US2069491A - Method for impregnating wood and other materials - Google Patents

Description

Feb. 2, 1937. B. o. HAGER 2,069,491

METHOD FOR IMPREGNATING WOOD AND OTHER MATERIALS Filed March 18, 1955 Patented Feb. 2, 1937 UNITED STATES METHOD FOR HVIPREGNATING WOOD AND OTHER MATERIALS Bror Olo'i Hitger, Stockholm, Sweden, assignor to Bolidens Gruvaktiebolag, Stockholm, Sweden, a limited joint-stock company of Sweden Application March 18, 1935, Serial No. 11,541

In Sweden ()ctober 8, 1934 '8 Claims.

It is a well-known fact that wood or other organic substances admitting of impregnation can be made resistant to attacks by funguses or other similar organisms, e. g. xylophagans, by that the objects are coated or impregnated with substances having a poisonous action on these organisms. The coating methods are economical to use, but the protective efiect obtained is very imperfect, which is due to the fact that the preservative penetrates inside the surface only in a small degree. Themethods of impregnation by means of pressure and vacuum treatment give a good distribution of the preservation agents in the objects, but the processes are always expensive in practical use.

It has been previously proposed to introduce, by double impregnation, difiiculty soluble substances e. g. into wood in such a manner that first a soluble matter is introduced by pressure treatment, the excess being removed by putting the objects being treated, under a vacuum, whereupon they are impregnated again, this time with a solution of a matter which gives with the first one a precipitate of a difiicultly soluble compound. This method is, however, in its execution so complicated and expensive that it has found but a small use in practice.

The present invention has for its object to avoid these inconveniences by carrying out the impregnation without pressure treatment, in open vessels, only by the aid of heat. The objects to be preserved, e. g. posts made of wood or the like,

are put down into a bath consisting of a certain solution suitable for the purpose, which solution is heated to a temperature settled by tests or experiments in eachindividual case. As a result of this heating to the desired temperature, air is expelled from capillaries and other hollow spaces in the objects in question and, besides, moisture possibly occurring in the objects evaporates and participates in the expulsion. When this process has advanced suniciently far, which for difierent materials occurs after periods of time of unequal length, the temperature of the solution is decreased. On this occasion, part of the water vapour which has been formed in the hollow spaces, condenses little by little so that vacuum arises therein, and, as a result, the impregnating solution is sucked in. This operation is interrupted when a suitable amount of impregnating solution is taken up by the material, and the objects are then rapidly taken out of this first bath and are immerged in a second bath or solution. This lattersolution (the fixing solution) has a lower temperature, so that a further condensation takes place in the capillaries, with the result that also this second solution will be sucked into "the capillaries or the hollow spaces in the objects in question. This latter solution contains. a matter which with the matter present in the first (oi. zi-sv) (hot) solution forms adifiicultly soluble compound that is fixed in the objects impregnated.

As will be more closely described in the following, it is possible, while applying the same process,

to carry out the method in such a manner that the objects which are going to be impregnated with the different solutions, instead of being moved from one tank into a second impregnating tank, are permitted to remain in one and the same tank during the two impregnations, the

solution used in the first impregnation, after this first impregnation has been brought to'an end, being removed from the tank and the second (cool) impregnating solution thereafter being introduced into the same. In practice, the process is conveniently carried out in such a manner that, while impregnation with the first solution third tank and the objects which are contained in the second tank and have been impregnated to a completion, are taken out and this tank is charged anew, while, after-the impregnation with the first solution in the first tank has been brought to an end, impregnation with the second solution is performed therein, and so on in succession. According to this form of the method the solution used for the first impregnation is drawn off from the tank before the second (cool) solution is introduced in the same tank, and the first solution brought into another tank inwhich the first impregnation is to take place, as will be nearer explained with reference to the drawing.

In order further to illustrate the principle of the present invention the following example may be given.

