How to use housed bearing units to save costs

Although originally developed by RHP over four decades ago, the housed bearing unit can be said to have truly 'come of age' in today's global market for manufacturing. The unrelenting pressures to reduce build times and costs have led to greater integration of component parts in all areas of manufacture. For example, in the automotive industry the onus is now firmly on suppliers to provide pre-engineered assemblies such as hub units that simply bolt onto the vehicle transmission system - which is, itself, usually pre-assembled.

Housed bearing units provide the same integrated benefits in general manufacturing industry, food processing, materials handling and agricultural applications. By providing units that are ready-assembled to bolt into place, they provide an easy and economical solution to bearing problems relating to component complexity, mounting, and also bearing maintenance and life in difficult environments.

A simple comparison supports the case for 'bolt-on' convenience. The typical mounting arrangement for a standard ball bearing includes a number of separate components, some having to be accurately machined. These components include a housing, stepped shaft, inner and outer ring retainer, and lock nut and thread. Not surprisingly, this arrangement is both expensive and time-consuming to install. In contrast, one of NSK's RHP range of self-lube units employs the same basic bearing, but integrates all other elements needed to assemble the bearing, together with facilities for sealing and relubrication. In practice, therefore, the housed bearing reduces the number of expensive components, simplifies assembly and cuts stock holding costs. But that is not all.

Specifications to suit applications

Self-lube units provide effective engineering solutions to other bearing problems too, including economical mounting, bearing maintenance and bearing life in difficult environments. Self-lube bearings conform to ISO standards and are available in different materials and configurations. Cast iron pillow block and flange types are used for normal and medium-duty applications, while zinc-plated pressed steel units are available for lighter duty operations. In addition, as many self-lube units are called upon to operate in harsh environments, NSK has introduced the Silver-Lube range of corrosion-resistant bearings and housings. These are excellent for applications where frequent washdowns are necessary, optimum hygiene standards are required and good chemical resistance is important.

Essentially self-lube housed bearing units consist of an insert, normally based on a 6200 series deep groove ball bearing with a cast iron (pillow block, flange or take-up unit) or pressed steel housing. The bearing insert can carry a combination of radial and axial loads in the same way as a standard ball bearing. It has an extended inner ring with an integral shaft locking device and a spherical outer ring that matches the spherical bore in the housing to overcome initial housing misalignments up to 0.030 radians.

A number of insert types are available for use in light and heavy applications and high- and low-temperature operating conditions. Heavy-duty types are used in equipment such as pumps and fans. Designed with a wide inner ring they facilitate a broad choice of locking methods. The simplest of these, set screw locking, is suitable for most applications except those where vibration is a problem. Where vibration does occur an eccentric locking collar mechanism is supplied. Alternatively, in applications where a positive concentric lock is required, or when heavy vibration or shock loads are present, a taper lock system is preferred. With all these locking arrangements, standard shafting can be used - there is no need for a precision interference fit.

Temperature extremes

In applications where self-lube bearings are required to operate in high or low temperature conditions, HLT inserts come into their own. These units provide opportunities to reduce maintenance, downtime and replacement costs at temperatures as high as +180degC and as low as -40degC.

Especially suited to high-temperature applications, HLT inserts are designed with C5 radial internal clearance and high-temperature grease and seals to give maximum life even at +180degC.

As self-lube bearings are widely used in operating environments that are dirty and wet (for example, materials handling, agriculture and textiles) they are provided with a choice of effective sealing systems. The standard S type seal consists of a robust steel pressing with a nitrile sealing lip that is designed to retain grease within the bearing and keep contaminants out.

For more hostile environments a flinger seal has been developed. This gives increased levels of protection to the standard single-lip seal to extend bearing life in arduous conditions without any loss in speed capability. Finally, offering the highest levels of protection of all is the triple-lip seal. A highly efficient seal having three nitrile sealing lips, this component is recommended where a high degree of contamination is present.

The self-lube range can also be supplied with protection of another kind, this time for factory personnel against the dangers posed by rotating shafts. A Protector end cover is available for easy fitting to most standard self-lube housed bearing units. Manufactured in mild steel, the patented Protector is difficult to dislodge, yet can be removed without damage and used again repeatedly.

For more information about NSK's RHP Self-Lube housed bearing units, go to www.eu.nsk.com/ENG/products/product_ballBearingUnit_2.asp.