A ROLLER MILL FOR GRINDING GRANULAR MATERIALS, PARTICULARLY CEREALS

Abstract: A roller mill for grinding granular materials, particularly cereals, is described and comprises at least one pair of contrarotating rollers (2) between which a gap (3) is defined for the passage of the material to be ground, and a screening device (10) associated with the rollers (2) for separating the products of the grinding according to the dimensions of the ground material. The screening device (10) comprises a screening surface (14a) positioned lower down to the rollers in such a position to be directly supplied by gravity, by falling of the material ground by means of the rollers (2).

Description: A roller mill for grinding granular materials, particularly cereals Technical Field The present invention relates to a roller mill for grinding granular materials, particularly cereals, according to the preamble to main Claim 1. Background Art Within the field of milling technology, towards which the present invention is particularly but not exclusively directed, there are known mills which have one or more pairs of contrarotating rollers spaced apart by a predetermined distance such that a gap is defined between their respective cylindrical surfaces for the passage of the material to be groun . In these mills, there is generally provision for several successive stages of grinding of the cereal until flours ground to the desired extent are produced. In this case, between one grinding stage and the next, there is a stage in which the products of the grinding are classified to separate the finer material from the coarser material in a manner such that the products thus separated are sent to subsequent grinding stages provided according to the dimensions of the ground material . From the European patent application No. 949003 it is known a mill for grinding cereals, comprising, in succession, two separate milling passages with respective contrarotating rollers and a sifting device interposed between the passages . The sifting device comprises a rotating member which affects the product that leaves the first milling passage so as to propel it against a screening surface in order to separate a significant amount of product before the second milling passage. In the roller mill disclosed in this document it is further provided that the product propelled through the screening surface and the product which leaves the second milling passage are successively combined and sent to a separation and classification unit, for example to a plansifter. In regard to this last feature, the known mills have conveyor devices for transporting the material ground by the rollers into special screening devices. For example, it is known to provide for the products of the grinding to be transported and lifted to the inputs of separators having one or more screens with meshes of different sizes disposed one above another so that, as the product poured in from the top falls down, it is separated into grades having homogeneous dimensions . An arrangement of this type, which requires the provision of conveyors and lifting devices between the rollers and the separator for each grinding stage, is fairly onerous and also leads to a degree of structural complexity. Moreover, since the conveyors permit a localized and concentrated discharge of the material onto the screens of the separator, a constant and uniform distribution of the material on the screen cannot be ensured, necessitating a larger screening surface to avoid the risk of excessive supply and interruptions in the supply of the material and a consequent reduction in efficiency and output yield. Disclosure of the Invention The technical problem upon which the present invention is based is that of providing a roller mill for grinding granular materials, particularly cereals, which is designed structurally and functionally to overcome the disadvantages complained of with reference to the prior art mentioned. This problem is solved by the invention by means of a roller mill formed in accordance with the appended claims, Brief Description of Drawings The characteristics and the advantages of the invention will become clearer from the detailed description of an embodiment thereof, given with reference to the appended drawings, provided by way of non-limiting example, in which: - Figure 1 is a partially-sectioned perspective view of a roller mill according to the invention, - Figure 2 is a partially sectioned side elevational view of the mill of Figure 1, -Figure 3 is a perspective view corresponding to Figure 1. Best Mode of Carrying out the Invention With reference to Figure 1, a roller mill for grinding cereals, such as corn, wheat and the like, formed in accordance with the present invention, is generally indicated 1. The mill 1 comprises one (or more) pairs of contrarotating rollers 2 between which a gap 3 is defined for the passage of the material to be ground, and a feed device, generally indicated 4, positioned above the rollers 2 and including a vibrating hopper 5 for holding the material to be ground as well as supplying it and directing it into the gap 3 by means of deflector elements 6. The rollers 2 are supported rotatably on a framework 7 of the mill and are located inside a body 8 which, below the rollers, has walls 8a inclined so as to converge at an outlet 8b aligned vertically with the gap 3. Drawer-like bodies, indicated 9, positioned between the rollers 2 and the outlet 