Non-woven article made of a heat-resisting material, method for manufacturing the article and apparatus for implementing the method

Abstract: An article manufactured from ceramic fibres, glass fi­ bres or mineral fibres or a mixture thereof includes randomply directed discontinuous fibres formed of such materials and brought together with a dry process by means of an air flow, and possibly includes also a binder for binding these fibres. In a method for manufacturing such an article, the dis­ continuous fibres, possibly intermingled with fibres serving as a binder, are couched into a mat in a manner that the discontinuous fibres are advanced into contact with an air flow which carries them to a level (36) so that the fibres become randomly directed and said fibre-­ carrying air flow is passed through said level (36). An apparatus for implementing the method comprises a web-forming unit (D) provided with a level (36) consist­ ing of an air-permeable wire or the like as well as feeder means (33) for advancing the fibres into a space (37) aligned with said level and connected with a flow duct (41) for passing the fibre-carrying air flow into said space.

Description: The present invention relates to a method for manufacturing a non-woven article wherein ceramic fibres, glass fibres or mineral fibres or a mixture thereof, possibly intermingled with fibres serving as a binder, are couched into a matlike structure, said method comprising relatively short fibres of predetermined length being advanced by means of an air flow which carries them to a first conveying level, said level being adapted to let said air flow pass therethrough. Such method is known from GB-A-2,125,450. Fire-resistant fibres like mineral, glass or ceramic fibres are presently used for manufacturing mineral felt in essentially two ways. According to a first method the fibres are, just after their manufacture sucked onto a suction wire to form a web. The article manufactured in this way, has a compact texture and a high weight per unit area. This method cannot be applied for manufacturing thinner web-like articles. Another drawback is the formation of granular and bead-like impurities in the articles. It is further not possible to admix bonding fibres in the article and final bonding of the article is effected by means of adhesives, which evaporate at low temperatures and, thus, make the use of such article difficult at high temperatures. According to another technique which is presently applied mineral, glass or ceramic fibres are used for manufacturing a web by means of water, in a way which is similar to manufacturing paper. Although, in this method, it is possible to include other fibres as well, long (over 50 mm) synthetic fibres as composite or bonding fibres cannot be employed. Another major drawback of this method is that, when emerging from a machine, the non-woven web is wet and especially thick qualities require high-powered drying, resulting in less economic production. Also in this method, the final bonding for providing a firm article can only be effected by using an organic binder with all the above-mentioned drawbacks. The weight per unit area or the density of articles produced by these methods is quite considerable, the strength product weight ratio being far from the optimum. When using such article as an insulating material, the density of that article is of importance. In the above-mentioned GB-A-2,125,450 a method of and an apparatus for the manufacturing a non-woven article is described, according to which mineral fibres are conducted beneath a binder adding station and then passed into a fiberizing device, comprising a mat forming zone or chamber. This chamber is delimited by two foraminous conveyors, which include a sharp angle and are brought together at a nip opening, at which point a mat-like or felted mixture is leaving the mat forming zone. The fibres entering said zone or chamber are entrained by an air flow towards and onto the two foraminous conveyors. The mat-like structure obtained by this rather simple method shows insufficiently randomly orientated fibres, which is a drawback especially when producing thin products. An object of the invention is to provide a method for manufacturing a non-woven article from mineral, glass or ceramic fibre in a manner that does not involve large amounts of water whereas the article produced shows excellent qualities and is adapted to be used as an insulating or building material in many applications that require fireproof fibre. Another object of the invention is to provide an apparatus for implementing the method for manufacturing the above-described article. In order to achieve the above objects, the method according to the invention is characterized in that the fibres are formed into a uniform mat on a first conveying level which advances the mat forward, whereafter the mat is picked up by means of a fibre carrying air flow which passes through said first conveying level and is directed to a second conveying level, which is placed opposite to said first conveying level and advances the fibres forward, the fibres being removed from said first conveying level and being randomly distributed and couched as a mat against said second conveying level, said fibre-carrying