WO2001046053A1

WO2001046053A1 - Apparatus and method for stiffening a web leading edge

Info

Publication number: WO2001046053A1
Application number: PCT/US2000/034440
Authority: WO
Inventors: Timothy J. Custer
Original assignee: Marquip Inc
Current assignee: Marquip Inc
Priority date: 1999-12-21
Filing date: 2000-12-18
Publication date: 2001-06-28
Anticipated expiration: 2002-06-21
Also published as: AU2278201A

Abstract

A continuous web (12) being cut into sheets (11) by a rotary knife having upper (13) and lower (14) knife cylinders is provided with a temporary transverse corrugated lead edge to stiffen the web and prevent the lead edge from rising at high line speeds and sagging at low line speeds. The temporary transverse corrugating effect is provided by spaced alternating deflection strips (31) on both knife cylinders (13, 14), located immediately behind the cutting blades (15, 16), and engaging the lead edge of the web (12) immediately after the preceding sheet (11) has been cut.

Description

APPARATUS AND METHOD FOR STIFFENING A WEB LEADING EDGE

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention pertains to a rotary cut-off knife and, more particularly, to an apparatus and related method for temporarily creating a stiffened leading edge in a web traveling through a rotary knife.

Rotary knives comprising a pair of counterrotating knife cylinders carrying interengaging helical cut-off blades are well known in the art. Such rotary knives are particularly useful in processing paper and paperboard webs whereby a continuous running web is cut into successive sheets of a given length. The speed of the rotary knife cylinders is timed to the speed of the running web depending on sheet length, and the cylinders are rapidly accelerated or decelerated to cutting speed and, after the transverse cut is made, rapidly decelerated in preparation for the following cut. Such rotary knives are used to produce sheets from webs of substantially varying thickness, including solid fiber board stock having a caliper of .046 inch (1.17 mm) to fine paper having a caliper of .002 inch (.051 mm). Depending on the line speed of the web, the leading edge of the web exiting the rotary knife after the preceding sheet has been cut may droop, remain relatively horizontal, or tend to fly upwardly. The problem becomes more acute as paper caliper (thickness) drops. Typically, the leading edge of a fine paper web will droop at low line speeds (e.g. below 200 fpm or 65 m/min) and fly upwardly at higher line speeds (e.g. greater than 700 fpm or 227 m/min). In the intermediate speed range, the web may remain relatively flat or move in an unpredictable manner. There may be several causes for this phenomenon in addition to the inherent stiffness of the web material, including gravity, curl in the web, windage from the knife cylinders, and the uncontrolled area between the knife and the downstream outfeed sections before the leading edge of the web is nipped or otherwise engaged. There have been many attempts in the industry to solve the problem including directed air blasts both in the knife and in the outfeed area, stripper bars on the knife cylinders, foam strips on the cylinders and blades, a rotating brush in the knife outfeed area, and a doctor pan or transfer pan positioned extremely close to the outfeed of the lower knife blade tip. Some of the foregoing solutions have been marginally satisfactory. If great care is not exercised, paper sheets may be creased or wrinkled or may even jam the system, sometimes with serious damage. SUMMARY OF THE INVENTION

In accordance with the present invention, the leading edge of the web is provided with a transverse wave or corrugated effect in the rotary knife and immediately after the preceding sheet has been cut. The edge effect provides a stiffening of the web, inhibits drooping or rising, and eliminates many of the problems in the prior art. The wave or corrugated lead edge effect disappears as the sheet relaxes after passage through the knife, such that before the lead edge is engaged in the next downstream apparatus, it has resumed a flat, planar configuration.

The knife cylinders are provided with web deflection strips which are attached rotationally behind the cutting blades. The deflection strips are spaced axially along each knife cylinder and positioned such that the strips on one cylinder are axially between the strips on the other cylinder. The strips extend radially outwardly to define overlapping web-engaging surfaces such that the leading edge of the web is provided with a temporary transverse wave shape. The deflection strips are preferably made of a soft material such as felt. When applied to a rotary knife utilizing helical blades, the deflection strips are mounted to follow the helix of each blade. The strips may comprise semicircular ring segments and the strip material is chosen so as not to mark the web.

Lightweight carrier segments, made for example of plastic, are attached to the knife cylinders and the web-contacting ring segments are attached to the carrier segments. The carrier segments may be made of any suitable rigid material, but lightweight materials are preferable.

