US2990314A

US2990314A - Pulp molding method and apparatus

Info

Publication number: US2990314A
Application number: US613475A
Authority: US
Inventors: Ammon M Leitzel
Original assignee: Pacific Pulp Molding Co
Current assignee: Pacific Pulp Molding Co
Priority date: 1956-10-02
Filing date: 1956-10-02
Publication date: 1961-06-27
Anticipated expiration: 1978-06-27

Description

June 27, 1961 A. M. Lx-:rrzEL PULP MOLDING METHOD AND APPARATUS 2 Sheets-Sheet 1 Filed Oct. 2. 1956 FlG.l

LA 5. .E G n+ H T D 5 /MWL w jmM. m m N n m A 0 42M w/zA M/L, a? Qv/ UHVU VU o w June 27, 1961 A. M. LEITZEL PULP MOLDING METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed Oct. 2. 1956 INVENToR. AM MoN M. LE lTzEL BY M #v A T TORNEKS United States Patent 2,990,314 PULP MOLD1NG-MEFHOD AND APPARATUS Ammon `M. Leitzel, Portland, O reg., assiguor :to Pacific Pulp VMolding Company, Portland, Oreg., a corporatQgQf, ,Washiasfon Filed Qct. 2, '1956, Ser, No. 613,475

6, Claims. 1.(Cl. 162-220) 'Ihe present invention relates to a method and appara- -tusfor molding `pulp articles. The invention is concerned with suction molding of generally planiform articles such as Aegg flats, fruit trays, plates, compartmentedserving trays, cushion ilats, packing pads and the like, all of -which are of considerable width and breadth compared to any variations in depth. Such articles usu ally"have projections above, and depressions below, a medianp'lane, particularly those used for packing eggs or`fruit or as cushioning member. In Vthe formation of such articles a suction"`mold yis employed, there usually being'aplurality of such molds -mounted upon a large wheel, or upon 'a chain or other mechanism, whereby .each of the molds is successively dipped into a slurry tank and alayer of pulp depositedthereon by suction applied through the mold, the layer being maintained upon the surface of the mold until suiiciently dried to .permit its removal from the mold 'without being torn apart or deformed.

The present inventionis concerned with the formation of articles of this character which have substantially smooth surfaces, without the employment of expensive mating dies. Mating dies are usually employed for the purpose of compacting the pulp and smoothing the exposed surface of the layer of pulp on the suction molds, and are usually rheated s o Ythat drying may be accomplished while the article is undergoing an ironing effect. Not only are such mating dies expensive, since 'they must be accurately formed and rigid, but they must be applied accurately tothe surface of the article and maintained in registry with the suction mold for a considerable period of time. Usually, these requirements are met by a complicated machine employing `a number of mating dies. The present invention Vis distinguished therefrombyV the use of a single mating die which'is applied to the article for a short period of time, and which is so inexpensive that Yit may b e discarded andreplacedif a defect should develop in Athe mating die. This singlemating die is resiliently forced against the exposed surface ofthe article while itis maintained by suction on the suction mold, for a shortperiod of time immediately succeeding the deposit of the pulp layeron the suction mold. vThereafter substantial 'drying .of the article is accomplished, not only by direct radiation but by the drawing of heated `air through the article, rapid drying being thus accomplished. i

When molded pulp articles are formed `upon suction molds, the outer surface of the layer of pulp initially presents a rough or uneven appearance-because the distribution of the pulp fibers on .the `mold is not entirely uniform, and valso because a considerable 4number ofthe =outer fibers areoriented at a large angle with `respect to 4the outer surface of Vthe layer of pulp. The mating dies Yforce these fibers into the plane of the article and iron out the irregularities in the surface of the article, and also compact the .entire article to some extent. lhe `present invention vaccomplishes these results much more `rapidly than by any method or mechanism heretofore known.

