Need some advice...

Hello bill12780,

A bearing surface is only as good as it is clean, and so you want a bearing having at least some form of good wiping action. Teflon foam works, but better yet, try Teflon felt. Order samples and give 'em a try.

Good luck!

-e

I am confused (not to worry it happens often) . Do you want a bearing, a bearing race, a bearing seal?

No matter - Teflon, UHMW and urethanes as well as Nylon are all knee jerk responses. Composites and ceramics are also available

A little more info/specifics : load bearing? subject to pressure, loads, deformation? strictly swimming pool levels of chlorine or higher concentrations.

C'mon you can tell. I'm still a year or two away from purchasing the equipment to start my own production. And I'm kinda busy right now, so go ahead - whatcha fixin, building, breaking?

Hi TC!

The OP mentioned that one of the bearing surfaces is acrylic. Seems to me that composites and ceramics would scratch acrylic. Given his mention of pool chemicals and the needed resistance to UV, I suspect the bearing will be exposed to the elements - and all that comes with it; dirt, grime, debris and so forth. Fabric was one of the candidates he'd mentioned. Seems to me that a hard surface against acrylic would be vulnerable to gouging from dirt and grime. I suspect also that he wants the acrylic scratch-free so that folks can easily see through it (possibly an underwater pool window over which something slides, perhaps? Just guessing here.)

Take care,

-e

I am not on board with the Teflon felt. Not in a chlorinated, wet environment anyway.

I actually was unaware of such a beast until I followed the links (the first offered no hits).

Hmm.. now I'm scratching my head wondering where in my home I could use some of the stuff. Not for it's intended purpose of course (no billiard table). Maybe as a very slick rug that eggs wont stick to?

Why not simply line the acrylic edges with some hard material (like steel/ aluminium frame) and use it as the bearing surface ?

I think above answer by sb is spot on.

You likely will never find a bearing material that will not scratch Acrylic which is pretty soft on any hardness scale. Perhaps cloth or felt would do. With oil soaked seals to prevent any dust or particles from entering. Then comes the question is the bearing sleeve 360 degrees or only over a much lesser angle, which would perhaps mean the acrylic tube is just laid down? If the bearing sleeve is 360 degrees you could not look trough anyway Too many unknowns here.

Substituting a metal bearing seem a way around your problem.

I think our OP should say a little more about his application. My take on it is that he wants the transparency of acrylic but needs a way to slide something across it without scratching the surface.

"...Seems to me that composites and ceramics would scratch acrylic..." - mostly, but not always.

If you get composites to rub other type composites, you're relatively safe.

Zytel^®, used today in knife and tool handles is such composite (Nylon-soaked glass-fiber) versus, say ComAlloy Hiloy^® used in scratch-proof sinks and baths - (Polycarbonate-soaked hollow carbon-tubes) - and you have both materials relatively scratch-proof - one of those (polycarbonate) acrylic, both compound and composite.

Just about any material will do what you ask..it's not the material but the finish or the dirt it has picked up which will scratch.

You compound your error by saying it would be ok if it polishes....polishing is no more than very fine scratching.

A soft material like Felt/ptfe/SRBP (sythetic resn bonded paper/cloth) would work well but will hold contaminants.
A hard material, steel or brass will work well but must have a good surface finish and smoothed edges.

So I think the problem is one of maintaning cleanliness more than material choice.
If you force me to suggest a material.... Nylon (Acetal)

Del (feel free to abuse my ideas on this )

so tempted to give up a GA for that one!

definitely wins points for creative use of household items!

Well, dammit! Give me a GA already!

There you go.

It cost me nothing, so what the...

Hello europium:

I think soap is a pretty good answer so a GA to you. I am not sure if a bar once wet will make like a 'chalk' line as it is moved. Should that be a 'soap' line?

A few more details would be nice.

My first thought was he was a pool man and had to keep a pool cover clean. But your answer seems to have a ring to it, so I will go with that!

Take care....................

If I was to write* something like:

"...To whom it may concern.

I herewith offer to sell GA's for a dime each. I know I'll never get reach with that, but if I gave these for free, people might disregard them alltogether, so there.

Heck, I'll donate it to charity, just don't bite my head off..."

Would I be kicked off CR4 ?

*_{A JOKE dammit !}

Any body been to the beach the came home and had the sand imbedded into the soap bar after a shower?

That's a problem, to be shore. Life can be a real beach sometimes.

Careful! Any of the thermoplastics will suffer scoring if the surface area localised pressure is sufficient. I think the metalurgists call it "galling" but I'm not sure.

Every plastic has a pressure/velocity point at which it locally melts (plasticises) and will appear as a scratch.

Even the teflon foams and other suggestions could cause localised problems. While those suggestions are all good, there are still limitations that only you can define in your specific application.

How 'bout a water bearing? Like an air-bearing, only wet.

