CH615407A5 - Process and plant for the manufacture of fibres from a thermoplastic material - Google Patents

Abstract

A main gas stream (12A) and a gas jet emerging from an orifice (36), entering the main stream transversely and creating an interaction region therein are generated. A lace of thermoplastic material in the drawable state, for example of molten glass, is taken from a crucible (200) by an orifice (37) into the region of interaction in order to be drawn and converted into fibres therein. To avoid the adhesiveness of the fibres to the equipment components situated in their path, an additional gas jet is brought by an opening (300) into contact with the flow resulting from the main stream and the secondary jet. <IMAGE>

Description

The invention relates to the manufacture of fibers from a thermoplastic material such as glass, by drawing by means of gas streams. French patent FR 2223318 describes a process for manufacturing fibers consisting in generating a main gas stream and at least one secondary gas jet of smaller dimension but of kinetic energy per unit of volume greater than that of the main current, in directing the secondary jet transversely to the main current so that it enters there by creating an interaction zone, and to introduce the thermoplastic material in a stretchable state into the interaction zone to stretch it and transform it into fibers.

The invention aims to prevent the adhesion of the fibers on the material elements placed in the vicinity of their trajectory. To this end, the invention provides the method and the installation, defined respectively in claims 1 to 5.

The patent mentioned above provides for the use of a surface or a plate constituting a limit to the main current, downstream of the arrival of the molten material, this surface being able to be inclined to bend the flow resulting from the current. main and secondary jets.

However, when such a downstream plate is used, the fibers tend to adhere to it, all the more so since the plate forms a greater angle with the initial direction of flow of the main stream.

It is obviously desirable to reduce the tendency of the fibers to adhere in particular to the downstream plate or to pile up there. To obtain this result, according to one embodiment of the installation, the additional gas jet, consisting for example of air, is brought into contact with the main current interaction zone immediately downstream of the supply orifice. in material, at the upstream edge of the plate. This air intake near the upstream edge creates a layer of gas on the surface of the plate licked by the main current, a layer which tends to avoid adhesions and the accumulation of material on the plate.

In an embodiment of the installation comprising a plurality of fiber drawing stations staggered transversely to the

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main stream and each comprising a secondary jet which enters the main stream and a molten material supply orifice, the member for emitting the additional jet is provided with a discharge opening formed for example, either of a series of orifices emitting individual jets, each aligned with a fiberizing station, or a gas supply slot transverse to the direction of flow of the main stream. In both cases, the supply of additional air tends to create a curtain or a layer of air on the surface of the downstream plate exposed to the main current and also tends to promote greater penetration of the thread of thermoplastic material into the interaction area.

According to another variant of the installation, a unitary structure is used in the region where the secondary jet and the thermoplastic material are both introduced into the main stream. Such a unitary structure makes it possible to obtain and maintain at each fiberizing station a precise alignment of the emission orifice of the secondary jet and of the material supply orifice in the upstream-downstream direction of the main stream: this Alignment is particularly important for manufacturing uniform fibers in the case of an apparatus comprising a plurality of fiberizing stations mounted in series and staggered transversely to the direction of flow of the main stream.

In French Patent No. 2223318, a technique is provided for obtaining the precision of the alignment of the emission orifices of the secondary jets and of the material supply orifices in the upstream-downstream direction of the main stream; it consists in using a series of separate secondary jets, associated with a slot for supplying material, this slot being placed transversely to the main stream and downstream of the jets with respect to its direction of flow. In this case, the molten material is brought, from the slot, and under the influence of the individual secondary jets, to points precisely located downstream of each of these jets.

According to another embodiment of the installation, when a crucible or a die equipped with a series of orifices staggered transversely to the main current is used instead of a slot, the installation is provided with a structure comprising a series of holes arranged transversely to the main stream, with respect to its direction of flow and each located upstream of a material supply orifice. Preferably the structure is an integral part of the crucible. The secondary jet emission generator is equipped with emission tubes which each penetrate a hole in the structure to introduce a secondary jet into the main stream, the opening for discharging the additional jet being placed downstream of the orifices d material supply. By using such a common unitary structure, in which the holes for the supply of thermoplastic material and those for the supply of the secondary jet are drilled, it is easier to obtain a precise alignment of the pairs of orifices. Due to the proximity of these orifices, the temperature of the secondary jet influences the temperature of the thread of thermoplastic material, which makes it possible to adjust the latter by modifying the temperature of the secondary jet.

