US2299686A - Hydraulic press - Google Patents

Description

Oct. 20, 1942. ERNST 2,299,686

I I HYDRAULIC PRESS Original Filed Jan. 15, 1940 6 Sheets-Sheet l INVENTOR WALTER ERNsT ATYORNEYS Oct. 20, 1942. w. ERNST 2,299,686

HYDRAULIC PRESS' Original Filed Jan. 15, 1940 6 Sheets-Sheet 2 INvEN'ro R WALTER ERNST ATTORNEY5 HYDRAULI C PRES S Original Filed Jan. 15, 1940 s Sh eets-Sheet 5 Iu v; NTOR WALT ER ERNST BYZ Z Z ATTORNEYS 0a. 20, 1942. w ERNST 2,299,686

HYDRAULI C PRES 5 Original Filed Jan. 15. 1940 6 Sheets-Sheet 4 WORK RCQD KNLI In l6 INVENTOR Waum iRNsT BY Z Z r ATTORNEYS Oct. 20, 1942. w. ERNST v 2,299,636

HYDRAULIC PRESS -Original Filed Jan. 15, 1940 s Sheets-Sheet 5 luvimoa WALTER [mm ATToRuiYa Oct. 20, 1942. w. ERNST 2,299,536

HYDRAULIC PRESS Griginal Filed Jan. 15. 1940 6 Sheets-Sheet 6 .IIBzE fin-.7

I-Qvnnon WALTER, Erma" Bvz Ammuavs Patented Oct. 20, 1942 HYDRAULIC rmass Walter Ernst, Mount Gilead, Ohio, assignor to The Hydraulic Development Corp., Inc., Mount Gilead, Ohio, a corporation of Delaware Original application January 15, 1940, Serial No.

Divided and this application November 28; 1940, Serial No. 367,645

2 Claims.

jection molding, die casting and the like. Heretofore where a relatively long working stroke at high pressures has been necessary, particularly in 'connection with forging presses, it has necessitated the use of a very large operating system of hydraulic accumulators, the first cost of which was prohibitive. Also, due to the relatively short portion the working cycle is of the total cycle of operations the system was highly inefiicient.

The object of this invention is to provide a movement to the work at low pressure and high speed, giving a rapid traverse stroke; and to thereafter provide continued high speed at high pressure in order to impart tremendous pressures to the work, preferably without sudden shock, as is required in the case of forging metal billets, compressing plastics, etc.

It is a further object of this invention to traverse a hydraulically operated press platen to the work at relatively low pressure.

It is an object to provide, preferably, an independent hydraulically-operated system for this purpose.

It is an additional object to utilize the movement to the work by the platen to release at a given position into the platen operating system a high pressure such as that of a compressed gas, which in turn applies high pressures to another portion of the hydraulic system, which in turn supplies a reserve quantity of high pressure fluid to maintain the platen at high speed and to give it a very high pressure stroke.

It is an object to provide an independent hvdraulic system for creating sufilcient hydraulic pressure in the independent high speed system by compressing a gas or its equivalent, which, when released, applies its pressure to the high speed system hydraulic fluid and the fluid will in turn apply its pressure for the final stroke of the platen.

It is an object of this invention to provide a relatively high-pressure pump and hydraulic system for operating a press platen to give a quick movement to the work at low pressure, and to assist in the subsequent high speed, high pressure movement of the platen.

It is an object to provide a second pumpadapted to supply fluid at similar high pressures and to operate an accumulator piston in an accumulator cylinder for compressing a gas, such as nitrogen.

It is an object to provide means controlled by the movement of a platen at a predetermined point in its stroke to release this gas pressure so that it in turn will apply its pressure to its hydraulic system that is brought in communication with the platen of the press to accomplish the final very high speed and high pressure stroke. It is therefore possible with relatively small, standard pumps to secure efiiciently all of the advantages of very large and cumbersome and ex pensive accumulator systems while at the same time maintaining a high cycle rate with pumps of small size occupying a small space and utilizing well-known pressures.

It is a further object to provide means of returning the press platen to its initial position at a speed as high as its initial movement to the work, while utilizing the same source of fluid pressure for this purpose as is applied to the pressing piston during this initial movement to the work.

The object of this invention is to secure the advantages of a closed circuit with a reversible pump so that .the direction of movement can be reversed without shock while securing the advantages of sudden high pressure. Thus shock is eliminated at the end of the reverse of the stroke which is characteristic of the accumulator type of press.

It is a further object to secure (through the metering valve) a constant speed irrespective of work resistance, whereas with the old type of press systems, the press slowed down as the resistance increased, or sped up as this resistance decreased.

It is a further object to make possible the adjustmentr of the final high speed movement of the press platen, by providing a manually ad- It is a further object to subject the pump control to accumulator pressure, and thus to stop pump delivery, when the position of the piston of the accumulator indicates that the latter is fully charged; and to prevent subjection of the pump control to accumulator pressures at all times when the position of the piston indicates less than full charging, thus permitting the pump to deliver fiuid at its maximum rate to the accumulabor.

It is a further object to cause the pump associated with the accumulator to deliver at its full capacity immediately after the release of stored accumulator pressure, thus supplementing this stored pressure in producing a high speed, high pressure movement of the platen.

It is'a further object to, utilize the full discharge of the two pumps, as well as the discharge of the accumulator, in the execution of the final high pressure stroke of the press.

It is a further object to keep the size of the accumulator at a minimum by storing therein, only as much fluid as is required, along with the output of both pumps, to effect the final high speed,

. high pressure stroke of the press, all other movements of the press being produced solely by one of the pumps.

It is a further object to provide electrical control means for maintaining an open passage for the transfer of accumulator pressure to the press between the time of initiation of this transfer by platen actuated means, and its termination by pressure actuated means.

