US1955411A - Cellulose board - Google Patents

Description

April 17, 1934, w

w. A. DARRAH CELLULOSE BOARD Original Filed Au 10, 1929 -2 Sheets-Sheet vl o l o o R! o M April 17, 1934. w. A. DARRAH- 1,955,411

CELLULOSE BOARD 1 Original Filed Aug. 10, 1s. .9 2 Sheets-Sheet 2 Patented Apr. 17, 1934 UNITED STATES CELLULOSE BOARD William A. Dari-ah, Chicago, 11].

Original application August 10, 1929, Serial No, 384,850, now Patent No. 1,819,771, dated August 18, 1931. Divided and this application July 13,

1931, Serial No. 550,382

9 Claims.

This application is a division of application serial No. 384,850 filed August 10, 1929 now Patent #1,s19,771 dated August 18, 1931.

This invention relates to processes, apparatus and product produced in a novel method of forming a sheet or board. Some of the objects of this invention are to provide economical, and effective methods for rapidly producing a strong uniform sheet or board. My process also permits of forming board with considerably greater margins than is ordinarily possible and avoids many limitations present in the usual commercial methods now obtaining.

Some of the objects of this invention areto make possible the formation of the board or sheet from materials which would produce a board or sheet only with great difiiculty with the present methods. Another object of this invention is to produce a stronger, tougher board than would be possible from the same materials using present methods. My invention produces a density and interlocking of fibers or particles which is superior to that now obtained. My invention also makes it possible to readily produce a board having a different surface condition from the interior. My process also makes possible the formation of a board containing cementing materials in a manner much superior to present known processes.

The product resulting from the practice of my invention is superior in many ways to present boards. If desired it may be made harder, denser and stronger although my process permits'the formation of a light board such as is used for insulation. My invention will be described in connection with the formation of board such as is know as wallboard, but it should be understood that by making obvious changes in the process and materials I may produce thinner boards, sheets, paper or if desired extremely thick and heavy blocks.

My invention also permits a material shortening of the time of the processes and a material shortening of the subsequent drying withja great saving in heat in the drying operation and. a material reduction in the cost of drying equipment. Other objects of this invention will be apparent from the specifications, claims and drawings attached hereto.

Referring to the drawings Figure 1 shows in'section partly broken away a portion of one form of my equipment in side elevation, I

Figure 2 shows a portion of the same equipment in end elevation also partly broken away.

iii

Figure 3 shows a detail of a portion of the rotating member while,

Figure 4 shows a vertical elevation partly in section of a portion of the equipment shown in Figure 1 with certain conditions as will be later described.

Figure 5 shows a side elevation partly in section of a roller table, press and dryer which form other steps in my process.

In the drawings, 1 represents the housing of a centrifugal rotating member which is carried on shaft 2, which runs in bearings 3 and 4. supported on pedestal 5. The equipment may be driven from pulley 6 through a belt or in any conventional manner. The centrifugal 1, consists of a back or web member 7 supporting a side member 8 enclosed in a housing or shell 9 which is intended primarily to prevent the throwing of moisture or other materials about the room. A perforated member 10 is ruggedly supported in member 8 and preferably carries a screen member 11. In order to obtain a greater strength under some conditions I may extend shaft 2 as indicated by 12 and apply braces or other reinforcing members as indicated by 13. A drain or outlet 15 is so provided in the lower portion of housing 8 for recovering the white water.

A supporting member 16 which may conveniently take the form of an I-beam or channel member serves to carry movable support 17 which 35 for purposes of illustration is indicated as a trolley consisting of a frame 18 carried on wheels 19 and 20. The frame 18 supports arms 21 and 22 which carry beam member 23 on which is mounted head box 24. A flexible hose or pipe g0 member 25 delivers stock to head box 24 from any desired source as for example tank 60 the level in which may be varied to adjust the hydrostatic pressure on head box 24 for purposes to be later described. A work table 26 carries a series of live rolls 27 which may be driven in any desired manner as for example-by sprocket 28 by means of a chain in the usual manner.

Itwill be evident that movable member 17 and therefore head box 24 may be moved out of position within the cylinder. In Figure 4 the head box is shown in position within the centrifugal 1 whereas in Figure 1 the head box is shown removed and a second movable member 29 carrying frame 30 on wheels 31 and 32 serves to support frame 33 by means of arms 34 and 35.

