FR2801241A1 - Treatment of wood for timber preservation uses a succession of hot and cold baths with transfer in a shrouded environment to give the required impregnation more rapidly and with low energy consumption - Google Patents

Abstract

The process to treat wood, or similar material, uses heat and impregnation. The wood (4) is initially made wet to give a water content of \-25 mass%. The heating stage gives a strong evaporation of the contained water within the wood structure, followed by a dwell time in a controlled ambient environment for cooling. When cool, the wood is given a rapid chilling action by immersion in a bath of a preserving medium. The wood is heated to a level of at least 10 kW/m<2> or 2 MW/m<3>, for the surface or the vol. The moisture content of the wood (4) is raised to 40-80 mass% of the dry mass. The heating and cooling is effected by successive immersion in two baths of oil (3,6), with a min. transfer time of 30 secs. from the first bath to the second, and pref. min. 10 secs. The first bath is held at a temp. of 110-250 deg C, and the temp. of the second bath is 10-70 deg C. Before the heating stage, the ends of the wood (4) are covered or treated to make them liquid-proof, or the longitudinal wood fibers are shrouded to give an inner pressure within the wood material during heating and reduce the scope for some of the wood to be untreated. The wood processing time is from 30 mins. to 4 hrs., with a cooling phase which is longer than the heating stage. The heat is applied to the wood surface with a flow density of 10-300 kW/m<2> by contact with a hot liquid, infra red rays or superheated steam (at 140-300 deg C) or air at a high temp. of 150-300 deg C, by high frequency or very high frequency waves at a density of 2-20 MW/m<3>. The cooling phase is by water where the wood has a dry mass content of 60% to 20%. An Independent claim is included for a wood processing assembly with a heating stage (7) to raise the temp. of the wood (4) with a flow of at least 10 kW/m<2> or 2 MW/m<3>, to give a strong evaporation of any moisture within the wood material. A cooling stage (8) reduces the temp. of the wood by immersion in a liquid (6). A transfer system (9) moves the wood (4) between the stages (7,8), which prevents any significant dwell time in a non-processing environment such as ambient air, to give the best impregnation during the rapid cooling action. Preferred Features: The assembly has a basin (2) for a bath (3) with a heater (7) such as a heat exchanger, and a mechanism (10) to ensure that the wood (4) is immersed within the bath (3). There is relative movement between the wood (4) and the bath (3) liquid by a recirculation pump or a wood agitator. A second basin (5) holds a bath (6) with a cooling unit (8) such as a heat exchanger, and a system (12) to keep the wood (4) immersed together with a recirculation pump and/or a conveyor to give a relative movement between the wood (4) and the bath (6) liquid. The transfer unit (9) between the two baths has a conveyor (14) or a traversing unit with a sieve or a lock. A hood (16) shrouds the two basins (2,5) at least partially and the transfer system (9) between them. Non-contact heat for the wood is provided by a microwave generator or an infra red radiator. A hot gas is fed (18) into the shrouding around the processing stages (2,5). The assembly can contain at least two alternating heating (2) and cooling (5) basins, with transfer units for the wood between them. A further Independent claim is included for the wood where at least a part is impregnated with a used preservation oil at a rate of 0.05-2.0 kg per kg of dry non-oily material. The oil is a composition of used or contaminated oil and pref. a vegetable oil. Preferred Features: The wood has an outer roasted layer with a thickness of 0.5-2.0 cm. The layer of impregnated wood has a thickness of 10-100% of its dia., with a water content of <= 0.4 kg per kg of dry material.

Description

Method and device for the treatment of wood or similar materials The present invention relates to a method and to a device for the heat treatment and impregnation, essentially by immersion, of wood or similar ligneous materials.

There are many methods of preserving wood in order to improve its resistance to attack by biological agents such as termites or other xylophagous insects and rots (cubic, fibrous or soft). They are distinguished on the one hand by the agent or the impregnation solution used, and on the other hand by the process allowing to introduce and fix this agent (or the solution to be impregnated) inside. parts or structures of wood to be treated.