It is a further object to provide electrical control means for preventing release of accumulator pressure upon the main pressing piston, during the retraction stroke of that piston.

It is a further object to provide make-up means whereby the pump directly associated with the pressing piston may draw fluid from the reservoir in excess of that available in the push-back cylinder, the amount of fluid thus supplied to the pump being dependent upon the speed of the press during its working stroke, this speed in turn being dependent upon the predetermined flow of accumulator fluid to the press.

It is a further object to open and close a valve between the accumulator and the'press by means of the pressure within the accumulator, the direction of application of this pressure being governed electrically in response to the beginning and ending of the final working stroke of the press.

It is a further object to provide means for momentarily relieving the high pressure above the working piston, and simultaneously by-passing the pump associated directly with the press, to prevent shock upon the press and system at the time of reversal of the press movement.

It is a further object to protect the press and the entire system against the accidental development of undue pressures, by the provision of safety valves at the necessary points in the system. I

The press of this invention is especially intended for operations in which it is desirable or imperative to execute a relatively long high pressure stroke at high speed. Examples of such operations are found abundantly in forging, injection molding, or die casting. A specific example taken from the field of power forging, is the making of long steel shells. In this case a billet, heated to the correct temperature, is placed in the cavity of the lower die member, the first of two or more pressing movements being immediately thereafter initiated. This first movement might, for example, bring the upper male die member into the cavity of the lower die member to press the heated billet downwardly, forcing it to assume the shape of the lower portion or the cavity. The length of stroke necessary to accomplish this operation might be from several inches to more than a foot, depending on the particular work-piece in process. must be executed rapidly, to prevent too great cooling of the part, in view of further pressing strokes yet to be performed.

The first male die member must then be with drawn, again at a high rate of speed, and a second die member moved into place. This done, another stroke of the press is efi'ected, either by manual or automatic control means, for example to form the interior of the shell by displacing some of the previously formed metal upwardly into the space between the two die halves. This operation, although requiring high pressures acting through a long stroke, must, as before, be performed with great rapidity, to prevent the cooling of the shell tothe point of shrinking upon the punch. Similarly, any subsequent pressing strokes will require rapid press action, the more numerous and the deeper these are, the more imperative becoming the high speed.

It is to meet the requirements of such a pressing operation, and to do this with ecenomy of equipment and space, and with smoothness and efliciency, that this press has been invented.

This application is a. division of my application Serial No. 313,852, filed January 15, 1940.

Referring to the drawings: '7

Figures 1 to 5 are diagrammatic views of the press and its operating system, showing the significant stages of apressing operation.

Figure 1 illustrates the idling stage of the press and system, preparatory to a working stroke] Figure 2 illustrates the initial stage of a working stroke, in which the press platen is caused to approach the work at a rapid rate, and under no pressure.

Figure 3 illustrates the second stage of a working stroke, in which the press platen encounters the resistance of the work and proceeds downwardly at a rapid rate, but under high pressure generated by a primary and an auxiliary pressure system.

Figure 4 illustrates the reversing stage, the platen having completed its work, and the press controls being operative to initiate its return.

Figure 5 illustrates. the stage in which the platen is returning to its idling position, and the auxiliary pressure system is storing working energy for the subsequent pressing cycle.

Figure 6 is an enlarged view of a portion of the press of Figure 1 showing more fully the details of certain control valves.

Figure 7 is a diagram of of this invention.

Referring in detail to Figures 1 to"5 of the drawings, the numeral I designates the pressing plunger of a hydraulic press, having at its upper end the double-acting piston 2. This piston reciprocates within the cylinder 3. At the lower end of the plunger 1 13 mounted a platen 4 upon which, in turn, is mounted the upper member of any suitable work-engaging means, such as a die or injection plunger. Disposed above the cylinder 3 and mounted thereon is a reservoir 5 adapted to store part of the fluid medium by which the pres is operated. a

The movement of the platen 4, and the presthe electrical circuit At any rate, the stroke sures exerted by it upon the work, are iie'rermined by twoindependent' pressure generating systems, and by a third interconnecting hydraulic control system. There are thusthree distinct, butinterrelated, hydraulic systems provided for the control of the press; a primary pressure system, a secondary or auxiliary pressure system, and an interconnecting control system. For the purpose of making clear the separate actions of these systems, they will first be described under separate headings.

Primary pressure system and a self-centering spring cy inder 8, the .design of which is well known, and does not constitute a part of the present invention.

The pump delivers fluid to the differential areas of the press piston 2 in accordance with the setting of its shift ring. That is, the pump may deliver through lines 9 and ID to the main pressing area of piston 2, withdrawing fluid from the push-back area through line I I, and thus effect a downward stroke of the piston; or, it may deliver into line Ii, withdrawing from lines 9 and I0, and thus effect the reverse orupward stroke of the piston, depending upon the setting of the shift ring to the right or left of the center of the pump.

The position of the shift ring is primarily determined by the action of the operating solenoid the hydraulically actuated piston within cylinder 1, this piston being adapted to move directly, in direction and extent. with the pilot plunger.

The source of fluid pressure for this servomotor action is the constant delivery pilot pump II, which draws fluid from the reservoir 5 through lines l8 and I9, discharging it through line 20 to one of the ports of a relief valve 2|. requirement of the servomotor for operating fluid is intermittent, as determined by solenoid l2 and control rod [3, this relief valve normally by passes the discharge of pilot pump l1 into line 22 and back to the suction side of the pump through line I9. When, however, the control elements l2 and I3 act to cause movement of the pilot plunger 16 in either direction, fluid pressure within the 'servomotor is momentarily lowered, and the spring within the relief valve 2| moves the valve plunger to close the passage between lines 20 and 22. This results in directing the output of the pilot pump into the servomotor through line 23, effecting the required movement of the pump shift ring. The exhaust of fluid from the servomotor is by way of lines 24 and 22, either to pump I! or reservoir 5.

