6. The validity period was lifted according to Protocol No. 3-93 of the Mechanized State Council for Standardization, Metrology and Certification (IUS 5-6-93)

7. EDITION (September 2007) with Amendments No. 1, 2, 3, approved in December 1987, September 1988, February 1990 (IUS 3-88,1-89, 5-90)


An amendment was made, published in IUS No. 12, 2013

Amendment made by database manufacturer

This standard applies to lumber coniferous species and installs technical requirements to lumber intended for use in the national economy and export.

The standard does not apply to resonance and aircraft lumber.

(Changed edition, Amendment No. 3)

1. MAIN PARAMETERS AND DIMENSIONS

1.1. Lumber is divided into edged, unedged, boards, beams and beams.

Terms and definitions - according to GOST 18288.

1.2. Nominal dimensions of lumber and maximum deviations from nominal dimensions are in accordance with GOST 24454.

By agreement with the consumer, lumber with gradations in length, size and permissible deviations established in GOST 9302 and GOST 26002 are allowed for the domestic market.

(Changed edition, Amendment No. 2).

1.3. Symbol should consist of the name of the lumber (board, block, timber), a number indicating the grade, the name of the wood species (coniferous or individual species - pine, spruce, larch, cedar, fir), a digital designation of the cross section (for unedged lumber - thickness) and designations of this standard.

Examples of symbols:

Board - 2 - pine - 32x100 - GOST 8486-86

Board - 2 pieces - 32 - GOST 8486-86

2. TECHNICAL REQUIREMENTS

2.1. Lumber must meet the requirements of this standard and be made from the following wood species: pine, spruce, fir, larch and cedar.

(Amendment. IUS N 12-2013).

2.2. Based on the quality of wood and processing, boards and bars are divided into five grades (selected 1, 2, 3, 4th), and beams - into four grades (1, 2, 3, 4th) and must meet the requirements specified in the table .

Purpose of lumber different varieties given in the required appendix.

(Changed edition, Amendment No. 1, 3).

2.3. Sawn timber of selected, 1st, 2nd, 3rd grades is produced dry (with a moisture content of no more than 22%), raw (with a moisture content of more than 22%) and raw antiseptic. During the period from May 1 to October 1, the production of raw antiseptic and raw lumber is allowed by agreement with the consumer (customer).

The moisture content of grade 4 lumber is not standardized.

Antiseptic treatment - according to GOST 10950.

2.4. Assessment of the quality of lumber, with the exception of deck timber, should be made according to the face or edge that is worst for a given board, and timber and beams square section- on the worse side.

2.5. The surface roughness parameter of lumber should not exceed 1250 microns for selected, 1st, 2nd and 3rd grades, and for 4th grade - 1600 microns according to GOST 7016.

2.4, 2.5. (Changed edition, Amendment No. 3).

2.6. Non-parallelism of faces and edges in edged lumber, as well as faces in unedged lumber, is allowed within the limits of deviations from the nominal dimensions established by GOST 24454.

2.7. Additional requirements for lumber intended for special shipbuilding

Norms for limiting vices

Notes:

1. Knots less than half the maximum allowed size are not taken into account.

2. In lumber with a thickness of 40 mm or more (except for selected grades), oblong and stitched knots with a size along the minor axis of up to 6 mm and a depth of up to 3 mm are allowed without limiting the size along the major axis.

3. The stepson is allowed according to the norms of unfused knots. Not allowed in selected variety.

4. The size of a knot is determined by the distance between the tangents to the contour of the knot, drawn parallel to the longitudinal axis of the lumber. The size of an oblong and stitched knot on the faces of lumber and on all sides of the beams and beams is taken to be half the distance between the tangents drawn parallel to the longitudinal axis of the lumber.

5. In lumber longer than 3 m, it is allowed to have one knot of the size specified in the standards of the adjacent lower grade.

6. On a section of lumber with a length equal to its width, the largest sum of the sizes of knots lying on a straight line intersecting the knots in any direction should not exceed the maximum size of permitted knots.

Continuation

Notes:

1. Warp standards are established for lumber with a moisture content of no more than 22%. With higher humidity, these norms are halved.