The impregnation of the wood material with preservatives depends on the composition and structure of the latter. The impregnation capacity is very variable from one species to another; beech, maple and hornbeam are fully permeated while the heart of other species is difficult to access and only the sapwood can be significantly impregnated with preservative substances. Finally, certain species, such as fir, spruce or douglas, can be very difficult to impregnate.

The effectiveness of an impregnation treatment can be assessed by both the amount and the depth of penetration of the preservative absorbed into the piece of wood. Among the methods ensuring a shallow depth of penetration, let us cite in particular: the external application of the preservative using a brush, by sprinkling or spraying, by direct immersion in the treatment solution containing the preservative preservation. The increase in the depth of penetration and the impregnated quantities is generally obtained from an autoclave treatment such as the process described by the document Guide to the preservation of wood, Michel RAYZ AL, March 1998, Center technique du bois et. of furniture (CTBA) - 75012 PARIS, pages G2-67.

The major drawback of these treatments lies in the use of an enclosure and of pumps allowing the performance of vacuum-pressure cycles, the investment and operating costs (mainly energy) of which are high. In addition, achieving a given impregnation quality requires prior drying of the wood - energy-intensive and time-consuming - as well as delicate control and control of the pressure and vacuum cycles.

The autoclave treatment times are also long (several hours) and require long downtime of the equipment.

The object of the present invention is to provide an improved method of treating wood and a device for its implementation.

Another object of the present invention is to remedy, at least in part, the drawbacks of the known methods.

In a method of treating a piece of wood according to the invention, said piece is heated in order to obtain an intense vaporization of part of the water contained in the material. Before the water content at the heart of the part is below the saturation point of the fibers (between 30% and 40% mass / dry mass), said part is suddenly cooled by bringing it into contact with a "cold" liquid medium. (the temperature of which is much lower than the boiling point of water at working pressure) containing the preservative (s). This last step is preferably carried out by immersing the solution in a bath (liquid) with which it is sought to impregnate the part.

It has been observed experimentally that, during this cooling, the treatment liquid penetrates to a significant depth in the piece of wood. This penetration results from the strong depression created by the sudden condensation of the residual vapor previously created. The suction power (or suction) thus generated allows significant impregnation of the initial voids or left by the departure of water during the first stage.

In other words, the invention is based on the generation of a high pressure drop in the wood fabrics (induced by the intense vaporization) in the presence of high heat flux densities and a higher material temperature or equal to the boiling temperature of water at the working pressure. This first step is followed by bringing into contact as quickly as possible with the treatment solution at a temperature much lower than the boiling point of water. The internal overpressure of the first step is followed by a depression during the second step which is used for the impregnation of the pores and vessels of the piece of wood by capillary flow of the treatment solution in contact with its outer surface.

For this purpose, it is essential to avoid the prolonged contact of the heated part, during its transfer to the cooling bath containing the preservative (s), with a non-treating intermediate phase (gaseous, in particular with ambient air), which would be likely to "fill" the wood vessels instead of the treatment product. Preferably, this transfer should be carried out in less than 30 seconds, in particular in less than 10 seconds, for example in less than 3 or 5 seconds. This effect can, if necessary, be limited or even avoided by waterproofing or covering the ends of the part to be treated where the longitudinal fibers of the wood are flush with the grain and which offer low pressure drops to gases and liquids. Likewise, maintaining the temperature of the environment through which the material passes, during its transfer, at a temperature above the boiling point of water (at the working pressure) by spraying liquid, hot steam air or by additional heating (by infrared, high frequencies, microwaves) will prevent early condensation of the steam trapped in the porous matrix. The latter can finally be prevented by a transfer of the material with the atmosphere used during the first step by means of a nacelle, a lock or any other suitable device.