When a downward, pressing stroke of piston 2, is to be effected, the solenoid I2 is energized (by means vto be hereinafter described), its resultant mot-ion (see Figure 2) being transmitted to the shift ring of pump 6 through the servomotor as described above, the pump then supplying fluid to line 9, and withdrawing it from Since the has been completed, the solenoid is de-energized (see Figure 4) and the pump is shifted to reverse its delivery by means of a spring within the servomotor, thus to effect an upward, return motion of the piston 2. As this-piston nears the limit of its upward travel, the control rod I3,

which is carried by platen 4, acts through an adjustable collar 25 to move lever l4 and ultimately the pump shift ring to their neutral positions, in which both pump 6 and piston 2 are caused to idle. Should any leakage of fluid occur to permit piston 2, with plunger land plate 4, to descend of their own weight, control rod I3 and collar 25 will correspondingly descend, permitting the pump to again deliver to the pushbackside of piston 2, restoring it to its idling position. This condition of the press is shown in Figure l.

In addition to the press controls thus far described, there are provided certainother controls, one of which is a surge valve, generally designated 26. This valve is situated in the upper wall of cylinder 3, between the fluid reservoir 5 and the pressing area of piston 2, its pur posebeirig to open a direct passage between this area and the fluid in the reservoir at certain stages of a pressing cycle. For example, when piston 2 and platen 4 move downwardly at the beginning of a pressing cycle, they do so under the influence of gravity, and at a rate determined by'the suction of the pump 6 drawing fluid from the lower end of press cylinder 3. As the area in this end of the cylinder is relatively small, being only as large in cross section as the pushback side of piston 2, the piston tends to travel downwardly at a speed considerably greater than that at which the pump 6 delivers fluid through lines 9 and, ID to the upper, pressing side of the piston 2. This tendency creates a suction in the space above piston 2, which suction draws the valve member 21 downwardly a ainst the spring 28, opening a passage between the fluid in reservoir 5 and the space above piston 2 by way of ports 29 and 30 (see Figure 6 for details). The

' space above the piston is thus filled as rapidly as the pump 6 can remove fluid from the lower end of cylinder 3, making the advance of the platen towards the work as rapid as possible.

As soon as the platen 4, or the work-engaging member carried by it, contacts the work, pressure is developed in the upper end of cylinder 3 above piston 2, closing the surge valve 26 by moving the member 21 upwardly to cut off the passage between ports 29 and 30. The valve remains in th s state until the reverse motion of the platen is begun, at which time it again opens, although by a different action than previous'y. As the piston 2 is driven upwardly by fluid pressure bearing against its push-back area, this pressure is communicated by the lines 3|, 32 and 33 to the head of a plunger 34 in the upper part-of the surge valve 23. The plunger is moved downwardly against the compression of spring 35, its lower extremity striking the upper surface of the valve member 21, forcing it open against spring 28. This opening 'of the surge valve again assists in a rapid motion of piston 2, in this instance by providing a free passage into the reservoir for fluid above the piston in excess of that required by pump 6 to fill the push-back area of cylinder 3.

At the moment of reversal of platen 4, two other control valves, seen in enlarged form in Figure 6, are operative. One of these, the tonnage control valve, is designated generally 36.

This valve, in fact, initiates the reversal of the platen by causing the de-energization of the soleacid H! upon the attainment of the desired pressure upon the work. This pressure is communicated to the valve through lines 31 and 38, which are branches of the main pressure line H! leading to the area above piston 2. From line 381 the pressure is directed against the end of the plunger 39, lifting it in opposition tothe force exerted by a compression spring 46. This movement of plunger 39 is transmitted to a cam 4| carried at its upper end, the cam being adapted to trip a normally closed limit switch 42, in series with the contactor circuit for the solenoid l2. The valve 36 is maintained in this position as long as pressure in line 38 exceeds the compression of spring 40, the flow of fluid through the valve being exhausted by the line 43 to the reservoir 5.

It is to be understood that the tonnage control valve just described may be replaced, for the purpose of reversing the motion of the platen, by a limit switch responsive to the position of the platen. The other valve which becomes operative at the time of press reversal is located within the reservoir 5, and is generally indicated at 44. Its purpose is to relieve the intense working pressure existing in the space above piston 2', and, while doing this, to by-pass to the reservoir the delivery of pump 6 into line H toward the pushback area of piston 2. This pressure-relieving and pump by passing action provides a shockless reversal of the press. The valve 44 consists of the balanced plungers 45 and 46, both of which are urged toward the right (see Figure 6) under spring pressure. Normally, the spring pressure upon plunger 45 positions this plunger so as to block the port 41 opening into the reservoir, as well as one end of an internal passage 48. Likewise, the spring pressure upon plunger 46 normally positions it so as to block the port 49' opening into the reservoir.

During the working stage of the press, the plunger 46 shifts to the left, pressure within cylinder 3 being transmitted to it through lines I8, 31 and 59, overcoming the spring tension urging it to the right. When the working pressure reaches its predetermined limit and the tonnage control valve acts to reverse the delivery of pump 6, pressure within push-back line H is transmitted by lines 3| and 5| to the right end of plunger 45, shifting it to the left against its spring tension. Plungers 45 and 46 being thus shifted, port 41, passage 48,'and port 49 are all uncovered, whereupon working pressure standing in line 31 is relieved through port 41 to the reservoir, and the delivery of pump 6 is by-passed through lines 3| and 5|, passage 48, and port 49 to the reservoir. Working pressure having been relieved, plunger 46 is spring-returned to its normal right-hand position, blocking port 49* and causing the delivery of pump 6 to be directed against the push-back area of piston 2. Also, since this pressure above the piston 2 is relieved, push- -back pressure in line 33 is now enabled to open the surge valve, whereupon piston 2 proceeds to move upwardly to the starting position.

