||Steel Standard Measures Angle of Repose of Mold Powders
C 1444, Standard Test Method for Measuring the Angle of Repose of Free-Flowing
Mold Powders, has been approved within Subcommittee C08.11 on
Fluxes and Materials for Metallurgical Casting, within Committee C08 on Refractories.
This test method indicates the ability of a mold powder to flow
freely. Mold powders are used in the continuous casting of steel
and the flowability of a mold powder is an important property,
says Materials Technology Manager Trevor Hardy, involved with
product development and materials technology for 30 years with
Foseco, Inc., Brookpark, Ohio.
A mold powder is defined as a powder or granular material added
to the top of molten steel in the continuous casting mold, explains
Hardy, which partially melts forming a liquid layer next to the
molten steel. This liquid, now known as a mold flux, protects
the steel from reoxidation, absorbs the non-metallic inclusions,
lubricates the steel shell as it passes through the mold, and
controls the heat transfer from the solidifying steel shell to
the mold. Particle size, shape, and bulk density will affect the
flowability of powder material.
The angle of repose is the greatest angle measured from the horizontal
to the slope of a cone-shaped pile of free-flowing material. Test
Method C 1444 determines the angle of repose of free-flowing mold
powders; at angles greater than this angle of repose, the mold
powder will flow. A table of precision statistics in C 1444 provides
values for the:
--Average angle of repose;
--Standard deviations within and between; and
--95 percent repeatability and reproducibility intervals.
When the mold powder is applied on the top of molten steel in
the continuous casting mold, it has to flow over and completely
cover the exposed surface of the molten steel, which is particularly
important when automated flux feeders are used, notes Hardy.
If the mold powder does not readily flow then some steel surface
will remain exposed. The result is insufficient thermal insulation
and an increased reoxidation of the steel and a reduced tendency
for the mold powder to absorb non-metallic inclusions.
Hardy says the test method was developed by a C08.11 task group
of manufacturers, suppliers, and users of mold powder, and academicians
from École Polytechnique, Canada. All participated in the ruggedness
and interlaboratory testing to collect data for the repeatability
and reproducibility described in the standard.
For further technical information, contact Trevor Hardy, Foseco, Inc., 20200 Sheldon Rd., Brookpark, OH 44142 (440/816-7102).
Committee C08 meets October 19 at the Imperial Palace, Las Vegas,
Nev. For meeting or membership details, contact manager Felicia Quinzi, ASTM (610/832-9738). //
Copyright 2000, ASTM