Drying chamber for lumber air. Do-it-yourself drying chamber for lumber

Any woodworking enterprise cannot do without such a procedure as wood drying. And so that no defects appear in the process, a special drying chamber for lumber should be used. Such a dryer will also be useful for those who are engaged in the production of wood products at home, in such cases it can be done by yourself.

Importance of drying for wood

Wood for the manufacture of various products must first be dried so that it is suitable for subsequent use. So, if your furniture is made on the basis of too wet wood, then it will quickly dry out and become unusable. And if the tree is too dry, then, for example, the door will quickly swell and will not close.

Also, drying a tree is useful for the following reasons:

the material is protected from fungal attack;
change in size and shape is prevented;
improve the mechanical and physical properties of the material.

Drying is a lengthy process, the wood is heated with hot air or superheated steam. After drying, the tree can be stored and transported longer, it will not be deformed.

Drying chamber for lumber

Kiln drying is a key way to dry wood. With the help of dryers, deciduous and coniferous species are dried to different types quality. The most common and economical drying technique is as follows. Free and bound moisture is removed from the wood by supplying heat to the damp wood using hot air. Further, the removal of excess evaporated moisture occurs with the help of humidified and partially cooled air.

The drying chamber is a complete plant equipped with all necessary equipment for work. By their design, such chambers are prefabricated metal or assembled from building materials. The latter are made directly in the workshops or as free-standing buildings based on industrial materials.

The chamber can be entirely made on the basis of monolithic reinforced concrete, the walls can be made of solid red bricks, and the ceiling can be made of reinforced concrete.

If several chambers are used in production, they can be combined into one block, which has a corridor with heat supply wiring and a system automatic control. Depending on the volume of loaded wood, the air circulation can be horizontal-transverse or vertical-transverse.

Lumber can be loaded into the chamber on trolleys along the rail track or as packages using a forklift. Heat is transferred to wood in the following ways:

through the air;
through the products of combustion;
using superheated steam;
radiant warmth;
solid body;
through current;
through an electromagnetic field.

The equipment for this device is basic and additional. The main includes the following:

fan system;
heating system;
humidification and supply and exhaust ventilation.

Additional equipment includes:

blocks (door, psychrometric and insulated);
fan drive electric motor;
stacked carts.

The drying control process can be automated, which helps to maintain the temperature and humidity inside the chamber at a certain level. The temperature is regulated by supplying the coolant to the heaters or by turning the electric heater on or off.

Humidity can be adjusted using a remote moisture meter, which allows you to check the condition of the material remotely at several points at once. If there are no external sources of heat supply, then autonomous heating means powered by electricity, coal, gas, lumber or diesel fuel can be used.

Structure classification

In convection-type chambers, energy enters the wood through the air cycle, and heat transfer occurs through convection. Such structures are tunnel or chamber.

Tunnel dryers have a greater depth, they push stacks of stacks from one end (wetter) to dry. They are obligatory filled from one end, and emptied from the other. Stacks are pushed one at a time every 4-12 hours. These dryers are used for large sawmills and help carry out transport drying.

Chamber dryers are shorter; during the drying process, the same parameters are maintained throughout the chamber. If the blowing depth is from 2 meters, then in order to equalize the drying conditions, the method of reversing the ventilation direction is used. The chamber is filled and emptied from one side if there is only one door. Lumber can be dried any to different indicators of humidity. It is these designs that are most often used in our country.

The condensation type of dryer is different in that the moisture that has arisen in the air begins to condense on special coolers, and then the liquid is removed. The efficiency here is high, but the cycle is long, since devices with a high temperature do not work and large heat losses are observed. These types of equipment are more suitable for processing small volumes of materials or drying wood of dense species - ash, beech or oak. But condensation chambers also have a number of advantages:

no need for a boiler room;
the cost of the camera and the cost of operation are low.

Drying chambers also differ in the way of circulation and the nature of the drying agent, the principle of operation and the type of fence.

For example, circulation can be natural or forced. The designs of the first type are outdated and inefficient, it is almost impossible to control the modes, and the uniformity of the drying of the material leaves much to be desired. At modern requirements it is better not to use such dryers.

By the nature of the drying agent, the chambers are:

air;
gas;
high temperature.

Drying modes

Depending on the quality requirements, lumber drying in a special apparatus is carried out in different modes, which differ from each other in temperature. If it is a mini chamber, then in the process the temperature slowly rises and the relative humidity of the agent decreases.

One or another mode is selected taking into account the following factors:

There are modes of high-temperature and low-temperature process. In low-temperature applications, moist air is used as an agent, the initial temperature is less than 100 degrees. There are three categories of these types of modes:

soft - drying is carried out without defects, the mechanical and physical properties of the wood are preserved, including its color and strength;
normal - drying is also carried out without defects, strength is retained almost completely, color may vary slightly;
forced - the strength for static bending, tension and compression is maintained, but the strength for chipping and splitting with darkening may decrease.

In high temperature conditions there is a two-stage change in the agent's indicators, it is possible to switch to the second stage from the first only when the wood reaches a transitional moisture content of 20 percent.

Such modes are assigned depending on the species and thickness of the wood, and are assigned for drying materials used in the production of load-bearing structures of buildings and those products where dark wood with reduced strength can be used.

Before starting work on a particular mode, the lumber must be heated with steam supplied through humidifying pipes with fans running, closed exhaust ducts and heating devices.

Be sure to calculate the chamber for lumber. The temperature of the drying agent at the beginning of heating should be 5 degrees higher than the first stage of the mode, but not higher than 100 degrees. The saturation level of the environment for a material with an initial moisture content of 25% is 0.98−1, and if the humidity is below this indicator, then 0.9−0.92, respectively.

The duration of the initial period depends on the type of tree. For conifers, it is up to 1.5 hours per centimeter of thickness. For soft hardwoods it will be 25 percent more, and for hard hardwoods it will be half as much compared to softwoods.