'Frame 33 carries a series of material supports '36, 37 and 38 which for convenience in description are shown as being portions of a substantially cylindrical surface. Work supports 36,

the size of the opening 44 in slice 42.

37 and 38 are carried respectively by arms 39, 40 and 41.

Head box 24 is provided with a slice 42 provided with adjusting screws 43 designed to. control 45 indicates a frame extending from support 33 and carrying doctor 46 which may be of any conventional design as for example a roller.

Perforated member 10 is formed integrally with the centrifugal device 1. Perforated screen 11 or Fourdrinier wire is held in place by wedge members 4'7 and 48 provided with a locking member 49 which may take the form of a cylindrical rod or key.

Referring more specifically to Figure 5 the table member 26 carrying live rollers 27 is shown receiving a piece of board or sheet 50 preparatory to passing it through press member 51 which for purposes of illustration is shown formed from rolls 52 and 53, and which serve to press and thereby'harden the board. A dryer device 55 is shown in position to receive the board after leaving press member 51, the board for purposes of illustration being carried on live rolls 56 and leaving dryer 55 on live rolls 57.

One method of operating the equipment here described and practicing my invention consists in putting centrifugal device 1 into rotation and then sliding carriage 18 along support 16 until head box 24 is in approximately the condition shown in Figure 4. It should be noted that direction of rotation of centrifugal 1 should be approximately the same as the flow of stock from head box 24. Direction of rotation is indicated by the arrow on Figure 3. Having then adjusted the opening 44 of slice 42 by means of screws 43 to obtain the desired flow of stock, valve 58 is opened allowing the stock to fiow in head box 24.

The stock employed may be formed from a great variety of materials and by many wellknown methods. One satisfactory form of stock is that now used in the preparation of board or paper depending upon the characteristics of the product which it is desired to produce. In case it is desired to make a board the stock may consist of ground wood to which has been added sizing materials and if desired a portion of filler and long fiber. One of the materials which I prefer to use as a source of fibers in making a product in accordance with my invention is the cellulose fibers obtained from submitting wood to a disintegrating or defiberizing action.

These fibers may be obtained either by submitting the woodto grinding in the wellknown stone grinders or by equivalent means such as hammer mills, disintegrators, fiberizers, etc. These fibers when used in the manufacture of board in accordance with my invention are of course in the so-called hydrated state and suspended in water. As mentioned elsewhere I prefer to use the coars er fibers for the skeleton or structure of my board. For example the fibers which would be obtained by running chips and wooden blocks through two hammer mills would constitute an excellent skeleton for my board. It is frequently an advantage as in the case of paper manufacture to cook these fibers before making up the board, but this is not essential. A light cooking increases the strength .of the board. A wide range of materials may be employed in my process and I do not wish to be restricted to any special raw material. Such substances as ground wood, ground straw, sugar cane residue, corn stalk fibers or many other materials may be employed.

Those substances usually used in the manufacture of paper and board may be employed for filler. One of the materials which I prefer to use is a fine ground wood fiber or Wood fiour. Other materials I have found equally satisfactory are starch, clay, gypsum, whiting, etc. It is preferable to prepare a portion of the material in such a manner as to produce a considerable percentage of fairly long fibers. Methods of obtaining this result are wellknown in the art of producing board,'paper and similar products and form no part of this invention. It is important to know, however, that owing to the characteristics of the process which I have invented a much wider range of materials may be used than is permissible in presentstandard practice. As the stock is delivered through opening 44 of head box 24 it falls upon Fourdrinier or screen 11 which may be constructed of wire in the manner similar to present commercial Fourdriniers or if desired a piece of canvas or fabric may be employed.

The centrifugal action due to the rotation of the device subjects the stock to a very powerful force which tends toseparate the water of the stock and leave the solid material on the screen. I prefer to adjust the speed with which the stock leaves opening 44, so that as far as possible the velocity of the stock leaving opening 44 will approximate the lincar velocity of screen 11. This arrangement is of some importance in rapidly building a smooth uniform sheet without ripples or lumps and without creating an unbalance in centrifugal device 1, which in the speeds and sizes employed is quite susceptible to unbalanced conditions. I do not wish to be limited to any particular velocity in device 1, as in general I have found that I can produce a board most rapidly the higher the linear velocity of device 1. On the other hand, if I wish to produce a relatively hard dense board the faster screen 11 travels the more satisfactory the results and the essential limit under the conditions I have described is the strength of the materials and the structure formed therefrom.

