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maple lumber. (This is why it’s best to either air-dry maple completely or to saw it and put it into the dry kiln immediately.) There are variations on this schedule that have been worked out by different investigators, and I’ve included them as Appendix D in this manual. Both The Dry Kiln Operators Manual and Drying Hardwood Lumber contain a variety of schedules for common species and thicknesses. They also describe how to compile a schedule for a wide variety of North American species, but the procedure can be a little confusing when you first look at it. I recommend that you use the schedules in Drying Hardwood Lumber in preference to those in the Dry Kiln Operator’s Manual. The schedules in Drying Hardwood Lumber are more recent and take into account the lower quality and narrower boards that are commonly dried nowadays. Another publication that you should know about is Dry Kiln Schedules for Commercial Woods – Temperate and Tropical19; it contains schedules for about 500 different North American and tropical species that you might refer to for less common species. Special schedules have been formulated for achieving the whitest hard maple possible, for drying both upland and lowland red oak, for drying weak, bacterially-infected oak and so forth. These schedules work reliably, but understanding what’s happening with your lumber will help you avoid the sort of problems you get when all you know is how to follow the “cookbook.” Understanding how drying procedures and drying defects are related will also help you to understand and explain what happened when you receive a load of air-dried lumber from someone else that turns out to have a lot of surface checks or stain! The schedules in both books were developed with operators of steam kilns in mind. I’ll demonstrate how to modify these schedules to take advantage of the lower drying temperatures possible with DH kilns in the next section. HOW DO CONVENTIONAL AND DEHUMIDIFICATION KILN SCHEDULES COMPARE? You can run conventional steam kilns and dehumidification kilns on identical schedules, within the upper temperature limits of the DH equipment, but it’s sometimes useful for brightness considerations to be able to take advantage of the lower temperature at which you can start to dry in a DH kiln. To convert a conventional kiln schedule to one suitable for a dehumidification kiln, lower the starting temperature to something you’re comfortable with but keep the RH% the same. If you consult the EMC chart you will find that this changes the kiln EMC very slightly (see the first lines for conventional and DH kiln schedules in Table 8 for an example). Use your common sense to increase the temperature as your sample boards dry, keeping the EMCs roughly the same as the conventional schedule you’re using as a reference. Table 8 compares a conventional steam kiln schedule with a possible DH kiln schedule for 4/4 and 5/4 upland red oak (including Appalachian red oak). (These schedules would be followed by equalization and conditioning as needed.). The DH schedule shown starts at a lower dry bulb than the conventional kiln; the RH and EMC values for each MC step are about the same as the conventional schedule until the wood is nearly dry. 19 Boone, R. Sidney; Kozlik, Charles J.; Bois, Paul J.; Wengert, Eugene M. 1988. Dry kiln schedules for commercial woods-temperate and tropical. General Technical Report FPL-GTR-57. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 158 p. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr57.pdf 87PDF Image | HARDWOOD DRY KILN OPERATION A MANUAL FOR OPERATORS OF SMALL DRY KILNS
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