EP3223934B1 - Device for reprocessing and cooling foundry sand - Google Patents

Description

The present invention relates to a device for cooling warm particle beds, in particular foundry sand.

Used foundry sand can be reused if the foundry sand is processed. To do this, it is necessary to cool down the used sand.

Such a device is for example from the DE 1 508 698 known. The device described there consists of a mixing container and two vertically arranged drive shafts for a mixing tool. The foundry mold sand to be cooled is introduced into the mixing container on one side and removed on the other side. While the foundry sand to be cooled passes through the device, the foundry sand is mixed using the mixing tools. In addition, the mixing container has an opening for supplying air directly on the container base in the container wall.

With this device, an attempt is made to generate an air-flowed, mechanically supported fluidized bed sprayed with water in order to cool the foundry sand, which has been heated up to 150 ° C. by the preceding casting process, to the operating temperature of approx. 45 ° C. by evaporative cooling.

The mixing container is integrated in a machine frame. The mixing container itself has two mutually penetrating polygonal sections. A corresponding rotating mixing tool is arranged in the center of each of the two sections. The mixing blades attached to the shaft typically have plate-shaped blades that are moved on vertically arranged holders by radially extending rotating support arms. The plate-shaped blades only have an effect on a circular path with a small extent, which is delimited essentially locally around the blade. At the in the DE 1 508 698 described device penetrate the two sections, so that when controlling the two mixing tools, care must be taken that they do not collide with one another, which makes coordinated movement control necessary.

In particular when very large quantities of foundry mold sand are to be cooled with the device and therefore the container diameter is made correspondingly large, the known devices only achieve uneven cooling, which clearly limits the quality of the foundry mold sand to be used. Improved molding sand quality can be achieved, for example, by using vacuum mixers, which are, however, relatively expensive.

In the inexpensive devices, as in the DE 1 508 698 are shown, the cooling air introduced at the edge only blows flow channels through the sand bed in the immediate vicinity of the inlet openings and escapes upwards in a relatively short way without fulfilling the actual task of uniformly fluidizing the bed and cooling with high efficiency. The center of the mix in the middle of the container is not at all reached by the air, since it only comes into contact with the air flowing out and up on an outer circular path in the immediate vicinity of the air inlet openings. Due to the substantially higher flow resistance of the bed in the radial direction towards the mixer shaft, the air flows vertically upwards after exiting the slot-shaped opening and following the lowest pressure loss. In the center of the mixing container, the sand is only slightly mixed by the rotating blades due to the prevailing low circumferential speed and speed differences, and slowly pushed radially outwards by the outward-pointing blade inclination in order to convey it into the cooling zone.

As a result of the speed differences, the residence time of the mixed material also shows great differences between the material located in the middle of the container and on the outer circumference. In the worst case, the mixed material travels through the cooler from the addition opening located on the central axis to the opposite discharge opening in the area of the drive shafts without substantial contact with the supplied cooling air. In addition, the locally emerging vertical flow channels in the wall area observe very high exit velocities from the bed of mix, which entrain a large amount of solid particles due to the high velocity and fluctuation of the flow.

Therefore is already in the DE 199 25 720 Described to draw the cooling air through a generally centrally arranged opening in the housing cover by a suction fan and to clean it in a generally voluminous gas cyclone downstream of the cooler. The sand and additive components carried in the gas stream are largely separated in the cyclone and applied to the sand discharged from the cooler. Due to the mode of action of a gas cyclone, the large and heavy sand particles are preferably separated there, while the fine particles in suspension such as bentonite and carbon follow the gas flow and are completely discharged. Complete separation of the particles does not take place. Due to the undefined composition of the fine fractions that are later separated in a filter, these fractions have to be disposed of and compensated for by adding new additives. The sand, which is usually rather dry, removed from the bottom discharge of the cyclone is placed on the conveyor belt on the cooled sand. These discharged sand particles are no longer mixed with the moistened sand, which can lead to problems in the molding machines if there is no further sand homogenization and moistening.

The US 3,456,906 A and the US 3,050,795 A show mixing tanks of the prior art.

Starting from the prior art described, it is therefore an object of the present invention to provide an improved device with which a more uniform fluidized bed is achieved as far as possible over the entire cross section of the mixing container, and in addition the proportion of the solid particles entrained with the gas stream , should be reduced.

