EP0166228A2 - Installation for carrying out a full-mould casting process - Google Patents

Abstract

1. An apparatus for carrying out the full-mould casting process having a plurality of moulding boxes (6), in which patterns (28) which can be gasified under the action of poured-in melt are surrounded by granular moulding material (13), which is loosened by compressed air during the moulding of the patterns and during the demoulding of the castings and is hardened under vacuum during the casting process, each mould cavity (12) of the moulding boxes (6) being connected to chambers for the gaseous working media by means of partition walls at least partially limiting said cavity, and in which the moulding boxes (6) can be moved by a circulating, intermittently controlled means of transport to several work-stations forming a closed work system, characterized in that the moulding boxes (6) are connected fixedly to the means of transport (1) and each moulding box has a plurality of mutually independent gaspermeable partition walls (15, 33, 36) with chambers (16, 32, 37) lying therebehind in each case, via which compressed air and vacuum are applied separately to the mould cavity (12) at correspondingly designed work-stations (A to J).

Description

The invention relates to a device for carrying out the full mold casting process with several mold boxes, in which gasified models are surrounded by granular molding material under the action of the poured melt, which is loosened with compressed air during molding of the models and during demolding of the castings and solidified under vacuum during the casting process , wherein each molding space of the molding box is connected via these at least partially delimiting partitions with chambers for the gaseous working media, and in which the molding box can be moved with a rotating, intermittently controlled means of transport which has several work stations.

Such a device is known from CH-PS 524 415. The molding boxes used in this known device each have a one-piece base plate made of sintered metal, which divides the molding space of the molding box filled with molding material from an underlying prechamber, which can be acted upon alternately with compressed air or with a vacuum at the individual work stations.

Furthermore, from DE-PS 17 58 521 a device for carrying out the full molding process is known, in which a molded box provided with a gas-permeable base plate is used, in which additionally the nocn Sidewalls are gas permeable. The majority of the combustion gases produced during casting are to be removed via the gas-permeable side walls provided here, so that only small amounts of hot gases can get into the vacuum pump via the base plate.

However, it has been shown that the sintered materials used in such mold boxes are relatively easy to smear due to the combustion gases flowing through them, since the gases also contain vapors which condense in the fine cavities of the sintered material. The latter is less apparent when casting relatively small models, since the amount of gas generated here is also relatively small. With relatively large models, however, these circumstances must be taken into account, since here the gas permeability of the partitions used decreases over time due to the passage of an increased amount of gas, and thus also the service life of the molding boxes.

When using molding boxes with relatively large dimensions of the molding space, it has also been shown that sometimes a completely satisfactory formation of the so-called fluidized or fluidized bed is not achieved in the molding space. One reason for this is likely to be that the base plate made of sintered metal has a comparatively low flow resistance, so that the flow resistance of the compressed air rising overall in the molding space is mainly determined by the flow resistance of the molding material. If the molding material is present in the mold space at different bed heights at the start of the compressed air supply, the compressed air introduced seeks the path of least resistance, for example in the region of a depression on the surface of the molding material, while molding material accumulations in the molding space are no longer sufficient to form the fluidized bed be flowed through. There there are confusing flow conditions in the base plate as a result of locally different flow resistances, especially after a long period of use, for example if gases extracted through the base plate impede the flow through deposits in the sintered material of the base plate.

This is where the invention begins, which is based on the object of providing a device for carrying out the full mold casting process, with which it is possible to produce medium-sized castings, such as e.g. Cylinder heads of water-cooled four-cylinder automotive engines or cast grapes, largely automated economically to manufacture by the full mold casting process, while at the same time a complete whirling of the molding material must be guaranteed when the compressed air is introduced even with a long period of operation.

The solution to this problem essentially results from the characterizing features of claims 1 and 4.

Because the molding chamber of the molding box can be pressurized separately with the media compressed air and vacuum at the corresponding work stations, each work step can be precisely defined at the individual work stations. Furthermore, there is no danger that the gas-permeable partition walls used in connection with the production of a fluidized bed will clog after a short time; the latter furthermore requires that the intensity of the loosening of the molding material remains precisely controllable in the long term, thus ensuring reliable automation. This in turn results in the advantage that the molding material can remain in the molding box after the casting has been removed from the mold, since it can be cooled in a simple manner at several work stations by re-blowing compressed air. The mold box must therefore not be completely emptied as usual after removal from the mold, so that it is sufficient to fix it with the To connect means of transport, that is, an automatic tilting device for the molding box can be saved. It should also be emphasized that with a stationary arrangement, the dust that otherwise arises when the molding box is dumped is advantageously not produced here.

