WO2013150362A1

WO2013150362A1 - Apparatus to feed inert material in a concrete mixing plant or an asphalt production plant

Info

Publication number: WO2013150362A1
Application number: PCT/IB2013/000580
Authority: WO
Inventors: Renzo Salvadori; Angelo Zinutti; remove to
Original assignee: Le Officine Riunite - Udine Spa
Priority date: 2012-04-05
Filing date: 2013-04-03
Publication date: 2013-10-10
Also published as: EP2834416B1; EP2834416A1; ITUD20120058A1

Abstract

An apparatus (10) to feed inert material in a concrete mixing plant or an asphalt production plant comprises a weighing tank (17) configured to weigh on each occasion a desired quantity of inert material and a belt transport device (19) disposed in cooperation with the weighing tank (17) to transport the weighed quantity of inert material toward a mixing unit (11) in a desired direction of feed (F).

Description

"APPARATUS TO FEED INERT MATERIAL IN A CONCRETE MIXING PLANT OR AN ASPHALT PRODUCTION PLANT"

FIELD OF THE INVENTION

The present invention concerns an apparatus to feed inert material in a concrete mixing plant or an asphalt production plant.

More precisely, the apparatus is advantageously but not exclusively applied to the weighing tanks of a concrete mixing plant, or an asphalt production plant, used to weigh the desired quantities of inert material to be sent to the mixing unit of inert material.

BACKGROUND OF THE INVENTION

It is known that concrete, or concrete mix, is obtained by mixing water, a hydraulic binder such as cement, inert material or stone aggregates and possibly chemical additives, in suitable proportions.

Concrete mixing plants are known, used to prepare the concrete, which comprise a mixing unit in an elevated position to mix the inert material with the cement, the water and the possible chemical additives, and an apparatus to feed the inert material toward the mixing unit which normally comprises a storage tank for the inert material, which can be divided into one or more compartments for dosing various types of inert material, in the shape of a truncated pyramid funnel, loaded continuously or intermittently with a determinate quantity or variety of inert material.

The storage tank has shutters at the lower part which can be selectively opened to intermittently feed a weighing tank disposed below the storage tank. The weighing tank has the function of containing and weighing, by means of suitably disposed load cells, the necessary and dosed quantity of inert material to be sent on each occasion to the mixing unit.

Transport means of the belt type associated below the weighing tank are provided for moving the mass of inert material weighed.

The belt type transport means, which include one or more belts, are inclined to move the weighed inert material from below, under the weighing tank, upward to the mixing unit.

The belt type transport means are generally equipped with drawing and return devices able to promote the movement of the belts.

One disadvantage of the known solutions is that it is necessary to bring the inert material from the lower exit position of the weighing tank to the elevated loading position of the mixing unit.

Indeed, obtaining a single belt made from a first horizontal segment and a second inclined segment with a constant gradient would cause difficulties in correspondence to the change of gradient of the belt, with consequent problems in the configuration of the belt and in containing the material inside a limited zone of the belt.

For this reason normally two consecutive independent belts are used.

In this known embodiment, a first belt, defined collecting belt, assumes a horizontal configuration below the weighing tank, while a second belt, defined loading belt, assumes an inclined configuration with a constant gradient such as to bring the material falling from the collecting belt to the loading point of the mixing unit.

This configuration entails the need to lift the whole storage plant and/or to make at least an excavation to house at least the collecting belt and part of the loading belt.

In other cases, the known solutions usually use weighing tanks with an inclined belt, to unload the inert material into the other loading belt, or in a loading hopper which can be lifted by a winch. However, the inclined weighing tanks have a limited loading capacity, as well as having a large vertical bulk.

In all cases known in the state of the art, the costs and necessary spaces are considerably increased.

A further drawback connected to the longitudinal configuration of the belt described above concerns the damage and wear of the belt itself. In fact, to make this longitudinal configuration of the belt, flat belts are normally used, cooperating with a return pulley or roll, on each of the two external edges of the belt. Using rolls or pulleys of reduced diameters, the belt is excessively tensed and therefore, the presence of residues of inert material can damage it. There is therefore considerable stress on the belt, consequently increasing the possibility of damage and wear.

