US2620776A

US2620776A - Variable stroke final slow closing and initial slow opening hydraulic ram

Info

Publication number: US2620776A
Application number: US88124A
Authority: US
Inventors: Groves Walter Robert
Original assignee: British Industrial Plastics Ltd
Current assignee: British Industrial Plastics Ltd
Priority date: 1948-04-23
Filing date: 1949-04-18
Publication date: 1952-12-09
Anticipated expiration: 1969-12-09

Description

Dec. 9, 1952 w. R. GROVES 2,520,776

' VARIABLE STROKE FINAL SLOW CLOSING AND INITIAL SLOW OPENING HYDRAULIC RAM Filed April 18, 1949 4 Sheets-Sheet l PEEP/15? K94 r:

DEL/l) VE- v Pomp (2W F .5. M 1: mam W M- w. R. GROVES 2,620,776 VARIABLE STROKE FINAL SLOW CLOSING AND INITIAL SLOW OPENING HYDRAULIC RAM 1 Filed April 18, 1949 4 Sheets-Sheet 2 Dec. 9, 1952 64 29 A A 120 A fl ma/rrfio z Z7 Z3 2.5 ogrL Z p 7 29 120 L 20 f2] J Dec. 9, 1952 w. R. GROVES 2,620,776

' VARIABLE STROKE FINAL SLOW CLOSING AND INITIALSLOW OPENING HYDRAULIC RAM Filed April 18, 1949 4 Sheets-Sheet 5 DELAY ZAL v5 00,97] 4/ 30 33 m? K11 07/: 774' Ua .4 m2? m Fae? 70 4 Dec. 9, 1952 w. R. GROVES I 2,620,776

- VARIABLE STROKE FINAL sLow CLOSING AND INITIAL sLow OPENING HYDRAULIC RAM Filed April 18, 1949 4 Sheets-Sheet 4 Patented Dec. 9, 1952 VARIABLE STROKE FINAL SLOW CLOSING AND INITIAL SLOW OPENING HYDRAULIC RAM Walter Robert Groves, London, England, assignor to British Industrial Plastics Limited, London, England, a company of Great Britain Application April 18, 1949, Serial No. 88,124 In Great Britain April 23, 1948 9 Claims.

This invention relates to improved means for controlling application of pressure to hydraulic rams which are biassed to move in the direction of the operative stroke, e. g. biassed by gravity as in down-stroke hydraulic moulding presses.

The object of the invention is to control the application of pressure so that the ram, whilst being allowed to move at relatively fast speeds towards and away from the work, will be caused to move slowly when nearing engagement with the work to which high static pressure is required to be applied. The achievement of this object is particularly desirable in the case of moulding presses in order to prevent damage to the mould parts due to dynamic impact.

A further object of the invention is to cause the ram to move slowly at the commencement of its withdrawal from engagement with the work so that time and energy may be saved or operations facilitated, in the case where re-engagement with the same work is desired, as in the case of moulding presses when the moulds are opened one or more times during the course of the moulding process to allow the material in the moulds to breathe.

The invention is characterised by the provision of a high pressure liquid feed which leads through a constriction to the cylinder working space, i. e. at the top of the head of a ram which works with a down stroke, and which conveys, without a delaying constriction, high pressure liquid to counteract upon the ram in the direction of the return stroke, so that the ram can be caused to move at a slow speed in the opera tive direction and, when obstructed, will be sub- J'ected to the high pressure which will build up in the cylinder working space less the high pressure counteracting upon the ram.

The extent of the constriction may be made adjustable by means of a valve so as to regulate the slowness of the ram speed.

Means are preferably provided for automatically opening the delivery of the high pressure liquid to the said feed at the desired moment for slowing down the ram. For example, a valve may be interposed between-the high pressure supply and the feed which is mechanically engaged and moved by the ram or a member carried by the ram when the latter reaches a particular point in its working stroke. Such valve may be also adapted to short-circuit the constriction when not engaged by the ram..

The high pressure liquid which is conveyed to counteract upon the ram is preferably received in .an annular space around the body portion of 2 the ram under the head of the ram, the crosssectional area of the annular space being small (e. g. 10% or less) of the area of the head of the ram exposed to the cylinder working space.

