Moisture content of wood and dry lumber. Natural moisture content of wood Natural moisture content 1 grade

Determination of moisture content and drying of wood

1. DETERMINATION OF MOISTURE OF WOOD.

There are several ways to determine the moisture content of wood. To determine the humidity, you can use a special device - an electric moisture meter. The operation of the device is based on the change in the electrical conductivity of wood depending on its moisture content. The needles of the electric moisture meter with electrical wires connected to them are inserted into the 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. Electrohygrometers EVA-2M, which determine humidity in the range of 7 - 60%, are widely used.
Many experienced carpenters determine the moisture content of the tree by eye. Knowing the types of wood, its density and others physical properties, you can determine the moisture content of wood by weight (weighing several identical blanks of the same species in turn), by the presence of cracks at the end or along the fibers of the wood, by warping and other signs.
With the weight method, from the board (control sample) at a distance of 300 - 500 mm from the end, a moisture section 10 - 12 mm thick is sawn off, thoroughly cleaned of burrs, sawdust and weighed, the result is recorded in a journal, and the section is placed in drying cabinet with temperatures up to 103 °C. After 6 hours of drying, the section is weighed and the mass is recorded in a log, then dried again and weighed every 2 hours after drying. If, after repeated weighings, the mass of the section does not change, this means that the section is dried to an absolutely dry state with a moisture content W 0 = 0% and a mass P.

The initial moisture content of the sample wood is determined by the formula:

W \u003d (P n - P s): P s * 100%,

where W - initial humidity, %;

P n and P s - the initial mass and mass in an absolutely dry state of the sample.

Also, checking the current humidity during the drying process can be carried out by weighing control samples with a length of at least 1000 mm, which are also sawn out of the boards to be dried at a distance of 300 - 500 mm from the end, cleaned of bark, burrs, sawdust, after which the ends are painted with paint . The sample is weighed to the nearest 5 g.
When processing lumber with a planer, its thin shavings, compressed by hand, are easily crushed - which means that the material is wet. If the chips break and crumble, this indicates that the material is dry enough. When transverse cutting with sharp chisels, they also pay attention to chips. If they crumble or the wood of the workpiece itself crumbles, this means that the material is too dry.
The complete saturation of wood with water is called the hygroscopic limit. This stage of humidity, depending on the type of wood, is 25-35%.
In practice, wood is distinguished: room-dry (with a moisture content of 8-12%), air-dry artificial drying (12-18%), atmospheric-dry wood (18-23%) and wet (humidity exceeds 23%).
The wood of a tree that has just been felled or has been in water for a long time is called wet, its moisture content is up to 200%. There are also operating humidity corresponding to the equilibrium moisture content of wood in specific conditions.

Wood moisture requirements in products

Table 1.

Name of products	GOST	Humidity, %

outer and vestibule door frames
boxes internal doors
door panels


sashes, vents valves, blinds
flashings, layouts
Profile details:
floor boards and bars, plinth, window sill
internal architraves
platbands and outer lining
handrails, exterior trim
handrails, exterior trim
Wooden floor beams:
solid wood
glued wood

The moisture content of freshly cut wood (having the moisture of a growing tree) depends on the species and the location of sampling along the trunk section. At conifers the moisture content of wood in the peripheral part of the trunk (sapwood) is greater than the moisture content of wood in the central part of the trunk (core). In hardwoods, the moisture content is approximately the same throughout the entire section of the trunk.
The moisture content of driftwood is generally higher than that of overland delivered wood, with the moisture content of driftwood being higher than that of freshly cut wood. So, the moisture content of the sapwood part of pine logs after the alloy increases to 150%, the core part of the logs - up to 50%.
As you know, wood has cellular structure. Moisture in wood can fill cell cavities, intercellular space and impregnate cell walls. Moisture that fills cell cavities and intercellular space is called free, and impregnating cell walls - related, or hygroscopic.
Freshly cut wood has both free and bound moisture. When drying wood, free moisture is first removed, and then bound.

