IMPROVED ROLLING MILL WITH DIRECT DRIVE MOTORS AND METHOD FOR OPERATING SAID ROLLING MILL

Abstract

The invention is a mill or rolling mill for processing cereals, granular materials, mixtures of cereals and similar products, comprising at least one pair of parallel cylinders (C, C) positioned side by side, wherein each cylinder (C, C) of each pair is provided with a torque motor that in turn is mounted or assembled directly on the shaft of the respective cylinder (C, C), and at least one control circuit (Z) suited to select which one of said two cylinders (C, C) of each pair rotates faster.

Claims

1. A mill or rolling mill for grinding and processing cereals, granular materials, mixtures of cereals and similar products, comprising at least one pair of parallel cylinders (C, C) positioned side by side, wherein each cylinder (C, C) of each pair is provided with a torque motor, in turn mounted or built directly on the shaft of the corresponding cylinder (C, C), and at least one control circuit (Z) suited to supervise the rotation parameters of said cylinders (C, C) of each pair, wherein said at least one control circuit (Z) selects which one of said two cylinders (C, C) of each pair rotates faster, wherein said faster cylinder (C, C) can selectively be the first or the second cylinder (C) according to the type of processing to be obtained.

2. The mill or rolling mill according to claim 1, wherein said motors are of the synchronous type with permanent magnets, each having the rotor integral with the end of the shaft (A, A) of each cylinder (C, C) and the stator constrained to the fixed supporting structure (S) of the shaft (A, A) of each cylinder (C, C), and wherein said rotor comprises permanent magnets (M, M) arranged in proximity to at least one end of the shaft (A, A) of each cylinder (C, C), said permanent magnets (M, M) being arranged along the circumference of said shaft (A, A) in such a way that they are equidistant from each other, while said stator comprises coils or windings (B, B) fixed to said supporting structure (S) and arranged radially around the end provided with permanent magnets (M, M) of each shaft (A, A), and wherein each set of permanent magnets (M, M) of said shafts (A, A) and each set of said coils or windings (B, B) are arranged radially around said permanent magnets (M, M) without contact during rotation.

3. The mill or rolling mill according to claim 2, wherein said coils or windings (B, B) are fixed to said supporting structure (S) through flanges (H, H) and/or are constrained with at least one reaction arm in order to limit their rotation and transmit the desired torque to the rotating shaft (A, A).

4. The mill or rolling mill according to claim 1, wherein each set of coils or windings (B, B) of each motor is connected to said control circuit (Z), and wherein said control circuit (Z) controls the power supply and change of polarity or power intensity of said coils or windings (B, B) of each motor in an independent manner through corresponding control units (L, L).

5. The mill or rolling mill according to claim 1, wherein said cylinders (C, C) have a grooved surface (C1), comprising a plurality of projections (D, D) with cross section substantially in the shape of saw teeth, meaning an asymmetrical triangular cross section, each projection defining a cutting edge, or blade (D1), and an inclined surface, or back (D2), and wherein by making the first cylinder, or front cylinder (C) rotate faster it is possible to obtain a type of processing that is different from the type of processing obtained by making the second cylinder, or rear cylinder (C) rotate faster.

6. The mill or rolling mill according to claim 1, comprising means for measuring the clamping force of said two cylinders (C, C) of each pair, suited to communicate said values to said at least one control circuit (Z) that controls the management parameters of the motors of said cylinders (C, C).

7. The mill or rolling mill according to claim 1, comprising one or more means or devices suited to serve as an interface with the user or with an external terminal, for the insertion and/or setting and/or modification of data and controls related to the processing parameters.

8. The mill or rolling mill according to claim 1, wherein said control circuit (Z) controls the power supply and the change of polarity of the coils or windings (B, B) of the motors of each pair of cylinders (C, C) by transmitting a higher rotation speed and torque for one of the two cylinders (C, C), while the other cylinder (C, C), which is slower, is braked by its own motor, and wherein the control unit (L, L) of the slower motor, through the feedback connection (R) of the DC-BUS or other type of carried out downstream of the power rectifiers, makes part of the energy recovered available to the motor of the faster cylinder (C, C), transmitting it directly to the respective control unit (L, L).

