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Alternative Materials to Bronze for high-load bushings... are there any?

snowshooze

Hot Rolled
Joined
Sep 15, 2010
Location
Anchorage, Alaska, USA
ISO 17842-1:2015, “Safety of amusement rides and amusement devices —Design and manufacture”, etc. Go talk to the latest manufacturers of the ride or a PE. “Specifications should match the manufacturer’s instructions.” There‘s a lot packed into safety design requirements for component replacements, and failure analysis includes two forms, “general safe state failure and dangerous failure.” The bushings might be important and their undoing might precipitate other stresses causing failures, eventually. Seems there’s a number of Spider and Spider-type carnival ride failures.

2002 Columbus, OH

* “[Spider-like Spinning] cars rotate in groups of three at the end of spider-like arms, which spin at a top speed of 24 mph. The men were thrown about 20 feet from the ride. Both were treated for injuries and released.

"We started off slow and then picked up momentum and Jim says, 'Well, it looks like this is going to be a fun one,"' said Dennis Nielsen, whose head was bandaged and his right eye swollen. "I feel sore all over."

I wouldn’t put my kids on a carnival ride w armatures spinning that’s been built using forum-advised parts, as minor or ‘insignificant’ as the components might be thought to be, even if gotten right. However, suggestions are a good talking point to discuss w those who would sign-off on replacements to conform to and meet inspection requirements.
And you think I am gonna do something stupid.
Quit it.
 

snowshooze

Hot Rolled
Joined
Sep 15, 2010
Location
Anchorage, Alaska, USA
There are people who could do the calcs here. There are people that could stamp the drawings here. But there are NOT people with enough clairvoyance to do that based on the information given.

Making parts to print is one thing. This is not that. Be careful.
I asked about materials.
My interest is in compressive loading and coefficient of friction.
Nothing else.
I trust China?
Nope.
This job calls for a Machinist.
Here I am.
 
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Strostkovy

Stainless
Joined
Oct 29, 2017
I don't think material or quantity of lubrication is the issue, I think it's an issue of geometry and effectiveness of lubrication.
I obviously don't have all of the details. But I think the bushings need to be made with the ID and OD slightly oversized, and pressed into a reamed hole with a slight interference fit that shrinks the ID to a snug tolerance around the shaft that slips in. There are many charts floating around that determine the fit quality based on the bushing load. There needs to be a means to inject lubricant in the joint itself, with grooves to carry that lubricant along the surface. I think there is no chance of getting a square ended pin or even a tapered pin into the snug slip fit of the bore. I would have a ball shaped end on the shaft that fits first, and then guides the radiused taper the rest of the way. Protective sleeves mounted to the machine to plop the pins in for transport will go a long way towards keeping them clean and in spec, as well as a spare somewhere.
I am not an engineer, and am learning just like everyone else. But every bushing issue I've ever had was lubrication not making it's way into the joint or a sloppy fit.
 

Strostkovy

Stainless
Joined
Oct 29, 2017
I drew up an example of the "wangshaft" geometry I like but seldom see used. This example will self center with up to 19 degrees of initial misalignment on installation. I like a flange on the square end that stops the pin at full insertion, and then a sliding gate with ball detents that retains it. But that's all up to you to figure out.
For lubrication of the bushing I've seen a real simple approach where a shallow, coarse thread is cut into the bushing and grease is injected into a crosshole in the middle. One of the easiest shapes to machine for this purpose IMO.

wangshaft.png
 

hanermo

Titanium
Joined
Sep 28, 2009
Location
barcelona, spain
Em..
The easiest solution perhaps is just to make the bushings 6" in diameter, vs 3".
This will likely make them 4x-8x stiffer and stronger and last 12x+ longer.

Rigidity and strength and longevity tend to be diameter power of 3, or power of 4.
Cost tends to be linear per size.

If it´s easy, and cheapish, I would also make them longer, to maintain the 1:1 D/L ratio.
So 6" in D, and 6" in length.
This is likely about 40x stronger and 40x longer lived.

There are many fudge factors involved, thats why 4-8x vs 16 x in strength.

And almost always, something vastly stronger than "peak load" lasts nearly forever.
Every (good/decent) lathe on the planet is a good example.

Lathe peak loads are 2% of failure/deformation loads.
Mills and VMCs are about the same.
A good manual lathe lasts 50-100 years, give or take.

Another option is std bearings, stacked, perhaps in elastomeric mounts.


Doubling the D will greatly increase the surface speed and R rating of the bushings, but the rides have very low rpm.
Should not have any effect, imho.

Fwiw, I built a carnival ride, and had it professionally inspected and certified and insured, ...
 
Joined
Jan 15, 2005
Location
The Netherlands
Like I said before Lock the pin LOCK THE PIN
A good solution would be this Easy to take the pin out
Easy to fabricate But you can also buy these at Nord-Lock
BTW The bearing swivels just a bit Like 45Dgr or so
At least that is how I see it

Peter
expander-system_pivot-pin.png
 
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Comatose

Titanium
Joined
Feb 25, 2005
Location
Akron, OH
If anything EVER happens with the ride, the first people the inspectors are going to call in is the manufacturer. Whether your bushings had anything to do with it or not. The manufacturer is going to pretty much immediately flag your parts as being an unauthorized modification, which will absolve them of responsibility. The state inspector is then going to ask the carny for the paperwork approving the modification. The carny will point the your way.