This structure with upstream plate, or heel, integral with the crucible or the die, also comprises separate tubes for the emission of secondary gaseous jets, these jet tubes having an outside diameter slightly smaller than the diameter of the holes in the upstream heel for penetrate slightly without, however, crossing them. It is preferable to mount these secondary jet tubes in groups. For example, with a die comprising about 80 glass supply orifices, the tubes are arranged and mounted in groups of about twenty and each group thus formed is preferably supplied separately with gas. Although, for most glass composition formulas, it is envisaged to use a die and an upstream plate or heel made of platinum alloy, the assembly which has just been described above, from the moment that the secondary jet tubes are insulated, allows the manufacture of the die / heel assembly in platinum alloy, while the tubes and the accessory assemblies and the gas supplies are made of less expensive metal, for example stainless steel. It is also advantageous especially when the crucible and the plate are made of platinum and the jet tubes of stainless steel, to provide an assembly and a supply in groups representing a portion of the total, associated with a die with multiple orifices, because this division into groups adapts more easily to differential thermal expansions and contractions such as between the assembly of the crucible or die on the one hand and the supply assemblies on the other.

In order to protect the jet tubes in the region where they penetrate into the corresponding openings of the upstream plate formed integrally with the crucible and the die, it is recommended to coat each tube with an insulating material, for example alumina .

Examples of embodiments of the invention are described below.

In this description, reference is made to the attached drawings in which:

fig. 1 is an elevational view, partly in vertical section, showing the means for supplying glass, the means for producing a gas stream and a secondary jet, as well as the means for introducing a additional air jet;

there fig. 2 is a plan view in section along 2-2 of FIG. 1; fig. 3 is an enlarged vertical section of the crucible or the die, with the plate which is integral therewith; this section, along 3-3 of fig. 4, also shows the relationship between the devices for supplying the secondary jet and the additional air;

fig. 4 is a plan view on which one can observe from below certain parts of FIG. 3, views along line 4-4 of FIG. 3;

fig. 5 is a schematic view of certain parts shown in FIG. 3 and shows in particular the fiberizing effect produced by the use of the main current and the secondary jet, and also the action of the additional air;

fig. 6 is a perspective view of certain gas supply and distribution means used to supply gas to the secondary jets;

fig. 7 is a horizontal section of various parts of the fiber drawing stations, the central part not being shown and the section representing the arrangement of certain elements constituting a fiber drawing installation at several stations;

fig. 8 is a perspective view of the apparatus used to mount a certain number of tubes used for supplying gas to the secondary jets;

fig. 9 and 10 show a modified form of the device intended to bring the additional air, FIG. 9 being a section along 9-9 of FIG. 10 and fig. 10 being a section along 10-10 of FIG. 9;

fig. 11 and 12 are partial views established as in FIG. 3, but showing other embodiments of the device for supplying additional air;

fig. 13 and 14 show still other arrangements of the parts for creating the fiber-drawing stations arranged according to the invention, FIG. 13 being determined generally as in FIG. 1, and fig. 14 being a partial plan view showing certain parts shown in FIG. 13.

The general arrangement (see in particular FIGS. 1 to 4) comprises a fiber-drawing crucible 200 in association with a fore-body 201 for feeding the glass, it being understood that instead of bringing the glass from the front - body of a glass furnace, an electrically heated melting crucible can be used to melt the glass and ensure its supply.

The crucible is provided with a series of glass outlet orifices 37, intended to bring the glass into the zone of interaction between the main stream and a series of secondary or carrier jets. Each secondary jet is associated with each glass supply orifice in order to produce a corresponding number of fiberizing stations. The main current is indicated by the arrow 12A (fig. 5)

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and the secondary or carrier jets are emitted from supply tubes through orifices 36. These supply tubes and orifices will be described in detail below.

The main stream is brought through line 202. This stream is produced following the combustion of a fuel in the combustion chamber 203 (fig. 1) which can be supplied with a mixture of gas and air at 204 .

A burner 205 supplied with a mixture of gas and air at 206 supplies the gas which is conveyed through the orifices 36 (FIG. 5) via the tubes mentioned above. The arrangement of these parts which constitute each of the fiber drawing stations is shown in more detail in FIGS. 3 and 4. As shown, it can be seen that the jet tubes 207, which are supplied from the burner 205 in the manner described below, penetrate a little into the holes 36a and emit gas jets transversely in the current 12A leaving the conduit 202. As shown by the embodiments of FIGS. 1 to 8, the holes 36a are drilled in a wall or heel 208, contiguous with the limit of the current 12A and, preferably, forming an integral part of the crucible 200.

