AU718773B2 - Improvement to devices for manufacturing mineral fibres by free centrifuging - Google Patents

Description

IMPROVEMENT TO DEVICES FOR MANUFACTURING MINERAL FIBRES BY FREE CENTRIFUGING The invention relates to a device for the manufacture of mineral fibres from a drawable material by centrifuging.

Techniques called free-centrifuging techniques are known in which the material to be fiberized is conducted in the molten state from the outside to the periphery of fiberizing rotor [sic] and is driven by these rotors in order to separate therefrom in the form of fibres due to the effect of the centrifugal force.

In these techniques, 3 or 4 centrifuging rotors arranged close to one another are generally used. The molten material is poured onto a first rotor, accelerated and sent on to the next rotor. The drawable material thus passes from one rotor to another, each rotor converting part of the molten material into fibres and sending the excess onto the next rotor.

These techniques are more especially employed for the industrial production' of rock wool from basaltic glasses, blast-furnace slags or more generally from any material having a high melting point.

Many improvements have been proposed for these techniques, and mention should especially be made here of those forming the subject of European Patent EP-B2-0,059,152.

The centrifuging rotors are subjected to high temperatures because of their contact with the molten material. However, these high temperatures must not be such that they lead to deformation and/or wear prejudicial to the positioning of these. rotors. This is why conventional devices described in the aforementioned application include cooling means consisting in particular of providing a flow of water through the .s-,,-shaft of the rotor and as far as the internal face of -i peripheral part of the rotor.

2 Two types of cooling are known, either with recycling of the liquid or with the liquid being lost.

That is to say, in the latter case, that the liquid, generally water, after having flowed through the rotor is ejected therefrom via apertures. The process of the invention falls within this second type of cooling.

In document EP-B-0,195,725, the cooling water, after its contact with the rim of the centrifuging rotor, is evacuated (possibly in the form of steam) via apertures arranged on both sides of the rotor. The fact, on the one hand, of expelling the cooling water and, on the other hand, of doing this close to the hottest points of the centrifuging rotor has many advantages. Firstly, the flow of the liquid, which is in one direction, is thereby greatly simplified and, secondly, the exiting water can vaporize, resulting in more effective cooling by virtue of the very high latent heat of vaporization.

European Patent EP-B-0,195,725 presents in detail the system for feeding cooling water to a centrifuging rotor which also possesses, inside the rotor, a binder feed intended to ensure mutual cohesion of the fibres within the mat which they form. In the case of the water feed, provision is made for the pipe, concentric with the axis of the rotor, which supplies the water to terminate in the plane of symmetry of the rotor, in an enlarged cavity from which the water escapes via a hole in order to reach the internal space in the rotor and be directed by the centrifugal force onto the orifices which emerge, on each side, on the lateral faces.

The cooling system common to the two preceding documents fulfils its role perfectly and enables the lifetime of the centrifuging rotors to be appreciably extended. However, although the cooling is globally effective, there are large temperature gradients on the rim where the liquid vitrifiable material is deposited.

§\RAhis is because the material is deposited and remains o a strip having a certain width before being 3 expelled, either in the form of fibres or in the form of drops projected onto the next rotor. Insofar as the relative position of the jet emanating from the melting member and of the rotors stays the same, a large temperature difference is established between the substrate of [sic] the centre of this strip, which is very hot, and that beneath its edges; at the point where the thickness of the molten material is smaller, it stays cooler since the mass is greater while the surfaces for heat exchange with the outside are virtually the same. It would be beneficial to decrease this gradient since it is a source of wear because of the stresses which it introduces into the fiberizing rotor.

Patent Application WO 95/07243 proposes a centrifuging rotor, intended to produce mineral fibres, which is, in itself, very different in design from the previous ones. It has more the shape of a drum than that of a wheel, its thickness along the axis being substantially greater than its largest diameter. In addition, the diameter of the region which is covered by the material to be fiberized can be varied. The molten material is deposited at one of the ends of the drum, at the point where the diameter is small, and progresses along the axis as far as the region of fibre formation, at the other end, where the diameter is larger. In the latter region, orifices are provided, lying at the periphery of the drum, which allow the water to escape in the form of steam. The purpose of the entire device is to obtain fibres whose diameter varies little from one fibre to another.

