US2651419A - Vibrating screen - Google Patents

Description

Sept. 8, 1953 G. ovERs'rRoM Er AL VIBRATING SCREEN 3 Sheets-Sheet 1 Filed June 30, 1950 d www W l M@ u ms@ m n WEQEQT n OO. III E V TMMQN y ZW a o Sept. 8, 1953 l G. ovERsTRoM Er AL y 2,651,419

VIBRATIG SCREEN Filed June 30, 1950 SvSheets-Sheet 2 INVENTORS. 62504965 Ovsesreom CoA/@Ao OVEQSTQOM GUSTA vs' A. OVEeszeo/w,

Sept. 8, 1953 G. OVERSTROM E1- A.. 2,551,419

VIBRATING SCREEN Filed June 3o, 195o 3 sheets-sheet 3 (il l INVENTORS. a 13 @Eo/26E Ovsesneo/w, if' CoA/@Ao OvEesneo/w,

@warm/E A. OVEQSTHOM, 1c Q' Patented Sept. 8, 1953 VIBRATING SCREEN George Overstrom, Alhambra, Conrad Overstrom. Altadena, and Gustave A. Overstrom, Alhambra, Calif.

Application June 30, 1950, Serial N0. 171,458 15 Claims. (Cl. 210-196) This invention relates to improvements in vibrating or oscillating screens or analogous apparatus particularly suited to the screening of physical mixtures of liquids and finely divided solids, as for example vegetable oils of the edible variety such as palm oil, corn oil, olive oil and peanut oil.

An important Object of this invention is to provide a novel combination of elements forming a screening apparatus in which the elements are so related that there is imparted to the screen cloth forming part of the combination a motion which will agglomerate the finely divided solid content of a liquid feed and continuously cause this agglomerate to travel to the reject end of the screen cloth without interruption in its forward travel and at the same time drive the liquid portion of the mixture substantially free of solid content through the screen cloth.

Another impor-tant object of this invention is to provide a combination of this nature in which the motion of the screen cloth is such as to agglomerate the fragile solid content of a liquid and convey this solid content the length of the screen clothv Without disintegrating it, even though it may be relativelyk easily disintegrated.

Another object of this invention is to provide a screen combination in which the component parts are so arranged as to produce a motion in the screen box and the screen cloth mounted therein that tends to drive the liquid ingredient of a feed of a mixture of liquid and solid material through a fine mesh screen cloth and at the same time agglomerate the solid content of the mixture so that it will not pass through the meshes of the cloth even though line enough to do so in its original state.

Another object of this invention is to provide a vibrating screen combination for screening liquids with a solid content by a motion of the screen cloth which will agglomerate the solid content suspended in the liquid and cause this agglomerate to pass off the end of the screen cloth even though the openings in the cloth are larger than the particle size of the solid content of the mixture passing over the screen cloth.

Another object of this invention is to provide a vibrating screen combination including a screen cloth which imparts a motion to the cloth such as will drive the liquid component of a mixture of liquid and solids through the fine mesh of the screen cloth while at the same time rejecting the undersized solid content of the mixture.

Another object of this invention is the provision ofV a novel method of imparting motion to a screen cloth so that a liquid feed having nely divided solid material suspended therein fed to the screen cloth will have imparted to the liquid a motion which will cause the liquid to be driven through the screen cloth and its solid content to agglomerate and travel to the reject end of the screen cloth without interruption in its forward motion along the cloth.

Other objects of this invention will be made apparent from the following description of several forms of screening apparatus combinations in accordance with this invention.

In the accompanying drawings,

Figure 1 is a side elevational view of one form of screening apparatus in accordance with this invention; l

Figure 2 is a transverse, cross-sectional view taken on the line 2 2 of Figure 1;

Figure 3 is a cross-sectional detail view taken on the line 3-3 of Figure 1 Figure 4 is a. vertical, central, longitudinal, cross-sectional view through the apparatus of Figure 1;

Figure 5 is a side elevational view somewhat diagrammatic in form illustrating a modied screening apparatus in accordance with this invention;

Figure 6 is a similar view of a still further modification of this invention;

Figure 7 is a similar view of a still further modified form of apparatus in accordance with this invention;

Figure 8 is a detailed cross-sectional View taken on the line 8-8 of Figure 7 Figure 9 is a side elevational view of another modification of this invention showing the screen box supported from above; v

