Lightweight Interchangeable Magnetic Sleeve and Method of Manufacture Thereof

Abstract

A lightweight interchangeable magnetic sleeve and method of manufacture thereof are disclosed. The sleeve assembly comprises an annular tube in the exterior surface having recesses filled with comparatively rigid magnetic means which are firmly adhered therein. The sleeve assembly includes a tubular radially compressible liner component, relatively slightly shorter than the tube, and bonded inside and substantially axially centrally within the tube thus leaving interior cylindrical end regions of the tube exposed beyond the annular end surfaces of said liner. The remaining exposed interior cylindrical surfaces of the tube are rebated back from the liner exposing annular shoulders within the tube. The rebates are tapped so that correspondingly sized threaded end rings of a more structurally robust, rigid and resilient material than the tube material, can be fitted into the tube ends and tightened against the annular shoulders created by the rebating, placing the entire sleeve assembly under slight compression.

Claims

1. A sleeve assembly (2) comprising a cylindrical tube (4), formed from one of: an engineering plastics material, a metal or an alloy thereof, having a density less than 3.5 g/cm.sup.3 and having exterior and interior cylindrical surfaces extending generally between a pair of annular end surfaces (4A), said tube having machined or otherwise provided therein a plurality of recesses (12) substantially completely occupied by comparatively rigid magnetic means (20) which are firmly secured therein, said recesses being of substantially uniform depth along their length, and being uniformly spaced apart circumferentially of the tube and extending axially from one end of the tube to another end of the tube over substantially the entire axial length of the tube, wherein said sleeve assembly further comprises a tubular radially compressible liner (6) which is shorter in axial length than the cylindrical tube and which is bonded inside said tube to the interior cylindrical surface thereof axially centrally thereof thus leaving interior cylindrical end regions (4B) of the tube exposed beyond the annular end surfaces (4A) of said liner, said interior cylindrical end regions having rebates (8) extending radially outwardly from the circular interface between said liner and said tube so as to define annular shoulders (4D) within the interior of the tube at either end thereof, said interior cylindrical end regions being provided with screw threads (4C) so as to be capable of receiving a pair of correspondingly threaded end rings (10) constituted of a material having a modulus of elasticity which is at least twice that of the material of which the cylindrical tube is constituted, and having an inner diameter which is greater than the inner diameter of the compressible liner thus allowing the interior cylindrical surface of said liner to be radially expanded towards a position in which the interior cylindrical surface lies substantially flush with an inner cylindrical surface of said end rings, and wherein said annular shoulders (4D) are provided internally of the tube at a relatively shallower axial depth from the respective annular end surfaces (4A) of said tube than the axial distance between the terminal end of at least one of the recesses (12) and the annular end surfaces of the tube most proximate thereto, the arrangement being that when said end rings are screwed fully into said rebates and into abutting relationship with the annular shoulders and tightened thereagainst, not only do said end rings exert axial compression on the cylindrical tube, but said end rings also provide underlying structural support for the end regions of the sleeve assembly underneath said at least one recess.

2. The sleeve assembly (2) according to claim 1, wherein the annular shoulders (4D) are provided internally of the tube at a relatively shallower axial depth from the respective annular end surfaces (4A) of said tube than the axial distance between the terminal ends of all the recesses (12) and the annular end surfaces of the tube most proximate thereto.

3. The sleeve assembly (2) according to claim 1, wherein the annular shoulders (4D) provided at either end of the tube lie substantially flush with the annular end surfaces of said liner (6).

4. The sleeve assembly (2) according to claim 1, wherein the modulus of elasticity of the end rings (10) is one of: at least a factor of 2 greater; at least a factor of 3-5; and at least one order of magnitude greater than the material of which the cylindrical tube (4) is constituted.

5. The sleeve assembly (2) according to claim 1, wherein the cylindrical tube (4) is constituted entirely of Aluminium and the end rings are constituted entirely of steel.

6. The sleeve assembly (2) according to claim 1, wherein the cylindrical tube (4) is constituted of an engineering plastics material, being a synthetic polymer which is both non-fibrous and not fibre-reinforced, said synthetic polymer being one of, or some combination of: an acetal-based homopolymer or copolymer, a polyamide, and a polyester, and the end rings (10) are constituted entirely of steel.

7. The sleeve assembly (2) according to claim 1, wherein the exterior cylindrical surface of the liner (6) is securely and firmly bonded to the interior cylindrical surface of the tube by means of a high strength epoxy-based adhesive which, once cured, provides an effective and rigid bridge between the adjacently disposed cylindrical surfaces of said liner and said tube respectively, over substantially the entirety of those surfaces.

8. The sleeve assembly (2) according to claim 1, wherein the axially outermost annular end surfaces (10A) of the end rings (10) lie substantially flush with the annular end surfaces (4A) of the cylindrical tube (4).