With regard to the temperature gradients on the external sleeve of the drum of WO 95/07243, it is [sic] increased rather than decreased compared to the prior art since the molten material cools substantially during its progress from one end of the sleeve to the other. The function of the orifices via which the steam is expelled does not seem to be preferentially that of ling, since the hottest region, at the point where 4 the molten material is deposited, does not have any orifices, but the stated objective is to avoid, opposite each orifice, contact with the metal and thus to create, very locally, kinds of pimples in the molten material, each pimple being the origin of a fibre.

Although this is not their primary function, the orifices which allow steam to escape facilitate the cooling of the material to be fiberized which covers them as well as of the sleeve itself in this region. Since it is at this point that the material to be fiberized is coolest, the effect of the escape of steam via the orifices is to increase the thermal gradient on the sleeve.

The objective which the invention intends to achieve is to decrease the thermal gradients in the axial direction of the rim of the centrifuging rotors.

o According to the present invention there is 20 provided a fiberizing rotor for use in a machine for the manufacture of mineral fibres by external centrifuging, the rotor including a rim on the outside of which the material to be fiberized in the molten state is supplied either from oo a distributing rotor or from another fiberizing rotor, the rotor including an internal liquid circuit with orifices for the evacuation of the liquid provided on the rim, wherein the orifices are provided on that part of the rim where the material to be fiberized is poured or thrown by the distributing rotor or another fiberizing rotor.

This arrangement of the cooling orifices makes it possible to decrease the temperature of the substrate at the point where it is hottest. The consequence of this is a decrease in the corresponding temperature gradients.

Preferably, the orifices are arranged on the rim 'RA in at least two rows lying in parallel planes and, H:\Caroline\Keep\Speci\P 2 309 3 .doc 3/02/00 4A advantageously, the rotor includes two rows lying symmetrically with respect to the plane of symmetry of the rim.

This arrangement in parallel rows, especially when they are centred symmetrically on the rotor of the oa H:\Caroline\Keep\Speci\P2309 3 .doc 3/02/00 5 invention, allows effective cooling of the centre of the region where the molten material is deposited.

The invention also provides liquid-distributing means which make it possible to feed each of the rows of orifices and, advantageously, the distributing means feeding a row of orifices being [sic] a row of distributing holes lying in a plane parallel to that of the row of orifices.

The result of this is that all the rows of orifices are definitely fed. One way of achieving this result consists in making provision for the rows of orifices to be separated from each other by continuous partitions, each row of holes thus feeds [sic] a row of orifices without affecting the neighbouring row of orifices.

The preferred embodiment of the rotor of the invention makes provision for it to include a two-part liquid feed chamber, a feed compartment and a distributing compartment, these then being connected via the distributing holes. In a general way, the distributing holes have in total a cross-section of less than the total cross-section of the orifices on the rim. In general, in respect to both compartments, provision is made for the rate at which liquid is fed to the motor to be adjusted so that a reserve of liquid is formed in the feed compartment.

In order to ensure optimum cooling of the interior of the rotor, it is advantageous for the distributing holes to be distributed in two rows lying in planes which are on each side of the planes of the rows of orifices on the rim, which are also two in number. Likewise, provision is made for the internal walls of the rotor, which lie on the one hand on the side where the fibres are ejected and on the other hand on the opposite side, to move closer together on going from the interior of the rotor to its periphery so that the liquid emanating from the distributing holes preads out over them as it progresses towards the S o1 ices on the rim.

6 Thus, before its escape, the liquid has extracted the maximum possible heat from the rotor.

In the case of cooling on the fibre-extraction side, at the point where the blowing air, heated by it passing above the molten material, leaving the rotor, heats it, provision is made laterally for the rotor to include direct escape holes, distributed in a circle centred on the axis of the rotor, these lying on that side of the rotor where the fibres are ejected, and preferably for the direct escape holes to feed into a circular groove of larger radius. In this case, it is advantageous for the total cross-section of the direct escape holes and that of the distributing holes to be of the same order, the second one preferably being greater. These direct lateral escape holes lie in general on the flange which forms the side wall of the rotor.

