Vacuum drying of wood. Methods and equipment for professional wood drying Container design for vacuum wood drying

All photos from the article

A do-it-yourself dryer for boards is made if it becomes necessary to process a large amount of unprepared wood. Of course, you can immediately purchase blanks with optimal moisture content, but in this case, the cost of purchasing the material will be very high. So the building special device can be quite effective from an economic point of view.

In our article we will tell. How wood is dried, and we will give recommendations for self-arrangement of the drying chamber.

Theoretical aspects

Moisture in wood

Before proceeding with the design of the dryer, we need to understand why it is needed. As the name implies, such devices are designed to remove excess liquid from wood, and here it is worth paying attention to theory.

All moisture in wood is divided into two groups:

• free - is located in the cavities of cells and in intercellular spaces. The content of free moisture is primarily determined by the conditions in which the tree grew, as well as the storage conditions of the sawn blanks. When drying, free moisture leaves the wood rather quickly;
• bound (structural) - a liquid that is part of the cell walls. Each tree species normally has its own level of moisture content in the structure. In this case, the removal of the bound liquid occurs very slowly, because in vivo drying can take from several months to several years.

As a rule, the limit of saturation of wood with moisture is at the level of 30%. A tree with a higher moisture content is considered damp and is almost never used for work.

Humidity readings for different material differ:

Why drying is necessary

So, we figured out the moisture itself, now let's analyze why we need to reduce it.

1. When moisture is removed in a natural way, the configuration of wood fibers changes, due to which the size of the board decreases - it “dries out”.
2. In this case, the workpiece loses moisture unevenly, because the deformation can also occur in different planes at different speeds.
3. Due to this, stress lines are formed inside the wood, which later give rise to cracks.

Note!
As a rule, the board cracks along the fibers, starting from the end.
This is due to the least strong bonds between the longitudinal fibers.

1. In addition to cracking, transverse deformation of the board is also possible: the part either bends in an arc, or the so-called “propeller” is formed due to uneven raising of the edges. This behavior is explained simply: not all fibers dry out at the same time, which means that their length also decreases in different ways.

As you can see, if used to build structures or craft various designs wood with a high moisture content, over time, individual parts may become unusable. This can be avoided in one way - before starting work, prepare the raw materials by drying it in one way or another.

Drying modes

The use of drying chambers can significantly reduce the time required to prepare lumber for work. At the same time, by controlling the dehydration mode, we can control the operational properties of the resulting material.
To date, experts distinguish three drying modes:

Creation of a drying chamber

Finished premises

So, we argued the thesis that lumber must be prepared for use by drying. Now let's figure out how to make a dryer for boards with your own hands.

First, we need to choose a room in which the drying process will take place:

1. Since the removal of moisture from wood requires significant energy costs, the area of ​​the dryer must be selected based on the planned volumes of material..
2. The optimal height of the room is 2 - 2.5 m (so as not to bend over). The width should allow the placement of one or two stacks of boards of 1.8 - 2 m with a passage between them.
3. The windows in the dryer must be laid with bricks. We expand the doors in such a way that we can freely load the processed material.

Note!
For ventilation, either a small window is left, or a vent, into which we will later lead the air duct.

1. If the drying of the boards is planned in sufficient large room, then it is desirable to make a separate partition in it. We build partitions of brick or a sufficiently thick beam to provide thermal insulation.

Building a dryer

However, it is not always possible to find a suitable room (most often a garage or a barn plays this role).

That is why it will be useful to learn how to make a board dryer from scratch:

1. We lay a strip or column foundation under the structure. Since the mass of the structure will be small, then we make the base shallow.
2. After the foundation concrete has dried, we assemble the frame from an aluminum or galvanized steel profile. We connect the frame parts with the help of bolts and special brackets.

Note!
The price of aluminum structures is much higher, but at the same time they are significantly more resistant to corrosion in a warm and humid environment.
So the use of more expensive load-bearing elements is fully justified.

1. Walls and roof sheathing steel sheets, which we fix to the frame with metal screws (with a drill). For maximum efficiency, we perform double cladding, laying a layer of mineral wool insulation between the metal sheets with a capacity of 100 - 150 mm.

1. On the floor we lay a dense waterproofing membrane, which is covered with a layer of sawdust.
2. We install doors that should close as tightly as possible. For additional sealing, you can reinforce the door frame with bars with attached rubber sheets.
3. As in the case of using an already finished room, we must equip ventilation products for air circulation.

