The invention relates to the woodworking industry, namely to the technology of drying bog oak wood, and can be used, for example, in the production of furniture. To implement the method, at the first stage, bog oak wood blanks 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 workpieces are placed in a sodium chloride solution at a temperature of 20-22°C and kept at atmospheric pressure for 1.5-2.5 hours. The blanks removed from the solution are placed in a convective wood drying chamber and convective drying is carried out until the final moisture content of the wood blanks is 7.9-8%. Drying modes are selected depending on the thickness of the workpieces. The invention should reduce drying time and improve 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 production of furniture.
Technological processes for producing high-quality dried lumber and bog oak blanks are characterized by complexity and long duration.
There are several approaches to solving this problem. One of them represents convective drying of lumber under low-temperature conditions in periodic chambers and includes technological operations of heating, drying, moisture-heat treatment and conditioning of wood. The known technology provides for a stepwise change in the parameters of the drying agent depending on the moisture content of the wood ("Guide technical materials (RTM) on the technology of chamber drying of wood." - Arkhangelsk, 2000).
There is a known method of drying difficult-to-dry tree species, including oak, improving the known technology (description of patent RU 2263257, IPC 7 F26B 1/00, F26B 3/04, 04/19/2004, prototype). To speed up the drying process and eliminate cracking, the known method additionally provides for the formation of outer surface blanks of a layer of hygroscopic substance, providing an optimal difference in humidity between the outside and inner surface workpieces in the process of stepwise convective drying. To do this, before convective drying with a four-stage temperature increase, lumber is boiled at atmospheric pressure in a 15-17% sodium chloride solution for 2.5-3.0 hours.
The known method is long-lasting and does not provide high quality dried products. This is explained by the fact that the specificity of bog oak wood is not fully taken into account, associated with the presence of till 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.
In addition, the welding operation in the known method requires additional costs to improve production conditions, in particular, to ventilate production premises.
The purpose of the invention is to develop an effective technological process drying bog oak wood.
The technical result from the use of the invention is a reduction in drying time, improved quality of dried workpieces and improved 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 and held for 1-2 h at a temperature of 120-122°C and a pressure of 1.4-1.5 atm, and in the second, the heated wood is immersed in a sodium chloride solution at a temperature of 20-22°C and maintained at atmospheric pressure for 1.5-2.5 hours.
The essence of the technical solution is that at the stage of heating wood in an autoclave with dry saturated steam and holding it at a temperature of 120-122°C and a pressure of 1.4-1.5 atm, conditions are created for the destruction of till in bog oak wood and during subsequent stages drying creates conditions for the unhindered removal of moisture from the wood. The holding time is selected experimentally depending on the size of the workpieces and the initial moisture content of the wood within an interval of 1-2 hours, which is optimal for the destruction of till in the selected autoclave processing mode.
At the second stage, when heated wood is immersed in a solution of sodium chloride at a temperature of 20-22 ° C and atmospheric pressure, due to the difference in temperature and external pressure during the holding process, favorable conditions not only to form a hygroscopic layer on the outer surface of the workpiece, but also to remove moisture from the wood. Two-stage hydrothermal treatment of bog oak wood in selected modes makes it possible to reduce the initial moisture content of the workpieces before convection drying by 2-3% compared to the prototype and significantly reduce the duration of the drying process. Thus, with a stepwise convective drying process, the number of temperature increase steps is reduced by at least one.
Examples of method implementation.
Three batches of blanks made of stained oak wood in the form of bars measuring 19×100×500 mm, 32×100×500 mm and 50×100×500 mm with an initial humidity W n =90% at the first stage of hydrothermal treatment were placed in an autoclave and hydrothermal treatment was carried out treatment with dry saturated steam, heating them to a temperature of 120-122°C and further holding them under 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 workpieces were placed in a sodium chloride solution with a concentration of 15-17% at a temperature of 20-22°C and the first batch was kept at atmospheric pressure for 1.5 hours, the second for 2 hours and the third for 2.5 hours.
