Patent Description:
Web materials such as polymer film, paper, nonwoven or woven textile, metal foil, sheet metal, and others, are used to manufacture a variety of products. The web materials are generally provided in the form of large rolls or coils formed by winding the web material about a winding core. The core is generally paperboard, though it may be reinforced with a plastic outer shell or the like. The paperboard core may be formed of low, medium or high strength paperboard plies.

A roll of paper or the like wound onto the core typically has a weight above a half ton and can exceed five tons. Typical core sizes are a nominal internal diameter (ID) of <NUM> in. to <NUM> in. (<NUM> to <NUM>) and a length of about <NUM> to <NUM> inches ( about <NUM> to <NUM>,<NUM>). Other cores, such as tissue cores and cores for carrying sheet metal, can have IDs ranging from <NUM> in. to <NUM> in. (<NUM> to <NUM>).

To begin the winding process, a leading edge of a web is attached to the winding core and the core is rotated about its axis to wind the web into a roll. The rolls are subsequently unwound during a converting or similar process.

Web converters continually strive to increase productivity of converting processes by increasing the total amount of web throughput per unit time. To this end, there has been a continual push toward higher web speeds, roll widths and roll weights, which leads to winding cores that must rotate at higher rotational demands. Thus, paper converting can place extreme demands on the stability of current winding cores.

During a winding or unwinding operation, a core is typically mounted on a rotating expandable chuck that is inserted into each end of the core and expanded to grip the inside of the core so that the core tends not to slip relative to the chucks as torque is applied therebetween. Typically, the rotation of the core is achieved by means of a drive coupled to one or both of the chucks, and the core is rotated to achieve web speeds of, for example, <NUM> fpm to <NUM> fpm (<NUM>/s to <NUM>/s) or more. The chucks generate torque (rotational force) on the core as they rotate the core during a winding operation. Torque also can be generated by the web during an unwinding operation, and by braking tension applied to the core by the chucks or other core engaging elements.

Currently in many winding and unwinding (converting) operations, cores are used in combination with chucks that have smooth expanding elements. These smooth expanding elements do not always engage the core properly, or the maximum torque transmission is exceeded, and as a result, the chuck will break free and slip inside the core. When the slippage is excessive, the ends of the core that contact the chucks can be damaged or destroyed, the material carried on the core cannot be used, and the speed of the converting process is negatively impacted. Debris generated during unwanted slippage can also cause chuck performance and maintenance issues. Even a mild case of slippage can lead to reduced throughput, lower converting speeds and causing an excessive waste of material.

<CIT> teaches a tubular core in which the chuck-engaging surface of the core is made from a softer material than the body of the core, such that the chucks can "penetrate" ("dig in and grip") the soft chuck-engaging surface. This penetration of the chucks into the softer chuck engaging surface increases the physical engagement of the core and chucks and prevents the chuck from slipping while the core is rotating. <CIT> teaches using a softer layer for the mechanical engagement between the chucks and the core. <CIT> teaches using at least a <NUM> thick layer to allow for this improved engagement. See <CIT> at Paragraph <NUM>. <CIT> teaches applying a softer layer of material to the entire chuck engaging surfaces.

<CIT> discloses an improved core for mounting on one or more core engaging elements, the core having an inner surface and an outer surface adapted to accommodate sheet material wound thereon, the core having two axially opposed ends (see <FIG>), the core comprising one or more inner plies that form engaging elements. <CIT> teaches a method of making a hollow cylindrical core comprising the steps of: spirally winding one or more inner plies around a forming mandrel; spirally winding one or more additional plies around the forming mandrel to form a continuous core that moves axially along the mandrel before coming off the mandrel; cutting the continuous core into individual cores, each core having two axially opposed ends, an inner surface comprising one or more engaging surfaces near each end and an outer surface adapted to accommodate a material wound therein. <CIT> discloses a winding core that has high stiffness by virtue of being formed predominantly of fiber-reinforced plastic (FRP) such as fiber glass material or the like. In particular, the winding core comprises a tubular shell of FRP, which is substantially stiffer than a paperboard tube of the same dimensions. However, expandable chucks cannot readily dig into and grip the FRP shell because of its hardness. Accordingly, the winding core also includes a pair of generally tubular end fittings bonded to the inner surface of the shell at the opposite ends, the end fittings comprising a material having a durometer hardness substantially lower than that of the shell and being positioned to be engaged by winding or unwinding chucks. Each end fitting has an axial length that is a relatively small fraction of the length of the shell. <CIT> describes coating being disposed on the inner surface along the entire length of the core. <CIT> shows a method of making a hollow cylindrical core, the core having a length, comprising the steps of: spirally winding one or more inner plies around a forming mandrel, spirally winding on or more additional plies around the forming mandrel to form a continuous core that moves axially along the mandrel before coming off the mandrel, cutting the continuous core into individual cores, each core having two axially opposed ends, an inner surface comprising one or more engaging surfaces near each end, and an outer surface adapted to accommodate a material wound therein.