Figure 10 is a diagrammatic side elevational view of the screen box of any one of the forms of apparatus herein disclosed showing the positions along the screen at which cards of motion were taken;

Figure 11 is a diagram of the motions of the screen box and screen cloth contained therein at the points along the screen box as indicated in Figure 10; and

Figure 12 is a diagram of motion of an orthodox screening machine showing the motion 0f the screen box and the cloth contained therein at the feed and discharge ends, Such as is produced in vibrating screens of the type illustrated in United States Patent No. 1,621,949 granted March 22, 1927, to Gustave A. Overstrom, and United States Patent No. 1,995,435, granted March 26, 1935, to Gustave A. Overstrom.

after a short travel along the screen path sothat a separation of this solid content fromthe. liquid carrier could not be effected.

The screening machines otk this. invention-are.-

so constructed that the motion of the. screen.

cloth is such as not to permit the solid content of hot palm oil, for example, to pausednlits trail/.el

along the screen cloth, with the'result that it quickly agglomerates without disintegration and` is discharged over the end-g f the cloth While the liquid. component. is driven through the cloth substantially.- free of.` solid-z content.

Prior tothis invention ithas not, been possible to free palm oil Qfitsundesirable solid content by` means of screens off the vibrating type. lldible` oils are generally. expelled through such machines asAndersonorlirench expellers, although in some cases solyent. extraction and high pressure steam. extraction have. been used. None. of; these. methodsare, completely satisfactory for.- many reasons. weil. understood in the art. For example, when. edible. oils of this type are expelled there-.isa dry Ine-alv discharged from one end of theexpeller ande an. oil bearing an undesirable quantity of. meal-.discharged from the other end of the expeller. In an effort to remove thismealafrom the. oil-.itis placed in settling tanks and thesupernatant liquidis drawn off-butt asiswell known, this liquid still contains minute particles which..in-.the.case-of palm oil areE phosphatides Asis well understood phosulla.tittN are .triehydr-ic. and. one OH. component generally goes with any glycerine-Dresf. ent, andl another goesito.` form a fatty or oleic acid.V ares/ult. these componentsy are. easily subject tov oxidation.. resulting in. decomposition which is the source of an undesirable stench. Prion to. this. invention: no. effective method or apparatus has been. developedto sufficiently eliminate. these. difcultieswitn the result that it .has been. commontoshipedible oils such as palm oil under refrigeration.

Iffthe ysolidgcontentl .of such oils whichv average l0 microns in size-.can be4 removed or substantially-` so, such oxidation is sloweddown andfurther.- pr-,ocessingA simplified.

Since the solid contentof. such oilsis as fineasllO4 microns in size, the vibratingscreening ma. chines.;ofgthisinyention employ iinemesh screen cloths.. of;v al mesh, for. example, of 120 andfiner. InLsuome;case;.screns. of 20u square mesh have been used. As disclosed herein when such fine screen cloths. are vibrated. through. paths. of. H- tionsuch as .wilLbe hereinafter disclosed these finel particles. are.. caused to agslomerate and travel continuously along the screenclothto thev rejectend.- The. liquid` component of such Oils for.v examplenthat passesthrough the screen cloth` is further processed ina centrifuge.V It iscommon. practice .td centrifuge the oil after asmuch of thelsolidvcontentdas possible has .beenremoved' therefrom. TheK oil recovered by prior. processinghas contained sufficient solidcontent to cause the.` centrifuge to. plug atp its jets. Without the.;

use of the. Screening, machines.. o this. invention 4 the centrifuge had to be shut down after a Short run and the bowl cleaned. Centrifuging the liquid component recovered from the screens of this invention has been simplified by reason of the fact that the running time of the centrifuge without cleaning has been increased from a fraction of an hour to a total time between bowl cleanings, as shownl by the followng table:

10Q; 10U mesh 120 x 120 mesh 150 x 150 mesh 200 x 200 mesh yhouriY l 3 hours 8 hours 4i hours tudinal side membersconnected. by suitable crossbraces such as thev angle irons 23. A pair-Voi brackets 3 are attachedtof the feed end of; the-V screen box I at opposite sides andon-the bottom thereof, and similarly apair of brackets 3'are attached to the opposite end of the screen boxY I on opposite sides thereof at thertop. Each of" these brackets has mounted therein a transversely extendingpintle' which may be mount'- ed on their respective brackets in any. suitable manner. Mountedonthe pintlesA 3" at the centers are the involutelycoiled .springs 4 vhaving tangential tailsV which are, firmly attached by means of suitable clamps 4'.' to.. the base frame 2; The base frame` may` bev built up. in any suitable and well known mannerto provide a support for the screen box through. thespringsA. Mounted' on the side frames ofthe screen boxl toward the discharge end of, the screen box are a pair of brackets 5.. which. are constructedv to provide a mounting forl the-driving-member 6 which imparts vibration to-.thev screenbox. This driving.

member in principleconsists .of a rotating unbalyanced weight which may. be provided in various forms, a very suitableone of which is disclosedin United States Patent4 No. 2,304,198A granted December 8, 1942, toGustave A. Overstrom et al. This driving mechanism for imparting vibration to the screen box as shownin detail in-that patent is entirely suitable for usefin thevarious. screening combinationsherein disclosed.

On the end of theunbalanced shaft forming part of the driving-.mechanism 6*, is mounted a pulley 'l connected by a belt 3 to; a drive'pulley mounted on the shaftof. the drivingmotorl 9,-

which motor in turn is-gsupported by a suitable cradle 9', attached tdthesideofthebase frame 2, as shown in Figure 1.

At the feed end.of.the.screenboxl is a framework l0 of any suitable-constructioncomprising vertical and crossmembersgrmly securedtothe base frameV 2 and-supporting aliquiddistribur..

tor box Il having arlfeed pipe connection.. I2.

a sheet trzuisverselyA .ofthe .screen box. ontothe onto 'the screen cloth la. This screen doin isr mechanism. The cloth itself is provided at each,

end with a reinforcing strip I4 of hook shaped formation in cross section, Ias clearly shown in Figure 4. Likewise attached to the longitudinal side edges of the screen cloth are reinforcing strips I4a of hook shaped formation in cross section, as clearly shown in Figure` 3. Extending longitudinally of the side members of the box I are a pair of angle irons I (see Fig.3) attached to the box side members in any suitable manner, as by welding in the case of metal. The screen cloth I3 extends transversely ofthe box and rests at its reinforced side edgeson the angle supports I. The screen cloth is stretched transversely by means of U-shaped channel members I extending longitudinally of the screen cloth and fulcrumed on their upper edges on the box side members I, as clearly shown in Figure 3. The opposite longitudinal edge of the channel members I5 engages in the hook shaped reinforced edge I4EL of the screen cloth throughout its length. Bolts I1 pass through a strip I5 extending along the outer faces of the channel members I5, properly positioned by means of dowel pins I5" mounted in the members I5. The bolts, of which there are several, as indicated in Figure ll, are engaged by means of nuts I6 bearing on suitable formations in the box side members I so that as the nuts are tightened the channel members I5 fulcrum in a direction to stretch the screen cloths I3 transversely. A series of U-shaped springs 40 lie between the channel members I5 and the frame members I, so that the terminal ends of each spring engages in socket 4| secured to the member I, and the closed end bears against the inner face of the channel member I5 and passes under pin I5. These springs aid in the outward fulcrum movement of channels I5 as the nuts I6 are eased off, and the member I5 is supported by the pins I5" resting on them.

The screen Icloth I3 is stretched longitudinally in the following manner. An angle iron I8 extends transversely of the box side members I and is permanently secured between them in a position so that the hook reinforcing strip I4 at the feed end of the screen cloth is engaged thereover, as shown in Figure 4. On similar principles channel member I8' is secured adjacent the discharge end of the screen. The reinforcing hook shaped strip I4 at this end of the screen cloth engages in hooks or projections on a tubular member I9 which rests on the channel I8 and is rotatable on its axis. A series of clamping devices comprising nuts and bolts 20 and clamping blocks engaging the tube I9 are provided to clamp this tube in various rotated positions on the fixed angle iron I8. Thus with reference to Figure 4, it will be seen that by rotating the tube I9 the screen -cloth I3 can be stretched longitudinally against the resistance of its anchored opposite end. When stretched to the proper degree longitudinally the tube I9 is clamped by means of the nuts and bolts 2U'. As indicated in Figure 4, the bolts 20 pass through diametrically aligned slots in the tube I9 of sufficient length to permit of sufficient rotationalmovement of the tube I9 to insure proper tensioning.

