FIELD OF INVENTION:

The invention relates to the general field of shearing and in particular to the shearing of metal plates and strips.

BACKGROUND OF THE INVENTION:

The use of hydraulically operated shearing machines to cut sheet metal is well know. For example, GB 2405118 A describes a hydraulically actuated shearing machine which achieves a rocking type shearing action by using a curved shear blade and two separately controlled hydraulic cylinders. A simplified cross section is illustrated in Figure 1. The piece of material that is to be cut 1 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. Two hydraulic cylinders 6 and 7 of a hydraulic actuating-mechanism are connected between the upper support beam 4 and the lower support beam 5. Each of the hydraulic cylinders 6 and 7 engages the upper support beam 4 in one engaging-area, hydraulic cylinder 6 in the engaging area on the left end of upper support beam 4, and hydraulic cylinder 7 in the engaging area on the right end of upper support beam 4. By controlling 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 is being cut. With a raked shear blade the distance the shear blade has to move is the thickness of the material plus the width of the material multiplied by the tangent of the rake angle. Typically 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 full 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 hydraulically operated shearing machine like the one in Figure 1 has three primary parameters which determine the necessary size of the hydraulic fluid pump system and of the valves which supply fluid to the hydraulic cylinders. The first parameter is that the combined annulus area of the hydraulic cylinders must be sufficient to generate the overall 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 typically must be able to work with a cutting cycle time of about 3 seconds and a reset-time of about 7 seconds.

For thin and/or 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 is very expensive and needs a lot of space, and the operation of large pumps and valves is energy-intensive and high-maintenance.

Applicants patent application 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 1 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/min. 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.

Hydraulic cylinders having internal flow paths are known. For example, US 5,237,916 discloses a regenerative hydraulic cylinder having several passages between opposite piston faces. A valve member is switchable, via a hydraulic pilot line, between a flow impeding orientation and a flow enabling orientation.

The present invention avoids these problems seen in prior art metal shearing machines by providing a metal shearing machine having the features of claim 1 attached hereto.

In a preferred embodiment, the first hydraulic piston includes a detachable cylinder rod.

In a preferred embodiment, the valve in the hydraulic piston may be supplied with fluid via a conduit in the corresponding cylinder rod. 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 according to the present invention is located in a cylinder 9, piston 8 and cylinder 9 being arranged to define chambers 10. Piston 8 includes 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 skilled in the art that the invention is equally 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 typically 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.