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Reasons and Solutions of Wood Cracking

source:未知 edit:admin time:2017-08-12
Wood is a natural material, trees in the growth process often subject to a variety of factors outside the factors, resulting in abnormal wood structure, there will be such as the coating of the defects, trees due to illness, insects and other violations caused by material changes (called parasitic Sexual defects), these are the natural defects of wood.
 
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Common wood natural defects include knots, discoloration, insects, cracks and so on. These will cause damage to the coating, so they must be cleaned and remedied before painting.
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Rupture is due to the external force of wood or temperature, humidity changes, resulting in the phenomenon of separation of fibers.
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There are several forms of wood cracking: split, split, split and crack. Here we simply understand the reasons for the occurrence of these types of cracking:
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One, split:
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Refers to the surface cracks, surface cracks refers to the original wood or finished surface cracks. Cracks are usually limited to chord and develop radially. When the wood is dry, the moisture is evaporated from the surface, and when the surface layer moisture content falls below the fiber saturation point, the surface wood begins to shrink, but the moisture content of the adjacent inner wood is above the fiber saturation point and does not shrink. The shrinkage of the surface wood is limited by the inner wood and can not shrink freely, resulting in internal stress in the wood: the surface wood is pulled and the inner wood is pressed. The more dry the conditions, the higher the moisture content of the inner and outer layers, the greater the internal stress. If the tensile stress of the surface layer exceeds the tensile strength of the wood grain, the wood tissue is torn, and since the tensile strength of the wood-like tissue is smaller than that of the adjacent wood fibers, the cracks are first generated along the wood rays.
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Second, split:
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Ie internal cracks. Cracks are also known as cell fissures. The internal cleansing occurs at a later stage of drying and sometimes occurs during the storage of the dry material. Usually not easy to find from the outside of wood, but serious, can be judged by the concave surface of the material. The internal fracture is caused by the tensile stress of the inner layer of the wood.
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Three, split:
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That is, surface cracks. Or only to the end of the wood, or to one or both sides of the end, which are commonly referred to as splitting. The main reason is that the direction of water in the direction of the wood is far greater than the direction of the stripes, when the wood is dry, the moisture from the end of the evaporation than from the side much faster. The end of the water content is lower than the middle, the end of the shrinkage by the central wood restrictions, and thus produce tensile (tensile) stress at the end, when the tensile stress exceeds the tensile strength of wood, the end surface cracking.
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Fourth, the rotation:
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This crack develops along the growth wheel and often extends to several adjacent wheels. Cracks usually occur at the beginning of the drying, appearing on the end of the wood, with the deep progress of the cracks deepening and lengthening. Sometimes in the interior, but in the late drying, is due to severe internal tensile stress caused.
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Measures to deal with cracking of wood
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1, the use of high-temperature qualitative treatment:
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The method of reducing the internal friction of wood can be used to qualify the high temperature, and the residual deformation of the surface of the wood surface can be eliminated by high temperature and high humidity treatment before the end of the drying process. In the treatment, the wood surface due to humidification expansion and compression generated residual deformation, with the original residual deformation of the offset, wood cracks and therefore eliminated.
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2, mechanical anti-cracking:
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In the dry wood with wire bundles, the use of anti-crack ring, the combination of nail plate, etc., with the mechanical method to force the wood not to expand and shrink, so you can also prevent the cracking of wood.
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3, brushing waterproof coating:
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In the end of the wood and the surface brushing waterproof coating, slow down the evaporation of wood surface strength, which can reduce the moisture content inside and outside the wood gradient, can also reduce the cracking of wood.
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4, with a waterproofing agent for infiltration treatment:
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A more effective method is to use a waterproofing agent for pressurized treatment, so that the waterproof agent into the wood deep, in order to achieve a good anti-cracking effect of durability.
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5, to improve the material when the saw method:
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Wood anisotropy, in the same temperature and humidity changes in the case of its wet, dry shrinkage coefficient is the largest chord, followed by radial, vertical changes in the smallest, so the next saw when the production of some diameter cutting board, Can reduce cracking. Especially when the plate with the heart of the heart is prone to serious splitting, which is due to the radial direction of the chord near the chord caused by the difference, the best way is to avoid the production of pulp with the heart of the plate.
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