For cutting a fine paper web, the felt deflector strips preferably overlap by about 1/8 inch (3.2 mm). As the caliper and inherent stiffness of the web increases, the offset may be decreased. The corresponding method for temporarily stiffening the leading edge of a continuous web traveling generally horizontally through a rotary knife having a pair of upper and lower knife cylinders carrying interengaging helical cutting blades includes the steps of (1) deflecting the web along the cut edge in an alternately upward and downward direction with respect to the horizontal plane of the web immediately after cutting a sheet to provide the lead edge of the web with a temporary transverse wave shape as the edge moves downstream from the knife, (2) permitting the lead edge to relax and return to the plane of the web, and (3) nipping the lead edge for continued web processing. The deflecting step preferably comprises providing the knife cylinders with raised surfaces portions positioned rotationally behind the cutting blades, spacing said raised portions axially and oriented alternately along the cylinders, and extending beyond the plane of the web.

In a variant method for temporarily stiffening the leading edge of a web traveling through a rotary knife to successively cut sheets from the web along a traverse cut edge, the method includes the steps of (1) providing the knife cylinders with raised portions located rotationally behind the cutting blades, said raised portions spaced axially along each cylinder and positioned such that the raised portions on one cylinder are axially between and radially overlapping the raised portions on the other cylinder, and (2) driving the knife cylinders to cut a sheet from the web along the transverse cut edge and to cause the raised portions to engage the web leading edge and create a temporary transverse web shape along said leading edge. The method preferably includes the steps of (1) maintaining the transverse web shape along the web leading edge for a distance downstream of the knives, (2) permitting the leading edge to return to a generally planar shape, and (3) engaging the leading edge for continued web processing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a generally schematic side elevation view of a web handling system including a rotary knife equipped with the apparatus of the subject invention.

FIG. 2 is an enlarged partial sectional view taken on line 2-2 of FIG. 1 showing the lead edge of the web after a transverse cut has been made.

FIG. 3 is an elevation view of the rotary knife taken on line 3-3 of FIG. 1. FIG. 4 is a vertical section taken on line 4-4 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, a rotary knife 10 is operative to continuously cut sheets 11 from a running paper web 12. The rotary knife 10 includes upper and lower knife cylinders 13 and 14 to each of which is respectively mounted upper and lower helical cutting blades 15 and 16. The helical cutting blades are configured to provide a transverse slit from one edge of the web to the other and the knife cylinders are driven to correspond to the speed of the running web 12, all in a manner well known in the art.

The web is driven and moved through the rotary knife 10 by a lower drive roll

17 cooperating with an upper nip roll 18 to capture the web in an upstream nip 20. The web is carried between the nip 20 and the rotary knife on an infeed transfer pan 21.

The knife cylinders 13 and 14 are accelerated or decelerated to line speed and timed to continuously cut sheets 11 of a selected length. After each transverse cut is made, the knife cylinders are decelerated in anticipation of the next cut, all in a well known manner. The downstream edge of the sheet 11 is fed into a downstream nip 22 comprising, in the construction shown, upper and lower conveyor belts 23 and 24 operating over nip rolls 25. The belts 23 and 24 are entrained respectively around upstream infeed idler rolls 26 and 27 positioned to cause the belts to converge toward the nip. The belts are operated at a slight overspeed with respect to line speed so that a gap is pulled between the cut sheets.

When the web 12 is a fine paper, having a thickness in the range for example of

.002-.004 inch (.05-.10 mm), the sheets 11 may tend to drift vertically from the horizontal plane of the web, either upwardly or downwardly, usually depending on line speed. At higher line speeds, the sheets tend to be lifted upwardly whereas, at lower line speeds, the sheets tend to droop under the influence of gravity. In either case, the sheets may collide with one or the other of the infeed belts 23 or 24 and be bent or wrinkled. Significantly greater deflection in either vertical direction may result in folding or jamming of the sheets. Once a single sheet has been so damaged, succeeding sheets may pile up behind it and cause a potentially catastrophic jam. In lieu of or in addition to operating the lower conveyor belt 24 around an infeed idler roll 27, an outfeed transfer pan 28 may be utilized to support the web and the sheet once it is cut from the web. However, even with an outfeed transfer pan 28, uncontrollable vertical movement of fine paper sheets at high and low web speeds remains a problem.

Referring also to FIGS. 2-4, the apparatus and method of the present invention are operative to provide a temporary wave shape or corrugated effect transversely to the leading edge 30 of the web 12 immediately after the transverse cut has been made by the rotary knife 10. The upper and lower knife cylinders 13 and 14 are each provided with a series of axially spaced raised ring segments 31 immediately behind and upstream of the cutting blades 15 and 16. The ring segments are constructed and positioned to engage the leading edge 30 of the web in a manner to provide the wave effect or transverse corrugation 32, best seen in FIG. 2. The transverse wave shape is formed only temporarily, but provides a significant stiffening effect permitting the lead edge 30 of the web to be maintained more nearly horizontal, thereby virtually eliminating any tendency to raise vertically upwardly at high speeds or to droop vertically downwardly at low line speeds.

