What can be cooked from squid: quick and tasty

The tree is natural material susceptible to fluctuations in temperature and humidity. Its main properties include hygroscopicity , that is, the ability to change humidity in accordance with environmental conditions. They say that wood "breathes", that is, it absorbs air vapors (sorption) or releases them (desorption), responding to changes in the microclimate of the room. The absorption or release of vapors is carried out by the cell walls. With an unchanged state environment the moisture level of wood will tend to a constant value, which is called equilibrium (or stable) moisture.

The ability to absorb moisture is influenced not only by the microclimate of the room, but also by the type of wood. The most hygroscopic species are beech, pear, kempas. They react most quickly to changes in humidity levels. In contrast, there are stable species, for example, oak, merbau, etc. These include the bamboo stem, which is highly resistant to adverse climatic conditions. It can even be laid in the bathroom. Different types of wood have at different levels humidity. For example, birch, hornbeam, maple, ash have low moisture content (up to 15%) and, when dried, tend to form cracks. The moisture content of oak and walnut is moderate (up to 20%). They are relatively resistant to cracking and do not dry as quickly. Alder is one of the most drying-resistant species. Its moisture content is 30%.

Moisture is one of the main characteristics of wood. Under humidity wood is understood to be the ratio of the mass of water to the dry mass of wood, expressed as a percentage.

Absolute humidity wood is the ratio of the mass of moisture in a given volume of wood to the mass of absolutely dry wood. According to GOST, the absolute humidity of the parquet should be 9% (+/- 3%).

Relative humidity wood is the ratio of the mass of moisture contained in wood to the mass of wood when wet.

There are two forms of water in wood - bound and free. They add up to the total amount of moisture in the wood. Bound (or hygroscopic) moisture is contained in the cell walls of wood, and free moisture occupies half of the cells and intercellular spaces. Free water is removed more easily than bound water and affects the properties of wood to a lesser extent.

According to the degree of moisture, wood is distinguished into the following types:

Wet wood. Its moisture content is over 100%. This is only possible if the wood has been in the water for a long time.

Freshly cut. Its humidity ranges from 50 to 100%.

Air dry. Such wood is usually stored in the air for a long time. Its humidity can be 15-20%, depending on climatic conditions and the time of year.

Room-dry wood. Its moisture content is usually 8-10%.

Absolutely dry. Its moisture content is 0%.

During prolonged drying, water from the wood evaporates, which can lead to significant deformations of the material. The process of moisture loss continues until the moisture level in the wood reaches a certain limit, which directly depends on the temperature and humidity of the surrounding air. A similar process occurs during sorption, that is, moisture absorption. A decrease in the linear volumes of wood when bound moisture is removed from it is called shrinkage. Removal of free moisture does not cause shrinkage.

Shrinkage is not the same in different directions. On average, the complete linear shrinkage in the tangential direction is 6-10%, and in the radial direction - 3.5%. With complete shrinkage (that is, one in which all bound moisture is removed), the moisture content of the wood is reduced to the hygroscopic limit, that is, to 0%. With an uneven distribution of moisture during drying of wood, internal stresses can form in it, that is, stresses that arise without the participation of external forces. Internal stresses can cause changes in the size and shape of parts when machining wood.

The properties of wood directly determine the properties of wood products. With excessive or insufficient moisture, wood usually absorbs or gives off moisture, respectively increasing or decreasing in volume. With high humidity indoors, wood can swell, and with a lack of moisture, it usually dries out, so everything wooden crafts, including floor coverings, require careful maintenance. To prevent deformation of the floor covering, the room must be kept at a constant temperature and humidity. This is beneficial not only for quality and durability. floor coverings and wooden furniture but also on people's health. With a sharp change in the temperature and humidity conditions in the room, internal stresses arise in the wood, which lead to cracks and deformations. Optimum temperature in a room with parquet flooring should be approximately 20 0 C, and the optimum air humidity is 40-60%. Hydrometers are used to control the room temperature, and the relative humidity in the room is maintained with humidifiers.

DETERMINATION OF WOOD MOISTURE

There are several ways to determine the moisture content of wood. V living conditions use a special device-electric moisture meter. The operation of the device is based on a change in the electrical conductivity of wood depending on its moisture content. The needles of an electric moisture meter with electric wires connected to them are introduced into a tree and passed through them electricity, while on the scale of the device, the moisture content of the wood is immediately noted in the place where the needles are inserted. Many experienced carvers measure wood moisture by eye. Knowing the types of wood, its density and other physical properties, it is possible to determine the moisture content of wood by mass, by the presence of cracks at the end or along the grain of the wood, by warping and other signs. By the color of the bark, its size and the color of the wood, you can recognize ripe or freshly cut wood and the degree of its moisture. When processing a s / m with a plane, its thin shavings, compressed by hand, are easily wrinkled - this means the material is wet. If the chips break and crumble, this indicates that the material is dry enough. When cross-cutting with sharp chisels, attention is also paid to the shavings. If they crumble or the wood itself is chipped off, this means that the material is too dry. Very damp wood is easy to cut, and a wet mark is noticeable at the cutting site from the chisel. But it is unlikely that it will be possible to get a high-quality thread in the end, since cracking, warping, and other deformations cannot be avoided.

DRYING WOOD

Drying wood - the process of removing moisture from wood to a certain percentage of moisture.

