US2560581A - Shielding shoe for drums and similar filters - Google Patents

Description

July 17, 1951 N- G. LEFFLER SHIELDING SHOE FOR DRUMS AND SIMILAR FILTERS Filed March 6, 1946 2 Sheets-Sheet 1.

a,Fuly E7, 1951 N. G. LEFFLER 2,560,581 SHIELDING SHOE FOR DRUMS AND SIMILAR FILTERS Filed March 6, 1946 2 Sheets-Sheet 2 \NVE\\\`TOR @NA @MQW Patentedl .uly 17, l 195 sHlELDING-snon FORDRUMS AND WSIMILAR FILTERS Nils GustavLeiiler, sS undsvall; Sweden p'plication Marche, 1946, Serial No. 652,464 "In 'Swedenilanuary 12, 11942 (CL 2id-.199)

The present `invention relates to-ltersfoff the typed embodying Va'movable perforated nlterrnember adapted to pick up on its one'side solids from a `suspension and to discharge suspension liquid at its other side after passage through'the fo'penings't'hereof'under the influenceof a differential pressurel between said sides.'V 'Such a' filter is usually, :but `not always,v formed as 'a' rotary v cylindrical drum the peripheral surface of "which :is perforated-and provided 'with 'a ne mesh -`wire fabric for 'picking `up the solids of the suspension in which the drum ispartially submerged, hand wherein the Ydifferentialpressure" is produced either by evacuating the interior of Athe'd'runi 'or subjecting the outer surface thereof to "a superatmospheric pressure. The 'invention is especially adapted for embodiment inrotary druinflters 'for picking up solids',s`uch as bers, powders and granules, from suspensions in liquids and is more particularly concerned wthan improved construction of a 'shieldingshoe for such lters.

' It is an ob'ject of the inventionto provide a shield shoe of the kind defined which will secure a sufficiently vgood sealing Aaround that vportion of thewire fabricwhere the taking off takes place. It is anctherobject so to construct the shoethat it will in high degree be independent ofvariations said difference in pressure. It is also an object' to provide means for pressing a' sealing member of the shoe'againstthe Efilter rnerr'iber at a constant pressure.,Y A further object is Yto improve the sensitivity of the shoe," and a still further object is top'rovid'e a sealing shoe-which will close olf A'the take off 'portion "effectively in filter drums 'even if'the drum is not v'perfectly circular.

The invention will now be described 'more in detail with reference to the accompanying 'drawingsv illustratingY various lembodiments by which the invention may be realized in connection with vacuum drums for paper making but it is to be understood that the Yinvention is not limited to the features so yshown but has to be 'taken in its broadest scope.

In the drawings'Fig. 1 is a cross sectional side elevation of the takingeoff portion of a yii'lter dr'um ofthe 'cell-"free type Vand the shielding shoe according to the invention and Fig. '2 shows this slioefrorn the right, the drum" being removed and a portion `of the shoe being broken away to 'show details of construction.' Fig. A3 is a cross vsection of the shoe along the '-line A-A in Fig. 1. Fig. 2l-sh'ows an alternative ilexible Yconnection between thelstationary and 'the 'movable parts of lthe shoe. Figs. to 7 show inthe same way as Figs. 1v to 3, respectively, another embodiment-,of the invene erection of the arrow inlFig. l` and is submerged jint'o the lber vsuspension 1.- `T-h`e filter fin'elfrrber -i is-'according to this einbodilnentf'providedFwith franges vf2connected to the disc-like ends 3 of the drum'by 'means `of bolts 4. The drum is in the yusual A"way supported by-ihollow shafts or 'trun nionsrofta-ting in bearings outside the druni-in the suspension vat 'which "details are *not'sho'wn in the drawings. The iil'trate or liquid 'freed from 2bers is withdrawn in the `usual way fron''t'he interior of the drumthrough one orbcthfof :the t'runnionstosucking tubes leading to arl'sealing tank.

