PROCESSING OPERATIONS IN FOREST-BASED INDUSTRIES IV-B Flashcards
the process of drying wood by mechanical or natural means
WOOD SEASONING
OBJECTIVES OF WOOD SEASONING
- reduce the occurrence of wood defects
- minimize effect of shrinkage and swelling of wood
- increase strength properties of wood
- facilitate application of preservatives
- improve machining and finishing qualities
- increase thermal and electrical resistance
- improve nail holding capacity of wood
- reduce weight for easy transportation and handling
- enhance resonance quality of wood for acoustic applications
- reduce bond failure in glued-wood products
METHODS OF WOOD SEASONING
a. Natural drying
b. Artificial drying
Natural drying:
i. Air seasoning
ii. Water seasoning
iii. Solar seasoning
- oldest, traditional and simplest method of seasoning wood
- based on the principle that the piece of timber is stacked in a way to allow plenty of air to circulate around each piece of timber
Air seasoning
- process of placing logs in a river with thicker ends pointing upstream side of the river for seasoning purposes
- the sap of the timber is washed over a span of 2-4 weeks by the river water
Water seasoning
- a solution provided for the low energy requirement of air drying and the speedy operation of kiln drying
- slower and gentler form of kiln drying
Solar seasoning
Artificial drying:
i. Seasoning by boiling
ii. Chemical seasoning
iii. Electrical/ Rapid seasoning
iv. Kiln seasoning
drying of wood thru mechanical means or with the use of equipment and/or chemicals
Artificial drying
- wood is immersed in water and then boiled for about 3 – 4 hours under supervision
- the needed amount of sap in the water is removed during boiling
Seasoning by boiling
- timber is stored in suitable salt solution for some time
- the salt solution used has the tendency to absorb water from the timber
- So, the MC is removed and then timber is allowed to drying
Chemical seasoning
- timber is subjected to high frequency alternating currents
- the resistance of timber against electricity is measured at every interval of time
Electrical/ Rapid seasoning
- seasoning of wood in a chamber using artificially controlled temperature and humidity
- the hot air circulates in between the timber logs and reduces the moisture content
Kiln seasoning
Kiln seasoning:
a. Progressive kiln seasoning
b. Compartmental kiln seasoning
- timber enters at one end and moves progressively through the kiln much as car moves through a tunnel
Progressive kiln seasoning
Progressive kiln seasoning:
a. Draft kilns
b. Forced draft kilns
– heated air is allowed to rise through the material by natural convection
Draft kilns
– fans are employed to force the air through the wood
Forced draft kilns
- a single enclosed container or building, etc.
- the timber is loaded into the kiln and remains in place throughout the drying process
- a kiln in which the total charge of lumber is dried as single unit
Compartmental kiln seasoning
- process employed to prevent drying defects during kiln drying
KD Quality Control
KD Quality Control:
a. Conditioning treatment
b. Equalization treatment
– steam introduced to relieve stresses prior to end of KD
Conditioning treatment
– temperature is lowered with steam to have a more uniform final MC of stocks
Equalization treatment
- QC test performed to determine drying stresses in wood
Prong test
– occurs when the core is in tension while the surface is in compression
Casehardening
- are carefully worked-out set of progressively increasing kiln temperature and decreasing relative humidity which a KD operator can use as a guide to dry specific wood products at a satisfactorily rate without causing objectionable drying defects
KILN DRYING SCHEDULES
KILN DRYING SCHEDULES:
a. General KD schedules
b. Special KD schedules
– employed for lumber used in general construction
General KD schedules
– developed to attain specific objectives for special uses
Special KD schedules
