EP0366902B1 - Method of and installation for compacting foundry mold material - Google Patents

Description

The invention relates to a method and devices for compressing foundry molding material which has been heaped up in a molding space above a model by means of a compressed gas which suddenly relaxes into the molding space with a relatively lower, then with a high pressure gradient and compresses the molding material as a result of the pressure surge.

This so-called air pulse process has generally proven itself in the compression of foundry molding material. It is now essentially a question of homogeneously compacted forms with high Ensure hardness even with difficult models with abrupt differences in height of the model contour or with a small edge distance.

For this purpose, it has become known from DE-OS 33 17 196 to arrange a gas-permeable layer above the molding material surface, the gas permeability of which is lower in the area above the model than in the model-free edge area. This results in a significantly improved adaptation of the mold hardness to the conditions of the model.

Then it is known from DE-OS 37 40 775 to bring about the compression not with one but with two successive pressure surges, the pressure gradient of the first pressure surge being smaller than that of the second pressure surge. However, this double pressure surge leads to an increase in the cycle time of the molding machine.

Finally, a two-stage compression process is known from CH-PS 659 012, in which compression is carried out first with the conventional air pulse and then by mechanical raising of the molding box.

Proceeding from this, the object of the present invention is to provide a method and a device for the compression of foundry molding material which is distinguished on the one hand by good compression values in critical model areas and on the other by a short cycle time.

This object is achieved with respect to the method in that the differently high pressure gradients are generated within a single pressure surge. The area of the pressure curve which rises with the high pressure gradient directly adjoins the first, flatter area of the pressure curve.

Investigations by the applicant have surprisingly shown that a pressure pulse controlled in this way gives significantly better compression values than a conventional pressure pulse. The reason for this is probably the following explanation: The first, relatively flat area of the pressure increase essentially only fluidizes the molding material, that is to say, improves its flowability without causing any noteworthy compression. The subsequent further pressure increase, which takes place with the steep pressure gradient customary for compression, benefits from the improved flow properties of the molding material, because it seamlessly connects to the pressure previously reached within the same pressure surge. This significantly improves the compressibility, especially in narrow areas between individual models or between model and molding box. The cycle time of the method according to the invention remains almost the same, because all processes take place with one and the same pressure pulse.

The first section of the pressure curve expediently runs from atmospheric pressure to an intermediate value of 1 to 3 bar gauge pressure, the subsequent section from this intermediate value to the final pressure, which, as usual, is approximately 4 to 6 bar.

Different control mechanisms can be used so that a pressure increase with the desired different pressure gradients can be realized within one and the same pressure surge. It is particularly favorable to generate the pressure surge to generate the first, flatter pressure increase in such a way that the relaxation of the pressure surge from the pressure chamber into the molding space is artificially throttled during this period. If the second section should then begin with the higher pressure gradient, this throttling effect only needs to be canceled. This procedure has the advantage that it is possible to work with the valve constructions that have already been tried and tested in practice and that one only has to delay the opening movement of this valve somewhat at the beginning. This then automatically results in an initially flat pressure rise, which then, when the valve opens further and without delay, changes to the steeper pressure rise already practiced.

A particularly expedient development of the invention consists in generating the pressure surge with its two differently steep sections only over the area of the molding material which is essentially above the model or the models, whereas the molding material in the edge area with the usual continuously steep pressure surge, without throttling.

This division of the mold space delays the sand movement over the model, which means that the sand can reach its final compaction at the same time, both on the model and on model-free sections. An ideally homogeneous compaction is thus obtained.

Various implementation options are available as a device for carrying out the method. In the simplest case, the conventional molding machine with a pressure pulse (DE-A-3518 980) is used, in which the valve between the pressure chamber and the molding space is actuated by a hydraulic and / or pneumatic pressure medium. In order to bring about the intended delay at the beginning of the opening movement of this valve, an adjustable throttle valve need only be installed in a pressure medium line for controlling this valve.

In such molding machines, for example according to DE-OS 33 17 196 above the undensified molding material have a gas-permeable layer with reduced gas permeability in the area of high model contours, it is most advantageous to design this layer as a mechanical throttle element whose gas permeability is adjustable. As a result, a reduced gas permeability and thus the desired change in the rate of pressure rise can also be brought about at the beginning of the pressure pulse.

The flow cross section of the throttle element should be adjustable from about 0% to about 50%, in particular up to about 30% of the free cross section. The opening time of the throttle element is adjustable to adapt to the model contour. The throttle element can be opened at least partially during the opening movement of the pressure chamber valve.

From a design point of view, it is recommended that the throttle element be formed by perforated plates which are displaceable relative to one another. In one position the perforated plates cover the holes of the neighboring plate, in the other position the perforated plates are aligned.