Wooden posts are heated in an aqueous solution of sodium arsenate to a temperature immediately below the boiling point (for example, in the vicinity of 100 0.), and are maintained at this temperature during about five hours, whereupon the solution is cooled down to about C. After one hour or so the posts are taken up and are quickly transferred to abath containing zinc sulphate, and having a temperature of e. g. 10 to 20 0., and are left there until they have absorbed the desired amount of liquid. As a result, zinc arsenate,which is an effective preservative against rot funguses and is not extracted. by water, deposits on the fibres in the posts.

Of course, instead of sodium arsenate an alkaing a metallic ion capable of forming diflicultly soluble metallic arsenite or arsenate may be used. Thus, besides zinc salts soluble salts of barium, calcium and magnesium and the like are suitable. Also arsenious acid or trioxide of arsenic may be used in the first (hot) solution, if the second (cool) solution contains such a substance that a difllcultly soluble compound is formed. For example, arsenious acid or alkaline arsenate gives with alkaline bichromate a precipitate of difiicultly soluble chrome arsenate. 0n the whole, all kinds of soluble arsenic compounds which give with another soluble substance a difilcultly soluble compound, can be used.

In the above example it has been stated that certain salts have to be used in the first impregnating solution and other salts in the latter solution, but the process may, of course, also be carried out in reverse order.

Instead of or together with one or several of the metallic compounds contained in the fixing solution and stated above by way of examples, also soluble salts of copper and/or of manganese, e. g. solutions or copper sulphate or of chloride of copper, of manganese sulphate or of manganese chloride or other solutions in connection with said metals and being adapted to the purpose may be used.

The following combinations may be stated as examples:

Solutions of or solutions containing:

(A) Copper sulphate and copper chloride (an example of the combination of salts of the same metal with difierent acids).

(B) Manganese sulphate and zinc chloride (an example of the combination of salts of different metals and difierent acids).

(C) Calcium chloride and zinc chloride (an example of the combination or salts of different metals with the same acid).

Also a combination of three or, if desired, a greater number of salts may be used. Salts of calcium cannot, however, be used in combination with sulphates.

In the following, some examples of individual salts and of combinations of salts which may be used, are given:

(1) Examples of single salts:

CuS04 CuCh MnSO;

MnCla ZnSOr ZnClz (2) Examples of two salts used together:

In order to reduce the losses of heat in the hot bath when said bath consists of an aqueous solution, an oil of suitable consistency may be poured out onto the surface and be allowed to spread thereon. The oil impedes evaporation, and the heating costs will be considerably reduced. Temperatures and time of treatment as well as the concentration or the solutions are fixed in each individual case with regard to the nature of the objects being impregnated and of the solutions as well as other circumstances that may exercise an influence upon the desired result.

In a view to further elucidate the method and the manner in which it may be carried out in practice, two different embodiments of arrangements suitable for that purpose are shown, by way of examples, in the accompanying drawing.

Figure 1 shows diagrammatically, in side view, part of the plant, as viewed along the line I-I in Figure 3 in the direction of the arrows.

Figure 2 shows a cross-section through the line IIII in Figure 1.

Figure 3 shows a top plan view of the plant according to Figure 1.

Figures 4, 5, 6 show in similar manner a second embodiment of the plant being equipped with three impregnating tanks so arranged that in two of said tanks impregnation may proceed simultaneously, with the first and the second solution, respectively, while impregnated material is taken out of the third tank and while the same is being loaded with fresh material.

The invention will first be described with reference to Figures 1, 2, and 3.

A and B designate the tanks in which the impregnation takes place. 0 and D designate tanks for receiving the difierent solutions by means of which the impregnation is effected. As shown by the drawing, the two tanks A and B are disposed parallel with each other, and the tanks C and D are arranged on a bed i at such a height that liquid can, by gravity, flow from the solution tanks into the difierent tanks A, B through pipes 2, 3 provided with shut-off valves 4, 5.

