Several years ago, Schaeffler's linear technology specialists from Homburg developed a re-lubrication and sealing component kit that contained a metering system for minimising lubricant consumption and sealing requirements, providing optimum sealing of the lubricant duct for the standard INA-branded roller monorail guidance systems. More recently, the company announced an interesting upgrade to its RUE-E range of linear recirculating roller bearings and guidance systems, essentially equipping these units with special lubricant metering valves, which provide precise doses of lubricant under all operating conditions, regardless of the guide's mounting position.
With conventional roller monorail guidance systems, the re-lubrication duct between the lubrication hole on the linear guide and the rolling elements can become empty, depending on the mounting position and operating conditions, so more lubricant is required during re-lubrication to ensure reliable operation. With centralised lubrication systems, only one specific dose is provided per impulse, which can lead to the lubricant arriving late at the rolling elements or even result in lubricant starvation. This problem is exacerbated when the guide is mounted vertically, often resulting in insufficient supply of lubricant to the upper rolling element rows. In extreme cases, this can cause damage to the rolling elements and raceway, leading to the complete failure of the linear system.
The O rings in a standard linear guidance system can now be replaced with the latest SMDS metering valves, a paper seal being placed between the end plate and the lubrication duct, to prevent lubricant leaking from the ends. According to Schaeffler UK’s linear product specialist, John Loonam, this configuration reduces lubricant consumption by more than 25% compared with more conventional designs. Only one valve per side and rolling element loop is required and one lubrication connector per carriage.
A key design feature of this novel upgrade is the special injection moulded saddle plate, which, combined with the various connection options for re-lubrication at the front, rear and side of the carriage end, ensures that lubricant is directed precisely at the rolling elements.
The SMDS development made its UK debut at the recent Machine Building show in Birmingham. At the same event, Schaeffler also showed a range of linear guidance systems and lubricants, which it has developed exclusively for the clean room market. It is perhaps surprising that determining the suitability of machine elements for clean room duties – essentially by measuring particle emissions – is not covered by international standards. Instead, it is up to individual manufacturers to test their products and classify them accordingly for such applications.
Schaeffler uses the services of independent research bodies such as the Fraunhofer Institute to measure particle emissions from its linear and rotary bearing products and help in the classification process. These analyses also include outgassing behaviour, ESD performance and mechanical efficiency. The metal parts of Schaeffler’s monorail guidance systems for clean room application can be made from corrosion resistant martensitic steel, while the use of special lubricants based on synthetic oils and polyurea thickener, such as Schaeffler’s Arcanol Clean M multi-purpose grease offers significantly lower particle emissions compared with standard greases.