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HANDBOOK OF MECHANICAL DESIGN 



Design of Helical Springs 



Condensation of the standard specifications and design procedure adopted by the Atlas Imperial Diesel Engine 

 Company as set forth by W. M. Griffith, product engineer of that company, in March and April 1937, Product 

 Engineering. 



CLASSES OF SPRING SERVICE 



Class I. Rapid, continuous deflection over a uniform stress range from zero to a 

 maximum or from an intermediate stress to maximum — as in engine valve springs. 



Class II. Rapid deflections over a variable stress range that may be from zero to 

 intermediate, intermediate to maximum, or zero to maximum — but with only 

 intermittent operation — as in springs for engine governors. 



Class III. Statically loaded at maximum stress or infrequent deflections with 

 stress range from zero to intermediate, intermediate to maximum, or zero to 

 maximum — but with only infrequent operation — as springs for relief valves. 



PURCHASE SPECIFICATIONS FOR SPRING WIRE 



The minimum physical properties given in these specifications are 95 per cent of 

 the average values determined by tests. Thus the minimmn physical properties here 

 specified are well within commercial limits. 



SWEDISH STEEL SPRING WIRE SPECIFICATIONS 



Generally used for Class I extension or compression springs and Class II and 

 Class III extension springs, in wire diameters from 0.1055 in. up to 0.262 in. This 

 material can be used for springs of larger or smaller wire diameter, but generally 

 music wire is used for the smaUer wire diameters and carbon steel for the larger wires. 



1. Steel Manufacture 



This steel is to be of Swedish manufacture according to approved practice by the 

 acid open-hearth or electric-furnace process. 



2. Chemical Composition 



Carbon 0.60-0.70 Phosphorus 0.025 max. 



Manganese 0.45-0.65 



Silicon 0.15-0.25 



Sulphur 0.025 max. 



3. Physical Properties 



Range of wire diameter, in. 



0.1055 and under. 

 0.1205-0.1350... 

 0.1483-0.1920... 

 0.2070-0.2625... 

 0.2812-0.3437... 

 0.3625-0.4375... 

 0.4615-0.5625 .. . 



Minimum tensile 

 strength, lb. per sq. in. 



Ultimate 



212,000 

 202,000 

 187,000 

 175,000 

 164,000 

 155,000 

 146,000 



Elastic 

 limit 



154,000 

 146,000 

 136,000 

 126,000 

 119,000 

 112,000 

 106,000 



Alinimum 

 strength, lb. 



torsional 

 per sq. in. 



Ultimate 



184,000 

 175,000 

 163,000 

 151,000 

 142,000 

 135,000 

 127,000 



Elastic 

 limit 



112,000 

 106,000 

 99,000 

 92,000 

 86,000 

 82,000 

 77,000 



Reduction of area, 48 per cent minimum. Elongation in 10 in., 5 per cent minimum. 



