EP1529617A2

EP1529617A2 - Improved concrete-mixing process and plant with mixing of components

Info

Publication number: EP1529617A2
Application number: EP04078074A
Authority: EP
Inventors: Vittorio Merli; Adriano Savorelli
Original assignee: Vortex Hydra Srl
Current assignee: VORTEX HYDRA S.R.L.
Priority date: 2003-11-06
Filing date: 2004-11-05
Publication date: 2005-05-11
Also published as: ITMI20032143A1; EP1529617A3

Abstract

Improved concrete-mixing process and relative plant with the mixing of components in the field of the mixing of cement and non-cement aggregates with the mixing of components in the dry state thus allowing a fine homogenization of the compound, but with perfectly dosed single elements.

A process is provided together with a plant subdivided into two areas or basic phases.

The first area or phase consists in dry mixing batches of components, batchwise, the second area or phase consists in the continuation of the mixing and continuous hydration of the compound by means of a mixer-feeder.

Description

The present invention relates to an improved concrete-mixing process and a relative plant with the mixing of components.
The known existing concrete-mixing plants are generally characterized by the use of pre-established quantities of components by weight or volume, which are such as to provide a reasonable quantity of mix at the end of the mixing process.
For each mixing cycle and with as accurate means as possible, the established quantities of components are provided and are then introduced into the main machine called "mixer" in order to homogenize the mixture of components as much as possible with water to obtain the final mixture, called concrete mix.
There are a wide range of means for preparing the quantities of components and also methods for their mixing which have been known and adopted for a long time. The best mixtures (or mixes) as far as quality and homogenization are concerned, are obtained by weighing each single component. There are also various ways of optimizing the mixing and the introduction of water, by evaluating the best result with respect to the final resistance of the mix.
Both the inert starting materials and their proportions can vary, as also the sequence, i.e. the order with which the components are put together, but above all the homogenization of the mix must be well supervised before the mixing water is added.
In order to guarantee this homogenization, different types of mixers were produced in the past, also depending on the type of mix to be obtained (wet, normal or semi-dry).
Fixed and mobile mixers (for example auto-concrete-mixers) with a rotating container, mixers with a fixed container with stirrers and/or mixers of the mix with fixed blades, rotating blades, counter-rotating blades and fixed blades (planetary turbo-mixers), were in fact produced.
Finally, for large quantities and for medium-low quality concretes, concrete-mixing plants were also set up with counter-rotating screw mixers which, although mixing the components introduced in continuous, are not able to guarantee a sufficient homogenization of the components themselves. There are, in fact, variations in the cement content and water/cement ratio which, in some cases, make their use unadvisable.
The main limitations of current mixing plants are listed hereunder:

They are batch plants and consequently the mixer must be dimensioned not for the immediate capacity requested but for the integral value relating to the minimum preparation and mixing cycle time of the single quantities.
The addition of water to the mixture however obtained, in any case involves a downtime which must be added to the cycle.
The same consideration can also be made for the time interval necessary for charging the components and for discharging the mix obtained.
The mix obtained is discharged into a specific container which is dimensioned to receive up to double the quantity envisaged for the single mix, in order to ensure continuous supply for the plant downstream.
The reduction in possible mixing times and the necessity of having reasonable quantities of mix (so as to ensure a continuous supply) inevitably leads to a compromise between time available and mixing efficiency of the dry product and mix with water. The presence of cement granules and/or colour, a non-homogeneous distribution, the presence of only slightly wet clots, have, in fact, been observed.
In addition to what is specified above, the result of using moderate quantities is an increase in the power applied which becomes increasingly more onerous, also economically, with an increase in the plant potentiality.
The difficulties in running present plants are also quite important: for example, in the case of a sudden lack of energy, the mixer becomes blocked and the mix must be unloaded as soon as possible with manual methods. The same thing is necessary in the case of malfunctioning of the plant using the mix itself: hardening of the cement is, in fact, only a question of time; once the water has been added to the mix, it hardens in short times, in approximately an hour, and in order to save and preserve the machines, the mix must be discharged as soon as possible; the mix is completely useless with a consequent economic loss.

