JPH04258367A - Method and device for cleaning powder and particles - Google Patents

Abstract

PURPOSE: To clean the particle surfaces of contaminated powder and granular materials, particularly thermally reconditioned used molding sands without the particle destruction thereof although these surfaces contain undesirable particulates, such as carbonized resins, additives and chamotte. CONSTITUTION: The method is to load gas under superoverpressure (=pressurized gaseous flow) on the powder and granular materials to be cleaned or recleaned, putting the powder and granular materials 2 into a fluidized state by such loading of the pressurized gas, preventing the particles from receiving impact load or collision load by a fixedly arranged wall or movable wall and executing the cleaning only by the abrasive property or frictional surface stress of the particles. Or the apparatus is equipped with a vessel 3 having a powder and granular material inlet and a powder and granular material outlet. This vessel has a gas permeable inflow bottom 5 for the purpose of forming a fluidized layer 8. The apparatus is connected to a pressurized gas source arranged upper than the inflow bottom and has at least one nozzle 9 directing this pressurized gas stream toward the inside of the fluidized bed.

Description

[Detailed description of the invention]

[0001] The present invention aims to improve particle surfaces (single particles) of dirty powder particles.
The present invention relates to a (mechanical) cleaning method, in particular a (re)cleaning method for thermally (pre)regenerated sand, especially for used foundry sand. The invention further comprises a container having a granular material inlet and a granular material outlet, the container being provided with a gas permeable inlet bottom for the purpose of forming a fluidized bed, the bottom having a source of fluidizing gas. The present invention relates to an apparatus for carrying out the method, in which a fluidizing gas can be loaded from the source.

As is well known in the professional field, in a wide variety of technical processes using granular materials (such as, for example, and in particular sand), this granular material is generally contaminated after carrying out the process. In this case, not only would they previously be classified as waste products, but they could also be disposed of, where appropriate, by being dumped in a dump or otherwise removed (and possibly partially extracted for reuse). It has been processed.

This applies, for example, and especially to old foundry sand, which has been and is occurring in increasingly large quantities, and which has been treated as a molding material with organic binders and/or inorganic chemical binders. However, after casting, it gets dirty especially from the binder added in advance, and old casting sand gets dirty (
In other words, it cannot be easily reused (without recycling). The reclamation and therefore (at least partial) recovery of the contaminated granular material means that in the above example case the binder coat and other impurities of the sand particles consisting essentially of quartz are separated and removed from the sand particles. Assumed.

[0004] In the case of foundry (old) sand organically bound to molding sand, such a binder coating is caused especially by bentonite, which is generally added as a molding substance, depending on the heat load during casting. ---This is because chamotte (oleitization) causes it to adhere to the surface of sand particles in a substantially shell-like manner. Furthermore, the bright carbon and the additives that form it continue to become impurities in the molding sand used in casting (=old foundry sand).

[0005] Insofar, German Patent Publication No. 4
008 849, German Patent Application No. 31 03 030, no.
No. 8 15 877, No. 30 19 069, and U.S. Patent No. 2 783 511 have already proposed techniques for regenerating old foundry sand, but these techniques are insufficient from both a technical and economic point of view. But it did not produce satisfactory results. German Patent Publication No. 4 008
No. 849 itself proposes a method and apparatus for regenerating old foundry sand, which brings significant technical and therefore economical improvements over the prior art, as will become clear below. It has been found that there is still room for improvement: the quality of the recycled product is particularly important in terms of its unrestricted reuse (as far as possible) in various molding methods, and in particular in the parameters - pH value - Ooliticization. - Sludge material - Total carbon content - Loss on ignition - Characterized by particle size <90μ and (acceptable) of these parameters
Limit values are defined or established for each molding method based on corresponding experience. Beyond these parameter limits, reuse of the regenerated old foundry sand is in principle still possible, but only in suitable so-called molding material circuits.

[0006] Therefore, it is always necessary to check the concrete problems, or, taking the concrete problems into account, to check which limit values have to be maintained in the concrete application case.

