PDF Publication Title:
Text from PDF Page: 006
MONITORING THE DRYING For information on drying schedules and schedules for specific species and thicknesses, see the reference to the Dry Kiln Operator’s Manual and the Dry Kiln Schedules for Commercial Woods: Temperate and Tropical. In measuring the rates of moisture loss, it is impractical to weigh every board in the kiln and electric meters are not accurate above 30 percent moisture content. Therefore, the sample board method should be used to determine the moisture content of lumber in the kiln. This method uses short, carefully chosen sample boards sawn from larger pieces of lumber and these sample boards are weighed periodically and estimated moistures are calculated. Since the wettest or slowest drying lumber in the kiln has the highest risk of splitting and cracking, the sample boards should represent this kind of lumber. Use samples from the most recently cut wood, the widest and thickest boards, lumber with the most heartwood, and boards that are quartersawn whenever possible (see Appendix C: Procedures for Cutting and Using Sample Boards). PROCESS While the kiln described in this publication is designed for simple operation, you will still need to closely monitor the drying process. Monitoring the moisture loss and quality of the wood during the drying process will help you maximize the efficiency of the kiln. Simply explained, when drying lumber you want to dry fast enough to prevent stain and long drying times, yet slow enough to prevent checks and other drying defects. The prevalence of certain defects is influenced by the species, thickness, moisture content, and drying conditions. Monitoring the moisture content during the drying process is important to avoid drying too rapidly (which results in quality loss) and to know when the load has reached the desired moisture content. Measure the sample boards daily to determine the daily rate of moisture loss. This loss should be compared with the safe drying rate for that species (see Figure 7 for hardwoods). If the drying rate is too fast, then it may be necessary to increase the relative humidity setpoint of the dehumidifier or turn two of the four fans off. Lumber should be dried to the maximum safe drying rate without exceeding the daily loss. The safe drying rate refers to the moisture loss in one day, not the average loss over several days. Figure 7 lists the safe drying rate for common one inch thick North American hardwoods. Softwoods are typically able to dry at a much faster rate and moisture content losses above 10 percent per day are quite common. When lumber is at its highest moisture content, it is important to adhere to the safe drying rate. Most unwanted checking and splitting in drying lumber occurs as the wood loses the first one-third of its moisture content. Once the lumber dries below 22 percent moisture content, the risk of creating new cracks and splits is low. Dry lumber for interior use to a moisture content of six to eight percent for most areas of the country. This will limit the amount of dimensional changes that would occur when the wood is processed and in service. Lumber used for exterior purposes is usually dried to 12 to 15 percent moisture content. Softwood lumber used for framing is commercially dried to 19 percent moisture content. However, fewer building defects would result if softwood framing lumber were Figure 7: Safe Drying Rates for North American Hardwoods. SPECIES Ash, White Beech Birch, Yellow Cherry Elm, American Gum, Red Maple, Hard Maple, Soft (Sapwood) Oak, Red Lowland Oak, Red Upland Oak, White Upland Poplar, Yellow Tupelo (Black Gum) Walnut MAXIMUM RATE OF MC LOSS PER DAY (%) 1” Thick 2” Thick 4.1 1.8 2.4 2.3 4.1 2.1 2.6 5.5 - 1.5 1.0 5.5 4.3 5.5 10.4 4.5 6.1 5.8 10.4 5.3 6.5 13.8 1.0 - 2.5 3.8 2.5 13.8 10.9 8.2 5 dried down to 12 percent moisture content.PDF Image | DH Drying for Small Woodworking Firms and Hobbyists
PDF Search Title:
DH Drying for Small Woodworking Firms and HobbyistsOriginal File Name Searched:
dhkilns.pdfDIY PDF Search: Google It | Yahoo | Bing
5,000 BF Shipping Container Lumber Dry Kiln For Quality Lumber The 5,000 BF container kiln consists of one 40 foot high-cube aluminum shipping container... More Info
Shipping Container Lumber Dry Kilns by Global Energy Global Energy designed and developed the container kiln back in 1991. The purpose is to give access to portable sawmill owners, furniture makers, and small business the value added profit of dry kiln lumber and quality hardwoods... More Info
Vacuum Kiln Conversion Kit for Lumber and Wood Dry Kilns Convert your existing conventional dry kiln into a fast drying vacuum kiln. Similar to vacuum bagging in the boat building and aircraft industry, we have come up with a proprietary process which allows you to build a very simple vacuum kiln at a fraction of the price, and without the intensive conventional metal chamber structure... More Info
Vacuum Pump Cart System for Bagging Clamping Wood Drying and more Vacuum Cart with 2HP Pump and Dual Pistons with multiple multiplex vacuum ports and liquid reservoir... More Info
Vacuum Bagging Basics Vacuum bagging is a method of clamping, which has traditionally been used in the composites industry, but can also be used for vacuum drying materials, including wood products... More Info
CONTACT TEL: 608-238-6001 Email: greg@globalmicroturbine.com (Standard Web Page)