EP0255475B1 - Shot sleeve for a pressure die-casting - Google Patents

Description

The present invention relates to a filling sleeve for a hot chamber die casting machine according to the preamble of claim 1. Die casting machines have been known per se for a long time. A distinction is made between hot chamber and cold chamber die casting machines.

In a type of hot-chamber die casting machine, the casting device or metal pump hangs on a carrying device and dips into the metal melt in the crucible, as a result of which the metal pump is kept at the casting temperature. This filling sleeve essentially consists of a vertically standing pressure cylinder with a pressure piston driven from above by the same carrying device and a so-called gooseneck connected to the lower part of the pressure cylinder, which ensures the connection to the casting mold. In another type of machine, the pressure cylinder is attached to the bottom of the crucible and the outlet channel is placed in the wall of this container.

Usually pressure cylinders, pressure pistons and goosenecks are made of ferrous metals, eg cast iron, and are therefore only suitable for casting molten metals which do not attack these materials. According to Ernst Brunhuber, "Praxis der Druckgussfertigung", 3rd edition, 1980, pages 42 and 48, this condition is generally fulfilled for the die casting of lead, tin and magnesium alloys. In the case of zinc alloys, however, a solution attack on iron and steel parts is only prevented if they contain aluminum as an alloy component in sufficient amounts, which is why alloys are used for zinc die casting with about 4% aluminum. In contrast, aluminum and brass melts cannot be cast with hot chamber die casting machines of a known type.

The use of ceramic materials which are chemically resistant to such melts has long been proposed with the intention of expanding the application possibilities of hot-chamber die casting machines to such attacking metal melts as aluminum melts.

According to GB-PS 773 009 for a hot chamber die casting machine with a hanging metal pump it was already proposed in 1954 to manufacture the pump and crucible from silicon carbide and to line the running surface of the pressure cylinder and the piston with wear-resistant zirconium boride, or to manufacture the pressure piston entirely from zirconium boride. The fact that this proposal has not been implemented in practice is obviously due to the fact that, because of the low tensile strength of the ceramic material, the ceramic pump could not withstand the desired casting pressure. A particularly critical point is the attachment of the ceramic pump to the metal support device.

In a hot-chamber die-casting machine with a pressure cylinder attached to the crucible bottom and an outlet channel made of cast iron in the crucible wall, DE-OS 28 42 543 proposed in 1977 to manufacture the pressure cylinder from ceramic and to line the channel with an insert tube made of ceramic. Because in such a cast iron crucible, uneven dilatations and therefore slight deformations the crucible wall is unavoidable, it can be expected that the highly fragile ceramic tubes will disintegrate very soon under such stresses.

In cold chamber die casting machines, the casting set is outside the liquid metal. The pressure chamber is usually arranged horizontally and extends with a constant diameter to the mold dividing surface. The solidified metal residue remaining in the cylinder after the casting process is expelled at or after opening of the mold by moving the pressure piston. This rest has a relatively large volume compared to the casting and therefore means a high waste rate with each casting.

In vertical cold chamber machines, the chamber is closed at the bottom by a counter piston. The melt is ejected laterally through an opening in the cylinder wall to the casting mold; the counter-piston is lowered to remove the solidified metal residue.

According to E. Brunhuber, loc.cit., An important advantage of cold chamber machines is that all die-cast metals and alloys can be cast on them, in particular aluminum alloys and brass, as well as magnesium, zinc, lead and tin alloys.

However, these machines have the disadvantage that the metal melt in the pressure cylinder is exposed to a more or less rapid cooling. For this reason, the pouring process must be carried out quickly and practically in a shot-like manner after the filling sleeve has been filled, which leads to turbulence in the air and casting vapors which disturb the quality of the casting into the molten metal and entrainment of already solidified metal particles from the pressure chamber into the casting mold. If the system is to be vented using a vacuum pump, it must be carried out in parallel with the casting process. Despite the short dwell time in the impression cylinder, aluminum melts attack the wall and absorb iron. This iron absorption, which also takes place in part in the casting mold, may be undesirable for the quality of the casting due to the formation of needle-shaped crystalline iron aluminum precipitates and also represents a problem for the recycling of the die casting waste (E. Brunhuber, loc.cit., P. 326 -327). Furthermore, the attack of the melt on the steel cylinder means a reduction in its service life. A certain remedy is provided by the lubrication of the cylinder wall before each shot. However, the decomposition of the lubricant in contact with the liquid metal, in particular aluminum, produces gases which lead to pore formation in the casting. Therefore, the castings cannot be properly heat treated, which also limits the number of alloys suitable for die casting.

