GB2052310A - Grading machine for particulate commodity - Google Patents

Abstract

The machine comprises feed table 10, sorting table 11, and hopper system 12 for collecting the graded particles. Sorting table 11 comprises a perforate deck 18 having two separate zones, the perforations in the first zone (A) being smaller than those in the second zone (B). The table is vibrated in a direction to cause particles to pass along the deck. The deck is made from expanded metal sheet 45 in zone A, and from a woven metal material having larger apertures in zone B. The particles are fed onto zone A via weir arrangement 29 comprising a pair of diverging square-section transverse bars 60 and 61 mounted over round- section rods 68 forming a grid for dispersing the particles. This arrangement prevents dust and smaller particles being retained on top of the mass of larger particles on the deck 18 which occurs where conventional feed arrangements are used. <IMAGE>

Description

SPECIFICATION Grading machine for particulate commodity The present invention relates to a device for grading a particulate commodity by size; more particularly, but not exclusively, the invention relates to a machine for separating a chopped commodity of a desired size from undersized particles, oversized particles and dust produced during the chopping operation. The device is particularly suitable for grading chopped nuts into desired particle sizes.

Grading machines are known which comprise a continually vibrating deck formed from open mesh material onto one end of which a particulate commodity is delivered. The apertures in the mesh increase in size towards the far end of the deck, and the vibrations cause the commodity to move along the deck towards this end. The smaller particles pass through the small perforations in the first part of the deck, and the larger particles pass over these holes and are separated when they encounter the larger apertures located further along the deck.

Products like nuts contain substantial quantities of vegetable oil, and the dust which is produced when nuts are chopped leads to frequent clogging of the mesh screens which are used for the deck in conventional machines. In addition, it is often difficult to ensure that the dust produced during the cutting and chopping operation actually passes through the perforations in the preliminary part of the deck; instead, the dust sometimes lies on top of the chopped products and is carried through into the following zones without being separated from the larger particles.

The present invention provides a grading machine for sorting a particulate commodity by size in which these disadvantages are minimised or substantially eliminated.

According to the present invention, there is provided a device for the grading of a particulate commodity by size, comprising a substantially horizontal perforate deck, delivery means for delivering the particulate commodity on to the upper surface of the deck, and vibrator means for vibrating the deck to cause the particulate commodity to move towards one end thereof, whereby the deck comprises a first zone formed from a perforated sheet material and having apertures therein through which small particles of the commodity can pass, and a second zone downstream, in the direction of movement of the commodity along the deck, of the first zone and formed from a mesh material having apertures of a larger size than those in the first zone, and means for collecting the grade commodity passing through the apertures in one or both of said zones, the delivery means being adapted to disperse the commodity as it is fed onto the upper surface of the deck to cause the smaller particles to pass through the apertures in the deck in the first zone thereof.

In order to avoid the clogging of the preliminary part of the deck which occurs when conventional mesh materials are used for oil-containing products such as chopped nuts, a perforated sheet material is used for the first zone in the device according to the invention. Preferably, this material is an expanded sheet metal material. It has been found that the sharp, stamped edges of the expanded sheet metal mesh are much less prone to clogging than conventional mesh materials. Preferably, the expanded sheet metal comprises steel sheet of between 0.5 mm and 0.65 mm thickness formed with parallelogram-shaped apertures having opposite sides with an average dimension of between 3 and 4 mm, the other sides having a dimensions of between 6 and 7 mm. Although the deck may be made from stainless steel, this is not essential where oil-containing products are being graded.

Preferably, the second zone comprises an open mesh woven metal material having an average aperture size of between 4 and 5.5 mm square. The second zone is used for collecting the chopped particles of the required size which are being extracted in the grading operation. These particles are too large to pass through the expanded sheet preliminary zone, and are collected after falling through the woven mesh. Suitably, an opening is provided at the end of the second zone through which even larger particles can be passed. These larger particles are usually agglomerated dust and smaller particles which have become consolidated due to the stickiness of the oil-containing product.

It is most important that the particles are dispersed onto the upper surface of the vibrating deck in the correct manner from the feed mechanism to ensure that the dust and smaller particles pass through the perforations in the first zone. It has been found that in some instances the smaller particles and the dust generated during the cutting operation, instead of falling through the perforations in the first zone, remain on top of the larger particles which are passing forwards towards the second zone, and as a result separation does not take place.The delivery means are designed to prevent this, and in a preferred embodiment of the invention they comprise a feed table which may be inclined towards the deck and which is located at a higher level than the deck, and a weir arrangement located at the edge of the feed table over which the particles must pass before they fall onto the upper surface of the deck.

