Note that the defects of sawn timber can be divided into two main types – natural, that is, related to the defects of the wood itself, and those that appeared during wood processing, in the process of creating sawn timber, that is, depending on the human factor. A special GOST 2140–81, developed back in 1981, still operates in Russia. This GOST includes all visible wood defects.
The most common flaw in lumber is the familiar knots. Actually, this is a part of the tree that was inside the trunk, which did not in the best way affect its quality and appearance. Although sometimes knots can even decorate a tree cut, experts try to avoid such options. There are many types of knots that can be in lumber:
- Round, oval, oblong.
- According to their location in the sawn tree, knots can be edging, stitching, ribbing, bed, end.
- There are through, through all the lumber, and one-sided knots.
- Branched, grouped and scattered over the entire surface of the sawn timber knots.
- Non-intergrown with the surrounding wood, intergrown and partially intergrown knots.
- Rotten, tobacco, rotten and healthy knots.
It should be noted that not all of the above types of knots have a catastrophic effect on the quality of lumber. For example, if a knot is quite healthy, intergrown with the rest of the wood, then it stands out only externally and will not affect the quality of the lumber. But a stitching knot, that is, a knot that penetrates the entire edge or face, extending to two edges, is very bad. Experts also consider group knots, that is, located close to each other, to be very harmful for the quality of sawn timber..
The second common flaw in lumber is cracks. They represent a break in the wood, cracks are much more common along the fibers, and not across. In small assortments, it is impractical to distinguish cracks by type, they are considered a single defect. In large assortments, the following types of wood breaks can be distinguished:
- Metic cracks.These are radial cracks inside the shafts. Most often found in beech, larch and pine. They can reach 10 meters, often the crack goes from the butt to the living crown. On the lateral surface of round timber blanks, metic cracks are not visible, but on the ends of sawn timber they can be noticeable. There are simple metic cracks and complex.
1 – simple label; 2 – cruciform mark
- Stunning cracks.They are gaps in the annual layer of wood, found in all tree species. Flaw – an arcuate or annular crack, not filled with resin.
- Frosty cracks.As the name implies, they appear during a sharp drop in temperature in winter, spread radially into the depth of the trunk.
- Shrinkage cracks.This is the case when human intervention is the cause of the crack. Such cracks occur during wood drying as a result of drying stresses. They are smaller in length and depth, usually appear at the ends of the lumber due to uneven drying..
It is also customary to distinguish between end cracks, lateral, deep and not, through, closed and diverging. The appearance of cracks significantly reduces the strength of the wood; in addition, fungi, mold, and moisture can penetrate into the sawn timber through cracks. Therefore, tears, especially deep and clearly visible, are considered a serious defect..
GOST also indicates the presence of defects in the tree trunk itself, which, as a result, can affect the quality of sawn timber, make their harvesting more difficult, and the consumption is much more significant. The following trunk defects are distinguished:
- Displacement.This is a reduction in the diameter of the tree from the butt to the top. In general, this is normal, as the barrel is always thinner at the top. But if the diameter decreases by more than a centimeter every meter of height is already a vice.
- Consistency.One of the types of tapering is that the trunk is noticeably wider at the bottom. The consistency can be round and ribbed.
- Ovality.The shape of the end of round lumber in the form of an ellipse is also considered a defect..
- Growths, that is, the thickening of the trunk may be bumpy or smooth.
- Curvature.A crooked barrel is much more difficult to work with, and bends can be simple and complex.
As a result, the indicated defects of the trunks can cause the radial inclination of the fibers in already prepared sawn timber and veneer.
There are also many defects in the structure of wood:
- Tangenal slope of fibers, which is informally called the natural cross-bed. In this case, the wood fibers are located either along a slope or in a spiral. The oblique layer can cause warping and increased longitudinal drying..
- Cutting annual layersor radial inclination of fibers.May occur when incorrect sawing of generally normal timber or due to the curvature of the trunk and stiffness.
- Roll.These are changes in the structure of branches and trunk, typical for conifers. It manifests itself in darkening and thickening of annual layers, leads to cracks, reduces the strength of the wood and interferes with its processing. The appearance of sawn timber also deteriorates..
- Broad-layer.The annual rings are too wide, this wood is softer, it is fragile.
- Traction wood.Too thick, sharply enlarged annual rings, are expressed in hairiness, sometimes the wood changes color. May cause cracking, warping, mossiness.
- Curliness.The wood fibers are arranged irregularly, sinuous. Such material is fragile, it is more difficult to process it. But in finishing lumber, curliness is even appreciated for the unusual appearance and structure of the tree..
- Curls on annual layers.They reduce the strength of the wood, curls can be through, that is, extending to both sides of the lumber.
- Eyes.They can be dark and light, well noticeable and not so, scattered and group. In general, these are traces of dormant buds, which never became shoots. Eyes are usually not considered a serious defect..
- Resin pocket.This is a cavity that has arisen between the annual layers and is filled with resin. It is inconvenient that the resin flowing from such pockets stains the instrument and spoils the surface of wooden products.
- Wrong corewood, offset or double.
1 – displaced core; 2 – double core
Wood wounds include dryness, sprouting, cancer. All these are serious lesions that affect both the appearance of the wood and its quality..
1 – open cancer; 2 – closed cancer
During the processing of wood itself, in addition to cracks, which we wrote about above, the following defects may occur:
- Change in wood color. This can happen if hardwoods are dried at too high a temperature. Often even a burn may occur on a tree..
- Change of shape. Of course, during drying, the wood will still change its shape, but it can be achieved that the changes are minimal. To do this, you should strictly adhere to the drying technology, proceed with caution.
- Grinding. If there were resin pockets or the wood itself is tarred, then the resin at a high temperature – above 60 degrees – will simply flow. In general, resinification will not affect the technical properties of wood..
- Shrinkage of cells. Note again that you should not dry wood at temperatures above 60 degrees, this will have a detrimental effect on its properties..
- Warpness. It can occur not only during drying, but also during improper storage, sawing.
In addition, wood can acquire abnormal coloration during tanning and chemical processes. This phenomenon is called chemical coloring, the physical properties of the wood do not change, but the appearance is seriously affected..
Fungal damage to wood and biological damage, such as wormholes, are very harmful. In addition, defects in lumber may appear already during transportation, as a result of careless handling, improper cutting and processing. This is also a human factor.
Fungus damage to wood
Mechanical damage to lumber, for example, nicks, scratches, pricks, chips, tears, dents, snags, often occurs during manual processing. Automation of the process and the use of special devices when sawing and sanding wood help to avoid such problems..