SOME PHYSICAL PROPERTIES OF WIPING SOLDERS 111 



any conclusions from the solid-liquid ratios regarding the plasticity 

 to be expected or regarding the quality of the solder must be dismissed. 



Comparison of Workahility and Temperature Gradient of Plasticity 



In Fig. 5 are shown the plasticity-temperature gradients for the 

 various solders. Here comparative values of plasticity for any one 

 solder are taken as given by the sample heights after ten minutes of 

 compression. It is seen that solders No. 1, 2 and 3 show good (low) 

 gradients, with No. 3 seeming to be superior, while Nos. 5, 6 and 

 especially No. 4, show a large variation in plasticity with temperature. 

 Since, if it is to be properly worked, a wiping solder must not vary 

 rapidly in consistency with temperature, this can be used as one 

 criterion for choosing a satisfactory solder, and on this basis the 

 solders tested should be placed in an order consistent with Fig. 5. 



Such a rating is quite in agreement with actual working charac- 

 teristics, which rank solder No. 3 first. No. 4 last, the others falling in 

 between in essentially the order which Fig. 5 would indicate. 



It is now of interest to determine if there exists any relation between 

 the rapidity with which the plasticity varies with temperature and 

 the values of h, the slope of the log rate vs. log height curve. Reference 

 to Table II will show that there is a wide divergence in the values of 

 h found for the different solders. It is further seen that the difference 

 exhibited from one alloy to the next is greater than the difference 

 between individual runs on one solder at different temperatures. This 

 virtual constancy of h for any one solder justifies, it may be noted in 

 passing, the use of sample heights after fixed intervals of compression 

 as comparative measures of plasticity, as in Figs. 4 and 5. There 

 would be no such justification for using such sample heights in com- 

 paring different alloys having different values of b. 



If then h is regarded as a constant for any one solder, independent 

 of temperature, mean values of b for each solder may be computed 

 from the values obtained at different temperatures. Such mean 

 values have been computed, and are included in Table II. Com- 

 parison of these with the curves of Fig. 5 shows a striking agreement 

 between the order of the solders based on increasing temperature 

 gradients and that based on decreasing values of b. This suggests 

 that the temperature gradient of plasticity is the lower, the more 

 removed is the character of the flow from that of a strictly viscous 

 liquid. Furthermore, it is apparent that if the value of b is an inverse 

 measure of the temperature gradient of plasticity, and if the latter is 

 in turn an inverse measure of the workability of a solder, then the 

 value of 6 is a direct measure of workability. 



