WO2008122860A1

WO2008122860A1 - A method for temporarily storing powder mixtures and storage silos for actuating the method

Info

Publication number: WO2008122860A1
Application number: PCT/IB2008/000795
Authority: WO
Inventors: Vainer Marchesini; Massimo Passerini; Lamberto Vincenzi
Original assignee: Wam S.P.A.
Priority date: 2007-04-06
Filing date: 2008-03-12
Publication date: 2008-10-16
Also published as: CN101678292A; ITMO20070129A1; CN101678292B

Abstract

A method for temporarily storing powder mixtures and a storage silo for actuating the method, the method comprising stages of: introducing a powder mixture internally of a storage silo (1) and extracting the powder mixture from a discharge mouth (3) located on a bottom of the silo (1), and an intermediate stage of moving the powder mixture internally of the storage silo (1). The stage of moving, which has the aim of preventing selective depositing of powders having different granulometries belonging to the mixture, comprises a main stage of raising at least a part of the powder mixture from the bottom and towards a top of the storage silo (1), which main stage is performed using a vertical screw (2).

Description

A Method for Temporarily Storing Powder Mixtures and Storage Silos for Actuating the Method.

Technical Field

The invention relates to a method for temporarily storing powder mixtures and a storage silo for actuating the method.

In particular, the invention relates to storage of pre-mixed materials for building, for example mortar and cement mixes. Background Art

Prepared materials of this type are usually stored internally of storage silos, generally of considerable size. These storage silos comprise a lower hopper, usually truncoconical, on a bottom of which a discharge mouth opens for extraction of the stored material. A disadvantage of the storage of powder mixes internally of the above- described type of silo relates to the risk of stratification of the various powders of different granulometry constituting the mixture. The selective depositing of the powders might cause substantial alterations in the material extracted from the discharge mouth with respect to the original composition thereof. In practice, considering the case of storage of a pre- mixed preparation for mortar, it can happen that the material extracted contains a percentage of bond which is not sufficient for a direct use thereof. A further drawback normally connected with storage of powder material internally of silos of the present type relates to the extraction of material by force of gravity. In effect, the descent of the material internally of the lower hopper can be obstructed by the formation of static structures on the part of the material itself. These structures, which are like architectural arches, originate when the loose material becomes arranged above the discharge mouth, creating a statically-balanced vaulted conformation. During the stage of extraction, therefore, the formation of these vaults have to be prevented from forming up in the material; or at least they have to be broken up. There exist various methods for obtaining this aim, the simplest and most widely-used thereof is percussion on the external walls of the silo to generate pressure waves which propagate towards the inside of the structure. This solution, however, apart from requiring frequent maintenance of the silo, is not particularly effective and the times required for the extraction of the material in the presence of high moisture levels can be very long.

The aim of the present invention is to provide a method for temporary storage of powder mixtures, and a relative storage silo therefor, which can guarantee homogeneous distribution of the various powders constituting the mixture extracted at the end of the storage period. An advantage of the method and relative apparatus described relates to the ease of extraction of the mixture of powders stored in the silo, as the lasting formation of vaults and bridges is excluded. Disclosure of Invention

Further characteristics and advantages of the present method and relative apparatus for actuation thereof will better emerge from the detailed description that follows, made herein with reference to the accompanying figures of the drawings, given by way of non-limiting example and in which: figure 1 is a view in vertical elevation of a storage silo of the present invention, partially sectioned; figure 2 is a section of an upper part of a storage silo during a stage of introduction of the powder mixture internal of the silo according to the method of the invention; figure 3 is a second of an upper part of a storage silo during a stage of movement of the powder mixture internal of the silo according to the method of the invention; figure 4 is an exploded perspective view of a lower part of a silo of the present invention; figure 5 is a section of the discharge mouth of a silo of the present invention, at a formation of a vaulted arch by a build-up of the stored powder mixture; figure 6 is a section view of the discharge mouth of a silo at a stage of extraction of the powder mixture contained according to the present method. With reference to the figures of the drawings, we describe a storage silo 1 for actuating the method for temporarily storing powder mixtures of the present invention. In the following description, for the purpose of the interpretation of the relative positions of the elements, the storage silo 1 must be considered in the normal operating configuration thereof, i.e. vertically assembled with the discharge mouth facing downwards. The operating configuration is shown in figure 1.

