ASTM D3215-93(2002)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
An American National Standard
Designation: D 3215 – 93 (Reapproved 2002)
Standard Test Method for
Measurement of the Specific Electrical Impedance of
Electrical-Grade Magnesium Oxide for Use in Sheathed-Type
Heating Elements
This standard is issued under the fixed designation D 3215; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope the current in the material to the root mean square of the
current density, and equal to the product of the measured
1.1 This test method covers the determination of specific
impedance Z and a geometrical shape factor F. (The impedance
electrical impedance of electrical-grade magnesium oxide by
is essentially resistive and phase effects are ignored).
externally heating a test cell to elevated temperatures using
typical materials.
4. Summary of Test Method
1.2 The values stated in SI units are to be regarded as the
4.1 The specimen of magnesium oxide is poured into a
standard. The values given in parentheses are for information
length of tubing around a centrally located rod, and the
only.
assembly is compacted to form a test cell simulating a sheathed
1.3 This standard does not purport to address all of the
heating element. The test cell is placed in a heated furnace.
safety concerns, if any, associated with its use. It is the
Voltage is applied across the magnesium oxide in the test cell
responsibility of the user of this standard to establish appro-
in series with a known resistance. The leakage current is
priate safety and health practices and determine the applica-
measured in milliamperes. The leakage current and the geo-
bility of regulatory limitations prior to use.
metric factor are used to calculate the specific impedance.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards:
5.1 The specific electrical impedance can be used to indicate
B 344 Specification for Drawn or Rolled Nickel-Chromium
whether or not the magnesium oxide provides sufficient im-
and Nickel-Chromium-Iron Alloys for Electrical Heating
pedance to perform satisfactorily in high-temperature heating
Elements
elements.
D 2755 Test Method of Sampling and Reduction to Test
Weight of Electrical Grade Magnesium Oxide
6. Apparatus
3. Terminology 6.1 Tube Furnace, horizontal, having a uniformly hot zone
at least 178 mm (7 in.) long. A maximum temperature spread
3.1 Definitions of Terms Specific to This Standard:
of 65.5°C (610°F) between three thermocouples is accept-
3.1.1 measured impedance, Z, n—the ratio of the root mean
able.
square of the voltage applied between two electrodes that are in
6.2 Tube Loading Devices (see Fig. 1 for suggested design).
contact with the specimen to the root mean square of the
6.3 Swaging Machine.
current distributed throughout the volume of the specimen
6.4 Swaging Dies, 12.06 mm (0.475 in.), 11.43 mm (0.450
(neglecting phase effects).
in.), and 11.18 mm (0.440 in.).
3.1.2 shape factor, F, n—the ratio of the test cell length to
6.5 Metal Trimming Device.
the logarithm of the ratio of the test-cell diameters, relating the
6.6 Vibrator.
current flow per unit length to the logarithmic mean potential
gradient across the insulation.
3.1.3 specific electrical impedance, Z , n—the ratio of the
s
root mean square of an alternating potential gradient parallel to
A Lindberg Single Zone Tube Furnace, Type 59545, 12 in., 500 to 1500°C,
available from Lindberg Co., 304 Hart St., Watertown, WI 53094, with Temperature
Control using Type R Thermocouple and suitable Ceramic Tube and Plugs, or
This test method is under the jurisdiction of ASTM Committee D09 on equivalent, has been found suitable for this purpose.
Electrical and Electronic Insulating Materials and is the direct responsibility of Size 4 swaging machines available from either the Torrington Co., 59 Field St.,
Subcommittee D09.14 on Electric Heating Unit Insulation. Torrington, CN 06790, or the Fenn Mfg. Co., 200 Fenn Rd., Newington, CN 06111,
Current edition approved March 15, 1993. Published May 1993. Originally or their equivalent, are satisfactory for this test method.
published as D 3215 – 73. Last previous edition D 3215 – 83. The L & A vibrator, Model F-769, Type B, Size 3, available from the Pressed
Annual Book of ASTM Standards, Vol 02.04. Steel Co., 705 N. Pennsylvania Ave., Wilkes-Barre, PA 18703, or its equivalent, is
Annual Book of ASTM Standards, Vol 10.02. satisfactory.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 3215
6.10 Tubing, 177.8 6 8 mm (7.0 6 0.03 in.) long by 12.70
6 0.08 mm (0.500 6 0.003 in.) in outside diameter by 0.89 6
0.08 mm (0.035 6 0.003 in.) in wall thickness.
6.11 80 Nickel-20 Chromium Alloy Rod, 203.2 6 0.8 mm
(8.0 6 0.06 in.) long by 4.11 mm (0.162 in.) in diameter (AWG
6), in accordance with Specification B 344.
6.12 Rubber Plugs, 12.70 mm (0.500 in.) long by 11.0 mm
(0.430 in.) in outside diameter by 3.2 mm (0.125 in.) bore.
6.13 80 Nickel-20 Chrome Wire, 0.51 mm (0.20 in.) diam-
eter (AWG 24), in accordance with Specification B 344.
7. Sampling
7.1 Obtain the sample of magnesium oxide (approximately
50 g) in accordance with Test Method D 2755.
FIG. 1 Test Cell Loading Devices
8. Procedure
8.1 Clean the tube and rod using standard laboratory clean-
ing procedures. Measure the tube initial outside diameter, OD ;
6.7 Spot Welding Machine.
inside diameter, ID ; and initial length, L .
1 1
6.8 Thermocouples, three, Type R, No. 24B&S gage,
8.2 Assemble the rod and tube in the loading device and fill
0.510-mm (0.020 in.) diameter with appropriate potentiom-
the tube with the specimen of magnesium oxide. Vibrate 2 min
eter.
to assist densification.
6.9 Test Circuit, (see Fig. 2), capable of measuring tempera-
8.3 Pour out the first load of magnesium oxide and repeat
8.2 using new magnesium oxide. Vibrate 7 to 10 min.
8.
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