Some Physical Properties of Wiping Solders * 



By D. A. MCLEAN, R. L. PEEK, Jr., and E. E. SCHUMACHER 



The plasticity of a number of solders at wiping temperatures has been 

 determined by compression tests between parallel plates. The character of 

 the flow is found to be that corresponding to a linear relation between shear- 

 ing stress and a fractional power of the velocity gradient. This corresponds 

 approximately to a relation between rate of compression (dh/dt) and 

 sample height (h) given by the equation: dh/dt = kh^, in which k and b are 

 constants, of which b is independent of the test conditions. For viscous 

 materials & = 5.0; for most solders b is greater than 5.0, and increasing values 

 of b are associated with lower temperature gradients of plasticity. It is 

 shown that a solder must have a low temperature gradient of plasticity in 

 order to be properly wiped, and that determination of the value of b by 

 means of a plasticity test can therefore be used to evaluate the working 

 properties of a solder. 



A number of factors upon which the plasticity of wiping solders and 

 the porosity of wiped joints may depend have been investigated. In par- 

 ticular, it is shown that segregation is not responsible for porosity, but that 

 the latter may be dependent upon the particle size of the solid phase at 

 wiping temperatures. The relation of particle size to the wetting power of 

 the liquid phase is discussed. 



A WIPING solder is one used in joining sections of lead (or lead 

 alloy) piping or sheathing, such as that used for telephone 

 cables. As such, it must wet the sheathing readily, must be coherent 

 and plastic enough to be worked with the hands over a considerable 

 temperature range, and must form a strong, non-porous joint. The 

 desirable qualities for a wiping solder have been more fully enumerated 

 by Schumacher and Basch,^ but the above will suffice for consideration 

 in connection with this paper. 



One phase of a general investigation of wiping solders has been a 

 study of their plastic properties in the temperature range in which 

 they are wiped. In this study consideration has been given not only 

 to the working properties which a solder must have in order to be 

 properly wiped, but also to certain other properties which may affect 

 the character of the wiped joint, particularly those which may result 

 in porosity of the joint. 



The temperatures at which the tests described below were made lie 

 in the wiping range, and are intermediate to those represented by the 

 solidus and liquidus lines in the respective equilibrium diagrams of the 

 solders investigated. At such temperatures the alloys form two phase 



* Presented before the Society of Rheology, Rochester, New York, December 28, 

 1931. Published in Jour, of Rheologv, January, 1931. 



1 E. E. Schumacher and E. J. Basch, Ind. & Eng. Chem., 21, 16 (1929). 



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