AU1869701A

AU1869701A - Method and device for forming mineral wool by internal centrifuging

Info

Publication number: AU1869701A
Application number: AU18697/01A
Authority: AU
Inventors: Pascal Decker; Daniel Guyot; Laurent Pierucci
Original assignee: Saint Gobain Isover SA France
Current assignee: Saint Gobain Isover SA France
Priority date: 1999-11-24
Filing date: 2000-11-22
Publication date: 2001-06-04
Anticipated expiration: 2020-11-22
Also published as: KR20020049012A; WO2001038245A1; NO20022394L; NO20022394D0; RU2002116704A; FR2801301B1; AU778802B2; AR026601A1; KR100661062B1; CA2392338A1; BR0015756B1; PL197681B1; CA2392338C; FR2801301A1; RU2252199C2; HUP0203462A2; PL355499A1; ATE245129T1; EP1255702B1; DE60003953D1

Description

WO 01/38245 - 1 - PCT/FRO0/03243 PROCESS AND APPARATUS FOR FORMING MINERAL WOOL BY INTERNAL CENTRIFUGING The invention relates to techniques for forming 5 mineral fibres or other thermoplastics by the process of internal centrifuging combined with extension or attenuation by a high-temperature gas blast. It applies especially to the industrial production of glass wool intended, for example, to form part of the composition 10 of thermal and/or acoustic insulation products. The fibre-forming process to which the invention relates consists in introducing a stream of molten glass into a spinner, also called a fiberizing dish, rotating at high speed and pierced around its 15 periphery by a very large number of holes through which the glass is thrown out in the form of filaments due to the effect of the centrifugal force. These filaments are then subjected to the action of an annular high temperature, high-velocity attenuating blast along the 20 wall of the spinner, which blast thins down the filaments and converts them into fibres. The fibres formed are entrained by this attenuating gas blast towards a receiving device generally consisting of a gas-permeable conveyor belt. 25 This process has formed the subject of many improvements. Thus, the patent EP 0 189 354 B1 relates to an improved burner generating the annular attenuating blast, namely an internal combustion burner comprising an annular combustion chamber. 30 Patent WO 97/15532 also relates to an improvement to this burner, the improvement consisting in that the attenuating gases have a radial temperature gradient, by being hotter close to the spinner. Patent EP 0 519 797 B1 relates to the addition 35 of a blowing ring placed at some radial distance from the axis of the spinner greater than that of the burner generating the attenuating gases, this blowing ring emitting individual and divergent jets of gas which - 2 meet below the lowest row of holes of the spinner and which have the function of generating a cold gas layer which channels the hot-attenuated fibres. The invention relates more particularly, but 5 without any limiting character, however, to thermal and/or acoustic insulation products having particularly high mechanical properties, for specific applications requiring such properties. These are especially insulation products which support masonry elements and 10 which consequently have to withstand high compressive loads, such as the elements used for the insulation of flat roofs allowing traffic. This is also the case with products which are used as exterior insulation and which must be able, in particular, to withstand tearing 15 forces. To achieve such performance, this type of insulation product generally has a high density, for example at least 40 kg/m 3 , and has undergone, after the fiberizing operation proper, an operation whose purpose 20 is to ensure that the fibres inside the felt assume directions as varied as possible without appreciably modifying excessively the overall orientation of the layer of fibres coming from the centrifuging. This operation consists especially in "creping" the fibres, 25 this being obtained by passing the layer of fibres between two series of conveyors which define its upper and lower faces, a longitudinal compressive force resulting from the layer passing from a pair of conveyors driven at a certain speed to a pair of 30 conveyors of lower speed than the previous pair. This type of operation is described, for example, in patent EP 0 133 083. However, it has been found that this creping operation does not always allow the expected 35 improvement in mechanical properties to be obtained. The object of the invention is therefore to improve the mechanical properties of thermal and/or acoustic insulation products (or at the very least to ensure that the constancy of these properties from one - 3 product to another is improved), without degrading their insulation properties, by concentrating more particularly on the high-density insulation products that have undergone a creping operation. 5 Instead of seeking to modify the parameters of the usual creping process, the inventors of the present application have studied the reasons why this creping operation is not always satisfactory. They came to the conclusion that, after creping, it turns out that the 10 fibres did not sufficiently have the isotropic orientation hoped for, this being due to the fact that, in particular, their dimensions were not necessarily the most suitable: excessively long fibres were difficult, by simple creping, to reorient as randomly 15 as was necessary to ensure the best tear strength and compressive strength. The invention therefore consists in modifying the fiberizing conditions in order to adjust the dimensions of the fibres so that they lend themselves 20 better to creping, especially by making them shorter. This modification has, inter alia, relied on the way in which the fibres, having undergone the hot gas attenuation, are channelled, as described below. Thus, the subject of the invention is firstly 25 an apparatus for forming mineral fibres by internal centrifuging, comprising: e a spinner which can rotate about an axis, especially a vertical axis, and the peripheral band of which is pierced by a 30 plurality of holes; e a high-temperature gas attenuating means in the form of an annular burner; e a pneumatic means, for channelling/adjusting the dimensions of the fibres, in the form of 35 a blowing ring. The invention furthermore provides for the channelling/adjustment of the dimensions of the fibres, adjusted by the said pneumatic means, to be supplemented by at least one other means, including a - 4 mechanical means comprising a cool wall placed around the spinner at least opposite its peripheral band. The annular burner may, for example, be of the type described in the aforementioned patent 5 EP 0 189 354. The blowing ring may, for example, be of the type described in the aforementioned patent EP 0 519 797. This patent has already explained that the layer of gas at ambient temperature emitted by the 10 blowing ring enveloping the jets of attenuating gas from the annular burner had the role of channelling the fibres and of gripping the torus formed by the fibres between the moment when they are ejected by the spinner and that when they are gathered by the receiving device 15 located beneath the spinner. In fact, schematically this layer of gas is not an "impermeable" pneumatic barrier in that all or some of the fibres are driven with a sufficient centrifugal force to pass through it. On the other hand, this 20 pneumatic barrier brakes them and possibly inflects the direction of their movement, but also varies their dimensions: when the fibres strike the layer of cold gas, the resulting shock is high enough for the fibres to be possibly broken. 