WO1997031151A1

WO1997031151A1 - Method and device in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust separated from the web

Info

Publication number: WO1997031151A1
Application number: PCT/FI1997/000091
Authority: WO
Inventors: Jens Petter Enkvist
Original assignee: Valmet Corporation
Priority date: 1996-02-22
Filing date: 1997-02-13
Publication date: 1997-08-28
Also published as: FI960808A0; FI98389B; FI98389C

Abstract

The invention concerns a method and a device in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust and equivalent separated from the web (W). According to the invention, the space placed around the device (10) or equivalent that produces dust is encapsulated by means of a box construction (13) at least from one side of the web (W), and dust and equivalent are removed from the interior of the space provided with a box construction (13) along with the exhaust air as an exhaust air flow through an exhaust air duct (14). In the invention, the space provided with a box construction (13) is sealed, in the running direction of the web (W), at the outlet side by means of an air-curtain jet (P), which extends substantially across the entire width of the web (W).

Description

Method and device in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust separated from the web

The invention concerns a method in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust and equivalent separated from the web, in which method the space placed around the device or equivalent that produces dust is encapsulated by means of a box construction at least from one side of the web, and dust and equivalent are removed from the interior of the space provided with a box construction along with the exhaust air as an exhaust air flow through an exhaust air duct.

Further, the invention concerns a device in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust and equivalent separated from the web, which device comprises a box construction, which has been formed around the object that forms dust at least at one side of the web and which box construction is provided with an exhaust air duct for removing the dust and equivalent along with the exhaust air flow.

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 dust separated from the fibre mesh in the web and from the fillers in said mesh. The dust spreads into the environment and is partly also carried into the web reel. Also, upon manufacture of paper, dust and contaminations adhere to the face of the paper web, such as debris and fibres derived from the dryer section of the paper machine. An important source of dust is the slitting process, and dust problems also occur in the manufac- ture of tissue paper, in particular in connection with crέping by means of a doctor, wherein the paper web is separated from the face of a steam-heated yankee cylinder by means of a doctor blade, in which connection a particularly large quantity of dust is separated from the web, which dust is drawn along by the paper web and spread around into its environment.

Dust and contaminations cause problems in further processing, for example in printing, because keeping the printing rolls clean is of essential importance from the point of view of the quality of printing.

Also, dust spreads both in the paper mill and in the further processing into the environment and can involve drawbacks for occupational health, because the dust can contain various filler particles.

From the prior art, for prevention of spreading of dust, among other things, solu¬ tions are known in which the object that forms dust is encapsulated, the function of the encapsulation being to confine the detrimental dust to its site of formation. The housing can be designed mainly in two ways. Either the whole machine can be placed inside the housing, or the dust-forming part of the machine or device is placed inside the housing. From the interior of the housing, the dust is removed along with the exhaust air through the exhaust air duct. In this way, in the interior of the housing, as a rule, a vacuum arises, which may cause problems of runnability of the paper web, for example fluttering. The principle of encapsulation and the dimensioning of the air flows are known from a number of basic textbooks in this field, for example from the publications Teollisuuden kohdeilmanvaihto , VTT/Hel- sinki 1982 ('Ventilation in industrial sites', Technical Research Centre of Finland, Helsinki 1982) and Tyόpaikkojen ilmastointi , Vakuutusyhtiό Pohjola 1979 ('Air- conditioning at Working Sites', Pohjola Insurance Company, 1979).

However, by means of arrangements of encapsulation, it is not possible to remove the dust that is carried along with the air flow on the web faces or the dust adhering to the web face. For example, static electricity can affix dust to the web face. Thus, the object of the present invention is to provide a solution in which the carriage of dust and contaminations along with the web out of the housing space is eliminated or at least minimized.

It is a further object of the invention to suggest a solution by whose means the problems of runnability arising from the vacuum present in the interior of the housing space can be eliminated.

