EP0110941B1 - Method for mixing a plastic containing concrete to be sprayed in a mixing tube and mixing tube for implementing such method - Google Patents

Abstract

In the method for mixing dry material with water, particularly concrete, for its projection, the material is axially fed to a projection device, the projection air and water and supplied transversally to the injection channel (34). Optionally, a second injection channel (35) is provided for compressed air.

Description

The invention relates to a method for mixing a plastic-containing dry sprayed concrete according to the preamble of patent claim 1 and to a mixing tube according to the preamble of patent claim 6 or 8 which is used in particular to carry out this method.

In the method known from DE-A-31 36 737 for mixing a plastic-containing shotcrete during dry concrete spraying, inadequate mixing of the dry substance with the water supplied from the side and the synthetic resin emulsion also supplied from the side is achieved. When spraying plastic concretes dry, the proportion of synthetic resin and the proportion of water must be regulated interdependently, for example in order to be able to spray a concrete rich in synthetic resin, for example, during renovation work, which has a higher adhesiveness and possibly a water barrier capacity, and then, but fresh on fresh, then a lower synthetic resin To be able to apply dry shotcrete. It is always tried to keep the amount of resin added as low as possible, because the resin is relatively expensive. Due to the different viscosities of water and synthetic resin emulsion, it has proven difficult to achieve the same mixing quality of the mixture of synthetic resin emulsion and water supplied at the side as with a relatively synthetic resin-rich mixture with a synthetic resin and water mixture low in synthetic resin. For the latter, the injection channels would have a larger internal cross-section than for the low-resin mixture, so that a comparable outlet pressure from the injection channels is achieved and so that the mixing is qualitatively equivalent to a relatively low-resin mixture.

From the aforementioned DE-A-31 36 737 a mixing tube for concrete dry spraying is also known, which has two axially spaced sets of injection channels, each starting from an annular space and each having an outlet opening on the inner wall of the spray nozzle. The two sets of injection channels are arranged at an axial distance from one another which is greater than half the total axial length of the mixing tube. The first set of injection channels at the front in the conveying direction is intended for the supply of plastic emulsion, while the second set of injection channels is intended for the supply of water.

Due to the predefined internal cross sections of the injection channels, a sufficiently deep injection of water or synthetic resin emulsion into the dry mixture stream and thus homogeneous mixing is no longer achieved if the amount of liquid added per unit time is below a certain threshold value. In addition, sufficient mixing of water and synthetic resin emulsion is not achieved.

Proceeding from this, the object of the invention in terms of the process is to improve the known process for mixing a plastic-containing shotcrete in such a way that a uniform mixing of dry mixture, synthetic resin emulsion and water is achieved regardless of the respective addition amounts. In terms of the device, the object of the invention is to improve the known mixing tube in such a way that the more uniform mixing of dry mixture, synthetic resin emulsion and water is achieved.

This object is achieved with regard to the method by the features specified in claim 1 and with regard to the mixing tube by the features of claims 6 or 8.

Further features of the invention are the subject of dependent claims 2 to 5, 7 and 9.

According to the invention, it is possible to achieve thorough mixing regardless of the amount of water or amount of synthetic resin emulsion added. The negative impact on the mixing result of water pressure and water quantity or pressure of the synthetic resin emulsion and their quantity in the known mixing method or the known mixing tube is excluded because the mixing of water and synthetic resin emulsion takes place in advance and the mixing of this mixture with the dry mixture mainly through which compressed air is reached. The liquid mixture is entrained by the compressed air and transported, so to speak, that it can penetrate deep enough into the dry mixture flow and sufficient mixing is achieved.

The influence of the compressed air fed in from the side on the mixing process can be deduced from this and the excellent mixing of compressed air and liquid fed in from the side can be seen from the fact that when the mixing tube is operated without dry flow, to which only compressed air and, for example, water are fed laterally, there is before the outlet end of the mixing tube a tail of about 1 m in length (depending on the operating parameters) of finely divided water. Individual water droplets are no longer recognizable, rather a water mist is formed from finely atomized water droplets. This very fine atomization of the water is a good prerequisite for an excellent mixing result of the water with the dry mixture.

