JP2727135B2 - Impulse dryer roll with shell with high thermal diffusivity - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a papermaking machine and a calendar. In particular, the invention relates to rolls used in papermaking machines to transfer heat to a paper web. Furthermore, the present invention relates to a heating roll for use in papermaking machines and calendars, with improved heat transfer to the paper web.

BACKGROUND ART Paper manufacturing is an important industry. In the past, efforts have been made to increase paper productivity by increasing the width of paper webs produced by papermaking machines. Another trend to increase paper productivity is to increase the speed of the web through the paper machine. The width of the web can be increased by making the papermaking machine and paper handling rolls wider. Also, increasing the production speed of the paper web causes problems in the dryer section of the papermaking machine. As the web speed increases, the heat transfer from each dryer cylinder to the dry paper web decreases. Thus, the dryer section of the papermaking machine must be made longer while increasing the web speed.

One solution to the problem of making the dryer section longer is an impulse dryer. This impulse dryer uses a high-temperature roll heated to at least 232 ° C (450 ° F). The heated roll is used to form a wide nip between the roll and the shoe. The paper web will come into contact with the hot surface of the roll. The paper is supported by a press felt, which in turn rests on a blanket which rests on a lubricating film on the shoe. By using an impulse dryer having such a wide nip, the length of the dryer section of the papermaking machine can be greatly reduced.

Further improvements to this impulse dryer require increased heat transfer between the roll and the paper web. Increasing the temperature of the roll surface requires increasing the temperature of the entire roll. This has an adverse effect on the strength of the roll. Increasing the temperature of the roll has the disadvantage of complicating the use of an internal crown support mechanism using a hydraulic mechanism. Further, when the temperature is increased, the press felt is easily burnt, the fibers on the web surface are loosened, the stress of the roll head becomes excessive, and the bearing is easily overheated. Thus, in U.S. Pat. No. 4,324,613 to Wahren, it is recognized that the impulse dryer roll is more effective when formed from a material having relatively high thermal conductivity. Warren also teaches that it is desirable to use a roll with a low conductivity surface to achieve high surface temperatures. Warren has also proposed material selection criteria for at least the roll surface layer, stating that aluminum is less preferred than steel or nickel. Warren ignores copper as unfit for his roll.

Riihinen, U.S. Pat. No. 4,613,794, describes rolls for use with individually heated calenders. This roll uses a non-magnetic insulating layer between the outer ferromagnetic layer and the inner core of the roll. Lihinen heats the calender rolls by induction and allows access to the interior of the rolls for crown control, but does not disclose how to use increased heat transfer to improve heat transfer. Not.

No. 4,738,752 to Busker et al. Discloses a press roll used in a heated wide nip press having a first concentric layer and a second concentric layer extending around the first layer. Suggests. The second layer has a higher thermal conductivity than the first layer. The first layer is a material having a low coefficient of thermal conductivity, and the second layer is a metal. It further suggests that the first layer is ceramic and the second layer is metal.

For buscars and others, the second outer layer is 0.0127-0.127 cm (0.005-
0.050 inch). Busker et al. Do not disclose how to calculate the appropriate thickness of the metal outer shell over the inner metal base shell. Basker does not teach how important heat diffusion is in selecting the material of the outer shell or its thickness.

What is necessary is to use a roll having high heat transfer in an impulse dryer or a calendar.

DISCLOSURE OF THE INVENTION The roll of the present invention consists of two parts. One is a metal base shell, which is made of a usual spun-cast steel alloy. The second portion of the roll has a thin outer shell, i.e., a few tenths of an inch, which is in intimate contact with the surface of the steel alloy base shell.

The outer shell is composed of a highly heat diffusing material. Thermal diffusion is proportional to heat conduction and inversely proportional to the specific heat and density of the material. Examples of high thermal diffusivity materials include copper and aluminum.

One way to construct the roll of the present invention is to flame spray a surface of the roll with a copper layer of about two-tenths of an inch. This roll is used for the wide hot press nip of the impulse dryer. The wide nip is formed by a shoe. The shoe has a smooth arcuate surface with a curvature slightly greater than the surface of the roll of the present invention. A wide nip blanket is pulled on the surface of the shoe at a speed equal to the surface speed of the roll. The paper web moves near the surface of the roll and a press felt is positioned between the blanket and the web. The effect of the shoe is to hold the paper web against the roll on a 5 foot diameter roll, perhaps over a 10 inch perimeter distance. The roll is rotated to produce a surface speed of 914 meters / minute (3,000 feet / minute). The wide nip blanket, the press felt and the paper web all pass through the roll at the same speed.

