How to dry bog oak. Shrinkage of bog oak wood under various processing conditions. Features of oak wood: what should be the result of drying

We ask you, if possible, to send us recommendations for drying oak (what features should be paid attention to when drying this type of wood).

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Natalia Titova

The technology for drying oak wood is not fundamentally different from the technology for drying coniferous and softwood species. Distinctive feature is that when switching from one drying stage to another, it is necessary to equalize the moisture content of individual boards in a stack, taking into account that drying is carried out on the wettest material. The process of drying wood in a drying chamber is divided into several stages: I. Initial heating of wood. II. Actually drying wood. III. Moist heat treatment. IV. Conditioning. Drying always begins with warming up the wood, regardless of the initial moisture content of the lumber. During heating, water (steam) is supplied to the chamber through humidifying pipes with the heat exchangers turned on, the fans running and the supply and exhaust channels closed. The humidity of the drying agent is maintained at a level close to saturation. After warming up, the moisture content of the lumber is additionally measured, according to which it is judged from which stage to start the actual drying. It should be borne in mind that drying is carried out on the wettest material. It is forbidden to switch to another drying stage until the moisture content of all boards has reached the transitional moisture content. The drying of wood itself is divided into steps. In the initial stage of the process, it is necessary to maintain a small thickness moisture difference, which is achieved by using a drying agent with a high degree of saturation. As the wood dries, it is advisable to lower the degree of saturation in order to bring the material to a given final moisture content. The transition from stage to stage in the presence of a moisture meter is judged by its testimony. The temperature of the medium towards the end of drying should be increased. With a decrease in humidity, an increase in temperature will not cause a decrease in strength, but at the same time it will significantly speed up the process. Drying itself ends when the final moisture content is reached according to all sensors. Then they move on to the stages of moisture heat treatment and conditioning treatment. Moist heat treatment is necessary to remove or reduce the "residual" internal stresses that occur in the wood during drying. To create an environment high humidity the following is supplied to the drying space of the chamber: steam or sprayed water with the heaters turned on, the fans running and the supply and exhaust channels closed. The humidity of the drying agent is maintained at a level close to saturation. When drying hardwoods, conditioning treatment is required. Conditioning is carried out to equalize the moisture content of the wood according to the volume of the stack and the thickness of the lumber. In the drying chamber, with the help of heaters and humidifiers, such a state of the environment is maintained in which under-dried assortments dry out, and over-dried ones are moistened. After leveling the final moisture content of the lumber, the stacks must be cooled at closed door and open supply and exhaust channels. Fans are allowed in summer.

The invention relates to the woodworking industry, namely to the technology of drying bog oak wood, and can be used, for example, in the manufacture of furniture. To implement the method, at the first stage, blanks made of bog oak wood are placed in an autoclave and hydrothermal treatment is carried out with dry saturated steam when heated to a temperature of 120-122 ° C and under a pressure of 1.4-1.5 atm with exposure, respectively, for 1- 2 hours. At the second stage, the heated blanks are placed in a sodium chloride solution at a temperature of 20-22°C and maintained at atmospheric pressure for 1.5-2.5 hours. The blanks extracted from the solution are placed in a convective forest drying chamber and carry out convective drying to the final moisture content of wood blanks of 7.9-8%. Depending on the thickness of the workpieces, drying modes are selected. The invention should reduce the drying time and improve the quality.

The invention relates to the woodworking industry, namely to the technology of drying bog oak wood, and can be used, for example, in the manufacture of furniture.

Technological processes for obtaining high-quality dried lumber and blanks from bog oak are characterized by complexity and long duration.

There are several approaches to solving this problem. One of them is convective drying of lumber with low-temperature conditions in batch chambers and includes technological operations heating, drying, moisture heat treatment and wood conditioning. The known technology provides for a stepwise change in the parameters of the drying agent depending on the moisture content of the wood ("Guiding technical materials (RTM) on the technology of chamber drying of wood". - Arkhangelsk, 2000).

