The invention relates to a cleaning device for cleaning a dewatering screen in a wet or dry section or a wet felt in a press section of a paper making machine, said device comprising at least one rotatable spray nozzle, which is cou¬ pled to an air and/or liquid supply means. During the production of paper a dewatering screen and/or a wet felt is contaminated with paper residue, size- residue and other contaminants. In order to obtain a proper operation of the paper making machine, the dewatering screens and/or wet felts need to be cleaned by means of a cleaning device.

A cleaning device of this kind is inter alia known from German Gebrauchsmuster DE-U-29517859. The cleaning device shown and described therein includes a rotatable spray nozzle which is driven by the (cleaning) water. The cleaning device furthermore contains means for supplying air, which air is blown into a hood, in which the rotatable spray nozzle is disposed, in order to provide exhaustion of the detached dirt and/or the mist or the residual water into an discharge room. One disadvantage of this known cleaning device is the fact that a particular amount of cleaning water is required to obtain a required/desired rotational speed of the spray nozzle. This may cause the screen or the felt to become wetter than may be desirable, which has a negative effect on the paper production process and/or may lead to malfunctions. Another disadvantage of this known device is the fact that the exhaustion of the detached dirt and/or the mist or the residual water does not function adequately, because the matter to be exhausted is carried from under the hood along with the screen or the felt. The object of the invention is to provide an improved cleaning device which does not exhibit the above disadvantages. In order to accomplish that objective a cleaning device according to the invention is characterized

in that said cleaning device includes a motor for rotating said spray nozzle.

By using a motor for effecting rotation of the spray nozzle instead of the liquid and/or air being supplied (as is done in the aforesaid German Gebrauchsmuster) , it becomes possible to adjust the amount of air and/or liquid being supplied and the desired pressure to the screen or the felt to be cleaned, without this having an effect on the rotatio¬ nal speed of the spray nozzle. Furthermore this makes it possible to freely select the orifice of the spray nozzle, independently of the required/desired rotational speed.

One embodiment of a cleaning device according to the invention is characterized in that said motor is an electro- motor.

This enables easy adjustment of the rotational speed of the spray nozzle in dependence on the degree of contamination, the type of screen or felt, the necessary cleaning operation, etc. One embodiment of a cleaning device according to the invention is characterized in that said motor includes a rotatable hollow shaft, which is coupled to the spray nozzle. Another embodiment of a cleaning device according to the invention is characterized in that said cleaning device furthermore includes at least two air jet nozzles, which jet nozzles are disposed on either side of the rotatable spray nozzle.

This enhances the cleaning operation of the rotatable spray nozzle, because the dirt detached by the spraying of the spray nozzle is removed from the screen or the felt by the air jets. In addition to that an overpressure is generated near the screen or the felt, which automatically causes exhaustion.

Another embodiment of a cleaning device according to the invention is characterized in that said cleaning device includes a row of air jet nozzles extending transversely to said screen or said felt, which air jet nozzles are positioned in the direction of movement of said screen or

said felt with respect to said rotatable spray nozzle, and which comprise outlet openings, which blow in operative condition, in a direction opposed to the direction of movement of said screen or said felt. This provides additional certainty that (detached) dirt, residual water, etc. cannot be carried along with said screen or said felt, but is discharged through an exhausting hood. Furthermore the invention relates to a cleaning device wherein said device comprises an exhausting hood, which hood terminates near or in a discharge drain (save-all) disposed at some distance from said screen and/or said felt and parallel to the transverse direction thereof. Said cleaning device is according to the invention characterized in that said exhausting hood comprises at least one plate-shaped end piece, which end piece is in contact, at least with its free end, with the inner side of the discharge drain (save-all) during operation. Thus the detached contaminations being carried off through said exhausting hood are collected only at the ends of the discharge drain (save-all) , and said discharge drain (save-all) will not become clogged in the working area of the cleaning device. This leads to a considerably improved operation of the cleaning device, whilst at the same time minimizing shut-down and/or unnecessary standstill of the cleaning device. According to one aspect of the invention the free end of the plate-shaped end piece is configured to have a shape which substantially corresponds with the shape of the inside of the discharge drain (save-all) . This leads to a considerably improved displacement and removal of the contaminations to the ends of the discharge drain (save-all) , whilst preventing the discharge drain (save-all) from becoming clogged.

