Vacuum drying of wood technology. Advantages of vacuum drying wood. wood drying process

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.

For many centuries, wood has been the main material in the manufacture of furniture.
The furniture was made from wood that had been cut down a few years ago.
In the case of using raw, non-dried wood, the boards dry out quickly and become covered with cracks.
When dried, the tree shrinks, therefore, structures erected from initially raw material may squint over time, lose strength, and geometry.
Damp wood is a great place for mold to grow.
At the same time, an excessively overdried building material is also bad, since such material actively absorbs moisture, 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. At the same time, steam or hot air is supplied to the surface of the lumber. This process takes long time and is quite expensive for the manufacturer. Largely because of this, furniture made on the basis of natural wood is significantly 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 can be used various modes. 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.

Soft dry. Here lumber retains its characteristics and properties. Therefore, changes in color or strength parameters of the product are not observed.
Normal drying. Color may vary, but only slightly. Strength parameters are somewhat reduced.
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 right level lumber moisture.

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.

Build with your own hands easier system where is used natural air exchange. At the same time, its efficiency indicators are significantly inferior forced circulation air. 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.

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. Similar designs 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.
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 that requires detailed study. specifications 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 necessary for construction and repair are obtained. different thickness. 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 House master will always be provided quality material to perform 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:

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.
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.
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:

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.
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.
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.
The thermal insulation is installed mineral wool 10-15 cm thick.
The floor is covered waterproofing film and sawdust.
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.
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.
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:

You need to choose a room in which there is a fireplace or stove. You can use electric fireplaces and stoves.
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. For forced circulation warm air install fans.
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

The chamber cannot be immediately warmed up to high temperature. In normal mode, it works like this:

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.
When the temperature reaches 45°C, open the air supply one third and exhaust system ventilation. In about 2 days the temperature rises to 50°C.
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 capable of working with cameras different size 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 dry various breeds 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 are more advantages to this method. The use of vacuum drying avoids the destruction of lumber, their cracking, warping or other possible defects. In this case, a piece of wood will dry out evenly, regardless of its thickness and length. This will take relatively less time, because the evaporation of moisture from wood in a rarefied environment occurs very quickly.

The equipment required for this is easy to transport and install, so that it can be used in the most different places, even directly on deforestation.

However, vacuum drying equipment is expensive, so small businesses and households can almost never afford it. Despite the small volume of the chambers (up to 10 cubic meters), the device consumes a lot of electricity. Perhaps this is the limit of its shortcomings.

professional drying

The body of the professional wood drying chamber is made of stainless steel. For complete sealing, its top is covered with elastic rubber, framed in a metal frame. Sensors are installed inside to measure humidity.

The specialist controls the camera from the outside - the equipment necessary for this is placed in a separate vestibule. Be sure to have a vacuum pump, the power of which is enough to pump out air and accumulated condensate.

Used for heating aluminum radiators(in the form of plates) with water, which is heated using a boiler outside the chamber. Due to the lack of complex elements, it is easy to operate such a machine.

Temperature and vacuum sensors are used to control the process. If something goes wrong, the specialist will track it according to the readings on the monitor.

But professional equipment it is expensive - you will have to pay an amount of 3 million rubles for a medium-sized camera. But it copes with damp wood in just two weeks, while natural drying wood dries for years.

The specific drying time depends on the type and condition of the wood:

boards from freshly cut oak will dry for about a month, and a fresh log house and a thin cut - 15 days;
wet (30%) Oak planks dry from 16 days, but in a thin version (25 mm) - a little more than a week;
boards from freshly felled pine dry for 8 days, and lower humidity (30%) - only 6 days;
building timber with dimensions less than 150 x 200 mm and a humidity of 65% will dry in 12 days, but thick types (200 x 300 mm) - about 21 days.

Times also vary due to differences in instrument settings for different breeds. Some breeds are hardy, while others should be treated gently, gradually, slowly.

Operation of the vacuum dryer

Vacuum drying of wood is divided into several stages. First, the wood is loaded into the chamber. In this case, lumber is placed in layers between aluminum plates for heating. The specialist adjusts the drying parameters (temperature and pressure). This is required to work with different breeds tree, after which you can turn on the device. During drying, the pressure is maintained at the same level, and the temperature may vary.

Note! During the warm-up stage, normal pressure is used, the vacuum pump is turned off. This is necessary to prevent defects.

When the wood is heated to the required temperature, the vacuum pump is turned on. It removes air from the drying chamber, thereby creating the desired pressure. The moisture in the wood moves from the center to the outer layers. Since the material is moistened, use additional funds not required. Even distribution of moisture saves wood from damage.

The moisture released to the surface of the material evaporates due to the high temperature, settles on the walls of the case and is removed by the pump.