Each fiberizing station established as just described operates generally in the manner described in the patent referred to above, and the parameters, including the kinetic energy of the gas stream and the secondary jet in its operational area and the temperatures and speeds of the current and the jet, as well as the temperature of the glass, the ratio between the dimensions of the orifices of the glass and the jet, their spacing and others, can all correspond to the parameters described in said patent .

One of the improvements concerned by the present invention relates to the downstream wall or plate element provided in the embodiments described in the patent cited in reference. Such a plate is designated as the downstream plate because it is located, with respect to the direction of the current 12A, downstream of the fiberizing station, that is to say downstream of the orifice 37 for supplying the glass, which itself is downstream of the jet orifice 36. The downstream plate is more particularly shown in FIGS. 1,3 and 5, where it is designated under the reference 209. As can be seen in FIG. 1, the downstream plate is mounted using adjustable supports 210, which makes it possible to adjust the position and the inclination of the plate. The plate 209 is thus positioned so that its inclination bends the current after it passes in front of the glass supply orifice.

The downstream plate (fig. 3 and 5) has a conduit 211, with fittings 212, which allows the circulation of a water cooling agent, for example, through this conduit 211. This circulation therefore provides cooling of the plate downstream.

As indicated above, the use of a wall or plate downstream of the fiberizing stations tends to produce contact between the fibers and the plate, hence a tendency to accumulate a deposit of glass. on the surface of the plate. With the improvement according to the invention, this tendency is considerably reduced thanks to the particular conditions under which air is supplied, preferably in the form of a fluid layer along the underside of the downstream plate or along the leading edge or upstream edge of the plate. The air or gas used for this purpose is referred to as the addition], and the jet produced is referred to as the additional jet.

In the realization of fig. 1 to 8 the leading edge 213 is placed at a certain distance from the lower part of the crucible 200, so as to form a slit between the crucible and the leading edge, slit through which the additional gas can be brought into a zone which, relative to the direction of movement of the current, is downstream of the orifices 37 for supplying the glass. The plate 209 comprises a duct 214 which is arranged there with fittings 215 for supplying additional gas, air for example. A series of orifices 216 communicate with the supply duct 214, and bring the air in the direction of the leading edge of the downstream plate, thus supplying the air which passes through the slot adjacent to the crucible. In order to close the gap between the crucible and the downstream plate and thus ensure that the additional gas cannot escape and will be brought through the slot in the leading edge of the plate, a sheet metal plate 217 is connected to the structure of the assembly 218, the lower edge of the plate being raised in the vicinity of the lower wall of the crucible, so as to thereby provide a cavity containing an insulating material 219 with high thermal resistance such as alumina fiber. It may be advantageous to make this stainless steel cover having a certain resilience. With this assembly and with the cover 217, the downstream plate can be positioned as described above while remaining in contact with the cover 217.

The action of the additional jet is indicated in fig. 5, in which flow lines appear not only the current 12A and the secondary jet of the jet tube 207, but also the additional jet brought from the passage 216 towards the leading edge of the plate from which the additional air passes through the slit and enters the system at the limit of the current, producing a fluid current or layer at the level of the underside of the plate 209. This apparatus includes a certain number of fiberizing stations of the kind of that of FIG . 5, spaced from each other transversely to the current. It is planned to bring an additional gas passage 216 aligned with each secondary jet orifice 36 and its associated glass supply orifice 37. With a certain number of additional gas supply passages, the additional gas from several passages tends to merge and therefore to form a more or less continuous gas curtain during its passage through the slot and its flow along the underside of the downstream plate at the limit of the current. As a result, the fibers being formed are effectively prevented from coming into contact with the surface of the downstream plate.

It will also be noted that the presence of the gas conduit 214 and the passage of additional gas on the faces of the downstream plate contribute to cooling the plate, so that the action of additional gas, in combination with the action of the agent cooling circulating in the conduit 211, will keep the plate at a relatively low temperature, which is also beneficial because it avoids sticking of the glass on the surface of the plate.

In an installation in which a large number of fiber drawing stations are spaced transversely to the current, for example about 80 stations, it is preferable to divide the downstream plate. As can be seen in fig. 2 and 7, the downstream plate, as a result of the multiplicity of the illustrated fiberizing stations, is sectioned and formed of three parts, each provided with a cooling duct 211 and an additional gas duct 214, respectively provided with fittings supply for air and water circulation as described above. By dividing the plate into such sections, efficient and precise circulation of the cooling water is made easier and a precise repetition of the additional air supply is guaranteed, thereby helping to keep the operating conditions within narrow limits. tolerance.

