Elastomers for High Temperature Fluid Sealing Applications
|Publication Date:||1 August 2018|
Nothing in this standard supercedes applicable laws and regulations.
In the event of conflicts between the content/intent of this document and a supplier version, this and only this document shall take precedence.
The words must, shall or will as used in this document mean a mandatory requirement. This specification covers elastomers used in static sealing of high temperature gasket and seal components (e.g., turbo, exhaust gas recirculation, etc.,) in engine oil or coolant. For high temperature application requirements specific to turbo charging see GMW16189 Sealings in Turbo Charger Applications.
Materials covered by this specification are divided into Classes and Types of oil and coolant resistant elastomers. Table 1 describes the Class (Class A, Class B, etc.,) of elastomers meeting the designated temperature range and Type 1 and Type 2 meeting the designated application of gasoline or diesel engine. Part performance requirements are in 3.8 and Table 6. See 1.4 Remarks
Identify the elastomer nomenclature using ASTM D1418 or ISO 1629.
See Table 1. Press-in-place and O-ring elastomers with high immersion test temperatures. Only parts fitting the scope and application may use this specification.
Table 1 currently represents compounds in the 70 hardness range to 80 hardness range.
Approved compound properties for each type of elastomer are listed in Table 4, Table 5 and Table 6. Table values by type are a compilation of data from multiple approved compounds and hardness ranges.
For fluorocarbon rubber (FKM/FPM) polymer types, in methanol and ethanol diluted conditions, the percent fluorine level is most important. In biodiesel diluted conditions with oil, the cure type and no metal oxides take precedence over percent fluorine.
This global standard was developed with careful consideration to cost containment, legal considerations, best practices, lessons learned, etc., to establish consensus material quality and performance. Because this is a global standard, the elastomer supplier is only required to generate data for the initial approval using the CG5498; High Temp Data Sheet for this standard, avoiding numerous regional and divisional requirements and expense.
Turbo System Oil Pressure.
The oil impulse pressure conditions can reach 1400 kPa ± 100 kPa, (14 bar ± 1 bar or 203 psi ± 15 psi) for the 5 s of oil circulation which occurs immediately following cold start-up. Expect oil pressure at 800 kPa ± 100 kPa (8 bar ± 1 bar or 116 psi ± 15 psi) during circulation.
Turbo System Coolant Pressure.
The maximum coolant impulse pressure conditions can reach 517 kPa ± 50 kPa (5.2 bar ± 0.5 bar or 75 psi ± 7 psi) which occurs immediately following cold start-up. Expect coolant pressure at 150 kPa ± 50 kPa (5.2 bar ± 0.5 bar or 22 psi ± 7 psi) during circulation.
O-rings. 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 inner diameter (ID) to cross section width should be a ratio of nine (9) to one (1) or greater (see Table 3).
The ratio for SAE AS568, the 214 size is seven (7) to one (1). Of greater interest is tensile stress at 20% elongation to 50% elongation because it is closer to the insertion and removal performance of the O-ring.
For a 70 hardness compound to an 85 hardness compound, the maximum fluid pressure limit applied to an O-ring is 10.3 MPa. A back-up ring is preferred at a 7.8 MPa (78 bar or 1 131 psi) pressure or higher. The maximum joint gap, see Figure 1, for a 70 nominal hardness compound without an additional/back-up O-ring is 0.15 mm at 7.8 MPa maximum pressure and 0.35 mm for 3.4 MPa maximum pressure