EP0729780A2 - Installation for mixing liquids with solid materials - Google Patents

Abstract

A predetermined quantity of liq. is mixed with a predetermined quantity of solid, e.g. pigment, in a plant having a storage container (1) for the liq. and a mixer (4) with a mixing shaft (9) powered by a drive motor (11). A liq. supply line (34) connects a supply pipe (13) of the mixer to the container and a solid metering device (29) opens into the pipe. The required ratio of solid to liq. is obtd. by several passages of the liq. through the mixer. The mixer is separate from the container and has an outlet (24) connecting to the storage container via a return line (25).

Description

The invention relates to a system for mixing a predetermined amount of liquid with a predetermined amount of powdered solid.

In practice, for example in the paint industry, the problem arises time and again of premixing a predetermined amount of liquid with a predetermined amount of powdery, dust-prone solid, usually pigment, in a dust-free manner. Such mixtures are then usually milled and dispersed in agitator mills. If the addition of pigment to liquid is concerned, paint or varnish is produced in the subsequent agitator mill. The problem of dust-free mixing of such solids and liquids has so far not been satisfactorily solved in practice. In addition, when the entire batches, that is to say the entire predetermined amount of liquid and the total predetermined amount of powdery solid, are combined at the same time, strong agglomerate formations generally also occur, which in turn make the subsequent grinding and dispersing process more difficult or more complex. In this application, the terms “liquid” and “solid” also encompass the majority thereof.

From PCT WO 92/21436 a device for wetting and dispersing powdery solid in liquids is known, which has a disk-shaped rotor in a dispersion chamber. On one side of the disc-shaped rotor is an inlet for the powdery solid and the inlet for the liquid is provided on the other side of the disk-shaped rotor. The pulverulent solid is brought together with the liquid in a wetting space in the outer edge region of the rotor disk. An outlet for the liquid-powder mixture is located on the outer edge of the wetting chamber surrounding the rotor disk. The liquid and the powdery solid are supplied by suction using the high-speed rotor disc. The powdery solid can be from a funnel arranged above the device and / or by means of a hose from a bag, storage container or the like. be sucked in. From the magazine SÖFW Journal Cosmetics Detergents Specialties, April 2, 1992, pages 2 to 4, it has also become known for this known device to connect the outlet of the device to the liquid storage container so that the liquid is circulated through the device is and the solid is thereby concentrated in the liquid. The announcement of the powdery solid is relatively difficult and depends on numerous influencing variables, for example the flow behavior of the powdery solid.

The invention is therefore based on the object of creating a system of the generic type which can be operated in such a way that dusting on the one hand and pronounced agglomerate formations on the other hand are largely avoided.

This object is achieved by the features of claim 1. The essence of the invention is then that a batch of powdery, dust-prone solid and a batch of liquid are brought together quasi-continuously in such a way that the liquid circulates several times, and in many cases, and the solid is distributed over these multiple cycles in the liquid is concentrated. The solid is metered, inevitably supplied. Solid and liquid are brought together in the feed nozzle, so that there is already a pre-mixing. This avoids the formation of larger agglomerates. Dusting is prevented by the way the solid is fed.

Numerous advantageous and partially inventive configurations result from the subclaims.

Fig. 1

eine Anlage zum Mischen von Flüssigkeit und Feststoff mit einem Vorratsbehälter, einer hiervon gesonderten Mischeinrichtung und einem Zuführstutzen mit Dosiereinrichtung und

Fig. 2

eine weitere Ausführungsform einer Anlage zum Mischen von Flüssigkeit mit Feststoff mit einem als Mischeinrichtung dienenden Vorratsbehälter und einem in den Vorratsbehälter mündenden Zuführstutzen mit Flüssigkeitszuführung und vorgeordneter Feststoff-Dosiereinrichtung.

