US2668621A - Clamp for screen frames - Google Patents

Description

Feb. 9, 1954 P. M. THOMPSON 2,668,621

CLAMP FOR SCREEN FRAMES l l l /24z 75253 /06 /z "022 98 98@ w' 28 C@ /5 mq "5% Q6 /OZ /02 S25/a2| n /z y wf lL/ M20 75 .52 7'47 EMoR. zo 25 42 76 02%?, 7%7Z0wum 2 Sheets-Sheet P. M. THOMPSON CLAMP FOR SCREEN FRAMES Feb. 9, 1954 Filed Nov. 14, 1949 Ill/I 4 A\\\ IIIIIIIII Patented Feb. 9, 1954 CLAMP FOR SCREEN FRAMES Peyton M. Thompson, Lockport, N. Y., assignor to Richmond Manufacturing Company, Lockport, N. Y., a corporation of New York Application November 14, 1949, Serial No. 127,090

11 Claims. l

This invention relates to sifters and'particularly relates to an equalizing holddown for the stacks of sifters in which a plurality of stacks of superposed screens are mounted for high speed gyration as a unit.

This application is an improvement on the Sifter described and claimed in the co-pending application of David Crampton, Serial No. 144,090, filed February 14, l1950. It is an object of the present invention to provide a sifter of the type described with an improved mechanism for clamping the stacks of screen frames together and holding them securely to the sifter frame.

A further object of the invention is to provide a sifter of the type described in Which the clamping means for the stacks of screen fra-mes is readily accessible and easily operated.

Another object of the invention is to provide means for raising the top frame or cover of each of the stacks of screen frames and supporting the top frame in an elevated position to permit replacement or substitution of screens.

Another object is to provide such a holddown in the nature of alinkage having a iloating con- -nection with its anchorage and capable of moving to exert an equalized pressure on the corners of the stack so that uniform clamping pressure is applied tothe corners of the stack as a function of tightening the holddown.

Another object isto provide guides to insure substantially true vertical movement of the top frames when being elevated or clamped down thereby to insure that each top frame is accurately brought intol proper register with its stack of screens as it is lowered.

A still further object of the invention is to provide a simple clamping mechanism which Armly holds each stack of screen frames against vertical motion by rods attached adjacent to the corners of the covers thereof.

Other objects and advantages of the present invention will appear from the following description and drawings in which:

Fig. 1 is a side elevational view of one end of a sifter embodying the present invention.

Fig. 2 is a top plan view of the end of the sifter shown in Fig. 1.

Fig. 3 is a vertical sectional view on the line 3-3 of Fig. 2.

Fig. 4 is an end elevational view of the sifter shown in Fig. 1 with parts broken away the better to show certain structure.

Fig. '5 is a fragmentary enlarged View showing in vertical section thedetails of the cover clamp- L f g ing mechanism used on the ends of the sifter, this section being taken on the line 5 5 of Fig. 1.

Fig. 6 is a view similar to Fig. 5 showing details of the cover clamping mechanism used between stacks of screen frames, this section being taken on the line 6--6 of Fig. 3.

Fig. 7 is a fragmentary end elevational view showing the arrangement of the port for providing access to the clamping device between the stacks of screen frames.

This application provides improvements in sifter constructions which are particularly useful with high-speed siitersof the type shown and described in the copending application of Peyton M. Thompson, Serial No. 562,753, for High Speed Sitters, led November 10, 1944, now Pat. #2,511,885, and the improvements have been illustrated as applied to a sifter of that type. The apparatus required for imparting gyratory circular motion to the sifter and a number of other details of sifter construction which are not pertinent to the present invention are not illustrated or described herein. It will be understood that the above mentioned application may be referred to for such details or that, if desired, any other suitable construction may be employed.

