US2635301A - Web or mat forming device - Google Patents

Description

April 21, 1953 D. L. SCHUBERT EI'AL WEB OR MAT FORMING DEVICE Filed Sept. so, 1948 6 Sheets-Sheet 1 IN VEN TORS 001.5 4 Scnuszzr By 191.:s1er H. DEMEERLEER M w M April 21, 1953 D. SCHUBERT EI'AL 2,635,301

WEB OR MAT FORMING DEVICE 6 Sheets-Sheet 2 Filed Sept. 30, 1948 April 21, 1953 D. L. SCHUBERT ET AL 2,535,301

WEB OR MAT FORMING DEVICE Filed Sept. 30, 1948 6 Sheets-Sheet 3 inventor an: L. c/vusznr 671.5522" 1 1- 0EMEERA ER April 21, 1953 D. L. SCHUBERT ET AL 2,635,301

WEB 0R MAT FORMING DEVICE Filed Sept. 30, 1948 6 Sheets-Sheet 4 Zmnemor 081.5 L, Scuussxzr H4552? H. DENEEIZLEER WWW April 21, 1953 D. L. SCHUBERT ET AL 2,635,301

WEB OR MAT FORMING DEVICE 6 Sheets-Sheet 5 Filed Sept. 30, 1948 3nnentou 001.: L. SGHUBERT 191.55 H. Us/155121.551: 1 u w 1/ d noun-us .Apnl 21, 1953 D. SCHUBERT ETAL 2,635,301

WEB OR MAT FORMING DEVICE Filed Sept. so, 1948 s Sheets-Sheet a 31m mot 0:91.12: 4. scnuafin 2' 61.55197 H. OENEEBLEER WWW Cmornegy Patented Apr. 21, 1953 WEB OR MAT FORMING Dale L. Schubert and Albert H. De Meerleer, Tacoma, Wash., assignors to Plywood Research Foundation, Tacoma, Wash., a non-profit corporation of Washington Application September 30, 1948, Serial No. 51,938

r This invention relates to a mat or web forming device and more particularly to a device for providing or laying up a mat of lignocellulose material. Such lignocellulose material may be such annual products as straw, sugar cane, corn stalk, and the like. However a most suitable product is the fiber obtained from trees and hereinafter reference will be made to wood fibers but it is to be understood that this term is being employed as illustrative of lignocellulose materials and not as a limitation. a i

There are a number of mechanical grinders or fibrators on the market today to grind or provide fibers from wood products. These are sold under various trade names by various companies. By way. of illustration, suitable devices are sold by companies generally known as: Bauer,

Allis-Chalmers, Sprout-Waldron, Sutherland and Robinson Mfg. Co. These grinders are preferably fed with steamed or chemically treated chips and mechanically fibered wood is exhausted in a continuous process.

It is an object of this invention to take such mechanically fibered wood products and lay them up in a mat or web so that they can be pressed to form hardboard products. Generally, a suitable binder is admixed with the wood fiber so that the. final products will have the desired cohesion between the aggregate particles. A typi cal binder giving desired results is a thermoset type such as a phenol-aldehyde which sets up under the desired heat and pressure. The type of binder, indicated is the type that iscommonly employed-inthe plywood industry to adhere together the various veneers which make up the plywood panel. This type of adhesive is employed where there is so-called hot-pressing of the panels or plywood. As the present invention does not involve any particular adhesive, only onetype of the many adhesives which may be employed is described and that by way of example.

While the thickness of the mat to be provided will vary with the material employed and the nature of its treatment, it can be stated that in a general way a mat from about 5 to 8 inches thick is provided if a finished hardboard having a thickness of approximately a quarter of an inch is desired. It is an object of this invention to intermesh or intertwine the various individual fibers so that a substantially uniform mat or web ,isprovided to-provide the desired strength to thefinal hardboard .product.

