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Kiln ScheduleModification
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– 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
• Solution– 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
– 315/470-6832