The body of the sifter embodying the present invention is shown as cf generally square, boxlike form and as carrying four stacks of screens, although it will Ibe understood that the invention is applicable to sifters in which a greater or fewer number of stacks of screens are employed. Since the construction of the screen stacks is the same except for the necessary reversal of parts,v the same reference numerals will be used to designate similar parts on the two stacks of screens shown in the drawings and on the frame.

' The main supporting frame for the sifter of the present invention comprises a pair of horizontal channel beams 20 which are arranged on opposite sides of the sifter and are preferably disposed in a horizontal plane intersecting the center of gravity of the sitter. The channels of the beams 20 face outwardly, and adjacent the center of the sifter are rigidly connected by a pair of horizontally spaced transverse channel beams 22, the ends of which are preferably welded to the side channel beams 20.

Topsupport the main frame for the usual vibratory or gyratory motion in a horizontal plane, each of the ends of the longitudinal side channel beams 20 is supported by a plurality of vertically disposed wooden reeds 24. The upper ends of each group of these wooden reeds 2li are suitably anchored to the ceiling of the room in which ,the

sifter is housed (not shown) or to other suitable supporting means. The lower ends of each group of reeds 24 are secured to the outer face of one of the longitudinal side channel beams 25 by a block and clamping plate 26 which are held in position and in clamping engagement by screws or bolts 28. As pointed out in the co-pending application above referred to, the connections between the reeds 24 and the main longitudinal side beams 20 of the frame should preferably be at places which lie in a plane intersecting the center of gravity of the sifter, for the reason that greater gyratory speed can be secured and vibration will be minimized.

At spaced intervals along each of the main longitudinal side channels 20 of the sifter frame the reduced upper ends 29 of depending tie rods 30 extend upwardly through the flanges of the beam 20 and are secured to nuts 32 supported on the upper flange of this beam with the shoulders separating the reduced ends 29 and lower portions 3l of the rods 36 in contact with the lower flanges of the beams 20. The lower ends of the tie rods 39 extend through the side angle `bars 34 of a supporting platform frame 36. The frame 36 comprises the side angle bars 34, the end transverse angle bars 38 which connect the ends of the bars k34, and ,intermediate transverse vangle bars 4l! which connect the side angle bars 34 at places directly below the transverse chanl.

nel beams A22 of the main frame of the sifter. The platform frame 36 and the platform 42fon the bottom side thereof are supported by nuts 44 at the lower ends of the vertical tie rods 30.

'I'he platform 42, as shown in the drawings, .carries lat each end intermediate the reeds 24 .and the channel beams 26 two stacks of screen vrate, screen, or grade the material being handled .into different sizes. Holes in the bottom of the platform 42 provide communication with outlet `spouts 48 through which the sifted or graded material is Withdrawn.

Three of the corners of each stack of screen frames 46 are embraced by vertical angle bars .56, 52, and 54. The vertical angle bars 56 nt into the corresponding corners between the longitudi- 1nal channel beams 26 and the transverse channel `beams 22 of the main frame of the sifter.

The vertical angle bars 52 have their lower ends inside the transverse angle bar T of the platform frame f and intermediate their lengths are preferably attached as by welding to the transverse channel beams 22 of the main sifter frame. At Atheir upper ends the bars 52 are preferablyattached to the transverse angle bars 23 which lie above .and parallel to the beams 22 and bars 46 and which are connected at their ends bythe longiltudinal members 25. The bars 52 embracefrespectively, the adjacent inside corners of the Vstacks-of screen frames 46.

At the outside corners of the stacks of frames 46 which are adjacent to the corners of the platform 42 vertical angle bars 54 are provided, the

'bars 54 being arranged-inside of the main longitudinal channel beams -20 and .the platform frame angle bars 34 and 38. The angle bars 56, 52, and

54 may be secured in position by any suitable means. If desired the vertical bars `52 maybe permanently fixed in position, as-by bolting, welding, or riveting, and the barsf can be :adjustably moved toward these bars 52 to clamp the screen frames therebetween by the clamping means shown in the application above referred to.