The boiler G (or other heating apparatus suitable for the purpose) communicates with the impregnating tank A, in which impregnation with the first solution is carried out in such a manner that the solution, through the action of the pump 6, can be brought to circulate from the tank A through the pipe I, the pump 6, the boiler. or other heating apparatus G and the pipe 8 back to the tank A. Between the pipe 8 and the pipe 1 there is provided a branching pipe 9 capable of being cut oil by means of a valve l0, and in each of the pipes I and 8, there is provided a valve II, which valves are so arranged that, if the valve ii is shut off and the valve iii opened, the solution can be brought to circulate in the manner apparent from the drawing, without passing through the boiler G.

I! designates the material to be impregnated.

The method proper is carried out e. g. in the following manner:

Aiter the tank A has been loaded with material l2,whlch is going to be impregnated, and the tanks C and D have been loaded with the dinerent solutions (see above) intended for the impregnation and the tank A has been filled with the solution intended for the first impregnation, this last-mentioned solution is rapidly heated from about 70 C.-which temperature it has in the continuation of the work from the preceding impregnating process "carried out in the same tank-by means of the heater or boiler G which is strongly heated for this purpose. After about an hour or two (the time varies, of course, according to the nature of the material, the capacity of the tank, etc.) and after the temperature in the tank A has risen to about 95C., the firing, or heating effected otherwise, of the boiler G may be lessened. After 4 to 5 hours the circulation through the boiler is out 01f and cool solution from the tank C is allowed to enter, this in order to bring about a slight fall of temperature in the hot solution so that the logs or material in question, in the manner indicated more in detail in the preceding, will be brought to absorb suitable amount of solution. The added amount of solution is as great as the amount absorbed by the'material being impregnated in each singleaimpregnation operation.

The period of time during which the material has to remain in the tank to absorb a sufficient amount of solution, is dependent on the fall oif temperature obtained. In order that the cool.- ing shall be as uniform as possible, the solution is brought still to circulate, at this instant not through the boiler G, however, but whilst passing by said boiler in the manner indicated above, i. e. by closing the valves ii and opening the valve it.

When the impregnation of the charge con tained in the tank A has been terminated, the material is rapidly transferred, by means of suitable lifting or transporting devices, to the tank B, which contains impregnating solution from the tank D, remaining from a preceding process and completed by fresh supply from the tank D, and the material is allowed to remain in this solution during a period of time adapted to the purpose, 6. g. about 12 hours, whereupon the material is ready impregnated and taken out. After the material has been transferred from the tank A to B, the tank A is loaded with fresh material (which, after impregnation has taken place therein, is then transferred to the tank B after the material has been removed from said latter tank.

It ought to be understood that for each new impregnation process new solution from the tanks C and D must be added to the tanks A andB, respectively, to an amount corresponding to the amount of solution absorbed by the amount in the preceding process.

.In order to maintain the material immersed in the solution during the treatment, it is loaded with weights or locked by means of suitable holding-down devices.

The plant shown in Figures 4, 5, 6 is, in the essentials, similar to that described above with reference to Figures 1, 2, 3, with the distinction, however, that three impregnating tanks ESE, H are provided and communicate with the boiler G and the solution tanks C, D in such a manner that, as indicated above, the impregnation with the first solution can take place in any of said tanks E, F, H, while at the same time the impregnation with the second solution takes place in another of said tanks and the taking-out of impregnated material and the introduction of fresh material can take place in the third tank, in unbroken succession.

For this purpose, the tank C is, via a pipe 3 capable of being cut off by means of a valve 2, connected with a branching pipe which is provided with branching pipes i5, I6, I"! capable of being cut oif, so that in a manner known per se solution from the tank C can, according to wishes,

, be supplied to any of the tanks E, F, H.

In similar manner, the solution from the tank D may be supplied, via the pipe 2 capable of being cut off by means of the valve l9 and communicating with the branching pipe 20 capable of being cut off, to any of said tanks, E, F, H in the manner stated above with relation to the solution from the tank C. These tanks communicate in turn, via pipes 2!, 22, 23 having shut-off valves v 24, with a branching pipe 25 which in turn, via a pipe 31 capable of being cut off and provided with a valve 26, communicates with the boiler or other heating apparatus G, so that said boiler can be brought to communicate with any of the tanks H.

