EP1370412A2

EP1370412A2 - Embossing roll with removable plates

Info

Publication number: EP1370412A2
Application number: EP02707974A
Authority: EP
Inventors: Jeremy James Michael Papadopoulos
Original assignee: Paper Converting Machine Co
Current assignee: Paper Converting Machine Co
Priority date: 2001-03-09
Filing date: 2002-03-07
Publication date: 2003-12-17
Also published as: WO2002072340A3; WO2002072340A2

Abstract

An embossing roll (85) includes a roll body (86) and a plurality of plates (87) which are removably secured to the roll body. Each plate (87) includes an outer surface which is provided with an embossing pattern. The plates (87) can be secured to the roll body (86) by vacuum and/or mechanical devices.

Description

EMBOSSING ROLL WITH REMOVABLE PLATES

Background

This invention relates to embossing rolls for tissue or plastic film or other webs, and, more particularly, to an embossing roll with removable embossing plates.

Paper products such as bathroom tissue and kitchen towels are commonly formed on a rewinder line in which one or more jumbo rolls of webs are unwound, perforated, and rewound into retail sized rolls. Many rewinder lines include an embosser for forming embossments in one or both of the webs and perhaps a glue deck to bond webs together.

The embosser conventionally includes one or more embossing rolls having an embossing pattern and a cooperating backup roll which presses against each embossing roll. The cooperating roll can be, for example, a meshing steel or paper roll or a compliant smooth rubber-covered roll. A paper roll is formed from compressed paper or cloth. Steel and paper cooperating rolls are formed with recesses which mesh with the projections on the embossing roll. Each web is advanced between an embossing roll and its cooperating roll, and the embossing pattern is embossed into the web.

In most present commercial embossers, the embossing roll is manufactured integrally. That is, a roll body with journals is fabricated, and then the outer surface of this roll is engraved with an embossing pattern, commonly using acid and a resist, and/or indentation by a patterned tool. The problems with an integral embossing roll relate to cost and changeover time:

1. To get a new pattern, it is necessary to create an expensive new roll body.

2. To replace an old pattern, the heavy and expensive roll must be taken out of commission and shipped, for machining to a smaller size, and re- engraving.

3. Damage or wear in a limited surface region requires replacing the entire pattern.

4. When switching embossing rolls to produce a few days' worth of product with a different pattern, the exchange of rolls takes a considerable amount of time, perhaps longer than a working shift.

Covering a smooth precise roll with a removable (slightly undersized) sleeve the surface of which bears an engraved pattern is common in the printing art. It is also known in the embossing art, see, for example, U.S. Patent No. 6,173,496 and EP 0 836 928 Al . However, this approach has at least several disadvantages:

1. Fabrication of sufficiently well- fitting steel engraved sleeves has been difficult, so printing technology has been used to make the sleeves, e.g., fiberglass sleeves, covered with hard nitrile rubber and laser-engraved. For ordinary production, these sleeves are not considered to be durable enough to be worth the expense.

2. A durable steel sleeve, thick enough for deep engraving, is very difficult to expand temporarily for installation on, and removal from, the supporting roll. In particular, the conventional compressed-air "flotation" method of Miller Graphics U.K., Ltd., Stork Screens America, Inc., Charlotte, North Carolina, or Strachan and Henshaw Machinery, Inc. is inadequate.

3. Removal of an entire sleeve can be accomplished quickly only if the embosser was designed specifically to support the roll body in a cantilever fashion, i.e., to hold a heavy roll at one end only, with clearance for the sleeve to be withdrawn over the other end. Furthermore, there must be enough space beside the machine to withdraw the entire length of the sleeve.

Summary of the Invention.

The invention provides an embossing roll with embossing plates which are removably secured to a roll body. The removable plates provide the following advantages:

1. When changing embossing patterns, only the surface, i.e., the plates, is changed, not the entire roll body. Therefore, less investment is needed, and storage/shipping costs are reduced. This makes it feasible for converters to stock alternate or backup engraved patterns, and to take on smaller jobs, profitably.

