EP0128974B1 - Moulding machine for producing moulds or cores from moulding sand - Google Patents

Abstract

1. A moulding machine for producing casting moulds or casting cores from moulding sand by vacuum injection, the machine comprising : a moulding box or core box (1) having a baseplate (4) and a top plate (12) and formed with slit-like nozzles (3, 5, 13) ; clamping jaws (8) engaging the moulding or core box (1) laterally ; and a lifting table (7) pressing the moulding or core box (1) into engagement with a sand filler (10 or 44), the sand filler (10 or 44) having an injection head (11) or a fluidizing head (46) and a gassing plate (35), the latter being adapted to be pushed over the moulding or core box (1), the plate (35) being connectable by way of valves (39, 40) to a supply of carrier gas or to scavenging air, the slit-like nozzles (3, 5, 13) being connected by way of a suction line (24) to a vacuum device, characterised in that individual auxiliary suction lines connected to the slit-like nozzles (3, 5, 13) extend to a tubular main (23) connected, by way of the suction line (24) and of an associated valve (25) and also by way of a parallel auxiliary suction line (28, 31) having a control valve (32) and an absorber (30), to a vacuum tank (26).

Description

The invention relates to a molding machine for producing casting molds or cores from molding sand according to the vacuum shooting principle, which consists of a mold or core box provided with a base plate and a top plate and slot nozzles, clamping jaws acting laterally on the mold or core box and a mold or core box against a lifting table pressing a sand filling device, the sand filling device being equipped with a shooting head or a fluidizing head and a gassing plate which can be pushed over the mold or core box and which can be connected via valves to a carrier source or to purging air, and wherein the slot nozzles are connected to a via a suction line Vacuum device are connected.

In the known molding machines of this type, the molding sand is usually introduced and compressed into the molding or core box with a very high air or gas pressure, the slot nozzles arranged in the box frame, the base plate and the top plate depending on the shape of the model Venting during the compression process and the removal of the gases formed during the hardening of the binder added to the molding sand and the purge air. The gases emerging from the slot nozzles are often harmful to health and must therefore be extracted and rendered harmless by means of large interception hoods covering the molding machine. However, suction devices of this type have the disadvantage that usually not all harmful gases are suctioned off and removed. From DE-OS 26 21 153 it is known to condense the catalyst gas used for curing mold parts for the purpose of recovery and reuse in a cold trap. Another disadvantage is that the one-sided application of compressed sand to the molding sand requires long processing times during compression and curing.

On the other hand, from DE-OS 30 08 235 a method is known in which two adjacent box parts are provided with air discharge openings and one vacuum chamber each, each of which is connected to a suction device via a suction line. The upper part of the box is connected to a sand reservoir via a shot opening and a closure device. The mold cavity is filled with molding or core sand according to the vacuum firing principle by means of a vacuum created suddenly in the chamber. If necessary, a subsequent compression and / or curing with a reaction or catalyst gas and a flushing with air then take place according to the air pressure pulse principle. This embodiment also has the disadvantage that the molded or core sands, the nature of which often changes and the flowability of which is very temperature-dependent owing to the admixed binders, are not sufficiently compacted. Curing by means of a reaction or catalyst gas blown into the compressed core is relatively slow. There is also a need to shorten the curing time for faster series production.

The invention is therefore based on the object of designing a molding machine of the generic type in such a way that the compaction can be adapted to different and / or changing operating conditions and properties of the molding sand and the curing time is shortened.

This object is achieved according to the invention in that individual auxiliary suction lines connected to the slot nozzles open into a collecting tube which is connected to a vacuum container on the one hand via the suction line and an associated valve and on the other hand via a parallel additional suction line equipped with a control valve and an absorption apparatus is.

This training has the essential advantage that the filling and compacting of the molding sand can be adapted as best as possible to the operating conditions, in particular the type and nature of the molding sand, by filling and compacting either only by vacuum or in conjunction with the compressed gas, so that a substantial larger pressure difference is formed. Even poorly flowable molding sands can be injected evenly and quickly with the simultaneous use of vacuum and compressed gas. For curing, the effect of the vacuum has the advantage that the reaction is accelerated and less binders and catalyst substances are required. The reason for this is a more uniform gas flow through the molding or core mass. Furthermore, the vacuum device is advantageously used for degassing, so that the exhaust gases can no longer escape into the open, but are discharged in a closed system. During the filling and compression process, the vacuum can be applied directly to the slot nozzles, whereas the gases extracted during curing are passed through an absorption device for the purpose of separating harmless components.

