Technical field

The present invention relates to a grinding mill with rollers, in particular for grinding hard materials, such as glass, ceramic materials or the like.

Technological background

The invention can be applied in particular to the technical field of grinding materials generated as manufacturing scraps in tile production processes. However, the invention can be applied to all types of grindable hard materials.

As tile production scraps are now considered as waste, producers need to provide a disposal plan possibly involving reusing them in the production cycle. The use of roller mills makes it possible to grind these manufacturing scraps to a preselected size of the material being output that allows to reuse them in the tile manufacturing processes.

A type of mill widely used in this ceramic field derives from a technical solution adopted in the industry of the so-called glass frits, where ground glass material is used for producing ceramic glazes for tiles.

This solution provides that the mill consists of at least one pair of counter-rotating grinding rollers, typically made of steel, which are rotatably supported on a supporting structure, one of the rollers is driven in rotation by a motor while the other roller is supported as idle and is dragged by friction by the motorised roller. Thanks to this configuration, the grinding action occurs mainly by compression of the material, and partly by friction .

While, on the one hand, this type of grinder proves to be simple and cheap to use, on the other hand, it has some limiting aspects. These include, for example, the fact that the adjustment of the spacing between the rollers is purely mechanical and therefore not particularly smooth and easy to perform.

In addition, the grinding effect can hardly adapt to the different amount or size of the material instantly feeding the rollers.

The stress generated by the rollers is therefore discontinuous, depending on the amount or size of the material passing through them, and the mill may consequently undergo irregular stresses that increase wear thereof. In addition, in case of large, non-grindable foreign materials passing through, the rollers are subjected to considerable impacts, which promote rapid wear thereof .

As a partial solution to the above-mentioned problems, mills have been arranged in the state of the art wherein the rollers are pressed together by hydraulic or pneumatic pistons, whereby it is possible to adjust the pressure. Such a solution also allows the rollers to be moved apart in case of non-grindable pieces or other particularly hard foreign objects passing through them.

Adjusting the pressure of the rollers also makes it possible to control and program the size (particle size) of the ground material (a higher pressure between the rollers corresponds to a finer particle size) being output. These improvements, which originally made the grinding mills used for the production of glass frits more efficient, in the ceramic colouring sector, still leave some problems unsolved when applied to the grinding of pottery shards and scraps. In fact, ceramic tiles (e.g. porcelain stoneware) are mechanically stronger than glass materials and the grinding capacities required to the grinder are typically very high (they can reach several tons per hour). A ceramic grinding mill thereby provides rollers that are longer, even twice as long as the rollers of mills for grinding glass.

A plant for grinding ceramic tiles may for example provide four pairs of rollers, a first pair of shaped rollers being intended for "crushing", while the other three pairs of rollers, in cascade, are intended for "grinding", such a configuration differing from that provided in the field of glass grinding, where the plant typically provides only three pairs of smooth "grinding" rollers.

Other limitations may also arise due to specific problems occurring while grinding tiles. In this respect, in plants producing ceramic tiles, other scrap materials such as wood, plastic or iron are sometimes improperly thrown into the scrap tile pile. In a grinding plant a step of control sieving is generally provided between the exit of a crushing machine and the entrance to the grinding mill. In the crusher, entire shards are crushed into smaller pieces (of the order of a few centimetres), then in the mill the material is reduced to powder (with the required size normally less than a millimetre) . Among the aforementioned materials or foreign bodies, rubber and wood tend to compress but are not ground due to their elastic behaviour, while iron is often so hard that it cannot be crushed by grinding rollers, even if they are made of strong steel.

Typically, despite the precautions taken (including the provision of magnets capable of intercepting and removing ferrous materials directed between the rollers), it is very difficult to prevent a foreign piece, normally rubber, wood or iron, from entering the mill and impacting the rollers. In each pair of opposite rollers, one roller is fixed while the opposite roller is movable and connected to pneumatic or hydraulic pistons, which apply adjustable pressure.

When the rollers are pressed by pneumatic pistons, a certain amount of clearance in the relative displacement between the rollers is possible, also related to the compressibility of the air, which allows foreign parts to pass through. However, if a foreign object falls laterally between the rollers, it causes a tilted displacement of the movable roller with respect to the fixed roller. In other words, the movable roller does not maintain its axis parallel to the axis of the fixed roller while moving away. This leads to misalignment in the transmission of motion between the motor coupling and the shaft of the movable roller and in the rotation of the shaft on the bearing, resulting in excessive impacts, friction and wear, or even breakage.

Description of the invention

A main object of the invention is to make available a grinding mill with rollers of the above-mentioned type, structurally and functionally designed to overcome the limitations highlighted with reference to the above- mentioned prior art.

