Rope Guides 



The MT 75 is designed for use on wire ropes from 3/8- to 3/4-inch 

 in diameter by using different size rope guides. The rope guides perform 

 a two-fold function: (1) they concentrate, in the wire rope, the magnetic 

 field generated by the strong permanent magnets, and (2) they guide the 

 rope through the search coils. A test was conducted on 1/2-inch wire 

 rope to observe the effects of tight and loose fit on each of the search 

 coil sizes. The search coil is available in four sizes: 3/8, 1/2, 5/8, 

 and 3/4 inch. The test results showed that the best signals occurred 

 when the search coil's fit was as snug as possible without it touching 

 the wire rope. Figure 8 shows that the closer fitting coil (1/2-inch 

 diam) produces the best signal-to-background noise ratio. 



FIELD TESTING 



Tests were performed to evaluate the MT 75' s field inspection 

 capabilities. The first test was on a load line of a 35-ton truck crane 

 which was recently inspected by the visual-rag technique shown in Figure S 

 The MT 75 shown in (Figure 10) detected broken wires and an area of 

 corrosion which were missed on the earlier inspection. Several other 

 small capacity cranes were also inspected with similar findings. Inspec- 

 tion time was on the order of one sixth that required using the "visual 

 and rag" method. Some of this time was used for a close inspection of 

 those areas which were in the worst condition. Wire ropes on overhead 

 cranes, lift slings, winch wires and elevators were also tested. 



The MT 75 was loaned to a Public Works inspection division for two 

 months. The inspectors were given several hours of training on its use 

 and signal interpretation. After the two months, the inspectors provided 

 a brief evaluation of the device. The concensus was that the device was 

 much faster than the standard method. About 8 hours were required for a 

 "visual and rag" inspection of truck crane and only 1.5 hours for the 

 MT 75. Because of the MT 75 's light weight, it is easy to handle and 

 the inspectors were inclined to carry it with them and use it in their 

 daily inspections. 



CONCLUSIONS 



1 . The MT 75 provides useful information than cannot be obtained 

 from rag and visual inspection methods, e.g., internal broken wires, 

 corrosion pitting, peening, and nicking. 



2. Field tests have shown that the time required for wire rope 

 inspections may be reduced by as much as 80% over that required by the 

 visual and rag method 



3. The wire rope can be inspected at higher rope speeds and only 

 those areas that "sound" bad need to be inspected closely. 