The advantages of the mixing process according to the invention become clear by comparison with the properties of the known Procedure. This is dealt with in the following:

1. The material stream mixed according to the invention is mixed more homogeneously and moistened more uniformly than the stream mixed according to the known method. In the latter, stripes are often seen laterally in the jet cone, the lower area of the jet cone is typically more thoroughly mixed than the upper area. In contrast, layers of this type cannot be seen in the method according to the invention, which indicates better mixing and more uniform moistening.

2. In the known mixing process, the application thickness to be applied in one operation is approximately 3 to 4 cm for vertical surfaces. Due to the forced and much better mixing, application thicknesses which are significantly above these values, for example 20 cm, are achieved in the method according to the invention. It is no longer necessary, as in the conventional method, to work in several layers for larger thicknesses.

3. The rebound is relatively high in the known mixing process and is known to consist mainly of aggregates, so that the rebound quantity means not only a loss of material, but also must be taken into account in the composition of the finished product, since the proportions of the individual substances in the Dry mix are different than in the applied material. The rebound can be significantly reduced in the process according to the invention, it is considerably below the values given for the known process. This saves material on the one hand, but on the other hand the mixing ratio of the finished product can be specified more precisely. Due to the much better mixing of the liquid mixture and the dry mixture, the risk is avoided that material that is too dry gets onto the application surface, where it can rebound, but at least causes an unevenness in the finished spray product. Areas that are too damp and could slip or drip are also avoided.

4. In the case of the mixing tubes operating according to the known mixing method, irregularities in the material flow emerging from the mixing tube are frequently found, and this emerges in packets, that is to say in the form of strands or plugs. The dry mix is not evenly supplied to the mixing tube by the dry spraying machine used, because the machine mostly works discontinuously. The nozzle operator feels the uneven material flow as pneumatic impacts, i.e. as recoil. Surprisingly, these pneumatic impacts are reduced in the mixing process according to the invention, the spray jet is much more uniform and does not cause any recoil on the mixing tube.

5. In the mixing process according to the invention, the water addition can be significantly less than in the conventional process, which improves the water cement value which is decisive for the finished product. Because of the significantly improved mixing, the addition of water no longer has to be based on the fact that the partial stream lying in the upper jet region, which in the known mixing process is less humid than the areas below it, is sufficiently wetted.

6. Due to the better mixing, the dust generated by the dry spray process is better bound, so the nozzle guide breathes less dust.

7. In the conventional method, splash shadows are observed behind reinforcements and nests in corners. Both could be caused by material that is too dry, as well as by rebounding of the material. Surprisingly, these effects do not occur in the mixing process according to the invention.

In the mixing tubes according to the invention, liquid mixture and compressed air flow from separate channels into a common mixing area. This mixing area can be located in the interior of the mixing tube or directly on its inner wall (hereinafter referred to as V-mixing tube), or it can be separated from the interior, in this case the mixed product of compressed air and liquid mixture flows through common injection channels into the interior of the mixing tube (in called the following Y mixing tube). In the case of the V mixing tube, due to the very closely adjacent outlet openings of the injection channels for liquid mixture and compressed air, the compressed air influences the outflow of the liquid mixture from the first injection channels and entrains the water escaping there, so that sufficient mixing occurs regardless of the intensity of the liquid jet of dry mix and water is reached. The compressed air jets emerging from the second injection channels cause an intensive swirling of the dry mixture flow, which also improves mixing.

When steel fibers are added, the rebound on steel fibers is significantly reduced in the process according to the invention, and no hedgehog formation of the steel fibers could be observed.

