IE47241B1 - Manufacture of fibres from an attenuable material by means of gaseous currents - Google Patents

Abstract

The process consists in generating at least one secondary gas jet, in diverting it along a curved trajectory and guiding it sideways into a baffle member (8) which comprises a gutter-shaped component (9) whose cocavity is turned towards the inside of the trajectory of the jet, and in bringing a lace of ductile substance (S) towards the jet in the region where the latter flows into the baffle member. In a second stage each diverted jet enters a main gas stream (B) forming a zone of interaction into which the partially drawn fibre is introduced to be subjected to additional drawing. The process is employed especially for making fibres from glass.

Description

This invention relates to the technique of manufacturing fibres from an attenuable material ano it concerns more particularly the attenuation of various thermoplastic materials, particularly mineral materials such as glass or similar compositions which are converted into the molten state by heating. Xt also applies to the formation of fibres from certain attenuable organic materials such as polystyrene, polypropylene, polycarbonates and polyamides. Since the apparatus is more particularly of interest for the attenuation of glass and similar thermoplastic materials, the description will refer to this particular use by way of example.

Certain techniques using whirling currents to manufacture fibres by the attenuation of molten glass have already been described, for example in the publication of French Patent No. 2,223,318. This publication describes a process utilizing the formation of pairs of counter rotating tornadoes in a zone of interaction produced by directing a jet of gas (referred to as a secondary jet or carrier jet) to a main gas current of larger dimension and causing it to penetrate therein, a stream of molten glass being delivered into this zone of interaction to be attenuated there. In the apparatus used for carrying out this process, the glass supply orifice which directs the stream of glass to the zone of interaction is situated at 47341 or very close to the boundary of the main current. It is also possible, however, as described in Patent No. 43347 to place the glass supply orifice at some distance from the boundary of the main current and deliver the stream of glass to the said zone of interaction by gravity.

It has also been envisaged to place both the glass supply orifices and the emission orifices for the secondary jets at some distance from the boundary of the main current, the streams of glass being then delivered to the jets and subsequently introduced into the corresponding zones of interaction by the action of the jets. The streams are thereby subjected to two stages of attenuation, one in the secondary jet and the other in the main current. This arrangement is described in particular in Patent Nos. 43838 and 45953 Furthermore, according to Patent No. 45953 , a stable zone of laminar flow is produced in the secondary jet (or carrier jet) which carries the glass into the zone of interaction with the main current, this zone of laminar flow being situated between the counter rotating tornadoes of one and the same pair of tornadoes formed before penetration into the main current. The stream of glass is delivered to this laminar zone and then enters the region of the tornadoes which subsequently merge downstream of the carrier jet before the latter reaches the main current. The first stage of attenuation therefore takes place when the stream of glass is carried into the tornadoes of the carrier jet and subjected to their action whereas the second stage, which is advantageous but may in some cases be optional, takes place in the zone of interaction formed with the main current after entry of the carrier jet and of the partially attenuated stream of glass.

In Patent No. 45953 , the tornadoes of the carrier jet and the zone of laminar flow are produced by a disturbance of the jet at each fibre forming centre, which disturbance generally causes it to be deflected. This disturbance is produced by interposing a deflector or guiding device in the path of the jets so that these jets are deflected simultaneously This helps to stabilize the introduction of glass into the system and renders the operation regular in spite of the distance between the main current and the point at which the glass is delivered into each carrier jet.

One particularly important object of the present invention is to stabilize the stream of glass or other attenuable material by the formation of a zone of laminar flow between the tornadoes produced in a gaseous flow.

However, the deflector devices provided by the invention are of a different type from those in Patent No. 4ty53 , and provide various specific, particularly interesting advantages which will be referred to hereinafter.

Although these deflector devices are at the same time guiding devices and jet emission devices, the term deflector will be used in the description to denote them.

According to the present invention, an individual deflector device is used for each fibre forming centre. Each jet flows down a concave deflector device resembling a channel advantageously in the form of a bent tube from which the wall of smaller, radius or inner wall has been removed, and the stream of attenuable material is introduced into the flow of the jet in the region where the tube does not have an inner wall. The stream of attenuable material is thus delivered to the jet in the region where the latter flows in the concave deflector guide in the form of the channel.