In order to confine the material transported inside the space comprised between the return pulleys, and avoid damaging the belt, so called cup belts are often used, which are rather costly and tend to accumulate residues of inert material, or orthogonal tapes are introduced which can be applied directly on the belt, or on an external device.

In the first case the tapes are made fan-like, so that they can be wound on the drawing and return drums, and they also tend to gather dirt, especially when adhesive products are being treated.

In the second case, part of the material can escape containment and, especially in the case of abrasive materials, can get into the interstices and consequently ruin and wear out the belt.

Moreover, the pulleys and/or other possible return devices able to make the concavity normally have reduced sizes, for example in the order of a few centimeters or decimeters, considerably increasing the power needed for drawing the belt and increasing the stress to which the belt is subjected, increasing the wear and the possibility of deterioration.

Another drawback is that the belt must be used flat. This entails that a limited quantity can be transported.

Asphalt production plants, in which it is necessary to weigh the desired quantities of inert material or stone aggregates to be mixed to the bituminous components, have similar problems to those already discussed, with particular reference to the belt type transport means.

Document DE-A-3128569 is known, which describes a transportable dosage plant mounted on two vehicles. DE-A-3128569 proposes to solve the problem of transportability dividing the plant on two transport means, and does not discuss the modalities of obtaining the belt which transports the material from one vehicle to the other. The conveyor belt itself is fed in a conventional way through a dosage system to one, two or more loading hoppers. The conveyor belt in DE- A-3128569 is configured with a bend toward the top of the belt which does not define a big bending radius, nor is it rounded by any radius of curvature. Moreover the configuration described in DE-A-3128569 is not able to impede the upward lifting of the belt, and the consequent loss of tension when it is loaded behind the angled bending point. The reduction in the tension of the belt can cause the belt to slide because it loses adherence on the motorized drum, which is usually located at the head of the belt. A collateral effect of the lifting of the belt, especially in flat belts, is that the transported material is dumped laterally.

Document WO-A-2004/050514 is also known, which describes some methods of obtaining a frame made of sheet metal for a belt, and essentially a frame for a belt made by bending sheet metal in an S or a Z shape in the cross section. WO- A-2004/050514 provides attachments with threaded holes of the cover and tapes of the belt in relation to the frame made by bending metal sheets transversely in a Z or C shape. The containment tapes of the material are not able to prevent the loss of tension and the upward lifting of the belt. Moreover, WO-A-2004/050514 conventionally provides a common loading hopper to contain the fed material. The hopper is rectilinear and is interrupted at the point where the angled belt changes gradient upward, with the risk that the belt, drawn by the motorized drum, can form a sharp edge with the end of the hopper, with a consequent possible increase in the power required and damage to the belt.

One purpose of the present invention is to obtain an apparatus to feed inert material in a concrete mixing plant or an asphalt production plant which reduces the spaces needed and the costs of production.

Another purpose of the present invention is to obtain an apparatus which is resistant to wear and at the same time guarantees that substantially all the material to be transported is contained.

Another purpose of the present invention is to obtain an apparatus which needs limited drive power.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, an apparatus according to the present invention, which overcomes the limitations of the state of the art and eliminates the defects therein, is used particularly, but not exclusively, to feed inert material in a concrete mixing plant or an asphalt production plant. The apparatus of the present invention comprises a weighing tank configured to weigh on each occasion a desired quantity of inert material and a belt transport device disposed in cooperation with the weighing tank to transport the weighed quantity of inert material to a mixing unit in a desired direction of feed.

According to the present invention, the belt transport device has a longitudinal development, in the direction of feed, with a curvilinear configuration inclined upward, from a position below the weighing tank toward the mixing unit having at least a curved segment of belt, or a plurality of segments of belt, rectilinear or curved, the envelope of which reproduces overall a curved segment of belt, shaped with a high radius of curvature.

In one form of embodiment, the curved segment of belt is provided downstream of the segment of belt, typically rectilinear and horizontal, aligned to the weighing tank which receives the material discharged from above.

This disposition allows both to improve the possibility of loading the belt transport device at low heights, and also to maintain the support ground unaltered and to use an apparatus which is not very bulky.

In other words, it is possible to keep the plant low, and at the same time to avoid having to make excavations for housing at least part of the transport unit. Furthermore, it is not necessary to use a plurality of conveyor belts.

These features allow to obtain a plant comprising a reduced number of components, thus reducing both the costs and the bulk.

