US2925178A - Screener for dry powders - Google Patents

Description

R. H. DRESHMAN SCREENER FOR DRY POWDERS Feb. 16, 1960 Filed Feb. 8, 1957 Feb. 16, 1960 Filed Feb. 8, 1957 R. H. DRESHMAN SCREENER FOR DRY POWDERS 3 Sheets-Sheet 2 INVENTOR 76 @r /ers//MAW BY f/ ATTORNEYS Feb. 16, 1960 R, H, DRESHMAN 2,925,178

SCREENER FOR DRY POWDERS Filed Feb. 8, 1957 3 Sheets-Sheet 3 /fff .ZT

ATTORNEY/5 Aated. As ently known units `mass eccentrically journalled in overhanging The present invention relates to screeners and more particularly to a machine for dry screening Avery fine powders and the like.

Gyrator vibratory screenings as proposed by United `States Patent 2,284,671 to G. H. Meinzer and United States Patent 2,132,165 to` F. B. Henry has been used for screening relatively coarse granular and powdery materials but found negligible application `in dry screening operations` for fine and very ne powdered materials of a mesh of the order of 325 x 32S because of caking which occurred in prior art machines. Such caking occurs shortly after operation of the prior art machines Ais initia consequence, approximately 98% of all presfor sifting tinev mesh materials resort to a lwet process requiring addition lof acetone or naphtha. Bo 'of these additions create hazardous operating conditions ,and require additional costly drying steps to be performed on the screened material.

The screener of this invention is particularly useful for sifting tine powders such as tungsten carbide powder, paratin and similar materials. VIt is characterized by support structure having universally resilient `mountings disposed in angularly spaced relation to support a screen holder frame ring, preferably at its periphery, a rotating protruding relation to a peripheral edge of the frame ring on an axis paralleling the planes of the frame ring faces and substantially intersecting the vertical axis ofthe centroid of mass of the frame ring and its supported screen and contents and a plurality of pairs of vertically opposed mating abutment members respectively carried by the support structure and the frame ring. Rotation `of the eccentrically journalled mass effects vibratory oscillation of the frame ring` and its screen in its resilient mountings in a path to cause successive violent engagement of said pairs of abutment members and resulting superimposed vibra- 4tory movement of the frame ring and its supported screen and contents at right angles to the plane ofthe ring faces andthe screening surface. For purposes of ,simplified explanation, the compound movement produced in `this machine is made up of a high speed gyratory movement of the frame ring, its supported screen and` contents around an axis paralleling the plane `of the` screening surface due to rotation of the mass and an imposed vertical vibratory movement due to periodic successive hammer-like blows created by engagement of the respective mating pairs of abutment members. The imposed Vibratory motion acts in conjunction with the gyrator motion to impart a vertical beating movement ofthe material against the screen in addition to therside-to-side sifting movement produced by the rotation of the eccentric mass. This beating movement is etfective to prevent caking lof the tine powdered material prevalentin sifting operations attempted with the prior art screener machines. It has been found in practice that this compound movement is far superior forV screening tine mesh powders dueto ,this non-caking the'frame' ring mountingsare more uniformly resilient l. L,

feature and thefact that 2,925,178 Patented Fee. 1e, 1960 -basis thereby eliminating unproductive time necessitated by cleaning screens clogged by caked powders and drying material screened by the commercial wet processes in use with `prior proposed machines.

Still another object of the present invention `is to4 provide a vibratory dry screener in which the component parts are arranged for easy and ready removal and replacement and are of simple construction and small size to assure easy repair and adjustment and a compact rugged unit capableof use either as a portable machine orfas a permanent installation.

Another object of this invention resides in the provision of a screener ofgenerally triangular configuration incorporating a novel structural arrangement of the gyratory mechanism relative to the screen holder mountings.

A furtherobject resides in the provision of -abutments `disposed relative to the screen holder of the gyrating screen to imparta plurality of successive hammer-like blows kvertically relative to the screen during the periods of vertical movement of the screen and its holder.

Still another object of` this invention resides in the provision of a screen holder iixed on novel universally resilientimounting members with a rotating mass journalled on an eccentric axis parallel to a plane containing the mountingV points and substantially perpendicular to a vertical line` containing the centroid of mass of the screen holder, screen and its contents.

