Wear pairs.

[MikeR C]

The picture below is the first engine I ever build, right after I got a lathe. It wasn't built for anything in particular, more practice than anything.
When I built this engine I tried to use materials that would wear well and not gall. I was pretty successful except for the valve\port face. I used bronze for the face and 360 brass for the valve and they do not get along, it does not seem to matter how much oil I use, the portface seems to gall.
The point of this whole post is that I used to have a chart with different metals listed and how well the metals would wear in pairs. I think each pair was rated poor, good, and excellent. I am hoping someone has a copy or something similar as I have lost mine. I would appreciate any help with this.

Thanx
MikeR C

 

[black85vette]

Nice engine. I like the valve action. Kind of a variation on the wobler. Sorry, can't help with the info you need.

 

[Quickj]

wow, Interesting engine. It is an oscillator, but instead of the cylinder oscillating on the frame, the valve unit osscillates on the fixed cylinder. First time I have seen this design. Where did you find these plans?

In regards to your actual question, I have always heard that similar metals (like Aluminum piston in aluminum cylinder) is a bad combo. I will try to scrape up the information i Have on the subject.

Thanks for the engine Photo, Something else to contemplate building.

 

[MikeR C]

Unfortunately it has been too long since I put it together and I don't remember where the plans came from. I have a ton of old magazines and books and I was looking for something quick to put together. I ran it a bit to make sure it would behave itself and put it on a shelf, where it's been for better than fifteen years...

 

[ghart3]

 

[mu38&Bg#]

The Machinery's Handbook says that you want the journal to be 100 points harder minimum in Brinell hardness. Another website I recently looked at said that the two sliding surfaces won't gall if there is a difference of 7 points minimum on the Rockwell C which is roughly 200 points Brinnell.

 

[cobra428]

ghart3
Thanks for that chart. It puts me at ease with the tool steel to alum cam and crankshaft bearing surface I have in the middle of my engine
Tony

 

[Kermit]

It's interesting that Cast Iron, Nickle Steel, and Drill Rod, show as Excellent with themselves and everything else listed.

I would have thought certain combo's with cast iron would be better together than cast iron with itself. But it is a rather simplified chart I suppose.

I do see that the bronze bearings I was going to use with the 303 stainless crankshaft would be better made of cast iron. Nice, since I have a small lump or two of the stuff. ;D


Kermit

 

[dparker]

Mike: That is a neat engine. I like the way you did the valving, I have not seen that style of design before and to me it is unique.
I really like your design and build and the answers you have received are a good help to all the rest of us.
Thank you for bringing up this subject. May you have years of fun building fun projects in your shop. Show us more in the future as you have fun building.
don

 

[mklotz]

From the shop data file on my computer...

			Coefficients of Friction

dry (unlubricated) condition
				static		sliding

aluminum	aluminum	1.05-1.35	1.4
steel		brass		0.51		0.44
steel		aluminum	0.61		0.47
steel		steel		0.74		0.57
steel		graphite	0.1
cast iron	cast iron	1.1		0.15

 

[MikeR C]

ghart3,
That's the one! Thank you very much for going to the trouble to post it. I think I'll have it tattooed on my forehead so I don't lose it again!

mklotz,
I have seen coefficient of friction tables before, but, I'm not sure what conclusions I can draw from the info. It makes sense to me that if the friction is low that it would wear well, but I see aluminum\aluminum shows low but if you really slide them together the would destroy each other. Can you give some hints of what I should take away from your table?

Thanx
all for your help,
Mike

 

[mklotz]

I have seen coefficient of friction tables before, but, I'm not sure what conclusions I can draw from the info. It makes sense to me that if the friction is low that it would wear well, but I see aluminum\aluminum shows low but if you really slide them together the would destroy each other. Can you give some hints of what I should take away from your table?

First, a correction... Al on Al shows a high, not low, friction which is a bellwether of galling but, more importantly, a good reason not to use this combination in a low power model engine.

The rest of the table is meant as a guide for material choice in model engine building. While less of a concern in steam/air engines, friction is a serious concern in low power Stirlings and similar engines.

 

[MikeR C]

Sorry, I missed the "1" in front of the ".05", my mistake (NOT the first ) I am assuming the table is available on your website, I will go look for it. I expect it may fine tune the chart above.

Thank you,
MikeR C

 

[mklotz]

Actually, that table is not on my website.

I had started to put it together a long time ago but could find only a few entries so delayed putting it on the site until I could flesh it out. Today, there's far more information available quickly on the web, for example:

http://www.engineeringtoolbox.com/friction-coefficients-d_778.html

 

[thayer]

Unfortunately it has been too long since I put it together and I don't remember where the plans came from.

If anyone is still looking, this engine is very similar to the Compressed Air Motor on page 8 of Rudy Kouhoupt's first Shop Wisdom volume. I don't have any idea when the original article would have been published. On Rudy's the valve is on the outside of the engine and driven off the crank pin with a narrow fork instead of the wide one on an eccentric. Wouldn't be tough to reproduce Mike's example based on the photo and Rudy's article.

Thayer

 

[MikeR C]

Well I'll be, Thayer you are right. I dug out my copy of Rudy's book and the page 8 has a couple of oil stains, a sure sign that I actually had used it . Assuming anyone is interested, I could make drawings of the altered parts...

Thx
MikeR C