GB1592683A - Process and apparatus for the manufacture of fibres from attenuable materials - Google Patents

Abstract

A gas jet emitter (20) emits, through a series of orifices (21), a row of gas jets which are diverted and spread by a deflecting plate (40). The spreading of the jets is however limited by impact with the adjacent jets, which gives rise in each jet to counter-rotatary vortices (45, 48) surrounding a laminar flow zone (44) at low pressure, into which a thin stream (S) of molten thermoplastic material is sent. The jets are directed against a main gaseous flow (18) into which they penetrate, forming interaction zones. The thin streams are thus stretched successively in two steps, but the second step may be omitted. The method applies in particular to manufacturing glass fibres. <IMAGE>

Description

(54) PROCESS AND APPARATUS FOR THE MANUFACTURE OF FIBRES FROM ATTENUABLE MATERIALS (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 the technique of manufacturing fibres from an attenuable material by attenuation with gaseous currents, according to which a pair of whirls rotating in opposite senses, or counter-rotating tornadoes, are employed.

According to this technique, described in British Patent No. 1,454,061 a main gas current or blast is produced and a gas jet, referred to as secondary or carrier jet, is directed transversely to the main gas current. This jet has a smaller cross-section and high kinetic energy per unit volume than the main current. The secondary gas jet therefore penetrates the main current, producing a zone of interaction in which a pair of counter-rotating tornadoes develops as a result of the interaction. Between these tornadoes, a zone of relatively low pressure is established at the boundary of the main current, close to and downstream of the point of penetration of the jet. A stream of attenuable material is delivered to the zone of low pressure.This stream then enters the zone of interaction, where it is subjected to high velocity currents of the tornadoes, which cause the stream to be attenuated, finally to form a fibre.

One object of the present invention is to obtain good stability of the supply of attenuable material while avoiding the reciprocal influence of the temperatures of the different elements of the apparatus delivering the attenuable material and the gas.

Thus, according to this invention we provide a process for manufacturing fibers from attenuable materials, comprising generating at least one gaseous jet and modifying the flow of the jet so that lateral spreading of the modified jet is limited, thereby inducing in the jet at least one pair of spaced tornadoes, and delivering a stream of attenuable material into a zone located between the tornadoes to subject the stream to attenuation.

We also provide apparatus for manufacturing fibers from attenuable material comprising a supply source provided with at least one orifice for supplying at least a stream of attenuable material, a generator having at least one orifice for discharging a gaseous jet, means for modifying the flow of the or each jet to develop therein a pair of spaced tornadoes, said modifying means being located in the path of the jet between the discharge orifice and the stream of attenuable material, and the material supply orifice being directed towards a zone situated between said tornadoes. Thus, a gas flow or jet is produced, within which a pair of counter-rotating tornadoes, so-called "jet tornadoes", are produced by disturbance of said flow by means of a guide structure or deflector.This structure is arranged so that between these jet tornadoes there is produced a zone which is characterised both by a quasilaminar flow and by low pressure, thereby causing a powerful induction of air. This guide structure generally causes deviation of the gas jet and will therefore be referred to in the following description as a deflector. It should be noted that these counter-rotating jet tornadoes are produced by a deflector exerting an influence on the gas jet and not by penetration of a jet into a main current as has been described in the British Patent mentioned above. The action of this deflector not only produces the tornadoes but also establishes the zone of quasi-laminar flow and low pressure situated between these tornadoes.The present invention provides for the delivery of a stream of attenuable material, for example of molten glass, into a position where it is subjected to the influence of the induced air by the said zone of laminar flow. This stream is consequently first introduced into the laminar flow between the tornadoes and is then subjected to the influence of the high velocity currents of the pair of tornadoes (or whirls). Attenuation of the stream into a fibre is thereby brought about.

The process of attenuation described above, comprising the creation of counter-rotating tornadoes within a gas jet, may constitute the first stage of a two-stage attenuation operation. In this case the second stage is effected by transversely directing the jet and the attenuating fibre carried thereby into a main current or blast of larger cross-section, the jet still having sufficient kinetic energy per unit volume to penetrate the main current and there set up a zone of interaction similar to that described in the above mentioned Patent. As a result, the fibre, having been subjected to the primary attenuation operation, is introduced into the zone of interaction of the secondary jet with the main current, where it is subjected to a supplementary attenuating action.

In the course of this process, although each individual stream of attenuable material is subjected to two successive attenuating stages, each comprising the action of high velocity currents produced by the pairs of successively produced tornadoes, only a single fibre is formed from each individual stream of material.

It will be recalled here that according to the Patent mentioned above, in order to deliver or introduce the stream of attenuable material into the zone of interaction, the feed orifice of the said material is placed at or very close to the boundary of the main current. One important object of the present invention is to provide a separation between the feed orifice of the attenuable material and the boundary of the main current while maintaining stable delivery of attenuable material.

The employment of the process according to the invention has numerous advantages.

Above all, it follows from what has been said above that the use of jet tornadoes produced by the action of a deflector on the jet in the first stage of the attenuating operation makes it possible at the same time to introduce the attenuating fibre into the zone of interaction between the jet and the main current (the zone of interaction described in Patent No.

