A few weeks before Christmas, our festive favourites – Christmas trees – can be found in homes, in squares or in front of public buildings. However, pine, spruce, etc. not only decorate the surroundings, but are also an important material for the construction and furniture industries. With the help of harvesters, the trees are quickly transported from the forest to the sawmill, where they are automatically cut into boards using modern sawing systems.
Dense pine and spruce forests as far as the eye can see are a common sight in Sweden. In total, more than half of the country is covered by forest. Woodworking and wood processing represent important industries. In addition to being used as Christmas trees or for making furniture, wood is often used as a building material. For example, it is used to clad the facades of houses or to lay floors.
From forest to sawmill
Mobile harvesters are used for harvesting wood in the forest. The machines securely fasten the trees and saw them off with an integrated chainsaw. They then remove branches and leaves. Lorries transport the logs to the sawmill.
Before the actual sawing takes place, the logs are sorted according to diameter, so that the sawing system can be suitably adjusted later. The tree bark is also removed. Computed tomography is then used to check the wood. It examines the wood and determines whether there is any ingrown foreign matter, such as rocks, which could damage the system’s saw blades. In addition, the tomography checks the quality of the logs. In this way, knots or rotten spots can be detected and cut out in the best possible way when sawing.
Automatically processed into the right shape
The sawing system consists of four stations. The logs are transported on conveyor belts along the line and bandsaws cut boards on the right and left. Between each sawing station, rollers driven by pneumatic Festo DNC cylinders align the logs in such a way that natural bends in the wood are compensated for. A so-called displacement encoder, which is integrated into the pneumatic cylinders, supports this process. It determines the exact dimension of the log so that it is precisely positioned and the boards are always cut straight. In total, the sawmill processes 56% of the log, the rest being sawdust and tree bark. By the year 2020, the annual output is set to be 270,000 m³ of sawn boards.
More than 100 pneumatic, servopneumatic and hydraulic drives are integrated into the entire system, all of which are controlled by the CPX automation platforms and the functionally integrated CPX/VTSA valve terminals from Festo. They are supplied with various fieldbus modules that translate the signals of the control unit for the valve terminals. Different providers are preferred in different countries. Depending on the provider, a different CPX fieldbus module is used. This enables the Festo product to communicate with all fieldbus protocols. In addition, fieldbus technology allows several pieces of information to be transmitted via one cable. This makes it possible to put the system into operation very quickly and flexibly.
Packaging and delivery
After passing through the system, the boards are cut to a standard length and dried in a hall. Bark and sawdust are used to heat the drying hall. Finally, packaging and dispatch take place. Spruce wood is mainly used as a building material for the domestic market – for example, to clad facades on houses. Most of the pine boards are exported to countries such as Africa, Japan, China and Great Britain. The sawdust can also be reused in the pulp and paper industry.