air flow passing through said second conveying level. According to this method the fibres of a finished article are randomly orientated giving the produced web a particular loft and elasticity. If the starting material comprises mineral fibres that are not pretreated and contain beads and possibly sand, this material can be pretreated for producing a highly clean web comprising only separate fibres of a predetermined length and possibly composite fibres. In the article manufactured in this way its essential texture is formed by separate fibres, said separate fibres being directed in the three-dimensional structure of said article in arbitrary directions relative to each other, without forming any distinguished areas, in which the fibres lie in a common plane, as e.g. in paper. A web-like article, produced in this way, contains a considerable number of fibres that are directed crosswise and angularly relative to the plane of said web. In this way pockets between the fibres are produced, which decrease the density of an article. Heat-resisting separate fibres are used exclusively, then the article can only be bonded by needle-punching. However, the article can also have a binder admixed therein which is included in the texture in the form of melting or softening fibres, the share of the separate fibres in the basic material being in this case at least 70% by weight. The method according to the invention can be implemented in an apparatus comprising means for couching fibres into a mat-like structure including a web-forming unit, comprising feeder means for the fibres, a conveying level after the feeder means for forming the mat. According to the invention said apparatus is characterized in that said web-forming unit includes a first foraminous conveying level serving as a fibre-carrying means, a second foraminous conveying level placed opposite to said first conveying level and adapted to carry the fibres forward, said conveying surfaces delimiting therebetween a vacant space, said web-forming unit further comprising a flow duct, located outside of said space and directed towards the foramina of said first conveying level for passing an air flow through said level into said space as well as a flow duct located on the opposite side of said space, said flow duct being open towards the conveying surface of said second conveying level for passing the air flow from said space through said second level. A web manufactured by the method according to the invention can be subjected to a known after-treatment. Thus, the fibres can be bonded by needlepunching only or, if bonding fibres are admixed, it is possible to use both needlepunching and thermal binding. The finished article can have the shape of a mineral wool type of fluffy or lofty insulating material. The web can however also be used for manufacturing boards, beams etc. used as building elements by compressing superimposed non-woven webs into a more compact texture during thermal binding. In the latter case, the density of such article will be lower than that of similar articles manufactured by traditional methods. The method and apparatus according to the invention will now be described in more detail with reference to the accompanying drawing, in which Fig. 1 shows diagrammatically an entire fibre production line for implementing the method according to the invention, and Figs. 2-5 show more detailed views of different sections of the production line shown in Fig. 1. Reference character A in Fig. 1 indicates a pretreatment unit, character B indicates a separating unit, character C indicates a supply unit and character D indicates a web-forming unit, with character E indicating per se known after-treatment equipment. Fig. 2 shows a pretreatment assembly A at the forward end of a production line in a perspective view and partially cut away. Bundles of fibres are forwarded onto a conveyor 1, automatically controlled by photocells. From conveyor 1 the fibres travels to a pinned elevator 2 whose pins or studs lift the fibres up along a fast-rotating smoothing roll 3. The smoothing roll 3 throws the unopened bundles of fibres back down until they are opened and the fibres are able to pass between smoothing roll and pinned elevator 2. Thereafter, the fibres hit a fast-rotating release roll 4 which flings the fibres down onto a conveyor belt 5. This is followed by a second set of the same operations, i.e. conveyor belt 5 is followed by a pinned elevator 6, a smoothing roll 7 and a release roll 8 for flinging the completely opened fibres down onto a conveyor belt 9. This conveyor carries the fibres between feeding rolls 10 for advancing the fibres towards the surface of a fast-rotating pinned roll 11. The pinned roll is formed by coating a roll with a strip on which a great number of pins or studs are placed at a very small pitch. The roll has a surface speed of circa 800-1100 m/min and a mechanical impact provided by the studs produces such an effect that impurities, such as beads, carried by the fibres, are removed from the rest of the fibre and, thus, a suitable fibre material can be separated from raw material. The raw material to be used comprises fire-resisting separate fibre, glass fibre, ceramic fibre or any mixture thereof, the average length of fibres