Details of the invention result from the following description of two exemplary embodiments with reference to the drawing. It shows

Fig. 1

a system for mixing liquid and solid with a storage container, a separate mixing device and a feed nozzle with metering device and

Fig. 2

a further embodiment of a system for mixing liquid with solid with a storage container serving as a mixing device and a supply nozzle opening into the storage container with liquid supply and an upstream solid dosing device.

The system shown in the drawing has a storage container 1 which has a volume sufficient to hold a predetermined amount of liquid 2. An agitator 3 which can be driven by a drive (not shown) is arranged in the storage container 1.

Furthermore, a screw mixer 4 is provided, the essentially cylindrical housing 5 of which is surrounded by a temperature jacket 6 with an inlet 7 and an outlet 8 for a temperature medium for heating or cooling. A mixing shaft 9 is arranged in the housing 5 and can be driven by a mixing drive motor 11 via an upstream transmission 10.

At one end of the housing 5, a feed pipe 13 opens into its interior 12. In the area of the feed connector 13 and over a considerable part of the housing 5, the mixing shaft 9 is designed as a worm shaft with a helical screw shaft 14 running around it. In this area, the housing 5 can also be provided with a so-called clearing wheel which meshes with the screw webs 14 in order to ensure proper transport of the materials to be mixed through the interior 12 in the conveying direction 15. Such clearing wheels are known for example from DE 24 32 860 C2 (corresponding to US Pat. No. 3,957,210). Instead of a single-shaft machine with a clearing wheel, the screw-mixing machine 4 can also be designed as a double-screw machine, which is of a type that is forcibly conveying.

An intensive mixing section 17 adjoins the screw section 16 of the mixing shaft 9 which is provided with a screw web 14 and in which the mixing shaft 9 is occupied with short peg-like or strip-like mixing tools 18 which are assigned counter tools 20 attached to the inner wall 19 of the housing 5 . The mixing tools 18 and the counter tools 20 are each arranged on alternating circles around the central axis 21 of the mixing shaft 9. The smaller the distance of the mixing tools 18 from counter tools 20 adjacent in the direction of the central axis 21, the greater the dispersing effect.

At the rear end of the housing 5 in the conveying direction 15, a return conveyor 22 is provided, which comprises a pump conveying wheel 23 attached to the end of the mixing shaft 9, which conveys the liquid 2 into an outlet channel 24 opening out tangentially from the housing 5. The outlet channel 24 is connected to the reservoir 1 via a return line 25. If the mixing machine 4 is arranged directly above the storage container 1, then naturally no return conveyor must be provided.

The feed connector 13 consists of a lower funnel-shaped section 26 which is flanged to the housing 5 and opens into the interior 12 and which widens upwards, and an upper, approximately cylindrical section 27. A solid material projects into the upper cylindrical section 27 of the feed connector 13. Feed pipe 28 concentrically into which free-flowing, powdery solids are introduced from at least one solids metering device 29. These solids emerge from a lower outlet opening 30 of the feed pipe 28 into the funnel-shaped section 26 of the feed connector 13. A ring line 31, which surrounds the cylindrical section 27 of the feed connector 13 and is provided somewhat above this lower outlet opening 30, is provided by an approximately C-shaped jacket in cross section 32 is formed with a ring shape. The way bounded annular space 33 of the ring line 31 is connected to a liquid supply line 34 which leads to the reservoir 1. At least one liquid passage opening 35 is formed in the wall of the cylindrical section 27 of the feed connector 13, for example in the form of an adjustable gap. From the annular space 33, a pump 36 flows from the storage container 1 through the feed line 34 and through the through openings 35 into the cylindrical section 27 of the feed connector 13. It runs down the inner wall 37 of the cylindrical section 27 into the funnel-shaped section 26 The downward flowing solid 38 is completely enveloped by the liquid 2 running off on the inner wall 37. The liquid 2 is fed to the mixing machine 4 in the feed nozzle 13 under gravity. It also serves as a transport medium for the solid 38, which is also fed under the force of gravity. A certain pre-mixing of liquid 2 and solid 38 already takes place in the feed nozzle 13. This configuration of a feed nozzle 13 for feeding solid and liquid into a treatment machine is known per se, namely from DE 30 18 729 C2 (corresponding to US Pat. No. 4,394,980).