When the cylinder working space is open to exhaust, high pressure liquid acting upon the annulus on the underside of the head of the ram will operate the return stroke. A separate line, passing through a main control valve, may be provided in order to deliver this high pressure liquid to the annular space during the major part of the return stroke (and subsequently to exhaust the space), the aforementioned mechanically engaged valve sealing off the high pressure supply which is controlled by it and which has effected the first part of the return stroke. The connection between the constriction and the cylinder space above the ram head passes through the main control valve, and it is a function of this valve to connect the annulus space to the cylinder space, for ram down, or to exhaust the cylinder space and connect the annulus to pressure by the separate feed for ram up.

In order to delay the initiation of the fast speed of the return stroke, the main exhaust from the cylinder working space is, according to a further feature of the invention, controlledby a prefiller valve which is actuated by a piston operated by high pressure liquid supplied through a hydraulic delay valve. The latter is constructed with a differential piston whose portion of smaller area governs by its movement a connection between high pressure supply and the prefiller value actuating piston whilst the portion of larger area operates in a dashpot device having an adjustable liquid leak between the two sides of this piston portion. This has the advantage over a delay device consisting of an adjustable constriction in a direct high pressure supply to the piston of the prefiller valve in that the liquid leak is under relatively low pressure and can therefore be of relatively large area of flow so that it has no tendency to clog, and the time delay remains constant.

A preferred embodiment of the invention is illustrated in the accompanying drawings in which:

Figs. 1a and 1b jointly constitute a diagrammatical view, partly in section of the entire hydraulic system. e V v Figs. 2, 3 and 4 are sectional views of valves included in Fig. 1. g g

Figure 5 is a diagrammatic view si ilar to Figure 1b showing the second position of the main control valve.

Referring to the drawings the lower fixed platen of a down-stroke hydraulic moulding press is indicated at I and the movable upper platen or ram table is indicated at 2. A ram 3, operable in a cylinder 4 by high pressure liquid to raise or lower the ram table, is formed with a head portion 5 and a body portion 6 beneath the head portion of smaller diameter than the latter so that an annular space I is left between the ram body and the cylinder wall. This annular space is connected by a feed conduit 8 to a chamber 9 formed around an adjustable needle valve 9a which is in turn connected by a short passage II) to an automatic piston-type valve I I hereinafter-referred to as the slow close valve. The piston I2 of valve II has a reduced portion I3 providingan annular space I3a which, when the piston is in .the position shown, connects the short passage I to a passage I4 which is in restricted communication at Ma with the chamber 9 and passage Iil through the needle valve 9a. A conduit I coneotspassage I4 to the port A of a main control valve indicated at I6.

The piston I2 of the slow close valve I I is adapted to be moved downwardly by an-arm I! carried by the'ram table2, which armis engageable with a-projection I 8 carried by the piston I2. The piston I2 is biased by a spring I9 to move upwardly when the press opens and the arm I! is disengaged from the projection I8.

Valve II is further connected at port B by a conduit 26 to a high pressure liquid supply conduit 2I which is supplied with pressure from a source (not shown) but which may be a low pressure'vane pump giving a pressure of 1000 lbs. per square inch. Conduit 2I is connected through a non-return valve 22 of known construction to port C of the main control valve I6.

This control valve comprises three axially aligned

pistons

23a, 23b and 230 formed on a common connecting rod 24 and operable in a cylinder 25 to open or close ports therein by means of a piston (not shown) operable in a cylinder 26 by air pressure and connected to the connecting rod 24. The air pressure is regulated by a cycle controller (not shown) of known construction, that is, an automatic controller of the cycle of operations of a hydraulic press, e. g. an apparatus for causing a number of air circuits to be energised or de-energised at predetermined intervals so that a cycle of operations may be repeatedly carried out in exactly the same order. The space on one side of piston 23b is in communication with the space on the other side by means of a passage 21 formed in the connecting rod 24. Suitable packing 28 at either end of the valve cylinder prevents leakage of liquid around the projecting portions of the connecting rod 24.

