GB1566992A - Shearing press with shock damping system - Google Patents

Description

(54) SHEARING PRESS WITH SHOCK DAMPING SYSTEM (71) We, GULF & WESTERN MANUFACTURING COMPANY, a Corporation of the State of Delaware, of 23100 Providence Drive, Southfield, Michigan 48075, U.S.A., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the art of presses and, more particularly, to a shearing press having a hydraulic fluid shock damp mg system.

In a shearing press, as is well known, cooperable cutting die or shearing components are mounted on the press slide and bed to achieve cutting or shearing of material therebetween in response to movement of the press slide through the downward portion of its total stroke. Upon engagement of the die component on the slide with the material to be severed a load is placed on the press which progressively increases to a maximum which is reached at the point of break-through of the die components with respect to the material therebetween. This load is imposed on the press through the slide, and movement of the slide toward the press bed is retrained during the severing operation. This restraint is removed upon breakthrough, whereupon slide movement toward the press bed is accelerated as a result of the toad build up. In the absence of a restraining force with respect to such accelerated movement of the slide, objectional shock loads and vibration forces are set up within the press. Such shock and vibration is detrimental to press life as well as maintenance expenses in connection with component parts of the press. Moreover, these shock and vibration forces result in objectionably high noise levels and impart undesirable vibration to other equipment and to the personnel working in the vicinity of the press. Moreover, it will be appreciated that these undesirable characteristics are repeated with each stroke of the press and are related in degree of objectionability to the size of the press.

Efforts have been made heretofore to damp such shock and vibration forces experienced with the operation of a shearing press. While some success has been achieved in connection with reducing shock and vibration, the systems heretofore proposed for this purpose do not provide optlmum efficiency with regard to vibration and noise abatement over a desirable period of continuous use of a given press. Additionally, system heretofore proposed have characteristics which are detrimental to press life and economical press operation. With regard to such prior art efforts, it has been proposed, for example, to employ a hydraulic shock absorbing system including one or more piston and cylinder units interposed between the press bed and slide to define chambers receiving hydraulic fluid under pressure. During movement of the slide toward the bed to achieve a shearing operation fluid is expelled from the chamber or chambers through a variable restricted passageway incorporated in the piston component and adjusted to provide a predetermined restriction to flow from the chamber at the point of breakthrough of the material being severed. Such a system enables continuous, though restricted, movement of the slide following breakthrough and, thus, the imposition of some shock and vibration forces on the press. Moreover, if two or more such piston and cylinder units are employed in a given press, the adjustment thereof must be extremely accurate to avoid eccentric loading of the slide as a result of different pressure drops across the restrictions of the different units. Still further, the accuracies required in these units makes the system extremely expensive, and continuous operation of the press results in a require ment for frequent adjustment of the units whereby down time of the press is undesirably high as is maintenance time and expense. Additionally, continuous operation of the press with continuous flow of hydraulic fluid from the cylinder chambers each time the slide strokes results in undesirably high fluid temperatures which may necessitate the use of a cooling system therefor, thus adding to the cost of production and expensive operation of the press. Still further, even if just one piston and cylinder unit is employed to avoid the possibility of eccentric loading of the slide, the accuracy required with regard to adjusting the point of maximum restriction to coincide with the point of material breakthrough is impractical.

Other systems heretofore proposed have included a fixed orifice in the hydraulic system operable to pass hydraulic fluid from a fluid receiving chamber to a tank or the like by a low pressure drop during initial cutting of the material and at a high pressure drop when breakthrough occurs. The high pressure drop provides a restraining force against the slide. Systems of the latter character have poor efficiency with regard to reducing shock and noise and, additionally, generate excessive heat in the fluid due to the substantially continuous flow thereof under pressure.

The present invention aims at eliminating or substantially reducing the disadvantages of previous shock damping systems provided in connection with shearing presses, and accordingly provides a shearing press having an hydraulic shock damping system comprising a variable volume chamber connected to a source of hydraulic fluid under pressure and operable under compression in response to breakthrough of material being sheared to restrain the resulting accelerated movement of the press slide, a normally open shutoff valve in fluid flow communication with said chamber, and means for closing said valve in response to said accelerated movement of the press slide to prevent any fluid flow from said chamber.

