The present invention generally relates to the technical field of producing mineral fiber-insulating plates. Mineral fibers generally comprise fibers such as rockwool fibers, glass fibers, etc. More pre¬ cisely, the present invention relates to a novel technique of producing a mineral fiber-insulating web from which e.g. mineral fiber-insulating plates or products are cut. The mineral fiber-insulating plates or pro- ducts produced from the mineral fiber-insulating web produced in accor¬ dance with the present invention exhibit advantageous characteristics as to mechanical performance, such as modulus of elasticity and strength, low weight, reduced content of bonding agents, and good thermal-insulat¬ ing property. The mineral fiber-insulating webs are normally produced as webs from mineral fibers which are expelled from a mineral fiber generating means and transferred to a collector conveyor by means of an air stream. The mineral fibers, of which the mineral fiber-insulating web is com¬ posed, are normally linked together by means of droplets and/or particles of a heat-curable bonding agent which are cured by exposure to heat. For providing a mineral fiber web of adequate mechanical perfor¬ mance and mechanical integrity, such as elasticity and strength, a cer¬ tain amount of cured bonding agent has to be present. Hitherto, an ex¬ cessive amount of bonding agent has normally been used for providing adequate mechanical performance and integrity such as an amount of bond¬ ing agent of the order of 10% - 30% by weight of the bonding agent of the mineral fiber web.

The conventional methods of producing mineral fiber-insulating webs from mineral fibers which are transferred from a mineral fiber generat- ing means to a collector conveyor by means of an air stream result in serious waste or environmental problems as the air stream by means of which the mineral fibers are transferred from the mineral fiber generat¬ ing means to the collector conveyor includes a large amount of droplets and/or particles of the heat-curable bonding agent. Unless the droplets and/or particles of the heat-curable bonding agent, which droplets and/- or particles are carried along with the air stream after the transfer of the mineral fibers from the mineral fiber generating means to the collector conveyor, are separated from the air, which is later on

expelled into the atmosphere through a chimney or a similar air- expelling outlet, the droplets and/or particles of the heat-curable bonding agent which are carried along with the air may cause severe en¬ vironmental pollution. An object of the present invention is to provide a novel method of producing a mineral fiber web from which mineral fiber containing pro¬ ducts may be produced, in accordance with which method the above- described waste or environmental pollution problems are substantially eliminated. A further object of the present invention is to provide a novel method of producing a mineral fiber web from which mineral fiber con¬ taining products may be produced, according to which method the necessity of separating excess droplets and/or particles of the heat- curable bonding agents, which excess droplets and/or particles are carried along with the air stream after the formation of the mineral fiber web, is radically reduced or preferably eliminated to any substantial extent.

A further object of the present invention is to provide a novel method of producing a mineral fiber web from which mineral fiber con- taining products may be produced, which method renders it possible, in an online production plant, to produce mineral fiber containing products which are of a structure equal, in terms of mechanical performance, to prior art mineral fiber products, still including a reduced amount of bonding agent. A further object of the present invention is to provide a novel method of producing a mineral fiber web from which mineral fiber con¬ taining products may be produced, which method renders it possible, in an online production plant, to produce mineral fiber containing products which exhibit improved mechanical performance, such as modulus of elasticity and strength, as compared to conventional mineral fiber con¬ taining products of the same content of bonding agent.

A particular advantage of the present invention relates to the fact that the novel method of producing a mineral fiber web according to the present invention may to any substantial extent eliminate any waste of heat-curable bonding agent from a plant in which the method is performed further to any substantial extent eliminate any environmental pollution problems caused by waste of excess heat-curable bonding or coupling agent material to the environment from the plant, and still further to

any substantial extent eliminate the necessity of separating excess heat-curable bonding agent material from the exhaust air outlet of the plant.

A further advantage of the present invention relates to the novel mineral fiber containing product according to the present invention and produced in accordance with the method according to the present inven¬ tion, which mineral fiber containing product, as compared to prior art mineral fiber containing products, includes a smaller amount of bonding agent and is consequently less costly than the prior art mineral fiber containing products, and still exhibits advantages as compared to the prior art mineral fiber containing products relating to mechanical per¬ formance and thermal-insulating properties.

A further advantage of the present invention relates to the fact that the amount of bonding agent used for producing a mineral fiber con- taining product of a specific type is reduced in accordance with the method according to the present invention, as the amount of bonding agent may be reduced in a mineral fiber containing product according to the present invention as compared to a prior art mineral fiber contain¬ ing product of similar properties in terms of mechanical strength and thermal-insulating properties.

A particular feature of the present invention relates to a unique efficient utilization of the heat-curable bonding agent presented as droplets and/or particles to the mineral fibers which are transferred from the mineral fiber generating means by means of an air stream pro- viding substantially no environmental problems caused by excess bonding agent material which is expelled to the atmosphere.