The workpieces removed from the solution were placed in a convective forest 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 workpieces was carried out with a three-stage increase in the temperature of the drying agent. Drying modes were selected according to the "Guidelines" technical materials(RTM) using the technology of chamber drying of wood", - Arkhangelsk, 2001, transitioning to the next stage of increasing the temperature of the drying agent as the current moisture content of the wood decreases to the transition value relative humidity. The final moisture content of wood blanks in batches was 7.9%. The drying time for the second batch of blanks was 2.5 days, the third - 4 days.
The dried blanks in all batches corresponded to the second quality category.
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.
Similar patents:
The invention relates to drying technology, and in particular to methods for drying liquid-viscous and pasty products and materials, and can be used in various industries (food, chemical and others).
The invention relates to methods for drying high-moisture materials of plant and animal origin: vegetables, fruits, vegetable greens and medicinal herbs, meat, fish, using heating with IR emitters in a pulsed heating-cooling mode.
Aralova O.V.(VGLTA, Voronezh, Russian Federation)
Shrinkage of a wood fumed oak’s values that was subject to preliminary thermochemical processing and raw are investigated. Conformities to the lawof influence to processing modes on shrinkage size are established.
Bog oak wood has a very beautiful appearance, and for this reason it is a valuable, decorative material. Highly artistic products and crafts are made from this material. IN Lately There has been an increase in demand for bog oak wood.
The high price of this material is due to the complexity of its extraction, storage and processing. Perhaps the greatest problems in the technology of wood processing are associated with the process of its drying. Traditional methods do not provide high-quality drying of bog oak wood.
For a number of years, the Department of Timber Science of the Voronezh State Forestry Academy conducted research on the development of a technology for drying bog oak wood. The developed technology of chamber drying with preliminary thermochemical treatment provides high-quality drying of bog oak wood. Wood dried in this way has high dimensional stability.
However, during the preliminary thermochemical treatment, a thin layer of a hygroscopic solution is formed on the surface of the wood, which affects the hygroscopic properties of the wood.
Shrinkage is one of the main physical properties of wood that affects the dimensions of products and depends on the amount of absorbed wood moisture. The purpose of this work was to study the amount of shrinkage of wood treated in this way.
Experimental studies were carried out on the wood of bog oak, taken from the river. Voronezh.
Wood selection was carried out in accordance with GOST 16483.21−72. Billets with a section of 20x20 mm were sawn from round timber of bog oak wood for further research.
One part of the samples, the latter measuring 20×20×60 mm along the fibers, was subjected to preliminary thermochemical treatment in a hygroscopic solution for 3 hours. Then all the processed blanks were sawn into samples 20x20x30 mm in size, the latter along the fibers. The second part of the blanks, not processed, was sawn into samples of the same size and used for control. Then the samples were placed in desiccators, on the bottom of which sulfuric acid of a given concentration was poured to maintain a given relative humidity.
Desiccators with acid solution and samples above it were placed in drying cabinet, in which a constant temperature of 50 °C, 80 °C and 20 °C was maintained. The relative air humidity in the desiccators was maintained at 52-54%.
The results of experiments to determine shrinkage are presented in Fig. 1 and 2.
Figure 1- Dependence of shrinkage of thermochemically treated bog oak wood in the tangential direction on humidity, at different temperatures drying
Figure 2 - Dependence of shrinkage of untreated stained oak wood in the tangential direction on humidity, at different drying temperatures
Analysis of the results shows that Drying of thermochemically treated wood is significantly less compared to untreated wood. The greatest reduction in shrinkage is observed when drying at a temperature of about 50 °C. In this case, the shrinkage value for the treated wood was 3.5% and 7.2 % – for unprocessed. At a drying temperature of 80 °C, the shrinkage was 6,1%, and with atmospheric drying in room conditions(20 °C) the shrinkage amount was 7,1 %.
For untreated wood, shrinkage at temperatures of 20 °C and 80 °C was respectively8% and 8.5 %. The least shrinkage of stained oak wood, and therefore its greater dimensional stability, was observed when dried at a temperature of 50 °C, for both treated and untreated wood.