After completion of work, we check the tightness of the room, if necessary, eliminating defects in the skin. Now it remains for us to equip our drying chamber.

Note!
In a closed dryer, there should be no gaps that allow uncontrolled air currents to enter.
This is due to the fact that the presence of the slightest draft can provoke uneven processing of the boards, causing them to crack or deform.

Equipment

Instructions for arranging a dryer can be very different, because the equipment of the chamber largely depends on both our requests and financial capabilities.

But still general scheme put it realistically:

1. To begin with, we make supports on which a stack of boards will be installed. We fix on the floor, allowing you to raise the material to be dried by about 10-15 cm above the floor level, the proportion of circulation in the lower layer of air.

1. Instead of supports, you can use wall racks. At the same time, we fix metal brackets on the bearing surfaces, designed for laying stacks along the walls of the drying chamber.

Note!
This option is most often used when temporarily converting a part of an outbuilding to a dryer.

1. Next, install the heater. It can be a stove, a fireplace, heat gun, fan heater, etc. - it all depends on your preferences. The key parameter will be the power of the device, which is calculated based on the volume of loaded wood: for drying 1m3 of boards, at least 3 kW of thermal energy is needed, respectively, the more raw materials we need, the more powerful the device we need.
2. Together with heating devices, we install fans that will provide air movement. Of course, you can save on the purchase ventilation system and get by with a natural hood, but in this case, the time for preparing the boards for work will increase significantly, which means that the cost of heating the chamber will also increase.

1. We position fans and heating devices in such a way that warm air flows across the air flow. This installation allows you to significantly reduce the aerodynamic drag of the system, so that the dryer will work more efficiently.

Since our camera requires a large amount of electricity to function, it is advisable to connect a separate power cable to it. At the same time, we connect all used units to the switchboard through the RCD with the corresponding power partners. Such a precaution would not be superfluous, since a tree, even if not completely dried, can catch fire from the slightest spark that appeared during a short circuit.

Advice!
It is also desirable to install an automatic temperature and ventilation control system.
It is quite expensive, but its use allows you to control the parameters of the internal environment of the dryer, thereby ensuring the maximum quality of wood processing.

Dryer use

If the drying chamber was assembled in accordance with all the rules, then it will be quite simple to use it. To do this, we lay the boards in a pile, laying bars up to 20 mm thick between the rows, and load the pile into the dryer.

After that, we begin to change the temperature, gradually increasing the heat.

There are many drying schemes, but novice craftsmen should use the low-temperature mode, as it provides maximum quality with minimal risk of marriage:

1. Heating - raise the temperature to 45 - 50 0C at a speed of 5 - 70 C per hour.
2. Exposure - we keep 50 0C for 5 hours.
3. Drying - we reduce the moisture content of the wood from 30 to 8%, gradually increasing the temperature to 60 0C. This step takes about 48 hours. supply and exhaust ventilation turns on at half power.
4. Conditioning - we maintain the temperature at 600C for another 12 hours. Ventilation must be active.
5. Cooling down to ambient temperature with heating and ventilation off.

As a result, we should get boards suitable for most types of carpentry and joinery.

Conclusion

As you can see, a do-it-yourself dryer for a board is quite simple (but, admittedly, with certain financial costs). At the same time, the use of this device makes it possible to obtain a large amount of building materials, which, if purchased from a manufacturer, would cost much more.

For a more detailed acquaintance with the technology of chamber drying of wood, we advise everyone who is interested in this topic to study the video in this article.

Drying kilns for lumber are indispensable equipment in the production of wood-based blanks. Before sending a tree for processing, it must be dried. Otherwise, the risk of deformation, deterioration in quality increases significantly. finished products. Drying is carried out in special chambers under certain conditions. At the same time, many people assemble drying chambers with their own hands for use at home.

Not everyone knows exactly why to dry a tree before processing. Therefore, we will tell you some of the nuances of this process.

1. For many centuries, wood has been the main material in the manufacture of furniture.
2. The furniture was made from wood that had been cut down a few years ago.
3. In the case of using raw, non-dried wood, the boards dry out quickly and become covered with cracks.
4. When dried, the tree shrinks, therefore, structures erected from initially raw material may squint over time, lose strength, and geometry.
5. Damp wood is a great place for mold to grow.
6. At the same time, an excessively overdried building material is also bad, since such material actively absorbs moisture and increases in volume due to swelling. Therefore, to furniture, other structures, an effect occurs that is the opposite of drying.

