Metal Finishing and Buffing Brass

Brass:  This is common for household building materials such as lock sets and door hinges. It is also very common for kitchen faucets and other plumbing components.  When properly processed, it can be buffed to levels that rivals that of buffed precious metals used in jewelry.  Because of the active, corrosive surface exposed by buffing, brass requires plating or clear coating to protect the finish.

Brass is commonly made from a combination of copper and zinc with other alloys often added for strength and/or additional corrosion resistance.  (Yellow Brass has a ratio of roughly 70% Copper and 30% Zinc).  The relatively low melting point of 1560 to 1725 °F makes it good for both casting and machining.  It also makes it a good metal for either the aggressive (higher temperature) tangential buffing or (the cooler) mush buffing.  Since the metal can go ether way the type of buffing is usually determined by the geometry of the part:

• Flat Parts or Round Brass Parts:  (The round parts here are often made from bar stock on screw machines.)  Often these parts buffed using Tangential Buffing Operations.  The round parts are often placed on a rotary table where Sisal Buffs or Hard Treated Buffs can apply high pressures quickly and make short work of the buff process. The flat parts may be buffed on reciprocating tables or in off-hand operations.
• Complex Castings or Tubular Brass Parts:  Often buffed using Mush Buffing Operations.  These are either buffed in off-hand operations or use large slow buffing heads in the Mush Buff Automatic machines.  These operations often use a treated poly/cotton buff to find the proper balance between contouring to the part and providing an aggressive cut & color buff operation to smooth the part. This is often followed by an all cotton “wipe-off” or “Clean-up” buff head to provide the clean bright finish before the part is sent to plating.

Although not quite as reactive as zinc, brass will still oxidize (or tarnish) over a short period of time.  If there is no protection applied to the surface of the part and the time between buffing and plating is too long then the part will oxidize on the surface making it impossible to properly plate or clear coat the part.  It is possible to use an anti-oxidant in the buffing compound that can protect the part for several days (and maybe even weeks) before the part is plated.