Field of the Invention

This invention relates to a processing roll apparatus and method arranged to engage a material to be processed in heat exchange relationship, and more particularly to such an apparatus and method where the roll defines an enclosed chamber to contain a condensable heat transfer medium to transmit heat to the outside surface of the roll, such as a roll that is used in the pulp and paper industry to engage paper sheets and/or corrugating medium (i.e. a continuous web of paper formed into a corrugated shape) to heat and/or shape the same.

Background of the Invention

There are various industrial applications where cylindrical rolls are used for such things as forming and/or drying sheet material, such as paper, pulp or corrugating medium. One specific application for such rolls is to form corrugated paper which is then bonded to upper and lower paper web to form a corrugated sandwich structure (cardboard) . The exterior surface of the roll is made with longitudinally aligned ridges separated by recessed portions or grooves. The interior surface of the roll defines a closed chamber which is pressurized with a condensable heat transfer medium which is generally steam.

In operation pressurized steam is directed through an inlet which is commonly formed at an end wall of the roll with a rotary pressure seal, with the steam being at a temperature and pressure as high as possibly 400°F and 200 pounds per square

inch. As the steam condenses on the interior surface of the cylindrical side wall of the roll it transmits heat through the side wall and thus heats the paper or cardboard which is in contact with the roll side wall. As the steam condenses on the interior surface, the water is removed from the chamber by a siphon pipe or other removal mechanism and discharged through an outlet which can have a rotary seal joint. A common arrangement for corrugating rolls is for a set of three rolls to be horizontally aligned, one above the other, with the elongate ridge portions of each roll fitting into the matching valley or recessed portions of the other roll. As these rolls are rotated, the paper or web is fed into the region between the rolls to have heat applied thereto and to be formed in a corrugated pattern. As the resulting corrugated sheet moves from the location between the rolls, it is then bonded to upper and lower paper web to form a corrugated sandwich structure.

By way of further background information, various heat transfer media for this type of rolls have been tried in the past, but substantially all cylinders or rolls used for heating, drying or forming pulp or paper are generally heated by steam condensing on the inner surface of the roll that defines a closed pressure chamber. However, there are possible alternatives to using steam, for example, organic vapors such as Dowtherm and special heat transfer oils. The heat transfer coefficient for film type condensation of steam on stationary surfaces ranges from one thousand to three thousand

BTU/ (hr) (square feet of surface) (°F) difference in temperature between the steam and the surface being heated) . The corresponding range for organic vapors is 200 to 300 and for oils 10 to 30. Condensation is a constant temperature process, with the temperature depending upon the pressure. Because the internal volume of the roll is large compared with the rate of steam flow, the pressure is constant throughout. Thus, (provided there are no noncondensable gases) the heat leaves the steam at the same temperature at all points throughout the inner surface of the shell, thus, helping to maintain uniform heat transfer and drying at the water surface of the roll. As the steam condenses on the interior surface of the roll, heat is transferred first from the steam to the condensate film, then through the film to the metal wall that forms the roll. If the steam is super heated, its temperature will drop before it condenses, but condensation will occur at the same temperature as though it had been saturated at the same pressure. Researchers have established that with about 180°F super heat the rate of heat transfer to a given area is only about three percent more than for saturated steam at the same pressure. The ideal steam supply and condensate removal system should supply pure steam (no noncondensables) and maintain a thin, uniform condensate film. If noncondensables are present, and if liquid condensate alone is discharged from the cylinder, the noncondensables accumulate. Since the presence of noncondensable gas reduce the heat transfer capacity and uniformity, special consideration

should be given to insuring that the noncondensable gases are not allowed to accumulate. This can be accomplished in various ways. For example, by "blowing through" perhaps twenty percent of the steam supply with the condensate, a steam velocity high enough to purge noncondensables from the entire chamber within the roll can usually be achieved. Certain special problems must be taken into account in applying well known heat transfer data and steam technology to steam heated rolls. Let it be assumed that the roll is stationary, pressurized steam is being fed into the roll, and a certain amount of condensate (liquid water) has formed and rests on the lower part of the interior surface. As a roll begins to rotate, this tends to move the condensate in the direction of rotation of the roll; inertial forces tend to retard any change in motion of the condensate; centrifugal forces tend to hold the condensate against the inner periphery of the cylinder; and gravity tends to pull the condensate to the bottom of the cylinder. At very low speeds, the gravitational forces cause the condensate to run down the cylindrical side wall in a thin film that forms a puddle at the bottom of the roll. At slightly higher speeds, the viscous forces drag some of the condensate from the puddle part way up the ascending side wall of roll, but it continues to run down to the puddle. As the speed increases still further, the condensate is dragged higher up the interior surface of the side wall, and centrifugal forces hold the condensate to the side wall in the upper quadrant of the ascending side wall. However, gravity still prevails, and the

condensate breaks away from the cylinder wall and "cascades" back to the bottom of the dryer.