According to the invention, this is achieved by a device according to claim 1. According to the invention, the mixing tool has at least two mixing blades which are spaced apart in the vertical direction and at least one mixing blade has a mixer blade which is inclined with respect to the horizontal and which is preferably inclined downwards in the direction of rotation of the mixing tool. The direction of rotation is predetermined by the drive device of the mixing tool. The drive device of the mixing tool is therefore designed such that it drives the mixing tool in such a way that the mixing tools are inclined downwards in the direction of rotation. In an alternative embodiment, the drive device can also be designed such that the direction of rotation of the mixing tool can be changed if necessary.

The use of mixing flights offset in the vertical direction leads to better mixing of the material to be mixed. The mixing blades preferably extend in the horizontal direction from the drive shaft. The inclination of the mixer blade takes place in such a way that the mixer blade, which is inclined downwards in the direction of rotation of the mixing tool, leads to the fact that the material to be mixed is lifted during mixing, as a result of which a cavity is formed directly behind the mixer blade within the material to be mixed, in which the air supplied can be distributed over the entire width and length of the mixer blade in the mix. Therefore that extends Mixer blade preferably over at least half the radius of the circle, which the outer section of the mixer blade describes when rotating. In one embodiment it is provided that the mixer blade extends from the container wall to the drive shaft.

In order to improve the mixing of the cooling air with the material to be mixed, the mixer blade extends in a preferred embodiment essentially up to the container wall. The distance between the mixer blade and the container wall is preferably less than 100 mm and is best between 20 and 60 mm. This measure results in a layer-by-layer loosening along the tool profile in the sand bed. It is also possible for a preferably flexible attachment to be attached to the mixer blade, which projects radially over the mixer blade in the direction of the container wall and touches it, so that the attachment slides over the container wall during operation.

It is also provided that the container wall is inclined, so that the container cross section increases from the container bottom upwards. Each mixing blade has a mixer blade, the distance between the mixer blade and the container wall being the same for both mixer blades. Due to the inclined container wall and the arrangement of the two mixer containers at different heights, this has the consequence that the mixer blade arranged further up must extend radially further outwards. In terms of flow technology, the mixer blade is designed in such a way that the material to be mixed is lifted upwards, so that a cavity is formed on the side of the mixer blade which is remote from the flow and serves as a flow channel for incoming air. Ideally, the air can now flow over the cavity between the drive shaft and the container wall and rise on the side facing away from the solid flow through the falling mix due to gravity behind the mixing tool, so that the mix is evenly flowed through to the center of the container by the inflowing air. With a sufficiently high peripheral speed of the tools, this constellation essentially prevents local inflow of air only in the area of the air outlet openings. Tests have shown that the drive for rotating the mixing tool is preferably designed such that the mixer blade has a peripheral speed at its radially outer end of between 2 and 75 m per second and preferably between 30 and 60 m per second.

In a further preferred embodiment, at least one mixer blade of each mixing tool is arranged essentially on the bottom of the container.

With a suitable number and arrangement of mixer blades one above the other in connection with the selection of a suitable mixing tool peripheral speed, mechanical support of the fluidized bed can be achieved in such a way that the air flows through the sand bed largely homogeneously over the entire cross-section and the sand is evenly cooled.

Due to the good and even distribution of air over the entire cross section of the sand bed, the flow velocities on the surface of the bed are also reduced, so that the discharge of particles with the air flow is significantly reduced.

In a preferred embodiment, the mixing container has at least two mixing sections, a mixing tool which can be rotated about a drive shaft being provided in each mixing section, each mixing tool preferably having at least two mixing blades which are spaced apart in the vertical direction.

The peripheral speed of the mixing blades and the direction of rotation in the individual mixing sections can be different.

In this embodiment, the inlet for the foundry mold sand to be cooled is in one section, while the corresponding outlet is in the other section, so that the foundry mold sand has to pass through both mixing sections in succession. In a preferred embodiment, each mixing tool has a mixer blade arranged essentially on the container bottom, the two mixing tools being so far apart from one another that the two mixer blades arranged on the container bottom do not touch in any position of the mixing tools. In the narrowest case, the circular paths of the two mixer blades arranged on the tank bottom are tangent to one another.

