The invention also relates for example to the shoe element of a shoe roll according to the preamble of claim 4.

A shoe calender consists of a stationary body, around which an endless belt rotates.

A shoe roll comprises a shoe element that is supported on the body of the shoe roll in the roll nip between the shoe roll and its backing roll by means of hydraulic cylinders beneath the shoe element. It is possible to pressurize the shoe element of the shoe roll by means of the hydraulic cylinders attached to the body to provide a so-called nip pressure in the roll nip between the shoe element and the backing roll of the shoe roll.

To decrease the friction between the shoe element of the shoe calender and the endless belt that rotates on top of its stationary body, and to cool the shoe element of the shoe calender, fluid lubrication is usually arranged between the shoe element and the endless belt that rotates on top of it, next to the roll nip. Depending on the type of the shoe element, the method of lubrication is either dynamic or stationary, or partly stationary and partly dynamic. All these methods of lubrication have it in common that oil is brought from a hydraulic power unit through the shoe element to the roll nip or its immediate vicinity. In the dynamic or partly dynamic method of lubrication in particular, the majority of the lubricating oil drifts along the surface of the shoe element from the first side of the roll nip to the second side of the roll nip, and further to an oil collector trough integrated with the body of the shoe roll, whereby air is mixed with it at the same time, which is harmful to the pumping ability and the lubricating and cooling properties of the lubricating fluid, such as lubricating oil, and which must be removed before the lubricating oil is returned to the lubrication circulation. Because of the air contained by the lubricating oil, the hydraulic power units must be dimensioned so that their pipes are large and power is high.

In addition to calendering, the shoe rolls are used, when water is pressed from the fibre web.

The purpose of the invention is to eliminate the disadvantages of prior art.

Accordingly, the main object of the invention is to provide a lubricating system for the shoe roll, wherein the tube size and the power of the hydraulic power unit is essentially lower than in known lubrication solutions.

The above-mentioned objects are achieved by the lubrication system according to the invention and the shoe element used in it. The invention relates for example to the cooling arrangement of the shoe element of the shoe roll according to claim 1.

The invention also relates for example to the shoe element of the shoe roll according to claim 4.

The shoe roll comprises a stationary body, on top of which an endless belt is arranged to rotate. Next to the roll nip between the shoe roll and its backing roll, the shoe roll is provided with a shoe element, which is supported on the body by means of the hydraulic cylinders below it. At least two separate liquid circulations run through the shoe element. At least one of the liquid circulations is a lubricating liquid circulation arranged between the shoe element and the endless belt that rotates on top of it. At least one cooling liquid circulation is also arranged to cool the shoe element and to balance the temperature differences of the shoe element.

The liquids circulating in the lubricating liquid circulation and the cooling liquid circulation are not essentially mixed with each other inside the shoe element. The shoe element of the shoe roll comprises at least one flow channel for the lubricating liquid circulation, leading to the outer surface of the shoe element. Furthermore, the shoe element comprises at least one flow channel for the cooling liquid circulation, leading through the shoe element so that the cooling liquid circulating in the flow channel of the cooling liquid is not mixed with the lubricating liquid flowing in the flow channel of the lubricating liquid.

In some cases in the text, the flow channel of the lubricating liquid circulation and the flow channel of the cooling liquid circulation are also called the lubricating liquid flow channel and the cooling liquid flow channel, respectively.

The present invention is based on the fact that the lubricating and cooling liquid circulations of the shoe element of the shoe roll are separated from each other, whereby only enough lubricating liquid is fed into the lubricating liquid circulation to decrease the friction between the shoe element and the endless belt rotating on top of it. The cooling of the shoe element is arranged by means of a separate cooling liquid circulation, which is impermeable to air, whereby considerably less air goes from the cooling and lubricating liquid circulations of the shoe element to the liquid circulation than before.

The lubricating arrangement and the shoe element according to the invention provides the advantage over prior art that the power of the hydraulic power unit needed for circulating the liquids and the size of the transfer pipes are considerably smaller than those used before. This is because air enters the liquid circulation from the lubricating liquid circulation only, whereby the time for removing the air from the liquid circulation in an oil tank is considerably shorter than if the lubricating liquid circulation would be used both for decreasing the friction between the shoe and the belt, and for cooling the shoe; in the latter case, the volume of the lubricating liquid circulation is considerably larger, whereby the volume of air entering it also grows in proportion. The pressure of the cooling oil can be low, whereby the heating of oil caused by pressure drops is minor. The main advantage of smaller hydraulic power units is a lower price and simpler equipment.

In this connection, it should be noticed that the shoe roll and the shoe element refer to the shoe roll and its shoe element used both in shoe calendering and in connection with pressing a wet fibre web. The machine direction in this application refers to the direction of propagation of the fibre web.

