Inspection and repair project on RENK HSUSL-1020 gearbox

This client from The Netherlands came to us with this RENK HSUSL-1020. We inspected the gearbox and performed a repair. After a succesful testrun we shipped the gearbox back to the client.

Upon arrival on the vessel in Las Palmas, preparations were made to disassemble the gearbox. Only upon arrival at anchorage the disassembly could be started.

The gearbox showed no signs of serious damage or wear, beside normal wear on bearings and impact marks on the gears, from running without load. The pto-shaft bearing (pos. 5370) however was found heavily damaged, most likely caused by slipping of the rollers.

It is suspected that the damage was caused by an undersized shaft journal on which the bearing was seated, resulting in additional internal bearing-clearance.

After reassembling the gearbox, the gearbox was flushed, prior to performing a test-run.

During the test-run, temperatures were monitored and recorded. The gearbox reached an acceptable and stable operating temperature.

Recommendations

- It is essential to recondition (lasercladding) the shaft journal of the pto-shaft, in order to help prevent future damage to the bearing(s) and gearbox as a whole.
- Keeping the running hours into consideration (> 50.000 h.)
- it is recommended to open the complete gearbox for an extensive inspection and replace all the roller bearings and seals;
- Replace oil filter elements as instructed in the oil filter manual;
- It is recommended to check the oil filters and clean the oil filters regularly as instructed in the oil filter manual;
- It is recommended to perform a visual inspection and oil analysis annually to monitor the micropitting found on the main gears, after 6 – 9 months
- Realign the Shaft Generator, because this alignment is bad for the bearings and Coupling.

Because no shims where available it was not possible to align the generator.

Cause of damage In order for the bearing to work properly, it has to be mounted on the shaft with a shrink-fit (shaft diameter larger than the bore of the bearing). The shrink-fit makes sure the bearing is mounted firmly only the shaft, to prevent the bearing from sliding/slipping. But the shrink-fit is also important to obtain the correct amount of internal (radial/axial) clearance within the bearing.