Document VKEm0rXxxe6NpJ27jwry6nkY4

Ropes, Chains, and Slings cold-working of the metal Wrought iron chain (commonly called iron crane or dredge chain) used to be the ac cepted material for slings, hoists, cranes, power shovels, and marine purposes where human life or property would be endangered by failure However, since the introduction of alloy chain m 1933, the use of wrought iron has declined steadily and has nearly dis appeared Because of this lack of commercial importance, it is not considered here Heat-treated carbon steel is sometimes used for sling chains It has high strength, high impact resistance, and good abrasion resistance Special purpose alloy chains are made from stainless steel, monel metal, bronze, and other materials They are designed for use where resistance to corrosive substances is required, or where their other special proper ties are desirable Proof coil chain (also known as common or hardware chain) is used for miscellaneous purposes where failure of the chain would not endanger human life or result m senous damage to property or equipment Proof coil chain should never be used for slings Properties of alloy chain Alloy chain is produced from heat-treatable alloy steel in conformance with ASTM spe cifications A391-58 Types and amounts of the alloying elements may vary according to requirements of die individual chain manu facturer Chain after heat treatment has typical mechanical properties as follows Tensile Strength Elongation 125,000 psi minimum 15 per cent minimum Table 23-] shows the recommended work ing load limits, proof test loads, and the minimum breaking strengths of alloy steel chain The working load limit (safe load strength) is arrived at by dividing the breaking strength (ultimate strength) by a specified safety factor The values shown in Table 23-J represent the maximum loads that should ever be applied m direct tension to a length of alloy chain All alloy chain is proof-tested m direct tension under the proof test loads shown, pnor to final inspection and shipment The data for other types of chain may be obtained from TABLE 23-J WORKING LOAD LIMITS, PROOF TEST LOADS AND MINIMUM BREAKING LOADS FOR ALLOY STEEL CHAIN Nominal Size of chain (in ) Working Load limit (lb) Proof Test (lb) Minimum Break (lb) V. 3.250 6,500 10,000 Ve 6,600 13,200 19,000 V, 11.250 22,500 32,500 Ve 16,500 33,000 50,000 V, 23,000 46.000 69,500 7/e 28,750 57,500 93,500 1 38,750 77,500 122,000 1 Ve 44,500 89,000 143,000 IV. 57,500 115,000 180,000 1Ye 67,000 134,000 207,000 IV, 80,000 160,000 244,000 IV. 100,000 200,000 325,000 Source Specification for Alloy Cham, American Society for Testing and Materials, A-391-65 AUoy Steel Cham Specifications, No 3001, Natrona! Association of Chain Manufacturers the National Association of Chain Manu facturers specification No 3001 Stress on each leg of a multi-branch sling is increased appreciably when the angle between the chain and the horizontal is de creased The effects of angle of loading on the working load limit of a two-leg alloy sling are shown in Fig 23-8 The tensile strength of alloy steel chain increases m proportion to its hardness (pro duced by heat treating) Resistance to abra sion also increases proportionately with hardness Impact conditions caused by faulty hitches, bumpy crane tracks, and slipping hook-ups can materially add to the stress m the chain If severe impact loading may be encountered, a lower working load limit should be used, regardless of the chain type Alloy steel chains are suitable for high temperature operations However, continu ous operation at a temperature of 800 F (the highest temperature for which continuous operation is recommended) requires a re duction of 30 per cent m the regular working load limit These chains may be used at temperatures up to 1000 F at 50 per cent of 654