US2403391A - Hydraulic press - Google Patents

Description

2 Sheets-Sheet l w. P. Mum HYDRAULIC PRESS Filed June 13, 1942 Jul 2, 1946.

INVENTOR may 2 Sheets-Sheet 2 Filed June 15, 1942 HNVENTOR V MUER BY I,

ATTOBNE Patented July 2, 1946 HYDRAULIC PRESS William P. Muir, Hampstead, Quebec, Canada, as-

, signor to Dominion Engineering Works Limited,

La'chine, Quebec, Canada Application June 13, 1942, Serial No. 446,994 In Canada April 11, 1942 2 Claims. 1

This invention relates to control mechanism for regulating the tonnage or working pressure of a hydraulic press to suit the work being done and to prevent overloading of the work or tooling.

Various methods of regulating the tonnage or working pressure of hydraulic presses have been proposed and adopted prior to this invention. In some cases the discharge of a variable stroke pump which feeds the hydraulic press circult is gradually reduced as the working pressure increases so that, when the desired maximum working pressure is attained, the pump stroke will be Just suflicient to maintain this maximum pressure against leakage. In other cases the discharge of a variable stroke reversible pump feeding the hydraulic circuit is maintained substantially constant until the working pressure is'built up to the required maximum value whereupon the pump discharge is stopped or reversed through the agency of a suitable pressure operated pump stroke neutralizing and reversing mechanism. In

other cases pressure-operated controls are pro-, vided for automatically operating the main control valve of the press to transfer the pump discharge from the pressing cylinder to the return cylinder or cylinders when the working pressure in the pressing cylinder has been built up to the desiredmaximum value, such operation of the main control'valve also serving to establish connections through which pressure fluid is relieved from the pressing cylinder during the return stroke of the press.

The foregoing and other methods of "tonnage regulation now practiced are open to the objection that there is an appreciable time lag between the development of the desired maximum working pressure in the pressing cylinder and the actual operation of the pump stroke adjusting mechanism, control valve, or other control element relied upon to limit the rise of the working pressure. If there is any irregularity'in the op-- eration of such pump stroke adjusting mechanism, valve or other control element, th delayed action thereof may permit the working pressure to exceed the desired maximum value to a sufficient extent to overload the work or tooling. The method of regulation which involves the gradual reduction of the pump discharge as the working pressur increases is also open to the objection that it slows down the building up of the working pressure vto the required maximum value' and thus reduces the operating speed of the press. 7

With the foregoing in mind, an important object of this invention is the provision of adjustable "tonnage or working pressure regulating mechanism which functions instantly and independently of the pump-stroke controlling mechanism and the main control valve to prevent furpump to be utilized in rapidly building up the working pressure to the required maximum value.

A further object is the provision of a tonnage or working pressure regulating mechanism which, while permitting the full discharge capacity of the feed pump to be utilized in building up the working pressureto the required maximum value, also includes means whereby the pump discharge is automatically reduced after the desired maxi-' mum working pressure is attained.

A further object is the provision of a "tonnage" or working pressure regulating mechanism including means for effecting either immediate or delayed operation of the main contro1 valve from a power stroke to a return stroke position, the arrangement being such that any delay or lag in the operation of said valve to its return stroke 'position has no effect on the instantaneous operation of said regulating mechanism to prevent .iurther increase of the working pressure when the latter has been built up to the desired maximum value.

A further object is the provision of a tonnage" or working pressure regulating mechanism including means whereby the operation of the reversing valve to effect a return stroke of the press may be delayed to permit the press to dwell on the work at constant pressure for as long as may be desired.

A further object is the provision of a tonnage" or working pressure regulating mechanism which functions automatically in direct and instant response to the development of a predetermined working pressure in the pressing cylinder and hydraulic circuit to prevent further rise of pressure by establishing a relief connection through which the full discharged the pump may be bypassed even when the pump is operating at maximum discharge capacity. This protects both the press and the pump from overloading under any conditions of operation.

A further object is the provision of a "tonnage or ,working pressure regulating mechanism includug a main pressure regulating relief valve through which the discharge of the feed pump is by-passed when the working pressure in the pressing cylinder and hydraulic circuit reaches a predetermined maximum value and a supplementary back pressure regulating relief valve through which the discharge-from the main relief valve is passed, said back pressure regulat- I port 40 of a main pressure regulating relief valve 4| is connected to line 20 by a suitable pipe connection. The discharge port 43 of valve 4| is connected, by suitable pipe connection 44, to the inlet port 45 of an auxiliary back pressure regulating valve 46, the discharge port 41.0f which is connected, by pipe 48, to the previously mentioned relief line 25. The valve 4|, pipes 42 and 44, valve 46 and'pipe 48 conjointly provide a valve controlled relief line connection between the main fluid line '20 of the pressing cylinder and the relief line 25. As here shown,

valve 4| comprises a casing 49 containing a ver-' tically movable valve 50 which is normally closed against its seat 5| by a valve closing spring 52, the compression of which may be varied. by adjustment of the spring compressing nut 53. The valve member 46 also comprises a casing 55 containing a valve 56 which is held to its seat 51 by a valve closing spring 58, the compression of which may beregulated by adjustment of the spring compressing nut 60. From'this it will be apparent that the valves 4| and 46 may be spring loaded by suitable adjustment of the nuts 53 and 60 to open when the fiuid pressure acting to unseat said valves reaches a predetermined maximum value. v