In the following, the invention is described in detail with reference to the appended drawings.

Fig. 1 is a schematic cross-sectional view of a shoe roll comprising a Convex-type shoe element as viewed from the end of the pair of rolls.

Fig. 2 is a cross-sectional view of a shoe roll comprising a stationary lubricating zone as viewed from the end of the pair of rolls.

Fig. 1 shows one embodiment of the cooling arrangement of the shoe element of the shoe roll according to the invention. The figure shows the implementation of the cooling and lubricating liquid circulations in the vicinity of the shoe element only.

Fig. 2 shows another embodiment of the cooling arrangement of the shoe element of the shoe roll according to the invention. The figure illustrates in detail the feeding and return routes of the lubricating and cooling liquid circulations of the shoe roll, and also the hydraulic liquid circulation, which is used to pressurize the rows of hydraulic cylinders below the shoe element to provide nip pressure between the shoe element and the backing roll.

Fig. 1 shows a Convex-type shoe element 1 of the shoe roll 4, and a backing roll 2 on the opposite side of the element. A roll nip N is left between the shoe element 1 and its backing roll 2, wherein the surface of the fibre web W is calendered, when the roll nip between the shoe roll and its backing roll is pressed closed. The fibre web runs from left to right in the lubricating arrangement according to the figure.

The shoe roll 4 comprises a stationary body (not shown in this figure), on which the shoe element shown in the figure is supported by means of the hydraulic cylinders 7 below the same. The hydraulic cylinders are used to arrange a desired nip pressure in the roll nip N between the shoe roll and its backing roll, and the hydraulic cylinders are formed from two rows of hydraulic cylinders 7; 7a and 7; 7b, which at their lower parts are supported on the body of the shoe roll. An endless belt 6 is arranged to rotate on top of the body of the shoe roll 4. In the figure, the belt rotates from left to right in the direction of movement of the fibre web W. To prevent the belt 6 from wearing, lubrication must be arranged in the roll nip N between the outer surface la of the shoe element and the endless belt. Lubrication is arranged by means of lubricating liquid circulation 3, wherein lubricating oil is pumped from a hydraulic power unit (not shown in the figure) through a lubricating oil flow channel 3"to the outer surface la of the shoe element. The figure only shows the portion of the lubricating oil circulation that runs through the shoe element. On the outer surface la of the shoe element, the lubricating oil mainly drifts between the shoe element 1 in the roll nip N and the endless belt 6, and further away along the second edge B of the shoe element to a collector trough (not shown in the figure).

Part of the lubricating oil also drifts directly along the first edge A of the shoe element to the collector trough. The lubricating oil that has exited the edges of the shoe element is partly mixed with air and these streams of lubricating oil are thereafter conducted to the hydraulic power unit (not shown in the figure), where air is removed from the lubricating oil, after which the lubricating oil is fed back into the lubricating oil circulation 3. As the lubricating oil moves from the lubricating oil flow channel 3; 3", which runs through the shoe element, directly to the roll nip and further away from the roll nip, the lubricating oil circulation described above has a hydrodynamic character. In the shoe element according to the figure, there is also a separate cooling liquid circulation 5, in which the same lubricating oil circulates than in the lubricating oil circulation. In the arrangement according to the figure, the cooling liquid circulation 5 of the shoe element is formed from two parallel cooling liquid circulations 5; 5a and 5; 5b, wherein the lubricating oil runs in opposite directions to ensure a steady temperature of the shoe in the machine direction. The figure shows only the cooling liquid flow channels 5a ; 5a"and 5b ; 5b"of the cooling liquid circulation, which run through the shoe element. The cooling liquid flow channels are located in the shoe element 1 perpendicular to the machine direction, i. e., in the direction of the longitudinal axis of the shoe element.

The lubricating oil moves from the cooling liquid flow channels 5a"and 5b"to the hydraulic power unit through a suitable transfer pipe system of the cooling liquid, from where it is pumped back either to the same or another cooling liquid

circulation. Before pumping to the cooling circulation 5, the cooling liquid must generally be cooled by a suitable heat exchanger. Generally, the liquid running in the cooling liquid circulation and the lubricating liquid circulation is the same lubricating oil, or at least lubricating oils, which easily mix with each other, whereby minor oil leakage in the liquid circulations does not disturb the functioning of the liquid circulations.

As can be seen in the lubricating and cooling liquid circulations shown in Fig. 1, air enters the liquid circulations only by means of the lubricating liquid circulation, because the cooling liquid circulation 5 in the vicinity of the shoe element is essentially airtight. In the embodiment described above, the cooling liquid that circulates in the cooling liquid circulations 5; 5a and 5; 5b does not mix with the lubricating oil that flows in the lubricating liquid circulation even in the hydraulic power unit.

The basic structure of the shoe roll 4 shown in Fig. 2 is similar to that shown in Fig.

