US20070042884A1

US20070042884A1 - Optimized heat roll apparatus

Info

Publication number: US20070042884A1
Application number: US11/507,108
Authority: US
Inventors: Rene Larive; Bruce Taylor
Original assignee: Comaintel Inc
Current assignee: Comaintel Inc
Priority date: 2005-08-22
Filing date: 2006-08-21
Publication date: 2007-02-22

Abstract

One embodiment of the heated roll apparatus uses an optimized roll whose surface layer is composed of a material responsive to being heated, particularly by external magnetic induction, and the depth of which, as well as the construction of the rest of the roll, uses one or more other materials whose properties are optimized with respect to maximizing the roll's rate of temperature change, minimizing energy usage, and performing the intended application. A thin outer ferrous layer over top of a thicker ceramic, insulating layer may be used. The roll may also include an outer layer that is responsive to heating, particularly by magnetic induction, and one or more inner layers of different material(s) chosen to increase the roll's rate of temperature change and reduce energy usage, but which are further selected to promote rapid lateral heat conduction to reduce lateral temperature variations. This roll could include a thin outer ferrous layer over top of a thicker aluminum core. The roll may instead be constructed of a single contiguous material (such as a carbon-fiber composite) that is particularly responsive to heating by magnetic induction, and which has a higher strength-to-weight ratio than ferrous alloys (i.e. cast iron or steel), thereby allowing it to be lower in weight and more thermally responsive than conventional heated rolls. The roll may also have a surface layer or contiguous depth composed of a material responsive to being heated, particularly by magnetic induction, but which in addition has a minimal outside diameter (regardless of its internal construction) in order to minimize its mass, so that it can be heated more quickly to a higher temperature, by a given heat input rate generated by any means, than would be possible with a larger, conventional heated roll.

Description

FIELD OF THE INVENTION

This invention relates to heated rolls used in web processing operations such as: calendering; drying; laminating; embossing; pre-heating; corrugating; curing; heat-setting, shrinking; bonding; etc. It has particular application to roll surface materials responsive to high temperature induction heating, where energy losses associated with conventional, indirect heating systems can be significantly reduced.

