US3438239A - Hydraulic control devices for bending presses - Google Patents

Description

April 5, 1969 s. SALVAGNINI 3, 3

HYDRAULIC CONTROL DEVICES FOR BENDING PRESSES Filled May 4, 1966 INVENTOR:

Guide 80. Ia n) MMmZX YM United States Patent 3,433,239 HYDRAULIC CONTROL DEVICES FOR BENDING PRESSES Guido Salvagnini, 45 Via Cenisio, Milan, Italy Filed May 4, 1966, Ser. No. 547,663 Claims priority, application Italy, Jan. 26, 1966, 13,832/ 66 Int. Cl. B21j 9/12 U.S. Cl. 72-453 3 Claims ABSTRACT OF THE DISCLOSURE A device fitted on a hydraulic bending press to prevent the inclination of the movable bending plate or beater in respect of the press base, from suffering variations larger than a pre-set limit in the course of the working stroke and at the end thereof. Two laterally spaced hydraulic jacks control the beater with a pump for each of the jacks feeding approximately equal amounts of oil to the jacks. A first valve is connected in series with a second valve which opens when a condition of non-parallelism of the beater in respect of the base exists. A first duct connects each pump with the cylinder of the corresponding jack. The first valve has a piston slidingly fitted in a cylinder having an outlet with resilient means cooperating with the piston to prevent oil from flowing toward the outlet. A second duct extends through the piston and a pipe extends from the first valve to the second valve whereby oil delivered by the pump is fed to the second valve having an outlet so that the second valve is open to its outlet when the jack located at the corresponding side of the beater is advanced in respect of the other jack while said second valve at the opposite side of the beater remains closed.

Bending presses are machines that serve to variously bend metal sheets. It is known that in the more conventional bending presses to which the device of the invention is applied, the bending takes place by effect of the pressure upon the sheet of the border of a movable frame or heater having alternate vertical rectilineal movement.

In some bending presses during the bending operation, the beater moves from top to the bottom; in other bending presses the beater moves from bottom to the top. This invention however applies to both said presses, although the specification particularly refers to a press with bending movement from top to the bottom.

The fundamental problem of the bending press is the maintenance of the parallelism between the border of the beater plate and the rest plane for the sheet both during the bending movement and at the end of said movement, even it the sheet is outside the middle line of the beater plate.

In bending presses with hydraulic control, the beater plate is moved by two parallel axis jacks and the parallelism between the beater plate and the rest plane of the sheet is obtained if the rods of the two jacks move at any instant with equal speeds. There exist various devices which obtain said purpose with more or less great approximations; the one according to the present invention 1s simple and permits a precision higher than the minimum acceptable.

It is therefore an object of the present invention to provide a device capable of preventing that in a bending press with hydraulic control the inclination of the beater plate in respect of the bed-plate during the working movement and at the end thereof undergo variations exceeding a predetermined limit, the beater plate being moved by two jacks, each fed by a pump or anyway by oil flows approximately equal. The main feature of said device is that a valve, in series with a second valve acting in non-parallelism condition of the beater plate in respect of the bedplate, is offtaken on the duct connecting each pump with the cylinder of the relating jack.

Said first valve essentially comprises a rod slidingly fitted in a body; resilient means provided to maintain said rod in position to intercept the oil flow toward a discharge port; a duct of little diameter being provided, preferably across said rod, preventively sending the oil, through a further pipe departing from the said first valve, from the pump to the said second valve; said second valve being opened or closed according to whether the relating jack is advanced or back in respect of the other jack.

Said second valves advantageously comprise each a rod rigid with the piston of the relating jack or, according to a further embodiment form, with the machine basement, the end of said rod being cone or ball-shaped, and a body sliding upon said rod and suspended on a guide traverse compulsorily moving parallelly to itself and to the basement. Said guide traverse is supported by that one of the said rods having upper end, the supporting seat acting also as seat for tight closing of the valve.

The appended diagrammatical drawing shows an example of embodiment of the press according to the present invention.

FIG. 1 shows an elevational view of the press, in which some parts appear to be in section taken along a vertical plane;

FIGS. 2 and 3 shows respectively two elevational views, at from each other, of a detail relative to a possible form of practical embodiment of a movable guide traverse.