9. The sleeve assembly according (2) to claim 1, wherein the recesses (12) provided in the exterior cylindrical surface of the cylindrical tube (4) are axially aligned with the longitudinal axis of the sleeve assembly as a whole, with each recess containing an generally elongate arrangement of multiple magnet-keeper pairs (22, 24) which, as a unit, substantially fill and are adhered within said recesses, the uppermost surfaces of all said magnet-keeper pairs lying substantially flush with lands (4E) defined between each adjacent pair of recesses and thus disposed circumferentially to one or other side thereof.

10. The sleeve assembly (2) according to claim 1, wherein the end rings (10), in addition to being screwingly fitting into the ends of cylindrical tube (4), are adhered in place by means of a suitable curable adhesive composition, applied between one or both of threaded and unthreaded surfaces (4B, 4C) of the cylindrical tube (4) ends, and corresponding threaded and unthreaded surfaces of said end rings.

11. The sleeve assembly (2) according to claim 1, wherein at least one of the pair of end rings (10) is provided with one or more of: one or more registration notches (4F); and a radially extending visible indicator.

12. The sleeve assembly (2) according to claim 11, wherein the exterior cylindrical surface of the cylindrical tube (4) is provided with at least one pair of plate positioning formations (14, 16), each of said pair of formations being provided within a land (4E) defined between a pair of adjacent recesses (12), and both of said formations being both axially aligned with the longitudinal axis of the sleeve assembly and accurately circumferentially located with respect to a registration notch (4F) provided in the end ring (10).

13. The sleeve assembly (2) according to claim 2, wherein the annular shoulders (4D) provided at either end of the tube lie substantially flush with the annular end surfaces of said liner (6).

14. The sleeve assembly (2) according to claim 2, wherein the modulus of elasticity of the end rings (10) is one of: at least a factor of 2 greater; at least a factor of 3-5; and at least one order of magnitude greater than the material of which the cylindrical tube (4) is constituted.

15. A method of manufacturing a sleeve assembly (2), the method comprising the following steps, performed on a cylindrical tube (4) formed from one of: an engineering plastics material, a metal or an alloy thereof, having a density less than 3.5 g/cm.sup.3 and having outer and inner diameter dimensions respectively greater than and less than an ultimately required outer diameter/inner diameter dimensions of the finished sleeve assembly, counterboring the tube to a precise inner diameter dimension, adhesively bonding a tubular compressible liner (6) having an outer diameter of the order of 0.2-1.5 mm less than the inner diameter of the tube, and being of comparable length, within said tube to create a combined sleeve assembly, cutting at least one length from the combined sleeve assembly, said length being of the order of 0.5-4 mm longer than an ultimately required axial length of the sleeve assembly, machining out rebates (8) at either end of the sleeve assembly, said rebates having an axial depth of at least 8 mm back from annular end surfaces (4A) of the tube (4), said machining comprising complete removal of liner over said axial depth as well as some amount of a tube interior, said amount being between 4-25% of an annular thickness of the tube such that annular shoulders (4D), lying substantially flush with adjacent annular end surfaces of the liner (6), are defined within the sleeve assembly at both ends thereof, machining threads on exposed internal cylindrical surfaces (4C) of said rebates (8); screwing end rings (10) into each sleeve assembly end and tightening said end rings against the annular shoulders (4D) such that the tube is axially compressed between said end rings to a predetermined degree, said end rings being of an axial depth which is marginally greater than the axial depth of the rebates, machining a plurality of magnet-receiving recesses (12) in the exterior cylindrical surface of the sleeve assembly (2), said recesses being of a depth greater than between 50%-90% annular thickness of the annular end surfaces of the tube and extending substantially axially from one end of the sleeve assembly to the other, and furthermore being generally evenly spaced circumferentially around said exterior surface, such that a remaining surface area of the tube is less than 50% of an original cylindrical exterior surface area, said recesses terminating, at both ends, in a location which is axially more distant from the most proximate annular end surface of the tube than that at which said annular shoulders are disposed, adhering within every one of said recesses a plurality of magnet and magnet keeper pairs (22, 24) so as to completely fill said recesses, machining the exterior cylindrical surface of the sleeve assembly, with magnet assemblies adhered in place therein, such that the outer diameter of the sleeve assembly is precisely determined relative to a datum axis of machining, and machining the annular end surfaces of the sleeve assembly at both ends, including said end rings, such that any portions of said end rings which stand axially proud of the adjacent annular end surfaces of the tube are removed, and such that the sleeve assembly is machined down to a precise, predetermined axial length.

16. The method according to claim 15, further comprising the step, prior to screwingly inserting an end ring (10) into one or other end of the sleeve assembly (2), of applying an adhesive compound over one or more of: the surfaces of the annular shoulders (4B) of the rebates (8), the exposed annular end surface (6A) of the liner (6) inside the sleeve assembly, some or all of the unthreaded interior cylindrical surface (4B) of the rebate (8) provided in the tube at the said one or other end of the sleeve assembly, some or all of interior threaded regions (4C) provided on said rebate, and some or all of exterior threaded regions of the end ring (10).