The main control valve is connected at port D by a conduit 29 to port E of a hydraulic delay valve generally indicated at 30 and shown in detail in Figure 2. This valve comprises a piston 3I of small diameter movable in a cylinder 32 by high pressure liquid and secured to a larger hollow piston 33 movable in a cylinder 34. This larger piston and cylinder form a dashpot device, one side of the piston, space 33a, being in communication with the other side, space 34a, by means of an adjustable needle valve 35 and

passages

36, 31, 38 and 39 formed in the valve body. Movement of the pistons is biased by a spring 40 fitted within the larger piston and bearing on the end wall which closes the cylinder 34 and which contains the needle valve. The cylinder space 34a in cylinder 34 is in communicaiii) tion with a small annular space 4I formed around a reduced portion 42 of the small piston 3I the communication being by means of a longitudinal passage 43 formed within the small piston and leading to a further reduced portion 43a of said piston and to space 34a. A non-return valve I00 is provided in a seating I We in the piston 33 which when open also connects space 33a to space 34a by way of passage 43 and the reduced portion 43a. The cylinder 32 is closed by a removable limiting stop plug 32a.

The delay valve is connected at port F by a conduit 44 to port G of a valve assembly generally indicated at 45 and shown in detail in Figure 3, which-assembly is positioned within a prefiller tank 46 secured on a platform 41 above the ram cylinder 4, the platform 41 forming the cylinder head. The valve assembly 45 comprises a piston 48 operable in a cylinder 49 by high pressure liquid to move downwardly a hollow pistonlike cross head 5011 contained in a cylinder 5I. The stem 52 ofazpoppetvalve 52a, hereinafter referred to as theprefiller valve is pressed against the underside of the .cross head bya ,light spring 55 bearing on avalve'tappet on the end of valve stem 52. The upper-"end of cylinder 49 is closed by a removable plug 53, and the lower end of cylinder 5'I is..closed 'by an end plug 54. Upward movement of the crossheadand piston 48 is biased by the light spring 55 and a larger spring 50 provided in the cross head .and bearing on the end plug 54. The lower-part of the cylinder 5| has ports therein 45aithrough which liquid from the tank .enters freely and high pressure liquid leakage past piston 48 can escape to the liquid in the tank 46 at atmosphere pressure. The said end wall has a central hole 56 therein in which is secured .a sleeve'5'lextending downwardly into a port 58 formed in a collar 59 secured in an open- 1119; 6D in the cylinder head '41. The prefiller valve 52a is reciprocable in the sleeve 51 to open and close the port 58, the head 52a of the valve being adapted to seat on a seating 6| formed on the co1lar'59. The sleeve 51 is supported centrally within the port 58 by means of a spider member 62 carried by the sleeve and reinforced by a web 63 which spider bears on the top of collar 59.

The tank 46 is connected by means of a conduit '64 to port H of the main control valve I5 and an overflow conduit 65 is provided in the tank wall leading to a drain (not shown).

The delay valve 30 is connected at port J by a conduit-66 to .a hydraulic intensifier generally indicated at :61, the conduit 66 being connected to exhaust, i. -e. the tank 46 at junction 66a by way of conduit 64. The construction of the intensifier forms no part of this invention but may be adapted to give different ratios of intensification (see British patent specification No. 634,980). A conduit 68 connects the intensifier to an air operated hydraulic inlet valve 69 (shown in detail in Figur 4) which is adapted to supply the intensifier with high pressure liquid from the pressure supply conduit 21 by way of a conduit '26 connected to port K of the inlet valve. The valve comprises a block II provided with two chambers Ila and Nb connected by a port 12 and connecting the conduit 68 to the high pressure inlet port K. The port "I2 is closable by a poppet valve member 13 which is reciprocated by a hollow piston 14 the .head of which abuts against the end of the stem 15' of the valve member 13. The piston I4 is operable in a cylinder I6 by air pressure and is biased by a spring 11.

The air pressure for operating piston 14 may be regulated by manual means or by the cycle controller (not shown) regulating the main control valve.

A conduit I connects the output side of the intensifier to the supply conduit 2I at a junction I9 on the main control valve side of the nonreturn valve 22 and to the conduit 20 leading to the valve II.

The cylinder working space 89 in the ram cylinder 4 is connected by conduit F8 to port L of the main control valve.

