ASTM B845

ASTM B845 – Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts

Description:

Significance and Use

4.1 Preservation of a conducting surface on electrical contact is vital to the continued functioning of such contacts. Contamination of the surface with insulating layers formed by corrosion processes is one potential hazard. Laboratory testing of contacts in MFG tests is used to assess the effectiveness of design features and materials.

4.2 MFG tests are used in development studies of processes and materials for contacts. For example, coupon specimens may be exposed to MFG tests to evaluate new contact materials, layers of new coating materials on a supporting substrate, reduced coating thicknesses, or protective surface treatments.

4.3 MFG tests are also employed to test the durability of a finished product with respect to atmospheric corrosion. For example, finished connectors may be exposed to a MFG test and their performances compared against each other or against a set of fixed requirements. Relays or switch contacts may be exposed in the operated and non-operated conditions to compare performance.

4.4 MFG tests are useful for determining the effectiveness of connector housings and shrouds as barriers to ingress of atmospheric corrodants to the contact surfaces. These tests can also be used to assess the screening of the metal-to-metal contact areas of mated connectors.

4.5 MFG tests are employed as qualification tests to determine connector failure rates in application environments for which correlation between test and application has previously been established.

4.6 This guide provides test conditions which are to be applied in conjunction with Practice B827 which defines the required test operation and certification procedures, tolerances, and reporting requirements. Where the test specifier requires certifications or tolerances different than those provided in Practice B827, the required certifications or tolerances shall be part of the test specification. Differences from the specifications in Practice B827 shall be reported in the test report provided by the test operator to the test specifier. Specification of one of the test conditions defined in this document in the form of a statement such as, “Parts shall be tested in accordance with ASTM B845 Method Z,” implicitly requires test condition, Z, applied according to Practice B827.

Scope

1.1 The techniques described in this guide pertain to mixed flowing gas (MFG) tests containing species that are applied to evaluate devices containing electrical contacts such as slip rings, separable connectors, electromechanical relays or switch contacts. These techniques may be relevant to other devices, but it is the responsibility of the user to determine suitability prior to testing.

1.2 The MFG tests described in this guide are designed to accelerate corrosive degradation processes. These accelerations are designed such that the degradation occurs in a much shorter time period than that expected for such processes in the intended application environment of the device being tested. Application environments can vary continuously from benign to aggressively corrosive. Connectors and contacts within closed electronic cabinets may be affected by an environment of different severity than the environment on the outside of such cabinets. In general, indoor environments are different than outdoor environments. The MFG tests described herein, being discrete embodiments of specific corrosive conditions, cannot be representative of all possible application environments. It is the responsibility of the test specifier to assure the pertinence of a given test condition to the specifier’s application condition.

1.3 The MFG tests described herein are not designed to duplicate the actual intended application environment of the device under test. An extended bibliography that provides information which is useful to test specifiers to assist them in selecting appropriate test methods is included in this guide. The bibliography covers the scope from application condition characterization, single and multiple gas effects, and material and product effects to key application and test variables as well as discussions of atmospheric corrosion processes.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.