EP0793554B1 - Method of producing light metal castings and casting mould for carrying out the method - Google Patents

Abstract

PCT No. PCT/EP96/03691 Sec. 371 Date Apr. 25, 1997 Sec. 102(e) Date Apr. 25, 1997 PCT Filed Aug. 22, 1996 PCT Pub. No. WO97/07914 PCT Pub. Date Mar. 6, 1997A method for producing light metal castings, in particular cylinder heads, cylinder blocks and/or crankcases for internal combustion engines, includes a sand mold which forms a mold cavity for the casting. The sand mold includes outer mold parts, at least one core and at least one feeder for forming a riser, wherein the mold is provided with an in-gate for receiving the metal melt and the metal melt is filled into the mold cavity under the effect of gravity. A cover core (5) is fitted onto the mold that is at least in partial regions designed to be impermeable to gas and which contains at least one feeder, and wherein immediately after the filling operation, the feeder filled with metal melt is admitted with a pressure via a pressurized gas.

Description

The invention relates to a method for manufacturing of light metal castings, in particular cylinder heads, Cylinder blocks and / or crankcases for internal combustion engines, with a mold cavity for the casting forming lost form based on sand that Outer mold parts, at least one core and at least one Has feeder to form a pressure mass, the Form is provided with a gate for the molten metal and the metal melt under the influence of gravity in the Mold cavity filled and then with a compressed gas is applied.

It is known in the manufacture of castings Light metal and both lost forms based on sand as well as permanent forms, so-called molds, as well as forms too use, which consist of permanent molded parts, so-called half molds, and sand moldings are assembled. Here lies for the serial production of castings the main advantage of lost molds based on sand in the high production speed the production of the sand molds on the one hand and also the high production speed at Pouring in relation to the pouring stroke on the other hand, as opposed to it for casting the mold, cooling the mold until it is used again do not wait after each pouring process got to. Since it is possible to also manufacture the Recycle mold parts and cores used sand recently castings made of light metal, such as cylinder heads for internal combustion engines, with high productivity poured in lost molds based on sand. The The molten metal is poured into the sand mold always under the influence of gravity, mostly in the so-called Floor pouring. To improve the structure, feeders are used on the mold used in mass castings of high quality of the casting contain appropriate feeder mass, which acts as a so-called pressure mass. This is considered a disadvantage the somewhat coarser structure as well as possibly occurring Microporosity when pouring into sand molds compared to that Pour into molds in purchase.

The low pressure casting of light metal melts is also known in permanent molds, with a Pressurizing the melt in the mold with a gas a fine, dense structure can be achieved (DE-A-21 33421, DE-A-28 18 442). Pressurization poses because of the Strength of the mold is not a problem. However, since the mold have a very long cooling time is - for high Production speeds - a very large number very expensive molds required. With the frequently occurring changes the castings are then a large number of molds to change; also make new.

From DE-B-11 35 619 it is known to have a common sand mold fixed top box and fixed bottom box to be used, whereby to produce metal castings with a dense structure Upper box and lower box composite sand mold with one sealed hood is covered or top box and the sub-box sealed to connect with each other and on the free box surface also a sealed hood after the mold cavity with the molten metal has been filled. The interior of the hood is pressurized applied, which then about the porosity of the molding sand, but especially about the free melt surfaces in the area the feeder and riser condensing onto the melt acts. Despite the use of sand molds, this procedure is time consuming since either complete each Hood must be placed over the sand mold or when putting it together the sand form must be taken care of that lower box and upper box as well as the ones placed on them Pressure hood connected to each other in a perfectly sealed manner are.

From US-A-2 960 736 it is used to solve the sealing problems known to put a pressure hood on the feed opening, which is provided with a sealing collar that goes into the melt immersed in the feeder. The disadvantage of this system is below other in that for the purpose of sealing in the end part of the feeder regardless of the size of the castings to be cast a relatively large enamel surface is available must be so that after separating the feeder from the finished Cast a correspondingly large amount of material again must be melted.

