US2882766A

US2882766A - Control mechanism for hydraulic presses

Info

Publication number: US2882766A
Application number: US526155A
Authority: US
Inventors: Towler Frank Hathorn
Original assignee: Electraulic Presses Ltd
Current assignee: Electraulic Presses Ltd
Priority date: 1955-08-03
Filing date: 1955-08-03
Publication date: 1959-04-21
Anticipated expiration: 1976-04-21

Description

April 21, 1959 J. M. TOWLER 2,382,766

v CONTROL MECHANISM FOR HYDRAULIC PRESSES Fil ed Aug. :5, 1955 4 Sheets-Sheet 1 0 nwszvme I JOHN Malawi-I ,TOWLER, DECEASED 8) FRAN K HATMR Tou/LER, EKECUTOR Filed Aug. 3, 1955 April 21, 1959 J; M.- TOWLER, 2,882,766

CONTROL MECHANISM FOR HYDRAULIC PRESSES M yE/vroe JOHN mumps Town-1R, DECEASED 5) F'IPANK HATHORN TowLER, EYECUTOR )4 Tree/v96 4 Sheets-Sheet 2 April 21, 1959 J. M. TQWLER 2,882;766

CONTROL MECHANISM FOR HYDRAULIC PRESSES Filed Aug. 3, 1955 4 Sheets-Sheet 3 JOHN MAURICE FOWLER, DECEASED BY FRANK HATHORN TDWLER, EXECUTOR ATTORNEX April 21, 1959 J. M. TOWLER 2,882,765

CONTROL MECHANISM FOR HYDRAULIC PRESSES Filed Aug. 3, 1955 4 Sheets-Sheet 4 m vs/vroe JOHN MAumcE TOM/LEI?) DECEASED 8) FRANK HATHORN TOWLER, EKECUTQR ATTORNEY United States Patent 6 CONTROL WCHANISM FUR HYDRAULIC PRESSES John Maurice Towler, deceased, late of London, England, by lh-ank Hathorn Towler, executor, Otley, England, assignor to Electrauiic Presses Limited, Rodley, near Leeds, England, a limited-liability company of Great Britain Application August 3, 1955, Serial No. 526,155

7 Claims. (Cl. 78-42) This invention relates to control mechanism for hydraulic presses, particularly for hydraulic forging presses, and has for its object to provide means for limiting the working stroke of the press and for reversing the motion of the tool by automatic means so that the press driver may have direct control over the thickness of the workpiece or forging.

A further object of this invention is to provide for automatic compensation for the tilting of the moving table of a large press, so that the position of the centre of the table is controlled rather than the position of one extremity of the table as in other known controls.

A still further object of this invention is to provide for compensation for the stretch of the press columns and deflection of the tables under varying loads, so that the position of the moving tool is controlled in relation to that of the fixed tool and not in relation to some other part of the press frame which moves relatively to the fixed tools under varying loads as in other known controls.

Another object of this invention is to provide control mechanism having more than one operative position, each operative position corresponding to a pre-selected thickness of the resulting forging, and means whereby the press driver can move the control mechanism from one operative position to another prior to a forging stroke.

A further object of this invention is to provide the press attendant with a means for suppressing the action of the stroke control, without altering its adjustment, whenever he may desire to do so.

Broadly the invention consists in a control gear for a hydraulic press which will permit the press to operate automatically on a workpiece until the workpiece is reduced to a thickness which has been predetermined, said control gear comprising a tappet which reciprocates with the movable head of the press, a tappet rod adapted to be contacted by the tappet and thereby displaced when the workpiece has been reduced to a predetermined thickness and a valve operable by said displacement of the tappet rod to cause the movable head to have its motion stopped and/or reversed whereby the workpiece is not further reduced in thickness.

In a preferred embodiment the valve is operated by means comprising a crosshead which is acted upon at both ends simultaneously by levers which are tilted in unison, through an operative connection, by tappet rods to displace the crosshead bodily when the workpiece has a predetermined thickness to cause the valve to stop and/ or reverse the press ram.

