DESCRIPTION

The present invention relates to a roller milling machine for grinding food products, notably food grains, in particular for grinding cereals, such as for example, but not only, wheat and maize.

The use of flour is very widespread in the food sector, both for human use and for animal use. Since ancient times, already in the fertile crescent and in the Mediterranean region where civilisation originated, it was very common to produce flour from cereals, in order to be able to produce therefrom breads, cakes and similar items. The flour enabled easier transport and longer preservation, as well as enabling the preparation of the aforementioned specialities, being easier to eat and digest than cereals as such.

To date, flours from cereals are known, such as wheat and maize flour especially, but also flours from barley, rice, buckwheat, oat, rye, millet, sorghum and spelt. There are flours from plants other than cereals, such as lentils, peas, almonds and chestnuts. This list is far from exhaustive and there are many other types of flours available; a large part of them have become commercially important since it became known that gluten can entail problems of intolerance (coeliac disease) and alternatives have been studied which may result in products similar to traditional products, possibly without loss of quality of taste. There are also animal flours, generally used to supplement feed, even though their use is sometimes controversial, as clearly emerged during the episodes of "mad cow disease".

To be able to obtain flour, the material to be ground, normally cereals, but sometimes different material such as desiccated chestnuts and almonds, is introduced in the grinding device and subject to a mechanical grinding action. Generally, such an action is achieved by placing the material, as grains or in pieces, between two hard objects, moving one with respect to the other. In the past, this occurred by placing the material to be ground on a rather large stone and crushing it, exerting a compression with a normally smaller stone. This work was somewhat demanding and brought about a very coarse grind, which made the subsequent preparation of breads, cakes and similar items rather difficult, giving rise to areas that were baked very differently to how neighbouring areas were baked, and to a product that was sometimes not completely edible.

A later improvement was in the use of large stones, called millstones or grindstones, normally disc-shaped, driven mechanically by external forces, such as water, wind or animal traction (for example using donkeys). Thus, the hard effort became alleviated by the use of a kind of external engine, and the weight of the millstones or grindstones made the flour much finer, finally giving rise to a more uniform end product than that obtained manually.

In more recent times, more refined machines have been developed, such as the cereal roller milling machine, to which field the present invention applies in its own right.

A cereal roller milling machine is a machine comprising two counter-rotating rollers, normally made of metal or metal alloy. The distance between these rollers is adjusted according to the size of the material to be ground and the granulometry of the flour which is desired to be obtained. Usually, the material to be ground is inserted into a first roller milling machine, in the space between two rollers and these rollers are driven to rotate, as mentioned in opposite directions to one another. The coarsely ground material is sent to a second roller milling machine, with a shorter distance between the rollers, often truly minimal if not zero, where the coarsely ground material is further ground, so as to become finer and more uniform. The operation is repeated, passing through finer and finer roller milling machines, until a more suitable granulometry is attained, so as to obtain the desired end product.

Some machines of this type provide for two rolling stages in series, the entry of the second stage corresponding to the exit of the first.

Often, more roller milling machines are provided, often more than 20, which work together and in a coordinated manner, and the product of one roller milling machine, as previously mentioned, is fed to the next one to obtain a finer product which can be fed to another roller milling machine and so on, until the desired granulometry for the flour is achieved.

Usually, above the pairs of grinding rollers there is arranged a system for distributing the material to be ground which comprises, for example, a hopper or similar and a distribution roller, so as to distribute the material as uniformly as possible over the length of the roller and at a speed controlled according to the quantity of material to be ground, so as not to have overloaded areas close to areas completely lacking in material to be ground.

The milling rollers are rotated by pulleys and belts, with an inversion device for the roller moving in the opposite direction, which in turn are rotated by an electric motor, generally a three-phase asynchronous motor. Such a motor is normally hung from the ceiling of the premises where the grinding is carried out; therefore at least two walkable floors are to be provided in the plant where these roller milling machines are used. Generally, the system of pulleys and belts places only one of the two rollers of the roller milling machine in motion, the other one being moved by transmission and inversion means. The distribution system is, on the other hand, controlled by a gear motor, coupled directly to the distribution roller and with its speed being controlled by an inverter. These motors normally develop power levels from 7.5 kW to 37 kW, which is somewhat high, and therefore develop significant quantities of heat through the Joule effect and due to the frictions at play. It is clear that the energy consumption in a large milling plant, of this type, is rather heavy and it is therefore clear that even a small saving on the required energy for an individual stage can have a significant effect on the overall management of the plant over time. Bearing in mind that a milling plant often provides for a high number of these roller milling machines and that there are therefore many motors hung from the ceiling, it is clear that there is a floor which is wasted and subject to stresses that are far from insignificant, bearing in mind also the effect that the vibrations of the motors can have on the statics of the floor and, therefore, of the building, especially if vibrations are created at frequencies close to the natural frequency of the floor.