From JP-A-61 052 978 a sand casting process is known in which the molten metal is poured into the sand mold under gravity and then pressurized with a pressurized gas. To be able to carry out the pressurized gas application, is as A molded part made of temperature-resistant material based on aluminum-alumina-silica-iron oxide put on. This feeder is made of metal produced, in the sand mold in addition to the molded food part molded pressure chamber enclosed. This pressure chamber is connected to a compressed gas supply. At the The molded molded part must be shaped from the cooled casting and the pressure chamber is first removed from the sand mold, before it is completely disassembled and the sand if necessary can be worked up again.

The invention has for its object the casting of castings made of light metal under the influence of gravity and in lost forms based on sand regarding the Quality of the casting produced, especially in relation to a particularly dense and fine-grained structure with avoidance of improving microporosity as well as volume the feed material in the form of a pressure mass to reduce. Light metal in the sense of the invention includes in particular Aluminum and aluminum alloys.

The invention achieves the stated object in relation to the Procedure in that a lid core on the mold Sand base is placed, which contains at least one feeder and at least in the areas that can be pressurized with compressed gas is designed gas-impermeable and that immediately after the filling process, the one filled with molten metal Feeder pressurized with the compressed gas becomes.

With the procedure according to the invention it is possible even with lost forms made of sand, the structure of the solidifying Molten metal through additional pressurized gas to improve, condense and refine it because of the arrangement of an airtight Lid core an immediate possibility for the supply of compressed gas given is. At the same time, the volume or Mass of the pressure mass compared to the conventional casting process can be reduced by up to half if the shape is lost, so that a high saving of circulating material can be achieved can. The term "gas impermeable" in the sense of the present In addition to a gas impermeability in the invention Word sense also a gas permeability with high flow resistance, the desired when pressurized with gas Pressure build-up above the melt at a reasonable level ensures low leakage losses.

Advantageous further developments of the method according to the invention are given in claims 2 to 8. In a preferred version the method according to the invention provides that the pressurization of the molten metal in the feeder during the first critical solidification phase of the molten metal is executed, d. H. while the molten metal is still hot is, so that a corresponding influence by the pressure exerted the still flowable melt in the entire molding space is possible. This first critical solidification phase goes up to a cooling temperature of the light metal melt of 500 ° C, below this temperature Pressurization only limited effect (claims 5 and 6).

To a pressurization according to the invention in a simple manner to reach the molten metal in the feeder at the time in which the filling process ends, the filled metal melt but has not yet solidified, it is proposed above the feeder and the one containing the feeder To divide the core of the lid, to seal it and then with a connection for the admission of compressed air to be provided (claim 7). After pressurizing the Feeder is finished, this divided cavity in one further process step can be used to then apply a vacuum to this space above the feeder and at the same time the hot pouring, especially to extract gases escaping from the molds (claim 8th).

According to the invention, a (lost) mold is also used the features of the preamble of claim 9 for implementation proposed the method according to the invention, the marked is by at least one containing a feeder Sand-based lid core, on one of which the dining area sealing pressure mask can be placed, and wherein the Cover core gas-impermeable at least in the contact area of the pressure mask is trained.

To ensure perfect pressurization even during training of the lid core on the basis of sand proposed in a development of the form according to the invention, that the one containing the feeder was made on the basis of sand Cover core by one on its surface at least Core coating applied in the area of the print mask is designed to be gas-impermeable. The lid core itself can again composed of several individual cores to form a lid core be, each individual core formed gas-impermeable is, and wherein the individual cores at least in the area the feeder must be tightly connected. This Lid core or the lid cores make it possible, according to Filling the mold with metal on the in the lid core attached feeders to exert pressure by means of compressed gas, to be an improved finer and denser in this way Microstructure of the casting produced at the same time lower feeder volume - pressure volume - during the To achieve solidification.

According to a further advantageous embodiment, the lid core through an appropriate choice of the molding material and to design the binder so that it can withstand a pressure withstands up to 1 bar. To exercise the invention Process are only low pressures below up to 1 bar required to achieve the desired density and fine grain to achieve the structure.

