FR2459783A1 - Fiberising glass using orificed centrifugal spinner - feeding glass to spinner via rotating basket with single row of apertures - Google Patents

Abstract

In fiberising moltent glass by the centrifugal projection of streams of glass through rows of perforations in the peripheral wall of a spinner positioned on an upright axis within a downwardly directed annular gas blast, all the molten glass is feed to the inside of the peripheral wall of the spinner in the plane of the uppermost row of perforations. An downwardly flowing layer of glass is thus formed on the inside of the peripheral wall of the spinner. A rotating distributing basket with a single row of apertures in its peripheral wall located in the plane of the uppermost row of perforations of the spinner is located in the spinner wall. Used for fiberising glass, mineral and other thermoplastic materials.

Description

 The present invention relates to a hollow centrifuge for fiberizing thermoplastic materials, in particular glass, centrifuge whose axis is oriented vertically and into which a stream of glass is introduced which, during the rotation of the centrifuge, is directed towards the surface. - The inner wall of the centrifuge, in which are arranged a multiplicity of orifices so that the glass is projected in the form of nets or "primary fibers" at the outlet of said orifices.Il is provided means for producing a an annular stream of drawing gas at the outlet of a combustion chamber, said annular stream being directed downwardly along the outer surface of the perforated strip of the peripheral wall of the centrifuge so that the glass threads are stretched and the downwardly drawn fibers in the drawing stream for depositing, generally coated with a binder, on the upper face of a convoy Perforated receiving conveyor, usually positioned to form the bottom wall of a collection chamber. In a particular installation, suction boxes are provided under the conveyor, so as to facilitate the formation of a sheet or mat of fibers thereon, this sheet being evacuated for further treatment, packaging, etc. .

 In commonly used systems of this type, it is conventional to use so-called soft glasses, that is, glass compositions which are especially designed to have temperature and temperature characteristics. viscosity allowing free passage of the glass through the openings of the wall of the centrifuge at a much lower temperature than that at which the centrifuge material is able to withstand without excessive corrosion and deformation.

 To achieve the objective defined above, appreciable amounts of one or more compounds of barium, boron or fluorine which tend to lower the melting temperature, the devitrification temperature or liquidus and viscosity and are therefore effective in avoiding the use of excessively high glass melting temperatures.

 Typical contents of barium, boron and fluorine oxides presently used in the glasses used are approximately 3 *, 6 * and 1.5 * respectively, but the boron and fluorine compounds which are commonly used are volatile at the melting temperatures adopted in the manufacture of glass and even, for fluorine, at the glass temperatures used during the fiberization, so that to obtain these levels, it is necessary to initially introduce larger quantities of ingredients. during the preparation of the composition. The use of substantial amounts of these compounds is therefore hampered by the fact that they increase the cost of the fibers produced, because they are of a high price, in particular the barium compounds.

 On the other hand, the use of compositions containing these substantial amounts of. boron or fluorine or even barium requires precautions. In particular, in the case of boron or fluorine, troublesome volatile constituents are discharged from the molten glass production plant and in order to avoid polluting the atmosphere, it is necessary to treat the evacuated gases especially with a view to separating them. and properly removing these constituents.

 Finally, the relatively soft glasses obtained produce fibers that do not have all the desirable strength at high temperatures.

 The object of the invention is therefore to overcome the aforementioned drawbacks of the known embodiments.

 Thus, the objective of the invention is to increase the production capacity of a given centrifugal drawing installation of the type described, by practically eliminating certain sources of pollution, and by providing the possibility of using low cost glass to produce fibers with better thermal resistance characteristics.

 With fibers produced using a conventional centrifuge from compositions of known types, the insulating products can only be used in applications where they are subjected to temperatures slightly above 4000C. With fibers produced from certain compositions according to the invention, the corresponding temperature may instead be up to about 4800C.

 The above general problems can be solved by adopting a number of the important improvements provided by the present invention, individually or in various combinations, including the operating conditions, the method and equipment used for the introduction and distribution of the glass in the process. centrifuge, the construction of the actual centrifuge and also the composition of the glass, as well as the composition of the alloy which is formed the centrifuge. Different characteristics are interrelated, as will be explained below.

 Considering first the composition of the glass (examples will be given later), and although the method and equipment, using the centrifuge, can be used with compositions currently used, it falls within the scope of the invention that this composition may not contain fluorine and little, if any, barium and boron. Such glass compositions correspond to "hard" glasses having higher melting and devitrifying temperatures.

As a result, these fluorine and even boron or even barium-free compositions, which did not allow fiber drawing by the prior drawing technique, can be fiberized by the process and equipment according to the invention. In addition, these hard glasses are interesting from the point of view of their increased resistance to temperature.

 Such "hard" glass compositions, which have high devitrification temperatures and only reach a viscosity suitable for fiber drawing at elevated temperatures, require special processing and special fiberizing equipment and the invention relates to to a number of important improvements to the construction of the centrifuge, to the method and means for supplying and dispensing the glass in this centrifuge and to the operating conditions established in the centrifuge, facilitating the manufacture of the fibers from said glasses "hard" and even allowing the fibering of some very "hard" glass compositions that it would be difficult, if not impossible, to fiber with techniques and centrifuges of known types.

 It is also worth noting that some of these perfec-.

Structural and operative operations, while being of particular advantage and importance for fiberizing "hard" glasses, are also advantageous when applied to other types of glasses which can be fiberized by the centrifugation technique in question.

