MANUFACTURE OF MINERAL WOOL PRODUCTS

Abstract: Thermal insulation product which comprises air laid man-made vitreous fibre material through which is distributed a particulate additive for improving the insulation properties may be made using a cascade spinner in which a primary air blast is discharged over each fiberising rotor with a velocity of at least 100m/sec.

Description: MANUFACTURE OF MINERAL WOOL PRODUCTS This invention relates to the manufacture of thermal insulation products which comprise air laid man-made vitreous fibre (MMVF) material wherein one or more additives which improve the thermal insulation properties of the product are distributed substantially homogeneously throughout the MMVF material . Preferred products of this type are described in our applications PCT/EP99/ and PCT/EP99/ which are being filed even date herewith under our references PRL04151 O and PRL04293 O. It is known, for instance from GB-A-1 , 559 , 117 and WO92/06047 to make air laid MMVF products using apparatus which is generally known as a cascade spinner and comprises a set of at least three rotors mounted on a housing each for rotation about a different substantially horizontal axis and arranged such that when the rotors are rotating melt poured onto the periphery of the top rotor in the set is thrown onto the periphery of each subsequent rotor in turn and fibres are thrown off the rotors, and air supply means for blowing the fibres axially along the chamber and which comprise an air supply orifice slot associated with each subsequent rotor wherein each slot has an internal diameter substantially the same as the external diameter of the periphery of its associated rotor and is constructed for discharging a primary air blast substantially parallel to that periphery as a wall jet. The MMVF products are made using this apparatus by a process in which fibres are formed by pouring melt onto the top rotor while the rotors are rotating and the air blasts are being discharged and thereby forming a cloud of fibres traveling forwards from the spinner, and collecting the fibres from the cloud as a web, and if necessary converting the web to the insulation product. This conversion may include cross lapping, and may include curing any binder. It is known to incorporate, for instance, binder in the web by spraying it on to the fibres as they are thrown off the rotors and carried forward from the rotors. The primary air which provides the wall jets serves predominantly to promote fibre formation, and also to provide some transport air to carry the cloud of fibres away. Various velocities have been proposed in the literature for the primary air for these purposes. The incorporation of graphite or other particulate insulation- improving additive into the air laid MMVF product improves insulation properties when a substantially homogeneous distribution is achieved. However it would be desirable to achieve the greatest possible improvement, and we have now surprisingly found that the level of improvement in insulation properties can be influenced by the conditions under which the cloud of fibres is formed. In particular, when the particulate additive is being supplied through additive supply means on or adjacent to the spinner for spraying additive on to the fibres as they are thrown off the rotors and carried forward from the rotors, thereby forming a cloud of fibres and additive travelling forwards from the spinner, improved properties are obtained when at least one of the primary air blasts, preferably each of the primary air blasts, emerges from its associated air supply orifice with a velocity of at least 100 meters per second. The velocity may be up to 150, 200 or even 250 meters per second. We surprisingly find that the use of these high velocities (and the associated high volume and impulse) of the air which forms the wall jets results in improved insulation properties. We believe this is due to an improved distribution of the insulation- improving additive and that this may be due to the increased primary air velocity. The improvement is manifested particularly when the insulation product has relatively low density, usually below 100kg/m 3 and generally in the range of 5 to 60kg/m 3 , preferably around 10 to 40kg/m 3 . It is surprising that it is beneficial to make these relatively low density products at these high air blast velocities. When examining the effect of air velocity on product quality we have found that, with the exception of these particular products, it is usually preferred for the lower density products to be made using primary air blast velocities well below lOOm/s and so it is surprising that the higher velocities are beneficial in these particular products . The insulation- improving additive may be the only active ingredient which is sprayed on to the fibres during the process, for instance as a slurry in water, optionally with a surfactant to promote dispersion of the additive in the water. Generally however the particulate additive is sprayed as a mixture with a binder. The binder may be a conventional MMVF binder, for instance an aqueous curable binder resin. The amount of binder can be an amount typical for the air laid material or increased slightly to provide bonding of the additive. For instance the typical amount may be in the range 1 to 5% by weight of the product, and the extra amount may be 0.1 to 0.5%, often around 0.25% for each 1% of particulate additive that is added. For instance the amount is usually in the range 1.5 to 6%, by weight. A preferred