US3601902A

US3601902A - Drying cylinder for webs

Info

Publication number: US3601902A
Application number: US877124A
Authority: US
Inventors: Christian Schiel
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1968-11-20
Filing date: 1969-11-17
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31
Also published as: GB1238757A

Abstract

The specification discloses a drying cylinder having a jacket constructed to exhibit high strength and having bodies or members of high heat conductivity embedded in the jacket to conduct heat from the inside of the jacket to the outside surface thereof. The heat exchange connection of the inserted bodies, or members, with the jacket may be improved by a heat conductive filler material disposed between the bodies, or members, and the surface of the holes in the jacket in which they are mounted. In one modification of the invention, the bodies, or members, inserted into the cylinder jacket serve also at least to assist in supporting heating coils on the inside surface of the jacket.

Description

United States Patent Inventor Appl. No.

Filed Patented Assignee Priority DRYING CYLINDER FOR WEBS 18 Claims, 11 Drawing Figs.

US. Cl

Int. Cl

[50] Field of Search Primary ExaminerFredrick I... Matteson Assistant Examiner-Theophil W. Streule AttarneyMelvin A. Crosby ABSTRACT: The specification discloses a drying cylinder having a jacket constructed to exhibit high strength and having bodies or members of high heat conductivity embedded in the jacket to conduct heat from the inside of the jacket to the outside surface thereof. The heat exchange connection of the inserted bodies, or members, with the jacket may be improved by a heat conductive filler material disposed between the bodies, or members, and the surface of the holes in the jacket in which they are mounted. In one modification of the invention, the bodies, or members, inserted into the cylinder jacket serve also at least to assist in supporting heating coils on the inside surface of the jacket.

PATENTED M1831 |97| 3.601.902

sum 1 [1F 3 Fig. l

, mm m u-muu (XXXXXXY X) X X) XXYXYXXX X XXX XXYYI PATENTEU AUGBI IHYi 3.681.902

SHEET 2 0F 3 INVENTOR.

CHRDTMN SCHIEL MAM PATENTED M1831 |97| SHEET 3 [IF 3 INVENTOR. (HRWTMN MHML BY MAM DRYING CYLINDER FOR WEBS cylinder is equipped with at least one hollow trunnion for the introduction therein and the removal therefrom of a heating medium, such as saturated steam. There also have been employed peripherally heated drying cylinders, in which heating coils are located in the region of the internal surface of the cylinder jacket.

In either case, the heat from the heating medium passes radially outwardly through the cylinder jacket and acts on the web passing about the jacket to cause the d ying thereof.

The selection of a suitable material for the jacket of such a cylinder is important because the jacket must be smooth and have a high surface hardness and the material from which the jacket is made must have high strength. Furthermore, the material selected for the cylinder jacket should have a high coefficient of thermal conductivity.

I-Ieretofore, no material employed for making cylinder jackets for drying cylinders. has been entirely satisfactory because all of the aforementioned requirements have not been met in all materials. Cast iron is quite often employed for making the jackets of drying cylinders because it can be smoothly finished and the surface is hard and the frictional properties of cast iron are suitable for drying cylinder jackets. However, the thermal conductivity of cast iron is relatively low in comparison with the thermal conductivity possessed by other materials. Other materials having higher thermal conductivity have, however, been defective in some of the other properties referred to above.

With the foregoing in mind, a primary objective of the present invention is the provision of a drying cylinder of the type referred to above which will meet all of the important requirements referred to.

A particular object of this invention is the provision of a drying cylinder having at least the jacket portion thereof formed so as to have proper surface qualities and adequate strength, while at the same time, having desirably high thermal conductivity.

A still further object of the present invention is the provision of an arrangement for increasing the thermal conductivity of a body of metal employed as the jacket for a drying cylinder and to promote uniform distribution of the heat on the external surface of the cylinder jacket.

The foregoing objects, as well as other objects and advantages, of the present invention will become more apparent upon reference to the following detailed specification taken in connection with the accompanying drawings in which:

FIG. I is an axial section through a drying cylinder for a paper machine and constructed according to the present invention;

FIG. 2 is a fragmentary axial section through a cylinder according to the present invention;

FIGS. 3 to 5 show various arrangements of high heat conductivity bodies mounted in the cylinder jacket from the inside thereof;

FIG. 6 shows a body inserted into the jacket of a drying cylinder with a ring of low melting point material surrounding the body;

FIG. 7 shows the arrangement of FIG. 6 after the low melting point material has melted and flowed radially outwardly about the body;

FIG. 8 is a fragmentary view showing a development of the inside of a drying cylinder jacket with heating coils applied to the jacket surface;

FIG. 9 is a section indicated by line IXIX on FIG. 8;

FIG. 10 is a fragmentary axial section through a cylinder jacket illustrating a modification; and

FIG. 11 is a sectional view indicated by line XI-XI on FIG. 10.