being circa 4 mm but there may be included fibres having a length of up to 20 mm. In this context, the term "separate fibres" refers to precisely dimensioned fibres which are produced in precise dimensions during the actual fibre production (mineral fibres and ceramic fibres) or which are cut to a precise dimension from a filament (glass fibre). In order to produce a desired article, length of the fibres must be in any case less than 60 mm. As fibres are being fed in a pretreatment assembly, it is possible to admix therein at the same time some fibre, such as some synthetic fibre, which serves as a binder during a thermal bonding process effected later and whose length can be up to 120 mm, whereby said fibre can be any fibre, according to a particular application e.g. PET (polyester) or glass. The binder forming fibre must have a lower melting point than the fibre forming the actual product texture and glass fibre can used as a binder provided that the rest of the fibre comprises ceramic fibre or mineral fibre. The fibres, impurities removed therefrom and possibly other matter drifting along, are carried from pretreatment assembly A to a separation assembly B, shown in fig. 3 in a side view. In fig. 2 there is shown the end of an intake duct 12 which is in communication with the surface of pinned roll 11, the other end of said intake duct being in communication with separation assembly B. The separation assembly comprises a closed box 14 which receives the intake duct 12 coming from pinned roll 11 and from which issues an intake duct 13 connected with a source of suction, such as a conventional fan. By means of suction supplied through duct 13, the fibres are sucked through the box into duct 13 in such a manner that the fibres, being lighter in weight, rise up into said duct 13. For this purpose, the inlet of intake duct 12 is located lower than the outlet of intake duct 13 and, furthermore, between these ports is mounted a horizontal flow baffle 14' which blocks a linear flow in the box between said ports, creating a bend in the flow path and this enhances the separation of heavier matter from the fibres. The beads and other impurities, such as sand, removed from the fibre fall through the holes of a screen-like conveyor belt 15 fitted below said horizontal baffle 14 into a receptacle chute 15' from which they can be removed from time to time. The heavier matter, such as unopened bundles of fibre, remains however on top of conveyor belt 15 which carries it outside said box 12 for passing it to a fan 16 which blows it along a line 17 shown in fig. 1 back to pretreatment assembly A. Fig. 4 illustrates a supply or feeding assembly C located downstream of separation assembly B. Here, the other end of flow duct 13 coming from separation assembly B is passed through a cyclone 18 for separating the fibres from finer solid matter which is carried away through a vacuum pipe 19. The refined fibres fall into a box 20 below the cyclone. The box contains a horizontal conveyor belt 21 which receives the falling fibres and pushes them onto a pinned belt 22 which carries the fibres obliquely upwards and at the top section of this belt loop the fibres travel between smoothing roll 23 and belt 22. The smoothing roll 23 distributes the fibres uniformly in lateral direction, whereafter a release roll 24 drops the fibres vertically into a volume feeding chute 25 whose movable back wall 26 presses the fibre web or mat to uniform density. The chute 25 opens at its bottom above a conveyor belt 27 and the fibre mat travels upon conveyor 27 forward from below said chute 25 between a roll 28 shown by dash-and-dot lines and the conveyor, the former compressing the web uniformly onto conveyor 27 which carries it forward to the following unit. At this point, it is also possible to adjust a desired weight per unit area for the finished non-woven web by adjusting the speed of conveyor 27, the fibre volume in the feeding chute being constant. Fig. 5 is a side view of a web-forming unit D. The conveyor 27 carries the fibre from below a slow-rotating feeder roll 29 towards the surface of a fast-rotating pinned roll 30. The pinned roll is coated with a pinned or studded strip and the studs are positioned at a very small pitch and their length is circa 2 mm. The surface speed of said pinned roll is circa 2000-2500 m/min. To the surface of said pinned roll, at the point where the fibres come into contact with it, is blown a powerful air jet which is passed through an air duct 31 which is in communication with the space below pinned roll 30 towards the surface of a conveyor wire 32. The fibres are thus carried along with the air flow and remain on top of wire conveyor 32 while said air flow is sucked through the wire. Thus, the fibres build a relatively uniform mat or web on wire 32 which carries them forward onto a foraminous conveyor belt 33. At this point, the mat has some corrugation in it and still includes some areas wherein the fibres extend in parallel direction, which results from turbulence of the air flow. Conveyor belt 33 carries the fibre mat forward to a point 34, at which a powerful air flow is supplied below conveyor belt 33 by means of a fan 35 along a duct 41 opening below said belt 33, said air flow penetrating through