EP3166740A1

EP3166740A1 - Core, use of a core, and mehtod for the production of a core

Info

Publication number: EP3166740A1
Application number: EP15753438.9A
Authority: EP
Inventors: Valentin DIEL; Detlef Kube; Gerald KLAUS
Original assignee: Nemak SAB de CV
Current assignee: Nemak SAB de CV
Priority date: 2014-07-09
Filing date: 2015-07-06
Publication date: 2017-05-17
Anticipated expiration: 2035-07-06
Also published as: PL3166740T3; US10850321B2; US20170173670A1; KR101889053B1; DE102014109598A1; JP2017521256A; JP6246954B2; WO2016005806A1; ES2814149T3; CN107073563B; CN107073563A; HUE050240T2; KR20170023185A; EP3166740B1

Abstract

The invention relates to a core (1) made of a molding sand, the grains of which are conglomerated by a binder, said core (1) being used for forming a cooling duct (41, 42, 43, 44) in a cylinder block (26) for an internal combustion engine. Also disclosed are a use of a core (1) and a method for producing a core (1). The core (1) of the invention can be produced in a simple and safe manner and makes it possible to use a casting process to create even ducts that are no more than 3 mm wide at the narrowest point thereof. To achieve said aim, the core (1) comprises a supporting portion (2), two neck portions (11, 12) which project from a lateral surface (10) of the supporting portion (2) and are located at a distance from one another, and at least one bridge portion (15, 16) which is retained by the neck portions (11, 12) at a distance from the supporting portion (2) and which has a minimum thickness (dmin) of no more than 3 mm in a region (23, 24) between the neck portions (11, 12), said minimum thickness (dmin) being defined as the distance between the lateral surfaces (17, 18) of the at least one bridge portion; furthermore, at least in the region of the bridge portion (15, 16), the core (1) is made of a molding sand of which the grains have a maximum mean diameter of 0.35 mm.

Description

Casting core, use of a foundry core and method of making a foundry core

The invention relates to a casting core, which is formed from a molding sand whose grains are interconnected by a binder, and which is intended to image a cooling channel in an engine block for an internal combustion engine.

Furthermore, the invention relates to a use of such a casting core and a method for its production, in which by means of a core shooter, a molding material comprising a molding sand and a binder, shot into a mold cavity of a core mold and then the binder is cured to the

Gießkern give the required dimensional stability.

Casting cores of the type in question form as part of a casting mold in the component to be cast channels, cavities and other recesses. So are for engine blocks for internal combustion engines using

Casting cores, for example, leading the cooling water

Channels, but also the cylindrically shaped

Combustion chambers formed.

Engine blocks of modern high-performance engines must be cooled intensively in operation to the large Amount of heat that arises due to the high power density, purposefully dissipate. This is especially true for engine blocks that consist of a

Alloy material, such as made of an aluminum alloy. At the same time, especially in the field of passenger cars, there is a desire for ever more compactly built vehicles

Drive units, on the one hand to save weight and on the other hand to be able to accommodate engines with high performance in bodies in which only a small space is available.

The compact design leads to a closely spaced arrangement of the cylinder recesses of a cylinder bank. This results in correspondingly thin

Cylinder partitions. These are especially in the

Range associated with their cylinder head

End portions exposed to increased thermal stress. In order to prevent the occurrence of heat-related cracks or other damage, it is necessary, including in the relevant vulnerable

Area to carry out intensive cooling.

One way, the required cooling channel in the between two cylinder chambers of an engine block

Inserting the remaining thin intermediate wall is to drill the cooling channel in the block after completion of the casting process. Although this method allows precise production even very small and narrow-dimensioned channels, but manufacturing technology is complex, since it requires a large number of additional operations. This leads to high costs. One Another disadvantage is that it

manufacturing technology is difficult in the upper

Area of existing between adjacent cylinder recesses partition of an engine block a

To introduce a channel bore with minimized diameter, in which the highest thermal load arises in use.

To avoid this effort, are different

Proposals have been made as to how thin and narrow channels can be introduced into the regions of an engine block that are subject to high thermal loads during operation during casting production. This is how cores look like

Various molding compounds have been proposed, which have been selected in each case with the goal, on the one hand a sufficient dimensional stability of the filigree

Core section that is to map the respective channel in the casting, on the other hand, to ensure that the core material after the

Solidify the engine block as easily as possible so that a proper flow is ensured. However, the use of cores made from molding compounds encounters limits imposed by the dimensional stability and mechanical strength which the cores must possess in order to ensure sufficient productivity even under the conditions prevailing in a foundry operation.

