Evaluating the service parameters of crucible induction furnaces with graphite-bearing crucibles

Conclusions

We observed significant differences in the magnitude of the electrical resistivity of the (crucible) material in the zones of the diametric section of the graphite-bearing crucibles having unidirectionally oriented natural-graphite flakes, but differing in their location with respect to the direction of pressing.

In order to obtain a more uniform distribution of the ρ(t) values along the walls of a crucible designed for working in the medium frequency furnaces, its production technology must provide for a more isotropic structure, a more uniform densification in the wall along its entire height, and an identical material composition. It is desirable to carry out the melting process in the crucible under an atmosphere avoiding oxidation of graphite, or taking into account its possible burnup and the consequent increase in the electrical resistance of the crucible and its destruction during service.

The obtained data permit one to evaluate the order of magnitude of the electrical resistivity in the crucible zones which are of particular interest during induction heating: side walls close to the inductor and the outer corners of the top and the bottom parts. However, the specific features of the crucible texture give a basis to propose that the results of the electrical resistivity measurements carried out on the crucible material using the contact method (in particular, the dc measurements) must be specified more accurately for the calculations concerning heating of the metal-filled crucibles under medium frequencies. It is necessary to determine the effective electrical resistivity of the crucible material developed under these conditions using a special noncontact method under the most commonly used frequencies for the induction furnaces working with conducting crucibles.