YIn accordance with-the ,present invention, thematiug Adie comprises a substantially rigid, but .slightlyeexible die member. The matingdie member lcanfbe manufactured of rsheet metal, plastics, and other `suitable materials, `provided lthat the material has vsuiicient ilexi- :bility anddurability to be centrally bowed from a slightly concave condition tor a slightly convex condition successively in rapid order for many hours 'of operation, .and

"atthe same time have suicient rigidity to accomplish its function. One suitable material is a .glass-fiber v'reinforced`polyethylene plastic such as is commonly yused `for boat hulls, automobile bodies and the like, the member being built up to a thickness of about one-'eighth of au inch vfor molding a planiform article of about 12 by 20 inches andhaving'projections rising above, and depressions below, its median plane to an extent of about three quarters of an inch in each direction, Vsuch as a tray. Such a mating die, when clamped aroundits periphery in a rigid frame will sustain the Weight of a' grown man Without perceptible deliection, but when fluid pressure in vthe order "of ten to twenty pounds per square y"inch 4is vapplied to its surface it will flex to a 'position .tenance Ashutdowns rather than to chance having `it fail during an operating period. A member formed 'of'polyethylene plastic ofthe same type and dimensions as .that described above, withoutthe :glass liber reinforcing therein, khas also proven to be satisfactory.

The present invention is illustrated and described in conjunction with a molding machine of the character described and claimed in my copending applicationSeril No. 547,713, filed VNovember 18, l9`55 ,'but it will be readily apparent that the invention maybe employed iin conjunction with any suitable suction molding apparatus.

yItis therefore a principal object'of the present invention to provide `improved pulp-molding lapparatus for forming molded pulp articles having smooth surfaces.

Another object o f the invention .is to provide pulp molding apparatus of the suction molding type in which molded pulp articles are smoothed and compacted withyout the employment of expensive, rigid mating Ad 1' =s, a.rld mating die application mechanism. i

Another vobject of the invention is .to provide pulp molding apparatus of the suction molding type in which a substantially rigid, slightly ilexible, .matingdie member is employed to compact and smooth the molded .pulp article. A A further object lof the present invention is ,to provide a method for'forming compacted and smooth surfaced molded pulp articles. `Other objects and advantages will appear in the following description of a preferred embodiment of 'thein- .upon which to practice the present method, .greater details of which may ybe ascertained from the above-mentioned copending application, and illustrating the mecha- .nisrn of the present invention.

FIG. 2 is a partial plan VieWtakensubStaDtially along linevZT- ZofFIG l.

FIG. k3 isan enlarged vertical section taken ,substanytially along line 3-3 of FIG. 2, illustrating themechagnismY at the instant of application` of thefmating rdie mem- .berto-thelayercfpulpon the suction mold immediately after it rhas emerged from ythe slurry tank.

FIG. 4 is a view similar to FIG. 3 illustrating the removal of the mating die member from the layer of pulp on the suction mold; and

-FI-G. 5, is a schematic diagram of acontrol circuit-for theV means eifectingV the application and removalA of Ythe .'mating die member. v v

`In the drawings the numeral 10 generally refers to `a continuous molding wheel comprising a plurality of ,"peripherallyA disposed suction vmolds 12. The molding wheel has a hollow -hub portion 14 which is provided 'with suitable axle extensions (not shown) whereby the wheel is mounted for rotation about a horizontal axis. Such rotation can be produced-in any desired manner, ffor example, as illustrated and described in the above identified application. i -A slurry tank 16 is provided, into which a pulp slurry ir'itroduced through any suitable conduit such as the j conduit 18.v The suction molds are successively dipped l :Sinto Athe slurry in tank 16 and then withdrawn therefrom, suction being applied through each of the suction 'molds while in the slurry vso as to cause the depositof a `j'layer of Wet pulp thereon. 'l The molds 12 are secured at -their edges to support elements 20 at the periphery of the wheel 10,V the support elements being mounted on the outer ends of radially vextending spokesA 22 which extend from iianges 24 -atthe opposite ends of the hollow hub 14. Each of the molds 12 comprises a back plate 26 and a separable mounting rim 28, the two

