Pin on Steel bearing - tough one.
Pin on Steel bearing - tough one.
(OP)
I'm struggling with this one..
I've got a sprung loaded pull lever (for a switch) the motion of which is governed by a pin in a slot profile. (This provides detents and self centring etc.) The environment is difficult (unsealed unit on landing gear of aircraft) and I'm having problems with galling on the 4mm dia pin - I can't use lubicants (attract dirt- washes off etc.) I need the pin to slide accross the angled slot surface under the load of the spring.
I've tried:
Phosphor bronze pin onto chemically polished stainless.
(Failed quite quickly)
Stainless steel pin onto chemically polished stainless - both suface treated with oil impregnation.
(Much better but failed at about 15k ops)
I need at least 40k ops - low temp performance (-55dgC to 80degC).
I don't want a little bearing in there as dirt and dust will cause problems.
I would love to use a machined plastic for the slot carrier but delrin will creep (constant load from spring) and glass filled will abrade the pin.
Any suggestions?
I've got a sprung loaded pull lever (for a switch) the motion of which is governed by a pin in a slot profile. (This provides detents and self centring etc.) The environment is difficult (unsealed unit on landing gear of aircraft) and I'm having problems with galling on the 4mm dia pin - I can't use lubicants (attract dirt- washes off etc.) I need the pin to slide accross the angled slot surface under the load of the spring.
I've tried:
Phosphor bronze pin onto chemically polished stainless.
(Failed quite quickly)
Stainless steel pin onto chemically polished stainless - both suface treated with oil impregnation.
(Much better but failed at about 15k ops)
I need at least 40k ops - low temp performance (-55dgC to 80degC).
I don't want a little bearing in there as dirt and dust will cause problems.
I would love to use a machined plastic for the slot carrier but delrin will creep (constant load from spring) and glass filled will abrade the pin.
Any suggestions?





RE: Pin on Steel bearing - tough one.
If you can create an joint using plastic on metal, that's your best bet. If stresses are high and creep is a problem, I might suggest some highly filled plastics. I've used Vespel CR6100 which has a very high strength and modulus for a plastic. It's a carbon fiber impregnated Teflon, but that's not a particularly good description.
If you have to have a metal on metal joint, I'd suggest one of the parts being Nitronic 60. I've used that for a stainless valve guide, unlubricated, and it works very well without lubrication. Nitronic 60 is a special anti-galling austenitic stainless with much higher strength than 300 series stainless.
RE: Pin on Steel bearing - tough one.
Russell Giuliano
RE: Pin on Steel bearing - tough one.
ht
http://www.magnaplate.com/coatings/index.html
RE: Pin on Steel bearing - tough one.
The original trials with stainless steel on both sides went better than you might exppect so I'm now trying hardened a silver steel pin (its an easy test I can do now).
I think a graphite based coating is a possiblity but I am worried about the surface pressures. I've got 30N on a 4mm Dia pin running on two slots cut in a cylinder.
I have electro-polished the slot to give a good surface.
I'll have a look at the coatings you've suggested - please keep them coming!
From a small bearing point of view - I've only got 4mm Dia and imagine the super-fine dust you get in the desert.. I've done my best to baffle the entry but over 20 years of use it will get in there along with ice, de-iceing fluid and all sorts.
RE: Pin on Steel bearing - tough one.
RE: Pin on Steel bearing - tough one.
Can you make that interface a flat surface to reduce contact stress? If you can make it even a mm or so wide, the contact stress drops by an order of magnitude or more and the resulting wear should easily drop by an equivalent amount. The pin could be square in cross section instead of round, or flats machined into the round where it contacts the slot.
RE: Pin on Steel bearing - tough one.
Don
Kansas City
RE: Pin on Steel bearing - tough one.
1/ Silver Steel is a high nickel 1% carbon steel which has a hardness of 65 Rockwell C when hardened. Its pretty old school.
2/ The slot isn't a straight line - more of a wierd zig-zag, I would need multiple flats on it which would be difficult - but not impossible. Its likely that they would be out of position slightly and it would run on an edge. I take the point though, flat would be better.
3/ I don't know anything about garolite. Most switches are made with a thermoset aren't they? I need to machine my parts from stock I'm afraid.
RE: Pin on Steel bearing - tough one.
Mike Halloran
Pembroke Pines, FL, USA
RE: Pin on Steel bearing - tough one.
http://www.kolene.com/applications/adc.asp
One other that you might try is your "silver steel" vs a hard chrome plated "silver steel" pin. Heat treat both then hard chrome plate the pin.
RE: Pin on Steel bearing - tough one.