The print mask that is on the lid core to make one Cavity is provided for pressurization can can also be used in a further development of the invention due to the thermal influence of the molten metal to vacuum the molding sand and the core sand. It is therefore designed so that immediately after solidification of the molten metal and termination of the pressurization the pressure gasses a negative pressure to that of the Print mask covered cavity can be created. For this the print mask is provided with a further connection to be provided, which can be connected to a suction device.

An advantageous embodiment of the seal of the lid core consists of using a core size as a dispersion Apply diving or spraying. The surface treatment with a core size also causes an improved Strength of the lid core. Core sizes are fundamental for the equipment of sand cores for the production of Cast iron castings to achieve smoother and non-porous Known surfaces.

For the equipment of a lid core according to the invention, um Making these gas-impermeable will become core sizes based on a dispersion of refractory fillers in provided an organic solvent. These core sizes can also contain graphite. As refractory fillers come for example silicate refractories, such as zirconium silicate, magnesium and / or aluminum silicate in question. In addition, iron oxide can also be used as refractory filler can be contained in the core size. The core sizes also contain minor ones Amounts up to 1% by weight of a synthetic resin.

Possible core sizes are the dispersions explained above, however, other material compositions are also can be used which has a gas impermeable surface of the sand cores cause.

Based on the microstructure in the inventive form of sand for light metal castings will continue to improve suggested the mold outer parts made of sand, at least partially comprehensive support shells that can be moved towards and away from the mold assign. The support shells, which preferably consist of one durable material, for example metal, serve to support the pressure from the outside of the mold during of casting and pressurization in the critical first solidification phase of the molten metal in the casting mold.

The casting mold according to the invention enables a new and economical Process for making castings from Light metals by gravity casting, especially also of such complicated parts as cylinder heads and cylinder blocks of internal combustion engines with high quality castings using sand molds for both the outer shape for the cores as well. By means of immediately after termination of the casting process in addition to the casting on the The molten metal in the feeder is pressurized it, a dense fine structure evenly throughout to produce cast part, so that on the one hand the advantages of the lost forms based on sand can and on the other hand the high quality is achieved like otherwise it can only be achieved with castings in permanent mold casting.

Fig. 1

schematisch die Darstellung einer Gießform,

Fig. 2

die Ausrüstung der Gießform gem. Fig. 1 mit einer Druckmaske,

Fig. 3

eine schematisierte Explosionsdarstellung einer Gießform in Seitenansicht für ein Kurbelgehäuse,

Fig. 4

eine schematisierte Darstellung der Gießform gem. Fig. 3 in zusammengebautem Zustand,

Fig. 5

die Darstellung gem. Fig. 1 mit zusätz licher Glocke für die Absaugung.

The invention is explained in more detail with reference to schematic drawings of exemplary embodiments. Show it

Fig. 1

schematic representation of a casting mold,

Fig. 2

the equipment of the casting mold acc. 1 with a print mask,

Fig. 3

2 shows a schematic exploded view of a casting mold in side view for a crankcase,

Fig. 4

a schematic representation of the mold according to. 3 in the assembled state,

Fig. 5

the representation acc. Fig. 1 with additional bell bell for suction.

In Fig. 1 is a mold 1 in cross section for a simple rotationally symmetrical casting with a mold cavity 2 shown. Form 1 is a lost form with outer mold parts 3.1, 3.2 and a core 4 used and provided with a lid core 5, the feeder 6 for Has formation of the pressure mass. The outer mold parts 3.1 and 3.2 are put together in the parting lines 7, likewise The core 4 can be composed of several parts to form a core package his. The number and subdivisions of the outer mold parts and the cores 7 or core packages produced according to the shape of the casting to be cast. Furthermore, a gate 8 for the molten metal on the Mold 1 formed. The lid core 5 can also consist of several Core parts are put together and one or have several feeders 6.

2 is the shape 1 after pouring the molten metal and filling the mold cavity to create a Casting 9 shown, being in the feeders of the lid core 5 the pressure masses 10 are present.

