WEBS OF MAN-MADE VITREOUS FIBRES

Abstract: Particulate additive is included within an MMV fibrous web by forming a cloud of MMV fibres by fiberising a vitreous melt using at least one centrifugal fiberising rotor, carrying the cloud of fibres by an air stream to a permeable collector, blasting the particulate additive into the cloud at a direction against the direction of travel of the cloud, and collecting the fibres and additive as a web on the collector.

Description: Webs of Man-Hade Vitreous Fibres This invention relates to the production of MMVF (man- made vitreous fibre) webs containing a particulate additive substantially uniformly distributed throughout the web and bonded into it. It is standard practice to make an MMVF web by forming a cloud of fibres by fiberising a vitreous melt by use of at least one centrifugal fiberising rotor, carrying the cloud of fibres by an air stream from adjacent the rotor to a permeable collector, and collecting the fibres as a web on the collector. Binder is usually sprayed into the cloud and the web is subsequently subjected to curing so as to cure the binder and bond the fibres into the web, optionally after lamination or compression or both. It is often desired to include a particulate additive substantially uniformly throughout the web. One way of doing this involves spraying the additive into the cloud of fibres outwardly from a spray which is coaxial with the rotor. Such systems are described in, for instance, O90/15032, EP 530843 and U.S. 2,944,284. Unfortunately known methods such as these tend to be unsatisfactory for achieving uniform distribution of significant amounts of additive, partly because of the difficulty of introducing sufficient particulate additive coaxially with a fast rotating rotor. A common way of including particulate additive is to scatter it into the cloud of fibres between the formation of the cloud and the collection of the fibres on the collector. Examples of doing this when the rotor rotates about a substantially vertical axis, such that the cloud generally travels downwardly, are given in GB 1,234,075. When the rotor rotates about a substantially horizontal axis (for instance as in a cascade spinner) the cloud generally travels substantially horizontally towards the collector. The particulate additive may then be dropped into the cloud from above or may be blown into the cloud from behind the rotor. In GB 2,173,523, particles entrained in a flow of gas are directed transversely towards and into a downwardly moving cloud of fibres formed using a rotor which rotates about a vertical axis. The drawing shows that the stream of particles is ejected outside the cloud and drops downwardly into the outer edges of the cloud. It is an unfortunate fact that none of these known methods are capable of providing a satisfactory air-laid MMFV web containing a significant amount of uniformly distributed particulate additive trapped within the web. Instead, the additive (if present in large amounts) tends to be distributed non-uniformly and, when the web is a bonded web, the additive tends to be bonded non-uniformly. There is a particular problem when the additive is fibrous, since it tends to collect in the web as large tufts or flakes in the web and smaller tufts or balls gathered in loose lumps or ridges in the web, rather than as individual fibres or very small tufts uniformly distributed throughout the web. Trivial and insignificant amounts of additive may be introduced without impairing the properties, but any attempt at introducing useful amounts of additive will have the inevitable consequence of impairing the properties of the web. Attempts at minimising these problems are described in EP 461995 but attempts at introducing significant amounts of fibrous or other particulate additive by that technique will still result in a tufted, balled or other non-uniform distribution of the additive in the web. It would therefore be desirable to provide a way of introducing fibrous or other particulate additives into an MMVF web in such a way that there is little or no impairment of the properties of the web even when large amounts of the additive are incorporated. According to the invention, we make an MMVF web containing particulate additive by a method comprising forming a cloud of fibres by fiberising a vitreous melt by use of at least one centrifugal fiberising rotor, carrying the cloud of fibres by an air stream from adjacent the rotor or rotors to a permeable collector, blasting the particulate additive into the cloud of fibres at a direction against the direction of travel of the cloud towards the collector, and collecting the fibres and additive as a web on the collector. Thus, in the invention, we do not merely scatter the additive into the cloud or force it into the cloud perpendicular to or co-directional with the cloud, but instead we blast the additive into the cloud against the direction of travel of the cloud. The additive can be blasted into the cloud with a relatively wide spray angle of, for instance, 30 to 90°, but this is unnecessary and, instead, it is simpler and adequate merely to blast the additive from a simple duct