Non-destructive testing methods in veneer-based products manufacturing

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Toni Antikainen Name of the doctoral dissertation Non-destructive testing methods in veneer-based products manufacturing Publisher School of Chemical Technology Unit Department of Forest Products Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 100/2015 Field of research Wood Product Technology Manuscript submitted 7 April 2015 Date of the defence 28 August 2015 Permission to publish granted (date) 23 June 2015 Language English Monograph Article dissertation (summary + original articles) Abstract In modern veneer-based product manufacturing non-destructive testing (NDT) measurement methods are of importance. The great variation in wood (and veneer) material properties brings challenges in production and in the quality of the end product. By using NDT measurements methods the aim is to detect key material properties and grade the raw material into different predefined categories to obtain an end product with good properties having as low a deviation in these properties as possible. The aim of this study was to investigate approaches to the non-destructive and potentially on-line evaluation of i) veneer moisture content (MC), ii) lathe check depth (LCD) and grain angle (GA) in veneer and iii) adhesive spread rate (SR) on veneer. The study began by investigating the accuracy and precision of two existing industrial veneer MC measurement devices (Metriguard DME and Mecano MVA) and was followed by the development of the NDT methods. The MC of birch veneer was estimated with infrared (IR) technology. Veneers with different MC were imaged with an IR camera after drying and the relationship between the temperature data and veneer MC was then modelled. When estimating veneer MC with independent data not used in modelling it was found that the root mean square error (RMSE) was 1.2 %. Based on the results of this study, it was concluded that the spatial resolution of the IR method is better than microwave based methods but that the IR technology is more sensitive to the environment where the measurement is done and the accuracy is worse. Veneer strength properties may be characterized by the tensile strength perpendicular and parallel to the grain. The tensile strength perpendicular to the grain correlates strongly with LCD and tensile strength along grain with GA. In this study LCD and GA were measured simultaneously with laser trans-illumination imaging. LCD and GA were recognized from images using image analysis techniques. RMSE was found to be 7.4 % when measuring LCD. Absolut average error was 1.1 ° when measuring GA. Adhesive spreading is also an important process phase. The adhesive must be spread equally over the veneer to obtain the best strength properties. A fluorescence based measurement method to estimate adhesive spread rates was developed. RMSE was found to be13 g m-2 suggesting that this method could be an option when developing automated real-time adhesive SR measurement for processes. The proof-of-concept methods presented showed some promising results. The knowledge obtained through this dissertation increases the chances of developing real-time NDT measurement methods for veneer-based product manufacturing processes.In modern veneer-based product manufacturing non-destructive testing (NDT) measurement methods are of importance. The great variation in wood (and veneer) material properties brings challenges in production and in the quality of the end product. By using NDT measurements methods the aim is to detect key material properties and grade the raw material into different predefined categories to obtain an end product with good properties having as low a deviation in these properties as possible. The aim of this study was to investigate approaches to the non-destructive and potentially on-line evaluation of i) veneer moisture content (MC), ii) lathe check depth (LCD) and grain angle (GA) in veneer and iii) adhesive spread rate (SR) on veneer. The study began by investigating the accuracy and precision of two existing industrial veneer MC measurement devices (Metriguard DME and Mecano MVA) and was followed by the development of the NDT methods. The MC of birch veneer was estimated with infrared (IR) technology. Veneers with different MC were imaged with an IR camera after drying and the relationship between the temperature data and veneer MC was then modelled. When estimating veneer MC with independent data not used in modelling it was found that the root mean square error (RMSE) was 1.2 %. Based on the results of this study, it was concluded that the spatial resolution of the IR method is better than microwave based methods but that the IR technology is more sensitive to the environment where the measurement is done and the accuracy is worse. Veneer strength properties may be characterized by the tensile strength perpendicular and parallel to the grain. The tensile strength perpendicular to the grain correlates strongly with LCD and tensile strength along grain with GA. In this study LCD and GA were measured simultaneously with laser trans-illumination imaging. LCD and GA were recognized from images using image analysis techniques. RMSE was found to be 7.4 % when measuring LCD. Absolut average error was 1.1 ° when measuring GA. Adhesive spreading is also an important process phase. The adhesive must be spread equally over the veneer to obtain the best strength properties. A fluorescence based measurement method to estimate adhesive spread rates was developed. RMSE was found to be13 g m-2 suggesting that this method could be an option when developing automated real-time adhesive SR measurement for processes. The proof-of-concept methods presented showed some promising results. The knowledge obtained through this dissertation increases the chances of developing real-time NDT measurement methods for veneer-based product manufacturing processes.