ASTM B692-18(2023)

Standard Specification for 75 % Silver-25 % Graphite Sliding Contact Material

ABSTRACT
This specification defines the criteria for the chemical composition and other requirements (including physical properties, microstructure, superficial hardness, and specific resistance ) for silver-graphite brushes for sliding electrical contacts. The percentage of silver, graphite, ash in graphite, and total metal impurities are prescribed. The minimum acceptable values for the physical properties such as density, determined by measurement and weight method, and shear strength are given. Typical Rockwell hardness and specific resistance for the material are also specified.
SCOPE
1.1 This specification defines the criteria for composition and other requirements for brushes with a nominal silver content of 75 weight % with the balance being substantially graphite.  
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to become familiar with all hazards including those identified in the appropriate Safety Data Sheet (SDS) for this product/material as provided by the manufacturer, to establish appropriate safety, health, and environmental practices, and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2023
• ICS: 77.120.99 - Other non-ferrous metals and their alloys
• Technical Committee: B02 - Nonferrous Metals and Alloys
• Drafting Committee: B02.05 - Precious Metals and Electrical Contact Materials and Test Methods

Relations

• Refers: ASTM E18-18 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Jul-2018
• Refers: ASTM E18-17 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Jul-2017
• Refers: ASTM E18-12 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Dec-2012
• Refers: ASTM B613-76(2012) - Standard Guide for Preparing Specifications for Miniature Brushes of Composite Materials for Sliding Electric Contacts
• Effective Date: 01-May-2012
• Refers: ASTM E18-11 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Nov-2011
• Refers: ASTM E18-08a - Standard Test Methods for Rockwell Hardness of Metallic Materials <a href="#fn00002"></a>
• Effective Date: 15-May-2008
• Refers: ASTM E18-08 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 15-Jan-2008
• Refers: ASTM E18-07 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Apr-2007
• Refers: ASTM B613-76(2006) - Standard Guide for Preparing Specifications for Miniature Brushes of Composite Materials for Sliding Electric Contacts
• Effective Date: 01-Jun-2006
• Refers: ASTM E18-05e1 - Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
• Effective Date: 01-Apr-2005
• Refers: ASTM E18-05 - Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
• Effective Date: 01-Feb-2005
• Refers: ASTM E18-03e1 - Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
• Effective Date: 10-Jun-2003
• Refers: ASTM E18-03 - Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
• Effective Date: 10-Jun-2003
• Refers: ASTM E18-00 - Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
• Effective Date: 10-Jan-2002
• Refers: ASTM E18-02 - Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
• Effective Date: 10-Jan-2002

Overview

ASTM B692-18(2023): Standard Specification for 75 % Silver-25 % Graphite Sliding Contact Material defines essential requirements for the chemical composition and physical properties of silver-graphite brushes used in sliding electrical contacts. These brushes, consisting of a nominal 75% by weight silver with the balance being graphite, are designed for high-performance electrical contact applications where durability, conductivity, and specific mechanical characteristics are critical.

The specification addresses requirements for:

• Chemical composition (including allowable impurities and ash content)
• Physical properties (density, shear strength, hardness, and specific resistance)
• Microstructural soundness and manufacture consistency

ASTM B692-18(2023) improves product reliability by specifying rigorous criteria for electrical sliding contacts, aiding manufacturers, quality assurance teams, and end-users in meeting international best practices.

Key Topics

Chemical Composition Criteria

• Silver content: 75% by weight (±3%)
• Graphite: balance of the composition
• Maximum total metal impurities: 1%
• Maximum ash content in graphite: 5%

Physical Properties Standards

• Density: minimum 4.6 g/cm³ determined by measurement and weight method
• Shear Strength:
  • Rectangular parts: minimum 2000 psi (14 MPa) in both normal and transverse directions
  • Cylindrical parts: minimum 1000 psi (6.9 MPa) in the longitudinal direction
• Typical superficial hardness: Rockwell 15W50 (as per ASTM E18)
• Typical specific resistance: 6 × 10⁻⁶ Ω-in. (1.5 × 10⁻⁷ Ω-m)

