moved, the flux leakage intersects the search coils and if there is an 

 anomality in the wire rope, such as a broken wire, corrosion, pitting, 

 etc., the flux field is distorted. This induces a signal in the search 

 coils which is then conditioned and displayed. In the case of the MT 75 

 the data are transmitted to headphones as "clicks" and "crackles". The 

 data can also be recorded on a 1 -channel, brush-type recorder for a 

 permanent record. The recorder, however, does not come with the MT 75 

 and must be obtained elsewhere. 



LABORATORY TESTING 

 Test Procedures 



New wire ropes, of 6x25 right-regular-lay-fiber-core construction, 

 with diameters of 1/2 and 3/4 inch were used for the laboratory testing. 

 They were modified with simulated broken wires. The gaps in the crown 

 wires were made with a special chisel that produced clean square breaks. 

 Gap spacings were initally less than l/128th of an inch and were increased, 

 by filing, in 1/16-inch increments to a maximum of 3/8 inch. 



NCEL's wire rope test track was used to move the test wire rope 

 through the MT 75. The test track was designed to accommodate 100-foot 

 loops of wire rope from 1/8 to 2-1/2 inches in diameter. The speed of 

 the wire rope was changed by a variable speed transmission powered by a 

 1-3/4 horsepower electric motor. The wire rope speeds were varied from 

 to over 800 fpm. Each end support consisted of three 1-foot diameter 

 sheaves that simulated a 4-foot diameter sheave. The larger sheave 

 diameters were needed for wire rope with larger diameters to provide 

 adequate bend radius. 



Gap Configuration 



A broken wire can, depending on the cause, have various end config- 

 urations. For example, a fatigue break produces square ends, a tensile 

 break produces necked down ends, and a shear break produces angular 

 ends. The various types of gap configurations are shown in Figure 3. A 

 series of tests were conducted to determine the effective gap size for 

 all four types of configurations. The results indicate that the signal 

 loudness depended on the clear gap space size in the longitudinal direction. 



Gap Orientation 



Gap orientation is the location of a broken wire or any other 

 abnormality in relation to the two halves of the search coils located 

 180 degrees apart in the MT 75. In these tests a wire break could be 

 directly under a search coil or up to 90 degrees from the coil. To 

 determine the effect of gap orientation on signal size, a 1/2-inch wire 

 rope, with two simulated wire breaks about 3 yards apart, was run on the 

 wire rope test track. The broken wires maintained the same orientation 

 after each completed loop. Break A was a broken crown wire and break B 

 was a broken filler wire. The MT 75 was then rotated from to 90 degrees 

 in 22.5-degree increments. The signals were compared to observe any 