Moreover, the low tensions required to keep the belt in a longitudinally concave or curvilinear position are either generated by the weight itself of the inert material transported, or, when the belt is empty, by suitable upper and lower positioning means which are distanced from each other to define a space or play for the belt, so that the latter is not subjected to excessive tensions, avoiding risks of damage or wear.

Moreover, advantageously, the feeding apparatus according to the present invention can be developed and made in a modular manner to adapt to configurations which have a plurality of loading compartments in series, providing to associate the curved segment of belt to the end section of the last compartment, before the mixing unit, while the preceding compartments are associated with rectilinear segments of the belt transport device. In a variant, the belt transport device transversely has a concave section.

Predisposing the belt transport device in such a way, the quantity of material transportable is greater than that in the state of the art, which very often uses flat belts, and moreover, the material is contained laterally in the concavity while it is moved.

In accordance with some forms of embodiment described here, the belt transport device comprises:

- a conveyor belt mobile in the direction of feed and disposed along a curvilinear path inclined upward coordinated with the curvilinear configuration;

- lower positioning means of the conveyor belt comprising groups of successive adjacent idle rolls, disposed along the curvilinear path of the conveyor belt, each group of rolls comprising an idle central positioning roll and idle lateral positioning and return rolls disposed angled at the sides of the central positioning rolls;

- upper positioning means of the conveyor belt.

According to some forms of embodiment of the present invention, the positioning and return rolls and the upper positioning means are configured to define both the curvilinear path of the conveyor belt in the longitudinal direction, inclined upward coordinated with the curvilinear configuration, and also the conformation with the concave cross section of the belt transport device.

Moreover, according to some forms of embodiment of the present invention, the upper positioning means also act as delimiting means associated with the weighing tank and cooperating with the belt transport device to define a transport chamber which develops longitudinally along the curvilinear configuration inclined upward, through which transport chamber the inert material is conveyed. The upper positioning means are disposed in cooperation with the conveyor belt in proximity or in substantial correspondence to angled regions between the central positioning roll and the lateral positioning and return rolls.

In one form of embodiment, the belt transport device includes a single closed- ring conveyor belt, mobile in said direction of feed and disposed along a curvilinear path inclined upward coordinated with the curvilinear configuration. Advantageously, the conveyor belt is made of anti-wear rubber or of a polymeric material which is resistant to wear and relatively flexible and deformable, in order to adapt to the desired curvilinear configuration, both longitudinally and transversely to the direction of feed.

According to the present invention, thanks to the relatively flexible nature of the conveyor belt included in the belt transport device, the concavity spontaneously defines lateral side walls which prevent the material from exiting from the belt. Therefore, costs are reduced, because it is not necessary to use cup type belts and/or orthogonal tapes to contain the material.

According to one form of embodiment, the belt transport device is equipped with a pair of drawing and return pulleys.

According to one form of embodiment, the positioning means include lower and upper positioning means.

Advantageously, the low tensions needed to keep the belt longitudinally in the concave or curvilinear position are either generated by the weight of the transported inert material itself, or, in the segments in which the belt is empty, by the suitable upper or lower positioning means which are preferably distanced, or vertically staggered with respect to each other to define a space or play for the belt, so that the latter is not subjected to excessive tensions, reducing the friction and the interference of possible residues of inert material which can get in between, avoiding risks of damage and wear.

In a variant embodiment, the longitudinal curvilinear path of the conveyor belt is defined, at least in part, by the longitudinally staggered position of the lower and upper positioning means, disposed along a path mating with the desired curvilinear path.

In a variant embodiment, the positioning and return rolls of the idle type are disposed longitudinally along the conveyor belt, each having its own axis of rotation transverse to the direction of feed.

In a variant embodiment, the successive adjacent groups of rolls are configured to define, transverse to the direction of feed, a concavity suitable to position the conveyor belt with the desired concave conformation to contain the inert material.

According to one form of embodiment, in order to define the concavity, each group of successive rolls comprises a set of three rolls, which comprises the central positioning roll and the two lateral positioning and return rolls. In a specific variant, the central positioning roll is substantially horizontal, parallel to the direction of feed, while the two lateral positioning and return rolls are reciprocally inclined with respect to the central positioning roll, converging downward.

