GB2143751A

GB2143751A - Size grading screens

Info

Publication number: GB2143751A
Application number: GB08414607A
Authority: GB
Inventors: John Carruthers
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1983-07-20
Filing date: 1984-06-08
Publication date: 1985-02-20
Also published as: GB8414607D0

Abstract

A grading screen comprises a plurality of generally I-shaped elements 10, the cross-parts of which are hollow to accept coupling rods 14. Other forms of rod-embracing elements are also described and illustrated. <IMAGE>

Description

SPECIFICATION Size grading screens The present invention relates to size grading screens, and in particular, but not exclusively, to grading screens for potatoes and like agricultural produce.

Chain screen graders are already known in which rods bent into a square waveform shape have the tops and bottoms of their waveforms clipped to transverse coupling rods. These latter additionally close the open waveform shapes of the waveform rods to provide square open-bottomed receptacles for produce being graded.

The principal disadvantage of this known design is that the rod diameter is small (4 mm) and cannot be sheathed in plastic and the spring steel clips used to attach the waveform rods to the transverse rods invariably present hard sharp edges or corners which can damage the produce being graded.

It is an object of the present invention to provide a grading screen in which this risk is minimised.

According to the present invention, a grading screen e.g. for potatoes or like agricultural produce, comprises a plurality of rod-embracing elements connected together in an endless belt-like configuration providing successive rows of openbottomed accurately-shaped receptacles.

As compared with the previously known graders discussed above, the grading screen of the present invention has the advantage of facilitating the use of relatively large diameter material for the square open-bottomed receptacles with substantially no sharp edges being presented to the produce being graded.

In practice, seed and ware potatoes have to be size graded over an upper and lower square mesh grading screen before being offered for sale and under-and over-sized tubers should not represent more than 22% by weight of the sample.

Screen wear on the upper sized screen allows oversized tubers to pass into the sample and screen wear on the lower sized screen means that valuable tubers which could be sold are lost in the undersized rejects. This is very costly when high quality seed tubers are being graded.

No method of taking up the wear on existing conventional wire screens is possible and therefore these screens have to be replaced when they wear and stretch and become oversized.

The provision of individual rod-embracing elements in accordance with the present invention does not in itself solve the problem as small amounts of wear on the rubbing surfaces of adjacent elements tends to lead to bunching of the elements in the individual rows of elements.

Thus whereas in the apparatus of the present invention the amount of error introduced by element wear would be perfectly acceptable if fairly evenly spread across the full width of the screen, it is not acceptable if, as actually happens in practice, bunching results in all the error being accumulated at individual squares of the screen. Element wear is especially a problem when the elements are made of plastics materials but for convenience of manufacture and other reasons these are still the preferred materials for the elements and hence it is desirable to provide some means of lessening the undersirable effects outlined above without resorting to other less attractive materials.

Thus in a preferred embodiment of the invention, adjustment means are provided for reducing the effective length of the rods embraced by the elements by an amount substantially equal to he aggregate amount of wear that has taken place on the elements embracing that rod at the time of adjustment.

Conveniently, the adjustment means referred to above is provided by the rods themselves, each rod having an end portion bent back through at least a right angle and into contact or closely adjacent to the outer side of a side element of the screen.

Conveniently, continued wear on the elements is accommodated by an appropriate further bending of said end portion of the rod to maintain it in contact with or closely adjacent to the outer side of the relevant side element.

Clearly, the effective working life of the screen can be prolonged, if desired, by having the initial receptacle size of the screen set to give the maximum acceptable width dimension to the receptacles.

Conveniently, in preferred embodiments of the invention, the receptacle-defining elements are generally I-shaped elements, the lateral sides of the receptacles being provided by the stems of the generally I-shaped elements and the leading and trailing sides of the receptacles being provided by the cross-parts of the generally I-shaped elements which are staggered so that the cross-parts of the elements in any one row or elements are spaced apart by the cross-parts of the elements in the adjacent two rows of elements.

In an alternative arrangement, the elements are of modified I-shape with the cross-parts extending more to one side of the stem than to the other side.

In another arrangement, the elements are of rectangular C-shape with the cross-parts extending wholly to one side of the stem.

In modifications of these arrangements, the elements each comprise an assembly of smaller sections e.g. respectively comprising the stem and cross-parts referred to above.

Conveniently, the cross-parts and any part of the stem in line with these parts are hollow so as to accept transverse coupling rods which hold the elements together in said belt-like configuration.

Alternatively, however, the cross-parts and any part of the stem in line with these parts can be of C-shaped or other suitable cross-section allowing them to be clipped on to the coupling rods with the open part of their cross-section remote from the produce-bearing faces of the elements.

Conveniently, the limbs of the elements are substantially circular in cross-section although elements of any other suitable shape lacking sharp edges or corners in its receptacle-defining regions may be used instead if desired.

Conveniently, the elements are moulded out of polypropylene although other plastics materials such as nylon would also be satisfactory.

