METHOD AND APPARATUS FOR HEAT-TREATMENT OF A FIBER PRODUCT - NOZZLES ARE ELONGATED IN MACHINE DIRECTION

Abstract: A method and an apparatus for treating a fibre product containing a thermocuring binder wherein oppositely directed gas streams are introduced into the fibre product opposites sides thereof in at least one zone from and wherein the gas streams introduced into the fibre product leave the fibre product on the same side as and in zones which are adjacent to the zones into which the gas streams are introduced into the fibre product.

Description: Method an apparatus for heat-treatment of a fiber product - nozzles are elongated in machine direction The invention relates to a method of thermally treating a mineral fibre product using a gaseous medium, wherein oppositely directed gas streams are introduced into the fibre product from opposite sides thereof in at least one zone. DK patent application No. 2558/78 discloses a curing oven comprising means for passing a hot gas stream through a mineral fibre web arranged between two gas permeable conveyor belts in a direction perpendicular to the web plane. It is known that the amount of heat which is transmitted from the hot air to the thermocuring binder contained in the mineral fibre web is proportional to the pressure at which the hot air is intro¬ duced into the mineral fibre web. Therefore, attempts have been made to increase the curing capacity of curing ovens of the type mentioned above by increasing the air pressure on the inlet side of the web. In case of heat treatment of mineral fibre webs and in particular mineral fibre webs with a low density, an increase in the different¬ ial pressure may result in irregular compressions of the mineral fibre web which compressions are probably due to the fact that the mineral fibres are displaced relative to each other in areas where there is a comparatively low fibre density under the influence of the high differential pressure and that the curing of the binder is insufficient at this point. Such compressions may easily result in the formation of an uncon¬ trollable amount of cavities in the fibre web imparting thereto an unacceptable appearance and an uneven insulating capacity. DE patent publication No. A 22753 describes a method of the above- mentioned type. In this known method hot gas streams introduced from opposite sides of the mineral fibre web and through slot openings which extend perpendicularly to the direction of movement of the mineral fibre web are forced to move parallel to the web plane in the direction of movement of the mineral fibre web or opposite thereto before the gas is passed away from the fibre web through slot openings which extend perpendicularly to the direction of movement of the web. It is stated that the purpose of this forced movement of hot gas parallel with the web plane is to maintain the gas within the mineral fibre web for as long as possible thereby allowing it to release as much heat as possible. The invention is based on the discovery that, as a consequence of the exceptionally large surface area of the mineral fibres, typical¬ ly 500 m 2 /kg, an almost instantaneous change of the mineral fibre temperature occurs when the fibre web is exposed to the influence of hot or cold gas streams. Therefore, there is no need to force such gas streams to remain within the fibre web for a long period. Contrary to the teachings of DE publication No. A 22753 it has been shown that the gases may be allowed to escape immediately after their contact with the mineral fibres. This means that the travel- ling distance to be overcome by the gases in the mineral fibre web may be made short and that the gases may be introduced under a high pressure without ensuing compression of the fibres. Thus, the method according to the invention is characterized in that the gas streams introduced into the fibre product are released from the same side as they are introduced and in zones adjacent to the zones into which the gas streams are introduced into the fibre product. The terms "gas" and "gases" as used herein mean that they comprise any hot gaseous medium, including water vapour. The method according to the invention is particularly suitable for curing the binder of a mineral fibre product containing an uncured thermocuring binder and in the following it will be explained more in detail in connection with a curing process wherein hot gases are used to effect curing of a thermocuring binder. However, it should be understood that the method is also suitable for other thermal treatments, including cooling, of a mineral fibre product by introducing hot or cold gases into the mineral fibre product. The method according to the invention is particularly suitable for thermal treatment of fibre webs, and the gas flow pattern obtained by heat treating a fibre web according to a preferred embodiment of the method according to the invention is illustrated in the drawings wherein Fig. 1 is a sectional view of a fibre web 1 which is moved by two gas permeable conveyor belts 4 in a plane perpendicular to the paper plane. Through air inlet zones 2 which are elongated and extend in the direction of movement of the fibre web 1 hot gas streams which, following deflection so as to move parallel with the web plane, are once again deflected so as to move out of the fibre web 1 through the outlet zones 3 located adjacent to the air inlet ducts 2. The establishment a flow pattern such as the one shown in the drawing allows for an increase in the curing capacity of from 2 to 3 times compared to curing by means of hot gas streams which are passed transversally through the fibre web. As mentioned in connection with the description of the drawing, the gas inlet zones and the adjacent gas outlet zones may be elongated and extend in the direction of movement of the fibre web. The zones mentioned may, however, also extend transversally or diagonally to the direction of movement. It is preferred that the zone into which hot gas is introduced from the one side of the fibre web is located just opposite the zone into which gas is introduced from the opposite side, but the two zones may be positioned slightly displaced relative to each other. Furthermore the opposite zones should not necessarily be of the same size. Usually, however, at least 25% of the area of the smallest zone should be overlapped by the opposite zone. The pressure difference between the gas inlet zone and the adjacent gas outlet zone(s) may be provided in different manners. However, it is preferred to use a pressure which exceeds the atmospheric pres¬ sure in the gas inlet zone and atmospheric or subatmospheric pres¬ sure in the gas outlet zone(s). However, it may also be convenient to use a subatmospheric pressure in the gas outlet zone(s) and an atmospheric pressure in the gas inlet zone. It is essential that the differential pressures in the adjacent zones are maintained within suitable ranges. When elongated gas inlet zones extending in the direction of move¬ ment of the fibre web are used, the widths of said zones are prefer¬ ably larger than or equal to the widths of the adjacent gas outlet