PRESSING ARRANGEMENT FOR A MOVING WEB

Abstract: The invention concerns a pressing arrangement for a moving web (6), comprising a press roll (1) which forms a press zone (7) with a moving elastic belt (5) which is endless and supported by a counter body (2, 9). The outside of the belt is surface finished to a roughness which is more uniform than the side of the web contacting it. The press roll is heated to a temperature of at least 100 DEG C. The arrangement is principally intended for surface finishing of fiber mats such as paper or board. A method is indicated whereby preheating of the web prior to the press zone is achieved.

Description: Pressing arrangement for & moving web Technical field The present invention concerns a pressing arrangement for a moving web in accordance with the preamble of claim 1. The unit is principally < intended for surface finishing of fiber mats such as paper or board which under pressure pass between the press roll and the moving belt. The press roll is heated to a temperature of at least 100° Celcius. Technical stand A press arrangement for a moving web is known thru International Application PCT/SE92/00041 wherein a shoe is under applied pressure via a glide belt between a press roll and a counter roll, the shoe having a concave form following the contour of the press roll on the press roll side and a nonconcave contour on the supporting counter roll side. Further in prior art, a press arrangement is known thru U.S.Patent 4,287,021 wherein a concave shoe is under pressure via a carrying belt guided over a plurality of guide rolls and an endless guide belt guided over an annular shell supported by a beam structure or over guide rolls. The carrying belt receives water from the web in the press zone. In both of these references the press arrangement is piincipally intended for removing water from a moving web on a carrying belt and thus the moving belt will not come into contact with the web. As a consequece, surface uniformity and elasticity of the belt are unimportant and not called for properties. Additionally in prior art, a calendering arrangement is known thru Offenlegungsschrift DE 3632692 Al wherein a web is transported thru a calender nip formed between two rolls where both rolls are controllably driven and a soft belt encloses one of the rolls. An "ironing" action is achieved on the web by pressing the rolls very lightly against eachother and driving them at different speeds so as to produce a satinating effect \ thru friction. With this arrangement the surface improvement of the web * is obtained" solely thru a speed difference and frictional polishing action between the web and the roll facing the web. SUBSTITUTE SHEET Description of JJIS invention One main purpose wih the present invention is to achieve a pressing arrangement of the general type indicated in the introduction wherein the moving web is pressed against the press roll with a uniform pressure independent of variations in the thickness of the moving web. Another purpose is to achieve effective cooling of the belt. A further purpose is to provide the possibility of preheating the web in a controlled manner prior to the press zone. To achieve the main purpose, the invented pressing arrangement has the characterizing features set fort in the main claim. In this manner one obtains a smooth and uniform web surface on the side facing the press roll, irrespective of variations in the thickness of the web. The moving web is subjected to pressure in the press zone formed between a press roll and an elastic belt which is supported by a roll of suitable diameter or a stationary glide body or shoe. To obtain desired effects average unit pressures in the press zone have to be relatively high, i.e. a minimum of approximately? MPa and the surface temperature of the press roll at least 100° Celsius, preferably between 150 and 250°C. The web facing side of the belt would be surface finished to a roughness of typically 2 microns but importantly to a finish which yields • a; more uniform surface structure than that of the side of the web in contact with it in the press zone, e.g. at least the same, suitably 50%, preferably 25%, and especially 10% of the average pore size of the web. The high unit pressures in the press zone cause the smooth elastic belt to follow the contour of the less uniform side of the web facing it, thus resulting in a very even pressure on the web. As a cosequence this will enhance the uniformity ,>and -■- evenness of the pressing action on the side of the web facing the press roll. The pressing action would typically cause a minimum thickness reduction in the belt equal to about 3% in the middle of the press zone. This would normally represent an indentation which is considerably more than the deepest nonuniformity in typical paper or board. The cooling action on the backside of the moving belt by means of coolant in the supporting counter body protects the belt from overheating in the middle where where the reinforcing structure normally is located. SUBSTITUTE SHEET To achieve the additional advantage of preheating the moving web prior to the press zone the moving web is pressed against the heated press roll by the moving belt following said roll ahead of the press zone. This pressure is a function of the tension in the belt and can thus be considerable depending on the physical properties of the belt and certainly much higher than if the moving web alone (without the belt) would be contacting the press roll. It is also desirable to control the time of contact (preheating) prior to the press zone which can be done by adjusting the guide roll guiding the belt ahead of the press zone. In a preferred embodiment of the present invention the supporting counter body constitutes a cylindrical roll and thus the inside of the belt, facing this roll, could have a relatively nonuniform surface as said surfacecontacts a moving surface (roll) instead of sliding over stationary parts in the press zone. With the counter body constituting a roll, a desired length of the press zone can further be achieved by selecting a proper diameter for the roll. The bigger the diameter of both the press roll and the counter roll, the longer will be the press zone. The length of the press zone is also a function of the elasticity and thickness of the moving belt which encloses the counter roll. In practice, the length of the press zone can be between approximately 1 and 10 centimeters. 10 cm press zone lengths could be achieved with the use of relatively large (diameter = about 1,5 meters) rolls in conjunction with an elastic belt 1 cm thick. The indentation in the belt could then be about 1 mm. The surface roughness of the side of the belt facing the web is suitably 5 microns, preferably 2 microns, and most preferably 1 micron. The counter roll could be cooled by water whereas oil, circulating in a closed loop including an oil cooler, could preferentially be utilized when the supporting counter body constitutes a glide shoe or glide body. Brief description Q£ lbs drawings The invention shall now be elucidated in the following with reference to schematically illustrated nonlimiting examples of pressing shown on the attached drawings. Thus on the drawings: fig. 1 is an endview of the embodiment of the invention as a partial crossection with a roll constituting the supporting counter body, SUBSTITUTE SHEET fig. 2 is an endview of an alternative embodiment of the invention as a partial crossection with a glide body constituting the supporting counter body, fig. 3 is an endview of a partial crossection illustrating an adjustable guide roll to obtain a preheating zone of an adjustable length prior to the press zone. Description oi preferred embodiments In the drawings, identical reference numbers are used to indicate the same or similar details. Fig. 1 shows a pressing arrangement for a moving web, formed between a cylindrical press roll 1 and a belt 5 supported by a counter body constituting a., roll 2. A moving web 6 is passed between the rotating press roll and the moving belt. A guide roll 3 and a stretch roll 4 are provided for guiding the belt and maintaining it under proper tension. The press and counter rolls are forced against eachother by arbitrary, known loading mechanisms not shown here, thus producing the press zone 7. The press roll is heated to a temperature of at least 100°C The counter roll can be cooled by known means not shown here. In fig. 2 the counter body constitutes a glide body 9 which is supported by a beam 15. A lubricating duct 10 and lubricating nozzles 12 are provided for lubricating the area between the glide body 9 and the moving belt 5. A duct 13 is indicated for a cooling fluid which transfers heat within a closed loop including a heat exchanger. Arbitrary, known loading mechanisms for applying load between the press roll and the glide body are not shown here. The glide body can be adjusted from the end flanges 50 as indicated by the arrows 52. The moving web 6 passes between the press roll 1 and the moving belt 5 in the press zone 7. In fig. 3 an adjustable 14 guide roll 16 is shown and has been included for the purpose of obtaining a preheating zone 8 of variable length prior to the press zone 7. The moving belt 5 encloses guide roll 16. With the exception of this guide roll the arrangement is similar to that shown in fig. 1. When practical solutions of details in the pressing arrangement according to the invention have not been described more comprehensively, they fall within known or customary practice in the art to which this invention pertains and are easily perceived by someone skilled in the art. SUBSTITUTE SHEET