This and other objects which will clearly appear below are achieved, according to the present invention, by means of a grinding mill with rollers having the characteristics set forth in the appended claims. According to a main aspect of the invention, a grinding mill with rollers comprises at least one pair of rollers likely to be driven in relative counter-rotation about the respective main rotation axes thereof, the material to be ground being supplied by falling between the rollers, the first of said rollers being rotatably supported by a pair of first supports which are fixed to respective abutments of the mill, the second of said rollers being rotatably supported by a pair of second supports, which are mounted on the abutments in a manner slidingly guided in a direction perpendicular to the rotation axes, the mill comprising first pneumatic cylinder/piston means which are operatively associated with the pair of second supports and configured to generate a preselected thrust pressure of one roller against the other, or with an adjustable spacing in order to obtain the desired degree of grinding of the material, and hydraulic cylinder/piston means which are operatively associated with the pair of second supports and which are configured to at least oppose the thrusts which tend to move the rollers away from each other and which are caused by foreign bodies which pass between the rollers during the grinding.

According to another aspect of the invention, the hydraulic cylinder-piston means are configured to keep the corresponding piston in contact with the corresponding second support, without applying any pressure to the second roller, by opposing a resistance if the second roller is moved away from the first roller following the passage of foreign bodies between the rollers during grinding. According to another aspect of the invention, the hydraulic cylinder-piston means are configured to generate a preselected thrust pressure between the rollers, in cooperation with or with deactivation of said pneumatic cylinder-piston means. According to another aspect of the invention, the pneumatic means and the hydraulic cylinder-piston means are configured in such a manner that the resistance applied by hydraulic means is greater than the resistance applied by pneumatic means. According to another aspect of the invention, the respective cylinders of the hydraulic means are connected, with fluid communication, to a respective hydraulic accumulator which acts as a damping means.

According to another aspect of the invention, the respective cylinders of the hydraulic means are connected, with fluid communication, to each other and to a hydraulic accumulator which acts as a damping means.

According to another aspect of the invention the cylinders of the hydraulic means are configured as double-effect cylinders, each cylinder including a lower operating chamber and an opposite upper operating chamber, the cylinders being connected to each other, with fluid communication, in such a manner that the lower chamber of a cylinder which is associated with one of the first supports is connected to the upper chamber of a cylinder associated with the other of the first supports so that the thrust, away from the rollers, generated by an impact at one of the axial ends of the rollers, also tends to urge the rollers, with mutual movement apart, at the other opposite axial end of the rollers, thereby opposing the displacement from the condition of parallelism of the axes of the rollers. According to another aspect of the invention, the hydraulic accumulator is provided with a gas bellows.

According to another aspect of the invention, the mill comprises a plurality of grinding modules, wherein each module is provided with a pair of said rollers, each module being selectively able to be configured in such a manner that the respective hydraulic cylinder/piston means perform only the function of security counter to thrusts which tend to move the rollers apart from each other as a result of the passage of foreign bodies or generate the thrust pressure between the rollers in cooperation with or by excluding the respective pneumatic cylinder/piston means. The hydraulic cylinders can thereby operate by exerting the thrust on the rollers, selectively on the different modules of the mill. This feature proves effective when, for example, higher closing thrust pressures between the rollers must be achieved for finer grinding or higher productivity. In the same mill, modules with rollers pressed by pneumatic pistons where the hydraulic pistons only act as a security device without applying pressure can coexist with modules where the rollers are instead pressed by hydraulic pistons in cooperation with or excluding the pneumatic pistons. According to another aspect of the invention, one or some or all of the modules of the mill may be provided with both pneumatic and hydraulic cylinder-piston means, so that it is possible to choose, depending on the application, whether to press with the pneumatic cylinders while retaining the hydraulic cylinders for security or to press with the hydraulic cylinders while possibly deactivating the pneumatic cylinders. For this purpose, the design of hydraulic cylinder-piston assemblies alternately acting as a security device or exerting their thrust will be appropriate.

According to another aspect of the invention, the hydraulic cylinder-piston means are spaced apart from the corresponding supports and the spacing between the hydraulic cylinder-piston means and the corresponding supports is adjustable. According to another aspect of the invention, the piston of the hydraulic cylinder-piston means is extended externally to the corresponding cylinder in a respective operating rod and said operating rod is integral to the corresponding first support.

According to another aspect of the invention, the cylinders of the hydraulic means are configured as double-effect cylinders, each cylinder including a first operating chamber and an opposite second operating chamber, the cylinders associated with the supports being fluidically connected with a slide valve to selectively connect the first chamber of a cylinder associated with one of the supports with the second chamber of a cylinder associated with the other of the supports. According to another aspect of the invention, the cylinders of the hydraulic means associated with a respective support are connected to a discharge conduit on which an adjustable discharge valve is provided, the opening of which is controlled by the pressure drawn from the corresponding discharge conduit of the cylinder associated with the other respective support.

