SNL plummer (pillow) block housings are available with different standard sealing solutions.
The housing size determines which sealing solutions can be used. Table 1 provides an overview of the characteristics and suitability of each sealing solution. The detailed information about each sealing solution should be used as a guideline, and does not substitute for testing a seal in its application.
Four-lip seals (TSN .. L)
Four-lip seals (fig. 1) replace the former double-lip seals (TSN .. G). When compared to double-lip seals, the new seals are more effective. They also generate less friction, which enables higher shaft speeds. Four-lip seals are horizontally split and easy to mount.
The permissible angular misalignment for seals mounted on shafts ≤ 100 mm in diameter is approximately 1° and approximately 0,5° for larger shafts.
The characteristics and suitability of four-lip seals are provided in table 1.
V-ring seals (TSN .. A)
V-ring seals (fig. 2) consist of a V-ring and a sheet steel sealing washer with a vulcanized rubber lip. The rubber lip fits into the seal groove in the housing. The washer is protected against corrosion.
V-rings can accommodate circumferential speeds up to 7 m/s. For circumferential speeds between 7 and 12 m/s, they should be located axially on the shaft. At speeds above 12 m/s, a support ring must be used to prevent the seal from lifting. Recommended dimensions for appropriate support rings for axial and radial location are provided in table 2. Housing sizes 205 to 211 and 306 to 314 cannot be used with a support ring and are therefore not suitable for V-ring seals at operating speeds above 7 m/s.
The permissible angular misalignment for V-ring seals is approximately 1,5° for a 50 mm shaft decreasing to approximately 1° for shaft diameters ≥ 150 mm.
The axial movement of the shaft relative to the housing is limited to ±1 mm for shaft diameters up to 65 mm, to approximately ±1,2 mm for shaft diameters up to 100 mm and to approximately ± 1,5 mm for larger shaft diameters.
For arrangements with a vertical shaft, the V-ring of the lower seal should be mounted inside the housing.
The characteristics and suitability of V-ring seals are provided in table 1.
Felt seals or strips
In applications where bearings are mounted on a plain shaft with an adapter sleeve, split felt ring seals are typically used.
If the bearings are to be installed on a stepped shaft with a cylindrical seat (housing sizes 205 to 218 inclusive), loose felt strips can be used. The strips are 170 mm in length. They should be cut to the correct length and soaked in hot oil for a few minutes prior to mounting. The required number of strips per housing (for both sides) is listed in the product tables for bearings on an adapter sleeve and for bearings with a cylindrical bore.
The characteristics and suitability of felt seals and strips are provided in table 1.
Labyrinth seals (TSN .. S)
For applications where there are high speeds or extreme temperatures, SKF recommends using labyrinth seals. Labyrinth rings (fig. 5), mounted on the shaft, form a multi-stage labyrinth seal with the housing seal grooves. Hollow, silicone rubber cords (2 x 4 mm), supplied with the rings, hold the rings in place on the shaft.
The characteristics and suitability of labyrinth seals are provided in table 1.
Taconite heavy-duty seals with a radial labyrinth
For bearing arrangements that must operate under highly contaminated conditions, such as those encountered in mining, taconite heavy-duty seals (fig. 6), which can be filled with grease, are recommended. Grease enhances the sealing effect and extends the service life of the seals.
Taconite heavy-duty seals are labyrinth seals combined with a V-ring seal. The inner ring of the labyrinth seal is solid but the outer ring is split. They can be relubricated via a grease fitting in the main body of the seal.
The axial movement of the shaft relative to the housing is limited to ±1 mm for shaft diameters up to 65 mm, approximately ±1,2 mm for shaft diameters ranging from 100 mm, and ±1,5 mm for larger shaft diameters.
The characteristics and suitability of taconite heavy-duty seals are provided in table 1.
End covers (ASNH)
Housings at the end of a shaft should have an end cover (fig. 7) that fits into the seal groove in the housing.
For applications where temperatures exceed 110 °C (230 °F), steel end covers should be used. These can be cut from sheet steel and placed in the seal groove. Use a hollow silicone rubber cord to hold the cover in place. Seal groove dimensions are provided in table 3.
The characteristics and suitability of end covers are provided in table 1.
Details of the permissible length of the shaft end are provided in table 4.