US3282423A - Clamping means for grain cleaning apparatus - Google Patents

Description

Nov. l, 1966 R. D. MITCHELL CLAMPING MEANS FOR GRAIN CLEANING APPARATUS 5 Sheets-Sheet 1 Original Filed Nov. 22, 1961 Nov. 1, 1966 R. D. MITCHELL 3,282,423

` CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Original Filed Nov. 22, 1961 5 Sheets-Sheet 2 INVENToR.

ROBEIISQYT D. Mr-VCHELL @MQL/ww Nov. 1, 1966 R` D. MITCHELL.

CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Original Filed Nov. 22, 1961 5 Sheets-Sheet 5 mmv mw mw] .mm/w@ INVENTOR. ROBEYRT D MWCHELL W4/5W ATTORNEKSL.

Nov. 1, 1966 R. D. MITCHELL. 3,232,423

CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Original Filed Nov. 22, 1961 5 Sheets-Sheet 4 INVENTOR. Roai; D. MWCHELL MAGL/band ATToe/vEY-s.

Nov. l, 1966 R. D. MITCHELL.

CLAMPING MEANS FOR GRAIN CLEANING APPARATUS 5 sheets-sheet 5 Original Filed Nov. 22, 1961 INVENTOR. ROBERT D. M TCH ELL ATTORNEYS.

United States Patent O 3,2s2,423 i CLAMPING MEANS FOR GRAIN CLEANING APPARATUS Robert D. Mitchell, Buffalo, N.Y., assigner to S. Howes Co., Inc., Silver Creek, N.Y. Original application Nov. 22, 1961, Ser. No. 154,245. Divided and this application Apr. 29, 1965, Ser. No.

2 Claims. (Cl. 209-319) This application is a division of my copending application, Serial No. 154,245, filed November 22, 1961, now abandoned.

This invention relates to apparatus for cleaning dry granular material by removing therefrom various undesirable material. For inst-ance, the apparatus may be usefully employed in cleaning lcereal grain by separating therefrom dust, chaff, seeds, undersize grain, dirt, and other foreign matter.

The apparatus of the present invention, spe-aking :generally, employs several superposed vibratory classifying screens in conjunction with air currents for carrying off chaff and other light undesired particles and material. The use of this general arrangement for cleaning grain is well known and the present invention is directed, among other things, to an improved general arrangement and cooperation of several of the functional components of grain cleaning apparatus of the gener-al type indicated above.

While this application discloses and discusses the improvements of the present invention particularly with reference to cleaning apparatus for cereal grain, certain of the novel principles and teachings of the invention are applicable to apparatus for grading and separating other dry granular material according to different types and sizes and are also applied to combined apparatus for both grading and cleaning the grain or other dry granular material.

An object of the present invention is to provide a novel retention and locking arrangement for the screen members and means are provided whereby a single control may be manipulated to lock all of the several screen members of any number of principal screen surfaces of the screen deck in operating position or to release all of the screen members simultaneously by a single manipulation. The sc-reen retaining means is further so arranged that releasing movement thereof raises the screen sections from their seats in the screen frames to further facilitate their removal from the apparatus.

Other objects and advantages of the grain cleaner apparatus of the present invention will become apparent to those skilled in this art from a study of the exemplary form hereinafter set forth. However, while a particular embodiment is illustrated in the accompanying drawings and is described in detail in the following specification, it is to be understood that such embodiment is by way of example only and that the principles of the invention may be variously applied and employed. The spirit and scope of the invention is not to be considered as limited to the form set forth herein by way of example nor otherwise than as dened in the appended claims.

4In the drawings:

FIG. 1 is a general side elevational view of one form of the grain cleaner apparatus of the present invention;

FIG. 2 is an end elevational view of the `appar-atus of FIG. 1 viewed from the right hand end of FIG. 1;

FIG. 3 is a schematic view taken similarly t-o FIG. 1 showing the air ow passages and other portions of the apparatus diagrammatically;

FIG. 4 is a fragmentary top plan View of a portion of 3,282,423- Patented Nov. l, 1966 ICC the screen and screen housing structure of the apparatus of FIGS. 1 and 2, partly in cross-section; and

FIG. 5 is a fragmentary cross-sectional view taken generally as indicated by the line V-V of FIG. 1 but on a larger scale.

