GB2080090A

GB2080090A - Improvements in and relating to the treatment of granular material

Info

Publication number: GB2080090A
Application number: GB8115817A
Authority: GB
Original assignee: Christy & Norris Ltd
Current assignee: Christy & Norris Ltd
Priority date: 1980-05-28
Filing date: 1981-05-22
Publication date: 1982-02-03
Also published as: GB2080090B

Abstract

Apparatus for treating granular material, to remove at least part of an outer layer from individual grains of the material, comprises a trough (1), a pair of overlapping discs (4) situated in the trough, each disc being mounted for rotation in shafts (2, 3) about an axis perpendicular to the plane of the disc, the two axes of rotation being parallel to one another and the two discs of the pair overlapping one another, but neither disc overlapping the other as far as the axis of rotation of the other, the facing surfaces (11) of the discs of the pair of discs being generally planar, and means or causing the discs to rotate about the said axes, the arrangement being such that the granular material is treated by interaction with the facing surfaces of the pair of discs. The apparatus may be used for hulling rice, when the disc pairs are close together and the discs rotate in opposite directions, or for polishing rice, when disc pairs are spaced and the discs rotate in same or opposite directions. Preferably there is more than one pair of discs separated by weirs (8) over which the rice passes. <IMAGE>

Description

SPECIFICATION Improvements in and relating to the treatment of granular material The invention relates to the removal of at least part of an outer layer of material from individual grains of granular material, especially vegetabie material. Thus, for example, the invention includes paddy hulling, that is to say, removing the husk from paddy grains to give brown rice, and the polishing of rice, that is to say, the removal of bran from brown rice to give white rice. Other granular, vegetable materials that can be treated in accordance with the invention include, for example, wheat, oats, maize, mustard, sorghum, soya and ground-nuts.

The invention provides apparatus for treating granular material to remove at least part of an outer layer from individual grains of the material, which comprises a trough into which the material to be treated can be introduced and from which treated material can be removed, a pair of overlapping discs situated in the trough, each disc being so mounted as to be rotatable about an axis perpendicular to the plane of the disc, the two axes of rotation being parallel to one another and the two discs of the pair overlapping one another, but neither disc of the pair overlapping the other as far as the axis of rotation of the other, the facing surfaces of the discs of the pair of discs being generally planar, and means for causing the discs to rotate about the said axes, the arrangement being such that the granular material is treated by interaction with the facing surfaces of the pair of discs.

The invention also provides a method for treating granular material to remove at least part of an outer layer from individual grains of the material, which comprises introducing the granular material to be treated into the trough of apparatus in accordance with the invention, causing the overlapping discs to rotate and removing treated granular material from the trough.

The invention further provides granular material whenever produced by the method of the invention.

The construction and manner of operation of the apparatus depends upon the nature of the granular material to be treated and upon the nature of the treatment to be carried out.

The main variables are the axial separation between the facing surfaces of the overlapping discs, the nature of the overlapping portions of the faces of the discs, and the relative directions of rotation of the discs. The significance of those variables in relation to particular applications is discussed hereinafter.

Advantageously, there is provided, within the trough, one or more additional pairs of such overlapping discs, the pairs of overlapping discs being spaced apart from one another in a generally axial direction. Preferably, the arrangement is such that granular material introduced into the trough is subjected to the action of the different pairs of overlapping discs in turn, when the proportion of grains that are treated satisfactorily during a single passage through the trough is increased with the result that in some applications it is practicable to achieve a result in which the proportion of grains that are treated satisfactorily is high enough to render recycling unnecessary.

The axes of rotation of the discs of the additional pair or pairs advantageously each coincide with one or other of the axes of rotation of the discs of the first-mentioned pair. Preferably, the discs are each mounted on one or other of two rotatably mounted shafts of which the axes are parallel to one another.

Advantageously, when a plurality of pairs of overlapping discs are provided within the trough, the trough is provided with one or more plates or like members which extend transversely with respect to the said axes and which, when the trough is so mounted that the said axes extend substantially horizontally, serve as weirs over which the granular material has to pass in order to pass from one pair of overlapping discs to the next. Further, the trough is advantageously provided with removable closure means for the top of the trough.

The trough is also advantageously provided with inlet means through which granular material to be treated can enter the trough in the vicinity of one end pair of overlapping discs and outlet means through which treated granular material can leave the trough in the vicinity of the other end pair of overlapping discs. The inlet means may comprise an opening in the closure means in the vicinity of one of the two end pairs of overlapping discs, and the outlet means may comprise an opening in the bottom of the trough in the vicinity of the end pair of overlapping discs remote from the inlet means. If desired, there may also be an opening in the closure means at the end thereof remote from the inlet means.

There is advantageously provided, in the upper part of the trough, deflector means arranged to tend to cause granular material passing over a weir to be deflected downwardly into the region between that weir and the next pair of overlapping discs in the direction from the inlet means to the outlet means. The deflector means may comprise one or more plates, one for the or each weir, situated one over the or each weir and so inclined as to extend downwardly in the direction from the inlet means to the outlet means.

Instead, the deflector means may comprise one or more plates, one for the or each weir, extending substantially vertically and between the or each weir and the pair of overlapping discs on the downstream side of the weir with respect to the movement of granular material from the inlet means to the outlet means.

Advantageously, the axes of rotation of the discs of the each pair of overlapping discs lie, when the apparatus is in its operating position with the axes horizontal, substantially in the same horizontal plane. Further, the discs being (as is preferred) circular and mounted for rotation about their centres, the inner surface of the trough as seen in a cross-section taken perpendicular to the axes of rotation of the discs, although not in contact with the discs, preferably conforms generally to the peripheries of the discs, at least over their lower, outer quadrants. This, together with the presence of weirs and the deflecting means, ensures that a higher proportion of the granular material than would otherwise be the case is subjected to the action of the or each pair of overlapping discs during its passage from the inlet to the outlet.

It has been found that, with regard to the main variables referred to hereinbefore, there are two broad categories of apparatus, with corresponding categories of method, that are especially useful. The two categories can conveniently be exemplified with reference to the treatment of paddy and rice, a typical example of one category being suitable for the hulling of paddy to give brown rice and a typical example of the other category being suitable for the polishing of brown rice to give white rice.