A still further object of the invention resides in the provision of alternateembodiments of rotating masses eccentrically journalled from the screen holder of a vibrartoy dry screening machine.

Anotherobject of the present invention resides in'th'e provision of a novel triangular support frame providing a universally resilientthree point suspension means for a vibratory screen holder frame having an` integrallil mounted eccentric actuating mass.

A more complete 4and thorough understanding of the objects and features ofthis invention may be had from the following detailed description and appended claims en read in conjunction with the accompanyingdraw ing showingA a preferred embodiment thereof `in which:

Figure l is a front elevational view of a triangularly supportedvibratory screener incorporating-the features of this invention with certain parts in section forclarity of illustration; Figure 2 is a top plan` view of the in Figure 1;

Figure 3 is an enlarged sectional view taken` on line 3.-3 of Figure-2 showing details of` one embodiment of arotating eccentric b ody and details of its support on the screen holder; p

Figure4 is an-enlarged sectional view taken-online 4 4 of` Figure 2 illustrating details of one ofthecresil ient 'mounts and a pair ofthe impact abutments; `and f t ",ligure 5 fis a view. similar to `Figure 3 .illustrating fa modified embodiment ofa rotating eccentricbody.

With particular referencerto Figures `1 and 2 `the screen ing machine 10 hasya` horizontally,` disposed screenfrcapa bleef gyratorymotion around a substantiallyA horizontal axis `to accomplish screening of` powderedas `welles granular material. For easeofmanufacture, assembly ausl-.Operational cooperation :between tpartsntheubasefand mounting, of this machinerhasgbeen arrangedras` a point suspensonand as anrequilateral manglar. i :zeil

screener :illustrated Screening machine 10, as illustrated has a heavy triangular base 12, preferably made in the form of an equilateral triangle of cast iron, with vertical bosses 14 disposed on the upper surface at the apices of the base.

Each boss 14 has a central vertical bore 16 receiving the reduced end 18 of a support column 20. Set screws 22 ineach boss rigidly hold the three columns 20 in the base -12. The illustrated machine being a portable embodiment, three rubber pads 24 are inset on the underside horizontal. Immediately below the holder 30, aA funnel v36 rests in a frus'to-conical funnel support ring 38, xed by bolts and nuts 40 through a support ring ange 42 and support brackets 44 fixed to the columns 20. Support brackets 44 have integral collars 46, disposed with a sliding lit around a respective column. Set screws 48 are provided for fastening the collars at a desired 'height above the base. The funnel 36 may be shifted relative -to the screening frame 30 by varying the height of the funnel support ring 38 and support brackets 44.

One of the funnel support brackets 44 has an integral .'lateral arm 50 with a fixed collar 52 at itsffree end. YAdjustably fastened in collar 52 by set screw 54 is a post 56 carrying a motor supportl table 58.' An electric motor 60 is bolted on table 58 and furnishes the drive power for a gyratory vibration mechanism 61 ixedl in a hollow sleeve projection 62 (Figures 2 and 3) von Vthe side of the frame 30. Gyratory mechanism 61 is a separable unit in the form ofv a shaft'73 journalled'in frame sleeve 62 by bearings 68 and 70 inset in recesses 71 and 72 at opposite ends of sleeve 62 with one end 74 projecting beyond the end of frame sleeve 62. Clip rings 76 cooperate with appropriate grooves, in shaft 73 adjacent the outer side of each inner bearing race to retain both bearings 68 and 70 within their respective recesses 71 and 72 and also axially fix the shaft 73 relative to sleeve 62.

End 74 of shaft 73 in the embodiment of'Figur'e 3 is reduced in diameter to provide an annular shoulder 78. A pulley 80 is disposed on shaft end 74 and abuts against shoulder 78. The apertured hub 82 of an eccentric counterweight 84 is placed on the shaft end -74 abutting pulley 80. A screw 86 threaded in the shaft end 74, cooperates with a washer 88 to clamp the counterweight hub 82 and pulley 80 against the shaft shoulder 78. Although the counterweight, shaft and pulley can depend for unitary rotation upon the frictional force of clamping exerted by the screw 86, conventional splines or set screws may be utilized to positively lock the rotatable members together.

