GB1577979A

GB1577979A - Grinding machine for cereals and legumes

Info

Publication number: GB1577979A
Application number: GB14649/78A
Authority: GB
Original assignee: Buehler Miag GmbH
Current assignee: Buehler Miag GmbH
Priority date: 1977-04-15
Filing date: 1978-04-13
Publication date: 1980-10-29
Also published as: JPS5739189B2; DD136704A5; ES468832A1; JPS53130163A; DE2716637C2; IT1094399B; MX144707A; DE2716637A1; IN150207B; IT7822361A0

Description

(54) GRINDING MACHINE FOR CEREALS AND LEGUMES (71) We, BÜHLER-MIAG G.M.B.H., a body corporate organised under the laws of the German Federal Republic, of 19, Ernst-Amme-Strasse, 3300 Braunschweig, German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a grinding machine for grinding cereals and legumes.

It has been proposed to provide a grinding machine comprising a cylindrical grinding rotor composed of a number of grinding discs and driven by a motor around a vertical shaft and a screening jacket surrounding and radially spaced from the rotor, so as to define a grinding chamber for the product. The machine also comprises a housing which accomodates the grinding rotor and the screening jacket and serves as a bearing or supporting point for them, the housing having a product inlet and a product outlet and being connected to a fan for cooling the grinding rotor and carrying away the grinding dust.

These grinding machines which have a vertical grinding body, do not grind the grains at their tips but roll them thereby enabling them to be ground at their flanks.

Grinding the flanks of the grains is more advantageous because when this is done there is a smaller quantity of broken grains and only the losses of substance caused by the grinding operation itself result.

A large number of different designs of vertical grinding machines have been proposed in most of which the product to be ground is moved in and through the grinding chamber only by gravity, so that the residence time in the grinding chamber, the grinding time, is determined exclusively by gravity. With these machines it is not possible to influence the grinding output and the degree of grinding.

However, it has also been proposed to provide grinding machines in which the product is moved positively in or through the grinding chamber by one or more conveying means. With these machines it is possible for the throughput of product to be varied by altering the speed of the conveying means, but it has been found that the grinding effect or degree of grinding is more or less random.

Vertical grinding machines have also been proposed which have means for baffling the product in order to make it possible to regulate the residence time in the grinding chamber and consequently the grinding effect. When this is done, either a radial product outlet channel located at the bottom end of the grinding chamber is regulated in its throughflow cross section by means of an adjustable or spring-loaded flap or else a ring-shaped product outlet aperture of the grinding chamber is varied by means of manually operated slides. A further machine of this kind has at the bottom end of the grinding chamber a baffle ring which can be adjusted axially on wedgeshaped control surfaces and, according to its position, it releases or blocks to a greater or lesser extent the throughflow cross-section for the product.According to the above, the previously proposed vertical grinding machines therefore have either a positive feed or a positive passage of the product to be ground in and through the grinding chamber with the help of a conveyor or a control for the residence time of the product in the grinding chamber, using a baffle.

It has been found in practice that this design is inadequate if high machine outputs, that is to say a maximum product throughput, and an accurate control of the grinding operation or a definite degree of grinding as well as a uniform treatment of the product are required, which is expected from a modern machine of this kind.

According to the present invention there is provided a machine for grinding cereals and/or legumes, wherein the machine comprises a cylindrical grinding rotor composed of a number of grinding discs and arranged to be driven around a vertical shaft and a screening jacket surrounding and spaced from said rotor so as to define an annular cylindrical grinding chamber for the material to be ground, the machine also comprising a housing which supports the grinding rotor and the screening jacket and serves as a bearing or support for same the housing having an inlet for material to be ground and an outlet for ground material, there being fan means for cooling the grinding rotor and carrying away dust arising during grinding and wherein a conveyor for the positive inward feed of the material to be ground into the grinding chamber is arranged upstream of the grinding chamber in an axial extension and control means are located after the grinding chamber for controlling the through-put of the material being ground.

The present grinding machine is preferably designed in such a way that the said requirements - optimum throughput of product and also accurate control of the grinding operation - are fulfilled. A basis for such a design is that the quantity of product introduced into the grinding chamber per unit time must be defined and must be constant if a given output is to be achieved, while the product must be retained in the grinding chamber and the retaining action must be uniform over the entire crosssection of the grinding chamber if an adequate effect and an accurate control of the grinding process are to take place with all the products which are concerned. Furthermore, all the grains of product must pass along a path of the same length and must have the same residence time in the grinding chamber if - as is desired - all the grains of the product are to be ground to the same degree.