The present disclosure relates to an improved core for mounting on core engaging elements such as a shaft or a pair of chucks, and a method of making an improved core. The core is adapted to wind and unwind material thereon.

The object is achieved by an improved core according to one of the claims <NUM>, <NUM> and <NUM> and by a method according to claim <NUM>. Advantageous further developments are subject-matter of the dependent claims.

While this invention may be embodied in many forms, there is shown in the drawings and will herein be described in detail one or more embodiments with the understanding that this disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention as defined by the claims.

The following definitions are intended for the ease of understanding of the disclosure and are not intended to be limiting.

Arbor: A shaft or axle upon which a sheet may be wound.

Coating: When used herein as a verb, the word "coating" may refer to any suitable means of applying a material onto a surface. When used herein as a noun, the word "coating" may refer to any suitable material applied to a surface, such as the inner surface of a core, including without limitation liquids, powders, compounds, mixtures and treatments.

Coefficient of Friction (abbreviated COF, CoF or Cof): As used herein, coefficient of friction generally means the frictional force between a core and the core engaging elements when the two are stationary.

Core: A cylindrical structure, usually hollow, for carrying sheet or strand material thereon. The core may be made of fiber (such as wound paper), plastic, metal or any suitable material. Sometimes referred to as a tube or spool. The cores described herein may be used to hold and dispense any suitable material, including without limitation paperboard (such as for use in making packaging, sheet grade paper, and tissue grade paper), metal sheets, plastic films and textiles.

Chew Out: Damage to the inner surface of a core caused during a winding or, especially, an unwinding operation when the core engaging elements rotate independently of the core. Chew out usually happens when maximum torque is exceeded.

Core engaging elements: The structure or structures that engage (contact) the core to hold the core during winding and unwinding operations. May include without limitation chucks, solid shafts, differential shafts and arbors, either with or without expanding elements.

Engaging surface(s): The surface(s) on the inner surface of the core that engage (contact) the core engaging elements.

High-COF: The term "High-COF" (or "High COF") is used herein to describe a coating or other composition that tends to increase the COF between two surfaces, such an the inner surface of a core and the core engaging elements.

Maximum torque: The amount of torque that can be applied to a core before slippage (between the core and the core engaging elements) occurs.

Recoiler: A machine used to wind sheet material, particularly metal sheets, onto a core or spool.

Shafts: In contrast to chucks, shafts generally extend through the entire length of the core to hold the core. Differential shafts are shafts having sections that can rotate at different rotational speeds.

Torque: As used herein, torque generally means the rotational force applied to a core. Torque can generated by the core engaging elements as they rotate the core during a winding operation. Torque also can be generated by the web during an unwinding operation, and by braking forces applied to the core engaging elements.

Turning to the drawings, there is shown in <FIG> a perspective view of a portion of a core <NUM> used for carrying material <NUM> thereon. The material <NUM> can be any suitable strand or sheet material such as but not limited to paper, film and textiles. The core <NUM> may comprise spirally wound paper (such as in fiber based cores) and has an inner surface <NUM> and an outer surface <NUM>. The core <NUM> extends longitudinally (axially) between two ends <NUM> and may be any suitable length.

