US1995145A - Manufacture of artificial boards and like structures - Google Patents

Description

o. w. FROST March 19, 1935.

' MANUFACTURE OF ARTIFICIAL BOARDS AND LIK STRUCTURES Fied Maron 2e, 1932 l', gnap* VIII n mm, @mf

Patented Mar. 19, 1935 .l

UNITED STATES MANUFACTURE oF ARTIFICIAL BOARDS AND LIKE STRUCTURES Orcutt W. Frost, Cloquet, assignerto Wood Conversion Company, Cloquet, Minn., a

corporation of Delaware t Application March 26,

' 5 v Claims.

The present invention relatesv to fiber products,

such as insulation for heat and sound, and to artificial lumber, such as boards, shingles, and like forms which may be cut up, and to formed or molded articles of various sizesV and shapes which may or may not be` suitable for size reduction. t

It has particular reference to the forming of board, or sheet material of'- uniform thickness, that is with parallel surfaces, which can be cut into various sizes and shapes for use as a substitute for sawn lumber. Such material is hereinafter referred to as sheet lumber.

Dense hard boards of the lprior art which are used as artificial lumber, or Wall board, and which are formed of wood ber, or other cellulosic material, are ordinarily heavier and denser than ordinary sawn lumber. The latter averages about 30 lbs. per cu. ft. while the artificial boards referred to run from 40 to 50 lbs. per cu. ft., some vbeing well known which have a density of 1, or over 60 lbs. per cu. ft. Much of the material is so compressed and located that it is not efficiently used in carrying stresses. By the present invention, the material is so allocated in a structure that less dense, and stronger sheets may be made from the'same amount of material.

An important feature ofthe invention as it is used in connection with sheet lumber, is the use.

of a core layer, and of one or two surfacing layers of suitable material. The invention incorporates in artificial fibrous products, the principle of mechanics which is effective in steel structures, such as channel bars, angle bars, T-bars, H- beams, I-beams, andthe like, wherein: greatv strength is obtainable with a minimum of maerial.

In other words, in the present invention,- the material is so composed, and/or formed that it is most eiiicient where strength is required. In particular for sheet lumber, at least one strong surface layer is backed' by askeleton structure have a skeleton connecting vto wet masses of the fibers, the mass itself acts 1992, ,serial No. 601,411

as a plastic body and dries into a unitary body. Sometimes a binding agent is added, or one may be present in the ber mass, naturally, or formed therein by the process employed. From'experiments which I have conducted I have shown that when the fibers of Wood, ligne-cellulose, or cellulose are hydrated by working mechanically in water, the self-cementing action of the fibers increases with the amount of hydration. In this invention IY may employ such hydration processes to increase ,the self-cementing .properties of a cellulosic material, `or Vl may add a cementing agent, -or the cementing agent may be derived from the fibers during the process.

The sheets made heretofore have employed a substantially uniform mixture of base materials.

The sheets, or other shapes, have been made in sheet is thoroughly dry. The pressure applied y in part effects the density; A ysubstantially uniformity maybe obtained throughout the thickness of the sheet. Other lsheets have been made with cessation -of heat andpressure, either one or the other, or both, before complete drying of the sheet, so that the outside surfaces have a different texture than the interior. Y

vOne defect of such` prior articles is Athe utilization of the same materials on the entire interiorl of the board or sheet as is used on the exterior. The requirements and the functions of the outer' layers and the inner layers are not the same, and the differences-are such that the inner layer in particular may be in part dispensed with, and may includecheaper material.

Another defect of prior art materials is th necessary density for the required strength. Where 'thick boards are desired, too-much material is wastefully-used in the prior art processes and structures. -f

One object of the present invention is the provision of a board or like article having at the surface material suitable for `the requirements of the surface, and a less dense and a cheaper body supported and carried by the material of the surface, said surface material extending into the body and connecting the two surfaces.

Another object of the inventionv isthe provision of a skeleton core in a board or like article. One particular object of the invention is the provision of voids in the core of the article. I

Another particular object of the invention' is the of a composite structure by' separately making (1) a core-forming base, and (2) one or two surface-forming bases, combining them after they have assumed some independent form, and thereafter treating the composite structure to producev a unitary, composite structure.

The present invention may be carried out in numerous ways, and differently appearing structures may result.. all of which, however, involve the fundamental idea of this invention.

