EP0211230A2 - Installation for mixing solid materials and liquids - Google Patents

Abstract

An apparatus for mixing solids with one another and with liquids, in particular for the production of molding sand mixtures, consists of a circular, fixed trough and at least two groups of mixing tools which engage at different distances from the trough axis and from the bottom of the trough and which rotate around the trough axis and against the tangent of their. Orbit are set at opposite angles. In order to achieve both a horizontal and a vertical movement of the material to be mixed with the greatest possible throughput, the mixing tools are formed in a blade-like manner from partially cylindrical shell segments with an approximately horizontal axis of curvature, the mixing blades of the outer group with their concave side inwards and that of the inner group show outside. Separate, also circumferential wall wipers are provided for the inner and outer wall of the trough.

Description

The invention relates to a device for mixing solids with one another and with liquids, in particular for the production of foundry molding sand mixtures, consisting of a circular fixed trough with a vertical axis and at least two groups of mixing tools attached to arms, which are at different distances from the trough axis and from the Bottom of the trough at a relative speed, preferably in opposite directions, and are inclined at opposite angles to the tangent of their orbit such that the mixing tools of the outer group convey the mix to the inside, the mixing tools of the inner group convey the mix to the outside.

In a device of the aforementioned structure (DE-A-26 03 057 = US-A-4 154 540), the drive of the mixing tool groups is located in the area of the trough axis, each group of tools being assigned its own drive. The mixing blades are connected to the drive shaft via support arms. Are there any gears still connected between the drive and the support arms _? planned. This well-known mixer, which is particularly suitable for mixing building materials, e.g. concrete mixes, is determined, has an inner and an outer group of mixing tools rotating in the same direction of rotation above the trough bottom and a group of mixing tools rotating in their overlap area and above them in the opposite direction. The mixing tools are simple plates standing perpendicular to the trough bottom, which are set at an angle to the tangent of their orbit. Dur i _d different adjustment of the mixing tools is taken along the mixed material from both the outer as well as from the inner portion of the Togs always transported in the direction of Oberlappungsbereichs of the two first mixing tool groups and there by the overlying mixing tool group in the opposite direction.

Compared to mixers with mixing tools rotating only in one direction or with stationary tools and rotating trough, the mixer described above has the great advantage that the material to be mixed is not only moved alternately from the outside in and vice versa, but is also subjected to constant shear stress. As a result, a homogeneous mixture with high throughput is achieved for a large number of starting components.

In foundry molding sands, however, there are considerable problems in that, in addition to the quartz sand present as the main component, various solid, mostly dust-like additives and liquid binders of different viscosities have to be processed. The individual solid and liquid components have very different specific weights, with the result that layers of different component enrichment are formed within the mixer by sedimentation movements, which are difficult to dissolve. In contrast to concrete mixtures, each individual particle in molding sand mixtures should be surrounded by a binder layer, which on the one hand means a corresponding contact time between the binder and the molding sand particles, and on the other hand corresponding Forces, such as frictional forces, are required which lead to the binding of the binder on the particles. A mixer of the abovementioned construction cannot fulfill these functions, or can do so only inadequately. It has also been shown that the mixing material no longer runs quickly enough with increasing toughness, but rather is carried along over a longer distance, so that the longer the mixture, the longer the mixing time. Finally, the mixing tools, which only rotate in two levels, limit the filling height and thus the throughput per mixing cycle.

Mixers of special construction have therefore been developed in the past that take into account the special circumstances in foundry sands. Thus, it is known (DE-C-1 204 632) to arrange various mixing and kneading or rolling tools within a rotating trough, which in turn are driven around axes that run parallel to the trough axis — partly in opposite directions, partly in the same direction. Through this training, the mixture components are exposed to different movements and forces, which should lead to a good mixture quality. In a further known mixer (DE-B-2 318 692 = US-A-3 964 733), star-shaped mixing arms with scoops are circulating over the bottom of the stationary trough, which transport the mixing material in the circumferential direction and also raise it against the direction of rotation . Above these mixing arms, rotating centrifugal tools reach into the trough eccentrically to the axis, which continuously tear open the upper layer of the mixture and spin the mixture in opposite directions. This mixer also leads to a satisfactory mixing quality, but requires considerable driving forces and leads to heavy wear.

