The referenced U.S. Pat. No. 4,913,048, Tittgemeyer, the disclosure of which is hereby incorporated by reference, illustrates a printing roller or cylinder of the type to which the present invention relates. A sleeve-like cylinder is expanded by compressed air, so that it can then be pushed on a cylinder core, or a cylinder rotary structure. The core need not be a solid core but, itself, can be hollow and furnished with shaft ends or a through-shaft for retention in suitable bearings of the side wall of the printing machine. In accordance with the Tittgemeyer patent, the sleeve is expanded only to the extent that, after venting the compressed air, the sleeve engages the core or core structure similar to a shrink fit. Alternatively the cylinder sleeve is heated so that it will expand, slipped over the surface of the core structure, and cooled so that, again, a shrink fit will result. The sleeve thus is engaged by frictional engagement and stressed engagement on the core or core structure of the printing cylinder.
The sleeve, as well as the core, may be made largely of steel. Thus, the thermal coefficient of expansion of the core as well as of the sleeve will be the same. The sleeve, thus, cannot separate from the core in operation of the printing machine, since the increase in temperature will be essentially uniform both for the sleeve as well as for the core structure, or at least the surrounding surface, as the machine operates. Cylinder sleeves made of aluminum, however, have found wide acceptance. They have advantages, for example due to lesser environmental damage or pollution in their manufacture, with respect to cylinder sleeves made of steel. Aluminum, however, has a thermal coefficient of expansion which is about twice that of steel, and it has been found that, in operation, an aluminum sleeve may separate from the steel core when in printing operation. It is hardly possible, for manufacturing and assembly reasons, to manufacture a cylinder sleeve which is slightly undersized with respect to the steel cylinder, and expand such a sleeve sufficiently to permit it to be fitted over a steel cylinder core.
It has been proposed, see for example also the referenced Tittgemeyer U.S. Pat. No. 4,913,048, to increase the diameter of the core by a hydraulic system in order to ensure tight frictional fit of the cylinder sleeve on the core structure, after the cylinder sleeve has been mounted on the core structure.
It has been found, in actual operation, that it is difficult to increase the diameter of the surface of the cylinder core, due to problems with pressure application, sealing, and the like. Additional sealing problems arise. If printing media, for example damping fluids such as damping water, ink or solvents or other cleaning fluids penetrate between the printing cylinder sleeve and the cylinder core, cohesion forces may result which will cause the printing cylinder to adhere on the core by suction. It then becomes practically impossible to remove the printing cylinder sleeve without damage thereto or, usually, complete destruction thereof.