[0001] 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.
[0002] 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.
[0003] The invention further concerns a process for manufacturing centrifuged castings using
such machine.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] The devices of the above mentioned type exhibit a number of shortcomings and drawbacks.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] Further advantageous characteristics are claimed in the dependent claims.
[0015] 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.
[0016] 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).
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] From the above the advantages of the invention with respect to the conventional prior
art machines become evident.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
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.