The rimming condition is achieved when the centrifugal force becomes sufficiently greater than gravity, allowing the condensate to "go over the top" . The speed at which this occurs is greatly dependant upon the amount of condensate present in the dryer, a thin layer being rimmed at a slower speed than a thicker layer. However, on the ascending and descending walls of the cylinder, gravity respectively decelerates and accelerates the condensate layer. This results in a condensate layer that is thickest at the top and thinnest at the bottom and in a relative motion of the condensate (with respect to the side wall) best described as "sloshing". At speeds just above the rimming speed, sloshing is considerable. As the speed is increased, the sloshing diminishes, until, at very high speeds, where the gravitational force is overwhelmed by the centrifugal force, sloshing becomes almost negligible.

Fluid flow within the roll has a marked effect on the heat transfer properties of the condensate. Under non-rimming conditions, droplets of condensations can form on the upper portions on the inner roll surface. With dropwise condensation there is no film, and droplets of condensate form and flow in rivulets in the puddle. There is much less resistance to heat transfer from the steam to the metal than with film condensation. The general requirement for dropwise condensation is a non- wettable surface.

Under rimming conditions, heat transfer is governed both by the thickness of the condensate and by fluid flow characteristics. The thinner the layer and more turbulent the flow, the less the resistance to heat transfer. Thickness of the condensate depends on the design, size, location and clearance of the siphon which extracts the condensate from the interior of the roll, roll speed and diameter, condensating rate and differential pressure. Turbulence depends on the condensate thickness and roll speed and diameter. Minimizing the condensate thickness, although resulting in a minimum of turbulence, will result in a lower resistance to, and greater uniformity of, heat transfer.

To illustrate one of the significant problems in operating such steam heated rolls, let us take the example of a paper corrugating operation where a quantity of paper is being fed between a set of two rolls. The steam in the rolls is at a predetermined pressure and temperature, and as indicated above, with the rolls being rotated at a sufficiently high speed, the condensate that has formed will reach a "rimming" condition where the liquid is distributed substantially uniformly (by centrifugal force) against the interior surface of the cylindrical side wall of the roll. In this condition, with the temperature within the roll being substantially uniform throughout and with heat transfer being substantially uniform through all areas of the cylindrical side wall, the temperature of the outside surface of the cylindrical side wall is

substantially uniform over the entire outer surface of the side wall.

However, let it now be assumed that it is desired to feed a different size or type of paper sheet through the corrugating rolls . It is necessary to stop the rolls, and it may take approximately five minutes or so (with the rolls being stationary to make the change over to feed the second paper material through the rolls. During this approximate five minute or so changeover time, the condensate (i.e. water) will have accumulated at the bottom part of the roll, and may reach a depth of, for example, 1/4 inch or greater at the lowest point in the interior surface of the roll. Since liquid water is a relatively poor conductor of heat, that portion of the cylindrical wall of the roll that is beneath the liquid water that has accumulated in the bottom of the roll experiences a significant temperature drop in comparison with the other portions of the side wall of the roll (e.g. possibly several 10°F) . This uneven temperature will cause the roll to be distorted out of a perfectly round shape.

Thus, when the rolls are again starting to rotate, with the paper sheet being fed between the rolls, there will be substantial variations of the temperature at the side wall outer surface that engages the paper sheet. The result is that for a period of time (e.g. one to two minutes) until the surface temperature around the entire side wall surface of the roll becomes uniform, disturbing vibration of the roll will occur, the result being that this portion of the product must be discarded

or run at a much lower speed. As the rolls continue to rotate and pick up speed, then the "rimming" occurs, and the temperature around the entire side wall again becomes substantially uniform so that the operation can be carried on in a suitable manner. _t In addition to the problem noted above of obtaining substantial uniformity of surface temperature along the outside surface of the side wall of the roll, there is also the overall consideration of optimizing the heat transfer from the heat transfer medium (generally steam) within the roll to the outside surface. One avenue which has been explored extensively to accomplish this is to remove the condensate (i.e. liquid water) from the interior of the roll as effectively as possible so that the liquid film that accumulates on the interior surface of the roll during the rimming condition is as thin as possible. However, the overall problem of obtaining proper heat transfer is complex, and certain facets of this will be discussed later in this text.

It is with the above consideration and others in mind that the apparatus and method of the present invention has been developed.

Summary of the Invention

The roll assembly of the present invention is designed to engage a material to be processed in heat transfer relationship, such as a sheet of paper or the like.

The roll assembly comprises a roll structure mounted for rotation and defines an enclosed chamber to contain a condensable heat transfer medium. The

roll structure comprises a cylindrical side wall having an outside generally cylindrical contact surface to engage the material in heat transfer relationship and an inside generally cylindrical surface which is exposed to the heat exchange medium in the chamber in heat exchange relationship. The medium condenses on the inside surface and heat is conducted through the side wall to the outside surface. First and second end walls are located at first and second ends of the side walls.