After preheating, it is necessary to bring the indicators of the drying agent to the first stage of the operating mode. Then drying is switched on directly in compliance with the selected mode. Humidity and temperature can be controlled using valves on the steam lines or dampers on the supply and exhaust ducts.

During the operation of an infrared dryer, residual stresses appear in the materials, which can be removed by intermediate and final moisture and heat treatment in an environment of high humidity and temperature. It is necessary to process those lumber that are dried to operational performance and then need to be machined.

Intermediate moisture heat treatment must be carried out during the transition from the second stage to the third, or from 1 to 2 when using a high temperature. Coniferous species 60 mm in thickness or hardwood with a thickness of 30 mm or more are subjected to such processing. The temperature of the medium should be 8 degrees higher compared to the second stage, but not more than 100 degrees, provided the saturation is 0.95-0.97.

When the final average moisture content of the material is reached, the final moisture heat treatment can be performed. It is carried out at a temperature of 8 degrees above the previous stage, but not higher than 100 degrees. Further, the tree must be kept in the chamber for another 2-3 hours at the parameters of the last stage of the mode and only then stop the operation.

Drying chamber manufacturing

If you are engaged in the manufacture of wood products at home, then you will need to dry the material yourself. You can also make your own dryer., but you must follow all the rules of work. For manufacturing you will need:

camera;
heating device;
fan;
insulation.

One wall and ceiling of the chamber should be made of concrete, and the remaining walls will be made of wood, they will need to be insulated. There will be several layers:

Styrofoam;
boards wrapped in foil.

Now you need to install a heating element, it can be in the form of batteries. Water can be supplied to them from the stove in a heated form at a temperature of 60 to 95 degrees. Best to provide continuous process circulation of water by means of water pumps in the heating element. You will also need to install a fan in the chamber, with the help of which warm air will be distributed throughout the room.

It is imperative to provide a method for loading wood into the chamber. For example, it can be a rail cart. To control the temperature and humidity in the work area, you need to install wet and dry thermometers. And also inside the dryer You need to put shelves to expand the workspace.

During processing, a sharp change in temperature should not be allowed, otherwise the wood may crack or warp.

Work on the construction of the chamber must be carried out in compliance with fire regulations, so be sure to install fire extinguishers.

And instead of a heating element you can use an electric stove with two burners. The walls of the chamber can be insulated with wood shavings, and instead of foil, you can take penofol, which can reflect heat well from the surface of the walls. Drying in such a chamber is carried out within 1-2 weeks.

Thus, there is a large number of various modifications of drying chambers for wood. One or another option should be chosen depending on the material itself and the expected results. And if we are talking about the manufacture of various wooden products at home, then the camera is easy to do with your own hands.

One of the mandatory stages in the production of wood materials is harvested wood, produced in the open air and in special chambers, which protects the lumber from fungus, prevents deformation and changes in parameters.

Drying kilns for lumber operate in a certain mode, which is selected depending on the initial humidity, wood species, board thickness, planned use, taking into account the design features of the dryer.

The unit can also dry firewood, which is used in heating solid fuel boilers, fireplaces.

Drying modes

During the drying process, the oven can operate in low temperature, normal or high temperature mode.

Low temperature and normal mode

Processing wood in a low-temperature way is carried out at 45 °. This is the softest method, it preserves all the original properties of the tree to the smallest nuances and is considered a high quality technology. At the end of the process, the moisture content of the wood is about 20%, that is, such drying can be considered preliminary.

As for the normal mode, it proceeds at temperatures up to 90 °. After drying, the material does not change shape and size, slightly reduced color brightness, strength. This is the most common technology used for various types of wood.

High temperature mode

In this mode, drying occurs due to the action of superheated steam (temperature over 100 °) or hot air. The high-temperature drying process reduces the strength of the wood, gives it a darker shade, so the material is used to create secondary building and furniture components. At the same time, drying with superheated steam will be more gentle than with the use of air.

Types of drying chambers

The dryer for boards can be with natural and forced air exchange. At the same time, the first option is inefficient and unpredictable. Therefore, in order to avoid unjustified risks, chambers with natural drying are almost never used at present.

According to the principle of operation, the following types of dryers can be distinguished:

convective;
condensation;
vacuum;
aerodynamic;
microwave cameras.

The difference between the chambers in wood dryers is what equipment is used to heat the air, circulate it and lower the pressure.

convective

The drying chamber of the convective (convection) type is a rectangular insulated container with powerful ventilation in the ceiling edge, due to which the air is distributed through the heaters and wood. As a result of heating, the moisture of the lumber turns into steam, then leaves the chamber through special valves. This process of heat energy exchange is called convection.

Convective dryers are produced in two types: tunnel and chamber. In the first design, the boards enter the chamber from one side and are unloaded from the opposite side. Such models are mobile and designed for operation in large sawmill companies.

Chamber dryers provide for the launch and unloading of lumber through one door.

Convection chambers have the following features:

in one cycle, 20 cubic meters of wood can be processed, provided that the volume is completely filled;
all types of lumber can be dried, stacked in stacks with gaps;
after drying, it is possible to perform steaming, impregnation of products;
when connecting a solid fuel boiler for heating, the process will be more economical;
the design has big sizes, therefore it is intended for stationary work(no exit).

The advantages include the high quality of drying, but if the chamber is not filled to 100%, then there will be a high probability of obtaining poorly dried wood (with overheating or high humidity) due to the uneven passage of hot air flows through the products. A possible disadvantage is the high power consumption.

Condensation

Drying chambers of condensation type are similar in design to convection ones, but differ in the principle of operation. Wet steam, which occurs during the drying of wood, turns into water (condenses), which is collected in special containers. This technology is achieved due to the tightness of the drying chamber. The produced water is used for space heating.

Despite the cost-effectiveness of condensing units, the drying process takes a long time (about 2-3 weeks), while in convective units it takes from 1 to 2 weeks. Another disadvantage is the high cost of the unit.

vacuum

The dryer works on the principle of vacuum removal of excess moisture, the drying process consists of three stages: heating (preparatory), drying (with humidification), cooling. For a complete drying period, about 250 identical cycles are performed. The presence of a vacuum softens the impact high temperatures and prevents the wood from cracking.

