CHAPTER IV 

 THE TIN BRASSES 



Ternary alloys of copper-zinc and tin have been estab- 

 lished in commercial use for many years. Many, 

 including Hoyf*''*, Guillet, Hudson, and Jones'^"', and 

 Campbell'^", have investigated their sti-uctural charac- 

 teristics and established phase relationships. 



There are many tin brasses in use but the following 

 are the more important of those commercially available 

 in wrought form. 



Most common name 



Bearing or weatherstrip bronze 



Chain bronze 



Pen metal 



Admiralty metal 



Tobin bronze 



Government naval brass 



Hard naval brass 



Low-leaded naval brass 



Medium-leaded naval brass. . . 

 High-leaded naval brass 



Copper, 



% 



90 

 87 

 83. 

 71 

 60 

 60 

 61 

 60 

 60 

 60 



Tin, 



% 



0.50 

 1.25 

 1.50 

 1.00 

 0.75 

 0.75 

 0.75 

 0.75 

 0.75 

 1.00 



Lead, 

 % 



0.20 



0.50 

 0.75 

 2.00 



Zinc, 



% 



Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 

 Balance 



Properly to be included with the above are the so-called 

 "manganese bronzes." These alloys are actually tin 

 brasses in which manganese is present only as a residual 

 deoxidant. The more important alloys of this type are 

 the following. 



Bearing or weatherstrip bronze is largely used as a 

 bushing material involving light bearing loads and also 

 for weatherstrip applications. The presence of the tin 

 in the alloy slightly increases its resistance to atmospheric 

 tarnish and corrosion and moderately improves its tensile 

 strength. 



This alloy has excellent cold-working properties and 

 is most commonly fabricated in strip form by cold rolling. 

 The more important physical properties and a sum- 

 marization of mechanical properties may be found in 

 Table 1. Charts 1 to 10 on pages 134 to 136 give in 

 detail the influence of cold working and the effect of 

 various annealing treatments on the mechanical prop- 

 erties of this alloy. 



Chain bronze and pen metal are most commonly 

 used for the manufacture of brass chains and pen points. 

 The tin additions are made in both cases for the purpose 

 of improving strength, color, and corrosion resistance. 

 These alloys are also cold-working alloys and can be 

 hot-worked only with difficulty. They are seldom 

 fabricated in other than strip form. Tables 2 and 3 on 

 pages 137 and 140 indicate the more important physical 

 properties and give a general summary of their mechan- 

 ical properties. Detailed mechanical properties of cold- 

 rolled and annealed material may be found in Charts 

 11 to 32 on pages 137 to 143. 



Admiralty metal was developed as a condenser-tube 

 material by the British Navy in 1890 as an improvement 

 over 70-30 copper-zinc, which up until that time was the 

 most important commercial condenser-tube alloy. 



Research indicated that the presence of 1 per cent of 

 tin in 70-30 brass produced an alloy that had slightly 

 better mechanical properties than plain brass and, in 

 addition, had the property of developing a more protec- 

 tive film in contact with salt or brackish waters. Since 

 that time the use of admiralty metal in heat exchanger 

 applications has grown continuously. Today approxi- 

 mately 75 per cent of the total poundage of condenser 

 tubes sold in the United States is admiralty metal. 



In 1922, British investigators determined that the 

 presence of 0.02 to 0.05 per cent of arsenic in. admiralty 

 metal effectively prevented a type of corrosion known 

 as "dezincification." Since then it has been standard 

 English practice to include a small amount of arsenic in 

 • all admiralty-metal condenser tubes. Early in the 1930's 

 American fabricators of this alloy adopted similar prac- 

 tice. The presence of arsenic in no way influences the 

 working or structural properties of the metal. 



Admiralty metal is also used extensively for tube 

 sheets in heat exchangers of all types. It is used occa- 

 sionally in strip form for the fabrication of stamped or 

 drawn articles. 



Admiralty metal is essentially a cold-working alloy 

 although it can be fabricated hot if especial care is taken. 

 If hot-working operations, such as rolling, are to be per- 

 formed, it is absolutely necessary that lead be kept to a 

 trace, otherwise serious cracking will occur. Because 

 of the tin content and also because of the copper-zinc 

 range, hot working can be carried on in a limited tempera- 

 ture range only. Hot extrusion of tubes is usually per- 

 formed at temperatures of 1350 to 1400°F. and hot rolfing 

 at a range of 1350 to 1450°F. Prior to any hot-working 

 operation it is essential that castings be soaked at a 

 temperature of from 1350 to 1450°F. for several hours 



132 



