GMW GMW14751 PDF

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.