Vacuum drying of wood at the enterprise

The key specificity of the scheme for drying wood in a vacuum is considered to be a reduction in the time required to complete the operation provided, while maintaining absolutely all the properties of the final lumber product, and in some cases, including increasing resistance to certain operating conditions. The formation of a rarefied atmosphere in the internal size of the working chamber, in which moisture is removed from the wood, completely changes the physical properties of the heat treatment and drying process. The typical degree of vacuum at which thermal drying of wood is carried out is 0.95 mPa, and the speed of the agent of the released steam does not exceed 0.3 m3/s. Under such forcedly developed circumstances, there is absolutely no need to assemble fans, thermometers and moisture level regulators. The progress of the drying process is controlled by special sensors that set the level of readiness for the released moisture based on its number per 1 m3.

What is vacuum drying?

This type of drying is one of the varieties of this kind of technology for processing and preserving various types of materials and food products. A characteristic feature of this technology is the ease of use of drying, processing efficiency, low cost of the process itself and the speed of obtaining the required result.

The principle of influencing the processed material using vacuum drying is based on a minimum temperature level, which is much lower than the boiling point. Thus, in the absence of thermal influence on the material, which can change the structure of the processed raw material, excess moisture is removed from it than during thermal drying.

Design of vacuum chambers

Another key aspect of creating a vacuum chamber is design. Most manufacturers of truly high-quality raw materials face this problem.

In reality, it can be difficult to find useful information on this subject. There are manufacturers who are ready to share materials for the production of drying chambers. In addition, many companies offer design services for such equipment, as well as improvements and restoration of outdated installations.

Design of vacuum chambers

According to the projects, the design of such equipment is represented by the following elements:

Doors;
Heating components;
Thermal and vacuum units;
Automation;
Installation of a solid fuel tank that runs on wood, coal and the like.

If you have an outdated or ineffective installation, it can be restored by specialized services. Such services, as mentioned earlier, are offered by many companies.

Vacuum drying of wood

This type of drying is organized through the evaporation of moisture from the internal cavity of the wood. Due to natural conditions, during the growth of a tree, its internal metabolism is carried out by circulating fluid along the entire length of the trunk. If a tree is cut down, this circulation stops, the moisture begins to evaporate and, accordingly, the wood dries. But if drying takes place under natural conditions, it takes a lot of time, which, given the volume of processed wood consumed by humans, cannot provide the required amount of finished material. For these purposes, artificial dehumidification is used, which significantly speeds up this process, minimizes fungal damage to the wood, virtually eliminates the appearance of cracks and increases the service life of lumber.

Depending on the level of moisture in wood, it is divided into several categories, such as:

Wet. Refers to the type of materials that are constantly in water. The moisture level of such a tree is one hundred percent;
Recently felled. The degree of humidity varies from 40 to 100%;
Air dry. Wood that has been lying in the open air for a long time, but under a canopy. Its humidity can range from 15 to 20%;
Room dry. If the wood is stored indoors, then the temperature regime here is often the same, which dries the material faster, creating a humidity level of 8-10 percent;
Completely dry. It has zero moisture content, which can only be achieved by artificial drying.

For some types of production, the flexibility of wood is an important factor. The higher the humidity, the easier it is for the tree to bend. In this case, before vacuum drying, it is necessary to give the material the desired shape and fix the workpiece in this position, and then place it in the working chamber.

Vacuum chamber container

One of the main elements of making a drying chamber is the choice of container. To choose the right container, it is important to consider several important criteria.

Material used. Each element must be made of metal that does not corrode. More often the compartment is equipped with aluminum and stainless steel alloys;
Sealing. It should be remembered that the material used must be protected from moisture and atmospheric air by means of a seal;
Ventilation system. The engines of the installations must smoothly blow the raw materials, which will ensure a stable air flow intensity;
When each of the points described above is taken into account, then it will be possible to choose truly high-quality and reliable lumber equipment.

Vacuum chamber container

The principle of vacuum drying of wood

The process of vacuum drying wood includes a number of production stages. To understand the overall picture of this technology, each of the stages is described in detail below:

First of all, it is necessary to load the wood to be processed into the drying chamber. To do this, timber or round timber is laid on special carts in layers, each layer being layered with aluminum plates with heating elements;
The next step is to set up the equipment, which determines the required level of moisture in the output wood. To do this, depending on the further use of the material and the type of wood itself, the required temperature and degree of vacuum are set. Throughout the entire procedure, the pressure level does not change, only the degree of heating varies;
When the procedure starts, pressure is not created in the chamber, but only the lumber is heated. This technology is required to prevent board deformation;
After heating the wood to a certain temperature, the vacuum pump starts, which pumps out all the air from the internal volume of the chamber. When an absolute vacuum is reached, moisture from the deepest part of the tree gradually rises to its top layer, which ensures the necessary humidification process to avoid defective finished products. This eliminates the need to use additional humidifiers. After the liquid reaches the surface of the material, under the influence of temperature it quickly evaporates and settles on the walls of the drying chamber, from where it is pumped out as condensate. Evaporation of moisture under vacuum conditions occurs at a temperature of +40 degrees, and the maximum threshold throughout the entire wood drying process does not exceed +70 degrees.
To further speed up drying, rubber layers are located on the inner walls of the chamber, which, when a vacuum is created, begin to be drawn into the chamber, simultaneously squeezing the wood. Thanks to this, drying is accompanied by additional pressure;
The final stage of drying consists of lowering the temperature of the material being processed. In order to prevent its deformation, the heaters are turned off, but the vacuum is maintained. In this position, the tree continues to be under pressure and cools down at the same time. When the temperature of the lumber is compared to room temperature, the vacuum is released and the finished product is removed from the unit.