The press comprises a basement 1 carrying the lower portion of the die, upon which the sheet to be bent is made to rest; the upper portion of the die, namely the movable frame or heater 2, is controlled, in its descending movements, by two jacks 3, each comprising a cylindrical casing 4, fixed with respect to the basement 1, a piston 5 and a rod 6 (rigid with the piston 5), the lower end of which is fixed to the heater 2 with hinge means.

For each jack there is foreseen a pump 7 placed in a fixed position with respect to the basement; from each pump there departs a conduit 8 branched into two conduits El and 10 directed to the jack 3 and to a valve 11. In lieu of the two pumps there might be provided one single pump only with a device distributing the flow into two approximately equal portions.

The valves 11 comprise a body 12 fixed in respect of the basement, a cylindrical rod 13 axially sliding and oiltight in the suitable chamber of body 12, a spring 14 acting on rod 13, a cone-shaped needle closing the passage 16, a spring 17 and an adjusting screw 18 thereof acting on needle 15. The rod 13 under load action of the spring 14 is normally in the position indicated in FIG. 1, to close the passage between the conduit 10 and the outlet duct 19. The rod 13 presents inside an axial cylindrical bore 20 of little diameter connecting the chamber 21 with the chamber 22 of the valve 11. Two flexible conduits 23 connect the chambers 22 with the valves 24. A traverse 25 rigid with bodies 26 of the valves 24, is movable along a vertical plane and is guided by suitable means causing it to rest thoroughly horizontal, i.e. at any instant said traverse is parallel to the plane P of the basement supporting the metal sheet. A cavity 27 of the body 26 communicates with the conduit 23 and, through a cylindrical bore 28, with the outlet conduit 29. The closing and opening member of each valve 24, particularly of the bore 28, is represented by a head 30 integral with a rod 31; said rod is rigid with the beater 2 and can slide in sealing relationship, with an upper section thereof, in said body 26. The traverse 25 rests on the heads 30 with the bodies 26, whereby it descends and rises with the beater 2.

' According to the example of FIGURES 2 and 3, the traverse 25 is constituted by a rigid cylindrical body 32, that carries at its two ends a pin 33 rotatable in a bearing 34 inside a support 35 rigid with a valve body 26. For each end of body 32 there is provided a fixed upright 36 with respect to the basement and there are moreover provided a flexible and inextensible tape 37 fixed at 38 and 39 respectively to the upright and to the body 32 and a similar tape 40 fixed at 41 and 42 to the upright and to said body. In such a manner, the traverse 25 is caused to roll without dragging on the uprights 36, whereby it remains at any instant parallel to itself.

Consider the pumps 7 to be in action, and assume that the beater be not perfectly horizontal: the two heads 30 therefore are not at the same level, whereby the traverse, which is perfectly horizontal, rests upon the higher head 30 through one of the two bodies 26, whose valve 24 is thereby in closing condition; the other valve 24 is consequently open, that is to say the respective head is lowered with respect to the border of the bore 28. The flow rate of that pump 7, that corresponds to said closed valve, completely goes into the respective jack 3 and the fiow of the other pump instead finds an outlet or way of escape through the corresponding bore 20 and said open valve; the piston 5 corresponding to the latter advances therefore more slowly than the other one, until closure of said valve. If the load under the beater is perfectly centered and if the flow rates of the pumps are perfectly equal (which is not attainable in practice), once the parallelism between the heater and the basement is attained, namely the closure of the valve 24, the movement of the beater continues uniformly and parallel.

If instead the flow rates of the pumps are slightly different, or the load under the beater is not centered, whereby different pressures are produced in the pump-s and therefore different volumetric efficiencies are obtained, the valve 24 corresponding to the pump with greater delivery or smaller charge remains somewhat open, discharging the excess of flow; said excess of flow goes through the bore 20 to reach the valve 24 in opening condition. By dimensioning the valves 24 conveniently, it is possible to reduce to values smaller than the admissible tolerance for lack of parallelism of the beater, the lift of the head from its seat, namely the vertical distance between the lower border of the bore 28 and the line of the conical surface of the head 30 destined for the contact with said border. This is possible because the flow rate of oil which is to be controlled by valves 24 results in the difference between the flow rates of said two pumps; if each valve destined to parallelism should have to control the complete flow rate of a pump, as it occurs in other devices attempting to solve the same problem, the gage of parallelism should be more eater. Due to the smallness of flow which flows 4 in the bores 20 during the bending movement, it is also possible to size said bores 20 and springs 14 in such a manner that the difference between the oil pressures in two chambers 21 and 22 be insufficient to cause the mo ment of the rod 13 against the action of the spring 14.