In order to fill the mold cavity with the molten metal a densification and homogenization of the structure and to avoid microporosity is about the feeder 6 on the molten metal forming the pressure mass 10 a gas pressure P is exerted. This pressure P can be up to to be 1 bar.

To this pressure on the feeder 6 on the molten metal to be able to exercise in the mold cavity until it solidifies a pressure mask 11 is placed in a sealed manner on the cover core 5. The print mask 11 has a connection 12 for the compressed air supply.

The one based on sand in a known way Cover core 5 is usually microporous and therefore air-permeable. In order to exert pressure via the feeder 6 To allow compressed air to the molten metal melt, is the lid core 5 at least on its surface in the coverage area through the pressure mask 11 by means of a Core size coated and thus in the coated area gas impermeable. This seal the surface of the lid core 5 can, for example, by immersing the lid core 5 in a core size. With the help of the core size, for example, based on a refractory dispersion Fillers in an organic solvent, such as Zirconium silicate and carbon, small amounts of synthetic resin and isoropanol, denatured with acetone and some water containing, the surface of the lid core 5 becomes so dense and made stable that the lid core 5 is airtight and that, as shown schematically in Fig. 2, via the print mask withstands the additional pressure P applied.

It is essentially only necessary to cover the core 5 sealing in all areas by coating and to make it airtight, in contact with the compressed air come. However, an economical process is the lid core in its entirety in a corresponding core size to dive, which not only has an appropriate sealing effect on the surface of the lid core but also causes increased strength.

If the lid core 5 is composed of several parts is, each part is assembled before using a Sealing core sizing externally.

The core size applied to the lid core must be in front dry and harden using the lid core.

Applying the pressure P to the cast part by means of the print mask 11 placed on the mold is done in this way long until the solidification process of the light metal melt comes to an end, d. H. to a temperature below 500 ° C is achieved. This time depends on the size of the Workpiece that is manufactured, for example in a Cylinder block with a casting weight of approx. 20 to 22 kg for internal combustion engines approx. 1.5 minutes.

In Fig. 3 is the application of the invention to the manufacture of a crankcase for internal combustion engines in exploded view of the mold parts required for this shown. The outer mold is hereby formed by the upper mold block 3.4, the side Moldings 3.5 and the lower mold parts 3.6, which in turn can be composed of individual core parts, depending on the configuration. The core block 4.1, also the crankcase core block is again made up of individual core parts composed. The upper end of the form is the Lid core 5. All mold parts and the core block 4.1 and the lid core 5 are based on sand as lost Shape. The lid core 5 can be a additional part 13, namely a cylinder liner, included, which remains in the cast casting later.

The lid core 5 contains at least one feeder 6 for the pressure mass and is further on the top with the Print mask 11 can be covered. The print mask 11 is sealed placed on the lid core 5 and so over the lid core 5 formed cavity 14 can then by means the compressed air supplied via connection 12 Pressure are applied, so that additionally on the molten metal a pressure on the molten metal in the feeder area can be exercised in the form until it solidifies.

The lid core 5 can also be on the opposite Side of the crankcase so that the shape is 180 ° is rotated.

In order to increase the dimensional accuracy during casting Stabilize casting mold and add pressure from the outside to support the casting mold, support shells 16 can be provided be that act on the outer mold parts 3.4, 3.5, 3.6. These support shells 16 can be removed before the cast mold after solidification, for example of can be folded away from the pouring station.

In Fig. 4 the lost shape is schematically based of sand, as described in Fig. 3 for a crankcase, in the assembled state schematized in section shown. The arrow 17 is the direction in which the Ejector after the support shells have been moved sideways 16 works. The cover core 5 is also on here its surface coated with a core size and treated so that it is airtight and sealed the application of a pressure of up to 1 bar by means of the Print mask 11 is enabled.

After pressurizing the lid core 5, d. H. to Completing the same, it is possible to go through a second one Port 18 in the formed by the print mask 11 Cavity 14 above the lid core 5 accumulated flue gases, which are called especially by the action of the Escape and collect melt from the molded parts and cores, suck off.

