Manufacturing of drying chambers. Using a wood dryer

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

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

The installation 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

Low-temperature wood processing is carried out at 45°. This is the softest method, it preserves all the original properties of the wood down 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 occurs at temperatures up to 90°. After drying, the material does not change shape and size, the brightness of color and strength are slightly reduced. 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 more than 100°) or hot air. The high-temperature drying process reduces the strength of the wood and gives it a darker shade, so the material is used to create minor construction and furniture components. In this case, drying with superheated steam will be more gentle than using air.

Types of drying chambers

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

Based on 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 reduce pressure.

Convective

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

Convection dryers come in two types: tunnel and chamber. In the first design, boards enter the chamber from one side and are unloaded from the opposite. Such models are mobile and designed for use in large sawmills.

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

Convection chambers have the following features:

• in one cycle you can process 20 cubic meters of wood, provided that the volume is completely filled;
• All types of lumber can be dried by placing them in stacks with gaps;
• after drying, it is possible to steam and impregnate the products;
• when connecting a solid fuel boiler for heating, the process will be more economical;
• The design is large in size, therefore it is designed for stationary work (without traveling).

The advantages include high quality of drying, but if the chamber is not filled to 100%, then there is 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 high power consumption.

Condensation

Condensation-type drying chambers are similar in design to convection ones, but differ in operating principle. Wet steam generated during 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 resulting water reserves are used for heating the premises.

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

The features of a vacuum drying chamber are:

• quick drying of wood;
• saving energy costs as a result of increasing the temperature of functional heating plates placed between the lumber.

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

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 using a special aerodynamic propeller, which transfers 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, and lack of temperature control.

Microwave cameras

Microwave drying technology has been developed relatively recently. The installation 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 because it can be placed in any in the right place premises. Thanks to the powerful effects of electromagnetic waves, drying wood takes no more than 6 days.

The advantage of a microwave installation is also the high quality of drying when the mode is correctly selected.

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

DIY making

Drying wood privately requires a special chamber, which you can make yourself. If you are going to build a wood dryer with your own hands, then you need to allocate an area of ​​about 10 m2 on a plot of land for installation. You will need concrete for the foundation, material and thermal insulation for the walls, polyurethane foam, a ventilation system, a boiler and auxiliary equipment.

Construction stages

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

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

Such work will be justified if the finished object is used regularly. The drying chamber will need to be fully loaded and the drying technology must be strictly followed.

Foundation construction

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

After marking the site, it must be concreted so that the floor level of the chamber is approximately 10 cm above the ground level. The concrete site is made with sides protruding by half a meter. To prevent water from accumulating in the drying chamber, the foundation must be made with a slight slope. It is also necessary to provide for filling the rails for transporting the cart with products.

Walling

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

The height of the wood drying chamber consists of the height of the stacks, a 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.

Heating of the installation requires the presence of a source of thermal energy, therefore, when installing walls, it is necessary to build an extension for the boiler and its auxiliary equipment.

Roof insulation and installation

An effective and economical thermal insulator material can be dry shavings or sawdust, which are applied to the walls in the form of a mixture with cement and an antiseptic. To preserve heat, the floor is covered with shavings.

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

Equipment installation

Fans should be positioned vertically along the width of the ceiling to ensure uniform heat supply. The next row will consist of radiators. To retain heat in the drying chamber, you must first seal the cracks with foam.

Heat is supplied to the radiators from the boiler, which can run on electricity, liquid or solid fuel. Typically, a wood boiler is used to heat the drying chamber. Pipes are connected to the boiler, then an anti-explosion valve is installed to regulate the operation of the equipment.

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

The domestic market has a very wide selection of chambers for forced drying of wood, operating according to various technologies, both Russian-made and imported.

This confronts the customer with a difficult choice problem.

In this article I will talk about what I have encountered over three decades of work associated with various drying chambers. Perhaps the information provided here will help someone not to make a mistake in this matter.

Don't underestimate the importance of drying

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

This is explained by the fact that it is qualitatively organized process drying allows you to minimize the amount of defects, improve the quality of the final product and, accordingly, ensures its sale at higher prices, and also contributes to an increase in the number of regular customers.

The approach to financing forced drying technology based on the residual principle is categorically incorrect. The result of such a decision may be low profitability (even bankruptcy) of a timber processing enterprise equipped with the most modern machine tools.