members

26 and 28 being secured together and attached to the `support elements 20 :by means of studs 30..'The member 28 is provided 'with au openingof substantially the size of the article Ytobe molded andisprovided with a peripheral ledge 32 uponwhichis mounted a perforated, rigid mold 34 forming theprincip'al element of the suction mold. The Yelement .34 is covered by a closely matching screen 36, jthe. periphery of which is clamped to the mounting plate 128byY a peripheral clamp frame 38 and a plurality of studs 40. The screen is of such iiue mesh as to-pre- 'vent vrthe passage oflibers therethrough, but permits substantially uniform suction to be applied to the slurry. Whejnthe suction mold is immersed in the pulp slurry ak suction valve 42 inrits base is opened to permit withfdrawal `of water through a suction outlet 44. Ihe interiorvof the hollow hub 14 is maintained under '..vacuum atallptimes. Suitable connection between the v'hub'and a vacuum pumpis provided by any of the usual means such as disclosed in the above-identified applicat ion,` YThe conduits 44 from the suction molds are conjn'ected to-waterycollection drums 50` mounted within the periphery of the wheel. Y Each collection drum 50 is con- 'nectedby'a conduit 52V'and a valve chamber-54,10 the Linterior, o r. suction chamber` 56, of the mold 12' Twhich isroire Vstep forwardly. of such collection chamber inthe direction of rotation of the wheel 10.V Each valve chamber 54 mounts thevalve 42 of such mold, the valve be- VingV urged toward closed position by a spring 57. The `valv e 42 for each suction mold is opened at an ap- 'r-propriate time by valve actuating mechanism including "a stationary cam 60 mounted onY the frame of the machine. Cam followers 62 mounted onpthe ilange 24V eny"ga'ge the VVcam 60,V and'through a suitable linkage system operate links 64V extending radially outward toward the collectionV chambers 50. The links 64 are linked to Acranks mounted upon the collection chambersy where- 'by rockshafts 66 mounted on the collection chamber -are'partially rotated-at suitable times 4to operate pairs of valve cranks 68 and 70'eXtending in opposite direc- Ztions in the vdirection of rotation of the forming machine. The mechanism is such that when-crank 68 is rockedvin one direction Vit will depress spring 57 -to thus Aopen valve 42 and connect, the'suction mold to the source -oflvacuum Simultaneously therewith crank 70 is rocked fin .the opposite. direction. whereby a" valve `7.. is released, and the valvef/Zis `closed-bya. spring 74.' The valve 4 72, when opened, permits the passage of air under pressure into the interior of the suction chamber through a tube 76 connected to a main pressure pipe 78, of annular form, mounted upon the wheel and connected to 5 a source of pressurethrough the connection 80 and other suitable means (not shown).

The valve controlling mechanism is such that each suction mold is connected to the source of vacuum prior to its entry into the slurry, and vacuum is maintained constantly throughout the greater portion of travel of the suction mold. When the mold has traveled substantially 270- away from its deepest immersion in theslurry, -the suction is cut oli and air under pressure introduced thereinto, whereby the partially dried article is ejected lfrom the surface of the mold onto a vsuitable removing means such as exemplified by the suction .transfer head 90 and continuous belt conveyor 92. Pressure need only be applied momentarily when the transfer head 90 is in 4alignment withthe mold, and then suction reapplied. j'As the mold travels from the removal conveyor position back ltoz the slurry tank it `is preferably washed by I fluid forced thereagainst through spray heads 94.

lt isto be appreciated that only the essential elements Iof the machine necessary for an understanding thereof have been herein illustrated and described, greater details being available in the above-identified application. l5In the` above-identified application smoothing and compacting 'of the article is achieved by means of afresilient vtraveling.. belt, which is replaced herein by mechanism vof the present invention which will now be described. The mating die 96 ofthe present inventioncomprises ,a-mating die element, 100 matching the contours of the Vjsuction mold, projections thereon being of lesser dimensionsthan the depressionsin the suction mold, and devpressions therein being of greater dimensions than the corresponding projections of the suction mold, whereby a uniform layer of moist pulp may be interposed between the suction mold and the mating die elementwhen they are in mating position. This layer of pulp, indi- `cated at 102 in FIGS. 3 and 4, is rough and uneven fwhen' it emerges from the slurry, but becomes smooth and, even through the action of the mating die. The `mating die element comprises a peripheral, vertical flange '104 which is provided with a horizontal rim 106, speakfing with reference to the general plane of the mating ldie felement ,100. The mating element isa substantially rigid,Y slightly exible, impervious member .of'uniform ,thicknessthroughou which maybe formed of thin-sheet f metal r or various plastic compositions, but is preferably formed of fiber glass ,reinforced polyethylene-plastic-of Qthegtype used ,for making boat-hulls-and automobile 'bodies. 'Its rigidity is such thatwhen the-peripheral rim 1,06 on` a :mating die of approximately 12 by 20 .inchesinoutline is clamped in a rigid frame, a man mayV stand on it without material deilection of the cen- `tra1 portion thereof, but its ilexibility is such that. itrma'y be centrally bowed as much as one-quarter to threeeighths of an inch in eitherdirection when lluid pressure `in the order of ten to twenty pounds per square inch is applied uniformly thereto. TheY mating die element, is mounted upon a rigid mounting plate 110 by means of Va mounting frame 112 clamping the entire rim 106 to the mounting plate, such clamping being accomplished through a plurality of studs 116. The mounting plate 110 is provided with a pluralityvof apertures 118 Where,-

