IE47242B1 - Manufacture of fibres by means of gaseous currents with economy of energy - Google Patents

Abstract

The process of manufacture of fibres from a mineral thermoplastic substance employs a main gas stream (27) and a secondary gas jet (29). The section of the secondary jet is smaller than that of the main stream but the kinetic energy per unit volume of the secondary jet is higher than that of the main stream. The secondary jet is directed transversely to the main stream and enters it to create a zone of interaction (Z) which includes turbulent streams. A lace of ductile substance (34) is brought into this zone by the secondary jet. In the interaction zone the streams of gas contain oxidising fuel components introduced from the duct (35) by the nozzle (36) in proportions which result in a combustible mixture. The lace of ductile substance is brought into the zone (Z) at a temperature which is at least equal to the ignition temperature of the mixture. The process is employed especially for making fibres from glass.

Description

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, more particularly mineral materials such as glass or similar compositions which are melted by heating. However, since the apparatus according to the present invention is more particularly of interest for the attenuation of glass and similar thermoplastic materials, the description will be given with reference to glass by way of example.

Certain techniques employing whirling currents to produce fibres by the attenuation of molten glass are already known.

In particular, the publication of French Patent No. 15 2,223,318 describes the formation of pairs of counterrotating tornadoes in a zone of interaction produced by • . directing a gaseous jet known as secondary jet or carrier jet to a main gas current of larger dimensions and causing ' * it’to pfenetrate said current, a stream of molten glass being a delivered into this zone to be attenuated there.

Various types of apparatus used for the attenuation of a material in a zone of interaction have already been described in the above mentioned patent and in Patent Nos. 43838 and 45953 · In all these cases, a gaseous flow or jet which has a greater kinetic energy per unit volume than a main current is caused to penetrate this main current, the jet also having a smaller cross-section transversely to the main current than the latter. A stream of attenuable material is introduced into the zone of interaction of the jet with the main current either directly by gravity or by first delivering the stream into the gaseous jet to be thereby carried into the zone of interaction.

In the analysis which follows, account will be taken of the fact that attenuation of thermoplastic materials such as glass must of necessity be carried out at a high temperature. The glass is thus melted by heat, for example at a temperature above ca. 1250°C., and, in order to obtain high yields, the temperature of the attenuating gas in contact with the stream of material and with the forming fibre should also be sufficiently high to maintain the glass at the high temperature required for attenuation.

In the publication of French Patent No. 2, 223,318, the secondary gas jet and the main current are both at relatively high temperatures, for example about 800°C for the jet and 1580°C for the main current.

Although Patent No. 43838 describes the possibility of using low temperatures for the jet, for example in the region of room temperature, it provides relatively high temperatures for the main current, such as those mentioned above.

However, given that, on the one hand, the main current contains large volumes of gas and, on the other hand, only a portion of this gas is used for attenuation of the thermoplastic material in the zone of interaction, heating of all the gas in the main current to relatively high temperatures entails considerable losses of energy or heat.

TO This energy loss is prevented by the technique according to the present invention which, in contrast to the known technique, not only enables a jet to be employed at a low temperature but also enables a main current at a relatively low temperature to be used. According to the present invention, localised combustion of a fuel is effected in the immediate vicinity of the stream of material in the zone of interaction of the jet with the main current so that the desired temperature of attenuation may be reached and maintained in this zone without the whole of the main current having to be heated. The temperature of the gas emitted by the main current generator may therefore be considerably reduced, with a consequent saving in energy.

The technique of the present invention, referred to as localisation of energy, results in a substantial economy of energy as well as having other advantages. For example, it makes possible the rapid cooling of the fibres after attenuation, whereby the mechanical resistance of the fibres is .increased in the case of a large number of thermoplastic materials. This characteristic also enables very long fibres to be obtained, a result which is particularly desirable for certain applications.

Other advantages of the invention will appear in the course of the description relating to various embodiments of the apparatus illustrated in the drawings.

Figure 1 is a schematic view in elevation of the main elements of an apparatus which may be used according to the invention for the formation and reception of the fibres, in which apparatus a pair of jets is employed at each fibre forming centre, certain parts of the apparatus being shown in section; Figure 2 is a schematic perspective view on a larger scale, illustrating the mode of operation of the fibre forming apparatus of Figure 1; Figure 3 is a vertical section on an englarged scale of the elements constituting a fibre forming centre, taken through the plane of the jet emission orifices; Figure 4 is a vertical section through the elements of a fibre-forming centre of another embodiment of the apparatus which may be used according to the invention 47243 which has also been described in the above mentioned Patent No. 45953 Figure 5 is a schematic view in perspective illustrating tlje mode of operation of the apparatus of Figure 4; Figure 6 is a plan view of several adjacent jets and portions of the main current corresponding to Figure 4 and 5 but omitting the supply of glass and the fibres in the course of formation,Figure 7 is a view similar to that of Figure 4 but containing an additional part; Figure 8 is an elevational view partly in vertical section representing the adaptation of characteristics of the present invention to a fibre forming apparatus such as that shown in Figure 11 of French Patent Publication No. 2,223,318. Figures 9a and 9b are schematic sections through a fibre forming centre, Figure 9a illustrating the conditions and process of fibre formation in a zone of interaction without localisation of energy while Figure 9b represents the same fibre forming centre but using the technique of localisation of energy according to the invention; Figure 10 is a graph showing an advantage of the present invention obtained when it is applied to the formation of fibres from certain types of mineral 47342 thermoplastic materials.