outlet as a stream of particles having a substantially zero cone angle or a small angle, for instance 0 to 20, usually 0 to 10, degrees. The volume of particles introduced by this stream can be such that, if the stream is discharged from a duct outlet at an inappropriate position or inappropriate angle it will be easy to see that non-uniform deposition of particulate material is occurring on the collector, but the position of the duct outlet and the direction of the stream is so selected that the web does, instead, appear substantially uniform. Thus, if the duct outlet is at the wrong position or the wrong orientation the stream of particles will be carried into the web as a stream and will be apparent as a ridge or other non-uniform distribution in the web but adjustment of the angle and position of the duct from which the stream is discharged is made until the web has a surface appearance showing uniform distribution. Apart from any colour change due to the particles, the surface appearance of the web is therefore preferably substantially the same irrespective of whether or not the stream of particles is being blasted into the cloud of fibres. When there is a single fiberising rotor, it may be convenient to have a single stream emerging from a single duct outlet, but in many processes, especially when there is more than one fiberising rotor, there may be more than one duct outlet each generating a stream of particles. Accordingly each of the outlets needs to be oriented satisfactorily such that the web appears substantially uniform. The angle at which the or each stream is blasted into the cloud of fibres must be greater than 90° to the direction of travel of the fibres adjacent the duct outlet or other point at which the stream is blasted into the cloud. Generally the angle is at least 100° and preferably at least 110° to the direction of travel of the fibres at the point where the stream emerges from the duct. Ejecting the stream perpendicular to the cloud or the axis of the rotor, or at a smaller angle (co-directional) with the cloud gives inferior results. In particular, it is preferred that the or each stream of particles should emerge from its associated duct outlet along an axis that intersects the fiberising rotor or the front profile of apparatus on which the fiberising rotor is mounted. The preferred way of blasting the particulate additive into the cloud of fibres is as a stream of the particles entrained in air. It has sometimes been considered desirable to minimise the turbulence of the air stream in which the cloud of fibres is carried from the rotor to the collector and so it is surprising that it is satisfactory to blast the additive into the cloud as a stream entrained in air travelling against the direction of the main air stream carrying the cloud. However the amount of air needed for entraining even quite a large amount of additive is usually less than 5%, typically 0.2 to 2%, the amount of air which is carrying the cloud of fibres from the fiberising rotor to the collector and this relatively small amount of counterflowing air does not result in unacceptable turbulence of the air stream. Indeed, the counterflowing air may contribute to the uniform distribution of the additive within the cloud. Any suitable MMVF fiberising rotor can be used in the invention. Thus it can be, for instance, a spinning cup which is mounted for rotation about a substantially vertical axis and which has apertures in its walls through which fibres are extruded. The resultant cloud of fibres are generally carried downwardly by an air stream towards a collector which passes beneath the cup, in which event the stream of additive particles should be blasted into the cloud against its direction of movement away from the rotor upwardly into the downflowing cloud, for instance at an angle of 100 to 160°, often around 110 to 140°, to the axial direction of the cloud. In some instances the blast can be almost directly against the movement of the cloud from the rotor, or the axis of the rotor, and so the angle may be as much as 180°. Preferably, however, the fiberising rotor is mounted about a substantially horizontal axis and the cloud of fibres is carried forwards from the rotor towards the collector positioned in front of the rotor so that the fibres travel in a generally horizontal direction, towards the collector. There can be a single centrifugal fiberising rotor, with the rotor for instance being a Downey rotor or a jet blast rotor by which fibres are formed by the combination of centrifugal force and a jet blast. Preferably, however, the fibres are formed using a cascade spinner comprising a first rotor on to which melt is poured and off which it is thrown centrifugally and at least one subsequent rotor on to which the melt is thrown from the preceding rotor and off which fibres are thrown and wherein each of the rotors rotates about a substantially horizontal axis. The collector is a continuously moving conveyor located in front of the cascade spinner and the fibres are carried by the air stream from around the cascade spinner on to the conveyor. There can be two or more cascade spinners each forming