EP1105236B1 - Casting tool for casting shapes from non-ferrous metals - Google Patents

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

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. molds or casting molds needed to transfer an almost finished component.

Such components can be used as semi-finished products, as construction components, as finished parts or the like of further processing or the actual use are fed. 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 pipes, Pyrometer protection tubes etc.) made of these materials to withstand the high loads often not growing due to the intensive contact with liquid light metals are. Damage to the surface and thus the replacement of worn out Casting tools are the result. This damage manifests itself in washouts and fire cracks. Washouts are caused by erosion, corrosion and Weldments. Fire cracks are a result of thermal fatigue involved materials.

Erosion is the mechanical wear that is caused by high Flow velocities of light metals like aluminum and magnesium is caused during casting. The erosion of the casting tools is all the more lower the more resistant the materials used among the conditions are used.

The term corrosion summarizes all physical effects that the Favor dissolving of the casting tools. This mechanism is the Based on the fact that most of the alloying elements of steel in the Light metals aluminum and magnesium are soluble. This resolution carries along the time for a significant material removal.

Welding or gluing occurs when a Light metal casting solidifies in contact with the mold surface. At the Ejecting from the mold can then damage the mold surface arise.

With the washouts there is a carryover of material into the casting connected. These contaminants can have serious consequences to have.

It has now been shown that components made of non-ferrous metals in particular Aluminum or magnesium and their alloys, which are made using such molds and molds have been manufactured in further processing - in particular in automotive engineering - lead to significant difficulties and beyond show a strong tendency to corrosion.

For example, between body parts cast from aluminum in a simple way not to make permanent, welded connections. A Another difficulty has arisen when painting from magnesium or Magnesium alloys existing prefabricated parts, such as those used for Automobiles e.g. in the form of door and case lid handles, yield; such parts only partially take the applied parts when painting Colors on and corrode very quickly after their production.

JP 05 000 354 discloses a shaped body which essentially consists of tungsten is sintered. On the surface of the molded body, the cavity in which a Cast part is poured, an oxide layer forms. About the The shape of the particles from which the shaped body is sintered is not disclosed here.

a) Technical task

The object of the invention is to remedy this.

b) solving the problem

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

Based on the knowledge gained from many experiments that causative for the difficulties mentioned at the outset, the kidnapping and washing out of alloy components from the mold or mold during the casting process Non-ferrous metals and their transfer into the surface layer of the respective casting or injection molded part, this task is performed according to the Invention solved by the use of high-melting heavy metals as a material for the production of casting molds for the casting of molded parts Non-ferrous metals.

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

Here, the molds or casting molds can be completely removed from the high-melting heavy metal or the heavy metal alloy or Steel exist, the effective non-ferrous metal during the casting process facing surfaces with the high-melting heavy metal or whose alloys are sufficiently coated.

According to the invention, the alloys of tungsten consist of at least 30% Tungsten (W) and beyond mainly from the alloying elements Nickel (Ni), iron (Fe) and copper (Cu).

Using the casting tools according to the invention, at least, however, only to a minor degree of washouts and fire cracks Gießwerkzeugwerkstoffs. There are several properties of the material for this responsible. Due to its high warm hardness and good temper resistance he high mechanical wear caused by flowing liquid metals Resistance to. Therefore, there are significantly fewer signs of erosion than when using conventional materials. The heavy metals especially tungsten and molybdenum, go with the used Pouring temperatures and times in very small quantities in solution, so that hardly any corrosion can be observed. It also hampers those used Casting temperatures oxidation of the heavy metals takes place to a small extent welding the light metals to the mold. Damage to the This effectively prevents the casting mold from being welded on. Its structure and its mechanical properties but also its comparatively low Thermal expansion also make the material very resistant to thermal fatigue. It is therefore hardly susceptible to fire cracks.

As a result, that used to manufacture the molded parts Light metal is not or only very slightly contaminated and the mold or Shape does not wear or wears out only slightly.

This allows casting light alloys with a higher purity than before possible manufacture. It has been shown that the weldability of Light metal alloys significantly improved and at the same time the tendency to corrosion is greatly reduced.