And if this is combined with the manager’s erroneous ideas about how to dry the forest “correctly” and the priority of “saving” money on the purchase of equipment, the result will be disastrous. There will be a camera. But you won’t get high-quality dry lumber at the output.

I have worked 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 strives by any means to “snatch the ruble” here and now, without thinking at all 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 place 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 it yourself

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

However, a number of beginning timber processors strive, in order to save money, to make a drying chamber themselves.

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

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

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

To confirm this thesis, I would like to cite an incident that I witnessed in 2002-2003 (I don’t remember more precisely). At that time I had just gotten a job at a company that was still called “sharashki” before and today. It positioned itself as a diversified enterprise producing garden furniture, gazebos, fences and lumber.

Having heard that chamber-drying material could be sold at a higher price, the owner appointed three “smart guys” as developers and manufacturers of a convection-type chamber.

The “masterpiece” of design thought was sculpted in less than a month. Moreover, with a huge number of flaws and gross violations that were visible even to the naked eye (I already had some work experience at that time). I tried to bring this to the employer's attention. But the opinion of the “smerd” was not taken into account, and they insisted, creating problems for themselves out of the blue. I didn't.

Examples. The fans did not have the ability to reverse rotation, many metal elements of the structure “forgot” to be grounded, and the air heaters were of different power. And a young Tajik was appointed responsible for the operation, who had not the slightest idea about it. He also dealt with loading and unloading issues.

The creation worked for a little more than a week and ingloriously ended its short production history with a powerful fire, in which not only our owner’s property burned, but also the customer’s raw materials, which he had to dry.

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

At the end of this section, a few wishes for those who decide to make a drying chamber themselves.

Before starting to manufacture a structure in a material, you need to obtain at least minimal theoretical knowledge. Fortunately, today the Internet provides enormous opportunities for this. There are many very good tutorials on this topic. Among them, I would like to mention the books by Krechetov and Tsarev (co-authored with Peich). It would also be a good idea to familiarize yourself with the provisions of the current regulations. For example, SP114.13330.2016, which sets fire safety standards for storing timber.

When creating a project for your own dryer, you must calculate:

• optimal material for its walls;
• ensure that the gate closes tightly;
• determine the optimal method for loading materials for drying;
• select the type and power of fans, calculate their installation locations and the required quantity;
• 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, automation should be provided. As a last resort. Semi-automatic control of the drying process. But these are quite complex issues that require deep specialized knowledge.

Practice has shown that one of the most common mistakes made by manufacturers of home-made drying devices is water, when splashed dropwise, hitting the humidity sensor. As a result, the automation receives distorted commands. The result is marriage.

The second most common problem is the fact of “forgetting” that fans are powered by electric drives, which constantly have to be in conditions of high temperature and humidity. therefore, it will not work here to take any that are suitable in terms of power. Only special models required.

Pros and cons of different types of wood drying kilns

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

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

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

• drying period to a given moisture content;
• the occurrence of internal stresses during the drying process and the possibility of its relief;
• the difference in the moisture content of the outer and inner layers of lumber after the drying process is completed.

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

1. Convection drying chambers for wood

Cameras of this type are most common in Russia, and in all regions. Therefore, experience with such chambers forms the basis of my experience in servicing products for forcibly reducing 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 stream of hot air. The latter is heated by electric heaters (in the vast majority of models). The flow of the required strength and direction 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).

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

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 do not have time to release moisture with the same intensity. The result of this imbalance is internal stresses, which can provoke the occurrence of cracks.

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

If the alternation of these stages takes place in a timely manner, after completion of processing the resulting material has approximately equal moisture content throughout the entire 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, installation is carried out in the presence of a company representative, and operation is carried out strictly in accordance with 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 of finished products and, as a result, profits companies.

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

• the presence of models with significant one-time capacity (about 1000 m3), which is essential for large companies;
• the ability to fine-tune the control process, providing for changing the values ​​of essential parameters at any stage of drying;
• process control in automatic or semi-automatic modes;
• minimizing production costs.

Among the shortcomings I cannot fail to mention:

• sufficiently long drying times;
• the need for trained personnel to service the device.

1. Condensation drying chambers for wood

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

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

If available, moistening is carried out after completion of the first stage of drying, which allows minimizing the internal stress that has arisen in the upper layers of the 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 smoother and more uniform release of moisture from the wood). In other cases, it will not be possible to prevent cracking of products undergoing drying.