The above objects, the above advantages and the above feature to¬ gether with numerous other objects, advantages, and features which will be evident from the below detailed description of preferred embodiments of the invention are, in accordance with a first aspect of the present invention, obtained by a method of producing a non-woven mineral fiber web, comprising the following steps: melting a mineral material and producing a stream of molten mineral material, directing said stream of molten mineral material to a mineral fiber generating means so as to generate mineral fibers from said molten mine¬ ral material by solidifying said mineral material, expelling said solidified mineral material as mineral fibers from

said mineral fiber generating means, directing a carrier air stream past said mineral fiber generating means for carrying said mineral fibers away from said mineral fiber ge¬ nerating means, generating and spraying droplets and/or particles of a bonding agent or a coupling agent onto said mineral fibers of said carrier air stream so as to cause said droplets and/or particles to impact said mineral fibers, said droplets and/or particles predominantly having diameters larger than a minimum diameter corresponding to a droplet and/or particle showing substantially no tendency to impact said mineral fibers of said carrier air stream, and collecting said mineral fibers of said carrier air stream on a mi¬ neral fiber web collecting surface, thereby forming said non-woven mine¬ ral fiber web. In the present context, the term droplets and/or particles is to be construed including small size bodies of liquid or solid material con¬ ventionally known as droplets or particles, respectively, however, also including small size bodies including a mixture of liquid or solid mate¬ rial. In the present context, the term diameter is a generic term not only including the specific term referring to a sphere but also relating to an outer overall dimension of any arbitrary body of a specific geometric configuration including spheres, cubes, ellipsoids etc. and combinations thereof and representing a relevant outer dimension re¬ presenting the overall dimensions of the body in question. Furthermore, in the present context, the term bonding agent or coupling agent is to be construed including any material capable of coupling or binding the mineral fibers together, of causing the mineral fibers to adhere to one another, and further of providing any specific characteristic or property of the mineral fibers prior to the bonding of the mineral fibers together or after the mineral fibers have been bonded together, such as characteristics or properties regarding bonding capability, affinity, impregnation, such as water suction/absorption/repelling cap¬ ability and protection of the mineral fibers etc. Examples of bonding agents or coupling agents are heat-curable resins conventionally used within the industry for producing mineral fiber products and specific types of oils or tensides (surface tension controlling agents) capable of providing specific characteristics or properties.

According to the teachings of the present invention, it has been

realized that the droplets and/or particles of the bonding agent or coupling agent which are sprayed onto the mineral fibers which are carried along with the carrier air stream have a reduced tendency to im¬ pact the mineral fibers provided the diameter of the droplet and/or par- tide is smaller than a specific minimum diameter of the droplet and/or particle determined basically by the velocity of the carrier air stream. In accordance with the terminology used within the technical field of applying fertilizers by means of carrier air streams, the criterion ac¬ cording to the teachings of the present invention, according to which the droplets and/or particles of the bonding agent or coupling agent which is sprayed on to the mineral fibers carried along with the carrier air stream, may be defined as droplets and/or particles having a diameter larger than a specific diameter of the droplets and/or particles, which diameter corresponds to a droplet and/or particle being airborne at the specific air stream velocity as will be evident from the below discussion. Within the above mentioned technical field, it has been realized that a specific diameter threshold exists below which particles or droplets which are sprayed by means of an carrier air stream are simply carried along with the carrier air stream without i - pacting any obstacles, which characteristic property is characterized as the droplet and/or particle being airborne.

In accordance with the conventional techniques of applying droplets and/or particles of a bonding agent or coupling agent to mineral fibers which are carried along from a mineral fiber generating means by means of a carrier air stream, which droplets and/or particles may have diameters within a varying and unspecific droplet and/or particle dia¬ meter range, the present invention is based on the realization that droplets and/or particles of the bonding agent or coupling agent having a diameter smaller than a specific lower diameter threshold have no ten- dency to impact the mineral fibers carried along with the carrier air stream, and are consequently similar to the above-described fertilizer technique wasted as airborne droplets and/or particles, and have to be separated from the exhaust air which is exhausted into the atmosphere through e.g. a chimney or a similar exhaust device, or are exhausted into the atmosphere in case the exhaust air is not rinsed, which of course may cause a severe environmental pollution problem. Thus, the droplets and/or particles of said bonding agent or coupling agent may have diameters within a diameter range, the lower limit of which is

identical to or larger than said minimum diameter or alternatively or additionally, said droplets and/or particles of said bonding agent or coupling agent having diameters within a diameter range, the mean value of said diameters being somewhat larger than said minimum diameter, and more than 75%-95% of said droplets and/or particles, such as 80-95%, preferably 90% having diameters larger than said minimum diameter, pre¬ ferably said minimum diameter being of the order of 10-75 μ , such as 25-50 μm.

In a conventional method of producing non-woven mineral fiber webs from mineral fibers which are carried by means of a carrier air stream from a fiber generating means to a collector means such as a collector conveyor, the net volume of the bonding agent or coupling agent used for a specific production may be divided into a first volumetric part, cor¬ responding to those droplets and/or particles which are wasted, and a second volumetric part, corresponding to the droplets and/or particles which actually impact the mineral fibers and are to a large or small ex¬ tent utilized for bonding the mineral fibers together within the mineral fiber web. The droplets and/or particles which are wasted may, as will be described in greater details below, be wasted for various reasons. Although the droplets and/or particles which constitute the above- described first volumetric part are substantially smaller than the droplets and/or particles which constitute the above-described second volumetric part, the ratio between the first volumetric part and the total volume used for specific production may amount to a percentage of the order of 1-2%, which in comparison with the total amount of bonding agents or coupling agents used within the mineral fiber production industry amounts to a fairly large figure, which in the first place causes a severe environmental pollution problem in case the waste droplets and/or particles are not separated from the waste air vented from a production plant and, on the other hand, necessitates the utilization of elaborated filtering techniques for preventing the waste bonding agent or coupling agent material from being expelled into the atmosphere, causing the above-described environmental pollution problems. The method according to the present invention may be implemented in accordance with any production technique well known in the art per se as the mineral fibers may be generated by means of a spinning wheel, a cen¬ trifugal spinner, a nozzle dispensing the mineral fibers or similar mi-

neral fiber generating means. Various structures of mineral fiber gene¬ rating means are disclosed in the prior art, and reference is made to the below references, of which the listed US patents are hereby further incorporated in the present specification by reference. The list in- eludes the following references: DK 158,612, US 4,434,299, EP 0059 152, GB Patent Appln. 9001124.8 (published 18 July, 1991), GB 1,515,511, GB 2,004,204, GB 2,004,205, GB 2,004,205, GB 2,004,205, GB 2,004,206, GB 2,026,104, GB 2,043,489, GB 2,118,866, GB 2,142,844, GB 93/00053, DD 155,897, SE 452,150, SE 463,817, DK 5318/89, DK 5317/89, EP 0530843 and US 5,123,949.

