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. Using traditional technologies, wood is 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, wood species, final moisture content, quality category of the wood being dried and chamber design.
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 regimes, a three-stage change in the parameters of the drying agent is assumed, and from each stage to the next transition can be made only after the material reaches a certain level humidity, which is provided by the regime.
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%. High temperature regime 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 for drying coniferous and hardwood wood 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.
Drying chamber It is a completely ready-made 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 the 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; solid body, if you organize contact with a heated surface; current that passes through wet wood; high frequency electromagnetic field, which 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 external sources Heat supply for 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. Batch drying chambers are characterized by the fact that they can be fully loaded to simultaneously dry all the material, and the wood drying mode changes over time, depending at the moment remaining the same for the entire camera.
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. Based 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. Coniferous species with a thickness of 60 millimeters or more and deciduous species with a thickness of 30 millimeters or more are subjected to moisture and heat treatment. 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 maintain the temperature of the environment 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 in 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 a 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.
Drying is a mandatory stage in preparing wood before processing. To prevent logs from becoming deformed, they are dried under certain conditions, which are created in drying chambers. For your home workshop, you can make a wood dryer with your own hands.
The importance of drying
Since ancient times, wood that was cut down several years ago was used to make wood products. Furniture made from damp or improperly dried boards will warp or dry out and crack. When drying, the material shrinks, raw wooden beams will begin to move over time, and cracks the width of a palm will appear in the walls of the log house. Mold grows in damp wood. But overdried boards are also bad - the material begins to absorb moisture and swells.
Drying is carried out with hot air or steam, the process is long and expensive, but it gives the wood additional strength, prevents changes in shape and size, and the lumber is stored longer.
Drying modes
There are several modes of drying lumber. In self-made chambers, the temperature increases in stages, removing moisture from the raw materials. Drying technology is selected taking into account:
- wood species;
- dimensions of lumber;
- final and starting humidity;
- dryer features;
- raw material quality categories.
The drying process can be high temperature or low temperature. In the second case, primary processing is carried out at a temperature not reaching 100 degrees.
Low temperature regimes are divided into categories:
- soft - during the drying process, lumber retains all its properties, strength and color do not change;
- normal - color changes slightly, strength decreases slightly;
- forced - when chipped and split, brittleness is possible, the color darkens.
The change in ambient temperature at low temperature occurs in three stages. The transition to the next stage is possible when the wood reaches the specified moisture content.
High-temperature treatment is carried out in two stages. The second stage occurs when the moisture content of the raw material decreases to 20%. This technology is used when preparing wood for the construction of secondary structures, allowing for color changes and a decrease in strength.
Types of drying chambers
Drying of wood on an industrial scale is carried out in special chambers. Moisture is removed from the lumber by heated air and carried outside. Happens in the device full cycle drying wood. The room can be:
- prefabricated metal;
- constructed from building materials.
The latter are installed directly in carpentry shops or as free-standing buildings. The walls are made of reinforced concrete or brick. On large enterprises set up several chambers combined into a module with common system control and communications. Air circulates in the dryer horizontally or vertically-transversely. Wood can be transported to industrial dryers on rails on carts or laid out using forklifts.
Heat sources in the dryer:
- hot steam;
- radiant heat from special devices;
- heated shelves;
- electric current that passes well through wet logs;
- high frequency electromagnetic field.
The camera is equipped with basic and additional equipment. The main consists of systems:
- supply and exhaust ventilation;
- heat supply;
- hydration.
Additional equipment includes insulation of walls and doors, trolleys for laying material, psychometric equipment, and electric drive.
Industrial dryers are controlled automatically, small homemade dryers are controlled manually. Humidity is regulated by supply and exhaust ventilation and humidifiers. To measure the humidity in a room, a moisture meter is installed that collects data simultaneously in several places.
The following energy sources can be used to heat air: electricity, wood processing waste, liquid and solid fuel.
Types of dryers
According to the method of air movement, chambers are divided into:
- with natural;
- with forced air exchange.
Chambers with natural air exchange are low-performing and the process in them cannot be controlled. Therefore, they are used less and less.
Based on the principle of action, the following are distinguished:
- convective;
- condensation dryers.
In convection chambers, the wood is blown with streams of hot air, and heat is transferred by convection. They can be deep tunnel or chamber. Logs are loaded into tunnel chambers from one end and unloaded from the other, moving through the chamber, the material is gradually dried. The cycle duration ranges from 4 to 12 hours. Such cameras are installed in large sawmills. Chamber dryers are more compact; a single microclimate is maintained throughout the entire volume. Allows you to prepare any type of wood to the required condition. Therefore, most industrial dryers are chamber type.
Using condensation drying technology, moisture released from the material is deposited on coolers, accumulates in containers and is drained outside. The efficiency of such a device is very high, but the process is long and accompanied by high heat losses. The technology is good for preparing hard lumber in small batches. The price of equipment and the cost of condensation drying are lower than convective drying.
