US2064965A - Method and means for treating wood - Google Patents

Description

Dec. 22, 1936. H. E. WILL 2,064,965

METHOD AND MEANS FOR TREATING WOOD Fild Dec'. 14,1932 3 Sheets-Sheet 1 ATTORNEY Dec. 22, 1936. H. E. wu

METHOD AND MEANS FOR TREATING WOOD File d Dec. 14, 1952 3 Sheets-Sheet 2 acts/? uwl l t .W

INVENTOR ATTO R N EY Dec. 22, 1936. H, E, w L 2,064,965

' METHOD AND MEANS FOR'TREATING WOOD I Filed Dec. 14, 1952 3 Sheets-Sheet s Rig 4.-

. MM W' ATTO R N EY Patented Dec. 22, 1936 UNITED STATES PATENT OFFICE I v v v iMETHEOB AND TREATING I I Application December 14, 1932, Serial No. 647,287 In Germany December 14, 1931 6 Claims.

This invention refers to a method and means for treating wood and similar materials and also relates to an article produced by said method and means and known in the art under the name of "Lignokompakt, said article consisting of a compressed and otherwise treated wood which is nonswelling and non-shrinkable.

Methods used heretofore for impregnating dry heart-wood by means of steam or vapor have not 10 been successful since steam is liable to condense in the exterior layers of the wood and to form liquid stoppers which prevent the uniform and evenly distributed penetration of the impregnating substance into the wood.

In prior art wood was dried by means of evaporation taking place at the exterior surfaces of the wood, so that the interior of the wood re- 7 tained more moisture than the exterior layers;

the interior, therefore, shrank less than the exterior and this developed tension and forces within the wood whch caused cracks and fiaws.

To prevent the wood from cracking the drying process had to be interrupted by a steaming process after which the drying was resumed for some time.

An object of this invention is to provide an improved method of treating wood and similar materials, said method being free from drawbacks inherent in the previously known methods;

Another object is to provide means for producingan absolutely non-porous and non-swelling article made of wood, the pores of which have been closed by a thermical and mechanical treatment which does not include the use of a filling substance.

A further object is to provide an article which is made of wood but which has from three to six times as much strength, toughness and specific weight than normal wood, with a corresponding increase in the module of elasticity.

My method of treating wood comprises the steps' or processes of drying it, impregnating it by vapors and then compressing and cooling it. Some of these steps or any parts thereof may be steps will now be described in detail.

, My process ofdrying wood differs from those known in prior art in that I do not steam it.

After the drying process has begun, it may be with steam having a certain high temperature I omitted or used in a different sequence. These and pressure, depending upon the nature of the wood and other conditions. The steam passes with high velocity through the wood and should not have a high degree of moisture, so that it may not deposit any condensate on the wood fibres. 5 The deposition of the condensate is also prevented by heating the wood to a suitable temperature and by the high pressure of the steam. The drying process is practically or completely stopped while the wood is being softened.

The softened wood is dried by overheated steam or a mixture of hot steam and air. This process is carried out below thesaturation point of the wood fibres and at a temperature which is at least equal to the so-called specific temperature of 15 swelling 1. e. a temperature at which the wood begins to lose its hygroscopic properties. During this process the temperature of the exterior surfaces of the wood is kept higher than the temperature of the interior of the wood and is also 20 higher than the temperature of the saturated steam.

One of the important features of my invention is the fact that duringthe drying process the drying agent, namely the steam or the mixture of 25 steam and air, is passed at a high velocity, 1. e. a velocity of many meters per second, over the treated wood. The actual velocity depends on the size and quality of the treated article, etc. and is varied in the course of. the treatment. The. steam is superheated to an extent depending on the selected velocity. Due to this arrangement the heat is transmitted in a steady current from the drying agent to the interior of the wood, so that on a diagram the heat current would be represented by a straight line ending at zero, while a temperature diagram would be a parabolic curve.- The moisture contained in the wood vaporizes uniformly and in equal amounts throughout the entire cross-section of the wood, so that 40 the interior tension is not increased and no cracks appear in the treated article. The air contained in the interior of the wood is driven out by this inner vaporization process. Due to this feature of my method I am able to dispense with the usual step of removing the air, which was usually introduced between the drying and the impregnation steps.

My drying process is carried out below the saturation point of the fibres, the temperature of the treated material being higher than the range of the cooling temperatures; The'diflference between the temperature of the material and the cooling temperature is directly proportional to the percentage of the dry portions of the treated material and inversely proportional to the amount.

