EP3166740B1 - Core and mehtod for the production of a core - Google Patents

Description

The invention relates to a method for producing a casting core designed according to the preamble of claim 1, in which the work steps specified in the preamble of claim 1 are carried out.

The invention also relates to a casting core produced using this method.

Casting cores of the type in question form channels, cavities and other recesses as part of a casting mold in the component to be cast. In engine blocks for internal combustion engines, for example, the channels carrying cooling water, but also the cylindrical-shaped combustion chambers, are formed with the aid of casting cores.

Engine blocks of modern high-performance engines have to be cooled intensively during operation in order to remove the large amounts of heat that arise due to the high power density. This applies in particular to engine blocks that are made of a light metal material, such as an aluminum alloy. At the same time, there is a desire, particularly in the area of passenger cars, for ever more compact structures Drive units to save weight on the one hand and to be able to accommodate high-performance engines in car bodies where only limited space is available.

The compact design leads to a closely adjacent arrangement of the cylinder recesses in a row of cylinders. This results in correspondingly thin cylinder walls. These are exposed to an increased thermal load, in particular in the area of their end sections assigned to the cylinder head. In order to avoid the occurrence of heat-related cracks or other damage, it is necessary to also carry out intensive cooling in the relevant hazardous area.

One way of introducing the cooling duct required for this into the thin intermediate wall remaining between two cylinder spaces of an engine block is to drill the cooling duct into the block after the casting production has been completed. Although this method allows precise production even of very small and narrow channels, it is technically complex because it requires a large number of additional operations. This leads to high costs. Another disadvantage is that it is difficult in terms of production technology to make a channel bore with a minimized diameter in the upper region of the partition wall of an engine block between adjacent cylinder recesses, in which the highest thermal load arises in use.

In order to avoid this effort, various proposals have been made as to how thin and narrow ducts can be introduced into the areas of an engine block that are thermally highly stressed during operation during the production of the casting technology. Cores from a wide variety of molding compositions have been proposed, each of which has been selected with the aim of ensuring adequate dimensional stability of the filigree core section, which is intended to represent the respective channel in the cast part, on the one hand, and ensuring that the core material is solidified after the engine block has solidified can be removed as easily as possible so that a proper flow is guaranteed. However, the use of cores made from molding compositions reaches limits which are set by the dimensional stability and mechanical strength which the cores must have in order to ensure sufficient productivity even under the conditions prevailing in a foundry.

In order to be able to map channels with even smaller diameters in light metal engine blocks, is in the EP 0 974 414 B1 have been proposed to represent these channels through a correspondingly dimensioned glass tube which is inserted into the casting mold and is enclosed by the casting melt during casting. The material of the glass tube is selected in such a way that it breaks into many small parts under the stresses that occur during the solidification of the casting material, which can then be easily rinsed out. Other proposals aimed in this direction provide for the channels to be represented by sheet metal or wire inserts, which are then pulled out of the finished casting.

The above-mentioned possibilities have proven themselves in the prior art with more or less great technical and economic success for the production of channels which, despite their limited dimensions, are sufficiently large and accessible to be able to remove the remaining fragments of the core material which forms them.

In the case of a new generation of internal combustion engines cast from aluminum material, however, the thickness of the intermediate walls is reduced to such an extent that the cooling channels required therein have a clear width of less than 3 mm in their narrowest section. In engine blocks of this type cast from aluminum material, the clear width of the cooling ducts in the area where the intermediate wall between two cylinder spaces is narrowest is in the range of 1-2 mm.

A generic core and a method for its production are from the US 4,693,294 A known. With the known casting core, cooling channels are to be introduced into the cylinder wall between two cylinder openings of an internal combustion engine, which in the finished state has a total thickness of at most 9 mm, in particular less than 8.5 mm. The between the channel introduced into the cylinder wall and the adjacent one The remaining wall of the cylinder has a wall thickness of 2.5 mm or less, so that the inside width of the cooling duct introduced into the wall is> 3 mm at its narrowest point. In order to cast a cooling channel of this dimension, a casting core designed in the manner of a bridge is formed from a zircon sand according to the prior art, the mean grain size of which is 0.15-0.2 mm.