BACKGROUND OF THE INVENTION

The surface layer of most heated rolls is typically thick-walled and made of a ferrous alloy, while other more specialized, usually unheated rolls use other metals (e.g. aluminum) as well as non-metal materials such as granite. Heated rolls are typically heated internally, using hot water, hot oil, or steam, and may also be heated externally using steam jets, gas flames, hot air impingement, infra-red radiation, or magnetic induction. The depth of the surface layer of conventional heated rolls is typically greater than is necessary for the application at hand. While this may be due to strength considerations, it is often due to a lack of appreciation of the how this depth affects the process response time, energy consumption, and required heating system size. The applied heat may also be free to migrate in the cross-direction through the roll's thick outer wall at a rate higher than is optimal for the specific application. Or, conversely, the relatively low thermal conductivity of ferrous metals may limit the lateral heat conduction to a rate lower than is optimal for a specific application. The following are examples of these various situations;
Web Calendering Applications
In some continuous sheet producing industries (such as papermaking and metal sheet or foil manufacturing), in one of the final steps, commonly referred to as calendering, the web is passed between heavy, stiff rolls that are loaded against one another to compress the web and make it more dimensionally uniform. Calendering rolls are typically thick-walled and made of a ferrous alloy and are most commonly heated by a hot internal fluid flow, using hot water, hot oil or steam. The historical use of internal heating fluids, and the need for high roll stiffness during calendering has resulted in conventional heated calendering rolls being relatively thick-walled (typically with wall thickness of more than one inch, or solid throughout), with elaborate and expensive cross-bored fluid channels and rotating seals. Furthermore, conventional heated calendering rolls are made of an essentially homogeneous, moderately thermally-conductive material, such as steel, throughout their full wall thickness, to permit unimpeded heat conduction from the inside to the outside. The external fluid heating systems that accompany conventional heated calendering rolls are also relatively inefficient due to piping circuit heat losses and energy conversions losses (their original source of energy is often natural gas or heating oil, requiring energy conversion with attendant combustion and heat exchanger inefficiencies). Requisite external fluid temperature control systems must also be able to cool the fluid (to enable precise roll temperature control, and to remove the heat quickly during stoppages), which adds to the overall complexity and cost.
A primary limitation of conventional heated calendering rolls is that they are relatively thermally-conductive throughout their substantial depth, requiring that their whole mass be heated up to attain a desired outer surface temperature. Furthermore, the large mass of internal fluid used by conventional heated calendering rolls also has to be heated before it can heat the roll, or cooled before it can cool the roll. The large roll and fluid mass, and the long radial conductive path throughout the depth of the roll, thus produces a large thermal inertia that reduces the response time of roll temperature controls to process disturbances on continuous operations, and which furthermore thus imposes a severe setup and change-over delay on discontinuous, batch-type calendering processes. A further consequence of this large thermal inertia is that external fluid cooling and heating systems must be significantly over-sized to cool and heat the rolls fast enough before and after stoppages. Over-sizing these fluid-cooling and heating systems beyond what steady-state conditions require adds significantly to their size, complexity and initial cost, and further aggravates their inherent energy inefficiencies. A further limitation of conventional heated calendering rolls is that they are homogenous across their width, and the internal fluid paths are continuous across their entire width, making it impossible to locally heat just one cross-direction region of the roll. Even if a localized external heating means, such as magnetic induction or forced-convection heating using hot air impingement, is used to heat just one cross-direction region of the roll, the applied heat will conduct laterally through the roll, diminishing the localized effect.
Web Drying Applications
While there are many types of webs that are dried using heated rolls or heated metal cylinders, a typical one is a wet paper web, where in the case of paper manufacturing, it is upstream of the calendering process described above, and the web is typically first dried by passing it around steam-heated metal cylinders that are typically referred to as dryer cans. To permit heat conduction from the inside to the outside, dryer cans are usually made of a ferrous material such as cast iron, and are usually relatively thick-walled to support their own weight and that of the internal condensate, and to withstand the internal steam pressure.
The response time and cross-direction heat migration limitations mentioned above for web calendering applications apply equally to web drying applications.
Web Converting Applications
In certain web converting processes, such as web embossing, web laminating, or paper corrugating, a common manufacturing step is to pass individual web layers around one or more heated, ferrous, relatively thick-walled preheating cans or rolls to dry and pre-heat the layers before they are embossed or laminated together. The two or more rolls that form the embossing or laminating nips through which the web passes are also typically heated.
In embossing applications the purpose may be to thermally soften the web to make it more malleable. On laminating applications the purpose may be to preheat and dry the individual layers after rewetting or coating to reduce or prevent curl of the final laminated product, or to simply add heat to the process to facilitate intra-layer bonding during laminating. On all laminating and embossing applications it is generally desirable to ensure a very uniform (i.e. +/−1% of process) roll surface temperature profile across the width of the process. If the roll temperature is not sufficiently uniform it may impart a non-uniform temperature profile to the web(s) before or during laminating or embossing. This in turn may affect the web's localized compressibility, malleability, and dimensional stability, leading to variable finished product quality. While on high throughput web manufacturing operations such as papermaking it is cost effective to measure and control web properties in narrow zones across the width, such investments are usually not viable on converting applications that are typically much narrower and slower. Consequently, narrow zone control of effective roll heating means such as external magnetic induction, is often not commercially viable on converting applications. The common solution is then to use enhanced internal heat conduction means, such as helical fluid channels or phase change heat pipes, to promote lateral heat conduction and minimize lateral temperature variations. Unfortunately, such rolls are relatively expensive to build, they often require fluid connections, and they typically require a significant internal structural mass, which along with the internal fluid itself, adds to their thermal inertia to lengthen their heat-up response.
In paper corrugating applications the purpose is typically to heat and dry the individual paper layers in a controlled manner before gluing them together. Controlled drying of the outer paper layers during corrugating prevents or reduces warp of the combined final product, while controlled heating of both the inner and outer paper layers supplies the precise amount of process heat to gel, but not prematurely crystallize, the starch-based adhesive.
The response time and cross-direction heat migration limitations mentioned above for web calendering applications apply equally to web converting applications, especially in that preheating cans are homogenous across their width, with a single internal steam chamber, making it difficult to locally heat just one lateral region of the preheater can to localize the drying or heating effect in a given lateral region of the web.
Web Curing and Heat-Setting Applications
In certain other web producing and handling industries, many of which are discontinuous, batch-type processes (such as for bonded nylon fabric production for mesh or textile manufacturing), a common manufacturing step is to pass the web around one or more internally-heated metal rolls to dry and cure the material, to achieve a final target moisture, set and cure adhesive bonds, and shrink the web to its final, stable dimensions.
As with the previously described heated calendering applications, the historical use of internal fluids has resulted in conventional curing/heat-setting rolls being relatively heavy-walled with elaborate and costly internal fluid channels and rotating seals. These curing/heat-setting rolls are also made of a homogeneous, thermally-conductive material, such as steel, throughout their depth, and are also typically accompanied by an expensive and over-sized external fluid cooling and heating system to quickly remove and add heat before and after stoppages. Curing/heat-setting rolls are also homogenous across their width, and the internal fluid paths are continuous across their entire width, making it impossible to locally heat just one cross-direction region of the roll. This has a unique, negative implication on curing/heat-setting applications. Web shrinkage is typically a somewhat non-uniform phenomenon, occurring more freely and uniformly at the edges, and less easily and uniformly near the center of the web due to friction between it and contacting machine elements, such as rolls. This cross-direction non-uniformity often produces wrinkles in the web as it shrinks, which in turn may have a deleterious effect on the final quality of the web. If the curing/heat-setting roll could be heated in the center first, and then the heating application gradually broadened out toward the edges at an optimum, controlled rate, web wrinkling problems could perhaps be reduced or eliminated.
The above examples clearly illustrate that on many web manufacturing and converting applications the design of conventional heated rolls, and their method of heating, imposes significant limitations, and that these limitations will apply equally or in part to other web applications involving heated rolls.
Induction Heating
As mentioned above, and as disclosed in U.S. Pat. No. 4,384,514, ferrous metal rolls used on web manufacturing and converting applications can be externally heated by magnetic induction, whether or not the roll is also simultaneously heated by an internal heated fluid flow. Recent advancements in induction heating technology permit very reliable operation at high power densities (>50 kW power transmission/meter of roll width), to enable very reliable and efficient, rapid external heating of the surfaces of ferrous metal rolls to much higher temperatures than was previously attainable. Unfortunately the above-described conventional rolls cannot fully exploit the benefits of this new induction heating technology.
The heavy mass of conventional steel rolls or cans, the heat capacity of their thick steel walls, and the volume and heat capacity of internal cooling and heating fluid, all add to the substantial thermal inertia of these systems. Even though state-of-the-art induction technology heats just the surface region of a steel roll, where the thermal energy is actually needed by the process, that heat must unfortunately migrate into the roll and internal fluid, and heat up the entire combined mass before the surface temperature can be stabilized at a target value.
It is therefore an object of the present invention to provide a new apparatus using any one of a family of rolls, all consisting of a relatively thin outer layer that can be rapidly heated by any of the various external heating modes mentioned above, and a supportive core structure that will not easily absorb or conduct heat, that is fabricated of lighter-weight material with a much lower specific heat and thermal conductivity.
Another object of the present invention is to provide heated rolls in which the supportive core structure is fabricated of a material with a relatively high thermal conductivity, such as aluminum.
Still another object of the present invention is to provide heated rolls fabricated of a single contiguous material that is both responsive to eternal magnetic heating and also relatively lightweight.
A still further object of the present invention is to provide heated rolls that are of minimal diameter so that its surface and end wall heat losses are minimized, thereby allowing it to be heated to a higher temperature.
Another object of the present invention is to provide heated rolls that have a relatively lower thermal inertia than conventional rolls presently used for the same purposes, so that substantially less power will be needed to heat their surfaces to a given temperature in a given time period, and then maintain it there.
Yet another object of the present invention is to provide rolls with minimal thermal mass to facilitate more rapid cooling (which will be particularly advantageous on discontinuous, batch-type processes) by simple means, such as an external, inexpensive, forced-air convection cooling plenum, thereby eliminating the need for complex and expensive internal fluid cooling systems.
A further object of the present invention is to provide composite rolls that can be segmented in the cross-direction dimension to allow adjacent external heating elements to selectively heat given regions of the roll.

