Dry-Running Bushings Keep Printing Presses Clean

One oil drip from a bushing above the impression cylinder can contaminate hundreds of printed sheets before anyone notices. That risk is why PTFE-lined, self-lubricating bushings have become common in printing machinery, where they run dry and eliminate oil leakage near paper paths and ink systems. According to ISK Bearings, SF-1 type self-lubricating bearings are widely used in textile and printing machinery, with a working range of -195 degrees C to +270 degrees C and no external lubrication required.

How the DU Three-Layer Structure Works

The classic DU design bonds three layers into one thin wall: a steel backing for strength, a porous sintered bronze middle layer, and a PTFE/MoS2 overlay on the sliding surface. During the run-in phase, PTFE transfers a solid film onto the shaft, and the bearing then rides on this film under boundary lubrication. Ahcell's DU bushings carry a static load rating of 140 N/mm2, a dynamic rating of 60 N/mm2, and a PV limit of 3.6 N/mm2.m/s in dry operation, with a temperature span of -195 degrees C to +280 degrees C.

Wrapped and composite bushings of this type are manufactured to ISO 3547, the international standard for wrapped bushes, which defines dimensional tolerances and test methods for the flanged and plain cylindrical forms used in press frames.

Where Self-Lubricating Bushings Serve in a Press Room

Offset, gravure, and flexo presses share the same problem: every bearing is a potential leak point, and wash-up solvents attack conventional grease. Printers typically fit dry-running bushings in folder units, roller trunnions, ink roller journals, and side-frame linkages, while oil-lubricated positions remain only where speeds and loads demand them. Bijur Delimon International, a Timken company, supplies automatic lubrication systems for offset presses precisely because bearing replacement is costly and causes unexpected downtime, a cost that oil-free bushings avoid altogether at low and medium speed points.

• Folder and delivery unit pivot bushings, where paper dust accumulates
• Ink roller and dampening roller journals, where oil must never reach the sheet
• Side-frame and impression cylinder linkages with oscillating motion

SKF's press industry coverage notes that lubricated positions often need annular grooves and lubrication holes in the outer ring; dry-running bushings skip that plumbing entirely.

How to Size a DU Bushing for a Press Roller

Calculate the operating PV value by multiplying the specific bearing pressure in N/mm2 by the sliding speed in m/s. If the result stays below the DU limit of 3.6 N/mm2.m/s at the worst case, a maintenance-free bushing will survive; if it approaches the limit, add a margin by increasing the bearing length or switching to a graphite-plugged JDB bronze bushing.

Press builders that standardize on dry-running plain bearings also simplify spare parts. One DU sleeve family covers most roller journals, and because the PTFE layer protects the shaft, hardened chrome rolls last longer between regrinds.