The operation of the moulding press by means of the hydraulic circuit and devices described above is as follows:

One cycle of operation of the press, i. e., closing and opening of the moulds is effected in 5 distinct stages which are respectively (1) fast closing of the press, (2) slow closin of the press as it approaches the closed position, (3) press closed and intensification applied, (4) slow opening of press and (5) fast opening of press.

In the drawings the press is shown in the last of these stages, stage 5, with the ram 3 nearing completion of its upward stroke in the cylinder 4. The prefiller valve 52a has been moved downwardly to open the port 53 in the cylinder head by high pressure liquid at 1000 lbs. per square inch, hereinafter referred to as the circuit pressure, which has been supplied to the piston 48 of the valve assembly 45 by the pressure pump (not shown) by way of the pressure conduit 2|, port C in the main control valve I5, the passage 21 in the connecting rod 24 of pistons 23a, 21-, c, of the valve I6, port D in the valve IS, the conduit 29 leading to port E of the delay valve 39, cylinder 32 of this valve (where it has moved the piston 3| to open port F) and through port F to conduit 44 leading to port G of the valve assembly 45. Liquid at atmospheric pressure in the cylinder working space 83 above ram 3 therefore passes through port 58 to exhaust, i. e., into the tank 46.

The main control valve, when in the position shown, permits high pressure liquid at circuit pressure entering at port C from the conduit 2i, to pass to port A in the valve and then through conduit I5, the passage I4, the annular space I3a in the slow close valve now acting as a channel, passage Iii, chamber 9 of the needle valve 5a and conduit 8 to the annular space I around the body 6 of ram 3. As the cam arm I? is not in contact with the projection I8 of piston I2 of the slow close valve II, the piston is in its uppermost position, as shown, and has cut off high pressure liquid entering port B from conduit 2! The cylinder space 85 is also connected to exhaust, i. e. the tank 45, by means of conduit 18, port L in the main control valve I6, cylinder and port H of this valve I6 and conduit 64. Port H is permanently connected to tank 46 way of conduit 64.

Port J in the delay valve 39 is permanently connected to tank 45 by way of conduit 65. The passages 35, 3'1, 38, 39 in the valve body and the spaces 33a. and 34a on both sides of the piston 33 contain liquid at atmospheric pressure.

High pressure liquid has been cut off from the intensifier Bl by the valve member '33 of the inlet valve 65! closing on its seat 12 as the spring 'Il' has returned the piston E4 to the position shown. This is because air pressure to cylinder 75 has been cut off by the regulating cycle controller or by manual means. The intensified pressure in the system is reduced and the liquid pressure in conduit 68 has fallen to a low value.

When the ram 3 reaches the top of its stroke in cylinder 4 the whole circuit is static until the main control valve I6 is next moved to the ram down position. 'The cycle of operation is therefore ready to recommence on stage 1 of the cycle.

Stage 1.-Fast closing of press The main control valve I5 is operated, by means of air pressure moving the piston in cylinder 25 and regulated by the cycle controller to the ram down position. In this position, as shown in Figure 5, the

pistons

23a, 23b and 23c are moved to the left in the drawing so that piston 23b cuts off, at port 0, the high pressure liquid at circuit pressure passing to the annular space I around the body 6 of the ram 3 by way of port A and conduit I5, slow close valve I I and conduit 8 as already described. The annular space 1 is then connected to the cylinder space 80 above the ram 3 by way of conduit I5, port A in the main control valve IS, the space in the cylinder 25 around the connecting rod 24 between

pistons

23a and 23b, port L and conduit I8. At the same time high pressure liquid passing by way of port D, the conduit 29 and port E of the delay valve 30 to port G of the valve assembly 45 in tank 46, is out off at port D and the spring in the delay valve returns the large piston 33 from the position shown in the drawing, to the other end of the cylinder 34. The non-return valve I30 opens during this movement of piston 33 and liquid passes directly from space 34a through passage 43 and valve seating IIIIla to space 33a, thus bypassing the

passages

36, 31, 38 and 33 in the valve body and the needle valve 35, and allowing the spring to return the piston quickly, almost with a snap action.