25 This is therefore one means of controlling the length of the fibres. However, it has proved to be insufficient for truly obtaining a fibre length short enough to allow creping under ideal conditions without correspondingly compromising their insulation 30 capabilities. The additional mechanical means recommended by the invention has been shown to be highly effective in supplementing the action of the blowing ring and in increasing the options for controlling the length of the fibres. What is involved 35 here is therefore the addition to the pneumatic barrier of the blowing ring of another barrier which this time is a mechanical barrier, based around the spinner beyond the pneumatic barrier, and which also fulfils two roles: firstly, it channels all the fibres - all - 5 those that have already been able to break through the first pneumatic barrier beneath the fibre-receiving device and then it allows the length of the gathered fibres to be more finely adjusted: the impact of the 5 fibres against the physical wall allows them to be very effectively shortened in order to obtain optimum creping. Apart from the easier creping, the invention also makes it possible to obtain fibres whose dimensions are less dispersed, the histogram of the 10 sizes of which tends to be narrower. Finally, the shorter fibres also have a lesser tendency to form agglomerates of mutually bonded fibres, which bonded fibres reduce both the thermal and mechanical behaviour of the final product, most particularly its tear 15 strength. In fact, when high-density insulation products are manufactured, the diameter of the fibres is a less crucial parameter for obtaining a good level of thermal insulation than for the lighter products: it is 20 possible to "avail oneself" of coarser fibres for better mechanical strength. The diameter is a characteristic that can especially be controlled by the choice of operating parameters of the annular burner and by the flow rate of glass feeding the spinner. 25 However, the coarser the fibres the longer they are in general. It is here the invention comes into play, the mechanical wall being used, very schematically, to chop these coarse fibres in order to facilitate their creping while maintaining their mechanical properties. 30 However, the invention applies more generally to fibres of any dimension and any diameter. The pneumatic barrier and the mechanical barrier work in combination, the first one making it possible to vary the velocity and direction of movement 35 of the fibres, or indeed already to chop them, the second one stopping them from expanding radially and completing their length adjustment. Generally speaking, most of the fibres ejected from the spinner, especially at least 80 to 90% of the fibres, will strike the - 6 cooled wall, the remainder having mostly been stopped by the gases from the blowing ring. Just like the pneumatic barrier, the configuration and the parameters of this wall, especially its geometry and its position 5 relative to the spinner, to the annular burner and to the blowing ring, may be varied very freely. This wall is cooled so that there is no risk of the fibres which come into contact with it, and which are still relatively hot, becoming stuck thereon. 10 Advantageously, the outer surface of the cooled wall, facing the spinner, is mainly made of metal, especially one based on stainless steel. Preferably, this outer surface is concentric about the axis of the spinner and made of one or more 15 parts fastened together by mechanical linking elements. This outer surface is preferably at least partially cylindrical or in the form of a truncated cone. (In the latter case, the cone is preferably flared in its upper part. Throughout the present text, the terms "lower" 20 and "upper" refer, by convention, to a height projected on a vertical axis) . This conicity is favourable since it allows the fibres to be pulled back down better and makes it easier for them to interact with the gases emitted by the blowing ring, as will be explained in 25 detail below. Advantageously, the cooled wall is at least partly in the form of a truncated cone inclined at an angle ui, with respect to the axis Xi of the spinner, of between 0 and 300, especially strictly greater than 00, for example between 2 and 200 or 30 between 5 and 150. (In the cases most often encountered, the axis of the spinner is vertical or close to vertical). The cooled wall may also be characterized with respect to the axis X 2 along which the jets of gas (or 35 the layer of gas) emanating from the blowing ring are projected. Thus it may be advantageous to have an angle of inclination a 2 of the wall in the form of a truncated cone with respect to the axis X 2 which is - 7 between 0 and 60 or 700, especially between 2 and 20 or 300, or between 5 and 150. The angle O3 that the axis X 2 makes with the vertical may be equal to 0. In this case, given the al 5 and/or a 2 values described above, the gases from the blowing ring will converge on the cooled wall. However, this angle a 3 may differ from 00. Advantageously if a3 is between +300 and -300, the situation remains as in the aforementioned case of 10 convergence of the gases from the blowing ring onto the cooled wall. On the other hand, if a 3 has a magnitude greater than 300 (up to 900), the situation may therefore be one in which there is no longer, necessarily, convergence of the gases emanating from 15 the blowing ring onto the cooled wall, but rather convergence of these gases on to the plane on which the peripheral band of the spinner, pierced with holes, lies. Preferably, the height of the cooled wall 20 measured along a vertical axis is greater than that of the peripheral band of the spinner, the distance measured vertically between the lower end of the said wall and the lowest row of holes of the spinner being at least half the height of the peripheral band, 25 especially between half and twice the said height. The wall thus provides a surface large enough to confine the path of the fibres beneath the spinner, in order to better accompany and channel their paths towards the receiving member and to guarantee that all 30 or almost all the fibres are affected by the presence of this wall, even those emanating from the lowest rows of holes of the spinner. The simplest embodiment of this cooled wall consists in incorporating it into a mechanical device 35 having a cavity provided with a cooling system based on the circulation of a fluid of the water type, especially a device of the water-jacket type. An annular water jacket is also used around and below the spinner.