It is also noted that the transmission belts and pulleys commonly used for these machines can, owed to wear, become loose over time and, during operation, can slip and produce sparks which can cause, in the worst cases, fires. It is to be noted that the flour which can be scattered around these roller milling machines in the form of dust is extremely flammable and, in some circumstances, can even lead to explosions, for this reason creating an industrial environment that is traditionally already very dangerous; hence, it is understood how serious this problem can be.

W02017/089870 discloses a mill of this type, with an electric motor mounted directly on the rollers, each roller having its own motor. Unfortunately however, this type of mill, which would address the drawback of the cluttering of the ceiling and additional floor, does not work out, creating serious risks of explosion owed to the high temperatures which develop; therefore this type of mill is not as widespread as one would have imagined and to date remains almost unused.

CN 108187813 discloses a crusher with rollers, guided by a synchronous motor with permanent magnets, which comprises a frame, a fixed roller and a moving roller, the synchronous motor being not able to be fitted directly to the rollers, but there being provided a moving threaded shaft, a moving frame and a driving mechanism. The two ends of the moving roller are arranged in a moving support by means of roller bearings and the moving support is connected with the moving frame. The permanent magnet synchronous motor, which does not have special centring bushings, is adopted as a motor directly geared with the crusher with rollers, so as to reduce the intermediate drive linkage. However, this motor cannot be adapted for already-existing machines. In this crusher, the rollers are not in tight contact with one another and tolerance levels that are quite high are required.

W090/014165 cites a roller mill for refining granular food materials. It comprises a motion transmission system among two rollers which run at different speeds. Substantially, the patent relates to a speed switch for one of the two rollers, normally for the rear one.

EP 1158188 relates to a roller driving unit, in particular for the paper industry. It cannot be used in rollers for the grinding of cereals, since it provides rollers in white cast iron, subjected to a high amount of wear and requiring frequent disassembly in order that it can undergo continuous adjustment and ruling interventions. The continuous and fast depletion of these rollers would make the system too fragile for the grinding of cereals and grains.

The problem underlying the invention is to propose a roller milling machine structure for the production of flour which overcomes the drawbacks mentioned and provides for reducing the spatial size, increasing yields and operating in complete safety, minimising or completely eliminating the risks of explosion associated with the working environment. This aim is achieved by a roller milling machine for grinding food products, comprising a motor, floating-mounted with the aid of a torque arm directly on one of the grinding rollers, characterised in that said motor has particular centring bushings, in that said grinding rollers can operate in contact with one another, and in that said motor is liquid-cooled. The present invention relates also to a method for producing a roller milling machine as described above, characterised in that it provides for adapting a pre-existing roller milling machine, according to the steps of substituting an appropriately dimensioned motor, which has centring bushings and is floating-mounted directly on one of its grinding rollers, directly for the pulley mechanism of the pre existing systems and so as not to interfere with the other components of the roller milling machine, said motor being water-cooled; constructing a torque arm to enable a floating installation, interfacing the control drive with the existing electronics, so as to move the rollers apart in the event of overloading of the motor and interfacing temperature sensors with the existing protection management electronics. The dependent claims describe preferred characteristics of the invention.

Other features and advantages of the invention will become clearer from the following detailed description of a preferred embodiment, given purely by way of example and in a non-limiting manner, and illustrated in the appended drawings in which:

Figure 1 is a front view, partly in cross-section, of a roller milling machine according to the prior art;

Figure 2 is a side view, partly in cross-section, of the roller milling machine of Figure 1;

Figure 3 is a front view of a roller milling machine according to the present invention;

Figure 4 is a side view, partly in cross-section, of the roller milling machine of Figure 3; and

Figures 5A and 5B are perspective views of some components of the machine of Figures 3 and 4.