In the present machine the conveyor is preferably arranged so that its conveying surface directly adjoins the grinding chamber and the inlet cross-section for the material to be ground in the zone of the conveying means, the grinding chamber cross-section and also the cross-section of the outlet for ground material upstream of the control means are at least of approximately the same dimensions, the conveyor preferably being a screw conveyor, the external diameter of which is approximately the same as the mean diameter of the grinding chamber. The conveyor mounted directly in front of the grinding chamber in a rectilinear extension forces the material directly into the grinding chamber and acts over the entire cross-section of entry so that the pressure of the column of material in the grinding chamber is uniform at all points.

The control means is preferably designed so as to be self-regulating and because of this design ensures at the outlet end of the grinding chamber a definite constant counter-pressure which determines the residence time of the material in the grinding chamber and also the degree of grinding. The control means is preferably a flat baffle plate, the position of which is set by a predetermined external force. The baffle plate may be mounted centrally relative to the grinding chamber axis and is under the action of an adjustable weight in order to achieve an undisturbed flow of the ground material from the grinding chamber and an accurate guiding of the baffle plate or an accurately defined direction of movement and to make it possible to vary the packing pressure by adjusting the weight.In order that material shall be maintained in a state of flow between the outlet of the grinding chamber and the baffle plate and no undesirable backlash occurs when the machine is in operation, there are allocated to the baffle plate means for maintaining a minimum clearance at the outlet from the grinding chamber. Preferably the baffle plate is provided with entraining units which impart to it at least at times a rotary movement around the axis of rotation of the grinding rotor according to the movement of the material. It has been found to be advantageous for these entraining units to be axial pins which are spaced on the baffle plate from one another and contrary to the flow of material.The entraining units are for at least part of the time, carried along by the rotating material and in turn rotate the baffle plate, this being achieved by the fact that various vertical loads act on the circumference of the baffle plate but not always on the same point.

The grinding discs of the grinding rotor have only a definite working life which depends upon the use of the machine; this means that after a certain period of wear they must be replaced by new ones. In order to avoid a fairly long standstill of the machine when doing this and to make it possible to carry out the replacement of the grinding discs in the shortest possible time, the screw conveyor is preferably fixed releasably on to the grinding rotor and forms together with it a unit which can be dismantled as a whole.The grinding rotor conveniently comprises a shaft mounted in two bearings with several radial centreing vanes distributed uniformly around its circumference, which are firmly joined together at their top and bottom ends by rings and hold both the grinding discs and the screw conveyor so as to rotate integrally, the lower ring forming at the same time the vertical support for the grinding discs. The grinding rotor is preferably designed so as to be open at the top and bottom and its grinding discs are spaced from one another in order to allow them to be acted upon at the same time by the cooling air sucked through the housing and also to have them cooled correspondingly.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Figure 1 is a front elevation of a grinding machine, partly in section along its centre line, Figure 2 is on the right hand side, a plan view of the machine shown in Figure 1 with some parts removed, and, on the left hand side, a cross-section along the line II-II in Figure 1.

Figure 3 is a cross-section through the machine along the line III-III in Figure 1 on a larger scale, and Figure 4 is a central longitudinal section to the same scale as Figure 3 of a detail of the machine.

Referring now to the drawings, there is shown a grinding machine the main components of which comprise a housing 1, a grinding rotor 16 and a screen basket 44 held by the grinding rotor, a conveyor 22 for feeding the product into the grinding chamber, control means 47 for controlling the residence time of the product in the grinding chamber and drive means 35.

The housing 1 of the grinding machine may be made of sheet steel and is in the form of a cylindrical casing 2 having two column-like extensions 2a, and 2b a cover 3 and a bottom 4.

The cover 3 has an inlet 5 for the product to be ground and underneath its bottom 4 has an outlet hopper 6 which is retained by a number of fixtures 7 on a cover 9 connected to the bottom 4 by bolts 8. In order that the parts of the machine located in the housing 1 may be serviced, the casing 2 has two large rectangular apertures 10 which are opposite one another, and each of which is closed by a removable closing flap 11. Immediately above the bottom 4 there is provided on an extension 2a of the housing 1 a lateral outlet 12 with a connecting flange 13 which is connected to a suction fan (not shown in the drawing).Diametrally opposite the outlet 12 there is in the extension 2b a channel 14 which is closed by a lid 15 and which, for the purpose of removing any particles of product and dust which may accumulate on the bottom of the housing 4, can be connected for a short time with the atmosphere by removing the lid 15. so that the impurities are sucked out via the outlet 12.

