GMW GMW17286 PDF

Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. Measure the nitrogen leak rate in standard cubic centimeters per minute (SCCM) at the measured clamp load in megapascals (MPa) of Rubber Coated Metal (RCM). Continue load measurements until the leak rate reaches the specified cubic centimeters per minute minimum. Nitrogen leak sensitivity is not a direct measure of fluid sealing performance. It is more sensitive to mating joint surface to gasket coating conformability and suitable for defining minimum sealing design load.

Applicability. Characterization of the load required to seal at a specified surface finish. The use of this information may be compared to the surface finish and joint load needed by production joints. Machined joint surface finishes will be different between transmission and engine at a component or part level.

Method A – Pressure Decay. Measure the candidate to specific application leak rate (print or bill of material designated). Test pressure and fixture finish conditions are specified by the test requester. If no information is provided the default finish is used capturing the load in kilopascals (kPa) required to reach 0.1 SCCM at 6 bar pressure for engines. This method is used where the mating joint surface finish, internal pressure and flange pressure of production application are known. See Table 1.

Method B – Minimum Sealing Load Characterization. This method allows the surface finish limit bracketing of RCM for nitrogen sealing capability. It applies to new products/sources to better determine the optimum surface condition for that RCM. The surface finish performance range will vary by product and source. Using Table 1, measurement is made using the minimum sealing load starting at 0.9 μm and continuing in 5 μm steps through a given surface finish and coating thickness to reach the sealing target. Use the test pressure following 4.3.13 requirements. The boundary condition is found using multiple test fixture finishes in micrometers with the appropriate roughness average (Ra), average maximum height of the profile (Rz), and maximum surface roughness (Rz1max).

Remarks. The default finish method used here may not represent the production machining process or finish roughness variation. The information will assist for comparative purposes and general design knowledge.