CORA' - Timber trade and manufacturing.

Unit of Measurement: the thicknesses and widths given in the text are expressed in mm, differently from the lengths which are measured in cm. As an example, the measurement “27x100x240” describes boards that are 27 mm thick, 100 mm wide and 240 cm long

Other Names: this title gives the local or colloquial names that appear on the loading documents and which are generally accepted in the lumber sector. This fact becomes particularly important when the name is in a foreign language and is the only one recognised in the country of origin. In addition to the country of origin, however, the production zone and the loading port are also very important: the quality of lumber from the same species varies according to local conditions, the growth rate, the climate, the felling methods, the conversion rapidity, the selection level and the skill of the exporter. To confuse ideas even more is the fact that many countries unite species that are parented from a botanical point of view and place them all under the same group name. In consideration of all these factors, sector operators throughout the world always rely more on the botanical name when identifying the essences in a precise manner.

Aspect: the surface aspect of an essence is the result of the interaction of different natural elements: the different density that exists between spring and late developing wood, the quantity of the annual rings, the pigments and other colouring substances in the structure; the reaction of trees to stress (the stretching and compacting they undergo all through their life), torsion near knots, outgrowth, branches. All these characteristics, together with the differences in the types of grain and the cutting technique used, create the figure.

Short lengths: this expression identifies boards of shorter length. Considering that the reference parameters vary according to the area from which the essences come, it is impossible to establish a single value to identify a given product as Short length. An average value (which is flexible at a sales level) can be given as 200 cm. It must be remembered that short lengths of any species of wood can be purchased, exceptions excluded.

Average specific weight: the specific Weight (Density) of the wood depends on the water content (level of humidity, moisture content) per unit of volume. The supplied figure was calculated considering an average humidity level of 12%. The Specific weight of wood depends on its state (trunk stripped to the ground or not, sawn, dried) and also the environment in which it is present. To calculate the Specific weight at a level other than 12% but always between 5% and 25%, a correct approximation is to increase or decrease the specific weight by 0.5% for each point above or below the given humidity level. The density of wood can vary greatly even in the same botanical species, therefore the average value was taken as a reference. The Specific Weight can also be expressed in terms of Relative density, which expresses the Specific weight of the given volume of a substance relative to the weight of an equal volume of water. As water has a Specific weight of 1000 kg/m³, the Relative density is obtained by creating the ratio of the Specific weight as to this value.

Marketed woods are placed in different classifications according to their density.

 

Density

 

 

Specific weight (Relative density) at a humidity level of 12%

Exceptionally light

Lower than 300 (0.3)

Light

300 - 450 (0.3 – 0.45)

Average

450 - 650 (0.45 – 0.65)

Heavy

650 - 800 (0.65 – 0.80)

Very heavy

800 - 1000 (0.80 – 1.00)

Exceptionally heavy

1000 (1.0) or above


Distribution
: even though many species grow in countries that are not the country of origin, this term refers to the territory that is the main source of supply of a given Species.

Durability: this term refers to the natural ability of timber to resist attacks from fungi when it comes into contact with the soil or in the presence of high levels of condensation, when the humidity penetration can exceed 20%. Wood for outdoor use, but which does not come into contact with soil, lasts longer.

 

Natural durability of short boards

 

 

Approximate life in contact with soil

Excellent

More than 25 years

Good

15 – 25

Moderate

10 – 15

Scarce

5 – 10

Null

Less than 5 years

Grain: this term indicates the natural formation of wood grain, in other words how it “runs” in relation to the main trunk axis. Different types of grain exist:

  • Straight: the grain runs parallel to the main axis of the tree
  • Crossed: the grain is not parallel to the main axis of the tree
  • Interlocked: the grain spirals round the axis of the tree but changes direction to the left and to the right alternately (the spiral direction changes every few years).
  • Spiral: the grain moves in spirals in one direction only, producing a twisted effect
  • Fiddleback: the grain is wavy and regular.
  • Quilted: the grain is wavy and irregular.
  • Irregular: the grain wraps around the knots and other irregularities.
  • Diagonal: indicates a milling fault in straight-grain trunks, which is also found in axes sawn tangentially with a spiral grain.


Uses
:a summary of the typical uses for each type of wood is supplied, which is intended as a guide and not a definitive list.

Workability: the classifications of resistance to cutting and smoothing with tools refer to oven-dried material with a 12% humidity level. The term indicates the ability of the wood to hold nails and screws and the holding characteristics are evaluated; the results can be good, variable or difficult.