17. The method according to claim 15, further comprising the steps of: machining out at least one circumferential registration notch (4F) of predetermined circumferential width and axial depth dimensions in an annular end surface (4A) of at least one of the end rings (10), whereby said notch can receive a correspondingly shaped and dimensioned registration formation provided on a mandrel assembly on which said sleeve assembly (2) is to be mounted, machining out at least one pair of recesses adapted to receive a pair of accurately machined plate-locating formations (14, 16), said recesses being arranged in axially perfect alignment with the central axis of the sleeve assembly and at a precise angular position relative to the angular position of the registration notch, and thereafter inserting said pair of plate-locating formations into said recesses, and accurately positioning and securing said formations therein.

18. The method according to claim 17, wherein two pairs of recesses is machined out from the exterior cylindrical surface of sleeve assembly (2), the second pair of recesses also being adapted to receive said plate-locating formations (14, 16) and being firstly disposed in perfect axial alignment with the central axis of the sleeve assembly and secondly disposed in precisely diametrically opposed relationship to the first pair of recesses.

19. The method according to claim 16, further comprising the steps of: machining out at least one circumferential registration notch (4F) of predetermined circumferential width and axial depth dimensions in an annular end surface (4A) of at least one of the end rings (10), whereby said notch can receive a correspondingly shaped and dimensioned registration formation provided on a mandrel assembly on which said sleeve assembly (2) is to be mounted, machining out at least one pair of recesses adapted to receive a pair of accurately machined plate-locating formations (14, 16), said recesses being arranged in axially perfect alignment with the central axis of the sleeve assembly and at a precise angular position relative to the angular position of the registration notch, and thereafter inserting said pair of plate-locating formations into said recesses, and accurately positioning and securing said formations therein.

20. The method according to claim 19, wherein two pairs of recesses is machined out from the exterior cylindrical surface of sleeve assembly (2), the second pair of recesses also being adapted to receive said plate-locating formations (14, 16) and being firstly disposed in perfect axial alignment with the central axis of the sleeve assembly and secondly disposed in precisely diametrically opposed relationship to the first pair of recesses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 shows a perspective view of a partially completed sleeve construction according to the present invention, comprising in particular a cylindrical tube with compressible liner bonded therein,

[0080] FIG. 2 shows a perspective view of the sleeve construction of FIG. 1 in a later stage of completion, wherein end rings have been fitted (one of which is visible in the Figure) and axially aligned, spaced-apart recesses have been machined out of the exterior cylindrical surface of the tube,

[0081] FIGS. 3A, 3B, 3C shows respectively a perspective view, an end elevation, and a plan view of an elongate magnet-and-keeper assembly of suitable axial length, width and depth dimensions to be relatively snugly received in any one of the recesses illustrated in FIG. 2,

[0082] FIG. 4 shows a perspective view of a completed sleeve construction according to the present invention around which a printing or coating plate is firmly magnetically secured to the exterior cylindrical surface of the sleeve construction, and

[0083] FIGS. 5A, 5B show respectively sectional elevations through the sleeve construction as indicated in FIG. 4 at V-A, B, said sectional elevations “A” and “B” respectively illustrating different possible embodiments of the invention, in particular as regards the relative axial relationship between the terminal ends of the recesses and the extent to which said recess are (or are not) undercut by the internal rebates provided internally of the sleeve construction at either end and in which the end rings are disposed.

DETAILED DESCRIPTION

[0084] Referring firstly to FIG. 1, there is shown a sleeve assembly indicated generally 2 and illustrated in a partially completed state. As will be seen in the Figure, and as a result of the perspective view, only the near end is fully illustrated, but it is to be assumed by the skilled reader that the arrangement and configuration of the alternate (far) end of the sleeve assembly is identical in practically all respects, and that, in the condition illustrated in FIG. 1 at least, the sleeve assembly is completely symmetrical, i.e. longitudinally about its axial mid-point, and axially about any diametral section. In this specific description, almost exclusive reference is made to the tube being of a plastics material, specifically an engineering plastics material. However, the reader should understand that for some indeed many applications, it may be more preferable to manufacture the tube entirely and completely in Aluminium or another similarly lightweight, low density metal. Thus where “plastics” or similar or cognate expressions in the following specific description, the reader should understand that the term “Aluminium” could be used instead, and a sleeve assembly incorporating an Aluminium tube as opposed to one constituted of a plastics material is entirely within the scope of the present invention. Regardless of the particular lightweight material chosen, the advantages, benefits and effects of the invention still apply. Preferably, the material has a density of less than 3.5 g/cm3 at room temperature.

[0085] Specifically, sleeve assembly 2 consists essentially of a plastics material outer cylindrical tube 4 having and extending between annular end surfaces, one of which is referenced at 4A, and within which is bonded, for example by means of an epoxy- or other high-strength resinous adhesive, a cylindrical tubular compressible liner 6 which also has, and extends axially between, a pair of annular end surfaces, one of which is referenced at 6A. Ideally, the plastics material chosen for the tube is one which is both structurally and dimensionally stable and thus rigid, resilient, but not brittle, and one which can be machined with relative ease and without cracking, tearing or without experiencing extensive plastic deformation. Suitable plastics materials include, without limitation, Delrin®, Nylon 6, Nylon 6, 6 or other Polyoxymethylene (POM), acetal, polyacetal, and polyformaldehyde, polyamide, or polyester.

