IE892269A1 - Screening apparatus - Google Patents

Abstract

A screen deck (11) for a screening apparatus has a base portion (12) formed from a plastics material such as nylon for attachment to a drive arrangement which imparts a cyclical motion to the screen deck. The floor of the deck is defined by metal rods (13) which extend in cantilever manner from one side of the elongate base portion (12). The ends of the rods (13) are engaged within apertures (14) provided in the elongate base portion (12). These apertures are dimensioned so that the ends of the rods (13) are positively held within the apertures, such as by force fitting, where the resilient deformation of the plastics on entry of the rod end ensures a positive engagement thereof. Retention may be enhanced by providing a groove (15) in the rod.

Description

COMPLETE SPECIFICATION Patent Application No. 2269/89 SCREENING APPARATUS11 APPLICATION No. SPECIFICATION FILED vsn-lQI U PUtfL C INSPECTION UNDER MOTION 69 AND RULE 117 '. ;L, NO * ul, -gr nF ie /, / s ι BORD NA MONA, an Irish Statutory Corporation, established under the provisions of the Turf Development Act, 1946, of Lower Baggot Street, Dublin 2, Republic of Ireland. 0153S -1IE 892269 This invention relates to screening apparatus. In particular, the invention relates to screen decks, especially screen decks for vibratory screening apparatus.

Screening apparatus typically includes a series of screen decks, each of which is driven in a vibratory or oscillatory or combined vibratory and oscillatory manner for advance of material from one screen deck to a following screen deck, with fines material falling through each screen deck under the action of the motion of the deck, and remaining unscreened material being forwarded to the succeeding deck. Each screen deck is typically a sieve-like structure, for example formed from a network of bars or mesh or defined by a perforated plate or a web of piano wire. The product to be screened, such as peat, is supported on the screen deck during vibration or motion thereof.

Fine material falls through and larger material remains on top of the screen deck to be advanced to the next deck. The screening size of each deck, i.e. the size of the interstices in the screen grid, may be same or varied at each stage of the screening apparatus.

The cleaning or clearing of screen decks of known constructions has long been a perennial problem for many users, especially those handling wettish or damp products such as peat. In a known method of preventing clogging of screen decks, an operative with cleaning equipment is stationed alongside the screens, to free them whenever blinding or clogging occurs. An alternative cleansing method uses automated brushes, which perform an effective cleaning operation on the screen decks when functional, but lead to structural complications in the screening apparatus with consequent difficulties in the reliability of the cleansing system itself.

It is known to provide screen decks having an array of rods extending in cantilever manner so that their free ends are unsupported. British Patent Specification No. 307,268 provides an arrangement of this kind in which a screen for eliminating stalks from tea consists of one or more sections, each in the form of a wire or sheet metal comb. A rocking motion is imparted to the screen when in operation to achieve the required sifting action.

British Patent Specification No. 687,499 describes a somewhat similar structure, in which there is a series of comb-like screens arranged in succession, the elements of each comb-like screen being in the form of resilient tongues, similar to leaf springs, capable of vibrating freely.

British Patent Specification No. 931,110 shows yet another arrangement of this kind, particularly directed to the screening of garbage, in which each array of cantilevered rods slopes downwardly from the fixed upper ends of the members, for downwards cascading of material to be screened during operation. Finally, the vibratory screening apparatus of British Patent Specification No. 2,134,415A provides a series of transverse screening decks, each of which is defined by finger-like members projecting from a base member, with diverging spaces being defined between the fingers.

Further cantilever-form screens are described in British Patent Specification No. 805,506, where the rods are said to diverge towards their free ends, British Patent Specification No. 856,966, where the spaces between the teeth diverge and the rods defining the teeth are of trapezoidal cross-section, British Patent Specification No. 1,075,025, in which the inclinations of individual rods differ so that the spacing between them increases from their feed ends towards their discharge ends, British Patent Specification No. 1,334,785, which provides another cascade arrangement, and British Patent Specification No. 1,555,028, where the lower ends of the screening members rest loosely against a frame portion.

It is an object of the present invention to provide screening apparatus, and in particular a cantilever-type screen deck, suitable for the reliable screening of a multiplicity of particulate materials, in particular peat, offering an improved and simplified construction as compared with known screen decks and apparatus of this kind.

According to the invention, there is provided a screen deck comprising a base portion for attachment to drive means for imparting a cyclical motion to the screen deck, and a plurality of rods extending in cantilever manner from said base portion, the base portion being an elongate member, from a side of which the rods extend to define a substantially planar array, the base portion being formed from a plastics material and the rods being formed from a metal, and the base portion being provided with a plurality of apertures dimensioned for retentive accommodation of end portions of said rods. Thus the free ends of the rods are unsupported in any way by any other structural portion of the screen deck. Suitably the screen deck of the invention is incorporated in screening apparatus in which a driving mechanism is arranged to drive a single screen deck or each of a plurality of screen decks in a vibratory and/or oscillatory manner to achieve the screening action.

