Transcript Seasoning of Timber - Industrial Techniques grade 8

Seasoning of Timber
Grade 8
Seasoning logs
What is seasoning of timber
When a tree is cut down the wood contains
a large amount of moisture. It would not be
wise to use the wood in this wet state. The
moisture must be dried out and the
controlled process of doing so is called
seasoning.
How does moisture affect timber?
• The water will affect timber in many ways, for
example
• Strength properties will be reduce
• Fungal attack is over likely
• The timber is vulnerable to some species of
wood destroying insects
• There excessive weight due to the amount of
water present
• The surface finish is unsuitable to receive either
paint or polish
• Adhesives will have minimal holding properties
Methods of seasoning
There are two methods of seasoning:
• air seasoning, sometimes called natural
seasoning,
• kiln seasoning.
Air seasoning
•
The easiest way, but not the most effective method of seasoning timber, is
to stack it outside. The timber is laid out as seen in the diagram below. It is
normally placed in a hut / building, with two sides open to allow air to
circulate. The roof and two other sides keep the timber relatively dry. The
circulation of the air slowly dries the timer. However, this techniques does
not give a precise moisture content. This is because air circulates freely and
carries moisture, depending on the weather and the time of year.
The spacing sticks keep the seasoning boards a short distance apart. The
air flows between each of the seasoning boards, allowing them to dry
slowly. In this way warping is kept to a minimum.
The seasoning time varies depending on the thickness of the wood boards
and the time of year. Usually three to four months for 25mm softwoods. The
time is doubled, for wood twice as thick. Hardwoods of 25mm thickness
require about six months and up to at least a year for 50mm boards.
Air seasoning
Air Seasoning- Advantages
Advantages of Air Seasoning
• No expensive equipment needed
• Small labour cost once stack is made
• Environmental friendly-uses little energy
Air Seasoning- Disadvantages
Disadvantage of Air Seasoning
• It takes much longer than kiln seasoning
• Large area of space reqired for a lot of
wood
• it is notable to produce timber not dry
enough for use in the dry, centrally heated
air of modern buildings
Kiln Seasoning
• In this method the wooden pieces are kept on
huge trolleys and then it is placed inside the hot
chamber of a furnace known as kiln. In this way
wooden pieces are kept in a controlled
atmospheric conditions for two weeks. The time
depends upon the type of wood and initial
moisture content. Blowers are also used. It is a
quick drying method and the moisture is reduced
to 10%. Since seasoning is done at a lesser time
through artificial means so the quality of wood is
inferior in comparison to seasoned wood
through natural seasoning.
Kiln Seasoning
Kiln seasoning
Kiln seasoning
Advantages of Kiln Seasoning
• It is dries quickly
• It can be controlled
• Achieve a lower moisture content
• Defects associated with drying can be
controlled
Kiln seasoning
Disadvantage of Kiln Seasoning
• It is an expensive method
• Requires supervision by a skilled operator
• Uses a lot of energy
summary