CHAPTER III 

 THE LEADED BRASSES 



Lead is virtually insoluble in alloys of copper and zinc 

 and, when present, occurs as finely divided and dis- 

 tributed metallic particles. Its presence in brass does 

 not appreciably influence the mechanical strength or cor- 

 rosion resistance of the parent alloy but it does drastically 

 reduce the ease of flaring, upsetting, cold-heading, and 

 bending operations, all of which can be performed with- 

 out difficulty on most of the unleaded copper-zinc alloys. 

 The one reason why lead is added to brass is to improve 

 its machinability. Copper-zinc alloys, because of their 

 ductility, machine rather poorly. The chips are long 

 and tough, tool wear is high, and lubrication problems 

 are difficult. Lead uniformly distributed in a brass 

 alloy causes the chips to break off and, since the chips of 

 leaded brass are practically undistorted and are only in 

 momentary contact with the tool face, very little heat is 

 transmitted to the cutting edge of the tool during 

 machining. 



With leaded brasses, friction between the chip and the 

 tool is reduced to a minimum. Experiments conducted 

 on leaded brass indicate that, at any feed with cutting 

 speeds up to 500 feet per minute, the principal factor 

 determining the cutting life of the tool is the linear dis- 

 tance traveled by the cutting edge in contact with the 

 work.*"' 



In selecting leaded brass for a particular application, 

 however, thought must be given not only to the matter 

 of machinability, but to the question of the influence of 

 lead on future operations or on the service life or per- 

 formance of the fabricated part. 



Brass that is to be cold-headed should contain little 

 if any lead. Careful control of lead is required in brass 

 that is to be brazed, welded, or silver-soldered. Where 

 spinning, heavy knurling, or heavy roll-threading opera- 

 tions are to be performed, a high lead content should be 

 avoided. There are available brass rods either lead- 

 free or semi-leaded that are satisfactory for operatio^as of 

 this type. 



Lead in brasses definitely improves shearing, blanking, 

 and piercing operations. 



Lead in the alpha brasses renders them hot short and 

 unsuitable for fabricating by hot-working methods. 



The alpha-beta brasses containing between 55 and 

 60 per cent of copper can be hot-rolled if the lead does 

 not exceed 1 per cent and can be successfully hot-forged 

 with up to 2 per cent of lead. If greater amounts of lead 

 than this are present, cracking in forging may occur. As 

 the copper content increases beyond 60 per cent, smaller 



Superior figures in parentheses refer to the numbered items in the 

 Bibliography, pages 331-332. 



amounts of lead can be tolerated. When the limit of the 

 beta phase is reached, between 63 and 64 per cent of cop- 

 per, lead must be kept to a trace if hot-working proper- 

 ties are to be retained. 



In the annealing of leaded brasses care must be taken 

 to avoid sudden exposure of cold-worked parts or 

 material to high temperature as the presence of lead 

 makes brass more sensitive to "fire cracking" (see 

 Brasses). 



There are available today a wide range of composi- 

 tions in leaded brass to cover a multiplicity of require- 

 ments. The most common commercial leaded brasses 

 are as follows: 



Most common name 



Hardware "bronze" 



Lancashire brass 



Leaded high brass 



Brass rod (leaded) 



Heavy-leaded sheet 



Engraver's brass 



Leaded brass 



Riveting and turning rod 

 Free-cutting brass rod . . . 



Low-leaded rod 



Deep-drilling rod 



Forging rod 



Extruded shapes 



Architectural "bronze". . 



Red brass 



Copper, 

 % 



87-90 



73 



65 



64 



64 

 63.50 



62 



62 

 61.50 



63 

 61.50 



60 



59 

 56.60 



Lead, 



% 



1-2 



2.50 



0.90 



1.25 



2.50 



1.50 



1.50 



1.60 



3.00 



0.50 



3.75 



2.00 



2.00 



2.20 



1.50 



Zinc, % 



Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 



Balance 

 Balance 

 Balance 



Al, 0.3%; Zn, 



balance 

 Balance 



Hardware bronze, so-called because it is used in the 

 manufacture of hardware, is most commonly fabricated 

 in rod form. This material has excellent cutting proper- 

 ties and has a color closely approximating that of the 

 more expensive tin bronzes. In addition, it has corro- 

 sion- and tarnish-resistance properties approximating 

 that of copper. The most important physical and gen- 

 eral mechanical properties are given in Table 1 on 

 page 9L Detailed data on the effect of cold working 

 and annealing on the mechanical properties are given on 

 Charts 1 to 7 on pages 91 to 93. 



Lancashire brass is widely used in the fabrication of 

 clock parts. The presence of the lead in this alloy 

 causes it to shear and punch with clean, smooth edges. 

 It is most commonly fabricated in strip form only. 

 Physical properties and general mechanical properties 

 are given in Table 2. More detailed data are given 

 in Charts 8 to 20 on pages 94 to 97. 



89 