Claims: Cl ms 1. A pressing arrangement for a moving web (6) icluding a press zone (7) for the moving web (6) formed between a cylindrical press roll (1) and belt (5), said belt being endless and supported by a counter body, CHARACTERIZED in that the belt (5) is elastic and has a surface which is more uniform than the surface structure of the moving web (6), and in that the surface temperature of the press roll is at least 100°C 2. A pressing arrangement as claimed in Claim 1, CHARACTERIZED in that the surface structure of the side of the belt (5) facing the web (6) has a pore size which is at least the same, suitably 50%, preferably 25% and most preferably 10% of the average pore size of the moving web (6), and/or that the surface roughness of the side of the belt (5) facing the web (6) is at least 5 microns, preferably 2 microns, and most preferably 1 micron. 3. A pressing arrangement as claimed in Claim 1 or 2, CHARACTERIZED in that said counter body is provided with cooling means. 4. A pressing arrangement as claimed in Claim 1, 2, or 3, CHARACTERIZED in that said counter body constitutes a roll (1). 5. A pressing arrangement as claimed in Claim 1, 2, or 3, CHARACTERIZED in that said counter body constitutes a stationary glide body (9). 6. A pressing arrangement as claimed in anyone of the above claims, CHARACTERIZED in that the moving belt (5) is guided into the press zone (7) via the press roll (1) thus providing a preheating zone (8) prior to the press zone (7). 7. A pressing arrangement as claimed in Claim 6, CHARACTERIZED in that the moving belt (5) is guided into the press zone (7) via the press roll (1) by means of a guide roll (16). 8. A pressing arrangement as claimed in Claim 6, CHARACTERIZED in that the length of the preheating zone (8) is adjustable. 9. A pressing arrangement as claimed in Claim 7 and Claim £', CHARACTERIZED in that the length of the preheating zone (8) is adjusted by means of the guide roll (16). 10. A pressing arrangement as claimed in anyone of the above claims, CHARACTERIZED in that the thickness of the moving belt (5) in the center of the press zone (7) is less than 97% of the thickness of the unloaded belt. SUBSTITUTE SHEET

Inventors: NYKOPP ERIK, NYKOPP, ERIK
Applicants: NYKOPP ERIK, NYKOPP, ERIK
Application year: 1993
Main classification: D21F3
IPC codes: D21F1, D21F3, D21F9, D21G1