A dowel is a cylindrical rod made of wood, plastic, or metal. They are often cut into shorter lengths called dowel pins. These pins are used in a wide range of applications for reinforcing structures or supporting weights.
Metal dowel pins are machined to very tight tolerances, and are used as precise locating devices in machine applications. Pins either have a smaller diameter than the corresponding hole so that they can slip in, or a larger diameter so that they must be pressed in (interference fit). Engineers use dowels as reference points to create repeatable assembly processes and limit the variation between manufactured products. The advantage of dowels over bolt threads is that they permit less mechanical play (loosening of connections over time).
Black Oxide Coated Dowel Pins
The problem with metal dowels, though, is that they can rust over time and do not handle friction very well. Black oxide dowel pins are uniquely designed to address both of these issues. The black oxide coating protects the pins from rust and reduces friction between the hole and the pin, resulting in better functionality, less wear and tear, and therefore a longer service life. Also, because of the material’s low coefficient of friction, they can be slightly oversized, creating a superior tight connection.
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Other benefits of the black oxide coating are galling/cracking/peeling prevention, and a lightweight construction. Because of these features, dowel pins that have been coated in black oxide are often used in precision manufacturing for surgical instruments, hydraulic valves, cameras, microscopes, and other sensitive scientific research equipment.
Black Oxide Coating Process
Hot black oxide is applied using a sodium hydroxide oxidizer nitrite/nitrate bath. The steel is immersed in the 285-degree F bath for between 10 and 20 minutes. The result is an abrasion resistant surface finish complete with a rich dark blue color, which meets Military Specification 13924D, ASME B18.8.2, and AMS 2485.
A-Z Supply Can Help!
We carry an impressive selection of black oxide dowel pins in various shapes, sizes, and tolerances, with features such as beveled or rounded edges. Please visit our online catalog to explore what we have in stock, and contact us if you have any questions.