US2042826A - Process of treating wood - Google Patents

Description

June 2, 1936. Y F. G. BRIGHT 2,042,825

PROCESS OF TREATING WOOD Filed May 3l, 1934 2 Sheets-Sheet 2 Patented June 2, `1936 PATENT OFFICE PROCESS OF TREATING WOOD Frank G. Bright, St. Jean, Quebec, Canada, as-

signor to The Singer Manufacturing Company, Elizabeth, N. J., a corporation of New Jersey Application May 31, 1934, Serial No. 728,382 In Canada September 8, 1933 5 Claims.V (Cl. 21-12) This invention relates to improvements in the method of treating wood, and has for its primary object to provide a commercially practicable process of coloring lumber as well as relatively thin Wood pieces such as veneers and the like, under conditions resulting in the requisite uniformity of coloring of the treated wood throughout its Width and thickness.

Another lobject of this invention is to provide an improved method of reducing the moisture content of wood to a desired percentage of moisture. A further object of the invention is to provide a process of coloring wood by impregnation under conditions controlled to predetermine the desired moisture content of the wood after being colored. Other and more specic objects of the invention will be apparent from the following description and claims.

'For the purpose of obtaining a better understanding of the invention, there is somewhat diagrammatically illustrated in the accompanying drawings one embodiment of apparatus particularly adapted for practising the improved wood-coloring process comprising the present invention, it being understood of course that the invention is not limited to the specic details of construction and the arrangement of parts of an-apparatus as herein described, and that modi-l fications thereof or other forms of construction may be employed in practising the present improved wood-treating process.

In the drawings, Fig. 1 is a longitudinal vertical section, partly in side elevation, 0f a preferred embodiment of the apparatus. Fig. 2 is an end elevation of the apparatus as viewed from the right in Fig. 1. Fig. 3 diagrammatically illustrates the connections for the heat radiating means within the receptacle. Fig. 4 is a detail view in side elevation of the door clamps and showing the cylinder and door flanges in section.

According to the present improved process, it is vnot essential that the wood before being treated be either initially partially or wholly dried, as a separate operation, valthough it is desirable that all the wood treated in one run has approximately the same percentage of moisture to insure' the same degree of coloring throughout. v The wood to be treated is piled or stacked upon a truck or other suitable carrier, with superposed layers or pieces of the Wood separated by suitable spacing strips. The truck or carrier supporting the wood is placed in a suitable receptacle which is then closed preparatory to treating the wood.

As illustrated in the accompanying drawings, a

preferred embodiment of the receptacle referred to lcomprises a substantially horizontally disposed cylindrical body I having at its opposite ends removable doors 2.

The doors 2 are each secured in receptacleclosing position by a plurality of releasable 5 clamps comprising bolts 3 extending through notches or slots 4 provided in juxtaposed peripheral end-flanges -5 and 6 of the body I and the respective doors. The bolts 3 for each door are body I adjacent to the end flanges 5 thereof,

said bolts being secured in door clamping position by suitable nuts 8. Preferably a suitable gasket 9 is disposed between the anges 5 and 6 .hinged upon an endless cable 1 embracing the 10 to tightly seal the end openings of the cylindrical 15 der I that there is a gravitational tendency for 25 the doors 2 to swing slightly away from the ends of the cylinder I, so that said doors may be readily shifted by movement of the trolleys I2 to l completely expose the ends of the cylinder. Draw-bridge rails I4 pivotally connect oor rails I 5 with rails I6 provided within the cylinder I for a truck I1 upon which the wood W (Fig. 2) to be treated is piled.

After the wood to be treated-has been placed in the receptacle and the doors 2 have been tightly closed, a forced circulation of the atmosphere within the receptacle is induced by starting the operation of fans preferably disposed interiorly of the receptacle and herein later described. At the same time steam is admitted 40 to heat radiators, also later described, it being understood that when treating Wo'od in successlve runs the receptacle temperature may be approximately 200 F. before said 'steam admission, due to the heated condition of the recep- I i tacle in the previous treatment and the temperature drop incidental to opening the receptacle doors for removal and insertion of wood.

At about the same time that steamV is admitted into the radiators and the operation of the fans started, a vacuum of approximately 26" is created in the receptacle by any suitable means such as an air-pump, ejector or syphon evacuator, the air-within the receptacle and a considerable quantity of the air in the wood interstices being withdrawn therefrom through a pipe I8 and a pipe I9 connected therewith, thus effecting by the reduction of external pressure a lowering of the boiling point of any moisture in the wood, and of course also reducing the temperature limit at which rapid evaporation of said moisture begins. While it is preferred, in order to expedite the process, to start the operation of the fans and to admit steam into the heat radiators before-the vacuum step, it is obvious that the order of procedure up to this point may be Wholly or in part reversed.