<FIG> a partial plan view of an apparatus <NUM> for making a core such as the core <NUM> of <FIG>. In general, the core <NUM> may be formed by spirally (or convolutely) winding a plurality of fiber based plies about a mandrel <NUM>, adhering the plies together, and severing portions or sections of the continuous core as it comes off the mandrel <NUM> to form individual cores <NUM>. The plies are drawn from respective creels (not shown) and routed along a path to the mandrel <NUM>. Each ply may have an adhesive applied to it at an adhesive applying station (not shown) such as a glue pot for adhering to adjacent plies.

In the illustrated apparatus, an inner ply <NUM> is applied to the mandrel <NUM> and spirally wound to form the inner layers of the core. Downstream from the inner ply <NUM>, a plurality of intermediate or body plies <NUM> are applied on top of the inner ply <NUM> and spirally wound to form an intermediate zone of the core <NUM>. After applying the last intermediate layer <NUM> and forming the intermediate zone, one or more outer plies <NUM> are applied on top of the intermediate zone and spirally wound to form an outer zone of the continuous core <NUM>. A cut-off station (not shown) may be included to cut the continuous core <NUM> into discrete lengths to form individual cores <NUM>.

A winding belt <NUM> may be used to rotate the continuous core <NUM> in a screw fashion such that the continuous core <NUM> advances down the mandrel <NUM>. To facilitate movement of the continuous core <NUM> along the stationary mandrel <NUM>, a lubricant may be applied to the inner surface of the innermost ply <NUM> using a lubricating station (not shown). The lubricant may be any suitable lubricant, including but not limited to a waxy solid, a liquid or a powder.

<FIG> is a cross-sectional side view of a portion of a paper converting apparatus <NUM>, including a core <NUM> mounted on two chucks <NUM>. The core <NUM> has an inner surface <NUM> that engages the chucks <NUM> and an outer surface <NUM> that carries wound material <NUM> such as paper, plastic film or metal foil. The chucks <NUM> are located at either end <NUM> of the core <NUM> and have expandable elements <NUM> (sometimes referred to as "jaws") that engage engaging surfaces <NUM> of the core <NUM>. The engaging surfaces <NUM> are located at each end <NUM> of the core <NUM> and are part of the inner surface <NUM> of the core <NUM>.

Chucks come in numerous types and geometries. Some chucks are substantially cylindrical and some have cone-like extensions. As noted above, many chucks have expandable elements that engage the inner surface <NUM> of the core <NUM>.

The inner surface <NUM> is typically a paperboard material, although the inner surface <NUM> could be any suitable material for the core <NUM>. Typically, the paperboard material has a density of between about <NUM>/cm<NUM> to about <NUM>/cm<NUM>, but the density can and sometimes does fall outside this range. The core <NUM> could be a "heterogeneous" tube wherein different materials (such as different grades of paper) form different parts (typically layers) of the core <NUM>, or it may be a "homogeneous" tube wherein the entire core wall is formed of a single type of material, which is typical of most paperboard winding cores.

A typical outer diameter of the winding core <NUM> may be about <NUM> in. (<NUM>) and a typical inner diameter of the core <NUM> may be about <NUM> in. Winding cores typically come in standard diameters to accommodate uniform tooling, but it should be understood that the winding core may have various dimensions for both the inner and outer diameters of the core <NUM>, as well as the thickness of the core <NUM>. The length of the core <NUM> in one embodiment is about <NUM> in. ), while typical core lengths range from <NUM> in. (<NUM>) to <NUM> in. However, it should be understood that the core <NUM> could be any suitable dimensions depending on the specific web material being wound or other factors.

<FIG> is a perspective schematic view of one end <NUM> of the core <NUM> of <FIG> with the body portion of the chuck <NUM> removed for clarity. The chuck <NUM> in <FIG> and <FIG> includes three expandable elements <NUM>. Each expandable element <NUM> is capable of expanding radially outward from the chuck body. The expandable elements <NUM> may be arranged about the entire circumference of the chuck <NUM>. Thus, the expandable elements <NUM> may be spaced uniformly about the entire inner circumference of the core <NUM>.