In the detailed description which follows, reference will first be made to the apparatus represented in the drawings, and the aspects relating to the localisation of energy in the operation of this apparatus will then be analysed.

Referring first to Figure 1, it represents schematically a main current generator 8 such as a burner equipped with a nozzle 9 which emits, a main current 10 in an approximately horizontal direction although the current may, of course, be emitted in other directions.

A collector 13 connected to a jet manifold box 11 by a connection 12 supplies the said manifold box with compressed gas, for example, compressed air. As can be seen in Figures 2 and 3, the jet mainfold box 11 comprises pairs of orifices 14 and 15 for the emission of jets, successive pairs of orifices being indicated by the references 14a - 15a; 14b - 15b; 14c - 15c; 14d - 15d; 14e - 15e. The jets emitted from these pairs of orifices are indicated by the corresponding letters. Figure 2 shows in perspective view three pairs of jets, whereas Figure 1 and 3 show only one pair of jets a - a. To each pair of jets corresponds one 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 and 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 progresses downwards and penetrates the main current 10, producing with the latter a zone of interaction which is used for a second stage of attenuation.

A source of supply of glass is indicated 10 schematically at 16 in these figures. It comprises a bushing 17 having a series of glass supply tips 18 arranged at intervals, each comprising a feed orifice 18a and, upstream thereof, a metering orifice 19. The glass is thus delivered in the form of bulbs G from which the streams of glass S flow downwards, each fibre forming centre comprising one bulb and one stream of glass. The fibres formed from a series of fibre forming centres distributed transversely over the width of the main current 10 are subsequently deposited on a perforated conveyor or belt 20 in the form of a mat of fibres B. The distribution of the fibres on this conveyor is brought about inside a chamber bounded, for example, by a wall 21, by the action of the suction chambers 22 preferably situated below the conveyor 20 and connected by conduits 23 to one or more suction fans represented schematically at 24. The formation of fibres carried out with the above apparatus is explained and analysed in more detail with reference to Figures 2 and 3.

As already mentioned above, the process proper to each fibre forming centre is preferably connected to the action of the jets of adjacent centres. Figure 2 represents the complete process of attenuation for the fibre forming centre corresponding to the jets b - b and only part of the process for the fibre forming centres corresponding 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 mode of operation, it should first be recalled ' that any gas jet induces a movement of surrounding air when it is emitted from an orifice. Each of the jets a therefore comprises a central part or core j surrounded by an envelope of gas containing the induced air indicated by the letter i. This envelope rapidly grows in size as the flow of the jet progresses while the core of the jet remains the relatively short central part in the form of a cone. The gas forming the core of the jet has a velocity equal to that of the jet at the moment when it leaves the orifice although the velocity of the gas in the envelope diminishes progressively as the flow progresses. The arrows represented in Figures 2 and 3 indicate the influx of air caused by the flow of the jets and by the flow of the main current.

When a pair of jets having approximately the same kinetic energy per unit volume and preferably also approximately the same dimension is used and the two jets have their axes situated in the same plane and converging so that they impinge against each other, preferably at an acute angle, the combined flow spreads out laterally downstream of the region of impact of the two jets, that is to say they spread out in directions transverse to the plane of the axes of the jets.

The pair of the jets or the planes containing their axes are sufficiently close together so that at each fibre forming centre the lateral spreading out of the combined flow from a pair of jets is restricted or limited by impact on the flow of pairs of adjacent jets as they spread out. This impact between adjacent combined flows results in the development of two pairs of small tornadoes in each flow, the origins of the tornadoes of a pair being situated at some distance from each other on either side of the plane of the axes of the jets.

Upper and lower pairs of tornadoes are represented schematically in Figures 2 and 3. The tornadoes of the upper pair, indicated by the reference tu - tu, are formed by currents turning towards each other in the upper part of the tornadoes and away from each other in the lower part. The tornadoes of the lower pair, on the other hand, which are indicated by the letters tl - tl, turn in the opposite senses to those of the upper pair.

Between the two pairs of tornadoes, in the region of impact between the jets, there is formed a zone L of laminar flow associated with these tornadoes, at the level of which zone the influx of induced air is very intense, and it is precisely in this zone of laminar flow, beside the upper tornadoes, that the stream of glass S is introduced. This stream is formed from the bulb or cone of glass G which is somewhat shifted in position from the jet emitter. However, since the bulb of glass G is in an attenuable or fluid state when it leaves the supply tip, the stream of attenuable glass S is carried from the initial position of the bulb towards the zone of laminar flow L due to the intense influx of induced air, and this effect ensures that the stream of attenuable material will be taken into the laminar zone. Consequently, even if there is a slight fault of alignment of the glass supply tip 18 in relation to the pair of jets, the influx of induced air will automatically compensate for this fault and carry the stream of glass into the appropriate position.