If, on the other hand, I wish to form a light somewhat porous board it is desirable to operate at somewhat lower speeds.

Obviously the most satisfactory speed for any given product will depend upon the nature and conditions of the stock, the rate at which it is fed from head box 24 and the desired characteristics of the product being produced. As an illustration of operating conditions, I have found that linear velocities in the neighborhood of 3000 to 4000 feet per minute give satisfactory results with certain stock consistencies.

In operating the equipment, I prefer to place a given charge of stock in tank 60 and so adjust the hydrostatic head produced by the liquid in tank 60, that the velocity of the stock leaving opening 44 approximates the linear velocity of the member 11. I prefer to use for tank 60 a container which is relatively shallow so that the hydrostatic head will not vary between wide limits during the emptying of tank 60. Many obvious mechanical expedients may be employed to accomplish this result such as raising or lowering the tank 60 to compensate for changes in level of the contents. If desired I may also pump the stock from tank 60 and depend on the pressure delivered by the pump to control the velocity of the stock leaving opening 44. It is to be understood of course that opening 44 extends substantially the entire width of the sheet which is to be formed.

After the desired amount of stock has been appliedto Fourdrinier ll through head box 24 in order to build up the required thickness of sheet, I find it advantageous in many cases to add a new supply of a different grade of stock to tank 60. For example in forming a commercial wallboard I prefer to use a rough relatively coarse fiber for the interior portion of the board and I may add such fillers as are desired'to this material. The first portion of stock will tend to segregate, the finer portions going to the inner surface of the Fourdrinier and the coarser fibers building up to form a felt or mat. The subsequent addition of other portions of stock tends to fill in a portion of the voids between the coarser fibers with the result that the product at the end of this stage usually exhibits a hard dense surface adjacent to the walls of the centrifugal or the Fourdrinier and a more porous surface on the inner side. Inasmuch as it is commercially usually desirable to produce a board or sheet having a high degree of finish on both sides, I frequently prefer to add to tank 60 after the board is substantially formed, a new portion of stock which preferably composed of finer fibers and particles and serves to give a smooth, dense, uniform coating to the surface of the board. For this purpose I may use such materials as sulphite or other forms of wood pulp as prepared for making paper or I may use such materials as gypsum cement, plasters, etc. depending on the required characteristics. If a paper pulp is employed for this purpose, the resultant product presents a smooth and finished appearance which is very desirable and gives a surface which is relatively hard and dense.

One form of sheet which I have found very satisfactory may be made by mixing with the stock a quantity of caustic burned magnesite. The quantity of this material may vary within wide limits, but satisfactory results may be obtained when the ratio of magnesite to cellulose fiber in the finished product is in the neighborhood of one to six.

The stock is then formed in the way previously described and if desired the finishing coating may have a proportionate amount of caustic burned magnesite. After as much water as possible has been removed from the material due to the centrifugal action resulting from the rotation of device 1 a limited portion of magnesium chloride may be applied to the sheet through head box 24 or in any other desired manner the quantity of magnesium chloride being designed to be suflicient to cause a strong set with the caustic burned magnesite.

Having completed the forming operations and no longer requiring the use of head box 24, carriage 18 may be rolled out of position and frame 29 which carry work supports 36, 37 and 38 may be moved into position. shown in Figure 1. This frame also carries a doctor 46 which may be employed to smooth or finish the top surface of the sheet as required.

After the sheet is properly formed and acted upon by the doctor centrifugal device 1 is brought to a stop preferably with wedge members 47 and 48 near the lower portion. The board is then loosened from screen 11 by inserting a. doctor or slice between the board and the screen. If de-- sired this may be held in position by arm 45 and the centrifugal I slowly rotated to loosen the board. Many other methods of accomplishing this result will be apparent to those skilled in the art.