[0086] The geometric planes in which the annular end surfaces 4A, 6A lie are most preferably exactly orthogonal to the central longitudinal axis of the sleeve assembly as a whole, referenced “C.sub.L” in this and other Figures. Importantly, and as can be seen in the Figure, the liner 6 is axially shorter than the tube 4 within which it is bonded so that, when the liner 6 is initially slid completely within the tube 4 prior to bonding and disposed substantially axially centrally and thus symmetrically therein, the annular end surfaces 6A of the liner are set back from those of the tube so that a pair of identical annular rebates (one of which is referenced at 8) is automatically created at either end of the sleeve assembly internally of the tube 4. Said rebates 8 are defined, on one hand, by those portions of the interior cylindrical surface 4B of the tube 4 which remain exposed and extend beyond the annular end surfaces 6A of the liner 6, and on the other hand by said liner annular end surfaces 6A.

[0087] In accordance with the invention (and as can be seen more clearly in FIG. 5), once the liner is firmly bonded to and within the interior cylindrical surface of the tube, and the adhesive has cured, the remaining exposed interior cylindrical surfaces of said tube are subjected to further machining, for example a grinding operation carried out around substantially the entire interior cylindrical surface of the tube so as to slightly (for example by an amount of between 1-5 mm, depending on the overall outer diameter of the sleeve assembly, and the annular thickness of the tube) enlarge the internal diameter in end regions thereof. As a result of this machining/grinding out operation, which is effected to an axial depth from the annular end surfaces of the tube which is either marginally less than, or about the same as that at which the annular end surfaces of the liner are disposed, annular shoulders, one of which is referenced at 4D, are created in the interior of the tube at both ends thereof. Said shoulders are important because they provide a surface against which end rings can abut and be tightened against, thus placing the sleeve assembly in a state of non-negligible axial compression between said end rings, and without engaging (at least significantly) with, and thus also axially compressing, the annular end surfaces of the liner. The specific configuration of end rings, the annular shoulders, and the respective annular end surfaces of both tube and liner will be explained further below.

[0088] In some embodiments of the invention, and depending on whether there exist remnants of cured adhesive at the interface between the annular end surfaces of the liner and the immediately adjacent cylindrical surface of the tube, it may be necessary or preferable to additionally machine, for example by grinding, the annular end surfaces of the liner, both to remove such adhesive remnants, and also to ensure that the annular end surfaces of the liner lie in a plane which is exactly orthogonal the central (datum) axis of the sleeve assembly as a whole. It is to be mentioned here that it is of course equally if not more important that the geometric plane in which the annular shoulders machined into the interior of the tube as mentioned above and described more fully below lie is also exactly orthogonal to the central (datum) axis of the sleeve assembly as a whole because any offset of the/those places from orthogonality would immediately compromise the axial compression which the end rings apply on the tube between them, with the result that the tube could be subjected instead to undesirable torsional and shear forces.

[0089] In further accordance with the invention, screw threads 4C are machined into the said interior cylindrical surfaces 4B, said threads being provided over at least some of the axial length of those interior cylindrical surfaces as illustrated, preferably between 25%-75% of the axial length thereof. Preferably, the pitch of the threads machined into this surface is at least 0.5 mm, more preferably at least 1 mm, and most preferably in the range 1-2.5 mm, this being on account of the fact that machining threads of very fine pitch (e.g. less than 0.5 mm, and commonly less than 1 mm) in plastics materials is exceedingly difficult if not impossible, at least with standard thread-machining equipment. Obviously the particular requirement for larger thread pitch does not apply for tube constituted of metal or alloys thereof, as such can generally be machined with much greater precision.

[0090] Once the threads 4C have been machined in the partially complete sleeve assembly of FIG. 1, it is ready to receive the end rings.

[0091] At this point, it is useful to provide exemplary dimensions for a conventional metal decorating sleeve assembly—the sleeve assembly illustrated in the Figures and in particular FIGS. 1, 2, and 4 may have overall axial length of 180 mm, effective/final outer diameter of 227 mm, and an inner diameter (i.e. the inner diameter of the liner) of 197 mm. The liner axial length may be of the order of 156 mm, thus defining internal rebates at either end of the liner at an axial depth of 12 mm. Further machining of these rebates outwardly by a radial amount of about 1.9 mm naturally produces annular shoulders having that radial dimension completely around the interior exposed cylindrical surface of the tube, at a 12 mm axial depth. The end rings themselves are thus 12 mm in axial depth, and have outer diameter (on which threads are machined) may have an effective outer diameter of 214 mm, and in some embodiments the end rings may be provided with an enlarged outer lip having a diameter of 215 mm which may be received in a corresponding seat surface of similar radial dimension (1 mm) milled into the end surface of the tube (not shown).

