CH637175A5 - CYLINDER USED IN THE PRODUCTION AND PROCESSING OF CORRUGATED CARDBOARD. - Google Patents

Description

The present invention relates to cylinders used in machines for processing and producing corrugated cardboard.

The cylinder of the present invention is intended for use as an overlapping cylinder in the bonding portion of a corrugating machine, a pressing cylinder in the heating zone, a supply cylinder disposed before a rotary knife, and a feed cylinder in corrugated board processing machines such as a printer, folder-gluer and rotary cutter.

In general, corrugated cartons are likely to have their corrugations crushed or deformed when pinched between the rolls. This tendency is particularly marked when the lining used is thin.

In the corrugated industry, it has so far been a great problem to prevent such deformation of the corrugations, thereby keeping the thickness of the corrugated board constant, which is vital.

In the bonding part of a corrugating machine for producing corrugated cardboard, a gluing cylinder applies the glue to the tops of the corrugations of a sheet of corrugated cardboard on one side coming from the previous station or station. Above the gluing cylinder is placed a heavy steel overlapping cylinder. The overlapping cylinder, having its axis supported by a lever, is usually adjusted to lightly press the sheet against the gluing cylinder to avoid poor bonding which would be due to irregular application of the glue.

The overlapping cylinder presses the sheet on the side of its lining. In addition to the irregularity due to the height of the groove (so-called top-bottom) formed during the waving process, the surface of the lining is not equal, but tends to be lower to the parts opposite the bottoms of the undulations than to the parts opposite their peaks. In addition, the traditional straddle cylinder is

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in contact with the sheet substantially along a line or tangentially. Therefore, the overlapping cylinder is usually adjusted so that its bottom is in contact with the lowest parts of the liner or at an even lower position for bonding. The lever mechanism supporting the overlapping cylinder is provided with a stopper to prevent the overlapping cylinder from lowering from its preset position. The lever allows an upward movement of the overlapping cylinder, but it is too heavy to be moved up. Because the device is as explained above, the corrugations are more or less deformed when the sheet of corrugated cardboard is pinched between the gluing cylinder and the overlapping cylinder.

Likewise, with the traditional steel overlap cylinder, since it has to be adjusted to lightly press the sheet, there is a tendency for more glue than necessary to be applied to the tops of the corrugations. This means poor savings or wastage and too much moisture absorption from the one-sided sheet.

Excessive moisture absorption is undesirable for the following reasons. First, the corrugated sheet would soften so much due to the excess moisture that it would be even more likely to have its ripples deformed as it passed between the cylinders in successive phases.

Second, the sheet should absorb more heat in the heating step that comes after the sticking step. This means gain or loss of thermal energy. Likewise, the sheet should stay in the heating part longer. This decreases the speed of the machine and therefore the production per unit of time. In addition, the pressure applied to the sheet against the heating plates must be increased to have better absorption of heat. This increases the risk of deformation of the corrugations of the sheet.

Third, excessive moisture can cause warping of the corrugated sheet, which can cause machine breakdowns and produce a defective sheet.

When changing the lining, the space between the gluing cylinder and the overlapping cylinder must be readjusted. This adjustment is very painful and requires a high degree of specialization. The readjustment of the spacing is also necessary when changing the type of corrugation or groove. Therefore, a set of overlap and glue rollers with a pre-adjusted spacing is usually prepared for each type of groove.

In the heating part of the corrugating machine, numerous steel pressure rolls are arranged to press the sheet of corrugated cardboard against the heating plates by means of a cotton belt or strip to improve thermal conduction. Each pressing cylinder has its axis which is supported by a lever or a wedge to allow adjustment of the pressure applied to the sheet.

The greater the pressure applied by the pressure rollers on the sheet, the better the bonding and the higher the speeds, but the greater the risk of deformation of the corrugations. Since the pressure rollers press the sheet through the cotton strip in a line or tangentially, the pressure applied to the sheet is very great, even if the sheet is not pressed directly, but through the strip of cotton or through it.

When the joints of the cotton strip where the sections of the strip are joined by lacing and its convex parts where foreign bodies are attached pass under the pressure rollers, the rollers will jump, thus applying excessive pressure on the sheet and causing deformation of its undulations.

Also in the heating part, the space between the pressing rollers and the heating plates must be readjusted in accordance with the type of groove or groove, the material, etc., of the corrugated sheet.