BRIEF SUMMARY OF THE INVENTION In the present invention a hollow drying cylinder for drying webs, such as paper or textile webs, is provided. The cylinder has a cylindrical jacket portion and end members secured to the jacket portion and carrying support shafts or trunnions for the cylinder. 7

The present invention is particularly concerned with improving the rate of heat flow from inside the jacket to the outside where the heat can act upon a web passing over the jacket. The transfer of heat through the jacket from the inside to the outside thereof, and the uniform distribution of the heat on the outer surface of the jacket is augmented by the insertion of members into the jacket which exhibit a high rate of heat conductivity. Such members will permit the flow of heat through the jacket from a fluid heating medium, such as steam, supplied to the inside of the jacket throughone of the trunnions and such members, when employed in connection with heating coils inside the jacket, also improve the flow of heat from the heating coils outwardly through the jacket. The

' members referred to can be in the form of pin, or peglike bodies inserted into the inside jacket surface, or they can be in the form of rings set into annular grooves formed in the outside jacket surface.

GENERAL DISCUSSION OF THE INVENTION According to the present invention, a material is selected for the jacket of the drying cylinder which will exhibit the necessary strength and surface hardness and surface smoothness and frictional properties and the thermal conductivity of the jacket is enhanced by distributing in the jacket, bodies or members, having higher thermal conductivity than the material of the jacket.

Normally, by placing the bodies in blind holes extending outwardly from the inside of the jacket, the formation of hot spots on the outer jacket surface is avoided. However, the bodies may extend completely through the jacket to the outer surface thereof and then, if a heat sensitive material, such as a paper web, is passed over the jacket, an insulating member is inserted between the web and the outer surface of the jacket, such as a belt, or the like.

The bodies referred to above may advantageously be in the form of cylindrical or rodlike members and this simplifies the formation of the bores in the jacket cylinder for receiving the bodies. However, ithas also been found-that the bodies could be in the form of rings or annular segments extending generally in the circumferential direction of the cylinder. In this last-mentioned case, the rings, or segments, may be inserted into grooves extending into the cylinder jacket from the outer surface thereof. Such rings, or segments, are advantageously formed with the greatest cross-sectional dimension in the radial direction so as to serve efficiently for guiding the heat from the inside of the jacket surface radially outwardly to the outer surface of the jacket.

In the case of rings, or segments, set into grooves opening to the outside of the jacket, localized overdrying of the web being treated is prevented by providing an insulating region between the jacket surface and the web, such as the belt, or the like, referred to. Such rings or segments are preferably flush with the outer surface of the jacket. In the drying cylinders of the type to which live or saturated steam is supplied, a film or condensate forms on the internal surface of the cylinder jacket and this film, as is known, offers resistance to the flow of heat from the steam in the cylinder to the cylinder jacket.

The present invention takes this into account by mounting the bodies internally of the cylinder jacket in such a manner that they protrude radially inwardly through any such film of condensate and thereby have their radially inner ends directly exposed to the steam.

It has been found important to maintain good thermal contact between such inserted bodies and the jacket to bring about good heat transfer'to the outer surface of the jacket. One way of bringing this about is to press fit or shrink fit the bodies in the jacket, but all efforts to bring about the very best thermal contact between the bodies and jackets in this manner has met with limited success.

The present invention proposes to augment the rate of heat transfer between the inserted bodies and the jacket, namely to minimize the temperature radiant across the interface therebetween by placing between the inserted bodies and the jacket in the recesses in which the bodies are placed a filler agent which is a good conductor of heat and which may, within the range of the highest temperatures at which the cylinder operates, become flowable. By highest temperature is meant that temperature at which the cylinder will not become damaged, nor the heating medium become decomposed.

Such a filling agent will fill in all crevices and recesses and pores that might exist between the inserted bodies and the surfaces of the bores in which they are mounted and the rate of heat transfer between the bodies and the cylinder jacket will, therefore, not depend simply upon the formation of extremely smooth, close fitting surfaces on the body and its bore but, instead, even if the body fits loosely in its bore in the jacket, good heat transfer will take place between the body and the jacket.