Cameras of this type are optimal choice, if you have to dry mainly thick lumber, or products made from dense wood (for example, ash or oak).

If you plan 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 lot of disadvantages. Main:

• very long drying times, which are several times higher than those of convection-type chambers;
• the emergence of additional costs due to the use of freon;
• the quality of the 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 sterilization of workpieces).

1. Aerodynamic drying chambers 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.

The air is heated due to the heat generated by operating fans (the mechanical energy of the rotating rotor is transformed into thermal energy).

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

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

It is strictly not recommended to use such lumber in carpentry. When you try to “dry” such a material, it is guaranteed to burst (crack).

Of course, we can refer to the fact that the problems of internal stresses are inherent in any drying technology. But in the variant under consideration, 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 include:

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

The disadvantages are:

• unsatisfactory drying quality;
• long drying time;
• very significant costs for paying for electricity.

1. Infrared drying chambers for wood

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

In summer, drying in this way can be carried out under canopies 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 available to me for drying and processing wood.

The results obtained, in general, can be called satisfactory. But the technology “didn’t look good.” And for industrial use, this solution is absolutely unacceptable, due to the duration and complexity of the preparatory stage of laying and subsequent selection of finished lumber.

The advantages include:

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

As disadvantages, you should pay attention on the:

• significant difficulties in organizing control over drying parameters;
• Possibility of use on bookmarks with limited volumes not exceeding 5 m3.

1. Microwave drying chambers for wood

The wood in them is dried by implementing a process similar to what occurs in a household microwave oven. The only difference is in the sizes of the products.

High-frequency radiation does not damage the wood, facilitating the delicate and uniform removal of moisture throughout almost the entire depth of the workpiece. The time it takes for finished lumber to reach a given level of moisture content is quite short.

Out of curiosity, I worked with friends on a similar installation (new knowledge is never superfluous). The results turned out quite good. 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, the small volumes of one-time loading make such a solution unprofitable either for large-scale production or for private owners.

The latter is especially true if you estimate how much it costs to maintain such cameras, especially if you have to replace a broken magnetron generator.

But, as they say, “it depends on 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 consumption of electricity.

Among the shortcomings, I would first of all name:

• insignificant one-time loading capacity, not exceeding -7-10 cubic meters;
• very complex control over the progress 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 water boiling at lower temperatures. Therefore, the required drying effect can be achieved with “little loss” without using high temperatures.

This automatically reduces heat loss in a chamber of this type and allows for a very slight change in the color of the material undergoing drying.

The design features of such products depend on who manufactured them. For example, Italian WDE Maspell dryers, which are often used by Russian timber processors, and some domestic kilns have water heaters. Other domestic manufacturers prefer electric heating elements.

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

This technology makes it possible not to use aggressive 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 workpieces after drying is completed is determined not only by the selected technology and type of drying chamber, but also by correctly selected technological modes, which are included by manufacturers in each model and properly functioning automation.

In addition to this, an important factor is the choice of a reputable manufacturer with the necessary technological know-how and drying experience. The technology is complex and, unfortunately, I have encountered more than once when the owner chose a manufacturer after superficially understanding the issue. As a result, I received equipment that was more pain than work. The declared characteristics did not correspond to reality. I had to either modify the camera myself and spend time and money on it, or I had to resign myself to working on this equipment.

Despite the fact that in such chambers the impact on wood occurs more gently, there remains a possibility of cracking of the material undergoing drying. It is always there and in any drying mode. Since wood is a living material, in which it can simultaneously form different kinds stress. These processes are influenced by the type of wood and the place of its harvesting, the technology of cutting the log and the age of the tree.

Well, in terms of drying time, 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 never seen such a speed in any technology, perhaps only in microwave.

Advantages of vacuum type cameras:

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

Disadvantages (unfortunately, she also has them):

• manual loading and unloading;

The importance of reliable automation in drying chambers

I want to say something about this separately. Drying wood is a very complex process. Therefore, manufacturers automate high-quality modern cameras to the maximum. But no machine or automation can completely replace a person.

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

As a rule, defects appear at the final stage, when it is no longer possible to correct anything.

Therefore, a thorough approach to the choice of the camera to be purchased, as well as to the training of personnel, is required.