Moisture content of freshly cut wood

Table 2

wood species	Humidity, %
wood species	Kernels or ripe wood	Sapwood	Medium


Larch

2. DRYING THE WOOD.

When making any kind of joinery, the wood must be dry. Dry wood has high strength, warps less, does not rot, easily glues, finishes better, is more durable, finished products do not crack. Any wood of the most various breeds very sensitive to changes in environmental humidity. 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. Therefore, for joinery, wood must be dried to the degree of moisture that is assumed in the future during their operation. Indoors, wood moisture up to 10% is sufficient, and under open sky- no more than 18%.
Drying is the process of removing moisture from wood by evaporation. Drying lumber can be natural or artificial.

NATURAL DRYING

Natural drying occurs under the influence of atmospheric circulating air, which evaporates moisture from the wood. Natural drying of lumber is combined with storage. It is necessary to dry the 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 damp. Due to the difference in stresses, cracks form, the tree quickly warps. Wet lumber is dried immediately after sawing. This prevents the appearance of wormholes and rot.
Stacked materials dry less well in spring than in summer. This process is more intense in June. The drying time of softwood lumber in natural conditions up to 18 - 22% humidity is given in the table.
The time required to dry to 18-22% moisture content of lumber stacked with spacers:

Table3

Month of laying lumber for drying	Number climate zone	Drying time in days with lumber thickness, mm
Month of laying lumber for drying	Number climate zone
March April May




June July



Aug. Sept

Note: For larch, the drying time is increased by 60%.

Climate zones

1st - Arkhangelsk, Murmansk, Vologda, Kuibyshev, Perm, Sverdlovsk, Sakhalin, Kamchatka, Magadan regions, the northern half of the Western and Eastern Siberia and Komi, the northern part of the Khabarovsk Territory and the eastern part of the Primorsky Territory.

2nd - Karelia, Leningrad, Novgorod, Pskov regions, the southern part of the Khabarovsk Territory and Western part Primorsky region.

3rd - Smolensk, Kaliningrad, Moscow, Tver, Orel, Tula, Ryazan, Ivanovo, Yaroslavl, Nizhny Novgorod, Bryansk, Chelyabinsk, Vladimir, Kaluga, Kostroma, Amur region, the southern part of Western and Eastern Siberia, the republics of Chuvashia, Mari El, Mordovia, Tatarstan, Bashkotorstan, Udmurtia.

4th - Kursk, Astrakhan, Samara, Saratov, Volgograd, Orenburg, Voronezh, Penza, Tambov, Rostov, Ulyanovsk regions, the North Caucasus.

Natural drying of lumber has been sharply reduced since mid-August. Spruce lumber dries faster than pine lumber. Thin materials dry faster than thick materials. Softwood lumber 16 mm thick after 4 days of drying lose half of the initial moisture, then the drying intensity drops sharply. Lumber with a thickness of more than 20 mm evaporates most of the moisture after 20-30 days of drying.
The stacking begins with the device of the base, with a height of at least 50 cm together with the lags. The top of the base must be horizontal. The base supports are placed in increments of 1.5 m to prevent deflection of the lumber. The shape of the stacks is a square or a rectangle.
Stacks of lumber are protected by a roof that protects the material from atmospheric precipitation, direct impact sun rays and dust.
Timber is laid on dry softwood pads 25x40 mm in size. The extreme gaskets are laid flush with the ends of the boards, and the rest at a distance between them of no more than 70 cm. To create better ventilation of the stack, all gaskets are laid in a strictly vertical row along a plumb line. Between stacked boards or bars, gaps (spaces) of the same width are left, forming vertical channels along the entire height of the stack. The width of the spacing, depending on climatic conditions and the section of the boards, is set for lumber up to 45 mm thick from 1/2 to 3/4 of the lumber width and for lumber with a thickness of over 45 mm from 1/5 to 1/3 of the lumber width. For uniform drying of lumber along the height of the stack, at a distance of 1 and 2 m from the bottom row of boards, air vents 150 mm high are arranged. The boards are laid with the inner layers up to reduce their warpage. To prevent cracking, it is recommended that the ends of the boards be carefully painted over. oil paint or soak several times with hot drying oil to protect the pores of the wood .. It is necessary to process the ends immediately after the cross cuts to size. If the tree is different high humidity, then the end is dried with a blowtorch, and only then painted over.