1,454,061). This first stage therefore represents a means of bringing the attenuable material into the attenuating operation which takes place in the zone of interaction. The following advantages are thereby obtained: The various elements of the apparatus can now be clearly separated, in particular the means for producing the main current, the means for producing the secondary jets and the feed device for supplying the attenuable material. Now the separation of these elements is advantageous for various reasons. In particular, it reduces the heat exchange between the three elements of the system, and this provides greater flexibility for maintaining the temperature differences between the means for producing the main current, the means for producing the secondary jet and the feed device for supplying the attenuable material.

Moreover, such a reduction in the heat exchange enables fibre formation to be carried out under favourable conditions in the case of substances such as hard glass which require relatively high temperatures to be converted to the molten state or to the desired consistency for attenuation.

The separation of the elements provided in the present invention also reduces or eliminates the formation of particles which have not or only badly been shaped into fibres due to sticking of the attenuable material against hot surfaces. More uniform fibre formation and more uniform products can therefore be obtained. Moreover, the employment of a two-stage process in which the first stage serves to deliver the attenuable material into the zone of interaction of the jet and the main current is advantageous since this first stage constitutes a means for stabilizing feed of the material to the zone of interaction in spite of the considerable space between the device which supplies the material and the boundary of the main current, and this is an important factor for obtaining uniform fibre formation in the zone of interaction.In the first stage, considered as the means for feeding the material, the formation of the zone of quasilaminar flow at low pressure enables the stream of material to be supplied regularly and with precision into the region situated between the jet tornadoes produced by the action of the deflector, and this precision is maintained even in the event of faulty alignment of the feed orifice supplying the attenuable material with the zone of laminar flow.

Due to this "automatic" compensation of irregularities in the position of the point of supply of the attenuable material, certain elements of the apparatus, such as the device for supplying a stream of molten glass, need no longer be constructed with a so great precision.

This is a considerable advantage, since, as is known, high precision in machining is difficult to reconcile with the very high temperatures encountered in the handling of molten glass, particularly in the formation of fibres from hard glass or other materials such as slag or certain rocks.

The technique according to the present invention also has the advantage of being able to be applied to a wide variety of attenuable materials, including not only various mineral materials, as indicated above, but also certain organic attenuable materials, such as polypropylene, polystyrene, polyamide or polycarbonate.

In the present invention, it is also provided to employ certain more particularly interesting operating conditions relating to the temperature and velocity of the secondary jet in relation to those of the main current. It is preferred to impart to the secondary jet a velocity and a temperature substantially lower than those provided in the examples of the publication of Patent No. 1,454,061 with a view to obtaining additional characteristics and advantages which will be explained hereinafter.

Although it is in most cases envisaged according to the present invention to carry out the formation of fibres from attenuable material in two stages, it should be noted that for certain applications the material may be subjected to the first stage alone, that is to say to the stage of fibre formation resulting from the feed of the attenuable material into the zone situated between a pair of counter-rotating tornadoes produced by disturbance of the jet by means of the deflector. The omission of the subsequent stage of penetration of the jet into a larger main current simplifies the apparatus.

The present invention is applicable to any attenuable material but is particularly suitable for attenuable thermoplastic materials such as glass and similar compositions heated to the melting point or to a suitable consistency for attenuation.

The embodiment represented and described hereinafter is particularly suitable for attenuating glass or similar compositions and, unless otherwise indicated, everything referring to glass in the following description may also be applied to any other attenuable material.

The description given below with reference to the accompanying drawings clearly explains the manner and means of obtaining the objectives and advantages described above. The figures illustrate the preferred embodiments of the apparatus according to the invention and represent schematically the important stages of the action of the jet, the action of the main current and the attenuating operation itself.

Figure 1 is a schematic overall view in elevation with several partial sections showing the general layout of the main elements of an apparatus according to the present invention.

Figure 2 is a vertical section on an enlarged scale of the elements of one of the fibre forming centres taken on the line 2-2 of Figure 4.

Figure 3 is a detailed plan view on an even larger scale of several jet outlet orifices and glass supply orifices taken on the line 3-3 of Figure 2.

Figure 4 is an elevational view of part of the apparatus represented in Figures 1 and 2, taken from the right side of Figure 2.

Figure 5 is a plan view taken on the line 5-5 of Figure 4.

Figure 6 is a perspective view on an enlarged scale of a jet manifold box used in the apparatus represented in Figures 1 to 5.

Figure 7 is a schematic view in perspective, illustrating the mode of operation of the process and apparatus according to the present invention.

Figure 8 is a longitudinal section through one of the fibre-forming centres of Figure 2, illustrating certain phases of the action of the jet and of the main current or blast in attenuating glass delivered from an orifice situated in the upper part of the figure.

Figure 9 is a plan view of several jets and portions of the main current, corresponding to Figure 8 but omitting the supply of glass and the glass fibre being formed.

Figure 10 is a schematic transverse section through three adjacent jets, illustrating the directions of rotation of the counter-rotating jet tornadoes.