Like characters of reference denote like parts throughout the several figures of the drawings. In the exemplary embodiment of the invention set forth herein to illustrate the various novel principles and features of the invention a rigid framework of horizontal and vertical structural members designated. generally by the numeral 20 supports the Various operating components of the machine in their proper relative positions.

.In general the upper portion of the machine includes a feed box or entry arrangement for the grain to be cleaned and a blower or fan with appropriate duct work for Connecting the suction side thereof to take up relatively light undesired matter from the grain being cleaned. This upper portion is shown schematically in FIG. 3. The lower portion of the machine is given over principally to a so-called screen deck which comprises a series of slightly inclined superposed. vibratory or reciprocatory screens with brush means for maintaining the screens clear .and effective to accomplish their screening functions. The screen deck structure and the brushing mechanism are illustrated mainly in FIGS. 4 and 5.

Mounted generally centrally of the upper portion of the machine is a centrifugal fan or blower designated generally by the numeral 21 and having its axis of rotation extending lengthwise of the machine, that is, from the feed end to the delivery end. Blower 21 has two axial inlet ports designated 22 and 23 which are directed, respectively, toward the head or feed end of the machine and toward the tail or delivery end.

Blower 21 discharges laterally, as at 24, air which in normal operation has picked up and subsequently discharged chaff, light dirt and dust and other foreign matter which it draws from the grain and is separated from in a manner which will presently appear. The rotor shaft of fan or blower 21 is shown at 25 in FIG. 2.

As will be noted from a consideration of FIGS. 1 and 3, blow-er inlet port 22 communicates with a head chamber 26 and blower inlet port 23 communicates with a t-ail chamber 27. Mounted .alongside of the head chamber 26 at the extreme right hand side of the machine as viewed in FIG. 1 is a feed. box 30 into which the grain to be cleaned is deposited.

As schematically indicated in FIG. 3 the hoods which form the head and tail chambers 26 and 27 are separable from the underlying duct structure generally along a horizontal plane through the axis of blower rotor shaft 25. Thus removal of the head and tail chamber hoods exposes the air passage duct portions for ready access for cleaning or other purposes.

Referring to the schematic view, FIG, 3, a desired ilow4 of grain from feed box 30 passes into the lower portion of a vertical duct or suction leg 31 which leads upwardly to the head chamber 26, the grain dropping to the head end of a screen deck or housing shown generally in FIGS. 1 and 3.

The feed box 30 land the means for cont-rolling the rate of grain feed therefrom are best shown in FIG. 3 wherein the numeral 32 designates an entry or ller duct and the numerals 33 and 34 designate a pair of inclined wall members which converge downwardly to fonm a restricted grain passageway. y

A helical screw conveyor distributor member 35 is disposed in the apex formed by the wall members 33 and 34 and the helical formations thereof are of opposite hand in both directions outwardly from the center of the screw member toward its ends. Accordingly, grain owingl downwardly to the screw member 35 is distributed outwardly toward the opposite ends of the trough formed by the wall members 33 and 34 so that the grain is more or less uniformly distributed along the feed box 30 which is elongated in a direction perpendicular to FIG. 3.

From the aforesaid trough the gain falls to a further pair -of inclined trough-forming walls members 37 and 38, the former of which is xed within the feed box 30 and the latter of which is attached to several arms 39 which are fixed to an adjusting rockshaft 40 mounted in bearings at the outside of feed box 30. A feed wheel 41 is mounted in the trough formed by the wall members 37 and 38 and is provided with vanes which extend downwardly therealong in an axial direction whereby grain is fed downwardly -through the trough by rotation of feed wheel 41.

Means are provided for regulating the rate of feed of the grain independently of the speed of rotation of the feed wheel 41 by moving the adjacent portion of the wall member 38 toward and awayfrom feed wheel 41 to reduce or enlarge the passageway. It will be noted from FIG. 3 that rockshaft 40 is provided with control arms 44 which terminate in cam followers 45 which engage adjustable control cams 46. Extension coil sprin-gs 47 hold followers 45 in engagement with cams 46.

The springs 47 also provide a yieldable means for urging the movable wall member 38 toward the fixed wall member 37. Thus when unusually large pieces of material must pass between these wall members the wall member 38 may move resiliently away from wall member 37 to permit such passage, by rotation of feed wheel 41, without damage to the plates or associated mechanism. After the large piece has passed between the wall members the spring 47 will return wall member 38 to its adjusted position.

