Wood defects- These are natural deficiencies of individual sections of wood, reducing its quality and limiting its use.
Defects are the defects of wood of mechanical origin that arise in it during the process of harvesting, transportation, sorting, stacking and mechanical processing.
One of the wood defects is fiber inclination- used to be called cross-layer. As is already clear from the name, this defect consists in the deviation of the fibers from the longitudinal axis of the trunk. The inclination of the fibers can be either tangential or radial.
Traction wood characterized by a change in structure in the extended zone of trunks and branches, manifested in a sharp increase in the width of the annual layers. Under the influence of light, such areas of wood are colored Brown color. As a rule, traction wood is typical for hardwood trees.
Curlyness- tortuous or random arrangement of wood fibers. Occurs in everyone tree species, more often in deciduous trees.
Curl- local curvature of annual layers near knots or shoots. It can be one-sided or through, reducing the strength of wood. The same " side effects"They also give ocelli - traces of dormant buds that have not developed into shoots. Their diameter does not exceed 5 mm. The ocelli are scattered and grouped, light and dark.
Pocket- density within or between annual layers, filled with resin or gums.
Core- a narrow central part of the trunk, consisting of loose tissue of brown or lighter color than the surrounding wood. At the ends of the assortment there are spots of about 5mm various shapes, on the radial surface - in the form of a narrow strip.
Displaced core- eccentric location of the core, accompanied by curliness.
Double core- the presence in the assortment of 2 or more cores with independent systems annual layers surrounded on the periphery by one common system.
Dry-sidedness- a section of the trunk surface that has become dead during the growth of the tree as a result of damage.
Sprouting- a healing or overgrown wound.
Cancer- a depression or swelling on the surface of a growing tree as a result of the activity of fungi or bacteria.
False core- a dark, unevenly colored zone, the border of which does not coincide with the annual layers, separated from the sapwood by a dark border.
Wood spotting- coloring of sapwood of deciduous trees in the form of spots and stripes, close in color to the color of the core.
Internal sapwood- adjacent annual layers located in the core zone, their color and properties are close to the color and properties of sapwood.
Water layer are called areas of core or mature wood with a high water content.
The hardness of wood primarily depends on the type of wood, and also to a large extent on the growth conditions of the tree, humidity, etc. Within one type, the spread of values can be quite significant. Usually the average relative Brinell hardness values are indicated as a percentage relative to oak, the relative hardness of oak is taken as 100%.
Strength is the ability of wood to resist destruction under mechanical loads. It depends on the direction effective load, wood species, density, humidity, presence of defects and is characterized by tensile strength - the stress at which the sample is destroyed.
There are main types of forces: tension, compression, bending, shearing.
Thus, when choosing materials and wood products, you should take into account the above characteristics and not purchase products with defects and defects in wood. As a rule, low-quality wood is not used for the production of products, but only your vigilance will help you avoid purchasing low-quality products that do not meet norms and standards.
TYPES OF CUTTING LOG
There are two main types of cutting wood (logs) into boards (lumber):- radial;
- tangential,
as well as three additional types:
- mixed;
- semi-radial (rustic);
- central.
Scheme of types of log cutting
DESCRIPTION OF TYPES OF LOG CUT
Radial cut- this is a cut in which the axis of the cut passes through the core of the log and, as a result, the lines of annual rings in the section of the board form an angle of 76 - 90 degrees. with its faces (two main planes of the board). The wood of radial cut boards is quite uniform in color and texture. Such boards practically do not deform when dried and do not swell when moistened, because the change in wood dimensions occurs mainly along the line of the rings (across the grain), and for radial cut boards they are located along the thickness. Radial cut lumber has the highest performance indicators compared to lumber of other types of cut.
Tangential cut- This is a cut that is made along tangents to the lines of the annual rings of the trunk at some distance from its core. The surfaces of such boards have a pronounced texture and a bright wave-like pattern of annual rings. For tangentially cut boards, the coefficients of shrinkage and swelling due to moisture are twice as high as for radially cut boards, which causes their significant deformation when the humidity state changes. For this reason, tangential cut boards are less preferable for use in wet conditions than radial cut boards.
Rustic (semi-radial) and mixed cuts- these are cuts with signs of two main types of cuts at the same time: radial and tangential and, as a result, have indicators averaged between them. In a rustic cut, the lines of annual rings have the form of straight lines located at angles of 46 - 75 degrees. to the layers, and in a mixed cut these lines change from straight at the edges (along the width) of the board to arched in the middle.
Central cut- This is a cut made directly in the center of the trunk and including its core. Considering that the core of the trunk consists of the least durable wood, center-cut lumber has the most heterogeneous structure in terms of strength of all the types considered.Useful articles
Lumber - wood materials (beams, boards and whetstones) obtained by sawmilling. There are lumber of radial, tangential and mixed sawing. Lumber with sawn edges is called edged, while lumber with unsawed edges is called unedged.
