US3402449A

US3402449A - Printing cylinder and process of manufacturing the same

Info

Publication number: US3402449A
Application number: US452555A
Authority: US
Inventors: Schroder Hans
Original assignee: Windmoeller and Hoelscher KG
Current assignee: Windmoeller and Hoelscher KG
Priority date: 1964-05-08
Filing date: 1965-05-03
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24
Also published as: DE1229548B

Description

Sept. 24, 1968 H. SCHRDER 3,402,449

PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME Filed May 3, 1965 5 Sheets-Sheet l #507s gavovder @/MW 27a/@www Sept-24,1968 H.SCHRDER 3,402,449

PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME Filed May 5, 1965 5 Sheets-Sheet 2 Pfg. 5

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PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME Filed May 3, 1965 5 Sheets-Sheet 4 1@ ai@ wim m @fyfs Sept. 24, 1968 H. SCHRDER PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME 5 Sheets-Sheet 5 Filed May 3, 1965 zcf:

United States Patent O 3,402,449 PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME Hans Schrder, Lengerich, Germany, assignor to Windmoller & Hulscher, Lengerich, Nordrhein-Westfalen, Germany Filed May 3, 1965, Ser. No. 452,555 Claims priority, application Germany, May 8, 1964, W 36,749; Nov. 16, 1964, W 37,967 12 Claims. (Cl. 29-123) ABSTRACT OF THE DISCLOSURE A self-contained hollow printing cylinder for printing machines including at least three superimposed layers of material. The inner layer includes a thin glass liber cylinder carrier; the middle layer is deposited on said carrier and includes a mixture of thermosetting plastic material and glass strands; and the third or outer layer includes a pure thermosetting plastic material. The peripheral surface of the outer layer is smooth.

In the manufacture of printing cylinders, such as are used in aniline printing as carriers for the rubber printing plates, aluminium is usually employed as a material for cylinders relatively large in diameter so that the reduction in weight facilitates the manipulation when printing cylinders must be interchanged, as is required Whenever the printing pitch is changed. In spite of the reduction in weight obtained by the use of aluminium as -a material of construction, the weight of the conventional printing cylinders large in diameter is still so heavy that two persons are often incapable of performing the interchange because human strength is insufficient for lifting the printing cylinders and their shafts from the bearings. Lifting gear must be employed so that the interchange of the printing cylinders takes a very long time and involves undesirably long interruptions in production.

Besides, the manufacture of the known printing cylinders is highly uneconomical because expensive casting molds must be procured for the printing cylinders, which must be made only from time to time and in small quantities. One casting mold is required for each size of printing cylinders used in practice. As there is no mass production of the cylinders, these casting molds cannot be fully utilized. Besides, the keeping of the casting molds in stock is extremely expensive. For instance, for various printing pitches and the corresponding printing cylinders differing in circumference by increments of one centimeter, the difference between the diameter of a given cylinder and that for the next smaller or larger printing pitch is 3.18 mm. For the manufacture of all conventional printing cylinders having diameters from 180-800 mm., 195 molds must thus be kept available. This large number of molds, each of which has substantially the volume of the printing cylinder to be made therewith, requires obviously a very large space.

Another disadvantage of the conventional manufacture of printing cylinders resides in that the bores in the cylinder end walls must be finish-turned when the cylinder has been completed to ensure an exact centering of these bores for receiving the shaft. This additional operation is complicated and expensive. Finally, the known printing cylinders of aluminum must be rotationally balanced on special rotational balancing machines when the cylinders have been completed so that the costs of the machinery and of the manufacturing process are further and considerably increased.

It is an object of the invention to provide a printing cylinder which has such a light weight that even cylinders 3,402,449 Patented Sept. 24, 1968 ICE relatively large in diameter can easily be interchanged by hand, and has much lower manufacturing costs than conventional printing cylinders of aluminum whereas it meets all requirements as to the mechanical properties of printing cylinders. More particularly, it is an object of the invention to provide a novel manufacturing process wherein the previously required, expensive procuring and stocking of casting molds for the various cylinder diameters is no longer necessary.

