The principle of operation of a vacuum drying chamber for wood. Homemade wood dryer

Drying of wood lumber is carried out mainly using a vacuum drying chamber. Technological operation It consists in the fastest possible evaporation of moisture at the lowest possible pressure.

The drying chamber itself looks like a metal cylinder, it is made from boiler iron. The length of the device is up to 40 m, and the diameter is approximately 2 m. The chamber is hermetically sealed, the temperature inside it can be set in the range from 50° to 90°. Heating occurs by supplying water vapor through pipes that are evenly spaced along the internal walls cylinder.

As raw materials, boards up to 25 mm thick are loaded into the device, while heating takes place within 1 hour. If boards with a thickness of 50 mm are used, the duration of the warm-up stage is increased to 2 hours. After that, the steam supply is completed and the pumping of air from the chamber begins. Due to the fact that it is hermetically sealed, a 90% vacuum is formed. This state lasts 2 times longer than the previous stage and ranges from 2 to 4 hours. Evaporation of residual moisture occurs with a concomitant decrease in temperature. When the sensors inside the chamber show 30°, the work stops vacuum pump. Next, iterations are repeated from heating to pumping out air, from 7 to 12 such cycles pass with breaks between them.

Total time it takes to dry pine board thickness of 75 mm to a moisture content of not more than 10% is 3 days with an initial moisture content in the timber of 70%. If boards with the same moisture content are dried, but their thickness does not exceed 25 mm, then the duration of the process is reduced to 24 hours.

Adjusting the drying mode in the above vacuum chamber is difficult, which makes the device applicable only to work with homogeneous raw materials.

When developing a vacuum compression chamber for drying, the latest technological solutions were used. The device combines the best features of classic cameras and useful innovations. Basic hallmark such a chamber is its versatility, because it can dry boards of the most diverse quality levels. The process is faster than in a standard convection chamber. Drying of a whole round timber is permissible, while the appearance of cracks both outside and inside is excluded.

Drying in a compression chamber makes it possible to make changes in the color of the material at the request of the customer, the change can be so radical that the original rock becomes completely unrecognizable.

Drying can also reduce the hygroscopicity of lumber, thus leveling the lack of raw materials, which depends on fluctuations in atmospheric humidity that occur during the growth of the tree. The compression chamber allows you to work with boards of a given non-linear shape. The values of the working pressure inside the device are low, so the device does not fall into the area of attention of the Boiler Supervision Inspection.

During the drying cycle, a permanent increase in air temperature occurs, which causes an increase in the moisture content of the drying agent. The removal of moisture from the board is fully automatically regulated. Evaporation of liquid from a bar is explained by the influence of a difference in the level of humidity and depends on the coefficient of moisture conductivity. The moisture content of the drying agent increases with its pressure: this occurs together with the increase in temperature values in order to ensure the safety of the drying process. The higher the pressure of the drying agent, the higher the boiling point of water (at a given temperature). The heat supply ends at the moment when the predetermined parameters are reached, among which the equilibrium moisture content of the board under certain conditions (in the physical environment of hot steam under conditions high pressure). The calculation of the required parameters is based on the diagram of the equilibrium moisture content of a tree for atmospheric pressure.

Until the heat supply was cut off, the principle of operation of the vacuum convection drying chamber did not differ from the standard convection drying with a few exceptions. Higher temperature values are used, which allows you to speed up the drying process itself; the possibility of moisture exchange with the elements is excluded external environment, this is possible by increasing the moisture capacity inside the device itself. The automatic start-up of the condensing unit takes place. It, in accordance with the previously set program, changes the temperature to a lower side, and there is also a programmatic decrease in the pressure and humidity level of the drying agent. The decrease in temperature values and pressure occurs at the pace that is set by the thickness of the board and what kind of wood is drying in this moment. Between the pressure inside the beam itself and the external pressure, significant difference. Next, moisture is squeezed out of the timber due to the pressure difference. Further, due to the temperature difference, the surface of the board is cooled. And after that, the device starts to function as a vacuum chamber of standard design with a small difference in intensity (due to the use of higher temperature values). In the process, condensate appears, for which it is provided automatic system plum. Moisture is discharged when it reaches a certain volume, the pressure in the drying chamber decreases first to atmospheric level, and then even lower. At this time, no energy costs are incurred to create a rarefied one. Wednesday, technological process from that moment on, it flows according to the classical thermodynamic laws. The equilibrium moisture content of the drying agent is maintained, which is in accordance with the predetermined final value of the wood moisture percentage. Conditioning is in progress: the humidity is distributed evenly both on the scale of one bar and the total volume of lumber.

