EP0429117B1

EP0429117B1 - A machine for producing centrifuged castings of nonferrous alloys

Info

Publication number: EP0429117B1
Application number: EP90202947A
Authority: EP
Inventors: Primo Righeschi; Francesco Zumbo; Sergio Pisotti
Original assignee: CABE SpA
Current assignee: CABE SpA
Priority date: 1989-11-16
Filing date: 1990-11-07
Publication date: 1996-02-28
Anticipated expiration: 2010-11-07
Also published as: DE69025549D1; ES2086363T3; IT8922408A0; IT1237777B; EP0429117A1; DE69025549T2

Description

The present invention relates to a machine for producing centrifuged castings of nonferrous alloys such as articles of costume jewelry, pewter and small metal parts, buckles, buttons and the like.
Devices are known for injecting under pressure a molten metal into a metal mold.
For example from CH-A-311310 it is known a machine and a process for feeding a continuous flow of molten metal from a reservoir to a centrifugal metal mold, through a coaxial channel, with the molten metal being supplied upwardly by means of pressure or vacuum.
Patent Abstracts of Japan, Vol. 7, No. 50 (M-197)(1195) & JP-A-57 199 557 discloses a devices for centrifugal casting employing a pressurized injection of molten metal at the center of a metal mold.
A.C. Street in "The diecasting book", 2nd Edition, 1986, pages 52 & 53 discloses a plunger for the injection of molten metal under pressure into the fixed metal mold of a diecasting machine.
On the other hand, the present invention concerns a machine, also known in the art as automatic casting complex, and that allows for the manufacture of the above mentioned articles and other, through the melting and the casting in suitable rotating dies or molds of nonferrous metals, such as tin, zinc, lead and the like.
Typically the molds of such machines are built of casting rubbers, e.g. silicon rubber for zinc and tin/lead alloys, or natural or synthetic rubbers for tin/lead alloys.
There are known and currentely employed machines comprising a base supporting a disc-shaped multiple impression mold that is rotated by a rotating cylinder for obtaining the required centrifugal casting. In the known machines the melted alloy metal is maintained in a crucible housed in the upper part of the machine, at a height of 1-2 meters, and connected to the mold by a conduit or pipe that is substantially vertical. In use a predetermined volume of melted metal flows down under the action of gravity to the center of the rotating mold, and is divided into a plurality of radial pouring channels or runners feeding the single molds through the centrifugal force. The preamble of claim 1 is based upon these known machines such as for example models TR2350/F200 and TR8350/F400 manufactured and marketed by the applicant.
In such machines the feeding takes place by means of a cup or ladle actuated by an ascent-descent cylinder that is dipped into the crucible and then raised up to a pouring zone wherein the melted metal is tapped through a gate of the ladle and poured into the metal pouring spout. Suitable fixtures and dishes are provided in the base allowing for the loading and the rotation of one, two or more molds that are then unloaded in turn at the end of a production run.
The devices of the above mentioned type exhibit a number of shortcomings and drawbacks.
Firstly the crucible is housed at a considerable height (about 1.7 meters) above the floor and therefore the (rather frequent) loading operation is quite inconvenient for the operator, besides the fact that the machine as a whole has a considerable height.
Further, in case a crack or a hole is formed in the crucible, one can easily realize how much the underlaying parts of the machine can be severely damaged by the melted metals dripping thereon. Moreover also a worn-out pouring pipe can cause damages, particularly to the nearby heating resistors.
From the viewpoint of the production quality the liquid metal undergoes a partial oxidation when contacting the air of the pouring pipe and reaches the casting molds 2-3 seconds after being drawn from the crucible, thus cooling and reducing its flowability. Moreover the articles so obtained tend to exhibit a low molecular coesion which results in surfaces being rough and porous. In order to mitigate these inconveniences it is necessary to employ alloys containing larger amounts of metals that favours the flowability and the casting quality, and such metals appreciably raise the cost of the alloy.
An object of the present invention is to overcome the above mentioned drawbacks and shortcomings of the known machines, and more particularly to realize a machine that is easy to be used and able to improve the surface quality and the mechanical characteristics of the casted articles even when cheaper alloys are employed.
According to the invention these objects are achieved through a machine for producing centrifuged castings as claimed in claim 1.
Further advantageous characteristics are claimed in the dependent claims.
The invention will now be described with reference to a preferred but non limiting embodiment, illustrated in the attached drawings, in which:

Fig. 1 is a schematic diagram of the machine according to the invention; and
Fig. 2 illustrates the device for feeding the melted metal, in an enlarged scale.