The vertically higher mixer blades of different mixing tools are preferably arranged at different axial heights. They are designed so that their circular paths overlap. The different arrangement in the vertical direction prevents a collision from occurring. The design described enables all tools to be designed close to the wall. In addition, both mixing tools can be driven independently of one another at different speeds, without fear of a collision. This means that the mixing tools in the individual mixing tank sections can be assigned an optimum speed for the predominant process engineering task. In this way, the tool speed of the mixing chamber section on the material inlet side can be optimized for the efficient mixing in of the water, while the speed of the tool in the subsequent mixing chamber section can be coordinated with the optimal flow of cooling air through the sand bed with reduced particle discharge, since here the stickiness of the particles due to the moisture reduction has already subsided. The geometry of the mixing tool can also be designed differently in the different levels and mixing chamber sections, so that a corresponding optimization with regard to the flow through the sand bed is achieved while the solids discharge from the bed is minimized at the same time.

For example, the air supply can have openings in the container wall through which air can be blown into the interior of the container. The openings are preferably arranged at the same vertical height as the mixer blade which extends essentially to the container wall.

In an alternative embodiment it is provided that the air supply is supplied via the mixing tool itself, which for example has a hollow shaft. For example, the mixer blade can have corresponding air outlet openings on its side oriented opposite to the direction of rotation. Of course, a combined air entry via openings in the container wall and via openings in the mixing tool would also be possible.

Due to the design, the peripheral speed of the mixer blade increases with increasing distance from the drive shaft, with the result that the mixing effect increases in the direction of the container wall. If the cross-section of the mixer blade remains the same, the mixing intensity will also increase as the effective diameter increases, since the peripheral speed increases with increasing radius. This physical law can be countered by suitably designing the cross-sectional shape of the leaves from the inside out. For example, the mixer blade can have a width that increases in the radial direction. Alternatively or in combination, the angle of inclination of the mixer blade to the horizontal can decrease in the radial direction.

The mixer blade can be flat or curved. The angle of inclination with respect to the horizontal is preferably between 15 ° and 60 ° and particularly preferably between 20 ° and 50 °.

In a further preferred embodiment, the mixer blade is designed as an angled profile, the inner angle being arranged opposite to the direction of rotation of the mixer blade and preferably being between 90 ° and 180 °. With this measure, a larger cavity facing away from the solid flow can be formed, so that the air flowing from inside or outside into the channel formed in this way can penetrate to the end of the air channel formed with a simultaneously reduced pressure loss.

Alternatively, the mixer blade can also be a substantially closed polygon profile, such as a rectangular or triangular profile, with corresponding air outlet openings being arranged on the side facing away from the flow, so that the cooling air can be introduced into the material to be mixed via the profile.

In a further embodiment, ploughshare-like attachments are attached to radially inner sections of the mixing blade to compensate for the lower peripheral speed, in order to increase the lifting and overflowing of the mixture on the one hand and to achieve an improved mixing effect on the other. In combination with air outlet openings located below the plowshares, a falling sand curtain can be created which, due to its larger heat and mass transfer area, achieves a higher cooling capacity when it comes into contact with the outflowing air.

In particular with fine sand qualities, it can be advantageous if the mixer blade of the uppermost mixing blade is tilted in the opposite direction, so that the mix is directed downwards in order to counteract excessive swirling and, consequently, excessive discharge from the cooling device with the exhaust gas flow.

The distance between the air inlet openings arranged in the mixing container and the radially outer end of the mixer blade should be as small as possible in order to avoid that too much of the cooling air escapes upwards before reaching the mixer blade.

Tests have shown that the average flow velocity of the cooling air in the outlet area of the air inlet openings should be between 15 and 35 m / s and particularly preferably between 20 and 30 m / s. Even if the angle of inclination of the container wall can in principle take any value between 0 and 45 °, the inclination is preferably between 15 and 35 ° and particularly preferably between 20 and 30 ° with respect to the vertical.

