Wood cracking reasons and solutions
wood is a natural substance, the trees in the growth process influenced by outside factors, timber organization structure is unusual, can appear such as adverse to the coating defects, trees caused by disease, insect and other violations of material changes ( Called parasitic defects) , these are part of the natural defects of wood.
common wood natural defects including her, discoloration, bug, crackle and so on. All the coating has a harmful effect, so must be to remove them before coating and remedy.
rift is due to the wood by external force or the influence of temperature, humidity, the phenomenon of fiber separated from each other.
wood craze has the following several forms: table, inside crack, crack and crack. Below we simply know that several cracking occurs in the form of:
a crack, table:
refers to the surface crack, table split refers to the original wood crack on the surface of the body or timber. Cracks are usually confined to the string, and along the radial direction development. Wood drying, the first to evaporation from the surface, when the surface moisture content is reduced to less than the fiber saturation point, the surface of wood began to shrink, but at the moment, the lining of the adjacent wood moisture content is above the fiber saturation point, not shrink. Surface contraction is limited by the inner wood lumber, not free shrinkage, thus produce internal stress in wood: surface tension lumber, inner wood compression. Dry conditions more severe, the moisture content of timber reach to the inside and outside layers, the greater the resulting internal stress. If wood surface tensile stress than horizontal grain tensile strength, the timber organization torn, because along the wood ray organization the tensile strength of a nearby wood fiber strength is small, so the crack produced along the wood rays in the first place.
the internal crack. Internal crack also often called honeycombing. Internal crack produced in the late dry, sometimes produced in dry material storage period. Usually not easy to found outside the from wood, but serious when, can be made of materials to determine the sag. The crack is caused by tensile stress in inner layer of wood.
three, side crack:
the transverse crack. End to crack or is limited to the end face of lumber, or extend to the end of one side or both sides, the latter is often referred to as splitting. The main reason is due to hydraulic conductivity along the grain direction of wood is much greater than the horizontal grain direction, when wood drying, moisture evaporation from end face than much faster evaporation from the side. End moisture content is below the middle, and end the shrinkage restricted by central wood, so in the end ( Stretching) Stress, when the tensile stress exceeds the tensile strength of horizontal grain of lumber, transverse crack.
4, wheel crack:
the cracks along the growth direction, often spread to the adjacent a few round of growth. Wheel crack usually occurs in the early stage of drying, in the face of lumber, with the progress of the dry crack, extended. Sometimes happens on the inside, but appeared in the late dry, is caused by serious internal tensile stress.
to deal with the solution of the wood craze
1, using high temperature qualitative processing:
cut wood crack method can be used in high temperature qualitative processing, produce crack in the wood surface residual deformation can be done before the end of the drying process for high temperature and high wet processing to eliminate the wood. In processing, wood surface for humidifying expansion and compression residual deformation, and the presence of the original residual deformation offset, wood inside crack thus eliminated.
2, mechanical method of crack:
in the dry wood with wire bundles on the end, nail plate, etc. , using a combination of anti-cracking ring, don't use the method of mechanical force wood expansion and contraction, it also can avoid wood craze.
3, besmear to brush waterproof coating:
at the end of lumber and surface coating waterproof coating, slow evaporation intensity on the surface of the wood, which reduces the moisture content of lumber, both inside and outside gradient, can also reduce the cracking of lumber.
4, the antiseptic treatment with waterproofing agent:
more effective method is to use pressurized waterproofing agent, waterproofing agent deep into the wood, in order to achieve good anti-cracking effect of persistence.
5, improve the method of sawing lumber current:
wood anisotropic, at the same temperature and humidity changes, the wet up, the largest is the chordwise shrinkage coefficient, followed by the radial and longitudinal changes in the minimum, so next saw cutting board, to produce more diameter can reduce the cracking. Especially with the pith of plank dry prone to serious split, this is because the pith radial chords to the shrinkage difference caused by the nearby, is the best way to avoid when lumber production sheet with pith.