SUMMARY OF THE INVENTION

A web processing apparatus of the present invention includes (A) a roll consisting of (i) a composite annular structure, having a thin outer shell or sleeve, typically less than a ¼ inch thick, made of a first material capable of being heated to the desired temperature by a known external heating method, and an inner, typically thicker sleeve or core, made of a second material that is highly non-conductive in both electrical and thermal respects and able to withstand said desired temperature; said composite annular structure being suitably constructed and reinforced so that the exterior surface of the outer sleeve is exposed, and the outer sleeve and inner sleeve or core are adequately anchored to one another, enabling the composite annular structure to perform the desired function effectively and reliably; and (ii) a final suitable structure supporting said composite annular structure to permit mounting and rotation of the roll; (B) a device for externally heating the outer sleeve of the composite roll.
In another embodiment of the present invention the inner sleeve or core of the web processing apparatus is made of a second material that is highly thermally conductive and able to withstand said desired temperature. The web processing apparatus could also include (A) an optimized roll manufactured from a contiguous material such as carbon-fiber composite, which thereby has a significantly lower thermal mass, higher strength-to-weight ratio, and higher surface emissivity than conventional rolls manufactured from ferrous alloys, and (B) a device for externally or internally heating such optimized roll.
In another embodiment of the present invention, the web processing apparatus includes (A) an optimized roll manufactured from a material responsive to heating by external magnetic induction (such as steel or carbon-fiber composite), that has a minimal outside diameter (typically <12″ diameter) in order to minimize its thermal mass, so that it can be heated by a given induction-generated heat input (typically >20 kW/meter roll width) to a higher temperature (typically >>150° C.) than would be possible with a larger, conventional heated roll, and (B) an external magnetic induction heating device with a power output (typically >20 kW/meter roll width) that is sufficient to heat the roll of the present invention to a relatively high temperature (typically >>150° C.).
The optimized heated roll apparatus of the present invention may be beneficially applied and heated by any external (i.e. steam jets, gas flames, hot air impingement, and infra-red radiation) or internal method (i.e. internal magnetic induction, or hot fluids such as hot water, hot oil or steam). However, the various embodiments described herein of the present invention are particularly suited to heating by external magnetic induction, which is typically simpler to apply and/or more energy efficient than other potential heating methods.
The optimized heated roll apparatus of the present invention is generally designed to enable faster, more controllable heating, to a higher temperature, with lower energy expenditure, and cooled more quickly with a simpler cooling system, than conventional rolls that are predominantly manufactured from ferrous alloys. The preferred embodiments of the present invention therefore each provide some combination of the following core advantages;

- Lower thermal mass (mass×specific heat) than conventional heated ferrous rolls, enabling faster heating by external induction and faster cooling by any suitable means.
- More conductive interior material properties than conventional heated ferrous rolls, enabling higher lateral heat conduction to reduce lateral temperature variations.
- Smaller diameter than conventional heated ferrous rolls, enabling heating by external induction to higher temperatures
- Higher surface emissivity than conventional heated ferrous rolls, allowing the roll's surface temperature to be measured by non-contact Infrared means.

