December 17, 2008
Knocking on a gearbox at output RPM
I have an odd problem with a gearbox.
It is a Farrel SR158A, 2.72:1 ratio (106T/39T), single reduction, herringbone gears. It is driving a calendar roll (via a drive shaft) for our paper machine. The gear box is not old: about 2 months since installation. It is rebuilt, to what extent, I don’t know, but the gears look new. It has been making a sharp knocking noise at the output shaft frequency since the rebuild (output shaft = 533 RPM). The highest amplitude is vertical on the input shaft (1449 RPM).
We don’t see any gear fault frequencies on either shaft. The Gear Mesh and 1st harmonic is modest (< 20% of overall).
We were sure there was damage on the output gear (there seems to be a rash of them lately). So we pulled the inspection cover off of it, and examined the teeth. We slowly turned the gear around and did not see any significant wear or damage on the teeth, just a few very small dinks, and no uneven wear. We took an oil sample and it had no visible metal or crud in it (it’s still out for analysis).
We pried on it radially and axially to see if it had play: none. We have run out of time on this shut down, but next chance we get we’ll put a dial indicator on the gear to see if it’s cocked on the shaft, though I don’t think that’s the problem.
Any other ideas on where we should look?
Carson