2. Wood defects not mentioned in this standard are allowed.

2.7.1. Lumber for plating parts and connections of sea boats, boats of seagoing vessels, gliders, high-speed lake and river boats and sports vessels of the 1st class must meet the requirements of selected grade with the following additions:

the core part in the middle of the length of the lumber must be on the inner face: in the longitudinal sheathing - at least 50%, in the diagonal - at least 25% of the width of the face;

the dimensions of the fused, partially fused and unfused knots taken into account should not exceed 10 mm;

the number of fused knots taken into account should not exceed 1 piece. on any one-meter length of lumber, and partially fused, unfused - 1 piece, per 2 m length of lumber;

the knots taken into account are allowed no closer than 10 mm from the edges of the lumber;

pockets on the outer face of lumber are not allowed.

2.7.2. Lumber for decking of marine vessels must meet the requirements of select and first grades for external decks and first and second grades for internal decks with the following additions:

on the best faces of lumber with a width of up to 100 mm inclusive, intended for external decks, the sapwood part is allowed to be no more than 30 mm wide, and the surfaces of the faces must be sawn radially or close to it (without wedge cuts of annual layers);

the knots taken into account are allowed: fused - no closer than 10 mm, partially fused and unfused - no closer than 15 mm from the ribs of the outer face;

on the worst face and the lower halves of the edge area of ​​lumber, fused knots are allowed without limitation, and partially fused and unfused knots are allowed up to 1/3 of the width of the face;

cracks are allowed in lumber for external decks up to 1/4 of the thickness; for internal decks - 1/3 of the thickness of lumber. Cracks in deck lumber are not limited in length;

blunt wane is allowed in deck lumber with a size of no more than 5 mm;

cancer on the best faces and upper halves of the edge area, and pockets on the best face of lumber for external decks are not allowed;

core within the bottom half of deck lumber is permitted.

Note. The quality of deck lumber is assessed by the best face and the upper halves of the edge area.

(Changed edition, Amendment No. 1).

2.8. Lumber must be sorted by type of processing into edged and unedged, by size and grade (each grade separately).

At the request of the consumer, lumber can be sorted into groups of grades in accordance with the purposes established in the mandatory annex to the standard.

Lumber for export must be sorted in accordance with the work order of the foreign trade organization.

2.9. The grade, nature of processing, size and type of wood must be indicated in the consumer specification.

3. ACCEPTANCE RULES AND CONTROL METHODS

3.1. Acceptance rules and control methods - according to GOST 6564.

APPENDIX (required)

APPLICATION
Mandatory

Electronic document text
prepared by Kodeks JSC and verified against:
official publication
Lumber. Specifications:

Sat. GOST. - M.: Standartinform, 2007

Revision of the document taking into account
changes and additions prepared
JSC "Kodeks"

Wood is a natural material that is 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 vapor (sorption) or releases it (desorption), reacting to changes in the microclimate of the room. The absorption or release of vapors occurs due to the cell walls. In an unchanged state environment The moisture level of wood will tend to a constant value, which is called equilibrium (or stable) moisture content.

The ability to absorb moisture is affected not only by the microclimate of the room, but also by the type of wood. The most hygroscopic species include beech, pear, and kempas. They respond 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 very resistant to unfavorable climatic conditions. It can even be installed in the bathroom. Different types of wood have different moisture levels. For example, birch, hornbeam, maple, and ash have low humidity (up to 15%) and, when dry, tend to form cracks. The moisture content of oak and walnut is moderate (up to 20%). They are relatively resistant to cracking and dry less quickly. Alder is one of the most drying-resistant species. Its humidity is 30%.

Humidity is one of the main characteristics of wood. Under humidity wood is understood as a percentage ratio of the mass of water to the dry mass of wood.

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

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

There are two forms of water found in wood - bound and free. These 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 the interior of the cells and intercellular spaces. Free water is easier to remove than bound wood and has less effect on the properties of wood.

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

Wet wood. Its humidity is more than 100%. This is only possible if the wood for a long time was in the water.

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

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

Room-dried wood. Its humidity is usually 8-10%.

Absolutely dry. Its humidity is 0%.

During prolonged drying, water evaporates from wood, which can lead to significant deformation 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, absorption of moisture. A decrease in the linear volume of wood when bound moisture is removed from it is called shrinkage. Removing free moisture does not cause shrinkage.