In the case of molding boxes with larger dimensions of the molding space, it may be advantageous in connection with the cooling of the molding material that, according to a further feature of the invention, a suction device is provided at the demolding work station for a partial removal of the molding material from the molding box. By reducing the amount of hot molding material by about a third, the swirling of the remaining molding material is facilitated and thus the cooling is accelerated. In addition, the swirling in of larger models is also facilitated, since the molding space is not completely full. In such a procedure, it is therefore provided according to a further feature of the invention that a filling device is provided at the molding work station for the remaining filling of the molding box with molding material. The measures described have the great advantage that, in contrast to the prior art, it is not necessary to cool the entire molding material separately.

A further significant improvement of the device according to the preamble of claim 4 takes place in that a perforated plate with a flow resistance which is preferably higher than the base plate is provided below the bottom plate of each molding box. Such a design results in an equalization of the local supply pressure of the compressed air in the prechamber on the surface of the perforated plate, so that each hole of the perforated plate receives essentially the same supply of compressed air. The compressed air then passes through the perforated plate at the discrete points corresponding to the holes in a core flow lying transversely to the plane of the perforated plate and thus flows through the underside of the Base plate with relatively low flow resistance in a variety of individual nozzle-like jets. As a result of the comparatively lower flow resistance of the base plate, there is a uniform outlet of the compressed air above the base plate, so that there are no speed peaks, ie where the compressed air penetrates deeply into the molding material with comparatively high energy and causes a so-called harmful "bubbling", which the use of a pure perforated plate would be the case. This creates clear, favorable flow conditions for the formation of the fluidized bed over the entire area above the base plate and thus reliably achieves a fully developed fluidized bed, even if the molding material should be present in the molding space at significantly different bed heights at the start of the compressed air supply.

Further details, features and advantages of the invention result from the following description of an embodiment with reference to a drawing.

• Fig. 1 eine Draufsicht auf eine vereinfachte Darstellung einer erfindungsgemäßen Einrichtung zur Durchführung des Vollformgießverfahrens,
• Fig. 2 einen Schnitt nach Linie II/II gemäß Fig. 1,
• Fig. 3 in schematisch vereinfachter Darstellung einen Vertikalschnitt durch einen erfindungsgemäßen Formkasten und
• Fig. 4 die Einzelheit aus Kreis IV in Fig. 3 in vergrößerter Darstellung.

It shows

• 1 is a plan view of a simplified representation of a device according to the invention for carrying out the full molding process,
• 2 shows a section along line II / II of FIG. 1,
• Fig. 3 shows a schematic simplified representation of a vertical section through a molding box according to the invention and
• Fig. 4 shows the detail from circle IV in Fig. 3 in an enlarged view.

As can be seen from FIGS. 1 and 2, the device for carrying out the full mold casting process essentially consists of a rotary system 1 which forms a closed system in the sense of the working steps. It has a stand 3 resting on a base plate 2, on which a turntable 5 is rotatably mounted with a bearing ring 4. In the present example, nine molding boxes are attached to the turntable 5 at the same distance and cannot be tilted.

As can also be seen from Fig. 2, a drive shaft 7 of an electric motor 8 meshes with a non-rotatable ring gear 9 of the turntable 5. Routed by the electric motor 8, the rotary movement of the turntable 5 is controlled intermittently by control means, not shown, in such a way that a respective Molding box 6 at the work stations labeled A to J in FIG. 1 makes timed stops.

At work station A, the molding steps take place, i.e. Create a fluidized bed, then fill the remaining molding material into the molding box and finally pour. The filling takes place with the aid of a filling device, not shown, which is symbolized by the arrow 10. At workstations B and C, the work steps solidify, but the number can be expanded. At D, the step of demolding, i.e. Whirling up the molding material and removing the casting, carried out, in which case the additional step of partially removing the molding material from the molding box takes place. For this purpose, a suction device 11 symbolized by the arrow 11 is used, which can work in a known manner on the principle of a vacuum cleaner. Finally, work stations E to J (or others) follow, in which the molding material is cooled to 40 ° C to 50 ° C by creating a fluidized bed.

Each molding box 6 has a circular cross section and an inner molding space 12 for receiving the granular molding material 13, which in the present case consists of binder-free sand. The molding material 13 is filled into the molding space 12 through an upper opening 14 and rests on a bottom plate 15 on the underside of the molding space 12.