It has also already been proposed for horizontal cold chamber machines to provide the pressure chamber with a lining made of ceramic material, with the purpose of protecting the steel cylinder against the attack of the molten metal. For example, US Pat. No. 3,664,411, based on a proposal from 1969, describes such a device which is suitable for the casting of ferrous metals, in particular cast iron at temperatures of approximately 1300 ° C. or cast steel at temperatures of approximately 1600 ° C. Pressure from about 350 to 420 kg / cm² is suitable. According to this document, for the manufacture of the printing cylinder, the one-piece inner lining or a plurality of rings that abut one another on the end face, in particular made of silicon nitride, is introduced into a heated steel jacket. The subsequent shrinking of the steel jacket immovably holds the ceramic lining in such a way that it is still under radial compressive stress later at operating temperature. The document also shows that, just as in the case of unclad, horizontal cold chamber machines, at the end of the casting process, a remainder of the metal melt solidifies in the front part of the pressure chamber, which is then ejected with the pressure piston.

From DE-A-24 49 428 a filling sleeve for a die casting machine is known which, in addition to an outer cooling bar metal jacket made of steel, has a hollow cylinder fitted therein. Recesses for an integrated heating are provided in the inner surface of the metal jacket over the circumference of the hollow cylinder.

US-A-3 672 440 discloses a die casting machine, the cylinder liner of which is formed with lined up annular segments made of, for example, a molybdenum alloy. If individual segments are damaged by the thermal shock that occurs when the liquid metal is poured in, they can simply be replaced.

In view of these circumstances, the inventors have set themselves the task of developing a filling sleeve of the type mentioned at the outset for a hot chamber die casting machine, with which it should be possible to cast aggressive metal melts, such as those made of aluminum alloys, titanium alloys, Cr-Ni steel as well as alloys that can also be hardened by thermal treatment, in a hot chamber process, and with better quality than can be achieved on cold chamber machines. In addition, the heat losses caused by the heat flow to the metal jacket are to be reduced.

A filling sleeve of the type mentioned with the characterizing features of claim 1 leads to the solution of the stated problem. Further preferred embodiments of the filling sleeve according to the invention result from the dependent claims 2 to 6.

Suitable materials for the inner ceramic hollow cylinder are materials which are chemically resistant to aggressive metal melts, in particular aluminum melts, such as silicon nitride, Si-Al-ON, borides and others.

However, such ceramic materials known today have only a limited thermal insulation capacity, so that they allow a certain heat flow to the metal jacket and therefore require a correspondingly high heating output.

In order to reduce these heat losses, according to the invention the ceramic hollow cylinder is divided into at least two hollow cylinders in the radial direction, in that a pressure-resistant intermediate cylinder made of a ceramic material with a high insulating capacity, such as e.g. Zirconia or other.

It has also proven expedient to subdivide the ceramic hollow cylinder (s) in the axial direction into rings. This initially facilitates the manufacture of the individual ceramic components. Furthermore, this subdivision allows the ceramic lining to be better adapted to any Slight bending of the metal jacket due to slight differences in elongation.

Furthermore, the chamber should be as tight as possible. For this purpose, according to a further development of the invention, the metal jacket is provided at one end, preferably at its end facing the casting mold, with an inwardly directed annular shoulder, which acts as an axial support for the ceramic hollow cylinder. At the other end of the metal jacket, after the ceramic hollow cylinder has been installed, a displaceable pressure ring which rests against its end face is arranged, which is under the action of clamping means supported on the metal jacket. After the filling sleeve has been assembled, an axial pressure is exerted with this clamping means via the pressure ring on the hollow cylinder, or in the case of a multi-layer version at least on the hollow cylinder which determines the tightness of the chamber, which presses the ceramic components tightly against one another.

When the filling sleeve is brought to operating temperature with the heater, the ceramic lining, in particular the inner layer thereof, of course expands not only in the radial but also in the axial direction, which also contributes to the tightness.

