EP4357013A1 - Method and colloidal mixer for the colloidal preparation of a suspension - Google Patents

Abstract

The invention relates to a method and a colloidal mixer 10 for the colloidal processing of a suspension, in particular processing of building materials, with a colloidal mixer in which at least one liquid is introduced into a mixing trough 12, at the lower area of which an outlet opening 22 with a mixing device 30 with a mixing rotor 32 is arranged, which is driven in rotation. According to the invention, at least one powdered solid component is introduced into the mixing trough, the at least one liquid mixed with the at least one powdered solid component by the rotatingly driven mixing rotor is set into a flow and is discharged from the mixing trough through the outlet opening, the mixture being returned for a certain time via a return line 40 to an upper area of the mixing trough for further mixing and, after reaching a desired mixing state, the mixture is discharged as a finished suspension from the outlet opening by means of a discharge line 50. According to the invention, it is provided that air is deliberately introduced into the at least one liquid and/or the mixture. is incorporated in a finely divided form, whereby a specific density of the liquid or mixture is reduced.

Description

The invention relates to a method for the colloidal processing of a suspension, in particular processing of building materials, with a colloidal mixer, in which at least one liquid is introduced into a mixing trough, at the lower area of which an outlet opening with a mixing device with a mixing rotor is arranged, which is driven in rotation, at least one powdered solid component is introduced into the mixing trough, the at least one liquid is mixed with the at least one powdered solid component by the rotatingly driven mixing rotor, set in a flow and discharged from the mixing trough through the outlet opening, the mixture being returned for a certain time via a return line to an upper area of the mixing trough for further mixing and after reaching a desired mixing state, the mixture is discharged as a finished suspension from the outlet opening by means of a discharge line, according to the preamble of claim 1.

The invention further relates to a colloidal mixer for the colloidal processing of a suspension, in particular for the processing of building materials and in particular for carrying out a method according to the invention, with a mixing trough which has an upper feed opening for feeding at least one liquid and at least one powdered solid component and a lower outlet opening, a mixing device which has a rotatingly drivable mixing rotor and is arranged in a lower region of the mixing trough, wherein the at least one liquid and the at least one powdered solid component are mixed to form a mixture by the mixing rotor and a flow of the at least one liquid or mixture can be generated towards the outlet opening, a return line which extends from the outlet opening back to the upper feed opening of the mixing trough, a discharge line for discharging a finished suspension from the mixing trough and a control valve device by means of which the return line and the discharge line can be opened or closed in particular alternately, according to the preamble of claim 7.

A colloidal mixer for the colloidal preparation of a suspension, especially for the preparation of building materials, is for example based on the EP 2 363 200 B1 out.

The suspensions produced with these colloidal mixers consist of one or more liquid components, usually water, and one or more mostly mineral solid components such as cement, bentonite, rock flour, fly ash, etc.

The use of such colloidally dissolved suspensions is applied in a wide variety of industrial sectors, such as special foundation engineering, mining, building renovation, tunnel construction, mining, exploration for mineral resources and much more.

Initially, continuous colloidal mixers were developed which could only process one liquid and one solid component.

These suspension mixers are mainly used in diaphragm wall construction, for the production of supporting fluids (bentonite suspension), but also for diaphragm wall suspensions in the single-phase diaphragm wall process.

Newly developed construction processes resulted in new requirements for suspension qualities. Suspensions made up of several liquid and solid components were also required.

This meant that the solids content in the mixture formulations exceeded the liquid content several times over, and suspension densities of 2 kg/dm ³ and above were required. The available batch mixing systems are ideal for this. their performance limits. In particular, so-called turbo mixers (mixing pumps) or circulation systems with Venturi nozzles are no longer able to produce these required suspensions in the required mixing quality reliably and economically.

Depending on the fineness of the grinding, powdered solids have a very large surface area and tend to form lumps (agglomerates) when wetted with liquid.

Depending on the loading condition of the mixing vessel and the density of the suspension already formed in the mixing system, these lumps begin to float on the surface of the suspension in the mixing vessel and are hardly or not at all broken down.

This leads to poor quality suspensions in which important rheological parameters are not achieved.