According to the invention, these objects are accomplished in that a printing cylinder for printing machines consists according to the invention of a hollow cylinder, which comprises essentially a thin cylindrical carrier of glass liber mat or the like and thermosetting plastics material deposited on this cylindrical carrier. Such a printing cylinder has the strength required for its use, particularly when, in a development of the invention, a mixture of thermosetting plastics material and chopped glass strands, with an optional admixture of quartz powder, is deposited on the cylindrical carrier, whereas the outside peripheral surface consists suitably of pure thermosetting plastics material in order to avoid a formation of pores. The thermosetting plastics material which is reinforced with chopped glass strands and to which quartz powder may be admixed, if desired, is about three times lighter than aluminum but still has an extremely high strength. The admixing of chopped glass strands and quartz powder serves also to minimize the shrinkage of the plastics material during curing.

Because the printing cylinders according to the invention need not be cast but the plastics material is deposited in a plastic state on the cylindrical carrier, it is no longer required to provide casting molds for each size of printing cylinder which is used in practice but the cylindrical carrier may be separately made for each size of printing cylinder so that a stocking of casting molds is entirely superfluous.

The end walls of the hollow cylinder may also consist having a cylindrical carrier of cured glass fiber mat, these reinforcing rings may consist of cardboard tubes, on which glass fiber mats impregnated with thermosetting material are wound, followed by curing.

In the process according to the invention for the manufacture of printing cylinders, a stiff cylindrical carrier is made, which consists of thin, originally fiat material and has the same length and inside diameter as the printing cylinder to be made, the end Wall members of the cylinder are mounted, the cylindrical carrier is suspended for rotation about a horizontal axis, thermosetting plastics material, or a mixture containing thermosetting plastics material, is applied to the outside peripheral surface of the rotating cylindrical carrier, and finally the plastics material is cured and the printing cylinder is finish-turned or ground. As has been mentioned hereinbefore, it is particularly desirable to apply to the peripheral surface of the cylindrical carrier initially a mixture of chopped glass strands and thermosetting plastics material and, when this layer has been cured, to apply to the outside thereof a thin layer of pu-re thermosetting plastics material. For a `rapid curing of the plastics material, a stream of hot air may be directed against the rotating cylinder during the application of any or both layers.

The intermediate layer may be applied by spraying with a spray gun. The spraying apparatus may comprise in known manner a device for cutting and admixing chopped glass strands. In accordance with the invention, however, the pasty material for the interlayer may alternatively be fed to an applicator bar, which contacts the peripheral surface of the cylindrical carrier along a generatrix and which is adjustable in its distance from the axis of such cylindrical carrier, which bar serves for spreading the material on the cylindrical carrier. The applicator bar may be used as a doctor blade for the pure thermosetting plastics material, which is applied to the cylindrical surface by another applicator. This layer consisting of pure thermosetting plastics material may be colored in any suitable manner according to the invention.

The cylindrical carriers for the printing cylinders according to the invention may be made particularly easily and at particularly low costs if at least two supporting discs having a suitably selected diameter and central bores are fitted on a shaft, a mold shell consisting of individual bar elements extending parallel to the shaft is formed around the supporting discs, a fabric layer consisting preferably of chopped glass strands and impregnated with thermosetting plastics material is wound around the mold shell and cured, whereafter the mold is removed and the end wall members of the cylinder are mounted. In this case it has proved particularly desirable to use channelsection bars in making the mold shell, which bars are fitted one into the other alternately with inwardly and outwardly facing bases and are held together by rubber bands or the like. In a development of the invention, the supporting discs may be split along a diameter and their halves may be easily detachably connected. When the cylindrical carrier is to be removed from the mold, these halves can be separated from each other so that the mold collapses and can be removed with great ease from the cured cylindrical carrier.

In the manufacture of each reinforcing ring for particularly light-weight printing cylinders having a cylindrical carrier of glass ber mat, glass ber mat impregnated with thermosetting plastics material may be wound around a exible cardboard tube and this tube may be formed into a circle corresponding to the inside diameter of the cylindrical carrier, preferably with the aid of the supporting discs used for the manufacture of the cylindrical carrier. When the resulting reinforcing rings have been cured, they may be embedded in the cylindrical carrier by casting with thermosetting plastics material.

A further improvement may be obtained according to the invention if the cylindrical carrier is double-walled and a spacing and stiffening interlayer is disposed between the two walls of the cylindrical carrier. As a result of the double-walled structure of the cylindrical carrier, provided with the reinforcing interlayer, the printing cylinder has the strength and stiffness required for its use without need for providing separate reinforcing elements inside the cylinder, even in relatively long cylinders. Besides, the thus improved printing cylinder will resist even very high pressures, which could result in a slight deflection between the reinforcing rings in the printing cylinders according to the embodiments described hereinbefore.