At thetakingsoff portionjof thelter 'where the doctor 5 is provided and Vdownv/ards Vto the l-evel of the suspension 1 the shielding shoek is arranged. The functionof the'shoe is 17o-shut olf thepoinrnunica'tion between `the interior" -of the drum and the 'outer' atmosphere part'lyffor"acil'r tating' the' removal oftheeake'and partly fo'r pre'- venting air from Ypassing vthe naked portion of the ilter'rnember' before the latter submerges .again into the suspension. In theperipheral'di'- 'rection of the 'drurnthe'shoe extends beyond this Staking'off place'bth ways and in 'theaiia'l direc# tion the-shoe is substantially' coeiitensive `w'itlfi-the length of the'drum'or atleast so asv to 'cverall inward-openings o`f the filter portion. As shown in the drawing lthe shoe is submergedrin'tothe filtrate 8 in the drum but this is not necessary for the satisfactory operation of thel shoe." in Ylter drums having low ltrate exhaustion where, consequentlm the filtrate level is low the vshoe does not reach Vor submerge into the fil-trate. Y The shielding shoe consists principally vof two main par-ts, the stationaryshield member `or support 9 bei-ng- `shaped iand=constructedso as lto withstand the' pressure differences encountered in Vvacuum filters, and' the movable sealingmember` I-IJ being 'shaped-and constructed substantially airtightly toiclose off'the take-oit yportion and 4adjacent portions of the vlilter by' sliding against and closingupwthe fsi'eving or Aperforated. section of the drum.

suited for water lubrication.

In the embodiment illustrated in Fig. 1 the support 9 and the sealing member I0 enclose a substantially liquidtight or airtight chamber I I which communicates with the outer atmosphere or with a source of pressure medium (a gas or a liquid) by means of the conduit I2. So as readily and, if desired, controllably to secure the shoe to a bracket or the like, not shown, the support 9 is equipped with attaching feet I3 having borings I4 for securing bolts. The brackets may be secured to a stationary shaft arranged in the centre of the drum. By turning this shaft, which may, if desired, be done during operation, the position of the shoe in the peripheral direction can be regulated according to requirements and running conditions.

'Ihe taking off portion of the drum being usually situated near the level of the suspension the shoe will usually have a vertical position. The sealing member I is pivoted about two pins I5 arranged in the axial direction of the drum at the lower end of the support 9, the holes receiv- ,ing said pins in either the support 9 or the sealing member Ill being oblong in cross section with their elongated dimension extending substantially perpendicular to the support 9, i. e. radially of the drum. Being movable about these .pins I5 to and from the filter member I of the drum the sealing member I9 can be resiliently pressed against sealing surfaces of the filter member, for instance by means of springs I6. In

order to reduce the pressure against the lter or,

if desired, to obtain a small interspace between the sealing surfaces of the shoe and the lter portion rolls I1 may be provided on the sealing part Ill pivoted about pins I9 in brackets 26 secured to the upper portion 2| of the sealing member I0 in such a manner that the rolls I1 will run along peripheral portions of the lter member outside its perforations. In order to facilitate the regulation of the position of the rolls in bracket 20 the pin shaft I9 is preferably so shaped that the axis of rotation of the roll I1 is eccentric to that portion of the pin I9 Which bears in bracket 20 whereby the roll I1 can be moved in the radial direction of the drum simply by rotating the pin I9 more or less. By using for the roll I1 ball bearings the wear of the roll will practically be limited to its outer running surface and the wear of that surface will in any case be less than that of the sliding tightening portions of member I0. For diminishing the risk of jamming, the portions of the sealing member I0 sliding against the drum or the sliding surface of the drum may consist of or be coated with some suitable, relatively soft material such as hard rubber, soft rubber or artificial resin products. Along with the wear of roll I1 the sliding surfaces will then be successively ground so as to t closely to the friction surface of the filter member independently of the wear of the roll.

In order further to insure a good sealing in the axial direction of the drum between the outer atmosphere and the interior of the drum, i. e. to prevent leakage of air into the drum by a flow axially along the surface of the sealing member I9 to the ends thereof and thence around the ends into the drum, the sealing member I0 may be provided with grooves 22 for housing sealing bars 23, which are resiliently pressed against the peripheral running path I8 of the filter member, for instance by means of springs 24. The

bars 23 are preferably made from a material In the embodiment shown in Fig. 1 the lower .edge 25 of the sealing bar 23 and the end of the groove 22 on Which said edge rests are bevelled downwardly toward the surface I8 of the lter member so that the friction between the surface I8 and the bar will cause the latter to be wedged against the former.