2. The plates can be made of steel so that there is no sacrifice in durability.

3. Small gaps between plates accommodate thermal expansion and manufacturing inaccuracies better than a sleeve.

4. The plates are held to the roll with a fixturing system of vacuum suction and/or mechanical devices. Because the engraved surface is not in sleeve form, it is possible to attach/remove it from a roll without cantilevering that roll or removing it from the embosser (and without requiring substantial side clearance) .

5. If the fixturing system includes quick-change features, it will be possible to change embossing patterns in minutes rather than hours.

6. There is no need to invest in a new embosser to utilize the removable plates. The invention will retrofit easily to most existing embossers .

The removable plates may be made of any sufficiently durable material. A key requirement is to provide means to hold them accurately, firmly, and safely against the surface of a fast-turning roll, while they are being pressed against a co-operating roll (which creates heat and "creeping tendencies") . Any holding method should permit reasonably quick changes and advantageously ensure safety in case power or vacuum is lost.

One embodiment uses vacuum to hold the plates, locating pins to guarantee precise location and prevent creeping (unimportant in some applications) , and quick-change mechanical interlocks to retain the plates safely when vacuum is turned off. Other embodiments use vacuum alone or omit vacuum and use only mechanical attachments. Description of the Drawing

The invention will be explained in conjunction with illustrative embodiments shown in the accompanying drawing, in which --

Figure 1 illustrates conventional prior art rubber-to-steel embossing of a tissue web to add decoration and bulk;

Figure 2 illustrates a prior art two-ply embossed paper product ;

Figure 3 is a schematic side view of a prior art embossing machine for producing foot-to- foot embossments;

Figure 4 is a schematic side view of a prior art embossing machine for producing nested embossments ,-

Figure 5 is a perspective view of one embodiment of an embossing roll which is formed in accordance with the invention;

Figure 6 is a fragmentary end view of the body of an embossing roll which is similar to the embossing roll body of Figure 5;

Figure 7 is a fragmentary plan view of adjacent vacuum areas of the roll body of Figure 6;

Figure 8 is a view similar to Figure 5 of another embossing plate configuration;

Figure 9 is an exploded sectional view of one embodiment of an embossing roll;

Figure 10 is an exploded sectional view of another embodiment of a small embossing roll;

Figure 11 is a plan view of a curved embossing plate with hidden fixturing studs;

Figure 12 is a fragmentary view of a rod for removably retaining the embossing plate on an embossing roll;

Figure 13 is a top view of the rod of Figure 11;

Figure 14 is an exploded sectional view of another embodiment of a small embossing roll;

Figure 15 is an end view of the vacuum control system for the roll body of Figure 13;

Figure 16 is an exploded fragmentary sectional view of the roll body of Figure 14;

Figure 17 is an exploded perspective view of the small embossing roll of Figure 14;

Figure 18 is another perspective view of the small embossing roll of Figure 14; and

Figure 19 is a perspective view of a cylindrical steel sleeve which can be used to make embossing plates.

Description of Specific Embodiments A. General Description of Embossing

Figure 1 illustrates conventional rubber- to-steel embossing of a tissue web W to add decoration and bulk. The web can be wound into retail sized rolls of bathroom tissue or kitchen toweling.

An embossing roll 31 includes an engraved surface 32 which is engraved with an embossing pattern. The embossing roll 31 cooperates with a rubber-covered backup roll 33. A web W is advanced between the cooperating rolls, and the embossed surface 32 presses the web into the rubber-covered roll and forms embossments 34 in the web. The roll 33 is adjustable to vary the pressure on the web.

Figure 2 illustrates a two-ply web W₂ which has been embossed by the rolls 31 and 33. The embossing of the two webs may create a minimal mechanical bond between the webs. A multi-ply web having more than two plies can also be embossed.