The annular space 4| formed around the reduced portion 42 of the small piston 3| is now placed in communication with port F and conduit 44 leading to port G of the valve assembly 45, and cylinder I9 is therefore connected to exhaust by way of port F, passage 43 formed in the small piston 3|, space 34a of cylinder 34 and passage 39 leading to port J. The intensifier remains inoperative and high pressure liquid, at circuit pressure, remains in conduit 20.

The large spring 50 (Fig. 3) in the valve as sembly 45 returns quickly the cross head a and the piston 48 to their uppermost position in cylinders 49 and BI respectively and the crosshead is moved clear of the valve tappet on the end of valve stem 52. This allows the prefiller valve 52a to be reseated gently and positively by the light spring 55 only. As the ram 3 falls quickly by gravity the bulk of the liquid in the tank is drawn through port 58 into the cylinder working space 81), valve 52a opening as atmospheric pressure acts on the back of the valve head against the action of spring 55.

Stage 2.Slow closing of press As the ram 3 descends, and at a predetermined position in its descent, the arm I! carried by the ram table 2 engages the projection I8 carried by the piston I2 in the slow close valve I I and moves the piston downwardly against the action of spring I9. The upper part of piston I2 cuts off the direct communication between conduit 3 and conduit I5 that existed by way of passage I0, annular space I3a and passage I4, and therefore cuts 01f communication between the annular space 1 around ram 3 and the cylinder working space 80. This causes the outgoing liquid from the annular space I to pass to conduit I5 by way of the constriction at Ma between the needle valve "chamber 9 and passage N and consequently the quick descent of the ram 3 is abruptly slowed down. At the same time, however, the lower part of piston l2 clears port B and the high pressure liquid in conduit 20 passes, by way of annular space 13a of piston l2, passage l0, chamber 9 and conduit 8, to the annular space I so that not only is the quick descent of the ram slowed down, but instantly under the high pressure of the liquid in the annular space 1 all downward movement of the ram is stopped and the ram tends to move upwardly. It cannot do this, however, because the prefiller valve 52a, under the pressure of liquid in the cylinder space 80, instantly shuts like a non-return valve, and the cylinder space 80 is than closed except for the connection to the high pressure liquid in conduit 8 by way of conduit 18, ports L and A of the main control valve i0, conduit 15, passage l0, and the constriction at Ma, leading to the chamber 9. A pressure is thus built up in the cylinder space 80 depending for its intensity on the ratio between the ram area and the annular space area. This pressure is approximately t; that of the circuit operating pressure, which in this case is 1000 lbs. per square inch, and thus the pressure of the liquid in the cylinder space 80 will be approximately 100 lbs. per square inch. High pressure liquid will, therefore, leak through the constriction at Ma and pass to the cylinder space 80 by way of conduits l5 and i and the main control valve 66, and the ram will now move downward slowly. The instant the ram table 2 is checked by an obstruction such as the moulds of the press meeting, the pressure of liquid in the cylinder space 80 quickly builds up, due to the leak or" liquid through the constriction at to the circuit pressure of 1000 lbs. per square inch, and the pressure in the space 80 and the annular space i is equalised. The effective area or" the ram for the pressing operation will then be that of the body portion projecting through the cylinder 4, i. e. about 90% of the diameter of the head portion 5 of the ram.

Stage 3.Pre'ssi'ng and intensification The switching in and out of the intensifier 67 at this stage of the cycle, may, as already stated, he eiiected by manual operation or by the cycle controller (not shown) regulating the main control valve #0. switching in and out is done separately so that greater flexibility of the operation is obtained. It is clearly undersirable to have a continuously acting intensifier working unnecessarily (i. e. lifting the press or coming in early during the slow close stage etc). Apart from this, the wear on the valves will be less and the needle valve will be less and the needle valve in the slow close valve II will control flows much better than at the circuit pressure, i. e. 1000 lbs. per square inch than at the 2000 lbs. or 3000 lbs. per square inch obtained from the intensifier. Intensification, therefore, only takes place as a final clamp to the moulds after the press is closed and pressure already applied to the moulds by the circuit high pressure.