It is known that this undesirable situation can be reduced by installing additional rotating tools in the mixing container to break up these agglomerates. The disadvantage, however, is that the mixers are complex to construct and material accumulates on these additional tools in the form of incrustations, leading to extreme caking, particularly in the case of solids containing binders. This results in significantly higher cleaning and maintenance costs.

Another well-known method is to increase the circulation flow. This method increases the kinetic flow energy. This leads to a partial, but not complete, dissolution of agglomerates. The disadvantage of this is that part of the kinetic energy enters the suspension in the form of heat, which is undesirable in some cases and can have a negative impact on hydration, especially in the case of cement.

The invention is based on the object of specifying a method and a colloidal mixer with which a colloidal preparation of a suspension can be carried out particularly efficiently and economically.

The object is achieved on the one hand by a method having the features of claim 1 and on the other hand by a colloidal mixer having the features of claim 7. Preferred embodiments of the invention are specified in the dependent claims.

The method according to the invention is characterized in that air in finely divided form is deliberately incorporated into the at least one liquid and/or the mixture, whereby a specific density of the liquid or the mixture is reduced.

A basic idea of the invention is to specifically reduce the specific density of the liquid or mixture when producing the mixture by incorporating air in finely distributed form into the liquid or mixture. This means that powdery solids that are on the surface of the liquid or mixture sink faster and more reliably and thus no longer float on the surface of the liquid, especially if the mixture has an increased density due to additives. This causes comprehensive wetting of the powdery solid particles and they can be absorbed more quickly into the liquid/mixture and processed to form the colloidal suspension. Overall, a colloidal suspension with high mixing quality can be quickly produced in a particularly efficient manner without providing a large number of additional mixing tools. As the solid components sink more quickly, they reach the area of the mixing device earlier, which results in faster and better mixing. Conglomerates can be broken up efficiently.

The adjustment of the specific density of the mixture by incorporating air depends in each individual case on the recipe and on the liquid and solid components used. According to a further development of the invention, it is particularly advantageous that the specific density of the at least one liquid or mixture is reduced, whereby the volume of the liquid or mixture is increased by 2 percent to 15 percent by adding air. By incorporating air, a corresponding Increase in volume of the liquid or mixture. The specific density is set in such a way that solid particles on the surface of the liquid or mixture sink immediately or very quickly into it and can no longer be held back or can hardly be held back by the physical surface tension.

In principle, air can be incorporated in various suitable ways. In particular, an air supply device can be provided with which air can be introduced into the liquid or mixture in a finely distributed manner via one or more supply nozzles.

According to a further development of the invention, it is particularly advantageous that the return line has a mouth opening which is directed towards an inner side of the mixing trough, whereby the returned liquid or mixture impacts on the inner side. When the liquid flow impacts, the surface of the liquid increases and swirls, causing air from the surrounding atmosphere to be incorporated.

It is particularly advantageous that a return flow from the return line hits the inside of the mixing trough approximately perpendicularly. This flow guidance alone, with an impact on the inside wall of the mixing trough at approximately a right angle, can achieve the desired integration of air and a corresponding reduction in the specific density.

According to one embodiment of the invention, a particularly good integration of air is achieved in that a return flow from the return line is essentially divided into two partial flows when it hits the inside of the mixing trough, which flow in opposite directions along the inside of the approximately drum-shaped mixing trough. The mouth of the return line and the arrangement in relation to the inside of the mixing trough can be designed in such a way that the return flow is divided into approximately two equal partial flows, which then flow in the circumferential direction along the inside of the drum-shaped, preferably cylindrical, mixing trough. A first partial flow therefore flows clockwise along the inside of the mixing trough and a second partial flow flows in the opposite direction along the inside of the mixing trough.

The mixing trough can preferably have a diameter of between 1 meter and 2 meters and be designed to accommodate a batch of 1t to 3t of material/medium. Preferably 300l to 800l of liquid can be fed in at a feed rate of preferably 20 l/s to 100 l/s. The remaining material component, which depends on the recipe, is formed by one or more solid components, which are added via conveyor devices at a feed rate of preferably 10 kg/s to 20 kg/s. Smaller or larger diameters of the mixing trough for different batch sizes are also possible in principle.