For present purposes it will be assumed that the spring loading of the valve 4| is adjusted so that this valve will open only when the working pressure developed in the hydraulic circuit and the pressing cylinder 1 during the working stroke of the press reaches a maximum value of approximately 2000 lbs. per square inch. The

circuit and the pressing cylinder I. In' this connection it will be readily understood that the power consumption and the load on the pump is considerably reduced by reducing the volume of the pump discharge following attainment of opening of this valve in response to theestablishment of such pressure permits the excess discharge of the pump to be passed therethrough and thus prevents further rise of pressure in the. hydraulic circuit and the pressing cylinder. In this connection it may be explained that the valve 4| is preferably made of sufllcient size to by-pass the full discharge of the pump even when the latter is working at maximum discharge capacity. The discharge from the valve 4| passes through the auxiliary back pressure relief valve 46, the spring loading of which is adjusted to maintain an intermediate pressure of, say, 200 lbs. per square inch in the relief line connection 44 between the two valves. .As hereinafter described the intermediate pressure thus established in the portion 44 of the pressure regulating relief line is utilized to operate the valve II and also the stroke regulating mechanism No of the feed pump i0. It is also available for operating other controls.

The intermediate pressure established in the portion 44 of the relief line is transmitted, through pipe 6| and valve 62, we piston 63 operating in a cylinder 64 and serves to move the piston downwardly against the resistance of the piston biasing spring 65. The piston 63 is provided with a stem or rod 66 which, during the downward movement of the piston, acts against one of the members of the toggle 39 to operate the toggle to a collapsed position ermitting the valve member |3 of valve II to be shifted to its'return stroke position by'its operating spring 35. When it is desired to permit the press to .dWell on the work for a given period subsequent to the development of the desired predetermined workin pressure, this is accomplished by operating the valve 62 to throttle the flow of pressure iluid In this way the collapsing through the line 6|. of the toggle 39 by the downward movement of the valves 4| and 46.

maximum working pressure in the system. The flow of pressure fluid through the line 10 is controlled by a suitable regulating valve When the valve element i3 of the main control valve is in its right hand or return stroke position the pressure regulating valves 4| and 46 are isolated since, in this position of valve element i3, the fluid line 20 is connected to the exhaust line 25. In the return stroke position of valve element i3, the intermediate pressure in pipe connections 44, 6| and i0 is relieved via bleed valve l2, pipe 48 and exhaust line 25.

In the foregoing arrangement the discharge from the-main pressure regulating valve 4| is so regulated by the action of the auxiliary back pressure regulating valve 46 that the desired intermediate pressure in the portion of the relief line between the two relief valves is maintained constant from the moment the valve 4| opens until the press platen 5 is operated on its return stroke. Since this intermediate pressure is maintained practically constant irrespective of the volume of discharge through the valves 4| and 46 it provides an ideal source of hydraulic energy for operating the main control valve and the pump stroke adjusting mechanism Ma.

It is important to note, at this point. that when the desired maximum working pressure is built up in the hydraulic circuit and the pressing cylinder 7, the valve 4| opens instantly to .prevent further rise of this pressure. It will thus be seen that a very close regulation of the maximum working pressure developed in the system may be obtained by appropriate adjustment of the spring loading of valve 4| and that this regulation is not aileoted by any time lag in the operation of the main control valve i to its return stroke position nor by any time lag in the operation of the pump stroke adjusting mechanism i011. Consequently, if the valves 4| and 46 are made of such size as to be capable of discharging the full capacity of the pump, it is possible to delay the operation of the main valve II to its return stroke position so as to permit the press to dwell on the Work at constant pressure for as longas may be desired. During such dwell periods the by-passing of the full pump discharge through the valves 4| and 48 prevents overloading of both the press and the I pump.

Another advantage of the arrangement described herein is that the maximum working pressure, as determined by adjustment of the valve 4|, remains constant irrespective of the setting of the valve 46 or the rate of the flow through The utilization of the intermediate pressure established between the valves 4| and 46 for reducing the pump discharge makes it possible to economize power and to prolong the life of the pump when operating at long pressure dwells.

