Method for carrying out the ejection cycle of the air stored between die and billet in a billet extruding press

Abstract: The invention relates to a method of carrying out an ejection cycle for air trapped between a billet and a die in a generic metal extrusion press (1) which comprises a carrier (5) for a billet (b) and a plunger (2) provided with respective actuating hydraulic cylinder/piston assemblies (6;3 and 4). For carrying out the method, the press (1) is provided with hydropneumatic accumulators (11,15) adapted to supply the cylinder/piston assemblies (4 and 6) with oil under such a pressure as to resist the thrust forces of the carrier (5) against the extrusion die (M) and of the plunger (2) against the billet (b) as the latter is being extruded.

Description: This invention relates to a method for carrying out the ejection cycle of the air stored-up between die and billet in a billet extruding press of the type which comprises a billet carrier reciprocable toward and away from said die along a longitudinal extrusion axis of the press, a plunger reciprocable toward and away from said carrier along said axis, said carrier and plunger being respectively provided, the former with secondary hydraulic cylinder/piston assemblies, and the latter with a primary hydraulic cylinder/piston assembly and associated secondary hydraulic cylinder/piston assemblies, and a hydraulic oil transfer system extending between pumping means and said hydraulic cylinder/piston assemblies. During a generic metal, specifically aluminum, extrusion operation, there exists a need to eject the air trapped between the metal billet held in the carrier and the extrusion die as the plunger is moved forward against the billet to deform the metal material forming the billet and, hence, have the billet extruded. This is made necessary by that trapped air would attain very high pressure levels apt to prevent the deformed metal from passing through the die, so that the extrusion process as a whole is brought to a standstill. The overall operation cycle of extrusion presses currently includes a secondary, air ejection, cycle, which consists of sequentially stopping the press and discontinuing the extrusion process, de-pressurizing the working oil to the plunger, retracting the plunger, and retracting the carrier. These cycle steps take place upon suitable valves provided in the oil feed line to the plunger being opened and the feed to hydraulic cylinder/piston assemblies which drive the carrier and the plunger being reversed. The backward movements of the plunger and the carrier, which actually occur over a few millimeters distance, require that, on resuming the extrusion operation after an air ejection or, equivalently, venting cycle has taken place, the carrier and plunger be returned to the positions they occupied before the stop. Consequently, the operational time of the press related with the extrusion has been increased by the time required to restore the press to the same conditions that were established prior to discontinuing the extrusion process for the air-venting cycle. Since this fact involves energizing and reversing the operation of some parts of the hydraulic system, such as shut-off valves and pumping means, a series of downtime and operational transient states of the press significantly lengthen the air-venting cycle as a whole to the detriment of the press productivity. The underlying technical problem of this Invention is to provide an extrusion method and press having, respectively, such functional and structural features as to carry out an air ejection cycle during the extrusion of a billet, while overcoming the above-mentioned drawbacks with which the prior art is beset. This technical problem is solved by a method according to the invention being characterized in that it consists of temporarily resisting the thrust of the plunger against the billet during the extrusion process, as well as the thrust of the carrier against the extrusion die, without thereby inducing backward movement of the carrier and the plunger to allow said ejection of air from between the billet and the die. For carrying out the above method, the invention also provides a press defined in the claims which follow this description. Further features and the advantages of the invention will be more clearly apparent from an embodiment thereof, being described herein below by way of a non-limitative example with reference to the accompanying drawing, whose single figure shows diagramatically a press according to the invention. With reference to the drawing, generally shown at 1 is a press according to the invention which comprises a plunger 2 provided with a primary hydraulic cylinder/piston assembly 3 and two secondary hydraulic cylinder/piston assemblies 4. The secondary hydraulic cylinder/piston assemblies 4 are each comprised of a double-acting piston 4a movable within a cylinder 4b where it defines