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Description / Abstract:
Material Description. Commercial compounds are
divided into the following types:
Type A. All 35% to 43% acrylonitrile (ACN),
Hydrogenated Nitrile Butadiene Rubber (HNBR) gasket or Oring
compound(s) in contact with cooling water and engine oil for
application temperatures with a functional temperature range of -5
°C to 150 °C as defined by ASTM D1329 TR10 and SAE J2236
respectively.
Type B. All 25% to 34% acrylonitrile ACN HNBR
gasket or O-ring compound(s) with a functional temperature range of
-29 °C to 150 °C as defined by ASTM D1329 TR10 and SAE J2236
respectively.
Symbols. Identify the elastomer nomenclature
using ASTM D1418 or ISO 1629.
Applicability. This standard covers the use of
hydrogenated nitrile elastomer whose function is to seal the
cooling system (water pump, oil cooler, or front engine cover,
etc.) and engine oil system openings with one (1) part. Type A is
used where maximum oil resistance is required (see 1.4.1). Type B
has slightly less oil resistance, but improved low temperature
flexibility.
Remarks.
The ACN content of HNBR, influences the oil resistance of the
compound. High ACN (35% to 43%) provides excellent oil resistance
but sacrifices low temperature flexibility. Low temperature HNBR
typically has an ACN of 18% to 23%.
Some prints/drawings identify "D" or race track shapes as
O-rings. To avoid confusion, testing and table data only apply to
the ASTM D1414 definition of an O-ring.
Tensile and elongation properties of O-rings are measured by
spool separation, however, during this step, the elongation across
the specimen width is not uniform. To minimize data variation, the
recommended ratio of O-ring inside diameter (ID) to cross section
width should be 9 to 1 or greater.
Note: The ratio for SAE AS568-214 size is 7 to
1. Of greater interest is tensile stress at 20% to 50% elongation
because it is closer to the performance range of the
O-ring.
Rubber Adhesion to Carrier (Edge Molded
Design). Rubber must be secure to the carrier over the
entire contact length. On a fully cured part, attempts to remove
the rubber using pliers or other gripping tools in a 90 degree or
180 degree pull (to the carrier) shall result in tearing of the
rubber. A cut (up to 12 mm) between the rubber and carrier is
permitted to facilitate gripping of the rubber. A clean adhesive
failure (rubber to carrier) is not acceptable. Nondestructive test
alternative using an interference fit, post die for small openings
or a straight segment rule die that deflects or bends the edge
bonded rubber is permitted. For open segment tests, the carrier
must be securely clamped to prevent movement during deflection of
the edge bonded elastomer. The interference of the die edge to the
elastomer profile must make contact at the mid-point of the
flexible extension from the bonded edge. One (1) pass (downward and
upward) is sufficient. There must be no loss of elastomer to metal
adhesion or elastomer cracking under 2x magnification.
Elastomers used in part of assembly (POA) are usually selected
by supplier specific criteria and often remain unspecified or
unidentified on end user prints and drawings. As the original
equipment manufacturer (OEM) end user, GM reserves the right
(through directed buy) to define common rather than source specific
requirements. Use this document in the appropriate Statement of
Requirements (SOR) Appendix C, and corporate prints and drawings
using Section 8 Coding.