Apparatus in the first category has the facing surfaces of the discs of the or each pair of overlapping discs relatively close together in relation to the dimensions of the grains to be treated, the frictional properties and possibly also the resilience of the overlapping portions of the facing surfaces of the discs are important, and the discs of the or each pair of overlapping discs are arranged to be driven in opposite senses. Apparatus in the second category, on the other hand, has the facing surfaces of the discs of the or each pair of overlapping discs relatively far apart in relation to the dimensions of the grains to be treated, the abrasiveness of the facing surfaces of the discs is important, and the discs of the or each pair of overlapping discs may be arranged to rotate either in opposite senses or both in the same sense.

Where the granular material to be treated is paddy or rice, an important distinction between the two operations of hulling and polishing is that, whereas in hulling each husk is usually split into two parts when it is removed, in polishing the bran is removed as a fine powder, and it is believed that that distinction will be found to be of significance in deciding which category of apparatus will prove to be suitable in other cases. Thus, where the outer layer is relatively weakly secured to the remainder of the grain except because it substantially surrounds the remainder of the grain and it has itself a relatively high degree of coherence, apparatus in the first category can reasonably be expected to be suitable for removing the outer layer.

Where, on the other hand, the outer layer is relatively strongly secured to the remainder of the grain, but has itself a relatively low degree of coherence (for example, it may be capable of existing as a continuous layer only because it is secured to the continuous surface of the remainder of the grain), apparatus in the second category can reasonably be expected to be suitable for removing the outer layer.

Although it is to be understood that the apparatus of the invention has uses other thar, the treatment of paddy and rice, and that the method of the invention is not limited to the treatment of those materials, it is convenient - to use the terms "hulling" and "polishing", respectively, to denote the two broad categories of apparatus referred to above.

As examples of other operations that can be undertaken using hulling apparatus, there may be mentioned removing the husk from oats, mustard and soya, and removing the shells from ground-nuts. As examples of other operations that can be undertaken using polishing apparatus, there may be mentioned removing bran from wheat, millet and sorghan, and removing the skin from maize.

Referring first to hulling apparatus, the means for causing the discs to rotate about the said axes is advantageously such as to ensure that the discs of each pair of overlapping discs rotate in opposite senses. For example, where the discs are each mounted on one or other of two shafts, the means for causing the discs to rotate about the said axes may comprise two gear wheels meshing with one another, one of the gear wheels being non-rotatably mounted on one of the said shafts and the other gear wheel being nonrotatably mounted on the other of the said shafts.

Further, experiments have shown it to be preferable for the means for causing the discs to rotate to be such that, in operation, the portions of the discs of a pair of overlapping discs that, at any given moment, are overlapping one another, move upwardly rather than downwardly at that moment.

Advantageously, the discs are so mounted that the axial separation between the facing surfaces of the or each pair of overlapping discs is adjustable. This makes it possible to adjust the apparatus both to render it suitable in turn for granular materials having different grain sizes and to adjust the apparatus to take account of wear to the facing surfaces of the discs.

For many applications, it is advantageous if the axial separation between the facing surfaces of the or each pair of overlapping discs is, or can be adjusted to be, a distance not exceeding 5 mm. For the shelling of ground nuts, however, an axial separation of approxi mately 10 mm gives good results. For hulling paddy, the optimum axial separation between the facing surfaces is usually within the range of from 1.5 to 3 mm.

Again, for many applications, it is advantageous if the discs, being circular and mounted for rotation about their centres, have diameters within the range of from 1 5 cm to 60 cm. (Diameters within this range may also be advantageous for the discs in polishing apparatus.) In order to promote the required hulling action of the overlapping discs on the granular material, at least the portions of the facing surfaces of the discs of each pair of overlapping discs that overlap one another are preferably made of rubber or a plastics material, which is preferably resilient. To impart the desired rigidity to the discs at the same time, the discs are preferably made of metal with at least the said overlapping portions of the facing surfaces of the discs being covered with rubber or a plastics material.Preferably, the said portions of the discs are covered with polyurethane. If desired, for each disc the entire disc may be covered in, or may be made of, a resilient plastics material, for example polyurethane. The surface of the rubber or plastics material is preferably formed with indentations (which when the material is in the form of a layer on a metal disc, may pass right through the layer) and/or protrusions. (It will be appreciated, however, that such indentations and protrusions leave the facing surfaces of the discs of each pair of discs generally planar.) In that way, the apparent frictional forces between the discs and the grains can be considerably increased with generally much better results.The frictional forces are described as "apparent" because, if the size of the indentations and/or protrusions is of the same order as the size of the grains being treated, the forces involved may not in fact be purely frictional. The resilience of the rubber or plastics material lessens the risk of grain breakages.

The treated granular material may be removed from the trough in admixture with removed layer material, the treated granular material being thereafter separated from the layer material. Alternatively, the removed layer material and the treated granular material may be separated in the trough, the trough being provided with a first outlet for the treated granular material and a second outlet for the removed layer material.

For some applications it is advantageous to provide means for cooling the interior of the hulling apparatus, for example by causing a current of air to pass through the apparatus.

As is indicated above, in an especially important form of the process, the granular material to be treated is paddy, the outer layer removed from the individual grains is husk, and the treated material is brown rice.

When, as is approximately the case for paddy and some other naturally occurring granular materials, the material to be treated comprises grains of which the shape is substantially that of an ellipsoid of revolution, the axial separation between the facing surfaces of the or each pair of overlapping discs is advantageously so chosen as to be substantially equal to or slightly larger than the minor axis of the said ellipsoid of revolution. It will usually be found desirable to choose an axial separation that is slightly larger, rather than slightly smaller, than the said minor axis. If the axial separation is too small, damage to the treated grains is caused, but test results suggest that if it is so chosen that it would appear to be slightly too large, the resultant gap is filled by other material, presumably, removed layer material, and the hulling efficiency is not markedly reduced.