Against the background of the prior art, the task has arisen of specifying a method which makes it possible to produce casting cores which can be produced in a simple, reliable manner and which also allow channels which are at their narrowest point at most 3 mm wide are to manufacture by casting.

The method that achieves this object according to the invention is specified in claim 1.

With the method according to the invention, casting cores can be produced which have at least the features specified in claim 2. A casting core according to the invention can advantageously be used in a casting mold for the cast-technical production of an engine block for an internal combustion engine by pouring an aluminum melt into the casting mold, the web section of the casting core in the engine block forming a cooling channel arranged between two cylinder spaces of the engine block, the clear width of which is at most 3 mm is.

Advantageous refinements of the invention are specified in the dependent claims and are explained in detail below, like the general inventive concept.

A casting core according to the invention, which is provided for forming a cooling channel in an engine block for an internal combustion engine, is accordingly formed entirely from a molding sand, the grains of which are connected to one another by a binder. According to the invention, the casting core now has a support section, two peg sections which protrude from a side surface of the support section and are arranged at a distance from one another, and at least one web section which is held at a distance from the support section from the peg sections and whose minimum thickness, measured as the distance between its side surfaces, is in one area between the pin sections is at most 3 mm. The casting core is formed at least in the region of its web section from a molding sand, the grains of which have an average diameter of at most 0.35 mm.

A casting core according to the invention thus consists entirely of molding sand, the grains of which are connected to one another in a manner known per se by means of a suitable binder in such a way that they form a solid body.

The support section of the casting core allows the casting core to be gripped, transported and inserted into a casting mold without any problems despite the filigree design of its web section. So he can Casting core according to the invention can also easily be part of a casting mold designed as a core package. In the same way, it can be used in any other casting process, in which filigree channels with minimal dimensions are to be formed in or on the respective casting.

The pin sections carried by the carrier section form the inflow and outflow channel in the engine block to be cast, via which the narrow, narrow-dimensioned cooling channel is supplied with coolant, which is represented in each case by the web section carried by the pin sections in the engine block. Its thickness is reduced to a maximum of 3 mm in a critical area, and in practice the minimum thickness in this area is 1-2 mm. The relevant critical area, in which the web section of the casting core according to the invention is narrowest, is assigned to the area of the respective intermediate wall of the engine block to be cast, where the intermediate wall is thinnest and the cylinder spaces separated by the intermediate wall come closest.

It is crucial for the practical implementation of the invention that the casting core is formed from a fine-grained molding sand at least in the area of its web section. Its grain size is selected so that the web section disintegrates finely in the solidified casting after the casting, so that the remaining core fragments either trickle out of the solidified engine block automatically or can be rinsed out.

Surprisingly, it has been shown that the casting cores can not only be produced in a conventional manner by shooting in a core shooter, but also offer a surface texture in the area of the narrow web section, which produce sufficiently smooth inner surfaces in the cooling channel to be produced without this being necessary complex finishing job required. This applies in particular if the average diameter of the grains of the molding sand is at most 0.27 mm, in particular at most 0.23 mm.

As already mentioned, casting cores according to the invention can be produced on an industrial scale by using a core shooter to shoot a molding compound, which comprises a molding sand and a binder, into a mold cavity of a core mold and then to harden the binder in order to give the casting core the required dimensional stability, whereby According to the invention, a molding sand whose grains have an average diameter of at most 0.35 mm is used as molding compound at least for the web area of the casting core. Here too, for the reasons explained above, it goes without saying that the average diameter of the grains is optimally not more than 0.27 mm, in particular at most 0.23 mm.

According to the invention, optimal work results are 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 coated with a binder, with the middle also being applicable here The diameter of the shaped sand grains coated in this way is not greater than 0.35 mm. Shaped sands coated with binder of the type processed according to the invention are still used today for the so-called "croning process", also called "mask molding process" in technical terminology, and for example under the designation VS744 (average grain size 0.29 mm +/- 0.02 mm ) or VS1264 (average grain size 0.21 +/- 0.02 mm) from Hüttenes-Albertus Chemische Werke GmbH, Düsseldorf. Hüttenes Albertus Chemische Werke GmbH also published the paper "The Mask Molding Process: A German Innovation in Casting Production" by Ulrich Recknagel, which shows the technology and history of the mask molding process.