As is well known in the art, the cooperating backup roll could have an outer surface which is harder than rubber. For example, the surface could be steel or other metal or paper. Hard surfaces are generally formed with cooperating or matching recesses into which the projections of the embossing roll extend. Figure 3 illustrates a conventional embossing machine for producing two-ply paper products with foot-to-foot embossments. A top web 44 which is unwound from an unwind stand (not shown) passes between an upper rubber-covered roll 45 and a steel embossing roll 46. The embossing roll is engraved to provide embossments or radially outwardly extending projections 47 and unembossed areas 48 between the projections.

The embossing roll 46 is rotatably mounted in a frame 49 of the embossing machine, and as the embossing roll 46 and the rubber covered roll 45 rotate, projections 47 on the embossing roll 46 press the upper web into the rubber-covered roll 45 and form embossments 50 on the upper web. Adhesive or glue is picked up from an adhesive fountain (not shown) by a transfer roll 51, and the glue is transferred by transfer roll 52 to an applicator roll 53. The applicator roll 53 contacts the embossments 50 of the upper web and transfers glue to the embossments .

A lower web 54 is unwound from another unwind stand and passes between a lower rubber- covered roll 55 and a second steel embossing roll 56. The embossing roll 56 is also provided with embossments or projections 57 and unembossed areas 58. The projections 57 on the second embossing roll press the lower web into the rubber-covered roll 55 and form embossments 59 on the lower web.

The two embossing rolls are geared so that the embossments of the two webs are aligned and are pressed together where the projections of the embossing rollers meet at the nip 62 between the embossing rolls. As the embossments of the webs are pressed together, the adhesive on one of the embossments 50 secures the two plies together. The resulting laminated two-ply embossed product 63 advances away from the embossing machine for further processing operations, for example, in a rewinder line .

The second embossing roll 56 is rotatably mounted in the frame of the embossing machine. The second embossing roll is also advantageously pivotable relative to the first embossing roll 46 so that the nip 62 can be adjusted. The rotational or longitudinal axes 46a and 56a of the embossing rolls are parallel.

Figure 4 illustrates a conventional embossing machine for producing two-ply paper products with nested embossments. An upper web 65 from an unwind stand advances over a spreader roll 66 and around an upper rubber-covered roll 67. An upper embossing roll 68 having projections or embossments 69 presses the upper web into the rubber-covered roll 67 to form embossments in the upper web.

A lower web 71 is advanced from another unwind stand over a bowed roll 72 and around a lower rubber-covered roll 73. A lower embossing roll 74 having projections or embossments 75 presses the lower web into the rubber-covered roll 73 to form embossments in the lower web.

Adhesive is applied to the embossments of the lower web (while they are still supported by the projections) by an adhesive-applying roll 76 which is supplied with adhesive by transfer rolls 77 and 78 and a fountain (not shown) .

The axes of rotation 68a and 74a of the upper and lower embossing rolls are parallel, and the rolls are separated to provide an open nip 80. The projections 69 on the upper embossing roll are offset from the projections 75 on the lower embossing roll so that the projections of the two embossing rolls mesh at the nip 80. The embossed upper web 65 leaves the upper embossing roll 68 at the nip 80 and meshes with the embossed lower web 71 on the lower embossing roll. The two webs are pressed together at a nip 81 between a rubber-covered marrying roll 82 and the projections of the lower embossing roll 74, and the adhesive on the embossments of the lower web is pressed against unembossed areas of the upper web to secure the two webs together. The rolls are rotatably mounted in a frame 83 of the embossing machine .

B. The Inventive Embossing Rolls

Figure 5 illustrates an embossing roll 85 which is formed in accordance with the invention. The embossing roll includes an elongated, generally cylindrical roll body 86 and a plurality of embossing plates 87. The particular roll illustrated includes 16 plates arranged in four longitudinally extending rows or quadrants and four circumferentially extending rows. The outside surfaces of the embossing plates form a cylindrical surface, and an embossing pattern is engraved on the outer surface of the plates .