Upon examining Figures 1 and 2, the general case of a known type of roller milling machine is seen. The roller milling machine 1 comprises a pair of milling rollers 2, 3, placed in rotation by transmission belts, 4 and 5 respectively, which in turn are made to rotate by motors 6, 7, usually arranged hung from the ceiling of the premises where the roller milling machine 1 is contained.

Figures 3 and 4 illustrate a roller milling machine 8, according to a preferred embodiment of the present invention.

In this embodiment, there are a motor 9, mounted directly on the head of the grinding roller 10, and a motor 11, mounted directly on the distribution roller. Said motor 9 is floating- mounted with the aid of a torque arm (not shown in the drawings). Preferably, said motor 9 is directly fitted to said roller 10 and the other motor 11 is directly fitted to the distribution roller, so as to completely eliminate every type of transmission. The roller milling machine 8 can arrive at the plant already assembled by the manufacturer during the production stages and if necessary also pre-tested, given that the presence of an external motor and belts with which to connect it are not required. Furthermore, the roller milling machines 8 can be arranged as desired in the premises, according to requirements, without needing to place them by a motor, and therefore spaces can actually be optimised. If desired, the arrangement of the roller milling machines 8 in the same premises can be changed from time to time, according to circumstances. Figure 5a shows in perspective view a motor 9. As is seen, a coolant inlet 12 and a coolant outlet 13 are present. Another grinding roller 14 is provided. The distance between the rollers 10 and 14 can be adjusted and they can work in tight contact with one another.

Figure 5B shows a motor 11 for the distribution rollers, which is different from the motor 9.

Preferably, the motor 9 is a liquid-cooled three-phase synchronous motor with permanent magnets, and has a centring bushing fitted. As an alternative, it can be a switched reluctance synchronous motor, also liquid-cooled. In any case, these are preferably motors with an efficiency of class IE4. Generally, the coolant is water, but can also be an aqueous solution, for example a solution of water and ethanol or a solution of ethylene glycol. The specific heat of water, however, certainly makes the liquid more suitable for this purpose.

Preferably, the motor 11 is a motor similar to the motor 9, but it is not liquid-cooled. Thus, there are further energy savings.

Preferably, the motor 9 is mounted on only one (10) of the milling rollers, preferably on the one mounted at the front, as seen from the access area of the roller milling machine 8.

Preferably, the other roller (14) is driven in rotation by a system of transmission belts 15. The combination of these last features avoids having to make the other roller 14 act as a brake (as it would do if it were also motorised like the roller 10), since it rotates at a lower speed than the roller 10, in order to maintain a fixed turns ratio. While the motor 9 would be dimensioned as if the other motor were not there, the latter would be almost impossible to dimension.

Preferably, the food products are grains and/or cereals.

When the roller milling machine 8 according to the present invention is used, the material to be ground (grains or other, such as dry chestnuts, animal remains or other), is introduced in a known way, for example by means of a hopper that is not depicted, in the area of the distribution rollers. The distribution rollers are put into motion by the motor 11 and, by rotating, have the effect that the material to be ground is fed to the grinding rollers 10 and 14, being distributed uniformly along their entire lengths, such that it is always present at every point of each of the two rollers 10, 14 in the same quantities (with the exception of the start and stop steps, in which clearly such uniformity is not possible), so as to ensure a grind that is uniform and without differences in granulometry of the flour obtained.

The front roller 10 is placed in rotation by the motor 9. Coolant flows into the cooling jacket of the motor 9 by the inlet 12, circulates inside said cooling jacket, so as to maintain a constant temperature, so as to prevent the motor from possibly seizing up due to excessively heating up. The coolant, in cooling the motor, heats up and leaves by the outlet 13 at a higher temperature and cools back down to then be recirculated at the inlet 12. Such recirculation can take place using (before the coolant is reintroduced via the inlet 12) the heat passed to the coolant in other parts of the plant, for example for space heating of the premises or for heating water for sanitary use for bathrooms present in the plant, making the coolant pass through a heat exchanger, of a type known per se, such as a shell and tube exchanger or a concentric tube exchanger. In any case, the roller milling machine 8 according to the present invention provides for the continuous and constant removal of heat produced by the machine 9 in a very efficient manner, even in very hot places, and this is why the motor 9 can be mounted directly on the roller 10, which was not possible in roller milling machines of the prior art, including the roller milling machine disclosed in W02017/089870, achieving results as promised by that patent, but which it failed to maintaining them.