Mike -
If all of this was bigger, I would do just as you suggest. The whole pin arrangement would need to be approx 4x4mm with a central spindal within that. This thing needs to be durable and reliable in a harsh environment and I just can't feel condfident about such small parts. I know you haven't got visibility of this unit but the whole thing can be held in one hand.
unclesyd -
Generally I've steered away from nitride solutions because of poor corrosion resistance (I need 500 hours salt mist). I need to find out more about Nitronic 60. What is 17/4 ?
Galling and wear are the biggest issues I'm facing. The pin seems to take most of the wear so I've hardened that and I'm just about to put it back into the test chamber but it won't run until next week now...
RE: Pin on Steel bearing - tough one.
http://www.matweb.com
and at materials suppliers like Carpenter Technologies:
http://www.cartech.com
AK Steel:
http://www.aksteel.com
and Allegheny Technologies:
http://www.alleghenytechnologies.com
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Pin on Steel bearing - tough one.
RE: Pin on Steel bearing - tough one.
Another possibility is make either part out of hardened 440C SS. This material has given some excellent wear and galling resistance in some sliding applications.
RE: Pin on Steel bearing - tough one.
I'm in the UK and, looking at the materials you've mentioned, they seem easier to get in the US. I'll talk to my supplier about UK friendly equivalents for anti-galling, hardenable stainless steels.
Screwman - I like the Nickel plus PTFE coating idea. Do you have any suppliers or a brand name for that?
Chris
RE: Pin on Steel bearing - tough one.
RE: Pin on Steel bearing - tough one.
This has been suggested a few times - the problem is that its a long, small diameter pin. Even with a good bearing in the centre, the pin wouldn't rotate as the small torque due to the small OD wouldn't overcome the bending forces trying to jam it. Added to that, this is an unsealed unit which will get jammed up with fine dust.
There are plastic bearing materials which I could use which wouldn't creep (Nylon 4.6, PEEK) but looking at the abuse the unit might get in the field a steel solution is far more confidence inspiring albeit harder to get right.
My current thinking, based largely on the feedback I've had from this forum, is to make both the pin and the slot from a gall-resistant hardened steel and then apply a surface treatment to both which is wear resistant and self-lubricating. If I can I'll make the pin a little larger and the slot a little wider to help things along.
RE: Pin on Steel bearing - tough one.
http://www.armoloy.com/nyflon25.html
Hope this helps.
RE: Pin on Steel bearing - tough one.
I did speak to Armaloy and got a quote. I've looked into lots of different surface treatments and its suprising how similar a large range of chemically different processes can be for a given application.
My current favourite is the hard graphite coating. One thing I like about it is that (to my thinking) if it does begin to flake, its still a lubricant. Some of the other coatings are ceramic and I worry that if they start to go they'll put an abbrasive dust all over the surface which will cause a rapid decilne.
The Armoloy coating and some others are very diificult to get a feel of their failure modes as they are a proprietary blend of unknown origins.
Some other processes (like ion based ones which are line of sight) don't give a warm and fuzzy feeling with regards to evenly coating the insides of a slot.
RE: Pin on Steel bearing - tough one.
http://
RE: Pin on Steel bearing - tough one.
Where I'm going with this is that even the best coatings fail when the substrate fatigues away from under them. You have to reduce the contact stress, by reducing the force or by reducing the curvature.
When the cost of manufacturing a super- hard, exotically curved pin is finally revealed, some money might, er, fall out of the sky so to speak, for redesigning the entire mechanism.
I'm reminded of some guys who think they mass- produce big yachts. Truth is, whichever installation crew reaches a hull first gets to pick where their stuff goes, so the last trade to reach a particular hull faces a really knotty problem of snaking their pipes or cables or hoses or structure around whatever's already been installed. A friend of mine runs a fleet of them, all the same model, and they're all different; it drives him nuts.
Analogously, you've been suckered into patching a design that really should be re-done from scratch, with all affected specialties participating in the balancing act at the same time.
Mike Halloran
Pembroke Pines, FL, USA
RE: Pin on Steel bearing - tough one.
Lots of points there - taking them in order..
I know the pin doesn't have to be round but if you could see the detail of the design you'd see that either you let the pin wear to a flat without galling or you'll be running on an edge from flat misalignment. This is largely due to the scale of the mechanism and the simlplicity it needs due to the need for reliability under dust ingress.
You're right about substrates - that's why I need a hard substrate to support my finish, this will also help with wear. A larger pin is possible but this weakens the slot carrier.
I'm afraid the design is all mine and it was done from scratch. Its got to a point where its very simple now and, ironically, the issues I've now got are more to do with failure in qualification rather than failure in the field. (I prefer it that way around).
RE: Pin on Steel bearing - tough one.
RE: Pin on Steel bearing - tough one.
I haven't looked at it although aren't those specialist PE variants all moulded and fairly pricey?
I must admit I'd worry about chemical attack in this application and abuse by users but its a good suggestion and I'll have a look. I know that stuff is tough.
RE: Pin on Steel bearing - tough one.
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