US3032820A - Method and apparatus for the manufacture of particle board - Google Patents

Description

May 8, 1962 E. s. JOHNSON 3,032,820

METHOD AND vAPPARATUS FOR THE MANUFACTURE OF PARTICLE BOARD ERNESTSIGURD JHNSON May 8, 1962 E. s. JOHNSON 3,032,820

METHOD AND APPARATUS FOR THE MANUFACTURE OF PARTICLE BOARD Filed May 27, 1958 4 Sheets-Sheet 2 INVENTOR ERNEST SIGURD JOHNSON May 8, 1962 E. s. vJOHNSON 3,032,820

METHOD AND APPARATUS FOR THE MANUFACTURE OF PRTICLE BOARD Filed May 27, 1958 4 sheets-sheet s 9'7 G5 lNvENToR ERNEST SGURD JOHNSON Y* /,14]

May 8, 1962 E. s. JOHNSON 3,032,820

METHOD AND APPARATUS FOR THE MANUFACTURE OF PARTICLE BOARD Filed May 27, 1958 4 Sheets-Sheet 4 lNVE NTOR ERNEST SIGURD JOHNSON Unite States arent METHGD AND APPARATUS FOR THE MANU-v FACTURE OF PARTICLE BARD Ernest Sigurd Johnson, 2404 Hillsboro St., Raieigh, NIE.;

Wachovia Bank 8s Trust Company, executor` of `said Ernest Sigurd Johnson, deceased Filed May 27, 1958, Ser. No. 738,206

6 Claims. (Cl. 18--47.5)

This invention relates to a method and apparatus for producing artificial lumber. It more particularly relates to a process for manufacturing wood particle board from a mixture of wood chips and a suitable adhesive.

In the furniture manufacturing industry there is ia considerable amount of waste wood available which is suitable for the manufacture of wood particle board. Such waste wood may consist for example of slabs, edgings kand trim, cull lumber, veneer bolt trim-olf, scrap veneer, veneer cores and planer shavings. The manufacture of wood particle board from these sources not only offers a use for the Waste material but also results in a valuable product from materials which might otherwise he usedV only as fuel.

The manufactured wood particle board has a number of uses. It may be used as core stock for veneer furniture parts. It may also be used in cabinet work as core material where the cabinet is later covered with some type of plastic material or the like. In addition, the particle board may be -used inthe manufacture of household doors and as wall board. Further uses have been made of particle board las sulaiioon'ng, subroong and sheathing. However, these latter uses have been limited due to the relatively high costs of particle board.

The largest use of Wood particle board is as core board for 'veneer furniture parts. This represents a particularly useful application of the products of my invention since the scraps from wood used in the manufacture of furniture parts may beused to manufacture particle board Within the same factory. This particle board is in turn used to manufacture the cores for veneer furniture. Moreover, since many furniture manufacturers customarily useparticle board cores in veneer furniture because of the lack of suitable hardwood stock, it represents a considerable economy for the manufacturer to make his own particle board within his own factory lby using wood scrap from the manufacture of other furniture.

Various methods have been proposed for the manufacture of wood particle board. All of these methods contain the essential step of forming wood chips, coating the wood chips with a suitable adhesive, spreading the wood chip on a flat surface and compacting the layer of chips under heat and pressure to form the wood particle board. The problems involved in such processes are to obtain a particle board of uniform density throughout and having straight edges thereby requiringno trimming of edges with its resulting waste. In order to overcome these problems'it is necessary to maintain a uniform mixture of wood chips, that is to prevent the separation of the fine material `from the larger wood chips or lalso the segregation of one from the other. It is also necessary to form a mat of chips of uniform thickness and density prior to pressing. Numerous attempts have been made to'solve these problems in the past such as the use of rotating cylinders to level od the mat of wood chips prior to pressing. However, such devices do not insure a uniform mixture of the mat. Various types of feeding devices have been proposed for depositing a uniform mat such as paddle wheels, toothed circular discs which deposit small tufts of material, and rotating cylindrical screens containing the Wood chips, none of which guarantee a mat which will provide a particle board of a uniform density throughout.

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v ing a uniform mixture of wood chips and adhesive over a caulboard to permit the manufacture of particle board of uniform density therefrom.

Another object of this invention is a method for forming a mat of wood chips and adhesive of uniform thickness which may bepressedinto a particle board of uniform density.

