Concentric double sleeve for a rotary printing cylinder

Abstract: A sleeve (3) for a rotary rotogravure or flexography printing cylinder (1), said cylinder (1) comprising a generally steel mandrel (2) to be rotated about its axis (K) when used in a printing machine, said sleeve (3) being able to be mounted on said mandrel (2). The sleeve (3) comprises two cylindrical portions (5, 6) removably associated with each other and forming, during the rotation of the mandrel (2), substantially a single body in the sense of being torsionally locked together.

Description: This invention relates to a rotary printing cylinder in accordance with the introduction to the main claim. A printing cylinder for rotogravure or flexography is known to comprise a generally steel mandrel on which a sleeve is mounted. This latter carries the printing elements (recessed or in relief). The sleeve is generally of tubular cylindrical form and can be mounted on the mandrel by various methods, involving for example surface deformation of the mandrel or the use of air to facilitate the mounting of the sleeve on the mandrel. The sleeve is of small thickness to allow it to be easily handled. EP-A-0 623 466 relates to a printing cylinder having a cylindrical core and a removable outer sleeve. The latter comprises a layered body having an inner layer (or base element) made of reinforced thermoplastic material and an outer layer made of copper or of copper alloy. The first layer is integral with the second layer and forms with the latter a sole piece. The use of the aforesaid known cylinders has however various drawbacks deriving in particular from their use for different print developments. In this respect, when the print development changes the cylinder diameter must be changed. As the sleeves, as stated, are of small thickness, the diameter change is necessarily achieved by replacing the sleeve. In other words, the change in print development is achieved by replacing the mandrel with one of the desired diameter and mounting an appropriate sleeve on it. This operation is however difficult to carry out because of the weight of such mandrels (which as stated are of steel), and involves considerable cost. An object of the present invention is to provide a sleeve for rotary printing cylinders which enables the print development to be changed quickly at low cost. A further object is to provide a sleeve of the aforesaid type which is easy to handle. These and further objects which will be apparent to the expert of the art are attained by a sleeve for a rotary printing cylinder in accordance with the accompanying claims. The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which: Figure 1 is a longitudinal section through a sleeve according to the invention taken during its assembly; Figure 2 shows a printing cylinder provided with the sleeve of the invention. With reference to said figures, a printing cylinder is indicated overall by 1 and comprises a mandrel 2 on which a sleeve 3 open at its two ends 3A, 3B is mounted. The mandrel, generally of steel, is arranged to rotate about its axis K driven in any known manner. According to the invention the sleeve 3 comprises two cylindrical portions 5 and 6, the portion 5 (the outer) being mounted about the portion 6 (the inner) and being arranged to support the printing matrices if these are not already an integral part of said portion 5. Said portions 5 and 6 are both cylindrical and tubular to enable them to be fitted together and to be mounted on the mandrel. Specifically, the outer sleeve portion 5 is of very small thickness and is constructed for example of glass fibre and epoxy resin. In contrast in the illustrated embodiment the sleeve portion 6 consists of three concentric cylindrical layers 8, 9 and 10, the layers 8 and 10 (outer and inner) being of high rigidity material such as carbon fibre, and the intermediate layer being of expanded rigid polyurethane. In the portion 6 there are provided at one of the open ends 3A, 3B of the sleeve 3 a plurality of channels 12 opening into the outer surface 13 of this portion and communicating with the inner cavity 14 of the sleeve 3. These channels (of diameter for example between 1.5 and 3 mm) are arranged to feed compressed air from the interior of the sleeve 3 to said surface 13 to enable the portion 5 to be fixed onto and released from the portion 6. To facilitate the mounting of the portion 5 onto the inner portion, this latter has a surface part 15 close to the end 3A inclined (for example by an angle alpha - α - of between 12° and 20°) to the remaining surface 13. This hence provides a lead-in for mounting the portion 5 onto the portion 6. It will now be assumed that a sleeve 3 according to the invention is to be assembled; for example it will be assumed that a previously used print character supported by a first portion 5 is to be changed to a different character supported by a different portion 5. To release the components of the sleeve 3, it is firstly separated from the mandrel 2, after which its ends 3A, 3B are closed by usual closure elements (such as frusto-conical plugs 20 and 21), one of which is provided with a through channel 23. These plugs seal against the wall 14A of the inner cavity 14 of the sleeve. Compressed air (at a pressure of up to 12 bar) is then fed into the cavity 14 through the channel 23 (arrow F in Figure 1). This air penetrates into the channels 12 and reaches the surface 13 on which the portion 5 is located. The air pressure does not change the diameter (inner or outer) of the portion 6 because of the rigidity (and considerable thickness relative to that of the portion 5) of the layers 8, 9 and 10. The portion 5 has an inner diameter A very close to the outer diameter B of the portion 6 and is coupled to this latter by an interference fit. This fit is such as to make the two portions act as one, so that the sleeve 3 behaves as though it were in one piece from the torsional stress viewpoint. In other words, during the rotation of the cylinder 1, the portions 5 and 6 undergo no relative slippage, neither is there any relative slippage (deriving from torsional forces) between the portion 6 and the mandrel 2. On feeding air onto the surface 13, the portion 5 becomes detached (by virtue of its own elasticity) from the portion 6. The portion 5 can hence be withdrawn from the portion 6 by maintaining the air feed into the channels 12. To mount a new portion 5 onto the portion 6 the procedure is analogous to that carried out for the aforesaid withdrawal. Furthermore the lead-in present on the surface 13 of the portion 6 facilitates the mounting of the portion 5 onto this latter. This mounting is hence done while maintaining the compressed air feed into the cavity 14 and hence into the channels 12, said air on reaching the surface 13 causing a slight elastic expansion of the portion 5, enabling the said mounting to be achieved. When mounting is complete, air feed into the sleeve 3 is interrupted on which, by elastic return, the portion 5 becomes coupled to the portion 6 as an interference fit. As stated, this fit is such as to prevent relative slippage between said portions. The sleeve 3 formed in this manner, being extremely lightweight because of its constituent materials, can be mounted on the mandrel 2 to obtain a printing cylinder of the required development (ie with a required diameter L). If said development is to be changed, the sleeve 3 is withdrawn from the mandrel 2 and a new sleeve is used having its portion 6 of a different diameter B but with its inner diameter C equal to that of the withdrawn sleeve. A corresponding portion 5 is fitted to the portion 6. This substitution can be achieved quickly and at low cost in that a set of different diameter portions 5 and 6 costs considerably less than a corresponding set of different diameter mandrels (which in any event would require the use of sleeves also of different inner and outer diameters). Consequently, the print development can be changed using the same mandrel and replacing only the sleeve. This operation is facilitated by the low sleeve weight. The portion 5 separated from the portion 6 withdrawn from the mandrel 2 can be stored for subsequent repetitive printing. One particular embodiment of the invention has been described. Other embodiments can however be provided in which the portion 6 can be of a single layer rather than of several layers as described. The portion 6 in particular can also be of metal (aluminium, titanium and their alloys or steel) or of rigid plastics (rigid PVC, ABS etc.).

