|Gary Wooding||05/10/2018 13:39:19|
|669 forum posts|
I have to make a wheelchair to transfer disabled people from the changing rooms to a lift that lowers them, wheelchair and all, into a chlorinated swimming pool. And getrs them out again.
The real problem is the wheel and caster bearings. Ordinary steel bearings will simply rust, so what bearings should I use. I'm thinking of solid bearings of, say, plastic, brass, or bronze. Nylon is probably unsuitable because it absorbs water, but what about Delrin? It's only about 50mtrs from the changing rooms to the pool. What do the experts recommend?
Do stainless bearings exist?
|1445 forum posts|
Would it be possible to use a modified conventional framed chair that could be fixed/clamped in some way to a framed set of castors to transport the people to the pool edge, attach the chair to the lifting device and release the chair to castor frame before lifting the chair over and into the pool.
This would avoid the need for any bearings to enter the chlorinated water, just a thought.
|Senior Yates||05/10/2018 14:06:14|
|34 forum posts|
Try Nylacast I would recommend Aquanyl PA6/12 as it doesn't absorb water. No link to this company but I have used their material many times.
|Jeff Dayman||05/10/2018 14:20:23|
|1789 forum posts|
Delrin would be a good material choice I think.
There are stainless bearings available but unless silicone grease is used, and ALL bearing parts are stainless, there could be issues. I've been stung before with using stainless bearings in a freshwater marine application where the races and balls were stainless but unknown to me, the carrier was plated mild steel. Didn't last long. It was a shock to see orange rust pouring out of that supposedly stainless bearing!
|David George 1||05/10/2018 14:21:52|
1190 forum posts
Have you thought of fitting stainless ball bearings you can get 30 mm x 12 mm x 8 mm bearing for about £10.0 each from simply bearings
|Neil Wyatt||05/10/2018 14:47:26|
17712 forum posts
Something like these, nylon races with stainless steel balls, designed for use in harsh environments.
(Advantage is needs no lubrication, and you don't want oil/grease in a swimming pool).
Edited By Neil Wyatt on 05/10/2018 14:48:21
|duncan webster||05/10/2018 14:47:57|
2538 forum posts
I'd just use Delrin on SS axles. It has very low water absorption and is dead easy to machine
|David Jupp||05/10/2018 14:49:38|
|723 forum posts|
There are also ceramic or ceramic/plastic ball bearings available which wouldn't suffer from corrosion.
|47 forum posts|
How about lignum vitae as it is water lubricated.
2631 forum posts
+1... Plus have you thought about Teflon sleeve bearing … self lubricating & water proof
|Nick Taylor 2||05/10/2018 16:50:37|
|102 forum posts|
I would opt for plain PTFE bearings, zero maintenance and close tolerances possible without too much friction.
|5616 forum posts|
No need for lignum vitae or anything home-made. Try searching for 'Waterproof Bearings'. You can get plastic ball bearings specifically designed for low maintenance in wet environments. They're also resistant to most chemicals.
I like Mick's BANZAI suggestion, and you should take up his kind offer to be test-pilot. Please video his Kamikazi off the high-board so we can all improve by watching Charity in action.
|Swarf, Mostly!||05/10/2018 17:13:15|
|526 forum posts|
My choice would be a fabric reinforced grade of Tufnol, with the grain going the right way. There used to be a material trade-named 'Ferrobestos' used for propellor shaft stern tube bearings but I guess the 'bestos' bit makes it a No-No nowadays.
On the strength of many years experience, I'd say that metal items don't have to be immersed to suffer corrosion in a chlorinated swimming pool environment.
However, I thought 'the modern thing' with swimming pools was ozone or ultra-violet sterilisation.
|535 forum posts|
Have a word with Igus, very helpful on material selection for their bushes and not expensive. Their catalogue is good if you can navigate your way through it.
|Carl Wilson 4||05/10/2018 19:38:51|
670 forum posts
|316 stainless steel running in ptfe bush. I have extensive experience of this running in seawater. Lasts forever.|
|Howard Lewis||05/10/2018 19:41:49|
|3146 forum posts|
Presumably Staimnless for the shafts and housings, and then a composite, (or could sealed , 2RS, ball races be used?
I liken the suggestion of lignum vitae. Water lubricated, has been used as a thrust bearing for ships propellor shafts for many years. Don't use it as a bouyancy aid, denser that water!
|Carl Wilson 4||05/10/2018 19:44:18|
670 forum posts
|You don't need the complication of ball races etc for a submersible application.|
|jason udall||05/10/2018 21:34:01|
|2023 forum posts|
|Dry bearings would be the way to go.|
Because any kind of lubrication will upset risk assessment bods.oil or the hint of a risk of oil ib the pool .Even PTFE built into plastics .. would be called a lubricated solid..just avoid that discussion So choose a self lubricated solid. Though avoid leaded bronze or similar...
Edited By jason udall on 05/10/2018 21:36:00
|Gary Wooding||06/10/2018 10:03:23|
|669 forum posts|
Thanks for all the good advice. Here's the background to my requirements.
I do voluntary work for the Remap charity (the church-door handrail shown in last month's MEW was one of mine) and neither the swimming club nor the charity can afford to spend much. The hydraulic lift consists of a large platform, level with the side of the pool, which can be lowered into the pool. The wheelchair must be of conventional design so that people with sufficient upper-body strength can propel it themselves. The frame of the wheelchair will be made of PVC pipe and the wheels and casters I have obtained are plastic, but they have conventional steel bearings. There are 12 bearings in all, of three different sizes. Since cost is a major consideration I thought that machining them from solid would be the most cost-effective solution. Delrin or PTFE seem the way to go, but if I could get some lignum vitae at a suitable price....
|Ian S C||06/10/2018 10:36:50|
7468 forum posts
Lignum Vitae, very old lawn bowls, stick to the plastic bearings on 316 stainless shafts, make sure all metal parts are stainless or plastic, and probably best to over engineer the chair as they can have a rough time from some staff, or patients.
There was a Kiwi bloke Rob Buchanan making low priced plastic wheel chairs that were suitable for being immersed in salt water. Ron set up a Charitable trust called MEND, I don't know if the e-mail address is still ok,
Ian S C
Edited By Ian S C on 06/10/2018 11:00:26
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