This roll consists of a metal cylinder with strong walls. This cylinder wall typically has a thickness of several inches. The roll is heated upstream of the wide nip by an induction heater that heats the roll surface. When an analysis of the heat transfer between the roll and the web was performed, it was found that only the outermost portion of the roll was exposed to temperature changes. If the roll surface is 232 ° C by induction heater
When heated to (450 ゜ F), the entire interior of the roll is 23
A uniform temperature of 2 ° C (450 ° F) is reached.

The surface of the roll in contact with the web should be 93 ° C or 149 ° C (200 ° C
(゜ F or 300 降下 F). However, this temperature change is only experienced at one-tenth to three-tenths of an inch of the surface of the roll. Thus, the only effective heat transfer portion of the roll is the thin outer annulus. With conventional rolls, the only way to improve heat transfer was to increase the temperature of the roll, extend the length of the nip, or slow down the web. All three of these approaches are expensive and have their associated drawbacks. Accordingly, the present invention seeks to increase the thermal diffusivity of the roll by providing the roll with a copper layer having an accurately calculated depth, thereby improving heat transfer between the roll and the web.

Accordingly, an object of the present invention is to provide an impulse dryer roll with improved heat transfer to the paper web to be dried.

It is another object of the present invention to provide a roll for use in a calender that has improved heat transfer to the paper web for a given roll surface temperature.

It is another object of the present invention to provide a roll for use in the dryer section of a papermaking machine that requires only a shorter portion.

Still another object of the present invention is to provide a roll for use in an impulse dryer that reduces the loosening of fibers on the web surface.

It is still another object of the present invention to provide a roller for use in an impulse dryer, which has reduced roll head stress.

Further objects, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of a large area, or long nip, or wide nip type papermaking machine using a two-layer roll of the present invention.

FIG. 2 is a schematic cross-sectional view of a wide area, ie, long nip, or wide nip papermaking machine utilizing the rolls of FIG. 1 using a wide nip blanket.

FIG. 3 is a graph showing the relationship between temperature and time at various depths from the surface of the roll of FIG.

FIG. 4 is a schematic cross-sectional view of a calendar using the two-layer roll of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION In particular, the same reference numerals in FIGS. In these figures, an impulse dryer 20 is shown. The impulse dryer 20 has a press roll 22 that forms a nip 26 with a shoe 24. This shoe 24 has a concave surface facing the roll 22, which is
It is mounted so as to be pressed toward 22. Press nip 26 is formed between roll 22 and shoe 24.
The paper web 28 passing through the nip 26 receives a pressing force for a long time. The press felt 32 moves under the web 28, and the loop belt 30 passes over the shoe 24 under the felt 32.

Oil is supplied between the shoe 24 and the belt 30. The oil creates a hydrodynamic fluid wedge between belt 30 and shoe 24. The fluid wedge lubricates the movement of the web 28 through the nip 26 while simultaneously transmitting pressure to the web. Press felt 32 under paper web 28,
Moreover, it is on the belt 30 and passes through the nip 26. The paper web 28, the press felt 32, and the belt 30 are rolled.
Since they are located in one place together with 22, they are driven at the same speed. Thus, the paper web 28 is not subjected to such a large force as to deflect. This is because no relative movement occurs between the surface of the web 28, the surface of the press felt 32, and the surface 34 of the press roll 22. Thus, the paper web 28 is primarily subjected to compressive forces as it passes through the wide nip 26. The effect of this compression force is to bring the web into close contact with the surface 34 of the press roll 22.

