NL1025943C2 - Wood processing method, especially for robinia, comprises maintaining moisture content of wood above given limit from chopping until drying stage - Google Patents

Abstract

The moisture content of the wood is kept above a given limit from the chopping stage right up to the drying stage, when it is reduced to below this limit. A method for processing wood, especially robinia wood, comprises chopping and sawing the wood, stacking the wood in a drying arrangement and placing the latter under tension, transporting the drying arrangement to a dryer installation and steam drying the wood. The moisture content of the wood is kept above 30% until the drying step and then reduced to less than 30% during drying.

Description

METHOD FOR PROCESSING WOOD

The invention relates to a method for processing wood, in particular Robinia.

Tropical hardwood is used extensively in all kinds of fields. Tropical hardwood has the advantage that it is durable and not very sensitive to rot. Tropical hardwood is harvested in natural areas in the tropics and this logging causes considerable damage to nature there. Due to the global demand for tropical hardwood, these areas where tropical hardwood is growing are at great risk.

10 Much is being done to reduce the production of such tropical hardwood forests, so that nature suffers little damage. However, this has the consequence that the demand for tropical hardwood is many times higher than the supply thereof.

15 There are currently few or no alternatives for tropical hardwood. In Europe, the Robinia wood species is growing, which can be seen as an alternative to tropical hardwood. At least, Robinia has the same durability. The disadvantage of this type of wood, however, is that it is difficult to machine because it easily warps and that it has a green color. The customers for the tropical hardwood want a brown color because they are familiar with it. The green wood color is therefore not desired.

An advantage of Robinia, on the other hand, is the limited growing time of 25 years as opposed to tropical hardwood with growing times of more than 80 years.

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It is now an object of the invention to provide a method for processing wood, in particular Robinia, which reduces the aforementioned disadvantages.

This object is achieved with a method according to the invention, which comprises the steps of: - cutting down the wood; - cutting the wood; - stacking the wood into a drying package and tensioning the drying package; - transporting the drying package to a drying device; and steam drying the drying package, wherein the moisture content of the wood from cutting down to steam drying is kept above 30% and reduced to below 30% during steam drying.

When the dried wood is used for interior, the moisture is reduced to around 10%. For outdoor applications up to around 18%.

By keeping the wood, in particular Robinia, from the hood 20 until it is dried in a drying package by means of steam at a moisture content of above 30%, the wood is prevented from involuntarily warping and thus difficult to be processed. By subsequently drying the wood in a drying package, the moisture content is reduced to an acceptable value, without the wood warping, since it is clamped in a drying package.

In a preferred embodiment of the method according to the invention, the wood is dried with an overheated steam. The temperature of the steam is preferably in the range of 105 ° C to 115 ° C. The advantage of steam drying is that the moisture in the core of the wood rises above the boiling point and is thus driven out of the wood. The use of steam prevents the outside of the wood from drying out earlier than the core, which could cause cracks in the wood.

In a preferred preferred embodiment of the method according to the invention, the wood is dried within 144 hours. Typically, wood is dried very slowly for periods of more than 60 days. This is done to prevent discolouration of the wood.

In contrast to the usual practice, the method according to the invention attempts to dry the wood as quickly as possible, whereby a discoloration as large as possible occurs. The advantage with Robinia is that as a result the green color disappears and a brown color develops, which is strongly reminiscent of the color of tropical hardwood.

In yet another embodiment of the method according to the invention, the step of steam-drying the drying package is preceded by post-tensioning the drying package. This ensures that the drying package is optimally under tension when the drying package goes into the steam drying oven. This way, the wood is prevented from warping as much as possible during steam drying.

In addition, the fibers in the wood will stick to each other as a result of steam drying. Because the wood is tensioned, the fibers will be fixed in this tensioned state, whereby the properties of the wood improve.

It is possible to add chemical components to the steam during steam drying, thereby influencing certain characteristics of the wood. For example, it is possible to add certain chemical components to the steam in order to increase the durability of the wood. 1026943 η 4 is also possible to add dyes to the steam, whereby the color of the wood is further influenced.

When Robinia is processed with the method according to the invention, a product is formed that exhibits great similarities with tropical hardwood in durability, color, strength and weight. However, the advantage is that a non-endangered wood species is used, making it easy to meet the current demand for sustainable wood.

In the table below, an exemplary embodiment is given of a method for drying wood. The wood is then heated in the first phase, then steamed, after which it can be dried and cooled. In this embodiment, the wood with a moisture content MC of above 30% is reduced to a moisture content of about 10%. Moreover, it can be seen that the wet bulb temperature during drying is 100 *. This means that the wood is dried from the inside and therefore cannot be previously dried on the outside, thereby preventing cracking.

Warming_Steam_Drying_Cooling Phase

Time [h] _ 6-10_ 60-120_ 60-80_ 6-18 T dry bulb [° C] 10-99__99_ 100-120 30_ 25 T gradient [° C / h] 5-20 __ <10 __- 5_ RH_ 80- 95_> 95__50-60 T wet bulb [° C] ___ 100__ MC [%]> 30 10 _ 30 It is important that the wood is properly tensioned during this process. In view of the aggressive acids that are released during this drying process, steel straps are less preferred, since this can cause stains on the wood. Therefore, plastic straps are preferably used, which are tensioned to between 2000 and 3000 N.

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The example given above relates to wood with a thickness of 27 tm.

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Claims (5)

A method for processing wood, in particular robinia, which method comprises the steps of: - cutting down the wood; - cutting the wood; 5. stacking the wood into a drying package and tensioning the drying package; - transporting the drying package to a drying device; and steam drying the drying package, wherein the moisture content of the wood from cutting down to steam drying is kept above 30% and reduced to below 30% during steam drying. The method of claim 1, wherein the wood is dried with superheated steam. The method of claim 2, wherein the temperature of the steam is in the range of 105 ° C to 115 ° C. The method of any one of the preceding claims, wherein the wood is dried within 144 hours. A method according to any one of the preceding claims, wherein the step of steam drying the drying package is preceded by post-tensioning the drying package. 0269 4 3