In view of achieving the objectives stated above and those that will come out later, the method in accordance with the present invention is mainly characterized in that, in the method, the space provided with a box construction is sealed, in the running direction of the web, at the outlet side by means of an air-curtain jet, which extends substantially across the entire width of the web.

On the other hand, the device in accordance with the invention is mainly character¬ ized in that the device further comprises a blow device for sealing the space pro¬ vided with a box construction by means of an air-curtain jet, and that the blow device is placed, in the running direction of the web, at the side of outlet of the web out of the space provided with a box construction.

According to the invention, an air jet that extends across the web is blown against the web, which air curtain closes the space subjected to a vacuum in the interior of the box. By means of the air jet, the housing space is sealed against the web and, moreover, the effect of the web speed on the flows is reduced significantly and any loose particles are passed into the exhaust air flow. By means of the air curtain, the vacuum in the housing space is controlled to the desired level and, moreover, by means of the air curtain it is possible to separate poorly adhering fibres from the web face.

According to a preferred further characteristic feature, by means of the air curtain jet and a guide face in the device, the air flow following along with the web can be turned towards the exhaust air flow, whereby the removal of air is enhanced. According to a second preferred further characteristic feature, static electricity is separated and removed from the web by means of a remover of static electricity, in which connection any dust particles adhering to the paper web by the effect of static electricity are also detached.

In the arrangement in accordance with the invention, the vacuum in the vacuum space is measured and the air curtain blowing is regulated based on the measurement result, so that the vacuum in the space remains at such a level that it does not cause problems of runnability. In this connection, it is also possible to take into account, for example, that in various slitters/cutters and winders/reel-ups the web speed varies periodically, for example, 0...35 metres per second, depending on the winding/ reeling stage, and based on the measurement results, by means of the air curtain blowing, the pumping effect arising from these cycles can be compensated for. The device in accordance with the invention is suitable for use in different applications in paper machines or equivalent, for example, in connection with the removing of dust from the doctors placed in the final end of the dryer section, in finishing devices, such as a slitter-winder, and/or in connection with the detaching creping doctor in a tissue paper machine and in other suitable applications in which the dust and contaminations carried along with the web or separated from the web cause problems.

In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being not supposed to be strictly confined to the details of said illustrations.

Figure 1 is a schematic illustration of an arrangement in accordance with the invention fitted in connection with a slitter.

Figure 2 is a schematic illustration of a blow device in accordance with the inven- tion. In Fig. 1 the slitter is denoted with the reference numeral 10 and the web guide rolls with the reference numerals 11 ,12. The web W runs in the direction indicated by the arrows S . The area of the slitter 10 has been encapsulated by means of a box construction 13, which housing can, if necessary, be formed as a separate box 13 of its own, or as a part/parts of the housing it is possible to use suitably placed frame constructions of the machine. In connection with the housing 13, an exhaust air duct 14 is provided, in which a suction flow is arranged by means of a blower 15, whereby the space inside the housing 13 is subjected to a vacuum. In Fig. 1 , the arrows J schematically illustrate the air flows passing in the interior space in the housing 13.

In accordance with the invention, at the outlet side of the web W in the housing 13, a blow device 20 is fitted, by whose means an air curtain jet is blown towards the web W, which curtain jet extends substantially across the entire width of the web W. The air duct in the blow device 20 is denoted with the reference numeral 21 and the connected blower with the reference numeral 22. By means of a measurement device 24, the vacuum present in the interior space in the housing 13 is measured, and by means of the regulation and control devices 23 the blower 22 of the blow device 20, and thereby the intensity of the air curtain jet blowing P, are controlled, based on the measurement results obtained with the measurement device 24, so that the vacuum in the interior of the housing 13 remains at the desired level.