Drying is carried out in drying chambers. In this case, steam is supplied to the surface of the lumber or hot air. This process takes long time and is quite expensive for the manufacturer. Largely because of this, furniture made on the basis of natural wood, much more expensive than MDF, chipboard, etc.

The use of drying chambers allows you to obtain the following properties of lumber:

• Increased strength;
• Protection against the likelihood of changing forms;
• Preservation of primary dimensions during application;
• Extended service life etc.

The task of drying chambers is to improve the quality characteristics of lumber. Therefore, drying is an obligatory stage of wood processing.

Process Features

For drying lumber, various modes can be used. In do-it-yourself chambers, the temperature rises in stages, which allows you to gradually remove excess moisture from the material.

The mode and features of the drying process in the chambers are determined taking into account the analysis of the following parameters:

• The type of dried wood;
• Dimensions of materials;
• Initial humidity indicator;
• Humidity index to be achieved;
• Design and technological features of drying chambers used for processing;
• Quality category of processed lumber.

Types of drying

Do-it-yourself drying of wood inside the chamber is of two types:

• Low temperature;
• High temperature.

The high temperature treatment process is carried out in two steps. The transition to the second stage occurs when the moisture content of the workpiece drops to 20 percent. This technology relevant when using wood as materials for the construction of secondary structures.

Low temperature mode is divided into three categories.

1. Soft dry. Here lumber retains its characteristics and properties. Therefore, changes in color or strength parameters of the product are not observed.
2. Normal drying. Color may vary, but only slightly. Strength parameters are somewhat reduced.
3. Forced drying. Performing splitting or chipping of raw materials dried in forced mode, it can become brittle. The color also changes, the wood becomes dark.

Heat sources

Drying chambers can use different heat sources, the task of which is to achieve the desired level of moisture in the lumber.

The following heat sources are distinguished:

• Heated fell;
• Radiant emitters;
• Heated racks;
• Electricity;
• High-frequency electromagnetic field.

A constructive chamber necessarily includes three components:

• Ventilation and exhaust system;
• Heat-saving unit;
• Humidification system.

Dryers

Dryers differ from each other in the way air moves inside the chamber. Based on this parameter, the following varieties are distinguished:

• Systems with natural air movement;
• Drying systems where the forced air exchange principle is used.

It is easier to build a system with your own hands that uses natural air exchange. At the same time, its efficiency indicators are significantly inferior to forced air circulation. For this reason, cameras of the natural type are becoming less and less common.

Dryers are distinguished by the principle of their operation. This is one of the main characteristics that you should pay attention to when choosing drying equipment or designing a drying chamber for building it yourself.

1. convection chambers. Inside them, the lumber is blown by hot air currents. Heat transfer is carried out by the convection method. Such dryers are divided into chamber and tunnel. The tunnel chamber involves loading wood from one end and unloading it from the other. Gradually, moving on the dryer, the material acquires the necessary characteristics and moisture parameters. The drying cycle in tunnel chambers is 4-12 hours, they are used in large sawmills. The chamber type of dryers is compact, inside they maintain a uniform microclimate throughout the entire volume of the chamber. Such structures make it possible to achieve desired characteristics lumber various types. This has led to the fact that the vast majority of industries that work with wood use chamber equipment.
2. condensation chambers. Here, the moisture that is released from the lumber settles on the cooler, after which it accumulates inside a special container and is discharged outside. Such dryers are characterized by an increased efficiency. At the same time, the process of preparing wood takes a lot of time and there are impressive heat losses. Condensation technology shows itself best when preparing small batches of wood, which is characterized by increased hardness. The cost of the equipment itself and the cost of operating condensation chambers make it preferable compared to convective units.

The choice of equipment for drying wood is a rather serious issue, requiring a detailed study of the technical characteristics of the chambers themselves and the features of the process of preparing lumber for their further processing. Therefore, if you have any questions, we recommend consulting with specialists.

Sometimes making a dryer with your own hands is preferable to buying factory equipment. But if you decide to assemble the device with your own hands, strictly adhere to the manufacturing technology. Violation of the guidelines may result in backfire for wood and funds invested in the manufacture of equipment.

