Felt seals for bearings, shafts and oil retention

Why use a felt seal instead of a rubber lip seal?

A felt seal forgives what a rubber lip seal does not.

Felt seals need relatively little shaft pressure and keep a constant sealing pressure despite wear, end play, minor misalignment or an out-of-round shaft. The fibers also hold oil, so the seal lubricates the shaft it touches.

Rubber lip seals win when fluid is under pressure. Felt is the better choice for grease retention, dust exclusion and slow or intermittent shafts, where low friction and a little self-lubrication matter more than a pressure rating.

What types of felt seals do you make?

• Full ring seals: the classic felt ring seal, pressed into a bearing housing groove.
• Split C-rings: a felt seal ring cut through once, so it slips around a shaft without taking the assembly apart. Handy for maintenance kits.
• Wiper strips: clean slides, rods and guide rails as they move.
• Oil wicks: carry oil from a reservoir to a bushing by capillary action.

How does a felt seal fit a bearing housing?

A felt seal for a bearing housing is a full ring pressed into a groove in the housing bore or end cover. The groove squeezes the felt so its inner edge presses on the turning shaft. That keeps grease in the bearing and dust out, and the contact holds as the felt wears.

• Where they go: plummer (pillow) block housings and bearing end covers.
• Groove: many housings use a tapered felt ring groove to DIN 5419. Send the groove size, or the standard size, and we cut the ring to fit.
• Shaft size: give the shaft diameter where the seal sits, not at the bearing seat, if the two differ.
• Repairs in place: split C-rings work as felt seals for shafts that cannot be pulled out of the housing.

Which felt grade makes a good seal?

SAE F-1 is the default grade for a felt bearing seal. It is at least 95% wool, has the highest tensile strength in the SAE range and stays dense enough to keep contact as it wears. F-5 has the same wool content at lower weight and suits lighter duty.

Softer grades pack down on a turning shaft and open a gap. The SAE felt density and strength table shows how quickly strength drops above F-7.

How fast can a shaft turn against a felt seal?

For a plain felt ring seal in a bearing housing groove, keep the shaft surface speed at or below about 5m/s (980fpm).

That is the limit Koyo, the bearing maker, gives for felt seals in its sealing guide. Machine Design’s 2002 review of felt seals puts the usual working limit higher, at 2,000fpm (about 10m/s), and up to 4,000fpm in some designs. Design to the lower figure unless your own tests on the assembly support more.

To check a design, work out the speed at the seal: π × shaft diameter × rpm ÷ 60. A 50mm shaft at 1,500rpm runs at about 3.9m/s, inside the limit. Above that, a rubber lip seal is usually the better choice.

What temperature and fluids can felt seals handle?

SAE wool felt works from -80 to 200°F (-62 to 93°C). Wool tolerates mineral oil and grease well. For acids, bleaches or constant damp, needle-punched polyester felt is the safer choice: it resists organic acids, mildew and bleaches, and runs continuously at up to 300°F (149°C).

Condition	SAE wool felt	Polyester felt
Grease and mineral oil	Good, holds oil	Good
Acids, mildew	Poor	Good
Temperature	-62 to 93°C (-80 to 200°F)	Up to 149°C (300°F)

Flat seals that sit under a bolt rather than on a turning shaft are covered on the custom felt washers page. Grease delivery to gear teeth uses felt lubrication gears for rack drives instead.

Felt seal FAQ