Seasoning of Wood

Name: Seasoning of Wood
Author: Wagner, J. B. (Joseph Bernard)

Wagner, J. B. (Joseph Bernard)

Lumber -- Drying

Some of the advantages of kiln-drying to be secured over air-drying in
addition to reducing the shipping weight and lessening quantity of
stock are the following:

     1. Less material lost.
     2. Better quality of product.
     3. Prevention of sap stain and mould.
     4. Fixation of gums and resins.
     5. Reduction of hygroscopicity.

This reduction in the tendency to take up moisture means a reduction
in the "working" of the material which, even though slight, is of
importance.

The problem of drying wood in the best manner divides itself into two
distinct parts, one of which is entirely concerned with the behavior
of the wood itself and the physical phenomena involved, while the
other part has to do with the control of the drying process.


           Physical Conditions governing the Drying of Wood

     1. Wood is soft and plastic while hot and moist, and becomes
     "set" in whatever shape it dries. Some species are much more
     plastic than others.

     2. Wood substance begins to shrink only when it dries below
     the fibre-saturation point, at which it contains from 25 to
     30 per cent moisture based on its dry weight. Eucalyptus and
     certain other species appear to be exceptions to this law.

     3. The shrinkage of wood is about twice as great
     circumferentially as in the radial direction; lengthwise, it
     is very slight.

     4. Wood shrinks most when subjected, while kept moist, to
     slow drying at high temperatures.

     5. Rapid drying produces less shrinkage than slow drying at
     high temperatures, but is apt to cause case-hardening and
     honeycombing, especially in dense woods.

     6. Case-hardening, honeycombing, and cupping result directly
     from conditions 1, 4, and 5, and chemical changes of the
     outer surface.

     7. Brittleness is caused by carrying the drying process too
     far, or by using too high temperatures. Safe limits of
     treatment vary greatly for different species.

     8. Wood absorbs or loses moisture in proportion to the
     relative humidity in the air, not according to the
     temperature. This property is called its "hygroscopicity."

     9. Hygroscopicity and "working" are reduced but not
     eliminated by thorough drying.

     10. Moisture tends to transfuse from the hot towards the
     cold portion of the wood.

     11. Collapse of the cells may occur in some species while
     the wood is hot and plastic. This collapse is independent of
     subsequent shrinkage.


                         Theory of Kiln-drying

Public-domain text, read in full here on John Shaqi.

Opening the text

Seasoning of WoodWagner, J. B. (Joseph Bernard)

Science

Seasoning of Wood

Wagner, J. B. (Joseph Bernard)

Lumber -- Drying

Some of the advantages of kiln-drying to be secured over air-drying in
addition to reducing the shipping weight and lessening quantity of
stock are the following:

     1. Less material lost.
     2. Better quality of product.
     3. Prevention of sap stain and mould.
     4. Fixation of gums and resins.
     5. Reduction of hygroscopicity.

This reduction in the tendency to take up moisture means a reduction
in the "working" of the material which, even though slight, is of
importance.

The problem of drying wood in the best manner divides itself into two
distinct parts, one of which is entirely concerned with the behavior
of the wood itself and the physical phenomena involved, while the
other part has to do with the control of the drying process.


           Physical Conditions governing the Drying of Wood

     1. Wood is soft and plastic while hot and moist, and becomes
     "set" in whatever shape it dries. Some species are much more
     plastic than others.

     2. Wood substance begins to shrink only when it dries below
     the fibre-saturation point, at which it contains from 25 to
     30 per cent moisture based on its dry weight. Eucalyptus and
     certain other species appear to be exceptions to this law.

     3. The shrinkage of wood is about twice as great
     circumferentially as in the radial direction; lengthwise, it
     is very slight.

     4. Wood shrinks most when subjected, while kept moist, to
     slow drying at high temperatures.

     5. Rapid drying produces less shrinkage than slow drying at
     high temperatures, but is apt to cause case-hardening and
     honeycombing, especially in dense woods.

     6. Case-hardening, honeycombing, and cupping result directly
     from conditions 1, 4, and 5, and chemical changes of the
     outer surface.

     7. Brittleness is caused by carrying the drying process too
     far, or by using too high temperatures. Safe limits of
     treatment vary greatly for different species.

     8. Wood absorbs or loses moisture in proportion to the
     relative humidity in the air, not according to the
     temperature. This property is called its "hygroscopicity."

     9. Hygroscopicity and "working" are reduced but not
     eliminated by thorough drying.

     10. Moisture tends to transfuse from the hot towards the
     cold portion of the wood.

     11. Collapse of the cells may occur in some species while
     the wood is hot and plastic. This collapse is independent of
     subsequent shrinkage.


                         Theory of Kiln-drying

Public-domain text, read in full here on John Shaqi.

Seasoning of Wood

Seasoning of Wood

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