The embossing roll has a length L and a diameter D. The length of the embossing roll depends on the width of the web which is being embossed. Typical embossing rolls may have lengths of up to 100 or 110 inches or more and diameters of up to 18 to 20 inches or more .

The roll body 86 includes a pair of ends 88 and journals 89 which extend away from the ends along the longitudinal axis of rotation 90 of the embossing roll. A vacuum rotary union 91 is mounted on the end of one of the journals and is connected to a vacuum pump or other vacuum source by vacuum line 92.

Referring to Figure 6, the vacuum rotary union 91 is connected to four vacuum control valves 94 by an internal passage 95 in the journal 89. (Advantageously, in the case of a roll with hollow construction, internal passage 95 will extend to communicate with the roll interior, which can be used as a vacuum reservoir.) Optimally these are 3-way valves, which connect plate-suction areas either to vacuum (for holding) or to atmosphere (to release) . Each vacuum control valve is connected through an opening 96 in the journal 89 and an internal passage 97 in the roll body 86 to deep longitudinal and shallow transverse vacuum grooves 98 and 99 in each quadrant of the outer surface of the roll body. Each quadrant also includes at least one rectangular or oval groove 100 for a sealing gasket to form a vacuum suction area for holding a plate.

Subsequent plates axial of the first plate are conventionally secured with the same vacuum valve. However, each requires its own separate seal area or areas. The seal areas to be controlled by one single valve are conveniently connected by shallow-angle holes as in Figure 7.

Referring to Figure 7, two axially adjacent embossing plates are held against adjacent oval sealing glands 100a which surround longitudinal vacuum grooves 98 and transverse vacuum grooves 99. Adjacent longitudinal grooves 98 are connected by two shallow-angle drilled holes 98a and 98b which meet at 98c so that the vacuum areas for one longitudinal row of plates may be controlled by one valve. The drilled holes 98a and 98b intersect below the surface of the roll body.

In Figure 5 the embossing plates 87 include straight longitudinal and transverse side edges 101 and 102. However, straight-cut side edges might cause a minor disruption of the engraved pattern.

Figure 8 illustrates an embossing roll 103 which is similar to the embossing roll 85. However, the embossing plates 104 of the roll 103 have nonlinear side edges 105 and 106 which avoid the important areas of the embossing pattern. While the non-linear side edges might not avoid all of the engraved portions of the plates, the disruption to the embossing pattern is substantially reduced or minimized. The side edges 105 and 106 are shown in zig-zag fashion for illustrative purposes only. The actual preferred contour of the non-linear edges will depend on the embossing pattern.

Figure 9 is an exploded cross sectional view of an embossing roll 108 in which embossing plates 109 are removably secured to roll body 110 only by vacuum. A vacuum source communicates with the surface of the roll body through internal passages 111, and shallow transverse surface grooves 99 in combination with deeper longitudinal grooves 98 (see Figure 6) distribute the vacuum force over substantially the entire surface of each plate. Each plate is sucked by vacuum against a flexible and resilient sealing gasket 113.

One or more cylindrical locating studs 114 extend radially inwardly from each plate. Each locating stud is inserted into a circular opening 115 in the roll body. The locating studs prevent the plates from "walking" or "creeping" under the ironing influence of the moving band of pressure which is exerted on the embossing roll by the rubber-covered backup roll.

To guard against the danger of vacuum interruption while the roll is spinning, an electrical or mechanical sensor is used to halt the machinery if vacuum is lessened, and in addition, a check valve placed after the rotary union slows air leakage when the hose is cut.