Due to the combined action of the deflection of the jet and its lateral confinement by the walls of the deflector in the form of the channel and the induction of the surrounding gas, a central zone of quasi-laminar flow is formed in each jet, situated between two tornadoes, and the stream of attenuable material is carried into the zone of laminar flow bounded by the pair of tornadoes and is thus subjected to a primary attenuation in the jet.

Although the attenuation achieved with the system of flow briefly described above would be effective in producing certain types of fibres, the invention also provides for the use of the gaseous jet and its associated deflector in combination with a main current to carry out attenuation in two stages, v/hich respresents the preferred embodiment of the invention and enables very fine fibres to be obtained. The main current is then directed so that it encounters the jet, which has a greater kinetic energy per unit volume than the main current and is smaller in size in a direction transverse to the main current than the latter so that the jet penetrates the current to form a zone of interaction. This has been described in the publication of French Patent No. 2,223,318 It comprises two counter rotating tornadoes which enable a second stage of attenuation to be performed.

In Patent No. 45953 mentioned above, a series of jets is produced, these jets being spaced apart from each other at a suitable distance in the transverse direction so that successive jets impinge on each other at least downstream of the deflector is such a manner that their impact with each other promotes the development of pairs of counter rotating tornadoes bordering on the opposite sides of a zone of quasi-laminar flow. According to the present invention, on the other hand, the pair of tornadoes bordering on the zone of quasi-laminar flow is produced without mutual impingement of adjacent jets and it is therefore no longer necessary to observe a particular distance between the jets.

Due to the formation of tornadoes in the curved part of the deflector and the particular form of the deflector, the two tornadoes produced in each jet have the same sense of rotation as those produced in the zone of interaction of the jet with the main current.

Consequently, any residual movement of rotation of the tornadoes formed in the jets will reinforce the tornadoes of each corresponding zone of interaction.

The process and apparatus briefly described constitute effective means of converting an attenuable material into fibres by subjecting each stream of material to an attenuation preferably comprising two stages without any intermediate fragmentation being produced. The various other objects and advantages of the invention will become evident in the course of the following description given with reference to the drawings. 472 Figure 1 is a schematic view in perspective, partially in section and interrupted, showing two main elements of an apparatus according to the invention for the formation of fibres and their collection, comprising a plurality of fibre forming centres.

Figure 2 is a view in perspective on a larger scale of one of the jets, the guiding device and the flow produced, illustrating the delivery of a stream of attenuable material to the flow of the jet.

Figure 3 is a longitudinal section in elevation on an enlarged scale of the elements of a fibre forming centre, taken through the plane common to the jet and the source of supply delivering the stream of attenuable material. The figure also shows part of the generator for producing the main current and in particular it indicates certain dimensions which are to be taken into consideration to establish the operating conditions for carrying out the preferred embodiment of the present invention.

Figure 4 is a transverse view in elevation taken on the line 4./4. of Figure 3.

Figure 5 is a horizontal section through a tip supplying attenuable material taken on the line 5/5 of Figure 3, again showing certain dimensions to be taken into consideration.

As already mentioned, since the technique of the present invention is more particularly adapted to the attenuation of glass and similar thermoplastic materials, the following description will be given with reference to the use of glass.

The overall view of Figure 1 represents an installation using six fibre forming centres. A generator 6 emitting a main current B consists, for « example, of a nozzle connected to a burner to produce 10 a hot main gas current from products of combustion. The width or transverse dimension of the main current is greater than that of the row of jets described below.

A manifold box 7 supplying the gaseous jets, for example compressed air, is situated at some distance from the main current generator and comprises a wall having a series of orifices each of which is equipped with a deflector device 8. As also shown in Figure 2, each deflector device 8 is advantageously formed by a bent tube having a constant radius of curvature, one end of which is fixed to the corresponding orifice of the manifold box. The radius of curvature of the tube may, however, be variable. The part situated on the inner side of the tube and constituting, for example, about half the tube, has been removed. The deflector device also comprises a part in the form of a channel 9 constituting the outer part of the bent tube and thus having a curvature whose concavity is turned towards it axis.

Associated with each deflector device is a bulb or cone of glass 10 issuing from a suitable source of supply indicated schematically in Figures 3 and 4 which is in the form of a bushing 11 which is preferably wide enough to cover the row of jets. This bushing is provided with a series of tips for delivering glass, each having a metering orifice 12 opening into a feed cup 13 the edge of which constitutes the supply orifice 13a.