- 8 Advantageously, the configuration of the pneumatic means and that of the wall are such that the jets of gas emanating from the blowing ring have an emission direction on leaving the ring which converges 5 on the cooled wall, the convergence preferably occurring at a height below that of the middle of the peripheral band. In fact, the jets of gas may be designed so as at least partly to hug the wall. Since these jets are generally emitted vertically, the 10 conicity of the abovementioned wall makes it possible for the jets of gas to converge gradually and constrains them to hug the wall, at least in its lower part. As mentioned above, this convergence is not systematic and certain embodiments forming part of the 15 invention include a divergence, the jets of gas emitted by the blowing ring possibly being directed towards the wall of the spinner rather than towards the cooled wall according to the invention. Preferably, provision is made for the upper 20 edge of the cooled wall to be further from the axis of the spinner than are the points of emission of gas from the blowing ring. Preferably, the cooled wall may be configured so that its upper edge is beside the points of emission of the gases from the blowing ring, which 25 points of emission are, for example, in the form of holes in an annular pipe, of nipples or of nozzles, as will be explained in detail below. The upper edge may also be moved slightly further away; advantageously, it is at a distance x, (measured radially with respect to 30 the axis of the spinner) from the axes of projection of the gas jet (or, in other words from the centres of the holes emitting the jets of gas) of at most 40 mm, especially at most 20 mm and at least 0.5 mm. The preferred blowing ring comprises elements 35 generating preferably individualized and divergent jets of gas which meet below the lowest row of holes of the peripheral band. Two embodiments are preferred: a tubular ring pierced with holes, to which nipples are fixed, or a series of nozzles.

