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SONL plummer (pillow) block housings are designed for two methods of oil lubrication:

  • oil bath lubrication with a pick-up ring
  • circulating oil
The lubricant should be selected based on the operating conditions of the bearing. For additional information, refer to Lubricant selection.

Oil bath lubrication with a pick-up ring

Oil bath lubrication with a pick-up ring is typically used with SONL housings (fig. 1). It provides a uniform supply of lubricant to the bearing.
This oil lubrication method uses a ring that hangs loosely from the labyrinth seal shaft sleeve on one side of the bearing. It hangs deep into the oil reservoir in the bottom half of the housing. As the shaft rotates, the ring follows, picking up oil from the sump and bringing it to a collecting trough. The oil then flows through the bearing and back into the oil sump.
In the fifty years that this lubrication method has been used, there has not been any record of wear where the ring contacts its seat on the labyrinth seal shaft sleeve – regardless of the shaft dimensions, or speed of the application.
Oil quantities

Housings should be filled with the recommended oil quantities listed in table 1. Markings on the inside of the housing base and on the oil level gauge indicate the correct oil level. To avoid leakage, do not exceed the recommended oil level. The oil pick-up ring enables a wide range between maximum and minimum oil levels. This results in a correspondingly long period between refills or oil changes.

The minimum and maximum levels indicated on the oil level gauge apply to standstill. The oil level may drop during operation and may vary even more during start-up. If oil is replenished during operation, keep the level 5 mm below the maximum mark.

Precaution after machine stops

Before start-up, the oil level should be filled to the maximum mark on the oil level gauge. This is even more important after longer machine stops to avoid the possibility of dry-running the bearing until the oil pick-up ring delivers a sufficient amount of lubricant.

After shorter machine stops, a sufficient amount of oil remains in the oil sump and in the bearing to provide lubricant during start-up.

Magnetic plugs
Each seal kit contains a magnetic plug. The plug can be fitted in one of the oil outlet holes in the housing base. The plug attracts metal contaminants in the oil, to extend bearing service life.
Special oil pick-up ring for use on shafts with electromagnetic clutches
If shafts with electromagnetic clutches are to be supported in SONL housings, the standard steel oil pick-up ring must be replaced by a brass ring (GH-TSO ...-.../MB). Appropriate brass rings are listed in table 2.
Oil cooling tubes

In high temperature applications, where an oil pick-up ring is used, auxiliary cooling tubes should be installed (fig. 2). They use water, which has to be provided via an external system, to cool the oil in the housing. The pressure of the cooling medium should not exceed 4 bar.

Oil cooling tubes are available in different sizes (table 3). Depending on the need, one or two cooling tubes can be installed via the oil outlet holes in the housing base. Detailed mounting instructions are provided with the products.

Oil cooling tubes are identified by the basic designation AVA-0001 followed by a size identification, e.g. AVA-0001/3.

Oil outlets
Tapped holes in the housing base that are not used for the oil level gauge or cooling tubes can be used as oil outlets.

Circulating oil lubrication systems

Circulating oil lubrication systems are generally preferred when high speeds generate an excessive amount of heat, or when there are high ambient temperatures. For this lubrication method, the oil pick-up ring should not be used and the oil level gauge is not needed.
A circulating oil lubrication system typically has supply lines attached to the housing cap and drain lines attached to the base (fig. 3). Circulation is normally produced with the aid of a pump. After the oil has passed through the bearing, it drains from the housing and flows into a tank. It is filtered and, if required, cooled before being returned to the housing. Proper filtering and cooling of the oil are important factors for bearing and oil service life, and can provide improved machinery performance as well as cost savings.
SKF supplies different standard solutions for circulating oil lubrication systems. For smaller systems, e.g. 1–2 fans or pumps, the SM-100 Oil Circulating Unit is available. For larger systems, SKF Flowline is available.
Relevant abutment dimensions for connecting a circulating oil lubrication system to an SONL housing are listed in table 4.
Using a circulating oil lubrication system with spherical roller bearings

SONL housings have two tapped holes in the cap that can be used as oil inlets. The hole in the centre of the cap should be used to lubricate spherical roller bearings with a relubrication feature (a lubrication groove and holes in the outer ring).

The housing base has four tapped holes that can be used as oil outlets.

Using a circulating oil lubrication system with CARB and self-aligning ball bearings

In a circulating oil lubrication system, CARB toroidal roller bearings and self-aligning ball bearings, which are relubricated from the side, require another design compared to spherical roller bearings, to allow the oil to pass through the bearings. Therefore, SONL housings with the designation suffix RA (→ Housings for circulating oil lubrication systems) are recommended.

SONL .. RA housings have two tapped holes in the cap that can be used as oil inlets. For CARB toroidal roller and self-aligning ball bearings, always use the offset oil inlet hole in the housing cap, and two oil outlet holes on the opposite side of the housing, to make sure the oil has to pass through the bearing and to get enough outlet capacity.

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