EP0616839A1 - Method and device for continuously mixing of several solid and/or liquid components especially for making concrete - Google Patents

Abstract

Process in which the solid components are each delivered to a gaseous carrier medium individually or combined in appropriate groups and the mass flows or volume flows of the components are then combined at high flow velocity in a mixing section in such a way that the mass flow or volume flow of the component or components having the quantitatively largest portion is first fanned out and directly afterwards the mass flows or volume flows of the remaining components to be mixed are fed into this fanned out mass flow or volume flow which is then reunited in an impact-like manner and led off for further use. The mixing device for carrying out this process has a pear shape, a central flow divider (2) for fanning out the quantitatively largest mass flow or volume flow, lateral inlet ports (10) for the remaining components to be mixed and an outlet port (7) for the finished mixture. <IMAGE>

Description

The invention relates to a method and the associated device for mixing several solid and / or liquid substance components, the substance components being fed to the mixing device in precisely metered quantities in continuous mass or volume flows and the finished mixture being discharged from the mixing device in a continuous volume flow. A preferred field of application of the invention is the production of concrete, in particular high-strength and / or fast-setting concrete.

When mixing substances, two fundamentally different methods are preferably used, and therefore two groups of machine devices. In one group, the mixing process takes place in vessels or containers in which agitators with plate, blade, screw or whisk-like agitating tools are arranged. The mixing process can be carried out discontinuously (DE 26 11 054 A1) or with continuous flow through the mixing device (DE 31 42 053 A1). In order to be able to thoroughly mix the aggregate, cement and make-up water required for the production of concrete to a dough-like paste, the discontinuous process is predominantly used today, whereby the mixing the dough is formed by means of paddle or screw-shaped agitators in appropriately shaped vessels and usually takes between 0.5 and 3.0 minutes. The long mixing times are necessary in order to achieve good moistening of the cement particles on the one hand within the doughy mass and on the other hand to achieve as complete a coating of the aggregate parts as possible with cement milk.

In the continuous-flow mixing devices, the material components are filled in on one side of the mixing vessel and discharged on the other side. Transport and mixing are almost always carried out using the same mechanically moving parts such as agitators, blades or screws. Gravity is also often used to support the flow through the mixing device, in which case the agitators or the mechanically moving mixing tools usually rotate about a vertical or almost vertical axis. In the production of concrete, importance must also be attached to these mixing devices that the residence time of the pasty mass in the mixing devices is long enough to moisten the cement particles and to coat the aggregate parts with cement milk. To achieve this goal, stowage elements and stowage chambers are often provided.

The known mixing devices of the two above-described processes with discontinuous and continuous flow have the disadvantage in the production of concrete that relatively long residence times are required in the mixing device. Because of the long dwell times, the mixing devices described above are not at all suitable for the production of quickly setting concrete.

Such concrete comes from the expansion of underground cavities, such as tunnels, caverns, canals or routes used in mining for temporary or permanent securing of the exposed surfaces as shotcrete. Since the usual concrete paving techniques cannot be used, special spraying methods have been developed, whereby a distinction is made between dry and wet spraying methods. In the dry spray process, a dry mixture of cement, aggregate and powdery solidification accelerator is conveyed by means of compressed air to a spray nozzle, where the make-up water is added. If necessary, a liquid solidification accelerator is also only added at the spray nozzle. In the wet spraying process, ready-mixed fresh concrete with a soft consistency is usually conveyed to the spray nozzle by means of a pump, compressed air for increasing the spraying speed and a liquid solidification accelerator being supplied to the spray nozzle.

In dry spraying, the dosing devices are often too imprecise to ensure adequate wetting of all cement particles. Supported by the compressed air expanding in and behind the spray nozzle, considerable amounts of unwetted cement dust and also the chemical solidification accelerator get into the air and lead to a long-term unacceptable health hazard for the persons carrying out the spraying.

