METHOD AND DEVICE IN A PAPER MACHINE OR EQUIVALENT OR IN A FINISHING DEVICE OF SAME FOR REMOVAL OF DUST

Abstract: The invention concerns a method in a paper machine or equivalent or in a finishing device of same for removal of dust, in which method a blowing (P) is directed at the web (W), which blowing separates dust from the web (W), and in which method a suction effect is applied to the web (W) for removal of the dust that is separated out of connection with the web. In the method, before the dust separating blowing (P) in the running direction of the web (W), a vortex flow (P2) is produced so as to prevent carriage of the dust into the environment and to compensate for the suction effect. Further, the invention concerns a device in a paper machine or equivalent or in a finishing device of same for removal of dust, in which device (10) there are blow elements (11, 13, 20) for producing a blowing (P) that separates dust from the web (W) and suction elements (14, 16, 15) for producing a suction effect so as to remove the dust that is separated out of connection with the web. The device (10) comprises an arrangement (20, 17, 18) for producing a vortex flow (P2) before the dust separation blowing (P) in the running direction of the web (W) so as to prevent carriage of the dust into the environment and to compensate for the suction effect.

Description: Method and device in a paper machine or equivalent or in a finishing device of same for removal of dust The invention concerns a method in a paper machine or equivalent or in a finishing device of same for removal of dust, in which method a blowing is directed at the web, which blowing separates dust from the web, and in which method a suction effect is applied to the web for removal of the dust that is separated out of connection with the web. Further, the invention concerns a device in a paper machine or equivalent or in a finishing device of same for removal of dust, in which device there are blow elements for producing a blowing that separates dust from the web and suction elements for producing a suction effect so as to remove the dust that is separated out of connection with the web. In paper machines, at both sides of the web, which usually moves at quite a high speed, a boundary layer of air is formed, which carries along with it dust that has been separated from the fibre mesh of the web and from the fillers in the web. The dust spreads in the environment and is partly also carried to the web reel. Moreover, after the manufacture of the paper, dust and contaminations, such as debris and fibres, adhere to the face of the paper web, which contaminations come from the dryer section of the paper machine. One important source of dust is the slitting process, in which an abundance of dust is separated from the web when the web is slit into component webs in the longitudinal direction. Problems of dust also occur in the manufacture of tissue paper, in particular in connection with creping by means of a doctor, wherein the paper web is separated by means of a doctor blade from the face of a steam-heated yankee cylinder, in which connection a particularly large quantity of dust is detached from the web, which dust is drawn along by the paper web and spread into the environment. Dust and contaminations cause problems in the further processing, for example printing, because it is of vital importance from the point of view of the quality of printing that the printing rolls remain clean. Also, dust spreads both in the paper mill and in further processing into the environment, and dust may involve risks for occupational health, because it may contain various particles of fillers. With respect to the prior art, reference is made to the US Patent No. 3,239,863, in which a web cleaning device is described in which a chamber space is used, in which two air nozzles have been formed directed at the web, the space between the nozzles being closed so that it forms an exhaust chamber for the air coming out of the nozzles and for the dust separated from the web. In this prior-art arrangement, it is one of the problems how to produce a sufficiently high air blow rate to separate the dust adhering to the web as well as that the device has had to be constructed so that it is placed quite far from the web, in which case it is mainly suitable for general removal of dust, but not for detaching dust or contaminations from the web. One prior-art solution for the problems described above is described in the appli- cant's FI Patent No. 95, 611, in whose dust removing method and equipment it has been considered novel that the web has been subjected to a high-pressure blowing so as to separate the dust from the web and that, in the running direction of the web, before and after said high-pressure blowing, dust and equivalent that has been separated from the web is absorbed. The object of the present invention is further development of said solution so that a more efficient and simpler solution is obtained, whose cost of manufacture is also lower and which is also suitable for cleaning the paper web from both sides across the entire width of the web. It is a further object of the invention to suggest a solution in which there are no problems of runnability, for example, arising from the vacuum necessary for sucking the dust, and by whose means it is possible to prevent access of dust as leakage flow back onto the web and into the environment. In view of achieving the objectives stated above and those that will come out later, the method in