With the above system, maximum restraint of slide movement following breakthrough is achieved by quickly and positively blocking fluid flow from hydraulic fluid receiving chambers interposed between the press slide and bed. This maximum restraining force provides increased efficiency in reducing shock and noise by minimizing the load energy released and thus slide movement following breakthrough. Moreoever, by positively blocking fluid flow from the chamber or chambers there is very little heat generated in the system fluid. Accordingly, the necessity of cooling systems are avoided as is the danger of excessive heat in the system without such a cooling system.

Preferably, such shutoff of fluid flow from a fluid chamber at the point of breakthrough is achieved by a flow sensitive valve in the fluid system which is responsive to acceleration of the slide at the point of breakthrough to block fluid flow from the chamber or chambers. Further, the shock and vibration loads imposed on the press by energy release at breakthrough can be further reduced by using a minimum volume of hydraulic fluid in the system, by using a fluid having a high bulk modulus, and by rapid response of the flow sensitive valve. Preferably, the flow sensitive shutoff valve provides restricted flow from the chamber or chambers with minimal pressure drop during the cutting operation up to the point of breakthrough. At the point of breakthrough, acceleration of the slide positively shuts the valve producing a rapid counterload against slide movement, thus reducing the energy release experienced at breakthrough and maintaining the load on the press through the slide, thus to minimize shock, vibration and noise.

The present invention also provides a method of suppressing shock in a shearing press having cooperable shearing means and wherein shock is occasioned by breakthrough of the shearing means relative to material being severed, comprising: interposing an hydraulic fluid receiving variable volume chamber between a slide and a bed of the press so that the fluid under pressure is expelled therefrom as the slide moves toward the bed to perform a shearing operation, stopping fluid flow from the chamber upon breakthrough of the material being severed, and returning fluid under pressure to said chamber during movement of the slide away from the bed.

Also in accordance with the invention there is provided a shearing press comprising a frame including a bed and supporting a reciprocable slide, wherein, in use, material is severed between cooperable shearing means supported by said bed and slide, said slide means being accelerated in the direction of said bed upon breakthrough of the shearing means through the material being sheared, and an hydraulic shock damping system including a variable volume chamber mounted between said slide and said frame and including means displaceable to reduce the volume of said chamber during movement of said slide toward said bed to sever material between said shearing means, said displaceble volume reducing means being arranged to be accelerated by said accelerated slide movement, a source of hydraulic fluid, means for delivering hydraulic fluid from said source to said chamber under pressure, and a fluid pressure actuated shutoff valve in fluid flow communication with said chamber and actuable to close in response to an increase in fluid pressure caused by acceleration of said displaceable volume reducing means to prevent any fluid flow from said chamber.

Some preferred embodiments of the invention are described in detail below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a shock damping system in accordance with the present invention associated with the slide and bed components of a shearing press; Figure 2 is a graph showing slide displacement and press load curves during the working stroke of a shearing press without shock damping; Figure 3 is a graph showing slide displacement and press load curves during the work stroke of a shearing press having a shock damping system in accordance with the present invention; and, Figure 4 is a schematic illustration of a modification of the system shown in Figure 1.

Referring now in greater detail to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the present invention only and not for the purpose of limiting the same, a hydraulic fluid shock damping system is schematically illustrated in Figure 1 and in conjunction with a shearing press 10 operable, for example, to cut blanks from metal sheets. The structure and operation of tresses of this character are of course well shown in the art. and details regarding the structure and operation are not necessary to an understanding of the present invention.