For securing an eicient sealing between the support 9 and the sealing member I9 sealing rods 26 are movably provided in grooves 21 of the sealing member I0. Such rods are preferably provided at the upper part and along both sides of the sealing member. The grooves 21 may communicate with chamber I I through hole 28 whereby the sealing rods will be exposed to the pressure prevailing in chamber I I and, thereby be pressed against the sealing surfaces 29 and 3|] of the support 9. It is, of course, possible to provide sealing rods also at the bottom of the shoe but in the embodiment shown in the drawing the contact surfaces 3| and 32 are preferably by being ground to each other arranged to seal suiciently and effectively against each other. Said contact surfaces are preferably cylindric having their axis of rotation coinciding with the centre of the pivot pins I5.

Since the movement between the support 9 and the sealing member I0 is usually relatively small the connection between these parts may be carried out alternatively as shown in Fig. 4. A flexible plate 33 is liquidtightly or airtightly secured to the support 9 and the sealing member IU by means of bolts 34. For preventing the bolt heads 34 from cutting down into the plate 33 ribbons 35, for instance of iron, may be interposed along the plate 33. By this means an absolutely airtight but nevertheless flexible connection can be obtained.

By providing a channel or the like 36 in the surface of the sealing member I9 facing the filter member at the upper portion of the shoe it is possible to connect that portion of the filter I having already7 been freed from the ber cake and consequently been opened to the atmospheric pressure to adjacent portions still covered by the bre cake and therefore still being under vacuum. By this means the lter cake will be loosened beforehand and its removal by the doctor 5 will be facilitated. Although valuable in cell-free devices or apparatus of the kind shown in the drawings having a foraminous plate I for supporting the wire fabric said connection channel is much more important in cell filters where the shielding shoe slides against the inner portions of the various big cells or compartments into which the periphery is subdivided in that case. By connecting the channel 36 with a source of pressure medium this effect can be further increased and the cake can be, so to say, blown away from the lter. medium to channel 36 the pipe 31 is by means of flexible pipe 38 connected to the inlet nipple 39 of the channel 36. In case gaseous pressure medium is used in chamber I I it will be sufficient to connect channel 36 with chamber II whereby the conduit 31, 38, 39 can be dispensed with.

In case the fluid or pressure medium in chamber II is water supplied through pipe I2 all seals between the support member 9 and the sealing member III can be made with relatively great clearance so that the different parts are more easily movable relative each other, because the leakage of water from chamber I I to the interior of the drum will within certain limits not have any detrimental influence on the operation of the apparatus.

For supplying pressure aseogssi "When fthe :shielding shoe Vsubnfierged inrthe filtrate liquid the sealing will usually beusufficient at 'the lower end. Sometimes, however, some Aair may leak into the filter drum around Athe .bottom of `the shoe and for counteracting `such leakage, particularly when the ltrate "level is near vtor below the bottom of the shoe, water can be injected as by the perforated pipe 4U supplied with 'pressure water through pipe 4l either from outside or. as the case may be, from chamber Il. The perforations should be placed so that'the injected water will be supplied to the place r.of leakage.

It A.often happens that the .big filter drums are not exactly circular .but :are instead `more .or less irregular in shape. Foreliminating, at least partly, this irregularity the inner portions of the sealing member lf! may, according -to one embodiment of this invention, be made flexible or elastic. Thus the portion between the sealing details proper, that is, between the upper 4part 2l and the bottom part, for instance down to theA pins I5.' and between the grooves 22, may be made of flexible material such as thin steel plate. In a further development a flexible sealing member is secured about its `entire periphery directly to the stationary member 9 and is then resiliently movable against the filter and performs its sealing function by abutting against the surface to be shielded off. 4Such a construction would be similar to that illustrated in Fig. 4, modified to the `extent that the grooves 22, bars 23 and springs 24 would be omitted and the Vmember I0 would be formed of a suitable flexible material.