1. The figure also shows the stationary body 10 of the shoe roll, which the rows of hydraulic cylinders 7; 7a, 7b are supported on, and the collector tray 11 of the lubricating oil. The figure shows the lubricating, cooling, and hydraulic liquid circulations to the hydraulic power unit H and back. In the shoe roll 4 according to the figure, a mainly stationary lubricating zone is formed between the shoe element 1 and the endless belt W rotating on top of it by means of a pocket formed on the outer surface la of the shoe element. The lubricating liquid circulation 3 of the shoe element and the endless belt is arranged so that the lubricating oil is fed from the hydraulic power unit through the lubricating oil feed channel 3; 3'into the lubricating oil flow channel 3; 3"approximately in the middle of the shoe element, and from there further to the essentially stationary zone (pocket) between the shoe element and the endless belt. The lubricating oil moves on the outer surface la of the shoe element from the pocket located next to the roll nip and along the outer surface of the shoe element to the oil collector tray 11, from where it returns further to the hydraulic power unit H through the lubricating oil discharge channel 3; 3"'.

Air is mixed with the lubricating oil, when it moves from the outer surface of the shoe element into the oil collector tray. The cooling liquid circulation 5 of the shoe element, instead, is arranged so that cooling oil is fed from the hydraulic power unit H through the cooling liquid feed channel 5; 5'to the cooling liquid flow channel 5; 5"leading through the shoe element. In this case, the cooling liquid circulation of the shoe element is formed from only one cooling liquid circulation 5 and the flow channel 5"in it, which is now located transversely to the longitudinal axis of the shoe element, i. e., in the machine direction. The cooling oil is conducted from the

flow channel 5"back to the hydraulic power unit through the discharge channel 5"'of the cooling liquid. The hydraulic liquid circulation 8 as such is conventional and the hydraulic liquid is pumped from the hydraulic power unit H through the feed channel 8; 8'of the hydraulic liquid to the hydraulic cylinders 7, from where the excess is returned through the discharge channel 8; 8"'of the hydraulic liquid back to the hydraulic power unit. The hydraulic liquid flowing in the feed and discharge channels of the hydraulic liquid circulation 8 is cooled by a heat exchanger 9 that has water circulation. The same oil is preferably used both in the hydraulic, cooling, and lubricating liquid circulations.

A noteworthy fact in the cooling, lubricating, and hydraulic liquid circulations described above in particular is that air enters the liquid circulations only by means of the lubricating liquid circulation, which decreases the size of the liquid transfer pipes and that of the hydraulic power unit H, and the required pumping power of the liquid.

In the embodiment of the invention shown in Fig. 2, the streams of liquid coming from the various liquid circulations to the hydraulic power unit preferably consist of the same lubricating oil, whereby they can be allowed to mix in the hydraulic power unit after air has been removed from the lubricating oil returning from the lubricating oil circulation, whereby the structure of the hydraulic power unit becomes simpler.

Only one lubricating arrangement of the shoe element and the shoe element of the shoe roll according to the invention are shown above. However, it is clear to those skilled in the art that the invention can be implemented in many other ways within the scope of the claims.

Accordingly, the lubricating and cooling liquid circulations of the shoe element above are shown for only certain, typical shoe rolls currently used. If the shape of the shoe element deviates from the one described above, the structures of the liquid circulations are also changed, however, keeping the lubricating and the cooling liquid circulations separate. The lubricating oil circulations as such are well known in the art and numerous different, partly dynamic, partly static or purely dynamic or static lubricating oil circulations for various shoe elements are described in the literature of the field. The lubricating, cooling, and hydraulic liquid circulations can either be fully separate or fully or partly the same. In partly or fully the same circulation systems, the liquid circulations are preferably combined inside the hydraulic power unit. For example, the lubricating and hydraulic liquid circulations of the shoe roll can be combined, but the cooling liquid circulation separate.

In the cooling liquid circulation, the shape of the cross-sectional profile of the cooling liquid flow channels can deviate from round, if appropriate. The number and the direction of the flow channels can also vary; for example, in some cases, the cooling channels can run through the shoe element so that their direction deviates both from the machine direction and the direction of the longitudinal axis of the shoe roll.

Generally, the cooling liquid circulating in the cooling liquid circulation is preferably cooled by means of a heat exchanger comprising water circulation, which is located in the feed channel of the cooling liquid circulation.

The embodiments described above relate to the shoe elements used in shoe calendering and their lubricating arrangements. However, pressure apparatuses with the same structure as the shoe calender are also used when removing water from the fibre web. In that case, the water is absorbed by wires above and below the fibre web or, in some cases, conducted inside a pressure apparatus that has a similar structure to the shoe roll. The shoe element and the lubricating arrangement according to the invention can also be used in connection with such pressure apparatuses.