An example of the convention technique of applying droplets and/or particles of a bonding agent or coupling agent to mineral fibers which are carried along from a mineral fiber generating means by means of a carrier air stream is disclosed in the above listed Swedish patent application No. 8,503,805, publication No. 452,150. In the reference, it is stated that the bonding agent or coupling agent which is applied in particulate state is dispensed from the same side as the mineral fibers and introduced into the carrier air stream at a location before the carrier air stream impacts the mineral fibers. The reference is, however, totally mute regarding any consideration relating to any dependency of the droplets or particles of the particulate bonding agent or coupling agent of the carrier air stream.

In US patent No. 4,433,992, a technique of a spraying bonding agent or coupling agent onto mineral fibers carried along in a carrier air stream is described. According to the reference, is is stated that the liquid composition constituting the bonding agent or coupling agent is projected in the form of drops into the gas current carrying the fibers, transversely to the current, as the drops have sufficient energy to penetrate the gas current to then become finally divided by the higher velocity of the latter. According to the technique described in the US reference, it is comtemplated that the high energy gas current or carrier air stream is capable of dividing the larger diameter drops into finally divided droplets provided the drops are introduced into the gas current or carrier air stream in a direction transversely relative to the direction of the gas current or carrier air stream. The teachings of the US reference is in total disagreement with the basic realization of the present invention as it has been realized according to the teachings of the present invention that drops of bonding agent or coupling agent

have a very small tendency of being divided into smaller droplets or particles even when exposed to a high energy carrier air stream resulting in an inadequate utilization of the amount of bonding agent or coupling agent used for the production of the mineral fiber web provided the bonding agent or coupling agent is supplied to the carrier air stream as drops.

In US patent No. 5,032,334, US patent No. 5,123,949 and US patent No. 4,592,769, various techniques of producing mineral fiber webs are disclosed. The techniques involve spraying a particulate bonding agent or coupling agent onto the mineral fiber web which is collected on a conveyer. Reference is made to the above Swedish patent and the above US patents, and the above US patents are hereby incorporated in the present specification by reference.

Dependent on the specific type of fiber generating means and on the direction of the mineral fibers expelled from the mineral fiber ge¬ nerating means relative to the vertical direction, the air stream may fulfil certain requirements as to the transfer of the mineral fibers from the mineral fiber generating means to the collection site, at which the mineral fibers are collected for the formation of a mineral fiber web. Thus, the carrier air stream may define a specific direction and a specific air velocity past the mineral fiber generating means for carry¬ ing the mineral fibers being expelled from the mineral fiber generating means along a predominant direction or along predominant directions, as the specific directions of the carrier air stream may be substantially coinciding with the predominant direction or predominant directions, may be substantially perpendicular to the predominant direction or pre¬ dominant directions or may alternatively define an angle with the pre¬ dominant direction or predominant directions.

Depending on the air velocity of the carrier air stream, by means of which the mineral fibers are transferred from the mineral fiber generating means to the mineral fiber web collecting surface, the drop¬ lets have to have a diameter above a specific minimum diameter in order to comply with the minimum diameter requirement characteristics of the present invention. In the preferred embodiment of the method according to the present invention, the droplets and/or particles have diameters within the range 10 - 300 μm, preferably within the range 25 - 200 μm, further preferably within the range 50 - 150 μm. In accordance with the above mentioned preferred embodiment of the method according to the

present invention, the specific air velocity of the carrier air stream is of the order of 50 - 250 m/sec.

It is to be realized that the requirements as to a specific minimum diameter are in contradiction to certain requirements as to maximum utilization of the bonding agent or coupling agent through the subdivi¬ sion of the droplets and/or particles of the bonding agent or coupling agent into a plurality of minor droplets and/or particles for increasing the number of bondings or couplings within the mineral fiber web as com¬ pared to a mineral fiber web including the same amount of coupling agent or bonding agent, however, including larger droplets and/or particles. A certain analysis of conventional methods of producing mineral fiber webs from mineral fibers, on which analysis the present invention is based, has revealed that a compromise between, on the one hand, the requirement as to eliminating droplets having diameters below the critical minimum diameter characteristic of the present invention and, on the other hand, the utilization of the total amount of bonding agent or coupling agent through sub-division of the bonding agent or coupling agent droplets and/or particles into a plurality of minor droplets and/or particles is established, provided the droplets and/or particles have diameters with- in the range 50 - 150 μm. By using fairly small droplets and/or par¬ ticles, the increased internal cohesion due to surface tension of said droplets and/or particles as compared td larger droplets and/or particles is utilized for ensuring that the droplets and/or particles are not unintentionally divided into extremely small droplets and/or particles which might be wasted as discussed above due to the reduced tendency of the smaller droplets and/or particles to impact the mineral fibers. According to a particular advantageous embodiment of the method according to the present invention, the droplets and/or particles are dispensed from a rotating droplet dispenser as the utilization of a rotating droplet dispenser renders it possible to produce droplets ex¬ hibiting a substantially constant diameter and not only a diameter with¬ in a specific range. By the utilization of a rotating droplet dispenser, droplets of a specific diameter of e.g. 70 μm, +/- 10 *m ma be produced as the number of particles differing more than +/- 1° P ^m f ^rom the speci- fie diameter of the droplets produced by means of the rotating droplet dispenser constitutes less than 1% of the total amount of droplets pro¬ duced by the rotating droplet dispenser. According to a further advantageous embodiment of the method according to the present inven-