For hand operation the intensifier may be brought in by a special valve operated automatically by the pressure in the cylinder space 80. For example, the intensifier is energised when the pressure in the space 80 reaches 600 lbs. per square inch.

As an example, the moulds may be brought together at a pressure of 50 tons and after an dwell the pressure liquid can be stepped In both cases it is desired that the up to 100 or 150 tons at a 2 to 1 or 3 to 1 ratio by the intensifier. Air pressure in the inlet valve moves the piston 14 of the inlet valve 69 against the action of spring 11 and moves valve member 13 off its seat to open the port 12 and connect the conduit 68 to port K. High pressure liquid at circuit pressure, 1. e. 1000 lbs. per square inch passes from the high pressure supply conduit 2| by way of conduit 70, port K, chambers Ha and Nb and conduit 68 to the intensifier. Intensified high pressure liquid at 2000-3000 lbs. per square inch, depending on the degree of intensification required, passes from the intensifier, by way of conduit I20, junction 19 and conduit 20, to the slow close valve i i. From thence it passes by way of annularspace [3a, passage l0, chamber 9 and conduit 8 to the annular space 1, and by way of the constriction at Ma, conduit l5, ports A and L of the main control valve I6 and conduit 18 to the cylinder space 00. Pressure is thus equal on the ram head 5 and in the annular space I. After the required period of intensification the intensifier is switched out of the circuit (by manual means or by the cycle controller as hereinbe'fore stated). When air pressure to the piston 74 is cut off the spring :7 returns the piston to the top of the cylinder, and the valve member 13 is reseated by the high pressure liquid acting upon its underside. The intensifier is connected to exhaust by way of conduits 66 and 65, and the intensified pressure in the circuit is reduced to circuit pressure, i. e. 1000 lbs. per square inch.

Stage 4.*Slow opening of press Air pressure regulated by the cycle controller is cut off from the cylinder 26 and the piston therein moves to the right and through connecting rod 24 the main control valve is operated to ram up position. In this position the

pistons

23a, 23b and 230 are moved to the right to restore them to the positions shown in Fig. l of the drawing.

Three things now happen: (1) The cylinder space is connected to exhaust, i. e. the tank 46 by way of conduit 78, ports L and H of the main control valve I6, and conduit 64; (2) high pressure liquid at circuit pressure, i. e., 1000 lbs. per square inch is connected to the annular space 1 by way of conduit 20, the annular space 13a in the slow close valve Ii, passage i0, chamber 9, and conduit 8, and by way of ports C and A of the main control valve 15, conduit [5, passage 1 and the constriction at Ma into chamber 9; (3) high pressure liquid at port C is connected by way of passage 21 in the connecting rod 24 to the space between pistons 23b and 230 which is in communication with port D and then passes through conduit 29 to cylinder 32 of the delay valve 30 by way of port E.

The passages through the main control valve for the liquid being exhausted from the cylinder space 80, (these are ports L and H and the an nular space around the connecting rod 24 in the cylinder 25), are inadequate for rapid flow, particularly that from the comparatively low pressure lbs. per square inch) that exists in the cylinder space 80 so the ram 3 begins to move upwards slowly. The liquid at circuit pressure passll'lg through the constriction at Ma to the annular space 1 by way of conduit 8 is unimportant as long as the slow close valve H is engaged by the cam arm I! and the liquid is supplied direct to the space 1. As the ram 3 moves upwardly the piston I2 is urged upwardly by the action of the spring l9 and port B is gradually cut off from space I 3a. When the ram 3 has moved upwardly far enough for the lower part of piston l 2 to completely cut off the annular space l3a from the liquid, at circuit pressure, at port B, the liquid at circuit pressure passing through the main control valve and conduits l5 and 8 to the annular space I is the only motive power to raise the ram 3, and as this passes to the annular space I by way of the constriction at Ma, as already explained, the upward movement of the ram 3 is still very slow.

