EP1105236A1

EP1105236A1 - Casting tool for casting shapes from non-ferrous metals

Info

Publication number: EP1105236A1
Application number: EP99946021A
Authority: EP
Inventors: Fidelius Greiner; Marion Von Cetto
Original assignee: Gesfuer Wolfram Industrie Mbh
Current assignee: *GESELLSCHAFT FUER WOLFRAM-INDUSTRIE M.B.H.; Plansee SE
Priority date: 1998-08-25
Filing date: 1999-08-25
Publication date: 2001-06-13
Anticipated expiration: 2019-08-25
Also published as: ES2178471T3; DE59901818D1; EP1105236B1; ATE219400T1; PL346151A1; PL191290B1; WO2000010752A1; DE19838561A1

Abstract

Shapes cast from non-ferrous metals, such as the light metals aluminium or magnesium, can present paintability or weldability problems if the casting tools, e.g., the mould, consist of iron. According to the invention, the casting tools, e.g., the mould, are therefore either produced from a heavy-metal alloy such as a wolfram alloy or coated with said alloy on the contact surface up to the shape. In particular, the heavy metal alloy is in the form of a sintered shape which is subsequently treated on the contact surface, especially mechanically treated, particularly by cutting.

Description

Casting tool for casting molded parts from non-ferrous metals

I. Technical background

For the production of molded parts from non-ferrous metals, in particular from aluminum or magnesium, by casting, casting tools, e.g. Chill molds or casting molds are required to transfer an almost finished component.

Such components can be supplied as semi-finished products, as construction components, as finished parts or the like for further processing or the actual intended use. The molds or casting molds required for this consist of suitable steels, i.e. from ferrous metals.

It has been shown that casting tools (molds, crucibles, suction tubes, pyrometer protection tubes, etc.) made from these materials are often unable to cope with the heavy loads caused by intensive contact with liquid light metals. This results in damage to the surface and thus the replacement of worn casting tools. This damage manifests itself in washouts and fire cracks. Wash-out occurs due to erosion, corrosion and welding. Fire cracks are a result of thermal fatigue in the materials involved.

Erosion is the mechanical wear caused by the high flow velocities of light metals such as aluminum and magnesium during casting. The erosion of the casting tools is all the more the less resistant the materials used are under the conditions used.

The term corrosion summarizes all physical effects that favor the dissolving of the casting tools. This mechanism is based on the fact that most of the alloying elements of steel are soluble in the light metals aluminum and magnesium. This dissolution leads to considerable material removal over time.

Welding or gluing occurs when a

Light metal casting solidifies in contact with the mold surface. At the

Ejection from the mold can then damage the mold surface.

With the washings a carryover is connected in the casting. These contaminants can have serious consequences.

It has now been shown that components made of non-ferrous metals, in particular made of aluminum or magnesium and their alloys, which have been produced by means of such molds and molds, lead to considerable difficulties in further processing - in particular in automobile construction - and moreover a strong tendency to corrode demonstrate.

For example, permanent, permanent welded connections cannot easily be made between body parts cast from aluminum. A further difficulty has arisen when painting finished parts made of magnesium or magnesium alloys, as are required in particular for automobiles, for example in the form of door and case lid handles; such parts only partially take on the applied colors during painting and corrode very quickly after their manufacture. a) Technical task

The object of the invention is to remedy this.

b) solving the problem

This object is achieved by the characterizing features of claim 1. Advantageous embodiments result from the subclaims.

Based on the knowledge gained from many tests that the causes of the difficulties mentioned at the outset are the carryover and washing out of alloy components from the mold or mold during the casting process of the non-ferrous metals and their transfer into the surface layer of the respective cast part or injection molded part, this task is performed accordingly solved the invention by the use of high-melting heavy metals as a material for the production of casting molds for the casting of moldings from non-ferrous metals.

According to a further feature of the invention, tungsten, tungsten alloys, molybdenum or molybdenum alloys are used as the heavy metal.

