WO2015155417A1

WO2015155417A1 - Method for passing web tail from one paper machine section to another and apparatus therefor and construction thereof

Info

Publication number: WO2015155417A1
Application number: PCT/FI2015/050247
Authority: WO
Inventors: Kimmo Loippo; Antti ELO
Original assignee: Runtech Systems Oy
Priority date: 2014-04-11
Filing date: 2015-04-10
Publication date: 2015-10-15
Also published as: FI20145349A; EP3129549A1; US20170022021A1; EP3129549A4

Abstract

The invention relates to a method and apparatus for passing a web tail being threaded from one paper machine section to another by way of guiding the tail with the help of an air jet from a transfer plate (1). An essential feature of the invention is to employ a construction (3) rising from the surface (2) of the transfer plate (1) to a height (5) with the shape of a linear ramp or a droplet for guiding the web tail in its travel direction (9) thereby minimizing the contact area between the web tail and the transfer plate (1).

Description

METHOD FOR PASSING WEB TAIL FROM ONE PAPER MACHINE SECTION TO ANOTHER AND APPARATUS THEREFOR AND CONSTRUCTION THEREOF The invention relates in accordance with the preamble of claim 1 to a method for passing a web tail being threaded from one paper machine section to another by way of guiding the tail with the help of an air jet. Furthermore, the invention relates to an apparatus in accordance with the preamble of claim 9 and the construction thereof in accordance with claim 17.

Tail threading in paper/newsprint or tissue machines is typically implemented with the help of carrier ropes, vacuum-supported belt conveyors or air-assisted transfer surfaces. Of these methods, carrier ropes represent the oldest technology, whereby it also is becoming obsolete due to safety problems.

Vacuum-supported belt conveyors are technologically good and safe, but require extremely intensive care and expensive to construct and maintain. Air- assisted transfer plates are gaining ground in the market owing to their generally secure runnability as well as cost-efficient construction and use. However, their most common handicap is a relatively short rope run with respect to machine speed and wide spectrum of web types. If the machine running conditions change in regard to web speed, basis weight or other qualities, generally the system must be readjusted to minimize web broke. Details of prior-art technology are discussed in patent application FI20060757, and in patents Fl 123352 and Fl 122377.

In the art are known different kinds of arrangements aimed to improve the transfer of web tail from one machine section to the next. Conventional constructions of the prior art have been hampered by a plurality of disadvantages such as, e.g., it has been impossible to achieve a favorable air flow velocity between the transfer plates and the web tail or, alternatively, removal of blown air has disturbed the tail threading process. Resultingly, the performance of state-of-the art apparatus has not seen essential improvements. It is an object of the present invention to provide a cost-effective and

maintenance-free apparatus to perform tail threading in different paper machine sections at various speeds and web types. In practical tests it has been found necessary to create a relatively high vacuum between the web/tail and the web transfer plates by means of an air jet blown in the direction of the web travel, whereby the vacuum is preferably in the range of 5 - 300 Pa. With the help of induced vacuum, the web/tail is attracted to an immediate vicinity of the transfer plate, that is, at a distance of about 0 - 5 mm from the plate surface to the tail surface. In this fashion, the tail path can be controlled so that the tail is directed to the desired direction. As to the tail path control, a maximally high vacuum would obviously be advantageous. However, at the same time friction between the threading apparatus and the web should be minimized in order to prevent tail threading speed from falling below the running speed of the process (i.e., machine speed). Inasmuch as the tail/web transfer plate is essentially a fixed accessory while the web travels at machine speed, the mutual speed difference between their surfaces may possibly be very high at this point. Hence, it is necessary to avoid or at least minimize an intimate contact between the tail/web and the transfer plate. Friction is directly related to the attractive force of the induced vacuum and the resultant local contact between the tail/web and the transfer plate. The greater the area of the contact, the higher the generated friction. Resultingly, it is necessary to apply a larger volume and pressure of the air flow to achieve a sufficient attractive force and to compensate for the frictional force.

In regard to the above, the present invention aims to solve three problems:

1 . Minimization of possible contact surface area between the tail/web and the transfer plate.

2. Induction of a proper vacuum (5 - 300 Pa) between the tail/web and the transfer plate. 3. Generation of maximally effective transferring force on the tail/web by means of air jets.