Vacuum dryer is another modern invention that allows you to quickly and efficiently dry wood. But the scope of its application is not as wide as that of an infrared dryer. Let us consider in more detail the properties of both devices.

One of the properties of wood is hygroscopicity, the ability to absorb moisture. A freshly felled tree is saturated with moisture, and raw wood is unsuitable for making furniture and creating building structures. It is highly susceptible to biological damage, warping and cracking.

For further use, freshly harvested lumber must be dried. Natural drying- this is a long process, so equipment was invented to speed up the drying of wood.

Different dryers differ from each other in the principle of operation and performance. You can choose the optimal equipment for specific operating conditions by comparing them. In this article, we will focus on infrared and vacuum dryers, figure out how they work, how much lumber and how long they can dry, how much energy they consume, and what is their market price.

Principle of operation

IR dryers develop infrared rays, which, by heating the wood, dry it to the required moisture level. These rays are of the same nature as visible light. They pass freely through the air. Nitrogen and oxygen molecules do not absorb infrared radiation, so all the energy is directed to warming the wood, not the air.

This method of drying does not involve the use of a coolant, which eliminates the need to monitor its performance and equip the equipment with complex automation.

Infrared heat acts gently on the wood, without causing strong internal stresses and warping.

Vacuum dryers The market offers two main types: with cyclic and contact heating of the material. The principle of operation of the former is based on convective heating of wood and vacuum removal of excess moisture. The operating temperature usually does not exceed 65°C, but a pressure of 0.09 MPa causes moisture to boil already at 45.5°C. Vacuum allows lumber to dry without exposure to high temperatures, so that the tree does not crack. During drying, when the temperature reaches 65°C, the boiler switches off automatically. The surface of the wood begins to cool, and moisture from the inside flows to drier areas. Over the entire drying period, shutdown and restart occurs many times, while moisture is drawn out evenly.

In contact heated dryers, heat is transferred to the material by means of thermoset plates which are stacked. The plates are heated either by water or electricity.

Appearance

infrared dryer- this is a set of thin thermoactive cassettes that are stacked in a pile of lumber in a certain sequence and connected to a power source. The stack prepared for drying is covered with a material with a reflective layer so that the condensate drains outside the stack. The drying process is controlled by a temperature controller responsible for maintaining the set temperature. The equipment is compact and easy to use, if necessary, can be easily transported from place to place in the trunk of a car

vacuum dryer is a sealed chamber made of stainless steel, made in the form of a cylinder or parallelepiped. The chamber of the first type is tightly closed with a door, the second one is covered with a rubber membrane in a metal frame.

In dryers with contact heating, the boards are laid inside the chamber in layers, alternating with heating plates. When used as a heat agent hot water, its circulation in the plates is provided by a water pump. The water is heated by a boiler, and the vacuum is created by a liquid vacuum pump.

In cylindrical chambers of large volume, material is loaded along a rail track, which is mounted inside and outside.

Size and weight

Convenience infrared dryers are their small size and weight. One thermoactive cassette has a size of 1230x650x1.5 mm, that is, it is a thin plate of a small area. The weight of the cassette is 5.7 kg. A standard set for drying 1 m³ of lumber includes 12 cassettes with a total weight of 69 kg. With the crate, control panel and cabling, the weight of the equipment does not exceed 130 kg. Its transportation does not require the use of special equipment.

vacuum the press dryer, even with a small load volume, has a significant larger size and weight. Thus, a parallelepiped-shaped unit with a loading volume of 4 m³ has dimensions of 4800x1700x2005 mm and weighs 2300 kg without aluminum plates. The size of the heating plate is 4000×1400 mm. To transport such equipment, a rail or road container is required.

Autonomy of work

IR dryer works completely offline. By installing and connecting the equipment correctly, you will not have to perform additional control of operating parameters. You only need to set the drying mode, based on the quality of the source material, and in the future, the thermostat will monitor the maintenance of the set temperature.

