Abstract:
Screen separators and a screen tensioning system for separators that facilitates rapid measurement of screen tension. Each separator subframe screen is suspended between opposed subframe walls. Suitable linkages distribute vibration during the aggregate sifting process. Screen edge flanges are secured by tensioners that control a screen suspension bracket. A carriage bolt fitted through bracket orifices and the walls coaxially receive a resilient grommet captivated by an adjustable sleeve nut. As the nut is tightened, screen tension increases and the grommet diameter increases. A portable gauge with an internal U-shaped measurement sleeve is fitted over the deformed grommet to measure screen tension. A plurality of gauge calibration points bordering the deformed grommet determine applied screen tension.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to vibrating screen separators for processing commingled mixtures and separating and assorting their solid constituents. More particularly, the present invention relates to separator screen machines, and to methods and apparatus for adjustably tensioning the vibrating screens they use for sifting and separating aggregates. 
   2. Description of the Related Art 
   Numerous screen separator devices are known in the art for processing commingled mixtures. With machinery of this nature, aggregates of various desired sizes are separated from differently sized portions of an incoming raw mixture. Typical separator devices are associated with suitable bulk handling equipment, including chutes, conveyors and the like, that deliver raw material to the separator, and thereafter transfer separated constituent elements away from the separator stages for further processing or storage or shipment. Screen separators designs involve multiple generally planar, screens that are mounted on subframes and vibrated during operation. Screens or groups of screens may be stacked vertically, or arranged serially in a processing plant. Elements of materials traversing the vibrating screens gravitationally drop below for further collection and processing. Numerous successive screening steps are often accomplished with laterally adjacent or vertically stacked screen decks. Typically the separator screens are tightly mounted and supported within an encircling subframe that is secured to the machine framework. Vigorous agitation in the form of screen vibration and/or oscillation is imparted through a variety of different mechanical systems causes material movement and enhances the separation effects. 
   Prior art vibrating screen separators are seen in prior U.S. Pat. No. 4,274,953, issued Jun. 23, 1981, and U.S. Pat. No. 5,199,574 issued Apr. 6, 1993, both of which are entitled “Vibrating Screen Separator.” Both of these patents are assigned to J &amp; H Equipment, Inc., the instant assignee. The latter reference discloses a vibrating screen separator having a generally planar sifting screen that is forcibly vibrated. The separator may be configured with stacked decks and serially connected sections involving multiple sifting planes. In the latter patent reference, the emphasis was upon a means of tuning the interconnecting vibratory apparatus for maximum sifting effects by optimizing vibrational energy control. In the separator sheets, cloth is tensioned between subframe sides by mounting rails that are tightened by eye nuts externally accessible at the sides of the frame. Material gravitationally flows over the vibrating screens towards a discharge position. The screen cloth is shaken by an elongated, center strip that is oscillated by a vibrator drive system. 
   Vibrating screen separators are subject to continuous wear and tear during operation. The screen sections must be mounted tightly in proper alignment. Screen tension is controlled by the multiple peripheral eye nuts or mounting hardware that surrounds the subframe. Adjustments are required periodically, and during routine maintenance or the replacement of screen sheets, the multiple eye nuts must be tediously inspected and adjusted to insure proper operational tension. No simple means for simply and quickly measuring screen tension has hitherto been available. 
   A system for easily maintaining proper screen tension with a minimum of operator effort is desirable. An adequate screen tensioning system should be quickly and easily adjustable, and means must be provided enabling an operator to quickly discern the setting of the tensioning hardware. A screen separator having tensioning elements whose settings can be readily determined visually, for example, would significantly ease the maintenance and operation burdens imposed upon the machine operators. 
   BRIEF SUMMARY OF THE INVENTION 
   Our invention provides an improved screen separator, and an improved tensioning system for securing and stretching separator screens used for material processing. The preferred tensioning system provide a highly visibly and easily measured indication of screen tension. 
   A preferred separator has at least one separator subframe comprising a screen that is adapted to be tensioned between a pair of subframe walls. Suitable vibrations are transmitted through appropriate linkages to distribute vibration. Relatively large aggregates that cannot drop through the screen travel across it to a laterally spaced-apart delivery point, and those particles dropping through it gravitationally can be recovered below, or can be conveyed by lower screens to an appropriate remote location for offloading. 