Differences of the vacuum drying chamber are:

fast drying of wood;
saving energy costs as a result of increasing the temperature of the functional heating plates embedded between the lumber.

Vacuum chambers are expensive to purchase and maintain, so it is unprofitable to dry pine or spruce in them.

Aerodynamic

The installation is a metal box with high-quality thermal insulation. The moisture formed as a result of drying flows into a special collection. Heated air circulates in a closed space with the help of a special aerodynamic screw, which gives its energy to the drying process.

The chamber must be fully loaded with lumber, only then the quality of work will not suffer. Maintenance of an aerodynamic wood dryer does not require specific knowledge, the installation is fully automated.

The disadvantages are the relatively long drying process (about 20 days), high energy consumption, lack of temperature control.

microwave cameras

Microwave drying technology has been developed relatively recently. The unit is a closed metal container with a door in the end wall and operates on the principle of a microwave oven. Microwave radiation heats the wood, from which water molecules are squeezed out under pressure.

The camera is convenient in that it can be placed anywhere in the room. Thanks to the powerful effect electromagnetic waves drying wood takes no more than 6 days.

The advantage of the microwave installation is also in the high quality of drying with the right mode.

The dryer is expensive due to the high consumption of electricity and the need from time to time to change the main spare part - the magnetron (a device for emitting electromagnetic waves).

DIY manufacturing

Drying wood in a private way requires a special chamber, which you can make yourself. If you have to build a dryer for wood with your own hands, then on a plot of land you need to allocate an area of \u200b\u200babout 10 m 2 for installation. You will need concrete for the foundation, material and thermal insulation for the walls, mounting foam, a ventilation system, a boiler and auxiliary equipment.

Stages of construction

The construction of a mini-dryer consists of successive stages:

preparation of the foundation for installation;
walling;
thermal insulation;
installation of the roof and doors;
installation on the ceiling of radiators and fans;
installation of the boiler in compliance with safety regulations, laying pipes.

Such work will be justified with regular use of the finished object. The drying chamber will need to be fully loaded and the drying technology strictly observed.

Foundation construction

The site is marked out taking into account the length of the lumber and the total width of the stacked stacks, plus a loading allowance of about 30 cm.

After marking the site, it must be concreted in such a way that the floor level of the chamber is about 10 cm higher than the ground level. A concrete platform is made with sides protruding half a meter. To prevent water from accumulating in the drying chamber, the foundation must be made with a certain slope. You should also provide for the filling of rails for the transport of carts with products.

Walling

As a material, you can use brick, sandwich panels, railway container. The most common material is wood. Three walls are made from it, and it is desirable to make the fourth from concrete.

The height of the wood drying chamber is the sum of the height of the stacks, the loading allowance of 30 cm and the height of the fans and radiators. When building a small chamber, the height is calculated taking into account the filling of the entire volume.

The heating of the installation provides for the presence of a source of thermal energy, therefore, when installing the walls, it is required to build an extension for the boiler and its auxiliary equipment.

Roof insulation and installation

Dry shavings or sawdust, which are applied to the walls in the form of a mixture with cement and an antiseptic, can serve as an effective and economical heat insulator material. To keep warm, the floor is covered with shavings.

The roof of a makeshift room is mounted with a slope so that the snow does not linger on it. Then the doors are installed by hanging on an I-beam or hinged.

Equipment installation

Fans should be positioned vertically across the width of the ceiling to distribute heat evenly. The next row will consist of radiators. To keep the heat in the drying chamber, you first need to seal the slots with mounting foam.

Heat is supplied to the radiators from a boiler that can run on electricity, liquid or solid fuel. Usually, a wood-burning boiler is chosen to heat the drying chamber. Pipes are brought to the boiler, then an anti-explosion valve is installed that regulates the operation of the equipment.

Mandatory and proper drying in a home-made or purchased drying chamber is a reliable guarantee of the quality of lumber.

In the domestic market, there is a very wide choice of chambers for forced drying of wood, operating on various technologies, such as Russian production, and imported.

This puts the customer in front of a difficult choice problem.

In this article, I will talk about what I had to face in three decades of work related to various drying chambers. Perhaps the information given here will help someone not to make a mistake in this issue.

Don't Underestimate the Importance of Drying

My experience of working in several companies involved in the drying of various woods, allows me to speak about the importance of this technological stage in the finished lumber production chain.

This is explained by the fact that it is a well-organized drying process that allows minimizing the number of defects, improving the quality of the final product and, accordingly, ensuring its sale at higher prices, and also contributes to an increase in the number of regular customers.

The approach to financing forced drying technology according to the residual principle is categorically wrong. The result of such a decision may be low profitability (up to bankruptcy) of a timber processing enterprise equipped with the most modern machine park.

And if this is superimposed on the manager’s erroneous ideas about how to dry the forest “correctly” and the priority of “saving” funds on the purchase of equipment, the result will be disastrous. The camera will. But you won’t wait for high-quality dry lumber at the exit.

I had to work under various bosses (owners). And it must be recognized that the personality of the leader plays a colossal role in the correct solution of this issue.

One seeks by any means to "grab the ruble" here and now, completely without thinking about tomorrow. Another purposefully invests in the development and equipment of production, being content with minimal profits and, ultimately, gets a highly profitable company that occupies a stable position in the market for providing such services, demonstrating positive development dynamics even in the off-season and with a decline in consumer demand.

Buy or make your own

In order to get a quality product, you should use a high-quality tool, one of which is a drying chamber.

However, a number of novice wood processors tend, in order to save money, to make a drying chamber on their own.

I assume that this is possible. But only if there are specialists who are able to correctly and fully carry out preliminary calculations (and such, at woodworking enterprises, can be found infrequently). And when it is required to periodically dry small volumes of wood.

In all other cases, such decisions lead to unjustified financial losses, a significant amount of marriage and the loss of regular customers.

