ASTM D2900-90(1997)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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e1
Designation:D2900–90(Reapproved 1997) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Accelerated Life Test of Electrical Grade Magnesium Oxide
as Used in Sheathed-Type Electric Heating Elements
This standard is issued under the fixed designation D2900; 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.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 length of time the test cell operates before failure occurs is
recorded as its life.
1.1 This test method covers the accelerated life testing of
electrical grade magnesium oxide (MgO) under conditions
4. Significance and Use
involving thermal cycling to an elevated temperature. The test
4.1 The insulating quality of the magnesium oxide at high
determines both the rate at which electrical insulation imped-
temperatureandduringthelifespanofaheatingunitisamost
ance (Note 1) or test current through the insulation changes
significant aspect of the material to the user. Accordingly, a
with time and the time span resulting in complete failure of a
means is specified for determining the insulating quality in a
test cell incorporating the sample under test.
relatively short time, with magnesium oxide being the only
NOTE 1—At test temperatures, capacitive and inductive reactance are
intended variable.
negligible, and therefore impedance values are considered essentially
resistive.
5. Apparatus
1.2 This standard does not purport to address all of the
5.1 Loading Machine, vibratory-type, with suitable loading
safety concerns, if any, associated with its use. It is the
devices.
responsibility of the user of this standard to establish appro-
5.2 Rolling Machine, capable of roll reducing to 6.35 mm
priate safety and health practices and determine the applica-
(0.250in.)diameterthroughfivepassesof7.62mm(0.300in.),
bility of regulatory limitations prior to use. For specific safety
7.24 mm, (0.285 in.), 6.86 mm, (0.270 in.), 6.60 mm (0.260
precaution, see 9.4.1.
in.),and6.35mm(0.250in.),withnosubsequentsizingrolls.
1.3 The values stated in acceptable metric units are to be
5.3 Fusion or Spot Welding Machine.
regarded as the standard.
5.4 Variable A-C Power Source, (approximately 124 V)
with voltage-regulation to 61V and meter for measuring.
2. Referenced Documents
5.5 Variable A-C Test Voltage, supply of approximately 600
2.1 ASTM Standards:
V max.
B344 Specification for Drawn or Rolled Nickel-Chromium
5.6 Voltmeter,A-C, 1000 V/V, 600 V full-scale deflection.
and Nickel-Chromium-Iron Alloys for Electrical Heating
5.7 Thermocouple,ANSI Type K, No. 26 B&S gage, 0.408
Elements
mm (0.0159 in.) in diameter with appropriate potentiometer.
D2755 Test Method of Sampling and Reduction to Test
5.8 Milliammeter, A-C rectifier type 0-10 ma full scale
Weight of Electrical Grade Magnesium Oxide
deflection.
5.9 Voltage Divider, Rheostat, 50W, 500 V.
3. Summary of Test Method
3.1 The specimen of magnesium oxide is loaded into a test 6. Materials
cell, which is formed into an operative heater of specific
NOTE 2—To reduce the number of variables from one test to another, it
construction. The test cell is thermally cycled by internal
heating under conditions designed to accelerate deterioration
and promote failure in a period of several months. Electrical
resistance of the insulation is measured periodically. The total
A suitable loading machine is a three-station Oakley loader, manufactured by
Oakley Industries, Inc., 7315 N. Linder Ave., Skokie, IL.
A suitable rolling machine is an Oakley rolling machine, manufactured by
Oakley Industries, Inc., 7315 Linder Ave., Skokie, IL. Although roll reducing is
This method is under the jurisdiction of ASTM Committee D-9 on Electrical
preferred,swagingisoptional.Suggestedsizesofreductionare7.62mm(0.300in.)
andElectronicInsulatingMaterialsandisthedirectresponsibilityofSubcommittee
D09.14 on Electric Heating Unit Insulation. 7.24mm(0.285in.),6.86mm(0.270in.),6.60mm(0.260in.),and6.35mm(0.250
Current edition approved August 31, 1990. Published October 1990. Originally in.) If swaging is used, the sheath tube length must be increased about 3% and the
published as D2900–70. Last previous edition D2900–84. helix resistance increased about 4%. A suitable swaging is a Size 4 Torrington
Annual Book of ASTM Standards, Vol 03.04. machine manufactured by the Torrington Co., 59 Field St., Torrington, CT.
