Further Trials of Roll-Feed, High Temperature Dryers for 8/4 Southern Pine

Studs dried by four configurations of roll-feeding mechanisms (for a continuous kiln similar to a roll-feed veneer dryer) were compared to conventionally stickered studs. The roll-feed arrangements were as follows: (1) studs fed flat between smooth rolls and guided between fixed steel bars; (2) studs fed flat under smooth top rolls guided between high-shouldered rings on bottom rolls only; (3) spool-shaped rolls on top only (spools having 45-degree faces), with studs fed flat; and (4) studs fed on edge between low-shouldered rings mounted on both top and bottom rolls. Studs were charged into a cold kiln. The kiln was heated to 240?F/160?F and held for 21 hours after startup; the load was then steamed for 3 hours at 195?F/185?F and discharged. The green studs, which were surfaced S4S to 1.74-inch thickness and 3.82-inch width, averaged 81.5 percent in moisture content and 19.0 pounds in weight. Crook, bow, and twist, when green, averaged 0.06, 0.11, and 0.08 inch. Specific gravity of the studs was 0.46 based on green volume and ovendry weight. Dry studs averaged 8.5 percent in moisture content, with range from 3.8 to 16.0 percent and standard deviation of 2.3 percent. Average stud weight on discharge was 11.6 pounds, with range from 8.8 to 14.9 pounds. Roll-dried studs averaged less crook (0.14 inch), bow (0.17), and twist (0.16) than those conventionally stickered (0.22, 0.26, and 0.34 inch respectively). The data seem to favor the dryer configuration in which studs are roll-fed on edge and guided by double low-shouldered rings. With studs fed on edge, thickness shrinkage was least of any configuration, averaging only 0.05-inch. Disadvantages of roll-feeding studs on edge between double low-shouldered rings include some damage to corners of twist-prone lumber, an extra 1/10 inch of width shrinkage, and poorer control of twist and bow than when studs are fed flat. The grading rules which allow only 1/4-inch of crook compared to 3/8-inch of twist and 1/2-inch of bow appear to place emphasis on crook control. The major disadvantage of all four of the roll-fed configurations tested is the necessity for accurately sizing each green stud in width and thickness before admitting it to the kiln.

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