tion, the droplets and/or particles are produced by means of a centrifugal spinning wheel producing the mineral fibers. In order to provide an advantageous distribution of the droplets and/or particles as the droplets and/or particles mingle with the carrier air stream carry- ing the mineral fibers away from the centrifugal spinning wheel produc¬ ing the mineral fibers, the droplets and/or particles are preferably, in accordance with teachings well known in the art per se, produced at the outer diametrical range of the spinning wheel in order to produce the droplets and/or particles as close as possible to the origin of the mineral fibers. Thus, the droplets and/or particles are preferably generated within the diametrical area 50 - 100% of the diameter of the spinning wheel, such as within the range 80 - 100% of the diameter of the spinning wheel .

In order to prevent that the droplets and/or particles, which are sprayed onto the mineral fibers, which are expelled from the mineral fiber generating means after solidifying the molten mineral material, are cured due to the high temperature of the mineral fibers or the air of the air stream which has been heated by the mineral fibers, the mine¬ ral fibers expelled from the mineral fiber generating means are pre- ferably further cooled by said air stream, by a separate cooling air stream optionally including steam or an alternative cooling medium or by spraying droplets of water onto said mineral fibers of said carrier air stream.

The step of cooling the mineral fibers is preferably carried out prior to the step of spraying the droplets and/or particles onto the mineral fibers of the carrier air stream in order to prevent that the mineral fibers exhibit an extremely high temperature as the droplets and/or particles are caused to impact the mineral fibers which might cause unintentional evaporation or solidification of the droplets and/or particles.

The cooling of the mineral fibers by means of the droplets of water may preferably be carried out in accordance with the basic teachings of the present invention as, in accordance with a first advantageous embodiment of the method according to the present invention, the droplets of water have diameters larger than a minimum diameter of a droplet of water showing substantially no tendency to impact the mineral fibers. Consequently, the cooling of the mineral fibers is generated by causing the droplets of water to impact the mineral fibers. In

accordance with the above advantageous embodiment of the method accord¬ ing to the present invention, the droplets of water preferably have diameters within the range 10 - 300 μm, preferably within the range 25 - 200 μm, further preferably within the range 50 - 150 μm. In accordance with an alternative advantageous embodiment of the method according to the present invention, the droplets of water have diameters smaller than a minimum diameter of a droplet of water showing substantially no tendency to impact the mineral fibers. In accordance with the above alternative advantageous embodiment of the method accord- ing to the present invention, the cooling of the mineral fibers is generated by preventing the droplets of water from impacting the mineral fibers and instead by carrying the droplets of water along with the carrier air stream for causing the carrier air stream to be cooled through a cooling water droplets mist. According to the above alternative advantageous embodiment of the method according to the present invention, the droplets of water preferably have diameters smaller than 250 μm, preferably smaller than 200 μm, further preferably smaller than 150 μm, such as having diameters within the range 10-250 μm, preferably within the range 20-150 μm, further preferably within the range 30-100 μm. Provided the droplets of water to be sprayed onto the fibers of the carrier air stream is produced by means of a centrifugal spinning wheel producing the mineral fibers, the droplets of water are preferably in accordance with teachings well known in the art per se, produced at the outer diametrical range of the spinning wheel in order to produce the cooling water droplets as close as possible to the origin of the mineral fibers and consequently cool the mineral fibers as quick¬ ly as possible after the generation of the mineral fibers by means of the spinning wheel. Thus, the cooling water droplets are preferably generated within the diametrical area 50-100% of the diameter of the spinning wheel, such as within the range 80-100% of the diameter of the spinning wheel .

The above objects, the above advantages and the above feature to¬ gether with numerous other objects, advantages, and features which will be evident from the below detailed description of preferred embodiments of the invention are, in accordance with a second aspect of the present invention, obtained by a a method of producing a mineral fiber web, com¬ prising the following steps: melting a mineral material and producing a stream of molten mineral

material, directing said stream of molten mineral material to a mineral fiber generating means so as to generate mineral fibers from said molten mine¬ ral material by solidifying said mineral material, expelling said solidified mineral material as mineral fibers from said mineral fiber generating means, directing a carrier air stream past said mineral fiber generating means for carrying said mineral fibers away from said mineral fiber ge¬ nerating means, generating and spraying droplets and/or particles of a heat-curable bonding agent or coupling agent onto said mineral fibers of said carrier air stream so as to cause said droplets and/or particles to impact said mineral fibers, said droplets and/or particles predominantly having diameters larger than a minimum diameter corresponding to a droplet and/or particle showing substantially no tendency to impact said mineral fibers of said carrier air stream, collecting said mineral fibers of said carrier air stream on a mi¬ neral fiber web collecting surface, thereby forming a non-woven mineral fiber web, and heating said non-woven mineral fiber web to an elevated temperature so as to cause the droplets and/or particles of said heat-curable bond¬ ing agent or coupling agent to cure for bonding said mineral fibers of said non-woven mineral fiber web to one another, thereby forming said mineral fiber web. The above objects, the above advantages and the above feature to¬ gether with numerous other objects, advantages, and features which will be evident from the below detailed description of preferred embodiments of the invention are, in accordance with a third aspect of the present invention, obtained by a plant for producing a non-woven mineral fiber web, comprising: melting means for melting a molten mineral material and for pro¬ ducing a stream of molten mineral material, mineral fiber generating means, means for directing said stream of molten mineral material to said mineral fiber generating means so as to generate mineral fibers from said molten mineral material by solidifying said mineral material and expelling said solidified mineral material as mineral fibers from said mineral fiber generating means,