'byiluid may be introduced into or withdrawn from the space 120 between the mating die and the mounting plate. A iiexible diaphragm 126 is mounted in back of. the Amounting plate 110, the periphery thereof being clamped tothe back ofthe mounting plate 110 by a dish-"shaped backing member 128 and aplurality of studs 130. The backing member lis provided with a nipple 132 to which `is clamped aihose k13,4. A central partition 136Y in mem- 2ber128 is provided with .a pluralityof apertureslSS -whereby 'suctionor uid pressure may? be applied th the diaphragm 126, and when the diaphragm is withdrawn -from the mounting plate i110, as illustrated in FIG. 3, -it will-'not Vbe subjected .to extreme deformation'at any one Vpoint and is limited yin its outward exing movement.

As illustrated in FIG. 3, `the valve V42 `is open at the linstant that the mating dieelement is applied, and at the same time suction has beenapplied to'theinterior of the backing member 128 whereby -uid contained in the space 120 between the mating die 100 and the diaphragm 126 is partially withdrawn through thev apertures 118. The vacuum applied throughthe valve 42 is withdrawing water from the layer of pulp lbut the pulp is still in a very moist condition-at this instant, having just been withdrawn from the-slurry. The vacuum exerted against the diaphragm v118 has caused the vertical ange 4104 to give slightly inwardly and the central portion of the mating die to `be bowed, or inother words, the mating-dieelement 100 has assumed a slightly dished conditionv of concavity whereby the periphery of the mating vdie rst makes contact with the periphery of the layerfof pulp on the suction die. Shortly thereaftenthe source of vacuum is ldisconnected from themating die and air under pressure is introduced through the nipple .132,vthereby-causing the surface of the mating die element to progressively contact and iron the surface o-f the layer of pulp inwardly from its rim in all directions uniformly toward its center. The amount of uid trapped between the mating .die element and the diaphragm 126 is such thatwhen the diaphragm 126 is forced at against the mounting plate 110 the mating die has assumed a slightly dished condition of conveXity, the peripheral portions thereof being tirst withdrawn from the-molded pulp layer and then its surface being peeled progressively inwardly and uniformly throughout until the central portion of the mating die Velement alone remains in contact, whereupon the mating die element li-s withdrawn to a distance. It is to be appreciated that this action will not affect the layer of pulp in any fashion other than to smooth it and compact it uniformly. Suction being constantly maintained through the suction mold holds the layer of pulp in its smooth condition as the mating die is withdrawn therefrom increment by increment.

The state of flexure of the mating die element may be reversed without departing from my invention. In other words, it maybe convex when applied and concave when Withdrawn.

Suitable means are provided to maintain general'planes of the suction mold and mating die in parallelism during the entire application of the mating die. The means comprises -a pair of mounting arms 140* extending diagonally downward beyond the slurry tank in the direction-of rotation of the machine, being pivotally mounted coaxially of the machine at 1142, one on each side of the wheel-10. The arms 140 extend beyondthe -mating die and are connected together by a crossrod 144 at their outer Yextremies. At each end of the mating die backing member 128 there is a longitudinally slotted radially extending arm 146, the slot 1'48 thereof receiving a crank pin 150. The-end of the arm 146 is seated in a socket -152 at the inner end of a telescoping rod 154 slidably -journaled in -a tube l156 projecting inwardly from the crossrod-144 and firmly urged against the end of the arm 146 by afstrong spring 158. A pin 160 mounted on the member 146 projects laterally into a slot 162 lin the radial arm 140. It'will be apparent from the foregoing thatthe mating die is thus maintained tangentially of the wheel 10, butthat the spring 158 may be compressed to permit withdrawal of the mating die from themachine in order thatreplacements'may be effected.

