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Post by Ruston92 on Nov 23, 2014 21:08:33 GMT
Probably a obvious answer, but why are engineering plastics such as PTFE not used as cylinders/cylinder liners?
I was having a chat with a couple of friends the other day about different ways to make cylinders, one mentioned using an Oilite bush for a liner, but I would have thought the oil would just pour out at the temperature and the bush would disintegrate.
Does anyone have anything to say on this topic? Alternative |
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Post by Deleted on Nov 23, 2014 21:13:28 GMT
Hello young chap----- do you still want this little blower or shall I sell it on ??---------just a yes or no will do..Thanks..Alan R
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Post by Roger on Nov 23, 2014 21:18:07 GMT
PTFE isn't that rigid when it gets hot, it's liable to move around and end up getting destroyed. It's one thing to make piston rings from it and quite another to line a cylinder. You might get away with it on an engine with solid PTFE cylinders using wet steam, but it's not heavy and it's probably almost as expensive as Cast Iron or Leaded Bronze.
I don't think having a porous material for a steam cylinder makes logical sense. I can see why you might want microscopic indentations to retain oil but that's about all.
Something I've not heard of being used is Hard Anodised Aluminium. That would be cheap and easy to make, but who want's something light on a locomotive where you need adhesion?
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pault
Elder Statesman
Posts: 1,496
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Post by pault on Nov 23, 2014 21:18:20 GMT
trouble with oilite as a liner is it is porous, lubrication of cylinders is not an issue,
so its a non starter
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Post by vulcanbomber on Nov 23, 2014 22:35:01 GMT
PTFE isn't that rigid when it gets hot, it's liable to move around and end up getting destroyed. It's one thing to make piston rings from it and quite another to line a cylinder. You might get away with it on an engine with solid PTFE cylinders using wet steam, but it's not heavy and it's probably almost as expensive as Cast Iron or Leaded Bronze. I don't think having a porous material for a steam cylinder makes logical sense. I can see why you might want microscopic indentations to retain oil but that's about all. Something I've not heard of being used is Hard Anodised Aluminium. That would be cheap and easy to make, but who want's something light on a locomotive where you need adhesion? Cant think of much worse to make a cylinder from.... |
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Post by Rob on Nov 23, 2014 23:53:08 GMT
Cant think of much worse to make a cylinder from.... Cheese?  In all seriousness and for my benefit as I don't know, why not aluminium, besides weight and possibly thermal conductivity? Aluminium with liners works for car engines, is there a particular reason it wouldn't work for a steam engine? |
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Post by Ruston92 on Nov 24, 2014 7:07:22 GMT
I once saw a locomotive with ali cylinders. It was seized up as the bore had oxidised.
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Post by joanlluch on Nov 24, 2014 8:17:50 GMT
I attempt to use stainless steel for the cylinder block (bore) and PTFE for the piston rings.
On the one hand, stainless is a heavy, hard, durable, non thermal conductive material, so it has all the properties we want on a cylinder.
Also PTFE plays really well with stainless and has a very low friction rate. The only constraint is that stainless may be slower to machine but we are not producing mass volume cylinder quantities, right?
Joan
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Post by albert on Nov 24, 2014 8:26:51 GMT
Hello,
Nothing beets good old cast iron.
Albert
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Post by vulcanbomber on Nov 24, 2014 19:02:53 GMT
Cant think of much worse to make a cylinder from.... Cheese? In all seriousness and for my benefit as I don't know, why not aluminium, besides weight and possibly thermal conductivity? Aluminium with liners works for car engines, is there a particular reason it wouldn't work for a steam engine? The rate it expands at, and the fact that hard anodised its still as soft as melted butter would be my main reasons, along with the fact it has no bearing qualities. Stainless is also utterly useless for cylinders. |
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Post by Rob on Nov 24, 2014 19:45:37 GMT
Thanks vulcanbomber  Presumably the user of a liner would solve these problems, though? I am just playing devil's advocate, of course, as I'm using good old cast iron for my cylinders! |
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Post by andyhigham on Nov 24, 2014 19:47:36 GMT
Aluminium car and motorcycle cylinders use either a cast iron liner or a hard chrome plating on the bore.
The reason for using aluminium in cars/bikes is lightness. The reason for chrome bore is improved thermal conductivity. Neither of these properties are an improvement over cast iron in a steam loco. There is a good argument for using aluminium pistons, the less the reciprocating weight the easier it is to get a better balance
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Post by Deleted on Nov 24, 2014 20:16:10 GMT
But there's Aluminium------and then there's Aluminium !!.........Something like this would be called for }---------- en.wikipedia.org/wiki/Lo-Ex ----------- |
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Post by Deleted on Nov 24, 2014 20:17:48 GMT
Aluminium car and motorcycle cylinders use either a cast iron liner or a hard chrome plating on the bore. --------------------------------------------- or chrome plated piston rings as well.. |
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Post by andyhigham on Nov 24, 2014 20:29:59 GMT
Chrome rings can be used on iron cylinders - NEVER use chrome rings on chrome cylinders. Iron rings can be used on either iron or chrome cylinders
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Post by Deleted on Nov 24, 2014 20:47:23 GMT
Quite right !!
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Post by joanlluch on Nov 24, 2014 21:56:17 GMT
Stainless is also utterly useless for cylinders. please can you explain it? I am going to use stainless steel, why is it not suitable? |
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Post by vulcanbomber on Nov 24, 2014 22:01:01 GMT
Stainless is also utterly useless for cylinders. please can you explain it? I am going to use stainless steel, why is it not suitable? Stainless in general is very good at "picking up". Its one I find very difficult to explain actually but from the motion of a piston rubbing up and down will scratch the surface and the hole effect escalates very quickly into little lumps. Cast Iron if I were you. |
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Post by joanlluch on Nov 24, 2014 22:08:38 GMT
please can you explain it? I am going to use stainless steel, why is it not suitable? Stainless in general is very good at "picking up". Its one I find very difficult to explain actually but from the motion of a piston rubbing up and down will scratch the surface and the hole effect escalates very quickly into little lumps. Cast Iron if I were you. I fully know this, but I am using PTFE in the rings, not metal. Also cast iron can oxidize no? |
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Post by andyhigham on Nov 24, 2014 22:08:43 GMT
The perfect material for cylinder liners is cast iron
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