This weir arrangement preferably comprises one or more bars arranged transverse to the feed direction and having a geometrical section (such as square or triangular) over which the particles are pushed as they are fed onto the deck. Preferably, a pair of diverging bars are provided, with their apex located adjacent the feed table and on the centre-line of the machine, and these are supported on a grid system comprising horizontal support rods disposed in the plane of the bed at an angle to the direction of travel of the particles.

The combination of the sharp edges of the transverse bar or bars and the grid arrangement described ensure that the dust and smaller particles do not adhere to the surfaces of the larger particles as the commodity passes from the feed table onto the deck, and the dust and smaller particles rapidly fall through the perforations in the first zone leaving the larger particles to pass onto the second zone.

In order that the invention may be more fully understood, embodiments in accordance therewith will now be described by way of example with reference to the accompanying drawings, in which Figure 1 shows a side elevation of a grading machine according to the invention; Figure 2 shows a plan view of the grader of Figure land Figure 3 shows part of the grader, to a larger scale, viewed along the line Ill-Ill in Figure 2.

Referring to the drawings, these show a grading machine for sorting or grading a particulate commodity on a size basis. The machine shown in the drawings is designed for separating chopped nuts of a particular size from dust and smaller particles produced in the chopping operation.

Generally the grading machine comprises a feed table 10 onto which the particles pass from the chopping machine, a sorting table 11, and a hopper system 12 for collecting the graded particles. The base of the sorting table 11 comprises a deck 18 which is formed with perforations through which the particles may pass, the deck having two separate zones A and B, the perforations in zone A being smaller than those in zone B. Vibration of the sorting table 11 causes particles delivered onto the deck 18 from the feed table to pass along the deck in the direction of arrow 20. The smaller particles pass through the perforations in zone A (as shown by arrow 21 in Figure 1) before they reach zone B. The larger particles pass through the openings in Zone B (arrow 22). The particles are collected separately by hopper system 12.

Referring now in detail to the drawings, the sorting table 11 comprises a generally channel-shaped support having a base which is formed by the perforated deck 18, side walls 25, 26 and end walls 27,28.

The sorting table includes a support comprising a honeycomb structure 30 (shown in Figures 1 and 3) consisting of intersecting slats located beneath the deck 18 and which are rigid with the side walls 25 and 26. This support 30 is provided to ensure that the relatively thin material of the deck 18 remains flat and rigid during operation.

The sorting table 11 is mounted resiliently in a frame 32 (shown only partially in the drawings) by means of leaf springs 34. These leaf springs comprise relatively inflexible plates of a platics material secured at their upper ends to lugs 35 fixed to the side walls 25 and 26 and at their lower ends to brackets 36 on the frame 32. As shown in Figure 1, the leaf springs 34 are inclined at an angle cur to the horizontal. A single leaf spring 34a atthe same inclination is provided at the narrow end of the feed table 10 to prevent whipping, and further support may be provided by tie-rods connecting the feed table 10 to the sorting table 11.

Also inclined at the same angle a are a pair of out-of-balance motors 41 and 42 which are mounted on the side walls 25 and 26 respectively to form part of the resiliently-mounted sorting table 11. The motors, which run at around 2,900 r.p.m., are counter-rotating and are located at the centre of gravity of the system; they are intended to agitate the product on the deck 18 and cause the particles to move along the deck in the direction of arrow 20.The inclination a of the motors and the leaf springs is between 65" and 85" (preferably 70 ) and induces both horizontal and vertical components of vibration into the sorting table 11, these components being in a vertical plane so that there is substantially no vibrational motion of the table in a horizontal direction perpendicular to the longitudinal axis thereof.

In this way, the particles are moved along the deck as weli as vibrated up and down, but they have no sideways motion towards the walls 25, 26. Three bars (one shown at 44) interconnect the two motors 41 and 42 in a triangular formation to neutralise the compressive and tensile forces introduced by the motors and to reduce any tendencies of sideways motion of the particles.

Particles for grading are delivered onto the feed table 10 which is associated with the sorting table 11.

These particles have previously passed through a chopping machine (not illustrated in the drawings) which chops up the nuts into particles of the required size. Inevitably, during the chopping operation a substantial amount of dust and fine particles are generated, and these are passed from the chopping machine onto the feed table 10. From the feed table, which is connected to the table 11 and thereby continuously vibrated by means of the out-of-balance motors, the commodity passes, as will be described, over the weir arrangement generally indicated at 29 and onto the upper surface of the first portion A of the deck 18.

The deck 18 is a composite structure, the first zone (A) of which is made from an expanded metal sheet 45 which has been flattened on at least one surface; the flattened, smooth surface is disposed uppermost. The aperture in the deck sheet are smaller than the desired "accept" product so that the smaller size particles can pass through these apertures before the "accept" product is collected. The apertures are parallelogram-shaped and have an average size of 3.6 x 6.9 mm. The sheet may be stainless steel, although this is generally unnecessary where the product contains a substantial amount of oil which resists corrosion of the surface.One of the problems inherent in known designs of grader has been that the dust and other small particles produced during the chopping operation have tended to clog the holes in the preliminary part of the deck, where the concentration of dust and stickly particles is high.