As this invention is particularly useful in conne tion with providing a web or mat, it is an 3 Claims. (Cl. 19-156) object of this invention to provide a relatively traveling supporting means and means to toss unmatted wood fibers into the air and allow the same to descend by gravity or to be urged toward the relatively traveling belt by reasons of a vacuum means and lay up a web or mat on the supporting member and to provide a web or mat of a desired thickness.

Itis a further object of this invention to provide a mat where a relatively slight longitudinal angle is provided during formation of the mat,

so that there will not be too steep an incline to It is a further object of this invention to provide a traveling surface, such as a cylindrical surface, or an oval surface, or a caterpillar type endless moving bed, with tines thereon so that matted wood fiber can be unmatted and air separated to provide a felt or mat of substantially uniform thickness and wherein the individual fibers are intertwined and matted to provide a,

mat of substantial strength and uniformity to the end of obtaining the greatest strength in the final hardboard product.

It is a further object of this invention to provide such traveling tines in combination with adjustable restricted passageways so as to adjust the volume of wood fibers which are fed to a relatively moving supporting means therefor on which the mat is being laid up.

It is a further object of this invention to provide comb means in association with said tines so as to adjust the throw or tossing of the fibers in their air separation.

It is a further object of this invention to provide deflector vane means disposed in the fiow of wood fibers as said fibers are being air separated and to thus control the height or, thickness of the mat crosswise considered.

It is afurther object of this invention to provide a diverging discharge chute for the unmatting driven tines to minimize the length of .the-

rotor supporting the tines. By shorteningthe length of the unmatting rotor, the same is suit 3 able to high speed work and the quality of the mat produced thereby is increased.

It is a further object of this invention to provide a mat of an initial thickness slightly greater than that finally desired and to scrape ofi or remove a portion of the upper surface thereof to produce a final matjof a predetermined uniform thickness.

It is a further object of this invention to provide a traveling scraper, which may be in the nature of a traveling endless band. or a driven.

rotor in combination with a conveyor,'which may be in the nature of a screw type conveyor or an endless traveling belt. a

The above mentioned general objects of this invention together with others inherent in the same are accomplished by the devices set forth in the accompanying drawings throughout which like reference numerals indicate like parts:

Figure 1 is a perspective view, with parts broken away, of a device embodying'this invention;

Fig. 2 is a fragmentary view, partly in section and partly in elevation, and on a larger scale than Fig. 1 showing an. unmatting rotor and a fragment .of. associated parts;

Fig.33 is a View somewhat similar to Fig.. 2 showing a modified form of anunmatting rotor that may be employed in this invention and substituted for the. corresponding parts shown in Fig. 2;

Fig. 4 isa fragmentary view partly in' elevation and partly in section and on a larger scale than Fig. 1 and showing the mat scraper memher. and some of the parts associated therewith;

Fig. 5 is a fragmentary perspective view illustrating a modified form of a mat scraping means employed to remove excess material over a predetermined thickness of mat;

Fig. 6 is a fragmentary plan view taken substantially on broken line 5-6 of Fig. 2;

Fig. 7 is a fragmentary .elevational view, taken substantially on broken line l'l of Fig. 2;

Fig. 8 is a perspective view, with parts broken away, of a device embodying a modified form of this invention;

Fig. 9 is a somewhat schematic view with parts in; elevation of a still further modified form of this invention;

Fig. 10 is a longitudinal sectional view, with parts in elevation, taken through a precompressor 44 ofFig. 1 and showing details omitted from Fig. 1.in interest of clarity; and

'Fig. 11 is a sectional view taken substantially on broken line II--II of Fig. 10.

Referring now to Fig. l of the drawings, a housing It is employed. Ground fiber is delivered to the device from the inlet conduit means II. This device is designed for continuous production and the capacity of the device should be coordinated or synchronized with production of fiber from a grinder or grinders so that the grinder output is slightly in excess of the amount of material to provide a mat of a given thickness. Thus the inlet conduit II is connected to the desired size of grinder or the desired number of grinders.

Alined with inlet conduit means II to receive material exhausting therefrom is a conveyor means I2 (see also Fig. 2). The conveyor I2 delivers wood fiber to rotor I3 either under said rotor I3 as shown in Figs. 1 and 2 of the drawings or over said unmatting rotor I3 as indicated inFig. 3 of the drawings.