Conveniently, where the grading screen is intended for use with potatoes or other products of like size and shape, then the stems of the elements will be 12 mm diameter. The stems of the elements for a 40 x 40 mm aperture grading screen will be 64 mm long and the cross-parts will be about 24 mm long. In this case, each cross-part may be pierced by a bore of about 4.2 mm diameter to accept a 4 mm diameter coupling rod. Larger diameter, say 16 mm, stems could be used for a larger (say 85 x 85 mm) aperture grading screen.

For a smaller, say 20 mm x 20 mm aperture, grading screen, the stems might be 10 mm for example.

The invention also includes an element for use in the grading screen of the present invention and especially such an element when having the dimensions and/or one or some of the optional features outlined above.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1 to 4 show plan views of parts of different designs of grading screen according to the present invention; Figure 5 shows a schematic side view of a grader using one of these screens; Figures 6, 7, 8 and 9 show perspective views of the elements used in the grading screens of Figures 1 to 4; Figure 10 shows a modification of one of these elements; Figure 11 is a plan view of the embodiment of Figure 1 showing the cumulative effect of prolonged wear; Figure 12 is a plan view of the embodiment of Figure I modified by the inclusion of adjustment means for the cross-rods of the screen; Figure 13 is a detail of the Figure 12 embodiment showing different settings of the adjustment means; and Figure 14 shows an end view and a side view of a tool used for resetting the adjustment means.

Thus referring first to Figure 1 of the drawings, a first grading screen according to the present invention comprises a plurality of generally I-shaped elements 10, the cross-parts of which are hollow, as shown at 12 in Figure 6, to accept coupling rods 14. Plastic encapsulated fasteners 15 are fitted at the ends of each rod to secure the elements in position.

It will be observed from Figure 1 that each receptacle of the endless belt-like configuration formed in this way, has its lateral sides provided by the stems of the elements in the associated row of elements while its leading and trailing sides are provided by the cross-parts of those same elements and by the cross-parts of the elements in the adjacent two rows of elements. This is indicated in Figure 1 for one such receptacle 20 where reference numerals 22, 23 indicate the lateral sides of the receptacle and reference numerals 25, 26, 27 and 29, 30, 31 indicate the cross-parts providing the leading and trailing sides respectively.

Figure 2 shows a second grading screen according to the present invention in which modified Ishaped elements 10 have been used, each with its cross-parts extending further to the right of the stem than to the left (see also Figure 7).

Figure 3 shows a third grading screen according to the present invention in which rectangular Cshaped elements 10 have been used, each with its cross-parts extending to one side only of the stem (see also Figure 8).

Figure 4 shows a fourth grading screen according to the present invention in which the elements, generally I-shaped in this case (see also Figure 9) are made up of an assembly of smaller sections 2, 4. In other variations, not shown, the elements of the earlier embodiments are also divided up into smaller sections in an analogous fashion.

Turning now to Figure 11, this shows, by way of example how in the embodiment of Figure 1, small amounts of wear on the rubbing surfaces of the plastic I-section elements 10 tend to accumulate in one square and the affected squares cross back and forth across the screen in a diagonal fashion.

On a 40 mm square mesh upper screen with 17 squares across its width this means that 6% by number of the tubers can be oversized and this is an unacceptably high figure.

Figure 12 shows a modification of the Figure 1 embodiment in which the end portions 32 of the rods 14 extend through apertures into the slots 33 of slotted side elements 34 of the screen. There they are bent back through at least a right angle to bring them into contact or closely adjacent to the outer sides of elements 34.

Rebending the end portions of the rods 14 to take up further wear is illustrated in Figure 13 where reference numerals 35 indicate the accumulated wear for two rows of elements 10 while reference numerals 36 indicate the end portions of the next pair of rods bent back to a further extent than previously so as to take up this wear and once again bring all the associated elements 10 into engagement with one another. Readjustment of the rods in this way can greatly increase the life of the screen because the small amounts of wear on each mesh square (say 0.2 mm), does not significantly affect the grading accuracy of the screen.

Rebending the wires can easily be accomplished on the farm by hammering the end portions 32(36) further over with a tool 37 of the type shown in Figure 14. This is essentially a block having a grooved end 38 for fitting over the end portions of the wire and an opposite end 39 for hammering.

The width of the block is such as to allow it to enter the slots 33 and its height is such as to ensure that the end 39 will project from the slot for hammering.

The modiciation of Figure 12 may, of course, equally well be incorporated in the other embodiments and variations described herein and/or illustrated in the drawings.

In modifications of the arrangements and varia tions described so far, the cross-parts and any part of the element stem in line with these parts may be of C-shape or other suitable cross-section allowing them to be clipped on to the coupling rods with the open part of their cross-section remote from the produce-bearing faces of the element. By way of example, Figure 10 shows such a modification of the I-shaped element of Figure 6.

Turning now to Figure 5, this shows a side view of a complete root crop grader using the grading screen (8) of any of Figures 1 to 4 or a variation or modification of these designs as above described.

In this Figure, reference numeral 40 indicates a delivery conveyor to the screen 8; reference numeral 42 indicates a transverse conveyor for removing undersize produce which has passed through the apertures of the screen 8; and reference numeral 44 indicates a series of inspection rollers for produce conveyed by and discharged from the screen in the direction shown in the drawing. Vertical agitators (not shown) for the top run of the screen 8 are also preferably included.

