Metal Shearer with Adjustable Side Link

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:

To perform a cut with a shearing machine at least one shear blade has to be moved towards another shear blade with a force which is named overall actuating-force, the overall actuating-force being sufficient to overcome the resistance of the material to be cut, the resistance being named cutting force. When shearing wide metal plates and strips a straight cut of the full width of material would require an enormous overall actuating-force which would not be practical. Consequently shearing machines for shearing wide material generally use either a raked shear blade, or a curved shear blade for a rocking type shearing action.

The present invention is concerned with improvements to apparatus and methods for employing the rocking type shearing action.

When employing a rocking type shearing action the major components of blade movement are determined by cranks or hydraulic cylinders. Lateral position of the top blade assembly is controlled by a side link or perhaps a pin or other sliding part moving against a slideway.

The problem with these prior art methods is that they do not allow the blade to execute a perfect rolling cut motion. There is always some lateral movement of

the blade causing a deviation from the ideal rolling action. This lateral movement leads to a poorer quality of cut and increased blade wear.

The invention addresses these problem of the prior art by providing, according to a first aspect of the invention, a metal shearer comprising the features recited in claim 1 attached hereto.

According to a second aspect of the invention, a method of shearing metal comprises the steps set out in claim 9 attached hereto.

The invention will now be described with reference to the appended figures in which:

Figure 1 is a schematic representation of a conventional rolling cut mechanical shear, employing cranks to control the rolling cut motion of the shear;

figure 2, is a schematic representation of a hydraulically operated rolling cut shear;

figure 3 shows the error between the ideal lateral position of the upper blade (for a perfect rolling cut) and the actual position when the upper blade is constrained by a side link of fixed length and

figure 4 shows a schematic representation of a rolling cut shear according to the invention.

The figures are not to scale and are not intended to represent the relative sizes of components. Any component which appears in more than one figure is lablelled with the same numeral throughout.

Referring to figure 1 , a conventional rolling cut mechanical shear comprises an upper blade 1 and a lower blade 2 mounted on a support beams 3 and 4 respectively. The rolling cut motion of upper blade is determined by cranks 5 and side link 6.

Referring to figure 2, in a hydraulically operated rolling cut shear, the rolling cut motion of the upper blade 1 is determined by cylinders 7 and 8 and by side link 6. In figure 2, only one cylinder is located at each end of the support beam (for clarity) but in some installation two or more cylinders, having different capacities may be employed at each end. Such equipment is detailed in, for example, applicants co-pending application EP 0725358.8.

In the systems illustrated by figures 1 and 2, the fixed length of side link 6 prevents the upper blade 1 (and associated support beam 3) from executing a perfect rolling action. Instead, a degree of lateral movement of blade 1 with respect to the object being cut is caused.

Figure 3 plots the error between the ideal lateral position of the blade for a perfect rolling cut and the actual position as a result of the fixed length link. In practice, typical errors range from about -20mm to +30mm.

Further description of the invention is made using the example of a hydraulically operated shear but the principles illustrated apply equally to other rolling cut shears such as the type illustrated in figure 1.

Referring to figure 4, in a rolling shear according to the present invention, the fixed length side link is replaced with link of variable length 9. In the example illustrated, the variable length link is realised as a hydraulic cylinder. The stroke of the hydraulic cylinder is controlled by a servo-valve 10 and an electronic control system 11.

A position transducer (not shown) which is mounted on cylinder measures its stroke and the control system 11 adjusts the stroke to the desired value by sending an appropriate signal to the servo valve. The reference stroke for the cylinder is adjusted during the rolling cut motion in synchronisation with the movement of the upper blade in order to achieve a good rolling cut action with minimal lateral movement of the upper blade relative to the sheet being cut.

Electronic control system can be realised as a computer programmed to send the necessary signals to servo valve 10, in response to varying position of the support beam 3 and the stroke of cylinder 9.

It will be apparent to those skilled in the art that alternative implementations of the variable length link are possible. For example, instead of utilising a hydraulic cylinder, the variable length link 9 could be realised as a screw jack (e.g. an electrically driven screw jack) or an eccentric cam. In light of the present disclosure, the implementation of such alternative embodiments of the invention is within the capabilities of a person skilled in the art.

Nevertheless, the use of a hydraulic cylinder to provide the variable length link may be particularly suited to systems employing hydraulic cylinders elsewhere (for example the system of figure 4), and which include the necessary elements of a hydraulic system anyway. A prior art system employing such cylinders (e.g. figure 2) particlurly lends itself to a post market upgrade, employing a further

cylinder and associated control equipment to create a system such as that illustrated by figure 4.