It will thus be understood that by the formation of at least one pair of tornadoes bordering on a zone of ίΰ tt . *3 re laminar flow at each fibre forming centre and by the delivery of the material in an attenuable state into a region adjacent to the said zone, the stream of material is automatically carried into this zone by the currents of induced air which, as mentioned above, automatically compensate for any faults in alignment, so that the introduction of attenuable material into the system is stabilized. This stability is achieved even when the glass supply tips are placed at some distance from the jet emitters, which distance is desirable in that it helps to control and maintain both the glass supply tips and the jet emitters at the desired temperature.

Downstream of the laminar zone L, the two tornadoes tu - tu as well as the tornadoes tl - tl tend to merge and as the flow progresses downstream they tend to lose their identity, as represented in Figure 2 in the portion showing the two pairs of tornadoes which originate from 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 from the pair of jets b - b. The resulting combined jet then forms the zone of interaction with the main current inside the latter, as has already been analysed in detail in the Patent publication No. 2,223,318 mentioned above. This zone contains an additional pair of tornadoes T.

It should be noted that each plane containing the axes of jets of one pair intersects the main current preferably in a straight line virtually parallel to the direction of .propagation of the latter.

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 subsequently subjected to an additional attenuation in the zone of interaction of the aforesaid flow with the main current. It will be seen from the figures that these two stages of attenuation take place without fragmentation of the stream of glass, so that each stream produces a single fibre.

In order that the process described above may be achieved at each fibre forming centre, particularly the formation of pairs of tornadoes each bordering on a zone of laminar flow, there is used a pair of jets which preferably have the same kinetic energy per unit volume. The cross-sections of these two jets also preferably 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 practically the same. Furthermore, the cross-sections of the tvzo 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 direction parallel to and in the direction perpendicular to the plane containing their axes, and these dimensions need not necessarily be 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 close to each other in the core of the jet and in both jets of one fibre forming centre. Furthermore, it is desirable that adjacent pairs of jets have substantially the same dimensions in order to enable uniform formation of pairs of tornadoes bordering on the zones of laminar flow to take place when each combined flow impinges on the adjacent flow when spreading out laterally. Having the jets of successive fibre forming centres identical enables uniform and homogeneous fibre forming conditions to be obtained in the various zones of interaction produced by penetration of the jets into the main current .

In order that penetration may take place, the combined flow must have a kinetic energy per unit volume greater than that of the main current when it reaches this current.

It will also be noted that the jets grouped into pairs should have certain specific characteristics in order to form the zone of laminar flow in which the stream of glass can be introduced without fragmentation. In fact, it is important that the axes should be situated virtually in the same plane and meet in this plane preferably at an acute angle.

In the system described above with reference to Figures 1, 2 and 3, the characteristics relating to the localisation of energy may be used in various ways. Firstly, it is provided according to the present invention that the currents of gas in the zone of interaction formed by penetration of the jet into the main current should contain combustible components and combustion-supporting components in such proportions that the mixture is combustible. The combustible and the combustion-supporting components are preferably present in approximately stoichiometric proportions in the immediate vicinity of the attenuable material. The manner of introducing these components into the zone of the interaction will be described in detail later after the description of the other embodiments of the apparatus represented in the drawings.

Reference will therefore be made to the apparatus shown in Figures 4, 5 and 6, which has also been described in * Patent No. 45953 . In the latter, a series of secondary gas jets or carrier jets is produced and a deflector is associated with them. The jets are thereby deflected or directed towards a main current which they penetrate, and the streams of glass are introduced into the flow of the jets to be carried by them into the corresponding zones of Interaction formed in the main current. Referring first to Figure 4 which illustrates schematically the main elements of a fibre forming centre, the left part of the figure shows part of a burner or generator 25 comprising a nozzle 26 emitting a main current 27. A jet manifold box 28 has a series of emission orifices 29 through which the jets indicated by the letters a, b, c and d in Figure 5 are emitted. The manifold box 28 may be supplied with fluid under pressure by way of the connection 31 connected to the supply pipe 30. On this manifold box 28 is mounted a deflector plate or flap 40 which covers the series of jets and the edge 41 of which is in such a position that the jets impinge against the deflector.

A bushing 32 associated with a forehearth 33 or other suitable means of supplying glass comprises supply tips 34, and a stream of glass is directed to each flow of jet described below, to be carried downstream to the zone of interaction with the main current 27. As explained in the description, fibre formation takes place in the jet but also in the main current, and the latter then delivers the fibres to the right as represented in Figure 4 to form a sheet or mat which is deposited on a perforated conveyor belt or the like.