Other advantages and characteristics of the invention will be demonstrated in the remainder of the description, given by way of advantageous but nonlimiting example, with reference to the appended drawings in which
FIG. 1 is a vertical section, in elevation, showing a fiber production installation comprising a centrifuge arranged in accordance with a preferred embodiment of the invention and provided with a blowing generator producing an annular gas stream. stretching downwards along the peripheral wall of the centrifuge
FIG. 1a is a fragmentary view on a larger scale of another characteristic part that can be incorporated in the embodiment of FIG. 1
FIGS. 2, 3, 4, 5 and 6 are sections similar to FIG. 1 and each show an embodiment of the centrifuge and glass feed members inside the centrifuge.
FIG. 7 is a detail view, in section, on an enlarged scale showing a mounting arrangement of a glass supply member inside a centrifuge such as that of FIG. 6;
FIG. 8 is a detail view showing on a larger scale the arrangement of another form of glass delivery member, corresponding to the version of FIGS. 4 and 5;
FIG. 9 is a partial perspective view of a reinforcement chord of centrifuges such as those of FIGS. 4 and 5, and
FIGS. 10 and 11 are variant sections of the perforated strip of the peripheral wall of the centrifuge.

GENERAL STRUCTURE
In the embodiment of Figure 1, there is provided a vertical shaft 10 centrifuge support which carries at its lower end a hub 11 for mounting the centrifuge. The centrifuge itself has been designated as a whole by the reference 12. It consists of a strip or peripheral wall 13 comprising a multiplicity of rows of fiberizing orifices and whose upper edge is connected to the hub 11 by the central portion The holes in the wall of the centrifuge have been shown only in the sectional portions of the wall of the device, but it goes without saying that there is a multiplicity of orifices distributed in several rows spaced vertically. On its lower edge, the centrifuge is provided with an inwardly projecting flange 15 to which is connected the upper edge of a cylindrical element 16 which performs a reinforcing or shoring function, as will be specified in FIG. the following.

 Inside the centrifuge, there is provided a distribution basket 17, rotating with it and having a single series of dispensing orifices 18 which are placed substantially in the plane of the upper row of orifices of the peripheral wall of the centrifuge. As indicated, the basket 17 is mounted on the hub 11 by means of tabs 17a directed downwards. A stream of glass is introduced downwards, in the center, through the structure supporting the centrifuge, as indicated in S, so as to arrive inside the basket 17 and to spread laterally on the bottom to the perforated peripheral wall of the basket, the glass then forming inside this wall a layer from which designated nets 19 are cut through the orifices radially outwardly towards the inner surface of the peripheral wall of the centrifuge in an area adjacent to the upper row of orifices; from this zone, the glass flows downwards on the inner surface of the centrifuge wall. This flow directed downwards is carried out unhindered because there is no containment wall or chamber to the interior of the peripheral wall and the flow, when observed with stroboscopic illumination, has laminar characteristics with uniform wave appearance.

It is from this laminar flow without retention or confinement that the glass penetrates the orifices formed in the peripheral wall of the centrifuge and is projected from all these orifices in the form of a multiplicity of primary threads which are stretched by the annular stream of gas established by the equipment which will be described in the following.

 FIG. 1a shows a variant of the dispenser basket 17b, which comprises two rows of orifices 18a arranged in staggered rows but all close to a common plane in order to bring the glass into the zone of the upper row of orifices of the centrifuge wall.

 Regarding the arrangement of the dispenser basket (17 in Figure 1 and 17b in Figure la), it should be noted that most of the dispensing baskets used in the known methods are provided with several rows of orifices spaced vertically the each other to ensure a distribution of the glass towards the perforated peripheral wall of the centrifuge over most of the vertical dimension of this wall. However, the Applicant has found that by adopting, according to this known technique, a multiplicity of orifices for effecting the vertical distribution of the glass, certain disadvantages and difficulties were encountered, in particular when using centrifuges of relatively large dimensions, at the same time. both with respect to the diameter and the vertical height of the perforated peripheral wall.

 One of the most important difficulties lies in the heat lost by the glass threads during their journey between the dispenser basket and the inner surface of the centrifuge peripheral wall. This heat loss is directly proportional to the total area of the nets being cut. With a large number of small nets, as in previous systems, the total area is much greater than that corresponding to the arrangement according to the invention, wherein the dispenser basket is provided only with a row of larger orifices. dimensions, which allows the same amount of glass to be cut for a much smaller total area.

Thus in a particular case, the system according to the invention makes it possible to bring a given quantity of glass in the form of nets, the surface of which corresponds to only 1/7 of the surface of the prior systems.

 Thanks to the invention, therefore, the excessive heat loss occurring in the transferred glass of the dispenser basket is eliminated on the peripheral wall of the centrifuge while this constitutes a major disadvantage of prior equipment. In addition, because of the small dimensions of the glass nets created in these known embodiments, the heat loss occurring during the passage of the dispenser basket to the peripheral wall of the centrifuge is much less uniform between the different nets that in the case where produces a smaller number of larger nets, as in the arrangement according to the invention.

 Although the aforementioned difficulties concerning heat losses have not been considered prohibitive when using soft glasses of known methods, these heat losses are not tolerated during the use of the hard lenses considered here.

 Another important factor is that the present invention makes it possible to increase the diameter of the centrifuge. With the basket dispenser known systems that produces small diameter glass nets, increasing the diameter of the centrifuge tends to produce a floating nets and therefore to alter the uniformity of the operating conditions. By using, according to the invention, a smaller number of larger nets, this floating is remedied, but other means for reducing this tendency to float will also be described hereinafter with reference to the embodiments shown in FIGS. Figures 2 to 6.

