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Accessories for the aluminum industry cast-houses

Use of SonicByte^TM for quality control of the accessories used in the aluminum industry cast-houses

Accessories used in cast-houses

The aluminum cast-houses used several pieces as accessories for the transfert of liquid metal, its filtration, its temperature measurement and others (see Fig. 1). These pieces, with various shapes, sizes and geometries are produced from refractory materials shaped by casting and then fired beyond the operating temperature. In service, these pieces are subjected to the action of severe induced stresses due to the temperature variations they face. Their longevity is directly related to the number of temperature cycles required to cause their fracture. The maximum number of cycles to failure varies inversely with the length of their original critical defects, which defines their initial level of damage.

Fig. 1: Examples of accessories used in aluminum cast-houses.

Initial damge level characterization using SonicByte^TM

Pieces initial level of damage characterization can be made using SonicByte^TM, either through their elastic modulus measurement or simply by referring to their resonance periods under different vibration modes. In the first case, the acoustic signals detected by SonicByte^TM must be treated either analytically or numerically. For geometrically simple pieces such as spouts, tap hole blocks and thermocouples shields, analytical processing allows their characterization regardless of their size. For pieces of complex geometry, such as launders and grid plates, numerical processing is required for each different dimensional format.

Characterization of the progessive damage in service using SonicByte^TM

The progressive damage of the pieces in service can also be quantified using SonicByte^TM. For example, Figure 2 provides the resonance period (under longitudinal mode) of six spouts, three of them being previously subjected, during their use in a cast-house, to different numbers of temperature cycles. The spout designated "Used-1" is the one that suffered the greatest number of cycles in service. It is also the one whose resonance period, detected by SonicByte^TM, is the highest.

Fig. 2: Resonance periods of original and used spouts.

The SonicByte^TM thus offers the possibility for users to determine the opportune moment for taking such pieces out of service. Traditionally, this decision is based on qualitative criteria, which often underestimate and sometimes overestimate the pieces' longevity. In the first case, pieces still usable are replaced unnecessarily, thereby increasing operating costs. In the second case, the liquid metal loss caused when pieces break can cause serious accidents.