Reducing shrinkage defaults andor drying time thanks to oscillating conditions

1
Reducing shrinkage defaults and/or drying time
thanks to oscillating conditions

• Mariella DE LA CRUZ LEFEVRE
• Daniel ALEON
• Romain REMOND
• Patrick PERRE

2
Summary

• Wood drying an industrial delicate process
• Mechanosorption
• and oscillating drying conditions a brief
  synopsis
• Experimental work
• Results
• Conclusions
• Perspectives

3
Wood drying an industrial delicate process
Wood drying is an essential operation in wood
industry.
ISCHP 2009, September 28th - 29th, Paris
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Wood drying an industrial delicate process
Drying defaults are a consequence of the
mechanical stresses related to wood shrinkage.
collapse
Drying schedules should consider the mechanical
behaviour of wood
Process duration as short as possible Good
product quality
checking
ISCHP 2009, September 28th - 29th, Paris
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Wood drying an industrial delicate process
How to reduce the drying stresses and the
deformations?
Activation of the viscoelastic creep
High temperature drying above the glass
transition temperature
Patent EMBRAPA-ENGREF process (Brazil, 2000)
ISCHP 2009, September 28th - 29th, Paris
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• Mechanosorption
• and oscillating drying conditions a brief
  synopsis

Mechanosorption
ISCHP 2009, September 28th - 29th, Paris
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• Mechanosorption
• and oscillating drying conditions a brief
  synopsis

Oscillating drying conditions
First reference Haygreen (1965) Empirical
schedules quality drying time
Disparate results
Adequate periods and intensities are essential to
obtain significant improvements
ISCHP 2009, September 28th - 29th, Paris
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Experimental work
Wood material

• Beech wood (Fagus sylvatica)
• In France, it is the second dried hardwood after
  oak (Quercus sp.)
• It has a very elevated shrinkage coefficient and
  thus an elevated risk of drying defaults.

ISCHP 2009, September 28th - 29th, Paris
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Experimental work
FCBA dryer and schedules
Conventional
thermocouples
fans
Oscillating 1
Wet temperature oscillations
Oscillating 2
ISCHP 2009, September 28th - 29th, Paris
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Experimental work
Sampling
Conventional schedule
Oscillating 1
Oscillating 2
ISCHP 2009, September 28th - 29th, Paris
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Experimental work
Boards measurement and instrumentation
Mass Deformations (bow, spring, twist and
cup) Slicing test (after drying)
MC monitoring
ISCHP 2009, September 28th - 29th, Paris
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Results
Final MC homogeneity
Standard deviation
ISCHP 2009, September 28th - 29th, Paris
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Results
Deformations
Mechanosorptive creep, activated through MC
oscillations, produces a more important
relaxation of stress inside the boards
ISCHP 2009, September 28th - 29th, Paris
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Results
Slicing test
After 48h
Significant reduction of internal stresses thanks
to the oscillations
After 1 week or more
Influence of periods
ISCHP 2009, September 28th - 29th, Paris
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Results
Slicing test
Immediately 0.66mm After 48h 2.28mm After 1
week 2.53mm After 21 weeks 2.89
After 48h
After 1 week or more
48h storage long enough?
ISCHP 2009, September 28th - 29th, Paris
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Conclusions

• Results prove the potential of oscillating
  drying to improve the quality of wood
• final MC homogeneity
• final MC gradient
• residual stresses (gap)
• global deformations

• Influence of amplitude, alone or combined to
  periods, should be studied
• Adequate periods and intensities are essential
  to obtain significant improvements

ISCHP 2009, September 28th - 29th, Paris
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Perspectives
ISCHP 2009, September 28th - 29th, Paris
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• Thank you

ISCHP 2009, September 28th - 29th, Paris