The particular advantage of using croning molding materials results from the fact that the binder covering of the respective molding sand grains has a spherical shape according to the invention. The spherical shape ensures a particularly good behavior of the molding material when shooting cores according to the invention in a conventional core shooting machine. In this way, casting cores according to the invention can be produced with a high level of operational reliability, despite their minimized dimensions.

Especially when using the more fine-grained molding sand with an average grain size of 0.19 - 0.23 mm, not only can casting cores be easily produced in a core shooter, but it also shows that the surface of the thin cooling channels shown by their web section in the engine block cast in each case adequate quality on a regular basis has, without the need for sizing or other surface-improving aids, such as talc or the like.

If, when using coarser sands with average diameters of their preferably binder-coated grains of 0.27 mm and more, it turns out that the surface quality of the cooling channels shown in the cast part is not sufficient, this can usually be used by applying a thin coating or another to improve the surface Be fixed by at least on the web section. With grain sizes of more than 0.35 mm, however, casting cores with the dimensions specified according to the invention can no longer be reliably fired, and the effort to compensate for the coarse surfaces becomes so great that an application is no longer sensible even from an economic point of view. For this reason, molding sands whose grains coated with binder have an average diameter of less than 0.27 mm, in particular less than 0.25 mm, are optimally used for the production of casting cores according to the invention.

The binder with which the grains of the molding sand used according to the invention for the production of the casting cores are coated is typically a resin which, as a result of the application of heat, bonds and hardens with the resin of the respectively adjacent grains, so that a firm bond is produced.

A reliable production by conventional shooting of the cores in a core shooting machine also contributes if, according to one embodiment of the invention, the side surfaces of the casting core according to the invention each transition into the peripheral surface of the pin sections in a jump-free transition and its thickness starting from a maximum thickness assigned to the respective pin section Longitudinal direction of the web section decreases continuously to the minimum thickness. The jump-free connection of the web section to the tenon sections supporting it and the continuous reduction in thickness help to ensure that the molding material, despite the minimized dimensions in the core shooter, also fills the cavity securely and sufficiently tightly, which forms the narrow web section of the casting core.

The jump-free connection of the web section to the pin sections can be simplified in that the pin sections have a cross-sectional shape shaped like a cam, the tip of which faces the respective other pin section. In this way, the side surfaces of the web section can easily nestle against the peripheral surface of the pin sections, which in turn supports the filling of the web section with molding sand during core shooting.

In the manner according to the invention, casting cores can be produced which, in their critical, minimally thick region, not only have a thickness of at most 3 mm, in particular 1-2 mm, and are therefore suitable, Show cooling channels with a clear width of 3 mm and less, in particular 1.5 +/- 0.5 mm, in the cast part to be created, but where the height is also minimized in the critical area. In the case of a casting core according to the invention, the height of the web section in the region in which it has its minimum thickness can be limited to a maximum of 4.5 mm.

Basically, it is conceivable to form only the web section of a casting core according to the invention from fine-grained molding sand according to the invention, while the other sections of the casting core consist of a coarser molding sand. For this purpose, for example, the web section could be shot from the fine-grained sand separately from the other sections of the casting core and then connected, for example by gluing, to the remaining sections of the casting core which were shot from coarser sand. However, it is simpler in terms of production technology if, according to a further embodiment of the invention, the casting core is in each case completely formed in one piece from a molding sand which meets the requirements according to the invention.

If this requires the amount of heat to be dissipated, a casting core according to the invention can also be easily designed so that it depicts more than one narrow pouring channel in the thin intermediate wall of the engine block to be cast. For this purpose, two or more spaced web sections can be carried by the pin sections, each of which has an area in which their minimum thickness is at most 3 mm. It goes without saying that here, too, significantly smaller minimum thicknesses, for example 1-2 mm, are possible for the additional web sections.