Cams 46 are xed to a camshaft 49 and a handwheel 50, shown in FIG. l, regulates the angula-r positions of cams 46 by way `of a worm and wheel connection with camshaft 49 as at 51. The distributing screw member 35 and the feed wheel 41 are belt connected as shown at 53 in FIG. 2 for rotation in the same direction at approximately the same speed, the screw member 35 being driven from feed wheel 41 as will later appear.

As shown in FIG. 2, an electric driving motor 60 mounted on the top of framework 20 is belt connected as at 61 to the rotor shaft 25 `of blower 21 to drive the same. A further belt connection 59 from shaft 25 extends to a speed reducing gear unit 62 having an output shaft 63 and feed wheel 41 is belt connected to the latter as indicated at 64 in FIGS. l and 2.

Reference will now be had to the screen deck structure, Va h-ousing for which is indicated generally by the reference numeral 65 in FIG. l and further details of which are shown more particularly in FIGS. 4 and 5.

Referring to FIG. l, the screen deck structure c-omprises generally a housing having side walls 66 and top and bottom walls 67 and 68. The side walls 66 extend generally longitudinally and in a downwardly inclining direction toward the tail end o-f the machine, the left hand end as Viewed in FIG. 1. At the right hand end the housing is enlarged upwardly as clearly shown at 69 in FIG. 1, thus forming a receiving chute for material falling from the feed box 30.

The screen housing is suspended for reciprocatory movement in a generally left-to-right horizontal direction as viewed in FIG. 1 by pairs of f-ore and aft exible steel straps designated 70 and 71, respectively, which straps are attached to the machine framework at their upper ends and to the screen housing structure at their lower ends. The screen housing structure is adapted to be rapidly reciprocated for effective vibratory screening action by a conventional eccentric drive mechanism designated 73 in FIG. 1. A typical drive of this type, known in the art as a Buhler drive, is shown in Roth Patent No. 1,517,587.

In the present instance the eccentric drive mechanism 72 is driven from a countershaft 75 by a belt connection 76 and the countershaft 75 is driven from the output shaft 63 of speed reducer 62 by a belt connection 77.

Supporte-d between the side walls 66 of the screen housing structure are a series of three superposed screens including a relatively short scalper screen 80, shown in dot and dash lines in FIG. 3, which is positioned in the upwardly extending right hand portion 69 of the screen housing and inclines downwardly to the right as viewed in FIGS. 1 and 3. The remaining two screens, one above the other, are designated 81 and 82 and incline downwardly to the left as viewed in FIG. l. The upper screen 81 is generally called the main screen and the lower screen 82 is called the sand or seed screen. Each of these screens in the present instance comprises two screen units in edge -to edge relation, as will later appear.

The scalper screen 80 receives the grain falling from the feed box 30 by way of the suction leg 31 and since the scalper screen is -of relatively coarse mesh it passes all excepting the larger pieces of foreign matter -or debris, the latter being discharged from 4the machine by way of a chute designated in FIG. 1.

The main screen 81 is of such mesh as to pass good grain but hold thereon all undesired matter larger than the good grain. The lowermost screen 82 which finally receives the grain through Ithe main screen is of relatively fine mesh and merely passes sand, seeds and similar fine impurities which are generally of smaller particle size than the good clean grain. Foreign matter held on main screen 81 discharges through a chute 83 and nes falling through screen 82 to bottom pan or wall 68 pass out 0f the machine through a duct 84.

The screen deck structure is fthe subject of further novelty as to the means and method of mounting and releasably securing the screen elements therein and as to the means provided forbrushing the bottoms of the screens to maintain the same clear and unclogged for performing their screening functions. Further details of the screen structure will be described later herein, following a description and discusison of the general structure and operation of the grain cleaner generally. In this connection reference will now be had to the diagrammatic View, FIG. 3, which presents the grain cleaner as viewed in FIG. 1 but in schematic form.

The feed box 30 and its adjunots and the suction leg 31 adjacent thereto have been previously described, as

has the blower 21 and its two inlet ports 22 and 23 and its discharge duct 24. It will be noted from FIG. 3 that good grain from the lower end of the nal screen 82 discharges into the lower end of a vertical duct 85 called herein the tail air suction leg. It will be noted also that the head and tail suction legs 31 and 85 discharge at their upper ends into the head and tai- l chambers 26 and 27, respectively.