As the board is loosened it falls by reason of its own weight upon work supports 36, 37 and 33. Frame 29 is then moved along I-beam 16 until the board is over live rolls 27. It is then released by rotating work supports 36, 37 and 38 about member 33 thus placing the formed board gently and without distortion upon the live rolls 27 of table 26. The board is then moved by means of live rolls 27 through press member 51 into dryer 55. The rolls 52 and 53 may be so proportioned as to straighten and flatten the board 50 thus compensating for the curvature resulting from the formation of the board in centrifugal device 1. This operation is preferably carried on while the board is wet and with proper care, as otherwise the fibers and structure of the board is likely to be damaged. While I do not wish to limit my invention to any specific sizes, as these may obviously vary with the requirements in each particular case, I have found that when producing board which in its finished stage may be approximately one-half inch thick it is convenient to use a centrifugal having an internal diameter ranging from twenty to thirty feet. A width of ten feet for the Fourdrinier also gives convenient commercial results- A wide range of dimensions are possible,. however, without exceeding the scope of my invention.

It will be evident from the description here given that the process which I have invented makes possible the formation of boards and sheets from a wide range of materials which have hitherto been excluded. An example of this condition arises from the fact that in forming board or sheets under commercial conditions the characteristic known as freeness is of vital importance. If a given stock is not free enough the time required for forming the sheet will be excessive and the production with a given investment in equipment will be materially reduced. This also means that the thickness of board which it is possible to form may be kept below the desired figure. On the other hand, in forming commercial sheets by the present method a fiber which has a desirable amount of freeness is likely to be coarse and form a sheet which is weak and poor in appearance. Present commercial methods, therefore, it will be noted involve a balance between therate of forming the board, the thickness of the board or sheet and the strength of the final product. Limitations of this class are largely overcome by the device which I have invented, quite largely for the reason that the powerful forces avaiiable make it possible to quickly form a board of almost any desired thickness independent of the freeness characteristic.

Another advantage obtained from the process I have described is the much greater amount of water which can be removed from the sheet or board. In the case of commercial board practice it is not unusual for the product leaving the Four drinier or forming machine to contain 60 to70% of water and only 30 or 40% of solid material. By means of the process which I have invented the ratio of solid material to water can be immensely increased so that by proper manipulation if desired, I can produce a sheet or board containing as little as 15 to 25% of water.

This results in large savings of heat and time in the drying operation. The saving in heat results in a reduction in operating cost while the saving in time makes possible the use of shorter and smaller dryers.

The process which I have here disclosed also makes possible the formation of a board or sheet which is much denser and harder than can be obtained by the present commercial methods. This appears to be due partly to the'large forces available for removing the water, partly to the outward pressure of the fibers against the Fourdrinier and partly to the filling of the voids between the fibers It will be noted that none of these factors are available in any where near the same degree with present methods.

I am aware that the use of a vacuum has been advocated in connection with the forming of board the vacuum being applied either to the inside of a cylindrical, moving, perforated drum and the stock being delivered to the outside of the drum. In some cases a vacuum has been applied under a Fourdrinier wire acting to draw out the water.

The maximum effect of the vacuum cannot of course exceed atmospheric pressure or in the neighborhood of fourteen pounds per square inch and most experiments in this line have been conducted with an effective difference of pressure amounting to not over six or seven pounds.

It will be apparent of course that with the device which I have devised the force available for removing the water and compressing the board is limited only by the strength of the materials and the structure formed therefrom. If desired, I may utilize forces which are 1000% or more in excess of those available by present methods.

I am aware that many efforts have been made to accomplish the results which I obtain by means of carrying relatively high pressure on the head box or delivery of the stock. Such efforts have been unsuccessful and apparently are likely to prove unsuccessful for the reason that the desired result must apparently be obtained by someforce which tends to draw the water from the felt which is formed rather than to force it' into the felt. The distinction is obvious as some of the effects resulting from the pressure system are a destruction of the felt and serious dislocation of the fibers from their natural position, the blocking of the felt so that it becomes nearly water tight due to the closing of the pores, and the'obvious mechanical difficulties of controlling the equipment.