The nozzle 26 which emits the main current has a wide outlet orifice. The bushing 32 is also preferably large in the direction perpendicular to the plane of Figure 4 and is capable of supplying glass to all the tips 34.

The jets emitted from the emission orifices 29 are deflected or guided by means of a deflector which cooperates with these jets to produce pairs of counter15 rotating tornadoes which are used at least for the primary attenuation but also for conducting the partly attenuated streams into the zones of interaction produced by penetration of the jets into the main current. The deflector plate 40 is associated with a group of jet emission orifices for the purpose of producing the pairs of counterrotating tornadoes in the jets. As may be seen particularly in Figure 5, the deflector plate preferably takes the form of a bent sheet, one part of which covers the jet manifold box to which it is fixed while the other part has a free edge 41 placed in the path 2 42 of the jets which are emitted from the orifices 29 and advantageously placed along a line which occupies the axes of these jet orifices.

This position of the deflector plate 40 and of its 5 edge 41 causes each of the jets to impinge against the inner surface of the plate 40, thereby causing the said jets to spread out. Figure 5 shows the flow of four of the jets emitted from the orifices a, b, c and d, and it will be noted that each of these jets spread out sideways as it approaches the edge 41 of the plate.

It is provided that the emission orifices 29 for the jets should be sufficiently close together and the deflector should be so arranged that at the moment when adjacent jets spread outwards, they impinge against each other in the region of the edge 41 of the plate.

Preferably, as shown in Figure 5, this mutual impingement of adjacent jets takes place as closely as possible to the free edge 41 of the deflector plate 40. This results in the formation of pairs of counter-rotating tornadoes which are represented in Figure 5 in association with each of the three jets emitted from the orifices a, b and c.

To analyse the formation of tornadoes in each jet, particular reference will be made to the tornadoes 42b and 43b associated with the jet from the orifice b. It will be noted that these tornadoes have their origins situated substantially at the edge of the deflector plate 40, on opposite sides of the jet, close to the zone in which the jet on spreading out impinges against the adjacent jets emitted from the orifices a and c which are also spreading out. The tornadoes 42b and 43b are counter-rotating and enlarge as they progress until they meet at some distance downstream of the edge 41 or the deflector plate. These tornadoes 42b and 43b also have a component directed downstream.

Due to the distance between the origins or points of formation of the tornadoes 42b and 43b and their progressive increase in size, an approximately triangular zone 44b forms between the tornadoes and the edge of the deflector plate. This triangular zone is at a relatively low pressure and is subjected to a powerful influx of induced air, but its flow nevertheless remains quasilaminar. It is in this zone that the stream of molten glass or other attenuable material is introduced, and, due to the laminar nature of the flow in this triangular zone, the stream of glass is not fragmented but is carried into the region situated between the two tornadoes.

The senses of rotation of the currents in the tornadoes of jets 42b and 43b are opposite to each other, the tornado 42b rotating clockwise as represented in Figure 5 while the tornado 43b rotates counter-clockwise.

The currents in these tornadoes therefore move towards each other in the upper part and then flow downwards in the direction of the central or laminar zone 44b.

The senses of rotation described above are indicated by arrows in the pair of tornadoes 45a and 46a associated with the jet issuing from orifice _a, Xt should be understood that the flow of the jet from the orifice a is represented by a section taken at the level of the dotfntstream end of the zone of laminar flow 44a, that is to say close to the zone in which the two tornadoes begin to merge after they have increased in size, this phenomenon of merging increasing progressively as the jet flows downstream. It will also be clear that the flow of the jet from the orifice a comprises not only the pair of tornadoes 45a and 46a but also a pair of tornadoes 47a and 48a which also rotate in senses opposite to each other, as represented in Figure 5, but the tornado 48a rotates clockwise while the tornado 47a rotates counterclockwise. It should be understood that such double pairs of tornadoes are produced by each of the jets and one such double pair is associated with each jet.

With reference to Figure 5, it will be noted that when the flow progresses from the plane representing the tornadoes associated with the orifice a, the four tornadoes tend to merge and reform a less well defined flow, as shown by the section 49c taken across the flow of the jet from orifice c. The whirling movements decrease in intensity and the whole flow, including the laminar flow from the central zone of the jet, merges in the region indicated as 49c, the jet then progressing downstream towards the main current 27.

In Figure 5, the representation of the various portions of the jet has been schematised for the sake of clarity. For example in the zone situated slightly downstream of their origin, the pairs of tornadoes formed in a jet appear to be at a slight distance from the pair of tornadoes formed in each adjacent jet although in reality the various tornadoes are virtually contiguous.

