Crop shear knife and method of operating same

Claim 1

In crop shear apparatus for severing relatively thick and resistant stock, said apparatus comprising a pair of knife supports arranged to rotate synchronously in opposite angular directions around parallel axes, a pair of knives one of which is carried by each of said supports and each of which knives has an outer cutting edge extending longitudinally generally parallel to the axis of rotation of its support, said knives being rotatable in circular orbits of like radius into and out of a cutting edgeabutting position which corresponds to maximum stock penetration without substantial overlap of the knives, the novelty which comprises a trailing knife having a forwardly directed shearing face extending inwardly from said cutting edge and inclined rearwardly with respect to a radius at an angle which is so related to the radius and to the thickness of the work that the included forward angle between said shearing face and the work at the position of initial effective contact with the work just prior to penetration is substantially 90* and increases during continued rotation, and a leading knife having a rearwardly directed shearing face extending inwardly from its cutting edge at an included rearward angle which decreases during continued rotation and which, at said position of initial contact, is not less than 90* to the plane of the work and not greater than the angle between the plane of the work and a radial line projected from the cutting edge to the axis of rotation.

Claim 7

The method of shearing plate stock in a crop shear which comprises determining the radius of the orbits of the knives and the thickness of the work, arranging the forwardly facing shearing face of the trailing knife to substantially intersect the shearing edge and at an angle such that at its position of initial operative engagement with the work the included angle between the shearing face and the plane of the work is equal to or greater than 90*, arranging the rearwardly facing shearing face of the leading knife to extend inwardly from its shearing edge at an included angle to the work which at said position is not less than 90* to the plane of the work and not greater than the angle between the plane of the work and a radial line projected from the cutting edge to the axis of rotation, and rotating the knives synchronously in opposite angular directions around parallel axes to bring their shearing edges into edge abutting position without substantial overlap and shearing the work while increasing the first-mentioned included angle and decreasing the second-mentioned included angle.

Claim 8

The method of shearing plate stock in a crop shear which comprises determining the radius of the orbits of the knives and the thickness of the work, arranging the forwardly facing shearing face of the trailing knife to substantially intersect the shearing edge and at an angle such that at its position of initial operative engagement with the work the included angle between the shearing face and the plane of the work is equal to or greater than 90*, arranging the rearwardly facing shearing face of the leading knife to extend inwardly from its shearing edge at an included angle to the work which at said position is not less than 90* to the plane of the work and not greater than the angle between the plane of the work and a radial line projected from the cutting edge to the axis of rotation, and rotating the knives synchronously in opposite angular directions around parallel axes to bring their shearing edges into edge abutting position without substantial overlap and shearing the work while increasing the first-mentioned included angle and decreasing the second-mentioned included angle.

Claim 10

The method of severing heavy metal plate stock or the like with a rotary shear of the type having paired leading and trailing shearing knives orbitally synchronously rotatable in opposite angular directions about parallel axes toward and from a closely adjacent position at an interposed pass line while the stock is moving therebetween along the pass line which comprises determining the length of a straight line from the axis of rotation of the trailing knife to the nearest point on the surface of the stock, determining the length of a radial line from said axis to the pass line, determining the angle corresponding to the cosine of the angle between said lines when a right triangle is constructed therefrom having its hypotenuse corresponding to said radial line and its third side corresponding to a line on the surface of the stock closest to the trailing knife, arranging a forwardly facing shearing surface on the trailing knife at such an angle to a radial line projected to its shearing edge that said shearing surface slopes rearwardly and inwardly with respect to said last-mentioned radial line at an angle which is not materially less than the angle corresponding to such cosine, and shearing the stock in the shear between said knives.

Claim 11

The method of severing heavy metal plate stock or the like with a rotary shear of the type having paired leading and trailing shearing knives orbitally synchronously rotatable in opposite angular directions about parallel axes toward and from a closely adjacent position at an interposed pass line while the stock is moving therebetween along the pass line which comprises determining the length of a straight line from the axis of rotation of the trailing knife to the nearest point on the surface of the stock, determining the length of a radial line from said axis to the pass line, determining the angle corresponding to the cosine of the angle between said lines when a right triangle is constructed therefrom having its hypotenuse corresponding to said radial line and its third side corresponding to a line on the surface of the stock closest to the trailing knife, arranging a forwardly facing shearing surface on the trailing knife at such an angle to a radial line projected to its shearing edge that said shearing surface slopes rearwardly and inwardly with respect to said last-mentioned radial line at an angle which is not materially less than the angle corresponding to such cosine, and shearing the stock in the shear between said knives.