According to another aspect of the invention, the cylinders of the second pneumatic cylinder-piston means are configured as double-effect cylinders. Brief description of the drawings The characteristics and advantages of the invention will become clearer from the following detailed description of some of its preferred embodiments shown, by way of exemplary non-limiting example, with reference to the accompanying drawings, wherein:

- Figure 1 is a perspective view of an example of a grinding mill with rollers made according to the present invention,

- Figure 2 is a side elevation view of the mill of

Figure 1,

- Figure 3 is an exploded perspective view of some details of the mill of the previous figures,

- Figure 4 is a schematic view of a mill detail according to the invention in an embodiment,

- Figure 5 is a schematic view of the detail of Figure 4 of the mill according to the invention in a further embodiment,

- Figure 6 is a view corresponding to that of Figure 1 of a further example of a mill with rollers according to the invention,

- Figure 7 is a perspective view of a further example of a grinding mill with rollers, including several modules of overlapped pairs of rollers,

- Figures 8A and 8B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention,

Figures 9A and 9B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention,

Figures 10A and 10B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention,

Figures 11A and 11B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention,

Figures 12A and 12B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention,

Figures 13A and 13B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention,

Figures 14A and 14B are partial schematic views respectively in side elevation and in plan view from above of a further embodiment of the mill according to the invention.

Preferred embodiments of the invention

Referring at first to Figures 1 and 2, 1 globally refers to a first embodiment of a grinding mill with rollers according to the present invention, comprising a supporting structure formed by a pair of opposite plates 2 connected to each other by respective abutments, each abutment including a respective pair of beams 3, extended parallel and spaced apart from each other. The mill 1 is designed to grind hard materials including, in particular, ceramic material scraps, derived from tile manufacturing scraps, in order to obtain a powdered material suitable for re-use in the tile manufacturing cycle. The mill 1 comprises a pair of counter-rotating rollers, referred to by 4 and 5, with cylindrical shells and having their respective main rotation axes XI, X2 parallel to each other. Between the rollers 4, 5 an opening 6, of adjustable width, may be defined for the passage of the material to be ground, or the rollers may be pressed into contact with each other.

The rollers 4, 5 are designed as smooth-surface rollers, other conformations being provided depending on application requirements. For instance, an example of a mill with rollers 4, 5 with a shaped surface is shown in Figure 6. The pair of rollers 4, 5 thus configured constitutes a so- called grinding mill "module", and depending on the specific application requirements, several modules can be combined. For example, Figure 7 shows a mill configuration comprising four horizontal roller modules of the aforesaid type, wherein the material to be ground is fed by gravity, by means of a feeder device (not depicted) positioned above the highest vertically positioned module, normally equipped with shaped rollers. Below the upper module, three smooth roller modules are positioned in a vertical cascade, each module carrying a single motorised roller.

Hereinafter, any use of the terms "lower", "upper", "horizontal" and "vertical" will therefore refer to this specific configuration of horizontal rollers, wherein the material to be ground is fed by gravity in a substantially vertical direction, and the above terminology will be understood to be related to this spatial arrangement.

In the mill module 1, between each pair of beams 3, a respective pair of first supports 7 supporting the roller 4 and a respective pair of second supports 8 supporting the roller 5 are mounted in a facing position.

In particular, the roller 4 is otherwise referred to as a "fixed roller", in that it is rotatably supported by the supports 7 integral with the abutments, without any possibility of relative movement with respect to the beams of the abutments, while the roller 5 is otherwise referred to as a "movable roller" in that the supports 8, on which it is rotatably supported, are mounted on the abutments in a sliding manner guided along the corresponding beams 3 in a direction perpendicular to the rotation axes of the rollers.

In greater detail, each support 7 and 8 comprises a respective parallelepiped bearing-holder block. 7a refers to both bearing-holder blocks of supports 7, which are rigidly constrained to the beams 3 of the corresponding abutments.

8a refers to both bearing-holder blocks of the supports 8, on each block 8a a pair of seats 10 being obtained, provided on opposite faces of the block and intended to slidingly couple with the respective beams 3 of the corresponding abutment, so as to create a linear guide to slidingly guide the bearing-holder block 8a along the beams 3 of the corresponding abutment. The roller 4 is arranged to be driven in rotation, about its axis XI, by a motor 11 connected to a rotation shaft (not depicted) of the roller, through a reduction unit 11a. The roller 5 is mounted with its shaft (not depicted) supported as idle between the supports 8 and is dragged in counter-rotation to the roller 4 by the frictional action of the material to be ground passing through the opening of the rollers or by the roller itself if they are pressed together against each other.