Finally, it is known (DE-A-1 557 252) to use a plurality of planar mixing tools rotating about vertical axes in a revolving trough and to move the mix from the outside inwards by stationary guide plates. In addition, there are mixing tools which have a plurality of planar blades arranged at a distance from one another on a vertical axis, which force the mix to be moved vertically. With this mixer, horizontal and vertical movements are superimposed in the mix. In this, as in the majority of the above-mentioned embodiments, it is disadvantageous that the differently working mixing tools also each require their own drive, so that the accessibility of the trough from above is considerably impaired. Furthermore, due to the asymmetrical arrangement of the mixing tools, there are dead spaces or spaces in which the mixed material is only exposed to a certain force or movement component, so that the different effects on the mixed material take place at different geometric locations and there is no real superimposition of these effects . As a result, the dwell time is correspondingly long and the mixer volume is used insufficiently.

The invention is based first of all on the known fact that optimum mixing quality, particularly in the case of foundry mold sands, requires both horizontal and vertical movement components within the mixture. The mixture should also be subjected to constant shear stresses in order to effectively counteract the formation of agglomerates. Proceeding from this, the object of the invention is to communicate the aforementioned movement and force components to the material to be mixed by means of simply constructed mixing blades and to increase the performance compared to conventional mixers.

Starting from the device of the structure mentioned at the outset (DE-A-26 03 057 = US-A-4 154 540), this object is achieved according to the invention in that the mixing tools are shovel-like as shell segments of a circular cylinder with approximately horizontally arranged axis and the mixing blades of the outer group with its concave side inwards, the inner group with its concave side facing outwards and give the mix a twisting movement and that the inside of the outer wall and the inner wall of the trough are assigned peripheral wall wipers .

The shovel-shaped mixing tools according to the invention peel a partial stream out of the material to be mixed by means of the leading cutting edge and, depending on the angle, deflect it inwards or outwards. At the same time, a swirl movement is imposed on this subset, within which the mixture components are moved both horizontally and vertically. At the same time, this "peeling process" creates shear and compressive forces that imprint the binder on the molding sand particles. This process creates patties within the material to be mixed, which partly disintegrate again after leaving the trailing edge of the mixing blade or are dissolved again by the other mixing blade groups. Because the mixing blades of the two or more groups, as is known per se, are placed at opposite angles to the tangent of their orbit, the required radial movement from the inner region of the trough to the outside or from the outer region to the inside is also imposed on the material to be mixed . Due to the swirl movement, even with viscous mixtures, it is avoided that the mix is only taken along in the direction of circulation over longer distances and is not circulated. By arranging the mixing blades, in particular the inner group at different heights above the trough bottom, a high filling level is possible, but at the same time it ensures that there is constant transport from top to bottom and vice versa. Because the mixing blades consist of jacket segments of a circular cylinder, they are easy to manufacture in terms of production technology. This is supported by the further measure that separate wall wipers are provided in addition to the mixing blades, in that they have a simple nnear structure can point, which, due to the fact that these components are subject to greater wear, makes it easier to readjust or replace them, while the more complicated shaped mixing blades are only exposed to the mixing forces.

Mixers with curved mixing blades with a horizontal axis of curvature are known (DE-C-801 618), but they are located in only one plane, so that the filling height is very low. Furthermore, transport mainly takes place in a horizontal plane. The mixing blades are not partially cylindrical, so that their production is relatively complex. After all, the innermost and outermost mixing blades act as wall wipers and are therefore exposed to heavy wear. This is all the more so as they also act as a floor scraper, like all other mixing blades.

According to a preferred embodiment it is provided that the mixing blades have a leading cutting edge inclined in the opposite direction of rotation and an approximately horizontally running lower cutting edge, it also being advantageous that the leading cutting edge merges into the lower cutting edge via an arcuate curved edge. This means that the jacket segment forming the mixing blade is cut back to the absolutely necessary area in order to obtain the desired movements, and unnecessary pressure and frictional forces that do not bring about a mixing effect need not be overcome. Caking on the leading cutting edge is also avoided in this way and the partial flow to be set in a swirl movement is cut _/ at different heights. According to a preferred embodiment of the invention, the mixing blades are inclined with respect to the horizontal plane in the opposite direction to their direction of rotation. This measure allows the mixed material to be given an even more pronounced vertical movement component.

In a further advantageous embodiment, the mixing blades of the outer group consist of two or more jacket segments of a circular cylinder arranged one above the other, which are connected along a jacket line. As a result, the mix can be gripped on the outside by a single tool over the entire filling level and divided into two or more partial flows, each of which is set in a swirling movement. In this embodiment, the connecting line of the two jacket segments has a greater radial distance from the trough axis than the outer edges delimiting the jacket segments.