The solids metering device 29 has a funnel 40 which either has a volume which is sufficient to hold the entire batch of solids 38 or to which the predetermined amount of solids is continuously fed during a complete mixing cycle. The dosing accuracy of the solids dosing device 29 is not particularly demanding. The metering device only has to be adjustable in such a way that it inputs the predetermined amount of powdered solid over a predetermined period of time into the feed nozzle 13. The metering device 29 can have a volumetrically conveying screw or a gravimetrically conveying screw or a gravimetrically conveying belt conveyor. In the simplest and sufficient version, a volumetrically conveying screw is provided. Such metering devices are known and commercially available. In principle, it is also sufficient if a setpoint for the solid volume to be dispensed per unit of time can be set.

If it is to be reliably avoided that air is drawn into the mixing machine 4 when solid 38 and liquid 2 are added, then the screw mixing machine 4 must always be completely filled. In order to make this possible, a fill level measuring device is arranged in the funnel-shaped section 26 of the feed nozzle 13, which has a fill level probe 41 that operates without contact. This probe 41 continuously sends fill level signals to an input 42 of a control device 43. These signals are processed in the control device 43 in such a way that a control signal corresponding to a minimum fill level 44 and a maximum fill level 45 is generated which is output via outputs 46, 47 for alternative or cumulative control the drive motor 11 of the mixing shaft 9 and / or a pump drive motor 48 is supplied. If the probe 41 reports that the minimum fill level 44 has been undershot, then either the speed of the mixing shaft 9 and thus the throughput of the mixing machine 4 is reduced by driving the drive motor 11 or the speed of the drive motor 48 of the pump 36 and thus its delivery rate is increased. If, on the other hand, the probe 41 reports that the maximum fill level 45 in the feed connector 13 has been exceeded, then either the speed of the drive motor 11 and thus the throughput of the mixing machine 4 is increased or the speed of the drive motor 48 of the pump 36 and thus the liquid supply are reduced. Both measures can also be taken simultaneously. In principle, it is also possible to control the drive 50 of the solids metering device 29 via an output 49 of the control device 43 in such a way that when the liquid throughput is reduced, the solids supply is also reduced and vice versa. Otherwise, the above-mentioned target value for the volume to be supplied to the supply nozzle 13 by the metering device 29 or the corresponding amount of solid 38 is likewise set in the control device 43.

wobei V_Feststoff und V_Gemisch den Volumenstrom an Feststoff und den Volumenstrom an Gemisch aus Feststoff und Flüssigkeit bezeichnen. Wenn die Mischmaschine 4 in der zuvor geschilderten Weise mit vollständiger Füllung arbeitet, dann gilt $${\text{V}}_{\text{Mischmaschine}}{\text{= V}}_{\text{Feststoff}}{\text{+ V}}_{\text{Gemisch}}\text{.}$$

In principle, it is also possible to operate the mixing machine 4 with relining, ie less liquid 2 and less solid 38 are fed to it than its conveying capacity V corresponds to the _{mixing machine} . So in this case $${\text{V}}_{\text{Blender}}{\text{> V}}_{\text{Solid}}{\text{+ V}}_{\text{mixture}}\text{,}$$

where V _solid and V _mixture denote the volume flow of solid and the volume flow of mixture of solid and liquid. If the mixing machine 4 operates in the manner described above with complete filling, then the following applies $${\text{V}}_{\text{Blender}}{\text{= V}}_{\text{Solid}}{\text{+ V}}_{\text{mixture}}\text{.}$$