[0092] Referring now to FIG. 2, sleeve assembly 2 is illustrated in a more advanced state of completion. Specifically, steel end rings, one of which is generally referenced at 10, and being provided around their exterior cylindrical surfaces with threads corresponding to the threads 4C provided on the interior cylindrical surfaces of the tube 4 in the end regions thereof, are screwed into the rebates 8 of the sleeve assembly at both ends thereof. As will be understood by the skilled person, and can be seen in FIG. 2 (and in more detail in FIG. 5), the most preferable and required arrangement of the end rings after they have been completely and axially compressingly screwed in place within the sleeve assembly is that their outermost annular end surfaces 10A lie precisely, exactly flush with the immediately adjacent and respective annular end surfaces 4A of the tube, at both ends. In order to achieve this configuration, it is preferable that, initially, the axial depth of the end rings 10 is slightly (e.g. 0.5-1.5 mm) greater than the axial distance between the annular shoulders 4D and the annular end surfaces 4A of the tube. In this case, even after the end rings are firmly and compressingly screwed into the sleeve assembly, the annular end surfaces of the end rings will stand proud some amount, e.g. 0.4-1.4 mm, proud of the adjacent annular end surfaces of the tube. Therefore, most preferably, both the ends of the sleeve assembly are subjected to a yet further machining step which not only removes any proud-standing portion of the end rings, but also ensures that both adjacent respective annular end surfaces of the tube and end rings lie exactly flush with one another, in the same geometric plane, and (in some embodiments) an exact, predetermined/desired axial distance from one another thus providing a sleeve assembly having a precise overall axial length.

[0093] One further dimensional feature of the end rings deserves mention. It can be seen in the Figure (and also in more detail in FIG. 5) that the interior diameter of the end ring 10 is greater than the corresponding dimension of the liner 6 adjacent which each end ring 10 is ultimately disposed, and thus some small portion (e.g. 0.5-2 mm wide) of the annular end surface of the liner remains exposed, visible and not concealed behind the ring. As the skilled person will appreciate, this configuration is regarded as essential because in order for the sleeve assembly to be “blown” (by compressed air) onto an air mandrel, the compressible liner must be capable of being elastically radially expanded (and thus compressed) slightly before the liner, and thus the sleeve assembly as a whole can be slid onto and over the mandrel. Once the sleeve assembly is in the correct position, both axially and circumferentially, on the mandrel, the source of compressed air is released, and the liner then elastically relaxes into firm and secure engagement with the mandrel, and thus the sleeve assembly is firmly and securely mounted on the mandrel.

[0094] Turning now to the exterior cylindrical surface of the sleeve assembly illustrated in FIG. 2, it can be seen that a plurality of elongate recesses 12 being substantially rectangular in cross-section have been machined in or otherwise cut into the exterior cylindrical surface of the tube. Said recesses are substantially dimensionally identical and substantially evenly circumferentially spaced apart around the entirety of the exterior cylindrical surface of the tube, each being machined out to a particular uniform depth, typically of the order of 7-15 mm. As previously mentioned, the machining out of the recesses is conducted after the end rings 10 have been firmly secured in place at each end of the sleeve assembly so that its structural strength is thereby enhanced, particularly at the end regions thereof. In the configuration shown in the Figure, the recesses are most preferably substantially axially aligned with the central axis of the sleeve assembly, but it is possible, in some embodiments that the recesses may be machined in spiral fashion, i.e. such that there is some relative circumferential offset between the opposing terminal ends of each recess. It is also possible in some embodiments that the recesses may be axially open-ended, in that they do not have axially opposed terminal ends.

[0095] However, the illustrated, axially aligned, terminated configuration of the recesses is preferred because straight-sided recesses can readily accept a pre-assembled similarly straight and appropriately dimensioned magnet assembly as illustrated in FIGS. 3A, B, C and described further below, and closed-ended recesses can much easier contain a fluent adhesive composition which may be spread or poured thereinto prior to insertion of a magnet-keeper assembly (see below). Regardless of the particular shape and orientation of the recesses, their depth and overall axial length are important because [0096] (a) generally speaking, the depth of the magnets and keepers, or of the magnet-keeper assembly, which each of the recesses receive is a significant factor in determining the overall magnetic field strength which they provide, and [0097] (b) the recesses must extend over substantially the entire axial length of the sleeve assembly to ensure that any ferromagnetic printing or coating plate which is to be magnetically mounted on and secured to the exterior cylindrical surface of the sleeve assembly is firmly magnetically held in place thereon over substantially the entirety of its width, which will, in most cases, be only slightly less than the overall axial length of the sleeve assembly itself.

[0098] For these reasons, not only do the recesses terminate axially very close (e.g. of the order of only a very few mm) to the annular end surfaces of the tube, but their depth is also comparatively a significant proportion of the overall annular thickness of said tube, for example being anything from 50-90% of that thickness. Thus without the structural reinforcement being provided by the already secured-in-place interior liner and encapsulating end rings, it would be generally impossible to machine out all the recesses to the required lengths, widths, and radial depths without structurally damaging or indeed destroying the tube.

