In Eastern Canada, black spruce (Picea mariana (mill.)) lumber is often used by companies producing engineered wood products. Since it has only recently been utilized for finger-jointing, there is a need to examine this species with a view to optimizing the manufacturing parameters that influence the finger-jointing process. Key parameters influencing the finger-jointing process for softwoods such as black spruce were identified following visits to five finger-jointing plants in the Québec region.
The key parameters selected for study included: finger-joint geometry, curing time, pressure, machining parameters and moisture content and temperature of the jointed wood. Bending and tension tests were used to evaluate the finger-joints as per NLGA-SPS1-2000. Test results indicated a strong influence of finger-joint geometry on bending strength and, to a lesser extent, on tensile strength of finger-jointed black spruce. Optimum pressure was achieved at about 500 psi. Results on curing time of isocyanate adhesive indicated that mean tensile strength increased slightly with curing time until it stabilised at around 24 hours following joint assembly. More than 90% of finger-joint mean tensile strength was achieved after 5 hours of curing time at room temperature.
Results on the influence of machining parameters on the performance of finger-joints indicated no significant influence of cutting speed on tensile strength. Chip-load, however, was found to have some effect following a parabolic trend where the optimum value was achieved at 0.034 inch and at a feed speed of 60 feet/min. No clear trend on the influence of moisture content and temperature conditioning was observed for the combinations tested. However, the two combinations tested at -5oC exhibited the lowest mean tensile strength among all other combinations. There is a need to expand on this study to include more combinations of moisture content and temperature before concrete conclusions can be made.