In one embodiment, it is provided that both smooth rollers 4, 5 are driven in rotation by respective motors, as is the case with the shaped roller module shown in Figure 6, which is designed to be placed in the highest position of the multi-module mill configuration of Figure 7. This is in order to be able to make greater use of the frictional action and friction in the grinding process, which may be appropriate for certain types of material. In Figures 6 and 7, details similar to those of the mill module in Figure 1 are marked with the same numerical references.

The mill module 1 is provided with pneumatic cylinder- piston means, globally referred to by 15, which are operatively associated with the pair of supports 8, to generate a preselected thrust pressure of the movable roller 5 against the fixed roller 4, in order to obtain the desired degree of grinding of the material. A predetermined thrust pressure between the rollers 4, 5 corresponds to a corresponding size of the material ground by the mill. Pneumatic cylinder-piston means can be configured to urge the rollers against each other or at an adjustable spacing by means of appropriate end stops. In greater detail, the pneumatic means comprise a pair of cylinder-piston assemblies, each assembly comprising a piston 16 mounted and guided within a respective cylinder 18.

Due to their structural identity, only one of the pneumatic cylinder-piston assemblies will be described in detail.

The piston 16 is extended, outside the cylinder 18, into an operating rod 19, the free end of which is connected, by means of a hinged coupling, to a pusher member 20.

21 refers to a crosspiece, conveniently made from a "C"- section profile, which is extended transversely between the mill abutments. The pusher members 20 are positioned and constrained in the intrados part of the crosspiece 21.

Each cylinder-piston assembly 18, 16 is also positioned at the respective bearing-holder block 8a, in such a manner that the crosspiece 21 is arranged for surface contact against the bearing-holder blocks 8a of the pair of supports 8. In such a configuration, the pneumatic cylinder-piston units 18, 16 can be activated to press, through the pistons 16, the crosspiece 21 against the blocks 8a and consequently generate a preselected thrust pressure of the roller 5 against the roller 4, in order to obtain the desired grinding degree.

In this respect, it is noted that the thrust direction of the pneumatic cylinder-piston assemblies 18, 16 coincides with the linear sliding direction of the bearing-holder blocks 8a in relation to the mill abutments.

The cylinder-piston assemblies 16,18 are conveniently configured as double-effect cylinders and by adjusting the thrust pressure, obtained by feeding compressed air, via a pneumatic circuit, into the operating thrust chambers of the cylinders 18, the particle size of the ground material is adjusted accordingly. The chamber opposite to the thrust is instead activated if the rollers are to be moved apart, obviously not under normal working conditions. In a preferred embodiment, the chambers of the pneumatic cylinders 18 are connected to each other, with fluid communication, and to a source of compressed air for operative control of the pistons. With such a fluidic connection, the synchronous movement of the pistons is also ensured.

In an alternative embodiment, it may be provided that the operating chambers of the pneumatic cylinders 18 are fed, independently, the air supply being controlled and regulated by means of a control unit (not depicted), suitable for ensuring the movement of the pistons 16 as well as for generating the desired thrust pressure.

As shown in the figures, the pneumatic cylinder-piston assemblies 18, 16 are preferably arranged externally to the corresponding plate 2 of the supporting structure, said plate being provided with through openings 22 through which the respective rod 19 of the cylinder-piston assembly 18, 16 can extend in the direction of the corresponding bearing-holder block 8a.

The mill module 1 further comprises hydraulic cylinder- piston means, globally referred to by 25, which are operatively associated with the pair of supports 8, mainly to counteract the thrusts tending to move the rollers 4, 5 apart from each other and caused by foreign bodies or pieces (non-compressible or non-grindable) passing between the rollers during the grinding.

In greater detail, the hydraulic means 25 comprise two pairs of hydraulic cylinder-piston assemblies, each assembly comprising a piston 26 guided within a respective cylinder 28. Each piston 26 is extended externally to the corresponding cylinder 28 in a respective operating rod 29.

In the example described, it is provided that on each support 8 a corresponding pair of hydraulic cylinder-piston assemblies 28, 26 is operatively associated, the operation of which will be described in detail below.

With reference to the embodiment described herein, at each abutment of the mill, the two hydraulic cylinder-piston assemblies 26, 28 are positioned at vertically opposite parts with respect to the crosspiece 21, with each cylinder 28 in abutment and constrained to the plate 2 and with the corresponding piston 26 bearing the respective operating rod 29 facing the bearing-holder block 8a.

The cylinder-piston assemblies 28,26 are configured, primarily, to maintain the corresponding piston 26 in substantial contact with the corresponding bearing-holder block 8a of the support 8, without however exerting any active pressure on the block and consequently on the roller 5, opposing a resistance if the roller 5 is moved away from the roller 4 following the passage of foreign bodies or pieces (incompressible or non-grindable) between the rollers during the grinding.