This choice of flow rates, which are of the same order, between the liquid escaping from the rim and that escaping from the side of the rotor, the latter being however much less heated by the molten material, shows the effectiveness of the main cooling system of the invention at the hottest point.

The description and the figures which follow will enable the invention to be understood and its advantages appreciated.

Among the figures, Figure 1 shows a view of a fiberizing machine with two fiberizing rotors, Figure 2 shows a section through a centrifuging rotor according to the invention and Figure 3 shows an estimated distribution curve for the temperatures at the surface of the rim of the same rotor.

Figure 1 depicts a fiberizing device of the type used according to the invention, comprising three centrifuging rotors 1, 2, 3, two successive rotors rotating in opposite directions from each other.

Devices of the same type with four centrifuging rotors re also commonly used. The material to be fiberized 4, the molten state, is poured either via a shute 5 or 7 from the orifice of a stabilizing reservoir onto the first centrifuging rotor 1, which is also called the distributing rotor since it produces virtually no fibres and its function is essentially to accelerate and distribute the material to be fiberized 4 over the next rotor 2 onto which it is sent and where it partially adheres. The adhering molten material separates from the rotor 2 due to the effect of the centrifugal force and then forms filaments which are entrained by the gas stream generated by the orifices of the blowing ring 6 and/or by a drawing lip, while the non-adhering material is sent on to the next centrifuging rotor 3 for the production, in the same manner, of a complement of fibres.

The gas stream carrying the fibres is directed transversely to the direction of projection of the fibres from the rotor. By virtue of the projecting member 7, the binder compound is centrifugally projected in the form of droplets into the gas stream which divides it up finely so that the fibres formed are uniformly coated.

These centrifuging rotors are water-cooled, preferably using flow rates of cooling water which are set for each rotor depending on the equilibrium temperature to be obtained. Normally, the temperature of the rotors in contact with the molten material decreases on going from the first 1 to the final 3 [sic].

The invention relates to the centrifuging rotors and their liquid-circulation cooling system.

Conventional centrifuging rotors, like those described in Patent EP-B-0,195,725, usually consist of a hub through which the fluids cooling water and binder are supplied, of a rim at the periphery of which the material to be fiberized, in the molten state, is distributed and of two flanges, on both sides of the rotor, which are associated on the one hand with the hub and on the other hand with the rim in order to R brm a kind of internal chamber (the rotor is hollow),

I

8 inside which the coolant flows before being ejected via orifices generally lying in the flanges. The fiberizing rotors also generally include, in addition, in the central part of the rotor on the fibre-extraction side, a member 7 for projecting the liquid binder (see Patent EP-B-0,059,152) which will not be discussed here.

It is the system for cooling the centrifuging rotors, of the above type, which the invention allows to be improved.

The centrifuging rotor of the invention, unlike the prior systems, is equipped with orifices for escape of the coolant water in most cases on the periphery of the rim itself. Such orifices maybe seen in Figure 2 at 8, 9, these being drilled through the rim in regions 10, 11 which have been especially thinned. This configuration allows very effective cooling of the central part of the rim, at the point where the supply of heat by the molten material to be fiberized is greatest. These orifices emerge in the surface of the rim with its usual structure. In the figure, the rim is depicted with circular ribs 12 lying in planes perpendicular to the axis of the rotor, but any other structure favourable to good fiberizing is compatible with the invention.