Typical dimensions and materials for the elements 10 have been given in the introductory portion of the specification. A typical overall screen width for a potato conveyor according to Figures 1, 2, 3 and 4 might be 600, 900 or 1200 mm for ex- ample.

At least the preferred embodiments of the grading screen according to the present invention have the advantages of minimal damage to the produce being graded, high grading accuracy, the ability to adjust for wear, hard-wearing and non-corrosive materials, and individual elements which are easily replaced, cheap to manufacture, and easily assembled to make up any length or width or grader screen.

Claims

1. A grading screen comprising a plurality of rod-embracing elements connected together in an endless belt-like configuration providing successive rows of open-bottomed accurately-shaped receptacles.

2. A grading screen as claimed in Claim 1 including adjustment means for reducing the effective length of the rods embraced by the elements by an amount substantially equal to the aggregate amount of wear that has taken place on the elements embracing that rod at the time of adjustment.

3. A grading screen as claimed in Claim 2 in which the adjustment means is provided by the rods themselves, each rod having an end portion bent back through at least a right angle and into contact or closely adjacent to the outer side of a side element of the screen.

4. A grading screen as claimed in Claim 3 in which continued wear on the elements can be accommodated by an appropriate further bending of said end portion of the rod to maintain it in contact with or closely adjacent to the outer side of the relevant side element.

5. A grading screen as claimed in any of Claims 2 to 4 in which the initial receptacle size of the screen is set to give the maximum acceptable width dimension to the receptacles.

6. A grading screen as claimed in any preceding claim in which the elements are generally Ishaped elements, the lateral sides of the receptacles being provided by the stems of the generally Ishaped elements and the leading and trailing sides of the receptacles being provided by the crossparts of the generally I-shaped elements which are staggered so that the cross-parts of the elements in any one row or elements are spaced apart by the cross-parts of the elements in the adjacent two rows of elements.

7. A grading screen as claimed in any of Claims 1 to 5 in which the elements are of modified Ishape with the cross-parts extending more to one side of the stem than to the other side, the lateral sides of the receptacles being provided by the stems of the elements and the leading and trailing sides of the receptacles being provided by the cross-parts of the elements which are staggered so that the cross-parts of the elements in any one row or elements are spaced apart by the cross-parts of the elements in the adjacent two rows of elements.

8. A grading screen as claimed in any of Claims 1 to 5, in which the elements are of rectangular Cshape with the cross-parts extending wholly to one side of the stem, the lateral sides of the receptacles being provided by the stems of the C-shaped elements and the leading and trailing sides of the receptacles being provided by the cross-parts of the C-shaped elements which are staggered so that the cross-parts of the elements in any one row or elements are spaced apart by the cross-parts of the elements in the adjacent two rows of elements,

9. A grading screen as claimed in any preceding claim in which the elements each comprise an assembly of smaller sections.

10. A grading screen as claimed in Claim 9, in which the smaller sections respectively comprise the stem and cross-parts of the elements.

11. A grading screen as claimed in any preceding claim in which the cross-parts and any part of the stem in line with these parts are hollow so as to accept transverse coupling rods which hold the elements together in said belt-like configuration.

12. A grading screen as claimed in any of Claims 1 to 10 in which the cross-parts and any part of the stem in line with these parts are of Cshaped or other suitable cross-section allowing them to be clipped on to transverse coupling rods with the open part of their cross-section remote from the produce-bearing faces of the elements, said transverse coupling rods being effective to hold the elements together in said belt-like config uration.

13. A grading screen as claimed in any preceding claim in which the limbs of the elements are substantially circular in cross-section or are of any other suitable shape substantially lacking sharp edges or corners in its receptacle-defining regions.

14. A grading screen as claimed in any preceding claim in which the elements are moulded out of polypropylene or other plastics material.

15. A grading screen as claimed in any preceding claim for use with potatoes or other products of like size and shape, in which the elements define receptacles having a length dimension of about 64 mm in the direction of travel of the screen and a width dimension of about 24 mm in the transverse direction.

16. A grading screen as claimed in Claim 15 in which each cross-part is pierced by a bore of about 4.2 mm diameter to accept a coupling rod of 4 mm diameter.

17. A grading screen substantially as hereinbefore described with reference to, and/or as illustrated in, Figures 1 to 4 of the accompanying drawings or as hereinbefore described with reference to, and/or illustrated in, Figures 1 to 4 when modified by reference to Figure 10 or 12 and 13.

18. An element for use in the grading screen of any of Claims 1 to 17.

19. An element substantially as hereinbefore described with reference to, and/or as illustrated in Figures 6 to 10 of the accompanying drawings.

20. A grader including a grading screen as claimed in any of Claims 1 to 17.

21. A root crop grader substantially as hereinbefore described with reference to, and/or as illustrated in, Figure 5 of the accompanying drawings.

22. A rod-bending tool substantially as hereinbefore described with reference to, and/or as illustrated in, Figure 14 of the accompanying drawings.