REMOVING AND COLLECTING DUST FROM TRAVELING MATERIAL
United States Patent 3775806
Apparatus for removing and collecting dust from a travelling sheet or web of material including a blow box having means for impinging jets of clean air against the sheet in directions both in the direction of travel of the sheet and opposite thereto. A suction box cooperates with the blow box to form suction gaps withdrawing the air after its engagement with the material to thereby remove the dust from the material. The suction in the suction box is sufficient to withdraw additional air from the surrounding atmosphere through the spaces which exist between the material and the suction box, and means is provided to remove the dust from the air withdrawn by the suction box. An alternate embodiment provides guide elements in the suction gaps which support the material at these points through a film of air.
US Patent References:
Method and apparatus for stabilizing an air-borne web
Wallin et al. - January 1966 - 3231165
Method for drying fibrous sheet material
Dungler - April 1952 - 2590849
Pneumatic dust removal machine
Hollick - July 1950 - 2515223
Coating glass sheets
Shoemaker - December 1940 - 2224236
Method and apparatus for stabilizing an air-borne web
Wallin et al. - January 1966 - 3231165
Method for drying fibrous sheet material
Dungler - April 1952 - 2590849
Pneumatic dust removal machine
Hollick - July 1950 - 2515223
Coating glass sheets
Shoemaker - December 1940 - 2224236
Inventors:
Olbrant, Goran (Farsta, SW)
Citron, Bengt (Vendelso, SW)
Rosby, Sven-olof (Vaxjo, SW)
Sandblad, Krister (Vaxjo, SW)
Citron, Bengt (Vendelso, SW)
Rosby, Sven-olof (Vaxjo, SW)
Sandblad, Krister (Vaxjo, SW)
Application Number:
05/199112
Publication Date:
12/04/1973
Filing Date:
11/16/1971
View Patent Images:
Export Citation:
Assignee:
Aktiebolaget, Svenska Flaktfabriken (Stockholm, SW)
Primary Class:
Other Classes:
15/345, 15/347
International Classes:
A47L7/00; B08B5/04; B41F23/00; D06G1/00; D21F5/00; B08B5/00; A47L9/10; A47L5/38; A47L5/14
Field of Search:
15/301,303,36A,307,308,309,312,345,346
Primary Examiner:
Morse Jr., Wayne A.
Assistant Examiner:
Moore C. K.
Parent Case Data:
The present application is a continuation-in-part of the co-pending U. S. application of the same inventors, Ser. No. 11,755 filed Feb. 16, 1970 and entitled "Arrangement for Sucking Dust from Web Material", now abandoned.
Claims:
We claim
1. Apparatus for sucking dust from horizontally traveling material in sheet or web form by simultaneously blowing on clean air and sucking off dust-laden air adjacent the surface of the material, comprising a suction box extending across the width of the material in its path of travel, a fixed wall substantially parallel to and adjacent the path of travel of the material, said wall being coextensive in length with said box and cooperating with said box to provide at opposite sides of said wall suction gaps extending across said path of travel, said fixed wall having at least three rows of blow openings for blowing jets of clean air between the path of travel and the fixed wall, said rows being parallel to said suction gaps, said jets having their horizontal components substantially parallel to the wall and to the direction of motion of said sheet, said jets being directed in opposite directions concurrent and countercurrent to the direction of travel of the material respectively, the jets in the two outermost of said rows having a minimum vertical component to blow jets of air substantially parallel to the direction of motion of the material, the jets in the central row having a sharp angular vertical component to project jets of air to impinge against the confronting surface of the material at a substantial angle so as to dislodge dust from the surface layer of said material to improve the dust removal effect, said intermediate row including openings directed in opposite directions to provide horizontal components paralleling the direction of movement, and means to withdraw said blown air through said suction gaps including a filter to collect the dust from said withdrawn air, said withdrawing means operating to withdraw a quantity of air greater than the air supplied through said jet means whereby ambient air is drawn into said air gap from the side of the box remote from said fixed wall.