It will be sufficient to appreciate that the press has a frame 12 providing a press bed 14 and that the frame supports a slide 16 for reciprocation toward and away from bed 14 a suitable drive arrangement being provided to achieve such reciprocation. As is further well known in the shearing press art, bed 14 supports a shearing component 18 and slide 16 supports a shearing component 20 cooperable with component 18 to cut material therebetween during downward movement of slide 16 to the bottom dead center position thereof. Cutting takes place, of course, from a point along the slide stroke above the bottom dead center position at which shearing component 20 engages the material to a second point along the slide path just ahead of the bottom dead center at which shearing components 18 and 20 cooperatively breakthrough the material being cut. As is well known to those skilled in the art of presses, engagement of material to be cut between shearing components 18 and 20 during downward movement of the slide imposes a load on the press through the slide and which load is suddenly released upon breakthrough of the material, whereupon downward movement of the slide is accelerated in the direction toward the bottom dead center position thereof. This is of course accompanied by release of the energy stored by loading of the press during the shearing operation.

In accordance with the present invention, a shock damping system is associated with the slide and frame components of the press to minimize downward displacement of the press slide following breakthrough, thus to minimize the release of energy resulling from loading of the press up to the point of breakthrough. The shock damping system, designated generally by the numeral 22 in Figure 1, is a hydraulic system including hydraulic fluid receiving variable volume devices 24 mounted on or supported relative to the press bed for actuation by slide 16 during downward movement thereof toward the bottom dead center position. In the embodiment shown, each variable volume device 24 is in the form of a piston-cylinder assembly including a cylinder 26 supported on the press bed and a piston 28 supported within cylinder 26 for vertical reciprocation relative thereto. The space in cylinder 26 behind piston 28 defines a fluid receiving chamber 30. and cylinder 26 is provided with a common inlet and outlet passage 32 opening into chamber 30. Slide 16 carries an actuator pin 34 for each piston, and each pin 34 has its upper end screw threadedly interengaged with a support collar 36 on the slide so that the Din is vertically adjustable relative to the slide for the purpose set forth hereinafter.

Chambers 30 of variable volume devices 24 are connected to a common source of hydraulic fluid under pressure. More particularly, in the embodiment shown in Figure 1 a motor-pump unit 38 is adapted to deliver hydraulic fluid under pressure to chambers 30 from a source 40 through a flow line system including a flow line 42 and branch lines 44 and 46 connected thereto and to one of the passageways 32 to variable volume devices 24. A one way check valve 48 prevents backflow to source 40, and a pressure responsive unloading valve 50 is operable at a predetermined pressure between valve 48 and the motor-pump unit to return hydraulic fluid to the source when valve 48 is closed and the pressure between the latter valve and motor-pump unit 38 exceeds the setting of valve 50.

A normally open fluid flow sensitive shutoff valve 52 is provided in flow line 42 to control fluid flow through the latter line.

Valve 52 includes a restricted passageway 54 permitting restricted fluid flow in the direction between chambers 30 and source 40 when valve 52 is in the open position illustrated in Figure 1. Valve 52 further includes a closed passageway 56 which is adapted to block fluid flow through line 42 when valve 52 is in the closed position in which passage 56 would be shifted to the right in Figure 1 to a position in alignement with flow line 42. Valve 52 is normally biased to the open position such as by a spring 58 and is adapted to be biased to the right in Figure 1 by fluid under pressure from branch lines 44 and 46 acting thereagainst through a feed line 60, as described in greater detail hereinafter. For the purpose set forth hereinafter, a low pressure hydraulic fluid receiving accumulator 62 is connected to flow line 42 between valves 48 and 52, and a high pressure hydraulic fluid receiving accumulator 64 is connected in fluid communication with line 42 and branch lines 44 and 46 between valve 52 and chambers 30 of variable volume devices 24.

Operation of the shock damping arrangement described above will be best understood by referring to Figures 2 and 3 of the drawing together with Figure 1. Briefly, Figures 2 and 3 are graphs showing slide displacement and press load during movement of the slide through the shearing stroke. Figure 2 shows the effect of no shock damping of the slide, and Figure 3 shows the effect of the shock dampening system described above and the effect of prior art shock damping systems In both graphs, the point 1 represents the time during the slide stroke at which, in the system disclosed herein, pins 34 engage pistons 28 during movement of the slide toward the bottom dead center position thereof which is indicated BDC in Figures 2 and 3. Point 2 represents the time at which the shearing components engage the material to be severed, and point 3 represents the time at which breakthrough of the material by the shearing components occurs. Curve L represents the load imposed on the press during a severing operation, and curve D represents the position of the slide during the severing operation relative to bottom dead center. If the press was not loaded by the interposition of material to be cut between the shearing components, slide displacement curve D would be arcuate throughout its extent and thus would follow the arcuate portion D' between point 2 and BDC in Figure 2 and between points 2 and 4 in Figure 3. The significance of point 4 is set forth hereinafter.