There is shown in Figurev 3 one'of several 1on-` 6. gitudinally extendingV substantially .if-shaped beam members 22 which are mounted uponv the transverse reinforcing members 23 of the screen box. The longitudinal top edge of each of the members 22 is covered with a resilient covering such as soft neoprene rubber to minimize the Wear of the screen I3 at the point of engagement with these supports for the screen cloth.

Supported under the screen box and in the base frame 20 is a stationary collecting and drain pan 24 having a discharge connection 25 through which the liquid which passes through the screen can be withdrawn. A drip strip 24 insures that liquids are directed into the drain pan 24.

Several of the more important structural features and relationship of component elements of this structure are best emphasized at this point. From the above description it will be seen that the frame forming the screen box and in which the screen cloth I3 is mounted for vibration therewith, is supported at each corner by means of involutely coiled springs which in turn are fixed upon the base frame 2. It will be noted that the driving means 6 which imparts vibration to the screen box is mounted towards the :screen cloth I3 terminates at its high end at a point somewhat spaced from the supporting springs for the high end of the screen box and terminates at its other end at a point spaced inside of not only the supporting springs 4 for the lower end of the box but of the driving mechanism 6. Thus the driving member 6 is mounted relatively close to the supporting springs at the lower end of the box and near to or beyond the reject or discharge end of the screen cloth. These are Very important relationships of elements in order that there be imparted to the screen cloth itself a motion which will effect the separation of solids from liquids of the type previously described in a highly efficient manner.

As those skilled in this art will appreciate or can learn by simple test, there can be some variation in the location of the driving member 6 with respect to the adjacent screen box support while attaining satisfactory results, but it is essential to the type of operation desired by the mechanism herein disclosed that the driving element 6 be mounted on the screen box beyond the reject or discharge end of the screen cloth. This relationship of the driving element to the screen cloth will be found in all the modifications to be hereinafter described. In part at least it is due to this relationship that the finely divided solid content of a liquid will be agglomerated without disintegration and caused to travel continuously to the discharge end of the screen cloth. In the modification illustrated in Figure 5, the general construction of the parts is similar to that previously described. A box base frame 2 of any suitable construction is provided on which is mounted the screen box I. In this case the lower end of the inclined screen box is supportedV case the driving element E which isthe same ask that previously described; is also mounted on the( aces1,419-- screenbox I, but a somewhat spaced rela--VY yond the reject end ofthe screen I3. The dif- .ference in this construction over those previously described is in the fact that' the involutely coiled .springs d for the 'high endof the box are mounted on opposite sides as in the'case of Figure 1 and are attached to the top edges` of the side members of the box I. Inorder toaccomplisli this the base frame 2 is provided with rigid uprightsy 2' of sunicient height to provide a supe port for the tails of the involuted springs- 4 through the agency of the clamps 4.

The modification of Figure 7 is similar to that of Figure l with two exceptions, the iilst of which involves some spacing of the driving element S from the adjacent resilient supports for the screen box and yet beyond the discharge end of the screen cloth I3, asin all previous cases. The real difference in the construction herein illustrated is in the resilient mountings for the screen box l. In the arrangement of Figure i the resilientvsupports comprise involutely coiled springs, whereas in the arrangement of Figure 7 they consist of resilient discs 2'! of rubber or other suitable material. The supports for these discs in this case have been modified to accommodate'this vdiiference in construction and consist of circular housings 543 mounted on the base frame 2 in Whichthe resilient discs 27 are mount-V ed. The screen box is provided with brackets'S as in the case of Figure l, andasrclearly shown in Figure 8, are providedwith transversely extending pintles 3' which lie in central apertures in the discs' 21. Thus these resilient discs or bushings 21 Serve to support the screen box for freedom to effect the desired motions of .the screen box under the driving forces of the vibrator E in a manner quite similar to the -motions accomplished when using the involutely coiled springs.

As illustrated in Figure 9 the screen box may be supported from overhead. 'The screen box, asin previous cases, is provided with the tiri-v ing element 6 mounted 'beyond the dischargeend of the screen I3. The 'box itself is supported .at each corner from the ceiling or any V.suitable overhead structure 28fby means of 'helically coiled springs 29 and suitable attaching links at their respective ends. It will be seen ithatthegen'eral arrangement and location of the supporting spring elements, the vibrator element `and the screen cloth is the same as that previously -escribed, the difference being that Ithescreen box is 'provided with a hanging. support.