A known method of drying difficult-to-dry tree species, including oak, improving the known technology (description to the patent RU 2263257, IPC 7 F26B 1/00, F26B 3/04, 04/19/2004, prototype). To speed up the drying process and avoid cracking, the known method additionally provides for the formation of outer surface blanks of a layer of a hygroscopic substance that provides an optimal moisture difference between the outer and inner surfaces of the blanks in the process of stepwise convective drying. To do this, before convective drying with a four-stage temperature increase, the lumber is boiled at atmospheric pressure in a 15-17% sodium chloride solution for 2.5-3.0 hours.

The known method is long and does not provide high quality dried blanks. This is due to the fact that the specificity of bog oak wood, associated with the presence of til in vessels that prevent the removal of moisture from the wood, and the achievement of maximum humidity due to a long stay in fresh running water, is not fully taken into account.

In addition, the operation of welding in the known method requires additional costs to improve production conditions, in particular, to ventilate industrial premises.

The objective of the invention is the development of an effective technological process drying oak bog wood.

The technical result from the use of the invention is a reduction in the duration of drying, an increase in the quality of dried blanks and an improvement in production conditions.

The technical result is achieved by the fact that in the method of drying bog oak wood, which involves hydrothermal treatment in a solution of sodium chloride and convective drying, hydrothermal treatment is carried out in two stages, while at the first stage heating is carried out in an autoclave with dry saturated steam with exposure for 1-2 h at a temperature of 120-122 ° C and a pressure of 1.4-1.5 atm, and on the second - heated wood is immersed in a solution of sodium chloride at a temperature of 20-22 ° C and kept at atmospheric pressure for 1.5-2.5 hours.

Essence technical solution is that at the stage of wood heating in an autoclave with dry saturated steam with exposure at a temperature of 120-122 ° C and a pressure of 1.4-1.5 atm, conditions are created for the destruction of til in bog oak wood and during the subsequent stages of drying, conditions are created for unhindered removal of moisture from wood. The exposure time is selected empirically, depending on the size of the blanks and the initial moisture content of the wood within the range of 1-2 hours, which is optimal for the destruction of til in the selected mode of autoclaving.

At the second stage, when heated wood is immersed in a sodium chloride solution at a temperature of 20-22 ° C and atmospheric pressure, due to the temperature difference and external pressure, favorable conditions are created during the holding process not only for the formation of a hygroscopic layer on the outer surface of the workpieces, but also for removing moisture from wood. The two-stage hydrothermal treatment of bog oak wood in the selected modes makes it possible to reduce the initial moisture content of the blanks before convection drying by 2-3% compared to the prototype and significantly reduce the duration of the drying process. So, with a stepwise process of convective drying, the number of temperature rise steps is reduced by at least one.

Examples of the implementation of the method.

Three batches of blanks from bog oak wood in the form of bars with dimensions of 19×100×500 mm, 32×100×500 mm and 50×100×500 mm with an initial moisture content W n = 90% at the first stage of hydrothermal treatment were placed in an autoclave and hydrothermal treatment was carried out. processing with dry saturated steam, heating them to a temperature of 120-122 ° C and further exposure under a pressure of 1.4-1.5 atm, respectively, for 1 hour for the first batch, 1.5 hours for the second and 2 hours for the third .

From the autoclave, the heated blanks were placed in a sodium chloride solution with a concentration of 15-17% at a temperature of 20-22°C and kept at atmospheric pressure for the first batch for 1.5 hours, the second for 2 hours and the third for 2.5 hours.

The blanks extracted from the solution were placed in a convective wood-drying chamber.

Drying of the first batch was carried out at a temperature of 64°C. When the workpieces reached a moisture content of 8%, drying was stopped. Drying time was 18 hours.

Drying of the second and third batches of blanks was carried out with a three-stage increase in the temperature of the drying agent. Drying modes were chosen according to the "Guidelines technical materials(RTM) according to the technology of chamber drying of wood", - Arkhangelsk, 2001, carrying out the transition to the next stage of increasing the temperature of the drying agent as the current moisture content of the wood decreases to the value of the transitional relative humidity. The final moisture content of wood blanks in batches was 7.9%. The duration of drying for the second batch of blanks was 2.5 days, the third - 4 days.

