Nondestructive Quality Assurance of Ceramic Filters Using Noncontact Dynamic Characterization

Ceramic candle filters are stiff cylindrical structures arranged in rosettes in a hot gas vessel. Custom-made with strong composite materials, these filters are designed to withstand heating and cooling cycles of very high temperature gradients during coal energy production processes. To ensure consistency in the manufactured filters, noncontact dynamic characterization using laser vibrometry is proposed as a factory quality control technique. To evaluate the proposed technique, a sensitivity study using both contact and noncontact vibration measurements is first conducted. The shift in natural vibration frequencies is used as a quality indicator for likely manufacturing variables. Six candle filters are tested using dynamic impact tests. Contact and noncontact results are compared with theoretical natural frequency values, which show that laser results were “noisier” due to dropout from speckle noises. The results are used to establish the sensitivity of the technique, which indicates that dynamic characterization is a valid nondestructive testing technique for quality assurance of the ceramic filters, provided that the manufactured filters have a quality variation greater than 3.21%.