US1283105A - Wood-preservative treatment. - Google Patents

Description

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WOOD-PRESERVATIVE TREATMENT.

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No Drawing.

To all whom it may concern:

Be it known that I, J UDsoN an]: Cnw, a,

subject of the King-of Great Britain, and resident of the city of Montreal, in the Province of Quebec and Dominion of Canada, have invented certain new and useful Improvements in NVood-Preservative Treatment, ofwhich the following is a full, clear, and exact description.

This invention relates to the treatment of wood products such as ties, timbers or the like, in order to preserve them from the effects of moisture, fungi or other destructive agents, thereby introducing new qualities of resistance to both decay and mechanical wear.

It is well known that timbers or Wood blocks for pavements, when fully impregnated with oily materials, such as creosote oil, are not made waterproof thereby. This has been proved by the fact that drybloeks, when fully impregnated with oil, would expand after being laid in the ground to such an extent as to destroy a laid pavement. This is due to the fact that moisture can be absorbed by the cell Walls of a wood structure, even though they are impregnated with and surrounded by oil. It has been shown and is generally recognized that the normal conditions of cell wall saturation in oil impregnated timbers is one wherein the lignocellulose material contains approximately 20% moisture. This is called the normal point of saturation.

It is also known by extensive tests for determining the strength of timbers at various points of saturation that an absolutely dry specimen of timber will show approximately twice the mechanical strength of timbers carrying the normal amount of water saturation. It is also a well established fact that moisture is requisite for the decay and destruction of timbers by means of ferment or fungi, and the dry timbers will last indefinitely. If it is possible, therefore, to maintain wood in an absolutely dry condition, the maximum strength and resistance to wear can be maintained.

The object of my invention is to reduce the wood products first to a bone dry condition, and then to impregnate and cover the surface of the wood in such a manner that moisture cannot again enter the wood and be absorbed by the cell walls thereof.

The method of carry g t my pr cess is Specification of Letters Patent,

Application filed. August 11, 1916.

Patented (lot. 29, 1918.

Serial No. 114,449.

as follows :-The specimen is first immersed ina solution of hot coal tar pitch or tar and is left submerged therein until the air and moisture, which is contained in all green or air CllledllllllbBI'S, has been driven off. To .accomphshthis, the pitch or tar solution must be heated to a temperature of 212 Fahrenheit, or higher, depending upon the rate at which the moisture is to be expelled. Dry wood will commence to char when heated to atemperature above 250 F but this cha rring will not take place when moist timbers are being heated, and the steam is pass ing constantly from the outside surface to the specimen. It is only after the moisture is practically all driven out from the speci men that char-ring of the, surface will take place, and when this action is noticed, this portion of the treatment may be terminated.

The specimen is then taken out of the tank or other receptacle. and allowed to cool until.

the average temperature is below the boiling point of water, when a practical vacuum will exist in the cells within the specimen. If, now, the entire specimen is again heated until the pitch on the surface is in a liquid condition, it will be drawn into the cells of the wood to fill-this vacuum. This second heating step can be carried out by immersing it for a second time in the molten coal tar pitch at a proper temperature, or by heating it in a chamber in which the ten'iperature is controlled by means of air or steam, and in which pressure may also be applied. Owing to its viscosity, a deep impregnation will not be obtained when using a material such as coal tar pitch, but this is not necessary nor desirable, as long as the impregnation is sufficiently deep to thoroughly plug and waterproof the exterior portions of the material, then, the inner part of the wood will be preserved from both moisture and decay. It is desirable to obtain not only a limited depth of impregnation but also a surface coating, which will prevent the exposure of the cell walls to atmospheric influences. The resultant procluct of my invention is a timber in which the heart of the specimen is dry, sterile and under partial vacuum. The surface comprises a layer of impregnated wood covered with a coating which prevents access of moisture. If the impregnating pitch used is of a soft and sticky consistency when cold, an. additional surface coating may be given by dipping the specimen into a tank of very hard pitch in a hot molten condition.

The first part of my process is carried out in open tanks so arranged that the specimens, either singly or in bundles, can be immersed and held below the surface. The second part of the process consists either in the application of heat and pressure within a closed cylinder tank in order to forcethe soft pitch into the cells of the wood, or it may consist of successive heating and cool ing operations by dipping the specimen intermittently into the hot material, in which case the hot pitch will be forced into the cells by means of atmospheric pressure. The wood product thus treated will be harder and stronger than wood treated by the usual processes on account of its bone dry condition.

Having thus described my invention, what I claim is y 1. A process of treating wood, which consists in heating the wood in solution of coal tar pitch at practically a charring temperature, expelling the water of saturation from the fibers 0f the wood, impregnating the outer portion of the wood with the material in which it is immersed, coating the surface with a harder pitch at higher temperatures and leaving sufficient coating on the surface to keep the surface fibers of the wood from contact with moisture.

2. A process of treating wood, which consists in heating the wood to a sterilizing temperature, removing the water of saturation from the cell walls of the fibers, impregnating the outer portion of the wood with a solution of coal tar pitch, and coating the surface of the wood with a harder pitch at higher temperatures to prevent the fibers from again absorbing the water of saturation.

3. A process of treating wood, which consists in heating the wood at a sterilizing temperature until the water of saturation is removed, impregnating the outer portion with a solution of coal tar pitch which is fluid at temperatures below 212 Fahrenheit, and finally dipping in temperatures above 212 Fahrenheit.

In Witness whereof, I have hereunto set my hand, in the presence of two witnesses.

J UDSON A. DE OEW.

Witnesses:

S. R. W. ALLEN, G. M. MORELAND.

u Copies of this patent may be obtained for five cents each, by addressing the Commissioner of IPatents,

Washington, I). G.