According to a further embodiment of the invention, it is particularly advantageous that the two partial flows are generated at a flow rate such that the partial flows meet at a point in the mixing trough that is approximately opposite the outlet opening, forming turbulence. The two partial flows flow in opposite directions, approximately around half the inner circumference of the mixing trough, until both partial flows meet again and collide. Additional turbulence is formed in this area, with corresponding enlargements of the surface area of the partial flows. This promotes the further incorporation of air in finely distributed form into the respective liquid or mixture.

The liquid or mixture can then sink again within the mixing trough, the bottom of which is preferably conical, and sink to the mixing device with the rotating mixing rotor in the area of the outlet opening. The mixing paddles of the mixing rotor are preferably designed and driven in a rotating manner in such a way that cavities are formed in the liquid or mixture in a targeted manner, i.e. short-term cavities with negative pressure. This further supports the finely distributed incorporation of air and the wetting of the solid particles.

The rotating mixing rotor also works as a kind of pump, through which the mixture formed can be conveyed out of the outlet opening and returned via the return line to the upper area of the mixing trough for a further mixing and processing step. As soon as a desired mixing quality is reached, which is usually after one to two minutes, the return line can be closed and the finished mixture can be discharged from the mixing trough as a suspension via the outlet opening using a discharge line. The suspension thus formed can then be transported directly for further processing or for short-term interim storage. A further batch of suspension can then be formed by introducing at least one liquid and at least one powdered solid component.

The colloidal mixer according to the invention is designed to specifically incorporate air in finely distributed form into the at least one liquid or the mixture in order to reduce a specific density of the liquid or the mixture. The colloidal mixer according to the invention can be used in particular for carrying out the previously described method according to the invention. The previously described advantages can be achieved in this way.

An advantageous development of the colloidal mixer according to the invention is that the return line has a mouth opening which is directed towards an inner side of the mixing trough. The returned medium can hit a drum-shaped inner wall of the mixing trough at a flow speed which can be several meters per second, preferably 10 m/s to 20 m/s, whereby turbulence and a corresponding incorporation of ambient air occur.

Alternatively or additionally, according to an embodiment of the invention, it can be provided that an air supply device with at least one supply nozzle is arranged for injecting air into the liquid or mixture. The at least one supply nozzle can be provided at any suitable location on the colloidal mixer, in particular in a lower region of the mixing trough. Preferably, a plurality of supply nozzles can be provided, whereby ambient air can be injected under pressure in a finely distributed manner into the liquid or mixture, in particular in the region of the mixing rotor.

A further preferred embodiment of the invention consists in that the mixing rotor is arranged in a recess at the bottom of the mixing trough in front of the outlet opening. The mixing rotor with its radially directed mixing blades can be A corresponding design of the edges and surfaces of the mixing blades can create the desired turbulence and also cavities in the liquid or mixture. This achieves a particularly good mixing effect. Openings or perforations can be formed in the mixing blades of the rotor to further improve the mixing effect. At the same time, the mixing rotor can serve as a pump to suck in the liquid or mixture from the upper area of the mixing trough and transport it to the outlet opening at a predetermined flow rate.

According to one embodiment of the invention, it is particularly advantageous that the depression with the mixing rotor is arranged centrally or eccentrically on the bottom of the mixing trough to its central axis. A central arrangement of the depression with the mixing rotor to a central axis of the mixing trough leads to symmetrical flow conditions within the colloidal mixer. An eccentric arrangement of the mixing rotor to the central axis of the mixing trough can lead to an additional turbulence effect.

According to a preferred embodiment of the invention, particularly good mixing is achieved in that a rotor axis of the mixing rotor and a center axis of the drum-shaped mixing trough lie in a center plane of the mixing trough and that a return flow from the mouth opening of the return line strikes the inside of the mixing trough approximately parallel to the center plane.

The newly developed colloidal or suspension mixer can have a dispersion zone, the actual colloidal mixing device, in which the breakdown of the components takes place, and a convection zone that holds the actual batch volume, the so-called mixing container. These two zones can be designed in different cylindrical diameters and are preferably connected to one another via an asymmetrical cone.

