US2500966A - High-speed sifter - Google Patents

Description

March 1950 P. M. THOMPSON 2,500,966

HIGH-SPEED SIFTER Original Filed Nov. 10, 1944 4 Sheets-Sheet l all,

March 21, 1950 P. M. THOMPSON 2,500,966

HIGH-SPEED SIFTER Original Filed Nov. 10, 1944 4 Sheets-Sheet 2 77 J57 mmvrm ATTORNEYS" March 21, 1950 P. M. THOMPSON 2,500,966

HIGH-SPEED SIFTER Original Filed Nov. 10, 1944 4 Sheets-Sheet 5 A. T TORNE'YS March 1950 P. M. THOMPSON ,500,

HIGH-SPEED SIFTER Original Filed Nov. 10, 1944 4 Sheets-Sheet 4 v uvvmron @922; m. fi

ATTOR/VEYS Patented Mar. 21, 1950 HIGH-SPEED SIFTER Peyton M. Thompson, Lockport, N. Y.,- assignor to Richmond Manufacturing Company, Lockport, N. Y., a corporation of New York Original application November 10, 1944, Serial No. 562,753. Divided and this application December 6, 1945, Serial No. 633,202

Claims.

This invention relates to a high speed sifter and more particularly to means for securing a stack of sieves in place in a sifter which is suspended from reeds and which includes an eccentrically weighted rotary shaker for imparting a rotary movement in a horizontal plane to describe perfect circles of adjustable diameter or amplitude. Features of the invention can be advantageously utilized in sifters other than the particular type shown, however.

This application is a divisional application of my copending application Serial No. 562,753, filed November 10, 1944, for High speed sifters.

One of the objects of the invention is to provide a sifter which will operate at high speed without undue strain on any of the parts, particularly such strains as are liable to cause breakage.

Another aim of the invention is to provide such a sifter in which a plurality of stacks of screens can be mounted, and which will handle any desired large volume of materials and in which the stacks of screen frames are reliably clamped together as masses separate from the frame and each mass clamped to the frame without irregular strain thereon.

A further feature of the invention is to provide a holding mechanism for the top frames of the stacks of screens which automatically raises when released. By this means each relatively heavy top frame is raised automatically when released thereby rendering the screens of the stacks directly accessible without having to lift the top frame free from the sifter. as has been necessary heretofore.

. Another object is to provide a'master clamp for each stack of screen frames and which is simple in construction, readily accessible and is so designed as to avoid all danger of breakage of either the clamp or the part of the frame to which the clamp is anchored.

Another object is to provide a simple and readily accessible end clamp for each stack of sieves, which clamps to the stack as a group without strain upon the frame and holds the stack solidly without strain upon the frame, all frame strains tending to cause crystallization of the frame members.

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

Fig. 1 is a side elevational view of a high speed sifter embodying the present invention.

Fig. 2 is an end elevatlonal view.

Fig. 3 is a top plan view, showing the supporting reeds in section.

Fig. 4 is a vertical sectional view taken on line i l, Fig. 3 and showing some of the screens in elevation.

Fig. 5 is an enlarged horizontal sectional view, taken on line 5-5, Fig. 2.

Figs. 6, 7 and 8 are fragmentary, vertical sectional views, taken on the correspondingly numbered lines in Fig. 5.

Fig. 9 is a fragmentary view similar to Fig. 1 and showing one top frame released and lifted by its supporting springs to render accessible the.

screen frames of the corresponding stack.

The body of the high speed sifter embodying the present invention is generally of rectangular boxlike form and is shown as carrying a stack of screens at its opposite ends, although it will be understood that four stacks of screens could be provided, two at each end, to double the capacity of the sifter. Since the body is of identical construction at its opposite ends, the same reference numerals will be used to designate similar part at each end.

The main supporting frame for the sifter comprises a pair of horizontal side channel beams 20 which are arranged on opposite sides of the sifter and which are arranged in a horizontal plane intersecting the center of gravity of the sifter. The channels of these channel beams 20 are shown as facing outwardly and at the center of the sifter these side channel beams are shown as rigidly connected by a pair of horizontally spaced transverse channel beams 2|, the ends of which can be welded to the side channel beams '20 and reinforced by gussets 22 which serve to hold the channel beams 20 and 2! in rectangular relation. A pair of horizontal channel beams 23 are arranged centrally of the sifter to extend foreand-aft and are secured at their ends, by bolts 24 or in any suitable manner, to the upper and lower sides of the transverse channel beams 22.