The close contact between the web 28 and the surface 34 of the press roll under pressure facilitates rapid heat exchange between the surface 34 of the roll 22 and the web 28. The rapid heat transfer between the roll 22 and the web 28 results in a drying mechanism that is not yet fully understood, characteristic of an impulse dryer. Rapid heating of the paper web causes some of the moisture contained in the web to evaporate. The steam generated from the web moisture is transferred to the surface 34 of the roll 22.
And between the paper web 28. The only way out is from paper web 28 to press felt 32. Paper web 28
This has the effect of rapidly moving the steam downward from the upper surface of the web to the felt 32 and blowing the moisture contained in the web 28 onto the felt 32. This process, ie, impulse drying, causes the paper web 28 to quickly remove moisture.

The press roll 22 of the impulse dryer 20
Has an improvement effect over the ordinary impulse dryer. Roll 22 has a metal base shell 38 constructed of a conventional steel alloy. Its base shell 38
Is covered with an outer shell 40 made of a material having a high thermal diffusion property such as copper. The illustrated rolls are not drawn to scale, and for purposes of illustration, the relative thicknesses of the base shell and the outer shell are exaggerated. The outer shell 40 is in close contact with the outer surface 42 of the base shell 38. The metal base shell 38 provides the structural support for the outer shell 40. The high thermal diffusivity of the outer copper layer doubles the effective heat transfer between the roll 22 and the paper web 28. A typical impulse dryer is a press roll
The press nip is configured to reach a surface temperature of 93 ° C to 149 ° C (200 ° to 300 ° F) or more, preferably 232 ° C to 288 ° C (450 ° to 550 ° F). A typical impulse dryer may also use a wide nip press with a shoe that presses an impermeable blanket toward an induction heating roll. The high surface temperature heats the wet web rapidly as it passes through the nip, softening the paper fibers. This significantly enhances the dewatering action and gives rise to the strength properties of the paper sheet.

Enhancing the heat transfer effect by using a thin outer shell 40 with high thermal diffusivity allows the impulse dryer to be designed to achieve the selected effect. First, a lower surface temperature of the roll 22 still provides the same heating level. This overcomes several problems caused by high shell temperatures. That is, when the temperature becomes high, burning of the press felt, loosening of the shell on the web surface, excessive thermal stress of the roll, and overheating of the bearing occur. Second, more heat can be supplied to the paper to remove more moisture. Third, the speed of the web 28 can be increased while keeping the impulse and drying effects constant. In a practically suitable design using a press roll 22 with an outer shell with high thermal diffusivity, 3
All three effects include lower press roll temperature, faster operating speed, and more complete drying of the paper web 28.

FIG. 1 is a cross-sectional view of an impulse dryer 20 using a press roll 22, taken along the direction of travel of the paper web 28. As will be appreciated by those skilled in the papermaking arts, the width in the cross-machine direction of the paper web 28 is typically 100-400 inches, and components of the impulse dryer, such as the roll 22, are required for certain functions. As is generally said, it is somewhat longer.

Loop belt 30 and its support 44 are conventional and are described in U.S. Patent No. 4,673,461 (Roerig).
More details are described in (Outside). The belt 30 is a continuous loop whose width in the cross machine direction is a press roll
Being wider than 22, the end of the belt (not shown) is sealed to a circular closure (not shown) that seals the end of the belt, thus containing the nip lubricant in the sealed belt 30 . The fixed beam 33 is included in the belt 30. The beam adjustably supports the shoe 24 by the hydraulic piston chamber 35. A piston 37 is positioned in the hydraulic piston chamber 35. The shoe is pivotally supported on roller pins 39. The roller pin 39 is seated in the downward groove of the shoe 24 and the upward groove of the piston 37. The piston is pushed upward by the fluid pressure below the piston in the hydraulic piston chamber 35. The hydraulic piston chamber is in the form of an elongated slot, which slidably receives the piston,
Extending across the entire width of this machine under 24. The belt 30 is guided by side guides 41 and 43, upper guides 45 and 47, and lower guide 49. These guides are adjustably mounted on beams 33 to stabilize belt 30 during startup. These guides also have the effect of stabilizing the belt 30 in the event of any rattling or instability during normal operation.

Once the belt 30 has reached its operating speed, the belt 30 will assume its natural shape except for the part that moves across the nip 26 between the shoe 24 and the press roll 22 due to the action of centrifugal force. Thus, as the speed increases, the belt 30 is held at a slight distance from the guides 41, 43, 45, 47, 49 due to the action of the centrifugal force.