One embodiment of the cleaning device according to the invention is characterized in that the plate-shaped end piece is made of a flexible material, for example a rubber or a plastic. This material can be readily processed at low cost, whilst at the same time providing a satisfactory cleaning of the discharge drain (save-all) .

Another embodiment of the cleaning device according to the invention is characterized in that the outlet opening of the exhausiting hood is in the form of a venturi tube. This provides a considerably improved discharge of the contamina- tions from the exhausiting hood, so that the occurrence of clogging, failure and/or unnecessary standstill of the cleaning device is considerably reduced.

Hereafter the cleaning device will be explained by way of example with reference to the accompanying figures, in which:

Figure 1 shows a first embodiment of a cleaning device according to the invention;

Figure 2 is a more detailed view of a part of an embo¬ diment of a cleaning device; Figure 3 is a more detailed view of another embodiment of a cleaning device according to the invention; and

Figure 4 shows another embodiment of a cleaning device according to the invention.

Figure 1 shows an embodiment of a cleaning device 1 including a rotatable spray nozzle 3. Said spray nozzle is driven by a motor 5 in order to obtain the required/desired rotational speed. Spray nozzle 3 is coupled to a hollow shaft 51, which forms part of the rotatable part of the motor. The rotational speed can be adjusted thereby in dependence on e.g. the extent of contamination, the type of screen or felt, the spray nozzle used, the amount and/or the pressure of the liquid (e.g. water) and the air pressure used.

The cleaning device is placed near a screen or felt 7, which moves over a roll 9. The cleaning device furthermore includes an exhausting hood 11, which is coupled to a fan 21.

A cleaning device furthermore includes supply means 13, which are on the one hand coupled to a liquid supply pipe 131 and an air supply pipe 132, and which on the other hand supply the liquid to spray nozzle 3 via an outlet 15. Supply means 13 furthermore include an outlet 17, which is coupled to air supply means 19. Said air supply means 19 include a portion 193, which blows air along the liquid sprayed onto the screen or the felt by the spray nozzle. Air supply means

19 furthermore include a portion 191, which blows air in the form of a so-called air knife after the screen or the felt has passed spray nozzle 3. The supplied air and the detached dirt, residual water etc. are exhausted via a fan 21. Four parameters are of essential importance for the necessary cleaning of screen or felt 7, viz. the speed at which the paper, and thus the screen or the felt are trans¬ ported, the amount of medium (air, water and/or other liquid) that is required, the pressure of the medium and the rotational speed (power) of spray nozzle 3.

The possibility to select the amount of medium and the pressure of said medium independently of the rotational speed of the spray nozzle with the cleaning device according to the invention provides a great deal of freedom in the selection of the above parameters for different types of screens or felts, different types of contamination/cleaning requirements, different belt speeds, different requirements with regard to the allowed amount of liquid, etc.

Figure 2 is a more detailed view of a part of an embo- diment of a cleaning device according to the invention. Those elements that correspond with the elements shown in Figure 1 are indicated by the same reference numerals.

The rotatable spray nozzle 3 covers a spraying area 31. Beside this spraying area air jet nozzles 4 forming part of portion 193 of air supply means 19 are provided, which air jet nozzles assist in soaking off/detaching contaminations from the screen or felt 7. Said air jets 41 furthermore cause the dirt to be moved from the screen or felt 7 into the exhausting hood 11 disposed thereabove. Instead of using two air jet nozzles 4 it is also possible, of course, to use four air jet nozzles or a row of air jet nozzles disposed on an imaginary circle.

Figure 3 is a more detailed view of a part of an embo¬ diment of a cleaning device according to the invention. In this embodiment portion 191 of air supply means 19 is in the form of a row of air jet nozzles, which blow air jets 195 at an angle towards screen or felt 7, in a direction opposed to the direction of movement of said screen or said

felt. This provides a so-called air knife, by means of which the detached dirt and/or the mist or the residual water is removed from said screen or said felt.