In an embodiment where the core <NUM> is about <NUM>. in length, a roll of paper <NUM> wound on the core <NUM> can approach a weight of <NUM> tons. The expandable elements <NUM> on each chuck <NUM> located at the top of the core <NUM> support the weight of the winding core <NUM> in addition to the weight of the web material <NUM> that is wound on the winding core <NUM> at any given time. Consequently, the expandable elements <NUM> are capable of producing a substantial amount of force on the core <NUM> to both rotate and support the winding core <NUM>.

Torque may be applied to the core inner surface <NUM> in a number of ways and at different times during winding and unwinding operations. In a winding operation, one or both chucks <NUM> may be coupled to a motor or the like to drive the core <NUM> in rotation to wind the web <NUM> around the core <NUM>. This driving action applies torque to the core inner surface <NUM>.

The chucks <NUM> also may apply torque to the core inner surface <NUM> during an unwinding operation. When unwinding material <NUM> from the core <NUM> during, for example, a paper converting operation, the expandable elements <NUM> engage the engaging surfaces <NUM> of the core <NUM>, applying a pressure to hold the core <NUM> in rotational engagement. In a paper converting operation such as that shown in <FIG>, the web <NUM> may be unwound from the core <NUM> via a machine driven apparatus not shown in <FIG>. During unwinding at least one chuck <NUM> is coupled to a brake (not shown) that acts to slow or stop the winding core <NUM> from rotating. The core <NUM> is typically rotated at peripheral speeds of <NUM>/s to <NUM>/s, although various other speeds, including much higher speeds, may be employed. It is possible that during an unwinding operation the web itself may cause torque as it is pulled off the roll.

Although the chucks <NUM> shown in <FIG> include expandable elements <NUM>, it should be understood that the chucks <NUM> could have other configurations and may alternatively not expand hydraulically, but rather expand pneumatically or mechanically inside the hollow of the core <NUM>, as is known by those skilled in the art. The expandable elements <NUM> may also have different designs, sizes and shapes to accommodate different winding cores <NUM> or a specific winding/unwinding application. Different types and sizes of chucks <NUM> could also be implemented for different sized winding cores <NUM> or for different types of winding core materials.

The expandable elements <NUM> can impart very high forces on the core <NUM>. <FIG> is a perspective end view of a core <NUM> after a partial unwinding operation. The ID (inner surface <NUM>) of the core <NUM> bears visible impressions/indentations <NUM> caused by pressure exerted on the core <NUM> by the expandable chuck elements <NUM>, but otherwise is basically undamaged. These indentations are a function of the radial force applied to the core <NUM> by the expandable elements <NUM>, as well as the grade, density and hardness of the paper used.

As the torque on the core inner surface <NUM> increases, the likelihood of slippage between the core <NUM> and the chucks <NUM> increases. In general, many cores can withstand a torque force of <NUM>-<NUM> lbf-ft (<NUM>-<NUM>) and some cores can withstand much higher torque forces. Chucks have been designed to mitigate slippage by, for example, designing expandable elements <NUM> to increase the contact area between the expandable elements <NUM> and the core <NUM> and. more particularly, the engaging surfaces <NUM> of the core inner surface <NUM>.

<FIG> is a perspective end view of another core <NUM> after a partial unwinding operation. During the unwinding operation, torque on the core <NUM> increased to the point where the chuck <NUM> rotated independently of the core <NUM> and damaged the inner surface <NUM> of the core <NUM>.

This damage may involve multiple inner plies, and is sometimes referred to as "chew out. " Slippage can also result in "burnout", wherein the friction caused by the chucks <NUM> against the core <NUM> burns or scorches the core <NUM>, rendering it unsuitable for further use.

When chew out (or burnout) occurs, the user can't control the web of material <NUM> coming off the core <NUM>, which can require slowing or shutting down the paper converting operation and adjusting the core-chuck interface. Sometimes the user will place a shim or other device between the core <NUM> and the chucks <NUM> to try to eliminate further slippage, web breaks, vibration or other converting issues resulting from chuck slippage and/or core chew-out. Sometimes the user must run at a lower speed to try to avoid slippage. Also, sometimes the user will splice the web to a new roll of paper early. Repeated slippage can cause the user to splice out of rolls prematurely.

