Device and method for manufacturing of castings

The invention relates to a device and a method for the manufacturing of a cast part. Particularly the invention relates to a device with a moulding box filled with moulding sand in which, for the manufacturing of the cast part, a cavity tillable with metal is formed with at least one cooling body being arranged between the wall of the moulding box and the cavity, the cooling body being compounded from a material of high caloric conductibility.

Such a device for example is known from DE 102 42 559 A1 in which it is proposed, for influencing of the cooling to carry out the density distribution of the material inside of the cooling body inhomogeneous, at least in a section.

From US 5,072,773 it is known to arrange metal plates between the cam surfaces of a crankshaft and the wall of a moulding box, so that the surfaces of the crankshaft corresponding to the surfaces of the metal plates facing toward the cavity cool down. A similar principle is also known from WO 93/05908.

With the devices described, by the quick cooling of surface sections, material hardenings can be generated, which are desired for certain applications.

However, often it is necessary, particularly at the manufacturing of very large cast parts, that the material structure of the whole cast part is homogeneous. For this the known cooling bodies are not suitable. On the other hand, it is desirable that particularly very large cast parts could be cooled down quick as a whole, so that less room is needed in a foundry for the storage of cast parts to be cooled down. A quick cooling of the cast part also helps acheive a more homogeneous distribution of the carbon content in the cast material.

Taking this as a starting point, the object of the present invention is to provide a device for the use in casting moulds, with which it is feasible to cool down cast parts as quick as possible, so that a more homogeneous material structure is caused.

According to the invention this object is achieved in that, in an intermediate area, the cooling body and the cavity are positioned at a distance from each other, and that in the

intermediate area there is arranged an intermediate body, which is made from a material different to the material of the cooling body.

In contrast to the prior art, the cooling body with its surface faces towards the cavity so that it does not form a part of the cavity, but it is located at a distance from the cavity. As a result, the sections of the material of the cast part, which are located adjacent to a cooling body, will not be cooled down too fast, and thereby hardening of the material of the cast part in sections, will not occur. Thus, while quick cooling of a cast part is achieved the material structure of the cast part is homogeneous and lacking in stress. Particularly with very large cast parts this has advantages, for example with a hub for the bedding of wind power wheels.

By the use of the cooling bodies the time required for the cooling of the cast part can be reduced considerably. The cooling-down time can decisively be influenced by the geometry and the volume of the cooling bodies as well as by the initial temperature of the cooling body and the temperature of the metal to be cast.

The intermediate body fulfils a multifunction: On the one hand it provides a contact surface for the cooling of the cast part, on the other hand the intermediate body covers the actual cooling body and protects it from temperatures being too high. Due to the fact that the material of the intermediate body is different to the material of the cooling body, the intermediate body can be constructed so that it is insensitive as against high temperatures and at the same time is able to conduct the heat from the cast part to the cooling body.

Preferably the distance between the cooling body - that means that surface of the cooling body which is closest to the cavity - and the cavity itself is at least 50 mm, in particular at least 70 mm. By choice of the distance a compromise can be found between a good cooling effect and the avoidance of the local hardening of the material of the cast part.

According to an embodiment of the invention the intermediate body is made from moulding sand. The moulding sand has a caloric conductibility which is many times lower than the caloric conductibility of the cooling body. Nevertheless the moulding sand can transmit heat energy towards the cooling body from the cast part to be cooled.

The values quoted above concerning the distance between the cooling body and the cavity correspond to the extent of the intermediate body. With use of moulding sand it transpires

that with the quoted values, especially at a value of 80 mm, it is guaranteed, that the moulding sand can be well rammed. This ramming is important for the avoidance of bubbles, the dimensional stability of the cavity and for the surface quality of the cast part.

On the other hand the above-mentioned values are low enough to guarantee, that sufficient heat transport between the cast part and the cooling body can take place. It has turned out by experiments that a cooling-down time of a bulk cast part could be reduced by about 20%.

According to a further embodiment of the invention the intermediate body is made out of a material with a high quota of iron, for example out of steel or gray cast iron. This material is insensitive to heat.

According to a specially preferred embodiment of the invention the intermediate body is made out of a material with a high quota of carbon, especially graphite. The quota of carbon of the intermediate body preferably amounts to more than 50%, further preferably more than 80%, in particular 100%. Such a material is extremly insensitive to heat and has a high caloric conductibility (129 W/m*K). Surprisingly it transpires| out that with the use of an intermediate body of graphite cooling-down times can be reduced up to 40%.

It is suggested that the intermediate body is made of a material, the melting point of which is above 1400 ⁰ C to guarantee that the intermediate body does not melt.

If the intermediate body is made of a material the caloric conductibility of which is at least 10 W/m*K, quick and effective heat dissipation is achieved.

It is advantageous, if the intermediate body is fastened to the cooling body, to guarantee that the intermediate body does not become displaced during the casting action.

In an advantageous way the intermediate body is made of a material, the melting point of which is above 300 ⁰ C. Since the cooling body does not come in contact directly with the part to be moulded, it is not necessary that the melting point is particularly high. Materials with a lower melting point can thus be used too. Especially it is possible to use materials having a caloric conductibility of at least 100 W/m*K.