The dispersion zone can have a tangential outlet, which can be connected, in particular by means of a connected Y-piece, to a return or circulation line to the convection zone and to an emptying line. Both outlets on the Y-piece can preferably be closed and controlled by means of a pneumatic pinch valve depending on the operating state.

The mixing device contains a rotating rotor with special mixing paddles, also known as mixing blades. This rotor, preferably driven by a three-phase motor with a toothed belt drive, describes a circular movement at a defined peripheral speed. This leads to the transmission of movement and power and thus to the acceleration of the liquid or liquefied components in the mixer (such as water, powdered solids).

The following operating states can be set as examples:

Operating mode Mixing

The rotor rotates and the components are accelerated. The pinch valve of the circulation line is open, while the pinch valve of the discharge or emptying line is closed. A defined circulation of the liquid medium in the system takes place.

Operating state Emptying

The rotor rotates and the components are accelerated. The pinch valve on the return or circulation line is closed and the circulation is stopped. The pinch valve on the discharge line is opened. The liquid medium in the system is pressed into the discharge line and discharged from the mixing system.

The colloidal mixer preferably has a cover structure with various inlet openings for liquids, solids, additives and, among other things, for the circulation line. A so-called deflection pipe can be attached to the outlet opening for the circulation line.

In the mixing operating mode, the mixing medium circulates between the mixer and the mixing tank preferably in a defined volume flow of up to 200 m ³ /h. The deflection pipe, which is installed at a defined position and inclination, can divide the volume flow into two partial flows of approximately equal size. This is done by deflecting the volume flow to the cylindrical wall of the mixing tank. The two partial flows move in opposite directions along the cylindrical wall of the mixing tank and meet opposite the deflection pipe.

The meeting of the two partial flows now causes the backflow to continue in the middle of the mixing tank above the inlet of the mixer and the suction of the mixing medium by the mixer is promoted.

At the beginning of each mixing batch, water is preferably dosed into the mixing system as a liquid component. During the water dosing, the mixing system may already be in the mixing mode. This means that from the beginning, the circulation described above occurs from a certain fill level. Since the resulting volume flow hits the liquid level from above, a lot of air is now drawn into the liquid (water) and fed to the mixer by the resulting flow.

Due to the high currents, the air cannot escape and now passes through the mixer (dispersion zone) together with the dosed water.

Since the mixer generates cavitation due to its technical design, which was determined using a high-speed camera, the air in the water is distributed particularly finely. This effect helps to artificially reduce the specific density of the dosed water. This takes place for all mixture components during the entire mixing and dosing process.

Evidence of this effect can be seen in the fact that the water in the mixing system becomes cloudy and milky. If the mixing system is switched off, the water is immediately or very quickly deaerated, countless tiny air bubbles rise and the water becomes clear again in no time.

If powdered mineral solid is added as a further dosing step, the solid can sink more quickly in the water and is thus more easily sucked into the mixer (dispersion zone).

The cavitation acting in the colloidal mixer ensures that every single solid particle is wetted with water and can thus be broken down almost optimally. A large positive effect in terms of the dosing of mineral solids can also be seen. Cavitation is caused by the negative pressure generated behind the mixing blades, in which the liquid evaporates, creating vapor bubbles. When these enter a zone of lower pressure, the Steam returns and the volume is reduced significantly. This creates a short-term, extreme pressure difference with the environment, so that agglomerates of solid particles in particular are sucked into the resulting cavity and broken down. This enables and/or improves the wetting of the individual solid particles with liquid and ensures a particularly homogeneous mixture.

All mineral solids tend to form agglomerates (lumps) when dry due to storage or mechanical influences. Furthermore, mineral solids usually have a bulk density of around 1kg/dm ³ . Due to this technical fact, solid agglomerates would float on the water surface and would be difficult to influence by currents or mechanically break down into their individual particles. By reducing the density of the water according to the invention, the floating of these solid agglomerates is completely prevented or at least significantly reduced.

The solids and the agglomerates contained therein are thus specifically fed into the dispersion zone and are broken down there very efficiently.

Due to the high circulation capacity in the mixing system, this also ensures that the entire batch content, consisting of water and solids, passes through the dispersion zone several times, thus ensuring very good homogenization.

