. Seasoning of wood; a treatise on the natural and artificial processes employed in the preparation of lumber for manufacture . difficulties should be encountered in suc-cessfully drying the materials at hand. The Pipe or Moist-air Dry Kiln While in the blower class of dry kiln, the circulation isobtained by forced draft with the aid of fans or blowers,in the Moist-air kilns (see Fig. 31); the circulation is ob-tained by natural draft only, aided by the manipulationof dampers installed at the receiving end of the dryingroom, which lead to vertical flues through a stack to theoutside atmosphere
. Seasoning of wood; a treatise on the natural and artificial processes employed in the preparation of lumber for manufacture . difficulties should be encountered in suc-cessfully drying the materials at hand. The Pipe or Moist-air Dry Kiln While in the blower class of dry kiln, the circulation isobtained by forced draft with the aid of fans or blowers,in the Moist-air kilns (see Fig. 31); the circulation is ob-tained by natural draft only, aided by the manipulationof dampers installed at the receiving end of the dryingroom, which lead to vertical flues through a stack to theoutside atmosphere. The heat in these kilns is obtained by condensing steamin coils of pipe, which are placed underneath the material TYPES OF DRY KILNS 189 to be dried. As the degree of heat required, and steampressure govern the amount of radiation, there are severaltypes of radiating coils. In Fig. 32 will be seen the SingleRow Heating Coils for live or high pressure steam, whichare used when the low temperature is required. Figure 33shows the Double (or 2) Row Heating Coils for live orhigh pressure steam. This apparatus is used when a. Fig. 31. Section through a typical Moist-air Dry Kiln. medium temperature is required. In Fig. 34 will be seenthe Vertical Type Heating Coils which is recommendedwhere exhaust or low-pressure steam is to be used, or maybe used with live or high-pressure steam when high tem-peratures are desired. These heating coils are usually installed in sections,which permit any degree of heat from the minimum tothe maximum to be maintained by the elimination of,or the addition of, any number of heating sections. Thisgives a dry kiln for the drying of green softwoods, or byshutting off a portion of the radiating coils— thus re-ducing the temperature — a dry kiln for drying hard-woods, that will not stand the maximum degree of heat. In the Moist-air or Natural Draft type of dry kiln, any 190 SEASONING OF WOOD
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