The storage silo 1 comprises a main storage chamber 10 which inferiorly communicates with a hopper 11 provided with a discharge mouth 3. The storage chamber 10 is preferably cylindrical, with an internal diameter which is equal to the maximum internal diameter of the hopper 11, preferably truncoconical, with which it communicates. The storage silo 1 further comprises an opening 6 for the introduction of the powder mixtures to be stored in the main storage chamber 10. The storage silo 1 of the present invention further comprises a vertical screw 2, rotatably associated to the longitudinal axis x of the silo and predisposed for moving the powder mixtures stored internally thereof. The screw 2 comprises a propeller 16 which couples to a central shaft 13. The central shaft 13 extends along the longitudinal axis x of the storage silo 1, starting from the top of the silo down to in proximity of the discharge mouth 3. The central shaft 13 is advantageously connected at an upper end 13b thereof with the top of the storage silo 1. The central shaft 13 is operatively connected to a motor 14. The motor 14 is preferably arranged outside the storage silo 1 and is connected via a gear reducer 15 to the upper end 13b of the central shaft 13. The central shaft 13 is preferably made of a metal material. The propeller 16 is associated to the external surface of a hollow cylindrical element predisposed to couple axially with at least a part of the extension of the central shaft 13. The propeller 16 and the hollow cylindrical element on which it is fashioned are advantageously realised in a deformable plastic material, preferably a techno-polymer. The propeller 16 comprises an initial tract 16a at the lower end of the central shaft 13, and a final tract 16b which is interrupted before the upper end 13b of the shaft. The storage silo 1 of the invention advantageously comprises internally thereof a vertical central channel 7, provided with a lower mouth 7a and an upper mouth 7b. The screw 2 is arranged inside the central channel 7; the function of the central channel 7 is to serve as a guide for the powder mixtures moved by the screw 2. The central channel 7, arranged coaxially to the screw 2, is constituted by a simple cylindrical tube. The internal diameter of the central channel 7 is substantially coincident, or just above, the maximum diameter of the propeller 16. The central channel 7 covers the screw 2 for at least part of the longitudinal extension thereof; the central canal 7 is advantageously interrupted nearby the initial tract 16a and the final tract 16b of the propeller 16.

The storage silo 1 comprises a spoke-type centring device 17 associated to the screw 2 in the operating configuration of the silo. The spoke-type centring device 17 enables easy mounting of the screw 2 and the various vertical components associated thereto (central channel 7, central shaft 13, propeller 16). The centring device comprises a plurality of spokes 17a of a same length, radially departing from a central sleeve 17b predisposed to be crossed by the screw 2. The spokes are preferably angularly equi-spaced. The ends of the spokes 17a are predisposed to be constrained to the internal walls of the storage silo 1. In the described preferred embodiment, the spokes 17a are three in number. The free ends thereof are shaped such as to be constrained restingly on the inclined internal walls of the truncoconical hopper 11. The central sleeve 17b is externally placed over the central channel 7, with respect to which it is slidingly constrained. The central sleeve 17b is connected by means of a compression spring 17c to a fixed sleeve 17d, rigidly constrained about the central channel 7 above the central sleeve 17b. During an assembly stage of the silo, the hopper 11 is assembled to the cylindrical body of the storage silo 1. During this stage, the free ends of the spokes 17a come into contact with the inclined internal walls of the hopper 11, realising the centring of the central channel 7 and the elements inserted internally thereof (screw 2, central shaft 13, propeller 16). The elements to be centred must be already present internally of the storage silo 1 and constrained to the top of the silo itself. The storage silo 1 of the present invention comprises a lower deflector 5, rotatably associated to the longitudinal axis x of the silo itself in proximity of the upper opening 7b of the central channel 7. The element is predisposed to project at least a part of the powder mixture raised by the screw 2 along the central channel 7 distancing from the longitudinal axis x of the storage silo 1 such as to redistribute it homogeneously above the whole free surface of the powder mixture stored internally of the storage silo 1. The lower deflector 5 is advantageously rigidly constrained to the central shaft 13, and it is thus solid in rotation with the central shaft 13. As previously described, as the upper opening 7b of the central channel 7 near the final tract 16b of the propeller 16, the lower deflector 5 is arranged, with respect to the central shaft 13, immediately above the final tract 16b of the propeller. The lower deflector 5 has a substantially truncoconical shape, with the larger base turned upward and the smaller base equal to the diameter of the cylindrical surface on which the propeller develops 16. The tapered surface of the lower deflector 5 can comprise, or not, reliefs for facilitating the projection of the powder mixture in a distancing direction from longitudinal axis x. The tapered surface can further exhibit a slight concavity. The upper deflector 4 is rigidly constrained to the central shaft 13 and is thus solid in rotation with respect thereto.

