EP0326870B1 - Method and machine for compacting foundry sand - Google Patents

Abstract

With this method and the machine for carrying out the method, it is possible to achieve optimum compaction of foundry sand (24) for the production of castings, both as regards the hardness of the mould and as regards gas permeability. Matched to the respective foundry sand quality established by means of a standard test piece using the Brinell ball impression method, flexible settings for a plurality of vibratory pressing phases are possible, in which a plurality of pressing surfaces, such as a frame of a press housing (12), a top plate (13), and a plurality of press rams (14) can be used individually or in groups, simultaneously or in succession with adjustable pressing forces. In addition, unbalance motors (9) of a vibration unit are connected to a continuously adjustable frequency converter so that the vibrations required for the corresponding vibratory pressing phase can be set. <IMAGE>

Description

The invention relates to a method and a device for carrying out the method for compacting foundry molding sand, in which a progressive compression takes place in the vibratory pressing method, with a vibrating table, a molding frame, a filling frame that absorbs the excess sand, a multi-stamp consisting of a press housing with a large number of press dies. Press head and a vibration unit supported by springs and equipped with unbalance motors.

There is a whole series of known processes for compacting foundry mold sand for the production of sand molds in mold boxes, as well as for boxless mold parts, all of which have the same goal, the most uniform possible distribution of hardness in the mold sand over the entire area, especially in the edge zones of the sand mold and regardless of the shape of the model body, in order to obtain a perfect cast when the mold is subsequently poured off.

In addition to the tried and tested tamping by hand, mechanical presses, in particular high-pressure presses, mechanical shaking with post-presses, vacuum presses and the so-called shooting process, in which the molding sand is shot into the molding box under excess pressure, are known above all for automatic series production.

The most advantageous method with a satisfactory degree of compaction for each model form has proven to be the vibrating press method, as a combination of two methods in which the advantages of a mechanical vibrating device are paired with the advantages of a compaction head.

• In einer ersten Stufe wird ein Modell in einen Formkasten auf dem Vibrationstisch eingelegt;
• in einer zweiten Stufe wird Formsand mit einem Bindemittel bis an den oberen Rand des Formkastens eingefüllt;
• in einer dritten Stufe wird die Tragplatte mit den Pressstempeln nach unten verschoben, bis die Pressstempel auf der Oberfläche des Formsandes lose aufliegen;
• in einer vierten Stufe werden die Unwuchtmotoren eingeschaltet, wobei der Formsand durch die Vibration und die lose durch ihr Eigengewicht auf dem Formsand aufliegenden Pressstempel gefestigt wird.
• Sobald die gewünschte Festigung des Formsandes erreicht ist, werden die Unwuchtmotoren stillgesetzt, die Pressstempel hochgehoben und der Formkasten kann weggeführt werden.

Such a method and such a device for the production of foundry molds in mold boxes is known from GB-A-2 130 511. The device comprises a vibration table with unbalance motors, which rests on springs, for receiving a molding box, and a press device fastened to a yoke above the vibration table with a plurality of press rams which are adjustable in height. The press rams, individually vertically displaceable, rest in a support plate that can be adjusted in height by means of piston-cylinder units. They hang loosely in the support plate and, due to their own weight, act on the surface of the molding sand filled in the molding box when the support plate is moved downwards.

• In a first stage, a model is placed in a molding box on the vibration table;
• in a second stage molding sand is filled with a binder up to the top of the molding box;
• in a third stage the support plate with the press rams is moved downwards until the press rams lie loosely on the surface of the molding sand;
• In a fourth stage, the unbalance motors are switched on, the molding sand being fixed by the vibration and the press rams lying loosely on the molding sand due to their own weight.
• As soon as the desired strengthening of the molding sand is achieved, the unbalance motors are stopped, the press rams are raised and the molding box can be removed.

With CH-PS No. 662 072 A5, another machine for the production of casting molds has become known, which also provides this vibratory pressing method. The machine comprises a frame construction through which a horizontal conveyor leads, which serves as a feeder and guide for the objects to be treated by the machine. The frame construction carries a ramming device at the top with a so-called compression head consisting of a plurality of fluid cylinders and a vibration device at the bottom. The vibrating device has an anvil supported on springs, which can be brought into engagement with the mold-making station by a lifting means and is effectively connected to a shock-vibrating device also supported on springs. During operation, the objects and materials required for mold production are fed in via the conveyor. As soon as they have taken the correct position in the mold production station, the vibrating device is switched on and the vertical oscillating movements are transmitted to the anvil or to the mold production station.