The effectiveness of the mixer can be further increased by, for example, the mixing blades of the inner group being at different distances from the trough axis and / or from the bottom of the trough. Furthermore, the vertical movement component can be influenced or amplified in that, for example, the mixing blades of the inner group are driven about an axis inclined to the trough axis. It is also possible to drive the mixing blades of the inner group about an axis arranged eccentrically to the trough axis.

According to a further feature of the invention, the outer group of mixing blades is assigned further partially cylindrical mixing blades with a perpendicular axis of curvature, the leading edge of which is at a greater radial distance from the trough axis than the trailing edge. The mixing blades with a vertical axis of curvature guide the mix primarily inwards, while those with a horizontal axis of curvature give the mix an inward twisting movement.

It is preferably provided that a partially cylindrical mixing blade with a vertical axis of curvature is connected to a mixing blade with a horizontal axis, the latter being arranged at the top, while the former extends approximately to the bottom of the trough. This ensures, in particular, that specifically lighter components, which mainly collect on the surface, are constantly circulated and mixed in, while in the lower area with the vertical mixing blades there is no significant vertical transport, i.e. the light components are not transported back to the surface. This effect is particularly pronounced when the mixing blade with the horizontal axis of curvature protrudes above the surface of the material to be mixed. The vertical mixing blades also make it easier to empty each batch.

In a further preferred embodiment it is provided that the wall wipers for the inner wall of the trough with the mixing blades of the inner group and those for the outer wall of the trough with the mixing blades of the outer group rotate synchronously. The mixing blades and wall wipers can thus be supplied by the same drive.

A wall scraper for the outer wall of the trough is preferably arranged in the circumferential direction behind each mixing blade of the outer group. Characterized in that the wall scraper runs after the mixing blade, the stripped material falls into the free space which has been generated by the leading mixing blade, which displaces the material inwards. This stripped material is then gripped by the subsequent mixing blade and transported inwards. This ensures that no material remains in the area near the wall for a long time.

Finally, the wall wipers can have replaceable and / or adjustable wear strips.

• Figur 1 eine schematische Ansicht einer Ausführungsform der Vorrichtung;
• Figur 2 eine schematische Ansicht einer weiteren Ausführungsform;
• Figur 3 eine den Figuren 1 und 2 entsprechende Ansicht einer dritten Ausführungsform;
• Figur 4 eine schematische Draufsicht auf einen Sektor des Trogs der Vorrichtung;
• Figur 5 eine schematische Seitenansicht des Trogsektors gemäß Figur 4;
• Figur 6 eine der Figur 4 entsprechende Ansicht eines Trogsektors bei anderer Ausbildung und Anordnung der Mischschaufeln;
• Figur 7 eine schematische Seitenansicht zu Figur 6
• Figuren schematische Darstellungen zur Geometrie ⁸ und ⁹ einer Ausführungsform der Mischschaufeln;
• Figur 10 einen Axialschnitt durch einen Mischer und
• Figur 11 eine Draufsicht auf die Mischer gemäß Fig. 10.

The invention is described below with reference to several exemplary embodiments shown in the drawing. The drawing shows:

• Figure 1 is a schematic view of an embodiment of the device;
• Figure 2 is a schematic view of another embodiment;
• Figure 3 is a view corresponding to Figures 1 and 2 of a third embodiment;
• Figure 4 is a schematic plan view of a sector of the trough of the device;
• FIG. 5 shows a schematic side view of the trough sector according to FIG. 4;
• FIG. 6 shows a view corresponding to FIG. 4 of a trough sector with a different design and arrangement of the mixing blades;
• FIG. 7 shows a schematic side view of FIG. 6
• Figures are schematic representations of the geometry ⁸ and ^{9 of} an embodiment of the mixing blades;
• Figure 10 shows an axial section through a mixer and
• FIG. 11 shows a top view of the mixer according to FIG. 10.

The mixer shown in Figures 1 to 9 consists of a fixed trough 1 with a cylindrical jacket 2 and a horizontal bottom 3. The axis of the trough is designated by 4. Several - in the exemplary embodiment shown, two - groups 5 and 6 of mixing blades engage in the trough from above, group 5 having mixing blades 7 and 8 and group 6 having mixing blades 9. The mixing blades are shown in Figures 1 to 3 for ease of illustration only as a rectangular structure. Their actual shape is described with reference to FIGS. 4 ff.