'rial becomes equal to the pressure of the saturated steam at a higher, temperature; in other words, these two pressures become equal to each other at a temperature higher than that which would have existed had the dry substance been absent.

fact that an increase in the amount of heat supplied to the exterior surfaces of the article is not compensated by an increase in vaporization. This may be explained by the supposition that a part of the steam situated in the interior of the wood acts catalytically in a different way from the part of steam situated in the exterior layers of the wood, the first-mentioned part of the steam being more saturated than the secondmentioned part, while the second-mentioned part is more super-heated than the first-mentioned part of the steam; thus the wet steam in the interior of the wood precipitates the vaporization, while the superheated steam in the exterior layers retards the vaporization process.

Practical experiments have shown that in the course of my drying process a great part of the moisture contained in the wood is removed by vaporization and 'not by a flow of moisture towards the surfaces of the wood which takes place in prior art methods.

I prefer to operate at temperatures which are higher than 100 C. and are close to the abovementioned temperature of swelling since the features which have just been described become more apparent at these temperatures.

A characteristic feature of my method of "treating wood is, consequently, a very quick and short drying step during which the hygroscopic properties of the wood are further diminished.

My drying process may be successfully em-' ployed in treating green wood. The time necessary for drying green wood is shorter'than that necessary for drying ordinary wood. In both cases the vaporization takes place not only at the exterior surfaces but also in the interior of the wood and can be regulated so that the moisture is evenly and uniformly removed from the entire cross-section of the wood, and, consequently, no inner forces can arise within the wood. When a fir-timber 50 millimeters in thickness is used, its water content of 42% may be reduced to 8% in 64 hours, 300 kilograms of water being removed per cubic meter of timber. If a well preserved wood is not required, the drying period of 64 hours may be further reduced to 50 hours, while methods known in pror art require triple or quadruple the amount of time for the 65 same result.

The wood is usually aged towards the end of the drying process. At the time the drying step is practically interrupted for a time while the wood is being subjected to a high temperature. The inner forces still existing within the wood disappear and its elasticity is diminished; chemcal reactons take place within the wood fibres, resulting in a hardening of its cells.

As already mentioned, my steps of ripening, drying and aging wood may be used for treating any other material which contains moisture, even if this moisture-is bound in a colloidal'form.

' After my drying process has been completed, there is usually no necessity for the introduction of a separate step of removing air from the interior of the wood, althoughin some cases the treated article may be placed under vacuum for some time. 1

.Next the wood is treated by suitable gaseous binding and fluxing means and impregnated. These binding means act as catalysts and cause an absorption process which begins at the exterior portions of the treated article and gradually proceeds towards the center thereof. The temperature in the interior of the article is maintained at the condensation temperature of the gaseous means, while the temperature at the external surfaces is kept at a higher level in the beginning of the absorption and is then gradually lowered.

Due to this arrangement no liquid deposits are formed within the treated article at the beginning of the treatment so that vapors and gases can freely penetrate into the wood and reach its central portions which are maintained at a temperature closeto the condensation temperature.

I accomplish this important feature of main:

taining the temperature of the external wood layers at a higher level than the temperature of the interior, by passing the superheated vapors at a high velocity over the external surfaces of the article. This velocity should be equal to at least a few meters per second and should be varied in the course of the treatment. The vapors should be superheated to an extent depending on the selected velocity. Thus I increase the co efficient of heat transmission and am able to select a suitably high amount of heat transmitted to the external layers of the treated article. The

amount of transmitted h'eat depends, obviously,

on the'selection of a suitable temperature of the super-heated vapor and the temperature of the surfaces of the article. On the other hand, the transmitted heat increases the temperature of the exterior layers of the treated article to such an cells of the wood, and so that the excessive amount of the liquid is immediately transformed into vapor again by the heat passing through the article in a direction towards the exterior thereof. This vapor is super-heated by the dry and porous wooden article which plays the role of a superheater in this respect.

After this treatment has been continued for some time, I diminish the velocity of the gases by reducing the action of the blasting means, which will be describedmore fully hereinafter, and thus diminish the coefficient of heat transmission and lower the tempeiature of the external surfaces of the article. Then the superheating tempera-.

ture also becomes lower and the absorption increases in a direction towards the exterior of the treated article.

This treatment can be successfully used for producing a high class article such as Lignokompakt and in that case the impregnating sub-.

stance must be completely absorbed by the wood. I

If an article of lesser or different qualities is required any desired amount of the impregnating substance may be supplied to the wood which may be impregnated to any desired extent.