9. The mill or rolling mill according to claim 1, further comprising means suited to control the speed of the feeding roller, that is, of the roller that feeds said at least one pair of cylinders (C, C) with the material to be processed, in order to synchronize the speed of the feeding roller and the speeds of said cylinders (C, C) for the purpose of guaranteeing that the grinding speed exceeds the feeding speed.

10. A method for operating the mill or rolling mill according to claim 1, wherein said control circuit (Z) controls the power supply and the change of polarity of the coils or windings (B, B) of the motors of each pair of cylinders (C, C) by transmitting a higher rotation speed and torque to the front cylinder (C) or to the rear cylinder (C) of each pair, according to the type of processing to be carried out.

11. The method according to claim 10 for operating the mill or rolling mill, wherein with said cylinders (C, C) arranged in a matching manner, meaning so that the blades (D1) of the teeth (D) of the first cylinder or front cylinder (C) are directed downwards, while the blades (D1) of the teeth (D) of the second cylinder or rear cylinder (C) are directed upwards: the blade-blade type of processing is obtained with said front cylinder (C) rotating at a higher speed than the rear cylinder (C); and the back-back type of processing is obtained with said front cylinder (C) rotating at a lower speed than the rear cylinder (C).

12. The method according to claim 10 for operating the mill or rolling mill, wherein with said cylinders (C, C) arranged in a specular manner, meaning so that the blades (D1) of the teeth (D, D) of both cylinders (C, C) are directed downwards: the blade-back type of processing is obtained with said front cylinder (C) rotating at a higher speed than the rear cylinder (C); and the back-blade type of processing is obtained with said front cylinder (C) rotating at a lower speed than the rear cylinder (C).

13. The method according to claim 10 for operating the mill or rolling mill, wherein said control circuit (Z) comprises a plurality of predefined programmes or recipes comprising one or more sequences of operating parameters.

Description

[0074] According to the invention, the rotation direction of one or both of the cylinders can be inverted, for example in case of blockages in the machine or for cleaning purposes.

[0075] As the torque motors operate in a reversible manner, owing to the driving action exerted by the faster cylinder on the slower cylinder, which takes place through the product being ground, it is possible to recover part of the energy supplied by the mains, due exactly to the difference between the rotation speeds of the two cylinders.

[0076] By properly connecting the two control units using a connection of the DC-BUS type or another type, carried out downstream of the power rectifiers, it is possible to obtain, from the slower motor, the generation of energy that is immediately made available to the faster motor. The slower cylinder and, consequently, the motor connected to it are driven by the product being ground, which acts as a driving element for the faster cylinder.

[0077] The advantages achieved by the new improved rolling mill are the following.

[0078] First of all, the possibility to change the speed ratio between the two cylinders automatically through the control circuit, with no need to stop and above all to disassemble the machine, revolutionizes the grinding process known up to date. In fact, according to the type of product to be ground and to the starch damage level to be obtained, it will be possible to vary the speed and possibly even the rotation direction of each one of the two cylinders, as well as their rotation ratio, according to the finished product to be obtained.

[0079] In addition to the above, high energy savings are obtained owing to the recovery of the energy supplied by the slower cylinder. Furthermore, differently from the motors of the traditional rolling mills that absorb 40% of the installed power when running idle, the motors of the new rolling mill that is the subject of the invention absorb 10-12% of the installed power. Therefore, all the power saved in order to maintain the rolling mill running idle compared to the traditional motors will be available during the grinding step. Furthermore, during the grinding step further 30% energy can be saved owing to the recovery action performed by the motor installed on the slower cylinder. This means that, compared to traditional motors, the system with two torque motors allows the slower motor to make part of the electric energy taken from the electricity mains available for the faster motor.

[0080] The application with the new motors provides the control circuit with a whole series of parameters that make it possible to manage the grinding process in an optimal manner. In fact, through the two control units it is possible to control the following:

[0081] a. torque of each motor;

[0082] b. number of revolutions;

[0083] c. power absorption;

[0084] d. temperature;

[0085] e. speed ratio.

