EP0192234B1 - Mixing method for making concrete and/or mortar, and device for carrying out this method - Google Patents

Description

The invention relates to a method for mixing fractional mineral additives, hydraulic binders and optionally polymeric additives with mixing water to concrete and / or mortar, preferably for use in mobile mixing systems, in which the pre-metered additives and the Binder and the pre-metered mixing water, optionally with polymer additives, are introduced into the interior of the mixing device and the mixture is discharged after mixing through an opening in the mixing trough.

The mixing of fractional mineral aggregates, hydraulic binders and possibly polymeric additives with mixing water to concrete and / or mortar takes place at least in medium and large-scale construction projects exclusively in batches with so-called compulsory mixers. This is because so far it has not been possible to ensure a sufficiently homogeneous mixing with continuous mixing processes and thus a consistently high quality of the mix. In particular, unavoidable variations in the dosage of the additives or the binder lead directly to fluctuations in the composition of the mix. Continuous mixers are therefore not officially approved for the production of quality concrete. Due to the discontinuous operation, a sufficient throughput rate often requires oversized mixing systems and the connection of buffer stores if the mixed material is discharged using continuously operating means of transport, such as concrete pumps or belt conveyors. This requires a relatively high effort in the construction and correspondingly high operating costs. This is particularly problematic in the case of mobile mixing plants, as are often installed on medium-sized and larger construction sites. The progress in construction technology requires high performance on the one hand, but has also led to a significant reduction in construction times, so that conventional mixing systems often either underperform or are too cumbersome and too long compared to the effective operating time Set-up times. The establishment of the necessary foundations is usually associated with high costs.

According to the most frequently used mixing process, the aggregates and the binding agent are metered out of the storage containers in a quantity-controlled manner and fed to a premixer with a belt conveyor belt. Another conveyor brings the premixing into the weighing container of a batch scale, from which the entire batch is fed into the mixer trough. The premixing is necessary in particular because otherwise the homogenization of the batch, which is given up as a whole, would take too much time. The weighing container of the batch scale also serves as a buffer container so that the mixer can be quickly refilled after the mixer has been emptied. After adding the pre-metered amount of mixing water and the mixture, the mix is removed as quickly as possible so that the mixer is free for the next batch. With the frequent use of continuously operating conveyors for the mix, such as concrete pumps or conveyor belts, the addition of a buffer container is necessary. Usual batch sizes are in the range of one to several cubic meters, which results in an output of approximately 60 to several 100 cubic meters per hour with an average mixing time of approximately 45 seconds per batch. Conventional mixing plants for such services are comparatively complex and cumbersome.

GB-A-986 884 discloses a method of the type mentioned at the outset and an apparatus for carrying out this method, in which the respective mineral additives, hydraulic binders and, if appropriate, polymeric additives are accommodated in individual silos above a conveyor belt. To compile a mixture, a single silo, for example a silo for a mineral aggregate, is opened so that a desired amount of the substance falls onto the conveyor belt and can be transported to a transport container by means of this conveyor belt. In the same way, the silos of the other constituents of the mixture are opened one after the other and the quantities removed therefrom are conveyed to the transport container by the conveyor belt until the desired mixture has been compiled. The transport container is then brought to a mixer in which the mixture is mixed. In this known method, operation is therefore carried out batchwise, the problems described at the outset occurring. In particular, the throughput rate in this method is relatively low.

It is an object of the present invention to provide a mixing process and a device for mixing fractional, mineral aggregates, hydraulic binders and possibly polymeric additives with mixing water for concrete and / or mortar, which, while maintaining the quality of the mix and small plant dimensions, result in higher throughputs allow.

The above object is achieved in a mixing process of the type mentioned above in that the additives and the binder are continuously added to the belt conveyor in layers one above the other, and that the discharge is also continuous it is done that the throughput per minute is between 40% and 400%, preferably between 80% and 200%, of the average mixer filling quantity and that the mixer contents are subjected to a compulsory mixing treatment and a vibration at the same time.

