Idler survey on a 4.2 km overland conveyor
Two days walking the line with an infrared thermometer and a notebook found 61 failed rollers and one genuine alignment problem.
Overland conveyors fail quietly. A seized roller on a 4.2 km run is not audible from the head end, and the first symptom is usually a belt cover gouge that nobody can explain. The only reliable way to find them is to walk the line.
Method
We walked it in two days with an infrared thermometer, a torch and a paper log. Every idler set was checked for surface temperature differential against its neighbours, shell wear was graded on a three-point scale, and anything with visible shell flat-spotting was marked for immediate change.
Sixty-one rollers were failed or failing out of roughly nine hundred — around seven percent, which is high but not unusual on a line that has never had a systematic survey. More interesting was where they clustered.
The cluster told the real story
Thirty-eight of the sixty-one sat inside one four-hundred-metre section. That is not a roller quality problem; that is a structural alignment problem loading one side of the carry idlers. We surveyed the stringer through that section and found it had settled by eleven millimetres over roughly forty metres.
Replacing thirty-eight rollers without correcting the stringer would have bought about eight months. Correcting the stringer first turned a recurring cost into a one-off.