 In addition, when a large number of small glass threads are directed to the inner surface of the perforated peripheral wall of the centrifuge over most.

As a result of the perforated area of this wall, some of the threads arrive on the perforated wall in the ori- entation of the orifices of the wall, while other nets arrive on the perforated wall in the intermediate zones. establishes non-uniform flow conditions that tend to disturb the uniformity of the fibers produced.

 This being so, according to the invention instead of using a large number of vertically distributed nets on the peripheral wall of the centrifuge, a layer of molten glass flowing downwards is established and maintained without being impeded or confined to the surface. interior of the perforated peripheral wall, the supply of the glass being effected towards the upper edge of this layer and the latter progressing downwards in a laminar manner by passing over all the perforations of the wall of the centrifuge, so that the conditions of Projection of the glass mesh through and out of each orifice of the peripheral wall is substantially the same, eliminating a cause of nonuniformity of the produced fibers.

 This establishment of the downwardly unfurling layer is ensured by the dispenser basket described above with reference to FIGS. 1 and 1c, ie using a dispenser basket in which all the glass to be converted into fibers. is fed to the centrifuge wall through a single series of orifices near or in a plane at or near the upper series of orifices in the centrifuge wall. This single row of orifices advantageously comprises from 75 to 200 holes only in total, which corresponds to a number between one tenth and one third of that commonly used in multi-row dispensing baskets.

 The establishment of the desired uniform conditions for passage of the glass through the openings of the centrifuge wall is further improved by certain other preferred operating conditions which will be defined later, in particular the maintenance of temperature conditions which create viscosity essentially. uniform glass in the upper and lower areas of the centrifuge wall.

 To ensure the drawing of the glass threads, the device represented in FIG. 1 comprises an annular chamber 20 provided with an annular nozzle 21, this chamber 20 being fed by one or more combustion chambers such as 22, which are provided with appropriate means burning fuel to produce the hot drawing gases. This produces a downwardly directed annular draft gas stream which is in the form of a curtain surrounding the centrifuge. The design details of the structure supporting the centrifuge and the blowing generator need not be given in the present description because they are well known to those skilled in the art.

 As indicated in FIG. 1, the equipment also includes means for heating the lower edge of the centrifuge. This means may be in a variety of forms and preferably comprises a ring-shaped high frequency heater 23, as shown in the figure. This heating ring preferably has a diameter greater than that of the centrifuge and is preferably located at a short distance below the bottom of this device.

OPERATIVE DATA
The conditions and operating parameters will now be described.
Considering the operation of an embodiment of the invention such as that shown in FIG. 1, it should be noted first of all that although various features of the invention may be involved in centrifuges of all sizes, in the context of the invention to give the centrifuge a diameter greater than that of conventional centrifuges. For example, it is possible to adopt for the centrifuge a twist diameter of 400 mm, compared to the value of 300 mm commonly adopted in a large number of prior devices. This allows to provide a much greater number of glass delivery orifices in the peripheral wall of the centrifuge, so that it is possible to advantageously increase the number of glass nets projected by this centrifuge into the surrounding annular blowing stream for their drawing.

Due to the relatively high rotational speeds of centrifuges of this type, this apparatus is subjected to a very great centrifugal force and since it operates at high temperature, the median zone of the peripheral wall always tends to curve towards the outside.

This tendency is counterbalanced by using reinforcement or shoring means, of which several forms will be described in the various embodiments shown in the drawings. In the embodiment of FIG. the shape of an annular element 16 fixed via the flange 15 bent inwardly on the lower edge of the peripheral wall. The reinforcing action of this annular element 16 can be well understood taking into account that, since the central zone of the peripheral wall 13 tends to curve outwards under the action of the centrifugal force, it tends to also to bend the flange 15 upwards and inwards around its line of junction with the lower edge of the wall 13.Si (as in the known centrifuges), the annular element 16 was not provided, a This bending of the flange 15 upwards and inwards would result in the formation of a slight undulation of its relatively thin inner edge.

On the contrary, the presence of the annular element 16 on the inner edge of this collar prevents this undulation, thereby ensuring a strengthening of the centrifuge wall.

The angular junction of the element 16 with the collar 15 also contributes to creating the desired reinforcement.

 For the purpose that has just been defined, the annular element 16 preferably has, in the axial direction of the centrifuge, a dimension greater than the average thickness of the peripheral wall of the centrifuge. In addition, in order to effectively counterbalance the curvature of the peripheral wall towards the outside, the annular element 16 is preferably mounted in a position projecting downwards from the inner edge of the collar 15.

Advantageously, it is given a vertical dimension greater than the maximum thickness of the wall 13. It has been found that the reinforcement of the centrifuge carried out in this way makes it possible to delay the bulging of the wall of the centrifuge and consequently to increase the duration of the service of this device.

 Other figures which will be described in the following other arrangements for performing this reinforcing action are shown.

Before describing the operation of the embodiment of the equipment according to the invention shown in FIG. 1, it should be noted that, in a known process of using a centrifuge with a relatively soft glass, it is usual to introduce the glass in a dispenser basket mounted in the central zone of the centrifuge and having a peripheral wall provided with several vertically spaced rows of glass dispensing orifices so that the glass discharged by the basket reaches the peripheral wall of the centrifuge at least on most of its vertical dimension. a substantial difference in temperature is then established between the upper edge of the peripheral wall and its lower edge
As a result, the upper edge is at higher temperatures than the lower edge, mainly because this upper edge is located near the birth zone of the draw stream. In addition, the peripheral wall is commonly the same thickness over the entire height or even in some cases it is thicker towards the upper edge than towards the lower edge. In addition, in this known technique, there may be certain differences in size (diameter) between the orifices of the upper rows of the centrifuge and those of the lower rows. The known embodiments of these various factors have already been taken into account in order to obtain that the threads The upper apertures are projected at a higher flow rate than the threads of the lower apertures in order to obtain what has been called "umbrella" fiber drawing, as described, for example, in the French patent 1,382,917 (FIG. 3). . This prevents the fibers from intertwining, thus becoming entangled and welded together in the fiberizing zone, as is the case when the glass threads are projected at the same distance by the upper rows and the lower rows of orifices.