The significant improvement in the weldability of aluminum castings Use of the casting molds according to the invention is particularly advantageous in the Manufacture of cast aluminum chassis and composite parts Bodies for the automotive industry.

Another advantage of the invention has resulted from the fact that in particular Magnesium alloys can now be painted. The vanishingly small Dissolution of the molding material also leads to a significant increase in tool life the mold or casting mold during the manufacturing processes.

The casting tools to be made from the high-melting heavy metals, Chill molds, printing and casting molds can be of any shape and Training according to the manufacturing process used and for have the manufacturing process material to be used.

In addition, it has proven advantageous to use the high-melting Heavy metal alloys, especially the tungsten alloy, as Shaped element or coating of the shaped element or contact part for to be produced molded part not within the molded element as a cast Part, but instead of a sintered part, which is made of a framework of microscopic particles, especially monocrystals of heavy metal, which is firmly linked to each other by a binding matrix are connected, and which also contains the heavy metal.

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

The quantitative relationships in the shaped element, or the shaped element, which consists of a heavy metal alloy, the sintering process should be selected is to be carried out so that a molded element with high mechanical strength and at the same time a small proportion of the Alloy elements added to the contact surface between heavy metal Shaped element and molded part is achieved.

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

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

As the diameter of the particles decreases, the risk of Removing such e.g. Tungsten particles from the sintered shaped element when casting the molded part out of the contact surface with the consequence of a Storage in the near-surface areas of the molded part. This Contamination would again lead to undefined changes in the Corrosion behavior, abrasion resistance, machinability and Paintability.

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

It must also be taken into account that the sintering process in Dependence on the addition of alloying elements, which are made up of the elements 22 to 29 or 40 to 47 or 72 to 79 of the Periodic Table of the Elements should be selected, and in particular from the group of elements 25 to 29 or 46 and 78 should be chosen, and if possible no more than include three alloy elements in total, so that a dense Material arises.

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 that too Heavy metal is dissolved to a small extent - 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 into solid phase remain.

When manufacturing molded parts from aluminum, copper should in particular be considered Part of the alloy can be dispensed with, since copper is in the molding at the same time is made of aluminum, and therefore to establish a connection with the Molding tends.

In addition to the disadvantage of decreasing tensile strength when the particle diameter is too large heavy metal also increases the diameter of the contact areas that are generated by the binding matrix. The smaller these bond matrix contact areas are, the greater the probability that due to mechanical abrasion, sticking to the molded part, etc. Particles detached from the binding matrix and in the molded part in areas close to the surface be stored.

The specified diameter size of the heavy metal particles therefore represents one optimal middle ground.

Furthermore, the proportion of the surface of the heavy metal particles can be on the contact surface at the expense of the binding matrix proportions can be increased by the contact area of the molded element towards the molded part after sintering the molded element mechanically processed, for example by machining acceptance such as Milling or grinding, but also by eroding.

As a result, the particles consisting of heavy metal on the contact surface capped, so that their spherical shape on the contact side is a flat surface having. Because during sintering the spherical particles adhere to the outer surface of the Creating a sintered mold is the area percentage compared to this initial structure the particle is larger than the proportion of binding matrix in the contact area, and thereby also the width of the binding matrix contact areas to a maximum of 1 µm to 5 µm reduced.

The large wetting angle between tungsten and the light metals like Al and Mg in connection with the small web widths of the binding matrix prevented a rinse and thus the removal of heavy metal particles.

Whether the heavy metal alloy on the shaped element as a thin, in particular coating applied in the non-solid state, i.e. powdered or liquid can be applied, or in the form of a sheet-like thin Plating depends on the deformability of the heavy metal alloy and / or whose melting point compared to the melting point of the base part of the Form 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 welding of the tungsten neither in liquid nor in powdered state possible (by sintering), but probably by thermal Syringes such. B. plasma spraying.

