Hardening my piston

[plumbgun]

Hi folks, I wonder if a kindly member can put me straight regarding case hardening of a piston that I have recently had made for a vintage Webley Air Rifle? (A MK I ) Failing that, does anybody know a firm that offers the service at a reasonable cost? All comments gratefully received, and a Happy New (airgunning) Year to all!

Paul M.

[steveyb]

Might struggle spent years trying to harden my piston !!

[mel h]

I'll forgo the temptation to comment on my age or the state of my piston.
Case hardening is a process where the low carbon steel item is completely encased in high carbon dust (Casenite, if my memory is correct) within a container which is heated in a furnace for quite a long time, till some of the carbon is soaked into the surface of the workpiece, only a few thou but enough to produce a hard (and pleasingly coloured) surface when quenched. It is a fairly simple job where small articles are concerned, but something the size of an airgun piston needs some carefull thought about the size of the container and the time required.
Mel.

[plumbgun]

Never had much of a problem, mate, until recently - but a touch of prostate cancer followed by radiotherapy and it's a different matter. I was hoping for serious replies though (sigh*)

[airgunnut]

spent years trying to harden my piston !!

You can get pills for that!

[airgunnut]

I was hoping for serious replies though (sigh*)

This is the bbs ya'know! Whitty and/or sarcastic comments are given as freely as the insults




(I know a few who have/recovering from prostate cancer so, I wish you and those close to you nothing but the best)

[airgunnut]

You can get case hardening powder, you heat the metal to cherry red then put into the powder, let cool for a few mins then repeat, or you could use, used engine oil, (the high carbon content of the used oil is supposed to be absorbed in to the metal (were talking microns here) but the heating and quenching will harden the metal more than the oil
My only concern is that pistols take a hell of a pounding, 0- umpteen 100 feet per second then back to 0 in less than a second with a vertuly instant and violent stop, hardened metal (not tempered) is usually brittle and brittle metal does not handle shock well (can shatter)
I think case hardening might be the wat to go (that way you have the hardend surface and the relatively soft metal underneath to take the shock)

[ccdjg]

You can get case hardening powder, you heat the metal to cherry red then put into the powder, let cool for a few mins then repeat, or you could use, used engine oil, (the high carbon content of the used oil is supposed to be absorbed in to the metal (were talking microns here) but the heating and quenching will harden the metal more than the oil
My only concern is that pistols take a hell of a pounding, 0- umpteen 100 feet per second then back to 0 in less than a second with a vertuly instant and violent stop, hardened metal (not tempered) is usually brittle and brittle metal does not handle shock well (can shatter)
I think case hardening might be the wat to go (that way you have the hardend surface and the relatively soft metal underneath to take the shock)

You can still just about get case hardening powder off fleabay, but you have to be sure it is the sort that you can just dip the red hot piece into and it is not charcoal mixed with accelerators, as the latter might need more than an hour of baking at red heat in a furnace. One of the names for the fast stuff was Kasenite but it is no longer available because it was thought to be poisonous. In fact it was a ferrocyanide salt and practically non-toxic, but that's what health and safety legislation is doing to us. You can buy pure potassium ferrocyanide off fleabay which will work - just handle it sensibly and don't inhale any fumes. The ferrocyanide method is a nitriding process rather than a carbonising process.

You really only need to case harden that part of the piston that contacts the sear, so it should be easy to do with a good propane blowtorch.

A useful link is here http://www.technologystudent.com/equip1/heat2.htm

[JustinThyme]

The old case hardening powder I used many years ago as an apprentice went by the name of "casenit" if i remember correctly, also banned some time later for some strange reason or other due to its arsenic content .... dont know whats available now

[plumbgun]

Well, thanks for the info and good wishes. Kasenite as far as I recall ( and which I have) was supposed to be a mixture rich in hoof and horn chippings, which ties in well with the old timers' method of using leather in an iron box, heated to red heat in a fire. As for the ferrocyanide, as a chemist, I have acces to that too (as well as ferricyanide which might work also?!) but had never heard of using it; it makes sense though, and thanks for that. What I was hoping for was someone who had actually done the job to share their experience. A piston bought from a well known air rifle spares supplier says that the "piston will have to be hardened after fitting", and I just thought that this was a much more common operation than it now seems to be. My cute little Webley MK I is well worth the trouble though, and I'm sure that somehow I'll get it going again.

Paul M.

[johnbaz]

Hi

I think you can use old leather or bonemeal but it does have to go in (I believe ) an iron box too, The longer it's in the furnace the deeper the case hardening penetrates

I wonder if someone could turn one one on a lathe in annealed carrbon steel so that it could be tempered afterwards??



John

[edbear2]

Paul, I have some proper Kasenit dating from the 1980's. It is in the original 2L size steel drum (think big paint tin). This is maybe 1/4 full, and recently I gave some to someone who told me it still worked fine.

I can photo and scan the original graphics / instructions printed on the tin for you to. Basically it's heat to temp, dip roll and leave in the powder for a spell, re-heat and quench, then repeat to increase depth of case if required.

You have to find out what carbon content your piston is made from, as Kasenit can cause problems with alloy (higher carbon) steels, and even cracking.

In the case of oil hardening, this will only work if the steel again has an elevated carbon content. If a free cutting or mild grade you can heat and dip in oil for the rest of your life on an hourly basis, all that will happen is that the part will go black, but it won't get any harder

It's all about the base metal used.

Anyhow, if you want to play, P.M. me the dimensions (roughly) of the piston unit, and an address and I will get some off to you

ATB, Ed

(oops...just read you have some, but if you want the original instructions I can post them later).

[walnutfarmmick]

You can get pills for that!

Swallow them fast or you'll get a stiff neck!

On a more serious note I've vague memories of reading about charred leather or even sugar being used as a source of carbon. I'll have a poke through a few older books once it gets light and see if I can find anything.

ATB, Mick

[walnutfarmmick]

How about nitriding it?

That might just be a more commercially available process. Possibly an engine reconditioner might know of a firm that does it. In the early '80s I used to handle a lot of commercial crankshafts so I know that Leyland ones were usually treated so.

ATB, Mick

[deejayuu]

Not trying to muddy the water but if it only needs local hardening, as suggested, then why not try simple heat treatment at that point.
If the base metal has insufficient carbon then it won't harden/temper but no real harm done.
(crawls back into bunker)