TechArchive

Original article date: June 2000

The performance capacity of linear bearings can no longer be measured simply in terms of their load carrying capacity, rigidity and accuracy. Due to economic and environmental pressures, there is a clear trend towards design solutions which run with little or no maintenance whilst achieving a long operating life. This can give savings not only in terms of lubricant costs and machine downtime, but also in the design and components required to incorporate relubrication facilities in the machine.

While the operating life of a guidance system is determined by factors including the fatigue behaviour of the material, this does not always give the whole picture. Based on practical experience and extensive tests carried out at INA, it was shown that only a very small percentage of linear guidance systems fail as a direct result of rolling contact fatigue. By far the greatest proportion of failures are due to contamination and defective lubrication.

This leads to an important but surprisingly simple conclusion: if the bearing arrangement itself is correctly designed, a long operating life can be achieved primarily by ensuring optimum lubrication and sealing. If a standard guidance system is used under conditions where lubrication is critical, it may be concluded that it will not run satisfactorily for very long, because the volume of lubricant in the carriage is too small. Increasing the operating life requires relubrication at frequent intervals.

Applications involving severe contamination pose a different set of problems. If the rolling element system is not adequately protected against contamination, rapid wear of the raceways and rolling elements is only to be expected, with a considerable reduction in operating life. In order to achieve a sufficiently long life, additional and often very expensive modifications must be made to be adjacent construction. In order to address these problems, INA has devoted considerable time and resources to the optimisation of bearings and guidance systems so that they can achieve maintenance-free operation under a wide range of application conditions.

The maintenance-free concept was originally developed for the KUVE monorail guidance system. A lubricant groove is provided along the raceway of each of the four rows of recirculating balls, significantly increasing the total volume of lubricant within the carriage. As a result, the guidance system can operate without relubrication for very long periods and, in many applications, is maintenance-free throughout its entire operating life.

This is, however, only one aspect of the maintenance-free concept. For applications involving a high level of contamination, special double lip wipers can be fitted to the ends of the carriage, and the sealing strips fitted as standard to the underside of the carriage can be supplemented by an extra set in contact with the top of the guideway.

In those applications where lubrication is critical, the large volume of lubricant already held within the carriage can be further supplemented by fitting a long-term lubrication unit, which comprises a housing containing an absorbent material and devices which then release the stored lubricant onto the raceways. This unit is fitted to both ends of the carriage in conjunction with the special wipers described earlier. This has the decisive advantage that a large quantity of lubricant is held in close proximity to the raceways and is released in a controlled manner, while highly effective double lip wipers hold this lubricant within the carriage. The lubricant is therefore not distributed along the length of the guideway and lost as a result, additionally leading to contamination of the machine environment. This is in contrast to other systems on the market which use large volume porous seals to provide additional lubricant to the guideway but have no means for retaining the lubricant within the carriage itself.

These innovations represent a quantum leap towards achieving guidance systems which can run with zero maintenance in most applications, so it was logical that they should also be applied to other monorail guidance systems from INA.

The KUE and KUSE monorail guidance systems, with two and six rows of balls respectively, now include the lubricant reservoirs in the carriage as standard, which greatly increases the relubrication intervals of these guidance systems. For more demanding applications, these systems and the roller monorail system RUE are available with double lip wipers, lower sealing strips and long-term lubrication units. The roller monorail system RUE is also available with an additional sealing strip. This represents a fundamental upgrade of the INA range of monorail guidance systems, taking account of the drive towards maintenance-free operation whilst retaining high levels of load capacity, accuracy and rigidity. While the double lip wiper component and the long-term lubrication unit obviously increase the overall length of the carriage, the design envelope and mounting dimensions are otherwise unaffected. In the unlikely event that relubrication is required in critical operating conditions, even where these measures are used, they still represent a significant and beneficial increase in the relubrication intervals. In the majority of applications, however, the use of these innovative modular components to increase lubricant volumes and prevent the ingress of contamination should allow long-term, maintenance-free operation right up to the limit of the system’s fatigue life.

Further information on the INA range of maintenance-free monorails is contained in INA publication MAI 61.

• INA Bearing Company Ltd
  Forge Lane,
  Minworth,
  Sutton Coldfield,
  West Midlands B76 1AP.

• Telephone: 0121 351 3833
  Fax: 0121 351 7686.
• Web:www.ina.co.uk

< p class="received">June 2000