Jim, Hugo
Issue:
LLO have a BSC-ISI that is under-loaded by 400lbs. They noticed that its small blades where lifted from their clamp-plates. They measured this gap by inserting shims at the blade/clamp-plate junction. A 1.5 mils-thick shim could be inserted by approximately 18/64” in the whole length of that junction.
Test:
We did the same test here at LHO on BSC6, which is reasonably loaded, in order to help LLO diagnose. The access was limited. Only two blades were tested. They could only be tested along 2” of the junction’s length.
Result:
Observations are the same for both of the blades that were tested. A 1 mil-thick shim could be inserted by approximately 28/64”, and a 2 mils thick shim could be inserted by approximately 19/64”.
Conclusion:
The gaps measured on LHO-BSC6 are similar to the ones measured on the unit studied at LLO. Hence, the space measured between the blades and their clamp-plates doesn’t seem to be a justification for a BSC-ISI to be under-loaded.
Suggestion:
Further discussion revealed that our bolts were lubricated before torqueing. Lubrication allows reaching a higher level of compression before tripping the torque wrench. It also revealed that our bolts were torqued to a higher torque value.
Higher torque allowed LLO to increase their mass budget
As the shim test performed did not appear to be impacted by the torque difference, it might be interresting to see if torque impacts the value of the thickest shim that can be inserted in that gap.
Jim, Hugo,
Gaps were re-measured today. The measurement consisted in trying to insert the thickest shim possibe in the blade/clamp-plate junction. We were able to insert a 5mils shim while LLO managed to insert a 6.5mils shim before re-torquing their blades.
The effect of torque seems more noticable at the edge of the blade/clamp-plate junction.