Setting up a homemade dryer
In order to make a dryer with your own hands, you can do without drawings. It is necessary to provide:
- camera room;
- insulation;
- heat source;
- fan.
The area of a dryer built by yourself usually does not exceed 9 square meters. meters. In a square-shaped room it is easier to ensure optimal movement of warm air. It is desirable that one wall of the chamber be made of concrete slabs, the others made of wood. All walls are insulated from the inside in two layers: polystyrene foam and foil board. An excellent and free insulation material is wood shavings. And the foil can be replaced with penofol, which perfectly reflects heat.
You can build a separate drying room with your own hands from aluminum; such a structure will last a long time. The frame is made of profile, it is sheathed with sheet metal, which is insulated from the outside. The thickness of the insulation is at least 15 cm. The floor is covered with roofing felt, and a thick layer of shavings is poured on top as thermal insulation.
Care must be taken to thoroughly seal the front door!
The heat emitter can be made in the form of pipes or heating radiators. The water temperature should be 65-95 degrees. It is heated by an electric boiler, wood stove, or gas boiler. For a small chamber, even a two-burner electric stove is sufficient. If the stove is located directly in the room, you need to line it with bricks. The brick will accumulate heat and gradually radiate it into the dryer. It’s easy to equip a convection chamber with your own hands by installing a fan heater as a heat source.
When setting up a dryer for your home woodworking workshop with your own hands, it is important to observe preventive measures. fire safety. There should always be a fire extinguisher near the building.
Constant circulation of warm water, which is provided by the pump, is important. To ensure that heat is evenly distributed throughout the room, a fan is installed. Workroom Equipped with a wet and dry thermometer.
To make it easier to load the board into the chamber, you can use a trolley on rails. And to increase the usable area, shelving is built on the walls.
The step-by-step instructions are as follows:
- We are building the foundation.
- We are building the frame.
- We cover the frame with sheets of metal.
- Installation of thermal insulation.
- Cover the floor with film and sawdust.
- Installation of supports from bars.
- Installation of heaters and fans.
The design of a homemade chamber for drying lumber in the video:
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 and 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 principles. 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 impact electromagnetic waves Drying wood takes no more than 6 days.
The advantage of the microwave installation is also high quality drying in the correct mode.
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, ventilation system, 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 regularly used. 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 drying chamber is the most important equipment in woodworking enterprises, as it allows you to remove moisture from lumber, thermally treat the wood to prevent biological destruction, impart resistance to rotting, maintain mechanical strength at the lowest density, and create minimal thermal and electrical conductivity in the wood.
What are drying chambers and complexes?
Drying chambers are industrial equipment used for drying various types lumber and wood species, deciduous or coniferous, for fumigation of pallets. To process large volumes of wood, modular chambers are combined to create large-sized drying complexes.
Types of drying chambers and drying modes
MAKIL PLUS LLC offers drying chambers for lumber, with boilers (heating units) that burn (recycle) wood waste, which are divided into two types, depending on the coolant used:
- Coolant - water. These installations consist of a boiler and water heaters, circulation pumps, automation adapted for use in cold weather (anti-freezing system), and a water treatment system. The system copes well with water softening, and the boiler power is selected based on the volume of drying chambers and additional consumers. Based on the above, a drying complex for drying water-type lumber has a high initial cost of the project, since it includes many expensive elements and requires specialized installation.
- Coolant - air. The system includes an air heating unit with a capacity of 100 - 500 kW, a centrifugal fan and an air duct system. The initial costs for this equipment are included in the price of the camera; the customer receives a ready-made solution without additional capital investments. The universal air heating unit has a higher efficiency compared to a water boiler and is capable of producing both minimum and higher temperatures than a water-type wood drying chamber.
To process wood in drying complexes, three main modes can be used: soft, medium and forced. When maintaining a soft mode with a temperature of up to 55°C, during the drying process the wood retains all its properties without changing in strength or color. When using the average (normal) mode with temperatures up to 67-70°C, the shade of the wood changes slightly. For high temperatures up to 85-90°C with forced mode, rapid drying is characteristic, but with darkening of the wood.
Technologies used by the company in the manufacture of cameras
The main advantage of drying kilns for wood is:
- Autonomous operation of the system in the absence of heating networks
- Minimum costs for fuel with simultaneous waste disposal
- Compact placement of main and auxiliary equipment
- Possibility of dismantling equipment and moving it to a prepared foundation
- High degree of thermal insulation of the chamber as a whole, tightness and insulation of sliding gates
- Fast warm up to required temperature
- Minimum heat loss through structures
- The drying agent and coolant are both air and water.
- Possibility of quick conversion to coolant.
- Easy to maintain, easy to control.
- Possibility of drying in any mode.
- Drying complexes are made of 80% Russian materials not requiring a long wait when replacing.
- The modular design allows you to add new drying chambers without stopping existing chambers.
- Thermally protected reversible axial fans with Siemens/ electric motors
- Litouch drying process control system from the world leader Logika concern
- The ability to program the controller up to 16 phases of lumber drying, which allows you to create special climatic conditions inside the chamber for the drying process.
