33Figure 12-12.-Lattice boom terminology.removed from service. When the main cords of tubularboom sections are damaged in any manner, includingslight dents, they are severely weakened and have failedat loads significantly below capacities. As outlined inthe 11200.1, structural repairs will not be made withoutwritten approval from COMSECOND/COM-THIRDNCB equipo offices.In the NCF, sections normally come in 10- to20-foot lengths.When adding several sections ofdifferent lengths, check the operator’s manual for boomsection configuration. If this information is not in theoperator’s manual, a rule of thumb used when mixingshort boom sections with long sections, you install theshorter sections closest to the boom butt; for example,if you use two 10-foot sections and one 20-foot section,install the two 10-foot sections closest to the boom butt.The boom sections are bolted by plate (flange)connections (fig. 12-13, view A) or pin and clevisconnections (fig. 12-13, view B). The most common isthe pin and clevis.All boom sections that come with a crane will havean attachment identification number attached thatassigns the boom section to a specific crane.Boom Angle IndicatorsBoom angle indicators are normally mounted on theboom butt, visually readable by the operator. On mostmodels in the NCF, the boom angle indicator is a metalplate with degree numbers (0 to 90 degrees) and a freelyswinging arm that reacts as the boom angle changes (fig.12-14). The numbers and arm should remain clean andvisually readable at all time.The capacities that are listed on the crane load chartsare also based on and vary with the boom angle of thecrane. On hydraulic cranes, the boom angle is the anglebetween the bottom of the boom butt and the horizontalFigure 12-13.—Boom sections connection.Figure 12-14.—Boom angle indicator.12-7
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