means for generating and directing a carrier air stream of a speci¬ fic direction and a specific air velocity past said mineral fiber gene¬ rating means for carrying said mineral fibers away from said mineral fi¬ ber generating means, means for generating and spraying droplets and/or particles of a heat-curable bonding agent or coupling agent onto said mineral fibers of said carrier air stream so as to cause said droplets to impact said mineral fibers and adhere thereto, said droplets being generated pre¬ dominantly having diameters larger than a minimum diameter corresponding to a droplet showing substantially no tendency to impact said mineral fibers of said carrier air stream, and means for collecting said mineral fibers carried by said air stream, thereby forming said non-woven mineral fiber web.

The above objects, the above advantages and the above feature to- gether with numerous other objects, advantages, and features which will be evident from the below detailed description of preferred embodiments of the invention are, in accordance with a fourth aspect of the present invention, obtained by a plant for producing a mineral fiber web, com¬ prising: melting means for melting a molten mineral material and for pro¬ ducing a stream of molten mineral material, mineral fiber generating means, means for directing said stream of molten mineral material to said mineral fiber generating means so as to generate mineral fibers from said molten mineral material by solidifying said mineral material and expelling said solidified mineral material as mineral fibers from said mineral fiber generating means, means for generating and directing a carrier air stream of a speci¬ fic direction and a specific air velocity past said mineral fiber gene- rating means for carrying said mineral fibers away from said mineral fiber generating means, means for generating and spraying droplets and/or particles of a heat-curable bonding agent or coupling agent onto said mineral fibers of said carrier air stream so as to cause said droplets to impact said mineral fibers and adhere thereto, said droplets being generated pre¬ dominantly having diameters larger than a minimum diameter corresponding to a droplet showing substantially no tendency to impact said mineral fibers of said carrier air stream,

means for collecting said mineral fibers carried by said air stream for forming said non-woven mineral fiber web, and heat-curing means for curing said droplets and/or particles of said heat-curable bonding agent or coupling agent so as to cause said droplets and/or particles to cure for bonding said mineral fibers of said non-woven mineral fiber web to one another, thereby forming said mineral fiber web.

The above objects, the above advantages and the above feature to¬ gether with numerous other objects, advantages, and features which will be evident from the below detailed description of preferred embodiments of the invention are in accordance with a fifth aspect of the present invention obtained by a mineral fiber product containing mineral fibers, said mineral fibers being bonded together in an integral structure sole¬ ly through a bonding agent or curing agent initially present in uncured, non-woven mineral fiber webs from which said product is produced as droplets having a diameter within the range 10-300 μm, preferably within the range 25-200 μm, further preferably within the range 50-150 μm.

The mineral fiber product according to the present invention ex¬ hibit properties as expressed in terms of e.g. mechanical performance or mechanical integrity, such as elasticity and strength which characteris¬ tics constitute a substantial improvement of the mineral fiber product as compared to similar, conventional mineral fiber products or alternatively provided the characteristics of the mineral fiber product according to the present invention is identical to the characteristics expressed e.g. in accordance with the above terms identical to the characteristics of a similar conventional mineral fiber product still including a radically reduced content of cured bonding agent or coupling agent consequently improving the price of the product as compared to the conventional product and also improves the fire resistance characteristics of the product as compared to the conventional product. The present invention will now be further described with reference to the drawings, in which

Fig. 1 is a schematic view illustrating a plant according to the present invention of producing a non-woven mineral fiber-insulating web, Fig. 2 is a schematic view illustrating a part of the plant also shown in Fig. 1 and representing specific production parameters,

Fig. 3 is a schematic and partly cut away view of a spinning wheel also shown in Figs. 1 and 2,

Fig. 4 is a schematic and sectional view of a rim segment of the spinning wheel shown in Fig. 3,

Figs. 5-7 are reproductions or photographs illustrating the genera¬ tion of droplets of a bonding agent or a coupling agent by means of the spinning wheel shown in Fig. 3,

Figs. 8 and 9 are perspective views- illustrating alternative em¬ bodiments of the plant according to the present invention of producing a non-woven mineral fiber web, and

Fig. 10 is a diagrammatic view illustrating the tendency of a drop- let of a specific diameter as to impact an object when exposed to a spe¬ cific carrier air stream.

In Fig. 1, a first embodiment of a plant for carrying out a method according to the present invention of producing a non-woven mineral fiber web is shown. The plant centrally comprises a rotating spinning wheel designated the reference numeral 10 in its entirety which is caused to rotate at a high rotational speed such as the speed of 5- 15,000 rpm round a substantially horizontal output shaft 12 of a rota¬ tion generating motor 14. The spinning wheel 10 defines an outer cylindrical surface 16 which is used for producing mineral fibers from a stream of molten mineral material which is expelled from a spout 18 as a stream of molten mineral material 20. The spinning wheel 10 is rotated in a direction indicated by an arrow 15. The spinning wheel 10 is as will be described in greater details below cooled to a temperature below the melting point of the mineral material of the molten stream 20 and consequently causes the molten mineral material to solidify as the material is contacted with the outer cylindrical surface 16 of the spinning wheel 10.

