93 



CuSn 



3o i5 Toe S^ 



Percentage of Copper 



Part of Provisionol Copper -Antimony -Tin Diagram. 



Ki;;-. :'. 



Fig. 1. e-tin-<-t)i»ii('r ;ils(. is liard. has a lower speciflc sravity tliaii that of 

 tin anil forms first of all t-rystals of the alloy of this comi)Ositi(in. on a fall- 

 ing temperature, along the branch E-F of the liquidus of Fig. 2. 



These crystals grow rapidly at temperatures within their formation 

 ranges. On account of their relatively low specific gravities flotation in the 

 still liquid portions readily occurs. It may easily happen that a given bear- 

 ing may have its hard, wear-resisting components so large that they become 

 broken in use and so distributed as to iwssess quite different properties at 

 different points. Figs. 4. .1. c. 7 and s illustrat(- the rapidily of flotation.* 

 .Metal was melted and immediately poured on a warm iron plate. A sheet 

 about one-fourth inch in thickness solidifled in less than thirty seconds. 

 Figs. 4, 5. 6 and 7 show the cast, unpolished upper surface. Fig. 8 the lower 

 surface, polished and etched with nitric acid. Even in the short time that 

 elapsed between pournig and solidification, segregation of -crystals has 

 occurred to so great an extent that none at all are present in the lower 

 surface layer. Figs. \) and 10 illustrate the extent of growth under unusual 

 conditions, although it may be noted that such conditions might easily be 

 brought about by inadequate control of furnace conditions. 



Rapid growth and segregation at liigher temperatures are well recognized 

 jihenomena. In the experiments described in this paiier an attempt was 

 made to determine the relative rates of growth and segregation of the two 

 systems of crystals here mentioned, in temperature ranges near the re- 

 spective solidi. 



AVorking specimens were first prepan'd by melting a quantity of the 

 alloy at (iHO" (.'.. stirring thoroughly with a stick of wood and immediately 

 casting in chill molds of cast iron. This resulted in the formation of fine 

 crystals, as shown in Figs. 11 and 12, taken after poli.shing and etching 

 sections of two of tlie jneces. Tliese specimens were then heated to stated 

 temperatures and either chilled or slowly cooled after certain periods of 



