Anatomia De Maderas

Wood quality
Wood product streams
The classical definition of wood quality is the suitability of a given piece of wood for a specific end use, and, accordingly, individual wood characteristics are not usually seen as universally good or bad.
The exact set of characteristics that constitute high or low quality varies depending on the specific use. Some examples of desirable characteristics aresoundness (lack of decay) straight rain small scattered knots or the complete absence of knots, and dimensional stability (a tendency to dry without warping and to remain straight in use) some examples of undesirable characteristics are decay, large or unsound knots, lack of dimensional stability, and poor mechanical properties .some wood products are very forgiving of variation in woodcharacteristics. Others require raw material with a narrow range of wood characteristics. Consequently, it makes sense to begin a discussion of wood quality by thinking about the broad categories of wood products and the characteristics that are important for each group. A convenient way to do this is to divide all possible wood utilization options into a small number of “end product streams” with similarraw material requirements, for example(1) heat and chemicals,(2) fibers and particles, and (3) solid products
Heat and chemicals
The energy production stream is the least demanding in terms of Wood characteristic. Raw materials with lower moisture contents and higher specific gravities are more desirable but fuelwood can include a variety of low quality raw materials. These could come fromsmall stems, crooked stems, stems with large numbers of knots, or stems with high proportions of defects such as cross grain, rot reaction wood (wood associated with leaning or deformed stems)
Many chemicals used every day are derived from wood bark extractives, or foliage. Raw materials used for their production must be cleaner than for energy and, although some species work better than otherbecause of their chemical composition, fiber characteristics or other wood properties are relatively unimportant

Fiber and particles
Composite Wood products such as oriented strand board (OSB) parallel strand lumber (PSL) waferboard, particleboard medium density composites wood cement composites and pulp for paper and paperboard are included in the fiber and particle product stream. Manufacture ofthese products requires cleaner raw material than energy production, although perhaps not mere so than chemical production. In most cases, bark is seen as detrimental, so ease of bark removal from round wood is an important feature. Manufacture of fiber and particle based products is also less tolerant of decay, reaction wood, pitch pockets, or other irregularities. It is, however technicallyfeasible to make these products from small stems or stems with substantial grain deviation as long as it is not associated with reaction wood and does not interfere with debarking or primary processing such as waferizing
Solid products
This stream is divided into structural products and appearance products. Solid products include round wood such as post and poles sawn lumber and veneer in some waysthe structural product stream is the most demanding. Products in this stream must meet engineering standards such as specified mechanical requirements and they are intolerant of grain deviations or decay. On the other hand they can contain some knots and discoloration without adversely affecting their performance
The raw material requirements for structural products have change greatly during thetwentieth century. Technological improvements now allow sawing of logs as small as 9 cm in diameter on the small and although economic constraints often preclude processing logs quite so small. Techniques were also developed to use weaker or less stiff lumber in parts of engineered products where mechanical properties were less important and abundant fast growing species such as aspen (populous...