GB2463045A - Hydraulic piston with internal bypass valve - Google Patents

Abstract

A hydraulic piston 8 is disclosed having a valve 11 and conduits 12 embedded therein so that when the piston 8 moves within a cylinder 9 in a non-operation mode (for example when the piston 8 follows the movement of a component being driven by other means, such as a second hydraulic piston) the valve 11 can be opened to allow hydraulic fluid to pass from a fluid chamber 10 on one side of the piston 8 to a fluid chamber 10 on the other side of the piston 8. The piston 8 may comprise a detachable piston rod 14 or cylinder rod 15 which includes a bore or passageway 13 arranged to supply fluid to actuate the valve 11. Location of the valve 11 within the piston 8 eliminates the need for external fluid connections to the cylinder 9. The piston 8 is suitable for use in a metal shearing machine.

Description

Internal Bypass Valve for Hydraulic Cylinder HELD OF INVENTION: The invention re'ates to the genera' fie'd of shearing and in particu'ar to the shearing of metal p'ates and strips.

BACKGROUND OF THE INVENTION:

The use of hydrauicay operated shearing machines to cut sheet meta' is we know. For examp'e, GB 2405118 A describes a hydrauicay actuated shearing machine which achieves a rocking type shearing action by using a curved shear b'ade and two separate'y controUed hydrau'ic cynders. A simplified cross section is ifiustrated in Figure 1. The piece of material that is to be cut I is positioned between an upper curved shear b'ade 2 and a tower straight shear b'ade 3. The upper curved shear blade 2 is attached to an upper support beam 4 and the tower straight shear b'ade 3 is attached to a tower support beam 5.

Two hydrau'ic cy'inders 6 and 7 of a hydraulic actuating-mechanism are connected between the upper support beam 4 and the sower support beam 5.

Each of the hydrau'ic cy'inders 6 and 7 engages the upper support beam 4 in one engaging-area, hydrau'ic cy'inder 6 in the engaging area on the eft end of upper support beam 4, and hydraulic cylinder 7 in the engaging area on the right end of upper support beam 4. By controing the stroke of hydraulic cylinders 6 and 7 separately but in a synchronized manner the upper shear blade 2 can be made to execute a rocking type shearing action. The same type of shearing machine could be used with raked shear blades instead of curved shear blades in which case the two hydraulic cylinders move synchronized in the same direction to achieve the cutting action.

A consequence of using a raked shear blade or a rocking type shearing action is that the distance which the shear blade has to move to complete the cut is much greater than for a straight full width cut with a straight shear blade. For such a straight cut the shear blade only has to move through at most the full thickness of the material which s being cut. With a raked shear blade the chstance the shear blade has to move s the thickness of the material plus the width of the material multiplied by the tangent of the rake angle. Typicay the rake angle is only about 2 degrees and consequently for wide material the shear blade movement required is many times greater than for a straight cut. Similarly for a rocking type shearing action as illustrated in Figure 1 the movement of the hydraulic cylinders 6 and 7 is many times greater than would be required for a straight fuU width cut.

The actuating-force of a hydraulic cylinder 6 or 7 which is operated with the cylinder rod in tension is the product of its annulus area multiplied by the available supply pressure of the hydraulic fluid. In a shearing machine according to Figure 1 the combined annulus area of the hydraulic cylinders 6 and 7 must be sufficient to generate the required overall actuating-force for the thickest and strongest material that is to be cut with the available supply pressure of the hydraulic fluid.

In a practical shearing line for metal plates and strips it is important that the throughput of the shearing machine can keep pace with the other production units which deliver the material to be cut and process the cut material.

Throughput is the mass of material processed per time unit, i.e. output per time unit. The throughput of a shearing machine depends on a number of factors including the width and thickness and strength of the material being cut, the number of cuts required, the time it takes to perform the complete cut, which is called the cutting cycle time, and the time it takes to reset the shear blades which are moved for shearing to their starting position and to move the piece of material between cut positions, which is called the reset-time.

The strength of a material is defined by parameters such as yield strength and elongation to fracture.

As a result of these factors a hydraucally operated shearing machine like the one in Figure 1 has three primary parameters which determine the necessary size of the hydrauc fluid pump system and of the valves which supply fluid to the hydrauc cynders. The first parameter is that the combined annulus area of the hydraulic cyhnders must be sufficient to generate the overaU actuating-force required for the strongest and thickest material that is to be cut. The second parameter is that the stroke of the hydraulic cylinders must be sufficient to cut the widest and thickest materiaL The third parameter is that for all kinds of materials to be cut the shearing machine must be able to provide cutting cycle times and reset-times which allow fulfilling the throughput demands. The sum of cutting cycle time and reset-time must permit the hydraulic shearing machine to perform the number of cuts per time unit necessary for the desired throughput.

For example, to achieve sufficient throughput a shearing machine for metal plates typicay must be able to work with a cutting cycle time of about 3 seconds and a reset-time of about 7 seconds.

For thin andfor narrow material per tonne of output more cuts are required than for thick or wide material, and consequently the same throughput requires more cuts per time unit than for thick and/or wide material. Therefore, the hydraulic system of pumps, valves and cylinders of a shearing machine like the one in Figure 1 has to be dimensioned such that it can provide the short cutting cycle time and reset-time required for the thinnest and/or narrowest material to be cut.