It will be seen, therefore, that each fibre forming centre comprises a jet emission device associated with a glass supply tip, both cooperating with the main current, each of the fibre forming centres producing a single filament.

The process taking place at each fibre forming centre is represented in Figure 2 which illustrates what takes place at the moment of emission of each jet. Due to the curvature of the jet deflecting device and the fact that this jet is guided and confined on its lateral surfaces in the element which is in form of a channel 9, the tornadoes 14 develop along opposite walls of this concave channel. The sense of rotation of these tornadoes is represented by arrows. The origins of the tornadoes 14 are situated on the lateral walls of the concave channel and the tornadoes increase in size downstream of the jet and progressively merge with the intermediate portion L of quasi-laminar flow. The zone of quasi-laminar flow of the jet is accompanied by a substantial influx of induced air which is indicated schematically by arrows. This induction of air tends to attenuate the bulb 10 into a stream of glass and carry the latter into the jet, more precisely into the zone of laminar flow situated between the tornadoes 14.

In Figure 2, the zone represented as torn away downstream of the reference numeral 14 shows that the tornadoes progressively merge downstream of the jet, becoming progressively less distinct, as indicated by the broken lines.

The delivery of the stream of glass into the zone of laminar flow situated between the tornadoes of the jet is indicated by the latter S in Figure 2. The stream is then carried along by the action of the tornadoes and is subjected to a primary attenuation in the jet, in particular in the zone situated between the tornadoes of a pair, so that it is progressively reduced in cross-section to form a filament. The fact that the stream of glass S is carried into the zone of quasi-laminar flow has various advantages. In particular, it prevents the fragmentation of the stream of glass by virtue of the absence of turbulence in the zone where the glass is introduced, thus favouring the manufacture of filaments or fibres of considerable length. Furthermore, the induced air currents in the vicinity of the zone of laminar flow tend automatically to drive the stream of glass into the median region situated between the tornadoes, and this process is powerful enough to compensate automatically for any faults in alignment of the glass supply orifice with the jets. As indicated by the arrows, the induction of air continues downstream along the path of the jet.

Although attenuation of the stream of glass effected in the jet may be sufficient to produce suitable fibres for certain applications, it is preferred to carry out an additional attenuation using a main gas current so that the fibres are subjected to two stages of attenuation As can be seen in Figure 1, the second stage of attenuation results from the fact that each jet directed obliquely to the main current, encounters the latter and penetrates it to produce a zone of interaction. The second stage of attenuation is produced in this zone of interaction, described in particular in the publication of French Patent No. 2,223,318, Patent Nos 43347, 43838 , and 45953 A comparison of Figures 1 and 2 also shows that the two tornadoes formed in each jet have the same sense of rotation as the pair of tornadoes produced by the penetration of the jet into the main current.

In order that penetration may take place, the jet must have a greater kinetic energy per unit volume than the main current. Furthermore, its cross-section, or at least the dimension of the section in a direction transverse to the main current, should be smaller than that of the latter. These relationships of dimension and kinetic energy must exist in particular at the level of the zone of penetration of the jet into the main current. Consequently, since the flow in this region is constituted by merged tornadoes 14a and by induced air, it is necessary to use jets which have an even higher kinetic energy at their point of origin, that is to say on leaving the orifices of the manifold box 7.

On penetrating the main current, each flow issuing from a jet produces therein the formation of a pair of tornadoes indicated at 15 which, in one and the same pair, are also counter rotating in the sense indicated in Figure 1. At each fibre forming centre, the partially attenuated stream or filament is thus subjected to an additional attenuating force under the influence of the high velocity currents constituting the tornadoes 15, whereby a second stage of attenuation can be effected and a fine fibre can be produced.

The fibres thereby produced at various fibre forming centres of such an installation are gathered together, for example on a perforated fibre receiving. device such as a conveyor belt 16 moving over one or more suction chambers 17 so that the fibres can be collected in the form of a mat or web F on the moving belt of the conveyor.

If desired, a suitable binder such as a resin 10 binder may be sprayed over the fibres, for example in the region where Figure 1 has been cut. The mat of impregnated fibres is then taken to a treatment station such as a furnace for polymerising the binder.

As already explained above, the jet should have a 15 higher kinetic energy per unit volume than the main current, no matter what the temperature of the gas. It is possible, for example, to use gas supplies connected to burners so that the main current and the jet are both at high temperatures and therefore both have a low density.

