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FLEXO Magazine : August 2011
24 FLEXO august 2011 www.flexography.org sleeve suppliers will offer an extended warranty on dimensional stability, taper and TIR concerns, as long as proper material movement and storage prac- tices are being employed. In the narrow and mid web arena, there is now an aluminum-cladded print sleeve available. This will greatly improve the dimensional stability of the sleeve, decrease the taper and TIR con- cerns related to atmospheric conditions and offer prolonged life expectancy of the sleeve—beyond the traditional three-year period. Just be sure that the added weight of the aluminum-cladded sleeve does not overcome the inertia mismatch of the servo motor designed for the press. MOUNTING & FITTING Most all sleeves are now pneumati- cally loaded on the press mandrels. Compressed air is used in the range of 60 to 90 PSI (6 bar) to compress the expansion layer of the inner diameter of the sleeve. This allows the sleeve to slide on the mandrel like an air hockey puck slides across the table. Once the air is turned off, the expansion layer returns to its original state, securing the sleeve to the press mandrel. The way this works is due to the designed inter- ference fit of the inner diameter of the sleeve to the outer diameter of the press mandrel. Typically, the ID of the sleeve will be .001-in. smaller than the OD of the press mandrel. When compressed air is introduced it expands the inner layer, thus compressing the expansion layer allowing it to slide on. As you can imagine, any contamina- tion between the ID and OD will allow a sleeve to get stuck requiring it to be forced off. Housekeeping is the best practice for eliminating stuck sleeves and sleeve damage. The last thing you want to do is pry off a new composite sleeve with a metal pry bar. Carrier sleeves or bridge mandrels can also be used to reduce sleeve thickness, weight and also to reduce cost of larger re- peats. All these types of sleeves can be suited to fit all plate material and back- ing combinations. Servo driven sleeves can also offer tighter on press toler- ances as the effects from mechanical drive systems, gear backlash and worn bearings will no longer be a factor in print performance. These performance increases will be seen in both running speeds and color-to-color registration. PRECISE REGISTER POSSIBLE In the round direct imaging (ITR) on plate sleeves is gaining a lot of traction. This process allows for plate sleeves to be imaged digitally ITR. A continuous layer of photopolymer is applied to the sleeve with an integrated laser ablated mask (LAM) layer and then exposed and processed. There are many great advantages to this technology. There will be no plate seam that can lift on smaller repeats thus eliminating any gap or plate bounce. With the elimination of flat plate imaging there is no need for a distortion factor to Print sleeves can be imaged in the round.