PERMANENT MOLD FOR MELTING LIGHT METAL FOUNDRY MATERIALS AND USING THE TYPE OF PERMANENT MOLD AND A MATERIAL OF
FOUNDRY
DESCRIPTION OF THE INVENTION The present invention relates to a mold for the melting of light metal casting materials. The invention also relates to the use of such a mold and the use of an inherently known cast iron material. The principle of using molds in casting molds, in particular in sand casting molds, is known to specifically cool more substantially a molten material, cast in the casting mold, in particular a light metal casting material, such as a aluminum or magnesium material, in the contact area between the casting material and the shell, which the sand mold is capable of doing (Stephan Hasse, Ernst Brunhuber: "Giesserei Lexikon" [Casting Plant Encyclopaedia], page 735, 18a edition, 2001). In this way, a specifically directed solidification of the casting material is achieved, taking as a base the areas of the casting material that come into contact with the mold. In addition to this, the accelerated cooling achieved by the use of shells allows a microstructure of the solidified cast iron to be obtained which is improved with respect to its properties Ref. 184747
mechanical, in particular more dense, in the area cooled by the shell. The shells are therefore usually used in such sections of the casting mold which form areas of the casting that will be formed in which particularly high demands are placed on the properties of the microstructure. This applies in particular to the manufacture of technical casting of engine blocks or cylinder heads of combustion engines from a light metal alloy. A typical example for the sector of casting molds, in which the shells are used for local improvement of the microstructure, is the cylinder chambers of combustion engines. The travel surfaces of the cylinder chambers are subjected to heavy loads when they are in operation, so that high demands are placed, in particular, on their properties of wear resistance, hardness and strength. Conventional shells are made of cast iron material. In terms of casting technology, they can be manufactured in a simple and economical way. In practice, however, cast iron shells have proven problematic with the casting of light metal castings, such as aluminum or magnesium fusions, due to the coefficient of
Lower thermal expansion of cast iron compared to light metal casting material. During casting, the shell which comes into contact with the melting of light metal is heated and its coefficient of thermal expansion expands accordingly. If the temperature falls during the subsequent solidification process, the shell shrinks back to its initial volume. If the melting and the molds have different coefficients of thermal expansion, stresses or even relative movements can occur in the contact areas between the shells and the solidified melting material, as a result of this the defects are caused in the finished function. In particular, porosities and other comparable surface defects can occur. Such defects prove to be problematic in particular in situations in which particularly high loads occur in the individual foundry when in operation. Added to this, is the fact that the tensions which occur between the shell and the casting can be too great that the shell can only be separated from the solidified cast iron with relatively high stress, which has a negative consequence particularly in the manufacture Automated light metal foundries.
Attempts have been made to solve the inherent problem with the use of gray cast iron cores using molds formed of bronze. The principle is known from DE 195 333 529 Al, for example, of forming cylinder chambers of combustion engines by means of bronze shells inserted in a sand mold proposed for melting aluminum fusions. The composition of the bronze of these known molds in this case is preferably determined in such a way that they have coefficients of thermal expansion of at least 20 x 10"6 K" 1, which conform to that of a fusion of Al. Since the The thermal expansion coefficient of the molds is adjusted to that of the aluminum which will be melted, it can be guaranteed that the mold and molten cast material will expand and contract to essentially the same degree. In this way, the stresses between the cast iron and the shell can be reduced to a minimum. A disadvantage of the known bronze molds is their high price and their unfavorable wear behavior. Its handling is also heavy, since the bronze molds can not be maintained with magnets, for example. With automatic manufacturing techniques in particular, this makes it difficult to provide casting molds which are equipped with bronze molds. To avoid the adherence of the molten material to the mold, and to obtain a surface quality
optimal, it is necessary in practice, as a rule, that the surface of the mold be provided with a rigging. This procedure also leads to a complication of the manufacturing process, which inevitably incurs additional costs. Taking the prior art described hitherto as a basis, the object of the invention is to provide a shell capable of being economically manufactured, which possesses optimized properties of use and at the same time makes possible optimized casting results. In addition to this, a preferred application is described for such a shell. Finally, the object to be solved by the invention also consists in describing a new possibility of application for an inherently known casting material. With respect to the shell for the casting of light metal casting materials, this object is solved because it is made of a cast iron material alloyed with Ni and / or Mn, of which the content of Ni and / or Mn content is it dimensioned in such a way that the coefficient of thermal expansion of the shell is adjusted to the coefficient of thermal expansion of the light metal melting material which will be melted in each case. A shell provided in accordance with the
The invention can preferably be used as a constituent part of a sand casting mold for casting a cylinder block of a light metal casting material. The invention takes advantage of the possibility to alloy molten iron in such a way that its coefficient of thermal expansion corresponds to the coefficient of thermal expansion of the melting of the light metal that will be melted in each case. Properly alloyed cast iron is already inherently known. Accordingly, for example, in the German published application DE 27 19 456 Al a cast iron material is already described which has a coefficient of thermal expansion of between 16.0 x 10"6 and 21.0 x 10" 6 K "1 at temperatures between 20 ° C and 100 ° C. This corresponds, for example, to the coefficient of thermal expansion of typical molten aluminum alloys in the related temperature range Until now, however, such cast iron materials have only been used for structural components which melt in or shrink on, or are compressed with, light metal elements.Therefore, for example, an example of typical use for the known alloy of DE 27 19 456 A1 is in the manufacture of slots of ring, used as sealing elements in light metal pistons for combustion engines.