Shrinkage is not the same in different directions. On average, complete linear shrinkage in the tangential direction is 6-10%, and in the radial direction - 3.5%. With complete drying (that is, one in which all bound moisture is removed), the moisture content of the wood is reduced to the limit of hygroscopicity, that is, to 0%. If moisture is unevenly distributed 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 during mechanical processing of wood.

The properties of wood directly determine the properties of wooden products. When there is excess or insufficient moisture, wood usually absorbs or releases moisture, increasing or decreasing in volume accordingly. At high humidity indoors, wood can swell, and if there is a lack of moisture, it usually dries out, so all wooden products, including floor coverings, require careful care. To prevent deformation of the floor covering in the room, it is necessary to maintain a constant temperature and humidity. This has a beneficial effect not only on 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 a room, internal stresses arise in the wood, which lead to cracks and deformations. The optimal temperature in a room with parquet flooring should be approximately 20 0 C, and optimal humidity air - 40-60%. Hydrometers are used to monitor room temperature, and room relative humidity is maintained using humidifiers.

DETERMINATION OF WOOD MOISTURE

There are several ways to determine wood moisture content. IN living conditions use a special device - an electric moisture meter. The operation of the device is based on changes in the electrical conductivity of wood depending on its humidity. The needles of an electric moisture meter with electrical wires connected to them are inserted into the wood and an electric current is passed through them, while the moisture content of the wood is immediately marked on the scale of the device in the place where the needles are inserted. Many experienced carvers determine the moisture content of wood 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 wood fibers, 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 content. When processing with a plane, its thin shavings, compressed by hand, are easily crushed, which means the material is wet. If the chips break and crumble, this indicates that the material is dry enough. When making transverse cuts with sharp chisels, also pay attention to the shavings. If they crumble or the wood of the workpiece itself crumbles, this means that the material is too dry. Very wet wood is easy to cut, and a wet mark from the chisel is noticeable at the cutting site. But in the end it is unlikely that it will be possible to obtain a high-quality thread, 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 content.

Dry wood has high strength, warps less, is not susceptible to rotting, is easy to glue, is better finished, and is more durable. Any wood is the most various breeds reacts very sensitively to changes in environmental humidity. This property is one of the disadvantages of timber. At high humidity, wood easily absorbs water and swells, but in heated rooms it dries out and warps. In the room, the wood humidity is sufficient up to 10%, and under open air- no more than 18%. There are many ways to dry wood. The simplest and most accessible - natural look drying - atmospheric, airy . Wood should be dried in the shade, under a canopy and in a draft. When dried in the sun, the outer surface of the wood quickly heats up, but the inner surface remains damp. Due to the difference in stress, cracks form and the wood quickly warps. Boards, timber, etc. are stacked on metal, wooden or other supports with a height of at least 50 cm. The boards are stacked with their inner layers facing up to reduce their warping. It is believed that boards placed on the edges dry faster, since they are better ventilated and moisture evaporates more intensely, but they also warp more, especially material with high humidity. It is recommended to compact a stack of p/m, prepared from freshly cut and live trees, with a heavy load on top to reduce warping. During natural drying, cracks always form at the ends; to prevent cracking and preserve the quality, it is recommended to carefully paint the ends of the boards oil paint or soak with hot drying oil or bitumen to protect the pores of the wood. The ends must be processed immediately after cross-cutting into the cut. If the tree is different high humidity, then the end is dried with a flame blowtorch, and only then paint over it. The trunks (ridges) must be debarked (cleared of bark), only small collars-muffs 20-25 cm wide are left at the ends to prevent cracking. The bark is cleaned so that the tree dries out faster and is not affected by beetles. A trunk left in the bark in relative heat with high humidity quickly rots and is affected by fungal diseases. After atmospheric drying in warm weather, the wood moisture content is 12-18%.

There are several other ways to dry wood.

Way evaporation Or steaming has been used in Rus' since ancient times. The blanks are sawn into pieces, taking into account the size of the future product, placed in ordinary cast iron, sawdust from the same blank is added, filled with water and placed in a heated and cooling Russian oven for several hours, “languishing” at t = 60-70 0 C. In this case, “leaching” - evaporation of wood; Natural juices come out of the workpiece, the wood is painted, acquiring a warm, thick chocolate color, with a pronounced natural texture pattern. Such a workpiece is easier to process, and after drying is less likely to crack and warp.