It is also provided that pneumatic means 15 and hydraulic means 25 are configured in such a manner that the resistance opposed by hydraulic means 25 is greater than the resistance opposed by pneumatic means 15.

In one embodiment it is provided that the cylinders 28 of the hydraulic means are connected, with fluid communication, to a respective hydraulic accumulator 30 bearing a gas bellows 31 (schematically depicted in the figures) having a damping function of the gas bellows type. As an alternative to the gas bellows, other types of damping systems are anyhow possible.

In the figures, the conduits of the hydraulic circuit, which connect the operating chambers of the hydraulic cylinders with a manifold 33 which is in turn fluidically connected to the accumulator 30, are referred to by 32. The hydraulic circuit is configured to convey the hydraulic fluid, e.g. pressurised hydraulic oil, along the conduits 32 from and to the operating chambers of the hydraulic cylinders.

In the example described, the configuration depicted has two hydraulic cylinders for each side of the mill, consequently there are four hydraulic cylinders for each mill module, however it is possible to have one cylinder for each side (so two hydraulic cylinders for each module) or a different configuration.

On the movable roller 5, at the bearing-holder blocks 8a, the pneumatic pistons 16 which exert the adjustable thrust between the rollers are active, as well as the hydraulic pistons 26 which do not exert any active thrust against the roller 5 during normal operation, but as soon as the roller 5 moves away from the roller 4 and the block 8a comes into contact and presses the corresponding hydraulic piston 26, the latter opposes a resistance. Such a resistance, which has an elastic behaviour due to the action of the hydraulic accumulator, is greater than the resistance that the pneumatic piston can oppose. Thereby, the displacement, both on-axis and off-axis, of the roller 5 is limited and slowed down, thereby reducing or avoiding undesirable stresses on the roller shafts, bearings and motor transmission couplings.

In one embodiment, the respective hydraulic cylinders 28 connected, with fluid communication, to each other and to the hydraulic accumulator 30 having a damping function. Alternatively, the hydraulic cylinders 28 may be configured without any fluidic connection between them, thus acting independently, and each being connected to a respective accumulator, the accumulators possibly also having different charges. In one embodiment, the hydraulic cylinders 28 are configured as double-effect cylinders, each cylinder 28 including a lower chamber 28a and an opposite upper chamber 28b, the cylinders being connected to each other, in fluidic connection, such that the lower chamber 28a of a cylinder 28 associated with one of the supports 8a is connected to the upper chamber 28b of a cylinder 28 associated with the other of the supports 8a. Thereby, the thrust, away from the rollers, generated by an impact at one of the axial ends of the rollers, also tends to urge the rollers, with mutual movement apart, at the other opposite axial end, thus opposing the displacement from the condition of parallelism of the axes of the rollers.

In other words, by means of the crossed fluidic connection described above (schematised in Figure 5), the thrust generated by an impact occurring at one of the axial ends of the rollers, causes a thrust away from the rollers at the opposite end of the rollers, with the advantage of maintaining a greater parallelism between the rollers, opposing the relative displacement. It must be noted that, for particular application requirements, in other embodiments it may be provided that the pressure generating the thrust of one roller against the other, suitable for regulating the grinding effect, is carried out by means of the same hydraulic cylinder-piston assemblies and this function operatively alternates with the function of damping the stresses generated by the impacts caused during the grinding by foreign bodies passing through.

In this operating mode it may also be provided that the thrust function of one roller against the other is carried out exclusively by the hydraulic cylinder-piston assemblies (excluding the pneumatic cylinder-piston units) or in cooperation with the pneumatic cylinder-piston assemblies. In a multi-module mill configuration, such as the type shown in Figure 7, it may be provided that the hydraulic cylinders can operate by exerting a thrust on the rollers, selectively on the different modules of the mill. This occurs, for example, when higher closing pressures between the rollers are required for finer grinding or higher productivity. Thus, in the same multi-module mill there may be modules with rollers pressed by pneumatic cylinders where the hydraulic cylinders are only active with a damping security function and modules where the rollers are pressed by hydraulic cylinders in cooperation with the pneumatic cylinders or excluding the pneumatic cylinders.

In a multi-module mill embodiment, it may be provided that one or some or all of the mill modules may be provided with both pneumatic and hydraulic cylinders, with the operational possibility of selecting, depending on the application, whether to exert thrust with the pneumatic cylinders, keeping the hydraulic cylinders in the security damping function, or exert thrust with the hydraulic cylinders, possibly deactivating the pneumatic cylinders. In this case, the design of the hydraulic cylinders, which can alternately act as a security device or exert a thrust, must be appropriate.