To support this main frame for gyratory circular movement in a horizontal plane, each end of each of the main longitudinal side channel beams 20 is supported by a plurality of wooden reeds 25. The upper ends of each group of these wooden reeds Z5 is shown as anchored in a support 26 secured to the ceiling framework of the building in which the sifter is housed and the lower end of each group of reeds 25 is secured by a block and clamping plates 28 to the outer face of the corresponding longitudinal side channel beam 20 by screws 29 or in any other suitable manner.

To gyrate the main frame, in a horizontal plane to traverse such perfect circles, a shaker mechanism is provided which is preferably constructed as follows:

A vertical shaft 36 is journaled in the longitudinal central channel beams 23 by a thrust bearing 3! carried by the upper longitudinal central channel beam 23 and a bearing 32 carried by the companion lower central longitudinal channel beam 23. This lower bearing 32 need not be a thrust bearing since in operation the shaft 39 floats so that the upper bearing 3| is made in the form of a thrust bearing to support the shaft when the sifter is at rest. It is important, however, that the shaft 36 intersect the center of gravity of the sifter. At this point of intersection of the shaft 30 and the center of gravity of the sifter, a drive pulley 33 is fast to the shaft 30, this pulleythereby being disposed in the center of gravity of the sifter. This drive pulley 33 is arranged between the two longitudinal central channel beams 23 of the sifter frame, as shown in Fig. 4. This pulley 33 has a lower flange 34 to support a drive belt 35, the two stretches of which belt can pass horizontally outward from either side of the sifter through a pair of openings 36 provided in each of the main longitudinal side channel beams 20 for this purpose.

Outside of these openings 38, idler pulleys 38 and 39 are mounted on the corresponding main longitudinal side beam 20 and from these pulleys the corresponding stretches of the belt are shown as passing under pulleys 40 carried by a bed or support 4| and thence passing around a drive pulley 42 on the shaft of a motor 43.

The pulley 39 on the tight side of the belt 35 can be secured to the corresponding main longitudinal side beam 20 of the frame by a bearing bracket 45 of any suitable character but the pulley 38 on the loose side of the belt 35 is shown as being adjustable to permit of tightening the belt.

For this purpose, the pulley 38 is shown as rotatably mounted between the arms of a yoke 43, the upper end of this yoke being pivoted to a bracket 48 which is in turn secured to the top flange of the adjacent main longitudinal side channel beam 29. To the lower end of one arm of this yoke 46 is pivotally secured one end of a horizontal adjusting rod 49 which extends horizontally across to the other side of the sifter and through an opening provided in a bracket 59 secured to the opposite main longitudinal side channel beam 20. The free end of the adjusting rod 49 is threaded and works in a hand adjusting nut 5| which is rotatably mounted, but held against axial movement by the bracket 50. It will be seen that turning the nut 51 by hand serves to move the adjusting rod 49 axially thereby to swing the yoke 46 and its pulley 38 inwardly or outwardly, this, in turn, tightening or loosening the slack stretch of the belt 35 which passes over this pulley 38. v I

The shaft 30 is eccentrically weighted at its opposite ends to cause the frame, suspended by the reeds 25, to gyrate in a horizontal plane in perfect circles. As these eccentric weights are identical in construction, a description of one will be deemed to apply to both.

The numeral 58 represents an H-shaped rectangular head or block fast to the correspond-' ing end of the shaft 30 and in the arms of which a pair of horizontal parallel rods 59 are slidably mounted. To the corresponding ends of these rods 59 is secured a D-shaped weight 63, the

flat side of this D-shaped weight bearing a ainstthe corresponding face of the supporting block or head 58 so that this weight is always eccentric to the axis of rotation of the shaft 30. The rods 59 project from the opposite side of the supporting block or head 58 and have threaded extremities which receive an adjusting nut BI and a lock nut 62. Interposed between each adjusting nut GI. and the supporting block or head 58 is a helical compression spring 63, this spring surrounding the corresponding rod 59 and the metal or. wire forming its convolutions being rectangular in cross section.