Figure 11 is a longitudinal section in elevation of the main elements, illustrating in particular certain dimensions which must be taken into account to establish the operating conditions for carrying out the preferred embodiment of the present invention.

Figure lia is a sectional view of a detail, showing the space between two adjacent jet orifices.

Figure lib is a section through part of the feed device for supplying the attenuable material.

Reference will first be made mainly to Figure 1, which represents schematically a typical overall arrangement of the apparatus suitable for carrying out the technique of the present invention. On the left of Figure 1 may be seen schematically, at 15, part of a burner or generator producing a main current or blast 18 and having a nozzle 16 with an outlet orifice 17 large enough to enable several fibre forming centres to be associated with the main current 18. A feed pipe 19 for supplying a gaseous fluid under pressure is connected to the jet manifold box 20 which serves to supply gas to the emission nozzles for the secondary jets, one orifice of which is represented at 21.

A bushing 22 connected to a forehearth or other suitable means for supplying glass, indicated at 23, has tips or the like for supplying glass 24, by means of which a stream of glass is directed towards each jet flow to be carried downstream to the zone of interaction in the main current 18. As already explained in the description, fibre formation takes place in the jet but also in the main current and the main current carries the fibres to the right as shown in Figure 1 to form a sheet or a mat which is deposited on a perforated conveyor belt 26. Underneath the upper section of this belt is a suction chamber 27 which is connected to a suction fan indicated schematically at 28 to facilitate the deposition of the sheet of fibres on the perforated belt 26.

The various fibre forming organs are shown in more detail in Figures 2 to 6 which will be referred to hereinafter. The devices for generating the main current and the secondary jets are advantageously mounted so as to be adjustable in relation to the supporting structure, indicated schematically at 29, in order that the relative positions of the main current and of the secondary jet can be adjusted in the vertical direction and preferably also in the upstream-downstream direction of the main current 18.

As can be seen particularly in Figures 4 and 5, the nozzle 16 for the main current is relatively wide and therefore has a large outlet orifice 17. As shown in Figure 4, the bushing 22 for supplying the glass, which is situated under the forehearth 23, is also preferably large in the direction perpendicular to the plane of Figure 2 to enable it to supply glass to a plurality of glass supply devices or tips 24.

Figures 2 and 3 show clearly how each tip 24 has a metering orifice 24a and preferably also an elongated lower reservoir 24b situated downstream of the metering orifice. The reservoirs or cups 24b are preferably elongated in the plane of the fibre forming centre, that is to say in the plane containing the glass supply tip 24 and the orifice 21 which emits the associated jet.

The orifices 21 are formed in the anterior inclined walls of a series of jet manifold boxes 20 carried by support rods 30 which are mounted on the supporting structure 29 of the apparatus and extend the whole length of the bushing 22. The rods also pass through apertures 31 formed in the mounting lugs 32 provided at each end of each jet manifold box (see also Figure 6). The various jet manifold boxes, four in number in the apparatus represented here, may be shifted to the right or to the left, as can be seen from Figures 4 and 5.

The positions of the jet manifold boxes on the support rods 30 are determined by means of additional rods 33, 34, 35 and 36, each of which is threaded at one end to fit into a threaded hole in one of the lugs 32 of the jet manifold boxes. Three such threaded holes are shown at 37 in Figure 6. At its end 38, each of the rods 33 to 36 is mounted on a bearing which fixes its axial position, and it is provided with a slot by means of which it can be turned to displace the corresponding jet manifold box and thereby adjust the position of the latter in the lateral direction. It is thereby possible to adjust the relative positions of the jet emission orifices 21 in relation to the glass supply tips 24, particularly with the object of compensating for differences in thermal expansion.The fact that the jet orifices are distributed among several jet manifold boxes enables the orifices to be correctly aligned with the glass supply orifices on lines parallel to the flow of the main current. This alignment may not be perfect, but this is acceptable with a device of the type represented and conforming to the present invention in which the streams of glass are delivered into quasilaminar zones between jet tornadoes, which zones are represented at 44b in Figure 7.

In fact, as already explained earlier, the delivery of the streams of glass into these zones enables slight inaccuracies in the relative positions of the glass orifices and jet orifices to be automatically compensated.

Each of the jet manifold boxes 20 is connected to the pipe 19, which supplies the fluid for the jets, by means of two flexible connections 39, so that the position of the jet manifold box can be adjusted independently of the position of the feed pipe 19.

As already indicated above, the present invention provides that the jets delivered from the emission orifices 21 should be subjected to a deviation or a guiding action by means of a deflector which cooperates with the jets to produce the pairs of counter-rotating tornadoes used for at least the primary attenuation but also for feeding of the partially attenuated threads into the zones of interaction produced by the penetration of the jets into the main current. For producing the pairs of counter-rotating jet tornadoes, the present invention proposes the use of a deflector such as a deflector plate 40 associated with and common to a group of jet emission orifices. In cases where the jets are subdivided into groups, with each group associated with a jet manifold box 20, each of these manifold boxes preferably has a deflector plate 40. As shown particularly in Figures 7 and 8, the deflector plate preferably assumes the form of a bent metal 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 of flow or core of the jets emitted from the orifices 21 and advantageously placed along a line which intersects the axes of these jet orifices.

