WO2000067921A1

WO2000067921A1 - Improved grading screens

Info

Publication number: WO2000067921A1
Application number: PCT/GB2000/001741
Authority: WO
Inventors: David Rankin; Anne Shanks
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-11
Filing date: 2000-05-11
Publication date: 2000-11-16
Anticipated expiration: 2001-11-11
Also published as: GB9910859D0; AU4592400A; GB2364003A; GB0126920D0

Abstract

A grading screen is formed from one or more sheets (10) of wear-resistant, non-metallic, material in which a plurality of closely spaced apertures (12) are provided. One elongate sheet (10) is formed into a continuous belt with its ends joined together by fastening means. The fastening means comprises two parts (30, 32). Both parts (30, 32) are of reflexive section and having two limbs (34) with one part (30) being secured to each end of the sheet (10) with a limb (34) above and below the said end of the sheet (10). One part (30) is provided with a lengthwise series of hook elements (36) and the other part (32) is provided with a correspondingly spaced lengthwise series of apertures (38) through which extends and is secured a rod (40) around which each hook element (36) is engageable and is held.

Description

IMPROVED GRADING SCREENS

This invention relates to an improved grading screeen, primarily but not necessarily, for use in grading potatoes, other vegetable or fruit.

Heretofore, potato grading is achieved by using wire mesh screens. Unprotected wire mesh screens have inherent problems when used in grading potatoes due to the nature of the potato, particularly causing skin damage and bruising but also cutting into the potato, for example when a substantially round potato becomes stuck in a rectangular mesh aperture i.e. 'pegging'. While some new screens are coated with a synthetic plastics material, or rubber or synthetic rubber material to overcome these problems, such coatings wear through leaving the unprotected wire mesh. While using plastic covered screens may prevent some skin damage and bruising, it does not obviate the problem. This is disadvantageous- An object of the present invention is to obviate or mitigate this disadvantage.

Accordingly, the present invention is a grading screen formed from one or more sheets of wear-resistant, non-metallic, material in which a plurality of closely spaced apertures are provided.

Preferably, one elongate sheet is formed into a continuous belt with its ends joined together by fastening means. The fastening means beneficially comprises two parts, both parts being of reflexive section and having two limbs with one part being secured to each end of the sheet with a limb above and below the said end of the sheet. One part is desirably provided with a lengthwise series of hook elements and the other part being provided with a correspondingly spaced lengthwise series of apertures through which extends and is secured a rod around which each hook element is engagable and is held. The elongate sheet is preferably arranged around a set of three or more rollers, at least one of which is adapted to be driven, the items to be screened being fed onto the upper flight of the belt. Movement means may be provided to vibrate at least the upper flight of the belt. Alternatively, the screen is for use as a flat bed grader having a vibratory, oscillatory or reciprocatory movement in a grading apparatus, and has two opposite lateral sides each having strap securing means therealong and at least at one end of the strap securing means, a tensioning bar extends between mountings provided on the strap securing means to maintain the sheet taut.

Preferably also, the apertures in the or each sheet are similar and are provided in a regular pattern across the sheet. The sheet is beneficially formed of a multi-layered material, the topmost layer being of a soft rubber or synthetic rubber compound- Embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:-

Fig. 1 is a side perspective view of a screen according to a first embodiment of the present invention;

Fig. 2 is an exploded perspective view of a fastening means; Fig. 3 is a perspective view of a part of a grading screen according to a second embodiment of the present invention; and

Fig. 4 is an end elevational view of the screen in the direction of arrow A. Referring to the drawings, a grading screen particularly, but not exclusively, for grading potatoes is formed from one or more sheets 10 of wear-resistant, non- metallic material. The or each sheet 10 has a plurality of similar apertures 12 spaced in a regular pattern across the sheet 10. The apertures are substantially square, hexagonal or round. Square apertures have typically a 10mm radius on each corner. The sheet 10 is formed of a multi-layered material, the topmost layer being of a soft rubber or synthetic rubber compound. The material is constructed using layers of pre-tensioned synthetic fabric, such as polyester bonded together in layers of rubber or synthetic rubber. This forms the carcass and is of conventional conveyor belt construction and gives the sheet a combination of strength, load-bearing capacity and stability. This carcass is encased between a top and a bottom covering of rubber or synthetic rubber. The bottom covering conforms to standard conveyor specification DIN 22102 Type Y or British Standard BS490. This is a wear resistant conveyor belt suitable for highly abrasive applications. On a shore hardness test, it has a shore hardness rating of 60 + or - 5% which is typical for a standard conveyor rubber. The top covering is made of a high quality super-soft rubber compound which has the advantage of reducing damage and bruising on the potato or other vegetable or fruit being graded to a minimum. On a shore hardness test it measures 40 shore hardness + or - 5%. As a potato falls onto the sheet it will be cushioned by the top covering and so will incur little or no damage as it hitsv or moves across the sheet. The top layer is made of a high grade mnatural rubber compound which is cured to give a soft texture but which still has excellent resistance to abrasion- The softness of the rubber is dependant upon variations in temperature pressure and time taken during the curing process. This top covering is bonded to the other layers of the sheet producing a very soft surface. This material combines the strength and wear resistance of a heavy duty rubber conveyor with the advantages of a hard wearing but highly shock absorbent, cushioned surface.

