Drying

In many countries unseasoned wood are traded, but in Sweden all sawn timber is wiped at the sawmill. Drying kilns are most commonly used in the drying; about 95 percent of production is dried in them.

Wood kilns are divided into batch kilns and walking kilns. Today's batch kilns are the most commonly used method. The amount of batch kilns at walking wiper increases due to the proportion of special dried timber has risen sharply in recent years.

Drying Process

Normal drying aims to dry timber to about 18% moisture content so called shipping dry. The goal is to lower the moisture content of the wood without wood cracking and to such moisture content that can be stored or transported without damage. As drying wood shrinks, the cutting process must therefore be done with excess in relation to the final product dimensions.

Some wood pieces deformed during drying. That's because the wood shrinks differently in different directions. This can be counteracted in a variety of ways, for example by drying at higher temperature than normal and under mechanical pressure of drying package as well as the subsequent voltage balancing conditioner. Drying at higher temperatures and voltage regulation has become increasingly common in recent years.

During the drying process the temperature and humidity in dryers are controlled by computers. Artificial drying of wood takes about 6 days for 50 mm thick planks. The center exchanges reach the desired moisture content faster than lateral exchanges because the kernel from scratch has lower moisture content than splints. Drying for a specific purpose, which requires lower moisture content than shipping dry, takes longer. In the past it was customary to wipe such as carpentry wood in two steps, first down to 18% in sawmills, finally dried to 7-9%. Today, it is becoming more common to dry down to final moisture content directly in the kilns at the sawmill. To dry directly to final moisture content produces a better quality from fracture point.

Conditioning

After drying the wood is conditioned, so that moisture content differences and tension leveled. Conditioning takes place in wood dryer and takes 2-3 days.

Batch kiln
Batch kiln
Walking drying process
Walking drying process

 
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