Another Objectis a method for prepressing a mat composed of a mixture of wood chips and adhesive to permit the manufacture of particle board of uniform density and having straight edges therefrom.

Another object of this invention is to provide an apparatus for distributing la layer of a mixture of wood chips and adhesive of uniform thickness and having a uniform density by Weight throughout the layer on a caulboard.

A further object of this invention is to provide 4an apparatus for forming a mat of wood chips and adhesive having uniform thickness and uniform distribution of wood particles throughout for the manufacture of particle board of uniform density.

Various other objects and advantages of the invention will be made apparent as this Vdescription proceeds.

I have found that the problems of the prior manufacture of particle hoard. may be overcome and the above objectives attained by the use of my method and apparatus. In my invention the first step is the formation of usable wood chips. ln connection with furniture manufacturing, suitable sources of waste are saw end trimmings and rip saw edge waste (including poplar, gum syCamore, elm and walnut). Scrap from band saws and veneer trimmings often are used, and planer shavings can be used if necessary.

The waste wood is first conveyed to a conventional flake cutter and from there to a hammer hog where it is first reduced in size. lf the Waste wood is small enough to start with, the ake cutter may be by-passed. From the hammer mill or hog, chips are yautomatically conveyed to a tangential separator which separates chips and dust sending the chips to chip storage Iand the dust to boilers as fuel.

The chips are next transferred to a separating screen of the horizontal three-separation gyro-centric type. Chips which do not pass the irst screen 'are returned to the hammer mill for Vfurther size reduction. Chips passing through all screens are passed to the boiler for fuel and chips of the proper size which remain on the third screen are passed through a magnetic separator to remove metal particles therefrom and from thence to a finish chip storage bin. Provision is made for withdraw-al of chips from the storage bin for a test of moisture content which should be about 6 to 8% and for removal or addition of moisture as required. Chips are removed from the storage bin into yan automatic weigh hopper which collects accurately weighed batches. The weighed batch of chips is then dropped intothe blender where itis mixed with the correct amount of a suitable adhesive, for example, urea formaldehyde glue. 4

The automatic weigh hopper and blender are coordinated so that the automatic weigh hopper refills after the doors close and the blending operation is in progress. The mixture of chips and adhesive is then transferred by belt conveyor to the spreading machine or chip spreader` where the chips are spread on aluminum caulboards having aluminum strips on all four edges.

The use of the caulboards and a uniform spreader permit the formation of a chip board having uniform density from the center to the edges so that no trimming is necessary. The thickness of the mat deposited on the caul is about five times Vthat of the iinal board. In order to contain this mat prior to pressing operations, a special chip loading frame is attached to the caul. This frame rests on the rim of the caul and is high enough to hold the entire layer of chips. The caul with the loading frame added is moved under the chip spreader by a` power roller conveyor. The moving caul trips a limit switch that starts the spreader which deposits an equal weight of chips over the entire width and length of' the caul.

The spreader consists of a hopper which contains the chips and has a rotating toothed cylinder at the bottom thereof. The rotating cylinder is provided with transverse pockets, around its circumference, each of which extends along the entire length of the cylinder. The walls of these pockets are inclined toward the direction of rotation of the cylinder. As the cylinder rotates each pocket passes through the bottom of the hopper and is lled with the woodchip-adhesive mixture which is slightly compacted in each pocket and is subsequently deposited on the caul below the cylinder in equal increments having uniform density by weight.

After the chips have been deposited on the caul, a separate prepress form is placed inside the chip loading frame. The prepress form is bevelled downward towards the outer edges on the lower side which contacts the wood chips. The caul with the prepress form is then moved into a prepressing press where pressure is applied for a Vpreliminary forming of the chip board. The caul is then removed from the prepress after which the chip loading .frame is also removed from the caul. The bevelled prepressed form provides a mat having `greater density at its edges. This has been found to make possible a `finished board having uniform density throughout and straight edges, after the hot pressing step.

The caul with the prepressed board thereon is then lined up to enter the hot press. v The hot press may be of any type but a two-opening shuttle type hot press has been found to be particularly suitable. When both ends of the two-opening hot press have been opened, a caul with a prepressed board is inserted in each opening and the press is closed. The press exerts a pressure of from 150 to 200 p.s.i. at 300 to 350 F. for 5 to l5 minutes depending on the thickness and density of the board being produced. yAfter pressing, the caul and pressed boards are removed from the press, the finished boards are removed from the cauls and the cauls are returned by a roller conveyor to the chip spreader station.