With regard now to the operation of the shock damping arrangement described hereinabove, the components of the press and hydraulic system are in the positions illustrated in Figure 1 prior to a shearing operation. Hydraulic fluid is delivered under pressure from source 40 to chambers 30 through flow line 42, restricted passage 54 of valve 52 and branch lines 44 and 46, and the fluid under pressure in chambers 30 biases pistons 28 upwardly. As slide 16 moves downwardly toward bed 14, pins 34 engage pistons 28 just before shearing components 18 and 2() engage the material therebetween to be severed. The adjustability of pins 34 enables setting the pins in this respect. As mentioned above, the material is engaged at point 1 in the graphs of Figures 2 and 3 and at this time the slide is located a distance S above BDC. Continued downward movement of slide 16 causes downward movement of pistons 28 in cylinders 26 thus forcing the hydraulic fluid in chambers 30 into branch lines 44 and 46 through cylinder passages 32. This fluid from chambers 30 flows back toward source 40 through restricted passage 54 of valve 52 and, since one way valve 48 is closed against return of fluid to source 40, accumulator 62 receivers the back flow fluid under pressure and stores the latter for return towards chambers 30 as set forth hereinafter. During this movement of the slide toward its bottom dead center position the slide has a normal velocity which is a known factor in connection with a given press, and shutoff valve 52 is structured for this normal velocity to produce a minimal pressure drop through restricted passage 54, whereby the opening bias is sufficient to maintain valve 52 open.

Continued downward movement of slide 16 brings shearing components 18 and 20 into engagement with the material therebetween, thus initiating the imposition of a load on the press through the slide. This engagement with the material is represented by point 2 in the graphs, and at this time the slide is spaced a distance W above the bottom dead center position thereof. As the shearing components cut the material, pins 34 continue to depress pistons 28 and the loading of the press restrains advancement of the slide and reduces the velocity thereof.

Accordingly, the piston displacement is gradual causing a continuance of the foregoing fluid flow from chambers 30 through restricted passage 54 of valve 52 to accumulator 62. As will be seen from load curve L in the graphs, the press is loaded from zero to a maximum as the shearing components move through the material during the period of slide displacement represented between points 2 and 3. At the same time, it will be seen that the material between the shearing components restrains displacement of the slide in the downward direction towards the bottom dead center, as repre sented by portion D2 of the displacement curve in the graphs.

The shearing components breakthrough the material at point 3 whereby the load is removed from the press and the stored energy of the load is imposed on the slide causing a rapid acceleration of the slide towards its bottom dead center position. In the absence of any shock damping of the slide at this point, the slide is immediately accelerated to bottom dead center, thereby imposing shock on the press and bounce of the slide resulting in the imposition of a series of reverse direction loads on the press as indicated by the portion of load curve L to the right of point 3 in Figure 2.

A shock damping system in accordance with the present invention advantageously restrains slide displacement toward BDC following breakthrough and minimize the energy release so as to maintain a load on the press during completion of the severing operation. In this respect, with reference to Figure 1, acceleration of the slide which occurs upon breakthrough is transmitted to pistons 28, thus suddenly accelerating displacement of the pistons in the direction to reduce the volume of chambers 30. This suddent displacement increases the velocity of the hydraulic fluid flowing from chambers 30, whereby valve 52 is actuated through feed line 60 to close the valve and thus positively block fluid flow from chambers 30. Thus, as seen in Figure 3, load energy release is stopped at point 5 following breakthrough and the slide is restrained from reaching BDC, as represented by portion D3 of the slide displacement curve.