The press felt 32 is supported on an in-feed roll 46 and a press-out feed roll 48. The infeed press felt roll 46 and the outfeed roll 48 typically have a diameter of 0.61 meters (2 feet), but the corresponding diameter of the press roll is 1.52 meters (5 feet). These rolls 46,48
It serves to send the press felt through the nip 26 of the impulse dryer 20 to the position to be sent. After leaving the outfeed roller 48, the press felt 32 is processed by a felt dryer (not shown). The felt dryer removes moisture and excess moisture from the felt 32 before the felt is returned to the infeed roller 46 for reuse.

The press roll 22 of FIG.
The hydraulic crown control mechanism 50 having the following is used. The crown support beam has an oil supply port 54. The oil supply port 54 is connected to the inner surface 60 of the metal base shell 38 by a piston 58.
Oil is supplied to the piston space 56 for driving the piston. Central beam, i.e. piston 58 spaced along axis 50
Gives a constant pressure between the press roll 22 and the shoe 24. In FIG. 1, an induction heater 62 is schematically illustrated. The heater 62 is a coil excited by a high-frequency current.
Has 64. Induction heater 62 is conventional. It uses an oscillating magnetic field generated by a high frequency alternating current, which causes an eddy current on the surface 40 of the roll 22. The resulting eddy currents create resistive heat at the surface 40, which heats the surface to the desired temperature.

In terms of heat transfer, Ciel 40 is a "semi-infinite plate"
(Semi-infinite plate). This is because a given segment of the roll will be in the nip for a very short time. The external induction heating of the shell 40 causes the entire roll to operate at a uniform temperature from the inside 60 to the outside 34, except for a thin outer layer whose temperature fluctuates periodically. The effective depth of this outer layer can be expressed by the following equation.

In the above equation, X = depth of the layer where the periodic temperature change occurs, and the unit is feet.

S = surface speed of press roll, unit is meter / hour (feet / hour) L = length of nip, unit is feet a = heat diffusivity of outer surface, unit is square meters / hour (square feet / hour) This depth Is approximated assuming that the surface temperature changes stepwise. Indeed, the change is not dramatic, so the above estimate seems to be higher than it really is.

FIG. 3 is a graph showing the relationship between the temperature change of the roll surface and the time, and is further deepened continuously at three points. In FIG. 3, the vertical axis is temperature and the horizontal axis is time. Curve 66 at the top represents the relationship between roll surface temperature and time. Since the press roll 22 is about 5 feet in diameter,
The circumference is about 16 feet. The nip 26 in FIG.
Inches, the result is that the roll requires only about 5% of the time it takes for the paper web to rotate around the roll.
Exposure. The upper curve 66 has a sawtooth waveform 68 which represents the surface temperature when the drum 22 makes one revolution.

From the starting point, the temperature drops steeply. This indicates that the surface 34 of the roll 22 has contacted the paper web 28. The total contact time of the web in this case corresponds to 5% of the wavelength 68, and the decrease in surface temperature is basically instantaneous. The surface 34 of the roll 22 maintains the temperature of the web 28 as the web is heated by contact with the roll.

As some point on the surface exits the nip, heat flows from the interior of the roll toward the cooler surface, causing the temperature 72 to gradually increase. Finally, when the roll surface passes through the induction heater 62, the roll surface rises in temperature, as shown at 74, after which the temperature rises, as shown by the roll surface at 70.
It is constant until it comes into contact with the paper web 28 again.

The thermal diffusion (a) is defined by the following equation. That is, Where a = thermal diffusivity k = thermal conductivity c = specific heat p = density A second graph 75 represents the temperature profile of any point that has moved a distance in the depth direction from the surface of the roll 22. The wavelength 76 of the second curve 75 is the same as the wavelength of the surface temperature curve 66. However, the temperature change is not as steep as the first curve because the point represented by curve 75 is somewhat distant from the surface.

The third curve 78 has a wavelength 80, which is the same as the wavelengths 76 and 68, which wavelength is governed by the rotational speed of the roll 22. This curve represents the point that has traveled farther from the roll than curve 75, which is deeper into the roll and how small the temperature change caused by the periodic nature of the surface 34 that contacts the roll and is heated by the induction heater 62. Indicates whether it is.