The roller 10 rotates driven by the motor 9, while the roller 14 rotates, driven by the transmission belts 15, at a similar speed, but in the opposite direction of rotation. Thus, there are two counter-rotating rollers 10, 14 which, by rotating, take in the material to be ground between them, taking it in and crushing it, until it is ground to a size which depends on the distance between the rollers 10, 14. If the flour obtained still has too high a granulometry, provision can be made for a second grinding stage which gives rise to a further grinding, so as to obtain flour of the desired granulometry. The flour thus produced can be collected in a known way and be arranged for sale or for other possible processing stages, possibly including further grinding steps, to be carried out in machines with rollers 10, 14 that are closer together to obtain a finer granulometry, until the two rollers 10, 14 are brought in direct contact with one another.

At the end of the grinding, the motors 9, 11 can be stopped, causing also the rollers 10, 14 and the distribution roller to stop, thus halting the grinding. The presence of an inversion device means that the rollers 10, 14 can temporarily be driven in the opposite direction to the execution direction, thus arriving at cleaning said rollers 10, 14 in a simple and effective manner.

By virtue of the fitting of the motors 9, 11 to the grinding roller 10 and the distribution roller respectively, and the system of transmission belts 15 which drive the second grinding roller 14, the motors driving the machines 8 need not be hung from the ceiling, thus saving the need for a second floor, and also enabling the use of smaller premises or enabling the ceiling to be exploited in a different way. Having eliminated losses through transmission, an energy saving is additionally obtained, which previously could not be hypothesised.

Furthermore, the absence of transmission belts, which hence cannot become loose and slip in the pulleys (as well as reducing maintenance costs), makes the roller milling machines 8 much more reliable than the known roller milling machines 1, since sparks become much rarer and a series of accidents and explosions become more unlikely, with a net increase in work- related safety and without the need for any protective guards which today are present on the roller milling machines 1 according to the prior art. There is also a net reduction in wear of the bushings of the motors 9 and 11. Furthermore, energy losses are lower, and therefore the saving is even higher and, given the large number of machines generally present in a plant and the power levels generally at play, such a saving is significant and much greater than the highest production and installation costs of these machines 8 as compared with the roller milling machines 1 of the prior art.

The liquid cooling, for example with water, has made all this possible, which was impossible with the traditional air cooling of these motors.

The roller milling machine 8 according to the invention can be produced as a completely new machine or as a reworking and adaptation of devices that are already existing and present in the plant, by simply fitting the motor (for example by keying it on) to the head of one of the grinding rollers, presently driven by the system of belts and pulleys. Thus, the present invention is very versatile in how it can be applied, and the renewal of the installed machines in already-existing plants (with greater energy efficiency and considerably fast amortisation) can be deferred in time while the replacement of machines already in use is not required as being essential. This manner of working, possible according to the present invention, is however not possible with the means of the prior art, such as for example the crusher according to CN 108187813 which, on the contrary, cannot be adapted in any way to pre-existing systems.

The motor 9 is dimensioned so as to be able to directly replace the pulley mechanism of pre-existing systems and not interfere with the other components of the roller milling machine; this would not be possible with a motor different from a water-cooled motor 9, since the large sizes involved would prohibit it. A very small number of modifications are to be introduced, such as the construction of a torque arm to enable a floating installation, the interfacing of the control drive with the existing electronics, so as to move the rollers 10, 14 apart in the event of overloading of the motor 9 and the interfacing of temperature sensors with the existing protection management electronics.

It is understood that the invention must not be considered to be limited to the particular arrangement illustrated above, which forms only one examplary embodiment thereof, but that various variants are possible, all within the capabilities of a technician skilled in the art, without thereby departing from the scope of protection of said invention, which scope is defined in the claims that follow.

LIST OF REFERENCE CHARACTERS

1 Roller milling machine (according to the prior art) 2 Milling roller (for 1)

3 Milling roller (for 1)

4 Transmission belt (for 2)

5 Transmission belt (for 3)

6 Motor (for 4) 7 Motor (for 5)

8 Roller milling machine for grinding 9 Motor (of 10)

10 Grinding roller

11 Motor

12 Coolant inlet (for 9) 13 Coolant outlet (of 9)

14 Grinding roller

15 Transmission belt (for 14)