An advantageous embodiment of the colloidal mixer according to the invention is that the mixing rotor has mixing blades which are provided with a hole pattern. The mixing blade is preferably formed from a base sheet, wherein several through holes are introduced into the base sheet through the hole pattern, preferably by machining, (laser) cutting or punching. The holes of the hole pattern can preferably have a circular contour in whole or in part. The holes can have a diameter between 5 mm and 50 mm and can be arranged in particular in a grid with a uniform grid spacing. Other hole sizes and in particular other hole contours, such as square or polygonal, are possible.

The hole pattern in the mixing blades results in a significant increase in the effective flow edges on the mixing blade. This increases the turbulence effect and in particular the formation of a large number of relatively small cavities. Preferably, the hole pattern with the through holes can form a total opening area which accounts for between 25% and 35%, particularly preferably between 26% and 28%, of the total area of the mixing blade. Here, the ratio of the effects of the flow edge length to the flow resistance is most favorable. The holes are located in particular in the lower approx. 65%, preferably 62% to 66%, of the blade height. The dimensions of the mixing blades are based on the dimensions of the recess or receptacle in the mixer, with the edge of the mixing blades running as close to the wall as possible. The mixing blade can preferably be approximately rectangular and in particular have a width of 50mm to 400mm and a height of 150mm to 700mm. Other dimensions are possible depending on the shape of the mixer.

Another positive effect is that the change in flow resistance reduces the energy required to rotate the mixing rotor at a given speed. This means that the mixing and homogenization effect of the colloidal mixer can be improved with a reduced energy requirement. The mixing rotor can preferably be driven at a speed of between 100 rpm and 800 rpm. Deviations are possible depending on the recipe of the mixture.

The mixer and/or the mixing blades can preferably be formed with a durable stainless steel, in particular a Hardox material.

Fig. 1

eine Seitenansicht eines erfindungsgemäßen Kolloidalmischers;

Fig. 2

eine Querschnittsansicht durch einen erfindungsgemäßen Kolloidalmischer nach Fig. 1;

Fig. 3

eine Draufsicht auf den Kolloidalmischer von Fig. 1, jedoch ohne Deckel;

Fig. 4

eine vergrößerte Darstellung eines Mischblattes in Seitenansicht mit einem Lochbild;

Fig. 5

eine Frontalansicht des blechförmigen Mischblattes von Fig. 4;

Fig. 6

eine vergrößerte Darstellung des Details A von Fig. 4; und

Fig. 7

eine vergrößerte Darstellung des Details B von Fig. 4.

The invention is described in more detail below with reference to a preferred embodiment which is shown schematically in the accompanying drawings. In the drawings:

Fig.1

a side view of a colloidal mixer according to the invention;

Fig.2

a cross-sectional view through a colloidal mixer according to the invention Fig.1 ;

Fig.3

a top view of the colloidal mixer of Fig.1 , but without lid;

Fig.4

an enlarged view of a mixing blade in side view with a hole pattern;

Fig.5

a front view of the sheet-like mixing blade of Fig.4 ;

Fig.6

an enlarged view of detail A of Fig.4 ; and

Fig.7

an enlarged view of detail B of Fig.4 .

In the Figures 1 to 3 an embodiment of a colloidal mixer 10 according to the invention is shown with a drum-shaped mixing trough 12, which is arranged on a frame 11. The drum-shaped mixing trough 12 has a cylindrical inner side 13 or inner wall in its upper area and is closed off at its top with a lid 14. A lower section of the mixing trough 12 is formed by a conical base 16, which passes via an opening into a downwardly directed receptacle or depression 20 with a mixing device 30. The opening with the depression 20 is arranged eccentrically to a center axis of the cylindrical upper area of the mixing trough 12, as can be clearly seen from Fig.3 emerges.

The mixing device 30 in the recess 20 on the underside of the mixing trough 12 has a rotatingly driven mixing rotor 32 with a rotor hub 33 and radially directed mixing blades 34 attached to it. The mixing rotor 32 with the mixing blades 34 is designed overall in such a way that at least one liquid component introduced into the mixing trough 12 is mixed with at least one powdered solid component fed into the mixing trough 12 by the rotating mixing rotor 32. A peripheral speed of the mixing rotor 32 is set in such a way and the shape of the mixing blades 34 is designed in such a way that cavities are formed in a targeted manner in the at least one liquid or the mixture being formed, which cavities further support a mixing effect and a fine distribution of air.