Unlike autoclave processes which use, during vacuum-pressure cycles, the variation in the specific volume of the gases initially present in the material, and therefore prior drying, it is essential, in a process according to the invention, that the parts to be treat are not dry; it is essential that the parts to be treated have a humidity greater than 25%, in particular of the order of 40% to 80% (mass / dry mass); for this purpose, the parts can, if necessary, be re-humidified before treatment by prolonged immersion in a tank of liquid water at room temperature.

In order to obtain rapid cooling, the latter is carried out in a liquid medium in the treatment solution at a temperature much lower than that of the surface of the heated piece of wood. The difference between these last two temperatures is generally chosen to be greater than 40 C, in particular greater than 60 C. In the first step, the piece of wood is heated for this purpose to a temperature above the boiling point of surface water (of the order of 110 to 180 C if the operation is carried out at atmospheric pressure) and at a core temperature close to the boiling temperature of water (depends on the working pressure and In the second step, the temperature of the bath is maintained, thanks to a cooling unit, at a temperature generally below 70 C at atmospheric pressure, more precisely in the range of 20 C to 60 C. These operations, in particular that of cooling, are preferably carried out at atmospheric pressure or at a pressure close to the latter. In the particular case where the heating is carried out in a closed enclosure, the water vapor leaving the piece of wood can be used to induce an increase in the working pressure in the enclosure and thus increase the heating in the room. treat ; the condensation of the vapor during the second stage will then result from the simultaneous action of the cooling and the return to atmospheric pressure (isenthalphic condensation of the vapor in the latter case).

The treatment bath, in which the rapid cooling of the submerged parts to be treated is carried out, may consist essentially of an aqueous phase supplemented with hydrophilic preservatives (such as Copper - Chromium - Arsenic), by creosotes diluted in water. petroleum, by an emulsion or a dispersion of these same agents in aqueous or hydrophobic phases, by one or a mixture of organic solvents. However, the use of an oil bath (s) (mineral oils, vegetable oils or animal fats) supplemented with hydrophobic preservatives is preferred (for example pyrethroids and pyrethroids). Cooling in an oil bath (s) makes it possible to greatly reduce the costs of the treatment solution and to ensure rapid cooling, of around fifty degrees in less than 30 minutes, in particular in less than 10 minutes, under natural convection conditions (oils are very thermodilatable fluids). In order to facilitate the circulation of the solution and to homogenize the treatment between the pieces of wood (batch treatment), a tangential movement of the cold treatment medium is induced with respect to the pieces is carried out, either by displacement of the pieces, or by flow. bath, or by a combination of these means (moving the pieces of wood on rails or mats combined with recirculation of the treatment solution in the cooling tank).

According to one characteristic of the invention, the total duration of the treatment does not exceed four hours; for example the duration is of the order of 30 minutes to 1 hour (depending on the dimensions and the initial water content of the parts to be treated. However, depending on the desired quality objective (quantity impregnated and / or depth of penetration ), it is possible to repeat the heating-cooling sequence several times. We can in the same way depending on the anisotropy of the treated wood material and the desired objective (impregnation by one or the ends, impregnation only on the surface) if necessary partial or total waterproofing of the ends of the piece of wood (by chemical, physical or mechanical stealing).

According to another characteristic of the invention, the heating is carried out in the presence of high flow densities and must lead to a boiling of the water in the material (ie vaporization of the water at the core of the material under the effect of strong heat flux) ; the flux densities are generally located in the range of 10 kW / m - to 300 k @, '/ m - (power referred to the external surface of the treated parts), and / or in the range of 2 i @ Ït '/ m; at 20 IIW / mj (power relative to the volume of the parts treated). Heating can be obtained by different processes which can be combined if necessary: radiation (infrared, high frequencies, ultra high frequencies), exposure to very hot air (e.g. combustion gas) or superheated water vapor immersion in a fluid at high temperature (between 110 and 300 C at atmospheric pressure) whose boiling point is much higher than that of liquid water; in the latter case, the parts are preferably immersed in a bath similar in nature to that used for cooling, in particular an oil bath (for temperatures between 110 and 250 ° C. at atmospheric pressure).

