GB2469288A

GB2469288A - Apparatus for shearing which offsets repulsive forces

Info

Publication number: GB2469288A
Application number: GB0906006A
Authority: GB
Inventors: Peter Walker
Original assignee: Siemens VAI Metals Technologies Ltd
Current assignee: Primetals Asset Management UK Ltd
Priority date: 2009-04-07
Filing date: 2009-04-07
Publication date: 2010-10-13
Also published as: GB0906006D0

Abstract

Apparatus for shearing comprises first and second blades (2, 3, fig 1) mounted on respective support arms; and a means for applying a first force to a first support beam in a first direction 4, which causes the first blade to perform a shearing action on the object, and which also gives rise to a repulsive force between the blades in a second direction 5. At least one blade is arranged with a vertical offset 8 and a horizontal offset 7 from a torsion axis 6 of its respective support beam. The vertical and horizontal offsets are selected to provide a total torque on the respective support beam to provide displacement of the at least one blade, which at least partially offsets the displacement arising from distortion of the respective support due to the repulsive force.

Description

Shear with Blade Offset The invention is concerned with shearing machines as typicaUy used in, for example, the processing of sheet or strip metaL A typical shear (shearing machine) includes an upper blade and a lower blade, each being mounted on a respective support beam. The blades are arranged, one on each side of a vertical plane and the action of a vertical force on one (usually the upper) blade causes the two to come together and slide past each other, thereby providing a shearing action on a suitably arranged object such as a metal plate.

In addition to the vertical force, a horizontal force arises from the action of the blades on the object. This force tends to push the blades apart.

Typically, the magnitude of the horizontal force is about 25 -30% of that of the vertical force. On large modern shears the vertical force can be about l6000kN so the horizontal forces can be 4000kN or more.

The vertical and horizontal forces cause deflection of the blades and the beams that support them. The horizontal deflection causes distortion of the cut so that the edge of the sheared plate has an undesireable curve and slope instead of being straight and square.

The prior art approach to this problem has been to employ robust, stiff structures for the bladelsupport beam assembly, which are less susceptible to distortion by these horizontal forces.

The present invention provides an alternative approach to this problem, which provides less distortion of the cut edge and allows for lighter support beams.

According to the invention apparatus for shearing an object comprises the features set out in daim 1 attached hereto.

The invention wi now be described by non-'imiting examp'e with reference to the appended figures in which: figure 1 shows a cross-section of a shear according to the prior art; figure 2 iIustrates the distortion of b'ade and suport beam arising from the repu'sive forces between the b'ades according to the prior art; figure 3 shows a perspective view of a blade and support beam assemb'y according to the invention; figure 4 shows a plan view of a blade and support beam assemb'y according to the invention; figure 5 shows a cross-section of a b'ade and support beam assemb'y according to the invention; Referrring to figure 1, in a shear according to the prior art a p'ate 1 is sheared by a top b'ade 2 and a bottom b'ade 3. This produces a vertica' cutting force 4 and a horizontal force 5 the iatter tending to separate the blades and increase the gap between them.

Referring to figure 2. even when robust supporting structures are emplyed, the horizonta' force causes disrortion of the b'ade to varying degrees a'ong its ength, the distortion typicay being greatest near the centre of the b'ade.

n the present invention, the b'ade and supporting beam assemb'y is designed such that the action of torsion on the beam during operation counteracts the deflection due to the horizonta' force.

Referring to figure 3. a support beam 10 and blade 2 assemb'y according to the invention is iliustrated in a perspective view. This example is concerned with the top blade and the shear is of the hydrauc type, where the vertical cutting force is provded by hydraulic cylinders acting on the ends of the beam.

Referring to figure 4, the horizontal force 5 causes a tendency for the blade/beam assembly to bend as indicated by the dotted lines. The deflection of the blade can be calculated as a function of the stiffness of the assembly.

Referring to figure 5, in a cross-sectional view of the support beam 10 and blade 2 according to the nvention, the vertical and horizontal forces are shown by 4 and 5 respectively.

The blade 2 is located relative to the torsion axis 6 of the assembly as indicated by hodzontal and vertical offsets 7 and 8 respectively. The vertical force 4 produces a negative (clockwise) torque on the beam, which is the product of the force 4 and the hodzontal offset 7. At the same time, the horizontal force 5 produces a positive (anticlockwise) torque on the beam, given by the product of the horizontal force 5 and the vertical offset 8. The overall torque on the beam can be set by selecting the correct ratio of offsets 7 and 8, having regard to the ratio of forces 4 and 5.