Particularly serious disadvantages in both wet and dry spraying are the rebound, which is around 30%, and is mainly due to the fact that the mixing is imperfect, and the fact that the water-cement values are responsible for the quality of the concrete are of crucial importance, are very difficult and often cannot be adhered to in practice.

Furthermore, the solidification accelerators used to date increase the leachability of the concrete, so that at Contact between corresponding concrete components and the groundwater more components are leached out of the concrete, which can then pollute the groundwater.

Recently, low-gypsum special cements have therefore been developed that have setting times of less than 10 seconds without chemical setting accelerators. These cements cannot be used in the known shotcrete processes. In the wet spraying process, the fresh concrete produced using this cement would solidify on the way to the spray nozzle. In the spraying process, this cement would come into contact with the moisture naturally contained in the aggregates, so that there would be a first partial reaction before the addition of the make-up water. Because of this partial reaction, the reactivity of the special cement would be impaired in such a way that the solidification and strength development of the applied concrete could no longer meet the requirements for rapid rock protection.

So far, it has been used to dry the additives in the dry spraying process, i.e. to remove any moisture that could lead to a premature reaction with the special cement before adding the make-up water. Of course, this is a very complex solution in terms of device, time and energy.

In addition to the first group of mixing devices described above, there is a second group of mixing devices which works without mechanically moving parts and uses the physical principle of mechanical whirling (DE 37 39 976 A1). In this case, the components to be mixed are usually introduced into a vessel or a container into which compressed air is additionally introduced via nozzles or nozzle bottoms, so that mechanical swirling and, at the same time, mixing of the Material components is achieved. This form of mixing is characterized in that the proportion of the substances to be mixed in a unit volume of the mixing vessel is relatively small, and that a relatively rapid, preferably vortex-like movement of the substance particles takes place, which results in good mixing in a relatively short time. Such mixing devices are also available for a continuous run.

The principle of mechanical intermingling has so far only been used for mixing solid, mostly fine-grained material components. This process technology in the forms known so far is not suitable for the production of concrete.

Starting from this prior art, the invention is based on the task of thoroughly or almost completely mixing a plurality of solid and / or liquid substance components continuously, extraordinarily quickly and with exactly predetermined mixing ratios which are to be observed very precisely over long periods of time.

According to the invention, this object is achieved by a method of the generic type in which the solid substance components, individually or combined in suitable groups, are each given to a gaseous carrier medium and the mass or volume flows of the substance components are then combined in such a way at high flow velocity in a mixing section that the masses - or volume flow of the substance component or substance components with the largest quantitative proportion is first fanned out and the mass or volume flows of the other substance components to be mixed are then fed into this fanned-out mass or volume flow, which is then brought together in a crash-like manner and discharged for further use.

According to the present invention, the kinetic energy of the mass or volume flows is used both for the supply of the substance components to be mixed to the mixing section, for the mixing process itself and for the discharge of the finished mixture. Due to the high flow velocity of the mass or volume flows, the mixing process is completed in a very short time, usually in less than a second.

The fanning out of the mass or volume flow of the material component with the largest proportion in terms of quantity causes an extremely favorable ratio between the volume of material and the total volume on the mixing section for the mixing process. A volume ratio that is favorable for the mixture is always given when the proportion of the volume of material in the total volume is as small as possible and thus it is ensured that there is a great deal of space between the individual material particles, through which the components of the other material components to be mixed and the particles of the fanned out Mass or volume flow can be supplied. This is where the mixing process begins, which is completed by the crash-like merging of the fanned-out mass or volume flow in such a way that there is then a complete or almost complete mixture which is used for further use.

In an advantageous embodiment of the method, at least two mass or volume flows of the other substance components to be mixed are premixed before they are introduced into the fanned-out mass or volume flow, which further increases the mixing effect.

It is particularly useful to use the method according to the invention for the production of concrete. The aggregate and the cement are introduced into the air streams with high dosing accuracy, and the aggregate-air volume flow fanned out in the mixing section following the transport route and the volume flows of cement-air and make-up water are introduced into the fanned-out aggregate-air volume flow with great kinetic energy.

