Plastic(?) for bearing to run in water

Thinking of making a pedal-powered boat, stainless shafts, suggestions
for bearing materiel please. And sources for suitable plastic mitre
gears in qty=2 pairs, smallparts has some but they may be too small.
Reply to
xpzzzz
Loading thread data ...
IIRC, the navy has used both Lignum Vitae (oily enough by itself) and hard maple vacuum impregnated with oil. Both will probably wear better than plastics.
Delrin, umhw or acetal (which may be delrin again, off-brand) might all work from the plastic end, I generally prefer the moly-filled versions. Teflon is slippery, but a bit on the soft side.
Reply to
Ecnerwal
"Ecnerwal" wrote in message news: snipped-for-privacy@news.eternal-september.org...
If you don't have a vacuum chamber, heating the wood in oil (or wax) forces out the water and much of the air, and the liquid will be sucked in as it cools.
jsw
Reply to
Jim Wilkins
I've seen ceramic bearings advertised and wonder if they'd be good in a watery scenario. Ball bearings would be much better than bushings.
-- Stay centered by accepting whatever you are doing. This is the ultimate. -- Chuang-tzu
Reply to
Larry Jaques
No answers to your questions, however something you may be interested in.....
I saw some video of a pedal powered kayak thingo on TV the other night. It had "push pedals" (left pedal went down / right came up sort of thing) and flaps underneath rather than a rotary propeller. It seemed quite efficient and worked very well.
I could not find any images online but I found this link which discusses rotary v flap propellers.
formatting link

Reply to
Dennis
I've used ceramic bearings in hot corrosive service, but not submerged. I think the difficulty in getting a complete seal and particulates in the water would cause ball bearings to fail sooner and more catastrophically than bushings.
Dad tried roller bearing pillow blocks on his rice field levee rollers once(4500# concrete spool, mild steel axle). They failed in less than a year. Big loads, lots of dirt, slow speed, side of the field storage. The maple blocks we boiled in old oil usually lasted at least a decade.
Pete Keillor
Reply to
Pete Keillor
But would they have worked as well on a pedal-powered unit? ;) Anything you can do to reduce friction or inefficiencies on a human-powered device is a real must.
-- Stay centered by accepting whatever you are doing. This is the ultimate. -- Chuang-tzu
Reply to
Larry Jaques
PV will be VERY low... on stainless, HDPE, UHMWPE, or acetal will all work submerged. Nylon is a No-No, because it absorbs water, and will swell.
LLoyd
Reply to
Lloyd E. Sponenburgh
Some of the plastics are pretty slick, especially in water. A low friction ball bearing isn't so low friction when it fails, which is what I think would happen. Ceramic ball bearings are pretty expensive, too.
I don't know what type of pedal powered boat he's considering. The old paddle wheel things are horribly inefficient anyway, but good exercise. Due to the miter gears, I'd guess he's planning on using a prop. You'd only need the plastic for an outboard bearing, but the major drag on efficiency would be a shaft packing gland or seal, followed by the miter gears themselves.
A prop for pedal power would probably be larger diameter and higher pitch due to the low speed. If he could avoid the miter gears, it'd help. Maybe a timing belt with a twist? and angle the shaft enough to avoid a seal, although that introduces another source of inefficiency.
I don't know how good the pedal powered kayaks are. Where I use a kayak fishing, I think they'd draw too much. A lot of it is very skinny water.
Personally, I'd stick with paddles or oars.
Reply to
Pete Keillor
FWIW, these are home-made stainless steel needle bearing wheels on a hydraulic lift that lives in an area outdoors that floods every spring:
formatting link
It's made of stainless pipe, round stock and TIG welding rod, and fitted loosely enough to tolerate mud.
You also need a prop thrust bearing unless you plan to misuse the miter gears for it.
Reply to
Jim Wilkins
I've used UHMW blocks just drilled for the stainless shaft for 25 years now in my apple water bin dump. No lube, never maintained. look like they may wear out in another 25 years or so.
Karl
Reply to
Karl Townsend
The standard "cutless" bearing on a prop shaft is a hydrodynamic bearing made of rubber. The bearing surface is a number of flat pads with grooves between that draw a layer of water between the shaft and bearing. They work fine with both bronze and stainless shafts.
formatting link
Re plastic ball bearings:
formatting link
Plastic ball bearings have been used on sailboat blocks for many years. The first I remember seeing had Delrin balls and hard anodized aluminum races.
If the shaft speeds are too low for a cutless bearing, I'd go to Igus' website and go thru the selection procedure to pick the best material. Igus has no minimum and is very reasonable for small orders.
formatting link
Reply to
Ned Simmons
Since you are pedaling the boat the best material will be Delrin AF. Delrin AF is teflon filled and is very low friction. The next choice would be UHMW or nylon. Nylon absorbs water so it is best to rough machine, soak in water for a week, and then finish machine. Then keep the bearings submerged or put the boat in the water a week before the season starts. But I would strongly suggest Delrin AF because it performs VERY WELL with water as a lubricant when running stainless shafting. Eric
Reply to
etpm
I built a wet bearing for a pump in an etching machine entirely out of Plexiglas. It worked very well, but was used for continuous rotation with minimal side thrust. I'd think delrin, nylon or similar material should work fine. W. M. Berg, SDP and such outfits have all sorts of gears in plastic, but again, fairly small sizes and certainly not cheap.
Jon
Reply to
Jon Elson
Most pedal boats use Delrin for the bushings, usually they are 1-1.5" wide They are set up so they don't run below the waterline as well.
formatting link
will give you some drive ideas.
Reply to
Steve W.

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.