An analysis of the nature of shrinkage of stained oak wood at temperatures of – 20 °C, 50 °C and 80 °C and a relative air humidity of 52-54% showed that the amount of shrinkage of stained oak wood is the same as that of natural oak. Minimal shrinkage of bog oak wood is observed when drying at a temperature of 50 °C and a relative air humidity of 52-54%. Maximum - when drying in natural conditions (temperature 20 ° C and 80 ° C, and relative humidity 52-54%. Maximum shrinkage in natural conditions is due to the absence of internal stresses that restrain shrinkage. When high temperature and relative air humidity of 52.5%, the increase in shrinkage is presumably due to the appearance of collapse, as in natural oak wood due to the destruction of some anatomical elements.
Thus, as a result of the experimental studies, it was found that in order to reduce the shrinkage and increase the dimensional stability of products made from it, it is advisable to subject the bog oak wood to preliminary thermochemical treatment and drying to the required final moisture content in chambers at a temperature of about 50 °C. The layer formed on the surface (about 0.5 mm) from the hygroscopic solution is easily removed by subsequent mechanical processing.
Literature
1. Kuryanova, T.K., Platonov, A.D., Petrovsky, V.S. Drying of solids hardwood with preliminary thermochemical treatment [Text] / T. K. Kuryanova, A. D. Platonov, V. S. Petrovsky // Forest Journal. – 2004. - No. 4. – P.58–63.
Oak is a very popular material that is widely used:
- Construction.
- Finishing work.
- Making furniture.
- Making art objects and souvenirs.
Naturally, not just felled and sawn wood is used in the work, but processed and qualitatively dried material. This is a prerequisite to avoid future cracking, changes in the shape and size of the product. Oak, which is used in construction or furniture business, must have certain physical and mechanical properties.
Therefore, when the sawing is completed, the question arises: “ How to dry oak correctly" We will answer this in this article.
Features of oak wood: what should happen as a result of drying
Oak lumber is quite capricious, it is difficult to dry naturally. It is not enough just to leave the stack under a canopy or in the open sun in order to get the desired result after a certain time.
Before how to dry oak boards, you need to understand the features of the material:
- Oak wood is susceptible to drying. This means that when the moisture level drops below a critical level, internal and external cracks can form.
- The most difficult thing to dry is freshly sawn oak, whose humidity exceeds 25%.
- Temperatures above 55 degrees are not allowed early stages drying. This leads to the collapse of wood capillaries, that is, to the appearance of multiple internal cracks.
- It is not recommended to send freshly sawn material with a humidity above 40% for drying.
- Proper drying of oak requires maintaining a certain level of temperature and humidity.
Features of drying oak wood are such that to obtain quality material without defects with a certain percentage of humidity, it is necessary to draw up a preliminary plan for this procedure and use special means.
There are several tasks for drying oak:
- Shrinkage with prevention of changes in linear dimensions. Here the humidity is reduced to 30%.
- Drying to transport humidity of 20-22%.
- Full volume drying for immediate use. The humidity level should be 6-12%.
Methods of drying oak: chamber and chamberless methods
From all of the above, it is obvious that obtaining wood from a freshly felled oak that meets all the necessary parameters is a labor-intensive and time-consuming process.
There are many ways to reduce the moisture content of boards, logs and beams, but they can all be divided into two large categories:
- Tubeless (atmospheric) drying.
- Chamber drying.
Atmospheric drying is ideally the most affordable and natural way to reduce moisture levels. The technique has been used in sawmills and wood processing industries for centuries. It is believed that naturally dried wood is of the highest quality and can be used for decades without changing its original qualities. But the method has one significant drawback - it takes a long time.
Since modern life is very dynamic, buyers are interested in purchasing material as quickly as possible. Logging enterprises, in turn, prefer to sell wood as quickly as possible. Therefore, in the 19th-20th centuries, many techniques were invented using electrical energy. Chamber drying is carried out in convection chambers, condensation method and vacuum drying are also used. 
