Page 296 - The Tribology Handbook

Soft piston seals B27

Table 27.2 Seals derived from basic types Table 27.3 Special seals
~~
Double-acting, one-piece, narrow width, Material
but preswre can be trapped between
lips and seal may jam. Needs Rubber
composire piston
Dynamic seal on piston

Similar, but no pressure trap and can be
fitted to one-piece piston
‘\“‘ Register between body Polyethylene
sections
Static seal in body
sections
Dynamic seal on piston
Derived from ‘0’ ring. Less tendency to
roll. Improved and multiple sealing
surfaces. Sealing forces reduced and Piston head seal Polyethylene
parting line flash removed from
working surface

Multiple sealing lips to obviate leakage
due to curl
SPRING Fits ‘0’ ring groove. Usually
Use internally or F’TFE
externally. Suitable for
_. -. .
rotational movement.
~
e~
‘W’ section. Good for hydraulic
applications and high pressures. Can
be used internally or externally

Table 27.4 Mating surface materials
Materials ryPe Finish Remarks

0.6 pm max. 0.2 to 0.4 pm 0.2 pm rnax. 0.05 to
(8 to 16 pin) preferred 0.1 prn (2 to 4 ,pin)
preferred
Brass As drawn Best untreated materials. Improve
J with use.

Copper As drawn J High cost.

Aluminium As drawn J Liable to SCUE and corrode.
alloy Low cost
Polished J

Anodised / Short life
Hard / Abrasive, therefore polish
anodised
J Low cost.
Mild steel As drawn Corrodes.

Honed Corrodes readily
Hard chrome J Very abrasive, polish before and
plated after plating. High cost.
d
Ground Used mostly for piston rods
~~
Stainless steel Ground J
Notes: Anodising and plating can be porous to air causing apparent seal leakage. The finish on the seal housing can be 0.8 pm. Use rust
prevention treatment for mild steel in storage.
B27.2