Dried blanks in all batches corresponded to the second category of quality.

A method for drying bog oak wood, involving hydrothermal treatment and convective drying, characterized in that hydrothermal treatment is carried out in two stages - at the first stage, heating is carried out in an autoclave with dry saturated steam with exposure for 1-2 hours at a temperature of 120-122 ° C and pressure 1.4-1.5 atm, on the second - the heated wood is immersed in a sodium chloride solution with a temperature of 20-22 ° C and kept at atmospheric pressure for 1.5-2.5 hours.

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Bog oak is one of the most valuable types of wood. It is used for making art and decorative items. But the extraction and processing of bog oak is a long and costly process. Therefore, the price of the material is high. Dry stained wood traditional ways problematic due to the peculiarities of its structure. We will tell you more about how to dry bog oak in compliance with all technologies.

Bog oak is mined on the banks of rivers. Wood can lie in water for more than a hundred years, and then it is taken out and processed. Products made of stained material have a pleasant dark color and are durable. In terms of density, moraine material is compared with iron, so it is even difficult to cut it. Humidity of freshly mined product can reach 117%. Compared to the natural humidity of 50-65%, the figure is impressive.

Material is obtained in three ways:

1. At the bottom - deep works- the most costly and painstaking.
2. When developing peatlands - less laborious.
3. Manufacturing in specialized workshops is the simplest, but multi-stage method.

The weight of wet oak wood is 1500 kg / 1 cu. Therefore, immediately after extraction from the water, the material is cleaned of silt and sand and sawn into small pieces. Otherwise, transportation becomes more difficult.

The tree is afraid of sharp contact with hot air and direct sunlight, so drying is done in a gentle mode. A proven old-fashioned way to dry bog oak is to place small bars in the grain in the fall and leave until spring. Natural drying is also allowed, but it must be carried out in a room with good ventilation and constant indicators of humidity and temperature. It became possible to dry the material in a short time only in the last 10 years, with the advent of new technical means.

For drying bog oak in a short time, the following methods are used:

1. Vacuum chamber.
2. Pulse.
3. Adsorption.
4. Infrared.

But when drying in the chambers, the moraine material becomes discolored and becomes not so dark. Therefore, many criticize methods of unnatural drying. But with natural drying, the areas where the sun hit, also brighten. Chamber drying of bog oak saves time, and if it is carried out in accordance with the technology, then cracks will not appear and the product will not be subject to internal stress.

When chamber drying to a different moisture index, slight changes in geometric shapes are allowed. But if you pre-process the product chemical composition, then the changes decrease. Details are shown in the table below:

As chemical processing a penetrating antiseptic solution is used. In it, the product is soaked for 2-3 hours. And also the shrinkage is affected by the temperature regime in the chamber and the humidity of the air. The maximum allowable temperature is 50 degrees - shrinkage is maximum. Smaller changes are allowed at temperature regime 25 degrees.

Main processing steps

How oak is dried different ways we'll tell you more. The technology is followed step by step and it is unacceptable to skip one of the stages. Otherwise, the wood will crack and become brittle.

Vacuum exposure

vacuum drying oak is carried out in special chambers, where, under the influence of low atmospheric pressure, wood is pulled out excess moisture. It takes place in several stages:

1. Bog oak is soaked in an antiseptic solution for 2-3 hours. Sanezh will do.
2. The product is placed in a drying chamber, where it is kept at a temperature of 25 degrees and a humidity of 50% for 5 to 10 days. Temperature and humidity must be constant.
3. The oak is placed in a sealed chamber, where, under the influence of a vacuum, it is secondarily treated with an antiseptic solution.
4. Dried at a temperature of 35 degrees and humidity not higher than 25% for 10 days.

The method has advantages:

• Oak wood dries to a predetermined temperature.
• Color change is only 2-7%.
• Complete readiness within 4-5 weeks.