zones. Whatever elongated gas inlet zones used extend in the direction of movement of the fibre web, transversal or diagonal thereto, they are preferably divided in the longitudinal direction to form separate sections and different pressures may be maintained in adjacent sections. Thus, it is advantageous to maintain a lower pressure difference between the first section in a gas inlet zone and the corresponding gas outlet zone than between the subsequent sections and the cor¬ responding gas outlet zone(s). During the initial heat treatment the areas of the fibre web in which the fibre density is lowest are most exposed to fibre com¬ pression. It is therefore important that this initial heat treatment is carried out under a comparatively low differential pressure. As the gas flow is strongest in the said areas having low fibre density, curing and an ensuing fixture of the fibres is quickly effected in these areas. In this manner these areas obtain such high degree of resistance to fibre compression that increased differ¬ ential pressures may be applied in the subsequent sections without a risk of fibre compression. The increased curing capacity mentioned above is not conditioned by the entire curing operation being carried out as described above. Thus, it has been found that the increase in the curing capacity may be obtained by such modifications of portions of existing curing ovens, e.g. 20-90% and particularly preferred the first half there¬ of, that the curing therein is carried out by the method according to the invention. It has also been found that it may be advantageous to allow the first portion of the curing operation to be effected by heat con¬ duction, viz. by supplying heat to the gas permeable belts which are usually used to move mineral fibre webs through a curing oven, so as to form thin cured surface layers by contact of the belts with the fibre web surfaces. By initially carrying out the curing as de¬ scribed above, following formation of said thin set surface layers, higher differential pressures may be applied without the risk that recesses are formed in the fibre web surfaces. According to the invention the mineral fibre web is preferably maintained between two gas permeable belts, such as lamella belts, while it is treated with the gas streams supplied at the opposite sides. The term "mineral fibres" as used herein comprises inorganic fibres produced from minerals. Examples of such fibres are rock wool fibres, glass wool fibres and slag fibres. The method according to the invention is suitable for thermal treatment of fibre webs having densities which are comprised within wide ranges, but it is particularly suitable for the treatment of light products of e.g. mineral fibre webs having a density of down to 7 kg/m 3 , but preferably a density of 15-60 kg/m 3 . The fibre webs may be composed of one or more fibre layers. FI-B-80102 discloses a method for drying a fibre web wherein a fibre web arranged between two air tight heat conductive belts is heated by heat supply to the belts. GB patent No. 867530 discloses an apparatus for drying a textile fibre web wherein the fibre web is kept freely suspended in a drying zone wherein hot air is blown against the fibre web sides through slotted nozzles located on opposite sides of the fibre web. The invention further relates to an apparatus for carrying out the method described above. The apparatus comprises means for supporting a fibre product containing a thermocuring binder between two gas inlet openings for introducing heated gas streams into the same area of the fibre web from opposites sides thereof and it is character¬ ized in that proximall to each gas inlet opening and on the side where there is provided an outlet duct is provided for gas which leaves the fibre product. According to the invention each gas outlet duct is preferably connected to one or more gas inlet openings through a conduit wherein a gas pump and optionally heating means are provided. This embodiment permits the gas flowing out of the fibre product to be recycled optionally following renewed heating and to be reintro- duced into the fibre product, thereby minimising the heat loss. As indicated above, the method and the apparatus according to the invention is particularly suitable for use for curing a continuous binder-containing mineral fibre web, but it may also be used for curing a series of successively moved separate mineral fibre el¬ ements. They may also be used for the curing of binder-containing separate elements or stacks thereof. The invention will now be described more in detail with reference to the drawings, wherein Fig. 2 is a vertical sectional view of a preferred embodiment of the apparatus according to the invention, and Fig. 3 is a partial perspective view of the apparatus according to Fig. 2 wherein some parts are shown in a sectional view. The apparatus according to Figs. 2 and 3 comprises an upper endless gas permeable belt 10 and a lower endless gas permeable belt 12, which may serve to move a mineral fibre web 14 through a curing chamber 16. The apparatus further comprises an inlet duct 18 for the supply of hot gas. The duct 18 divides into an upper branch duct 20 and a lower branch duct 22. The upper branch duct 20 is connected to an upper gas inlet zone which is divided into sections 24 by longitud¬ inal gas outlet ducts 26 which are open at the ends. In a similar manner the lower branch duct 22 is connnected to a lower gas inlet zone which is divided into sections 28 by longitud¬ inal gas outlet ducts 30 which are open at the ends. At the ends the gas outlet ducts 24 and 30 are connected to gas collecting zones 32 and 34 which, through communication ducts 36 and 38, respectively, are in communication with an outlet duct 40. As will appear from Fig. 2 the outlet duct 40 is connected to a reheating apparatus 42 comprising a burner 43, which may be used for reheating the gas passed out of the curing chamber 16. The supply of gas to the apparatus 42 and the supply of hot gas to the inlet duct 18 is effected by means of a centrifugal blower 44. The apparatus disclosed operates as follows: Hot gas from the reheating apparatus 42 is blown through the duct 18 by means of the blower 44 and on through the branch ducts 20 and 22 to the sections 24 and 28, respectively. From here the hot gas passes through the belts 10 and 12 into the mineral fibre web 14 and from here into the adjacent gas outlet ducts 26 and 30 while forming a gas flow pattern corresponding to the one shown in Fig. 1. From the ducts 26 and 30 the gas passes to the gas collecting zones 32 and 34 and on through communication ducts 36 and 38, respectively, into the outlet duct 40 and back to the apparatus 42. As will appear from the above explanation, the hot gas leaves the mineral fibre web 14 immediately following its introduction. This means that the operation may be carried out using small pressure differences between the sections 24,28 and the gas outlet ducts 26 and 30, respectively. Thus, the apparatus permits efficient heat treatment of the mineral fibre web 14 without the ensuing risk of recess formation in the fibre web surfaces.