- High maintainability during operation
These technologies not only make it possible to dry lumber without changing color or cracking, but also ensure trouble-free operation of the equipment.
Economic payback of wood waste chambers
Economic payback is one of the benefits of equipment from the MAKIL PLUS company. A wood drying complex, on average, pays for itself within a year, since the cost of drying 1 cubic meter, including the cost of servicing the device, is about 450 rubles. In addition, purchasing a completely ready-to-use installation solves the problem of wood waste disposal. At the same time, mixed waste even with a high percentage of moisture is suitable for work.
The MAKIL PLUS company produces drying equipment with chambers with a volume of 10 to 140 m 3, which are manufactured according to ready-made projects, and according to individual customer requirements. Drying complexes for wood “MAKIL PLUS” are already operating in every region of Russia and are becoming more in demand every day.
More information on this equipment and its purchase can be obtained by contacting the managers of our company.
How to make a cheap vacuum dryer for wood with your own hands
Hello dear readers and subscribers of Andrey Noak's Blog! Do you know what is most important about wood materials? This is high quality drying.
Each enterprise uses a special drying technology. But if you want to dry the material yourself, then I will tell you how to make a vacuum dryer with your own hands. But first, a little theory.
Wood is a hygroscopic material, this is due to the fact that wood absorbs water evaporation from the air.
Each wood material has varying degrees of moisture content, depending on storage conditions and the environment.
Why dry wood?
Drying is the process of removing moisture from a material through evaporation.
When a tree grows, its metabolism is carried out by the circulation of moisture through the trunk. When cutting, the circulation stops and the moisture begins to evaporate.
In order to build a house or make any wooden product, you need to properly dry the logs.
Purchased vacuum dryer
Well-dried material is protected from fungi, damage and cracks, and its service life will significantly increase.
If the drying was of high quality, then the product will serve you for many years.
Wood is divided into categories depending on the degree of moisture:
- wet is considered to be one that has been in water and its humidity is one hundred percent;
- freshly cut, with humidity ranging from 50 to 100%;
- air-dry, in cases where the material has been exposed to air for a long time.
The moisture content of such wood is approximately 15-20%;
- room-dry, with humidity 8-12%
- absolutely dry, the humidity of which is exactly 0.
Wet material will be difficult to process, but is flexible and elastic.
Properties of dry wood
Dry material has greater biological resistance. After drying, strength increases and withstands load better. It is easy to process, and the products do not crack after processing, unlike raw wood, in which the process of rotting may even begin under suitable conditions.
Ancient drying methods
A long time ago, people used only wood to build houses.
In houses you can find wooden utensils. Therefore, it was necessary to come up with ways to properly dry logs as the main building material.
At that time, people used several drying methods.
For this method, they took the necessary piece of wood, water and sawdust. The water was heated to 70 degrees, the workpiece was placed in it, then it was covered with sawdust and left for a certain time so that the material was steamed.
After drying, the workpiece did not crack, and the structure became denser and more flexible.
Paraffinization is another method that has been widely used for a very long time.
Here, wooden blanks were dipped into paraffin heated to 40 degrees and left for several hours. It was important to maintain the same temperature of the substance.
After the procedure, the wood should dry for several days. The properties of the material change after drying. The workpiece does not crack, does not rot, and acquires an original tinted shade.
Craftsmen used this drying method to make wooden utensils, then finished product skillfully painted.
Wood moisture content, measurement methods
There are many ways to determine humidity.
To accurately determine the moisture content of wood, special instruments are used. Electric moisture meters are capable of determining humidity with an accuracy of 2-3%. The basic principle of such devices is based on the fact that wood of different moisture content has different electrical resistance.
There are many more “folk” ways to determine humidity, but only professionals use them:
- By weight, weighing identical pieces of wood of the same species in hand or on scales one by one.
- Experienced specialists determine humidity “by eye”, by the presence of cracks and breaks.
- According to the shavings.
When processing lumber, small shavings are compressed in a fist. If it wrinkles easily, then the material is wet. Dry wood is indicated by the fragility of the chips, but if the chips crumble, then most likely the wood has been overdried.
- By cutting. If, when processing wood with a chisel, a wet mark is noted, and the material is easily and smoothly cut, then it is not dried. It is better not to carve on such a surface, as cracks and flaws will appear when it dries.
Assembling a vacuum dryer at home
It is very profitable to dry the wood yourself, and if you do this using a vacuum dryer, the drying time will be reduced significantly.
But buying vacuum drying from factories is quite expensive, and I will tell you how you can make it yourself, and also save on it.
Drying at home takes place in special chambers.
To set it up, you will need a large room, a heat source, and a fan to distribute the heat inside the structure.
The floor, walls and ceiling of such drying must be very strong; reinforced concrete or an iron conveyor is best.
If you take a cheap used iron conveyor for example with railway, then this will even be a very cheap option. Or, for example, to reduce the cost, you can weld the conveyor yourself from old iron.