In accordance with one form of embodiment, the upper positioning means comprise curvilinear shaped guides, or return rolls, or again blocks, disposed along the desired curved development.

The invention also concerns a method to feed inert material in a concrete mixing plant or an asphalt production plant, which provides to weigh on each occasion a desired quantity of inert material by means of a weighing tank and to transport the weighed quantity of inert material to a mixing unit in a desired direction of feed by means of a belt transport device disposed in cooperation with the weighing tank. The method according to the present invention provides that the inert material is transported along a conveyor belt defining a path with a curvilinear configuration inclined upward, from a position below the weighing tank toward the mixing unit. The conveyor belt is kept positioned at the lower part by successive adjacent groups of idle rolls, disposed along the curvilinear path of the conveyor belt. Each group of rolls comprises a central idle positioning roll and lateral idle positioning and return rolls disposed angled at the sides of the central positioning roll. Moreover, the conveyor belt is kept positioned at the upper part by upper positioning means disposed in cooperation with the conveyor belt in proximity or in substantial correspondence to angled regions between the central positioning roll and the lateral positioning and return rolls, to define a transport chamber which develops longitudinally along the curvilinear configuration inclined upward, through which transport chamber the inert material is conveyed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of some forms of embodiment, given as a non- restrictive example with reference to the attached drawings wherein:

- fig. 1 is a front view of an apparatus to feed inert material according to the present invention associated with a concrete mixing plant;

- fig. 2 is a lateral view of the feeding apparatus in fig. 1 ; - fig. 3 is an enlarged detail of fig. 1 ;

- fig. 4 is an enlarged detail of fig. 2;

- fig. 5 is a plan view of the feeding apparatus in fig. 1.

DESCRIPTION OF SOME FORMS OF EMBODIMENT

With reference to the attached drawings, a feeding apparatus 10 of inert material according to the present invention is usable in a concrete mixing plant 60 to make concrete for building structures. However, the feeding apparatus 10 can also be used in an asphalt production plant or similar or comparable productions in which it is necessary to feed a dosed quantity of material.

The feeding apparatus 10 is configured to feed a suitable quantity of inert material, such as for example sand, or gravel or other stone aggregates, to a mixing unit 1 1, suitable to mix the inert material with water and cement, or similar hydraulic binder, and possible added chemicals, in suitable proportions, in order to obtain concrete.

The mixing unit 1 1 is provided with a first station, which receives the material fed by the feeding apparatus 10 and also comprises a frame 38 along which a hopper 41 moved by a winch is able to slide, by means of vertical guides 39. The hopper 41 transports the inert material received from the feeding apparatus 10 from the first station to the next work station. Fig. 1 shows the hopper 41 indicated by a continuous line, in the position in which it receives the inert material from the feeding apparatus 10, and by a dotted line in the intermediate and final positions along which the hopper 41 is moved.

The feeding apparatus 10 comprises a storage tank 12, which can be divided into one or more compartments to also dose various types of inert material, in this case shaped like a substantially truncated-pyramid funnel. The storage tank 12 is supported by an upper frame 13 and is able to be loaded from above, through an upper aperture, with the inert material which subsequently has to be sent, in dosed quantities, to the mixing unit 1 1.

In its lower part, the storage tank 12 has discharge mouths 14, which can be selectively opened and closed using shutters, or other known opening and closing means 40, depending on the quantity and the moment of the cycle, in order to discharge an inert material in a weighing tank 17 suitable to weigh, in a known manner, an appropriate quantity of inert material to make the concrete. The weighing operation can be carried out using load cells 29 installed on vertical uprights 30 that support the weighing tank 17.

The feeding apparatus 10 comprises a belt transport device 19 disposed so as to transport the weighed quantity of inert material discharged from the weighing tank 17 to the first station of the mixing unit 11, in a desired direction of feed F.

In this case, the belt transport device 19 is supported by a support frame 34 in cooperation with the vertical uprights 30.

According to the present invention, all in all the belt transport device 19 has a longitudinal development, in the direction of feed F, with a curvilinear configuration inclined upward, from the position below the weighing tank 17 as far as the mixing unit 1 1. The curvilinear configuration from the bottom upward has at least a curved segment of belt 26 shaped in particular like the arc of a circle with a high radius of curvature, advantageously comprised between about 0.5 meters and 10 meters. Otherwise, several rectilinear or curved segments of belt can be provided, with an envelope that all in all reproduces the curved segment of belt 26. It is believed that the high radius of curvature allows for example to prevent lateral escape of the inert material and also allows to operate with a limited absorption of power.

