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The Brinell hardness indicates the average hardness or compressive strength of wood species. The value is given in Newtons per square millimeter - i.e. N/mm². This value is important, among other things, in order to be able to select the hardness and thus the type of wood suitable for the intended use and to be able to plan accordingly. The resilience of floors or furniture, for example, is directly dependent on this. Above all, but not only for larger construction projects, the Brinell value should therefore be taken into account.
Brinell and resilience
Brinell hardness is given in Newtons per square millimeter and is often given the abbreviation HB or HBW (Brinell hardness). It indicates how high the compressive strength is and thus when a wood begins to be damaged by pressure and weight.
For example, if the hardness is 22 N/mm² like that of European birch, a square millimeter can be loaded with 2.2 kilograms without being damaged. That doesn't sound like much at first, but in more common dimensions, the load-bearing capacity and resilience become clearer:
22 N/mm² is already 22 tons converted to decimetres, which can be carried on an area of 10 by 10 centimeters - the corresponding wood is therefore comparatively hard.
Hardness testing - formula and identification
The Brinell wood hardness is determined using an appropriate measuring device and method. A standardized solid - a hard metal ball - is pressed into the wood with the force F. The diameter of this metal ball and the diameter of the impression made in the wood are used for the calculation.
The method according to Johan August Brinell already existed in the 19th century. The Swedish engineer presented it at the Paris World Fair in 1900. The procedure and specification of the values have not changed since then. The formula is still:
The following Calculation example shows how hardness can be determined using this formula:
The exposure time of the solid in combination with the force is normally 10 to 15 seconds. Only if it lasts deviations exists, the duration is added to the degree of hardness as the last piece of information. However, the duration does not appear in the formula. With a detailed and standard-compliant labeling, this could look like this:
44.9 HBW 2.5/31.25/20
- 44.9 HBW - indicates the Brinell hardness.
- 2.5 - corresponds to the diameter of the sphere, i.e. the diameter of the solid that is used for the test.
- 31.25 - test force in kp (kilopond)
- 20 - different test or exposure time of 20 seconds.
If the duration is not specified, the designation would be limited to Brinell hardness, ball diameter and test force and would therefore look like this in this example:
44.9 HBW 2.5/31.25
Hardness of German species
How hard are the types of wood?
When using wood, it is important to know how hard each type is. Anyone who also wants to support sustainable and regional forestry will focus primarily on types of wood cultivated in Germany. For this reason, we have compiled common types together with the associated degrees of hardness:
The 3 hardest types of wood in Germany
yew
HBW: 50 N/mm² - This particularly hard wood is only commercially available in small quantities. Initially it is yellowish white, later reddish brown. Due to its properties and the rather inconspicuous grain, it is particularly popular for musical instruments, sculpture and carving.
Black Locust
HBW: 46 N/mm² - The tree, which originated in America, has also been planted in Europe for several centuries and is used, among other things, to improve the soil. The heavy and resilient wood is hard and has a golden brown color when dried. It is very versatile. Parquet, stairs, garden furniture, small furniture, but also gates and fences are used.
ash
HBW: 38 N/mm² - Ash wood is whitish, golden yellow or reddish to chocolate brown and extremely versatile. Floors and furniture can be made from it, as can paneling on ceilings and walls.
Robinia pseudoacacia, black locust
Other types of wood and their hardness
- Beech: 34 N/mm²
- Douglas fir: 18 N/mm²
- Alder: 12 N/mm²
- Aspen: 21 N/mm²
- European oak: 34 N/mm²
- European larch: 19 N/mm²
- Spruce: 12 N/mm²
- Pine: 19 N/mm²
- Cherry: 29 N/mm²
- Lime: 16 N/mm²
- Walnut: 32 N/mm²
- Poplar: 20 N/mm²
- Giant tree of life 35 N/mm²
- Fir: 20 N/mm²
- Walnut: 26 N/mm²
- Hornbeam: 36 N/mm²
In addition to the explicit number, the growth rate be included. Fast-growing woods are usually much softer - i.e. have a low hardness value. These include mainly softwoods. On the other hand, if the trees grow slowly, the wood is usually harder.
However, this also results in higher costs and the wood is more difficult to process. For these reasons, too, it is advisable not to choose the hardest types of wood - but to make an appropriate decision or even carry out your own hardness test if necessary.
Pinus parviflora, White Pine
The extra tip with a difference:
Comprehensive and expert advice on the degree of hardness of wood is always useful when larger projects are to be carried out. Floors, but also furniture or particularly stressed areas and objects must withstand a lot - but the hardest wood is not always necessary. An expert and coordinated decision can save both costs and effort.