A sealing device has been well known which is interposed between a stationary side member such as a bearing unit and a rotary side member in order to prevent water and dust from entering in the wheel suspension of vehicle wheels. Several measures have been recently taken so as to realize fuel efficient vehicles and the reduction of rotary torque is sought for the bearing unit. A seal lip is provided so as to elastically and slidably contact a slinger fixedly fitted to the rotary side member of the sealing device. If the force of seal lip elastically and slidably contacting the slinger is made large, it is point out the friction of the slinger and the seal lip is increased to exert influence on the rotary torque and to inhibit low torque.
According to some prior arts, the slidably contacting face of the slinger with the seal lip is processed to reduce the friction with the seal lip so as to reduce the torque.
FIG. 7a and FIG. 7b diagrammatically show a partially enlarged sectional view of the prior art, namely a partially enlarged view of the slidably contacting face of the slinger and the seal lip. The reference numeral 70 in the figure shows a slinger fixedly fitted to the rotary side member and constituting a sealing device, 730 shows the slidably contacting face of the slinger and 750 shows an adhesive layer made of adhesive agent.
There are several ways for surface processing of the slidably contacting face 730 of the slinger 70. When edges are formed concave and convex by roughening the slidably contacting face 730 as shown in FIG. 7a, there arises such a problem that the slidably contacting seal lip is worn away.
When a tone wheel made of magnetic rubber is provided on the outer face of the slinger 70 and constitutes a magnetic encoder together with a magnetic sensor, the tone wheel is integrally attached to the slinger 70 with adhesive. In case of bonding, the tone wheel is attached after the slinger 70 is entirely soaked in adhesive, so that an adhesive layer 750 is formed on the slidably contacting face 730 even if the roughening process is executed on the slidably contacting face 730 as shown in FIG. 7b, thereby deteriorating the reduction effect of the rotary torque.
Japanese Patent Publication 2003-148626-A (Patent Citation 1) describes that the slidably contacting face of the slinger with the seal lip has a predetermined surface roughness, wherein concavity and convexity are transferred on the surface of the slinger when the slinger is rolled with a roll executed with concavo-concave treatment and the surface of the slinger is processed to be a predetermined surface roughness.
The Japanese Utility Model Publication 1991-43174-U1 (Patent Citation 2) discloses that the slidably contacting face of a slinger with a seal lip is processed in order to improve the sealing ability.
The patent citation 2 describes spherical objects having an appropriate grain size are shot on the slidably contacting face to obtain predetermined surface roughness.