It is possible for the filling agent to have a melting point above the operating temperature of the jacket. In this case, by a short-time overheating of the jacket the filling agent changes state and penetrates into the crevices between the bodies and the recesses, whereafter, upon cooling to the operational temperature of the jacket, the filling agent will solidify. In such a case, the melting point of the filling agent should not be too high, so as to avoid thermal stresses in the jacket upon cooling.

The melting point of the filling agent may even be below operating temperature of the jacket and during operation of the cylinder be in a more or lessflowable state so that, under the action of the centrifugal force of the revolving cylinder, it will flow into the radially external regions of the crevices.

As a filling agent there may be used a paste which conducts heat. If, however, the heat conducting bodies are inserted from the direction of the internal jacket surface, then a metal is preferable as filling agent. Such a metal is preferably solid at room temperature and liquid at the operating temperature of the drying cylinder. Such a metal, upon the shutting off of the heating medium which precedes any halting of the machine, will solidify and, therefore, will not ooze out at the internal jacket surface. A paste, on the other hand, may have a rather low viscosity over a wide temperature range and, therefore, might rather easily leak from the sealer-filled crevices.

It is of importance for heat to flow radially through the jacket and the bodies, therefore, extend principally in the radial direction.

In a further development of the invention, the bodies are in the form of radially arranged spikes, pins, or pegs, which, in the cross section, are preferably circular. Such an arrange ment leads to a satisfactory heat flow density, even if the pegs, or spikes, or pins, have a rather small cross section compared to the wall thickness of the jacket, so that the loss of strength of the jacket can be kept rather low. By experimentation, it has been ascertained that the heat flux density of a jacket equipped with copper pegs is about percent higher than that of a similar jacket which is equipped with ribs.

In order to accommodate these pegs, or pins, or spikes, bores are provided which pass completely through the jacket. Such bores may be drilled from the outside of the jacket, thus permitting the use of a drilling device which is commonly used for making suction rollers of paper machines.

With sensitive webs, like those of paper or similar materials,

and to prevent in this way, the arising of corrosion. The bores can be sealed by fitting each peg rather accurately into its bore or by employing a heat conducting sealer mass to seal the bore. If the bores do not pass all the way through the jacket and are, instead, blind bores which are drilled outwardly from the inside of the jacket, sealer materials on the inside are not required.

Further, it may be possible to eliminate insulation bet een the web and the jacket surface because such blind bores may eliminate hot spots on the outside surface of the jacket.

An advantageous development of the invention is'the one which provides both ribs in the jacket and also the pegs, or spikes, or pins, mounted on the ribs. The ribs bring about the creation of a large surface and this way a good heat transfer from the heating medium to the jacket material, while the pegs, or pins, or spikes, bring about, in addition, an improvement in the thermal conductivity of the jacket. If the pegs are inserted in the ribs only down to about the foot of each rib, they will not cause a significant lowering of the strength of the jacket, so that the jacket does not have to be constructed any thicker for jackets in which the pegs, or pins, or spikes are absent.

The choice of pins, or pegs, .or spikes, as bodies render it possible to introduce the tiller mass into the jacket in a rather simple manner, namely, in the shape of sheaths which can be mounted on the pegs, while the recesses, or bores, in the jacket to receive the pegs are large enough to accommodate the pegs and the sheaths which surround them. Each peg, or pin, or spike may be equipped with several sheaths or sleeves which are arranged axially behind each other.

Furthermore, it is of advantage for a sheath or sleeve to be shorter than the pinlike member on which it is mounted, and to be arranged close to the internal jacket surface, and to create the volume of the crevice spaced between the pinlike member and the bore radially outside the sleeve, at least approximately equal in volume to that of the sleeve. During operation, the radially external regions of the crevice space are thus completely filled by the material of the sheath, or sleeve.

It is preferable to form the recesses for the members as blind bores extending outwardly from the internal surface of the jacket and to seal the members inserted in the bore to the bore at the radially inner end, as with a seal which will prevent loss of the filling agent from the bore.

As mentioned, the present invention is also applicable to drying cylinder in which heating coils are mounted o'n the internal jacket surface. In this case, the invention is practiced by forming the inserted members as supports for the heating coils and connected thereto in heat exchange relation. The members will thus receive heat from the heating coils and transfer it directly to the jacket, while simultaneously anchoring the heating coils to the jacket. In order to improve the heat transfer in this case, a heat conducting filler agent may be provided in the bores of the jacket and surrounding the members mounted in the bores.

