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(11) | EP 1 685 933 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Mixer for concrete, mortar and similar materials, provided with small unloading hopper |
| (57) The present invention refers to a mixer for concrete, mortar and similar materials,
provided with a parallelepiped tank in which two mixing shafts are horizontally mounted
in parallel, which rotate inside basically cylindrical chambers, with a longitudinal
overturned V-shaped profile in intermediate lower position, whose continuity is interrupted
by the presence of a small central rectangular trap, with a hopper fixed in lower
external position on the tank and provided with an upper mouth slightly larger than
the length of the trap; it being also provided that the trap is equipped with a tilting
lid to guarantee closing and opening by means of a suitable actuator.
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[0001] The present patent application refers to a mixer for concrete, mortar and similar materials, provided with a small unloading hopper in lower position.
[0002] Mixers for concrete, mortar and similar materials are commonly used in the building industry to prepare large volumes of the said conglomerate materials preferably designed to be loaded on concrete mixer trucks.
[0003] In particular, traditional mixers consist in a large parallelepiped tank with metal structure, in which two large shafts with horizontal axis operate, being parallel and contra-rotating, fixed between the two sides of the tank.
[0004] Each contra-rotating shaft supports a series of radial arms used to support mixing blades that, during the rotation of the shafts, repeatedly mix and amalgamate the components of the mixture loaded in the tank.
[0005] It must be noted that according to the traditional technique, the two transversal shafts rotate inside corresponding cylindrical intersecting chambers housed inside the mixer at a certain height from the bottom wall.
[0006] The two cylindrical chambers are bordered by corresponding semi-cylindrical casings that represent the external and lower lateral walls of the cylindrical chambers, which communicate in the symmetrical axis of the parallelepiped tank and are open on top to permit loading the mixture components in the tank.
[0007] In traditional mixers, a rectilinear gap extending from one side to the other side of the tank exists between the longitudinal lower borders of the two semi-cylindrical casings.
[0008] The rectilinear gap provides the opening through which the mixed material is poured by gravity under the tank into a suitable conveyor hopper.
[0009] Evidently, the rectilinear opening is closed by means of a tilting lid until mixing is completed, which acts as connection between the lower longitudinal borders of the semi-cylindrical casings of the two chambers that house the mixing shafts.
[0010] The presence of the lid between the two chambers creates structural continuity between the same chambers, in order to allow the mixing material to be transferred from one chamber to the other chamber by means of the mixing shafts.
[0011] This type of mixers is normally supported by a suitable support at a suitable height, so that the concrete mixer truck to be loaded can be placed exactly under the concrete mixer.
[0012] As soon as the conglomerate material is sufficiently mixed, the lid is opened so that the mixture contained in the mixer can be poured by gravity into the conveyor hopper that acts as funnel and transfers the mixture into the loading mouth of the concrete mixer truck.
[0013] The material transfer is favoured by the action of the two mixing shafts, since the inverse rotation makes them work as augers that continuously move the mixture from one side to the other side of the tank, while conveying it towards the centre of the tank, that is to say towards the unloading opening in intermediate position between the two semi-cylindrical chambers.
[0014] In spite of their functionality, the mixers of the aforementioned type are impaired by the characteristics of the opening used to unload the mixture.
[0015] The central unloading opening traditionally extends from one side to the other side of the mixer, that is to say covering the entire extension of the mixer bottom wall.
[0016] In this way, once the lid that closes the opening is removed, the mixture contained in the mixer (from one side to the other side) is poured into the conveyor hopper below, thus emptying the mixer completely.
[0017] However, the presence of such a large opening used for unloading determines some specific characteristics in the design of the said mixers.
[0018] First of all, the lid associated win the opening must be removed very slowly by suitable electronic components installed on board.
[0019] This is done to prevent the entire quantity of the mixture (or at least the majority of it) from falling in the hopper at once, thus clogging the hopper.
[0020] Moreover, the fact that the opening used for unloading extends from one side to the other side of the mixer tank determines the large dimensions of the conveyor hopper.
[0021] On one side, the upper mouth of the hopper must have a basically identical surface extension as the bottom wall of the mixer and on the other side, the hopper must have a considerable height.
[0022] The considerable height is determined by the need to give a strong inclination to the hopper walls, in order to make the mixture "slide" with the required fluidity towards the lower unloading mouth, whose diameter is imposed by the dimensions of the loading mouth of concrete mixer trucks.
[0023] Based on the above considerations, it appears evident that traditional mixers are severely impaired in terms of production costs, structural and installation complexity.
[0024] Another disadvantage is that the handling mode of the lid associated with the unloading opening must be studied, together with the need to have a conveyor hopper with large dimensions.
[0025] As a matter of fact, this results in high production costs for the hopper and requires the use of a support with considerable height (and therefore considerable cost) in order to place an ordinary concrete mixer truck under the hopper, in spite of the large vertical dimension of the hopper.
[0026] The purpose of the present invention is to devise a new technology capable of overcoming the aforementioned drawbacks of the prior technique.
[0027] More precisely, the structure of a traditional mixer with two shafts is modified in order to use a conveyor hopper characterised by smaller structure and lower height.
[0028] The present invention is based on the idea of providing an opening used to unload the mixture characterised by limited length and configured as a trap in central position with respect to the length of the tank of the mixer of the invention.
[0029] Being understood that the trap is placed in intermediate position between the two basically cylindrical chambers that house the two mixing shafts, it must be noted that it only extends in a short central section of the tank, and not from one side to the other side of the tank (such in the case of the prior technique).