The very short mixing times and the complete or almost complete mixing thereby make the process according to the invention highly suitable for the production of fast-setting concrete, as it is e.g. is used for mountain protection in tunnel construction. In particular, low-gypsum cement can be used, since it is fed to the mixing device separately from the naturally moist aggregate by the method according to the invention. The elaborate predrying of the aggregate previously required when using low-gypsum cement can thus be dispensed with. It is of course also possible to use the method to process normal setting cement with the addition of a chemical setting accelerator.

It is particularly expedient if the rapidly setting concrete is fed to a centrifugal device immediately after its production, which accelerates the concrete and transfers it to its destination without wires.

In addition to concrete, in particular quick-setting concrete, the centrifugal device can also be used to apply other mixtures produced by the process according to the invention.

Advantageous refinements of the method according to the invention result from the further subclaims.

To carry out the method according to the invention, a mixing device is proposed which is rotationally symmetrical, and in the axis of symmetry of which there is an inlet connection for the mass or volume flow of the substance component with the largest proportion and an outlet connection for the finished substance mixture are arranged, a flow divider being provided centrally within the mixing device and at least two lateral inlet connections for the mass or volume flows of the other substance components to be mixed, which are present open into the mixing device in the region of the end of the flow divider facing the inlet or outlet for the mass or volume flow of the substance component with the largest proportion by volume.

The mass or volume flow with the largest proportion of substance in terms of quantity is fanned out by a flow divider which is arranged centrally within the mixing device and is preferably of streamlined design. The remaining material components to be mixed are fed into the mixing device at several points, specifically in an area in which the mass or volume flow of the material component with the largest proportion in terms of quantity has already been fanned out. This is where the mixing starts, which is completely or almost completely completed by the crash-like merging of the fanned-out current.

In a further embodiment of the invention, the mixing device is pear-shaped, in such a way that its radius of curvature on the output side is smaller than its radius of curvature on the input side. The resulting flow contour of the mixing device is favorable for the fanning-out effect in its entrance area and produces a particularly intensive crash effect in its exit area.

In a further embodiment of the mixing device, two lateral inlet connections are provided for the other material components to be mixed, which are diametrically opposed and expand in width towards the mixing device in such a way that that its width at its junction with the mixing device corresponds to its diameter at this point. This ensures that all flow parts of the mass or volume flow of the substance component flowing through the mixing device are hit with the largest quantity by mass or volume flows of the other substance components to be mixed.

Further advantageous refinements of the mixing device, in particular for the production of concrete, result from the further subclaims.

Fig. 1

einen Schnitt durch ein vorteilhaftes Ausführungsbeispiel der Mischeinrichtung mit zentraler Zufuhr für die Komponente mit dem mengenmäßig größten Anteil und seitlicher Zufuhr für die übrigen zu vermischenden Komponenten;

Fig. 2

ein Verfahrensschema für die Herstellung von Beton, bei dem Zuschlagstoff und Zement mit Druckluft als Trägermedium und das Zusatzwasser jeweils getrennt der Mischeinrichtung zugeführt werden;

Fig. 3

einen Schnitt durch einen Teilbereich der Mischeinrichtung mit seitlichem Zufuhrstutzen und Anordnung der Düsen für das Zusatzwasser und das Zement-Luft-Gemisch sowie mit äußeren Düsen für die Luftzufuhr zur zusätzlichen Beschleunigung des Volumenstromes;

Fig. 4

einen Schnitt B-B nach Fig. 3 mit einer Ansicht der Düsenanordnung;

Fig. 5

eine Draufsicht auf einen Düsenblock, der die Düsen gemäß Fig. 3 und Fig. 4 enthält, von der Mischeinrichtung her gesehen,

Fig. 5.1

einen Schnitt durch den Düsenblock gemäß Fig. 5,

Fig. 6

einen Schnitt A-A durch die Mischeinrichtung gemäß Fig. 1 und Fig. 3;

Fig. 7

einen Schnitt durch den unteren Teil der Mischeinrichtung mit einem Einlegestück zum Richten und zur Fortleitung der Teilvolumenströme und

Fig. 8

eine Kombination der Mischeinrichtung mit einer Schleudermaschine, vorzugsweise zur Herstellung und zum Auftragen von Beton.