 Although, in some known systems, the bottom edge of the centrifuge is subjected to heating in addition to that resulting from the action of the annular drawing current and the introduction of molten glass, the production of In the known embodiments, an "umbrella" fiber pattern most often requires a difference between the temperatures of the glass on the upper edge of the centrifuge and on its lower edge. The upper edge of the centrifuge is subjected to a higher temperature. because of the aforementioned factors while the bottom edge of the centrifuge is usually at a lower temperature, even if additional heating is created; because of this difference between the temperatures which are for example about 10500C at the top of the centrifuge and 9500C at the bottom, the resulting viscosity of the glass is lower at the top than at the bottom and this results in easier flow through the upper openings so that the glass threads are projected farther up than at the bottom of the centrifuge, which allows to obtain the desired "umbrella" fiberization.

 In the known techniques using soft glasses, such a difference in temperature between the upper edge and the lower edge of the centrifuge could be established to achieve the aforementioned objectives, because with these soft glasses, even when the temperature substantially exceeds the temperature However, it is not sufficiently high to produce serious damage to the centrifuge metal (for glass located in the area adjacent to the upper rows of orifices).

 On the contrary, with a hard glass, it is not possible in practice to operate with a large temperature difference between the upper and lower edges of the centrifuge. This is because if the temperature on the lower edge was kept sufficiently high enough to devitrify the temperature to prevent the glass from crystallizing, and thus not obstructing the lower rows of orifices, it would be necessary for establish the temperature difference frequently used in known systems to obtain umbrella fiberization, bring the temperature of the glass in the area adjacent to the top edge of the centrifuge to such a high value that the centrifuge would be subject to corrosion, erosion and / or or excessive deformation.

 According to the invention, given these factors, and when using hard glass compositions, the desired umbrella fiberization is obtained in a new way. Instead of using a difference in temperature between the upper and lower edges of the centrifuge, approximately the same temperature is set on the upper and lower edges of the centrifuge and this temperature is maintained at a level (eg 10500C) which is greater than the devitrification temperature while being relatively close thereto.The viscosity of the glass is therefore essentially the same in the areas of the upper and lower rows of the centrifuge orifices, for example about 5000 poises; however, according to the invention, the desired increase in resistance to the projection of the glass threads through the orifices of the lower rows is established in a different manner. Thus, unlike the prior art, a peripheral wall is used in the centrifuge which has a greater thickness in the direction of the lower edge than in the direction of the upper edge, as clearly shown in FIG.

As a result, larger length orifices are obtained in the direction of the lower edge which, for a given viscosity of the glass, oppose greater resistance to the flow of the threads under the action of the centrifugal force. Because of this difference in flow resistance, the glass threads are projected further on the upper edge of the centrifuge than on the lower edge, thereby producing the desired umbrella fiberization. If necessary, it is possible to increase the flow resistance of the glass threads through the orifices of the lower rows by reducing their diameters.

 To establish the desired temperature along the lower edge of the centrifuge, it is carried out according to the invention a more intense heating of the lower edge of the centrifuge in the known embodiments. Thus the heater 23 shown in Figure 1 has a power at least double or triple that of the devices used in the past. it is appropriate to use a heater with a power of 60 kW at 10000 Hz.

 In the preferred embodiment of the present invention, conditions are maintained establishing in the upper and lower areas of the centrifuge peripheral wall a glass temperature which is about 10 to 200 ° C higher than the devitrification temperature.

 In most applications, the lower zone of the peripheral wall of the centrifuge is further given a thickness at least about 1.5 times that of its upper zone; in some cases, it may be desirable to give the lower zone a thickness of the order of 2.5 times that of the upper zone. A thickness of the lower zone of the centrifuge wall double that of the upper zone is a typical value for the practice of the invention. For example, in a particular device, the thickness of the upper zone may be 3 mm and that of the lower zone 6 mm.

 Although the increase in thickness may be essentially uniform from top to bottom, as shown in FIG. 1, it is also possible to adopt the variant indicated in FIG. 10 which represents on an enlarged scale a cross section of the peripheral wall of FIG. a centrifuge also having a thicker thickness in its lower zone than in its upper zone. In this case, the wall has the highest thickness in the lower zone, the minimum thickness in the median zone and an intermediate thickness in the upper zone. This partitioning of the wall thickness advantageously makes it possible to establish in an even more precise manner the desired effect of umbrella fiberization. In this respect, it should be noted that the two main sources of heating of the peripheral wall are formed at the top by the annular stream of drawing gas and bottom by the induction heating device 23. As a result, the median zone of the peripheral wall takes a temperature a little lower than that of the upper or lower edges and that the viscosity of the glass in the middle zone is increased in correspondence. A wall thickness variation such as that shown in FIG. 10 thus facilitates the establishment of the desired degree of flow and projection of the glass, i.e., a maximum degree in the upper zone, an intermediate degree in the middle zone and a minimum degree in the lower zone.

 Although FIGS. 1 and 10 show the outside wall surface as having a conical profile, that is to say a slightly larger diameter at the bottom than at the top, it goes without saying that this external surface may have a cylindrical shape as shown in Figure 11.