In a first embodiment of the invention, said apertures are dimensioned for retention of said end portions of said rods by means of force fitting, the end portions being retentively engaged by gripping action of the plastics material of the base portion resulting from resilient deformation of said plastics material on insertion of the rod end portions. Preferably, said apertures are drilled apertures. In an alternative embodiment, the base portion is formed by moulding plastics material around said end portions of the rods, said apertures being defined during the moulding operation. In either embodiment of the invention, the base portion may be formed from nylon. Preferably, each of said rod end portions is provided with a formation for enhancing retention of the rod end portion within a said aperture. Said formation is suitably defined by a circumferential groove extending around the external periphery of the rod in an end region thereof.

The rods may be of one or more of a diversity of cross-sections, including circular, rectangular and triangular, or any other cross-section appropriate for a particular screening need. The length of the free portion of each rod extending from the base portion of the screen deck may be varied in dependence on the required dimensions of the screen deck. The spacing between each two adjacent rods in an individual deck may be varied, to suit the dimensions of the screen deck and the particular properties of the material to be screened. The rods are most suitably formed from steel. The cross-sectional dimensions of each rod in an individual screen deck array are most suitably identical, so that for a circular cross-section rod, each rod is of the same diameter.

The screen of the invention thus provides a series of bars extending from a supporting block, the free ends of the bars being unsupported. The fact that this structure has the free ends of the bars or rods unsupported results in these rods or bars themselves vibrating during vibratory or oscillatory drive of the screen deck in use of the screening apparatus, so that the screen becomes self-cleaning. Any tendency for the material being screened to clog or blind or to occupy the spaces between the rods is overcome by the vibrating movement of the rods in the array. The dimensions and spacing of the rods may be chosen, as also their cross-sections and the manner of their mounting in the base portion, to provide particular resonant frequencies in the structure, which may be matched to the drive cycle of the unit, so that especially effective anti-blinding or anti-clogging properties may be developed in the screen deck of the invention.

In another aspect, the invention provides screening apparatus comprising a plurality of screen decks as hereinbefore defined together with means for driving each deck in a cyclical manner to achieve advance and screening of material received on the screen deck, wherein the dimensions and/or configuration of the screen decks and the drive characteristics of the apparatus are matched to achieve a desired vibratory motion of the rods of the screen decks during use of the apparatus.

An embodiment of the invention will now be described having regard to the accompanying drawings, in which Figure 1 is a diagrammatic pictorial view of a screening apparatus incorporating a plurality of screen decks, Figure 2 is a side view of the screening apparatus of Figure 1, Figure 3 is a pictorial view of a portion of a screen deck according to the invention, Figure 4 is a sectional view through the base portion of the screen deck of Figure 3 showing the manner of mounting of a rod member therein, Figure 5 is a top view of a screen deck according to the invention, Figure 6 is a front view of the screen deck of Figure 5, Figure 7 is a side view of the screen deck of Figures 5 and 6, and Figure 8 is a sectional view of the screen deck of Figures 5 to 7 on the line A-A of Figure 5.

As shown in Figures 1 and 2, in a screening apparatus 1, a series of screen decks 2a to 2e are arranged in an array, each screen 2b to 2e being located forwardly and downwardly of the preceding screen 2a to 2d in the direction of advance of the material to be screened during use of the apparatus, so that the material 4 to be screened, in this case peat, travels forwardly and downwardly along the screening apparatus 1 and falls from one screen 2a to 2d to the next screen 2b to 2e in succession during the screening operation. Each screen deck 2a to 2e is driven in vibratory and/or oscillatory motion, as indicated by arrows 3, to impart an agitating motion to the material 4 to be screened, indicated diagrammatically for screen 2d only in Figures 1 and 2. Under the influence of this driving action of each screen deck 2, fines material of a size determined by the grid or mesh of the screen deck falls through the screen deck, this being indicated by reference 5 for screen 2c in Figure 2. The remaining material on the upper side of each screen deck continues to advance forwardly and tumbles over during its passage from each screen deck 2a to 2d to the succeeding deck 2b to 2e, as indicated by arrow 6 in Figures 1 and 2. Conventional screen decks typically include a grid or mesh-like structure, formed by perforated plates, webs of piano wire, or the like.