5 shows a further development of the invention, with a further suction bell 19 on the pressure mask 11 Distance is applied so that this second suction bell also covers the area of the outer mold parts in the upper area, so that all escaping from the form, evolving from the heat of smoke under the Suction bell 19 are sucked off via the connecting piece 20 can. It is possible to use the pressure mask 11 and the suction bell 19 to connect to each other via supports 21. Both the pressure mask 11 and the suction bell 19 are sealed to the lid core 5 or the outer mold parts put on. Ports 12 and 20 are connected to corresponding ones Pressurized gas supply and suction devices connected.

Claims (15)

1. A process for manufacturing castings of lightweight metal, in particular cylinder heads, cylinder blocks and/or crankcases for internal combustion engines, with a sand-based lost casting mould forming a mould cavity (2) for the casting, which mould has outer mould parts (3), at least one core (7) and at least one riser (6) for forming a pressure pig, the casting mould being provided with a runner gate (8) for a molten metal and the molten metal being poured into the mould cavity (2) under the action of gravity and then being pressurised, characterised in that a sand-based cover core (5) is laid on the casting mould, which core contains at least one riser (6), which is made impermeable to gas at least in the regions which can be acted upon by compressed gas, and that immediately after the filling operation has ended the riser (6) filled with molten metal is pressurised using the compressed gas.
2. A process according to Claim 1, characterised in that once the filling operation has ended a feed means for the compressed gas is placed in sealing manner against the partial regions which are made impermeable to gas in order to pressurise the riser (6) filled with molten metal.
3. A process according to Claim 1 or 2, characterised in that the riser (6) filled with molten metal is pressurised by a compressed gas up to about 1 bar.
4. A process according to one of Claims 1 to 3, characterised in that the impermeability to gas of the cover core (5) is brought about by applying a core dressing at least to partial regions of the cover core (5).
5. A process according to one of Claims 1 to 4, characterised in that the pressurisation of the molten metal in the riser (6) is effected during the first critical solidification phase of the molten metal.
6. A process according to one of Claims 1 to 5, characterised in that once a temperature of the metal poured into the casting mould which is below 500°C is reached, the pressurisation of the molten metal in the riser (6) is terminated.
7. A process according to one of Claims 1 to 6, characterised in that to pressurise the riser region a cavity (14) located above the cover core (5) and sealed off therefrom is pressurised with the compressed gas.
8. A process according to one of Claims 1 to 7, characterised in that once the pressurisation at the cavity (14) which can be pressurised has ended a partial vacuum is applied.
9. A casting mould for manufacturing castings of lightweight metal, in particular cylinder heads, cylinder blocks and/or crankcases for internal combustion engines, with outer mould parts (3), at least one core (4) and at least one riser (6) for forming a pressure pig, which can be connected to a means for pressurising using a pressurised gas, for performing the process according to one of Claims 1 to 8, characterised in that a sand-based cover core (5) containing at least one riser (6) is provided, on which a pressure mask (11) sealing off the riser region can be placed, and that the cover core (5) is made impermeable to gas at least in the contact region of the pressure mask (11).
10. A casting mould according to Claim 9, characterised in that the sand-based cover core (5) containing the riser (6) is made impermeable to gas by a core dressing applied to its surface at least in the region of contact for the pressure mask (11).
11. A casting mould according to one of Claims 9 or 10, characterised in that the sand-based cover core (5) withstands a pressure of up to 1 bar when the riser region is pressurised.
12. A casting mould according to one of Claims 9 to 11, characterised in that the core dressing is applied to the cover core (5) as a dispersion by means of dipping or spraying.
13. A casting mould according to one of Claims 9 to 12, characterised in that the outer mould parts (3) are allocated supporting shells (16) which at least partially surround them and move towards and away from the mould.
14. A casting mould according to one of Claims 9 to 13, characterised in that the pressure mask (11) has a connection (18) for extracting gases.
15. A casting mould according to one of Claims 9 to 14, characterised in that a bell (19) which can be placed hermetically over the pressure mask (11) on the casting mould, at least extending over the cover core (5), with a connection (20) for producing a partial vacuum, is provided.

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