A clamping plate 56 is pivotally mounted at each end of the platform 42. The member 56 comprises a ilat face plate 58 which is provided adjacent its lower end with a pair of outwardly extending lugs 66 which are secured toa mounting block 62 by the hinge pin 64 and nut 66. The blocks 62 are preferably welded to the bars *38 of the platform frame 36. The face plate 56 has integrally attached thereto on the rear side thereof a pair of spaced inwardly extending flanges 68. The clamping member 56 is adapted e to be swung around a horizontal axis on hinge pin 64. When in normal vertical position the member 56 has the face plate 58 overlapping and flush `against the sides of the adjacent stacks of screen frames 46 with the inwardly extending flanges 68 serving to prevent sidewise displacement of the frame 46.

In effect, the clamping member 56 provides a pair of angle bars mounted on a single pivoted plate. The clamping member 56 is provided with a handle 'l0 and is held in vertical position by a plurality of wing nuts "i2 which are secured on the threaded ends of the tie rods T4. The `tie rods 14 are secured at their inner ends to a vertical plate 16 which extends transversely substantially the full Width of the sifter and is secured to the transverse channel beam 22 and transverse angle bars 23 and 46 by welding or other suitable means. The tie rods F4 pass through the vertical plate 16 and are held thereto by nuts 'I8 screwed on the threaded ends of the tie rods yon each side of the plate i6. Tightening of the wing nuts 12 on the tie rods 14 results in the face plate 58 exerting pressure on the corners of the screen frames 46 and drawing them into close engagement with the vertical angle bars 52. Since the sifter is subject `to rapid gyratory motion it is essential that the screen frames 46 be firmly clamped in alignment. Clamping of the adjacent sides of the two stacks of frames carried at each end of the sifter yis i ,obtained by the clamping members .as above described.

To each end of each of the main longitudinal side beams 20 of the main frame of the Vsifter there is secured a clamping -plate 86 .which is L- shaped in horizontal section. Each of the L- shaped clamping plates 66 is provided with a Apair of vertically spaced, outwardly extending ears 62 which are secured for pivotal movement to the outwardly extending flanges of the adjacent channel beam 253 by means such as Ya pivot pin or bolt-66. The clamping plates 86 can thus be swung to embrace Ythe corners of the vertical angle bars y54.

Each clamping plate Sil is provided with a lug 86 which projects outwardly from the corresponding end of the sifter. Each of the lugs Sil is provided-with an upwardly directed slot 86, the slots 88 in the two clamping plates Sii-at each end of the sifter being in horizontal alignment and in the same vertical plane. A rod Se threaded at both ends for the mounting of handwheels 92 is received within the slots 88 with the handwheels on the outer sides` of the lugs B6. When the hand wheels 92 are turned on the screw threaded ends of the rod 66 the-hubs 63' of said Wheels are brought to lbear against the lugs 66 and in pulling the lugs together cause the vertical angle bars 54 embraced by the Vclamping plates 86 to press against the corners off=the screen frames 46 and thus to clamp the stack of frames securely between the vertical angle bars.

Although the screen frames 46 are clamped between the member 56 and the angle bars 50, 52 and 54 to prevent horizontal shifting with respect to platform 42, it is also necessary to hold the screen frames firmly down against the platform frame 36. By the present invention there is provided mechanism for securely clamping the screen frames 46 downwardly against the platform frame 36 by means attached to the top frame 96 with vwhich each stack of screen frames is equipped.