Industrial production of significant volumes requires the use of cameras made by professionals. Self-activity in this matter is tantamount to suicide.

To confirm this thesis, I want to cite a case that I witnessed in 2002-2003 (I don’t remember exactly). Then I just got a job in a company that is still called "sharashka" before and today. It positioned itself as a diversified enterprise producing garden furniture, gazebos, fences and lumber.

Hearing that the material of chamber drying can be sold more expensive, the owner appointed three "intelligent men" as developers and manufacturers of the convection-type chamber.

The "masterpiece" of design thought was sculpted in less than a month. And with huge amount flaws and gross violations that were visible even to the naked eye (I already had some work experience then). I tried to bring this to the employer's attention. But the opinion of the "smerd" was not taken into account, but to insist, creating problems for himself out of the blue. I didn't.

Examples. There was no possibility of reverse rotation on the fans, many metal structural elements were “forgotten” to be grounded, the heaters were of different power. And a young Tajik was appointed responsible for the operation, who did not have the slightest idea about this. He also dealt with the issues of loading and unloading.

The creation worked for a little more than a week and ingloriously ended its short production biography with a powerful fire, in which not only the property of our owner burned down, but also the raw materials supplied by him, which he had to dry.

But that didn't teach him anything. This citizen continued to build his business on the principle: “There are only two points of view on the question, mine and the wrong one.” After working for a while, I thought it best to change jobs.

At the end of the section, a few wishes for those who decide to make a drying chamber on their own.

Before proceeding with the manufacture of a structure in a material, it is required to obtain at least minimal theoretical knowledge. Fortunately, today the Internet provides a huge opportunity for this. There are many very good teaching aids on this topic. Among them, I would like to mention the books of Krechetov and Tsarev (co-authored with Peich). It will not be superfluous to familiarize yourself with the provisions of the current regulations. For example, SP114.13330.2016, which sets fire safety standards for the storage of timber.

When creating a project for your own dryer, it is imperative to calculate:

optimal material for its walls;
achieve tight closing of the gate;
determine the optimal method of loading materials for drying;
choose the type and power of fans, calculate their installation locations and the required number;
resolve the issue with the coolant and the implementation of the humidification system;
be sure to install a psychrometer and humidity sensors in the chamber.

Ideally, there should be automation. As a last resort. Semi-automatic control of the drying process. But that's enough difficult questions requiring deep specialized knowledge.

Practice has shown that one of the most common mistakes committed by manufacturers of homemade drying devices, is the ingress of water, when it is dripping, onto the humidity sensor. as a result, automation receives distorted commands. The result is marriage.

The second, in terms of frequency of occurrence, is the fact of "forgetting" that the fans are powered by electric drives, which constantly have to be in conditions of high temperature and humidity. therefore, taking any suitable in power will not work here. Only special models are required.

Pros and cons of different types of drying kilns for wood

Small companies mainly use Russian-made cameras. In addition, Czech and Italian are quite often used, less often Finnish (mainly in the north-west of the European part of Russia). This preference is explained by the following factors:

the optimal ratio of performance, performance, durability and cost;
opportunities for the rapid acquisition of spare parts and the availability of after-sales service(the vast majority of dryer manufacturers have a wide network of representative offices in the CIS countries, including Russia);
minimum delivery times, relatively low customs and delivery costs, the possibility of installation supervision and staff training.

Regardless of the principle implemented in the design, which is the basis of the drying technology (convective, condensing, vacuum, etc.), any design solves the same problem - it evaporates the moisture contained in it from the wood. That is why, when considering the quality of forced drying, first of all, they pay attention to such indicators as:

drying time to a specified moisture content;
the occurrence of internal stresses during the drying process and the possibility of its relief;
difference in humidity between outside and inner layers lumber after the drying process is completed.

I would like to say a few words about the specific drying technologies that I had to deal with.

Convection kilns for wood

Cameras of this type are most common in Russia, and in all regions. Therefore, the experience with such chambers forms the basis of my experience with the maintenance of products for the forced reduction of the percentage of moisture in lumber.

The technology underlying this drying principle is very simple. Moisture. Contained in the tree, it is removed from it by blowing it with a jet of hot air. The latter is heated by electric heaters (in the vast majority of models). Flow necessary strength and directivity is formed by blocks of powerful fans, the number of which can reach ten or more units.

An important advantage of chambers of this type is the structurally provided possibility of steaming wood. This allows you to minimize internal stresses (ideally, completely zero them).

For all cameras with which I had to work, the parameters internal environment, created inside, were measured by the installed psychrometer, and the built-in automation controlled the drying process.

The process is divided into several stages, at each of which the moisture content of the material and the magnitude of internal stresses are different.

The upper layers of lumber, when blown with hot air, dry faster than the inner ones. And the layers near the core part do not have time to give up moisture with the same intensity. The result of this imbalance is internal stresses that can induce cracks.

To compensate for this negative process, almost all convective chambers have an additional stage of moisture treatment, when moisture is sprayed onto the surface of the material undergoing drying. Further, the drying process by supplying hot air continues again.

If the alternation of these stages takes place in a timely manner, after processing is completed, a material is obtained that has approximately the same moisture content throughout the volume.

However, this is in theory. But in practice, a lot depends on who made the camera, its model and the notorious "human factor".

If the product is purchased from a reliable manufacturer, the installation is carried out in the presence of a company representative, and the operation is carried out strictly according to the manufacturer's recommendations, then in such devices it is possible to obtain finished lumber with negligible internal stresses, which eliminates its cracking, increases the yield finished products and as a result, the profit of the company.

To the advantages of the considered types of cameras, I would attributed:

availability of models with a significant one-time capacity (about 1000 m 3), which is essential for large companies;
the possibility of fine-tuning the control process, providing for changing the values of essential parameters at any stage of drying;
process control in automatic or semi-automatic modes;
minimization of production costs.

Among the shortcomings I can not but mention:

sufficiently long drying time;
the need to train trained personnel to service the device.

Condensation kilns for wood

The main difference between this technology and the one discussed above is the following technical features. Moisture from the wood undergoing drying, released into the air of the chamber, condenses on the special coolers available in the design, is collected in special drainage channels and removed from the chamber, and the air dried in this way continues the closed wood blowing cycle.

Coolers are charged with freon. Operating temperatures in these dryers are ≤ 45 °C. This significantly increases the drying time of one bookmark, even in comparison with convection chambers. Depending on the selected model of the device, it may or may not have a humidification option.

If available, wetting is carried out after the completion of the first stage of drying, which minimizes the internal stress that has arisen in the upper layers of lumber.

In models where humidification is not provided, this issue is solved by the presence of inverters on the fan motors, which allow you to change the speed of the supplied air flow (This is done in order to ensure a smoother and more uniform release of moisture from the wood). In other cases, it will not be possible to exclude cracking of products undergoing drying.

Cameras of this type are the best choice if it is necessary to dry mainly thick lumber, or products made from dense wood (for example, from ash or oak).

If it is planned to dry wood for subsequent use in carpentry, such a solution can hardly be called the best.

The advantages of the method include:

low power consumption;
almost 100% elimination of cases of warping of lumber.

There are quite a few shortcomings. Main:

very long drying times, which are several times higher than those of convection-type chambers;
the appearance of additional costs due to the use of freon;
the quality of finished materials cannot be called ideal;
wood treated in this way has low resistance to pathogenic microflora (low temperatures in the chamber do not allow blanks to be sterilized).

Aerodynamic kilns for wood

Twice I had to work on similar cameras. They have the simplest design compared to other types of products. This is an ordinary metal box with fans installed in it.

Air heating is carried out due to the heat generated by the operating fans (the mechanical energy of the rotating rotor is transformed into thermal energy).

When the required humidity is reached in the chamber, the fans stop. This is the easiest DIY solution. However, this drying technology has many disadvantages. Therefore, I would not recommend purchasing such cameras.

The main disadvantage is that fact. That blowing hot air dries the wood unevenly. While the upper layers are already almost dry, the inner ones still have a fairly high degree of moisture. The result of this imbalance is a significant internal stress in the finished products.

The use of such lumber in carpentry is categorically not recommended. When you try to "dry out" such material, it is guaranteed to burst (crack).

Of course, one can refer to the fact that the problems of the occurrence of internal stresses are inherent in any drying technology. But in the considered version, they are the most significant and expressed as clearly as possible.

There are advantages to be found in any method.

The advantages of aerodynamic drying can be considered:

ease of installation and low cost of operation (it is enough to connect the unit to a 3-phase 380V network);
drying is carried out with considerable intensity;
the cost of such drying chambers can be considered low (compared to other types of products), if costs are not considered. Which entails subsequent operation.

The cons are:

unsatisfactory drying quality;
long drying time;
very significant cost of electricity.

Infrared kilns for wood

The main difference of the drying technology under consideration is the absence of the requirement to create a closed volume room (the actual chamber). To remove moisture, special designs called infrared cassettes are used. When laying a stack for drying, they are placed between the layers of stacked wood. The infrared radiation created by them evaporates moisture from the tree to its entire depth.

In summer, drying in this way can be carried out under sheds in the open air, having previously protected the stack from direct rain.

I had to work with such devices privately, in my own workshop. I really like to test new technologies of wood drying and processing available to me.

The results obtained, in general, can be called satisfactory. But the technology didn't look good. Yes, for industrial use this decision absolutely unacceptable, due to the length and complexity preparatory phase bookmarks and subsequent sampling of finished lumber.

Benefits include:

autonomy and compactness of technology;
ease of bringing into working condition;
high economy.

As disadvantages, attention should be paid on the:

significant difficulties in organizing control over drying parameters;
the possibility of using on bookmarks with limited volumes, not exceeding 5 m 3.

microwave ovens for wood

The wood in them is dried due to the implementation of a process similar to what is happening in a household microwave oven. The difference is only in the size of the products.

High-frequency radiation does not damage the wood, contributing to the delicate and uniform removal of moisture over almost the entire depth of the workpiece. The terms for reaching a given degree of moisture content of the finished lumber are quite short.

For the sake of curiosity, I worked with friends on a similar installation (new knowledge is never superfluous). The results are good enough. However, the complexity of the device, the rather high cost, the high cost of components (the price of the same magnetrons starts from 300,000 rubles, and the service life, unfortunately, is not long) and, most importantly, small volumes of a single load make such a solution unprofitable for anyone. large-scale production, nor for private traders.

The latter is especially relevant if you consider how much the maintenance of such cameras costs, especially if you have to replace a broken magnetron generator.

But, as they say, "the taste and color ...". The choice is yours.

The advantages of such installations are:

high drying speed and excellent quality of the output material;
economical use of electricity.

Of the shortcomings, I would, first of all, name:

an insignificant one-time loading capacity not exceeding -7-10 cubic meters;
very difficult control over the course of the process;
high cost of magnetron generators.

I fell in love with these cameras. The structures are completely sealed (in the vast majority of models). During the drying process, a pressure below atmospheric pressure is created inside them. Therefore, drying can be carried out at relatively low temperatures (up to 65 °C).

This is explained by the fact that a decrease in pressure leads to boiling water at lower temperatures. Therefore, the desired drying effect can be achieved with "little blood" without using high temperatures.

This automatically reduces the heat loss in this type of chamber and allows for very little color change in the material being dried.

The design features of such products depend on who they are made by. For example, in Italian WDE Maspell dryers quite often used by Russian timber processors and some domestic cameras are water heaters. Other domestic manufacturers prefer electric heating elements.

Home distinctive feature Drying using vacuum technology is a curious situation when the temperature to which the board is heated, passing drying, exceeds the boiling point of water vapor (other name, saturation temperature). As a result, all processes taking place inside the board are significantly accelerated, and the latter dries faster.

This technology makes it possible not to use the aggressive effect of high temperatures on the material during the drying process.

