Crucible for annealing cast iron piston rings

I made some piston rings for my Gypsy engine and I want to heat treat them using a crucible [Trimble method I believe].

Reading on the internet I see reference to a formula which gives the dimensions of the crucible for a given ring size, does anyone one know were I can find this formula?

Also does the crucible have to be made out of cast iron or can I use steel

Hi David,

I made one of these over 20 years ago, I used 303 stainless steel. The information is in a Strictly I C magazine.

I have all of these and will have a look for it over the weekend.

John Feeney

Thanks John, would be useful but I can probably work it out for myself if I need too so don't spend too much time looking.

I made rings for my steam launch engine using this method. The rings were sprung over a cylindrical piece with a key set in it with the right thickness, then the whole lot was enclosed in an airtight container made from stainless steel tube with cast iron end caps, held on by a bolt through the middle. That helps keep the air out, which will reduce scaling. High temperature anti seize compound can be used too. I had to make several sizes, as there are four sizes of ring in the engine, ranging from 1.625" up to 5 inches. (low and high pressure pistons, and low and high pressure piston valves.) Each container was then heated up to a dull red heat and then kept there until I was confident that the heat would have soaked all the way through

Apart from the rings themselves, I don't think the material is critical provided it won't melt on you. The resulting rings are working well so far, I've taken the covers off enough to peer in at the bores and it all looks pretty good. The ring proportions are actually based on IC engine practice. The ones in the valves are apparently happy running over the ports.

John

Trimble wrote up 'his' method for piston ring manufacture in Model Engineer V153, No 3735, 17 Aug 1984 and later in Strictly IC V2, No 7, 8, 9, 1989. The method is very similar to that written up by Prof D H Chaddock (of Quorn fame) in Model Engineer V133, No 3319, 21 April 1957. I don't remember Trimble's ME article, but I'm pretty sure that he did not acknowledge Chaddock in his SIC articles, although it seems rather unlikely that he was unaware of Chaddock's method. Another example of Americans thinking they invented everything first (computers, powered flight, "Moore-pattern" scraping, etc., etc.)? I wouldn't be surprised if they claim to have been first to set foot on the moon... [with a nod to a recent thread, I should explain that this unnecessary, silly image is included for those who can't appreciate innocent tongue-in-cheek comments and sarcasm without help.]

A useful overview, which hopefully gives the information you seek, can be found at **LINK**

Oops! Too late to edit a slip-up in my post. Correction: Chaddock's method described in 1967, not '57.