To promote precipitation of chaff and other light materials from the air passing from the suction legs 31 and S5 through the head and tail chambers 26 and 27 and to the blower 21 the head and tail chambers are each provided with a series of bales which cause the air to pursue a Itortuous expanding path through the head and tail chambers. This expansion of the area of the flow path in the direction of ow reduces the velocity of the air whereby solid particles entrained therein fall into hoppers 86 and 87 at the lower ends of these chambers, from whence it is moved laterally from the machine by means of a pair of conveyor screws 88 and 89, respectively.

Referring to the head chamber 26, a pivoted damper plate 90 regulates the passage area between the suction leg 31 `and chamber 26. A similarly located pivoted damper plate 91 is provided in the tail chamber 27 to regulate the flow area between tail suction leg 85 and chamber 27 and manual adjusting control means for the damper plates 90 and 91 are provided externally of the machine as shown at 92 and 93, respectively, in FIG. l.

Air passing into the blower inlets 22 and 23 from the head and tai-l chambers goes by way of fan or blower inlet chambers designated 95 and 96, respectively, which communicate at their upper ends with the head 4and tail chambers, such communication being under the control of slide dampers 98 and 99, respectively, which are regulated vertically by screw mechanism designated 100 and 101, respectively.

It is desiredthat air entering the headand tail chambers flow downwardly, thence upwardly to the blower inlet chambers, to further promote precipitation of solid matter entrained in the air. Accordingly the head and tail chambers are provided with fixed bales designated 102 and 103, respectively, which extend downwardly from the upper ends of these chambers medially between their entry and discharge sides.

It will be noted that air passes upwardly through the scalper screen 80 to suction leg 31 to entrain chaff, dust and other light impurities from the grain as it enters the screen structure. Again at the discharge end, the screened grain falls into the tail suction leg wherein air is passing upwardly to the blower to entrain chaff and other relatively light material which has not been previously separated or which was removed from the grain in the course of the cleaning and screening process.

As shown in FIG. 1, the chaff hopper screw conveyors 88 and 89 are connected for joint rotation by a belt 104, the conveyor screw S8 being driven from the output shaft 63 of speed reducer 62 by a belt connection 105.

The effective suction at the head and tail ends of themachine may be independently regulated by means of a pair of sliding valve plates 107 and 108 located against upper wall portions of the blower inlet chambers 95 and 96, respectively. The valve plates 107 and 108 and the underlying wall portions of the inlet chambers each have Va multiplicity of perforations, as indicated in FIG. 3, and the inlet chambers may thus be selectively vented to atmosphere in varying degrees by reason of the fact that the perforations of the valve plates are in registry with the underlying perforations in the inlet chamber walls in greater or less degree, according to the horizontal positions of adjustment of the valve plates. The valve plates 107 and 108 may be entirely closed by moving the plates so that the respective perforations of the plates and the wall portions are entirely out of registry.

Flow of good grain from screen 82 into tail leg 85 by way of a chute 110 may be controlled or arrested as desired by vertical adjustment of a sliding valve plate 109 associated with the ta'il leg 85.

Reference will now be had to further details of the construction and operation of the screen deck structure illustrated particularly in FIGS. 4 and 5. As indicated earlier herein, both the main screen 81 and the lowermost screen 82 comprise two screen sections lying in abutting relation, each section extending the full width of the screen deck. The manner in which these screen sections are supported and retained in the screen deck housing is shown in detail in FIG. 5, wherein the numeral 120 designates an angle iron rail member fixed to the interior wall of a side wall 66 of the screen housing 65. It is to be understood that two pairs of rail members 120 are provided, an upper and a lower rail member at the inter-ior of each side wall 66 to provide ledges for supporting the opposite side edges of the screens 81 and 82.

The screen member 82 which is illustrated fragmentarily in FIG. `5 includes a frameV portion 121 of channel cross section which extends thereabout and is adapted to rest on the rail members 120 at opposite sides of the screen housing. In the illustrated instance frame portion 121 is tapered as shown to it between wedge shaped longitudinal gasket members 122 `of rubber or the like whereby the screen members fit snugly between the houssing side walls 66. For conveniently and securely locking the screen members 81 4and 82 in assembled position and for releasing them when desired the following locking arrangement is provided.