To channels with even smaller diameters in

It has been proposed in EP 0 974 414 B1 to image light metal engine blocks, these channels through a correspondingly dimensioned glass tube Imaged in the mold and inserted in the mold

Casting is enclosed by the casting melt. The

Material of the glass tube is chosen so that it breaks under the stresses occurring in the course of solidification of the casting material into many small parts, which can then be easily rinsed.

Other proposals in this direction provide for the channels to be formed by sheet metal or wire inserts, which are then pulled out of the finished casting.

The above-mentioned possibilities have in the prior art with more or less large

technical and economic success for the

Production of channels proven, despite their

limited dimensions are sufficiently large and accessible to remove the remaining fragments of the imaged core material can.

In a new generation of aluminum alloy cast internal combustion engines, the thickness of the

However, intermediate walls reduced so that the required cooling channels in their narrowest section have a clear width of less than 3 mm. In engine blocks cast of Al material of this type, the inside width of the cooling channels is in the area where the partition wall between two cylinder chambers on

narrowest, in the range of 1 - 2 mm.

Against the background of the prior art, the object of the invention was to provide a casting core, which can be manufactured in a simple, reliable manner and thereby allows to produce also channels which are at their narrowest point at most 3 mm wide, by casting.

In addition, a preferred use and method of making cores that do so should be indicated.

With respect to the casting core, the invention has this

Problem solved in that such a casting core is formed according to claim 1.

Advantageously, a casting core according to the invention can be used in a casting mold for casting technology

Production of an engine block for a

Using an internal combustion engine by pouring an aluminum melt into the casting mold, wherein the web portion of the casting core in the engine block one between two

Cylinder chambers of the engine block arranged cooling channel, the clear width is at most 3 mm.

The solution to the above problem with respect to the method is finally that the

Production of a casting core according to the invention

Assignment of claim 12 takes place.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail. A casting core according to the invention, which is intended to image a cooling channel in an engine block for an internal combustion engine, is therefore completely formed from a molding sand whose grains are connected to one another by a binder. According to the invention, the casting core now has a support section, two

Journal sections extending from a side surface of the

Carrier portion protrude and are arranged at a distance from each other, and at least one spaced from the support portion of the journal portions held web portion whose distance as its

Side surfaces measured to each other minimum thickness in a lying between the pin portions area

3 mm at the most. Here is the casting core

formed at least in the region of its web section of a molding sand whose grains have a middle

Have a diameter of at most 0.35 mm.

A casting core according to the invention thus consists entirely of foundry sand, the grains of which in a manner known per se with one another by means of a suitable binder

are connected, that they form a solid body.

The support portion of the casting core makes it possible to easily grasp the casting core despite the filigree design of its web section, to transport and insert it into a mold. So can the

Be mold core according to the invention also readily part of a mold formed as a core package. Likewise, it can easily be used in any other casting process, in or on the particular casting filigree channels are to be formed with minimized dimensions.

The journal sections carried by the support section form the supply and to be cast in the engine block

Outflow channel through which the narrow, narrow-dimensioned cooling channel is supplied with coolant, each supported by the pin sections

Bridge section is shown in the engine block. Its thickness is reduced in a critical range to at most 3 mm, in practice, the minimum thickness in this range is 1 - 2 mm. It is the

relevant critical region in which the web portion of the casting core according to the invention is narrowest, associated with the region of the respective intermediate wall of the engine block to be cast, on which the intermediate wall is thinnest and which through the intermediate wall

separate cylinder rooms come closest.

Decisive for the practical implementation of the invention is here that the casting core is formed at least in the region of its web portion of a fine-grained molding sand. Its grain size is chosen so that the

Web section after the casting in the solidifying casting finely divided, so that the remaining

Core fragments either automatically trickle out of the finished solidified engine block or can be rinsed out.

Surprisingly, it has been shown that the

Casting cores not only in a conventional manner

Shooting in a core shooting machine, but also offer a surface texture in the region of the narrow web portion, which produce sufficiently smooth inner surfaces in the cooling channel to be produced, without requiring a complex

Finishing order required. This applies in particular if the average diameter of the grains of the molding sand is not more than 0.27 mm, in particular not more than 0.23 mm.