3 6
Annual Book of ASTM Standards, Vol 10.02. Asuitable voltmeter is a type DP2X manufactured by the General Electric Co.
D2900
is recommended that a stockpile of materials be maintained for making
8.6 Determine the density of the magnesium oxide as
life test cells.
loaded. (The loaded density will vary with the magnesium
6.1 The material specifications shall be followed as closely oxide being tested. However, a density of 2.30 g/cm would
as possible. However, due to variations in the magnesium normally be considered a minimum.)
oxide being tested, adjustments may be necessary in the tube
8.7 Roll reduce in rolling machine to 6.35 mm (0.250 in.)
length, terminal length, and helix resistance to obtain the
using the steps outlined in 5.2. Do not anneal.
dimensions and the wattage of the final test specimen as
8.8 Removetheendwashersbysuitablemechanicalmeans.
outlined in Section 8.
8.9 Spot weld the electrical connectors to the terminals.
6.2 Helix:
8.10 Radiographs or X-ray photographs of the test cell are
6.2.1 Material—Resistance wire in accordance with Speci-
optional, but desirable, as a means of detecting an off-center
fication B344, (80 Ni-20 Cr).
helix or irregular helix pitch before life testing. Two X-rays
6.2.2 Wire Size—No. 29 B&S Gage, 0.287 mm (0.0113 in.)
should be taken with the test cell rotated 90° around the
in diameter.
longitudinal axis for the second X-ray.
6.2.3 HelixOutsideDiameter—2.41mm(0.095in.)asclose
8.11 Finished Dimensions and Specifications:
wound.
8.11.1 Diameter—6.35 6 0.05 mm (0.250 6 0.002 in.).
6.2.4 Total Resistance—32.8 V (approx.).
8.11.2 Heated Length—260 6 3 mm (10.25 6 0.125 in.).
6.2.5 Resistance as Assembled and Welded—32.3 V.
6.3 Sheath Tube—Incoloy 800 or equivalent, bright as 8.11.3 Sheath Length, Nominal—394 mm (15.5 in.).
welded, annealed temper, 7.926 0.05 mm (0.3126 0.002 in.)
8.11.4 Wattage, Nominal at 124 V—655 W.
inoutsidediameter,0.635mm(0.025in.)wallthickness,296.8 2
8.11.5 Watt Density—12.6 6 0.4 W/cm (81.4 6 2.5
mm (11.687 in.) long. 2
W/in. ).
6.4 Terminals—SAE 1006 or 1010 steel, 2.34 mm (0.092
8.11.6 Resistance, Nominal, Cold (As-rolled)—21.6 V.
in.) in diameter, 73.03 mm (2.875 in.) long; fusion end 1.91
8.11.7 Magnesium Oxide Density, Nominal—3.05 g/cm
mm (0.075 in.) in diameter, 6.35 mm (0.250 in.) long.
(0.110 lb/in )
6.5 Closing Washers—Fiber or polyethylene, 7.62 mm
(0.300 in.) in outside diameter, 1.96 mm (0.077 in.) in inside
9. Insulation Impedance (Note 1) and Current
diameter, 1.57 mm (0.062 in.) thick.
Measurement Methods
6.6 Degreasing Agent—Acetone or similar solvent.
6.7 Electrical Connector—9.53 mm (0.375 in.) wide, 19.05
9.1 Any one of the three methods described in 9.2, 9.3, or
mm (0.750 in.) long, 1.98 mm (0.078 in.) thick, No. 8-32
9.4 may be used. The magnitude of the insulation impedance
tapped hole, or other suitable connector. values will vary according to the method used. It is necessary,
then, to report the method of measurement used. Sections 9.2,
7. Sampling
and 9.3 are insulation impedance methods, and 9.4 is a current
7.1 Obtain sample of magnesium oxide in accordance with
measurement method.
Test Method D2755.
9.2 Voltmeter Method with Quadrature Test Voltage—(S
...