Laser incising of Canadian softwood to improve treatability

Laser-incised black spruce and Douglas-fir lumber was successfully treated with chromated copper arsenate (CCA) type C preservative. However, the high number of incisions required, together with the relatively slow speed of the incising process, combine to limit the potential of this technology. Air-dried black spruce and kiln-dried Douglas-fir boards were incised using a carbon-dioxide laser. It was established that a laser of 125 watts with a beam duration of 0.03 second produced incisions with a depth of 10 mm. The incision diameter at the surface was approximately 0.7 mm. Increasing the energy of the laser increased the surface browning, due to the heat developed during the vaporization of the wood by the laser. CCA pressure treatment of black spruce boards incised with 13,888 incisions per square meter did not produce an integral shell of treated wood. Reducing the longitudinal separation of incisions from 72 mm to 36 mm or 24 mm improved the treatment sufficiently to allow the samples to exceed the requirements of the Canadian wood preservation standard. The penetrations and retentions in Douglas-fir boards, incised with dense patterns having longitudinal spacings of incisions of 24 mm and 18 mm, exceeded those required by the Canadian standard. Increasing the laser energy and the beam duration resulted in complete penetration of the board. An energy-time combination of 200 watts times seconds was found to provide the 42-mm penetration necessary to penetrate the board.

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