As already mentioned, can be inventive

Making cores industrially by means of a core shooter a molding material, the one

Molding sand and a binder, shot in a mold cavity of a core mold and then the binder is cured to the casting core the required

To give dimensional stability, wherein according to the invention as a molding material at least for the web portion of the casting core, a molding sand is used, the grains of a

have a mean diameter of at most 0.35 mm. Again, for the reasons explained above, it is understood that the average diameter of the grains is optimally not more than 0.27 mm,

in particular at most 0.23 mm.

Optimal work results can be achieved with molding compositions in which the molding sand and the binder are not present as a mixture, but in which the grains of the molding sand are each covered with a binder, which also applies here that the middle

Diameter of the molding sand grains coated in this way is not greater than 0.35 mm. Molded sands coated with binder of the type processed according to the invention are still in use today for the so-called "croning process" in which

Technical language also called "askenformverfahren",

used and for example under designation VS744 (average grain size 0.29 mm +/- 0.02 mm) or VS1264 (average grain size 0.21 +/- 0.02 mm) from the Hüttenes- Albertus Chemische Werke GmbH, Dusseldorf, offered. Hüttenes Albertus Chemische Werke GmbH has also published the treatise "The Mask Forming Process: A German Innovation for Cast Production" by Ulrich Recknagel, which describes the technique and history of the mask molding process.

A particular advantage of the use of croning molding materials arises when the binder coating of the respective molding sand grains has a spherical shape. The spherical shape ensures a particularly good behavior of the molding material when shooting of the invention

Cores in a conventional core shooter. Thus, casting cores according to the invention can be used with high reliability despite their minimized dimensions

getting produced.

Especially when using the fine-grained molding sand with a mean grain size of 0.19 - 0.23 mm not only cores can be easily in one

Core shooting machine produce, but it also shows that the surface of the thin coolant channels shown by their web section in each cast engine block regularly a sufficient quality

owns, without that sizing or other

surface improving agents such as talc or the like may be needed. Should be preferred when using coarser sands with average diameters of their

binder-coated grains of 0.27 mm and more

turn out that the surface quality of the

Casting pictured cooling channels is not sufficient, this can be resolved by applying a thin sizing or other commonly used to improve the surface agent at least on web section. With grain sizes of more than 0.35 mm, however, casting cores can no longer reliably shoot with the dimensions specified in accordance with the invention and can be driven to compensate for the coarse surfaces

Effort becomes so great that an application no longer makes sense from an economic point of view. Therefore, for the production of casting cores according to the invention, such molding sands are optimally used, and their binder-coated grains have on average one

Diameter of less than 0.27 mm, in particular less than 0.25 mm.

The binder with which the granules of the molding sand used according to the invention for the production of the cores are preferably coated or mixed is typically a resin resulting from

Heat is bonded and cured with the resin of each adjacent grains, so that a solid composite is formed.

For a reliable production by

conventional shooting of the cores in one

Kernschießmaschine also contributes, if according to an embodiment of the invention, the side surfaces of Gießkerns invention each in a jump-free transition into the peripheral surface of the

Pass over pin sections and its thickness, starting from a respective pin section associated

Maximum thickness in the longitudinal direction of the web section

continuously decreases to the minimum thickness. The jump-free connection of the web section to the journal sections carrying it and the continuous

Dickenabnahme contribute to ensure that the molding material in spite of the minimized dimensions in the core shooting machine and the cavity safely and sufficiently tight fill, which images the narrow web portion of the casting core.

The jump-free connection of the web section to the journal sections can be simplified in that the journal sections one after the manner of a cam

having shaped cross-sectional shape, the tip of which faces the respective other pin portion. In this way, the side surfaces of the web portion can easily cling to the peripheral surface of the pin portions, which in turn the filling of

Footbridge section with molding sand during core shooting

is supported.

In the manner according to the invention, casting cores can be produced which are in their critical, minimal thickness

Not only a thickness not exceeding 3 mm,

in particular 1 - 2 mm, and thus are suitable, in the casting to be created cooling ducts with a clear width of 3 mm and less, in particular 1.5 +/- 0.5 mm, depict, but in which in the critical area and the height is minimized. So can at a According to the invention, the height of the web section in the region in which it has its minimum thickness is limited to a maximum of 4.5 mm.

