As part of our overall stern tube seal offering, we provide chrome steel liners suitable for all standard systems.
Our aft and forward chrome steel liners are OD-finished, and other machining can be carried out by the customer.
The stern tube seals in oil-lubricated lip-type systems run on a bush or liner. Over time, the seals create grooves in the liners, which shows that the liner is doing its job of protecting the propeller shaft.
When seals are replaced during the overhaul process, the new seal should run on a fresh liner surface. In the aft system, this can be achieved by adding or removing a distance ring between the seal housing and the stern tube, moving the entire seal box to a different position on the liner.
Our AFT and FWD chrome steel liners follow the industry standard design and are compatible with the following stern tube systems:
Once there are two sets of grooves on the liner, it can be removed and machined to produce a fresh surface. This leaves it ready for another two seal overhaul periods (generally five years each time).
Usually, a distance ring will have been installed during the initial build process. At the five-year dry-dock, this distance ring will be removed, allowing the seal to run on a fresh surface.
At the ten-year dry-dock overhaul, the liner will be removed from the shaft and machined in the workshop. The distance ring can then be reinstalled, and the liner may be used for another ten years.
These issues include coatings chipping off and damaging the seals, as well as severe wear and signs of overheating on the stern tube seals.
We concluded, in consultation with our supplier, that the stern tube liner needs a certain amount of surface roughness to distribute oil correctly and provide proper lubrication. We have established a guideline safe range for the surface roughness between 0.4 and 0.8 Ra.
A brand-new ceramic-coated liner is likely to meet this roughness standard, but after five or ten years of operation, the polished track on the liner will likely no longer be within this range. In these cases, we recommend installing a distance ring if possible. If this is impossible, we recommend replacing the liner with a new chrome steel liner.
If a ceramic coated liner has already been in operation and a distance ring cannot be installed, and if the customer does not wish to replace the liner, the surface roughness must be measured.
RM Propulsion will not grant any warranty on the stern tube seal overhaul with a ceramic coated liner.