Claims: C 1 a i s 1. A method of thermally treating a mineral fibre product with a gaseous medium, wherein oppositely directed gas streams are intro- duced into the fibre product from opposite sides thereof in at least one zone, c h a r a c t e r i z e d in that the gas streams intro¬ duced into the fibre product are released from the same side as they are introduced and in zones adjacent to the zones into which the gas streams are introduced into the fibre product. 2. A method according to claim 1 wherein the fibre product is a fibre web, c h a r a c t e r i z e d in that the gas inlet zones and the adjacent gas outlet zones are elongated and extend in the direction of movement of the fibre web transversally or diagonally to the latter. 3. A method according to claims 1 or 2, c h a r a c t e r i z e d in that it is used for the treatment of a mineral fibre product containing a thermocuring binder with hot gas streams having a temperature above the curing temperature of the binder to cure the binder. 4. A method according to claim 3, c h a r a c t e r i z e d in that the area into which hot gas is supplied from the one side of the fibre product is located exactly opposite to the area into which gas is introduced at the opposite side. 5. A method according to claim 3, c h a r a c t e r i z e d in that the zone through which a hot gas stream is introduced into the fibre product from the one side thereof partially overlaps the zone into which a hot gas stream is introduced into the fibre product from its opposite side. 6. A method according to claim 5, c h a r a c t e r i z e d in that the area in which the two zones overlap each other constitutes at least 25% of the smallest of the two zones. 7. A method according to any one of claims 3 through 6, c h a r ¬ a c t e r i z e d in maintaining a pressure in the areas into which hot gas is introduced which exceeds the atmospheric pressure and in maintaining an atmospheric or subatmospheric pressure in the gas outlet zone(s). 8. A method according to claims 1, 2 or 3, c h a r a c t e r ¬ i z e d in that the gas inlet and gas outlet zones are elongated and extend in the direction of movement of the fibre web. 9. A method according to claim 8, c h a r a c t e r i z e d in that the widths of the gas inlet zones are larger than or equal to the widths of the adjacent gas outlet zones. 10. A method according to claim 2, c h a r a c t e r i z e d in that the elongated zones are divided longitudinally to form separate sections. 11. A method according to claim 10, c h a r a c t e r i z e d in that different pressure differences are maintained between a section in a gas inlet zone and the corresponding gas outlet zone and between the remaining section(s) and the corresponding gas outlet zone(s) in adjacent sections. 12. An apparatus for carrying out the method according to claim 1 comprising means (10,12) for supporting and moving a mineral fibre web (14) between two gas inlet openings (24,28) for introducing gas streams into the same area of the fibre product (14) and from opposite sides thereof, c h a r a c t e r i z e d in that proxim- ally to each gas inlet opening (24,28) and on the side there is provided an outlet duct (26,30) for gas which leaves the fibre product. 13. An apparatus according to claim 12, c h a r a c t e r i z e d in that each gas outlet duct (26,30) is connected to one or several gas inlet openings through a conduit (40,18) wherein a gas pump (44) and optionally heating or cooling means (42) are provided. 14. An apparatus according to claim 12 or 13, c h a r a c t e r ¬ i z e d in that the gas inlet openings (24,28) are elongated and extend in the direction of movement of the mineral fibre web (14).

Inventors: HOGENHAVEN ARON PER, HOEGENHAVEN, ARON, PER
Applicants: HOGENHAVEN ARON PER, ROCKWOOL INT, ROCKWOOL INTERNATIONAL A/S
Application year: 1993
Main classification: D06B5
IPC codes: D06B19, D06C7, F26B13