kann eine vollständige Füllung der Mischmaschine 4 dadurch erreicht werden, daß über die Rücklaufleitung 25 ein Rückstau auf die Mischmaschine 4 ausgeübt wird. Hierzu ist in der Rücklaufleitung 25 eine einstellbare Drossel 51 mit einem zugeordneten Manometer 52 vorgesehen. Die Drossel 51 ist auf einen Ausgang 53 der Regeleinrichtung 43 geschaltet. In diesem Fall wird bei vorgegebener hoher Unterfütterung der Mischmaschine 4 die Drossel 51 so gesteuert, daß der Minimal-Füllstand 44 nicht unterschritten und der Maximal-Füllstand 45 nicht überschritten wird, wobei das Manometer 52 dazu dient zu überwachen, daß ein maximal zulässiger Druck im System nicht überschritten wird.In the last case, where applies $${\text{V}}_{\text{Blender}}{\text{> V}}_{\text{Solid}}{\text{+ V}}_{\text{mixture}}\text{,}$$

A complete filling of the mixing machine 4 can be achieved in that a back pressure is exerted on the mixing machine 4 via the return line 25. For this purpose, an adjustable throttle 51 with an associated manometer 52 is provided in the return line 25. The throttle 51 is connected to an output 53 of the control device 43. In this case, the throttle 51 is controlled at a predetermined high relining of the mixing machine 4 so that the minimum fill level 44 is not fallen below and the maximum fill level 45 is not exceeded, the pressure gauge 52 being used to monitor that a maximum permissible pressure in the System is not exceeded.

Basically, the setting is such that when the liquid 2 in the storage container 1 is completely circulated through the mixing machine 4 and back to the storage container 1, only a fraction of the solid 38 to be added to the liquid 2 is added. Depending on the nature of the solid 38 and the liquid 2 and the desired homogeneity, two to ten circulations of the liquid 2 may be appropriate until the solids 38 have been completely added. If a fineness of dispersion of the mixture is desired, then in many cases more than ten cycles are required. It should be added at this point that the term liquid also includes the mixture of liquid 2 and solids 38 formed during the circulation. A pure liquid 2 is only present at the beginning of the process. As described, this is mixed with solids 38 and thus forms a flowable liquid-solid mixture, which for the sake of simplicity is also referred to as liquid.

When talking about amounts of liquid, it can be both volumes and amounts by weight. The same applies to solids 38.

The agitator 3 in the reservoir 1 serves to bring about a concentration compensation in the reservoir 1, that is to say to ensure a uniform concentration of solid 38 in liquid 2 in the entire reservoir 1.

An eccentric screw pump or a conventional mixer provided with conveying devices can also be used as the mixing machine 4. It is essential that it has its own funding, that is, it gives the liquid 2 and the solid 38 a delivery pulse.

To the extent that the same parts are used in the exemplary embodiment according to FIG. 2, they are identified with the same reference numerals as in FIG. 1. As far as functionally identical but structurally different parts are used, they are identified by the same reference number with a prime. Reference is made to the previous description.

In the exemplary embodiment according to FIG. 2, no mixing machine separate from the storage container is provided; rather, the storage container 1 'is provided with an intensive agitator 3', which causes an intensive circulation of the liquid 2 in the storage container 1 '. Such agitators 3 'are known; These are, for example, so-called spiral agitators, which in particular also exert a pronounced pull-in effect on the surface of the liquid 2 on the latter. The storage container 1 'is provided with a lid 54 in which a vent opening 55 is provided, for example for a pendulum vent.

The feed nozzle 13 in the embodiment described in FIG. 1 is mounted in the lid 54 and ends above the liquid 2. It is arranged so far above the liquid 2 that even after the entire solid 38 has been completely mixed into the liquid 2, it does not Mixture immersed.

