Automated control of cellulose fibre cement boards with a non-contact ultrasound scanner

• A non-contact ultrasound method using Lamb waves, for the quality control of cement boards is presented.
• An original test methodology developed for testing cellulose fibre cement boards is included.
• The methodology was verified by laboratory tests on specimens, and in real production conditions.
• The distribution of moisture content in the boards and Lamb wave characteristics were compared.

This paper presents a non-contact ultrasonic method using Lamb waves, for the automatic quality control of cellulose fibre cement boards during their production. The causes of typical material imperfections: delamination, cracks, material heterogeneity and areas of excessive moisture content, disqualifying such boards from sale, are described. Tests were carried out using an ultrasound scanner specially constructed to identify the imperfections. The Lamb wave amplitude-signal registration position characteristics were determined and the defective areas were identified on their basis. Also the influence of board moisture content on ultrasonic test results was taken into account. The moisture content in the boards was measured in all the stages of their production and maps showing the distribution of average mass moisture content in the finished cellulose fibre cement boards were plotted. The studies have shown the non-contact ultrasound method based on Lamb waves to be a suitable tool for the testing of all the boards being in production without halting the latter.