Figure 10 illustrates an embossing roll 117 in which embossing plates 118 are removably secured to roll body 119 by only quick-change mechanical devices. Each plate includes two or more locating and gripping studs 120 (see also Figure 11) which cooperate with a notched rod 121 (see also Figures 12 and 13) which extends longitudinally through the entire roll body. The studs are cylindrical in cross section and include hook-shaped notches 122.

The studs are inserted into cylindrical openings 123 in the roll body, and the rods 121 extend through portions of the openings. Referring to Figure 12, each rod is provided with a semicircular notch 124 for each stud. When the notches 124 in the rods are aligned with the opening 123, the studs 120 can be inserted into the openings. The rods are then rotated one-half turn so that solid portions of the rod enter the hook-shaped notches of the studs and draw the studs into openings 123 and draw the plates against the roll body.

Referring to the upper left portion of Figure 10, each plate advantageously has a radius of curvature which is less than the radius of curvature of the roll body when the plate is not secured to the roll body. The curvature of the unattached plate is shown in solid outline. The plate will therefore flatten out and seat irmly against the roll body, to eliminate rattling and maintain contact despite centrifugal force in high speed operation, when it is drawn against the roll body by the rod 121. The curvature of the attached plate is shown in dotted outline. The bending stiffness of the plate must permit the draw-down to develop a preload higher than the centrifugal force on the plate when the embossing roll rotates.

In the embodiment illustrated, the rods 121 are rotatably supported in longitudinal grooves 125 which are machined in the surface of the roll body. The grooves extend angularly with respect to a radius of the roll body. One end of each rod can include a head or shoulder which bears against a shallow recess at one end of the roll body, and the other end of the rod can be threadedly engaged with a nut which bears against a shallow recess in the other end of the roll body. The rod can be manually rotated to a latching or unlatching position, for example by a key or wrench fitted to an appropriate feature at the threaded end, and, while its orientation is held, the rod can be locked in place by tightening the nut.

Many other attaching devices can be used, for example, sliding rods, screws, dovetails, any of a variety of releasable latch mechanisms, and equivalents thereof. The disclosed studs and rotating rods have the advantages of quick change; no loose parts which might drop to floor, or be forgotten, or work loose to damage the cooperating roll; end actuation; and easy machining into a roll surface, i.e., no long drilled holes. Many other sufficiently strong attaching mechanisms are possible, with or without a draw-down feature. For example, projecting grippers on the roll body can engage cooperating recesses or cavities in the plates. Any such locking system must have a feature to prevent unexpected loosening due to vibration.

Figure 14 illustrates an embossing roll 126 which uses both vacuum and mechanical devices to attach embossing plates 127 to roll body 128. Each plate includes two or more locating studs 129 as described with respect to Figure 10. The studs are inserted into openings 130 in the roll body and are captured by rotatable notched rods 131 as described with respect to Figure 10. The positions of the studs relative to the openings are precise for locating purposes. However, the fit to the cooperating notched rod is loose to assure easy working. As is well known, for slidably engaging pairs, angular clearance is necessary to prevent binding in the eventuality that the plate is slightly tilted.

The rods 131 are not designed to draw the plate down against the roll body. That is the function of the vacuum system. Rather, the rods serve to retain the plates when the vacuum is turned off or power for the vacuum source is interrupted. For safety, if this should occur while the roll is rotating, the plates must be provided with enough bending strength (by virtue of adequate thickness) to bear the cantilevered centrifugal force.

Two vacuum regions are provided under each of the plates 127. Each vacuum region is defined by a sealing gasket 133. Vacuum communicates with each region through a longitudinal internal passage 134 and branched internal passages 135. The branched passages communicate with grooves 136 in the surface of the roll body.

Figure 15 is an end view of the embossing roll 126 of Figure 14. Three-way vacuum control valves 137 are connected to the vacuum passages 138 in the journal 139 of the roll and to the longitudinal passages 134.