Figure 2 depicts the preferred embodiment of the invention, that is to say that, on the one hand, the, rows of orifices are separated by a kind of partition 30 which allows each row to be fed separately and that, on the other hand, the hollow part inside the rotor is separated into two compartments, a feed compartment 13 and a distributing compartment 14. The two compartments 13, 14 communicate via connecting holes 15, 16. The feed compartment 13 receives the coolant conventionally via the hub of the rotor, not depicted. Due to the effect of the centrifugal force, the liquid is projected to the periphery of the compartment 13, at the point where there are the holes 16. The coolant feed flow is preferably such that .ayt allows the creation of a reserve of liquid in the 9 compartment 13, which guarantees that there is permanent flow from the holes 15, 16 and 19 and that this is the same over the entire periphery of the compartment 13. On leaving the holes 15, 16, the liquid is projected by the centrifugal force along the axis of these holes and preferably strikes the walls of the distributing compartment, respectively 17, 18, which close up towards the periphery of the rotor and thus allow the coolant to progress again by virtue of the centrifugal force towards the orifices 8, 9, "licking" the walls 17, 18 which it cools before leaving the interior of the rotor, onto the rim. The "partition" 30, between the two rows of orifices guarantees that each of the rows is fed. The two compartments are depicted in the figure as if they formed sealed boxes. This is not a necessity since the centrifugal force systematically drives the water in a radial direction parallel to the plane of symmetry of the rotor.

In the prototype rotor, having a diameter of 350 mm, the orifices 8, 9 formed two circular rows of 120 holes, each having a diameter of 1.2 mm. A first row 8 lay on one side of the plane of symmetry of the rotor, the other row 9 lying symmetrically on the fibre-extraction side. The wall separating the two compartments 13, 14 was itself drilled with two circular rows of 10 holes, each having a diameter of 0.9 mm. It is thus found that the set of orifices on the rim has a total cross-section of 271 mm 2 while they are fed, by virtue of the connecting holes 15, 16 with 2 a much smaller overall cross-section, namely 12.7 mm This choice of the respective cross-sections prevents the coolant from stagnating in the distributing chamber where it would run the risk of heating and possibly vaporizing with the problems which could arise therefrom. The formation of a reserve of liquid in the feed compartment, by virtue of the adjustment in the ,-flow rate of the liquid, makes it possible to ensure a -'13ermanent feed.

rl) 10 The two compartments, namely the feed compartment 13 and the distributing compartment 14, constitute one embodiment of the invention. It is also possible to feed the rows of orifices 8, 9 directly from the regions 10, 11, these being separated by the partition 30, by installing feed holes which act in the same manner as the holes 15, 16, but which lie on the pipe concentric with the axis of the rotor (cf.

document EP-B-0,195,725) Other tests were carried out with rows of orifices on the rim which are arranged unsymmetrically with respect to the plane of symmetry of the rotor. The results were equally satisfactory.

Figure 2 shows a hole at 19 which forms part of a circular row of direct escape holes, it [sic] provides additional cooling of the outside of the side wall of the fiberizing rotor, on the fibre-extraction side. The holes 19 in the prototype have a diameter of 0.9 mm and they are 10 in number. Their overall crosssection is thus 6.4 mm 2 which is less than the overall cross-section of the connecting holes 15, 16 (12.7 mm 2 but not too far from this cross-section. As may be seen in the figure, above the holes 19, a circular channel 32 has been made which collects the liquid emanating from the hole 19 and distributes it over a wider sector. Likewise, the hole 19 emerges set back with respect to the channel 32 and above all with respect to the edge of the rim, enabling the liquid to extract heat from a large area of the side face of the rotor with [sic] leaving it.

Compared to a conventional cooling system (using holes lying in the flanges on each side of the centrifuging rotors), the system of the invention, as has just been described, is much more effective .and makes it possible to use only 250 litres of water per hour instead of the usual 350 400 litres.

Figure 3 depicts the probable profile of the t emperatures at the surface of the rim. It is very dfficult to measure the actual profile of the 11 temperatures of the metal at the surface of the rim beneath the molten material. Here, this is an estimate, the most probable one, which is completely compatible with the results of the experiments on the centrifuging rotors according to the invention in production, results which will be discussed later.

Two curves are depicted: 22: a curve of the temperature distribution under running conditions in the case of conventional centrifuging rotors; 23: distribution on the rim of the rotor according to the invention.

With the old system, the cooling is less effective at the centre of the rim, between the limits 20, 21 between which the molten material is deposited.