These and other features and advantages of the invention including various details of construction and preferred embodiments thereof are described more fully in the following description and the accompanying drawings illustrate a contemplated mode of operation of -my invention but are not intended to be limited thereto in which:

FIG. l represents a schematic plan of the chip board manufacture.

FIG. 2 represents a cross-sectional side view of the chip spreader.

FIG. 3 represents a cross-sectional perspective view of a segment of the chip spreader cylinder illustrating the `pockets.

FIG. 4 illustrates the particle stirrer of the chip spreader. .i

FIG. 5 illustrates a perspective and cross-sectional view of the' chiploading tray.

FIG. d is a perspective and cross-sectional view of a caulboard.

FIG. 7 illustrates a partial end view of the assembly of the chiploading tray and caulboard illustrating the latch mechanism.

FIG. 8 illustrates the latch mechanism shown in FIG. 7, from a side view.

FIG. 9 is a cross-sectional view illustrating the caulboard and chiploading tray assembly, the' prepress form, and a prepressed mat of wood chips.

FIG. l-O represents a partial end view of the caulboard and prepress form assembly, the chiploading tray holder and the mat ejector, illustrating the latch mechanism `for attaching the tray to the holder.

Referring urtherto the drawings, FIG. 1 illustrates one form of iow diagram of the overall process for the manufacture of wood particle board from waste wood; it will be understood, however, that other types of plant layout may be used equally well in the practice of my invention.

The production of wood particle board begins with the production of suitable chips. End trim `from cut oit saws and edgings and scrap from rip saws are the primary sources of scrap. The scrap from band saws and veneer trimming is also used. 1E'laner shavings can be used if necessary. This scrap is fed by means of rubber belt conveyors and pneumatic collectors into the hammermill hog 2 which breaks it into chips. The scrap may first be passed through a flake cutter 1 if necessary, after which it enters the hammer hog. The chips fall into the bottom of the hammer hog and then are pneumatically conveyed in line 3 to a tangential separator 4. This separator is designed to allow all the chips and dust to fall into an air lock 5 which dumps them into bin 6 below. By lowering the eiciency of this separator some of the fines can be talten directly to the boiler, not shown, since the exhaust side 7 of the separator is connected to the main line clust collection system 8.

The chips fall from the airlock S into storage bin 6 directly under the separator 4. This bin allows a buildup of chips so that there will be a constant flow of chips into the separating screen 9. The chips are dropped onto the separating screen by means of a variable speed screw conveyor It?. The separating screen is preferably a horizontal, three-separation, gyrocentric type. .The screen is suspended by cables so that it is entirely `free to shake. The first screen is 1A mesh, and the chips which fail to pass through it drop out onto a conveyor 11 which moves them back to the hog for further reduction in size. The second and third screens are preferably mesh size Ma" and 1/16". Material that passes through this nal screen is considered too small and drops into a dust pipe 12 which carries the dust -to the boiler. The chips which do not pass the final screen are those which will be used to make the particle board. The average length of these chips is about 1/2. These chips fall into a chute 13 which conveys them to a cyclone collector 14 above the finish chip storage vbin 18. The chips pass through a mag netic separator 15 in order to remove any metal particles that are mixedin the chips and are then pneumatically conveyed by means of fan 17 to collector 14.

The sized chips are stored in a large sheet metal bin 18 which preferably has a storage capacity of approximately cu./ft., or more depending on the size of the chip board mill. A l2 hours supply of dry chips is preferably kept in the bin 18. Built into the bin 18 is a small pipe 19 which will release chips so that they can be tested for moisture content. It is best that the moisture content be between 6 and 8%, based 0n Oven dry weight. lf necessary, the chips may be dried or moistened to the correct moisture content. l A screw conveyor 2u is built into the bottom of the bin13 for removal of the chips when they are needed. Screw c011- veyor 29 drops the chips into an automatic weight hopper 21, which automatically stops the screw when the desired amount of chips are in the hopper. This batch size must be correctly predetermined. With the use of counter-balances a limit switch controls the feed of dry chipsinto the weight hopper.v Since storage bin 18 and hopper 21 are usually located on a oor above the 5 ing operation, a signal light, not shown, is provided that will burn while the hopper is being loaded and turned olf when the loading is complete. This signal light is connected with the same limit switch that controls the feed of dry chips from bin 1h into weight hopper 21.

