EP3320999A1 - Production method with a vacuum sand mould - Google Patents

Abstract

The invention relates to a manufacturing method for producing cast parts from metal with a sand mold (1). The sand mold (1) is in this case produced in a molding box (2) by means of a vacuum molding process. According to the invention, the sand mold (1) located under reduced pressure in the molding box (2) is first filled with liquid metal (5). The molding box (2) is then subjected in whole or in part wholly or partially to a cooling liquid (4) to the sand casting mold (1) which is under reduced pressure, and is opened at points in which cooling liquid is applied, simultaneously or before the cooling liquid is applied. As a result, cooling liquid (4) is absorbed into the sand casting mold (1) which is under reduced pressure, as a result of which the solidifying casting (3) is very quickly quenched.

Description

The present invention relates to a method for producing cast parts from metal with a sand mold according to the preamble of claim 1.

In particular, the present invention relates to casting production with sand casting molds made by a vacuum molding process. Casting method for producing castings of metal, e.g. Of iron, aluminum or magnesium alloys are well known. Typical casting methods that require sand casting molds are gravity casting or low pressure casting.

In low-pressure casting, a molding box is positioned with a vacuum or negative pressure sand casting mold via a Druckvergiesseinrichtung. The molding box with the standing under vacuum / vacuum sand mold is then docked over the sprue of the mold box at the furnace outlet of the Druckvergiesseinrichtung and connected to this non-positively. By a controlled pressure build-up in the furnace interior, liquid metal rises via an oven riser into the furnace outlet of the Druckvergiesseinrichtung and flows through the sprue of the molding box in the sprue of the sand mold. The sprue of the sand casting mold leads into a sprue area, which distributes the flow of liquid metal over a channel system and optimally fills the mold cavities of the sand casting mold. So that turbulence does not occur during flow of the liquid metal or material-specific critical velocities are exceeded, which negatively influence the later component mechanically or chemically (oxidation processes), the flow velocity of the liquid metal is regulated by the pressure in the pressure casting device. After the casting has been completed, the mold is allowed to cool until the casting produced is sufficiently solidified that it can be unpacked from the molding box. For example, the sand mold is passed over a vibrating table to release the sand from the casting.

In gravity casting, a sand mold is filled from above with liquid metal. Thanks to gravity - mostly turbulent - the metal flows into the sprue of the sand casting mold and is also distributed in the sprue area via distribution channels into the cavities of the casting mold. Through the use of appropriate filters in the sprue of the sand casting mold, a laminar flow can also be generated during gravity casting. The filters have the additional advantage that even impurities or oxidation products can be filtered out of the liquid metal.

The described low-pressure casting method or gravity casting is used in particular for the casting of light metals, e.g. Aluminum alloys, used.

For casting on an industrial scale, it is important to operate the casting plant as efficiently as possible. Therefore, it is important to achieve short cycle times for the production of the individual castings. An important factor for the cycle time is the cooling rate of the manufactured component. The faster the casting solidifies or is rigid enough to unpack it from the sand mold or the molding box, the more efficiently the casting plant can be operated.
However, faster quenching or solidification of the liquid metal also brings about improved mechanical properties for the casting produced. This means that a fast and targeted cooling of the melt produces metal structures with better mechanical properties (eg hardening of the casting).

In order to accelerate the cooling of the sand mold, prior art solutions are already known.

The font US 7121318 suggests that after filling a sand mold (a sand stock conglomerate with binder) with liquid metal, the sand mold comes into contact with a solvent, eg water. As a result, the liquid metal is cooled faster in the edge zones and begins to solidify there. Of the Edge area of the casting with a solidified surface also comes into direct contact with the solvent and is thereby further quenched. The solvent also dissolves the sand mold in the cooled area. The US patent suggests that the sand mold is immersed in a bath filled with the solvent.

In another document, the US Pat. No. 7,216,691 , It is proposed to spray a filled with liquid metal sand mold with water or immerse in a water bath for faster cooling of the mold or faster solidification of the casting contained therein. The purpose of this is also the dissolution of the sand casting mold. Targeted loading of individual areas of the sand casting mold with the coolant also achieves a zonal deterrent and thus also zonally better mechanical properties on the casting produced.

