US2166319A - Hydraulic press with variable retraction for platens - Google Patents

Description

y P. c. POCOCK ET AL 9 HYDRAULIC PRESS WITH VARIABLE RETRACTION FOR PLATENS Filed Dec. 8, 1957 3 Sheets-Sheet l INVENTORS A TTORNEYJ.

July 18, 1939. P. C. bcock AL 11 5 3 79 HYDRAULIC PRESS WITH VARIABLE RETRACTION FOR PLA'I'ENS Filed Deg s, 1937 3 Sheets-Shet 2, l

Ill

A TTORNE Y5,

1 22 v INVEN7DRSQ Patented July 18, 1939 UNITED STATES PATENT orFicE HYDRAULIC PRESS WITH VARIABLE 'RE- 7 TRACTION FOR PLATENS Paul C. Pocock, Marion, and Victor S. Shaw,

Mount Gilead, Ohio. assignors to The Hydraulic Press Corp., Inc., Wilmington, Del., a corpora-' tion of Delaware Application December 8, 1937, Serial No. 178,772

10 Claims.

Another object is to provide a hydraulic press with means for automatically applying a relatively large retracting force to the platen at the start of the retraction operation, and subsequently to apply asmaller retraction force.

Another object is to provide a hydraulic press having a plurality of retraction plunger areas for providing different amounts of retraction force at different portions of the retraction part of the operating cycle.

Another object is to provide a hydraulic press with a retraction plunger and an auxiliary retraction plunger, together with means for bringing the auxiliary retraction plunger into and out of operation, for applying a larger amount of retraction pressure in a predetermined portion of the retraction stroke.

Another object is to provide a hydraulic press with means responsive to the attainment of a predetermined pressure upon the retraction stroke to apply an additional retraction force to the press platen.

Another object is to provide a hydraulic press with a double-acting main plunger having a retraction area and a retraction plunger having an additional retraction area, together with means responsive to the attainment of a predetermined pressure upon the retraction stroke for applying both of said retraction areas to the work of retracting the press platen.

Another object is to provide a method of press-.

ing workpieces, including temporarily applying an additional force to separate the pressing members at the completion of the working stroke.

In the drawings: l Figure 1 is a central vertical section through one embodiment of a hydraulic press according to the present invention.

Figure 2 is an enlarged central vertical section through the four-Way operating valve shown in Figure 1.

Figure 3 is an enlarged central vertical section through the three-way auxiliary retraction valve shown in Figure 1.

Figure 4 is an enlarged central vertical section through the pressureresponsiveswitch shown in Figure 1.

Figure 5 is a modification similar to the righthand portion of Figure l, but showing mechanical means for shifting the retraction valve.

Figure 6 is an enlarged vertical section through the retraction valve shown in Figure 5.

Figure 7 is an enlarged vertical section through a modified retraction valve for use in the circuit 10 of Figure 1, wherein the retraction valve is shifted by hydraulic means; I

General arrangement In general, the hydraulic press circuit of this 15 invention consists of a hydraulic press having a main plunger for moving the platen upon a working stroke, and a'plurality of retraction plunger areas for retracting the plunger, certain of said areas being inserted in. the circuit during a pre- 20 determined portion of the-retraction stroke in order to apply a greater retraction force during one portion of the retraction stroke than during another portion. Means, such as a pressureresponsive switch, and an electrically operated 25 valve are provided for distributing pressure fluid to the additional retraction plunger area in response to the attainment of a predetermined pressure upon the retraction stroke.

Inperforming certain kinds of pressing oper 3U ations with hydraulic presses, a considerably larger force is needed in the initial part of the retraction stroke thanis subsequently needed for the remainder of the retraction stroke. This problem is present in hydraulic metal-working n3 presses having dies for forming .or drawing metal parts. At the end of the working stroke of such a press the two dies are so firmly engaged with the Work-piece that a considerably greater force is necessary for separating the dies than for sub- (in sequently retracting the platen and main plunger against the forces of friction and gravity.