Now the arrangement according to the invention is capable of presenting a comprehensive solution to the above-mentioned prerequisites in a single embodiment that also optimizes the operation of the apparatus. The inventiveness of the present apparatus is based on the unique arrangement of the transfer plate air ducts serving to guide and control the air flow. An essential feature of the air ducts is their entirely novel construction for threading the web tail from one machine section to the next.

More specifically, the invention is characterized by what is stated in the appended claims. In the following, the invention is described in more detail with the help of appended drawings, wherein

Figs. 1 - 5 show a simplified construction view of a transfer plate for threading a web tail from one machine section to the next; and

Figs. 6 - 18 show schematic views of different embodiments of the air duct construction according to the invention.

The arrangement illustrated in appended drawings 1 - 18 now provides a novel approach to a maximally optimal solution capable of overcoming the above- listed problems.

As shown in Figs. 1 - 5, an air duct system 3 is adapted in a transfer plate 1 further including a hole or similar nozzle acting as an air ejection opening 7, wherefrom air is directed to surface 2 of the transfer plate 1 in the travel direction 9 of the web tail. The outlet nozzle shape in the air duct system 3 resembles a frog's eye allowing the frog eye shape of openings to be called a frog eye 3. It is an essential feature of the invention that the number and placement of frog eye structures 3 in the transfer plate 1 can be varied to meet different requirements. In the configuration of Fig. 1 , frog eyes 3 are located equispaced in a row over the entire width of the transfer plate 1 . In Figs. 2A and 2B is shown a preferred embodiment having frog eyes 3 located equispaced over the entire width and length of transfer plate 1 .The frog eyes 3 are situated in rows interspaced at 5 - 150 mm over the width of plate 1 and in columns having the rows interspaced at 10 - 300 mm along the length of plate 1 . An alternative embodiment has the frog eyes 3 interspaced randomly however so that the entire area of the surface 2 of plate 1 is covered, whereby the openings are spaced in the xy-directions at 30 - 100 mm from each other.

In the embodiment variants shown in Figs. 2A and 2B, the frog eyes 3 are located in a mutually symmetric pattern, either in the tail travel direction 9 or at a desired angle thereto. In Figs. 3 and 4 is shown another variant having the frog eyes 3 located in an unsymmetrical pattern. In the variant of Fig. 3 the frog eyes 3 are formed covering only a given partial area of transfer plate 1 , while in the variant of Fig. 4 the frog eyes cover the entire area of the transfer plate, however, in groups that are placed in a dispersed fashion. In Fig. 5 are shown two connected transfer plates 1 comprised of a combination of the embodiments of Figs. 1 and 4.

Obviously, the number of these different variants and combinations can be modified in plural ways. Essential to the invention is that use of different variants or their combinations are selected to suite the point of application. A particular aim of using different variants is to achieve a significant increase in the transfer force moving the tail forward. For instance in accordance with Fig. 4, the dispersed location of air jet openings over the entire area of transfer plate 1 allows when necessary to form a substantially greater number of web-pulling air jet openings than by the configuration of Fig. 2 having straight-lined openings. Moreover, the unsymmetrical placement of openings permits increasing or decreasing the number of web-pulling points at desired locations of transfer plate 1 , whereby the pulling efficiency can be further enhanced by combining differently configured transfer plates with each other as shown in Fig. 5.

In accordance with Figs. 6 - 18 the air flow is directed with the help of the frog eye structure 3 onto the surface 2 of transfer plate 1 in an entirely novel fashion. Structure 3 begins seamlessly at point 4 on the surface 2 of transfer plate 1 and rises in the form of a linear ramp or a water droplet upward from surface 2. In the structure 3 is formed one or a plurality of holes or an equivalent nozzle serving as air exit opening 7. The exit opening 7 is shaped to meet the needs of different processes, whereby its simplest form can be a round hole, but alternatively, it can have for instance a semicircular, droplet-like, oval, triangular, square, rectangular or any other cornered shape.

