EP3322547B1 - Method for producing a casting core, and a casting core - Google Patents

Description

The invention relates to a method for producing a casting core for the casting production of a casting and a casting core as such. In this case, the casting core in each case consists of a molding material which is mixed from a binder and a foundry sand and optionally added additives.

Cast cores of the type in question are typically used for the casting production of castings from a molten metal. They are referred to as "lost parts" because they are destroyed when the casting is removed from the mold.

Such as in the DE 102 09 183 A1 described, is poured to produce a casting molten metal in the mold cavity enclosed by the respective mold cavity. After or in the course of the solidification of the molten metal to the casting, the casting mold is separated from the casting.

Usually, a casting mold comprises several casting cores. These form cavities, channels and other recesses within the casting. For molds that are so However, they also form the outer contour of the casting from.

The cores are made in molds called "core shooters" which comprise a core box divided into upper and lower core box halves. The core box delimits with its core box halves a mold cavity which depicts the casting core to be produced. In this mold cavity, a molding material is shot with the core box closed with pressure. This process is called "core shooting". Subsequently, the casting core is cured in the core box. Then, the core box is opened by moving at least one of the core box halves to remove the casting core. If their size permits, in industrial mass production usually several casting cores are molded simultaneously in a core box.

Molded materials used for the production of casting cores of the type in question are usually mixed from a molding base material, for example an inorganic refractory molding sand, and a binder. In practice, inorganic or organic binders are used for this purpose. When using inorganic binders, the curing of the molding material in the core box by heat and moisture removal ("hot box process"), whereas using organic binder, the cores are gassed in the mold with a reaction gas to a chemical reaction of the binder with the Reaction gas to cause the solidification ("cold box process"). Both based on inorganic and on organic binder systems molding materials are available in the market in a variety of designs. If necessary, such molding materials contain additives in order to adjust their properties, in particular with regard to storability, flow behavior, etc.

With the known, for example, in the already mentioned DE 102 09 183 A1 described and commercially available molding materials, it is possible to produce filigree shaped, ie small diameter, elongated thin sections and also finely shaped branching having cores whose dimensional stability is sufficient to be transported from the Gießkernherstellung to mold, to keep safe in the respective mold and also to absorb the loads occurring during the pouring of the melt. However, the nature of their preparation and the molding material used to make them implies that the cores are highly brittle and therefore fragile.

The above-described conventional industrial-scale manufacturing approach and reusable-mold-based manufacturing method involves some limitations in the molding of the cores. So Ausformschrägen must be provided in the mold cavity of the core box to allow a reliable, non-destructive removal of the finished casting core from the core box. When using a usual two-part core box in practice, the cores can have no undercuts that would hinder the demolding. Should Nevertheless, casting cores are produced with such undercuts, multi-part core box structures must be used, which require a high technical complexity and a correspondingly high investment investment.

In order to depict undercuts in the known Gießkernfertigung, so-called "loose parts" are used (s. Foundry Lexicon, 19th edition, 2007, specialist publisher Schiele & Schön , Keywords "Losteil" / "Ansteckteil"). These are inserted into the core box, then enclosed with molding material and removed with the casting core from the core box. Due to the interlocking of loose part and molding material of the casting core caused by the respective undercut, the release parts can only be pulled out of the casting core after removal. In addition to the associated with their use additional operations have such Losteile from a production point of view in mass production the disadvantage that a lot of loose parts must be in circulation to ensure a proper, timely workflow.

In addition, even with the use of multi-part core boxes, freedom in shaping the casting cores is limited. Thus, in any case, it must be ensured that the molding material can be shot into the core box cavity so that it completely fills the mold cavity and is sufficiently compacted.

With the conventional Gießkernherstellung therefore certain core geometries, such as, for example, according to Art an hourglass, in the manner of a helical spiral geometries or comparable complex shaped body, not at all or only with extreme effort to be made. In spite of the principally high degree of freedom of design, which offers a core production based on the principles of original molding, it is not possible to exploit the full design potential that would theoretically be possible when casting with lost cores.

An example of the attempt to assemble complex shaped core cores from several core parts is in DE 297 17 661 U1 described. The composite core parts to the casting core are locked against each other by means of a Spreitzelements.

According to the DE 10 2008 023 336 A1 The strength of filigree casting cores can also be increased by applying a foil to the circumference of the cores.

Against the background of the above-described prior art, the object has arisen to give a method that allows the production of complex shaped or optimized in terms of their quality cores in a simple manner.