Any lumber is obtained by longitudinal sawing of a log. As a result, bars, slats, boards of various thicknesses necessary for construction and repair are obtained. Only dry lumber is used in construction. They are of higher quality. For drying wood at home, a special do-it-yourself lumber dryer can be equipped. The process of building this structure will take a lot of time. But as a result, the home master will always be provided with high-quality material for performing various jobs.

The quality of the timber depends on how dry the wood is. The moisture content of the timber should be 12%.

Dryer construction

The construction of the simplest dryer for drying small amounts of wood with your own hands in natural conditions consists of several stages:

1. It is necessary to select and prepare the area for the placement of the building. It is possible to build a dryer on the adjoining land plot. Suitable for building a small dryer flat roof. The floor can be made of several layers of roofing material, sprinkled with sawdust.
2. The wood to be dried is stacked in a stack no wider than 120 cm. Optimal size its width is 80 cm. The stacking height is 50-70 cm. Separate layers of boards or beams are laid with slats at least 2 cm thick. It is recommended to stack the stack across the air flow in this area.
3. Provides protection from rain and snow. Dry wooden bars with a cross section of approximately 50x50 mm. Iron is placed on them, which is pressed with the same bars.

In such a dryer, the material is blown with air, the moisture gradually evaporates, the humidity level decreases.

Drying chamber

The wood is most effectively dried in a special drying chamber. It can install automatic systems, which control the entire process of drying wood of specific species. At the output, the lumber will have a predetermined moisture level. Such a camera can also be built with your own hands. But this building will cost a lot of money. For construction you will need:

• aluminum profile;
• sheet metal;
• material for thermal insulation;
• waterproofing film;
• sawdust;
• thermal construction gun.

Construction is carried out in the following order:

1. You should start with the construction of a foundation of any type. It can be pile, tape. For its construction, you can use brick, concrete, metal pipes and other materials. It all depends on the size of the camera.
2. A frame is built on the foundation. The best way to do this is to use aluminum profile. It is assembled with bolts and nuts. Other methods of connecting frame elements are possible.
3. The finished frame is sheathed with aluminum or steel sheets. They are fastened with screws, bolts, welding. The walls can be made of brick, concrete, other materials.
4. The thermal insulation is installed mineral wool 10-15 cm thick.
5. The floor is covered with waterproofing film and sawdust.
6. For stacking lumber stacks, supports are prepared from bars in the form of a kind of well. This is done in order to raise the bottom row of the stack above the floor level.
7. Lumber prepared for drying is stacked through wooden spacers. Air must pass freely between the rows of boards. The height of the stack is only limited by the height of the ceiling.
8. For forced circulation of heated air, fan heaters or other heating devices are installed. The air flow must be directed across the boards in the stack. This contributes to a more efficient drying process.

Dryer inside the house

A small number of boards can be dried inside the house or cottage. The dryer is set up like this:

1. You need to choose a room in which there is a fireplace or stove. You can use electric fireplaces and stoves.
2. The room is separated from the rest of the house by partitions. Tightly closing doors are installed. Ventilation may be needed for ventilation. All cracks must be sealed, as extraneous air flows and drafts adversely affect the quality of the dried material. The walls are also recommended to be insulated. On top of the insulation, they can be lined with brick, which maintains heat well from the stove and from electric heaters. Fans are installed to force the circulation of warm air.
3. Raw lumber is stacked on specially made durable metal shelves.

Before drying, you need to check the moisture level of the material. This is done using a moisture meter. high humidity causes early deterioration of buildings, the appearance of mold and fungus. Overdried wood is deformed due to moisture absorption and swelling. Drying of wood is usually carried out to a moisture level of about 8-12%. So that it does not crack, experts recommend treating the ends of the boards with a mixture of drying oil and sifted chalk. The consistency of the mixture resembles thick sour cream.

Lumber can be dried with or without bark. You just need to remember that birch, aspen, poplar and beech in the bark can be affected by rot. In general, the drying process can take up to 2 weeks. During this time, temperature fluctuations in the dryer should not be allowed. There must be a fire extinguisher in the dryer room. This is required by the safety rules.