For adjusting the coefficient of thermal expansion of iron and light metal melting material which is sufficiently accurate for the purposes of the invention, preferably the deviation between the coefficient of thermal expansion of the particular cast iron material used for the shell and the The thermal expansion coefficient of the particular light metal melting material is restricted to a maximum range of ± 0.4 x 10"6 / K. Surprisingly, it has been shown that cast iron materials alloyed according to the model of the material known with manganese and / or nickel can be adjusted with respect to their thermal expansion behavior in such a way that the manufactured shells thereof have optimum performance in a casting mold, in particular a sand casting mold, with respect to the foundry result that This is not foreseeable, since in the prior technique in each case, with respect Regarding the expected individual functional functioning, the focus has been on the essential mechanical and microstructural properties of the known cast iron material. In contrast, the invention is based on the discovery that cast iron alloys obtained in this way are especially well suited, due to the thermal expansion behavior that expands beyond the mechanical and microstructure properties, being
used as material for the manufacture of shells. The use of a cast iron material according to the invention, alloyed with Mn, Ni, in each case alone or by a suitable combination of these elements, for the manufacture of shells, can minimize the stresses in the contact area between the shell and the solidified cast material, which otherwise rise with the shells when the light metal fusions are being melted. Due to the adjustment of the coefficient of thermal expansion of the shell to that of the light metal casting material, the stresses which occur during the solidification of the casting material between the mold and the casting material are reduced to a minimum. At the same time, with the shells, the inherently known advantageous effects of the prior art with respect to the controlled solidified microstructure are reliably achieved. In this situation, the molds according to the invention can be economically manufactured in an inherently known manner and have a wear resistance which is much higher than that of the known bronze molds. On the basis of their magnetic properties, they are easier to handle for automated processing, with the result that they have significantly improved utility in the light metal casting sector in relation to the
known types. It is of particular significance for current practice that the surface qualities of the foundry achieved with the use of casting molds according to the invention are too good that the elaborate preparation of the molds with the prior art prior to the casting process is not required more time. According to the invention, it is both possible to add only nickel or only manganese to the cast iron material, as well as to provide both elements as alloying constituents. The decisive factor is that the coefficient of thermal expansion of the shell is adjusted to the coefficient of thermal expansion of the casting material. The shells according to the invention are particularly well suited for use when melting aluminum alloys, since the coefficient of thermal expansion of the mold material can be adjusted particularly well to that of the aluminum alloys. The shells, however, can also be used in the casting of other light metal alloys, such as, for example, magnesium alloys. Preferably, the shells according to the invention are well suited for use in sand casting molds for casting a cylinder block made of a light metal casting material. In this situation, the shells which are
In accordance with the invention, they can be used in particular to form the cylinder cavities of a molten cylinder block for combustion engines. This is the case regardless of whether the cavities themselves serve as cylinder travel surfaces or if the additional cylinder liners are provided. If the internal walls of the cavity themselves serve as the cylinder path surfaces, after the solidification of the casting, the internal cavity walls can be coated in a manner inherently known with a material, such as nickel or silicon, to increase its resistance to wear. It is also possible, however, to use as a casting material an inherently known hypereutectic alloy which precipitates silicon, wherein the shells according to the invention reliably guarantee that the desired precipitations of Si occur in the area of the travel surfaces. of the cylinder thanks to accelerated solidification induced in a controlled manner by means of the shells. Of course, it is possible in this situation, after the solidification of the casting, that the machining of the traversing surfaces is performed to expose the precipitated silicon in a manner also inherently known. According to a preferred embodiment, the material
