Lumber Manufacturing---Debarking
• Purpose—Increase value of byproducts
--Scrapes and edgings → chips without bark → pulp
--Bark particles → burn (energy)
• Types of debarkers
--Drum debarker: removing bark from pulp logs
--Ring debarker: removing bark from saw- and veneer logs
--Pole shaver: shave bark off utility poles
Drum Debarker
• To remove bark from pulp logs
Corrugated interior tumbles the logs and scrapes off bark;
logs rub against each other to knock off bark; water shower
softens bark and washes bark out of the drum. Because of
gentle rubbing action
very little removal of
quality fibers from surfaces.
Ring Debarker
• To remove bark from saw- and veneer-logs
Logs are centered in a ring of rosser
heads with projecting teeth; bark is
removed with a pressure about 30 to
50 psi. Bark is removed at high speed
with substantial surface removal of
wood but does not affect lumber or
veneer yield.
Pole Shaver
• To move bark from utility poles to obtain smooth surfaces
Pole rotates as it passes under a floating
peripheral-milling cutterhead, removing
the bark with a minimum of wood loss
and retaining the natural taper.
Primary Breakdown—Head saws
•
Band saw: Able to handle large logs,
provide straight cuts and thin saw kerf
increase lumber yield.
•
Circular saw: Saw diameter limits log sizes,
thick saw blades for stability (1/4”)
large saw kerfs
reduces lumber yield.
Saw Mills
• Scragg Mills
Consists two or four circular saws on a common arbor. Distance
between blades can be adjusted to produce 4-, 6-, or 8-inch cants.
The logs are commonly moved through saws by a conveyor.
• Multiple Band Mills
Similar to scragg mills except that breakdown is done by 2 or more
opposing bandsaws, producing two slabs and one cant if two bands
are used.
• Chipping Headrigs
Logs pass through a set of side cutterheads to remove excess
wood into chips, followed by another set of top/bottom cutterheads to produce a cant. Chips are to be used for pulp & paper.
Chip-N-Saw
Designed to process small straight
Logs 6 to 16 inches in diameters.
Logs first pass through two pairs
side and top/bottom) chipping
cutterheads to square or shape
logs, followed by passing the cant
through a series of circular saws
mounted on a common arbor to
produce multiple pieces lumber.
High-Tech Mills
• BOF (Best Opening Face)
For high efficiency: Electronic hardware (scanner & computer) and good computer
software; machine that is able to position logs quickly & saw accurately with thin kerf.
Resawing
• Ripping—Ripping is to saw lumber along the grain. Slabs
produced by headrigs are cut with a pair of circular saws (called
an edger) to square the edges to a specific width simultaneously.
Large slabs are rip into multiple pieces with a series of circular
saws mounted on a common arbor (gang saws).
• Rough trimming—Trimming is to saw lumber across the
grain to a specific length. Rough trimming follows the ripping
to cut green lumber into pre-determined lengths, usually done
with a pair of hollow ground circular saws.
Sorting & Drying
• Sorting—This operation is to sort cut lumber into different
grades, species or species groups, thickness, length and
sometimes according to moisture content.
• Drying (seasoning)
--Reasons to dry : Seasoned wood is dimensionally stable
Dry wood is durable against inscets & decay
Dry is stronger
--Air-dried lumber: moisture content >15% ≤19%
--Kiln-dried lumber: moisture content ≤15%