As already mentioned elsewhere, the throttle element does not have to extend over the entire cross section of the molding space, but is recommended if it is only in the area above of the model is arranged. In contrast, the rest of the area can remain free. Usually this is the edge area - however, the situation is reversed when shaping bathtubs.

So that the zones of different gas permeability are also delimited from one another in the vertical direction, it is recommended that the throttle element have bulkheads which plunge down into the molding material. These bulkheads extend through the filling frame and, if necessary, also a piece into the molding box.

Another device for performing the method according to the invention is based on DE-A-33 17 196 and is characterized in that two valves are provided between the pressure chamber or the pressure chambers on the one hand and the molding space on the other hand and that the one valve on the inner area of the molding space is connected, which is essentially above the model, whereas the other valve is connected to the model-free edge area of the molding space. This enables a largely individual pressurization of individual areas of the molding space depending on the model conditions there. Due to bulkheads that dip into the sand, mutual influence of the pressure conditions is largely limited to the end of the pressure pulse.

In the case of large cross sections of the molding space, it is within the scope of the invention to work not only with two, but with more valves and in this way in particular to divide the inner region of the molding space into several rooms.

• Figur 1 den erfindungsgemäßen Druckverlauf über der Zeit;
• Figur 2 eine Formmaschine im Vertikalschnitt;
• Figur 3 daß dazugehörige Steuerschema;
• Figur 4 einen Ausschnitt einer Formmaschine mit einem anderen Ventil und
• Figur 5 einen ähnlichen Ausschnitt mit zwei Ventilen.

Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the drawing; shows

• Figure 1 shows the pressure curve according to the invention over time;
• Figure 2 is a molding machine in vertical section;
• Figure 3 that associated control scheme;
• Figure 4 shows a section of a molding machine with another valve and
• Figure 5 shows a similar section with two valves.

In Figure 1, the ordinate shows the pressure (P) in the mold space above the sand surface and the time (T) on the abscissa.

According to the invention, the pressure in the molding space is first increased with an unusually low pressure gradient of 30 to 100 bar / sec until a pressure of approximately 1 to 3 bar is reached. This first pressure section 1 then merges seamlessly into a substantially steeper pressure section 2, which has the pressure gradient of approximately 100 to 600 bar / sec that is customary in pulse compression. The pressure equalization between the pressure chamber and the molding space is as before at around 3 to 6 bar. The pressure reduction then begins, in which the compressed gas escapes through gaps in the molding space and / or through deliberately provided openings, and is optionally extracted. The latter comes into consideration if a reaction gas is used as the compressed gas which brings about a chemical hardening of the molding material.

The section 1 upstream of the conventional pressure increase 2 causes intensive fluidization of the filled molding material. The resulting improved flowability benefits the pressure section 2, which is decisive for the compression, because this pressure section joins directly before the air from the pressure section 1 leaves the molding space. In contrast, in the known method by means of two successive pressure surges, the ventilation by the first pressure surge has already largely decayed when the second pressure surge begins.

The pressure curve according to the invention is therefore particularly suitable for molds with deep bales.

In order to demonstrate that the pressure curve according to the invention can also be subsequently implemented in existing molding plants, the known valve control according to P 35 18 980.0 is used for further description. This system is shown in FIG. 2, only the parts of the compression device necessary for understanding the invention being shown.

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 thus formed is a pressure vessel 5 - in the exemplary embodiment for receiving compressed air - which is connected via a connection 6 from a pressure accumulator or from the company Compressed air network is fed.

The pressure vessel has a plate which is provided with a plurality of openings 8 in a rust-like manner in the area above the molding space. A frame 9 is flanged to the top 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 on the other hand can be moved relative to one another in order to be able to fill the molding space with molding material up to just below the bottom 7. Before compression, the two assemblies are brought together and pressed tightly together at their interface.

A closure member in the form of a rigid valve plate 11, which likewise has a multiplicity of openings 12, interacts with the bottom 7 or its area having the openings 8. In addition, a sealing covering 13 is attached to the underside of the valve plate within the area of the openings 12. The openings 8 in the bottom 7 and the openings 12 in the valve plate 11 are offset from one another in such a way that they block each other in the closed position.

The valve plate 11 is seated on a guide rod 14, which at the same time forms the piston rod of a piston 15 of a pressure medium cylinder 16. This and the control system are described below with reference to FIG. 3.

The pressure medium cylinder 16 is arranged in a hydraulic circuit, the pressure source of which is designated 17. This is, for example, a hydraulic pump that is fed from a tank 18. From the pressure source 17, the pressure medium reaches the pressure chamber 22 of the pressure medium cylinder 16 via a control slide 19, a check valve 20 and the feed line 21.