An overall method of mitigating slippage and the damage it can cause is to change the coefficient of friction (COF) between the inner surface <NUM> of the core <NUM> and the core engaging elements. COF, often represented by the variable µ, may be represented by the following formula: <MAT> where:.

There are two kinds of µ, static and kinetic. In the discussion that follows, µ (or COF) is generally the static µ (or static COF). It should be understood that, while the processes disclosed herein generally increase static µ, they also generally increase kinetic µ as well.

The COF between the inner surface <NUM> of the core <NUM> and the chucks <NUM> is a function of many variables, some of which can be controlled to improve the core-chuck interaction and thus mitigate damage to the core <NUM>. There have been developed and will now be described various improved cores as well as methods of improving core-chuck interaction.

In one aspect a core <NUM> and method of making a core <NUM> involves using a high COF material ("coating") <NUM> that is applied or otherwise disposed on the inner surface <NUM> of the core <NUM>. The high COF coating <NUM> is adapted to increase the coefficient of friction (COF) between the inner surface of the core <NUM> and the core engaging elements such as the chucks <NUM>. The coating <NUM> may be applied over the lubricant (if present) and/or directly onto the "bare" inner surface of the core <NUM>.

<FIG> is a perspective view of a core <NUM> after a high COF coating <NUM> has been applied to a portion of the inner surface <NUM>. As explained further below, the high COF coating <NUM> may be applied in any suitable pattern and to all or less than all of the engaging surfaces <NUM> of the core <NUM>.

<FIG> is a graph showing the relationship between maximum torque and the coefficient of friction (COF) between the core and the core engaging elements. The data in <FIG>, obtained using finite element analysis (FEA), shows that maximum torque increases as COF increases.

Increasing the COF between the inner surface <NUM> of the core <NUM> and the core engaging elements (such as chucks <NUM>) increases maximum torque, that is, the amount of torque (rotational force) that can be applied to the core <NUM> by the chucks <NUM> before slippage occurs. In other words, adding a high COF coating <NUM> to the inner surface <NUM> of the core <NUM> causes the chucks <NUM> to better grip the core <NUM>.

<FIG> is a graph showing the effect of the COF (between the inner surface <NUM> of a core <NUM> and the core engaging elements <NUM>) upon the maximum torque for a core <NUM> having an inner ply <NUM> made from a first grade of paperboard (designated "Board <NUM>"). As <FIG> shows, maximum torque generally increased with the COF. Here is the same data in table form:.

<FIG> is a graph showing the effect of the COF (between the inner surface <NUM> of a core <NUM> and the core engaging elements <NUM>) upon the maximum torque for a core <NUM> having an inner ply <NUM> made from a second grade of paperboard (designated "Board <NUM>"). Again, torque generally increased with COF. Here is the same data in table form:.

The high COF coating may be any suitable material that increases the COF of the core <NUM> and the core engaging elements <NUM>. The coating <NUM> may be applied in the form of a liquid, powder, slurry or any suitable physical form. The coating <NUM> may be suitable for use with most if not all chuck designs. Suitable coatings include but are not limited to aqueous dispersions of anti-skid agents and silicates, latex coatings and adhesives.

<FIG> is a graph showing the effect of the concentration of high COF material on torque, that is, the effect of the weight percent of high COF material in the coating applied to <NUM>% of the chuck engaging surface area <NUM> on torque. As the figure shows, for at least one coating / paperboard combination, increasing the concentration of the high COF material in the coating <NUM> increased torque. Here is the same data in table form:.

The coating <NUM> may be applied to all or a portion of the inner surface <NUM> of the core <NUM>. For example, the coating <NUM> may be applied only to the chuck engaging surface <NUM> near each end <NUM> of the core <NUM>, or along the entire axial length of the core <NUM>.

<FIG> is a graph showing the effect of surface area on torque, and, in particular, the effect of the percent of the core inner surface <NUM> that is covered with high COF material <NUM> on maximum torque. The coverage, that is, the area on which the coating <NUM> is applied expressed as a percentage of the total area of the core inner surface, varied from <NUM>% to <NUM>%. The maximum torque varied from <NUM> to <NUM>. As the figure shows, torque performance generally improved with surface area coverage. Here is the same data in table form:.