As shown in Figs. 1 - 18, an essential feature of the frog eye opening is that its linearly or droplet-like ramping contour begins seamlessly 4 from surface 2 of transfer plate 1 and rises to a desired height 5 from surface 2, wherefrom its shape continues essentially parallel with the surface of transfer plate 1 and travel direction 9 of the web tail. The air exit opening 7 formed into the frog eye 3 is most advantageously located either to above the plate surface 2, parallel to the level of surface 2 or below the level of surface 2 in the fashion shown in Figs. 6, 8 and 9. An alternative embodiment is such that the frog eye 3 has a plurality of air exit openings 7, e.g., as shown in Fig. 7, both above the surface 2 of the transfer plate as well as to the underside 6 of the transfer plate surface 2. Also the frog eye 3 may possibly have, in addition to the arrangement of the embodiment, the air exit openings 7 also located to the center or any alternative way as shown in Figs. 6, 8 and 9. Hereby the air exit openings 7 may also be differently shaped at different points of the same frog eye 3. In this fashion the air exit opening(s) 7 that guide the air onto the transfer plate surface 2 can direct the air flow substantially parallel to the transfer plate 1 and travel direction 9 of the web tail. In accordance with the above discussion, the structure of frog eye 3 can be implemented such that it is located entirely flush with the surface 2 of transfer plate 1 or alternatively at the level of surface 2 of transfer plate 1 or just above thereof. An alternative embodiment has a given portion of the frog eye structure 3 situated below the underside 6 of the surface 2 of transfer plate 1 .

As shown in Fig. 6, the frog eye 3 has a height of 0.3 - 10 mm, most advantageously 3 - 6 mm with a width of 2 - 10 mm, most advantageously 3 - 8 mm and a length of 2 - 150 mm, most advantageously 10 - 50 mm. The shape shall be such that starts seamlessly 4 from surface 2 of transfer plate 1 and rises as a linear ramp or a droplet to form a frog eye 3, preferably with a round contour to a desired height 5. The diameter of the air exit opening 7 is 0.5 - 5 mm, most advantageously 1 - 3 mm, most preferably located in the center of frog eye 3. As described above, the number and shape of air exit openings 7 in frog eye 3 can be varied to meet different requirements. As shown in Figs. 10 - 14, the number of air exit openings 7 in a single frog eye 3 can be one or a plurality of, whereby their shape can be slit-like, circular, oval or fanned. The shape of air exit opening 7 may be different as seen from the air inlet side compared with the shape at the air exit. For instance, the inlet side opening can be shaped as a single larger hole, while the exit opening of the same air duct may be spread laterally in a fan-like fashion into a oval opening.

Analogously, the shape of frog eye 3 proper illustrated in Figs. 6 - 18 may be varied. As seen from the direction of air exit opening 7, it may have a semicircular, circular, droplet-like or oval shape, while alternatively it can have a triangular, square or other cornered shape.

More particularly, the shape of frog eye 3 and location of air exit opening 7 are dictated by the requirements posed by a specific application. One particularly advantageous embodiment is the frog eye 3 shown in Figs. 14 and 15 having a substantially droplet-like shape. This embodiment is with a high probability the most optimal transfer plate arrangement in regard to controlling the air flow. The slanting angle of the frog eye outer surface with respect to the surface of transfer plate 2 may vary within 10 - 170 deg., most advantageously within 45 - 135 deg. An entirely droplet-like contour is achieved by making the outer surface of frog eye 3 continuously curved.

In the embodiment according to the invention, air flow from frog eye 3 is directed essentially immediately onto the surface of transfer plate 2, parallel to the transfer plate 1 and the travel direction 9 of the web tail as seen from aside the plate. Correspondingly as seen from above the transfer plate 1 , the air flow exits from frog eye 3 essentially directly onto the transfer plate surface 2, either parallel thereto or inclined to transfer plate 1 and the web tail travel direction by -60 - +60 deg., most advantageously by -45 - +45 deg. As shown in Figs. 16 - 18, the openings of frog eye 3 are drilled at different angles from two directions, i.e., from below 10 and from above 2 of transfer plate 1 . Resultingly, the opening as seen from above 2 of the transfer plate is either parallel to the plate or slightly inclined to the plate 1 by -10 - +10 deg., most advantageously by -5 - +5 deg., while as seen from below 10 of the transfer plate the opening is inclined by 10 - 170 deg. to the transfer plate, most advantageously by 45 - 135 deg. The opening is continued as a duct through the frog eye 3 ending as an air exit opening 7 on the transfer plate surface 2. In this fashion the present arrangement can substantially improve directional injection of the air flow parallel to the transfer plate surface.