A longitudinal locking or clamping Ibar overlies each rail member 120 and is provided with inwardly projecting yoke portions 126 at its opposite ends which are pivoted to the upper ends of the rock arms, the rock arms at the feed end being designated 127 in FIG. y1 and the rock arms at the delivery end being designated 128 in FIGS. 1 and 5. The rock arms 127 at the feed end of the screen housing are fixed to the inner ends of rock shafts 130 which are jointly oscillated to effect locking movements of the screen members 81 and 82 in `a manner which will now be described.

Exteriorly of the sidewalls 66 of the screen housing the rock shafts 130 are connected for joint rocking movement by arms 131 and a connecting link 132. As shown in FIG. l, an operating screw 135 is mounted at the feed end of screen housing 65 as at 136 for free rotation but in a manner to prevent -axial movement. An operating handle 137 is provided at the outer end of screw 135 and its inner end engages an internally threaded arm (not shown) on a rock shaft 138. Rock shaft 138 has operating connection with the rock shafts 130 at opposite sides of the screen housing 65 by means of rock arms 140 and 141 and a connecting link 142.

From the fore-going it will be seen that operation of screw 135 in one direction or the other by manipulation of handle 137 will rock the several arms 127 in opposite directions. Since each arm 127, its companion arm 128, and the connecting locking or clamping bar 125 form, in conjunction with the side wall 66 to which the arms 127 and 128 are pivoted, a parallelogram linkage, rocking movements of the 4arms 127 are automatically duplicated in the several arms 128. v

. Thus all of the locking yor clamping bars 125 are jointly raised and lowered in a parallel manner by manipulation of handle member 137 of screw 135. This operation either clamps the lower flanges of the several screen framing channels 122 to the supporting rail members 120 or releases them. Raising movements of the locking bars 125 causes them to engage the upper interior portions -of the screen framing channels 121 to raise the screen sections clear of the supporting rail members 120 for ready removal.

In grain cleaners of the prior art it is customary to provide means for continuously brushing the under surfaces of the screens to maintain their effectiveness. The apparatus of the present invention provides novel means for -accomplishing this function in the form of fluid pressure actuated motor means which acts directly upon the brush supporting structure to reciprocate the same without mechanical connection to or transmission from the screen housing structure generally.

This is of particular advantage because of the vibratory action of the screen structure and the desirability of isolating the same from the remainder of the machine as far as is practically feasible. In the `arrangement of the apparatus of the present invention the supporting and driving means for the brush mechanism is mounted independently of the screen structure itself.

Refe-rring particularly to FIGS. 4 and 5, a general-ly rectangular brush supporting frame is -designated by the numeral and a plurality of longitudinal rows of lbrush members is designated 151. The lateral spacing of the r-ows of brush members is -approximately equal to or slightly less than the degree of lateral reciprocation of the brush supporting frame 150 so that the entire under surface of the screens is kept clear and it will be noted that the individual brush members of each row are spaced from each other a short distance whereby they clear a series of lateral reinforcing angle members 152 0f the screen members 81 land 82.

The supporting and reciprocating means for the brush supporting fname 150 is illustrated in FIG. 4, to which reference will now be had. As indicated above, the

brush frame support is independent of the remainder of the screen structure, including the screen housing. A pair of tubular brush frame support shafts 155 and 156 extend laterally through the screen housing just below each of the screen members 81 and 82 and the two pairs of shafts 155 :and 156 are xed at their opposite ends to the general framework of the apparatus as indicated in FIG. 4.

Fixed to the underside of each brush frame 150 adjacent to its four corners are bearings 160, preferably of the lineal ball type, which mount the brush f-r-ame on the tubular shafts 155 and 156 for lateral sliding movement. Reciprocation of each brush frame 150 is effected by an air cylinder 161 which is attached at one end to the machine framework 20 las at 162 and has a piston rod 164 which is attached at its outer end to the brush frame 150 as at 165. It will be seen from the foregoing that both the reciprocable mounting of each b-rush frame and its reciprocating means are supported entirely independently of the screen housing generally.

Each cylinder 161 is double acting and is provide-d with conventional conduit and passage means for supplying operating air pressure alternately to its opposite ends. The means for shifting the valve positions at each end of the lateral movement of the brush frame will now be described. A valve shifting rod 168 extends through the tubular brush frame mounting shaft 156 and engages a shifting lever 169 of a valve shifting mechanism 170.

A pair of valve shifting collars 171 and 172 are slidably mounted -on shaft 156 at each side of the screen housing just inwardly -of the side walls 66 thereof and studs 174 extend through the collars 171 and 172 and into valve shifting rod 168 whereby the collars 171 and 172 and the valve shifting rod 168 are fixed for joint axial movement. The studs pass through longitudinal slots in shaft 156 to permit such movement independently of shaft 156.

