US2033411A - Manufacture of artificial lumber and pressed and molded products - Google Patents

Description

Man'ch 19, 136. F ARsm ZMBAM MANUFACTURE OF ARTIFICIAL LUMBER AND PRESSED AND MOLDED PRODUCTS Filed Sept. 6, 1.932 2 Sheets-Sheet 1 ramp California Redwood splinterysawdust m mixture Similar Material H at and 9 Chemically Treat Screen through Add Coarse Screen. Hot mate m Top 9f Mold 7 Screen Through 6 Fine Screen I Invert Mold and Contzants.

Mix Coarse Screened Particles with Part of Fluid Binder.

Add and Hix Fine Particles and Rest of Binder.

Screen Mixture 7 Into Cold. Mold.

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Patented Mar. 10, 1936 UNITED STATES PATENT OFFICE MANUFACTURE OF ARTIFICIAL LUMBER AND PRESSED AND MOLDED PRODUCTS Application September 6, 1932, Serial No. 631,919

4 Claims.

The present invention lies in a novel process of producing artificial fiat boards and shapes in any desired thickness and to any reasonable dimensions, and further lies in the production of a product greatly improving any and all comparable materials now commercially produced,

The invention will be described with the aid of the accompanying drawings in which:

Figs. 1 and 1a. are diagrammatic chain views jointly showing the various steps in the process.

Fig. 2 is a perspective view showing a small section of the product.

Fig. 3 is a fragmentary plan view showin part of one of the mold plates.

As my aggregate, I preferably select California redwood sawdust, preferably as now produced as wastage of the lumber industry, by those saws engaged in ripping with the grain of the wood rather than across the grain, because the preferred sawdust is of the splintery variety rather than the granular character of particles which are produced by cross-cut saws. In place of such sawdust however, I may use any vegetable material placed by mechanical means in a splintery condition resembling the sawdust described.

I prefer sawdust from wood dried to a point wherein it contains approximately twelve percent of thenatural moisture of the tree, or a subsequent drying of the green sawdust to that percentage. Those skilled in the art will recognize that the moisture content of twelve per cent means that the wood particles will at that point be completely dry to the touch, yet retain the.

full measure of the strength of the wood, which would not be true were the drying carried to a point below twelve per cent moisture content.

A characteristic of this wood, and also of many other vegetable materials of like character, is that it contains a considerable quantity of water soluble tannates, lignins, and/or dye stuffs,

which through their uneven distribution, coupled sometimes with soluble pitchy or adhesive substances, require a definite chemical treatment for the purpose of neutralizing and rendering the same insoluble. I have, therefore, elected to so render inert the dye stuff, and the like and perforce must therefore destroy any natural resin, gum or adhesive, this wood or other utilized vegetable substances may contain. The loss of the natural adhesive content of the wood is of small moment, however, because very little pitch or resin exists in this material and what little there is, is in isolated locations not evenly spread throughout and would, therefore, if utilized, present a continuous problem of variables to a manufacturing process.

In that the time of addition of those materials to the sawdust which will neutralize natural adhesives, or render inert the soluble dyes and resins contained therein, and render them insoluble and infusible under temperatures which I employ is a convenient moment for the performing of other chemical results, I at this time add those materials which eliminate the hygroscopic feature of this wood and render said wood highly fire resistant. I may effect all of these results in the following ways.

I place the sawdust in a closed mechanical mixer equipped for heating and with vacuum and spray equipment, with the mixer in action, I heat the sawdust to 200 F. and may spray (in a fog) a solution of water, acetic acid, di-ammonium phosphate and magnesium fluorosilicate, which solution has been heated to that same temperature.

My purpose is'to add the di-ammonium phosphate at a rate of 20 pounds per ton of sawdust; acetic acid at the rate of five pounds per ton of sawdust, and magnesium fluorosilicate at the ratio. of ten pounds per ton of sawdust (all weights approximate). To accomplish the same, I must use approximately one-hundred pounds of water per ton of sawdust, which water, after ten minutes mixing, I draw off by the coincident application of the heat and vacuum in the usual way, leaving a moisture content in the sawdust at approximately the original twelve per cent set which will be set forth in detail in the followins:

The magnesium fluorosillcate is well known as a germ proofing and termite proofing agent, as well as rot resisting agent.