According to the invention it is now possible to use a larger air volume and/or speed to create a vacuum. Resultingly, the present arrangement can reduce the effect of friction by way of minimizing the area of contacting surface with the help of higher vacuum. Also the distance of the web tail from the transfer plate surface 2 can be controlled accurately. The web tail makes contact only with the highest point 5 of frog eyes 3 inasmuch as the spaces between the web tail and the transfer plate 1 are filled with the air flow exiting from the frog eyes. In the manner described above the arrangement according to the invention now is capable of overcoming the three problems listed earlier. Firstly, the area occupied by frog eye 3 seen from above transfer plate 1 is extremely small, whereby the possibly occurring area of contact between the web and the transfer plate remains minimal. Resultingly, as the contact area between the web tail and the transfer plate is minimized, this represents one of the essential features included in the arrangement according to the invention. A second essential feature of the invention comprises creating an advantageous level of vacuum at 5 - 300 Pa between the web tail and transfer plate 1 . The vacuum between the web tail and transfer plate is dictated by the air flow, i.e., the differential speed of air flow with regard to the web tail speed and amount of injected air. Owing to the structure of frog eye 3, the invention permits the use of a higher air flow rate or speed to establish a greater vacuum. In contrast, arrangements according to prior art inject the air flow from air exit openings at an angle from the transfer table surface. As a consequence, a portion of the air flow induces a lifting effect off the transfer plate on the web tail, while only the remaining portion serves to pull the web tail in the downstream direction of the transfer plate and create a vacuum.

Thirdly, the invention is characterized by providing a maximally great forward- pulling force on the web tail with the help of directed air flow. An essential feature herein is to direct the air flow parallel to surface 2 of transfer plate 1 . This can be achieved by locating frog eyes 3 over the entire surface of transfer plate 1 either in an equidistantly spaced, unsymmetrical and/or in a dispersed fashion or only on a selected area of transfer plate 1 .

The arrangement according to the invention offers essential improvements in regard with prior-art constructions wherein air is ejected through the transfer plate via holes drilled at an acute angle thereto.

Claims

WHAT IS CLAIMED IS:

1. A method for passing a web tail being threaded from one section to another by way of guiding the tail with the help of an air jet from a transfer plate (1 ), characterized in that an air exit structure (3) rising from the surface (2) of the transfer plate (1 ) to a height (5) with the shape of a linear ramp or a droplet guides the web tail in its travel direction (9) thereby minimizing the contact area between the web tail and the transfer plate (1 ).

2. The method of claim 1 , characterized in that, from one or more air exit openings (7) of a frog eye structure (3) arising seamlessly (4) from transfer plate surface (2), the air flow is directed essentially parallel (9) to the web tail travel direction, whereby simultaneously is created an advantageous level of vacuum at 5 - 300 Pa between the web tail and transfer plate (1 ) so that with the help of the vacuum the web tail is kept in the immediate vicinity of surface (2) of the transfer plate (1 ), most advantageously at a distance of about 0 - 5 mm.

3. The method of claim 1 or 2, characterized in that onto the transfer plate (1 ) are formed a plurality of frog eyes (3) suited to create a maximally high air flow released from air exit openings (7) serving to transfer the web tail forward, whereby the height (5) of frog eye (3) is 0.3 - 10 mm, most advantageously 3 - 6 mm, with a width of 2 - 10 mm, most advantageously 3 - 8 mm and, in the web tail travel direction (9) over transfer plate (1 ), a length of 2 - 150 mm, most advantageously 10 - 50 mm, whereby the frog eye (3) has an essentially droplet-like shape wherein the angle of its slanting surface in respect to surface (2) of transfer plate (1 ) is 10 - 170 deg., most advantageously 45 - 135 deg.

4. The method of claim 3, characterized in that as seen from above the transfer plate (1 ), the air flow exits from frog eye (3) essentially directly onto surface (2) of transfer plate (1 ), either parallel thereto or inclined to transfer plate (1 ) and the web tail travel direction (9) by -60 - +60 deg., most

advantageously by -45 - +45 deg.

5. The method of any of claims 1 - 4, characterized in that the frog eyes (3) are located on surface (2) of the transfer plate (1 ) interspaced apart from each other by 5 - 150 mm laterally and by 10 - 300 mm longitudinally either in an equispaced, unsymmetrical and/or dispersed fashion in the xy-directions at a distance of 30 - 100 mm from each other, either over the entire area or only a given partial area of one or a plurality of transfer plates (1 ).

6. The method of any of claims 1 - 5, characterized in that from the air exit openings (7) the air flow is directed essentially parallel to the web tail travel direction (9) so that the frog eyes (3) are formed either essentially flush with the level of surface (2) of the transfer plate (1 ) or just above the same or, alternatively, a portion of the frog eye structure (3) extends below (6) the surface (2) of transfer plate (1 ).