The deformation of the corrugations is more likely to occur during treatments where the sheet contains relatively a lot of moisture, i.e. in the bonding part and in the heating part.

Next, a pair of steel feed rollers is arranged upstream of a rotary knife of the corrugator to bring the sheet of corrugated cardboard to the rotary knife. The feed rollers rotate at a slightly higher speed than the sheet feed speed so as not to allow the sheet to accumulate in front of the rotary knife. Thus, the sheet is fed on the rotary knife while being slightly pulled by the feed rollers.

With the traditional steel supply cylinder, the upper and lower supply cylinders are in contact with the corrugated sheet substantially tangentially on a transverse line. Therefore, in order to advance the sheet while pulling it slightly, the pair of feed rollers must pinch the sheet with considerable pressure, thereby causing the sheet of corrugated cardboard to warp.

Pairs of steel feed rollers are also used in other corrugated board processing machines such as a printer, folder-gluer and rotary die cutter. Also on these machines, deformation of the corrugations can occur due to the gripping force applied by the feed rollers. This can also occur at the auxiliary feed rolls and the process rolls mounted on such machines.

An object of the present invention is to provide a cylinder for use in machines for processing and producing corrugated cardboard having elasticity on its outer periphery to prevent deformation of the corrugations, without having to frequently readjust the space between the cylinders if we change the material, type of groove, etc. The cylinder according to the invention is defined by claim 1.

The characteristics and advantages of the present invention will become apparent from the following description given with reference to the appended drawings in which:

fig. 1 is a schematic view showing how a cylinder according to the present invention is to be used in the bonding part and the heating part of a corrugating machine;

fig. 2 is a schematic view showing how it is used in the next part of the corrugator;

fig. 3 to 18 are partial clear views of various embodiments of the present invention;

fig. 19 is a sectional view of an alternative embodiment of FIG. 18, and fig. 20 is a sectional view of another alternative of the embodiment of FIG. 18.

In the drawings, identical or similar reference numbers are used to designate similar or corresponding parts.

Fig. 1 shows a bonding part A and a heating part B of a corrugating machine where the cylinders 1 according to this invention are used as overlapping cylinders and pressing cylinders, respectively.

The bonding part A generally consists of a glue bowl 2, a glue cylinder 3 partially immersed in the glue of the glue bowl 2, a metering cylinder 4 to adjust or dose the amount of glue applied to the cylinder glue, and a rider 5 which rotates in contact with the glue cylinder 3 with a sheet of single-sided corrugated cardboard S pinched in between to be glued.

A lining L adheres to the sheet passed with glue and the double-sided sheet S 'is then dried in the heating part B where it is pressed by the pressing rollers 6 against the heating plates 7 through a strip of cotton 8.

Fig. 2 shows a part of the corrugating machine where the sheet of double-sided corrugated cardboard S 'passes through a splitter-marker C and is brought by a pair of feed rollers 9, 10 to a rotary cutter D. The cylinder lower supply can be replaced by a guide plate. The feed cylinder5

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upper tation 9 is usually set to a speed of rotation slightly higher than the speed of the sheet so as to pull it.

Although, in the example of fig. 2, the cylinder 1 according to this invention is only used as an upper supply cylinder 9, it can be used for the two supply cylinders or for the lower supply cylinder 10.

Several cylinder embodiments according to this invention will be described with reference to Figs. 3 to 20.

The first group of embodiments illustrated in figs. 3 to 7 are cylinders which comprise a cylinder body covered with one or more tubes made of natural or synthetic rubber or flexible synthetic resin, said tubes being adapted to be inflated by gas to give elasticity to the cylinder.

With reference to fig. 3, the cylinder 1 comprises a cylinder body 11 and two tubes 12 wound in a spiral around the cylinder body, said cylinder body having a gas inlet passage 13 for introducing gas such as air into the tubes 12. Each end of the tube can be connected to the passage 13 by means of a connector which also serves to fix the tube. The tube can be fixed by any other means such as adhesives and adhesive tapes.

Gas can be introduced into the tube through a pipe (not shown) connected to the gas supply passage 13 via a rotary connector.

The body of the cylinder 11 is provided with a spiral groove 15 in its external periphery to partially receive the tubes 12 to fix the latter and into which forced air has been introduced.