In order to prevent the development of dangerous pressures within the primary system, there are provided two safety valves 52 and 53. Valve 52 stands in the branch line 32, protecting the push-back side of the system, while valve 53 stands in the branch line 31, protecting the working side of the system. Both safety valves discharge into the reservoir.

There is also provided a check valve 54, its purpose being to permit fluid stored within the reservoir to be drawn into the line 3| and through it and line H to the pump '6, this passage of fluid taking place at certain times during the actual working stage of a pressing operation. Its action will be more fully described later in connection with a summary of the combined actions of all three hydraulic systems of this invention.

As stated above, the primary pressure system is operative at all times during a cycle of the press. From the description of this system it will be evident that this is the case; that the system is operative immediately upon the energization of the solenoid l2 to advance the platen toward the work, that it is operative during the working stage to drive the platen downwardly at high pressure, and that it is operative, upon de-energization oi the solenoid l2, to return the platen to its idling position and to maintain it in this position until the initiaton of a new cycle. The primary pressure system is, indeed, solely operative to produce the first rapid work-approaching stroke of the press, and the entire return stroke. It is in the second, or working stage of thepress that the primary pressure system is augmented by the auxiliary pressure system acting through the controls of the interconnecting system, and these systems will now be considered.

Auxiliary pressure system The auxiliary pressure system has its pressure source in a pump 55. This is a variable delivery high pressure pump, and may be of any wellknown type. It is fitted with a pressure control which consists ofa pressure cylinder 56 and a spring cylinder 51. The spring in cylinder 51 tends to hold the shift ring of the pump on full stroke, so that the pump will draw fluid from the reservoir 58 through the line 59 and deliver pressure through line 66. The pressure cylinder 56 is connected by the line 6| to a part of the pressure circuit in a manner later to be described, so that when pressure is built up in this part of the circuit to a point determined by the tension of the spring in cylinder 51, the pressure will overcome the spring tension and return the shift ring of the pump to neutral position, or nearly to neutral position. Under these conditions, the pump will deliver just sufiicient volume to maintain pressure in the system as determined by the setting of the spring in cylinder 51. Two hand wheels, 62 and 63, are provided, one for adjusting the stroke of the pump, and one for adjusting the tension of the spring. The design and operation of this control is well known by those versed in the art.

A relief valve 64 is provided as a protection to prevent excessive pressures being built up in line 60 or in other parts of the auxiliary pressure system, in the event the pump control should fail from any cause. This relief valve exhausts through line 65 to reservoir 58. The shut-oi! valve 66 is provided in line 66 merely for the purpose of disconnecting the pump for repairs, without draining the system; it is fully opened when the system is in operation.

Pressure fluid from pump 55 is delivered through line 66 to an elastic pressure accumu-' lator, generally designated 61. This accumulator consists of a high pressure cylinder 68, having a bore 69 in which is fitted piston 10; and of an enlarged cylinder 1| having a bore 12 in which is ,fitted piston 13. The two pistons, 10 and 13, are rigidly interconnected by the rod 14. In the drawings the cylinder 1! is shown broken above piston 13, to indicate that the-height oi this portion of the cylinder is dependent upon the particular pressure drop to be allowed between the uppermost and lowermost positions or the piston. For instance, if a 20 per cent drop is decided upon, the total height of the cylinder will be five times the stroke of the piston.

The space above piston 13 is filled with an elastic fluid medium, as for example with air, or some inert gas suchas nitrogen, helium or neon. It will be readily recognized that as fluid pressure is pumped into the bore 59 of the accumulator 61, piston '18, rod 1.4 and piston 13 will be pushed upwardly to compress the elastic mediumin bore 12 above piston 13.

Attached to piston 10, as by rod 15, is a cam 15 which is located outside the accumulator 51 and is adapted to actuate the control valve 11, this valve being located in the line and being designed to control the stroke of pump 55. Valve 11 contains a piston 18 on the right end of which is mounted a ball, or roller, for contacting cam 15. Piston 18 is forced to its extreme right-hand position by a spring 19, this position of the piston being seen in Figures 3, 4 and 5. While in this position, the piston shuts oil passage of fluid from the line 80 to the line 5|, the line 80 being a branch of line 8| leading to the fluid pressure bore 69 of the accumulator 51. At the same time, line 5i, which is connected to the pressure cylinder 56, is in communication with line 82, in turn connected to exhaust line 83, which leads to the reservoir 58. Under this condition, no pressure can exist in cylinder 55, and pump 55 will be held on full stroke position by the spring in cylinder 51, so that the full delivery of the pump is directed into the accumulator 61, stor-' ing pressure fluid in the bore 59.

In Figure-5, the accumulator is shown nearly filled, with the piston 18 of valve 11 standing in its extreme right-hand position. A slight additional upward movement of the accumulator piston, which position is illustrated in Figure 1, will bring cam 16 into contact with a roller on the end of piston 18, forcing this piston to the left against the pressure of spring 19. This action of the piston will close connection between lines 6! and 82, and will open the connection between lines GI and 80 allowing pressure from accumulator 61 to act in the pressure cylinder 55 of pump 55. v

This pressure willovercome the setting of the spring in-pump cylinder 51 and will shift the ring of the pump toward the left, or to neutral.

Under this condition, the pump will deliver just sufilcient fluid into the accumulator 51 to maintain it fully charged.

