Comparison of Kiln Schedules for Drying Spruce

Eighteen charges of nominal 2-inch spruce [Picea glauca (Moench) Voss and Picea engelmannii Parry] from the British Columbia Interior were dried using six temperature-classification schedules: conventional, low-high, low-variable high, constant high, superheated steam and air-drying. Air circulation was varied from 250 to 900 fpm. A method of quality assessment was devised based on the presence of seasoning checks, splits, warp, loose knots, and honeycomb. Mechanical test specimens were cut from all dried boards, and tested in static bending and compression parallel to grain, after appropriate equalization periods. Drying rates (l percent MC loss/hour) were calculated for each of the schedules employed. Four conventional-temperature charges making use of 250 fpm air circulation increased the average drying rate to 0.53 percent per hour. Low-high temperature schedules employing variable air circulations of 900 and 250 fpm, improved average, drying rate to 0.73 percent/hour. When a combination of 900 and 500 fpm air circulation was used with a low-high temperature schedule, the drying rate increased to 0.82 percent/hour, a gain of 105 percent over the drying rate observed using the conventional schedule. Grade fall-down ranged from zero to 5.0 percent in conventionally dried charges utilizing the lowest circulation of 250 fpm. Low-high temperature schedules generally resulted in less than 5.0 percent severe degrade, regardless of rate of drying. Constant high temperature (max. 232?F), low-varying high temperature (max. 265?F) and superheated-steam drying schedules produced an excessive amount of honeycomb, therefore precluding their use. There was evidence that modulus of rupture, modulus of elasticity or maximum crushing strength of clear specimens were affected by drying conditions except in one instance, where exposure to low-varying high temperatures (max. 265?F) showed a statistically significant reduction of 8.2 percent in modulus of rupture.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member