The interlayer consists suitably of spacer portions arranged to maintain a considerable spacing in the peripheral direction of the cylindrical carrier from each other, except at the connection points. This results in a printing cylinder having a particularly light weight because only a relatively thin layer of thermosetting plastics material must be applied to the double-walled cylindrical carrier, which is very light owing to the large interstices within the interlayer. In one embodiment of the invention, the inner wall of the cylindrical carrier is surrounded by a helically wound cardboard tube, which has been impregnated with thermosetting plastics material and cured, and this tube carries the outer wall of the cylindrical carrier. In a particularly preferred embodiment, stilening and spacing strips extending at right angles from the inner wall and interconnected, preferably in a honeycomb structure are provided between the two walls of the cylindrical carrier. The connection of the cardboard strips in a honeycomb enables a satisfactory bending of the material out of its plane without destruction of the joints between the cardboard strips and without endangering the rigidity of the connection between the two walls of the cylindrical carrier.

In a further development of the invention, each wall of the cylindrical carrier may consist of glass rovings, which have been impregnated with thermosetting plastics material, helically wound in a cylindrical surface, and cured. Each of these rovings consists of a plurality of glass laments. The rovings may be wound by a suitable apparatus about the mold which serves for the manufacture of the cylindrical carrier and enable an operation without waste, different from glass fiber mats, which must be cut to suit the circumference and length of the printing cylinder to be made.

It is also proposed according to the invention to make the end lwall members of the cylinder from annular discs, which are separately cast from thermosetting plastics material, preferably reinforced with glass fibers, and after curing are bonded to the cylindrical carrier. The manufacture of the cylindrical carrier and the casting and curing of the cylinder ends may be carried out at the same time rather than in succession, as in the embodiments described hereinbefore, which results in a considerable saving of time.

Further embodiments of the invention will be explained more fully and by way of example in the following description with reference to the drawings, in which FIG. 1 is a front elevation showing an embodiment of a printing cylinder according to the invention,

FIG. 2 shows a coordinated side elevation,

FIG. 3 is a longitudinal sectional view showing the cylinder according to the invention of FIGS. l and 2 on a larger scale.

FIG. 4 is a longitudinal sectional view showing a mold designed according to the invention and used for manufacturing the cylinder of FIGS. 1 to 3.

FIG. 5 is a side elevation showing the mold of FIG. 4.

FIG. 5a is an elevation of the channel section bars used in the manufacture of the mold.

FIG. 6 is a top plan view showing the mold for manufacturing the end wall ymembers of the cylinder.

FIG. 7 is a sectional view taken on line A-B of FIG. 6 and showing an annular stiffening insert.

FIG. 8 is a longitudinal sectional view showing the cylinder according to the invention during the manufacture of the end wall members.

FIG. 9 is a top plan view showing the cylinder of FIG. 8.

FIG. l0 is a longitudinal sectional view showing a further embodiment of a printing cylinder according to the invention.

FIG. ll is a side elevation showing the printing cylinder of FIG. l0.

FIG. l2 is a longitudinal sectional view showing a third embodiment of a printing cylinder according to the invention during the manufacture thereof.

FIG. 13 is a longitudinal sectional view showing the printing cylinder according to FIGS. l0 and 1l during its manufacture.

FIG. 14 is an elevation showing the cardboard honeycombs used in making the printing cylinder according to FIGS. l0, l1 and 13.

In the embodiment of a printing cylinder according to the invention as shown in FIGS. 1 to 3, the cylindrical body 101 (FIG. 1) is composed of a plurality `of layers. The inner layer 102 (FIG. 3) is formed by a glass fiber mat impregnated with thermosetting material. The intermediate layer 103 consists of a thermosetting material, which contains chopped glass strands. The outer finish layer 104 consists only of thermosetting material. The

end walls

105 and 106 of the cylindrical body 101 consist also of a plurality of layers, namely, an inner cardboard disc 107, which is reinforced by glass fiber mats 108 impregnated with thermosetting plastics material, an intermediate layer 109 of thermosetting material containing chopped glass strands, and an outer finish layer 110 of pure thermosetting material. The