Hitherto, when sufficient retraction plunger area has been provided to insure sufficient force for separating the dies under such conditions, i.) this area has been unnecessarilylargefor use throughout the remainder of the retraction stroke. As a; consequence. there has been a serious loss of speed in the retraction stroke resulting from the large size of the retraction area .1 and the largev volume of pressure fluid required to serve this large retraction arqa. Alternatively. it has been necessary to provide an additionally high capacity pressure system. such as an additional hydraulic pump and. motor for slip a;

plying the additional force needed for separating the dies at the start of the retraction stroke, but unnecessary during the subsequent portion of the retraction, Accordingly, with the previous arrangements of separating the diesby using a constantrain area on the retraction stroke, much power has been wasted, and unnecessarily large and extensive equipment has been required to supply the pressure fiuid necessary to apply the requisite retraction force for separating the dies and for maintaining the desired speed of retraction.

By the provision of an auxiliary retraction plunger area, according to the present invention, and by making it possible to insert and withdraw this auxiliary retraction plunger area from the stroke, it is possible to utilize the additional area only for separating the dies. Once the dies have been separated, however the additional area is withdrawn from the circuit and the platen is subsequently retracted at a higher speed without requiring additional pumping equipment of high capacity. According to the present invention, therefore, the desired speeds of operation are maintained with smaller capacity pumping equipment than has hitherto been necessary, because the maximum retraction power. is appliedonly during the short portion of the retraction stroke during which it is required. According to the present invention, furthermore, two separate and distinct retraction plunger areas are provided for retracting the main plunger and platen, valves being provided for. selectively admitting pressure to one or both of these retraction plunger areas, as required by the forces demanded at different portions of the retraction stroke.

Press construction Referring to the drawings in detail, Figure 1 shows a preferred embodiment of the press circuit of thisinvention. In this embodiment the pressis; provided with a bed H] and head forming bottom and top press members, and interconnected by strain rods |2 having nuts |3 threaded uponthe upper and lower ends, respec- .tivcly. The press head contains a main cylinder.

|4 having a main cylinder bore l5, within which a main plunger i6 is reciprocable. The latter is provided with a piston head having a forward or working area l3 and a retraction or return area IS. A packing 20, urged into contact with the plunger |6 by the gland 2|, prevents leakage around the main plunger l6 at the entrance to the main cylinder bore l5.

Mounted upon the main cylinder is a surge tank 22 for supplying the working fluid to the circuit. The main cylinder I4 is also provided with an aperture23, within which is inserted a surge valve 24 having a surge valve member 25 urged upwardly by a coil spring 26 in the direction of closingthe passageway through the valve. The surge valve 24 also contains aplunger 21, urged upwardly by the coil spring 28 and downwardly by pressure fiuid supplied thereto in order to forcibly maintain the surge valve member 25 in an open position, directly upon the return or retraction stroke of the press,- and responsive to the supplying of pressure fluid to the. retraction cylinders. This surge valve 24 in itself forms no part of the present invention, and is disclosed in the Ernst Patent No. 1,892,568 of December 27,

Likewise mounted upon the press-head H is a four-way operating valve, generally designated 29, and a three-way retraction control valve, gen- -to the bracket upon the press bed I0.

eraily designated 30. Both of these valves are described subsequently in detail. Secured to the 'main plunger I6 is a platen 3|, suitably guided and glands for the prevention of leakage.

Die construction The press construction of this invention is adapted to handle any kind of pressing operation, equipment suitable for metal drawing being shown purely for purposes of illustration and not by way of limitation. To this end the platen 3| is provided with a punch 36 cooperating with the bore 31 of a die 38 mounted upon the press bed II). In Figure 1 the press is shown as having performed a pressing operation upon a workpiece 39, represented as a deep cylindrical shell of metal closed at one end. The operation which the press is shown to have performed upon this workpiece has consisted in smoothing the outer surface of the workpiece 33 by pushing it through the bore 31 by means of the punch 36. The die 38 is provided with transverse sockets 40 containing pawls 4| urged by springs 42 inwardly to positions engaging the top of the workpiece after the pressing operation has been concluded,