The method according to the invention and the associated device are explained in more detail below on the basis of exemplary embodiments illustrated in the drawings, in particular relating to the production of concrete. It shows:

Fig. 1

a section through an advantageous embodiment of the mixing device with a central feed for the component with the largest amount in terms of quantity and lateral feed for the other components to be mixed;

Fig. 2

a process diagram for the production of concrete, in which the aggregate and cement with compressed air as the carrier medium and the make-up water are each fed separately to the mixing device;

Fig. 3

a section through a portion of the mixing device with lateral supply nozzle and arrangement of the nozzles for the make-up water and the cement-air mixture and with external nozzles for the air supply for additional acceleration of the volume flow;

Fig. 4

a section BB of Figure 3 with a view of the nozzle arrangement.

Fig. 5

3 shows a plan view of a nozzle block, which contains the nozzles according to FIGS. 3 and 4, from the mixing device,

Fig. 5.1

5 shows a section through the nozzle block according to FIG. 5,

Fig. 6

a section AA through the mixing device according to FIG. 1 and FIG. 3;

Fig. 7

a section through the lower part of the mixing device with an insert for straightening and forwarding the partial volume flows and

Fig. 8

a combination of the mixing device with a centrifugal machine, preferably for the production and application of concrete.

1 shows the mixing device on which the invention is based in a particularly advantageous embodiment, the mixing device being referred to below as mixing pear 1 because of its pear-shaped housing. Due to the pear-shaped housing and the streamlined guide element 2, which is held centrally in the rotationally symmetrical mixing bulb 1 by means of a plurality of fastening ribs 3, the mass or volume flow of the material component fuses with the the largest proportion in terms of quantity, which flows in at the inlet nozzle 4 at high speed and with air as the carrier medium, in such a way that an extraordinarily favorable ratio between the volume of material and the total volume is achieved within the mixing bulb 1.

In the lower part of the mixing pear 1, its radius of curvature becomes smaller, so that the partial mass or partial volume flows 5 collide in the region 6 and bring about the final mixing in a crash. The mixture of substances is then transferred to downstream facilities via the outlet nozzle 7.

So that the mass or volume flow is always maintained and there can be no stoppages and thus blockages, additional nozzles 8 can be arranged on corresponding parts of the mixing pear 1, via which additional air is blown in to accelerate the flow process. This is particularly necessary because for certain applications - for example for the production of high-strength, fast-setting concrete for lining tunnels - the mixing pear 1 must work without any problems in any spatial position.

The guide element 2 and also other parts of the mixing pear 1 which are not marked and are exposed to wear are provided with abrasion-resistant wear protection pads 9 which can be designed to be interchangeable or are made entirely of wear-resistant material. Even parts that only show greater wear over longer periods of time are built in such a way that they can be easily replaced with only minor interruptions in operation.

On the side of the actual mixing pear 1 there are inlet connections 10 for supplying the remaining material components which are to be mixed with the material component supplied via the inlet nozzle 4. In the case of concrete manufacturing The make-up water and the cement are supplied via the inlet nozzle 10 and premixed within these inlet nozzle before entering the actual mixing bulb 1.