It will also be noted that with present commercial methods the rate of travel of water through the felt which is formed on the Fourdrinier gradually decreases until it reaches a point where the flow of water is so slow as to beimpractical. If under these conditions the attempt is made to add a surface coating of some other material, the pores being already filled with fine material, the rate of fiow of moisture through the board already formed will be so slow as to make the process prohibitive. On the other hand, by utilizing the centrifugal principle this difficulty is entirely elimnated owing to the much greater forces which are available.

In describing my invention I have utilized certain specific terms and descriptions for the purpose of clearness. I do not wish to be confined to the exact structure shown or described or the exact method outlined as many departures from my invention will be apparent to those skilled in the art. Such items as dimensions, speeds, pressure, thicknesses and other characteristics are, of course, subject to variation with the operating conditions and the product which it is desired to form. The mechanical structure shown is intended to be diagrammatic and illustrates principles and many obvious equivalents may be employed without departing from the spirit of my invention.

A further feature of my invention consists in the fact that I am able to produce a. board or sheet containing cementing material such as magnesium oxy-chloride. In order to successfully produce a board or sheet containing a material of this nature it is necessary to first remove the major portion of the water and then add a new portion of the cement forming material such as the magnesium chloride. Such a procedure is entirely impractical with present commercial methods and equipment, but is extremely simple in the process I have invented.

It will be apparent from the description given above that one form of sheet which I am able to produce has an interior formed from long, strong and relatively coarse fibers and an exterior formed from fine and more refined fibers interlocked, however, with the coarser fibers. The resultant board, therefore, has the strength, stiffness and resilience which results from the use of coarserfibers in the central portion, but the hard, smooth, dense surface which results from the interlocked layer of finer fibers.

It should be pointed out that the surface layer of finer fibers is intermingled at the junction in such a manner that there is no sharp lamination, but a gradual gradation as distinguished from the condition in which a sheet of finer fibers, as for example a layer of paper, is attached to an interior portion of coarse fibers.

The use of the applicant's process and the product resulting therefrom involves a considerably lower first cost, a stronger attachment between the various grades of fiber with a resultant increase in strength.

It is well known that laminated sheets have a definite tendency to part or shear along the point of attachment. This is particularly true in the case of sheets formed by attaching a separately made layer of fine fibers such as paper to another separately made interior layer. On the contrary, the structure I have devised owing to the interlocking of the two types of fibers, is substantially free from this difficulty.

As a result of this construction, the board I have made is stiff, strong, hard, light and presents a good appearance. It is also practically free from the tendency of the outer surface portion to separate from the interior portion of finer fibers.

Having now fully described my invention what I claim as new and wish to secure by Letters Patent in the United States is as follows:

l. A hard dense homogeneous and unlaminated board formed from defiberized wood fibers felted together and having coarser wood fibers in the interior and wood fibers made by the sulphite process on the outside.

2. A unitary board of homogeneous structure formed principally from ground wood cellulose fibers with a preponderance of relatively coarse fibers in the central portion thereof and a preponderance of relatively fine fibers adjacent the surface thereof, and a thin smooth layer of sul- 5. A unitary board of homogeneous structure formed principally from defiberized wood fibers with a mineral binder distributed-there-among, the fibers in the central portion of said board being relatively coarse and having appreciable spaces therebetween while the fibers in the outer portion are finer than in said central portion made from sulphite wood fibers and arranged more closely together, thus forming a smooth, dense, hard surface.

6. A cellulose product of homogeneous unitary structure formed from wood fibers felted together, the fibers in said central portion being relatively coarse and spaced apart while the fibers in the outer portion are relatively fine and spaced close together, said inner and outer portions being directly interlocked one to the other without an intermediary binder, said finer fibers serving to form a smooth, dense, hard surface to the product.

7. In a cellulose product of homogeneous unitary structure a relatively hard dense surface layer formed of relatively fine sulphite fibers from wood directly interlocked with a relatively softer central portion of coarser cellulose fibers.

8. A cellulose product formed of felted defiberized wood fibers having a relatively hard dense water proof surface of relatively finer fibers of sulphite stock and a central portion of coarser fibers said outer portion and central portion being felted together, to form a unitary interlocked structure. I

9. A unitary board formed principally of cellulose fibers felted together and bonded with magnesium oxychloride, the surface of said board being composed of finer fibers than the central portion thereof, said inner and outer fibers being interlocked together to form a homogeneous structure.

A. DARRAH.

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