The rotating mixing rotor 32 discharges the at least one liquid or the mixture being formed to a lateral outlet opening 22 with a Y-pipe section 24, on the two outlet nozzles of which a return line 40 and a discharge line 50 are arranged. An adjusting device 38 can be used to control whether the mixture formed is returned to the mixing trough 12 via the return line 40 to continue the mixing process or is discharged from the colloidal mixer 10 via the discharge line 50.

To form the actuating device 38, a first pinch valve 42 is arranged on the return line 40 and a second pinch valve 52 is arranged on the discharge line 50, which can be closed or opened in particular by supplying a pressure medium, in particular compressed air.

If the first pinch valve 42 is opened and the second pinch valve 52 is closed, liquid or mixture is led from the Y-pipe section 24 via the return line 40 through a feed opening 15 in the cover 14 back into an upper area of the mixing trough 12, as clearly shown in the Figures 2 and 3 is shown.

The free end of the return line 40 has a deflection pipe or a mouth opening 44 which is directed towards the inner side 13 of the mixing trough 12. When the liquid or mixture which emerges from the mouth opening 44 impacts on the inner side 13 of the mixing trough 12, ambient air is incorporated into the liquid or mixture in a finely distributed manner. This is supported by the fact that the return flow is divided into two partial flows by the orientation of the mouth opening 44, which flow in opposite directions along the inner side 13 of the mixing trough 12 in the circumferential direction. At a flow speed of several meters per second, the partial flows can thus meet again in an opposite area on the inner side 13 of the mixing trough 12, with additional air being incorporated into the liquid or mixture through additional turbulence.

The incorporation and fine distribution of the air is, as already described above, further achieved by the rotating movement of the mixing rotor 32 with the mixing blades 34. increased. The mixing process can preferably last between 100 seconds and 200 seconds.

After the desired consistency or homogeneity of the mixture has been achieved, the first pinch valve 42 on the return line 40 can be closed and the second pinch valve 52 on the discharge line 50 can be opened. In this way, the fully formed mixture or suspension is discharged from the outlet opening 22 via the discharge line 50 from the colloidal mixer 10 by the pumping action of the mixing device 30.

After emptying the mixing trough 12, another mixing process for a new batch can be started.

In the Figures 4 to 7 a possible embodiment of a mixing blade 34 is shown, which can be used on a mixing rotor 32 of a mixing device 30 of the previously described colloidal mixer 10. For fastening the mixing blade 34 to a rotor hub 33 of the mixing rotor 32, fastening elements 37 are shown schematically on one fastening side. These serve for the detachable fastening of the mixing blade 34 to the rotor hub 33. In Fig.6 Detail A with fastening element 37 is made of Fig.4 shown in more detail.

The mixing blade 34 is formed from a base sheet 35 with a thickness d, as can be clearly seen from Fig.5 The thickness d can be between 3 mm and 20 mm. In the actual mixing area of the mixing blade 34, a hole pattern 36 with a large number of through holes is formed. The side surfaces of the mixing blade 34 can be surface-treated.

The diameter of the through holes can be between 5 mm and 50 mm. The material webs between the through holes can be a few mm in size. Overall, the hole pattern 36 with the through holes can form a total opening area which makes up between 40% and 80% of the total area of the mixing blade 34.

In Fig.7 a partial area of the hole pattern 36 is shown in more detail, wherein the hole pattern 36 is formed from a plurality of through holes arranged in rows next to one another in a grid. Between the through holes remain Grid or material webs with corresponding flow edges, which ensure good turbulence and a particularly finely distributed formation of cavities over the surface of the mixing blade 34. In principle, a web width between the holes can be between 10% and 40%, preferably between 16% and 33%, of the hole diameter. A sheet thickness can be between 20% and 75%, preferably between 33% and approximately 66%, of the hole diameter. The hole diameter is preferably between 10 mm and 20 mm, particularly preferably around 12 mm.

According to Fig.7 a lower corner area of the mixing blade 34 can be chamfered or angled.