Due to the form of flow of the jet in the laminar zone and in the pairs of tornadoes and particularly in the upper pair of each group, introduction of the stream of attenuable material indicated by the reference S for the fibre forming centre containing the jet orifice b results in delivery of this stream into the laminar flow of the central zone. This carries the stream into the zone of high velocity situated between two tornadoes and consequently the stream is attenuated as shown in Figure 5 This attenuation takes place substantially in a zone corresponding to the plane P. The pairs of tornadoes of a 47243 jet exert a whipping action on the attenuated fibre substantially in the zone of plane P so that the forming fibres are not thrown against adjacent jets.

The jet then flows through the upper boundary of 5 the main current 27, carrying with it the fibre which is in the process of attenuation, and this jet must have a sufficient kinetic energy per unit volume to penetrate the main current.

A second stage of fibre formation then begins, which takes place according to the principles set forth in detail in the above mentioned French publication 2,223,318.

It should be understood that in the region of penetration of the secondary jets into the main current, the flow and velocity of each jet still remain sufficiently concentrated near their axis so that each of the jets develops its own individual zone of interaction with the current. In Figure 5, therefore, a pair of counterrotating tornadoes indicated by TT is produced in the zone of interaction, which causes the formation of currents which effect additional attenuation of the forming fibre. This fibre is then carried to some suitable means of reception, for example, the conveyor 20 of Figure 1, by the combined flow of the jet and the main current.

In Figure 5, the induction of air is represented by arrows directed in the sense of the flow of the jet, and it will be seen not only that the air is induced in the laminar zone adjacent to the edge of the deflector plate but also that this induction continues as the jet flows downwards.

The operating conditions which may be employed in the process according to the invention with the apparatus described above are given in the description which also defines the ranges within which these conditions may vary.

As with the first embodiment of the apparatus described above, the combustible and combustion-supporting components may be introduced into the system of Figures 4, 5 and 6 in different ways which will be described later.

The description will first refer to the apparatus represented in Figure 7 which carries the same reference numerals as Figure 4 for the parts which they have in common.

An additional device appears in Figure 7 for the introduction of the combustible or combustion-supporting components into the zone of interaction. A feed pipe 35 for fuel and/or combustion-supporting component is connected to a series of emission nozzles 36 which are spaced apart and directed towards the main current so as to deliver the fluid into a region adjacent to the zone of interaction Z and immediately upstream thereof. In 47342 Figure 8, the main current produced by a generator 50 is delivered by a nozzle 51 into a zone which is limited above by a plate 52 and below by a plate 53 which is curved downwards away from the midplane of the main current Cooling tubes 53a may he mounted on this lower plate if desired. a bushing 55 for supplying glass is provided with a series of orifices 56 arranged at intervals along the width of the main current transversely to the direction of propagation so as to deliver the streams of attenuable material into this main current. Just upstream of the glass supply orifices, the upper plate 52 has a series of jet emission orifices 29 each of which is associated and aligned with a corresponding glass supply orifice. The orifices 29 are supplied with compressed fluid from a collector 54 connected to the conduits 54a and 54b.

The plate 52 also comprises another collector 57 connected to a series of successive orifices 57a arranged transversely to the main current and each associated and aligned with a glass supply orifice 56 and the corresponding jet emission orifice 29.

This collector 57 is supplied with gaseous fuel by a conduit 59 which may be connected to a main supply 60.

A plate 58 arranged downstream along a peripheral region of the main current constitutes an upper boundary to the latter and has a cooling tube 58a. Some of the elements of this apparatus are analogous to those represented in Figure 11 of the prior Patent publication NO. 2,223,318.

In the embodiment of Figure 8, the fuel is introduced through, for example, the orifices 57a while the air used for the secondary jets arrives through the orifices 29 so that a mixture of fuel and combustionsupporting component can be obtained in the zone of interaction with the main current.

Furthermore, an additional supply of air may be introduced into the main current upstream of the zone of interaction through upper and lower feed channels 61 and 62, respectively, situated in the region where the main current generator 50 is connected to the nozzle 51. Each feed channel ends in a slot or plurality of feed orifices indicated schematically at 63. This introduction of additional air into the main current serves in particular to afford certain advantageous conditions, for example a suitable temperature of the main current, which conditions are connected with the technique of localisation of energy. When combustion of the fuel takes place in the zone of interaction, it is not necessary to use main current at such a high temperature as that required in the absence of this localised combustion.

A considerable saving in the fuel required for the formation of the main current can therefore be achieved.

It is obvious that for producing a main current at a relatively low temperature and at the desired velocity, it is possible, instead of having recourse to the introduction of additional air,' to eliminate the use of a burner completely and replace it by an other system comprising for example, a device with a heat exchanger in which the gas for the main current is heated.

Before considering other means of carrying the fuel and combustion-supporting component reference will first be made to Figures 9a and 9b which will be compared to analyse the process of localisation of energy according to the invention and the resulting saving in energy or fuel.