In this preferred embodiment two or more tappet rods of different lengths are carried by a turret which is rotated, preferably by a hydraulic motion, to bring a tappet rod of selected length into position for engagement by the reciprocating tappet thereby to enable the press to operate automatically to reduce a workpiece to the thickness corresponding to the selected tappet rod.

A control gear according to this preferred embodiment is easily adapted to provide automatic compensation both for stretch of the press frame and tilting of the moving table of the press as will hereafter appear.

In order that the invention may be clearly understood and carried into effect two embodiments thereof will now be described by way of example, by aid of the accompanying drawings in which:

Figure 1 is an elevation of a vertical downstroking hydraulic press showing part of the tappet gear in a control mechanism according to the invention.

Figure 2 is a plan of the press base shown in Figure 1.

Figure 3 is a sectional view of the control valve.

Figure 4 illustrates a suitable form of hydraulic motor for turning the turrets carrying the sets of tappet rods of different lengths.

Figure 5 illustrates schematically a modified form of valve operating gear which will provide the aforesaid automatic compensation for stretch and tilt.

Referring to the drawings, Fig. 1 shows a down stroking hydraulic press having a press head 1, a moving table 2 and a press base 3. The press head and base are connected by upright columns 1a which may serve as guides for the table 2 which is advanced toward the base in well-known manner by introduction of pressure fluid into a cylinder incorporated in the head and accommodating a ram 2a attached to the table. A bracket 4 projecting laterally from the table, preferably at or near one corner, carries a tappet 5 which is slidably mounted for endwise movement in the bracket and has a heavy head 6 supported by the upper surface of the bracket which serves to locate the vertical position of the tappet. Another bracket attached to and projecting laterally from the base 3 supports a turret 8 which is mounted on a vertical spindle and provided with suitable turning gear 10. In the exemplary embodiment the turret 8 carries three

tappet rods

11, 12 and 13 mounted in upright position and slidable axially in the turret and so arranged that by turning the turret any one of the tappet rods may be moved into vertical alinement with the tappet 5 and with a spring tappet 14 slidably mounted in a recess in the bracket. The tappet 14 is biased upwardly by a spring 14' against the tappet rod selected for use and its lower end is positioned to engage the upper end of a lever 15 fixed to a cross shaft 16. This cross shaft is utilized to operate the stroke control mechanism as will appear presently. Thus, it will be seen that by providing

tappet rods

11, 12, 13 of different lengths together with means for positioning them selectively between the movable tappet 5 and the spring tappet 14 the press may be quickly set to forge to three different finished thicknesses.

To compensate for any possible deflection of the press table by unevenly applied loads the tappet assembly above described is duplicated at the opposite side of the press. Moreover, the tappet assemblies are interconnected through suitable linkages for joint operation of the press control valve. Referring more particularly to Fig. 2 of the drawings a laterally projecting bracket 7' at the corner of the base 3 diagonally opposite the bracket 7 carries a turret 8' similar in all respects to the turret 8. The turret 8 like the companion turret carries tappet rods 11', 12' and 13' of the same dimensions as the other tappet rods and spaced so that they may be interposed selectively between a table carried tappet (corresponding to the tappet 5) and a spring tappet (corresponding to the tappet 14). The latter is positioned for cooperation with the upper end of a lever 15' fixed to a rock shaft 16'.

The

shafts

16 and 16 constitute a part of the linkage through which the tappet assemblies act jointly to actuate a servo valve 19 (Fig. 3) which controls press operation in well-known manner. For this purpose the shafts 16 and 16' are supported by suitable brackets on the side of the press body to converge toward one corner actuated.

