EQUIPMENT FOR CLEANING THE WEBS OF A PAPER MACHINE
The present invention relates to equipment for cleaning the fabrics of a paper machine, which equipment is intended to be installed especially in an unsupported section of the fabric, such as a belt sleeve, transfer belt, or similar, and which equipment includes a doctor arranged, in its operating position, against the fabric.
In paper machines, the fabrics are continually cleaned to maintain the quality of the paper and to increase their operating life. At some of the cleaning points, the fabric is in between its support points, which are generally rolls. In such cases, an ordinary doctor with blades cannot be easily used, because in such positions there is insufficient support or no support at all on the opposite side of the fabric. In such an unsupported section, the fabric ^lives' , i.e. flutters. A conventional doctor set in this position does not adapt sufficiently to the movement of the fabric, instead the fabric strikes repeatedly against the doctor blade. This wears the fabric a great deal and the fabric may even tear. At the same time, however, the cleaning is inefficient and uneven.
Equipment for clearing fabrics of paper machines, especially in their unsupported sections, is known from utility model 3076. In the equipment in the publication, the member that actually cleans the fabric is a brush roll. After the brush roll, the equipment also has a vacuum chamber, into which the pulp that has detached from the fabric is sucked.
Bristles of varying stiffness can be selected for the brush roll, but the continuous brushing movement nevertheless wears the fabric. In addition, the upper part of the vacuum chamber is open, which increases the vacuum required. At the same time, the brush roll lifts a curtain of mist around the equipment. This takes place especially, if the brush roll is rotated
against the direction of movement of the fabric. The vacuum chamber seals too continually rub the surface of the fabric. This wears the fabric and increases the need to service the seals .
The invention is intended to create a new kind of equipment for cleaning the fabrics of a paper machine, which will achieve a better cleaning result with simpler equipment and with less wear to the fabric. The characteristic features of the invention appear in the accompanying Claims. In the equipment according to the invention, all the cleaning takes place in an enclosed space, so that moisture or dirt does not spread into the surroundings. Various combinations of devices can be used as the cleaning members, according to the cleaning requirement and the fabric. In addition, seals that do not wear the fabric are used to seal the enclosed space. The equipment according to the invention is suitable for fabrics requiring cleaning. In particular, fabrics can be easily cleaned with the equipment in their unsupported sections and, if necessary, the equipment can even be installed on both sides of the fabric.
In the following, the invention is described in detail with reference to the accompanying drawings illustrating some embodiments of the invention, in which
Figure la shows a side view of a cross-section of equipment according to the invention arranged in the unsupported section of a fabric, Figure lb shows a side view of a cross-section of equipment according to the invention arranged in connection with a shoe press roller, Figure 2 shows a cross-section of one embodiment of equipment according to the invention, Figure 3 shows the embodiment according to Figure 2 partly altered.
Figures la and lb show equipment according to the invention applied in two different locations. In general, the equipment can be installed in a paper machine in any part of the journey of a fabric, in which there is sufficient space. In the 5 application, the term paper machine also refers to board machines. In addition to a belt sleeve and a transfer belt, other paper machine fabrics include wires and felts.
In Figure la, the equipment is arranged to clean transfer belt
10 10 and in Figure lb the belt sleeve 11 of shoe press roller 9.
In both places, there is insufficient space behind the fabric to permit a normal doctor. However, the cleaning member in the equipment according to the invention is a normal doctor 12.
This is possible, because doctor 12 is situated in a vacuum
15 chamber 13, which is set against the fabric. In this case, vacuum chamber 13 is formed inside a special nozzle 14. During cleaning, the internal vacuum in nozzle 14 pulls the fabric onto the edges 15 of nozzle 14, when the movement of the fabric becomes less violent and the fabric becomes flat over nozzle
20 14. This allows a doctor to be used in the equipment according to the invention, even though the fabric is not actually supported from its opposite side.
When the equipment is used, moisture and dirt do not spread to 25 the surroundings, because all the cleaning members are located inside the nozzle. In addition, the entire equipment is arranged in such a way that it can be moved in relation to the fabric. Thus, the equipment can be moved further away when the fabric is being changed or during the servicing of the 30 equipment itself. However, the nozzle generally remains in place during operation. On the other hand, the nozzle, the doctor, or both can be equipped with an oscillating device, which will improve the result of the cleaning.
35 In Figures la and lb, nozzle 14 is set at a slight upward angle. This allows water and dirt to travel by gravity from the
cleaning equipment to vacuum chamber 13, and from there away from the equipment. However, a sufficient vacuum will cause water and other material to rise upwards too, so that the equipment can be installed in all positions, even vertically downwards. However, an unnecessarily great vacuum will stress the fabric, because the edges 15 of nozzle 14 lie against the fabric.