Dry wood has high strength, shrinks less, does not rot, sticks easily, finishes better, and is more durable. Any wood of a wide variety of species is very sensitive to changes in the humidity of the environment. This property is one of the disadvantages of timber. At high humidity, wood easily absorbs water and swells, and in heated rooms it dries out and warps. Indoors, the moisture content of wood is sufficient up to 10%, and in the open air - no more than 18%. There are many ways to dry wood. The simplest and most affordable - natural look drying - atmospheric, air ... It is necessary to dry wood in the shade, under a canopy and in a draft. When dried in the sun, the outer surface of the wood heats up quickly, while the inner remains moist. Due to the difference in stress, cracks are formed, the wood quickly warps. Boards, beams, etc. p / m are stacked on metal, wooden or other supports with a height of at least 50 cm. Boards are stacked with inner layers upward to reduce their warpage. It is believed that the drying of boards placed on the edges is faster, since they are better ventilated and the moisture evaporates more intensively, but they also warp more, especially material with high humidity. It is recommended to compact a pile of p / m, harvested from freshly cut and live trees, with a heavy load from above to reduce warpage. With natural drying, cracks always form at the ends, to prevent their cracking and preserve the p / m, it is recommended to carefully paint over the ends of the boards oil paint or soak in hot linseed oil or bitumen to protect the pores of the wood. It is necessary to process the ends immediately after the cross cuts into the cut. If the tree is distinguished by high humidity, then the end is dried with a blowtorch flame, and only then painted over. Trunks (ridges) must be debarked (cleaned of bark), only at the ends small belts-couplings with a width of 20-25 cm are left to prevent cracking. The bark is cleaned so that the tree dries out faster and is not affected by beetles. The trunk, left in the bark, in relative warmth with high humidity, quickly decays and is affected by fungal diseases. After atmospheric drying in warm weather, the moisture content of the wood is 12-18%.

There are several other ways to dry wood.

Way evaporation Or steaming has been used in Russia since ancient times. The workpieces are sawn into pieces taking into account the size of the future product, they are laid in ordinary cast iron, sawdust from the same workpiece is poured, poured with water and placed for several hours in a heated and cooling Russian stove “languishes” at t = 60-70 0 C. This occurs "Leaching" - wood evaporation; natural juices come out of the workpiece, the wood is colored, acquiring a warm thick chocolate color, with a pronounced natural texture pattern. Such a workpiece is easier to process, and after the end of drying it cracks and shrinks less.

Way waxing ... The workpieces are immersed in melted paraffin and placed in an oven at t = 40 0 C for several hours. Then the wood dries out for a few more days and acquires the same properties as after parking: it does not crack, does not warp, the surface becomes tinted with a distinct texture pattern.

Way steaming in linseed oil. Cookware made of wood steamed in linseed oil is very water-resistant and does not crack even with daily use. This method is still acceptable today. A blank is placed in a container, poured with linseed oil and steamed over low heat.

Wood is a “living” material that changes its properties not only during growth, but for a long time after felling. Moisture is one of the most important characteristics of wood for its use. This material is highly susceptible to environmental changes. One of its properties is "breathing" - the absorption and release of gases by the cell walls of the material. By the same principle, these cells absorb and release moisture.

What can affect the moisture content of woody tissue? There are 3 main factors:

Wood species

The time of year at which it was cut down;

Features of the climate.

Let's consider the most commonly used concepts of wood moisture.

Natural wood moisture

This is the level of moisture contained in the tree. at the time of the cut... It is also called "initial moisture". This value is used as a basis for further actions with the batch of material: for example, you can calculate the drying time and conditions. Moisture content may vary under different conditions from 25 to 80%... When determining the natural moisture content of a particular batch of wood material, we will always keep in mind "moisture under specific conditions".

Equilibrium humidity

When wood is in the same air environment for a long time, without significant changes in air humidity and temperature, the material reaches an equilibrium humidity. This is a state when the process of drying or saturation with moisture in these conditions has stopped, and the percentage of moisture has become constant. It should be noted that different breeds trees in the same conditions reach practically equal indicators of internal moisture.

Depending on the different conditions contents distinguish 5 degrees of wood moisture:

Wet- humidity is more than 100%, this state is achieved by long-term storage of wood in water.

Freshly cut- moisture level from 50 to 100%.

Air dry- from 15 to 20%. Such indicators are achieved when stored in air, they differ depending on temperature and precipitation.

Room-dry- from 8-10%. The moisture level is established when stored indoors.

Completely dry- wood with a moisture content of 0%.

Free and bound moisture

There are 2 types of liquid in wood tissues:

Bound moisture- is located inside the cells of the tree.

Free moisture- the one that fills the pores and channels of the tissues, but has not yet been absorbed by the cells.

Saturation point of wood grain

Associated with these two concepts is the so-called fiber saturation point: that percentage of wood moisture when all free moisture is removed from it, but at the same time bound liquid remains in it.

For different types of wood, this degree is determined from 23 to 31%.

Ash - 23%

Chestnut, Weymouth pine - 25%

Pine, Spruce, Linden - 29%

Beech, larch - 30%

Douglas fir, sequoia - 30.5 -31%

This value is important, since the volume and size of wood changes with moisture content from 0% to saturation point. After the cells are completely filled with water, the volume of the tree will not increase significantly.

Measuring wood moisture with a moisture meter

Absolute moisture content of wood

Let's consider the concepts of absolute and relative humidity.

Let's take a wooden block.
Absolute moisture is the ratio of the mass of the internal liquid to the mass of the fully dried bar.
The value is calculated by the formula:
W = (m - m 0) / m 0 x 100,
where, (m) and (m 0) - the mass of the wet and dried bar.
GOST 17231-78 interprets this value simply as "moisture". But this concept is inconvenient to use in calculations, since the amount of water refers specifically to the dry mass, and not to the total weight. As a result, discrepancies arise: for example, 1000 g of wood contains 200 g of moisture, but the absolute moisture is calculated as 25%.

Wood relative humidity

This is a more convenient concept for calculations, since it reflects the ratio of the mass of the internal fluid to the total mass of the bar. The calculation formula is the simplest:

W rel. = m water / m sample x 100.

