Ball bearing used as roller 3

[Haarg]

We want to use a ball bearing with the outer race running directly on a flat surface. The bearings will be loaded to about 1000 lb. Travel is 35 in, and frequency is under once per day.

We have one mechanism that has been used for several years, but early on, one of the bearings (6204) broke its outer race; there have been no further incidents.

We're building several more of the mechanisms and we'd like to have a better reason for using a particular bearing than TLAR. Any suggestions would be most welcome.

We can get 6204-2RS bearings for $6 each, and we can get 6204-2RS bearings for $0.93 each. Are cheap bearings always junk, or are they usable in this sort of application? A broken bearing would be just inconvenience.

Thank you for your anticipated help.

Haarg

 

[israelkk]

The bearing material is very brittle therefore, when the outer race is loaded in a line it deflects the deflection may be more than the bearing can tolerate because it doesn't have a plastic zone. I you can press fit a hardened and tempered (~50RC) thick ring (at least thick as the outer race) over the bearing outer race it will support the bearing and reduce the bearing deflection by ~90%.

 

[Tmoose]

I believe "Cheap bearings" are risky in standard applications like electric motors where substandard finishes make noise and smoky metallurgy shortens life.

How many bearings per unit? If I was really satisfied with the life, I'd keep on doing what I've been doing. The potential $5 Saving per bearing can quickly be eaten up testing (or just talking about) the cheaper ones, or good will lost to customer "inconvenience." I'd apply my cost reduction and reliability improvement efforts elsewhere.

1000 lbs is a lot for a 6204. Properly supported the static load (incipient race denting) limit is about 1500 lbs.

http://medias.ina.de/medias/en!hp.ec.br.pr/62..-2Z_FAG*6204-2Z_FAG

As Israelkk said, The outer race really needs a steel housing at least 2X the race thickness. If the material that interacts with the roller OD is not showing distress, I'm not sure fancy materials are needed. heat treating does not change steel housing's stiffness.

Rather than fabricate an outer housing I'd be looking at roller follower type bearings. Note how thick their outer races are.

http://www.thk.com/eng/products/class/rollerfollower/index.html

Your 6204's OD is 47 mm.

Buying cam follower bearings come with a mounting stud.

http://www.thk.com/documents/us_pdf/products/generalB/CamFollower/en_B_808.pdf

 

[diskullman]

For this type of application, usually the cheapest bearing available is used, regardless of quality. These bearings are usually designed to run in electric motors at 1750 RPM for hours at a time. You want to look into unground bearings as well, but precision bearings are cheaper due to larger production quantities.
A good example of what is used would be pallet jack wheels. They usually have a 6205-2RS bearing of the cheapest variety, as it is used mostly for it's size and it's ability to roll, even just slowly. They typically use the cheapest chise bearings available.

Russell Giuliano