Oil lube for low speed spindle with angular contact bearings

So I'm planning on making a vertical hollow spindle with two 7318 angular contact bearings with a 90mm bore and I'm looking for lubrication ideas. It's going to be a sand mixing machine that dumps the sand through a vertical hole through the middle of a tube supported on the two angular contact bearings. Ideally there would be a rotating seal below the two bearings to keep a supply of oil for the bearings. This will turn about 60-100 R.P.M. with the two bearings under an oil bath for lubrication. There will be lots of abrasive dust and moisture and occasionally salt air.

So my questions are: will ball bearings be ok running completely immersed in oil at low speeds?. What rotating seal technology exists to keep the oil in and the dirt out?. I was thinking along the lines of stellite face seals that Caterpillar makes, for the bottom seal rather than a rubber shaft seal that will eventually leak and need replacing.

for such a low speed you could make a seal out of a traditional packing material such as wool or hemp, and pump grease into the bearings every few weeks.

if you need an environmentally friendly solution, rapeseed oil is as good as any 10w-30 motor oil.

the issue with filling a bearing full of oil or grease is simply heat generation. at 100rpm a 90mm bore bearing completely packed full of grease might be 10 watts of heat. (heat goes up with the cube of the rpm with regard to oil or grease churning)

as for keeping contaminates out you may want an air gap between the rotating seals and the bearings. if you can't do this then keeping the bearing under positive pressure with oil or grease should push contaminates out of the bearings into the product.

johansen said:

for such a low speed you could make a seal out of a traditional packing material such as wool or hemp, and pump grease into the bearings every few weeks.

if you need an environmentally friendly solution, rapeseed oil is as good as any 10w-30 motor oil.

the issue with filling a bearing full of oil or grease is simply heat generation. at 100rpm a 90mm bore bearing completely packed full of grease might be 10 watts of heat. (heat goes up with the cube of the rpm with regard to oil or grease churning)

as for keeping contaminates out you may want an air gap between the rotating seals and the bearings. if you can't do this then keeping the bearing under positive pressure with oil or grease should push contaminates out of the bearings into the product.

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I had a bit of a think about it while going for a walk this afternoon and came to a similar conclusion. I'm not a big fan of sisal packing after seeing marine prop shafts get chewed up by sisal and corrosion so I'm thinking of a rubber or viton lip shaft seal and some NLGI 00 semi-fluid grease inside. That way even if the seal wears a bit the grease should stay in place. I could even stack two lower seals to keep the inner one a bit cleaner and have some fixed steel cup/hat to keep the sand/dust away a bit.

Ive had plenty of experience with abrasive grit......I suggest the Cat face seals with labrynth shields are the only viable way to make this.Any kind of soft seal will embed with grit and chew out both seal and mating surface......ive tried all these things with garnet processing equiptment.