Furthermore it is advantageous, if the cooling body is at least partly, and particularly completely, made of aluminium. Aluminium has a very good caloric conductibility (237

W/m*K) and, as a result, can dissipate great amounts of heat from the cast part. In addition a cooling body can be produced easily and at a reasonable price, for example by producing it separately or by casting process. For manufacture by casting process metal plates can be welded into the moulding box to form hollow spaces, into which can be put solid aluminium parts. The cooling bodies can then be formed by melting open the aluminium parts, so that the aluminium can adapt to the form of the hollow spaces.

According to a further advantageous embodiment of the invention the side of the cooling body which is faces towards the intermediate body can be provided with a protective layer, which is made of a material with a high melting point, especially of a material with a high quota of iron. In this way it can be avoided that the cooling body deforms as soon as a great amount of hot metal is being filled into the cavity and the heat energy being dissipated through the intermediate body would be to great, or if the intermediate body possibly contains defective flaws in the form of hollow spaces, into which possibly molten metal of the cast part could penetrate.

In order to avoid melting of the material of the cooling body, it is advantageous that this material is, at least in sections, surrounded by a material with a high melting point. It is particularly advantageous if the material with the high melting point completely surrounds the cooling body. In this case it is even possible that the material with the high caloric conductibility melts, however it can not deform or leak because it is surrounded by the material with the high melting point. Therefore the molten core of a cooling body can solidify again, so that the cooling body is usable again as soon as a certain temperature is reached.

To further improve the cooling effect it is suggested, that the cooling body and the wall of the moulding box rest on each other. Thus the moulding box itself can absorb heat energy and convey it to the ambience of the moulding box so the cooling effect will be further improved. Additionally or optionally to this the cooling body can, at least with a section, extend over and above the moulding sand. Because of this the cooling body can be in direct contact with the ambient air and, as a result, can quickly convey a great amount of heat. This effect can be increased further if the section extending over and above the moulding sand is provided with surface extensions, especially cooling webs. With that the cooling body can rest at the wall of the moulding box - as described above -, however it does not need it.

Further the invention relates to a method for the manufacturing of a cast part, particularly by use of a device as described above, which method comprises the following steps: A moulding box will be filled with moulding sand, including the formation of a cavity; between the wall of the moulding box and the cavity at least one cooling body of a material with a high caloric conductibility will be arranged in the moulding box in a manner such that the cavity and the cooling body, in an intermediate area, are at a distance from each other; in the intermediate area an intermediate body will be arranged, which is made from a material different from the material of the cooling body; the cavity will be filled with metal. It is clear that the first-mentioned steps (filling of the moulding box and arrangement of the cooling bodies and the intermediate bodies in the moulding box) also can be carried out at the same time or in another order.

A further embodiment of this method provides, that the method will firstly be carried out without cooling bodies, while during filling of the cavity the temperature is measured in at least two different sections of the moulding sand. In this way it can be determined in which sections of the moulding sand particularly high temperatures occur. This information can be used to arrange the cooling body - or the cooling bodies - in the moulding box with regard to the temperatures measured in the moulding sand.

This method will be the more precise, the more measuring points are used. Of course instead of single temperature values also increases in temperature can be measured, so that still more precise understanding about the heat distribution in the moulding sand can be acheived.

Further advantages, features and details of the invention arise from the following description, in which with reference to the drawing a particularly preferred embodiment is described in detail. The features shown in the drawing and mentioned in the claims and the description can be essential for the invention individually or in any combination.

The drawing shows a perspective view of a device according to the invention. As a whole it is indicated by reference 2. The device 2 is provided with a moulding box 4 consisting of several parts and shown only in sections, the wall 6 of which limits a volume which can be filled with moulding sand.

Inside the moulding box 4 a sand core 8 is arranged, which defines the inner surfaces of a cast part 10. The represented cast part 10 is a hub for the bedding of a wind wheel.

Altogether six bulk cooling bodies 12 are arranged within the moulding box 4. Three of the cooling bodies 12 are shown in the drawing; the remaining three cooling bodies are arranged at the bottom of the moulding box 4, but not shown in the drawing in the interests of clarity. The back of the cooling body 12 rests on the wall 6 of the moulding box 4. Essentially the cooling bodies 12 consist of aluminium and are provided with a protective layer 14 on the side which faces towards the cast part 10, which layer 14 is made of a very ferruginous material. Furthermore inside the moulding box 4 a feeder 16 is arranged via which cast material can be fed to the cast part 10 being freshly cast in order to compensate for material shrinkages.

The remaining sections of the moulding box 4 are filled with moulding sand 18. A cavity 20 is provided within the moulding box 4 as indicated in the drawing by a broken line. For the manufacturing of the cast part 10 this cavity can be filled with liquid metal using a pouring basin 22. A slag runner 24 with filters 26 is arranged between the pouring basin 22 and the cavity 20.

As is clearly visible in the drawing, the cavity 20 is spared by an intermediate section 28 a distance 30 from the cooling body 12. The distance 30 between the cavity 20 and the cooling body 12 amounts to about 80 mm. Also the intermediate section 28 is filled with moulding sand 18. This moulding sand forms an intermediate body. In the intermediate section 28, there can also be arranged a dishlike intermediate body of graphite and with a wall thickness of about 80 mm.

Regardless of whether an intermediate body out of moulding sand 18 or out of graphite is being arranged in the intermediate section 28, the distance between the cooling body 12 and the cavity 20 will enable the cast part 10 to cool down in such a way, that a material structure results which is highly homogeneous. In this case the cooling-down time is much shorter than when manufacturing without use of the cooling bodies 12. With an intermediate body of graphite a maximum shortening of the cooling-down time can be achieved.