In a screening apparatus of this kind, the actual vibratory motion imparted to the screens may vary. There is always a component in the direction of advance or flow of the material, as designated by the horizontal arrow or arrows 3 of Figures 1 and 2, but at least two further motions are possible to provide up to three individual driving movements of the screen deck. In many installations, an up and down and forward motion of each individual vibrating screen deck is provided in combination, as indicated by the arrows 3 of Figures 1 and 2. The angle of tilt of each individual screen deck may also be varied. This angle may be positive or negative with respect to the direction of material advance, or the screen deck may be horizontal.

As shown in Figures 1 and 2, each screen deck 2a to 2e provides a slight upward gradient against advancing material. A relatively shallow angle of inclination is depicted, but steeper angles may be provided.

The screen deck 11 of the invention is shown in Figures 3 to 8. It is defined by a generally planar array of rods 13 extending from a base portion 12 in a cantilevered manner. Thus one end of each rod 13 is received within base portion 12 and the opposite end of the rod is free and unsupported. The base support or portion 12 from which the cantilevered rods or bars 13 of the screen according to the invention extend is formed from plastics material and is most suitably a nylon plastics product. This facilitates ready production of the unit of the invention, since no tolerance is required on the bores 14 provided in the nylon support 12. These holes are simply drilled to nominal size, and the ends of the rods 13 to be retained in the base portion 12 are forced into the holes 14, where they are retained by the gripping action of the plastics material, which expands slightly when the rods are forced in. The resilience of the plastics material then serves to hold the rods 13 in position.

At the gripped end of each rod or bar 13, where it is inserted into the plastics material portion 12, a retaining formation defined by a circumferential or peripheral groove or depression 15 is however suitably formed about 10 mm short of the end face of the rod, so as to provide an improved grip or engagement within the plastics material of the base portion 12. This groove is indicated by reference 15 in Figure 4 only. It may be formed in relatively simple manner during the production process by briefly rotating the rod end in contact with a grindstone. Alternatively, the process may be automated. On insertion of the rod end, the plastics material initially expands slightly outwardly and then springs back inwardly so that the inner wall of the aperture or bore 14 within which the rod end is received grips into or engages in the depression or recess defined by groove 15 and provides a positive grip on the retained end of the rod.

The base portion 12 when formed from plastics material may also be moulded around the ends of the rods, these being initially located in a jig and the plastics material then formed around the ends of the rods to be retained in the support 12. However, for many purposes drilling the plastics support 12 and force fitting the rods 13 represents a preferred manner of construction of the screen deck 11 of the invention.

The cantileveredly extending rods 13 are suitably without any transverse mutual interconnection between them throughout their lengths outwardly of the base support portion 12. Thus in a favoured configuration of the invention, the length of each cantilevered bar 13 is relatively short in comparison with the elongate dimension of the base 12, which dimension corresponds to the overall width of the screen deck 11. The dimensions of the screen deck 11 can be chosen together with the number of screening stages and the spacing of the screen stages so as to allow any material which becomes matted on any individual screen deck, i.e. material which has gathered itself into a non-readily separable mass, to undergo a tumbling action where it leaves the front of each screen stage to fall onto the next stage. In the course of tumbling or turning over during this transition over the free front ends of the bars to the next screen deck, there is a tendency for any matted-together masses to become separated, so that the screening action on the next stage is facilitated and proceeds more effectively.

As shown in the present drawings, the cross-section of the bar or rod 13 in the present embodiment is circular, to provide an elongate thin cylindrical rod. This configuration is favoured, but other cross-sections may also be employed. Square rods, triangular cross-section rods, and oval rods are all suitable for use with the screen deck of the invention. A square section rod may enable blinding to be completely eliminated, in that parallelsided passages are defined between each two adjacent rods for the passage of screened material. Triangular section bars are especially suited for the provision of finer and more uniform gaps for the passage of granulated material of closely regulated size. In all cases, the free ends of the bars are de-burred, to eliminate sharp edges which might possibly lead to retention of material undergoing screening, while a peripheral retaining groove is preferably formed near the mounting end of the rod.

The length, spacing and diameters or cross-sections of the cantilevered bars 13 of the screen deck 11 of the invention are all variable. The material used may also be selected to meet the particular screening demands in question. Spring steel or stainless steel may be employed, but alternatively non-metallic metals may be used. In general, the more rigid the cantilevered rods, the better the granulation. For high quality screening, where the size of the recovered material is critical, then the spacing of the bars and the overall flatness of the generally planar array are also important. Thus the bars should not be susceptible to being readily bent out of their initial structural positions in which they define portions of this planar array. For other products, for example, moss peat, the quality of granulation is less important, but since the screen of the invention provides an enhanced self-cleaning capability, as compared with known cleaning methods, which is an especial feature of the present invention and provides greatly enhanced performance in all modes of application of the invention, it is therefore of utility in screening installations of all kinds and for use in handling materials of all types.