accordance with the invention is mainly characterized in that, in the method, before the dust separating blowing in the running direction of the web, a vortex flow is produced so as to prevent carriage of the dust into the environment and to compensate for the suction effect. Further, the device in accordance with the invention is mainly characterized in that the device comprises an arrangement for producing a vortex flow before the dust separation blowing in the running direction of the web so as to prevent carriage of the dust into the environment and to compensate for the suction effect. In the arrangement in accordance with the invention, the face of the blow device that is placed facing the web has been shaped so that part of the cleaning jet is turned back towards the nozzle slot, in which case, by means of the vortex formed, it is possible to control the vacuum in the space and thereby to avoid problems of runnability caused by an excessively high vacuum. In the arrangement in accordance with the invention, the suction chamber has been shaped and dimensioned so that the high-speed cleaning jet has time and space enough to be turned into the exhaust air duct, whereby access of dust as a leakage flow back onto the web and into the environment are excluded. The arrangement in accordance with the invention is suitable for cleaning the web from both sides and, moreover, if necessary, in particular when a web wider than normal is being run, in view of cleaning the web edges by means of the dust removing device, the ends of the device can be provided with side blow nozzles. In the arrangement in accordance with the invention, the exhaust air duct is preferably shaped so that an intensive vortex is formed in the duct, whereby the duct remains clean and, moreover, the bottom of the pressure chamber has been shaped so that, with an adequate flushing velocity, adhering of dust to the faces in the device is prevented. In the arrangement in accordance with the invention, the blow nozzle slot has been designed so that the slot is adjustable, in which case the intensity of the dust separation blowing can be regulated readily. The blow device in accordance with the invention has also been arranged inclinable in the running direction of the web in compliance with the angle of arrival of the web and with the paper grade that is run, so as to obtain an optimal cleaning result. The device in accordance with the invention extends preferably across the entire width of the machine and, if necessary, for example when placed at spreader rolls after a slitter, it can be bent to the desired form, for example to the form of deflected rolls, and the bending can be controlled, for example, by means of measurement of distance from the web face. In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being, however, by no means supposed to be strictly confined to the details of said illustrations. Figure 1 is a schematic vertical sectional view in the machine direction of a device in accordance with the invention. Figure 2 is a schematic illustration of a device in accordance with the invention in the direction of width of the web. Figure 3 is a schematic illustration of an arrangement of the device in accordance with the invention at both sides of the web. Figure 4 is a schematic illustration of a further exemplifying embodiment of the face of the suction chamber in a device in accordance with the invention. Figure 5 shows a second further exemplifying embodiment of the face of the suction chamber in a device in accordance with the invention. In the exemplifying embodiment shown in Fig. 1, the air is passed into the dust removing device 10 along the intake air duct 11 , from which the air is passed into the blow-air chamber 13 and from it through the nozzle opening 20, as a high- pressure air jet P, towards the paper web or equivalent W. The running direction of the web W is denoted with the reference arrow S, and the air flow travelling along with the web is denoted with the reference arrow PI. The exhaust air chamber of the dust removing device 10 is denoted with the reference numeral 14, and into said chamber a vortex chamber 16 has been shaped, which produces an intensive vortex in the exhaust air chamber 14, which vortex keeps the exhaust air chamber 14 clean. From this chamber the air is passed into the exhaust air duct 15. The dust removing device 10 is placed near the web W so that a space 25 is formed, in which a vortex air flow P2 is formed by the joint effect of the dust separation blowing P at the bottom face 17 of the device and the air flow PI carried along with the web W, by means of which vortex P2 the access of dust as a leakage flow back along with the web W and, thus, into the environment is prevented. The vortex P2 is formed by means of the dust separation blowing P, by means of the air flow PI travelling along with the web W, by means of the shape of the face 17 of the suction chamber 14 of the dust removing device 10 placed facing the web W, and by means of the dimensioning of the vortex space 25, for example, by regulating the distance of the device 10 from the web W. Dust is separated from the web when a sharp air jet, a dust separation blow P, is blown out of the nozzle opening 20, which jet penetrates through the boundary layer and separates the particles of dust from the web face. The separated dust is removed into the suction chamber 14, and the air that contains dust particles is passed to cleaning, for example, in a wet separator. The blow pressure of the dust separation blowing is 2 kPa ... 