In principle, it is conceivable to form only the web portion of a casting core according to the invention of fine-grained molding sand according to the invention, while the other portions of the casting core consist of a coarser molding sand. For this purpose, for example, the web portion of the fine-grained sand separated from the other

Fired portions of the casting core and then connected, for example, by gluing with the shot of coarser sand remaining portions of the casting core. However, it is simpler in terms of manufacturing technology if, according to a further embodiment of the invention, the casting core is in each case formed completely in one piece from a foundry sand which satisfies the specifications according to the invention.

If this makes the amount of heat to be dissipated, a casting core according to the invention can also be easily designed such that it images more than one narrow casting channel in the respective thin intermediate wall of the engine block to be cast. For this purpose, two or more of the pin portions may be used

be spaced apart web portions supported, each having a region in which their minimum thickness is no more than 3 mm. It goes without saying that for the additional web sections significantly lower

Minimum thickness, for example 1 - 2 mm, are possible. A casting core according to the invention is particularly suitable for use in a casting mold for the production of an engine block for a casting method

Internal combustion engine by casting an aluminum melt into the casting mold, wherein the web portion of the casting core in the engine block depicts a cooling channel arranged between two cylinder chambers of the engine block, whose inside diameter is at most 3 mm.

With the invention can be in each

Combustion engine block, in which between two

Cylinder openings a narrow partition is formed, thin channels in the partition in question

contribute. Of course, this includes the

Possibility, in the technical production of engine blocks having more than two cylinder openings, in each of the between adjacent

Cylinder openings existing partitions by means of a respective casting core according to the invention to image at least one thin channel.

Hereinafter, the invention with reference to a

Embodiment showing drawing explained in more detail. Their figures show each schematically:

1 shows a casting core in a view from below;

Fig. 2 the casting core in one against his one

Broadside view;

Fig. 3, the casting core in one against his one

Narrow-side view; 4 shows a detail of a casting mold in one

Longitudinal section;

Fig. 5 shows a detail of an engine block in

Top view .

The casting core 1 has a support section 2, which has the basic shape of a narrow pyramidal stipple with opposite broad sides 3, 4 and likewise opposite narrow sides 5, 6, which connect the broad sides 3, 4 to one another.

Adjacent to the upper end face 7 are at the

Broad sides 3.4 laterally projecting holding sections 8,9 formed, which extend approximately over a fifth of the height of the support section 2.

At its lower plan face 10 are at the

Carrier portion 2 also formed two pin portions 11,12 which extend axially parallel to each other and aligned perpendicularly from the end face 10th

protrude. The pin sections 11, 12 have a

cam-shaped cross-sectional shape, the cam tip 13,14 each in the direction of the other

Journal section 12,11 points.

Between the pin portions 11,12 extend in the longitudinal direction of the pin portions 11,12 spaced from one another and the end face 10 of the support portion two web portions 15,16. The longitudinal axes L1, L2 of the web sections 15, 16 are aligned parallel to one another and to the end face 10 of the carrier section 2. With their ends go the web portions 15,16 in the respectively associated pin portion 11,12. For this purpose, the side surfaces 17,18 of the web portions 15,16 so to the peripheral surface 19,20 of the respective

Tongue section 11,12 nestled. They run tangentially and without jolts into the circumferential surface section 21, 22 of the journal sections 11, 12, which extends between the cam tip 13, 14 and the respectively thickest point of the cross section of the journal sections 11, 12.

At the respective junction where the

Web portions 15,16 are connected to the respective pin portion 11,12, corresponds to the distance of their side surfaces 17,18 measured thickness d of

Web portions 15,16 a maximum thickness dmax of approx.

5 mm, in practice, the thickness dmax may also be greater. Starting from this maximum thickness dmax, the thickness d of the web sections 15, 16 continuously decreases in the direction of the respective other journal section 11, 12, until it lies in a middle position between the webs

Spine portions 11,12 arranged center region 23,24 of the web sections 15,16 reaches its minimum thickness dmin of about 1, 5 mm.