A disadvantage of the latter is that the shaking movement is generated by the impact of the anvil or hammer on the underside of the press table, which results in a very strong impact delay and considerable noise.

A disadvantage of both known devices is that the compacting head, which consists of a large number of press cylinders, compresses the sand, particularly in the area of the compacting heads, while unpressed and partially loose sand predominates between the individual compacting heads and around the compacting heads themselves. It has also been shown that most known devices for the production of casting molds cannot take full account of the given sand properties.

The invention is therefore based on the object of improving the inadequate consideration of the sand properties in various operating sands and to propose a method and a device for carrying out the method for compacting foundry mold sand for the production of mold parts, with which a procedural and operational optimization of the sand-dependent shape parameters is achieved can be so that there is both a sufficient mold hardness and an ideal gas permeability of the molded parts.

This object is achieved by the invention characterized in claims 1 and 2.

The advantages achieved by the invention are essentially to be seen in the fact that a flexible adjustment of the compression parameters in the case of changing sand properties, in accordance with a hardness of the shape determined beforehand on a standard test specimen using the ball indentation method using the Brinell method, and uniformity in the case of widely varying model contours Compression is also possible with molded parts with very different model contours that overpressing or underpressing in extreme areas and the so-called bridging are prevented and clean and small casting puddles can be carried out.

With the frequency of the unbalance motors of the vibration unit, which can be infinitely adjusted via a frequency converter, it is also possible to replace the noise-intensive anvil strokes known from conventional vibratory press machines with an almost silent and more effective vibro excitation of the subject matter of the invention. By reducing the vibration frequency during the final pressing phase, when the vibration unit is placed on the stop bar, the unbalance motors can be run continuously, which besides the practically silent transitions also enables a rational clock sequence.

On the accompanying drawings, an embodiment of the invention is shown, which is explained in more detail below.

• Fig. 1 einen Aufriss einer Vorrichtung zur Herstellung von Giessformteilen im Schnitt dargestellt, in einer ersten Phase, der Vorvibrierphase,
• Fig. 2 einen Aufriss der Vorrichtung wie Fig. 1, in einer zweiten Phase, der Konsolidierungs- und Entlüftungsphase,
• Fig. 3 einen Aufriss der Vorrichtung wie Fig. 1 in einer dritten Phase, der Vorverdichtungsphase,
• Fig. 4 einen Aufriss der Vorrichtung wie Fig. 1 in einer vierten Phase, der Press-Verdichtungsphase,
• Fig. 5 einen Aufriss der Vorrichtung wie Fig. 1 in einer fünften Phase, der Endverdichtungsphase.

Show it:

• 1 shows an elevation of a device for the production of mold parts in section, in a first phase, the pre-vibrating phase,
• 2 shows an elevation of the device as in FIG. 1, in a second phase, the consolidation and venting phase,
• 3 shows an elevation of the device like FIG. 1 in a third phase, the pre-compression phase,
• 4 shows an elevation of the device as in FIG. 1 in a fourth phase, the press-compression phase,
• Fig. 5 is an elevation of the device like Fig. 1 in a fifth phase, the final compression phase.

1, 2, 3, 4 and 5, 1 denotes a vibrating table. A model plate carrier 4 with a model 5, a molding frame 2 and a filling frame 3 is fastened on the vibration table 1. The model plate carrier 4 is used to hold a positive or a negative model plate 22. Above the model 5, molding sand 24 is filled in the molding frame 2 and in the filling frame 3. The vibrating table 1 is supported on prestressed reactor springs 8 on an exciter frame 6. The excitation frame 6 itself is supported on insulation springs 7 which rest on a machine foundation 19. On the exciter frame 6, two unbalance motors 9 are arranged with opposite directions of rotation. At least one solid is on the machine foundation 19 Stop bar 10 constructed with a support plate 20, which interacts with a support chuck 21 of the vibration table 1. A vertically movable multi-punch press head 11 is provided above the vibrating table 1. The multi-die press head 11 consists of three press units, the press housing 12, a mother plate 13 and a number of press dies 14. Each of these press units can be actuated individually and independently of the others. The press housing 12 has an outer piston / cylinder unit 16 with a pressure cylinder 17 and a pressure piston 18 and can be moved in the vertical direction. The mother plate 13 is slidably guided in the press housing 12 on the inner walls and is moved parallel to the direction of movement of the press housing by a plurality of inner pistons / cylinder units 25 installed in the press housing 12. The press punches 14 are slidably guided in the mother plate 13 parallel to the direction of movement of the mother plate 13 and are likewise moved by an inner piston / cylinder unit 26 installed in the press housing 12. The supply lines 27, 28 for a pressure medium to the inner piston / cylinder units 25, 26 of the press housing 12 are integrated in the cover 15 of the press housing 12.

