Referring to Figures 1 to 4, a double acting cylinder 10 is shown having a piston 12 attached to a piston rod 14 for reciprocating within the cylinder 10. The cylinder 10 has a first end 16 through which the piston rod 14 extends and a first passage 18 leading from the first end 16 to a first valve 20. A second end 22 of the cylinder 10 has a second passage 24 leading to a second valve 26. The first valve 20 and the second valve 26 have first opening ports 28 and 30 respectively which open into a molten metal tank 32 as shown in Figure 4. Whereas the molten metal tank is not shown in Figures 1, 2 and 3, this tank is omitted for ease of illustration. However, the first opening ports 28 and 30 from the first valve 20 and the second valve 26 open under the molten metal level within the tank 32 so that molten metal enters the valves.

Second opening port 34 in the first valve 20 and second opening port 30 in the second valve 26 connect to passageways 38 and 40 respectively which join into an injection passageway 42 leading to a nozzle attachment 44 which in turn connects to a die 46.

As shown in more detail in Figure 4, the piston 12 is attached to the piston rod 14 which moves up and down powered by a pneumatic cylinder 50. The cylinder 50 is double acting and has adjacent to it and joined by a bridge 52, a hydraulic cylinder 54 with a hydraulic valve 56 having a stepper motor 58 to open and close the hydraulic valve 56 and thus effect speed control of the piston 12. This provides a variable speed piston stroke in both directions. The pneumatic cylinder 50 powers the piston in both directions and the speed of the piston is set by the stepper motor 58. A microprocessor 60 operates the pneumatic cylinder 50, controls the speed of the piston 12 in the cylinder 10 by the stepper motor 58 and operates a first solenoid operator 62 for the first valve 20 and a second solenoid operator 64 for the second valve 26 to ensure the correct sequence of steps occurs in the casting process.

The pneumatic cylinder 50 controls the pressure applied to the piston 12, so that the pressure is sufficient to push the molten metal into the die 46 so that there is substantially no pressure in the die, just sufficient to replace the air in the die 46. ' Whereas a pneumatic cylinder 50 and stepper motor 50 are shown to control the speed and pressure of the piston 12 in the cylinder 10, it will be apparent to those skilled in the art that a mechanical equivalent system with a pressure relief mechanism in the injection passageway 42 or the other passages may be provided. The system controls speed of the piston 12 to ensure the filling occurs at the required rate, and pressure on the piston so there is no build up of pressure in the die during the injection step and a predetermined pressure is maintained on the piston 12 after the injection step while the metal solidifies.

Each of the valves 20 and 26 has a valve chamber 70 in which a cylindrical valve member 72 with sealing faces at top and bottom, is supported by a valve stem 74 and moves from a first position where the valve member 72 closes the first port 28,30 about the stem 74, and a second position wherein the valve member 72 closes the

second port 34,36. The valve member 72 is moved by the solenoid operator 62,64 attached to the stem 74.

The cylinder 10 is shown incorporated into one assembly 80 having the first valve 20 and the second valve 26 built therein. Thus, the piston rod 14 and the two valve stems 74 extend up above the level of molten metal in the tank. The valves 20 and 26 are positioned above the cylinder 10 and, as can be seen, the cylinder is shown to be mounted with a vertical axis. Whereas a vertical axis is shown herein it would be apparent that the cylinder need not be mounted vertically but may be at an angle or horizontally, depending upon the specific requirements of the machine itself.. For instance, a shallower tank could be provided if the cylinder was positioned horizontally.

The integral valve assembly 80 has the first passage 18 from the first end 16 of the cylinder 10 therein and also a portion of the second passage 24 from the second end 22 of the cylinder 10. Furthermore, the injection passageway 42 extends to a connector 82 which in turn is connected to a flexible hose 84. The flexible hose is insulated and has heating coils 85 surrounding it, thus it is kept at an even temperature to ensure that the molten metal does not cool while being transferred from the tank 32 to the die.

In the embodiment shown the nozzle attachment 44 is mounted on a support arm 88 adapted to move vertically up and down on shaft 90. Hydraulic cylinder 92 connected to the support arm 88 moves the nozzle attachment 44 up and down and a control valve 94 is operated by the microprocessor 60 to ensure the movement of the nozzle attachment 44 is controlled to match the movement of the piston 12 and valves 20 and 26.

