SOME PHYSICAL PROPERTIES OF WIPING SOLDERS 105 



temperature is frequently checked, and can be controlled within 

 ± 1° C. by adjusting external resistances. The sample height is 

 measured at inter\-als by an Ames gauge which moves with the plunger, 

 a complete record of sample height vs. time being thus obtained. 

 With one exception, the tests here reported were continued for 30 

 minutes. 



The sample size used was one which has been found convenient — a 

 cylinder 1.374 inches (3.490 cm.) in diameter and .300 inch (.762 

 cm.) high. Samples were obtained from a single cast of each solder, 

 tested for blow-holes and inclusions by density measurements. 

 Samples were milled to dimensions with a tolerance of ± .001 inch 

 (.0025 cm.). The weight of the plunger and load was 30 lbs. (13.63 

 kg.). 



Character of the Flow 



The data directly obtained in a typical run, readings of sample 

 height vs. time from start of run, are plotted in Fig. 1, together with 

 tangents to the curve fitting the points plotted. By computing the 

 slope of such tangents there are obtained values of the rate of com- 

 pression, dh/dt, corresponding to various values of sample height, //. 

 If these are plotted logarithmically, log dh/dt vs. log h, as in Fig. 2, 

 a straight line is obtained. This shows that under the test conditions 

 employed, the relation between sample height and rate of compression 

 is of the form: 



(ih , , , 



where k and b are empirical constants. All the tests made on solders 

 gave results that could be fitted with an equation of this type. At 

 any one temperature the value of b was constant for a given solder, 

 while the value of k varied with the load and sample volume but was 

 independent of the initial sample height. A limited number of tests 

 have indicated that all runs made on any one solder at a given tem- 

 perature can be represented by an equation of the type: 



dh ^ Wh'' 



dt^"^-^' (2) 



where W is the load, V the sample volume and K, a, b, and c are 



constants characteristic of the material. 



It has been shown both theoretically ^ and experimentally ^- ^ that 



"O. Reynolds, Phil. Trans., Land., 177A, 157 (1886). 

 *Ormandy, "The Engineer," 143, 362, 393 (1927). 