CHAMBER DRYING OF Lumber

Chamber drying is the main method in which sawn timber is dried in drying chambers having the necessary equipment and devices. Temperature, humidity and air circulation are controlled in the chambers.
Atmospheric drying serves to pre-dry lumber and is usually combined with a wood drying chamber.
Sawn timber can be stacked in stacks in piece or batch way. When forming a stack in a piecewise way, dry (with a moisture content of not more than 18%) calibrated coniferous and hardwood strips with a section of 25 x 40 mm and a length equal to the width of the stack are laid between the rows of boards. Stack height spacers must be laid perpendicular to the boards and strictly vertically one above the other.
The stack is formed from boards of the same breed and thickness. The number of spacers stacked along the length of the stack is given in the table:

Number of spacers stacked along the length of the stack

Table4

Note: In the numerator - the number of pads for stacks of softwood, in the denominator - of hardwood.

Ways of laying lumber in piles depend on the direction (circulation) of the drying agent. For drying chambers with countercurrent circulation, lumber is laid at intervals (spaces), and for chambers with transverse reverse and countercurrent rectilinear circulation - tightly.

Drying modes

Drying of lumber takes place under a certain temperature and humidity regime, which is understood as a regular alternation of the processes of temperature and humidity effects on wood in accordance with its moisture content and drying time.
During the drying process in the chamber, the air temperature gradually rises (in steps) and the relative humidity of the drying agent decreases. Drying modes are prescribed taking into account the type of wood, the thickness of the lumber, the final moisture content, the quality category of the materials being dried and the structures (type) of the chambers.

Depending on the requirements for lumber, the modes are divided into:

· soft M, with soft modes, defect-free drying is obtained with the preservation of the physical and mechanical properties of wood and color;

normal H, under normal conditions, defect-free drying is obtained with a possible slight color change in coniferous wood, but with the preservation of strength;

· forced F, with forced drying modes, wood is obtained with the preservation of bending, tensile and compression strength, but with a decrease in chipping and splitting strength by 15 - 20% and with possible darkening of the wood. For these modes, a three-stage change in the parameters of the drying agent is provided, and the transition from each stage of the mode to the next can be made only when the material reaches a certain moisture content provided for by the mode.

Modes of high-temperature drying process for batch chambers
provide for a two-stage change in the parameters of the drying agent, and the transition from the first stage to the second is carried out when the wood reaches a moisture content (transitional) of 20%. The high-temperature regime is determined depending on the breed and thickness of the lumber.
High-temperature regimes can be used for drying wood used for the manufacture of non-load-bearing elements building structures, in which a decrease in strength and darkening of wood is allowed.