DIVERSE PARAMETERS
Before describing other embodiments of the invention and other corresponding features, which are highlighted in Figures 2 to 9, it is desirable to define certain additional parameters, including ranges of structural and operating characteristics of the inyention.

 Although various features of the invention may be used in conjunction with centrifuges having a perforation coefficient (ratio of the total perforation area to the total area) of the peripheral wall of the order of magnitude of that adopted in Known embodiments, certain features of the invention are advantageously used in combination with a centrifuge having a greater number of orifices per unit area of the peripheral wall. By such an increase in the coefficient of perforation, it is possible to increase the capacity of the centrifuge, that is to say the total amount of glass converted into fibers by this centrifuge.

 When analyzing this subject, it should be remembered that the rate of delivery of the glass through the apertures of the centrifuge wall is strongly influenced by the viscosity of the glass feeding them. An increase in viscosity slows the flow in each orifice but, by increasing the coefficient of perforation, it is possible to maintain a given overall capacity for a centrifuge, even with glass of higher viscosity. Consequently, the increase in the perforation coefficient makes it possible to use glasses with a viscosity greater than that commonly used on centrifuges, without resulting in a reduction of the overall fiber drawing capacity.

 The fiberizing capacity also depends on the diameter of the orifices, but it is possible to maintain, even with orifices of reduced diameter, a given fiberizing capacity if the perforation coefficient is sufficiently increased.

 According to the invention, it is even possible to increase the overall production capacity of a given centrifuge and this while simultaneously reducing the speed of passage of the glass through the individual orifices of the peripheral wall. This result can be obtained partly by increasing the coefficient of perforation (as indicated above) but also by certain other factors which will be specified later; as a result, the erosion and deterioration of the centrifuge is reduced despite the increase in the overall fiber capacity. Erosion is obviously concentrated in the individual orifices, but it is surprising to see that despite the increase in the coefficient of perforation (which should produce a weakening of the centrifuge), the capacity and the service life of the centrifuge are not reduced and can be even slightly increased compared to the known achievements.

 In addition, reducing the speed of flow of the glass in the orifices, it is not necessary to give the drawing current generated along the outer surface of the peripheral wall of the centrifuge a speed as high as if it existed. a greater flow rate through each orifice. This translates into a double benefit. In the first place, it is possible to produce fibers of greater length because, as is well known, the length of the fibers produced by a centrifuge of the aforementioned type is generally inversely proportional to the speed of the drawing gases. Secondly, the speed reduction of the drawing gases makes it possible to save energy.

 An increase in the coefficient of perforation also makes it possible to stretch a larger number of filaments in a given volume of drawing gas, which also results in energy savings. It has been found that, in the practice of the invention, notwithstanding the increase in the number of filaments per unit volume of drawing gas, the fibers produced do not form pockets or areas of agglomeration of fibers but the The fibers remain isolated from one another during the entire stretching phase, making it possible to produce fibrous products, for example insulating products, of high quality.

 In the practice of the invention, it is appropriate to adopt in most cases a perforation coefficient corresponding to at least 15 orifices per square centimeter of the perforated portion of the peripheral wall, for example a value between 15 and 4 or 50 holes per square centimeter. A preferred value is of the order of 35 orifices per square centimeter. The diameter of the orifices used is preferably between about 0.8 and 1.2 mm.

 Although certain features of the invention can be applied to centrifuges of any diameter, it is contemplated in many applications of the invention an increase in the diameter of the centrifuge compared to known apparatuses. Thus, although in the known centrifuges a diameter of about 300 mm is adopted, the centrifuges arranged according to the invention can be given a diameter of at least 400 mm and up to 500 mm.

 Increasing the diameter of the centrifuge also offers advantages. Thus, for a given perforation coefficient and for the same fiber-drawing capacity of the device, an increase in diameter results in a reduction in the flow velocity of the glass through each orifice. As indicated above with respect to increasing the coefficient of perforation, the decrease in flow velocity in the orifices may even allow some increase in the viscosity of the fiberglass. For the same capacity of the centrifuge, however, a higher viscosity of the glass does not produce excessive wear due to the reduction in flow velocity in the orifices.

 Although certain features of the invention can be exploited in centrifuges whose peripheral wall has any desired vertical dimension, it is also possible to envisage, in certain applications, an increase in the height of this peripheral wall, up to twice as great as the realizations. known; for example, the centrifuge band height can be increased from about 40 mm to 80 mm. This increase in height makes it possible to increase the total number of orifices, an extremely advantageous result since an increased number of glass threads are projected into the drawing gas stream, which results in a new energy saving.

DETAILED DESCRIPTION
Are now described in detail Figures 2 to 9
Considering the embodiment shown in Figure 2, we see that there is again provided a central shaft 10 supporting the centrifuge and at the lower end of which is mounted the hub 24 which has the function of supporting the centrifuge designated in 25 as in the first embodiment, there is provided an annular chamber 20 having an annular nozzle 21 for emitting the drawing current along the peripheral wall of the centrifuge. In Figure 2, the diameter of this centrifuge is a little larger than in Figure 1 and the peripheral wall 26 also has a greater thickness in the lower zone than in the upper zone.On the lower edge of the peripheral wall, there is provided a flange 27 curved inwards and whose thickness gradually increases radially inwards, its inner edge having, in the axial direction of the centrifuge, a dimension at least equal to the average thickness of the wall 26 and preferably greater than the maximum thickness of this wall. This creates a reinforcement intended, as described above, to prevent the peripheral wall 26 from bulging outwardly in its central zone.

