STRESS BALANCING MOUNT FOR A KNIFE ON A CUTTER ROLL IN A WEB PROCESSING MACHINE

Abstract

A roll cutting device for a web processing machine having a cutter roll with only one knife affixed thereto, the cutter roll being rotatably mounted to the machine and configured to perforate or cut the web once per revolution of the cutter roll, and a stress balancing member mounted to the cutter roll in diametric opposition to the knife, the knife and the stress balancing member being connected to the cutter roll by similar connection means so that mechanical stresses caused by connection of the knife and the stress balancing member are balanced and the cutter roll rotates without stress-induced eccentricity.

Claims

1. A web cutting roll for use in a web processing machine, comprising: an elongate cutter roll arranged on a roll centerline and rotatably connected to the web processing machine and transversely spanning a moving web; a knife connected to the cutter roll at a first position by a first connector arrangement so that the knife rotates with the cutter roll to define a peripheral path in which transverse contact with the web occurs once per revolution of the cutter roll; and a stress balance member connected to the cutter roll in a position opposite of the knife relative to the roll centerline, the stress balance member being connected by a second connector arrangement, the first and second connector arrangements being substantially similar so that static mechanical stresses imposed upon the cutter roll by the connection of the knife and the stress balance member are substantially the same thereby balancing static mechanical stress forces in the cutter roll.

2. The web cutting roll of claim 1, wherein the cutter roll is symmetrically configured about the roll centerline.

3. The web cutting roll of claim 2, wherein the knife and the stress balance member are substantially similar in dimensional configuration.

4. The web cutting roll of claim 3, wherein the first and second connector arrangements each comprise a plurality of fasteners uniformly spanning the length of the knife and stress balance member, respectively.

5. In a web processing machine having a frame supporting a plurality of transverse rolls defining a feed path along which a web of material is moved and a web cutting means transversely spanning the web, the web cutting means configured to perforate the web as it is moved along the feed path, the improvement in the web cutting means comprising: an elongate cutter roll rotatably connected to the web processing machine; a knife connected by a first connector arrangement at a first position on the cutter roll so that the knife rotates with the cutter roll to define a generally cylindrical peripheral path in which transverse contact with the web occurs once per revolution of the cutter roll; and a stress balance member connected to the cutter roll in diametric opposition to the knife, the stress balance member being connected by a second connector arrangement, the first and second connector arrangements being substantially similar to balance static mechanical stresses imposed upon the cutter roll by the connection of the knife and the stress balance member and minimize eccentricity of the peripheral path as the cutter roll rotates.

6. The improvement of claim 5, wherein the cutter roll is symmetrically configured about the roll centerline.

7. The improvement of claim 6, wherein the knife and the stress balance member are substantially the same in physical configuration.

8. The improvement of claim 7, wherein the first and second connector arrangements each comprise a plurality of fasteners uniformly spanning the length of the knife and stress balance member, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:

[0011] FIG. 1 illustrates a conventional web cutting device on which the present invention is useful;

[0012] FIG. 2 illustrates the web cutting device of FIG. 1 upon which the present invention is shown incorporated;

[0013] FIG. 3 is a plan view of the web cutting device of FIG. 2;

[0014] FIG. 4 in an elevation view of the web cutting device of FIG. 3;

[0015] FIG. 5 is a section view of the web cutting device of FIG. 4 taken along cut line 5-5; and

[0016] FIG. 6 is a second view of FIG. 5 illustrating thermal displacement in the roll cutter mount and the effect on cutter alignment with the present invention;

[0017] FIG. 7 is a partial elevation view of the prior art web cutting device of FIG. 1 illustrating stress-induced deflection in the cutter roll that may occur in the absence of the present invention; and

[0018] FIGS. 8 and 9 illustrate the effect of instant invention on cutter roll deflection and roll cutter perforation quality.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0019] Many of the fastening, connection, processes and other means and components utilized in this invention are widely known and used in the field of the invention described, and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art, and they will not therefore be discussed in significant detail. Also, any reference herein to the terms up or down, or top or bottom are used as a matter of mere convenience, and are determined as the machine would normally rest on a level surface. Furthermore, the various components shown or described herein for any specific application of this invention can be varied or altered as anticipated by this invention and the practice of a specific application of any element may already be widely known or used in the art by persons skilled in the art and each will likewise not therefore be discussed in significant detail. When referring to the figures, like parts are numbered the same in all of the figures.