From the weight hopper, the chips are dumped into the mixer 22 by opening the weight hopper doors controlled with an air valve. The lower weight hopper doors are then closed and screw 21 is again started to reiill the hopper. Before the upper hopper door is opened, the mixer door, also operated by an air valve, is closed. When the weighed chips are Vin the mixer a predetermined amount of glue is pumped through the lines from glue tank 23 and sprayed through nozzles, not shown, located in mixer 22. This mixing continues from 2 to 6 minutes, depending upon the weight and type of chips and amount and type of adhesive. Added with each 70 pounds of glue preferably urea-formaldehyde are 16 pounds of a non-odor catalyst and 24 pounds 'of water. When the mixing is completed, the prepared chips are dropped onto a belt 24 which moves them to the hopper 25 above the spreader 26. A revolving serrated cylinder, not shown, is attached to the outside of mixer 22 and is located directly above belt 24. This cylinder is driven by the idler pulling on belt conveyor 24. By adjusting the cylinder up and down a uniformly thick mat is formed on the belt 24 giving a constant flow of chips into the hopper 25 of the chip spreader. It is desirable to have this constant flow, sincethe spreader operates much more eiciently if a constant level of chips is maintained in hopper 25. The chip spreader is described more fully in subsequent paragraphs.

To begin the actual spreading and pressing cycle it is necessary to have a number of aluminum caulboards, usually from 4 to 8, size 66 x 110, or any other preferred size. These aluminum Sheets 6i) (FIG. 6) have side strips 61 of aluminum l Wide and 1%" thick ser cured around all four edges. The caulboards and prepress forms hereafter described are designed to produce a board that has density and other characteristics which are uniform from the center to the edges so that no trimming is necessary. The caulboards produce an actual board size of 64" x 108". rlhis size may be varied by the use of iller strips of a hard species of wood that are dressed to 3A thickness or by the use of different size caulboards. These variations make it necessary to have on hand chiploading frames and forms for the sizes that are to be made. The aluminum strips 61 have a slight bevel inside, as shown in FIG. 6, t allow for ease in v removal of the linished board.

In loading the caulboard 60 a chiploading frame 62 (described in greater detail hereafter, see FIGS. and 6) is attached to the caulboard. Frame 62 tits on the caulboard rim 61 and in the embodiment illustrated is 2%" high. It is lined with 16-gauge sheet metal and flared at the top so that chips falling on the edge will be guided onto the caul. The frame 62 is attached to the caul by hooks 65 at the four corners and is kept in alignment by means of dowel pins 66 in the frame which it into holes 63 in the caulboard rim. This frame is attached to the caul prior to the spreading of the Vgluetreated chips thereon. After the chiploading frame is attached, the power conveyor 30 is started, moving the empty caul under the spreading unit 26. The moving caul 60 trips a limit switch, not shown, which starts the spreader and at the same time belt 24 which conveys chips to the spreader from mixer 22. The spreader 26 is designed to seize and deposit an equal weight of chips per unit area so that an equal Weight of chips is uniformly deposited over the entire larea of the caulboard. When forming a 5%." finished particle board, the spreader deposits a mat approximately 31/2" thick on the caulboard. As the trailing end of the caul passes from under the spreader the limitl switch stops the spreader and conveyor belt 24, and the caul continues on roller conveyor 30 towards prepress 27 for the formation of the prepressed mat. In the prepressing operation, a prepress form 69 (see FIG. 9) lined with sheet metal 70 is used. This form tits inside the chiploading frame attached to the caul. The form is made up of lumber cores edgeglued to a thickness of 5". A beveled piece 79 is attached around the edges before the sheet metal covering is attached. This form results in a prepressed mat with the desired characteristics to obtain a final chipboard of uniform density.

The loaded caul 60 is pushed into the prepress 27 as carefully as possible to avoid shifting the chips. Removable pins, not shown, are located on each corner of the prepress and serve as stops to position the caul for the prepressing operation. Once the caul is in position the control switch is closed to start the prepressing. The press closes and builds up a pressure of p.s.i. and holds this pressure for one minute before opening automatically.

The pressed form is then removed from prepress 27 on- Vto transfer 3l where chiploading frame 62 is removed from the caulboard.

