During this procedure, the material changes its physical, mechanical, technical and operational qualities. The ratio of the extractives contained in the material also changes. The process is aimed at improving all available properties.
The drying process takes several stages.
First, moisture evaporates from the surface of the wood, then the turn of the layers located in the depths of the wood comes. Thinner parts dry out faster, moisture begins to move from thickened places to thinner, already dried out.
If the process is technologically wrong, thin layers of wood begin to shrink, as it were.
The result is that the wood cracks and warps. To prevent this from happening, wood blanks are treated with a mixture of chalk and drying oil, which are applied to the sections of the blanks, from their end.
Therefore, it is better to harvest wood in the form of beams, boards and other geometric shapes.
Rigs, stumps and other parts that are prepared for the production of dishes, volumetric sculptures, it is more convenient to process immediately after cutting, while the tree is still damp and lends itself to the influence of various devices and tools.
None of the operations required for processing causes such significant changes in the properties of wood as drying it. Various modes of this process are due to the species and other features of sawn timber: the area of growth, the density of the tree, the place of cutting, etc. The mode selected at once often needs to be corrected during the drying process.
The selection of the appropriate mode depends on the wood species and thickness source material. So that the boards do not warp or crack during the procedure, they are pre-steamed in chambers with wet steam.
First, the material is heated well for one to two hours at t 50 °. Then it is raised to 60 °, and the steaming procedure is repeated. It can be repeated up to three times as needed.
For soft breeds, use a temperature t ° from 40 to 75 degrees, for hard varieties from 35 to 55. In any case, this indicator should not be higher than 80 ° C. If the temperature rises higher, irreversible changes occur in the surface layers of the material. The wood is, as it were, hardened, which significantly complicates its further processing with tools.
At the very beginning of the process, the air has a fairly high humidity and low temperature.
The higher the initial moisture content of the wood, the more moisture must be in the air entering the chamber. This is necessary in order to prevent cracking of the material. As the rock dries up, the temperature of the air is gradually increased, while the moisture content in it, on the contrary, is reduced.
There is a strict relationship between the humidity of the air and the moisture content of the material.It can be determined using a special device - a psychrometer, which is used to determine the humidity and temperature of the air in drying chambers.
The latter are called dryers. There are various methods for drying wood.
The factory method involves the use of special chambers for drying. These are batch-type steam-air dryers with reverse circulation. The resulting material, unloaded from there, is aged for two or three days in the production shop.
At this time, the material is normalized, that is, it is released from the surface and internal stresses acquired during the drying process.
There are also gas chambers for drying wood material. In such batch devices, a special smokeless gas is used to get rid of unnecessary moisture.
It is obtained by burning raw wood waste in furnaces. With the help of a high-pressure axial fan, through special gas ducts, it is fed to the lumber stacks.
The system is designed with a steam humidifier.
In the woodworking industry, gas devices operating on natural gas are used. They are equipped with a firebox, the temperature in which during combustion reaches 1300 ° C. But before entering the dryer, the mixture circulates and cools, acquiring a temperature of 100 degrees by the time it enters the chamber. The working mixture is smokeless.
If the work of such a chamber is well-adjusted, then the lumber dried in it remains light. Each of them can accommodate four large stacks of boards. They are also used for conventional, ordinary drying of conifers.
Electric dryers are used for high-speed drying of building material, in which high-frequency currents are applied. This procedure does not last long - the drying time is only a few hours, and its quality is high.
The wood dries evenly: no flaws, warpage or cracks. The number of rejects with this method of drying turns out to be much less than with the gas and steam method - its indicator is less than five percent.
Features of heating dielectrics and semiconductors (wood belongs to them) in a high-frequency electric field are that the temperature of the entire processed material rises noticeably in a short period of time. A damp board can be heated up to 100 degrees throughout its entire thickness in three minutes. The power of the current absorbed by the material is regulated by the parameters of the electric field (by changing it through regulation).
In addition to industrial methods of drying wood, there are also household ones.
Using a microwave
The advantages of this method are that when using it, tiny cracks are not formed in a wooden block, which can turn into scrap up to one and a half centimeters of material from each end, and in some cases even break the workpiece into pieces.Under the influence of microwave heating, changes occur in the lignin fibers, due to which the object dried in this way loses its sensitivity to sudden changes in humidity.
For the drying procedure, a not very powerful, budget microwave model without unnecessary options is suitable. The main thing is that it has a low power mode.
It usually corresponds to the "defrost" or "defrost" mark. The chamber must be large enough to accommodate crafts or wooden blanks. The chamber is often larger in width than in depth.
It is more convenient to dry individual workpieces whole, some are better to saw. If it is already known what they are intended for, then they are sawing according to the size of future products, with an allowance.
It is allowed to dry a pre-processed workpiece, which must also have at least a small allowance. It should be remembered that the product may deform during the drying process. A round object may become more oval.
Those who often work with wood gradually gain experience. Craftsmen can guess what reaction to expect from what kind of wood, how exactly what kind is deformed, and make the appropriate allowance.
If you leave a processed raw workpiece on the table, it can burst.
During breaks in work (for example, when threading) or before drying in the microwave, put the product into a plastic bag.
Before starting the procedure, the workpiece is weighed and the weight is recorded. Wrapped in a plastic bag with holes made, the item is placed in the middle of the oven, the minimum power is set. Processing time depends on the size of the item.
Then the workpiece is cooled directly in the bag and warmed up again. Condensation is drained from the bag, the item is weighed.
The whole cycle is repeated several times until the mass becomes constant, ceasing to decrease.
If in the first attempt the thing cracks, it is necessary either to reduce the power even more, or to seal the ends of the workpiece. The trays are wrapped in newspapers before being placed in a bag.
You can also do this with other blanks: this will reduce the likelihood of wood cracking.
After cooling down, before the next cycle, the newspapers are changed to new ones. If there are resin pockets in the array, the latter can, boiling, break it and stain the oven with resin. Wrapping in paper will also help here.
If you continue the process of heating an already dried tree, it can char and even catch fire.
This is an affordable and extremely easy way. Boards are stacked under a canopy so that they do not fall on precipitation and sunlight. For them, a special flat base must be prepared, for the equipment of which you can use rails, logs, thick pipes or bars. Lumber is laid across this base.
Between the ground and the bottom layer of the boards there should be a distance of 0.
3 m. It is better to cover the ground under the pile with sheets of roofing material, straw or hay. The forest dries up for a long time: this process can take up to several years. In warm weather, the process is more active.
The ends of the forest are covered with a special mixture containing lime.
From the sides, the stack is sheltered from streams of oblique rain and from strong winds. Special measures are taken to prevent rapid drying and cracking of the material. Across the boards, between the layers of the dried wood, at a distance of a meter from each other, spacers are laid: the outermost of them are located flush with the ends of the boards in a stack.
With this method of drying wood with your own hands, obligatory cracks form at the ends of the boards. For this reason, the length of the blanks should be slightly larger than the planned products.
After all, after the end of drying, the cracked ends of the boards will have to be cut down. With this drying, carried out in dry and warm conditions, the moisture remaining in the wood is about 20 percent.
Material to be used for interior work should be moved to a heated room for final drying.
The disadvantage of such a simple method is obvious: the impossibility of drying the material completely, plus the dependence on the season and weather. The advantage lies in simplicity and low cost.
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