Parker O-Ring Handbuch Seite 151

7. Applications
Compound Lubrication
DIN ISO 1629 with mineral
oil base
NBR 100
HNBR 150
HNBR 150
1)
FKM 200
1)
FKM Hiflour 200
6)
FFKM 200
6)
EPDM not compatible
VMQ 150
1)
FVMQ 175
1)
ECO 135
ACM 150
1)
CR 100
Table 7.11 Comparison of elastomers in a compatible contact medium and max.
allowable temperatures °C
at these temperatures lubricants degrade after a short time
1)
special compound
2)
high swelling at room temperature, hydrolysis at high temperatures
3)
medium to high swelling according to temperature
4)
in water/steam
5)
compound has a higher heat resistance, but at these temperatures lubricants
6)
degrade after a short time
7.14.2 Low Temperatures
When being cooled, rubber compounds lose their elasticity. At
very low temperatures they harden and have glasslike brittle-
ness, eventually shatterable if struck. As long as they are not me-
chanically disturbed they remain intact. Upon returning to normal
temperatures they regain their original properties; the condition
being fully reversable.
The low temperature flexibility of a compound can be slightly im-
proved if a contact medium causes swelling and softening. Sof-
tening can occur through dissolving of plasticiser.
Water Air
70 90
100 150
2)
150 150
130 200
2)
180 250
2)
230 320
2)
150 (180) 150
5)
100 200
100 175
50 135
- 150
3)
80 90
4)
151
According to the Medium Compatibility Table, silicone (S 604-70)
and fluorosilicone (L 677-70) are to be selected for low tempera-
ture applications. These compounds have poor wear resistant
properties and are recommended only for static applications.
Further elastomers with good cold flexibility are CR, EPDM and
special NBR compounds.
Tests for hardness, rebound and compression set can be used
(Fig 7.2) to compare and review the flexibility of O-rings at low
temperatures. There are many methods of testing the low tem-
perature flexibility of elastomers but only a few enable a practical
comparison with other applications. The TR
ASTM D 1329 (or ISO S 2921) have proved a realistic measure-
ment of cold flexibility. This involves 100% stretching of a speci-
men and its freezing in stretched condition. Then the specimen
is released at one end and the temperature is allowed to rise at a
controlled rate. Upon being warmed the elastomer begins to re-
turn to its original shape. When 90% of its elongation is reached,
the corresponding temperature is the TR
10% return of elasticity. Continuing the test, 50% equals TR
etc., see example in Fig. 7.3.Temperature at the TR
be taken for all elastomers to determine a minimum functional
temperature.
In practice a static seal may have a minimum functional tempera-
ture of about 15°C lower than the TR
designed gland.
tests carried out to
10
point. This means
10
,
50
point can
10
point assuming a correctly
10
O-Ring Handbook
Parker Hannifin GmbH
O-Ring Division Europe