Livarski vestnik 55 / 2008 št. 2

Zoran Glavaš, Faruk Unkić, Dragutin Lisjak:
THE PREDICTION OF THE AS-CAST DUCTILE IRON IMPACT TOUGHNESS BY USING THERMAL ANALYSIS AND ARTIFICIAL NEURAL NETWORKS

Sandor Lukacs, Friedrich Klein:
POSSIBILITIES AND LIMITS TO PRODUCE DIE CASTING PARTS WITHOUT DEFECTS

Karlo Raić, Rebeka Rudolf, Ivan Anžel:
CORROSION OF REFRACTORIES USED IN SECONDARY ALUMINIUM MELTING FURNACES

Zoran Glavaš 1, Faruk Unkić 1, Dragutin Lisjak 2
1) Faculty of Metallurgy, University of Zagreb, Aleja narodnih heroja 3, 44103 Sisak, Croatia
2) Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10002 Zagreb, Croatia

THE PREDICTION OF THE AS-CAST DUCTILE IRON IMPACT TOUGHNESS BY USING THERMAL ANALYSIS AND ARTIFICIAL NEURAL NETWORKS

Abstract

This paper presents the application of artificial neural network (ANN) in the foundry process. A two-layer feedforward neural network which is trained using backpropagation algorithm that updates weights and biases values according to gradient descent momentum and an adaptive learning rate (Backpropagation Neural Network – BPNN) have been established to predict the as-cast impact toughness of ductile iron (DI) using the thermal analysis (TA) parameters as inputs. The generalization property of the developed ANN is very good, which is confirmed by a very good accordance between the predicted and the targeted values of as-cast impact toughness on a new data set that was not included in the training data set.
Key words: ductile iron, impact toughness, artificial neural networks, thermal analysis

Dr.-Ing. Sandor Lukacs, Prof. Dr. Dr. h.c. Friedrich Klein

POSSIBILITIES AND LIMITS TO PRODUCE DIE CASTING PARTS WITHOUT DEFECTS

Abstract

Shrinkage cavities can be minimized if different local solidification times are achieved by suitable die material combinations.
On the basis of the measurements it could be proven that in accordance with the Chvorinov equation the solidification time constant depends not only on the thermo physical characteristics of the melt and the die, but also on the local wall thickness. The smaller the local wall thickness of a cast part, the larger is the appropriate solidification time constant.
By the prepared connections the solidification time coefficient can be easily determined from the wall thickness and the surface temperature of the die.
For the aluminium alloy AlSi9Cu3 the wall thickness was aimed at which is attainable with an identical solidification time by the change of the heat conductivity, selecting a hot-working steel with different thermo physical characteristics and the temperature of the cooling agent. The definition of the wall thickness correction factor (FKT) allows to determine the increase possible of the rigid wall thickness ton the basis of different heat conductivities of the die material at same solidification time and temperature of the cooling agent.
Due to the investigations about the influence of the cooling agent temperature on the solidification time, a calculation method was developed, with the assistance of the temperature of the cooling agent, in order to ensure an identical solidification time for cast part ranges with different thicknesses, within the usual wall thickness range.

Karlo Raić 1, Rebeka Rudolf 2,3, Ivan Anžel 2
1) University of Belgrade, Faculty of Technology and Metallurgy, Karnegijeva 4, 11000 Belgrade, Serbia
2) University of Maribor, Faculty of Mechanical Engineering (FME), Smetanova ul. 17, 2000 Maribor
3) Zlatarna Celje d.d., Kersnikova ulica 19, 3000 Celje, Slovenia

CORROSION OF REFRACTORIES USED IN SECONDARY ALUMINIUM MELTING FURNACES

Abstract

This paper discusses the internally (chemical, structural and physical) and externally (thermal stress, mechanical stress and electrical power) affected mechanisms during refractories’ corrosion in secondary aluminium melting furnaces.
Chemical corrosion occurs due to redox processes which destroy the refractories’ oxide content. A refractory’s heterogeneous surface structure has a catalytic effect on the corrosion of its wall. Physical corrosion starts with the penetration of an aluminium molten mass into the wall.
Thermal stress on the refractory leads to crack nucleation and/or propagation and resulting in loss of strength. In addition mechanical stress, i.e. the rotative action in a tilting rotary furnace, can also be a reason for a refractory wall’s corrosion. Similarly, any higher specific electrical power of the induction furnace could accelerate corrosion.
Practical methods are presented for avoiding the corrosion of a refractory’s wall. In this context, the influence of additives is discussed as well as protective coatings on the corrosion resistance of an alumino silicate refractory.
Key words: refractory corrosion, secondary aluminium, melting furnaces