additive is graphite in the form of particles, especially lamellar particles. Air-laid MMVF products comprising graphite are described in our co- pending application no. PCT/EP 99/ (reference PRL04151WO) , claiming priority from European patent application no. 98307761.1 and British patent application no. 9916175.4. In the present invention the graphite may have any of the features described in that application. The present invention may be applied to produce any of the products described in that application and other graphite- containing products. Further products containing other preferred additives are disclosed in our co-pending application PCT/EP 99/ (reference PRL04293WO) , claiming priority from British patent application no. 9916174.7. The additives include silicon, aluminium (powder or flakes) , mica, silica and titania and mixtures thereof. They may have any of the features described in that application. Any of the products described in that application may be made by the method of the present invention, as may other products containing these additives . Other additives known for improving thermal insulation in different products may also be used in the invention, for instance germanium, carbon black, fibrous potassium titanate, amorphous silica, fumed silica, precipitated silica and fused silica. They may be used alone or mixtures may be used, for instance of graphite and one or more other insulation- improving additives. In general, additives which are flake-shaped or lamellar-shaped are preferred. The particle size is preferably very small, for instance as indicated in those applications . The total amount of additive is usually between 0.2 and 15%, usually between 0.5 and 10%, by weight. Reference should be made to the text of each of the aforesaid PCT applications for full disclosure of the products and their composition, and the entire disclosure of each of the PCT applications is herein incorporated by reference . The air which provides the wall jets promotes attenuation of the fibres during their initial formation, and also provides air for transporting the cloud of fibres away from the spinner. This air is conveniently referred to as the primary air. Each slot may be provided by a series of adjacent nozzles. Each of the subsequent rotors generally has a diameter of from 150 to 400mm, often in the range 220 to 350mm. The area in the spinner of the orifices through which the primary air is blasted on each subsequent rotor is generally in the range 100 to 400, often around 150 to 250 or 300, cm 2 for the spinner, which usually has four rotors. Preferably there are secondary air slots displaced outwardly from the primary air slots for providing a secondary air stream, predominantly to facilitate transport of the cloud of fibres forwards from the spinner. These air slots also may be a series of nozzles. The velocity of the secondary air as it emerges from its nozzles or other air supply orifices is generally from 50 to 100% of the velocity of the primary air. The secondary air slots are preferably substantially concentric with the primary air slots and often extend over substantially the same angular areas of each of the subsequent rotors as the primary air slots. The outward displacement of the secondary slots is generally such that their innermost edge is from 50 to 500mm, often from 100 to 300mm from the periphery of the rotor. The area of the secondary air slots in the spinner is generally in the range 50 to 150, typically around 100, cm 2 . The primary and secondary air slots may each have a width typically of 5 to 30mm, preferably 10 to 15mm. The primary air flow on the cascade spinner is usually above 6000 and preferably above 7000 or 8000Nm 3 /hr. It may be up to, for instance, 12000 or 15000Nm 3 /hr. Best results are obtained with values of around 9000 to 10000Nm 3 /hr. The impulse due to the primary air is generally above 200N and generally above 250N, for instance up to 400N or even 500N. Values of around 280 to 380N are often preferred. The volume of secondary air on the cascade spinner is generally above 3000Nm 3 /hr, preferably above 3500 up to, for instance, 7000Nm 3 /hr, with best results generally being obtained with around 4000 to 6000Nm J /hr. The impulse due to the secondary air is generally above 8 ON and usually is above 100N. It may be up to, for instance, 250 or 350N, with best results generally being obtained with values in the range 120 to 20ON. It is not essential that there should be secondary air on each (or any) of the subsequent rotors. For instance, it can be preferred to have primary air only on the first subsequent rotor and secondary air on the remaining two subsequent rotors (when the spinner consists of four rotors) . Generally the secondary air slots (and the primary air slots) extend over 1/3 to A of the periphery of each of the subsequent rotors which each is associated. Irrespective of whether or not secondary air (as explained above) is provided on any rotor, it can be preferred to have tertiary air, for instance the air described in W096/38391 and which is blown or induced around the spinner. The primary air may emerge from its respective slots wholly in the axial direction but often it has a tangential component over part or all of the length of each of the primary air slots, for instance as described in GB-A- 1,559,117 and in WO92/06047. The secondary air may have a direction which is wholly axial as it emerges from the secondary air slots or it may emerge with an angle of, for instance, up to 10° or 