Figure 9a represents the conditions under which attenuation takes place -in a zone of interaction between a jet and a main current in the absence of the technique of localisation of energy. An emission nozzle 64 produces a main current which is preferably of considerable width, that is to say large in a direction perpendicular to the plane of the figure, so that several pairs of glass supply devices 66 and jet emitters 65 may be associated with the main current to produce a large number of fibres. The stream of glass and the secondary jet are indicated by the reference S and J respectively, and the zone of 47342 interaction between the jet and the main current is indicated by the reference Z. With such a system and using a conventional glass composition, the temperature of the jet may be either about 800°C (as described in Patent publication No. 2,223,318) or very much lower and close to room temperature (as in Patent No. 43838 . In both cases, the temperature of the main current varies from 1500 to 1750 °C according to the of the jet so that the desired temperature temperature/for attenuating the stream of glass is obtained in the zone of interaction. On Figure 9a is indicated a temperature of 1700 °C in the vicinity of the lips of the nozzle for the main current, the core C of which current extends to the zone of interaction with the jet although the zone in which attenuation properly speaking takes place is at a temperature between that of the main current and that of the jet. Downstream of the zone of interaction, the successive isothermal lines represent the progressive fall in temperature, for example, 1600, 1400 and 1200°C.

Figure 9b exactly represents the same elements of the apparatus as Figure 9a but it shows the conditions which prevail when the technique of localisation of energy according to the present invention is employed.

For this purpose, the jet emitter 65 may be supplied with a mixture under pressure containing a combustible gas while additional air or oxygen may be carried by the nozzle 64 providing the main current, the gases for the main current being at a much lower temperature at the moment of their emission than the temperature employed under the conditions of Figure 9a. For example, the temperature of the main current may be about 600°C at the outlet of the nozzle, as shown by the isothermal lines, and the temperature of a large proportion of the gas then decreases, for example to values of about 400, 300 and 200°C, in the zones situated downstream of the nozzle, which correspond to those of the isothermal lines 1600, 1400 and 1200eC in Figure 9a.

Although it would be possible to carry the fuel with the main current, it is preferred that this fuel constitutes part of the secondary jet, that is to say that it be introduced into the gas of the secondary jet, as described above. The jet J therefore serves not only to produce the zone of interaction into which the stream of glass S is delivered but it also carries into this zone a combustible component which is intimately mixed with the combustion-supporting component, in particular with the excess of air, which is brought into the zone of interaction by the main current. By virtue of the presence of whirling currents in the zone of interaction, it is possible to obtain the very intimate mixture desired.

As regards the proportions of fuel and combustion-supporting component, it should first be noted that stoichiometric proportions are preferably used. However, a combustible mixture may also be obtained with proportions which are not stoichiometric.

In the case of a mixture with natural gas, for example, the quantity of air may vary within a range of 0.8 to 1.7 times the quantity of air corresponding to stoichiometric proportions. These suitable quantities of combustion-supporting component and fuel form a combustible mixture in the zone of interaction whose ignition point is lower than the temperatures of the compositions of molten glass normally employed for fibre formation, so that the stream of glass carried into the zone of interaction is capable of igniting the combustible mixture formed therein. The desired temperature, for example 1700°C, can therefore be reached in the zone of interaction Z so that attenuation of the stream of material and its conversion into fibres can be carried out although the temperature of the main current both downstream and upstream of the said zone is very much below this value. It will also be noted that the zone of interaction produced with each of the jets may comprise only a very small proportion of the total volume of main current. Since it is only this proportion which must reach the high temperatures required for attenuation, a very great saving in energy is achieved by the technique according to the invention compared with the systems in which the total volume of main current is raised to the attenuation temperature.

It is also important to note that the technique of attenuation in a zone of interaction is particularly well adapted to the localisation of thermal energy due to the presence of a region of low pressure and low velocity which is formed in the immediate vicinity of each stream of glass and generally surrounding the latter without the need to interpose any other material element.

The fuel or the combustion-supporting component may thus be injected into the zone of interaction to form the combustible mixture while the presence of hot glass enables the mixture to be ignited. The current swirling at high velocity, or tornadoes, which are characteristic of the zone of interaction, are used in the technique of localisation of energy to effect intimate mixing of the fuel and combustive, as already described above. Furthermore, since these whirling currents move sometimes in the same sense as the current and sometimes in countercurrent thereto, regions of relatively low flow velocity compared with that of the main current inevitably exist in the zone of interaction. The existence of such regions of low flow velocity constitutes one of the conditions for ignition of the combustible mixture and maintenance of stable combustion. The importance of this characteristic will be underlined by recalling that with a mixture of natural gas and air, the velocity of propagation of the flame is from about 0.3 to several metres per second at 20°C. Although this velocity of propagation of the flame increases with an increase in temperature, it always remains very low compared with the velocity of the main current.

Nevertheless, since the zone of interaction is also characterised by the presence in certain regions of a flow at a lower velocity than the velocity of propagation of the flame, it is possible to ignite the combustible mixture and maintain stable combustion. The reasons given above appear to explain the phenomena of ignition and of stability of combustion in the zone of interaction but other explanations for this phenomenon can probably be found.

