The main objective of this project was to determine practical methods for enabling veneer mills to continuously monitor glue spread over the entire veneer surface during production and to alert mill personnel to problems as they occur.
Several mills were visited to determine the main factors affecting glue coverage and uniformity for roll spreaders, curtain coaters, foam extruders and spray applicators. For each of these applicator types, the feasibility for online spread measurement was assessed based on observations and discussions with mill personnel. It was observed that with all applicator types, problems are a common occurrence due to a wide range of factors ranging from viscosity fluctuations and flow blockages to veneer surface roughness.
It is apparent that mills could greatly benefit from having an automated system for real time monitoring of glue application quality for detecting glue deficiency and providing valuable feedback for the mill to minimize problems such as poor bonding, delamination, etc.
From the experimental phase of the project, it was demonstrated that near IR (infra-red) light could be used to probe through phenolic glue coatings on veneer with results linking the degree of IR light absorption to the coating thickness (R² > 0.95). Tests also showed the feasibility of using this method for urea formaldehyde (UF) glue mixes.
Based on the findings a computerized, optical scanning system was developed using tungsten halogen work lights as an IR source and an IR sensitive camera as the detector. For the setup, lights were angled downward at 45 degrees to illuminate the full width of the veneer surface with the camera mounted directly above the illuminated area to measure the IR reflectance. A computer with imaging software developed by Forintek was used to record the readings and calculate the glue spread. To simulate mill conditions, the entire system was mounted on a laboratory veneer conveyor and then used for scanning full-size veneer sheets at production line speeds.
Pilot plant tests and a subsequent mill trial demonstrated that the scanning system was effective for continuous, online measurement of phenolic glue spread over the entire surface area of 4x8-foot veneers.
Following this project, Forintek has planned to facilitate the transfer of this technology to industry through involvement with a project to install an advanced prototype scanning system at a Forintek member mill.