a full-section chamber 4c and an annular chamber 4d. Throughout this specification and the appended claims, full-section chamber 4c means the volume enclosed between the walls of the cylinder 4b and the piston 4a and intended to be filled completely with oil; likewise, annular section chamber 4d means the volume enclosed between the cylinder and the piston walls which is partly occupied by a piston rod, not referenced in the drawing. The press 1 also comprises a carrier 5 for a billet (b) which is linked to a respective pair of secondary hydraulic cylinder/piston assemblies 6; similarly to the previous ones, each hydraulic cylinder/piston assembly 6 comprises a double-acting piston 6a movable within a cylinder 6b where it defines a full-section chamber 6c and an annular chamber 6d. The same considerations apply to chambers 6c and 6d as have been made for the corresponding chambers of hydraulic cylinder/piston assemblies 4. The plunger 2 is reciprocable toward and away from the carrier which is, in turn, reciprocable toward and away from an extrusion die M; the plunger and carrier are moved along the same direction, which coincides with the extrusion axis of the press. In addition, the press 1 is provided with a hydraulic system 7 for circulating oil through said hydraulic cylinder/piston assemblies, which system may be basically composed as follows. A first branch 8 of the hydraulic system 7 connects the primary cylinder/piston assembly 3 and the full-section chambers 4c of the secondary cylinder/piston assemblies 4 to a set of main supply, displacement pumps 9, 10. A second branch 8a of the hydraulic system 7 connects a first hydropneumatic accumulator 11 to the annular chambers 4d of the secondary cylinder/piston assemblies 4 for the plunger 2; the accumulator 11 is provided with a pilot solenoid valve 12 for a cartridge valve 13. A third branch 14 of the hydraulic system 7 extends from the full-section chambers 6c of the secondary hydraulic cylinder/piston assemblies 6 for the carrier 5 to said pumps 9 and 10; similarly as above, there is also a fourth branch 14a connecting a second hydropneumatic accumulator 15 to the respective annular chambers 6d of cylinder/piston assemblies 6. Lastly, the second hydropneumatic accumulator 15 is also provided with a pilot solenoid valve 16 for a corresponding cartridge valve 17. Located at an oil inlet 18 to the primary cylinder/piston assembly 3 for the plunger 2 is a pre-fill valve 19 having a pressure relief valve 20 associated therewith. The pumps 9 and 10 have respective by-pass blocks 21 and 22 to be explained later in connection with the operation of the invention. A third, actuation and hold-up hydropneumatic accumulator 23, provided with a respective hold-up solenoid valve 24, is connected to the full-section chambers 6c of the hydraulic cylinder/piston assemblies 6 driving the carrier 5. An additional pump 25 has a delivery side 25a connected to the accumulators 11, 15 and 23; a set of corresponding check valves 26, 27 and 28 make the connection of said delivery side 25a to each accumulator 11, 15 and 23 independent of the other two accumulators. A pressure transducer 29 is associated with the pre-fill valve 19. The operation of the above press during an air election cycle will be now described. The condition attained during the extrusion of a billet b presented in the carrier 5 is assumed for the initial reference condition of the press 1. That condition is incurred when the billet b in the carrier 5 is compressed by the plunger 2 occupying an advanced position toward the carrier and being pressed on it; the carrier 5 is, in turn, at an advanced, juxtaposed position to the extrusion die M against which it is pushed. Under the initial condition, the primary cylinder-piston assembly 3 and the full-section chambers 4c and 6c are respectively supplied with pressurized oil from the pumps 9 and 10; solenoid valve 24 is energized. Starting from this initial condition, the pressure relief valve 20 is opened to lower the pressure in the chambers 4c and the primary cylinder/piston assembly 3; in addition, the hold-up solenoid valve 24 is de-energized. The pressure transducer 29 detects the pressure drop in the oil supply to the primary cylinder/piston assembly 3, and on a predetermined pressure level being attained, energizes the solenoid valves 12 and 16 to operate the corresponding cartridge valves 13 and 17. At the same time, the main pumps 9, 10 are by-passed by the respective blocks 21 and 22 inhibiting the delivery of oil to the two branches 8, 14 of the hydraulic system 7, while holding them in their steady-state operational condition entered during the extrusion process. The hydropneumatic accumulators 11, 15 are placed, upon the valves 13, 17 being opened, in communication with the annular chambers 4d, 6d of the respective secondary cylinder/piston assemblies 4, 6 of the plunger 2 and the carrier 5. Within