This formula is used in the calculation of a heating engineer to determine the volume of water evaporated from firewood. According to him, at a moisture content of 20%, a 1000 - gram bar contains 200 grams of moisture and 800 grams of dry fibers - quite a logical result.

Wood species moisture

One of the factors affecting humidity is the type of wood. Due to the different structure of fibers, some rocks instantly react to changes in the external environment, absorb and release water. Others are more stable and become saturated with moisture very slowly.

The most actively absorbing rocks are beech, pear, kempas.

Oak, merbau are considered stable and resistant to changes.

The drier rocks tend to crack when shrinking. Moderately moist, such as oak, are more resistant to such phenomena, less change in their properties when conditions change.

When sawing under normal conditions, the moisture content of different types of wood has the following average values:

Wood moisture content for pellet granulation

Pellets and fuel briquettes appreciated thanks to low level moisture in the fuel. The moisture content in it is 8-12%. With these characteristics, a minimum amount of smoke is generated during combustion.

The optimum moisture level of wood for pellet production is 12-14%. Hammer crushers also work with wood chips up to 65% moisture, but with such moisture it is impossible to grind the material to the required fraction, therefore grinding takes place in several stages. To bring the crushed sawdust to the required condition, complexes with drying drums are used.

Wood is a "living" material, constructions made of it breathe and can change their moisture content. This is its main difference from brick, concrete, metal ... This feature determines the presence of some problems when using building materials from wood, especially when it comes to changing the percentage of moisture.

Moisture: the concept of free and bound moisture

In wood, the bulk of the water is in the cavities of cells, intercellular spaces, in channels, voids, cracks - this is free moisture. A certain amount of water is present in the thickness of the cell membranes - bound moisture.

Free (capillary) moisture in the tree is retained by simple physical and mechanical bonds, it easily evaporates during normal drying. This is the water that wood can absorb and release. When it comes to the moisture content of lumber, we mean the amount of free moisture.
Bound (microcapillary) moisture is retained in the tree by complex physicochemical processes, its removal is associated with huge energy costs. In nature, it evaporates from wood during combustion or natural aging, that is, when cells are completely destroyed.

The moisture percentage of sawn timber is one of the most important technical characteristics affecting the quality and scope of products. In addition, the moisture indicator can translate the board or timber into one of five grades. So, in GOST 8486-86 it is said that the selected and first-third grades include sawn timber with a moisture content of up to 22 percent (dry) or from 22% (raw, treated with an antiseptic), and only the 4th grade is not standardized for this indicator.

Allocate absolute and relative humidity. In construction practice, attention is mainly paid to the absolute, which is defined as the ratio of the mass of moisture contained in the tree to the mass of dry wood.
It is customary to distinguish several types of moisture:

wet wood (floatable) - 100 percent or more;
freshly sawn - from 50 to one hundred percent;
air dry - up to 20 percent;
room-dry - 7-10 percent;
absolutely dry - 0 percent.

There are also the concepts of "semi-dry" lumber, wood products "transport moisture" - about 22%.

Why you need to know the percentage of moisture in lumber

Wood moisture is unstable. Wood is hygroscopic, it always strives to come into balance with the environment. Moisture exchange occurs constantly, when the humidity of the air rises, the lumber absorbs water from it, and when it decreases, it gives it away. This interaction causes a number of processes to change the structure and shape of the material, such as:

swelling;
shrinkage;
warpage;
cracking.

During shrinkage, lumber shrinks due to the evaporation of moisture from the wood. Moreover, the volume decreases in direct proportion to the decrease in humidity. The tree dries out unevenly in different directions, least of all along the fibers (by 0.1-0.3%), in the radial direction - 4-8%, in the tangential direction - 6-10%. Volumetric shrinkage on average can be 12-15 percent. So that, after drying, the manufactured lumber has required sizes, when sawing logs, for example, on a bar or board, allowances are made. At the same time, it is taken into account that shrinkage depends on the density of the wood - the higher it is, the more it dries out. By the way, different breeds react differently to changes in the humidity regime, distinguish among them more or less resistant, and some are characterized by carpenters and joiners as "nervous".

Swelling is an increase in volume of wood products, that is, a process opposite to shrinkage. It occurs when the tree is operated in high humidity conditions. The increase in volume in itself does not affect the strength of the wood as such, but it can lead to a violation of the shape / integrity of the structures assembled from it.

The property of wood to swell and dry out with a radical change in humidity is considered negative. However, in some cases, for example, swelling is useful - it ensures the tightness of the connection of parts, for example, during manufacturing wooden boats, barrels, etc.

Street wooden structures the processes of swelling and shrinkage undergo periodically, with the change of seasons. Therefore, they are particularly susceptible to processes such as cracking and warping, which are the result of constantly changing humidity.

During shrinkage, uneven distribution of water in the layers of wood can form, as a result of which tension arises in different directions, leading to the formation of cracks. Due to shrinkage, the curvature of the product is often observed - warping. It can be longitudinal or transverse, it appears unevenly in different directions. Curved lumber complicates installation and can lose load-bearing capacity. They even distinguish (GOST 2140 81) a specific visible flaw of the board - "winged", that is, helical buckling.

Choosing lumber by percentage of moisture

Lumber of a certain moisture content is intended for certain purposes. It is allowed to use a board / timber with a moisture content of 20-30 percent for the construction of any outdoor structures - fences, gazebos, sheds, fences for animals, and the like. In addition, a timber and a board of natural moisture is suitable for arranging some structural elements during the construction of houses and repair work... For example, for arranging rafter system or lag under the flooring. In this case, the reliability of the fastening will not allow cracks and warpage to appear when drying. And to protect against fungus, products are treated with special antiseptic compounds.