Shine: this term indicates how the wood reflects light, giving brightness to the surface. Compact and smooth wood are shinier than rough wood. Radial surfaces in general are shinier than tangentially sawn wood. The brightness of wood is not necessarily connected to its level of shine.

Mineral stains: some wood can be subject to black or brown mineral stains both when it comes into contact with ferrous composites through the soil and when it is used in damp environments. This fact is caused by the chemical reaction between the iron and tannin or similar compounds (such as polyphenols) that are naturally present in wood. Soft wood in general does not contain much tannin but other species such as Douglas and Redwood contain similar substances and can be subject to stain formation.

Movement: calculation is based on the sum of the tangential and radial movements resulting from a variation in the relative humidity between 60% and 90% at 25°C, and corresponds to the movement or dimensional variations of seasoned wood that is subject to atmospheric changes while in use. It was found that the return during seasoning and movement during use are not directly connected: as an example, timber that shrinks a great deal during drying could record only slight movement during use.

 

Type of movement

 

Percentage variation

 

Slight

Less than 3%

Medium

3 – 4.5%

Elevated

Above 4.5%


Botanical name
: each tree has a Botanical Classification that allows it to be identified precisely. Taking Walnut as an example, the correct scientific denomination should include the following:

Kingdom  Plantae
Division       Angiospermae
Class         Dicotyledonae
Order          Juglandales
Family Juglandaceae
Type Juglans
Species Regia

In practice only two names are used, the first being the Type and the second the Species (Binominal System). In the example given above, the European Walnut should therefore be called Juglans Regia.

Permeability for preservation treatments: wood that undergoes a preservation treatment, if carried out correctly, usually lasts slightly longer than harder natural wood. Timber that contains an external layer of permeable alburnum is to be preferred to hard wood that in general is more resistant to preservation treatments. The most used classifications are:

  • Permeable: can be penetrated completely by both hot and cold processes, carried out in the open air
  • Moderately resistant: it is quite easy to carry out lateral penetration (up to 18 mm in approx. 3 hours).
  • Resistant: difficult to penetrate beyond 6 m even after a long period of treatment.
  • Extremely resistant: cannot be penetrated even after an extended pressurisation phase.


Bending properties:this is the minimum radius of curvature at which a moderate percentage of bending can be obtained without defects in 25 mm-thick sections that have undergone saturated steaming at an atmospheric pressure for at least 45 minutes before the bending operation.

Radius of curvature at which breakage, during bending, should not exceed 5% (mm)

 

 

Bending property classification

Lower than 150

Very good

150 – 250

Good

260 – 500

Moderate

510 – 750

Modest

Higher than 750

Very modest

Mechanical properties: the knowledge of specific mechanical properties is necessary for determining the resistance and suitability of a species for a particular use. These are

  1. Maximum bending resistance required for transversal bending
  2. Rigidity or elasticity module, essential for determining the resistance of a strut or long standard
  3. Resistance to collision from loads applied unexpectedly.
  4. Resistance to parallel grain pressure, which determines the ability to resist loads on the head grain, very important when the wood is used for props or short standards.

Classification at a humidity content of 12%

Resistance to bending (N/mm2)

Rigidity (KN/mm2)

Maximum resistance to compression (N/mm2)

Resistance to collision (m)

Very low

Lower than 50

Lower than 10

Lower than 20

Lower than 0.6

Low

50 - 85

10 - 12

20 - 35

0.6 – 0.9

Average

85 – 120

12 – 15

35 – 55

0.9 – 1.2

High

120 – 175

15 - 20

55 - 85

1.2 – 1.6

Very high

Higher than 175

Higher than 20

Higher than 85

Higher than 1.6

Seasoning: the drying rate is based on the time needed to oven-dry planks that are 25 mm thick, starting from the fresh state until a humidity content of 12% is obtained. The seasoning speed varies according to the type of essence and the thickness.

Tangential cut: the trunk is cut in a tangential direction as to the yearly rings that form, with the cutting line, an angle that is equal to or greater than 40 degrees. This type of cut gives a “fiammato” effect.

Radial cut: the cutting line creates a 90 degree angle with the annual rings and runs parallel to them. The trunk is first sawn into pieces the size of a quarter of the trunk, giving a “rigatino” effect.

Texture: the texture of the wood surface is the result of the difference between the size of the pores and the width and quantity of rings. Wood with large vessels and wide rings has a rough texture, while wood with narrow vessels and thin rings has a fine texture. Referring to Soft (Resinous) wood, the texture is the result of the difference between spring wood and late wood, while for Hard (Broad-leaved) wood the texture is defined as being regular if it has widespread pores, and irregular if ring-shaped pores are present.