Thick boards, like lumber, are frequently desirable, but the prior art processes of making thick boards are not economically adapted for operation to effect this result. 'Thick boards are frequently desirable, because the transverse strength is proportional to the square of the thickness, and the surfaces bear the greatest stresses. Just as an I-beam becomes stronger by increasing the width of the web connecting the flanges, so the board of the present invention becomes stronger by increasingthe thickness of the skeleton core between the surface layers.- In making boardsvor sheet lumber, or like articles, by the present invention, I provide at least one sufficiently strong surface layer, but preferably two,` and a backing or connecting core of sufiicient strength to support or carry the surface layer or layers, or the stress layer, as it will hereinafter be referred to. In sheet lumber, two

parallel stress layers are carried and connected by a suitable core. The greatest variations in the invention as herein described are variations in the character and formation of the core. Of course, a stress layer may vary widely in density, composition, and other properties, just as the artificial sheets of the prior art may vary.

, In connection with the general and detailed description of methods, apparatus and products, which have been chosen to illustrate the present invention, the accompanying drawing is referred to. In the drawing:

Fig. 1 illustrates diagrammatically the arrangements of mechanical elements which may be used lin carrying out the invention.

Fig. 2 represents an artificial board containing in the core particles like sawdust as a filler.`

Fig. 3 represents a similar product containing in the core shredded particles, such as excelsior.

Fig. 4 represents an artificial board in which the filler comprises systematically arranged solid elements such as wooden strips.

Fig. 5 represents an artificial board in which voids are formed by removal of the elements present in the core during formation of the board.

Fig. 6 represents an artificial board in which there is an intermediate layer likea surface layer sandwiched between two core layers.

The materials for the stress layerrmay be the same as is used in any prior art board, and may include fiber and a cement-ing agent. The latter may be added, or may be by nature an ingredient accompanying the original fiber source, or may be onefformed incidentally or intentionally in the process of preparing the fiber. I prefer to use a cellulosic iiber, and to treat it by a hydrating process to form a cellulose hydrate. This may be a gelatinous film on some or all of the fibers, or it may be a liquid mass of completely gelatinized nbers'added to less hydrated, or to unhydrated fibers.. I prefer. to use as the body of the fiber, a partially digested wood, or semi-chemical pulp, such as ligno-cellulose, so termed to distinguish it from more completely cooked wood which is' substantially "cellulose in character. Where wood, ,or wood waste, or straw and the like as a raw material, is cooked wlthchemicals, lignocellulose is preferred to cellulose, because of the higher yield of fiber to be obtained. Where ,hy-

dration is practiced to yform pulp-bonding material, either ligne-cellulose or cellulose may be hydrated. If ground wood pulp, or other mechanically undigested wood, or other cellulosic material, is employed, hydration of the cellulosic material may be effected, irrespective of the specific character of thecellulosic material.

As material for the core, any kind of pulp may layers, but the core as a body may have an4 average density which is less than the density of the stress layers.l The non-pulp part of the core may be void space, or any filling material eithervgranular or fibrous, and preferably, if fibrous, it is to be in the form of aggregates of fibers rather than fibrated material. Flakes of paper, coarse sawdust, shreds of Wood, wood shavings, slivers of wood, and the like, may be used. Excelsior is most desirable because of its flexibility. A very coarse grade of such excelsior may be used. It is to'be understood that a pulp ce-v menting agent is present in the lpulp part of the core to bind the pulp part together into a network, or a unit around a filler. Preferably, such cementing agent is the same as is used 'in the pulp of stress layer, and a hydrated cellulose is suitable for both. By using the same bond in the pulp of the stress layer and in the pulp of the core an integral substance is established extend; ing as a skeleton or net work throughout the unit, and it-may be made integral by the one process of uniting and curing the different elements of the composite structure.

In practicing the invention the weaker core may be effected by creating voids therein, either systematically, as by some mechanicalrmeans, or heterogeneously, as by controlling the character of its composition. In the mechanical method I may incorporate solid material as a part of the structure to define the voids and to resist and to transmit compression,l and then remove the solid means, either bodily, in fragments, or otherwise. I may use elongated rods or bars v'vhich may be removed endwise from the voids formed thereby in the completed product.' I may use volatile or decomposable crystalline material, which remains in solid form in the process, and remove it wholly or partly as a gas or vapor through the poresof the completed unit. I may use a leavening agent in the core which may be either soluble or insoluble in water. i

