Reduced weight magnetic cylinder

A magnetizable cylinder has a cylinder body formed from a magnetizable material with an outer cylindrical surface configured to receive a flexible cutting die. The cylinder body has first and second axial ends spaced apart by the outer cylindrical surface and a hollow interior. First and second journals are joined to the cylinder body with interference fits. At least one of the first and second journals has a weep hole extending through the journal into the hollow interior of the cylinder body. The interference fit of the journals to the cylinder body result from thermal changes of at least one of the first journal, the second journal, and the cylinder body prior to joining the first journal to the cylinder body and the second journal the cylinder body.

SUMMARY

This disclosure is directed to a magnetic cylinder used in connection with flexible dies for the converting industry. The magnetic cylinder comprises a magnetizable stainless steel, hollow cylindrical body with hardened steel journals. The construction allows for a significant reduction in weight of the magnetic cylinder in comparison to conventional magnetic cylinders formed from solid stainless steel, while preserving demanding requirements for tolerances of run-out tolerances and cylindricity. The magnetic cylinder may be formed by shrink fitting the hollow cylindrical body onto the journals. The magnetic cylinder and journals may meet the requirements for shrink fitting in accordance with ISO S7/h6.

DETAILED DESCRIPTION

FIG. 1shows a magnetizable or magnetic cylinder20. The magnetic cylinder20comprises a hollow cylindrical body22with an outer diameter cylindrical surface and opposite axial ends24,26. The hollow cylindrical body22provides a mounting surface for the flexible die (not shown). The hollow cylindrical body22may also have an inner diameter cylindrical surface, for instance, a straight bore (e.g, a uniform continuous cross-section) as shown, or other inner diameter surface profile. Journals28,30may be arranged at the axial ends24,26to support and drive the magnetic cylinder20in converting press machinery. The cylindrical body axial ends24,26may be configured to receive the journals with an interference fit. The interference fit may be in accordance with ISO S7/h6. The journals28,30may be configured to be inserted in the hollow cylindrical body22in accordance with ISO S7/h6. As shown in the drawings the inner surface of the cylindrical body has a straight bore that is located on a shoulder31formed on an inner face of each journal. Rather than a bore of a uniform, continuous cross section, the cylindrical body may have a counter bore in one or both of its axial ends to receive the shoulder31formed on the inner face of the corresponding journal26,28. The cylinder body22may be made from a stainless steel, for instance, a 416 series stainless steel, or another material magnetizable steel. The journals28,30may be made from hardened alloy tool steel such as AISI 4150 or D2.

One or more of the journals28,30may have threaded holes32to allow attachment of a timing or a spur gear34to the journal with one or more mechanical fasteners (not shown). InFIGS. 3 and 4, the spur gear34is removed for ease of illustration. The journals28,30may also have threaded jackscrew holes36. Jackscrews (not shown) may be directed through the jackscrew holes36to allow disassembly of each of the journals28,30from the hollow cylindrical body20. The journal may be formed with shoulders and other locating surfaces38on its outer faces as necessary to support any attached timing or spur gear(s). At least one, and preferably both, of the journals28,30includes a weep hole40that communicates with the interior of the hollow cylindrical body22when the journals are press fit into the axial ends24,26of the hollow cylindrical body. A plug42may be temporarily inserted in the weep hole, as will be explained below in greater detail. For instance, the weep hole40may be threaded to accept a set screw42allowing the weep hole to be sealed and opened as desired, as explained below.

In forming the magnetic cylinder, the journals28,30are finish ground to specification to receive centers46, finish the locating shoulder31on the inner faces of the journals, finish locating surfaces38on the outer faces of the journals for any spur gears34t, and to receive the axial ends24,26of the hollow cylindrical body22with an interference fit in accordance with ISO S7/h6. The hollow cylindrical body22has the interior surfaces of its axial ends24,26finish ground to receive the journals28,30with an interference fit in accordance with ISO S7/h6. Then, prior to installation with the hollow cylindrical body22, the journals28,30are cooled to a surface temperature of approximately −110 degrees Fahrenheit for a period of approximately 15 minutes, and the hollow cylindrical body22is heated to a temperature of approximately 300 degrees Fahrenheit. The journals28,30are then pressed or slip fitted together with the hollow cylindrical body22. When the hollow cylindrical body22cools to room temperature and the journals28,30return to room temperature, the components are held together with an interference fit with an acceptable amount of hoop stress and able to withstand necessary axial displacement forces during operation of the converting equipment.

The weep hole40allows pressure inside the interior of the hollow cylindrical body22to be relieved during assembly of the journals28,30with the cylindrical body. For instance, as the journals28,30are pressed onto the axial ends24,26of the hollow cylindrical body, the weep hole40allows air entrapped in the interior of the hollow cylindrical body22to escape. The weep hole(s)40may be threaded to accept the set screw42so as to allow the weep hole to be sealed after assembly. This allows the magnetic cylinder20to undergo any finish machining/grinding/magnetizing operations while preventing any material(s) from entering the interior of the hollow cylindrical body22through the weep hole40during such finishing processes. The set screw(s)42may be removed from the weep hole(s)40in the journals28,30during normal operation of the converting equipment to equalize pressure between the atmospheric condition in which the converting equipment is location and the hollow interior of the cylindrical body thereby preventing distortion of the magnetic cylinder20. The effect of distortion may be more pronounced when the converting operations occur at a location with a higher elevation that the location in which the magnetic cylinder was manufactured. While the rate of equalization is dependent upon temperature, barometric pressure, altitude and relative dimensions of the magnetic cylinder and weep hole diameter, the weep hole40may be size to accommodate a wide range of these factor and considerations. For instance, the weep hole may be a ANSI 10×32 threaded hole with a diameter of 0.159 inches for an 8 inch nominal diameter magnetic cylinder20. Such a size accommodates most sizes of magnetic cylinders and operating conditions of converting equipment.

The exemplary magnetic cylinder20provides a reduced weight compared to conventional solid magnetic cylinders. This provides many benefits in comparison to conventional solid magnetic cylinders in that the exemplary magnetic cylinder allows for a reduction in cylinder inertia during operation of the converting equipment. This in turn allows for the use of less torque for acceleration and deceleration in the drive system of the converting equipment which in turn allows for lower operating stresses on the converting equipment. Additionally, the exemplary cylinder20when compared to similarly sized conventional cylinders reduces the reflective inertial load to the drive system thus providing greater registration control of the die station. All of the benefits are achieved without sacrificing the dimensional and structural integrity of the magnetic cylinder. For instance, for a 8 inch nominal size magnetic cylinder20, the wall thickness of the cylinder body may be 1 inch which allows for the elimination of a significant amount of weight.

The embodiments were chosen and described in order to best explain the principles of the disclosure and their practical application to thereby enable others skilled in the art to best utilize the disclosed embodiments and with various modifications as are suited to the particular use contemplated. As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.