From dry lumber (room-dry humidity at the level of 7-10 percent), planed small and large moldings (lining, block house, plinths, corners, casings) are made for external and internal door leaves, window transoms and frames, parquet, furniture.

Woodworkers have such a concept as "transport moisture". Its indicator should not be more than 20-22 percent. If the moisture content of sawn timber is higher, then it is not permissible to transport them over long distances, since transportation will take a long time, during which wood decay is possible.

In practice, absolutely dry wood with an indicator of 0 percent does not occur. This concept is applied only when using one of the methods for determining moisture - weight.

Basic methods for determining moisture

To find out the moisture content of sawn timber, two main methods are used today - by weight and using a moisture meter.

Weight method

The moisture content is determined as follows - a small sample (control sample) with a width of 20-25 mm is cut out of a bar or board. It is very important to take it not from the very edge, but from the middle, since the end parts always have less moisture. The sample is cleaned of sawdust and weighed on a technical balance capable of giving ultra-precise readings (up to one hundredth of a gram). The resulting weight is recorded - this will be the initial mass of the sample (IMP).

Then the sample is dried in a special drying cabinet at 100-105 degrees. After five hours, it is taken out and weighed, fixing the weight, dried again, checking the indicators every 1-2 hours. When the weight stops changing, the wood is completely dry - the final mass of the sample (MCM) is recorded. Further, the moisture content of lumber is determined as follows: the difference between NMP and KMP is divided by the KMP indicator, the resulting figure is multiplied by 100 - the initial moisture indicator is obtained.

The main advantage of the method is that it gives very accurate indicators (the error is no more than 1 percent). Minuses:

the analysis can take a long time;
you will need to cut a sample of the material, which is unacceptable for finished products.

Using a moisture meter

A moisture meter is an electrical device specially designed for measuring humidity. There are two types of it:

contact (needle) - the work is based on the conductometric method;
non-contact - the work is based on the dielectric method.

The needle moisture meter has two sharp metal needles that are immersed in the wood. Then the button is pressed, closing the circuit. The device measures the electrical resistance, which changes depending on the level of moisture in the material. Further, according to a special formula stored in the memory of the moisture meter, the percentage of moisture is calculated. Measurements in this case are carried out locally, therefore, the procedure must be carried out in several places of the product to obtain accurate results.

The main working element of a non-contact moisture meter is a radio frequency generator. Measurements are carried out using built-in contact pads, therefore, unlike the needle model, the device does not leave traces of the product. The work is based on measuring the dielectric constant of wood - water itself is characterized by a high dielectric constant, which makes it possible to obtain accurate indicators of the percentage of moisture in the material.

The main advantages of using moisture meters are ease of use and the ability to quickly get a result. Non-contact instruments are also perfect for measuring the moisture content of finished products. The main disadvantage is that the indicators of moisture meters are not very accurate, the error can be from 2 to 7 percent.

Basic methods of drying sawn timber

Drying of wood is the most important operation aimed at improving its technological and consumer properties. Even if the product is overmoistened, the former dry lumber is much less likely to warp and crack, it is easier to handle and install. A dry tree perfectly resists infection by harmful fungi. The weight of the products turns out to be less, while the strength and hardness increase, and the thermal insulation qualities are also noticeably improved.

Today in the woodworking industry there are two main methods of drying - natural (atmospheric) and forced (chamber).

Natural drying

In atmospheric drying, lumber is stacked under the canopy on outdoors... When forming a pile between rows of boards, beams, etc. put spacers. The stacks are installed with openings for air circulation. The ends of the products, in order to avoid the appearance of cracks, are treated with special compounds. In addition, hardwood lumber must be antiseptic before stacking.

The drying agent in this case is air, although, unlike the forced method, it is impossible to control its parameters (temperature, humidity). It all depends on the weather and the time of year. An important point is how tightly the stacks are stacked. The denser, the higher the relative humidity in them and the lower the temperature, which means that the wood will dry out more slowly.

Atmospheric drying makes it possible to obtain products with a moisture content of 18-20 percent at the outlet. The speed of the process will depend on the initial moisture content of the wood, the season, the type of wood and the section of the lumber.

The main advantage is the relatively low cost of the process. No special equipment and air heating costs are required. In addition, residual stresses during shrinkage will not be so strong, and cracks will not form - this is especially important when drying wood with initially high humidity.

Minus - lumber dries for a long time, it is impossible to control temperature and humidity. With a prolonged increase in the humidity of the ambient air, there is a risk of fungal infection.

Forced drying

The most technologically advanced high-performance method that allows you to obtain wood with a moisture content of 7-12 percent in a short period of time. Its essence lies in the fact that specially formed piles of sawn timber are placed in special chambers, in which the required temperature and humidity conditions are maintained for a certain time. The drying agent can be steam, heated air or flue gases, their movement can be both natural and forced.

What is wood? It is a material consisting of hydrophilic components with a capillary-porous structure, and therefore it constantly contains a certain amount of water. If we consider a living tree, then here water is needed to maintain its life, since it plays a major role, as in the human body. The amount of water in the tree is called the moisture level. And in fact, this is one of the main and most important characteristics of a tree.

The moisture index is directly related to the quality of the material, has a great influence on its properties and, accordingly, on its suitability for use in certain construction works.

The moisture level is indicated as a percentage, and is the ratio of the mass of water in the wood, to its dry mass.

Humidity also has an effect and the interaction of the material with water is quite significant characteristics, especially for mechanical or chemical processing, for example, painting, impregnation with solutions, alloying and storage, etc.

Wood has a high cellulose content and water has an effect when it is activated. Through this interaction, paper is produced. First, the wood is ground by mixing with water, and then, during molding, water is removed, due to this, strong interfiber bonds are formed in the finished material.

