Plain bearing use and greasing design

[dawz]

Dear all,

This is on greasing design for plain bearings.

background story: A scissor lift. 2x deep groove ball bearing stacked on each side (each track). one of the deep groove ball bearings busted suspected due to irregular track surface. Now intend to use plain bearings.
thread:

https://www.eng-tips.com/viewthread.cfm?qid=516801

For the plain bearing, is an "outer shell" required for it to roll over the track? Just like how it was used in a cylinder jack.

Also, are rubber seals necessary for plain bearings?

 

[3DDave]

I was wondering why this design seemed weird; other makers don't use it as it doesn't support the bearings as well as possible.

See

https://youtu.be/-JZmhSHFkxs?t=204

Notice the lack of grease that tends to capture debris that can damage the bearing.

 

[dawz]

I was wondering why this design seemed weird; other makers don't use it as it doesn't support the bearings as well as possible.

See

https://youtu.be/-JZmhSHFkxs?t=204

Notice the lack of grease that tends to capture debris that can damage the bearing.

that looks like a solid steel roller.. hmm.

I have concerns that debris will instantly kill the plain bearings if not sealed.

Maybe I am wrong in designing it this way.

 

[dawz]

What about the "anti-abrasion" sliders? Looks like a combination of engineering plastic with metal core on the inside.

https://youtu.be/Dj8aDX74Rrw?t=65

 

[3DDave]

What about specifying what the application you have is?

 

[dawz]

It's basically a crawler, carrying things like fruits and sand/rock. The bearing sits inside the track circled in red. Load on bucket is about 2 ton max.

 

[3DDave]

Looks fun.

I wonder if that dumper on top is adding a large impact load that scissor lifts rarely have. I don't see any springs to lessen the resulting force. That particular arrangement may be hitting the sliding portion like a big hammer unless there is some control in the cylinders in the dumper to slow it down to a crawl before setting all the way level.

I think you could use a UHMWPE plate to slide on and an aluminum bronze block foot in double-shear with a side catch to the channel to prevent overturning. Specify a polished finish on the aluminum bronze face that is against the plastic plate and it should last a long time.

 

[dawz]

Fun.. but risky if not designed well.

there's no suspension to dampen and bearing will take a lift and knock on track if scissor wobbles at the highest position. Z axis Clearance for the deep groove ball bearing in the track right now is 1mm.

Won't UHMWPE break under high pressure?

 

[3DDave]

Yes. At 100 Million psi it will break. So will a hardened bearing.

Use more than the end of a needle as the bearing area and it will be fine.

I'm not going to argue about my recommendation.

 

[dawz]

Yes. At 100 Million psi it will break. So will a hardened bearing.

Use more than the end of a needle as the bearing area and it will be fine.

I'm not going to argue about my recommendation.

Alright.

I just need to decide a design at this point. If plain bearings without greasing (or minimal greasing) does the job.. i'll go with that, it's a more economical approach in my region here.

I have never tried sliders/blocks before, but i'm open to the idea.