Patent Publication Number: US-4321760-A

Title: Nozzle structure for moistening or impregnating a web

Description:
This is a continuation, of application Ser. No. 912,614, filed June 5, 1978 now abandoned. 
    
    
     The present invention concerns a process for moistening, impregnating or refining a web of paper, carton, foil etc. and is more particularly concerned with an apparatus having an improved nozzle construction for carrying out this process. 
     Drying equipment for thin webs, using nozzles which keep the dry web in a suspended state is known, per se. In the USA and in Switzerland, such drying nozzles are commercially available under the name of &#34;Airfoil&#34;. These work according to Bernoulli&#39;s theorem of the wings of an aeroplane. It is known that the static pressure above such as Airfoil nozzle is lower than above the web, and the latter is thus kept motionless through the air flow. A stable state of equilibrium is achieved which guarantees a perfect contact-free web guidance even where varying widths are concerned. 
     The process of the present invention for the moistening, impregnating or refining of a web of paper, carton, foil etc. is characterised by the web being treated by steam through the condensation effect of liquid being supplied via nozzle bodies, and by a precipitate being produced. 
     The apparatus of the present invention for carrying out this process comprises nozzle bodies arranged in a casing and connected to a steam supply, each containing in front of the nozzle outlets a heater for overheating the liquid or the gas in a practically pressureless condition; and the apparatus also includes cooling elements for cooling the web being treated as said is led past the nozzle bodies whereby a condensation and thus a precipitate is produced on the surface of the web. dr 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawing represents an exemplified embodiment of the plant required for carrying out this process, of which 
     FIG. 1 represents a diagrammatic representation of a nozzle body constructed in accordance with the present invention, and shown in partial section; 
     FIG. 2 represents a vertical section of the nozzle body of FIG. 1 on a larger scale, and 
     FIG. 3 contains a schematic representation of an apparatus employing the improved nozzles of the present invention, which apparatus includes several nozzle bodies, with the web being fed through the apparatus past said nozzle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIGS. 1 and 2 of the drawing, a nozzle 1 is formed by an oblong housing 4 which is provided with a slot-like nozzle outlet 2 for the delivery of hot water vapor to a moving web 11 of paper or the like. The outlet 2 is formed by the upper edge 3 of the wall of the housing 4 and a pipe 5 arranged in the upper part, said pipe 5 extending in a direction parallel to and closely adjacent to one face of moving web 11 (see FIG. 2) and being used for the delivery of steam to the nozzle for the moistening or refining of web 11. The pipe 5 is fixed to the upper edge of the front wall 4&#39; of the housing 4 by a welded joint (FIG. 2), and is provided with discharge ports 6 on its bottom surface through which the steam in pipe 5 can escape downwards. The elements 7, 7&#39; constitutes an oblong heater developed as a radiator and arranged along the bottom of the pipe 5, over which the steam coming out of the discharge ports passes. A liquid or gaseous heating medium passes through the pipe 7 of the radiator. An electric heater may also be fitted in pipe 7. A separating wall fixed to pipe 5 and dividing the hollow space of the nozzle body into two longitudinal halves; this separating wall does not extend right down to the housing base but forms a gap 9 for the entry of the hot gasses into the circulation space 10. There, the hot gasses rise and escape through the nozzle outlet 2. 11 represents the web to be treated passing the nozzle body 1. 12 represents a drip edge for the condensate formed during the operation of the apparatus, this drip edge projecting downwards and being formed by an extension of the rear wall of the housing 4. 
     The heater 7, 7&#39; serves to overheat the liquid or the gas in front of the nozzle outlet 2. This effect is of large, even decisive significance for the process and the apparatus used for this purpose. E.g. if one operates with wet steam which has a relatively low heat content, and if this steam is overheated, the heat content only increases insignificantly. Consequently, the substratum being treated is not heated quickly. As experience has shown overheated steam with a small heat content also cannot give off much heat. 
     As shown in FIG. 3, the web 11 to be treated is passed within a casing 13 between the walls of the wide sides 13&#39; and 13&#34; respectively on one hand, and groups of nozzle bodies 1 each of which is constructed in the manner described above and each of which is arranged at a distance from these casing slides on the other hand. Guide and deflector rolls 14 are arranged above and below the casing 13, these rolls being at the same time developed as cooling rollers. With the exception of slots 15 for the passing through of the web, the casing 13 is sealed on all sides. A discharge pipe 16 with an associated suction element 17 emanates from the top of the casing 13. 
     As shown in FIG. 2, the slot-like nozzle outlet 2 developed between the edge 3 of the housing wall 4 of each nozzle body 1 and the associated pipe 5 is directed in a downwardly inclined manner adjacent the web moving downwards, subjecting the latter--as it is the case with the Airfoil nozzle--to a suspension effect. The steam flowing between the web 11 and the casing walls 13&#39; and 13&#34; respectively as well as between the groups of nozzle bodies, produces in the area of the nozzle outlet 2--similar to the Airfoil principle--a bigger static pressure than in the remaining area of the web. Since the static pressure is smaller next to the nozzle outlet 2 than it is on the side of the web which is turned away, the web is kept suspended by the air flow. This results in a stable state of equilibrium which safeguards a perfect and contact-free web guidance, even where varying widths are concerned. 
     The apparatus can be built both for one-sided as well as double-sided application onto the web 11. It also permits applications where the rear of the web must not be thermally loaded. 
     The moistening is also necessary if the web 11 e.g. was treated on one side and there are difficulties with the plane surface. Moistening should also take place if for technical reasons a hard-drying of the web becomes necessary and a normal degree of moisture has subsequently got to be reached again. Water in the wet to saturated steam is particularly suited for moistening purposes of the web. Of course, any other liquid convertible into a vapor may be used. The liquid could, furthermore, be a solution which refines or impregnates the web in order to make it e.g. water-tight, water-repellent, flame-resistant, moth-proof or rot-proof. It does not matter of what material the web to be treated does consist; paper, carton, foils etc. are particularly suited for treatment by the present invention.