GB1181782A - Improvements relating to Grinding - Google Patents

Abstract

1,181,782. Snagging. NORTON ABRASIVES Ltd. 1 March, 1967 [11 March, 1966], No. 10908/66. Heading B3D. A method of snagging a workpiece, e.g. a steel slab or billet prior to rolling it into sheet or strip form, comprises contacting said workpiece with the peripheral surface of a rotating snagging wheel, said peripheral surface including a first surface area of relatively high grinding efficiency and a second surface area of relatively low grinding efficiency, said first surface area being located at a different radial distance from the wheel axis than said second surface area, while effecting relative movement between said workpiece and said wheel such that said workpiece is contacted by said second surface after being contacted by said first surface area, said relative movement including a component of movement parallel to the axis of rotation of said wheel, whereby to impart to said workpiece a surface finish superior to that which would be achieved by contacting the workpiece solely with said first area while achieving a grinding efficiency greater than that which would be achieved by contacting the workpiece solely with said second area. A snagging wheel, Fig. 1a for use in a reciprocating type of snagging operation, has outer ayers 2 of high grinding efficiency comprising a relatively coarse abrasive material and an inner layer 3 of lower grinding efficiency comprising finer or more friable abrasive material. The layers may be moulded as a single wheel, the layers may be made separately and cemented together to form a single wheel or the layers may be made as separate wheels and mounted on a single spindle. The wheel may be formed with a convex contour; if formed cylindrically, it acquires the convex contour when snagging is started. Thus, the layer 3 determines the nature of the finish. In a modification, Fig. 2a (not shown), a wheel has outermost layers (5) of high grinding efficiency, intermediate layers (6) of lower grinding efficiency and a middle layer (7) of still lower grinding efficiency. In a further modification, Fig. 3a, a wheel for use in a unidirectional type of snagging operation, has a leading layer 9 of high grinding efficiency and a trailing layer 10 of lower grinding efficiency. A wheel according to Figs. 1a, 2a or 3a may be moved across the surface of a workpiece 11 with its median plane at right-angles to the surface, Fig. 4, or at an acute angle to the surface in the direction of movement, Fig. 5. The wheel may be reciprocated; in the case of Fig. 4, no change of attitude of the wheel at the end of each pass is necessary but in the case of Fig. 5, the tilt of the wheel must be reversed at the end of each pass; moreover, a wheel as in Fig. 3a would have to be rotated through 180 degrees at the end of each pass. The arrangement of layers may be reversed, so that the high grinding efficiency area is further from the axis than areas of lower grinding efficiency. Such a wheel is moved across the workpiece surface with its median plane at an obtuse angle to the surface in the direction of. movement, Fig. 6. When the wheel is reciprocated, the angle of tilt is reversed at the end of each pass. The layers may comprise the same abrasive material but of different particle sizes, different abrasive materials of the same particle sizes, or different abrasive materials of different particle sizes. The preferred abrasive material is sintered bauxite but others such as fused alumina may be used. The binder may be resin. There may be a continuous gradation of grinding efficiency from one peripheral edge of the wheel to the opposite edge of the wheel.