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 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 wood-drying chamber and convective drying is carried out until the final wood moisture content of the blanks is 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 sawn timber by low-temperature conditions in chambers of periodic action and includes technological operations of 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 surface blanks 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 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 production facilities.
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, involving 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 holding 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.
The essence of the technical solution lies in the fact that at the stage of heating wood in an autoclave with dry saturated steam with holding at a temperature of 120-122 ° C and a pressure of 1.4-1.5 atm, conditions are created for the destruction of the til in the bog oak wood and during the subsequent stages drying, conditions are created for the unhindered removal of moisture from the 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 the 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 not only to form a hygroscopic layer on the outer surface of the blanks, but also to remove moisture from the 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 of 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 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 holding 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 workpieces 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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Aralova O.V.(VGLTA, Voronezh, RF)
Shrinkage of a wood fumed oak’s values that was subjected to preliminary thermochemical processing and raw are investigating. conformity 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 is 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 is highly dimensionally stable.
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 according to 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 humidity in the desiccators was maintained at 52-54%.
The results of experiments to determine the shrinkage are shown in fig. 1 and 2.
Figure 1- Dependence of shrinkage of thermochemically treated bog oak wood in the tangential direction on humidity, at various temperatures drying
Figure 2- Dependence of shrinkage of untreated bog oak wood in the tangential direction on humidity, at different drying temperatures
An analysis of the results shows that drying of thermochemically treated wood is significantly less compared to untreated wood. The greatest decrease in shrinkage is observed during drying at a temperature of about 50 °C. In this case, the shrinkage value for treated wood was 3.5% and 7.2 % - for raw. At a drying temperature of 80 °C, the shrinkage was 6,1%, and with atmospheric drying in room conditions(20 °C) the amount of shrinkage was 7,1 %.
For untreated wood, the shrinkage at temperatures of 20 °C and 80 °C was, respectively,8% and 8.5 %. The smallest shrinkage of bog oak wood, and hence its greater dimensional stability, was manifested during drying at a temperature of 50 ° C, both for treated and untreated wood.
An analysis of the shrinkage nature of bog oak wood at a temperature of -20 °C, 50 °C and 80 °C and a relative air humidity of 52-54% showed that the shrinkage of bog oak wood is the same as that of natural oak. The minimum shrinkage of bog oak wood is observed when drying at a temperature of 50 ° C and a relative 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 a 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 treatment.
Literature
1. Kuryanova, T. K., Platonov, A. D., Petrovsky, V. S. Drying of solid 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.
- Creation of furniture.
- Production of 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 sawing is completed, the question arises: “ How to dry oak". We will answer it in this article.
Features of oak wood: what should be the 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 subject to drying. This means that when the moisture level falls below a critical level, internal and external cracks can form.
- The hardest thing to dry is freshly sawn oak, the moisture content of which exceeds 25%.
- Temperatures above 55 degrees are unacceptable early stages drying. This leads to the collapse of woody capillaries, that is, to the appearance of multiple internal cracks.
- It is not recommended to send freshly sawn material with a moisture content above 40% to dry.
- Proper drying of oak requires maintaining a certain level of temperature and humidity.
Features of drying oak wood are such that in order to obtain quality material without defects with a certain percentage of moisture, it is necessary to draw up a preliminary plan for this procedure, use special tools.
There are several tasks for drying oak:
- Shrinkage with warning of changes in linear dimensions. Here, the humidity is reduced to 30%.
- Shrinkage to transport humidity of 20-22%.
- Full volume drying for direct use. The humidity level should be 6-12%.
Oak drying methods: chamber and tubeless technique
From the foregoing, it is obvious that obtaining wood from a freshly cut oak that meets all the necessary parameters is a laborious and lengthy process.
There are many ways to reduce the humidity of boards, logs and beams, but all of them can be divided into two broad categories:
- Chamberless (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 woodworking industries for centuries. It is believed that a naturally dried tree is of the highest quality and can be used for decades without changing its original qualities. But the method has one significant drawback - prolongation in time.
Since modern life is very dynamic, buyers are interested in acquiring material as quickly as possible. Logging companies, in turn, prefer to sell wood as soon as possible. Therefore, in the XIX-XX centuries, many techniques were invented using electrical energy. Chamber drying is carried out in convection chambers, the condensation method and vacuum drying are also used. 
All work is carried out in industrial conditions, as a rule, are divided into the following stages:
- Warming up
- Drying directly.
- Cooling, obtaining a predetermined humidity threshold.
Chamber drying is similar to repeatedly 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 it is possible only in industrial conditions.
Fortunately, not so long ago infrared dryers, which allow to reduce the time of atmospheric drying, to 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 placed inside stacks, and can also be used to dry 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 those of atmospheric-dried wood:
- 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 everyone can use IR dryers, you do not need to have special skills to get the result. The equipment is powered by conventional 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 indicator is reached, the infrared dryers turn off. Oak can immediately be used for its intended purpose.
Oak wood is quite capricious when drying, in order to get the best 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 breeds and a valuable resource that is widely used for the manufacture of decorative and artistic 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, to obtain high-quality stained wood with natural drying is quite problematic. 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 reconnaissance of river channels, and production is assigned only for the time of the low level water in the river.
Apart from natural methods, to obtain bog oak, a simple but multi-stage technology for harvesting material in special workshops is used.
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 is difficult to tolerate the effects of a large flow of hot air and a direct hit sun rays, and when naturally dried 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 wood, before drying it is recommended to pre-place it for 2 hours in 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 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:
- Connection of two or more conductors from the end sides of each workpiece.
- 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 the required level of 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:
- 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 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%. To disadvantages vacuum technology can be attributed to 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:
- Oak is soaked in a solution with an antiseptic for at least 3 hours.
- Then it is placed on flat surface, so that the heat from the infrared heaters is distributed between the workpieces.
- 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 material, but special granules with mineral composition. Drying with adsorbents is carried out in several steps:
- 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.
- Extraction of rock from solution and drying 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 and covered with new sheets of paper every day. Drying by the adsorption method takes from 1 to 2 months. During this time, the tree reaches the desired 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 the industrial and home production timber will be successful, maintaining performance at the highest level.
Dear Sirs,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).
Thanks in advance,
Sincerely,
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. wood drying process drying chamber 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.
