis lying in the direction of flow of the main current 12A, see Figure 3.

With the arrangement for the supply of glass described with reference to Figures 2 and 3, the calibrating aperture 37c may form the actual orifice for the supply of glass, or its control orifice.

In the embodiment of Figures 2 and 3, the pressure of the carrier jet is advantageously a little higher than in the known apparatus, due to the distance between the orifice 36 and the main current. Consequently, pressures for the carrier jet of from 2 to 10 bars may he used with an orifice 36 °f about 2 mm. diameter; with an orifice 36 of 1 mm, the pressure may he from 2 to 25 bars.

The possibility of using high pressures and high kinetic energy for the carrier jet makes it possible to increase the quantity of glass supplied by the orifices 37 and to improve uniformity of glass flow as well as stability of the bulbs of glass formed, resulting in improvement in the uniformity of the fibres produced.

Further, the possibility of using high pressures for the carrier jet and the fact that tbe orifices 36 and 37 are at a distance from the main current, is of importance in making it possible to have greater interaxial distancos between the orifices 36 and 37- In addition, these factors also facilitate the use of orifices 37 which are larger than those of the orifice 36, for example, 1 to 2 times the dimensions of the orifice 36, when carrier jet pressures of up to 12 bars are used, and of 2 to 3 times when carrier jet pressures of from 12 to 25 bars are used.

In the embodiment of Figures 2 and 5, the width of the reserve pocket or reservoir measured transverse to the direction of flow of the main current, may in a typical case bo 1.3 times the diameter of the orifice 36 and its length ma)' be double its width.

With the embodiment of Figures 2 and 3 production was carried out with operating parameters and results given in the following Table:- Glass production: 35 to 40 kg per day per glass orifice Micronaire reading: (British Standard 3181 : 1968) 4.0 / 5 grammes Diameter of fibres: 5 to 6 microns Main current 12A: - Temperature: 155O°C - Pressure: 0.2 bars - Velocity: 450 m/s Carrier jet: - Temperature: 6oo°c - Pressure: 7 bars • - Velocity: 560 in/s Orifice diameter: 2 mm Ratio of kinetic energy: Carrier jet = 6 Main current (Micronaire (or Micronary) determining fibre fineness by refers to a method an air flow method) of In the embodiment of Figures 4, 5 and 6 a crucible 200 is combined with a hopper 201. A structure 202 directs the main current 12A in a generally horizontal direction below the crucible. The crucible is fitted with two staggered rows of orifices 37Λ and 37b, Figure 6. Tho supply duet 204 lias 347 branches with orifices 36B for the carrier jets adjacent the orifices 37B, and with branches for orifices 36A associated with the orifices 37A. All the orifices 36A, 36B, 37A and 37B are located at a distance above the upper boundary of the main current 12A. This construction does not only comprise a plurality of attenuding stations in staggered formation, but it is also possible to provide for a vertical distance between the orifices and the boundary of the main, current.

In the embodiments described above, the glass streams or filaments can tend to pass through the main current 12A without being fully attenuated, and some of the filaments can solidify prematurely, and result in the presence of thick fibres in the products obtained. This fault can be avoided by the embodiment of Figure 7, in which the main components are arranged the same general way as in Figures 2 and 3, . but in addition a plate 208 is situated at the outlet of the source 202 of the main current. This plate extends under the main current and curves downwardly away from it, as shown. This plate is followed by an extension plate 209 which has a .slit 2Ϊ0 for admission of a sheet of air or other gas supplied by a duct 211, In this embodiment the curved surfaces of the plates 208 and 209 produce a boundary effect which deflects the main current, resulting in an increase in the free space between the orifice 37 and the main ourrent.

In this way, tbe thickness of the main current is increased in the attenuating zone, so as to avoid the tendency for the glass to pass through the main current and to eliminate - 12 ^3347 premature cooling of fibres before the required attenuation lias taken place. In Figure 7, the pressure of the air at the slit 210 may be from 3 to 6 bars.