Valve arrangement The four-way operating valve 29 and three-way retraction control valve 30 are of the piston type, having heads arranged upon valve rods for con trolling the distribution of the fluid passing therethrough. The four-way operating valve 29 (Figure 2) consists of a casing 44 having a bore 45 and end plugs 46 with apertures 41 for the reciprocation of a valve rod 48 with spaced piston heads 49 and 50 thereon. Packings 5| and glands 52 revent leakage around the valve rod 48. The casing 44 is provided with -five annular enlargements 53, 54, 55, 56 and 51. The end enlargements 53 and 57 are interconnected by the passageway'58, terminating in the exhaust port 59. The lower end of the valve rod 48 is threaded, as at 60, for the connection of a threaded collar 6|, into which is inserted the upper threaded end 62 of the control rod 63. The latter is provided with adjustable collars 64, and 66, adjustably secured thereto. The upper and intermediate collars 64 and 65 are arranged to be engaged by the platen arm 61, secured to the platen 3|. The lower collar 66, however, is engaged by the arm 68 of a bellcrank h'and lever 69 pivoted, as at 10, The control rod 63 is guided in its reciprocation by the bored bracket 12 extending transversely from the bed Ill.

The three-way retraction control valve 30 (Figure 3) is of similar construction to the four-way operating valve 29 and is similarly provided with a casing 13, with a bore 14 closed by end plugs 15 with packings T6, and having four annular enlargements T1 to 80, inclusive. The end enlargements l! and are interconnected by the passageway 8|, terminating in the exhaust port 82, whereas the central enlargements l8 and 79 fill terminate in the ports 83 and 84.

Glands 85 similarly prevent leakage around the valve rod 88, which passes therethrough. The valve rod 86 is provided with spaced heads 81 and 88 for controlling the distribution of the fluid tothe various ports of the retraction control valve 30 according to the position of the valve rod 86..

On the upper end of the valve rod 86 is a flange 89 serving as an abutment for one end of the coil spring 90, the opposite end of which engages one of the glands 85 and serves to urge the valve rod 86 upwardly. Connected to the lower end of the valve rod 86, as at 9|, is the armature plunger 92 of a solenoid 93, having a winding 94 which when energized serves to pull the armature 92 and valve rod 80 downwardly against the urge of the coil spring 90. The solenoid 93 is mounted upon a bracket 95, secured to the press head II.

The winding 94 of the solenoid 93 is energized by the lines 98 and 91 leading to the contactsof the switch bars 98' and 99 of the contactor switch I00. The opposite contacts thereof are connected by the lines IOI and I02 to the power lines I03 and I04, respectively. The contactor switch I00 is provided with an operating coil I05 connected by the line I08 to the power line I03, and likewise connected by the line I01 to the contacts of the switch bar I08 of the pressure-responsive switch I09. From the opposite contact thereof the line IIO leads to the power line I04. The pressure-responsive switch I09 (Figure 4) is mounted upon the press bed I0, and is provided with a cylinder bore III, reciprocably receiving a plunger II2, the upper end of which is enlarged at II3 to engage one end of a coil spring II4, the opposite end of which engages a brack et H5. The coil spring II4 urges the switch plunger H2 and the switch rod II6 attached thereto in a downward direction, tending to separate the switch bar I08 from its contacts. The

pressure-responsive switch I09 is therefore a normally open switch: and closes only when the I pressure within the cylinder bore III rises to a point suflicient to overcome the thrust of the coil spring II4. A port II1 serves for the admission of pressure fluid to the cylinder III.

