ASTM B781-93a(2006)
(Guide)Standard Guide for Silver-Cadmium Oxide Contact Material
Standard Guide for Silver-Cadmium Oxide Contact Material
SIGNIFICANCE AND USE
Silver-cadmium oxide is a popular contact material that has been used in a wide range of applications in switches, relays and contactors for switching lamps, motors and resistive loads. Silver-cadmium oxide is a composite material consisting of a metal matrix, silver, with a metal oxide, cadmium oxide, dispersed throughout the matrix. Compositions of up to 30 % cadmium are made, but most applications use silver-cadmium oxide in the range of 10 to 15 % cadmium oxide by weight. Several different processes are used for manufacturing silver-cadmium oxide material and it should be understood that the manufacturing method has an influence on the properties of the material such as arc erosion resistance, welding resistance, arc mobility and contact resistance. Since the performance of contacts in a device is dependent on numerous factors outside the contact itself (opening speed, closing speed, contact pressure, contact bounce and many more device parameters), the guide cannot ensure performance in specific applications.
Arc erosion resistance and welding resistance are improved by the addition of cadmium oxide to the silver matrix. The contact resistance is raised by this addition but still is low. Cadmium oxide and silver do not alloy so the silver matrix retains its high conductivity. Silver-cadmium oxide contacts are used in current ranges of a few amperes to several hundred amperes.
Silver-cadmium oxide contact material is available as wire, silver-clad wire, sheet, strip, toplay, inlay and overlay sheet or strip, discrete contact parts, brazed contact assemblies, solid and composite rivet contacts and clad contact tapes.
Materials with higher cadmium oxide contents have lower material costs but may have higher processing costs due to lower formability.
SCOPE
1.1 This guide provides guidelines for users and manufacturers of silver-cadmium oxide material produced in strip, rod, wire, and part form for electrical contact applications.
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 Material Safety Data Sheet (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety and health practices , and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B781–93a(Reapproved2006)
Standard Guide for
1
Silver-Cadmium Oxide Contact Material
This standard is issued under the fixed designation B781; 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 relays and contactors for switching lamps, motors and resistive
loads. Silver-cadmium oxide is a composite material consisting
1.1 This guide provides guidelines for users and manufac-
of a metal matrix, silver, with a metal oxide, cadmium oxide,
turers of silver-cadmium oxide material produced in strip, rod,
dispersed throughout the matrix. Compositions of up to 30 %
wire, and part form for electrical contact applications.
cadmium are made, but most applications use silver-cadmium
1.2 This standard does not purport to address all of the
oxide in the range of 10 to 15 % cadmium oxide by weight.
safety concerns, if any, associated with its use. It is the
Several different processes are used for manufacturing silver-
responsibility of the user of this standard to become familiar
cadmium oxide material and it should be understood that the
with all hazards including those identified in the appropriate
manufacturing method has an influence on the properties of the
Material Safety Data Sheet (MSDS) for this product/material
material such as arc erosion resistance, welding resistance, arc
as provided by the manufacturer, to establish appropriate
mobility and contact resistance. Since the performance of
safety and health practices , and determine the applicability of
contacts in a device is dependent on numerous factors outside
regulatory limitations prior to use.
the contact itself (opening speed, closing speed, contact pres-
2. Referenced Documents sure, contact bounce and many more device parameters), the
2
guide cannot ensure performance in specific applications.
2.1 ASTM Standards:
4.2 Arc erosion resistance and welding resistance are im-
B311 Test Method for Density of Powder Metallurgy (PM)
proved by the addition of cadmium oxide to the silver matrix.
Materials Containing Less Than Two Percent Porosity
The contact resistance is raised by this addition but still is low.
B476 Specification for General Requirements for Wrought
Cadmium oxide and silver do not alloy so the silver matrix
Precious Metal Electrical Contact Materials
retains its high conductivity. Silver-cadmium oxide contacts
C914 Test Method for Bulk Density and Volume of Solid
are used in current ranges of a few amperes to several hundred
Refractories by Wax Immersion
amperes.
NOTE 1—Test Method B311 is applicable to fully dense forms. Speci-
4.3 Silver-cadmium oxide contact material is available as
fication B476 is applicable to strip, rod, or wire only. Test Method C914
wire, silver-clad wire, sheet, strip, toplay, inlay and overlay
is applicable to forms less than 99 % dense.
sheet or strip, discrete contact parts, brazed contact assemblies,
solid and composite rivet contacts and clad contact tapes.
3. Terminology
4.4 Materials with higher cadmium oxide contents have
3.1 lot, n—(usage involving discrete manufactured parts)—
lower material costs but may have higher processing costs due
allpartsofthesameform,anddimensions,fromthesamealloy
to lower formability.
melt or batch of particulate (if manufactured by consolidation),
processedunderthesameconditions,andsubmittedforinspec-
5. Manufacture
tion at the same time.
5.1 Since the manufacturing method has a significant influ-
4. Significance and Use ence on the properties and microstructure of silver-cadmium
oxide materials, it is important to understand some basic
4.1 Silver-cadmium oxide is a popular contact material that
information on the types of manufacturing. Silver-cadmium
has been used in a wide range of applications in switches,
oxide manufacturing can be first divided in two categories:
Internal Oxidation and Power Metallurgy.
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This guide is under the jurisdiction of ASTM Committee B02 on Nonferrous
5.1.1 Internal oxidation means that the cadmium oxide
Metals and Alloys and is the direct responsibility of Subcommittee B02.05 on
particles are formed by diffusion of oxygen into the silver alloy
Precious Metals and Electrical Contact Materials.
to combine with cadmium atoms to form cadmium oxide
Current edition approved June 1, 2006. Published June 2006. Originally
approved in 1987. Last previous edition approved in 1999 as B781 – 93a (1999).
particles. This process can be further divided into the catego-
DOI: 10.1520/B0781-93AR06.
ries of post and pre-oxidized materials. The post-oxidized
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or
process consists of
...
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