8b, are mounted removably on the body 8 and serve for collecting samples of the ground material output by the rollers. The mill 1 also comprises a screening device, generally indicated 10, mounted beneath the rollers 2 by means of a framework 11. Defined in the device 10 are a first chamber 12 in communication with the outlet 8b and a second chamber 13 separated from and in communication with the chamber 12 by means of a perforated screening surface 14a of a screen 14. The screen 14 comprises a substantially semicylindrical frame 14b extending parallel to the longitudinal axes of the rollers and having a length substantially corresponding to the axial length of the rollers . This represents a preferred selection, although the screen may have an orientation and an axial dimension different from those of the rollers . The frame 14b is fixed to the framework 11 removably and a net or a cloth with interwoven threads, constituting the perforated screening surface 14a of the screen, is stretched over it . In the first chamber 12 there are also stirring means comprising a rotor 15 with radial blades 16 and with an axis of rotation preferably parallel to the axes of rotation of the rollers 2 and spaced from a vertical plane tangential to the rollers in the region of the gap 3. Each blade 16 comprises a plurality of appendages 16a projecting radially from the rotor 15 in a rake-like configuration. The positioning of the rotor 15 inside the chamber 12 is selected in a manner such that the free ends of the blades pass close to the perforated surface of the screen 14 on their circular path. Brushes 17 are also provided at the free ends of the blades 16 to constitute means for cleaning the surface of the screen. On the opposite side to the screen 14, the chamber 12 has a polygonal-profiled configuration defined by a pair of inclined deflectors 18, 19 the second of which also constitutes means for directing the flow of ground material supplied to the chamber 12 through the outlet 8b. Concerning this, it should be noted that, by means of the deflector 19, the ground material is directed to fall by gravity on the screening surface 14a with a path substantially directed tangentially to the surface (Figure 2) . The chamber 12 is also in communication with an end of a duct 20, through an opening 21 from which the material rejected by the screen 14 is discharged, as will be explained further in the following description. The opposite end of the duct 20 is connected to a conveyor means 22, for example of the vertical screw type, provided for lifting the ground material rejected by the screen up to the hopper 5. The second chamber 13 comprises side walls 13a which are inclined so as to converge at an output opening 23 beneath which a horizontal conveyor 24, for example of the screw type, is disposed. The conveyor 24 is provided for transporting the ground material into a pneumatic conveyor 25 which in turn is intended to transport the material to subsequent processing stages in accordance with the preselected grinding pattern. In addition to the functions described above, the rotor 15 with radial blades serves, as a result of its rotation, to give rise to an intake of air through one or more intakes positioned in the upper portion of the body 8, which are for example formed by a perforated portions 8c of the body. The air drawn in is discharged through one or more outlets positioned at the side walls 13a of the chamber 13, labeled by the reference 13b, and at the output of the conveyor 24 in the region of the intake of the pneumatic conveyor 25. By virtue of the intake of air discharged in the region of the output of the conveyor 24 and of the side walls of the chamber 13, a circulation of air, the function of which will become clearer from the following description, is also induced and drawn through the rollers 2 as well as through the first and second chambers 12, 13. This air circulation takes place through the above-mentioned air-intakes. In Figure 3 , the flow direction of the forced circulation of air is schematically indicated by arrows labelled A. In operation, the material ground by the rollers 2 falls into the chamber 12 of the screening device by gravity and is separated by means of the screen 14. The separated material falls into the chamber 13 where it passes through the outlet 23 and is collected by the conveyor 24 and transported to the intake of the pneumatic conveyor 25 which transports the material to subsequent processes, whilst the material rejected by the screen 14 is moved and transported into the duct 20 by the bladed rotor 15 in order to be lifted up to the hopper 5 by the vertical conveyor 22 and to be ground further by another pair of rollers of a subsequent passage. It should be noted that the transportation of the rejected material into the duct 20 is facilitated by the deflectors 18, 19 provided in the upper portion of the chamber 12. During the rotation of the rotor 15, the brushes 17 provided at the ends of the blades 16 keep the perforated surface 14a of the screen clean so as to facilitate the separation of the ground material which falls into the chamber 12 continuously by gravity. Moreover, the rotation of the rotor is such as also to create swirling air movements inside the chamber 12 which, by drawing air from the upper portion of the body 8, induce a circulation of air through the rollers, in the body, as well as through the chambers of the separator. This circulation of air, to