Now considering the mounting of the secondary jets as shown in FIGS. 1 to 8, it should be emphasized that it is better for the upstream plate 208 or heel to be an integral part of the crucible 200. It is preferable that this part is made of platinum alloy when using glass composition formulas usually used for the manufacture of fibers, and especially to ensure the regularity of the formation of fibers at each of the multiple stations; it is important to ensure a precise upstream-downstream alignment of the secondary jet orifices 36 and of the glass supply orifices 37. In one of the embodiments described in the patent mentioned above, this precision of alignment in the upstream direction -value of the secondary jet and the current of glass to be fiberized is obtained automatically by the use of a narrow slot for the entry of the glass, rather than a series of glass supply orifices arranged separately as is already noted above. The assembly shown in fig. 1 to 8 also allows precise alignment of the secondary jets with the glass threads, but

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in this case, the alignment precision is obtained despite the adoption of separate holes for the glass. This precision is obtained by making the wall or upstream plate 208 and the crucible 200 integral. As the holes 36a of the secondary jets and the orifices of the glass are both drilled in the same part, the alignment precision is obtained and preserved even in variable conditions of thermal expansion or contraction of the various parts of the part.

The alignment accuracy is further facilitated by other arrangements included in the embodiment illustrated in FIGS. 1 to 8. We see from fig. 2, 3, 4, 7 and 8 that each secondary jet is emitted from a jet tube 207 which enters the hole 36a, the diameter of the jet tube 207 being slightly less than the diameter of the hole 36a. The jet tubes 207 are separated into groups; four of these groups are seen in the drawings and each group is mounted on a fluid supply pipe 220 connected to the supply pipe 221. By dividing the total number of tubes 207 and by mounting each group separately, the expansion and thermal contraction of the tubing 220, which serves as support and supply for each group, it is easier to give a margin than if all the tubes were mounted on a single support for the entire series of fiberizing stations. In addition, by using jet tubes 207 which penetrate into each separate hole 36a, and by using tubes with an outside diameter slightly smaller than the diameter of the holes, more room for expansion and contraction is reserved. The grouping of jet tubes and their arrangement as well as their assembly as described in order to reserve a margin for expansion and contraction are especially important when, as for example one can envisage, the crucible 200 and the upstream plate 208 are made of platinum alloy and the jet tubes and accessories are made of a less expensive metal such as stainless steel because these different metals have different coefficients of thermal expansion or contraction.

As best shown in fig. 8, each group of jet tubes 207, in combination with the tubing on which it is mounted and the associated supply fitting 221, forms an assembly which resembles a rake, and this assembly is adapted to be mounted at the end of the supply connection 221. As can be seen in fig. 1 and 2, the supply connections 221 are made so as to be connected to the burner 205 to produce the secondary jet gas and preferably an attempt is made to introduce air into the gas stream which enters each supply connection 221. This is achieved by supplying by means of a gasket 223 (see also fig. 6) interposed between the combustion chamber 205 and the mounting plates 222 of the supply fittings 221 for groups of jet tubes. This combustion gas diluter, the role of which is to lower the temperature of the combustion gases coming from the burner 205 to a temperature compatible with the behavior of the jet tubes, comprises: air supply pipes 224 which are connected to tubes 225. Several of these supply pipes 224 are distributed along the flue gas diluter, the tubes 225 bringing the air to the passages 226, a passage 226 being provided for each of the groups of secondary jet tubes . In this way, the jet tubes receive the products from the combustion chamber 205 diluted by the air introduced by the pipes 224.

As can be seen by referring to figs. 2, 4 and 7, an additional secondary jet orifice 36 is provided and a secondary tube 207 disposed laterally outside each end of the line of the glass supply orifices 37. This arrangement is in accordance with what has was described in the patent referenced above and guarantees a uniform fiber drawing activity at the glass supply orifices at the opposite ends of the series. In addition to this arrangement, provision is made, according to the arrangements described in this patent, for a comparable arrangement relating to the additional gas supply passages. In other words, as can be seen in Figs. 2, 4 and 7, there is an additional gas supply passage placed sideways with respect to each end of the series of glass supply orifices, this assembly being provided for reasons similar to those mentioned concerning the secondary jet ports placed sideways or additional.