The filler can described can be arranged horizontally or vertically. If it is arranged horizontally, it is expedient if the annular shoulder is designed immediately as an end plate with an outlet nozzle for the melt, the latter preferably being placed flush with the apex of the chamber. On the chamber side, there is an insulating ceramic lining on this support disk. As a result, the warm chamber is formed in the filling sleeve between the support disk and its insulation on the one hand and the pressure piston, which is likewise to be made of ceramic, which can be supplied with the required amount of molten metal via a suitable inlet opening. After the inlet opening has been closed by partially displacing the pressure piston, the air can be evacuated in the casting mold and in the warm chamber by means of a vacuum pump and only then can the actual casting process be carried out at the most suitable casting speed.

• Weil der Metallmantel ausserhalb des Schmelze-Vorratsbehälters angeordnet werden kann, kommt er mit seiner äusseren Fläche nicht in Kontakt mit der Metallschmelze und braucht sofern keine Schutzverkleidung dagegen.
• Weil der Metallmantel durch die Kühlung auf einer mässigen Temperatur gehalten werden kann, z.B. unterhalb 100°C, jedenfalls unterhalb 300°C, besteht kein Risiko eines Weichglühens des dafür verwendeten Metalls. Es wird also möglich, für die Herstellung des Metallmantels hochfeste Legierungen, inkl. Stahl, einzusetzen und somit die Dicke der Mantelwand unter voller Ausnützung der Metallfestigkeit weitgehend zu beschränken.
• Weil mit der Heizung die keramische Warmkammer auf Betriebstemperatur gehalten werden kann, besteht keine Gefahr, dass die eingefüllte Schmelze sich darin abkühlt. Die Schmelze kann auf der für das Giessen bestgeeigneten Temperatur gehalten werden. Die Operationen "Einfüllen in die Kammer", "Evakuieren der Luft", "Entgasen der Metallschmelze" und "eigentlicher Giessvorgang" können eine nach der anderen ohne gegenseitige Störung vorgenommen werden. Auch kann die Geschwindigkeit des eigentlichen Giessvorgangs ohne Gefahr einer Abkühlung in der Kammer unter alleiniger Betrachtung der bestgeeigneten Einfüllbedingungen der Giessform angepasst werden.

The heatable filling can according to the invention offers the following advantages:

• Because the metal jacket can be arranged outside the melt storage container, its outer surface does not come into contact with the metal melt and, provided that there is no protective covering against it.
• Because the metal jacket can be kept at a moderate temperature by cooling, for example below 100 ° C, in any case below 300 ° C, there is no risk of soft annealing of the metal used for this. It is therefore possible to use high-strength alloys, including steel, for the production of the metal jacket, and thus to largely limit the thickness of the jacket wall while making full use of the metal strength.
• Because the ceramic warm chamber can be kept at operating temperature with the heater, there is no danger that the melt will cool down in it. The melt can be kept at the most suitable temperature for casting. The operations "filling into the chamber", "evacuating the air", "degassing the molten metal" and "actual casting process" can be carried out one after the other without mutual interference. The speed of the actual casting process can also be adjusted without risk of cooling in the chamber by considering only the most suitable filling conditions of the casting mold.

Further details of the invention will now be given below are explained in more detail using exemplary embodiments and corresponding schematic figures:

- Fig. 1 -

die neue Füllbüchse mit ihren wesentlichen Bestandteilen sowie die Giessform, im Längsschnitt;

- Fig. 2 -

eine weitere Ausführungsform der Füllbüchse, bei der die keramische Auskleidung in Ringe unterteilt ist, im Längsschnitt;

- Fig. 3a und b bis 7a und b -

verschiedene Ausführungsbeispiele für die Anordnung der Heizung, im Längs- und im Querschnitt;

- Fig. 8a und b -

eine Füllbüchse mit drei coaxialen Keramikzylindern, z.B. zur weiteren Erhöhung der Verschleissfestigkeit, im Längs- und im Querschnitt.

Show it:

- Fig. 1 -

the new filling can with its essential components as well as the casting mold, in longitudinal section;

- Fig. 2 -

a further embodiment of the filling sleeve, in which the ceramic lining is divided into rings, in longitudinal section;

3a and b to 7a and b -

different embodiments for the arrangement of the heater, in longitudinal and in cross section;

8a and b

a filling sleeve with three coaxial ceramic cylinders, for example to further increase wear resistance, in longitudinal and cross-section.

In Fig. 1, the filling sleeve 5 is shown with the mold for a horizontal die casting machine.