The realization of fig. 3 is suitable for winding two tubes 12 in a spiral around the body of the cylinder in opposite directions, starting from the center towards each end, to prevent warping of the sheet.

The realization of fig. 4 is substantially the same as the embodiment of FIG. 3, except that a single tube 12 is spirally wound around the body of the cylinder in the spiral groove 15 in one direction. In the case of a high cylinder speed or a relatively small width of the cylinder, the sheet does not warp, even if the tube is wrapped around the body of the cylinder in one direction as in this embodiment.

The realization of fig. 5 comprises a cylinder body 11 provided with a plurality of annular grooves 15 in its outer periphery and as many annular tubes 12 mounted in said annular grooves.

In the embodiments of FIGS. 3, 4 and 5, gas can be sent through a gas supply orifice 14 having a plug which will be described later with reference to FIGS. 6 and 7. In this case, of course, the passage 13 and the fitting or rotary joint are not necessary.

The realization of fig. 6 comprises the cylinder body 11 and a plurality of tubes 12 mounted on the cylinder body parallel to each other and to the axis of the cylinder body, each of said tubes being provided with a gas supply orifice 14 having a plug.

In the embodiment of FIG. 7, a plurality of tubes 12 are mounted on the body of the cylinder 11 at an angle to the axis of the body of the cylinder.

The achievements of fig. 4 to 7 can be provided with a gas supply passage 13, grooves 15, fittings for connecting the tubes 12 to the gas supply passage 13, and a rotary connector for connecting a pipe to the supply passage gas if the need arises, although some of them are not illustrated in the drawings.

Instead of sending gas through a plug-in gas supply orifice 14, the gas can be injected into the tube with an injector or a syringe if the thickness of the wall and the material of the tube 12 are such that they ensure gas tightness after removing the injector from the tube.

In the embodiments of FIGS. 3 to 7, the distance between the adjacent tube sections should be such that it would not interfere with the advancement of the sheet of corrugated cardboard.

The second group of embodiments will be described with reference to FIGS. 8 to 11. They have one or more tubular sheets placed on the body of the cylinder and fixed at each end, the gas being introduced into a space formed between the tubular sheet and the external periphery of the body of the cylinder, thus giving elasticity to the cylinder surface. The tubular sheet is made with a flexible material but not permeable to gas, such as natural or synthetic rubber or a synthetic resin material.

The realization of fig. 8 comprises the body of the cylinder 11, a tubular sheet 16 mounted on the body of the cylinder, and strips 17 for fixing the tubular sheet on the body of the cylinder at each of its ends. The strip can be replaced by an adhesive or an adhesive strip. Air is introduced into the space formed between the tubular sheet 16 and the body of the cylinder 11 through the gas supply passages 13 axially and radially formed in the body of the cylinder. The tubular sheet is provided, on its internal wall, with annular ribs 21 as sealing means for dividing the above-mentioned space into a plurality of sections. This separation serves to prevent a barrel-shaped bulging of the tubular sheet 16 when gas is sent into space.

The realization of fig. 9 comprises the body of the cylinder 11, a plurality of relatively narrow tubular sheets 16 'mounted on the body of the cylinder, sealing means such as bands 17 for fixing the tubular sheets to each of the ends of the body of the cylinder and making it watertight gas spaces formed between the cylinder body and the tubular sheets. Gas is sent into the spaces through the gas supply passage formed in the body of the cylinder 11. If the distance between the inflated parts of the tubular sheets 16 'is too great for a smooth advance of the corrugated sheet , separate elastic elements (not shown) can be mounted between the adjacent tubular sheets 16 'to fill the valleys formed therebetween.

The realization of fig. 10 comprises the body of the cylinder 11, a tubular sheet 16 mounted on the body of the cylinder, fixing bands 17 for fixing said tubular sheet on the body of the cylinder at each of its ends, and sealing means comprising a plurality of strings 18 wrapped around the tubular sheet at suitable intervals to separate the space formed between the tubular sheet and the cylinder body into a plurality of gas-tight sections. The realization of fig. 10 is similar to that of FIG. 9, except that only one tubular sheet is used and that strings 18 are used as sealing means instead of wider strips 17.

The realization of fig. 11 is almost the same as that of FIG. 10, except that a single string 18 is spirally wound around the tubular sheet 16.