There is therefore preferably either tungsten as a heavy metal component the entire shaped element made of the tungsten alloy, or one with the base part (e.g. made of iron) screwed or otherwise positively connected Contact part. It should be noted that due to the different Thermal expansion behavior of tungsten on the one hand and e.g. Iron, on the other hand no warping of the contact part made of the heavy metal alloy takes place when heated, which yes - for reasons of material savings with the Tungsten alloy - only relatively thin dimensions will be used while the mechanical stability and compressive strength through the outside adjacent base part should be guaranteed.

c) working examples

Fig. 1:

eine Schnittdarstellung durch den Kontaktbereich zwischen Formelement und Formteil,

Fig. 2:

die Darstellung eines anderen Gefüges innerhalb des Formelementes und

Fig. 3:

unterschiedliche Formelemente.

An embodiment according to the invention is described in more detail below by way of example with reference to the figures. Show it:

Fig. 1:

2 shows a sectional view through the contact area between the molded element and molded part,

Fig. 2:

the representation of another structure within the form element and

Fig. 3:

different form elements.

In Fig. 1 it can be seen that that consisting of the heavy metal alloy Form element or the part of the form element that is to be manufactured with Molded part 3 comes into contact (contact part 5), from a large number of small, spherical, in particular spherical particles 6, which by a Binding matrix 7 filling gaps are held together.

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

The temperature prevailing during sintering lies e.g. B. below the melting point of each heavy metal used, e.g. B. tungsten, but above the melting points the other alloying elements, e.g. B. nickel and iron. This Alloy elements are thus in the form of a melt, which also means that part of the Tungsten goes into solution in the melt, leaving the binding matrix initially is present overall in solution and solidifies when the sintering process is ended and thus forming the well-known molecular lattice structure of a metal alloy.

The fact that the spherical, exclusively consisting of the heavy metal in particular, glue spherical particles directly to one another and additionally the existing voids between the particles formed by the described binding matrix are filled, which is also a very high Adhesion to the heavy metal framework arises a sintered body, the mechanical properties, in particular tensile strength is significantly higher than that of pure heavy metal, in particular tungsten.

Because elongation and tensile strength decrease with increasing heavy metal content and for the brittleness to increase, the heavy metal content should be one Do not exceed the 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, the surface of the particles 6 forms a 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 with respect to the molded part 3.

Because the mechanical processing of the contact surface 10 up to round particles 6 are leveled at the contact surface, this will The proportion of the area is increased and in contrast the proportion of the area of the binding matrix 7 reduced at the contact surface 10. In addition, the binding matrix shares viewed in depth at the contact surface, preferably funnel-shaped educated. At the beginning of the use of the contact part 5 or shaped element becomes - as shown in dash-dotted lines - an increasing Release of material from the binding matrix 7 from the contact surface 10 take place, so that here a formation of cavities in the contact surface 10 in Area of the binding matrix 7 will take place.

As a result, however, that which is freely available towards the contact surface 10 becomes available at the same time Material of the binding matrix 7 is becoming less and less, and so is the triggering and Migration into the molded part 3 is becoming ever slower with increasing Use of the form element without reducing the probability breaking out of particles 6 which lie directly on the contact surface 10, increases dramatically.

3 shows different form elements:

3a shows a casting mold with its mold halves 1a, 1b. There is each mold half 1a, 1b on the one hand from a cavity for the later Molded part 3 facing contact part 5a, 5b, which on its back by a corresponding base part 4a, 4b is reinforced. The base part 4a, 4b can be made of Iron or steel material, while the contact part 5a, 5b from heavy metal alloy according to the invention. The two parts lie preferably along a flat or at least straight in one direction Contact surface 8 to each other and are positive or material connected with each other.

This makes it possible to dimension the base part 4 relatively weakly and thus reducing the material requirements 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 exists made of the heavy metal alloy according to the invention, but is in its wall thickness again kept thin as it is surrounded by an outside Contact part 5, which can be made of iron or steel, is supported. The Connection between the two parts can be analogous to that of casting molds respectively.

3c shows an example of a mold half again, e.g. 1a one 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. The contact area 8 is channel-shaped with a hat-shaped cross section. The for that Contact part 5 heavy metal alloy used, e.g. Tungsten alloy, is - even when used as flat strip material or sheet metal - only flexible to a limited extent, so that the radii of curvature of the contact surface 8 depend on this flexibility Heavy metal alloy must be turned off and not be too small. A strip material with a constant thickness is preferably made from the Heavy metal alloy used and applied to the base part 4, the Thickness of the tape material used is so large that the cross section of the to be produced contact surface 10 still completely within the cross section of the strip material 9 lies.