A pre-chamber 16 with a connection 17 for the supply of compressed air according to arrow 18 is provided below the molding space 12 or the base plate 15. The compressed air flowing into the pre-chamber 16 is present on the underside of the base plate 15. The base plate 15 is gas-permeable, so that the compressed air can penetrate through the base plate 15 into the molding space 12 and swirl the molding material 13 there, so that a fluidized or fluidized bed is formed.

It has been shown that the compressed air passes through the bottom plate 15, which consists, for example, of sintered metal, when it forms the sole separation between the molding space 12 and the pre-chamber 16, in a very different local flow. Such differences in the flow through the base plate 15 can result from locally different flow resistances of the sintered material, and in particular from locally different pouring heights of the molding material 13 in the molding space 12. Accumulations of the molding material 13 in the molding space 12 become due to the higher flow resistance of the compressed air only in one Fluidization no longer flows through sufficient intensity, so that the full formation of the fluidized bed is hindered.

To produce a homogeneous fully formed fluidized bed, a perforated plate 19, for example made of metal, is therefore arranged below the base plate 15 and has holes 20 for the passage of air. The flow resistance of the perforated plate 19 with the holes 20 is ins overall relatively high; in any case higher than the flow resistance which is present in the base plate 15, which is made of sintered material, for example. The perforated plate 19 thus forms the main flow resistance for the compressed air in the pre-chamber 16 and forms a throttle, in front of which a relatively high supply pressure builds up over the surface of the perforated plate 19, which can have a height of, for example, up to 5 bar. The supply pressure on the underside of the perforated plate 19 presses the compressed air through the holes 20 in discrete flows, which thus act in a similar manner to nozzles, so that the underside of the bottom plate 15 is flowed towards in the manner indicated by arrows 21 in FIG. 4. If the base plate 15 were now missing and the core flow directly into the molding material 13 according to arrows 21, this would result in a speed profile of the inflowing compressed air, as is illustrated in FIG. 4 by a dash-dotted line 22 and corresponding speed arrows 23. In this way, a core flow according to the arrows 21 and the speed profile 22 would be achieved in the area of each hole 20, which penetrates into the molding material 13 in an approximately lance-like manner and penetrates deeply into it, so that the speed profile 22 causes excessive swirling and thus dust formation of the molding material 13 arises that must be avoided.

The combination of base plate 15 / perforated plate 19 eliminates this disadvantage of so-called "bubbling", and advantageously a uniform speed profile of the compressed air flowing into the molding material 13 is obtained, as is also shown in FIG. 4 with the dashed line 24 and corresponding speed arrows 25 . The holes 20 provided in this connection have a diameter between approximately 2 and 6 mm, preferably between 3 and 5 mm and in the illustrated example case of 4 mm. They are at a mutual distance of several cm, preferably between 3 and 5 cm, in the example at a distance of 4 cm.

On the comparatively thin perforated plate 19, the considerable supply pressure lies in the antechamber 16, so that spacers 26 are provided for the rear support of the perforated plate 19, which are arranged in a grid-like manner in the example and thus form a flat-looking rear support for the perforated plate 19. The spacers 26 arranged in a grid-like manner each delimit square chambers 27, a hole 20 of the perforated plate 19 being assigned to a chamber 27 in the center. The fact that the spacers 26 largely seal the adjacent chambers 27 against one another ensures in particular that the compressed air per chamber 27 exits evenly through the base plate 15, so that the uniform flow profile 24 is obtained.

1 and 2 is the following, the mode of operation of a molding box 6 and its particular further embodiments being described in principle for the time being.

In operation, the molding material 13 located in the molding space 12 is fluidized in the manner described by compressed air supply according to arrow 18. In this state, the molding material 13 behaves essentially like a liquid, so that a model made of expanded polystyrene, as is customary in the case of full molding, can be inserted through the opening 14 easily and without damage into the fluidized molding material 13 and is completely washed by the latter even with complicated undercuts or the like. After interrupting the compressed air supply according to arrow 18, the molding material 13 settles and surrounds all surfaces of the model, which is indicated at 28 in FIG. 2. During the throttling of the compressed air supply, a vibrating device 29 can also be switched on, which sets the molding material in vibrations of a certain amplitude and frequency in order to further compress it, so that the molding material 13 follows the contours of the outer surfaces of the model 28 cleanly and tightly even with complicated shapes. The combination of the formation of a fluidized bed, on the one hand, and a final shaking, on the other hand, ensures that even the most unfavorably lying surface areas are acted upon cleanly by the molding material, on the one hand, by the general upward movement of the molding material in the fluidizing bed and, on the other hand, by the compacting settling movement during shaking.