' In Figs. 5-8 another embodiment -.of the invention is illustrated. Whereas in the embodiment previously described the main members of the shielding shoe were hinged to each other at the bottom by means of pins I5 and sealing member HJ of the latter embodiment is movably connected to the support member 9 by means of -a pair of arms 43 or 54, respectively, each of 'which connects, preferably, an intermediate point 42 of member lil with a point 45 on the support member more or less at the end of the shoe, .pref-v erably at the upper end. The sealing member I of Fig. is pivotally attached to arms 43 by means of the .pins 42 and the other end of each arm 43 is pivotally secured to a bracket 44 on the supporting member Si by means of the pin 45. By virtue of this mode of attachment the sealing member id is movable against the filter member l not only unilaterally about the pins 42 lbut through its entire length. VIt is, .of course, possibleinstead to connect an intermediate point of the stationary member 9 with the upper or the lower end of member lll.

By rep-lacing the pins 42 and 45 by round balls 46 and 4l, respectively (Fig. 8), the sealingmember l) will be movable in all directions. The balls 45 and il are journaled in spherical bearings '48 and 49, respectively, having spherical covers 5d and 5|, respectively, secured to the bear-ings by means of bolts 52 and'53,frespectively. The balls 46 and 41 are-connected to each other by -the arm '54. Preferably two such connections are vv`provided in about the same place as the arms 43 of Figs. 5J?, although a single connection of this construction positioned centrally of the shielding shoe would vobviously enable substantially universal movement of -the sealing memberl.

When water is used inside the shielding shoe leakage nwater V'may escapeatthe upper .portion of the shoe and wet the-driedfibeicake. "For protecting the latter a baille `2l is .provided .at .the top fof `the sealing member I0 preferably by shaping -t-he top= of that `member adequately.

Apart from the hinging means characteristic to .this embodiment the various details disclosed in connection with the description of vthe embodiment according to Figs. 1 4 may :be .applied to the present embodiment. Thus the variousseali'ng bars 23 and 26 may be provided and runner rolls lil caribe used at the top aswell as at the bottom,

In :any of the embodiments the chamber Il may freely communicate with the vspace between the sealing member 1.!! and the filter member fl provided a ysubstantially atmospheric pressure' is prevailing in chamber I l.

Although particularly described in connection with 'filter drums submerged Yin a suspension of ber it is to be understood that the invention 'can be employed equally `well in conjunction with othertypes of `pickingxup machines forsuspended solids where these are picked up on a foraminous member by the action `of a pressurediierence between-opposite sides of the foraminous member. Used in connection with iilter drums in which the suspension is poured into the interior ofthe drum and the filtrate is drawn of outside by the aid-0f a lower outside pressure the shielding shoe ofthe present invention shall be arranged at the outer side yof the drum and be shaped accordingly. Employed with cell lters in ywhich the cells open at lthe one or 'both ends of the drum the shoev of the invention will Vbe placed over an appropriate number of `such cell openings at the end or ends of the drum.

As' used in the specification and claims hereof, the words seal and sealing are `notintended to apply solely to conditions in which a perfect seal is eifected, because frictional seals .are seldom, Vif ever, absolutely airtight or watertight. Instead, these words should be interpreted to mean'that the leakage of air, water or other fluid is inhibited to the maximum Adegree practicable in'structures of the character'd'e'scribed, and that where the seal is made vby frictional engagement between relatively movable members, a limited lamount of leakage may exist without seriously--impairing the utility of the invention.

What Yis claimed is:

l'. A shielding shoe for filtersof the type embodying a movable perforated iilter member adapted to pick up on its one side solids from'a suspension and to discharge `suspension liquid 4at itsother side after passage through the-openings thereof under the influence oi Va diiferential pressure between said sides, said shoe comprising -a stationary shoe member having walls forming a 'chamber having an opening facing said filter member, `a sealing shoe member interposedbetween said lter member and said stationary shoe member and so supported by the latter as to 'be capable of limited movement relative theretoy toward and awai7 from said nlter member, said sealingshoe member having anend wall at least a portion of which is adapted to engage one side of said filter member to shield off a limited nu'mber of :the discharge openings thereinand alperipheral wall portion juxtaposed to the wall iportionzof said stati-onary `shoe member surrounding said chamber opening, and means for sealing the space 'between the juxtaposedl wall portionsy of said stationary and-sealing shoefmembera'whe'reby said members form an enclosure for the space within saidchamber and 'that between the chamber opening andthe adjacent portion of `said lter member, .the outer surface of vsaid sealing :shoe

member between the portion of the end wall adapted to engage the lter member and said sealing means having substantially no portion thereof exposed to an uncounterbalanced pressure component perpendicular to the lter member and arising from the atmosphere surrounding both shoe members.