At the same time the small piston 3| in the delay valve is moved against the action of the spring 48 by the high pressure liquid at circuit pressure entering at port E. The large piston 33 must also move and to do this the liquid in the space 33a must be forced through the needle valve and by way of

passages

36, 31, 3B and 3-9 in the valve body pass back to space 34a on the other side of the large piston 33. Therefore, the liquid in space 33a is placed under a slight pressure. In Fig. 2 of the drawing the ratio of areas of the small and

large pistons

31 and 33 respectively is approximately 1 to 30 so that the pressure in space 33a is only approximately 65 lbs. per square inch. As the liquid under pressure in space 33a is forced through the needle valve 35 into passage 35 the reduction in pressure which occurs ensures that the period of delay is constant. A reasonable period of delay, for example, is approximately 1 to 2 seconds. As the pistons 3i and 33 move under the circuit pressure in the cylinder 32 the piston 3| clears port F and the liquid at circuit pressure passes through conduit 44 and port G of the valve assembly 45 and acts upon the piston 38 in cylinder 39. Piston 48 is moved downwardly against the action of the springs 50 and and the prefiller valve 52a is moved oii its seat (H. The high pressure liquid in the cylinder space 80 at a pressure of about 10% that of circuit pressure, i. e., 100 lbs. per square inch passes through port 58 now open and this allows the ram 3 to move upwards quickly.

The cycle of operation of the press has now reached stage 5 which is fast opening of the press and has been described above.

The cycle is now ready for repetition.

The hydraulic moulding press circuit described not only produces a press that can be operated by hand with the greatest of ease, as the operator has not to perform any elaborateoperations with the controls to obtain the most delicate mould closing and opening, but the same delicacy of action can be obtained from the simplest cycle controller. With automatic operation, only two types of intelligence need be converted from the cycle controller to the main control valve, i. e. either up or down.

The supply pressure is easily obtainable from a simple low pressure vane pump, and one such pump may supply 12 presses and circuits as described with eiliciency.

The lifting of the ram by pressure applied to the annular space 1, means that no push-back rams are needed and servicing is reduced. Presses having push-back rams can be adapted to use the circuit described herein, the cylinder space of the push-back rams being substituted everywhere for the annular space 1. A second hydraulic cylinder may be fitted to the lower platen for transfer moulding.

The combination of the various components described above is cheap to make, simple and trouble-free to operate and capable of carrying 10 out the most intricate moulding technique under automatic control. It is versatile, not only in moulding technique but also in pressure application, when the variable ratio intensifier is used, as it combines in one press three loadings, i. e. 50, and tons without the expense of individual variable pumps or the power wasting character of reducing valves.

I claim: 1. In a hydraulic operating circuit having a cylinder and a ram reciprocable therein, said ram having a head portion and a rod portion, said head portion dividing said cylinder into a head chamber and a rod chamber, said ram being biased to move relatively freely in an operative stroke away from said head chamber and movable in the opposite direction in a return stroke, a high pressure liquid feed means for said ram, a source of high pressure liquid connected to said feed means, means controlling the supply of high pressure liquid to said feed means, a first high pressure liquid feed passage connecting said feed means to said rod chamber, a second high pressure liquid feed passage for connecting said source to said head chamber, means providing a constriction between said controlling means and said second high pressure feed passage, means operative'by said ram when it reaches a predetermined point in its operative stroke for operating said controlling. means to convey pressure liquid through saidv first high pressure feed passage to said rod chamber to subject said ram to a counteracting force in the direction of the return stroke of the ram and to simultaneously supply pressure liquid through said constriction and said second high pressure liquid passage to said head chamber, the pressure area of said ram subject to pressure in said head chamber being greater than the area of said ram subjected to pressure in said rod chamber whereby said ram in its operative stroke beyond said predetermined point will move slowly depending upon the rate of flow of liquid through said constriction, and whereby when movement of the ram is substantially halted by saidcounteracting force, pressure will be built up in said head chamber to exert on the ram a force equal to that exerted by the ram by pressure in said head chamber less said counteracting force.

2. Means for controlling the application of force to a hydraulic ram as claimed in claim 1 including a valve for adjusting the extent of said constriction so as to regulate the slowness of the rams speed.

3. Means for controlling the application of pressure to a hydraulic ram as claimed in claim 1 in which said controlling means comprises a valve interposed between said source of high pressure liquid and said high pressure liquid feed means, said means for operating said con-trolling means comprises portions carried by said ram and said valve and engage-able with each other in the operative stroke of said ram when said predetermined point is reached.