While any solid may be used, such as sand, mineral fibers, animal fibers, and metal shreds or fibers, I prefer waste products, and especially light-weight waste,-such as material which is less dense than pulp parts. in their ultimate form. Coarse sawdust, shavings, or shredded wood, exemplified by coarse excelsior, are suitable lightweight materials.' The. more elongated is the form of such filler, the more it functions as a mechanical reinforcement. It is of such a character that whenvcompressed it forms interstices,

. which in the nal product are filled with cemented pulp integrally united to cemented pulp in the stress layers. p

To make such a board, I form a pulpy mass, preferably by treating wood waste, in any way to form a wet fibrated mass. The flbration may be mechanical, chemical, or both. Ground wood may be used. Cellulose pulp, such as paper stock, may be used. Semi-chemical pulp may be used, such as wood chips softened by a partial chemical digestion, and then mechanically separated as in a rod mill. All or part of the pulp may be treated to form cellulose hydrate, as by the mechanical action of a beater (Hollander), a Claiiin, or a Jordan, or otherwise. A part of the pulp, or any other cellulose pulp, may be completely hydrated to a gelatinous solution without fibrous form, or it may b e very highly hydrated, and such cellulose hydrate may be added to less hydrated pulp or to unhydrated pulp. By any method, a self-cementing pulp mixture is formed, exemplified by a mixture of fibre, or pulp, and gelatinous cellulose hydrate. drated 'to form a gelatinous skin about each of them. Such material isa plastic mass when wet,

owing asa plastic mass.

The plastic mass described is used in part by itself to form wet pulp laps for the surface layers. It is also used `as the essential part of the core in admxture with the solid filler. For example 60% of` shredded wood and 40% of self-cementing pulp (air dry weights) form a suitable core. In practice three machines are used, one to form the wet mat of core, which may be about 2 inches thick, vand two others, such as cylinder machines, one above and one below the core former, for forming and discharging a wet lap of adhesive pulp onto the opposite surfaces of the wet core lap. The surfacing laps may be 1/8 inches thick when wet. The three laps are united, pressed through squeeze rolls to eliminate surplus water, and then passed to a press. The process may be continuous, or intermittent according to machines employed. If intermittent the formed sheets may be made initially of size suitable for the press. If continuous, the composite sheet may be cut to fit the press.

Multiple presses suitable `for the process are well-known and some may operate simultaneouslycupon as many as twenty such sheets. They are capable of using pressures up to 1500 lbs. per sq. inch, and of being heated by steam at a pressure up to 100 to 150 lbs. per sq. inch. They may also be electrically heated. A,

The pressure and temperature which may be employed generally arenot critical in practicing this invention and may be varied according to the results desired. For certain products fixed conditions may be specified. It is preferred -that the temperature should be sumcieht to boil out the excess water. Air drying or evaporation is l vnot excluded, however, and it may be ldesirable for .certain special types. It has been found that the air-dried product is better when hydrated cellulose is present, as the'concentration of the hydrated or gelati-nized cellulose is increased. The

inch and a mechanical pressure .of 250 lbs. is san- 'isfactory for V,a general purpose sheet lumber.

When pressure and a boiling temperature are applied, the applications arepreferably simultane- Preferably all the bers are hyous, andare continued until liquid water in the mass has been boiled out. Such drying converts the cellulose hydrate into a hardhorny mass which -is integral as a continuous masser net. work from face, through core tofacefbeing substantially uniform in` character through its indensity from face to face, with the 'same pulp maSS.

Breaking point f d. t under Poun s ransversc bonded Composi- Thck' Pounds load Item pulp r on ness face per cu. applied Sq. to Iacex tt at center of 6 in. span 4 inches wide Per cent l 635 pulp... .137 in. 43. 5 46. 7 lbs. 2 432 55pulp...

. 45 shred-- .260 in. 31.0 85. 5 lbs.

wood 3 573 45 pulp v o5 Shred-- 553 in. 2,5. 6 135.0 lbs.

The foregoing tableclearly demonstrates that a less dense board containing a less quantity of bonded pulp, may be stronger' than the same area of board containing more of such pulp.

As a detailed example of carrying out the indischarged and may be couched over to aV conveyer belt, preferably in the form of a screen 12, under which there is a suction box 13. The mat is thus made more dense and less wet.

Additional felting means, such as Olivers l5y above the mat 11 and 16 below the mat il, form thinner sheets or mats l'l and 18 of pulp, preferably identical with that used in adrniuzturer with the sawdust.l These laps are couched to conveyer belts 19 and 20 to bring., them-toward the core-mat 11, at which they are properly directed to form facings on the core mat. The

three mats move uniformly together as one sheet 21 over a. conveyer 22, preferably a screen, to squeeze rolls 23for removal of surplus water, and for a uniting compression of the mats. The sheet may then be out intosizes ksuitable for the hot press. In the press vthey may be subjeced to a continuous pressure of 250 pounds per' square inch, and a drying heat produced by a '10 pound steam pressure within the platens of the press.

