data from break B changed signal size for each orientation. Regardless 

 of the differences between breaks A and B, the signal size was dependent 

 on gap orientation. 



Gap Space 



New Rope . A series of tests was conducted on new wire rope to 

 determine LF signal size as a function of longitudinal gap space. A 

 hammer and chisel were used to make wire breaks in crown wires. The 

 initial gap space was about 1/128 inch, but a file was subsequently used 

 to widen the gap spacings to 1/2 inch in l/l6-inch increments. 



Tests were conducted on wire rope 1/2, 3/4, 1-1/8, 1-1/2, 2, and 

 2-1/2 inches in diameter. Rope speed was 200 ft/min in all cases, 

 except for the 2-1/2-inch-diameter wire rope. For that rope, the sensor 

 head was pulled over the wire rope because the drive wheel of the test 

 stand could not develop sufficient traction to maintain movement of the 

 rope. 



A condensation of the data for the various tests is shown in Fig- 

 ures 4 through 9. From these data, LF signal-to-noise ratios were 

 obtained for each gap space. The background noise was defined as an 

 average of the peak values for each rope. 



Figures 10 through 15 show LF signal-to-noise ratio as a function 

 of gap space. Interestingly, the LF signal-to-noise ratios ranged from 

 2 to 4 for a gap space of about zero. Therefore, one would expect to 

 easily detect a broken wire even when the gap space is extremely small, 

 but this is not necessarily true because of two conditions: (1) the 

 above data were collected on new wire rope, and (2) the background noise 

 was the average of the peak values. 



New wire rope is fairly clean of background noise; once surface 

 corrosion occurs, however, background noise increases. As a wire rope 

 is worked, the strands and wires seat themselves relative to one another. 

 Internal and external wear, along with peening and nicking, is another 

 cause for background noise. Heath and Sherwood propose to track the 

 growth of background noise as an indication of the condition of the wire 

 rope (see the Appendix). Data on the growth of background noise are not 

 available, but it is expected that LF signals for small gap sizes would 

 quickly be lost in the background noise. 



The other condition -- that of using average peak values for back- 

 ground noise -- means that above-average background-noise signals can 

 appear to be LF signals. Many times, confusion exists when studying a 

 signal as to whether it is an LF or a background noise signal. This 

 occurs most frequently in heavily used wire ropes. 



In summary, LF signal size is dependent on the gap space, and 

 broken wires with extremely fine gap spacings can be detected in new 

 wire rope. 



Used Rope . The difficulty of distinguishing between LF signals 

 from small gap spacings and background noise was investigated by non- 

 destructive testing and then by disassembling a used wire rope. A 

 1-1/8-inch-diameter, 6x31 fiber-core wire rope, which had been retired 

 from a mine elevator hoist, was used in the test. A 100-foot-long 

 section was mounted on the test stand. Magnograph data were obtained at 