2. Apparatus for sucking dust from horizontally traveling material in sheet or web form by simultaneously blowing on clean air and sucking off dust-laden air adjacent the surface of the material, comprising a suction box extending across the width of the material in its path of travel, said box including side walls disposed substantially perpendicular to the plane of the traveling material, a fixed wall substantially parallel to and adjacent the path of travel of the material, said wall being coextensive in length with said box and having side edges spaced from the side walls of said box to provide at opposite sides of said wall suction gaps extending across said path of travel, guide means overlying said suction gaps spaced intermediate said side walls and said side edges to project above the same below the path of travel of the material, said fixed wall having means for blowing jets of clean air between the path of travel and the fixed wall substantially parallel to the same and to the direction of motion of said sheet, said jets having their horizontal components directed in opposite directions concurrent and countercurrent to the direction of travel of the material respectively, and means to withdraw said blown air through said suction gaps including a filter to collect the dust from said withdrawn air, said guide means deflecting at least a substantial portion of said blown air downwardly into said suction gaps, said withdrawing means operating to withdraw a quantity of air greater than the air supplied through said jet means whereby ambient air is drawn into said air gap from the side of the box remote from said fixed wall said guide means also cooperating with said side walls to direct ambient air into said suction gaps.
3. Apparatus according to claim 2 wherein said guide means comprise cylindrical elements operable to assist in the provision of a film of air intermediate said guide means and the material to support the latter in its path of travel without scraping engagement with the apparatus.
4. Apparatus according to claim 2 wherein said side walls disposed to terminate in lips which are adjustable toward and away from said path of travel of the material to thereby vary the clearance for the admission of ambient air into said suction gaps.
5. Apparatus according to claim 4 wherein said lips are turned at an angle to assist in the deflection of ambient air into said suction gaps.
1. Apparatus for sucking dust from horizontally traveling material in sheet or web form by simultaneously blowing on clean air and sucking off dust-laden air adjacent the surface of the material, comprising a suction box extending across the width of the material in its path of travel, a fixed wall substantially parallel to and adjacent the path of travel of the material, said wall being coextensive in length with said box and cooperating with said box to provide at opposite sides of said wall suction gaps extending across said path of travel, said fixed wall having at least three rows of blow openings for blowing jets of clean air between the path of travel and the fixed wall, said rows being parallel to said suction gaps, said jets having their horizontal components substantially parallel to the wall and to the direction of motion of said sheet, said jets being directed in opposite directions concurrent and countercurrent to the direction of travel of the material respectively, the jets in the two outermost of said rows having a minimum vertical component to blow jets of air substantially parallel to the direction of motion of the material, the jets in the central row having a sharp angular vertical component to project jets of air to impinge against the confronting surface of the material at a substantial angle so as to dislodge dust from the surface layer of said material to improve the dust removal effect, said intermediate row including openings directed in opposite directions to provide horizontal components paralleling the direction of movement, and means to withdraw said blown air through said suction gaps including a filter to collect the dust from said withdrawn air, said withdrawing means operating to withdraw a quantity of air greater than the air supplied through said jet means whereby ambient air is drawn into said air gap from the side of the box remote from said fixed wall.
2. Apparatus for sucking dust from horizontally traveling material in sheet or web form by simultaneously blowing on clean air and sucking off dust-laden air adjacent the surface of the material, comprising a suction box extending across the width of the material in its path of travel, said box including side walls disposed substantially perpendicular to the plane of the traveling material, a fixed wall substantially parallel to and adjacent the path of travel of the material, said wall being coextensive in length with said box and having side edges spaced from the side walls of said box to provide at opposite sides of said wall suction gaps extending across said path of travel, guide means overlying said suction gaps spaced intermediate said side walls and said side edges to project above the same below the path of travel of the material, said fixed wall having means for blowing jets of clean air between the path of travel and the fixed wall substantially parallel to the same and to the direction of motion of said sheet, said jets having their horizontal components directed in opposite directions concurrent and countercurrent to the direction of travel of the material respectively, and means to withdraw said blown air through said suction gaps including a filter to collect the dust from said withdrawn air, said guide means deflecting at least a substantial portion of said blown air downwardly into said suction gaps, said withdrawing means operating to withdraw a quantity of air greater than the air supplied through said jet means whereby ambient air is drawn into said air gap from the side of the box remote from said fixed wall said guide means also cooperating with said side walls to direct ambient air into said suction gaps.
3. Apparatus according to claim 2 wherein said guide means comprise cylindrical elements operable to assist in the provision of a film of air intermediate said guide means and the material to support the latter in its path of travel without scraping engagement with the apparatus.
