1. Field of the Invention
This invention relates generally to processes and equipment for galvanizing threaded rods and more particularly concerns a method and apparatus for dipping cleaned and prepared threaded rods in molten zinc, efficiently removing excess molten zinc from the dipped threaded rods and then cooling the threaded rods to solidify the molten zinc coating thereof. Even more particularly the present invention concerns a method and apparatus for achieving sufficient rotational velocity of threaded rods, immediately following molten zinc dipping, to cause removal of excess molten zinc by centrifugal force as the rods move from a zinc dipping station to a cooling station.
2. Background of the Invention
Within the hot-dip galvanizing industry, there exists a need to galvanize threaded rod material in large quantities. Manual hot-dipping of threaded rods is too slow and too labor intensive to allow for competitive pricing of the rods when sold to the end user. In addition, it is imperative that the threads of the finished galvanized rod be clean and smooth so as to allow for the application of a nut. This is known as `nut-ability` and is the single, most crucial requirement in the process of hot-dip galvanizing of threaded rods. To achieve nut-ability the excess molten zinc that typically adheres to threaded rods after the rods have been removed from the molten zinc bath must be removed so that the resulting solidified zinc material will not interfere with application of nuts to the threads of the rods.
Existing Methods Within the Industry
Currently, two methods are typically used to achieve hot-dip galvanizing of threaded rods. One method is to manually dip the rods in molten zinc using hooks and to then "sling" off the excess molten zinc as best as possible using a variety of manual methods. As mentioned above, this process is slow, quite costly from the standpoint of labor and the results are varied, producing a very low yield of usable product. The second most common method is to hang the rods vertically, typically in rod support cage devices, depending on rod thickness, and then dipping them into a molten zinc bath. As the threaded rods are lifted from the zinc, a motorized device above spins cage device containing the rod or rods and slings off the excess molten zinc from the threads, thus removing the excess molten zinc centrifugally. This zinc removal process is followed by dipping the hot rods in cold water to quench the rods and solidify the molten zinc. This process produces superior results from the standpoint of quality but the process is limited by the number of rods that the spinning device can handle at one time. In addition, the cages for holding the rod or rods must be cleaned of excess zinc and manually loaded and unloaded for each batch so that labor requirements for this type of galvanizing process are typically significant. This cleaning, loading and unloading is a time consuming process that depends on significant human interaction and is therefore susceptible not only to various yields of finished product, but increases the chance for injury to workers and damage to the product.