In one embodiment the inside surface of the side wall is formed with a plurality of elongate ridges defining elongate valleys between each pair of adjacent ridges to receive condensate that condenses from the medium on the inner surface and provide flow paths for the condensate. The inside surface further provides a collecting location in communication with the valleys to receive the flow of the condensate along the flow paths . There is condensate collecting means to collect the condensate from the collecting location. Also there is a chamber inlet means through which the medium passes into the chamber and chamber outlet means through which condensate of the medium passes from the chamber.

In one preferred form, the ridges and valleys are aligned with a longitudinal center axis of the roll structure about which the roll structure rotates. Also, the ridges and valleys are formed so that the flow paths provided by the valleys slope away from the longitudinal axis toward the collecting location.

Further, in a preferred form the collecting location comprises a surface region recessed relative to the ridges and extending continuously in a 360° curve around the inner surface of the side wall. The condensate collecting means comprises a tubular member having an inlet position adjacent to the recess region.

Also, in the preferred form, the collecting location is positioned between two sets of ridges and valleys, with each set of ridges and valleys having outer locations spaced farther from the collecting location toward the end walls, and inner locations positioned adjacent to and capable of directing flow of condensate into, the collecting location. Also in a preferred form, the ridges have a crest portion closer to the longitudinal axis, extending along a lengthwise dimension of its related ridge, and ridge side surfaces extending away from the crest portion away from said longitudinal axis divergently. Thus, condensate forming on the crest portions of the ridges flows awayj from the longitudinal axis along said side surfaces, in a condition where said roll structure is rotating so that the condensate is in a rimming condition distributed substantially entirely around the interior surface of the roll.

In the particular configuration first shown herein, the crest of the ridges have a narrower width dimension adjacent to the collecting locations, and the width dimension increases in a direction from the inner end of the ridges toward the outer end of the ridges.

Also, in the preferred embodiments shown herein, the side wall comprises an outer cylindrical shell, and at least one generally cylindrical insert positioned in heat transfer contact with the shell. The ridges and valleys are formed at the inside surface of the insert.

In the particular embodiments shown herein, the roll structure is a corrugating roll having an outer surface of a plurality of longitudinally extending ridges separated by recesses. Also, the insert itself may be made in two separate portions, spaced from one another, so that the collecting location is between the two separate insert portions and is defined by the interior surface of the shell. In a preferred form of the present invention, the inside surface of the side wall is formed with a plurality of elongate longitudinally extending grooves which provide flow paths for flow condensate longitudinally along the roll structure, and also a plurality of laterally extending grooves which lead into said longitudinally extending grooves. The longitudinally extending grooves having a depth greater than said lateral grooves so that there is flow from the lateral grooves into said longitudinally extending grooves. The inside surface has a circumferential collecting recess which connects to said longitudinally extending grooves said collecting recess having a depth at least as great as that of the longitudinally extending grooves so that condensate is able to flow from the longitudinally extending grooves into the collecting recess. The lateral grooves can be circular or in a continuous spiral.

In the method of the present invention, a roll assembly is provided such as noted above. While the roll is stationary, the condensate collecting on the interior surface of the roll flows into the valleys to the collecting location, where the condensate is removed. In the rimming condition, the centrifugal force causes the condensate to flow into the valleys and to the collecting locations where the condensate is removed. In both instances, there is improved heat transfer through the roll, and also more uniform heating throughout.

Other features of the present invention will be come apparent from the following detailed description.

Brief Description of the Drawings

Figure 1 is a longitudinal sectional view of a portion of a prior art steam heated roll with one type of condensate removal (siphon) system; Figure 2 is a longitudinal sectional view of another prior art steam heated roll assembly having a different condensate removal device;

Figure 3 is a longitudinal sectional view showing yet a third prior art steam heated roll assembly;

Figure 4 is a longitudinal sectional view of the apparatus shown m figure 3;

Figure 5 is a longitudinal sectional view of yet a fourth prior art steam heated roll; Figure 6 is a transverse sectional view of the apparatus of Figure 5 ;

Figure 7 is a longitudinal sectional view of a prior art steam heated roll, which is stationary, thus forming a "puddling" condition;

Figure 8 is a sectional view similar to Figure 7, but showing the condensate film formed during the rimming condition;

Figure 9 is a longitudinal sectional view of a portion of a prior art steam heated roll, showing the thickness dimensions (i.e. radial dimensions) of the various components substantially enlarged for purposes of illustration;

Figure 10 is a longitudinal sectional view of a prior art steam heated roll that is stationary, showing the depth distribution of the puddle formed at the bottom of the roll;

Figure 11 is a longitudinal sectional view of one preferred embodiment of the present invention;

Figure 12A is a sectional view taken along line 12-12 of Figure 11, showing the roll in a rimming condition;

