Free-Cutting Brass (Alloy 360) for Automatic Screw Machine Products

Free-Cutting Brass, Copper Alloy No. C36000 (“Alloy 360”), is a standard alloy of copper and zinc containing about three percent lead. The basic 60-40 mixture of copper and zinc forms an alloy with good strength and corrosion resistance; the small amount of lead provides the superior machinability that gives the alloy it familiar name. With these three constituent elements – copper, zinc and lead – the alloy is completely recyclable.

Free-Cutting Brass is an old and thoroughly understood alloy. It is one of the most widely used of the copper metals; hundreds of millions of pounds of it are consumed annually in the USA, year after year. But Alloy 360 is also a very modern engineering material, especially in light of today’s production economics. In short, Free-Cutting Brass is an available, affordable, compatible alternative to leaded steel for screw machine products.

Free-Cutting Brass is strong; some design engineers are surprised to learn that the strength of half-hard Alloy 360 falls in a range between hot-rolled and cold-drawn G12144 leaded steel (formerly AISI 12L14), brass’s major competitor. (“Half-hard” describes the strength condition, or “temper,” which is usually specified for brass rod for screw machine products.) And, being a brass, Alloy 360’s ductility is significantly higher than steel’s. The numbers, taken from the SAE Handbook1, are tabulated below.

Most screw machine products are not designed to meet high strength requirements. Steel screw machine parts, for example, are not ordinarily heat treated. In fact, strength requirements for common screw machine parts are generally modest compared with the values tabulated above. Surveys have shown that Free-Cutting Brass can be substituted directly for leaded steel in more than half of all screw machine products without sacrificing strength or safety.

Therefore, if a part is currently being made from G12144 steel, chances are good that a simple change to Free-Cutting Brass will produce a part of at least equivalent performance.

But why change to brass, even if it is just as strong as steel? Isn’t brass expensive? Isn’t brass simply too exotic for the kind of screw machine products made from leaded low-carbon steel?

No, it is none of the above.

First of all, Free-Cutting Brass is not expensive; in fact, typical screw machine parts made from Free-Cutting Brass cost less than the same part made from leaded steel. Copper vs. Steel– True or False? shows how specifying Free-Cutting Brass can save you money. It also provides a few other facts about Free-Cutting Brass to think about when selecting the material for your next screw machine product, or when re-ordering an existing steel part.