Bearings and Bearing Units with Solid Oil
In most applications, ordinary greases and lubricating oils will provide satisfactory lubrication to the bearing giving it an acceptable service life. However, there may be cases where lack of accessibility means that relubrication is virtually impossible, or where very good contaminant exclusion is required. Solid Oil - the third choice of lubrication - may be the answer, as it provides "lubrication for life" and good sealing.
Solid Oil has been very beneficial in outdoor lifting equipment, cranes and traverses, and in vertical shaft arrangements or where bearing arrangements cannot be reached for relubrication.
Bearings and bearing units with Solid Oil
Most SKF ball and roller bearings as well as bearing units (fig 1) can be supplied with Solid Oil and are identified by the designation suffix W64.
Bearings fitted with large-volume cages made of polyamide or machined brass are less suitable for Solid Oil. This also is the case with CARB toroidal roller bearings, which will lose their axial displacement properties when filled with Solid Oil.
Features of Solid Oil
Solid Oil consists of a polymer matrix, which is saturated with lubricating oil.
The polymer material has a structure with millions of micro-pores, which hold the lubricating oil. The pores are so small that the oil is retained in the material by surface tension. Oil represents an average of 70% by weight of the material.
The oil used as standard is very high quality synthetic oil, which meets the needs of most applications.
The oil-filled polymer material is moulded into the bearing. A very narrow gap will form around the rolling elements and raceways during the moulding process, enabling the bearing components to rotate freely. The oil, which seeps into the gap, provides good lubrication for the bearing right from the start. Solid Oil completely fills the internal space in a bearing and encapsulates the cage and rolling elements. Solid Oil uses the cage as a reinforcement element and rotates with it.
Solid Oil keeps the oil in position and brings more oil to the bearing than grease. A metallic surface sliding against Solid Oil is provided with an even and consistent oil film. A moderate increase in temperature causes oil to be pushed towards the surface of the polymer matrix, as the thermal expansion of the oil is greater than that of the polymer matrix. The viscosity of the oil also decreases with increasing temperature. When the bearing stops running, the polymer matrix reabsorbs excess oil.
In addition, Solid Oil is environmentally friendly and keeps contaminants out of the bearing, even without seals (fig 2). However, for those applications where very good contamination exclusion is needed, the use of bearings with Solid Oil and integral contact seals is recommended. But in all cases maintenance will be unnecessary because no relubrication is needed.
Dimensions, tolerances, internal clearance
Dimensions, tolerances and internal clearance of bearings or units with Solid Oil are the same as for the corresponding standard products.
Load carrying capacity
- Deep groove ball bearings
- Angular contact ball bearings, single row
- Angular contact ball bearings, double row
- Self-aligning ball bearings
- Cylindrical roller bearings
- Needle roller bearings
- Tapered roller bearings
- Spherical roller bearings
- Thrust ball bearings
The basic dynamic and static load ratings for the Solid Oil bearings are the same as for the corresponding standard bearings.
To achieve satisfactory operation, bearings or units with Solid Oil, like all bearings or units, must always be subjected to a given minimum load, which should be slightly higher than for the standard bearings or units. The recommendations for calculating the requisite minimum loads for the different standard bearing types are provided in the text preceding each table section.
An indication of the limiting speeds for bearings with Solid Oil is provided in table 1 by the speed factor
A = n dm
A = speed factor mm/min
n = rotational speed, r/min
dm = bearing mean diameter
= 0,5 (d + D), mm
The speed limits indicated by the factor A apply to open (unsealed) bearings. For bearings with integral seals 80% of the quoted values should be used.
It is important to remember that the higher the speed, the higher the operating temperature. It may therefore be necessary to limit the bearing speed for high temperature operation so that the temperature limit for the Solid Oil is not exceeded.
Generally, when bearings with Solid Oil are to operate under extreme conditions, it is advisable to contact the SKF application engineering service for advice and support.
The standard oil normally used for Solid Oil is a very high quality synthetic oil. Its important properties are listed in table 2.
Oils having other viscosities can also be used successfully, e.g. special oils for the food industry, heavily loaded or low temperature applications etc. Additives, such as rust inhibitors, can be added to Solid Oil to provide extra protection.
Before deciding upon oil type and ordering, please consult the SKF application engineering service.