Figure 16 illustrates the notched studs 129 of Figure 13 which are provided with circular notches 140 which are designed to latch the plates rather than draw the plates downwardly against the roll body. When the studs are inserted into the openings 130 and the rod 131 is rotated, the solid portions of the rod rotate into the notches 139. It will be understood that variations in the contours schematically indicated at 140 and 131 may advantageously provide draw-down, ejection, and over- center locking functions.

Figures 17 and 18 are exploded perspective views of the embossing roll 126. Each of the embossing plates is drawn against the embossing rolls by two vacuum regions which are defined by oval sealing gaskets 133. The ends of the rotating rods 131 extend beyond the ends of the roll body 128 and can be rotated by any convenient mechanism.

The embossing plates fully cover the surfaces of an embossing roll over which the web travels so that the continuous web is embossed with the embossing pattern without interruption. Although adjacent embossing plates are separated at their edges, the side edges of the plates create little if any interruptions or discontinuities in the embossing pattern. When surface heating is expected, a slight gap of approximately .010" or more between plates may be intentionally provided to prevent the plates from buckling, and (for the case of locating stud aligned in an axial row) , slight clearance in the axial direction of the roll may be provided in the locating holes. Any interruptions in the embossing pattern can be further reduced or minimized by contouring the side edges of the embossing plates to avoid the important areas of the embossing pattern as illustrated in Figure 7. Preferably the contour would be placed close to protrusion bases, where the rubber roll never penetrates. To eliminate circumferential gaps altogether between axially neighboring plates, the plates can be urged together axially by springs or any other loading means.

The embossing plates can be formed from steel to maximize durability. The thickness of the steel plates can be made sufficient so that the embossing protrusions are not flexed or fatigued by the periodic pressure of the rubber roll .

Referring to Figure 19, the embossing plates for a complete embossing roll can advantageously be formed by first forming an integral steel sleeve 142. For example, a steel sleeve having a wall thickness of 0.25 inch, a diameter of 18 to 20 inches or more, and a length of 100 to 110 inches or more can be formed depending upon the dimensions of the embossing roll.

The sleeve is prepared for later sectioning and precise mounting by drilling holes 114 at precise locations for future studs. If large holes are drilled, the holes can be tapped for installing threaded studs . Small holes can be welded closed on the outside surface of the sleeve, and the inside openings can be used to precisely position studs for welding.

The sleeve is then engraved with the embossing pattern, for example, by match engraving which is a low-force engraving method which will not damage a thin sleeve. Other possible methods are photoengraving of brass or magnesium, spray etching of steel with laser-ablated resist, laser ablation of any plate with surface of polymer or ceramic, or any other low force engraving method which is known in the art .

The engraved sleeve is then cut into a plurality of plates. The thinnest possible kerf, e.g., 0.008-0.020 will minimize disruption to pattern. The plates can be cut with straight side edges as indicated by the dashed lines 144 and 145 in Figure 19, or the edges can be contoured to minimize disruption of the pattern. The plates can be cut either manually, for example, by a jigsaw, or automatically, for example, by laser or water jet.

As an alternative approach, the plates may be cut first and engraved second while held in position on a roll body. In this case higher-force engraving methods may be used. This approach of engraving separate plates also offers the advantages of manufacturing curved plates by rolling flat plates; and eliminating any need for narrow-kerf sectioning.

The embossing plates can be retrofitted to a previously formed conventional embossing roll by removing the previously engraved layer and providing the embossing roll with the vacuum and/or mechanical latching mechanisms. All of the embodiments described herein involve relatively simple surface features and short holes which can be formed in an existing embossing roll by surface machining and drilling.

The thickness of the embossing plates can vary depending upon various criteria:

1. If the objective is to ensure that the plates will survive loss of vacuum when the embossing roll is spinning rapidly, the centrifugal force acting on the cantilevered plate halves on either side of the attaching studs, e.g., 114, 120, 129, should not cause the plates to yield. For high rotational speeds, i.e., speeds substantially higher than current's speeds, this requires a heavy, rigid plate. In fact, the plate would be too heavy, to be held by vacuum alone .