I have above named acetic acid, di-ammonium phosphate and magnesium fluorosilicate, but any weak acid or metallic salt, such as commercial alum or blue-stone, will serve, though in the case of a metallic salt, the solution containing that ingredient must be sprayed upon and absorbed into the sawdust partic es before the application of the solution containing the di-ammonium phosphate, because the intermingling of these two liquids would cause a chemical reaction which would defeat my purpose.

I may introduce into the sawdust, in the mixer, a solution containing aluminum sulphate for the purpose of rendering insoluble the heretofore soluble tannates, pectins, dye stuff and soluble lignins, etc., of said wood particles. While this is my primary purpose the addition of this aluminum sulphate under the influence of heat in the mixer and subsequently heat and high pressure to which the mixture is in a later step subjected, likewise renders inert any pitchy or adhesive substance the wood may contain, and through its widely known astringent action, cures the hygroscopic tendency of this wood. Further, the alum content of the wood particles reacts with a later described binder which I spray into the mass, rendering the water soluble binder insoluble, partially so reacting when in the mixture and partially so reacting in the subsequent operations.

I then add the solution containing the diammonium phosphate and the magnesium fluosilicate, sixty pounds of water containing the same; this raises the moisture content to nineteen percent and the sawdust is still dry to the touch. Notez-Sawdust, such as I have described, begins to feel damp with approximately twenty-five percent moisture content.

In that the di-ammonium phosphate is held in this condition of dryness and fixed position in relation to the alum, it follows that the chemical change instant on contact in water solutions of the two, cannot take place in the sawdust except in a very minor degree negligible in my process.

As a later step, the addition of my glutinous, or viscous binder, takes up almost the entire capacity of the alum as a precipitant which will be later apparent.

It is possible to use sodium or potassium tungstate to replace the di-ammonium phosphate with equal results. I can use the metallic chlorides with equal fire-proofing results.

In that I only use five pounds of alum per ton of sawdust, I need only forty pounds of hot water containing the same for the fine spray (fog), and in that the sawdust is dry (12% moisture content) this solution is immediately absorbed integrally, only adding approximately 2% additional moisture, leaving said sawdust still in a condition of apparent dryness.

For my binding agent, I may use a solution of water soluble urea formaldehyde condensation resin (gravity about 22 B at 65 F.) produced by the usual well known methods. I use this binder to a total of between 10% and 30% of the entire mixture dependent upon the absorbent qualities of the sawdust, i. e. the absorbent qualities of sawdust from some logs (usually light weight second growth logs) being far greater than the I keep the two grades separate.

absorbent qualities of the butt logs from older growths.

The soluble urea formaldehyde resin on being tion, and upon subsequently being subjected to high pressure and squeezed onto, and into, each particle of sawdust, forms an ideal binding medium which may, at this moment, by continuation of the application of heat and pressure, be entirely converted to the completely insoluble and infusible state; or a product may be pro duced at this point containing a binder which is rigid when cold but pliable and plastic when heated, the above referred to rubbery state, through the fact that sufficient time under heat and pressure has not been given to render the binder completely infusible. In other words, the product may, at this point, be produced in a thermo-plastic condition, or in a condition of rigid iniusibility and insolubility.

I screen the chemically treated sawdust through a fourteen mesh screen, rejecting for regrinding all remaining on said screen. I then screen the screened sawdust through a thirty mesh screen. I prefer to use sawdust of such graduation that approximately 75% lies between fourteen and thirty mesh and approximately 25% passes the thirty mesh, though this is only for economizing in the use of binder, which is subsequently added, in that the fines are absorbent to a higher degree than the coarse particles. Therefore, a larger percentage of fines will require a larger proportion or binder.

I introduce the coarser particles of screened sawdust into the above described mixer and mix cold five minutes with one-third of the binder required for the whole batch. I next introduce the fine material and the remainder of the binder and mix for fifteen minutes. The binder, in all cases, is sprayed into the mixture in as fine a spray (fog) as is possible.

The preferable type of mixer is a rotary drum type equipped with baffles to cascade the saw dust from the top to the bottom continuously as it revolves to assure contact of all particles with the fog of binder sprayed therein as the mixer n revolves.

The purposes for which it may be necessary to produce the board containing the binder in the rigid, infusible and insoluble condition will be further described.

For a binder, I can equally as well use the cresylic, phenol, glycol, tung, or vinyl resins, or the like resins, condensed with the aldehyde, or natural gums, or resins, or the like, in the same way as binders. Also the animal and vegetable glues are likewise adaptable to my purpose. Also the cellulose, nitrates, acetates and xanthates are likewise easily adaptable.