belt 33 by virtue of its foramens and blowing the fibres at this point to an air-permeable wire conveyor 36 above. The top surface of conveyor belt 33 carrying the fibre mat in the beginning and the bottom surface of wire conveyor 36 intended for the final build-up of a fibre mat are at this point located opposite to beach other and delimit therebetween an open space 37 wherein the air flow passed through said conveyor belt 33 picks up the fibres from the top surface of belt 33 to the bottom surface of belt 36. Above said wire conveyor 36, in other words on the backside of a fibre mat in view of its build-up surface, there is a suction duct 38 into which the air flow is passed from space 37 through wire 36. All of the air flow blown through conveyor belt 33 is passed through wire 36 and, for this purpose, said space 37 is sealed as tightly as possible both at the side edges of conveyor belt 33 and those of wire conveyor 36 and also upstream of the point of blowing and downstream of the point of blowing by only leaving the gaps for allowing the fibre mat into space 37 above belt 33 and from space 37 to the bottom surface of wire 36. The conveyor belt 33 comprises a wire structure, e.g. a conventional nylon wire having foramina that are circular and relatively large in diameter, circa 1,5 mm in diameter. The upper section in a wire conveyor may consist of a normal wire but a particularly preferred and uniform setting of fibres is obtained by using a so-called honeycomb-type of wire. The air flow in space 37 has a speed of circa 10-30 m/s which is sufficient to provide a sufficient intermingling of the fibres and to blow them in random directions onto and against wire conveyor 36. Conveyor belt 33 and wire conveyor 36 travel in the same directions and a relatively even mat that lies first on lower conveyor belt 33 leads to the formation of a product having a uniform weight per unit area also on upper wire conveyor 36. Following said space 37, a fibre mat on wire conveyor 36 is advanced between said wire and a nip roll 39 onto a conveyor belt 40 for carrying the finished article forward. Following the above-described formation of a web, said fibre mat is advanced to after-treatment equipment, used for final bonding of the fibres and designated in fig. 1 with reference E. In case the fibre mat consists exclusively of mineral fibres or the like, it will only be bound by needlepunching in a conventional needlepunching machine in which the binding is effected mechanically by punching with needles. If the structure includes binder-forming bonding fibres as mentioned above, such as glass or polyester fibres, it is possible to employ also thermal bonding in addition to needlepunching. Thermal bonding can also be accompanied by other additional operations, such as compressing fibre mats into sheets, beams or similar rigid structures. The above-described method can be applied for manufacturing from mineral glass or ceramic fibres or their mixtures some mat-shaped or sheet-like articles, whose weight per unit area is within the range of 60-3000 g/m². The best way of comparing articles of the invention with traditional heat-resisting non-woven products is to compare their densities to each other. The density of both mat-like articles and those compressed into sheets and beams is circa 5 times less than that of the products manufactured from the same materials using known methods. However, the strength qualities are in the same order. By adjusting the process conditions (air flow rate, compression in after-treatment) this ratio can be increased up to 10-fold. When bonding fibre is used, its share of the product is always less than 30 %. It should be noted that glass can be used either as a structure-forming fibre, the binder comprising a synthetic fibre, such as PET, or glass can be included in the articles as a binder, the main structure consisting of mineral fibres and ceramic fibres which melt at higher temperatures than glass. The articles can be used in all fire-resisting materials, such as interior carpets underlying carpets and sound-proof surfaces in ship-building industry, roofing felt, PVC-coating bases as well as building boards. One important application of these articles includes high-temperature insulations, e.g. products for replacing health-hazardous asbestos. It is conceivable to employ fibre material pre-refined already at an earlier stage, whereby such material can be directly fed into feeder assembly C. In addition, a web-forming unit D of the invention may be of a different design for producing a force in the direction of the mat-forming level by means of air flow. In the web-forming unit D shown in the drawings, for example, the planes or levels need not be necessarily located as a first conveying plane below a second conveying plane but what is required is that the surfaces of these conveying planes be directed towards each other for providing therebetween a space, wherein the above-described air carrying feature of the fibres can be effected. However, in view of the most economic use of space and practical aspects, it is preferable that said planes be located above each other in vertical direction and preferably as described above, i.e. the first conveying plane below the second conveying plane.