 In the embodiment of FIG. 2, a dispenser basket 28 is mounted in the center of the centrifuge and is provided with a row of peripheral ports 29. The glass stream S enters the basket from the top, as 1, and the rotation of the basket 28 radially projects the glass threads 30 outwards.

 Instead of the threads 30 being fed directly into the peripheral wall of the centrifuge, the embodiment of FIG. 2 provides a relay device interposed between the basket and the peripheral wall of the centrifuge. This relay device is in the form of an annular hopper 31 open towards the inside and having in the bottom a row of relay holes spaced so as to emit glass filaments, indicated at 32, towards the peripheral wall. centrifuge.

As in the first-described embodiment, the outlets of the threads 32 should be positioned to direct all the fiberglass into the upper region of the perforated wall of the centrifuge, thereby establishing the laminar free flow described below. upper.

 In the embodiment of FIG. 2, the diameter of the distributor basket 28 is given a value lower than that of the basket 17 of FIG. 1, notwithstanding the fact that the diameter of the centrifuge of FIG. 2 is greater than the diameter of the preceding one. This proportioning of the parts in question is advantageous because, even with a basket with a diameter equivalent to that indicated at 17 in FIG. 1, the distance separating the perforated wall of the centrifuge from the dispenser basket would alter the uniformity of the threads being cut and would produce a flutter and therefore the arrival of a portion of the glass to an area of the wall placed below the upper edge.This is undesirable because, in the practice of the invention, all the glass must be brought essentially in the plane of the upper rows of orifices of the wall of the apparatus in order to establish from the top to the bottom of the peripheral wall of the centrifuge the free downward flow in superposed laminar layers that is desired.

 By using a dispenser basket 28 with a diameter slightly smaller than that of FIG. 1 and by further employing a relay device such as the annular hopper 31 of FIG. 2, it is possible to ensure a more precise transfer of the glass towards the region of the upper row of fiber drawing ports. The hopper 31 can be mounted on a portion of the hub 24 by means of a thermally insulated carrier structure 31a as shown at 46 in FIGS. 7 and 8.

 As in FIG. 1, a high frequency induction heating device 23 can be used in FIG. 2 to equalize the temperatures in the upper and lower regions of the perforated wall of the centrifuge.

 Figure 3 shows an embodiment similar to that of Figure 2 and corresponding numerals have been adopted to designate identical or very similar parts. In fact, the centrifuge 25 and also the dispenser basket 28 are of identical construction to that of FIG. 2, but instead of using the annular hopper 31 open towards the inside, a relay device 33 is adopted. This device 33 comprises, mounted on the hub by means of thermally insulated supports 33a, an annular cup having an open channel inwards so as to receive the glass nets 30 coming out of the basket 28. and the lower edge of the channel is provided with a weir or weir 34 so that the glass arriving in the drip edge 33 overflows and is transferred by centrifugation to the inner surface of the peripheral wall of the centrifuge. Preferably the relay drip edge 33 is arranged so that the weir dam ensures the transfer of the glass in the plane of the upper row of orifices of the peripheral wall.

 The operation of the embodiment of FIG. 3 is similar to that of FIG. 2, except that, in the case of the hopper of FIG. 2, the orifices provided at the base of the funnel discharge nets of separate glass 32 while in Figure 3 the glass is discharged by the relay device in the form of a sheet, as indicated in 35.

 Referring now to the embodiment of Figure 4, we see that the centrifuge 36 shown has a vertical dimension substantially increased compared to that of the centrifuges of Figures 1, 2 and 3. In Figure 4, a basket is used 28 similar to that of FIG. 3 and this basket delivers glass threads 30 to the annular relay drip edge 33, of a structure similar to that described above with reference to FIG.

However, in FIG. 4, the relay device 33 does not discharge the glass directly to the inner surface of the centrifuge wall; on the contrary, it conveys it inside an annular hopper 37 which is open towards the inside and which is mounted on a support member 38 situated inside the centrifuge and connected thereto in the zone of its upper edge. .

 The chord 38 has a cylindrical shape and its upper edge is fixed on the neck of the apparatus while its lower edge is provided with a groove 38a for receiving the edge 36a, oriented downwards and provided on the lower flange of the centrifuge. The chord 38 is also connected to a base plate -38b. As can be seen, the chord 38 and the base plate are preferably provided with spaced holes. Anchoring members or brackets 39 distributed on the periphery (see also FIG. 9) protrude inwardly from the central part of the peripheral wall of the centrifuge and serve for fixing a ring 39a which comes engage in a grooved shoulder 38c integral with the frame 38.The peripheral spacing of the consoles 39 avoids any appreciable effect of retention or disturbance on the laminar flow of glass progressing on the inner surface of the peripheral wall of the centrifuge. The engagement of the members 36a-38a and 39a-38c is designed to allow the chord 38 and the peripheral wall of the centrifuge to expand and contract freely with respect to each other. This frame, in particular thanks to the members 39, 39a and 38c, provides effective reinforcement of the peripheral wall of the centrifuge, thus opposing a bulge outwardly of this wall under the action of the centrifugal force.

 An advantage of this structure is that the reinforcing elements are maintained at a relatively low temperature; for example, while the temperature of the peripheral wall is about 10500C during operation, that of the frame will be about 6000C so that this frame will remain more rigid.

 In the enlarged cross-sectional view of FIG. 8, certain constructional details of the relay hopper 37 and the chord 38 are shown. It can be seen that the transfer ports 40 provided at the base of the funnel are arranged so as to pass glass threads through orifices 41 radially aligned formed in the frame 38.

