ENCYCLOPÉDIE DE LA RECHERCHE SUR L’ALUMINIUM AU QUÉBEC 2013 | Page 70

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DÉVELOPPEMENT, OPTIMISATION ET INTÉGRATION DES PROCÉDÉS DE FABRICATION ET DE CONCEPTION
Static and kinetic friction
DEVELOPMENT, OPTIMIZATION AND PROCESS INTEGRATION OF MANUFACTURING AND DESIGN

coefficients of the carbon paste

COEFFICIENTS DE FRICTION STATIQUE ET CINÉTIQUE DE LA PÂTE DE CARBONE
with a lubricated steel mould at
EN UTILISANT UN MOULE LUBRIFIÉ EN ACIER À HAUTES TEMPÉRATURE ET PRESSION

high temperature and pressure

STATIC AND KINETIC FRICTION COEFFICIENTS OF THE CARBON PASTE
WITH A LUBRICATED STEEL MOULD AT HIGH TEMPERATURE AND PRESSURE
1
1

Stéphane Thibodeau , Jeffrey Dubois , Donald
Ziegler2, Houshang D. Alamdari1 and Mario Fafard1
Chaire de recherche industrielle CRSNG/Alcoa MACE3,
Centre de recherche sur l’aluminium - REGAL
Alcoa Primary Metals, Alcoa Technical Center, 100 Technical Drive
Alcoa Center, PA 15069-0001, USA
1

2

Introduction

Method
Two tests were performed. The first one gives the global friction
behavior of the paste and Teflon combined. The second test,
that generates a second system of equations, utilises a steel
plate under the paste. Rp (eq. 4) can be defined, with known
parameters, by subtracting equations 2.1 and 2.2. Now, only
μp/s is unknown by replacing equations 1 and 4 into 2.2.

Historically, the Hall-Héroult process used the
Söderbergh technology which consists in
constantly regenerating a continuous anode
while adding pitch on the top. Today, the primary
aluminum industry uses prebaked anodes due
to their higher performance. These anodes are
pressed or vibrated in a lubricated steel mould.
Modelling the forming process is a valuable
approach which will help improve the process
and the anode itself.
1

Problematic
During the forming process, the carbon paste is
confined and high normal stresses in the paste
at the interfaces with the mould are developed.
Friction forces result at the mould wall and
paste interface whether using a lubricant or not.
The friction restricts the movement of the
paste causing density gradients within the
carbon blocks.

Objective

PRIX // AWARD
Chaire de recherche Alouette,
UQAC sur le carbone

Determine the static and kinetic friction
coefficients at the mould/paste interface. The
industrial forming process requires a high level
of stress and a temperature of 150
C.
Because the literature is incomplete in regard to
the friction coefficients of the paste/steel
interface at both the target temperature and
high stress level, an apparatus has been
developed.

Material
Stéphane Thibodeau
Jeffrey Dubois
Houshang Alamdari
Mario Fafard
Centre de recherche
sur l’aluminium - REGAL,
Université Laval
Chaire de recherche
industrielle
CRSNG/Alcoa MACE3
Donald Ziegler
Alcoa Technical Center

Comparative
tests

Paste friction
test

FApp = Rp + Rm

2

FT = fp + fT
FT = Rp·μp/s + Rm·μt/s

3

Rm = Pi·S ·μp/s

2.1
4

FT = Rp·μp/s + Rm·μt/s
F – FT
Rp = T1
μs/s - μp/s

2.2
5

FT1 = Rp·μs/s + Rm·μt/s

FT1 = FApp μt/s + (μs/s - μt/s)

FT1 – FT
μs/s - μp/s

The friction coefficients of the
Teflon/steel and steel/steel interfaces were obtained by
means of the same apparatus using an empty mould. Two
different steel/steel friction coefficients were found due to
the apparatus limitations. Coefficients were selected
based on the similarities in the test behaviours. A second
experiment, where the Teflon and steel plate were
inverted, was done in order to validate the results. The
figure on the right summarizes the entire employed
method. A lubricant was used during each test.

Results
The first graph presents typical curves of the force needed to generate the
displacement of the mould. Colored lines represent the pressure applied on the paste.
The second graph shows the friction coefficients obtained from the two different
approaches. The asterisk is related to the second experiment using µs/s*.

FApp
Ft

Kinetic
Static

Conclusion
o The developed apparatus was able to reveal the friction behavior of the carbon paste
under as large pressure as 6,5 MPa and at a temperature of 150 C;
o The tests permitted to obtain the static and the kinetic friction coefficients of the anode
carbon paste with the mould wall which are respectively 0,15 and 0,13.
o The friction coefficients found will be introduced in the simulation of the forming
process, based on the model developed by Hicham Chaouki, with the aim of improving
the quality of the anode block and the process itself.

Journée des étudiants – REGAL

In the aluminum industry, the anode blocks manufacture represents an important
Dans l’industrie de l’aluminium, la fabrication de blocs anodiques représente un
grand défi en termes de qualité. La friction de la pâte carbonée avec lede Montréal, challenge in 22 octobre 2013 The friction of the carbon paste with the mold restricts
Palais des congrès moule
QC, Canada, terms of quality.
its movement and cause density gradients within the anode. Numerical modeling
restreint le mouvement de cette dernière et cause des gradients de densité à
provides a great opportunity to predict the mechanical behavior of the paste
l’intérieur des anodes. La modélisation numérique offre une belle opportunité
when subjected to external stresses. To properly simulate this behavior, the static
de prédire le comportement mécanique de la pâte lorsqu’elle est soumise à
and kinetic coefficients of the paste with the mold must be defined. This poster
des contraintes externes. Afin de simuler adéquatement ce comportement, les
presents the work that led to the characterization of the tribological behavior of
coefficients de friction statique et cinétique de la pâte avec le moule doivent être
the paste at high temperature and stresses. An apparatus has been developed to
définis. Cette affiche présente les travaux qui ont conduit à la caractérisation du
perform