- Hydraulic circuit The hydraulic circuit interconnecting the hydraulic elements previously described is shown in Figure 1. Pressure fluid is provided by a hydraulic pump I I8 of any suitable type. The pump IIB receives fluid from the surge tank 22 over the suction line I39, and discharges pressure fluid through the pressure line I leading to the central port I2I of the operating valve 29. The pressure line I20 also leads to the upper port 83 of the retraction control valve 30. From the upper 'port I22 of the operating valve 29, line I23 leads to the port I24 in the head of the main cylinder I4. From the lower port I25 of the operating valve '29, the line I26 leads to the ports I21 in the retraction cylinders 33. A branch I28 leads to the top of the surge valve 24 for actuating the valve opening plunger 21 upon retraction stroke of the press. From the remaining or exhaust port 59 of the operating valve 29, the exhaust line I29 runs back to the surge tank 22. i

In the position shown in Figure 2 the operating control valve has been lifted into its neutral position by the platen arm 61, so that fluid from valve 30 is connected by the exhaust line I30.

to the surge tank 22. The remaining port 84 thereof is connected by the line I3I to the lower port I32 in the main cylinder I4 on the opposite side of the piston head I1 from the head port I24. The spring 90 normally urges the valve heads 81 and 88 of the retraction control valve 30 into the position shown in Figure 3, wherein the pressure fluid from the line I20 normally is entrapped between theheads 81 and 88. When the solenoid 93 is energized, however, and the valve rod 86 'is drawndownwardly, the heads 31 and 88 move into positions connecting the pressure line I20 and pressure port 83 with the port 84 and line I3I leading to the auxiliary retraction area I9 of the main piston head I1.

Operation In the operation of the press circuit of the present invention the auxiliary retraction area is ordinarily out of the operating circuit, and is brought into the circuit by the retraction control valve 30 only when its additional force is necessary. Let it first be assumed that the various elements of the press circuit are in the positions shown in Figures 1, 2 and 3. The operator r'emoves the workpiece, which has been finished in the previous operation of the press, and places a new workpiece upon the punch 36, above the aperture 31 in the die 30. The operator now shifts the hand lever 89 to the left, causing the arm 68 to lift the collar 86 and. control rod 63, thereby from, the retraction cylinders 33, back to the surge tank 22, by way of the line I26, the operating valve 29 and the line I29. main plunger I6 and platen 3| to descend by gravity. The suction thereby createdabove the main plunger head I1 causes the surge valve member 25 to push against the thrust of the coil spring 28, thereby permitting fluid to pass inrectly through the surge valve 24, into the space above the main plunger head I1. This permits the main cylinder to fill rapidly with fluid, without depending upon the fluid supplied thereto by the pump IIB.

When the punch 36 encounters the workpiece 39 and resistance is built up, the main plunger I6 and platen 3| cease to move by gravity. Pressure is then built up in the head of the main cylinder I4 above the piston head I1, this pressure automatically closing the surge valve member 25, assisted by the coil spring 26. The pump H9 thereafter continues to supply pressure fluid to continue-the pressing operations upon the workpiece 39 until these operations have been completed. Just before the completion of the pressing operation and when the platen has neared the lower limit of its Working stroke, the platen arm 61 engages the collar 85 upon the control rod 63,

moving the latter downwardly and shifting the This permits the I of fluid.

sure through the branch line I23,from the line I26, enters the surge valve 24 and urges the plunger 21 thereof downwardly, forcibly opening the surge valvemember 25. The pressure fluid entering the retraction cylinders 33 engages the retraction plungers 32 and urges the platen 3I upwardly upon its retraction stroke.

If the force required to separate the punch 36 from engagement with the workpiece 39 and die 36 does not exceed the normal operating pressure within the retraction cylinders 33, the platen 3I rises and proceeds upon its retraction stroke until the platen arm "engages the collar 64 and raises the control rod 63. This shifts the valve rod 48 and heads 49 and of the operating valve 29 into the neutral position thereof, thereby entrapping the pressure fluid from theline I20 within the operating valve 29, and holding the platen 3| in its retracted position.