In a further embodiment, fixed, alternatively also spring-loaded, radially movable extensions made of, for example, plastic are located on the radially outer ends of the mixer blades, which rub against the container wall and thus establish direct contact between the air outlet opening and the side of the mixing blade facing away from the flow of solids ,

In a further preferred embodiment, even more than two, namely three or even more mixing chamber sections are arranged one behind the other, through which the material to be mixed flows in succession. In such an embodiment, the mixing and the homogeneous distribution of the water is essentially carried out in the first inlet-side chamber, while intensive ventilation of the sand bed and thereby evaporative cooling is achieved only in the second chamber. The quality of the cooled sand can be corrected in the third or each subsequent chamber by adding water or other additives, for example. For example, the foundry sand should then have a residual moisture between 3.0 and 3.5% around the sand when leaving the device enveloping bentonite, which brings about the forming properties of the molding sand, and to enable direct use in the molding machine. In this case, it can be advantageous if the mixing tool in the third mixing chamber section, that is to say the section through which the material to be mixed flows last, has mixer blades which are inclined upwards in the direction of rotation, thereby ensuring that it becomes one in the last mixing chamber section shear stress on the mix. As a rule, it is also not necessary in the last mixing chamber section for air to be supplied, so that corresponding openings can be dispensed with in this section. It can also be advantageous for some applications if the mixing chamber tool in the third mixing chamber section is designed with the direction of rotation opposite to the mixing chamber tool of the second mixing chamber section.

As already mentioned, the local flow rate is significantly reduced by the measures according to the invention, with the result that fewer solid particles are entrained and carried away by the air flow.

Nevertheless, in a particularly preferred embodiment it can be advantageous if the rising gas flow in the housing is freed as much as possible of the entrained solid particles. It is therefore provided in a preferred embodiment that a solids separator is arranged above the mixing tool. In a preferred embodiment, the solid particles are separated in a vortex flow, for example in a rotary flow generated by a rotor. The forced rotary flow creates a corresponding centrifugal field, which can be adjusted in strength by selecting the speed of rotation of the rotor. This gives you the option of setting the separation capacity and the size of the separating grain. Thus, for example, if the rotational speed is increased sufficiently, the particularly fine additive components contained in the gas flow can also be almost completely recycled.

The solution according to the invention achieves a very compact design of the cooler, with almost all solid particles being retained in the mixer at the same time.

Figur 1

eine Schnittansicht einer ersten erfindungsgemäßen Ausführungsform einer Kühlungsvorrichtung,

Figur 2

eine Schnittansicht einer zweiten erfindungsgemäßen Ausführungsform,

Figur 3

eine Detailansicht eines Mischers mit mehreren unterschiedlichen Mischerblättern,

Figuren 4 bis 8

Querschnittsansichten verschiedener Mischerblätter.

Further advantages, features and possible uses of the present invention will become apparent from the following description of preferred embodiments of the invention. Show it:

Figure 1

2 shows a sectional view of a first embodiment of a cooling device according to the invention,

Figure 2

2 shows a sectional view of a second embodiment according to the invention,

Figure 3

a detailed view of a mixer with several different mixer blades,

Figures 4 to 8

Cross-sectional views of various mixer blades.

In Figure 1 a first device according to the invention is shown in section. The device 1 for processing and cooling foundry mold sand has a mixing container 2 which is arranged in a housing 3. The mixing container 2 has two mixing sections, in the center of which a drive shaft 4 is arranged, which in turn each have a plurality of mixing blades with corresponding mixer blades. The device 1 has an inlet 5 and an outlet 5 ', via which hot foundry sand can be introduced into the mixing container 2, for example by means of a conveyor belt 6, or the processed sand can be discharged from the mixing container 2 again. A number of cooling air openings 7 are introduced in the inclined container wall 2, via which cooling air can be introduced into the mixing container 2. The two drive shafts 4 each have mixing blades near the ground, which extend in opposite directions and on each of which a mixer blade 8 is mounted. The two drive shafts 4 are arranged at a distance from one another in such a way that the mixer blades 8, which are arranged near the ground, cannot collide with one another in any rotational position. In the vertical direction spaced apart from the mixing blades close to the floor, further pairs of mixing blades are arranged, which are also each equipped with corresponding mixer blades. In the embodiment shown, all mixer blades are inclined downwards, so that when the drive shaft is rotated in the intended direction, the foundry mold sand located in the mixing container 2 is raised and flows over the inclined mixer blade surface. The mixer blades of the second and third levels are arranged at a height which corresponds to the vertical height of the air inlet openings 7 in the container wall 2. In addition, the mixer blades of levels 2 and 3 are arranged so that they extend almost to the air inlet openings 7. The two drive shafts 4 are driven by means of the drive motors 9. A solids separator 11 is arranged in the cover of the housing 3 and consists of a wheel provided with lamellae, which wheel can be rotated with the aid of the drive motor 10. The suction of the cooling air supplied via the air inlet openings 7 then takes place via the spaces between the lamellae of the solid matter separator 11. The driven wheel of the solid matter separator 11 generates a vortex flow in which the solids contained in the air to be extracted are separated and fall back into the mixing container ,