An operating device 56 is also provided, by means of which the delivery rate of the pump 36 can be adjusted on the one hand by correspondingly adjusting the speed of the pump drive motor 48 and on the other hand the metering rate of the metering device 29. As a result, it can be determined overall that the contents of the predicate container 1 'are pumped several times, while the solid 38 is added by the metering device 29 via the feed nozzle 13. With this configuration, it is in particular possible to pump the liquid 2 or the mixture of liquid 2 and increasing proportion of solid 38 more than 10 times before the entire amount of solid 38 has been added. In this context, the mixing of liquid 2 and solid 38 takes place exclusively in the predicate container 1 'by means of its agitator 3'; there is no dispersion here. Sufficiently thorough mixing can, however, be carried out for many applications.

In the exemplary embodiment according to FIG. 2, an agitator drive motor 57 has the function of a mixed drive motor which drives the agitator shaft 59 of the agitator 3 'serving as a mixing shaft by means of a V-belt drive 58. In the exemplary embodiment according to FIG. 2, the storage container 1 'with agitator 3' thus serves not only as a storage container, but also as a mixing device.

Claims (19)

System for mixing a predetermined amount of liquid with a predetermined amount of powdered solid with the following features: - a predicate container (1, 1 ') for the predetermined amount of liquid (2), a mixing device (4) with a mixing shaft (9, 59) which can be driven by a mixing drive motor (11, 57), a liquid supply line (34) connecting a supply nozzle (13) of the mixing device (4) to the storage container (1), - A solids metering device (29) opening into the feed pipe (13) and - Such an adjustability of the feed rate of the solid dosing device (29) and the throughput of the mixing device (4) that the predetermined amount of solid (38) of the predetermined amount of liquid (2) over several runs of the liquid (2) through the mixing device (4th ) is added. System according to Claim 1, the mixing device being designed as a mixing machine (4) separate from the storage container (1) and having an outlet (outlet channel 24) which is connected to the predicate container (1) by means of a return line (25). System according to claim 2, wherein the mixing machine is designed as a screw mixing machine (4) which has a mixing shaft (9) which has a screw section (16) in the region of the feed connector (13) and adjoining it. System according to claim 2 or 3, wherein the mixing shaft (9) in the area in front of the outlet (outlet channel 24) has an intensive mixing section (17). System according to claim 4, wherein the mixing shaft (9) is provided in the region of the intensive mixing section (17) with peg-like or strip-like mixing tools (18). Plant according to claim 5, wherein in the area of the intensive mixing section (17) the mixing tools (18) are assigned stationary counter tools (20). System according to one of claims 2 to 6, wherein in the region of the outlet (outlet channel 24) of the mixing machine (4) a return device (22) is provided which is connected to the return line 25. System according to claim 7, wherein the return device (22) comprises a pump delivery wheel (23) attached to the mixing shaft (9), to which an outlet channel (24) connected to the return line (25) is assigned. System according to one of claims 1 to 8, wherein an agitator (3, 3 ') is arranged in the predicate container (1, 1'). System according to one of claims 2 to 9, wherein a control device (43) with outputs (46, 47) for changing the amount of liquid (2) supplied to the feed nozzle (13) per unit time and / or the per unit time in the mixing machine (4 ) enforced amount of liquid (2) is provided. System according to claim 10, wherein a fill level measuring device (fill level probe 41) is arranged in the feed pipe (13) and is connected to an input (42) of the control device (43). Plant according to claim 10 or 11, wherein an output (49) of the control device (43) is connected to a drive (50) of the solids metering device (29). System according to one of claims 2 to 12, wherein an adjustable throttle (51) is arranged in the return line (25). System according to claim 13, wherein the throttle (51) is adjustable. System according to claim 1, wherein the storage container (1 ') is designed as a mixing device into which the feed connector (13) opens. System according to claim 1 or 15, wherein an intensive agitator (3 ') with a pronounced pull-in effect is arranged in the storage container (1'). System according to one of claims 1 to 16, wherein the solids supply and the liquid supply line (34) open freely above the mixing device in the supply nozzle (13). Plant according to claim 17, wherein the solids feed opens into the feed connection (13) within the liquid feed. Installation according to one of claims 1 to 18, wherein the predicate container (1 ') is closed with a lid (54).

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