This position of the deflector plate 40 and of its edge 41 causes each of the jets to strike against the internal surface of the plate 40, so that the jet spreads out. Figure 7 shows the flow of four jets emitted from the orifices a, b, c and d, and it will be noted that each jet spreads out laterally as it approaches the edge 41 of the plate.

According to the invention, the jet emission orifices 21 are placed sufficiently close together and the deflector is arranged so that at the moment when the jets spread out laterally, adjacent jets impinge upon each other in the region of the edge 41 of the plate.

Preferably, as shown in Figure 7, the adjacent jets make contact with each other as close as possible to the free edge 41 of the deflector plate 40. This results in the formation of pairs of counter-rotating tornadoes represented in Figure 7 in association with each of the three jets emitted from the orifices a, b, c.

To analyse the formation of the jet tornadoes, reference is made particularly to the tornadoes 42b and 43b associated with the jet from the orifice b. It will be noted that the tornadoes have their apex situated substantially at the edge 41 of the deflector plate 40 on opposite sides of the jet, close to the zone in which the jet, as it spreads out, impinges upon the adjacent spreading jets emitted from the orifices a and c. The tornadoes 42b and 43b are counter-rotating as indicated in Figure 10 and they become progressively larger as they move on until they meet at some distance downstream of the edge 41 of the deflector plate.

These tornadoes 42b and 43b also have a component directed downstream.

Due to the space between the apices or points of formation of the tornadoes 42b and 43b and on account of the progressive enlargement of the tornadoes, an approximately triangular zone 44b forms between the tornadoes and the edge 41 of the deflector plate.

This triangular zone is at a relatively low pressure and undergoes a substantial influx of induced air but its flow nevertheless remains quasilaminar. It is into 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 advanced in the form of a single attenuating thread into the region between the two tornadoes.

It is to be noted that the senses of rotation of the currents in the jet tornadoes 42b and 43b are opposite to each other, the tornado 42b rotating clockwise as shown in Figure 7 while the tornado 43b rotates counter-clockwise. The currents in these two tornadoes therefore approach each other in their upper part and then flow downwards in the direction of the central or laminar zone 44b.

For the pair of tornadoes 45a and 46a associated with the jet from the orifice a, the senses of rotation are indicated by arrows as in the previous case. It should be understood that the section which represents the flow of jet from the orifice a has been taken at the level of the downstream 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 widened out, this phenomenum of fusion or merging progressing as the jet flows progressively downstream.The figure referred to above also shows clearly how the flow of the jet from the orifice a comprises not only the pair of tornadoes 45a and 46a but also another pair of tornadoes 47a and 48a which rotate in opposite senses as represented in Figures 7 and 10 but in this case the tornado 47a situated on the left in Figure 7 rotates in the counter-clockwise sense while the tornado 48a situated on the right rotates clockwise. Such double pairs of tornadoes are produced by and associated with each of the jets. The origin of the formation of the lower pair of jet tornadoes is different from that of the upper pair, as will be explained with reference to Figure 8.

With regard to Figure 7, it should be noted that as the flow progresses from the plane in which the tornadoes associated with orifice a are represented, the four tornadoes tend to merge and to reform into a less differentiated flow, as indicated by the section 49c taken across the flow of the jet from the orifice c. The whirling movements decrease in intensity and the whole flow, including the laminar flow of the central zone of the jet, intermingles in the region indicated at 49c, the jet then progressing downstream in the direction of the main current 18.

In Figure 7, the section through the various portions of the flow of the jet has been represented schematically for the sake of clarity. For example, in a zone situated slightly downstream of their origin, the pairs of tornadoes which take their origin in each of the jets appear to be slightly removed from the pair of tornadoes starting in each adjacent jet although in reality the various tornadoes are virtually contiguous.

In Figure 8, the fibre forming centre represented is the centre which originates at the jet emission orifice b of Figure 7. It therefore contains the tornado 43b and the laminar zone 44b. The pair of lower tornadoes takes its origin in the region situated below the deflector plate 40, Figure 8 merely showing the lower tornado 48b which originates behind the zone 44b. The rotation of the lower tornadoes results from the combined action of the jet against the internal surface of the plate 40 and of the induced air currents which join up with the flow of the jet, this rotation does not appear to have any influence on the delivery of the stream of attenuable material.However, in the upper tornadoes the direction of the currents has a predominant influence on the attenuating process when the stream of molten material is first delivered into the laminar zone and subsequently into the flow of jet downsteam of the point where the tornadoes merge.

Due to the form of flow of the jet in the laminar zone and in the pairs of tornadoes, particularly in the upper pair of each group, the introduction of the stream of attenuable material S into the fibre forming centre comprising the jet orifice b results in the stream being carried into the laminar flow of the central zone. This conducts each stream into the high velocity zone situated between the tornadoes of each pair so that the stream is attenuated as shown in Figure 7. This attenuation takes place mainly in a zone corresponding to the plane P indicated in the same figure. The action of the pairs of jet tornadoes causes a whipping of the attenuated fibre substantially in the zone of the plane P so that the fibre being formed is not thrown from side to side and into neighbouring jets.