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 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);
• is it possible for the operator to intervene in the operation of the automation, allowing for prompt adjustment of the drying process at any time;
• It is highly desirable to have a digital display on the automation, which displays the main characteristics of the process (humidity, temperature, etc.) in real time;
• Do manufacturers provide the ability to record the progress of the chamber drying process with recording of all parameters and its subsequent display in the form of a graph (this allows for subsequent analysis, if necessary);
• built-in automation must be “smart”, that is, eliminate the possibility of making “wrong” decisions. For example, do not issue a command for humidification when the ventilation curtains are open;
• Is it possible to control the camera remotely?
• presence of light and sound indication and emerging malfunctions.

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

At the right time, taking into account the readings of control devices, the humidity, temperature, and level of air conditioning in the internal volume of the chamber must change. All this will have a positive impact on the quality of the finished product.

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

14 points to pay attention to when buying a drying chamber

You can distinguish a good camera from a bad one, in each specific situation, not only by its type, but also by who made it. Without naming any brands here, I will dwell 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 transferring heat to wood;
• also, heating plates must be made of stainless steel or aluminum, which is highly resistant 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 air external environment and atmospheric moisture must be guaranteed to be excluded;
• the existing heat and vapor barrier must be of high quality and installed correctly;
• steam removal from the chamber should be carried out as efficiently as possible;
• operate 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 disrupted. 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 defects and a decrease in profits.

• The installed automated control system should allow the operator's participation in the process to be reduced to a minimum, and the available SDUK should make the drying process easier and more predictable;
• The entire drying process should be displayed on the PC in the form of graphs for analysis in case of failure;
• There must be online monitoring 24/7 from the manufacturer.

An ideal camera, in my opinion, must meet the following fundamental criteria:

• ensure the highest possible quality of finished products (dried lumber);
• require minor expenses for its construction, equipment and commissioning;
• have a low cost of drying one cubic meter of forest (in terms of);
• the entire drying process should not have a negative impact on the environment;

Important: long service life (the housing 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 environments inside and the housing began to “siphon”, each It took me a month to weld it 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, under the influence of corrosion, “collapsed like tin" The camera's reinforcement ribs could not withstand it. The manufacturer simply made the calculations incorrectly.;

The best decision for a person who decides to purchase a drying chamber is preliminary stage careful preparation, during which:

• you should determine the required annual drying volume (today and in the future);
• study the issue of the presence and quantity of wood waste in production, and the possibility of using it to heat the coolant for the chamber (installation of an autonomous solid fuel boiler);
• analyze the possibility of atmospheric (open) drying;
• develop a layout of chambers, storage areas for raw materials and finished products.

Remember. Not everything depends on equipment, even the highest quality and most expensive. At least half of the success is due to the camera operators and repairmen (their qualifications directly affect the result). For example, how they organize the storage of raw materials and finished lumber.

Defects of lumber due to incorrect drying conditions

Some leaders. Due to lack of awareness. Drying processes are considered to be quite simple and do not deserve special attention. He put the board down, turned on the airflow and heating for a certain time, and took out the finished product.

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

In fact, for “incomprehensible” reasons, in one cell there is almost no defect, and in the second, its percentage goes off scale beyond the acceptable limit. To understand why this happens, sometimes you need to spend a significant amount of time (and the marriage is progressing). 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 purchases and choosing the optimal cost/performance ratio, and not even the possible prospects for its operation. The main thing is to understand whether the dryer is capable of bringing the moisture content in the lumber to the required levels in a short time throughout the entire depth of the wood, evenly, and whether it is capable of stabilizing the geometry (in size and shape).

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

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

Hard species (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 likelihood of marriage is high.

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

If the stack is not stacked correctly, warping can add to the cracks.

What problems have we encountered most often with 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 made by a well-known brand and quite expensive. Most often, these are leaks in various pipes caused by corrosion, downtime caused by a malfunction and lack of necessary spare parts (for imported cameras this problem is very relevant) or waiting for a specialist. Quite often problems arise with fans.

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

• Wood is heated in different chambers, from different manufacturers, with different agents (water, air, radiation waves, etc.), heating structures various types As a result, lumber dries differently.
• The moisture evaporated in the wood must be collected 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 for quite a long time. But most often it is:

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

In the first case, installing fans with reverse rotation often helps to solve the problem. 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 redesigned. Only professionally performed calculations and competent design (modification of the camera) can help. In my experience, this is a lot of time and money wasted.

The main thing to understand is that

NOBODY has yet managed to completely solve ALL the problems of drying uniformity and quality of finished products!