You'll either have a piece of paper stamped by a PE signing off on the modification, or you won't. If so, then it becomes his problem. But you won't, because a PE doing the analysis properly, from scratch, without support from the factory will cost more than the value of the machine in its entirety.

I'm not at ALL risk averse, product wise or personally. Could give you a list. But, my professional opinion as an engineer is that what you are planning to do is not a well considered, calculated risk. It is ignorant, stupid and reckless. The fact that you're being combative about it just reinforces that in my mind.

Compressive loading and coefficient of friction is NOT all there is to this design. People here are trying to tell you that.

You COULD do this right, but you are clearly SwissMak levels of "don't know what you don't know." Except that in this case, you're risking other people's kids instead of your own kneecaps.

But hey, can't fix stupid.


I asked about materials.
My interest is in compressive loading and coefficient of friction.
Nothing else.
I trust China?
Nope.
This job calls for a Machinist.
Here I am
 

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
The Factory bushing are junk when they are new.
Junk.

I take this to mean that you have dimensionally inspected the bushings and found that they fail to meet the specifications called out by the manufacturer, not that the pins and/or housings have been sufficiently worn by use to give a fit different than that which was intended by the OEM.

Every time the bushings are replaced with fresh ones made to the same size, the fit will be a little looser. This effect will be accelerated as the overall wear increases. I'm sure you know this because your first idea was not to make wild guesses as to what completely different material will magically fix everything, but to study the original specifications and make a "high mileage" set of parts which are altered from the original design only to account for accumulated deviation over the life of the equipment. Right?
 

Joe Gwinn

Stainless
Joined
Nov 22, 2009
Location
Boston, MA area
Talk to these guys: https://thordonbearings.com/
They have some amazing materials. The one I'm familiar with is called 'Thordon Blue'. It is very resistant to abrasive contaminants. It is also very expensive. Biggest problem for your application would be that it is normally an interference fit. Sounds weird but it works, and if it lasts long enough maybe the installation hassle would be ok.
It may also be only for flooded bearings, such as marine propeller shafts.

It appears to be some kind of polyurethane alloy: "US20090098179A1".
 

Strostkovy

Stainless
Joined
Oct 29, 2017
There seems to be a lot more respect for the original engineers here than I would expect. How do we know the engineers didn't spec out loose garbage because it would run long enough and was cheaper, or they simply made a bad call?
Is nobody else constantly redesigning crap that someone engineered terribly to begin with?
I bet the pin was made a small OD for an easily assembled slip fit that wears too quickly.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
My wife and kids love riding rides. Myself, I like looking at the rides, seeing how they're built and how well they break down for travel. Even how fast they can load and unload victims. Fascinates me.

Not all, but probably 80% of them look like they were built out of Bubba's backwoods scrapyard, liquor and gun emporium.

My wife won't let me do it, but I really want to take a bunch of old rusty bolts with me and toss a handful under rides, leave some on the floor as I get out, etc. and see what the Carnies do about it.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Most OE stuff in my experience is spec'd for quick and easy assembly. Not long life. They will sell you as many replacement parts as you are willing to buy... I'd be perfectly comfortable with modifying the material on this one as long as I could keep an eye on it and the specs of the material were equal or better. If I was making bushings for something I'd never see again, I'd probably stick with the bronze too.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
My wife and kids love riding rides. Myself, I like looking at the rides, seeing how they're built and how well they break down for travel. Even how fast they can load and unload victims. Fascinates me.

Not all, but probably 80% of them look like they were built out of Bubba's backwoods scrapyard, liquor and gun emporium.

My wife won't let me do it, but I really want to take a bunch of old rusty bolts with me and toss a handful under rides, leave some on the floor as I get out, etc. and see what the Carnies do about it.

The carnies probably wouldn't even notice. They have guys that come in before the fairs start and set up the rides, and then come back after the fairs to take them down. They'd notice, I should hope.

And, uh... You need your wife's permission? :D
 

Strostkovy

Stainless
Joined
Oct 29, 2017
My wife and kids love riding rides. Myself, I like looking at the rides, seeing how they're built and how well they break down for travel. Even how fast they can load and unload victims. Fascinates me.

Not all, but probably 80% of them look like they were built out of Bubba's backwoods scrapyard, liquor and gun emporium.

My wife won't let me do it, but I really want to take a bunch of old rusty bolts with me and toss a handful under rides, leave some on the floor as I get out, etc. and see what the Carnies do about it.
There are almost always bolts and cotter pins sitting around near rides when I look around.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
And, uh... You need your wife's permission? :D

I trust my wife's decisions when it comes to what things we should and should not expose our kids to. Watching dad fuck with the carnies would probably make an unforgettable memory, but it also sends the wrong message. My kids learn a lot about human behavior through my actions. Something I don't think my dad ever took into consideration and I hope to do better.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
I trust my wife's decisions when it comes to what things we should and should not expose our kids to. Watching dad fuck with the carnies would probably make an unforgettable memory, but it also sends the wrong message. My kids learn a lot about human behavior through my actions. Something I don't think my dad ever took into consideration and I hope to do better.

Having 2 kids myself, I understand that completely. I feel the same way. If I was going to do it, I just wouldn't let the kids see! :D But I probably wouldn't do it either. It's actually not that easy to pull one over on my kiddos.
 








 
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