Machinery's Handbook, 31st Edition
Spring Materials
305
Spring Materials The spring materials most commonly used include high-carbon spring steels, alloy spring steels, stainless spring steels, copper-base spring alloys, and nickel-base spring alloys. High-Carbon Spring Steels in Wire Form.— These spring steels are the most commonly used of all spring materials because they are the least expensive, are easily worked, and are readily available. However, they are not satisfactory for springs operating at high or low temperatures or for shock or impact loading. The following wire forms are available: Music Wire, ASTM A228: (0.80–0.95 percent carbon) This is the most widely used of all spring materials for small springs operating at temperatures up to about 250°F. It is tough, has a high tensile strength, and can withstand high stresses under repeated loading. The material is readily available in round form in diameters ranging from 0.005 to 0.125 inch and in some larger sizes up to 3 ∕ 16 inch. It is not available with high tensile strengths in square or rectangular sections. Music wire can be plated easily and is obtain able pretinned or preplated with cadmium, but plating after spring manufacture is usually preferred for maximum corrosion resistance. Oil-Tempered MB Grade, ASTM A229: (0.60–0.70 percent carbon) This general- purpose spring steel is commonly used for many types of coil springs where the cost of music wire is prohibitive and in sizes larger than are available in music wire. It is readily available in diameters ranging from 0.125 to 0.500 inch, but both smaller and larger sizes may be obtained. The material should not be used under shock and impact loading condi- tions, at temperatures above 350°F, or at temperatures in the sub-zero range. Square and rectangular sections of wire are obtainable in fractional sizes. Annealed stock also can be obtained for hardening and tempering after coiling. This material has a heat-treating scale that must be removed before plating. Oil-Tempered HB Grade, SAE 1080: (0.75–0.85 percent carbon) This material is similar to the MB Grade except that it has a higher carbon content and a higher tensile strength. It is obtainable in the same sizes and is used for more accurate requirements than the MB Grade, but is not so readily available. In lieu of using this material it may be better to use an alloy spring steel, particularly if a long fatigue life or high endurance properties are needed. Round and square sections are obtainable in the oil-tempered or annealed conditions. Hard-Drawn MB Grade, ASTM A227: (0.60–0.70 percent carbon) This grade is used for general-purpose springs where cost is the most important factor. Although increased use in recent years has resulted in improved quality, it is best not to use this grade where long life and accuracy of loads and deflections are important. It is available in diameters ranging from 0.031 to 0.500 inch and in some smaller and larger sizes also. The material is available in square sections but at reduced tensile strengths. It is readily plated. Applica- tions should be limited to those in the temperature range of 0 to 250°F. High-Carbon Spring Steels in Flat Strip Form.— Two types of thin, flat, high-carbon spring steel strip are most widely used although several other types are obtainable for specific applications in watches, clocks, and certain instruments. These two composi- tions are used for over 95 percent of all such applications. Thin sections of these materials under 0.015 inch having a carbon content of over 0.85 percent and a hardness of over 47 RC (Rockwell C scale) are susceptible to hydrogen-embrittlement, even though special plat- ing and heating operations are employed. The two types are described as follows: Cold-Rolled Spring Steel, Blue-Tempered or Annealed, SAE 1074, also 1064, and 1070: (0.60 to 0.80 percent carbon) This very popular spring steel is available in thicknesses ranging from 0.005 to 0.062 inch and in some thinner and thicker sections. The material is available in the annealed condition for forming in 4-slide machines and in presses, and can readily be hardened and tempered after forming. It is also available in the heat-treated
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online