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

Way steaming in linseed oil. Wooden utensils steamed in linseed oil are very waterproof and do not crack even with everyday use. This method is still acceptable today. The workpiece is placed in the container and poured linseed oil and steamed over low heat.

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, wood is sensitive to temperature fluctuations and changes in humidity. It’s not for nothing that they say that wood breathes - it absorbs and releases air vapor during 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 don't change.

Rock 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 finishing of swimming pools, bathrooms, and other rooms with high humidity.

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

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

Alder is the most resistant to drying out; its moisture content is 30 percent.

Absolute and relative humidity

Consumers often confuse these two concepts, so let's look at them in detail.

Absolute humidity is the ratio of the mass of moisture to the mass of dry wood. U parquet board this figure 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.

Humidity levels

There are five degrees of wood moisture content:

1. Wet wood with a moisture content of 100 percent or more. This is rare because such indicators are possible when the tree has been in water for a long time.
2. Freshly cut wood. Humidity levels at this stage are 50 percent or more, depending on the type of tree.
3. Air dry. This degree of humidity occurs when the wood has been left in the air for a long time. The humidity level is on average 20 percent.
4. Room-dried wood. This degree is characterized by a humidity of no more than 10 percent.
5. Absolutely dry wood - 0 percent humidity.

What does humidity affect?

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

How to determine humidity?

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

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

For example, shavings removed from a log and easily crushed by hand indicate that the wood is damp. And brittle shavings mean that the wood is dry.

If pieces of wood are chipped during processing, it means it is too dry. If the saw glides through it like butter, the wood is very wet.

What kind of wood to use in construction?

One of the most frequently asked questions arising during construction frame house- what kind of board to build it from.It is clear that in any case the board will be edged, and not “slab”. But which one exactly? edged board take - natural humidity, dry, or maybe dry planed?Actually, it all comes down to the difference in price, the accuracy of the dimensions and the “geometry” of the board. In this article we explain the difference between different options boards for building a frame house, pros and cons.

Frame made from natural moisture boards - advantages and disadvantages.

Let's start with the cheapest material - natural moisture board (EB).Why is it the most popular? Because it is the cheapest and requires minimum investment. Roughly speaking, they sawed the log into boards and, please, the finished product. In fact, the only advantage of natural moisture boards is that they are cheap. What does natural humidity mean? This means that the moisture content in the board corresponds to the moisture content in the tree when it was still growing and was saturated with juices, moisture received through the root system.That is, this is the natural moisture content of a living, uncut tree. The raw tree was cut down, quickly transported to the sawmill, cut into boards andthis board, from which juice often flows, has been sold.The board's natural moisture content is about 40%. Humidity also depends on the season. Moreover, contrary to popular belief, in winter (the so-called “winter forest”) the moisture content of wood is highest, and lowest in August.You can see this for yourself by searching the Internet for information about wood moisture content by season.However, seasonal fluctuations in wood moisture content are not so great. Winter or summer – it’s still a “damp” forest. Is it possible to use a board with natural humidity in frame house? It is possible, but understanding well what you are doing and understanding the possibilitynew consequences.All consequences will be in one way or another connected with the natural process of drying of the damp board, the loss of that very natural, natural moisture.

Disadvantage number 1 - shrinkage. What will happen to the board during the drying process?Firstly, this is shrinkage - the moisture leaves, the wood “shrinks”, changing its size. Let's say there was a board of natural humidity 50x150mm.After drying, it will become, for example, 46x147.Shrinkage rarely occurs evenly, so some part of the board will be 46x147, some 48x143, some 43x149.Now imagine that this happens to all the boards and everyone has different shrinkage. Moreover, shrinkage can be different even for the same board.There is one at one end, another in the middle, etc. Let's add to this that the board could initially have been sawn with a wide range of sizes - which is very likely, since the equipment of most sawmills leaves much to be desired. As a result, you will have a fairly significant spread in the sizes of the boards -Accordingly, it is already difficult to talk about any kind of “evenness” of the frame.Something that can easily come out during finishing work.And you will have to deal with this using additional sheathing, leveling pads, etc. - which in turn is time and money. The RUSSIP Association uses in construction only wood that has been transport-moistened and sawn into professional equipment(using a disk, not a “ribbon”).