The drying process in vacuum chamber is also automated, but in this case more complex automation is used, since it is necessary to monitor the parameters of the coolant (if any) and pressure. In some types of dryers, the process can be carried out manually. In most models, an alarm condition indication is provided, which is activated when the temperature is exceeded, the degree of vacuum decreases, the coolant parameters change, etc.

Drying time

The drying time depends on the wood used and its initial moisture level. The process of drying a pine board to a moisture content of 8% using infrared equipment can last from 3 to 7 days. The thinner the boards, the faster they dry.

AT different types vacuum dryers the time indicators are slightly different, but on average, the drying time of a pine board with an initial moisture content of 50% to a final moisture content of 8% lasts 16-18 hours.

Loading volume

IR cassettes can be used to dry any amount of lumber.

Vacuum chambers are offered with different loading volumes: from 4 to 20 m³.

Source of power

infrared cassettes are connected through the control panel to the 220 V network, the voltage of 380 V is also suitable.

Vacuum chambers Requires a 380V power supply.

Power and electricity consumption

Max Power infrared dryer- 3.3 kW/m³. During the drying time of 1 m³ of lumber, from 200 to 400 kWh of electricity is consumed.

Average power consumption vacuum chambers is 15-37 kW. Unfortunately, cameras with truly fantastic energy costs are often found on the market - from 50 kW / m³.

Price

Price is a weighty argument when buying equipment.

Prices IR dryers FlexiHIT is very affordable:

a set for drying 1 m³ of a three-meter board - 59,288 rubles;
a set for drying 1 m³ of a four-meter board - 69,329 rubles;
set for drying 1 m³ of a six-meter board - 70,007 rubles.

Prices vacuum chambers of domestic production fluctuate between 500 thousand-1.5 million rubles, imported equipment costs 3-4 times more.

findings

IR dryers easy to use, can be used in production and at home, suitable for drying any amount of lumber and have a reasonable price.

in vacuum chambers wood dries quickly and evenly, does not deform and even levels out, its color remains unchanged. But due to the high cost and high energy consumption, it is advisable to use them mainly for drying expensive wood species.

The quality of the products made from this material. Do-it-yourself vacuum drying of wood can significantly save time spent on drying wood raw materials.

With this method of drying wood, the possibility of various deformations of the dried wood is largely excluded.

The process of drying wood in a vacuum environment has its positive aspects:

significant acceleration of the processes of drying wood raw materials;
lower cash costs for energy expended;
more uniform methods of drying wood.

This equipment is quite simple in its management, does not require special training of personnel.

Mini vacuum dryer

The vacuum drying method also has some negative parameters:

large overall dimensions of the equipment itself;
no way to control for drying different breeds wood;
characteristic of large industries.

How to build a vacuum dryer with your own hands?

In most cases, novice businessmen do not have enough money to purchase a factory installation for the vacuum drying method, so we will take a closer look at such an option as do-it-yourself vacuum drying of wood.

To equip home-made vacuum dryers for wood, you must have suitable premises, as well as the presence of any container.

It needs to be hermetically sealed. Or you can build this dryer using reinforced concrete structures: with this option, one of the walls is made of wood.

Should be produced thermal insulation the camera itself - for this you can use a variety of types mineral wool or use regular foam. You should also cover the insulation with a special film, which will help reflect heat flows into the chamber.

Radiators for heating should be used as heating elements - at the same time, these radiators should warm the water up to seventy degrees. It will be necessary to install a fan of sufficient power: given element contributes to a more correct flow of air masses inside the chamber.

Homemade vacuum dryer

To heat the water mass, a boiler is used, from which, using a water pump, water will be supplied to heating elements. In addition, it will be necessary to mount an apparatus to create a vacuum environment. Humidity sensors will also be needed.

The system that controls this equipment is moved outside the chamber itself - usually, some separate vestibule is made. Drying material can be loaded and unloaded either manually or using a forklift.

Adjustment needs to be made temperature regime so that changes in this parameter occur at a smooth pace.

Features of a homemade chamber for the vacuum drying method

When building this equipment on our own, it is necessary to create special technological parameters inside the chamber. When drying in a homemade oven, the drying time can take more than two weeks.

Materials loaded into the chamber should be treated with special solutions, including chalk and drying oil.

When building a home-made vacuum installation, fire safety parameters should be carefully observed, otherwise you may encounter irreparable consequences.