But, while praising this or that technology, I urge future users not to forget that the minimum number of defective blanks after drying is determined not only by the chosen technology and type of drying chamber, but also by correctly selected technological modes that are laid down by manufacturers in each model and properly functioning automation.

In addition to this, an important factor is the choice of a conscientious manufacturer with the necessary technological developments and drying experience. The technology is complex and, unfortunately, I have not once encountered when the owner chose the manufacturer after superficially sorting out the issue. As a result, I received equipment with which more torment than work. The claimed characteristics did not correspond to reality. I had to either modify the camera myself and spend time and money on it, or dare to work on this equipment.

Despite the fact that in such chambers the impact on the wood is more gentle, there is a possibility of cracking of the material being dried. It is always there and in any drying mode. Since a tree is a living material, in which different kinds stresses. These processes are influenced by the type of wood and the place of its harvesting, the technology of cutting logs and the age of the tree.

Well, in terms of drying, I can say that we dry a “fifty” pine board in a vacuum-type chamber (at the last workplace) from 50 to 8 percent in just 2 days. I have not seen such a speed in any technology, perhaps only in microwave.

Advantages of vacuum chambers:

excellent quality of dried materials;
record fast speed drying;
high performance;
suitable for both small enterprises (models from 1-8 cubic meters), medium-sized enterprises (models from 8-18 cubic meters), large enterprises(models from 18-36 cu.)

Disadvantages (unfortunately, she also has them):

manual loading and unloading;

The importance of reliable automation in drying chambers

I want to talk about this separately. Drying wood is a very complex process. Therefore, quality modern cameras manufacturers automate as much as possible. But no machine and automation can completely replace a person.

Therefore, an operator is needed in any case. And better, a competent operator. Since a mistake made at any stage of drying can turn into an irreparable marriage at the exit, or lead to an emergency.

As a rule, marriage manifests itself at the final stage, when it is no longer possible to fix anything.

Therefore, it is required to approach the choice of the purchased camera, as well as the training of personnel, thoroughly.

Automation allows you to get rid of a significant number of problems, so I consider this component in the design of the drying chamber to be very important. Especially if drying is planned to be carried out on an industrial scale.

When choosing a camera, be sure to pay attention to the following:

is it possible to organize automatic control, providing for the task different modes drying and the ability to download new templates (custom programs that you create for your production);
whether it is possible for the operator to intervene in the operation of automation, which allows you to quickly adjust the drying process at any time;
it is highly desirable to have a digital display on the automation, on which the main characteristics of the process (humidity, temperature, etc.) are displayed in real time;
whether manufacturers provide for the possibility of recording the course of the chamber drying process with fixing all the parameters and then displaying it in the form of a graph (this allows for subsequent analysis, if necessary);
built-in automation should be "smart", that is, exclude the possibility of making "wrong" decisions. For example, do not give a humidification command when the ventilation shutters are open;
whether it is possible to control the camera remotely;
the presence of light and sound indication and malfunctions.

When the automation is set and works correctly, an environment is formed and maintained in the chamber that is optimal for a particular drying stage.

At the right time, taking into account the readings of control devices, humidity, temperature, and the level of air conditioning in the internal volume of the chamber should change. All this will positively affect the quality of the finished product.

When choosing automation, the main thing is not to overdo it. Do not make "butter oil". Automation installation required. But only under certain conditions. On cameras, for example, of a convective type, with a volume of less than 20 cubic meters of a single load, its installation is economically unprofitable, since it will pay off for a very long time. On such cameras, the best solution is to use semi-automatic devices.

14 Points to Consider When Buying a Dryer

It is possible to distinguish a good camera from a bad one, in each specific situation, not only by its type, but also by who it was made by. Without naming any brands here, I will focus on the main issues of choosing this product using the example of a vacuum chamber. There are not many of them:

heating elements must be structurally calculated and have an optimal design for heat transfer to wood;
also the heating plates must be made of steel stainless grades or aluminum, which has a higher resistance to corrosion;
registers connecting elements must be coated with anti-corrosion compounds;
the gates in the chamber and its enclosing surfaces must ensure maximum tightness of the internal volume. Contact with the air of the external environment and atmospheric moisture must be guaranteed excluded;
the existing heat and vapor barrier must be of high quality and installed correctly;
removal of steam from the chamber should be carried out as efficiently as possible;
work from a solid fuel or gas boiler.

Otherwise, an increase in heat loss and, automatically, electricity consumption is inevitable. And, most importantly, the drying technology is violated. And the most intelligent automation will not be able to cope with violations caused by the presence of such defects. As a result, an increase in the volume of marriage and a decrease in profits.

The installed automated control system should make it possible to reduce the operator's participation in the process to a minimum, and the existing SDUK should make the drying process easier and more predictable;
The whole drying process must be displayed on a PC in the form of graphs for analysis in case of a malfunction;
There should be online monitoring 24/7 by the manufacturer.

Ideal, in my opinion, the camera must necessarily meet the following fundamental criteria:

ensure the highest possible quality of finished products (dried lumber);
require insignificant expenses for its construction, equipment and commissioning;
have a low cost of drying one cubic meter of wood (in terms of);
the entire drying process should not adversely affect the environment;

Important: long service life (the case and components must be designed and made from high-quality materials), in the case of vacuum chambers this is especially important, more than once I have seen how the chamber rusted after 2 years under the influence of aggressive media inside and the case began to “siphon”, each I had to weld it for a month and make metal patches. After 5 years, such a building looked like a colander. In the Rostov region, there was a case when, after 3 years, in the process of creating a vacuum, the chamber “collapsed like a tin can” under the influence of corrosion. The camera amplification ribs failed. The manufacturer simply incorrectly made the calculations.;

The most correct decision for a person who decides to purchase a drying chamber is preliminary stage thorough preparation, during which:

needs to be determined annual volume drying (today and in the future);
study the issue of the presence and quantity of wood waste in production, and the possibility of their use in order to heat the coolant for the chamber (installation of an autonomous solid fuel boiler);
analyze the possibility of atmospheric (open) drying;
to develop a layout of chambers, places of storage of raw materials and finished products.

