Artificial (kiln) seasoning

Kiln drying of lumber is perhaps the most effective and economical method available. Drying rates in a kiln can be carefully controlled and defect losses reduced to a minimum. Length of drying time is also greatly reduced and is predictable so that dry lumber inventories can often be reduced. Where staining is a problem, kiln drying is often the only reasonable method that can be used unless chemical dips are employed.

Kilns are usually divided into two classes:

1.    Progressive

2.    Compartment

Both methods rely on the controlled environment to dry out the timber and require the following factors:

§  Forced air circulation by using large fans, blowers, etc.

§  Heat of some form provided by piped steam.

§  Humidity control provided by steam jets.

Amount and Duration of Air, Heat and Humidity depends upon:

1.    Species

2.    Size

3.    Quantity

1. Progressive Seasoning:

In the progressive kiln, timber enters at one end and moves progressively through the kiln much as a car moves through a tunnel. Temperature and humidity differentials are maintained throughout the length of the kiln so that the lumber charge is progressively dried as it moves from one end to the other. Progressive kilns may be further subdivided into natural draft kilns in which heated air is allowed to rise through the material by natural convection, and forced draft kilns in which fans are employed to force the air through the wood. A progressive kiln has the stack on trolleys that ‘progressively’ travel through chambers that change the conditions as it travels through the varying atmospheres.