rings

111 and 112 are prefabrcated from a suitable material-plastics material or metal-and are suitably slightly tapered internally for a close fit on the shaft. These rings are centered in the

end walls

105 and 106. The cylindrical body 101 has a plurality of stiffening rings 113, which are adhered to the inside wall surface of the cylinder and serve as reinforcements. The number of these rings depends on the length of the cylindrical body. At least two stiffening rings 113 are provided at the two ends of the cylindrical body and are suitably spaced from the two outer ends of the cylinder 101 by a distance corresponding to the thickness of the

end walls

105 and 106 so that they form a backing for the cardboard disc 107, which forms the inner layer of the end walls. The starting material for the reinforcing rings is suitably a commercially available, flexible cardboard tube, which contains a reinforcing layer consisting of a glass filament band impregnated with thermosetting material.

To make the mold (FIGS 4 to 5a) which is used according to the invention in the manufacture of the cylindrical carrier of the printing cylinder described hereinbefore, a series of circular discs of wood 116 are fitted on a shaft 115 in a length which corresponds to the length of the mold. To facilitate the stripping from the mold, these discs are split and held together by adhesive tape 117. The mold shell generally designated with 118 in FIG. 7 comprises channel-section bars 119, Iwhich are fitted one into the other and applied around the wooden discs 116. The narrow channel-section bars 119 (see particularly FIG. 5a) enable the formation of a rigid mold shell 118 and constitute an ideal expedient for easily making a mold of any desired diameter by adding or removing bars 119 and using wooden discs having a suitable d1- ameter so that it is not necessary to keep molds on stock. The mold shell is held together by two

rubber bands

120 and 121, which are applied around the channel-section bars 119 at both ends of the lmold. Besides, these

rubber bands

120 and 121 determine the exact length of the cylinder to be made. A 'cellophane sheet 122 applied about the resulting mold skeleton serves as a parting layer between the mold and the cylinder material and prevents a contamination of the mold. A glass fiber mat impregnated with thermosetting material is wound around the mold over the cellophane sheet 122. When the thermosetting material has cured, the tube forming the cylindrical carrier can now be stripped from the mold. For this purpose, the two

rubber bands

120 and 121 are removed from the mold and the split wooden discs 116 are ejected with a rod. The thrust destroys the adhesive joints 117 so that the wooden discs 116 together with the shaft 115 and the section bars 119 can easily be removed. The cellophane sheet serving as a parting layer is then removed from the inside of the cylindrical carrier, which conslsts of the glass fiber mat impregnated with thermosetting material.

The stiffening rings 113 can then be made (see FIGS. 6 and 7). The mold to be used for making the stiffening rings 113 in the process according to lthe invention consists essentially of one of the split wooden discs 116, wh1c h has already been used in the manufacture of the cylindrical carrier consisting of the glass ber mat 102 impregnated with thermosetting material. The wooden disc 116 is suitably placed on a horizontal surface. To ensure that the outside diameter of the stiffening ring 113 equals the inside diameter of the tube 102, blocks 123 consisting of a suitable material and having the same thickness as the channel-section bars 119 used in manufacturing the cylin- `drical carrier are applied around the wooden disc 116. A steel band 124 held together by adhesive tape is then applied tightly around the blocks 123 so that the band protrudes to a suitable extent the surface formed by the wooden disc 116 and the blocks 123.. A glass filament Iband 114 impregnated with thermosetting material is then wound around a fiexible cardboard tube 113. This tube is placed along the inside of the -mold and held therein by clips 125. This ensures that the stiffening rings have an exactly circular shape and after curing have an outside diameter which corresponds exactly to the inside diameter of the cylindrical carrier 102. The stiffening lrings 113 are then fitted into the interior of the cylinder 102 in the `desired intervals and are aligned and embedded in cast thermosetting material (FIG. 3). This ensures the required stiffness of the cylindrical carrier 102.

To manufacture the end walls 105 and 106 (FIGS. 8 and 9), the tube 102 is placed in an upright position so that, eg., the end wall 105 is cast first and the end wall 106 thereafter. To make the end wall, a cardboard disc 107 is provi-ded, which is impregnated with 'thermosetting material and corresponds in diameter to the inside diameter of the tube 102. This disc is placed on the stiffening ring 113, which is at the top end of the upright tube and is offset by the thickness of the lend wall from the rim of the tube 102. The cardboard disc 107 has a central opening 126, which is required to enable the fitting of a shaft through the end walls -in a subsequent stage of manufacture.