- 9 Advantageously, the temperature of the attenuating gases emitted at the exit of the annular burner is at most 1600 0 C, especially between 1350 and 1450OC; this is a temperature which may therefore be 5 lower than that possibly encountered in the internal centrifuging, the temperature of the attenuating gases generally being at least 15000C and, rather towards 1600C. "Cooler" attenuating gases, apart from the resulting energy saving, have the advantage of causing 10 less damage to the binder which it is desired to spray onto the fibres beneath the spinner, the fibres having in fact a lower temperature at the time of spraying. It is also probable that fibres attenuated at temperatures below the usual temperatures would be mechanically more 15 "brittle", something which would make them easier to chop into short fibres during their passage through the cold layer emitted by the blowing ring and then to impact against the mechanical wall according to the invention. This choice of attenuation temperature thus 20 would also help, indirectly, in adjusting the dimensions of the fibres. An optional additional means for channelling/adjusting the dimensions of the fibres is structural: it consists in adjusting the piercing of 25 the peripheral band so that the size of the holes, arranged in concentric rows, varies from the top down over the height of the spinner in the centrifuging position, this hole size decreasing and then again increasing over the said height. 30 According to a preferred embodiment, the holes are distributed in groups of concentric rows with, from the top down, at least one first group of ni "high" rows of circular holes having a diameter di, a second group of n 2 "intermediate" rows of circular holes 35 having a diameter d 2 less than di and finally a third group of n 3 "low" rows of circular holes having a diameter d 3 greater than the diameter d 2 , where ni, n 2 , n 3 1 and especially between 3 and 10. Preferably, the - 10 following relationship exists between the diameters di, d 2 and d 3 @ - di is close to d 3 , with di = d 3 ± 0.2 mm, especially di = d 3 ± 0.1 mm, 5 d3 - d2 ~ di - d2, - d 3 - d 2 is between 0.1 and 0.5 mm, especially where d 3 - d 2 > 0.1 mm or > 0.2 mm. The subject of the invention is also a process for forming the fibres, using especially the apparatus 10 described above and consisting of internal centrifuging combined with high-temperature gas attenuation in which the material to be fiber [sic] is poured into the spinner which rotates about an essentially vertical axis and the peripheral band of which is pierced by a 15 plurality of holes, from which the material is ejected and then attenuated by a high-temperature gas blast emitted by an annular burner, the fibres being channelled and dimensionally adjusted by a pneumatic device in the form of a blowing ring. The process is 20 such that this channelling, this dimensional adjustment are supplemented by at least one other means which include a mechanical means forming a physical barrier to the propagation of the fibres radially with respect to one [sic] of the spinner: this is the cooled wall 25 described above. The process of the invention consists in adjusting the configuration of this mechanical means, the parameters of the attenuating gas and of the gases from the blowing ring, and optionally the piercing of 30 the peripheral band of the spinner by [sic] the manufacture of mineral wool having a micronaire of between 3 and 8 under 5 grams. The mean diameter of the fibres forming the mineral wool is advantageously between 4 and 13 pm. 35 The invention also relates to the application of the process and of the apparatus which are described above to the manufacture of thermal and/or acoustic insulation materials having a density greater than - 11 40 kg/M 3 , especially from 40 to 160 kg/m 3 , the mineral wool of which has especially been creped. The invention also relates to these high density insulation products themselves, especially 5 those intended for making insulation panels for a car roof. In general, for a thickness of 50 mm, a density of 80 kg/m 3 and a binder content by mass with respect to the glass wool of approximately 6%, the following are obtained: 10 - a tear strength of approximately 20 ± 3 kPa; - a 10% compressive strength of approximately 60 ± 5 kPa; - a thermal conductivity of at most 38 W/m.K The invention will be described in greater 15 detail below with the aid of the following figures: - Figure 1: a schematic vertical sectional view of the fiberizing plant according to the invention, - Figure 2: an enlarged schematic vertical 20 sectional view of the spinner according to a first embodiment, - Figure 3: an enlarged schematic vertical sectional view of the spinner according to a second embodiment. 25 Figure 1 shows highly schematically a fiberizing plant suitable for implementing the invention and similar to the teaching of patent EP 0 519 797 with regard to the spinner, the annular burner and the blowing ring. This plant essentially 30 consists of a bottomless spinner 1, the peripheral band 2 of which is pierced by a large number of holes, fixed to a hub fastened to the spindle 3 for rotating about an axis X 1 , mounted vertically and driven by a motor (not shown). The stream of molten glass feeds the 35 spinner, passing via the hollow spindle 3 and flows into the solid-bottomed basket 5 provided with a cylindrical wall pierced by a small number of relatively large holes, by drilling, and for example, having a diameter of about 3 mm by means of which holes - 12 the molten glass is delivered in the form of primary streams 7 directed towards the inside of the peripheral band from which it is [sic] expelled due to the effect of the centrifugal force in the form of filaments 8. 