While the rotor I3 is shown as a cylindrical member havingv a plurality of projecting tines I4 4 on its periphery, it is to be understood that spiders may support the cylindrical surface which mounts the tines It or an endless track of the caterpillar type may be employed to mount said tines I4 as a mechanical equivalent of the cylindrical member I3. The tines I4 are disposed in a succession of circular paths for purposeswhich will be described. I

Referring now to Fig. 6 which is a fragmentary view taken substantially on broken line 66 of Fig. 2, a comb I5 has teeth IS. The teeth I6 scrape rotor I3 and the space between the teeth I6 provide a passageway for tines I 4 to travel therethrough. Thepurpose of the comb I5 is to prevent dischargeof material out of the housing IQ.

If itis desired to enclose all parts of the rotor I3, then a cover I! and screen means I8 are employed (see Fig. 2). The purpose of screen means I8 is to vent out, any air under pressure caused by reason of the movementof the-rotor is in the space directly'below the cover II.

Another comb I9 having teeth ZiS-cQnfines-the wood fibertherebelow. disposed in spaced relation to the-under side:

(as shownin Fig. 2) of the rotor I3; Prefere ably theplate 2| is angularly movable towardthe rotor I3 and is also movable with the conveyor.

I2 away from the rotor I3: This may be accomplished by providing a plate 22 at :each end of the machine and each plate 22 rotatablysupports the cross shaft 23 of the conveyor means .12 and also pivotally supports, by pivot means 24,.one end of the plate 2I. with a keyhole slot 25. The'plate 22 is connected to the main housing by reason of a cap screw 26. Thus when cap screw 26 is loosened, the plate'22- and parts carried thereby may be moved relatively to the rotor I3 and the desired size of throat between the rotor I 3' and the arcuate plate 2I' may be obtained. The end portion 2'! of the plate 2| (see Fig. 7) is secured to the main frame or housing III by nut and bolt means 32 operating in a keyhole slot in the main housing"); so that.

the plate 2I can be adjusted about the pivot means 24' (see Fig. 2) and can also move with the plate 22 and after a desired adjustment has been made, then the portion 21 can be again secured to the main frame or housing II) and adssired adjustment which has thus been madecan be maintained.

.Preferably an arcuate plate 28 is pivoted to the plate 2| by pivot means 29. Adesiredamgular position between plate 28 and plate 21 may be obtained by proper adjustment. of the. set

screws 39 which are threaded in. the The plate 28 carries a comb 3 I.

As shown in Fig. 7, which is a fragmentary plate: 28.

view looking in the direction of the arrowsI-l' of Fig. 2, the comb 3| scrapes the surface of the rotor I3 between the alined tines i4 and the space between the teeth of the comb 3| permits travelof the tines I4 therethrough. The comb 3| projects through an opening in the plate 2| so that the comb 3| can be movedradi'ally toward and away from the rotor IS.

The purpose of thecomb BI is to -provide-re- An arcuateplate 2-I The plate. 22. is provided 5. caused to form a mat in which the individual fibers are'intertwined and thus we have stability and interweaving of the fibers in forming the mat. Under many circumstances the comb 3I will be adjusted so as to be inoperative and the size of throat between rotor I3 and plate 2| will control the unmatting of fibers.

Instead of discharging the fibers below the rotor I3 as is indicated in Figs. 1 and 2 of the drawings, they may be discharged over the rotor I3 as is indicated in Fig. 3 of the drawings. In Fig. 3 of the drawings, a plate 33 is employed which plate will be used in place of cover I? and screen means I8 and bolted to the main frame or housing Ill. The plate 33 has an arcuate shape portion 34 which forms a throat or passageway between such portion 34 and the rotor 13 The size of the throat between the portion 34 and the rotor I3 may be adjustable as indicated with the under feed as shown in Fig. 2. In the interest of simplicity, no adjustment is shown in Fig. 3 of the drawings for the arcuate shape portion 34 of the plate 33 in view of the showingof adjustable means in connection with the plate 2I of Fig. 2. Also a comb functioning similar to the comb 3i may be employed in connection with an over feed if desired. v