The caul with its prepressed mat is then loaded into press 2S for the hot pressing step to form the finished chipboard. The hot pressing cycle is conducted at a pressure of to 200 p.s.i. at 30W-350 F. for 5 to 15 minutes, depending upon the thickness and density of the board being produced and the curing or polymerization time of the glue used. After the pressing, the finished chipboard is removed from the cauls and the empty cauls are returned to a point on the conveyor 30 ahead of the spreader 2.6 where they may have a chiploading frame 62 attached thereto and be again passed under the spreader 25 for the making of another chipboard.

By the use of a shuttle type hot press such as the Fjellman American Automatic shuttle feeder and suitable conveyor lines, chipboard may 4be produced at an increased rate. The shuttle type press may be loaded at both ends, and two boards are, pressed at the same time. Moreover, the press is loaded with new prepressed mats simultaneously with the unloading of iinished chipboards. Thus, new cauls may be spread with chips and placed on the press racks while the pressing cycle is in operation so as to be ready for insertion in the press as soon as one pressing operation is finished. The entire operation is thus substantially continuous.

Using a twelve minute press cycle it is, therefore, possible at 100% capacity to manufacture lO boards per hour of size 64" x 108". This gives 48()` sq. iit. per hour or 3840 sq. ft. per 8 hour day. By :decreasing the press cycle to 8 minutes production will be 5760 sq. ft. per day at 100% capacity. By technical procedures, developed through laboratory experiments, high quality 3A" thick boards have been vproduced with a press cycle of 8 minutes.

The chip spreader 26, illustrated in greater detail in FG. 3 consists of a cylinder 4@ of a length equal to the Width of a caulboard. In the embodiment illustrated the cylinder 49 is six feet long and one foot in diameter and has tooth-like recesses 41 on its periphery running the length of the cylinder. The cylinder is mounted for rotation in the bottom of a hopper 25 lled with chip particles coated with glue. The teeth d1, or serrations, seize a uniform quantity of the glue treated chips and deposits them on acaulboard passing beneath the spreader 26.

The serrated cylinder 40 is mounted on a shaft 40A driven by a gear reduction motor. The motor is started and stopped by limit switches actuated by the caulboards passing beneath the spreader Z6. The framework 4 2 of the spreader is made of channel and angle steel and mounted over the caulboard conveyor 30. The spreader framework 42 supports the serrated cylinder 4G, the drive motor, not shown, the hopper 25 which feeds the panticles to the cylinder recesses 4l iand-the particle stirrer 43 (see FIG. 4), located near the bottom of the hopper 25.

work of the spreader.

aosasao The particle stirrer is preferably a 2" square steel bar to which steel teeth 44, /m" thick by 11/2" long have been Welded. The axis of the particle stirrer is located in the hopper 25 so that the particle stirrer teeth revolve 25/8" about the teeth d1 of the serrated cylinder titl. The serrated cylinder teeth openings 41 in the embodiment illustrated, are 3A" deep by 2" from front to back and extend the entire length of the cylinder 40 (see FlG. 3). The faces of the teeth have holes 45 drilled `at 6 inter* vals so that metal plates or angles can be bolted to the face of the teeth if their depth needs to be increased due to a change in specifications of the particles being used.

The sheet metal hopper 25 holds the glue-treated chips or particles and feeds them into the teeth 4l of the serrated cylinder 40. The hopper is 221/2 deep by 30" wide at the top and the length is the same as that of the scrrated cylinder 49. The back side of the hopper is provided with a vibrator plate 46 made of a plywood faced with 16 gauge sheet steel with a strip of 1A" thick belting 47 secured to the bottom edge and extending 21/2 beyond the edge of the vibrator piate 46 and resting on the teeth 41 of the cylinder 4l). The front side of the hopper is formed by a spacer 48 made of Ma" plywood faced with 14 gauge sheet steel and reinforced at the bottom with a formed solid wood block 49 also faced with 14 gauge sheet steel. A 5 Wide strip of 1A." thick belting is bolted to the front bottom edge of the hopper 2S and protrudes 1/2 beyond the edge of the spacer reinforcing block 49 to form a packer 56 for packing the chip particles into the serrated teeth 41. The end of the packer 56 clears the edge of cylinder teeth 41 by a distance which is regulated by adjustable screws 51 mounted in the front frame- The clearance is adjustable from to depending upon the characteristics of the chip particles being used and the mat being formed and this spacing controls the degree of packing or compaction of the particles in the teeth 41.

