Machinery's Handbook, 31st Edition
Stresses in Springs
315
120 110 100
90 80 70 60 50 40 30 20 10 0 Initial Stress, Due to First Load, Corrected for Curvature, 1000 psi 0 5 1015202530354045505560 Fig. 11. Endurance Limit Curves for Compression Springs Notes: For commercial spring materials with wire diameters up to 1 ∕ 4 inch except as noted. Stress ranges may be increased by approximately 30 percent for properly heated, preset, shot-peened springs. Materials preceeded by * are not ordinarily recommended for long continued service under severe operating conditions. Working Stresses at Elevated Temperatures.— Since modulus of elasticity decreases with increase in temperature, springs used at high temperatures exert less load and have larger deflections under load than at room temperature. The torsional modulus of elastic- ity for steel may be 11,200,000 pounds per square inch at room temperature, but it will drop to 10,600,000 pounds per square inch at 400 ° F. and will be only 10,000,000 pounds per square inch at 600 ° F. Also, the elastic limit is reduced, thereby lowering the permis- sible working stress. Design stresses should be as low as possible for all springs used at elevated tempera- tures. In addition, corrosive conditions that usually exist at high temperatures, especially with steam, may require the use of corrosion-resistant material. Table 2 shows the permis- sible elevated temperatures at which various spring materials may be operated, together with the maximum recommended working stresses at these temperatures. The loss in load at the temperatures shown is less than 5 percent in 48 hours; however, if the temperatures listed are increased by 20 to 40 degrees, the loss of load may be nearer 10 percent. Maxi- mum stresses shown in the table are for compression and extension springs and may be
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