4. Apparatus according to claim 2 wherein said side walls disposed to terminate in lips which are adjustable toward and away from said path of travel of the material to thereby vary the clearance for the admission of ambient air into said suction gaps.
5. Apparatus according to claim 4 wherein said lips are turned at an angle to assist in the deflection of ambient air into said suction gaps.
Description:
The present invention relates to apparatus for removing and collecting dust from the surface of a sheet or web of material such as paper and the like. The invention has particular application to material which is sensitive to the touch such as materials which have coatings or a surface texture which may be damaged if it rubs against the apparatus as it is advanced therethrough.
The present invention utilizes principles disclosed in U. S. Pat. No. 3,231,165 issued Jan. 25, 1966, wherein oppositely-directed jets of gaseous medium are impinged against a travelling web to stabilize the travelling material against fluttering as it is treated by the gaseous medium.
In the industrial treatment of sheet material, for example in cutting machines, printers and rewinders for paper, problems arise because of dust formation on the surface. Not only does the dust formation reduce the quality of the product, but in certain cases it also gives rise to interruptions in the treatment of the material by clogging the machines used. Special dust-removing apparatus has been used with varying success, but it has been virtually impossible to use such conventional apparatus for elimination of dust from continuously-running webs of material which are sensitive to the touch, inasmuch as such apparatus permits rubbing of the material against the nozzle or other projecting parts uncontrolledly.
The present invention provides apparatus for sucking the dust off from the web or sheet and simultaneously stabilizing the web or sheet spaced from the stationary apparatus at the optimum distance for achieving the best possible dust removal effect.
In particular, the primary object of the invention is characterized by a blow box having at least one row of blow jets, preferably openings of the eyelid type, extending transverse to the path of travel of the material. The openings are disposed within a fixed wall parallel to and adjacent the path of the material. The blow box is connected with means for supplying clean air at a sufficient quantity to blow jets of air between the material and the fixed wall substantially parallel to the direction of motion of the material so as to impinge against the material with a scrubbing effect. Removal of the dust is effected by a suction box having a suction gap parallel with the blow openings immediately adjacent the blow box to thereby achieve effective dust removal in combination with an effective stabilization of the material at the proper spacing relative to the fixed plane.
More specifically the present invention provides blow openings to project the jets of air both in the direction of motion of the material and in the direction opposite thereto and the suction gaps are disposed both in advance and behind the blow box.
In accordance with another feature, means is provided to admit atmospheric air into the suction boxes in amounts regulated to insure non-engagement of the travelling material with the stationary parts of the suction and blow boxes and to provide a film of air which separates the film from the fixed elements of the apparatus.
All of the objects of the invention are more fully set forth hereinafter with reference to the accompanying drawing wherein:
FIG. 1 is a longitudinal sectional view along the direction of travel of the material illustrating the blow box and suction box in cross section as seen from the line 1--1 of FIG. 2;
FIG. 2 is a plan view illustrating the blow openings and suction gaps as seen from the line 2--2 in FIG. 1;
FIG. 3 is a view partially in section illustrating the combined blow box and suction box and the respective connections to sources of pressure and suction, including the means to collect the dust removed from the material; and
FIG. 4 is a view similar to FIG. 1 illustrating the modified embodiment of the combined blow box and suction box made in accordance with the invention.
Referring to the drawing, the material 1 to be cleaned of dust, as shown in the embodiment of FIGS. 1 to 3, inclusive may consist of a continuous web of material being advanced as indicated by the arrow 1a along a predetermined path of travel. However the material may also be individual sheets which are fed along the path of movement. A fixed wall 2 is disposed parallel to and adjacent the path of movement of the material 1 so as to be disposed in confronting relation with the surface of the web or sheets transported therein. The wall is provided with means for projecting jets of clean air against the confronting surface of the material, in the present instance three rows of blow openings 3 which extend transverse to the web 1. The blow openings 3 located in the outermost rows 3a blow air jets between the web and the fixed wall substantially parallel to the direction of motion of the web, thereby to position the web in the predetermined path of travel. The blow openings 3 in the row 3b between the outermost rows 3a are adapted to eject air jets in directions having a greater inclination to the web than the first mentioned jets so as to penetrate into the surface layer of the web and release dust therefrom, thereby contributing to an improvement of the dust removal effect. The openings in the row 3b are alternately turned in opposite directions parallel to the travel of the web, blowing jets both in the direction of travel and oppositely thereto.
