GB2051635A - Hydraulic multi-cylinder press - Google Patents

Abstract

A hydraulic press, e.g. a forging press, has a plurality of working cylinders 2, 3, 4 with operating pistons 2a, 3a, 4a which can be optionally activated either together or individually or in groups by pumps 7, 8, 9. Retraction cylinders 5, 6 retract the movable press member 1a and the main working piston 3a into the top dead centre position. The other pistons 2a, 4a are separated from the movable press member and can be locked in their top dead centre position using a pump 10 and a duct 44 connected to the cylinders 2, 4. <IMAGE>

Description

SPECIFICATION Hydraulic multi-cylinder press, more particularly forging press The invention relates to a hydraulic press, more particularly a forging press with a pressure source, a plurality of working cylinders which can be optionally activated either together or individually or in groups, and with retraction cylinders for retracting the movable press member and the working piston into the top dead centre position. Presses of this kind are constructed either to reduce the consumption of pressure medium when using an accumulator drive if a lower press force can be used for the work which is to be carried out, or to increase the operating speed with a direct pump drive if only part of the operating cylinders are required for the work which is to be carried out.

It is common practice to select a threecylinder construction with three identical operating cylinders which permit the use of 33 1/3%, 66 2/3% and 100% pressure stages or the middle main cylinder is constructed to have 66 2/3% of the total piston surface area and the two side cylinders are constructed to have a combined piston surface area of 33 1/3% of the total piston surface area. Three identical power stages can be selected in both cases.

The pistons of the inactive operating cylinders of known multi-cylinder presses of this kind move in no-load operation; the cylinders are filled through separate charging valves with a separate pressure fluid. In high speed hydraulic presses, for example free-forging presses, these charging valves have large dimensions and, because of the brief reversal times required, give rise to operating defects.

It is the object of the invention to develop a hydraulic multi-cylinder press of the kind described hereinbefore so as to avoid the need for charging valves and thus to improve the operational reliability.

According to the invention this problem is solved in that the piston of the operating cylinder or cylinders which can be optionally activated is or are separated from the movable press member, i.e. they can be locked without any high-tensile connection and in their top dead centre position. The invention therefore proceeds from the idea that the unused operating pistons are to be released from their rigid connection to the movable press member so as to obviate the need for filling the associated cylinders in no-load operation, so that the trouble-prone charging valves are also eliminated.

Hydraulic or mechanical means can be provided for locking the operating pistons in the top dead centre position. According to the invention a preselector valve for activating the selected operating cylinder or cylinders and simultaneous connection to a return or relief duct of the operating cylinders containing the working pistons, which are to be locked, is recommended according to the invention for hydraulic locking.

Hydraulic locking of inactivated operating cylinders, which are not required, is preferred within the scope of the invention. To this end the invention provides that the operating pistons of the inactivated operating cylinders are connected with hydraulic pressure devices which can be biased from a pressure source via an additional preselector valve and are adapted to act against the operating stroke.

Embodiments of hydraulic pressure devices for locking operating pistons in the top dead centre position are disclosed in claims 4 and 5.

Three embodiments of the invention are illustrated in the accompanying drawing in which: Figure 1 shows a three-cylinder press with a floor-mounted drive, Figure 2 shows a three-cylinder press with an underfloor drive and Figure 3 shows a press according to Fig. 1 with a different retraction drive.

In the example according to Fig. 1 the press comprises three operating cylinders 2, 3 and 4 with operating pistons 2a, 3a and 4a, of which the pistons 2a and 4a of the side cylinders 2 and 4 are constructed as stepped pistons and have no high-tensile connection with the movable press member la, i.e. they are separated therefrom. The piston 3a of the middle operating cylinder 3 can be rigidly connected to the press member 1 a in conventional manner, because in the exemplified embodiment it cannot be optionally activated but is constantly driven. Retraction of the movable press member 1 a is performed by retraction cylinders 5 and 6 which are subjected to the constant pressure of an accumulator 11.

The press 1 is driven by three pumps 7, 8 and 9 which are connected parallel with each other, have a variable delivery rate and a reversible delivery direction. In the course of the press stroke the pumps draw hydraulic fluid from a tank 1 4 and transfer it through a delivery duct 42 to the press, through which retraction fluid also flows after reversal of the pumps, if the press member 1 a moves in the upward direction under the action of the retraction cylinders 5 and 6. Retraction can also be performed by the pumps 7, 8 and 9 or one of the said pumps, as shown in the exemplified embodiment illustrated in Fig. 3, in a manner already known from valveless control procedures by means of pumps whose delivery direction is reversible.