Hence for cutting materials with a wide range of width, thickness and strength with a certain throughput in a hydraulic shearing machine like the one in Figure 1, the hydraulic cylinders must have a large annulus area and a large stroke and are required to move with the short cutting cycle time and reset-time which is needed for the thinnest or narrowest material. Hydraulic cylinders with large stroke and large annulus area have a large volume. Consequently, the volume of hydraulic fluid to be pumped for moving the shear blades is large and has to be pumped quickly, which requires large hydraulic pumps and valves.

A hydraulic system with large pumps and valves s very expensive and needs a lot of space, and the operatbn of large pumps and valves is energy-intensive and high-maintenance.

Appcants patent appcation number EP 0725358.8 describes an arrangement which addresses the wide range of demands made by a system which can provide the actuating force necessary to deal with thick and, or wide material but which can also achieve the cutting cycle times and reset-times typically required when cutting thin and, or narrow material.

A hydraulic actuating mechanism is described in which at least one hydraulic cylinder can be switched in and out of operation mode, independently of at least one other hydraulic cylinder of the mechanism. For example, the mechanism may comprise at least one cylinder having a relatively small effective area, and at least one cylinder having a relatively large effective area, the latter being switchable in and out of operation mode.

Such an arrangement is shown in Figure 2, in which a piece of material that is to be cut I is positioned between an upper curved shear blade 2 and a lower straight shear blade 3. The upper curved shear blade 2 is attached to an upper support beam 4 and the lower straight shear blade 3 is attached to a lower support beam 5. instead of having one hydraulic cylinder in each engaging area as shown in Figure 1, the shearing machine has two hydraulic cylinders 6a and 6b in the engaging-area in the left half of the support beam, and two hydraulic cylinders 7a and 7b in the engaging area in the right half of the support beam.

The combined effective areas of all hydraulic cylinders is sufficient to generate the overall actuating-force required for the thickest and strongest material that is to be cut. The effective area of the smaller hydraulic cylinders 6a and 7a is chosen such that it is sufficient to generate the overall actuating-force required for cutting products which require the fastest cutting speed and consequently the shortest cutting cycle time.

When not in operation-mode, cylinders 6b and 7b are isolated from the hydraulic circuit (by valves not shown) and typically follow the movement of the support beam to which they are engaged (during shearing and reset). Thus, hydraulic fluid which is not under working pressure flows in and out of these cylinders and EP 0725358.8 discloses the provision of a bypass valve to allow such fluid to pass from one side of the piston to the other.

However, the inventors have found that the flow required through the bypass valve can be very large -of the order of 12000 litres/mm. Handling this large flow not only requires a large valve but it also requires large pipes to connect it to the cylinder. This is made even more difficult by the fact that the cylinder moves during operation so that flexible pipes are required.

The present invention avoids this problem by providing a hydraulic cylinder having the features of claim 1 attached hereto.

The invention will now be described by way of example, with reference to the following figures in which: Figure 1 shows a simplified cross section of a prior art hydraulic shearing machine with curved shear blade.

Figure 2 shows a simplified cross section of an exemplary embodiment of a hydraulic shearing machine having at least one hyadraulic cylinder which is switchable between operation and non-operation modes according to the demands being placed on the apparatus and Figure 3 shows a preferred embodiment of hydraulic piston and cylinder arrangement according to the present invention.

Referring to figure 3, a piston 8 accorchng to the present invention is located in a cylinder 9, piston 8 and cylinder 9 being arranged to define chambers 10. Piston 8 indudes a valve 11 operable in cooperation with conduits 12 to provide fluid communication through piston 8.

In the embodiment shown, valve 11 is actuated by pressure transmitted via hydraulic fluid supplied through conduit 13 and controlled by a solenoid (not shown).

The cylinder-piston arrangement show in figure 3 is of the through rod' type but it will be apparent to those skied in the art that the invention is equaUy applicable to other types such as single rod cylinders.

In applications where the piston rod is heavily loaded during operation, a rod 14 and the piston 8 are typicay realised as a single casting or forging. However, where a rod 15 is only lightly loaded, the inventors have found that it is conveniently realised as a removable component allowing for easier installation and maintenance of valve 8.

The rod 15 may be attached to the piston by (for example) bolts 16.

Moreover the conduit 13 is conveniently realised as a drilling or pipe through rod 15, thus minimizing the connections required only a hose connection (not shown) to the rod 15 is necessary.

Claims (7)

1. Claims 1. A hydraulic piston 8 characterized by at least one conduit 12 in the piston and a valve 11 in the piston, the valve being operable to provide, in cooperation with the conduits, a fluid path through the piston.
2. 2. A hydraulic piston according to claim 1, located in a cylinder 9, the piston and cylinder being arranged to define chambers 10 on a first and second side of the piston and within the cylinder, the valve being operable to allow fluid to pass from one chamber to the other chamber without exiting the cylinder.
3. 3. A hydraulic piston according to claim 2, being a first hydraulic piston in an apparatus, said apparatus having at least a second hydraulic piston, wherein the first hydraulic piston is switchable in and out of operation-mode, independently of the operation mode status of the at least second hydraulic piston.
4. 4. A hydraulic piston according to claim 3, where the apparatus is a metal shearing machine.
5. 5. A hydraulic piston according to any of claims I -4, further comprising a cylinder rod 15, the cylinder rod being detachable from the piston.
6. 6. A hydraulic piston according to claim 5, wherein the cylinder rod includes a conduit arranged to supply fluid to the valve.
7. 7. A method of operating a hydraulic piston 8, comprising the steps of switching the piston from an operation mode to a non-operation mode and characterized by operating a va've 11, ocated n the piston, and thereby aUowing fluid to pass through the piston, via at least one conduit 29 in the piston.