In the point of bending stroke wherein the beater is required to stop, the motion of traverse 25 is stopped by an adjustable dog, rigid with the base, whereby two valves 24 are simultaneously opened. Now, the opening of said valves is such that, while being the deviation from a true parallelism kept within admissible limits, however the flow rate that flows through the bores 20 results in head loss between the chambers 21 and 22, sulficient to shift the rods 13, whereby a communication is established between the ducts 10 and the outlet ducts 19. The flow rate of each pump in excess of that amount which is delivered through the respective bore 20 and valves 24i.e. the major portion of the total flow rate-is exhausted through the duct 19; oil is no more fed to upper chambers of cylinders 3, and the pistons 5 are stopped (stop in a floating position). Thus, also the stopping of beater-i.e. the total release of pump flow rate-is obtained by a very small lift of valves 24-i.e. with a very small deviation from the true parallelism, Owing to the fact that the small lifting of valves24results, as explained above, in the total lifting of valves 11, which have wide ports.

Said valves 11 are designed to act also as safety valves. In fact, when the valve 24 is closed, and the further operation of jack is prevented because the resisting force exceeds the max. force that can be exerted by the jack, then the needle 15 is lifted by the oil from its seat, and a release occurs through the ducts 16 and 43; such exhausted oil also flows through the bore 20, thereby causing a pressure differential across the chambers 21 and 22,-sufficient to lift the rod 13, and thus to open the passage from the chamber 21 to outlet duct 19. In such a manner, the oil pressure can never exceed the max. value which is pre-set by the tension of spring 17, i.e. by the adjustment of screw 18.

A variant of this invention, by which the basic principle thereof is left unchanged, consists in having the rods 31 of valves 24 secured to the base, while the uprights 36 are fixedly connected with the beater. Even in thi latter case, any deviation from a true parallelism results in the opening of one of the valves 24, with all the consequences as stated above. For simplicitys sake, the means by which the heater is returned back to its initial position after each bending stroke, will be not described; at any rate, many already known devices are available, with which the press in question can be fitted for said purpose.

Obviously, rnany modifications and variations of the present invention are possible in the light of the above teachings. Therefore, it is to be understood that the invention is not limited in its application to the details specifically described or illustrated, and that within the scope of the appended claims it may be practised otherwise than as specifically described or illustrated.

.What I claim is:

1. A device adapted to be fitted on a hydraulic bending press to prevent the inclination of the movable bending plate or beater in respect of the press base, from suffering variations larger than a pre-set limit in the course of the working stroke and at the end thereof comprising a heater, two laterally spaced hydraulic jacks controlling said heater, a pump for each of said jacks for feeding approximately equal amounts of oil to said jacks, a first valve connected in series with a second valve Which opens when' first valve to said second valve whereby oil delivered by said pump is fed to said second valve having an outlet so that said second valve is open to its outlet when the jack located at the corresponding side of the beater is advanced in respect of the other jack while said second valve at the opposite side of the beater remains closed.

2. A device according to claim 1 wherein said second valve comprises a piston fixed to a piston of its related jack, and a body slidingly fitted on said piston, a traverse from which said second valve is hung, the weight of said traverse and of said bodies supported thereby cooperating with said piston of said second valve for a tight closing of said second valve. 1

3. A device according to claim 1 wherein said second valve comprises a piston fixed to said beater, a body slidingly fitted on said piston and a traverse from which said second valve is hung, the weight of said traverse and of said bodies supported thereby cooperating with said piston of said second valve for a tight closing of said second valve.

References Cited UNITED STATES PATENTS 2,759,330 8/1956 Broekhoven 10046 2,859,591 11/1958 Zimmerman 100-46 3,070,146 12/1962 Ferranti 10046 1O RICHARD J. HERBST, Primary Examiner.

G. P, CROSBY, Assistant Examiner.

US. Cl. XR

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