SNL housings in the 30, 31 and 32 series with labyrinth or taconite seals are intended for grease lubrication. For oil lubrication, housings with oil seals (→ Housings for oil lubrication
The lubricant should be selected based on the operating conditions of the bearing. For additional information, refer to Lubricant selection
Initial grease fill
If no other requirements exist, the free space in the bearing should be completely filled with grease and the free space in the housing should be filled to 20 to 40% of its volume. A 40% grease fill is required when bearings have to be relubricated from the side, while a 20% grease fill is used when bearings are relubricated via the outer ring.
The housing base has markings to show the height of a 40% grease fill (fig. 1
). For highly contaminated environments and slow speeds, fill the housing to 70–80%. For best protection against contaminants, use the SKF Three-Barrier Solution
. For additional information, contact the SKF application engineering service.
Quantites for 20 and 40% grease fills are listed in table 1
. The values are valid for a typical lithium grease (about 0,95 g/cm3
). They include the grease for the bearing, but not the grease to fill the seals. For sealed bearings, the values have to be adjusted.
In most applications, the initial grease fill will adequately lubricate the bearing until the grease is exchanged during the next planned maintenance interval.
SNL plummer block housings enable relubrication of the incorporated bearings and seals. There are three drilled and tapped holes for an AH 1/8-27 PTF grease fitting: two in the cap (one centred and one offset), and one in the base. Each hole is sealed at delivery with a threaded plug.
Dimples cast into the top of the housing cap indicate alternative positions where holes can be drilled and tapped to accommodate a grease fitting. The two dimples on the outer sides of the central ridge indicate the position for lubrication holes for the seals.
The following items are supplied with each housing:
a grease fitting, designation AH 1/8-27 PTF, with a plastic cover (fitting protector)
a grease fitting, designation M1 G 1/8
an adapter, designation LAPN 1/8
The adapter transforms the 1/8-27 NPSF thread to a G 1/4, which enables the use of grease lubricators such as SKF MultiPoint.
Relubrication via the outer ring
The hole in the centre of the cap or the hole in the base should be used to relubricate spherical roller bearings with a relubrication feature (a lubrication groove and holes in the outer ring) (fig. 2
). When applying grease via the relubrication feature, the shaft should be rotating. Narrow bearings (dimension series 13 and 22) in the locating position can be axially displaced, so that the relubrication groove in the bearing does not line up with the relubrication hole in the housing cap. Make sure the bearing is sufficiently centred when relubricating.
Relubrication from the side
When relubricating from the side, which is typically necessary for CARB toroidal roller bearings, the offset hole in the housing should be used (fig. 3).
When bearings mounted on an adapter sleeve have to be relubricated from the side, the grease should be introduced from the side opposite the lock nut.
When bearings mounted at the end of a shaft have to be relubricated from the side, the grease should be applied at the point closest to the end cover.
Grease escape holes
If frequent relubrication is required, SKF recommends having grease escape holes (fig. 4
). Dimensions can be found in table 2
. SNL housings supplied with grease escape holes are identified by the suffix V, e.g. SNL 3134 V.
SNL housings in the 30, 31 and 32 series can be used in applications where there are relatively high speeds and the bearings are lubricated via an oil bath or circulating oil lubrication system.
The housings must be modified to accommodate one of the following oil seals:
Recommended oil levels can be found in:
table 3 for SNL housings in the 30 series
table 4 for SNL housings in the 31 series
table 5 for SNL housings in the 32 series
Housings modified for oil lubrication are not stock items. Check availability prior to ordering.