On the other hand, it is more effective on the side of the wheel where the peripheral blowing takes place (machine side) and virtually identical on the fibreextraction side.

The temperature gradient at the region 20, 21 has been depicted by 24 and 25 for the prior art and for the invention respectively, the latter temperature gradient being markedly less steep than the former.

Comparative tests were carried out with conventional compositions, such as are normally used for' fiberizing rock wool, and also with special compositions which are more fluid, having a steeper viscosity curve and/or a narrower "working range".

The conventional fiberizable masses for manufacturing rock wool have compositions by weight of the type: Si02 A1 2 0 3 12% CaO 28% MgO 6% 3 Various oxides The fiberizable compositions of the above type 11xhibit quite a slow variation in viscosity as a 12 function of temperature. Thus the viscosity goes from loglo 1, at the point where the temperature is 1493 0 C, to logio0 3 for a temperature difference of approximately 380 0 C. It is assumed that the working range is the temperature region which separates the temperature at which the viscosity corresponds to loglo 1 from that of the liquidus, at the point where devitrification starts. This second temperature is, in this case, 1230 0 C, that is to say that the working range is 260 0

C.

Such a fiberized [sic] composition on the centrifuging rotors according to the invention makes it possible to obtain substantially longer fibres than with conventional rotors. More specifically, during a test lasting 40 hours, with rotors according to the invention driven at a rotational speed of 60-00 revolutions per minute, a fibre elongation was observed such that it allowed the surface density of the primary mat to be reduced from 300 g/m 2 to 220 g/m 2 with the identical binder level for a given fineness index ("fasonaire"). The elongation of the fibres also allows the binder level to be reduced.

The "fasonaire" is a quantity used by all rock wool producers, which enables the overall fineness and length of the fibres to be evaluated. This quantity is measured using a so-called "fasonaire" apparatus, for example that from the company AVIATEST NIEBERDING in Germany. The test piece is a tuft of mineral wool, free of binder or oil, of a given mass, which may include non-fibrous components (slugs, sand, etc.) dictated by certain fiberizing processes. It is- compressed in a cylindrical chamber of predetermined volume. A gas stream dry air or nitrogen is passed over the test piece. The gas flow rate being held constant, the pressure drop across the test piece is measured using a column of water graduated in conventional units.

The primary mat is a step in the manufacture when mats are manufactured in two steps, the formation RA71 f a primary first web of fibres and of liquid binder 13 (this web being as thin as possible) followed by deposition of several thicknesses of the primary web, in a zigzag fashion, perpendicular to the axis of the final mat. The performance characteristics of the finished mat are better the larger the number of primary webs, that is to say, all things being equal, the lower the individual .surface density. Normal production is limited towards the low end of the surface density of the primary web (below this minimum value, the web tears and holes appear), [lacuna] the invention itself makes it possible, under the same production conditions, easily to go down to lower values, thereby substantially improving the quality of the finished mat. It may also be stated that, for a given quality, that is to say for a given number of plies of primary web in the finished mat, it is possible to decrease the amount of binder since it is the liquid binder which ensures cohesion of the primary web.

Other tests were performed with a composition which is more fluid in the molten state. This is a product which includes a high proportion of blastfurnace slags with low iron content, making it possible to obtain clear fibres which are desired for some applications, especially for spraying. A typical composition by weight is, for example: SiO 2 44% A1203 11% CaO 38% MgO 3 <1% Various oxides >1% The temperature difference corresponding to the viscosity r1 such that logon0 1 and the liquidus is, in this case, 90 0 C, corresponding to a narrow "working range". In order to work properly, it is necessary to keep the molten material during fiberizing within a 2 R very narrow temperature range. With the centrifuging 14 rotors of the invention, it is found to be much easier to keep the plant under proper production conditions.

Some rock wool compositions are particularly difficult to fiberize. This is the case in particular for those which dissolve more rapidly in biological liquids.