In the embodiments of FIGS. 8 to 11, also, gas supply passages formed in the cylinder body, a rotary connector for connecting a gas supply tube to the gas supply passage, and a gas supply port for introducing gas directly into each section (instead of the gas supply passage and the rotary connector) is provided, although some of these are not illustrated in the drawings.

In the embodiments of FIGS. 8 to 11, a shut-off valve (or similar device) can be provided for each section of the space between the cylinder body and the tubular sheet to prevent the gas from escaping through a possible broken part of the sheet tubular.

The third group of embodiments will be described with reference to FIG. 12. In this group, a tubular sheet of synthetic resin having a multitude of air bubbles on it or inside is mounted on the cylinder body. In other words, the tubular sheet used has elasticity in itself.

The realization of fig. 12 includes the cylinder body 11 and a tubular sheet 19 having a multitude of independent air bubbles 20 thereon and mounted on the cylinder body to enclose

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its outer periphery and fixed to the body of the cylinder at each of its ends by means of strips, twines, adhesive strips or the like.

This type of tubular sheet can be replaced by a porous sheet having a multitude of continuous air bubbles like a sponge.

The fourth of the embodiments will be described with reference to FIGS. 13 to 17. They have a cylinder body whose external periphery is enclosed by at least one intrinsically elastic member.

The realization of fig. 13 comprises the cylinder body 11 and two elastic elements 22 in the form of strings wound in a spiral around the cylinder body. The elastic elements can be attached to the cylinder body 11 by means of an adhesive, an adhesive tape or any other suitable means of attachment. Preferably, the cylinder body 11 should be provided with spiral grooves 15 so as to partially receive the elastic elements 22. This provides stable support or support for the elastic elements on the cylinder body. In the embodiment of FIG. 13, two elastic members are spirally wound in opposite directions, starting from the center of the cylinder, to prevent warping of the corrugated sheet.

The realization of fig. 14 is substantially the same as that of FIG. 13, except that a single elastic member 22 is spirally wound in one direction. In the case of a high cylinder speed or a narrow cylinder, the cardboard sheet still does not warp, even if the elastic element is wound in one direction.

In the embodiment of FIG. 15, a plurality of annular elastic elements 22 are mounted in annular grooves 13 formed at the outer periphery of the cylinder body 11 at suitable intervals.

In the embodiment of FIG. 16, a plurality of elastic elements 22 are mounted on the cylinder body 11 parallel to the axis of the cylinder body and between them. Grooves 15 are formed in the periphery of the cylinder body 11 to ensure the stable maintenance of the elastic elements.

The realization of fig. 17 differs from that of FIG. 16 only in that the elastic elements 22 are mounted on the cylinder body 11 at an angle to the axis of the cylinder body.

In the embodiments of FIGS. 13 to 17, the distance between the elastic elements 22 should not be too great so as not to impede the advance or the smooth passage of the sheet of corrugated cardboard. In all embodiments, the elastic elements can be attached by adhesives, adhesive tapes or any other suitable means of attachment.

In the embodiments of FIGS. 13 to 17, the elastic element 22 is a cord or twine having a circular or rectangular section. Consequently, this group of embodiments has the advantage of having an elastic element of greater elasticity and of less material used.

The realization of fig. 18 comprises the cylinder body 11 and a tubular elastic member 23 mounted on the cylinder body enclosing its external periphery and attached to the cylinder body by means of tapes, adhesive tapes or other means. Since the elastic element is in sheet form, this embodiment is more advantageous in that the contact surface with the cardboard sheet is larger.

If it is to be fixed to the body of the cylinder 11 by adhesive means, the adhesive tubular element 23 can advantageously be provided with an adhesive layer 24 on its internal surface as shown in FIG. 19.

The cylinder of fig. 20 is the embodiment of FIG. 18 having the tubular elastic element 23 provided with a layer of lining 25 on its external surface to increase the resistance, the abrasion resistance and facilitate the cleaning of foreign bodies caught on its surface. The ease of cleaning is particularly important for the overlapping cylinder which is liable to be stained by splashes of glue. This lining is required in particular if the elastic element 23 is made of foam plastic.