Well if we are to get that technical, drill the ends of the Acrylic and insert a steel rod. May as well just go with a magnetic bearing. No wear, smooth action, good glide, at reasonably high cost.

"Well if we are to get that technical, ..."

Technical? My car has four of them.

Try teflon in one of it's many forms.

Hi. I would have to say you are probably looking at PTFE (Teflon). It is a material with one of the lowest coefficients to friction. The other characteristic it has is that is inherently UV resistant. In tests it has withstood the Florida sun for over 30 years with no degradation. I would not recommend Nylon as it has a tendency to absorb water ian is not really suited to UV exposure. Most polymers are not suitable for this reason unless you buy a grade that has been specifically formulated wth a UV stabilizer.

That's all I have to say about that.

Al

I WOULD USE DELRIN FROM DUPONT CHECK ON LINE FOR PROPERTIES OF DELRIN

WOW!

I am always amazed at the response I get here at CR4. I can tell you how much I appreciate all your experts help!

Let me give you some more information.

This is for a product we build that is a automatic spa cover. It "slides" over the spa on the edges. The Plastic that we use for the panels scratches the acrylic that the spa is made of. We have in the past had a spring loaded roller to lay down a fabric called Keeter has the panels move across the top of the spa. This is expensive, unreliable, and adds a lot of "labor" to the manufacturing and maintenance.

What I am looking at is adding either a adhesive backed material on the spa itself OR to the bottom of the panels.

My fear with putting them on the bottom is that the tape or material may peel up has it slides back and forth over time.

Also I should mention that retooling to add a channel is not an option. Also, permanently "changing" the spa is not an option. (hence my tape idea, it could be changed and remove as needed)

Sorry about not being more detailed in my first post. I had no idea I would get such a huge response.

I am looking at all the suggestion, But would like any revised ideas you all may have.

Thanks to all!

bill12780

Well, then! That simplifies things a bit and gives you a lot more options.

Funny thing is, here on CR4 the more detail one supplies, the fewer the answers (generally. Sometimes - often - the thread wanders off-track. Like a bar of bath soap. )

So, this cover slides across the top of the spa and scratches the surface. I think as long as you are sliding anything across the spa's top surface you will get scratches as many others have mentioned. It will either be dirt or residue from spa chemicals etc. that scratch it.

When you are retracting the cover, does it stay horizontal to the ground all the way across or does it pivot up or down at the "back" end.

You need to check up on the concept used for MHOS scale of hardness. In truth all this say is that a harder substance will scratch a softer one. Teflon could be the answer but you need to suck it and see - any abrasive dust will cause scratching - what I would think best would be to use a lubricant possibly a good quality car polish - be liberal don't put it on and polish it off. A teflon spray or powder could be used regularly. Possibly teflon powder in a wax polish base would be better.

The paste or wax must be renewed regularly to ensure there is an active layer.

Maybe a daft idea - if you can get some but glass beads as used in reflective (road-line) paints might help - I believe this has been used to move heavy machinery.

Ever thought about wheeled cover ? say small wheel on two ends guided on rails. When the cover reaches end, the wheels drop down in small slots and the cover is tight. (Since it is top cover, you don't have problem of leak-proofness while sliding). It don't have to slide along the edges while movement (or you may think like retractable wheels a la aircraft)

Rubber or soft urethane ( a big wide contact area- if kept moist will slide) ... or consider wheels/rollers (a long axle full of rubber or wood/ wheels or a rolling pin type of wheel (small diameter rolling pin wheels- one right behind the other).

"The choices you make might be mistakes but it's never too late to turn around." Tony Lang - musician PS You need to disclose the end purpose or object so's others can offer proper input...

Sorry I did not identify myself earlier... at any rate it occurred to me that a rolling assembly that 'rolls out' a covering- sort of like the way artificial turf gets installed (& returned to the spool for storage). Very little if any rubbing or scrathing possible this way. Carlos

"The choices you make might be mistakes but it's never too late to turn around." tony Lang - musician

Float "IT" on air.....whatever "IT" is.........

Just the thought process my mind was leading to.

Ideally if the cover is horizontal jets of air or water can float the cover without any friction. We have moved ships by this technique using air.

When the air is stopped the bearing effect disappears. Note that the lift is proportional to area under support.

You must use a material that is softer than the acrylic you are trying to protect. Seems obvious, but not to everyone. Depending on your application, indoor/outdoor carpet may be your best best as it does not require special tools or talents to use.

Hope this helps joe@w3ig.net

urethane coated or Teflon coated bearings or wheels should do the trick with fore and aft wipers/brushes.

Both Teflon and UHMW have the lowest co-efficient of friction. They are primarily used for sliding applications so those would probably be good choices. Found a website that could help you more with spec sheets and everything.

Both Teflon and UHMW have the lowest co-efficient frictions of plastic. They are both used primarily for sliding applications so try those. Found a website with more specs and data for you.