5 The spinner is surrounded by an annular burner 9 and by a blowing ring 10. The rows are distributed in three groups from the top down: the intermediate rows have a smaller hole diameter than the high and low rows by at least 0.1 or 0.2 mm. 10 The annular burner 9 (in accordance with the teaching of patent EP 0 189 354) generates a gas jet whose temperature at the lips of the burner is about 14500 C. The fineness of the fibres is determined by the 15 value of their micronaire (F) under 5 g. The micronaire measurement, also called the "fineness index" takes into account the specific surface area by virtue of the measurement of the aerodynamic pressure drop when a given amount of fibre extracted from an unsized blanket 20 is subjected to a given pressure of a gas, generally air or nitrogen. This measurement is commonplace in mineral fibre production units; it is standardized (DIN 53941 or ASTM D 1448) and it is performed by an apparatus called a "micronaire apparatus". 25 The blowing ring 10 consists of a tubular ring, the holes of which are provided with nipples 11 fastened by welding, for example. By allowing prolonged guiding of the jets, the nipples lead to greater stability of the individual-jet emission conditions and 30 consequently the operating uniformity of the ring is thereby favourably affected. According to the invention, and as is shown more clearly in Figure 2, there is an annular device 12 comprising a stainless steel outer wall 13 facing the 35 spinner 2 and in the form of an upwardly flared truncated cone. This wall makes an angle ai of about 5 to 12o with respect to the vertical. In the non limiting particular case shown in Figure 2, the vertical axis is coincident with the axis of rotation - 13 X 1 of the spinner and with the axis of emission X 2 of the jets of gas emanating from the blowing ring 10. The upper edge 14 of the wall 13 is beside the wall of the nipples 11 of the blowing ring. Its lower 5 edge is at a significantly lower height than that of the lowest row of holes of the spinner. This wall 13 therefore belongs to a device of approximately annular shape placed opposite the spinner, which is of the "water jacket" type; it is 10 provided in its cavity with a water-circulation cooling system in order to ensure that the wall with which the fibres come into contact remains at a temperature low enough for them not to remain stuck to the wall, but to "rebound" and possibly be broken under the impact. 15 In operation, the fibres in the course of being formed for the most part break through the layer of cold gas emitted by the blowing ring 10 and strike the wall 13 so as to be taken back down, in a convergent direction towards the receiving device (not shown). 20 Also not shown, since it is conventional, is the binder-spraying ring below the spinner. The mineral wool gathered in the form of a layer is then conventionally heat-treated, especially to crosslink the binder, and then undergoes a creping operation 25 according the teaching of patent EP 0 133 083. The fibres obtained have a micronaire of approximately 7 under 5 grams. Their thermal and mechanical performance at 80 kg/M 3 was mentioned above. 30 Moreover, it has been found that the mechanical properties of this type of heavy insulation product was as good, or indeed better, when, for the same spinner, the output of 22 tons/day is increased to 35 tons/day. This is quite remarkable insofar as the opposite 35 tendency is generally observed, namely a progressive deterioration in the mechanical properties when the production output increases in the case of so-called lightweight or low-density products (that is to say a density of less than 40 kg/m 3 ). This is a surprising - 14 and advantageous consequence of the invention, which may perhaps be explained by the fact that the higher the output of glass ejected from the spinner, the more substantial/violent the impact of the fibres on the 5 cold wall and the greater the size reduction of the fibres. Figure 3 repeats the structural elements already described in Figure 2. In this embodiment, the jets of gas emanating from the blowing ring 10 are 10 emitted along an axis X 2 which makes an angle aX 3 of approximately 60O with the vertical. These jets are directed towards the peripheral band 2 of the spinner and not towards the cooled wall 13. The two embodiments shown in Figures 2 and 3 do 15 not limit the invention - many other configurations are possible. Thus, the element 12 and the ring 10 with its nipples 11 may be configured so that the approximately horizontal surface of the upper part of the element 12 lies at a higher level with respect to the vertical 20 than the end of the nipples 11 (either by modifying the geometry of the nipples, for example by inclining them, or by modifying the geometry of the upper region of the element 12, especially that of its edge 14): thus, the element 12 is "raised" with respect to the nipples 11. 25 It is also possible to take the opposite approach, by slightly "lowering" the element 12 with respect to the said nipples 11, the sole constraint being, however, to prevent the fibres from being able to pass above the cooled wall 13.