Referring now to Fig. 1, a preselector valve 1 2 disposed in the delivery duct 42 and set in position I in Fig. 1, in which all three cylin ders 2, 3, 4 are biased, is provided for preselection of the power stage. In the second control position II only the middle cylinder 3 is biased, but the side cylinders 2 and 4 are connected to a relief or return duct 43 which extends to the tank 14. In the first control position I of the preselector valve 12, which is provided only for preselecting the power stage and is not operated during the normal operating cycle of the press, the latter will therefore operate with the full press force and with an operating speed defined by the sum of the delivery rate of the three pumps 7, 8 and 9.

The pressure medium disposed in the annular chambers of the annular piston surface areas 2b and 4b of the stepped pistons 2a and 4a is thus delivered via a duct 44, a second preselector valve 1 3 in control position I and a duct 44a to the tank 15.

On the other hand, the annular piston surfaces areas 2b and 2b together with the duct 44, the preselector valve 1 3 and a pump 10, associated with the tank 15, comprise a hydraulic pressure device for locking the stepped pistons 2a and 4a in the top dead centre position if the cylinders 2 and 4 are inactivated by virtue of the preselector valve 1 2 being set into the second control position il, i.e. by being switched to the return duct 43.

Under these conditions the second preselector valve 1 3 will be simultaneously set to the control position 2 so that the delivery duct 45 of the pump 10 communicates with the duct 44 and the annular piston surface areas 2b and 4b are biased. Accordingly, the pistons 2a and 4a remain in the top dead centre position when the biased piston 3a of the middle operating cylinder 3 descends and the movable press member 1 a is lifted off the locked pistons 2a and 4a, to which it is not connected in high-tensile manner.After an operating cycle at maximum press force it is possible for the preselector valves 1 2 and 1 3 to be set into their control positions II while the press member 1 a is still being retracted by means of the retracted cylinders 5 and 6; the operating pistons 2a and 4a, which are not required during the next operating cycle with inactivated operating cylinders 2 and 4 are then driven into the top dead centre position by pressure means obtained from the pump 10 and independently of the retraction cylinders 5 and 6 and remain locked in said dead centre position.

The embodiment according to Fig. 2 shows a three-cylinder press in which the movable frame 20 is operated by an underfloor drive in relation to a stationary foundation plate 35 which supports the three operating cylinders 21, 22 and 23. Three parallel-connected, variable and reversible pumps 24, 25 and 26 are again provided as a drive and are connected via a delivery duct 42 to a power station preselector valve 37 and are adapted to draw pressure medium from a tank 39 or to deliver it thereto. A return duct 43 for relieving the inactivated operating cylinders extends into the said tank 39 in a manner similar to that of the exemplified embodiment illustrated in Fig. 1. Retraction cylinders 27 and 28, biased by the constant pressure of an accumulator 41, are provided for the retraction of the movable frame 20.

The operating pistons 21a, 22a and 23a of the operating cylinders 21, 22 and 23 are plunger pistons which can be locked in their top dead centre position by means of hydraulic pressure devices comprising stationary auxiliary cylinders 29, 30 and 31, whose piston rods 29a, 30a and 31a are connected to lockable operating pistons 21a, 22a and 23a.

The said auxiliary cylinders are connected by means of cross-members 32, 33 and 34 to the stationary foundation plate 35 (not shown). The auxiliary cylinders 29, 30, associated with the two side cylinders 21, 22, are connected via a common duct 46 to a preselector valve 38 and the middle auxiliary cylinder 31 is connected to a duct 47 to the said preselector valve 38 which is associated on the inlet side with a delivery pump 36 having a delivery duct 48 and a return duct 49 which extends into a tank 40.

The preselector valves 37 and 38 differ from those illustrated in Fig. 1 by having three different control positions I, II and Ill instead of two such control positions. in the middle control positions I, illustrated in Fig. 2, the pumps 24, 25, 26 operate via the delivery duct 42 and the parallel-connected ducts 50 and 51 on the output side of the preselector valve 37 to all three operating cylinders and all auxiliary cylinders 29, 30, 31 are controlled via the duct 47 and the preselector 38 in the middle, corresponding control position I to retraction via the duct 49. In the corresponding control positions II of both preselector valves, only the middle operating cylinder 23 is biased, but the side cylinders 21, 22 are relieved via the ducts 51, 43. The lateral auxiliary cylinders 29, 30 are biased with pressure via the ducts 48, 46 to lock the inactivated side cylinders in the top dead centre position and the middle auxiliary cylinder 31 is driven via the ducts 47, 49 to retraction in accordance with the operating stroke of the middle operating cylinder 23.