The groups 5 and 6 of mixing blades 7, 8 and 9 run at different radial distances from the trough axis 4. For this purpose, they sit on support arms 10 and 11, which in turn are connected to a drive via drive shafts 12, 13, if necessary with the interposition of gears. As indicated by the directional arrows A and B, the mixing blades 7 and 8 of group 5 rotate in opposite directions to the mixing blades 9 of outer group 6.

As can further be seen from FIG. 1, the mixing blade 7 of the inner group 5 can have a greater radial distance from the trough axis 4 than the mixing blade 8 of the same group. Likewise, the two mixing blades 7, 8 of group 5 can dip into the trough at different depths, as can also be seen from FIG. 1.

The embodiment according to FIG. 2 differs from that according to FIG. 1 essentially only in that the different radial spacing of the mixing blades 7, 8 of the group 5 can also be achieved by axially displacing the drive shaft 12 with respect to the trough axis 4. This also creates an eccentric orbit.

In the embodiment according to FIG. 3, the drive shaft 12 of the inner group 5 with the mixing blades 7 and 8 is inclined by the angle 06 with respect to the trough axis 4 or the drive shaft 13 of the external group 6, so that the mixing blades 7, 8 are different on the one hand Are arranged height and on the other hand give the mix both a horizontal and a vertical movement component.

In addition to the groups 5 and 6 of mixing blades 7, 8 and 9 already described, the device, as shown in FIGS. 4 to 9, additionally has at least one wall scraper 14 lying against the outer wall 3 of the trough, a horizontally lying floor scraper 16 and one of the Inner scraper 17 assigned to inner wall 18 of trough 1. These wipers can consist of simple slanted strips.

The mixing blades 7, 8 and 9 are partially cylindrical or formed by cylinder cutouts. The generation of the blades 7, 8 of the inner group 5 is indicated schematically in FIGS. 8 and ₉ . A cylinder 20 is shown there with dashed lines, the blades 7, 8 being formed from a segment 21 of this cylinder, ie having a curvature with the radius r (FIG. 8). The other contour of segment 21 can be seen from the projection according to FIG. The direction of rotation A of the blade 7 or 8 is also indicated. The blade 7, 8 has a leading cutting edge 22, which is inclined to rise in the direction of rotation 14, and a further horizontal cutting edge 23.

In the exemplary embodiment shown, the cutting edge 22 merges via an arcuate section 25 into a section 24 of the horizontal edge 23 rising to the rear. The apex line or the parallel axis of curvature of the blades 7, 8 is indicated by 26 in FIG.

As can be seen from FIG. 4, the apex line or axis 26 of the blade 7, 8 is set at an angle with respect to the tangent of the orbit, so that the mixed material captured by the mixing blade 7, 8 is transported from the inside to the outside and at the same time is guided in a swirling motion . The mixing blades 9 are formed from two superposed partial cylinders 27, 28, which are connected to one another along a surface line 29, which in turn lies further outside than the outer boundary edges 30, 31 of the two partial cylinders 27, 28. In the exemplary embodiment according to FIGS. 4 and 5 the axes 26 of the mixing blades 7, 8 of the inner group 5 and the axes of the partial cylinders 27, 28 of the mixing blades 9 of the outer group are arranged horizontally.

In contrast to this embodiment, in the exemplary embodiment according to FIGS. 6 and 7, the axis of the partial cylinders 27, 28 is shown rising in the opposite direction of rotation 15. Furthermore, the mixing blades 7, 8 are inserted radially further outwards and they engage less deeply in the trough.

10 and 11, a structural design of the mixer is shown. The same parts are provided with the same reference numerals, so that only different features are to be described here. 11 that the inner group has, in addition to the mixing blades 7 and 8, a third mixing blade 15 of the same contour. These three mixing blades are arranged at different radial distances from the trough axis 4 (FIG. 11) and at different heights (FIG. 10) above the trough bottom 3. They all run in the direction of A. Furthermore, the outer group 6 has two diametrically arranged mixing blades 9 with a horizontal axis of curvature, which are each attached to a support arm 11 together with a wall scraper 14 for the outer trough wall 2. As shown in FIG. 11, the wall scraper 14 runs behind the respective mixing blade 9 in direction B and transports the material into the space created by the mixing blade. The wall wipers 14, like those for the inner wall and the trough bottom, have adjustable and exchangeable wear strips 32.

