WO2002002287A1

WO2002002287A1 - Method and equipment for preserving wooden poles

Info

Publication number: WO2002002287A1
Application number: PCT/IB2001/001171
Authority: WO
Inventors: Libère Nitunga
Original assignee: Innovis International; NIYONIZIGIYE, Déogratias; Ndayikengurukiye, Godefroid
Priority date: 2000-07-04
Filing date: 2001-07-02
Publication date: 2002-01-10
Also published as: CA2451489A1; MXPA03000410A; AU6935001A; OA12584A; AU2001269350B2; BR0112496A

Abstract

The invention concerns a method for preserving sap or more less dry wood, which consists in impregnating the wood longitudinally and radially, a longitudinal injection following the raw sap circuit for preserving the whole timber, and a radial injection following the processed sap circuit for specific and more intense impregnation reserved for the part of the timber most exposed to biological alteration.

Description

PROCESS AND EQUIPMENT FOR PRESERVING WOOD POSTS

DESCRIPTION Previous situation

Wooden poles are widely used worldwide, mainly as supports for power and telephone lines. To give them a sufficient lifespan, it is necessary to apply a preservation treatment to them before their implementation. This treatment consists in incorporating into the wood cells an insecticide and fungicide product, in order to make the wood inedible for the microscopic fungi responsible for decay, as well as for insects. To achieve this objective, the processes used are very varied, but they can be grouped into two main categories: dry wood treatment processes and sap wood treatment processes.

a) Treatment procedures for dry wood (in a closed vessel or autoclave)

They use alternating vacuum and pressure to force the chemical into the dry wood cells.

Following the shrinking of the sap circuits during the drying process, these processes need to use high treatment pressures (10 bars). These are industrial processes widely used worldwide. However, they have the following 2 drawbacks:

. A penetration depth generally limited to 2 cm for most round timber;

. The impossibility of adapting the intensity of impregnation to the possible specific needs of a certain part of the wood to be protected (collar of posts and stakes for example).

b) Processing methods for sap wood (sap displacement processes)

They are applied to freshly felled roundwood in which the internal circuits of the sap are still largely open. These methods consist in applying the antiseptic solution to the large end of the trunk under a slight pressure of the order of 1 bar; the preservative penetrates through the rising sap circuit (longitudinal impregnation).

These processes have the following main disadvantages:

. Need to treat freshly felled wood;

. Impossibility of adapting the intensity of impregnation to the possible specific needs of part of the wood; . With versions prior to the present invention, low level of production, high labor intensity and environmental pollution.

There are also techniques for impregnating wood in sap by vacuum and pressure alternating in an autoclave, but they are closer to methods of treating dry wood than methods of treating by displacement of sap.

Major post problem that remains despite these treatments

It can be considered overall that the treatment methods described above leave substantially the same density of chemical in the different parts of the post. However, we know that the part of the post by far the most exposed to attacks by wood destroying agents is the area of embedding in the ground which, in reality, needs an impregnation about 3 times more intense than the rest of the post. .

We then resort massively to additional treatments of the base of the post to strengthen its protection. Research on these additional treatments continues to this day, which shows that the problem has not yet been resolved satisfactorily. These treatments are applied as a preventive measure before the installation of the post and systematically with a periodicity of 5 to 10 years, and / or as a curative treatment on posts showing the beginning of deterioration.

The main weaknesses of additional post base treatments

Conventional post-autoclave treatment methods rely on additional treatments to ensure the posts have a suitable life. However, these additional treatments have the following weaknesses in particular:

1 ° Their operating principle excludes the use of preservatives which enter into chemical reaction with wood to form highly insoluble complexes, because these would quickly form a barrier which would prevent the further diffusion of the product in the wood. We must therefore fall back on other products, whose resistance to washing leaves something to be desired, it is for this reason that the collar recall treatments must be repeated several times, with an interval of 5-10 years.

2 ° Their mode of application requires the release of the base of the post to a depth of about 50 cm. On the one hand, this represents a non-negligible volume of work, given the large number of posts in service, particularly when they are installed on the sidewalks; and on the other hand, this operation regularly weakens the foundation of the posts.

3. Pitting processes affect the fibers of the wood, and therefore the mechanical strength of the post to a certain extent, precisely in the most vulnerable area from the mechanical point of view.

Contribution of the present invention

The present invention relates to a method for preserving wood in sap or more or less dry, which impregnates the wood in the longitudinal direction and in the radiai direction: a longitudinal injection following the circuit of the raw sap for an overall preservation of the piece of wood; and a radial injection following the elaborate sap circuit, reserved for a specific area or for the whole piece of wood, for an additional and more intense impregnation chosen according to the risks of biological alteration which are specific to it.

This process is characterized in particular by:

1 ° The use of wood in sap. In these latter the internal circuits of water and sap circulation are still largely open and for this reason they generally permeate much better than dry wood. The new process also applies to more or less dry wood thanks to the high performance of the equipment used, but these are special cases. This is particularly the case with longitudinal injection of timber felled a long time ago, or radial injection into the collar of posts in service.

2 ° A special impregnation located at the level of the part most exposed to biological alteration, which makes it possible to adapt the concentration of the product used to the intensity of the risks specific to this area.

3 ° The possibility of using, particularly in the intense and specific injection phase of the most exposed part, products which are fixed permanently in the wood, in particular tar or their derivatives as well as salts which enter into reaction chemical with wood - CCA type salts for example. It is with such products that the greatest resistance to washing is currently registered. These products cannot be used with the conventional methods of additional treatment specific to the collar of the posts for example (punctures, bandages), because the insoluble compounds which would result from their chemical reaction with the wood, would be opposed to a diffusion of the product beyond their point of application.