In Figure 2 a schematic sectional view of an alternative embodiment of the invention is shown. The same reference numbers were used for the same elements. At the in Figure 2 In the embodiment shown, the cooling air is supplied once via a drive shaft 4 designed as a hollow shaft, in which air is fed into the duct 15 and via the duct into corresponding openings within the mixer blades 8, 8 ′, 8 ″ and 8 ″ ″ by means of the feed 12 the Flow the mix. Additionally or alternatively, air can be brought into the housing via the air supply 13 and into the mixture via the air inlet openings 7. It can be clearly seen in this embodiment that the mixed blades of the upper levels have a longer radial extension than the mixed blades of the lower level.

The mixer blades 8, 8 ′, 8 ″ and 8 ″ ″ essentially extend as far as the container wall. However, in order to avoid damage to the mixer blades, a small gap must remain. For a mixer blade, for example, it is shown that the mixer blades have an extension 14 can have made of plastic, which can also be pressed with the help of springs on the container wall to reduce the proportion of the cooling air supply that flows directly vertically upwards.

In Figure 3 Various embodiments of mixer blades are shown by way of example. In principle, as shown in the embodiment provided with the reference number 17, the mixer blade could extend uniformly from the drive shaft to the container wall. Of course, however, curved shapes, as in the embodiment denoted by the reference number 15, or fan-like shapes, such as in the embodiment denoted by the reference number 16, would also be possible.

In the embodiment provided with the reference number 18, ploughshare-like attachments 19 are provided on the mixer blades.

Figure 4 shows a cross-sectional view through a mixer blade 20, which here consists of a single inclined surface. Behind the mixer blade, when the mixer blade 20 moves, a zone is formed which is essentially kept free of the mix, into which the cooling air introduced into the mixing container through the air supply openings 7 can flow radially inwards along the mixer blades. The contour of the air outlet opening 7 is ideally selected so that, in combination with the geometry of the mixer blade, the most uniform and long-lasting air inflow into the zone behind the mixer blade which is kept free from the material to be mixed can take place.

In Figure 5 A cross-sectional view of a second embodiment of a mixer blade 21 is shown. Here the mixer blade consists of an inclined surface and an angled, essentially horizontal surface.

In Figure 6 a cross section through a third embodiment of a mixer blade 2 is shown. Here, too, an inclined surface is provided, which essentially adjoins in one direction vertically extending section and in the other direction an opposite inclined section.

In Figure 7 a cross section through a further embodiment of a mixer blade 23 is shown. The mixer blade 23 again has an inclined surface. It is mounted here on an essentially tubular element, through which cooling air can likewise be introduced into the mixing container.

In Figure 8 an embodiment is shown as an example, in which different mixer blades 24 to 26 are mounted on the drive shaft in three different planes. The mixer blade arranged in the lowest level has a downwardly inclined blade surface and a section running essentially perpendicularly to it. In the middle level, a mixer blade 25 with a cross section is used, which forms a kind of cavity through which cooling air can be transported radially outward from the drive shaft. In the uppermost level, a mixer blade 26 is used, which is inclined upwards in order to prevent the mixed material from being whirled up too strongly. Of course, other geometries are possible for the design of the mixer blade.