And, in the foreseeable future, there is no solution to this problem. Therefore, the main goal that every manufacturer strives to achieve is to minimize the percentage of defects and 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 is much more likely to break. These products are characterized by lower efficiency and require more thorough and frequent maintenance.

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

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

RESULT

Toward the end of my story, I decided to break my obligation not to name specific models and manufacturers. With a clear conscience, I can recommend FALCON vacuum chambers (of almost any model) to small and medium-sized and even large manufacturers. There were the fewest problems with these Russian products.

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

Related articles:

There are many technologies for high-quality drying of wood, but each of them has its own disadvantages and advantages. Of course, it is the positive indicators that make them relevant, but still there is a difference between them and it is quite significant.

Types of equipment for drying wood

The type of drying chambers depends on the size of the lumber, its type, and the nature of the qualities that the wood should be endowed with. But still, all technologies can be divided into 2 main categories:

• – heating of lumber is carried out directly by heating the wood with special heaters that are in contact with the surfaces of the layers of the stack.
• Air - heating of wood is carried out by heating the air that circulates inside the chamber.

Also, for drying wood, equipment should be divided according to heating method:

• Direct - heating of lumber is carried out due to electrical or alternative sources, which generate direct heat. These types of dryers include convection chambers, aerodynamic chambers, steam chambers and gas chambers.
• Electrophysical – technologies in which lumber is dried without heating the wood. These types of equipment include cameras /, and.
• Combined - a type of equipment that combines two physical processes: excess pressure and temperature. These varieties include pulsed vacuum drying units and vacuum chambers.

Our company offers custom-made production of vacuum chambers for drying lumber. . and up to 6 m long. We also carry out orders with individual requirements for loaded wood, both in length and volume. The technology consists of contact heating at low temperatures, while the wood does not crack or deform. The resulting humidity indicator is 6-8% for three with a defect rate of about 1%. For each breed, an individual drying regime is established.

See also:

Contents Options for organizing drying Benefits of self-drying Alternative to drying wood at home In order for the structure to be durable, reliable and comfortable, it is important to properly prepare construction lumber. After cutting, it contains a large amount of moisture, on average about 60%. It is not practical to carry out construction with such material. During service, it is subject to linear deformations, which will gradually lead to its deterioration, [...]

Contents Nuances when drying Wood shrinkage table Shrinkage and swelling coefficients Shrinkage allowances for lumber of tangential or mixed sawing species: spruce, pine, cedar, fir When does shrinkage occur? During the drying process, wood significantly changes its physical parameters. It becomes lighter, changes its shape and its geometric dimensions are slightly distorted. All this together is called shrinkage and the main task when [...]

Contents Quick drying using a forced mode Quick drying of boards in drying chambers Quick drying of wood/firewood at home One of the main requirements in the development of new equipment for harvesting high-quality lumber is the rapid drying of wood, but not all technologies can perform this with equal quality. When wood is suddenly heated, and especially overheated, it not only [...]

Lumber can be called high-quality only if its equilibrium moisture content is about 15%, the correct geometry is observed on the cut and there are insignificant deviations from linearity. If all this is clearly expressed, then this indicates that the drying process was not followed. Therefore, there are a number of requirements for the equipment and its operating personnel, consisting […]

Industrial processing of wood is possible only after it has been pre-dried. Dry wood is protected from fungal damage, retains its size and shape, and has better physical and mechanical properties. This stage of lumber production is long and complex, so special drying chambers or, as they are called in the professional environment, “dryers” are used to carry it out. Currently, the range of equipment in this category is presented quite widely, which makes it easy to select equipment for specific tasks. The main difference between the models is the method of moisture evaporation: vacuum or convective.

Technical features of drying chambers

A significant advantage of modern devices is the ability to use both ordinary and exotic types of wood for drying, which require especially careful treatment. These are such popular samples of raw materials as teak, wenge, rosewood, beech, anegri and others, from which high-quality lumber and boards are produced, and which are used in interior decoration and furniture production. During processing, the workpieces are not subject to cracking or warping, fully retaining their external and practical advantages.

Advantages

The KAMI company carries out direct supplies of industrial drying chambers for wood from the world's leading manufacturers. With the help of our specialists, you can easily select and purchase the appropriate equipment for a small or large workshop aimed at constantly increasing production volumes. Prices are kept at an affordable level, which will avoid additional costs and rationally arrange production. And effective logistics from KAMI is a way to receive your purchase as quickly as possible, regardless of whether you are in Moscow or another city in Russia.