As is well-known, rotation of an eccentric mass creates a gyratory vibrational effect in the rotating mass normal to its axis of rotation. Such vibrational effect is transmitted through the support bearings and is normally absorbed or damped in the supporting structure. If the support structure is itself resiliently mounted, it will assume a gyratory movement from the rotating eccentric mass. By constructing the screen frame 3.0 so the axis of the eccentric mechanism 61 lies in a vertical plane-'which passes through the approximate centroid of inertia of the combined screen frame ring 30, screen holder 32rand screen 34, the combined assembly will assume and retain a substantially gyratory path of movementaround the axis of shaft V73. By properlyvleveling the frame supporting members, this axis can be made horizontal and laterally centered so there is no tendency for the material being screened to shift more to Oneside than the other of the screen due to gravity effects.

To accomplish the most convenient structure utilizing a parallel position, gyratory movement of a screening device, frame ring 30 is constructed as an annular ring with a dependent annular flange 90 (Figure l) and a substantially horizontal radial flange 92. At three equiangularly spaced locations around the edge of frame ring 30, annular open ended vertical housings 94 are integrally formed with flanges 90 and 92. Clearly illustrated in Figure 4 the upper end of each housing 94 is provided with a narrow integral inwardly Ydirected annular shoulder 96. A hat ring 98 is fastened by screws 100 to the lower end of each housing 94 to provide a removable inwardly directed annular shoulder 102 spaced below shoulder 96.

Shoulders 96 and 102 define a vertical bore substantially exceeding the major diameter of support columns 20 and are adapted to encircle the reduced upper ends of the respective columns 20. These reduced ends are threaded part Vway toward the axially facing shoulder formed at the juncture of the reduced end with the main 'corresponding roughly to that normally used in tire cas.

ings or rubber spring shackle and torque rod sleeves.

4Shoulder 96 rests on the upper face of upper rubber ring 105 while shoulder 102 bears firmly against the underface of lower rubber ring 105 when screws 100 are drawn home to secure ring 98 in place. A s will be clear from the description just given, frame ring 30 is resiliently supported by the spaced pairs of rings 105 at the three points of connection to columns 20 so as to maintian the frame ring resiliently related to the support columns for limited and substantially uniform relative movement in all directions thereby defining a universal resilient mounting with respect to each of the columns 20.

As will be apparent to those skilled in the art rotation of eccentric 84 by belt 111 cooperating with pulley 80 and motor pulley 112 insofar as the structure so far described is concerned would tend to moveframe 30, as viewed in Figures 1 and 4, to the right and downward as the eccentric mass 84 moves from its uppermost vertical position clockwise to a position 90 from that shown in Figure 3, then further downward and tothe left until it reaches its lowermost vertical position then upwardly and to the left until it reaches a position 90 clockwise removed from its lowermost position and then further upward and to the right to its initial or starting position. Such movement is freely permitted by the resilient mountings just described. Assuming a rotational speed of the eccentric mass 84 approximating 1800 r.p.m., it will be appreciatedthat this movement would result in an extremely rapid side-to-side and vertical up and down movement of the frame ring and its supported screen and screenable material. However, since gravity forces are involved causing the material to rest more or less on kthe screen for unitary up and down movement therewith, it will be appreciated that the only effective relativemovement between the material and the screen as a result 7g interposes between each of the housings 94 andthe sup,-

port brackets 44 `for the funnel 36 a second support .an nl mmu sin set screws 48 similar to those bracket 115 having an integral collar 116 slidingly fitted around the respective columns and fixed theretoby previously described. Each of the support brackets 115 at ythe free end of its arm has kintegrally formed thereon a vertically extending housling 117 centrally apertured and tapped to receive an externally threaded, hardened abutment screw 118 having a wrench head 119` adapted to permit it to be lengthwise adjusted in the housing 117 and a lock nut 121 adapted to lock it in adjusted position relative to housing L117. Each of the housings 94 has a thickened formation 123 disposed in overlying relation to its related housing 117 drilled in opposed aligned relation to its relatedscrew 118 and counterbored from its underside as indicated by numeral 124 to receive a` hardened metal plug 125. Plug125 is preferably secured in the counterbore `by means of -a driven lit and forms with screw 118 a pair of relatively adjustable, vertically opposed abutments. In normal operation these abutments interrupt the nor.- mal downward gyratory movement of the frameg and its supported screen holder 32 and screen 34 ,through a sharp abutting engagement simulating a hammer blow on frame 30. Preferably these spaced pairs of abutments are adjusted to assure independent successive engagement so that a series (in the illustrated-embodiment `three) of distinctive hammer-like blows are imparted to frame 30` as it nears the lowermost point in its gyratory movement.