Disadvantage number 2 - changes in geometry. Second difficulty.During the drying process, internal stresses arise in the board, which often lead to a change in the geometric dimensions of the board. That is, there was a flat board rectangular shape, became curved, twisted, skewed - the most typical changes in geometry are “saber”, “propeller”, boat.

Typical types of geometry changes - board warping

It is very difficult to work with such a board - usually boards with lost geometry are cut into shorter ones. For example, from one six-meter “propeller” you can make two relatively even 3-meter boards, or three 2-meter boards. But this is ideal.In practice, not all crooked boards can be cut into small pieces and often they simply end up as waste. It is very difficult to predict changes in geometry, since it largely depends on the drying conditions, sawing technology and the original quality of the wood from which the board is made. But when drying in a stack using the “natural” method in air, there is a significant possibility thata significant part of the board will then go to waste due to “geometry”. When constructing SIP panels, we use paired boards to fasten them together; this allows us to avoid torsion.

Disadvantage number 3 - biological damage. Damp wood is an excellent breeding ground for microorganisms, mold and various fungi.At sawmills, the degree of “biocontamination” is very high. That is, very often, boards with natural moisture from the sawmill already arrive contaminated with fungal or mold spores. And the further development of these microorganisms depends on the combination of humidity and temperature. If a frame is built from a damp board and left to “dry”, the likelihood of mold and mildew developing is not so high.

Yes, you can treat wood with antiseptics. But the efficiency of processing wet wood is very low, the board is damp and does not “absorb” the antiseptic.And finally, antiseptic treatment costs money. Which again we add to the cost of the board.

Let's summarize on the natural humidity board. So you pay inexpensively for the material itself, but you may end up with a crooked, cracked, moldy frame.And it’s not a fact that you will see it.You will feel the cracks by how the house will lose heat, and a moldy frame will shorten the life of the house. When choosing such a board, you need to be aware of possible consequences and that the initial cheapness can be more than compensated for by correcting the shortcomings that have arisen.

We build from transport moisture boards.

That is, when before sale, the board is specially dried in a special drying chamber, to the so-called transport or equilibrium humidity of 8-22%.This humidity is called equilibrium mainly because it is in a more or less equilibrium state with atmospheric humidity.There is no point in drying more, up to 6-8% (furniture humidity), since it takes much longer and, accordingly, is more expensive, and there is a possibility that during construction, the board will return to equilibrium humidity, absorbing moisture from the atmosphere. Wood with this degree of drying is usually used only in carpentry and furniture production. By the way, one of the popular questions is why use a dry board if during the construction process it will still get wet, for example in the rain. Here you need to understand that the board has natural moisture - they have this moisturein bulk.A dry board, even in heavy rains, will not “get wet” through, it is not a sponge.Yes, the surface layer will be wet, but it will only be a few millimeters, which will dry out in 1-2 days.In other words, a dry board will never return to its natural moisture unless you specifically soak it in water for a long period of time.

Board in the drying chamber

Advantages of transport moisture boards:

2. Size and Geometry -What will happen to a board of natural humidity when drying has already happened to a board of transport humidity of 90%.What should have been crooked was crooked, the board has shrunk and will no longer change its dimensions significantly. In fact, you receive a “finished product” and there will be no cracks or twisting of elements in the frame.Since all defects are clear at the time of purchase, you can only select the right board without paying for unnecessary marriage.

Disadvantages of the board transport humidity:

1. The price is 20 percent higher than boards with natural humidity.

2. If you do not sort the board (discarding defects in geometry), then building from such a board is not very convenient.Sorted transport moisture board - best option for economical and high-quality construction.There is only one problem - such a board (precisely sorted) is not so easy to find.But also unsorted suitable option for construction than natural humidity. If only because its “behavior” is more predictable - there will be no further shrinkage and loss of geometry, or it will be insignificant. For our work, timber is supplied to us by trusted suppliers with a mandatory guarantee and quality.

Construction from dry planed boards.