Of the minuses stand out high costs on electricity and the complexity of the process. If you do not keep track of humidity or temperature, then the wood will crack and become unusable.

Pulse method

The impulse method of drying bog oak is rarely used in Russia due to high costs. But it is considered effective and the material dries evenly.

It is carried out in the following steps:

1. Conductors are connected to the wooden blank on both sides.
2. The second ends of the conductors are connected to a special electrical appliance that will supply current.
3. Under the influence of electrical impulses, the workpiece gradually dries up to the required moisture content.

If you have the skills and knowledge, then you can assemble such a device with your own hands and use it for work.

adsorption method

The adsorption method resembles the old grandfather method and is available to everyone at home. To dry, a small piece of oak is placed in a material that absorbs moisture as much as possible. Craftsmen use special mineral granules. But newsprint will do.

Drying is carried out in the following steps:

1. Small blanks are soaked for 3-4 hours in a container with an antiseptic solution. But do not use solutions with bleaching effects, otherwise the black color valuable breed will disappear.
2. The blank is wrapped in several layers of paper and placed in a well-ventilated and dry place.
3. Each day, the product is unfolded and folded into new newspaper sheets.

Drying is carried out for 1-2 months. The wood will not crack and retain its noble hue.

infrared plates

The infrared light heats the wood evenly and the drying process is gentle. The workpiece does not heat up and no internal deformation is observed. The method is available at enterprises and at home. It is enough to purchase several infrared heating elements and place them on a frame made of timber or metal.

Drying is carried out in the following steps:

1. The workpiece is soaked in an antiseptic solution for 3-4 hours.
2. Placed on a flat surface under infrared heaters.
3. Once an hour, the workpieces should be turned over so that the heat is evenly distributed.

Humidity is checked with a handheld moisture meter. When the product dries out, it is allowed to rest for 3–4 days in a dark and cool place with a humidity of 15–25%. Then use as directed.

Of the advantages of drying under infrared plates stand out:

• Wood does not warp or crack.
• Does not lose its black color.
• Drying occurs evenly over the entire depth and length.
• Energy costs are minimal.

The method has no disadvantages, but because of its novelty, it is little trusted. The video below details one of the available ways drying hardwood:

How to properly dry bog oak is the secret of wood carving masters. It was passed down from father to son and carefully preserved. But with the advent of new technologies, it is not difficult to dry stained wood at home. The main thing is to follow the technology and follow our instructions.

Bog oak is one of the most precious rocks and the most valuable resource, which is widely used for the manufacture of decorative and art products. It has excellent aesthetic characteristics, increased hardness, but also a high cost due to the complexity of the drying process. Due to the high density of the structure, it is rather problematic to obtain high-quality stained wood during natural drying. But modern technologies allowed to dry the wood, taking into account all the characteristics of the material in a short period of time and with a minimum percentage of rejects.

Features of processing bog oak

Extraction and processing of bog oak is a non-standard process that is very different from the harvesting of spruce, pine or other ordinary wood. blank this material can be carried out in natural conditions during the extraction of peat or deep works in river channels. In the first case, wood extraction is carried out in the process of developing a peat bog. In the second case, oak deposits are determined by careful exploration of river channels, and extraction is assigned only at the time of the lowest water level in the river.

In addition to natural methods, a simple but multi-stage technology for harvesting material in special workshops is used to obtain bog oak.

As a result of a long stay under the water column, the oak acquires a noble dark color and a density comparable to iron. Only a carbide tool is suitable for cutting it. Moreover, the drier the material, the harder it becomes.

Due to the high natural humidity wet oak, reaching 117%, its weight is 1500 kg per 1 cu. This makes it difficult to transport it, so the tree is cut almost immediately after it is taken out of the water, and only then is it sent for shrinkage. Bog wood does not tolerate exposure to a large stream of hot air and direct sunlight, and when naturally dried, it requires a stable temperature, good ventilation and a huge amount of time. But modern technologies have made it possible to dry the material efficiently and as soon as possible, using the following methods:

• impulse;
• vacuum (chamber);
• infrared;
• adsorption.