Remember. Far from everything depends on the equipment, even the most high-quality and expensive. Not less than half of the success is the merit of the operators and repairmen serving the camera (their qualifications directly affect the result). For example, how they organize the storage of raw materials and finished lumber.

Lumber rejects due to incorrect drying conditions

Some leaders. By virtue of lack of awareness. Drying processes are considered quite simple and do not deserve special attention. Put the board down, turned it on certain time blowing and heating, took out the finished product.

In this case, I want to cite the wise thought of my grandson: “The taste and color ... all felt-tip pens are different.” If it were that simple, then the problem with choosing a camera would not exist in principle.

In fact, for "incomprehensible" reasons, there is almost no marriage in one cell, and in the second, its percentage goes off scale beyond the permissible limit. To understand why this happens, sometimes it takes a considerable amount of time (and the marriage goes on). And anything can affect the quality, from design defects to improper loading.

The main task that you have to solve when choosing a camera is not only and not so much saving money on the purchase and choosing the optimal cost / performance ratio, and even the possible prospects for its operation. The main thing is to understand whether the drying room is able to bring the moisture in the lumber to the required levels in short term throughout the depth of the wood evenly, whether it is able to stabilize the geometry (in size and shape).

Any wooden product made from poorly dried material will fail very quickly. And hidden defects become noticeable only after a certain time. About what they were. You will recognize by warping and cracking, peeling paint and other "charms".

It is considered on average. That a cubic meter of freshly harvested wood contains about 300 liters of liquid, which the chamber should evaporate. But in such a way as not to damage the material. Most of this volume is in the capillaries, a smaller part, in the cells of the wood tissue, which these capillaries form. Removing moisture at the cellular level is the most difficult task. It is the violation of technology on this stage leads to cracking of lumber.

Hard rocks (oak, ash, beech) are the most difficult to dry. Their top layer dries much faster and forms a crust that does not allow moisture to pass through from the inner layers. As a result, the probability of marriage is high.

That is why it is extremely important to comply with the standard technological modes of drying (for example, timely leveling of humidity). This process is very complicated. Even the same board dries unevenly in length and volume with a spread of up to 2%.

If the stack is not properly stacked, buckling can be added to the cracks.

What are the most common problems faced by modern drying chambers?

During my rather long practice in various industries, I had to deal with various nuances of operation.

Problems can arise when working with any camera. Even produced famous brand and quite expensive. Most often, these are leaks in various pipes due to corrosion, downtime caused by a malfunction and lack of necessary spare parts (for imported cameras this problem highly relevant) or the expectation of a specialist. Quite often there are problems with fans.

But the main problem, in my opinion, is the uniform heating of the stacked stack to the full depth and the effective extraction of moisture:

Wood is heated in different chambers of different manufacturers with different agents (water, air, radiation waves, etc.), heating structures various types, as a result, lumber dries differently.
The intake of moisture evaporated in the wood should occur as efficiently as possible at the right time.

These 2 problems had to be solved more often than others, since it is inherent in almost all types of cameras (to varying degrees).

The reasons can be listed long enough. But most of the time it's:

under-dried material at the end of the stack and over-dried at its beginning, or at the top of the stack and in the middle.
the drying agent between the rows of the stack can practically not penetrate or differ significantly in temperature, which reduces the process to the level of natural drying in terms of time and quality.

To solve the problem, in the first case, the installation of fans with reverse rotation often helps. You can "play" with their placement and total number to determine the optimal solution. But this cannot be called a panacea. The desired result is not always achieved.

In vacuum chambers, everything is much more complicated; the design of the heating elements and the moisture removal system will have to be redone. Only a professionally performed calculation can help and competent design(camera modification). This is in my experience a lot of time and money wasted.

The main thing to understand is

Completely solve ALL problems of drying uniformity and quality finished products so far NOBODY succeeded!

And, in the foreseeable future, a solution to this problem is not expected. Therefore, the main goal, which every manufacturer strives to achieve, is to minimize the percentage of rejects and to bring the parameters as close as possible to ideal ones.

In the case of convection chambers, make sure that the fans inside are not remote. They have a long shaft, which breaks much more often. These products are less efficient and require more thorough and frequent maintenance.

Moisture protection of fan motors must be of class "H" (at internal temperatures in the chamber ≤ 130 ° C) or "F" (at temperatures below 85 degrees).

It is obligatory to have a reverse with an efficiency of about 90%.

TOTAL

At the close of my story, I decided to violate the obligation not to name specific models and manufacturers. With a clear conscience, I can recommend FALCON vacuum chambers (practically any models) to small and medium-sized and even large manufacturers. With these Russian products, there were the least problems.

By performance characteristics. In terms of performance and durability, they are comparable to models of international giants in this market segment. Unlike them, they have a whole set of additional advantages:

In this article:

Wood is a hygroscopic material that contains moisture naturally and has the ability to absorb it from the atmosphere. Sawn timber goes on sale in two forms: natural moisture and dried. Of course, the latter are more expensive, so many entrepreneurs, when equipping a sawmill, think about ways to dehydrate wood.

Humidity indicators

According to the degree of moisture, the following states of the tree are distinguished:

wet(100% humidity) - logs that were long time in water (for example, transported by alloy);
freshly cut humidity depends on natural conditions plant growth, and ranges from 50-100%;
air dry- the material that is stored in the air (under a canopy) reaches the parameters of 12-20%;
room dry(8-12%) - drying in a closed, heated and well-ventilated area;
dry(humidity less than 8%) - prepared by the method of forced release of moisture.

Why is proper drying so important?

Boards of natural moisture are larger than dried boards in size, but are cheaper. This is because lumber manufacturers set a tolerance for future shrinkage and trimming.

Humidity standards:

for building and carpentry materials - 10-18%. In the manufacture of building materials, the production moisture content of wood should be equal to or be 1.25-3.5% lower than the operational one in order to avoid natural shrinkage.
For furniture production – 8-10%.