In a still further develop ment of the invention, each individual pinlike member is equipped with a head which surrounds the adjacent region of the corresponding heating coil.

Only a general increase of the heat flux density of the jacket of a drying cylinder has so far been discussed, but the invention may be used also for the improving of the jacket of a drying cylinder in another manner. As is known, drying cylinders, when formed of cast iron, are cast in a vertical position. When this is done, the pressure of the liquid iron at the lower end of the mold is greater, so that the cast material is more dense at the lower end than at the upper end, and there is a corresponding thermal conductivity over the length of the finished cylinder. Specifically, the conductivity decreases from the denser end of the jacket toward the less dense end.

By the practice of the present invention, the heat flux density passing through the jacket can be equalized from end to end of the jacket and differences in the thermal conductivity which arise in the jacket can be compensated in a simple manner. To accomplish such compensation, the size and/or the number of the inserted bodies increases towards this end of the cylinder which is less dense and which, therefore, has the smaller thermal conductivity. Also, compensation can be accomplished by causing the bodies towards said less dense end to penetrate more and more deeply into the interior of the cylinder.

The end regions of a drying cylinder, which are formed rather thick for reasons of strength, may be equipped with a greater number of inserted members so that the heat flux density in that region will reach the desired value. In such instances, the jackets are originally designed to carry the inserted members.

The introduction of bodies or members of a high thermal conductivity into the jacket of a drying cylinder may also take place in a restricted region or regions, so that the thermal conductivity in the region, or regions, is modified, while in all other regions of the jacket the thermal conductivity is determined solely by the nature of the jacket material itself.

Thus, if the jacket of a cylinder, due to a faulty casting, or for other reasons, proves to have low thermal conductivity, only such regions may be provided with bodies, or members, of an increased thermal conductivity. Heretofore, jackets were scrapped and considerable loss was sustained from this cause. By the practice of the present invention such cylinder jackets may be compensated and used in drying units.

From the foregoing, it will be seen that the general concept of the present invention might be expressed as follows: The thermal conductivity of the jacket of a drying cylinder can be brought to a desired level, even in selected regions, by inserting, or imbedding in the jacket in heat exchange relation therewith and, preferably, with the heating agent which supplies heat to the jacket, a plurality of bodies of a material which has a thermal conductivity differing from the-thermal conductivity of the jacket material, whereby the desired thermal conductivity is created in the said jacket regions.

DETAILED DESCRIPTION OF THE DRAWINGS The drying cylinder shown in FIG. 1 has a cylindrical jacket 1, end members 2, a hollow support shaft 4 equipped with steam outlet openings 3, and syphon tubes 5 inside the jacket.

Bearings 6 outside the cylinder support the assembly. Inserted into jacket 1 from the inside are radially arranged members in the form of copper pegs 7.

The pegs 7 (shown schematically) are distributed uniformly across the full jacket surface and may have a diameter of about 10 mm. The arrows indicate the direction of flow of the steam into the cylinder and the direction of flow of the condensate and of the cylinder.

InFlG. 2, the cylinder jacket 1 shown is equipped on the inside with ribs 3 into which copper pegs 7 are imbedded. The end of the jacket ll increases in cross section towards the end member 2, and is equipped with copper pegs 17, which become longer as the jacket cross section increases so that the thermal flux which can pass radially through the jacket 1 to the outer surface thereof in the thicker edge region of the jacket will have a value corresponding to that of the thinner regions of the jacket and high enough to effect drying of the web 9.

In FIG. 3, sleeve 10 having a central tapering hole'is inserted into bore ll of jacket 1. A tapered copper pin 7 has been pressed or driveninto the hole in sleeve 10 so that pin 7 is held in sleeve 10, while sleeve 10, in turn, is expanded into tight engagement with the surface of bore 11.

The inserted pinlike member 7" in FIG. 4 is equipped with annular ribs at its radially inner end larger in diameter than bore 11, which during the act of hammering or pressing the member in place in the bore are deformed so as to seal bore 1 l at the mouth end thereof. At the upper end of the pinlike member 7 is a conical bore 14 in which a conical pin 15 is disposed, which bottoms in bore 11 as the pinlike member 7" is put in place.

Pin 15 will expand the bottom end, or radially outer end of pinlike member 7 so that with a correctly machined area lid in bore 11, pinlike member 7" will make good heat exchange contact with the wall of the bore 11.