For the heating oil bath, it is possible to use an oil or a mixture of oils of animal, vegetable or mineral origin, in particular used vegetable oils, by-products of the food industry such as frying oils. used. These inexpensive products are already thermodegraded and therefore rich in surfactants (free fatty acids), they allow the use of hydrophilic or hydrophobic preservatives indifferently in the cooling bath.

Likewise, the use, for the cooling step, of an oil or of a treatment solution having the same hydrophobic character, makes it possible to greatly reduce the costs of the impregnation solution and to protect the treated wood from subsequent re-humidification and its effects during outdoor use (drying-re-humidification cycles). These effects are responsible for the appearance and the propagation of cracks on the periphery of the treated wood and constitute preferential routes of penetration of biological agents of degradation of the wood.

The oil is used for its excellent properties as a heat transfer fluid in a two-phase environment (i.e. in the presence of steam) during the first stage. At high temperature, this first step can be accompanied by the strong fixation of the fatty acids of the bath on the celluloses and hemicelluloses of the wood, a very favorable reaction to the preservation of the wood. During the cooling step, the impregnation of the material with very thermodegraded substances such as frying oils very strongly reduces the biological availability of the wood substrate for microorganisms and insects. In addition, the use of oils offers outlets for by-products of the agro-food industry that are little valued and makes it possible to impregnate the material with biodegradable substances which will allow better compatibility of the materials produced with the environment during processing. their use or recycling. The use of a frying step (thus named by analogy with the use of oils in the food industry) quickly followed by immersion in the medium (the solution) with which one seeks to impregnate the material (wood) makes it possible to carry out at the same time - a drying, or even an additional drying of the material, - a light heat treatment leading to a relaxation of the mechanical stresses in the material and to a slight roasting of the wood (making it possible to obtain a partial reduction in food reserves that is sought organisms responsible for the degradation of the ligneous material), - deep impregnation not requiring the use of a pressure variation cycle of the medium surrounding the part to be treated, as is the case in an autoclave.

Compared to other surface heating methods (infrared, superheated water vapor) or volume (microwave, high frequencies), the step of immersion in a bath brought to a temperature above the boiling point of water is interesting for the proposed impregnation process because it allows - strong heat fluxes absorbed by the material, (which allow high evaporative flow rates and a high (transient) overpressure in the material, - rapid treatment (a few minutes to tens of minutes), - easy implementation, - direct treatment of green wood (ie wet and not impregnable as it is by the processes described above), - heat treatment and stresses generated are likely to improve the impregnability of the material by the continuous opening of the cellular network (opening of lids, etc.), - low investment and operating costs.

The step of immersion in the solution to be treated after partial vaporization of the water contained in the material allows - the use of a dynamic depression due to the modification of the liquid-vapor balance during cooling, - a deep impregnation in the presence of strong pressure gradients which are difficult to generate by conventional processes, - reduction in treatment time, - reduced investment, easy to use, - the use of a wide variety of impregnation solutions ( aqueous or hydrophobic) including oils and alcohols which can hardly be used in conventional autoclave vacuum-pressure processes (in the case of the use of alcohol with added preservatives, the carrier solvent can be secondarily removed by air drying).

According to another aspect, the invention consists of a device for treating wood which comprises - means for heating pieces of wood in the presence of high densities of heat flow, in a first enclosure or container, - means for rapid cooling of pieces of wood produced in a (second) enclosure or container, preferably separate from the first enclosure or container, - means of rapid transfer (movement) of the pieces of wood from the enclosure (or container) where heating is carried out to the enclosure (or container) where the cooling is carried out.

