EP0552354B1 - Device for the dry regeneration of used foundry sand - Google Patents

Abstract

PCT No. PCT/EP92/01858 Sec. 371 Date Jul. 12, 1993 Sec. 102(e) Date Jul. 12, 1993 PCT Filed Aug. 13, 1992 PCT Pub. No. WO93/03872 PCT Pub. Date Mar. 4, 1993.An arrangement for the dry reconditioning of used foundry sands in which used sand is fluidized with air or an air/gas mixture and flung against a precipitator to separate and remove substances covering sand particles. The precipitator has several planar baffle elements arranged in concentric circles around a conical deflector. A jet of used sand/air directed toward the deflector expands radially outwardly toward the baffle elements so that the jet is decelerated several times by the deflector and the baffle elements and, in a confined space, split into individual streams and swirled to provide heavy mechanical friction between sand particles and between sand particles and the baffle elements.

Description

The invention relates to an arrangement for dry regeneration of foundry sands with the features of the preamble of claim 1.

Such arrangements are known, for example from DE-PS 28 56 536, DE-OS 39 09 535, EU-A1-00 60 394, US-PS 42 66 673 or DE-OS 22 33 111.

As is apparent from DE-PS 28 56 536, the aim of these arrangements is not only to remove the binder coatings from the sand grains, but also to separate the sand from the detached coatings and other contaminants within the arrangement and during the treatment. In the last-mentioned publication, additional outlet openings for a secondary gas flow are arranged around the riser pipe in a certain way in order to achieve a locally limited, uniformly uniform flow all around. A baffle bell is used as the separating device, which is arranged at a distance above the outlet mouth of the riser pipe. A plurality of separator cells are arranged in a common upper housing box, an outlet chamber being arranged above the impact bell for each separator cell, into which the gas emerging from the impact bell enters with the detached material particles and which are connected to a common exhaust air collector. At a distance below the outlet mouth of the riser pipe, each separator has an umbrella-like catching device which is designed such that it passes on a partial flow of the stream of sand falling from the impact bell in a veil-like manner into the next separator cell, while the other partial flow is returned to the inlet nozzle of the riser pipe . This arrangement is complex overall and leaves something to be desired with regard to the separating cut in the sighting.

Another disadvantage is that high forces have to be exerted to separate the binder casings, which lead to the sand grains being partially destroyed on the impact bell and an undesirable change in the sand grain structure occurring.

In order to reduce the effort, a special swirl floor is assigned to the outlet end of the riser pipe in the arrangement according to the aforementioned publication. As a result, the escaping air flow is to expand partially radially, taking contaminants contained in the old sand with it, and thereby hit the mass of sand, dust and air falling out of the impact hood, so that the fine particles can be better removed. To improve this effect, the impact bell is pulled relatively far down and constricted at the lower outlet end. This does not improve the detachment of the binder coatings from the grains of sand.

It is an object of the invention to develop an arrangement with the features of the preamble of claim 1 so that, with a space-saving arrangement, both the release of the binder coatings from the individual grains of sand and the sighting can be significantly improved, so that the effectiveness of the regeneration in each separator cell can be increased significantly, while the sand grain structure should be preserved as completely as possible.

This object is solved by the features of claim 1.

The arrangement is particularly suitable for dry regeneration in a plant in which the used sand is treated with air or an air / gas mixture of a relatively low temperature of a maximum of 550 ° C., preferably significantly below, so that the clay-like binders in particular and the brighteners that are released from the sand grains of the old sand can largely be used again as binders.

Due to the design of the new arrangement, in particular the configurations according to the subclaims, the separator of each separator cell counteracts a large number of friction and swirl surfaces against the braked and deflected material jet emerging from the riser pipe, which divides this material jet into a plurality of partial flows of the friction surfaces, swirling strongly and causing the grains of sand in the area of the separator to move together in a strongly stirring manner Get relative movement. Due to the division into partial flows and their strong swirling in a small space, a high degree of efficiency is achieved when loosening the binder coatings. At the same time, however, the solid particles are already classified in the area of the separator and its flat elements. In this way, the coarser particles or grains of sand remain in the area of the radially flat elements, while the loosened binder particles and the fine impurities are carried along with the air flow flowing outward through the baffles formed by the flat elements and carried out upwards. The separation of the finer particles is further improved by the division into partial streams and the associated intensive enlargement of the surface of the flowing mixture. The various grains of sand, which are guided downwards on the flat elements at different distances from the axis of the riser pipe (cf. claim 2) with friction, are subject to a strong friction effect and a further screening when leaving the deflection element, since part of the carrier air or the carrier air / Gas mixture flows downwards and, when leaving the flat elements of the separator, flows outwards and upwards to the outlet, taking finer parts with it upwards. You get not only a very intensive cleaning effect but also a reliable and effective screening. Additional expansion rooms or facilities for supplying additional air for viewing are not required.

