ASTM B70-90(2007)

Standard Test Method for Change of Resistance With Temperature of Metallic Materials for Electrical Heating

SIGNIFICANCE AND USE
The change in resistance with temperature for heating element materials is a major design factor and may influence material selection. The measurement of this change is essential to ensure that heating elements perform as designed. This test method was designed to minimize the effect different manufacturing processes have on resistance change, thereby yielding results that are reproducible.
SCOPE
1.1 This test method covers the determination of the change of resistance with temperature of metallic materials for electrical heating, and is applicable over the range of service temperatures.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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 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.

General Information

• Status: Historical
• Publication Date: 30-Apr-2007
• ICS: 27.010 - Energy and heat transfer engineering in general
• ICS: 97.100.10 - Electric heaters
• Technical Committee: B02 - Nonferrous Metals and Alloys
• Drafting Committee: B02.10 - Thermostat Metals and Electrical Resistance Heating Materials

Relations

• Replaces: ASTM B70-90(2001) - Standard Test Method for Change of Resistance With Temperature of Metallic Materials for Electrical Heating
• Effective Date: 01-May-2007
• Replaced By: ASTM B70-90(2013) - Standard Test Method for Change of Resistance With Temperature of Metallic Materials for Electrical Heating
• Effective Date: 01-May-2013
• Referred By: ASTM B603-07(2018) - Standard Specification for Drawn or Rolled Iron-Chromium-Aluminum Alloys for Electrical Heating Elements
• Effective Date: 01-May-2007
• Referred By: ASTM B344-20 - Standard Specification for Drawn or Rolled Nickel-Chromium and Nickel-Chromium-Iron Alloys for Electrical Heating Elements
• Effective Date: 01-May-2007

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B70 − 90 (Reapproved2007)
Standard Test Method for
Change of Resistance With Temperature of Metallic
Materials for Electrical Heating
This standard is issued under the fixed designation B70; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope end, shall be attached by welding, at a distance from the
corresponding current lead not less than one tenth of the length
1.1 This test method covers the determination of the change
of the specimen between the potential leads.
of resistance with temperature of metallic materials for elec-
trical heating, and is applicable over the range of service 3.2 When the resistance is to be measured with a Wheat-
temperatures. stone bridge, only the current leads are required.The resistance
of the leads in this case shall not exceed 1 % of the resistance
1.2 The values stated in SI units are to be regarded as
of the specimen and the leads shall be made of the same type
standard. No other units of measurement are included in this
of alloy as the test specimen. For both methods of
standard.
measurement, the leads shall have a length within the heated
1.3 This standard does not purport to address all of the
zone of the furnace of at least 50 times their minimum
safety concerns, if any, associated with its use. It is the
transverse dimension, in order to avoid disturbance of the
responsibility of the user of this standard to become familiar
temperature of the specimen by conduction of heat to the
with all hazards including those identified in the appropriate
colder parts of the furnace.
Material Safety Data Sheet (MSDS) for this product/material
as provided by the manufacturer, to establish appropriate
4. Electric Furnace
safety and health practices, and determine the applicability of
4.1 The furnace for heating the specimen shall be of such a
regulatory limitations prior to use.
type that the temperature can be controlled over the range from
room temperature to the maximum desired. It shall be so
2. Significance and Use
constructed that the specimens and the thermocouples can be
2.1 The change in resistance with temperature for heating
maintained at a uniform and constant temperature at desired
element materials is a major design factor and may influence
points within the working range. The specimen and thermo-
material selection. The measurement of this change is essential
couples shall be so shielded as to prevent direct radiation from
to ensure that heating elements perform as designed. This test
hotter, or to colder, parts of the furnace.
method was designed to minimize the effect different manu-
4.2 In order to test the uniformity of the temperature in the
facturingprocesseshaveonresistancechange,therebyyielding
region to be occupied by the test specimen, a typical specimen
results that are reproducible.
and thermocouple shall be prepared and mounted in the center
of this region.The furnace shall then be heated to its maximum
3. Test Specimen and Leads
temperature and maintained at this temperature until equilib-
3.1 Thetestspecimenshallbepreparedfrommaterialasleft
rium is reached. The specimen shall then be moved in the
by the manufacturing process, and in a form suitable for
furnace in the direction of the maximum temperature gradient
measuring its resistance in an electric furnace. When the
through a distance equal to the maximum dimension of the
resistance is to be measured with a Kelvin bridge,
largest specimen and thermocouple assembly which is to be
potentiometer, digital ohmmeter, or equivalent, a current lead
usedinthisfurnace.Thetemperatureofthetypicalspecimenin
shall be welded to each end of the specimen in such a manner
this position shall not differ from that in the normal position by
that there will be no change of current distribution in the
more than 10°C.
specimen during measurements. Potential leads, one at each
5. Resistance Measurements
5.1 A Kelvin bridge, potentiometer, digital ohmmeter, or
This test method is under the jurisdiction of ASTM Committee B02 on
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
equivalent shall be used when measuring specimens having
B02.10 on Thermostat Metals and Electrical Resistance Heating Materials.
resistances less than 10Ω . AWheatstone bridge may be used
Current edition approved May 1, 2007. Published May 2007. Originally
with specimens having resistances greater than 10 Ω. The
approved in 1927. Last previous edition approved in 2001 as B70 – 90 (2001). DOI:
10.1520/B0070-90R07. resistance of the specimen shall be measured with an accuracy
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B70 − 90 (2007)
of 0.1 %. The measuring current shall be so small that the ture of test for the alloy in question, and hold at this value until
resistance of a specimen is not changed thereby as much as the resistance of the specimen remains constant except for the
0.
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