In the case where the heating and / or cooling are obtained by soaking the pieces of wood in a bath, each container receiving the bath comprises means for maintaining the pieces of wood in total immersion (the buoyancy of the material depending on the composition of the material and in particular its water content). These devices can be fixed or mobile, in the latter case they also serve to move the parts in the bath. The two containers (or bins) should preferably be contiguous; they can be obtained by fitting a tank with a partition wall physically and thermally isolating the heating bath from the cooling bath. This separation can be total or partial. In the latter case, the transfer of the parts from the first to the second bath can be obtained without contact with the gaseous atmosphere present above the baths; to this end, the device may include an airlock (or "lock") provided (c) with devices for maintaining the parts in immersion during their transfer. The tanks are preferably covered, at least in part, by a cover making it possible to reproduce a confinement enclosure under slight overpressure. This allows i) to maximize the impregnation during the cooling step, ii) to limit the risks of projection, 11i) to increase the temperature of the atmosphere crossed by the material during its transfer (s' it takes place in the gaseous phase) and to limit the air circulation which could induce premature condensation of the vapor contained in the material, iv) to carry out a possible sprinkling of the material with superheated water vapor, very hot air, high temperature oil. In all cases, the devices and their conduct must make it possible to maintain the overpressure in the wood material and thus limit the filling of the vessels with a gaseous phase during the transfer.

According to another aspect, the invention consists of a piece of wood, which can be obtained, directly or indirectly, by a process according to the invention, of which at least part (or peripheral layer) is impregnated with a preservative, characterized in that said part or layer is impregnated with an impregnation vector chosen from mineral oils, animal oils, vegetable oils, solvents (creosotes, tars, mineral oils obtained from the fractionation of petroleum products, extracts in mineral or non-mineral solvents), In addition, a surface part (layer) can be roasted (partial carbonization), as a result of surface heating, in particular in an oil bath at high temperature (between 110 and 250 C at atmospheric pressure). Generally, the average water content of the part (in particular of said layer in the peripheral part) will be less than 0.3 kg of water per kg of non-oily dry matter, in particular less than 0.1 kg / kg. The average content of impregnation solution (in particular of oil) of said impregnated layer will generally be of the order of 0.05 to 2 kg of oil per kg of non-oily dry matter. The thickness of the impregnated layer is of the order of 1 to 100 mm depending on the cutting direction of the pieces of wood relative to the orientation of the cellular elements of the wood, in particular of the order of 5 to 50 mm for a 200 mm diameter log. The average thickness of the roasted surface layer, characterized by an alteration of the molecules of hemicelluloses and amorphous cellulose (significant decrease in the number of hydroxyl groups associated with partial crosslinking) and the appearance of pyrolysis products, may be order of 0.5 to 2 cm (it depends very much on the times and temperatures of treatment).

Other advantages and characteristics of the invention will be understood through the following description which refers to the appended drawings, which illustrate, without any limiting nature, preferred embodiments of the invention.

Figures 1 to 6 schematically show 6 examples of embodiments of the method according to the proposed invention, Figure 7 shows a schematic cross section of a piece of wood treated according to the invention.

Each of the devices 1 comprises a tank 2 containing the bath 3 for heating the pieces 4 of wood, and a tank 5 containing the bath 6 for cooling and treating these same pieces.

To this end, the tank 2 is equipped with a heat exchanger 7 connected by conduits 50 to a heating device (not shown) of a heat transfer fluid circulating in the exchanger 7 and the conduits 50.

Similarly, the tank 5 is equipped with a heat exchanger 8 connected by conduits 51 to a cooling unit (not shown) of a coolant circulating in the exchanger 8 and the conduits 51.

In order to keep the pieces of wood (such as boards, beams, stakes or posts) immersed in each bath 3, 6, each tank 2, 5 is respectively equipped with a member 10, 12 ensuring the immersion.

This member 10, 12 may be fixed and be in the form of a rail flush with the surface of the bath or immersed therein; alternatively, this member may be mobile and may be in the form of a belt, chain or cable conveyor; in this case, it can be equipped with projecting members forming fingers capable of driving the parts 4 in motion in the baths, as schematically represented by arrows 11, 13.

One or two conveyor (s) 14a, 14b, 14c (figures 1 and 3) of similar structure can be used (s) to quickly transfer parts 4 from bath 3 to bath 6: each of these conveyors has a cable 52 equipped with fingers 53 for driving parts 4; conventionally, each cable shaped as a closed loop, extends between two pulleys or rollers driven in rotation by an actuator along axes perpendicular to the plane of the figures.