, As shown in Fig. 3 the servo valve 19 has a casing with an inlet 20 for servo pressure fluid and a movable valve member or plunger 21 operative to open or close a passage from the fluid inlet 20 to a servo pressure outlet 22. In the particular valve shown the plunger 21 is biased to a closed position by a spring 21'. The crosshead 18 is provided with a central recess or socket 'adapted to coact directly with the projecting end of the pending application, Serial No. 403,354, filed January 11, 1954, with which the present control gear may be used. In the preferred form of the control gear the turrets 8 and 8' are turned by means of a rack and pinion turning gear and 10' (Fig. 4). Each rack and "pinion is operated by opposed cylinder and

piston actuators

23, 24 for the

turret

8 and 23', 24 for the turret '8'. The supply of pressure fluid to the actuator cylinders is controlled by a manually operable control valve 25 which may be of any preferred type.

or to interrupt advance of the same as shown in our 00- The mechanism above described compensates for uneven movement or tilting of the press table 2 by averaging the movements of opposite corners of the table and utilizing the result for controlling purposes. This averaging is done by the crosshead 18 and the linkages including the

shafts

16 and 16 which transmit movements from the tappet rods 11 at opposite corners of the table to opposite ends of the crossheads. Displacement of the central portion of the crosshead which is in direct engagement with the plunger 21 of the control valve is thus proportioned to the average advance of the two corners or, more particularly, to the advance of the center of the table. Accordingly, the control valve 19 is actuated to interrupt table movement when the center of the press table has advanced through the stroke required to reduce the work to a predetermined thickness as determined by the particular set of control elements 5 and 11-13 selected for operation.

The thickness of the finished workpiece, of course, is determined by the

particular tappet rod

11, 12 or 13 positioned for engagement by the tappet 5. Since the tappet and the rods are mounted in fixed relation to the table and the press bed respectively the stroke of the press and consequently the finished thickness of the work is determined by the length of the tappet rod in use. Thus, assuming that the end of the tappet 5 is flush with the working face of the table, a tappet rod that presents its upper end one inch above the working face of the base 3 will act to stop the table advance when its separation from the base is one inch minus the small increment required to depress the tappet rod and actuate the control valve 19. Since the above mentioned increment has a fixed value, the tappet rods can be precisely dimensioned to provide any desired work thickness.

The stretch of the press frame is clearly proportional to the pressure in the hydraulic press cylinder or in other words proportional to the force exerted by the press ram. If it is desired to compensate for the stretch of the press frame, this may be done by mechanism such as illustrated in Fig. 5, in which a lever 26 is interposed between the crosshead 18 and the valve spindle 21 of the valve 19 and the other end of the lever 26 is supported by a piston 27 which is subject to the same pressure as that in the hydraulic cylinder of the forging press, being connected thereto by the inlet 28. The free end of the lever 26'is also supported on a blade spring 29 which is fulcrummed on a piston 30 which in turn is supported by hydraulic pressure in a cylinder 31 and controlled by a valve 32. The function of the valve 32 is to release the fulcrum piston 30 so as to make the mechanism inoperative.

The spring 29 is deflected by the force applied by piston 27 which is subject to the pressure in the forging press cylinder and therefore the force of piston 27 is proportional to the force applied by the press ram. Thus by suitably proportioning blade spring 29 the said deflection of the spring 29 will compensate for the stretch of the press frame. More particularly, the end of the lever 26 supported by the spring 29 will be shifted vertically an amount proportioned to the pressure in the press cylinder which is a proportionate measure of the stretch of the press frame. Since the press control mechanism actuates the valve 19 through the lever 26, such shifting of the end of the lever will correspondingly affect the movement that must be imparted to the level by the controls in order to actuate the valve. The proportioning of the spring 29 and levers 15, 17, 18 and 26 is such that the change in the position of the lever delays operation of the valve 19 until the center of the press table has moved a distance equal to that called for by the setting of the control system, plus a distance corresponding to the stretch of the press frame under the pressure prevailing in the press cylinder. On the other hand, it will be understood that unequal stretching of the press frame, such as to cause the press table 2 to tilt or move out of parallel with the press base 3, will be compensated by the crosshead 18 which is free to rock in relation to the valve spindle 21 as above explained.

In the operation of forging presses of the above general character it is not always possible to center the workpiece precisely with respect to the press table. Due to the high pressures developed between the table 2 and base 3, such off-center loading of a workpiece results in the development of high eccentric forces which tend to tilt the table from parallel relation to the base. In the case of automatically controlled presses, this tilting of the table affects the finished dimensions of the workpiece, the finished piece being oversize or undersize, depending on the location of the controls at the low or high side of the table.