[0007] The regenerated material obtained from thermal regeneration of old foundry sand is basically or generally already of relatively high quality, but still contains the components of the carbonized resin, the additives and/or the particle surface chamotte and undesirable particulate matter (because it is a nuisance). It may therefore be necessary or highly desirable to remove at least some or most of these impurities from the recycle product in order to optimally adjust the per se desirable or required quality of the recycle product. The same obviously applies to other regeneration methods.

[0008] When considering mechanical (re)cleaning in such (re)cleaning, it must be confirmed that the cleaning effect is achieved in the case of mechanical cleaning that protects the particles, which is always desirable for powder and granular materials. It is well known that this is essentially due to an abrasive effect or a frictional effect, that is, when the individual powder particles (that is, the sand particles in the case of the above example) move relative to each other while abrading each other. Excessively high relative velocities between the particles of the granular material or relative to other cleaning factors means that if the particles of the granular material to be (re)cleaned move too strongly, the particle size will decrease and the particles will be destroyed. Dangerous, insofar as particle surfaces are damaged and/or the cleaning parts can undergo considerable abrasive destruction due to impact effects, especially at corresponding (too high) pulse energies.

Several methods and devices are known for mechanically removing such impurities. Impacting and abrasive effects of the sand particles on each other are caused, similar to what occurs with fixed or moving parts of the device. Examples here include impact crushers, ball mills, vibrating vessels, tumblers, and the particularly frequently used Jacob, Simpson and Weyback impact cleaners. In order to keep the breakage and destruction of the particles as small as possible, attempts are generally made to keep the impact forces low and to make the polishing effect more effective by suitable measures, such as the oblique position of the impact surfaces.

A significant drawback common to all of these devices or the methods carried out with them is the relatively large degree of particle destruction, which is generally greater the more stringent the quality conditions required for the regeneration. This is because the more stringent the quality conditions, the more logically and therefore consistently the impingement speed will be set correspondingly higher or the number of passes through the cleaning device will be increased, but at the same time inevitably the cleaning effect will be comparatively This is because, in addition to improving the accuracy, the degree of particle destruction also increases.

SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a method of the type mentioned at the outset, which makes it possible to clean or reclean (mechanically) dirty particle surfaces of granular materials effectively and while protecting the particles. It is to provide equipment suitable and designated for carrying out the same.

According to the present invention, as a solution to the part related to the method of the above-mentioned problem, a gas flow under excessive pressure is applied to the granular material to be cleaned or recleaned, and the granular material is caused to flow due to this gas load. cleaning is carried out solely by the abrasive or abrasive (surface) stress of the particles, preventing the particles from being subjected to impact or collision loads on fixedly arranged or movable walls; The solution in question is a device according to a similar concept for carrying out the method, comprising at least one unit arranged above the inflow bottom and connected to a source of pressurized gas, directing the pressurized gas flow into the interior of the fluidized bed. It features a nozzle.

The present invention is thus, as it were, a very advantageous complement to the thermal regeneration described in German Patent Application No. 40 08 849 (see in particular Example 2 and the technology described in connection therewith in this publication). According to the present invention,
As will be described in more detail below, it is proposed to bring the granular material to be cleaned or the granular material to be recleaned into a fluidized bed state.

[0014] At that time, the front pressure in front of the nozzle is about 2.3 absolute pressure.
bar (back pressure of the fluidized bed is approximately 1.15 bar absolute)
r) the gas sonic velocity has already been achieved in the nozzle, the inflow velocity (=sonic velocity) remains constant as the prepressure increases, and on the other hand, as the pressure increases, the incoming gas mass (and therefore the pulse) increases (and) I would like to point out that.

It is of particular importance here that, in contrast to the prior art methods mentioned above, the residence time during which this frictional effect is effective can be extended virtually arbitrarily. It can be seen that, according to the method of the invention, the ideal type of mechanical sand regeneration sought is achieved exclusively by abrasion of adhering binder shells or other impurities.

[0016] In one embodiment of the invention, the nozzles can be arranged vertically and/or laterally offset to avoid impingement of sand streams accelerated by opposing air jets.