The font DE 11 2006 000 627 T5 describes another method and a sand mold with improved heat dissipation, preferably for the production of castings from aluminum alloys. The sand mold and the cores are made of quartz sand, which are mixed with a water-soluble binder, so that the quartz sand remains in the desired shape. For purposeful hardening of certain parts of the casting to be produced, water-soluble cores are used at corresponding points of the sand casting mold. If, after the casting process, the sand casting mold is splashed with water at the points where the water-soluble cores are used, the water-soluble binder dissolves and the cores are washed away. As a result, not only in a relatively short time a solidified edge zone forms on the casting, but the casting is quenched at this point even faster, as soon as the core is washed away and the water jet comes into direct contact with the solidified casting surface. This can also take place a local hardening of the casting.

The font US 4,222,429 describes a cooling method for a vacuum sand mold. Here, the under-pressure sand mold is filled with liquid metal. By means of the negative pressure in the sand casting mold, which persists through the suction, additional gases (vaporizing styrene resin) are evacuated from the sand casting mold during the casting process. To cool the sand casting mold, a gas is subsequently rinsed through the (porous) casting mold and then sucked out of it again, which causes additional cooling or quenching of the casting mold and the cast part. As a cooling gas, for example, air is used, which is pumped by means of a compressor in the sand casting mold. It can also be rinsed with water vapor instead of air. This rinse of the sand mold results in heat removal. In addition to flushing the sand mold with a cooling gas or air, the sand mold can be sprayed with water from the outside.

The present invention is therefore based on the object to provide a method for the production of castings, which greatly improves the cooling of sand casting molds produced by means of vacuum molding and the castings solidifying therein.

This object is achieved by the method for producing castings according to claim 1.

• Herstellung der Sandgussform in einem Formkasten mit einem Unterdruck-Formverfahren
• Füllung der hergestellten Sandgussform im Formkasten mit flüssigem Metall
• Kühlung der Sandgussform und des darin erstarrenden Gussteiles mit einer Kühlflüssigkeit (z.B. Wasser).

Known casting methods for producing cast parts with a sand casting mold include the following steps:

• Production of the sand mold in a molding box with a vacuum molding method
• Filling the manufactured sand casting mold in the molding box with liquid metal
• Cooling the sand casting mold and the casting solidifying therein with a cooling liquid (eg water).

• die sich unter Unterdruck befindliche Sandgussform im Formkasten wird zunächst mit flüssigem Metall gefüllt
• der Formkasten wird anschliessend mit der sich darin unter Unterdruck befindlichen Sandgussform ganz oder teilweise mit einer Kühlflüssigkeit beaufschlagt
• der Formkasten wird - nach oder unmittelbar vor der Kühlflüssigkeitsbeaufschlagung - an Stellen mit Kühlflüssigkeitsbeaufschlagung geöffnet, so dass die Kühlflüssigkeit in die sich unter Unterdruck befindliche Sandgussform gesogen wird und dadurch das erstarrende Gussteil abschreckt.

However, the process according to the invention still contains the following specific Steps:

• the vacuum mold sand mold in the mold box is first filled with liquid metal
• the mold box is then wholly or partly pressurized with a cooling liquid in the sand mold located therein under reduced pressure
• the molding box is opened - after or immediately before the coolant application - at locations with Kühlflüssigkeitsbeaufschlagung so that the cooling liquid is sucked into the located under negative pressure sand mold and thereby deters the solidifying casting.

