Some time ago I asked SKF's engineering about this.
Here's their reply to me:
educated guess is that the seals are not an issue in
this application. The problem is with the Bronze bushing
that is being used as a sealing surface. Bronze is
generally quite soft and might not have the required
hardness of Rockwell C 30 or higher. You have a few
options to solve this issue:
can put SKF speedi-sleeve gold on the shaft (P/N 99830).
You will probably have to install multiple sleeves as
you have 3 seals next to each other.
can replace the bronze bushing with a hardened wear
sleeve for better abrasion resistance. We can offer you
a custom wear sleeve if needed.
can plate your bushing with a harder material (Chrome,
ceramic, etc) to make it wear resistant.
the harder the shaft is, the less grooving it will see.
I also suggest you to make sure that you grease pack the
area between the seals to make sure that the seals not
in contact with the oil are well lubricated. A lack of
lubrication can cause the seal and surface to wear
quicker. Finally I would arrange the seals with 2 facing
the water and one facing the oil as long as there is no
regards, Jaydeep Laljani, Application Engineer, SKF USA
back and said:
thanks for your analysis. Frankly, I have wondered why
the manufacturer used Bronze in the first place and not
stainless - they actually call it a "wearing-out
bushing" (but then they do charge a lot for replacements
month I'm returning to the boat, which is in Turkey, and
I can easily have a local shop turn a new bushing in 316
Stainless (the same material as the shaft and propeller,
so no electrolysis issues.) I think that would solve the
problem without going to sleeves or plating.
the orientation of the seals, I like your suggestion of
two facing the water and will do that the next time I
change the seals. After all, we're really trying to keep
the water out more than keeping the oil in. And, yes,
indeed, I always pack the seals with a good water-proof
grease and that helps, I'm sure. "
think you might not get as much life as you want with
316 SS as it is still not up to the required hardness.
If you want to go Stainless I recommend 17-4 Stainless
steel which is harder. If you are going with the 316 SS
I would recommend you to passivate it to improve
corrosion resistance. "
Hope that's helpful.
Cheers, Craig Briggs, SN#68 Sangaris
Hardness of stainless steel 316 does not
vary tangible. Bushing from stainless 316 will
definitely last longer, but the bushing will cost
much more. 316 steel is expensive and hard to
machin. But it is very good corrosion resistant
material, good for salt water. If people are
interested I can find mashin shop that can make
them. We have to order 100 bushings or more.
Otherwise setup cost is too much.
"LIFE IS GOOD"