[0020] Referring to FIGS. 1 and 2, there is shown a web cutting device 10 of the type commonly used in roll converting machines in which a continuous web 5 is moved to the web cutting device 10, severed or perforated by interaction with a knife 30 on a roll cutter 20, and moved away from the cutting device 10 by a discharge conveyor, if severed. A conventional frame 100 is provided for rotatably supporting the cutting device and appropriate drive(s) 105 for rotating the roll cutter 20 at a speed required to sever/perforate the web into sheets of a desired length. The roll cutter 20 is supported by bearings (not shown) at opposite ends thereof to enable rotation of the roll cutter about a roll axis 200 that is generally transverse to the web 5. The bearings are connected to and supported by the frame 100 of the roll converting machine by bearing support blocks 40. A cutting anvil 50 is also connected to the frame 100 of the roll converting machine, preferably sharing a common anchorage with the bearing support blocks 40 to preclude relative movement between the cutting anvil 50 and the roll cutter 20 during operation. Alternatively, the anvil 50 may comprise a roll similar to the roll cutter with a peripherally disposed anvil surface which interacts with the knife as the adjacent rolls rotate, rotation being synchronized to enable the knife and anvil to interact.

[0021] The roll cutter 20 and cutting anvil 50 extend for at least the width of the web 5. In practice, web widths ranging from 36 to 72 inches are common.

[0022] Desired production rates in modern web converting machines require web travel speeds ranging from 200 to 700 feet per minute. Upward pressure for production efficiency improvements pushes development of machines using even higher web speeds. With higher web speeds comes increased heat generation in the bearings and other friction interfaces.

[0023] Maintaining close spatial tolerance in the gap between the knife 30 and the anvil 50 of the web cutting device 10 is essential for high production efficiency, especially for perforation of the web. The web converting machine 10 may be required to handle web thicknesses ranging from 0.005 to 0.100 inches. This gap G (see FIGS. 5 and 6) must be maintained within a tight tolerance throughout the operating temperature range of the machine since movement on the order of the web thickness being processed will negatively affect roll cutter performance.

[0024] Thermal displacement in the frame 100 caused by heat transfer from the roll cutter bearings can cause movement of the roll cutter centerline 200 away from the anvil 50 (shown as arrow A in FIG. 1) thereby causing gap G (best shown in FIGS. 5 and 6) to increase. This is illustrated in FIG. 1 wherein thermal expansion of the bearing support blocks 40 displaces the roll centerline upward, opening the gap spacing between the knife 30 and the anvil 50. A first aspect of the present invention addresses this problem, illustrated in FIG. 2, by reorienting the connection interface 101 between the bearing support block 40 and the frame 100 to generally perpendicular to the web passing tangential to the knife roll. This bearing block mount orientation results in thermal expansion in the bearing support block causing displacement of the roll cutter centerline 200 primarily along an axis that is generally parallel to the web, shown as arrow B in FIG. 2. Note that an axis parallel to web 5 is also generally perpendicular to a cutting plane 120 in which the knife 30 and anvil 50 interact, as is best illustrated in FIGS. 5 and 6. Cutting plane 120 is defined by the edge of the anvil 50 and the roll cutter centerline 200 and may thus vary slightly from perpendicular to the web. Thermal effects thus do not dramatically alter the vertical spacing between the anvil and the roll cutter centerline, but simply cause the cutting plane 120 to be angled slightly as thermal expansion occurs.

[0025] Further limitation of thermally induced effects on knife positioning and gap G is provided by incorporating a thermal isolator 60 between the bearing support blocks 40 and the frame 100 to limit heat transfer from the support blocks 40 to the machine frame 100 which might otherwise contribute to thermal expansion of the frame members along an axis perpendicular to the web feed path.

[0026] In FIG. 5, the edges of the knife 30 and anvil 50 align on the cutting plane 120, producing a clean cut or perforation. FIG. 6 illustrates the thermal shift of the roll cutting centerline 200 that occurs due to thermal expansion of the support block 40. Though shown exaggerated for illustration purposes, the shift (T.sub.2-T.sub.1) may be on the order of 0.001 to 0.005 inches due to thermal expansion, but rather than directly increasing the gap between the knife 30 and anvil 50, the shift causes the cutting plane 120 to be angled slightly with reference to the web while minimizing the effect on the vertical spacing between the knife 30 and anvil 50. The altered orientation of the main axis of thermal growth reduces the adverse impact of cutting quality due to thermal growth. The initial orientation of cutting plane 120 may also be adjusted so that the knife 30 and anvil 50 align on the preferred perpendicular cutting plane when the machine is at operating temperature so that a greater proportion of web cuts are may under optimal conditions.

[0027] The thermal isolator 60 is preferably constructed of a material that is thermally stable and has a low coefficient of thermal conductance, significantly lower compared to the ferrous material comprising the frame and bearing support blocks and preferably lower by one or more orders of magnitude. In one embodiment, a thermal isolator 60 is fabricated from mica, which has a thermal conductance approximately two orders of magnitude less that iron or steel, has demonstrated acceptable results.