This device has, in a known manner, a fixed mold platen 1 with the mold plate half 2 fixed thereon and a movable mold platen 3 actuated by a pressure system (not shown) with the movable mold plate half 4 fixed thereon. The filling sleeve 5 according to the invention is fastened to the fixed platen 2, which also has an outlet opening 6 is connected to the pouring system 7 of the actual mold cavity 8 and is further equipped with the displaceable pressure piston 9 for pressing the molten metal located in the chamber 10 of the filling sleeve 5 into the mold.

In the exemplary embodiment shown, the wall of the filling sleeve 5 can be cooled by an outer, e.g. composed of a steel tube formed metal jacket 11 and an inner ceramic hollow cylinder 12 fitted therein, which has recesses 13 distributed around the circumference for integrated heating.

At its end facing the casting mold, the filling sleeve 5 is fastened to the metal jacket 11, e.g. metal disc 14 screwed therein, the outer surface of which rests on the fixed mold plate half 2. On the chamber side, the metal disk 14 bears a ceramic disk 15, against which the end face of the ceramic hollow cylinder 12 lies tightly. In the metal disk 14 and the ceramic disk 15 thus acting as a fixed axial support for the ceramic hollow cylinder, the outlet opening 6, which is preferably arranged flush with the upper surface line of the chamber 10, is recessed, which can be lined with a ceramic mouthpiece 16.

At the other end of the filling sleeve 5 there is a rear ceramic perforated disk 17 on the end face of the ceramic hollow cylinder 12 and this has a displaceable pressure ring 18 which is under the action of clamping means which are supported on the metal jacket 11, for example a clamping nut 19 provided with an external thread. Perforated disk 17 and pressure ring 18 have channels 20 as access to the recesses 13. This exemplary embodiment shows that the chamber 10 of the filling sleeve 5 can be supplied with flux metal from above through the filling opening 21.

For the liquid metal leakage between the piston 9 and the wall of the chamber 10, a small outlet opening (not shown) can be provided in the rear part of the filling sleeve 5, below.

In operation, the metal jacket is cooled by the ambient air. If this effect is not sufficient, liquid cooling can be provided, e.g. a cooling coil 22 are used.

The ceramic hollow cylinder 12 and the ceramic disks 15, or at least the front one of them, are made of a material that is chemically resistant to the melt to be cast, e.g. made of silicon nitride. In order to increase the thermal insulation, as indicated in the figure by the dash-dotted line, the wall thickness of the ceramic hollow cylinder 12 is divided into two layers, namely an inner hollow cylinder 12a made of the chemically resistant material and an intermediate cylinder 12b made of a ceramic material with a higher thickness thermal insulation, e.g. Zirconium oxide. For a similar purpose, the front ceramic disc 15 can be subdivided analogously. The rear ceramic ring 17 then expediently also consists of the ceramic material with a higher thermal insulation capacity.

In the device shown in Fig. 2 with another Embodiment of the filling sleeve, many components of the device according to FIG. 1 are adopted and provided with the same reference numbers. In a further development of the embodiment according to FIG. 1, the ceramic hollow cylinder 12 is here divided into concentric cylinders 12a and 12b and these are also divided into individual rings. In this case, the inner rings 25, which are made of ceramic material that is resistant to the melt, lie directly against one another on the end face by being under the action of the pressure ring 18 and the clamping nut 19. These rings 25 are decisive for the tightness of the chamber 10. The outer rings 26 made of ceramic material with a higher thermal insulation capacity can have the same length as the rings 25 and also lie against one another on the end face. However, it often happens that the insulating material of the rings 26 has a greater expansion coefficient than the material of the inner rings 25. This could occur at operating temperature and, although the rings 26 take an average temperature between that of the rings 25 and that of the metal jacket 11 lead that the rings 26 effectively expand more in the axial direction than the inner rings 25 and thereby push them apart, which would be disadvantageous for the tightness of the chamber 10.

With the intention of avoiding such phenomena, according to a further development of the invention, if the corresponding thermal coefficients require it, or as a precautionary measure, the rings 26 are made less long than the rings 25, so that, as illustrated in FIG. 2, each is smaller Gap 27 remains between the rings 26. Nevertheless, the rings 26 do their full job as thermal insulators and support for the inner rings 25. So that the rings 25 always lie correctly in the rings 26, the rings 25 and 26 can be paired for assembly by shrink-fitting and thus inserted into the metal jacket. It is also possible to insert spacers 27 made of a resilient material in the spaces.