Also, the properties of wood directly determine the properties of products from it. When using such a material, it is necessary to select wood based on the humidity of the air in the room, since it tends to adapt to the microclimate of the room. Thus, with a lack of moisture, it will absorb it from the air and swell, with an excess of moisture, on the contrary, dry out. After the selection of wood and its installation, it is necessary to constantly maintain the humidity and temperature conditions of the room.

Wood moisture is divided into 2 types:

Relative
Absolute

Relative humidity is defined as the percentage of the mass of water to the mass of the entire material.

Absolute moisture is the ratio of the water contained in the tree to the dry mass of the wood itself, the ratio is also expressed as a percentage. For example, parquet, the absolute humidity should range from 6 to 12%, for the maximum manifestation of its operational abilities, this figure should be 9%.

The concept of completely dry wood means a material that has been dried to constant weight at a temperature of 102 to 106 degrees Celsius. In this case, the values of the relative humidity are also needed, they are used in calculating the mass fraction of the components of the material as a percentage of the absolutely dry material. This type of moisture is used to characterize wood samples by comparing them with respect to water content.

Wood moisture levels

Wet. The moisture content of such a material exceeds 100% (this may be the case if the wood has been in water for a long time).
Freshly cut. The moisture content of such wood varies from 50 to 100%.
Air dry. Wood, dried naturally... The moisture content of such material can range from 15 to 20 percent, depending on climatic conditions and the time of year, respectively.
Room-dry. Such wood also dries naturally, but in a dry room, due to which it has a moisture content of 8-10%
Absolutely dry. The conditions for its drying were indicated earlier. Humidity is 0%

You can notice uneven distribution of water in different parts of the tree. Thus, the trunk contains less water than the roots and branches; The lower and upper parts of the trunk are larger than the middle; sapwood coniferous trees contain more water than ripe and hearty wood. In conifers, in turn, the moisture content of the core is less than that of deciduous trees, and the moisture content is cross section distributed less evenly. Considering the bark, there is a significantly lower moisture content of the crust than the bast, about 7-10 times.

Regarding the moisture content of freshly cut wood, it is 80-100%, for driftwood this indicator is 2 times higher. And on the example of conifers, the moisture content of the kernel is 2-3 times less than the moisture content of sapwood.

In the construction industry, degrees of humidity are distinguished by slightly less than in general consideration.:

Freshly cut. The moisture content of such wood, depending on the microclimate, soil and felling time, ranges from 50 to 100 percent.
Air dry. Naturally air dried wood. The moisture content of such wood is comparable to the air humidity in the region where it was dried and can average 15-20%.
Room-dry. Wood dried in a heated room, the absolute humidity of such material is 10-14%; it is also possible to note wet wood, obtained in the process of a long stay in water, the absolute humidity of such wood is up to 200 percent and more.

The types of water in wood are also distinguished, it can be hygroscopic and capillary. From these types, the moisture level of the material is added. Hygroscopic moisture is located in the cell walls, capillary, in turn, directly in the cells themselves. Free, or capillary water is removed from wood several times less, and also less affects the properties of the material.

The moisture saturation of the wood at the initial level is carried out with the help of hygroscopic water and only after the full filling of the cell walls begins the filling of the cells themselves. For this reason, it is the change in the bound (hygroscopic) moisture that is the reason for the slowing down, stopping or accelerating the processes of warping, shrinkage, and changes in the properties of strength and elasticity. At that moment, as a change in the level of free moisture practically does not affect any properties and processes.

Water absorption is the unique ability of wood to absorb water when it is in direct contact with it for a long time. Since wood is a natural material, it is highly susceptible to changes in microclimate. The main property that provides the ability to adapt to different climatic conditions is hygroscopicity, i.e. the ability of a material to change the level of moisture, adapting it to the level of the environment.

Wood has the so-called "breathe" property, that is, it releases or absorbs air pores when the microclimate of its environment changes. These processes take place thanks to the cell walls. It should also be noted that with a constant, unchanging microclimate, the material will gradually tend to a constant level of humidity, which is called stable or equilibrium.

Hygroscopicity - the property of wood to adapt, i.e. change the level of its humidity, corresponding to the change in the humidity of its environment. In most wood species, the hygroscopicity index is 30% at a temperature of 20 degrees Celsius.

As mentioned earlier, moisture in wood is divided into two types: bound and free. It is the amount of bound moisture that indicates the level of hygroscopicity, and its maximum amount is the limit of hygroscopicity. This limit may fluctuate depending on temperature regime, at 20 о С it is 30%, when the temperature changes, the bound moisture turns into free and vice versa.

The moisture level of the material is reduced by drying. Also, chemically bound moisture can be present in wood, usually these are substances that are part of the material, they can be eliminated by chemical processing.

The hygroscopicity limit does not differ depending on the type of wood. In most cases, it makes up 30% of the wood mass (at a temperature of 20 degrees Celsius), this is a kind of saturation point. The rest of the wood saturation with water occurs due to free moisture.

When the moisture level changes, depending on the nature of the change, the wood may dry out when the moisture level decreases, or swell when it increases.

In most cases, a visible change in size is observed along the cross section, less often it is noticeable along the longitudinal section. Speaking of dense wood, it is fashionable to note its greater weight and, accordingly, a greater level of swelling or shrinkage.

The cavity of the wood cells contains free moisture, which is bound in the cell walls, respectively. The standard saturation limit of wood is 30%, and as the moisture level decreases, the material dries out accordingly.

If the saturation limit for all rocks is practically the same, then the ability to absorb moisture depends directly on the individual structure of the material, and, accordingly, on the rock. Some of the most hygroscopic species are beech, kempas and pear. They react as quickly as possible to changes in the microclimate and immediately begin to change themselves.

There are also stable species of rocks that are practically not amenable to change (if there is no global change in temperature and humidity conditions), such as oak, merbau, and so on. They also include bamboo wood, which has high level resistance to changes in climatic conditions and adverse environmental influences, this is one of the few types that can even be laid on the bathroom floor.