The blow openings 3 in the wall 2 are in communication by way of a blow box 4 with air supply means operable to supply pressurized clean air to the blow box. As shown in FIG. 3, the connection is by way of a duct 12 to a blower 13 having a motor 14 and a pressure regulator 15 in the suction side of the blower. The pressure regulator 15 has an operator 16 to adjust the pressure and quantity of the clean air supplied to the blow box 4. In this manner, jets of pressurized clean air are impinged against the confronting surface of the material 1 and the dust in the surface layer is removed by the parallel flow of clean air generated by the rows 3a between the wall 2 and the material 1.
In order to collect the dust removed from the surface layer of the material 1 and to prevent the redepositing of the dust onto the web or sheets of material, suction gaps 5 are provided on both sides of the fixed wall 2, as seen in the direction of motion of the material. The suction gaps 5 are defined between the leading and trailing ends of the fixed wall 2 and upstanding walls 7 of a suction box 6 which surrounds the blow box 4 and is in communication with a source of suction. As shown in FIGS. 1 and 3, the suction box is connected by ductwork 17 to a filter 18 having removable filter cartridges 19 therein. Air is drawn through the filter 18 by a blower 23 having a motor 24 and a pressure regulator 25 with an operator 26. Thus operation of the blower 23 withdraws the dust-laden air from between the wall 2 and the material 1 into the filter 18 where the dust particles are collected, for example by the cartridges 19.
The wall 2 along its edges adjoining the suction gaps 5, is beveled as indicated at 2a at approximately 15° to facilitate the deflection of air and dust into the suction gaps. The walls 7, in the illustrated embodiment, may be raised and lowered to adjust the distance between the upper edge of the wall and the material in accordance with the flow of air and the character of the material. Preferably the suction provided by the blower 23 operates to withdraw a greater quantity of air than is supplied by the blower 13 so that substantially all of the air impinged against the web from the openings 3 is drawn into the suction gap along with atmospheric air from the other side of the upright walls 7. The flow of air over the tops of the walls 7 is facilitated by the inturned lips 27 on the walls. The flow of air forms a cushion which resists displacement of the material into scraping engagement with the wall 7, thereby avoiding the possibility of damage to the material from such engagement, for example when the character of the surface of the web is sensitive to the touch, as, for example, undried coatings.
It should be noted that by the use of the eyelid shape openings in the upper wall 2, arranged as set forth, the material is conveyed in its path of travel substantially free from fluttering. The form of the openings 3 insures the scrubbing action of the air jets impinging against different spots of the travelling material surface, thereby scrubbing the surface free from lint and dust and simultaneously conveying the lint and dust away from the surface. By controlling the position of the walls 7 and the pressure and suction of the blowers 13 and 23, effective collection of the dust removed from the surface layer of the material is obtained.
To further insure against scraping engagement of the material with the walls 7, a modified embodiment of the invention has been provided, as shown in FIG. 4. In this embodiment, the blow box 4a and its connection to the pressurized clean air is identical to the blow box 4. The suction box 36 has been modified as indicated but its connection to the suction and collecting arrangement is identical to the previously-described embodiment, as indicated at 17a.
In accordance with this embodiment of the invention, the suction box 36 is provided with upstanding adjustable walls 37 which terminate at their upper extremities in outturned lips 38. The lips 38 cooperate with guiding means 39 in the form of fixed tubes or bars extending transversely with respect to the direction of movement of the material. The guide elements 39 are preferably circular in cross section and are not mounted for rotation. Their position overlying the suction gap 35 between the blow box 4a and the wall 37 generates a film of air indicated at 40 between the guiding means 39 and the material. This film of air separates the material from the guiding means and is effective to "lubricate" the material passing the guiding means.
The guiding means 39 also serve to deflect a major portion of the air discharged from the space between the blow box 4a and the material into the suction gap 35 so as to avoid any tendency of the major part of the air to follow along the path of movement of the material. The outturned lips 38 cooperate with the guiding means 39 to facilitate the injection of atmospheric air into the suction box to insure against discharge of dust-laden air into the surrounding atmosphere. The walls 37 are adjustable similarly to the walls 7 of the previous embodiment for the same purpose.
While particular embodiments of the present invention have been herein illustrated and described, it is not intended to limit the invention to such disclosure but changes and modifications may be made therein and thereto without departure from the invention, as defined in the following claims.