The storage silo 1 comprises means for projecting a powder mixture introduced into the silo through the opening 6 in the direction of an upper deflector 4 predisposed to deviate at least a part of the powder mixture at the longitudinal axis of the storage silo 1, such that the free surface of the powder mixture deposited is convex. The upper deflector 4 is rotatably associated to the longitudinal axis x of the storage silo 1, and exhibits a concave lower surface 4a. The upper deflector 4 is umbrella-shaped and axialsymmetric, with the concavity, as mentioned, facing downwards. The lower surface 4a thereof can comprise, or not, reliefs for facilitating the projection of the powder mixture in a distancing direction from the longitudinal axis x. The upper deflector 4 is arranged on the central shaft 13 in proximity of the upper end thereof, above the lower deflector 5. The means for projecting the powder mixture in the direction of the upper deflector 4 comprise a directed tube 8, associated at one of the ends thereof at the opening, the other end being arranged in proximity of the upper deflector 4 and facing towards the lower surface 4a thereof. The end of the tube associated to the opening 6 is arranged below the other end.

The internal surface of the hopper 11 is at least partially defined by at least an elastically deformable wall 12. The elastically deformable wall 12 is preferably arranged in proximity of the discharge mouth 3 of the silo. The wall is predisposed to facilitate exit of the powder mixture from the discharge mouth 3, and does so by transmitting an elastic pulse to the powder mixture adjacent thereto at an elastic return of the elastically deformable wall 12, originating from a reduction in the powder load of the mixture bearing thereon, due to a raising along the central channel 7 on the part of the screw 2 of the powder mixture. Further explanation follows for the sake of clarity. During discharge of the silo, it can happen that the powder mixture stored forms a vaulted arch at the discharge mouth 3 (as previously explained). In this condition, the silo is full and the loading of the powder mixture on the elastically deformable wall 12 causes the deformation thereof. If the previously-described screw 2 is set in rotation, a raising of part of the stored powder mixture is originated, and precisely in the part stored in proximity of the discharge mouth 3. The raising necessarily causes a reduction in the load bearing on the elastically deformable wall 12; it follows that the wall returns into its non-deformed state. The elastic return of the wall causes a thrust on the powder mixture adjacent thereto, with a consequent breakage of the bridge and detachment of the product on the wall, with a consequent exit of the material from the discharge mouth 3 of the silo. In the described embodiment of the present invention, the elastically deformable wall 12 is constituted by a first hollow truncoconical basket made of a deformable plastic material (preferably a techno-polymer) which constitutes the terminal part of the hopper 11. The storage silo 1 further comprises at least a rigid cage 9, externally associated to the at least a deformable wall 12, with functions of supporting and limiting the deformation of the wall 12. In the described embodiment of the present invention, the rigid cage 9 is constituted by a second hollow truncoconical basket predisposed for housing the first basket, the internal walls of the second basket being slightly concave in order to enable deformation of the deformable elastic wall 12 associated thereto. The two baskets are both flanged, both superiorly in order to enable fastening thereof to the rest of the hopper, and inferiorly in order to enable fastening of an element for selective occlusion of the discharge mouth 3. With reference to the previously-described storage silo 1, the method for temporary storage of powder mixtures of the present invention necessarily comprises a stage of introduction of the powder mixture internally of the storage silo 1 and a stage of extraction of the powder mixture from the discharge mouth 3 located at the bottom of the silo 1. As previously discussed, during the course of the two described stages and the storage period of the mixture, a stratification of the constituents of the mixture can occur, due to the selective depositing of the powders having various granulometries. In order to prevent this stratification, the method further comprises a stage, intermediate with respect to the two previously- described stages, of movement of the powder mixture internally of the storage silo 1. The movement stage comprises a main stage of raising at least a part of the powder mixture from the bottom towards the top of the storage silo 1 actuated by means of the vertical screw 2. During the raising stage, the screw is thus set in rotation in the correct direction and raises the powder mixture from the bottom towards the top of the silo, by activation of the motor 15 operatively connected to the central shaft 13. During the course of the main raising stage, the part of the powder mixture which is raised is displaced by the screw 2 through the vertical central channel 7 having a guide function. The raised powder mixture is collected in the vicinity of the lower mouth 7a of the central channel 7, and exits from the upper mouth 7b.