In place of a water soluble urea formaldehyde condensation resin as a binder, preferably with redwood sawdust as described, I can use for a like purpose any of the other binders named, or like materials, even though many of them are not water soluble. The binders named which are not soluble in water can all be produced in liquid condition by the use of proper solvents. In solution of proper viscosity, each one may be sprayed into and onto my treated vegetable particles and may be thereby adapted into my process without serious alteration in said process. Also each water insoluble binder named in a solution of its proper solvent is emulsifiable with water, by the use of proper agents, and in that condition is adaptable directly into my process with my treatknown in the art).

ed vegetable fibre, without'further serious change in my process.

If I use animal glue as a binder, I prefer to use such glue in the proportion of 7%, or less, in a water solution, and to add thereto sodium bichromate or potassium bichromate to the quantity of 5% of the weight of dry glue contained. The bichromate of glue so produced ondrying is harder than it would ordinarily be (a fact well This glue is sensitive to sunlight (a fact also well known in the art). It is also sensitive to the direct rays of the tungsten electric incandescent bulb, and to the action of heat, facts heretofore unknown in the art, insofar as I know. I, therefore, with the use of this material make my mixture in the presence of high candle power, tungsten electric light, tumbling and stirring the mix so as to activate the said bichromate of glue in such way that upon the subsequent subjecting of the mat to heat, pressure, reheating and chilling, as my process outlined, the bichromate of glue becomes a water insoluble binder therein.

If I elect to use one of the water insoluble condensation resins, I do so by the use of emulsification. I proceed as follows, viz: I take an alcohol solution of the cresylic acid and formaldehyde condensation resin, say grams of the same, in a viscous condition, comparable to the viscosity of the ordinary sodium silicate solution of commerce at 40' B. I heat the same to about F; and into the same I melt one gram of stearic acid. I heat separately 100 c. c. of water to 150 F'., adding thereto one gram of caustic soda. I mix the cresylic solution into the water thereby producing a water thin emulsion in which the suspended particles are so fine as to have all the appearance of a solution not changing color while hot, but solidifying to an opaque jelly when cold. This emulsion is sprayed hot into the mixture previously described (containing acid) and the emulsion subsequently breaks the resin precipitating in a finely divided state on and in the particles of wood by reason of the acid action on the caustic soda portion of the emulsion, the resin thereby reconverting to the insoluble state.

The mass, on removal fro-m the mixer, is next run through a screen to assure freedom from lumps and/or uneven mixture. The mixture is still dry to the touch, or at most only slightly moist.

The mixed material is next weighed out in direct ratio with the size of the product to be pressed, i. e., a board A, thick requires approximately 340 grams of mixture per square foot of surface, and the batch is pressed in molds.

A novel feature of my process lies in the accomplishment of a uniform layer of sawdust of uniform density in the mold before pressing the same. The mixture is placed in a mold 5 equipped with a removable bottom plate 6, the contact surface of which has been oiled or waxed. This plate 6 is cold.

The accomplishment of a uniform layer of sawdust of the gradation specified herein, of uniform density all-over its area was found to be a most diflicult task to achieve. Its accomplishment was absolutely necessary because the product being pressed does not flow under heat and pressure, being of a fibrous character (splinters) and in no screen being equipped with square holes approxi mately each way, and screening the mixed sawdust therethrough into the mold. Upon the filling of the mold 5 the sawdust piles up until it touches the bottom of said screen which is at a predetermined point, calculated to produce a predetermined thickness of finished product. When the mold is filled, the screen 1 is removed.

It was found that loosely piled sawdust, upon compression, produces a sheet wherein one surface is more dense than the other and that the lack of uniform pressure shown thereby produces a sheet which subsequently warps.

The solution for this fault was found to lie in a preliminary compaction of the loose sawdust particles by vibrating from the top, for instance by tampers 8. By this method of compacting, the sawdust compresses to approximately onehalf the volume previously occupied and becomes a partly solid mass (splintery fibres intermeshed) without losing the prearranged uniform density over its area.

The fine material contained sifts away from the top surface leaving a thin layer of the coarse splinters on that top surface.