Accordingly, the major proportion of the load is maintained on the press following breakthrough. From the point of time in normal slide displacement at which BDC is reached the press load is progressively decreased as a result of movement of the slide drive components which would normally cause upward displacement of the slide from BDC. At point 4 in the graph of Figure 3, the slide drive components are in slide displacement positions corresponding to the displacement position in which the slide is he d by the piston-cylinder units 24.

Thereafter, the slide drive components move the slide upwardly and the load on the press is reduced to zero.

The load maintained on the press in this manner maintains the hydraulic fluid between chambers 30 and valve 52 under pressure to maintain valve 52 closed. Upon upward movement of slide 16, the fluid pressure in the system biases pistons 28 upwardly to reduce system pressure and thus provide for spring 58 to open valve 52.

Thereafter, fluid accumulated under pressure in accumulator 62 is released to flow through restricted passage 54 of valve 52 back into branch lines 44 and 46 and chambers 30 to fully bias pistons 28 to their uppermost positions. Motor-pump unit 38 is operable to replenish any fluid leakage from the system which might occur during operation of the press.

High pressure accumulator 64 is a safety device to prevent damage as a result of press overload. If, for example, there is some breakdown which causes the press slide to impose a high pressure on the hydraulic system between piston-cylinder units 24 and check valve 48, accumulator 64 is actuated to receive fluid under such excess pressure.

The embodiment of the present invention illustrated in Figure 4 is the same in many respects as that shown in Figure 1 and, accordingly, like numerals are employed in Figures 1 and 4 to designate like components. In the embodiment of Figure 4, restricted passageway 54 of shutoff valve 52 is in communication with source 40 and piston-cylinder units 24 through flow line 42 and a branch line 66 leading to the valve.

Additionally, fluid flow through restricted passage 54 in response to downward movement of pistons 28 prior to material breakthrough is released by a low pressure check valve 68 for flow to a sump or the like 70 leading back to source 40. In further comparison of this embodiment with that shown in Figure 1, high pressure accumulator 64 in Figure 1 is replaced by a pressure responsive relief valve 72 which is operable in response to an undersirably high fluid pressure in the system to dump fluid to a sump or the like 74 for return to source 40. Further, low pressure accumulator 62 in Figure 1 is replaced by a low pressure accumulator 76 positioned between motor-pump unit 38 and check valve 48 to accumulate fluid under pressure when shutoff valve 52 is closed to provide sufficient fluid for the system to return pistons 28 to their uppermost positions following a severing operation. It will be appreciated that accumulator 76 works in conjunction with motor-pump unit 38 in replenishing the system in this respect.

Operation of the system shown in Figure 4 insofar as blocking fluid flow from chambers 30 of piston-cylinder units 24 is the same as that for the system shown in Figure 1. In this respect, initial downward movement of pistons 28 prior to breakthrough is at the velocity of the press slide, whereby valve 52 remains open and fluid expelled from chambers 30 flows through check valve 68 to sump 70. Upon breakthrough, the sudden acceleration of slide 16 and the resulting velocity increase in the fluid flow closes valve 52 to block further flow or fluid from chambers 30 and thus stop downward displacement of the slide. When the slide reaches point 4 in the graph of Figure 3, system pressure is reduced whereby valve 52 is biased open and pistons 28 are biased to their uppermost positions in preparation for the next severing operation.

It will be appreciated in conjunction with both of the embodiments herein disclosed that the magnitude of the load energy release at point 3 in the graph of Figure 3 can be controlled toward minimization by using a minimum volume of hydraulic fluid in the piston-cylinder units and flow lines, by using a hydraulic fluid having a high bulk modulas, by using a rapid response flow sensitive shutoff valve, and by various combinations of these control possibilities.

While considerable emphasis has been placed on the specific embodiments herein illustrated and described, it will be readily understood that many modifications will be obvious and suggested upon reading the foregoing description and can be made without departing from the principles of the present invention. In this respect, for example, while two piston-cylinder units 24 are illustrated, one or more than two such units can readily be associated with a given press structure to provide the desired slide restraint function in response to breakthrough.