Here, the molds or casting molds can consist entirely of the high-melting heavy metal or the heavy metal alloy or of steel, the effective surfaces of which face the non-ferrous metal during the casting process are sufficiently strongly coated with the high-melting heavy metal or its alloys.

According to the invention, the alloys of tungsten consist of at least 30% tungsten (W) and moreover mainly of the alloying elements nickel (Ni), iron (Fe) and copper (Cu). When using the casting tools according to the invention, there is no, or at least only a slight washing out and fire cracking of the casting tool material. Several properties of the material are responsible for this. Due to its high warm hardness and good tempering resistance, it offers high resistance to mechanical wear caused by flowing liquid metals. Therefore, there are significantly fewer erosion phenomena than when using conventional materials. The heavy metals, in particular tungsten and molybdenum, dissolve in very small quantities at the casting temperatures and times used, so that hardly any corrosion can be observed. In addition, the oxidation of the heavy metals, which occurs to a small extent at the casting temperatures used, hinders the welding of the light metals to the casting mold. This effectively prevents damage to the mold by welding. Its structure and mechanical properties as well as its comparatively low thermal expansion also make the material very resistant to thermal fatigue. It is therefore hardly susceptible to fire cracks.

The consequence of this is that the light metal used to produce the molded parts is not or only very slightly contaminated and the mold or the mold is not or only slightly worn.

This means that light metal cast alloys can be produced with a higher purity than previously possible. It has been shown that this significantly improves the weldability of light metal alloys and at the same time greatly reduces the tendency to corrode.

The significant improvement in the weldability of aluminum castings by using the casting molds according to the invention is particularly advantageous in the manufacture of aluminum castings composed of chassis and bodies for the automotive industry. Another advantage of the invention has resulted from the fact that magnesium alloys in particular can now be painted. The negligible dissolution of the molding material also leads to a significant increase in the service life of the mold or casting mold during the manufacturing processes.

The casting tools, molds, printing and casting molds to be produced from the high-melting heavy metals can have any shape and design in accordance with the manufacturing process used and the material to be used for the manufacturing process.

In addition, it has proven to be advantageous not to use the high-melting heavy metal alloys, in particular the tungsten alloy, as a molded element or coating of the molded element or contact part to the molded part to be produced within the molded element, but instead from a sintered part , which consists of a framework of microscopic particles, in particular monocrystals of the heavy metal, which are firmly connected to one another by a binding matrix, and which also contains the heavy metal.

The particles or grains (monocrystals) are spherical, ideally spherical.

The proportions in the shaped element or the shaped element, which consists of a heavy metal alloy, are to be selected in this case, and the sintering process is to be carried out in such a way that a shaped element with high mechanical strength and at the same time a low proportion of the alloy elements added to the heavy metal is achieved on the contact surface between the molded element and molded part.

In particular with tungsten as the heavy metal used, this can be achieved if the approximately spherical particles of tungsten have a diameter of 10 μm to 40 μm, in particular of 20 μm to 30 μm. The size of these particles is influenced on the one hand by the percentage (all percentages given in the present application are percentages by weight) and on the other hand by the physical parameters of the sintering process.

If the particles, for example made of tungsten, had a larger diameter, the tensile strength of the corresponding sintered part would be too low, and thus its resistance to temperature changes would decrease.

As the diameter of the particles decreases, the risk of such, e.g. Tungsten particles from the sintered molded element when the molded part is poured out of the contact surface, with the result that it is embedded in the regions of the molded part near the surface. This contamination would again lead to undefined changes in the corrosion behavior, the abrasion resistance, the machinability and the paintability.

Since the grain size increases during sintering, the longer the duration of sintering and the higher the temperature at which the sintering takes place, the size of the particles of heavy metal can be controlled by the type of sintering process.

It must also be taken into account that the sintering process depends on the addition of alloy elements, which are to be selected from elements 22 to 29 or 40 to 47 or 72 to 79 of the periodic table of the elements, and in particular from the group of Elements 25 to 29 or 46 and 78 should be selected, and if possible not include more than three alloy elements in total, so that a dense material is formed.