Fig. 2 is a more detailed illustration of a blow air device 20, which is fitted in view of sealing the housing 13 at the side of outlet of the web W from the housing 13. The blow device 20 comprises a nozzle opening 25, out of which an air jet P is blown which extends across the web and which closes the interior vacuum space in the housing in the way of an air curtain. The air duct in the device 20 is denoted with the reference numeral 21. Into the device 20 an air flow guide face 27 is formed, by whose means the air flow J arriving along with the paper web W, which flow often contains an abundance of dust and contaminations, is turned towards the exhaust air duct 14. The device 20 can favourably also be provided with a remover of static electricity, by whose means, as is indicated by the arrow Q, static electricity is removed from the face of the web W, in which connection the dust particles adhering to the web face by the effect of static electricity are separated and carriage of said particles along with the web W is prevented by means of the air curtain P, by means of which air curtain blowing P the air flow is also turned rearwards and, thus, towards the exhaust air duct 14 (Fig. 1). Through the exhaust air duct 14 the dust is passed by means of the exhaust air to further treatment.

The device 20 in accordance with the invention extends substantially across the entire width of the web W in the cross direction of the web W.

The blow velocity of the air curtain blowing P depends on the basis weight and on the support of the web, and it can be 20...80 metres per second, preferably 30...50 metres per second, for example for a web of a weight of 150...180 grams per square metre. The blow direction can be oblique in relation to the running direction of the web, and its angle in relation to the running direction S of the web can be 30°... 90°, preferably 40°...50°.

Above, the invention has been described with reference to some preferred exemplify¬ ing embodiments of same only, the invention being, however, not supposed to be strictly confined to the details of said embodiments.

Claims

1. A method in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust and equivalent separated from the web (W), in which method the space placed around the device (10) or equivalent that produces dust is encapsulated by means of a box construction (13) at least from one side of the web (W), and dust and equivalent are removed from the interior of the space provided with a box construction (13) along with the exhaust air as an exhaust air flow through an exhaust air duct (14), characterized in that, in the method, the space provided with a box construction (13) is sealed, in the running direction of the web (W), at the outlet side by means of an air-curtain jet (P), which extends substantially across the entire width of the web (W).

2. A method as claimed in claim 1, characterized in that by means of the air curtain jet (P) the air flow which runs along with the web (W) and which contains dust and equivalent is turned towards the exhaust air duct (14), and that by means of the air curtain jet (P) dust and equivalent that adhere to the web (W) are detached.

3. A method as claimed in claim 1 or 2, characterized in that, in the method, static electricity is removed from the web (W) so as to detach dust that adheres to the web

(W) by the effect of static electricity before the air curtain blowing (P).

4. A method as claimed in any of the preceding claims, characterized in that the vacuum present in the interior space in the box construction (13) is measured and, based on the measurement results, the intensity of the air curtain jet (P) is regulated in order to keep the vacuum at the desired level.

5. A device in a paper machine or equivalent or in a finishing device of same for collecting and removing the dust and equivalent separated from the web (W), which device comprises a box construction (13), which has been formed around the object (10) that forms dust at least at one side of the web (W) and which box construction (13) is provided with an exhaust air duct (14) for removing the dust and equivalent along with the exhaust air flow, characterized in that the device further comprises a blow device (20) for sealing the space provided with a box construction (13) by means of an air-curtain jet (P), and that the blow device (20) is placed, in the running direction of the web (W), at the side of outlet of the web (W) out of the space provided with a box construction (13).

6. A device as claimed in claim 5, characterized in that the blow device (20) includes a remover of static electricity so as to remove static electricity present on the face of the web (W) and, thus, to detach dust that adheres to the web (W) by the effect of static electricity.

7. A device as claimed in claim 5 or 6, characterized in that the blow device (20) comprises a guide face (27) for turning the air flow (J_w) that flows along with the web (W) towards the exhaust air duct (14).

8. A device as claimed in any of the claims 5 to 7, characterized in that the device comprises a measurement device (24) for measurement of the vacuum present in the interior of the space (13) provided with a box construction and regulation and control devices (23) for controlling the intensity of the air curtain blowing (P) and, by means of said control, for keeping the vacuum at the desired level.