Fig. 2 shows another embodiment of the invention in which the stem of the main control pressed air will ,7 air through an "f'v'iously mentioned air lines" and 9|. The openin: of valve 88 permits compressed air to flow to 7 valve [3 is connected to an operating piston 15 working in an air cylinder 16. The operation of piston 15 is controlled by the action. of a pilot valve 11 working in a pilot valve casing '18 to which air under pressure is delivered through a main air line 19. when the pilot valve is in the position shown in Fig. 2 air under pressure is delivered to the right hand end ofcylinder 15 through pilot valve port .88, pilot valve casing port 8!, and line 82 the air previously supplied to the right hand end of air cylinder it being exhausted through line 83 and a suitable exhaust connection 84 provided in the pilot valve 11. The air thus applied to the right hand end of cylinder 18 acts against the piston lb to operate the main control valve 13 to the power stroke position shown in Fig. 2. When the pilot valve ll is shifted to the left the line 83 is connected to the main supply line 19 through the pilot valve port at so that air under pressure is now supplied to the left hand end ofcylinder l6 to operate the piston 15 and the main control valve element iii to a return stroke position. During this latter operation of the piston 15 the air previously supplied to the right hand end of cylinder 16 is exhausted through line 82 and an exhaust port 85 provided in the pilot valve 11.

The pilot valve 'Il may be operated manually through the agency of suitable normally closed push button valves 88 and 89. As here shown the inlet ports of these push button valves are connected in parallel with each other to the main air supply line 19 through the agency of a branch connection 80. The outlet port of valve 88 is connected to the left hand end of pilot valve cylinder I8 by a fluid line 9| while the outlet port of push button valve 89 is connected by pipe line 92 to the right hand end of the pilot valve cylinder 18. From this description it will be apparent that when push button valve 88 is opened against the resistance of its valve closing spring 880:. comof the pilot valve 11 to force the pilot valve to the right. Similarly, the opening of the push button valve 88 against spring 89a causes compressed air ot be supplied to the right hand end of-the pilot valve cylinder 16 to force left. V

In the arrangement shoviir'iin Fig. 2 the intermediate pressure established in the section ll of the work-pressure regulating relief line controlled by valves H and 46 is utilized to effect automatic operation ofthe pilot valve 11 in the direction necessary to operate the main control valve 13 to its return stroke position. Inthis connection it will be noted that the line Si is connected to the left hand end of a cylinder 94 con taining a piston 95 which is normally biased to the position shown in Fig. When the piston is moved to the right by the intermediate pressure established in line GI the stem 91 of said piston engages and opens a normally closed valve 9' which controls th flow of air line "connecting the prethe left hand end of the pilot valve cylinder I8 and'to operate the pilot valve 17 to the right thereby establishing the connections necessary to operate the main control valve element-,1 3 to its return stroke position. During the return stroke of the press the air supplied to cylinder 81 is exhaunted through the bleed valve 12. 1 g

2 by the spring 98.x

I valve through which pressure fluid is routed Having thus described what I now consider to be the preferred embodiment of this invention it will be understood that various modifications may be resorted to within the scope and spirit of the appended claims.

Having thus described my invention, what I claim is:

1. A'hydraulic press including a maincontl'il} effect a working stroke of the press in one position of said valve and to efiect a return stroke of the press in another position of said valve, 2. collapsible valve-actuating toggle connected to said valve and serving, when extended, to hold said valve in its first mentioned working stroke position, a fluid pressure toggle-collapsing device comprising a cylinder and a piston working in Said cylinder and connected to said toggle, biasing means arranged to shift said valve to the secand mentioned or return stroke position upon collapse of said toggle by said piston, a fluid line through which pressure fluid is conducted from said valve to the pressing cylinder of the press in the working 'str'oke' position of the valve, an

excess-pressure relief line connected to said first.

mentioned line at a point between the pressin cylinder and said valve, a normally closed working-pressure regulating valve arranged in said relief line and adapted to be instantly opened by the pressure fluid when the working pressure in the pressing cylinder is built up to a predetermined maximum value, said relief line and pressure regulating valve being of sufllcienig capacity to carry off from said first mentioned linall the pressure fluid in excess of that required to maintain the said predetermined maximum working pressure in said pressing cylinder, 9. back presbe applied to the left hand end I the pilot valve to the sure regulating valve included in said relief line at the discharge side of the working-pressure regulating valve and functioning, in the open position of said working-pressure regulating valve, to maintain a definite intermediate pressure in a portion of the relief line located between said valves, a valve-controlled fluid transfer line connected between the cylinder of the toggle collapsing device and the portion of the relief line located between the discharge side of the working-pressure regulating valve and the inlet side of the back pressure regulating valve and a valvecontrolled by-pass line having one end connected to said fluid transfer line and the other end connected to aid relief line at the discharge side of the back pressm-e regulating valve.

2. A hydraulic press at set forth in claim 1 including a variable stroke hydraulic pump having its discharge side connected to said main control valve to supply pressure fluid to the pressing cylinder of the press in the working stroke position of said valve, said pump being equipp d with a pressure responsive stroke adjusting mechanism and a pressure fluid line through which working fluid is supplied to and exhausted from said mechanism, said line being equipped with a control valve and being connected between said stroke adjusting mechanism and the aforesaid vfluid transfer line through which fluid is supplied to and exhausted from the cylinder of the toggle collapsing device. v

Images