Large, high-quality logs (these are logs from the bottom, butt part of the tree) provide the most valuable lumber. When sawing such logs, you need to decide on the thickness of the resulting boards in order to maximize the volume and cost of the resulting material. Since lumber prices depend on its thickness, and because cutting into thick timber produces less sawdust, this decision has a serious impact on income. However, if the quality of the thick material is lower, even if the best edge is almost pure, then sell it for good price It won't be easy. The sawyer should try to reduce the size of the material being cut when he sees that the quality of the wood begins to decline.
If the log is good, producing large lumber and railroad ties from the central part of the log is, to say the least, unwise. Because the price of timber is always less than the price of boards.
For high grade logs, circular sawing is recommended. In fact, cutting to the taper of the log and angling the log so that the cut is parallel to the bark is recommended for all "good" edges. The result will be clean wood along the entire length, more valuable pieces of lumber, and this will avoid the need to saw the clean wood later into short pieces. When you reach the low-grade part of the log, move on to the shape of the beam and minimize the operation of cutting the beam on the sides.
Durable but low-quality logs should be cut as quickly as possible. These logs are of little use - the profit is very small, or none at all, which means that these logs need to be removed from the machine, the faster the better. Any sawing method is suitable here. Most often they are sawed onto timber, or simply sawed right through. In this case, it is generally better to reduce log overturns to absolute zero.
Fragile logs provide such an insignificant profit and such a huge risk of breaking the product that it is better not to deal with them at all.
Logs of average quality can produce a significant amount of good lumber, and here a lot depends on the sawyer, on how he will turn the log. Here the decision to rotate the log is critical to profit.
First, you need to select the worst part of the log and cut it without taking into account the runoff. But you can't cut too much on this side. For small logs, you generally need to cut one layer, that is, cut once along the entire length of the log, or a layer and a short board, and then turn the log over to the opposite side.
Another way is to choose the best side of the log and start cutting taking into account the taper of the log. Then this particular part is sawed for a long time before the log is turned over.
Lumber is sawed from one side until the sawyer expects that the next board on that side of the log will be at least as good as the boards that can be obtained from the other side. There is an exception: if you start sawing from the worst edge of the log, you must saw until you get a completely smooth cut surface in order to turn the log over onto it. In other words, the good side of the log needs to be cut deeply, and the bad side is simply removed with a layer or layer and one board.
If we take a log with a diameter of 60 cm, although this is true for all logs of any size, when sawing with a 180° turn, we get 8 boards that need to be additionally trimmed on the sides, and using less effective method, always turning to the adjacent face, we get 13 such boards. This circumstance alone can already be a significant argument in favor of turning the log 180°, especially for small enterprises. In addition, this sawing method gives more wide boards, and they are usually more valuable. When flipped over to the adjacent edge, you get 8 tangentially cut boards, which are subject to severe warping when drying. Further, if it is walnut or red oak with a narrow sapwood part, then with a 180-degree turn of the log we will get 10 boards with sapwood, with another turning method - 13 boards. Sapwood causes problems during drying. And when the log is turned 180 degrees, the internal tension of the wood is relieved, which results in the avoidance of cracks and cracks.
Turning over to an adjacent edge may be easier, but from an economic and cutting safety point of view, rotating the log 180° is more beneficial.
After two opposite edges of the log have been sawn, you need to move on to the third and fourth. As usual, the worst of these edges is cut first, without taking into account the taper of the log. However, a good quality edge should always be sawn parallel to the bark to increase yield. good lumber from a log.
The width of the first layer when sawing from all four sides of the log is critical.
If the edge is of good quality, that is, the first sawn board can be classified as good grade, Then minimum width The sawn timber should be 15-1 cm. Of course, this depends on the size of the log itself. To take into account further processing of the board, planing or even cutting on the sides, 15-1 cm is recommended, and not 15 cm.
If the edge is of poor quality, then it makes sense to cut boards with a width of at least 10-1 cm. The length of such boards should be at least 1.2 m. In general, you need to produce boards of no less length at your sawmill.
When it comes to logs of frankly poor quality, it makes sense to cut them from the “belly” or from the “ears”, rather than looking for a good edge. The "ears" are usually removed in 1 or 2 passes of the saw, revealing smooth surface inside the log. Cutting from the “belly” requires more manipulation, and as a result you get several short but clean boards.
Timber has a number of advantages compared to thin boards. The timber often has a beautiful wood pattern that buyers love. When dried, it dries out half as much as boards (3% versus 6% for boards). Less cracking during drying. When humidity changes environment the timber is more stable. When the floor is covered with it, it hardly wears out.
Also, when sawing timber, the yield of useful product from the log is 20% lower. Its production speed is much lower. It requires 15% more drying time. The timber dries out in thickness 2 times more than narrow boards. Sharp branches that remain in the timber, in contrast to round branches in the boards, greatly reduce the strength of the material.