In the system described with reference to Figure 9b, the flame front tends to adhere to the source of ignition, that is to say to the stream of glass itself or to the stream of material which it is desired to raise to or maintain at the desired attenuation temperature. This attachment of the flame can be achieved, firstly because 47343 the temperature of the glass is very much higher than the ignition temperature of the mixture and may, for example, reach double the latter and secondly because a boundary layer of combustible mixture develops in contact with the surface of the stream of glass, which boundary layer is brought to the conditions of ignition by the heat released by the glass. Consequently, the glass is surrounded by a layer of combustion which releases in the adjacent layers and in the zone of interaction a localised and stable combustion which remains attached to the stream of glass during its attenuation.

Since a large part of the heat exchanges with the stream of glass takes place by contact of the hot gases with its surface, the technique according to the present invention is an efficient means of ensuring the transfer of heat necessary for maintaining the stream of glass in an attenuable state since the zone in which intense heat is released is precisely that which immediately surrounds the said stream.

Another advantage of the process according to the invention consists in that in the case of a large number of glass compositions the mechanical resistance of the fibres produced increases if the temperature of the fibre is rapidly reduced at the end of attenuation. These favourable conditions are here realised, as shown clearly by the isotherms in Figure 9b.

In the apparatus represented in Figures 1, 2 and 3, the pair of jets a-a may thus contain the combustible component necessary for attaining the desired result and it consequently serves not only to deliver the glass Into the zone of interaction with the main current but also to introduce the fuel into this zone, while the air may be conducted into the system by means of the main current 10 as in Figure 9b. In this way, and by choosing temperatures for the jet and the main current in the region of those indicated above with reference to this figure, the desired localisation of energy and fuel economy can be obtained.

In the embodiment represented in Figures 4, 5 and 6, it is possible, if desired, to introduce all the combustible component with the gaseous jet while the air may be carried with the main current, preferably with a simultaneous lowering of the temperature of said current to values such as those suggested above with reference to Figure 9b for the sake of maximum saving of energy.

In the embodiments of Figures 7 and 8, the fuel may be introduced independently of the jet, that is to say separately, as already mentioned. The combustionsupporting component, for example, air may be carried either by itself or by the main current or by both.

Figure 8 represents an embodiment of the apparatus used for introducing air with the main current, in which air is added to this flow close to the emission nozzle 51. By these means, the total volume of gas required and the desired temperature can be obtained by burning only a small volume of the gas provided for'forming the main current, the process of localised combustion according to the invention then taking place in the zone of interaction surrounding the streams of material so that the elevation in temperatures required for attenuation is produced locally, as explained with reference to Figure 9b.

The process of localisation of energy according to the invention has also had particular advantages for the attenuation of certain types of material, such as certain types of rocks and other natural mineral or synthetic materials for which the range of attenuation temperature is particularly narrow. In the graph in Figure 10 are entered the variations of viscosity ij as a function of the temperature t for two different types of attenuable material, 10a being the graph obtained for a glass conventionally used for fibre formation while 10b correspond to a natural rock for which the temperature range at which suitable viscosities are obtained is very narrow. It can be seen on this graph that the viscosity range between the points A and B within which attenuation can take place corresponds to a much wider temperature range (ta - t^) in the case of glass than in the case of the rock (temperature range t'a - t'b’· By introducing the fuel in a suitable quantity into the zone of interaction with the main current, the zone at which a suitable temperature for attenuation of the rock or any other suitable material is obtained can be extended downstream, thereby making it easier to maintain the desired viscosity for a longer period.

As regards the apparatus or the processes of attenuation represented in Figures 1 to 3, 4 to 6 and 7, in which the stream of attenuable material is subjected to the action of the jet before the jet enters the main current, it should be noted that even if the fuel and combustion-supporting component are both present in the flow at the point where the stream of attenuable material is conducted into this flow, ignition does not necessarily take place there. It may even, depending on the various operating conditions chosen, such as the temperature of the jet and its velocity, for example, only take place when the jet has reached the main current or has penetrated it.

The values for the various parameters given in the description correspond to the operating conditions which may he used according to the invention and they illustrate the invention without in any way limiting it.

In particular, although the fuel mentioned by way of example is natural gas, a synthetic gas or a mixture may be used and certain liquid fuels may also be used in an atomised or vaporised form.

With a fibre forming centre of the type represented in Figures 1 to 3, the main current 10 is produced from •10 heated and compressed air and is at a temperature of about 600°C. Its velocity is in the region of 300 m/s and its pressure approximately 0.18 bar. The axes of the two secondary jets are at an angle of 60°C. One of these jets contains a mixture of 1 part by volume of natural gas and 3 parts of air while the second jet consists of 4 parts by volume of air. The temperature of the jets is around 20°C and the jets have a velocity in the region of 330 m/s and a pressure of approximately 2.5 bar. The stream of glass is raised to a temperature of around 1300°C.