As the mineral material of the stream 20 is solidified, mineral fibers are generated which mineral fibers are caused to travel from the spinning wheel 10 towards a mineral fiber collector 22 constituted by a perforated conveyor belt 24 which is caused to move round two rollers 26 or 28 in a direction indicated by an arrow 25. Mineral fibers generated by means of the spinning wheel 10 are collected in a mineral fiber stream which is designated the reference numeral 30 in its entirety as the mineral fibers are carried along with a carrier air stream produced by means of air outlets 32 and 34 generating an air stream represented by arrows 35. The carrier air stream outlets 32 and 34 are preferably positioned circumferentially encircling the spinning wheel 10 as more

than two carrier air stream outlets are preferably provided such as 4-6 or even more carrier air stream outlets. The spinning wheel 10 serves two additional purposes apart from the purpose of solidifying the mineral material of the molten mineral material stream 20 for the generation of the mineral fibers of the mineral fiber stream 30, viz. the purpose of generating and spraying droplets of a bonding agent or coupling agent onto the mineral fibers of the mineral fiber stream and the purpose of spraying droplets of water onto the mineral fiber stream for causing a cooling of the mineral fibers. The droplets of the bonding agent or coupling agent are produced by means of a toothed front cup of the spinning wheel 10, which cup is designated the reference numeral 40, and comprises a toothed inner rim part 42 which constitutes an essential element of the generation of the droplets of the bonding agent or coupling agent. The droplets of the bonding agent or coupling agent are formed into a spray of droplets designated the reference numeral 44.

The cooling of the mineral fibers of the mineral fiber stream 30 is accomplished by means of droplets of water constituting a spray of water droplets 46. The spray of water droplets 46 is generated by means of water which is pumped into the interior of the rotating spinning wheel 10 for causing a cooling of the outer cylindrical surface 16 of the spinning wheel 10 which cooling water is expelled from a plurality of water droplets generating apertures 48 provided at a surface part of the cylindrical surface 16 of the spinning wheel 10, which surface part is positioned adjacent to the inner toothed rim part 42 of the bonding agent or coupling agent droplet generating cup 40.

The spray 46 basically serves the purpose of cooling the mineral fibers to a temperature below the curing temperature of the bonding agent or coupling agent of the spray 44 for preventing that the droplets of bonding agent or coupling agent of the spray 44 are cured as the droplets are contacted with the mineral fibers of the mineral fiber stream 30 without establishing linkage to any adjacent mineral fibers after the mineral fibers are collected on the conveyor 22 as a non-woven mineral fiber web which is designated the reference numeral 50.

Apart from the droplets of the bonding agent or coupling agent ge- nerated by means of the cup 40 of the spinning wheel 10, two or more directional adjustable nozzles 52 are provided for generating droplets of the bonding agent or coupling agent which droplets constitute a spray 54 of droplets of the bonding agent or coupling agent. The droplets of

the sprays 44 and 54 and preferably also the cooling water droplets of the spray 46 exhibit specific characteristics as to their minimum and maximum diameters in accordance with the teachings of the present inven¬ tion. Alternatively, the cooling water droplets of the spray 46 may ex- hibit characteristics as to a maximum droplet diameter causing a cooling effect as the droplets constitute a mist of droplets.

In Fig. 2, a larger scale segment of the plant of Fig. 1 is shown. In Fig. 2, the spray 44 is shown in greater details along with two dotted line boundary curves 60 and 62, the importance of which will be described below. In Fig. 2, three dot-and-dash lines 64, 66 and 68 are further shown which lines divide the mineral fiber stream 30 into two parts, A and B.

The dotted line curve 60 represents a curve along which a droplet of the bonding agent or coupling agent travels provided the droplet has a diameter smaller than a minimum diameter of a droplet of the bonding agent or coupling agent showing substantially no tendency to impact the mineral fibers at the air velocity of the carrier air stream generated from the carrier air stream outlet 32 and represented by the arrow 35. Provided the droplet has a diameter smaller than the above-mentioned minimum diameter, the droplet shows substantially no tendency to impact the mineral fibers of the mineral fiber stream 30 as the droplet is simply carried along with the carrier air stream. The dotted line curve 62 represents the curve along which a droplet of the bonding agent or curing agent travels provided the droplet has an extremely large dia- meter resulting in that the droplet due to its high diameter and further its high mass and inerthia may travel through the mineral fiber stream 30 without impacting any mineral fibers.

The curves 60 and 62, consequently, represent boundary lines corresponding to a specific range of droplet diameters within which range the droplets of the bonding agent or coupling agent generated by means of the spinning wheel 10 are to be represented. Droplets of the bonding agent or coupling agent having diameters smaller than the droplet corresponding to the curve 60 and having diameters larger than the droplet corresponding to the curve 62 should preferably not be generated as the droplet is most likely wasted as the droplet is simply carried along with the carrier air stream and as the droplet most likely travels through the mineral fiber stream 30 without impacting any mineral fibers due to the high inerthia of the droplet, respectively.

Similar to the bonding agent or coupling agent droplets, the cooling water droplets of the spray 46 preferably have diameters larger than a minimum diameter of a droplet of water showing substantially no tendency to impact the mineral fibers at the air velocity of the carrier air stream in order to provide a maximum cooling efficiency of the water cooling droplets. Alternatively, the cooling water droplets may con¬ stitute a water droplets mist which cools the carrier air stream and surrounds the mineral fibers of the mineral fiber stream 30, provided the cooling water droplets have diameters smaller than the above minimum diameter.

The sections A and B defined by the dot-and-dash lines 64, 66, and 68 preferably constitute separate areas of the mineral fiber stream 30 in which cooling of the mineral fibers is accomplished and in which the bonding agent or coupling agent droplets are caused to impact the mine- ral fibers of the mineral fiber stream 30, respectively.