Likewise, a correspondingly shaped casting core should be created.

With regard to the method, the invention has achieved this object by carrying out at least the steps specified in claim 1 during the production of casting cores.

A casting core which dissolves the abovementioned object is accordingly distinguished by the fact that it is made of a molding material which consists of a mixture of a binder and a foundry sand and optionally added additives, wherein the casting core is deformed by a deformation caused by an external force finished shape is brought. Such a casting core can be produced in particular by using the method according to the invention.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

1. a) Formen des Gießkerns durch Einbringen des Formstoffs in eine Gießkernform;
2. b) Verfestigen des Formstoffs;
3. c) Entnehmen des Gießkerns aus der Gießkernform;
4. d) Erwärmen des Gießkerns auf eine Verformungstemperatur;
5. e) Verformen des erwärmten Gießkerns durch Aufbringen einer Verformungskraft auf den Gießkern;
6. f) Abkühlen des Gießkerns.

The inventive method for producing a casting core consisting of a molding material, which is mixed from a binder and a foundry sand and optionally added additives, for the casting production of a casting comprises the following steps:

1. a) molding the Gießkerns by introducing the molding material into a Gießkernform;
2. b) solidifying the molding material;
3. c) removing the casting core from the casting core mold;
4. d) heating the casting core to a deformation temperature;
5. e) deforming the heated casting core by applying a deformation force to the casting core;
6. f) cooling the casting core.

The invention is based on the surprising finding, contrary to the previous estimates of the experts, that casting cores produced in a conventional manner can also be deformed at a suitable temperature if they have already been given their basic shape in a conventional core shooter. Deformation may be caused by bending, compression, tension, shear, torsional deformation, or any other deformation due to external forces applied to the respective core. The deformation according to the invention allows casting cores produced from commercially available molding materials to subsequently obtain a shape which can not be produced with conventional core shooting machines at all, only with limited quality or only with a particularly high outlay.

The invention thus provides a high degree of design freedom and complexity in casting development. This makes it possible to implement novel casting core designs in a technically simple way. In particular, the production of undercuts is possible by the inventive subsequent forming of the cores without the need for complex core boxes with loose parts are used.

The process according to the invention can also be used for the subsequent optimization of properties of the core cores obtained after core shooting. Thus, casting cores can be subsequently densified in the manner according to the invention with the result that they have a higher dimensional stability and improved surface properties.

Depending on the brittleness that still shows the respective molding material when heated, and taking into account the basic shape, which has the respective core after removal from the core shooting machine, the deformation according to the invention should be carried out at a slow deformation rate. The respectively suitable maximum deformation rate can be determined experimentally in a simple manner. By means of practical tests it could be shown here that even filigree casting cores can be reliably deformed according to the invention if the deformation speed is limited to 2 mm / s at the most, in practice deformation rates of at least 0.01 mm / s are the rule should. Optimal deformation speeds are in the range of 0.1 to 1.0 mm / s, in particular 0.3 to 0.7 mm / s. In particular, casting cores which have an elongated, filigree shape can be safely bent, twisted, pulled or compressed when these deformation rates are selected.

The deformation forces to be applied in the deformation according to the invention and acting on the respective casting core from the outside can also be determined by simple experiments. Practical tests have shown here that with deformation forces which are 8 mm in diameter of a sample which is circular in cross-section in the range of 5-100 N or correspond to specific strengths of the cores of 0.2-0.6 N / mm ² , Also filigree shaped cores can subsequently deform in accordance with the invention. This applies in particular if the deformation takes place at deformation speeds which are in the ranges mentioned in the preceding paragraph. Deformation forces of 20-80 N (corresponding to specific strengths of 0.1-0.4 N / mm ² ), in particular 30-70 N (corresponding to specific strengths of 0.15-0.35 N / mm ² ), have here proved to be particularly effective.

In principle, the invention can be applied to any type of foundry cores made of molded materials of the type in question. This applies both to mold materials containing an inorganic binder and to mold materials based on an organic binder. Practical experiments have shown here that the invention can be used particularly well in casting cores in which an organic binder is used. In this case, it is assumed that, in particular, such organic binders act in the manner of an adhesive as a result of the heating of the casting cores according to the invention and thus bond together the grains of the molding material from which the casting cores are formed.