As the wood fiberis being discharged from the rotor I3, it passes between a plurality of fiber directing vanes 35. The vanes 35 which are shown in Figs. 1 and 2 of the drawings are of a shape so that the discharging wood fiber from the rotor, I3 strikes an arcuate portion 36and thus the material does not tendto hang on the vanes. The vanes 31 shown in Fig. 3 of the drawings are of slightly different shape but again the vanes 31 are provided with an arcuate portion 38] for] the same purposes as the arcuate portion 36 of the vanes 35. m

e, As appears in Fig. 1 of the drawings, the vanes 35 diverge outwardly similar to the throat portion 39 of the housing III.

It has been found desirable to employ a rotor I3 having a length less than the width of the mat 40 being formed. When the rotor I3 is short, it is more suitable for high speed work and at high speed it has an output to provide a thickness of mat 40 greater than desired for hard board of the same width as the rotor I3 and hence the reasonfor the throat 39. Furthermore, if vanes 35 are employed, greater control obtains for providing a mat 46 of substantially uniform thickness crosswise considered.

In Fig. l of the drawings, the side walls ofthe housing II] are broken away in the interest of clarity. However, the side walls of the housing III act as side guides against which the mat 46 is laid up. Thus the vanes 35 can be shaped so that a suitable amount of material is laid up at th sides as well as at the middle of the mat 40 crosswise considered.

The bottom of the housing I is provided with arelatively moving member on which the mat 40 is laid up. This may be readily accomplished byproviding a conveyor means 4| which functions as the bottom of the housing member ID. Thus we have a relatively moving member on which a mat is laid up which relatively moves so far as the source of wood fibers being delivered from the rotor I3 is concerned. The various fibers which are provided by mechanically fibering or grinding wood are' heterogeneous. Theyare different in weight and are different in size. Thus they will be tossed different amounts by the rotor I3-some will be tossed further. than others. The. mat 46, as it is formed, has its uppe'rsurfa-ce angularly inclined upwardly, longitudinally considered, as respects its bottom surface and with the apex of the angle toward the rotor I3. If this angle is too great then there will be. a tendency for balls of wood. fiber to be formed which will roll downwardly on the top of themat and generally in a direction toward the rotor, I3 and if we have any balls so formed, an imperfect mat is formed. However, where the rotor I3 is driven at relatively high speed such as in the neighborhood of three thousand R. P. M., there will be such a. difference in the rate of travel of the individual fibers that the fibers in falling down, give much the same appearance as a snowstorm. This prevents too steep a longitudinal angle of the mat 40 andvery satisfactory results obtain. -As there is considerable turbulence of air in the housing Ill due to the rotation of the rotor I3, preferably screen means 42 is provided to exhaust airfrom within the housing I0. Also.

the top of the housing III decreases in height as the distance increases from the rotor I3. to thus generally follow the path of the falling wood fibers. As shown, the various portions of the top of the housing ID are inclined, however,

an arcuate shape may be employed if desired In order to insure a mat of a predetermined and uniform thickness, preferably the mat is formed to an initial thickness over. that desired and then the excess over' the predetermined thickness is scraped 'ofi orremoved. In Figs. 1 and 4, the scraper, device comprises adriven rotor 46 and a driven screw conveyor 41. A trough 48" cooperates with screw conveyor 41 so that materials being moved by the screw conveyor 41 will be delivered from right to left as viewedin Fig. 1 of the drawings and ;to a suitable dis-charge means. The rotor 46 may be similar in construction to the rotor I3 and is provided with a plurality of tines 49 disposed in a plurality of successive circular paths. Also a scraper or comb member 50 is provided which may be similar in construction to either of the members I5 or I9 (see particularly Fig. 6 of the drawings for details of comb I5). The ro tor 46 throws the wood fiber backwardly and upwardly andthose fibers going upwardly ride over the top ofthe rotor 46 and down comb member 56 to the driven screw 41 and then are discharged to the left of the machine as viewed;

in Fig. 1 of the drawings. From the conveyor 41, wood fiber can then be moved by any appropriate conveyor means and returned to the inlet conduit means II.

