This invention generally relates to a mechanism and a process for coating portions of articles have dissimilar external configurations. More specifically, the invention relates to the application of a thermoplastic layer to coat tapped holes in specialty articles such as metal stampings.
It is well known to apply a thermoplastic resin powder such as nylon to threaded articles to form a "patch" which retards disengagement of the patched fastener with a mating fastener, as shown, for example, in U.S. Pat. Nos. 3,787,222 and 3,858,262. Mechanisms have also been developed for applying a protective coating to standard internally threaded fasteners at relatively high production rates, such as disclosed in U.S. Pat. No. 4,888,214, the disclosure of which is incorporated by reference herein. Similarly, other mechanisms have been developed for applying coatings to both standard and non-standard fasteners at lower production rates, such as disclosed in U.S. Pat. Nos. 5,141,771 and 5,362,327, also incorporated by reference herein.
A common characteristic of the fasteners described in the patents listed above is that they possess only a single tapped hole (e.g., nuts), and their external dimensions are maintained within close tolerances.
There are many specialty articles, such as metal stampings, that contain multiple tapped holes and possess a relatively large variation in their external dimensions. While the tapped or threaded holes of such specialty articles can also advantageously utilize the protective coating or patch described above, prior art coating or patch applicators, including the mechanisms described in the above-referenced prior art patents, typically utilize external dimensions to position the threaded holes with the centerline of corresponding spray nozzles. Unfortunately, this approach is hampered with most stampings, for example, whose external surfaces often have burrs and rough edges which preclude precise positioning from these edges. In the past, to accomplish the coating of articles with varying external dimensions, the coating has been applied to manually positioned articles, at correspondingly low production rates.
It would, therefore, be desirable to provide an automated process, and an automated mechanism, for applying protective coatings or patches to threaded holes in articles having varying external configurations, while also providing a corresponding increase in production rates.