The optimum deformation temperature to which the cores are heated before the deformation according to the invention can also be determined by simple experiments. Practical experiments have shown here that deformation temperatures which are in the range of 150-320 ° C, in particular 180-300 ° C, are practical. The upper limit of 300 ° C proves to be particularly important for mold materials with organic binders because otherwise there is a risk of premature deterioration of the binder.

The deformation temperature should be kept within the above range during the subsequent deformation, optimally maintaining a constant temperature level.

The heating rate when heating the cores should be 1 - 15 ° C / s, especially 4 - 8 ° C / s.

For example, a heated tool, a convection oven or an infrared lamp can serve as the heat source for the heating according to the invention. Also conceivable is a general or local heating of the casting core by means of a concentrated hot air jet or the like.

The method according to the invention is also suitable for optimizing the shape of a casting core in the sense of a calibration. For this purpose, the casting core is heated in accordance with the invention after removal from the core shooting machine and deformed by external force so that it corresponds exactly to the respective specifications of its geometry.

Likewise, it is conceivable to add two cores positively or non-positively by an inventive deformation, which would otherwise have to be glued together. For this purpose, in the course of carrying out the steps a) -c), a first casting core can be produced, which has a recess. In addition, a second casting core is provided, which has a projection, which is adapted to the shape of the recess of the first casting core. The second casting core can now be joined to the first casting core such that the projection of the second casting core engages in the recess of the first casting core to form a joining zone. Subsequently, at least one of the casting cores passes through the work steps d) - f) and is thereby deformed in step e) such that in the region of the joining zone a dense positive connection is formed, by which the two casting cores are connected to each other. In this way, two or more cores can be interconnected by connections, which are formed for example in the manner of plug-in or snap-in connections.

As an alternative to providing a casting core with a projection adapted to the recess of the other casting core, it is also possible to properly position a casting core without pronounced projection on the first casting core provided with the recess and then feed material of the second casting core into the opening of the first casting core to press. For this purpose, according to a further embodiment of the method according to the invention by executing the steps a) - c), a first casting core with a recess (A) and a second casting core are provided, which is then positioned on the first casting core in a predetermined position, said after Positioning at least the second casting core the steps d) - f) passes through and is deformed in step e) by applying an external force such that material of the second casting core, which is arranged in the region of the recess of the first casting core, into the recess of the first casting core enters and fills this recess, so that a tight positive connection is formed, by which the two casting cores are interconnected. In this way, a positive or non-positive connection between the casting cores is created in the manner of a clinching process. It can of course on the casting, whose material in the Recess of the other core is pressed, marks, paragraphs, surveys or the like may be present to facilitate the proper positioning of the cores to each other. If the recess of the first casting core is a passage opening, it is also conceivable to push the material of the second casting core through the recess so far that it widens on the side opposite the second casting core and establishes a firm connection between the casting cores Type of riveted joint is created.

Fig. 1

einen stabförmigen Gießkern vor und nach einer Verformung in seitlicher Ansicht, wobei die Form vor der Verformung gestrichelt und die Form nach der Verformung durchgezogen dargestellt ist;

Fig. 2

einen quaderförmigen Gießkern vor und nach einer Verformung in seitlicher Ansicht, wobei die Form vor der Verformung gestrichelt und die Form nach der Verformung durchgezogen dargestellt ist;

Fig. 3a

einen weiteren stabförmigen Gießkern mit einer Vielzahl von daran angeformten Abzweigungen vor einer Verformung in seitlicher Ansicht;

Fig. 3b

den Gießkern gemäß Fig. 3a in stirnseitiger Ansicht;

Fig. 4a

den Gießkern gemäß Fig. 3 nach einer Verformung in seitlicher Ansicht;

Fig. 4b

den Gießkern gemäß Fig. 4a in stirnseitiger Ansicht;

Fig. 5a - 5d

zwei Gießkerne in den verschiedenen Arbeitsschritten, die beim Verbinden dieser Gießkerne durchgeführt werden, jeweils in seitlicher, teilgeschnittener Ansicht.

The invention will be explained in more detail with reference to an exemplary embodiments showing drawing. Their figures show each schematically:

Fig. 1

a rod-shaped casting core before and after a deformation in a lateral view, wherein the mold is shown in dashed lines before the deformation and the shape after the deformation is shown drawn through;

Fig. 2

a cuboid casting core before and after a deformation in a lateral view, wherein the mold is shown in dashed lines before the deformation and the shape is shown drawn through after the deformation;

Fig. 3a

another rod-shaped casting core with a plurality of branches formed thereon before deformation in a lateral view;

Fig. 3b

the casting core according to Fig. 3a in frontal view;

Fig. 4a

the casting core according to Fig. 3 after a deformation in a lateral view;

Fig. 4b

the casting core according to Fig. 4a in frontal view;

Fig. 5a - 5d

two casting cores in the different work steps that are performed when connecting these cores, each in a side, partially cutaway view.