Dry planed board is the material from which houses are built throughout the civilized world.The board has already dried to required humidity, sorted by grade,the geometrically crooked boards went somewhere else, and the rest were planed to the same size.The size variation of planed boards according to GOST is within 2mm. That is, from a planed board you will get a neat, dry, even frame that will stand for many years and will not mold, twist, etc. Disadvantages of dry planed boards: 1) high price (2-3 times more expensive than wood with transport humidity), 2) it is necessary to find a quality supplier who will give a guarantee for the timber, guaranteeing that the drying technology was followed, 3) there are few offers on the market in terms of “ price-quality”, the choice is not great.

Dry planed board - exact dimensions and geometry, optimal humidity

Conclusions.

1. Construction from boards of natural moisture is a lottery with unpredictable consequences, andeliminating the consequences often kills all the initial savings, more than surpassing the cheapness of the board.

2. A good option for building a house is to use transport moisture boards. But such a board must be purchased only from a trusted and professional supplier.

3. The best and at the same time expensive -use of dry planed boards.

Wood is a rather porous material containing a large number of capillaries filled with moisture. In practice, wood moisture content is defined as the ratio of the weight of water contained in the tree to the weight of absolutely dry wood. There is a concept of “free” and “bound” moisture. “Free” moisture is contained in the pores and capillaries of the tree. “Bound” moisture is that contained directly in the cells of the tree.

When drying, the tree shrinks - it decreases in size (volume). In this case, there is practically no decrease in size along the fibers (along the length of the board), but in the direction transverse to the grain, there is a significant change in size (along the thickness and width of the board). The magnitude of this change depends on the type of wood and the specific value of the change in wood moisture content. In life, the most unpleasant surprises are associated with changes in the width of the board.

For example, if you lay a floor with a board that has natural moisture, then the decrease in its width over time can be so significant that two adjacent boards will lose their grip on each other. In this case, to remove the cracks, you will have to tear off all the boards from the joists and lay them again, fitting them end to end.

“What humidity should the board have?” you ask. It’s simple - any wooden product, during its operation, tends to the so-called “equilibrium humidity”. “Equilibrium humidity” is determined by the temperature and humidity of the air in the environment where the board will be located. You can see the values ​​of this humidity in the table. For a residential premises it averages 8-10%, for a street it averages 12-14%. It logically follows from this that a damp board will dry out indoors, losing its width, on the other hand, a dry board will be moistened outdoors, expanding.

Natural moisture content, final wood moisture content

Natural humidity- this is the moisture inherent in wood in a growing or freshly cut (sawn) state, without additional drying. Natural humidity is not standardized and can range from 30% to 80%. The natural moisture content of wood varies depending on growing conditions and time of year. Thus, the natural humidity of freshly cut trees in a “winter” forest is traditionally less than the humidity of freshly cut trees in a “summer” forest.

Initial humidity- the same as natural humidity. A freshly felled tree has a maximum moisture content, which for different species can even exceed 100%. Balsa wood can have a freshly cut moisture content of up to 600%. In practice, we deal with smaller values ​​(30-70%), because After cutting, some time passes before the tree is sawed and placed in the dryer, and it, of course, loses a certain amount of water. We take the initial moisture content to be the moisture content of the wood that it has before being sent to the drying chamber.

Final humidity- this is the humidity we want to get after full cycle drying. In this case, the purpose of the product made from dried wood is taken into account.

First of all, wood drying is the process of removing moisture from wood by evaporation.

Drying wood is one of the most important operations in the wood processing process. The wood is dried after sawing, but before wood processing. The wood is dried in order to protect it from damage by wood-staining and wood-decaying fungi during its further storage and transportation. Drying prevents wood from changing shape and size during the manufacturing and use of products made from it, improves the quality of wood finishing and gluing. The humidity to which wood is dried depends on the scope of its further use. The whole point is to bring the moisture content of the board to the same value that a product made from this board would reach over time during operation under these conditions. This humidity value is called “equilibrium humidity”; it depends on the humidity and temperature of the surrounding air. For example, the board from which parquet and other products used indoors will be made should have a humidity of 6-8%, since this is the humidity that will be equilibrium. For products that will be used in contact with the atmosphere (for example: wooden windows, external cladding of the house) the equilibrium humidity will be 11-12%.

