GB2249043A - Surface abrasive treatment of small objects - Google Patents

Abstract

Apparatus is disclosed for use in the abrasion of small objects, e.g. rice grains, to remove surface material, e.g. bran, therefrom. A chamber (2) has a bottom formed by an abrasive drum (14) which passes under a transverse wall (12) of the chamber. An inlet (22) is provided for objects to be abraded. An outlet (24) is provided for abraded objects. In use, objects recirculate in the chamber and material removed from said objects passes under the transverse wall. An auger (26) feeds objects through or from the inlet to generate pressure on the recirculating objects to press the lowest objects against the moving drum.

Description

SURFACE ABRASIVE TREATMENT OF SMALL OBJECTS This invention relates to apparatus and method for use in the surface abrasive treatment of small objects, for example, seeds, including cereals, legumes, nuts and the like; cleaning aggregate and objects of wood, plastics, mineral or metal.

Apparatus for such purpose has been proposed which has a chamber; means for providing an abrasive moving bottom which passes under a transverse wall of the chamber; an inlet for objects to be abraded; and an outlet for abraded objects, in use, objects recirculating-in said chamber and material removed from said objects passing under the transverse wall. The chamber has a top, opposed to the bottom, the top being sufficiently close to the bottom that, in use, pressure is exerted on the recirculating objects to press the lowest objects against the bottom In use of the prior proposed apparatus it is found that the pressure is generated on the objects in only a small area of the chamber.As the area in which pressure is exerted has the greatest effect on the removal of surface material it is desired to enlarge the area to improve the efficiency of the apparatus.

To this end, in accordance with the invention there is provided apparatus for use in the abrasion of small objects to remove surface material therefrom, comprising: a chamber; means for providing an abrasive moving bottom which passes under a transverse wall of the chamber; an inlet for objects to be abraded; means for feeding particles from or through the inlet into the chamber; and an outlet for abraded objects, in use, objects recirculating in said chamber and material removed from said objects passing under the transverse wall, the chamber having a top, opposed to the bottom, the auger generating Y pressure, contained by the top, on the recirculating objects to press the lowest objects against the bottom.

In a particular embodiment of the invention, the means for feeding particles is an auger. Sufficient pressure may be generated by use of the auger, that pressure is generated over a larger area in the chamber thereby improving the efficiency of the apparatus. The apparatus preferably includes means for restricting the flow of abraded objects from the outlet in which case the pressure generated depends on a balance between the affect of the auger (e.g. its speed of rotation) and the degree of restriction of the outlet.

The invention also extends to a method of abrading small objects to remove surface material therefrom comprising; supplying objects to a chamber having an abrasive moving bottom which passes under a transverse wall of the chamber, so that objects recirculate in said chamber and material removed from said objects passes under the transverse wall; operating an auger to exert pressure on the recirculating objects to press the lowest objects against the bottom; and removing abraded objects from an outlet to the chamber.

The means for providing an abrasive moving bottom may include an endless abrasive belt or, more preferably, a drum having an abrasive covering or coating.

Means are preferably included for drawing a vacuum outside the chamber, to remove material, abraded from the objects, from the means providing an abrasive moving bottom.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a cross section of apparatus embodying the invention; Figure 2 is a detail of the apparatus of Figure 1, and Figure 3 is a section on A-A of Figure 1.

A chamber 2 is defined by a box 4 having side walls 6,8 and transverse walls 10,12. A drum 14 (only part of which is llustrated) covered by an abrasive sheet 16 constitutes an abrasive moving bottom or floor of the chamber. In use the drum 14 rotates about an axis (not shown) normal to the plane of the paper in Figure 3. The top or outer surface of the sheet 16 has a coating of abrasive sand or grit. The drum passes underneath the transeverse walls 10, 12 and the side walls 6,8 with a gap 18 in between. The gap between the transverse wall 10,12 and the drunk 14 may be of the order of 10 thousandths of an inch. The gaps between the other walls and the drum are not so critical but are preferably of the same order. The box has a semicylindrical top 20 which closes the chamber.

