US2938718A

US2938718A - Hydraulic cushion for the die pad of a ram type press

Info

Publication number: US2938718A
Application number: US815832A
Authority: US
Inventors: Floyd M Williamson
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-05-26
Filing date: 1959-05-26
Publication date: 1960-05-31
Anticipated expiration: 1977-05-31

Description

May 31, 1960 F. M. WILLIAMSON 2,938,713

HYDRAULIC CUSHION FOR THE DIE PAD OF A RAM TYPE PRESS Filed May 26, 1959 Z g g- IN V EN TOR. 7' WZY/Zkmsazz FTTGH'A/EXS United States Patent HYDRAULIC CUSHION FOR THE DIE PAD OF A RAM TYPE PRESS Floyd M. Williamson, 12921 E. Jelferson Ave., Detroit 15, Mich.

Filed May 26, 1959, Ser. No. 815,832

4 Claims. (Cl. 267-1) This invention relates to hydraulic cushions for die pads of ram type presses.-

In ram type presses having conventional hydraulic cushions, the pressure relief valve tends to bounce or vibrate on closing of the press due to the sudden rise in pressure and velocity of the hydraulic fluid on the high pressure side of the system and this causes frothing of the hydraulic fluid and generates excessive heat, both of which are objectionable.

The present invention substantially eliminates such bounce or vibration of the pressure relief valve upon closing of the press and thus minimizes, if not entirely eliminates, frothing and generation of excessive heat due to such valve action.

A principal object of the invention is to provide a new and improved hydraulic cushion for die pads of ram type presses.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawing which by way of illustration shows a preferred embodiment of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used Without departing from the scope of the present invention as set forth in the appended claims.

In the drawing:

Fig. 1 is a schematic view of part of a hydraulic cushion embodying my invention; and

Fig. 2 is a schematic view illustrating the remainder of the cushion and showing a section of the pressure relief valve taken along the line 2-2 of Fig. 1.

This application is a continuation-in-part of my prior copending application Serial No. 455,270, filed September 10, 1954, for Mechanisms for Hydraulically Controlling Movement of Pads in Dies, now Patent No. 2,890,669.

A hydraulic cushion embodying my invention comprises in general one or more hydraulic cylinders 12, each provided with a reciprocating plunger or piston 14 therein arranged to react on the die pad of a ram type press, a tank 16 of hydraulic fluid under pressure, a pressure relief valve indicated generally at 18, a hydraulic fluid connection 20 between the tank 16 and the valve 18, a hydraulic fluid connection 22 between the valve 18 and each hydraulic cylinder 12 whereby hydraulic fluid under the pressure to which it is subjected in the tank 16 (say 80 to 100 pounds per square inch) is supplied to the hydraulic cylinders 12 and plungers 14 for biasing the die pad 10 to its extended position.

The hydraulic fluid connection 20 is connected at one end to the bottom of the tank 16 and at its other end to the cross passage 26 of a manifold 24. The valve 18 is provided with a plurality of parallel bores or recesses 28, each of which is connected by a passage 30 to the cross passage 26 of the manifold 24. The bores 28 are interconnected by passages 32 which form part of a one-way by-pas's around the pilot valve indicated generally at 34 and the unloading valve indicated generally at 36. Each of the hydraulic fluid connections 22 is connected to a manifold 38 having a manifold passage 40 therein. A passage 42 extends between the manifold passage 40 and one end of each of the bores 28. The by-pass just referred to includes a cross passage 44 intersecting and interconnecting the passages 42 and a plurality of passages 46 extending between the cross passage 44 and the passages 32.

A one-Way check valve 48 associated with each passage 46 permits flow of hydraulic fluid from the passage 32 through the passage 46 into the cross passage 44 and the passages 42 under the pressure to which the hydraulic fluid in the tank 16 is subjected, but prevents return flow of such fluid from the passage 44 to the passage 32 through the passages 46. The

valves

34,36 and 48 normally separate the low pressure side of the system from the high pressure side thereof where the pressure may rise during the closing of the press to 1000 pounds per square inch or whatever pressure the valve 18 is set for. Thus hydraulic fluid under the pressure to which it is subjected in the tank 16 reacts on the plungers 14 for biasing the die pad to its extended position.

