Engineering Competence

Bearing housing family extended with model suitable for oil lubrication

Creating a new standard housing for oil-lubricated applications has resulted in the SONL housing – a new member of the SKF SNL high-performance-class housing family. This latest addition is a modern bearing housing designed specially for oil lubrication and for today’s demands for simplicity, function and total economy.

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Creating a new standard housing for oil-lubricated applications has resulted in the SONL housing – a new member of the SKF SNL high-performance-class housing family. This latest addition is a modern bearing housing designed specially for oil lubrication and for today’s demands for simplicity, function and total economy.

Oil lubrication has growthpotential as an alternative for grease under certain conditions, though it does tend to require more care in setting up and running than grease-lubricated systems. Oils generally tend to be more uniform in their characteristics than greases, and the choice of oil is based on its operating viscosity, this being dependent on bearing size, rotational speeds and loads as well as the operating temperature.

The SONL housing has been designed to overcome the inherent disadvantages associated with oil lubrication, such as oil bath splashing and difficult sealing of the side covers, resulting in a large number of components and the need for different executions, depending on the design of the arrangement. The housing has been developed following customer requirements for a simple economic design that has good performance. The result is a modern split housing consisting of just two halves, top and bottom. It is easy and convenient to assemble. In addition, there is no need to consider whether the housing will be used for a bearing in the locating or non-locating position or whether it will be for a through shaft or at the end of the shaft. The same housing can be used in every situation.

The new SONL housing is characterized by an excellent oil lubrication system and incorporates a design for effective heat removal, enabling high bearing speeds such as those encountered in high-speed industrial fans operating in difficult and often hot environments.

Successful lubricationis one of the key elements for bearing systems; the oil needs to be delivered to the bearing in the right quantities, continuously, without the risk of overheating or leakage. Supplying too much oil can result in an excessive churning action, leading to unwanted heat generation. In the SONL housing, the maximum oil-bath level is lower than the bearing rolling elements in the lowest position. This simply means that there is no direct contact between the rolling elements and the oil reservoir. SONL housings make use of the simple principle, and proven method, of an oil pick-up ring. The ring hangs loosely next to the bearing; when the shaft turns, the ring turns with it. The ring picks-up the oil from the oil reservoir and brings it directly to the bearing, no matter what the dimensions of the shaft are, or how fast it’s turning. Wear has never been observed where the pick-up ring contacts its seating.

Another important feature of the SONL housing is its deep reservoir, which holds a large volume of oil. This results in a lower oil bath temperature, but it also contributes to better heat exchange. Lower oil bath temperature means increased viscosity and consequently longer bearing service life.

The housing also has an oil level indicator on the bottom half of the housing, and this helps in establishing the correct amount of oil while the housing is open.

Also, if needed, a cooling element can be incorporated into the housing for additional cooling in difficult operating conditions such as very high speed, heavy loads or environments with high ambient temperatures.

SONL housings can also be equipped with an oil circulation system. In this case the oil pick-up ring is not required. Instead, oil pipes are connected to the holes on the top of the housing for the oil inlet and on the holes on the bottom half for the oil outlet. In applications where a CARB® bearing is used in conjunction with an oil circulating system, SKF supplies a variant of the SONL housing designated with the suffix RA.

Bearing mountingand housing assembling are operations that must be properly carried out in order to provide correct bearing performance. The simplicity of the SONL design enables mounting and assembly to be effected in a logical and time-saving manner. The housing has a perpendicular base to facilitate alignment. Cast markings indicate the centre of the bearing, thus eliminating the need to measure and score the housing. Cap bolts between the housing halves are loosened on delivery, so time is saved in opening the housing. The SONL housing is designed to cut the number of potential faults associ-ated with assembly to an absolute minimum. The old problem of first putting the side covers onto the shaft is gone. Both the side cover gasket and cover bolts that had to be tightened to the right torque are gone. The split housing design has the side covers integrated into the housing.

Sealing is an important aspect in any housing design. Between the housing and the shaft is a very reliable labyrinth seal. In tough laboratory testing and real-life applications it has proven extremely tight. The oil stays in and the dirt is kept out, thus preventing oil contamination and potential environmental damage through oil leakage. As the SONL housing has the side covers integrated with the top and bottom halves, the risk of leakage through covers does not exist.

The SONL bearinghousing is designed on the building-block principle. One single basic housing design is suitable for all executions. It is suitable for self-aligning ball bearings, spherical roller bearings and CARB toroidal roller bearings; for bearings with direct mounting on a cylindrical seating or onto a sleeve on a cylindrical seating; for bearings in the locating or non-locating position; and for mounting on through shafts or at the end of a shaft. The SONL housing is designed for oil bath lubrication, but the standard housing can also be used for oil circulating lubrication, in case of CARB bearings, with a small modification.

Overall, the SONL housing is an important addition to the SKF family, as it is intended to give those applications requiring oil lubrication the same level of performance and security of operation that SKF has established for grease-lubricated systems.

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