To preserve heat inside the chamber, we reinforce the walls with foam plastic and line them with clapboard.
Instead of polystyrene foam, you can use mineral wool or other insulation.
To reflect heat, you need to lay a special material. You can use foil, but penofol will also work, especially since its heat-reflecting and preserving qualities are much better.
We proceed to installing the heating device.
The entire heating system must be installed separately from other heating circuits and must be constantly running. You can use a heating radiator, with which the water is heated to 65-90 degrees.
In order for the heat in the chamber to be equally distributed, a fan is required, otherwise there will be uneven drying of the raw materials and, accordingly, low quality.
One more point, the temperature in the chamber should change smoothly and gradually.
When building your own drying facility, you must comply with all fire safety rules.
An important point is the construction of a system for loading lumber into the chamber. You will be loading large and fairly heavy boards. Carts that move on rails or a forklift work well for this. The material inside is placed on shelves or simply on the floor. To control the drying process you must install special sensors, and these are thermocouples and vacuum (pressure) sensors.
If you do everything correctly, you can get very high-quality wood with a good presentation.
The main point in the construction of a dryer is to achieve the necessary parameters inside the chamber, and the materials and equipment that were used do not matter.
In your chamber you can reduce the drying process of raw materials to 2 weeks.
How does vacuum drying work?
After you have placed the material in the drying chamber and closed the door tightly, you can begin drying. Air is extracted from the chamber to create a vacuum of about 9 - 10 bar. It is known that when pressure decreases, water boils faster.
Thanks to this technology, bound and free moisture will move evenly from the center to the periphery, thereby ensuring high-quality and uniform drying of the material, regardless of location.
Dry top wood cells will absorb moisture from those located in the core.
First, thin places dry out, then moisture from thicker layers moves to the dry ones, thereby moisturizing them. If this process is interrupted, the material may collapse as thinner layers begin to shift.
Coating the ends of thick lumber to prevent rapid release of moisture and the formation of cracks during drying.
To prevent displacement, lumber is treated with a special mixture made from chalk and drying oil.
Often the end parts of workpieces need to be processed.
Drying excludes the use of humidification systems, and thermometers should not be installed in the chambers. The process can be controlled using special sensors, which are controlled externally, often in a separate vestibule.
Very often, vacuum installations are used for drying expensive species such as oak, merbau, padauk, wenge, and zebrawood.
It is very convenient, since the wood is practically not destroyed when dried.
My help
I have the opportunity to provide advice on drying technology, selection of new and used equipment.
You can contact me through SUPPORT.
My new book was recently published, which provides recommendations on the operation of drying systems in production. The information given in the book is simply unique, you definitely won’t find it anywhere else.
More information about the book can be found in the “MY BOOKS” section.
Good luck and see you again!
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Purpose of modular wooden drying chambers.
Drying chambers SCM series, students in the "100" category best products in Russia.", They are designed for drying wood from hardwood and softwood in accordance with quality categories 0, 1, 2, 3 depending on the purpose of the wood. Drying chambers our products certified and answer " General requirements to monitoring and control systems environment drying chambers" and "Requirements for quality drying" in accordance with the Russian Technical Material (RTM) guidelines for chamber drying in wood.
Installation, design features of SCM wooden dryers.
Striving for maximum speed assembly and speed wooden drying chamber partially included in SCM models. Modular design wooden drying chamber simplifies delivery and installation.
To meet the wishes of the company's customers, many standard sizes Drying chambers. Now TERMOTECH develops and produces wooden drying chambers and complexes with pneumatic load from 6 to 180 m³ operating on thermal energy generated by burning wood waste or stationary boiler houses.
Drying chambers with a load capacity of up to 20 cubic meters. They have a body in the form of a complete container with a supporting frame, the dimensions of which can be shipped by road or rail.
High mobility and low cost installation work allow you to build a heated drying cabinet with a heated floor. When renting production areas wooden drying chambers with underfloor heating is more practical. With a low probability of frequent disassembly, for example. If we have our own space, we can offer a version of the drying chamber body without floor insulation. The cost of chambers without floor insulation is lower, we need more work for installation.
It is necessary to clamp the cement cement independently along the height of the already welded track at our company's location, on the transverse stiffener. mollusk Drying chambers volume 20 cubic meters up to 180 m3. They are made in the form of modular blocks, are easily transported, and are easily connected with screw connections. The time required to assemble a modular drying chamber ranges from 4 to 8 hours, proportional to the number of modules.
Seams are sealed when installing drying modules using a special rubber profile and silicone sealant, which is delivered to the customer along with the drying chamber.
The roof of modular wooden drying chambers, depending on the loading volume, is made one-sided or two-sided. All SCM drying chambers are equipped with a condensate collection and removal system, which increases the service life of the fence. For better sealing Wooden loading doors of the drying chamber are made with a floating hinge, closing the door door at four points using screws.