A modified form of the downstream plate and of the supply of the additional jet is shown in FIGS. 1,9 and 10. Here, the downstream plate, represented at 227, is equipped with a circulation duct for coolant 228 with fittings 229, and also with an air supply duct 230, with fittings supply 231. The individual passages or orifices 231 which bring the additional air from the duct 230 are connected to the base of a groove or slot 233 having a border facing the leading edge 234 of the downstream plate and placed just above above this edge. It is easily understood that this structure is intended to be mounted relative to the fiber drawing stations in the same general manner as that described above with regard to FIG. 1. The downstream plate of fig. 1, 9 and 10 is also intended to adjust to a structure to close the gap between the downstream plate and the crucible in a similar manner to that indicated in 217 and 219 in FIGS. 1,3 and 5. A slot such as that shown in 233 can be used to promote the spreading of the additional gas along the upstream edge of the plate, and thus promote the formation of a sheet of additional gas on the surface of the plate exposed to the interaction flow.

In fig. 11 shows another modified form of construction of the downstream plate and the additional gas supply. As shown, the lower part of the crucible 200 has a slightly modified profile and the shape of the downstream plate 234 is also modified to adapt to the lower part of the crucible in the manner indicated below. The plate 234 is provided with a coolant conduit 235 with fittings 236 and the additional gas supply conduit 237 with supply fittings 238 opens into passages 239 which communicate with a narrow chamber in the form of a slot or passage formed between the leading edge of the plate 234 and the lower portion of the crucible. Conformation means are arranged between the plate and the crucible to ensure the flow of the additional gas in the desired direction and out of the slot at the leading edge of the plate.

In fig. 12 shows another assembly of the downstream plate. In this embodiment, the crucible 200 is an integral part of an upstream plate or heel 208 provided with holes 36a corresponding to jet tubes 207. Here, the construction of the downstream plate 209 is essentially the same as that which has been described more top referring to fig. 1 to 8, but the system for shaping the space between the plate and the crucible is different. For example, the lower part of the downstream plate is lined with a metal strip 240 which extends over the entire length of the plate 209 and contributes with the upper part of the plate to delimit an elongated slot for the passage of the additional gas. in the current. This assembly is insulated against the heat of the crucible by means of an insulating layer extending over the wall 240, as shown at 241. Such insulation of this kind, like the insulation 219 described above, is advantageous from the made of the reduction of calorific losses for the crucible.

In all of the embodiments described in the above,

each time jet tubes 207 entering the holes forming an integral part of the crucible are used, it is desirable to provide thermal insulation between the jet tubes and the holes. This insulation can be obtained by covering the tubes with a thermal insulator such as alumina for example. Such insulation not only helps to limit heat loss from the crucible, but also protects the metal of the jet tubes.

All the provisions described in the foregoing also apply to a general type installation shown in FIG. 1 in which the crucible is mounted under a glass supply fore-body 201; the crucible is separated or isolated from the glass supply structure by a ceramic element 242,

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in which is taken a tube for cooling agent 243 (fig. 1 and 2). It is also advantageous to use insulation made of fibrous material 244, as indicated, on the lower part of the contiguous surfaces of the fore-body to slow down the heat losses in this area.

In certain cases at least it is advantageous to establish electrical assemblies as indicated in 245, connected to the ends of the crucible 200 and allowing the heating of the crucible by electrical resistance.

Figs. 13 and 14 show another embodiment comprising the supply of additional air. In this embodiment, the glass supply fore-body or equivalent is indicated at 246 and the crucible with the die at its lower part is shown at 247. The glass supply orifices bear the reference 37 and in this embodiment the secondary jets are supplied by the orifices 36 formed in the projections 248 which leave from the pipe 249 supplying the gas jets. A supply conduit 250 is connected to the tubing 249.

The current 12A is emitted by the assembly 251, the upper limit of the current being close to the secondary jet orifices and of the glass, 36 and 37.

On the downstream side of the orifices 37 is an assembly comprising a downstream plate shown at 252, this assembly being hollow with a tube 253 supplied by a conduit 254; the tubing is provided with a series of raised studs 255, the orifices 256 of which serve for the emission of additional air in a position which, relative to the direction of the current, is downstream of the fiberizing station established by the glass and secondary jet orifices.

As can be seen in fig. 14, the jet orifices, the glass supply orifices and the additional gas orifices are mounted in groups aligned with each other in an upstream-downstream direction, each group constituting a fiberizing station.