The process according to the invention has numerous advantages over known casting processes. Thanks to the use of sand casting molds produced by the vacuum process, no binder is required (cost savings). The sand preparation is very easy. There are no expensive and bulky sand processing plants needed. The sand consumption is low with the inventive production method and accordingly environmentally friendly, because no additives are needed. Sand casting molds produced by means of vacuum molding require less draft and, in contrast to other sand casting molds, can also have undercuts. As the sand casting molds produced by the vacuum process contain no water, no water vapor is generated during the casting process. Thus, even lower wall thicknesses can be cast on the casting. In addition, castings produced thereby have a higher dimensional accuracy and can have a very fine surface, since sand with a small particle size can be used. Even burr-free production is possible. The castings then do not necessarily have to be sandblasted.
The inventive production method can also be used in all known and common casting.
In the production process according to the invention, the quenching of the casting with water or another cooling liquid is brought to a very high level by the resulting suction effect. The cooling liquid penetrates much faster and deeper into the porous sand casting mold, so that significantly higher cooling rates The castings are effected as with conventional cooling methods. By touching the edge-solidified casting in the sand mold with the cooling liquid, the heat is dissipated abruptly. Due to the extreme cooling rate, both primary dendrite formation and eutectic solidification are very fine-grained. The suction effect is also improved by the fact that the cavities between the grains of sand are not blocked by binders. The sand mold is thus much more porous and the cooling liquid is sucked by the negative pressure abruptly into the sand casting mold, without being hindered in the flow.

Figur 1

Herstellung einer Sandgussform mit bekanntem Unterdruck- oder Vakuum-Formverfahren

Figur 2.1 und 2.2

Bereitstellung des Formkastens mit der sich unter Unterdruck befindliche Sandgussform

Figur 2.2

Füllung der Sandgussform mit flüssigem Metall

Figur 3.1 und 3.2

Erfindungsgemässes Abkühlen und Auspacken der sich unter Unterdruck befindlichen Sandgussform

Figur 4.1 und 4.2

Weitere Variante für das erfindungsgemässe Abkühlen und Auspacken der sich unter Unterdruck befindlichen Sandgussform

The production process according to the invention and its mode of action will be explained below on the basis of exemplary embodiments. However, it should be expressly pointed out that the inventive method and the inventive idea is not limited to the embodiments shown in the examples. Show it:

FIG. 1

Production of a sand mold with known vacuum or vacuum molding process

FIGS. 2.1 and 2.2

Provision of the mold box with the under-pressure sand mold

Figure 2.2

Filling the sand mold with liquid metal

FIGS. 3.1 and 3.2

Cooling and unpacking of the present under negative pressure sand casting mold according to the invention

Figures 4.1 and 4.2

Another variant for the inventive cooling and unpacking the located under negative pressure sand mold

The FIG. 1 shows first the production of a sand casting mold after the vacuum forming process. The illustrated method is state of the art and can also find application in the inventive manufacturing process. The first picture shows the provision of a vacuum box with a model half of the casting mold to be produced. On the model half a casting funnel is attached, through which the liquid metal should later flow into the sand casting mold. The second picture shows a first process step for the production of the sand casting mold. In this case, a film or model film is heated until it becomes plastically deformable. Subsequently, the model film is lowered from above over the Giesstrichterform and the model half. By means of suction on the lower case model plate, a negative pressure is created (see arrow), which sucks the model foil to the model half and to the pouring funnel. The model half and the pouring funnel shape can be offset with small holes for better suction of the model film. The model film cools and remains in the modeled form. Optionally, sizing can then be applied to the model film. In the 4th to 6th pictures it is shown how the top of the mold box is positioned over the half of the model with mounted model foil and filled with sand, eg quartz sand, and finally closed with an upper cover foil. In the upper part of the flask, a negative pressure is now generated by the air being sucked out of it (see arrow in the figures). The vacuum or negative pressure in the molding box upper part is kept stable by means of pumps, so that the negative pressure remains in the upper part of the molding box. The top of the flask is now removed from the half of the model and the casting funnel shape (see 7th picture). The mold half made of sand hereby remains in its shape due to the negative pressure exerted, similar to a vacuumed food packaging. The resulting benefits have already been explained above. The bottom of the mold box with the lower mold half is made in the same way. The flask top is anschießend assembled with the associated lower part of the molding box and connected to each other non-positively. The mold box with the sand mold in it under vacuum is now ready for filling with liquid metal (see 8th picture). After the liquid metal has solidified to the casting, the negative pressure can be released and the manufactured casting removed from the molding box (see 9th image).