An inlet 22 extends from a hopper (not'shown) into the chamber adjacent the side wall 6. An outlet 24 is provided in the oposite side wall 24, spaced laterally across the drum. In a preferred arrangement the outlet extends in the side wall 8, from transverse wall 10 to transverse wall 12, and is thus adjacent the transverse wall 12. In other arrangements the outlet may not extend the full extent between the transverse walls but is preferably located adjacent the wall 12 towards which the drum rotates.

Under and thus partly in the inlet 22, and extending into the chamber 2, is an auger 26. In use, the auger 26 is rotated to feed small objects to be abraded from the inlet into the chamber 2. In other arrangements the auger may be situated only in the inlet in which case it acts to feed the small objects through the inlet into the chamber. The outlet is of reduced size compared to the cross-section of the chamber, so as to restrict the flow of objects leaving the chamber, such that a significant pressure is generated in the chamber, the pressure being contained by the top of the chamber. The pressure urges the objects against the abrasive surface of the sheet 16 on the rotating drum 14. The pressure generated depends on the action of the auger, eg how fast it rotates, and on the restriction provided by the outlet.

Pressure can be generated to urge the lowermost objects against the drum substantially right across the drum from the inlet to the outlet and over the full extent of the chamber from the wall 10 to the wall 12.

Small objects to be abraded are loaded into the hopper and fed to the inlet 22. By way of example, the small objects may be grains of rice from which the outer layers, part or all of the bran layers, are to be removed. In this example, drum 14 is run to produce a surface speed of about 10 metres/sec. Rice grains are fed via the inlet 22 into the chamber. The grains are transported by the auger across the chamber to generate pressure as described above. The grains recirculate under the action of the drum, in the direction of the arrows in Figure 3, so that they contact the drum 14 repeatedly and an outer layer is removed.

As illustrated, the shaft 42 of the auger extends right across the box 4 into a bearing in the side wall 8, although the auger 26 extends only partly across the box. Optional paddles 44 extend approximately radially from the shaft 42 for rotation therewith to ensure rotation of the grain in the chamber.

Referring to Figure 3, the material removed passes under the wall 12 through the gap 13 and the grains leave the chamber at the edge of the drum through the outlet 24. Material removed and the grains may thus be collected separately by means (not shown). In the example illustrated baffles 28 form a plenum chamber 30 with the transverse walls 10,12. A partial vacuum is drawn in the plenum chamber via an outlet (not shown) so that air is drawn in via the slot 18 removing material from the drum 14. A similar wall 28 forms a plenum chamber adjacent the other transverse wall 10 so that the apparatus may be operated with the drum 14 rotating in either direction.

In an alternative (not illustrated) two chambers 2 are positioned back to back across the drum, with their inlets adjacent or common and their outlets at opposite edges of the drum. Left and right hand augers are rotated on the same shaft to transfer the small objects in opposite directions to towards the respective outlets.

-The gap 18 is sufficiently small, that only material which has been removed passes through. Thus in the case of polishing rice, any "fines" caused by grains breaking, will remain with the rice and not pass into the bran. In this way, the surface material is removed from and separated from the small objects. In practice the gap 18 is as small as possible preferably, for example, 10 thousandths of an inch. The gap would not normally be larger than 30 thousandths of an inch.

Because of the recirculation of the grains, they are well polished without breakage or being heated up.

At the transverse wall 12, forward motion of the objects is arrested and they progress upwards and recirculate in the direction of the arrows in Figure 3. The top 20 contains the pressure generated between the auger and the restricted outlet, to press the lower objects against the drum 14. The lid illustrated is shaped to accommodate the auger, but may be rigid or flexible, planar or shaped. A flexible lid may be subjected to pressure on its side exterior to the chamber, and thus act as a diaphragm.