, 2. A shielding shoe as claimed in claim 1 wherein the area of said enclosure as projected on a plane substantially parallel to the filter member is substantially equal to that of the filter member engaging portion of said sealing shoe member as projected on the same plane.

1 .3. A shielding shoe for filters of the type embodying a movable perforated lter member adapted to pick up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the innuence of a differential pressure between said sides, said shoe comprising a stationary shield plate, a sealing member movable in a direction substantially perpendicular to said shield plate and having a restricted area of its outer surface adapted to engage one side of said filter member to seal off a limited number of the discharge openings therein, and means for sealing said shield plate and sealing member to each other to form a substantially watertight chamber between them, the outer surface of said sealing member between said sealing means and said restricted area being so shaped that all components of pressure exerted against said surface perpendicular to said restricted area are substantially counterbalanced.

4. A shielding shoe as claimed in claim 1 including means for supplying fluid under pressure to said enclosure.

5. A shielding shoe for filters of the type embodying a rotatable drum having a pervious filter member adapted to pick up on its one side solids from a suspension and to discharge suspension fluid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a stationary shield plate, an arcuate sealing plate supported by said stationary shield plate and adapted with at least the border portions of a restricted area thereof to engage one side of said lter member to seal olf a limited number of the discharge openings therein, said sealing plate being movable relatively to said stationary shield plate toward and away from said filter member about an axis parallel to the axis of said drum, and means for sealing the space between the relatively movable edges of said plates, the geometrical projection of the area enclosed by said sealing means on the plane of said filter member being substantially equal to the geometrical projection of said restricted area on the same plane.

6. A shielding shoe as claimed in claim 5 including a pin tted at one end of said stationary shield plate and forming a pivotal connection between the latter and said sealing plate.

'7. A shielding shoe for filters as claimed in claim 6 wherein the shielding shoe is adapted to be mounted in a substantially vertical position and the pivot pin is located at the lower end of the stationary shield plate.

8. A shielding shoe as claimed in claim 5 including a pin parallel to the axis of said drum carried by said stationary shield plate at one end thereof, the adjacent end of said sealing plate having a hole in which said pin is received, the cross section of said `hole being oblong with its elongated dimension extending substantially r.- dially of said drum.

. 9. A shielding shoe as claimed in claim 1 including pressure means in said enclosure for resiliently urging said sealing shoe member away from said stationary shoe member in a direction substantially perpendicular to the side of the filter member adaptedto be engaged by said sealing shoe member.

10. A shielding shoe as claimed in claim 9 wherein said pressure means comprises at least one spring.

11. A shielding shoe as claimed in claim 1 including means for supplying a fluid under pressure to the enclosure formed by said shoe members for urging said sealing shoe member away from said stationary shoe member in a direction substantially perpendicular to the side of the filter member adapted to be engaged by said sealing shoe member.

12. A shielding shoe as claimed in claim 11 wherein the portion of the end wall of said sealing shoe member adapted to engage the filter member is provided with a depression of limited area lying wholly within the confines of said portion so as to provide a space between the depressed area of the shoe member and the adjacent side of the lter member, and which includes means for establishing communication between said space and the enclosure formed by said shoe members.

13. A shielding shoe as claimed in claim 11 including means for establishingI communication between the enclosure formed by said shoe members and a restricted area of the portion of the end wall of the sealing shoe member adapted to engage the filter member.

14. A shielding shoe for filters of the type embodying a movable perforated filter member adapted to pick -up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the inuence of a differential pressure between said sides, said shoe comprising a stationary shoe member, a sealing shoe member interposed between said filter member and said stationary shoe member and so supported by the latter as to be capable of limited movement relative thereto toward and away from said lter member, said sealing shoe member having a wall adapted to engage one side of said lter member lwith at least the border portion of a restricted area of the outer surface thereof to shield off a limited number of the discharge openings in said filter member, said stationary shoe member having a rigid wall portion adjacent the periphery of said sealing shoe member, and means for sealing the space between said rigid wall portion of the stationary shoe member and the periphery of said sealing shoe member to shield the inner surface of the latter from the pressure of the atmosphere surrounding both shoe members, the outer surface of said sealing member exposed to said pressure being so shaped that all components of force exerted thereby against said surface in directions perpendicular to the filter member are substantially counterbalanced and the geometrical projection of the area enclosed by said sealing means on the plane of said filter member being substantially equal to the geometrical projection of said restricted area on the same plane.