The grinding rotor 16 is arranged centrally in the housing 1 and comprises a vertical shaft 17 with three radial centreing vanes 18 which are firmly connected with one another at their top by means of a ring 19 welded to them and at their bottom by means of a ring 20 welded to them, and which carry both grinding discs 21 and conveying means consisting of a screw conveyor 22, the grinding discs 21 being supported vertically on the ring 20. The screw conveyor 22 has a cylindrical extension 23 which is connected so as to rotate integrally with the ring 20 by means of bolts 24. Each grinding disc 21 is fixed so as to rotate integrally by means of a pin 25 (Figure 2) on one of the centreing vanes 18 and consequently relative to the shaft 17.The grinding discs 21 are spaced a small distance apart in the axial direction and the top grinding disc 21 is spaced a small distance from the screw conveyor 22 so as to allow for the passage of cooling air between the discs, and this clearance is obtained by spacer pins 26 arranged at definite intervals around the circumferences of the discs. The shaft 17 of the grinding rotor 16 is mounted in two anti-friction bearings 27 and 28, of which the bearing 27 is a radial bearing and the bearing 28 is a radial and axial bearing. The bearing 28 is held in a cylindrical cap 29 which constitutes part of the housing 1 and is connected to the casing 2 by a number of radial arms 30. The bearing 27 engages in a cylindrical cup 31 which is firmly connected by radial arms 32 with a flange 33 which is fixed by means of bolts 34 on to the lid 3 of the housing 1.

The drive 35 for the grinding rotor 16 consists of an electric motor 36, a V-belt pulley 37 mounted so as to rotate integrally on a shaft, of the motor 36, a V-belt pulley 38 mounted so as to rotate integrally on the shaft 17 of the grinding rotor 16 as well as several V-belts 39. The electric motor 36 is fixed to a carrier plate 40 by means of bolts 41, and the carrier plate 40 is fixed by means of bolts 42 to the extension 2b of the housing 1 so as to be adjustable. A cover 43 covers the rotating parts of the drive 35.

The grinding rotor 16 is surrounded by a concentric screen basket 44 which consists of two radially adjustable screen basket halves 44a, 44b, each of which is releasably secured to the housing by means of bolts 45 in the interior of the housing 1. As can be seen from Figures 1 and 2, the grinding rotor 16 and the screen basket 44 define an annular cylindrical grinding chamber 16. It can also be seen that the screw conveyor 22 with its conveying surface in the shape of a screw worm directly bounds the grinding chamber 46 and its external diameter is approximately the same as the mean dia meter of the grinding chamber 46.Furthermore, it can be seen that the crosssectional area of the inlet for the product in the vicinity of the screw conveyor 22, the constant cross-sectional area of the grinding chamber 46 and the cross-sectional area of its outlet 46a upstream of the control means 47 are approximately the same.

The control means 47 for controlling the speed of throughput of the product in the grinding chamber 46 as can be best seen from Figures 3 and 4, is in the form of a baffle plate composed of a flat ring 47a incorporating the actual control means, four arms 47b, a hub 47c, and also a downwardly pointing supporting bracket 47d to which a pressure plate 47e is firmly connected by welding. The baffle plate 47 is arranged with the help of its hub 47c so as to be able to slide up and down on the bottom offset end of the shaft 17 of the grinding rotor 16 and is automatically retained in position by an external force in the form of a weight 48.

The weight 48 is mounted adjustably on a straight arm 49a of a two-armed lever 49, the other U-shaped arm 49b of which has a ball-shaped end resting on the pressure plate 47e of the supporting bracket 47d of the baffle plate 47, so that it is pressed against this from below and in this way holds in position the baffle plate 47, according to the setting of the weight 48, close in front of the outlet 46a of th grinding chamber 46.

The lever 49 is mounted in a support 50 fitted on the outlet hopper 6. In order to maintain a minimum clearance 51 (Figure 4) between the baffle plate 47 or its ring 47a and the outlet 46a of the grinding chamber 46 there are provided two adjusting screws 52 which are screwed against the cup 29 of the lower grinding rotor bearing 28 through suitable threaded holes in the hub 47c of the baffle plate 47; by screwing the adjusting screws 52 to a greater or lesser degree into the hub 47c it is possible to vary the minimum clearance 51.