In a corresponding manner, the height h of the web sections 15, 16 measured as the distance between the top and bottom of the web sections 15, 16 continuously decreases starting from a maximum height hmax at the respective connection point in the direction of the central region 23, 24, until a minimum height h min exists there is given by about 4, 3 mm. The casting core 1 has been fired in one piece in a conventional, not shown core shooting machine from a commercial so-called "Croning molding sand" whose quartz grains have a mean grain diameter of 0.21 +/- 0.02 mm (corresponding to AFS Kornfeinheitsnummer 68 + The molding sand was shot at a pressure of 2 - 6 bar into a core box heated to 200 - 350 ° C, in which the binder resin of the

Quartz sand grains in a row over the core box

successful heat supply zusammenackt and

are cured. After a required for this

Residence time of 30 - 120 s, the core 1 could be removed from the core box. He dismissed despite the

filigree shape of its web portions 15,16 on a sufficient dimensional stability in order to supply it for further use. He also had especially in the area of the web sections 15,16 a uniformly finely grained surface whose quality was so high that it could be fed directly to the re-use. The application of a size or other aid that would have been required for coarser surface textures to achieve the required quality was not required.

Cast cores 1 designed and produced in the above-described manner are used as part of a casting mold 25 which is only partially shown in FIG. 4 and otherwise conventionally designed as a core package, which likewise only serves to cast one in FIG

partially shown, from one Aluminum melt alloy cast engine block 26 for an internal combustion engine arranged in series

Cylinder chambers 27,28,29 are used. The cores 1 are arranged by means of cores 30,31,32 so between the cylinder chambers 27-29 mapping cylinder cores 33,34,35 that their web sections centrally in the upper, the cover cores 30-32 associated region of between the cylinder cores 33-35 existing narrow free space 36,37 is arranged. In the finished engine block 26, the respective free space 36, 37 forms in each case the cylinder intermediate wall 38, 39, through which the respectively adjacent cylinder chambers 27, 28; 28, 29 are separated from each other. In the area 40, in which the

adjacent cylinder spaces 27,28 / 28,29 come closest, the minimum thickness dmin of the respective cylinder intermediate wall 38,39 is about 5 mm.

After pouring the Aluminiumschmelzlegierung into the mold 25 of the aluminum casting material solidifies. As a result of the associated heating of the binder begins to disintegrate, which holds the grains of sand of the core 1 together. The registered on this way

As a rule, heat energy is only sufficient to start the decomposition process. If the resulting fragments of the casting core 1 are still too large to from the channels formed by the casting core 1 to

trickle, the nuclear material is then further comminuted in a known manner by a targeted treatment. For this purpose, a suitable, known in technical language under the keyword "thermal Entsanden"

Heat treatment can be carried out in which the disintegration of the binder by targeted heat supply for so long continue and, consequently, the compound is dissolved under the individual molding material grains until the molding material is free-flowing. Alternatively or additionally, the comminution of the casting core can also be mechanically supported by exposing the casting mold or the casting itself to hammer blows, knocking, shaking or vibrating. To the discharge of the crushed molding material of the casting core 1 from the

To optimize the respective channel, the respective channel can additionally be flushed with water or another liquid.

At least the pin and web portions 11,12,15,16 of the cores 1 disintegrate in this way finely divided that their molding sand trickles freely from the finished casting despite the minimized dimensions of the channels imaged by them or can be rinsed out if necessary.

The journal sections 11, 12 of the respective casting core 1 can be coupled to a water jacket core, not shown here, which engages in the engine block 26

Cooling channel images, over which the cylinder chambers 27-29 on its outside bounding walls of the engine block 26 are cooled. In this way, in practical use of the internal combustion engine, cooling water flows over the intake and exhaust ports represented by the journal sections 11, 12

Outflow channels 41,42 through the narrow by means of

Web sections 15,16 mapped, in the range 40 only about 1.5 mm wide and about 4.2 mm high cooling channels 43,44 in the cylinder intermediate walls 38,39 and ensures in the thermal highly loaded area of the cylinder intermediate walls 38,39 for effective cooling.