7. The method of any of claims 1 - 6, characterized in that the air flow is directed out from one or a plurality of air exit openings (7) of the frog eye (3) so that one or more of the openings (7) are formed either flush with the level of surface (2) of the transfer plate (1 ) or above the same or alternatively and/or below (6) the surface (2) of transfer plate (1 ).

8. The method of any of claims 1 - 7, characterized in that, in order to improve the direction of the air flow parallel (9) to the surface (2) of the transfer plate (1 ), into the frog eye (3) are formed openings from two directions, i.e., from below (10) and from above (2) of the transfer plate (1 ) so that one opening situated above surface (2) is aligned either parallel to the transfer plate (1 ) or at an angle of -10 - +10 deg. to the plate (1 ), most advantageously -5 - +5 deg., while as seen from below (10) of the transfer plate the other opening is inclined by 10 - 170 deg. to the plane of the transfer plate (1 ), most advantageously by 45 - 135 deg., whereafter the air flow path is continued as a duct through the frog eye (3) ending as an air exit opening (7) on the surface (2) of the transfer plate (1 ).

9. An apparatus for passing a web tail being threaded from one paper machine section to another by way of guiding the tail with the help of an air jet from a transfer plate (1 ), characterized by having an air exit structure (3) adapted thereto rising from the surface (2) of the transfer plate (1 ) to a height (5) with the shape of a linear ramp or a droplet, said structure guiding the web tail in its travel direction (9) thereby minimizing the contact area between the web tail and the transfer plate (1 ).

10. The apparatus of claim 9, characterized by having onto the surface (2) of transfer plate (1 ) seamlessly (4) rising from said surface (2) adapted a frog eye structure (3) incorporating one or more air exit openings (7) , wherefrom an air flow is directed essentially parallel (9) to the web tail travel direction, whereby simultaneously is created an advantageous level of vacuum at 5 - 300 Pa between the web tail and transfer plate (1 ) so that with the help of the vacuum the web tail is kept in the immediate vicinity of surface (2) of the transfer plate (1 ), most advantageously at a distance of about 0 - 5 mm.

1 1 . The apparatus of claim 9 or 10, characterized by having onto the transfer plate (1 ) formed a a plurality of frog eyes (3) suited to create a maximally high air flow released from air exit openings (7) serving to transfer the web tail forward, whereby the height (5) of frog eye (3) is 0.3 - 10 mm, most advantageously 3 - 6 mm with a width of 2 - 10 mm, most advantageously 3 - 8 mm and, in the web tail travel direction (9) over transfer plate (1 ), a length of 2 - 150 mm, most advantageously 10 - 50 mm, whereby the frog eye (3) has a dropletlike shape wherein the angle of its slanting surface in respect to surface (2) of transfer plate (1 ) is 10 - 170 deg., most advantageously 45 - 135 deg.

12. The apparatus of claim 1 1 , characterized by having, as seen from above the transfer plate (1 ), the air flow exiting from frog eye (3) is essentially directed onto surface (2) of transfer plate (1 ), either parallel thereto or inclined to transfer plate (1 ) and the web tail travel direction (9) by -60 - +60 deg., most

advantageously by -45 - +45 deg.

13. The apparatus of any of claims 9 - 12, characterized by having the frog eyes (3) located on surface (2) of the transfer plate (1 ) interspaced apart from each other by 5 - 150 mm laterally and by 10 - 100 mm longitudinally either in an equispaced, unsymmetrical and/or dispersed fashion in the xy-directions at a distance of 30 - 100 mm from each other, either over the entire area or only a partial area of one or a plurality of transfer plates (1 ).

14. The apparatus of any of claims 9 - 13, characterized by having the air flow released from the air exit openings (7) directed essential parallel to the web tail travel direction (9) so that the frog eyes (3) are formed either essentially flush with the level of surface (2) of the transfer plate (1 ) or just above the same or alternatively and/or below (6) the surface (2) of transfer plate (1 ).

15. The apparatus of any of claims 9 - 14, characterized by having the air flow directed out from one or a plurality of air exit openings (7) of the frog eye (3) so that one or more of the openings (7) are formed either flush with the level of surface (2) of the transfer plate (1 ) or above the same or, alternatively, a portion of the frog eye structure (3) extends below (6) the surface (2) of transfer plate (1 ).