Microstructure and Defect Control

• Free from structural defects, cracks, or abrasive particles
• Laminations aligned as ordered
• No particles that can sliver a metal-alloy ring under specified pressures

Certification and Traceability

• Producers must certify materials meet all specified requirements
• Consistency in source materials and methods of manufacture is essential

Applications

ASTM B692-18(2023) materials are crucial for:

• Sliding electrical contacts in industrial, railway, or automotive applications
• Generator and motor brushes where high conductivity and wear resistance are necessary
• Electrical machinery and power transmission equipment needing reliable, low-resistance current transfer

These high silver-content graphite materials ensure optimum electrical and mechanical performance, particularly in demanding environments that require stable contact under motion, minimized wear, and long part life. The standard promotes component consistency across manufacturers and suppliers.

Related Standards

ASTM B692-18(2023) is used alongside several related standards in the field of electrical contact materials, including:

• NEMA CB-1: Brushes for Electrical Machines (referenced for property definitions and testing methods)
• ASTM B613: Guide for Preparing Specifications for Miniature Brushes of Composite Materials for Sliding Electric Contacts
• ASTM E18: Test Methods for Rockwell Hardness of Metallic Materials

These standards collectively ensure a robust foundation for specifying, testing, and assuring quality in the production and application of sliding contact materials.

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By specifying material composition, physical properties, and testing protocols, ASTM B692-18(2023) supports the global electrical industry with universally accepted benchmarks for high-performance silver-graphite sliding contacts. Using compliant brushes enhances system reliability, safety, and longevity across a wide range of electrical machinery and equipment.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B692 − 18 (Reapproved 2023)
Standard Specification for
75 % Silver-25 % Graphite Sliding Contact Material
This standard is issued under the fixed designation B692; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 NEMA Standard:
CB-1 Brushes for Electrical Machines
1.1 This specification defines the criteria for composition
and other requirements for brushes with a nominal silver
3. Requirements
content of 75 weight % with the balance being substantially
graphite.
3.1 Chemical Composition shall be as follows:
Silver 75 ± 3 % (weight)
1.2 The values stated in inch-pound units are to be regarded
Graphite balance
as standard. The values given in parentheses are mathematical
Total metal impurities 1 % max
Percent ash in graphite (NEMA CB-1) 5 % max
conversions to SI units that are provided for information only
and are not considered standard.
3.2 Physical Properties—The following lot average proper-
ties must be met. Unless otherwise agreed between the pro-
1.3 This standard does not purport to address all of the
ducer and the user, the number of samples shall be five.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to become familiar
3.2.1 Density—The minimum acceptable density shall be
with all hazards including those identified in the appropriate 4.6 g/cm as determined by the measurement and weight
Safety Data Sheet (SDS) for this product/material as provided method defined by NEMA CB-1.
by the manufacturer, to establish appropriate safety, health,
3.2.2 Shear Strength:
and environmental practices, and determine the applicability
3.2.2.1 The shear strength for the normal and transverse
of regulatory limitations prior to use.
directions shall be measured for rectangular parallelepipeds
1.4 This international standard was developed in accor-
and shall be 2000 psi (14 MPa), minimum.
dance with internationally recognized principles on standard-
3.2.2.2 The shear strength for the longitudinal shear direc-
ization established in the Decision on Principles for the
tion shall be measured for cylinders and shall be 1000 psi
Development of International Standards, Guides and Recom-
(6.9 MPa), minimum.
mendations issued by the World Trade Organization Technical
3.3 Microstructure—Parts shall be visually free of structural
Barriers to Trade (TBT) Committee.
defects, cracks, etc., upon examination at 50×. The press
2. Referenced Documents direction, as evidenced by laminations, shall be as defined by
the purchase order. Also the brush material shall not contain
2.1 ASTM Standards:
abrasive particles that will sliver a metal-alloy ring with a
B613 Guide for Preparing Specifications for Miniature
hardness ≥110 HK when the brush force is equal to 30 g or
Brushes of Composite Materials for Sliding Electric
that necessary for 5.0 psi (34 kPa) pressure, whichever is
Contacts
greater. A sliver is defined as a loose wear particle with one
E18 Test Methods for Rockwell Hardness of Metallic Ma-
dimension ≥50× t
...