A Study of Bark Removal At Low Temperatures By Simulated Cambium-Shear Methods

Debarking of white spruce (Picea glauca) and balsam fir (Abies balsamea) at sub-zero temperatures was studied. Experiments were carried out in the laboratory on a single-tool, debarking apparatus simulating ring-type debarkers. Seven debarking tools were employed at tool pressures up to 400 pounds per inch of cutting edge, at log temperatures varying between -30 and 0?F. In general it was observed that white spruce offered greater resistance to bark removal than balsam fir and that at low temperatures bark removal appears to be dependent primarily on a) the force applied on the tool, and b) tool geometry. Temperatures below the -10 to -15?F range seem to be critical in terms of bark removal. Within the experimental limitations imposed by simulation techniques, results showed that the desired level of bark removal (0.5 percent bark remaining) may be obtained at various combinations of angle of attack and tool pressure. Depending upon species, the minimum value of the radial force component was between 50 and 55 lb./in. to obtain the above efficiency. From the standpoint of power – and maintaining acceptable barking efficiency – a tool angle of attack of approximately 75? – 80? should be used. Cutting edge radius was not studied extensively, although it will probably have an effect if it departs substantially from the 0.010 to 0.040 in. range. Within the range examined, tool sharpness and clearance angles had no detectable effects. Low levels of residual bark were usually accompanied by high wood losses. Thus, in commercial practice, a slightly higher residual bark value might be tolerated in order to obtain an acceptable value in the latter. Other factors having an effect on debarking quality are moisture content of the inner and outer bark, species (white spruce, although requiring more power, yields more acceptable results than balsam fir) and compression wood.

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