The provision of the-valve 11 in the auxiliary pressure circuit insures that whenever the accumulator is not fully charged, the pump 55 will supply pressure fluid to the accumulator 61 at its maximum output capacity. As indicated above, valve 11 is not actuated by cam 15, and the control 56 of the pump is not, therefore, subjected to pressures within the accumulator 61, until cam '15 has been carried by pistons and 13 almost to the upper limitof its travel, where the elastic medium above piston 13 has been compressed to the desired point, and the bore 59 has been completely filled with working fluid. Thus, although the pump 55 is shifted to its no; delivery, or neutral position, in response to fluid pressure within the bore 59, it is subjected to that pressure through the valve 11 only when the posi- 5 tions of pistons 18 and indicate that the pump has fully performed its charging function. It

will be noted that because of this provision, pump 55 will always be delivering at its maximum rate during a downstroke of piston 10, thus supplementing the stored volume of accumulator fluid in producing the high speed stroke of the press at high pressure.

For replenishing any of the gaseous medium that may be lost from the accumulator, there is provided a supply line Ila, in which is placed a shut-off valve llb.- Normally the valve lib is closed, the accumulator requiring no operating connection to its source of gas supply. When the addition of gas to the accumulator is found necessary, valve lib is opened to permit a flow from the gas source to the accumulator. The

pressure of the gas supply will be equal to the.

minimum gas pressure within the accumulator, that is, the pressure when piston 13 is at the bottom of its stroke.

The cylinder 1| is also provided, at its lower end, with a breather line He, the purposeof this line being to maintain atmospheric pressure on the underside of piston 13.

There is provided in the upper end of cylinder 68 a port 84 by which the drain line 83 is connected to the bore 69 above the piston head 10. This arrangement provides for conducting back to the reservoir 58 any fluid which leaks past the piston head 10 from the lower, high pressure end of the bore 69.

The reservoir 58 is joined with the reservoir 5 of the primary pressure system by the pipe line 85. Pressure fluid transferred from the accumulato-r to the press is ultimately returned to the reservoir 58 from which it originally was taken, by being expelled into the reservoir 5 upon the retraction stroke of the press, and then overflowing into the line 85.

Interconnecting control system The purpose of the system now to be described is to release, during the working stage of the press cycle, the kinetic energy of the gaseous medium compressed above piston 13 of the accumulater, and to expend this energy upon the work by conducting to the working area of piston 2 the fluid contained within the bore 59 of the accumulator.

The passage of fluid from the accumulator is through line 8| and valve 85 into line 81. The valve 85 is simply a service valve similar to the valve 66, and is normally fully open. Line 81 leads to a metering valve 88, pressure fluid being discharged from this valve through a choke valve 89 and thence, through line 98, to a pilot operated two-way valve 9|. A line 92 leading from this two-way valve joins the main pressure line I0, and it is by opening a passage into this line 92 from line 90 that the two-way valve 9i opens a passage from the accumulator 51 to the press.

The open or closed position of ,valve 9| is determined .by pilot pressure in the lines 93 and 94. This pilot pressure is taken from the pressure line 81 through branch line 95, choke valve 95, and line 91 to'the four-way pilot valve 98. Depending upon the setting of this pilot valve, fluid is conducted from line 91 into either pilot line 93 or 94, for controlling the position of the two-way valve 9|. The setting of valve 98 is determined by the energization or de-energization of a solenoid 99, and by the compression of a spring I00 opposing the solenoid. When energized, the solenoid 99 actuates the piston IOI of the valve 98 so as to connect lines 91 and 94, exhausting line 93 to the drain line 83. At this time, the compression of spring I is exceeded by thepull of the solenoid core. When, however, the solenoid 99 is de-energized, the spring I 00 actuates the valve piston I 0| so as to connect lines 91 and 93,. exhausing line 94 to the drain line 83.

The solenoid is shown in its de-energized state in Figures 1, 2, 4 and 5, being energized only in the operating stage shown in Figure 3. From these views of the drawings and from the foregoing description, it will be apparent that energization of the solenoid 99 results in the opening of, the two-way valve 9|, and that de-energization of the solenoid results in the closing of this valve, by directing pressure into pilot lines 94 and 92 respectively. The choke valve 96 standing in the inlet line 91 of the pilot valve 98, regulates the fluid velocity into the pilot lines 93 and 94, and consequently, the speed of opening or closing of the two-Way valve 9 I.

The purpose of the metering valve 08 and the .choke valve 09 is to regulate the transfer of fluid from the accumulator to the press, once that flow has been started by the energization of solenoid 99 and the consequent opening of valve 9!. The setting of the choke valve 89 is responsible for the general rate at which the transfer of fluid takes place, while the metering valve 00, in cooperation with the choke valve 89, serves to maintain that rate constant against varying resistances offered by the work, and also, at the moment of opening of valve'9l-, serves to cushion the impact ,or accumulator pressure upon the press.

Valves 8B and 89 may be regarded as two chokes in the pressure line between the accumulator and the press. Valve 89, after being manually adjusted, is a fixed choke, while valve 88 is a variable choke, its restriction of the presspre line increasing and decreasing inversely with pressures in line 90.

Briefly, the metering valve consists of a plunger I02 urged in one direction by a spring I03. The plunger I02 is provided with metering flutes or grooves I04, these flutes permitting more or less passage of fluid from the line 81 to the choke valve 89, as plunger I02 is raised and lowered, respectively. The pressure on the inlet side of the choke valve 89 is communicated to the end of the plunger I02 opposite the spring I00 by the line I05. The pressure on the outlet side of the choke valve 89, that is, the pressure identical with that exerted upon press piston 2, is communicated to the spring loaded end of the plunger I02 by the line I06.