All work is carried out in industrial conditions, as a rule, divided into the following stages:
- Warm up
- Drying directly.
- Cooling, obtaining a predetermined humidity threshold.
Chamber drying is similar to multi-accelerated atmospheric drying; the desired result is achieved many times faster. But the disadvantage is the high cost of the procedure. It is necessary to use expensive equipment; most often this is only possible in industrial conditions.
Fortunately, not so long ago infrared dryers, which allow you to reduce the time of atmospheric drying and obtain the desired result in a time comparable to chamber processing. At the same time, all features of drying oak wood, the material does not experience aggressive action that destroys the structure. At the end of the process, the humidity reaches the required level.
Infrared oak drying: the advantages of the modern method
Proper drying of oak Now it has become possible even at home. Infrared dryers manufactured under the FlexiHIT brand have a cassette form factor, are easily located inside stacks, and can also be used for drying small pieces of material. In this case, the volume of wood does not matter, it is enough to use required amount dryers and position them correctly. The result is achieved in 3-7 days.
The properties of infrared-dried oak correspond to the properties of wood dried by the atmospheric method:
- The material has a specified moisture content.
- The fibers do not warp, cracks and stressed areas do not form.
- Appearance matches appearance naturally dried oak.
It is noteworthy that anyone can use IR dryers; you do not need to have special skills to get results. The equipment operates on normal electrical network, while consuming very little. Drying one cubic meter of wood requires no more than 200-400 kW.
To check the humidity, it is enough to use a moisture meter; when the required value is reached, the infrared dryers turn off. The oak can be used for its intended purpose immediately.
Oak wood is quite capricious when dried, so to get the optimal result in the shortest possible time, it is better to prefer tubeless drying in combination with IR dryers.
Bog oak is one of the most precious species and a valuable resource, which is widely used for the manufacture of decorative and artistic products. It has excellent aesthetic characteristics, increased hardness, but also high cost due to the complexity of the drying process. Due to the high density of the structure, it is possible to obtain high-quality stained wood with natural drying it is quite problematic. But modern technologies made it possible to dry wood taking into account all the characteristics of the material in a short period of time and with a minimum percentage of defects.
Features of bog oak processing
The 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 of this material can be carried out in natural conditions during peat extraction or deep works in river channels. In the first case, wood is extracted during the development of a peat bog. In the second case, oak deposits are determined by careful exploration of river beds, and extraction is scheduled only for the duration of the low level water in the river.
Besides natural methods To obtain bog oak, they use a simple but multi-stage technology for harvesting material in special workshops.
As a result of a long stay under water, oak acquires a noble dark color and density comparable to iron. Only a carbide tool is suitable for cutting it. Moreover, the drier the material, the harder it becomes.
Due to high natural humidity wet oak, reaching 117%, its weight is 1500 kg per 1 cu. This makes it difficult to transport, so the wood is cut almost immediately after it is taken out of the water, and only then is it sent for drying. Stained wood is difficult to withstand the effects of a large flow of hot air and direct impact sun rays, and when dried naturally, 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 in the shortest possible time, using the following methods:
- pulse;
- vacuum (chamber);
- infrared;
- adsorption.
Some argue that unnatural drying leads to lightening of the material, but when drying under natural conditions this is also possible. At the same time, unlike the last option, chamber technology saves time, increases productivity, and reduces the likelihood of cracks. To reduce possible deformation of the wood, before drying it is recommended to first place it in a chemical solution 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 defects, each bog oak drying technology requires compliance with a certain stage. Failure to follow the step-by-step procedure will lead to internal stress in the material, which will make it brittle and provoke the formation of cracks.
Pulse Technology
The pulse technique involves exposing lumber to electric 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 procuring large volumes of material. Pulse drying includes two main stages:
- Connecting two or more conductors from the end sides of each workpiece.
- Connecting the free ends of the conductors to a device that supplies current in a pulsed mode. Under its influence, the wood gradually dries and is brought to the required moisture level.
