WHAT ARE LOG DEFECTS IN THE LAWN INDUSTRY?

WHAT ARE LOG DEFECTS IN THE LAWN INDUSTRY?

In wood processing industries, besides wood as the main raw material, generally materials such as glue, varnish, paint are used according to the product type to be produced. Therefore, the efficiency and quality of such products, as well as the log properties, are also effective in other raw materials used in their production. However, in products such as timber, solid parquet and cut veneer whose raw material is only timber, timber properties have a more significant effect on quality and yield, provided other production conditions are kept constant. In particular, the fact that the mowing operators cannot determine the appropriate mowing model according to the defect or characteristics of the log increases the losses.

In Ts En 844-2 (2000), round wood is defined as a product that is cut, with the exception of firewood, the end part is removed and all branches are trimmed and can be cut into shorter lengths if necessary. Unsorted trunk wood is round wood that has not been cut into shorter lengths. The best quality part of the unsorted trunk wood is the side closest to the root. Because as you move towards the tip (crown) of the tree, the diameter and amount of the knots increase. The log obtained from the thick end of the unsorted trunk wood is called the Bottom Log. Quality timber to be used in peeling veneer production and furniture is produced from this part. The end log is the log produced from the thin end of the unsorted trunk wood. End Log are more suitable for particle board industry. Those produced from the part between the bottom log and the end log of the unsorted trunk wood are called Second Log or Intermediate Log. The process of sizing logs is called logging.

2. Logging Defects and Its Effects on Timber Production: Logging should be done in a way to obtain maximum timber efficiency, taking into account the existing defects in the trunk. In addition, since the best quality part of a tree is the side closest to the ground, logging should be started from the bottom part. Mower operators, the properties of logs before mowing;
   a- The form of the log (cylindrical, curved)
   b- The surface of the bark (smooth or cracked, smooth or spirally fibrous, knotless or knotty, insect bites, swellings, twin pith, frost crack, tumors, etc.)
   c- They should examine the cross-section of the log (narrow or wide annual ring, eccentric growth, core or ring crack, rot, coloration) and classify them according to three main groups.

2.1. Rotten Hole: It is a defect caused by fungi. Usually, the sapwood part of the trees planted with this defect remains more robust. Some rotten cavities cannot be detected without cutting down trees. It is an effective defect that significantly reduces timber yield. If the core rot is minor, it should be left in a single plank from the core of the log. If the core rot is extensive, the rot should be removed with a prism cut. Especially in the production of radially sawn quality timber, core rot must be removed.

2.2. Coloration: It is especially effective on timber quality yield. As a result of incorrect storage in the forest or factory warehouses, various stains occur on the logs due to fungi. If the coloration is superficial, the colored parts should be removed from the log with a prism cut. Thus, quality parts can be obtained from heartwood. If the coloration is excessive, the logs can be cut with a sharp cut. In this case, the obtained parts are of 3rd or 4th class quality.

2.3. Annual Ring Irregularities: Annual ring width varies more or less in the cross section of the log. If this difference becomes too pronounced, it is a defect when narrow annual rings are suddenly followed by wide or wide annual rings by narrow annual rings, or when the ring width is constantly changing. This defect indicates that the properties such as working, hardness and texture of the wood material are not homogeneous. This affects the processing and drying properties of the material. In some trees, the fact that the annual rings take a wavy state is not considered a defect in every use. For example; Since the annual ring waviness, which occurs due to the wavy fibrousness encountered in Spruce and Fir growing in high mountains, creates beautiful shapes in the tangential section, it is considered a useful feature in the wood material used for decorative purposes. Spruce, which has annual rings indented from place to place, also constitutes a desirable material for making string musical instruments. Apart from the above-mentioned uses, the waviness in the annual rings is a defect because it makes the surface treatments difficult and in large-surface timbers, a large number of fibers are cut and split (Berkel 1970).