the hydropneumatic accumulators 11, 15, oil is under a predetermined pressure and can flow to the annular chambers 4d, 6d upon the corresponding valves 13, 17 being opened. The force developed by the pressure respectively applied by the oil contained in the accumulators 11 and 15 to the pistons 4a and 6a, is adequate to compensate the force originated by the pressure exerted by the oil still present in the full-section chambers 4c, 6c from the previous extrusion step initially performed by the press 1, on the corresponding pistons 4a and 6a. This force compensation holds the carrier and plunger in a state of equilibrium, the carrier and plunger forward stroke toward the extrusion die and the carrier, respectively, being then brought to a stop. In fact, by suitably timing the energization of the solenoid valves 12 and 16, the equilibrium of the forces acting within the secondary cylinder/piston assemblies 4 and 6 of the plunger and the carrier can be maintained without inducing backward movement in the carrier and the plunger. It should be noted that on the pressure relief valve 20 being opened, the pressure in the full-section chambers 4c and the primary cylinder/piston assembly 3 drops quickly also on account of the action of the pressurized oil from the accumulator 11. This pressure drop takes place in a succession of decreasing values and within a time period to be set by the user. In fact, the magnitudes of that time period and the pressure drop values are dependent on the emptying rates of the full-section chambers 4c and the primary cylinder-piston assembly 3, as well as on the storage pressure of the oil inside the accumulator 11; the higher the pressure within the accumulator 11, the faster will the oil flow from the accumulator 11 to the annular chambers 4d. The pressure of the air trapped between the billet b and the extrusion die M is such that, as the carrier ceases to be pressed against the die and the plunger no longer pushes on the billet in the carrier, the air can rush out of the space in which it was retained. Simultaneously with the ejection of air just described, the additional pump 25 will supply the hydropneumatic accumulator 23, whereto it is communicated by de-energizing the valve 24. Subsequently to air venting, the solenoid valves 12 and 16 are de-energized, the pressure relief valve 20 is closed, the pumps 9 and 10 are again connected to the branches 8 and 14 of the hydraulic system and the hold-up solenoid valve 24 is energized to communicate, during this phase, the accumulator 23 to the full-section chambers 6c of the hydraulic cylinder/piston assemblies 6 for the carrier 5. The press 1 is thus made ready to resume extrusion of the billet b as normal, with the carrier and the plunger at an unchanged position from the initial condition, that is the position taken during the extrusion step preceding the air venting cycle. Once the billet extrusion process is resumed, the additional pump 25 restores, with the aid of valves 24, 26, 27 and 28, the interiors of the accumulators 11, 15 and 23 back to their pressure settings, in readiness for a successive cycle of air ejection from the press. A press according to the invention can afford a number of advantages. The pressurized oil within accumulators 11, 15 and the actuating and hold-up accumulator 23 allows a pressure to attain predetermined high levels respectively in the annular chambers 4d, 6d and the full-section chambers 6c, and be at once available with no transients. In essence, the use of the hydropneumatic accumulators enables optimum control of each operation step of the press, and of the plunger and carrier movements, compared to that afforded by just displacement pumps. This movement control can be advantageously optimized by the adoption of a timing arrangement therefor which, as mentioned above, allows the equilibrium of the pressures acting in the annular 4d and 6d and full-section chambers 4c and 6c of the respective secondary cylinder/piston assemblies 4 and 6 for the plunger and the carrier to be kept constant over time. Also, the hydropneumatic accumulators have no operational of transient states as have the pumps 9, 10 and 25, and allow the duration of an air ejection cycle to be further reduced, thereby improving the press productivity. A further advantage of the invention is that, through the use or the hydropneumatic accumulators and their respective by-pass blocks, on resuming the extrusion process after completion of an air ejection cycle, the main pumps are already in an optimum steady-state operation condition without requiring any adjustment and attendant operation transient. Lastly, it should be emphasized that in order to have the air ejection cycle carried out, it has not been necessary to open the pre-fill valve, but to just energize the pressure relief valve, thereby affording additional savings in the time required to complete the whole ejection cycle.