In addition to the mixing pear, FIG. 2 also schematically shows the upstream process technology which is required for trouble-free, uniform and precisely metered concrete production. The aggregate as the largest proportion in terms of quantity of the later concrete is fed into a compressed air line 12 through a size-coordinated sluice device 11, the air as carrier medium conveying the aggregate via the feed line 13 to the inlet nozzle 4 of the mixing pear at high speed 1 forwards. The cement, in terms of quantity, is fed into the compressed air line 12 through a smaller, preferably similarly designed, sluice device 14 and passed on to the two inlet ports 10 via a feed line 15, which branches shortly before the mixing pear 1 at point 16. Since the aggregate has its own moisture, only the required amount of differential water may be supplied as additional water via line 17 to maintain an exact water-cement value, which is converted into a fine droplet mist in a correspondingly constructed nozzle 18 and transferred to the inlet nozzle 10 becomes.

Since the throughput of the mixing pear 1 has to be varied and adapted to the respective conditions in certain process sequences, for example in the manufacture of tunnel jacket shells made of concrete, it is necessary that the mass or volume flows of the aggregate, the cement and the make-up water can also be changed , however, regardless of the total amount of concrete produced, the mixing ratios must be observed exactly. For this purpose, either the infeed devices for the aggregate and the Cement designed to be sensitive or other control devices are present in the feed lines. The make-up water, the high pressure of which is generated by a corresponding pump, can be adjusted to the exact volume flow required in each case by control devices, also not shown. In addition to the devices for changing the mass or volume flow for the three material components, there are sensors with which the respective material flows can be measured. The sensors and the devices for changing the mass or volume flows are interconnected to form a complete, sensitive control system.

3 shows, for the advantageous exemplary embodiment according to FIG. 1, the technical details of the supply of the water, the cement-air mixture and the additional air required for acceleration, as well as the coincidence of the premixed mass or volume flow 19 from these components with the mass flow. or volume flow of the additive 20, which then together form the mass or volume flow 5. Cement and water are already premixed in a mixing vortex in the mass or volume flow 19 which is moved very quickly by the additional air used for acceleration. After the partial flows 19 and 20 meet, the mass or volume flow 5 is also a vortex flow, which serves for the further mixing of water, cement and aggregate. In order to favor the mixing processes, the flow rates are relatively high, so that the entire mixing process, i.e. the dwell time of the substances to be mixed in the mixing bulb 1 is less than one second.

On both sides of the water nozzle 18 there are supply nozzles 21 for blowing the cement-air mixture into the inlet nozzle 10, which envelop the water nozzle 18 in an arc. These nozzles can be arc-shaped flat nozzles 21 or consist of a number of smaller nozzles which are arranged on enveloping sheets on both sides of the water nozzle 18. To speed up the Cement, air and water existing volume flow in the inlet nozzle 10 are also arranged on both sides outside of the nozzle arrangement described above also arc-shaped air nozzles 22 which envelop the nozzle arrangement of water nozzle 18 and cement-air nozzles 21 and in another embodiment also from a number of smaller nozzles can exist, which are arranged on preferably two arcs.

FIG. 4 shows a section BB according to FIG. 3 through an inlet connector 10. This section shows the arrangement and shape of the individual nozzles for the supply of the additional water 18, for the supply of the cement-air mixture 21 and the supply of the additional air 22 recognizable for the embodiment in which the enveloping nozzles 21 and 22 are arcuate and the material supply to the nozzles takes place in an arrangement according to FIG. 3. The shape and mutual assignment of the nozzles 18, 21 and 22 produce a very rapidly flowing, turbulent, conically widening, flat volume flow 19 in which the extremely fine water droplets already mix with the cement particles and in which extensive cement moistening takes place before the mixing bulb 1 is reached.

5 and 5.1 show an embodiment of the nozzle arrangement according to FIGS. 3 and 4 which is particularly favorable in terms of production technology, in which, for reasons of cost-effective production, all the nozzles are combined in one nozzle block which - in order to easily clean the nozzles and protect the wear in to be able to exchange easily - is designed in two parts and is held together by fastening screws 23. For technical reasons, the supply opening 21 for the cement-air mixture is not curved, while the supply of the additional air required for the acceleration of the volume flow takes place via bores 22 arranged in an arc. The wear protection 24 for the cement feed nozzles can be opened when the nozzle is opened blocks can be easily replaced by loosening the screws 23. The nozzle block is attached to the inlet nozzle 10 by means of the fastening screws 25.

