Coating Trends For Fasteners

Paper #:
  • 1999-01-3072

  • 1999-12-01
Garcia, R. and Barboza, J., "Coating Trends For Fasteners," SAE Technical Paper 1999-01-3072, 1999,
General Motors Corporation has always made every effort so that our end products and processes and configuration of components could help preserve the environment.Along those lines, General Motors do Brasil started to develop a protective coating that is corrosion resistant and environment friendly. At first, this will be used for fasteners. This effort involves dramatic changes in attitude, such as our need to admit that we are responsible for managing resources and keeping our world habitable and healthy for the future generations.This study describes metallic and organometallic coatings with an increased resistance to corrosion associated to temperature, free of such harmful metals as cadmium, nickel, lead, chromium, etc. Also demonstrated here is the significance of the total friction coefficient and its composition, considering the friction coefficients inherent to the fastener threads/heads. The friction coefficient is also related to the performance (efficiency) of the screw joint.The coating is completely recyclable, special consideration being given to reduced energy consumption, reduced metal waste and simplified waste handling during coating application to control proliferation and usage of toxic substances.Friction coefficient is another characteristic of coatings. As the level of automation tend to be increasingly higher in assembly processes, specifications for fastener coating have been requiring a low friction coefficient within a well-defined range.Because the friction coefficient is established under coating specifications, we can assure that metallic joints will always be uniform in quality levels and Process Engineers will always benefit from torque values and tensioning forces within well-limited ranges.The coating incorporates lubricating media in the layer, which ensures well-defined, controlled friction coefficients. This in turn will enable automation of assembly operations and guarantee rigid, stable joints.The significance of the friction coefficient can be seen from DIN 946 - “Determination of Coefficient of Friction of Bolt/Nut Assemblies under Specified Conditions” - which has become a key document in relation with fasteners as a result of automated assembly processes.The coatings referred to herein are available in Brazil, where five different technologies have been approved so far and another one is under final tests. All of these techniques involve parts coated in Brazil.
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