Each of the top frames 96 is equipped with an inlet spout 80 in the top thereof through which the materials to be sifted or screened are admitted to the rectangular header |00 which is interposed between the top screen frame 46 in each stack and the top frame 96 and preferably projects upwardly above the tops of the angle bars 50, 52 and 54 andthe clamping plates 58. The headers |00 provide receptacles within which the material to be sifted or screened collects and from which the material is fed to the series of screens below. If desired, the headers |00 and top frames 86 can be attached or made integral to constitute a unitary structure. On opposite sides of each of the top frames 96 adjacent the corners thereof there are provided pins |02 which extend horizontally outwardly therefrom with the pins |02 on one side of each cover projecting over side beams 20. Mounted on the pins |02 and de#- pending therefrom are elongated rods or draw bars l|04 and |06. FA bracket |08, which is L-shaped in vertical cross section, is mounted at each end of the sieve platform adjacent the outer side of each of the stacksl of screen frames 46 thereon below the projecting pins |02. The shorter leg I|0 of the L preferably extends outwardly from the screen frames and is secured by bolts I I2 or other suitable means to the supporting platform frame 36. The longer, vertically extending leg of each of the brackets |08 is provided with a pair of converging diagonal slots I |4 which extend inwardly and downwardly from points adjacent the upper corners of said brackets. Associatedwith each of thev brackets `|08 is a horizontally disposed draw screw |I6 which is threaded substantially throughout its length .with the threads on one end thereof being directed oppositely from -the threads on the other end. Threadedly mounted on each threaded end of each draw screw |I6 is a. draw nut or shoe IIS. Each of the draw nuts or shoes I I8 is `provided with a cylindrical extension4 |20 which passes through one of the slots II4in one of the brackets |08, so as to have a floating connection therewith, and through the bottom end of one of. the draw bars |04, being held in place therein by a spring clip |22. To reduce friction, the cylindrical extensions |20 preferably carry rollers |23 which surround these extensions and ride in the slots ||4. The outwardly facing ends of the draw screws |I6 Yare provided with squared portions |24 which are adapted to be engaged by a key or a socket wrench. At eachy end ofthe sifter, between the two stacks of screen frames 46 and behind the face plates 58 there are provided L-shaped brackets 120 substantially like brackets |00. The brackets -|26 are equipped with slots II4, threaded draw screws II 6 and draw nuts I I8 in the same manner as' the brackets |00. The 'draw nuts IIS are connected, respectively,l to the lower ends' of a pair of draw bars |04. At the upper end of each of the brackets |26 there is mountedv another L-shaped bracket |28 which is secured to the bracket |26 by a pair of bolts |30 passing through the brackets |26 and |28.

Rigidity of the brackets |28 is provided by pairs of sleeves |32 which are mounted on the vbolts |30 between the brackets |26 and |28. kThe brackets |28 are provided like the bracketsv |08 and |26 with diagonal converging slots II4, threaded draw screws |I6, and draw nuts '|I8, the nuts ||8 having extensions |20 with rollers |23 passing through the slots II4 and connected to draw bars |06. The draw bars |04 and |06 are in all respectsidentcal except for length, the bars |06 being shorter than the bars |04 since the bracket |28 with which they cooperate is mounted above the other brackets |08 and |26.

As will be seen from the drawings, by proper rotation of the draw screws I I6 the pairs of draw nuts or shoes |18 threadedly mounted thereon will be caused to approach each other. Consequently, the extensions |20 on said shoes or nuts will move downwardly in the converging slots Y| I4 and, through the draw bars |04 and |06, all four corners of each of the top frames 96 will be pulled down, thus securely clamping the screen frames 46 and the header |00 in place and holding the same firmly down on the platform frame 36. Access to the squared ends |24 of the draw screws H6 mounted onl the brackets |26 and |20 is obtained by forming a vertically elongated opening |34 in the face plate 50, the vertical elongation ofA this opening |34 permitting direct access to each of the squared ends |24 of the corresponding draw screws ||6, regardless of their elevation at the time. Although the brackets |08 and |26 are illustrated as being mounted on the platform 42, they may be mounted in any other convenient manner. For example, the brackets |08 could be, if desired, mounted on main frame beams 20.

