Method and a device for sorting and dry cleaning wheat

Abstract

 The invention concerns a method comprising the following steps:

a) a first step of wheat accumulation and dwell;

b) a step of layering the wheat over a first vibrating screen having smaller size holes than the wheat size and being swept by an ascending air stream;

c) a step of separating the heavy wheat fraction by passing through a second vibrating screen having larger size holes than the wheat size and being swept by an ascending air stream;

d) a second step of wheat light fraction accumulation and dwell which did not go through said vibrating screen during step (c); and

e) a step of dropping the wheat from step (d), said dropping being in the form of a thin layer and in countercurrent with respect to an ascending air stream;

and a device comprising a loading well, two vibrating screens, a discharge well, and a suction channel.
The invention affords large power savings and considerable reduction of the whole wheat cleaning system vertical height.

Description

[0001] This invention relates to a method and a device for sorting and dry cleaning wheat for use, in particular, following preliminary processing through a grading machine for size.

[0002] Know are grading machines, as disclosed for example in Italian patent application No. 69426 A/79 claiming of Swiss priority No. 533/79 of 19th January, 1979, suitable for wheat processing, which can grade the wheat to separate small size particles (dirt, sand) from large size ones (maize, etc.).

[0003] Wheat that has been subjected to such a pre-treatment for grading contains, however, some amounts of dust and lightweight particles which require to be separated.

[0004] Known is a dust trap, as disclosed in Italian patent No. 777734 claiming of Swiss priority No. 14489 of 20th October, 1965. In general, this dust trap type is placed at the delivery end of the cited grader in order for all the wheat stream to be freed from dust.

[0005] The wheat thus treated must then be graded according to weight into a light fraction and a heavy fraction. This grading treatment for weight is generally conducted in a concentrator which separates a light fraction (amounting to about 30% by weight) and a heavy fraction (amounting to about 70% by weight).

[0006] The light fraction must then be further processed for removal of rye, barley, light wheat, whilst the heavy fraction shall have to be processed, in turn, on a stone trap for stone removal.

[0007] This known arrangement is not devoid of shortcomings, however, and in particular the dust trap and concentrator have high power requirements and require a large volume of air which is then to be purified of dust prior to being released to the atmosphere. This evidently require that adequate conditioning devices (cyclones, filters, etc.) be provided, which involves, in turn, added power consumption for adequate conditioning.

[0008] Furthermore, the cited concentrator has a considerable height dimension and spans the full height of a story of the building accommodating the cleaning equipment, thus involving a much higher first cost than the cost of the concentrator per se.

[0009] It is, therefore, an object of this invention to reduce the power requirements for supplying the stream of air utilised in the dust trap.

[0010] Another object is to reduce the overall size of the wheat cleaning apparatus as a whole, attenuating the necessity of a full story of the building which contains such apparatus.

[0011] These and other objects are achieved by the method of sorting and cleaning wheat which comprises the following steps:

a) a first step of accumulation and dwell of the wheat;

b) a step of layering the wheat over a first vibrating screen having a smaller hole size than the wheat size and being swept by an ascending air stream;

c) a step of separating the heavy wheat fraction by passing through a second vibrating screen having larger size holes than the wheat size and being swept by an ascending air stream;

d) a second step of accumulation and dwell of the light wheat fraction which did not go through said vibrating screen during step (c); and

e) a step of dropping the wheat from step (d), said dropping being in the form of a thin layer and in countercurrent with respect to an ascending air stream.

[0012] It has been unexpectedly found, in fact, that the heavy phase amounts to about 50-70% by weight and requires, after going through the vibrating screen in step (c), no further processing through a dust trap, thereby said heavy phase may be transferred directly to the stone trap.

[0013] Only the light phase, which only amounts to about 30-50% by weight of the total, is subjected to the dust freeing process of step (a), thus affording savings in power which can be as high as 70%.

[0014] Preferably during said steps (a),(b),(c) and (d), the wheat is kept in vibratory motion along a substantially horizontal path.

[0015] During said steps (b) and (c), the wheat is held preferably on a slightly inclined path to the horizontal direction.

[0016] The method described above is implemented of preference on a device including a loading well, a first vibrating screen having smaller size holes than the wheat size, a second vibrating screen having larger size holes than the wheat size, and being characterised in that it comprises a discharge well located at the end of said second vibrating screen having a laminar outlet for the wheat to flow out; a suction channel located at said laminar outlet; said laminar outlet being formed by the bottom of said discharge well and a wall of said suction channel.