Pinlike member 7", shown in FIG. 5, differs from the one shown in FIG. 4 in that it has a head 119' larger in diameter than bore Ill. An elastic seal 20 is arranged between the head l9 and the cylinder jacket 1.

FIGS. 6 and 7 show insection a fragment of a cylinder jacket lhaving an internal jacket surface 10 and an external jacket surface 1b. The jacket has drill-ed therein from the inside, blind bores, each of which has a radial, inner portion b as well as a radial, outer portion 9'. The diameter of portion 9' is smaller than the diameter of portion 8'. A copper pinlike member 4' having a head 5 and a neck region with circumferential ribs 6' larger in diameter than the radial, inner por" tion 8 of the blind bore is driven into the bore. Pin 4 is surrounded by a sleeve 7a of soft soldering alloy which, prior to the driving in of the peg 4' was mounted on the pin and is received inside portion 8' of the blind bore. When the jacket 1 is heated to the melting temperature of the sleeve, the sleeve becomes liquid and, under the action of centrifugal forces, moves outwardly. It then will occupy, as will be seen in FIG. "I the space between the radially outer end of pin 4 and the radial outer portion 9' of the blind bore, and may also occupy a part of the radial inner portion 8' of the: blind bore.

FIG. 8 shows two heating coils 2, 3' attached to the jacket 1. A number of pinlike members are inserted in bores in the jacket along the heating coils. These members have heads, some of which are identified at 4b, 5b, 6b and 7b in FIG. 8.

As will be seen in. FIG. 9, the heating coils 2', 3 pass through bores in the heads of the pinlike member, while the pinlike members themselves are driven into the blind bores 13 in the jacket 1 and are retained therein by peripheral ribs 15 which, before being driven into the bores 13', are larger in diameter than thesaid bores. The pinlike members, thus, serve at least partly to attach the heating coils to the jacket and also transfer heat from the coils to the jacket. Even if the pinlike members alone are sufficient to attach the heating coils to the jacket, as a safety factor, retention screws 16 and washers 17 may be provided to retain the pinlike members in places, and in this way, bring about a completely reliable attachment of the heating coils to the jacket.

The annular segments 27 shown in FIGS. 18 and 11, which may be made of copper, are driven into circumferential grooves 23 formed in the jacket 1. The outer surface of the jacket 1 is formed of a layer of sintered metal 24 which is machined after it is deposited on the jacket, and upon this layer rests the web 9".

Modifications may be made falling within the scope of the appended claims.

What is claimed is:

1. A hollow drying cylinder for use in drying webs, said cylinder having a cylindrical jacket and end members, and heat transfermembers mounted in longitudinally distributed relation in said jacket and said members being formed of a material having a higher thermal conductivity than that of the material of said jacket for facilitating transfer of heat from inside of said jacket to the outer surface thereof.

2. A hollow drying cylinder according to claim 1, in which said jacket is formed with grooves extending substantially circumferentially thereof and said members are arcuate and disposed in said grooves.

3. A hollow drying cylinder according to claim 1, in which at least some of said members have the inner ends thereof flush with the internal surface of said jacket.

4. A hollow drying cylinder according to claim I, in which at least some of said members project radially inwardly from the internal surfaceof said jacket.

5. A hollow drying cylinder according to claim 4 in which said filling agent is a metal which becomes flowable at about the highest operating temperature of said jacket and which is solid at room temperature.

6. A hollow drying cylinder according to claim 1, in which said jacket is provided with blind bores extending outwardly from the inside surface of said jacket to receive said members and at least some thereof being larger in diameter than the members mounted therein, and a heat conductive filling agent in each said bore which is larger in diameter than the member mounted therein filling the space around the member in the bore in at least the .radially outer region of the bore and establishing efiicient heat transfer relation between said jacket and the said members.

7. A hollow drying cylinder according to claim 1, in which said jacket is provided with internal circumferential ribs and at least some of said members are mounted in said ribs.

8. A hollow drying cylinder according to claim 1, in which said jacket has bores extending radially outwardly from the inside surface of the jacket and said members are pinlike and are mounted in the said bores in said jacket.

9. A hollow drying cylinder according to claim 6, in which each said bore is radial and each said member is pinlike, said filling agent is heat softenable and in unsoftened state is receivable in said bore in the form of a sheath arranged in surrounding relation to the respective member.