[0099] As can be seen in the figure therefore, the machining out of the recesses in spaced apart relationship leaves lands 4E of the tube 4 between each recess. Of course, the substantially circumferentially even spacing of the recesses is the most preferred arrangement to avoid any unwanted rotational inertial imbalance, and therefore it is most desirable that the width of each of the lands 4E is substantially identical over the entire exterior cylindrical surface. It is also desirable that the axial separation distances between the terminal ends of each and every recess and the respective most proximate annular end surface of the tube are also identical so that the sleeve assembly as a whole is essentially perfectly inertially symmetric. This condition of rotational or inertial balance is an important consideration, because in use, inertial forces arising from the high speed (many 10 s if not hundreds of revolutions per second) can be significant, and for lightweight plastics sleeves become of significantly greater concern, at least as compared to the more conventional but significantly heavier metal sleeve assemblies.

[0100] Typical dimensions for the recesses (such as may be provided around the exterior surface of the particular sleeve assembly having the specific dimensions abovementioned) may be (for all recesses): axial length 172 mm, width 20 mm, depth 6 mm, and a total number of slots, 26, in 2 sets of 13 on respective diametrically opposite halves of the sleeve assembly, such being separated by the pair of plate locating formations (see further description below).

[0101] A final feature of the partially completed sleeve assembly of FIG. 2 are the raised, proud-standing plate locating formations 14, 16, which are screwed or adhered in place within appropriately dimensioned recesses (not referenced) drilled or otherwise machined in at least one of the lands 4E between a respective adjacent paid of recesses 12. Although not illustrated in or immediately apparent from the Figure, in most preferred embodiments, the recesses 12 are uniformly sized and spaced apart so that the exterior cylindrical surface of the sleeve assembly is substantially diametrically symmetrical. Thus, about any diametral section taken through the sleeve assembly, exactly the same number of whole (and possibly part-) recesses 12 (and of course also lands 4E) would exist in each sectional half. In such an arrangement, each recess 12 and land 4E would automatically have a corresponding diametrically opposite recess and land, and in most preferred arrangements, one further pair of plate locating formations may be provided in that land being diametrically opposite that in which plate locating formations 14, 16 are provided.

[0102] Referring now to FIGS. 3A, 3B, 3C, there is shown one possible magnet-and-keeper assembly 20 comprising an alternating series of steel or other ferromagnetic material keepers 22 and intervening typically sintered ferrite magnets 24, each being disposed on a central locating (steel) rod 26 and all being sandwiched and contained between a pair of (steel) containing end pieces 28 firmly secured to said rod 26. The cross-sectional shape 30 of each of the magnets and keepers is shown in FIG. 3B, and the overall length of the assembly, measured from the ends of rod 26, may initially be slightly greater than the axial length of each and every recess 12 into which the assembly is adapted to fit, as a result of the manner in which the magnet-and-keeper assemblies are manufactured and assembled. Therefore, prior to insertion thereof into any recess, the tips of the rod 26 may be cut or otherwise machined off to allow the remaining assembly to be snugly received within any recess. Prior to such insertion, the interior of any receiving recess 12 may be part-filled with an adhesive bonding compound, for example an epoxy resin, so that when the magnet assembly is inserted and pressed firmly therein, the bonding compound flows around the sides of the recess and into the various interstices which may exist between the magnet-and-keeper assembly and the recess itself. Most notably, the depth “d” (see FIG. 3B) of the magnet-and-keeper assembly will be generally the same as the depth of each and every recess so that the upper surfaces of the magnet-and-keeper assemblies ultimately lie approximately flush with the surfaces of the adjacent lands lying on either side of any particular recess. Naturally, each and every recess receives an identical magnet-and-keeper assembly in this manner, and thereafter the adhesive is allowed to cure so that each magnet-and-keeper assembly is robustly secured within each recess.

[0103] Of course, it is equally possible, although less efficient, to manually fill the recesses with an alternating sequence of individual magnets and keepers, as is currently conventionally done, particularly for spirally arranged recesses. The important considerations for both methods of construction are merely that the magnets and keepers are substantially of the same depth, that depth is broadly identical to the depth of the recess, and that the recess is substantially completely filled over its entire axial length with magnets and their respective keepers. Regardless of the manner in which the recesses 12 are filled with magnets and keepers, once all the recesses are so filled, the entire exterior cylindrical surface of the sleeve assembly is then subjected to precision surface grinding whereby the overall outer diameter (OD) of the sleeve assembly is slightly reduced (e.g. by 0.5-1.5 mm) down to required ultimate OD, a critical dimension for operative performance. Notably, this grinding step also removes any cured adhesive residue extant on the surface, and furthermore results in the arcuate smoothing of the exterior-facing surfaces of the magnets and their respective keepers so that not only do the edges of the magnets and keepers lie precisely flush with the adjacent plastics material lands and thus the interface regions therebetween are perfectly smooth and thus essentially continuous, but the entire exterior surface of the sleeve assembly is rendered perfectly cylindrical about the central axis.