which any contribution provided by the suction means (not shown) associated with the pneumatic conveyor is added, is such as to bring about cooling of the rollers as well of the ground material . The invention thus solves the problem posed, achieving many advantages in comparison with known arrangements . A first advantage lies in the fact that, since the ground material is supplied directly onto the screening device of the mill according to the invention by falling by gravity, no conveyor and/or lifting means are required for supplying this device, with the consequence of structural simplifications as well as greater efficiency of the system by virtue of the related saving in energy and power. A second advantage is due to the fact that the material ground by the rollers falls on the screening surface of the screen substantially in the form of a continuous "film" which is uniform over the entire axial length of the rollers so as to tangentially cover (Figure 2) the screening surface of the screen with a uniform and even distribution, without excessive supply or interruptions, thus achieving an improved output yield of the material and requiring less maintenance . Another advantage consists of the fact that the circulation of air induced by the rotation of the screening device of the invention helps to keep continuously cooled the rollers and the cereal itself which tend to be heated during the grinding operations, so that the chemico-physical characteristics of the cereal are kept intact and an improved overall efficiency of the mill is achieved. Moreover, the air circulation permits a greater homogenization of the product during the grinding operations . Also another advantage is that the mill according to the invention allows a complete classification of the ground product without requiring any further classification unit (plansifter) or sifting machines, downstream to the mill. The installation plant costs are also reduced because the mill according to the invention involves overall spaces more limited than the known solutions in which the presence of plansifters or similar devices requires vertical extensions also of three or four times larger.

Claims: Claims 1. A roller mill for grinding granular materials, particularly cereals, comprising: - at least one pair of contrarotating rollers (2) between which a gap (3) is defined for the passage of the material to be ground, and - a screening device (10) associated with the rollers (2) for separating the products of the grinding according to the dimensions of the ground material, characterized in that the screening device (10) comprises a screening surface (14a) positioned lower down to the rollers (2) in such a position to be directly supplied by gravity, by falling of the material ground by means of the rollers (2) . 2. A mill according to Claim 1, comprising conveyor means (19) interposed between the rollers (2) and the screening surface (14a) to direct the material supplied by gravity, by falling from the rollers, along a falling path on the screening surface (14a) which is substantially directed tangentially to said surface (14a) . 3. A mill according to Claim 1 or Claim 2 , in which the screening device (10) comprises a first chamber (12) supplied with the falling material ground by the rollers (2) , a second chamber (13) separated from and in communication with the first chamber (12) by means of said screening surface (14a) , the second chamber (13) being intended to collect the material screened by means of said surface (14a) . 4. A mill according to Claim 3 , in which stirring means (15,16) are provided in the first chamber (12) for stirring and transporting the rejected material from the screening surface (14a) towards an outlet (21) from the first chamber (12) . 5. A mill according to Claim 4, in which first conveyor means (22) are provided for lifting up the ground material rejected by the screening surface (14a) and discharged through said outlet (21) , to a supply hopper (5) of the rollers (2) to be ground further by the rollers. 6. A mill according to Claim 4, in which the stirring means comprise a bladed rotor (15) and the screening surface (14a) extends at least partially along a portion of the path described by the rotation of the blades (16) . 7. A mill according to Claim 6, in which the rotor (15) has an axis of rotation substantially parallel to the axis of rotation of the rollers (2) . 8. A mill according to one or more of Claims 2 to 5, in which second conveyor means (24, 25) are associated with an outlet (23) of the second chamber (13) for the transportation of the material separated by the screening surface (14a) . 9. A mill according to Claim 8 , in which the conveyor means are pneumatic or mechanical. 10. A mill according to Claim 8, in which air-intake means are associated with said second conveyor means (24, 25) . 11. A mill according to Claim 10, in which said air- intake means comprise one or more intakes (8c) provided upstream to the rollers, the rotation speed of the rotor (15) being selected so as to induce and draw a forced air circulation through the rollers (2) . 12. A mill according to one or more of the preceding Claims, in which the screening surface (14a) is fixed in the screening device (10) removably.

Inventors: BARBIERI SILVANO, BARBIERI, SILVANO
Applicants: AGREX SPA, BARBIERI SILVANO, AGREX S.P.A., BARBIERI, SILVANO
Application year: 2000
Main classification: B02C4
IPC codes: B02C4, B02C23