Further advantages of the invention result from the following description of four exemplary embodiments for mixing tubes, which are not to be understood as restrictive. For this purpose, reference is made to the drawing, in which show:

1 shows an axial section through a Y mixing tube with premixing of air and water in an annular space,

2 shows an axial section through a Y-mixing tube corresponding to FIG. 1, but with premixing in the injection channels,

Fig. 3 shows an axial section of a V-mixing tube with first injection channels for water and second injection channels for compressed air, and

Fig. 4 shows an axial section of a mixing tube with premixing of air and water before the first injection channels and with second injection channels for compressed air (combination of Y and V mixing tube).

The mixing pipes for the concrete dry spraying shown in the drawing essentially consist of a tubular part, hereinafter called main piece 20, which has an end region 22 for the connection of a delivery line 24 and an end region opposite this on the axis 26 of the mixing pipe, which is the outlet end 28 forms. As shown in FIG. 1, the arrangement is such that the clear cross-section for dry mixture 30 conveyed in thin stream in the conveying line 24 practically does not change, only in the region of the outlet end does the main piece 20 converge slightly. An overall nozzle effect is therefore not sought.

A distributor ring 32 is screwed tightly into the main piece 20. In the exemplary embodiment according to FIG. 1, it has two sets of injection channels 34, both of which are V-shaped to one another and run at an angle of + 60 ° or -60 ° to the axis 26. Each set has a total of twenty injection channels 34, which end in the interior 36 of the mixing tube.

The other end of the injection channels 34 is located in an annular space 38, which serves as a mixing chamber in the exemplary embodiment according to FIG. 1. It is connected to a water annulus 42 via a plurality of water channels 40 and also to an air annulus 46 via a plurality of air channels 44 distributed over the circumference. These two annular spaces 42, 46 serve as a supply line and storage for water and air, they make it possible to supply water or air via a single external supply line. They are used to distribute the air or water. The water annulus 42 is connected via a bore 48 to a water connection 50, a controllable valve 52 is interposed. The air annulus 46 is connected to an air supply line 58 via a bore 54 and a controllable valve 56.

In practical operation, the water under a pressure of, for example, 6 bar in the water annulus 42 flows through the many water channels 40 into the annulus 38, where it meets a large number of compressed air jets. These come from the air annulus 46, which is under a pressure of slightly more than 6 bar, via a plurality of air channels 44. These water jets occur approximately transversely to the direction of the injection channels 34, whereby an additional swirl is achieved. In contrast, the compressed air jets flow into the annular space 38 approximately in the exit direction of the injection channels 34.

If necessary, a jet splitter, a sharp edge or a sieve can be provided in the annular space 38 and in the exit direction of the water channels 40 in order to mechanically support the destruction of the water. The shape of the annular space is chosen so that an optimal mixing of water and air is achieved in it. The diameter of the injection channels 34 is somewhat larger than in the known mixing tube, because additional air has to be let through. Instead, however, the number of injection channels 34 can be greatly increased compared to the known mixing tube. The annular spaces 42 and 46 are delimited to the outside by a union sleeve 60, which is screwed onto the main piece 20.

In contrast to the exemplary embodiment according to FIG. 1, the mixing process in the exemplary embodiment according to FIG. 2 does not take place in a special mixing space (annular space 38), but in the injection channels 34. The annular space 38 now serves as a water annular space and is connected directly to the interior 36 of the mixing tube via the injection channels 34. Its connection to the outside takes place via a bore 48 which merges into the valve 52 and the water connection 50 (not shown). As in the exemplary embodiment according to FIG. 1, the injection channels are formed in a distributor ring 32, they are approximately 60 ° to the axis 26 in the conveying direction. To form the air channels 44, a groove 62 is machined into the distributor ring 32 from the outlet end 28, which cuts all the injection channels 34. It communicates with air channels 44 which, like the water channels 40 in the exemplary embodiment according to FIG. 1, are formed and open into the air annulus 46.

Overall, in the exemplary embodiment according to FIG. 2, the premixing according to the invention between air and water takes place where the groove 62 intersects the individual injection channels 34.