The door seal is a heat-resistant 3-strip profile. supplied drying chambers Control system equipped with drying procedure, semi-automatic fully automated (computer-based), S control of fuel supply, boiler operation, blinds, ventilation curtains, etc.
proposed wooden drying chambers manufactured both in a state of rest and in a transitional version. Transitional version allows the customer to organize the most efficient continuous technological process and increase the productivity of drying chambers due to more rational use of loading and unloading time compared to blindness.
Loading wood into wooden drying chamber produced by standard wheels. Depending on the load capacity of the chamber, transportation of strings can be longitudinal or transverse. When drying wide untreated wood, excluding the cross-tip of the wood, the pedestal is equipped with a block-type clamping mechanism.
In this case, the force on the upper types of beams is equal to the force on the lower types of lumber. In numerical terms, this force is equal to the force of the fund's weight.
Heating system.
Modular drying chambers and wooden complexes produced by Termotech operate on thermal energy obtained from the combustion of wood waste in the heat generators of our industrial or stationary gas boilers. Water heated to 95°C by a pump is provided through a supply pipe to the side walls wooden drying chamber radiators, after passing through which it enters the boiler at a temperature of 75 ° C.
Useful water registers are single-sided double-sided bimetallic tube heaters (steel bolts with aluminum plates). It refers to the drying chamber of a specific boiler acting on the loaf (chips, leftovers, stove - 70 ... 100 vol.%) in a mixture of wood waste (30%).
When large number chips (100%) solid equipped with a boiler funnel - relying on sawdust, feeding a screw mixer or carburetor with mechanical load, which allows heating wood products of each fraction (slabs, shavings, shavings, bark). If there is insufficient wood waste, we can fill the supplied heat source directly to burners, gas or oil stoves.
For more efficient and stable operation of the boiler, a fan is installed in the turbine, and an ejector is installed in the chimney flues.
Air exchange system, fans, brackets.
For heat exchange between water registers and internal air wooden drying chamber A centrifugal fan is installed, the electric motor of which is mounted externally Drying chamber for drying wood.
The use of rotary fans made it possible to reduce energy consumption for ventilation in wooden drying chambers produced by TERMOTECH by 1.7 times compared to manufacturers of similar products. Drying chambers. Such effective results were achieved thanks to the rational redistribution of power when installing the fan. The abnormally high pressure was reduced, resulting in increased ventilator efficiency.
In addition, blood pressure was reduced in cubic dependence, and increase power - squared. With aerodynamic calculation wooden drying chamber The greatest losses occur when ventilation system ventilated.
The loss of fan motor power is directly proportional to the cubic speed of the drying agent. Therefore, further optimization was carried out from the condition: The speed of the drying agent next to the sawdust storage should be between 1 and 1.5 m/s. Based on quality conditions, the same speed is adjusted by CNIIMOD for drying wood under mild and normal conditions.
Because the domestic industry does not produce specialized fans for Drying chambers(high performance, low pressure) - all fan wheels are of their own shape.
Fan wheels are statically and dynamically balanced. In wooden drying chambers with a wood load of up to 12 m ³ The fan wheels are mounted directly on the motor shaft.
Fan for wooden drying chambers with a wood volume of more than 12 m ³, carried out through bearings and pulleys. The fan bearing bearing is the most heavily loaded device in the dryer chamber.
For greater reliability, we use FAG, the company is the world's leading carrier (Germany) of the BND series with FAG spherical bearings. These bearings have a labyrinth seal, grease nipple during maintenance and are centers that can withstand heavy loads, as originally developed for crushing and grinding machines, roller drives for presses and wind turbines.
The most optimal transverse extrusion of the chimney and temperature conditions inside drying dry baked lumber It comes with screens and external blinds. This design allows easy access to inspection and maintenance of the rotating fan and registers. To exchange air with the atmosphere in Ljubljana wooden drying chamber Aluminum inserts and exhaust valves are installed.
Fences, wall insulation.
Corps of all Drying chambers have optimal thermal insulation designed for the middle zone, a layer of solid mineral wool slab that does not absorb moisture and has a high degree of fire resistance.
All steel elements that prevent corrosion in the drying chamber are protected by a corrosion-resistant coating and a waterproof coating. When shipped In regions with different climatic conditions, it is possible to build a thickness that provides the necessary thermal insulation.
How to make a wooden drying chamber
In accordance with the technical task of the customer, there are technological possibilities for the production of monolithic polyurethane foam insulation from closed enclosures wood dryingFists, or a combination of thermal insulation consisting of rigid hydrophobic mineral wool (water absorption coefficient by volume - 1.5%), TIS mats - TIB TU 2123-299-89 and polyurethane.
Polyurethane foam has the best insulating properties, the lowest thermal conductivity coefficient (W 0.019-0.28 / M º K), low weight (40-60 kg / m³), high adhesive strength and corrosion protection.
