Pressing arrangement in the processing apparatus of a paper/board machine or finishing machine with a metal belt loop

The present invention relates to a pressing arrangement in the processing apparatus of a paper/board or finishing machine with a metal belt loop, where the fibrous web to be processed is led through a nip formed by the belt loop and a counter-element outside it, the fibrous web being subjected to pressing action within the processing zone between the metal belt and the counter-element and a local additional load within the said processing zone by means of at least one pressing element inside the belt loop.

In a metal belt calender, the fibrous web is pressed in the zone between the thermo roll and the metal belt. The additional load required is obtained by means of an additional load roll (preferably profiled) inside the belt loop, as disclosed, for example, in an earlier international application PCT/FI03/00066 of the Applicant of the present application. An additional load roll, such as a profiled sym roll, is a relatively expensive component. In a wet press nip, the fibrous web is pressed by means of a felt and wire. As a nip roll can be used an ordinary roll or a long-nip roll.

The aim of the present invention is to provide a solution by means of which the additional loading inside the belt loop can be realised in a relatively simple manner and which at the same time makes possible the formation of several nip points within the processing area.

To achieve this aim, the pressing arrangement according to the invention is characterised in that the internal pressing element in the metal belt loop is a load beam to which a support roll is rotatingly fitted in bearings by means of a hydrodynamic bearing system, which support roll can be brought into contact with the inner surface of the metal belt loop for exerting the local additional load force on the fibrous web being processed.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic view in principle of a pressing arrangement according to the invention when implemented in connection with a metal belt calender,

Figure 2 shows a diagrammatic view in principle of an embodiment of the pressing arrangement, and

Figure 3 shows a diagrammatic view in principle of another embodiment of the pressing element.

Figure 1 shows a metal belt calender comprising a calendering belt 2 made of metal, which rotates around guide rolls 3. The calendering belt 2 travels around a roll 5 arranged outside it, which means that the calendering zone N is formed between the belt 2 and the roll 5. The material web W to be calendered passes through the calendering zone, whereupon it is subjected to the desired pressure impulse and thermal effect as a function of time. Lines 9 and 9a in Figure 1 depict the peaks of the pressure effect when pressing elements 40 according to the invention are arranged inside the calendering belt, which press the belt against the roll 5. Broken line 8, on the other hand, depicts the shape of the pressure effect when the contact pressure effective in the calendering zone is formed by means of belt 2 tension alone, while the pressing elements 40 are out of pressing contact with the belt 2. Reference numeral 6 refers to heating means, such as an induction heater, an infrared radiator, a gas burner or a capacitive heater.

Figure 2 shows an embodiment of the pressing element according to the invention, where the element 40 consists of a support plate 46, in which is arranged a bearing housing profile 45 extending across the whole width of the web, in which profile is formed a groove 48 for receiving the support roll 41. The bearing housing profile has a body part 42, in which is formed a feed channel 43 and a discharge channel 44 providing hydrodynamic lubrication, the said channels opening into the groove 48. Between the groove 48 and the support roll 41 is formed a hydrodynamic lubrication medium film 49. The support roll may be loaded via the support plate 46 against the metal belt 2, the fibrous web W being processed running on the opposite side of the said metal belt. The support roll 41 is a thin, tubular or shaft- like means which is preferably arranged to be deflected to achieve profiling in the

CD direction. In the example embodiment in Figure 2, the deflection of the support roll may be based on, for example, deflecting the support plate 46 by means of suitable deflecting means (not shown), which may be, for example, hydraulic cylinders positioned between the support plate and the body structure of the machine in question, in which case the support roll will follow the curvature of the support plate.

In the example embodiment of Figure 3, the pressing element 50 consists of a solid support piece 51, which extends in the transverse direction of the machine essentially across the width of the fibrous web being processed, and in which support piece has been machined a groove 48 for receiving the support roll 41, in which groove is supplied lubricating medium along a feed channel 52 to form a lubricating medium film between the support roll 41 and the receiving groove 48. The support piece 51 may also be arranged to be deflectable for deflecting the support roll to achieve the desired profiling in the CD direction.

In the embodiments of both Figure 2 and 3, at the ends of the support roll are provided support bearings (not shown) which maintain the support roll in place in the groove 48. In conjunction with the groove 48 may be arranged sealing means extending in the longitudinal direction of the support roll on either side of the roll, thus preventing soiling of the lubricating medium and making the lubricating medium system an essentially closed one. The lubricating medium film is subjected to a pressure of the order of 0.1-0.5 MPa and the shear rate of the lubricating medium film is of the same order as in the sliding surfaces of the load elements of deflection compensated rolls. The lubricating medium may be lubricating oil, glycol or the like, or most preferably water. Water hydraulics is economical and safe and possible seepage flow will not cause soiling.

One or more pressing elements may be placed in succession inside the belt loop in the machine direction. Due to their small size, several pressing elements may be fitted per one backing roll, for example a thermo roll, whereupon several higher pressure zones can be provided per a single roll. By means of this pressing arrangement is obtained an extremely efficient calender with several nips in a very compact space. The lubricating medium system can be arranged to be heated or cooled. The solution relating to the invention is suitable, for example, for belt

calenders, shoe calenders - where the pressing element according to the invention may be used instead of a load shoe - a wet press nip and other devices for forming and pressing fibrous webs.