Bearings are the often overlooked components that ensure your printing and production systems don’t miss a single deadline.

Consider just a few of the systems that compose your operation: press cylinders, oscillators, lead rolls, ink fountain rolls, folders, splicers and conveyors.

There are a lot of parts that slide and rub against another object. This causes friction — friction that must be controlled in order to protect your systems against catastrophic failure.

Enter the bearing. Bearings eliminate these adverse effects. They provide trouble-free, low-friction rotation of all machine parts.

The parts of a bearing: Outer ring, inner ring, shield/seal, cage, balls and cage.
Graphics: SKF Printing Business Unit

What composes a bearing? There are several essential parts: inner and outer ring, rolling elements, cage and perhaps a shield or seal. Every rolling bearing has these essential parts, although their design varies substantially depending upon the bearing’s intended use.

Load direction critical

Among the considerations are the amount and direction of the load on the bearing, the expected speed, the environment, available space, life expectancy, lubrication, running accuracy and misalignment.

Let’s take a look at load direction. Load direction is critical when deciding what kind of bearing is required. Ball bearings, for example, are specifically designed for use in light to moderate radial (top-down or bottom-up) loads, limited-thrust (side-to-side) loads and are more suited for high speeds.

Roller bearings, by contrast, should be used in areas of heavy radial and thrust loads, and typically run at lower speeds.

Other factors also apply, depending upon how the ball or roller contacts the raceway and how the thrust or radial loads are distributed through the bearing.

Ball bearings have point contact between the ball and the outer raceway. Roller bearings have line contact; the contact that’s made between the rolling element and the outer raceway is proportionate to the load and speed the bearing can handle.

Finding what’s best

Two popular printing equipment bearings are deep-groove ball bearings (DGBB) and angular contact ball bearings (ACBB). DGBBs have one point contact at the center of the raceway to handle the lighter loads and high-speed demands.

ACBBs, as their name implies, contact the raceway at a prescribed angle, normally 40 degrees. To that end, ACBBs are better suited to handle heavy axial loads that travel in a single direction. ACBBs can also be added in matched pairs to increase their thrust load capacity in one or opposing directions.

Let’s examine four roller bearing units available on the market.

Spherical roller bearing

The spherical roller bearing, which is commonly used on printing cylinders, perforators, die-cutters and slitters, has two rows of rollers with a common raceway in the outer ring. The inner-ring raceways are inclined at an angle to the bearing axis (see Fig. 1).

Fig. 1

These bearings are self-aligning and consequently insensitive to nominal shaft deflection or bending. They are also immune from errors of alignment of the shaft relative to the housing. In addition to radial loads, the bearings can also accommodate axial loads acting in both directions.

Taper roller bearing

Conversely, the taper roller bearing has tapered inner- and outer-ring raceways between which tapered rollers are arranged. Its design makes taper roller bearings particularly suitable for combined (radial and axial) loads (see Fig. 2).



Fig. 2

Uniquely, a taper roller bearing’s inner ring, with roller and cage assembly, can be mounted separately from the outer ring. TRBs are generally incorporated onto the cylindrical shafts of a press’ cylinders or on embossing rolls.

Cylindrical roller bearing

The third type of roller bearing is the cylindrical roller bearing. The majority of CRBs have cages. This bearing can accommodate heavy radial loads and operate at higher speeds than other roller bearings.

Cylindrical roller bearings come in different designs.

There are four different flange designs in caged CRBs. To ensure the correct one is used, engineers must analyze the intended function of the equipment.

They should base their choice on whether the equipment requires axial expansion (side-to-side movement) of the shaft or if the equipment must have the ability to support light axial loads.

For example, ink-oscillating rollers require free movement of the shaft so flanges are not present on the inner ring.

Printing cylinder unit

The printing cylinder unit is a relatively new entrant into the bearing market. The PCU, developed by Steyr, Austria-based SKF Printing Business Unit, blends the flexibility of the cylindrical roller bearing, an eccentric sleeve and greased-for-life needle roller bearings into a single unit. In the past, these components were separately machined.

Many companies have adopted the PCU for plate and blanket cylinders, in part because they offer a number of advantages beyond the high-running accuracy of the CRB.

For example, PCUs boast zero clearance between side frame and sleeve. They are quick and easy to mount. Finally, the PCU offers smooth eccentric adjustment and low friction.

Paul Pirkle is printing business manager, North America, for SKF Printing Business Unit. He can be reached at Paul.R.Pirkle@skf.com. For information detailing recommended product ranges, technical features and other data regarding bearings used in the printing industry, visit www.printing.skf.com.