In the embodiment of Figure 8, the generator 202 is situated below a duct 212 which has a set of orifices 36 each supplying a gaseous carrier jet. The glass is supplied from a receptacle 213 filled by a supply pipe 214. The receptacle 213 has walls such as the wall 215 and it also has an over-flow lip 2i6. A sheet of molten glass flows over the lip 216 and then down to the carrier jets where it is divided into filaments 37S. Each filament is formed adjacent one of the carrier jets and each enters the interaction zone thus producing formation of fibres.

This embodiment is advantageous for the formation of fibres from very refractory or corrosive materials such as slag and other mineral compounds. Materials of this type have a.tendery to cause excessive orifice wear and consequently the crucible and other containers require frequent replacement, which involves interruption of the fibre-forming process.

As in the previous embodiments, the distance between the orifices 36 and the boundary of the main current may be from 5 to 10 mm. The distance between each orifice 36 and the respective point where sheet of glass leaves the lip 216 may be from 2 to 10 mm.

To facilitate handling of some types of attenuable material, particularly when the latter has a tendency to block the glass supply orifices or to corrode the material around them at high temperatures, an embodiment may be used which - 13 433 47 has components made of inert or corrosion-resistant materials, which are refractory, for example, materials with a chrome oxide or alumina basis. Such an embodiment will now he described with reference to Figures 9 and 10. A crucible 217 is made of a substance with a refractory oxide basis. It is supplied with attenuable molten material 218. One wall of this crucible is in the form of a lip with grooves 219 forming separate supply channels for each filament S.

A generator 220 supplies the main current through an outlet nozzle 202 in the form of a sheet or layer just below the grooves 219. Carrier jet orifices 36 are supplied from a duct 204 which is in turn supplied from a source 221. The orifices 36 are positioned to create interaction zones at points located approximately vertical to and below the 13 descending filaments S which enter the interaction zones and are formed into fibres.

The grooves 219 may he arranged exactly above the upper boundary of the main current, and spaced 50 to 100 mm therefrom, and the orifices 36 are located 5 to 10 mm above the !0 said upper boundary. With some attenuable materials which are prepared at very high temperatures, it may he desirable to provide cooling to reduce the material to the best temperature for formation of fibres. The distance at which the grooves 219 are located above the main current may itself provide -5 the necessary cooling, hut it is possible to provide supplementary cooling, for example by lowering the temperature of the gaseous carrier jets and for the main gaseous current. These may he either products of combustion (which may be - 14 cooled upstream of the supply point), air or steam.

Figure 11 shows another embodiment which is similar to that of Figure 1, but which has an additional carrier jet.

A jet pipe 222 with an orifice 223 is arranged at a point which, in relation to the direction of flow of the main current, is downstream of filament S. One pipe 222 can bo provided at each attenuating station, and may be supplied with gas through a duet 224 fed through a pipe 225. l'ho supplementary pipes 222 are used particularly when the distance of free fall of the filaments S is relatively great, and the supplementary carrier jets stabilise the filaments when they ai'rive near the interaction zones between the carrier jets from the orifices 36 and the main current 12A, With a supplementary carrier jet downstream, which has approximately the same dimensions as the first or upstream carrier jet and approximately the same pressure and velocity, the two carrier jets create induced currents as indicated by the arrows in Figure 11, these induced currents being distributed more or less symmetrically in relation to the filament S, and thus tending to maintain the filament in a stable position between the carrier jets as well as in relation to the point of entry into the interaction zone.

In all the abovo-deseribe.d embodiments, the orifice 36 is situated, in relation to the direction of flow of the main current, upstream of the glass supply means. Although this is the preferred position for the orifice 36, it is also possible to locate it in other positions in relation to the gliiss supply menus or in relation to the filament S. Tims, - 15 ί3347 the oi'ifice 36 may even he situated, in relation to the direction of fLow of the main current, in a position downstream of the glass supply means or of the filament S. In this case, the filament S will pass at the surface of the main current around and into the intci'action zone just downstream of the carrier jet, and will then he guided to the interior of the main current in this zone.