The warranty period for the insulation of aluminum polyurethane foam sandwich panels is 30 years. ( Detailed description And comparative characteristics rigid polyurethane foam and mineral wool, see here.) Internal walls wooden drying chamber made of aluminum sheet or steel with heat-resistant coating.
Outer envelope drying chamber walls made of galvanized, corrugated film 0.8 mm thick. Places where dew is likely to occur (the inner surface of the door, inlet and outlet valves) are made of aluminum.
Thermal treatment of wood.
At the request of the client for the production of dry wood from 0, 1, 2, 3 quality categories, wooden drying chambers they are done universal humidification, conditioning and steam system - development and production by TERMOTEH.
The diversity of the system is achieved by generating dry entropic steam and increasing the moisture content, i.e., creating the necessary and sufficient conditions for high-quality hardness and drying of wood, as well as thick conifers.
The processing device must remove the internal tension in the wood when the wood is already dry to ensure the stability of the workpiece geometry after processing in woodworking machines. This is a concept, a textbook. Very often, the storage conditions for carpentry products after sawing wood are violated, for example: lack of sunscreen for protection from the sun, uneven air flow of the chimney with natural air circulation, loading one drying chamber into several packages with different sawing periods (sometimes important - months).
Therefore, there is an uneven distribution of moisture throughout the volume of one plate and the volume of the foundation. This leads to tension and inappropriate drying conditions. Avoid rejection with moisture compensation, which is achieved by conditioning the wood treatment at the beginning of drying. For the solid beech process, a steam process is necessary to create a uniform color palette for the wood of different ages. The color intensity is proportional to the duration of the steam.
In any case, when heat treating wood, temperature acts as a catalyst (fast) in the process of uniform redistribution of moisture through the material (moisture transfer), and the high humidity of the desiccant slows down the drying process (stops the removal of moisture), moisturizes overdried wooden parts.
The duration of moistening depends on the thickness and type of wood. Woodworking recommendations for woodworking is “wood drying technology”, which is equipped with drying chambers for our products. CAM "Module C1", "C2-Module" includes the entire thermocouple drying program. In the absence of a water supply network, the humidification system, air conditioning system and water vapor can work in an unnecessary mode, an unnecessary tank with a consumer inside wooden drying chamber, whose volume is sufficient to complete the entire drying cycle.
In case of emergency in the event of a fire disaster, the same humidity should be used by a conventional fire extinguishing system wooden drying chamber in accordance with PPB-01-93 “Fire Safety Rules in the Russian Federation”.
If the client has available premises that are outdated Drying chambers for drying wood we are ready to provide technical solutions and equip necessary equipment for their conversion or modernization of drying chambers.
Convective drying chambers for wood
The presence of drying equipment for drying wood and lumber, as a rule, is one of the main attributes of modern woodworking production.
Board dryer: creating and using a drying chamber
Convection-type drying chambers have found wide application both in Russia and abroad. Convective wood drying technology makes it possible to obtain high-quality lumber with the required moisture content. Modern drying chambers are equipped with automation that allows you to control and monitor the drying process remotely.
Negotsiant-engineering company supplies drying chambers for wood Russian production.
The proximity of production, the introduction of the latest technologies and well-functioning service make it possible to provide our Customers with inexpensive and high-quality drying equipment. We sell both small (with small loading volume) drying chambers and major projects for various industries.
Features and advantages of drying chambers
Automatic control and monitoring of the wood drying process
Minimum delivery, installation and commissioning times for drying chambers
The design of the drying chambers is made of aluminum and stainless steel elements
The ventilation and heating system is equipped with reversible fans made in Germany
The walls of the drying chamber building are insulated with Finnish mineral wool with basalt fiber
Inspection door as standard
Sales and service of drying chambers
We supply, install and commission drying chambers.
We provide warranty and service.
Drying chambers are made to order at the request of the Customer
Loading volume from 45 m
We offer comprehensive solutions for organizing a wood drying area using boiler equipment and wood waste recycling equipment.
The cost of drying chambers is lower than competitive ones.
Technical characteristics of drying chambers
Optional
Supervision of installation and commissioning works
A specialist arrives to carry out installation supervision work, takes measurements of the foundations in accordance with the documentation provided in advance, and then begins assembling the drying chamber with the customer’s team.
Upon completion of assembly, the specialist puts the drying chamber into operation and trains the customer’s personnel.
Catalog drying chambers for wood
A detailed description of the design of a convective wood drying chamber can be downloaded here
Photos of completed projects for the installation of drying complexes
The drying mode depends on the type of wood and the thickness of the lumber. To prevent the boards from cracking or warping during drying, they are pre-steamed, for which wet steam is supplied to the chamber.
First, they are heated for 1-2 hours at a temperature of 50° C.
DIY lumber drying chamber
After steaming, increase the temperature to 60 ° C, then repeat the steaming and, if necessary, steam up to three times. With the correct drying mode, the wood does not undergo large deformation.
Rice.