In the embodiment shown in Figure 5, a nozzle attachment 44 of the type disclosed in United States patent application Serial No. 578,835 is shown. The nozzle attachment 44 has an internal stem 100 connected to a valve seat member 102. A base 104 of the nozzle attachment has a seat 106 onto which the valve member 102 seals. A flexible sleeve 108 joins the base 104 to a top portion 110, and a spring 112 holds the valve closed when the nozzle attachment is not in contact and being pushed upwards to engage the die 46. When the nozzle attachment is engaged in the die 46, then the sleeve 108 being flexible permits the stem 100 to move downwards and thus the valve opens to permit molten metal to pass through the nozzle attachment to the die.

.The operation of the double acting cylinder is illustrated in Figures 1, 2 and 3. In Figure 1 the first valve 20 is shown in the second position with the first port 28 to the tank 32 open and the second port 34 closed, thus as the piston 12 moves downwards, molten metal is drawn through the first port 28 of the first valve 20, along the first passage 18 and into the cylinder 10 above the piston 12. At the same time the second valve 26 has the first port 30 to the tank 32 closed and the second port 36 to the injection passageway 42 open. Thus, molten metal is pushed along the second passage 24 through the second valve 26 into the injection passageway 42 and through the nozzle attachment 44 to the die 46. The volume of molten metal which is pushed through the injection passageway is equivalent to the area of the piston 12 times the piston stroke.

In Figure 2 the first valve 20 is shown with the first port 28 closed and the second port 34 open. The second valve 26 is shown with the second port 36 closed and the first port 30 open, therefore, as the piston 12 rises, molten metal is pulled from the tank 32 through

- li ¬ the first port 30 of the second valve 26, and the second passage 24 to fill up the cylinder beneath the piston 12. At the same time, molten metal is forced through the first passage 18, the first valve 20 and the injection passageway 42 to the die 46. The volume of metal that is be forced out of the cylinder 10 in this stroke is representative of the area of the piston 12 minus the area of the piston rod 14 times the piston stroke.
In Figure 3 a third provision is made wherein the piston 12 is initially at the top of the cylinder 10. The cylinder is full of molten metal and both the first valve 20 and the second valve 26 have the first ports 28 and 30 to the tank 32 closed. When the piston 12 moves downwards, molten metal passes along the second passage 24 through the second valve 26 into passageway 40. A portion of molten metal passes through the injection passageway 42 to the die 46 and the other portion of molten metal passes through passageway 38, first valve 20, first passageway 18 and into the top of the cylinder 10. In this stroke the volume of molten metal passed to the die 46 is equivalent to the cross-sectional area of the piston rod 14 times the piston stroke. The injection step shown in Figure 3 provides a small flow of molten metal through the injection passageway and is used for small die capacities, as the movement of the piston produces a far smaller flow than shown in Figures 1 and 2.
The nozzle attachment 44 as shown in Figure 4 is positioned above the level of molten metal in the tank 32. Thus, should any of the valves 20, 26 or the valve in the nozzle attachment 44 fail to close, molten metal does not flow out of the nozzle attachment 44. Under normal operations, the injection passage 42 and all the passages within the tank remain full of molten metal. Even that portion of the injection passage 42 above the level of the molten metal in the tank 32 remains full
when the valve provided in the nozzle attachment 44 is closed.
A single piston stroke may be used to fill a die 46 in one embodiment. However, in other embodiments two or more piston strokes may be used or portions of a piston stroke. This enables different sizes of die to be utilized with the same equipment. There are three different capacities of molten metal delivery for the piston strokes as explained and illustrated in Figures 1, 2 and 3. Furthermore, by reversing movement of the piston, there is essentially no pause to refill the cylinder. When a die 46 is filled, then provision is made for pressure to be maintained on the piston 12 so that the molten metal solidifies under pressure. The die 46 fills preferably within a time of about 3 to 30 seconds and a flow rate of molten metal into the die is preferably in the range of about 0.01 to 1 kilogram per second. Substantially no pressure is required in the die during the filling step, however, once the die has been filled, then pressure is applied during the solidifying stage. Molten metal alloys for encapsulation and for use in meltable metal cores preferably has a melting temperature below about 350°C.
Various changes may be made to the embodiments shown herein without departing from the scope of the present invention which is limited only by the following claims. For more information,please visit http://www.bossgoo.com