The two following subfigures 2.1 and 2.2 show a schematic representation of the two-part molding box 2, wherein each mold box half 2 contains a Sandgussformhälfte which is held under negative pressure. Part 2.1 also shows how both sand mold halves are held in their formed by the model sheets 12 due to the negative pressure. The underprint in the two casting mold halves is held by the molding box 2, as well as a mold box cover film 7 and a model film 12. The schematic figures show at both mold box halves a suction point 11, by means of which air is sucked out of the mold halves and thus the negative pressure is generated. The molding box upper part also has a casting funnel 10, through which the melt is poured into the closed casting mold in a later step. According to part 2.1, the two mold box halves acted upon by negative pressure are stacked on top of each other and frictionally connected with each other. In the partial figure 2.2, both mold box halves are joined together. These are non-positively connected so that the sand casting mold does not open during the casting process. The two mold box halves form the actual mold box 2 with the sand mold 1 assembled therein from the two sand mold halves. The assembled sand mold 1 forms a cavity 13 which has the casting mold to be produced. The closed molding box 2 can now be filled with the melt, ie, solid metal 5. The present invention may be applied to any casting method, for example the gravity or die casting methods described above. Further common and applicable casting methods would be, for example, the tilt casting, the falling casting or the lateral casting. The sand mold 1 is now filled according to part 2.2 with liquid metal, wherein the liquid metal cools and - slowly begins to solidify in the edge zones to the sand mold.

The two subfigures 3.1 and 3.2 now show the inventive method step: The molding box 2 with the still located therein under vacuum sand mold 1, which is filled with liquid, teilerstarrtem metal is moved away from the casting device (not shown). The casting device will thus release for the next casting operation, ie filling of a further mold box. The filled molding box 2 is for this purpose, for example, by a robot, not shown, moved away from the casting apparatus and pivoted via a cooling device. The cooling device can, as shown in the two sub-figures consist of a large cooling pool or bath 6 (eg a water bath). In addition to the actual cooling basin 6, the cooling device can also have nozzles 9 for the cooling liquid admission, which spray the liquid metal filled molding box 2 from different directions, eg from above, with a cooling liquid. Typically, water is used as the cooling fluid or coolant.
The molding box 2 is now partially immersed, for example, in the cooling basin 6 and sprayed from above by means of the nozzles 9 with the cooling liquid. The mold box 2 can also be completely immersed in the cooling tank 6, in which case no additional nozzles are necessary. The molding box 2 with the sand casting mold 1, which is still under reduced pressure, is now opened according to the invention completely or even only at the locations with the application of cooling liquid. This is done by removing the mold box cover sheets 7. The invention now makes use of the suction effect of the negative pressure (typically -0.6 to -0.8 bar): By removing the cover sheets 7, water is immediately sucked into the sand casting mold 1, which instantaneously quenches the casting 3. Since the sand mold 1 is made of sand, ie quartz sand, and contains no blocking binder (eg Betonit) or other fines, the water can penetrate very quickly and deeply into the porous sand mold, ie between the individual grains of sand, thanks to the pre-existing negative pressure / vacuum. Although a sand casting mold is very compact, it is actually porous and has a theoretical cavity between the grains of sand, which can account for 33% of the total sand casting mold volume. Because of this, the inventive cooling or quenching effect is very high compared to the known cooling methods.
Of course, it is not excluded that the inventive method also applies to vacuum sand casting molds, which are provided with additives. As can be seen from the preceding statements, care must be taken here that the additives used do not adversely affect the porosity of the sand casting mold or its permeability to the cooling liquid, or at least do not influence it too negatively. Accordingly, Betonit should preferably not be used as additive / binder, because this when in contact with water closes the cavities between the grains of sand and makes the sand mold impermeable to water (despite the low pressure little or no water is sucked into the sand mold).
After the cover sheets 7 of the molding box have been removed, it is also conceivable for the molding box 2 to be immersed deeper into the cooling basin 6. The immersion of the molding box 2 in the water bath 6 offers the additional advantage that the immersion process can be controlled or regulated. That is, the cooling process can be influenced by the dipping direction and speed. For example, the molding box can be immersed horizontally in the casting position, obliquely or rotated through 180 degrees about a horizontal or a vertical axis. Accordingly, certain areas of the casting may be quenched faster via the dipping direction and / or speed.

