Lumber Drying • Reasons to dry lumber --Dimensional stability --Dry wood is stronger than wet wood --Dry wood is more durable against decay and insect damages • Methods --Air drying with natural elements (temperature, humidity, wind) Moisture Content ≤ 19% --Kiln drying: drying under controlled environments Moisture Content ≤ 15%
Drying Procedures • Sorting for Grades, thickness, species, sometimes MC based on drying rates • Stacking & stickering Good stacking & stickering ensures a successful drying operation • Air-drying
Kiln Drying • Basic Elements --A compartment to enclose lumber --Heating (coils) --Vents and steaming device to regulate relative humidity --Fans for air circulation
Planing Basics of planing Planing is done by passing lumber through a series of planer cutterheads. Surface qaulity is defined by length of knife marks (Ft) and depth of knife marks (h). Ft =12 x F NT Where F = feed speed N = Revolutions per minute T = Number of knifes on cutterhead Lumber is knife planed
Sanding (Machining with coated abrasives) • Basics Wood-based composite panels are finished with coated abrasive, which consists of backing, resin sizing and minerals (abrasives). • Abrasives --Garnet (Hardness 7.5) --Aluminum oxide (9.5) --Silicon carbide (9.6, diamond 10) • Grit size The higher the number the finer is the grits, 60, 80, 100,……
Lumber Grades and Grading • Hardwood Lumber Grades: • Hardwood lumber is graded according to size and appearance
Softwood Lumber grades • Softwood lumber is graded for strength
Methods of Grading Softwood Lumber • Visual Grading: Examining each piece for strength- reducing defects and assign a strength ratio • (% strength remained) relative to a piece without any defect. • Machine Grading: Flexing each piece to an extent not • to cause any damages, followed by calculating MOE • (modulus of elasticity) and estimating MOR (modulus • of rupture). Grading also can be done with ultrasound • Method. Both methods are non-destructive evaluation • (NDE) .