16. The apparatus of any of claims 9 - 15, characterized by having into the frog eye (3) formed openings from two directions, i.e., from below (10) and from above (2) of the transfer plate (1 ) so that one opening on the surface (2) is aligned either parallel to the transfer plate (1 ) or at an angle of -10 - +10 deg. , most advantageously -5 - +5 deg., while as seen from below (10) of the transfer plate the other opening is inclined by 10 - 170 deg. to the plane of the transfer plate (1 ), most advantageously by 45 - 135 deg., whereafter the air flow is continued as a duct through the frog eye (3) ending as an air exit opening (7) on the surface (2) of the transfer plate (1 ).

17. A construction (3) of a transfer plate (1 ) for passing a web tail being threaded from one paper machine section to another by way of guiding the tail with the help of an air jet from a transfer plate (1 ), characterized by having an air guiding construction (3) adapted thereto rising from the surface (2) of the transfer plate (1 ) to a height (5) with the shape of a linear ramp or a droplet, said construction guiding the web tail in its travel direction (9) thereby minimizing the contact area between the web tail and the transfer plate (1 ).

18. The construction of claim 17, characterized by having onto the surface (2) of transfer plate (1 ) seamlessly rising from said surface (2) adapted a frog eye construction (3) incorporating one or more air exit openings (7) , wherefrom an air flow is directed essentially parallel (9) to the web tail travel direction, whereby simultaneously is created an advantageous level of vacuum at 5 - 300 Pa between the web tail and transfer plate (1 ) so that with the help of the vacuum the web tail is kept in the immediate vicinity of surface (2) of the transfer plate (1 ), most advantageously at a distance of about 0 - 5 mm.

19. The construction of claim 17 or 18, characterized by having onto the transfer plate (1 ) formed a plurality of frog eye constructions (3) suited to create a maximally high air flow released from air exit openings (7) serving to transfer the web tail forward, whereby the height (5) of frog eye (3) is 0.3 - 10 mm, most advantageously 3 - 6 mm with a width of 2 - 10 mm, most advantageously 3 - 8 mm and, in the web tail travel direction (9) over transfer plate (1 ), a length of 2 - 150 mm, most advantageously 10 - 50 mm, whereby the frog eye (3) has a droplet-like shape wherein the angle of its slanting surface in respect to surface (2) of transfer plate (1 ) is 10 - 170 deg., most advantageously 45 - 135 deg.

20. The construction of claim 19, characterized by having, as seen from above the transfer plate (1 ), the air flow exiting from frog eye construction (3) is essentially directed onto surface (2) of transfer plate (1 ), either parallel thereto or inclined to transfer plate (1 ) and the web tail travel direction (9) by -60 - +60 deg., most advantageously by -45 - +45 deg.

21 . The construction of any of claims 17 - 20, characterized by having the frog eye constructions (3) located on surface (2) of the transfer plate (1 ) interspaced apart from each other by 5 - 150 mm laterally and by 10 - 300 mm longitudinally either in an equispaced, unsymmetrical and/or dispersed fashion in the xy- directions at a distance of 30 - 100 mm from each other, either over the entire area or only a given partial area of one or a plurality of transfer plates (1 ).

22. The construction of any of claims 17 - 21 , characterized by having the air flow released from the air exit openings (7) directed essential parallel to the web tail travel direction (9) so that the frog eye constructions (3) are formed either essentially flush with the level of surface (2) of the transfer plate (1 ) or just above the same or, alternatively, a portion of the frog eye structure (3) extends below (6) the surface (2) of transfer plate (1 ).

23. The construction of any of claims 17 - 22, characterized by having the air flow directed out from one or a plurality of air exit openings (7) of the frog eye construction (3) so that one or more of the openings (7) are formed either flush with the level of surface (2) of the transfer plate (1 ) or above the same or alternatively and/or below (6) the surface (2) of transfer plate (1 ).

24. The construction of any of claims 17 - 23, characterized by having into the frog eye construction (3) formed openings from two directions, i.e., from below (10) and from above (2) of the transfer plate (1 ) so that one opening on the surface (2) is aligned either parallel to the transfer plate (1 ) or at an angle of -10 - +10 deg., most advantageously -5 - +5 deg., while as seen from below (10) of the transfer plate (1 ) the other opening is inclined by 10 - 170 deg. to the plane of the transfer plate (1 ), most advantageously by 45 - 135 deg. , whereafter the air flow is continued as a duct through the frog eye (3) ending as an air exit opening (7) on the surface (2) of the transfer plate (1 ).