Claims (34)

1. CLAIMS;1. A process for making fibres from atfcenuable material comprising:- forming at least one stream of attenuable material and feeding it from delivery means; directing a main gaseous blast in a path transverse to the stream and spaced from the delivery means: directing at least one secondary gaseous jet of smaller cross section than that of the blast towards the latter, the secondary jet having a kinetic energy per unit of volume sufficient to cause it to penetrate the blast so as to form a zone of interaction, the stream of attenuable material being caused to pass across the space between the delivery means and the main blast so as to meet the blast at a point adjacent the zone of interaction.

2. A process according to claim 1, wherein the attenuable material is a thermoplastic material fed from the delivery means in molten state and wherein the said space is a free space and is such as to provide thermal insulation of the delivery means with respect to the main blast.

3. A process according to claim 1 or to claim 2, wherein the secondary jet is directed from a point in the space at a distance from an outflow orifice for the stream.

4. A process according to any preceding claim, wherein the stream passes by gravity across the space, the action of currents induced by the secondary jet facilitating guiding the stream into the interaction zone.

5. A process according to any preceding claim wherein the secondary jet is directed obliquely to tha stream so as to penetrate the boundary of the blast in the area where the stream meets the blast.

6. A process according to any preceding claim, wherein the space is enlarged by deflecting the path of the main blast in a direction away from the source of the stream.

7. A process according to any preceding claim, wherein the stream of attenuable material is downstream of the secondary jet relative to the direction of movement of the blast. 33 4 7

8. A process according to claim 1 or claim 2, wherein the tenuable material is caused to flow in the form of a layer, plurality of secondary jets being directed towards the blast as to form a plurality of zones of interaction, the secondary :s with the currents which they induce in the space dividing ί layer into streams which meat tha blast at points adjacent 3 zones of interaction.

9. A process according to any of claims 1 to 7 wherein jlurality of secondary jets are directed towards the blast so to form a plurality of zones of interaction, the attenuable :erial being fed over a notched overflow which produces a irality of streams which enter the zones of interaction .

10. A process according to any preceding claim, wherein additional gaseous jet is provided downstream of the or each earn of attenuable material in relation to the direction of w of the main blast, and is directed towards the interaction e to stabilise the stream entering that zone.

11. A process for the production of glass fibres comprising:plying by gravity a stream of molten glass from a supply fice; directing a main gaseous blast transverse to the stream a distance below the supply orifice; and directing a gaseous ondary jet of smaller cross-section than that of the main st and having a kinetic energy per unit of volume sufficient cause it to penetrate the blast so as to form a zone of interion, the secondary jet being directed from a point above the n blast obliquely downwards to create the zone of interaction in area in which the stream of molten glass encounters the main 3t.

12.. A process according to any preceding claim, wherein the Le of the or each secondary jet in relation to the main blast Less than 90°, which angle is included between the axis of the sach secondary jet and the direction of flow of the main blast.

13. A process according to claim 12. wherein the angle is

14. Apparatus for the production of fibres from attenuable rial, comprising:- first means to propagate a main gaseous t, second means to propagate at least one secondary gaseous 18 4-3 3 4 7 jet of smaller cross-section than that of the blast, which jet is directed so as to enter transversely into the main blast to form a zone of interaction, the kinetic energy per unit of volume of the jet being greater than that of the main blast; and delivery means including a supply orifice for delivering a stream of attenuable material and so positioned that there is a space between the blast and the delivery means, the supply orif ic e causing the stream to pass across the space to meet the blast at a point adjacent the zone of interaction.

15. Apparatus according to claim 14, wherein an outlet for the secondary jet is in the space above the upper boundary of the main blast and spaced from the supply orifice, the space being a free space.

16. Apparatus according to claim 14 or claim 15, wherein the orifice for the attenuable material is in the upper part of the free space and is arranged so that the stream passes by gravity across the free space.