4. Means for controlling the application of pressure to a hydraulic rain as claimed in claim 1 including an exhaust valve in said head chamber, and means for opening said exhaust valve during the return stroke of said ram.

5. Means for controlling the application of pressure to a hydraulic ram as claimed in claim 1 including an exhaust valve in said head chamber, and hydraulically operated means for opening said exhaust valve comprising a cylinder, a piston therein mechanically engaging said ex- H haust valve, and means for introducing pressure liquid into said last-named cylinder.

6. Means for controlling the application of pressure ts a hydraulic ram as claimed in claim 1 including an exhaust valve in said head chamber, and hydraulically operated means for opening said exhaust valve comprising a cylinder, a piston therein mechanically engaging said exhaust valve, means for introducing pressure liquid into said last-named cylinder, said means for introducing pressure fluid into said last-named cylinder comprising ahigh pressure liquid feed passage, and automatic valve means operative during a return stroke of said-ram for supplying high pressure liquid to said last-named liquid feed passage.

7. Means for controlling the application of pressure to a hydraulic ram as claimed, in claim 1 including anexhaust valve in said head chamber, and hydraulically operated meansv for opening said exhaust valve comprising a cylinder, a piston therein mechanically engaging said exhaust valve, means for introducing pressure liquid into said last-named cylinder, said means for introducing pressure liquid into said last-named cylinder comprising ahigh pressure liquid feed passage, and automatic hydraulic valve means for connecting said source of high pressure liquid to said last-named feed passage during a return movement of said ram, said hydraulic valve means comprising a, differential piston unit formed with a piston of large area and a piston of smaller area, cylinders in whcih such pistons reciprocate, the cylinder for said larger piston having a chamber on each side or such piston and the cylinder for the smaller piston having a chamber in one end thereof connected to said source of high pressure liquid and to said lastnamed high pressure liquid feed passage whereby movement of the piston of smaller area controls the supply of high pressure liquid from said source to said last-named high pressure liquid feed passa e, means connecting the chamber at one side of said piston of larger area with said last-named high pressure feed passage, a further liquid passage connecting the chambers of the cylinder of said larger piston, and an adjustable liquid leak in said last-namedpassage for controlling the speed of movement of saidlarger piston and thus of said smaller piston.

8. In a hydraulic operating circuithaving a cylinder and a ram reciprocable therein andhaving a head portion above which is a head chamber,

said ram below said head being reduced indiameter to provide a rod chamber, saidram bein biased for movement in anoperative stroke away from said head chamber and being movablein the opposite direction in a return stroke, conduit means affording relatively unrestricted ccmrnunication between said chambers through said conduit means during a substantial initial portionof the operative stroke of said ram, a. normally inoperative constriction operative for constricting communication between said chambers through said conduit means, and means operative by said ram at a predetermined point in its operative stroke for rendering said constricting means operative and for supplying pressure liquid tosaid conduit means between said constricting means and said rod chamber whereby, when said lastnamed means becomes operative, pressure in said rod chamber will substantially halt movement of said ram whereupon the flow of pressure liquid through said constricting means will build up substantial pressure in saidhead chamber to move said ram against pressure. in said rod chamber.

9. In a hydraulic apparatus according to claim 8, a liquid tank, said cylinder having a port between said head chamber and said tank, a valve controlling communication through said port, means biasing said valve to closed position and against which biasin means said valve opens to admit liquid from said tank to said head chamber upon an operating stroke of said ram, and means for positively opening said valve forthe displacement of liquid from said head chamber to said tank upon a return stroke of said ram.

WALTER ROBERT GROVES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 714,994 Baldwin Dec. 2, 1902 836,347 Tittelbach Nov. 20, 1906 1,585,529 Boving May 18, 1926 1,940,668 Ernst Dec. 26, 1933 1,946,503 Schafer Feb. 13, 1934 2,018,977 Spellman et al Oct. 29, 1935 2,285,069 Vickers June 2, 1942 2,335,809 Stacy Nov. 30, 1943 2,365,743 Curtis Dec. 26, 1944 2,368,769 Muller Feb. 6, 1945 2,465,758 Sedgwick et al. Mar. 29, 1949