This is followed by spark erosion or machining mechanical Processing the production of the contact surface 10 in the desired shape.

LIST OF REFERENCE NUMBERS

1a, b

mold

2

mold

3

molding

4

base

5

contact part

6

particle

7

binding matrix

8th

Touchpad

9

band material

10

contact area

Claims (17)

1. Casting tool such as shape member, suction pipe, crucible for producing shapes from non-ferrous metals, in particular from aluminium or magnesium, by means of continuous casting, chill casting or die casting, wherein the casting tool consists at least on the sides contacting the shape to be produced of a heavy-metal alloy, in particular a heavy-metal alloy with a high-melting heavy-metal, in particular of a tungsten or molybdenum alloy,
   characterized in that
   the part of the casting tool consisting of the heavy-metal alloy is sintered of spherical, in particular globular particles (6) of heavy-metal, and consists in the spaces between the particles of a binding matrix (7), whose mixture also contains the heavy-metal.
2. Casting tool according to claim 1,
   characterized in that
   the casting tool is a casting mould (1a, 1b).
3. Casting tool according to claim 1,
   characterized in that
   the casting tool is an iron mould (2).
4. Casting tool according to any one of the preceding claims,
   characterized in that
   in the heavy-metal alloy solely one heavy-metal is alloyed.
5. Casting tool according to any 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 remainder alloy elements.
6. Casting tool according to any one of the preceding claims,
   characterized in that
   the heavy-metal alloy contains at least 90% of tungsten and a maximum of 10% of alloy elements.
7. Casting tool according to any one of the preceding claims,
   characterized in that
   as alloy elements the chemical elements of columns 5 to 11 of the fourth to and including seventh line of the period system are used, and in particular the elements manganese, iron, cobalt, nickel, copper, palladium and platinum.
8. Casting tool according to any one of the preceding claims,
   characterized in that
   the casting tool completely consists of a sinter element and a binding matrix (7) present in the spaces between the sintered particles.
9. Casting tool according to claim 8,
   characterized in that
   the casting tool is constructed of a basic part (4) on the side turned away from the shape and a contact part (5) of the heavy-metal alloy on the side contacting the shape (3).
10. Casting tool according to claim 9,
    characterized in that
    the basic part (4) and the contact part (5) are areally joined to each other, particularly by form or material closure, in particular welded.
11. Casting tool according to any one of claims 9 or 10,
    characterized in that
    the basic part (4) is produced on the contact part (5) in the form of a surface coating.
12. Casting tool according to any one of claims 9 to 11,
    characterized in that
    the basic part (4) and the contact part (5) are joined to each other by form-closure, in particular by screwing.
13. Casting tool according to any one of claims 9 to 12,
    characterized in that
    after the joining to the basic part (4) the contact part (5) is surface-treated, in particular cut or eroded, on the contact side turned towards the shape.
14. Casting tool according to any one of the preceding claims,
    characterized in that
    the spherical particles have a diameter of 10 µm to 40 µm, in particular of 20 µm to 30 µm, and the heavy-metal content of the binding matrix (7) is larger than 0% and amounts to a maximum of 30% to 100%, in particular the heavy-metal content ranges between 20% and 30%.
15. Method for producing casting tools, which are used for the production of shapes from non-ferrous metals, in particular from aluminium or magnesium, by means of continuous casting, chill casting or die casting,
    characterized in that
    at least on the contact side turned towards the shape (3) to be produced the casting tool is produced by sintering a heavy-metal alloy, in particular a tungsten alloy, which forms a structure of particles after the sintering that consists of the heavy-metal and a binding matrix (7), which binds the particles (6) to each other and also contains the heavy-metal, with the particles (6) being spherical particles, in particular globular particles.
16. Method according to claim 15,
    characterized in that
    the diameter of the particles (6) ranges between 10 µm and 40 µm, in particular between 20 µm and 30 µm.
17. Method according to any one of the preceding method claims,
    characterized in that
    in shapes to be produced of aluminium the heavy-metal alloy and consequently also the binding matrix contains the least possible amount of copper, in particular no copper.

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