The ring segments 31 on the upper knife cylinder 13 comprise short semicircular carrier segments 33 to each of which is adhered an outer deflection strip 34, preferably comprising a narrow strip of felt. The carrier segments are preferably mounted to the outer surface of the knife cylinder 13 with machine screws and an adhesive. The felt deflection strip 34 may be attached to the outer surface of the carrier segment with a suitable adhesive or any other suitable fastening mechanism. Similarly, semicircular lower carrier segments 35 are mounted on the lower knife cylinder 14. Suitable lower deflection strips 36, also made of felt, are glued or otherwise fastened to the carrier segments 35. The ring segments 31 on each of the knife cylinders 13 and 14 are equally spaced in an axial direction, but the segments are positioned such that the deflection strips on the upper cylinder lie axially midway between the deflection strips 36 on the lower cylinder. Furthermore, the outer surfaces of the upper and lower deflection strips 34 and 36 which make contact with the web define cylinders of rotation which overlap, as may be seen in FIGS. 2 and 4 and the right hand portion of FIG. 3. The overlap results in alternate upward and downward deflections of the lead edge of the web across the full width of the web and the resultant transverse corrugating effect or wave shape shown in FIG. 2.

Referring particularly to FIG. 4, the ring segments 31 and the respective upper and lower deflection strips 34 and 35 are positioned immediately behind and upstream of the respective cutting blades 15 and 16. Because the blade holders 37 must of necessity be circumferentially spaced from one another (the lower blade holder trailing the upper in the embodiment shown), the lower deflection strips 36 trail somewhat behind the upper deflection strips 34. The radial outer surfaces of the upper deflection strips 34 lie approximately on the cylinder defined by the path of the upper cutting blade 15. The radial outer surfaces of the lower deflection strips 36 lie a cylinder of rotation slightly smaller than the diameter of the cylindrical path of the lower cutting blade 16. By recessing the lower deflection strips 36 slightly from the cylinder of the rotation of the lower cutting blade 16, the upstream edge of the outfeed transfer pan 28 (if used) can be located very close to the path of the lower blade edge without danger of the lower deflection strips striking the pan edge and being sheared off. However, if an outfeed transfer pan is not used, the lower deflection strips 36 could be made thicker to extend out to (or even beyond) the cylinder of rotation of the cutting edge of the lower blade 16.

Fine paper having a caliper in the range of .002-.006 (.05-.15 mm) inch may be deflected more and thus provided with a deeper corrugating effect than heavier papers or solid fiber board. For fine papers, an overlap between the upper and lower felt deflection strips 34 and 36 of about .125 inch (3.2 mm) has been used with good results. The mount of overlap may, of course, be varied simply by changing the thickness of one or both of the deflection strips 34 and 36. The sectional view of FIG. 4 shows the interengaging cutting blades 15 and 16 at the precise instant of cutting through the web 12. Because of the helical shape of the blade the view of FIG. 4 represents any point axially across the knife at the instant of cutting. In other words, the transverse cut progresses across the web from one edge to the other in a sort of scissors fashion. However, at high web and knife cylinder speeds and a relatively small helix angle, for example 3° or less, the cut proceeds extremely quickly. The ring segments 31 are positioned immediately behind the respective blade holders 37 and thus in the FIG. 3 view, the helical displacement of the ring segments axially along the knife cylinders 13 and 14 may be seen. The transverse wave shape or corrugating effect provided in the leading edge 30 of the web 12 (FIG. 2) is only temporary and as the lead edge travels downstream toward the nip 22, the web material relaxes and the wave shape disappears. The wave shape or temporary corrugating effect is completely gone before the leading edge enters the nip 22. However, the transverse wave shape is retained long enough to provide the stiffening and stabilizing effect described above.