The vacuum environment accelerates this process, because evaporation begins already at a temperature of 40 degrees - this would not happen at normal pressure. The air surrounding the wood is never heated to a temperature of more than 70 degrees. The upper rubber coating of the chamber, when pumped out, is drawn inward and presses on the boards, creating a kind of press.

The final step is conditioning. It is used only after the wood reaches the required moisture content. Heating is suspended, but the vacuum pump is not turned off. The wood gradually cools while continuing to be under pressure, which is necessary to prevent changes in the shape of the material. When the temperature reaches room temperature, the pump is turned off and the wood is removed from the device.

Do-it-yourself room equipment

A do-it-yourself vacuum wood dryer will cost less than buying a professional device. To do this, you need to select a chamber and equip it with a heat source and a fan.

Using inexpensive heat ventilation instead of a powerful pump is the main point of savings. Therefore, it is better to install the unit in spacious room. It must be ventilated so that the air inside the hull can be constantly renewed, covered and dry enough, otherwise the tree may become infected with mold or other diseases.

Camera

Most a good option cases for - iron conveyor. It is cheaper to use a used one (they are actively used on railway), but you have to take care of its cleanliness.

For the case, a container for sea transportation is suitable, you just need to look for a more airtight model. You can also use old scrap metal and weld the camera yourself. This is the most economical option.

To save internal heat walls must be insulated with foam and trimmed with clapboard. It is better to purchase a special insulating material for reflection, but you can use foil or penofol, while the second option is preferable.

Equipment

When the camera is ready, proceed to assembly and installation heater and vacuum pump. heating system dryers must be installed separately from the general heating circuit, because it must function stably and independently. A radiator is selected that can heat water up to 65-90 degrees.

Important! In order for the heat to be evenly distributed during drying, you will need to install a fan.

This is a mandatory step, as uneven heating spoils the quality of the wood. When building dryers with their own hands, great attention is paid to fire safety.

To facilitate the loading of the tree, a loading system is needed. So, you can use carts on rails or a forklift. Raw materials can be dried both on the shelves and directly on the floor. If the preservation of wood is important, then it is necessary to install temperature sensors, which will help control the process. This is especially important for expensive breeds tree. If the design is built correctly, then the temperature in the chamber will change evenly.

Qualitatively dried lumber has always been a guarantee of quality, durability and reliability of any structure in which wood occupies a significant share. But getting it in natural conditions is difficult and at the same time, so that it does not deteriorate. Drying time under normal atmospheric conditions can be from 6 to 12 months, depending on temperature and humidity. environment. During natural heat treatment, the material undergoes unwanted deformations, warping and cracking.

To improve the quality of lumber drying, many equipment options were invented, often they try to make a vacuum drying chamber for wood with their own hands - because. this technology is considered one of the most effective. But the problem is that it is quite difficult to make such a unit on your own. Nevertheless, there are craftsmen who make them from old tank bodies or thickened sheet steel. Basically, these are mini cameras with a loading volume of 5-10 cubic meters.

What is vacuum drying wood with your own hands?

Do-it-yourself vacuum wood dryer is quite possible if you have a case from a rocket, a tank, or any other similar type of product from which you can make a shell for equipment.

Main structural elements:

frame
Vacuum pump
heating elements (heaters, plates, steam generator, microwave radiators, etc.)
trolley for loading lumber
automation

You will need a pump to pump out air and create a vacuum. The lumber can be heated by any known method, which can be the contact method, air-gas and water vapor.

A do-it-yourself vacuum chamber is quite complicated in the technical part, because it will be quite difficult to find many details for its manufacture. And ordering them specifically is tantamount to ordering the camera itself. Therefore, before starting to design vacuum drying chambers for wood with your own hands, you should consider whether it is expedient or if it might be better to order it from a specialized company.

Do-it-yourself thermal chamber for wood - thermowood production

Thermal vacuum chamber technology has been around since the last century. The thermo dryer has much in common with the vacuum kiln for drying lumber.

To do vacuum chamber for thermowood, technical features must be taken into account:

Wood processing takes place at high temperatures
The chamber body must withstand high pressure

These 2 points are important to consider for the safety of personnel.

An important task is the choice of agent: oil or steam. Also technical modes. With incorrect modes, thermal drying takes place only on the surface of the wood, while lumber may not acquire the desired properties:

deep color change
fire resistance
increased resistance to decay

Making a homemade thermowood chamber, like thermowood itself, at home is a difficult task. Competent specialists ready to share their experience are unlikely to be found on forums, videos, or somewhere on the net. If you have any questions, please contact the manufacturers.

Vacuum dryers for wood: do-it-yourself or professional?

Our company is engaged in the production of high-quality and highly efficient drying chambers. vacuum type not the first year, so I'm ready to offer a really reliable and practical option.

But if you need a wood vacuum dryer small size for heat treatment small parts and you want to make it with your own hands, then there is a need for a drawing. Drawings on this topic are enough a rare event, from those that are found with a low probability, a camera capable of working in a production environment will come out.