An advantage for the embodiment of the present invention is that -- due to the stabilizing effect of the jets of the used gaseous medium -- there is no need for a stretching of the web, even if the material of the web is thin and very fragile, for instance consists of tissue.
The present invention utilizes principles disclosed in U. S. Pat. No. 3,231,165 issued Jan. 25, 1966, wherein oppositely-directed jets of gaseous medium are impinged against a travelling web to stabilize the travelling material against fluttering as it is treated by the gaseous medium.
In the industrial treatment of sheet material, for example in cutting machines, printers and rewinders for paper, problems arise because of dust formation on the surface. Not only does the dust formation reduce the quality of the product, but in certain cases it also gives rise to interruptions in the treatment of the material by clogging the machines used. Special dust-removing apparatus has been used with varying success, but it has been virtually impossible to use such conventional apparatus for elimination of dust from continuously-running webs of material which are sensitive to the touch, inasmuch as such apparatus permits rubbing of the material against the nozzle or other projecting parts uncontrolledly.
The present invention provides apparatus for sucking the dust off from the web or sheet and simultaneously stabilizing the web or sheet spaced from the stationary apparatus at the optimum distance for achieving the best possible dust removal effect.
In particular, the primary object of the invention is characterized by a blow box having at least one row of blow jets, preferably openings of the eyelid type, extending transverse to the path of travel of the material. The openings are disposed within a fixed wall parallel to and adjacent the path of the material. The blow box is connected with means for supplying clean air at a sufficient quantity to blow jets of air between the material and the fixed wall substantially parallel to the direction of motion of the material so as to impinge against the material with a scrubbing effect. Removal of the dust is effected by a suction box having a suction gap parallel with the blow openings immediately adjacent the blow box to thereby achieve effective dust removal in combination with an effective stabilization of the material at the proper spacing relative to the fixed plane.
More specifically the present invention provides blow openings to project the jets of air both in the direction of motion of the material and in the direction opposite thereto and the suction gaps are disposed both in advance and behind the blow box.
In accordance with another feature, means is provided to admit atmospheric air into the suction boxes in amounts regulated to insure non-engagement of the travelling material with the stationary parts of the suction and blow boxes and to provide a film of air which separates the film from the fixed elements of the apparatus.
All of the objects of the invention are more fully set forth hereinafter with reference to the accompanying drawing wherein:
FIG. 1 is a longitudinal sectional view along the direction of travel of the material illustrating the blow box and suction box in cross section as seen from the line 1--1 of FIG. 2;
FIG. 2 is a plan view illustrating the blow openings and suction gaps as seen from the line 2--2 in FIG. 1;
FIG. 3 is a view partially in section illustrating the combined blow box and suction box and the respective connections to sources of pressure and suction, including the means to collect the dust removed from the material; and
FIG. 4 is a view similar to FIG. 1 illustrating the modified embodiment of the combined blow box and suction box made in accordance with the invention.
Referring to the drawing, the material 1 to be cleaned of dust, as shown in the embodiment of FIGS. 1 to 3, inclusive may consist of a continuous web of material being advanced as indicated by the arrow 1a along a predetermined path of travel. However the material may also be individual sheets which are fed along the path of movement. A fixed wall 2 is disposed parallel to and adjacent the path of movement of the material 1 so as to be disposed in confronting relation with the surface of the web or sheets transported therein. The wall is provided with means for projecting jets of clean air against the confronting surface of the material, in the present instance three rows of blow openings 3 which extend transverse to the web 1. The blow openings 3 located in the outermost rows 3a blow air jets between the web and the fixed wall substantially parallel to the direction of motion of the web, thereby to position the web in the predetermined path of travel. The blow openings 3 in the row 3b between the outermost rows 3a are adapted to eject air jets in directions having a greater inclination to the web than the first mentioned jets so as to penetrate into the surface layer of the web and release dust therefrom, thereby contributing to an improvement of the dust removal effect. The openings in the row 3b are alternately turned in opposite directions parallel to the travel of the web, blowing jets both in the direction of travel and oppositely thereto.