<FIG> is a graph showing the relationship between coating pattern and maximum torque. As previously noted, the coating <NUM> may be applied to the inner surface <NUM> of the core <NUM> in various patterns or configurations. For example, the high COF coating (<NUM>) may be applied to the inner surface (<NUM>) in a pattern to achieve a desired level of surface area coverage. The coating <NUM> may be applied in a single spiral pattern (like in <FIG>), a multiple spiral pattern, in one or more annular rings, or in any suitable pattern. The coating <NUM> may also be applied only to all or part of the engaging surfaces <NUM>.

In the test results shown in <FIG>, coating the inner surface <NUM> of a core <NUM> with one, two or three <NUM>,<NUM> wide spirals resulted in maximum torque values of <NUM>, <NUM> and <NUM> respectively. Coating the inner surface <NUM> of the core <NUM> with one, two or three <NUM>,<NUM> wide spirals resulted in maximum torque values of <NUM>, <NUM> and <NUM> respectively. Coating the entire inner surface <NUM> of the core <NUM> ("full coverage") resulted in a maximum torque value of <NUM>. Here is the same data in table form:.

Although all of these results may be satisfactory, it may be surmised from this data that fuller coverage results in better core/chuck interaction, at least to a point.

<FIG> is a flowchart illustrating a method <NUM> of making an improved core <NUM>. The method may comprise the following steps:.

As noted above, the core <NUM> may be formed by spirally winding a plurality of plies <NUM>, <NUM>, <NUM> about a mandrel <NUM>, adhering the plies together to form a continuous core <NUM>, and severing portions or sections of the continuous core <NUM> to form individual cores <NUM>. A high COF coating <NUM> is disposed on at least the engaging surfaces <NUM> of the core <NUM> in one of several different ways. For instance, the coating <NUM> may be applied before, during or after the core making process.

If applied before the core making process, the coating <NUM> should be applied to the inner facing surface of the paper used to make the innermost plies <NUM>.

If applied during the core making process, the coating <NUM> may be applied either to the inner plies <NUM> that make up the inner surface <NUM> prior to winding the plies <NUM> around the mandrel <NUM>, or to the formed core inner surface <NUM> as the continuous core <NUM> moves along the mandrel <NUM>. If applied after the core making process, that is, after the continuous core <NUM> is cut into usable individual cores <NUM>, the coating <NUM> may be applied by any suitable means, including using a rag applicator, rollers, brushes, a squeegee applicator or a spray applicator. Preferably the coating <NUM> is applied near each end <NUM> where the chucks <NUM> engage the core <NUM>.

Preferably the coating <NUM> is applied on areas where the expanding core engaging elements <NUM> (chucks, shaft, etc.) are in contact with inside surface <NUM> of the core <NUM>. In the case of chucks <NUM>, this area generally is near each end <NUM> of the core <NUM>. With shafts, this area may extend most or the entire length of the core <NUM>. In some cases this area may be just one end <NUM> of the core <NUM> if that end experiences more torque (e.g., from a motor and/or brake).

In another aspect the method of improving core-chuck interaction involves using a specialty material for the inner ply or plies <NUM> of the core <NUM> or the engaging surfaces <NUM> of the core <NUM>. The specialty material can be a high COF, anti-skid paper or a paper having special properties. The special properties may include thickness, roughness and recycled paper content.

Tests were conducted to determine the effect of paper density on maximum torque. <FIG> is a graph showing the effect of the density of the core inner ply <NUM> on maximum torque. As the figure shows, in this brief set of tests, torque performance did not correlate well with density of the inner ply <NUM>. Here is the same data in table form:.

Tests were conducted to determine the effect of paperboard strength of the inner ply or plies <NUM> on maximum torque. <FIG> is a graph showing the effect of paperboard strength of the core inner ply <NUM> on maximum torque. As the figure shows, in this brief set of tests, torque performance did not appear to correlate well with paperboard strength. Here is the same data in table form:.