Drying chamber operating modes

Do not immediately heat the chamber to a high temperature. In normal mode, it works like this:

1. Within 15-20 hours, the air in the chamber is heated up to approximately 45°C. The ventilation system is not working yet. Moisture should appear on the walls of the chamber.
2. When the temperature reaches 45°C, the supply and exhaust ventilation systems should be opened by a third. In about 2 days the temperature rises to 50°C.
3. The dampers must be fully opened and the temperature brought to 55°C. This is usually sufficient for a normal drying process. As soon as the humidity reaches about 8%, all dampers must be completely closed, turn off the heat supply. Fans continue to work even during the day. After the temperature drops to 40°C, dry lumber should be obtained, ready for use.

Optional equipment

As additional equipment can be installed in the drying chamber automation. Its properties:

• the system is able to work with chambers of different sizes and with different heat sources;
• is relatively cheap;
• does not require special knowledge for its maintenance;
• is easy to install;
• measures the temperature and humidity in the chamber;
• provides fully automatic or semi-automatic operation of the drying chamber;
• automatically controls the operation of valves, dampers and fans.

For the system to work, it is enough to set the thickness and type of lumber, the desired final moisture content. The system helps to dry various types of wood: pine, spruce, oak, birch, beech, linden, ash, maple, alder, hornbeam, poplar, aspen, sycamore. Every 2 hours, automation takes readings of humidity and temperature and makes the necessary adjustments to the operation of all air heating and ventilation systems. The approximate cost of such a system ranges from $400-450.

Building a dryer with your own hands is quite troublesome and expensive.

But the result covers all costs. This is especially important for those involved in the manufacture wooden products like furniture and woodcarving. Dry wood costs several times more than raw wood. In addition, in your own dryer, you can achieve a certain moisture content of the workpieces. Everything can be done independently with a great desire and the availability of a suitable place.

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 yourself want to engage in the production of wood products, you will also need a drying chamber for drying wood. Today we will talk about how to do it right.

The need to dry wood

How to dry a board efficiently and quickly? This question has been of interest to every carpenter since ancient times. Since ancient times, people have been storing forests for many years in order to have time to evenly dry it. The grandfather prepared a tree for his grandson, using the very material that his grandfather had left him.

The importance of properly dried wood is enormous! For example, if wooden furniture, which 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 tree can dry out and shrink in size, which means it will deteriorate!

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

Drying wood is a long, complicated 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 is not deformed. Drying of boards is carried out in steam chambers, where the possibility of internal damage is excluded.

The concept of wood moisture

For full perception essence of the drying process is worth a little plunge 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 in the walls of cells and in their cavities, filling the microcapillary system. 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 moisture 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 averages 30%. If the moisture content of a tree is above 30%, then it contains free intercellular moisture. The wood of a freshly cut or growing tree has a moisture content greater than the saturation limit, that is, it is raw.

Depending on the purpose of the wood blanks, it is customary to dry the wood 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 joints that affect performance (ski, 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 weather. Wood dried to such a moisture content is mainly used in standard housing construction, in the production of ordinary containers and when there is no need for interchangeability during assembly.

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

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

Wood drying modes

Depending on the requirements that apply to the quality of wood, lumber can be dried in different modes, which differ in temperature level. In the mini wood drying chamber, 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 dried wood and the design of the chamber.

There are modes of low- and high-temperature process. 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 able to provide defect-free drying of the material while maintaining the natural physical and mechanical properties of wood, including color and strength, which is important for drying wood to the transport moisture content of export sawn timber.
• Normal mode guarantees a defect-free drying of wood with almost complete preservation of the strength of the material with slight color changes, which is suitable for drying lumber to the final moisture content.
• The forced mode retains strength for static bending, compression and tension, but some reduction in splitting or chipping strength with wood darkening is possible, which is intended for drying wood to operational moisture.

According to low-temperature regimes, 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 carried out only after the material reaches a certain level of humidity, which is provided for by the regime.

High-temperature regimes provide for a two-stage change in the indicators of the drying agent, and it is possible to switch 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 regimes can be used for drying wood, which is used for the manufacture of non-load-bearing elements of buildings and structures in which darkening of wood and a decrease in strength are allowed.

The concept of a drying chamber

Chamber drying is the main method of wood drying. Drying chambers are required for drying softwood and hardwood to different categories quality. 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 damp tree with hot air and carrying away the evaporated excess moisture by humidified and partially cooled air.

