SPRINGS 



131 



10 20 30 40 50 60 70 80 90 

 Lower S/ress in Thousands of Lb.perSq.ln. 



Fig. 249. — Allowable torsional stress range 

 Swedish steel wire. 



no 



100 



^ 50 



t ™ 

 i 60 



I 50 



for 



•o 40 



55 30 



E 

 E .20 



"5 



a 

 S 10 



Fig. 



10 20 50 40 50 60 70 80 90 100 110 

 Lower Stress in Thousandsof Lb. per Sq. In. 



251. — Allowable torsional stress range for 

 chrome-vanadium-steel wire. 



100 

 90 



r- 80 



'- 70 



; 60 



I 



I 50 



: 40 



! 30 

 i 20 



Fig. 



160 



d 140 

 & 



^120 



jii 



.J 



o 100 



-a 



c 



§ 80 

 o 



JZ 



i 60 



f 40 



^ 

 E 



i 20 



10 20 30 40 50 60 70 80 90 lOO 

 Lower Stress in Thousands of Lb. per Sq.la 



250. — Allowable torsional stress range for 



ordinary carbon-steel wire. 



. 20 40 60 80 100 120 140 160 



Lower Stress in Thousands of Lb. perSq.ln. 



Fig. 252. — Allowable torsional stress range for music 

 wire. 



SPRING FORMULAS 



In using the formulas given on pages 133 and 134 to design Class II and Class III 

 springs, a trial value of D/d is assumed and the corresponding Wahl factor is obtained 

 from the curve in Fig. 248. The material is selected and the allowable stress is taken 

 from the table on page 128. The larger value is used if the estimated wire size is 

 less than 0.2625 in. diameter. For larger Avires the smaller value is used. With 

 the outside diameter of the spring specified and the load W known, the wire diam- 

 eter d can be calculated. The spring index must then be checked to see if it is 

 on the safe side and approximates the index selected for the calculations. Likewise, 

 the diameter of the wire must be checked against the permissible working stress 

 selected. 