Thus the typical composition: Si02 52% Fe20 3 A1 2 0 3 2% CaO 31.5% MgO Na 2 0 4% Various has a particularly narrow working range which makes -it very difficult to control the fiberizing conditions with conventional rotors. This is because the temperature for logion 1 is 1360*Cand the liquidus is at 13400C, which gives a working range of 20'C. In plants equipped with rotors having coolant escaping from the side flanges, it is virtually impossible to stabilize the plant, which continues to oscillate between a fiberizable material which is too hot to fiberize or too cold, which devitrifies. The rotors of the invention have made it possible to stabilize the plant and to fiberize for hours without interruption.

They thus provide a solution to a major problem having an impact on health and the environment.

Moreover, in the three above cases, whether a conventional composition or a more difficult composition to fiberize, less wear of the centrifuging rotors is observed, the rotors having to be changed only after operating times which are approximately longer.

It may thus be seen that the device of the invention, by virtue of the reduction in the temperature gradients on the rim of the centrifuging RjN,%rotors, under the molten fiberizable material, allows 15 the manufacturing conditions to be appreciably improved, both in terms of the quality produced (length of the fibres and delay in the reduction in quality due to wear of the rotor) and in terms of the stability of the conditions (compositions with a narrow working range, in particular) or in terms of wear of the equipment.

Claims (13)

1. 2. A fiberizing rotor according to claim 1, in which the orifices are arranged on the rim in at least two rows lying in parallel planes. 3 A fiberizing rotor according to claim 2, in which S"the two rows lie symmetrically with respect to the plane of symmetry of the rim. A fiberizing rotor according to claim 2 or claim 3, in which the rotor is provided with liquid-distributing means for feeding each of the rows of orifices.
2. 5. A fiberizing rotor according to claim 4, in which the distributing means feeding a row of orifices is a row of distributing holes lying in a plane parallel to that of a the row of orifices.
3. 6. A fiberizing rotor according to claim 5, in which the rows of orifices are separated from each other by continuous partitions.
4. 7. A fiberizing rotor according to claim 5 or claim 6, further including a two-part liquid feed chamber, a feed compartment and a distributing compartments connected via H:\Caroline\Keep\Speci\P23093.doc 3/02/00 17 the distributing holes.
5. 8. A fiberizing rotor according to any one of claims to 7, in which the distributing holes have in total a cross-section of less than the total cross-section of the orifices on the rim.
6. 9. A fiberizing rotor according to claim 7, in which the rate at which liquid is fed to the rotor is adjusted so that a reserve of liquid is formed in the feed compartment. A fiberizing rotor according to any one of claims to 9, in which the distributing holes are distributed in two rows lying in planes which are on each side of the planes of the rows of orifices on the rim, which are also two in number. g
7. 11. A fiberizing rotor according to claim 10, in which the internal walls of the rotor, which lie on the one 20 hand on the side where the fibres are ejected and on the other hand on the opposite side, move closer together on going from the interior of the rotor to the periphery of the rotor and the liquid emanating from the distributing holes spreads out over the internal walls as the liquid progresses towards the orifices on the rim.
8. 12. A fiberizing rotor according to one of claims 1 to 11, in which laterally the rotor includes direct escape holes distributed in a circle centred on the axis of the rotor, lying on that side of the rotor where the fibres re ejected.
9. 13. A fiberizing rotor according to claim 12, in which the direct escape holes feed into a circular groove of a larger radius. o 14. A fiberizing rotor according to claim 12 or claim H:\Caroline\Keep\Speci\P23093.doc 3/02/00 18 13, in which the total cross-section of the direct escape holes and that of the distributing holes are of the same order.
10. 15. A fiberizing rotor according to claim 14, in which the total cross-section of the distributing holes is greater than of the direct escape holes.
11. 16. A machine for the manufacture of mineral fibres by external centrifuging including a fiberizing rotor of any one of claims 1 to
12. 17. A fiberizing rotor for use in a machine for the manufacture of mineral fibres substantially as herein described with reference to the accompanying drawings.
13. 18. A machine for the manufacture of mineral fibres substantially as herein described with reference to the accompanying drawings. Dated this 3rd day of February 2000 ISOVER SAINT-GOBAIN By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 3* H:\Caroline\Keep\Speci\P23093.doc 3/02/00