Radial called a cut, in which the plane of the cut passes through the core of the trunk. The wood of such boards is quite uniform in color and texture, the inter-ring dimensions are minimal. Radial cut boards are resistant to external influences, are practically not subject to deformation and have high wear resistance. The radial cut board has a shrinkage coefficient = 0.19% and a swelling coefficient = 0.2%. These indicators for radially cut lumber are twice as good as for tangentially cut boards. For a radial cut board, the process of shrinkage and swelling occurs along the width of the fibers - the thickness of the board, and for a tangential cut along the width of the board because the fibers of the “tangent” are located along the width. Accordingly, at the floor board, parquet board, imitation timber, block house, lining of radial cut, there are practically no cracks compared to similar products of tangential cut. Since the yield of radial cut boards is 10 - 15% of the total volume, their cost is quite high.
Radial cutting of wood is a method of cutting a log in which all the fibers in the board run along the direction of the annual rings. When radially cut, lumber has the best physical and mechanical properties. The strength and hardness of wood with radial cutting is higher than with tangential cutting.
The yield of radial cut boards is usually small (does not exceed 30%). On the UP-700 longitudinal sawing machines, the yield of radial cut boards reaches 60%. This high rate is achieved thanks to the cutting optimization system. Choosing among optimization criteria maximum output radial cut boards, conditions of radial and semi-radial cutting, the technologist determines the percentage of yield of the radial board.
Radial cutting can also be done using other equipment. But the percentage yield of a radial cutting board on other equipment depends on how the operator cut the log. Typically this figure is significantly less than 50%. Due to the microprocessor control system and optimization system on the UP-700, you can obtain the maximum possible number of radial cut boards.
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| Cut texture: 1 - tangential cut; 2 - radial cut; 3 - semi-radial cut. | ||
Tangential called a cut, in which the plane of the cut passes at a distance from the core, tangentially to the annual layer of the trunk. Such boards have a pronounced texture and a rich wave-like pattern of annual rings. Tangential cut boards have higher shrinkage and swelling rates, but are more affordable.
Sawing hardwood
The sawing operation involves decisions about board thickness, turning the log, and compensating for the log's taper. This depends on many factors: the type of wood, the quality of the log, its size, the design of the machine and the grade of lumber that needs to be obtained. There are 3 standard cutting patterns:
Simple sawing
The log is sawed until its core is exposed, and then turned 180° and sawed to the end. This is the fastest and easiest sawing method; however, with this method, each piece of lumber must be cut on the sides. Lumber sawn in this way is somewhat wider and heavier, of lower quality and has a lot of waste. It is extremely susceptible to warping during drying. Therefore, simple sawing or sawing through is justified only in the case of very low quality logs, when all of the above disadvantages are no longer particularly important.
Circular sawing
When sawing in a circle, a cut is first made, and the log is turned over to a new edge, sawed, and turned over again until at least 5 turns have occurred. From a financial point of view this is best way for logs of medium and high quality, although at the same time, at some sawmills it is difficult to carry out such a log turnover, and the daily productivity will be low. Of course, a machine with hydraulics solves this problem.
Sawing timber
Sawing timber maximizes productivity sawing machine(number of boards per day) and, as a rule, is used in industry when working with medium and large-sized logs. In this case, the log is first sawn as in circular sawing, but the central part of the log, which can have dimensions of 18x23 or 25x25 and so on, is either transferred for processing to another machine along the production line, or sold as a large and heavy beam. Basically, logs of medium and low quality are sawn in this way, when it is impossible to obtain valuable lumber from the central part of the log. This saves time and effort in producing a product that is not of very high quality and therefore not of very high price.
Deciding which side of the log to start cutting on, which cut surface to open first, is the most important part of sawing. We divide the log into 4 sides, each of which extends along the entire length of the log and occupies a certain part of its circumference. The choice of the first face is determined by the position of all the others.
When sawing in a circle and sawing timber, two basic rules apply:
The worst edge of the log is sawn first without any consideration for the taper of the log. Counting the slope of a log means raising or tilting the log so that the saw cuts parallel to the bark. Since this is the worst part of the log, this means that it will produce short boards and a lot of slabs. Since we do not take into account the taper of the log, this gives us the opportunity to do the opposite, the best side cut logs parallel to the bark, without lifting or tilting the log. This means that from this best part of the log more boards of high quality will come out, which also match the length of the log.
Cut the best edge of the wood first, taking into account the taper of the log. This means that the log needs to be raised or tilted so that the first cut is made parallel to the bark.