These hammer-like blows cause shock waves in a vertical plane tending to vibrate screen 34 thereby causing the powdered material to be thrown violently up and down with respect to screen 34. As a consequence, any

caked material resulting from the side-to-side sifting mo- -ltion of the frame and its screen will be dashed against the screen and broken up as fast as it forms. In order to limit the amplitude of the Vgy'fratory movement in a vertical plane and make sure that frame 30, its screen and screen holder and` the material being screened is not thrown bodily from supports 2.0 and from screen 34, the present invention provides a plurality of limit stops. These stops preferably take the form of dome shaped, centrally apertured bonnets 131 respectively secured in the upper ends of the bores provided by housings 94 by cap screws 132 threaded into suitably formed apertures in ring 30 and abutment washer and lock nut assemblies 133 threadedly mounted on the upper ends of studs 134 threaded into the internally tapped upper ends of columns 20. As clearly shown by numeral 135 in Figure 4, the spacing between the opposed faces of bonnets 131 and washer and lock nut assemblies 133 determines the stroke or amplitude `of movement in a vertical direction and is quite small, in actual practice being of the order of 1A in a machine having a 24 inch diameter frame ring 30. It will be appreciated, therefore, that further shock waves, but of substantially lesser force due to the counteracting gravity forces, will be imposed on ring 30 and its supported screen and screenable ma-` terial by these limit stops. The relative adjustment'of these limit stops is again preferably selected to assure successive engagement.

From the description so far given, `it will be appreciated that the gyratory movement normally resulting from rotation of the eccentric mass on its axis is resiliently restrained in a sidewise` direction by rubber discs 105 and is positively limited in a Vertical direction by the. limit stops andabutments 118, 125.` As a conse- `quence, a definite side-to-side sifting movement is per-4 mitted by the machine of this invention while a drastically limited, high frequency, erratic, vertical dancing movement is imposed on the sifting movement. As a result of the structureof this invention, a unique screening `action is provided to betteraccomplish dry screening of material of any grain size and which alone has bee'n found capable of dry screening very tine powders.

While screen holder 32 andscreen34 may take-any suitable form, the present invention contemplates a holder in the. form ofa peripherally recessed ring (Figure l) having a shoulder 141 adapted to peripherally overlap theinner margin of frame ring 30, an axially extending, externally tapered support flange 142 of lesser maximum diameter than thev bore of ring 30 depending from the main tbody of holder 32, a clamp ring 143 internally tapered to mate with flange 142 and a series of annularly spaced studs 144 threaded intothe main `body of `holder 32 and extending freely through clamp ring 143 to threadedly receive clamp and lock nut assembly 145. In use screen 34 is laid upon the free end of flange 142 with its peripheral edges overhanging and clamp ring 143 is pressed axially onto flange 142 and studs 144 bending screen 34 into clamped engagement between the mating surfaces, of ring 143 and ange 142. Clamp and lock nut assemblies are Vthen threaded home on studs 144l to draw the screening tightly across the end of the holder ring and clamp its edges between the mating surfaces of flange 142 and clamp ring 143. At diametrically lspaced points, the periphery of the body of the holder ring is provided with outwardly protruding ears; 146 of lesser thickness than the major diameter portion of vthe V'holder ring to provide handles for lifting the holder 32 with its attached screen out of frame ring 3i).

a The present invention contemplates that ring 30 will be provided'with a pair of upstanding, vertically ribbed lugs 147 located at 120 -intervals and having-inwardly disposed arcuate faces lying along a circle having a diameter equalling the major diameter of the holder ring 32 and a` clamp screw-assembly 148 disposed 120 away from lugs 147 for forcing the holder ring 32 bodily toward and into clamped engagement with lugs 147, to takeup all side play between holder32 and frame .30. Assembly 148 comprises a threaded shaft V149 journalled in a bearing block formed on theupper face of ring 30 at its periphery and having la removable bearing cap. 151 for removably securing shaft 149 in radially disposed relation on ring30. The inner end of shaft 149 threadedly engages a pressure block 152 slidably but non-rotatably bearingon the upper face of ring 30 in position to be moved radially into and out of engagement with the side face of ring 32. A hand wheel 153 is preferably secured to the opposite end of shaft 149 for operating shaft 149.