As a brush frame 150 reaches its limit of movement in either direction one of the bearings 160 thereof which slides on shaft 156 during such movement abuts an adjacent valve shifting collar 171 or 172, as the case may be, and thus moves valve shifting rod 168 to reverse the valve shifting mechanism 170 and thus reverse the direction of piston rod 164 and brush frame 150.

In FIG. 1 the numeral 180 designates an air pressure storage tank which may be employed to supply operating fluid pressure to the brush actuating cylinders 161, pressure thereafter being generated by an air compressor 181 driven from shaft 75 by a belt connection 182. If desired, side panel members may be attached to the exterior of framework 20 to enclose the working parts of the apparatus.

In FIGS. 4 and 5 the numerall 185 `designates a series of angle members which are secured to the upper surfaces of the frame portions 121 of the screen members in obliquely disposed position, as shown in FIG. 4. Grain tending to move downwardly along the screen frame portion is thus 4deflected inwardly. to the screen surface proper at various points along the side edges of the screen surfaces.

Iclaim:

1. In a grain cleaner, a screen housing comprising opposed side walls and opposed vertically spaced pairs of rails at the interiors of said side walls, a screen section adapted to seat on each pair of said rails, an opposed pair 0f llocking bar members disposed above each pair of said rails, longitudinally spaced rock yarms on each of said bar members mounting the latter for parallel movement toward and away from said rails linkage means connecting between a pair of vertically spaced rock arms at a corresponding longitudinally spaced position on at least one side of said screen housing forming with said bar members a parallelogram 'linkage 'at said one side, and common control means operable to simultaneously move each opposed pair of said locking bar members toward and away from said rails to selectively clamp and release said screen sections.

2. In a grain cleaner, a screen housing comprising opposed side walls and opposed pairs of rails at the interiors of said side walls, a plurality of screen sections adapted to seat marginally on said rails, a plurality of vertically spaced locking bar members disposed 4above said rails, longitudinally spaced rock arms mounting said bar members for parallel movement toward Iand away from said rails, and control means including linkage means connecting rock arms of the several locking bar members forming with said several locking bar members a parallelogram linkage and operable to simultaneously move said plurality of locking bar members toward and away from said rails to selectively clamp and release said screen sections.

References Cited by the Examiner UNITED STATES PATENTS 1,919,485 7/ 1933 Soldan 209-403 2,227,090 12/ 1940 Hughes 209-404 X 2,426,897 9/ 1947 Orton 209-405 X 2,477, 123 7/ 1949 `Gilson 209-319 3,022,893 2/1962 Hasley 209-319 X 3,087,617 4/1963 Forsberg 209-319 FOREIGN PATENTS 509,591 7/ 1939 Great Britain.

HARRY B. THORNTON, Primary Examiner.

Claims (1)

1. IN A GRAIN CLEANER, A SCREEN HOUSING COMPRISING OPPOSED SIDE WALLS AND OPPOSED VERTICALLY SPACED PAIRS OF RAILS AT THE INTERIORS OF SAID SIDE WALLS, A SCREEN SECTION ADAPTED TO SEAT ON EACH PAIR OF SAID RAILS, AN OPPOSED PAIR OF LOCKING BAR MEMBERS DISPOSED ABOVE EACH PAIR OF SAID RAILS, LONGITUDINALLY SPACED ROCK ARMS ON EACH OF SAID BAR MEMBERS MOUNTING THE LATTER FOR PARALLEL MOVE MENT TOWARD AND AWAY FROM SAID RAILS LINKAGE MEANS CONNECTING BETWEEN A PAIR OF VERTICALLY SPACED ROCK ARMS AT A CORRESPONSING LONGITUDINALLY SPACED POSITION ON AT LEAST ONE SIDE OF SAID SCREEN HOUSING FORMING WITH SAID BAR MEMBERS A PARALLELOGRAM LINKAGE AT SAID ONE SIDE, AND COMMON CONTROL MEANS OPERABLE TO SIMULTANEOUSLY MOVE EACH OPPOSED PAIR OF SAID LOCKING BAR MEMBERS TOWARD AND AWAY FROM SAID RAILS TO SELECTIVELY CLAMP AND RELEASE SAID SCREEN SECTIONS.

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