SNLN 30 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 radially split and easy to mount.
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.
The permissible angular misalignment for seals mounted on shafts < 150 mm in diameter is approximately 1,5° and approximately 1° for larger shafts. The axial movement of the shaft relative to the housing is limited to ±1,5 mm.
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 (TSN .. C)Felt seals (fig. 3) are simple and effective. At circumferential speeds above 4 m/s, a small gap forms between the felt and shaft, transforming the contact seal into a non-contact, gap-type seal.
The characteristics and suitability of felt seals 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. 4), mounted on the shaft, form a multi-stage labyrinth seal with the housing seal grooves. Hollow, silicone rubber cords, 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 (TSN .. ND, TNF ..)For bearing arrangements that must operate under highly contaminated conditions, such as those encountered in mining, taconite heavy-duty seals, 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 labyrinth ring is solid but the main body of the seal is split.
SNLN 30 housings from size 3024 to 3032 accommodate taconite seals with a radial labyrinth (fig. 5). SNLN 30 housings from size 3034 to 3056 accommodate solid taconite seals with an axial labyrinth (fig. 6). Both 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 ±1,5 mm for shaft diameters ranging from 110 to 150 mm, ±2 mm for shaft diameters ranging from 160 to 200 mm, and ±4 mm for larger shaft diameters.
The characteristics and suitability of taconite heavy-duty seals are provided in table 1.
End covers (ASNH .., ETS ..)Housings at the end of a shaft should have an end cover that fits into the seal groove in the housing.
For housings from size 3024 to 3032, the end covers are made of plastic (fig. 7) and are suitable for operating temperatures from –40 to +110 °C (–40 to +230 °F). 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.
For housings from size 3034 to 3056, the end covers are made of grey cast iron (fig. 8) and are suitable for operating temperatures from –50 to +200 °C (–60 to +390 °F). They are inserted, together with a hollow silicone rubber cord, in the housing seal groove.
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 3.