[0086] All the above and possible other parameters allow several preset programmes to be run on the control circuit. This makes it possible to obtain the desired product according to specifications that are perfectly repeatable and therefore not subject to errors due to manual management.

[0087] According to the type of cereal, it is thus possible to apply the preset or in any case presettable programme or recipe, in which all the processing parameters and the exact sequence of operations are defined in a precise and repeatable manner, wherein said parameters and operations will be set automatically controlling speed, torque and rotation direction of each cylinder of each pair.

[0088] Said programmes or recipes can successively be updated and in any case modified or added according to the type of product that has to be obtained from time to time. This is possible thanks to the new technology applied, which allows all the operating parameters to be controlled and completely, immediately and automatically modified.

[0089] The new rolling mill comprises also a device suited to control the clamping force of the grinding cylinders, which makes it possible to verify and reproduce the intensity of the grinding stress due to the adjustment of the distance between the two cylinders. This device consists of two load cells or another means suited to measure the clamping force of the cylinders. The force value that can be read on the control device is communicated to said control circuit that acts on the motor management parameters in such a way as to obtain the desired grinding intensity.

[0090] In particular, according to the power absorption and to the stress of the load cells, it is possible to manage also the feeding rate of the material to be processed.

[0091] The attached table shows a practical embodiment of the invention by way of non-limiting example.

[0092] FIG. 5 shows a pair of cylinders (C, C) of a rolling mill, but the explanation provided below is to be understood as valid for rolling mills equipped with two or more pairs of cylinders (C, C).

[0093] Each cylinder (C, C) is arranged with its shaft (A, A) parallel to the shaft (A, A) of the other cylinder (C, C).

[0094] The end of the shaft (A, A) of each cylinder (C, C) is housed and rotates in a support or supporting flange (F, F) that is integral with the structure (S) of the rolling mill.

[0095] The rotor of the magnetic motor is applied to the end of each shaft (A, A), and in particular a series of identical permanent magnets (M, M) are applied, mounted, connected or in any way joined to said end of the shaft (A, A), said permanent magnets being arranged along the circumference so that they are equidistant from each other.

[0096] Said permanent magnets (M, M), located on the generatrix of the end of the shaft (A, A) of the cylinder (C, C) and arranged longitudinally with respect to the shaft of the cylinder (C, C) itself, constitute said rotor of each torque motor.

[0097] A series of coils or windings (B, B) constituting the second part of each torque motor, meaning the stator, are fixed to the structure (S) of the rolling mill.

[0098] In the example shown in FIG. 5, said coils or windings (B, B) are fixed to the structure (S) of the rolling mill through a connection flange (H, H). Said coils (B, B) are, therefore, installed around the end with said permanent magnets (M, M) of the shaft (A, A), in such a way as to be arranged radially with respect to said permanent magnets (M, M).

[0099] All the coils or windings (B, B) of all the cylinders (C, C) are connected to a control circuit (Z).

[0100] Said control circuit (Z) controls and feeds the coils or windings (B, B) of each one of the two cylinders (C, C) independently, by means of the two control units (L, L).

[0101] The control unit (L) of the motor of the faster cylinder (C) serves the function of master, while the control unit (L) of the motor of the slower cylinder (C) is set as slave. In particular, said control circuit (Z) feeds the suitable coils or windings (B, B) with suitable intensity and frequency, or alternates the power supply sequence, in such a way as to transmit the desired torque and rotation speed to the permanent magnets (M, M) and thus to the cylinders (C, C).

[0102] The control circuit (Z) supervises the rotation parameters of the two cylinders (C, C), making it possible to set the same speed or different speeds for said two cylinders (C, C).

[0103] For example, said control circuit (Z) can set the same rotation speed for both of the cylinders (C, C), or it can set the rotation torque of each one of the two cylinders (C, C) at the same or different values, or it can set for one cylinder (C) a lower speed than for the other cylinder (C) coupled with it, so that the former cylinder is thus braked.