The arrangement can thus also be designed relatively simply and arranged in a space-saving manner.

The further sub-claims 3 to 10 contain features for a particularly favorable embodiment of the separator. The measures according to claims 15 and 16 result in a particularly simple material management and a compact arrangement which can be operated essentially automatically and continuously, in particular if the anode is designed according to claims 11 to 14.

The invention is explained in more detail below with the aid of schematic drawings using an exemplary embodiment.

Figur 1

schematisch eine Regenerierungsanlage für Gießerei-Altsand, bei der mit Vorteil die Anordnung gemäß der Erfindung eingesetzt werden kann;

Figur 2

im Ausschnitt die Anordnung gemäß der Erfindung in einer bevorzugten Ausführung, wie sie bei der Regenerierungsanlage noch Figur 1 eingesetzt werden kann;

Fig.3

im größeren Maßstabe und in Seitenansicht und Teilweise aufgebrochen eine Separatorzelle, wie sie bevorzugt bei den Separatoren noch Figur 2 in Reihenanordnung eingesetzt werden kann;

Fig. 4

den bei der Separotorzelle verwendeten Abscheider in Ansicht von unten;

Fig. 5

den in Figur 4 gezeigten Abscheider im senkrechten Schnitt und

Fig. 6

eine Einzelheit einer Abwandlung.

Show it:

Figure 1

schematically a regeneration system for foundry sand, in which the arrangement according to the invention can be used with advantage;

Figure 2

in section the arrangement according to the invention in a preferred Design as it can still be used in the regeneration plant Figure 1;

Fig. 3

on a larger scale and in side view and partially broken open a separator cell, as can preferably be used in the separators in FIG. 2 in a row arrangement;

Fig. 4

the separator used in the separator cell in a view from below;

Fig. 5

the separator shown in Figure 4 in vertical section and

Fig. 6

a detail of a variation.

The arrangement according to the invention is used with particular advantage in the dry regeneration of old foundry sands in systems in which the old foundry sand is only treated at relatively low temperatures of maximum 550 ° C. In a preferred embodiment, the used sand is treated in a first separator stage 1 with an air gas mixture with a temperature of approximately 300 ° C. Previously, the used sand is prepared in the usual way by separating metal parts and the like and introduced into the separator 1 at 2. The air gas mixture is supplied by a blower 4, which comes via line 3 from a heat exchanger 6, which is connected to a burner circuit 30, the exhaust air of which is discharged at 29. The separator 1 is connected with respect to the air gas mixture to form a closed circuit via a separator 5, in which the exhaust air emerging from the separator 1 is freed of dust and fine particles and is returned to the heat exchanger 6. The separated solids are derived at 7. In the regeneration system shown, the materials derived from 7 consist primarily of reusable active binder components which can be collected in corresponding silos.

Some of the separated substances can also be fed to the burner 30 as fuel. Part of the air can also be fed to the burner as the medium to be heated. In this case, a proportion of fresh air is supplied to the circuit mixture.

The sand treated in the separator 1 passes via the transfer line 12 into a second separator 10, in which the old sand is again in the circuit led air of significantly lower temperature is treated in the same way. The air is supplied via the blower 14, while the treated used sand 22 is fed to a cooler 20, in which the blower 21 cools the sand down to the desired operating temperature. From there the sand reaches a sand bunker via line 23. The circulating air passes from the separator 10 into a separator 15. The separated solids are fed to the burner, as is part of the air as fresh air. The fuel quantities still missing can be fed separately to the burner via line 31. The solid particles separated from the cooling air at 25 and collected at 27 can also be fed to the burner, while the cleaned cooling air is discharged into the atmosphere at 28.

The separators 1 and 10 are essentially the same. Each separator 1 or 10 consists of one or more rows of several separator cells 38a to 38f or 48a etc. connected in parallel. Each separator cell forms a separate unit which is separated from the other separator cells by a housing 60, 61 (FIG. 3) consists of a hollow cylindrical lower housing section 61 and an upper truncated cone-shaped housing 60.

As is evident from FIG. 2, the individual separator cells are arranged close together in the flow direction along a falling line. The supply lines 40a and 50a connected to the lower ends of the cells for the air / gas mixture and the process air, as well as the collecting lines 41 and 51 for the detached sheathing particles and foreign matter, with which the truncated cone is used, have a correspondingly relatively steep incline Housing part 60 is connected via the nozzle 77.

The feed point for the used sand shown in FIG. 1 at 2 is represented in FIG. 2 by a belt conveyor 35 and a bucket conveyor 36 or 46, the used sand being fed to the lower housing part 61 of the separator cell at 37 and via a corresponding transfer line 39 of falling inclination as shown by transfer line 68 in FIG.