With a fibre forming centre as described in Figure 7, the same conditions as those mentioned above may be used for the main current 27. The jet consists of air at a temperature of 20 °C, a velocity of 330 m/s and a pressure of 2.5 bar. In this case, natural gas is supplied by the emitter device 36 at a pressure of around 0.5 bar and a velocity of 200 m/s. The glass is supplied from the supply tip 34 at a temperature in the region of 1300°C.

Claims (20)

1. CLAIMS:1. Process for the manufacture of fibres from a mineral thermoplastic material, in which are produced a main gas current and a secondary gas jet whose cross-section transversely to the main current is smaller than the latter, the kinetic energy per unit volume of the secondary jet being greater than that of the main current, the jet being directed transversely to the main current and penetrating therein to produce a zone of interaction which comprises whirling currents and along which a stream of attenuable material is carried into the said zone, characterised in that the currents of gas in the zone of interaction contain combustible and combustionsupporting components in proportions suitable to produce a combustible mixture, and in that the stream of attenuable material is delivered into the said zone at a temperature at least equal to the ignition temperature of the said mixture.

2. Process according to claim 1, characterised in that the combustible and combustion-supporting components are in approximately stoichiometric proportions in the zone of interaction.

3. Process according to claim 1 or claim 2, characterised in that one of the said components introduced into the zone of interaction constitutes at least part of of the jet or of the main current.

4. Process according to one of the preceding claims, characterised in that one of the components introduced into the zone of interaction constitutes at least part 5. Of the jet, the other component introduced into this zone constituting at least part of the main current.

5. Process according to one of the preceding claims, combustible component characterised in that the / introduced into the zone of interaction constitutes part of the jet and the 10 combustion-supporting component at least part of the main current.

6. Process according to one of the claims 1 or 2, characterised in that the combustion-supporting component introduced in to the zone of interaction 15 constitutes part of the secondary jet or of the main current and in that the combustible component is introduced into the said zone, producing a jet of gaseous fuel under pressure directed towards the main current and entering the region of the zone of interaction. 20

7. Process according to claim 6, characterised in that the jet of fuel directed towards the main current enters the said current at a point situated upstream of the secondary jet.

8. Process according to claim 1 or claim 2, 25 characterised in that the combustible component is introduced into the zone of interaction, producing a jet of gaseous fuel under pressure directed towards the main current and entering therein upstream of the secondary jet, and in that the combustion-supporting 5 component is introduced into the main current in the form of air carried under pressure into the latter upstream of the said jet of fuel.

9. . Process according to one of the preceding claims, characterised in that the temperature of the main current 10. In a region situated upstream of the zone of interaction is lower than that of the stream of attenuable material carried into the said zone.

10. Process for the manufacture of fibres from a mineral thermoplastic material, in which are produced 15 a main gas current and at least one secondary gas jet whose cross-section transversely to the main current is smaller than that of the latter, the kinetic energy per unit volume of the or each secondary jet being greater than that of the main current, the jet or jets being 20 directed transversely to the main current and penetrating said current to produce a zone or zones of interaction containing whirling currents and in which a stream of attenuable material is conducted into the said zone or zones, characterised in that the currents of gas in the 25 zone of interaction contain combustible and combustion40 supporting components in proportions such that they form a combustible mixture, which mixture is ignited in the said zone.

11. Process according to claim 10, characterised in that the combustion-supporting component is introduced into the zone of interaction in the form of at least part of the main current, the combustible component being introduced into the said zone independently of the jet and of the main current.

12. Process for the manufacture of fibres from a thermoplastic material according to claim 10, in which there is produced a plurality of secondary gaseous jets.

13. Process according to claim 12, characterised in that each zone of interaction is supplied with fuel by the corresponding secondary flows.

14. Process according to claim 12, characterised in that each zone of interaction is supplied with combustionsupporting gas by the corresponding secondary flows.

15. Apparatus for the manufacture of fibres from a mineral thermoplastic material, comprising: A generator or main current; a device emitting a secondary gas jet, equipped with an emission orifice whose dimension or width transversely to the main current is smaller than that of the outlet orifice for said current, the jet being directed so as to intersect the main current and penetrate it to produce a zone of interaction; and a source of supply delivering a stream of molten material into the zone of interaction, characterised in that it comprises a device for introducing fuel into the zone of 5 interaction.

16. Apparatus according to claim 15, characterised in that the device for introduction of the fuel is provided with an orifice placed at the boundary of the main current.

17. Apparatus according to claim 15, characterised 10 in that the device for introduction of the fuel comprises an emitter whose orifice is situated at a distance from the boundary of the main current.

18. Apparatus according to claim 15, characterised in that the device for introduction of the fuel is 15 arranged so that it delivers the fuel into the main current upstream of the zone of penetration of the secondary jet.with said current.

19. ’ Apparatus for the manufacture of fibres according to claim 15, substantially in accordance with any of 20. Embodiments herein described with reference to and shown in the accompanying drawings.

20. A process for the manufacture of fibres according to claim 1, substantially as herein described with reference to the accompanying drawings.