Liquid metal can then be poured onto the plastic of the model 28 in order to gasify it and fill the mold cavity thus formed with solidified molten metal. In order to obtain a further improvement in the stability of the walls of the molding material 13 along the contour of the model 28, the molding material is subjected to negative pressure from below by suction, the suction also simultaneously evolving gases that are formed. For this purpose, a suction connection 30 separate from the pre-chamber 16 is provided on the molding box 6, from which air and gases are extracted according to arrow 31. The suction connection 30 opens into an annular space 32 in the lower region of the molding box 6 adjacent to the base plate 15, so that the suction according to arrow 31 results in a flow direction in the molding material 13 which is directed downward from the region of the opening 14. The annular space 32 is gas permeable

Circumferential wall 33 separated from the molding space 12 in such a way that no molding material 13 can penetrate into the annular space 32, but gases can be drawn off from the molding material 13.

The gas-permeable peripheral wall 33 is preferably designed as a so-called slotted perforated plate, the width of the slits being matched to the grain size of the molding material 13 in such a way that the diameter of the smallest grains of the molding material occurring is on the one hand significantly greater than the width of the slots but on the other hand significantly below the length of the Slots. In the present case, the molding material 13 made of sand has a grain size of 0.3 to 0.5, so that a slot width of 0.2 mm is selected with a slot length of 4 mm. Such slotted perforated sheets are known for other purposes and are commercially available, so that it is not necessary to go into them in detail.

Characterized in that the suction of the hot gases formed by the melt through the peripheral wall 33 adjacent to the base plate 15 is avoided that these gases must pass through the base plate 15 made of sintered metal. This fact prevents a gradual change in the flow resistance of the base plate 15 due to deposits from the gas stream, so that it maintains unchanged flow properties over a long period of operation. Furthermore, the two-part construction of the base plate 15 / perforated plate 19 on the one hand and the separate extraction of the hot gases on the other hand also make it possible to use a sintered plastic for the base plate 15, which has functional advantages and cost advantages over sintered metal.

As can also be seen from FIG. 3, the circumferential wall of the mold space 12, designated as a whole by 34, is formed differently from a cylindrical shape. In a central height range of the molding box 6, the circumferential wall 34 has a maximum diameter or maxi in an equatorial plane 35 paint the width and tapers in the example from the equatorial plane 35 both upwards and downwards. In the area of the equatorial plane 35, in the present case a further possibility is provided for extracting the combustion gases, namely a circumferential ring 36. This ring, like the circumferential wall 33, consists of a slotted perforated plate and delimits a chamber 37 with a pyramidal cross section, to which a suction connection 38 is provided.

The tapering of the molding box 6 downwards, which results in the shape of a truncated cone in the shape of a circular cross section of the peripheral wall 34, favors the compression of the molding material 13, in particular under the action of the vibrating device 29, since the inclination of the peripheral wall 34 during the settling movement by the vibrating means an additional component of the movement Molding material in the direction of the vertical central axis of the mold space 12, designated 39. The inclined formation of the circumferential wall 34 from the equatorial plane 35 upwards advantageously prevents any tendency of the molding material to rise, which is to be feared when, in particular, large-volume models are poured and metal of greater density underneath the upper sand layers, which are released by the model fills and thus exerts pressure on the sand. Such a "floating tendency" of the molding material effectively counteracts the frustoconical configuration of the peripheral wall 34 above the equatorial plane 35.

Finally, a cover plate 40 is shown in section in FIG. 3, which is used instead of the film that is usually used in order to favor the application of a vacuum. After the introduction of the cover plate 40 and a pouring funnel 41, the molding space 12 should expediently be filled up with molding material 13 up to the mark denoted by 42.

At the beginning of the operation of the device according to the invention for the full molding process according to FIGS. 1 and 2, a molding box 6 is located in the work station A, the molding space 12 of which is already filled with molding material 13. A model 28, consisting of a gasifiable foam, is now embedded in the molding material 13, while air flows into the mold space 12 from the pre-chamber 16, which is pressurized with compressed air, via the perforated plate 19 through the gas-permeable base plate 15 and causes the molding material 13 to swirl slightly. This swirl effect, which can be regulated by a control valve (not shown), brings the molding material 13 into a floating state, which allows the model 28 to be introduced into the molding material 13 with practically no resistance. Shortly before the compressed air is switched off, the molding material 13 is compressed by the vibrating device 29 attached to the side of the molding box 6. Then a cover plate 40 is placed on the molding material 13 and the pouring funnel 41 is placed on the model 28 and refilled with additional molding material up to level 42.