Figure 13A is a transverse sectional view taken at the same location as Figure 12A, but showing only a portion of the side wall insert, drawn to enlarged scale; Figures 12B and 13B are views similar to

Figures 12A and 13A, respectively, but showing the roll stationary in the "puddling" condition;

Figure 14 is a sectional view taken at line 14- 14 of Figure 11; Figure 15 is a sectional view taken along line 15-15 of Figures 11;

Figure 16 is a longitudinal sectional view of a steam feed/condensate removal fitting for the embodiment of Figure 11;

Figure 17 is a sectional view, drawn to an enlarged scale, of an outside surface portion of the side wall of the roll shown in Figure 12A, showing a modified form of the collecting area of the insert;

Figure 18 is a view similar to Figure 11, showing a modified form of the insert made as two seaport portions, with the condensate collecting area being positioned therebetween;

Figure 19 illustrates in transverse section the corrugated surface of the roll used in one preferred form of the present invention; Figure 20 is a view similar to Figure 12A, but showing the roll side wall 104 made as a single casting;

Figure 21 is a sectional view of a fourth embodiment of the present invention, this being a longitudinal sectional view which, for ease of illustration, illustrates only that portion of the roll on one side of the longitudinal center line, and also illustrating only one part of the roll, measured from a longitudinal center location to one end of the roll;

Figure 22 is a view similar to figure 21, but showing a modified version;

Figure 23 is a transverse sectional view, drawn to an enlarged scale, relative to Figure 21, taken along line 22-22 of Figure 21; and

Figure 24 is a view similar to Figure 23 and 21, but shows a further modified version.

Description of the Preferred Embodiments a. Brief Review of Prior Art Steam Roll Designs It is believed that a clearer understanding of the present invention may be achieved by first examining the common prior art steam heated rolls and their associated apparatus.

One such steam heated roll assembly 10 is shown in Figures 1, where there is a roll 12 having a cylindrical side wall 14 and end walls 16. Bearing members or trunnions 18 are provided at each end wall 16. There is a drive gear 20 connected to one bearing member 18 to rotate the cylinder. To provide for the steam to be fed into the roll and for removal of condensate, there is a steam joint 22 which attaches to a steam inlet pipe 24 and also to a condensate outlet pipe 26 positioned in one of the end bearing members 18. A steam inlet passageway is indicated at 28. Also, there is provided a siphon 30 that withdraws the condensate from the chamber 32 defined by the interior surface 34 of the side wall 14 and also the interior surfaces 36 of the two end walls 16. In operation, the steam enters through the conduit 24 and into the chamber 32 to condense on the interior surface 34 of the side wall 12 and also to some extent on the surfaces 36 of the two end walls 16. When the roll is stationary, the condensate collects on the bottom of the roll 12, where the siphon 30 removes the condensate. When the roll 12 is rotating at a sufficiently high velocity, so as to cause a rimming condition, the

siphon 30 draws out the condensate from the film of condensate passing beneath. Since there must be a certain amount of clearance between the inlet end 38 of the siphon and the side wall surface 34, the thickness of the condensate film in the rimming condition is generally between about one to three millimeters, depending upon the amount of clearance and the location within the roll 12.

A second type of a prior art steam heated roll assembly is shown at 10a in Figure 2. In this instance, the roll 12a has within it a siphon 30a where there is a longitudinally aligned siphon pipe 40b and oppositely extending and radially extending arms 42 that rotate with the roll 12a. A third type of prior art roll assembly 10b is shown in Figure 3 and 4, where there is a roll 12a having therein a siphon 30b having a horizontal arm portion 40b and a single radially extending siphon return arm 44. Yet a fourth prior art roll assembly 10c is shown in Figures 5 and 6. There are two generally semi-circularly curved siphon arms 46 which have condensate inlets at 48 that are nearly tangentially aligned with the interior surface 34c of the side wall 14c of the roll 12c. The inlets 48 are located so that these function to "scoop" the condensate into the inlet 48.

b. Heat Transfer Characteristics of Prior Art Roll Assemblies

Reference is now made to Figures 7 and 8 which show a prior art steam heated roll 12 in cross- section, having a single siphon 30. In Figure 7,

the roll 12 is stationary, and it can be seen that condensate has collected at 50 in the bottom part of the roll interior chamber 32. There is a small amount of moisture which collects in droplets along the top and side surface portions 52 of the interior surface 34, and these droplets in turn run down to the lower puddle at 50. Since any film that forms in the upper and side interior surface portions 52 is relatively small, heat transfer at those locations is relatively high. With water being a poor conductor of heat, the heat transfer at the lower puddle location 50 is relatively poor.

In Figure 8, the roll 12 is shown in the rimming condition. It can be seen that a substantially uniform film has formed at 54. The centrifugal force, with the roll 12 rotating at full speed, is higher than the force of gravity, so that the condensate film 54 is relatively uniform. As indicated above, generally this film 54 can be between about one to three millimeters, depending upon the clearance of the siphon with the interior wall 34, and the precise location on the wall 12, relative to the location of the siphon 30.