Because the web deflection strips 34 and 36 are positioned behind the cutting blades 15 and 16, the strips do not touch the web until after the cut has been made. Therefore, the strips do not have any effect whatever on cut quality. The temporary transverse wave shape and resultant stiffening effect has been found to work effectively to control the tendency for the lead edge of the web to move both downwardly and upwardly, depending on speed, web material, and other factors as previously discussed. This system has been tested on small caliper fine paper and on various paper thicknesses up to solid fiber board with a thickness of .046 inch (1.18 mm) with consistently good results. The deflection strips and associated mounting mechanism are completely passive and require no operator adjustments of any kind. For example, no air blast devices of any kind are required and, therefore, all of the detrimental secondary effects of air blast control may be eliminated. The lead-in angles between the upper and lower conveyor belts 23 and 24 may be decreased. A smaller angle requires less overspeed in the downstream nip 22 which has been shown to result in better cut quality, particularly on fine paper. A smaller lead-in angle also allows the nip 22 to be positioned closer to the cut point of the knife, allowing the system to cut shorter sheets. The use of rigid lightweight plastic ring segments 31 does not effect the balance of the knife cylinders. Further, the mass added by the ring segments has little affect on roll inertia which is an important consideration in a rotary- knife where the cylinders must be accelerated and decelerated rapidly. In another, but less desirable embodiment, the temporary transverse wave shape could be produced by air jets directed from the inside of the knife cylinders in an axial alternating arrangement, as previously described for the ring segments 31. However, any system utilizing air jets is substantially less desirable than the completely passive system of the preferred embodiment. Alternately, air jets could be used to replace the ring segments on one knife cylinder, while maintaining the ring segments and associated deflection strips on the other knife cylinder.

Claims

CLAIMSI claim:

1. An apparatus for providing a stiffening effect in the leading edge of sheets being cut from a continuous web moving through a rotary knife having a pair of counterrotating knife cylinders carrying interengaging cutting blades to provide a transverse cut edge, said apparatus comprising: web deflection strips attached to the knife cylinders rotationally behind the cutting blades; said deflection strips spaced axially along the cylinder and positioned such that the strips on one cylinder are axially between the strips on the other cylinder; said deflection strips having web-engaging radial outer surfaces that define overlapping cylinders such that the leading edge of the web defined by the transverse cut edge is provided with a temporary transverse wave shape.

2. The apparatus as set forth in claim 1 wherein said deflection strips are made of felt.

3. The apparatus as set forth in claim 1 wherein the cutting blades are of a helical shape and said deflection strips on the knife cylinders are mounted to follow the helices of the respective blades.

4. The apparatus as set forth in claim 1 wherein said deflection strips comprises semicircular ring segments.

5. The apparatus as set forth in claim 4 wherein said ring segments are made of a material which engages the web without marking.

6. The apparatus as set forth in claim 5 including carrier segments attached to the knife cylinders, and means for attaching said ring segments to said carrier segments.

7. The apparatus as set forth in claim 6 wherein said carrier segments are made of a rigid material of substantially lower density than the knife cylinder material.

8. The apparatus as set forth in claim 1 wherein, for cutting a web of fine paper having a caliper in the range of about .002 to .006 inch (.05 to .15 mm), the deflector strip overlap is about .125 inch (3.2 mm).

9. A method for temporarily stiffening the leading edge of a continuous paper web traveling generally horizontally through a rotary knife having a pair of upper and lower counterrotating knife cylinders carrying interengaging helical cutting blades operating to successively cut sheets from the web along a transverse cut edge, said method comprising the steps of:

(1) deflecting the web along the cut edge in an alternating upward and downward direction with respect to the horizontal plane of the web immediately after cutting a sheet to provide the lead edge of the web with a temporary transverse wave shape as the lead edge moves downstream from the knife; (2) permitting the lead edge to return to the plane of the web; and,

(3) nipping the lead edge for continued web processing.

10. The method as set forth in claim 9 wherein said deflecting step comprises providing the knife cylinders with raised surface portions rotationally behind the cutting blades, said raised portions being spaced axially and oriented alternately along the cylinders and extending beyond the plane of the web.

11. A method for temporarily stiffening the leading edge of a web traveling through a rotary knife having a pair of counterrotating knife cylinders carrying interengaging cutting blades operating to successively cut sheets from the web along a transverse cut edge, comprising the steps of: (1) providing the knife cylinders with raised portions rotationally behind the cutting blades, said portions spaced axially along each cylinder and positioned such that the raised portions on one cylinder are axially between and radially overlapping the raised portions on the other cylinder; and,

(2) driving the knife cylinders to cut a sheet from the web along the transverse cut edge and to cause the raised portions to engage the web leading edge and create a temporary transverse wave shape along said leading edge.

12. The method as set forth in claim 11 including the steps of:

(1) maintaining the traverse wave shape along the web leading edge for a distance downstream of the knives;

(2) permitting the leading edge to return to a generally straight edge shape; and, (3) engaging the leading edge for continued web processing.