The tube 12, the tubular sheets 16, 16 ′, 19, the elastic element 22 and the tubular elastic element 23 can be made of natural rubber, or of synthetic rubber such as ethylene vinyl acetate, rubber of butadiene (BR), butadiene stylene rubber (SBR) or acrylonitrile butadiene rubber (NBR), or a synthetic resin such as urethane or polyethylene, or a combination thereof. Preferably, they should have good characteristics of forming, processing, elasticity, thermal resistance, ease of cleaning of foreign bodies and resistance to abrasion. They can be built either in a single layer, or in two or more layers of the same material, or with different materials. They can also be reinforced by intermingling the material with canvas in the layer or between layers to increase the resistance. In particular, the tubular sheets 16 and 16 'can be intertwined with steel wires to keep them in good shape and ensure normal advance of the corrugated sheet.

The lining 25 can be made of synthetic resin such as polyester, nylon and silicon resin.

Natural rubber has greater elasticity than synthetic rubber because of its lower hardness, but synthetic rubber is better than natural rubber in terms of abrasion resistance and thermal resistance.

It is clear that the cylinders having an elasticity on their external periphery made with tubes and possibly elastic separating elements as described above, benefit from all the advances and configurations valid for tires, in particular rubber multilayers, the pressure, insertion of fabric and / or steel wire. These aspects have been mentioned in detail, but other typical features for tires can just as easily be used for these cylinders.

The advantages and effects of the cylinder according to the present invention will be described below.

First, if used as an overlapping cylinder in the bonding part of a corrugating machine where the single-sided corrugated sheet S passes between the bonding cylinder 3 and the overlapping cylinder 5 (fig. 1) to apply the glue on the tops of the corrugations, the cylinder 1 is in contact with the cardboard sheet not along a line, but on a surface, thanks to its elasticity, so that the pressure applied to a surface unit of the sheet S will be less than that applied with a traditional steel cylinder. Since the cylinder 1 has a certain elasticity on its outer periphery, it can absorb shocks, unevenness on the lining side of the cardboard sheet or variations in thickness of the corrugated sheet. This advantage exists particularly with embodiments using gas to give elasticity to the cylinder as long as the pressure of the forced gas is appropriate. The pinch pressure can be easily adjusted by adjusting the pressure of the feed gas which can be observed and read on a meter.

In contrast to the traditional steel overlapping cylinder which cannot absorb such changes or shocks, the cylinder according to this invention makes it possible to ensure sufficient pressure applied to the cardboard sheet by the cylinder, thus ensuring the application of a quantity appropriate glue without being excessive so as not to deform the corrugations. This decreases the risk of producing defective sheets such as deformed corrugated sheets or poorly glued or warped sheets and increases production. In addition, the adjustment of the space between the cylinders according to the change of the material, the type of groove, etc., is no longer necessary. This is particularly true for embodiments using gas to give elasticity to the cylinders.

If the cylinder according to the present invention is used as a pressing cylinder in the heating part of a corrugating machine, similarly the cylinder 1 is in contact with the sheet of corrugated cardboard not along a line, but on a surface, of so that the pressure applied to a unit area of the sheet will be much smaller than with the traditional steel cylinder, even if the total pinch pressure remains the same. This increases the pres5

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sion on the sheet of corrugated cardboard without fear of deforming the corrugations, thereby obtaining better heat transfer, higher machine operating speed and greater production per unit of time. In addition, as the cylinder according to this invention can absorb all the irregularities on the surface of the cotton strip at the laced and curved locations, there is no longer any need to readjust the position of the pressure rollers according to the changes in materials. , type of groove, etc.

Similarly, if the cylinder according to this invention is used as a feed cylinder upstream of the rotary cutter D io (fig. 2), the sheet of corrugated cardboard is in contact with the upper and lower cylinders on a surface, not along a line, so the risk of causing the deformation of the corrugations is extremely reduced. Since the contact surface between the cylinder and the sheet increases, a greater friction force required for the advancement of the sheet can be obtained. This decreases the clamping force required for the cylinders, thereby reducing the possibility of deformation of the corrugations. This is particularly true when a material having a high resistance to friction is chosen as the material for covering the cylinder body.

The cylinder according to the present invention can be used either as a cylinder large enough to cover the entire width of the sheet, or as a shorter cylinder covering only part of its total width, such as an auxiliary supply cylinder.