From the boiler G extends, in similar manner as above described, a pipe I! provided with a shutofi valve El and a pump 6 and communicating with opposite ends of the tanks E, F, H via the pipe Zll provided with branching pipes capable of being cut off, so that liquid from any of said tanks can be brought to circulate through the boiler G for the purpose of being heated.

The pipe 25 is provided with a valve H! which is kept closed when it is desired that the solution shall circulate through the boiler G, but if the valves Ill! and 26 are closed and the valve It! is opened, the boiler will be put out of the circulation, so that the solutions circulate only through the pump ii and the one of the diiferent tanks E, F, H which, in each individual case, is switched in for the time being.

When the impregnation in one of the tanks, e. g. in E, with the first (hot) solution has been terminated, the material will, according to this embodiment, not be transferred to one of the other tanks, but the impregnating solution is instead transferred from the tank E into one of the other tanks charged with fresh material-4n the present case, the tank H. The ready impregnated material contained in the tank-E can now be removed and fresh material be introduced and the impregnation with the second cool solution be going on simultaneously in the tank F and the impregnation with the first hot solution in the tank H as explained above.

When the impregnation with the second solution in the tank F and that with the first solution in the tank H have been terminated, the solution contained in the tank H is conveyed to the tank E and the secondsolution is conveyed from the tank F to the tank H.

The material in the tank F has now been impregnated to a completion, and the material can thus be removed from this tank and then fresh material be introduced into the same, and so on in succession.

It ought to be understood that fresh solutions are supplied to the different tanks from the tanks C, D is explained above, in order to cause lowering of the temperature when impregnating with the first (hot) solution, and in order to compensate for the solutions consumed during the IJI'OCESS.

The impregnating process in itself as regards heating and lowering of the temperature in the first tank, where the impregnation with the first, hot solution is going on, takes place in the same manner as above described with reference to Figures l to 3.

In order to bring about this transfer of. solution from one of the impregnating tanks E, F, H to another there is provided a pumping arrangement 30 indicated diagrammatically on the drawing, which arrangement communicates with a pipe 3| forming a continuous circuit and fitted with branching pipes 32, 33, 34 in which are provided valves adapted to the purpose, so that solutions may, in the manner stated above, be

transferred from one tank to another in desired sequence. The realization of the details of such a branching pipe will be evident to all those skilled in the art, so that a special description in this respect may be dispensed with.

It ought to be obvious that the tanks A, B, E, I", H and C, D are provided with suitable means for tapping of! the solutions contained therein, when required, e. g. at the end of the working.

Having thus described my invention I declare that what I claim is:--

1. A method of impregnating wood with solutions of metallic salts which comprises heating the wood to a suiiicient temperature to expel gas therefrom, decreasing the temperature of the wood while in contact with a metallic salt solution thereby sucking solution into the wood, interrupting the sucking action while the wood has capacity to absorb more solution by separating the wood and solution, and contacting the wood with a second solution of a metallic salt which is capable of reacting with the firstmentioned salt, said second solution being at a lower temperature than the first solution, there- 30 by enabling the sucking action to continue.

2. In the method of claim 1, heating the wood and the first-mentioned solution to a temperature of approximately 100 C., thereafter decreasing the temperature of said solution to about 70 to 80 C. and using the second solution at a temperature varying from to 20 C.

3. In the method of claim 1, maintaining wood in contact with the first-mentioned solution for a period-of about flve hours while at a temperature of approximately 100 C., decreasing the temperature thereof to within the range of about 70 to 80 C., and maintaining the temperature of the second solution within the range of 10 to 20 C.

4. In the method of claim 1, employing a solution containing an arsenic compound as the first-mentioned solution, and a second solution containing an ion capable of forming a dimcultly-soluble compound with arsenic.

5. In the method of claim 1, applying an oil of suitable consistency to the surface of the first-mentioned solution. I

6. In the method of claim 1, forming a compound of zinc in the reaction between the said salts.

7. In the method of claim '1, forming a compound of copper in the reaction between the said salts.

BRoR OLOF HAGER.

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