wood drying process

Before the drying process is carried out according to the selected mode, the wood is heated with steam supplied through the dampening pipes, with the heaters turned on, the fans running and the sugar-exhaust channels closed. At the beginning of heating, the temperature of the drying agent should be 5°C higher than the first stage of the mode, but not more than 100°C. The degree of saturation of the environment should be within 0.98 - 1 for wood with an initial moisture content of more than 25%, and 0.9 - 0.92 for wood with a moisture content of less than 25%.
The duration of the initial heating of wood depends on the type of wood and for sawn softwood (pine, spruce, fir and cedar) at an outdoor temperature of more than 0 ° C is 1 - 1.5 hours at a temperature of less than 0 ° C - 1.5 - 2 hours for every centimeter of thickness. The duration of warming up of soft hardwood lumber (aspen, birch, linden, poplar and alder) is increased by 25%, and for hard hardwood lumber (maple, oak, ash, hornbeam, beech) it is increased by 50% compared to the duration of warming up of softwood breeds.
After warming up, the parameters of the drying agent are adjusted to the first stage of the mode and then they start drying the lumber, observing the established mode. The temperature and humidity of the air are regulated by valves on the steam pipelines and dampers of the sugar-exhaust channels.
During the drying process, residual internal stresses arise in the wood; to eliminate them, intermediate and final moisture heat treatment is carried out in an environment of high temperature and humidity. At the same time, lumber is processed, dried to operational humidity and subject to further mechanical processing.
Intermediate moisture heat treatment is carried out during the transition from the second to the third stage or from the first to the second when drying in high-temperature conditions. Softwood sawn timber with a thickness of 60 mm or more and hardwood (depending on the species) with a thickness of 30 mm or more are subjected to moisture heat treatment. In the process of heat and moisture treatment, the temperature of the medium should be 8°C higher than the temperature of the second stage, but not more than 100°C, with a degree of saturation of 0.95 - 0.97.
The final moisture heat treatment is carried out only when the wood reaches the required final average moisture content. During the final heat and moisture treatment, the temperature of the medium is maintained at 8°C above the last stage of the mode, but not more than 100°C. At the end of the final moisture heat treatment, the dried lumber is kept in the chambers for 2–3 hours at the parameters provided for by the last stage of the regime, after which the chambers are stopped.

wood is natural material, which is very susceptible to changes in humidity levels and temperature regime. The main property of wood is its hygroscopicity, that is, the ability to change the level of humidity according to environmental conditions. This process is called the "breathing" of the tree, while it can absorb air vapor (sorption) or emit them (desorption). Such actions are a reaction to changes in the microclimate of the building. If the state of the environment does not change, then the moisture content of the wood will tend to a constant value, which is called the equilibrium (or stable) moisture content.

How to determine the moisture content of lumber

In order to calculate the moisture content of timber, there are several methods:

Several varieties of the concept of "humidity"

Humidity is one of the main characteristics of wood. Moisture is the ratio of the amount of liquid to the dry mass of wood, expressed as a percentage. The liquid in the tree is present in a bound (hygroscopic) and free state. From these values, the total amount of moisture in the wood is compiled. bound moisture is located in the walls of woody cells, and the free one fills the cavities in the cells and between them. Free water is easier to remove than bound water and has less effect on the properties of the timber. The moisture content of dry lumber should be between 8 and 16%.

There are several concepts of "humidity":

initial moisture is the amount of moisture in the wood before it is sent to dry. Freshly sawn wood has a maximum moisture level, which for different varieties tree can be higher than 100%. For example, balsa wood has a freshly cut moisture content of about 600%. Most often, the types of wood that are more familiar to us have an initial or natural moisture level ranging from 30 to 70%
final moisture is the moisture level to be obtained by drying
transport humidity of lumber is at the level of 20-22%. In order to transport timber of natural moisture, they must first be dried. Atmospheric drying of lumber is carried out in accordance with GOST. The drying process significantly increases the protective properties of timber, and also stabilizes their physical and mechanical parameters.
operational humidity is the humidity coefficient at which wooden products are operated.

What should be the natural moisture content of lumber? GOST 3808.1-80 regulates this indicator at the level of 22%. Timber at natural moisture levels can be created from almost any type of wood. Within the territory of Russian Federation such raw materials are produced mainly from wood coniferous varieties such as spruce, pine, cedar or larch.

Planed board and timber from these varieties are different increased level strength and resistance to the action of the environment on them, for this reason they are excellent for interior and exterior work in the building. Such material is produced by simple sawing of logs.

Do not forget that lumber of natural moisture can rot and be affected by microorganisms, so they must be subjected to protective treatment.

The beam is produced in a variety of sections, which makes it possible to purchase just such an option that is best suited for solving the tasks. The main advantages of natural moisture timber include high quality and affordable cost. Compared with the cost of dry timber, the price of wet material is almost 30% lower.

Operating humidity values for lumber and wood products

Natural moisture, final moisture, free moisture - all these terms characterize the quality of wood and lumber produced from it.