Turning now to the polishing, the discs of each overlapping pair of discs can, as mentioned above, either rotate in the same sense or in opposite senses. When they rotate in opposite senses, however, it is preferable that the portions of the discs of a pair of overlapping discs that, at any given moment, are overlapping one another, move downwards at that moment.

In order to promote that required polishing action of the overlapping discs on the granular material, the facing surfaces of the discs of the or each pair of overlapping discs are preferably abrasive in nature. While the desired abrasiveness can, in the case of metal discs, be achieved by applying a suitable finish to the facing surfaces of the discs, it is preferred that a layer of an abrasive, especially tungsten carbide particles, be applied to the facing surfaces of the discs.

In the case of polishing, the axial separation between the facing surfaces of the or each pair of overlapping discs is much less critical than in the case of hulling. Thus, while too small a separation will lead to damage to the grains being treated and too large a separation will result in a reduction in efficiency, there is a relatively wide range of separations over which successful operation can be achieved. When, as is explained hereinbefore and as is not infrequently the case with naturally occurring granular, vegetable material, the individual grains have a shape approximating to that of an ellipsoid of revolution, the said separation between the faces should normally be greater than the major axis of the ellipsoid of revolution.In the case of the polishing of brown rice, for example, a separation within the range of from 5 mm to 20 mm will be found to give acceptable results, although 5 mm may be found to be rather too small for some brown rice. In some applications it may be advantageous for the discs to be so mounted that the axial separation between the facing surfaces of the or each pair of overlapping discs is adjustable. Where a plurality of pairs of overlapping discs is provided and weirs are provided in the trough between adjacent pairs of discs, the separation between each disc and the adjacent weir may be approximately the same as the separation between the facing surfaces of the discs.

It has been found that, in the case of polishing, there should be a substantial depth of granular material in the trough if an acceptable throughput is to be achieved. Thus, when the trough is provided with an inlet and an outlet, the rate of supply of material to the inlet and/or the depth of the weirs (where they are present) is advantageously sufficient to ensure that the level of the granular material is at or above the level of the axes of rotation of the discs.

The invention still further provides a combination of first and second apparatus, each apparatus being for treating granular material to remove at least part of an outer layer from individual grains of the material and comprising a trough, a plurality of pairs of overlapping discs situated in the trough, the discs of each pair being so mounted as to be rotatable about an axis perpendicular to the plane of the disc, the axes of rotation being parallel to one another and the two discs of each pair overlapping one another, but neither disc of each pair overlapping the other as far as the axis of rotation of the other, the pairs of overlapping discs being spaced apart from one another in a generally axial direction, the facing surfaces of the discs of each pair of discs being generally planaer, and means for causing the discs to rotate about the said axes, the arrangement being such that the granular material is treated by interaction with the facing surfaces of each pair of discs, the trough of each apparatus being provided with inlet means through which granular material to be treated can enter the trough in the vicinity of one end pair of overlapping discs and outlet means through which treated granular material can leave the trough in the vincinity of the other end pair of overlapping discs, the outlet through which the granular material can leave the trough of the first apparatus being in communication with the inlet of the trough of the second apparatus through conduit means and there being provided means for separating layer material removed from the granular material in the trough of the first apparatus so that, in operation, substantially only the treated granular material from the first apparatus enters the trough of the second apparatus.

Advantageously, the first apparatus is situated above the second apparatus so that, in operation, granular material treated in the first apparatus falls under gravity to the second aparatus. The means for separating layer material removed from granular material in the first apparatus may comprise a fan arranged, in operation, to cause air to flow upwardly through the material leaving the trough of the first apparatus so that, while the treated granular material continues to fall, the removed layer material is carried up by the air to an outlet. If desired, the fan may be arranged to cause air to flow upwardly through the material before the material passes through the outlet of the first apparatus so that substantially only the treated granular material passes through the said outlet, the removed layer material leaving the trough through a second outlet.

In some cases it may be desirable to provide means for cooling the interior of the first apparatus. The means for cooling the interior of the first apparatus may comprise a fan arranged, in operation, to cause air to flow along the length of the trough. Where a fan is provided for separating layer material removed from granular material in the first apparatus this fan may also, if desired, be arranged to cause air to flow along the length of the trough, for example, from the inlet of the trough, or from an opening in the trough in the region of that inlet, to the outlet for removed layer material.

The speed of rotation of the discs can, for both hulling and polishing, and especially in the case of polishing, be varied over a wide range, but it will usually be found that a speed within the range of from 1 ,000 to 3,000 revolutions per minute will give satisfactory results. In the case of polishing apparatus with relatively small discs, say, 1 5 cm in diameter, however, a speed of, say, 5,000 revolutions per minute is acceptable.

The invention makes it possible to provide apparatus for treating granular material to remove at least part of an outer layer from individual grains of the material, for example for paddy hulling and rice polishing, which can be simple and cheap to manufacture and to operate. The invention also makes it possible to provide a method for treating granular material to remove at least part of an outer layer from individual grains of the material, for example for paddy hulling or rice polishing, which can be carried out cheaply and simply by relatively unskilled workers. Furthermore use of the apparatus and method of the invention may, for example, result in breakages of grain being kept to a relatively low level and in the removal of the outer layer being carried out in a relatively efficient manner, that is to say for a given power consumption a greater throughput of grain may be achieved.

Several forms of apparatus for treating granular material to remove an outer layer from individual grains of the material and constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of a first form of apparatus, which is suitable for hulling, with the cover removed; Figure 2 is a diagrammatic cross-section taken on the line ll-ll in Fig. 3; Figure 3 is a diagrammatic cross-section taken on the line Ill-Ill in Fig. 2; Figure 4 is a diagrammatic axial crosssection on a larger scale through one form of disc usable in the apparatus shown in Figs. 1 to 3; Figure 5 is a diagrammatic view of a disc taken in the direction of the arrow "A" in Fig.

4; Figure 6 is a diagrammatic axial crosssection on the same scale as that of Fig. 4 taken through another form of disc usable in the apparatus shown in Figs. 1 to 3; Figure 7 is a diagrammatic cross-section through a second form of apparatus, which is suitable for hulling, the section being taken on the line VII-VII in Fig. 8; Figure 8 is a diagrammatic cross-section taken on the line VIII-VIII in Fig. 7.

