EP0512201B1 - Process for manufacturing a sand mold - Google Patents

Description

The invention relates to a method for producing a sand mold in a molding machine according to the preamble of patent claim 1.

It is known from DE-AS 12 97 818 to compact the molding sand only by means of mechanical pressure forces via a press plate.

It is also known from DE-AS 26 08 740 to compress the molding sand in combination by compressed air and a press plate.

According to DE-A-3 226 171, the molding sand is compressed by pressure surge of a gaseous medium onto a molding sand loosely poured over a model device. Before the pressure surge is triggered, the pore volume on the top exposed to the pressure surge is reduced, for example, by spraying on a medium or by mechanically pressing the molding sand with a plate, so that the active area of the surface of the molding sand is enlarged and the gas pressure impact acting is thus offered an enlarged area of attack .

It is an object of the invention to achieve greater mold hardness while reducing the time required for producing the mold and thus with increased production output.

This object is achieved by the features of claim 1.

According to this solution, there is no pre-compression by air pulse or air flow, but the compression of the molding sand in this regard only begins when the mechanical compression of the molding sand begins or is already in progress. Surprisingly, this results in a greater mold hardness than in a procedure with which a pre-compression is first carried out by means of an air pulse or air flow and only then is the mechanical post-compression carried out by means of a press plate or a multi-die press head. This better mold hardening result is accompanied by less time required to produce the mold or mold half if the two compression processes are not carried out one after the other, but rather overlap one another.

Fig. 1a bis 1 d

in Folge verschiedener Einstellungen einer Formmaschine für das Sandeinfüllen (Fig. 1a), das Luftstromverdichten (Fig. 1b), das mechanische Verdichten mittels eines Vielstempelpreßhauptes (Fig. 1c) und das Trennen (Fig. 1d), wobei die Vorgänge gemäß Fig. 1b oder Fig. 1c dem Stand der Technik entsprechen, und

Fig. 2

ein Versuchsdiagramm.

The invention is explained in more detail below using an exemplary embodiment. It shows:

Fig. 1a to 1 d

as a result of various settings of a molding machine for sand filling (Fig. 1a), air flow compression (Fig. 1b), mechanical compression using a multi-ram press head (Fig. 1c) and cutting (Fig. 1d), the processes according to Fig. 1b or Fig. 1c correspond to the prior art, and

Fig. 2

an experimental diagram.

The method according to the invention was examined in comparison to the method according to the prior art on a molding machine from the applicant. This molding machine was characterized by the following essential data: Mold box size, mm 1200x1000x350 / 350 Filling frame height, mm 350 Type of press compaction Multi-punch press Number of press punches 7x9 = 63 Stamp / dimensions 130x145 Ram cylinder diameter 80 Ram piston rod diameter 65 Ram stroke max. 390 Hip distance between the press rams 5 mm Maximum hydraulic oil pressure, bar 60 Compressed air boiler volume, sqm 5 Airflow valve, NW in mm 2x150 Air pressure, bar 5.6 Valve opening time 0.3 sec

1 shows a part of the sand molding machine, namely with the model plate 10 in which there are throughflow openings 12, the actual molding box 14 and the filling box 16 located above it. In FIG. ie above the filling box, a sand bunker 18, from which the molding box 14 and the filling box 16 are filled with molding sand. Then this bunker 18 is moved away and the arrangement of model plate 10, molding box 14 and filling box 16 moves the compression unit, which consists of a multi-die press head 20 and an air supply device 22 for supplying the compressed air with which the molding sand is compressed. The press rams 20 are in their retracted position in FIG. 1b and in the lower press position in FIG. 1c. In Fig. 1d, the individual parts are in the extended position in which the molding box is separated from the model. It should be taken into account that the state of the art is shown in FIG. 1b, in which the air compression occurs mechanical compression takes place, whereas, according to the invention, air compression only begins when mechanical pressing has already started.

First of all, experiment A carried out measurements in connection with a method according to which compressed air was applied to the molding sand in the sense of airflow compression and then mechanical re-compression by hydraulic pressing. The series of tests yielded the following measurement results when 4 different special pressures were applied to the sand by the press rams: Table 1 spec. Press pressure on the molding sand kp / cm2 Mold hardness according to + GF + Degree of shape uniformity% Power requirement kW FH s 6 79 7.9 90 8.8 8th 84 4.3 95 10.2 10th 86 4.8 94 11.6 12th 90 2.8 97 12.9

On the basis of test B , the molding sand was compacted in that the air, in this case air flow, was applied by pressing at the beginning of the compression process. With the elimination of the air compression process step before the pressing process, there is also no pre-compression of the molding sand. The respective measurement results are shown in Table 2, the form hardnesses at the various specific pressing pressures the molding sand by the mechanical press of 6.8 and 12 kp / qcm gives higher values than experiment A. Table 2 spec. Press pressure on the molding sand kp / cm2 Mold hardness according to + GF + Degree of shape uniformity% Power requirement kW additional Press stroke mm FH s 6 82 9.1 88 8.8 2.3 8th 88 4.4 95 10.2 1.7 12th 91 3.0 97 12.9 -

2 shows in this test the dynamics of the oil flow in the hydraulic press for mechanical compression and the pressure in the compressed air tank for compression during 1 compression according to the experiment. When the press begins (second 1), the oil requirement increases immediately to a maximum value. It decreases continuously with the movement of the individual punches as a result of the progressive compression of the molding sand. At the moment the air flow is initiated (second 2), there is a pressure drop in the boiler, which is documented by curve L. The duration of the air flow can also be seen at approx. 0.3 sec. The oil flow thus rises again immediately, as curve H clearly shows.

The jump occurring at 1.5 seconds can be explained by the fact that not all punches start moving immediately and evenly. It should also be borne in mind that the Air pressure in the boiler was not measured at the point of compression, so that a certain hysteresis of the pressure display must be taken into account here. However, it can be seen that air compression commences clearly after the start of the mechanical pressing, which surprisingly results in better hardness values with a significant time saving in the production of the mold half.

Claims (4)

1. Method for the manufacture of a sand mould in a moulding machine by charging the mould sand into a mould box and compacting the mould sand by pressurising it with air and compacting the mould sand by the application of mechanical forces, characterised in that the compaction of the mould sand by pressurising it with air and the compaction of the mould sand by the application of mechanical forces overlap one another so that the compaction of the mould sand by pressurising it with air from the headroom located above the mould box begins only when the compaction by the application of mechanical forces begins or is already in progress.
2. Method according to Claim 1, characterised in that the pressurising with air takes place distinctly after the start of the mechanical pressing.
3. Method according to Claim 2, characterised in that the pressurising with air takes place within one second after the start of the mechanical pressing.
4. Method according to Claim 1, characterised in that at the same time as the mould sand, the surface of the mechanical press device facing away from the surface of the mould sand is acted on by the air.

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