In that case one would use a jet of higher velocity than that of the main current in order to obtain the desired relationship of kinetic energy. This relationship may also be obtained by using a gas at relatively low temperature and hence high specific density for the jet, for example compressed air at room temperature, while the main current consists of products of combustion at a high temperature, and in that case the velocity of the jet may be lower than in the previous case and may even be below that of the main current. This characteristic would still lead to the desired result, that is to say a jet having a higher kinetic energy per unit volume than the main current, so that it will penetrate the latter and produce the desired zone of interaction.

Figures 3, 4 and 5 indicate the relations between the three main elements of a fibre forming centre, namely the main current generator, the jet emitter and the source of supply of attenuable material. Various symbols are entered in these figures to identify various parameters and in particular certain dimensions and angles entered in the tables below which give both the suitable ranges of variation of the dimensions and the angles and the preferred values.

TABLE 1 Bushing and supply tip of attenuable material Symbol preferred value range (mm) 0-----10 F. dR 2 ' 1 ----5 D 5 1-----10 R TABLE IX Emission of jet Symbol preferred value (mm, degrees) rangedJ 2 0.5--- 41J 3 1 15YJ 5 at least 1.0 a D 45° 20 --- 90 % 2.5 2 --- 3 ξ TABLE III Main Current Symbol preferred value (mm) range ’έ 10 5 --- 20 TABLE IV Relative positions of the various elements Symbol preferred value (mm, degrees) range a JB 45 20 --- 90 Xbj - 5 + 10 ---- -20XJF 5 1 — 8ZJF 5 0 --- 15ZJB 20 15 --- 35ZDB 16 0 --- 30 ]d 2 1 — 3dJ As regards the symbol XRj, the negative values apply to the case represented in Figure 3 in which the outlet of the nozzle emitting the main current is situated upstream of the secondary jet emission orifice viewed in the direction of propagation of the main current.

As regards the dimension it may be noted that the value zero is given, which corresponds to a position ' of the lower edge of the deflector at the boundary of the main current; and the tornadoes of the jet continue and become more powerful in the zone of interaction produced with the main current, and better continuity of the actions of attenuation of the jet and of the main current is thereby obtained.

The number of fibre forming centres may be as much as 150 but in a normal installation for the formation of fibres from glass or a similar thermoplastic material, a suitable bushing would have, for example, 70 supply tips The term supply orifice for attenuable material used in the description should be interpreted in a very general sense. It may denote an isolated orifice delivering material to a jet flowing in a deflector device or it may denote a supply slot associated with a row of jets or a series of orifices. The row of orifices may in fact be replaced by a slot placed transversely to the main current downstream of a row of jets and associated deflector devices, the material issuing from the slot being then subdivided into a series of cones and streams under the influence of the jets and of the induced air currents, each stream being then carried into the zone of laminar flow of the corresponding jet.

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 formed into fibres. As indicated earlier, the invention is applicable to a wide range of attenuable materials.

The temperature of the bushing or of the source of supply will also vary according to the particular material to be converted into fibres, and, in the case of glass or other inorganic thermoplastic materials, it generally lies within a temperature range which may be between 1,400 and 1,800°C. In the case of a conventional type of glass composition, the temperature of the bushing is in the region of 1,480°C.

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

Certain values relating to the jet and to the main current are also important, as indicated in the table below in which the following symbols are used: 7241 ρ = pressure Τ = temperature V = velocity Ρ = mass per unit volume Symbol TABLE V Emission of jet preferred value range Pj (bar) 2.5 1 --- 50 Tj (°C) 20 10 -—1100 10 Vj(m/sec, 300 200 --- 900 pjV’jfbars) 2.1 0.8--- 40 Symbol TABLE VI Main Current preferred value range 15 Ρβ (mbar) 95 30 --- 250 tb (°C) 1450 1350 --- 1800 Vg (m/s, 320 200 — 550pBVg5 (bars) 0.2 0.06--- 0 If both the jet and the main current are employed, the 20 width and preferably the transverse section of the jet are smaller than those of the main current, as already mentioned above, and the jet must penetrate the main current to produce a zone of interaction in which the second stage of attenuation will take place. For this purpose, the jet must have a higher kinetic energy per unit volume than the main current in the region where they cooperate. A particularly suitable ratio of these kinetic energies per unit volume is in the region of 10/1, namely: In addition to certain advantages already provided in the above-mentioned earlier patents and applications, the technique according to the present invention affords several very specific advantages which are important for the formation of fibres from a very wide variety of materials, in particular from thermoplastic mineral compositions such as glass ;or other similar materials.

