ASTM D3026-94

Standard Test Method for Sinter Index of Electrical Grade Magnesium Oxide for Use in Sheathed Heating Elements (Withdrawn 2002)

SCOPE
1.1 This test method covers the determination of sinter index which predicts the sintering characteristics of electrical grade magnesium oxide for use in manufacturing sheathed heating elements.  
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
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 establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Withdrawn
• Publication Date: 31-Dec-1993
• ICS: 71.060.20 - Oxides
• Technical Committee: D09 - Electrical and Electronic Insulating Materials

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.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.
Designation: D 3026 – 94
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
Sinter Index of Electrical Grade Magnesium Oxide for Use in
Sheathed Heating Elements
This standard is issued under the fixed designation D 3026; 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 melting point. The rate of sintering is greater with smaller
particles than with larger particles.
1.1 This test method covers the determination of sinter
index which predicts the sintering characteristics of electrical
4. Summary of Test Method
grade magnesium oxide for use in manufacturing sheathed
4.1 The specimen of magnesium oxide is placed in a
heating elements.
magnesium oxide combustion boat and exposed to an elevated
1.2 The values stated in SI units are to be regarded as the
temperature in an oxidizing atmosphere for a specified time. It
standard. The values given in parentheses are for information
is then cooled and subjected to a weighted, specially shaped,
only.
probe that penetrates the body of the specimen.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
5. Significance and Use
responsibility of the user of this standard to establish appro-
5.1 The degree of sintering of the magnesium oxide at
priate safety and health practices and determine the applica-
elevated temperatures experienced in manufacturing sheathed
bility of regulatory limitations prior to use.
heating elements is important to the user. A high degree of
2. Referenced Documents sintering increases the tendency of the insulation to fracture
during bending of the heating element but a low degree of
2.1 ASTM Standards:
sintering reduces the thermal conductivity.
C 266 Test Method for Time of Setting of Hydraulic-
Cement Paste by Gillmore Needles
6. Apparatus
D 2755 Test Method of Sampling and Reduction to Test
3 6.1 Electric Furnace, capable of heating the entire combus-
Weight of Electrical Grade Magnesium Oxide
tion boat (6.3), to 10936 5°C (2000° 6 9°F). The furnace shall
D 3347 Test Method for Flow Rate and Tap Density of
be provided with a power supply and control to permit
Electrical Grade Magnesium Oxide for Use in Sheathed-
3 adjustment and maintenance of the desired test temperature.
Type Electric Heating Elements
The use of a nonswitching-type power supply is optional. The
E 220 Method for Calibration of Thermocouples by Com-
4 furnace shall be of one of the following types:
parison Techniques
6.1.1 Tube Furnace, having a minimum 305 mm (12 in.)
uniform heat zone, with a straight bore, open-ended, ceramic
3. Terminology
combustion tube measuring approximately 32 mm (1 ⁄4 in.) in
3.1 Descriptions of Terms Specific to This Standard:
outside diameter, by 25.4 mm (1 in.) in inside diameter, by 610
3.1.1 sinter index, n—a number that characterizes the de-
mm (24 in.) in length.
gree of sintering and numerically equals the weight in grams
6.1.2 Muffle Furnace, having a minimum internal dimension
that causes a specially shaped probe to penetrate the sintered
of 133-mm (5 ⁄4-in.) width by 203-mm (8-in.) depth and
body of a fired magnesium oxide specimen to a prescribed
95-mm (3 ⁄4-in.) height, and capable of heating twelve com-
depth.
bustion boats simultaneously. The furnace cavity should be
3.1.2 sintering, n—the welding together and growth of
checked to ensure a uniform heat pattern.
contact area between two or more initially distinct particles at
6.2 Combustion Plate, 102-mm (4-in.) by 203-mm (8-in.)
temperatures below the melting point, but above one-half of
by 13-mm ( ⁄2-in.) thick to support boats in the muffle furnace.
The combustion plate must be capable of withstanding the
temperature and thermal shock associated with the test.
This test method is under the jurisdiction of ASTM Committee D-9 on
Electrical and Electronic Insulating Materials and is the direct responsibility of 6.3 Combusion Boat, refractory type, magnesium oxide, 95
Subcommittee D09.14 on Electrical Heating Unit Insulation. 3
mm (3 ⁄4 in.) long, and having a flat bottom for at least half its
Current edition approved June 15, 1994. Published August 1994. Originally
published as D 3026 – 72. Last previous edition D 3026 – 86.
Annual Book of ASTM Standards, Vol 04.01.
3 5
Annual Book of ASTM Standards, Vol 10.02. Magnesium oxide combustion boats are available from Saxonburg Ceramics,
Annual Book of ASTM Standards, Vol 14.03. 100 Isabella St., Saxonburg, PA 16056.
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 3026
width (Fig. 1). Prior to use, the boat shall be fired at 10936
5°C(2000 6 9°F) for1hto remove trace material that may
affect the testing to follow. Magnesium oxide boats are
reusable until fractured.
6.4 Sinter Tester, cement set time tester in accordance with
Test Method C 266. The Gillmore needle is replaced by a
modified needle (Fig. 2).
6.5 Loading Funnel, having a minimum 60 degree taper on
the sides, an orifice diameter of 2.17 mm (0.086 in.), and no
stem. The fill hopper and orifice as specified in Test Method
D 3347 are satisfactory.
6.6 Straightedge, stainless steel, a minimum of 102 mm (4
in.) long.
6.7 Optical Pyrometer or Potentiometer, with 20B&S
gage, 0.82-mm (0.032-in.) diameter, ANSI Type K thermo-
couple, insulated with refractory thermocouple tubing, and as
long as necessary to reach a suitable cold junction location
when positioned as required in the furnace. Calibrate the
optical pyrometer to ensure required accuracy of 65°C
(69°F). Calibrate the ANSI Type K thermocouple in accor-
dance with Method E 220, or equivalent, to ensure required
FIG. 2 Penetrating Needle
accuracy of 65°C (69°F). Equivalent methods of measuring
temperature which have the accuracy specified above may be
accordance with Test Method D 2755.
used.
6.8 Timing Device, capable of measuring 1 h within 61 8. Preparation of Sample, Test Specimens and Control
min.
Standard
6.9 Balance, having a minimum capacity of 2000 g and a
8.1 Thoroughly mix the sample or control standard and pour
sensitivity of 0.5 g.
it into the funnel while holding a finger over the orifice.
6.10 Weighing Cup, of size and weight suitable for the
8.2 Prepare the test specimen by allowing the magnesium
expected range of test results, to be placed on the platform of
oxide powder to flow through the orifice into the combustion
the penetrating needle (Fig. 2).
boat beginning at one end and moving towards the other end
6.11 Weighing Media, magnesium oxide powder, No. 12
while filling to overflowing. Do not fill in layers.
lead shot, or equivalent.
8.3 With the stainless steel straightedge held vertical and
6.12 Control Standard, magnesium oxide, having a sinter
perpendicular to the longitudinal axis of the combustion boat,
index of approximately 100.
scrape off the excess magnesium oxide in one motion, flush
with the top surface of the combustion boat.
7. Sampling
7.1 Obtain a 75 to 100-g sample of magnesium o
...