[0017] According to a preferred embodiment, the support for the bottom of the loading - well, the first vibrating screen, second vibrating screen, and support for the bottom of the discharge well form a rigid unitary vibrating body. Thus, with a single vibration generating unit connected rigidly to said rigid body it becomes possible to keep all the active parts of the device in a vibratory state.

[0018] Said vibration-generating unit is preferably comprised of a pair of eccentric mass powered vibrators so arranged as to impart a force directed horizontally through the centre of gravity of the rigid vobrating body.

[0019] The invention will be better understood by having reference to the figures of the accompanying illustrative and not limitative drawings, where:

Figure I is a side sectional view of a plant which implements a known method not embodying this invention;

Figure 2 is a side sectional view of a plant which implements the method according to this invention; and

Figure 3 is a side sectional view of a device according to this invention.

[0020] With reference to Figure 1, a grader for size is provided which yields a stream 2 of small size particles, stream 3 of medium size particles consisting of wheat, and stream 4 of large size particles mostly comprising maize incidentally admixed to the wheat and large size impurities. The stream 3 contains about 98% of the wheat and represents, accordingly, the useful yield.

[0021] In this conventional embodiment of a wheat cleaning method, the stream 3 is directed to a dust trap 46 which operates on a vertical suction channel and an ascending stream of air, to be accomplished, for example, as disclosed in the above-mentioned Italian patent No.777734.

[0022] The stream of dust-free wheat is then processed through the concentrator 5, which delivers a light fraction 6 amounting to about 30% by weight, and a heavy fraction 7 amounting to about 70% by weight.

[0023] The light fraction 6 is then processed on a rubbing device 8 which exerts a powerful cleaning action in combination with one of crushing the empty grains and earth lumps. A successive dust trap 47 will improve the cleaning of said fraction.

[0024] The heavy fraction 7 is processed through the stone trap 10, which separates stones from the useful grain 11.

[0025] The overall cleaned wheat results from the combined streams 9 and 11.

[0026] With reference to Figure 2 which describes a method and a device according to this invention, a grader for size 12 is arranged to feed the loading well 13 of the device 14 of this invention, which yields the light fraction 6 and heavy fraction 7 which are processed through the devices 8 and 47 and the stone trap 10. The useful wheat is collected from the streams 9 and 11.

[0027] With reference to Figure 3, a loading well 13 is provided to collect the wheat infeed to be treated. The bottom 15 of the loading well 13 is carried on a support 16 which is connected rigidly to the rigid body 17 which is kept in vibratory motion by a pair of powered vibrators 18 of the counter-rotating eccentric mass type. The bottom 15 of the loading well 13 is made to yield to the weight of the wheat load and is adjustable by means of a spring 20.

[0028] The rigid body 17 bears on elastic means 19 which allow for its vibration.

[0029] The rigid body 17 carries directly the first screen 21 and second screen 22 which have smaller and larger holes, respectively, than the wheat grain size.

[0030] Through both screens, an ascending air stream is maintained which follows the path indicated by the arrows 23.

[0031] Of preference, both screens would slope slightly toward the discharge end from the horizontal direction.

[0032] Cleaning of the screens is accomplished according to a conventional method by employing rubber balls 24 which will bounce over a corrugated mesh 25.

[0033] The terminating portion of the second screen communicates directly with the discharge well 26, which has a laminar opening 27 formed by the bottom 28 of the discharge well and the wall 29 of the suction channel 30. The area of the laminar opening can be adjusted by shifting, upwards or downwards, the flat moulding 44.

[0034] According to the embodiment shown in Figure 3, the support 42 for the bottom 28 of the discharge well 26 supports the bottom 28 rigidly. The wall 29 is hinge mounted at 31 close to the top of the supporting structure, thereby its position can be controlled by operating a handwheel 32 which drives a'lever not shown in the drawing.

[0035] Adjustability of the wall 29 position affords, for a given ascending air flow, control of the suction force of the channel 30.

[0036] Valves 33,34 afford, moreover, additional adjustment of the airflow through the sieves 21,22 and the channel 30, respectively.

[0037] A hood 43 enables connection of the device to a suction fan which will generate the required vacuum to.provide the streams through the screens 21,22 and the channel 30.

[0038] Two chutes 35,36 allow the heavy fraction to be conveyed to a hopper 37.

[0039] A hopper 38 collects the light phase following the dust freeing treatment through the channel 30.

[0040] The method of this invention is preferably implemented through the use of the device shown in Figure 3, where the first step (a) of wheat accumulation and dwell is carried out in the loading well 13; the layering step (b) is carried out on the first screen 21; the separation step (c) is carried out through the second screen 22; the second step (d) of light fraction accumulation and dwell is carried out in the discharge well 26; and the step (e) of wheat dropping into a thin layer is carried out through the laminar opening 30 in the direction of the arrow 39.