During the idling stage of the press, when no flow of pressure fluid is taking place through valves 08 and 89, pressures in the control lines I05 and I06 are identical and spring I03 holds the plunger I02 in its uppermost position, where the flutes I04 present the least possible restriction to fluid flow. This position of the metering valve is seen in Figure 1. At the instant that two-way valve 9| is opened to discharge the accumulator, the pressure in line 90 on the outlet side of choke 89 will momentarily drop, and this change will be communicated 'to the metering valve through line I06. The effect of this sud den drop of pressure bearing upwardly against the plunger I02 will be to permit this plungerto move downwardly, pressure in line I05 still being relatively high. Because of this downward motion, the restriction through the flutes I04 is greatly increased, with the result that the tendency of accumulator pressure fluid to rush into the pressing area of cylinder 3 is checked. Gradually, as pressure rises in line 00, the restriction at valve decreases and the rate of flow to the press increases. The metering valve thus releases accumulator pressure without shock upon the press.

During the pressing operation, varying work resistances will be registered upon the metering valve plunger I02 through the line I06. Lbwered pressures in this line will permit the valve plunger to move downwardly under the influence of the pressure in line I05, this movement resulting in a greater restriction of the fluid passage along the flutes I04, thereby reducing the flow from line 81 to the choke 09. Increased pressures, on the contrary, cause the valve plunger to move upwardly, so that larger areas of the flutes I04 are exposed to the fluid passage. and the flow to valve 89 is increased. The press movement is thus maintained at a constant rate, namely, the rate predetermined by the manual adjustment of choke 89.

Energization of the solenoid 99, to Initiate the transfer of pressure fluid from the accumulator to the press, takes place just before the platen I engages the work. To provide for this accurately timed energization, there is attached to the platen a control rod I0I having the cam face I08, this cam face being adapted to engage and close a normally open limit switch I09. The position of this limit switch is adjusted to meet the requirements of different pressing operations.

The manner in which solenoid 99 is energized by the closing of switch I09, as well as the manner in which other electrical controls of the press are operated, will next be discussed.

Electricat control circuit Referring to Figure 7 of the drawings, there are shown the power lines IIO, III and H2 for supplying current to the electrical controls of the press. A starting switch H3 is placed in a circuit leading from the power line IIO, this switch representing any manual or automatic means for closing the circuit through the magnetic switch II4. Current flows through the coil H5 of the switch H4, and thence, by way of the normally closed limit switch 42 of the tonnage control valve 36 to the power line I I I. The essential parts of this valve are diagrammatically illustrated in connection with the switch 42.

Energization of coil II5 closes all the blades of the magnetic switch II4, these blades -normally being held open by the spring H6. The

closing of blade III upon its contact points completes a holding circuit through the coil II5 by way of line I I8, this circuit by-passing the starting switch H3 and permitting it to be opened.

Simultaneously with the energization of the holding circuit, the pump shifting solenoid I2 is energized by the closing of blades H9 and I20 of. the magnetic switch. Current passes through blade H9 from power line H2 and branch I2I, returning through blade I20 and branch I22 to the power line III. The circuit remainsin this condition throughout the work-approaching stroke of the press. It will be noted, however, that the circuit to the solenoid 99 has been partially completed by the closing of blade 9, the line I23 leading to the limit switch I09 now being connected to power line H2.

The contacting of limit switch I09 by cam I08 completes the circuit through solenoid 99, by way of lines I24, I25 and I50 to power line 0. At the same time, a circuit is made through the coil I26 of a second magnetic switch, current passing along line I21 to the coil I26, and thence along line I28 to join line I25, returning to power line IIO through line H8. Energizatlon of coil I26 results in closing blade I29 upon its contact points, thus by-passlng. the limit switch I09 and making a holding circuit through lines I30 and I2! to coil I26. The circuit to the solenoid 99 is now made through blade I29 and the line I3! 'to line I24, this circuit continuing to energize.

solenoid 99 after cam I08 has passed beyond limit switch I09, and this switch has opened.

'Current is thus flowing through all the controls of the electrical circuit during the engagement of work by the press. This condition ob.- tains until the working stroke has been completed, as determined either by a position limit switch actuated by the platen or by the setting 01 the tonnage control valve. When this valve is actuated by pressure wi hin the pressing area of main cylinder 3, the switch 42 is opened, and the entire electrical circuit is thereby de-energized. Opening of switch 42 breaks the circuit through coil H5, with which it is in series, and

blade II! and line H of the holding circuit. The spring I I6 then moves magnetic switch II4 to open all its blades, so that the circuit to solenoi'd I2 is broken, as well as the circuit through branch I23 to magnetic switch and solenoid 99. Although switch 42 of the tonnage control valve is only momentarily. opened, the circuit cannot be remade upon its return to closed position since the holding circuit through coil H5 is broken at the blade III,'and the starting switch H3 is standing open. Also, as limit switch I09 is actuated by the cam I06 upon the retraction of the press, solenoid 99- will not be re-energized, because the blade II9, in series with this limit switch is open. Transfer of fluid from the accumulator through the pilot controlled valve 9| is thus prevented during the upward movement of the press.

OPERATION or Connmno SYSTEMS Idling In describing a complete cycle of operations of the'press, attention is directed to Figures 1 to 5 of the drawings. In Figure 1, the press is seen in its idling state, the platen 4 being fully withdrawn from the work, and dwelling in this condition, although in readiness for, a pressing stroke. No appreciable flow of pressure fluid is taking place in the primary system, the pump 6 being held in its neutral, no-delivery position by the upward force of the collar 25 of the control rod I3 acting upon one end of the lever I4. Such flow as does occur is toward the push-back area of piston 2, and is due to leakage of pressure fluid from this area, with the consequent lowering of the platen and actuation of the pump through collar 25, to delivery into line II an amount of fluid sufl'icient to compensate for the leakage.