Displacement of the hydraulic fluid in the cylinders 12 by movement of the plunger 14 due to movement of the die pad 10 upon closing of the press is controlled by the unloading valve 36 and the pilot valve 34 which together form the pressure relief valve 18 whereby suitable resistance to displacement of hydraulic fluid from the cylinders 12 and the high pressure side of the system may be obtained so as to provide a hydraulic cushion for the die pad 10.

p The pilot valve 34 includes a piston valve member 50 which is normally seated on an annular seat 52 provided on a valve member 54, the seat 52 surrounding one end of a passage 56 in the valve member 54. The piston valve member 50 is reciprocable in a bore 58 provided in the body or block 60 of the valve 18, and a spring 62 disposed in the bore 58 is arranged to react on the piston valve member 50 and on one end of a pin 64 for seating the piston valve member 50 on its seat 52. The pin 64 is axially movable in a guide 66 secured in place by cap 68 suitably secured to the body 60, and an adjusting screw 70 is provided for reacting on the head of the pin 64 whereby the pressure at which the pilot valve 34 opens may be adjusted.

The unloading valve 36 comprises a cup-shaped valve member 72 and a plurality of circular valve ports 74 provided in the side wall of a sleeve 76 disposed within the bore 28 below the valve member 54. The ports 74 on the upstream side thereof are provided with V-shaped notches in the edges thereof first exposed on opening movement of valve member 72 so as to minimize frothing of the high pressure fluid as it escapes through ports 74. The sleeve 76 is of such a shape as to form an annular passage 78 between the outside of the sleeve and the inside of the bore or recess 28, with which the passages 30 and 32 and the ports 74 communicate. A spring 80 confined between the sliding valve member 72 and the valve member 54 biases the valve member 72 to its lowermost position and so as to close the ports 74. The interior of the sleeve 76 forms a valve bore, one end of which communicates with oneend of the passage 56 while the other end of which communicates with one end of the passage 42 which forms a part of the hydraulic fluid connection to the hydraulic clinders 12. The valve member 72 is provided with a passage 82 therethrough, such passage being of smaller efiective cross section than that of the passage 56.

A plurality of unloading valves 36 are illustrated, the same being arranged in parallel in a by-pass around the valve 34 and being of the same construction, .With the possible exception that only one of them need be provided with a passage 82. The number of valves 36 used depends upon the hydraulic fluid capacity of the high pressure side of 'thesystem. The bores internally provided by the sleeves 76 of the'other of the valves S6 areeach connected by a passage 84 to a cross-passage'- 86 which communicates with a cross passage 90in the valve member 54 which intersects the passage 56; -A' conduit 92 around the valve 34 interconnects the bore 58 adjacent the valve seat 52 with the annular passage 78 whereby fluid which passes the valve 34 when the same is open may return through the conduit 92, the annular pass'age w78, and the passage 30 to the hydraulic connection 20.

react on the fiuid in the system to cause the plungers 14 of the hydraulic cylinders to bias the die-pad 10 to its extended position. At this time the pressure throughout the system is equalized. The springs of the check valves .48 exert only sufiicient pressure on the valves to seat the same and hence offer little resistance to flow of fluid from the passages 46 into the passages 44and 42. Upon closing of the press the die pad 10 will be moveddownwardly and react on the plungers 14 so as to displace hydraulic fluid from the cylinders 12. The displacement of such fluid from the cylinders 12 and the high pressure side 'of the system will be resisted by the pilot valve 34 and unloading valve 36. However, the pilot valve 34 will open when the pressure on the high side ofth e system exceeds the resistance for which the .pilot valve 34 is set.

The variable speed of the ram during the closing of the'press so reacts on the die pad 10 and the .plungers 14 as to cause a very rapid and sharp increase in pressure and velocity on the fluid in the high pressure side of the system which creates a sudden impact upon thevalve member 50 of the pilot valve 34, thereby suddenly'opem ing the same in such a way that the valve 50 would bounce or vibrate except for the cushioning effect obtained by the unloading valve'36 which upon opening bypasses high pressure fluid from the high pressure 'side of the system around the presure relief valve 34. The resulting pressure drop on the spring side of the unloading valve member 72 attending the initial opening of valve 34 coupled with the resistance to flow of oil through passage 82 will cause valve member 72 to travel and uncover ports '74 a short time interval after the opening of valve 34,

thereby discharging oil from the high pressure side of the system through ports 74. This dissipates the effects of the sudden increase in pressure and velocity of the hydraulic fluid and the resulting reaction on valve 50, and 7 positions the valves and 72 for the steady relief. of oil from the high pressure side of the system. I have found that this arrangement minimizes, if not entirely eliminates, frothing and generation of excessive heat due to the bouncing action of the pressure relief valve encountered in conventional hydraulic cushions, and eliminates the necessity of water cooling such valves, as is sometimes necessary.