   Each generally rectangular screen subframe comprises a pair of rigid, spaced apart walls that receive and secure outer edges of the sifting screens. Each screen is mounted along its ends to opposite, internal surfaces of the subframe walls by a plurality of spaced apart tensioners that engage conventional screen edge flanges known in the art. The tensioning system preferably comprises a one-piece suspension bracket on inner subframe walls. The preferred bracket preferably has a planar, apertured center integral with a lower foot and an arm that angles upwardly away from the center. The bracket foot is coupled to the screen edge flange for imparting screen tension. 
   Each tensioner is secured by a suitable fastener, preferably an elongated carriage bolt, that is fitted through suitable bracket orifices and, aligned orifices in the subframe walls. The carriage bolt shank coaxially mounts a resilient grommet that is captivated by a washer and sleeve nut threadably coupled to the carriage bolt end. As the sleeve nut is tightened, screen tension increases. Concurrently, the resilient grommet is compressed and deformed, so that its diameter increases. Grommet diameter is directly related to applied screen tension. 
   A portable gauge adapted to be fitted around the grommet quickly and easily measures screen tension. The gauge has a pair of legs disposed on opposite sides of an elongated, U-shaped measurement channel that decreases in width towards the gauge top. A plurality of calibration points are defined along inner leg edges. When the gauge is fitted about a grommet, the grommet slides within the measurement channel until interference prevents further slidable movement. The larger the grommet, and the concomitant compression, the less the grommet can slide within the gauge measurement channel. Calibrations defined upon inner edges of the gauge feet provide a measurement of screen tension by directly measuring grommet diameter changes in response to axial compression. 
   Thus a basic object of our invention is to provide a system for easily maintaining proper screen tension in screen separators. 
   Another object is to minimize the amount of time and effort required of screen separator machine operators for maintaining correct screen tension. 
   A related object is to provide a screen separator tensioning system that is quickly and easily adjusted. 
   Another important object is to provide a tensioning system of the character described wherein the amount of tension imparted to the screen can be quickly and correctly measured. 
   It is also an important object to provide a screen tension adjustment system of the character described wherein relatively precision adjustment in screen tension may be readily insured by simple portable and tools. 
   Another basic object is to provide a screen tensioning system that simplifies the maintenance and service requirements associated with industrial screen separators. 
   These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views: 
       FIG. 1  is an exploded isometric view of a stacked screen separator machine with portions thereof omitted for clarity; 
       FIG. 2  is an enlarged, fragmentary, isometric view of a single screen separator subframe, showing our tension adjustment system; 
       FIG. 3  is an enlarged fragmentary, diagrammatic view taken generally along line  3 - 3  of  FIG. 2 ; 
       FIG. 4  is an enlarged, sectional view of a preferred tensioner, derived generally from circled region  4  in  FIG. 3 ; 
       FIG. 5  is an enlarged, sectional view derived generally from circled region  5  in  FIG. 4 ; 
       FIG. 6  is an enlarged, fragmentary exploded isometric view of the tensioning system, derived generally from circled region  6  in  FIG. 4 ; 
       FIGS. 7-9  are enlarged, fragmentary sectional views derived generally from circled regions  7 - 9  in  FIG. 6 ; 
       FIG. 10  is an enlarged, fragmentary plan view of a preferred tensioner set to a predetermined screen tension; 
       FIG. 11  is a fragmentary plan view taken generally along line  11 - 11  in  FIG. 10 ; 
       FIG. 12  is an enlarged, fragmentary plan view of a preferred tensioner set to an increased screen tension; 
       FIG. 13  is a fragmentary plan view taken generally along line  13 - 13  in  FIG. 12 ; 
       FIG. 14  is an enlarged, fragmentary plan view of a preferred tensioner set to a further increased screen tension; 
       FIG. 15  is a fragmentary plan view taken generally along line  15 - 15  in  FIG. 14 ; 
       FIG. 16  is an enlarged plan view of the preferred tension gauge; and, 
       FIG. 17  is a side elevational view of the preferred tension gauge take from a position generally to the left of  FIG. 16 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With initial reference directed to  FIGS. 1 and 2  of the appended drawings, a screen separator constructed generally in accordance with the best mode of the invention has been generally designated by the reference numeral  20 . This particular separator uses a pair of vertically stacked, generally rectangular separator subframes  22  and  24 . Each subframe is mounted to and deployed upon the separator machine frame and vigorously agitated by a vibrator system  26 . Vibrations are transmitted downwardly through linkages  27  and  28  to cross pieces  30 ,  32  that distribute vibrations to the screens  34 ,  36 . Portions of material traversing the screens are separated, with the larger particles traversing the screens and laterally exiting from upper screen edges, and with smaller aggregates dropping through the screen mesh gravitationally. One or more banks of separator screen assemblies may be laterally used in sequence. However, it will be understood that the invention is not limited to separators with multiple vertically stacked or laterally spaced-apart screens. Fuller design details of vibrating screen separators of this general type are discussed in prior U.S. Pat. No. 4,274,953, issued Jun. 23, 1981, and U.S. Pat. No. 5,199,574 issued Apr. 6, 1993, which, for purposes of disclosure, are hereby incorporated by reference. 
