Industrial seal self study guide - SKF.com

SEAL DESIGN GROUPS (cont.)
“OLD” DESIGN
“NEW DESIGN”
Older “clamp-type” seal (left) has
been replaced by newer hydrodynamic
Waveseal (right) (fig. 3qq).
General purpose design for lubricated
media and moderate pressure and
surface speeds (fig. 3rr).
Old vs. New Seal Designs
Following the “original” leather strap seals, the first engineered
designs were known as “assembled” or “clamp-type” seals. They were
assembled by laying two sealing elements and three metal spacer rings
into an outer shell and clamping these components together. They
were wide and sturdy in appearance, and tended to apply high lip
pressure to the shaft, creating shaft wear. A garter spring was placed
against the primary or retention element. The sealing lips were usually
trimmed to size, using a knife.
In today’s designs, the sealing element is molded to size, and
permanently bonded to a metal case (fig 3qq). In modern spring
loaded molded seals, a garter spring is snapped into a mold-formed
groove in the sealing member. Today’s seals are narrower, lighter
and less sturdy in appearance, but their designs give them uniform
compressive sealing force. Only a thin band of lip material rubs against
the shaft so they can operate at higher speeds with less friction.
PTFE seals
SKF PTFE seals (fig. 3rr and fig. 3ss) are assembled or machined,
made-to-order radial shaft seals based on PTFE (Teflon ® or
polytetrafluoroethylene). This thermoplastic material has properties
that exceed the capabilities of rubber compounds. PTFE seals can
accept high surface speeds, pressure and dry running conditions and
have high wear resistance and service life. Their temperature range
is very wide and they resist attack by nearly all acids, solvents and
chemical agents. They can be made for variety of inch or metric sizes
from small to large diameter, often without any tooling charge. PTFE
seals generally require a high quality shaft finish and hardness, and
are engineered to meet specific application conditions.
Pressure design for service to 5
psi (35 bar). Variations for vacuum
and high shaft speeds (fig. 3ss).
28