Qualitatively dried lumber has always been a guarantee of quality, durability and reliability of any structure in which wood occupies a significant share. But get it in vivo 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. You can warm up lumber with any known way, which can be a 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

Make a homemade thermowood chamber just like thermowood itself at home 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 has been manufacturing high-quality and highly efficient vacuum-type drying chambers for several years, so we are ready to offer a truly reliable and practical option.

But if you need a wood vacuum dryer small size for heat treatment of small parts and you want to make it yourself, then there is a need for a drawing. Drawings on this topic are enough a rare thing, 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.

Why dry wood?

Drying for lumber is extremely required process, without which wood simply cannot be used.

The quality of wood depends on proper drying.

If you have your own business related to the production of wood products, then you can not do without your own drying chamber. But first, let's try to understand why this dryer is needed, why lumber needs to be dried. It's all about natural humidity any tree. If you make a product from undried wood, then it will dry out over time, crack, and all that remains is to throw it away. In addition, a properly dried wood improves its working qualities, becomes stronger, more resistant to environmental influences and less susceptible to destructive mold. In the old days, to prepare the forest for use, it was dried not even for years, but for decades. Often, logs prepared for grandchildren were laid under a special canopy. Imagine, not even for children, but for grandchildren.

To our happiness modern technologies allow us to significantly speed up this process. And although this process is still quite long and complicated, it still cannot be compared with traditional technologies and the result is even better.

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Moisture content of lumber

It is important to understand that a tree is a living organism and its cells contain moisture while it is alive. In general, freshly cut wood has a moisture content of 30 percent or more. If we want to use wood, then we need to get rid of excess moisture. What kind of moisture is superfluous? It depends on what we are going to use the board or log prepared for production for. If the tree is used for the manufacture of products where the highest assembly accuracy is required (for example, for the production musical instruments, sports equipment, parquet and some types of furniture), then its humidity should be reduced to 6-8 percent. If you are just preparing lumber for long-distance transportation, for example, for export, then it is enough to reduce the humidity to 20 percent.

The same wood is also suitable for some types of buildings, for the production of containers and other goods. Other products require wood moisture between these two extremes. Floor boards, cashing, sheathing boards can have a moisture content in the range of 15 percent. BUT window frames, doors, stair elements or decorative items will require wood from 8 to 15 percent moisture.

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Making a dryer with your own hands

Consider, finally, the construction of the drying chamber itself. To begin with, in addition to the basic building materials for the manufacture of the camera room, you need to purchase a heating device, a fan and a good insulation.

The scheme of the drying chamber.

You can use a ready-made room for the construction of drying, or you can build it specially. It is desirable that the ceiling and one wall be made of reinforced concrete, while the rest of the walls are made of wood, which later need to be covered. thermal insulation materials: first we cover them with foam plates, sheathe them with clapboard and then cover everything with sheets of foil. The next step is to install some kind of heating device, for example, a heating radiator, in which the water should be heated to 65-90 degrees. Since continuous heating is necessary, it is better to immediately make the heating system autonomous, with its own furnace and pump for constant circulation of the coolant. Absolutely necessary in the drying chamber is a fan, which, dispersing the air around the room, should ensure uniform heating of the entire drying space and the laid wood.

In advance, you need to think over the issue of laying wood material for drying, how the wood will be brought into it, whether it will lie in the middle of the chamber or on special shelves, etc. good options for loading wood is a trolley on rails or a forklift. Take care of the availability of devices for recording humidity and temperature in the drying chamber, without which effective control over its operation is impossible.

Scheme of air temperature and wood humidity in the drying chamber.

When building, consider some more nuances. The temperature in the drying chamber should not fluctuate sharply, make sure that it changes smoothly. Otherwise, you run the risk of destroying all the stocks of wood laid in the drying. It can crack and warp. It is also worth remembering fire safety, because you are dealing with heating appliances and large stocks of dry wood. To do this, keep a fire extinguisher nearby. Of course, some of the above can be replaced with analogues available in the house, in particular, a water heating radiator can be replaced with electric heaters, up to an electric stove with a pair of burners on. Only again we remind you of fire safety, be careful. The walls of the dryer can be insulated not only with polystyrene, but also with others. suitable materials, up to the same wood shavings, and penofol can replace the foil, which is well able to reflect thermal radiation back into the camera.

The main thing during construction is to achieve the creation of suitable conditions inside the chamber, and what material or technology you used is not critical. In such home drying, lumber will dry for about 1-2 weeks.