Claims: A method for manufacturing a non-woven article, wherein ceramic fibres, glass fibres or mineral fibres or a mixture thereof, possibly intermingled with fibres serving as a binder, are couched into a matlike structure, said method comprising relatively short fibres of predetermined length being advanced by means of an air flow which carries them to a first conveying level (32,33), said level being adapted to let said air flow pass therethrough, characterized in that the fibres are formed into a uniform mat on a first conveying level (32,33) which advances the mat forward, whereafter the mat is picked up by means of a fibre carrying air flow which passes through said first conveying level and is directed to a second conveying level (36), which is placed opposite to said first conveying level (32,33) and advances the fibres forward, the fibres being removed from said first conveying level and being randomly distributed and couched as a mat against said second conveying level (36), said fibre-carrying air flow passing through said second conveying level. A method according to claim 1, characterized in that said first conveying level (32,33) is located below said second conveying level (36), the fibre conveying surface of said first level (33) facing upwards and the fibre conveying surface of said second conveying level (36) facing downwards said fibres being picked up from the top of said first conveying level (32,33) by means of an upwardly directed air flow to the bottom surface of said second conveying level (36). A method according to claim 1 or 2, characterized in that a uniform mat on the first conveying level (32,33) is provided by advancing a fibre mat by means of a feeder device (29) towards the surface of a rotating pinned roll (30), from which the fibres are advanced by means of an air flow to said first conveying level (32,33) said air flow being capable of passing through said first conveying level (32,33). A method according to claim 3, characterized in that the fibres are advanced by means of an air flow from a pinned roll (30) to an air-permeable wire conveyor forming the first section (32) of said first conveying level, from which the fibres are passed downstream of said first section (32) to a foraminous conveyor forming the second section (33) of said first conveying level, through which section an air flow is blown for carrying the fibres to the second conveyor level (36). A method according to any one of the claims 1-4, wherein the starting material comprises non-pretreated mineral fibres containing beads and possibly sand, characterized in that prior to forming a mat on said first conveying level (32,33), the beads contained in the fibres are removed by means of mechanical impact, caused by the studs of a rotating pinned roll (11), bundles of fibres being advanced towards the surface of said roll (11). A method according to claim 5, characterized in that after the first removal of beads, the fibres are separated from remaining beads and other possible impurities by entrapping the fibres in an air flow. An apparatus for implementing the method as set forth in claim 1, said apparatus comprising means for couching fibres into a mat-like structure including a web-forming unit (D), comprising feeder means (30) for the fibres, a conveying level (32,33) after the feeder means (30) for forming the mat, characterized in that said web-forming unit (D) includes a first foraminous conveying level (32,33) serving as a fibre-carrying means, a second foraminous conveying level (36) placed opposite to said first conveying level and adapted to carry the fibres forward, said conveying surfaces delimiting therebetween a vacant space (37), said web-forming unit (D) further comprising a flow duct (41), located outside of said space (37) and directed towards the foramina of said first conveying level (32,33) for passing an air flow through said level into said space (37) as well as a flow duct (38) located on the opposite side of said space (37), said flow duct (38) being open towards the conveying surface of said second conveying level (36) for passing the air flow from said space (37) through said second level (36). An apparatus according to claim 7, characterized in that the conveying surface of said first conveying level (32,33) faces upwards at the location of the fibre-carrying air flow (41,38) and the conveying surface of said second conveying level (36) faces downwards at that same location, said first conveying level (32,33) being positioned below said second conveying level (36). An apparatus according to claim 7 or 8, characterized in that said web-forming unit (D) further comprises a pinned roll (30) located upstream of said conveying levels (32,33; 36) a feeder means (29) for advancing the fibres towards the surface of said pinned roll (30) as well as a flow duct (31) located between the surface of the pinned roll and the first conveying level (32,33), air-flow producing means being connected to said duct (31). An apparatus according to claim 9, characterized in that said first conveying level (32,33) includes a first section (32) comprising an air-permeable wire conveyor located at the end of said flow duct (31) in the direction of travel of the fibres, as well as a second section (33) located downstream of said first section (32) and comprising a foraminous conveyor. An apparatus according to any one of the claims 7-10, characterized in that upstream of said web-forming unit (D) in the direction of travel of the fibres a pretreatment assembly (A,B,C) is present for removing impurities from the fibres, said assembly comprising a rotatable pinned roll (11) and feeder means (10), for advancing the fibres towards the surface of said pinned roll (11). An apparatus according to claim 11, characterized in that said pretreatment assembly includes a flow duct (12) located downstream of said pinned roll (11) and open towards the surface thereof, an airflow producing means being connected to said flow duct (12) which comprises also means (14,14') for separating the fibres from impurities.

Inventors: NIEMINEN JORMA, NIEMINEN, JORMA
Applicants: ROCTEX OY AB
Application year: 1989
Main classification: D04H1
IPC codes: D04H1