3, 4 and 5, a conical, cross-sectionally flat, rapidly moving volume flow is generated, which is fed through the inlet connection 10 of the mixing pear 1. In order to keep the proportion of the mist-shaped volume flow 19 consisting of a mixture of cement, make-up water and air, which comes into contact with the wall of the side inlet connection 10, as low as possible, the inlet connection 10 near the mixing pear is shaped as shown in FIG. 6 that it represents a wrapping of the volume flow 19 to a certain extent.

Fig. 6 shows a section A-A of FIG. 3 again. Those parts of the mist-shaped volume flow 19 which would come into contact with the wall of the inlet connection 10 are deposited there and would enter the mixing pear 1 as a liquid flow. The above-described shaping of the inlet connection 10 in the vicinity of the mixing pear 1 is intended to prevent this and, moreover, to cause the volume flow 19 consisting of a cement-water-air mixture to enter the mixing pear 1 and there with that from an additive. Air mixture existing volume flow 20 meets, still has its fog-like consistency. This ensures that the fast moving aggregate particles of the volume flow 20, which due to the fanning out have relatively large mutual distances from each other, from the mist, i.e. of cement milk, to be completely covered.

So that all volume flow parts of the aggregate-air volume flow 20 flowing through the mixing pear 1 are hit by the cement-additional water-air volume flow 19 the inlet nozzle 10 near the mixing pear 1 expanded so that its largest axis corresponds to the diameter of the mixing pear 1 at this point.

FIG. 7 shows an advantageous exemplary embodiment of the invention, in which an insert 26 is inserted into the lower part of the mixing bulb 1 in order to achieve a shape that is optimal for the respective application. In order to optimally design the impact of the partial streams in the crash point 6, and thus the mixing quality for each application, the guideways for the partial streams 5 can be changed by different inserts 26 in their surface and can thereby be adapted to the requirements of the respective mixing process. In addition, by using highly wear-resistant materials for the production of the insert 26, the frictional wear that occurs on the guideways due to the small radius of curvature in the lower part of the mixing pear 1 is reduced to a minimum.

Finally, FIG. 8 schematically shows the interaction of the mixing pear 1 with a centrifugal machine 27, the concrete emerging from the mixing pear 1 via the outlet opening 7 being passed axially into a known centrifugal wheel 28, which over the largest part of its circumference is enclosed with a circumferential housing strap 29. The concrete is accelerated in a form-fitting manner by the blades 30 of the rapidly rotating centrifugal wheel 28, discharged in a well-bundled jet 31 and transferred in a free throw to an application surface, for example a tunnel wall. The mixing pear 1 and the centrifugal machine 27 are combined to form a structural unit which can be arranged on a manipulator or a swiveling boom and guided along the tunnel wall.

Claims (19)