Figure 2 shows equipment, which is particularly suitable for cleaning a belt sleeve 11. Because a belt sleeve 11 does not stretch and contract very much, it is possible to use a relatively low vacuum. In this case, there is a small contact force between the edges 15 of nozzle 14 and the fabric 15, so that simple sliding surfaces 16 can be used in the edges 15. Sliding surface 16 may be a surfacing or a separate piece, which is made of slippery material that will not scratch the fabric. The need for a vacuum is also reduced by the fact that belt sleeve 11 is impermeable by air. Thus, even a low vacuum will hold the fabric 16 against the nozzle. In this case, however, care must be taken to ensure a supply of replacement air. There are gaps between the ends of the nozzle in the example and the fabric, through which replacement air can enter vacuum chamber 13. The equipment shown is suitable for cleaning other fabrics besides belt sleeves.
The nozzle itself can be made from a variety of materials and its shape can be varied according to the space available. In the example, nozzle 14 is attached to the paper machine by means of arm 17. Nozzle 14 can also be supported from its ends, in which case the space needed for the installation will be reduced. Depending on the embodiment, the vacuum is led to nozzle 14 through openings 18 in the ends, or through holes 19 drilled in arm 17. Connections can also be made to the sides of nozzle 14, through which a vacuum can be created in chamber 13 (not shown) . During cleaning, the vacuum, together with the replacement air, creates a flow that removes the water and dirt
detached from the fabric. In the application in Figure 2, the doctor 12 is attached to nozzle 14. This construction simplifies the handling of the equipment, but demands a strong nozzle. Alternatively, the doctor may be supported separately, 5 when a light nozzle may be used. It is preferable to arrange a water jet 20 inside nozzle 14 before the doctor, to clean the fabric and lubricate the blade of doctor 12. This will improve the result of the cleaning and reduce wear in the fabric. In addition to, or instead of the water jet, a steam jet can also 10 be used.
In addition to the doctor, there may also be a brush roll (not shown) according to utility model 3076 inside the nozzle. In the embodiment in Figure 3, there are also other additional
15 properties, which improve the operation of the equipment. One significant feature is the sealing of the edges 15 of nozzle 14. In the disclosure, the same reference numbers are used for components that are functionally similar. Unlike the previous embodiment, slit nozzles 21 or rollers 22 are used in the edges
20 15 of nozzle 14. The compressed air led through the slit nozzles 21 keeps fabric 10 away from the edges 15 of nozzle 14, but seals vacuum chamber 13 sufficiently. A nozzle 14 equipped with a gap jet 21 will scarcely wear fabric 13 at all. A corresponding feature can be achieved by fitting a rotating
25 roller 22 on edge 15. Roller 22 can rotate freely or incorporate a rotating device. If necessary, a single nozzle may incorporate various edge solutions.
In addition, the equipment according to the invention includes 30 devices arranged on the opposite side of the fabric to vacuum chamber 13 for pressing the fabric towards and against nozzle 14. Certain fabrics, such as felts and wires, permit air to pass through, so that replacement air comes through the fabric. Similarly, the necessary vacuum can be reduced by feeding 35 compressed air from the opposite side, for instance by means of slit nozzle 23. Compressed air is also used for moving the
fabric onto nozzle 14, when the cleaning starts. The vacuum needed in vacuum chamber 13 can also be reduced by using a pressurized tube 24, which is arranged to carry the fabric from the opposite side. In principle, tube 24 is similar in principle to the belt sleeve of a shoe press roller. The loading effect can be varied by adjusting the internal pressure in tube 24. The pressure devices described can be located either on the edges of the nozzle, or next to the cleaning device. Other alternative locations are also possible.
The equipment according to the invention is generally not in contact with the fabric, unless cleaning is required. Cleaning is started by arranging a vacuum in vacuum chamber 13, by means of which the fabric is sucked onto nozzle 14. If necessary, the entire equipment is also moved towards the fabric. Once the fabric has stopped fluttering, doctor 12 is run against the fabric, when the actual cleaning begins. If required, other cleaning devices arranged in nozzle 14 are also used. The doctor is adjusted in a known manner. The vacuum is also adjusted during cleaning. In addition to the vacuum, the fabric is also pressed against the nozzle by means of compressed air on the opposite side of the fabric or by means of some other adjustable device. In addition to pressure, the auxiliary devices in question also reduce the vacuum required.
The embodiments of the equipment can be varied in individual cases. However, the doctor is located inside the vacuum chamber, so that the equipment will achieve a good doctoring result, without dirtying again the surroundings of the equipment or the fabric being cleaned, and without wearing the fabric unnecessarily.