The density of wood is the most important characteristic of the material that allows you to calculate the load during transportation, processing and using wooden raw materials or items. This indicator is measured in grams per cubic centimeter or kilograms per cubic meter, but the snag lies in the fact that these indicators cannot be considered stable.
What it is and from what depends?
Wood density, if we speak dry definition language, is The ratio of mass of material to its volume. At first glance, it is not difficult to determine the indicator, but the density is highly dependent on the amount of pores in a specific tree of wood and its ability to retain moisture. Since water is a more dense substance than many types of dry wood and, naturally, more dense than emptiness between the fibers, the percentage of its content is strongly affected by the final indicator.
In view of the foregoing, two indicators of wood density are distinguished, which are close to the most common definition, but are more accurate.
- Specific gravity. This criterion is also known as basic or conditional density. For measurements take the so-called wood substance – this is no longer natural material in its original form, but a dry block, which is pressed under a large pressure to eliminate even emptiness. In fact, this figure characterizes the true density of wood fibers, but in nature, without preliminary drying and pressing, such a material will not meet. Accordingly, the density of wood is in most cases all the same above the specific weight.
- Volume weight. This indicator is already more close to reality, because the mass is estimated not even dried, and raw wood. This method is adequately adequate because in our country there can be an ideal dry wood in principle – the dried material has the property of choosing the missing moisture from atmospheric air, it becomes heavier again. In view of this volumetric weight, it is customary to determine for wood with a certain, clearly designated humidity level, which is normal for a particular variety. To such a state, the fresh substance should still be dried, but it does not put the task of achieving the zero level of humidity – stop at that indicator, which will still be ensured by the laws of physics when contacting air.
The density of the wood material is interconnected with some other physical properties. For example, the presence of pore means the presence of gas bubbles in the thicker of the tree – it is clear that they weigh less, occupying the same volume. Therefore, wood with a porous structure always has a density lower than that grade for which a large number of pores is not typical.
Similarly, there is a relationship of density with humidity and temperature. If the pores of the material fills heavy water, then the bar itself becomes harder, and vice versa – when drying, the material gives only a minor shrinkage in volume, but significantly loses in terms of mass. Temperature here is mixed in an even more complex scheme – when it is raised, on the one hand, forces water to expand, increasing the volume of the workpiece, on the other – provokes faster evaporation. In this case, the temperature decrease below zero turns moisture into ice, which, without adding in weight, slightly increases in volume. And evaporation, and frozen moisture in the wood structure are fraught with mechanical deformation of the bar.
Once came about the humidity, it is necessary to clarify that According to its level, three categories of seaved wood are distinguished. In this case, a freshly dredged material, the moisture content is usually at least 50%. In terms of indicators, more than 35% of the tree is considered raw, the indicator within 25-35% allows you to consider the material semi-dry, the concept of absolute dryness begins with 25% water content and less.
Up to absolute dryness, raw materials can be brought even with a natural drying under a canopy, but to achieve even lower water content will have to use special drying chambers. At the same time, measurements should be carried out with wood, Whose humidity does not exceed 12%.
The density is also closely related to Absorption, That is, the ability of the wood of a particular variety to absorb moisture from atmospheric air. The material with a high absorption of a priori will be denser – simply because It constantly takes water from the atmosphere and in normal conditions there can be no little much dry dry.
Knowing the density parameters of wood, you can roughly judge it about its thermal conductivity. Logic is very simple: if the wood is not dense, then there is a lot of air emptiness in it, and the wooden product will have good thermal insulation properties. If the air has low thermal conductivity, then water is just the opposite. Thus, high density (and therefore the moisture content) suggests that for thermal insulation, the concrete tree variety is completely not suitable!
In terms of flammability, in general, such a tendency is observed. The pores filled with air, they can not burn in themselves, but the process does not interfere, therefore the loose varieties of wood are usually burning pretty good. High density due to significant water content – this is a direct obstacle to the spread of fire.
A bit paradoxically, but less dense wood varieties are distinguished by increased resistance to deformation from impact. The reason lies in the fact that such a material is easier to squeeze due to a large number of empty internal voids. With a dense tree it will not work so – the displacement of heavy fibers will follow, because most often the billet from a strong blow will split.
Finally, dense wood in most cases is less susceptible to rotting. In the thickness of such a material, there is simply no free space, and the wet state of the fibers is the norm for him. In view of this, when processing wood sometimes even use soaking in ordinary distilled water, using it as a method of protection against influential biological factors.
If we consider the determination of the density of wood purely from the point of view of the mathematical formula, then The mass of the product multiplied by the humidity parameter is divided into volume, also multiplied by the same parameter. The humidity parameter is included in the formula due to the fact that, absorbing water, dry wood has a fool property, that is, it is increased in volume. It may not be noticeable to the naked eye, but to solve most tasks it is important to take into account every excess millimeter and kilogram.