A process for the continuous mixing of several solid and / or liquid material components, the material components being fed to the mixing device in precisely metered quantities in continuous mass or volume flows, and the finished mixture being discharged from the mixing device in a continuous mass or volume flow, characterized in that the solid material components, individually or in suitable groups, are each given to a gaseous carrier medium and the mass or volume flows of the material components are then combined in such a way at a high flow rate in a mixing section that the mass or volume flow of the material component (or material components) has the largest quantity Proportion is first fanned out and the mass or volume flows of the other substance components to be mixed are then fed directly into this fanned out mass or volume flow, which is there after being merged like a crash and removed for further use. Method according to claim 1, characterized in that at least two mass or volume flows of the remaining substance components to be mixed are premixed before they are introduced into the fanned-out mass or volume flow. Method according to one of the preceding claims, characterized in that the substance mixture emerging from the mixing section is passed directly to a centrifugal device (27, 28) which accelerates the substance mixture and transfers it to its destination without a wire. Process for the production of concrete according to one of the preceding claims, characterized in that aggregate and cement are introduced into air streams with high metering accuracy, that the aggregate-air volume flow is fanned out, and that the volume streams cement-air and make-up water with large kinetic energy in the fanned-out aggregate air volume flow can be initiated. A method according to claim 4, characterized in that the amount of make-up water supplied is precisely matched to the continuously measured moisture content of the aggregate, so that the total amount of water always corresponds exactly to the predetermined water-cement value. Method according to one of the preceding claims 4 and 5, characterized in that in the event of interruptions to the mixing process which become operational at short notice, the supply of cement and aggregate is interrupted directly and the supply of make-up water and air is initially maintained around the mixing device immediately after the interruption in operation to clean automatically. A method according to claim 6, characterized in that water is additionally introduced into the mixing device (1) for cleaning. Mixing device for carrying out the method according to one of claims 1 to 7, characterized in that it is designed to be rotationally symmetrical and that in its axis of symmetry there is an inlet connection (4) for the mass or volume flow (20) of the substance component with the largest proportion and an outlet connection (7) for the finished mixture of substances, a flow divider (2) being arranged centrally within the mixing device (1), and at least two lateral inlet connections (10) for the Mass or volume flows of the other material components to be mixed are provided, which open into the mixing device (1) in the region of the end of the flow divider (2) facing the inlet connection (4). Mixing device according to claim 8, characterized in that it is pear-shaped, such that its radius of curvature on the output side is smaller than its radius of curvature on the input side. Mixing device according to one of claims 8 and 9, characterized in that the flow divider (2) is of streamlined design. Mixing device according to one of claims 8 to 10, characterized in that two lateral inlet connections (10) are provided, which are diametrically opposed and expand in width towards the mixing device (1) such that their width at their point of entry into the mixing device ( 1) whose diameter at this point corresponds. Mixing device according to one of claims 8 to 11, characterized in that acceleration nozzles (8, 22) are arranged in the inlet connection (10), in the mixing device (1) and in the outlet connection (7), from which a carrier medium with high kinetic energy emerges, in order to ensure a perfect flow through the mixing device (1) and the discharge of the mixed substances, as well as to avoid flow stoppages and blockages. Mixing device according to one of claims 8 to 12, characterized in that its parts and areas which are exposed to particular wear due to the impinging or flowing material flows have a special wear protection (9) have, and are designed such that the wear protection itself and / or the parts in question are easily replaceable. Mixing device according to one of claims 8 to 13, characterized in that an easily replaceable insert (26) is arranged on the bottom of the mixing device (1), the contour of which for the forwarding of the partial volume flows (5) to the desired mixing process and crash effect (6 ) is cut, and which is preferably made of highly wear-resistant material. Mixing device according to one of claims 8 to 14 for carrying out the method according to claim 4, characterized in that in each inlet connection (10) a high pressure nozzle (18) for injecting the make-up water and at least one flat nozzle (21) or a corresponding number of smaller nozzles for blowing in of the cement-air mixture is provided. Mixing device according to claim 15, characterized in that the high-pressure nozzle (18) is arranged centrally in the inlet connection (10) and is surrounded in a circular or approximately circular manner by the supply nozzles (21) for the cement-air mixture, and in that the supply nozzles (21 ) are arranged at a predetermined angle to the longitudinal axis of the high pressure nozzle (18). Mixing device according to claim 16, characterized in that the feed nozzles (21) are enveloped by likewise arcuate flat nozzles (22) or a number of correspondingly arranged smaller nozzles, through which air is additionally blown into the side inlet connection (10). Mixing device according to one of claims 15 to 17, characterized in that the formation and arrangement of all the nozzles (18, 21, 22) in the lateral inlet connection (10) form a flat, conically fanned, turbulent volume flow (19) for the make-up water and the cement - Generate air mixture. Mixing device according to claim 18, characterized in that the shape of the inlet connection (10) shortly before the mixing device (1) corresponds to the external shape of the volume flow (19).

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