It enables a very stable introduction of glass to be achieved and consequently also a very stable cone of glass in spite of the considerable distance between the main elements of the system and more precisely the distance between the source of supply of glass, the jet emitter and the generator of the main current. The separation of these elements enables the desired temperature to be maintained for each one of these elements with the degree of precision desired for obtaining efficient and regular fibre formation.

The invention also enables very stable pairs of tornadoes to be formed in the flow of the jet, this stability being due in particular to the fact that the origins of the tornadoes are situated inside the deflector 47341 in the curved part which is in the form of a channel, and they are therefore fixed in a stable position. This results in great stability in the supply of attenuable material. The use of a deflector resembling a channel for each jet enables the tornadoes in each flow to be formed independently of adjacent jets. This has the advantage of being able to choose any distance between the jets.

Claims (13)

1. CLAIMS:1. Process for the conversion of an attenuable material into fibres by means of gaseous currents, characterised in that it consists of establishing at least one gaseous jet, deflecting it along a curved path and laterally confining it, thereby producing a pair of counter rotating tornadoes having their origins on the lateral surfaces of the deflected flow, and conducting the material in the form of a stream in the attenuable state to the concave surface of the path of the jet in the gas induced by the latter.

2. Process according to Claim 1, characterised in that the stream of material is introduced into a zone of laminar flow situated between the two counter rotating tornadoes in their upstream part.

3. Process according to one of the Claims 1 and 2, characterised in that a main gas current of greater width is produced, whose path intersects that of the deflected jet or jets, the jet having a higher kinetic energy per unit volume than the main current in order to penetrate the latter and thus produce a zone of interaction comprising a pair of counter rotating tornadoes, the stream of attenuable material being delivered into said zone of interaction by the deflected jet.

4. Process according to Claim 3, characterised in that the jet is deflected and confined so that the two tornadoes produced in the jet describe the totality of its cross-section and have a sense of rotation identical to that of the tornadoes of the zone of interaction.

5. Process according to one of the Claims 2 or 3, characterised in that deflection and lateral confining of each jet are effected at a distance from the boundary of the main current, each stream of material delivered into the zone of laminar flow being subjected to a primary attenuation in the deflected jet and to an additional attenuation in the zone of interaction with the main current

6. Process according to Claim 3, characterised in that deflection and lateral confining of each jet are effected close to the boundary of the main current in order that the tornadoes produced in the jet will continue and become more powerful in the zone of interaction formed with the main current.

7. Process according to one of the Claims 1 to 5, characterised in that the temperature of the gaseous jet is close to room temperature.

8. Apparatus for converting an attenuable material into fibres, comprising a source of supply of attenuable material equipped with at least one supply orifice and an emitter emitting at least one gaseous jet, said emitter being provided with at least one emission orifice, characterised in that it comprises at least one deflector device into which the jet is introduced and which comprises a curved element the concavity of which is directed to the inside of the path of the jet, the supply orifice for attenuable material being placed opposite the concave face of the curved element to deliver a stream of attenuable material to the jet in the region where the latter flows in the deflector device.

9. Apparatus according to Claim 8, characterised in that the curved element of the deflector device has the form of a channel, the concavity of the said element being turned towards the axis of the channel.

10. -Apparatus according to one of the Claims 8 and 9, characterised in that it comprises a generator producing a main gas current (B) of greater width in a direction which, downstream of the deflector device, intersects the path of the jet which has been deflected by said deflector device, the kinetic energy per unit volume of the jet being greater than that of the main current.

11. Apparatus according to one of the Claims 8 to 10, characterised in that the free end of the deflector element in the form of a channel is situated at some distance from the boundary of the main current.

12. Apparatus for converting an attenuable material into fibres according to Claim 8, substantially as herein described with reference to and as shown in the accompanying drawings.

13. A process for the manufacture of fibres according to Claim 1 substantially as herein described with reference to the accompanying drawings. MACLACHLAN & DONALDSON Applicants' Agents 47 Merrion Square