17. Apparatus according to claim 15 or 16, wherein the secondary jet is directed obliquely to the stream so as to penetrate the blast in the area where the stream meets the blast.

18. Apparatus according to any of claims 14 to 17 comprising means for deflecting the main blast in a direction away from the orifice.

19. Apparatus according to claim 18, wherein a curved plate is situated at that boundary of the blast which is opposite the delivery means and guides the main blast so as to cause the latter to veer away from the orifice.

20. Apparatus according to claim 18 or 19 having means for supplying an additional jet acting to affect that boundary of the main blast opposite to that which the stream and the secondary jet enter.

21. Apparatus according to any of claims 14 to 20, wherein the said second means is in a position which, in relation to the main blast, is upstream of the stream of attenuable material. 19 13347

22. Apparatus according to any of claims 14 to 21, wherein the said second means comprises an outlet orifice which is separated vertically from the main blast and horizontally from the supply orifice.

23. Apparatus according any of claims 14 to 22, wherein the distance between the supply orifice and the boundary of the main blast is from 10 to 100 mm.

24. Apparatus according to any of claims 14 to 23, wherein the axial spacing between the supply orifice and an orifice of the or each secondary jet in tha direction of flow of the main blast is from 4 to 10 mm.

25. Apparatus according to any of claims 14 to 24 wherein the or each secondary jet orifice is at a distance from the main blast of from 5 to 10 mm.

26. Apparatus according to claim 22, wherein the axial spacing between the supply orifice and an orifice for the or each carrier jet in the direction of flow of the main blast is 3 to 4 times the diameter of the or each secondary jet orifice

27. Apparatus according to any of claims 14 to 26, comprising additional blower means in tha space downstream of the stream or streams of attenuable material in relation to the direction of flow of the main blast, the additional blower means directing an additional jet or jets so as to stabilise the stream or streams entering the zone or zones of interaction.

28. Apparatus for making fibres comprising·- means for generating a main gaseous blast; a plurality of fiberising centres associated with the blast and including means for supplying attenuable material to the region of the boundary of the blast, and each fiberising centra further including means for.directing a secondary gaseous jet of smaller cross-section than that of the blast into the latter transversely thereof, the kinetic energy per unit of volume of the jet being greater than that of the blast, and the supply means being spaced from the boundary of the blast and comprising a supply reservoir and means providing for overflow from the reservoir adjacent to the gaseous jets, thereby supplying the attenuable material at a plurality of the centres. - 20 4 3 3 4 7

29. Apparatus according to claim 28, wherein the means providing for overflow is a lip providing for overflow of a layer of the attenuable material.

30. Apparatus according to claim 28, wherein the means providing for overflow comprises a weir having a plurality of overflow grooves respectively delivering streams of attenuable material to positions adjacent the respective secondary gaseous jets.

31. Apparatus for the production of fibres from attenuable thermoplastic material comprising:- means for generating a main gaseous blast and for directing it generally horizontally; a reservoir for supply of molten attenuable material and having a plurality of supply orifices for the material spaced above the main blast, the orifices forming two sets, the orifices of each set being separated in the direction of flow of the main blast, and means for generating a plurality of gaseous secondary jets each smaller than the main blast,the kinetic energy per unit of volume of each jet being greater than that of the blast, and for directing the jets downwards into the main blast so that each jet enters the main blast at a point where a stream of attenuable material enters.

32. Apparatus according to claim 31, wherein the means for generating the secondary jets includes a set of orifices for delivering the jets, each orifice being spaced above the upper boundary of the main blast at a point which, in relation to the direction of flow of the main blast, is upstream of a stream of attenuable material, each jet orifice having its outlet axis inclined towards the stream at an angle such that the jet penetrates the said upper boundary at the point where the stream of attenuable material penetrates it.

33. A process for making thermoplastic fibre substantially as herein described with reference to the accompanying drawings. •13 3 I 7

34. Apparatus for snaking thermoplastic fibre constructed and arranged substantially as herein described and shown in tha accompanying drawings.