   Referencing  FIGS. 2-4 , each screen subframe  22  comprises a pair of rigid, spaced apart and parallel walls  38 ,  39  between which the tensioned screen  34  is stretched. Walls  38 ,  39  include upper and lower flanged ends  40  that facilitate conventional mounting to the machine main frame (not shown). The screen is mounted along its ends to opposite inner surfaces  37  of the subframe walls  38 ,  39  by numerous spaced apart tensioners  42 . Referencing  FIGS. 5-7 , screen edges are securely fastened to an elongated mounting flange  44  that is mechanically coupled to the tensioner  42 . Rigid flange  44  has a generally V-shaped cross section (i.e.,  FIG. 5 ). Extreme edges  35  of a screen  34  are received between and compressively sandwiched by flange halves  46  and  47  ( FIG. 5 ). Each flange  44  can be pulled towards a given subframe wall  38  or  39  by a tensioner  42 , for stretching and tightening the sifting screens as hereinafter described. 
   As seen in  FIG. 1 , numerous spaced apart tensioners  42  serially mounted along the subframe walls  38  have external portions visible along outer subframe wall surfaces  41 . Preferably there is an elongated shelf flange  48  running along the inside of the walls  38 ,  39  immediately below the line of tensioners  42 . The cross section of flange  48  is generally L-shaped. During installation of the subframes, flange  48  provides a shelf function to aid in preliminary assembly prior to tensioning. Each of the tensioners  42  is secured inside walls  38  or  39  to an elongated suspension bracket  50  that bears against the internal wall surfaces. While bracket  50  preferably comprises an elongated extrusion, it will be apparent that the bracket function could be accomplished by a plurality of spaced-apart separate bracket elements of the same cross section. Bracket  50  preferably comprises a planar center  52  that is integral with a lower, in-turned foot  54  ( FIGS. 5 ,  6 ) and an upper, angled arm  55 . Center  52  is normally oriented substantially parallel with the walls  38  and  39 . There is an integral, curved terminal lip  56  (i.e.,  FIGS. 4 ,  9 ) at the edge of suspension bracket arm  55  that contacts the subframe inner wall surfaces. There are a plurality of spaced-apart orifices  53  defined in bracket center  52  (i.e.,  FIGS. 6 ,  9 ) which register with similar through-holes  51  ( FIG. 6 ) defined in the subframe sides. As best seen in  FIG. 5 , the lowermost foot  54  of the bracket  50  receives the screen edge flange  44  to control screen tension. Foot  54  is forced within flange vertex  58  ( FIG. 5 ) as the elements are tightened, and it is disposed above and substantially parallel with shelf flange  48  discussed previously. 
   With reference now jointly directed to  FIGS. 4 ,  8 , and  9 , the tensioners additionally comprise an elongated fastener  60  that is fitted through bracket orifices  53  and side holes  51  in assembly. The preferred fastener  60  is a carriage bolt whose head  61  abuts the planar center  52  of the suspension bracket  50 . On the outer side of the subframe walls  38  or  39  the carriage bolt shank  62  penetrates and coaxially secures a resilient grommet  64  that is compressed as tightening increases. As best seen in  FIG. 8 , a retainer washer  66  that bears against grommet  64  is compressed by tightening of a hex sleeve nut  68 . 