15. A shielding shoe as claimed in claim 14 including rolls carried by said sealing shoe member adapted to run on running surfaces associated with said filter member.

16. A shielding shoe as claimed in claim 14 wherein said seal shoe member includes elongated sealing elements yadjacent the edges thereof parallel to the direction of movement of said filter member and bordering said restricted area, and means for resiliently urging said elements outwardly from said sealing shoe member into engagement with said filter member.

17. A shielding shoe as claimed in claim 14 including means for connecting said sealing shoe member to said stationary shoe member for movement relative to the latter comprising at least one arm pivotally connected to both of said shoe members.

18. A shielding shoe as claimed in claim 17 wherein the pivotal connection of said arm to at least one of said shoe members is so constructed and arranged as to permit movement of said arm in a plurality of planes.

19. A shielding shoe as claimed in claim 14 wherein the portions of said sealing shoe member adapted to have engagement with said lter m-ember are provided with sliding surfaces consisting of a relatively soft material, such as rubber.

20. A shielding shoe for filters of the type embodying a movable perforated filter member adapted to pick up at its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a stationary shield member having walls forming a chamber open at one side facing said filter member, a sealing member supported by said stationary shield member and movable relative thereto, said sealing member having a wall extending across the open side of said chamber and adapted to engage one side of said filter member to shield a limited number of the openings thereof from said differential pressure, and means for connecting said sealing member to said shield member and completing the closure of the open side of said chamber to render the latter substantially liquidtight, said means comprising a flexible strip of liquid-impervious material xed both to the periphery of the wall of said sealing member and to said shield member.

21. A shielding shoe for filters of the type embodying a movable perforated lter member adapted to pick up at its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof Iunder the inuence of a differential pressure between said sides, said shoe comprising a stationary shield member having Walls forming a chamber open at one side facing said filter member, a sealing member supported by said stationary shield member and movable relative thereto, said sealing member having a wall extending across the open side of said chamber and adapted to engage one side of said filter member to shield a limited number of the openings thereof from said differential pressure, and means for completing the closure of the open side of said chamber and rendering watertight the spaces between the relatively movable portions of said sealing and shield members including a groove formed in one of `said members, a sealing element housed in the outer portion of said groove and projecting therefrom into frictional engagement with a cooperating sealing surface of the other of said members, and means including a conduit connected to the inner portion of said groove behind said sealing element foi1 supplying a liquid under pressure to said groove to hydraulically force said sealing element into engagement with said co0perating sealingI surface.

22. A shielding shoe as claimed in claim 14 including means for mounting said sealing shoe member for pivotal movement relative to said stationary shoe member about an axis substantially parallel to the direction of movement of said filter member.

23. A shielding shoe as claimed in claim 14 including means adjacent the end of the shoe where the filter member leaves the shoe for supplying liquid to the space between said end of the shoe and the filter member so as to prevent the leakage of air through said space.

24. A shielding shoe for filters of the type embodying a movable perforated lter member adapted to pick up at its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a stationary shield member having rigid Walls rformingI a chamber of substantial area open at one side facing said filter member, an impervious flexible sealing member secured at its periphery to the walls of said stationary shield member and cooperating therewith to close the open side of said chamber and render the latter substantially liquid-tight, the exibility of said sealing member rendering it movable in a direction substantially perpendicular to said filter member, and means in said chamber for pressing said sealing member away from said shield member and into contact with one Side of said filter member t0 shield a limited number of the openings thereof from said differential pressure.

NILS GUSTAV LEFFlLiER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,211,739 Miser Jan. 9, 1917 1,377,765 Elling May 10, 1921 1,627,882 Berry May 10, 1927 1,848,478 Haug Mar. 8, 1932 1,876,399 Catala et al. Sept. 6, 1932 1,937,426 Formaini Nov. 28, 1933 2,053,664 Hiller et a1 Sept. 8, 1936 2,274,641 Abbott et a1 Mar. 3, 1942 2,283,495 Evans May 19, 1942 2,285,649 Evans June 9, 1942 2,418,777 LeClair Apr. 8, 1947

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