Further, it will be appreciated that variable volume devices other than piston-cylinder units can be employed and that, in connection with piston-cylinder units, the pistoncylinder relationshlp can be reversed so that the cylinder is a movable component engaged by the press. Still further, while it is preferred to employ a flow sensitive shutoff valve permitting restricted fluid flow therethrough prior to breakthrough of the material being severed, it will be appreciated that other shutoff valve structures could be employed. Moreover, it will be appreciated that the shutoff valve could be controlled other than by system fluid. For example, the valve could be solenoid actuated to close at the point of breakthrough. It is only necessary in accordance with the present invention that the shutoff valve be actuated at the point of acceleration of the slide upon breakthrough to positively block fluid flow from the chambers of the variable volume devices.

WHAT WE CLAIM IS: 1. A shearing press having hydraulic shock damping system comprising a variable volume chamber connected to a source of hydraulic fluid under pressure and operable under compression in response to breakthrough of material being sheared to restrain the resulting accelerated movement of the press slide, a normally open shutoff valve in fluid flow communication with said chamber, and means for completely closing said valve in response to said accelerated movement of the press slide to prevent any fluid flow from said chamber.

2. A press according to claim 1, wherein said valve is fluid pressure responsive and said means for closing said valve means is actuable by the fluid flowing from said chamber means.

3. A press according to claim 1, wherein said valve includes a restricted passageway which communicates with said chamber when said valve is open to permit restricted flow of fluid from said chamber.

4. A press according to any one of claims 1 to 3, wherein said valve is connected in a fluid flow line between said source and said chamber and fluid pressure relief means is connected in said fluid flow line between said valve and chamber.

5. A press according to claim 4, wherein said relief means comprises fluid pressure responsive relief valve.

6. A press according to claim 4, wherein said relief means comprises fluid pressure responsive accumulator.

7. A shearing press comprising a frame including a bed and supporting a reciprocable slide, wherein, in use, material is severed between cooperable shearing means supported by said bed and slide, said slide being accelerated in the direction of said bed upon breakthrough of the shearing means through the material being sheared, and an hydraulic shock damping system including a variable volume chamber mounted between said slide and said frame and including means displaceable to reduce the volume of said chamber during movement of said slide toward said bed to sever material between said shearing means, said displaceable volume reducing means being arranged to be accelerated by said accelerated slide movement, a source of hydraulic fluid, means for delivering hydraulic fluid from said source to said chamber under pressure, and a fluid pressure actuated shutoff valve fluid flow communication with said chamber and actuable to close in response to an increase in fluid pressure caused by acceleration of said displaceable volume re

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. can be controlled toward minimization by using a minimum volume of hydraulic fluid in the piston-cylinder units and flow lines, by using a hydraulic fluid having a high bulk modulas, by using a rapid response flow sensitive shutoff valve, and by various combinations of these control possibilities. While considerable emphasis has been placed on the specific embodiments herein illustrated and described, it will be readily understood that many modifications will be obvious and suggested upon reading the foregoing description and can be made without departing from the principles of the present invention. In this respect, for example, while two piston-cylinder units 24 are illustrated, one or more than two such units can readily be associated with a given press structure to provide the desired slide restraint function in response to breakthrough. Further, it will be appreciated that variable volume devices other than piston-cylinder units can be employed and that, in connection with piston-cylinder units, the pistoncylinder relationshlp can be reversed so that the cylinder is a movable component engaged by the press. Still further, while it is preferred to employ a flow sensitive shutoff valve permitting restricted fluid flow therethrough prior to breakthrough of the material being severed, it will be appreciated that other shutoff valve structures could be employed. Moreover, it will be appreciated that the shutoff valve could be controlled other than by system fluid. For example, the valve could be solenoid actuated to close at the point of breakthrough. It is only necessary in accordance with the present invention that the shutoff valve be actuated at the point of acceleration of the slide upon breakthrough to positively block fluid flow from the chambers of the variable volume devices. WHAT WE CLAIM IS:

1. A shearing press having hydraulic shock damping system comprising a variable volume chamber connected to a source of hydraulic fluid under pressure and operable under compression in response to breakthrough of material being sheared to restrain the resulting accelerated movement of the press slide, a normally open shutoff valve in fluid flow communication with said chamber, and means for completely closing said valve in response to said accelerated movement of the press slide to prevent any fluid flow from said chamber.