It is desirable to guide the upper end of one of the draw bars |04 or I 06 at each side of each stack of screens so that the top frames 66 are constrained to move in a vertical path without lateral displacement or wobbling and so that each top frame is brought down in proper register with its stack of screen frames to fit properly thereon. For this purpose, a guide plate is shown as secured to the upper end of each of the corner angle bars and 02, each of these guide plates being vertically disposed and projecting along side the corresponding stack of screen frames 46 and alongside the adjacent draw bar |04 or |06. Each of these guide plates I35'is provided with an inclined slot |36 which inclines in the same direction as the slot I I4 associated with the same draw bar but at a lesser angle to the vertical. Each of these guide slots |36 guides a guide pin |30 projecting laterally from the adjacent draw bar |04 or |06 into the guide slot. It will be seen that as the lower end of each draw bar so guided by its guide plate |35 is moved vertically and laterally in following its slot |I4, its upper end is also moved vertically and laterally by the guide slot |36, the lateral movement of the upper end of the draw bar being less than its upper end as determined by the difference in distance of the slots |36 and I I4 from the pivots |02. By so guiding the upper ends of a pair of draw Abars asso ciated with each stack of screen frames, the tcp frame 86 thereof is constrained to move in a sub-v stantially true vertical path without wobbling or lateral displacement and the Vtop frame is brought down in accurately positioned register with `the steek of sereen trames so. as te. fit. properly thereon.-

the olarnelrie Plates .ttl would he 'swung outwardly ond beek the nit-f ated eine .or .holte 5- 'he v@nelle leere .te .would then, hereroored. `ongle would then te eleeeed from inward elemente .e sein nt with 3.211.@ Stack@ f t'lefls 1511.15 @tarllllmi llt@ 1.11# anism not being shown. Wing nuts ft2 would be nneoreweel end the Clamping niemeer 56 would be wung outwardly and downwardly on hinge pin E4. A suitable wrench or lgey would then .be ap? tilted .to the .Sonered ende 12.4 to torn .the .drew sorews l I5 associated vwith the brackets. 198, [25 and it in e direetlon to eeuee the drew nnte Htl to Vloe moved enert .end upwardly in the Slots l UL. there raisins the. top. frames. 96- The headers. it?. and any of the .Soreen trames i6 een then be withdrawn and other frentes substituted there for..

the .desired substitution of eereene hee lesen inode, the .elernnine member te ie reieed into yertieal position, with the rearwardly extending tiene ..8 passing between the Stacks of Sereen. from e s6, and the Wine .nuts l2.4 are applied to the.. threaded ende of vthe tie rode 74- The vertieel. angle fears 54 .are next placed in position om@ breeine; the outside oorners of the steekt of eoreen. frames and the clamping plates BQ mounted on the channel beams y2l) are swung around into position with the -liiee Bt extending forwardly .end the .slots 88 in alignment. The rod v9!! carrying the handit/peels 92 is thereupon placed in the slots t- Ihe .drew Screws H 6 are then rotated in the onnoelte direction with the result that the nnte .lili will he drew-n together and downwardly vin tite Slots n4 and the drew bers |04 and tilt will be moved downwardly to eeet the top. trainee .9.6 and ldraw them firmly down against the sereen trainee 4 .In snoh .movement the snide eine |38 on.; theiinner .ends of .e Deir of the drew here IBA and 1,06 .associated with each stack of sereen graines follow tneirguide grooves |36 i-n the guide platee end hence the top vfreine .Se is lowered .e substantielle tine Vertical Path .end is. broiight Vinto `aocurate register with the screen .frentes te te .Seat eeoure-.tely thereor-i-A The assem-V bly will Consequently be olttrnped firrnly against .the Platform .42-