The time required to draw the requisite vacuum is very short, and, dependent upon the character of the air-exhausting apparatus employed need take only a few minutes. Furthermore, the specified vacuum need not be held for any considerable period of time, but immediately after it is attained a denite quantity of ammonia gas may be introduced into the receptacle, which ammonia gas is promptly and thoroughly diffused throughout the itially rises at a decidedly more rapid rate than the pressure created by introduction of the ammonia gas and the formation of water vapors generated by the heating of the wood. This differential between the relatively low pressure l .within the receptacle and a pressure normally corresponding to the attainedl temperature is peculiarly favorable to drying the wood, because the heating of the wood under the low pressure permits an initial vaporization of -the surface moisture of the wood and, as the wood becomes gradually heated to a uniform temperature throughout its cellular structure, there results a continuous passage of moisture from the interior of the wood through the outer layers thereof and in a continuous evaporation of said moisture. As the wood is consequently progressively dried from the interior outward, premature hardening is prevented of the outer layers of the wood before the drying action iscompleted to the desired extent.

The temperature rise should preferably not exceed 350 F., and the above described drying action of the wood during the coloring thereof by impregnation is controlled, as hereinafter described, to meet the conditions incidental to the moisture content of the-wood at the beginning of the coloring operation and the desired moisture content at the. end of the operation. For this purpose, when the difference between the initial and final moisture content of the wood necessitates a drying action throughout the coloring operation, suitable relief valves provided upon the receptacle containing the wood may be em-.

ployed to limit the developed pressure below the pressure normally corresponding to the temperature attained at any degree of rise of the latter. The water vapors given olf by the wood being constantly circulated past the vheated radiators by the fans become superheated and serve as a further wood drying agent, so that while the drying of the Wood` is progressive it is nevertheless accelerated by the forced circulation. However, it is obvious that the drying' action may be ar- 'the coloring operation,

rested during the coloring operation, if desired, by setting the relief valves so that the gases or vapors introduced or liberated within the receptacle may build up a pressure in excess of the pressure corresponding to the attained temperature.

A- still more positive and more definitely controllable method of arresting the drying of the woodl at any time during the coloring `operation consists in introducing into the receptacle a pressure building medium such as compressed air, to superimpose a pressure upon the wood additional to that raised by water vapor and gas, whereby at any point in the coloring operation the pressure may be caused to exceed that normally corresponding to the temperature of steam in the receptacle, thus arresting further evaporation of moisture from the wood during continuance of When the wood to be colored initially has a moisture content which is substantially equal to the desired moisture content after the coloring operation has been completed, the compressed air may be introduced into the receptacle immediately after introductionof the aqua ammonia or ammonia gas, i. e., before the wood has become sufficiently heated to discharge some of its moisture by vaporization, thereby pref venting any wood drying action. The pressure developed, or incurred, holds a portion of the wood acids in the wood cells, which acids in conjunction with the heat and ammonia gas effect coloring of the wood. The compressed air may be introduced into the receptacle through the air-pump connection pipe I8, or by means of any other suitable connection between an air-supply line and the receptacle.

The heating of the wood in itself serves to change the'color thereof, but instead of employing the deleterious high temperature and length of treatment that would otherwise be necessary by heat treatment alone to obtain darker shades of coloring, the heat coloring action is supplemented by ammonia gas.` As the ammonia gas is introduced into the receptacle while the latter is under the vacuum drawn, as before noted, but primarily because of the highly turbulent gaseous condition induced throughout the interior of the receptacle by the fans, the ammonia gas is brought forcibly into contact with all of the wood within the receptacle, for the same length of time and to the same degree, thereby insuring a uniformity of absorption by the Wood of the gas and a uniform coloring action thereupon by the reaction of the gas with the wood constituents. The time required for the coloring operation depends upon the ydepth of color desired and also upon the nature of the wood, although the maximum'required time is short as compared with the operation time of previously known wood coloring processes.