The ring 127 is tapered on its outside and is centered on the cardboard disc 107 and adhered to the latter with thermosetting material. The cardboard ldisc is now reinforced by a layer 108 of glass fiber mats, which is impregnated with thermosetting material. Then the intermediate layer 109 is applied by casting. This layer consists of thermosetting material mixed with quartz powder and chopped glass strands. The admixture of quartz powder and chopped glass strands prevents to a large extent a shrinkage of the thermosetting plastics material during curing. In end walls having a relatively large diameter, the curing of the thermosetting material sets up higher stresses. In this case it has been found suitable to apply to the thermosetting material while the same is still plastic a further glass fiber mat 128 in order to avoid these stresses, which tend to shrink the material. For instance, when the manufacture of the end wall 105 has proceeded to this stage, the end wall 106 is similarly manufactured. When the

end walls

105 and 106 have been cured, the rings 127 are removed. Before the casting operation, these rings were provided with :a suitable release agent. The end '

walls

105 and 106 are thus formed with openings, which are closed toward the interior of the tube 102 only by the cardboard disc 107. The diameter of these openings is `desirably larger by a suitable amount than the internally tapered

rings

111 and 112, which will now be cast in the end walls.

For this purpose, the tube 102 is firmly secured to the rotatably mounted shaft 115 so that an axial displacement or radial movement of the tube relative to the shaft is prevented. Then the tube is adjusted to rotate exactly in a circle. For this purpose, the shaft 115 is rotated. A suitable ruler is held along the rotating tube 102 so that any deviation from an exact circular motion can be properly recognized and eliminated by slight blows on the tube. The adjusting of the tube 102 in this stage of manufacture eliminates the need for rotationally balancing the finished cylinder on expensive machines, which would have to be procured for this purpose, as well as the need for finish turning the

rings

111 and 112. These rings are then adhered into the

end walls

105 and 106 at several points with pasty thermosetting material. vWhen the bonds have been cured, the layers 103 and 104 (FIG. 3) are applied to the tube 102, which consists of a glass fiber mat impregnated with thermosetting material. For this purpose, the horizontally mounted shaft ]l15 and the tube 102 secured to said shaft are rotated. Thermosetting material mixed with chopped glass strands is then applied to the outside peripheral sur-face of the rotating cylindrical carrier by means of a suitable tool (not shown), which may consist, e.g., of a bar. This application is conducted so that the thermosetting material is evenly spread on the periphery of the cylindrical carrier and is smoothed as it is being applied. To accelerate the curing of the applied thermosetting material, the rotating cylindrical carrier is suitably contacted with a stream of Warm air during the application of the layer.

Thelayer 103 consisting of thermosetting material mixed with glass bers is applied in this process with a high degree of uniformity. This assists in avoiding a noncircular rotation of the cylinder and the need for rotationally balancing the finished cylinder. On the other hand, it is difficult to avoid blisters in this mixture. The same often has individual air pockets, which would result in pores if this layer were finish-turned. For this reason it has proved desirable to apply to the layer 103 when the same has cured a finish layer 104, which consists of a pure thermosetting material, which is preferably slightly colored by the addition of a suitable coloring material. This finish layer provides a perfectly homogeneous finish to the cylinder. The finish layer 104 is applied like the layer 103 by means o-f an applicator bar and while the rotating cylinder is being contacted with a stream of warm air. The contact with a stream of warm air accelerates the curing of the layer 104 and prevents a running of liquid thermosetting material from the cylinder body.

Alternatively, the

layers

103 and 104 may be applied with the aid of known s-praying apparatus to the rotating cylinder, which is contacted with a flow of warm air. The spraying apparatus used for applying the layer 103 is coupled in this case to a cutting mechanism for cutting glass strands.

When the manufacture of the cylinder has proceeded to this stage, the cylinder is then placed in an upright position on one of its

end walls

105 and 106 in order to provide them also with a iinish layer 110 of preferably colored thermosetting material. For this purpose, an adA hesive tape or the like is tightly applied around the end wall to be treated, in order to ensure a formation of neat edges. Then the thermosetting material is cast onto the end wall. At the same time, the

rings

111 and 112, which were previously only adhesively held in the openings 129 and 130, are yfirmly embedded in the cast material. When the finish layer applied to the end wa'lls has cured, the adhesive tape serving to define the edges is removed.