In a first embodiment, one elongate sheet 10 is formed into a continuous belt with its ends joined together by fastening means. The fastening means (Fig. 2) comprises two parts 30, 32. Both parts 30, 32 are of reflexive section, each having two limbs 34 with one part 30 being secured to each end of the sheet 10 with a limb 34 above and one below the said end of the sheet 10. The parts are of metal or hard-wearing plastics material. The two limbs 34 of each part 30, 32 are secured together trapping the respective end of the sheet 10. One part 30 is provided with a lengthwise series of hook elements 36 and the other part 32 is provided with a correspondingly spaced lengthwise series of apertures 38 through which extends and is secured a rod 40 around which each hook element 36 is engagable and is held. The elongate sheet 10 is arranged around a set of three or more rollers 42 ( four rollers 42 are shown, at least one of which is adapted to be driven. The items to be screened being fed onto the upper flight of the sheet 10. Movement means in the form of power driven agitators (not shown) are provided to vibrate at least the upper flight of the sheet 10. Conveying apparatus of conventional construction is/are provided to remove each grade of potatoes screened and any debris. The tautness of the sheet 10 is governed by the distance apart of the rollers 42 (one roller may be a jockey roller spring biased to take up any slack). Sides are provided along the length of upper flight of the belt with the lower flight spaced from the upper flight to allow collection hoppers or feed boots for other conveyors to be located under the upper flight to collect the rejected potatoes, soil and debris, passing through the apertures, for further processing.

Screens require to be frequently changed to allow grading of different sizes of potatoes. The two part fastener described above has been designed to be changed with the minimum of delay. It is advantageous to reduce the time taken for changing sheets on grading apparatus to a minimum since 'downtime' means lost production time. Normal conveyor fasteners are not designed to be released easily as conveyors are not usually changed frequently. In a second embodiment as shown in Figs. 3 and 4 in which like parts are denoted by like numerals, the sheet 10 is for securing across or around a frame (not shown) in a grading apparatus (not shown). The screen 10 is for use as a flat bed grader having a vibratory, oscillatory or reciprocatory movement in a grading apparatus, the movement causing any potatoes fed onto the screen to migrate thereacross with any soil and debris and potatoes smaller than the apertures 12 falling through the apertures 12, the potatoes larger than the apertures 12 passing across the sheet 10 and being collected at the discharge end thereof. The sheet 10 has two opposite lateral sides, each having strap securing means 14 therealong. The means 14 comprises two straps 14A, 14B secured together by a series of fastening devices 16, each for example a bolt and nut, at intervals therealong. At each of the two ends of the strap securing means 14, a tensioning bar 18 extends between mountings 20 provided on the strap securing mans 14 to maintain the sheet 10 taut. Each mounting 20 is an upright extension 20A of strap 14A at the inboard side of the strap 14A, the extension 20A having a threaded boss 22 through which one end of the bar 18 passes in threaded engagement as shown. The apertures 12 in each sheet 10 are similar and are provided in a regular patters across the sheet 10. In use of both embodiments, with a grading screen as described above fitted to a grading apparatus, potatoes to be graded are fed thereunto, for example from a hopper or from an elevator. As described above, by the movement imparted to the sheet 10, the potatoes migrate across the sheet 10 with potatoes smaller than the apertures 12 passing therethrough as well as any soil and debris. The larger potatoes are collected at the discharge end of the screen.

More than one sheets can be used, for example in a vertically spaced arrangement, the sheets in such an arrangement having apertures of lesser diameter from top sheet to bottom sheet to obtain different grades of potatoes.

Alternatively, a cascade arrangement of sheets can be placed in an end-to- end arrangement to obtain a series of different sized grades of potatoes.

Variations and modifications can be made without departing from the scope of the invention described above and as claimed hereinafter.

Claims

CLAIMS:

1. A grading screen formed from one or more sheets of wear-resistant, non- metallic, material in which a plurality of closely spaced apertures are provided.

2. A screen as claimed in Claim 1 , wherein one elongate sheet is formed into a continuous belt with its ends joined together by fastening means.

3. A screen as claimed in Claim 2, wherein the fastening means comprises two parts, both parts being of reflexive section and having two limbs with one part being secured to each end of the sheet with a limb above and below the said end of the sheet.

4. A screen as claimed in Claim 3, wherein one part is provided with a lengthwise series of hook elements and the other part is provided with a correspondingly spaced lengthwise series of apertures through which extends and is secured a rod around which each hook element is engagable and is held.

5. A screen as claimed in any one of Claims 2 to 4, wherein the elongate sheet is arranged around a set of three or more rollers, at least one of which is adapted to be driven, the items to be screened being fed onto the upper flight of the belt.

6. A screen as claimed in anyone of the preceding Claims, wherein movement means is provided to vibrate at least the upper flight of the belt.

. A screen as claimed in Claim 1 , wherein, the sheet is for use as a flat bed grader having a vibratory, oscillatory or reciprocatory movement in a grading apparatus, the sheet having two opposite lateral sides each having strap securing means therealong and at least at one end of the strap securing means, a tensioning bar extends between mountings provided on the strap securing means to maintain the sheet taut.

8. A screen as claimed in anyone of the preceding Claims, wherein the apertures in the or each sheet are similar and are provided in a regular pattern across the sheet.

9. A screen as claimed in Claim 8, wherein the sheet is formed of a multi-layered material, the topmost layer being of a soft rubber or synthetic rubber compound.

10. A grading screen substantially as hereinbefore described with reference to Figs. 1 and 2 or Figs. 3 and 4 of the accompanying drawings.