EP0131723B1 - Device for compacting foundry mould material by means of pressurized gas - Google Patents

Description

The invention relates to a device for compressing foundry molding material by means of pressurized gas, consisting of a pressure vessel forming a pre-pressure chamber for the pressurized gas, a molding space arranged underneath, consisting of a molding box, filling frame and a model plate with a model that closes the molding box below, on which the molding material is compressed prior to compression is loosely heaped up, and a valve with a large opening cross section arranged between the pre-pressure space and the molding space, the closure opening of which opens in the range of milliseconds.

A method and a device of the aforementioned construction are described in the applicant's patent application DE-A-32 43 951, the content of which is made the subject of the present application. It is a matter of loosely heaping the molding sand onto the model and the model plate without any additional auxiliary means, e.g. B. pressing devices or the like. To compress only by means of a pressure gas acting on the free surface of the molding material. A uniform and sufficiently high mold hardness can only be achieved with this method if a sudden increase in pressure is achieved within the molding space. The compression then takes place essentially by the exchange of momentum between the molding material particles, the braking thereof on the model plate and the top of the model and by an additional fluidization effect. A high pressure gradient, that is, a rapid build-up of pressure in the molding space, initially depends on the outlet pressure in the upstream pressure space. The higher this is, the sooner a high pressure gradient can be achieved, but the greater the structural effort to produce this form. With a representative high pre-pressure, such as in company compressed air networks, a high pressure ingredient can only be achieved by opening the valve between the pressure vessel and the mold in a few milliseconds. This alone requires special valve designs, as described in some embodiments in patent application P 32 43 951.

Another important parameter is the gas mass acting on the free molding material surface, which must be in a certain ratio to the molding material mass. For common mold box dimensions, the gas mass throughput must be more than 50 kg / s. The temporal pressure increase in the molding space should be more than 300 bar / s with a final pressure of up to approx. 8 bar. The required gas mass throughput, as well as the increase in pressure over time, require not only a quick-opening valve, but also a correspondingly large and sudden valve opening can in turn only be achieved if, despite the necessarily large closure member, its mass is kept as low as possible. This in turn means that the pressure gradient and the gas mass throughput can essentially only be controlled by the level of the admission pressure. This means that the mold hardness, which is directly dependent on these parameters, can only be regulated using the form. In view of the short cycle times of molding machines and in view of the fact that the compressed gas is generally provided in a constant pressure store or else is generated by an exothermic reaction of a fuel gas mixture, this is not possible or only with corresponding effort.

From the unpublished EP-A 0 129 210 (see Article 54 (3), EPC), from which the independent claim 1 is based, a device of the type mentioned is known. Here, a ring slide is arranged in front of the closure member, which is used on the one hand to close the pressure chamber after the opening stroke of the closure member, in order to be able to fill the pressure chamber again with compressed gas immediately after opening the closure member, and on the other hand it is provided for presetting the gas mass flow rate.

The invention has for its object to develop a device of the structure described above in such a way that the mold hardness is adjustable within wide limits.

This object is achieved in that the compression valve is associated with a control valve, the free opening cross-section is larger than the free cross-section of the valve opening, and which can be adjusted to a predetermined control cross-section by means of a control element before the opening movement of the closing member begins. The control valve is preferably arranged between the upstream pressure chamber and the compression valve, but it can also be connected downstream of the latter.

Although it would be obvious to design the valve between the compressed air tank and the molding space itself as a control valve, that is to say to control the overflow cross sections accordingly, this is practically not possible due to the special requirements mentioned at the outset which are placed on this valve. The invention therefore goes a different way by assigning a further control valve to the valve, the control cross sections of which can be preset, so that the gas mass flow rate can be regulated by the control valve at a given admission pressure. The actual compression valve, however, is not changed. The shape hardness that can be achieved during the relaxation process can thus be set within wide limits. The free opening cross section of the control valve should, if possible, be significantly larger than the free cross section of the compression valve, so that when the control cross section is completely released it is ensured that the maximum mold hardness is achieved or - given the mold hardness - the molding material is sufficiently compressed even with large dimensions of the molding box.

According to a preferred embodiment, the control valve can be closed by means of the control member after the opening stroke of the closure member.

In addition to its actual control function, the control valve thus also fulfills a safety function by ensuring that after the compression process and the venting of the molding space and when the molding box is lowered, the compressed gas cannot escape or only in a small amount. This is important because the pressure vessel and valve, on the one hand, and the molding box with filling frame, on the other hand, are separated from one another after the compression stroke in order to remove the compressed mold and to fill the molding box and filling frame again with molding material. The control member can in turn be controlled in such a way that it only reaches the open position when the compression valve has already reached its closed position.

An advantageous embodiment provides that the control valve is designed as a lifting bell, which engages over the compression valve and whose stroke can be preset.

If the valve opening is in the bottom of the pressure vessel, then according to one embodiment, an overflow space for the compressed gas is arranged above the valve opening, which is only open to the valve opening and is connected to the admission pressure space via the control valve. The overflow space serves to transfer the compressed gas from the upstream pressure space of the pressure vessel to the valve opening.