In this exemplary embodiment, two ceramic disks 28 and 29 of different diameters made of thermally insulating material and a ceramic disk 30 made of material which is chemically resistant to the melt are formed on the mold-side end of the filling sleeve 5, the two disks 29 and 30 being accommodated in the first ring 26. At the other end of the filling sleeve 5, two perforated disks 31 made of thermally insulating ceramic are arranged.

This exemplary embodiment also shows that the fresh melt can be filled into the chamber 10 through a thermally insulated riser pipe 32, it being possible for the desired amount of melt to be supplied by a suitable metering device (not shown). The residual melt remaining after the casting process can also be removed from the chamber 10 through this riser pipe 32.

Recesses distributed around the circumference serve to introduce the heating power. Different possibilities for the arrangement of electric radiators in a filling box according to FIG. 2 are illustrated in the further FIGS. 3 to 7 (respectively a and b).

To accommodate straight heating rods 35, as shown in FIGS. 3a and 3b, axial longitudinal bores 36 arranged concentrically within the wall of the rings 25 or, as shown in FIGS. 4a and 4b, 25 axial longitudinal grooves 37 in the lateral surface of these rings 25 milled or left out in the manufacture of these rings. Analogously, such longitudinal grooves 37 can also be arranged in the inner lateral surface of the insulating rings 26, as illustrated in FIGS. 7a and 7b.

As further shown in FIGS. 5a and 5b or 6a and 6b, there is also the possibility of providing recesses 38 for receiving a heating spiral in the outer lateral surface of the inner rings 25 or in the inner lateral surface of the insulating rings 26.

In all these different cases, the current is supplied through a recess through the rear ceramic disk 17 and the pressure ring 18, as shown in FIG. 1. However, the individual heating elements can be separated by an annular recess, e.g. in the front end face of the disk 17, are electrically connected in parallel, in which case only a single access channel 20 is required for the current supply through the pressure ring 18 and the disks 31.

The production of bores or grooves in the individual rings 25, as shown in FIGS. 3 to 5, means additional manufacturing costs. Because such elements are exposed to a certain, albeit slight, wear during operation, above all because of the friction of the pressure piston, it can prove to be advantageous, as shown in FIGS. 8a and 8b, additional rings 25 to install full-walled wear rings 39. Such wear rings can also be arranged flush with the rings 25 or, as shown, offset in the longitudinal direction.

Like the inner rings 25, these rings 39 can be produced from a material that is chemically resistant to the melt or from a different material quality, which has even better tribological properties compared to the ceramic material of the pressure piston.

Claims (6)

1. Shot sleeve for a hot-chamber pressure die-casting machine comprising an outer coolable metal shell (11) particularly of steel, and an inner heatable hollow cylinder (12) fitted therein and having recesses (13) distributed over its periphery for an integral heating system, characterized in that the hollow cylinder (12) is subdivided radially into at least two cocentrically disposed hollow cylinders (12a, b) of ceramic material, and the outer hollow cylinder (12b) disposed between the metal shell (11) and the heating system consists of ceramic material having a high thermal insulating power.
2. Shot sleeve according to Claim 1, characterized in that the ceramic hollow cylinders (12a, b) are subdivided in the axial direction into rings (25, 26).
3. Shot sleeve according to Claim 2, characterized in that the length of the outer rings (26) is at most as great as that of the inner rings (25).
4. Shot sleeve according to one of Claims 1 to 3, characterized in that axial recesses (36, 37) intended to receive heating rods (35) are provided inside the wall and/or in the outer peripheral surface of the inner hollow cylinder (12a) or of the inner rings (25) and/or in the inner peripheral surface of the outer, thermally insulating hollow cylinder (12b) or of the outer rings (26).
5. Shot sleeve according to one of Claims 1 to 3, characterized in that spirally extending recesses (38) intended to receive a heating coil are provided in the outer peripheral surface of the inner hollow cylinder (12a) or of the inner rings (25) and/or in the inner peripheral surface of the outer, thermally insulating hollow cylinder (12b) or of the outer rings (26).
6. Shot sleeve according to one of Claims 1 to 5, characterized in that inside the inner hollow cylinder (12a) or the inner rings (25) an additional solid-walled lining, for example consisting of rings (39), is also provided.

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