While this method is not suitable for large-scale preparations of bog oak, it is quite acceptable for drying single specimens. Moreover, a device of this type can be assembled independently, having special knowledge or having certain skills in installing electrical equipment.
Drying in a vacuum chamber
For this type of drying, chambers are used where moisture is removed from the wood due to low atmospheric pressure. The entire process should take place in the following order:
- The lumber is kept in an antiseptic solution with a penetrating effect for at least 2 hours.
- 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.
- After this period, the wood is moved 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 to the required moisture content in just a month with a color change of 2 to 7%. To the disadvantages vacuum technology This can be attributed to the complexity of this process and high energy costs.
Infrared drying
Drying using infrared rays is considered one of the most gentle. It allows you to dry lumber evenly without heating or deforming it. 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 only need to purchase a few infrared heaters, which are then placed on a pre-mounted metal or wooden frame. After erection of the structure, drying is carried out in several stages:
- The oak is soaked in a solution with an antiseptic for at least 3 hours.
- It is then placed on flat surface, so that the heat from infrared heaters is distributed between the workpieces.
- To obtain uniform drying, the lumber is turned over once an hour. The workpiece dries with equal humidity throughout its entire depth and length.
During the drying period, humidity is determined manually using a moisture meter. Once the desired humidity is achieved, 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 use at home. To dry by adsorption, oak wood is placed in a material that absorbs moisture well. Regular newsprint can be used as such material, but most often special granules with mineral composition. Drying using adsorbents is carried out in several steps:
- Pre-soak the lumber in an antiseptic solution for 3 or 4 hours. For this procedure, only antiseptics that have no whitening effect are suitable. Otherwise, the oak will lose its dark, valuable color.
- Extracting the rock from the solution and drying it with paper.
- 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 drying, bog oak is unrolled every day and covered with new sheets of paper. Drying by 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.
Let's summarize
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 home production wood will be successful, maintaining productivity at the highest level.
Dear Sirs,If possible, we ask you to send us recommendations for drying oak (what features should be paid attention to when drying this type of wood).
Thanks in advance,
Sincerely,
Natalia Titova
The technology for drying oak wood is not fundamentally different from the technology for drying coniferous and soft-leaved species. Distinctive feature is that when moving from one drying stage to another, it is necessary to equalize the moisture content of individual boards in the stack, taking into account that drying is carried out over the wettest material. wood drying process drying chamber divided into several stages: I. Initial heating of the wood. II. Actually drying the wood. III. Moisture and heat treatment. IV. Conditioning. Drying always begins with heating the wood, regardless of the initial moisture content of the lumber. During heating, water (steam) is supplied to the chamber through humidifying pipes with heat exchangers turned on, fans running and supply and exhaust ducts closed. The humidity of the drying agent is maintained at a level close to the saturation state. After warming up, the moisture content of the lumber is additionally measured, which is used to determine at what stage the actual drying should begin. It should be taken into account that drying is carried out over the wettest material. It is forbidden to move 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 stages. At the initial stage of the process, it is necessary to maintain a small value of humidity difference across the thickness, 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 the specified final moisture content. The transition from stage to stage in the presence of a moisture meter is judged by its readings. The temperature of the medium should be increased towards the end of drying. With a decrease in humidity, an increase in temperature will not cause a decrease in strength, but at the same time will significantly speed up the process. The drying itself ends when the final humidity is reached according to all sensors. Next they move on to the stages of moisture-heat treatment and conditioning treatment. Moisture-heat treatment is necessary to remove or reduce “residual” internal stresses that arise in 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 heaters turned on, fans running and supply and exhaust ducts closed. The humidity of the drying agent is maintained at a level close to the saturation state. When drying hardwood, conditioning treatment is required. Conditioning is carried out to equalize the moisture content of the wood over the volume of the stack and the thickness of the lumber. In the drying chamber, with the help of heaters and humidifying devices, an environmental condition is maintained in which under-dried assortments dry out, and over-dried assortments are moistened. After leveling the final moisture content of the lumber, the stacks must be cooled at closed door and open supply and exhaust ducts. In summer, fans can be turned on.