50 kPa, preferably 15 kPa ... 35 kPa, for example, when the dust removing device in accordance with the invention is used for removing dust from printing papers / boards. The blow velocity to be used in the dust separation blowing P is 50...400 metres per second, preferably 50...300 metres per second. Of course, the values to be used depend on the strength of the paper web that is being run, i.e. on the intensity of blowing that the web endures and on the intensity of blowing that is necessary to separate the dust from the web face. Of course, when softer paper grades are being run, lower values are used. The vacuum in the suction chamber 14 is 0.5...6 kPa, preferably 1...3 kPa, but, of course, the values of vacuum to be used in the suction chamber also depend on the paper grade that is being run. The distance of the blow device from the web face is 1...40 mm, preferably 2...10 mm. The nozzle slot 20 is preferably adjustable so that the intensity and the direction of the dust separation blowing P can be regulated by adjusting the nozzle opening 20. If necessary, the dust removing device 10 can also be inclined, which is indicated by the arrow R, in compliance with the angle of arrival of the web W and with the grade of the web W that is being run so that an optimal cleaning result is obtained. As is shown in Fig. 2, the dust removing device 10 extends substantially across the entire width of the web W, and, if necessary, it can be bent to the desired deflected shape, for example, of the spreader rolls after a slitter. The bending can be controlled, for example, by means of measurements of distance E' from the web W face, the regulation members 40 being controlled based on the measurement results and based on the control 50 so that the dust removing device 10 is bent to the desired shape. For cleaning of the edges of the web W, it is possible to provide the ends of the dust removing device 10 with side blow nozzles, out of which the blowing PS is blown. This arrangement is particularly advantageous when a web W wider than normal is run. In the exemplifying embodiment shown in Fig. 1, the vortex P2 has been produced so that the face 17 of the dust removing device 10 that is placed facing the web and that starts from the suction chamber 14 has, in the direction of arrival of the web W, first been formed as convex towards the web W, after which there follows a linear portion, which ends in the nozzle opening 20. The vortex P2 can be intensified by also shaping the face 18 of the dust removing device 10 that defines the inlet opening 21 of the air flow PI arriving along with the web W, for example, curved, as is shown in Fig. 1. The guide face 18 can also be shaped in some other way, compare, for example, Figs. 4 and 5. In the figures, on the whole, the air flows passing in the dust removing device 10 are denoted with arrows. Fig. 3 is a schematic illustration of an exemplifying embodiment in which the dust removing devices 10 are placed at both sides of the web W. This takes place preferably so that the blow openings 20 are placed facing one another, in which case the vortex spaces 25, in which the vortex flow P2 is produced by the effect of the lower face 17 of the device 10, of the dust separation blowing P, and of the air flow P2, are placed substantially one opposite to the other. Fig. 4 shows an exemplifying embodiment of the shape of the lower face 17 of the air chamber 13 in the dust removing device 10 so as to produce a vortex P2 in the space 25. In this exemplifying embodiment, the lower face 17 has been shaped concave in relation to the web W face from the suction chamber 14 to the blow opening 20. In this exemplifying embodiment, the guide face 18 that defines the inlet opening 21 for the air flow Pi has been bent so that it is substantially L-shaped in relation to the running direction of the web W. Fig. 5 shows a second exemplifying embodiment for producing a vortex air flow P2 in the space 20, and in this exemplifying embodiment the vortex flow P2 is produced, besides by means of the dust separation blowing P, the air flow PI travelling along with the web W, and the shape of the lower face 17, also by means of a blowing P3 through the nozzle opening 27, which blowing P3 is parallel to the lower face 17 and complies with the running direction S of the web and is of a direction substantially contrary to the direction of the dust separation blowing P. In this exemplifying embodiment the lower face 17 is substantially linear, and the guide face 18 is curved but bent towards the direction of arrival S of the web W. The scope of the invention, of course, also includes embodiments in which the embodiments are connected with guide faces 18 and/or lower faces 17 of different types and shapes. Above, the invention has been described with reference to some preferred exemplifying embodiments of same only, the invention being, however, in no way supposed to be strictly confined to the details of said embodiments. For example, a vortex flow can be produced in a number of different ways, besides the exemplifying embodiments illustrated in the figures, and from the point of view of the invention it is essential to produce this vortex flow in order to increase the dust removing efficiency of the device and, at the same time, in order to control any areas of vacuum that may possible deteriorate the runnability. Many variations and modifications are possible within the scope of the inventive idea defined in the following patent claims.