Downstream, the flow of the jet causes the jet to penetrate the upper boundary ofthe main current 18 while carrying the attenuating fibre, provided this flow maintains sufficient kinetic energy to effect this penetration. A second stage of attenuation then begins, which takes place in accordance with the principles described in detail in Patent No. 1,454,061.

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 remains sufficiently concentrated in the neighbourhood of the axis to cause each jet to develop individually a zone of interaction with the current. Thus in Figure 7, a pair of counter-rotating tornadoes indicated at TT is generated in the zone of interaction, producing currents which have an additional attenuating effect on the fibre being formed. This fibre is then carried by the combined flow of the jet and of the main current towards a suitable receiver, for example a perforated conveyor or belt (indicated by the reference 26 in Figure 1).

In Figures 7 and 8, the induction of air has been indicated by arrows directed in the sense of flow of the jet, and it can be seen that the air is induced into the laminar zone adjacent to the edge of the deflector plate and is induced to a progressively greater extent as the jet flows downstream. To elaborate in more detail the description of the apparatus and the process of the present invention, certain permissible variations and certain particularly interesting ranges of operating conditions are given below.

Firstly, as regards the relative positions of the jet emission orifices and of the deflector 40, these are adjusted to cause the jets to spread out so that neighbouring jets impinge upon each other substantially at the level of the edge 41 of the deflector. This arrangement is represented in Figure 7 and it will be noted that in such a case, the origins or apices of the upper pairs of jet tornadoes are situated at the edge 41 of the said deflector plate 40.

The Jets and the deflector plate may be arranged so that the jets impinge upon each other at points situated substantially upstream or downstream of the edge of the plate but it is preferred to keep the impact of adjacent jets with each other very close to this edge because in that case maximum stability of the jet tornadoes is obtained and consequently also maximum stability of the laminar zone of the jet. This stability of the laminar zone is in turn important for stabilising the supply of glass to the system.

Complete precision is not necessary although the following facts must be taken into account: If the point of impact of adjacent jets is situated at a considerable distance downstream of the edge of the deflector plate, the tornadoes become unstable because they then originate in a free space rather than at the edge of the plate. If, on the other hand, the apices are situated at the edge or close to the edge of the said deflector plate, the jet tornadoes appear to "attach themselves" to the edge in a stable position.

If, on the other hand, adjacent jets impinge upon each other at a point situated a considerable distance upstream of the edge of the deflector plate, the formation of tornadoes is obstructed by the plate itself.

In order that the pair of upper tornadoes may form on the edge 41 of the deflector plate, it is important to place this edge at the level of the central axis of the jets or close to this level. If the edge of the plate is slightly higher, the deviation diminishes correspondingly or may even disappear, and in this case no tornado will be produced. If, on the other hand, the edge of the deflector plate is situated too low down, for example, below the lower limit of the jet, formation of tornadoes tends to be less regular and the tornadoes are less organised.

If the tornadoes are created under the most favourable conditions, that is to say when their apices are "attached" to the edge of the deflector, they are at their most stable and supply of the stream of glass and its attenuation in the zone of the plane P described above will also be most regular and stable.

One of the advantages of the present invention is that it can be used for producing fibres with diameters varying within a very wide range. Fibres with smaller diameters than those produced by the process according to British Patent No. 1,454,061 can be obtained. One particularly important advantage of the present invention compared with this process is the possibility of manufacturing fibres of a given diameter at a substantially higher unit pull rate. The unit pull rate referred to is the "rate of fibre formation" per orifice or per delivery tip for the attenuable material and, according to the present invention, this unit pull rate may reach 150 kg per aperture per 24 h.Values for this parameter and other factors relating to the operating conditions are given below with particular reference to Figures 11, 11a and lib and the corresponding information represented in the form of Tables.

As already indicated above, the first attenuating stage of the process according to the invention may, if desired, be used independently of the second stage, and although it is not possible to obtain such fine fibres with the first stage alone than when both stages are used, one nevertheless obtains sufficiently fine fibres for certain applications, and these fibres may be produced at a relatively high unit pull rate.

Referring to Figures 11, 11a and 11b and the figures in the Tables, it should be pointed out first that the representation of the various elements of the system, in particular in Figure 11, is given to clarify the explanation of the ranges of dimensions and angles but does not necessarily indicate the preferred values in all the ranges.

In Figure 11, the three main elements, that is to say the main current generator, the jet emission device and the device for supplying attenuable material, are represented in the same sectional view as in Figures 2 and 8 but Figures 11, 11a and 11b contain symbols identifying certain dimensions and angles to which reference will be made in the Tables below.

