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Properties of wood

 
 

Wood of different breeds is non-uniform on the physical and mechanical properties. To physical properties carry humidity, heat - zvuko - and elektroprovodnost, and to mechanical - density and resistibility to splitting, compression, wear process, etc., and also ability to keep screws and nails.

The Big role is played by humidity of wood. Durability and durability of products, and also their weight depend on it. For example, 1м3 svezhesrublennoj oak wood weighs 1,04т, and in an air-dry condition - all 0,76т, a pine - accordingly 0,82 and 0,52, a fur-tree - 0,8 and 0,47. Wood well absorbs a moisture from air, thus it inflates, increases in volume and small cracks disappear. In the course of drying the moisture evaporates very slowly. The svezhesrublennyj oak contains from 5 to 70% of a moisture, in 6 months - 43, through 12-39 and in 18 months of natural drying-27%. Meanwhile humidity of the wood intended for joiner's works, should not exceed 10-18%. The humidity of a tree less, the longer products from it do not crack, do not rot, stick together is better.

Preparations, raskroennye on length and width with corresponding allowances, dry faster, than integral boards. Stroganye boards dry even faster, and edging - faster not edging.

To silnousyhajushchim to breeds the linden, a beech, an alder, a birch, a nut, ilm, a chestnut, a cherry, an apple-tree, a hornbeam, a pear, a box, to umerennousyhajushchim - an aspen, a pine, an oak, an ash-tree, a poplar, a maple, a yew, an acacia, to malousyhajushchim to breeds - a fur-tree, a larch, a fir, black and mahogany concern.

Wood at drying is jarred on and is frequent rastreskivaetsja. As external year layers dry faster, and internal more slowly, the warped boards always are turned by the convex party to a trunk core. In drawing 2 it is shown, how occur shrinkage and koroblenie raskroennogo logs depending on an arrangement of year rings. Raskraivajut or split logs in many ways of a different thickness: serdtsevinnye, central and lateral.

Serdtsevinnye of a board contain a core and a small amount of knots of all versions: healthy, grown and tobacco. Knots reduce value of wood, lowering its mechanical properties. These boards more often rastreskivajutsja. As a rule, them cut in the thickness 40мм and more from thick logs.

The Central boards receive at a cutting of a log along a core axis. Thus is better defects on internal plasti boards come to light. The central boards rastreskivajutsja it is less serdtsevinnyh.

Lateral boards (between serdtsevinnoj or the central boards and gorbylem) have no branched out knots and contain bolshee quantity zabolonnoj wood which on durability and water penetration does not concede jadrovoj to wood.

Each breed of a tree possesses colour inherent in it, shine, a structure. White, slightly yellowish colour the birch, a linden, an aspen, a fur-tree, a fir, brown tone - an oak, a chestnut, an elm, an ash-tree, a pear, a plane tree, etc. have, brown colour - a walnut, krasnovato-white - a beech, light yellow - a box.

Some breeds of a tree after cabin change the colour: the alder on air reddens, the oak in water darkens, and at long stay in the river or lake becomes almost black. Such wood named morenym an oak, is highly appreciated in furniture manufacture.

Heat conductivity of wood in comparison with other materials is very insignificant. For example, the factor of heat conductivity of a pine makes 0,14, and a brick - 0,45. Low heat conductivity of wood, especially dry, speaks that a tree has many time filled with air.

Damp wood - good enough conductor of an electricity. It should be considered at conducting of electric, telephone and broadcasting lines. If in advance not to consider all these features of wood, it is possible to admit marriage in work. To correct it often happens difficultly, and at times and it is impossible. Therefore to prepare details follows so that there was a maximum exit with the least waste. First of all boards plane, then mark, saw up and down. In this case the joiner sees all lacks and cuts preparations free of defects. At preparations from a crude material provide allowances in 5мм on all parties.

It is necessary to know ways of reduction koroblenija wood. A log split so that they were with serdtsevinnoj a board. Then them put in the form of a log and dry up. Drying up, boards are jarred on (fig. 2) from a core to a bark, forming as though trays. The board with a core is not jarred on, but dries out so that its middle remains to thickness of the ends, that is from the middle by the ends the board descends as though on a cone.

Koroblenie and usyhanie wood: 1 - serdtsinnaja a board; 2 - lateral boards; 3 - gorbyl

2. Koroblenie and usyhanie wood :
1 - serdtsinnaja a board; 2 - lateral boards; 3 - gorbyl

If of such boards to make a door or any board, having a board trays in one party products will have the form of a wide tray. Correction of a product by planing much more will reduce a thickness of boards that not always it is desirable.

Therefore it is better than a board to stack or have year layers every which way then the door or a board will turn out equal enough and to correct them much easier. When the door or a board produce from narrow boards, is not wider 100мм, having their year layers every which way traces koroblenija boards are almost imperceptible and to correct them strozhkoj easily enough.