ASTM-B507:14(R2021) pdf free download – Standard Practice for Design of Articles to Be Electroplated on Racks.
The average-to-minimum thickness ratio in these examples was 9.2 for the part with sharp corners and 5.6 for the part with the rounded corners.
6.4 Deep recesses will always have a thinner deposit than the surrounding external areas, as shown in the cross section of a concave part in Fig. 7(a). The average-to-minimum nickel thickness ratio for this example was 6.6. A more uniform deposit thickness can be obtained on a convex-shaped part, as shown in the example of Fig. 7(b). In this case the averageto-minimum nickel thickness ratio was 2.
6.5 Another example of an elongated curved surface (convex) is illustrated in Fig. 5(a).
7. Racking and Rinsing
7.1 Other factors besides metal distribution should also be taken into account when designing a part that will be rack electroplated. The parts must be attached firmly to the rack, so that all significant surfaces come in contact with the electrolyte.
7.2 The parts must be attached to a rack firmly enough to prevent falling off during electroplating, and the attachment should be with enough force to provide a continual low- resistance electrical contact. In many cases, parts are rigidly fastened to racks through spring clips, prongs or bolts. Little or no metal will deposit at the points of contact: therefore, it is important to select noncritical areas for attaching parts to racks.
7.3 Articles attached to racks should he oriented to permit electroplating to be free of roughness on significant surfaces. Roughness comes from insoluble debris suspended in an electroplating bath that becomes incorporated into the depositing metal, especially on upward facing surfaces. Thus, in many circumstances, it is advisable to have the significant surfaces in a vertical position, or even be inverted during electroplating.
7.4 Orientation of a part on a rack is also important to reduce opportunities for air entrapment in cupped areas. Air pockets will revent metal deposition on the exposed surface. Adequate drainage of parts on racks is also desirable to reduce dragout of the electrolyte to the rinses. Engineering design can incorporate holes at strategic locations to allow satisfactory runoff of solution.
7.5 Racks that are near the significant surface may interfere with the plating by robbing the surface of current and cause thin deposition. Robbers can be used to remove some of the current to increase the uniformity on the significant surface. These techniques can be used to produce a uniform deposit thickness on complex shapes.
8. Keywords
8.1 cathode; curreni density; fixture; rack; racking; uniformity.