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Chapter 28

Chapter 28. Hard Facing, Surface Treatment, and Protective Coatings. Hard Facing • Surface Treatment • Protective Coatings. Hard facing is used to combat adhesive wear and galling, gouging, erosion, cavitation erosion, and contact fatigue.

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Chapter 28

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  1. Chapter 28 Hard Facing, Surface Treatment, and Protective Coatings Hard Facing • Surface Treatment • Protective Coatings

  2. Hard facing is used to combat adhesive wear and galling, gouging, erosion, cavitation erosion, and contact fatigue.

  3. Hard facing materials are identified by AWS designations or commercial names.

  4. The four principal thermal spraying processes are flame spraying, spray and fuse, plasma spraying, and high-velocity oxyfuel thermal spraying.

  5. Conversion coatings are surface treatments that modify the surface layer of a metal through oxidation.

  6. Anodizing is the anodic oxidation of specific base metals to enhance their naturally formed oxide films.

  7. An electroplating bath consists of a tank, anodes, cathodes, and a rectifier. The tank is filled with the plating solution (electrolyte).

  8. During electroplating, positive ions in the plating solution migrate toward the cathode, where they are reduced to the metallic state and deposited on the cathode.

  9. The amount of metal deposited in electroplating is determined by its equivalent weight.

  10. Brush or selective plating is used to touch up damaged plating or to locally repair worn or scored shafts or other items in the field.

  11. Chromium plating causes a significant reduction of fatigue strength unless steps are taken to prevent the loss.

  12. Nickel plating exhibits a wide variety of properties depending on the composition of the plating electrolyte and the operating conditions.

  13. Ion implantation is performed in a vacuum using an ion accelerator.

  14. In sputtering, the target is bombarded by gas ions that have been accelerated at high voltage.

  15. In evaporation, the ions or molecules are obtained by vaporizing the source.

  16. With ion plating, dense coatings may be achieved.

  17. Coating components include resins, pigments, solvents, and various additives for improving desirable properties.

  18. An emulsion is a mixture of liquid droplets interspersed throughout a liquid, while a dispersion is a mixture of solid particles interspersed throughout a liquid.

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