Figure 9 is a diagrammatic plan view of a third form of apparatus, which is suitable for polishing, with the cover removed; Figure 10 is a diagrammatic cross-section taken on the line X-X in Fig. 11; Figure 11 is a diagrammatic cross-section taken on the line Xl-XI in Fig. 10; Figure 12 is a diagrammatic cross-section through a fourth form of apparatus, which is suitable for polishing, the section being taken on the line Xll-Xll in Fig. 13; Figure 13 is a diagrammatic cross-section taken on the line Xlll-Xlll in Fig. 12; Figure 14 is a diagrammatic side view of a first form of combination of a hulling apparatus with a polishing apparatus; Figure 15 is a diagrammatic end view of the combination of Fig. 14 taken in the direction of the arrow "B" in Fig. 14;; Figure 16 is a diagrammatic side view of a second form of combination of a hulling apparatus with a polishing apparatus; and Figure 1 7 is a diagrammatic end view of the combination of Fig. 1 6 taken in the direction of the arrow "B" in Fig. 16.

Referring now to the accompanying drawings, in which the same reference numerals are used to indicate corresponding parts of different forms of apparatus, and referring first to Figs. 1, 2, 3, 4 and 5, the first form of apparatus, which is suitable for hulling a granular material, for example, paddy, comprises a trough 1 which, when the apparatus is in use, extends horizontally. Within the trough 1 there are two rotatably mounted shafts 2 and 3, which run horizontaly along the length of the trough, are arranged side-by-side (so that in use their axes lie in the same horizontal plane) and extend through the end walls of the trough.

Each of the shafts 2 and 3 carries a plurality of (say, six) circular discs which are all similar and are indicated generally by the reference numeral 4 and which are coaxial with the shaft on which they are mounted. As can be seen in Fig. 1, each of the discs 4 mounted on the shaft 2 overlaps one of the discs 4 mounted on the shaft 3. As is explained hereinafter, the discs 4 of each pair of overlapping discs co-operate with one another to treat granular material in the trough 1. It will be seen that each disc 4 of a pair of overlapping discs does not overlap the other disc as far as the axis of rotation of the other disc. The discs 4 are so mounted on the shafts 2 and 3 that they can be removed and replaced by fresh discs, and so that the axial separation between the facing surfaces of the discs of each pair of overlapping discs can be varied.

As can be seen in Fig. 3, the discs 4 of each pair of overlapping discs together extend across substantially the entire width of the trough 1, which is so shaped that the inner surface of the trough conforms generally to the periphery of the discs over their lower, outer quadrants. If damage to the grains is to be avoided, the gap between the lower, outer quadrants of the discs 4 and the trough 1 should either be very small, say, 0.5 mm (which implies expensive manufacturing techniques) or relatively large, say, 6 mm, for hulling paddy. Similar considerations apply to the gaps between the shaft 3 and the peripheries of the discs 4 mounted on the shaft 2 and to the gaps between the shaft 2 and the peripheries of the discs 4 mounted on the shaft 3.Of course, smaller gaps corresponding to a larger degree of overlap are preferable because it is the overlapping portions of the discs 4 that effect the treatment.

The trough 1 is closed at the top by a cover member 5, which is removable and which is provided (see Fig. 2) with an aperture 6, which serves as an inlet for granular material to be treated. At the end remote from the inlet 6, the base of the trough 1 is formed with an aperture 7, which serves as an outlet both for treated granular material and for layer material that has been removed from the individual grains.

Extending across the width of the trough 1 at right angles to the axes of the shafts 2 and 3 are a plurality of vertical plates which serve as weirs 8 for the granular material. There is one weir 8 between each two adjacent pairs of overlapping discs 4 and also one between the outlet 7 and the pair of overlapping discs nearest to the outlet.

In the upper part of the trough 1 there is provided deflector means in the form of a plurality of plates 9, one above each weir 8, which extend across the width of the trough and which are inclined downwards in the direction from the inlet 6 towards the outlet 7. The plates 9 are welded to the cover member 5.

Each disc 4 comprises a metal backing disc 10 one side of which is covered with a layer 11 of polyurethane formed with indentations 1 2 (see Fig. 4 and Fig. 5, in which latter Fig.

the indentations 1 2 are shown only in two areas whereas they in fact extend over the whole outer surface of the polyurethane layer). In the case of each pair of overlapping discs 4, it is the facing surfaces of the discs that have the layer 11 of polyurethane. The layer 11 of polyurethane may be secured to the metal backing discs 10 by moulding or some other form of bonding.

If desired, the discs 4 may, instead of being as shown in Figs. 4 and 5, be as shown in Fig. 6. The form of disc shown in Fig. 6 is the same as that shown in Figs. 4 and 5 except that, instead of having a layer 11 of polyurethane provided with indentations, there is provided a layer 11 of polyurethane provided with protrusions 1 3. It will be appreciated that the difference between the two forms of disc 4 lies in the fact that, whereas in the form shown in Figs. 4 and 5 the outer surface of the polyurethane layer 11 further from the metal backing disc 10 is continuous (see Fig.

5), in the form of disc shown in Fig. 6, it is the outer surface of the polyurethane layer 11 nearer to the metal backing disc 10 that is continuous.

As is explained hereinbefore, the axial separation between the discs 4 is an important parameter in the context of hulling and, when the grains being hulled can be regarded approximately as ellipsoids of revolution, it should be so chosen as to be slightly greater than the minor axis of the grains. Thus, in the case of paddy of which t:ie grains have a minor axis of, say, 2.5 mm, the axial separation between the discs 4 of a pair of overlapping discs should be, say, 3 mm. The axial separation should be measured, in the case of discs 4 of the form shown in Figs. 4 and 5, from the continuous outer surface of the layer 11 on one of the discs to the corresponding outer surface of the layer 11 on the other disc.In the case of discs 4 of the form shown in Fig. 6, on the other hand, the axial separation should be measured from the top of the protrusions 1 3 on the layer 11 on one disc to the top of the protrusions 1 3 on the layer 11 on the other disc. Thus, in each case, what is measured is the minimum axial separation between the overlapping portions of the discs.

