Overview of the Possibilities and Limitations
of the Characterization of Ceramic Foam
Filters for Metal Melt Filtration
Claudia Voigt, Jana Hubálková, Are Bergin, Robert Fritzsch,
Ragnhild Aune, and Christos G. Aneziris
Abstract
The filtration of molten metal using ceramic foam filters
(CFF) is a purification method often used by the
aluminum industry to meet the increasing demands the
melt quality. CFFs are in most cases produced by the
replica method using polyurethane foam templates, which
are coated with a ceramic slurry of targeted composition
before being sintered into its final structure. Despite the
key role of CFFs in view of metal cleanliness, there are
only a few quality parameters for their evaluation. In the
present study, an overview of the different material
properties essential for CFFs, suitable measurement
methods, and their limitations are presented. The focuses
of this work are the different densities of ceramic foams
and the thermal expansion coef ficient measured by
dilatometry, as well as the filter porosities and microstruc-
ture measured through mercury intrusion porosimetry and
computer tomography, respectively. Moreover, elastic
(Young’s Modulus) and mechanical properties (compres-
sive strength) are discussed.
Keywords
Filtration
Ceramic foam filter
Ceramic
Introduction
Ceramic foam filters are used for melt filtration of aluminum,
iron, and steel since the 1960s [1, 2]. Despite the use of
millions of ceramic foam filters every year, there are only a
few specifications, guidelines, or papers about the require-
ments regarding the application as a metal melt filter. The
properties specified in the BDG guideline (Bundesverband
der Deutschen Gießerei—Industrie) [3] include several
parameters, e.g. filter dimensions, tolerances for the filter
dimensions, functional pore size, filter volume as well as
measurement guidelines for the cold compressive strength,
the amount of crumbs, and an impingement test.
In this study, an overview of “typical” and “untypical”
measurable ceramic foam filter properties is presented, dis-
cussed, and the limitations of the possible measurements are
described. These properties are explanatorily shown for a set
of commercially available ceramic foam filters for continu-
ous aluminum casting.
The mechanical properties of ceramic foams are often
used to develop new filter compositions and for production
quality control. The information about the mechanical
properties is gathered by measuring compressive (or crush-
ing) strength, bending strength, and Youngs Modulus,
whereby the compressive strength is the most frequently
measured mechanical property. Nevertheless, no standard
for measuring the compressive strength of ceramic foams
exists. Standards for measurement of the cold compressive
strength of shaped insulating refractory products (DIN
EN ISO 8895) [4] and dense shaped refractory products
(DIN EN 993-5) [5] could be applied for the ceramic foam
samples. These standards using samples with a size of
114 114 76 mm
3
or 114 114 64 mm
3
,
C. Voigt (&) J. Hubálková C. G. Aneziris
Institute of Ceramic, Glass and Construction Materials,
Technische Universität Bergakademie Freiberg, Agricolastr. 17,
09599 Freiberg, Germany
e-mail: claudia.voigt@ikgb.tu-freiberg.de;
Claudia.Voigt@ikfvw.tu-freiberg.de
J. Hubálková
e-mail: jana.hubalkova@ikgb.tu-freiberg.de
C. G. Aneziris
e-mail: aneziris@ikgb.tu-freiberg.de
A. Bergin R. Fritzsch R. Aune
Department of Materials Science and Engineering,
Norwegian University of Science and Technology (NTNU),
Trondheim, Norway
e-mail: are.bergin@ntnu.no
R. Fritzsch
e-mail: robert.fritzsch@ntnu.no
R. Aune
e-mail: ragnhild.aune@ntnu.no
© The Minerals, Metals & Materials Society 2021
L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series,
https://doi.org/10.1007/978-3-030-65396-5_103
785