The device described above for compacting foundry mold sand for the production of mold parts works as follows:

In a first phase, the pre-vibrating phase (see FIG. 1), a predetermined amount of molding sand 24, which is oriented towards the properties of the molding sand 24 and the shape and size of the model 5, is applied by a sand dosing device (not shown), with the multi-punch press head being moved 11 and with the unbalance motors 9 switched on, filled into the mold frame 2 or into the filler frame 3 via the model 5 arranged on the model plate 22. After the filling process has ended, the sand metering device moves and the multi-stamp press head 11 moves in its place. By the opposite direction of rotation of the unbalance motors 9, a sinusoidal force acts on the vibration system consisting of the vibrating table 1, exciter frame 6, insulation springs 7 and reactor springs 8, which resonates with the rhythm of the force acting and the forced frequency, with a linear, vertical oscillating movement from the exciter frame 6 to the Vibration table 1 is transmitted. The ideal oscillation deflection can be set by adjusting the pretensioning force of the reactor springs 8 and the rotational speed of the unbalance motors 9 which can be infinitely regulated by means of a frequency converter, not shown. The molding sand 24 is fluidized by the vibration and distributed evenly in the molding frame 2, in the filling frame 3 and along the contours of the model 5. The internal friction and adhesive forces of the molding sand to be compacted, which are essentially dependent on the moisture content, are reduced under the action of the oscillating movements, so that the individual grains of sand move downward under the action of gravity and the bulk material is compacted. At the same time, bridging of the molding sand is also ruled out, even with complicated models.

In a second phase, the consolidation and venting phase (see FIG. 2), the complete multi-punch press head 11 is lowered in the vertical direction with the aid of the piston / cylinder unit 16 and moved into the sand, the press housing 12, the mother plate 13 and the Die 14 lie in a common press plane and thus form a contour press head. In this state, the molding sand 24 is uniformly pre-compressed and deaerated in the press housing 12 by the multi-stamp press head 11 with an increasing pressure force of the outer piston / cylinder unit 16 with the same internal pressure of the inner piston / cylinder units 25, 26. The pressure forces of the hydraulic systems are set so that the resulting total deflection of the insulation springs 7 and the reactor springs 8 of the vibration system is less than the distance between the support plate 20 of the stop beam 10 and the support chuck 21 of the vibrating table 1, ie the oscillating system vibrates freely at a high frequency without colliding with the stop beam 10.

In a third phase, the pre-compression phase (see FIG. 3), the frame of the press housing 12 is immersed further in the molding sand 24 with the help of the outer piston / cylinder unit 16 and the press rams 14 with the aid of the inner piston / cylinder unit 26, while the mother plate 13 remains and the associated inner piston / cylinder units 25 are gradually compressed at a balanced pressure. The immersion depth of the individual press punches 14 depends on the contour of the model 5, on the characteristics of the molding sand 24 and on the inner contour of the molding box 2. Despite increasing pressure in the outer piston / cylinder unit 16 and in the inner piston / cylinder units 26, the vibration system vibrates with compressed insulation springs 7 and reactor springs 8 still free.

In a fourth phase, the press-compression phase (see FIG. 4), the pressure in the outer piston / cylinder unit 16 and in the inner piston / cylinder units 25 assigned to the mother plate 13 is further increased, the frame of the press housing 12 and the mother plate 13 further compress the molding sand 24. The vibration system is based on the stop bar 10 and the frequency of the geared motors 9 is reduced; the pressing phase begins.