As to the auxiliary pressure system, the pump 55 has moved the pistons 10 and I3 of accumulator 61 to their fully charged positions, and has itself been shifted to neutral position in response to pressure within bore 69. operative only to restore the accumulator to its maximum pressure state as fluid within the bore 69 is lost through leakage.

The accumulator is maintained in its passive condition by the blocking of its pressure fluid in the interconnecting system, specifically at the push-back fluid takes place.

It is, at this time, 1

valve 9|, which is closed. This valve is forcibly maintained in its closed position by the action of static fluid pressure from the accumulator, transmitted through valves 96 and 98, and pilot line 99.

Rapid traverse toward work When it is desired to start a pressing operation the operator closes switch II3, energizing the pump solenoid I2 through the closing of contactor II 4. The pump 6 is immediately actuated to deliver at its maximum rate into lines 9 and I0 toward the pressing side of piston 2. Its entire fluid supply is taken from the push-back side of this piston through line II. This piston, with plunger I and platen 4, drop of their own combined weights as rapidly as withdrawal of Since the volume of this fluid is much less than that required to fill the space above the piston 2, a suction is created in this space by the descending piston sufficient to draw piston 21 of the surge valve 26 down against the spring 29, opening the passage to reservoir 5, and permitting a surge of storage fluid into the pressing space.

Figure 2 of the drawings illustrates the condition just described, solenoid I2 being shown col lapsed, arrows indicating the direction of flow of fluid, the platen shown descending, and the surge valve shown diagrammatically in its opened position. No change in the condition of the.

Working stroke The distance from its idling position to thework piece having been traversed, the platen 4, through the rod I01 and cam I09, actuates the limit switch I09, closing-this switch, and energizing the solenoid 99 in the manner described above, in connection with the electrical circuit. By thi action, the platen of the press causes the interconnecting control system to release the stored energy of the auxiliary pressure system, directing it to the pressing side of piston 2. Figure 8 of the drawing shows the press and the system controls in the positions they assume im;- mediately after this release of accumulated energy takes place. The flow of pressure fluid is indicated by bold arrows, while the flow of pilot fluid is indicated by light arrows.

In the primary system, no significant change has occurred except that the surge valve has been closed by the development of pressure in the space above piston 2. Th pump, however, continues to withdraw from the push-back side of the ,piston 2, and to supply fluid, now under high pressure, to the main working area of the piston. I

Upon energization of solenoid 99, plunger IOI ofpilot valve 98 is moved so as to exhaust pilot pressure from line 93, directing it instead to line 94. The two-way valve 9I is thus moved to its open position and the flow of pressure fluid from line to lines 92 and I0 immediately ensues. The rate at which this flow takes place is governed by'the opening of the choke valve 89, and when this valve is appropriately adjusted by the operator, this rate will be such as to cause the pressing piston 2 to move into the work without a reduction of its previous rapid traverse speed. That is, the large volume of pressure fluid supplied by the accumulator, added to the smaller volume supplied by pump 6 will equal the previous sum of the make-up volume from the reservoir is delivered from the accumulator into the press cylinder, the press speed may tend to increase. In this event, pressure would be built up on the push-back side of the press. This pressure will act through line H and branch lines 3| and 5| into the valve 44, which valve will thus be opened to relieve excess pressure fluid in the press cylinder, just as at the time of press reversal. The action of valve 44 in this connection determines the maximum speed of pressing. v If the operator has opened valve 89 only partially, the working stroke of piston 2 will proceed at a rate slower than the work-approaching rate, and some fluid will be drawn from the reservoir 5 through check valve 54 by the pump 6. The amount of fluid so drawn from the reservoir will be that required by pump 5 in excess of that available in the push-back portion of cylinder 3. The impact of accumulator pressure upon the press is cushioned, in the manner described in detail above, by the metering valve 88. It will be noted that the plunger I92 of this valve: has been sharply depressed in Figure 3, this new position checking the flow along flutes H34. As the working stroke of the press is executed, and varying resistances are offered by the work, the flow of fluid through valve 89 will be kept at a constant rate by the self-adjustment of metering valve 88 in response to these variations.

Referring to the accumulator 61 in Figure 3, it will be seen that the moving element composed of pistons I0, 13 and rod I4 has dropped slightly from its uppermost position, the high gaseous pressure above piston 13 having initiated this movement upon its release by the opening of twoway valve 9|. It will continue to be forced downwardly under this pressure, and will continue to expel pressure fluid from the bore 69 to the press, through the interconnecting system. In its position in Figure 3, it has carried rod '15 and cam 16 to a point where the cam no longer engages the roller on piston 18 of valve 11. The spring 79 of this valve has, accordingly, moved piston 18 to its righthand position, in which it closes communication between lines GI and 89, exhausting the control pressure fluid in line 9! to the atmospheric. pressure of reservoir 58. In response to this action, the pump 55 has been shifted to full stroke position and is delivering its full output to bore 69 of accumulator 61. It will be noted that this delivery of the pump 55 is begun very shortly after the release of accumulator pressure.

Initiation of reversal downwardly to its limit for the particular work piece in the press, as likewise th moving element of the accumulator. Back-pressure in line 38 to tonnage control valve 36 has collapsed the spring within this valve, moving cam 4! into position to open limit switch 42. Asexplained above, opening of this switch breaks the circuit to all elee-- trical controls, and, consequently, solenoids I2 and 99 are now in their extended positions.

Solenoid l2, upon de-energization, has permitted the spring within the control I of pump 6 to shift the pump to its'full delivery position in through passage 48 and port 49 to the-reservoir,

the port 49 already being opened by the movement of plunger 46 to the left under the influence of working back-pressurein line 50. As soon as the movement of plunger 45 uncovers port 41, this back pressure is relieved, passage of fluid being from lines l0 to 31, and through port 41 to the reservoir. This action of valve 44 is only momentary, and serves to eliminate shock in the press due to its reversal of'direction.