The method further comprises a second stage of projection of at least a part of the powder mixture raised by the screw 2 during the main raising stage away from the longitudinal axis x of the storage silo 1, this stage being finalised to obtaining a homogeneous distribution of the part of powder mixture interested by the main raising stage above the free surface of the powder mixture stored internally of the storage silo 1. The redistribution of the powder mixture performed during this stage is necessary for preventing an accumulation of the shifted material at the central part of the site, which would threaten correct movement of the whole mass of material. Thanks to the redistribution, the free surface of the material internally of the silo is maintained substantially horizontal during the course of the distribution stage. The second projection stage is actuated by means of the previously- described lower deflector 5, against which the powder mixture raised by the screw 2 along the central channel 7 impacts. During this stage, both the screw 2 and the lower deflector 5 are set in rotation by means of activation of the motor 15 which is operatively connected to the central shaft 13. In the method of the present invention, the stage of introducing the power mixture internally of the storage silo is of particular importance. In particular, of crucial importance is that the free surface of the powder mixture deposited internally of the silo 1 should take on a convex shape at the end of the stage, in order to prevent accumulation of material along the walls, which would be difficult to shift. To this end, the stage of introduction of the powder mixture internally of the storage silo 1 comprises a first stage of projection of the powder mixture against the lower surface of the upper deflector 4, which as already mentioned is predisposed to deviate at least a part of the powder mixture impacting on the longitudinal axis of the storage silo 1. In this way, the free surface of the powder mixture deposited internally of the storage silo 1 during the stage of introduction is convex. This first stage of projecting of the powder mixture is done using known means, by sending the mixture under pressure into the opening 6 of the directed tube 8. Preferably during the course of this stage the upper deflector 4 is maintained in rotation by the activation of the motor 15 operatively connected to the central shaft 13. A further critical stage of the described method is the stage of extracting the powder mixture contained in the storage silo 1 through the discharge mouth 3. During this stage, as already mentioned, the formation of bridges in proximity of the discharge mouth 3 on the part of material to be discharged is prevented. In order to avoid this eventuality, as already mentioned when describing the function of the elastically deformable wall 12, the stage of extraction of the powder mixture from the storage silo 1 comprises an auxiliary stage of raising at least part of the powder mixture from the bottom towards the top of the storage silo 1 by means of the screw 2. This stage has the aim of reducing the load of powders in the mixture that bear on the at least an elastically deformable wall 12 arranged in proximity of the discharge mouth 3 of the storage silo 1, causing the elastic return of the wall 12 with the effect of transmitting an elastic pulse to the powder mixture adjacent thereto. The elastic pulse aids extraction of the powder mixture from the discharge mouth 3 of the storage silo 1, breaking any vaulted arches which might have formed in the mixture and the detachment of the product from the wall itself. During the course of this stage the screw 2 is thus maintained in rotation by means of the activation of the motor 15 operatively connected to the central shaft 13. In all of the above-described stages, it is obviously of fundamental importance to maintain a rotation speed of the central shaft 13 and the screw 2 connected thereto which does not achieve a separation by centrifuging of the powders in relation to relative granulometry.

Claims

Claims.

1). A method for temporarily storing powder mixtures, comprising stages of: introducing a powder mixture internally of a storage silo (1) and extracting the powder mixture from a discharge mouth (3) located on a bottom of the silo (1), wherein the method further comprises an intermediate stage of moving the powder mixture internally of the storage silo (1), the stage of moving comprising a main stage of raising at least a part of the powder mixture from the bottom and towards a top of the storage silo (1), which main stage is performed using a vertical screw (2), the stage of moving being aimed at preventing selective depositing of powders having different granulometry belonging to the powder mixture. 2). The method of claim 1, wherein during the main stage of raising, the part of powder mixture raised is displaced by the screw (2) through a vertical central channel (7) having a guide function.