The proposed method makes it possible, even in the area of the belt conveyor, to assign the individual mixing components in terms of quantity in accordance with the mixing ratio. The mixing effort is reduced accordingly, the mixing time can be reduced and the system volume can be reduced.

The invention also relates to a device for mixing fractional, mineral additives, hydraulic binders and possibly polymeric additives with mixing water for concrete and / or mortar, comprising a mixing device with a belt conveyor belt for continuously feeding the mixing device and a discharge device, with storage containers for the additives and storage containers for the binder and, if appropriate, for the additives are connected to the belt conveyor belt in succession by means of metering devices, a quantity control for the supply of the additives, the binder and possibly the polymeric additives being provided to the mixing device, and wherein a metering device for the Mixing water is provided.

The above object is achieved in this device in that individual quantity-controlling metering devices are each provided at the outlet of the storage container before the junction with the belt conveyor, that these individual metering devices are controlled in such a way that they continuously add the additives and the binder in layers on top of each other Place the belt conveyor belt so that the discharge device is designed for the continuous removal of the mixture from the mixing device and that a mixer and at least one vibrator arranged near the bottom of the mixing device are provided for mixing the contents of the mixing device.

The invention is described below with reference to the drawing, which shows several preferred embodiments of the subject matter of the invention without restricting it.

Fig. 1 shows a side view of a mobile mixing plant for performing the method according to the invention in a schematic representation.

Fig. 2 shows a cross section through a two-shaft compulsory mixer, which is set up to carry out the method according to the invention, in a schematic representation.

In Fig. 1, a semi-trailer 1 is shown, which can be placed with its front end for transport on a semi-trailer 2. The frame structure 3 of the semitrailer 1 can be supported for operation with protectors 4a, 4b and 4c. Storage containers 5a, 5b and 5c for the additives are built up in the rear part of the semitrailer 1. Dosing devices 6a, 6b and 6c are arranged below the storage containers 5a, 5b and 5c, which for example consist of belt scales can exist. A weighing container 7a is attached under a storage container 7 for a binding agent, from which the binding agent is fed onto a belt conveyor belt 10 with a binding agent metering device 8 in accordance with the set mixing ratio. The belt conveyor belt 10 runs underneath the storage containers 5a, 5b, 5c, 7 and takes up the metered additives and the binding agent, which are layered one above the other in accordance with the position of the individual storage containers 5a, 5b, 5c, 7. After the binder metering device 8, the belt conveyor belt 10 rises to a mixing device 9 which is arranged on the frame construction 3 at the front end of the semitrailer 1. A continuously operating transport device 11, for example a belt conveyor belt or a concrete pump, is used to remove the mixed material. The mixing water is metered out of a metering device 14 into the mixing device or into the mixer.

In contrast to the previously known, in the method according to the invention, the feeding of the mixing device and the discharge take place continuously, the throughput per minute being between 40% and 400%, preferably between 80% and 200% of the average mixer filling quantity. The metering of the starting material therefore does not have to be carried out in batches limited to the capacity of the mixer, but rather an entire removal unit, for example the loading quantity of one or more transport vehicles, can be preselected. The binder is filled from the storage container 7 into the weighing container 75 and from there added to the additives passing through on the belt conveyor belt 10. The quantities of the individual components are coordinated with one another by a regulating and control unit (not shown). The ratio according to the invention of the throughput per minute to the mixer filling quantity ensures that the continuously added raw materials which have not yet been mixed only make up a relatively small part of the total mixer content, its homogeneity little is disturbed by the addition. Any fluctuations in the composition of the primary material, which could not be corrected by the regulating and control device, are distributed over the entire mixer content and thereby largely offset each other.

