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DRYING AND WOOD QUALITY CHALLENGES.

Eduardo Stehling, biologist and researcher at the Bela Vista Forest.

Producing wood for sawmills is an activity that is attracting more and more investors. Many farmers are interested in the potential of species such as the Australian cedar and high market values, usually based on lumber prices, to make their profitability calculations and consider the feasibility of going into business. Getting good log volume and quality is the first step to success, also considered by many as the main step. However, there are other bottlenecks after producing the trees. Wood sawing and drying are also fundamental to define the end product.

Before sawing a tree, it is paramount to know what use will be given to the timber. Those who buy dry wood, usually acquire parts that are larger than the finished product. Similarly, when sawing the wood, one needs to consider surpluses, to make up for losses that will occur in the drying process, especially due to post-sawing defects.

It is highly important to have good quality sawing equipment. The thickness of the pieces must be constant, so as not to influence wood drying, and this depends on the saw. Depending on the type of saw and technique used, pieces of various dimensions (boards, planks, battens, etc.) and quality levels can be obtained from the same tree. For that purpose, it is vital to proper screen the trees during harvesting.

Once a log is sawn, the timber obtained proceeds immediately to the next step, drying. This can happen outdoors; in a covered shed; in commercial, crafted or improvised dryers; using heavy-duty fans, etc. Each type of drying has its own characteristics, and its particularities are important in the process. In general, regardless of location, the timber is dried in stacks. The green wood pieces are separated from each other within the stack by wooden battens known as partitions, which allow the flow of air and promote drying and fumigating. It is very important that the surface where the stacks will be mounted is regular and leveled.

The partition walls represent a major part of the drying process. They need to have quality and must have regular dimensions, with width and height proportional to the size of the parts that need drying. Thin boards require thinner partition walls than thicker boards. The partition length must be equal to the stack width. Stack height and width must also have dimensions that allow for greater stack stability and ease of displacement.

To avoid the uneven bending of the boards during drying, the partitions must have vertical alignment along the stack height and should be distributed in large numbers on the boards. Thinner boards require less distance between partitions than larger boards.

Wood pieces from different parts of a tree can have different behaviors during drying. Growth stresses existing on the wood may cause post-sawing defects such as warping, twisting, cupping, surface cracks, etc., especially in poorly assembled and poorly standardized stacks. After mounting a wood stack, tying already standardized parts reduces the occurrence of deformities during the drying process. Use partitions at the ends of the stacks to prevent torsion in this region, thus minimizing losses at the ends of the parts.

Wood drying time will depend on several factors, including the sizes of the wood parts, partition size, the stack, mounting, and the place where drying is to be held. In general, drying wood more slowly and under mild conditions reduces the occurrence of defects after sawing and drying. Therefore, it is preferable to keep the stack in a shed that is covered and open on the sides than out in the sun.

Finally, a well assembled, standardized and properly tied stack directly influences drying time and the quality of the wood produced.

With the marketing of Australian cedar timber, it necessary to acquire knowledge on the sawing techniques for the species. For a high added-value timber, improving quality is synonymous with optimizing profits. Since the trend is the marketing of products and not trees, sawing and drying can add much value. The good news for farmers working with this species is that the techniques used to dry the Australian cedar wood are simple and do not require large investments. Drying without using dryers have shown excellent results, as well as standard stacks for the production of boards, planks and laths for linings. The wood drying time is 6 to 12 months in a roofed-shed and can be accelerated to a few weeks with the use of handmade dryers. It should be noteworthy that selling green lumber can generate future complaints from buyers, as it is still subject to deformations and losses until drying is complete.

The most important lesson for farmers is that to market wood, one must understand the market, one’s product and, mainly, prepare oneself so that during the production of trees, one should work on the structure needed for drying wood, a technique that will surely multiply profits.

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