2.4. Knots: Since it creates various technical problems in the use of wood material, it is considered the most important defect after rot and reduces the quality. Knots are formed by the expansion of the trunk every year by forming an annual ring and increasing the diameter and embedding branches or branch protrusions into the trunk wood. The knots formed by embedding a living branch into the trunk are called fused knots because the branch is fused with the surrounding trunk wood. The knots formed by natural branch cleaning by breaking off and falling of dead and dry branches, and by burying the dry and dead branch protrusion left on the trunk by the incremental tree trunk, are called falling knots. Because such knots are not fused with the trunk, are denser than the trunk wood, and shrink more at the end of drying, they fall and leave a gap in the timber. This issue is mostly related to İ.Y.A. applies to It is mostly found in Spruce, Fir and Hybrid. Knots also have a reducing effect on both the static and especially the dynamic resistance properties of the wood material. It breaks the color uniformity in wood. They cause bluntness of knives and saws as well as their negative effects on the machinability properties of wood material. Some indications on the bark indicate the presence of knots in the stem. These symptoms are in the form of “Chinese mustache” on the bark in thin and smooth bark tree trunks (Beech, Poplar, Birch), and in tree trunks with rough bark scales, “bark roses” (Oak) indicate knots in the trunk.

If the thick knots are densely located on one side of the log, it should first be started to be cut from the knotless side.

2.5. Curvature: Curved logs reduce timber yield and increase operating costs. However, in some places of use, for example; Curvature can be a sought-after feature in chestnut logs in boat and boat construction. If possible, crooked logs should be cut with a sharp cut with irrigation. Lumber should be produced by fixing the curved part of the log on the log cart and sawing in this way, with the curved part facing upwards or downwards.

2.6. Cracks: Cracks in the wood material occur due to various reasons such as finding different working directions parallel to the fibers, radial and tangential to the annual rings as a result of drying, severe cold (frost) or heat, and the rotating effect of the wind.
a. Peripheral Crack: Many environmental cracks occur in the periphery and in the direction parallel to the fibers, due to the fact that the wood works more in the tangential direction to the annual rings during drying in the tree trunks whose bark has been peeled off after cutting. Deep perimeter cracks cause the removal of thick cover boards from the logs in timber production and thus the loss of main product. Small and medium-sized cracks should be left in the edge or cover boards. Deeper cracks should be given to the saw so that they remain on the cutting line.
b. Core Cracks: Core cracks occur that extend radially from the core to the environment, starting from the cross-sections, due to the drying of the tree trunk and its different workings in three different directions after cutting.

They reduce the use value of logs. This phenomenon is more common in beech, oak, alder, and eucalyptus in summer.
Excessive progression of such cracks reduces timber yield and quality. When sawing this type of log, the deepest crack should remain at the cutting line, or if a crack wider than the cutting line, it should be left in a plank.
c. Ring Crack: This type of crack is ring-shaped. They run parallel to the annual ring. They are especially found in Oak and Fir. Small ring cracks should be tried to be left in one piece, if possible.
D. Cracks Caused by Freezing: Especially seen in Oak, Elm, Ash, Chestnut, Walnut and rarely in Beech and Fir. It is found in older trees rather than young trees. When cracking occurs in the wood, an explosion similar to the sound of a gunshot is heard. The length of the cracks sometimes reaches several meters. It forms a protruding groove on the outer side of the body.

2.7. Fiber Curl (Spiral Fiber): In this case, instead of being parallel to the tree trunk axis, the fibers are spiraling around the trunk by forming a small or large angle. In spiral fiber logs, during sawing, a much higher number of fibers are cut and split in an inclination compared to smooth fiber trunks, thus reducing the resistance of the sawn material. Spiral fibrousness also reduces the splitting ability of the material, and also complicates the surface treatment and affects its processing ability in various uses.