Various devices are possible for connecting the vacuum device to the slot nozzles of the molded or core box and the base and top plate. In a preferred embodiment, a hollow slide is arranged under the base plate equipped with slot nozzles, the cavity of which is connected to the slot nozzles and the collecting tube, and the lateral clamping jaws have a cavity which corresponds to that on the relevant slot nozzles and the manifold in connection.

In order to achieve a tight connection between the slot nozzles of the form or core box and the clamping jaws, they are provided with sealing rings on their contact surfaces, which also serve to pull off and position the box halves laterally when their actuating cylinders are retracted with a suction cup-like effect.

• Fig. 1 eine Formmaschine, teilweise geschnitten, mit einer Vakuumeinrichtung,
• Fig. 2 den Form- oder Kernkasten aus der Fig. 1 in einem größeren Maßstab,
• Fig. 3 den Gegenstand der Fig. 1 in einem anderen Betriebszustand und
• Fig. 4 eine andere Sandfülleinrichtung für die in Fig. 1 dargestellte Formmaschine.

The invention is shown in the drawing, for example; it shows:

• 1 is a molding machine, partially in section, with a vacuum device,
• 2 shows the molded or core box from FIG. 1 on a larger scale,
• Fig. 3 shows the subject of Fig. 1 in a different operating condition and
• Fig. 4 shows another sand filling device for the molding machine shown in Fig. 1.

The molding machine shown in FIGS. 1 to 3 is assigned a molding or core box 1 which is formed in two parts in the cone and whose cavity 2 corresponds to the contours of the mold or core to be manufactured. Depending on the design of the cavity 2, both halves are provided with slot nozzles 3, which are each connected to a common outlet opening via small bores. The molded or core box 1 rests on a base plate 4 equipped with slot nozzles 5 and is covered by a top plate 12 provided with slot nozzles 13 and a central filling opening. The base plate 4 rests on a hollow slide 6, the cavity of which is connected to the slot nozzles 5 of the base plate 4 via small bores. The hollow slide 6 is connected via a suction line to a collecting pipe 23, the meaning of which is described in more detail below. The hollow slide 6 is supported on a lifting table 7 which can be raised and lowered by means of a lifting cylinder. Furthermore, lateral clamping jaws 8 are provided, which can be pressed against the two halves of the mold or core box 1 by means of an adjusting cylinder 9. The clamping jaws 8, like the hollow slide 6, are hollow, the cavity being connected via a bore to the outlet opening assigned to the slot nozzles 3 and also connected to the collecting tube 23. In a similar way, the slot nozzles 13 of the head plate 12 are connected to the collecting pipe 23 via channels.

The embodiment shown in FIGS. 1 to 3 is suitable for processing plastic molding sand. For this purpose, a sand filling device 10 with a shooting head 11 is arranged on an upper machine part, which has a common filling opening with the head plate 12. Above the shooting head 11 there is a shooting cylinder 14 which is provided with slits and which is surrounded by a jacket 18 at a distance. Above the jacket 18 there is the reservoir 15 for the molding sand and a sand slide 16 actuated by an actuating cylinder 17. A valve seat 19 is also incorporated into the jacket 18, to which a shooting valve 20 is assigned, which is acted upon by a compressed air pump 22 via a pressure line 21 becomes.

The manifold 23 connected to the slit nozzles 3, 5 and 13 is connected via a suction line 24 provided with a valve 25 to a vacuum container 26 which is kept at a pressure of approximately 0.95 bar by a vacuum pump 27. In parallel to the suction line 24, a suction line 28 equipped with a check valve 29 is provided, which is connected via an absorption apparatus 30, e.g. B. a washing machine, a suction line 31 and a control valve 32 is also connected to the vacuum container 26.

As can be seen in particular in FIG. 2, the contact surfaces of the clamping jaws 8 are provided with sealing rings 33, 34. The inner sealing ring 33 seals the vacuum line between the outlet bores of the slot nozzles 3 and the cavity of the clamping jaws 8. By pressing the clamping jaws 8 against the mold or core box 1, the sealing rings 33 and 34 of each clamping jaw 8 develop a suction cup-like connection to the Form or core box 1 and enables positioning and pulling apart of the two box halves with the aid of the actuating cylinder 9.