The method according to the invention also offers the possibility of carrying out the cleaning process even in the heat. This makes it possible, for example, to thermally remove organic components from the residue of a synthetic resin binder. In this way, it is also possible to burn off such organic compounds that contaminate the dust discharged from the fluidized bed with the exhaust gas into harmless residual substances. With this variant, the method of the invention thus offers the possibility of combining the thermal and mechanical steps of radical sand regeneration into a single step.

[0018] This economically very positive possibility is complemented by several still important advantages. In other words, it is important to note here that fluidized beds follow different laws from those of pneumatic conveyance. This results in an essentially favorable mode of operation. This is because only relatively small energy expenditures are required for fluidizing the solids. For air quantities entering from the side, a small amount of energy is still sufficient to produce the above-mentioned flow phenomena in the fluidized bed. Overall, the energy expenditure resulting from the method according to the invention is therefore only about 20% of that required for the conventional pneumatic method. These economic advantages are complemented by the advantage that a large amount of qualitatively valuable recycled sand is produced with low particle losses.

On the other hand, a major advantage is that there is less particle breakage and therefore less transportation, fresh sand and disposal costs. Approximately 15% fewer particles are destroyed by weight. The proportion of average particle size >0.09 decreases by about 10% during the cleaning process for a cleaning time of 1 hour.

[0020] In terms of method, it is preferred that the pressurized gas stream is guided onto the surface/inside of the granular material to be cleaned at at least one load point, with particular preference being given to the at least one load point being They are arranged in the edge area of each granular mass to be cleaned, but it is understood that they can also be provided inside it.

[0021] Furthermore, if the granular material to be cleaned is located within the range of (at least) a second substantially opposite gas flow--in some cases caused by multiple locations or multiple "source locations"-- It has therefore also turned out to be desirable to arrange at least one second pressurized gas loading point substantially opposite to the at least one first pressurized gas loading point in order to ensure particularly intensive (re)cleaning. In this case, the flow state of the (more or less relaxed) bed and the gas jet pulse (prepressure in front of the nozzle)
The impact effect can be (accurately) metered between particles (rather than by walls or built-in mechanisms) by simply selecting them according to different penetration depths into the layer, resulting in an abrasive or frictional effect. are superimposed.

Furthermore, one embodiment of the invention has proven particularly advantageous when the pressurized gas is guided substantially tangentially to the outer surface of the granular material to be cleaned at at least one pressurized gas loading point. In this way, especially when this measure is implemented in two or more places, the granules to be cleaned can be subjected to rotational movements that positively influence the desired effect, and suitable wear walls or wear assemblies can be used for this purpose. The polishing effect can be strengthened with the embedding mechanism.

It has proven to be extremely desirable if the load intensity of at least one (preferably all) pressurized gas loading points can be set in order to optimally adapt the pressurized gas loading to the respective technical task. did. Furthermore, pressurized gas
This is also the case when using compressed air, which not only solves the problem in question here in the most desirable way, but also is or can be provided inexpensively.

Therefore, in the apparatus of the present invention, at least one second nozzle is preferably arranged on the opposite side of the fluidized bed or the granular material to be cleaned with respect to at least one first nozzle. The flow strength of (preferably all) nozzles may be configurable, i.e. adjustable or adjustable.

As already mentioned above under the process-technical point of view, the device according to the invention can preferably be provided with a plurality of nozzles, each nozzle preferably arranged in pairs and arranged substantially oppositely. Moreover, the central axes of the nozzles form parallel lines, form an angle with each other, and are also on a common line.

Further preferred embodiments of the invention (both in terms of the method and in terms of the device) are specified in the dependent claims. The present invention will be further described below based on one embodiment with reference to the drawings.

Figure 1 shows thermally (preliminarily) regenerated foundry sand 2.
A device, generally designated 1, for mechanically recleaning is shown, which comprises a container 3 with a powder inlet and a powder outlet, not shown in detail, which container is arranged vertically. It has a substantially rectangular or conical shape about an axis of symmetry 4.

In order to form a fluidized bed in the area of the old foundry sand 2 to be recleaned, the vessel 3 is equipped with a gas-permeable inflow bottom 5, which consists of a spherical bed, for example, and which is supplied from a compressed air source (not shown). Fluidized vortex air is applied from below via conduit 6 in the direction of arrow 7.

