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Rotor debarking at sawmills and plywood mills

 

Rotor debarking is the most commonly used method of debarking in the sawmill and veneer industry (e.g. plywood and LVL).

Debarking at sawmills

The debarkers at sawmills are positioned either at the location of the saw infeed or at the beginning of the log sorting line, before the timber is sorted according to diameter. In the Nordic Countries, Russia and North America, the debarker is usually found in the saw line, whereas most Central and South European sawmills place it in the log sorting line.

Debarking at the saw infeed

Positioning the debarker in the saw line requires the machine to function reliably, as the entire line process is dependent on it. VK debarkers can ensure the smooth operation of the saw line in all conditions.

Saw line debarking enables:

  • the optimisation of the debarking speed according to wood size (the wood has usually been sorted by diameter)
  • the feeding of wood into the debarker end-to-end without space in between logs (which are usually turned top end first)
  • transferral of wood into the saw line as cleanly as possible (the debarked logs do not need to be lowered to the ground at any stage)

Storing wood at a log yard is also easier as wood is debarked only in the sawline. Logs are not as slippery when the bark is still on. The bark also protects the wood for as long as possible prior to sawing. It slows the drying of the wood in warm conditions and reduces surface damage caused by loaders.

Debarking in the log sorting line

Positioning the debarker in the log sorting line improves sawing results thanks to more accurate log measurement. In the log sorting line, the wood is always debarked before measuring, so bark percentage does not come into consideration. Instead, measurements are always correct.

However, the ideal positioning of the debarker depends on the pricing method used in the respective timber markets. In Central Europe, for example, sawmills pay for actual wood with bark not included. In this case, it is recommended to debark the wood before the measurement that defines the payment.

The third reason for positioning the debarker in the log sorting line is the sawmill’s capacity requirement. At a log yard, the operating time of the debarker is flexible and can be increased as necessary, thereby ensuring a sufficient supply of wood for the sawmill.

Valon Kone regularly supplies two and three-rotor Combi debarkers to sawmills all over the world in particular.

Debarking at veneer and plywood mills

In veneer production, it is essential to avoid damaging the surface and ends of the wood during debarking. Rocks and other impurities in the bark that enter the peeling knives cause the knives to wear out more rapidly and reduce the quality of the veneer. Debarking the wood before peeling means the knives are kept in considerably better condition. It ensures an uninterrupted production process, excellent level of quality and minimal knife maintenance costs.

Due to the considerably higher price of top veneer, the wood’s most valuable part is its surface. The difference is significant when compared to the production of sawn timber, for example, which usually involves producing woodchips of the surface layers.

In veneer production, the raw material is usually soaked before it is cut into veneer. For the debarking process, it is better to position the debarker after the soaking phase where possible. This means the debarking tools and feed rolls do not need to place as much pressure on the wood.  Debarking is recommended after soaking, particularly in areas where the wood is likely to freeze in winter. Some wood species, such as birch, must always be soaked before debarking.