Preferably, the rotor 46 and the screw 41 are grooves which have a tendency to form by reason of the tines 49 on the rotor are in effect wiped out and a more uniform surface obtains on the mat 49 as it leaves the rotor 46. Also if there are any voids, this angular position of members 46 and 41 moves sufiicient material to fill in voids The rotor 46 is positioned in vertical spaced relation to the top lap of the conveyor, means 4| so that the lowermost portion of'the. path of travel of the tines 49 determines the final thickness of mat. Thus, if the device is designed to make more than one thickness of mat, therotor 4'6 must be mounted for relative vertical adjustment ascrespects the top lap of acsaeor:

Reeferringnowto Fig.5 of the. drawings, which shows a fragmentaryperspective view of, a modi-v fiedformof scraper meanswhich maybe used in place of the. scraper means just described. in.

connection with Fig. l, the; main housing or.

is. providedwith a wall t which is inspaced.

relation toth'eupper lapof co'nveyormeansdl' and the spacing is the same-as the thickness of the final'mat 40; A driving pulley 52, connected to :a source of power. notshown, and a driven pulley 54 support a conveyor belt 53.. This conveyor' 'bel t' may be formed of. metal or it may bea conveyor'belt having a metallic. edge portion'5'5 Theupper-lap of the conveyor belt 53 travels in a trough 56. The edge lilofithe conveyorbelt 53 rides in close proximity to the iinner surface of the wallfil and at an. elevation in alinement with the lower edge of said 'wall 5|. As the mat 40' passes under the top lap of" the conveyor belt 53, edge 55 functions. to cut oil anyexcesssurplus material in the mat lover a given predetermined thicknessv and suchexcessmaterial is removed by the belt conveyor53. The belt conveyor 53 thus functions. as a cutter and as a conveyorbelt. Preferably, thereis thus employed a combination cutter and conveyor Y, belt. However; if it is. desired to. use d two memb'ers instead of one, then a traveling era-reciprocating cutter knife would be. em pIoyed insteadof the cutting edge: 55 of. the conveyor belt53 and the same would be followed by a suitable-conveyor belt or other type of. fiber removing means to remove fibers out ofi from the mat 40 over aipredetermi ned thickness. Fibers discharging from the trough Siimay be returned to the inlet conduit means It.

If the mat is to be later pressed in a hot press, it is desired to provide a preccmpressor so as to decrease the necessary opening of the press to receive themats 40 to be pressed. As illustration of precoinpressor', we have shown the pre compressor de which operates on the mat as after it leavesthescraper; either that shown in Figs; Ifland 4 of' thedrawings or that shown in Fig. Bot-the drawings; This precompressor 4:; may comprise an endless traveling belt 58, a

driving roll 59, andaplurality of driven rolls.

60, 6t; '62, 63' and 64: Preferably, the conveyorb'eltll 'is supported by a driven roll 6% at: the point: of greatest pressure between the conveyor belt 58 and the upper lap of th'e conveyorimeans 4|. The chamber provided between theconveyor belt: 5'& and the conveyor belt ti gradually decreases. to thepoint of greatest pressure. where. rolls-Birandfidare: opposite each other; Therolls 6t and El provideholding of thesame, size chambenprovided bBlIWEEIl IOHSrGE. and 64. and then the: chamber-opens between roll wand: roll. 59.

The; various parts of the; precomp-ressor 44 whiclrhave been described are illustrated inFigure .Lofi the drawings and other portions of the precompressor are shown more in. detail in Figs. 10. andlla. Thetraveling: belts: i it and 58' are pref erablyforaminousor perforate beltsso that steamobtainsrif it is applied; as indicated by the details:

thereofin'Figsl lc'and l1.