Moreover, the belt transport device 19 has transversely a concave section, advantageously curvilinear or comparable, to contain the inert material laterally.

In the case in question, the belt transport device 19 includes a single closed- ring conveyor belt 18, mobile in the direction of feed F and disposed along the curvilinear path inclined upward.

The belt transport device 19 is also equipped with a pair of drawing 20 and return 21 pulleys, a possible tensioner roll 33, and lower and upper positioning means of the single conveyor belt 18, disposed intermediate between the drawing pulley 20 and the return pulley 21, in order to define, particularly in the segments in which the conveyor belt 18 is empty, the above-mentioned curvilinear development in the longitudinal direction, as well as the conformation with concave cross section. On the contrary, when the conveyor belt 18 is loaded, the curvilinear conformation is also given by the weight of the inert material transported on each occasion.

The lower and upper positioning means are suitably disposed distanced from each other, in order to reduce the friction on the conveyor belt 18 and the interference of possible residues of inert material.

The lower positioning means are in this case formed by a plurality of positioning and return rolls 27, 28 of the idle type. The conveyor belt 18 cooperates on one side with the drawing pulley 20, in this case disposed in a higher position in correspondence to the mixing unit 1 1 , and on the other side, with the return pulley 21 which is disposed lower.

The conveyor belt 18, being the closed-ring type, follows an outward path from the return pulley 21 to the drawing pulley 20 and a return path from the latter to the return pulley 21, in order to feed the inert material in the desired direction of feed F.

The positioning and return rolls 27, 28 of the idle type are disposed longitudinally along the conveyor belt 18, inside the closed-ring path thereof, and each have their own axis of rotation X, transverse to the direction of feed F.

The positioning and return rolls 27, 28 of the idle type are disposed along a curvilinear longitudinal path, from the return pulley 21 to the drawing pulley 20, in order to define the desired curvilinear development of the conveyor belt 18.

Moreover, the positioning and return rolls 27, 28 of the idle type are configured to position the conveyor belt 18 so as to determine a concave cross section thereof, with a desired radius of curvature, to contain the inert material laterally.

In this case, the single conveyor belt 18 has a configuration such that a portion of belt which transports the inert material on each occasion, that is, the one that during use is aligned with the weighing tank 17, longitudinally follows an initial segment of horizontal rectilinear belt 24 and a segment of inclined rectilinear belt 25, which acts as a feeding ramp, connected by the above-mentioned intermediate curved segment of belt 26 which has the above-mentioned high radius of curvature in the order of sizes comprised for example between 0.5 meters and 10 meters.

According to one form of embodiment of the present invention, the conveyor belt 18 has the curved segment of belt 26 which connects the initial segment of horizontal rectilinear belt 24 with an angle comprised between about 10° and 25°.

In some forms of embodiment, the upper positioning means can be formed by curvilinear shaped longitudinal guides 31, or by low friction blocks, or by return rolls positioned along the curvilinear path.

The upper positioning means are associated to the lower part of the weighing tank 17.

The upper positioning means can also function as delimiting means which cooperate with the conveyor belt 18 in order to define a transport chamber 36 along which the inert material is conveyed.

In one form of embodiment the delimiting means are formed by two longitudinal guides 31 attached below the weighing tank 17, also having the function of guiding the inert material which is discharged from the weighing tank 17 along the curvilinear path which the single conveyor belt 18 follows longitudinally, as well as cooperating with the lower positioning means to define the curvilinear development of the conveyor belt 18, in particular in the segments in which the latter is empty.

The longitudinal guides 31 are advantageously made of low friction material.

The longitudinal guides 31, disposed in a position advantageously symmetrical to and more internal than the longitudinal peripheral edges of the conveyor belt 18, cooperate in their lower part with the conveyor belt 18, in particular with the corresponding rectilinear segment of horizontal belt 24 and the corresponding curved segment of belt 26.

Advantageously, the longitudinal guides 31 are shaped, in their lower part, according to a radius of curvature mating with that of the curvilinear path which the single conveyor belt 18 follows longitudinally.