Claims

1. Apparatus for forming mineral fibres by internal centrifuging, comprising: 5 * a spinner (1) which can rotate about an axis X1, especially a vertical axis, and the peripheral band (2) of which is pierced by a plurality of holes e a high-temperature gas attenuating means in the 10 form of an annular burner (9); e a pneumatic means for channelling/adjusting the dimensions of the fibres in the form of a blowing ring (10), characterized in that the channelling and adjustment of 15 the dimensions of the fibres performed by the said pneumatic means are supplemented by at least one other means, which includes a mechanical means (12) comprising a cooled wall (13) placed around the spinner (1) at least opposite its peripheral band (2). 20

2. Apparatus according to Claim 1, characterized in that the surface of the cooled wall (13) facing the spinner (1) is mainly made of metal, especially stainless steel.

3. Apparatus according to either of the preceding 25 claims, characterized in that the cooled wall (13) is concentric about the axis of the spinner (1) and has an outer surface which faces the spinner (1) and is at least partially cylindrical or in the form of a truncated cone, preferably flared in the upper part. 30

4. Apparatus according to one of the preceding claims, characterized in that the cooled wall (13) is at least partly in the form of a truncated cone inclined at an angle ai, with respect to the axis X 1 of the spinner (1), of between 0 and 300, especially 35 strictly positive and preferably between 2 and 200.

5. Apparatus according to one of the preceding claims, characterized in that the cooled wall (13) is at least partly in the form of a truncated cone - 16 inclined at an angle a 2 with respect to the projection axis X 2 of the jets of gas emanating from the blowing ring (10) of between 0 and 60 or 700 especially equal to 0 or between 2 and 20 or 300, or between 5 and 150. 5

6. Apparatus according to one of the preceding claims, characterized in that the projection axis X 2 of the jets of gas emanating from the blowing ring (10) makes an angle a 3 with the vertical which is 0 or differs from 0, especially by ± 300, or of greater 10 magnitude.

7. Apparatus according to one of the preceding claims, characterized in that the height of the cooled wall (13), measured along a vertical axis, is greater than that of the peripheral band (2) of the spinner 15 (1), the distance measured vertically between the lower end of the said wall and the lowest row of holes of the spinner (1) being equal to at least half the height of the peripheral band (2), especially between half and twice the said height. 20

8. Apparatus according to one of the preceding claims, characterized in that the cooled wall (13) forms part of a mechanical device (12) having a cavity provided with a cooling system based on a circulation of fluid, especially a device of the water jacket type. 25

9. Apparatus according to one of the preceding claims, characterized in that the configuration of the pneumatic means with respect to that of the cooled wall (13) is such that the jets of gas emanating from the blowing ring (10) have a direction of emission which 30 converges on the cooled wall.