The particles are kept at a specified level in the hopper by the belt conveyor 24 bringing a uniform stream of glue coated particles from the blender or mixer 22. The

belt conveyor 24 is regulated by the same limit switches which turn the spreader 26 on or oft". The stirrer 43 revolves in the particles preventing bridging and keeping the tines uniformly dispersed with the larger sized particles. The vibrator 46 shakes continuously due to the movement of the cylinder teeth past the belting 47 on the vibrator edge. This shaking motion causes the particles to move down the side of hopper 25 to the cylinder teeth 41. The cylinder teeth are filled with a quantity of particles and carry them past the spacer 48 and packer 50 out of the hopper and drop them on the caulboard passing beneath the rotating cylinder. The packer Sli operates to compact a uniform density of chip particles in each of the teeth .-41 so that as the chips in each tooth pocket are deposited on the caulboard a uniform weight or density distribution is secured. In effect a uniformly compacted triangular layer of chips extending the entire length of the cylinder 40 is deposited from each tooth 41 on the caulboard as the caulboard passes under the spreader 26. Consequently, each tooth deposits a uniform quantity of particles by Weight on each unit area of the caulboard as it passes beneath the chip spreader 26. The spacing between the cylinder teeth 41 and the packer Sti at the edge of the Vspacer reinforcing block 49 can be varied from one end of the cylinder to .the other, resulting in varying weight of chips being deposited along the length of the cylinder 4d as desired. It is thus possible to produce a board with uniform density or with higher density at the edges or in the center as required if the press is ydesigned. to produce uniform thickness panels of varying density as specified. Each tooth 41 compacts the uniformly dispersed particles against the packer 5) and deposits th-is toothful of particles on the caulboard Without allowing the fines to'settle to the bottom surface of the mat. The speed ofthe rotating serrated cylinder 46 can be regulated, the speed of the caulboard conveyor can be regulated and the clearance between the cylinder teeth 41 and the packer 50 at `the edge of the spacer reinforcing block 49 can be regulated. By regulating these speeds and the packer clearance the proper weight of particles per unit of caulboard area can be deposited for any type particle. The prepress 27 forms the mat 78 (see FIG. 9) into one mass of uniformly dispersed particles a few seconds after they have been deposited on the caulboard.

The caulboards 6i) and chiploading prepress frame 62 are illustrated in greater detail in FIGS. 5 and 6. The caulboards 6t9rare preferably formed of 1A aluminum sheets and :have l wide aluminum bars 61 secured around the four edges of each caulboard sheet 60. The bars 61 are the same thickness as the board being produced and act as a thickness spacer in the hot press. The bars 61 have a 3 vtaper on the inside to facilitate removal of the cured boards. When producing 3A" boards in a 66" by` llO" press, the caulboards have aluminum edges l" wide by 3A thick and produce nished boards 64" by 108". The edge bars 61 are cut into l2 long sections so that differential cooling speedsv between the lz thick base of the caulboards and the l thick edges will not produce stresses. The chiploading trays 62 lit on top of the edge bars 61 of the caulboards. The chiploading trays (FIG. 5) are preferably straight grained wood lined with 16 gauge sheet steel. A tray for a 1%." splinter type board to be made in a 66 by 110" hot press is a 2% high by 1%6" thick wood frame 55" by 110 outside dimensions. The sheet steellining is 64 by 108" inside dimension by 31/2" high. The top edge of the sheetl steel 64 is flared out to prevent particle spilling when being filled at the particle spreader 26. Near each of the four corners there are latches 65 (see FIGS. 7 and 8) on the trays and keepers 66 on the caulboard edges which lock the two together when being filled with particles and prepressed. At each corner of the trays 62 there is a vertical bar 67 (FIGS. 5 `and 10) with a notch at the top to the tray to be secured to a frame 68 when the tray is being removed from the caulboard. The frames 68 are then suspended from an overhead conveyor, not shown, by

which the chiploading trays 62 are conveyed back from the position between the prepress and the hot press where they are removed from the caulboards to a position in advance of the chip spreader 26 where they are again deposited on and secured to caulboards to be passed beneath the spreader 26.

The prepressis a single opening standard hydraulic press capable of exerting up to pounds per sq. in. pressure over the entire surface of the caulboard. Prepress `forms 69 are attached to the top surface of the press according to the. size and type board being produced. A form yfor a 64 by 108" 40 pound per cu. ft. 1%" thick splinter particle board consists of three lumber lcores 64" by 108 and two 5% lumber cores 108 by 64" cross laminated, bevel edges and covered with sheet steel. The bevel edge 76 is thick at the edge of the form with a 71/2 taper to 0 thickness towards the center of the form. The sheet steel 71 on the sides ofthe form can extend exactly to the edge or can extend as far as 3%; below for edge depending upon the characteristics of the particles being used.