The steam chest l0! comprises'anv upper wall" I02 which wall 102. is'sealed. at itsends-by sealing means [03 against rolls. 62 and 63a Thesteam chest MI is connected to a source of steam under pressure by conduit [04. In order to prevent escape of steam laterally end sealing means I 05 are employed (see particularly Fig. 11). Within the steam chest it! are a plurality of laterally spaced grids H36 which are supported by cross braces I91. From this construction steam passes downwardly from steam chest [0i into mat 4B and can. only escape by passing through a portion of said mat Gd. Thus the upper surface of the mat. can be subjected to heat and moisture.

Preferably the lower side of mat is also' subjected to heat and moisture and the parts of the steam chest I89 are similar to parts em-' ployed in connection with-steam chest NH. The steam chest loll comprises a lower wall I08, end

sealing means 5%, a plurality of laterally spaced 1 grids I I0, cross braces H l and steam entrance conduit i i 2.

While the mat dd may be subjected to heat and it, as has been described, p1ates may be laid on the conveyor e: and a unit or section of mat may" be laid upon each plate. However, our device has been designed for continuous operation and hence means will be provided to transfer the laid.

up mat as it leaves our machine for further processing. As the transfer means, which picks up the precompressed mat as it leaves ourmachine, forms no part of this invention nor the types of presses which press the mat, they are not further described.

Referring now to the form: of the invention.

shown in Fig. 8 of the drawings, the conveyor forms the bottom wall of a housing 66 and such parts correspond respectively to conveyor 4| and. housing Ill of the previous figures. In 8 .of'

the drawings, the main distinction between the.

construction there shown and that previously described is that the. material is laid up as a mat as it is discharged from the grinders.

As illustrative of the plurality of grinders, there is shown grinders 6'5.

Wood chips are delivered into the it is desirable to control the capacity of, the device at the grinders. This is. obviously also true of the construction shown in the previous figures.- Grinders to provide mechanical wood fibers generally have a. relative speed of substantially thirty-six hundred. revolutions. per minute be-;

tween the. cutting plates. Withthis relative speed. the wood fibers that. are thrown out of. the discharge chutes 6 9 obtain a: relatively highrate oftravel and may lie/tossed iorair separartionmuch likethey are tossed by the rotor +3 of the-previous figures. In theform of the'inven-r tion ShOWn lI1 i-g- 8, there is employed aplu-s rality of grinders 5 1. andeachi lays its ownlayer"! of the. mat as the traveling belt 55 provides'relativeymotion between itself and" av plurality of: alined grinders; The 'meansjfor distributing} crosswise-considered, the wood!fibers thematic being." discharged from a givengrinder embody 9 vanes 10 which function similarly to the vanes 35 and 310i the previous figures. In other words, the layer of mat H is laid up by the first grinder and successive layers are laid thereon by successive grinders until the mat reaches the grinder which is last in the series, and then there is a mat 12 which corresponds to the felt 40 just before it reaches a scraper means.

As the scraper means employed in connection with Fig. 8 of the drawings may be identical with 'those previously described, a fragment of the scraper means shown in Fig. l is illustrated and the parts shown are given the same numbers in Fig. 8 as they are given in Fig. 1. Also, as the same precompressor may be employed in connecmat; Wood fiber is delivered from the hopper 13ttothe belt of the conveyor 14, a fragment of which is shown. The rotor 15 is driven by means not shown and is similar in construction to the rotor 13. An arcuate bafile plate 16 is disposed belowthe rotor 15. The arcuate baffle plate 16 may be adjustable as disclosed in connection with the plate 2! of Fig. 2, but such details of course do not relate to the novelty of the construction of Fig. 9 and hence are not shown. Fragments of the housing 1'! are somewhat schematically shown. A comb "functions similar to the comb IQ of Fig. 2. A perforate grid 79 is disposed in -the path of travel of wood fiber being discharged from the rotor 15. A traveling conveyor comprises a driving roll or sheave 80 (connected to a source of power not shown), driven rolls or sheaves 8|, 82, 83, and perforate or screen-like endless belt 84.