Specific applications where the various embodiments of the present invention would apply include numerous continuous and batch-type web manufacturing processes, such as:

- web calendering applications, such as during papermaking, plastic film and sheet manufacturing, and metal sheet or foil manufacturing.
- web primary and secondary drying applications, such as during paper, fabric or film manufacturing.
- web converting applications, such as during paper labeling, laminating, or printing.
- corrugated board curing and drying applications, such as during constituent paper preheating or combined board curing and drying.
- web curing and heat-setting applications, such as during layered and/or bonded fabric production for mesh or textile manufacturing.

While the embodiments of the present invention apply particularly well to the applications listed above, they will apply equally or in part to other web manufacturing applications involving heated rolls.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings that schematically illustrate embodiments thereof.
FIG. 1 is a length-wise sectional-view of a preferred embodiment of the present invention in which an optional adjacent forced-convection air plenum is also shown.
FIG. 2 is a length-wise sectional-view of an alternate arrangement of the embodiment of FIG. 1 where the outer shell is divided into separate outer annular sections to reduce lateral heat conduction from one section to the next, and where an optional, adjacent, magnetic induction heating systems is shown consisting of individual inductors of limited width.
FIG. 3 is a length-wise view of an alternate arrangement of the embodiment of FIG. 1, where the outer shell's annular sections are inclined so that no position across the web is ever exposed to a continuous, potentially cool seam between adjacent annular sections.
FIG. 4 is a sectional-view of a length-wise portion of the preferred embodiment of FIG. 1, where the substantial space between a thin outer shell and inner supporting core is filled with an expandable, high-temperature, structural foam to form a composite roll.
FIG. 5 a is a sectional-view of a length-wise portion of the embodiment of FIG. 1 where the roll is constructed of individual disks, each composing a thin annular outer shell, an inner annular core, and intervening, high-temperature, structural foam.
FIG. 5 b is an elevational view of the embodiment shown in FIG. 5 a.
FIG. 6 is a sectional-view of an angular segment of a conventional roll used for curing/heat-setting applications.
FIG. 7 is a graph illustrating the typical time-wise response achievable with induction heating on a conventional curing/heat-setting roll of the type shown in FIG. 6.
FIG. 8 is a graph illustrating the relative improvement in time-wise response that would be achievable with induction heating on composite rolls of the types shown in FIGS. 4, 5 a and 5 b.
FIG. 9 a is a cross-sectional view of a preferred arrangement of an alternate embodiment of the present invention, showing an optimized roll and an adjacent magnetic induction heating device, wherein the roll is manufactured from a relatively thin outer layer consisting of a material that is particularly responsive to external induction, such as steel or carbon-fiber composite, and a relatively thick inner layer of a material that is less dense and that has a relatively high thermal conductivity.
FIG. 9 b is a sectional plan-view of the embodiment shown in FIG. 9 b.
FIG. 10 a is a graph illustrating the steady-state surface temperature produced by a variable heat input profile, derived using a finite element analysis of a composite roll consisting of a thin outer ferrous layer and a thicker inner aluminum layer, of the type shown in FIGS. 9 a and 9 b.
FIG. 10 b is a graph illustrating the steady-state surface temperature produced by the same variable heat input profile, derived using the same finite element analysis, of a steel roll with the same outside and inside diameter as the composite roll analyzed in FIG. 10 a.
FIG. 10 c is a graph illustrating the steady-state surface temperature produced by the same variable heat input profile, derived using the same finite element analysis, of a steel roll with the same outside diameter and weight as the composite roll analyzed in FIG. 10 a.
FIG. 11 a is a cross-sectional view of a another embodiment of the present invention, showing an optimized roll manufactured of a suitable contiguous material such as carbon-fiber composite, a web in contact with said roll, and a suitable, adjacent external heating device such as a sectionalized magnetic induction actuator.
FIG. 11 b is a plan-view of the arrangement shown in FIG. 1 a, showing in addition an adjacent, optional, forced-convection cooling air plenum.
FIG. 12 is a cross-sectional view of an alternate arrangement of the embodiment show in FIG. 1 a, showing an optimized roll manufactured of a suitable contiguous material such as carbon-fiber composite, with internal fluid-carrying channels that may be used to replace or supplement other roll heating and/or cooling means.
FIG. 13 a is a cross-sectional view of embodiment of the present invention, showing an optimized, small diameter roll manufactured from a suitable material such as steel or carbon-fiber composite, a web in contact with said roll, and an adjacent magnetic induction heating device.
FIG. 13 b is a plan-view of the embodiment shown in FIG. 13 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a preferred embodiment of the rolls 100 of the present invention is shown. While there are numerous ways in which suitable composite rolls 100 can be constructed by those skilled in the art of manufacturing rolls to meet the needs of specific applications, the arrangement illustrated in FIG. 1 is just one example involving the present invention.
Referring again to FIG. 1 the composite roll consists of a thin ferrous outer shell 1 (approximately 3/16 inch thick) surrounding a thicker (approximately 4 inch thick) non-metallic sleeve 2 made from a preferably cast, suitable material, such as cement, that is adequately non-conductive in both electrical and thermal respects. The material making up the sleeve 2 should have a thermal mass that is one half or less than the thermal mass of steel. The cement (or equivalent) may have reinforcing bars 3 within it, and/or the outer shell 1 may have metallic protrusions 4 or hooks that will anchor it within the cement to add strength to the composite annular structure. If the cement used has approximately the same coefficient of expansion as the outer shell 1, the outer shell 1 might be partially embedded in the thicker inner sleeve 2. Metallic end caps 5 might also be anchored into the inner sleeve 2, by means of fasteners 6. Shaft extensions 7 might then be welded on to the end caps 5 to permit mounting and rotation of the roll. The ends of the outer shell 1 should also be heat-insulated to avoid direct thermal contact with the metallic end caps 5. When very high surface temperatures are used the thermal expansion coefficient of the materials used in the outer shell 1 and inner sleeve 2 should be closely matched.