The fourth curve 82 indicates that the temperature-time relationship is constant. It represents such a depth that the above equation cannot predict the temperature fluctuation. It is also the depth at which heat diffusion is no longer important in controlling the flow of heat between the roll 22 and the paper web 28.

Alloy cast iron shells are approximately 0.066 square meters / hour (0.6-
0.7 square feet per hour), whereas aluminum has a thermal diffusivity of 3.3 and copper of about 4.4.

Referring to Table 1, column 1 has various thermal diffusive dispersions. 0.7 corresponds roughly to the typical material that makes up the press roll. A thermal diffusivity of 3 corresponds to aluminum and a thermal diffusivity of 4 corresponds to copper.

In Table 1, two common nip lengths are shown in inches, 10 corresponds to the wide nip of a typical impulse dryer, and 1 inch is the use of a typical calender as shown in FIG. Corresponding to Two web speeds in feet per minute are listed. 914 per minute
Meters (3,000 feet per minute) are typical speeds of today's paper machines. At 6,000 feet per minute,
An appropriate range of paper speeds discussed in the industry.

Table 1 shows that the appropriate radial maximum thickness of the outer shell 40 requires only about 2/10 inch thickness, as shown, along with a combination of thermal diffusivity, nip length and web speed. Is shown. With reference to FIG. 3, Table 1 also shows the two-layer structure of the press roll 22.

The volume specific heat, that is, the amount of thermal energy per unit volume, is roughly constant over a wide range of metals, as long as the low density metal has a high specific heat and the high density metal has a low specific heat. Thus, the volume of the substance to be subjected to the periodic heating is a good indicator of the total amount of heat supplied to the paper web by the roll 22 while the roll 22 is in periodic contact with the paper web.

FIG. 3 can be understood and referred to when the depth corresponding to the curves 75, 78, and 82 is twice as large as the effective depth as shown in Table 1. Thus, from an alloy steel roll with an effective depth of 0.218 cm (86/1000 inch),
Movement to copper with an effective depth of 0.525 cm (207/1000 inches) means that more than twice the volume of the material is undergoing periodic temperature changes. Thus, the heat flow during a given cycle is almost twice as high.

Table 1 shows that when the nip length is reduced,
Because the effective depth is also reduced, in a calender as shown in FIG. 4, where the nip 76 is very thin with a length of 0.5-1.5 inches, a dramatic improvement in heat transfer requires a highly thermally conductive outer surface. Ciel 78 is effective.

Press roll 22 is manufactured in a conventional manner by centrifugally casting an iron alloy into a chilled mold. Centrifugal casting on cold metal shells typically results in a highly rigid roll surface with ductility inside. The outer shell of a highly diffusible material such as copper or aluminum is sprayed onto the outer surface 42, preferably by spraying the surface with molten metal. A typical metal spraying method involves sandblasting the surface of a roll to create a surface to which the sprayed metal adheres, heating the wire of the desired metal with an arc or plasma,
Spraying the resulting metal onto the surface 42 of the metal base shell 38 is included. Typically, a metal spray operation is performed upon rotation of the base shell 38 to form a continuous layer of spray metal until the required thickness is achieved. After this, the rolls are surface-finished, producing the surface smoothness required for impulse dryer press rolls and calender rolls.

One method of forming the outer shell involves first spraying molten metal into a chilled centrifugal mold and then centrifuging the thin outer layer by casting a steel-based shell 42 into the outer shell 40. This method requires that no outer oxide coating be formed on the outer shell 40 in order to create a molecular bond between the outer shell 40 and the base shell 34.

Another method is to apply a chemical or electrical coating from a solution to the surface 42 of the base shell 38. In chemical coating, it is important that the coated metal does not have porosity. In particular, another method of forming very thin layers for use in calendering is vapor deposition.

FIG. 2 shows another impulse dryer 120 having a press roll 122, which forms a wide nip 126 between the shoe 124 and the surface 134 of the roll 122. Impulse dryer 120 is impervious wide nip blanket 1
Use 30. Shoe 124 has a concave surface facing the roll, which is mounted to be pushed up toward roll 122. Nip 126 is the paper web 1 passing through the nip
28, a long-term pressing force is generated. Nip blanket
130 passes through the nip between shoe 124 and roll 122.