You ask: “What will happen otherwise?” We answer: Otherwise, what happens all the time in Russia will happen, namely, the consumer will face problems. Imagine that you bought lining in order to sheathe the walls inside your country house or dachas. If you buy clapboard made from damp boards from a careless manufacturer and cover the walls of your house with it, it will begin to dry out slowly naturally in an already installed state. Let us turn to the table of equilibrium humidity and experience. If you heat a room in winter to 25 degrees Celsius, then with a typical indoor air humidity of 35% for winter, the equilibrium humidity value for a board in such a room will be 6.6%. At bases and markets, lining can very often have a humidity of 14% or higher (we have encountered 30%). Next, imagine that your lining begins to dry out, losing water from its pores. When drying, a process called “shrinkage” occurs and is expressed in a decrease in size. wooden product. The amount of shrinkage depends on the type of wood, the direction of the fibers in the product, etc. The main shrinkage occurs across the fibers (according to the thickness and width of your lining). When your lining dries in the installed state to equilibrium moisture, you, in the worst case, risk not only seeing that the lining has come apart in places, but getting gaps between the boards, almost the width of a finger.

The industry uses various technologies for drying wood, differing both in the equipment used and in the characteristics of heat transfer to the dried material.
The classification of types and methods of drying is usually based on heat transfer methods, according to which four wood drying technologies can be distinguished:

• convective drying technology;
• conductive drying technology;
• radiation drying technology;
• electric drying technology;

Each type of drying can also have several varieties depending on the type of drying agent and the characteristics of the equipment used for drying wood. There are also combined technologies for drying wood, in which they simultaneously use different kinds heat transfer (for example, convective-dielectric) or other characteristics are combined various technologies drying wood.

Independent drying technologies

Chamber drying

Chamber drying. This is the main industrial technology for drying wood, carried out in wood drying chambers various designs, where lumber is loaded in stacks. Drying occurs in a gaseous environment (air, flue gases, superheated steam), which transfers heat to the wood by convection. To heat and circulate the drying agent, drying chambers are equipped with heating and circulation devices.

With chamber wood drying technology, the drying time for lumber is relatively short (from tens of hours to several days), the wood dries to any given final moisture content at the required quality, and the drying process can be reliably regulated.

Atmospheric drying

The second most important and widespread method at sawmills is the method of industrial drying of wood, carried out in stacks placed in a special open area (warehouses), washed atmospheric air without heating. The advantage of atmospheric wood drying technology is comparatively low cost. In addition, this method is the most gentle. Disadvantages: seasonality (drying practically stops in winter); long duration; high final humidity. Atmospheric wood drying technology is used mainly for drying lumber at sawmills to transport moisture and at some woodworking enterprises for drying and leveling the initial moisture content of lumber before drying in wood drying chambers.

Drying in liquids

Drying in liquids is carried out in baths filled with a hydrophobic liquid (petrolatum, oil) heated to 105-120 °C. Intensive heat transfer from liquid to wood allows the drying time to be reduced by 3-4 times compared to chamber drying, all other conditions being equal. This method is used in wood preservation technology to reduce its moisture content before impregnation. Attempts to dry lumber in petrolatum at woodworking enterprises have not yielded positive results due to the fact that lumber after such drying does not meet the requirements for wood for furniture and joinery and construction products.

Conductive drying technology

Conductive (contact) wood drying technology is carried out by transferring heat to the material through thermal conductivity upon contact with heated surfaces. It is used in small volumes for drying, thin wood materials- veneer, plywood.

Radiation drying

Radiation drying of wood occurs when heat is transferred to the material by radiation from heated bodies. The effectiveness of radiation drying is determined by the flux density of infrared rays and their permeability in solid wet bodies. The intensity of the radiant energy flow weakens as it goes deeper into the material. Wood is a low-permeability material for infrared radiation (penetration depth 3-7 mm), therefore this method is not used for drying lumber. It can be used for drying thin-sheet materials (veneer, plywood), in addition, this method is widely used in the technology of finishing wood products for drying paint and varnish coatings. Electric stoves, electric heating elements, gas (flameless) burners, and incandescent lighting lamps with a power of 500 W and above are used as emitters.