A shaft 170 is mounted in xed bearings upon a suitable-support A172 between arms 140 and is driven by a chain-beltfdrive, indicated at 174. -Each end of the shaft 'l70drivesfa disc 176-upon which a'link 178is pivotally mounted, lthe ffree end of the link 178 carryingzthelcrank while still being held tangentially to the wheel, will move into contact with thepulp layer-and remain'insuch relation while the crank pin -rides-,loosely in the-,slot

k148 and the mating ,die travels with the suction mold.

The lost motion connection thus provided Apermits the close approach of the kbackingplate 110 as vvillustrated-.in FIG. 3 and its subsequent withdrawal as illustrated in FIG. 4, while pressure is constantly appliedrthereto through the-spring 158. The chain drive forthe disc`1 76 is suitably correlated with the drivemeans forthe wheel 10 so that'the `placement and withdrawal yof the Vmating die occurs during the timeallowed.

A schematic control diagram forthe actuation ofthe `mating die is illustrated in FIG. 5 --wherein it is'seenthat `the flexible hose 134 is connected to a pair of conduits,

conduit V180 leading to a sourcev of yairpressure indicated at 182 and conduit 184 connected to a source of Vvacuum indicated at 186. A valve 188 in conduit 180 is controlled -bya solenoid l190 and a valve 1927in conduit l'84is controlled by a solenoid 193. The solenoids are `controlled by a circuit including-main line A200 lwhich leads'to a relay solenoid 202 and a contact 204 which 'is adapted Ito be engaged by a'cam follower 206 engageableby a c am 208 on one of the discs `176, the contact 204 being mounted in a switch box 210 suitably mounted adjacent .the disc. When the cam follower 206 is down as illustrated in rFIG. 5 the relay bar 212 is makingfcontact with the branch line 214 and thus energizing solenoid 190 to yopen valve 188, t-hereby connecting the source of pressure 182 to the interior of the mating die96 to ,causeoutward :flexing of the mating die element. At this time'the lower contact vof the relay is open andsolenoid 193 de-energized whereby valve 192 is closed. Shortly before contact of -the mating die element with the layer of pulp cam follower 206 rides up on cam 208, thereby energizing relay solenoid 202 to de-energize solenoid 190 while energizing solenoid 193, thus `disconnecting the source-of pressure and connecting the vacuum source to the mating die whereby the mating die element assu-mes its position v.of concavity immediately preceding contactzwith the layerof pulp. Shortly thereafter the vacuum is cut. olf yand/pressure is reapplied while the mating die element' is .in contact with the pulp.

It is to be appreciated that cam 208 could be interrupted whereby a series of reversals of the mating die element from concavity to convexity would be accomplished during the time that contact is maintained, thereby causing a series of hammer blows to Vbe applied Ato the layer of pulp. However, I have been unable -:to yascertain any improvement in quality thus achieved, the one reversal being suicient to achieveasmooth surfaced,` compacted article.

The upper half -of the forming wheel lis surmounted by ay hood 220 which is spaced Ifrom vthe surface -of Athe wheel to allow free ow .of air between `t'he'hood and :fthe wheel. The hood is heavily insulated as indicated `lrat 222 and is provided Iwith a reectivelining v224finback of a plurality of yradiant heating elements l226. Thus the smoothened and compacted 'layer of rpulp is-not Lonly subjected to radiant, drying heat butis constantly being traversed by a stream of heated drying air whereby moisture .and steam ris rapidly conveyedfawayfrom 4"the pulp throughthe collectiony chambers. Asuflicient degree of rigidity is thus :imparted-'tothe vpulpfarticle lthatf-it may bersafely blown 'from the fforming ,moldonto the transfer mechanismf f90 "and thenffdroppedr lonto the oon*- ve'yorfbelt 92 without being torn or dented, The con- Eveywor belt 9 2 preferably conveys the varticles through a dryingove'n for complete drying prior Vto stacking Aor otlie-handling. i i -Having -illustrated and described a preferred embodi- -ment of the machine and the method of pulp forming innvolved, I claim as my invention all such modifications in 'detail and-arrangement which come within the true spirit and scope of the followingclaims:

I claim:

1. 'I'he method of manufacturing a molded pulp article having all .portions thereof adjacent a general plane, which process comprises sucking -a layer of pulp onto a suction mold providing a foraminous mold surface having a corresponding general plane by applying suction through said surface while said mold is immersed in a pulp slurry, withdrawing said `mold and layer from said slurry, pressing an impervious slightly flexible mating die element providing a smoothing surface having a corresponding general plane against said layer on said mold surface immediately after said mold has been withdrawn lfrom said slurry and Vwhile maintaining said suction, bowing said die element toa slightly dished condition to bow said smoothing surface in one direction from its general plane prior to pressing said mating die against said layer and then bowing said die element to an opposite slightly dished condition to bow said smoothing surface from its general plane -in an opposite direction while in contacty with said layer and while the general planes of said surfaces are main- 'tained parallel so that said smoothing surface is pro- `maintain said suction.

2. The method of manufacturing a molded pulp article `having all portions thereof adjacent a general plane, which process comprises sucking a layer of pulp onto a suction mold providing a foraminous mold surface having a corresponding general plane by applying suction through said surface while said mold is immersed in a pulp slurry, withdrawing said mold and layer from said slurry, pressing an impervious slightly fiexible mating die element providing a smoothing surface having a corresponding general 'plane yagainst said layer on said mold surface immediately after said mold has been withdrawn from said slurry and While maintaining said suction, bowing said die ele- 'ment in one direction to bow said smoothing surface from 'its general plane to a slightly convex condition prior to pressing said mating die against said layer and then bowing said dieV element in an opposite direction to bow said smoothing surface from its general plane to a slightly con- -cave condition while in contact with said layer and while the |general planes of said surfaces are maintained par- .allel so that said smoothing surface is progressively moved in opposed directions into contact with said layer and is Y then progressively peeled in opposed directions from said layer,`and withdrawing said die element from contact With said layer while continuing to maintain said suction.

i 3. 'I'he method of manufacturing a molded pulp article having all portions thereof adjacent a general plane, which process comprises sucking a layer of pulp onto a suction mold providing a foraminous mold surface having a corresponding -general plane by applying suction through said surface while said mold is immersed in a pulp slurry, withdrawing said mold and layer from said slurry, pressing an impervious slightly exible mating die element providing a smoothing surface having a corresponding general plane against said layer on said mold surface immediately afterv said mold has been withdrawn from said slurry and while maintaining said suction, bowing said die element in one ,direction to bow said smoothing surface from its general plane yto a slightly concave condition prior to pressing said mating Ydie -against said v,layer and, then bowing said die elementrin an opposite A direction to bow said Vsmoothing Vsurface its generalV planemto a slightly convex `condition ,while in contactwith said Iayerand while the general planes of said surfacesare maintained from said layer, and withdrawing-said die element lfrom said layer while continuing to maintain said suction.

4. The method of manufacturing a molded pulp article having all portions thereof adjacent a general plane, which process comprises sucking a layer of pulp onto a suction mold providing a foraminous moldl surface having a corresponding general plane by applying suction through said surface while said mold is immersed in a pulp slurry, withdrawing said mold and layer from said slurry, pressing an impervious slightly flexible mating die element providing a smoothing surface having a corresponding general plane against said layer on said mold surface immediately after said mold has been withdrawn from said slurry and While maintaining said suction, bowing said die element to -a slightly dished condition to bow said smoothing surface in one direction from its general plane prior to pressing said mating die against said layer and then bowing said die element to an opposite slightly dished condition to bow said smoothing surface from its general plane in an opposite direction While in contact with said layer and while the genera-l planes of said surfaces are maintained parallel so that said smoothing surface is progressively moved in opposed directions into contact with said layer and is then progressively peeled in opposed directions from said layer, withdrawing said die element from said layer |while continuing to maintain said suction, then drying said layer on said mold while continuing to maintain said suction until said layer is substantially dry, and then removing the resulting article from said mold.

5. In a pulp molding mechanism including a suction mold providing a rigid foraminous mold surface having all portions thereof adjacent a general plane, a container rfor pulp slurry, means to immerse said surface of said mold in said slurry and to withdraw said surface from said slurry, means for applying suction through said surface while said surface is immersed in and Withdrawn from said slurry to deposit a layer of pulp on said surface and to withdraw said layer from said slurry with a layer of .pulp on said surface, the improvement which comprises, a slightly exible and impervious mating die element providing a smoothing surface having a correspond; ing general plane, means for pressing said die element into contact with said layer and for maintaining the general planes of said surfaces parallel during said pressing, and means for bowing said element in one direction into a slightly dished condition prior to said contact and for then bowing said element in a-n opposite direction into an oppositely dished condition during said pressing to progressively move said smoothing surface in opposed directions into pressing contact with said layer and to then progressively peel said smoothing surface in opposed directions `from said layer, said suction means maintaining said suction during contact of said element with said layer.