The subfigures 4.1 and 4.2 show a further variant of the inventive method. Here, the filled with liquid metal molding box 2 is completely immersed in a water bath 6, before the cover sheets 7 are removed on the molding box. The suction effect for the quenching of the liquid or partly already randerstarrten casting 3 with the cooling liquid is exploited even more efficient. As shown in the sub-figures 4.1 and 4.2, the molding box instead of the cover sheets 7 also slide 8 may have. These slides 8 take over the function of the cover sheet. Depending on the application and mold size, the use of sliders - e.g. at the bottom of the box - be more advantageous than the use of cover sheets. The slides can also be reused without further ado.

In the foregoing description, it has been stated that the molding box is opened after the cooling liquid is applied by the removal of the cover sheets or the slider. Of course, the idea of the invention also includes the possibility that the (partial) opening of the molding box takes place before or immediately before or at the same time as the application of cooling liquid. The molding box can thus be opened before or after the cooling liquid application (preferably only at the points with Kühlflüssigkeitsbeaufschlagung). The invention naturally used suction and thus cooling effect is used most efficiently if the sand mold absorbs only or mostly only cooling liquid and not also ambient air (much lower heat capacity). It is therefore preferable that the molding box is opened only after the cooling liquid application by the removal of the cover sheets or slider.

The present invention is not limited to the explicitly stated possibilities and embodiments. These variants are intended rather as a suggestion for the expert to implement the idea of the invention as low as possible.

LIST OF REFERENCE NUMBERS

1

Sand mold

2

Mold box, mold box half

3

casting

4

Coolant, water

5

liquid metal

6

Cooling basin, water bath

7

Mold box cover films

8th

Molding box-shifter

9

Nozzles for the coolant supply

10

pouring cup

11

Extraction point Sand casting mold

12

model foil

13

Cavity of the sand mold

Claims (10)

Method for producing cast parts from metal with a sand casting mold (1), the method comprising the following steps: - Production of the sand mold (1) in a molding box (2) with a vacuum molding process - Filling of the produced sand casting mold (1) in the molding box (2) with liquid metal Cooling the sand casting mold (1) and the casting (3) solidifying therein with a cooling liquid (4),
characterized in that
the vacuum mold located sand mold (1) in the mold box (2) is first filled with liquid metal (5) that
the molding box (2) is then wholly or partly exposed to a cooling liquid (4) with the sand casting mold (1) located therein under reduced pressure, and
the molding box (2) is opened, at the same time or before the cooling liquid is applied, at locations with cooling liquid admission, so that the cooling liquid (4) is absorbed into the sand mold (1) which is under reduced pressure and thereby quenching the solidifying casting (3) , Process for producing cast parts (3) according to claim 1, characterized in that the cooling liquid (4) is water. Method for producing cast parts (3) according to claim 1 or 2, characterized in that the loading of the molding box (2) with the cooling liquid (4) takes place in a cooling basin (6), preferably a water bath,
Particularly preferably, the molding box (2) is partially or completely immersed in the cooling basin (6). Method for producing cast parts (3) according to one of the preceding claims, characterized in that the sand casting mold (1) is held in its shape by the negative pressure in the molding box (2). Method for producing cast parts (3) according to one of the preceding claims, characterized in that the sand mold (1) is formed from quartz sand, preferably without binder. Method for producing cast parts (3) according to one of the preceding claims, characterized in that the sand casting mold (1) contains no binder, in particular concrete, or sizing. Method for producing cast parts (3) according to one of the preceding claims, characterized in that the mold box (2) is opened by removing the mold box cover films (7) or by slides (8) located on the molding box (2). Method for producing cast parts (3) according to one of the preceding claims, characterized in that the molding box (2) is immersed horizontally in the casting position or at an angle of 0 to 180 degrees about a horizontal or vertical axis rotated position in the cooling basin (6) is, preferably the immersion in the cooling pool (6) takes place in a controlled manner. Method for producing cast parts (3) according to one of the preceding claims, characterized in that the casting method is a vacuum forming method or a gravity method. Casting plant for the production of cast parts (3) with a process according to one of the preceding claims.

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