It should also be noted that the arrangement, according to the invention, of a mill module as an individual unit, facilitates the assembly and dismantling of a mill with several overlapped modules, facilitating both initial assembly operations and subsequent maintenance operations on the mill. Acting on each individual module to dismantle or assemble the rollers or their components, once the module is isolated from the rest of the mill, is in fact simpler than in the known solutions. Figures 8A and 8B show, in a partial and schematic manner, a further embodiment of the mill according to the invention, wherein details similar to those of the previous examples are marked with the same numerical references. This example differs primarily in that for each cylinder- piston assembly 28, 26 of the hydraulic type, such as of oleodynamic type, the corresponding piston 26 is arranged at a predetermined spacing D (D >= 0) from the corresponding bearing-holder support 8 of the movable roller 5, said spacing D being also adjustable. In other words, the spacing D may be set in an adjustable manner, based on the specific functional requirements of the mill, so that the resistance opposed by the hydraulic cylinder- piston assemblies 28, 26 only intervenes after the roller 5 has moved across the spacing D, when the support 8 comes into contact and presses against the rod of the corresponding piston 26.

It must be noted that, as an alternative to or in combination with the spacing adjustment system D, it is possible to intervene by adjusting the charge of the accumulator 30 with a gas bellows, so as to adjust the intervention threshold of the hydraulic cylinder-piston assembly.

Figures 9A and 9B depict, in a partial and schematic manner, a further embodiment of the mill according to the invention, wherein details similar to those of the previous examples are marked with the same numerical references.

In this example, in order to counteract the displacement from the condition of parallelism of the axes of the rollers 4, 5 (due to the thrust, which tends to move the rollers away from each other, generated, for example, by an impact at one of the axial ends of the rollers), the cylinders of the hydraulic cylinder-piston assemblies 28, 26 are configured as double-effect cylinders and each piston is integral, with its own rod 29, to the corresponding support 8 of the movable roller. For this purpose the free end of the rod 29 is rigidly connected to the corresponding bearing-holder block 8a of the support. Referring to each cylinder 28, wherein the piston 26 divides the two operating chambers 28a, 28b, for the sole purpose of easing the identification of the chambers in the following description, the chamber 28b, wherein the rod 29 is slidingly associated, is also referred to as the "minor chamber" and the opposite chamber 28a of the cylinder is also referred to as the "major chamber".

It is provided that the major chamber and the minor chamber of each cylinder-piston assembly 28, 26 are connected, through respective conduits 32, with a pressurisation pump (not depicted), housed in a control unit 41, and it is also provided that each conduit 32 is fluidically connected with a corresponding hydraulic accumulator 30 with a gas bellows.

It is further provided that the major chamber of a cylinder 28 associated with one of the movable roller supports 8 is fluidically connected, via a conduit 32a, with the minor chamber of a cylinder 28 associated with the other opposite support of the movable roller. The diagram of these additional cross-connections may for example correspond to the one shown in Figure 5. This cross-connection diagram is configured to ease the realignment of the rollers when the movable roller 5 is moved away from the fixed roller 4, following the passage of foreign bodies between the rollers generating impacts that tend to displace the axis of the movable roller from the condition of parallelism with the axis of the fixed roller.

Referring to Figure 9B, in case, for example, a thrust is exerted by one of the supports of the movable roller, referred to by 8', in the major chamber 28a of a cylinder associated thereto, an over-pressure is generated by the thrust. This over-pressure, brought, through the fluidic connection, to the minor chamber 28b of the cylinder associated with the other support, referred to by 8", tends to move the piston and with it the rod 29 in a condition of support pull, with a consequent effect of realigning the movable roller to the fixed roller, towards a condition of parallelism between the axes of the fixed and movable rollers.

In an opposite condition, wherein the thrust away of the movable roller is undergone by the support 8", the displacement transmitted to the rod 29 of the piston constrained thereto, causes an expansion of the corresponding minor chamber 28b, and through the fluidic connection with the major chamber 28a of the cylinder- piston assembly associated with the other support 8', fluid is drawn outside said major chamber, with a consequent displacement of the support 8' towards the realignment of the movable roller with the fixed roller, in the condition of parallelism of the axes.

The effect of realigning the movable roller towards the condition of parallelism with the fixed roller can also be obtained in a further embodiment of the mill, schematically shown in Figures 10A and 10B, wherein details similar to those of the previous examples are marked by the same numerical references. In this example, it is provided that the major and minor chambers of a cylinder 28 associated with a support 8 are selectively put in fluidic connection with the minor and major chambers respectively of the cylinder 28 associated with the other support 8, by means of the action of a three-position hydraulic slide valve 42. The displacement between the positions of the valve is controlled by the over-pressure generated in the major chamber of the cylinder-piston assembly 28, 26 pressed by the opening movement of the movable roller (a movement which is related to the thrust generated by the passage of non-grindable or non-compressible foreign bodies between the rollers during the grinding). In Figures 10A and 10B, the pilot conduits, referred to by 43, which activate the movement of the slide valve are shown with a dotted line. It must be noted that in this example as well, the rods 29 of the pistons 26 are integral with the supports of the movable roller which, for their identification in the figures, are marked by 8' and 8".