Fig. 2 represents the product in cross-section.

The product has three zones 25, 26 and 21, `of which 26 is the core. 27 are substantially pulp layers, and the pulp substance extends from one layer to the ,other,l

The surface zones 25 and f through the core as an integral substance, designated in the core as 28. The parts 29 designate the sawdust, and represent generally whatever fller may be used. One surface layer in the press may be formed against a wire screen on the platen, as is well known, for aiding the liberation of steam in the drying process. Screen markings 30 are designated.

In `the manufacture above described it is not necessary to form two stress layers. The lower Oliver 16 and its product 18 may be omitted, and to some extent a less denite stress layer having a uniform surface, will be formed by gravity drainageof the pulp substance to the lower side of the unit.L The ultimate essential characteristics will however prevail in the resulting product Where a water-proofed product is desired the surface layers 1'7 and 18 may be suitably treated or sized, either in the pulp form before felting, or after felting, as desired. When such treatment is limited to the pulp in the stress layers only, there is economy in sizingA materials as compared to sizing all the pulp for the board, as practiced heretofore forthe uniform type of In Fig. 3 a similar product is 'shown in which vshreds of wood such as jexcelsior 32 is present in the core, contained in the hardened intejral matrix 33 which is comprised in the surface layers and which fills the interstices between the shreds.

Fig. 4 represents a departure from the forms of Figs. 2 and 3, in which the filler is systematically arranged. Wooden strips 35 of triangular cross-section are arrangedin complementary relation as shown. 'Ilhese may be left embedded in the product. The pulp 36 extends integrally from face layer 37 to face layer 38, and between 'the adjacent lengths of filler in the form of webs 39. In manufacture various expedients may be adopted for incorporating'the filler. It is to be noted that prior to compression in the press, the adjacent lengths may be more separated along the line of the thickness of the board, and in the process of compression the faces 40 and 415 aid in compressing the pulp in theweb.

In Fig. 5 a further modification is shown, similar in original form to that of Fig. 4. Rods auch as round metal rods 42 may be inserted in the core base and housed therein as the filler.

' They may `thereafter be withdrawn, leaving voids indicated as 43 in the core, to reduce its average density. Thus the entire substance 44 of the core and the stress layer is the same, is integral, and of the same density, but because of the voids, the average, density of the core is less. Likewise, strips shaped as in Fig.- 4 may be withdrawn, and they may be originally supr-pliedas metal -rods,.as in Fig. 5 for the purpose 'of easy withdrawal. The contraction of metal on cooling contributes tothe separation of the rods from the pulpv in the core.

'In'Fig. 6 it i`s shown that the'invention is not limited to unlled layers at the surface. Such layers may be arranged within the core in one or more layers, exemplified by asingle layer of pulp 46 sandwiched -between two core layers 47 and 48,the whole being integrally united by -the pulp substance with two surface layers 49 and 50 ofl pulp base. Y j In general discussion it may be stated that the sawdust particles,` and the shredded wood of Figs. 2 and 3, respectively, are not necessarily cemented to the pulp substance, and may Ibe vsqueezed therefrom into the surface layers lvoid. 'I'hey function in the process of forming as pressure-distributing means and as means for forming voids in the integral substance. Because of the cheap character ofthe filler, it may be left in the voids which it creates, and it is not detrimental to the desired character of the product if the filler particle draws away from and resides more or less loosely or detached in the void. The forms of Figs. 2 and 3 are the preferred forms for reasons of simplicity and economy in the process of manufacture.

'I'he product may exhibit a characteristic laminated structure in the planel of -the sheet at any part of thel body, but this is to be distinguished from the existence of separable and distinct layers. not cubical such laminations may readily occur to the extent that the fibers, or the filler, are elongated in character. y l

In generaldiscussion of the process of formation, it may be stated that mechanical pres- Because the compression is unilateral and each other and to the horny cement. Likewise,

high temperature is not essential to the formation of the'hard and horny mass from hydrated cellulose. It is material to the speed of drying. The transfer of heat to the-interior is quicker by higher heat. In the case of metal inserts the transfer of heat to the interior is quicker than in the case of less conductive filler in the core, such as wood, sawdust, shavings, shredded wood.4 The ,latter absorb some water, and this also must be driven oif as well as the water in the selfcementing pulp.