[0030] Evidently, the reduction in the length of the trap has permitted to reduce the width of the mouth of the conveyor hopper, since the said mouth only needs to "cover" the reduced length of the trap.
[0031] Most of all, the reduction in the width of the hopper mouth has in turn permitted to limit the vertical dimension of the hopper, without requiring modifications to the walls and diameter of the lower unloading mouth.
[0032] This allows to save on fabrication costs of the hopper and of the entire bearing structure of the mixer, because the lower height of the hopper determines the lower height of the mixer compared to the prior technique, without impairing the optimal access of concrete mixer trucks under the mixer.
[0033] Similarly, the reduction in the length of the trap has also has permitted to reduce the dimensions of the lid and simplify its operation (without the need for sophisticated electronic components), since the lid simply needs to go from total opening to total closing position at constant speed. This is due to the fact that the smaller section of the trap eliminates the risk to pour a large quantity of mixture able to clog the hopper, also in the case of instantaneous total opening.
[0034] However, the reduction in the length of the trap on the bottom wall of the mixer of the invention has determined the need to make specific modifications to the internal structure of the mixer.
[0035] In particular, a special solution has been provided to ensure structural continuity between the two cylindrical chambers, upstream and downstream the central trap.
[0036] The connection between the two chambers has been designed with the additional scope to ensure that the entire mixture is poured into the central trap, regardless of the limited length of the trap itself.
[0037] In particular, two semi-cylindrical casings of the chambers that house the mixing shafts are designed in such a way that the lower longitudinal borders of the casings converge upwards, thus coming into mutual contact and originating, from one side to the other side of the tank of the mixer of the invention, a profile with basically overturned-V shape that is interrupted in the central trap for a short section only.
[0038] The structural continuity between the two chambers is ensured by the lid of the trap in closed position during mixing.
[0039] The presence of the "double-slide" profile in intermediate position between the two chambers, upstream and downstream the central trap, ensures that the mixture being gradually pushed towards the centre of the mixer by the traditional mixing shafts tends to transfer alternatively from one chamber to the other chamber, as soon as it passes over the crest of the "double-slide" connection profile.
[0040] Because of this last condition, the mixture is constantly intercepted by the blade-holding arms of either one of the two mixing shafts.
[0041] The mixture intercepted by the arms is continuously transported from one side to the other side of the tank and therefore transferred above the central trap, so that it is poured into the conveyor hopper through the trap.
[0042] Evidently, if a simple horizontal flat partition was positioned upstream and downstream the trap, a considerable quantity of mixture would remain in the central horizontal partition, without being intercepted by the two mixing arms and conveyed towards the central trap.
[0043] For purposes of clarity the description of the invention continues with reference to the enclosed drawing, which is intended for purposes of illustration only and not in a limiting sense, whereby:
- figure 1 is an axonometric view of the mixer of the invention seen from below;
- figure 2 is a cross-section of the mixer of the invention with a transversal plane;
- figure 3 is an inside view of the bottom wall of the mixer of the invention.
[0044] With reference to the aforementioned figures, the mixer of the invention is traditionally provided with a parallelepiped tank (1) in which two mixing shafts (2) are mounted in parallel, provided with blade-holding radial arms (2a), with each arm (2a) that rotates inside a corresponding chamber (C) bordered by a semi-cylindrical casing (3) that ordinarily represents the external lateral wall and the lower wall.
[0045] Also in this case, the two mixing chambers (C) are connected and in communication, in order to permit continuous transfer of the mixture from one chamber to the other.
[0046] As shown in Fig. 2, the two chambers (C) are provided with lower longitudinal borders with ascending profile, thus converging in the symmetrical axis of the tank (1) and originating an overturned-V shaped profile that extends from one side to the other side of the tank (1).
[0047] Figure 3 shows that the continuity of the overturned-V profile (4) is interrupted in the central section of the tank (1) due to the presence of a small trap (5), with rectangular shape, designed to unload the mixture obtained in the mixer of the invention.
[0048] In particular, the mixture is poured through the small trap (5) into a conveyor hopper (6) fixed under the bottom wall of the tank (1) and provided with an upper mouth slightly larger than the length of the trap (5).
1. Mixer for concrete, mortar and similar materials, of the type provided with a parallelepiped
tank (1) in which two mixing shafts (2) are horizontally mounted in parallel and rotate
inside communicating chambers (C), each chamber being bordered by a semi-cylindrical
casing (3) that represents the external and lower lateral walls, characterised in that the two chambers (C) are provided with lower longitudinal borders with ascending
direction, thus converging in the symmetrical axis of the tank (1) and originating
an overturned-V shaped profile (4) that extends from one side to the other side of
the tank (1), whose continuity is interrupted by the presence of a small trap (5)
with rectangular shape, under which a hopper (6) is fixed in external position on
the tank (1), provided with an upper mouth slightly larger than the length of the
trap (5); it being provided that the trap (5) is provided with a tilting lid (7) to
guarantee alternate closing and opening by means of a suitable actuator.
2. Mixer as defined in claim 1, characterised in that the trap (5) is exactly located in the centre of the tank (1).
3. Mixer as defined in the first or both preceding claims, characterised in that the actuator used to actuate the tilting lid (7) consists in a shaft (8) controlled
by a jack (9) and pivoted at the base of the two sides of the tank (1) in which the
mixing shafts (2) are also pivoted.
4. Mixer as defined in the preceding claims, characterised in that the tilting lid (7) has an upper convex profile, similar to a roof tile, which guarantees
the perfect connection between the two chambers (C) in closed position.