Because air is blown in the direction of said screen or said felt, a high pressure (overpressure) is generated at the location of said screen or said felt, which results in the removal of dirt etc. from said screen or said felt. The fan (21, see Figure 1) takes care of the further transport and discharge of the dirt etc. Figure 4 shows another embodiment of the cleaning device according to the invention. The parts of the cleaning device of this embodiment are indicated by reference numerals that correspond with those of the embodiment of the cleaning device according to Figure 1. The contaminated screen or felt 7 is cleaned by means of rotatable spray nozzle 3, after which the detached contaminations are transported through exhausting hood 11 in the direction indicated by the arrows, possibly along with the cleaning liquid being used, by means of portions 191 and 193 of air supply means 19. As is shown in Figure 4, exhausting hood 11 terminates near or in a discharge drain 60 (save-all) , which discharge drain 60 (save-all) is disposed at some distance from the screen or felt 7 and parallel to the transverse direction thereof. In order to prevent accumulation of contaminations in discharge drain 60 (save-all) resulting in said discharge drain 60 (save-all) becoming clogged, the exhausting hood 11 is according to the invention provided with at least one end piece 61, said end piece 61 with its free end piece 61a in the operative position being in contact, at least substanti- ally so, with the inner side 60a of discharge drain 60 (save- all) . End piece 61 is preferably plate-shaped, so that the outflow of contaminations from exhausting hood 11 in the direction indicated by the arrows is hardly obstructed, if at all. Whilst screen or felt 7 is being cleaned in the opera¬ tive condition, cleaning device 1 is moved to and from along screen or felt 7, in the transverse direction thereof, in a known manner. The soaked-off contaminations are deposited

into discharge drain 60 (save-all) via exhausting hood 11, in the direction indicated by the arrows, from which location they are moved towards the two ends of said discharge drain 60 (save-all) by means of end piece 61 during the movement of cleaning device 1. Thus the soaked-off contaminations are collected only at the ends of discharge drain 60 (save-all) , and said discharge drain (save-all) will not become clogged in the working area of cleaning device 1, i.e. substantially in the centre of discharge drain 60 (save-all) . In addition to that the collected contaminations can be readily removed at the two ends of the discharge drain (save-all) , without having to stop cleaning device 1. This leads to a considerably improved functioning of cleaning device 1, whilst at the same time reducing the occurrence of failure and/or unnecessary standstill of the cleaning device.

The free end 61a of end piece 61 may have a shape which substantially corresponds with the shape of the inner side 60a of discharge drain 60 (save-all) . This leads to a considerably improved displacement and removal of the contaminations to the ends of discharge drain 60 (save-all) , thus preventing the discharge drain (save-all) from becoming clogged.

The plate-shaped end piece may be made of a flexible material, for example a rubber or a plastic, which exhibits sufficient rigidity for moving the contaminations.

Although the outflow opening of exhausting hood 11 of Figure 1 is provided with a fan 21, the exhaustion of contaminations from exhausting hood 11 may also take place in a different manner. As is shown in Figure 4, the outflow opening of exhausting hood 11 is made in the form of a venturi tube 62. As a result of the special converging configuration of venturi tube 62, the pressure generated within exhausting hood 11 is converted into velocity within said venturi tube, resulting in an improved exhaustion of the contaminations to discharge drain 60 (save-all) , as indicated by the arrows. In this manner the risk of clogging and failure of the cleaning device is strongly reduced.

It will be apparent that several minor modifications to

the cleaning device according to the invention are possible without departing from the essence of the invention.

Thus it will be possible to operate the cleaning device with air only (without liquid) , resulting in dry cleaning action.

Furthermore it will be possible to add chemicals to the cleaning liquid (e.g. water) .

It will also be possible, if desired, to drive several (liquid) spray nozzles by one and the same motor 5, or to configure said spray nozzle as a combined liquid and air spray nozzle.

Furthermore it will be apparent, that various configu¬ rations of the motor 5 used for rotating spray nozzle 3 are possible. Besides an electrically driven motor, as already described above, it is also possible to use an air-driven motor. In addition to that an (electro) motor reductor is also quite suitable for rotating spray nozzle 3.