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Claims (29)

637175 2 1. Cylinder used in the production and processing of corrugated cardboard, characterized in that it comprises a cylinder body and, mounted on the cylinder body, at least one flexible element which gives elasticity to the outer periphery of the cylinder. 2. Cylinder according to claim 1, characterized in that the flexible element comprises at least one flexible tube mounted on the cylinder body so as to cover at least partially the surface of the cylinder, the tube containing a gas such as air . 3. Cylinder according to claim 2, wherein the tube is wound in a spiral around the body of the cylinder. 4. Cylinder according to claim 2, wherein a plurality of these tubes are annularly mounted on the body of the cylinder. 5. Cylinder according to claim 2, wherein a plurality of these tubes are mounted on the body of the cylinder parallel to the axis of the body of the cylinder. 6. Cylinder according to claim 2, wherein a plurality of these tubes are mounted on the cylinder body at an angle to the axis of the cylinder body. 7. Cylinder according to one of claims 2 to 6, wherein the cylinder body is formed with at least one groove in its external surface to partially receive the tube or tubes. 8. Cylinder according to one of claims 2 to 7, wherein each of the tubes has a gas supply orifice through which pressurized gas is introduced. 9. Cylinder according to one of claims 2 to 7, wherein the cylinder body is provided with a gas supply passage and connection means for connecting the passage to each of the tubes. 10. The cylinder of claim 2, wherein said tube is made of natural or synthetic rubber or synthetic resin or a combination of the two and is constructed at least in one layer. 11. Cylinder according to claim 10, in which the tube material is reinforced by intermingling the material with canvas or steel wire. 12. Cylinder according to claim 1, characterized in that the flexible element comprises at least one flexible tubular sheet mounted on the body of the cylinder and attached to the latter at each of its ends, the tubular sheet containing a gas such as l air in a space formed between the tubular sheet and the cylinder body. 13. Cylinder according to claim 12, further comprising sealing means for dividing the space into a plurality of sections. 14. Cylinder according to claim 13, wherein the sealing means comprise a plurality of annular ribs formed integrally on the internal surface of the tubular sheet with an appropriate spacing between them. 15. Cylinder according to claim 13, wherein the sealing means comprise a plurality of bands or cords mounted annularly on the tubular sheet or sheets with an appropriate spacing between them. 16. Cylinder according to claim 13, wherein the sealing means comprise at least one strip or cord wound in a spiral around the tubular sheet. 17. Cylinder according to one of claims 12 to 16, wherein the tubular sheet has a gas supply orifice from which the gas is introduced. 18. Cylinder according to one of claims 12 to 16, wherein the cylinder body is provided with an axial gas supply passage and a plurality of radial passages communicating with the axial passage for introducing the gas to the interior of each section. 19. The cylinder of claim 12, wherein the tubular sheet is made of natural or synthetic rubber or synthetic resin or a combination of the two and is constructed in at least one layer. 20. The cylinder of claim 19, wherein the tubular sheet material is reinforced by intermingling the material with fabric or steel wire. 21. Cylinder according to claim 1, characterized in that the flexible element comprises a tubular sheet mounted on the body of the cylinder to cover, at least in part, its external surface, the tubular sheet being made of synthetic resin and having bubbles of air above and inside. 22. Cylinder according to claim 1, characterized in that the flexible element comprises at least one elastic element in the form of a cord wound around the body of the cylinder so as to at least partially cover the surface of the body of the cylinder. 23. Cylinder according to claim 22, wherein the cylinder body is formed with at least one groove on its external surface to partially receive the elastic element. 24. The cylinder of claim 22, wherein the elastic member is made of natural or synthetic rubber or synthetic resin or a combination of the two and is constructed at least in one layer. 25. Cylinder according to claim 1, characterized in that the flexible element comprises at least one elastic tubular sheet mounted on the body of the cylinder to at least partially cover its surface. 26. A cylinder according to claim 25, wherein the elastic tubular sheet is provided, on its external surface, with a coating. 27. The cylinder of claim 25, wherein the elastic tubular sheet is made of natural or synthetic rubber or synthetic resin or a combination of the two and is constructed with at least one layer. 28. A cylinder according to claim 27, wherein the elastic tubular sheet material is reinforced by intermingling the material with a fabric. 29. Cylinder according to claim 1, comprising several narrow tubular sheets mounted on the body of the cylinder and separate elastic elements mounted between the adjacent tubular sheets to fill the recesses existing between them.