6. Scheme of drying methods:
a - periodic air-steam dryer, b - electric dryer operating on high-frequency currents; 1 - air heaters, 2 - supply channels, 3 - pipes for steam release, 4 - exhaust pipes, 5 - special cart (track), 6 - damper, 7 - movable electrode, 8 - fixed electrode
Soft woods are dried at a temperature of 40-75° C, hard wood - at 35-55° C.
The drying temperature of lumber should not exceed 80° C, since at higher temperatures the structure changes surface layers wood, i.e., the material is, as it were, hardened. Such material is difficult to process with cutting tools.
At the beginning of drying, the air should have relatively high humidity and low temperature.
The higher the moisture content of the wood, the greater the amount of moisture the air introduced into the chamber must contain to avoid cracking of the wood. Then, as the material dries, the air temperature is increased and the humidity is reduced to a minimum.
For drying softwood and hardwood lumber different sizes In most factories, in model shops, periodic steam-air chambers with stimulating reverse circulation are used.
Unloaded lumber from drying (dried at a temperature of 60-70 ° C to a humidity of 10-12%) before putting it into production is kept in the conditions of the production workshop for 2-3 days to free the wood from internal and surface stresses (normalization) obtained in result of drying.
In addition to steam-air drying chambers, there are gas chambers.
In a batch drying gas chamber, smokeless gas is used to evaporate moisture, obtained in the furnace by burning raw wood waste, which is pumped through flues onto stacks of lumber using an axial high-pressure fan. The chamber design includes a steam humidifying device.
In the woodworking industry, batch gas dryers are used, operating on natural gas, with a furnace in which the gas temperature reaches 1000-1300 ° C, but after circulation in the chamber the mixture is supplied at a temperature of about 100 ° C.
The working gas mixture is smokeless. Lumber dried in properly operating gas chambers does not darken. Each of the drying chambers can accommodate 4 stacks of boards, each with a volume of 1.8X2.6X6.5 mm. Gas chambers are used for routine drying of softwood lumber.
Lumber can be dried using the high-speed method in electric dryers using high-frequency currents. Drying using high-frequency currents lasts only a few hours, and the material dries evenly, without cracking or warping.
Wood waste during such drying is significantly less than in steam and gas dryers, and amounts to no more than 5%.
The peculiarities of heating semiconductors and dielectrics, which include wood, in a high-frequency electric field are that heat is released directly in the heated material and the temperature of the material can increase within a short time.
For example, a wet board can be heated to 100°C in 3 minutes. The wood is simultaneously heated throughout its entire thickness. The current power absorbed by the material can be adjusted by selecting and changing the electric field parameters.
The following should not be considered a DIY tutorial. Homemade chambers for drying wood exist and there are quite a lot of them. But at the same time, the vast majority of them are far from perfect.
Drying chambers are calculated and designed, which means this must be done by specialists.
Even if you decide to make a drying chamber “with your own hands,” then at least, before building, order a project from specialists or find and study literature on the design of drying chambers.
Woodworking, its cost, and the quality of products depend on the quality of drying of lumber. In turn, high-quality chamber drying of wood depends not only on adherence to technology (correct laying of lumber, adherence to regimes), but also on the design of the drying chamber.
I hope that the information provided here will allow you to avoid mistakes when purchasing or help improve the convective wood drying chambers available in your production.
Next, we consider the design of a wood drying chamber with an overhead fan arrangement (vertical-transverse circulation of the drying agent), since in modern convective chambers for drying wood this is the most common aerodynamic design.
All calculations are given for easy-drying wood species: pine, spruce, cedar, and so on.
Lumber with a thickness of 50 millimeters is taken as conditional.
Convective drying chamber for wood
For uniform drying of wood along the height of the stack, the distance from the wall of the drying chamber to the stack of lumber must be at least a quarter of the height of the stack (see Fig.
figure), otherwise it is necessary to ensure a narrowing of the air channel from top to bottom.
Diagram of a convective drying chamber (sectional view)
With two or more stacks, the distance between them (in Figure A) should be at least 15 - 20 centimeters.
For uniform drying of lumber along the length of the stack (with a board length of 6 meters), drying chambers, as a rule, must have at least three fans.
Wood drying kilns must be designed to allow air to flow only through the stack of lumber.
Loose passages reduce the air flow through the stack (therefore drying the wood more slowly) and make it uneven, which increases the unevenness of the moisture content of the dried lumber.
The free passage of air on the sides, top, and bottom of the stack must be blocked by curtains, thresholds, etc.
It is recommended to install the side curtains in such a way that they overlap the stack by 10 - 15 centimeters from the ends, this will reduce cracking of the ends. It is advisable to make the top curtains movable, since drying the wood leads to a decrease in the height of the lumber stack.
Air circulation during chamber drying of wood
Circulation is carried out using fans, the air passes across the stack. The fan compartment is separated from the stacks of lumber by a false ceiling and has a baffle designed to prevent “short circuits” in the air flow. This is very important!
In some homemade drying chambers, this partition is missing, as a result, a significant part of the air is uselessly chasing over the false ceiling, without getting into the stack.