fibres which are collected onto the conveyor, in which event one or more streams may be directed towards one spinner and other streams may be directed to other spinners. Usually the conveyer is an upwardly inclined conveyor. Usually the direction of movement is upwards and away from the spinner. In this process, the particulate additive is blasted into the cloud of fibres as one or more streams of particles entrained in air each from a duct outlet located in front of the cascade spinner. Often the conveyor- collector is a lower wall of a collection chamber having the cascade spinner at one end, in which event the or each duct is generally located in a side wall of the chamber. One or more of the ducts may be in the roof of the collection chamber. One or more ducts may be in the base of the chamber, for instance discharging upwardly from a position between the spinner and the start of the conveyor collector. The or each stream is generally discharged from the duct along an axis that intersects the front of the cascade spinner. The or each stream is ejected at an angle which is generally 100-180°, usually 100-160° and preferably 110 to 140° to the direction of travel of the cloud away from the rotor and/or the axis of the rotor. When, as is preferred, the cascade spinner has first, second, third and fourth rotors arranged in conventional configuration, it is particularly preferred that at least one stream of particulate additive should be directed towards the fourth rotor. If there is more than one stream of particulate additive, preferably at least 30%, most preferably at least 50% and often at least 70% by weight of the additive should be added by one or more streams that are directed towards the fourth rotor. Any other streams are preferably directed towards the third rotor. If there is more than one cascade spinner, streams may be directed towards each fourth (or third and fourth) rotor. In such an apparatus, if the stream is directed inappropriately, it may be seen that the surface of the web which is being collected is not flat, for instance carrying a ridge due to excess particulate additive in a narrow region of the collector. Upon adjusting the duct, for instance its orientation towards the fourth rotor and optionally also towards the third rotor and/or its distance from the rotor, it will easily be found that there is an orientation at which the particulate additive is distributed uniformly into the cloud and the web acquires a uniform smooth appearance. The distance of the duct outlet from the rotor is generally limited by the design of the apparatus to, for instance, below 7m. Reducing the distance to, for instance, below 3m generally improves mixing but if the duct outlet is too close to the rotor (e.g., below lm) there is a risk that the duct may interfere with formation and transport of fibres and so a distance of 1.5 to 3m is generally preferred. Similarly, visual observation of the cloud and the additive travelling through the chamber towards the conveyor will easily show whether the additive is being uniformly mixed into the cloud. When, as is customary, the web is to be a bonded web, binder may be sprayed into the cloud of fibres in conventional manner. The binder added in this manner may be adequate for bonding the particulate additive into the web but it may be desirable to spray binder into the stream of particulate additive as it emerges from its duct outlet. The amount of particulate additive can be as much as 50% or more based on the weight of MMV fibres. Often it is in the range 10 to 50% based on the weight of fibres. The preferred particulate additive is recycled mineral wool, generally in the form of small tufts of waste bonded MMVF wool. The tuft size is generally below 25mm and often below 10mm. Generally the tufts are above 1mm and often above 5mm. Other particulate additives that can be added in similar manner can be fine or coarse and include clay, perlite, vermiculite, pigments, magnesium hydroxide, aluminium hydrate or any other additive useful to render the product suitable for any of the known MMVF uses such as fire insulation and protection, thermal insulation, noise reduction and regulation, construction, horticultural media or reinforcement or filler. The web is collected on the conveyor or other collector in conventional manner and is carried off this and is subjected to conventional post treatments such as lamination, compression and curing so as to make a fibre product having the desired final properties. Lightweight products typically having a density in the range 10 to 50kg/m can easily include 5 to 30%, often around 15 to 25% recycled fibre based on the weight of fibre formed from melt in the process without any significant change in the properties of the product. Prior processes, for instance when the fibre is merely scattered into the cloud, have resulted in inferior quality if more than about 5% of fibre is introduced. Heavy products, for instance having a density of 50 to 300kg/m , can include 10 to 60%, often around 35 to 50% recycled fibre whereas prior processes have resulted in deterioration of properties if more than about 15 or 20% recycled