Some argue that unnatural drying results in lightening of the material, but natural drying can also do this. At the same time, unlike the latter option, chamber technology saves time, increases productivity, and reduces the likelihood of cracks. To reduce the possible deformation of the wood, before drying it is recommended to pre-place it for 2 hours in a chemical solution of penetrating action. But, even with such preparation, it is necessary to accurately monitor allowable temperature, which can vary from 25 to 50°C.

Main processing steps

To minimize the overall percentage of rejects, each technology for drying bog oak requires compliance with a certain stage. Failure to follow the step-by-step methodology will lead to internal stress of the material, which will make it brittle and provoke the formation of cracks.

Pulse Technology

The impulse technique involves the impact on the lumber with a current. This technology is considered the most effective, as it guarantees uniform drying of stained wood without deformation. But, it has one significant drawback - high costs when harvesting large volumes of material. Pulse drying includes two main stages:

1. Connection of two or more conductors from the end sides of each workpiece.
2. Connection of the free ends of conductors to a device that supplies current in a pulsed mode. Under its influence, the wood gradually dries up and is brought to required level humidity.

If this method is not suitable for large-scale blanks of bog oak, then it is quite acceptable for shrinkage of single specimens. Moreover, a device of this type can be assembled independently, with special knowledge or with certain skills in installing electrical equipment.

Drying in a vacuum chamber

For drying of this type, chambers are used, where moisture is removed from the wood due to low atmospheric pressure. The whole process should go in the following order:

1. Lumber is kept in an antiseptic solution with a penetrating effect for at least 2 hours.
2. The prepared oak is placed in a drying chamber at a constant humidity of 50% and a temperature of 25°C, depending on the thickness of the blanks, for 5–10 days.
3. After this period, the wood is transferred to a completely sealed compartment for re-treatment with an antiseptic and drying at a humidity of up to 25% and a temperature of no more than 25% for 10 days.

Thus, the wood dries up to the required moisture content in just a month with a color change of 2 to 7%. The disadvantages of vacuum technology include the complexity of this process and the high cost of electricity.

infrared drying

Drying with infrared rays is considered one of the most gentle. It allows you to dry the lumber evenly without heating and deformation. Due to the availability of equipment and low energy consumption, this method is successfully used both in large enterprises and at home. To do this, you need to purchase only a few infrared heaters, which are then placed on a pre-mounted metal or wooden frame. After the construction of the structure, drying is carried out in several stages:

1. Oak is soaked in a solution with an antiseptic for at least 3 hours.
2. Then it is placed on flat surface, so that the heat from the infrared heaters is distributed between the workpieces.
3. To obtain uniform drying, the lumber is turned over once an hour. The drying of the workpiece occurs with the same humidity throughout the depth and length.

During the drying period, the humidity is determined manually using a moisture meter. Upon reaching the desired humidity, the wood is allowed to rest for about 4 days, placing it in a cool room with a humidity of up to 25%.

adsorption method

The adsorption method is one of the most ancient technologies. Its main advantage is the availability of application at home. For adsorption drying, oak wood is placed in a material that absorbs moisture well. Ordinary newsprint can be used as such a material, but special granules with a mineral composition are most often used. Drying with adsorbents is carried out in several steps:

1. Pre-soaking lumber in an antiseptic solution for 3 or 4 hours. For this procedure, only antiseptics are suitable, which have no whitening effect at all. Otherwise, the oak will lose its dark valuable color.
2. Extraction of rock from solution and drying with paper.
3. The wood is then placed in dry room with good ventilation and wrapped in 3-4 layers of paper.

In order to ensure high quality dried, bog oak is unrolled every day and covered with new sheets of paper. Drying by the adsorption method takes from 1 to 2 months. During this time, the tree reaches the required indicators of importance, completely retains its shade and does not crack.

Summarizing

Proper drying of bog oak requires not only knowledge of all the features of this material, but also precise adherence to technology. Only in this case, industrial and domestic wood production will be successful, maintaining productivity at the highest level.