[0104] It should be mentioned here that there is a further possible alternate arrangement for the recesses, namely that instead of being machined out or otherwise created in a generally linear, axial direction relative to the sleeve assembly as a whole, the recesses could of course be disposed circumferentially and axially adjacent each other along substantially the entire exterior cylindrical surface of the sleeve. Thus, in this alternative embodiment, the recesses would extend generally circularly around the sleeve exterior surface as opposed to the illustrated embodiment wherein the recesses extend generally axially linearly from one end of the sleeve to the other. Of course, a sleeve assembly with recesses arranged in this alternative way would still result in the exterior surface thereof being substantially magnetic once the recesses were occupied by suitable magnet-keeper assemblies, and thus capable of adequately securing a printing plate or other work component thereto. Also, aspects of the present invention which require that the end rings provide structural support in the region of, and possibly also directly underneath the recesses would still, at least to some extent, still apply in the alternate arrangement, because the two circular recesses most remote from one another and disposed at one or other end of the sleeve assembly would still of course be required to be provided very close to the ends of the sleeve assembly for exactly the same reasons as the linear recesses of the primary embodiment extend similarly very close to the ends of the sleeve assembly. Those two, but only those two recesses would still therefore require the structural support provided by the substantially more rigid end rings disposed immediately below them in the sleeve assembly.

[0105] Referring now to FIG. 4, there is shown a finally completed sleeve assembly 2 to and around which a ferromagnetic printing/coating plate 24 is wrapped and magnetically secured thereto. As can be seen, the length of plate 40 (a single plate in this instance) is slightly less than the circumferential dimension of the sleeve assembly, and the lateral (width) dimension of the plate is both slightly less than the axial dimension of the sleeve assembly and slightly greater than the axial length of the recesses 12 in each of which the magnet assemblies 20 have been adhered. As the plate length is less than the circumferential dimension of the sleeve assembly, 3 of the said magnet assemblies are exposed as seen in the Figure, the outline of the keepers 22 and end pieces 28 of which, being typically of steel or other ferromagnetic metal, can clearly be seen. In contrast, the magnets within the magnet assemblies are not clearly seen in the Figure, because typically being of a black sintered ferrite material and thus (in this particular embodiment at least) the magnets are essentially the same colour as the typically black plastics material of the tube 4 and therefore rendered somewhat invisible or not at all clearly distinguishable from said plastics material, particular after the exterior cylindrical surface is ground down to precise outer diameter. Specifically, this grinding process has the dual effect of somewhat polishing or rendering more distinct the steel elements of the magnet assemblies while simultaneously swaging or somewhat merging or blurring the edges of the magnets with the plastics material lying to either side thereof so the magnets thus become somewhat invisible within, or indistinguishable from, said plastics material.

[0106] In order that the plate 40 can be applied to and precisely mounted on and around the exterior cylindrical surface of the sleeve assembly, a pair of appropriately sized, shaped and dimensioned holes are punched though the plate, said holes being in precise alignment with the most proximate lateral edge of the plate, and spaced apart by exactly the same distance as that axial distance between the correspondingly shaped plate locating formations 14, 16. Thus, when the plate is to be mounted on the sleeve assembly, the plate is manoeuvred so that the punched holes therein are directly above the plate locating formations, and then the relevant edge of the plate is place in position so that the plate locating formations pass through the punched holes. Thereafter, the remaining length of the plate is wrapped around the exterior cylindrical surface of the sleeve assembly. The plate, being generally thinner than the distance by which plate locating formations 14, 16 stand proud of the exterior cylindrical surface of the sleeve assembly will therefore, as illustrated, lie beneath said plate locating formations, which thus also stand proud of the exterior surface of said plate. As a final means of ensuring that the plate 40 is precisely correctly positioned on the sleeve assembly, a scribe line 42 is created circumferentially completely around the exterior cylindrical surface of the sleeve assembly so that a scribe line registration formation 44 formed or otherwise provided on plate 40 can be aligned with the scribe line, and thus the plate can be axially and circumferentially precisely positioned on the sleeve.

[0107] One further final feature of the end rings, shown in FIG. 4, should also be mentioned. In particular, one (and usually only one) end ring is provided with a very precisely machined registration notch 4F, the dimensions and shape of which correspond exactly to a registration keyway or similar formation provided on the mandrel onto and over which the sleeve assembly is adapted to be mounted, thus ensuring that the sleeve is correctly circumferentially positioned on the mandrel. Furthermore, said registration notch is provided at a very precisely determined circumferential position on the sleeve assembly itself relative to the plate location formations 14, 16 so that the circumferential position of the plate 40 (or plates) relative to the underlying mandrel is also very precisely determined.

[0108] It is worth mentioning here that the end ring which is provided with the one or more registration notches 4F is generally always regarded as provided the “datum”, i.e. it is that end ring from which all other relevant dimensions of the sleeve are determined, particularly axially.

