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Specific considerations

Hydrostatic guide systems can be supplied in a maximum length of 3,000 mm standard and up to 5,900 mm by special request. Due to the pressurized nature of the carriages, joining guideway sections is not possible. In addition, carriages are matched to the rail and cannot be interchanged. The choke gaps are set based on the specific carriage and rail combination.

The oil feed pipe to the pressurized side of the carriage must have a larger diameter and be reduced down at the carriage input — so as to guarantee flow at the input side. Alternatively, in the return pipes, the resistance through the extraction pump must be uniform and as low as possible.

Once oil has left the carriage, the diameter of the pipe should expand to ensure that dynamic pressure in the extraction pipe does not exceed 0.2 bar. The hydraulic unit must also be fitted with a pressure switch linked to the machine's control system so that movement of the hydrostatic axis is permitted only when there is sufficient pressure.

Elastic double lip seals on the end faces and sealing strips on the carriage undersides protect against contamination and maintain the hydraulic oil in the carriage.

Interchangeability

Hybrid machine approaches are influencing decisions on the use of hydrostatic guide assemblies, as they allow manufacturers to more precisely define components (such as bearings) based on specific customer requirements. This maximizes flexibility in the selection of technologies appropriate to the specific application — including hydrostatic bearings where suitable.

The ultimate advantage is that these guides are interchangeable and comply with the same ISO/DIN mounting specifications for monorail guidance systems. This allows machine manufacturers to offer both options for the same machine platform.

For more information on Schaeffler Group HLE series hydrostatic compact linear guidance systems, call (803) 548-8500 or visit schaeffler.us.

Machining results: Hydrostatic versus conventional roller guides

In high-speed machining and, in particular, in high-precision grinding applications, hydrostatic bearings increase cutting capacities and speeds, and improve surface quality and machining accuracy. They also damp loads at the point where the load is applied to protect against vibration generated in machine tools by blade contact shocks, tool wear, regenerative effects, and other disruptive but common forces.

Because the latest hydrostatic guides fit DIN design envelopes and mounting dimensions for monorail guidance systems, they have identical geometrical mounting dimensions and profile outlines. This is a feature that allows engineers to supply several performance classes with one machine to cover various machining requirements. For example, standard guides can allow for perfect surface quality and accuracy in standard machining, or hydrostatic guides can be substituted to get an increased cutting rate, cutting depth, and tool life (while maintaining quality and accuracy) from the same machine.

The operating load in machine tools is similar to the standard monorail guidance system. This guidance system can support loads from all directions and moments about all axes — regardless of the direction of motion.