There is not a single woodworking enterprise that can do without the wood drying procedure. To prevent the occurrence of various defects, it is customary to use a special technology for drying wood in a drying chamber. If you want to produce wood products yourself, you will also need a drying chamber for drying wood. Today we will talk about how to do it correctly.

The need to dry wood

How to dry a board efficiently and quickly? This question has interested every carpenter since ancient times. People have long been engaged in storing wood for many years in order to have time to dry it evenly. The grandfather prepared wood for his grandson, using the very material that his grandfather left him.

The importance of properly dried wood is colossal! For example, if the wooden furniture that is in the room is made of too wet wood that has just been cut down, then it will dry out over time, because the wood can dry out and decrease in size, which means it will deteriorate!

If the door to the house is made of excessively dry wood, it will swell over time and will not be able to close! If the door panel is assembled from blanks that are unevenly dried in volume, then it may burst or warp! Therefore, it is recommended to dry all wood blanks. In addition, drying protects the material from damage by wood-destroying fungi, prevents the size and shape of wood, and improves the physical and mechanical properties of wood.

Drying wood is a lengthy, complex and expensive procedure. Tree by traditional technologies heated with superheated steam or hot air. Dried wood can be transported and stored longer. In addition, during operation it does not deform. The boards are dried in steam chambers, where the possibility of internal damage is excluded.

Wood moisture concept

To fully understand the essence of the drying process, it’s worth diving a little into the theory. The procedure for removing moisture from wood is not entirely simple, because there are two types of moisture in the material itself. Wood consists of elongated plant cells. Moisture can be found in the cell walls and in their cavities, filling the microcapillary system. The moisture that is present in the spaces between cells and in their cavities is called free intercellular, and moisture in the cell walls is called bound intracellular.

The content of bound moisture in wood is limited. The state when the cell walls are characterized by maximum humidity when in contact with liquid moisture is called their saturation limit. It is generally accepted that the moisture content of the saturation limit does not depend on the rock and is on average 30%. If the wood's humidity is above 30%, then it contains free intercellular moisture. The wood of a freshly cut or growing tree has a moisture content above the saturation limit, that is, it is raw.

Depending on the purpose of wood blanks, wood is usually dried in different ways. The wood is dried to a moisture content of 6 - 8%, when the material is needed for mechanical processing and assembly of products for high-precision critical connections that affect performance (the production of skis, parquet or musical instruments).

Transport humidity is 18 - 22%. It is with this water content that lumber is suitable for transportation over long distances in warm seasons. Wood dried to such a moisture content is used mainly in standard house construction, in the production of ordinary containers and when there is no need for interchangeability during assembly.

Carpentry dampness is divided into several subspecies. Molded products (deck boards, sheathing, floor boards, casing) must have a moisture content of 15 ± 2%. Wood products (windows, doors, stairs and interior elements) made from solid or laminated wood can withstand humidity fluctuations from 8 to 15%.

Furniture humidity, depending on the level of the product and the use of solid or laminated wood, is 8 ± 2%, because it is at this humidity that the wood exhibits the most optimal characteristics for processing, gluing and subsequent use. But it is usually customary to reduce the humidity to 7-10%, performing partial sterilization of the wood and taking into account the uniformity of humidity throughout the tree, preserving mechanical properties material, absence of surface and internal cracks.

Wood drying modes

Depending on the requirements for the quality of wood, lumber can be dried in different modes, which differ in temperature level. In a mini drying chamber for wood, during the drying process, the air temperature gradually increases in stages and the relative humidity of the agent decreases. Drying modes are selected taking into account the thickness of the lumber, the type of wood, the final moisture content, the quality category of the wood being dried and the design of the chamber.

There are low- and high-temperature process modes. The first modes involve the use of moist air as a drying agent, the temperature of which in the initial stage is less than 100 degrees. There are three categories of these modes:

• The soft mode is capable of ensuring defect-free drying of the material while maintaining the natural physical and mechanical properties of the wood, including color and strength, which is important for drying wood to the transport moisture content of export lumber.
• The normal mode guarantees defect-free drying of wood with almost complete preservation of the strength of the material with minor color changes, which is suitable for drying lumber to its final moisture content.
• The forced mode maintains strength for static bending, compression and tension, but there may be a slight decrease in splitting or spalling strength with darkening of the wood, which is intended for drying wood to operational humidity.