Oil is supplied between the shoe and the blanket 130. This oil creates a hydrodynamic fluid wedge between the blanket 130 and the shoe 124. This fluid wedge transmits pressure to the web while at the same time lubricating the movement of the blanket through the nip 126. Press felt 132 moves through nip 126 and is positioned under blanket 130 under paper web 128. Paper web 128 and press felt
The blanket 132 and the blanket 130 are driven at the same speed together with the roll by mutual connection by frictional force. Thus, the paper web 128 is not subject to any significant shift. This is because there is no relative movement between the surface of the web 128, the surface of the press felt 132, and the surface 134 of the press roll 122. Thus, the paper web 128 is primarily subjected to compressive forces as it passes through the wide nip 126. The effect of this compression force is to bring the web into close contact with the surface 134 of the press roll 22.

Similarly to the dryer 20, the press roll 122 of the impulse dryer 120 has an improvement effect over the conventional impulse dryer. Roll 122 has a metal base shell 138 made of a normal steel alloy. This base shell 1
38 is covered on the outside with an outer shell made of a material with high thermal diffusivity. This outer shell 140 is the base shell 138
Is tightly joined to the outer surface 142 of the. Metal base shell 1
38 constitutes the structural support of the outer shell 140.

Blanket 130 and its support 44 are conventional. Blanket 130 is a continuous loop. Because it is wider in the cross machine direction than the press roll 122,
The edge of the belt (not shown) extends beyond the edge of the paper web 128. The fixed beam 133 is located below the belt 130 and the shoe 124. The fixed beam 133 adjustably supports the shoe 124 by a hydraulic piston chamber 135 having a piston 137 therein. The piston 137 is pushed upward by the fluid pressure below the piston 137 in the hydraulic piston chamber 135. The hydraulic piston chamber is shaped like an elongated slot,
A piston extending slidably under the shoe 124 over the full width of the machine. The belt 130 is guided by upper guide rolls 141 and 143, lower guide rolls 145 and 147, and a stretcher roll 149. The stretcher roll 149 is adjustably mounted to change the pulling of the blanket 130.

The press felt 132 is supported on an in-feed roll 146 and a press-out feed roll 148. Infeed press felt roll 146 and outfeed roll 148
Is typically 2 feet in diameter, but here the corresponding diameter of the press roll is 5 feet. Rolls 146 and 148 press the felt into impulse dryer 120
To a position to be sent through the nip 126 of the After the press felt 132 leaves the outfeed roller 148,
Processed by a felt dryer (not shown). This felt dryer uses an infeed roller 146
Moisture and moisture are removed from the felt 132 before being returned to the for reuse.

The press roll 122 of FIG. 2 is not shown using a hydraulic crown control mechanism. Rather, the roll 122 is formed with a large central portion and a diameter that tapers in the axial direction. Crown roll 12
The disadvantage of using 2 is that the pressure only occurs for one level of pressure between the roll 122 and the shoe 124. Thus, if a range of drying pressures is desired, it is desirable to use an active crown. In FIG.
An induction heater 162 is schematically illustrated. It has a coil that is excited with a high frequency current. Induction heater 16
2 has the usual properties. It has an oscillating magnetic field created by a high frequency current that creates an eddy current on the surface 141 of the roll 122. The induced current causes resistive heating of surface 134 to the desired temperature.

FIG. 4 shows a case in which a roll 86 having an outer shell 87 having high heat diffusion is used for the calendar 84. The calendar is used to smooth and improve the surface finish of the paper web 82.

Figure 4 shows the machine stack calendar, or "on-machine"
FIG. 3 is a schematic diagram of a calendar 84. The calendar consists of a calendar stack constituted by calendar rolls 86,88,90,92, i.e. a stack of calendars. These calendars typically have hard nips between hard rollers,
Alternatively, a soft nip in which hard rollers 86 and 90 and soft rollers 88 and 92 made of elastic fibers are alternately arranged may be provided. This structure is conventional. Soft nip calendars are typically of length
It has a nip from 1.27 cm to 3.81 cm (1/2 to 11/2 inch). The calendar roll 86 is heated by infrared heating or induction heating. Using a calendar roll with a metal base shell 96 and a highly heat diffusible outer shell 87,
Heat transfer between the roll 86 and the paper web 98 is improved. This improves the effectiveness of the calendar 84.