As a further step in securing uniformity of appearance, texture, and grain in the two sides of the finished product, and before subjecting the same to pressure, it is necessary to install a waxed or oiled plate 9 on the top, this plate being preheated to the temperature at which pressure is to be applied. The wax or oil is applied to prohibit sticking or adhesion of the pressed product to the plate. The mold 5 is now turned over thus reversing surfaces and what is now the top plate 6 is removed. This plate, having been oiled, or waxed, on the contact surface, upon removal takes with it, adhering to its surface, the layer of dust (material less than thirty mesh size) sifted onto it by the compacting or tamping, leaving behind upon the surface of the formed but not as yet compressed sheet, the coarse particles matted and interlaced in the same condition and of the same appearance as those coarse particles previously described on the opposite side of said sheet. The reason for this result, (removal of the dust with the plate 6) liesin the fact that dust, hitting the waxed surface as the materials were screened into the mold, adheres to said waxed surface instantly and insulates said surface against adhesion of the larger particles. A new waxed plate Ill heated is now installed on the top surface of the mold and the mat of sawdust is now readyfor compression under a hydraulic press.

In that a usual size of product is approximately forty square feet in area, it follows that molds with plates, etc., are of too great a weight for economical handling by means other than mechanical. I, therefore, elect to have the molds installed upon a traveling surface and all operations conducted as they slowly travel toward the press. That method of operation, which I I believe originated in the automotive J be utilized for handling the molds.

industry, and is technically called "moving line production, is my preferred method.

The metal plates used as contact surfaces with the sawdust being constantly heated and cooled, show a great tendency to warp. I have cured this fault by grooving the back of each plate as at 11 to /2 of its thickness into a multiplicity of squares (see Fig. 3).

The press l2 may be of any desired vertical or horizontal form and is preferably of a plural platen type, and suitable mechanical means may The sandwiches formed by the compact mats of splintery fibres and binder and the mold plates are compressed by this press at a pressure of about 1250 pounds per square inch of cross-sectional area for approximately ten minutes, at a temperature just under 100 C. My reason for holding the temperature under 100 C. is that the slight water content of the mass (approximately 16% to by weight, including the water content of the urea formaldehyde resinous liquid binder) will not dissolve the lignose or dye content of this wood due to the acidification thereof, previously described, but trapped steam caused uneven colors to appear upon the surface of the final product, and in that temperature under the boiling point of water is sufiicient to accomplish my purpose, I use this temperature which in itself prohibits the production of steam. I have learned by practice that this method produces I a good uniform quality of product from the press.

The press, molds, and material, are now cooled to room temperature requiring approximately three minutes, and the molds containing the pressed sheets are extracted from the press. The molds continue on the moving line (belt or roller conveyors) and the mold frame and top plate are removed and conveyed to a cleaning and waxing table, also heating tables, then to the initial moving line for re-use. The pressed and cooled sheet is next removed from the bottom plate and continues forth for further processing. The bottom plate follows the top plate.

The pressed sheet is next subjected to a coating of a substance which on further processing Waterproofs the sheet, adds strength and conveys such coloring for the finished product as may be desirable.

For this purpose, I may use the vinyl resins, such as are on the market under the trade-name of Vinylite. I use these materials in solution because they are thermo-plastic when dry, soluble only in the aromatic-hydro-carbons and the like, and highly resistant to water infiltration, or to the action of caustic solutions or acid solutions, alcohols or oils, and are therefore ideal for ordinary commercial, industrial, or domestic utilization of the final product. Also they are moderately inexpensive and easily procurable in commerce.

This resin, dissolved in proper solvents to a consistency of 25% to 50% resin content in, for example, toluol and/or benzole, can be applied by means of rolls or sprays l3 to the advancing, pressed sheet M in a cold condition, and by the application of a warm dry air current t5, the highly volatile solvents are removed, and the resin coating made plastic; also, at this point, any free water contained within the pressed sheet is removed by evaporation. I use a resin with a softening point, about 200 F. or less. While the resin remains plastic I pass the sheet through heated compression rolls l6 which press the resin into the wood surface of the sheet. 1'

next pass the sheet through cold rolls I! which chill the resin into the pores of said wood surface. The resin under my process is integral with the surface of the sheet as it leaves the press, thereby forming an entire new surface which has a glossy finish and is impervious, as I have outlined, but which will take any paint finish.

By surfacing in this manner, I have produced a sheet useful in industry in its then existing condition, with great advantages over comparable sheet now commercially produced. My sheet is still in such condition that it can be pressed into any desirable shape when heated and if heat and pressure are applied in the usual way, i. e., two thousand pounds per square inch of surface, or less, at a temperature of approximately 300 F. for approximately ten minutes, the urea formaldehyde resin binder of the wood particles will take on that insoluble, infusible cooked set, which assures permanent rigidity and provides that great resistance to the passage of electricity so well recognized in that variety of products now on the market, for that purpose. I refer to the urea formaldehyde, cresylic acid formaldehyde, phenol formaldehyde, and the like, condensation resins sold under various trade names such as Bakelite, Redmonol, etc.