A casting core according to the invention is particularly suitable for use in a casting mold for the cast-technical production of an engine block for an internal combustion engine by pouring an aluminum melt into the casting mold, the web section of the casting core in the engine block forming a cooling channel arranged between two cylinder spaces of the engine block, the clear width of which is at most Is 3 mm.

With the invention, thin channels can be introduced into the relevant partition in each internal combustion engine block in which a narrow partition is formed between two cylinder openings. Of course, this includes the possibility, when casting engine blocks that have more than two cylinder openings, to image at least one thin channel in each of the partition walls between adjacent cylinder openings by means of a casting core according to the invention.

Fig. 1

einen Gießkern in einer Ansicht von unten;

Fig. 2

den Gießkern in einer gegen seine eine Breitseite gerichteten Ansicht;

Fig. 3

den Gießkern in einer gegen seine eine Schmalseite gerichteten Ansicht;

Fig. 4

einen Ausschnitt einer Gießform in einem Längsschnitt;

Fig. 5

einen Ausschnitt eines Motorblocks in Draufsicht.

The invention is explained in more detail below with reference to a drawing showing an exemplary embodiment. The figures each show schematically:

Fig. 1

a casting core in a view from below;

Fig. 2

the casting core in a view directed towards one of its broad sides;

Fig. 3

the casting core in a view directed towards its one narrow side;

Fig. 4

a section of a mold in a longitudinal section;

Fig. 5

a section of an engine block in plan view.

The casting core 1 has a carrier section 2, which has the basic shape of a narrow pyramid stub with opposite broad sides 3, 4 and narrow sides 5, 6 also opposite one another, which connect the broad sides 3, 4 together. Adjacent to the upper end face 7, laterally protruding holding sections 8, 9 are formed on the broad sides 3, 4 and extend approximately over a fifth of the height of the support section 2.

On its lower, planar end face 10, two pin sections 11, 12 are additionally formed on the carrier section 2 and extend axially parallel to one another and project from the end face 10 in a vertically aligned manner. The pin sections 11, 12 have a cam-like cross-sectional shape, the cam tip 13, 14 of which points in the direction of the respective other pin section 12, 11.

Two web sections 15, 16 extend at a distance from one another in the longitudinal direction of the pin sections 11, 12 and between the pin sections 11, 12 and to the end face 10 of the carrier section. The longitudinal axes L1, L2 of the web sections 15, 16 are parallel to one another and aligned with the end face 10 of the carrier section 2.

The ends of the web sections 15, 16 merge into the respectively assigned pin section 11, 12. For this purpose, the side surfaces 17, 18 of the web sections 15, 16 are nestled against the peripheral surface 19, 20 of the respective pin section 11, 12. They run tangentially and without jump into the peripheral surface section 21, 22 of the pin sections 11, 12, which extends between the cam tip 13, 14 and the thickest point of the cross section of the pin sections 11, 12.

At the respective connection point at which the web sections 15, 16 are connected to the respective pin section 11, 12, the thickness d of the web sections 15, 16 measured as the distance between their side surfaces 17, 18 corresponds to a maximum thickness dmax of approximately 5 mm, in in practice the thickness dmax can also be larger. Starting from this maximum thickness dmax, the thickness d of the web sections 15, 16 decreases continuously in the direction of the respective other pin section 11, 12 until it reaches its minimum thickness dmin in a central region 23, 24 of the web sections 15, 16 arranged centrally between the pin sections 11, 12 of about 1.5 mm.

Correspondingly, 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 from a maximum height hmax given at the respective connection point in the direction of the central region 23, 24 until a minimum height hmin there 4.3 mm.

