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FLEXO Magazine : March 2010
34 FLEXO MARCH 2010 www.flexography.org Impact damage from improper handling. while the remainder use a solid build-up style. Both have a composite core sleeve with a wall thickness of approximately 0.040in. The core expansion style relies upon a polyurethane foam expansion layer that compresses as the core expands when the mandrel air supply is applied. There is a secondary composite build-up layer applied to the foam expansion layer that allows the aluminum tube to be pressed and glued in place without compressing the foam, as that would render the sleeve too tight. The solid build-up style has no true expansion layer and relies upon a core that shrinks in wall thickness as the core is forced into internal cavities within the thicker aluminum tube mounted on top when the mandrel air supply is applied. The core is only attached to the aluminum tube at each end, which allows the core to move laterally as the core material expands into the internal cavities and causes the parts of the core in contact with the solid internal ribs to become "thin- ner" therefore allowing the sleeve to mount onto the mandrel. When air pressure is removed, the core in both styles relaxes and locks to the mandrel with an interference fit. Chamber leaks and end seal leaks result in ink getting into the vicinity of the core sleeve. In expansion layer styles, some designs have end rings to try to protect the foam expan- sion layer, but, inevitably, ink penetrates the foam layer and leads to problems. Since the foam layer is compressed in a mounted state, any ink that penetrates the foam and dries results in elasticity being compromised. This can have an effect on sleeve surface concentricity and possible future fit problems. In the solid build-up styles, any ink contamination on the inner core or leaking into the internal cavities compro- mises the thinning of the core and the ability to easily remove the sleeve from the mandrel. Additionally, internal wear due to the lateral movement of the core against the ribs can result in concentricity problems for the printer. The foam expansion layer is the weak link in any expan- sion style sleeve, plate or anilox. In the case of anilox sleeves, ink contamination or non-conforming cleaning procedures can lead to serious consequences to the printer. Sleeve faces should always be sealed when using dry media and liquid cleaning devices. Ultrasonic cleaning is not recommended for anilox sleeves as it can actually de-laminate the various build- up layers. Damage to the expansion layer by dry media or cleaning solutions can result in significant challenges to the printer, mainly in the form of TIR (total indicated runout). Efforts are being made by sleeve suppliers to permanently seal the foam expansion layers and internal cavities, but a significant breakthrough has yet to be made. Some anilox suppliers have developed methods to refurbish anilox sleeves by removing the ink-encrusted expansion layer and replacing it with a silicone type sealant, but this will not always return the sleeve to an acceptable TIR. The future of anilox sleeves likely lies in a hollow sleeve with a composite carbon fiber outer tube and hubs that "slide" on the mandrels without an expansion layer. Such sleeves are available to the industry as plate sleeve bridges and such technology in the anilox sector could significantly reduce ink and cleaner contamination and corrosion as well as allow press speeds greater than 2,500fpm. Sleeve suppliers are beginning to develop such composite anilox sleeves for the newer high speed, wide web presses. Adhering to supplier developed cleaning procedures will certainly extend the life of any anilox sleeve, but care in mounting/de-mounting and reducing ink spillage will also go a long way to preventing print related anilox sleeve problems for the printer. ---Michael Bell, Rossini NA TECHNOLOGIES & TECHNIQUES
Sustainable Winter 2010