EP0429117A1

EP0429117A1 - A machine for producing centrifuged castings of nonferrous alloys

Info

Publication number: EP0429117A1
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: 1991-05-29
Anticipated expiration: 2010-11-07
Also published as: IT1237777B; DE69025549T2; EP0429117B1; ES2086363T3; DE69025549D1; IT8922408A0

Abstract

A machine and a process for producing centrifuged castings of nonferrous alloys such as articles of costume jewelry, buckles, small metal parts and the like. The machine comprises a base (1) supporting rubber multiple molds (2) that are kept rotating and into which a predetermined amount of melted metal from a crucible (7) is injected at a central location.

The device for feeding the melted alloy comprises a sleeve (8) with a movable plunger (9) that takes the liquid metal (6) from a side opening (12) and conveys it under pressure to the rotating mold (2) along a feeding conduit (5) that is substantially horizontal.

Description

The present invention relates to a machine and a process for producing centrifuged castings of nonferrous alloys such as articles of costume jewelry, pewter and small metal parts, buckles, buttons and the like.
More precisely, the 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.
The invention further concerns a process for manufacturing centrifuged castings using such machine.
Typically the molds 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 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 of nonferrous alloys, particularly articles of costume jewelry, pewter and small metal parts, of the type comprising a support base for at least one mold with means for rotating said mold, and a crucible connected to said machine through a conduit for feeding a predetermined amount of melted metal, characterized by a feeding device of the melted metal comprising:
- a sleeve within which is sealingly movable a reciprocating plunger,
- at least a side opening in said sleeve in communication with the melted metal of said crucible, and
- an outlet opening connected to said conduit for conveying the melted metal under pressure to the mold.
The invention further consists in a process for producing centrifuged castings of nonferrous alloys, particularly articles of costume jewelry, pewter and small metal parts, through the pouring of a predetermined amount of melted metal alloy from a crucible into a rotating mold, characterized in that said amount of metal alloy is pressurized in order to be transferred to the rotating mold.
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 1 on which two or more con ventional 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.
Although the invention has been described with particular reference to a preferred embodiment, the invention is not to be intended as limited to this latter, but it extends to cover all the changes and modifications that will be evident to the skilled in the art.

Claims

1. A machine for producing centrifuged castings of nonferrous alloys, particularly articles of costume jewelry, pewter and small metal parts, of the type comprising a support base (1) for at least one mold (2) with means (3) for rotating said mold (2), and a crucible (7) connected to said machine (2) through a conduit (5) for feeding a predetermined amount of melted metal,
characterized by a feeding device of the melted metal comprising:
- a sleeve (8) within which is sealingly movable a reciprocating plunger (9),
- at least a side opening (12) in said sleeve (8) in communication with the melted metal of said crucible, and
- an outlet opening (15) connected to said conduit (5) for sending the melted metal under pressure to the mold (2).

2. A machine as claimed in claim 1, characterized in that said sleeve (8) provides 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).

3. A machine as claimed in claim 1 or 2, characterized in that said crucible (7) and mold (2) are located substantially at the same height with the feeding conduit (5) laying substantially horizontal.

4. A machine as claimed in claim 1 or 2, characterized in that said crucible (7) is located below said mold (2).

5. 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).

6. A machine as claimed in claim 5, characterized in that said actuator (10) is a pneumatic cylinder.

7. A machine as claimed in claim 5, characterized in that said actuator (10) is a hydraulic cylinder.

8. A process for producing centrifuged castings of nonferrous alloys, particularly articles of costume jewelry, pewter and small metal parts, through the pouring of a predetermined amount of melted metal alloy from a crucible into a rotating mold, characterized in that said amount of metal alloy is pressurized in order to be transferred to the rotating mold.