The moisture level of each of the breeds is also different. Wood with low moisture content up to 15% (maple, birch) tends to dry out quickly and further crack. Material with moderate moisture content, up to 20% (walnut, oak), dries more slowly and is more resistant to cracking. Taking into account the material with high moisture content, up to 30% (for example, alder), we can say that it has great resistance to drying, and, accordingly, the formation of cracks on the surface.

To determine the physical and mechanical properties of wood species, it is tested, bringing it to normalized humidity, on average, this value reaches 12%, by conditioning at a temperature of 18-22 degrees and an air humidity of 60-70%.

Determination of wood moisture

There are several ways to determine the moisture level of a material.

In a domestic environment, this is done using a special device - an electric moisture meter. The device determines the moisture content based on the readings of changes in the electrical conductivity of wood. Needles with diodes are drawn from the device, and inserted into a tree, after which an electric current is passed through them, based on the conductivity data, the device shows the level of humidity in the place where the needle is inserted.
Also knowing physical properties material, type of wood, its density, etc., you can determine this indicator by weight, warpage and other signs.
Taking into account the color of the bark, it is possible to determine freshly cut or ripe wood, as well as its moisture level.
If an accurate indicator of moisture is not needed, then it can be determined by the chips, if it crumples, then the material is wet, if it breaks or crumbles, then the material is dry enough
Wood with elevated level moisture is cut well enough, and wet traces remain in the place where the cutting was carried out.

The moisture content of sawn timber is determined by the following formula:

Where m with and m 0 is the mass of the original and dried material, respectively.

Those. in fact, this indicator is determined either by weighing or using a special device.

The moisture content of driftwood - 200%, freshly cut - 100%, air-dry - 15-20%.

Drying wood

Drying of wood involves the process of removing moisture from the material to a certain value.

The gloss of wood is the property of a material to reflect those falling on it Sun rays... Depends on the type of wood, the degree of its smoothness and the indicators of the lighting itself. A high level of possession of this property is distinguished by rocks, most of the surface of which is formed by heart-shaped rays. It is a decorative property and is taken into account when determining the type of wood.

The dielectric property of wood is an ability that characterizes the dielectric constant of a material.

The swell factor is the average swelling of the material when the moisture level is increased by one percent.

Drying factor is the value of the average drying when the moisture level is reduced by one percent.

Warping is the property of wood to change, that is, to lose its size and shape under the influence of the environment.

Warping is longitudinal and transverse. The transverse depends on the swelling and shrinkage relative to the radial and tangential directions, it is caused by several factors:

Location of annual layers
Cutting location
Cross-sectional shape

Longitudinal depends on the presence of wood defects: inclination of fibers, knots, etc.

Also warpedness different types occurs when the balance of stresses in the material is disturbed during further processing (milling, dividing into thinner boards, etc.)

Longitudinal warping most often occurs when a mechanical change in the shape of the section of materials that are cut from different parts of the tree, or when drying.

Dried wood has a high level of strength, is less prone to warping, is not susceptible to decay, sticks together quite easily, and is also more durable than wet.

One of the big disadvantages of lumber is a sensitive response to changes in the microclimate of their environment. In this connection, when the humidity rises, it absorbs water, and when it is in a dry room, on the contrary, it gives off moisture, as a result of which it dries up and warps.

In order to avoid destruction of the structure of the material, it is necessary to maintain a constant air humidity, for an open environment it is about 18%, for closed rooms 10%.

There are also many ways to dry wood. The first is natural drying, or atmospheric. In this case, the wood is dried in an open space. It is necessary to fold it in the shade, also provide for a canopy and the presence of a draft. It is impossible to dry the tree in the sun, because in this case the upper part dries quickly, while the inside remains damp, which has its drawbacks. As a result, due to the difference in stress, cracks appear on the surface, and the warping process is accelerated.

When drying timber or boards, they should be stacked in stacks on a foundation, or on any base with a height of at least half a meter. Boards are stacked inside upward, this reduces the chance of warping. When drying at the edges, of course, the process will go faster, but the level of warpage will be several times higher.

It is also recommended to place a heavy load on top of the stack to reduce warpage when drying wet. Also, the ends of the timber should be painted with oil paint or other water-repellent material, this will avoid cracking. The processing process must be started immediately after cutting.

If the material has a high level of humidity, the ends are pre-dried with a blowtorch, and only after that they are processed. The board itself is completely cleaned of bark for faster drying and prevention of insect damage. It should be noted that wood that is not cleared of bark quickly begins to rot and is exposed to fungal infection. Typically, after this type of drying, the moisture content of the material is 12-18%.

There are other ways to dry.

Evaporation. This method was used in the days of Russia. The essence of the process is as follows. The material was cut into pieces of the required size, and then placed in a cooled oven for several hours at a temperature of 65-75 degrees. Thus, this very evaporation took place. In the process, the material was removed natural juice and it took on a light chocolate color, thereby emphasizing the natural grain of the wood. Subsequently, such material was easier to process, and after completion of drying, it became less susceptible to cracking and warping.
The second way is waxing. It consists in processing the material with paraffin and further drying it in an oven at a temperature of 40 degrees for several hours, and then for several days at room temperature, later the material acquired the same properties as during evaporation.
Steaming in linseed oil. It provides for filling the container with linseed oil into which the workpiece is then lowered and steamed in it over low heat. After this procedure, the wood acquires a high level of water resistance and does not undergo cracking.
Linear drying - provides for a reduction in the linear dimensions of the material by removing bound water from the walls of the cells, the opposite options are also considered, swelling of wood by increasing the percentage of water.

