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Lubricating oils

To lubricate super-precision bearings, high quality lubricating oils without EP additives are generally recommended. The requisite viscosity of the oil can be determined following the recommendations in Lubrication conditions - the viscosity ratio κ, and is essentially a function of bearing size, speed and operating temperature.
Calculations can be made with the Viscosity calculator.
With oil-air lubrication systems, many oil types are suitable. Oils with a viscosity of 40 to 100 mm2/s at 40 °C (105 °F) are typically used as are oils with EP additives which are preferable, especially for roller bearings. Oils with a viscosity of 10 to 15 mm2/s at 40 °C (105 °F) are typically used for oil jet lubrication, whereas oil mist lubrication systems typically use oils with a viscosity of 32 mm2/s at 40 °C (105 °F).
The intervals at which the oil should be changed when using an oil bath, circulating oil or oil jet lubrication system, depend mainly on the operating conditions and the quantity of oil involved. When oil drop, oil mist or oil-air lubrication systems are used, the lubricant is supplied to the bearings only once.
The intervals at which the oil should be changed when using the oil bath, circulating oil and oil jet methods, depend mainly on the operating conditions and the quantity of oil involved. When oil drop, oil mist or oil-air lubrication is used, the lubricant is "lost" and is therefore supplied to the bearings only once.

Oil cleanliness

Oil cleanliness, which affects bearing service life and performance, requires an effective sealing system. Even with effective seals, however, the condition of the oil should be monitored on a regular basis. This is particularly true for oil re-circulation systems where the ingress of coolants, cutting oils, and other liquid contaminants can alter the lubricating properties of the oil.
Oil cleanliness requirements can be described by the number of particles per millilitre of oil for different particle sizes. ISO 4406:1999 provides a coding system for the level of solid contaminants. The oil cleanliness requirements for high-precision applications like electro-spindles go beyond this coding. The maximum particle size should not exceed 5 μm. The acceptable contamination levels can be specified as an extrapolation of the contamination codes to
ISO 4406:1999 (diagram 1):
  • 10/7, for new spindles
  • 13/10, after long use (~ 2 000 hours)
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