Heat treatment of electric melting refractory materials

The heat treatment process of fused cast refractories, the general heat treatment can be divided into two stages of crystallization and annealing:

1. Crystalline stage

The general hope exists a certain size and uniform distribution of internal grain products. And the precipitation of crystal to a certain temperature range and enough time, so in the crystallization temperature range (crystalline phase) should be insulated for a period of time, let the crystal full precipitation and growth.

2. Annealing stage

After casting electric melting refractory products in the cooling process, because each part of the heating is not uniform, the casting internal temperature gradients, the great stress, causing cracking products. The cooling speed is high, the internal temperature difference is bigger, will produce stress are larger, causing the cracking tendency is even more. Therefore, casting should slow cooling, heat treatment. There are two kinds of annealing methods, namely natural annealing and external heating annealing.

(1) Natural annealing

In the heat preservation, heat insulation layer using casting types of external (diatomaceous earth and rock hit) and thickness, the casting cooling slowly.

In the heat preservation of annealing is to rely on the heat of casting itself. Adjust the cooling system is very limited, only from the thickness and thermal physical properties and the thermal insulation box mold insulation layer choice adjusting casting early cooling conditions, and the later stage (about the cooling time of 80% ~ 90%) with different time intervals to adjust, in fact is not possible. Moreover, thermal insulation filler dust, the assembly and disassembly of the mold to manual labor, small volume or special-shaped product quality can not be guaranteed, the insulation box low turnover rate, low rate of finished products.

(2)External heating annealing

Using annealing tunnel kiln, which can reduce the temperature gradient of electric melting refractory products surface layer and the center, so that the quality product rate of not less than 80%.