In Fig. 3, the spinning wheel 10 is shown in greater details dis¬ closing certain parts of the spinning wheel. As is evident from Fig. 3, the output shaft 12 is a hollow shaft through which two tubes 70 and 72 extend, which tubes serve the purpose of supplying the cooling water and the bonding agent or coupling agent, respectively. The cooling water supplied through the tube 70 is expelled within the interior of a cylin¬ drical drum 74 defining the outer cylindrical surface 16 of the spinning wheel 10. The cylindrical drum 74 includes internal guiding vanes, not shown in Fig. 3, for guiding the cooling water supplied through the tube 70 to an inner cylindrical surface of the cylindrical drum opposite to the outer cylindrical surface 16 and for discharging the cooling water as cooling water droplets from the apertures 48. Through the tube 72, the bonding agent or coupling agent is supplied to the interior of the cup 40 as the bonding agent or coupling agent is guided through centrifugal force impact to the outer toothed rim of the rim part 42 and expelled as bonding agent or coupling agent droplets of a specific diameter range.

In Fig. 4, a segment of the inner surface of the toothed rim part 42 of the cup 40 of the spinning wheel 10 is shown comprising radially sloping toothed surfaces 76 which on the one side communicate with a radially outwardly sloping surface 78 along which the bonding agent or coupling agent is supplied as a bonding agent or coupling agent liquid film from a bonding agent or coupling agent supply aperture 80 and on

the other side communicate with toothed edges 82 which cause a separa¬ tion of the bonding agent or coupling agent film into droplets of a spe¬ cific diameter range.

Figs. 5, 6 and 7 are reproductions of photographs of a spinning wheel similar to the spinning wheel 10 described above with reference to Figs. 1-4, rotating at a high rotational speed of the order of 8-15,000 rpm and having a toothed droplets generating rim part similar to the rim part 42 shown in Figs. 1-4 for the formation of droplets of the bonding agent or coupling agent which droplets are initially generated as a li- quid line which thereupon breakes up into individual liquid droplets. It has surprisingly been realised that the toothed rim part 42 of the spin¬ ning wheel 10 described above renders it possible to extremely accurate¬ ly determine the diameter of the droplets of the bonding agent or coupl¬ ing agent generated by means of the toothed rim part of the spinning wheel. The basic technique of generating droplets of a specific diameter by means of a rotating toothed rim part is described in the above patent references to which reference is made and the US counterparts of which are hereby incorporated in the present specification by reference.

In Figs. 8 and 9, two alternative plants for producing a non-woven mineral fiber web in accordance with the teachings of the present inven¬ tion are shown. In Fig. 8, the plant which is basically of a structure similar to the structure of the plant described in US patent No. 5,123,949, to which reference is made, and which is hereby incorporated in the present specification by reference, include a spinning wheel 110 which is journalled on a vertical shaft 112. From a disc-shaped dis¬ penser 113 a stream 130 of mineral fibers is expelled. The mineral fiber stream 130 may be propelled by means of a carrier air stream as the mineral fiber stream 130 is travelling towards a collector surface 122. The spinning wheel 110 includes two additional sections 116 and 140 serving the purpose of generating a spray 146 of cooling water droplets and a spray 144 of bonding agent or coupling agent droplets, respective¬ ly. The section 140 includes a toothed rim part 142 similar to the toothed inner rim part 42 described above with reference to Figs. 1-4. The droplets of the bonding agent or coupling agent droplets spray 144 and the cooling water droplets of the cooling water droplets spray 146 have diameters within the relevant diameter ranges determined in ac¬ cordance with the teachings of the present invention for causing the bonding agent or coupling agent droplets to impact the mineral fibers of

the mineral fiber stream 130 and for causing the cooling water droplets to impact the mineral fibers of the mineral fiber stream 130 or alternatively for preventing the cooling water droplets from impacting the mineral fibers of the mineral fiber stream 130 and instead generat- ing a cooling water mist enclosing the mineral fibers of the mineral fiber stream. Apart from the bonding agent or coupling agent droplets spray 144, a bonding agent or coupling agent dispenser or directional adjustable nozzle 152 similar to the nozzle 52 described above with re¬ ference to Figs. 1 and 2 is shown for generating a bonding agent or coupling agent droplets spray 154 in accordance with the teachnings of the present invention as described above with reference to Fig. 1.

In Fig. 9, a further plant for producing a non-woven mineral fiber web in accordance with the teachings of the present invention is shown. The plant comprises a molten mineral material reservoir 160 in which molten mineral material 162 is enclosed. From a plurality of molten mi¬ neral material dispensing nozzles 164, a stream 166 of mineral fibers is expelled. The mineral fiber stream 166 is caused to travel towards a collector conveyor 172 similar to the collector surface 122 described above with reference to Fig. 8 and propelled by means of a carrier air stream causing the mineral fibers to be carried towards the collector conveyor 162. The mineral fiber stream 166 is cooled by means of cooling water spray or mist generated by means of nozzles 168. The spray or mist includes cooling water droplets preferably having diameters larger than the above described diameter of a water droplet being airborne at the specific air velocity of the carrier air stream. By means of the bonding agent or coupling agent dispensing nozzles 152, the bonding agent or coupling agent droplets spray 154 is sprayed onto the mineral fibers of the mineral fiber stream 166 for causing the bonding agent or coupling agent droplets to impact the mineral fibers of the mineral fiber stream 166 carried along by the carrier air stream. By means of the collector conveyor 172, a non-woven mineral fiber web 174 is collected and trans¬ ferred from the plant in a direction indicated by an arrow 175 to further processing, such as folding, compressing, compacting, separat¬ ing, curing etc. like the mineral fiber web 50 produced in Fig. 1. The carrier air stream is forced to travel through the collector conveyor 172 as indicated by arrows 177.