As mentioned above, those skilled in the art of manufacturing rolls could provide other ways to achieve the desired, annular, composite roll structure, and to design and manufacture an additional supportive structure to permit mounting and rotation of the roll.
Referring still to FIG. 1, an adjacent forced-convection air plenum 8 can also be added to provide inexpensive, external, non-contact cooling of the roll's outer shell 1 to facilitate a rapid response time and/or to act in combination with whatever external heating system is used to heat the roll (e.g. steam jets, gas flames, hot air impingement, or magnetic induction). In addition, when a preferred means of external heating is used, such as magnetic induction, the outer shell 1 would be manufactured from a ferrous alloy that is particularly responsive to magnetic induction.
Referring now to FIG. 2, the arrangement shown in FIG. 1 can be further enhanced by dividing the outer shell into separate annular sections 9 to reduce lateral heat conduction from one section to the next. Such annular sections 9 could be further thermally isolated from one another by narrower, intervening, ring-shaped insulating strips (not shown). Commercially available inductive roll heating systems typically consist of individual inductors of limited width, typically between 60 and 120 mm wide. Inductors of suitable design and specification are disclosed in U.S. Pat. No. 7,022,951 issued Apr. 4, 2006. The widths of the annular sections 9 shown in FIG. 2 could then be made to match those of the adjacent inductors 10, and be lined up with them, so that individual inductor control could be used to profile the temperature of the heated roll as needed across its width.
As in the case of the previous arrangement shown in FIG. 1, an external forced-air convection plenum could be added to the arrangement shown in FIG. 2, and also to all the arrangements described below, to quickly and inexpensively cool the roll's outer layer during stoppages, or whenever the external heating system generates a roll surface temperature that exceeds the desired target value.
The ability to localize the external heating effect, whether the heat is generated by induction or other means, could be quite beneficial on paper drying applications, to facilitate cross-directional profiling of the paper's moisture content. This ability could also be quite beneficial on laminating and corrugating applications, to facilitate cross-directional profiling of the moisture and temperature of the incoming paper layers, so as to maximize the flatness, bond strength and dimensional stability of the final combined laminate or board. Furthermore, this ability could be extremely beneficial on some web curing/heat-setting applications where it may be preferable to start heating in the center of the machine and progress outwards at a controlled rate, to shrink the web symmetrically, and from the center outward, to minimize or eliminate the formation of wrinkles.
Referring now to FIG. 3, the arrangements shown previously in FIGS. 1 and 2 can be further enhanced by inclining the outer shell's annular sections 11 so that no position across the web is ever exposed to a continuous, potentially cool, continuous seam 12 between adjacent annular sections 11.
Referring now to FIG. 4, an alternative embodiment of the present invention is shown that includes a relatively thin outer shell 13, an inner solid or annular core 14, and an intervening annular space filled with a specialized insulating material 15 chosen for its sufficient solidity, low density, and low thermal conductivity. A suitable insulating material 15 might be an expandable, high-temperature, structural foam, such as TEPIC™, that has been recently developed by the US Department of Energy's Sandia National Laboratories in Livermore, Calif. To facilitate external magnetic heating of the composite roll shown in FIG. 4, and to ensure adequate structural stiffness, the outer shell 13 would be manufactured from a ferrous alloy, and the inner core 14 from a sufficiently strong material, perhaps of the same ferrous alloy. In addition, the inner core 14 may be annular in shape, as shown, allowing it to act as a sleeve about a full-width axle 16 (not shown in cross-section). Alternatively, external pivots could be welded or otherwise fastened to the ends of a solid inner sleeve (not shown), in a manner analogous to that shown in FIG. 1, to facilitate rotation of the composite roll.
Referring now to FIGS. 5 a and 5 b, the arrangement previously shown in FIG. 4 can be further enhanced by segmenting the composite roll into individual, composite disks 17, that are each fabricated by placing outer 18 and inner 19 annular sleeves between two side plates 20 (that are only used during fabrication), then filling the resulting contiguous, annular cavity 21 with expandable, high-temperature, structural foam 22, then removing the temporary side plates 20. The resulting composite disks 17 can then be slid upon a common axle 23. Furthermore, the outer 18 and/or inner 19 annular sleeves could also be notched to interlock adjacent disks 17, then end caps 24 (only one end shown, in FIG. 5 a) could be used to compress the disks 17 together to ensure adequate roll stiffness.
As described above with respect to other arrangements, the individual disks 17 could also be lined up with segmented, external heating means, such as individual inductors, to facilitate zonal temperature control, and/or inclined to prevent exposure of the web to continuous “cold” seams between adjacent disks 17.
One could also modify the foregoing arrangements to make effective and responsive use of internal heating, by locating fluid-carrying chambers or channels between a first, relatively thin, thermally-conductive outer sleeve, and a thicker, thermally-insulating layer below it. To ensure heat transfers easily, and essentially solely, to the outer sleeve, the fluid-carrying chambers or channels could be in direct thermal contact with the underside of the outer sleeve, while being otherwise surrounded and embedded within the inner, thermally-insulating layer below, prior to connecting at the end of the roll to an external source of steam, hot water, or hot oil.