The binding matrix itself is a metal grid structure, which is made from the melt of the alloyed elements, e.g. There is nickel and iron, in which also that

Heavy metal is dissolved to a small extent - with tungsten up to 30% tungsten in the binding matrix. It is also possible to sinter at such low temperatures that the elements of the binding matrix do not pass into the melt, but remain in the solid phase.

When producing molded parts from aluminum, copper, in particular, should not be used as a component of the alloy, since copper is also present in the molded part made of aluminum and therefore tends to form a connection with the molded part.

In addition to the disadvantage of decreasing tensile strength in the case of excessively large particle diameters made of heavy metal, the diameter of those contact surfaces which are produced by the binding matrix also increases. The smaller these bonding matrix contact areas, the greater the probability that mechanical abrasion, sticking to the molded part, etc. Particles are removed from the binding matrix and stored in the molded part in areas close to the surface.

The specified diameter size of the heavy metal particles therefore represents an optimal middle way.

Furthermore, the area portion of the heavy metal particles at the contact surface can be increased at the expense of the binding matrix portions by mechanically processing the contact area of the shaped element towards the shaped part after sintering the shaped element, for example by machining removal such as milling or grinding, but also by eroding , is processed.

As a result, the particles consisting of heavy metal are capped at the contact surface, so that their spherical shape has a flat surface on the contact side. Since the spherical particles build up on the outer surface of the sintering mold during sintering, the area fraction of the particles is increased compared to the binding matrix portion in the contact area compared to this initial structure, and the width of the binding matrix contact areas is thereby reduced to a maximum of 1 μm to 5 μm. The large wetting angle between tungsten and the light metals such as Al and Mg in connection with the small web widths of the binding matrix prevents under-rinsing and thus the removal of heavy metal particles.

Whether the heavy metal alloy can be applied to the shaped element as a thin coating, in particular in the non-solid state, i.e. powdered or liquid, or in the form of a sheet-like thin coating, depends on the deformability of the heavy metal alloy and / or its melting point compared to the melting point of the base part of the shaped element.

When using tungsten as a heavy metal on a base part made of iron, because of the comparatively low melting point of iron compared to tungsten, it is not possible to weld the tungsten in liquid or powdered state (by sintering), but by thermal spraying, such as e.g. B. plasma spraying.

In the case of tungsten as a heavy metal component, it is therefore preferred that either the entire shaped element is made of the tungsten alloy, or a contact part screwed to the base part (e.g. made of iron) or otherwise positively connected. It should be ensured that due to the different thermal expansion behavior of tungsten on the one hand and e.g. Iron, on the other hand, does not warp the contact part made of the heavy metal alloy when heated, which - because of the material savings in the tungsten alloy - will only be used relatively thinly, while the mechanical stability and pressure resistance are ensured by the outer base part should.

c) working examples An embodiment according to the invention is described in more detail below with reference to the figures. Show it:

1 is a sectional view through the contact area between the molded element and molded part,

Fig. 2: the representation of another structure within the shaped element and

Fig. 3: different form elements.

It can be seen in FIG. 1 that the shaped element consisting of the heavy metal alloy or the part of the shaped element which comes into contact with the shaped part 3 to be produced (contact part 5) consists of a large number of small, spherical, in particular spherical, particles 6 exists, which are held together by a binding matrix 7 filling the spaces.

This composite is made by sintering. The particles 6 consist entirely or in particular largely of the heavy metal used, for example tungsten, while the binding matrix consists of a solid mixture of the added alloying elements, for example nickel and iron, and in turn the heavy metal used, for. B. tungsten.

The temperature prevailing during sintering is e.g. B. below the melting point of the heavy metal used, z. B. tungsten, but above the melting points of the other alloying elements, e.g. B. nickel and iron. These alloying elements are thus in the form of a melt, which means that part of the tungsten also dissolves in the melt, so that the binding matrix is initially in total solution and solidifies when the sintering process is ended, thus forming the known molecular lattice structure of a metal alloy. As a result of the fact that the spherical, in particular spherical, particles which consist exclusively of the heavy metal stick directly to one another and, additionally, the existing cavities between the particles which are formed are filled by the described binding matrix, which likewise have a very high adhesiveness to the structure made of heavy metal, a sintered body is formed whose mechanical properties, in particular tensile strength, are significantly higher than that of pure heavy metal, in particular tungsten.