 The distribution of the brackets 39 at intervals on the inner surface of the centrifuge wall enables the desired laminar flow of the glass to be established from the upper zone of the centrifuge to its lower zone, with a minimum of interruptions.

 The other parts of the equipment, for example the centrifuge mounting spindle, the annular chamber and the annular stretch gas passage and the heating element 23 may all be similar to that already described above. above.

 In the embodiment of FIG. 5, the centrifuge 42 is of a construction similar to that of the centrifuge 36 of FIG. 4, but it has a smaller diameter and, for feeding the glass, it comprises a dispensing basket. central 43 with a diameter slightly greater than that indicated at 28 in FIG. 4, the peripheral orifices of this basket delivering threads of glass 44 directly into the relay funnel 37 instead of through the drip This embodiment comprises a chord 38, a base plate 38b hollowed out at its center and connections with the peripheral wall of the centrifuge, as described above with reference to FIG. 4.

 Although different features of the embodiments of FIGS. 4 and 5 can be used with peripheral walls of uniform thickness, it is preferable to increase the wall thickness towards the lower edge, for the reasons already indicated.

 FIG. 6 shows an arrangement similar to that of FIG. 3 and of which the centrifuge 25 and the distributor basket 28 are identical, but a weir drip 45 is used as a relay ring (see also the detail of FIG. Figure 7) mounted directly on a part of the peripheral wall itself instead of being on the hub as in Figure 3.

 In the detail views of FIGS. 7 and 8, it can be seen that in the two cases of direct attachment of the relay device shown in FIGS. 4 to 6 (37 in FIG. 8 and 45 in FIG. 7) an intermediate layer of material isolator 46 serves to reduce the heat transfer from the relay device to the centrifuge and, also in the case of the embodiment of FIGS. 4, 5 and 8, to the supporting structure 38.

ALLOYS
Particularly for fiberizing the hardest glasses, having viscosities of the order of 1000 poises at temperatures greater than about 1150 ° C., and having a devitrification temperature of the order of 103 ° C., it is also contemplated, according to the invention. , to manufacture the centrifuge in a special composition alloy capable of withstanding the necessary temperatures. When the glasses are softer, the use of this alloy also increases the longevity of the centrifuge. This alloy can have the following formula, the parts being indicated in percentage by weight
Elements Ranges
C 0.65 - 0.83
Cr 27.5 - 31
W 6 - 7.8
Fe 7. - 10
If 0.7 - 1.2
Mn 0.6 - 0.9
Co 0 - 0.2
PO - 0.03
S 0 - 0.02
Ni (supplement) 59 - 50
It is particularly useful to adopt an alloy of this type for centrifuges of large diameter, for example with a diameter of at least 400 mm.

GLASSES
An important advantage of the invention is that its structural and functional characteristics allow it to be used in fiber drawing of a wide range of glasses.

 It is thus possible to use many known compositions of stretchable glass, especially soft glasses.

In addition, various structural and operative features of the invention may also be used individually and in combination with certain types of glass compositions which have not been commonly used in known fiber drawing processes involving a centrifuge for spraying threads. glass in a drawing stream. Indeed, the technique and the centrifuge according to the invention make it possible to conveniently use glass compositions which have not been used in practice with centrifugal fiber-drawing equipment of known types, for various reasons, in particular because of a temperature of relatively high devitrification which requires the use of a relatively high fiberizing temperature. This high fiberization temperature, when adopted in the centrifuges of known types, causes (by erosion and / or bulging outwardly of the peripheral wall) deterioration sufficiently rapid that the centrifuge can not be used industrially in the centrifuge. convenient. Accordingly, it may be said that it would be virtually impossible to perform with centrifuges of known types the fiber drawing of some of the glass compositions contemplated in the practice of the present invention.

 In the following table are indicated the compositions and the main characteristics of eight different glasses that can be fiberized using the present invention.

