Author Topic: Steel on Steel Moving surfaces  (Read 2081 times)

Offline Kim

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Steel on Steel Moving surfaces
« on: November 20, 2017, 03:50:38 AM »
I know there is a design guideline I've have heard that you should NOT have like materials moving against each other.  Like no aluminum on aluminum for example, or it is likely to gall.

But what about steel on steel?
As you may have heard me say, I'm looking at building Kozo's A3 Pennsy Switcher, planning to change a lot of the brass to steel.  The specific area in question at the moment is the cylinder drain cock mechanism.  Kozo has a series of linkages setup that will open and close the drain cocks by moving a lever in the cab.  This mechanism is not likely to see a high amount of use - I mean, it'll get used of course, but its not like the piston rod or the valve linkage which are in constant motion.  The valve cocks will get opened and closed a few times per run.

I'd like to change several of the larger brass brackets to steel brackets.  But these brackets act as a pivot point for a steel pin.  Will this cause me problems - this steel on steel movement?  Or is that no biggie for the 1/4 turn that the pin will see once or twice in a session?  Especially if it gets oiled every once in a while?

Thank you for any thoughts you would be willing to provided me on my current planning dilemma.
Kim

PS He's just full of these silly little questions, isn't he?  :Jester:  (where is that dunce cap emoji?)

Offline paul gough

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Re: Steel on Steel Moving surfaces
« Reply #1 on: November 20, 2017, 04:40:48 AM »
In my experience there are endless applications of steel on steel both in smaller sizes and full size. Brake rigging, reversing linkages, sanding gear, basically anything where there are no significant forces or heat generation. If there is a wear issue it can be rectified by using a harder material in the pin or the bushing depending on which is preferred. Sometimes a hardened pin or bush, or both are used. The only place I have experienced a problem with steel on steel linkage is with a regulator linkage inside the boiler of a 12 inch gauge loco, here the wear was stopped by bronze welding/brazing up the hole and redrilling it, it has now given thirty years service with negligible wear in that pivot linkage. So, I should not think you will have any problem moving to a more economical material like steel for many of Kozos components, I think he just likes brass, its easy to work, doesn't usually corrode etc. etc. but is expensive, hideously so in my part of the world. Sometimes no lubrication is better, places where dirt or dust can get to the wearing surface and act as an abrading medium. It is a matter of considering the application and the environment in which it operates to determine what is suitable. Hope this assists. Regards, Paul Gough.

Offline Kim

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Re: Steel on Steel Moving surfaces
« Reply #2 on: November 20, 2017, 05:00:46 AM »
Thanks for the quick response Paul, I really appreciate it!

And after thinking about it, the links are steel and the pins are steel - the only part that isn't steel is the bracket.  So even in his design Kozo has some steel-on-steel movement.  As I said, its not a lot of movement, but it makes me feel that using Steel for these brackets won't be that big of a deal.

And as you said, I could harden the pins which could help too.

Thanks,
Kim

Offline Ian S C

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Re: Steel on Steel Moving surfaces
« Reply #3 on: November 20, 2017, 09:24:48 AM »
I tend to shy away from steel to steel, if I have a steel rod I bush the hole for the steel pin.  Although an actuating lever might only be moved once or twice, its on a piece of vibrating machinery, so its actually moving all the time.  I believe that two different steels, one hard, one soft will have a lower coefficient of friction than two similar steels, The term glass hard is mentioned, this is untampered, hardened steel, an indication that case hardening in one form or other is the way to go for shafts or pins.
If you don't like bronze bushes, try cast iron.
Ian S C

Offline Florian Eberhard

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Re: Steel on Steel Moving surfaces
« Reply #4 on: November 20, 2017, 11:43:18 AM »
Hi Kim
If you use free machining steel for the Pins together with some steel which gives you ä good finish when reaming it should last for quite long - at least if you lubricate those joints from time to time.

Why free machining steel? Because they are made to have good Chip control and to keep Tool wear low if poasible. So for example those Grades that contain lead will have some kind of "dry lubrication" because of the lead.