For low-temperature modes, a three-stage change in the parameters of the drying agent is assumed, and from each stage to the next one the transition can be made only after the material reaches a certain level of humidity, which is provided for by the mode.

High-temperature modes provide for a two-stage change in the parameters of the drying agent, and you can move from the first stage to the second after the wood reaches a transitional moisture content of 20%. The high temperature regime is determined depending on the thickness and type of lumber. High-temperature conditions can be used to dry wood, which is used for the manufacture of non-load-bearing elements of buildings and structures in which darkening of the wood and a decrease in strength are allowed.

Drying chamber concept

Chamber drying is the main method of drying wood. Drying chambers are required to dry softwood and hardwood to different quality categories. One of the most popular and economical methods of artificial dehydration of lumber is drying, when bound and free moisture is removed from the tree by supplying heat to the wet wood with hot air and carrying away the evaporated excess moisture with humidified and partially cooled air.

The drying chamber is a completely finished installation that is equipped with all the equipment necessary for drying wood. According to their design, wood drying chambers are divided into prefabricated metal ones and those made of building materials. The latter are constructed directly in workshops or as separate buildings from materials that are widely used in industry. The chamber can be made entirely of monolithic reinforced concrete. Its walls can be made of solid red brick, and the ceiling can be made of monolithic reinforced concrete.

If several dryers are used, they are often combined into a single block, constructing a common control corridor where the heat supply distribution and automatic control system for all chambers are located. Depending on the volume of wood loaded into the chamber, there may be horizontal or vertical transverse air circulation.

Loading of lumber into the chamber can be carried out in the following ways: on trolleys in the form of stacks along a rail track, like packages with a forklift. Heat transfer to wood can be carried out: by air, combustion products or superheated steam; radiant heat that comes from special emitters; a solid body, if you organize contact with a heated surface; current that passes through wet wood; high-frequency electromagnetic field that penetrates wet wood.

Equipment for a wood drying chamber is divided into basic and additional. The main ones include a fan system, a heat supply system, supply and exhaust ventilation and humidification; additional ones include an insulated door and psychrometric unit, stacking trolleys, and an electric motor for the fan drive.

The process of controlling wood drying in a chamber can be automated. Automation is capable of maintaining the humidity and temperature of the environment in the dryer at a given level. The temperature is regulated by supplying coolant to heaters or by turning an electric heater on and off, and humidity by using supply and exhaust ventilation and a humidification system.

The wood drying control system may have the ability to remote control humidity and temperature in the chamber. When drying lumber in a drying chamber, it becomes necessary to control the moisture content of the wood, for which a remote moisture meter is used, which allows you to check the moisture content of the wood at several points without entering the chamber. In the absence of external heat sources, the dryer can use autonomous heating modules and use gas, coal, wood waste, electricity and diesel fuel.

Types of drying chambers

IN real life It is customary to use the following types of drying chambers. The necessary energy in convective drying chambers is transported into the material using the air cycle, and heat transfer to the wood occurs through convection. There are two types of convection chambers - tunnel and chamber.

Tunnel convection dryers are deep chambers where stacks of stacks are pushed from the wet end to the drier end. These chambers must be filled at one end and emptied at the other. Pushing the stacks (the process of filling the chambers and emptying them) is done one stack at a time with an interval of 4 - 12 hours. These chambers are designed for large sawmills and allow exclusively transport drying of wood.

Chamber convection drying chambers are shorter than tunnel and vacuum drying chambers for wood; during operation, the same parameters are maintained throughout the chamber. When the blowing depth is more than 2 meters, the technique of reversing the direction of ventilation is used to equalize the drying conditions for the wood. The emptying and filling of the chamber occurs on one side if it has one door. Other loading systems are also known that are similar to the procedure for loading tunnel chambers. Any lumber can be dried to any final moisture content, which is why 90% of wood in Europe and Russia is dried in chamber dryers.

The condensation drying chamber differs from the previous ones in that the humidity that arises in the air condenses on special coolers and water comes out of the drying process. The efficiency of such a process is large, but the cycle is long, because the devices do not operate at high temperatures, and the total heat losses are also significant. The condensation chamber is primarily suitable for drying small volumes of wood, or for drying dense wood species - oak, beech or ash. The big advantage of such chambers is that a boiler room is not needed, the price of a wood drying chamber and the cost of drying are lower.