Claims: Claims 1. A method in a paper machine or equivalent or in a finishing device of same for removal of dust, in which method a blowing (P) is directed at the web (W), which blowing separates dust from the web (W), and in which method a suction effect is applied to the web (W) for removal of the dust that is separated out of connection with the web, characterized in that, in the method, before the dust separating blowing (P) in the running direction of the web (W), a vortex flow (P2) is produced so as to prevent carriage of the dust into the environment and to compensate for the suction effect. 2. A method as claimed in claim 1 , characterized in that, in the method, the vortex air flow (P2) is produced by means of a joint effect of the dust separation blowing (P), of the face (17) of the dust removing device (10) placed facing the web (W), and of the air flow (PI) travelling along with the web. 3. A method as claimed in claim 1 or 2, characterized in that, in the method, the vortex flow (P2) is produced by means of a joint effect of the dust separation blowing (P), of the face of the dust removing device (10) placed facing the web (W), of the air flow (PI) travelling along with the web, and of an additional blowing (P3) produced by means of the dust removing device (10). 4. A method as claimed in any of the preceding claims, characterized in that, in the method, the vortex flow (P2) is produced at both sides of the web (W). 5. A method as claimed in any of the preceding claims, characterized in that, in the method, the distance of the dust removing device (10) from the web (W) is regulated on the basis of measurements of distance (E'). 6. A method as claimed in any of the preceding claims, characterized in that, in the method, the dust removing device (10) is inclined in the running direction of the web (W) based on the angle of arrival of the web and on the web grade to be run. 7. A device in a paper machine or equivalent or in a finishing device of same for removal of dust, in which device (10) there are blow elements (11, 13,20) for producing a blowing (P) that separates dust from the web (W) and suction elements (14, 16, 15) for producing a suction effect so as to remove the dust that is separated out of connection with the web, characterized in that the device (10) comprises an arrangement (20, 17,18) for producing a vortex flow (P2) before the dust separation blowing (P) in the running direction of the web (W) so as to prevent carriage of the dust into the environment and to compensate for the suction effect. 8. A device as claimed in claim 7, characterized in that the arrangement in the device (10) for producing the vortex air flow (P2) comprises a nozzle opening (20) for producing the blowing (P) that separates dust, a face of the dust removing device (10) placed facing the web, and a guide face (18) for directing the air flow (PI) that travels along with the web. 9. A device as claimed in claim 7 or 8, characterized in that the device (10) further comprises a nozzle opening (27) for producing an additional blowing (P3) before the nozzle opening (20) of the dust separation blowing (P) in the running direction of the web (W). 10. A device as claimed in any of the preceding claims, characterized in that the device (10) is formed as two units, placed at opposite sides of the web (W). 11. A device as claimed in any of the preceding claims, characterized in that the device comprises an arrangement (E',40',50) for measurement of the distance of the dust removing device (10) from the web (W) and for regulating the distance based on measurements (E') of the distance. 12. A device as claimed in any of the preceding claims, characterized in that the device (10) extends substantially across the entire width of the web (W).

Inventors: LEIMU JUHA, LINDSTROEM JAN, LEIMU, JUHA, LINDSTROEM, JAN
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1996
Main classification: D21G9
IPC codes: B08B5, B08B15, D21F1, D21G3, D21G9