Only the side cylinders 21, 22 are biased in the corresponding control positions III of both preselector valves 37, 38, but the middle cylinder 23 is relieved via the ducts 50, 43.

To lock the inactivated middle cylinder in the top dead centre position, the middle auxiliary cylinder 31 is biased with pressure via the ducts 48, 47, but the lateral auxiliary cylinders 29, 30 are driven into the retraction motion.

Only the two side cylinders can be activated in the exemplified embodiment illustrated in Fig. 1, but the exemplified embodiment ac cording to Fig. 2 permits optional shutting down of the side cylinders or of the middle cylinder, a feature defined by the three control positions I, II and Ill of the preselector valves 37 and 38. The press according to Fig. 1 can therefore operate with only two power and speed stages, but the press according to Fig.

2 can be operated with three different power and speed stages, more particularly since the piston surface area of the middle operating piston 23a is greater than each of the identical piston surface areas of the lateral operating pistons 21a and 22a.

The construction and method of operation of the exemplified embodiment illustrated in Fig. 3 corresponds to that illustrated in Fig. 1 with the difference that the retraction cylinders 5, 6 are not connected to an accumulator, but are connected via a duct 55 to the suction branch 56 of the reversible variabledelivery pump 7, which delivers into the suction branch 56, closed by a non-return valve 57, and therefore into the retraction cylinders 5, 6, when the movable press member 1 a is retracted in the upward direction. To this end, it is necessary to provide a stop valve 58 between the common delivery duct 42 of the pumps 7, 8, 9 and the relief or return duct 43 which extends to the tank 14.In the illustrated control position I the said stop valve is closed when, in the course of a working stroke of the press, the pumps 7, 8, 9 deliver into the delivery duct 42 which, during the retraction motion, functions as return duct for the pressure medium which is displaced from the operating cylinders 3 or 2, 3 and 4. During the working stroke the pump 7 draws its suction volume partially from the retraction cylinders and partially via the opening non-return valve 57 from the tank 14. If all three pumps are driven to press retraction, the valve 58 moves into the open control position II so that the ducts 42, 43 and more particularly the branch 43a and the tank 14 communicate and the excess quantity of pressure medium discharged from the operating cylinders and not absorbed by the suction side of the pump 7 when this delivers into the small retraction cylinders 5, 6, is able to flow via the ducts 42, 43a into the tank 14. When set into the open control position II, the stop valve 58 also functions as a decompression valve and is driven into position II immediately prior to the reversible pumps 7, 8, 9 passing through zero position after an operating stroke.

It will be understood that some ducts shown in the drawing must be connected to safety valves, a feature which is not shown in detail.

Claims (6)

1. A hydraulic press, more particularly a forging press with a pressure source, a plurality of working cylinders which can be optionally activated either together or individually or in groups, and with retraction cylinders for retracting the movable press member and the working piston into the top dead centre position, wherein the pistons of at least one or more optionally activated operating cylinder or cylinders are separated from the movable press member i.e. they can be locked without any high-tensile connection and in their top dead centre position.

2. A press as claimed in claim 1 wherein a preselector valve is provided for activating the selected operating cylinder or cylinders and for the simultaneous connection to a return duct of the operating cylinders with the operating pistons which are to be locked.

3. A press as claimed in claim 2 wherein hydraulic locking of the operating pistons associated with the inactivated operating cylinders is obtained by the operating pistons thereof being connected to hydraulic pressure devices which act against the operating stroke and can be biased by a pressure source via an additional preselector valve.

4. A press as claimed in claim 3 with a floor-mounted drive wherein the lockable operating pistons are constructed as stepped pistons whose annular piston surface areas can be biased as hydraulic pressure devices for locking purposes.

5. A press as claimed in claim 3 with a floor-mounted drive wherein the hydraulic pressure devices comprise stationary auxiliary cylinders whose piston rods are connected to the lockable operating pistons.

6. A press, substantially as herein described with reference to and as illustrated in the accompanying drawings.