The casting core 1 was shot in one piece in a conventional core shooting machine, not shown here, from a commercially available so-called "croning molding sand", the quartz sand grains of which had an average grain diameter of 0.21 +/- 0.02 mm (corresponding to AFS grain size number 68 + / - 3 and were coated with a synthetic resin serving as a binder 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 as a result of the over After a required dwell time of 30-120 s, the casting core 1 could be removed from the core box. Despite the filigree shape of its web sections 15, 16, it had sufficient dimensional stability to allow it to be used again It also had a uniformly fine-grained surface, in particular in the area of the web sections 15, 16 e, the quality of which was so high that it could be used directly. It was not necessary to apply a size or any other tool that would have been necessary with coarser surface structures in order to achieve the required quality.

Casting cores 1 designed and produced in the manner explained above are part of an in Fig. 4 only partially shown, otherwise used conventionally designed as a core package 25 mold for casting a in Fig. 5 engine blocks 26, also shown only in sections and cast from a molten aluminum alloy, are used for an internal combustion engine with cylinder spaces 27, 28, 29 arranged in series. The casting cores 1 are arranged by means of cover cores 30, 31, 32 between the cylinder cores 33, 34, 35 that represent the cylinder spaces 27-29 in such a way that their web sections are centered in the upper area of the area between the cylinder cores 33-35 that is assigned to the cover cores 30-32 existing narrow free space 36,37 is arranged. In the finished engine block 26, the respective free space 36, 37 each represents the intermediate cylinder wall 38, 39, by which the respectively adjacent cylinder spaces 27, 28, 28, 29 are separated from one another. In the area 40 in which the adjacent cylinder spaces 27, 28, 28, 29 come closest, the minimum thickness dmin of the respective intermediate cylinder wall 38, 39 is approximately 5 mm.

After the molten aluminum alloy has been poured into the mold 25, the cast aluminum material solidifies. As a result of the associated heating, the binder, which holds the sand grains of the casting core 1 together, begins to disintegrate. The thermal energy entered in this way is usually only sufficient to start the decay process. If the fragments of the casting core 1 thus obtained are still too large to move out of the channels represented by the casting core 1 trickle, the core material is then further crushed in a known manner by targeted treatment. For this purpose, a suitable heat treatment, also known in technical terms under the keyword "thermal desanding", can be carried out, in which the disintegration of the binder continues by means of targeted supply of heat and the associated connection between the individual molding granules is dissolved until the molding material is free-flowing . As an alternative or in addition, the comminution of the casting core can also be supported mechanically by exposing the casting mold or the casting itself to hammer blows, knocking, shaking or vibrating. In order to optimize the discharge of the comminuted molding material of the casting core 1 from the respective channel, the respective channel can additionally be flushed through with water or another liquid.

In this way, at least the pin and web sections 11, 12, 15, 16 of the casting cores 1 disintegrate so finely that their molding sand, despite the minimized dimensions of the channels they represent, can freely trickle out of the finished casting or, if necessary, be rinsed out.

The pin sections 11, 12 of the respective casting core 1 can be coupled to a water jacket core (not shown here), which forms a cooling channel in the engine block 26, via which the walls of the engine block 26 bordering the outside of the cylinder spaces 27-29 are cooled. In this way, in practical use of the internal combustion engine, cooling water flows through it the pin sections 11, 12 shown inlet and outlet channels 41, 42 through the narrow cooling channels 43, 44 shown in the area 40 by means of the web sections 15, 16, only about 1.5 mm wide and about 4.2 mm high, in the intermediate walls of the cylinders 38.39 and ensures effective cooling in the region of the cylinder partition 38.39 which is subject to high thermal loads.

REFERENCES

1

Pouring core

2nd

Beam section

3.4

Broad sides of the carrier section 2

5.6

Narrow sides of the carrier section 2

7

upper end face of the carrier section 2

8.9

Holding sections

10th

lower flat end face of the carrier section 2

11.12

Pin sections of the casting core 1

13.14

Cam tip of the pin sections 12, 11

15.16

Web sections of the casting core 1

17.18

Side faces of the web sections 15, 16

19.20

Circumferential surface of the pin sections 11, 12

21.22

Circumferential surface portion of the circumferential surface 19, 20

23.24

Center area of the web sections 15, 16

25th

Mold

26

Engine block

27,28,29

Cylinder rooms of the engine block 26

30,31,32

Cores

33,34,35

Cylinder cores

36.37

Free space between the cylinder cores 33-35

38.39

Cylinder walls of the engine block 26

40

Area in which the adjacent cylinder spaces 27, 28, 28, 29 come closest

41.42

Inlet and outlet channels of the engine block 26

43.44

Cooling channels in the cylinder partition 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