The first form of apparatus operates in the following manner.

Granular material, for example, paddy, to be hulled is introduced into the trough 1 through the inlet 6, which may be surmounted by a hopper (not shown), and falls into the region between the end wall of the trough adjacent to the inlet and the adjacent weir 8. At the same time, the shafts 2 and 3 are caused to rotate by any suitable means in the senses indicated by the arrows in Fig. 3.

It will be noted that, when the shafts 2 and 3 are driven in that way, the portions of the facing surfaces of each pair of overlapping discs 4 that, at any given moment, are overlapping one another, are moving upwards at that moment.

A part of the granular material between the end wall of the trough 1 that is adjacent to the inlet 6 and the adjacent weir 8 passes through the gap between the overlapping portions of the facing surfaces of the discs 4 there. In so doing, it is subjected to a rolling and/or rubbing action with the result that an outer layer of the material, say the husk in the case of paddy grains, is removed as is desired.

The rotating discs 4 tend to keep granular material in their vicinity in an agitated condition and some of the material flows over the first weir 8 into the space between that weir and the second weir where it is acted upon by the next pair of overlapping discs 4. Further, material leaving the gap between a pair of overlapping discs 4 tends to be thrown upwards.

Essentially, the granular material moves along the trough 1 from the inlet 6 to the outlet 7 partly as a result of random movements in either direction and, if a head of granular material is maintained above the inlet 6 (say, in a hopper), by something analogous to the pressure in a liquid. Any tendency which there may be for the material to be thrown along the trough 1 in its upper region, so that it is not subjected to the action of one or more pairs of discs 4 is reduced or prevented by the deflector plats 9 situated over the weirs 8.

The shafts 2 and 3 can be driven conveniently by a diesel engine, but other forms of propulsion (even bicycle power) are possible, and the shafts may be coupled together by means of meshing gear wheels, one fixed on each of the shafts, to ensure that they rotate in opposite senses.

The material leaving the outlet 7 will comprise a mixture of treated granular material, say, brown rice, and removed layer material, say, husk. After they have left the outlet 7, they can be separated in any convenient way.

Referring now to Figs. 7 and 8, the second form of apparatus, which is also suitable for hulling granular material, for example, paddy, is the same as the first form except that the inclined deflector plates 9 situated over the weirs 8 are replaced by vertical deflector plates 14, which also extend across the entire width of the trough 1 and which are situated between the weirs 8 and the pairs of cooperating discs 4 (which may, as in the first form of apparatus, be either as shown in Figs.

4 and 5 or as shown in Fig. 6) downstream of the weirs with respect to the direction of movement of the granular material along the trough 1 from the inlet 6 to the outlet 7. The deflector plates 14 are welded to the cover member 5.

The manner of operation of the second form of apparatus is the same as that of the first form.

In either or both of the first form of the apparatusn and the second form of the apparatus it may be found advantageous in some circumstances to replace the cover member 5 with a cover member which, in addition to being provided with the inlet 6, is provided at the end remote from the inlet 6 with an aperture 7a (as shown, for example, in Fig.

1 6 below) which is opposite the aperture 7 in the base of the trough, the aperture 7a serving as an outlet for layer material that has been removed from the individual grains. With such an arrangement, the separation, as is described in greater detail below with reference to Figs. 1 6 and 17, of the removed layer material (for example, the husk) from the treated granular material (for example, the brown rice) takes place in the trough 1 of the apparatus 1 6 rather than after leaving the trough.

Referring now to Figs. 9 to 11, the third form of apparatus, which is suitable for polishing granular material, for example, brown rice, comprises a trough 1 which, when the apparatus is in use, extends horizontally. Within the trough 1 there are two rotatably mounted shafts 2 and 3, which run horizontally along the length of the trough, are arranged side-byside (so that in use their axes lie in the same horizontal plane) and extend through the end walls of the trough.

Each of the shafts 2 and 3 carries a plurality of (say, six) circular discs which are all similar and are indicated generally by the reference numeral 4 and which are coaxial with the shaft on which they are mounted. As can be seen in Fig. 9, each of the discs 4 mounted on the shaft 2 overlaps one of the discs 4 mounted on the shaft 3. It will be seen that each disc 4 of a pair of overlapping discs does not overlap the other disc as far as the axis of rotation of the other disc.

Although the fact that each disc 4 of a pair of overlapping discs does not overlap the other disc as far as the axis of rotation of the other disc is inherent in this particular form of apparatus because any further overlap would be prevented by the shafts 2 and 3, there is in fact no upper limit to the degree of overlap that will, in the case of apparatus suitable for polishing, give satisfactory results. Accordingly, in the case of apparatus suitable for polishing, the invention includes apparatus in which each disc of a pair of overlapping discs overlaps the other disc as far as, or beyond, the axis of rotation of the other disc.

The discs 4 are so mounted on the shafts 2 and 3 that they can be removed and replaced by fresh discs.

As can be seen in Fig. 11, the discs 4 of each pair of overlapping discs together extend across substantially the entire width of the trough 1, which is so shaped that the inner surface of the trough conforms generally to the periphery of the discs over their lower, outer quadrants. If damage to the grains is to be avoided, the gap between the lower, outer quadrants of the discs 4 and the trough 1 should either be very small, say, 0.5 mm (which implies expensive manufacturing techniques) or relatively large, say, 6 mm, for polishing brown rice.

The trough 1 is closed at the top by a cover member 5, which is removable and which is provided (see Fig. 10) with an aperture 6, which serves as an inlet for granular material to be treated. At the end remote from the inlet 6, the base of the trough 1 is formed with an aperture 7, which serves as an outlet both for treated granular material and for layer material that has been removed from the individual grains.

Each disc 4 is made of steel and one side of the disc has applied to it an abrasive layer 15, which is in the form of a layer of tungsten carbide particles. In the case of each pair of co-operating discs 4 it is the facing surfaces of the discs that have the abrasive layer 1 5.

The third form of apparatus operates in the following manner.