In the embodiment illustrated in FIG. 1, such a conveyor 14a partially immersed in the bath 3, is used to move (arrow 55) the parts 4 along an inclined wall 54 of the tank 2, so as to cause them to fall ( arrow 56) in the bath 6.

In the embodiment illustrated in FIG. 3, two conveyors 14b, 14c similarly transfer the parts 4 from the tank 2 to the tank 5 by sliding and / or rolling on the inclined walls 54, 57 (respectively rising and falling) of these 2 tanks; the trays are joined by the common upper edge of the two walls 54, 57.

In the variant illustrated in FIG. 4, a single conveyor 14, the central part of the longitudinal profile of which is curved to extend substantially parallel to the inclined walls 54, 57 by which the bins are connected, fulfills both the function of driving in movement of the parts 4 in the baths 3, 6, keeping these parts immersed in these baths, and transferring the parts from the first to the second bath.

According to a variant not shown, one or more pumps and / or agitators can contribute to the relative movement of the pieces of wood with the treatment solution.

As illustrated in FIGS. 1 to 4 in particular, a cover 16 equipped with a nozzle 18 for injecting (arrow 58) of a hot gas, covers the zone 9 of transfer between the tanks.

The heating of the rooms 4 can be obtained and / or supplemented by the action of a device such as marked 17 which diffuses into the treatment chamber 59 delimited by the cover 16 and the trays 2, 5, microwaves or infrared radiation.

In the variant illustrated in FIG. 2, the transfer from one tank to the other is obtained by pivoting 60 along the axis 61 (perpendicular to the plane of the figure), of a basket 62 mounted at the end of an arm 63.

In the variant illustrated in FIG. 5, this transfer is obtained by a similar pivoting of a partially submerged lock comprising four flaps 64 whose transverse profiles form a cross; the ends of the two flaps located in the lower part slide, during the pivoting of the airlock, along a wall 65 in the form of a portion of a cylinder with a horizontal axis, which wall extends to the upper end of a partition 66 separating the trays 2, 5; the space 67 delimited by the two lower flaps and the wall 65 is adapted to receive one or more parts 4; the rotation of the airlock shutters according to the arrow (anti-clockwise) causes the parts to be transferred from bath 3 to bath 6 without emersion.

The device illustrated in FIG. 6 comprises two structures similar to that of FIG. 3, which are arranged end to end and connected by an additional transfer device capped by a protective structure 16, 18; this device allows a treatment comprising successively a first heating, a first cooling, a second heating and a second cooling.

The cross section of a post with axis 4b treated which is illustrated in FIG. 7 shows the layer 4c impregnated with thickness 4d, including the roasted peripheral part 4e of thickness 4f.

Example 1 To treat a batch of 3 debarked Douglas-fir stakes 0.15 m in diameter and 1.5 m long, the initial water content of which was close to 100% (mass / mass on a dry basis), two baths were used. rapeseed oil maintained respectively at 180 C and 35 C at atmospheric pressure. The posts, the ends of which had been waterproofed by soaking in tar, were immersed in the heating bath for 60 minutes, taking care to allow easy circulation of the oil between the posts by natural convection and an effective compensation of the oil. the temperature drop of the bath. The stakes clamped at their ends by metal frames were kept immersed in the bath by means of chains and removed from the bath by the same device. The transfer to the cooling bath was carried out with a passage through air of the order of 5 seconds. The material remained immersed in the treatment solution for about thirty minutes, taking care to limit the heating of the cooling bath below 50 C. This bath colored red to Sudan red contained pyrethrums as a preservative.

After leaving the bath and draining (without wiping), it was observed, in a cross section of the stake, an impregnation of the wood with the colored oil and the preservative to a depth of 3 to 6 cm (in all cases the sapwood is completely soaked with colored oil) depending on the condition of the outer surface and a light roasting to a depth of 5 mm maximum.