The nozzles 9 arranged in the region of the fluidized bed 8 above the inlet bottom 5 are arranged substantially opposite each other in pairs and are connected to a common throttle member in the direction of the arrow 10 from a pressurized gas source (not shown). 11, the member is supplied via compressed air supply pipe 12
an annular tube 13 located inside and connected to the nozzle 9;
supply to. The compressed air supply pipe 12, and therefore the annular pipe 13, can be connected to individual/single throttle elements 11 in order to set the load strength of the old foundry sand 2 to be cleaned uniformly on all nozzles 9. However, as shown in FIG. 2, a plurality of compressed air supply pipes 12'' (shown in a plan view in the example of FIG. 2) are branched from the compressed air supply pipe 12', and one throttle member 11 is inserted into each of the compressed air supply pipes 12''. can also be arranged in such a way that the load strength of the old foundry sand 2 to be recleaned can be set appropriately differently in different zones of the fluidized bed.As can be seen, there are suitable adaptation possibilities. not only can be provided in different zones of the fluidized bed--as in the case of the embodiment shown in FIG. When each nozzle 9 is provided directly with its own diaphragm element 11, it is possible to provide different load intensities within one band.

It should be pointed out here that the container 3 does not necessarily have to have a rectangular/conical cross section, but may have a circular cross section, for example. A circular cross-section of the container 3 (at least in the area of the fluidized bed 8) is most preferred, especially when the granular material 2 to be cleaned (or the fluidized bed 8) is in operation, e.g. This is particularly the case when the container 3 is arranged to perform a rotational movement about the axis of rotational symmetry 4, which is often particularly desirable.

It should be pointed out that in one embodiment of the invention, there are at least two free spaces inside the container 3 starting in the calming space 3' and extending immediately before the inflow bottom 5 of the fluidized bed 8. Partition walls can be placed to separate (or in some cases more) parts. This should prevent back-mixing of the already mostly cleaned powder with the newly charged material. At the same time, so to speak, several fluidized beds are provided one after the other.

In the case of fluidized beds of circular cross section, this separation can be achieved by concentric areas or by fluidized beds arranged one above the other. It should be further pointed out that in the case of the above embodiment, the discharge diameter of the nozzle 9 is 3.4 mm, but it may be smaller or larger.

By the way, it should be pointed out that the container 3 can be provided with a circumferential rubber lining 14 in the region of the fluidized bed 9, one or more circumferential rubber linings 14 in the upper region of the fluidized bed 8, above the nozzle of the container 3. A heat exchanger (not shown) can be arranged, which makes it possible to reuse or continue to use from the recleaning process, especially when a recleaning fluidized bed is provided after the thermal fluidized bed. Heat can be acquired (recovered).

According to arrows 7 or 10, conduit 6 or 12
Or the gas introduced into the device 1 through 12' advances from the fluidized bed 8 and therefore from the old sand 2 to be recleaned, and then enters the container 3.
3' and finally, according to arrow 15, device 1
Expanding from

Finally, with reference to FIG. 2, it should be noted that this figure can also show a side view (rather than a top view) of the preferred arrangement. With the present invention, the granules to be cleaned, which have generally already been used technically in advance, can be cleaned in the most desirable manner.
Moreover, a method and the most desirable apparatus for carrying out the same are provided, which can be cleaned or recleaned (mechanically) with extremely (adjustable) protection of particles with an incredibly effective cleaning effect. The object of the present invention has also proven to be highly desirable, in particular, for the recleaning of old foundry sands that have been previously thermally (but possibly otherwise) reprocessed.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of the device of the present invention.