Therefore, the longitudinal guides 31 delimit transversely a space which defines the transport chamber 36 within which the inert material is conveyed by the conveyor belt 18 as far as the end of the corresponding curved segment 26 in correspondence to the mixing unit 1 1.

As we said, according to an alternative solution, not shown, instead of the longitudinal guides 31 idle rolls or guide wheels, or blocks can be provided, disposed according to the desired longitudinal curvilinear development.

Thanks to the high radius of curvature of the longitudinal curvilinear development of the conveyor belt 18, the drive powers and tensions of the conveyor belt 18 are contained. Therefore, the possible material which is interposed between the conveyor belt 18 and the longitudinal guides 31 does not create perceptible abrasions on the conveyor belt 18.

A considerable advantage provided by the high radius of curvature of the longitudinal curvilinear development of the conveyor belt 18 is the possibility of loading the conveyor belt 18 at low levels, without having to make excavations.

In some forms of embodiment, the upper positioning means do not have any interruptions and are above the connected point where the gradient of the belt transport device 19 varies, allowing to achieve the high radius of curvature.

The belt transport device 19 in this case provides that the longitudinal curvilinear development of the conveyor belt 18 is defined by the vertically staggered position of the drawing pulley 20 with respect to the return pulley 21 and by the positioning and return rolls 27, 28 suitably disposed along a path mating with the desired curvilinear development.

In this case, the positioning and return rolls 27, 28 provide a plurality of adjacent successive groups of rolls 27, 28, disposed along the curvilinear path which the conveyor belt 18 must follow, and configured to define, transversely to the direction of feed F of the inert material, a concavity 35 suitable in its turn to position the conveyor belt 18 with the desired concave conformation to contain the inert material. The concavity 35 is advantageous to prevent, for example, lateral escapes of the inert material which is transported. In this way, the inert material can also pass under the upper positioning means, but without escaping laterally.

In this case, in order to define the concavity 35, each group of successive rolls 27, 28 comprises a set of three rolls, of which a central positioning roll 27 and two lateral positioning and return rolls 28, suitably disposed with respect to each other at the sides of the central positioning roll 27.

In particular, the central positioning roll 27 is substantially horizontal, parallel to the direction of feed F, while the two lateral positioning and return rolls 28 are reciprocally inclined with respect to the central positioning roll 27, converging downward, to define a "U" conformation, more open or laterally flared. In this variant, the longitudinal guides 31 are disposed in cooperation with the conveyor belt 18 in proximity or in substantial correspondence with the angled regions between the central positioning roll 27 and the lateral positioning and return rolls 28.

In a variant, not shown, in order to define the concavity 35, each group of successive rolls 27, 28 comprises only one pair of rolls converging downward, disposed substantially in a "V" shape.

In one form of embodiment, in order to adapt to the curvilinear development upward of the conveyor belt 18, the weighing tank 17 has a coordinated shaped part, inclined upward, in the direction of feed F.

This shaped part, inclined upward, of the weighing tank 17, also has shaped walls inclined transversely to the direction of feed F, defining overall a tapered profile 32 in the direction of feed F (fig. 5), in its part facing toward the mixing unit 11, that is, above at least the curved segment 26 of the conveyor belt 18. The tapered profile 32 confers a bigger gradient to the walls, promoting the discharge of the inert material downward, which is thus not retained along the walls.

It is clear that modifications and/or additions of parts may be made to the feeding apparatus 10 as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of feeding apparatus, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Apparatus to feed inert material in a concrete mixing plant or an asphalt production plant, comprising a weighing tank (17) configured to weigh on each occasion a desired quantity of inert material and a belt transport device (19) disposed in cooperation with the weighing tank (17) to transport the weighed quantity of inert material toward a mixing unit (11) in a desired direction of feed (F), characterized in that the belt transport device (19) has a concave section transversely and a longitudinal development, in said direction of feed (F), with a curvilinear configuration inclined upward, from a position below the weighing tank (17) toward the mixing unit (11), having at least a curved segment of belt (26), or a plurality of segments of belt the envelope of which reproduces overall a curved segment of belt (26), shaped with a high radius of curvature, said belt transport device (19) comprising:

- a conveyor belt (18) mobile in said direction of feed (F) and disposed along a curvilinear path inclined upward coordinated with said curvilinear configuration;

