SOLDERLESS WRAPPED CONNECTIONS — PART III 



603 



tests are shown on Figs. 5 to 9 inclusive. These charts show a plot on 

 arithmetic probability paper of stripping force against the cumulative 

 per cent of the sample below the indicated stripping force. The straight 

 lines shown there are actually drawn through the average and average 

 minus Sa points where a is the standard deviation of the observed read- 

 ings. In the cases shown, and in fact in practically all the tests made to 

 date the results have come out so that the experimental values fit very 

 well on the straight hne drawn through these points, thereby indicating 

 good normal statistical distributions of the data. 



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12 5 10 20 30 40 50 60 70 80 90 95 98 99 



PER CENT OF TERMINALS BELOW INDICATED STRIPPING FORCE 



Fig. 7 — Effect of terminal plating (tin) on stripping force. 



For example, Fig. 5 shows the effect of stripping force of rounding the 

 corners of the terminal. These curves are for a typical tinned nickel 

 silver relay terminal 0.031'' by 0.062" in crosssection. The terminals 

 represented by the upper curve were punched from sheet nickel silver 

 stock and the corners were sharp as is usually the case where shearing 

 operations are used. The lower curve represents connections where the 

 corners were rounded off to a 0.006'' to 0.008" radius. It is seen that on 

 the average the stripping force using the sharp corners is about 1,000 

 grams higher than with the rounded corners, although both set3 of 

 terminals met the 3,000 gram requirement for mechanical stability. 



The effect of terminal hardness on stripping force is shown in Fig. 6. 

 Here brass terminals were used and it is evident that the softer terminals 

 give considerably higher stripping force than the harder ones. Both 