However, if you are going to buy finished equipment, then the most effective option are chambers with contact technology for heating lumber along the entire length, the rejection rate is less than 1, and the drying time to 6-8% moisture content of a pine board 30 mm thick will be only about 60 hours.

What is drying for?

From time immemorial, when performing any wood crafts, timber cut down a few years earlier was used. Products from wet or under-dried boards will warp or become covered with numerous cracks.

When the tree dries, it shrinks, the raw wood material will “behave” over time, huge wide gaps will form in the log house. In under-dried semi-finished products, a fungus is likely to start. But it is also not advisable to overdry the tree, because it will begin to absorb water, which will lead to swelling.

What are the modes of drying chambers?

There is a whole list of drying modes for wood materials. In built with my own hands machines, the mode from the lowest to the highest changes gradually, removing all excess water from the semi-finished product. The drying process is carried out based on the following characteristics of the material:

tree species;
overall dimensions of the semi-finished product;
final and initial level of humidity;
unit specifics;
lumber quality indicators.

The drying operation can be characterized by high temperature or low temperature. The second case is notable for the fact that the primary drying is carried out at a regime that does not reach 100ºС.

Low temperature conditions can be as follows:

soft - after drying, semi-finished products have their original properties, without changing strength and color;
moderate - the color changes slightly, strength characteristics decrease slightly;
accelerated - in the process of subsequent processing (fracture, sawing, cutting), increased fragility is possible, the color fades.

Change temperature regime at low-temperature processing it is carried out on three stages.

Processing in high temperature mode is carried out in two stages. The second stage begins when the moisture level of the semi-finished product drops to 15%. Such technological process used if necessary, further design of secondary structures.

The main types of drying chambers

Drying of wood semi-finished products in industrial volumes is carried out in specialized dryers. Moisture is removed from the wood due to heated air, which subsequently goes into the atmosphere. The device provides the passage of a full cycle of lumber drying. The machine body can be:

solid / prefabricated metal;
made with building materials.

The latter are mounted directly in carpentry workshops in the form of a structure, or as freestanding. The walls are made with reinforcement and concrete mortar. Alternatively, bricks can be used. Large factories make a system of cameras, combining them into whole modules with centralized control and communications. The air moves inside the dryer in horizontal plane or vertically transverse.

Heat sources in the dryer:

radiant source from specialized units;
hot shelves;
electric current that passes through raw semi-finished products;
high frequency electromagnetic field.

The cameras are equipped with the main and auxiliary equipment. Main systems:

supply and exhaust equipment;
heat sources;
humidifiers.

According to the principle of operation, dryers are divided into:

convection equipment;
condensing equipment.

In convective machines, semi-finished products are "washed" with hot air waves, heat is directed by the convection method. Travel time full cycle varies from 5 to 13 hours. Similar units are mounted on large-scale sawmills.

Chamber-type dryers are more compact; a constant temperature and the environment as a whole are maintained throughout the volume. This type of dryer will allow you to dry any type of wood material to the required condition, which is why many entrepreneurs who are associated with the need to dry lumber choose chamber dryers.

Based on the technology of the drying process, the moisture that is released from the wood settles on the cooling elements, is sent to containers and then drained. The efficiency of such a unit is quite impressive, but time-consuming, leads to large heat losses. The pricing policy of machines and the profitability of condensation drying are lower than those of convective drying.

Drawing

Drying chamber for lumber: step by step instructions

To build a dryer with your own hands, you can not use technical documentation. It is only necessary to provide:

the area where the camera will be installed;
insulating materials;
source and communications to create high temperature;
blowing.

The area of a machine built personally, as a rule, is not more than 10 square meters. A square-section room is more suitable for moving warm air currents. It is preferable that at least one of the walls of the equipment be concrete, the others can be made of wood. Inside the chamber without fail gives in to warming. A great insulation material- wood shavings. If there is no foil at hand, then it can be replaced with penofol.

A separate extension for the dryer can be constructed from aluminum sheets, such a design will last a very long time. The base is made on the basis of profiles, it is covered with sheets of metal, which is further insulated. The thickness of the insulation must be at least 150 mm. The floor is covered with roofing material, a thick layer of shavings is poured on top, which will be excellent as heat saving.

The heat source can be supplied as a heating pipe system. The temperature of the liquid in the pipes should be at the level of 60 ... 90ºС. For an oversized chamber, a two-burner stove will be quite acceptable. If the source is right in the room, it must be overlaid with a brick. The brick is able to perfectly collect heat in itself and send it to the lumber drying machine.

The continuous circulation of the liquid is important, which is provided by the compressor or the whole station. The room must be equipped with wet and dry thermometers.

For more convenient loading of semi-finished products into the chamber cavity, you can use a rail trolley.

Video: do-it-yourself drying chamber for lumber.