The mixing blades 9, which, as shown in FIG. 10, are arranged at the top and reach up to or above the fill level of the mixer, are assigned further mixing blades 33, which are formed from partial cylinders with a vertical axis of curvature and extend to the bottom 3 of the trough 1. The horizontally and vertically arranged mixing blades 9 and 33 are connected to one another and fastened to the support arms 11. The leading edge 34 of the vertical mixing blade 33 has a greater distance from the trough axis 4 than the trailing edge 35.

Claims (17)

1. Apparatus for mixing solids with one another and with liquids, in particular for the production of foundry molding sand mixtures, consisting of a circular fixed trough with a vertical axis and at least two groups of mixing tools attached to arms, which are at different distances from the trough axis and from the floor of the trough at a relative speed, preferably in opposite directions, and are inclined at opposite angles to the tangent of their orbit in such a way that the mixing tools of the outer group convey the mixture to the inside, the mixing tools of the inner group to convey the mixture to the outside, characterized in that the Mixing tools (7, 8, 9) in the form of blades in the form of shell segments of a circular cylinder with an approximately horizontally arranged axis (26) and the mixing blades (9) of the outer group with their concave side inwards, the (7, 8) of the inner group with their concave Are facing outwards d impart a swirl movement to the material to be mixed, and that peripheral wall wipers (14, 17) are assigned to the inner sides of the outer wall (2) and the inner wall (18) of the trough. 2. Apparatus according to claim 1, characterized in that the mixing blades (7, 8) have a cutting edge (22) which is inclined counter to the circumferential direction and an approximately horizontally leading lower cutting edge (23). 3. Apparatus according to claim 1 or 2, characterized in that the leading cutting edge (22) over an arcuate curved edge (25) merges into the lower cutting edge (23, 24). 4. Device according to one of claims 1 to 3, characterized in that the lower cutting edge of the mixing blades (7, 8) consists of a horizontal section (23) and an inclined section (24) against the direction of rotation (A). 5. Device according to one of claims 1 to 4, characterized in that the mixing blades (9) with their axis of curvature with respect to the horizontal plane against their direction of rotation (B) are inclined to rise. 6. Device according to one of claims 1 to 5, characterized in that the mixing blades (9) of the outer group consist of two or more parallel shell segments of a circular cylinder (27, 28) arranged one above the other, which are connected along a shell line (29). 7. The device according to claim 6, characterized in that the connecting line (29) of the two jacket segments (27, 28) has a greater radial distance from the trough axis (4) than the outer segments (30, 28) delimiting the jacket segments (27, 28) , 31). 8. Device according to one of claims 1 to 7, characterized in that the mixing blades (7, 8) of the inner groups (5) have different distances from the trough axis (4). 9. Device according to one of claims 1 to 8, characterized in that the mixing blades (7, 8) of the inner group (5) have different distances from the bottom (3). 10. Device according to one of claims 1 to 9, characterized in that the mixing blades (7, 8) of the inner group (5) are driven about an axis (12) inclined to the trough axis (4). 11. Device according to one of claims 1 to 9, characterized in that the mixing blades (7, 8) of the inner group (5) about an axis to the trough axis (4) eccentrically arranged axis (12) are driven. 12. The device according to one of claims 1 to 11, characterized in that the outer group (6) of the mixing blades (9) are associated with further partially cylindrical mixing blades (33) with a vertical axis of curvature, the leading edge (34) of a greater radial distance from the trough axis (4) has as the trailing edge (35). 13. The apparatus according to claim 12, characterized in that a partially cylindrical mixing blade (33) with a vertical axis of curvature is connected to a mixing blade (9) with a horizontal axis, the latter being arranged at the top, while the former is approximately to the bottom (3) of the trough (2) is sufficient. 14. The apparatus according to claim 13, characterized in that the mixing blades (9) with a horizontal axis of curvature of the outer group (6) project beyond the surface of the material to be mixed. 15. The device according to one of claims 1 to 14, characterized in that the wall wipers (17) for the inner wall (18) of the trough (1) with the mixing blades (7, 8) of the inner group (5) and (14) for the outer wall (2) of the trough (1) with the mixing blades (9) of the outer group (6) rotate synchronously. 16. Device according to one of claims 1 to 15, characterized in that one wall scraper (14) for the outer wall (2) of the trough (1) in the circumferential direction behind each mixing blade (9, 33) of the outer group (6) is arranged . 17. Device according to one of claims 1 to 16, characterized in that the wall wipers (14, 17) have interchangeable and / or adjustable wear strips (32).

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