For temperature-raising purposes, the receptaclev is preferably provided with four heat-radiators extending substantially the entire length lnteriorly, of the receptacle and arranged perpendcularly to each other to together define a rectangular space for the wood-supporting truck l1. As illustrated in the drawings, each of the radiators which are, in turn connected to an 2,042,826 `'outlet pipe 25 by means of the pipe 26. The receptacle may be additionally provided with a perforated pipe 28 extending lengthwise along the bottom of the receptacle and suitably connected to a steam supply line 29, whereby in special-cases steam may be .directly introduced linto the receptacle.

For inducing the highly turbulent gaseous con- 'dition throughout the interior of the receptacle,

fans'3, 3|, 32, and 33 are installedwithin the receptacle and preferably, although not necessarily, behind the opposed vertically disposed radiators 20, 2|, said fans being disposed in staggered relationship alternately at opposite sides of ;the receptacle. 'Ihe fan shafts are journaled in the wall of the receptacle and -in suitable outer bearings 34, said fan shafts carrying pulleys 35 Lof which' the two pulleys at one side of the receptacle are connected by a belt 36, and the two pulleys at the opposite side of the receptacle are connected by a belt 31. One of thepulleys 35 is also connected by a belt 40 to a pulley 4I upon one end of a countershaft 42 journaled in suitable bearings at the under side of the `"receptacle, said countershaft being driven by` any suitable means and carrying at its opposite end a pulley 43 connected by a crossed belt 44 to a pulley 35 at the side of the receptacle ,opposite to that of the pulley connected to the belt 40.

The ammonia gas may be supplied by injecting aqua ammonia .directly into the bottom of the receptacle, for instance through a pipe connection 50, or -said aqua ammoniamay be injected into pans suitably disposed within the reeptacle.4 The heated condition of the receptacle effects evaporation of the aqua ammonia and thereby liberation of theammonia gas.l The quantity of aqua ammonia injected into thereceptacle is measured to generate approximately .from 25 to 29 lbs. of ammonia gas per- 1,000 board lfeet of Wood within the. receptacle.

If preferred, the specied quantity of ammonia gas may be supplied froman evaporator external to the receptacle and in which the gas is generated, as for instance by heating aqua ammonia. I'o this end, the apparatus may include an evaporator comprising a cylindrical-body 45, disposed below the receptacle I and interiorly provided with pipe coils 46 having a steam inlet line 41 and an outlet'line 48'. The aquay ammonia is admitted into the cylinder 45 through an inlet line 49 and the liberated ammonia gas is'directed into the receptacle I by the pipe 50.' By

` employment of Ythe external evaporator expedient, the ammonia gas is preheated before admission into the receptacle I, thereby minimizingy pheric pressure, the fans may be stopped, and both doors of the receptacle then opened, whereupon the truck containing the colored wood may be withdrawn from one end of the receptacle and directly followed by another truck load of wood 5 entering the receptacle at its other end, thereby not only expediting loading of the receptacle but also minimizing loss of receptacle heat. It may be mentioned that by introducing theammonia gas in a definite quantity, which has been determined by experiment to be adequate for obtaining the desired shade of coloring of the wood, any ammonia gas which may be left in the receptacle after relieving the pressure therein is so negligible that it may be disregarded and the doors may be promptly opened after the treatment.

Having thus set forth the nature of the invention, what I claim herein is:-

1. The process of treating wood, consisting in subjecting the wood in a closed receptacleto ammonia gas and to heat above the vaporization point of the moisture content of the wood, and governing the moisture content of the wood by introducing into the receptacle a pressure bullding medium suilicient to prevent evaporation of the moisture content of the wood at a predetermined stage in the coloring operation.

2. The process of treating wood, consisting in subjecting the wood in a closed receptacle to ammonia gas, raising the temperature in the receptacle above 200 F., inducing by fan action a .forced circulation of the atmosphere within the receptacle, and governing the moisture content of the wood by introducing into the receptacle a pressure building medium sufficient toprevent evaporation of the moisture content of Vthe wood at a predetermined stage in the coloring operation.

-3. The process of treating wood, consisting in subjecting the wood in a closed receptacle to ammonia gas, raising the temperature within the receptacle above 212 F. under a pressure in said receptacle lower than a. pressure correspond ing to the temperature attained, inducing a forced circulation of the atmosphere within the receptacle by fan action, and maintaining the heated condition of the receptacle and said forced circulation for a denite period.

4. The process of treating wood, consisting in n exhausting the air from a closed receptacle `con taining the wood, subjecting the wood to ammonia gas, raising the temperature within the receptacle above 212 F., inducing a forced circulation of the atmosphere within the receptacle,

'FRANK G. BRIGHT. 70

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