Normalized humidity - the level of material moisture achieved under standard conditions (humidity 60-70%, temperature 18-22 degrees)

Volumetric shrinkage - provides for the complete removal of bound water from the material.

Volumetric swelling - provides for an increase in the level of bound water in the cell walls to the limit.

Relative humidity - is defined as the percentage of moisture to the wet weight of the material. Since wood is a hygroscopic material, it strives for an equilibrium moisture content relative to the surrounding microclimate. For example, at an air temperature of 20 degrees and a humidity of 100%, the moisture content of wood in equilibrium with these values will be equal to 30%.

It should be noted that a rapid change in the moisture content of the wood will lead to warping or, on the contrary, to strong swelling.

The more massive the element, the more attention should be paid to its drying, since uneven drying leads to the formation of cracks. When operating wooden structures, sharp changes in temperature and climatic conditions should be eliminated if possible.

The amount of shrinkage is different for each direction. Thus, in the radial it is 4-6%, and in the tangential 6-12 percent. It is due to this unevenness, during the drying process, a slight warpage occurs.

You should also know that with a sharp change in microclimatic conditions, internal stress occurs in the material, which leads to deformation and cracking of wood. The recommended temperature of the room in which the wooden elements are equipped is 20 degrees Celsius, with a humidity of 40-60%.

The standard moisture level for wood used for construction purposes, especially for the production of glued materials, is 8-15%. Consequently, the material requires mandatory drying. In turn, natural drying takes more time, in this way drying a board 5 centimeters thick under standard conditions (temperature 18-22 degrees and humidity 50-60%) takes 30-40 days. Artificial drying will take several times less time - 5-6 days, and at elevated temperatures, the drying time will be reduced to 3-4 hours.

The moisture content of the material after drying must necessarily comply with the operational standards for a particular type of work.

With prolonged drying, moisture from the material evaporates, which can lead to significant deformation. The drying process itself lasts until the material reaches a certain limit in terms of moisture, the limit depends on the microclimate in which drying takes place. The process of moisture absorption takes place in a similar way. Also, in some cases, shrinkage is carried out - that is, resizing by removing bound moisture, while if free moisture is removed, shrinkage does not occur.

Like drying, shrinkage affects the linear dimensions not in direct proportion, thus shrinkage in the tangential direction is up to 10%, and in the radial direction only up to 3.5%

With a continuous drying process, the moisture in the wood is reduced to the hygroscopic limit, that is, to 0%. When carrying out such a procedure, it is necessary to carefully monitor the uniform distribution of moisture, otherwise internal stress may form, which will cause deformation, changes in dimensions during mechanical processing of wood.

The convective drying process itself causes an uneven distribution of moisture, which contributes to the uneven drying of the material, and in the future, the occurrence of internal stress.

Freshly sawn wood has natural moisture. But this does not mean that the moisture content of all wood is approximately the same.

A pine that grew in a dry place and a tree that was cut down in a swamp will have a completely different moisture content. The humidity can be even higher, for example, when, when rafting down the river, the tree has absorbed as much moisture as it could. If you make boards from such wood without first drying it, then the boards, of course, will work, but over time they will surely dry out and warp. As a result, you will have to tear off the cladding boards nailed to the wall - to sort out the cladding. And even if you use a lining with a Euro profile for upholstery, all the same, gaps will appear in the lining, which will be the larger, the wider the width of the lining used. True, the cracks themselves will be smaller. (The wider the lining, the fewer the slots, but they themselves are larger. And vice versa - the narrower, the fewer the slots, but the greater their number.) And this is if sheathed with dry material over the wet. If both the base material is raw and the cladding is raw, then the consequences will be even worse and sadder. This is just one of the options for throwing money down the drain.

When shrinking, a tree loses from 5 to 7% of its size in width and thickness, and only up to 1% in length. This means that if this year you built a log house with a height of 3 meters, then in a year its height may well turn out to be 10, or even 20 centimeters less. But in length and width, it will remain almost the same as it was.

It is for this reason that most construction companies offer their clients to lay down a house from a bar in the first year and only finish it next year.

To prevent all this from happening, it is necessary to pre-dry the wood.

That is why the GOST determines the moisture content of the wood used. So much for interior cladding wood with a moisture content of up to 15% should be used, for outdoor - up to 20%. The moisture content of the floorboard should also not exceed 15% moisture.

There are several ways to determine the moisture content of wood. In a domestic environment, they use a special device, an electric moisture meter. The operation of the device is based on a change in the electrical conductivity of wood depending on its moisture content. The needles of the electric moisture meter with the electric wires connected to them are introduced into the tree and an electric current is passed through them, while the moisture content of the wood in the place where the needles are inserted is immediately noted on the scale of the device. Many experienced carvers measure wood moisture by eye. Knowing the types of wood, its density and other physical properties, it is possible to determine the moisture content of wood by mass, by the presence of cracks at the end or along the grain of the wood, by warping and other signs. By the color of the bark, its size and the color of the wood, you can recognize ripe or freshly cut wood and the degree of its moisture.

The ability to absorb moisture is influenced not only by the microclimate of the room, but also by the type of wood. The most hygroscopic species are beech, pear, kempas. They react most quickly to changes in humidity levels. In contrast, there are stable species, for example, oak, merbau, etc. These include the bamboo stem, which is highly resistant to adverse climatic conditions. It can even be laid in the bathroom. Different types of wood have different moisture levels. For example, birch, hornbeam, maple, ash have low moisture content (up to 15%) and, when dried, tend to form cracks. The moisture content of oak and walnut is moderate (up to 20%). They are relatively resistant to cracking and do not dry as quickly. Alder is one of the most drying-resistant species. Its moisture content is 30%.

Humidity is one of the main characteristics of wood. The moisture content of wood is understood as the ratio of the mass of water to the dry mass of wood, expressed as a percentage.