In addition, the ratio of the throughput to the mixer content controls the average residence time of the material to be mixed in a mixer trough of the mixing device and thus the intensity of the mixing. For example, if the mixer content is 1.67 cubic meters and the throughput per minute is 100% of the mixer content, the average residence time of the material to be mixed in the mixer trough is 1 minute and the average mixer output per hour is 100 cubic meters. With a conventional batch mixer of the same size, due to the waiting times for filling and emptying, only a much lower output could be achieved, although the mixing times are usually shorter.

Another advantage of continuous feeding is the addition of the mixing water and any polymeric additives. Since in the previously known processes the entire amount is filled as quickly as possible, the mixing water added at the same time or afterwards is very unevenly distributed at the start of the mixing. In the method according to the invention, it can be sprayed directly into the incoming primary material in a controlled manner and can be distributed very evenly from the start.

Even the longer mixing time with the same performance results in better mixing compared to the previously known methods if a similar mixer type is used. So-called compulsory mixers of various types are usually used, in which the mixture by mechanically driven mixing arms or other activators or mixing units. Surprisingly, it was found that the mixing is significantly intensified if the material to be mixed near the bottom of the mixing trough is additionally excited by one or more vibrators. The vibration has an effect similar to an additional liquefaction of the mix, for example by a higher addition of mixing water, and thus a better mixability, without also having its disadvantageous consequences. In addition to greater performance, the method according to the invention therefore also results in a higher quality of the mixture than in the case of conventional batch mixing. Continuous processes could not be used at all because of the insufficient quality. The vibrators can be inserted, for example, near the floor into the interior of the mixing trough. However, it is also possible to design at least parts of the mixer base as a vibrator. The discharge opening for the mix can either be located in the side walls of the mixer trough near the ground or directly in the ground and can be provided with a controllable closing device.

Another advantage of the method according to the invention also results from the possibility of continuous discharge. Since batch mixers are only emptied batch-wise, it is not possible to remove the mix directly with a continuously operating funding. If, for example, the mix is to be drawn off with a frequently used concrete pump, it is necessary to interpose a buffer tank that can hold the entire mixer content. The additional space requirement and the foundations cause considerable difficulties, particularly for mobile mixing plants. The method according to the invention, on the other hand, enables the mixed material to be transported continuously, for example directly to the Processing point.

A particularly advantageous embodiment of the method consists in that, according to claim 2, a double-shaft compulsory mixer with horizontally arranged mixer shafts and in the overlapping region of the mixer arms raised bottom of the mixer trough is used as a mixing device in a manner known per se, the raised bottom region of the mixer trough at least partially as a vibrator formed and the discharge opening is arranged in the overlap area of the mixer arms near the ground or in the ground. This embodiment is shown schematically in FIG. 2. The mixer trough consists of two sections 21a and 21b, the inner contour of which is adapted to the path of the mixer arms 22a and 22b, which are driven by two horizontally arranged mixer shafts 28a and 28b. It rests on a frame 27 and is fed through the filling funnel 23. The paths of the mixer arms 22a, 22b overlap, the bottom of the mixer trough being raised in the overlap area in accordance with the circular path curves. The wall of the mixer trough is at least partially recessed in the area of the elevation and replaced by an inserted vibrator 24, which either extends over the entire length of the mixer trough or only over a partial area. For the elastic sealing of the joints between the vibrator and the wall of the mixing trough, an elastomeric sealing sheet 26, for example a rubber plate, is placed over the vibrator 24 and overlapping over the edge of the mixing trough and optionally fastened. The sealing can also be done with other aids without affecting the essence of the invention. The discharge opening 25 can either be provided, as shown, in the overlap area of the mixer arms 22a, 22b in the end wall of the mixer trough or also directly in the floor if the vibrator 24 does not extend over the entire length of the mixer trough. The mixer trough is always in operation filled with mixed material up to a certain filling level, into which the metered primary material continuously introduced by the filling funnel 23 is stirred by the mixer arms 22a, 22b. The required amount of mixing water is metered in by means of a device (not shown), optionally with polymeric additives, which can take place directly into the incoming raw material and thus result in a very uniform distribution. The vibration excitation of the mixed material by the vibrator 24 significantly improves the miscibility, increases the homogeneity of the discharged mixed material and thus ensures constant strength properties of the structures produced. Although in principle other types of compulsory mixers can also be used without impairing the essence of the invention, the mixing principle of the double-shaft compulsory mixer is particularly well suited for using the method according to the invention. The process-specific distribution of the continuously supplied primary material in the mixer contents up to the likewise continuous removal in the overlap region of the mixer arms 22a, 22b leads to a particularly good homogenization of the mixture.