In order to enable the restriction on the flow of rice from the outlet 24 to be controlled or adjusted closure members are provided in the form of a flap 32. Th flap is pivotally mounted by pins 34 on a plate 36 so that it may close the outlet 26 as illustrated in Figure 1, or may open the outlet (not illustrated). The flap 32 is operated by a rod 38, pivotally attached thereto by a pin 38a and block 40. The flap is biased towards the closed position, for example, by pneumatic pressure (not illustrated) or by a system of weights and levers (not illustrated).

The force on the flaps 36, 38 affects the amount of work applied to the objects and thus the amount of material removed.

Increasing the force on the flaps increases the amount of material which is removed. To this end the pneumatic pressure may be adjustable, as may be the weights.

In another alternative (not illustrated), a restriction to the flow of grain from the outlet 24 may be provided by a chute or tube, the lower end of which is fed by the outlet and from the upper end of which the grain is collected. The height of the chute or tube, which may be adjustable, partly determines the restriction.

In other examples, not illustrated, the drum is coated directly with an abrasive material. The drum may be replaced with an endless abrasive belt stretched between two rollers. An advantage of the use of a drum is opposed to the endless belt, is that the belt requires a backing plate which remains in the same place and becomes heated by the abrasive action of the belt on the objects, whereas the drum rotates in its entirety, giving each part of the drum an opportunity to cool between passes under the chamber.

Claims (18)

1. Apparatus for use in the abrasion of small objects to remove surface material therefrom, comprising: a chamber; means for providing an abrasive moving bottom which passes under a transverse wall of the chamber; an inlet for objects to be abraded; means for feeding particles through or from the inlet into the chamber; and an outlet for abraded objects, in use, objects recirculating in said chamber and material removed from said objects passing under the transverse wall, the chamber having a top, opposed to the bottoin, the auger generating pessure, contained by the top, on the recirculating objects to press the lowest objects against the bottom.

2. Apparatus as claimed in Claim l, wherein the abrasive moving bottom is provided by an endless abrasive belt.

3. Apparatus as claimed in Claim 1, wherein the abrasive moving bottom is provided by a drum having an abrasive covering or coating.

4. Apparatus as claimed in any preceding Claim, wherein the outlet is spaced laterally across the belt or drum from the inlet.

5. Apparatus as claimed in any preceding Claim, wherein the outlet is in a sidewall of the chamber.

6. Apparatus as claimed in any preceding Claim 4, wherein the outlet is adjacent te transverse wall.

7. Apparatus as claimed in any preceding Claim, including two outlets, one on each side of the inlet.

8. Apparatus as claimed in any preceding Claim, including means for restricting the flow of abraded objects from the outlet.

9. Apparatus as claimed in Claim 6, wherein the means for restricting the flow of abraded objects comprises an upwardly extending chute or tube.

10. Apparatus as claimed in Claim 9, wherein the height of the chute or tube is adjustable so as to adjust the degree to which flow is restricted.

11. Apparatus as claimed in any preceding Claim, wherein the means for restricting the flow comprises a closure member which is biased closed against the outflow of abraded objects.

12. Apparatus as claimed in Claim ll, wherein the bias is adjustable.

13. Apparatus as claimed in any preceding Claim, including means for drawing a vacuum outside the chamber, to remove material, abraded from the objects, from the means providing an abrasive moving bottom.

14. Apparatus as claimed in any preceding Claim, wherein the top is a flexible diaphragm subject to pressure exterior to the chamber.

15. A method of abrading small objects to remove surface material therefrom comprising; supplying objects to a chamber having an abrasive moving bottom which passes under a transverse wall of the chamber, so that objects recirculate in said chamber and material removed from said objects passes under the transverse wall; operating an auger to exert pressure on the recirculating objects to press the lowest objects against the bottom; and removing abraded objects from an outlet to the chamber.

16. A method as claimed in Claim 15, wherein the outlet is spaced laterally across the belt from the inlet.

17. A method as claimed in Claims 15 or 15, including restricting the flow of objects from the outlet.

18. A method as claimed in any of Claims 15 to 17, including drawing a vacuum outside the chamber, to remove material abraded from the objects, from the means providing an abrasive moving bottom.