3). The method of claim 2, wherein the stage of moving the powder mixture internally of the storage silo comprises a second stage of projecting at least a part of the powder mixture raised by the screw (2) during the main raising stage in a distancing direction from the longitudinal axis (x) of the storage silo (1), such as to obtain a homogeneous distribution of the part of powder mixture, involved in the main stage of raising, on a free surface of the powder mixture stored internally of the storage silo (1). 4). The method of one of the preceding claims, wherein the stage of introducing the powder mixture internally of the storage silo (1) comprises a first stage of projecting the powder mixture against the lower surface of an upper deflector (4), the upper deflector (4) being predisposed to deviate at least a part of the powder mixture impacting at the longitudinal axis of the storage silo (1) such that the free surface of the powder mixture deposited internally of the storage silo (1) during the stage of introduction is convex.

5). The method of one of the preceding claims, wherein the stage of extracting the powder mixture from the storage silo (1) comprises an auxiliary stage of raising at least a part of the powder mixture from the bottom towards the top of the storage silo (1) by means of the screw (2), the stage having an aim of reducing a load of powders of the mixture which bear down on at least an elastically deformable wall (12) arranged in proximity of the discharge mouth (3) of the storage silo (1), causing elastic return of the wall (12) with an effect of transmitting an elastic pulse to the powder mixture adjacent thereto, the elastic pulse aiding extraction of the powder mixture from the discharge mouth (3) of the storage silo (1). 6). A storage silo for temporarily storing powder mixtures, comprising: a main storage chamber (10) which inferiorly communicates with a hopper (11) provided with a discharge mouth (3); an opening (6) for introduction of powder mixtures internally of the main storage chamber (10); wherein it comprises a vertical screw (2) which is rotatably associated to a longitudinal axis (x) of the storage silo (1), predisposed for moving the powder mixtures stored in the silo.

7). The storage silo (1) of claim 6, wherein it comprises a vertical central channel (7) internal of the storage silo (1), provided with a lower mouth (7a) and an upper mouth (7b); the screw (2) being at least partially arranged internally of the central channel (7); the central channel (7) having a guide function for the powder mixtures moved by the screw (2). 8). The storage silo of claim 7, wherein it comprises a lower deflector (5), rotatably associated to the longitudinal axis (x) of the storage silo (1) in proximity of the upper mouth (7b) of the central channel (7), predisposed to project at least a part of the powder mixture raised by the screw (2) along the central channel (7) in a distancing direction from the longitudinal axis (x) of the storage silo (1) such as to redistribute the powder mixture homogeneously over a whole free surface of the powder mixture stored internally of the storage silo (1).

9). The storage silo (1) of one of claims from 6 to 8, wherein it comprises means for projecting a powder mixture introduced into the silo through the opening (6) in a direction of an upper deflector (4) predisposed to deviate at least a part of the powder mixture to at least the longitudinal axis of the storage silo (1) such that the free surface of the deposited powder mixture is convex.

10). The storage silo (1) of claim 9, wherein: the upper deflector (4) is rotatably associated to the longitudinal axis (x) of the storage silo (1), the upper deflector (4) exhibiting a concave lower surface (4a); the means for projecting a powder mixture introduced into the silo through the opening (6) in a direction of the upper deflector (4) comprising a directed tube (8), which directed tube (8) is associated at an end thereof to the opening (6) and at another end thereof is arranged close to the upper deflector (4) and faces towards the lower surface (4a) of the upper deflector (4) . 11). The storage silo (1) of one of claims from 7 to 10, wherein the internal surface of the hopper (11) is at least partially defined by at least an elastically deformable wall (12) predisposed to facilitate exit of the powder material from the discharge mouth (3), transmitting an elastic impulse to the powder mixture adjacent thereto at an elastic return of the elastically deformable wall (12) originated by a reduction of a load of the powder of the powder mixture bearing thereon due to a raising along the central channel (7) on the screw (2) of a part of the powder material.

12). The storage silo (1) of claim 11, wherein it further comprises at least a rigid cage (9), externally associated to the at least an elastically deformable wall (12), which rigid cage (9) has functions of supporting and limiting deformations of the wall (12).

13). The storage silo (1) of one of claims from 6 to 12, wherein it comprises a spoke-type centring device (17) comprising a plurality of spokes (17a) of equal length, radially departing from a central sleeve (17b) predisposed to be crossed by the screw (2), ends of the spokes (17a) being predisposed to be constrained to the internal walls of the storage silo (1).