Drying wood by digestion in salt + a couple more effective methods
In order to determine the quality of lumber, there is such a thing as wood moisture. It will indicate the quantitative ratio, which is expressed as the percentage of water in the wood structure in the mass of the sample.
We suggest talking about drying wood by boiling in salt.
Wood is a porous material that is dotted with pores and channels into which water enters, and thereby nourishes the plant with the minerals necessary for growth. This moisture is called "free".
It is removed from the wood structure even during atmospheric drying, but in addition to free space, there is also moisture bound in the wood. We are talking about that part of the water that is in the tissues and cells of wood, and takes part in the formation of sawn timber as a durable and reliable type of building material.
Such moisture is quite difficult to evaporate, and in most situations it is completely unrealistic, because it is located in microscopic pores that will remain inaccessible even with strong overheating by the air stream. If during the evaporation of free moisture the wood material does not change its physicochemical properties, then ..
when the bound moisture evaporates, the wood will be subject to changes:
- It changes its structure a lot.
- Loses its former durability.
- Changes in linear dimensions.
- The shape is changing.
Bound moisture can occupy a large share of the total, and if the total moisture level in the wood is more than 30%, then this will indicate the presence of free moisture in it, and therefore such lumber can will dry again. The wood is subjected to drying in order to carry out its subsequent processing and impart the required qualities. It is necessary to boil wood to prevent cracking and protect it from the ingress of putrefactive microbes. There are two of the most popular methods for digestion - drying in salt water, and digestion in oil and drying oil. In addition, drying in urea or urea (i.
e. in a hydrophobic solution) is often used.
Digestion of wood in salt is carried out using 25 % saline solution. The wood should be placed in a container filled with saline, and then it should be boiled over medium heat for 2-3 hours. The time may vary depending on how much wood you are trying to boil.
Drying of wood is carried out in salt water, the material is heated, which makes it possible to remove bound moisture with minimal losses to the geometry of the sawn timber.
Digestion of wood in oil makes it possible not only to prevent cracking in wood, but also to enhance the expressiveness of the wood material. When cooking, oil begins to push water and air out of the wood, because it enters the intercellular spaces. then the wood should be dried, and as a result it will be easy and simple to grind and polish. The boiling technology is quite laborious and requires direct human work, as well as further drying.
It is used for small samples, even for cuts. On an industrial scale, drying with oil or even salt will be completely impractical, and this is mainly used for domestic conditions. In the case of small industries, drying chambers are used, sometimes even vacuum ones.
.. + 250 degrees. So, oil, any oil, will act as a heating agent - it will evenly transfer heat to the wood and remove water vapor, as well as air that is actively released during boiling (this is drying), and also does not allow oxygen to the wood, which will prevent carbonization.
The main feature of this process is that it is impossible to cool wood in an oil bath, because inside the wood there will be water vapor heated to +250 degrees, which, when compressed to room temperature, will create a vacuum that sucks oil inside wood, and this is unacceptable.
The tree should be removed from the hot oil, while you will hear how it whistles in air (but there is a peculiarity - an example of boiling a 10 * 10 cm bar is described, and it cracked inside from a sharp removal).
As a result, after several hours of cooking, you get dried to 3-4% thermally modified wood, which does not undergo warping in the future. The oiled layer of the material will be about 0.5 cm, and it is usually cut off, and then they work with the wood, as usual - they glue it, soak it with wood stain, paint and varnish it.
Here is the result of the procedure: "A tree boiled in oil begins to be saturated with oil, but no more than 0.
5 cm (and usually 0.2 cm at all) on the surface, no more than 10 cm s the end (we are talking about deep impregnation to a dark color). The material in such a zone will highlight oil when pressed firmly or even when cutting - it has a dark brown color. Such places should be removed on a thicknessing tool, and the ends cut down. Inside the wood has a light yellowish tint, and moisture content is from 3 to 5%.
Epoxy resin holds such wood, and everything is perfectly skinned.
When covering with stain and alkyd varnish PF-283, adhesion problems were not noticed.A birch tree, which is more than 6 cm thick, can easily tear inside with oblique tears in the depth of the block (everything is whole outside, and such problems usually appear after sawing), but this is all due to the fact that the wood was taken out of the oil too quickly. "
And here's another result: "The board was only put in heated oil, the temperature of which was not less than +110 degrees. The mass temperature is +120 degrees.
Used the most simple oil, sunflower, from the store. You can try adding driers, but there is no point in them, because a 5 cm dried birch board will dry for 7.5 hours. By the way, controlling the process is not difficult at all. When the board is immersed, foam begins to stand out strongly, and by the end of drying, the board will practically not emit air bubbles.
With hard work, the moisture content of the board is from 2 to 4%. "
When heated to +250 degrees without air (it does not matter in what way - under an oil layer, in an atmosphere of inert gas, or even with water vapor) there is a change in the state of aggregation of such a substance in wood as lignin, as well as thermal destruction of polysaccharides, which 2> are excellent nutrients for bacteria:
+ 500 degrees.
All this contributes to a change in the woody cell structure. But the cellulose remains unchanged. During heat treatment, the decomposition of the carbohydrate part occurs and the moisture content inside the wood decreases, and this increases the resistance of the wood to the decay process. Under standard conditions, it is often with carbohydrates that it provides a nutrient medium for microscopic organisms.
Drying wood by boiling in salt is not as effective as the method with oil.
By the way, this is the same process as described above, but at the end the wood is cooled in oil, because of which it penetrates into the very depths of the wood.As a result of this, the material will be poorly adhesive and it will be necessary to thoroughly degrease the place of gluing, and not every adhesive composition is suitable for this. But on the other hand, such wood is not afraid of water at all, will not shrink and warp. This is exactly what is required for timber deck and deck grating.
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