It will be noted that this treatment is similar to that which I use for drying the wood, including the ripening and aging steps. The impregnation may include therefore the steps of preliminary impregnation, softening during the interruption, the resumption of the impregnation and aging It can be also used for treating any material similar to wood. The vapors of the impregnating means can be used as heat transmitting means for a subsequent final drying of the wood, al-

though as a rule steam or a mixture comprising hot steam is used for that purpose.

After the absorption has sufliciently progressed I prefer to increase the temperature for the purpose of accelerating the impregnation taking place within the wood fibres, and also for the under vacuum for a short time in, the same container in which it was dried and impregnated. The purpose of this vacuum treatment is to accelerate the action of the impregnating substance on the wood fibres. Then the wood is subjected to mechanical compression which takes place in a device to be described hereinafter.

i The article is compressed in such a way that the forces acting along the width and the length of the article correspond to the compressibility or the elasticity of the wood fibres within this area. The amount of compression is selected with the view to the elimination of the hollow spaces within the wood.

Since the specific weight of similar woods may vary to a great extent, I must adjust the compressing means for each density in order to arrive at the same results. I determine the coeflicient of compression in a way which will be demonstrated by the following two examples:

1st Ewample:-1 cubic meter wood was found to contain 360 kilograms wood paste (consisting of 245 kilograms cellulose and 115 kilograms lignine) having a specific weight of Ws=1.46, 5 kilograms, resins, oils and fats with Ws=l.06 and kilograms water with Ws=1. The wood is to absorb 13 kilograms of tar oil with Ws=l.07 and 7 kilograms of turpentine oil with Ws'=0.87. The specific weight of the treated wood before compression was found to be 0.42. The coeflicient of compression is determined from the following equation:

' The specific weight of the compressed wood is increased to 3.3 0.42 1.39 and no hollow spaces will be found in the treated article.

2nd Example:-1 cubic meter wood contains 410 kilograms wood paste, 7 kilograms of resins, oils and fats, lO-kilograms water, 15 kilograms tar oil and 8 kilograms turpentine oil, the specific weight of treated wood before compression being equal to 0.48. Then The specific weight of the compressed wood is equal. to 235x048: 1.37.

The above examples show that if the operator dimensions of the raw wood for a finished article of any size can be easily determined.

The three-dimensional coefficient of compression is composed of different linear coefficients which depend on the strength of wood in directions parallel to the wood fibres and perpendicular to them, parallel to the concentrical rings and radial to them etc. I

If the tension at the end of elasticity is equal to Te, the transverse pressure should be PtZCX Te In the. case of the above-described first example with Te=lcg/cm the transverse pressure becomes equal to If the Poisson constant m=4, the longitudinal pressure in the direction of the fibres will be equal to Pl=330 (4-1) =990 kg/cm The wood described in the second example will be subjected to practically the same pressure since in that case Tezi'l kg/cm After the article has been compressed, it is cooled while still remaining under the press.

After my process has been completed, the resulting article consists of a mass which is similar to wood fibres in appearance but the cells of which are hardened, bound and compressed.

The device used for treating wood comprises a cylinder or container provided with a steam generator or distributor, blasting means, and a superheater. The drying and impregnating steps of my method can be carried out entirely within this container. The device also comprises a separate heated press and cooling means. I also prefer to use some suitable means for preventing the wooden articles from cooling off on their way from the above-mentioned container to the heated press.

. The vapors, gases and steam used for treating wood are all introduced into or produced within the container, they are superheated and mixed there to the desired extent and brought in contact with the wooden articles at a predetermined velocity. The vapors cause an absorption process within the wood which begins in the interior of each article and gradually spreads out towards the external layers. The articles within the container can be subjected to a vacuum treatment and the pressure of the gases and vapors can be changed froma high value to sub-atmospheric pressure or vice versa while the articles remain within the container. The wood is dried in the same apparatus, the velocity and the temperature of the heat transmitting means within the container being regulated until a uniform vaporization of moisture is obtained. The heating of the wood and the ripening and aging processes are all carried out within the same container.

A preferred embodiment of the inventive idea is illustrated in the accompanying drawings, in which:

Figure 1 is a vertical cross-section of a dryin and impregnating apparatus.

- Figure '2 is partly a top view and partly a hori= separated from adjacent upper and lower rowsby intermediate slats d. The slats d are of such size that most of the exterior surfaces of the articles remain exposed to the air.

A plate e which is situated within the cylinder m above the articles 0, is supported by a wall I attached to the cylinderm and carrying a number of regulatable blasting devices 9. A heating device h is also carried by the cylinder m and is situated above the plate e. A device y is used for introducing air into the cylinder and a pipe not shown in the drawings serves for removing exv haust air.