fibre is incorporated by conventional techniques. The products all appear visually uniform. They are novel. The velocity of the additive particles, at the time at which they are blasted out of the duct utlets or other means for discharging them into the c _d of fibres, is generally at least 10 metres per second and is preferably at least 20 metres per second. It is usually unnecessary for it to be above 60 metres per second, and it is usually below 40 metres per second. The invention is illustrated in the accompanying drawings in which: Figure 1 is a diagrammatic cross section of an apparatus by which the invention can be performed and Figure 2 is a plan view of the apparatus of Figure 1. The apparatus comprises a cascade spinner 1 mounted in the end 2 of a spinning chamber 3. The spinning chamber has a roof 4 and side walls 5 and 6. Its base is defined by an inclined conveyor 7. There is a pit 8 between the cascade spinner 1 and the conveyor 7 and into which shot may drop. The cascade spinner has a first or top rotor 9 arranged to throw melt on to a second rotor 10. Some of the melt is thrown off rotor 10 as fibres while the remainder is thrown on to third rotor 11. Some of this melt is thrown off as fibres while the remainder is thrown on to fourth rotor 12, off which it is thrown as fibres. Any suitable arrangement for the cascade spinner can be used, and the spinner may be provided with means for supplying air jets close to the spinner, for instance all as described in WO92/06047. During normal operation, melt is poured on to the top rotor while air is sucked through the conveyor 7 and is blown from the cascade spinner through slots (not shown) around the rotors and optionally also is blown through the end wall 2. Fibres thrown off the rotors are carried in the form of a cloud towards the conveyor 7. The cloud is somewhat conical and is approximately confined within the area marked by the dashed lines 13, 14 and 15. It will be seen that the bottom of the cloud is defined by line 13 making an angle of, for instance, 5 to 20°, typically about 10°, to the axis of the cascade spinner. The top of the cloud is defined by line 14 at an angle of around 45 to 65°, typically around 55°, to the axis of the spinner. The sides of the cloud are defined by line 15 making an angle typically of 30 to 55°, often around 40 to 45°, to the axis of the spinner. The air stream carries the fibres in the cloud on to the conveyor 7 where the air is sucked through the conveyor and the fibres are deposited as a web. As is conventional, the conveyor 7 moves continuously upwardly and the web is taken off the conveyor at the top roller 16. Binder is blown into the cloud in conventional manner, for instance from binder sprays mounted on the axis of one or more of the rotors and/or from other sprays mounted around the front face 17 of the cascade spinner or elsewhere in the chamber in conventional manner. Waste bonded recycled wool is broken into tufts and is recycled into the spinning chamber. If it is merely dropped in through the roof of the chamber even quite small amounts (for instance 10% based on the weight of wool formed from the rotors 9 to 12) results in visible non- uniformity of the web on the conveyor 7. In the invention there is at least one duct 18, each terminating in a duct outlet 19 located in a corresponding aperture 20 in the side wall 5 or 6 or in the roof of the chamber at a position about 2-2.5 metres from the front of the rotors. Each duct is positioned at an angle of about 100 to 160°, preferably around 120 to 140°, to the axis of the cascade spinner and to the general direction of travel of the cloud from the spinner towards the conveyor. A binder spray 21 may be provided between the duct outlet 19 and the spinning chamber positioned to spray binder across the duct outlet so as to wet all material entering the spinning chamber from the duct 18. Although the drawings suggest 6 different positions in the side walls, these merely show possible positions and in practice they will not usually all be used. There may be duct 18 discharging upwardly from above the pit 8, between the spinner and the conveyor 7. The or each duct 18 is oriented so that its axis 22 intercepts the face 17 of the cascade spinner and preferably so that it intercepts the area of rotor 12 and/or rotor 11. Preferably the axis of the or each duct intercepts the area of rotor 12, the fourth rotor in the cascade spinner. If the cascade spinner only has three rotors, then the axis of the or each duct should preferably intercept the area of the third rotor. In a typical process, tufts of bonded mineral wool having a tuft size of about 5 to 20mm are blown in through the ducts at a speed of about 25m/s. The amount of air that is blown in through the ducts is sufficient to entrain the tufts and is about 1% of the total amount of air drawn through the spinning chamber. Preferably the ducts are mounted in the walls of the chamber such that their vertical and horizontal angular orientations can easily be adjusted, since the operator can then select an orientation which can be seen to be giving the roost uniform deposition on the conveyor 7.