Operating principle of vacuum press-drying chambers

Press-vacuum drying chambers operate using vacuum, which is further enhanced by pressure on the stack. The pressure is exerted by a special rubber membrane. A standard vacuum drying press chamber consists of the following components :

The working chamber in which the wood that needs to be dried is placed;
Special rubber membrane;
Rubber seal;
Metal frame;
Water pump;
Heating plates;
Vacuum pump;
Electric heater;
Thermal insulation material;
Microprocessor;
Rubber tubes;
Humidity sensors.

Many of the vacuum press dryers are equipped with a built-in microprocessor and control panel. With its help, you can set different drying modes in the dryer, regulate the humidity in the chamber, and set the pressure required by the technology. It is enough to set the drying program, and the vacuum drying chamber itself will set the desired mode, focusing on the indicators of numerous sensors. The microprocessor of the vacuum drying unit can be connected to a computer, due to which the process can be controlled remotely.

Most vacuum press-drying chambers are compact in size, which allows them to be used in small enterprises. This equipment is especially popular in the field of drying valuable wood. For large woodworking enterprises, vacuum press-drying units are made to order.

Drying wood: vacuum pump

There are a number of features when drying wood under vacuum conditions. These nuances directly affect the choice of a suitable vacuum pump that will fully provide air rarefaction under the required circumstances. Thus, the following types of vacuum pumps are used:

Screw vacuum pumps. This technology allows you to generate a fairly high degree of vacuum during one cycle. The most popular industries where such technology is used are the chemical and pharmaceutical industries. Another advantage is the good resistance of the units to the influence of high humidity, as well as the absence of lubricants, which prevent contamination of the created vacuum by exhaust gases. Screw technology also implies the presence of explosion-proof units. They are necessary for drying processes during which explosive vapors are released from the processed material.
Water ring vacuum pumps. They are widely used in enterprises whose main activity is the production and drying of ceramics or building materials. This is due to the fact that the only working fluid used by the pump is ordinary water.
Rotary vacuum pumps. Thanks to its technological features, it prevents the ingress of released moisture from the material into the working area of the pump, which ensures the absence of contact with already released moisture and the material being dried. This concept is popular in those industries where raw materials react negatively to repeated exposure to humidity, thereby losing their functional characteristics.

The above types of vacuum pumps are used in such types of processing as:

Production of powdered milk;
Drying of discharged waste during wastewater treatment;
Drying wood;
Bringing synthetic granules to the final condition and a certain level of moisture;
Drying parts and finished ceramic products;
Drying of components and individual spare parts.

Manufacturing of vacuum chambers

The procedure for creating vacuum chambers was formed in the last century. This installation has much in common with vacuum equipment for drying lumber.

To create such equipment, a couple of technical features should be taken into account. It is important to process raw materials at high temperatures. Also, the body of the machine must withstand significant pressure. These couple of points must be taken into account to ensure the safety of personnel.

Manufacturing of vacuum chambers

Another important aspect when creating is the choice of agent: oil or steam. It is also worth considering technical parameters. If the conditions are incorrect, drying is carried out exclusively on the surface of the lumber. Because of this, the raw materials used will acquire a number of properties, such as:

Full color change;
Fire resistance;
Improved rot resistance.

It is worth noting that you can create a drying chamber for processing wood yourself at home, but it is quite difficult.

Board dryer: creating and using a drying chamber

All photos from the article

A do-it-yourself board dryer is made if there is a need to process a large volume of unprepared wood. Of course, you can immediately purchase blanks with optimal humidity, but in this case the costs of purchasing the material will be very high. So the construction of a special device can be quite effective from an economic point of view.

In our article we will tell you. How to dry wood, and we will give recommendations on how to independently arrange a drying chamber.

To use dry wood, you don’t have to spend money on buying it - you can bring the humidity back to normal on your own

Using the dryer

If the drying chamber was assembled according to all the rules, then using it will be quite simple. To do this, we stack the boards, placing bars up to 20 mm thick between the rows, and load the stack into the dryer.

Stacks of lumber

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

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

Heating - raise the temperature to 45 - 50 0C at a speed of 5 - 70 C per hour.
Exposure – keep at 50 0C for 5 hours.
Drying – reduce the humidity of the wood from 30 to 8%, gradually increasing the temperature to 60 0C. This stage takes about 48 hours. Supply and exhaust ventilation are turned on at half power.
Air conditioning – maintain the temperature at 600C for another 12 hours. Ventilation must work actively.
Cooling down to ambient temperature with heating and ventilation turned off.

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

Processing result

DIY wood dryer: drawings

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

compact drying chamber

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.

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. The device carries out a full wood drying cycle. 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.

At large enterprises, several cameras are installed, combined into a module with a common control system and communications connections. 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;
smoke;
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.

According to the principle of action, the following are distinguished:

convective;
condensation dryers.

Convection dryer Condensation dryer

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

solar wood drying chamber

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 follow fire safety measures. 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. The workroom is 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: