EFFECTS OF MIXTURE COMPOSITION ON THE LINING
STABILITY OF A CRUCIBLE INDUCTION FURNACE
A. S. Zavertkin
Translated from Novye Ogneupory, No. 5, pp. 41 – 43, May, 2008.
Original article submitted March 16, 2006.
Research results are reported on the effects of components on the resistance of acid lining for the crucible
induction furnace. To raise the lining resistance, one needs to eliminate components that react with the silica
crucible. The extent of silicon reduction from the lining is dependent on the heating of the metal and the
contents of carbon and silicon in the liquid. Increasing the carbon content and reducing the silicon
concentration in the metal favor wear on the crucible. The slag components most actively influencing the
resistance of the lining are magnesium and calcium oxides, which are produced on modifying cast iron,
ferrous oxide, and manganese on account of reduction in the viscosity of the slag, increase in its wetting
power, and penetration into the pores and unevenness in the walls of the crucible.
Karelian Republic casting organizations melt cast iron in
induction furnaces working at line frequency or at frequ-
encies ³1000 Hz. The crucible material reacts with the
reagents in the induction oven in a fashion dependent on
various factors, mainly how the melting is conducted.
In induction melting, there are marked temperature
differences in the liquid, which moves under electromagnetic
mixing. The slag temperature is somewhat lower than the
metal temperature. The reactions may include ones either
envisaged or neglected involving the additives, the slag, the
atmosphere, and the crucible lining. Other effects come from
the temperature in the furnace, the concentrations of harmful
impurities that attack the lining, and the area of interaction,
all of which influence the reaction rates.
During use, the crucible lining acquires a zone structure.
The internal working zone facing the liquid metal and slag
tends to dissolve. Behind it lies a transitional zone, which is
fairly dense, and which is subject to lower temperatures by
comparison with the working contact zone. Then follows the
quartzite zone, or what is called the least-altered zone, in
which the grains of the quartzite lining are not connected one
with another because of the inductor cooling. Chemical
analysis indicates that the contact zone serves interaction
between the oxides of iron, manganese, magnesium, alu
minum, and other components of the metal on the one hand
and the acid lining on the other. Slag is not especially added
in an induction furnace with acid lining. However, the oxides
formed by oxidation of the charge components constitute a
form of scum or slag, which reduces the stability of the lining
in the upper part of the crucible and does not favor the
improvement of the metal quality. The slags with certain
exceptions are formed by the oxidation of iron, silicon, and
manganese in the charge, as well as from the attack on the
The electromagnetic stirring causes the layer of colder
oxides formed at the surface to be entrained in the recesses of
the crucible, where it is heated and attacks the lining.
The attack is the less the closer the composition of the slag to
that of the lining. The composition of the slag on heating cast
iron in an LFD-25 induction furnace is shown in Fig. 1 for a
lining composed of Pervoural=sk quartzite from the
Petrozavodskmash Company used up to 1400 and 1500°C.
The small grains of quartzite lining are the most rapidly
attacked by the liquid metal and slag. Table 2 gives the
contents of silica and other oxides in the fractions .1 and 0.1
mm in the lining mass.
Tables 1 and 2 show that the compositions of the slag and
the lining (fraction <0.1 mm) differ only slightly. Above
Refractories and Industrial Ceramics Vol. 49, No. 3, 2008
1083-4877/08/4903-0213 © 2008 Springer Science+Business Media, Inc.
Geological Institute, Karelian Scientific Center, RAS, Russia.
TABLE 1. Slag Composition
Oxide content, wt.%
FeO MgO Al
1400 73.90 9.07 3.26 8.07
1500 79.78 3.31 1.92 8.24