Reference is now made to Figure 9 , which shows a portion of the side wall 12 of a prior art roll in cross-section. For purposes of illustration and explanation, the thickness dimensions of the side wall and the various layers or films associated therewith are greatly exaggerated. There is the steam 56 in the roll chamber 32, and the condensate film 54 is shown in the rimming condition. Next to the condensate wall 54 is a layer 58 of scale and possibly contaminates which form against the

interior surface 34 of the side wall 14. Immediately adjacent to the outside surface 60 of the side wall 14, there is a layer 62 of dirt and air, and outside of this there is shown a flat sheet of paper 64 which in this instance is being heated and dried.

This is simply a rather schematic showing of temperature differentials across the various layers, and is not meant to be precise representations . The effect of the layer of condensate relative to heat transfer will be discussed in more detail below.

Reference is now made to Figure 10 which shows the prior art roll 12 of Figures 7 and 8 in longitudinal cross-section, with a siphon tube 30 being located at one end of the roll . In this instance, the roll 12 is stationary so that the condensate collects as a puddle 50 in the lower part of the roll side wall 34. It will be noted that the puddle 52 is higher at the far end 66, relative to the siphon 30 and shallower at a location 68 closer to the siphon 30. The reason for this is that there is only the force of gravity acting on the puddle 50 to cause it to flow to the siphon 30 as the water is being drawn out. Since water is a relatively poor conductor of heat, the temperature of the outer surface portion of the side wall 14 at the location of the deeper portion 66 of the puddle 50 would be somewhat lower than the temperature of the side wall portion adjacent to the thinner portion 68 of the puddle 50. Further, the temperature of the outer surface of the side wall at an upper and side locations would be somewhat greater than that which exists at the outer

surface adjacent to the puddle locations 68 and 66. As indicated previously in this text, this accumulation of condensate as a somewhat non-uniform puddle at the lower part of the roll 12 during period when the roll 12 is not rotating results in a non-uniform temperature at the outside surface of the roll side wall 14. Thus, as indicated previously, for a certain period after the roll 12 starts to rotate, this non-uniform temperature condition remains and is detrimental to the proper operation of the roll.

c. Description of One Preferred Embodiment of the Present Invention To describe one preferred embodiment of the present invention, reference is first made to Figures 11 through 17. As shown in Figure 11, there is the roll assembly 100 of the present invention comprising a roll 102, having a cylindrical side wall 104 and two end walls 106. The side wall 104 comprises an outer cylindrical shell 108 having an inner cylindrical surface 110, and an insert 112 positioned snugly within the outer cylindrical shell 108. The configuration and function of this insert is particularly significant in the present invention, and this will be described in greater detail later herein.

There is a siphon assembly 114, comprising a centrally located, longitudinally extending pipe 116 supported at opposite ends 118 within the end walls 106. At one end wall 116, there is provided a steam inlet and condensate outlet fitting 120 which is, or may be, of prior art configuration. Such a

fitting is illustrated in Figure 17 and it can be seen to comprise a inner condensate removal pipe 122 surrounded by an annular steam inlet passage 124. This particular fitting shown in Figure 16 already exists in the prior art, and is currently marketed by the Johnson Corporation. Accordingly, this fitting 120 will not be described in detail herein. Connected to the center of the middle feed and support tube 116 is a siphon tube 126 which extends radially downwardly from a center coupling 128 for the pipe 116 and has at its lower end an inlet 129. While only one siphon tube 126 is shown herein, there could, of course, be additional siphon tubes and various arrangements of the same would be possible, as shown in the prior art in Figures 1 through 6, or variations of the same.

To turn our attention back to the roll insert 112, as indicated previously, the structure and functional features of this insert 112 are particularly significant in the present invention. In general, this insert 112 substantially improves the heat transfer characteristics of the roll 102 both with regard to improved rate of heat transfer (both in the rimming condition and the stationary "puddle" forming condition) , and with regard to greater uniformity of temperature at the outer surface of the roll side wall 104.

The roll insert 112 is formed in a general configuration of a cylinder having open ends. As shown in Figures 12 and 13 The outer surface 133 of the insert 112 is cylindrically shaped and fits against the inside surface 110 of the outer side wall shell or cylinder 108 in close metal to metal

contact so as to ensure optimized heat transfer between the two. The insert 112 is formed with two opposed sets of longitudinally extending grooves or valleys 130 which are distributed evenly around the entire inside surface of the insert 112. These grooves 130 are arranged parallel and adjacent to one another so as to form a plurality of longitudinally extending ridge members 131 separated by adjacent valleys 130. In describing the arrangement of these ridges 131 and valleys 130, the term "upper" shall denote proximity to the longitudinal center axis 134 of the roll side wall 104, and the term "lower" shall denote a distance further away from the longitudinal center axis 134. The term "inner" shall refer to proximity to the longitudinal center location of the roll 102 (or shall denote a direction toward that location) , while the term "outer" shall denote proximity to one or the other of the end walls 106 or a direction toward either of the two end walls 106.

