US2075023A - Method of preparing wood for grinding - Google Patents

Description

March 30, 1937. w DAVID 2,075,023

METHOD OF PREPARING woon FOR GRINDING Filed Dec. 12, 1934 r I I S nun-n a R? R LE5 rE/e M. Del/l0 INFENTOR I I A TTORNEY atented Mar. 30, 1937 aorsnzs METHOD OF PREPG WOUD FOR GRWG 7 Claims.

This invention relates to a method of and means for grinding wood for the manufacture of news print paper. More particularly, the invention relates; first, to the treatment of the wood to render the fibers derived therefrom of longer length, greater in yield, stronger and of lighter color than is ordinarily obtained; and second, to a method of assembling and grinding pieces of wood of irregular form and of varying size, and particularly pieces that are of small diameter; it 10 being an object of this invention to provide a treatment for the wood that makes possible the production of fibers of such grade and color that the addition of sulphite pulp is not required for the manufacture therefrom of a superior grade of news print paper. Furthermore, it is an object of the invention to devise a method of grinding pieces of wood of irregular form so that there will be substantially no loss of tissue in the form of flour or slivers. Explanatory to the invention it will here be stated that ground wood, as ordinarily produced for the manufacture of news print paper by grinding wood in a raw or natural condition, is made up of a mass of material in which short fibers predominate; these fibers consisting of the torn fragments of the natural fibers of the Wood. Furthermore, due to the dark color of such fibers, as well as its lack of strength when made into paper, it is customary in making news print Paper under usual conditions, to add a certain proportion of sulphite pulp which is stronger, and of a lighter color. However, this addition of pulp incidentally increases the cost of manufacture of paper to a point materially higher than would be the case if ground wood alone were used.

Since this added expense is undesirable, it has been the principal object of this invention, as was previously stated, to pr duce a superior grade of paper without use of sulphite pulp, and to accomplish this object I have provided a method of treating wood, before it is ground, with certain chemical reagents dissolved in water which softens the binding material, or middle lamellae of the cells or fibers in normal wood, and at the same time renders those dark colored, encrusting materials normally present in the wood more soluble in water, so that the wood when thus treated can be ground with the resulting production of long, strong fibers that become -much lighter in color after washing in water than that produced from untreated wood.

Explanatory to another object of the invention, it is here stated that heretofore, in the 55 manufacture of paper, attempts have been made to grind material of relatively small dimensions, but these attempts have not been successful, mainly due to the difficulty attendant upon attempts to hold the material that is being ground against the surface of the grindstone. Therefore, it has been a further object of this invention to overcome this difliculty as fobllows: First, the material that is to be ground cleaned of all foreign matter and is barked, then the pieces are assembled in cars or other containers with the fibrous plant material disposed with the sclerenchymatous fibers presenting their main axes parallel to the longitudinal faces of the container. The wood is then subjected to a chemical treatment to soften it, and after treatment the wood is compressed into compact bales to fit within the pocket of the grinder.

In accomplishing the before mentioned and other objects of the invention, I have provided the improved mechanism as disclosed in the accompanying drawing, wherein- Fig. 1 is a diagrammatic plan of a portion of a plant arranged for treating and grinding wood in accordance with the objects of the present invention.

Fig. 2 is a cross section on line.22 in Fig. 1, showing the treating retort.

Fig. 3 is a cross section of a press for compressing the treated Wood into bales.

Fig. 4 is a perspective view of a bale removed from the press.

Fig. 5 is a sectional detail illustrating the placing of bales in a grinder.

Referring more in detail to the drawing- 8 designates what may be a conveyer whereby the wood selected to be ground for news print paper is conveyed to one or more barking drums 2 of a suitable kind. From the drums the barked wood, cleaned of foreign matter, is discharged onto a conveyer belt 3 which passes between unloading platforms 3 adjacent which car tracks 5-5 extend.

The tracks 5 lead from the platforms through elongated, tubular retorts 66 and there are cars or trucks i mounted for travel on these tracks, whereby the cleaned wood unloaded from the conveyer 3 and placed in the cars is conveyed into the retorts for the treatment previously recited as an object of the invention.

The retorts are of a construction permitting them to be tightly closed and preferably are of circular cross section, as seen in Fig. 2, and the cars may be the usual wheeled trucks with cradle like bodies, as shown, in which the pulp wood is piled lengthwise for treatment. After a string of trucks with wood piled thereon for treatment has been enclosed in a retort, the retort is filled with the chemical solution to a depth sumcient to cover the wood and the solution is placed 5 under pressure which is maintained until a specified amount of the solution has been forced into the wood. The wood. may be completely impregnated with the solution or only partially impregnated, dependent upon the particular characteristics of the paper which it is desired to produce.