In Figure 3, the distribution line for gas / air mixture or air is designated 62a. The separator cell 38/48 is connected to this via the lower inlet connection 62. The air or the air gas mixture could also be supplied at 62b, as indicated by the broken line in FIG. 3. In the lower part of the Housing 61 is provided with a valve-like installation 63, with which valve part 64, which is movable in the vertical direction via control device 65, cooperates in order to be able to close lower housing part 61 above the air supply device. The nozzle-shaped inlet opening 67 of a riser 66 is shown at a distance above the valve. The valve device is closed during start-up in order to prevent sand located in the housing part 61 from falling into the ventilation duct until there is sufficient air pressure below the valve in order to reliably entrain the sand into the riser pipe 66 when the valve is opened.

Below the transfer line 69 and above the inlet transfer line 68, a discharge device 70 is arranged in the lower housing part 61 in the form of a sheet which half covers the interior of the housing 61 and has the inclination of the outlet transfer line 69.

The sand conveyed up in the riser falls onto the discharge device 70 and can slide into the outlet transfer line 69. If the line does not take up the sand, the excess sand still falls below and is conveyed up again through the riser pipe 66.

At the end of each transfer line, a flap 90 can be provided, which is arranged at an angle α at an angle (FIG. 6) such that the sand sinking in the housing 61 closes the flap. The flap only opens again when the sand level in the housing 61 falls below the flap level.

The automatic flow through the entire system is achieved through this flap 90.

If you open the gate valve at the end of a separation row, the sand automatically begins to slide in all separators.

In this way, the dwell time of the sand in the plant and thus the regeneration time are regulated in a simple manner via the sand's throughput speed.

A separator 75 is freely arranged in the upper double-cone-shaped housing part 60, approximately at the height of the cylindrical central section of the largest diameter of the housing part 60.

In the preferred embodiment shown in FIGS. 4 and 5, the separator has a flat, preferably circular separator plate 80 which is arranged centrally above the outlet of the riser pipe 66 and transversely to the riser pipe axis. In the middle, the separator plate has a deflecting cone 82 tapering downwards. A plurality of individual flat elements project downward from the plate 80 perpendicular to the plate 80 and parallel to the axis of the riser pipe 66. Each flat element 84 or 86 is flat or curved inwards to concave.

In the preferred embodiment, the planar elements are each distributed over partial circles 83 and 85 of different radius. Two such partial circles are shown in the design. However, more than two partial circles can also be provided.

Each flat element preferably has an approximately rectangular outline, the center line of greater length running essentially parallel to the axis of the riser pipe. The center lines can also have a slight inclination inwards or outwards with respect to the riser axis.

However, the flat elements can also be at least partially replaced by V-shaped or semicircular elements which are arranged as described.

The flat elements 84, 86 of partial circles adjacent in the radial direction are set to a gap. The circumferential width of the elements 86 in the outer pitch circle corresponds approximately to the clear circumferential distance between these elements or is only slightly larger. The circumferential width of the planar elements 84 on the radially inner pitch circle 83 is approximately equal to the clear circumferential distance of the elements 86 of the first outer pitch circle or is preferably somewhat less.

The mass flow emerging from the riser 66 hits the deflection cone 82, is thus expanded and deflected and swirled over the surface and strikes the surface elements of the partial circle 83 lying there. The flat flow is broken up into a large number of partial flows, with some partial flows being deflected and swirled and thereby also influence and swirl the neighboring partial flows. The partial flows passing between the elements of the inner partial circle meet the elements of the outer pitch circle and are redirected and swirled there. In this way, a strongly swirled fluidized sand bed with strong internal friction of the grains of sand against one another and numerous friction surfaces on cone 82, plate 80 and elements 84 and 86 is created in a confined space.

This strong mechanical friction and swirling results in an intensive separation of the binder coatings and at the same time a classification of the grains of sand and a sifting between sand and detached coating particles and foreign substances. The sand particles fall down and enter the annular storage space between the housing part 61 and the riser pipe, while the removed fine particles and contaminants emerge radially from the baffle-shaped separator 75 and are supplied to the outlet port 77 with the air.

In some cases, it may be appropriate to arrange a downwardly conically tapering hollow truncated cone 66a below the deflecting element 75, on which the sand particles impact, which still have sufficient energy and movement to the outside through the air, while those that flow downward in part from the sheet-like elements Air flows upwards in this area transversely to the movement of the sand mass and can entrain further fine particles. The funnel element 66a guides the sand cloud into the annular space below.

The air and the fine particles are collected in the collectors 41 and 51, respectively, and fed to the separator. A coarse separator can be connected to this, through which coarser components are discharged prematurely and fed back to the feed point of separator 1 or separator 10 via line 41 or the like.