Meanwhile the space beneath the piston head I1 of the main plunger I6 has been in communication with the surge tank 22 by way of the line I3I, which is normally connected to the exhaust line I30 of the retraction control valve.30, as shown in Figure 3. Accordingly as the main plunger I6 moves downwardly upon its working stroke, the fluid beneath the main piston head I1 passes directly along the line I3I, through the detraction control valve 30 and the line I30, into the surge tank 22. On the normal return or retraction stroke, as described above, the fluid passes from the surge tank 22, along the line I30, through the retraction control valve 30 and line I3I, into the space beneath the main piston head I1, filling this space with the proper amount Accordingly, under normal operating conditions, the auxiliary retraction area I9 on the under side of the main piston head I1 has no effect upon the speed or force of the main plunger I6, and absorbs none of the pressure fluid deliv-= within the retraction cylinders 33 and is transmitted along the line I33 leading tothe cylinder III of the pressure-responsive switch I09. At a predetermined pressure suflicient to overcome the thrust of the, coil spring II4 the plunger H2 rises and causes theswitch bar I08 to engage its contacts, closing the circuit between the lines I I0 and I01, thereby energizing the operating coil I05 of the contactor switch I00. The switch bars 93 and 99 thereof then close upon their contacts, closing the circuit between the lines IM and 91, and also between the lines I02 and 96, respectively. winding 94 of the solenoid 93, causing the armature 92 thereof and valve rod 66 of the retraction control valve 30 to be drawn downwardly. overcoming the thrust of the coil spring 90.

When this occurs the valve.heads 81 and 88 are shifted so that the pressure line I20 now communicates with the line I3I leading to the lower part of the main cylinder bore I5. Accordingly, pressure fluid now passes from the pump II8, along the line I20, through the retraction control valve 30 and along the line I3I. through the port I32, into the space beneath the auxiliary retraction area I9 of the main piston head I1. At the some time the lower valve head 88 closes the connection between the line I3I and thee);- haust line I30 leading tothc surge tank 22v The pressure fluid passing into the lower part of the This energizes the main cylinder bore I5 engages the auxiliary retraction area I9 of the main plunger I6, and

adds this area to the area of the retraction plungers 32, thereby increasing the force available for lifting the platen 3I and separating the punch 36 from the workpiece 39 and die 30.

As soon as the punch 36 has been loosened from its engagement with the workpiece 39, the force required to retract the punch 36 and platen 3| greatly diminishes and accordingly the pressure in the retraction cylinders 33 drops. This pressure drop is transmitted along the line I33 to the cylinder III of the pressure-responsive switch I09, permitting the plunger II2 thereof to move downwardly under the urge of the coil spring I I4, separating the switch bar I03 from its contacts and opening the circuit between the lines I01 and H0. This deenergizes the operating coil I05 of the contactor switch I00, opens the circuit between its switch bars 96 and 99 and their contacts, and deenergizes the lines 96 and 91. The consequent deenergization of the solenoid 93 permits the coil spring 90 to move the valve rod 86 of the retraction control valve 30 upwardly to its original position, cutting off the further flow of pressure fluid from the line I20 to the space beneath the auxiliary retraction area IQ of the 'main plunger I6, and opening the latter to a supply of pressure fluid, reaching it by way of the exhaust line I30, the retraction control valve 30 and the line I3I.

With the auxiliary retraction area I9 thus removed from the circuit, the temporary slowing down of the platen 3I, due to its presence, is ended and the platen 3I continues to move swiftly upward, under the influence of the retraction plungers 3I alone. When the platen arm 61 engages the collar 64 and shifts the operating valve rod 48 to its neutral position, the pressure fluid from the line I20 is again entrapped between the valve heads 49 and 50, and the main plunger I6 is held in a stationary position until the control rod 63 is moved upwardly to start another working cycle.

In the circuit shown in Figure l the manually operated lever 69 is shown for simplifying the disclosure. It will be understood, however, that the four-way operating valve 29 may be shifted by other means, such as by any suitable electric or hydraulic arrangement. Similarly, the retraction control valve 30 may be shifted by means of manual or hydraulic means in order to insert and remove the auxiliary retraction plunger area from the circuit. It will also be understood that these valves may be shifted mechanically in response to movement of any suitable portion of the press. In place of the spring 90, other suitable means, such as a pressure cylinder, may be used for returning the valve rod 86 of the retraction control valve 30 to its upper position.