There may be a point where the inner ply paper density or paperboard strength is just as important if not more so than the COF between the core <NUM> and the core engaging elements <NUM> in mitigating chewout. For instance, the COF between the core <NUM> and the core engaging elements <NUM> may be increased to such a high level that chuck slippage isn't the primary concern but paper failure is. However, it is believed that this drastically increased level of COF - and thus maximum torque - is outside the normal operating levels in most paper converting operations.

In another aspect, the method of improving core-chuck interaction involves mechanically or (not claimed) chemically treating the core inner surface or just the engaging surfaces of the core to alter the coefficient of friction (COF). For example, the method may comprise mechanically or chemically treating the engaging surfaces <NUM> of a core <NUM> to increase the COF of the engaging surfaces <NUM>, thereby increasing the maximum torque between the core <NUM> and the core engaging elements <NUM>.

In one aspect, the inner surface <NUM> of the core <NUM> may be mechanically treated during or after the core making process, such as by mechanical abrasion to increase the roughness of the inner surface <NUM>.

In another (not claimed) aspect, the inner surface <NUM> of the core <NUM> may be chemically treated to increase the COF of the inner surface <NUM> during or after the core <NUM> is made. The treatment may involve chemically treating the material, such as paperboard, that forms the inner ply or plies <NUM> prior to making the core <NUM>.

In yet another aspect the method of improving core-chuck interaction involves placing or positioning a loose layer of material between the inside surface <NUM> of the core <NUM> and the core engaging elements <NUM>. In such cases the loose layer may be removed after winding.

The present disclosure relates to improved cores and methods of improving the interaction between cores and core engaging elements to reduce or eliminate damage to the core or operational problems. The cores and methods may be useful in numerous industries, including the paper industry (for example, with sheeting operations (fine paper, converting)), the liner industry, the sheet metal industry, and any industry involving winding or unwinding of materials carried on cores.

For example, in the paper industry where cores are often mounted at either end on chucks, it may be desirable to increase the coefficient of friction (COF) between the inner surface of the core and the chucks, either by increasing the COF across the entire inner surface of the core or just at the chuck engaging surfaces.

Likewise, in sheet metal carrying applications where Metallan™ cores are often mounted on a shaft, it may be desirable to increase the coefficient of friction (COF) along the entire inner surface of the core <NUM> or along less than the entire inner surface <NUM>, such as along just the middle portion of the inner surface <NUM> between the core ends <NUM>.

In industries that employ differential winding shafts, such as certain paper, film, and tape industries, it may be desirable to adjust the coefficient of friction (COF) of each individual core to achieve a desired level of web tension for each core during winding or unwinding. Differential shafts are shafts having sections that can move (rotate) relative to each other. Typically, multiple cores are placed on the various sections of the shaft at the same time. The differential shaft allows relative movement between the cores, and also allows relative movement or slippage between each core and its corresponding section of the shaft. In these applications it may be desirable to control the COF of each core using the techniques described herein to achieve the desired level of web tension for each core during winding or unwinding.

The cores and methods described herein may offer improved performance for all chuck types, including chucks having smooth expandable elements, non-smooth expandable elements or no expandable elements. Examples of non-smooth expandable elements include those that are profiled, roughened or serrated. While core engaging elements having smooth surfaces are more challenging, problems can also occur for example with elements include those that profiled, roughened or serrated.

It is understood that the embodiments of the invention described above are only particular examples which serve to illustrate the principles of the invention.

Claim 1:
An improved core (<NUM>) for mounting on one or more core engaging elements, the core (<NUM>) adapted for winding and unwinding material (<NUM>) thereon, the core (<NUM>) being hollow and cylindrical and having an inner surface (<NUM>) and an outer surface (<NUM>) adapted to accommodate the material (<NUM>), the core (<NUM>) having two axially opposed ends (<NUM>), characterized by
a high coefficient of friction (COF) coating (<NUM>) disposed on all or a portion of the inner surface (<NUM>) in one or more spiral patterns, the high COF coating (<NUM>) adapted to increase the coefficient of friction (COF) between the inner surface (<NUM>) of the core (<NUM>) and the core engaging elements.