The invention aims to correct this difliculty by pro viding a novel arrangement of control elements to come pensate for the tilting of the table insofar as it affects. the stroke of the press. It is to be particularly noted that this compensation is not to be confused with attempts to correct or prevent the tilt, which, in general, have proved to be impractical because of the large forces involved. In applicants press, tilting of the table is mini-. mized by the sturdy construction of the press frame which, of course, is built heavy enough to withstand any eccentric forces that might reasonably be expected to develop. Despite such sturdy construction, tilting of the table will occur upon eccentric loading. The novel control arrangement provided by the invention prevents such tilting from adversely affecting the press structure as described hereinafter.

What is claimed is:

1. In a hydraulic press having a fixed work supporting base and a table movable toward the base to reduce the thickness of the work, the combination of a pairof tappets supported at opposite sides of the table and movable therewith, a pair of tappet rods supported at opposite sides of the base in positions to be engaged and shifted by the respective tappets of said pair as the work is reduced to a predetermined thickness, a valve for controlling movement of the press table, a cross head positioned for actuating said valve, and linkages operatively thickness of the work, the combination of a tappet mounted on and movable with the table, a plurality of tappet rods of different length supported adjacent the base for movement selectively into a position to be engaged and shifted by said table carried tappet as the work is reduced to a thickness proportioned to the length of the selected rod, valve means for controlling the movement of the table, and an actuating linkage connecting the selected tappet rod with said valve means.

3. A hydraulic press as defined in claim 2 in which the plurality of tappet rods are mounted in a turret rotatable to position the selected rod for engagement by the table carried tappet.

4. In a hydraulic press having a fixed Work supporting base and a table movable toward the base to reduce the thickness of the work, the combination of a pair of tappets supported at opposite sides of the table and movable therewith, a group of tappet rods of different length supported at one side of the base for movement selectively into a position to be engaged and shifted by one of the tappets of said pair as the work is reduced to a thickness proportioned to the length of the selected rod, a second group of tappet rods of lengths similar to the rods of the first mentioned group supported at the other side of the base for movement selectively into a position to be engaged and shifted by the other tappet of said pair as the Work is reduced to a thickness proportioned to the length of the selected rod, a valve for controlling movement of the press table, a cross head for actuating said valve, and linkages operatively connecting the selected tappet rods with said cross head.

5. A press as defined in claim 1 in which the control valve has a member movable to control table movements and in which the cross head is in direct engagement with said movable member.

6. In a hydraulic press having a movable table and a pair of control members disposed on opposite sides of the table and adapted to be shifted by the table as it approaches a predetermined position in a pressing movement, the combination of a control valve having a member shiftable to control the movement of the press table, a lever fulcrumed intermediate its ends on the movable valve member, a cross head pivoted at its center on one end of said lever, linkages operatively connecting the respective control members to opposite ends of said cross head for bodily moving the same to shift said valve member, a spring blade bearing on the other end of said lever, and a plunger engaging said other end of the lever in opposed relation to said spring blade, said plunger being reciprocable in a cylinder connected to receive fluid at the pressure prevailing in the press whereby to automatically compensate for stretch of the press frame.

7. A hydraulic press as defined in claim 6 including a cylinder, a piston reciprocable in said cylinder and adapted when pressure fluid is supplied to the cylinder to engage the spring blade and hold it against the end of the lever and thereby enable the lever to actuate the control valve, said piston releasing the spring blade to render the valve actuating lever inoperative when pressure fluid is released from said cylinder, and manually operable valve means controlling fluid flow to and from said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 1,469,689 Prius Oct. 2, 1923 1,900,050 Ernst Mar. 7, 1933 2,283,447 MacMillin et a1. May 19, 1942 2,561,169 Bickelhaupt July 17, 1951 2,753,689 Biggert July 10, 1956 2,759,330 Brookhoven et al Aug. 21, 1956 2,809,543 Zeitlin Oct. 15, 1957 FOREIGN PATENTS 447,703 Italy Apr. 28, 1949