| 摘要 |
1,145,259. Etching. DOW CHEMICAL CO. 4 Aug., 1966 [4 Aug., 1965], No. 34925/66. Heading B6J. Curved plates used in the photo-engraving art (e.g. magnesium alloy plates) are etched by applying a resist image to the curved surface as a workpiece, impinging a liquid etching composition on to the surface, simultaneously rotating the workpiece about its axis of curvature while cyclically varying the angle between the said axis and the flightpath of the impinging etching composition in a repeated time cycle to provide a repeated sequence of flow in essentially all directions across each point of theworkpiece surface, continuing the rotation and cyclic motion until the required depth of etch is obtained, and rinsing the plate so etched. The cyclic motion may be effected by movement of the workpiece or of the flightpath of the etchant or of both simultaneously. In a preferred embodiment (Fig. 1) a first end 1 of a workpiece having a length L lies a given maximum vertical distance H from the second end 2 and the vertical disposition of the two ends with respect to one another is reversed twice (as shown by sequence 1-9) to restore the original distance H between the two ends while simultaneously rotating the curved surface about its axis of curvature. H may vary from 0.4 L to 1À0 L and the cycle may be repeated between 2 and 20 times per minute. Where the flightpath of the impinging etchant solution is varied the angle between its path and the axis of curvature may be cyclically varied between X‹ and 180-X‹ where X is between 10 and 80, and the cycle may be repeated from 0.5 to 120 times per minute. The peripheral speed of the workpiece about its axis of curvature may be between 70 and 250 feet (21 and 75 metres) per minute and the direction of rotation may be reversed between 0 and 60 times per minute. |