The general objective of the present invention is therefore to provide an extremely simple plant with easy control of the specific variables in order to obtain a continuous and reliable mixing system.
Other objectives of the invention are to identify a plant and process for obtaining optimum characteristics of the product obtained, easy calibration, simple handling of the start-up and shut-down, to be effected rapidly and/or instantaneously.
These objectives according to the present invention are achieved by providing an improved concrete-mixing process and a relative plant with mixing of the components as specified in the enclosed claims.
A preferred industrial embodiment of the invention and its industrial application are described hereunder, in particular with reference to the enclosed drawing which provides a schematic representation of the process and machines or parts of machines which form the essential part of the plant, set up for the continuous production of concrete mix with three or more components or starting raw materials.
It is in fact evident that, in order to produce a concrete plant, at least three components are necessary, such as cement, sand and water in reciprocal proportions appropriately determined, but various other additives are generally envisaged such as colour, fibres and other raw materials in general.
The embodiment, object of the present invention, is substantially characterized in having identified means and systems for the production of a controlled, constant and perfectly homogeneous mix of all the starting components except for water, and subsequently obtaining, by means of a continuous mixer with an open Archimedean screw, the continuous mixing of the product, mixed in the dry state with water in the desired ratio and proportions.
The preferred industrial application thus described also consists in availing of a plant provided with all the necessary means for the variable weight measurement of the single materials in order to calibrate the proportions and ratios, with particular reference to the water/cement weight ratio, as desired.
The plant described consists of a series of containers 11, 12, 13, 14, etc. or deposit areas 15, 15', etc. in which the various raw materials in the form of dry powder, such as pigments, fibres, accelerators, fluidifiers, cement, sand, other materials suitable for the cement mix, are contained or added. The containers 11, 12, 13, 14, etc. are equipped with extraction screws 16 (alternatively belts) which selectively feed them into a weighing and/or dosing area 17 and subsequently into a main hopper 18. As shown for illustrative purposes, the various raw materials are fed by gravity fall from the Archimedean screws 16 in the weighing and/or dosing areas 17 or directly by means of conveyor belts 19, 19', etc. for the sand or one or more Archimedean screws 20 for the cement to the main hopper 18.
In particular, the feeding to the main loading hopper 18 is effected, for example, in a time order according to the following sequence.
Sand, having various particle-sizes, is fed first, followed by cement and subsequently various basic components such as colour, fibres (to give the mix tensile strength).
Furthermore, said sequence can also envisage the addition of other additives such as fluidifiers, accelerators (which, always in the dry state, can be useful for the final mix in relation to the uses and end-product desired).
Once the charging of the various components into the hopper 18, in the required weighed quantities, has been completed, the whole combination of components is discharged from the loading hopper 18 into a mixer 21 which is in continuous movement. The discharging is effected by the opening of one or more outlet mouths 22 whose opening is controlled by rapid opening valves 23, for example of the snare type.
The continuous mixer 21 is produced, for example, with high speed rotating blades 24, always in motion, so as to homogenize and uniformly disperse the combination of various components discharged. Once the weighed or volume dosed single components have been charged into the mixer, they are amalgamated in the dry state for a certain period corresponding to the required cycle time.
When the homogenization has been completed, the continuous mixer 21 unloads the homogenous compound obtained by the opening of a door 25, for example of the twin-valve type, which allows the material to drop into a further hopper 26.
The process described so far allows a highly homogeneous compound or product to be obtained, with "successive and moderate" small batches, ready for use, with a saving of energy and components used.
The great mixing rapidity and efficiency obtained enables the resulting compound or mix, to be used continuously.
This compound or mix, contained in a further hopper 26, is fed in continuous by means of a belt 27 to a simple continuous screw mixer-feeder 28.
The mixing water is also introduced into the continuous screw mixer 28, by means of pulverizing nozzles 29, and can be continuously controlled and regulated by the plant operator by means of a control device 30 equipped with instantaneous visible control of the quantity of water supplied.
Due to the very short period of time that passes between the introduction point of the water into the compound or mix and the point of use over the utilization of the mix itself, for example with an extruder 31 of said mix, there is a consequent minimization of the process losses caused by interruptions or other problems in the functioning of the plant downstream.
The only part of the mix, in fact, which must be rapidly eliminated is that which is already wet and contained in the continuous screw mixer 28. This elimination can be effected by means of an opening 32, selectively openable, which allows the discharge of the mix contained in the mixer 28 into a trolley or container 33. Alternatively, the whole mixer 28 can be moved with one of its outlet openings 34 from the position above the extruder 31 to a position above the trolley 33, as it is situated on a trolley equipped with wheels 35.
This allows a dry mixing of components and insertion of the water into the compound to obtain the mix, in continuous and in times extremely close to the utilization of the mix.
All the drawbacks of the known plants described above are thus eliminated.
In particular, it should be noted how the plant and process of the present invention are fundamentally based on the fact that they are subdivided into two distinct areas or phases.
A first area or dry mixing phase of the components batchwise with doses of the components which can be easily established in relation to the demands.
A second area or hydration phase of the compound thus obtained, in continuous, with water inserted to obtain the mix only at the last moment.
In this way, there is also the possibility of dry mixing solids and fibres with a perfect homogenization. This operation in the dry state allows preservation of the compound for an indefinite period in the case of suspension of the process and stoppage of the plant. Furthermore, there is advantageously also the possibility of interrupting the process or stopping the plant with a minimum waste of material already hydrated.
The present invention is consequently particularly important in the field of automatic mixing plants for the production of extruded products, such as, for example, tiles made of coloured cement.
It is therefore possible to obtain limited productions of the end-product, without the necessity of cleaning interventions of the whole plant as was formerly the case.
It can thus be seen how an improved concrete-mixing process and relative plant for the mixing of components according to the present invention achieve the objectives indicated above. Furthermore, in practice, the devices and materials used, as also the dimensions and components, can vary according to technical demands.