Example 2 Example 1 was repeated with the following differences - a cooling bath containing an aqueous solution of chromium, copper arsenic colored with methylene blue, - a cooling bath maintained at 20 C.

In this case, we observed in this case an impregnation of the order of 2 to 6 cm in preservation solution and a roasting of the same magnitude.

Claims (14)

1. A method of treating a piece (4) of wet wood characterized in that it comprises a step of heating said piece to obtain a sudden vaporization of the water contained in the piece, followed by a step rapid cooling of the part by bringing it into contact with a liquid medium (6) containing a wood preservative (s). 2. The method of claim 1 wherein the rapid cooling is obtained by immersion in a bath (6) of oil whose temperature is below 70 C. 3. Method according to claim 1 or 2, in which one passes from heating to cooling when the ratio of the mass of water contained in the part to the dry mass thereof is within a range of 60% to 20%. . 4. Method according to any one of claims 1 to 3 wherein the heating and cooling are obtained by successive immersion in two baths (3, 6) of used vegetable oil, the transfer of said part (4) of the first bath with the second being carried out in less than 30 seconds. 5. The method of claim 4 wherein the first bath is maintained at a temperature between 110 C and 250 C, wherein the second bath is maintained at a temperature of 10 C to 70 C, and wherein the duration of the treatment is of the order of 30 minutes to 4 hours. 6. Method according to any one of claims 1 to 5 wherein the heating power is provided in a surface manner with flow densities of between 10 and 300 k @ X '/ m-' by contacting with a hot liquid. , by infrared radiation, by contact with superheated water vapor (140 to 300 C) or air at high temperature (150 to 300 C), or in the volume by high frequency radiation or very high frequencies with densities between 2 and 20 NnV / m3. 7. Device for treating pieces (4) of wood characterized in that it comprises - a device (7) for heating the pieces (4), - a device (8) for cooling the pieces (4), - a device (9) for moving the parts (4) relative to the heating and cooling devices (7, 8). 8. Device according to claim 7 which comprises - a tank (2) adapted to receive a bath (3), - a member (7) for heating the bath (3), such as an exchanger, - a member (10) for maintaining the parts (4) immersed in the bath, - a member (11) for relative movement of the parts (4) and the bath (3), such as a bath circulation pump or a parts movement conveyor, and which further comprises - a tank (5) capable of receiving a bath (6), - a member (8) for cooling the bath (6), such as an exchanger, - a member (12) for holding the parts (4) immersed in the bath (6), - a member (13) for relative displacement of the parts (4) and of the bath (6), such as a pump and / or a conveyor, and in which the device (9 ) displacement comprises a conveyor (14) or a conveyor (15) of the lock or lock type. 9. Device according to claim 7 or 8 which further comprises - a cover (16) for partial containment at least of the chamber (2, 5) of treatment and of the device (9) for displacement, a member (17) of heating of contactless parts (4) such as a microwave or infrared radiation generator, - a member (18) for introducing into the chamber (2, 5, 16) for processing a hot gas . 10. Device according to any one of claims 7 to 9 which comprises at least two heating tanks (2) and at least two cooling tanks (5) arranged alternately, each pair of contiguous tanks (2, 5) being provided with 'a means of transferring parts (4) from one tank to another. 11. Piece (4) of wood impregnated with a preservative characterized in that it is impregnated with an impregnation vector for the agent, which vector is chosen from oils or solvents. 12. Part (4) according to claim 11 wherein said carrier is a used vegetable oil, the content of which in the impregnated part of the part (4) is of the order of 0.05 to 2 kg of oil per kg. of non-oily dry matter. 13. Part (4) according to claim 11 or 12 which comprises a roasted surface layer whose thickness is of the order of 0.5 cm to 2 cm. 14. Part according to any one of claims 11 to 13 wherein the thickness of the impregnated layer relative to the half-diameter (or equivalent diameter) of a cross section of the part is 10% to 100%, and in in which the water content of this impregnated layer is less than 0.4 kg per kg of dry matter.