Hold down clamps 151 are also preferably providedat diametrically opposite points on frame 30. As here shown, hold down clamps comprise integrally cast blocks 152 formed on frame ring 30 with radially disposed recesses 153 in their top faces and elongated clamp plates 154 disposed in said recesses and extending radially, inward over the top edge of .holder ring 32. Plates154 are preferably removably secured to blocks 152 by `nut locking` assemblies 155 made up of studs set in blocks 15-2 and removable lock washers and nuts threaded thereon.

Referring further to Figures l, 2 and 3, a pulley and partial belt guard 156 is preferably secured to the end ofzslceve 62 by screws 157 in surrounding relation to eccentric 84 and pulley 80. Preferably guard` 156 has a; removable cover 158 in the area of eccentric 84 providing ready access to eccentric 84, pulley 80 and belt 111 for removal and servicing.

A similar pulley and partial belt guard 159 having la removable cover 161 is provided for motor pulleyV 112. While guard 159 may be mounted in any suitable manner, it is contemplated that it will be supported from table 58 through a suitable support leg 162.

In lieu of eccentric 84, the modified` eccentric 165 of Figure'S may be employed with equalfacility in4 this Screener. As there shown eccentric 165 comprises a shaftin the form of the well known crank shaft journalled adjacent its ends in bearings 68 and 70. With the exception that sleeve 62 is provided with aslightly larger bore and that the protruding shaft end 74a is slightly shorter since it is called-upon to mount pulley 80 only, this form of eccentric isotherwise identical to that -previously described` The inventionmay be embodiedin other specific forms without departing from the spirityor essential character stics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured `by United States Letters Patent is:

l. A Screener for dry powders and the like comprising a plurality of upright support legs; universally resilient suspension means carried by said support legs; screen support means mounted on said resilient suspension vmeans; screen means secured to said screen support means for supporting a mass of loose material for screening; journal means `on said screen support means having its axis at right angles to said support -legs and substantially intersecting a vertical line passing through the centroid of mass of said screen support means and its screen means; an eccentric mass rotatably mounted in said journal means and adapted upon rotation to impart gyrating forces to said screen support means tending to move said screen support means and screen means in a path to impart a relative lateral shifting movement to said material and said screen and a unitary upr and down movement to said screen support means, said screen means and said material; and abutment means secured to said legs and arranged to intercept said screen support means at a predetermined point adjacent at least one of its vertical limits of movement to impart to said screen support means a hammer-like blow and lset up vibrator shock forces in said screen means which transmit a high velocity vertical bodily movement to said laterally shifting material whereby said material will be repeatedly dashed against said screen means to prevent caking and assure effective uninterrupted sifting of said material through said screen meanS.

-clamp washer of substantially less diameter than said second rubber disc superimposed on said second rubber disc;

.and a clamp nut threaded on said support leg into engagement with said clamp Washer to clamp said rubber discs and said spacer sleeves tightly between said washers with their marginal, peripheral edges freev for supporting connection to said screen support means.

3. The Screener of claim l wherein said screen support means comprises a ring-shaped frame having a radially directed journal socket disposed at one point along its circumference to form said journal means, and axially directed, angularly spaced, hollow housing formations adapted to freely receive said support legs and supportingly engage said universally resilient suspension means; and the major portion of said screen means beingv disposed within said ring-shaped frame. l

4. The ScreenerV of claim l wherein said eccentric mass comprises a shaft having coaxially related end'porti'ons -of `cylindrical configuration in cross-section providing journal portions and a radially offset intermediate portionl Voi? substantial mass disposed betweenfsaid end portions. i

f5. VThe Screener of claim l wherein said support legs are three in number,V said screen support means comprises a ring-like frame having equiangularly spaced, axially directedxleg socketvho'usings therein adapted Vfor attachment to said universally resilientl suspension means, and

Y salaire said journal means is disposed equidistantly between an adjacent pair of leg socket housings with its axis lying in a plane containing the center of a circle passing through the axis of said leg socket housings.