In operation, if the support 8' is subjected to a thrust with a movement (directed to the left looking at Figure 10B) related to the opening of the movable roller (which due to an impact tends to move away from the fixed roller), such a thrust, pressing on the rods of the corresponding cylinders, tends to create an over-pressure in the major chamber of the corresponding cylinder. This over-pressure is used to control the slide valve 42 (which is moved to the right looking at Figure 10B) in the operative position wherein the aforementioned major chamber is fluidically connected to the minor chamber of the cylinder associated with the other support 8". This over-pressure then acts on the piston of the cylinder which, moving (to the left looking at Figure 10B) pulls the support 8", thus favouring the realignment of the rollers.

A similar operation is obtained if it is the support 8" that moves due to an opening of the movable roller, following an impact, also in this case the slide valve 42 being controlled to put in communication opposite chambers of the cylinder-piston assemblies, favouring the condition of realignment of the rollers. It must be noted that, under normal operating conditions, the fixed and movable rollers may be allowed to be misaligned to a certain extent, the realignment system described above being configured to intervene when preselected threshold values are exceeded. Such an adjustment of the realignment system may be obtained by suitably setting the accumulators 30 and in the slide valve 42 by setting the pilot pressure activating the slide valve.

Figure 10A, relative to a side view of the mill, shows the fluidic connections between the chambers of the pair of cylinder-piston assemblies 28, 26 associated with each of the supports 8' and 8", and between said chambers and the slide valve 42.

Figures 11A and 11B depict, in a partial and schematic manner, a further embodiment of the mill according to the invention, wherein details similar to those of the previous examples are marked with the same numerical references.

In this example, it is provided that the roller realignment system is configured in detail as described below. Each major chamber 28a of the cylinder-piston assemblies associated with a corresponding support 8 is connected with a conduit 32 which in turn branches into a pair of conduits 45, 46, the conduit 45 being configured as a loading conduit through the connection with a pressurisation pump 40, the conduit 46 being configured as a discharge conduit through connection with a respective adjustable valve 47. The valve 47 may be adjusted so as to discharge a selected pressure value (pilot pressure). It may further be provided that, once the valve 47 is opened, the discharge may take place at a second pressure value, other than zero and lower than the first value.

Each support 8 is therefore associated with a loading circuit (by means of pump 40) and a discharge circuit (by means of valve 47), and it is provided that, as pilot pressure of the valve 47 inserted in the circuit associated with one of the supports, it is used the over-pressure generated in the circuit of the other support when the movable roller is moved (away from the fixed roller) following a thrust due to the passage of foreign bodies between the rollers. In other words, this over-pressure is brought into the circuit associated with the other support (through the pilot conduit 43), to open the valve 47 to discharge the chamber 28a of the corresponding cylinder 26, thus allowing the respective support to move, favouring the realignment of the rollers towards the condition of parallelism of the axes.

It must be noted that, under normal mill working conditions, the fixed and movable rollers may be allowed to misalign to a certain extent, the realignment system described above being configured to act when certain threshold values are exceeded. Such an adjustment of the realignment system may be obtained by suitably setting the valves 47, whereby the value of the pressure which makes the roller realignment system act, can be chosen. It must be noted that, as an alternative to or in combination with the realignment system described above, it is possible to act by adjusting the charge of the hydraulic accumulators 30 with a gas bellows, which are in any case provided (but not shown in the figures). Maximum pressure valves (also not shown) may also be provided.

The following embodiments, referring to Figures 12A to 14B, relate to variants of the pneumatic cylinder-piston (18, 16) means (15) applicable to the grinding mill of the invention. Figures 12A and 12B show, in a partial and schematic manner, a further embodiment of the mill according to the invention, wherein details similar to those of the previous examples are marked with the same numerical references.

In this example, in order to oppose the displacement from the condition of parallelism of the axes of the rollers 4, 5 (due to the thrust, which tends to move the rollers away from each other, generated, for example, by an impact at one of the axial ends of the rollers), the cylinders of the pneumatic cylinder-piston 18, 16 assemblies are configured as double-effect cylinders and each piston is integral, with its rod 19 and the pusher member 20, to the corresponding support 8 of the movable roller.

Referring to each cylinder 18, wherein the piston 16 divides the two operating chambers, referred to by 18a, 18b, for the sole purpose of easing the identification of the chambers in the following description, the chamber 18b, wherein the rod 19 is slidingly associated, is also referred to as the "minor chamber" and the opposite chamber 18a of the cylinder is also referred to as the "major chamber".