Thereafter, the annular spaces 32 and 37 of the molding box 6 are placed under vacuum, as a result of which the strength of the molding material 13 is increased and the same is fixed during the casting process now taking place. The casting process takes place with combustion and gasification of the model 28 consisting of foam.

After completion of the casting process, the rotary table 5 moves one work station further, so that the filled molding box 6 just described moves to work station B. Here and also at the next work station C, the dwell time serves to cool and solidify the cast molding.

The molding is demolded at work station D, this demolding being facilitated by swirling the molding material, as when molding the model 28. The the casting thus demolded can then be fed to a work table, also not shown, by means of a lifting magnet (not shown). At the same time, about a third of the hot molding material 13 is sucked off at the work station D with the aid of the suction device 11 for separate cooling. This extracted amount is symbolically represented in FIG. 2 by means of the double arrow 43.

Thereafter, the molding box 6 described in the introduction passes through several dwell times on the workstations E to J, where compressed air is blown in via the antechamber 16 in order to swirl the remaining molding material 13 located in the respective molding space 12, thus cooling the molding material to 40 to 50 ° C.

The molding box 6 then arriving from the work station J with a molding space 12 filled only 2/3 of its height then goes through the same work steps as described at the beginning; only with the exception that after the molding of the model 28, the amount of molding material 13 removed at work station D is replenished, with the aid of the filling device 10, which is symbolically indicated in FIG. 2 by the double arrow 44.

Claims (12)

1. Device for carrying out the full mold casting process with several mold boxes, in which gasified models are surrounded by granular molding material under the influence of the poured melt, which is loosened with compressed air when molding the models and when the castings are removed from the mold and solidified during the casting process under vacuum, whereby each molding space of the molding box is connected via these at least partially delimiting partitions with chambers for the gaseous working media, and in which the molding box can be moved with a rotating, intermittently controlled means of transport which has several work stations, characterized in that the molding box (6 ) are fixedly connected to the means of transport (1) and have mutually independent gas-permeable partition walls (15, 33, 36) with chambers (16, 32, 37) behind them, via which the molding space (12) separated with the media compressed air and vacuum accordingly designed workstations (A to J) can be acted upon, which form a closed system in the sense of the work steps. 2. Device according to claim 1, character- ized in that a molding device (10) for the remaining filling (44) of the molding box (6) is provided at the molding station (A). 3. Device according to claim 1 or 2, characterized in that at the work station demolding (D) a suction device (11) for a partial removal (43) of the molding material (13) from the molding box (6) is provided. 4. Device according to one of claims 1 to 3, with molded box, the base plate is designed as a gas-permeable partition, which delimits on one side a prechamber, which is provided with a connection for supplying compressed air, characterized in that below the base plate (15) a perforated plate (19) with a flow resistance that is preferably higher than that of the base plate (15) is provided. 5. Device according to claim 4, characterized in that between the perforated plate (19) and the base plate (15) spacers (26) are arranged, which are designed as chambers (27) defining webs. 6. Device according to claim 5, character- ized in that each chamber (27) is associated with a hole (20) in at least approximately central arrangement to the chamber (27). 7. Device according to one of claims 1 to 6, characterized in that a suction connection (30) is provided on each molding box (6) for generating negative pressure in the molding material (13), and that the peripheral wall (34) delimiting the molding material (13) ) is designed to be gas-permeable in the lower region (33) of the molding box (6) adjacent to the base plate (15) and is in flow connection with the suction connection (30). 8. Device according to claim 7, characterized in that the gas-permeable region (33) of the peripheral wall (34) of the molding box (6) is designed as a slotted perforated plate. 9. Device according to claim 7 or 8, characterized in that the base plate (15) consists of a material of relatively low heat resistance such as sintered plastic. 10. Device according to one of claims 1 to 9, characterized in that the peripheral wall (34) of the molding box (6) surrounding the molding material is tapered upwards, starting from an equatorial plane (35) lying in a central height range. 11. Device according to one of claims 1 to 10, characterized in that the peripheral wall (34) of the molding box (6) bordering the molding material (13), starting from an equatorial plane (35) lying in a central height range, in particular when used a vibrating device (29), tapered downwards. 12. Device according to one of claims 1 to 11, characterized in that each molding box (6) additionally has a suction connection (38) for generating negative pressure in the molding material (13) and for extracting the combustion gases therefrom, which in the area of the equatorial plane ( 35) opens into a chamber (37) which is bounded to the molding material (13) by a circumferential ring (36) made of a slotted perforated plate.

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