Claims: A sleeve (3) for a rotary rotogravure or flexography printing cylinder (1) comprising a generally steel mandrel (2) to be rotated about its axis (K) when used in a printing machine, said sleeve (3) being able to be removably mounted on said mandrel (2) and be coupled in a torsionally rigid manner to this latter, characterized in that the sleeve (3) comprises two cylindrical portions (5, 6) removably associated with each other, a first outer portion (5) being mounted about the second inner portion (6), said portions (5, 6) being torsionally locked together so as to form a single body during the rotation of the mandrel. A sleeve as claimed in claim 1, characterised in that the cylindrical portions (5, 6) are tubular, the inner portion (6) having an internal cavity (14) enabling the sleeve to be mounted on the mandrel (2). A sleeve as claimed in claim 2, characterised in that its inner portion (6) is layered. A sleeve as claimed in claim 3, characterised in that its inner portion comprises an outer layer (8) and an inner layer (10) of high rigidity material, between said layers there being a further layer (9) of expanded polyurethane. A sleeve as claimed in claim 2, characterised in that its outer portion (5) supports usual print matrices. A sleeve as claimed in claim 4 or 5, characterised in that the high rigidity material is hardened carbon or glass fibre or Kevlar, bonded with epoxy or polyester resins. A sleeve as claimed in claim 2, characterised by comprising a plurality of channels (12) provided within the inner portion (6), said channels (12) opening at the outer surface (13) of said portion and into the inner cavity (14) of this latter. A sleeve as claimed in claim 7, characterised in that the channels (12) are provided in proximity to one of its ends (3A, 3B). A sleeve as claimed in claim 8, characterised in that the outer surface (13) of its inner portion (6) has a surface part (15), close to the end in the vicinity of which the channels (12) are provided, inclined to the rest of said surface to form a lead-in for mounting the outer portion (5) onto said portion (6). A sleeve as claimed in claim 1, characterised by a constant inner diameter (C) and an outer diameter (B) variable on the basis of the print development. A sleeve as claimed in claim 2, characterised in that the inner portion (6) is in one piece and is of a high rigidity metal or plastics material such as titanium, aluminium, their alloys, steel, PVC, ABS.

Inventors: ROSSINI FELICE, ROSSINI, FELICE
Applicants: ROSSINI ERMINIO SPA, ERMINIO ROSSINI S.P.A.
Application year: 1996
Main classification: B41F27
IPC codes: B41F27, B41F13