Considering the practical side of the measurements, repel from the fact that Before measurements, you must first achieve a moisture equilibrium – when excess water is removed from wood by drying, but the material is not too dry and will not pull the moisture from the air. For each breed, the recommended humidity parameter will be its, But in general, the indicator should not fall below 11%.
After that, the necessary primary measurements are made – the dimensions of the workpiece are measured and the volume is calculated based on this data, then an experienced piece of wood is treated.
Next, the workpiece is dumping in distilled water for three days, although there is another criterion for stopping the soaping – it is necessary to achieve the thickness of the piece of chickens at least 0.1 mm. Having achieved the desired result, the swollen fragment is again measured and weighed, getting the maximum volume.
The next step is a long drying of wood, ending the next weighing.
The mass of the dried billet is divided into maximum volume, which was characteristic of the same, but wakeful from the moisture of a piece. As a result, the most basic density (kg / m³) is obtained or the proportion.
The described actions are instructions recognized in Russia at the state level – The procedure for operations and calculations was recorded in GOST 16483.1-84.
Since each gram and millimeter are important, the standard regulates even the requirements for the workpiece – it is a lumber in the form of a rectangle with a length and 2 cm wide with a height of 3 cm. At the same time, for maximum measurement accuracy, the workpiece is subject to compulsory careful processing before starting experiments. Protrusions and roughness should not affect the testimony.
Density of different breeds
From the above, it was possible to make a predictable conclusion that the procedure for measuring and evaluating the density of wood – the task is quite complex and requiring very precise measurements. In most cases, the comprehensive work and suppliers perform all complex work – On the packages of the same edged or parquet board, all the basic properties of the material must be indicated.
It is more complicated if a person is even a blank of wood of various varieties is engaged in himself, because then there will be no informative packaging, but then you can find exemplary density indicators for each tree variety from which entire tables are compiled. It is important only to remember that The moisture content of each individual bar is influenced by many factors, separately described above, and therefore, in a particular case, the mass fluctuations are very likely.
In some cases, another situation is possible: when only the task is delivered to the master, but there is no wood to implement it. Raw materials have to be purchased independently, but it is necessary to figure out which breed will be the most effective.
Considering that the density affects many other practical qualities of wood, you can immediately decompose the predominant part of unsuitable applicants, oriented on a specific category of material. Especially for this allocate Three main types of wood varieties in density.
Low density is practical at least from the point of view that light wood is easier to harvest and transport and transport, and the movers will be grateful to the consumer for choosing exactly such a tree. According to the common classification, The upper density limit for a small density tree is 540, less often 530 kg / m³.
This category includes the bulk of industrial coniferous rocks, such as spruce and pines, aspen and many types of walnut, chestnut and cedar, Iva and Lipa. Cherry and alder, depending on the specific varieties and conditions, can relate to rocks with small and medium density, and the cherry – more often to the middle. Due to the comparative ease of transportation, such wood is cheaper. Another obvious argument in favor of its cheapness and demand is that A significant part of domestic forests is composed of precisely these breeds.
Specialists note that Trees with a small density of trunks most common in the northern regions. It is due to the fact that the regions in which the forests of the respective rocks grow, can not always provide a large amount of moisture to the plant world.
Adjusting to the existing conditions, plants with a low density of wood form trunks of relatively low humidity, which ultimately affects the mass.
Middle density wood is “Golden Mid” when choosing a material, which does not have any explicit advantages, except for that significant moment that it does not have obvious flaws. Not being too heavy, such a material demonstrates good compressive strength, not possessing explicit flaws of dense breeds, like good thermal conductivity.
The category of medium density includes lumber from larch and birch, apple and pears, rowan and maple, flashes and walnut, ash and poplar, cherry, beech and elm. Cherry and Olha have a significant run in the density indicator, which does not allow you to confidently put all the representatives of the breed in one category – both fluctuate between small and medium, and Olha turns out to be closer to low density. Indicators allowing to include a breed in the middle density category are 540-740 kg / m³.
As you can see, this is also very common in our edges of the tree of trees, which enjoy noticeable demand in various fields of industry and can boast of high qualities not only in practical, but also in the decorative sphere.
Increased wood density may seem deficiencies in view of the fact that items from it turn out to be very heavy and massive and cannot boast of good thermal insulation indicators, and they are also split from impact.
In this case, the material is able to withstand significant constant loads without deformation, and also different Comparatively low flammability and amazing durability. Among other things, such wood is also relatively susceptible to rotting.
To hit the category of dense rocks, the density of wood is needed at least 740 kg / m³. Of the common varieties of wood, the oak and acacia are first remembered, as well as Grab and Samshat. This should also include some breeds that are not growing in our latitudes, for example, pistachio and iron trees.
Please note: almost all of the listed breeds refer to the category of expensive and prestigious. Even their very significant weight does not prevent the material of the material to carry from another hemisphere, which only else affects the cost.
Output from here only one: With all its shortcomings, such wood has a number of advantages that are worth a generously pay.