of cast iron can have a nickel fraction of 0.1 to 13.0% by weight. With a nickel fraction, the adjustment of the coefficient of thermal expansion can be carried out in a particularly simple manner. The contents of Ni greater cause increased expansion of the molten iron in heating, while with lower Ni contents, which are combined with equally small amounts of Mn, if present, adjust lower thermal expansion coefficients. The coefficients of thermal expansion of the shells according to the invention which are particularly well adjusted to the thermal expansion behavior of aluminum-based fusions are produced if the Ni content is more than 6.0% by weight, in particular at least 6.5. % in weigh. The range of nickel contents can be limited upwards, in which the effects used by the invention occur particularly reliably, in the adjustment of the upper limit for this range to a maximum of 8.00% by weight, preferably less than 8.00% in weight. As an alternative or in addition, the cast iron material may also have a manganese fraction to adjust the coefficient of thermal expansion, which is in the range of 0.1 to 19.0% by weight. The contents of higher Mn lead to a displacement of the thermal expansion coefficient towards higher values, while lower Mn fractions, with at the same time
Low or non-existent fractions of Ni, cause a smaller expansion of the molten iron in heating. Preferably, the contents of Mn are in the range from 4 to 12% by weight, to ensure an optimum fit to the expansion behavior of Al fusions. To achieve optimum results with respect to the wear resistance of the cast iron material, the cast iron material can also, in an inherently known manner, as well as iron and unavoidable impurities, contain the following elements (in% by weight): C: 1.5 - 4.0%, Si: 0.5 - 4.0%, Cu: 0.3 - 7.0%, Cr: < 2.0%, Al: 0.3 - 8.0%, Ti: 0.01 - 0.5%. Accordingly, the solution to the object referred to hitherto, with respect to the use of an inherently known cast iron material of DE 27 19 456 Al, is that this material, in addition to iron and unavoidable impurities, contains (in%) by weight): C: 1.5 - 4.0%, Yes: 0.5
- 4.0%, Cu: 0.3 - 7.0%, Cr: < 2.0%, Al: 0.3 - 8.0%, Ti: 0.01
- 0.5%, as well as at least one element of the group Ni, Mn, with the condition that the content of complete Ni: 0.1 - 13.0% and
the content of Mn to: 0.1 - 19.0%, is used to manufacture a mold for melting light metal casting material. The invention is explained in more detail later on the basis of an exemplary embodiment represented in a figure. Figure 1 shows a block of molten cylinder 1 with a shell 2 inserted therein, in a cross section. 1 shows a block of solidified cylinder 1 terminated, cast in an inherently known manner in a sand casting mold, not shown, of a multi-cylinder combustion engine, in a cross section through one of the cylinder chambers. After solidification and cooling, the sand casting mold is removed from the cylinder block 1, being destroyed in the process. The cylinder block 1 is melted from a conventional AlSil7Cu4Mg alloy (Si: 16.0 - 18.0; Cu: 4.0 - 5.0; Faith: < = 0.7; Mg: 0.4 - 0.7; Mn: < = 0.2; Ti: < = 0.2; Zn: < = 0.2; S others: < = 0.2; rest Al, figures as% by weight). This casting material has a coefficient of thermal expansion of 19.4 x 10"6 / K. The shells 2 are made of a commercial cast iron alloy GGL-NiCr 20-2 known under the name" Ni-Resistant ". of the
contents of Mn and Ni, the shells have a coefficient of thermal expansion which is in the range from 20 ° C to 200 ° C, 18.7 x 10"6 / K. This coefficient of thermal expansion is located too close to the coefficient of expansion of 19.4 x 10"6 / K of AlSil7Cu4Mg alloy from which the engine block melts that the shells, in heating and cooling, behave in essentially the same way as the Al smelting material. As a consequence , only minimal stresses occur in the contact area between the casting and the mold in each case, and an optimum casting result is achieved. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.