The standards for Alloy 260 brass call for 68.5 to 71.5 percent copper, 28.5 to 31.5 percent zinc and no more than 0.05 percent each of iron and lead. In practice the ratio of copper to zinc is rounded off to 70-to-30, so that the alloy is often referred to as "70/30 brass."
The solid melting point of Alloy 260 is 1,750 degrees Fahrenheit, and its liquid melting point is 1,680 degrees Fahrenheit. Its density at 68 degrees Fahrenheit is 308 lbs. per cubic inch, and its coefficient of thermal expansion --- change in volume when heated or cooled --- is 0.0000111 unit per degree Fahrenheit.
Properties when Annealed
Alloy 260 brass is annealed --- treated with heat followed by a cooling bath --- between 800 and 1,100 degrees Fahrenheit in order to enhance its natural strength as well as its heat and electrical conductivity. When it is annealed, Alloy 260 conducts heat at a rate of 70 BTU per square foot per hour per degree Fahrenheit based on a starting point of 68 degrees Fahrenheit. The electrical resistance of annealed wire made with Alloy 260 is 37 Ohms per foot of 1/1000 of an inch of diameter, or per circular mil, at 68 degrees Fahrenheit. Its electrical conductivity is measured at 26 to 28 percent at 68 degrees Fahrenheit.
The tensile strength of Alloy 260 is 43,000 pounds per square inch and the yield strength is 10,900 psi. Shear strength is 31,000 psi, shear torsion/modulus of rigidity is 6,000,000 psi and its modulus of elasticity --- amount of force needed to change its form by stretching --- is 16,000,000 psi.
Hardness and Flexibility
Alloy 260 brass has a Brinnell hardness score of 68 HB; this is about twice the score of copper and about five times that of aluminum. Its machinability rating is 30, making it one of the easiest types of brass to shape and cut.
Other Specifications and Characteristics
The ideal temperature for molding hot brass is from 1,300 to 1,450 degrees Fahrenheit. It has a smooth yellow finish that can be polished or brushed. It is easily cut and finished with polishing and buffing compounds, and it is known for its resistance to corrosion.