In a fifth phase, the final compression phase (see FIG. 5), the back of the mold is pressed through the frame of the press housing with the help of the outer piston / cylinder unit 16 and the inner piston / cylinder units 25 at an optimal contact pressure with the vibration table 1 resting on the stop beam 12 and the mother plate 13 pressed up finally the lower edge of the frame of the press housing 12 falls below the parting line between the molding frame 2 and the filling frame 3 and the pressure in the outer piston / cylinder unit 16 is released via a drain valve, not shown.

Suitable risers and pouring pits are either molded into the sand or cut into the molding sand after compaction. The determination of the respective amount of molding sand, the setting of the various compressive forces for the individual pressing phases, the setting of the preload of the reactor springs 8 and the changes in the drive frequencies for the unbalance motors are coordinated with the respective molding sand properties, which are carried out before each start of work using a standard test specimen using the ball impression method according to Brinell method is determined.

It is readily conceivable to design the press housing 12 such that individual press punches 14 or groups of press punches 14 can be acted upon separately. By a certain distance between the individual press rams or by the optional omission of individual press rams during the pressing, a much better compression of the molding sand is possible, but the press heads known as multi-rams, equipped with directly adjacent press rams, work after a short press travel through the teeth of the sand grains (cutting angle) same as a flat press.

Claims (6)

1. Method, for the compacting or foundry moulding sand, in which a progressive compaction takes place by the vibratory pressing process,
characterised by a stepwise preliminary compaction, which is preprogrammed matched to the respective state of the moulding sand (24) ascertained at a test body by the Brinell method and in which

- in a first phase, a bias of reactor springs (8) is set, which is adjusted to a sand quality, to a pattern (5) and to a mould frame size, and the mould sand mass is filled into a mould frame (2) with running eccentric motors (9) driven at an appropriately set frequency by way of a frequency converter,

- in a second phase, the moulding sand charge (24) is compacted and ventilated by an outline press head, which forms a common press plane and consists of a press housing (12), a mother matrix plate (13) and a plurality of press dies (14), while the eccentric motors (9) are running at the same frequency,

- in a third phase, the press dies (14) and the frame of the press housing (12) are impressed into the moulding sand (2 ) at a predetermined pressure with the mother matrix plate (13) stationary, while the eccentric motors (9) are running at the same frequency,

- in a fourth phase, the moulding sand (24) is pressed further with constant pressure on the frame of the press housing (12) and on the mother matrix plate (13) and with slightly incresed pressure on the press dies (14), while the eccentric motors (9) are running at a reduced frequency, and

- in a fifth phase, the mould back is pressed further through the frame of the press housing (12) and through the mother matrix plate (13) with slow reduction in pressure on the press dies (14), while the vibrator unit is resting thereon and while the eccentric motors (9) are running at a frequency reduced once again.

2. Device for the performance of the method for the compacting of foundry moulding sand (24) with a vibratory table (1), a mould frame (2), a filling frame (3) taking up the excess sand, a multi-die press head (11) consisting of a press housing (12) with a plurality of press dies (14) and a vibrator unit supported by springs (7, 8) and equipped with eccentric motors (9),
characterised thereby,
that the multi-die press head (11) displays three press units each independent of the other and that a steplessly regulable frequency converter is associated with the eccentric motors (9).

3. Device according to claim 2,
characterised thereby,
that the three press units display a press housing (12), which is movable in vertical direction by an external piston-cylinder unit (16), a mother matrix plate (13), which is borne to be displaceable at the inward walls in the press housing (12) and parallelly to the direction of movement of the press housing (12) and which is movable by internal piston-cylinder units (25), and the press dies (14), which are borne in the mother matrix plate (13) to be displaceable parallelly to the direction of movement of the press housing (12) and movable by further internal piston-cylinder units (26).

4. Device according to claim 3,
characterised thereby,
that a separate feed (28) for a pressure medium to the press dies (14) is associated with each individual internal piston-cylinder unit (26) or a group of internal piston-cylinder units (26).

5. Method according to claim 1,
characterised thereby,
that in the third phase, groups of press dies (14) and/or individual press dies (14) are impressed into the moulding sand (24) in alternation by the same pressure force or by different pressure forces.

6. Method according to claim 1,
characterised thereby,
that in the third phase, groups of press dies (14) and/or individual press dies (14) are impressed into the moulding sand (24) in alternation to an equal adjustable depth or to different adjustable depths.

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