[0028] In addition to stabilizing the relative position between the knife and anvil overall, a second aspect of the invention is directed toward improving the spatial relationship between the knife 30 and the anvil 50 along the extent of its transverse span across the web. FIG. 7 illustrates the cutter roll 20 equipped with only a single knife 30, the preferred cutter roll arrangement wherein the web is severed or perforated with each revolution of the cutter roll. The rotational speed of the knife is determined based on the desired sheet length or perforation spacing desired so that the knife interfaces with the web on the desired spacing interval. For example, if a sheet length of one foot is desired and the web is travelling at 500 feet per minute, the knife roll needs to rotate at 500 rpm to achieve the desired sheet length. The knife roll must be sized so the circumferential speed is greater than the web speed, at least 15% greater is preferred.

[0029] The preferred knife arrangement on the cutter roll aligns the knife on a slight helix of the cutter roll so that the knife and anvil interact to produce a scissors-type of shearing of the web. The knifes are typically formed from flat metal stock which must then be twisted when attached to the cutter roll. The stresses introduced which attaching a knife formed from a two-inch wide strip of one-quarter inch thick plate to the helical mount on the cutter roll are significant and lead to bowing of the cutter roll.

[0030] A single knife 30 is secured to the cutter roll using a connector arrangement 70 comprising a plurality of fasteners 72 generally uniformly spaced along the knife-cutter roll interface for the entire length of the cutter roll to create a robust connection of the knife to the roll. The fasteners 72 are preferably positioned on approximately two to three inch spacing for the entire width of the roll cutter 20. Multiple fasteners (e.g., pairs) may be used at each lateral location. As a result, the fasteners 72 may easily number eight or more for every twelve inches of cutter roll width. Stresses introduced by bending the knife to securing it to the cutter roll 20 result in a static mechanical stress imbalance in the cutter roll that may cause slight deflection from its roll centerline 200. Cutter roll deflections induced by the knife mounting stresses may be compounded as the cutter roll temperature increases during operation.

[0031] Any deflection can cause the edge 32 of the knife 30 being slightly bowed from a straight-line interface with the anvil 50 which is typically greatest at mid-span of the cutter roll. Even though the maximum displacement may be only on the order of a few thousandths of an inch, the result in less than adequate cutting or perforation of the web by the knife, typically in the middle of the web width where the knife edge will be closer to the anvil than desired and potentially resulting in contact between the knife edge and the anvil which may damage the knife. This is best illustrated in FIG. 8 in which the peripheral path 150A defined by the knife edge 32 is illustrated on a cutter roll that is deflected by installation of the knife 30. Instead of a desired cylindrical profile, an eccentricity may be introduced in the cutter roll, displacing the peripheral path 150 further from the roll axis 200 at midspan of the cutter roll compared to the displacement closer to the bearing supported ends. In extreme conditions, the knife edge 32 may even contact the anvil 50. More commonly, the eccentricity causes the knife edge to be shifted away from the anvil in the mid-span portion of the cutter roll, best illustrated as gap P in FIG. 7. In this condition, the knife edge displacement may even result in the knife failing to contact the web in mid-span.

[0032] As is best illustrated in FIGS. 5 and 6, the second aspect of the present invention addresses this shortcoming by attaching a stress balancing member 35 in diametric opposition to the knife 30 on the cutter roll 20. The cutter roll 20 is configured to the knife 30 and the stress balancing member 35 in a physically and dimensionally symmetrical configuration in relation to the roll axis 200. Sans attachments, a symmetric cutter roll is balanced to minimize deflections when rotating. The stress balancing member 35 is, in essence, a knife that lacks a cutting edge so that it does not interact with the web when positioned adjacent thereto. The stress balance member 35 is similar in physical configuration (e.g., mass, dimensions) to the knife 30 with the exception of its lack of a cutting edge 32 to maintain rotational balance of the cutter roll. The symmetric positioning of the stress balancing member 35, the similarity of physical configuration, and the use of the same connector arrangement 70 as that attaching knife 30 to the cutter roll rotationally balances the cutter roll and also balance the static stresses applied to the cutter roll by connection of the knife and balance member thereby minimizing stress-induced deflection (eccentricity) of the cutter roll 20 peripheral path 150B resulting in minimized variation in the spacing between the knife edge 32 and the roll axis 200 along the length of the cutter roll. This is best illustrated in FIG. 9 which illustrated a generally cylindrically shaped peripheral path 150B that results in uniform spacing S along the entire length of the knife 30. This improvement remains as the cutter roll reaches operating temperature. The result is more uniform cutting interaction between the knife 30 and the anvil 50 along the entirety of the web width.

[0033] Naturally, the invention is not limited to the foregoing embodiments, but it can also be modified in many ways without departing from the basic concepts. Changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.