Referring now to FIGS. 6, 7 and 8, the probable value of the various embodiments of the roll 102 of the present invention, in terms of heating system size reductions, response time improvements, and energy savings, may be investigated and approximated by constructing and solving realistic, transient heat transfer models for representative conventional and proposed roll arrangements. Referring specifically now to FIG. 6, a typical curing/heat-setting roll 102 used in the fabrication of layered nylon fabrics (that are subsequently used in paper manufacturing to support the paper web during pressing and drying), would be fabricated of carbon steel and have an outer diameter 25 of about 48 inches. A typical such roll would be about 12 meters wide and would consist of outer 26 and inner 27 shells (each typically about ½ inch thick) joined together by intermittent spacer strips 28 (with typical ½ inch×½ inch cross-sections) to form intervening fluid channels 29 through which would flow the aforementioned roll heating and cooling fluids.
A finite difference model that assumes the conventional roll dimensions noted above, and accounts for induction heat input, convection and radiation losses to ambient from the surface of the roll 100, and contact conduction losses to the fabric being cured/heat-set, and which also assumes the fluid channels are empty and filled with air, produces the results plotted in FIG. 7. The initial high induction heating rate 30 raises the 12 meter wide roll's outer surface temperature 31 rapidly to the target value 32, then conducts deeper into the roll to eventually also raise the temperatures of the inner surface of the roll 33 and the intervening air void 34 (in the empty fluid channels). Once the target surface temperature 32 is reached, the induction power output 30 can be reduced to a level sufficient to maintain the roll surface temperature 31 at the target value 32 for the remainder of the production run. To accomplish this the model estimates an energy transfer 35 of about 147 kW-hours is needed to heat the roll to the target temperature 32, then about 60 kW-hours/hour is needed to keep it there. A typical production run consisting of a 20 minute heat-up period followed by a 3-hour curing/heat-setting period, would then consume about 325 kW-hours of energy (assuming 100% efficiency). Once the induction heat source is turned off, the hot roll would then cool down at a relatively slow rate due to the absence of an internal heating/cooling fluid flow, as indicated by the overlaid temperature trajectories 36.
The same finite difference model, when applied to either of the arrangements shown in FIGS. 4, 5 a and 5 b, then produces the results plotted in FIG. 8. Noticeably, only about 37 kW-hours of energy 37 is needed to raise the roll's surface temperature 38 to the same target level 39 in the same 20 minute time span, and then only about 56 kW is needed to keep it there. In addition, because the temperature 40 of the inner depths of the roll rises insignificantly, and because the thermal inertia of the roll is so much lower, external forced convection cooling using air impingement is expected to reduce the outer surface temperature 38 to its original value within a mere 20 minutes, as reflected by the convection cooling airflow's rapidly decreasing spent air temperature 41. The reduced energy demand 37 during the heat-up period thus allows the maximum power output 42 of the induction system to be decreased by about 75% (from about 37 kW down to 9 kW). As a result, the induction system's design capacity can be decreased from 50 kW/meter to about 10 kW/meter, to greatly reduce its size, complexity and initial cost. The ability to rapidly cool the roll with just inexpensive external air impingement would also provide the desired cool-down response without the need for expensive and complex internal fluid systems.
Referring to FIG. 9 a, a second preferred embodiment of the roll of the present invention is shown. The key difference from the roll 100 of the embodiment shown in FIG. 1 is that the inner layer of the roll 104 of the embodiment shown in FIG. 9 a is that the inner layer of the roll 104 shown in FIG. 9 a is constructed of a material selected for its relatively high thermal conductivity. As shown in FIG. 9 a the roll 104 includes a thin ferrous outer shell 43 (approximately 1/16 inch thick or less) surrounding a thicker (approximately ¼ inch thick or more) sleeve 44 made from a material that has relatively high thermal conductivity and strength-to-weight ratio, such as aluminum.
The outer, typically ferrous layer 43 can be formed by suitable means such as either spray or plasma coating of steel 43 onto the underlying, typically aluminum substrate 44, or by shrink-fitting a thin, typically steel tube 43 around a heavier-walled, typically aluminum core 44.
The roll's outer ferrous layer is typically heated by an external magnetic induction heating device 45. Said magnetic induction heating device 45 may be sectionalized, as shown in FIG. 9 b, to facilitate localized control of the roll's surface temperature across all or part of its width, thereby permitting active compensation for excessive non-uniformities resulting from factors such as an incoming web 46 with a extremely non-uniform input temperature profile. (Commercially available inductive roll heating systems typically consist of individual inductors 47 of limited width, typically between 60 and 120 mm wide. Inductors of suitable design and specification are disclosed in U.S. Pat. No. 7,022,951 issued Apr. 4, 2006.)
Referring now to FIGS. 10 a, 10 b and 10 c, the probable unique value of the embodiment shown in FIGS. 9 a and 9 b, in terms of improved lateral temperature uniformity, may be investigated and approximated by constructing and solving a representative finite difference model for three relevant alternative roll arrangements, as follows:
Arrangement “X”: An 8 inch outside diameter static roll, with surface emissivity 0.3, in a surrounding 70° F. environment, comprising a 0.020 inch thick steel outer surface layer and a 0.313 inch thick inner aluminum layer, and weighing 35 lbs/meter, heated to 300° F. by an average heat input rate of 3.6 kW/meter, that varies across the width by +/−5%.
Arrangement “Y”: The scenario of Arrangement “X”, but where the roll comprises a 0.020 inch thick steel outer surface layer and a 0.313 inch thick inner steel layer, and weighs 90 lbs/meter.
Arrangement “Z”: The scenario of Arrangement “X”, but where the roll comprises a 0.020 inch thick steel outer surface layer and a 0.106 inch thick inner steel layer, and weighs 35 lbs/meter.
