The economic feasibility of preheating Douglas-fir blocks prior to peeling Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w9505331h

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  • Past research and industrial sources have implied that preheating Douglas-fir Pseudotsuga menziesii (Mirb.) Franco prior to peeling veneer was economically feasible. To test this, the effect of treatment temperature on veneer yield and thickness variation for three diameter classes of low grade Douglas-fir logs was studied and related to the cost of preheating. Test results showed that pre-heating No. 3 Douglas-fir Sawmill logs to a peel temperature range of 50°F to 120°F had no statistical effect on veneer value, total yield, grade yield, or veneer sheet width yield of 12, 18, and 24 inch diameter blocks. Block diameter, however was found to have a highly significant effect on veneer value expressed as the value of the percentage of the block volume recovered as marketable green veneer. Eighteen inch diameter blocks had the greatest total, grade, and full sheet recovery per unit volume of initial block diameter. Twenty-four inch diameter blocks had the least recovery and value while the 12 inch blocks were intermediate. Veneer thickness variation was found to be independent of peel temperature but significantly influenced by block diameter. The reason for the block diameter-veneer yield and thickness variation interaction was not investigated but was probably due to a complex interaction of wood properties at various diameters and the changing in the lathe setting angles due to the differences between diameters. A microprocessor based data acquisition system was built to record the output of a non-contact infrared temperature sensing instrument that measured the block temperature profile during peeling. The variability of temperature found within the blocks suggest the effects of heating would vary greatly for any one block. The microprocessor proved to be a valuable research tool that has many research uses but more importantly, many industrial process control applications. The equation describing unsteady state transfer for an infinitely long cylinder was solved via numerical analysis to theoretically estimate heating times for veneer blocks. The model may not be applicable to wood because the assumptions used to solve the problem, i.e. constant diffusivity and homogenity of the material, are violated when dealing with wood.
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