Below its piston 15, the pressure medium cylinder 16 has a gas pressure chamber 24 which connects to one Gas pressure accumulator 25 is connected. This gas pressure accumulator 25 is divided by a movable piston 26 into a gas pressure chamber 27 and a hydraulic pressure chamber 28. The hydraulic pressure chamber 28 is connected via a control slide 29 to a high pressure source 30, which is fed from the supply tank 18.

The piston 15 of the pressure medium cylinder 16 is extended on the hydraulic side with a piston rod 31 passing through the pressure chamber 22. This upper piston rod 31 carries a cylindrical shoulder 32 and a conically tapered shoulder 33 directly on the shoulder of the piston 15, which forms a throttle with the cylindrical constriction 34 when the piston 15 moves upward.

The hydraulic feed line 21 also leads to a controllable check valve 23, the control line of which can be connected to the pressure source 17 via the control slide 19. In the unlocked switching state of the check valve 23, the pressure medium chamber is connected via a branch from the line 21 to an outlet tank 37 and a vent line 38 in a pressure-relieved manner. The drain line 39 of the drain tank 37 opens into the hydraulic tank 18th

In addition, the aforementioned branch goes from the feed line 21 to an adjustable throttle 35 and a downstream control slide 36, both of which are connected in parallel to the check valve 23 are and which allow a slow drain of the pressure medium from the pressure chamber 22.

As a result, the throttle 35, which initially only releases a small return cross-section and, in conjunction with the open control slide 36, brakes the stroke movement of the piston 15 and thus the valve plate 11 and the flat pressure section 1 in the pressure diagram of FIG. 1 can be realized.

After, for example, 50 milliseconds, the check valve 23 also jumps into the open position, so that the outflow from the pressure chamber 22 is released unhindered. The valve 11 then opens abruptly in the usual way up to the maximum opening position and thus generates the section 2 of the pressure curve.

The closing of the valve 11 and the other control functions are described in detail in DE-OS 35 18 980, so that reference can be made to avoid repetition.

The use of a proportional valve is particularly useful. It replaces the check valve 23, the throttle 35 and the spool 36.

FIG. 4 shows another implementation option for bringing about the pressure curve according to the invention. Only a schematic section of the molding machine is shown, consisting of model plate 1, model 2, molding box 3, filling frame 4 and a molding chamber opposite valve 40 closing pressure chamber 5.

The valve 40 is only shown schematically. This can be a construction according to FIG. 2 or any other valve construction. It is only necessary to ensure that this valve opens quickly enough to bring about a pressure rise rate of 100 to 600 bar / sec in the molding space above the molding material. In contrast, the valve 40 does not need to perform a delayed opening movement as described in FIGS. 2 and 3. The delayed rise in pressure at the beginning of the pressure curve is generated here in a different way and is limited to that area of the molding material which is approximately above the model.

In this area, a throttle element 41 is arranged in the space between the valve 40 and the top of the filled molding material. This throttle element consists of two adjacent, horizontally displaceable, rust-like perforated plates, the holes of which are arranged so that they are almost or completely closed in one position of the throttle element, but are open in the other position. Such grate plate valves and their actuation is known per se in molding machines, so that it need not be discussed in more detail here.

It is now essential that the throttle element 41 has baffles 42 projecting downwards. These baffles are immersed in the molded material and extend close to or into the molding box. They are positioned so that they are roughly aligned with the outer contour of the models.

The function of this throttle element is as follows: If the valve 40 is opened, the throttle element 41 is initially almost closed, so that the pressure pulse can only propagate unimpeded into the edge region A of the molding space. The inner region B, which is located below the throttle element 41, however, is only subjected to an attenuated pressure pulse, the pressure gradient of which corresponds to section 1 of the pressure curve in FIG. 1. After approximately 50 milliseconds, the throttle element 41 goes into its maximum open position and the pressure correspondingly increases with the pressure gradient of section 2 of FIG. 1.

The design according to FIG. 4 thus allows the pressure curve according to the invention to be used only in that area of the molding material which is essentially above the model, whereas the model-free edge area is subjected to a continuously steep characteristic curve by the conventional pressure pulse.

This solution can also be easily retrofitted to the already built production machines. It is only necessary to use the throttle element 41 of an intermediate flange between the filling frame and the pressure chamber.

The design according to FIG. 5 permits an even more individual pressurization of different areas of the molding space. Here, the edge area A and inner area B are each connected to their own valves 50 and 51, respectively. Both valves can be opened separately by an individual delay circuit. They are either connected to a common or separate pressure chambers.