Since elongation and tensile strength decrease with increasing heavy metal content and therefore brittleness increases, the heavy metal content should not exceed an upper limit of 98%, better 95%.

As can be seen in FIG. 1 from the mechanically machined, for example milled, contact surface 10 to the molded part 3, which is cast, for example, from aluminum, a temperature is formed on the surface of the particles 6 due to the temperature of approximately 700 ° of the cast-in aluminum thin layer of one or more oxides of heavy metal, for example WO ₂ , WO ₃ , which acts as a release agent compared to the molded part 3.

Since the spherical to round particles 6 on the contact surface are leveled out by the mechanical processing of the contact surface 10, this increases their surface area and, in contrast, reduces the surface area of binding matrix 7 on the contact surface 10. In addition, the portions of the binding matrix on the contact surface, viewed in depth, are preferably funnel-shaped. At the beginning of the use of the contact part 5 or shaped element, therefore - as shown in dash-dotted lines - there is an increasing release of material from the binding matrix 7 from the contact surface 10, so that here cavities are formed in the contact surface 10 in the region of the binding matrix 7 will be done.

As a result, however, the material of the binding matrix 7 which is freely available towards the contact surface 10 becomes less and less, and thus the triggering and Migration into the molded part 3 becomes ever slower with increasing use of the molded element, without the probability of particles 6 lying directly on the contact surface 10 increasing dramatically.

3 shows different form elements:

3a shows a casting mold with its mold halves 1a, 1b. Each mold half 1a, 1b consists on the one hand of a contact part 5a, 5b facing the cavity for the later molded part 3, which is reinforced on its rear side by a corresponding base part 4a, 4b. The base part 4a, 4b can consist of iron or steel material, while the contact part 5a, 5b consists of the heavy metal alloy according to the invention. The two parts preferably lie against one another along a flat or at least straight in one direction contact surface 8 and are connected to one another in a form-locking or material-locking manner.

This makes it possible to dimension the base part 4 relatively weakly and thus to reduce the material requirement for the heavy metal alloy.

In contrast, Fig. 3b shows a mold 2 for the continuous casting of z. B. aluminum. The base part 4 surrounding the continuous casting opening again consists of the heavy metal alloy according to the invention, but its wall thickness is again kept thin, since it is supported on the outside by a surrounding base part 4, which can be made of iron or steel. The connection between the two parts can be made in the same way as for casting molds.

3c shows an example of a mold half again, for example 1a, of a casting mold, which in turn consists of contact part 5 and base part 4 made of heavy metal alloy on the one hand and iron or steel on the other hand. The contact surface 8 is channel-shaped with a hat-shaped cross section. The one for that The heavy metal alloy used for contact part 5, for example tungsten alloy, is only flexible to a limited extent, even when used as flat strip material or sheet metal, so that the radii of curvature of the contact surface 6 must be based on this flexibility of the heavy metal alloy and must not be too small. In this case, a strip material with a constant thickness made of the heavy metal alloy is preferably used and applied to the base part 4, the thickness of the strip material used being so large that the cross section of the contact surface 10 to be produced is still completely within the cross section of the strip material 9.

The contact surface 10 is then produced in the desired shape by spark erosion or machining.

REFERENCE SIGN LIST

1a, b mold

2 mold

3 molding

4 base part

5 contact part

6 particles

7 binding matrix

8 touch surface

9 tape material 10 contact surface

Claims

PATENT CLAIMS

1. Casting tool such as molded element, suction pipe, crucible, for producing molded parts from non-ferrous metals, in particular from aluminum or magnesium, by means of continuous casting, permanent mold casting or die casting, characterized in that the casting tool is made of a heavy metal at least on the sides contacting the molded part to be Alloy, in particular a heavy metal alloy with high-melting heavy metal, in particular made of a tungsten or molybdenum alloy.

