|
When selecting elastomeric seals for specific applications,
there are a number of important selection criteria including
the anticipated service conditions, the design and inspection
requirements for the particular application and material
specification and traceability.
The service conditions to be
considered include:
1. Fluid to be sealed, including any contaminants or
additives.
2. Temperature rang including minimum and maximum operating
conditions, as thermal cycling and potential excursions.
3. Pressure range-including minimum and maximum operating
range with on error range and compression/ decompression
rate if the pressure is high.
4. Vacuum application- including where the vacuum is
applied and whether it is cyclic.
5. Motion- either static or dynamic. If it is dynamic,
describe the motion.
The design requirements of
the particular sealing application are also critical
including:
1. Component geometry/ description, like O-ring, gasket,
diaphragm, etc.
2. Chemical medias affect on the seal
3. Desired service life. If it is a replacement for
a failed seal, which material was used before and why
did it fail.
4. Assembly considerations including lubricants, installed
stretch, etc.
5. Critical dimensions and tolerances, including groove
dimensions and machining tolerances.
It is important to consider
the inspection requirements including:
1. De fining inspection criteria
2. Determining the need for lot sampling
3. Setting acceptable quality levels (AQLs)
4. Indicating the critical sealing surface.
Material specification and
traceability are also critical for proper seal selection:
1. Define material specifications by the American Society
for Testing and Materials (ASTM). Society of Automotive
Engineers (SAE), military specification or other recognized
standards.
2. Discuss with your seal supplier the procedure for
specifying and certifying sealing materials.
3. Ask your supplier if compound changes may without
a customers knowledge and how to protect yourself from
it. Are hardness buttons, tensile bars or other test
specimens required for incoming material verification.
Cost versus Value:
When selecting materials for your particular sealing
application, the guiding principle should be value-in-use.
When evaluating seal performance, seal life and maintenance
costs must be included. A performance, seal made from
EPM may be appropriate for many general applications
where heat and steam are encountered, but inappropriate
at higher temperatures when contaminated steam and frequent
maintenance are required. The relatively high price
of a fluoroelastomer or perfluoroelastomer will be recouped
many times over by a seals long service life. Specifying
the proper high performance seal can also prevent costly
unscheduled downtime and dangerous leakage. |
