[AT] OT: Rosebuds! The oxi-acetylene kind...

Fri Nov 15 07:36:50 PST 2013

It's a function of the material, the temperature, and the time-at-temp.
 This re-heating of a case-hardened gear that we're talking about... it is
basically a tempering process.  Relatively low heat (say, 400F range) will
temper out some of the surface hardness, but it will take time (measured
in, say, hours) and most likely this will not be a concern.  Higher
temperatures (say, above 600F) will convert significantly more of the
surface hardness to a softer phase, and quicker.  I'm not certain but I
think that the alloy grade will make some difference in the times and
temperatures as well; higher alloy carburizing grade (example 8620) will be
more resistant to the effects of heat.  Good practical questions you ask,
Charlie.  It might boil down to "don't get it too hot and don't let it sit
too long and none of this will matter"

As for cryogenics, I'm no expert, but my understanding is that it is not a
standalone treatment.  It is used after a conventional heat-treatment, and
the purpose of cryogenic cooling is to complete the transformation of
retained austenite (a particular shape of iron-carbon molecule, which is
soft) into martensite (same chemical composition but a different shape,
much harder).

SO

On Fri, Nov 15, 2013 at 10:06 AM, charlie hill
<charliehill at embarqmail.com>wrote:

> Thanks Steve.  Do you know what temperature it takes to damage the
> hardness?
> Also, what do you know about Cryogenic hardening as opposed to heat
> treating?
> As I understand it, the hardening process has more to do with the abrupt
> but
> controlled
> change in temperature and not the temp it's done at.  I know that a lot of
> the race car
> parts are now cryo treated instead of heat treated.  Just curious.  This is
> all off topic
> at this point I guess.
>
> Charlie
>
> -----Original Message-----
> From: Stephen Offiler
> Sent: Friday, November 15, 2013 8:10 AM
> To: Antique tractor email discussion group
> Subject: Re: [AT] OT: Rosebuds! The oxi-acetylene kind...
>
> Thing is, gears are case-hardened.  If you re-heat them (the BBQ fire in
> the tranny) to the point that you damage the case hardness, what you've
> done is converted the surface microstructure to a less desirable, softer
> form of carbon steel, but the surface is still carbon-enriched.  A second
> heat treatment would have to be done with care.  Some of the carbon from
> the original case hardening is going to want to diffuse further into the
> base material, meaning your second heat-treat process is going to need to
> be a case-hardening process again, in order to get the surface hardness
> back up, BUT, the case depth is going to increase, and this is likely to
> make the gear teeth brittle and prone to fracture.
>
> SO
>
>
>
> On Fri, Nov 15, 2013 at 7:19 AM, charlie hill
> <charliehill at embarqmail.com>wrote:
>
> > Possibly Tom.  I really don't know for sure about that.  Just
> > know what I've seen done and what I've done.  As for the
> > effect on the temper of the steel and the metallurgy, I won't
> > argue with you about that.  You may well be correct.
> > However, they can be heat treated again.
> >
> > Charlie
> >
> > -----Original Message-----
> > From: Tom
> > Sent: Friday, November 15, 2013 1:03 AM
> > To: Antique tractor email discussion group
> > Subject: Re: [AT] OT: Rosebuds! The oxi-acetylene kind...
> >
> > Only one problem, Charlie, the gear teeth will be the first to heat.
> > So they will lose their temper before the hubs will be hot enough to
> > free on the shafts.
> >
> > Tom
> >
> >
> >
> >
> >
> > >________________________________
> > > From: charlie hill <charliehill at embarqmail.com>
> > >To: Antique tractor email discussion group <
> at at lists.antique-tractor.com>
> > >Sent: Friday, 15 November 2013 12:43 PM
> > >Subject: Re: [AT] OT: Rosebuds! The oxi-acetylene  kind...
> > >
> > >
> > >Tom I don't think you have to get them that hot in terms of max temp.
> > >You just have to get enough heat into the mass of metal to make the
> metal
> > >expand and break the joint loose.  When you have a big mass of metal it
> > >takes
> > >a lot of BTU's.
> > >
> > >Charlie
> > >
> > >-----Original Message-----
> > >From: Tom
> > >Sent: Thursday, November 14, 2013 6:27 PM
> > >To: Antique tractor email discussion group
> > >Subject: Re: [AT] OT: Rosebuds! The oxi-acetylene kind...
> > >
> > >One would have to wonder how hard the gears & shafts were after that
> > >experience!
> > >
> > >Tom
> > >
> > >
> > >
> > >
> > >
> > >>________________________________
> > >> From: Mike <meulenms at gmx.com>
> > >>To: Antique tractor email discussion group <
> at at lists.antique-tractor.com
> > >
> > >>Sent: Friday, 15 November 2013 12:05 PM
> > >>Subject: Re: [AT] OT: Rosebuds! The oxi-acetylene  kind...
> > >>
> > >>
> > >>Interesting that you would bring that up Charlie, I was watching RFD-TV
> > >>the other night and they were interviewing a guy that had restored
> Power
> > >>Horse tractors.. Parts are apparently very hard to get for those
> > >>tractors, you either need to make them or have a parts tractor. Anyway,
> > >>he said when he got it the transmission gears were seized up, so he
> > >>filled the transmission with charcoal briquets and let it burn, same
> > >>type of idea. Those are neat little tractors by the way, made to be
> > >>controlled just like a horse using reins to control the tractor via two
> > >>levers.
> > >>Mike M
> > >>
> > >>On 11/14/2013 7:22 AM, charlie hill wrote:
> > >>> Dave if the part is such that you can do it without messing something
> > >>> else
> > >>> up
> > >>> you might find you have better success, and cheaper, by just building
> > >>> a
> > >>> big
> > >>> fire and throwing the part in the bed of coals for a while.
> > >>>
> > >>> Charlie
> > >>>
> > >>> -----Original Message-----
> > >>> From: Dave Johnson
> > >>> Sent: Thursday, November 14, 2013 12:31 AM
> > >>> To: at at lists.antique-tractor.com
> > >>> Subject: [AT] OT: Rosebuds! The oxi-acetylene kind....
> > >>>
> > >>> I'm pretty ok with cutting & brazing, but have never used a rosebud
> to
> > >>> heat
> > >>> something, and my experience today has me scratching my head.
> > >>> The project at hand is freeing up a cast iron wheel hub, stuck on a
> > >>> keyed
> > >>> 1"
> > >>> shaft. This is on an old Gilson / MW garden tractor transmission....
> > the
> > >>> idea is to liberate a set of 4 of these hubs to make dual adapters
> for
> > >>> use
> > >>> on another tractor with a FEL.
> > >>>
> > >>> I have soaked it for quite some time and have a puller tensioned on
> > >>> it,
> > >>> but
> > >>> it's not moving.... so now it's time for a little heat.
> > >>>
> > >>> I bought a new victor 8-MFA rosebud and lit it off as I would the
> > torch,
> > >>> but
> > >>> when I try to get a blue flame, it flames out with a pop!
> > >>>
> > >>> What's going on here? Do I not want a hot blue flame, or do I simply
> > >>> need
> > >>> to
> > >>> feed a lot more of both gases to the torch? Or??  Any insight into
> > these
> > >>> things would be appreciated!
> > >>>
> > >>>     btw, I'm on digest, so it'll take a day for me to respond (:<((
> > >>>
> > >>>
> > >>> Dave in Gilroy, CA
> > >>> webguydave at yahoo.com
> > >>> _______________________________________________
> > >>
> > >>
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> > >
> > >
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