The sharp edges of the expanded metal sheet 45 prevent this from occurring. Particles passing through the apertures in sheet 45 fall into hopper 50 and are subsequently collected.

At the same level as the metal sheet 45 forming zone A in the deck 18, is a woven metal gauze 48 which forms zone B. This is intended for accepting a larger size of particles than those passing through the perforations in zone A and comprises for example stainless steel wire woven into an average of 4.75 mm square openings. The hole size is constant throughout the gauze 48 and particles passing through this gauze (in this case the "accept" product) fall into a hopper 51 and from there pass into a container 52.

Particles which are delivered onto the deck and which are too big to pass through either the perforations in zone A or the openings in zone B (e.g.

agglomerated dust or particles which may become stuck together because of the high oil content in the nuts) pass over the bar 53 provided at the end of zone B and downwardly through opening 54 and onto chute 55.

The weir arrangement 29 which induces the dust and smaller particles to pass quickly through the zone A is illustrated in more detail in Figure 3. It comprises a pair of diverging square-section transverse bars 60 and 61 which are provided with raised sections 62 and 63 respectively at their apex. Bar 60 is fixed to side wall 26 and bar 61 to side wall 25.

Round-section bars 68, also angled at a direction to the centre line of the assembly, run from the front wall 27 of the sorting table 11 to the side walls 25 and 26, and form a grid for dispersing the chopped product. The mixture from the chopping device moves along the feed table 10 towards the weir 29 and is separated at the weir, some passing under the bars 60,61 and through the grid formed by the bars 48, and the rest piling up at the centre of the bars where the raised portions 62, 63 are located. The bulk of the particles pass over the bars 60 and 61 before they drop onto the upper surface of zone A.

The dispersion of the commodity by the weir 29 causes the dust and smaller particles to pass through the mass of larger particles and onto the deck 18, where they fall through the apertures into the hopper 50. The larger size chopped nuts are moved in the direction of arrow 20 towards zone B, at the same time being shaken free of any remaining dust particles. Thus effective separation of the product is achieved.

Claims (10)

1. A device for the grading of a particulate commodity by size, comprising a substantially horizontal perforate deck, delivery means for delivering the particulate commodity onto the upper surface of the deck, and vibrator means for vibrating the deck to cause the particulate commodity to move towards one end thereof, whereby the deck comprises a first zone formed from a perforate sheet material and having apertures therein through which small particles of the commodity can pass, and a second zone downstream, in the direction of movement of the commodity along the deck, of the first zone and formed from a mesh material having apertures of a larger size than those in the first zone, and means for collecting the graded commodity passing through the apertures in one or both of said zones, the delivery means being adapted to disperse the commodity as it is fed onto the upper surface of the deck to cause the smaller particles to pass through the apertures in the deck in the first zone thereof.

2. A device as claimed in Claim 1, wherein the perforate sheet material of said first zone comprises expanded sheet metal material of between 0.5 mm and 0.65 mm thickness.

3. A device as claimed in Claim 2, wherein said expanded sheet metal material is formed with parallelogram-shaped apertures having two opposite sides with an average dimension of between 3 and 4 mm, the other opposite sides having an average dimension of between 6 and 7 mm.

4. A device as claimed in any of Claims 1 to 3, wherein said second zone comprises an open mesh woven metal material having an average aperture size of between 4 and 5.5 mm square.

5. A device as claimed in any of Claims 1 to 4, wherein an opening is provided downstream of said second zone through which particles can pass which are unable to pass through the apertures in said first and said second zones.

6. A device as claimed in any of Claims 1 to 5, wherein the delivery means adapted to dispense the particles onto the upper surface of the deck comprise a generally horizontal feed table located with a free edge disposed above the deck, means for causing particles thereon to move towards said free edge, and a weir device disposed at or close to said free edge and over which particles must pass before they fall onto the upper surface of the deck.

7. A device as claimed in Claim 6, wherein said weir device comprises a generally horizontal wall member extending transverse to the direction of movement of the particles along the feed table, which wall member is provided with longitudinallyextending angular edges.

8. A device as claimed in Claim 7, wherein said generally horizontal wall member comprises a pair of diverging bars having a geometric cross-section arranged in a plane parallel to the plane of the deck with their apex on the centre-line thereof.

9. A device as claimed in Claim 8, wherein said bars are supported on an open grid disposed over the delivery end of the deck.

10. A device for the grading of a particulate commodity by size, substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.