In order to produce in at least temporary rotary movement of the baffle plate 47 there are arranged on its ring 47a a number of axial pins 53 which are distributed uniformly around the circumference and project into the grinding chamber 46. the pins 53 are threaded and are screwed into corresponding threaded holes in the ring 47a and secured by nuts 54.

In the operation of the grinding machine just described. the enncline rotor 16 is driven continuously by the electric motor 36 via the belt drive 37, 38 and 39 and the suction fan which is not shown is switched on so as continuously to draw cooling air through the interior of the grinding rotor 16 and the grinding chamber 46 in the direction of the arrows (Figure 1), so that both the grinding rotor 16 and the product are constantly cooled and any grinding dust as well as parts of pods etc. are sucked away through the outlet 12.The product which is constantly fed in through the inlet 5, for example rice in the form of cane rice or brown rice, flows to the screw conveyor 22 which rotates at the same speed as the grinding rotor 16 and which feeds the product into the annular cylindrical grinding chamber 46 from the top, the product covering the total annular cross-section of the grinding chamber 46.

The product, e.g. brown rice, is then acted upon by the grinding discs 21 which grind the flanks of the rice grains and thus remove the husks as a result of which the desired white rice is produced. During this grinding operation the rice grains move under the action of the column of product constantly newly produced by the screw conveyor 22 and the action of the grinding discs 21 which entrain the grains as a result of friction so as to pass downwards helically in the grinding chamber 46 on to the baffle plate 47.The baffle plate 47 has a baffling effect on the product in the grinding chamber 46, as it is pressed against the column of product from below under the influence of the weight 48 and it maintains the weight of the column of product in balance and in this way determines the magnitude of the annular outlet gap (see Figure 4) between its ring 47a and the outlet 46a of the grinding chamber 46.

The baffling effect of the baffle plate 47 is therefore the same over the entire crosssection of the grinding chamber 46. The product which reaches the outlet clearance without any deflection, the ground rice or white rice, falls as a uniform annular shower of product into the outlet hopper 6 from which it is carried away. As the individual rice grains pass along the same path in the grinding chamber, the grinding effect is the same for all of them or at least approximately so.

By varying the adjusting force acting on the baffle plate 47, that is to say by adjusting the weight 48 or its position on the arm 49a of the lever 49, it is possible to increase or reduce the outlet gap and thus the residence time of the product in the grinding chamber 46, on which the degree of grinding of the rice grains depends. In this way, it is possible, if desired, to achieve different degrees of grindings, for example with different types of product. the baffle plate 47 automatically maintaining the degree of grinding set constant so long as it is not varied by renewed adjustment of the weight 48. In order to regulate the quantity of product fed into the grinding chamber 46 and consequently the throughput of product through the machine, the speed of rotation of the grinding rotor 16 is varied. This can be carried out, for example, by altering the gear ratio of the belt drive 37, 38, and 39 for example by changing the two belt pulleys 37 and 38, or using a drive motor with an adjustable speed.

If a grinding disc 21 should break or if the grinding discs 21 become worn, they can be exchanged by first of all dismantling the belt pulley 38 of the drive 35. Then the bolts 34 are undone and the cup 31 together with the upper anti-friction bearing 27 is removed.

The grinding rotor 16 is then free and after the baffle plate 47 has been removed from the shaft 17, it can be lifted out of the housing the shaft 17 being pulled out of the lower anti-friction bearing 28. After undoing the bolts 24, the screw conveyor 22 can be pulled out of centreing vanes 18, so that the grinding discs 21 are freely accessible and can be taken out one after the other singly from the centreing vanes and can be replaced by new ones. The re-assembly of the grinding rotor 16 into the machine is then carried out in the reverse sequence.

With the present machine a high throughput of product or an optimum grinding effect can be achieved, and, advantageously, flank grinding of the product takes place.

In addition, an accurate control of the grinding operation and consequently the maintenance of a predetermined degree of grinding which is uniform for all the grains of the product can be achieved with a simple and robust construction which does not require any specially trained staff to operate and worn parts of which can be changed easily and in a short time.

WHAT WE CLAIM IS: 1. A machine for grinding cereals and/or legumes, wherein the machine comprises a cylindrical grinding rotor composed of a number of grinding discs and arranged to be driven around a vertical shaft and a screening jacket surrounding and spaced from said rotor so as to define an annular cylindrical grinding chamber for the material to be ground, the machine also comprising a housing which supports the grinding rotor and the screening jacket and serves as a bearing or support for same the housing having an inlet for material to be ground and an outlet for ground material, there being fan means for cooling the grinding rotor and carrying away dust arising during grinding and wherein a conveyor for the positive inward feed of the material to be ground into the grinding chamber is arranged upstream of the grinding chamber in an axial extension and control means are located after the grinding chamber for controlling the through-put of the material being ground.