FIG. 2 is a schematic circuit diagram showing clearly the path of the pressurized gas;

[Explanation of symbols]

1　Device 2　Old foundry sand (preliminarily recycled) 3 Container 3’ part (3’s) 4 Axis of symmetry 5 Inflow bottom (3) 6 Conduit 7 Arrow 8 Fluidized bed 9 Nozzle 10 Arrow 11 Aperture member 12, 12' Compressed air supply pipe 13 Annular tube 14 Rubber lining 15 Arrow

Claims (20)

[Claims] Claim 1: A method for cleaning particle surfaces (single or multiple) of contaminated powder or granules, especially a method for (re)cleaning thermally (pre)regenerated sand, especially old foundry sand, for cleaning or recleaning. Gas under excess pressure (= pressurized gas flow) is applied to the powder and granules to be processed, and the powder and granules are brought into a fluid state by the load of this (pressurized) gas, and the particles are subjected to impact loads or A method characterized in that cleaning is carried out solely by the abrasive or abrasive (surface) stress of the particles, avoiding exposure to impact loads. 2. A method as claimed in claim 1, characterized in that the pressurized gas stream is guided onto the surface/inside of the granular material to be cleaned at at least one load point. 3. A method as claimed in claim 2, characterized in that the at least one loading point is arranged in the edge region of each granular mass to be cleaned. 4. At least one second pressurized gas loading point faces the at least one first pressurized gas loading point,
Method according to one or more of the preceding claims, characterized in that their axes are angular, form parallel lines or are arranged on a common line. 5. The pressurized gas is guided substantially tangentially to the outer surface/external region of the granular material/volume to be cleaned at at least one pressurized gas loading point. A method according to any one or more of the preceding claims. 6. A method as claimed in claim 1, characterized in that compressed air is used as the pressurized gas. 7. Method according to claim 1, characterized in that the load intensity of the pressurized gas is adjustable. 8. A device for cleaning particle surfaces (single or multiple) of dirty powder or granules, especially (re)cleaning device for thermally (pre)regenerated sand, especially old foundry sand, which comprising a container with an inlet and a powder outlet, said container having a gas-permeable inlet bottom for the purpose of forming a fluidized bed, said bottom being loaded with a fluidizing gas from a fluidizing gas source; An apparatus for carrying out the method according to one or more of the preceding claims, which is arranged above the inlet bottom (5) and connected to a source of pressurized gas, the pressurized gas flow being 1. A device characterized by at least one nozzle (9) directing the fluidized bed (8) into the interior of the fluidized bed (8). 9. At least one first nozzle (9)
9. Device according to claim 8, characterized in that at least one second nozzle (9) is assigned on the opposite side of the fluidized bed (8) or of the granular material to be cleaned (2). 10. Claim 8, characterized in that the flow strength of at least one nozzle (9) is adjustable.
or the device according to 9. 11. Device according to claim 9, characterized in that the flow strength of all nozzles (9) is adjustable. 12. A plurality of nozzles (9) are provided, each of which is arranged in pairs substantially opposite each other, or whose center lines form parallel lines. 11. The device according to any one or more of 11. 13. Claim 8, characterized in that the inlet bottom (8) consists of a spherical bed or the like, as is known per se.
12. The device according to any one or more of 12. 14. The container (3) comprises at least a fluidized bed (
14. Device according to one or more of claims 8 to 13, characterized in that it has a substantially circular cross-section in the region of 8). 15. At least a part of the nozzle (9) is arranged so that the granular material (2) to be cleaned can perform a rotational movement during operation, particularly around the axis of rotational symmetry (4) of the container (3). The apparatus according to any one or more of claims 8 to 14, characterized in that: 16. The container (3) comprises at least a fluidized bed (
8) Device according to one or more of claims 8 to 13, optionally according to claim 15, characterized in that it has a rectangular cross section in the region of . 17. Claim 8, characterized in that a partition wall or the like is arranged within the container (3) at least in the region of the fluidized bed (8), which partitions the free space inside the container into at least two parts. 17. The device according to any one or more of items 16 to 16. [Claim 18] The diameter of the nozzle (9) is approximately 1 to 2 m.
Any one of claims 8 to 17, characterized in that m.
The device described in one or more of the following paragraphs. 19. At least the fluidized bed (
19. The device according to claim 8, wherein the area of 8) is lined with a cushioning material (14) such as rubber. 20. Device according to claim 8, characterized in that at least one heat exchanger is arranged above the clean area.