Page 261 - The Tribology Handbook

B2O Sealing against dirt and dust

Table 20.2 Sealing of rotary parts

Method Description Comments
~ ~~
Type A Metallic rubbing rings mounted between Very high level of protection and
rubber ‘0’ rings, spring diaphragms or durability, wet or dry. Satisfactory when
IF SHAFT ROTATES OUTER HOUSING LIP MUST rubber housings. submerged in sea water to at least 3 m.
ENVELOP INNER HOUYING TO ACT AS THROWER
Contact faces 2-3 mm radial width. Rubbing speeds of up to at least 3 m/s,
INNER HOUSING Surface finish not greater than 3 pm R, but essential to use oil lubrication. If
DIAPIIRAGMS Axial pressure between contact faces rubbing speed is restricted to not more
140-210 kN/m2 (2C-30 Ibf/in2). than 0.1 m/s grease may be used.
Hardness of contact faces not less than Standard parts available up to 250 mm
800 VPN dia.
Rings of special size readily obtainable as
r SHAFT METALLIC Material of rubbing rings: Highly abrasion and corrosion resistant.
precision castings which require only the
contact faces to be ground and finished
RUBBING
RINGS
2nd choice (a) Highly alloyed cast
OIL
L LEVEL AT ABOUT Q OF BEARIM~ . 1st choice Stellite or similar Use for worst conditions of operation
-.
irons (proprietary mixes)
(b) Hard facings applied to Much less corrosion resistant
rings of cheaper steels
Type B Similar to Type A, only one rubbing ring Occupies less volume but level of
CONTACT FACES AS FOR TYPE A flexibly mounted protection as for Type A. Requires more
careful mounting and fitting of fixed
1 RUBBER ‘0’ RING OR SPRING DIAPHRAGM annular ring

ANNULAR RING SECURED WITH ADHESIVE
OR BY SOME MECHANICAL DEVICE
Type c Three garter seals arranged as oil retainer Level of protection much lower than either
and dust excluders, with either rubber Type A or B, but less costly. Standard
RUBBER GARTER SEAL
ARRANGED AS OIL RETAINER or leather sealing elements. The rubber seals more easily obtainable. Directions
lipped seal is for oil retention only, the in which lips of seals are mounted are
adjacent leather lipped seal prevents critical. Leather sealing elements are not
EASE NIPPLE FOR
TER SEALS ONLY contaminated grease from entering the abraded away so fast as rubber by dirt
bearing cavity and the outer leather seal and mud, and must be used for dirt
allows fresh grease to escape carrying excluders. Not suitable for total
contaminated material with it immersion in any depth longer than a
few minutes unless oil is replaced and
fresh grease is applied immediately after
coming out of water. Limiting speeds
are as for general practice when using
seals of this type. In worst environment
grease replenishment required daily.
Pump in until grease is seen to exude
from outer housing
LEATHER GARTER SEALS
Af?RANGED AS DIRT EXCLUDERS

B20.2