For example, the overflow space can have a wall which extends vertically upwards and surrounds the valve opening and in which a plurality of openings forming the free cross section of the control valve are provided, the control member being guided on the wall and provided with a corresponding number of openings. This embodiment gives in particular the possibility of arranging the drive for the compression valve within the pressure container.

The openings in the vertical wall of the overflow space and in the control member are preferably designed as vertical control slots, the degree of coverage of which determines the gas mass throughput.

In order to obtain the largest possible free cross-section on the compression valve, this will generally correspond to the outline shape of the molding box and filling frame, ie the valve opening will have an essentially rectangular outline. In such a case, according to an embodiment of the invention, the control slots are arranged on at least two walls of the overflow space that each rise above a rectangular side, and the control member is designed as a displaceable slot plate.

Instead, the vertical wall of the overflow space can also surround the valve opening in a circle and be provided with control slots at a uniform distance, the control member being designed as a rotatable slot ring.

The invention is described below with reference to an embodiment shown in the drawing, wherein a longitudinal section through the compression unit is shown.

In the drawing, only the parts of the compression device of a foundry molding machine necessary for understanding the invention are shown. In particular, the machine stand, the device for lifting and lowering the molding box and filling frame and, if necessary, for ejecting the finished mold from the molding box are not shown. The facilities for bringing up the model and for filling in the molding sand are also not shown, since these components are known in foundry mechanical engineering.

On a model plate 1 with a model 2 sits a molding box 3 and on this a filling frame 4. Above the molding space is a pressure vessel 5 - in the embodiment shown for receiving compressed air - which is connected via a connection 6 from a pressure accumulator or - at low admission pressure - is fed from the company's compressed air network.

The pressure vessel has a stationary plate as the bottom 7, which is provided with a plurality of holes 8 in a rust-like manner in the area above the molding space. A frame 9 is flanged to the underside of the base 7, to which an exhaust air line with a valve 10 is in turn connected. The pressure vessel 5 with the frame 9 on the one hand and the model plate 1 with model 2, molding box 3 and filling frame 4 can be moved relative to one another in order to be able to fill the molding space with molding material. Before compression, these two assemblies are brought together and pressed together tightly at their interface.

A closure member in the form of a rigid plate 11, which likewise has a large number of coaxial holes 12, interacts with the bottom 7 or its area with the holes 8. Furthermore, on the top of the valve plate within the area of the holes 12, as well as the holes 8 in the bottom 7, there is a sealing coating 13. As can be seen from the left half of the illustration, the holes 8 in the bottom 7 and the holes 12 in the valve plate 11 offset so that they do not overlap in the closed position.

The valve plate 11 is seated on a guide rod 14, which by means of a reciprocating piston 15 sliding on it from the right reproduced opening position of the valve plate can be raised into the closed position shown on the left. Damping cylinders 17, with which a crosshead 18 fastened on the guide rod 14 cooperates, sit on the cylinder 16 for the reciprocating piston 15 which is stationary within the pressure container 5. The upper end face of the lifting piston 15 acts against this crosshead 18 during its upward movement. Furthermore, the guide rod 14 is assigned a clamping device, designated as a whole by 19, of which one clamping part 20 is axially movable within a housing 21 supported on the floor and the other clamping part 22 sits on the guide rod. The clamping parts can be wedges or the like.

A presettable control valve is assigned to the compression valve described above, and in this case it is arranged in front of the compression valve because its closure member opens into the molding space. On the bottom 7 of the pressure vessel 5 there is a support body 23 which delimits an overflow space 24 between it and the bottom 7. The overflow space is delimited on the circumference by a vertical wall 29 which attaches along the outer boundary of the compression valve 8, 11, 12. The wall can be circular or rectangular and it has coaxial control slots 25, which are overlapped on the outside by a control member 26, which also has slots 27. Depending on the course of the vertical wall 29, the control member can be formed from slidable plates or a ring or ring parts.

• In der in Figur wiedergegebenen Schließlage des Ventils, in der auch die Steuerschlitze 25 des Tragkörpers 23 von dem Steuerglied 26 verschlossen sind, wird der Druckbehälter 5 über den Anschluß 6 mit Druckgas gefüllt. Die Klemmeinrichtung 19 befindet sich in der Klemmlage, so deß also die Ventilplatte 11 dicht gegen den Boden 7 angepreßt ist. Formkasten 3 und Füllrahmen 4 sind mit Formstoff, z. B. Formsand, lose gefüllt. Zum Einleiten des Öffnungshubs wird zunächst das Steuerglied 26 so verstellt, daß dessen Schlitze 27 mit den Steuerschlitzen 25 des Tragkörpers 23 ganz oder teilweise in Deckungslage kommen (siehe rechte Hälfte der Darstellung), so daß das Druckgas in den Überströmraum 24 gelangen kann. Nachfolgend wird ein mechanischer Sicherheitsriegel 26 ausgefahren und der Hubkolben 15 bei blockierter Klemmeinrichtung 19 abgesenkt, wobei er auf der Führungsstange 14 nach unten gleitet. Anschließend wird die Klemmeinrichtung 19 hydraulisch gelöst und damit werden die Führungsstange 14 und die Ventilplatte 11 freigegeben. Des über die Löcher 8 auf der Ventilplatte 11 anstehende Druckgas beschleunigt diese schlagartig nach unten, so dan das Druckgas über die Löcher 12 und über den randseitigen Bereich der Ventilplatte in den Formraum entspannen kann. Die überströmende Gasmenge und somit die auf den Formstoff wirkende Gasmasse wird durch den mittels des Steuergliedes 26 voreingestellten Steuerquerschnitt (Ausman der Überdeckung der Steuerschlitze 25, 27) bestimmt.

