TM5-3810-305-10WireRopeInstallationChecking The DiameterIt is most important to check the diameter of the delivered rope before installation. This is to makecertain that the rope diameter meets the specified requirements for the given machine or equipment.With an undersize diameter rope, stresses will be higher than designed for and the probability of break-ing the rope will be increased; an oversize diameter rope will wear out prematurely. This happensbecause of abuse to the rope caused by pinching in the grooves of the sheave and drum. In checking,however, the “true” rope diameter must be measured. And this is defined as the diameter of the circum-scribing circle, i.e., its largest cross-sectional dimension. To insure accuracy, this measurement shouldbe made with a wire rope caliper using the correct method (B, Figure 4-21). For measuring ropes withan odd number of outer strands, special techniques must be employed.Design specifications for wire rope are such that the diameter is slightly larger than the nominal size,according to the allowable tolerances shown in Table 2.Table 2. 0versizeLimitso fWireRopeDiameters*Nominal Rope DiameterAllowable LimitsOver 1/4 in. and larger (6.35 mm and larger)-o+5%*These limits have been adopted by the Wire Rope Technical Board (WRTB), and are being consideredfor inclusion in the forthcoming revised edition of “Federal Standard RR-W-410.” In the case of certainspecial purpose ropes, such as aircraft cables and elevator ropes, each has specific requirements.In measuring a wire rope correctly, always measure the larger dimension. The “true” diameter (A) lieswithin the circumscribed circle (B). Avoid using incorrect measurement position (C, Figure 4-21).Figure 4-21.HowtoMeasure(orcaliper)aWireRope4 - 30
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