Florian

Offline Walsheng

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Re: Steel on Steel Moving surfaces
« Reply #5 on: November 20, 2017, 12:30:25 PM »
We use steel on steel all the time in injection molds and some molds I have made have many millions of cycles.  Some of the parts have a lot of movement, like cam slides and even knock out pins.
You can/should not use the same material but we have used the same material in some cases but a different hardness.
Case hardened on full hardened works well also.

John

Offline b.lindsey

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Re: Steel on Steel Moving surfaces
« Reply #6 on: November 20, 2017, 12:36:17 PM »
Kim, in this application I think the lubrication is the key and more critical than material choice. As you say the total number of cycles will be small, unlike a piston and cylinder.

Bill

Offline paul gough

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Re: Steel on Steel Moving surfaces
« Reply #7 on: November 20, 2017, 12:48:43 PM »
Kim, if you think it necessary to harden the pins, consider first which is the easier part to replace, the bush or the pin, it might be just as effective to make the bush harder and the pin somewhat sacrificial. Pins are usually very easy to replace and stock sizes can often be utilised to obviate any machining. Regards, Paul Gough.

Offline Kim

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Re: Steel on Steel Moving surfaces
« Reply #8 on: November 20, 2017, 05:08:52 PM »
Thank you all for the helpful insights.

...I believe that two different steels, one hard, one soft will have a lower coefficient of friction than two similar steels...
If you don't like bronze bushes, try cast iron.
Interesting thoughts.
Its not that I don't like brass and bronze.  I do!  They just happen to be quite expensive.  And it will all be painted, so I won't even get to look at the the beautiful, expensive brass!  But cast iron is an interesting idea. I'll have to look into that...

If you use free machining steel for the Pins together with some steel which gives you ä good finish when reaming it should last for quite long - at least if you lubricate those joints from time to time.

Why free machining steel? Because they are made to have good Chip control and to keep Tool wear low if poasible. So for example those Grades that contain lead will have some kind of "dry lubrication" because of the lead.
This goes along with what Ian was saying too. This is a very good possibility.  I was planning to use the free machining steel for all the round stock because it works so easily, so this is likely to happen.

Thank you John, Bill, and Paul, for the comments and thoughts.

Looks like I will probably find a good combo of steel types to use here.  And may look into cast iron.
Thanks!
Kim

Offline Vixen

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Re: Steel on Steel Moving surfaces
« Reply #9 on: November 20, 2017, 05:20:40 PM »
All the gears and ball/roller bearings in your car's gearbox and differential are hardened steel on hardened steel, the harder the surfaces, the longer they last. The same is true for the timings chain and gears.
The secret is adequate lubrication.
« Last Edit: November 20, 2017, 06:11:58 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Jasonb

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Re: Steel on Steel Moving surfaces
« Reply #10 on: November 20, 2017, 06:15:42 PM »
Steel on steel will be fine for drain cock linkages, if it was good enough for the full size that ran 365 days a year for many years it is more than good enough for a model that may get run for a few weekends a year. I used mild steel on the links for my Fowler thought like the full size I put a brass knob on the end.

Offline Kim

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Re: Steel on Steel Moving surfaces
« Reply #11 on: November 20, 2017, 09:59:14 PM »
Thanks Vixen and Jason!

Jason, this is a great picture - the exact type of mechanism I'm talking about.

I really appreciate everyone's help on this!

Thanks,
Kim

Offline steamer

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Re: Steel on Steel Moving surfaces
« Reply #12 on: November 21, 2017, 01:03:12 AM »
Wot Mike Said


High precision watchmakers lathe.

Hardened steel bushing on Hardened steel shaft....Like Glass hard

harder than woodpecker lips......

Will last forever with a modicum of lubrication

Dave

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Damned ijjit!

Offline Kim

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Re: Steel on Steel Moving surfaces
« Reply #13 on: November 21, 2017, 01:19:45 AM »
Thanks Dave!
Kim

 

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