6. The Screener of claim 1 wherein said screen means comprises a rigid ring-like holder frame having an annular, axially facing, support shoulder spaced from one end, a main body section yof cylindrical coniiguration extending axially away from said shoulder toward the other end, a peripherally conical end section of lesser external diameter than said main body section extending axially away from said main body section and terminating in a transversely disposed end face; a section of screen material of desired mesh size extending across the opening defined by said end section in abutting relation to said end face and beyond the outer peripheral edge of said end face to provide an overhanging peripheral marginal section of screen material; a clamp ring having a conical internal bore adapted to matingly cooperated with said conical end section telescoped on said end section and securing said marginal section of screen material between said bore of said clamp ring and the outer conical wall of said end section; and means for adjustably securing said clamp ring to said ring-like holder frame.

7. A screener for dry powders and the like comprising a plurality of upright support legs; universally resilient suspension means carried by said support legs; a sci-eener vframe mounted on said resilient suspension means and having a generally horizontally disposed screening area for freely supporting loose material for screeningtherethrough; journal means at one side of said frame with its axis at right angles to said support legs; an eccentric mass rotatably mounted in said journal means and adapted upon rotation to impart gyrating forces to said frame tending to move said screener frame and screening area in a path to impart a relative lateral shifting movement to said material and said screening area and a unitary up and `down movement to said support frame, said screening area and the material supported thereby `for screening; and abutment means secured to said legs and arranged to intercept said frame at a predetermined point adjacent at least one of its vertical limits of movement to impart to said frame a hammer-like blow and set up vibrator shock forces in said scre-ener frame and screening area which transmit a high velocity vertical bodily movement to said laterally shifting, freely supported material whereby said material will be repeatedly dashed against said screening area to prevent caking and assure uninterrupted effective sifting of said material through said screening area.

8. A Screener comprising a screen support; flat screen means removably disposed in said screen support; a frame member for said screen support; resilient means connecting said screen support to said frame member; at least three abutment elements in said screen support; means on said frame member disposed in vertical alignment and spaced a slight distance below said abutment elements -and adapted, upon operation of said screener, to be vio- 'lently engaged by said abutment elements to impart imtheabutmen't'ifaces of said abutment elements. n l 9. A dry powder Screener or the like comprising; a

material containingpmeans including a substantially at screen; support structure including universally resilient Vconnecting means mounting said material containing means; a rotatable member having'journal means including an axis of rotation eccentric to the centroidtof mass of the rotatable member; means supporting said journal means on said material containing means with said axis substantially parallel to said substantially flat screen means; at least three pairs of abutments, one of each pair disposed on said material containing means and the other of each pair disposed on said support structure adjacent its paired abutment, said pairs of abutments being spaced apart from each other; and means to rotate said rotatable member and impart gyrational movement to said material containing means in a manner to effect violent striking of said abutments whereby said material on said material containing means will undergo both a side-toside sifting action and a high velocity up and down shattering action with respect to said screen.

10. A dry powder screener or the like comprising: a ring support; a screen tray removably disposed within said ring support; a frame structure; universally resilient mounting means connecting said ring support to said frame structure so said ring support is disposed substantially horizontal; at least three hardened abutment members disposed on the lower part of said ring structure and circumferentially spaced apart; matching abutments disposed on said frame structure disposed a slight distance below said abutment members; journal means fixed to said ring support; and an operatively rotatable member journalled in said journal means to rotate about an axis eccentric to the centroid of mass of said member, said axis being disposed perpendicular to the axis of said ring support.

11. A dry powder soreener or the likeas claimed in claim 10, wherein said ring support includes an attachment member; said journal means and said rotatable member are unitarily assembled as a support, journal means in said support and a shaft, with an offset mass, journalled in said journal means; and the unitarily assembled journal means and rotatable member are removably fastened to said attachment member.

References Cited in the tile of this patent UNITED STATES PATENTS 456,585 Morse July 28, 1891 1,120,012 Bell Dec. S, 1914 2,194,721 Piper Mar. 26, 1940 2,248,042 Chamberlain July 8, 1941 2,456,248 Berry Dec. 14, 1948 2,723,753 Cook NOV. l5, 1955 FOREIGN PATENTS 52,759 Germany Nov. 29, 1889

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