Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-06-25
2002-08-06
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S113000, C164S312000, C164S094000
Reexamination Certificate
active
06427754
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
(Not Applicable)
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process and a device for producing a brake drum or a brake disk comprising a carrier element made from a light metal alloy which is readily castable and machinable, and a friction lining made from a fiber- or particle-reinforced light metal alloy.
2. Related Art
An axle-mounted brake disk for rail vehicles is described in German Patent 44 00 898. The axle-mounted brake disk is produced as a monobloc disk or as a disk which is composed of a hub and friction ring, preferably with internal ventilation, and has hard ceramic particles dispersed in an aluminum alloy matrix. In this axle-mounted brake disk, it is intended that at least the friction ring, and preferably also the cooling ribs which are connected thereto, and/or also the hub should consist of a hypoeutectic AlSi-base alloy reinforced with hard ceramic particles. If the axle-mounted brake disk is comprised of a hub and friction ring, the components are screwed together.
Aluminum alloys which are reinforced with hard ceramic particles are very difficult to machine, however, and the solutions proposed in German Patent 44 00 898 require considerable machining. In the case of the monobloc disk, the hub, which also consists of the aluminum alloy reinforced with hard ceramic particles, has to be machined. In the disk which is composed of a hub and friction ring, the joint between the hub and the friction ring has to be machined. In both cases, this machining work is difficult to carry out owing to the aluminum alloy reinforced with hard ceramic particles which is used.
Accordingly, there is a need for a process and a device for producing a brake drum or a brake disk comprising a carrier element made from an inexpensive light metal alloy which is readily castable and machinable and has a wear-resistant friction lining made from a fiber- or particle-reinforced light metal alloy, and in which only the friction faces of friction linings must be machined.
EP 0 662 361 A1 describes a die-casting device for producing a metal object, having a ceramic filler pipe arranged in a bottom die, a ceramic filler plunger inside the filler pipe, a sliding annular seal between the filler pipe and the filler plunger, an induction coil which is positioned around the filler pipe in order to produce a pool of metal above the filler plunger, and a movable top die. In addition, vertical, insulated and water-cooled conductors are arranged in the filler pipe, so that the combined effect of the vertical conductors and the induction coil is to melt a slug which has been placed in the filler pipe with simultaneous turbulence and lifting of the molten material off the wall of the filler pipe.
BRIEF SUMMARY OF THE INVENTION
The process according to this invention comprises:
introducing a predetermined quantity of casting material for the carrier element in the form of a slug of light metal alloy into a filler pipe of a die, and melting the slug therein;
producing the carrier element in a die by moving the molten light metal alloy from the filler pipe into the die;
cooling the molten material to a temperature at which it is dimensionally stable;
introducing a slug of light metal alloy for the friction lining into the filler pipe of the die, and melting the slug therein;
immediately afterwards, casting the light metal alloy for the friction lining onto the carrier element by moving the molten light metal alloy from the filler pipe into the die; and
cooling and removing the cast article.
According to either process described above, the materials may be introduced with the fill pipe in a molten state.
The process according to the invention makes it possible to produce a brake drum or a brake disk using a composite casting process. The fiber- or particle-reinforced light metal alloy friction lining is fixedly connected to the readily castable and machinable, as well as inexpensive, light metal alloy carrier element. Consequently, only the friction face of the friction lining requires special machining, while the machining steps for the carrier element do not entail any special costs and difficulties. Preferably, a short-fiber-reinforced light metal alloy can be used.
The carrier element or the friction lining can be produced in a first die, after which the casting-on or casting-around operation takes place in a second die.
Preferably, however, the carrier element or the friction lining is produced in a single die, with space created in this die for the friction lining or the carrier element, after the carrier element or the friction lining has cooled down, by moving parts of the die, in particularly core pullers, and the fiber- or particle-reinforced light metal alloy or the light metal alloy for the carrier element is introduced into this space.
A suitable hub structure ensures central access, which is optimum in terms of casting technology, for the metal which is to be cast on or around in the second cycle through the gates, which are easy to punch off.
In order to achieve a secure interlocking between the light metal alloy for the carrier element and the fiber and particle-reinforced light metal alloy during casting, projections, ribs and/or apertures may be provided, forming toothing between the light metal alloys which have been cast on or around one another.
It is particularly preferable if an intermetallic interlocking between the light metal alloy for the carrier element and the fiber- or particle-reinforced light metal alloy is produced during casting by means of a surface treatment carried out on the carrier element or the friction lining, this surface treatment preferably being exposure of the surface of the light metal alloy which is introduced into the die first to a flux, which may be present in a carrier fluid in the form of a suspension or a solution, immediately before the second light metal alloy is applied.
It is particularly preferable if the treatment with a flux is combined with the cooling of the light metal alloy which is introduced into the die first, by applying a flux-containing coolant, in particular flux-containing water, to this light metal alloy.
In order to reduce the oxidation of the surfaces of the carrier element and of the friction lining, a vacuum of 20 to 100 mbar absolute or protective gas comprising nitrogen or argon or the like can be applied to or introduced into the die shortly before casting.
Cooling of the light metal alloy which is introduced into the die first to a temperature at which it is dimensionally stable requires only small amounts of water, which evaporates immediately while the flux prepares the surface of this light metal alloy for casting on or casting around with the second light metal alloy. If necessary, compressed air may subsequently be applied to the cast surface. This allows the cooling and drying time to be reduced.
According to an advantageous casting process, individual slugs of a molten light metal alloy for the friction lining and fiber and particle reinforcement material may be introduced separately into a filler pipe on the die. The components may then be inductively heated, whereby the light metal alloy is mixed uniformly with the fiber and particle reinforcement material as a result of the turbulence in the melt brought about by the induction currents. Then, the mixed molten material may be introduced into the space which is provided for the friction lining. Therefore, it is not necessary to provide or obtain a composite light metal alloy which is already provided with fiber or particle reinforcement material, and one step in the overall process may be eliminated.
The fiber or particle reinforcement material is introduced into the light metal alloy by means of the molten flow when melting down the light metal alloy or by introducing the material into a turbulent flow of the melt, which is brought about by agitation from above or centrifugal force produced by the rotation o
Elve M. Alexandra
Honsel AG
Kerns Kevin P.
Ostrolenk Faber Gerb & Soffen, LLP
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