Single-stack drying chambers for lumber allow the use of non-reversible fans; for two or more stacks, the fans must be reversible.
Requirements for fans for drying chambers
If the fan electric motor is located inside the drying chamber, it must be made in a moisture-proof design and have a heat resistance class of “H” (up to 100 degrees); an electric motor that does not meet these requirements must be moved outside the chamber.
In homemade drying chambers, class F electric motors are often used. As a result, they fail at intervals of 3 to 6 months.
If the fan performance is insufficient, chamber drying of wood proceeds more slowly, and the unevenness of humidity across the width of the stack increases.
Heating of convective drying chambers.
The heat required to evaporate moisture from the wood is supplied by heaters, their power is determined at the rate of 3 - 4 kW per cubic meter of lumber.
To ensure this, the heat removal surface of the heaters should be about 3.5 square meters per cubic meter of lumber. It is not recommended to use electric heaters: drying wood will have a higher cost. Probably for many the best option will use a boiler running on wood waste.
It is desirable that the air entering convective drying chambers during ventilation should pass through heaters before entering the stack.
Therefore, if there is a reverse fan, the heaters are usually arranged in two rows, as shown in the figure. If the heaters are located in one row, and the fans are reversible, then the heaters should be located between the ventilation ducts of the pressure side and the vacuum side.
This drying chamber design is characterized by slightly higher heat losses, but lower manufacturing costs.
Chamber drying of wood requires less thermal energy if convective drying chambers are equipped with recuperators (heat exchangers). In the recuperator, heat exchange occurs between the incoming and outgoing air during ventilation. The use of a recuperator, in addition to saving thermal energy, reduces temperature fluctuations during ventilation, therefore, the drying of lumber will be of better quality.
Unfortunately, convective drying chambers for wood with recuperators are practically not produced in Russia.
Thermal insulation of drying chambers for wood.
Total temperature difference is 115 degrees. Consequently, if thermal insulation is poor, part of the money you pay for heat will go to heating the street.
In addition, if the thermal insulation is poor, moisture will condense on the walls, floor and ceiling of the drying chamber, which will not allow maintaining the air humidity set according to the regime at the initial stages of wood drying.
If possible, drying chambers should be installed indoors; this will reduce the possibility of cracking of lumber during unloading due to sudden temperature changes. But even when installed indoors, good thermal insulation is required.
Tightness of drying chambers for wood.
At the initial stages, chamber drying of wood is carried out at high humidity, so moist air should be removed if and only when it is required by the regime.
If the airtightness is poor, it is impossible to maintain the specified air humidity. Using a humidification system does not help: even if steam is supplied, a significant part of it falls out as condensation due to contact with cold air.
Therefore: wood drying chambers must be sealed, have no cracks, and sealing gaskets must be installed on the gates. Homemade drying chambers especially often have poor sealing.
In industrial chambers, deterioration of tightness usually occurs due to loose closing of the gate due to careless adjustment during installation.
Supply and exhaust ventilation during chamber drying
Typically, the design of drying chambers provides supply and exhaust ventilation due to excess pressure on the pressure side and reduced pressure on the vacuum side; additional fans are not used.
The required total cross-sectional area of the air ducts for such ventilation is approximately determined at the rate of 40 square meters. centimeters per cubic meter of standard lumber on the pressure side and the same amount on the vacuum side. The air ducts are equipped with curtains that open and close as needed.
To reduce the formation of condensation in air ducts, their thermal insulation is desirable.
Humidification system for chamber drying of wood
There is an opinion that drying of easily drying wood species can be carried out without moisture treatment.
Indeed, when drying freshly sawn wood, the air humidity required by the regime is gained in 6 - 12 hours. However, if chamber drying of wood is carried out, which after sawing has lain for 2-3 days, then this time can extend for a day or more, which is no longer desirable.
Drying chambers for lumber - choosing equipment for drying wood
Thus, a humidification system for chamber drying of lumber is still needed. For humidification, use steam or finely sprayed water (droplets hang in the air) using nozzles. A very common mistake in homemade drying chambers is that when spraying, water gets on the thermometer and air humidity sensor. As a result, the automation receives false information about climate parameters.
This is not acceptable.
About the requirements for gaskets.
Gaskets are not an element of the design of the drying chamber and, of course, are not supplied with it, but without complying with the requirements for them, high-quality drying of wood is impossible, so let’s talk briefly about gaskets.
The gaskets must be made of dry lumber and have strictly the same thickness. The thickness of the gaskets with a total stack width of up to 4.5 meters must be at least 25 millimeters, with more It is recommended to increase the thickness of the stacks to 30 - 35 millimeters.
If the thickness of the gaskets is insufficient, chamber drying of wood proceeds more slowly, and the unevenness of humidity across the width of the stack increases.
The width of the gaskets is 40 - 50 millimeters.
The surfaces of the gaskets in contact with the lumber must be planed.
High-quality drying of wood largely depends on the correct installation of lumber, so be sure to study this issue.
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