The in the FIGS. 1 and 3a - 4b illustrated casting cores G1, G3 are exemplary of elongated, delicate caster cores, for example, when filing cylinder heads for internal combustion engines filigree shaped Ölversorgungs- or coolant channels. Cylinder heads of this type are usually cast today from cast aluminum materials.

The in Fig. 2 illustrated cylindrical casting core G2 is intended to mold a cavity, for example, when casting a cylinder crankcase for an internal combustion engine.

The in the FIGS. 5a-5d illustrated cores G4, G5 stand for such cores, which are connected together to form a Gießkernkombination GK to complex shapes of cavities or channels in one of a Imagine any molten cast casting.

The casting cores G1 - G5 have each been produced in the so-called "PU cold box process".

The binder used in the PU cold box process comprises two components, namely phenol-formaldehyde resin as the first component and isocyanate as the second component. Fumigation with a tertiary amine causes a polyaddition of these two components to form polyurethane.

For the production of the molding material, the foundry sand is in a suitable mixing unit, e.g. a vibratory mixer or blade mixer, the phenol-formaldehyde resin and the isocyanate for two to five minutes, especially three minutes, mixed. The added amount of the two components of the binder may vary depending on the application and foundry sand. Typically, they are based on the added amount of molding material between 0.4 and 1.2% per part. A ratio of 0.7% per part has proved particularly favorable.

If "parts" is mentioned here as a metering measure, it is understood that the quantity of the component measured in each case is measured with the aid of a unit measure which is the same for all components and the "parts" provided in accordance with the invention for the individual components are the respective multiple denote this unitary measure.

The ready-mixed molding material has been formed into the casting cores G1-G5 in a conventional core shooter. Here, the molding material with a shooting pressure of about 2 - 6 bar, in particular 3 bar, shot in a core box and compacted there. Subsequently, the gassing cores G1-G5 in the core box were gassed with the gaseous catalyst, the tertiary amine, in order to effect the hardening of the cores. Curing was carried out until cores G1-G5 reached a strength of 150-300 N / cm ² typical for PU cold box cores. The target was an optimal value of 220 N / cm ² .

The rod-shaped casting core G1 thus produced had, for example, a circular cross-section of 10 mm and a length of 200 mm. The casting core G3 was dimensioned accordingly.

The casting cores G1-G3 obtained in each case have now been heated to a preheating temperature of 220 ° C. in a circulating-air oven at a heating rate of 5 ° C./s.

The thus heated casting cores G1 - G3 have subsequently been deformed.

The casting core G1 has been positioned with its end portions on two mutually spaced blocks B1, B2 with rounded supports. Subsequently, a force was applied by a force acting in the direction of force K. This external force K has been applied by means of a stamp not shown here in detail, the center is aligned with the longitudinal extent of the Gießkerns G1 and is rounded at its coming into contact with the casting core G1 face to avoid pressure load peaks of the Gießkerns G1 in the deformation. The load by the force K was quasi-static with a forming speed of 0.5 mm / s. The initiated force K was 40 N.

The forming process was terminated after the desired deformation angle β of about 20-30 degrees was reached. During the deformation process, the casting core G1 was kept constant in a range around the deformation temperature of 220 ° C ± 30 ° C.

The casting core G1 plastically deformed in this way has been cooled to room temperature in still air. Subsequently, it could be used in the casting process like a conventionally shaped casting core.

The casting core G2, like the casting core G1, has been heated in the manner described above and subsequently deformed by external force application KA with the aid of a punch-like tool, likewise not shown here, in such a way that it has the shape of an hourglass. There was a compression of the molding material, which had a positive effect on its dimensional stability and its surface texture. At the same time, the casting core has been calibrated so that its shape optimally met the geometric specifications.

The casting core G3 has also been heated to the deformation temperature in the manner described above for the casting core G1. Subsequently, the heated casting core G3 has been clamped with its one end in a holder and acted upon at its other end as an external force with a force acting about its longitudinal axis L torque M. In this way, the casting core G3 could be twisted about its longitudinal axis L by an angle of 90 °.