In the operation of all of these screensthe movement of the iscreen cloth under the action of the driving 'element 6 isfsubstantiall-ythe same andcldthfatthe points l toof Figure 10, the component ci vertical movement thereofV gradually` decreases from position Ik to a point midway of positions 3 and 4 (the neutral point), and then gradually increases from that midpoint to thediseharge end. This illustration applies espe'ciallyl to all of the forms of screens shown herein; with thc-exception'of that of Figure 5 in which the motion varies invits detail, but is substantially' the same in its over-all effects. As illustratedinzFigure 11, the screen cloth at the feedfendto theleft of-the neutral point vibrates in aclosed elliptical-path having a very small vvertical component of movement and a larger horizontai component of movement. The major axis of theellipse'is sharply inclined forwardly, forming a small angle with the horizontal. At points-nearer and'nearerto the neutral point, the vertical componentV of screen movement becomes smaller while thehorizontal movement becomes greater, so that at theV neutral point thereis no vertical component of movement. Frcm'the. neutral point towards the discharge end,-as illustrated, the vertical component increases and-the horizontal component decreases as illustrated by the elliptical paths of motion, the major axis of which beingr less and less inclined `to the horizontal.

At Vthe discharge end of the screen, these paths of motion are more nearly circular so that the horizontal component is the smallest at this point while the vertical component is at a maximum. It ywill be noted that this motion diagram is related to the horizontal and, since the screen cloth lies in an inclined plane from the feed to the discharge end, it will be seen that the longitudinal axis of motionisralways slightly away from the inclined screen surf-ace.` With this type of motion., vit is possible to eifect agglomeration of the solid content of a liquid, of the type hercinbefore referred to, at the feed end where the vertical motion of the screen is quite small. This vertical motion -s accompanied by a forward conveying action represented by the horizontal components of-movement, so that the forward motion of the agglomerated material becomes progressively greater in a vertical plane while remaining of the same length'in-aA 'horizontal plane. This action continues vuntil' the 4agglomerate reaches the point .at .which the unbalanced revolving shaft is'inountedon .the box when the paths of motion become more nearly circular, as will be seen progressively from point through point S. It is not necessary'that the motion of the screen begreater in'la rvertical direction than in a horizo'n'tal direction at the discharge end of the screen .but only that .the vertical motion be greater at .thedischargelend .thanat the -feed end wherethe motion, as previously explained, is practically horizontal.

AEi'lieover-.ail eifect fof Athe structure of Figure 5 is thelsameas that of ytheother figures vfor the purposes of this invention. It will be noted, however, .in .view -Vof 1the fact that y-the Ailexible leg 25de in-a vertical plane, vthat the neutral point of .thescreen ;.is .atthis leg. =In other lwords the screen .has ,no vertical -motion at this point, only a .horizontal component of movement. In other words thechart of .motion of Figure rll applies to the screen of Figure5, .assuming that the neutralpointlisat thevertical -leg 26. With this assumptionthe Vmotionfof the screen progressively to" the right-corresponds-.to theinotion at the pointsA'toSlinclusivefofffthat g'ure. Thus this screen'is las 'fully .effective Ifor ,the purposesof 9 this invention as are theother structures herein illustrated.

It is as a result of the type of motion thus described that the screen accomplishes the proper forward travel of the liquid feed, effects agglomeration of the finely divided material without substantial disintegration in the case of the fragile material, and the transmission of the liquid through the screen into the drain pan 24. In other words this type of motion tends to agglomerate the finely divided material in a liquid, very fast feed in, and-'then tor subject Ait to a progressive movement along the screen cloth without interruption in travel until it is rejected at the discharge end thereof. By comparison with Figure 12 it will be seen that the type of motion imparted to the screen cloth is distinctly different from that of orthodox vibrating screens such as illustrated in Patent No. 1,621,949 previously referred to.

