Corso Ottonaio

The brass maker is the craftsman who works brass, an alloy consisting essentially of copper and zinc with percentages of zinc varying from 5 to 45 ÷ 50%. It is necessary to distinguish between binary brasses, consisting of copper and zinc, ternary brasses in which there is a third chemical element characterizing the alloy and quaternary brasses in which other chemical elements are present. The machinability of the copper-zinc binary alloys on machine tools is good, but the toughness causes the formation of very long chips; to overcome this drawback, lead (Pb) is added which, insoluble and foreign to the crystalline structure, is dispersed at the edges of the grains: thus the shavings become short or even dusty and the tools undergo less wear and heating, resulting in an improvement in the quality and speed of processing. Lead brass is also called dry brass. The presence of lead in some countries limits or prohibits its use in sanitary and other applications in contact with humans. The influence of the alloying elements can be studied through the Guillet coefficients, i.e. the addition of a third alloying element can be considered equivalent to the addition or subtraction of zinc. For example, the addition of silicon (coeff. = 10) is equivalent to a 10 times greater quantity of zinc: it thus happens that if 1-2% silicon is added to a Cu Zn 30 binary brass (with total α structure), becomes a totally β structure. Nickel has a negative equivalence coefficient, while that of lead is zero, since,