Wood has a porous structure, in the capillaries of which moisture accumulates. The moisture content of wood and lumber is defined as the ratio of the weight of water to the weight of dry material.

like anyone natural material, the tree is sensitive to temperature fluctuations and changes in humidity. No wonder they say that wood breathes - it absorbs and releases air vapor with any changes in the microclimate.

There is such a thing as equilibrium humidity - its indicator is constant, any type of wood tends to it if climatic conditions do not change.

Breed and humidity

Each type of tree reacts differently to changes in humidity. Beech and pear are considered hygroscopic species, so any temperature fluctuations are reflected in their wood.

Oak and bamboo are characterized as stable species, so they are often used in the construction and decoration of swimming pools, bathrooms, and other rooms with high humidity.

Hornbeam, birch, maple have low humidity, its indicator rarely exceeds 15 percent. During the drying process, cracks often form on such wood.

Walnut is a tree with moderate humidity, its upper indicator is 20 percent. This type of wood has relative resistance to drying and cracking.

The most resistant to drying is alder, its moisture content is 30 percent.

Absolute and relative humidity

Consumers often confuse these two concepts, so let's dwell on them in detail.

Absolute humidity is the ratio of the mass of moisture to the mass of dry wood. At parquet board this indicator should be 9 percent, a deviation of 3 percent in any direction is considered acceptable.

Relative humidity is the ratio of the mass of moisture to the mass of wet wood. That is, until the lumber has gone through the drying process. These indicators are given in the previous section.

Degrees of humidity

There are five degrees of wood moisture content:

Wet wood with a moisture content of 100 percent or more. This is rare, because such indicators are possible when the tree long time was in the water.
Freshly cut wood. Moisture indicators at this stage are 50 percent or more, depending on the type of tree.
Air dry. This degree of humidity occurs when the wood has lain in the air for a long time. The humidity index is, on average, 20 percent.
Room dry wood. This degree is characterized by humidity no more than 10 percent.
Absolutely dry wood - 0 percent moisture.

What influences humidity?

Excess and deficiency of moisture adversely affect the quality of lumber. At excess moisture they swell, and if insufficient, they dry out and crack. In both cases, the deformation of the board, beam, logs occurs.

How to determine humidity?

The moisture content of lumber is determined by an electric moisture meter. This device measures the level of moisture based on changes in the electrical conductivity of the wood.

Experienced carpenters determine the percentage of moisture by eye. The presence of cracks, the location of these cracks, the weight of the board, the color of the wood and other features are taken into account.

For example, shavings taken from a log and easily crushed by hand indicate that the wood is wet. And brittle chips - that the wood is dry.

If pieces of wood crumble during processing, it means that it is too dry. If the saw slides like butter in it, the wood is very wet.

Wood is a very hygroscopic material that easily changes its moisture content. The moisture content of wood is the percentage of water (moisture) in it. The moisture content of wood does not depend on the type of wood. Moisture content of wood is a quantitative indicator of the moisture content in it.

Wood moisture

Moisture exchange takes place between wood and air all the time. Therefore, the moisture content of wood is a very unstable value, which changes with the humidity of the environment. If the moisture content of the wood is greater than the humidity of the surrounding air, the wood will dry out. Otherwise, hydration. And if the humidity and temperature of the environment (air) will have a constant value for a long time, then the humidity of the firewood will also stabilize and will correspond to the humidity of the surrounding air.

Moisture content of wood, at which the exchange of moisture between it and environment, called "equilibrium"

In nature, the equilibrium moisture content for wood is an extremely unstable state. Because, in nature it is impossible to find air with long enough constant parameters of temperature and humidity. However, the state of equilibrium humidity is easily achieved for wood that is in an artificial microclimate, for example, in a drying chamber or simply in any other room with a constant temperature and humidity.

Distinguish between absolute and relative humidity of wood

Absolute moisture content of wood

Absolute humidity is the ratio of the mass of moisture that a sample of wood contains to the mass of absolutely dry wood of the same sample. According to , the value of absolute humidity (W) is calculated after the study (drying) of the sample, according to the formula:

W \u003d (m - m 0) / m 0 x 100,

where, (m) and (m 0) - the mass of the sample, before and after drying.