While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the valve reciprocable in said bore and normally seating on said valve seat so as to close said passage, a second bore communicating at one end thereof with the other end of said passage, a conduit having one end thereof connected to said first bore and the other end thereof connected to a valve port in the side of said second bore adjacent the other end thereof, a springtbiased unloading valve member reciprocable in said'se'cond' bore and normally closing-saidvalve port therein, a first hydraulic lfluid xconnection between said tank and said conduit, a second hydraulic fluid connectionbetween the other end of said second bore and said hydraulic cylinder, aone-way bypass between said conduit and saidsecond hydraulic fluid connection'whereby hydraulic fluid under pressure is supplied from said tank to said hydraulic cylinder and plunger for biasing saiddie pad to its er (tended position, said unloading valve member being normally disposed between said second hydraulic connection to said second bore and the valve port in thesidethereof so as to be movable in response to the flow of hydraulic pressure fluid in said second fluid connection. produwd by movement of said plunger by said die pad upon closing of the'press, and an open passage having a portion thereof of smaller eflective cross section than that of said passage insaid valve member between said second hydraulic .fluid connection and said passage in said yalve member, a part of said by-pass including a fluid fiowpath around and in heat exchange relation with a part of said second bore whereby heat generated therein is absorbed by hydraulic fluid as it flows through said path toward said hydraulic cylinder. 7

2. Apparatus according to claim 1 wherein said second bore is provided by a sleeve in and spaced from the wall of a recess in said valve body, the space between said sleeve and recess wall forming said fluid flow path.

3'. In a ram type press having a die pad, a hydraulic cushion for said. die pad including at least one hydraulic cylinder provided with a reciprocating plunger therein arranged to react on said die pad, a tank of hydraulic fluid under pressure, a valve body having a first bore, a valve member having a passage therein, one end of which communicates with said bore, and an annular valve seat surrounding said end of said passage, a spring biased pilot valve reciprocable in said bore'and normally seating on said seat so as to close said passage, a second bore communicating at one end thereof with the other end of said passage, a conduit having one end thereof connected to said first bore adjacent said valve seat and the other end thereof connected to a plurality of valve ports in the side of said second bore adjacent the other end thereof, a spring biased cup-shaped unloading valve mem- ..ber reciprocable in said second bore and normally'closing said valve ports therein, a first hydraulic fluid connection'between said tank and said conduit, a second hydraulic fluid connection between the other end' ofsaid .second bore and said hydraulic cylinder, a one-way bypass between said conduit and said second hydraulic fluid connection whereby hydraulic fluid under pressure is supplied from said tank to said hydraulic cylinder and plunger for biasing said die pad to its extended position, .said unloading valve member being normally disposed between saidsecond hydraulic connection tosaid; second bore and the valve ports in the side thereof so asto be movable in response to the flow of hydraulic pressure fluid in said second fluid connection produced by'movement of. said plunger by said die pad upon closing of the press, said second bore and the valve ports therein and the unloading valve'member reciprocable in said second bore comprising an. unloading valve, a plurality of such unloading: valves being arranged in; parallel between said second hydraulic connection and said conduit, one of said unloading valve members having a passage therethrough of smaller effective cross section than that of said passage in said valve member.

iOn for said'die'pad including at least one'hydraulic 5 cylinder provided with a reciprocating plunger therein arranged to react on said die pad; a tank of hydraulic fluid under pressure, a fluid connection between said tank and said cylinder having a check valve therein whereby hydraulic fluid under pressure is supplied from said tank to said cylinder and plunger for biasing said die pad to its extended position but return flow through such connection is prevented, a second fluid connection between said tank and cylinder having a pressure relief valve therein whereby resistance to displacement of hydraulic fluid from the cylinder is provided so as to form a hydraulic cushion for said die pad, and a by-pass around said pressure relief valve and including a plurality of normally closed unloading valves disposed in parallel in said second fluid connection between said pressure relief valve and said cylinder, said unloading valves opening in response to a predetermined pressure differential across said valve following the opening of said pressure relief valve.

References Cited in the file of this patent UNITED STATES PATENTS 1,849,690 Rode Mar. 15, 1932 2,300,162 Maude Oct. 27, 1942 2,901,238 Williamson Aug. 25, 1959