The drying chamber is completely ready installation, which is equipped with all the equipment necessary for drying wood. According to the device, drying chambers for wood are divided into prefabricated metal and made of building materials. The latter are built directly in workshops or as separate buildings from materials that are widely used in industry. The chamber can be completely made of monolithic reinforced concrete. Its walls can be laid out of solid red brick, and the ceiling - from monolithic reinforced concrete.

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

Loading 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; solid if you organize contact with a heated surface; current that passes through wet wood; high frequency electromagnetic field that permeates wet wood.

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

The process of controlling the drying of wood in the chamber can be automated. Automation is able to maintain the humidity and temperature of the environment in the dryer at a given level. The temperature is regulated by the supply of coolant to the heaters or by switching on and off electric heater, and humidity - through the use of supply and exhaust ventilation and a humidification system.

The wood drying control system may have options 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 sources of heat supply for the dryer, autonomous heating modules can be used and gas, coal, wood waste, electricity and diesel fuel can be used.

Types of drying chambers

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

Tunnel convection kilns are deep kilns where stack stacks are pushed from the wet end to the dry end. These chambers must be filled from one end and emptied from the other. The pushing of the stacks (the process of filling the chambers and emptying) is done one by one with an interval of 4 - 12 hours. These chambers are designed for large sawmills and allow only transport drying of wood.

Chamber convection kilns are shorter than tunnel kilns and vacuum kilns for wood, the same parameters are maintained throughout the kiln during operation. With a blowing depth of more than 2 meters, the method of reversing the direction of ventilation is used to equalize the conditions for drying wood. Emptying and filling the chamber occurs on the one hand, if it has one door. Other loading systems are known, which are similar to the procedure for loading tunnel chambers. Any lumber can be dried to any final moisture content, so 90% of wood in Europe and Russia is dried in chamber dryers.

The condensation drying chamber differs from the previous ones in that the moisture that occurs 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 loss is also significant. The condensation chamber is mainly suitable for drying small volumes of wood, or for drying dense woods such as oak, beech or ash. The big advantage of such chambers is that there is no need for a boiler room, the price of a drying chamber for wood and the cost of drying is less.

Drying chambers 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 periodical action are characterized by the fact that they can be loaded completely for simultaneous drying of all material, and the drying mode of wood changes in time, in this moment remaining the same for the entire chamber.

According to the circulation method, there are chambers with incentive and natural circulation. Dryers with natural circulation are outdated, inefficient, the drying mode in them is almost uncontrollable, the uniformity of wood drying is unsatisfactory. For modern construction such devices are not recommended, and the existing ones must be upgraded. According to the nature of the drying agent, gas, air and high-temperature chambers are distinguished, which operate in an environment of superheated steam.

wood drying process

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

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

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

During the operation of the 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 process sawn timber, which is dried to operational humidity and subject to mechanical processing in the future.

Intermediate moisture heat treatment takes place during the transition from the second stage to the third or from the first to the second in high-temperature conditions. Moisture heat treatment is subjected to conifers from 60 mm thick and hardwood from 30 mm thick. The temperature of the medium in the process of heat and moisture treatment should be 8 degrees higher than the temperature of the second stage, but not higher than 100 degrees, at a saturation level of 0.95 - 0.97.

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

Drying chamber manufacturing

If you decide to make wood products with your own hands, then you simply need a drying chamber for wood. However, during the construction of the dryer, comply with all required standards. You will need a camera, a fan, a heater and a heater.

Build a dryer or allocate a separate room, one wall and ceiling of which will be made of concrete, and the other walls will be made of wood that need to be insulated. To do this, it is customary to create several layers: the first of them is foam, the second is wooden planks which are pre-wrapped in foil.

After that, 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 heat up to 60-95 degrees Celsius. It is desirable to continuously circulate water by means of water pumps in the heating element. Also, a fan should be placed in a home-made drying chamber for wood, which contributes to the distribution of warm air throughout the room.

Think about how the wood will be loaded into the drying chamber. One of the loading options can be a rail trolley. To regulate the humidity and temperature in the room of the drying chamber, you need to use working area corresponding thermometers - wet and dry. Provide shelves inside the dryer to increase the working space.

In the process of drying lumber, a sharp change in temperature in the working room is not allowed, otherwise this will cause the wood to warp or cracks appear in it. When building a drying chamber, it is extremely important to observe fire safety requirements. Therefore, in the immediate vicinity of the dryer in without fail install fire extinguishers.