Claims (13)

Method for the colloidal processing of a suspension, in particular processing of building materials, with a colloidal mixer (10), in particular according to one of claims 7 to 12, in which - at least one liquid is introduced into a mixing trough (12), at the lower region of which an outlet opening (22) with a mixing device (30) with a mixing rotor (32) is arranged, which is driven in rotation, - that at least one powdered solid component is introduced into the mixing trough (12), - the at least one liquid is mixed with the at least one powdered solid component by the rotating mixing rotor (32), set into a flow and discharged from the mixing trough (12) through the outlet opening (22), - wherein the mixture is returned for a certain time via a return line (40) to an upper region of the mixing trough (12) for further mixing and - after reaching a desired mixing state, the mixture is discharged as a finished suspension from the outlet opening (22) by means of a discharge line (50), characterized by
that air in finely distributed form is deliberately incorporated into the at least one liquid and/or the mixture, whereby a specific density of the liquid or the mixture is reduced. Method according to claim 1,
characterized,
that the specific density of the at least one liquid or mixture is reduced, wherein the volume of the liquid or mixture is increased by 2 percent to 15 percent by the addition of air. Method according to one of claims 1 or 2,
characterized,
that the return line (40) has an opening (44) which is directed towards an inner side (13) of the mixing trough (12), wherein the returned liquid or mixture impacts on the inner side (13). Method according to claim 3,
characterized,
that a return flow from the return line (40) strikes the inner side (13) of the mixing trough (12) approximately perpendicularly. Method according to claim 3 or 4,
characterized,
that a return flow from the return line (40) is essentially divided into two partial flows upon impact on the inner side (13) of the mixing trough (12), which flow in opposite directions along the inner side (13) of the approximately drum-shaped mixing trough (12). Method according to claim 5,
characterized,
that the two partial flows are generated with a flow velocity such that the partial flows meet, forming turbulence, at a point in the mixing trough (12) which is approximately opposite the outlet opening (44). Colloidal mixer for the colloidal preparation of a suspension, in particular for the preparation of building materials and in particular for carrying out a method according to one of claims 1 to 6, with - a mixing trough (12) having an upper feed opening (15) for feeding at least one liquid and at least one powdered solid component and a lower outlet opening (22), - a mixing device (30) which has a rotatingly drivable mixing rotor (32) and is arranged in a lower region of the mixing trough (12), wherein the at least one liquid and the at least one powdered solid component are mixed to form a mixture by the mixing rotor (32) and a flow of the at least one liquid or the mixture can be generated towards the outlet opening (22), - a return line (40) which extends from the outlet opening (22) back to the upper feed opening (15) of the mixing trough (12), - a discharge line (40) for discharging a finished suspension from the mixing trough (12) and - a control valve device (38), by means of which the return line (40) and the discharge line (50) can be opened or closed, in particular alternately, characterized,
that the colloidal mixer (10) is designed to deliberately incorporate air in finely distributed form into the at least one liquid or the mixture in order to reduce a specific density of the liquid or the mixture. Colloidal mixer according to claim 7,
characterized,
that the return line (40) has an opening (44) which is directed towards an inner side (13) of the mixing trough (12). Colloidal mixer according to claim 7 or 8,
characterized,
that an air supply device with at least one supply nozzle for injecting air into the liquid or mixture is arranged. Colloidal mixer according to one of claims 7 to 9,
characterized,
that the mixing rotor (32) is arranged in a recess (20) on the bottom (16) of the mixing trough (12) in front of the outlet opening (22). Colloidal mixer according to claim 10,
characterized,
that the recess (20) with the mixing rotor (32) is arranged centrally or eccentrically on the bottom (16) of the mixing trough (12) to its central axis. Colloidal mixer according to one of claims 7 to 9,
characterized,
that a rotor axis of the mixing rotor (32) and a center axis of the drum-shaped mixing trough (12) lie in a center plane of the mixing trough (12) and that a return flow from the mouth opening (44) of the return line (40) strikes the inside (13) of the mixing trough (12) approximately parallel to the center plane. Colloidal mixer according to one of claims 7 to 12,
characterized,
that the mixing rotor (32) has mixing blades (34) which are provided with a hole pattern (36).

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