ASTM C1276-94(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C 1276 – 94 (Reapproved 1999)
Standard Test Method for
Measuring the Viscosity of Mold Powders Above Their
Melting Point Using a Rotational Viscometer
This standard is issued under the fixed designation C 1276; 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 3. Significance and Use
1.1 This test method covers measurement of the viscosity of 3.1 The viscosity of a molten mold flux is a very important
mold powders above their melting point through the use of a property for the correct functioning of a mold powder. This
platinum spindle immersed in a platinum crucible containing procedureisdesignedforproducersandusersofmoldpowders
the molten mold flux. Developed by differential angular to develop the viscosity-temperature relationships of the mol-
velocity between the crucible and spindle, spindle torque is ten mold flux for quality control or specification purposes, or
measured and used to calculate the viscosity. Data are gener- both. Practices C 965 were developed for glasses that are
ally taken as a function of temperature to describe the significantly higher in viscosity than mold powders. Also,
viscosity-temperature relationship for the molten mold flux. sample preparation is very different for the glass products
1.2 This test method uses a high-temperature furnace and covered.
measurements on molten material. Personal protection equip-
NOTE 1—Warning: Use caution when discharging molten sample into
ment to wear include high-temperature resistant insulating
water since this can cause an explosion.
gloves, coveralls, and a full-face shield.
1.3 The values stated in inch-pound units are to be regarded 4. Apparatus
as the standard. The values given in parentheses are for
4.1 Electrically Heated Furnace, equipped with a tempera-
information only.
ture controller, temperature measuring equipment, a spindle, a
1.4 This standard does not purport to address all of the
crucible, a device to rotate the spindle, and equipment to
safety concerns, if any, associated with its use. It is the
measure the torque or viscosity.
responsibility of the user of this standard to establish appro-
4.1.1 Any electrically heated furnace capable of providing a
priate safety and health practices and determine the applica-
uniform and stable temperature in the testing zone of the
bility of regulatory limitations prior to use. Aspecific warning
furnace can be used. The furnace must be capable of maintain-
statement is given in Note 1.
ing a temperature 180°F (82°C) above the maximum test
temperature. The atmosphere in the furnace should be air or
2. Referenced Documents
oxidizing.
2.1 ASTM Standards:
4.2 Thermocouple, calibrated in accordance with Method
C 965 Practices for Measurement of Viscosity of Glass
E 220. It is preferred that the thermocouple be immersed in the
Above the Softening Point
molten mold flux, in which case only the bare metal of the
C 1095 Practice for Calculating Precision Data on Refrac-
thermocouple should be immersed, since immersion of the
tories (C08) from Interlaboratory Test Results
thermocouple sheath may result in a reaction between the
E 220 Method for Calibration of Thermocouples by Com-
sheathandthemoltenflux.Alternatively,thethermocouplecan
parison Techniques
be placed outside the crucible containing the molten mold flux,
E 691 Practice for Conducting an Interlaboratory Study to
providing that the temperature difference between the flux and
Determine the Precision of a Test Method
the position where the thermocouple is placed is no more than
9°F (5°C).
4.3 SpindleandCrucible,platinumoraplatinumalloy. The
spindle is attached to the rotating device using platinum
This test method is under the jurisdiction of ASTM Committee C08 on
extension wires inside the furnace and other suitable wires
RefractoriesandisthedirectresponsibilityofSubcommitteeC08.10onRefractories
for Glass. outside the furnace, for example, stainless steel.
Current edition approved June 15, 1994. Published August 1994.
Annual Book of ASTM Standards, Vol 15.02.
3 5
Annual Book of ASTM Standards, Vol 15.01. An alloy such as zirconia grain-stabilized (ZGS) platinum has been used
Annual Book of ASTM Standards, Vol 14.02. successfully.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1276 – 94 (1999)
4.3.1 The dimensions of the crucible and spindle shall be 6. Calibration of the Torque Viscometer
such that, when the crucible is filled with molten mold flux, the
6.1 Clean the spindle thoroughly prior to running this
body of the spindle can be immersed fully to at least a depth of
calibration test. Conduct this test out of the furnace at 77 6
0.4 in. (1 cm) and the distance between the spindle and the
0.2°F (25.0 6 0.1°C) using standard viscosity silicone oils.
crucible bottom and all crucible walls shall be at least 0.4 in. (1
This calibration procedure must be run with silicone oils of
cm). Such minimum dimensions will eliminate wall effects.
various viscosities and using various spindle r/min. The types
There are no limits on the maximum dimensions of the
of silicone oils tested should have viscosities in the same range
crucible. However, larger crucibles and consequently larger
as those of the molten mold flux. Fill the crucible with the
amounts of molten mold flux will take longer to stabilize at
standard viscosity silicone oil, and stabilize the temperature by
temperature. See Fig. 1 for a typical crucible/spindle configu-
placing into a water bath set at 77 6 0.2°F (25.0 6 0.1°C).
ration.
6.2 Lower the spindle into the crucible, and position it in
4.4 Device to Rotate the Spindle and Equipment to Mea-
such a manner that it meets the dimensional tolerances as
sure the Spindle Torque. This device should be accurate to
specified in 4.3.1.
within6 1 % of the full-scale range of the spindle/speed
6.3 Switch the viscometer on at a selected speed of rotation
combination in use. Reproducibility should be within 60.2 %.
(r/min). Observe the reading on the viscometer.
6.4 Calculate the calibration constant from the following
5. Preparation of Mold Flux Powder
formula:
5.1 Burn out any carbon in the mold powder by heating the
calibration constant 5~viscosity of standard!/
sample in air at 900 to 1400°F (471 to 760°C). The required
~viscometer reading! at given r/min
heating time will depend on the carbon content and types;
6.5 If the standard silicone oil has a viscosity of 3.0 poise
experiencehasshown3to24htobesufficient.Burningoutthe
and the viscometer reading at 30 r/min is
...