BOARD

<tb> COMPOSITION <SEP> O <SEP> 1 <SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5 <SEP> 6 <SEP> 7
<tb> SiO2 <SEP> 66.90 <SEP> 63.15 <SEP> 62.60 <SEP> 62.70 <SEP> 61.60 <SEP> 63.45 <SEP> 62.10 <SEP> 60 ,30
<tb> Al2O3 <SEP> 3.35 <SEP> 5.05 <SEP> 5.20 <SEP> 5.15 <SEP> 5.90 <SEP> 5.25 <SEP> 5.85 <SEP> 6 35
<tb> Na2O <SEP> 14.70 <SEP> 13.20 <SEP> 15.15 <SEP> 15.20 <SEP> 13.80 <SEP> 14.95 <SEP> 14.55 <SEP> 14 95
<tb> K20 <SEP> 1.0 <SEP> 2.10 <SEP> 2.30 <SEP> 2.30 <SEP> 2.45 <SEP> 2.25 <SE> 2.70 <SEP> 2 65
<tb> CaO <SEP> 7.95 <SEP> 5.90 <SEP> 5.25 <SEP> 5.50 <SEP> 5.95 <SEP> 5.40 <SEP> 5.75 <SEP> 6 25
<tb><SEP> 0.30 <SEP> 2.65 <SEP> 3.35 <SEP> 3.35 <SEP> 2.60 <SEP> 4.00 <SEP> 2.75 <SEP> 2, 40
<tb> traces <SEP> 2.90 <SEP> 4.85 <SEP> 2.70 <SEP> 3.20 <SEP> traces <SEP> traces <SEP> traces <SEP>
<tb> zone <SEP> 0.035 <SEP> 2.00 <SEP> traces <SEP> 1.50 <SEP> 3.05 <SEP> 3.00 <SEP> 3.40 <SEP> 2.90
<tb> Fe2O3 <SEP> 0.49 <SEP> 0.78 <SEP> 0.79 <SEP> 0.85 <SEP> 0.89 <SEP> 0.84 <SEP> 1.88 <SEP> 3 37
<tb> 503 <SEP> 0.26 <SEP> 0.55 <SEP> 0.50 <SEP> 0.52 <SEP> 0.45 <SEP> 0.51 <SEP> 0.40 <SEP> 0 36
<tb> aces <SEP> traces <SEP> traces <SEP> traces <SEP> traces <SEP> traces <SEP> traces <SEP> traces
<tb> B2O3 <SEP> 4.9 <SEP> 1.50 <SEP> traces <SEP> traces <SEP> traces <SEP> traces <SEP> traces <SEP> traces
<tb> VISCOSITY <SEP>#
<tb> T (log # = 2) C <SEQ> 1345 <SEQ> 1416 <SEQ> 1386 <SEQ> 1403 <SEQ> 1410 <SEQ> 1402 <SEQ> 1405 <SEQ> 1395
<tb> T (1og "= 2.5) <SEP> C <SEP> 1204 <SEP> 1271 <SEP> 1249 <SEP> 1264 <SEP> 1270 <SEP> 1265 <SEP> 1266 <SEP> 1257
<tb> T (qig = 3) <SEP> C <SEP> 1096 <SEP> 1161 <SEP> 1141 <SEP> 1156 <SEP> 1158 <SEP> 1160 <SEP> 1158 <SEP> 1150
<tb> T (log # = 3.7) <SEP><SEP> C <SEP> 975 <SEP> 1042 <SEP> 1028 <SEP> 1038 <SEP> 1042 <SEP> 1045 <SEP> 1038 <SEP> 1030
<tb> DEVITRIFICATION <SEP>
<tb> Liquidus <SEP> C <SEP> 970 <SEP> 1020 <SEP> 960 <SEP> 1015 <SEP> 1015 <SEP> I <SEP> 1040 <SEP> 1020 <SEP> 1025
<tb> Speed
<tb> maximal <SEP> m / min <SEP> 0.93 <SEP> 0.52 <SEP> 0.30 <SEP> 0.46 <SEP> 1.1 <SEP> 0.40 <SEP> 1 , 08 <SEP> 1.96
<tb> erection <SEP> of <SEP> C <SEP> 855 <SEP> 900 <SEP> 840 <SEP> 800 <SEP> 900 <SEP> 880 <SEP> 915 <SEP> 920
<tb> RESISTANCE
<tb> CHEMICAL <SEP> (DGG)
<tb> Attack <SEP> to
<tb> water <SEP> rtg <SEP> 13.6 <SEP> 10.8 <SEP> 16.5 <SEP> 16.8 <SEP> 11 <SEP> 16.4 <SEP> 12.86 <SEP> 14.9
<tb> Alcaibiitê <SEP> mg <SEP>
<tb> residual <SEP> Na2O <SEP> 4.6 <SEP> 3.6 <SEP> 5.9 <SEP> 5.9 <SEP> 3.6 <SEP> 5.6 <SEP> 4.8 <SEP> 4.9
<Tb>
The chemical compositions shown in this table are sample analysis results given by way of example.

 Although the composition 0 can be fiberized by certain known methods, it can not be done in a cost-effective manner from the industrial point of view because the pulling or production capacity is. too weak. On the other hand, it is obvious that the composition O can be fiberized with the device according to the invention under profitable conditions.

 It is practically impossible to carry out commercially by known centrifugal fiber-drawing techniques the fiber drawing of the other compositions which, on the contrary, are entirely suitable for use in the practice of the invention.

Claims (8)

 1. hollow centrifuge potier fibering thermoplastic materials, including glass, characterized in that the centrifuge has a peripheral wall 13 which is provided with orifices and whose thickness is increasing towards its lower edge.  2. Centrifuge according to claim 1, characterized in that the peripheral wall 13 is thicker at its lower part, thinner at its middle part and an intermediate thickness at its upper part.  3. Centrifuge according to one of claims 1 and 2, characterized in that the inner generatrix of the wall 13 is of curved shape.  4. Centrifuge according to one of claims 1 to 3, characterized in that the outer surface of the peripheral wall 13 has a substantially cylindrical shape.  5. Centrifuge according to one of claims 1 to 4, characterized by a reinforcing element 16 connected to the lower part of the peripheral wall 13, this element 16 having a section in the axial direction of the centrifuge 12 larger than the thickness. of the peripheral wall 13.  6. Centrifuge according to one of claims 1 to 5, arranged to rotate about a vertical axis within an annular stream of drawing gas, characterized in that it is made of an alloy having the following composition, in parts by weight  Elements Ranges  C 0.65 - 0.83  Cr 27.5 - 31  W 6 - 7.8  Fe 7 - 10  If 0.7 - 1.2  Mn 0.6 - 0.9  Co 0 - 0.2  P O '- 0.03  S O - 0.02  Ni (complement) 59 - 50 and has a peripheral wall 13 provided with a plurality of vertically spaced rows of orifices for the production of molten glass threads.  7. Centrifuge according to claim 6, characterized in that the orifices of the lower rows of the peripheral wall 13 are proportioned so as to oppose a greater resistance to the flow of the glass than the orifices of the upper rows, for the same viscosity of the glass.  8. Centrifuge according to claim 7, characterized in that the orifices of the lower rows have a diameter smaller than the orifices of the upper rows.