Drying kilns are also classified according to the method of circulation and the nature of the drying agent used, the type of enclosure and the principle of operation. Drying chambers periodic action characterized by the fact that they can be fully loaded to simultaneously dry all the material, and the wood drying mode changes over time, currently remaining the same for the entire chamber.

According to the method of circulation, there are chambers with incentive and natural circulation. Dryers with natural circulation are outdated, low-performance, the drying mode in them is almost uncontrollable, and the uniformity of wood drying is unsatisfactory. For modern construction, such devices are not recommended, and existing ones must be modernized. Depending on the nature of the drying agent, the chambers are divided into gas, air and high-temperature chambers that operate in a superheated steam environment.

Wood drying procedure

Before drying according to the selected mode, the wood is heated with steam, which is supplied through humidifying pipes, with fans running, heating devices turned on and exhaust ducts closed. First you need to calculate the drying chamber for wood. The temperature of the agent at the beginning of heating the wood should be 5 degrees higher than the first stage of the regime, but not more than 100 degrees Celsius. The level of saturation of the environment should be 0.98 - 1 for material with an initial humidity of more than 25%, and 0.9 - 0.92 for wood with a humidity of less than 25%.

The duration of the initial heating depends on the type of wood and for coniferous species (pine, spruce, fir and cedar) is 1 - 1.5 hours for each centimeter of thickness. The duration of heating of soft deciduous trees (aspen, birch, linden, poplar and alder) increases by 25%, and for hard deciduous species (maple, oak, ash, hornbeam, beech) - by 50% compared to the duration of heating of coniferous species.

After preheating, it is customary to bring the parameters of the drying agent to the first stage of the mode. Then you can begin drying the lumber, subject to the established regime. Humidity and temperature are regulated by valves on the steam lines and gates of the sugar-exhaust channels.

During the operation of an infrared drying chamber for wood, residual stresses arise in the wood, which can be eliminated by intermediate and final moisture-heat treatment in an environment of increased temperature and humidity. It is customary to subject lumber to processing, which is dried to operational humidity and is subject to further mechanical processing.

Intermediate moisture-heat treatment is carried out during the transition from the second stage to the third or from the first to the second at high temperature conditions. Subjected to moisture and heat treatment conifers from 60 millimeters thick and deciduous from 30 millimeters thick. The temperature of the environment during the heat and moisture treatment process should be 8 degrees higher than the temperature of the second stage, but not higher than 100 degrees, with a saturation level of 0.95 - 0.97.

When the wood reaches its final average moisture content, final moisture-heat treatment can be carried out. In this process, the temperature of the medium is maintained 8 degrees above the last stage, but not higher than 100 degrees. At the end of the final moisture-heat treatment, the wood that has undergone drying must be kept in the chambers for 2 - 3 hours at the parameters provided for by the last stage of the regime. Then the drying chamber is stopped.

Making a drying chamber

If you decide to make wood products yourself, then you simply need a wood drying chamber. However, when constructing a dryer, comply with all required standards. You will need a chamber, a fan, insulation and a heating device.

Build a drying room or select a separate room, one wall and ceiling of which will be made of concrete, and the other walls will be made of wood, which need to be insulated. To do this, it is customary to create several layers: the first of them is polystyrene foam, the second is wooden boards, which are usually wrapped in foil in advance.

After this, you should install a heating element, which can be made in the form of batteries. Water must be supplied to the batteries from the stove, in which it will be heated to 60-95 degrees Celsius. It is advisable to continuously circulate water using water pumps in the heating element. Also, a fan should be placed in a homemade wood drying chamber, which helps distribute warm air throughout the room.

Consider how the wood will be loaded into the drying chamber. One loading option could be a rail cart. To regulate the humidity and temperature in the drying chamber, you need to use the appropriate thermometers in the work area - wet and dry. Provide shelves inside the dryer to increase work space.

During the drying process of lumber, sudden changes in temperature in the working room are not allowed, otherwise this will cause the wood to warp or cracks to appear in it. When constructing a drying chamber, it is extremely important to comply with fire safety requirements. Therefore, be sure to install fire extinguishers in the immediate vicinity of the dryer.

And finally, remember that instead of heating element At home, you can use a two-burner electric stove. You can insulate the walls of the drying chamber yourself using wood shavings. Instead of foil in the chamber, you can use penofol, which can provide good reflection of heat from the surface. In such a dryer, the wood is pre-dried 1-2 weeks in advance.