Referring again to FIG. 10 a, the input power 48 to the roll (heat input per unit time) can be varied with lateral position 49 to produce a steady-state surface temperature profile 50. Referring now to FIG. 10 b, changing only the inner layer's material to steel significantly increases the variability of the steady-state surface temperature profile 51. Referring next to FIG. 10 c, reducing only the inner steel layer's thickness to produce a roll weight equal to that of the composite roll assessed in FIG. 10 a, further increases the variability of the steady-state surface temperature profile 52. This simple analysis validates that a composite roll consisting of an outer ferrous shell and an inner, thicker layer including a lighter, more thermally-conductive material, will result in a lighter roll that will exhibit a more uniform surface temperature profile in response to a non-uniform surface heat exchange.
Referring to FIGS. 11 a, 11 b and 12, other embodiments of the roll of the present invention are shown. While there are numerous ways in which suitable optimized rolls can be constructed by those skilled in the art of advanced material science and/or manufacturing rolls, the arrangements illustrated in FIGS. 11 a, 11 b and 12, are just examples involving the present invention.
Referring now to FIG. 11 a, the optimized roll 53 consists of a contiguous layer of a suitable material 54, such as carbon-fiber composite, having a lower thermal mass (herein defined as the mass of the roll multiplied by the effective average heat capacity of the material from which it is manufactured), and strength-to-weight ratio than a conventional roll manufactured from one or more ferrous alloys. The lower thermal mass should be one half or less than the thermal mass of steel. The roll 53 may be solid throughout its depth, or hollow, as shown in FIG. 11 a.
Referring still to FIG. 11 a, the external surface 55 of the roll 53 might, if needed, be finished or coated to produce a surface emissivity high enough to permit non-contact temperature measurement of the roll's surface 55. The external surface 55 of the roll 53 might also be polished to produce a surface 55 smooth enough to prevent abrasion or marking of the contacting web 56, and/or to facilitate a higher heat transfer rate between the surface 55 of the roll 53 and the contacting web 56.
Referring now to both FIGS. 11 a and 11 b, roll heating may be accomplished using a suitable means such as external magnetic induction, and said magnetic induction heating device 57 may be sectionalized, as shown in FIG. 11 b, to facilitate localized control of the roll's surface temperature across all or part of the roll's width. (Commercially available inductive roll heating systems typically consist of individual inductors 58 of limited width, typically between 60 and 120 mm wide. Inductors of suitable design and specification are disclosed in U.S. Pat. No. 7,022,951 issued Apr. 4, 2006.) An optional roll cooling device, such as an external forced-air cooling plenum 59, may also be incorporated, as shown in FIG. 11 b.
The ability to localize the external heating effect, whether the heat is generated by induction or other means, could be quite beneficial on paper drying applications, to facilitate cross-directional profiling of the paper's moisture content. This ability could also be quite beneficial on laminating and corrugating applications, to facilitate cross-directional profiling of the moisture and temperature of the incoming paper layers, so as to maximize the flatness, bond strength and dimensional stability of the final combined laminate or board. Furthermore, this ability could be extremely beneficial on some web curing/heat-setting applications where it may be preferable to start heating in the center of the machine and progress outwards at a controlled rate, to shrink the web symmetrically, and from the center outward, to minimize or eliminate the formation of wrinkles.
Referring now to FIG. 12, one could also modify the optimized roll 53 of the present invention to make effective use of internal heating and/or cooling, by locating fluid-carrying chambers or channels 60 within the depth of the contiguous material 54, and connecting said channels 60 to a suitable heating and/or cooling fluid source, such as steam, water, or oil.
Referring now to FIG. 13 a, an optimized roll 61 is manufactured from a material 62 that is responsive to heating by magnetic induction, such as steel or carbon-fiber composite, and has a relatively small diameter (typically <12″ diameter), and thus a lower thermal mass (herein defined as the mass of the roll multiplied by the effective average heat capacity of the material from which it is manufactured) and smaller surface area from which to lose heat to the environment and contacting web 63, than would a larger, conventional heated roll. The lower thermal mass should be one half or less than the thermal mass of steel. The roll 61 may be solid throughout its depth, or hollow, as shown in FIG. 13 a.
Referring now to both FIGS. 13 a and 13 b, high heat flux (typically >20 kW/meter roll width) roll heating is accomplished using an external magnetic induction heating device 64, and said magnetic induction heating device 64 may be sectionalized, as shown in FIG. 13 b, to facilitate localized control of the roll's surface temperature across all or part of the roll's width. (Commercially available inductive roll heating systems typically consist of individual inductors 65 of limited width, typically between 60 and 120 mm wide. Inductors of suitable design and specification are disclosed in U.S. Pat. No. 7,022,951 issued Apr. 4, 2006.) The ability to localize the external heating effect using a sectionalized induction heating device could be quite beneficial on paper calendering and finishing applications to facilitate cross-directional profiling of the paper's caliper and/or gloss and smoothness.
Although suitable materials from which to manufacture the various layers of the embodiments of the present invention would be steel, ceramic, carbon-fiber composite, and aluminum, those skilled in the arts of advanced material science and/or roll manufacturing may identify other suitable materials that will satisfy the objectives of the present invention, and which would fall within the scope of the present invention.
While the foregoing invention has been described with respect to its preferred embodiments, various alterations and modifications are likely to occur to those skilled in the art. All such alterations and modifications are intended to fall within the scope of the appended clause.