The end result of both methods will be approximately the same, but the second method has one advantage. In this case, it is easier for the sawyer to rotate the log, because the open edge is the cleanest and has no defects. In the case of the first rule, the best part of the tree is the part opposite the open edge. It is not visible, and it is impossible to accurately rotate the log. Usually, if the wood is of good quality, then both rules work almost the same. But if you encounter a worse log, it is better to use the second rule.
Sawing soft wood
Many methods used in sawing hardwood, are also suitable for soft varieties. But there are also some differences. Of course, safety considerations must take precedence over the desire to produce as much product as possible.
Position the log so that when sawing, minor defects in the material appear inside the lumber, of course, if these defects are not so serious as to affect the strength of the final product. If possible, you should cut so that all knots and defects are located on one side of the lumber, while the other side remains clean. True, in the case of building materials, a clean surface does not affect the final price of the product. But large branches or defects can affect the strength of the structure.
Select the worst side of the log and start sawing from there, producing short lumber. The first lumber will be the worst and therefore must be short to be salable.
After the log has been sawn from the bad edge along the entire length of the log, you need to move to the opposite edge and cut parallel to the bark. From a good edge, the width of the board being cut should be at least 15 cm. On smaller logs - less than 30 cm in diameter, the first board should be 10 cm wide. Huge logs will have fewer defects inside and therefore do not need to be transferred to large building structures.
You should always turn a log from one side to another if the lumber from the new side is best quality than from the one that was just sawed.
Logs from waste. It is necessary to cut the “ears” in one pass of the saw, then turn the log over onto its “belly”, perhaps at least a few short boards can be made from it.
TYPES OF CUTTING LOG
There are two main types of cutting wood (logs) into boards (lumber):- radial;
- tangential,
as well as three additional types:
- mixed;
- semi-radial (rustic);
- central.
Scheme of types of log cutting
DESCRIPTION OF TYPES OF LOG CUT
Radial cut- this is a cut in which the axis of the cut passes through the core of the log and, as a result, the lines of annual rings in the section of the board form an angle of 76 - 90 degrees. with its faces (two main planes of the board). The wood of radial cut boards is quite uniform in color and texture. Such boards practically do not deform when dried and do not swell when moistened, because the change in wood dimensions occurs mainly along the line of the rings (across the grain), and for radial cut boards they are located along the thickness. Radial cut lumber has the highest performance indicators compared to lumber of other types of cut.
Tangential cut- This is a cut that is made along tangents to the lines of the annual rings of the trunk at some distance from its core. The surfaces of such boards have a pronounced texture and a bright wave-like pattern of annual rings. For tangentially cut boards, the coefficients of shrinkage and swelling due to moisture are twice as high as for radially cut boards, which causes their significant deformation when the humidity state changes. For this reason, tangential cut boards are less preferable for use in wet conditions than radial cut boards.
Rustic (semi-radial) and mixed cuts- these are cuts with signs of two main types of cuts at the same time: radial and tangential and, as a result, have indicators averaged between them. In a rustic cut, the lines of annual rings have the form of straight lines located at angles of 46 - 75 degrees. to the layers, and in a mixed cut these lines change from straight at the edges (along the width) of the board to arched in the middle.
Central cut- This is a cut made directly in the center of the trunk and including its core. Considering that the core of the trunk consists of the least durable wood, center-cut lumber has the most heterogeneous structure in terms of strength of all the types considered.Useful articles
The cut of wood determines the texture of the parquet board and a number of performance characteristics. There are 3 main types of cuts: tangential, radial and rustic. Less often, mainly for artistic parquet, transverse or, as it is also called, end cutting of wood is used, in which entire growth rings are preserved. In addition, there are mixed cuts - semi-radial and semi-tangential.
The radial cut is made perpendicular to the growth rings, the layers are clearly visible on the die, they are located parallel along the length, the texture of the parquet board is uniform and monochromatic.
Advantages and disadvantages of radial cut
Due to the fact that the process of shrinkage and swelling occurs along the thickness, the coefficient is only 0.18 and 0.2 accordingly: the value is 2 times higher than that of tangential cut wood, which changes dimensions along the width.
Parquet has increased strength characteristics and exceptional stability in various climatic conditions. However, you have to pay for everything: the radial cut yield does not exceed 15%, which significantly increases the cost of lumber.
Tangential cut
The tangential cut runs tangentially to the annual layers, but bypasses the core of the log. The texture is heterogeneous and variegated; natural patterns are created on the dies that convey the uniqueness of the breed.
Pros and cons of tangential cutting
However, with all the originality of the parquet texture less resistant to humidity and temperature changes. Thanks to minimum quantity defective tangential cut boards are cheaper.
Rustic cut
The cut is made in any direction under acute angle to wood fibers: boards are obtained with a wide variety of textures. That is why the rustic cutting method is extremely rarely used in the production of parquet: it is almost impossible to select uniform dies that are comparable in color.
The cutting method determines the texture and color of each die, and also directly affects the stability and strength of the floor covering.