it will .pariularly be .noted that the 'holddown of .the present invention serves to equalize the .tlelnnin pressures the eornere of the steers ley :virtue of the floating conneotion of the shoes or mits `H8 with the slotted plates .|03 or 128, @returning that, eey the unser right .hendeorner of. the Steek of eoreen .frames es viewed .in Fis. i. is higher than the upper lett hand .eorne-r, on turning the .Screw H6 `the -ehoe or Init H3 et the left would be drown further down its slot YI 44 than the vshoeornut AI I5 on the right and the screw H6, in the nal position, would be at. alii @ingle to the horizontal, inelining down-.- wardly `toitlard its headed end. BY Vir-tue of this .distortion of the linkage .due to its f loatine eln- .elioxjaga tile holddown would. apply .the seme 3. downward eressitre et the-.o

spite. .ot the ...elet at. et than `.trie other, ass. holcldotvn applies te the terriers off the platform ..53 is.. sini win. .aso Yhe noted hat together as masses so of. the. trente .niet Ari portent tentureo des rileed: above ie the positive r tontfrentes et .from the ete .S ofi the regel-.heee tirer-eli le desorileed o.Y embed' tot; tnel? to ei sieve .ot eenerel. tree pleetionl serial stood. herleiten. that @ordination to other 4. modioatilon to adapt.; is within .the spirit off the. present inve lit will be further understood that, numerous modi-r cations of the details of' ,eonstrufztion shown and described herein may .be madefwithout de.Y parting from `the .spirit oi :the invention. Ae.-k eordingly.,- it is desired that. the invention should not be limited by the foregoing description and; the accompanying drawingsbut is to lbe accorded the full ranger of equivalents comprehended the accompanying claims. Ielaini: l 41. An equalizing holddown for a stack of' rectangular. screenframes? mountedon -a support and said stack havinga .topy frame, conslprising.at least one pair.v of .elongated Jtension members .at each oftwo vopposite sides of Vsaid stack and severallyy .connected at their uppert ends vto, the cor-ners of said top frame to swingparallel with, said opposite sides of .said staclg, .a guide member at each vof said opposite sides .of said steek and seeured to said support below` each pair y0I- tene sion members and having a pair of conteiging surfaces ine-lined with referenee to .the horizontal and extending generally parallel with said 0.9: posi-te. sides of said stack, .a pair Qf independentsly floating shoes severally Slide/bly .elltl .Q each pair. or said surfaces. for moxement .th along' independently of each. other. means @one nesting the lower end .Q' .each .o .Salti tkSQQIl members with a corresponding one of; Said shoesA and a pair of fleatinamaoua y' operable each connecting. the ranged .to positively moyesa toward and from eaeli other thereby to raise and lower said top fram to. .apply .serialized downward Presser. corners or" fre. i

.2- eenelirlne, .holddewn .eet torth .eleirn i wherein-eeen of erelid snide inemloere .it .in -tlie for-.n.1 et ...en esetendine .plete mounted said support and wle in each said of con:

surfaces of slots in each of said plates; and wherein a roller is rotatably secured to each of said shoes and rides in a corresponding slot.

3. An equalizing holddown as set forth in claim l wherein each of said guide members is in the form of an upstanding plate mounted on said support and wherein each said pair of converging surfaces are provided by the upper and lower surfaces of slots in each of said plates, wherein each of said shoes is in the form of a nut having a stud on which a roller is rotatably mounted with said rollers severally riding in said slots, wherein each said screw is threaded in a corresponding pair of said nuts, and wherein Veach of said nuts is arranged on the side of its tension member remote from its guide plate.