2. The thickness which is required for mechanical engraving is about 1/8 inch. If laser engraving or etching can be used, a thinner plate can be used.

3. If the plate will be attached only by mechanical devices along the centerline of the plate and not by vacuum, the thickness should be such that the centrifugal acceleration acting on the half plate freely cantilevered from the mechanical devices would not deflect the edges of the plate by an amount exceeding the drawn-down displacement of the mechanical devices. For high speeds this requires a thick, rigid plate.

4. The overall thickness t of the plate, including the height h of the embossments is preferably greater than 1.5h: t > 1.5 h

In general the thickness of steel plates is preferably within the range of 1/8 to 1/4 inch. Thicknesses of about 6 mm or 1/4 inch permit machining and provide sufficient plate strength at today's top operating speeds if the mechanical interlock is only in the center of the plate. If it is desired to use a thinner plate or operate at higher speeds, a more complex mechanical interlock system extending closer to the plate edges will be necessary.

1. The plates are heavy enough, and for some embossers require enough arms-outstretched maneuvering, that a supporting or counterbalancing system may be needed. One may use a small jib crane or support arm or temporary guide rails or many other obvious approaches .

2. If so, the plate has to gripped. And it is not practical to grip it in the normal way (pinching contact on front and back) since the back must be left clear for installation. (In fact, there is no access to the back side when trying to remove from a roll.) One could use an edge grip (e.g., on a small 2mm lip around the plate, or at least on the two edges formed by the circumferential cuts) . That is, draw together two shallow hooks which engage the lip from the front side. Int his favored approach the roll should possess ejection means, such as one or more springs trapped under each plate, or an ejection funciton of the mechanical securing devices. Preferably, the plates to be removed (typically 6mm thick) would automatically move outwards half their thickness. Exploiting the angular clearance needed to prevent binding, at the juncture between two axially adjacent plates, the plate to be removed can be tilted u (so its edge has moved outwards nearly one full thickness) while the adjacent plate can be tilted down (so as to uncover the lip, etc. of the plate to be removed.)

With such an approach, if plates are removed in sequence from one end, both edges can be exposed to the hooks for edge-gripping.

Alternate front-surface gripping means are vacuum (with highly flexible seals to prevent air leakage between pattern elements) and magnetic.

3. When plates are being installed and removed, they are not locked in place by the preferred mechanical safety interlock. To be sure that they do not tumble out in the case that the exchange is performed at a nearly vertical sector of the roll, it is desirable to have some temporary holding feature. One approach is to have a ball detent or other weak but reliable mechanical grip, to hold the studs partway in their respective holes. When it is desired to mechanically clamp the plates, either the vacuum or a mechanical drawdown feature is used to press them against the roll body. In particular, if they are installed in sequence starting at the vacuum distribution end, the normal vacuum system may be designed to provide some weak suction in spite of the air flow from the uncovered vacuum areas .

Alternatively, any of a number of obvious low-force attachment means (including a separate vacuum system) may be used to secure the plates from dropping when the primary holding systems (e.g., vacuum and mechanical) are switched off.

While in the foregoing specification a detailed description of specific embodiments were set forth for the purpose of illustration, it will be understood that many of the details hereingiven may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.

Claims

I CLAIM :

1. An embossing roll for embossing a web comprising: an elongated roll body having a central longitudinal axis, a plurality of plates removably mounted on the roll body, each of the plates having an outer surface which is provided with an embossing pattern, and means for removably securing the plates to the roll body.

2. The embossing roll of claim 1 in which said securing means includes means for applying vacuum to the plates.

3. The embossing roll of claim 1 in which said securing means includes means for locating said plates on said roll.

4. The embossing roll of claim 2 in which said securing means includes a mechanical attaching device for each plate.

5. The embossing roll of claim 2 in which said securing means includes a radially inwardly extending stud on each plate and an opening in the roll body for each of the studs.