Each ridge member 131 has an upper crest 136 formed by two adjacent walls 138 of that ridge member 131. Each valley 130 has a lower valley floor or apex line 140 which is formed by adjacent side walls 138 of adjacent ridge members 130. In Figures 12 and 13, the ridges 131 and valleys 130 are shown in transverse section across a longitudinal axis 134 at the center location of the roll 102.

The two sets of ridge members 131 and valleys 130 are separated at the longitudinal center of the roll 102 by a continuous circum erential collecting

groove or recess 142, the two side walls 144 of which are formed by the terminal faces 146 of the central end portion of the ridge members 131. The floor 148 of the central circumferential groove 142 is a flat cylindrical surface following a continuous uniform 360° curve around the insert 112. In Figure 11, the floor 148 of the recess 142 is shown as being at the same level as the lowermost location 149 of the apex line 140 of the valley where it meets the floor 148. In Figure 17 there is shown a modified version where the floor, (indicated at 148a) of the recess 142a is made slightly lower than the apex line location 149a to facilitate draining the condensate from the valleys 130a. Also, each groove or valley 130 slopes slightly downwardly from outer end locations 150 to a center end location 152 adjacent to the center groove 142. More particularly, as can be seen in the cross- sectional view of Figure 14, as the valley or groove 130 extends outwardly toward its related end wall 106, its lower apex line 140 slants upwardly, but the side walls 138 maintain their same angular orientation. Thus, the crest 136 of each ridge member 130 becomes wider, while the distance between the edges of each crest 136 becomes smaller. In a further end location as shown in Figure 15, it can be seen that at the outer end of each groove 130, the depth of each valley 130 has diminished to only about one fifth to one tenth of the depth of the valley 132 at the center location.

d. Operation of the First Preferred Embodiment of the Present Invention With reference to Figures 12A and 12B, let it first be assumed that the roll 102 is rotating at full speed so as to be in the rimming condition. It can be seen that the condensate will collect in the lower portion of each valley or groove 130. Since the valley floor or apex line at the bottom of each groove or valley 130 slopes "downwardly" (which means it slopes in a direction away from the longitudinal center axis 134 about which the roll rotates) , the centrifugal force is in a radially outward direction. This causes the condensate to flow down the grooves or valleys 130 to the center collecting groove or recess 142, where the siphon tube 126 carries the condensate outwardly through the pipe 116.

The steam in the chamber 132 condenses on substantially all of the surface areas of the interior of the roll 102. As the condensate collects on the side walls 138 of each ridge 131, it flows downwardly into the area at the valley floor or apex line 140. Condensate which forms on the flattened portion of the crests 136 of each ridge

131 has a very short distance to flow laterally into the adjacent grooves 130. Thus, there is at most a very thin film of condensate that forms on those flattened areas of the crests 136, since the centrifugal force exerted on the film tends to cause the flow into the grooves or valleys 130.

Thus, it becomes evident that any film forming on any of the interior surface portion of the insert

112 tends to flow into the grooves, and then longitudinally along the grooves toward the center circumferential groove 142 to be extracted by the siphon 126. The overall result is that this diminishes the film thickness in most all parts of the interior of the roll insert 112 to a rather small fraction of the film thickness that would exist in a conventional prior art roll during the rimming condition. To explore another facet of the heat transfer characteristics of the present invention, it is evident that with the formation of the valleys 130, there is increased total surface area of the interior surface of the insert 112. Since the rate of heat transfer has a functional relationship to the area on which the steam is condensing, this arrangement further enhances the rate of heat transfer.

Let us now examine the condition of the roll 102 when it is stationary so that a puddle forms in the bottom of the roll 102. Reference is made to Figures 12B and 13B. Since the valley floor or apex line 140 slopes from the end walls 106 toward the center collecting groove 142, there is gravity flow of the condensate collecting in the grooves 130

(which are positioned at a lower location) toward the center location, where the siphon 126 collects the condensate to discharge it to a location outside the roll 102. It is evident from viewing Figures 12B and 13B that the upper portion of the side walls 138 of the ridges 131 at a lower position have condensate only in the lower portion of each groove or valley 130, and substantial portions of the side

surfaces 138 are exposed directly to the steam for optimum heat transfer. Also, at the flattened areas of the crests of the ridges 131 (see Figures 14 and 15) , there is a very short distance for the condensate to travel to descend into the adjacent grooves 130. Thus, any film that forms in these locations would be relatively small.

To review further the heat transfer characteristics of the present invention, let us first consider approximate practical dimensions for a roll such as shown in Figures 12A-B and Figure 13A-B.