2. A grinding machine as claimed in Claim 1, wherein the conveyor is arranged so that its conveying surface adjoins directly on to the grinding chamber and the crosssection of the inlet for the material to be ground in the zone of the conveyor and the cross-section of the outlet for the ground material in front of the control means are at least approximately of the same size.

3. A gririding machine as claimed in Claim 2, wherein the conveyor is a screw conveyor, the external diameter of which is approximately the same as the mean diameter of the grinding chamber.

4. A grinding machine as claimed in any one of Claims 1 to 3, wherein the control means is designed so as to be self-regulating.

5. A grinding machine as claimed in Claim 4, wherein the control means is a flat baffle plate, the position of which is fixed by a pre-determined external force.

6. A grinding machine as claimed in Claim 5, wherein the baffle plate is located centrally relative to the grinding chamber axis and is subject to the action of an adjustable weight.

7. A grinding machine as claimed in Claim 5, or 6, wherein means are provided for maintaining a minimum clearance between the baffle plate and the outlet from the grinding chamber.

8. A grinding machine as claimed in Claim 6 or 7, wherein the baffle plate is provided with entraining units which are arranged to impart to it at least at times a rotary movement around the axis of rotation of the grinding rotor, depending upon the movement of the material.

9. A grinding machine as claimed in Claim 8, wherein the entraining units are adjustable axial pins which are spaced from one another and directed on the baffle plate against the intended direction of flow of material.

10. A grinding machine as claimed in any one of Claims 3 to 8, wherein the screw conveyor is fixed releasably to the grinding rotor and forms with it a unit which can be dismantled as a whole.

11. A grinding machine as claimed in Claim 10, wherein the grinding rotor comprises a shaft mounted in two bearings with a number of radial centreing vanes which are uniformly distributed around the circumference and which are firmly joined together at their upper and lower ends by rings, the vanes being arranged to rotate integrally both with the grinding discs and the screw conveyor, the lower ring serving at the same time as a vertical support for the grinding discs.

12. A grinding machine as claimed in Claim 11, wherein the grinding rotor is open at the top and bottom and its grinding discs are spaced from one another.

13. A grinding machine for cereals and/ or legumes substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. example by changing the two belt pulleys 37 and 38, or using a drive motor with an adjustable speed. If a grinding disc 21 should break or if the grinding discs 21 become worn, they can be exchanged by first of all dismantling the belt pulley 38 of the drive 35. Then the bolts 34 are undone and the cup 31 together with the upper anti-friction bearing 27 is removed. The grinding rotor 16 is then free and after the baffle plate 47 has been removed from the shaft 17, it can be lifted out of the housing the shaft 17 being pulled out of the lower anti-friction bearing 28. After undoing the bolts 24, the screw conveyor 22 can be pulled out of centreing vanes 18, so that the grinding discs 21 are freely accessible and can be taken out one after the other singly from the centreing vanes and can be replaced by new ones. The re-assembly of the grinding rotor 16 into the machine is then carried out in the reverse sequence. With the present machine a high throughput of product or an optimum grinding effect can be achieved, and, advantageously, flank grinding of the product takes place. In addition, an accurate control of the grinding operation and consequently the maintenance of a predetermined degree of grinding which is uniform for all the grains of the product can be achieved with a simple and robust construction which does not require any specially trained staff to operate and worn parts of which can be changed easily and in a short time. WHAT WE CLAIM IS:

1. A machine for grinding cereals and/or legumes, wherein the machine comprises a cylindrical grinding rotor composed of a number of grinding discs and arranged to be driven around a vertical shaft and a screening jacket surrounding and spaced from said rotor so as to define an annular cylindrical grinding chamber for the material to be ground, the machine also comprising a housing which supports the grinding rotor and the screening jacket and serves as a bearing or support for same the housing having an inlet for material to be ground and an outlet for ground material, there being fan means for cooling the grinding rotor and carrying away dust arising during grinding and wherein a conveyor for the positive inward feed of the material to be ground into the grinding chamber is arranged upstream of the grinding chamber in an axial extension and control means are located after the grinding chamber for controlling the through-put of the material being ground.