TABLE I Bushing for supplying attenuable material Symbol Preferred Value Range (mm) dT 2 1-5 1 1 - 5 1R 5 0 - 10 dR 2 1 - 5 DR 5 1 - 10 TABLE II Emission of jet and deflector plate Symbol Preferred Value Range (mm, degrees) dJ 2 0.5.- 4 13 7 1 close to the lower approximately end of the range 3 to approximately 4 1D 4 2 - 10 1JD 0 -0.06 - + 1 dj (mm, degrees) aJD 45 35 - 55 C1JB 10 0 -- 45 ZJD 3 2 - 5 LJD 3 2 - 5 As regards the values indicated by the ratio lJD/dJ, the value zero represents that position of the deflector plate at which the lowest part of the edge of the plate lies on the axis of the jets, the negative value corresponding to any position of the edge of the deflector above the axes of the jets.

TABLE III Main current Symbol Preferred Value Range (mm) 1B 10 5 - 20 In addition to the dimensions and angles given above for the three main organs of the system, certain relations between the three should be noted, corresponding data for which are given in the following Table.

TABLE IV Relative positions of the various organs Symbol Preferred Value Range (mm, degrees) ZJF 8 3 - 15 ZJB 17 12 - 30 XBJ - 5 - 12 - + 13 XJF 5 3 - 8 aDB 45 35 - 55 With regard to the symbol XBJ, it should be noted that the negative values correspond to the case represented in Figure 11 in which the outlet of the nozzle emitting the main current is situated upstream of the secondary jet emission orifice in relation to the direction of propagation of the main current.

As indicated above, it is envisaged according to the present invention that the carrier jets or secondary jets should be arranged sufficiently close together to impinge upon each other so as to produce pairs of tornadoes in each secondary jet. As many fibre forming centres may be produced as desired, each centre comprising a tip or an orifice for supplying attenuable material and an associated jet, and since each secondary jet must impinge on each side upon another jet, it will be seen that two jets must be added to the total number of tips supplying attenuable material, these two "additional" jets being situated at the two ends of the series of jets.

The series of tips or orifices for supplying attenuable material may be replaced by a continuous slot arranged transversely to the main current. In that case, the cones and streams of attenuable material will be formed by the action of the individual secondary jets, starting from the slot. Here again, and for the same reasons as above, two additional jets must be placed at the ends of the series of jets.

The number of fibre forming centres may reach 150, but in a normal installation for the formation of fibres from glass or a similar thermoplastic material, an appropriate bushing would comprise 70 tips or orifices. In that case, 72 jets would be required.

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

As indicated above, the invention is applicable to a wide range of attenuable materials. In the case of glass or other thermoplastic inorganic materials, the temperature of the bushing or of the tip will, of course, vary according to the particular material which is to be converted into fibres. The corresponding range of temperatures may be between 1400"C and 1800"C. In the case of a glass of conventional composition, the temperature of the bushing would be in the region of 1480"C.

The unit pull rate may vary between 20 and 150 kg/aperture per 24 h, 50 to 80 kg/aperture per 24 h being typical values.

Certain values relating to the jet and the main current are also important, as indicated in the Table below, in which the following symbols are used: T = temperature P = pressure V = velocity p = volumetric mass TABLE V Jet Symbol Preferred Value Range P, (bar) 2.5 1 - 4 T, ("C) 20 S - 1500 Vj (m/sec) 330 200 - 900 pJV2 (bar 2.1 0.8 - 3.5 TABLE VI Main current Symbol Preferred Value Range PB (mb) 95 30 - 250 TB (OC) 1450 1350 - 1800 Vn (m/s) 320 200 - 550 PBVB (b) 0.2 0.06 - 0.5 Concerning the jet and the main current, it will be recalled that according to the present invention, the deflected jet may be used alone for attenuation of certain materials without its action being combined with that of a main current. When a main current and a jet are used, the jet has a smaller cross-section than the main current and it penetrates the current to produce a zone of interaction in which the second phase of attenuation is carried out. For this purpose, the jet must have a higher kinetic energy per unit volume than the main current in the region where they cooperate.The jet may have a kinetic energy from 1.6 to 60 times that of the main current, the preferred ratio being 10:1, that is to say:

It will be noted that in TABLE V, the temperature and velocity chosen for the secondary jet are very much lower than those given in the examples of Patent No. 1,454,061, as has already been mentioned above. In the examples of that Patent, the secondary jet used to form the zone of interaction with the main current is at a temperature of 800"C and a velocity of 580 m/s while the main current is at 1580do and has a velocity of between 224 and 283 m/s.The values for temperature and velocity of secondary jet shown in Table V are substantially lower but are nevertheless sufficient to produce the ratio of kinetic energy per unit volume necessary to ensure penetration of the jet into the main current. If the temperature of the jet is lowered, for example to below 100"C or around room temperature, the specific gravity of the gas increases at the same time, so that the required kinetic energy per unit volume can be reached in spite of using lower velocities. It is even possible to employ a jet having a lower velocity than the main current.

The advantages obtained by employing a secondary jet at a relatively low temperature are considerable. Firstly, at temperatures below 100"C, it becomes possible to use a source of ordinary compressed air to supply the jet. Moreover, conventional materials such as stainless steel may be used for the apparatus emitting the jet, rather than the more sophisticated or more expensive materials which are necessary for high temperatures.