Timbers obtained from logs with excessive fiber curl should not be used as a carrier element in the building. The thickness of the timber obtained from such logs should not be less than 40 mm. Otherwise, the produced goods can easily crack and break into pieces. Apart from this, when sawing logs or timbers, diagonal fiber formation can be seen when the cutting direction should be parallel to the fiber direction. This causes the resistance of the material to drop.

2.8. Wolf Bite and Other Holes: There is a decrease in quality and quantity yield in timber obtained from such logs. If there are superficial insect holes in the log, the production should be made with the prism cut method, and in deep insect holes, with the sharp cut method.

2.9. Body Taper: Each log has more or less taper. The stems that are close to the cylinder and show a normal diameter decrease (1 cm./m.) as one goes up from the bottom are called plump or cylindrical stems. Conversely, logs that show more diameter decrease than normal as the body goes from bottom to top are called conical logs. It is an important factor reducing yield in timber production. The strength properties of timber obtained from conical logs are lower than timber obtained from fuller trunks. Fir comes first in terms of trunk fullness, followed by Spruce and Pine, respectively.

2.10. Formation of Corrugated Trunk: Some tree trunks are separated from the circular shape in cross-section and become rough, indented, protruding and corrugated in the environment. Corrugated trunk formation is hereditary in some tree species, for example in Hornbeam, Porsuk, Cypress and Elm, annual rings in the trunk cross-section are coarsely wavy, indented and the trunk surface is corrugated.

2.11. Duality: The resistance properties of two or more cored stems are different from the normal stems and their value is low. Such trunks are dispersed when sawing with timber. In production with sharp cuts, the small diameter should be parallel to the saw plate. Inner bark timber produced at the junction of two trunks should not be classified.

If lumber is to be produced by the sharp cut method, the larger diameter of the cross-section should be parallel to the saw plate in order to obtain a wider board for oval cross-section logs without reaction wood. If there is reaction wood formation, the larger diameter should be perpendicular to the saw plate. If a prism cut is made to produce flanked timber, the small diameter at the first cut should be parallel to the saw when sawing logs with oval cross-sections without reaction wood. Thus, it is possible to produce a wider board with sharp edges from the obtained prism. When sawing logs with reaction wood with a prism cut, the larger diameter should be parallel to the saw at the first cut. In the productions made in this way, no reaction wood formation is observed in every wood obtained. Large amounts of eccentrically developed stems are of low value and annual ring widths, spring and summer wood widths are irregular.

2.12. Eccentric Growth: Eccentricity is seen in two forms: oval growth with the core in the center of the cross-section and reaction wood formation in which the core is offset towards the periphery. According to both formations, a different way should be followed in sawing the logs in the band saw machine. The reaction wood seen in coniferous tree logs is called "pressure wood", and the reaction wood seen in leafy tree logs is called "tensile wood". If possible, thick timber should be cut from logs containing pressure wood. In addition, when fixing such logs in the log cart before mowing, compaction should be done from the faultless side. In other words, the pressure wood part should be cut first. Because the pressure wood part is difficult to detect with clamping hooks. When sawing logs with drawwood, the saw blade gets stuck and the saw teeth tend to tear the fibers rather than cut them. To avoid this, well-sharpened sharp saws should always be used when sawing drawwood.

2.13. Various Wounds: In addition to climatic factors such as storm, snow, hail, and lightning, some injuries caused by animals, transportation vehicles and people are factors that reduce the quality of the log.

3. CONCLUSION The quality class of the lumber produced decreases according to the ratio of defects such as insect hole, coloration, knots, cracks, rot and fiber curling as well as production defects such as thickness difference, surface roughness, crooked cutting and corrugation on the quality properties of the timber. The formation of defects in wood properties generally depends on the growing conditions of the log, as well as on the conditions of its storage in the forest or in the factory after cutting. In both cases, it is necessary to control and recognize the defects that occur in the timber production stage, especially by the main machine operators, and to cut them in the above-mentioned ways according to the log defect or properties in order to improve the properties of the timber.