MRO Magazine

Feature

Sealing out bearing contamination

Bearing seals are critical when used in combination with grease lubrication because they help keep the grease free from contamination. Contamination that reaches grease is trapped and will continually wear on the bearing.


Bearing seals are critical when used in combination with grease lubrication because they help keep the grease free from contamination. Contamination that reaches grease is trapped and will continually wear on the bearing.

Most seals are designed to prevent contaminants from entering the bearing. Some seals are designed to allow some grease to escape from the bearing – or ‘weep’. With these types of seals, the weeping action allows the grease to carry some of the contaminants out of the bearing. The grease that escapes from the bearing helps lubricate the seal, and forms an additional barrier to contamination.

Equipment inspection and preparation

Before installing any Timken lip seal, equipment should be thoroughly inspected. Follow the specifications below for best results:

Shaft surface finish (roughness average or AA [arithmetic average]): With the exception of PS-1 (Model 61), all seals should have a surface finish within 0.25-0.50 µm (10-20 µin.).

For PS-1 (Model 61), the surface finish should be within 0.10-0.20 µm (4-8 µin.). The surface finish direction for all seals must be perpendicular to the shaft axis of rotation.

Housing bore surface finish, Ra (roughness average or AA [arithmetic average]): The surface finish of all seals must be 2.54 µm (100 µin.). The surface finish direction for all seals must be perpendicular to the shaft axis of rotation.

Shaft surface hardness, Rockwell C-scale: For all seals, with the exception of PS-1 (Model 61), the shaft contact surface should have a hardness between 30 and 40 Rockwell C. For PS-1 (Model 61), the surface hardness must be within 50-70 Rockwell C.

Additional specifications: Both the shaft and housing bore should include an edge relief (preferably an edge chamfer). Both the shaft and housing bore should be clear of any defects, such as spiral-machining marks, burrs, sharp edges, nicks, scratches and corrosion. 

Typically, the shaft has a wear groove created from previous seals. Make sure the new sealing lip does not seal in the same location.

When drive features such as keyways or splines are present, they must be covered using an installation tool similar to the one shown in Fig. 2, and using Installation Method D shown in Fig. 2d. If the use of a tool is prohibited by the size of the shaft, use one of the following options:

  • Polyethylene tape
  • Brass shim stock with smooth edges
  • Wooden plug with smooth edges.

Inspect the sealing lip for any signs of damage, such as cuts, indentations and nicks. Make sure that the spring (finger or garter type) is retained within the seal (bonded or assembled). Inspect the seal O.D., looking for any signs of damage, such as cuts (in rubber seals), indentations and nicks.

Installation methods

Solid seal installation: Install the seal(s) using one of the proper installation methods shown in Fig. 64. When using installation tooling, the diameter, or contact area, should not be more than 0.254-mm (0.010-in.) smaller than the bore diameter. If the use of an installation tool is prohibited by the size of the seal, then:

  • Rest a block of wood on the seal and use a mallet to drive the seal into position. Do not hit the seal directly with the mallet, as it may cause damage.
  • When using this method, follow a star pattern (as shown in Fig. 3 to avoid cocking of the seal.
  • Place the ends of the wooden block at positions 1 and 2 (as shown in Fig. 3.
  • Hit the centre of the board with the mallet.
  • Continue by rotating the wooden block to the appropriate positions (3 and 4, 5 and 6, 7 and 8), hitting the centre of the block with the mallet each time.
  • Repeat the pattern until the seal is properly seated in the housing bore. The seal is fully seated when the difference between the seal surface and the housing surface is 0.254 mm (0.010 in.).

Split seal installation

Note: This applies to ambient pressure/non-flooded applications only.

  • Apply a thin coat of lubricant to the seal lip and shaft.
  • Split the seal along the axis of rotation (shown in Fig. 4 and place the seal around the shaft.
  • Beginning with the split ends, insert the seal into the housing bore. Make sure the splits ends of the seal are touching.
  • Working downwards on both sides, continue inserting the seal into the housing bore, finishing at the bottom.
  • Once the seal is properly seated in the housing bore, it should protrude from the housing surface by 0.381 mm (0.015 in.), as shown in Fig. 5. The 0.015 in. protrusion is built into the width of the seal. The depth of the bore housing should be machined to the seal width specified on the packaging.

Inspection

After installation, inspect the sealing areas for leaks, paying special attention to the area around the sealing lip and the O.D. Make sure that the sealing lip is not in the groove worn into the shaft from the previous seal.

Isolator installation

Before installing an isolator, all equipment should be inspected. First, disconnect all power to the machinery and follow standard safety procedures to avoid personal injury or equipment damage during installation.

Second, inspect the shaft and bore surfaces. The shaft finish should be better than 1.63 µm (64 µin.) with minimal lead, but a polished surface is not required. The bore surface should be 2.54 µm (125 µin.). Both the shaft and bore should have a chamfer or other edge relief to prevent the O-ring from shearing.

Third, check the shaft and bore for damage or imperfections. They should both be clear of burrs, nicks, indentations and any other defects. Clean all foreign debris from the area. Note that, in many cases, the previous seal may have worn a groove into the shaft. Make sure that the rotor O-ring of the new seal does not ride in this area.

Finally, if drive features such as keyways or splines are present on the shaft, they must be covered during installation. To do so, use an installation tool, polyethylene tape, brass shim stock with smooth edges or a wooden plug with smooth edges.

Seal preparation: Timken metallic and non-metallic bearing isolators are unitized, and any attempts to take them apart will not only cause seal damage, but will void the warranty on the product.

Before installation, inspect the O-ring’s O.D. and I.D., making sure they are free of any defects. Use the lubricant included with your isolator to lightly grease all the O-rings.

Installation: Using your hands only (no installation tool required) push the isolator evenly onto the shaft.

If your isolator has a drain port, rotate it to the 6 o’clock position. For isolators with an orientation slot on the O.D. of the stator, rotate it to the 12 o’clock position to ensure appropriate positioning of the drain port. Some non-metallic bearing isolators may be installed in any direction, and there is no need to position the seal. See Fig. 68 for clarification, or contact your sales representative if you require additional information.

Using your hands only (no installation tool required), push the isolator gently into the bore. If required, gently tap the isolator using a mallet. While flanged isolators are fully seated when the flange is flush against the housing, flangeless isolators can be installed at the bottom of the housing and are fully seated when they are flush with the bore face.

Post-installation

Inspection: After installation, inspect the sealing area for damage. Gently spin the shaft to make sure the rotor is working properly. Do not flood the isolator or block the expulsion ports, as these act
ions can cause seal damage and failure.

Removal: To remove an old isolator from your equipment, start from the back side of the seal and perform installation instructions in reverse. If access to the back side of the isolator is difficult, pry it from the housing a little at a time. Be careful not to damage the shaft or housing bore during seal removal. MRO

This article has been adapted from the Timken Industrial Bearing Maintenance Manual, a technical reference on bearing maintenance in industrial and other applications. For more information, use our online reader inquiry service at www.mromagazine.com/rsc.

Online Reader Inquiry No. 460