4 ° A particularly intense impregnation thanks to the cross injection; in the longitudinal direction following the circuit of the raw sap, on the one hand; and in the radial direction by the radiating circuit following the circuit of the sap produced, on the other hand.

5 ° The use of a relatively high injection pressure when necessary (several bars) using the equipment described in Figure 1. A pressure of the order of 3 bars allows very deep impregnation of the wood, especially when applied to sapwood.

The equipment of FIG. 1 comprises: a supply pipe (1) for treatment product under a pressure of a few bars, a pocket or waterproof cover (2) composed of two elements; a waterproof membrane and a flexible and resistant fabric reinforcement. One or more clamps (3) allow the tight pocket to be strongly applied against the debarked base of the trunk (4) and thus ensure the necessary seal and the retention of the device against the wood being treated. A layer of elastic bands (5) improves the sealing of the device.

The device for radial injection further comprises one or more pieces of curved sheet metal (6) in one or more pieces, for retaining the sealed bag while the device is under pressure. Said metal sheet can advantageously be replaced by a flexible and resistant strip (Figure 2) wrapped around the area to be treated, over the waterproof cover.

When the wood to be impregnated requires the use of a relatively high treatment pressure, it may prove necessary to add a safety device like that of FIG. 3. Under these conditions, it is also possible to adopt a longitudinal injection as shown in Figure 3. It differs from the previous device by the waterproof bag and the security system. The latter becomes systematic while the waterproof pocket this time has a different opening for the passage of the trunk to be treated on the one hand, and the treatment product on the other hand. A metal tip (7) welded to a circular plate (8) ensures the antiseptic solution the passage of the supply pipe (9) to the section of the debarked base of the trunk. One end of the sealed pocket (10) passes inside the metal end piece (7), before being folded back outside the same end piece. Another collar (11) makes it possible to seal between the supply pipe (9), the waterproof pocket (10) and the metal end piece (7).

The safety system must prevent the device from detaching under the pressure of the processing pressure. It comprises a metal frame (12) applied against the circular plate (8), and connected via the tensioners (13) to a set of two upper and lower rings (14 and 15), of a diameter significantly greater than that of the trunk to be treated, and forming a self-locking system with the latter, as illustrated in FIG. 3. In the case where the two rings are rigid, they must be extended by an arm which allows the traction force exerted on to be properly oriented. the rings for the self-locking system to work.

A variant of these devices for longitudinal and radial injection makes it possible to easily impregnate with the same advantages, all kinds of round or non-round wood (pilings, railway sleepers, etc.). Here too, care must be taken to ensure that one end of the piece of wood to be impregnated remains at atmospheric pressure, so that a flow of the antiseptic product can be established through said piece. Suction from this end is not necessary because the pressure difference between the inlet and the outlet of the product is sufficient for impregnation as rapid as desirable, and in depth.

For the injection of squared timber the main adaptations are as follows: the collars are replaced by rods connected two by two by two bolts placed on either side of the piece of wood, while the safety system for the radial injection is reinforced by devices of rectangular section.

The most important factor that allows the performance of both longitudinal and radial injection devices is the fact that all of the operations for sealing said devices are carried out in the open, which is facilitated by a single entry of the piece of wood to be treated and the supply pipe to the point of application of the antiseptic product (figure 1), or a layout as in figure 3 for longitudinal injection.

Claims

1. A wood preservation process which consists of impregnating it both in the longitudinal and in the radial direction without resorting to the use of closed vessels; on the one hand by a longitudinal injection following the raw sap circuit in order to preserve the whole piece of wood in case and to the extent necessary; and on the other hand by a radial injection following the circuit of the elaborate sap, which radial injection is done on part or the entire length of the piece of wood to be preserved, and aims to achieve on the area where it s apply, an impregnation whose intensity is chosen according to the risk of biological alteration specific to said area.

2. A wood preservation process according to part or all of claim 1, which consists in reusing the effluents leaving the wood under the pressure of the preservative during treatment, either directly for woods whose sap does not form precipitates with the treatment product, either after a special preliminary "desiccation" operation, which consists in making a longitudinal injection with water or any substance suitable for removing the resins and the sap.

3. A wood preservation method according to claim 1, characterized by the use of pressurized air for pressurizing the preservative (without passing by hydraulic pumps or by hydrostatic means), and which uses a or several chemical tanks connected in series, the inlet of each tank being placed at the top and the outlet at the bottom.

4. Devices for implementing the method according to claim 1, having one or the other of the following characteristics:

- all of the operations to ensure the tightness of said devices are carried out in the open thanks to a single opening for the passage of the wood to be treated and of the treatment product (waterproof bag), or else thanks to a variant as shown in Figure 3 where the two ends of the sealed bag are open, and one of them passes inside the metal tip and folds over the outer edge of the latter;

- an extremely simplified injection device, which practically comprises only a supply pipe, a waterproof pocket or cover and clamps; a security system as characterized in the description which may be necessary only in a few cases;

- a pocket or waterproof cover composed of a waterproof membrane and a reinforcement in flexible and resistant material, with a diameter clearly greater than that of the wood to be treated, in order to be able to adapt to a wide range of dimensions of the wood ;

- one or more curved sheets, in one or more pieces, which allows the waterproof cover to better hold the pressure developed by the preservative inside the radial impregnation device, which sheet can advantageously be replaced by any device security adaptable to a wide range of dimensions of the wood, for example a flexible and resistant band, wrapped around the part to be treated over the waterproof cover as illustrated in Figure 2.

5. A device according to claim 4, for the impregnation of dry wood, in particular the re-impregnation of wood in service whose level of protection is not or is no longer sufficient.