And finally, remember that instead of heating element at home, you can use an electric stove with two burners. You can insulate the walls of the drying chamber with your own hands using wood shavings. It can be used instead of foil in the chamber with penofol, which is able to provide good reflection from the heat surface. In such a dryer, the wood is dried in advance for 1-2 weeks.

All woodworking enterprises make a profit from the sale of manufactured products. And the deeper the wood processing, the more profitable the production. Before buying equipment, each entrepreneur asks questions: What are the drying chambers for wood, what devices are equipped with, and which one to choose for your production?

If you choose the wrong equipment, then the profitability, on the contrary, will fall. And the greater range of wood drying kilns on the market makes the selection task even more difficult.

The main types of drying chambers are:

1. Dielectric.
2. Convector
3. vacuum
4. Aerodynamic

Wood drying method different ways was invented back in the 60s, but due to the high cost of electricity and the complexity of the design, technologies have only recently begun to be used. Most often all over the world use convector-type dryers. Why is this happening? Other designs can be used with a number of restrictions and subtleties of use. The main disadvantages of using inductive, condensing and vacuum wood dryers are:

1. Aerodynamic chambers require more electricity;
2. Condensation structures are expensive, and drying in them lasts 2 times longer than in convector ones.
3. Vacuum dryers are expensive and also expensive to maintain.
4. Dielectric require high costs for electricity, although they are considered among the best.

Convector dryers

Convectors are used for drying wood of various species and sizes. Due to the simplicity of the design, convector chambers are inexpensive to maintain, which indicates reliability. Therefore, in order to increase profitability, in 90 cases out of a hundred they are purchased.

Working principle of convector dryer

Heating occurs from a gaseous carrier (drying agent). When heated, the raw material is tapped. The drying agent can be steam, flue gas, air. The moisture released from the wood serves as an additional moistening of the agent, the excess is drawn into the atmosphere with the help of ventilation.

The exchange of air in a convector dryer is not higher than 2% of the total, so the energy efficiency is noticeable.

Complete set and equipment of the convector dryer

There are many configurations from various manufacturers, but there are basic options:

1. Equipment for an already built or under construction hangar of a drying structure.
2. Fully design with hardware.

Equipment case

The body is completely made of metal, assembled on a monolithic-pillar foundation. The metal used for manufacturing is carbon steel or aluminum with an anti-corrosion coating. Outside and inside the hangar is lined with aluminum sheets. Separate elements inside the structure (deflectors, false flows, amplifiers, etc.) are also made of aluminum. The chamber is insulated with mineral wool in the form of plates.

The structure is assembled in compliance with GOSTs and SNiPa. Options requiring additions and extensions are made according to an additionally developed scheme. The basic assembly is designed for an average snow load.

Convection chamber models

Convection drying chambers are produced by domestic and foreign companies. The most common are Helios: ASKM-7, ASKM-10, ASKM-15, ASKM-25. They are used for drying any type of wood of drying categories I, II, III and 0. According to reviews, these models work quickly, since German fans are used in the mechanism. And installation and maintenance of ASKM models is simple. The price is from 700,000 rubles, depending on the size and power.

Vacuum drying chambers

Designs are designed specifically for expensive raw materials (teak, wenge, rosewood, oak, anger, etc.). Vacuum dryers can also be used for any softwood or hardwood.

Working principle of vacuum dryer

Works vacuum dryer from convector heating of wood and vacuum removal of excess moisture. Temperature regime maximum +65 0С. But because of the vacuum, 0.09 MPa boils at 45.5 0C. This allows the drying process to be carried out without the aggressive effects of high temperatures, which does not create high internal stress, and the tree does not crack.

In the process of operation, the temperature rises by 65 0С, the automation is activated and the electric boiler is turned off. Top part wood begins to cool, and moisture from the inside begins to flow to the drier parts. For the entire drying process, such processes can occur up to 250 times. So the moisture is evenly drawn out along the entire length and depth of the raw material. The maximum moisture difference in different parts of the tree can be 0.5-1.5%, and completely dried has a moisture content of 4-6%.