A typical corrugating roll 102 could be, for example, two and half meters long, and have an inside diameter of possibly two hundred fifty millimeters. The thickness (indicated at "a") of the outer steel shell 104 could be, for example, fifty millimeters. The total thickness (indicated at "b") of the insert 112 could be, for example, about twenty millimeters. The total depth of each groove or valley 120 (indicated at "c") in Figure 13B is approximately 15 millimeters. The thickness dimension from the valley floor or apex line 140 to the outside surface of the insert 112 (indicated at "d") in Figure 13b is approximately five millimeters.

While the depth of each groove 130 is fifteen millimeters at the maximum, the depth of each groove 130 at its outer end (adjacent to the end wall 106) is only about three millimeters. Obviously, these dimensions, and also the configuration of the grooves could be varied. For example, the valley floor or apex line 140 could be made somewhat wider

or somewhat rounded, and the same is true of the ridge crests 136. For ease in manufacture, the slope of the ridge side walls 138 is made uniform (so as to make an included angle) indicated at "e" in Figure 13B of approximately sixty degrees. This slope could be varied, and possibly be made different at certain locations. Or there could be a compound slope, such as forming the slope of the side walls 138 near the end walls at a shallower angle.

Desirably, for economic and structural reasons, the outer shell 108 is made of steel. The insert 112 is desirably made of aluminium, both for ease of manufacture costs and also thermal conductivity. Thermal conductivity can be measured according to the following relationship, namely:

BTU'S/(hr) (sq. ft) (°F)/per ft of thickness According to this measure of thermal conductivity, the thermal conductivity of certain materials are given below.

Aluminum 121

Steel 25. ,6

Copper 222

Dural (an alloy) 119

Water 0. .3

To put these relationships in perspective, let it be assumed that it is desired to transfer one thousand BTU's per square feet per hour through a film of water which is one millimeter thick. To accomplish this, there would have to be a temperature deferential of 8.6°F imposed. To accomplish this

same rate of heat transfer for steel which is fifty millimeters thick, it would take only 6.5°F temperature differential. To accomplish this rate of heat transfer for aluminum that is five millimeters thick, the temperature differential required would be 0.14°F.

An analysis of these relationships, relative to the distribution of the condensate and the condensate film in the rimming condition and the stationary "puddling" condition of the roll 102, clearly indicates that not only is the rate of heat transfer enhanced, but also the uniformity of the heat transfer (particularly to solve the problems of temperature differential at the outside surface at the "puddle" location) .

First, in the rimming condition, in the prior art roll 12 there is generally a film thickness between about one millimeter to three millimeters. On the other hand, in the present invention, during rimming, the great majority of the inside surface of the insert 112 has substantially little if any of the condensate film thereon, since the condensate collects in the apex lines 140 of the grooves 130. It is apparent that even with the significant effect of a one millimeter layer of condensate, this provides significant improvement in heat transfer.

In the puddling condition where the roll 102 is stationary, the condensate that collects in the grooves or valleys 130 is constantly flowing toward the center location. Further, the side walls 138 have a relatively steep slope, and thus have very little film condensate thereon. At the very central portion of the roll where the grooves or valleys

130 have a maximum depth, even though there will be a certain amount of collection in the lower part of these grooves 130, substantial portions of the side walls 138 will have very little (if any) condensate remaining thereon. Thus, even at the puddle location itself, there are significant areas having little if any film, thus providing a relatively large area for the flow of thermal energy without being obstructed by a layer of film condensate. A further modified form of the present invention is shown in Figure 18, where the insert 112 is made as two separate sections 112b and 112c. This is accomplished by deleting the material of the insert 112 that is at the location of the recess so that the inside surfaces 146b of the inner side walls of the insert sections 112b and 112c are spaced from one another and the exposed middle inside surface portion 152 of the inner surface of the shell 108b forms the surface at which the condensate collects.

This preferred embodiment was specifically designed for a corrugating roll, but within the broader scope of the present invention, the basic concepts of the present invention could be applied to other types of rolls such as drying rolls for pulp or paper, etc. To illustrate the configuration of a corrugating roll of the specifically disclosed embodiment, reference is made to Figure 19 which is drawn to enlarged scale and shows a portion of the roll 102 circled at Figure 112. It can be seen that there is on the exterior surface a series of ridges 160 separated by recessed portions or grooves 162. As indicated previously, a matching set of rolls is

positioned one against the other with the ridges and grooves of the rolls that are interfitting with one another to give the paper or cardboard its corrugated configuration. Also, it is to be understood that the side wall 104, instead of being made in two parts (i.e. as a shell 108 and an insert 112) , this could be made as a single casting, where the grooves 130 and the collecting groove 142 can simply be machined into the interior surface. This is illustrated in Figure 20.

