[TheForge] oil temps (one more time)

[Steve Bloom]

At 09:14 AM 11/18/2010, Mark wrote:
>  Great info, thanks Steve....Just curious as to why you are using 
> oil for Japanese style work? Doesn't that have an ill effect on the 
> hamon activity? I was always under the impression that using water 
> would produce the most pleaseing hamon activity? I could be worn, 
> and usually am!! Ha ha

The quench will be in heated water but the stress relief / tempering 
will be in oil.  I've discovered that if there is much hesitation 
between the quench and the stress relief (read that as a few seconds 
to admire the curve), there is a decided chance that I will hear 
'CRACK' ....so there is a need for quick acting stress 
relief.  Typically, I use salt baths for austempering (1550 F high - 
the lava pool) with a quench and soak in low-temp salt (475 F).  My 
gear can handle a blade up to 18" long, so tanto length pieces are 
doable with my usual setup but anything longer requires new gear.

  I've just completed one of the Don Fogg drum forges and have lined 
up a quench bath (a 40" long gun-blueing tank with a propane burner 
from a cheap $20 grill that can run the water up to 180 F), but I 
need a tempering facility.

The options appear to be air, salt, glass beads, and oil.

(1) Air won't be quick and doesn't have much thermal mass (but it 
doesn't burn or corrode);
(2) Salt won't burn but the melt is at 350-400 F ,is very corrosive, 
and for a 4"x4"x36" bath, the cost is ~ $240;
(3) Glass beads will need stirring and I have my doubts about the 
speed of heat transfer to the metal; and
(4) Oil will burn but is inexpensive, is fluid at the right 
temperature, and ought to have the right degree of heat transfer and 
thermal mass

  - so it looks like oil is the way to go (as long as I don't burn 
down the shop).  Since I'll be submerging a quenched blade in oil 
that is below the flash point, I don't see any real danger with the 
oil (and the bath will have a snuff lid anyway).  My low-temp salt 
pot runs off a 110V water heater element and maintains 475F with 
about the same total volume of fluid, so I don't expect any problems 
with getting the oil up to the temp I need.

Steve