[0041] Operation is as follows.

[0042] The granular material from the size grader 12 enters the discharge well 13, whose bottom 15 is vibrated along with the rigid vibrating body 17, being distributed across the machine length.

[0043] The vibrating bottom is also oscillated by a swivel joint 16 to afford continued adjustment of the breadth of the passage opening 40 to the incoming flow, for the purpose of keeping the level within the loading well 13 constant.

[0044] The first screen 21 performs layering of the wheat such that the light particles will move to the upper region by the combined effects of vibration and the upflowing stream of air.

[0045] After the first screen 21, the wheat will meet the second screen 22. In this section, the heavy particles, which had previously arranged themselves at the bottom of the wheat layer, will fall through the screen holes and be collected into the hopper 37; the light particles would instead be held suspended by the stream of air and reach the discharge well 26.

[0046] Thus, densimetric grading of the wheat is accomplished by removing from the stream of granular material a fraction enriched with the heavier particles. That fraction amounts to 50-70% of the infeed material.

[0047] From the discharge well 26, the light fraction is introduced, by virtue of the vibratory movement, in the form of a sheet into the channel 30 where it is swept by an ascending air stream effective to remove the lightest grains and dust. The so cleaned light fraction by treatment with air collects into the hopper 38.

[0048] The well 26 is of fundamental importance to the proper operation of the device. It is, in fact, occupied continuously by the light fraction which is effective to seal the air in. Lacking that seal, the air would tend to move, due to pressure differentials inside the hood 41 and the channel 30, through the port 27 in either direction, thus defeating formation of a uniform sheet or causing clogging of the terminating portion of the second screen 22.

[0049] The wall 29 of the channel 30 oscillates around the swivel joint 31 and affords construction of either a converging or diverging or parallel channel contingent on different air stream grading requirements.

[0050] It has been found in actual practice that the invention achieves all the objects set forth without bringing about any loss in the useful wheat output, and while a degree of wheat cleaning ability which is comparable with that to be obtained with the conventional method described hereinabove.

Claims

1. A method of sorting and cleaning wheat, characterised in that it comprises the following steps:

a) a first step of accumulation and dwell of the wheat;

b) a step of layering the wheat over a first vibrating screen having a smaller hole size than the wheat size and being swept by an ascending air stream;

c) a step of separating the heavy wheat fraction by passing through a second vibrating screen having larger size holes than the wheat size and being swept by an ascending air stream;

d) a second step of accumulation and dwell of the light wheat fraction which did not go through said vibrating screen during step (c); and

e) a step of dropping the wheat from step (d), said dropping being in the form of a thin layer and in countercurrent with respect to an ascending air stream.

2. A method according to Claim 1, characterised in that during the steps (a),(b),(c) and (d), the wheat is kept in vibratory motion, said vibratory motion following a substantially horizontal path.

3. A method according to Claim I, characterised in that during said steps (b) and (c) the wheat is subjected to follow a slightly sloping path from the horizontal.

4. A device for sorting and cleaning wheat, comprising a discharge well, a first vibrating screen having smaller size holes than the wheat size, a second vibrating screen having larger size holes than the wheat size, and characterised in that it comprises a discharge well located at the end of said second vibrating screen having a laminar outlet for the wheat to flow out; a suction channel located at said laminar outlet; said laminar outlet being formed by the bottom of said discharge well and a wall of said suction channel.

5. A device according to Claim 4, characterised in that the support for the loading well bottom, first vibrating screen, second vibrating screen, and the support for the bottom of the discharge well form a rigid vibrating unitary body.

6. A device according to Claims 4 and 5, characterised in that vibration of said rigid vibrating body is generated by a single vibration-generating unit connected rigidly to said rigid body.

7. A device according to Claim 6, characterised in that said vibration-generating unit generates a horizontally directed thrust.

8. A device according to Claim 6, characterised in that said vibration-generating unit generates a thrust force through the centre of gravity of said rigid vibrating body. _'

9. A device according to Claim 6, characterised in that said vibration-generating unit comprises a pair of eccentric mass powered vibrators.

10. A device according to Claim 4, characterised in that said wall of said suction channel is movable to vary the breadth of said suction channel.

11. A device according to Claim 10, characterised in that said movable wall is hingedly connected to a location close to the top of the supporting structure.

12. A device according to Claim 10, characterised in that said movable wall enables the breadth of the discharge well to be varied.

13. A device according to Claim 4, characterised in that said first screen is slightly inclined from the horizontal toward the discharge end.

14. A device according to Claim 4, characterised in that said second screen is slightly inclined from the horizontal toward the discharge end.

Drawing