Claims

1. A cylindrical roll for use in a heated roll apparatus, said roll comprising:

a surface layer constructed of a material responsive to being heated by external magnetic induction, said surface layer covering the lateral surface of the roll;

an inner layer supporting said surface layer, said inner layer being constructed of an insulating material having a thermal mass that is one half or less than the thermal mass of steel;

a heater for externally heating said surface layer.

2. The cylindrical roll of claim 1 wherein said insulating material is a ceramic material.

3. The cylindrical roll of claim 1 wherein said surface layer is constructed of a ferrous material.

4. The cylindrical roll of claim 1 wherein said inner layer has a greater thickness than said surface layer.

5. The cylindrical roll of claim 1 further comprising an forced-convection air plenum positioned adjacent said roll to provide inexpensive, external, non-contact cooling of said surface layer.

6. The cylindrical roll of claim 1 wherein said surface layer comprises a plurality of annular sections and said heater comprises a plurality of heaters.

7. The cylindrical roll of claim 1 wherein said heater is an induction heater.

8. A cylindrical roll for use in a heated roll apparatus, said roll comprising:

a surface layer constructed of a material responsive to being heated by external magnetic induction, said surface layer covering the lateral surface of the cylindrical roll;

an insulating layer supporting said surface layer;

an inner layer supporting said insulating layer;

a heater for externally heating said surface layer.

9. The cylindrical roll of claim 8 wherein said surface layer comprises a plurality of annular sections and said heater comprises a plurality of heaters.

10. The cylindrical roll of claim 8 wherein said heater is an induction heater.

11. A cylindrical roll for use in a heated roll apparatus, said roll comprising:

an aluminum core supporting said surface layer;

a heater for externally heating said surface layer.

12. The cylindrical roll of claim 11 wherein said surface layer comprises a plurality of annular sections and said heater comprises a plurality of heaters.

13. The cylindrical roll of claim 111 wherein said heater is an induction heater.

14. A cylindrical roll for use in a heated roll apparatus, said roll comprising:

a single cylindrical contiguous body of a material that is responsive to induction heating and has a thermal mass that is one half or less than the thermal mass of steel;

a heater for externally heating said surface layer.

15. The cylindrical roll of claim 14 further comprising fluid-carrying chambers within said single cylindrical contiguous body.

16. The cylindrical roll of claim 8 wherein said contiguous body is made from carbon fiber composite.

17. A cylindrical roll for use in a heated roll apparatus, said roll comprising:

a single contiguous cylindrical body constructed from a material responsive to heating by magnetic induction, said single cylindrical contiguous body having a diameter of less than twelve inches;

a magnetic induction heater for externally heating said surface layer.