Should the separator be shut down for inspection or repair purposes, the inclined air supply line 40a or 50a can be used to easily remove the sand still contained in the separator cells by lowering the valve elements 64.

Claims (16)

1. An arrangement for dry regeneration of used foundry sand, wherein the used sand, containing binder coatings and impurities, and air at ambient temperature or an air/gas mixture heated to a maximum of 550°C is adapted to be supplied to a mechanical purification stage in the form of a multi-cell separator and each separator cell comprises a rising pipe open at both ends, a separator disposed above and in line with the upper outlet mouth of the rising pipe and having surfaces which slow down and deflect the jet of used sand and air or used sand, gas and air, a fan for supplying the air or air/gas mixture, a delivery device for introducing the sand or transferring the sand from one separator cell to another, a device for discharging the sand from the separator cells and a device for collecting and discharging the accumulating coating materials and impurities, characterised in that the separator (75) in each separator cell (38 or 48), in addition to the surfaces (80, 82) for slowing down and deflecting the jet rising through the rising pipe (66), has a number of flat elements (84, 86) peripherally spaced around the axis of the pipe (66) so that each element projects into and slows down the flow of the deflected jet and splits it up into component jets and makes it turbulent.
2. An arrangement according to claim 1, characterised in that respective groups of flat elements (84 or 86) are distributed around the axis of the rising pipe (66) in a ring on at least two graduated circles of different diameter, maintaining predetermined peripheral spacings.
3. An arrangement according to claim 2, characterised in that the flat elements (84 or 86) on successive graduated circles (83, 85) in the radial direction are peripherally staggered relative to one another.
4. An arrangement according to claim 2 or claim 3, characterised in that, relative to the axis of the rising pipe (66), the clear peripheral spacing between flat elements (84 or 86), preferably on each graduated circle (83 or 85), is substantially equal to or especially only slightly less than the peripheral dimension of the flat element.
5. An arrangement according to any one of claims 2 to 4, characterised in that, relative to the axis of the rising pipe (66), the width of the flat elements (84) in the peripheral direction of an inner graduated circle (83) is substantially equal to, or preferably somewhat less than, the clear spacing, measured in the peripheral direction, between the flat elements (86) on the next outer graduated circle (75).
6. An arrangement according to any one of claims 2 to 5, characterised in that each flat element (84, 86) seen from the axis of the rising pipe (66), is a flat or slightly concave plate aligned parallel to the axis of the rising pipe (66) and with its surface substantially at a tangent to or concentric with this axis.
7. An arrangement according to claim 6, characterised in that each flat element has a rectangular shape and a greater length parallel to the axis of the rising pipe (66) than in the direction at a tangent to the axis.
8. An arrangement according to any one of claims 2 to 7, characterised in that the flat elements (84, 86) project downwards approximately at right angles from a substantially flat separator plate (80) having a preferably circular shape.
9. An arrangement according to claim 8, characterised in that the plate (80) has a preferably conical separator member (82) with its tip pointing downwards and coaxial with the rising pipe (66).
10. An arrangement according to claim 8, characterised in that the diameter of the plate (80) and the radii of the graduated circles (83, 85) are chosen in dependence on the speed and the diameter of the jet of material coming out of the pipe (66) so that in the zone determined by the separator (75), the sand is separated from loosened particles of coatings and impurities.
11. An arrangement according to any one of the preceding claims, characterised in that the flat elements of the separator are at least partly V-shaped, seen in the direction parallel to the axis of the rising pipe (66).
12. An arrangement according to any one of the preceding claims, characterised in that a metal sheet (70) in the casing of the separator parts is disposed in the direction of a transfer pipe to the next separator cell and only partly covers the casing cross-section but is disposed so that the used sand can slide along the metal sheet (70) into the discharge or transfer pipe.
13. An arrangement according to claim 12, characterised in that a valve (90, 91) is disposed at the end of each transfer pipe (68, 69) and is automatically closed by the sand sinking in the casing until the sand has fallen below the level of the valve.
14. An arrangement according to any one of claims 1 to 13, characterised in that the separator element (75) of each separator cell is disposed in a double conical part (60) of the separator-cell casing so that a gap having a width at least half the radial dimension of the flat plate (80) is left between the inner wall of the part (60) and the periphery of the separator (75), the upper truncated cone being connected to the device (77) for discharging the loosened coating materials or the like.
15. An arrangement according to any one of claims 1 to 14, characterised in that the cells in each separator (38) are disposed in a line, preferably clone to one another, along a downwardly sloping line, and the supply, discharge, and transfer pipes (39, 40a, 41 or 49, 50a, 51) have a corresponding slope.
16. A device according to any one of claims 1 to 15, characterised in that the supply pipe (40a, 50a) for air or air/gas mixture is also in the form of a pipe for emptying sand from some or all of the separator cells.

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