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Plummer block seals
The following is an extract from the SKF catalogue, edited for this Handbook.
A marked improvement compared with earlier plummer blocks is that different types of seal can be used. The standard seals supplied by SKF are 'V'-ring and felt seals. They are delivered in special packages together with the housings. Fitting is very simple.
SKF bearing housings are always supplied complete with seals comprising 'V'-ring seals, felt seals (felt strips unless otherwise stated) or labyrinth seals.
'V'-ring seals are suitable for peripheral speeds of up to 12 m/s and operating temperatures of -40 to +100 deg. C. Felt seals are normally employed for peripheral speeds of up to 4 m/s and temperatures of up to + 100 deg. C. Before using felt strips, they should be soaked in hot oil for a few minutes. Labyrinth seals are universally applicable and not subject to wear.
The different seal types are outlined below :-
i. 'V'-ring seals
The 'V'-ring, which is of synthetic rubber, has a thin sealing lip, which functions in an axial direction. The ring also acts as a flinger as it rotates with the shaft.
This type of seal can be used with both grease and oil lubrication and is extremely effective under most operating conditions including high speeds.
The 'V'-rings in SNA plummer blocks seal against sheet metal washers with a rust preventive coating and placed in the grooves of the housing.
Each washer has a rubber lip bonded around its periphery and which bears against the housing. However, in plummer blocks SNA 205 to SNA 218 the 'V'-rings seal directly against the housing; in this case the side faces of the housings are machined.
SNA plummer blocks with 'V'-ring seals are given the suffix TA, for example SNA 505 TA.
The 'V'-ring seals consist of a 'V'-ring (1) and a sheet steel washer (2), which has been treated to prevent corrosion.
The 'V'-ring is mounted on the shaft (3) and seals against the washer, which is mounted in a groove (4) in the plummer block housing (5).
The washer has a bonded rubber lip and seals against the housing.
For exacting operating conditions, the 'V'-ring and felt seals of housings SNA 505 to SNA 518 and SNA 605 to SNA 615 may be supplemented by a light alloy collar (6).
The collar prevents the seals from becoming damaged and also enhances their sealing effect. The bore diameter tolerance is H10. The collar is designated TSNA B, e.g.: TSNA505B.
ii. Felt seals
The felt seal is a simple but adequate seal which can be used with grease lubrication and at peripheral speeds of up to some 4m/s.
Plummer blocks of series SNA 5 and SNA 6 are obtainable with split felt seals consisting of oiled felt incorporated in a light alloy ring in two pieces. These are pressed into the housing grooves after first inserting rubber 'O'-rings, which serve both as an effective seal between the housing and the light alloy ring and also to prevent this from rotating.
Plummer blocks SNA 205 to SNA 218 may also be supplied with felt seals but they comprise loose felt strips that are fitted directly in the grooves, i.e. they have no metal backing.
SNA plummer blocks with felt seals are given the suffix TO, for sample SNA 505 TO.
iii. Labyrinth seals
The labyrinth seal type TS shown below, is recommended in cases where SKF standard seals cannot be used for one reason or another, for instance if they do not match the diameter of the shaft.
Depending on the radial space available for the collar, the (a) or (b) design should be chosen (refer to table below for dimensions) :-
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Design 'A' |
Design 'B' |
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Type 'TS'- Narrow Collar |
Type 'TS' - Wider Collar |
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Table showing dimensions for sealing collars for 'special' seals type 'A' and 'B'.