The D-shaped weights 6!) are arranged eccentric to the axis of the shaft 39 and hence when the motor 43 is started and the weights rotated, these weights tend to move radially outward, their rods 59 sliding in the supporting block or head 58 against the resistance of the square or rectangular springs 83. The further these weights swing out, the greater the orbit of oscillation of the sifter frame, the maximum outward position of the weights 60 being determined by the speed of rotation of the shaft 30 and the degree of resistance of the springs 83.-

At spaced intervals along each of the main longitudinal side channel beams 20 of the sifter frame, depending rods 66 extend upwardly through the flanges of this beam 29 and are secured to nuts 68 supported on the upper flange of this beam. These rods 66 extend through the side angle bars 69 of a supportin platform frame 19 composed of these side angle bars 69, end transverse angle bars H connecting the ends of the side bars 69, and intermediate transverse angle bars 12 connecting the intermediate parts of the side bars 69 at places directly below the transverse channel beams Zl-of the main frame of the sifter. The platform frame, composed of the angle bars 69, H and "i2 is supported by nuts 13 at the lower ends of the vertical rods 56.

At each end of the sifter a rectangular horizontal platform 76 is secured to the frame 10, each of these platforms being secured at its edges in any suitable manner, to the undersides of the adjacent rectangle of the angle bars 69, H and l2- of this platform frame. Each of these platforms is provided with spouts 15 through which the sifted material is discharged in separate streams and each platform 14 carries a stack of screens indicated generally at 16.

The screens of each stack can be of any suitable construction to sift, bolt, separate, screen or grade the material into different sizes. Each of these screens is shown as including an inner wooden frame 89 of square or rectangular form which is shown as provided on one of its longitudinal sides with a vertical "throughs passage 82 which may be divided into sections by a partition 33 and provided on its opposite longitudinal sides with vertical inner throughs channels "2 which may be divided into sections by a partition I83. At one of its transverse sides, the inner screen frame is shown as provided with a. vertical "overs channel or passage 84 which extends across the entire width of this frame and may be divided into one or more sections by a partition 85. The opposite transverse end of the inner screen frame is closed or unprovided with any vertical passage but the entire screen frame structure as above described is shown as enclosed by an outer rectangular frame 86 of the same height and connected therewith by corner blocks 88.

The inner screen frame 80 carries a pair of central cross bars 98 which are parallel with the sides of the inner frame and hence cross each other at the center of the frame and divide the frame into four equal square or rectangular screening areas. All of these areas are covered by a screen of bolting or sifting cloth 9|. this cloth being usually made of fine mesh woven silk, although, of course. other materials could be used. This bolting or screening cloth is secured at its edges to the side bars of the inner screen frame 89.

Below the bolting screen a cleaner carrier 92 is mounted on the inner screen frame 89, this cleaner carrier preferably consisting of agrate of coarsely woven wires upon which the screen cleaners (not shown) are loosely supported for cleaning the bolting screen cloth 9| from its underside. Below the cleaner carrier 92. a plate or sheet 93 of sheet metal can be arranged to enclose the bottom of the inner screen frame 89, this plate receiving the throughs and directing them into one or the other of the throughs passages or channels 82, I82 as determined .by the inclination of this plate and the side of the inner frame 69 left open above this plate. The various throughs and overs passages of the several screens I6 are arranged to deliver the segregated material to the proper spouts I in the platform I4 on which each stack of the screen frames I6 rests.

The top of each stack of the screens I6 is covered by a rectangular header 95 which has side walls 96 engaging the outer rectangular frame 86 of the uppermost screen and a top wall 98 provided with an inlet spout 99 connected to the supply of materials being screened by a stocking or flexible tube 91 and through which stocking 91 and inlet spout 99 the materials to be screened are admitted and deposited on the uppermost screen I6. Each stack of the screens I6, together with its header 95, is securely clamped to the sifter frame by means which are preferably constructed as follows:

At the center of the sifter each of the two corners of each stack of screens I6 is embraced by a vertical angle bar I99, each of these angle bars fitting into the corresponding corner between the main longitudinal channel beams 29 and the transverse channel beams 2I of the main frame of the sifter, as best shown in Fig. 5. Similarly the other two corners of each stack of screens I6 are each embraced by a vertical angle bar I 9|, these angle bars I9I being arranged inside of the main longitudinal channel beams 29 and the outer 1 members 69 and II of the platform frame I9. To the lower end of each of these vertical angle bars I99, I9I is fixed a laterally outward projecting pin I92 which fits into a jaw I93 on top of the corresponding side bar 69 of the platform frame I9, these jaws opening horizontally and fore-andaft of the sifter and the jaws for each stack of screens opening in'opposite directions, as best shown in Fig. 4.