L1, L2

Longitudinal axes of the web sections 15, 16

Claims (11)

1. Method for producing a foundry core (1) which is provided to form a cooling channel (41, 42, 43, 44) in an engine block (26)for an internal combustion engine, and which has a supporting section (2), two neck sections (11,12) which protrude from a lateral surface (10) of the supporting section. (2) and are arranged at a distance from one another and at least one bridge section (15, 16) which is held by the neck sections (11,12) at a distance from the support section (2) and the minimum thickness (dmin) of which measured as the distance between its lateral surfaces (17,18) is no more than 3 mm in an area range (23, 24) which lies between the neck sections (11,12), wherein in the method a core shooting machine is used to shoot a moulding material, which comprises a moulding sand and a binder, into a mould cavity of a core form and subsequently the binder is hardened to provide the foundry core (1) with the required shape stability, and wherein at least the moulding material used for the bridge section (15,16) of the foundry core (1) comprises a moulding sand, the grains of which have a mean diameter of a maximum of 0.35 mm and are coated with the binder and are spherical in shape with their binder coating.
2. Foundry core, produced using the method according to claim 1, which is provided to form a cooling channel (41, 42, 43, 44) in an engine block (26) for an internal combustion engine, wherein the foundry core (1) has

   - a supporting section (2),

   - two neck sections (11,12) which protrude from a lateral surface (10) of the supporting section (2) and are arranged at a distance from one another, and

   - at least one bridge section (15, 16) which is held by the neck sections (11, 12) at a distance from the supporting section (2),

   wherein the foundry core (1) is made of a moulding sand at least in the area of its bridge section (15,16), the grains of which moulding sand have a mean diameter of a maximum of 0.35 mm,
   and
   wherein the minimum thickness (dmin) of the bridge section (15, 16) measured as the distance between its lateral surfaces (17, 18) is no more than 3 mm in an area (23, 24) which lies between the neck sections (11,12).
3. Foundry core according to claim 2, characterised in that the lateral surfaces (17, 18) of its bridge section (15, 16) pass on in each case without a jump into the peripheral surface (19,20) of the neck sections (11,12) and the thickness (d) deceases starting from a maximum thickness (dmax) assigned to the respective neck section (11,12) in a longitudinal direction of the bridge section (15,16) continuously down to the minimum thickness (dmin).
4. Foundry core according to any one of claims 2 or 3, characterised in that the minimum thickness (dmin) of the bridge section (15,16) is a maximum of 2 mm.
5. Foundry core according to any one of claims 2 to 4, characterised in that the minimum thickness (dmin) of the bridge section (15,16) is at least 1 mm.
6. Foundry core according to any one of claims 2 to 5, characterised in that the height (h) of the bridge section (15,16) is a maximum of 4.5 mm in the area (23,24) in which it has its minimum thickness (dmin).
7. Foundry core according to any one of claims 2 to 6, characterised in that it is completely formed from moulding sand, the grains of which have a mean diameter of a maximum of 0.35 mm.
8. Foundry core according to any one of claims 2 to 7, characterised in that the mean diameter of the grains of the moulding sand is a maximum of 0.25 mm.
9. Foundry core according to any one of claims 2 to 8, characterised in that the mean diameter of the grains of the moulding sand is a maximum of 0.23 mm.
10. Foundry core according to any one of claims 2 to 9, characterised in that the neck sections (11,12) have a cross-sectional shape shaped according to the type of a cam, the tip of which (13,14) faces towards the respective other neck section (12,11).
11. Foundry core according to any one of claims 2 to 10, characterised in that two or more bridge sections (15,16) arranged at a distance from one another and held by the neck sections (11,12) each have an area (23,24) in which the minimum thickness (dmin) is a maximum of 3 mm.

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