A vacuum is provided through the lower lap of the belt 84 and this may be accomplished by providing a vacuum chamber 85, connected to suitable pumping means not shown, and sealing means 86 between the walls forming the vacuum chamber 85 and the belt 84.

A second conveyor comprises driving roll or sheave 81- (connected to a source of power not shown), driven rolls or sheaves 88 and 89, and an endless belt 90. Preferably sealing means 9! are provided between the housing I! and the belt 90. The sealing means 86 and 9! may be in the nature of packing to prevent the passage of air therepast.

As the wood fiber is tossed by rotor 15 into the air and in a direction toward the grid 19 it is retained against the belt 84 because of the vacuum means. A negative pressure is provided which will be sufiicient to retain the desired thickness of mat on the underside of the belt 84. The vacuum may be adjusted to produce mats of different thicknesses as desired. As the upper lap of the belt and the lower lap of the belt 84 travel to the right, as viewed in Fig. 9, the mat is progressively moved in the same direction. Due to the fact that the said laps of said belts converge toward each other as they approach driven rolls 82 and 88, there is a pre compressor at such area. The point of greatest pressure will be between driven rolls 82 and 88.

'ing between rolls 8| and 82.

Driven roll 8| maintains this pressure for a desired period which is determined by the spac- Thereafter the bottom lap ofbelt 84. diverges away from the top lap of belt 90 and there is thus formed a precompressed mat 92. The precompressed mat 92 is delivered from conveyor 90 to any suitable place similar to that described in connection with the preceding forms of our invention.

An advantage of the form of the invention illustrated in Fig. 9 of the drawings is that the thickness of mat may be adjusted by adjusting the minus pressure provided in vacuum chamber BBand in turn against the lower lap of the perforate conveyor belt 84. The minus pressure is self adjustingdueto the mat'building up tliicker on one portion of the mat causing less air passage at' that portion and in turn the slowing of the building'upof the mat at such portion. Thi eliminates the need of scraping or removing eircess material to provide a mat of a given thickness. l

Throughoutthe various forms of the invention the conveyor belts, as 4| of Figs. 1, 4, 5,

conveyor belt BEofFig'. 8, and conveyor belts andB4 of Fig. 9 may be driven at variable speeds to control the thickness of a mat if wood fibers are being provided at a variable rate. However, it has been found preferable to run the various conveyor belts at a uniform speed and to control the amount of wood fiber that is being delivered by control of the amount of chips that are being delivered to the grinders. As previously indicated, there is the-greatest density of product at this location and hence the more practical it isto provide controls at such. locaion. i

From the various foreging illustrations of devices embodying the invention, it is obvious that there is provided a plurality of traveling tines, as the tines carried by rotors E3 or T5. The mechanically obtaind wood fibers are a heterogeneous mass. Theyare not of uniform mass or dimension. When these fibers are tossed in the air either by the said tinesor by the grinders 5'! of Fig. 8, they are thrown unequal distances and directions. By having them tossed at relatively high speed, the difference in the mass and size of individual fibers causes them to travel unevenly. As they fall or as they are thrown upwardly, the appearance within the housing is much like that of a snowstorm. By providing individual fibers, and which are being air separated, they form a mat which is well intertwined and is very selfsustaining. As the mat 40 is being formed on the relatively traveling conveyor, such as 4| of Fig. 1, its upper surface is at a small longitudinal angle to the conveyor. In other words, the mat 40 slopes gradually upwardly from its initial end as it approaches the scraper rotor 45. If the angle is too steep, then the fibers tend to roll down an incline and a mat is ruined because the fibers in a ball cannot be intertwined and intermatte-d with the other fibers in the mat. It has been discovered that if the fibers are not thrown at a high rate of speed, so that advantage can be taken of their difference in mass and difference in dimensions, a good uniform mat is not produced. Thus, the process of forming the mat by tossing the heterogeneous fibers violently in combination with the relatively moving mat supporting means is also a part of the invention.

Other features of the invention have been described in the foreging specification and are inherent in the appended claims.

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