6. In a pulp molding mechanism including a suction mold providing a rigid foraminous mold surface having all portions thereof adjacent a genera-l plane, a container for pulp slurry, means to immerse said surface of said mold in said slurry and to withdraw said surface from sai-d slurry, means for applying suction through said sur- `face while said surface is` immersed in and withdrawn from said slurry to deposit a layer of pulp on said surface and to withdraw said layer from said slurry on said surface, the improvement which comprises a slightlyY liexible and impervious mating die element providing la smoothing surface having a corresponding general plane, means for pressing said die element into contact with said layer and for maintaining the general planes of said surfaces parallel during said pressing, means for bowing saidelement in one direction into a slightly dished condition 'prior to 9 said contact and for then bowing said element in an opposite direction into an oppositely dished condition during said pressing to progressively move said smoothing surface in opposed directions into pressing contact with said ylayer and to then progressively peel said smoothing surface in opposed directions from said layer, said suction means maintaining said suction during contact of said element with said layer, said means -for bowing said element including a casing having edge portions secured to the edges of said element in sealing relationship therewith and a bottom Wall spaced from said element to provide a uid chamber, and means for varying the pressure of the uid within said chamber in opposite directions.

References Cited in the le of this patent UNITED STATES PATENTS King Sept. 8, 1891 Sims Dec. 16, 1919 Hall Apr. 5, 1927 Chaplin Feb. 16, 1932 Hopkinson Mar. 6, 1934 Young Nov. 21, 1944 Gramelspacher May y18, 1948 Castel et a1. Aug. 28, 1951

Claims

1. THE METHOD OF MANUFACTURING A MOLDED PULP ARTICLE HAVING ALL PORTIONS THEREOF ADJACENT A GENERAL PLANE, WHICH PROCESS COMPRISES SUCKING A LAYER OF PULP ONTO A SUCTION MOLD PROVIDING A FORAMINOUS MOLD SURFACE HAVING A CORRESPONDING GENERAL PLANE BY APPLYING SUCTION THROUGH SAID SURFACE WHILE SAID MOLD IS IMMERSED IN A PULP SLURRY, WITHDRAWING SAID MOLD AND LAYER FROM SAID SLURRY, PRESSING AN IMPERVIOUS SLIGHTLY FLEXIBLE MATING DIE ELEMENT PROVIDING A SMOOTHING SURFACE HAVING A CORRESPONDING GENERAL PLANE AGAINST SAID LAYER ON SAID MOLD SURFACE IMMEDIATELY AFTER SAID MOLD HAS BEEN WITHDRAWN FROM SAID SLURRY AND WHILE MAINTAINING SAID SUCTION, BOWING SAID DIE ELEMENT TO A SLIGHTLY DISHED CONDITION TO BOW SAID SMOOTHING SURFACE IN ONE DIRECTION FROM ITS GENERAL PLANE PRIOR TO PRESSING SAID MATING DIE AGAINST SAID LAYER AND THEN BOWING SAID DIE ELEMENT TO AN OPPOSITE SLIGHTLY DISHED CONDITION TO BOW SAID SMOOTHING SURFACE FROM ITS GENERAL PLANE IN AN OPPOSITE DIRECTION WHILE IN CONTACT WITH SAID LAYER AND WHILE THE GENERAL PLANES OF SAID SURFACES ARE MAINTAINED PARALLEL SO THAT SAID SMOOTHING SURFACE IS PROGRESSIVELY MOVED IN OPPOSED DIRECTIONS INTO CONTACT WITHSAID LAYER AND IS THEN PROGRESSIVELY PEELED IN OPPOSED DIRECTIONS FROM SAID LAYER, AND WITHDRAWING SAID DIE ELEMENT FROM CONTACT WITH SAID LAYER WHILE CONTINUING TO MAINTAIN SAID SUCTION.