According to a further preferred embodiment of the subject matter of the invention, the pre-metered additives and the binder are premixed transversely to the transport direction by an additional curvature of the belt conveyor belt 10 in the area of the binder metering device. Belt conveyor belts are usually guided by support rollers so that they are more or less trough-shaped curved transversely to the transport direction. The smaller the transverse curvature, the more evenly the cargo is distributed over the belt width. According to the invention, it is proposed to increase the transverse curvature in the area of the binder metering device. This means that in the marginal areas of the Conveyor belt lying aggregates poured towards the center of the belt and mix with the binder added in this area. The rearrangement of the aggregates on the belt conveyor belt 10 therefore results in premixing with the simultaneous metering in of the binder and enables a reduction in the residence time of the material to be mixed in the mixer trough with the same mixing quality. As a result, a mixer with a smaller content and a lower drive power can be used with the same mixing power. In addition to other advantages, this reduces the start-up time at the start and the after-run time at the end of a mixing process.

It is particularly advantageous to arrange a device for carrying out the method according to the invention in a mobile mixing system in accordance with claim 5 in a compact design on a semitrailer 1 of a semitrailer 2 provided with protector devices 4a, 4b, 4c, the mixing device 9 on the side facing the semitrailer tractor 2 of the semitrailer 1. Since several space-consuming system parts, such as a pre-mixer, a batch weigher with a buffer tank and a buffer tank are not required for the mixture discharged from the mixer, and a smaller mixer can be used with the same output, in comparison with the previously known methods, and a smaller mixer can be used better for a compact design. With the previously known mixing methods, it was previously not possible to install all the necessary system parts on a single vehicle trailer, which had dimensions suitable for road transport without significant dismantling. The additional system components had to be delivered with their own transport vehicles and possibly set up on the foundations to be built. In addition to other disadvantages, a crane usually had to be available. Often there were also different ones Auxiliary structures are created, such as loading ramps. In the device according to the invention, only the storage container 7 for the binding agent has to be removed or folded over for transport, and the protector devices 4a, 4b, 4c have to be deactivated after the towing vehicle 2 has been coupled. Commissioning can also be carried out much more quickly without lengthy preparation work after uncoupling the towing vehicle 2, stripping off the semitrailer 1 and establishing the power connection.

A further advantageous embodiment of the device according to the invention consists in that, according to claim 6, the storage container 7 for the binder from a vertical position of use in front of the storage containers 5a, 5b and 5c for the additives in a substantially horizontal transport position inside and above the storage container 5a, 5b and 5c for the aggregates can be folded down. To do this, it is only necessary to at least partially fold over, pivot out or otherwise remove the intermediate walls 13a, 13b and 13c between the storage containers 5a, 5b, 5c and to make the support frame for the storage container 7 foldable about an axis of rotation 12. The folding can take place, for example, with an attached cable pull or with a hydraulic device without additional aids, for example a crane, having to be carried along. By this measure, the transport height of the device according to the invention can be kept so low that it is also possible to drive onto lower underpasses without an additional vehicle having to transport system parts.