It is provided that the chambers 18a of the pair of cylinders 18 are connected, through respective conduits 32', to a pressurisation pump 40'. It is further provided that the major chamber 18a of a cylinder 18 associated with one of the movable roller supports 8, is fluidically connected (through a conduit 32a') with the minor chamber 18b of a cylinder 18 associated with the other opposite movable roller support. This cross-connection diagram is at all similar to the one provided in the example of Figures 9A and 9B (referred to the hydraulic cylinder-piston assemblies) and is configured to favour the realignment of the rollers in the event that the movable roller 5 is moved away from the fixed roller 4, following the passage of foreign bodies between the rollers generating impacts that tend to move the axis of the movable roller from the condition of parallelism with the axis of the fixed roller. For the operative steps of the realignment system, please refer to the example of Figures 9A and 9B.

It must be noted that, in this example, it is not provided to associate any gas accumulator with the cylinder-piston 18, 16, pneumatic means 15, as it is sufficient to exploit the compressibility of the air present in the pneumatic circuit of the cylinders 18, for damping function purposes. The effect of realigning the movable roller towards the condition of parallelism with the fixed roller can also be obtained in a further embodiment of the mill, schematically shown in Figures 13A and 13B, wherein details similar to those of the previous examples are marked by the same numerical references. This example has the same functional principles as the example of Figures 10A and 10B, the difference being that in this case the roller realignment system is implemented in the pneumatic cylinder-piston means 15 rather than in the hydraulic means. In this example, it is provided that the major and minor chambers of a cylinder 18 associated with a support 8 are selectively put in fluidic connection with the minor and major chambers respectively of the cylinder 18 associated with the other support 8, by means of the action of a three-position hydraulic slide valve 42. The displacement between the positions of the valve is controlled by the over-pressure generated in the major chamber of the cylinder-piston assembly 18, 16 pressed by the opening movement of the movable roller (a movement which is related to the thrust generated by the passage of non-grindable or non-compressible foreign bodies between the rollers during the grinding). In Figures 13A and 13B, the pilot conduits, referred to by 43', which activate the movement of the slide valve are shown with a dotted line. It must be noted that in this example as well, the rods 19 of the pistons 16 are integral with the supports of the movable roller which, for their identification in the figures, are marked by 8' and 8".

The operative steps of the realignment system are at all similar to those already described above and referred to Figures 10A and 10B, and reference is therefore made to the description already provided in this respect.

Figures 14A and 14B depict, in a partial and schematic manner, a further embodiment of the mill according to the invention, wherein details similar to those of the previous examples are marked with the same numerical references.

This example has the same functional principles as the example of Figures 11A and 11B, the difference being that in this case the roller realignment system is implemented in the pneumatic cylinder-piston means 15 rather than in the hydraulic means.

Each major chamber 18a of the cylinder-piston assemblies associated with a corresponding support 8 is connected with a conduit 32 which in turn branches into a pair of conduits 45', 46', the conduit 45' being configured as a loading conduit through the connection with a pressurisation pump 40', the conduit 46' being configured as a discharge conduit through the connection with a respective adjustable valve 47'. The valve 41 may be adjusted so as to discharge a selected pressure value (pilot pressure). It may further be provided that, once the valve 41 is opened, the discharge may take place at a second pressure value, other than zero and lower than the first value. Each support 8 is therefore associated with a loading circuit (by means of the pump 40') and a discharge circuit (by means of the valve 47'), and it is provided that, as pilot pressure of the valve 47' inserted in the circuit associated with one of the supports, it is used the over- pressure generated in the circuit of the other support when the movable roller is moved (apart from the fixed roller) following a thrust due to the passage of foreign bodies between the rollers. In other words, this over-pressure is brought into the circuit associated with the other support to open the valve 47' so as to discharge the chamber 18a of the corresponding cylinder 16, thus allowing the respective support to move, favouring the realignment of the rollers towards the condition of parallelism of the axes.

It must be noted that the roller realignment system applied to the pneumatic cylinder-piston assemblies may advantageously be combined with a hydraulic damping system selected from those described above, so that in case of misalignments beyond a certain extent, the hydraulic means system can still act, with a greater effectiveness due to the resistance values it can assume in contrast to the thrusts that tend to move the rollers apart from each other in a misaligned manner.

The invention reaches the proposed objects by achieving the advantages set forth above if compared to known solutions. A further advantage derives from the fact that, according to the invention, it is equally possible to choose whether it is more appropriate for each mill module to provide a thrust pressure between the rollers of the pneumatic or hydraulic type, depending on the characteristics of the material to be ground, the grain size or the required productivity .