Granular material, for example, brown rice, to be treated is introduced into the trough 1 through the inlet 6, which may be surmounted by a hopper (not shown), and falls into the region between the end wall of the trough adjacent to the inlet and the adjacent weir 8. At the same time, the shafts 2 and 3 are caused to rotate by any suitable means in opposite senses and so that the portions of the facing surfaces of each pair of overlapping discs 4 that, at any given moment, are overlapping one another, are moving downwards at that moment. Alternatively, the shafts 2 and 3 may be caused to rotate in the same sense as each other.

A part of the granular material between the end wall of the trough 1 that is adjacent to the inlet 6 and the adjacent weir 8 is subject to polishing by the abrasive layers 1 5 on the two overlapping discs.

It will be noted that, whereas in the first and second forms of apparatus, which are suitable for hulling, the discs 4 of each pair of overlapping discs are separated axially by a relatively short distance, say, 3 mm when the granular material is paddy of which the individual grains have a minor axis (regarding them as being approximately ellipsoids of rev- olution) of say, 2.5 mm, in the third form of apparatus, which is suitable for polishing, the discs of each pair of overlapping discs are separated axially by a considerably greater distance, say, 1 2 mm when the granular material is brown rice of which the individual grains have a major axis (again regarding the grains as being approximately ellipsoids of revolution) of say, 8 mm.

It has bsen found that, in the third form of apparatus, when the trough 1 is filled with granular material, at least in some of the regions between two adjacent weirs, to a depth sufficient for the shafts 2 and 3 to be immersed in the granular material, there is a considerable axial force tending to separate the discs 4 of a pair of overlapping discs.

Accordingly, the discs 4 must be relatively rigid. In the case of steel discs 4 having a diameter of approximately 1 5 cm, a thickness for each disc of approximately 5 mm will be found to provide the necessary degree of rigidity.

Of course, there is little or no axial force tending to separate the discs 4 of a pair of overlapping discs if there is a sufficiently small depth of granular material in the trough 1 in the vicinity of the discs in question, but it has been found that, to achieve a reasonable efficiency, there must be a substantial depth of material in the trough, satisfactory results being achieved when the depth of granular material is sufficient for the free surface of the material to be above the axes of the shafts 2 and 3.

The rotating discs 4 tend to keep granular material in their vicinity in an agitated condition and some of the material flows over the first weir 8 into the space between that weir and the second weir where it is acted upon by the next pair of overlapping discs 4.

Essentially, the granular material moves along the trough 1 from the inlet 6 to the outlet 7, if a head of granular material is maintained above the inlet 6 (say, in a hopper), by something analogous to pressure in a liquid. Thus, the rate of introduction of granular material into the trough 1 and the height of the weirs 8 each play a part in determining the depth of material in the trough 1. It will be noted that the weirs 8 extend above the axes of rotation of the shafts 2 and 3.

Any tendency which there may be for the material to be thrown along the trough in its upper region, so that it is not subjected to the action of one or more pairs of discs 4 is reduced or prevented by the deflector plates 9 situated over the weirs 8.

The shafts 2 and 3 can be driven conveniently by a diesel engine, but other forms of propulsion (even bicycle power) are possible, and the shafts may be geared together to ensure that they rotate in opposite senses, or they may be arranged to rotate in the same sense.

The material leaving the outlet 7 will comprise a mixture of treated granular material, say, white rice, and removed layer material, say, bran. After they have left the outlet 7, they can be separated in any convenient way.

In the case of white rice and bran, a screen is.

a convenient means of separating them.

Referring now to Figs. 1 2 and 13, the fourth form of apparatus is the same as the third form except that the inclined deflector plates 9 situated over the weirs 8 are replaced by vertical deflector plates 14, which also extend across the entire width of the trough 1 and which are situated between the weirs 8 and the pairs of overlapping discs 4 downstream of the weirs with respect to the direction of movement of the granular material along the trough 1 from the inlet 6 to the outlet 7. The plates 14 are welded to the cover member 5.

The manner of operation of the fourth form of apparatus is the same as that of the third form.

Referring now to Figs. 14 and 15, there is shown there a first form of combination of two forms of apparatus for treating granular material, which are mounted one above the other.

The upper apparatus, which is suitable for hulling paddy, is indicated generally by the reference numeral 1 6 and is the same as the apparatus shown in Figs. 1 to 3, although it could instead have the form of the apparatus shown in Figs. 1, 7 and 8. Similarly, the individual discs 4 can either have the form shown in Figs. 4 and 5 or the form shown in Fig. 6.

The lower apparatus, which is suitable for polishing brown rice, is indicated generally by the reference numeral 1 7 and is the same as the apparatus shown in Figs. 9 to 11, although it could instead have the form of the apparatus shown in Figs. 9, 1 2 and 1 3.

Leading downwardly from the outlet 7 from the trough 1 of the hulling apparatus 1 6 is an outlet conduit 18, which is of rectangular cross-section and closed on all four sides until it meets a conduit 1 9 with which the outlet conduit 1 8 communicates as a result of one of its side walls terminating where it meets the upper edge of the lower end of the conduit 19.

After leaving the outlet conduit 1 8 generally horizontally, the conduit 1 9 turns so that it extends first upwardly and then again generally horizontally before it terminates in register with an aperture in a housing 20 for a fan, which is not shown, but which is mounted on the shaft 2 of the apparatus 1 6. The housing 20 is formed with a horizontally extending outlet 21.

Below the point where it joins the conduit 19, the outlet conduit 1 8 continues downwardly and terminates in an inclined chute portion 1 8a, of which the upper side is open and serves as an air inlet 22, which leads into one side of the upper end portion of an inlet conduit 23. The inlet conduit 23, which is open at its upper end, leads downwardly to the inlet 6 in the cover 5 for the trough 1 of the polishing apparatus 17.

The first form of combination operates in the following manner. The shafts 2 and 3 of the hulling apparatus 1 6 and the shafts 2 and 3 of the polishing apparatus 1 7 are each caused to rotate in the senses described hereinbefore, and paddy is supplied, for example, by means of a hopper (not shown), to the inlet 6 of the hulling apparatus 1 6.

