Relaxing Rings

A special section just for steam engines and boilers, as without these you may as well fit a sail.
Mike Rometer
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Relaxing Rings

Post by Mike Rometer » Tue Jul 17, 2018 7:24 pm

I have been musing! I have some commercially made piston rings to suit my twin, but I think that they exert more pressure on the bore than I would prefer. I know I could fairly easily make my own (I've done that before), but I'm wondering if they could be relaxed a little, and how that could be done. I have thought of one method that might work, but wondered what others might do, or if anyone has actually tried it.
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Re: Relaxing Rings

Post by RGSP » Wed Jul 18, 2018 8:09 am

I have tried putting such rings in a dummy bore into a pukka annealing furnace with a precise temperature cycle recommended by people who know a lot more about cast iron than me: it didn't work very well, in that despite the rings being cast iron, they ended up non circular. I think I was unlucky for some reason, and that it SHOULD have worked, but...
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Re: Relaxing Rings

Post by Mike Rometer » Wed Jul 18, 2018 8:19 am

RGSP wrote:I have tried putting such rings in a dummy bore into a pukka annealing furnace with a precise temperature cycle recommended by people who know a lot more about cast iron than me: it didn't work very well, in that despite the rings being cast iron, they ended up non circular. I think I was unlucky for some reason, and that it SHOULD have worked, but...

That sounds to me like there was a temperature gradient in the furnace and some parts got hotter quicker than others. How much comparative weight was there in your dummy bore and of what material?

My idea was similar but I was going to keep the dummy (somewhat oversize dia) bore to the absolute minimum, as I didn't want to draw heat from the ring. It certainly needs to come to a good red heat to have any affect.

I have a few spares, though not an endless supply, so I can perhaps afford to experiment a little.
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Re: Relaxing Rings

Post by RGSP » Wed Jul 18, 2018 10:40 am

It's a long while ago, but the dummy bore was just a plain piece of annealed thick walled tube (bored to size after annealing), and the heating and cooling parts of the cycle were several hours each, so I don't think temperature gradients were serious. I honestly don't know what went wrong, but if forced to guess I'd say the piston ring material was non-uniform. Rubbishy cast iron is not a new Chinese invention, despite what many people say!

If you have a few spares, give it a try. I'm in process of designing myself a new engine, and I'm trying hard to use commonly available commercial parts where possible - including piston rings, and possibly cylinder liners as well.
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Re: Relaxing Rings

Post by fredrosse » Wed Jul 18, 2018 1:19 pm

I have relaxed standard IC engine rings in a furnace with good success.

Buy IC engine rings that are matching the bore of your steam cylinder.

Machine the sleeve with a bore a couple % greater than the steam cylinder bore, put the new rings in the sleeve, then, most important, wrap the assembly with stainless foil or other insulating material so it is heated very slowly to a dull red heat in the furnace. Various stress relieving shops will do this for you if you pay.

After a few hours in the furnace, cool slowly, and your relaxed rings will be ready to use.

Understand that steam pressure will get behind the ring, and force it against the cylinder wall with pressure, so while the relaxing process is helpful, there is still some healthy force pushing the rings to the cylinder wall.
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Re: Relaxing Rings

Post by Mike Rometer » Wed Jul 18, 2018 3:35 pm

Cheers Guys, all good thoughts. I have had another one myself.

When making rings all I do is split the new blank and spring it onto a suitable sized piece of silver steel (drill-rod) hanging the ring against a firebrick and heat it till it drops off. Could the process be reversed? A small clamp to hold the ring ends to the required 'spring' and again heat it against a firebrick. It can't, of course, drop off, so judgement will be required for the right temp, but having done it before I have some sort of idea how far to go.

Fred, the same happens in I.C. engines the compression (top) rings rely on the cyl. pressure for added oomph, and to seal to the piston groove face! That is also why I think these are too stiff to start with. There is no need to strip the bore as the piston moves, only seal to it.

Any more for any more?
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Re: Relaxing Rings

Post by asal0312 » Wed Jul 18, 2018 8:41 pm

I did what Fred says to rings for a duplex pump only heated with a torch. Worked good.
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Re: Relaxing Rings

Post by Mike Rometer » Thu Jul 19, 2018 9:05 am

Having re-read Fred's post I can see he is suggesting doing all the rings in one go. That certainly should get them all the same. As I have no furnace or hearth, I'm stuck with a pile of firebrick and a blow-torch, I think individually is probably the way I will need to go.

I'm beginning to wonder if I should just make my own as then they'll be right from the start. I do enjoy this type of messing with ideas, to see what will work in the home 'shop. You can sometimes be surprised.
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Re: Relaxing Rings

Post by DetroiTug » Thu Jul 19, 2018 2:38 pm

I'm not understanding the desire to take the tension out of piston rings. I understand it as something to avoid and one of the pitfalls of superheating. A ring with tension isn't going to damage the bore, a ring with proper tension not only seals well, it serves as a wiper to displace any sort of foreign debris on the cylinder wall. A weak ring will allow contaminates to become trapped in between the ring and the wall and do considerable damage, above and beyond the issue of not sealing well.

Rule of thumb on piston rings, if they can be installed without a compressor, they should be replaced.

-Ron
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Re: Relaxing Rings

Post by Mike Rometer » Thu Jul 19, 2018 3:47 pm

I've been fitting rings to pistons for about 60 years, and these are too tight, by long chalk. With both rings fitted, I can barely move the piston by hand, and no, they are not butting ends. There is little need with a steam engine for rings that scrape the bore they will only wear themselves very quickly, or the bore, especially in low/no lube situations. Basically I'm being a T.A., free, is free when all said and done, or I'd just set to and make some how I think they should be, with a set gap of about 1/4" before fitting (2.5" Dia bore), and as I said I like exploring this sort of thing in between getting on with it.
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