The present invention relates to a device comprising an endless conveyor belt and a driving cylinder for feeding the conveyor belt, and means for generating the tractive force required for feeding the conveyor belt. Said device may for instance consist of a cellulose washer.

In conventional devices of the type above, the tractive force required for feeding the conveyor belt is generated by means of one or more non-driving cylinders.

In paper production, conveyor belts of various types are used, among other purposes, for dewatering, washing and forming cellulose pulp.

Conventional devices of the type described above, comprising one driving cylinder and one or more non-driving cylinders, have the drawbacks of high friction between the belt and stationary support means and of great mechanical stress on the belt, entailing high maintenance costs, due to wear of the belt, and high transport energy consumption, among other inconveniences.

A purpose of the invention is to eliminate the drawbacks of prior art devices mentioned above and to achieve an economical device with reliable operation.

This purpose is achieved with the present invention, whose main characteristics are disclosed in the accompanying claims.

Thus, the present invention relates to a device comprising an endless conveyor belt and a driving cylinder for feeding the conveyor belt, and means for generating the tractive force required for feeding the conveyor belt, the device being characterised in that the means comprise at least one closed space, in which hydraulic or pneumatic pressure higher than the ambient pressure is maintained within a portion of the feeding profile of the conveyor belt.

Consequently, unlike conventional devices, the device in accordance with the invention comprises one single cylinder, i.e. the driving cylinder.

In this conjunction, the feeding profile of the conveyor belt means the path defined by the feeding of the conveyor belt.

The feeding profile of the conveyor belt has preferably an essentially constant radius of curvature within the area where hydraulic or pneumatic pressure is maintained.

Said feeding profile preferably follows a circular path at the area where hydraulic or pneumatic pressure is maintained, then adopts a tangential path, subsequently readopts a circular path at the area of the driving cylinder, and eventually a tangential path.

In a preferred embodiment of the invention, the closed space mentioned above is surrounded by a supporting frame, the conveyor belt and for instance horizontal and vertical packings between the supporting frame and the conveyor belt.

The conveyor belt may be perforated, unperforated or partly perforated, depending on the purpose of use. The conveyor belt is unperforated at the closed area.

In a particularly preferred embodiment of the invention, the device consists of a device for filtering fibrous or fine-grained material, such as a cellulose washer, the conveyor belt being at least partly perforated in that case.

The driving cylinder axis may be substantially vertical or horizontal, but it may also be inclined.

The device in accordance with the invention may further comprise a means for guiding the driving cylinder perpendicularly to the force received by the driving cylinder from the conveyor belt. This provision ensures that the belt is retained on the driving cylinder.

The invention will be described in greater detail below with reference to the accompanying drawing, of which

figure 1 shows a top view of a device in accordance with the invention and figure 2 shows a section along line I-I in figure 1.

Figures 1 and 2 show a cellulose washer in accordance with the invention. The endless conveyor belt, consisting in this case of a steel screen, is marked with reference number I. Driving cylinder 2, consisting for example of a gummed roll, is

rotated about its axis, vertical in this example, by means of an actuator. This actuator comprises a gearbox 8 including a rotor 9 and a pull bar 10.

Conveyor belt 1, supporting frame 4 and horizontal and vertical packings 5 together form a closed space 3. Packings 5, which may be shaped as hoses, form a sliding surface against/contact surface with conveyor belt 1. Conveyor belt 1 is unperforated at this area.

The closed space 3 is connected to a pressure source (not represented), which in space 3 maintains hydraulic or pneumatic pressure higher than the ambient pressure.This pressure may for instance be somewhat higher than the ambient pressure. The hydraulic or pneumatic pressure generates the tractive force required for feeding conveyor belt 1, in other words, adequate friction is achieved between driving cylinder 2 and conveyor belt 1. The contact surface between packings 3 and conveyor belt 1 is very small, and thus the friction between packings 3 and conveyor belt 1 will also be low.

The cellulose washer described above operates such that a pulp bed is formed on the inner surface of the conveyor belt. After this, wash water is conducted through the pulp bed from the inside out while the conveyor belt is being fed.

To ensure that conveyor belt 1 is retained on driving cylinder 2 the device in accordance with the invention may be equipped with cylinder means 6 for guiding driving cylinder 2 perpendicularly to the force received by the driving cylinder from the conveyor belt. Cylinder means 6 may be connected to a means 11 indicating the position of belt 1 relative to driving cylinder 2. The upper end of driving cylinder 2 is provided with a mobile support 7, allowing horizontal movement of driving cylinder 2.