Each of the corner angle bars I99, I9I is provided near its lower end with an outwardly-projecting lug I94, these lugs projecting fore-andaft of the sifter and being provided on their upper sides with a groove to receive a tie rod I95. Each tie rod is provided with a head at one end engaging one lug I94 and is threaded at its opposite end to receive a wing nut I96, which 6 screens 16 therebetween. Similarly each of th corner angle bars I99, I9I is provided near its upperend with an outwardly projecting lug Ill, these lugs projecting fore-and-aft of the sifter and being apertured to receive a tie rod Ill. Each tie rod I99 is provided with ahead at one end and is threaded at its opposite end to receive a wing nut 9, which bears against the adjacent lug I98 of the adjacent corner angle bar I99 or I9I. It will therefore be seen that tightening the wing nuts II9 draws the upper ends of the corresponding pair of vertical angle bars I99 and I9I together to securely clamp the upper ends of the stacks of screens I6 therebetween.

To each end of each of the main longitudinal side beams 29 of the main frame of the sifter, is

- pivotally secured a clamping plate I I 5 which is L- shaped in horizontal section. For this purpose each of these L-shaped clamping plates H5 is provided with a pair of vertically spaced ears II6 each of which is secured by a vertical pivot bolt II8 to the corresponding flange of the adjacent main longitudinal sid channel beam 29 of the main frame of the sifter. As best shown in Fig. 5, these L-shaped clamping plates II5 are swingable to embrace the corners of the vertical angle bars IN and each is provided with an apertured ear II9 which projects longitudinally outward from the corresponding end of the sifter and the pair of these cars H9 at each end of the sifter receiving a rod I29 which is threaded at its opposite ends. On each threaded end of each of these rods is a threaded hand wheel I2I, the hubs of which bear against the sides of the ears II9 so that upon tightening these hand wheels the L-shaped clamping plates II5 are drawn together and into engagement with the vertical angle bars I9I.

To clamp each stack of screens I6 down upon its platform 14, each stack is capped or surmounted by a top frame indicated generally at I25, a feature of the invention residing in the automatic lifting of these top frames I25 when the wing nuts which fasten them down are released. This automatic elevation of these top frames makes it unnecessary for the operator to climb up and lift them down in taking out the stacks of screens I6, the self-lifting feature automatically lifting them free from the stack.

Each top frame I25 is made of angle irons connected to form a rectangle which tightly fits over the upper header of each stack of screens I6 so as to be secured thereto as best shown in Figs. 3, 4 and 9. At each side this top frame is provided with a. pair of slotted ears I26 through each of which a vertical rod I29 extends. The lower end of each of these rods I28 is threaded and screws into the corresponding nut 68, these nuts 68 supporting the rods 66 as previously described. Above the nut 68, a collar I29 is fixed to each rod I28 and a helical compression spring I39 is arranged around each rod I29 and is interposed between each collar I29 and the corresponding ear I26 of the top frame I25. The springs I39 are of sufiicientstrength that, when each top frame I25 is released, they lift this top frame and rectangular header 95 to the position shown in Fig; 9 in which position the stack of screens I6 are directly accessible for removal.

The flexible stockings 9I accommodate this lifting of the top frames I25 and headers 95. The lifting movement of these springs I39 is limited by a stop collar I3I at the upper end of each rod I29. It will be noted that the springs I39- not only render the screen frames I readily accesslble but also render it unnecessary to remove the stockings 91 in changing these screen frames as has been necessary heretofore.