In Fig. 10, a diagramme is shown illustrating a characteristic pro¬ perty of droplets of a specific material such as a droplet of water or a

droplet of a bonding agent or a coupling agent sedimenting vertically in a gravitational field in an atmosphere moving horizontally at a specific speed. Along the abscissa axis, the distance determined in any arbitrary measures such as cm or m, indicated by the letter L is represented. Along the ordinate axis, a vertical height is represented. A total of six curves are shown representing a curve of travel of a droplet having a diameter represented by a circular signature of the respective curve. Thus, the curve C represents a very small droplet, e.g. a small bonding agent or coupling agent droplet, which is expelled from a bonding agent or coupling agent dispenser. This droplet like the other droplets re¬ presented by the curves D-H is exposed to a carrier air stream and is solely caused to travel a fairly short distance until the droplet evaporates or solidifies due to exposure to heat from adjacent mineral fibers. The curve D represents a somewhat larger droplet which travels a somewhat longer distance before the droplet evaporates or solidifies. The curves E and F represents droplets which are able to travel along with the carrier air stream beyond the distance at which the droplet of the curve C evaporates or solidifies without evaporating or solidifying. The droplets of the curves F, G and H have sufficient inerthia to reach ground contact whereas the droplet represented by the curve E fails to reach ground contact within the distance represented along the abscissa axis.

The curves C-H shown in Fig. 10 so to speak represent the probabi¬ lity of a droplet and/or particle of any specific diameter to travel a specific distance within a carrier air stream before evaporating or solidifying and before reaching ground contact. On the basis of similar sets of curves representing droplets of specific diameters exposed to a specific carrier air stream velocity, the relevant range of diameters of droplets and/or particles may be calculated or determined, which particles, on the one hand, have sufficient mass and inerthia to prevent that the droplet and/or particle in question evaporates or solidifies or is simply carried along as an airborne droplet or particle by the carrier air stream, and which particles, on the other hand, have a mass smaller than the mass of a particle which simply travels on its own with a reduced probability of impacting a mineral fiber carried along by the carrier air stream.

Exa ple

A spinning wheel of the configuration shown in fig. 3 and having an outer diameter of 332 mm was used in a production plant for the pro¬ duction of a non-woven mineral fiber web which was eventually used for the production of heat insulating mineral fiber plates. The spinning wheel 10 was used as a substitute for a conventional spinning wheel used by the applicant and the amount of bonding agent or curing agent used for the production of the non-woven mineral fiber web was adjusted for reducing the amount of bonding agent or curing agent used still provid¬ ing mineral fiber plates which were of a type which did not exhibit inferior mechanical properties as compared to the conventional mineral fiber plates produced by means of the conventional spinning wheel.

Table 1

GLT Dens. SLR σ σNorm

% kg/m ³ kg/m ³ kN/m ² kN/m ²

Conventional heat insulating plate 2.57 34.1 31.1 12.1 9.1

Heat insulating plate according to the invention

Experiment 1 2.36 32.2 33.3 12.3 10.9 (-8%) (-6%) (+2%) (+20%)

Experiment 2 2.00 33.5 31.6 12.5 10.0 (-22%) (-2%) (+3%) (+10%)

Comments:

GLT represents the content of solidified bonding agent expressed in percentage by weight of the overall mineral fiber product.

Dens, expresses the density of the mineral fiber plate,

SLR is an abbreviation of "Standard Luftmodstands Rumvaegt" (in English language: Standard Air Resistence Density"), an industrial standard measure representing the air permeability coefficient of the heat in¬ sulating product. The SLR measure should preferably be identical to or even larger than the density of the actual product or plate.

σ is the tensile strength of the product or plate.

^σ Norm ^{is the normalized} tensile strength as the tensile strength is converted into a measure representing the tensile strength of comparable products as the tensile strength of the actual product or plate is converted into a normalized measure representing the tensile strength of the product including 2.4% GLT.

The overall result of the two experiments were most promising as accord¬ ing to Experiment 1 a reduction of the content of bonding agent of 8% resulted in an improved insulating product (increased SLR as compared to the conventional plate) and a radically improved tensile strength (+20% as compared to the conventional product). According to Experiment 2, a radical reduction of the bonding agent content (reduced by 22% as com¬ pared to the conventional product), resulted in a product exhibiting SLR basically identical to the SLR of the conventional product (31.6 of the plate produced in accordance with Experiment 2 as compared to 31.1 of the conventional product) and an increased tensile strength as compared to the conventional product (the tensile strength being increased by 10% as compared to the conventional product).

Although the present invention has been described above with refe¬ rence to specific and presently preferred embodiments of the method and the plant of producing a non-woven mineral fiber web in accordance with the teachings of the present invention, numerous modifications and

amendments are obvious to a person having ordinary skill in the art and having perceived the spirit of the present invention. Such modifications and amendments are to be construed part of the present invention as de¬ fined in the appending Patent Claims. It is further contemplated that the more accurate and exact dosage of bonding agent or coupling agent droplets and/or particles of a specific pre-selected diameter range may improve the characteristics of the products produced from a non-woven mineral fiber web produced in accordance with the teachings of the present invention as the content of bonding agent or curing agent of the final product may be reduced still providing a product of adequate mechanical properties as compared to similar conventional products or alternatively may result in the production of products having improved mechanical properties compared to conventional similar products of identical bonding agent or coupling agent contact.