With a secondary jet at a low temperature, the problems of thermal deformation or expansion are considerably reduced or may even be eliminated and the risk of oxidation is also reduced. Moreover, in an installation with multiple fibre forming centres, the employment of a low temperature for the secondary jet enables the temperatures of the different jets to be maintained more uniform in relation to each other.

The use of jets at low temperatures is particularly advantageous f6r the apparatus equipped with a deflector described in the present application. When the position of the deflector has been determined and fixed in relation to the jet emitting device, the low temperature enables the accuracy of the dimensional characteristics of the deflector and of its position in relation to the jet emission orifices to be more easily maintained.

Furthermore, when a jet is employed at a lower temperature, the fibres are more easily transferred to a relatively cold region at the end of the attenuating operation. This characteristic is important for the reasons already explained in Patent No. 1,454,061.

The possibility of using ordinary compressed air at a temperature below 100"C or around room temperature does away with the consumption of energy which would be required for heating the jet. Moreover, air is more economical than high temperature fluids such as gaseous combustion products or steam.

Although, in Table V, the temperature of the secondary jet is around room temperature, it will be understood that it need not necessarily be so low. It will generally be preferable to keep it at a temperature substantially lower than the softening point of the thermoplastic material which is to be attenuated. In the case of glass or similar mineral materials, the temperature chosen would preferably be below 200"C, a temperature below 100"C being particularly suitable.

Example A glass having the following composition in percentages by weight is formed into fibres in an apparatus having 70 fibre forming centres of the type represented in Figures 1 to 6: SiO2 63.00 Fe2O3 0.30 Al203 2.95 CaO 7.35 MgO 3.10 Na2O 14.10 K2O 0.80 B203 5.90 BaO 2.50 The temperature of the bushing is in the region of 1500"C and the temperatures of the jets and of the main current are, respectively, of the order of 209C and 1500"C. The ratio of the kinetic energy per unit volume of the jet to that of the main current is in the region of 10 and the operation is carried out at a unit pull rate of 55 kg/aperture per 24 h. Under these conditions, the average diameter of the fibres obtained at the end of the two attenuation stages is about 6 microns.

WHAT WE CLAIM IS: 1. A process for manufacturing fibers from attenuable material, comprising generating at least one gaseous jet and modifying the flow of the jet so that lateral spreading of the modified jet is limited, thereby inducing in the jet at least one pair of spaced tornadoes, and delivering a stream of attenuable material into a zone located between the tornadoes to subject the stream to attenuation.

2. A process according to claim 1, wherein the flow of the jet is modified by means of a mechanical structure.

3. A process according to claim 1 or 2, wherein a series of laterally-spaced jets is used, which jets are deflected to modify their flow and the distance between the jets is such that adjacent deflected jets impinge upon one another.

4. A process according to any of claims 1 to 3, wherein the or each modified jet is directed transverse to and intersects a larger main gaseous blast, the kinetic energy per unit of volume of the or each jet being greater than that of the blast so that the or each modified jet penetrates the blast and produces zones of interaction, and the stream of attenuable material is delivered into the zone located between the tornadoes of the or each modified jet so that it is conveyed to the zone of interaction of the jet with the main blast.

5. A process according to claim 4, wherein the or each jet is modified at a substantial distance from the edge of the main blast, and the stream of attenuable material is delivered toward the corresponding jet near the zone of modification, to cause a primary attenuation

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

Claims (21)

**WARNING** start of CLMS field may overlap end of DESC **. expansion are considerably reduced or may even be eliminated and the risk of oxidation is also reduced. Moreover, in an installation with multiple fibre forming centres, the employment of a low temperature for the secondary jet enables the temperatures of the different jets to be maintained more uniform in relation to each other. The use of jets at low temperatures is particularly advantageous f6r the apparatus equipped with a deflector described in the present application. When the position of the deflector has been determined and fixed in relation to the jet emitting device, the low temperature enables the accuracy of the dimensional characteristics of the deflector and of its position in relation to the jet emission orifices to be more easily maintained. Furthermore, when a jet is employed at a lower temperature, the fibres are more easily transferred to a relatively cold region at the end of the attenuating operation. This characteristic is important for the reasons already explained in Patent No. 1,454,061. The possibility of using ordinary compressed air at a temperature below 100"C or around room temperature does away with the consumption of energy which would be required for heating the jet. Moreover, air is more economical than high temperature fluids such as gaseous combustion products or steam. Although, in Table V, the temperature of the secondary jet is around room temperature, it will be understood that it need not necessarily be so low. It will generally be preferable to keep it at a temperature substantially lower than the softening point of the thermoplastic material which is to be attenuated. In the case of glass or similar mineral materials, the temperature chosen would preferably be below 200"C, a temperature below 100"C being particularly suitable. Example A glass having the following composition in percentages by weight is formed into fibres in an apparatus having 70 fibre forming centres of the type represented in Figures 1 to 6: SiO2 63.00 Fe2O3 0.30 Al203 2.95 CaO 7.35 MgO 3.10 Na2O 14.10 K2O 0.80 B203 5.90 BaO 2.50 The temperature of the bushing is in the region of 1500"C and the temperatures of the jets and of the main current are, respectively, of the order of 209C and 1500"C. The ratio of the kinetic energy per unit volume of the jet to that of the main current is in the region of 10 and the operation is carried out at a unit pull rate of 55 kg/aperture per 24 h. Under these conditions, the average diameter of the fibres obtained at the end of the two attenuation stages is about 6 microns. WHAT WE CLAIM IS:

1. A process for manufacturing fibers from attenuable material, comprising generating at least one gaseous jet and modifying the flow of the jet so that lateral spreading of the modified jet is limited, thereby inducing in the jet at least one pair of spaced tornadoes, and delivering a stream of attenuable material into a zone located between the tornadoes to subject the stream to attenuation.