   Screen tightening occurs by turning sleeve nut  68 , and as nut tension is increased, screen tensioning follows. Concurrently, with tightening of nut  68  the resilient grommet  64  compresses, and suspension bracket  50  deforms as well. Grommet compression results in both axial and radial deformation. The length of the grommet  64  decreases as tension rises, and concurrently the diameter of the grommet  64  increases. The diameter of the grommet is directly related to the amount of screen tension ultimately effectuated by sleeve nut  68 . Grommet diameter changes are visually apparent and easily-measured. Diameter changes are directly related to screen tension. 
   Therefore, a gauge  70  ( FIGS. 10-11 ,  16 - 17 ) is proposed for determining screen tension by measuring grommet compression. Gauge  70  is a lightweight metallic, calibrated instrument that can be hand carried. The rigid, preferably metallic or molded plastic body comprises a top  73  that is integral with a pair of projecting, generally parallel and spaced apart legs  76 ,  77 . There is a generally U-shaped void forming a measurement channel  78  between legs  76  and  77 . The width of the measurement channel  78  is largest at the bottom of the gauge  70  (i.e., at the right side of  FIG. 16 ), and smallest near the gauge top  73  (i.e., near the left in  FIG. 16 ). As seen, for example, in  FIG. 10 , the gauge  70  may inserted over the grommet  64  and pressed towards and against it. Gauge legs  76  and  77  will be disposed upon opposite sides of the grommet, and the gauge top  73  will slide towards the grommet as long as adequate clearance exists within measurement channel  78 . 
   Opposite inner edges of the gauge feet are preferably indexed or calibrated. For example, there are a plurality of calibrated indexing points  79  ( FIG. 13 ) formed on both inner leg edges. Innermost index points are designated with the reference numeral  80  ( FIG. 11 ). The intermediate index points have been designated with the reference numeral  81 , and the outermost index points have been designated with the reference numeral  82 . As the gauge  70  surmounts the grommet  64 , the diameter of the grommet  64  (which is proportional to applied screen tension) is indicated by the index points  80 ,  81  and  82 . Grommet compression is indicated by those indexing points proximate the grommet center when forced within the measurement channel. 
   In the position illustrated in  FIG. 11 , the sleeve nut  68  is barely tensioned, so grommet diameter is normal. Grommet  64  can slide fully within gauge channel  78  such that the grommet is positioned adjacent the starting index points  80 . At this time, the sleeve nut  68  has barely been tensioned, so that grommet compression and screen tension are minimal. At the same time the suspension bracket  50  has been barely compressed by the carriage bolt fastener  60 . The outermost portion of the convex carriage bolt head  61  will be spaced a distance “X 1 ” from wall  38  as indicated in  FIG. 10 . 
     FIGS. 12 and 13  show the positions of various components when the screen has been moderately tensioned. In this instance the gauge can be moved a lesser distance upon grommet  64 , as the diameter of the compressed grommet has increased. The grommet  64  comes to rest within gauge channel  78  adjacent the intermediate indexing points  81 , which correspond to an intermediate and desired operating tension for the screens. At this point the screen has been tensioned, and its edges have moved towards wall  38 . Thus, as indicated in  FIG. 12 , distance “X 2 ” that corresponds to the space between the carriage bolt head  61  and the subframe wall  38  has decreased (i.e., it is a smaller than distance “X 1 ” in  FIG. 10  discussed previously. Also apparent is the fact that tightening of sleeve nut  68  has drawn bolt  60  inwardly, such that a tip portion  84  is exposed. 
   Finally,  FIGS. 14 and 15  illustrate maximum desired screen tension. Here the channel  78  in gauge  70  barely fits the compressed grommet  64 , whose diameter has been substantially enlarged. Here grommet  64  comes to rest within gauge channel  78  adjacent the outermost indexing points  82 , corresponding to maximal operating tension for the screens. This maximal screen tension results in a reduced distance “X 3 ” ( FIG. 14 ) that is smaller than either distance “X 1 ” in  FIG. 10  of distance “X 2 ” in  FIG. 12  discussed previously. It can also be seen that maximum tightening of sleeve nut  68  has drawn bolt  60  further inwardly, exposing more of tip portion  84 . 
   From the foregoing, it will be seen that this invention is one well adapted to obtain all the ends and objects herein set forth, together with other advantages which are inherent to the structure. 
   It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
   As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.