Page 247 - The Tribology Handbook

B17 Piston rings

NON METALLIC PISTON RINGS

Metallic piston rings require lubrication for satisfactory applications, piston rings can be made from self-
operation. There are, however, many applications where lubricating materials. These materials can also be used in
lubricants would be considered a contaminant or even a lubricated applications where there is a risk of lubricant
fire hazard, e.g. in food-processing equipment. For these breakdown.

Ring materials
Table 17.5 Typical properties of ring materials

Tensile strength Typical coef$cients
Malarial MN/~~ SpeciJic gravity of expansion x 1 O-~/OC
Carbon-filled PTFE 10 2.05 55
Glass-filled PTFE 17 2.26 80

GraphitelMoS2 filled PTFE 20 2.20 115
Bronze-filled PTFE 13 3.90 I18
Resin-bonded PTFE 29 1.75 30
Resin-bonded fabric 110 1.36

Carbon 43 1.8 43
Resin-bonded carbon 20 1.9 20
* Material is anisotropic, thus the lower expansion is parallel to, and the alternative figure is normal to, the plane of pressing.

Table 17.6 Suggested operating conditions for various materials

Material
Terminal Maximum Maximum Average
pressure speed temp. coejjicient humidiQ Minimal
Matrix Filler of friction p,p,m, lubrication
bars mls "C
(4)
PTFE Carbon 200 6.0 250 0.1/0.15 3 Very good
Glass 200 6.0 200 0.1/0.15 3 Very good
~ ~ ~~
Graphite/MoS? 200 6.0 200 0.12/0.18 3 Very good
Bronze 100 4.0 200 0.15/0.2 40 Good
Resin-bonded PTFE 200 4.0 200 0.15 10 Very good
~ ~~
Resin-bonded fabric 100 3.0 150 0.15/0.2 40 Poor
Carbon 60 3.8 350 0.2/0.25 40 Poor
Resin-bonded carbon 100 4.5 180 0.2 40 Poor

Ring design

Table 17.7 Preferred number of rings
~~ ~~~~~~
Differential pressure bars 0-9 10-14 15-24 25-29 30-49 50-99 100-200
Minimum number of nngs 2 3 4 5 6 7 8
B17.6