With regard to the operation of the fiberizing system in the case of the use of the additional gas as just described, it should be noted that the additional gas used may have a pressure of the order of 0.5 to 2 bars, and preferably between about 0.8 and 1.2 bar.

In an installation of about 80 fiber drawing stations, according to the embodiment of FIGS. 1 to 8, the air flow used for the supply of additional gas can be of the order of 15 to 30 Nm3 per 20 hours, and preferably between about 17 and 25 Nm3.

The kinetic energy per unit volume of the additional jet must be considerably lower than that of the secondary jet.

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Claims (14)

615 407 1. A method of manufacturing fibers from a thermoplastic material according to which a main gas stream is generated and at least one secondary gas jet of smaller dimension, but of kinetic energy per unit of volume greater than those of the main stream, directs the secondary gas jet transversely to the main current so that it enters there by creating an interaction zone, the thermoplastic material being introduced in a stretchable state into the interaction zone, characterized in that a jet is brought additional gaseous in contact with the flow resulting from the main stream and the secondary jet, so as to prevent the adhesion of the fibers to material elements adjacent to their path. 2. Method according to claim 1, characterized in that the additional gas jet is brought into contact with the flow downstream of the point of introduction of the thermoplastic material. 2 3. Method according to one of the preceding claims, characterized in that the additional gas jet is brought into contact with the flow in the immediate vicinity of the point of introduction of the material, in the form of threads in the molten state, in the interaction area. 4. Method according to one of the preceding claims, characterized in that the additional gas jet flows along a surface extending downstream from the point of introduction of the thermoplastic material into the interaction zone. 5. Installation for implementing the method according to claim 1, comprising a first generator emitting a main gas stream through an outlet orifice, a second generator emitting at least one secondary gas jet of kinetic energy per unit of greater volume to that of the main stream, through an emission orifice of section smaller than that of the outlet of the main stream and directing the secondary jet transversely to the latter to create an interaction zone, a source of power in thermoplastic material comprising at least one supply orifice arranged so as to bring the material, in the stretchable state, into the zone where the secondary jet enters the main stream, characterized in that it comprises a member emitting a gas jet additional to the flow resulting from the main stream and the secondary jet through a discharge opening (300; 256). 6. Installation according to claim 5, characterized in that the discharge opening (300, 256) of the additional gas jet is disposed downstream of the orifice (37) for supplying material, relative to the direction of main current flow. 7. Installation according to one of claims 5 and 6, characterized in that the opening (300) for discharging the additional jet is placed so that the latter comes into contact with the flow in the immediate vicinity of the place where a net of material in a stretchable state is introduced into the interaction zone. 8. Installation according to one of claims 5 to 7, comprising a plate disposed, with respect to the direction of flow of the main current, downstream of the place where the material is introduced into the interaction zone, characterized in that that the discharge opening (300, 256) of the member for emitting the additional jet is located in the region of the upstream edge of the plate, so that the additional jet flows along said plate (209 , 227, 252). 9. Installation according to claim 8, characterized in that the plate contains a conduit (214, 230) for supplying additional gas communicating with at least one passage (216, 232) directed towards the leading edge (213, 234 ) from the plate. 10. Installation according to one of claims 5 to 9, comprising a plurality of orifices for emitting secondary jets arranged transversely to the main stream, the supply source of thermoplastic material being provided with a plurality of orifices for supply (37) each delivering a thread of material, characterized in that the discharge opening of the additional gas jet consists of a slot (300) extending transversely to the main stream along the material supply orifices . 11. Installation according to one of claims 5 to 8, comprising a plurality of orifices for emitting secondary jets arranged transversely to the main current, the supply source of thermoplastic material being provided with a plurality of orifices for supply (37) each delivering a thread of material, characterized in that the opening for discharging the additional jet consists of a plurality of orifices (256) separated from each other transversely to the main stream and arranged each downstream of a material supply orifice (37). 12. Installation according to one of claims 10 and 11, characterized in that it comprises a structure (208) comprising a series of holes (36a) arranged transversely to the main current, relative to its direction of flow and located each upstream of a material supply orifice (37) and in that the generator for emitting the secondary jets is equipped with emission tubes (207) which each penetrate a hole in said structure to introduce a jet secondary in the main stream, the opening for discharging the additional jet being placed downstream of the material supply orifices. 13. Installation according to claim 12, characterized in that the structure is integral with the material supply source. 14. Installation according to one of claims 12 and 13, characterized in that the emission tubes (207) of the secondary jets are combined in several groups.