De-energization of solenoid 99 immediately results in cutting oi the transfer ofpressure fluid from the accumulator to the press, this action proceeding from the upward shifting of plunger Hll of pilot valve 98, and the reversal of pilot pressure in the lines 93 and 94 to close the valve 9|.

The pump as is, of course, delivering at its full- Return stroke Figure 5 shows the return stroke of the press, and the simultaneous re-charging stroke of the accumulator. This view is representative of the entire press return movement, no change in the setting of the controls taking place until the idling position is reached.

The platen is returned solely by the delivery of pump 6 toward the push-back side of piston 2. Part of the fluid above this piston is drawn upon by the pump through lines 9 and ID, the remainder being exhausted through the surge valve 26 to the reservoir 5, from which the proper proportion is carried by the pipe line to the reservoir 58. The surge valve is forcibly held open by the push-back pressure communicated to it through branches 3| and 33 of line H. The action of the surge valve in this stage of the press cycle aids in producing a rapid motion of the platen, just'as in the work-approaching stage. In both stages, it serves to make up they difierence in the volumetric requirements of the cylinder 3 above and below the piston 2, the speed limit switch N19 is accomplished only when the circuit has previously been made through the blade H9 of the magnetic switch 4. As pointed out above, once the holding circuit for switch H4 has been broken'by opening of the tonnage control switch 42, the starting switch must be closed to again energize switch H4, closing its, contact blades. This does not, of course, occur until the beginning of another cycle; therefore, during the return of the platen to starting position, the actuation of limit switch I08 by.

Representative pressures The press as described lends itself to a wide range of pressures, of which the following are to be considered merely representative.

Pressure upon the piston 2 may be at about 1250 pounds per square inch during the working stage. Pump 6 and accumulator 61 will then be designed to deliver pressures somewhatin excess of the amount, to compensate for frictional losses in the working parts, the pipe lines and the control valves. It might, for example, be estimated that such losses between the accumulator and the main piston would total 100 pounds, in'which case the minimum pressure available within the accumulator would be 1350 pounds per square inch.

This is the pressure that would be exerted by the gaseous medium on the pressurefluid of the accumulator at the limit of the downward stroke of the accumulator pistons, or, in other words, when the gas had reached its'maximum allowable expansion. When the accumulator is fully charged and standing in its uppermost position, this pressure will, of course, be higher, a typical increase being about 20 per cent. In the present instance, this would give a maximum accumulator pressure of 1620 pounds per square inch.

Again allowing for frictional losses in the accumulator and the circuit, the pump 55 would be designed for pressures greater than this maximum. A loss of 100 pounds of pressure, for example, would require that this pump have a peak delivery of at least 1750 pounds per square inch.

It may be repeatedhere that the work-approaching stroke of the main piston is accom- Summary of main features The press platen of this invention is moved to and from the work at high speed by the pump of a primary pressure system, this pump also beand being charged by this pump at full delivery in all except its fully charged position. The pump stores hydraulic fluid in the accumulator, and at the same time compresses a gas therein. At the appropriate time in a pressing cycle, the pressure of this gas, reacting upon the body of hydraulic fluid, forces this fluid through an interconnecting system to the press.

The release of accumulator pressure fluid is timed by the position of the press platen acting through electrical control means to open a valve in the interconnecting system. This occurs just prior to the closing of the press upon the work.

The tendency of accumulator pressure to be released with shocking force upon the Dres is checked by a metering valve, responsive to pressures at the inlet and outlet or a choke valve,

the latter being the manual control of the trans fer rate of accumulator fluid. As the working stroke proceeds, and varying resistances are met, the metering'valve functions to prevent fluctuations in this rate.

When properly positioned, th choke valve in the fluid transfer line makes possible a pressing speed as high as the initial approaching speed of the press. This high speed is effective throughout as long a working stroke as the fluid response to the pressure or-position attained by the press. Shock due to reversal is eliminatedby a valve which momentarily opens to relieve the high working pressure above the press piston,

and to by-pass the pump which at that moment ing operative to assist in effecting the high pressure stroke.

There is provided an accumulator for adding pressure fluid to that supplied by the pump of the primary system, so as to produce a press working stroke of high speed as well as high pressure. This accumulator is part of an auxiliary pressure system, having aseparate pump has been actuated to deliver toward the pushback side of the piston.

An important advantage of the invention is that the bulk of the accumulator is kept at a minimum. This is accomplished by employing the accumulator fluid only during the high pressure stage of the cycle, by adding the total output of both pump jtc the accumulator output at this stage, and by charging the accumulator, if necessary, at the full rate of delivery or one pump, whenever the other pump is causing the press platen to advance toward the work, to retract from the work, or to stand in its idling position. The accumulator is made as compact as possible, in other words, by designing it to store only as much pressure fluid as is needed to produce, together with the two pumps, a high speed, high pressure strok of the press. The output or one of the pumps produces all other motions of the press, while the output of the other pump simultaneously charges the accumulator.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The combination in a press of acompression cylinder containing a piston, a platen secured to said piston, means including a first source of pressure fluid for initially moving the piston at a predetermined pressure and rate of speed, a second source of pressure fluid including an acthe 'pressur'e fluid from the second source and said accumulator to said piston in addition to, and in parallel with the pressure fluid from said flrst source of pressure fluid to continue the movement of the piston at a higher rate of speed.-

v I 2,299,oao cumulator, and means for subsequently applying.

second source of pressure fluid including a pump and an accumulator supplied thereby for storing up pressure, and means for subsequently applying the pressure fluid from said second pump and said accumulator to said piston in addition to and simultaneously with the pressure fluid 'supplied by said first mentioned pump to continue the movement of the piston at a higher rate of speed.

WALTER ERNST.

Images