The blow openings 3 in the wall 2 are in communication by way of a blow box 4 with air supply means operable to supply pressurized clean air to the blow box. As shown in FIG. 3, the connection is by way of a duct 12 to a blower 13 having a motor 14 and a pressure regulator 15 in the suction side of the blower. The pressure regulator 15 has an operator 16 to adjust the pressure and quantity of the clean air supplied to the blow box 4. In this manner, jets of pressurized clean air are impinged against the confronting surface of the material 1 and the dust in the surface layer is removed by the parallel flow of clean air generated by the rows 3a between the wall 2 and the material 1.
In order to collect the dust removed from the surface layer of the material 1 and to prevent the redepositing of the dust onto the web or sheets of material, suction gaps 5 are provided on both sides of the fixed wall 2, as seen in the direction of motion of the material. The suction gaps 5 are defined between the leading and trailing ends of the fixed wall 2 and upstanding walls 7 of a suction box 6 which surrounds the blow box 4 and is in communication with a source of suction. As shown in FIGS. 1 and 3, the suction box is connected by ductwork 17 to a filter 18 having removable filter cartridges 19 therein. Air is drawn through the filter 18 by a blower 23 having a motor 24 and a pressure regulator 25 with an operator 26. Thus operation of the blower 23 withdraws the dust-laden air from between the wall 2 and the material 1 into the filter 18 where the dust particles are collected, for example by the cartridges 19.
The wall 2 along its edges adjoining the suction gaps 5, is beveled as indicated at 2a at approximately 15° to facilitate the deflection of air and dust into the suction gaps. The walls 7, in the illustrated embodiment, may be raised and lowered to adjust the distance between the upper edge of the wall and the material in accordance with the flow of air and the character of the material. Preferably the suction provided by the blower 23 operates to withdraw a greater quantity of air than is supplied by the blower 13 so that substantially all of the air impinged against the web from the openings 3 is drawn into the suction gap along with atmospheric air from the other side of the upright walls 7. The flow of air over the tops of the walls 7 is facilitated by the inturned lips 27 on the walls. The flow of air forms a cushion which resists displacement of the material into scraping engagement with the wall 7, thereby avoiding the possibility of damage to the material from such engagement, for example when the character of the surface of the web is sensitive to the touch, as, for example, undried coatings.
It should be noted that by the use of the eyelid shape openings in the upper wall 2, arranged as set forth, the material is conveyed in its path of travel substantially free from fluttering. The form of the openings 3 insures the scrubbing action of the air jets impinging against different spots of the travelling material surface, thereby scrubbing the surface free from lint and dust and simultaneously conveying the lint and dust away from the surface. By controlling the position of the walls 7 and the pressure and suction of the blowers 13 and 23, effective collection of the dust removed from the surface layer of the material is obtained.
To further insure against scraping engagement of the material with the walls 7, a modified embodiment of the invention has been provided, as shown in FIG. 4. In this embodiment, the blow box 4a and its connection to the pressurized clean air is identical to the blow box 4. The suction box 36 has been modified as indicated but its connection to the suction and collecting arrangement is identical to the previously-described embodiment, as indicated at 17a.
In accordance with this embodiment of the invention, the suction box 36 is provided with upstanding adjustable walls 37 which terminate at their upper extremities in outturned lips 38. The lips 38 cooperate with guiding means 39 in the form of fixed tubes or bars extending transversely with respect to the direction of movement of the material. The guide elements 39 are preferably circular in cross section and are not mounted for rotation. Their position overlying the suction gap 35 between the blow box 4a and the wall 37 generates a film of air indicated at 40 between the guiding means 39 and the material. This film of air separates the material from the guiding means and is effective to "lubricate" the material passing the guiding means.
The guiding means 39 also serve to deflect a major portion of the air discharged from the space between the blow box 4a and the material into the suction gap 35 so as to avoid any tendency of the major part of the air to follow along the path of movement of the material. The outturned lips 38 cooperate with the guiding means 39 to facilitate the injection of atmospheric air into the suction box to insure against discharge of dust-laden air into the surrounding atmosphere. The walls 37 are adjustable similarly to the walls 7 of the previous embodiment for the same purpose.
While particular embodiments of the present invention have been herein illustrated and described, it is not intended to limit the invention to such disclosure but changes and modifications may be made therein and thereto without departure from the invention, as defined in the following claims.
An advantage for the embodiment of the present invention is that -- due to the stabilizing effect of the jets of the used gaseous medium -- there is no need for a stretching of the web, even if the material of the web is thin and very fragile, for instance consists of tissue.