The concept of the value "absolute humidity", according to GOST 17231-78, is interpreted simply as "humidity". Like everything “absolute”, the value of “absolute humidity” is divorced from real world and is an extremely indigestible form in heat engineering calculations. For example, with an absolute humidity of 25%, a kilogram of wood will contain 200 grams of water. Such a discrepancy between the numbers is confusing in the calculations.

More convenient and practical is the value of relative humidity

Relative humidity of wood

Relative (working) moisture content of wood is the ratio of the mass of moisture that a sample of wood contains to its total mass. According to GOST 17231-78, the value of relative humidity (W rel.) is calculated from the value of absolute humidity (W) of the sample, according to the formula:

W rel. = 100W / (100+W)

or easier,

W rel. = m water / m sample x 100

Relative humidity is a very simple and convenient form for accounting for evaporated water in wood-fired heat engineering calculations. The value of relative humidity directly indicates the quantitative content of water in wood. For example, one kilogram of wood at 20% moisture content will contain 200 grams of water and 800 grams of dry wood matter.

For comparison, let's collect a "live" example in a table. This is a table for the same our sample. Let us determine and compare the values of its absolute and relative humidity:

Absolute humidity = 25%, sample weight: before drying = 1kg (1000gr), after drying = 0.8kg (800g)	Relative humidity = 20%, sample weight = 1kg (1000g)
absolute humidity will be 25%,	- if one kilogram of wood contains 800 grams of dry wood substance and 200 grams of water, then its value relative humidity will be 20%,
Formula to determine W \u003d (m - m 0) / m 0 x 100 W = (1000 - 800) / 800 x 100 = 25%	Formula to determine W rel. = 100W / (100+W) W rel. = 100 x 25 / (100+25) = 20%
Conclusion Despite the fact that the value of absolute humidity is the primary source for determining the value of relative humidity, it is the value of relative humidity that has a greater practical use. Because, it (the value of relative humidity) more realistically represents the water content of the sample and is not confusing with mismatched numbers.

Degree of wood moisture

According to moisture, all wood is divided into three groups: raw (moisture more than 35%), semi-dry (moisture from 25 to 35%) and dry (moisture less than 25%). Initially, the moisture content of freshly cut trees is 50-60%. Then, during natural drying under a canopy in the air, the wood loses up to 20-30% of moisture within one and a half to two years and comes to a state of conditionally moisture. After that, the moisture content of the wood does not change significantly, and its value is ≈25%. Such wood is called air-dry. To reduce the moisture content of wood to the state of room-dry (7 ... 18%), it must be dried forcibly in drying chambers, or moved for a long time to an artificial microclimate with specified conditions (for example, transferred to a room or other room).

There are the following degrees of wood moisture:

floating(humidity 60% or more)
It may be a tree that has been in the water for a long time. For example, driftwood, or wood after sorting in a water basin, or just a well-soaked (damp) log.
Freshly cut(humidity 45...50%)
This is wood that has retained the moisture of a growing tree.
Air dry(humidity 20...30%)
This is wood that has been aged for a long time in the open air, with good ventilation.
Room dry(humidity 7...18%)
This is wood that has been in a living room or in another heated and ventilated room for a long time.
Absolutely dry(humidity 0%)
This is wood dried at a temperature of t=103±2°C to constant weight.

Calorific value of wet wood

The calorific value of wood is directly dependent on its moisture content. The humidity of firewood is one of the defining indicators of its quality. That dry firewood burns better than raw wood is known to many, if not all. And everyone knows that wet firewood can always be dried, and dry firewood, on the contrary, can be wetted. Accordingly, the quality of fuel will change - improve or deteriorate. But is it so important for modern heating equipment? For example, wood-fired pyrolysis boilers allow you to burn firewood with a moisture content of up to 50%, and even up to 70%!

The table shows the generalized indicators of the calorific value of wood for each degree of its humidity.