6. The embossing roll of claim 5 in which said securing means includes means for releasably retaining each of the studs in the associated opening in the roll body.

7. The embossing roll of claim 6 in which said means for releasably retaining includes a longitudinally extending rod which extends through a plurality of said openings in the roll body, the rod being rotatably mounted for rotation about a longitudinal axis and having a notch aligned with each opening .

8. The embossing roll of claim 2 in which said means for applying vacuum includes grooves in the roll body which are covered by the plates and seals mounted on the roll body which engage the plates .

9. The embossing roll of claim 1 in which said securing means includes a mechanical attaching device for each plate.

10. The embossing roll of claim 9 in which said mechanical attaching device includes means for drawing the plate against the roll body.

11. The embossing roll of claim 9 in which said securing means includes a radially inwardly extending stud on each plate and an opening in the roll body for each of the studs.

12. The embossing roll of claim 11 in which said securing means includes means for releasably retaining each of the studs in the associated opening in the roll body.

13. The embossing roll of claim 12 in which said means for releasably retaining includes a longitudinally extending rod which extends through a plurality of said openings in the roll body, the rod being rotatably mounted for rotation about a longitudinal axis and having a notch aligned with each opening .

14. The embossing roll of claim 1 in which each of said plates is formed from steel and is curved to form a portion of a cylindrical surface.

15. The embossing roll of claim 12 in which the outer surfaces of said plates form a substantially continuous surface.

16. The embossing roll of claim 1 in which each of said plates includes non-linear side edges to reduce disruption of the embossing pattern.

17. An apparatus for embossing a web comprising: a frame, an embossing roll rotatably mounted in the frame for rotation about a longitudinal axis, the embossing roll having an outer surface which is provided within an embossing pattern, a cooperating roll rotatably mounted in the frame for rotation about a longitudinal axis parallel to the longitudinal axis of the embossing roll, the cooperating roll pressing against the embossing surface of the embossing roll, means for feeding a web between the embossing roll and the cooperating roll, the embossing roll comprising a roll body and a plurality of removably mounted plates on the roll body which provide said embossing pattern, and means for removably securing the plates to the roll body.

18. The apparatus of claim 17 in which said securing means includes means for applying vacuum to the plates .

19. The apparatus of claim 18 in which said securing means includes a mechanical attaching device for each plate.

20. The apparatus of claim 17 in which said securing means includes a mechanical attaching device for each plate.

21. The apparatus of claim 17 in which said cooperating roll is a rubber-covered roll.

22. The apparatus of claim 17 in which said cooperating roll has a surface with cooperating recesses .

23. The apparatus of claim 22 in which the surface of said cooperating roll is metal.

24. The apparatus of claim 22 in which the surface of the cooperating roll is paper.

25. A method of forming an embossing roll for embossing a web comprising the steps of: forming a cylindrical steel sleeve having a curved outer surface, engraving an embossing pattern on the outer surface of the sleeve, cutting the sleeve to form a plurality of curved plates, and removably attaching the plates to a generally cylindrical roll body.

26. The method of claim 25 including the step of forming on the cylindrical sleeve means for positioning the plates on the roll body, said forming step being performed before the sleeve is cut .

27. The method of claim 25 in which the sleeve is cut non-linearly to reduce disruption of the embossing pattern.

28. A method of forming an embossing roll for embossing a web comprising the steps of: forming a cylindrical steel sleeve having a curved outer surface, cutting the sleeve to form a plurality of curved plates, and removably attaching the plates to a generally cylindrical roll body, and engraving an embossing pattern on the outer surface of the plates.

29. A method of forming an embossing roll for embossing a web comprising the steps of: forming curved steel plates, removably attaching the plates to a generally cylindrical body, and engraving an embossing pattern on the outer surface of the plates.