7

I am working on a piece of art that has parts that rotate slowly, at about 1RPM, thanks to a couple of bearings. There is a possibility that it might be installed beside a beach for about a week. The problem is that sand and bearings do not play together well.

Or do they? Is there a bearing type that can resist the ingress of sand, or failing that, a reasonably reliable and durable way of preventing sand entering?

Yes, I am considering covering it with boots, but this question is part of research to see if there is an alternative.

Steve
  • 187
  • 1
  • 6
  • 6
    What does "Yes, I am considering **boots**," refer to? – NMech Feb 23 '22 at 06:34
  • 2
    Is covering the bearing with seals acceptable? – Mast Feb 23 '22 at 14:27
  • 12
    @NMech A boot is an external shield (often rubber) over moving parts – RLH Feb 23 '22 at 17:23
  • 7
    @NMech - picture here https://www.indiamart.com/phogataxleengineering/drive-shaft-boot-clip.html – Michael Harvey Feb 23 '22 at 18:44
  • 4
    *sealed bearings* - like they should all be, always, on everything. – Mazura Feb 23 '22 at 18:45
  • 1
    yes all those strategies are options, depending on how far you want to take it. For an hour's operation maybe easier to let it be and go with a single seal and some thick goop. Bearings themselves could be a sealed model, besides that you could construct a double seal that allows rotation, and fill the intermediate space with *thick* grease to trap particles that make it thru the outer seal and stop them getting thru to the inner space where the bearing is. In the most extreme case (heavy construction equipment), lubrication under positive pressure – Pete W Feb 23 '22 at 20:30
  • 1
    Magnetic bearings are a thing. https://en.wikipedia.org/wiki/Magnetic_bearing . Cost and size might be prohibitive – Jeffrey Feb 23 '22 at 20:37
  • 1
    @Jeffrey Unless you have iron sand. – DKNguyen Feb 23 '22 at 21:30
  • Gosh, thanks all. So many great answers, i am not sure which to accept. I appreciate your input. – Steve Feb 23 '22 at 23:02
  • 1
    Considering how well the various bearings on the suspension and drivetrain/wheels of a dirtbike fare, I wouldn't worry about a rubber sealed bearing doing 1 RPM on a beach – Caius Jard Feb 25 '22 at 18:08

6 Answers6

16

A bearing with contact seals is reasonably robust against airborne dust. It is a rubber seal that contacts both the inner and outer ring, leaving no gap. Such bearings do not rotate as readily as unsealed bearings and non-contact seal bearings. This type of seal is identified by suffix -2RS in the bearing code.

Some bearings with contact seals additionally have IP69 rating. Most commonly these are sold as food safe bearings, because they have to stand to power washer cleaning in food production facilities. They are significantly more expensive than normal 2RS bearings.

jpa
  • 1,845
  • 7
  • 12
  • 3
    This. It’s the reason why industrial bearings on bicycles can last 10Mm and more. Probably still a good idea to make them easily replaceable and maybe use two side-by-side. – Michael Feb 23 '22 at 15:07
9

Since it's low speed you could just use bushings. Unlike ball bearings with open cavities inside for sand to get into, there shouldn't be any real open spaces for large grains of sand to get into if you have tight clearances

DKNguyen
  • 4,625
  • 1
  • 9
  • 22
  • 9
    Where there are large grains of sand small grains also exist. – Solar Mike Feb 23 '22 at 07:53
  • 5
    @SolarMike True, but at least small grains better embed into the softer material of a bushing better where they are a little more out of the way. – DKNguyen Feb 23 '22 at 14:18
  • 3
    Bushings are also cheaper and could simply be replaced. The asker did say it only needs to survive a week. – Tech Inquisitor Feb 25 '22 at 17:11
  • @DKNguyen small grains embedded into softer material is how the wear happens. This is how you polish diamonds and the small grains are not out of the way. – D Duck Mar 01 '22 at 09:14
  • @DDuck I am aware hence the "more out of the way" rather than outright out of the way. This mechanism produces less wear than a loose grain of sand inside a steel raceway. It's similar to how a stone or grinding wheel can be made to leave a smoother finish if you dress it so that the abrasive particles don't stick out of the binder as much or clog the space between abrasive particles so that it glazes and doesn't cut as effectively. – DKNguyen Mar 01 '22 at 18:38
8

With high enough mechanical advantage (presumably you're gearing wind power or a large motor down heavily to make 1RPM), it's unlikely the bearings would fail you within a week even if scraping away totally packed with sand.

Just plan to inspect and replace any that are clearly having a bad time after their journey.

If you want to avoid replacement, follow @jpa's advice, though IP69 is probably overkill and you can save cost with a lower rating.

If you want the bearings to last tens of thousands of hours, you may want a lubrication system and scheduled inspections, though this would be spectacular overkill for your project
For completeness, Timken has some good reading
https://www.timken.com/resources/5892-bearing-damage-analysis-with-lubrication-reference-guide/

Another potential danger for your installation is the local salt water spray at metal interfaces; the dissimilar metals and brine can form a weak battery, greatly accelerating corrosion
https://en.wikipedia.org/wiki/Galvanic_corrosion

ti7
  • 181
  • 4
4

Protect all the bearings.

Boots as used on cv joints will protect bearings.

But there are boots designed to mount on various surfaces.

Bearings that are not protected will suffer an increased rate of wear, as any wind will bring fine particles which act as a grinding material.

Solar Mike
  • 14,798
  • 1
  • 19
  • 29
2

Bearings are cheap and consumable.

Simply fit new bearings after the installation leaves the beach and it will be as good as new.

Otherwise -2RS sealed bearings should be fine for months in a sandy environment. 1 RPM is not enough to create any measurable heat so these are low speed bearings, and probably low-load too given its a removeable art installation.

Another option is to add an additional cup/cover over the bearing, if the art allows this. Even gluing a piece of plastic over might be sufficient to minimise sand ingress.

I would not cover the outside of the bearing in excess grease - that will hold any sand in the area.

Criggie
  • 430
  • 3
  • 10
  • 1
    Thanks, the issue isn't so much replacing the bearings, I just don't want it (literally) grinding to a halt during the installation. – Steve Feb 25 '22 at 01:54
  • 1
    @Steve that this device turns at 1RPM suggests there's a power delivery and a gearing train somewhere. Sounds like there's going to be a lot of torque. As a measure - if you can't halt the geartrain with your hands, sand certainly won't stop it. – Criggie Feb 25 '22 at 02:12
  • 1
    Thanks for that, I hadn't considered that aspect. Not that I care much, but assuming sand wouldn't stop the bearing, would it be destroyed? – Steve Feb 25 '22 at 02:52
  • 2
    @Steve eventually yes. The performance would slowly drop, the resistance would increase, and over time the temperature would rise if it were doing thousands of RPM. At 1RPM it might click a little if the bearing race got a dent. A grain of sand in there would get pushed into the grease or powdered, so the very low speed means you're probably fine. When the installation is over, compare the resistance of the bearing after with a before "feel" and post your observations here. If you change the bearings, cut an old one open and explore it - makes for excellent answers. – Criggie Feb 25 '22 at 07:17
1

Bering's by name bear all of the friction at a point of two or more surfaces grinding together. They will all wear out. Your use case is "by a beach for a few days". Just suck it up and save ur money. They will work just fine. The art piece is not meant to last if it has moving parts.

Christopher Cameron
  • 11
  • 1