When the cylinder made according to the process of the invention has completely cured, its peripheral surface and its end walls are finish-turned or -ground with a conventional apparatus. The end Wall edges are suitably slightly rounded to protect them from damage.

A further embodiment of a printing cylinder according to the invention is shown in FIGS. 10 and 11. This embodiment is composed of a plurality of layers 201 to 204. The inner layer 201 consists of a glass fiber mat impregnated with thermosetting plastics material. The intermediate layer 202 is formed by cardboard strips (see FIG. 14), which are also impregnated with thermosetting plastics material and connected in a honeycomb structure. The layer 203 on top of the layer 202 consists of the same material as the layer 201. The layers 201 to 203 form a double-walled, cylindrical carrier. The intermediate layer 202 of this carrier ensures the required strength and stiffness of the cylinder. The cylindrical carrier is provided with the outer -finish layer 204, which is made from pure, preferably colored thermosetting material and forms a smooth, non-porous outside cylindrical surface. The

end walls

205 and 206 of the printing cylinder consist of a layer 207 of thermosetting plastics material reinforced with glass fibers, and also of a finish layer 204 of pure thermosetting material in order to provide a' smooth, nonporous surface. The

openings

208 and 209 are centered Cir in the

end walls

205 and 206. These openings are internally tapered and serve for receiving a printing cylinder shaft.

To manufacture a double-walled cylindrical carrier (FIGS. 12 and 13), a'n annular disc 211 is fitted on each end of a tubular mold 210. As this arrangement is symmetrical, only one end of the mold is shown in FIGS. l2 and 13. The spacing of the discs 211 secured to the mold 210 corresponds to the length of the cylinder to be made. Each disc may be secured to the mold, eg., by a clamp screw. The discs 211 are inwardly recessed to form two end faces 212 and 213 extending in the peripheral direction of the discs and a backing surface 214 for the material formingthe cylindrical carrier. The length of the extension is suitably chosen so as to correspond substantially to the thickness of the end walls, which are subsequently applied. A `glass fiber mat impregnated with thermosetting plastics material is now wound'onto the mold tube 210 between the end faces 213 of the discs 211 to form the inner layer 201 of the cylindrical carrier. In the embodiment of FIG. 12, the cylindrical carrier is given a double-walled structure in that a fiexible cardboard tube 215 impregnated with thermosetting plastics material is helically wound around the layer 201. A Wire netting 216 is then stretched around the cardboard tube 215 to form a backing for the outer layer 213 of the cylindrical carrier. Just as the inner layer 201, the outer layer 203 consists of a glass fiber mat, which is impregnated with thermosetting plastics material and wound around the wire netting 216 so that both ends of the mat lie on the backing surface 214 of the two discs 211 and the mat conta'cts the end face 212 of the discs.

In the embodiment shown in FIG. 13, the doublewalled structure of the cylindrical carrier is obtained in that cardboard honeycombs 217 forming the layer 202 (FIG. 10) are wound around the layer 201 consisting of glass fiber mat impregnated with thermosetting plastics material. As is apparent from FIG. 14, the cardboard honeycombs 217 consist of cardboard strips 218, Which are arranged on edge and are adhered to each other at spaced points so that cells 220 are formed when the strips are expanded in the direction of the double arrow 219. When the honeycomb is wound about the inner layer 201 of the cylindrical carrier, these cells retain their shape because the thermosetting plastics material is cured. As has already -been described with reference to the embodiment shown in FIG. 12, the layer 203 consisting of glass fiber mat impregnated with thermosetting plastics material is then applied over the cardboard honeycomb 217 forming the layer 202. The use of the cardboard honeycombs rather than a cardboard tube as an intermediate layer of the double-walled cylindrical carrier has the advantage that an additional wire netting as a backing for the outer glass fiber mat layer 203 of the cylindrical carrier is not required because the glass fiber mat can cover the cells of the cardboard mats 217 without difficulty. Both materials are equally suitable to impart to the cylindrical carrier the required strength and stiffness.