The paddy is hulled in the hulling apparatus 16, and a mixture of brown rice and husk leaves the trough 1 of that apparatus through the outlet 7 and falls down the outlet conduit 18.

The direction of rotation of the fan in the housing 20 is such that air enters the chute 1 8a through the air inlet 22 and flows up the lower part of the outlet conduit 1 8 and then up the conduit 1 9 into the housing 20 for the fan. The rate of flow of air caused by the fan is such that, while the brown rice continues to fall downwards and so enters the inlet conduit 23 leading to the polishing apparatus 17, the husk is carried up through the conduit 1 9 into the housing 20 from whence it is discharged through the outlet 21.

The brown rice is polished in the polishing apparatus 1 7 and a mixture of white rice and bran leaves the outlet 7 of the trough 1 of that apparatus. It will be noted that, as compared with the outlet 7 of the hulling apparatus 16, the outlet 7 of the polishing apparatus 1 7 is relatively large, which facilitates the separation of bran from the white rice by means of a screen (not shown), which can be situated just below the outlet 7 of the polishing apparatus 1 7.

Referring now to Figs. 1 6 and 17, the second form of combination is the same as the first form of combination except that the fan is not mounted on the shaft 2 of the hulling apparatus 1 6 but is provided with a separate drive means (not shown) and conduit 19 is replaced by a conduit 1 9a which at the end remote from the fan 20, instead of communicating with the outlet conduit 1 8 (as does the conduit 19), communicates directly with the trough 1 of the hulling apparatus 1 6.

In the combination shown in Figs. 16 and 17, the cover member of the trough 1 of the hulling apparatus 1 6 is provided with an aperture 7a opposite the aperture 7 in the base of the trough. The outlet 7a serves as an outlet for layer material that has been removed from the individual grains. The conduit 1 9a leads upwardly from the outlet 7a and then turns so that it extends first downwardly and then generally horizontally before it terminates in register with an aperture in the housng 20 for the fan. In the second combination, the outlet conduit 18 is closed on all four sides throughout its length.

The second combination operates in the same manner as the first combination except that the brown rice and husk are separated in the trough 1 of the hulling apparatus 1 6 rather than in the outlet conduit 18.

The direction and speed of rotation of the fan in the housing 20 is such that air enters the chute 18a through the air inlet 22 and flows up the outlet conduit 1 8 and through the outlet 7 into the trough 1 of the hulling apparatus 16. The fan also causes air to enter the trough 1 of the hulling apparatus 1 6 through the inlet 6 and to flow along the length of the trough 1. The rate of flow of air caused by the fan is such that the brown rice leaves the trough 1 through the outlet 7 and falls down the outlet conduit 1 8 while the husk is carried through the outlet 7a and through the conduit 1 9a into the housing 20 from whence it is discharged through the outlet 21.

The combination shown in Figs. 1 6 and 1 7 has the advantage that, as the fan is not mounted on the shaft 2 of the hulling apparatus 16, the shaft 2 and the fan can if desired be caused to rotate at different speeds. Furthermore it is not necessary for a single drive means to cause rotation of both the discs 4 of the apparatus 1 6 and the fan: where a single drive means is used to cause rotation of the discs 4 and the fan, there may be circumstances where some difficulty might be experienced in obtaining satisfactory speeds of rotation of both the discs 4 and the fan.

The combination shown in Figs. 1 6 and 1 7 also has the advantage that the air which is caused to flow through the trough 1 of the hulling apparatus 1 6 from the inlet 6 to the outlet 7a also acts to cool the hulling apparatus, which may in some circumstances be advantageous or even, under some operating conditions, necessary.

Instead of having inclined deflector plates 9 of the kind shown in Figs. 2, 3, 10 and 11, the second form of combination shown in Figs. 1 6 and 1 7 could have vertical deflector plates as shown, and as arranged, in Figs. 7, 8, 1 2 and 1 3. Similarly the individual discs 4 can either have the form shown in Figs. 4 and 5 or the form shown in Fig. 6.

It will be appreciated that, although the discs 4 described with reference to the accompanying drawings are all true discs in that they are circular, and it is preferred that they be circular, it is not essential and the invention includes the use of "discs" that depart from circularity.

Claims

1. Apparatus for treating granular material to remove at least part of an outer layer from individual grains of the material, which comprises a trough into which the material to be treated can be introduced and from which treated material can be removed, a pair of overlapping discs situated in the trough, each disc being so mounted as to be rotatable about an axis perpendicular to the plane of the disc, the two axes of rotation being parallel to one another and the two discs of the pair overlapping one another, but neither disc of the pair overlapping the other as far as the axis of rotation of the other, the facing surfaces of the discs of the pair of discs being generally planar, and means for causing the discs to rotate about the said axes, the arrangement being such that the granular material is treated by interaction with the facing surfaces of the pair of discs.

2. Apparatus as claimed in claim 1, wherein there is provided, within the trough, one or more additional pairs of such overlapping discs, the pairs of discs being spaced apart in a generally axial direction and the axes of rotation of the discs of the additional pair or pairs of discs each coinciding with one or other of the axes of rotation of the discs of the first-mentioned pair.

3. Apparatus as claimed in claim 2, wherein the trough is provided with one or more plates or like members which extend transversely with respect to the said axes and which, when the trough is so mounted that the said axes extend substantially horizontally, serve as weirs over which the granular material has to pass in order to pass from one pair of overlapping discs to the next.

4. Apparatus as claimed in claim 2 or claim 3, wherein the trough is provided with inlet means through which granular material to be treated can enter the trough in the vicinity of one end pair of overlapping discs and outlet means through which treated granular material can leave the trough in the vicinity of the other end pair of overlapping discs.

5. Apparatus as claimed in both claim 3 and claim 4, wherein there is provided, in the upper part of the trough, deflector means arranged to tend to cause granular material passing over a weir to be deflected downwardly into the region between that weir and the next pair of overlapping discs in the direction from the inlet means to the outlet means.

6. Apparatus as claimed in any one of claims 1 to 5, wherein the discs are circular and mounted for rotation about their centres and the inner surface of the trough as seen in a cross-section taken perpendicular to the axes of rotation of the discs when the apparatus is in its operating position with the axes horizontal, although not in contact with the discs, conforms generally to the peripheries of the discs, at least over their lower, outer quadrants.