The sheet formed, pressed and surfaced as outlined, nowadvances to the automatic trim saw which cuts it inpredetermined dimensions, trims ofi wastage, edge fins, etc. This saw is an ordinary article of industry and is not a concern of this patentapplication insofar as the details of its construction or operation enter. The finished sheets are next stacked for storage or for convenient shipment.

Instead of the vinyl resins in connection with the formation of my integral surface, I can equally as well use any of the previously named resins, the nitro-cellulose products, or the cellulose xanthate products, or the cellulose acetate products, or the like, for the same purpose.

While I have limited myself to describing the production of sheets of approximate thickness, it will be apparent to all skilled in the art that my process is adaptable to produce sheets of any reasonable thickness and can be utilized to produce dimension sizes and thicknesses of products. Said products can be produced, set, infusible, insoluble and sealed, as to surface, or can be produced strong and rigid at ordinary temperatures, yet plastic, moldable, formable, and bendable, under the application of heat, and when subsequently cooled, will again take on the condition of rigidity, retaining their surface sealing as heretofore described. Also in a condition wherein by the subsequent application of heat and pressure, the product may be pressed into a variety of forms and produce pavement, electrical insulation products, furniture parts, ornamental members and/or the like-set rigid, insoluble, infusible, highly fire resistant and impervious, as above outlined.

Particular attention is invited to the chemical treatment of the aggregates; to the proportioning of the coarse and fine aggregates to obtain uniform mixture and maximum density of mix,

and uniform distribution of binder; to the screening of the treated aggregate to assure uniform mix without lumps; to the manner of filling the molds to obtain a uniform layer of uniform density; to the vibrating for securing maximum density before pressing to prevent warping of the final product; to the inversion of mold and removal of it coated top plate thereby removing the fine particles sticking to the coating to secure uniform texture on both sides of the finished product; to the advantageous binders and coatings used; to the adaptability of the process to produce a product hard when cold, and insoluble yet thermo-plastic for future molding or pressing, and capable of being at that time set into rigidity, infusibility and insolubility, or which may be produced in the first case set, rigid, infusible and insoluble.

I claim:

1. A method of preparing a molding composition which comprises treating redwood sawdust produced in sawing redwood logs in the direction of the grain and containing about 12 per cent moisture with an aqueous solution of acetic acid, (ii-ammonium phosphate and magnesium fluorosilicate while the said sawdust is at a temperature of 200 F., screening the treated sawdust through a fourteen mesh screen, screening the foregoing screened sawdust through a thirty mesh screen, mixing a cresylic acid formaldehyde binder with the coarser of the above screened sawdust, the said binder being applied in the form of a fog which is sprayed onto the sawdust, adding the finer grade of the above screened sawdust, the relative proportion of the coarser and finer grades of sawdust being approximately three parts of coarser to one part of the finer sawdust, adding another portion of the said binder, and screening the above mixture.

2. A, method of preparing a molding composition which comprises treating redwood sawdust containing moisture but sensibly dry with an agent capable of insolubilizing natural constituents of the sawdust, a fire-retarding agent and a parasiticidal agent, screening the treated sawdust to produce at least two grades of particle size, adding a binder of the class consisting of phenol formaldehyde condensation product, ureaformaldehyde condensation product, and a glue, to a coarser grade of the screened sawdust, admixing a finer grade of the screened sawdust, adding more of one of the above binders, thoroughly mixing the mass, and screening the mixture.

3. A process of preparing a molding composition which comprises preparing'sawdust by mixing coarser particles with a heat reactive binder, adding finer particles and additional heat reactive binder, thoroughly mixing the mass, and screening the mixture.

4. A process of manufacturing board which comprises preparing a molding composition from redwood sawdust by mixing coarser particles with a heat reactive binder, adding finer particles and additional heat reactive binder, thoroughly mixing the mass, screening the mixture, introducing the sawdust with admixed binder into a mold whose inner surfaces are coated with an oily material, the said mold having a removable base plate, tamping the mixture in the mold to homogenize the sawdust mixture and inverting the mold, removing the base plate and inserting a new base plate having an oily material on the inner surface thereof.

FRANCIS L. CARSON.

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