10. Apparatus according to one of the preceding claims, characterized in that the blowing ring (10) comprises elements for generating individual divergent jets of gas which meet below the lowest row of holes of 35 the peripheral band, the said ring especially consisting of a tubular ring pierced with holes to which nipples (11) are fixed or of a series of nozzles.

11. Apparatus according to one of the preceding claims, characterized in that the temperature of the - 17 attenuating gas emitted at the exit of the annular burner is at most 16000C, especially between 1350 and 1450 0 C.

12. Apparatus according to one of the preceding 5 claims, characterized in that an additional means is provided for channelling/adjusting the dimensions of the fibres, which structural means consists in making the size of the holes of the peripheral band vary, from the top down in the centrifuging position, by 10 decreasing and then by increasing over the height of the peripheral band (2).

13. Apparatus according to Claim 12, characterized in that the holes of the peripheral band (12) are distributed in three, high, intermediate and low groups 15 of rows having diameters di, d 2 , and d 3 which satisfy the following relationships: ( - di = d 3 , i 0.2 mm, preferably di = d 3 ± 0.1 mm, @ - d 3 - d 2 di - d2, - d 3 - d 2 of between 0.1 and 0.5 mm, especially 20 greater than 0.1 mm or 0.2 mm.

14. Process for forming mineral fibres by internal centrifuging, combined with high-temperature gas attenuation, in which the material to be fiberized is poured into a spinner (1) which rotates about an axis, 25 especially a vertical axis, and the peripheral band (2) of which is pierced by a plurality of holes, from which the material is ejected and then attenuated by a high-temperature gas blast emitted by an annular burner (9), the fibres being channelled/dimensionally adjusted 30 by a pneumatic means in the form of a blowing ring (10), characterized in that the channelling and the dimensional adjustment of the fibres is supplemented by at least one other means, which includes a mechanical means (12) forming a physical barrier to the 35 propagation of fibres radially with respect to the axis X 1 of the spinner (1).

15. Process according to Claim 14, characterized in that the physical barrier is a mechanical element providing a wall (13) placed around the spinner - 18 opposite the peripheral band (2), especially a wall which is cooled and mainly made of metal, at least on the surface.

16. Process according to Claim 14 or 15, 5 characterized in that the said wall (13) is at least partially cylindrical or in the form of a truncated cone, preferably flared in its upper part.

17. Process according to one of Claims 14 to 16, characterized in that the jets of gas emitted by the 10 blowing ring (10) converge on this wall (12) and/or at least partly hug it.

18. Process according to one of Claims 14 to 17 characterized in that the jets of gas emitted by the blowing ring (10) are individualized, divergent and 15 meet after the lowest row of holes of the spinner (1).

19. Process according to one of Claims 14 to 16, characterized in that the gases emitted by the blowing ring (10) converge on the peripheral band (2) of the spinner (1).

20 20. Process according to one of Claims 14 to 19, characterized in that the attenuating gases are emitted at the exit of the annular burner (9) at a temperature of at most 1600'C, especially between 1350 and 1450 0 C.

21. Process according to one of Claims 15 to 20 25 characterized in that most of the fibres ejected from the spinner strike the wall (12).

22. Application of the apparatus according to one of Claims 1 to 13 or of the process according to one of Claims 14 to 21 to the manufacture of mineral wood of 30 micronaire of between 3 and 8 under 5 grams.

23. Application of the apparatus according to one of Claims 1 to 13 or of the process according to one of Claims 14 to 22 to the manufacture of thermal and/or acoustic insulation material having a density greater 35 than 40 kg/M 3 , especially of the crepe type.

24. Thermal or acoustic insulation products having a density of at least 40 kg/m, especially between 40 and 160 kg/m 3 , which are obtained from mineral wool obtained with the apparatus according to one of - 19 Claims 1 to 13 or according to the process in accordance with one of Claims 14 to 22 and then creped, and especially having a tear strength of approximately 20 kPa and a compressive strength of approximately 5 60 kPa for a thickness of approximately 50 mm, a binder content of approximately 6% and a density of 80 kg/M 3 .