As shown in Table 1, due to the short nip length,
Requires a thin high thermal diffusivity shell of 0.152 cm (60/1000 inches). Thus, the relatively thin radial thickness of the outer shell facilitates roll formation. This is more convenient for chemical filming. The relatively thin film can also use a non-metallic, high thermal conductivity coating such as diamond, so that the roll can be coated with diamond by evaporation.

It should be understood that as the speed of the web increases, the thickness of the high thermal diffusivity outer shell will need to be smaller.

As shown in Table 1, the formula for the effective depth is
This gives the roll material the maximum effective depth of heat transfer, and the use of a depth less than the maximum effective depth can still increase the heat transfer capability of the roll 22.

The nip length, roll diameter, and roll temperature shown here are merely examples in the examples, and using other temperature ranges, roll sizes and nip lengths,
It should be understood that the rolls of the present invention can be used to advantage.

Although the crown support mechanism is shown and described, the roll has a machined crown surface,
A thin outer shell with high thermal diffusion can also be applied or formed thereon.

Also, it should be understood that materials such as copper and aluminum have a thermal diffusivity of 3 or more, but a thermal diffusivity in the 1 range may be practical in some situations.

It is to be understood that the invention is not limited to this structure or arrangement of the components illustrated herein, and that such variations are within the scope of the following claims.

Claims (6)

(57) [Claims] 1. A metal-based shell (38) comprising a first metal selected as having high strength and low thermal diffusivity.
Wherein the base shell (38) comprises a cylinder having a length, a radius, and a cylindrical surface, the base shell having a first thickness along a radial direction. 38) a second metal outer shell (40) located on and supported by said base shell (38), said outer shell (40) being said cylinder of said base shell (38); The second metal is selected to have a higher thermal diffusivity than the first metal, and the outer shell (40) has a radius of a base shell (38). The base shell (38) forms a support for mechanical loading, said outer shell (40) having improved heat transfer therethrough, having a smaller radial thickness than the directional thickness. Heating the outer shell (40); An induction heater located in close proximity to said outer shell (40), said outer shell (40) having a radial thickness of less than 0.1 inch (0.254 cm) and said second metal Is selected from the group consisting of aluminum and copper, the second metal of which is sprayed onto said base shell (38), said base shell (38) forming a support for the mechanical load and said outer shell (40). ) A heating roll for drying the paper in a papermaking machine, characterized in that the heat transfer to the paper web pressed in engagement therewith is improved. 2. The outer shell (40) formed by metal spraying the second metal onto the base shell.
The roll according to claim 1. 3. Passing the paper web through the papermaking machine in a first direction at a surface speed of S meters / hour (S feet / hour); formed between the cooperating element and the roll surface in the first direction. Passing the paper web through a nip having a length of L feet measured to the roll surface such that the paper web heats the paper as it moves through the nip between the roll and the cooperating element. Heating the roll having a high strength inner base and an outer shell having a thermal diffusivity of 1 or more, measured in square feet per hour, of the high diffusivity layer. A papermaking method wherein the radial thickness is X feet, where X is determined by the following equation: 4. A base shell (38) which is selected as having high strength and is made of a first material having low thermal diffusivity, has an inside diameter and an outside diameter, and constitutes a cylinder having a cylindrical surface; A second on the base shell and supported by it
An outer shell (40) of a material, wherein the first material is a steel alloy, and the second material is selected from the group consisting of aluminum and copper having a higher thermal diffusivity than the first material; The outer shell has an inner diameter and an outer diameter, a difference between the inner diameter and the outer diameter of the outer shell is made smaller than a difference between the inner diameter and the outer diameter of the base shell, and the base shell has a mechanical load. Wherein the outer shell engages and has improved heat transfer to the pressed paper web;
Heating rolls that process paper in papermaking machines. 5. The difference between the outer diameter and the inner diameter of the outer shell is 0.76.
5. The roll of claim 4, wherein the roll is no more than 2 cm (0.3 inches). 6. The outer shell is connected to the base shell by a second
The roll according to claim 4, wherein the roll is formed by metal spraying a metal.