The use of lumber of natural moisture - flagrant violation technological process . When the wood dries naturally, it will change the width, thickness and, accordingly, the geometry of the entire product.

For example, edged pine board 50 * 150mm with natural humidity more than 50% after a couple of months will have parameters of 48 * 138 mm (for tangential cutting) and 46 * 144 (for radial cutting). Even if we take into account that the length of the product will remain the same (on average, the deviation does not exceed 0.1%), the final difference is catastrophic!

Methods for professional wood drying

1. Convective (chamber) drying

The most popular type of drying equipment - convection chambers. About 80% of manufacturers use just such dryers.

Advantages: easy to use, high moisture evaporation rate, low voltage in the final product, high loading volume (up to 1000 m3).

Supply and exhaust ventilation and heating systems are installed in the room (usually heaters). Humidity parameters are measured psychrometer and adjusted automatically. Waste is used as a fuel for obtaining hot water or steam in small-scale production wood production: wood chips, croaker, sawdust. It is profitable to use electricity and gas only with large volumes of production, otherwise high consumption and cost of resources will significantly reduce the cost of lumber.

Centrifugal or axial (depending on configuration) fans provide uniform distribution of warm air and timely removal of excess moisture to avoid warping, cracking and obtaining top quality wood in the shortest possible time.

Price - from 160,000 rubles(depending on configuration and cargo capacity).

2. Atmospheric drying

The natural process of evaporation of moisture from wood, which requires a minimum investment, but a maximum of time. However, wood dehydrated by atmospheric drying is considered the most resistant to deformation. Most often, this happens like this: a tree cut down at the beginning of winter is disbanded into boards and aged under a canopy until the start of the construction season. For 4-6 months, the lumber has time to dry up to 15-20% moisture.

In order to avoid deformation of the boards during the drying process, the following conditions are necessary:

stacking on a horizontal flat surface;
to protect against excess moisture between the rows of stacks and in the area where drying is expected, waterproofing is laid;
so that the boards are well blown, the stack is installed on concrete blocks and laid with timber or unedged boards of the same thickness (see the figure below);
stacks are stacked at equal intervals and parallelism;
a prerequisite for preventing deformation is a uniform load, which is carried out using wedges or clamping cords (see figure below);
the finished stack is protected from atmospheric influences, covered with a profile or slate. With this arrangement of the dryer, edged board will reach 12-18% humidity in 4-5 months. The speed and quality of dehydration depends on the climate, the amount of moisture in the atmosphere and the thickness of the board. The rules for atmospheric drying are regulated by GOST 2808.1-80 for sawn softwood and GOST 7319-80 for hardwood.

Rice. Scheme of arrangement of the dryer in the air

Main disadvantages: the design takes up a lot of space, the drying process is uncontrollable, and in areas with high humidity, the risk of fungal infection of the lumber is high. For such an area, pre-treatment of the boards with an antiseptic is recommended.

3. Vacuum dryer

Used for drying large wood, hardwoods (e.g. oak), valuable wood that is prone to cracking. The dryer is a sealed chamber made of stainless steel, in which boards are placed between aluminum heating plates. The top of the chamber is closed with an elastic rubber cover attached to a metal frame.

Hot water continuously circulates over the plates, which is heated by an external boiler. The vacuum inside the chamber is provided by a pump that pumps moisture out of the room.

Rice. Scheme of operation of the vacuum chamber

A microprocessor is used to control the processes inside the chamber. For each type of wood, the operator sets its own vacuum level and plate heating temperature. For example, a beech board with a thickness of 32 mm reaches 8% moisture in 29 hours. And a pine board with a thickness of 25 mm in 17 hours. Therefore, the main advantage of vacuum drying is the speed of processing materials..

Flaws: small capacity of the chambers (up to 10 m 3), high energy consumption, high internal stress due to uneven distribution of the final moisture content over the thickness of the material. These shortcomings are eliminated in new vacuum models, where drying is carried out using hot steam.

But the price of such cameras is high: 250,000 rubles with a load volume of 1 m 3.

4. Microwave dryer

The essence of the "microwave" method: wood is saturated with moisture, which then evaporates at the level of cellular structures. Wood dehydration is carried out by high frequency currents - 915-2500 MHz.

The electromagnetic field acts on the stacked lumber in the space of the metal chamber. Heating of wood occurs at the level of 50-60 degrees, therefore it is considered close to natural conditions.

Main pluses:

mobility;
compact dimensions;
the drying speed is 30% higher than that of convective chambers, with relatively low energy costs (for drying 1 m 3 of pine - 550 kW / h, oak - 2000 kW / h).

Flaws:

small volumes of loading (up to 4.5 m 3 for hard hardwoods and up to 7 m 3 for conifers);
high price of magnetron generators with a rather small resource of their work (no more than 650 hours);
uneven drying;
the possibility of ignition of the material inside the chamber - the microwave method is quite new, and the drying modes have not yet been worked out.

5. Condensation drying

Innovative equipment that has no analogues in the domestic production of drying chambers (from imported manufacturers, the brands Nardi, Vanicek, Hildebrand-Brunner are represented on the market).

Dehydration of lumber is carried out by a closed cycle method - without air access from the outside.

The air inside the chamber is saturated with moisture evaporated from the wood, washes the surface of the freon cooler, and its temperature drops below the dew point. Moisture condenses, and the released heat is spent on heating the drying agent.

Rice. The principle of operation of equipment with condensing drying technology

Main advantage: energy consumption is 3 times less compared to intermittent dryers (up to 0.5 kWh per 1 liter of evaporated water). Such chambers are used in cases where electricity is the only available or the cheapest type of coolant.

Flaws: low productivity, the duration of the drying process is 2-3 times longer than in chamber equipment.

The choice of a suitable method and equipment for drying wood is considered individually for each business, as it depends on a number of factors:

climatic conditions of the area;
the size of the production area;
range of raw materials and manufactured lumber;
the cost of energy carriers, investment opportunities of a potential consumer, etc.