The chiploading tray holder and mat ejector (see FIG. 10) is designed to remove the chiploading `frame 62 from a caulboard 6ft and hold it in an elevated position until it is returned to a station in advance of the chip spreader 26 and attached to an empty caulboard to be passed under the chip Spreader 26. At the same time that the chiploading frame 62 is lifted from the caulboard the prepressed mat 78 is ejected from the chiploading frame 62 onto the caulboard while maintaining straight edges and full density at the edges of the mat. The ejector is an angle iron frame 76 attached by springs, not shown, to the chiploading tray holder 68. Rods 74 passing through sleeves 77 attached to the inside of the vchiploading tray holder 68 are attached to the top of the mat ejector. The

rods also pass through spiral springs 73 which push the ejector frame 76 below the chiploading tray holder 68 except when the ejector frame is forced upward. The chiploading frame holder has ratchet catches 75 on the -four corners which engage the four notched bars 67 at the corners of the chiploading frame 62. For release there is a system of four spring loaded cables 72 attached to each ratchet catch 75 and to a common release handle, not shown, so that the chiploading frames 62 may be released from the holders 68 at all four corners simultaneously to facilitate their being reapplied in horizontal position on the caulboards 60 on the conveyor 30.

The prepress form 69 (see FIG. 9) is provided with a bevel angle on the edge 70 which has been determined `by. calculations and experiments to produce the correct extra pressure on the prepressed matedge. 'Ihe extra cornpression on the edges combined with the retaining aluminum bar edges 61 of the caulboard resists the outward thrust on the particles when the hot press closes and applies full pressure on the mat. A correct amount olf extra compression, determined by the bevel angle ofthe prepress, will produce a board of uniform density from the center of the board to the extreme edge. The correct bevel 70 has been determined to be a 71/2 with a thickness of 1%" at the edge when producing a 40 pound per cu. ft. density board 3A to 1?/16" thickness from splinter type particles. Other bevels have been determined to be necessary for different type particles aud different thickness boards. The correct bevel may be readily established -by simple trial.

With some types of particles and adhesives it is neces- Sary to have the sheet steel covering 71 of the prepress -form extend `as much as below the form in order to form a mat that will not crumble on the edges before full pressure is applied in the hot press. The density, in this case, begins to fall off in the last 1A near the edges. When the sheet steel covering stops at the edge of the form, uniform density lis maintained to the extreme edge of the board. Y

After the mat is prepressed, the chiploading tray must be removed without disturbing the edgesof the mat. For this purpose the chiploading tray holder and mat ejector device 68 is used. IIhe prepressed mat 78 on the caulboard 60 with chiploading tray 62 attached is pushed out of the prepress 27 on the roller conveyor 31. The conveyor line 31 has an elevator which raises the caul, mat and tray until the vertical notched bars 67 at the corners of the trays 62 engage the ratchet catches 75 on the corners of the chiploading tray holder 68. As the elevator raises the caulboards the mat ejector frame 76 is forcibly pressed against the entire bevelled edge of the mat 78 within e of all outside edges. As soon as the ratchet Catches are engaged, the four latches on the corners of the tray are released and the elevator is lowered carrying the caulboard 60 with the repress mat 78 thereon downward into position for feeding into the hot press 2S. The springs 73 between the ejector frame 76 and the tray holder 68 force the ejector frame 76 against the beveled edge of the mat 78 as the caulboard with the mat is lowered, leaving the tray 62 hanging on the tray holder 68. The pressure on top of the beveled mat edges maintains a perfectly straight edge without crumbling around the entire perimeter of the prepressed mat. The caulboard with prepressed mat -is then transferred to the hot press loader to be pressed with the edges of the `same density as the balance of the board. Because of the straight edges and uniform density of the finished boards, no trimming of the board is required and the entire board can be used for any purpose for which particle board is useful. There is, therefore, no waste of the product and no unnecessary operations.