With reference to Fig. 1, the machine according to the invention comprises a support base on which two or more conventional multiple-impression molds 2 are positioned. Each multiple-impression mold is made of rubber and comprises a number of cavities (impressions) radially arranged around a central feeding channel. The mold is rotated by a rotary cylinder 3 housed within the base 1 and such rotation of the mold can be obtained in known manners by means of electromechanical, pneumatic or hydraulic devices (not shown).
The molds 2 could be of the static type either a one-piece or made up by more pieces to be assembled together, and of various materials. Preferably the molds are positioned between two metal pressure discs. The liquid metal alloy 6 is stored in a crucible 7, e.g. of cast iron, provided with a conventional heating means that has not been illustrated for simplicity sake. The crucible heating means can be electrical, gas burning, gas oil burning, fuel oil burning, etc.
As shown in Fig. 1, the crucible 7 is substantially at the same height of the mold 2, so that gravity is not used for the transfer of the melted metal into the mold. Alternatively, the crucible can be located at a height lower than the mold. The crucible is furter provided with a feeding device that will be described hereinbelow with more details.
The connection between the crucible 7 and the mold(s) 2 is realized by a feeding conduit or pipe 5 tht is substantially horizontal, and in case slightly inclined upwards from the crucible to the mold, as shown in Fig. 1.
According to the invention the feeding device for the melted metal comprises a sleeve or cylinder 8 at least partially sunk in the liquid bath 6, and a reciprocating plunger 9 within such sleeve 8 driven by an actuator 10, e.g. a pneumatic or hydraulic piston.
The sleeve 8 has an inner siphon structure that is better shown in Fig. 2. It provides for a main cylindrical cavity 11 within which the plunger 9 slides, this latter carrying steel sealing rings 16 and 17. A side opening or gate 12 is realized in the sleeve below the surface of the melted metal, so that the melted metal can reach the main cavity 11 when the plunger is raised above the gate 12. A channel 13 extends parallel to the cylindric cavity 11, the channel having a cross section area smaller than that of the cavity and being connected at one end with the feeding conduit 5, whereas at the other end it communicates with the cylindric cavity through a passage 14.
This way a siphon is obtained imparting a push to the melted metal in wich it is immersed when the plunger is lowered in such a way that the liquid metal is driven under pressure into the mold. The speed so gained by metal is added to the speed imparted by the centrifugal force of the rotating mold so that the liquid metal can reach even the smallest mold recesses as well as portions having complex shapes.
The machine can work according to an operating cycle that is repeatedly carried out, even under automatic control, with the automatic positioning of the molds on a suitably shaped and dimensioned table that is moved by a device applying a linear, swinging, reciprocating or rotating motion.
From the above the advantages of the invention with respect to the conventional prior art machines become evident.
Namely the machine of the invention achieves a very quick transfer of the melted metal, in the order of 0.3-0.7 seconds, thus reducing the heat loss and allowing for a lower temperature of the bath in the crucible with consequent reduction of the power consumption and an increase of the crucible life.
Moreover it is possible to employ alloys that are more resistant to breakage, twist and tensile stresses being less rich with components that while increasing their flowability are nevertheless strongly aggressive and therefore cause a rapid corrosion of the crucible.
The quality of the casted article is improved since:

the metal which is injected into the mold is that laying at the bottom of the crucible and is substantially slag-free;
the combined action of the centrifugation and the pressure at which the melted metal is introduced into the mold produces casted articles that are more compact and have a more uniform outer surface;
a better adjustment of the amount of the metal fed to the mold is achieved.

Finally, the crucible is substantially at the same height of the mold and easy to be refilled, while the feeding conduit is fas from the critical areas of the machine, being substantially external.

Claims

A machine for centrifugal casting of nonferrous alloys such as articles of costume jewelry, pewter and small metal parts, of the type comprising a support base (1) housing at least one rubber mold (2) with means (3) for rotating said mold (2) about a substantially vertical axis, and a crucible (7) connected to said machine (2) through a substantially horizontal conduit (5) for feeding from above a predeterminded amount of molten metal to said mold (2),
characterized by a device for feeding said predeterminded amount of molten metal comprising:
- a sleeve (8) at least partially sunk in the liquid bath (6) of said crucible within which sleeve a reciprocating plunger (9) is sealingly movable,

- at least a side opening (12) in said sleeve (8) in communication with the molten metal of said crucible, and

- an outlet opening (15) connected to said conduit (5) for feeding said predetermined amount of molten metal to the mold (2), said crucible (7) being substantially at the same height of the mold (2),
said sleeve (8) providing for a siphon path comprising a cylindrical cavity (11) within which said plunger (9) is slidable, and a channel (13) parallel to said cavity and having a cross section smaller than that of said cavity, communicating with said cavity through a passage (14).
A machine as claimed in claim 1, characterized in that said crucible (7) and mold (2) are located substantially at the same height.
A machine as claimed in claim 1 or 2, characterized in that an actuator (10) is provided for driving the reciprocating motion of said plunger (9).
A machine as claimed in claim 3, characterized in that said actuator (10) is a pneumatic cylinder.
A machine as claimed in claim 3, characterized in that said actuator (10) is a hydraulic cylinder.