ASTM D2858-70(1997)e1

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.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
e1
Designation: D 2858 – 70 (Reapproved 1997)
Standard Test Method for
Thermal Conductivity of Electrical Grade Magnesium Oxide
This standard is issued under the fixed designation D 2858; 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.
e NOTE—Section 13 was added editorially in October 1997.
1. Scope 5. Apparatus
1.1 This method covers the determination of thermal con- 5.1 Filling Machine, vibratory-type, with suitable loading
ductivity of compacted, granular, electrical grade magnesium devices.
oxide (MgO) under conditions which simulate the use of this 5.2 Swaging Machine, with 11.8-mm (0.465-in.) and
material as insulation in tubular heating units. 11.4-mm (0.450-in.) dies with 6-deg throat angle (12 deg
1.2 The values stated in inch-pound units are to be regarded included).
as the standard. 5.3 Metal Lathe, or other suitable equipment for cutting test
unit to length.
2. Referenced Documents
5.4 Spot Welding Machine.
2.1 ASTM Standards: 5.5 A-c Voltmeter, 10 V nominal, 61 % of full scale,
B 344 Specification for Drawn or Rolled Nickel-Chromium
5.6 A-c Ammeter, 300 A nominal, 61 % of full scale.
and Nickel-Chromium-Iron Alloys for Electrical Heating 5.7 Thermocouple, 26-gage, ANSI Type K, with appropriate
Elements
potentiometer(s) and thermocouple switch.
D 2755 Test Method of Sampling and Reduction to Test 5.8 Variable a-c Power Source, capable of handling 250 A at
Weight of Electrical Grade Magnesium Oxide
8V.
D 2771 Test Methods for Compaction Density of Electrical
6. Materials
Grade Magnesium Oxide
6.1 Degreasing Agent—Acetone or similar solvent.
3. Summary of Test Method
6.2 Hollow Rod, 80 Ni - 20 Cr alloy, in accordance with
3.1 The sample of MgO is compacted within the cylindrical Specification B 344, 4.06 + 0.08, − 0.00 mm (0.160 + 0.003, −
space formed by a tubular sheath and a concentric, inner,
0.000 in.) in outside diameter, 0.89 + 0.08, − 0.00 mm (0.035
hollow rod. The rod is heated electrically to produce a + 0.003, − 0.000 in.) in wall thickness, and 410 6 0.8 mm (16
temperature gradient across the insulation. Thermal conductiv-
6 ⁄32 in.) long, and straight within 0.42 mm/m (0.005 in./ft).
ity is calculated from measurements of internal and external 6.3 Rubber Plugs, 11.00 mm (0.430 in.) in outside diameter,
temperatures, wattage applied to the unit, and the dimensions
3.18 mm (0.125 in.) in inside diameter, and 12.70 mm (0.500
of the unit. in.) long.
6.4 Sheath Tubing, Incoloy 800 or equivalent, bright as
4. Significance
welded, 12.70 6 0.08 mm (0.500 6 0.003 in.) in outside
4.1 Thermal conductivity of the insulation affects the inter-
diameter, 0.89 6 0.08 mm (0.035 6 0.003 in.) in wall
nal temperature of tubular heating units; therefore, it influences
thickness, 3606 0.8-mm (14 6 ⁄32 in.) long, and straight
electrical leakage and life of the heaters.
within 0.43 mm/m (0.005 in./ft).
1 4
This test method is under the jurisdiction of ASTM Committee D-9 on A suitable filling machine is a three station Oakley loader, available from
Electrical and Electronic Insulating Materials and is the direct responsibility of Oakley Industries, Inc., 7315 N. Linder Ave., Skokie, IL.
Subcommittee D09.14 on Electric Heating Unit Insulation. Swaging machines found suitable for this purpose are size 4 swaging machines,
Effective Feb. 27, 1970. available from either Torrington Co., 59 Field St., Torrington, CT, or Fenn Mfg. Co.,
Annual Book of ASTM Standards, Vol 03.04. 200 Fenn Road., Newington, CT.
3 6
Annual Book of ASTM Standards, Vol 10.02. Incoloy, 800t is a registered trademark of the International Nickel Co.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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 2858
7. Sampling 9.15 Make a thermocouple from 26-gage ANSI Type K
wires. Insulate with alumina thermocouple tubing. Insert the
7.1 Obtain a sample of MgO in accordance with Test
couple into the hollow rod of the test cell, with one leg
Methods D 2755.
extending out each end and the bead in the center of the cell.
8. Test Sample
Use a new thermocouple for each cell.
8.1 A sample size of approximately 150 g is required for
NOTE 2—For improved accuracy, both thermocouples should be made
each test unit.
from the same spools of wire.
9. Procedure 9.16 Set up the test cell in a horizontal position in an open
but draft-free area, with the sheath thermocouple on top of the
9.1 Clean the sheath and rod in the degreasing agent. After
cell. Wrap the thermocouple wires one full turn around the
cleaning, handle the rod only at the ends.
sheath and weight if necessary to maintain the surface contact.
9.2 Assemble the sheath and the rod with the loading
Attach the thermocouples through the thermocouple switch to
devices to maintain the rod centrally within the sheath and
the potentiometer, or to two different potentiometers.
effect bottom closure.
9.3 Using a vibratory filling machine, load the sample into
9.17 Attach the voltmeter to the instrument leads. Attach the
the sheath, taking about 2 min to fill the unit. power terminals from the power s
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