While I have described a specific embodiment of my invention, it will be understood that this is merely for the purpose of illustration and the invention is not limited to this embodiment. Boards of different size and thickness 10 may be made, and the types and sizes of conventional items of equipment may be varied as required. It will be understood that various modifications may be made of my invention without departing from the spirit of the disclosure and the scope of the following claims.

l claim:

1. The method `for producing chipboard of uniform density and straight edges which comprises the steps of forming a mixture of wood chips and adhesive, forming a plurality of separate compacted longitudinal increments of said mixture, said compacted increments having equal density throughout and length equal to that of the desired width of the finished board, depositing said compacted increments successively transversely the desired length of the finished board in a parallel relationship on a substantially rectangular horizontal surface having substantially vertical sides at the four edges thereof to form a layer `of wood chips andadhesive, pressing said layer under a confined form having a downwardly projecting bevel at the edges thereof to produce a preliminary mat having a bevel and greater density at the edges thereof without disturbing the relative interlocking position of wood chips, and pressing said mat to form the final chipboard, whereinhorizontal movement of wood chips is prevented by the greater density at said beveled edges.

2. A method for producing wood particle board which comprises the steps of forming wood chips, coating said chips with adhesive, depositing a densiiied layer of said coated wood chips of uniform density on a substantially rectangular horizontal surface havingY substantially vertical sides at the four edges thereof for containing said layer, pressing said layer under a confined form having a downwardly projecting bevel at the edges thereof whereby said layer is compacted Without horizontal movement of Wood chips to form a preliminary mat with greater density at the edges thereof, and pressing said mat to form the final wood particle board, wherein horizontal movement of wood chips is prevented by the greater density at said beveled edges, and said finished wood particle board has straight edges and uniform density throughout.

, 3. A method for producing Wood particle board which comprises the steps of forming Wood chips, coating said chips with adhesive, depositing a densified layer of said coated chips on a substantially rectangular horizontal surface having substantially vertical sides at the four edges thereof for containing said layer by passing said chips through a spreader which compacts and deposits equal amounts by weight of the wood chips over the entire area of said horizontal surface, pressing said layer under a confined form having a downwardly projecting bevel at the edges thereof whereby said layer is compacted Without horizontal movement of wood chips to form a preliminary mat with greater density at the edges thereof, and pressing said mat between said vertical sides under heat and pressure to form the final wood particle board, wherein horizontal movement of wood chips is prevented by the greater density at said beveled edges, and said board has straight edges and uniform density throughout.

4. A method for producing wood particle board which comprises the steps of forming wood chips, coating said chips with adhesive, depositing a relatively thick densified layer of said coated chips on a substantially rectangular horizontal surface havingV substantially vertical sides at the four edges thereof for containing said layer by passing said chips through a spreader which compacts and deposits equal amounts by weight of the wood chips over the entire area of the horizontal surface as it passes beneath the spreader, pressing said layer under a confined form having a downwardly projecting bevel at the edges thereof to produce a preliminary mat having a bevel `and greater density at the edges thereof without disturbing the relative interlocking position of wood chips, and

pressing said mat between said vertical sides under heat and pressure to form the final wood particle board,

1 1 wherein horizontal movement of wood chips is prevented by the greater density at said beveled edges, and said finished board has straight edges` and uniform density throughout.

-5. In a process for producing wood particle board, the method for providing straight edges and uniform density to the iinal product which comprises depositing a densiied layer of wood chips and adhesive on a substantialiy rectangular horizontal surface having substantially vertical sides at the four edges thereof for containing said layer of wood chips, pressing said layer under a confined form having a downwardly projecting bevel at the edges thereof whereby said layer is compacted without horizontal movement of wood chips to form a preliminary mat with greater density at the edges thereof, and pressing said mat to form the iinal wood particle board wherein horizontal movement of wood chips is prevented by the greater density at said beveled edges.

6. In a process for producing wood particle board, the method for providing straight edges and uniform density to the tina] product whichcomp'rises depositing a densied `layer of Wood chips and adhesive on a caulboard having substantially vertical sides at the four edges thereof for containing said layer of wood chips, forming a preliminary mat having greater density at the edges by compacting said layer under pressure with a confined form adaptedto produce beveled edges on said preliminary mat, without disturbing the relative interlocking position of wood chips, and thereafter pressing said preliminary mat under heat and pressure into wood particle board, wherein horizontal movement of wood chips is prevented by the greater density of `said beveled edges and said particle board has straight edges and uniform density throughout.

References Cited in the tile of this patent UNITED STATES PATENTS ae'- e

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