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Pre-cast refractory blocks

 Use of SonicByte^TM for quality control of pre-cast refractory blocks used for the hearth lining of aluminum melting furnaces

Aluminum melting furnaces

Aluminum melting furnaces (see Fig. 1) are very often charged with heavy ingots that are droped into the furnace. The hearth of these furnaces should thus be lined with materials having a high mechanical resistance such as pre-cast refractory blocks. 

Fig. 1: Aluminum melting furnace.

Pre-cast refractory blocks

Pre-cast refractory blocks are curently made from mullite-based castables that are pre-shaped in form of hexagons which are then heat treated up to about 800°C prior their use (See Fig. 2).

Fig. 2: Pre-cast refractory blocks.

The mechanical resistance of such blocks may vary by more than 100% due to their heterogeneous nature as well as their large dimensions making difficult the achievement of uniform temperature distribution during their firing.

Problem experienced with the use of pre-cast refractory blocks

The use of the lower resistant pre-cast refractory blocks from a given batch may lead to furnace premature failure when the blocks quality variation, within this batch, exceeds a limit value. This problem happened in an aluminum melting furnace that failed after 3 months of operation.

Post-mortem analysis conducted with SonicByte^TM

Pre-cast refractory blocks taken from the prematurely failed furnace were first analysed with SonicByte^TM to determine their modulus of elasticity (MOE) under symetrical vibration mode. The same analysis was made on same type of blocks taken from a similar reference furnace that did not experience premature failure on service.

The obtained results showed that the blocks taken from the prematurely failed furnace had a maximum MOE lower than 30 GPa which was the minimal value obtained for the blocks taken from the refrerence furnace.

Pre-cast refractory blocks quality control using SonicByte^TM

Before restarting the prematurely failed furnace with new batches of pre-cast refractory blocks made from the same product, each block from these batches was submitted to quality control using SonicByte^TM. The results obtained from one of these batches are shown on Figure 3. It can be noted that about 50% of the blocks from this batch had a MOE lower than 30 GPa.

Fig. 3: MOE distribution of a batch of pre-cast refractory blocks.

Finally, from the overall tested blocks, only those having a MOE higher than 30 GPa  were installed inside the furnace. After several years of operation, no premature failure was then experienced with that furnace.