The top frames are drawn down to clamp the stack of screens I5 against the platform I4 by wing nuts. For this purpose the side angle bars of the top frame I25 are extended longitudinally fore-and-aft of the sifter to provide a pair of longitudinally slotted ears I35 at the inner corners of the top frame and a pair of longitudinally slotted ears I35 at the outer corners of the top frame. A swing bolt I38 is pivoted to each ear I00 of the inner vertical angle bars I00 and swings into the slot of the corresponding ear I35. Each swing bolt I38 is provided with a wing nut I39 and it will be seen that upon tightening these wing nuts I39, the inner ends of the top frames I25 are drawn downwardly to firmly clamp the rear of the stacks of screens downwardly against their platforms I4. To similarly clamp down the outer corners of each top frame I25, a cam I40 is rotatably mounted on each end of each horizontal rod I20, this cam I40 having a cam face I4I which engages the corresponding face of the adjacent vertical angle bar IOI when the cam member is rotated clockwise as viewed in Fig. 6. This rotation of this cam member thereby serves to provide horizontal end clamping pressure to urge the stack of screens 16 toward the center of theslfter. Each cam I40 also serves as the anchorage for the lower end of a rod I42 which extends upwardly through the corresponding slotted ear I36. The upper end of each of these rods I42 is threaded to receive a wing nut I43 which bears against the top of the corresponding ear I35. It will therefore be seen that screwing down the wing nuts I43 not only tightens down the outer ends of the top frames I but also rotates the cams I40 clockwise, as viewed in Fig. 6, to force the corner angle bars IOI horizontally toward the center of the sifter to provide a horizontally acting end clamp for each stack of screens I5.

The-clamping of each stack of screens I5 is completed by master clamps which urge the inner vertical angle bars I00 of the stacks toward each other. For this purpose a plate -I is bolted to the inner face of each of the transverse channel beams 2I of the main frame of the sifter. Each of these plates I50 has a threaded stud I5I which projects out through a hole provided in the corresponding main longitudinal side channel beam 20 of the main frame of the sifter. Each stud I5I extends through a clamping plate I52 housed in the channel of the corresponding channel beam 20 of the main frame and each stud is provided with a nut I54. The opposed ends of the clamping plates I52 are provided with laterally extending lugs l55 whichfulcrum against the outer faces of the channel beams 20 of the main frame and the opposite end of each clamping plate I52 carries two pins I56 which extend through holes in the channel beam 20 of the main frame to engage the side of the corresponding corner angle bar I00 of the stack of screens 15. It will be seen that tightening the nuts I54 draws the clamping plates I52 inwardly and, through their pins I55, forces the inner vertical corner angle bars I00 of the stacks toward each other to firmly clamp the stacks of screensIIi. It will further be seen that the strain on the main frame in providing this master clamping action is directly lengthwise of the transverse channel beams 2| of the main frame Ilu thereby to avoid all danger of crystalllzing the main frame in providing such clamping action. The avoidance of strain upon the main frame in clamping the stacks of screens I0 in position is of paramount; importance in providing a heavy duty high speed sifter.

The sides of the sifter can be'enclosed by upper and lower side plates I58 and I59 which can be secured in position in any suitable manner and the main longitudinal side channel beams 20 of the main frame can-likewise be provided with cover plates I60. These enclosing plates are provided with apertures for the various rods and other parts of the sifter.

It will be noted that the stacks of screens I5 are clamped together as a mass separate from the main frame and that each stack or mass of screens is clamped to the main frame in such manner as to avoid irregular stresses on the main frame. It has been found that the main frame soon breaks down, due to crystallization when such irregular stresses are present. In particular each stack or mass of screens I5 is principally clamped to the main frame by the master clamping plates I52 which fulcrum on the outer faces of the main longitudinal side beams 20 at I55 and have pins I56 which project through holes in the side beams 20 to engage and clamp against the inner corner angle bars I00 of the stacks of screen frames. It will be observed that these master clamping plates I52 are tightened from the studs I5I which project directly out from the ends of the transverse channel beams 2I of the main frame. The stress of this clamping is therefore borne almost entirely by endwise tension against the transverse channel beams 2I of the main frame and hence without undesirable strain.

A further feature of the invention resides in the supporting of the top frames I25 for the stacks on the springs I30 so that these top frames are automatically lifted when the clamping wing nuts I39 and I43 are removed. It will be noted that this self -lifting of the top frames is provided by the simple expedient of screwing upstanding rods I 28 in the same nuts 68 which carry the depending rods 56 which support the stack of screens. and threading helical compression springs I30 on these rods, these springs engaging ears provided on the top frames.

From the foregoin it will be seen that the stacks of screens are clamped together as separate masses and that these masses are clamped to the frame without destructive stresses thereon. Further the screens can be easily removed and replaced the top frames in particular being selfrising to render the screens accessible.