REFERENCE NUMBERS

1 casting core

2 support section

3.4 broad sides of the support section 2

5, 6 narrow sides of the support section 2

7 upper end side of the support section. 2

8.9 holding sections

10 lower planar end face of the support section. 2

11,12 pin sections of the casting core. 1

13,14 cam tip of the pin sections 12,11

15,16 web portions of the casting core 1

17,18 side surfaces of the web sections 15,16

19,20 peripheral surface of the pin portions 11,12

21,22 peripheral surface portion of the peripheral surface 19,20

23,24 middle region of the web sections 15,16

25 casting mold

26 engine block

27,28,29 cylinder chambers of the engine block 26th

30,31,32 cores

33,34,35 cylinder cores

36,37 clearance between the cylinder cores 33-35

38.39 cylinder partitions of the engine block 26th

40 area where the neighboring

Cylinder chambers 27, 28; 28, 29 come closest

41, 42 inlet and outlet passages of the engine block 26

43,44 cooling channels in the cylinder intermediate walls 38,39 d thickness of the web sections 15,16

dmax maximum thickness of the web sections 15, 16

dmin minimum thickness of the web sections 15, 16

h height of the web sections 15,16

hmax maximum height

hmin minimum height

Ll, L2 longitudinal axes of the web sections 15,16

Claims

P AT ENT TO SP RU CHE

1. Gießkern, which is formed from a molding sand, whose

Grains are interconnected by a binder, and which is provided in a motor block (26) for an internal combustion engine, a cooling channel

(41,42,43,44), d a d u r c h

The casting core (1) is the same as the casting core (1)

a support section (2),

- Two pin sections (11,12), of a

Side surface (10) of the support portion (2) protrude and are spaced from each other, and

- At least one at a distance from the support portion (2) held by the pin portions (11,12)

Web portion (15,16), whose measured as a distance of its side surfaces (17,18) to each other minimum thickness (dmin) in one between the

Pine portions (11,12) lying area (23,24) is not more than 3 mm,

and

the casting core (1) is formed, at least in the area of its web section (15, 16), from a molding sand whose grains have an average diameter of at most 0.35 mm.

2. Casting core according to claim 1, d a d u c h e c e n c e n e s, d a s s

Side surfaces (17,18) of its web portion (15,16) each in a jump-free transition in the

Peripheral surface (19,20) of the pin portions (11,12) pass over and its thickness (d) from one of the respective pin portion (11,12) associated

Maximum thickness (dmax) decreases continuously in the longitudinal direction of the web portion (15,16) up to the minimum thickness (dmin).

3. Casting core according to one of the preceding claims,

d a d u r c h e k e n e, that is, the minimum thickness (d min) of the land portion (15, 16) is at most 2 mm.

4. Casting core according to one of the preceding claims,

d a d u r c h g e k e n e, that is, the minimum thickness (d min) of the land portion (15, 16) is at least 1 mm.

5. Casting core according to one of the preceding claims,

That is, the height (h) of the land portion (15, 16) in the region (23, 24) in which it has its minimum thickness (dmin) is at most 4.5 mm.

6. Casting core according to one of the preceding claims,

characterized in that it is completely formed from a molding sand whose grains have an average diameter of at most 0.35 mm.

Casting core according to one of the preceding claims, characterized in that the mean diameter of the grains of the molding sand is at most 0.25 mm.

Casting core according to one of the preceding claims, characterized in that the average diameter of the grains of the molding sand is at most 0.23 mm.

Casting core according to one of the preceding claims, characterized in that the journal sections (11, 12) have a cross-sectional shape shaped like a cam, the tip (13, 14) of which faces the respective other journal section (12, 11).

Casting core according to one of the preceding claims, characterized in that two or more of the pin portions (11, 12) are present

spaced apart web sections

(15,16) are carried, each having a region (23,24), in which their inimaldicke (dmin) is in each case at most 3 mm.

11. Use of one according to one of the preceding

Claims procured casting core (1) in a mold (25) for the casting production of a

Engine block (26) for an internal combustion engine through

Pouring an aluminum melt into the casting mold (1), wherein the web portion (15, 16) of the casting core (1) in the engine block (26) has a space between two cylinder chambers

(27,28,29) of the engine block (26) arranged cooling channel (43,44), whose clear width is at most 3 mm.

12. A method for producing a according to one of

Claims 1 to 10 obtained casting core (1), in which by means of a core shooter, a molding material comprising a molding sand and a binder in a

Mold cavity of a core mold is shot and then the binder is cured to give the casting core (1) the required dimensional stability,

At least the molding compound used for the web region (15, 16) of the casting core (1) comprises a molding sand whose grains have an average diameter of at most 0.35 mm.

13. The method of claim 12, d a d u r c h

characterized in that the grains of the molding sand are coated with the binder.

14. Method according to claim 13, wherein the grains of the molding sand with their binder coating have a spherical shape.