- lower positioning means of the conveyor belt (18) comprising groups of successive adjacent idle rolls, disposed along the curvilinear path of the conveyor belt ( 18), each group of rolls comprising a central positioning idle roll (27) and lateral positioning and return idle rolls (28) disposed angled at the sides of the central positioning roll (27);

- upper positioning means (31) of the conveyor belt (18),

said positioning and return rolls (27, 28) and said upper positioning means (31) being configured to define both the curvilinear path of the conveyor belt (18) in the longitudinal direction, inclined upward coordinated with said curvilinear configuration, and also the conformation with the concave cross section of the belt transport device ( 19),

wherein said upper positioning means (31) also act as delimiting means associated to the weighing tank (17) and cooperating with the belt transport device (19) to define a transport chamber (36) which develops longitudinally along said curvilinear configuration inclined upward, through which the inert material is conveyed, said upper positioning means (31) being disposed in cooperation with the conveyor belt (18) in proximity or in substantial correspondence to angled regions between the central positioning roll (27) and the lateral positioning and return rolls (28).

2. Apparatus as in claim 1, characterized in that said high radius of curvature is comprised between about 0.5 meters and 10 meters.

3. Apparatus as in claim 1 or 2, characterized in that the belt transport device (19) includes a single closed-ring conveyor belt (18), mobile along said direction of feed (F) and disposed along a curvilinear path inclined upward coordinated with said curvilinear configuration.

4. Apparatus as in claim 3, characterized in that the belt transport device (19) is equipped with a pair of drawing and return pulleys (20, 21).

5. Apparatus as in claim 1, 2, 3 or 4, characterized in that the longitudinal curvilinear path of the conveyor belt (18) is defined by the position, reciprocally staggered longitudinally, of the lower (27, 28) and upper (3 1) positioning means, disposed along a path mating with the desired curvilinear path.

6. Apparatus as in any claim hereinbefore, characterized in that the positioning and return rolls (27, 28) of the idle type are disposed longitudinally along the conveyor belt (18), each having its own axis of rotation (X) transverse to the direction of feed (F).

7. Apparatus as in claim 6, characterized in that the groups of rolls (27, 28), are configured to define, transverse to the direction of feed (F), a concavity (35) suitable to position the conveyor belt (18) with the desired concave conformation to contain the inert material.

8. Apparatus as in claim 7, characterized in that, in order to define said concavity (35), each group of successive rolls (27, 28) comprises a set of three rolls which includes said central positioning roll (27) and said two lateral positioning and return rolls (28).

9. Apparatus as in claim 8, characterized in that the central positioning roll (27) is substantially horizontal, parallel to the direction of feed (F), while the two lateral positioning and return rolls (28) are reciprocally inclined with respect to the central positioning roll (27), converging downward.

10. Apparatus as in any claim hereinbefore, characterized in that the upper positioning means (31) comprise curvilinear shaped guides, or return rolls, or again blocks, disposed along the desired curved development.

1 1. Apparatus as in any claim hereinbefore, characterized in that the weighing tank (17) has a part with a tapered profile (32) in the direction of feed (F).

12. Method to feed inert material in a concrete mixing plant or an asphalt production plant, which provides to weigh on each occasion a desired quantity of inert material using a weighing tank (17) and to transport the weighed quantity of inert material toward a mixing unit (11) in a desired direction of feed (F) by means of a belt transport device (19) disposed in cooperation with the weighing tank (17), characterized in that the inert material is transported by the belt transport device (19) along a conveyor belt (18) defining a path with a curvilinear configuration inclined upward, from a position below the weighing tank (17) toward the mixing unit (1 1), and in that the conveyor belt (18) is kept positioned at the lower part by successive adjacent groups of idle rolls, disposed along the curvilinear path of the conveyor belt (18), each group of rolls comprising a central idle positioning roll (27) and lateral positioning and return idle rolls (28) disposed angled at the sides of the central positioning roll (27), and the conveyor belt (18) is kept positioned at the upper part by upper positioning means (31) disposed in cooperation with the conveyor belt (18) in proximity or in substantial correspondence to angled regions between the central positioning roll (27) and the lateral positioning and return rolls (28) to define a transport chamber (36) which develops longitudinally along said curvilinear configuration inclined upward, through which the inert material is conveyed.