Detection of glue deficiency in laminated wood with thermography

摘要

In the production process of gluing wooden layers, adhesion problems sometimes occur (Meinlschmidt et al., 1998). One explanation can be that the amount of glue is not sufficient or that glue is even missing in some areas. In order to minimise such quality problems, a non-destructive test method, which can give a continuous control of the process and/or the product, is needed. This paper presents results from measurements performed in order to evaluate the potential of heating up thermography as a method to detect glue deficiency in laminated wood. Defect depth, defect size, degree of glue deficiency and wooden species of the surface layer have been varied. Lack of glue with a thermal defect size, i.e. the quotient of defect size and defect depth, higher than 4 is detectable. Highest contrast is achieved for the largest defects (24 mm) below the thinnest (0,5 mm) surface layer made of the dark wooden species Merbau. Bright wooden species results in lower contrast. Starved glue joints show about half the contrast compared to areas with total lack of glue.