Claims

An improved concrete-mixing process with the mixing of components, wherein various raw materials in the form of dry powder, such as pigments, fibres, accelerators, fluidifiers, cement, sand, and other materials suitable for a concrete mix, are selected according to type and weight for a certain mix and are treated in two distinct phases, a first dry mixing phase, batchwise, in doses established for producing a compound, and a second hydration phase of the compound in continuous with water introduced for producing the desired mix only at the last moment.
The process according to claim 1, characterized in that said first dry mixing phase is preceded by a feeding phase in a hopper of pre-established doses of said raw materials in the form of dry powder.
The process according to claim 1, characterized in that said first dry mixing phase is continuous.
The process according to claim 1, characterized in that in said second hydration phase of the compound in continuous, the water is introduced by means of pulverization controlled and regulated in continuous.
An improved concrete-mixing plant with the mixing of components comprising a series of containers (11-15, 15') of raw materials in the form of dry powder, such as pigments, fibres, accelerators, fluidifiers, cement, sand, and other materials suitable for a concrete mix, with at least one weighing and/or dosing hopper (17, 18) which receives said raw materials, a mixer in continuous movement (21) which receives, homogenizes and uniformly disperses said raw materials in the dry state, a further continuous mixer-feeder (28) associated with pulverizing nozzles (29)for the mixing water.
The plant according to claim 5, characterized in that one or more extraction screws (16), conveyor belts (19, 19') and one or more Archimedean screws (20) are associated with said series of containers (11-15, 15') of raw materials in the form of dry powder.
The plant according to claim 5, characterized in that said pulverizing nozzles (29) of mixing water are continuously controlled and regulated by means of a control apparatus (30) of the quantity of water supplied.
The plant according to claim 5, characterized in that said further continuous mixer-feeder (28) comprises an opening (32), selectively openable, which allows the mix contained therein to be discharged into a trolley or container (33).
The plant according to claim 5, characterized in that said further continuous mixer-feeder (28) is situated on a trolley equipped with wheels (35).