The two casting cores G4, G5 have also been produced in the manner described above for the casting cores G1-G3. In this case, the casting core G4 has on its one end face a projection V, whereas in the associated end face of the casting core G5 a recess A has been formed, whose shape represents with a certain excess a negative of the shape of the projection V of the casting core G4.

Accordingly, the casting core G4 could be introduced with its projection V into the recess A of the casting core G5, so that the casting cores G4, G5 were joined in the region of a joining zone F delimited by the recess A.

Subsequently, at least the casting core G5 has been brought to a deformation temperature lying in the range of 180-300 ° C. by concentrated heating, for example in the hot air jet. Then, the casting core G5 has been acted upon by means of a suitable tool, not shown here, with an external force KX such that the material of the casting core G5 surrounding the recess A has been compressed. The material of the casting core G5 surrounding the recess A has been pressed against this projection against the projection V until the projection V is tightly enclosed by the material of the casting core G5 and a dense form-fitting connection is formed by which the casting core G4 is related in every degree of freedom fixed undetachably on the casting core G5 and the Gießkernkombination GK is formed.

REFERENCE NUMBERS

β

deformation angle

A

Recess of the casting core G5

B1, B2

bucks

F

joint zone

G1 - G5

cores

GK

Gießkernkombination

K, KA, KX

external forces

L

Longitudinal axis of the casting core G3

M

torque

V

Lead of Gießkern G4

Claims (11)

1. Method for producing a foundry core (G1 - G5) for casting a cast part, wherein the foundry core (G1 - G5) consists of a mould material which is mixed from a binder and a mould sand, as well as optionally added additives, comprising the following production steps:

   a) moulding the foundry core (G1 - G5) by introducing the mould material into a foundry core mould;

   b) hardening the mould material;

   c) removing the foundry core (G1 - G5) from the foundry core mould;

   d) heating the foundry core (G1 - G5) to a deformation temperature;

   e) deforming the heated foundry core (G1 - G5) by applying a deformation force (K, KA, KX, M) to the foundry core (G1 - G5);

   f) cooling the foundry core (G1 - G5).
2. Method according to Claim 1, characterised in that the deformation force (K, KA, KX, M) brings about a bending deformation, compressive deformation, tensile deformation, shear deformation or torsional deformation of the foundry core (G1 - G5).
3. Method according to any one of the preceding claims, characterised in that the deformation is carried out at a deformation rate of at most 2 mm/s.
4. Method according to any one of the preceding claims, characterised in that the deformation force is 5 - 100 N.
5. Method according to any one of the preceding claims, characterised in that the foundry core (G1 - G5) is fully hardened in production step b).
6. Method according to any one of the preceding claims, characterised in that the binder of the mould material is an organic binder.
7. Method according to any one of the preceding claims, characterised in that the deformation temperature is 180 - 300°C.
8. Method according to any one of the preceding claims, characterised in that the heating-up rate when heating the foundry cores to the deformation temperature is 1 - 15°C/s.
9. Method according to any one of the preceding claims, characterised in that by carrying out the production steps a) - c) a first foundry core (G5) is produced with a recess (A), in that a second foundry core (G4) is provided which has a protrusion (V) which is adapted to the shape of the recess (A) of the first foundry core (G4), in that the second foundry core (G5) is joined to the first foundry core (G4) such that the protrusion (V) of the second foundry core (G5) engages with the recess (A) of the first foundry core (G5) forming a joining zone (F), and in that subsequently at least one of the foundry cores (G4, G5) passes through the production steps d) - f) and in production step e) is deformed in such a way that in the area of the joining zone (F) a tight form-fit connection is formed, by means of which the two foundry cores (G4, G5) are joined together.
10. Method according to any one of Claims 1 to 9, characterised in that by carrying out the production steps a) - c) a first foundry core is produced with a recess (A), in that a second foundry core is provided and this foundry core is positioned on the first foundry core in a predetermined position, in that at least the second foundry core passes through production steps d) - f) and in production step e) by applying an external force is deformed in such a way that material of the second foundry core which is located in the area of the recess of the first foundry core enters the recess of the first foundry core and fills this recess, so that a tight form-fit connection is formed, by means of which the two foundry cores are joined together.
11. Foundry core which is produced from a mould material which consists of a mixture of a binder and a mould sand, as well as optionally added additives, characterised in that the foundry core (G1 - G5) is brought into its final shape by means of a deformation brought about by external application of force (K, KA, KX, M).

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