Claims: A method for carrying out the ejection cycle of the air stored between a die (M) and a billet (b) in a billet extruding press of the type which comprises a billet (b) carrier (5) reciprocable toward and away from the die (M) along a longitudinal extrusion axis of the press, a plunger (2) reciprocable toward and away from said carrier (5) along said axis, said carrier (5) and plunger (2) being respectively provided, the former with secondary hydraulic cylinder/piston assemblies (16), and the latter with a primary hydraulic cylinder/piston assembly (3) and associated secondary hydraulic cylinder/piston assemblies (4), a hydraulic oil transfer system (7) extending between pumping means (9,10) and said hydraulic cylinder/piston assemblies (6;3 and 4), characterized in that it consists of temporarily resisting the thrust of the plunger (2) against the billet (b) during the extrusion process as well as the thrust of the carrier (5) against the extrusion die (M), without thereby inducing backward movement of the carrier and the plunger to allow of said ejection of air stored between the billet (b) and the die (M). A press for carrying out the method of Claim 1, of a type which comprises a carrier (5) for supporting a billet (b), reciprocable toward and away from a die (M) along a longitudinal extrusion axis of the press, a plunger (2) reciprocable toward and away from said carrier (5) along said axis, said carrier (5) and plunger (2) being respectively provided, the former with secondary hydraulic cylinder/piston assemblies (16), and the latter with a primary hydraulic cylinder/piston assembly (3) and associated secondary hydraulic cylinder/piston assemblies (4), a hydraulic oil transfer system (7) extending between pumping means (9,10) and said hydraulic cylinder/piston assemblies (6;3 and 4), characterized in that it comprises a means of temporarily resisting the thrust of the plunger against the billet during the extrusion process as well as the thrust of the carrier against the extrusion die without thereby inducing backward movement of the carrier and the plunger, which means includes a source (11,15) of pressurized oil connected to the secondary hydraulic cylinder/piston assemblies (6 and 4) for the carrier (5) and the plunger (2), which source is effective to apply a predetermined force to both of the latter by means of said secondary hydraulic cylinder/piston assemblies (6 and 4) appropriate to temporarily resist the thrust forces brought to play by the billet (b) extrusion. An extrusion press according to Claim 2, characterized in that said source of pressurized oil comprises first and second hydropneumatic accumulators (11,15) respectively connected to said secondary hydraulic cylinder/piston assemblies (4 and 6) for the plunger (2) and the carrier (5) over second (8a) and fourth (14a) branches of the hydraulic system (7). An extrusion press according to Claim 3, characterized in that it comprises: a first branch (8) of said hydraulic circuit extending from said pumping means (9,10) to the primary (3) cylinder/piston assembly (3) and to respective full-section chambers (4c) of the secondary cylinder/piston assemblies (4) for the plunger (2); a third branch (14) of said hydraulic system extending from said pumping means (9,10) to respective full-section chambers (16) of the secondary cylinder/piston assemblies (6) for the carrier (5); a first valve device (12,13) associated with said first accumulator (11); a second valve device (16,17) associated with said second accumulator (15); an additional pump (25) for supplying oil to said first and second hydropneumatic accumulators (11 and 15); a pressure transducer for the oil supplied to the plunger (2), said first and second valve devices (12,13 and 16,17) being linked operatively to said pressure transducer (29). An extrusion press according to Claim 4, characterized in that said pumping means (9,10) comprise respective by-pass blocks (21,22) for the delivery flow to said first and third branches (8 and 14). An extrusion press according to Claim 5, characterized in that it comprises a third actuating hydropneumatic accumulator (23) provided with a respective hold-up solenoid valve (24) connected to respective full-section chambers (6c) of the secondary hydraulic cylinder/piston assemblies (6) for the carrier (5). An extrusion press according to Claim 6, characterized in that said first and second valve devices (12,13 and 16,17) respectively comprise a pilot solenoid valve (12 and 16) and a cartridge valve (13 and 17).

Inventors: SEMINARI RENATO, SEMINARI, RENATO
Applicants: INNOCENTI ENG SPA, INNSE INNOCENTI ENGINEERING SANTEUSTACCHIO S.P.A.
Application year: 1992
Main classification: B21C27
IPC codes: B21C27, B21C23