[0109] Referring to FIGS. 5A and 5B, it can be seen, firstly in FIG. 5A, that the recesses 12, terminal end walls of which are referenced at 12A, are machined to a depth (“t.sub.2” in the Figure) which is a significant proportion (of the order of 40-50, and possibly up to 90%) of the overall annular thickness of the tube 4, referenced as “t.sub.1” in the Figure. Furthermore, the axial locations of the end walls 12A of the recesses relative to the shoulders 4D provided within the interior of the tube 4 can be seen. In particular, in this embodiment, the axial depth at which the shoulders 4D are provided is such that the recesses 12 are undercut to some non-negligible extent. In some embodiments, the degree of axial separation, ie. The undercut distance, may typically be of the order of 5-15 mm. Thus from this Figure it can clearly be seen why the structurally much stronger steel end rings must be already secured in place when the machining of the recesses is performed in the comparatively much less structurally strong tube. As the skilled person will appreciate, the circular, continuous end rings provide a structurally strong, and thus highly elastically resistant reaction surface for the interior cylindrical surface of the tube in the end regions thereof, so much so in fact that the machine tool performing the machining out of the recesses at said end regions can successfully perform such machining without damaging or otherwise structurally compromising the tube, notwithstanding the fact that there is proportionally very little plastics material of the tube remaining between the base of the machining tool (i.e. the base of the recess) and the interior cylindrical surface of said tube, i.e. that region in which the interior threads are provided and into which the end ring is screwed.

[0110] From FIGS. 5A and 5B, the relative inner radial/diametral dimensions of the end ring 10 and the axially adjacent liner 6 should be noted. In particular, from the Figures it is clear that the liner (in its radially uncompressed condition) effectively protrudes radially inwardly of the end rings in its relaxed condition, and can thus be radially outwardly expanded until it becomes flush with the end ring 10.

[0111] Finally, as can again be seen from FIGS. 5A and 5B, the relative axial separation of the shoulders 4D from the annular end surface 6A of liner 6 should be noted. This axial separation gives rise to an annular interstice betwixt end ring 10 and said annular end surface 6A which (a) may be filled with a sealing gasket, O-ring or curable gasket/sealing composition 50, and (b) ensures that when the end rings are tightened against the shoulders 4D at both ends of the sleeve assembly, the respective annular end surfaces 6A of the liner are not also compressed, or even directly contacted by the end rings, as this can lead to undesirable rupturing or other deformation of the liner leading to a partial or complete compromise of the compressibility of the liner, especially at the end regions thereof. Finally, as regards to FIG. 5A, it can be seen that between the threads 4C and the corresponding threads (not referenced) provided on the end rings, there is provided an intervening sealing and/or adhesive composition, such as a curable epoxy resin, which effectively both seals the threaded region rendering it fluid-impermeable, and also simultaneously ensures an exceedingly secure connection between the end ring 10 and the tube 4 to the extent that the end ring effectively becomes inseparable therefrom, and (most importantly) cannot circumferentially rotate relative thereto. By such means therefore, the circumferential position of end ring relative to the tube to and within which it is screwingly connected is effectively permanently set once the adhesive/sealing composition cures.

[0112] Referring specifically now to FIG. 5B, a slightly modified configuration is depicted in which the terminal end walls 12A of the recesses 12 are disposed axially more distant from the annular end surfaces 4A, 10A of the tube and end ring respectively than the shoulders 4D. Even in this configuration, however, the end rings still play an important structurally supporting role, because as the machine tool which performs the machining out of the recesses approaches the end of its travel and thus the creates the terminal end walls 12A of the recesses, the action of said machine tool on the plastics material will nevertheless give rise to a bending moment in the vicinity of the end region, which of course the structurally much stronger end ring component can much better resist that the comparably structurally much weaker plastics material.

[0113] Thus, the present invention should be considered as covering both the above arrangements, and in particular any arrangement where the terminal ends walls of the recesses 12A are axially proximate the internal shoulders 4D, for example being within 1-5 mm of one another, measured on the longitudinal axis of the sleeve assembly.

[0114] It should also be mentioned here that although much of the foregoing description of the present invention has been couched in terms of the resistance that structurally much stronger, e.g. steel, end rings provides for the sleeve assembly as a whole, in terms of its being able to withstand the rigours of machining and machine tools working directly on and in the plastics material, it is of course possible that the tube 4 may be cast, formed, extruded, or otherwise created with the recesses already in place, i.e. created as a result of the casting or other forming process. In this case, there would of course be no requirement for the recesses to be separately machined. Despite this, however, there will generally always be the requirement that exterior cylindrical surface of the sleeve assembly be machined, for example by surface grinding, which itself can entail significant circumferential and radial forces which will inevitably be of most concern at the end regions of the sleeve assembly where, were it not for the existence of the structurally much stronger end rings and the robust manner in which they are secured within the sleeve assembly, the plastics material would be bound to fail.