US2854919A - Hydraulic press - Google Patents

Description

M. vL'rAvsK 'HYDRAULIC PRESS Filed Feb. 28, 1955 3 .I 13 5 l I 7 2 Y y 14 1 A i llnnllllm .mlmnh United States Patent mace HYDRAULIC PRESS Milan Vltavsky, Bratislava, Czechoslovakia, assignor to CKD, Ceska Lipa, narodni poduik, Ceska Lips, Czecho- Slovakia Application February 2S, 1955, Serial No. 491,065

2 Claims. (Cl. 1D0-269) This invention relates generally to hydraulic presses, and more particularly to hydraulic presses provided with minimum valve pressure accumulator means for effecting a rapid travel of the press ram during the final portion of its pressing stroke.

In hydraulic presses of various types, more particularly in welding presses and in presses for moulding plastic materials, it is necessary to provide for rapid progression of the press ram as soon as there appears a decrease of the inherent resistance of the moulded material as a result of its melting or softening. This action in the past has been obtained in the case of welding presses by the arrangement of a strong spring between the press piston and the press plate and in the case of presses for moulding plastic materials by the provision of a pneumatic accumulator. With such arrangements it may be necessary, in the case of welding presses, to reset the spring for changing its tension as the pressing force is altered, and, in the case of presses for working plastic materials, it may be necessary to re-adjust the control device maintaining the pressure in the pneumatic accumulator.

The object of the present invention is to provide a device which will automatically adapt itself to any change of the pressing force. A further object of the invention is to provide an improved hydraulic press system which will provide for quick completion of the pressure stroke of the ram upon decrease in material resistance by accumulator means arranged in the head of the press cylinder and acting directly upon the press piston.

The invention is diagrammatically illustrated in the accompanying drawing wherein the device is shown partly in section and partly in elevation.

Referring now to the drawing, the vertical press cylinder 1 is divided into an upper accumulator tank 6 and a lower piston chamber by a horizontal intermediate transverse wall. Slidably movable in the piston chamber is a press piston ram 2, the lower extremity of which extends through the bottom wall of the cylinder and is adapted to come into pressing engagement with a workpiece adapted to be positioned on the lower stationary platform. The intermediate transverse Wall has an opening therein providing communication between the tank 6 and the portion 5 of the piston chamber above the piston head of the piston ram 2. A minimum valve member 3 vertically movable within the accumulator tank 6 is biased by spring 4 into seating engagement with the opening in the transverse wall to close the same. The ram 2 is controlled by a slide valve 12 Slidably movable in housing 7 supplied by oil or other suitable hydraulic uid from a'purnp 8. The force of the compression spring 4 of the minimum valve can be adjusted by means of a set screw 16 threadably mounted in the top wall of the cylinder 1. During the pressing stroke of the ram the control lever 11 is pivoted clockwise either manually or automatically to the position shown in the drawing to displace the slide valve 12 to its upper position, thus enabling the hydraulic uid to enter the space above the ram 2 and after a certain pressure is attained 2,854,919 Patented Oct. 7, 1958 valve 3 will open partially to admit uid into the accumulator tank 6. As soon as the pressure in chamber portion 5 attains the magnitude of the adjusted moulding pressure, the minimum valve member 3 opens fully, as the upward pressure on the valve exceeds the downward pressure of the compression spring 4. In the space above the level of the hydraulic tluid in the tank 6 there is provided a permanent filling of compressed nitrogen or air which is compressed further by the hydraulic uid admitted by valve 3 to constitute a small pneumatic accumulator. The introduction of gas into the accumulator tank 6 is controlled by valve 15 in gas supply line 15a. Thus, when the piston is put under pressure by the pressure uid in chamber portion 5 the rapid completion of the piston pressing stroke will commence as soon as a decrease in the resistance of the moulded material occurs. This action or the piston travel is very quick, since the compressed gas and the tluid in the accumulator exerts pressure from the tank 6 directly through the open minimum valve 3 into the chamber portion 5. Once the pressing operation has been completed, the control lever 11 is rotated counter-clockwise to displace the slide valve 12 to its lower position, and hydraulic uid enters the lifting space 9 of the press cylinder 1 beneath the piston head of ram 2. The pressure of chamber portion 5 is reduced by communication thereof with the tank 14 through the slide valve housing 7 and discharge pipe 10. During this procedure a part of the hydraulic uid escapes out of the tank 6 through the opening in the transverse wall 1a. On a decrease of pressure inside the tank 6 below a magnitude corresponding to the force of the compression spring 4, the minimum valve 3 closes automatically thus preventing any further decrease of the pressure inside the tank 6 and any escape of compressed gas contained therein. Therefore a change in the moulding pressure brings about a pressure in the accumulator tank 6 of a magnitude equalling that of the moulding operation pressure.

As soon as the press piston ram 2 reaches its top position, the bottom edge of the piston head opens an overow conduit containing the return valve 13 and the hydraulic Huid escapes out of the chamber portion 9 through the return valve 13 and further through the housing 7 of the slide Valve 12 into the discharge pipe 10 and thence into the tank 14.

After a certain pressure is attained in the chamber 5, the valve 3 admits hydraulic uid to the tank 6 simultaneously with an increase in pressure in the chamber 5. The admission of tluid to the tank 6 results in compression of the gas in that tank, thereby reducing the rate of increase in downward pressure on the head of the ram 2. This feature is important in Welding in that it reduces damage caused by shock.

I claim:

l. A hydraulic press comprising a vertical cylindrical housing having top and bottom walls and a transverse wall dividing said housing into an upper accumulator tank and a lower piston cylinder, said transverse wall having an opening therein providing communication between said piston cylinder and said accumulator tank; a piston ram vertically reciprocable in said piston cylinder, the lower portion of said ram extending through an openin in the bottom wall of said housing and the lower extremity of said piston ram being arranged to come into pressing engagement with a stationary workpiece; means supplying hydraulic uid under pressure to the piston cylinder, said fluid supplying means including a slide valve for controlling the direction of piston ram travel within said cylinder; means supplying a gaseous uid under pressure into said accumulator tank; and minimum valve means in said accumulator tank controlling the opening in the transverse wall between the accumulator 3 tank 'ancl the piston cylinder 'comprising a vertically movable valve member located between 'th'e -top wall 'of isaid cylindrical housing and said transverse wall, spring means in said accumulator tank normally biasing .said valve member downwardly into 'seating engagement .with 'said transverse wall opening vto 'cl'ose the same, and 'an 'adjust- 'ing Vscrew 'threaaljly mounted within and extending through an opening inthe top Wall of said housing with 'the operating portion 'thereof extending 'above said housing fop 'Wall "for 'adjusting 'the t'ension "of sa'id spring to 'control the 'minimum pre's'sure 'of h'e hydraulic uid in .the piston Ycylinder vabo've'th'e piston ra'rn which will 'un- 'se'at said "valve member.

including conduit return meansf'or discharging hydraulic 15 ,4 uid in said piston cylinder below the piston head of the ram to said hydraulic uid supply means when -said piston ram is returned to its uppermost position in the piston cylinder after completion of a pressing stroke.

References Cited in the le of this patent UNITED STATES PATENTS 1,765,627 Stacy June 24, 1930 1,895,710 Ernst et a1 Ian. 31, 1933 2,164,640 Cannon --.ce Ily 4,1939

2,259,781 Shaw et al Oct. 21,1941

FOREIGN PATENTS 623,401 Great Britain May 17, 1949

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