'I'he invention is not limited to any particular-thickness'of the stress layers, or the core, or any particular ratio of thicknesses. A very thin face layer may be used, and some decorative features may result in regulating thicknesses. For example, when the stress layers are sufliciently thin, the pressure means in the core, whether rods, grids, sawdust, shredded wood, or whatever may be used, can be made to exhibit shadowy or clear-cut markings in the exposed face, due to slight deviations `from equal distribution of preure. Particularly with shredded wood a variegated net work of lines may appear having slightly darker shade where lengths of `shredded wood press against-the surface layer.

Colors may be incorporated into the surface layer, and may also, if desired, be incorporated into the shredded wood to be preferentiallay o cause a mottled design in' color. f

'I'he chips o r other filler may be previously coated with a water-excluding substance, or otherwise treatedto prevent useless absorption of water from the aqueous pulp. Parafiln may be used, and will so function until heat is applied. Upon application of' heat thel parain will melt and it is then distributed throughout the board by diffusion, making the -nal product more water-resiaant. I have found that paraffin and any similarly acting material increases the drying time because of the subsequent diffusion under heat. 'Howeven when 'a suitably heat-resistant substance like gilsonite is used to render the filler water-resistant,- the time of drying may be shortened, because there is no water in the filler to be removed.

The product may be made with the particular object of providing high thermal insulation properties. The less dense is the board,'tl1e more air spaceA there is within itand hence the more` eiective it is as a heat insulation. The forms which have large voids therein, such as unfilled air spaces, .and the more spongy forms, are particularly advantageous as heat insulation. It is also to be understood that the sound transmitting property is lessened, and the sound absorbing quality is increased, by the same factors which increase the heat insulating capacity. In other words, the acoustical and the4 thermal properties may be advantageously increased by decreasing the averageI density of the product.

Products of the present invention may be made to approximateflumber in physical characteristics, and may or may not be grained to some degree, according to the character of the filler. It has greater strength per unit weight than the boards of uniformly dense material. Because ofl the use of filler as described, the product may be made in thicker form with less problems incidental to dryingthan are met with in making boards of the same thickness yfrom uniformly homogeneous pulp masses. The

boards are cheaper to make per unit of thickness. 'I'here is less warping, expansion and contraction because of the lower average density of the core. The board will receive and'will hold nails at the edges, without splitting. The product has a higher thermal insulating value than the denser forms. It may have an attractive surface appearance subject to variation by slight changes in proportions and in materials employed in the process of construction. When sizing is desired, reconomies may be effected.

It is also to be understood that sizing vand water-proofing agents may be incorporated-.finto any of the laps for the surface, or the core. Materials for such purpose are well known. The fibers employed may be proofed against water,

fire, insects, and rot in any known manner, if

desired, and such other changes and modifications, and prior art practices may be adopted, without departing from the invention as expressed in the appended claims.

I claim: f

1. The method of makingan artificial boardlike product which comprises making a wet core by forming around particles of a filler a skeleton network of wet brous composition capable of a self-cementing action on drying, forming on said core a wetl surfacing layer consisting lsubstantially entirely of fibrous composition having cementing properties similar to the fibrous composition of the core, pressing the core and surface layer together, drying the resulting body into an integral unit, andremoving the filler to leave voids in said core portion of the unit. 2. The method of making an articial boardlike product which comprises making a wet corev by forming around elongated rod-like elements a wet fibrous composition capable of a self-cementing action on drying, forming on said core a wet surfacing layer consisting substantially enltirely of fibrous composition having cementing properties similar vto the brous composition of the'core, pressing the core and surface layer together, drying the resulting body into an integral unit, and removing .the rod-like elements from the core.-

3.,'1'11@ method of making an artificial boardf like product whichcomprises making a core by.y

forming around ller elements a skeleton network of a self-cementing mass of structural composition, forming on said core 'a surfacing layer consisting substantially entirely of the essential composition of said core, treating the united core and layer to cause setting and integral union of said core and layer by its self-cementing action, and removing the filler elements.

4. The method of making an artificial boardlike product which'comprises making a core by forming around filler elements a skeleton network of fiber and cementing bond, forming on said core a surfacing layerconsisting substantially entirely i of ber and a cementing bond having cementing I Aa surfacing layer consisting substantially entirely of highly hydrated cellulose and fibers. treating oacUTr W. FROST. I

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