2. A press according to claim 1, wherein said valve is fluid pressure responsive and said means for closing said valve means is actuable by the fluid flowing from said chamber means.

3. A press according to claim 1, wherein said valve includes a restricted passageway which communicates with said chamber when said valve is open to permit restricted flow of fluid from said chamber.

4. A press according to any one of claims 1 to 3, wherein said valve is connected in a fluid flow line between said source and said chamber and fluid pressure relief means is connected in said fluid flow line between said valve and chamber.

5. A press according to claim 4, wherein said relief means comprises fluid pressure responsive relief valve.

6. A press according to claim 4, wherein said relief means comprises fluid pressure responsive accumulator.

7. A shearing press comprising a frame including a bed and supporting a reciprocable slide, wherein, in use, material is severed between cooperable shearing means supported by said bed and slide, said slide being accelerated in the direction of said bed upon breakthrough of the shearing means through the material being sheared, and an hydraulic shock damping system including a variable volume chamber mounted between said slide and said frame and including means displaceable to reduce the volume of said chamber during movement of said slide toward said bed to sever material between said shearing means, said displaceable volume reducing means being arranged to be accelerated by said accelerated slide movement, a source of hydraulic fluid, means for delivering hydraulic fluid from said source to said chamber under pressure, and a fluid pressure actuated shutoff valve fluid flow communication with said chamber and actuable to close in response to an increase in fluid pressure caused by acceleration of said displaceable volume reducing means to prevent any fluid flow from said chamber.

8. A press according to claim 7, wherein said shutoff valve includes flow restriction means permitting restricted fluid flow from said chamber prior to said acceleration of said displaceable volume reducing means.

9. A press according to claim 7 or 8, wherein said means to deliver hydraulic fluid from said source includes a flow line connected to said chamber, and pressure overload relief means in said flow line between said source and said chamber.

10. A press according to claim 9, wherein said pressure overload relief means comprises a pressure responsive relief valve.

11. A press according to claim 9, wherein said overload relief means comprises a pressure responsive accumulator.

12. A press according to any one of claims 7 to 11, wherein said variable volume chamber includes a cylinder mounted on said press bed and piston reciprocable therein and constituting said displaceable volume reducing means.

13. A press according to claim 12,

wherein said cylinder includes a common inlet and outlet passage opening thereinto behind said piston and said means to deliver hydraulic fluid from said source includes a flow line connected to said common passage, a check valve in said flow line for preventing backflow toward said source, and fluid pressure actuated overload relief means in said flow line between said check valve and said passage.

14. A press according to claim 13, wherein said shutoff valve includes flow restriction means in fluid flow communication with said flow line between said check valve and said passage, said flow restriction means permitting restricted fluid flow from said chamber prior to said acceleration of said displaceable volume reducing means.

15. A press according to claim 13 or 14, including a fluid pressure responsive accumulator in said flow line between said shutoff valve and said check valve for receiving fluid under pressure in response to flow from said chamber prior to said acceleration of said displaceable volume reducing means, said accumulator being responsive to a pressure less than that of said overload relief means.

16. A method of suppressing shock in a shearing press having cooperable shearing means and wherein shock is occasioned by breakthrough of the shearing means relative to material being severed, comprising: interposing an hydraulic fluid receiving variable volume chamber between a slide and a bed of the press so that fluid under pressure is expelled therefrom as the slide moves toward the bed to perform a shearing operation, stopping fluid flow from the chamber upon breakthrough of the material being severed, and returning fluid under pressure to said chamber during movement of the slide away from the bed.

17. A method of suppressing shock in a shearing press substantially as herein described.

18. A shearing press having an hydraulic shock damping system substantially as herein described with reference to the accompanying drawings.