The modification shown in Figure 5 provides mechanical means for shifting the retraction control valve 30. The valve 30 is generally similar to the valve 30 in Figure 1, except that the spring 90 and the flange 89 are omitted. The valve rod 86, however, is connected to a control rod I36 by means of the connection I35, and is guided at its lower end by a lug I31 upon the bed I0 of the press.

Extending laterally from the platen 3I is a platen arm I38. arranged to engage coil springs I39 and I40, mounted respectively above and below the platen arm I38 and positioned by means of adjustable collars MI and I42, respectively The upper spring I39 is provided to permit the platen 3I-to continue to move upwardly after it has shifted the valve" to its uppermost position wi'thout causing damage to the control rod I36 or the parts actuated thereby. This provision is made because the'stroke of the platen CM is greater than the stroke of the valve 30.

w The lower spring I40 serves to move the control III) rodl36 and valve rod 86 do'wnwardlywhen the spring I49 is-engaged by the platen arm I36 on the downward stroke of the platen.

In adjusting the press for-operation, the collar I42 is moved along the control rod I36 into such a position that the spring I40 will be engaged by the platen arm I38 to shift the control rod I36 downwardly when the platen 3I nears the lower limit of its stroke. In this manner the auxiliary return area I5 is caused to be opened to the entrance of'pressure fluid by way of the valve'30 as soon as the return stroke of the platen 3| is started by admitting'pressure fluid to the lines I26 and I28, in response to the operation of the four-way operating valve 29. The upper collar MI is adjusted during the setting-up operations of the press to such a position along the control rod I36 that the latter will be moved upwardly when the platen "3| has returned a sumcient distance on its return stroke to-free the workpiece from the punch. I At that point the platen arm I38 engages the'coil spring I39,'and the latter movesthe collar HI and control rod I36 upwardly, together with the valve rod 86, shifting the valve 30 and shutting off the auxiliary retraction area l9 from pressure fluid. In this manner the auxiliaryretraction area I9 is removed from service at a predetermined point on the return stroke of the platen 3|.

In the modification shown in Figure '7, the valve 30 as a whole is similar to that of Figure I and has a similar coil spring 90. The upper end of the valve rod 86, however, is threaded, as at I43, and provided with a nut I44 and locknut I45, whereby the force of the spring 99 may be adjusted. On the lower end of the valve rod 86 I is a piston head I46, mounted for reciprocation in a cylinder I41, threaded as at I48 into a threaded flange I49 serving to close the lower end of the valve casing 13. The upper end of the cylinder I41 communicates, through a port I50, with a conduit I33, whereas the lower end of the cylinder is provided with a port I5I, communicating with a conduit, I52, whichhas a drain line leading back to the surge tank 22 for draining away fluid which escapes past the piston I46. The conduit I33 is connected to the return pressure fluid line I26 and is the same conduit as the conduit I33 employed for actuating the pressure switch I09 in Figure 1.

In the operation of the'modiflcation shown in Figure 7 the four-way operating valve 29 is shifted so as to admit pressure fluid into the lines I26 and I28 for retracting the. platen 3| by means of pressure fluid admitted to the retraction cylinders 33. The resistance to the withdrawal of the punch occasioned by the friction between the punch and the workpiece causes pressure to be built up within the retraction cylinders 33, and this pressure is transmitted along the conduit I33 into the chamber above the piston head I46 in the cylinder I41 (Figure '7) When this pressure becomes sufficiently great to overcome the thrust of the coil spring 90, it shifts the piston head I46 and valve rod 86 downwardly,"shifting the valve heads 81 and 86 for admitting pressure fluid from the line I26 and the line I3I, leading through the port I32 to the auxiliary retraction area I9 the conduit I20.

of the main plunger I6. As soon as the punch is Heed from engagement with the workpiece by the force of the auxiliary retraction area I9 added to the effect of the retraction plungers 32, the pressure within the retraction line I26 drops. The consequent drop in the line I33 permits the spring 90 to shift the valve heads 8'1 and 88 upwardly, thereby cutting off the auxiliary retraction area I9 from the supply of pressure fluid in The press platen 3| thenceforth continues its retraction stroke under the influence of the retraction plungers 32 alone.