Instead of the embodiments shown in FIGS. 1 and 2, the premixing according to the invention between air and water can also take place in the area of the water channels, the bore 54 or even further outside. The known mixing tube of the type mentioned at the outset can be converted, for example, to the premixing of air and water according to the invention by injecting compressed air into the (externally visible, curved) water supply line.

Although it is preferred according to the invention to supply the air or water under pressure, the suction effect of an air or water stream can also be used to suck in the other partner required for the premixing, such as the air-water mixing, for example in the case of outlet screw connections from Taps is reached.

A distributor ring 32 is also provided in the exemplary embodiment according to FIG. 3, but this has In addition to the first injection channels 34, second injection channels 35, which run in a V-shape with respect to one another, open into the interior 36 of the mixing tube with a common outlet hole 37, which are each arranged in the same axial position and are equally spaced over the circumference of the distributor ring 32, so that each Set of injection channels 34, 35 has twenty individual channels. To be more precise: Each injection channel 34 of the first set is assigned an injection channel 35 of the second set, that is to say for compressed air. Instead of a common outlet hole 37, there may also be a certain distance between the outlet openings of the injection channels 34, 35 arranged in pairs, but the distance should be at most one millimeter, at most two millimeters.

In the distributor ring 32, two annular circumferential, essentially square recesses are provided which, together with the recessed inner wall of the main piece 20, delimit two annular spaces, namely a water annular space 42 and an air annular space 46. The annular spaces 42, 46 serve for the uniform supply of the individual injection channels 34, 35 with water or compressed air and make it possible that only a water connection 50 and an air supply line 58 are necessary.

In practical operation, the water under a pressure of, for example, 6 bar in the water annulus 42 flows through the many first injection channels 34 into the interior 36 of the mixing tube. At the same time, compressed air, which is at a comparable pressure, flows out of the air annulus 46 via the second injection channels 35 into the interior 36. Because of the closely adjacent outlet opening, in FIG. 1 in the form of a common outlet hole 37, it acts at an acute angle Compressed air jet flowing out water jet onto the water jet and causes suction in the area of the first injection channels, whereby the water is additionally conveyed. In particular, the compressed air jets from the second injection channels 35 create a swirl zone through which the dry mixture 30 flowing in is swirled strongly.

In contrast to the exemplary embodiment according to FIG. 3, which shows a pure V mixing tube, a combination of a V and a Y mixing tube is shown in the exemplary embodiment according to FIG. However, the structure is fundamentally similar to the exemplary embodiment according to FIG. 1, only the distributor ring is axially longer and has a total of three annular circumferential recesses, which here, together with the inner wall of the main piece 20, have an air annular space 46 from left to right limit the mixture of air and water serving annular space 38 and a water annular space 42. This water annulus 42 is in turn connected to a water connection 50 via a bore 48. The water flow can be regulated via a valve 52. However, the water annulus 42 is not the starting point of the first injection channels 34 as in the exemplary embodiment according to FIG. 3, but the water first flows into the annulus 38 via water channels 40, which are designed as axial grooves cut into the outer wall of the distributor ring 32.

The air annulus 46 is also connected to an air line 58 via a bore 54 and a controllable valve 56. From it, compressed air can flow directly into the interior 36 via the second injection channels 35, but in addition air channels 44 are also provided, which are also designed as axial grooves and pass through the compressed air into the annular space 38. As a result, compressed air and water mix in the annular space 38, and the mixture flows through the first injection channels 34 into the interior 36. Because of the close proximity between the outlet openings of the injection channels 34, 35 arranged in pairs, the above-described interaction occurs. The additional feeding of compressed air into the first injection channels, which corresponds to the Y arrangement, has particular advantages when spraying plastic-containing concrete.

Surprisingly, particular advantages of the nozzles described above have been found when adding concrete additives, in particular quick binders to ready-mixed concrete. If ready-mixed concrete is applied to inclined surfaces, for example embankments, it is practically unavoidable that the still moist material will slip. Usually, a quick binder is added to the ready-mixed concrete, which, however, significantly reduces the quality of the concrete. Due to the use of a nozzle according to the application in a ready-mixed concrete delivery line and for the admixing of quick binders, an excellent mixing and thus the lowest possible addition of quick binders could be achieved, so that the reduction in the concrete quality could be kept within limits.