20° from the axial. Generally it emerges substantially parallel with the surface of the associated rotor, and thus substantially parallel with primary air as that emerges initially adjacent to the surface of the associated rotor. The cascade spinner can have conventional construction . The means for applying the additive may comprise one or more orifices in the front of one or more of the subsequent rotors so that the additive is sprayed outwardly onto the fibres as they are thrown off the rotor. Additive discharge orifices on a rotor may rotate with the rotor so as to throw the additive outwardly by centrifugal force. However it is not essential that all the additive should be discharged outwardly in this manner. Additive may be sprayed on to the fibres from outside the periphery of each rotor, for instance from fixed orifices in the front of the spinner or positioned elsewhere around the spinner. Binder is also usually sprayed onto the fibres, e.g. from the same or similar orifices as the additive. Ant- settling agent and/or dispersing agent and/or defoamer may be sprayed with the additive, usually from the same or similar orifices. The total apparatus generally includes a collecting chamber with a collector moving through it and on which the web is collected. Two, three or more spinners may supply the fibres to a single collecting chamber. The overall construction of the spinner and the overall apparatus may be conventional and may be as described in, for instance, WO92/06047 or W096/38391. The melt is preferably rock, stone or slag melt. Example As an example of the invention, a bonded stone wool insulation product having a density of about 30kg/m 3 can be made in conventional manner by including 3% graphite in the binder slurry which is sprayed outwardly from each of the subsequent rotors . In process A the velocity of the primary air is about 75m/sec, the amount of primary air is about 5400Nm 3 /hr and the amount of secondary air is about 2700Nm 3 /hr. In process B (according to the invention) the velocity of the primary air is about 130m/sec, the volume of primary air is about 9400Nm 3 /hr and the volume of secondary air is about 4700Nm 3 /hr. All other conditions remained unchanged. It is found that process A operated at the lower air velocity gave an improved λ (compared to the corresponding process in the absence of graphite) of 1.5mW/m°K, whereas the corresponding process B (of the invention) at the higher primary air velocity gave an increase of 2mW/m°K.

Claims: CLAIMS 1. A process for making a thermal insulation product which comprises air-laid material using apparatus comprising a set of at least three rotors mounted on a housing each for rotation about a different substantially horizontal axis and arranged such that when the rotors are rotating melt poured onto the periphery of the top rotor in the set is thrown onto the periphery of each subsequent rotor in turn and fibres are thrown off the rotors, air supply means for blowing the fibres axially along the chamber and which comprise a primary air supply slot associated with each subsequent rotor wherein each slot has an internal diameter substantially the same as the external diameter of the periphery of its associated rotor and is constructed for discharging a primary air blast substantially parallel to that periphery as a wall jet, and additive supply means on or adjacent the spinner for spraying additive outwardly onto the fibres as they are thrown off the rotors and are carried forward from the rotors , and in which process fibres are formed by pouring melt onto the top rotor while the rotors are rotating, the air blasts are being discharged and the additive is being sprayed outwardly, and thereby forming a cloud of fibres and additive traveling forwards from the spinner, and collecting the fibres and additive from the cloud as a web, and if necessary converting the web to the insulation product , characterised in that the additive comprises a particulate insulation- improving additive, at least one of the primary air blasts emerges from its air supply orifice with a velocity of at least lOOm/sec, and the particulate additive is distributed substantially uniformly throughout the air laid material. 2. A process according to claim 1 in which the additive supply means comprise at least one additive discharge orifice on each of the subsequent rotors positioned within the periphery of the rotor and rotating with the rotor. 3. A process according to claim 1 or claim 2 in which the density of the product is 5 to 60kg/m 3 . 4. A process according to any preceding claim in which the additive comprises binder and particulate insulation- improving additive. 5. A process according to any preceding claim in which the particulate insulation-improving additive comprises graphite. 6. A silicon, aluminium, mica, silica or titania, or mixtures including any of these. 7. A process according to any preceding claim in which secondary air supplied at a velocity of 50 to 100% of the velocity of the primary air through slots displaced outwardly from the primary air slots. 8. A process according to any preceding calim in which each primary air blast emerges from its slot with a velocity of at least lOOm/s. 9. A process according to any preceding claim in which the velocity of the primary air is from 150 to 250 metres per second.

Inventors: CRIDLAND IAN, CRIDLAND, IAN
Applicants: CRIDLAND IAN, ROCKWOOL INT, CRIDLAND, IAN, ROCKWOOL INTERNATIONAL A/S
Application year: 1999
Main classification: C03C25
IPC codes: C03C25, D04H1