By choosing the offsets 7 and 8 correctly, the horizontal displacement of the blade due to the resultant torque can be made equal in magnitude and opposite in direction to that arising from the bending of the beam illustrated in figure 4. Consequently, distortion of the blade gap is minimised.

There are two components to the overall movement of the blade: - 1 Horizontal deflection due to bending of the beam in the horizonal plane as illustrated in Figure 4. Consider the case where the offsets 7 and 8 are chosen to give zero net torque on the beam. In this case the horizontal deflection of the beam is equal to the horizontal force 5 divided by the stiffness of the beam (in the horizontal plane).

2. Movement of the b'ade due to torsiona' twisting of the beam. imagine app'ying torque to the beam by two equa' and opposite horizonta' forces. n this case the net horizonta' force wou'd be zero and hence there wou'd be no horizonta' deflection of the beam. But the torque wou'd twist the beam about Its axis and the angle of twist would be equal to the applied torque divided by the torsional stiffness of the beam. The movement of the blade in direction 9 would be equal to the angle of twist x radius of the blade from the torsional axis.

In the case of the invention, the offsets 7 and 8 are adjusted to that these movements are opposite and, in a preferred embodiment equal i.e. horizontal_force_5 1 horizontal_stiffness net_torque / torsional_stiffness * rad us_blade_from_torsion_axis Note the the beam still bends -as illustrated by the dashed lines in Fig.4 but the twist of the beam moves the blade itself back relative to the axis of the beam so that the overa movement of the blade in the horizontal direction is close to zero.

The ratio of vertical force 4, to horizontal force 5 varies with factors such as the material to be cut. In a preferred embodiment, the vertical and, or horizontal offsets 7, 8 may be adjusted for such variations by employing shims or packers. In an aRernative embodiment the offsets could be adjusted automaticaUy using for example a wedge mechanism.

The invention has been illustrated thus far with respect to only one blade in a shearing machine but it will be apparent to those skilled in the art that it may be applied to both blades in a shearing pair.

Both blades may be mounted on their respective support beams with vertical and horizontal offsets from a torsion axis of the beam so that displacement caused by the repu'sive force between the b'ades, caused by the shearing action, is counteracted by disp'acement arising from the overa torque on each b'ade.

n an aRernative embodiment on'y one of the b'ades may be mounted with horizonta' and vertica' offsets s&ected to offset distortion of both support beams.

Claims

C'aims 1. Apparatus for shearing an object comprising: first and second blades mounted on first and second support beams respectively; means for applying a first force to the first support beam in a first direction, thereby causing the first blade to perform, in cooperation with the second blade, a shearing action on the object, which shearing action gives rise to a repulsive force between the blades in a second direction and characterized in that at least one blade is arranged on ts respective support beam with a vertical offset and a horizontal offset from a torsion axis of said respective support beam, the vertical offset and horizontal offset being selected to provide a total torque acting on said respective support beam to provide displacement of the at least one blade which at least partially offsets the displacement arising from distortion of said respective support beam due to the repulsive force.
2. Apparatus according to claim 1, wherein both blades are arranged on their respective support beams, each with a vertical offset and a horizontal offset from a torsion axis of their respective support beam, the vertical offset and horizontal offsets being selected to provide a total torque acting on each support beam to provide displacement of each blade which at least partially offsets the displacement arising from distortion of their respective support beam due to the repulsive force..
3. Apparatus according to claim I or 2, where the first direction is substantially vertical and the second direction is substantially horizontal.
4. Apparatus according to claim 3, where the first blade is an upper blade of the apparatus.
5. Apparatus according to c'aim 5, further comprising means for adjusting at east one vertical offset or at east one horizonta' offset.
6. Apparatus according to c'aim 1, wherein at east one blade is arranged on its respective support beam with a vertical offset and a horizonta' offset from a torsion axis of said respective support beam, the vertica' offset and horizonta' offset being se'ected to provide a totai torque acting on said support beam to provide dispiacement of said b'ade which at east partiaUy offsets the disp'acement arising from distortion of both blades respective support beams due to the repulsive force.