This self-cleaning capability is now explained further and enlarged upon. By virtue of their cantilevered mounting, when the screen deck is driven during use in the screening apparatus in a vibratory and/or oscillatory mode, the fact that the free ends of the cantilevered bars are unsupported results in the bars themselves vibrating, so that the screen deck becomes self-cleaning by the vibratory action of the bars disengaging trapped material and throwing it free. In addition, this vibration may be especially intense at the free ends of the rods themselves, thereby further enhancing the tumbling action achieved in a series of screen decks, such as those shown in Figures 1 and 2, where coarser or remaining material on each screen stage is transferred to the next succeeding stage. The vibration of the tips of the rods results in this material being agitated or thrown around to an enhanced degree during this transfer or tumbling action.

A natural frequency or resonant situation may also be developed, depending on the drive speeds and the nature of the drive motion, as well as the characteristics of the rods and their manner of mounting in the screen deck. Where resonance is properly tailored to operating circumstances and the material to be filtered, it may provide a further advantageous enhancement of the invention. In the separation of fibrous products, such as peat moss and the like, intense vibration of the rods enhances the self-cleaning capability of the screen deck of the invention, which capability enables it to handle successfully wettish materials which are normally difficult to screen successfully.

In the screening apparatus incorporating the decks 11 of the invention, the width of the screen deck at each stage can be up to 6 ft., i.e. its dimension transverse to the direction of product advance. As against this substantial transverse dimension, the length of the screen bars in the direction of the travel may be 18 inches or less. Thus the screen deck of the invention provides a relatively short dimension in the direction of advance of the material to be screened. In the top or plan view of Figure 5, the screen deck of the invention resembles a comb of a fine-toothed nature, the teeth of the comb being disposed in a generally horizontal plane in use of the invention. As depicted, the bar spacing is relatively fine for many purposes, but for fibrous or moss-type products, a wider bar spacing of between 19 and 25 cm with an appropriately matched diameter of bar 13 may be favoured. - 10 IE 892269

Claims (12)

1. A screen deck comprising a base portion for attachment to drive means for imparting a cyclical motion to the screen deck, and a plurality of rods extending in cantilever manner from said base portion, the base portion being an elongate member, from a side of which the rods extend to define a substantially planar array, the base portion being formed from a plastics material and the rods being formed from a metal, and the base portion being provided with a plurality of apertures dimensioned for retentive accommodation of end portions of said rods.

2. A screen deck according to Claim 1, wherein said apertures are dimensioned for retention of said end portions of said rods by means of force fitting, the end portions being retentively engaged by gripping action of the plastics material of the base portion resulting from resilient deformation of said plastics material on insertion of the rod end portions.

3. A screen deck according to Claim 2, wherein said apertures are drilled apertures.

4. A screen deck according to Claim 1, wherein said base portion is formed by moulding plastics material around said end portions of the rods, said apertures being defined during the moulding operation.

5. A screen deck according to any preceding claim, wherein the base portion is formed from nylon.

6. A screen deck according to any preceding claim, wherein each of said rod end portions is provided with a formation for enhancing retention of the rod end portion within a said aperture.

7. A screen deck according to Claim 6, wherein said formation is defined by a circumferential groove extending around the external periphery of the rod in an end region thereof.

8. A screen deck substantially as described herein with reference to and as shown in Figures 3 to 8 of the accompanying drawings.

9. Screening apparatus comprising a screen deck according to any preceding claim and a driving mechanism arranged to drive said screen deck in a vibratory and/or oscillatory manner to achieve a screening action.

10. Screening apparatus comprising a plurality of screen decks, each of which is in accordance with any of Claims 1 to 8, and a driving mechanism arranged to drive each of said plurality of screen decks in a vibratory and/or oscillatory manner to achieve a screening action.

11. Screening apparatus comprising a plurality of screen decks, each of which is in accordance with any of Claims 1 to 8, and means for driving each deck in a cyclical manner to achieve advance and screening of material received on the screen deck, wherein the dimensions and/or configuration of the screen decks and the drive characteristics of the apparatus are matched to achieve a desired vibratory motion of the rods of the screen decks during use of the apparatus.

12. Screening apparatus substantially as described herein with reference to and as shown in the accompanying drawings. DATED THIS 12th day of July, 1990 BY: TOMKINS & CO., Applicant's Agents SIGNED: 5, Dartmouth Road, DUBLIN 6.