The mixing tubes according to the invention are characterized by simple handling, that is, low demands on the user.

In practical tests, mixing tubes without constrictions, i.e. without a nozzle effect, have proven particularly useful. However, the use of the premixing of water and air according to the invention and for constricted mixing tubes is expressly not to be excluded. In particular, discharge funnels, such as a Laval nozzle diffuser, also show improvements in the jet characteristics, for example in the case of special mixtures, such as those used in mining.

Claims (9)

1. A method for mixing a plastics-containing concrete to be sprayed in a mixing tube, wherein a dry concrete mixture flowing axially through the mixing tube is mixed upstream of the outlet from the mixing tube with an artificial resin emulsion and with water and mixed thoroughly, the artificial resin emulsion and the water flowing through a plurality of injection channels arranged transverse to the axial direction of the mixing tube and the ratio of artificial resin emulsion and water being adjustable, characterised in that the artificial resin emulsion and the water are mixed, that this mixture flows through the first injection channels (34), that compressed air is fed via additional second channels (35, 44) discharging in the immediate vicinity of each of the first injection channels (34), or in a common outlet aperture (37) or in a respective first injection channel (34) upstream of a common outlet aperture (37) and that the compressed air stream and the mixture of artificial resin emulsion are adjustable independently of one another.

2. A method according to claim 1, characterised in that where compressed air is admixed to artificial resin emulsion and water upstream of the outlet from the injection channels the premixing of air and water occurs in the injection channels or in an annular space formed as a mixing chamber.

3. A method according to claim 1, characterised in that when compressed air is fed in a common outlet aperture (37) or in the immediate vicinity of each of the first injection channels (34) water mixed with compressed air is fed via the first injection channels.

4. A method according to claim 1 or 3, characterised when compressed air is admixture via second injection channels (35) discharging in direct proximity of each injection channel (34) which the water jets flowing from the first injection channels strike the compressed air jets flowing from the second injection channels (35) in the inner chamber of the mixing tube at an acute angle.

5. A method according to any one of claims 1 to 4, characterised in that reinforcing members, for example steel needles, are added to the dry mixture.

6. A mixing tube for dry concrete spraying, one end region (22) of which forms a connection for a feed pipe for dried mixture fed in a fine stream, of which the other end region (28) axially facing the first forms the outlet end and has a water connection (50) and an annular chamber (38) which is connected via a plurality of injection channels to the inner chamber of the mixing tube, characterised in that an annular chamber (42) connected to the water connection (50) for water and an annular chamber (46) for air connected to an air connection (58) are disposed upstream of the annular chamber used as a mixing chamber, which are connected via water channels (40) or air channels (44) to the annular chamber (38).

7. A mixing tube according to claim 6, characterised in that in the annular chamber (38) and in the outlet direction of the water channels (40) a device mechanically assisting the atomisation of the water is provided in the form of a jet splitter, a sharp edge or a screen.

8. A mixing tube for dry concrete spraying, the end region (22) of which forms a connection for a feed pipe for dry mixture fed in a fine stream, the other end region (28) axially facing the first form the outlet end, which tube has a water connection (50) and an annular chamber (38), which is connected via a plurality of injection channels to the inner chamber of the mixing tube, characterised in that second injection channels for an admixture of compressed air are provided in the immediate vicinity of the outlet apertures of the first injection channels (34) or in a common outlet aperture (37) with the first injection channels (35), which second injection channels (35) originate from a second annular chamber (46) connectable to a compressed air supply and converge with the first injection channels (34) on top of one another at an acute angle, a first injection channel (34) being associated with each of a plurality of injection channels (35).

9. A mixing tube according to claim 8, characterised in that the outlet openings of the injection channels (34 and 35) discharging in direct proximity are arranged at a distance of a maximum of 2 mm.

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