Engineered wood is an alternative to sawn wood. If a tree is to be cut down for our use, then it is best to waste as little of it as possible. Producing sawn lumber is inherently wasteful because we are converting a tapered, conical log into a set of three-dimensional rectangular cuboids. Engineered woods are woods produced by gluing small pieces of wood together to make a new type of wood. Plywood is probably the most familiar: A log is placed in a giant lathe and rotated around its long axis while a knife cuts off a thin layer (a veneer) as wide as the log is long. This long, thin veneer is cut into large squares that are glued together in multiple layers to make either a thin flexible plywood or a very thick and sturdy one (FIGURE 24-55). To make a strong wood that resists shrinking and warping, the grain of each layer is oriented at right angles to the grains of the adjacent layers. To make a plywood that can be bent around a corner, the grain of each layer is parallel to that of all the others. Much plywood is used as large sheets in the construction of homes and offices, and its rough surface will be covered by siding, plaster, or wallpaper. More elegant plywood is made by covering the rough plywood with an outermost veneer of fine wood such as maple or birch. Making plywood uses almost the entire log with almost no waste; by selecting the proper glue, the plywood can be given specific properties such as being waterproof or especially durable. Particleboard is an engineered wood similar to plywood but logs are simply chipped into particles rather than cut into veneer. The particles are then glued together to make a board of any desired size or thickness. Particleboard is weaker than plywood, and if it is made from sawdust particles, it can be crumbled by hand. But often strength is not needed, and by covering particleboard on each side with a veneer of wood or plastic, the composite structure can be very strong. Oriented strand board is an engineered wood made by gluing together long thin strips of wood, with all strips running in the same direction. One of the first uses of this technique was to construct laminated beams: Even if only short logs are available, they can be cut into strips that are then glued together as overlapping pieces (FIGURE 24-56). Beams can be fabricated that are longer, thicker, and stronger then any available tree; by bending the strips as they are glued, a beam of any desired shape can be created. Laminated beams are often used to span large spaces in churches, theaters, gymnasiums, and auditoriums without needing internal pillars. Artisan woods are those valued for their beauty (FIGURE 24-57). They often consist mostly of richly colored heartwood such as black (ebony, walnut), red (mahogany), white (maple, holly), and purple (juniper, purpleheart). Care is often taken in the way that artisan woods are cut: Tangential longitudinal sections show the texture caused by rays and fibers, whereas radial longitudinal sections show the pattern of alternating earlywood and latewood. These are referred to as the wood’s grain. Knotty pine is cut tangentially to show off the many dark knots produced when the plant branched prolifically (FIGURE 24-58). The texture of bird’s-eye maple also results from numerous tiny knots. Artisan woods are used to create small objects of beauty such as boxes, musical instruments, bowls, and lamps.
Вы собираетесь прочитать отрывок из статьи о боевых искусствах. Одно предложение было удалено из статьи. Выберите из предложений A-H тот, который соответствует разрыву. Существует одно дополнительное предложение, которое вам не нужно использовать. Узнайте эффективной борьбы и самообороны системы Тони Чанг является мастер боевых искусств, который служил долгое ученичество в обоих внутренних и внешних искусств. Он пользуется уважением во всем мире как инструктор боевых искусств в кенпо, t'ai чи ch'uan и чи кунг и работает несколько своих дабов в Манчестере. Он также имеет несколько учебных видео и DVD-раз, к его чести. В самом деле, он был одним из пионеров преподавания боевых искусств Методы серии по всему миру в Интернете. ________________________________________________________<br>1. В результате такого опыта, все больше и больше людей принимают его.<br>2. Студенты, посещающие эти обучаются несколько методов обучения.<br>3. Делая это, они могут реагировать на нападение с относительной легкостью.<br>4. Большинство боевых искусств не являются уличными эффективными.<br>5. Многие другие в настоящее время последовали его примеру.<br>6. Если бы это было так, то более сильный, большой человек всегда побеждавал бы.<br>7. Это одна из самых грозных систем выживания на улицах, борьбы и самообороны, когда-либо изобретенных.<br>8. Если вы берете его. Вы узнаете, как попасть в это состояние, и вы сможете защитить себя независимо от вашего размера, возраста или пола.
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