4. An equalizing holddown for two closely spaced parallel stocks of rectangular screen frames mounted on a common support and each of said stacks having a top frame, comprising a tension bar connected at its upper end to each -of the four corners of each of said top frames to swing parallel with the space between said stacks and the lower end of each of said tension bars being disposed closer to said support than to said top frame, two pairs of said tension bars being arranged in said space with each pair close to the side of a corresponding stack and the other two pairs being each arranged close to the face of the corresponding stack opposite said space, a shoe pivotally secured to the lower end of each of said tension bars, a plurality of guide members mounted on said support severally below and projecting upwardly toward a corresponding pair of said tension bars, said guide members being provided below each ten sion bar with a slot having upper and lower opposing faces engaging, respectively, the upper and lower faces of a corresponding one of said shoes, the pair of slots associated with each pair of tension bars inclining in opposite directions with reference to each other and constraining each pair of tension bars and shoes to movev both upwardly and downwardly relative to said support independently of one another in response to horizontal movement of each pair of shoes toward and from each other, and four manually operable generally horizontal screw members arranged parallel with the space between said stacks and each having opposite ends operatively connected with the corresponding pair of shoes to move said pair of shoes horizontally toward and from each other thereby to raise and lower each top frame and to apply equalized downward pressures at said corners of said top frame against said stack of screen frames.

5. An equalizing holddown for two closely spaced parallel stacks of rectangular screen frames mounted on a common support and each of said stacks having a top frame, comprising a tension bar connected at its upper end to each of the four corners of each of said top frames to swing parallel with the space between said stacks and the lower end of each of said tension bars being disposed closer to said support than to said top frame, two pairs of said tension bars being arranged in said space with each pair close to the side of a corresponding stack and the other two pairs being each arranged close to the lface of the corresponding stack opposite said space7 a nut pivotally secured to the lower end of each of said tension bars, the threaded bores through said nuts being generally horizontal and parallel with the space between said stacks, a horizontal roller rotatably secured to the lower end of Veach of said tension bars, a plurality of vertical guide plates arranged generally parallel with said space and mounted on said support severally below and projecting upwardly toward a corresponding pair of said tension bars, said guide plates being provided below each tension bar with a slot having upper and lower faces engaging, respectively, the upper and lower faces of a corresponding one of said rollers, the pair of slots associated with each pair of tension bars inclining in opposite directions with reference to each other and constraining each pair of rollers, tension bars and nuts to move both upwardly and downwardly relative to said support independently of one another in response to horizontal movement of each pair of nuts toward and from each other, and four manually operable generally horizontal screws arranged parallel with the space between said stacks and each having opposite ends screwed into the corresponding pair of nuts and formed to move said pair of nuts horizontally toward and from each other thereby to raise and lower each top frame and to apply equalized downward pressures at said corners ofsaid top frames against said stacks of screen frames.

6. A structure as set forth in claim 5 wherein each of said nuts is arranged on the side of its tension arm remote from its guide plate.

7. An equalizing holddown for two closely spaced parallel stacks of rectangular screen frames mounted on a common support and each of said stacks having a top frame, comprising a tension bar connected at its upper end to each of the four corners of each of said top frames to swing parallel with the space between said stacks and the lower end of each of said tension bars being disposed closer to said support than to said top frame, two pairs of said tension bars being arranged in said space with each pair close to the side of a corresponding stack and the other two pairs each arranged close to the face of the corresponding stack opposite said space, a nut having a horizontal stud pivotally fitted in an opening at the lower end of each of' said tension bars to permit the nut to swing about a generally horizontal axis generally parallel with the normal pivot axes of the upper ends of saidtension bars, the threaded bores through said nuts being generally horizontal and parallel with the space between said stacks, a roller rotatable on each stud, a plurality of guide members mounted on said support severally below and projecting upwardly toward a corresponding pair of said tension bars, said guide members being provided below each tension bar with a slot having upper and lower opposing faces engaging, respectively, the upper and lower faces of a corresponding one of said rollers, the pair of slots associated with each pair of tension bars inclining in opposite directions with reference to each other and constraining each pair of rollers, tension bars and nuts to move both upwardly and downwardly relative to said support independently of each other in response to horizontal movement of each pair of nuts toward and from each other, and four manually operable generally horizontal screws arranged parallel with the space between said stacks and each having opposite ends screwed into the corresponding pair of nuts and formed to move said pair of nuts horizontally toward and from each other thereby to raise and lower each top frame and to apply equalized downward pressures at said corners 4 Y 11 of said top frames against said stacks of screen frames. 4

8. A structure as set forth in claim 7 wherein each roller has an extension tting the opening in the lower end `of the corresponding tension bar.

