Drying and gas or vapor contact with solids – Process – With nondrying treating of material
Patent
1998-03-23
1999-05-11
Bennett, Henry
Drying and gas or vapor contact with solids
Process
With nondrying treating of material
F26B7/00
Patent
active
059014636
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an improvement in methods of treating wood at high temperature and in particular in so-called curing treatments. It also relates to a sensor enabling said method to be carried out.
BACKGROUND OF THE INVENTION
It is known that, in the natural state, wood or the wood fibers which are in contact with a humid atmosphere, tend to be logged with water, going as far as absorbing it up to 100% of their weight. Such water absorption is accompanied, on the one hand, by a swelling and, on the other hand, by a loss of the mechanical qualities and qualities of cohesion of the material which, in certain cases, can go as far as an advanced disintegration thereof. This is why the habit is taken, before every step of machining wood, of effecting a drying step which, by eliminating the water therefrom, improves its dimensional stability.
Although the drying step enables the water to be eliminated from the wood, it in no way modifies the hydrophilic nature thereof, with the result that it is again likely to reabsorb the water eliminated during drying when it is again in a humid atmosphere.
In order to decrease the hydrophilic character of the natural wood and thus to give it a long-lasting dimensional stability, different techniques of heat treatment at high temperature have been proposed.
Among these techniques, it has been proposed to subject the natural wood to different steps of treatment including in particular a drying in open circuit followed by heating and maintenance at a temperature included between about 220.degree. C. and 300.degree. C. for a determined period. Such a technique of treatment, called curing, makes it possible to give the wood both a hydrophobic character and an excellent dimensional stability.
However, it has been ascertained that the operation of curing had to be carried out with the greatest rigour, on pain of decreasing the mechanical characteristics of the wood treated. In fact, it is known that this curing step has for its object to partly destroy the hemicellulose of the wood without being detrimental to the structure thereof, in other words without destroying the lignin.
Under these conditions, one of the major difficulties encountered during the curing treatment consists in determining the time during which the curing temperature must be maintained in order to destroy the hemicellulose without significantly destroying the lignin.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome this drawback by proposing a method for detecting the end of the treatment level of the curing phase.
The present invention thus has for its object a method of treating wood by heating, comprising at least one step in which the wood to be treated is maintained at a determined temperature so as to destroy at least in part the hemicellulose of the wood, characterized in that it consists in monitoring, all along said step, the existing amount of at least one of the gases resulting from the decomposition of the hemicellulose, and in interrupting this step of treatment as soon as this amount begins to reach a substantially constant value.
In one embodiment of the invention, the wood is disposed in a treatment chamber provided with a sensor sensitive to acetic acid and/or carbon dioxide and/or carbon monoxide.
The present invention also has for an object a sensor intended for carrying out this method of treating wood, characterized in that it comprises a detector element constituted by a metallic oxide of the type allowing the detection of the reducing gases. Interestingly, said metallic oxide is a tin or titanium dioxide.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will be described hereinafter by way of non-limiting example, with reference to the accompanying drawings, in which:
FIG. 1 is a graph which represents the variation of the temperature respectively of a treatment chamber and of the wood to be treated, as a function of time, during a curing treatment.
FIG. 2 is a graph which represents, for
REFERENCES:
patent: 5169687 (1992-12-01), Sunol
Patent Abstract of JP 3111749.
Bennett Henry
N O W (New Option Wood)--societe anonyme
Wilson Pamela A.
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