The above-mentioned components have the position shown in FIG. 1 for filling and compacting the plastic molding sand. After the lifting table 7 has been pressed against the base plate 4 of the mold or core box 1, the valve 20 controlling the compressed air and the valve 25 assigned to the vacuum device are briefly opened depending on the mold or core geometry, forming a large pressure difference. The valves 20, 25 are preferably linked in terms of control technology in such a way that they can be opened selectively and variably at the same time or independently of one another or overlapping in time. For example, depending on the type of molding sand, it may be useful to first generate a pre-pressure by introducing compressed air and then to connect the vacuum; With other plastic molding sands, a reverse procedure or simultaneous exposure to compressed air and vacuum can be advantageous.

After compaction, which takes about 0.5 to several seconds, depending on the shape or core design and the type of molding sand, the molding machine is prepared for the curing process. For this purpose, the lifting table 7 is lowered and a gassing plate 35, which is slidably mounted, for example, on guide rails 36, is pushed between the molded or core box 1 and its head plate 12; then the lifting table 7 pushed up again (see FIG. 3). The gassing plate 35 has a gassing channel 37 which is connected to a gassing line 38. The gassing line 38 is divided and connected on the one hand via a valve 40 to a carrier gas source and on the other hand via a valve 39 to a purge air line. A line equipped with a valve 42 for introducing catalyst gas is also provided on the branch assigned to the carrier. The gas passed through the gassing line 38 can be heated if necessary with a heating device 43.

After the preparation of the molding machine for the curing process, the control valve 32 assigned to the vacuum device and the valve 40 belonging to the carrier gas source are opened simultaneously. The binder contained in the molding sand is cured with only a small pressure difference, the vacuum on the vacuum side being able to be set by means of the control valves 32 as a function of the mold or core geometry and density. The choice of the carrier gas and the catalyst gas depends on the type of binder added to the molding sand. If the binder consists of water glass, for example, C0 _{2 is used} as the carrier gas. If, on the other hand, they are polymerizable synthetic resins, N ₂ can be provided as the carrier gas, to which a suitable catalyst gas is added as a hardener. Examples of suitable polymerizable organic synthetic resins for molding sand are phenolic resins, isocyanates, furan resins. If thermally curable synthetic resins are to be used, the molding or core box 1 and the associated top and bottom plates 4, 12 heating devices (not shown) are provided. During the curing process and the subsequent ventilation process, in which the valve 40 is closed and the valve 39 is open, the exhaust gases are passed through the absorption apparatus 30, in which harmful constituents can be separated off.

For flowable molding sands, the molding machine is equipped with the sand filling device 44 shown in FIG. 4 instead of the sand filling device 10 shown in FIG. 1. A fluidizing head 46 and a sand slide 47 are arranged at the lower end of the storage container 45. The flowable molding sand is compressed by simultaneously opening the valve 25 associated with the vacuum device and a compressed air valve 48 assigned to the fluidizing head 46. At the same time, a vibrator 49 mounted on the lifting table 7 can be actuated if necessary (cf. FIG. 1). ). The procedure for curing is the same as that explained in connection with FIGS. 1 to 3.

The individual operations of the molding machine are controlled logically. Depending on the molding or core mass and the type of binder, a work cycle usually lasts 1 to several minutes.

Claims (4)

1. A moulding machine for producing casting moulds or casting cores from moulding sand by vacuum injection, the machine comprising: a moulding box or core box (1) having a baseplate (4) and a top plate (12) and formed with slit-like nozzles (3, 5, 13); clamping jaws (8) engaging the moulding or core box (1) laterally; and a lifting table (7) pressing the moulding or core box (1) into engagement with a sand filler (10 or 44), the sand filler (10 or 44) having an injection head (11) or a fluidizing head (46) and a gassing plate (35), the latter being adapted to be pushed over the moulding or core box (1), the plate (35) being connectable by way of valves (39,40) to a supply of carrier gas or to scavenging air, the slit-like nozzles (3, 5,13) being connected by way of a suction line (24) to a vacuum device, characterised in that individual auxiliary suction lines connected to the slit-like nozzles (3, 5, 13) extend to a tubular main (23) connected, by way of the suction line (24) and of an associated valve (25) and also by way of a parallel auxiliary suction line (28, 31) having a control valve (32) and an absorber (30), to a vacuum tank (26).

2. A machine according to claim 1, characterised in that a hollow slider (6) is disposed below the base plate (4) formed with the slit-like nozzles (5) and the internal space of the slider (6) communicates with such nozzles (5) and with the tubular main (23).

3. A moulding machine according to claim 1 or 2, characterised in that the lateral clamping jaws (8) have a hollow interior communicating with the tubular main (23) and with the slit-like nozzles (3) on the particular side concerned.

4. A machine according to claim 3, characterised in that the clamping jaws (8) have ring seals (33, 34) on their contact surfaces.

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