2. Casting tool according to claim 1, characterized in that the casting tool is a casting mold (1a, 1b).

3. Casting tool according to claim 1, characterized in that the casting tool is a mold (2).

4. Casting tool according to one of the preceding claims, characterized in that the heavy metal alloy consists exclusively of the corresponding heavy metal.

5. Casting tool according to one of the preceding claims, characterized in that the heavy metal alloy contains 30% to 98%, in particular 90% to 95%, of heavy metal, in particular tungsten, and the rest of the alloying elements.

6. Casting tool according to one of the preceding claims, characterized in that the heavy metal alloy contains at least 90% tungsten and a maximum of 10% alloying elements.

7. Casting tool according to one of the preceding claims, characterized in that the chemical elements of columns 5 to 11 from the 4th to 7th row of the periodic table are used as alloying elements, and in particular the elements manganese, iron, cobalt, nickel, copper , Palladium and platinum.

8. Casting tool according to one of the preceding claims, characterized in that the casting tool consists entirely of the heavy metal alloy, and in particular the heavy metal alloy is present as a sintered element.

9. Casting tool according to one of the preceding claims, characterized in that the base part (4) and the contact part (5) are connected to one another in a planar manner, in particular by a form or material connection, in particular welded.

10. Casting tool according to one of the preceding claims, characterized in that the casting tool is formed from a base part (4) on the side facing away from the molded part and a contact part (5) made from the heavy metal alloy on the side contacting the molded part (3).

11. Casting tool according to one of the preceding claims, characterized in that the base part (4) is produced in the form of a surface coating on the contact part (5).

12. Casting tool according to one of the preceding claims, characterized in that the base part (4) and the contact part (5) are positively connected to one another, in particular by means of screwing.

13. Casting tool according to one of the preceding claims, characterized in that the contact part (5) after the connection to the base part (4) on the contact side towards the molded part is surface-machined, in particular machined or eroded.

14. Casting tool according to one of the preceding claims, characterized in that the contact part (5) consisting of the heavy metal alloy, in particular tungsten alloy, or the entire casting tool made of spherical, in particular spherical, particles (6) made of heavy metal and in the intermediate spaces between the particles consists of a binding matrix (7), the mixture of which also contains the heavy metal.

15. Casting tool according to one of the preceding claims, characterized in that the spherical particles have a diameter of 10 μm to 40 μm, in particular 20 μm to 30 μm, and the heavy metal content of the binding matrix (7) is between 0% and 30% and 100 %, in particular between 20% and 30%.

16. A method for producing casting tools which are used to produce molded parts from non-ferrous metals, in particular from aluminum or

Magnesium, by means of permanent mold casting, continuous casting or die casting, characterized in that the casting tool is achieved at least on the contact side facing the molded part (3) by sintering a heavy metal alloy, in particular a tungsten alloy, which after sintering has a structure of particles consisting of the heavy metal and a binding matrix which contains the particles (6) connects with each other, and which also contains the heavy metal.

17. A process for the production of casting tools, which are used for the production of molded parts from non-ferrous metals, in particular from aluminum or magnesium, by means of gravity die casting, continuous casting or die casting, characterized in that the particles (6) are spherical particles, in particular spherical particles.

18. Process for the production of casting tools which are used to produce molded parts from non-ferrous metals, in particular from aluminum or

Magnesium, by means of permanent mold casting, continuous casting or die casting, characterized in that the diameter of the particles (6) is between 10 μm to 40 μm, in particular between 20 μm and 30 μm.

19. The method according to any one of the preceding claims, characterized in that in the case of moldings to be produced from aluminum, the heavy metal alloy and thus also the binding matrix contains as little, in particular none, as copper.

20. Use of high-melting heavy metals, in particular tungsten, as a material for the production of casting tools which are used for the production of molded parts from non-ferrous metals, in particular aluminum or magnesium, by means of continuous casting, die casting or permanent mold casting.