' 10. A hollow drying cylinder according to claim 9, in which each said sheath is shorter than the respective member and is receivable in the respective bore near the inner surface of said jacket, the volume of the respective bore radially outward of the said sheath which is not occupied by said member being about equal to the volume of said sheath.

11. A hollow drying cylinder accordingto claim 9, in which said bores are blind bores extending into said jacket from the inside surface thereof, and means sealing between each said member and the respective bore at the radially inner end of the bore.

12. A hollow drying cylinder according to claim 8, which includes heating coils mounted on the inside surface of said jacket, said pinlike members being distributed along said heating coils and forming at least a portion of the support for holding the heating coils on the said inside surface of the jacket, said pinlike members being in efficient heat exchange relation with said heating coils. i

13. A hollow drying cylinder according to claim 12, in which each pinlike member has a head thereon inside the jacket, said heating coils extending through said heads.

14. A hollow drying cylinder according to claim 8, in which each said member is in the form of a sleeve in the respective bore, said sleeve having a bore which converges toward the radially outer end of the sleeve, and a tapered pin element driven axially into the bore in the sleeve to expand the sleeve into tight fitting relation with the bore in the jacket.

15. A hollow drying cylinder according to claim 8, in which each bore is closed at the radially outer end and each said pinlike member has a tapered. hole in its radially outer end, and a tapered pin in said hole which bottoms in the respective bore whereby upon driving the said member into the respective bore the tapered pin will expand the radially outer end of the member.

16. A hollow drying cylinder according to claim 15, in which each pinlike member has ahead at the radially inner end larger than the bore in the jacket, and a sealing element between said head and the inner surface of said jacket.

17. A hollow drying cylinder according to claim 15, in

which each pinlike member has radial n'b means near the radially inner end thereof larger in diameter than the respective bore in the jacket and deformable into sealing engagement with the radially inner end of the bore in the jacket when the member is driven into the bore.

18. A hollow drying cylinder according to claim 11, in which each pinlike member has radial rib means near the radially inner end thereof larger in diameter than the respective bore in the jacket and deformable into sealing engagement with the radially inner end of the bore in the jacket when the member is driven into the bore.

Claims

1. A hollow drying cylinder for use in drying webs, said cylinder having a cylindrical jacket and end members, and heat transfer members mounted in longitudinally distributed relation in said jacket and said members being formed of a material having a higher thermal conductivity than that of the material of said jacket for facilitating transfer of heat from inside of said jacket to the outer surface thereof.

4. A hollow drying cylinder according to claim 1, in which at least some of said members project radially inwardly from the internal surface of said jacket.

6. A hollow drying cylinder according to claim 1, in which said jacket is provided with blind bores extending outwardly from the inside surface of said jacket to receive said members and at least some thereof being larger in diameter than the members mounted therein, and a heat conductive filling agent in each said bore which is larger in diameter than the member mounted therein filling the space around the member in the bore in at least the radially outer region of the bore and establishing efficient heat transfer relation between said jacket and the said members.

10. A hollow drying cylinder according to claim 9, in which each said sheath is shorter than the respective member and is receivable in the respective bore near the inner surface of said jacket, the volume of the respective bore radially outward of the said sheath which is not occupied by said member being about equal to the volume of said sheath.

11. A hollow drying cylinder according to claim 9, in which said bores are blind bores extending into said jacket from the inside surface thereof, and means sealing between each said member and the respective bore at the radially inner end of the bore.

12. A hollow drying cylinder according to claim 8, which includes heating coils mounted on the inside surface of said jacket, said pinlike members being distributed along said heating coils and forming at least a portion of the support for holding the heating coils on the said inside surface of the jacket, said pinlike members being in efficient heat exchange relation with said heating coils.

15. A hollow drying cylinder according to claim 8, in which each bore is closed at the radially outer end and each said pinlike member has a tapered hole in its radially outer end, and a tapered pin in said hole which bottoms in the respective bore whereby upon driving the said member into the respective bore the tapered pin will expand the radially outer end of the member.

16. A hollow drying cylinder according to claim 15, in which each pinlike member has a head at the radially inner end larger than the bore in the jacket, and a sealing element between said head and the inner surface of said jacket.

17. A hollow drying cylinder according to claim 15, in which each pinlike member has radial rib means near the radially inner end thereof larger in diameter than the respective bore in the jacket and deformable into sealing engagement with the radially inner end of the bore in the jacket when the member is driven into the bore.