At the feed end of that screen the screen cloth travels in closed oval paths with the long axes thereof inclined forwardly and at the discharge end in a similar path with the long axes, however, inclined rearwardly and with a progression of inclination of this axis from the former to the latter at intermediate positions, This type of motion is detrimental in the screening of a liquid containing finely divided material where it is required to reject the finely divided material from the liquid. A motion of that type does not allo-w the material to :agglomerate but causes the finely divided material to pass through the screen cloth openings along with the liquid. The constructions of this invention on the other hand cause -agglomeration and prevent movement of the finely divided material through the screen cloth even though it be of a size smaller than the screen openings. The particles instead of going through the screen quickly agglomerate into larger masses which travel along the cloth and are discharged at the end thereof without any hesitation in their movement. All of the modications herein described so act but not all with the same eiciency.

By Way of comparison from actual experience the following relative efficiencies have been observed, although all the structures herein disclosed are commercially feasible to attain the objects herein set forth. The screen of Figures 1 to 4 inclusive which was first tried Was commercially satisfactory but turned out not to be so efcient as the screen shown in Figure 5 which was the second type of machine to be tried. The machine of Figure 6 which was next tried showed an increase in efciency over the two previous structures. In addition to this increase in efficiency there was gained a considerable reduction in manufacturing costs. For comparison purposes it was determined that the ratio of efficiency between the machines of Figures 1, 5 and 6 is about as 15 is to 23 is to 30 as far as throughput of oil is concerned. The reduction of impurities contained in the screened material was about in the ratio of 76.6% for the machine of Figure 1; 86% for the machine of Figure 5; and 94.3% for the machine of Figure 6, when processing hot palm oil. More specifically, when using the machine of Figure 6 it was possible to remove 94.3% of all solids in the hot palm oil above 6 microns in size when the oil temperature was approximately 180 F. It should be noted here that the utility of these screens is not limited to the processing of hot liquids containing finely divided solids, reference being 10 made to hot palm yoil because of the greater practical experience'with the processing thereof.

From the above description of the various modifications of our invention herein disclosed it will be apparent to those skilled in the art that construction of the elements and the relationship are capable of variation within the limits of novelty herein disclosed, and we do not, therefore, desire to be strictly limited to the specific embodiments herein illustrated, but rather to the scope of the claims granted us.

What is claimed is:

l. A screening machine comprising a support, an inclined screen box, resilient members attached to the screen box adjacent each end thereof and respectively secured to said support, a screen cloth mounted in said screen box between the points of attachment of said resilient members to said screen box and of a length less than the distance between said points, and vibration imparting means mounted on said screen box between the resilient members at the lower end of said box and the adjacent end of said screen cloth. y

2. In the combination of claim 1, said resilient members comprising involutely coiled springs.

3. In the combination of claim 1, said resilient members comprising involtuely coiled springs, and means for attaching said springs at their inner ends to said screen box and at their outer ends to said support.

4. In the combination of claim 1, said resilient members comprising involtely coiled springs, the springs at the higher end of the screen box being attached to the underside of the screen box and the springs at the lower end of the screen box being attached to the upper side of the screen box.

5. In the combination of claim 1, said resilient members comprising resilient discs. Y v

6. In the combination of claim 1, said resilient members comprising resilient discs, and means for attaching the discs at their peripheries to said support and at their centers to said screen box.

'7. In the combination of claim 1, said resilient members attached to the higher end of said screen comprising flexible struts and means for xedly attaching said struts at their respective ends to said box and support.

8. In the combination of claim 1, said resilient members attached to the higher end of said screen comprising fiexible struts and means for fixedly attaching said struts at their respective ends to said box and support, and said resilient members attached to the lower end of said box being involutely coiled springs.

9. In the combination of claim 1, means for delivering a liquid onto the feed end of said screen cloth in a sheet.

10. In the combination of claim 1, a drain pan mounted on said support below said screen cloth.

11. In the combination of claim 1, said vibration imparting means comprising a rotatably mounted unbalanced Weight.

12. In the combination of claim l, said vibration imparting means comprising a rotatable and eccentrically mounted shaft.

13. In the combination of claim l, said resilient members comprising springs for suspending said screen box from said support.

14. In the combination of claim 1, said resilient members comprising resilient discs, means for mounting said discs on said support, and means References` Cited' in the. 171ev of this patentv UNITED STATES `PATENTS Number Name Date Sorensen May 25, 1926 Rigdon etal Mar. 31, 1931 Sayers et a1 Aug. 24, 1937 Over-.strom Nov. 15, 1938 Symons Mar. 5, 1940 Overstrom June 11, 1940 Corwin Apr. 29, 1941 Overstrom'et a1. May 27, 1941

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