Date post: | 14-Apr-2018 |
Category: |
Documents |
Upload: | binaywatch |
View: | 219 times |
Download: | 0 times |
7/27/2019 scan0050r.pdf
http://slidepdf.com/reader/full/scan0050rpdf 1/1
DURA SEA L M A NUA L / SECT ION III / PA GE 6
SECTION 111.2
SECONDARY SEAL MATERIALS
Secondary seals applied to mechanical
sealsare defined more specifically asshaft pack-
ing and insert mounting. Because they are static
and are called upon to seal imperfect surfaces,
secondary seals must possessa degree of resili-
ency which will allow them to "seat" perfectly
against adjacent surfaces. The most elastic or
resilient of all secondary seals are elastomers
which Durametallic applies in the configuration
of "0" rings. However, the temperature and
chemical resistance of elastomeric materials
are often exceeded, thus requiring the use of
other lessresilient materials. Becausethese othermaterials lack the elasticity of elastomers, they
assumeconfigurations that tend to compensate
for their limited resiliency. The purpose of this
sub-section is to discuss the three types of sec-
ondary sealsoffered by Durametallic.
11 I.2 .1 E L AS TO MER " 0" R ING S
It has already been pointed out that elas-
tomers, asused for secondary seals by Durame-
tallic, assume the configuration of "0" rings.
Figure III-C illustrates the application of elasto-
mer "0" rings as shaft packing and insert
mounting.
F IG . I I I - C " 0 " R IN G S E C O N D A R Y S E A L S
BUNA N (NITRILE)
This material, often referred to as Nitrile,
is a copolymer of butadiene and acrylonitrile.
Buna N hasan excellent resistance to petroleum
products, also finding wide acceptance in water
applications.
Buna N can be exposed to temperatures
ranging from -40°F to +225°F (-40°C to
+107°C).
Inherently Buna N Does not possess good
resistance to ozone, sunlight, or weather. There-
fore, spareBuna N"0" rings should not be stored
in direct sunlight or adjacent to electrical equip-
ment that may generate ozone.
NEOPRENE
Neoprene, correctly called Chloroprene
rubber, was among the earliest of the synthetic
rubbers available to seal manufacturers. It con-
tinues to be used for refrigerants; such as, freon
and ammonia, and other mild services. Like
Buna N, Neoprene can be subjected to tempera-
turesfrom -40°Fto +225°F (-40°Cto +107°C).
BUTYL
This is an all petroleum product produced
by copolymerizing isobutylene and isoprene.
Butyl rubber will resist the deteriorating
effects of many mild liquids, such as MEK and
acetone, but should not be used in petroleum
oils. Its temperature range is -40°F to +225°F
(-40°C to +1078C).
SILICONE RUBBER
Silicone elastomers are made from silicone,
oxygen, hydrogen, and carbon. They usually dis-
play poor tensi Ie strength, tear, and abrasion
resistance.
Silicone "0" rings are not recommended
for use in most petroleum fluids or ketones.
They can be successfully applied to temperatures
ranging from -80°F to +4000F (-62°C to
+204°C).