Models of popular vacuum designs

The most common model of vacuum chambers is Helios. Drying chambers for wood Helios differ in power, load volume and other technical specifications. More about TX Helios in the table:

Aerodynamic chambers for wood drying

These drying chambers are reminiscent of a metal box finished with a professional aluminum deck. An aerodynamic chamber of various modifications is used for drying all types of wood, with a load of 3-25 m3. On request, you can purchase chambers of individual design with a load of up to 43 m3.

The aerodynamic chamber is good because the work is fully automated and a minimum number of workers is needed.

The frame of the aerodynamic chamber consists of solid metal, sewn on load-bearing frame. The chamber is made in the form of a quadrangular box, into which it is convenient to load wood by car or by rail. ways. The entire internal structure is equipped with automatic condensate collectors.

Principle of operation

Drying is carried out under the influence of aerodynamic energy. Heated air circulates in the chamber under the influence of a specially designed aerodynamic fan. The air in the chamber, due to compression, increases the temperature on the centrifugal fan, specifically on its blades. Thus, aerodynamic losses are converted into thermal energy.

Heat is forced into the chamber, depending on the design, in reverse or dead-end. The work of the aerodynamic chamber is started by one button “start” and opens only after the cycle is completed.

Models of aerodynamic dryers

The most common dryers of the aerodynamic type Gelos SKV-25F, SKV-50F, SKV-12TA, SKV-25TA, SKV-50TA, as well as Italian EPL 65.57.41, EPL 65.72.41, EPL 65.87.41, EPL 125.72.41, EPL 125.87.41. Developed by Helios, specifically for drying coniferous material. They cost from 1,500,000 rubles.

Dryers with microwave chamber

Microwave cameras have been invented quite recently. Such a dryer resembles a closed metal container. Operates under the influence of the reflective surface of microwave waves. Reminds me how it works microwave oven. Using a microwave chamber, you can dry the material of any section and size. microwave chambers have simple design and you can adjust the wavelength to any length. This made it possible to dry any raw material using a microwave chamber. The attenuation mode of the microwave wave allows you to adjust the temperature inside the chamber. And reversible fans remove excess moisture from the system. Microwave drying is compared with dielectric drying, which is considered the most efficient, but is not used in Russia due to high electricity costs.

The main disadvantages of microwave chambers include wood moisture control and the high price of microwave dryers and electricity costs.

Models of microwave dryers

In Russia, this drying technology is offered by the engineering company in Moscow "Investstroy" - "SVCh-Les". Such an installation costs from 1,300,000 rubles. It is necessary to service the microwave forest once every half a year, at a price of 100,000 rubles.

Only half of the future profit depends on which camera the buyer chooses. Building and insulating a box is only part of all the work. It is important that the component equipment is of high quality.

Equipment for drying chambers

Equipment for dryers can be divided into types:

1. Thermal system.
2. Exhaust and humidification system.
3. Rail structure for loading and unloading

Ventilation equipment performs the role of uniform distribution of heated air. Installing a low-quality fan entails uneven drying of raw materials. According to GOST, the air movement inside the chamber should be optimally about 3 m / s. This can be achieved using high-quality and powerful fans. All fans have a rotary or axial connection system.

This equipment depends on the capacity and model of the drying chamber. The heat generator can be an electric heater or a heat exchanger. They are installed only by specialists, and they are used to pump and transfer thermal energy to wood. A system, such as a mini-boiler house for liquid, gaseous or solid fuel, can also act as a heat generator. It is convenient when work is carried out on waste wood production.

The electra heater has a design consisting of a pipe and a chrome spiral wound around it. This generator has a small advantage: a simplified process for controlling the temperature inside the chamber.

Humidification system

To ensure a constant uniform humidity in the dryers, humidification and exhaust equipment is used. Humidification is carried out by complex system nozzles, piping, solenoid valve.

The hood is carried out using a fan (usually rotary). The equipment works according to the following technology: when the humidity drops, the fan automatically turns off and the hood does not function. At the same time, air humidification occurs by offsetting the evaporation of the liquid, which enters the nozzle automatically when the valve is opened.

When the humidity rises, on the contrary, the valve closes and the fan turns on.

Rail loading and unloading system

This equipment is installed at the stage of camera assembly. The system is made of rails, which are installed thoroughly. On top of them, stacked carts are attached, which are needed for storing wood. Raw materials are placed on them, and placed in a chamber, after drying, the carts are rolled out into the street and packaged.

When choosing a chamber for drying wood, it is better to use the services of professionals, but do not neglect the information of specialists on the network.