The absolute moisture content of the wood is the ratio of the mass of moisture in a given volume of wood to the mass of absolutely dry wood. According to GOST, the absolute humidity of the parquet should be 9% (+/- 3%).

Wood relative humidity is the ratio of the mass of moisture contained in wood to the mass of wood in a wet state.

According to the degree of moisture, wood is distinguished into the following types:

Wet wood. Its moisture content is over 100%. This is only possible if the wood has been in the water for a long time.
Freshly cut. Its humidity ranges from 50 to 100%.
Air dry. Such wood is usually stored in the air for a long time. Its humidity can be 15-20%, depending on climatic conditions and the time of year.
Room-dry wood. Its moisture content is usually 8-10%.
Absolutely dry. Its moisture content is 0%.

The properties of wood directly determine the properties of wood products. With excessive or insufficient moisture, wood usually absorbs or gives off moisture, respectively increasing or decreasing in volume. With high humidity indoors, wood can swell, and with a lack of moisture, it usually dries out, so all wood products, including floor coverings, require careful maintenance. To prevent deformation of the floor covering, the room must be kept at a constant temperature and humidity. This has a beneficial effect not only on the quality and durability of floor coverings and wooden furniture, but also on human health. With a sharp change in the temperature and humidity conditions in the room, internal stresses arise in the wood, which lead to cracks and deformations. The optimum temperature in a room with a parquet floor should be approximately 20 degrees Celsius, and the optimum air humidity should be 40-60%. Hydrometers are used to control the room temperature, and the relative humidity in the room is maintained with humidifiers.

The properties of wood also depend on seasonal changes in the indoor microclimate.

During the heating season, which lasts from October to April, the indoor temperature rises and the humidity decreases. The moisture level in the parquet falls below the permissible level of 25%. Such differences negatively affect the general condition of the wood. Parquet planks change in size, dry out, the seams between them can diverge and form small gaps. Cracks may form on the coating. You can eliminate such consequences by lowering the temperature and increasing the humidity in the room.

In summer, parquet flooring absorbs more moisture. Relative humidity can be up to 60%. During this period, the opposite process takes place: with an excess moisture content, the strips swell, find one on top of the other, their edges rise, and the coating is deformed. In this case, in order to restore the coating, it is necessary to regularly ventilate the room or use an air conditioner and turn on the heating in order to reduce the humidity.

The deformation of the rivets during the change of season can be very significant. When the relative air humidity changes to 30% in winter to 60% in summer at a temperature of 20 ° C, the equilibrium moisture content of wood can change by 5%.

You can control the humidity and temperature conditions in the room using a thermohydrometer. This will help to take timely measures and avoid deformation of the coating. The room temperature can be changed with an air conditioner. To increase the humidity, you can put open containers with water (aquariums, fountains, etc. are excellent for this purpose) or purchase special air humidifiers with built-in microclimate analyzers.

Humidifiers without significant energy consumption will create a favorable indoor climate by ensuring the proper level of humidity. Exists different kinds humidifiers (steam, ultrasonic), depending on the method of evaporation of water.

For parquet floors and wood furniture, ultrasonic or traditional humidifiers are ideal. They protect wood coatings and furniture from cracking and drying out of wood.

DRYING WOOD

There are many ways to dry wood. The simplest and most affordable - natural type of drying - atmospheric, airy. It is necessary to dry wood in the shade, under a canopy and in a draft. When dried in the sun, the outer surface of the wood heats up quickly, while the inner remains moist. Due to the difference in stress, cracks are formed, the wood quickly warps.

Boards, beams, etc. p / m are stacked on metal, wooden or other supports with a height of at least 50 cm. Boards are stacked with inner layers upward to reduce their warpage.

It is believed that the drying of boards placed on the edges is faster, since they are better ventilated and the moisture evaporates more intensively, but they also warp more, especially material with high humidity. It is recommended to compact a pile of p / m, harvested from freshly cut and live trees, with a heavy load from above to reduce warpage.

With natural drying, cracks always form at the ends, to prevent cracking and preserve the p / m, it is recommended to carefully paint the ends of the boards with oil paint or soak with hot linseed oil or bitumen to protect the pores of the wood. It is necessary to process the ends immediately after the cross cuts into the cut. If the tree is distinguished by high humidity, then the end is dried with a blowtorch flame, and only then painted over.

Trunks (ridges) must be debarked (cleaned of bark), only at the ends small belts-couplings with a width of 20-25 cm are left to prevent cracking. The bark is cleaned so that the tree dries out faster and is not affected by beetles. The trunk, left in the bark, in relative warmth with high humidity, quickly decays and is affected by fungal diseases. After atmospheric drying in warm weather, the moisture content of the wood is 12-18%.

There are several other ways to dry wood.

Evaporation method

Or steaming has been used in Russia since ancient times. The workpieces are sawn into pieces, taking into account the size of the future product, they are laid in ordinary cast iron, sawdust from the same workpiece is poured, poured with water and placed for several hours in a heated and cooling Russian stove “languishes” at t = 60-70C. In this case, "leaching" occurs - the evaporation of wood; natural juices come out of the workpiece, the wood is colored, acquiring a warm thick chocolate color, with a pronounced natural texture pattern. Such a workpiece is easier to process, and after the end of drying it cracks and shrinks less.
Waxing method

The workpieces are dipped into melted paraffin and placed in an oven at t = 40C for several hours. Then the wood dries out for a few more days and acquires the same properties as after parking: it does not crack, does not warp, the surface becomes tinted with a distinct texture pattern.
Steaming method in linseed oil

Cookware made of wood steamed in linseed oil is very water-resistant and does not crack even with daily use. This method is still acceptable today. A blank is placed in a container, poured with linseed oil and steamed over low heat.