7. Apparatus as claimed in any one of claims 1 to 6, wherein the means for causing the discs to rotate about the said axes is such as to ensure that the discs of the or each pair of overlapping discs rotate in opposite senses, and is such that, in operation, the portions of the discs of the or each pair of overlapping discs that, at any given moment, are overlapping one another, move upwardly at that moment.

8. Apparatus as claimed in claim 7, wherein the axial separation between the facing surfaces of the discs or each pair of overlapping discs is, or can be adjusted to be, a distance not exceeding 10 mm.

9. Apparatus as claimed in claim 8, wherein the axial separation between the facing surfaces of the or each pair of overlapping discs is, or can be adjusted to be, a distance within the range of from 1.5 to 3 mm.

10. Apparatus as claimed in any one of claims 7 to 9, wherein at least the portions of the facing surfaces of the discs of the or each pair of overlapping discs that overlap one another are made of rubber or a resilient plastics material.

11. Apparatus as claimed in claim 10, wherein, for each disc, the entire disc is covered in, or is made of, polyurethane.

12. Apparatus as claimed in claim 10 or claim 11, wherein the surface of the rubber or plastics material is formed with indentations and/or protrusions.

1 3. Apparatus as claimed in any one of claims 1 to 6, wherein the facing surfaces of the discs of the or each pair of overlapping discs are abrasive and wherein the means for causing the discs to rotate about the said axes is either such as to ensure that, in operation, the discs of the or each pair of overlapping discs rotate in opposite senses and such that the portions of the discs of the or each pair of overlapping discs that, at any given moment, are overlapping one another, move downwardly at that moment, or is such as to ensure that, in operation, the discs of the or each pair of overlapping discs rotate in the same sense.

14. Apparatus as claimed in claim 13, wherein the axial separation between the facing surfaces of the discs of the or each pair of overlapping discs is, or can be adjusted to be, within the range of from 5 mm to 20 mm.

1 5. A combination of first apparatus as claimed in both claim 4 and any one of claims 7 to 1 2 with second apparatus as claimed in both claim 4 and claim 1 3 or claim 14, the outlet through which treated granular material can leave the trough of the first apparatus being in communication with the inlet of the trough of the second apparatus through conduit means and there being provided means for separating layer material removed from the granular material in the trough of the first apparatus so that, in operation, substantially only the treated granular material from the first apparatus enters the trough of the second apparatus.

1 6. Apparatus for treating granular material to remove at least a part of an outer layer from individual grains of the material substantially as herein before described, more especially substantially as hereinbefore described with reference to, and as shown in, Figs. 1, 2 and 3 and either Fig. 4 and 5 or Fig. 6 of the accompanying drawings, or Figs. 1, 7 and 8 and either Figs. 4 and 5 or Fig. 6 of the accompanying drawings, or Figs. 9 to 11 of the accompanying drawings, or Figs. 9, 1 2 and 13, of the accompanying drawings, or Figs. 14 and 1 5 of the accompanying drawings, or Figs. 1 6 and

1 7 of the accompanying drawings.

1 7. A combination of first apparatus for treating granular material to remove at least part of an outer layer from individual grains of the material with second apparatus for treating granular material to remove at least part of an outer layer from individual grains of the material, the combination being substantially as hereinbefore described with reference to, and as shown in, Figs. 14 and 15, or Figs.

1 6 and 17, of the accompanying drawings.

1 8. A method for treating granular material to remove at least part of an outer layer from individual grains of the material, which comprises introducing the granular material to be treated into apparatus which comprises a trough into which the material to be treated can be introduced and from which treated material can be removed, a pair of overlapping discs situated in the trough, each disc being so mounted as to be rotatable about an axis perpendicular to the plane of the disc, the two axes of rotation being parallel to one another and the two discs of the pair of discs overlapping one another, but neither disc of the pair overlapping the other as far as the axis of rotation of the other, the facing surfaces of the discs of the pair of discs being generally planar, and means for causing the discs to rotate about the said axes, the arrangement being such that the granular material is treated by interaction with the facing surfaces of the pair of discs, the granular material to be treated being introduced into the trough, causing the co-operating discs to rotate and removing treated granular material from the trough.

1 9. A method as claimed in claim 18, wherein the granular material to be treated is introduced into the trough of apparatus as claimed in any one of claims 2 to 17, the cooperating discs are caused to rotate and treated granular material is removed from the trough.

20. A method as claimed in claim 18 or claim 19, wherein the speed of rotation of the discs is within the range of from 1 ,000 to 5,000 revolutions per minute.

21. A method as claimed in any one of claims 1 8 to 20, wherein the granular material to be treated comprises grains of which the shape is substantially that of an ellipsoid of revolution and the axial separation between the facing surfaces of the or each pair of cooperating discs is substantially equal to or slightly larger than the minor axis of the said ellipsoid of revolution.

22. A method as claimed in any one of claims 1 8 to 21, wherein the apparatus is as claimed in any one of claims 1 to 12, the granular material to be treated is paddy, the outer layer removed from the individual grains is husk, and the treated material is brown rice.

23. A method as claimed in any one of claims 18 to 20, wherein the apparatus is as claimed in any one claims 1 to 6 or claim 1 3 or claim 14, the granular material to be treated is brown rice, the outer layer removed from the individual grains is bran, and the treated material is white rice.

24. A method for treating granular material to remove at least part of an outer layer from individual grains of the material substantially as hereinbefore described, more especially as hereinbefore described with reference to Figs. 1, 2 and 3 and either Figs. 4 and 5 or Fig. 6 of the accompanying drawings, or Figs. 1, 7 and 8 and either Figs. 4 and 5 or Fig. 6 of the accompanying drawings, or Figs.

9 to 11 of the accompanying drawings, or Figs. 9, 1 2 and 1 3 of the accompanying drawings, or Figs. 14 and 1 5 of the accompanying drawings or Figs. 1 6 and 1 7 of the accompanying drawings.

25. Granular material whenever treated by a method as claimed in any one of claims 1 8 to 24.