Heat treat rings

[Gordon]

How do you folks heat treat piston rings. I seem to have a problem making acceptable rings. I have gotten the cast iron from McMastar Carr and MSC so it is not that I am using some junk. I have been using a propane torch and getting the rings red hot with a gag in the gap. They retain the set but when I install them they deform and do not seal. I have read numerous articles about how to make perfect rings but mine all turn out to be junk. Presently I am waiting for some rings from Debolt. I have used commercial rings before and they seem to have spring and retain their shape during installation.

Presently I am building an Atkinson Differential engine and have made the rings per his instructions and have even tried making them to expanded size and not heat treating but I am not having any luck. The size is 1 1/8 OD x 3/32 wide x .010 thick.

 

[doc1955]

If I do a bunch of rings I make a little holding jig and heat it until everything is cherry red. If I do 1or 2 I make a spacer block as you have and put them up against a backing plate then point the torch at the center on the backing plate it is critical that you keep torch in the center. That way the rings will heat evenly and not deform. You can also cold form them (I haven't tried that yet) I mostly use the backing plate method for my v-8 it was a fixture that worked pretty good to. Here is a photo of the ring jig I used for my v-8 http://i913.photobucket.com/albums/ac331/doc0455/My V8 build/ring18.jpg

 

[Gordon]

So how do you get the rings heated evenly? If I put a ring on a plate, or a fire brick in my case, with a spacer I have a problem with getting the ring hot enough because the backing plate carries away the heat. If you use the fixture as shown do you heat the entire fixture to red hot?

I have also used the method others have described where the ring is suspended on a spacer and then heated until it drops off.

It would seem like having something like a kiln would be the answer.

 

[doc1955]

Get the flame hitting back plate in center holding torch perpendicular to the back plate. The flame should bounce pretty evenly around and heat ring up. If you use a jig yes heat the jig to cherry red and then let cool slowly.

 

[WOB]

Red hot is too hot. 1100 deg.F is hot enough. Ideally you should use a temp controlled furnace and heat the entire ring stack on the fixture to temp and then air cool. If no furnace is available, a stack of fire bricks arranged in an open sided box to capture the torch heat will work. YouTube has a large number of examples showing how to make a simple propane fired furnace from fire brick. Overheating does no good and makes clean up harder due to scale formation. 1100 deg is dull brownish-red in normal room light. Polished cast iron rings heated to 1100 deg will not develop scale. When cooled, the rings should have good spring return to the original gap, when forced closed.

WOB

 

[Philipintexas]

I’ve completed several Hit-n-miss engines and of course they will probably never run more than a few hours, but I never heat treated the rings. Is it really necessary? They seem to have a natural spring to the cast-iron and wear-in slowly.

 

[WOB]

The classic method of making model engine cast iron rings was originally published by George Trimble in SIC magazine issues 7,8,&9( available as reprints) http://www.strictlyic.com/pit01.htm In order to make the rings apply uniform pressure on the cylinder walls, they must be heat treated in the expanded condition so that they can act as springs when compressed into the piston's ring grooves. Properly made and installed into a correctly finished cylinder, they will break-in and make a near perfect seal in the first few minutes of the initial run. There are a number of web pages with condensed versions and descriptions of the Trimble procedure that can be found by searching " cast iron rings by the Trimble method". However, the original articles are essential if you want to do it correctly.

I have made about 50 such rings over the years for use in glow and spark ignition engines with great success. Once the tools and fixtures are made, and you get some experience, rings can be fabbed fairly quickly.

RWO

 

[stevehuckss396]

I use Doc's fixture and WOB is correct about the heat. I heat my rings to 1100 degrees for 3 hours on the recommendation of a well respected metallurgist. Soaking for 3 hours ensures complete stress relief and maximum wall pressure. So im told.

 

[Gordon]

Thanks all. I find it interesting that there are so many opinions about how to make rings. Everything from super complicated to downright crude. I am ordering the back issues of SIC today.

I still am wondering about a good method of heat treating. Obviously we all have a simple propane torch but some of the methods involve holding a precise temperature for extended periods of time which is not going to happen with a hand held torch. I have looked at eBay and Craigslist for used kilns but either they are super expensive, too far away or too big. I do not want something taking up more space in my shop that is 2 foot in diameter and three foot high. I have not found any simple plans for a small home made unit.

 

[doc1955]

The rings I made for my first engines were made with the propane torch process and they still have very good compression. I think if you are only making a few rings the torch process works fine. That process was described back in the HSM magazine with the Odds And Ends engine planes in it not sure of the year and issue. But like I say does work fine.The secret to it is getting the torch close to center so the ring will heat up close to evenly as possible.
The process Steve describes would be under ideal conditions.

 

[a41capt]

In the same vein, but regarding full sized rings (I enjoy rebuilding vintage motorcycle engines), would the grey iron tube that MacMaster Carr sells be appropriate to make rings from?

I am soon to receive a bike that I can’t find rings for, and I thought I might like to try my hand at making my own. It might turn into a minor cottage industry during my retirement!

Thanks in advance for any info you can provide for this newbie!

John
Camp Verde, AZ

 

[Anatol]

I still am wondering about a good method of heat treating. Obviously we all have a simple propane torch but some of the methods involve holding a precise temperature for extended periods of time which is not going to happen with a hand held torch. I have looked at eBay and Craigslist for used kilns but either they are super expensive, too far away or too big.