I claim as my invention:

1. In a sifter, a frame including spaced main longitudinal horizontal side beams, horizontally spaced transverse beams connecting said side beams near the center of the frame, means sus pending said frame, means for moving said frame,

in a horizontal plane to describe circles, a platform at each end of said frame, a stack of rectangular screens on each platform and a clamping means for each stack of screens, comprising a corner angle bar embracing the inner corners of each stack of screens, a clamping plate arranged on the outside of each of said side beams adjacent each end of said transverse beams and fulcrumed at its inner end on the adjacent side beam between said transverse beams, means connecting the opposite outer end of each of said clamping plates with the adjacent inner corner angle bar, and screw means carried by said frame adjacent said transverse beams and projecting exteriorly of said side beams and 'engageable with each of said clamping plates at a point intermediate the ends thereof to move said clamping plate transversely of the corresponding side beam into clamping relation with the adjacent inner corner angle bar.

2. In a sifter, a frame including spaced main longitudinal horizontal side beams, horizontally spaced transverse beams connecting said side beams near the center of the frame, means suspending said frame, means for moving said frame in a horizontal plane to describe circles, a platform at each end of said frame, a stack of rectangular screens on each platform and a clamping means for each stack of screens, comprising a comer angle bar embracing the inner corners of each stack of screens, a clamping plate arranged on the outside of each of said side beams adjacent each end of said transverse beams, means connecting the opposite outer end of each of said clamping plates with the adjacent inner corne angle bar, a threaded stud secured to each end of each of said transverse beams and extending parallel therewith to a point exterior of the corresponding side beam and intermediate the ends of the corresponding clamping plate and embraced. thereby, and a nut on each stud to move the corresponding clamping plate into clamping relation with the adjacent inner corner angle bar.

screened are supplied to said stack of screens, a

top frame surmounting each top header and connected therewith to provide a removable unit,

means mounted on said first frame and releasably clamping said top frame and top header downwardly to clamp said stack on said platform, and means separate from said clamping means for raising said top frame and top header as a unit when released from said clamping means, comprising a plurality of helical compression springs arranged on each side of said top frame and interposed between said first frame and top frame to lift and. hold said top frame and top header as a unit in an elevated position to render accessible the screen frames of said stack without removal of said stocking.

Y top frame surmounting each top header and con- 3. m a sifter, a frame including spaced main longitudinal horizontal side beams, horizontally spaced transverse beams connecting said side beams near the center of the frame, means suspending said frame, means for moving said frame in a horizontal'plane to describe circles, a platform at each end of said frame, a stack of rec-. tangular screens on each platform and a clamping means for each stack of screens, comprising a corner angle bar embracing the inner corners of each stack of screens, a clamping plate arranged on the outside of each of said side beams adjacent each end of said transverse beams and fulcrumed at its inner end on the adjacent side a beam between said transverse beams, at least one pin on the opposite oute end of each of said clamping plates and extending through a hole provided in the corresponding side beam to engage the opposing face of the adjacent inner corner angle bar, a threaded stud secured to each end ofeach of said transverse beams and extending parallel therewith through an opening provided in the corresponding side beam to a point exterior of the corresponding side beam and intermediate the ends of the corresponding clamping plate, and a nut on each stud to engage the exterior face of the corresponding clamping plate to move said pin into clamping relation with the adjacent inner corner angle 4. In a sifter, a frame, means suspending said frame for horizontal movement, means for moving said frame in a horizontal plane to describe circles, a platform on said frame, a stack of screen frames on said platform, a top header for said stack of screen frames and having at least one inlet adapted to be connected by a flexible stocking through which the materials to be nected therewith to provide a removable unit, means swingably mounted on said first frame and releasablyclamping said top frame and top header downwardly to clamp said stack on said platform, and means separate from said clamping means for raising said top frame and header as a. unit when released from said clamping means, comprising a plurality of vertical rods carried by said first frame on each side of said top frame and extending upwardly through apertures in said top frame, a helical compression spring around each rod and interposed between said top frame and said first frame to lift and hold said top frame and top header as a unit in an elevated position to render accessible the screen frames of said stack without removal of said stocking, and stop means at the upper ends of said rods to limit the elevation of said top frame and top header.

, PEY'ION M. THOMPSON.

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

UNITED STATES PATENTS

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