[0104] Furthermore, said control circuit (Z) can provide a setting according to which the first cylinder (C) is set rotating at a determined speed while the motor of the second cylinder (C) rotates at a lower speed. In this way, the second cylinder (C) is driven by the motion of the first cylinder (C) and by the material introduced between the cylinders (C, C). Said second cylinder (C) is braked by its motor and then the corresponding control unit (L), through the feedback connection (R), makes part of the recovered energy available for the motor of the first cylinder (C), supplying it directly to the control unit (L).

[0105] FIGS. 6, 7, 8, 9 show how the type of processing can be changed without varying the arrangement of the cylinders (C, C), but simply varying their rotation speed, wherein the higher speed is indicated by a double arrow, the lower speed is indicated by a single arrow, and the direction of introduction of the material from above is indicated by a broken arrow.

[0106] Said cylinders (C, C) have a smooth or grooved surface (C1), as shown in FIGS. 6-9, that is, comprising a plurality of projections (D, D) with cross section substantially in the shape of saw teeth, that is, an asymmetrical triangular cross section, each projection defining a cutting edge, or blade (D1), and an inclined surface, or back (D2).

[0107] In FIG. 6 said cylinders (C, C) are arranged in a matching manner, that is, so that the blades (D1) of the teeth (D) of the first cylinder or front cylinder (C) are directed downwards, while the blades (D1) of the teeth (D) of the second cylinder or rear cylinder (C) are directed upwards. The blade-blade processing is obtained with said front cylinder (C) rotating at a higher speed than the rear cylinder (C).

[0108] FIG. 7 schematically shows how the back-back type of processing can be obtained without inverting the position of the cylinders (C, C), but simply making the rear cylinder (C) rotate faster than the front cylinder (C).

[0109] In FIG. 8 said cylinders (C, C) are arranged in a specular manner, that is, in such a way that the blades (D1) of the teeth (D, D) of both cylinders (C, C) are directed downwards. The blade-back type of processing is obtained with said front cylinder (C) rotating at a higher speed than the rear cylinder (C).

[0110] FIG. 9 schematically shows how the back-blade type of processing can be obtained without inverting the position of the cylinders (C, C), but simply making the rear cylinder (C) rotate faster than the front cylinder (C).

[0111] The new rolling mill preferably comprises also means or devices suited to serve as an interface with the user or with an external terminal, for the input and/or setting and/or modification of data and controls related to the processing parameters.

[0112] A further technological advantage lies in that it is possible to adjust the feeding rate of the material to be processed in the machine.

[0113] It is known that rolling mills, in their upper part, are provided with a roller device, or feeding roller, which collects the material to be ground from an accumulation hopper that is incorporated in the machine and conveys it to the underlying grinding cylinders. The speed of said feeding roller is variable and determines the capacity of the machine.

[0114] In traditional rolling mills, the speed of the faster grinding cylinder and the differential ratio of the two speeds are fixed parameters, which can be modified only by changing the mechanical structure of the machine. In several instances, if the grinding capacity of the rolling mill needs to be increased, the speed of the feeding roller is increased, but this is possible only until the maximum peripheral speed of the grinding cylinders exceeds the speed transmitted by the feeding roller to the product that is reaching the cylinders.

[0115] This relationship between the two speeds guarantees a grinding homogeneity that is fundamental to obtain an optimal finished product. In the opposite case, if the speed of the grinding cylinders were lower than the speed of the product reaching the cylinders, the material would accumulate on said cylinders, with consequent grinding non-homogeneity, increased vibrations and noise due to continuous hitting.

[0116] Thanks to the new rolling mill, which comprises also means for controlling the speed of the feeding roller, it is possible to synchronize the two speeds, meaning the speed of the feeding roller and that of the grinding cylinders. The object is to ensure that the grinding speed is always higher than the feeding speed, so that for all the operating speeds of the machine it is possible to obtain optimal grinding results with no vibrations and reduced noise.

[0117] These are the schematic outlines that are sufficient to the expert in the art to carry out the invention, consequently, in the construction step variants may be developed that do not affect the substance of the innovative concept introduced herein.

[0118] Therefore, with reference to the above description and the attached drawings, the following claims are expressed.