In the present process the solution containing the chemical reagent is injected into the wood at a temperature substantially below boiling point of water. The solution comprises water in which alkalies, such as sodium carbonate and salts of acids, such as sodium sulphite, is dissolved. However, I do not limit the process to any particular concentration of the chemical reagents in water as this is determined in many cases by experiment only. The solution causes a certain chemical reaction in the wood which softens and loosens the fibers. In the case of woods that consist largely of sapwood and which are subject to discoloration through the attack of such organisms as blue stain fungi, as for instance, various species of the genus Ceratostomella, I prefer to use as a chemical reagent a substance or substances dissolved in water that will inhibit the growth of such organisms, as for example, sodium carbonate.

After proper or desired impregnation of the wood has been effected, the hydraulic pressure is released and the solution is withdrawn from the 5 retorts. Then steam, saturated or superheated, is admitted into the retorts at a pressure above atmosphere, and this is maintained until the chemical reagents with which the wood is impregnated have reacted on the wood and the 0 wood softened to the desired degree. The steam is then allowed to escape from the receptacle and the treated wood is withdrawn by advancement of the cars along the tracks 5. The treated wood 5 s then ready for grinding and this may be done while it still is hot from the treatment or it may b allowed to cool first.

It will be apparent that by controlling the pressure of the steam, or the pressure and super- 5 heat of the steam and the duration of the treatment, the rate of the reaction between the chemical reagent or reagents and wood, or such components of the wood that will react, can be deflnitely controlled.

In the diagrammatic illustration, the storage tanks for the chemical reagent are indicated at l0 and pumps for delivering it and for withdrawing it from the retorts are indicated at II, while 42 and I3 designate the pipe connections with 0 the pump. A steam generating boiler is shown at I4 and this is connected to the retorts by a pipe 15.

After the wood has been treated in the retort as was heretofore described, it is transferred to a mechanical, or hydraulic, press and is compressed to an extent whereby all voids between individual pieces are closed but without compressing the individual fibers of the pieces. While 70 held under compression wooden hoops are placed about the compressed bales to hold them together when removed from the press.

In locating the wood in the press the pieces are laid lengthwise in the manner as heretofore described when placed in cars or containers for treatment, and bales of standard size are formed so that they may be placed in the standard types of grinding machines. In Fig. 3, I have shown in cross section a bale being compressed in a press. In this view 20 designates the wood pieces, 2| is the press chamber and ,22 the plunger actuated by a ram 23. Wooden hoops 24 are located in position for securing the bale after it has been fully compressed.

In' grinding, the bale is pressed against the stone as it revolves in such manner that the direction of the axis of the stone is parallel to the main axis of the lignified fibers present in the bundle, and the bale presents a maximum surface to the stone at all times.

Having thus described my invention, what I claim as new, therein and desire to secure by Letters Patent is:-

1. A process of treating wood preparatory to grinding, comprising barking and cleaning the wood of foreign matter, enclosing the wood in a closed container, filling the container with a chemical reagent suificient to immerse the wood, applying pressure to the reagent to efiect its initial impregnation of the wood, draining the reagent from the container and applying steam under pressure to cause complete impregnation of the wood.

2. A process of preparing wood for grinding, comprising cleaning the wood, treating it with a chemical solution for softening and loosening its fibers, bundling the wood and compressing the bundles into compact bales.

3. A process of preparing wood for grinding, comprising cleaning the wood of foreign material and bark, immersing the wood in a chemical solution under pressure to cause loosening and softening of its fibers, removing the solution and applying steam under pressure, then pressing the wood into compact bales.

4. A Wood bale made up of chemically softened wood pieces, compressed together in a compact bale wherein the fibers of the wood pieces extend substantially in parallel relation.

5. A wood bale made up of wood pieces of irregular size and compressed together in a compact bale to remove all voids between adjacent pieces and wherein the fibers of the pieces extend substantially parallel and lengthwise of the bale.

6. A bale as recited in claim 5 wherein wooden bands bind the bale together.

7. A method of preparing wood for grinding comprising, barking and cleaning the wood, conveying it into a closed container, applying a chemical solution to the container under pressure to cause an initial impregnation of the wood, withdrawing the solution and applying steam under pressure to complete the impregnation, withdrawing the wood, and compressing it while hot into bales wherein the fibers of the wood pieces are laid substantially parallel and lengthwise of the bale.

LESTER W. DAVE).

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