2. A process according to claim 1, wherein the flow of the jet is modified by means of a mechanical structure.

3. A process according to claim 1 or 2, wherein a series of laterally-spaced jets is used, which jets are deflected to modify their flow and the distance between the jets is such that adjacent deflected jets impinge upon one another.

4. A process according to any of claims 1 to 3, wherein the or each modified jet is directed transverse to and intersects a larger main gaseous blast, the kinetic energy per unit of volume of the or each jet being greater than that of the blast so that the or each modified jet penetrates the blast and produces zones of interaction, and the stream of attenuable material is delivered into the zone located between the tornadoes of the or each modified jet so that it is conveyed to the zone of interaction of the jet with the main blast.

5. A process according to claim 4, wherein the or each jet is modified at a substantial distance from the edge of the main blast, and the stream of attenuable material is delivered toward the corresponding jet near the zone of modification, to cause a primary attenuation

of said stream within the modified jet, additional attenuation taking place where this modified jet interacts with the blast.

6. A process according to claim 3, wherein the jets have substantially parallel paths.

7. A process according to any of claims 4 to 6, wherein the or each jet is situated above a substantially horizontal path of the blast and is deflected downwardly to meet the blast at an acute angle to the vertical, the or each stream of attenuable material being delivered vertically downwardly toward the corresponding jet.

8. A process according to claim 7, wherein the or each stream is delivered downwardly by gravity.

9. A process according to any preceeding claim, characterized in that the or each jet has a quasi-laminar flow zone bordered by the pair of tornadoes which are located on opposite sides of said zone, the diameters of the tornadoes increasing progressively so that they merge downstream of the quasi-laminar flow zone, and in that the stream of attenuable material associated with the or each jet is delivered towards said quasi-laminar zone.

10. A process according to claim 8, characterized in that the tornadoes of each pair rotate helically in opposite directions, said movements having components which converge on the side of the jet towards which the stream of material is delivered and axial components directed downstream of the zone of laminar flow:

11. A process according to claim 4, characterized in that the or each jet is deflected towards the blast by a deflector placed in its path, the deflector being located upstream of 'the stream of material with respect to the direction of flow of the jet.

12. A process according to any preceeding claim, characterised in that the temperature of the or each jet is below 200"C, the attenuable material being a thermoplastic mineral material such as glass.

13. Apparatus for manufacturing fibers from attenuable material comprising a supply source provided with at least one orifice for supplying at least a stream of attenuable material, a generator having at least one orifice for discharging a gaseous jet, means for modifying the flow of the or each jet to develop therein a pair of spaced tornadoes, said modifying means being located in the path of the jet between the discharge orifice and the stream of attenuable material, and the material supply orifice being directed towards a zone situated between said tornadoes.

14. Apparatus according to claim 13, wherein the generator is provided with a series of jet discharge orifices spaced laterally from each other, the means for modifying the flow of the jets comprising a deflector element to deflect the jets and cause them to spread laterally, the jet discharge orifices being sufficiently close together so that adjacent jets which have been deflected by the deflector impinge upon one other.

15. Apparatus according to either of claims 13 or 14 wherein the jet generator and the means for modifying the flow of the or each jet are associated with a generator for discharging a main blast of greater cross-sectional area than that of the jets in a direction transverse to the flow of the modified jets and intersecting their path, the main blast being spaced from the supply source for the attenuable material and its kinetic energy per unit volume being smaller than that of the or each jet so that the or each modified jet penetrates the main blast.

16. Apparatus according to claim 14, wherein the axes of the jet discharge orifices are substantially parallel.

17. Apparatus according to any of claims 13 to 16, wherein the means for modifying the flow of the jets comprises a deflector plate having a surface placed at an angle to the initial path of the jets.

18. Apparatus according to claim 16 wherein the deflector surface of the deflector plate forms an angle of from 35 to 55" with the axes of the jets.

19. Apparatus according to any of claims 14 to 18, wherein the axis of the or each jet is initially substantially in the same direction as the main blast.

20. Apparatus according to any of claims 14 to 19, wherein the attenuable material supply orifice is situated downstream of the or each jet discharge orifice with respect to the direction of flow of the main blast, the jet discharge orifice being disposed so as to emit the jet transverse to the stream of material.

21. Apparatus according to any of claims 13 to 20, including separate jet manifolds each supplying gas to a group of jet discharge orifices, these manifolds being associated with mounting and adjustment means for adjustment of their position transverse to the direction of the blast.