Rotary drying

Rotational drying of wood is based on the use of the centrifugal effect, due to which free moisture is removed from the wood when it is rotated in centrifuges. Mechanical removal of free moisture is achieved at a centripetal acceleration value of at least 100-500g (g is the acceleration of gravity). Such accelerations have not yet been achieved in practice due to the difficulty of accurately balancing a centrifuge with a stack; only experimental development of corresponding devices is underway. In known industrial rotary dryers, the centripetal acceleration does not exceed 12 g. Under these conditions, mechanical dehydration occurs to a small extent. However, intensification of the drying process in the humidity range above the hygroscopic limit is observed.

When installing a carousel in a drying chamber, the technology for drying lumber is the same as in conventional batch chambers. The duration of drying at the first stage (from the initial moisture content to the hygroscopic limit) is reduced several times depending on the thickness, species and initial moisture content of the wood compared to conventional convective drying under the same conditions. Although rotary dryers are economical and provide high quality drying, the rotary method has not yet found industrial use for drying lumber.

Vacuum drying

Vacuum drying at reduced pressure in special sealed drying chambers. Due to the complexity of the equipment and the impossibility of obtaining low final moisture content of wood vacuum drying has no independent meaning. It is used in combination with other drying methods and as an auxiliary operation in preparing wood for impregnation.

Dielectric drying

Dielectric drying is the drying of wood in an electromagnetic field of high frequency currents, in which the wood is heated due to dielectric losses. Due to the uniform heating of wood throughout its entire volume, the emergence of a positive temperature gradient and excess pressure inside it, the duration of dielectric drying is tens of times less than convective drying. Due to the complexity of the equipment, high power consumption and insufficient High Quality drying Dielectric drying itself is not widely used.

Combined wood drying technologies

It is more effective to use combined wood drying technologies, for example convective-dielectric and vacuum-dielectric. For mass drying, the use of these methods is uneconomical, but in some cases, especially when drying expensive, critical lumber and blanks made from difficult-to-dry wood species, these methods can be used.

Convective-dielectric drying

With a combined convective-dielectric technology for drying wood, high-frequency energy from a special high-frequency generator is also supplied to a stack loaded into a chamber equipped with thermal and fan devices through electrodes located near the stack.
The heat consumption for drying in the drying chamber is mainly compensated by the thermal energy of steam supplied to the heaters, and high-frequency energy is supplied to create a positive temperature difference across the cross section of the material. This difference, depending on the characteristics of the material and the rigidity of the given mode, is 2-5°C. The quality of convective-dielectric drying of lumber is high, since drying is carried out with a small difference in humidity across the thickness of the material.

Vacuum dielectric drying

This is another way of drying wood using high-frequency energy. This technology uses the advantages of both vacuum and dielectric drying. By heating wood in a high-frequency field at reduced pressure, boiling of water in wood is achieved at low wood temperatures, which helps preserve its quality. The movement of moisture in wood during vacuum-dielectric drying of wood is ensured by all the main driving forces moisture transfer: moisture content gradient, temperature, overpressure, which reduces drying time.

During vacuum-dielectric drying, a stack of lumber is placed in an autoclave or a sealed chamber, where a vacuum pump creates a reduced pressure of the environment (1-20 kPa). The lower the environmental pressure, the lower the evaporation temperature of moisture and wood during drying. Heat consumption for drying is provided by the supply of high-frequency energy to the wood. When using this wood drying technology, operational difficulties also arise - the complexity of the equipment, especially the setup and operation of high-frequency generators, high consumption electricity for drying. Therefore, when deciding on the use of vacuum-dielectric chambers, it is necessary to first develop a feasibility study based on the conditions of a particular enterprise.

Induction or electromagnetic drying of wood

The method is based on the transfer of heat to the material from ferromagnetic elements (steel mesh) stacked between rows of boards. The stack, together with these elements, is in an alternating electromagnetic field of industrial frequency (50 Hz), formed by a solenoid mounted inside drying chamber. Steel elements (mesh) are heated in an electromagnetic field, transferring heat to wood and air. In this case, a combined transfer of heat to the material occurs: by conduction from the contact of heated meshes with wood and convection from circulating air, which is also heated by the meshes.