4/8/2016
Kiln Schedule
Modification
Bill Smith
SUNY ESF Wood Products
Syracuse, NY
Use applications mostly require:
• Kiln dried hardwoods to 6-7% MC
– (North American market; export perhaps
somewhat higher)
• Eastern white pine perhaps to ~10-12% MC
• SPF dimension; KD-19
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Equilibrium Moisture Content
and Relative Humidity
• RH %
– 90
– 80
– 65
– 50
– 30
–0
• EMC %
– 20
– 16
– 12
–9
–6
–0
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Kiln Drying Schedules • The purpose is to dry as rapidly as possible,
to be economical.
• However, drying must be controlled to
avoid value reducing defects.
• Typically, the temperature and the relative
humidity (wood EMC) are controlled.
• Relative humidity is lowered and
temperature is raised and as wood dries.
Kiln Drying Schedules •
•
•
•
•
So, we know what we want.
And we know what we need.
Do we always get what we want?
Really, you can’t always get what you want.
But, do we get what we need!
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Kiln Drying Schedule
Modification - Issues
• Why modify – fix problems, improve?
• Do you really know what is wrong?
• Don’t fix what is not broken!
Some typical schedules -
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Some typical schedules -
Some typical schedules -
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Some typical schedules -
Some typical schedules -
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Making Modifications •
•
•
•
Make one change at a time.
Document, measure, change, measure.
Avoid “compensating errors”.
Be sure of the “problem” before making
the “change” / “modification”.
Making Modifications, examples
• Problem
– Surface checks
• Cause
–
–
–
–
–
Drying to fast
Too much heat
Too low %RH
Too much sun
Too much wind
• Solution
– Slow down air drying
– Improve stacking
strategy
– Use shade-dri, burlap
– Use pile covers
– Increase %RH
– Lower wet bulb
depression
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Making Modifications, examples
• Problem
– Stain, mold
• Cause
– Drying to slow
– Too high %RH
– Too little air flow
• Solution
– Speed up air drying
– Improve stacking
strategy
– Decrease %RH
– Increase wet bulb
depression
Making Modifications, examples
• Problem
– Warp
• Cause
–
–
–
–
–
Stacking procedures
Sawing pattern
Thick, thin boards
Wood species, log size
Schedules; perhaps
• Solution
–
–
–
–
Improves log size
Improve sawing
Improve stacking
Schedule change?
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Making Modifications, examples
• Problem
– Slow Drying
• Cause
– Final %MC target too
low?
– Stacking procedures
– Knowing %MC
– Temperature too low
– %RH too high
• Solution
– Improve air circulation
– Reduce %RH
– Raise temperature
• Early in schedule?
• Late in schedule?
• Plot data!
Making Modifications, examples
• Problem
– Moisture Variation
• Cause
–
–
–
–
–
–
Stacking procedures
Knowing %MC
Temperature variattion
%EMC, %RH variation
Wood variation
Mixed species, thickness,
history
• Solution
–
–
–
–
–
Improve air circulation
Measure air flow, fix
Measure temperature
Measure steam, fix
Use uniform species,
thickness, history
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Making Modifications, examples
• Problem
• Solution
– Early or Late in Schedule
• Cause
–
–
–
–
–
Low %RH too soon
High temperature too soon
High %RH too long
Low temperature too long
Species issues
• White woods, Oaks, White
Pine, SPF Dimension
– Measure actual
problem
– Fix actual problem
– Make incremental
changes, measure,
improve
– Schedule??
– Equipment??
Making Modifications •
•
•
•
Make one change at a time.
Document, measure, change, measure.
Avoid “compensating errors”.
Be sure of the “problem” before making
the “change” / “modification”.
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Kiln Drying Schedule
Modification - Issues
• Why modify – fix problems, improve?
• Do you really know what is wrong?
• Don’t fix what is not broken!
Thank you!
• Questions?
• Comments?
– Bill Smith
– [email protected]
– 315/470-6832
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