9. A structure as set forth in claim 4 wherein a second guide member is iiXed to said common support and is disposed adjacent the upper ends of at least one tension bar of each stack and wherein said second guide member constrains thetension bar associated therewith against lateralrmoveinent with reference to said stack to guidesaid top frame in its upward and downward movement relative to said stacks.

10. An equalizing holddown for the adjacent corners of two closely spaced parallel stacks of rectangular screen frames mounted on a common support and each of said stacks having a top frame, comprising a tension bar connected at its upper end to each oi the adjacent corners of said top frames to swing parallel with the space between said stacks and the lower end of each of said tension bars being disposed closer to said support than to said top frames, two pairs of said tension bars being thereby arranged in said space with each pair close to the side of a corresponding stack, a shoe pivotally secured to the lower end of each of said tension bars, at least one guide member mounted in said space on said support and projecting upwardly toward said pairs of tension bars, said guide member being provided belowr each tension bar with a slot having upper and lower opposing faces engaging, re-

spectively, the upper and lower faces of a co1'- responding one of said shoes, the slots associated with each pair of tension bars inclining in opposite directions with reference to each other and positively constraining each pair of tension bars and shoes to move both upwardly and downwardly relative to said support in response to horizontal 'movement of each pair of shoes toward and from each other, and a pair of manually operable generally horizontal screw members arranged parallel with the space between said stacks and each having oppositeends operatively connected with the corresponding pair of shoes to move said pair of shoes horizontally toward and from each other thereby to raise and lower the corresponding top frarne relative to its stack and I responding stack, a nut having a horizontal stud t pivotally iitted in an opening at the lower end of each of said tension barsto permit the nut to swing about a generally horizontal ax-is generally parallel with the normal pivot axes of the upper ends o f said tensionj bars, the threadedv bores through said nuts being generally horizontal and parallel with the space between said stacks, a roller rotatable on each stud, at least one guide member mounted in said space on said support and projecting upwardly toward said pairs of tension bars, said guide member being provided below each tension bar with a slot having upper and lower opposing faces engaging, respectively, the upper and lower faces of a corresponding one of said rollers, the slots associated with each pair of tension bars inclining in opposite directions with reference to each other and constraining each pair of rollers', tension bars and nuts to move both upwardly and downwardly relative to said support independently of each other in re1- sponse to horizontal movement of each pair of nuts toward andy from each other, `and apair of manually operable generally horizontal screws arranged parallel with the space between said stacks and each having opposite ends screwed into the corresponding' pair of nuts and form-ed to move said pair of nuts horizontally toward` and from each other thereby to' raise and lower the corresponding top frame and to apply equalized downward pressures at said corners of said top frames `against said stacliof screen frames.

PEYTON M, THOMPSON.

References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 385,427 Pugh Y Y July 3, 1888 2,092,663 Bach sept. 7, 1937 2,099,107 Fleming v Nov. 16, 1937 2,191,923 1 1940 2,284,671 194.2 2,477,123 Gilson July 26, 1949 FOREIGN PATENTS Number Country Date 8,510 Great Britain of 1906 24,106 Austria May 10, 1906 197,050 Germany Feb. 5, 1907 187,619 Germany f June 29, 1907 253,954 Germany Dec. 30, 1911 26,340 Great Britain of 1912 296,528 Germany Feb. 13, 1917 353,902 Germany May 29, 19242 373,167 Germany` -f July 18, 1922 205,965 Great Britain Nov. 1,- 1923 295,419 Great Britain Aug. 9, 192s

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