The separation between the areas of the molding space is made by walls 52 which enclose the outlet of the valve 51, then expand above the molding material to the cross section above the model and merge into the vertical guide plates 42.

This makes it possible to individually and independently compress the inner and outer mold area.

It is within the scope of the invention to use a hardening gas which reacts chemically with the molding material as the compressed gas.

Claims (17)

1. A method of compacting foundry moulding material, poured over a pattern in a moulding chamber, by means of a pressurized gas which expands into the moulding chamber in a sudden burst initially with a relatively low pressure gradient and thereafter with a high pressure gradient and compacts the moulding material as a result of the pressure impact,
   characterised in that
   the differently sized pressure gradients are generated within a single pressure impact.
2. Method according to claim 1,
   characterised in that
   the pressure curve in a first portion having a low pressure gradient rises from atmospheric pressure up to an intermediate value of from 1 to 3 bar excess pressure and in a second portion having a higher pressure gradient rises from the intermediate value to the final pressure.
3. Method according to claim 1 or 2,
   characterised in that
   the pressure impact for generating a first portion having a low pressure gradient is artificially throttled on expansion into the moulding chamber and this throttle action is removed in order to generate the second portion.
4. Method according to claim 3,
   characterised in that
   the throttling of the pressure impact is produced by delayed opening of a valve that blocks off the moulding chamber from the pressurised gas.
5. Method according to any one of claims 1 to 4,
   characterised in that
   the pressure impact with its two portions is generated only over a portion of the free moulding material surface, especially over the portion that is located essentially over the pattern, whereas the moulding material in the remainder of the region, especially in the region free of the pattern, is acted upon by the customary, continuously steep pressure gradient.
6. Apparatus for carrying out the method according to any one of claims 1 to 5, in which the moulding chamber is blocked off by at least one valve (11) from the pressurised gas stored in at least one pressure chamber (5) and the actuation of that valve (11) is effected by a hydraulic and/or pneumatic pressure medium and the pattern plate (1) optionally has ventilation holes,
   characterised in that
   a valve (35) with an opening of adjustable cross-section is built into a pressure medium line for controlling the valve (11).
7. Apparatus for carrying out the method according to any one of claims 1 to 5, in which the moulding chamber is blocked off by at least one valve (40) from the pressurised gas stored in at least one pressure chamber (5) and the pattern plate (1) optionally has ventilation holes and in which at least one gas-permeable throttle element (41) is arranged above the uncompacted moulding material,
   characterised in that
   the gas permeability of the throttle element (41) is adjustable.
8. Apparatus according to claim 7,
   characterised in that
   the throughflow cross-section of the throttle element (41) is adjustable from approximately 0 % up to approximately 50 %, especially up to approximately 30 %, of the free cross-section.
9. Apparatus according to claim 7 or 8,
   characterised in that
   the opening time of the throttle element (41) is adjustable.
10. Apparatus according to claim 7, 8 or 9,
    characterised in that
    the adjustment of the throttle element (41) in the opening direction is made at least partly during the opening movement of the valve (40).
11. Apparatus according to any one of claims 7 to 10,
    characterised in that
    the throttle element (41) is formed by perforated plates that rest against one another and can be displaced relative to one another.
12. Apparatus according to any one of claims 7 to 11,
    characterised in that
    the throttle element (41) is arranged only in the region (B) above the pattern (2).
13. Apparatus according to any one of claims 7 to 12,
    characterised in that
    the throttle element (41) has bulkhead walls (42) that extend downwards into the moulding material.
14. Apparatus according to either one of claims 6 and 7, in which the moulding chamber is blocked off by valves from the pressure gas stored in at least one pressure chamber and the pattern plate (1) optionally has ventilation holes,
    characterised in that
    at least two valves (50, 51) are provided, and one valve is connected to the inner region (B) of the moulding chamber that is located essentially over the patterns, whereas the other valve (52) is connected to the pattern-free region, especially the peripheral region (A) of the moulding chamber.
15. Apparatus according to claim 14,
    characterised in that
    the connection of the valves (50, 51) to the respective regions (A, B) of the moulding chamber is made by walls (52, 42) which partially extend into the moulding material.
16. Apparatus according to any one of claims 7 to 15,
    characterised in that
    where the moulding chamber is of large cross-section the inner region (B) of the moulding chamber is divided into several chambers with additional throttle elements or valves.
17. Apparatus according to any one of claims 7 to 16,
    characterised in that
    only the throttle element (41) or valve (51) for the inner region (B) generates in the moulding chamber the pressure curve in accordance with any one of claims 1 to 5.

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