When the thermosetting plastics material has been cured, the cylindrical carrier is stripped by removing the discs 211 and pulling the mold 210. In the meantime, the

end wall members

205 and 206 have been cast in a separate operation from thermosetting plastics material reinforced with chopped glass strands. These end wall members are now applied to the cylindrical carrier and adhered to it with thermosetting plastics material so thatthey contact on the inside the end faces of the

layers

201, 215 and 216 (FIG. 12), or 201 and 217 (FIG. 13), defined by the end face 213 of the discs 211 whereas that portion of the layer 203 which protrudes beyond the inner and intermediate layers of the cylindrical carrier overlies the outside peripheral edge of the discs.

Finally, the finish layer 204 consisting of pure thermosetting plastics material, which is preferably colored, is applied to the cylindrical carrier and the end Walls, as has been described herenbefore. When the printing cylinder has been cured, it is finish-turned or ground on a suitable, conventional apparatus.

The cylinder according to the invention distinguishes by an extremely light weight. Tests have shown that the weight of this cylinder of thermosetting plastics material reinforced with glass fibers is only about one third of the weight of a comparable cylinder of aluminum so that the diiiiculties mentioned initially hereinbefore involved in an interchange of the printing cylinders are minimized. The special advantage of the manufacturing process just described resides particularly in the fact that the mold for making the cylindrical carrier is simple and can be made with a very small expenditure and eliminates also the problem of keeping molds on stock because for the manufacture of cylinders having a given diameter it is sufficient to keep on stock only a set of wooden discs of the respective diameter-these discs require only a small space-whereas the other parts required for the manufacture of the mold, particularly the channel-section bars, can easily -be used in such a manner as to provide for any diameter which may be required.

What is claimed is:

1. A self-contained hollow printing cylinder for printing machines comprising at least three radially disposed layers, the inner layer comprising a thin glass fiber cylindrical carrier impregnated with thermosetting plastic material, the middle layer comprising a mixture of thermosetting plastic material and glass strands, said middle layer being deposited on said carrier, and the outer layer comprising pure thermosetting plastic material.

2. The cylinder of claim 1 wherein the outer peripheral surface of said outer layer is smoothed.

3. The cylinder of claim 1 wherein said middle layer further comprises an admixture of quartz powder.

4. The cylinder of claim 1 further comprising an annular wall disposed at each end of said carrier, each of said walls comprising a carrier material, a thermo-setting plastics material laminated on said carrier material, and a central opening for the cylinder shaft formed in each of said walls.

5. The cylinder of claim 4 further comprising a plurality of reinforcing rings secured to said carrier.

6. The cylinder of claim 5 wherein said carrier comprises a cured glass fiber mat and wherein said rings comprise a plurality of cardboard tubes, and a glass liber mat wound around said tubes, said thermosetting plastic material being impregnated in said ring glass fiber mat and said rings being cured.

7. The cylinder of claim 1 wherein said inner and middle layers are provided with a spacing and stitfening interlayer disposed therebetween to form inner and outer cylindrical walls.

8. The cylinder of claim 7 wherein said interlayer comprises a spacer member disposed around the peripheral surface of the inner wall of said carrier and lying between said walls.

9. The cylinder of claim 8 wherein said spacer member comprises a cardboard tube helically wound around said inner wall, and a thermosetting plastic material impregnated in said tube, said tube and lplastic material being cured.

10. The cylinder of claim 8 wherein said spacer member comprises a plurality of reinforcing and spacing strips extending at right angles from said inner wall, said strips being interconnected in a honeycomb arrangement.

11. The cylinderof claim 7 wherein each of said walls comprises glass rovings in which said thermosetting plastic material is impregnated, said combination then being helically wound in a cylindrical surface and cured.

12. The cylinder of claim 7 further comprising an annular disc disposed at each end of said carrier, each of said discs comprising a thermosetting; plastic material from which it is cast and a plurality of glass bers embedded in said plastic material to reinforce same, said material and fibers being cured.

References Cited UNITED STATES PATENTS 1,475,963 12/ 1923 Osterlind lOl-375 X 1,787,890 1/1931 Woodward 29-132 X 2,393,953 2/1946 Bacon 29-132 X 2,597,858 5/1952 Freedlander 29-130 2,647,300 8/1953 Thomas et al 29-131 X 2,718,583 9/1955 Noland et al. 219-38 2,739,917 3/1956 Schulze 156-69 3,074,111 1/ 1963 Wiltshire 18-26 3,152,387 10/1964 Macleod 29-1301 LOUIS O. MAASSEL, Primary Examiner.