I've not done this but may do it soon. I'd guess you could easily make a small furnace out of 8 firebricks and maybe some fireclay (might not be necessary). 4 bricks in a square would leave internal space about 1/2 a brick volume. Slide one brick in or sideways as the door. Two bricks across the top. Two bricks across the bottom. Top and bottom with gaps you could play with, for flue and inlet - or tiny gaps between bricks may suffice. I'd try a propane ring or camping stove underneath. You might look at downdraft designs to economise on gas...or just put a bbq or a kettle on top Some steel bars across to hold up workpieces.
I suggest looking online for DIY ceramics kilns.
You can get a thermocouple to measure up to ~2300F for $50
http://www.clay-king.com/pyrometer.htm
There's a $50 IR thermometer that says it goes to just over 1000F here.
https://www.thermoworks.com/IR-Gun?gclid=EAIaIQobChMItpLCqO3i3AIVhB5pCh2Y4Q9ZEAkYCCABEgIOQvD_BwE

Probably make the whole thing for $100?
If anyone tries it , start a new thread? I'll be interested.

 

[WOB]

In the same vein, but regarding full sized rings (I enjoy rebuilding vintage motorcycle engines), would the grey iron tube that MacMaster Carr sells be appropriate to make rings from?

John
Camp Verde, AZ

I think it would make good rings. It appears to be made from centrifugally cast hollow billets which is a plus.

WOB

 

[editor123]

The one thing George Trimble was wrong on was the annealing temperature. His recommended temperature will change the characteristics of the iron. 1100 Deg. F. for one hour is enough. My friend, Dwight Giles quenches his right out of the oven but they are inside a SS envelope to keep the air away. He makes hundreds of rings for himself and others. They all work very well even in a supercharged V-8 or a small hit'nmiss.

 

[johwen]

If I do a bunch of rings I make a little holding jig and heat it until everything is cherry red. If I do 1or 2 I make a spacer block as you have and put them up against a backing plate then point the torch at the center on the backing plate it is critical that you keep torch in the center. That way the rings will heat evenly and not deform. You can also cold form them (I haven't tried that yet) I mostly use the backing plate method for my v-8 it was a fixture that worked pretty good to. Here is a photo of the ring jig I used for my v-8 http://i913.photobucket.com/albums/ac331/doc0455/My V8 build/ring18.jpg

 

[johwen]

I have made many rings using the above type fixture it is important to have the gap set correctly otherwise when compressed to fit the bore the ring will distort from a true circle. Wrap some paper around the rings so it burns when the fixture is heated removing any oxygen and the rings sealing surface is not carburised. The outside sleeve must have clearance on the rings so the don't distort to the shape of the bore.
The gap the rings are set to is important too as if it is to big when the ring is compressed it will not be a perfect circle after heat treatment.

Heat the whole set up to a red heat for about 15 minutes and let cool slowly.

After removing the rings they should have a firm wall tension in the bore and should compress to the original true circle without any oxidised sealing surface through the removal of the oxygen via the bunt paper.

Hope this helps.
John

 

[Timehunter]

As far as looking for a kiln, you might try a stained glass supplier.
They use them after using special paint on glass then put it in the kiln to melt it into the glass.
Don't remember where I got it from but I bought my wife one years ago when she did stained glass.
It was an electric one about two square foot.

 

[Entropy455]

I have a pottery kiln that I've retrofitted with solid-state controls. The controls were about 250 dollars, and I paid 300 dollars for the kiln (used). I installed an SSR in lieu of relay. This means no moving parts (relay clicking during operation - and no relay to wear out). I have precise digital temperature controls between 500 degrees F, up to 2000 degrees F. And for controlling oxide formation, I use ATP 641 (http://www.advancedtechnicalprod.com/pdf/atp.pdf) simply brush it on, let it air-dry, then heat-treat your parts. You'll have zero oxide - even on S7 or D2 tool steel at 1800 degrees F! (they recommend 304 for tool steel, but 641 is a good all-around compound). The paste forms a thin glass-like substance at elevated temperatures, which completely shields the part from oxygen & nitrogen damage. The moment the part starts to cool however (either air-quench, water-quench, oil-quench - or simply ramping the oven temperature down) - the compound will shatter and flake off. Point being - it does not interfere with the quenching process. It also means you can make parts exactly to size, and have zero oxide damage to remove from heat treatment. Note that air-hardening tool steels (my favorite to work with) will permanently expand 0.001" per inch from heat treatment.

(https://www.auberins.com/) here's where I got my kiln controls. They've got great prices (thermocouples, PID controllers, SSRs, etc). If you build a digital controlled kiln/oven (which I highly recommend) - be sure you install an SSR on both hot wires, otherwise the entire heating element will remain electrically hot-to-ground - and that's the last thing you want to worry about when sticking metal parts into an electric kiln. . . .

 

[a41capt]

I think it would make good rings. It appears to be made from centrifugally cast hollow billets which is a plus.

WOB

I like the idea of no waste in the middle, and since the rings I will be cutting are between 2 1/2” and 3 1/2”, It sure does minimize waste and boring time!

John

 

[abby]

A small kiln for heat treatment can be very simply made using a sheathed element either salvaged from a redundant storage heater or purchased new.
Simply coil the element around a steel tube former and cover with fire cement.
When the cement has set remove the former , end caps can be made from fire cement rammed into wooden moulds
The sheathed element means no danger from electric shock and the maximum operating temperature of 800°C gives plenty of scope for piston ring heat treatment.
Dan,