A perforated tube 2' is situated within the container m between the heating pipes h and the blasting devices 9 and extends along the entire length of the cylinder m. This pipe is used for introducing vapors and gases which have been produced or collected outside the cylinder.

The pipe 2' is situated within the path of the steam current and the vapors emitted by said pipe are superheated by this current before they reach the-heating pipes h, which further increase the temperature of the vapors and the steam current.-

The vapors can be produced within the cylinder by providing hot surfaces between the heatingpipes 11. and the blasting devices 9' and by spraying liquids over said surfaces.

An outlet is is used for removing the condensate A from the cylinder m. The outlet is is adapted to be connected with an air pump in order to produce", a vacuum within the cylinder m..

Plates I act as dams and allow only a certain predetermined amount of the circulating gases to pass under the articles (this amount being sufiicient to heat the bottom of the articles) while the remainder is forced to circulate among rows of articles c.

The distances between the walls of the cylinder m and the various devices within said cylinder are selected with the view to enabling the gases to maintain the required velocity while circulating within the cylinder.

The press shown in Figure 2 comprises four dies n used for compressing the wooden article in directions transverse to its fibres. The number of dies should correspond to the number of the articles side surfaces. The dies nare movable in a direction towards the center of the article and are supported by a casing o. v

In Figure 2, two of the four. dies 12 are shown in inoperative positions while the remaining dies compress the article. The pressure of the dies n is transmitted to the pressing jaws p; needle bearings q are used to correct the direction of the pressure and to enable the members p to recede from each other while being operated. The'mem ,bers p are guided by guide plates rwhich are adjustably mounted in the casing o.

If thetreated articleis a square in cross-seccompressed wooden article."

tion, and if the forces of compression are equal to each other, the guide plates 1' are placed at angles of 45 to the dies n. If the compression'forces are unequal, the guide plates 1' must form smaller angles with the dies 11.. If, for instance, the wooden article is rectangular in cross-section and is twice as long as it is. wide, the plates 1' form an angle of about 25 with the dies n.

The needle bearings q are carried by plates s connected by screws with the members p and the intermediate pieces t situated between the round end-pieces of the dies 11. and. the members I). The plates s are provided'with slots containing the screws carried by members p and t, so that the plates s can slide with respect to the members i and 10 while the press is being operated.

A cage-shaped member u (Figs. 2, 3 and 5) provided with fork-shaped pieces 12 is used for holding the compressed article in position. The member u is moved until its pieces 2; are placed over the dies n and come in contact with the members t, keeping the compressed article underpressure during its removal from the press.

The press shown in Figure 2 is used for compressing the wooden article in directions perpendicular to its fibres. While this compression takes place the wood is also compressed by a similar press in a direction parallel to its fibres The dies of the second-mentioned press move only a small distance, but the pressure exerted by them on the article is considerably higher than the transverse pressure. As shown in.Figure 3, the shape of the treated Figure 5 shows three transverse presses similar to the press shown in Figures 1 and 2. These presses, situated one behind the other, are used for compressing a long wooden article. In that case I prefer to use two plates w extending along the entire article.-

What is claimed is: r

1. A method of treating wood, comprising the steps of ripening, drying and aging a wooden article, impregnating said article by placing it in the path of a gas mixture containing a superheated vapor of an impregnating substance, said vapor having a velocity of a plurality of meters per second and gradually increasing the temperature of the vapor during the last-mentioned step. I

2. A method of treating wood, comprisingthe steps of ripenin drying and aging a wooden article, impregnating said article by placing it in the path of a gas mixture containing a superheated vapor of an impregnating substance, said vapor having a velocity of a plurality of meters per second and gradually increasing the pressure of the vapor during the last-mentioned step;

3. A method of treating wood, comprising drying an article, impregnating said article by placing it in the path of a gas mixture containing a superheated vapor of an impregnating subthe temperature of the vapor during the lastmentioned step.

4. A method of impregnating wood, comprising placing 'a wooden article in the path of a gas mixture containing a superheated vapor 01' an impregnating substance, said vapor having 9. velocity of a plurality of meters per second, and gradually increasing the temperature of the vapor during the impregnation. 1 5. A method of treating wood, comprising drying an article, impregnating said article by placingitinthepathotagasmixture containing a superheated vapor of an impregnating substance, said vapor having a velocity of a plurality of meters per second, and gradually increasing the pressure of the vapor during the last-mentioned step. a

6. A method-of impregnating wood, comprising placing a wooden article in the path of a gas mixture containing a superheated vapor of an impregnating substance, said vapor having 8. velocity of a plurality of meters per second, and

gradually increasing the pressure of the vapor 10 during the last-mentioned step.

HEINRICH ERNST WILL.

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