A fourth embodiment of the present invention is illustrated in Figures 21 and 24. Components of this fourth embodiment which are similar to prior embodiment will be given like numerical designations, with a "c" suffix distinguishing those of the fourth embodiment.

With reference to Figures 21 through 24, for convenience of illustration, there is shown only the cylindrical sidewall 104c of the roll 102c of the entire assembly 100c. It is to be understood, however, that the roll 102c has end walls, and that there is a siphon assembly (these are not shown for ease of illustration) . In this fourth embodiment, there is a plurality of longitudinally extending grooves 130c along the interior surface 110c. However, there are fewer grooves 130c, and these are spaced further from one another. In the particular embodiment shown herein, there are sixteen longitudinal grooves 130c spaced 22 ° from one another. In this particular configuration, the grooves 130c have a uniform depth along the entire length of the roll 104c.

At the end of the roll 104c, there is a circumferential recess or groove 142c that is deeper than the longitudinal grooves 130c, to receive the flow of condensate from the longitudinal grooves 130c. As indicated above, it is to be understood that there is a siphon tube which would extend downwardly to be adjacent to the surface of the circumferential recess 142c to remove the condensate. In this fourth embodiment, the interior surface 110c of the roll side wall 104c is formed with a plurality of circular circumferential grooves 194 which are spaced at intervals along substantially the entire length of the roll 104c. Each of these circular grooves 194c is positioned in a respective plane transverse to the longitudinal axis of the roll 102c. Alternatively, as shown in Figure 22 these grooves 194 could be formed as one continuous groove which is formed in the inside surface 110c as a continuous helical groove extending from one end of the roll 104c to the other.

As shown in Figure 23, the depth of the circumferential grooves 194 is less than the depth of the longitudinal grooves 130c. Thus, the condensate collecting in the grooves 194 flows laterally into the grooves 130c.

To describe the operation of the roll assembly 100c, the roll 102c will first be considered in the rimming condition. The condensate will form on the interior surface portions 198 that are positioned between the longitudinal grooves 130c and the circumferential grooves 194. The centrifugal force will cause the condensate to flow partly into the

circumferential grooves 194 and also into the longitudinal grooves 130c. The condensate flowing into the circumferential grooves 194 will then flow into the longitudinal grooves 130c, and the condensate in the grooves 130c will flow toward the collecting location where there is the circumferential groove 142c that is below the depth of the longitudinal grooves 130c. The siphon removes the condensate from this collecting groove 142c.

With reference to Figure 23, let us now consider the operation when the roll 102c is stationary, and condensate begins to collect in the bottom of the interior surface 110c. The condensate that forms on the upwardly positioned surface portions 198 will flow by gravity into the adjacent longitudinal groove 130c and in turn flow toward the collecting location of the groove 142c. If the lowermost longitudinal groove 130c is positioned immediately below the longitudinal center axis of the roll 102c so as to be at the lowest position of the interior surface 110c, then the condensate that forms on the adjacent portions 198 will flow by gravity into this lowermost longitudinal groove 130c to again flow to the collecting location at the circumferential groove 142c.

In the situation where there are two lowermost grooves 130c positioned at a location where these are laterally spaced from the vertical plane along longitudinal center axis, as shown in Figure 23, the condensate formed on the lowermost positioned surface portions 198 along the length of the roll 102c will then flow into the groove portions 194

that are at the lowermost position. This situation is shown in Figure 23. The circumferential grooves 194 are of sufficient depths so that in the position of Figure 22, the edge portions 202 of the lowermost groove portion 194 are positioned below the lowermost center portion 204 of the lowermost portion of the groove 194. Thus, as the condensate forms on the lowermost surface portions 198 of the surface 110c, this condensed water will flow into the lowermost portion of the groove 194 and then over the edges 202 into the adjacent longitudinal grooves 130c to again flow into the circumferential collecting groove 142c where it is drawn out by the siphon. Accordingly, there is substantially no puddling at the lowermost location 204 of the lowermost section 198 since the condensate that forms on these lowermost sections 198 flows longitudinally into the two adjacent circumferential grooves 194. A certain amount of condensate will collect in the very lowermost portion of the groove 194, as shown at 206 in Figure 22. However, the total surface area of the grooves 194 is very small in comparison to the much larger surface area of the surface portions 198. Thus, there is very little impedance to uniform heat transfer within the roll 102c, and there is very little tendency for the lowermost part of the roll 102c to become cooler than the rest of the portions of the cylindrical side wall 104c of the roll 102c.

In a typical configuration, with a roll having an inside diameter of about 200 millimeters, and with sixteen evenly spaced longitudinal grooves; the

depth of the longitudinal grooves 130c would be at least about 5 millimeters or greater, and the depth of the circumferential grooves 194 would be at least about 3 millimeters. A further modification is shown in Figure 24, where the longitudinal grooves 130c slope downwardly toward the collecting location.

It is to be understood that various modifications could be made to the present invention without departing from the basic teachings thereof.