The operation of the device is described below:

• In the closed position of the valve shown in the figure, in which the control slots 25 of the support body 23 are closed by the control member 26, the pressure vessel 5 is filled with compressed gas via the connection 6. The clamping device 19 is in the clamping position, so that the valve plate 11 is pressed tightly against the bottom 7. Molding box 3 and filling frame 4 are with molding material, for. B. molding sand, loosely filled. To initiate the opening stroke, the control member 26 is first adjusted so that its slots 27 come fully or partially in register with the control slots 25 of the support body 23 (see right half of the illustration), so that the compressed gas can reach the overflow chamber 24. Subsequently, a mechanical safety latch 26 is extended and the reciprocating piston 15 is lowered when the clamping device 19 is blocked, whereby it slides down on the guide rod 14. Then the clamping device 19 is released hydraulically and the guide rod 14 and the valve plate 11 are released. The pressure gas present via the holes 8 on the valve plate 11 suddenly accelerates it downward, so that the pressure gas can relax into the molding space via the holes 12 and over the edge area of the valve plate. The overflowing gas quantity and thus the gas mass acting on the molding material is determined by the control cross section preset by means of the control element 26 (excess of the overlap of the control slots 25, 27).

During the opening stroke, the guide rod 14 is braked when the crosshead 18 strikes the damper 17. The valve plate 11 reaches the position shown in the right illustration. In the meantime, the molding sand is accelerated and at the same time braked on model plate 1 and model 2 and compacted in the process. After completion of the opening stroke, the control member 26 is brought back into the closed position for protection, so that a new filling process can begin without the compressed gas being able to overflow. By means of the lifting piston 15, the guide rod 14 with the valve plate 11 is then raised again via the crosshead 18 and fixed in the closed position (left half of the illustration) by means of the clamping device. The safety latch 26 is retracted. During this process, the compressed gas still present in the molding space is blown off via the valve 10.

Claims (9)

1. Device for compacting foundry mould material by means of pressurized gas, comprising a pressure tank (5) for the pressurized gas constituting an admission pressure chamber, a moulding zone positioned below it formed by moulding box (3), sand frame (4) and a pattern plate (1) with pattern (2) terminating the moulding box (3) at the bottom and onto which is loosely poured the moulding material prior to compacting and a valve with a large opening cross-section arranged between the admission pressure chamber and the moulding zone and whose closing member opens in the millisecond range and with which is associated a control valve (25, 26, 27), whose free opening cross-section is larger than the free cross-section of valve opening (8) and which can be adjusted to a given control cross-section by means of a control member (26) prior to the start of the opening movement of closing member (11).

2. Device according to claim 1, characterised in that control valve (25, 26, 27) is arranged between the admission pressure chamber (5) and the valve opening (8).

3. Device according to claims 1 or 2, characterized in that control valve (25, 27) can be closed by means of control member (26) following the opening travel of closing member (11).

4. Device according to one of the claims 1 to 3, characterized in that the control valve (25, 27) is constructed as a lifting or travel bell, which engages over the valve used for compression purposes and whose travel is preadjustable.

5. Device according to one of the claims 1 to 3, characterized in that when a valve opening (8) is provided in the bottom (7) of pressure tank (5) , an overflow zone (24) for the pressurized gas is located above the same and which is only open to the valve opening (8) and is connected by means of control valve (25, 27) to pressure tank (5).

6. Device according to claim 5, characterized in that the overflow zone (24) has a vertically upwardly extending wall (29) surrounding valve opening (8) and in which is provided a plurality of openings (25) forming the free cross-section of the control valve and that the control member (26) is guided on wall (29) and is provided with a corresponding number of openings (27).

7. Device according to claim 6, characterized in that the openings in the vertical wall (29) of overflow zone (24) and in the control member (26) are constructed as vertical control slots (25, 27).

8. Device according to claims 5 or 6, characterized in that in the case of a substantially rectangular valve opening (8), the control slots (25) are arranged on at least two walls (29) of overflow zone (24) rising in each case via a rectangular side and that the control member (26) is constructed as a slidable slotted plate.

9. Device according to claims 5 or 6, characterized in that the vertical wall (29) of overflow zone (24) surrounds the valve opening in circular manner and with uniform spacing is provided with control slots (27) and that the control member (26) is constructed as a rotary slotted ring.

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