Sawing and drying of hardwood lumber from small diameter logs.

摘要

With high stumpage prices, each year sawmills are processing more and more smaller diameter hardwood logs. Most of the mills do not know the lumber yield, lumber grade, or cost of processing these logs. This project investigates the processing and yield of small diameter (11"and lower small end diameter) black cherry (Prunus serotina), sugar maple (Acer saccharinum), and northern red oak (Quercus rubra) logs. The location of each board was mapped in relation to the profile of the logs. After being sawn every board was examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a pre-drying grade. Drying was conducted through the use of a conventional kiln drying schedule and two modified kiln schedules designed to dry the lumber under milder drying conditions compared to the conventional kiln schedule. The first modified kiln schedule lowered the final dry bulb settings, while the second decreased the initial and final dry bulb settings. Modifications were made to the conventional kiln schedules published in the Dry Kiln Operators Manual but maintained comparable equilibrium moisture content (EMC) conditions for drying steps of the conventional kiln schedules. After drying each board was again examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a post-drying grade. Other characteristics that were recorded included slope of grain, the presence or absence of pith, and location of the board by log quality zone. The project also investigated the development of milder kiln drying schedules by testing the modified kiln schedules. In addition the strength and dimensional stability of the lumber was measured to investigate and predict the performance of the lumber when exposed to in-service varying EMC conditions. This study will provide the wood products industry with a better understanding of processing and use of lumber from small diameter hardwood logs.