The table shows that the lower the moisture content of wood, the higher its calorific value . For example, air-dry wood has a working calorific value almost twice that of freshly cut wood, not to mention wet wood.

Wood with a moisture content of 70% or more practically does not burn.
Perfect option for wood heating- is to use firewood in a state of room-dry degree of humidity. Such firewood gives maximum amount heat. But, since drying firewood to such a state is associated with additional energy costs, the most the best option for heating, air-dry wood will be used. Bringing firewood to an air-dry state is relatively easy. To do this, it is enough to prepare them for future use and store them in a dry, ventilated area.
Finally, I would like to note that the moisture contained in firewood not only worsens their calorific value. The increased moisture content in the fuel adversely affects the combustion process itself. Excess water vapor serves as the basis for creating an aggressive environment, which causes premature wear of the heating unit and chimneys.
Manufacturers of modern heating equipment recommend using air-dry wood as fuel, with a moisture content of no more than 30-35%

What is drying? Drying lumber is one of the most important and integral operations in technological processes woodworking, and largely determines the quality and competitiveness finished products. wood containing a large number of water, is easily affected by fungi, resulting in decay. Dry wood is more durable. A decrease in moisture leads to a decrease in the mass of wood and an increase in its strength. Dry wood, unlike raw wood, is easily finished, processed and glued. It does not change its size and shape, which is important in the process of manufacturing and operating products.

As a result of drying, wood is transformed from a natural raw material into industrial material, which meets the most diverse requirements that apply to it in various production and living conditions. SIGNIFICANTLY EXPENSIVE RAW! They include the cost of drying, which is quite high, but all this pays off with the quality of the product, its demand in the market.

The moisture content of wood is the ratio of the mass of water to the mass of dry wood, expressed as a percentage, and is used to estimate the amount of water contained in the wood.

After cutting the tree and sawing it into boards, the wood tissue is more or less porous, depending on the type of wood, and more or less impregnated with lymph - water, just what is called in technical jargon "wood moisture".

A freshly felled tree has a maximum moisture content, which for various species can even exceed 100%. Usually they deal with a lower moisture content (30 - 70%), since after cutting it takes some time until sawing and placing it in the dryer, and it loses some water.

For the initial moisture content, the value that the wood has before being sent to the dryer is taken.

The final moisture is the moisture we want to achieve.

Humidity of 20-22% is called transport, and the humidity at which the product is operated is operational.

Operating humidity values for sawn timber and wood products:

Operating humidity table for lumber

So how is dry wood obtained? How is it dried?

Lumber drying and drying chambers.

Wood drying is a long and energy intensive process. Thermal energy for dryers is produced in boiler houses. The heat carrier here is steam or hot water. The parameters of the environment in drying chambers are usually measured with a psychometer. Management and regulation is carried out automatically. These are dryers of the classical type: convective with various systems supply and exhaust ventilation and types of coolant. Their advantages: low capital costs, simplicity of the process, convenience Maintenance, high quality drying.

Along with traditional convection chambers, vacuum, condensing, microwave and other dryers have gained some popularity, but their use does not always allow achieving the desired result.

AT recent times happened significant changes in the organization, technique and technology of drying. If earlier the main volume of drying fell on large enterprises, where large drying shops were built, now the bulk of the wood is processed at small enterprises, the need for which can be met by one or two chambers of small capacity. Many small firms are trying to create home-made simple drying devices that cannot provide high-quality drying of the material. However, The market is making increasingly stringent demands on the quality of wood products.

Poor drying quality due to unsatisfactory technical condition dryers and poor technological training of personnel, leads to a hidden marriage - an uneven distribution of the final moisture content, which can go unnoticed for a long time and affect when the product is already in operation.

Modern convective wood-drying chambers of both domestic and foreign production allow achieving high quality drying. They are equipped with a system automatic control process and are a complex set of equipment that requires qualified maintenance.

Now that we have clarified the questions as to what is dry lumber, You can safely start reviewing the market, draw up a construction or repair estimate and will no longer become a victim of unscrupulous lumber sellers.