Claims: CLAIMS 1. A process for making an MMVF web containing particulate additive comprising forming a cloud (13, 14, 15) of fibres by fiberising a vitreous melt by use of at least one centrifugal fiberising rotor (9, 10, 11, 12), carrying the cloud of fibres by an air stream from adjacent the rotor or rotors to a permeable collector (7) , adding the particulate additive into the cloud of fibres, and collecting the fibres and additive as a web on the collector (7) , characterised in that the particulate additive is blasted into the cloud of fibres at a direction (22) against the direction of travel of the cloud. 2. A process according to claim 1 in which the particulate additive is blasted from at least one duct outlet as a stream of particles and in which the position of the or each duct outlet and the direction of the or each stream are so selected that the web appears substantially uniform. 3. A process according to claim 2 in which the stream of particles from a duct outlet is blasted at an angle of 100 to 180° to the general direction of travel of the cloud of fibres adjacent the duct outlet. 4. A process according to any preceding claim in which the particulate additive is blasted into the cloud as a stream of the additive particles entrained in air. 5. A process according to any preceding claim in which the cloud of fibres is formed using at least one cascade spinner comprising a first rotor on to which melt is poured and off which it is thrown centrifugally and at least one subsequent rotor on to which the melt is thrown on the preceding rotor and off which fibres are thrown, wherein each of the rotors rotates about a substantially horizontal axis and the collector is an upwardly inclined conveyor located in front of the cascade spinner, and in which the fibres are carried by an air stream from adjacent the cascade spinner or spinners on to the conveyor and are collected on the conveyor, and in which the particulate additive is blasted into the cloud of fibres as one or more streams of particles entrained in air, each from a duct located in front of the cascade spinner. 6. A process according to claim 5 in which the or each stream is directed towards the front of the cascade spinner or one of the cascade spinners. 7. A process according to claim 6 in which at least one stream of particulate additive is directed towards the final rotor of the cascade spinner or of one of the cascade spinners. 8. A process according to any of claims 5 to 7 in which the or each cascade spinner has first, second, third and fourth rotors and at least half the particulate additive is in one or more streams directed towards the or each fourth rotor. 9. A process according to claim 8 in which substantially all the particulate additive is directed towards the or each third and fourth rotors. 10. A process according to any preceding claim in which the particulate additive comprises tufts of mineral wool. 11. A process according to any preceding claim in which binder is sprayed on to the additive as it is blasted into the cloud of fibres. 12. An air laid MMVF web which is uniform and which contains uniformly distributed recycled fibre or other additive, wherein the web has (a) a density of 10-50 kg/m 3 and includes 5 to 30% (preferably 15 to 25%) additive or (b) a density of 50-300 kg/m 3 and includes 10 to 60% (preferably 35-50%) additive.

Inventors: NIELSEN MORTEN HVID, NIELSEN, MORTEN, HVID
Applicants: NIELSEN MORTEN HVID, ROCKWOOL INT, NIELSEN, MORTEN, HVID, ROCKWOOL INTERNATIONAL A/S
Application year: 1997
Main classification: D04H1
IPC codes: D04H1