LIST OF REFERENCE NUMBERS

1

contraption

2

mixer blade

3

casing

4

drive shaft

5, 5 '

Inlet, outlet

6

conveyor belt

7

Air inlet openings

8, 8 ', 8 "

mixer blades

9

drive motors

10

drive motor

11

solids

12

feed

13

air supply

14

renewal

15-18

mixer blades

19

Essays

20-26

mixer blades

Claims (14)

1. Apparatus for treating and cooling foundry moulding sand, comprising a mixing container (2) and a mixing tool rotatable about a drive shaft, wherein there is provided an air feed for the feed of air into the container interior, wherein the mixing tool has at least two mixing vanes spaced from each other in the vertical direction and at least one mixing vane has a mixer blade (8) with a surface which is inclined relative to the horizontal, wherein the container wall is inclined so that the container cross-section becomes larger in an upward direction from the container bottom, characterised in that each mixing vane has a mixer blade (8), wherein the spacing between mixer blade and container wall is approximately the same for all mixer blades.
2. Apparatus according to claim 1 characterised in that the surface of the mixer blade (8) is inclined downwardly in the direction of rotation of the mixing tool.
3. Apparatus according to claim 1 or 2 characterised in that the mixing tool has at least two vertically spaced mixing vanes with mixer blades (8), wherein a mixer blade (8), preferably the uppermost mixer blade (8), has a surface inclined upwardly in the direction of rotation of the mixing tool.
4. Apparatus according to one of claims 1 to 3 characterised in that the mixer blade (8) extends substantially to the container wall, wherein preferably either the spacing between mixer blade (8) and container wall is less than 100 mm and at best is between 20 and 60 mm or there is provided an attachment which is associated with the mixer blade and which projects in the direction of the container wall beyond the mixer blade and contacts the container wall.
5. Apparatus according to one of claims 1 to 4 characterised in that there is provided a drive for rotating the mixing tool, wherein the drive is so designed that the mixer blade (8) has a peripheral speed at its radially outer end of between 2 and 75 m/s and preferably between 30 and 60 m/s.
6. Apparatus according to one of claims 1 to 5 characterised in that the mixer blade (8) is arranged substantially at the container bottom.
7. Apparatus according to one of claims 1 to 6 characterised in that the mixing container has at least two and preferably three mixing portions, wherein provided in each mixing portion is a respective mixing tool rotatable about a drive shaft, wherein preferably each mixing tool has at least two mixing vanes spaced from each other in the vertical direction.
8. Apparatus according to claim 7 characterised in that there is provided a drive device with which each mixing tool can be driven with a peripheral speed which is adjustable independently of each other at the mixing vanes, wherein preferably the drive device is so designed that at least two mixing tools can be driven in mutually opposite directions of rotation.
9. Apparatus according to claim 7 or claim 8 characterised in that each mixing tool has a mixer blade (8) arranged substantially at the container bottom, wherein the two mixing tools are spaced from each other so far that the two mixer blades (8) arranged at the container bottom do not touch each other in any position of the mixing tools, and/or that each mixing tool has a mixing vane with a mixer blade (8) which is not arranged at the container bottom, wherein the mixer blades (8) which are not arranged at the container bottom are arranged at different axial heights.
10. Apparatus according to one of claims 7 to 9 characterised in that at least one mixing vane of the one mixing tool describes a circular path which in a projection on to a parallel plane intersects with a projection of a circular path described by at least one mixing vane of the other mixing tool on to the same parallel plane.
11. Apparatus according to one of claims 1 to 10 characterised in that the air feed has openings (7) in the container wall, through which air can be blown into the container interior, wherein the openings (7) are preferably arranged at the same vertical height as the mixer blade (8) which extends substantially to the container wall, and/or that the air feed is effected by way of the mixing tool which has a hollow shaft.
12. Apparatus according to one of claims 1 to 11 characterised in that the mixer blade (8) is of a width which enlarges in the radial direction, and/or that the mixer blade (8) is in the form of an angled profile, wherein the inner angle is opposite to the direction of rotation of the mixer blade (8) and is preferably between 90° and 180°.
13. Apparatus according to one of claims 1 to 12 characterised in that the mixer blade (8) has air outlet openings on its side oriented in opposite relationship to the direction of rotation.
14. Apparatus according to one of claims 1 to 13 characterised in that a solids separator (11) is arranged above the mixing tool, wherein preferably the solids separator (11) is so designed that by means of a rotor it produces a rotational flow.

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