According to a further advantageous embodiment of the subject matter of the invention, the belt conveyor belt 10 is designed as a tubular belt conveyor belt for feeding the mixer, at least in some areas. With such tubular belt conveyor belts the transverse curvature of the belt is increased in a known manner by a suitable arrangement of the support rollers so that a tube forms from the open conveyor belt by overlapping. This makes larger transport gradients possible without slipping of the conveyed material, so that the overall length of the system according to the invention can be reduced or the storage container can be enlarged accordingly if the belt conveyor belt 10 is formed in the area of the rise from the metering devices to the mixer.

The method according to the invention thus enables the construction of mixing plants which are quite suitable for large construction sites in terms of their performance, but because of their compactness, short set-up times and great mobility, they can also be used economically in smaller construction projects.

In principle, it is also possible to set up on rail-bound vehicles if a locomotive is used instead of the tractor 2 and a conventional wagon is used instead of the semi-trailer 1. In this way, it is particularly advantageous to assemble entire processing units which, because of their low transport height, can be used on electrified railway lines without having to switch off the power or remove overhead lines.

Claims (7)

1. A method of blending fractionated mineral additives, hydraulic binders and possibly polymeric additives and mixing water to produce concrete and/or mortars, preferably for use in mobile mixing plants, in which a belt conveyor carries the previously measured out additives and the binder as well as the previously measured out mixing water perhaps with polymeric additives into the interior of the mixing apparatus, the materials being mixed being carried out after the mixing process and through an aperture of the mixing trough, characterised in that the additives and the binder are placed onto the belt conveyor continuously in superposed layers and in that discharge is also accomplished continuously and in that the throughput per minute amounts to between 40% and 400%, preferably between 80% and 200% of the average mixer contents and in that the mixer contents are at the same time subjected to a positive mixing treatment and a vibration.
2. A method according to claim 1, characterised by the use of a double-shaft positive mixer with a vibrator in its bottom region.
3. A method according to claim 1 or 2, characterised in that the conveyor belt undergoes a tubular curvature in the region of the binder feed.
4. An apparatus for mixing fractionated mineral dditives, hydraulic binder and possibly polymeric additives with mixing water to produce concrete and/or mortars, comprising a mixing apparatus with a belt conveyor for the continuous charging of the mixing apparatus and a discharge apparatus, storage containers (5a, 5b and 5c) for the additives and storage container (7) for the binder and possibly for the additives being connected serially to the belt conveyor through interposed dispensing means (6a, 6b, 6c, 7a and 8), means being provided for controlling the supplied quantity of additives, binder and possibly polymeric additives to the mixing apparatus (9), a device (14) being provided for measuring out the mixing water, characterised in that there are at the outlet from the storage containers (5a, 5b, 5c and 7), individual quantity-controlling dispensing means (6a, 6b, 6c, 7a and 8) are provided in each case in front of the point of discharge onto the belt conveyor (10) and in that these individual dispensing means (6a, 6b, 6c, 7a and 8) are so controlled that they place the additives and the binder in superposed layers and continuously onto the belt conveyor and in that the discharge apparatus (11) is constructed for the continuous removal of mixture from the mixing apparatus (9) and in that for mixing the contents of the mixing apparatus a mixing mechanism is provided together with at least one vibrator disposed close to the bottom of the mixing apparatus.
5. An apparatus according to claim 4, characterised in that it is disposed in the manner of a mobile mixing installation of compact construction on a semi-trailer (1) of a tractor and provided with means (4a, 4b, 4c) for measuring out percentages, the mixing apparatus (9) being disposed on that side of the semi-trailer which is towards the associated tractor (2).
6. An apparatus according to claim 5, characterised in that the storage container (7) for the binder is constructed so that it is switchable from a vertical position of use in front of the storage containers (5a, 5b and 5c) for the additives and into a horizontal transport position within and above the storage containers (5a, 5b and 5c) for the additives.
7. An apparatus according to one of claims 4 to 6, characterised in that the belt conveyor for charging the mixing apparatus (9) has at least portions which are constructed as a tubular conveyor.

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