It will be understood that we desire to comprehend within our invention such modifications as come within the scope of the claims of the in vention.

Having thus frilly described our invention, what we claim as new and desire to secure by Letters tracti'on stroke of said main retraction means for temporarily amplifying the force of said main retraction means.

2. In a hydraulic press circuit, a platen, a main plunger connected thereto, main retraction means for retracting said mainplunger, auxiliary retraction means selectively insertible in said circuit during a minor part of the retraction stroke of said main retraction means for temporarily amplifying the force of said main retraction means, and means responsive to the attainment of a predetermined pressure in said main retraction means for rendering said auxiliary retraction means operative.

3. In a hydraulic press circuit, a platen, a main plunger connected thereto, a main retraction plunger connected thereto, an auxiliary retraction plunger area, and a valve for selectively admitting pressure fluid to said auxiliary retrac tion plunger area during a minor part of the retraction stroke of said main retraction plunger for temporarily amplifying the force of said main retraction plunger.

' 4. In a hydraulic press circuit, a platen, a main plunger connected thereto, a main retraction plunger connected thereto, an auxiliary retrac tion plunger area, a valve for selectively admitting pressure fluid to said auxiliary retraction plunger area during a minor part of the retraction stroke of said main retraction plunger for temporarily amplifying the force of said main plunger, and means responsive to the attainment of a predetermined pressure in said main retraction plunger for shifting said valve to admit pressure fluid to said auxiliary retraction plunger area.

6. In a hydraulic press circuit, a platen, a main plunger connected thereto, a main retraction plunger connected thereto, an auxiliary retrac tion plunger area, a valve [or selectively admitting pressure fluid to said auxiliary retraction plunger area during a. minor part of the retraction stroke of said main retraction plunger for temporarily amplifying the force of said main retraction plunger, electrical means for shifting said valve, and means responsive to the attainment of a predetermined pressure in said retraction plunger area for energizing said electrical means to shift said valve to admit pressure fluid to said auxiliary retraction plunger area.

7. In a hydraulic press circuit, a platen, a main plunger connected thereto, a main retraction plunger connected thereto, an auxiliary retraction plunger area, a valve for selectively admitting pressure fluid to said auxiliary retraction plunger area during a minor part of the retraction stroke of said main retraction plunger for temporarily amplifying the force of said main retraction plunger, a tank for supplying fluid to said circuit, said valve being normally positioned for maintaining communication between said auxiliary retraction plunger area and said tank, and means responsive to the attainment of a predetermined pressure in said retraction plunger for shifting'said valve to admit pressure fluid to said auxiliary retraction plunger area and cut of! communication thereto from said tank.

8. In a hydraulic press circuit, a platen, a main plunger connected thereto, main retraction means tor retracting said main plunger, auxiliary retraction means selectively insertable in said circuit during a minor part of the retraction stroke of said main retraction-means for temporarily amplifying the force of said main retraction means, and means responsive toa predetermined motion or said platen for withdrawing said auxiliary retraction means from the circuit.

9. In a lwdraulic press circuit, a platen, a main plunger connected thereto, main retraction means for retracting said main plunger, auxiliary retraction means selectively insertable in said circuit during a minor part of the retraction stroke of said main retraction means for temporarily amplifying the force of said main retraction means, and hydraulically-actuated means responsive to the attainment of a predetermined pressure in said main retraction means for rendering operative said auxiliary retraction means.

10. In a hydraulic press circuit, a platen, a main plunger connected thereto, main retraction means for retracting said main plunger, auxiliary retraction means selectively insertable in said circuit during a minor part oi the retraction stroke of said main retraction means for temporarily amplifying the force of said main retraction means, and hydraulically-actuated means responsive to the attainment of a predetermined pressure in said main retraction means for rendering operative said auxiliary retraction means and responsive to a pressure drop below said predetermined pressure for rendering inoperative said auxiliary retraction means.

PAUL C. POCOCK. VICTOR 8. SHAW.

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