Salt Bath Annealing?

[Dahonis]

Hi,

I have just read a few articles on the above, one article by The Gun Pimp I think

Has anyone else tried it?

Regards

Chris

[ovenpaa]

I read the article myself quite recently and found it intriguing so I would also be interested to hear from anyone who has tried it.

[jmc67]

I've not tried it, but apparently it is used quite widely in industry for annealing.

While I'm not normally one for banging on about caution when trying something, as a chemist please make sure anyone thinking about this is aware of the hazards involved with it. As a technique it is certainly not without its risks. A molten salt bath contains a vast amount of stored up energy. Any water, oils, anything flammable etc gets into this and there is an explosion risk. Heat it up too high and the salts can break down and release some pretty nasty gases.

This is a link to a paper from 1982, about a lab in the US which was destroyed when one of these went wrong (granted a bigger one that most would use at home, but not a particularly high temperature);

https://pubs.acs.org/doi/abs/10.1021/cen-v060n041.p029

And a quote of the main points; "A University of California, Berkeley, lab has been rebuilt and is ready for use again after being demolished in late July by the explosion of a molten salt bath. Berkeley chemistry and chemical engineering faculty members are concerned that many researchers are unaware of the potential dangers of these commonly used heat-transfer media.

The explosion involved a glass polymer-synthesis apparatus immersed in a fused salt bath containing 3 lb of sodium nitrite and 1 lb of potassium thiocyanate. The bath had been heated above 270 °C using a hot plate. The experiment was being conducted in a closed fume hood.

The explosion, which Berkeley faculty members estimate had the force of about 1 lb of dynamite, caused more than $200,000 damage to the new lab. The doors of the fume hood were imbedded in a wall 20 feet from the point of explosion and the interior walls of the lab were bulged outward. "

[dromia]

I played with it years ago when I was experimenting with molten lead annealing as well.

Besides the hazzards warning above, especially the one about it not getting over temperature a real risk in cheap non thermostatically/PID controlled pots like the Lee, I found the dipping process awkward to control for sufficient consistency. I am sure knacky people could rig up jigs and the like but that was just extra chew on for me. I find that a blow torch and a turntable to work just fine for me, simple and repeatable without the added hassle of watching pot temperature as well.

Also be aware that from my experience these salts are corrosive and hard on the pots and iron things around them.

Be worth looking at shipping as well, I got mine form a hot bluing materials supplier and I believe the bluing salts at least are expensive to send nowadays.

[The Gun Pimp]

One or two Diggle members are now using salt bath annealing so I asked one of them to write up the process for Target Shooter.

It is certainly a bit cheaper to get set-up compared to the carousel/blow-torch type. As quite a few shooters already have melting pots for lead casting, it makes it even cheaper.

[phaedra1106]

I have all the bits to do it, got a plate made to fit the small Lee pot etc.

I tried it once but the nasty high temperatures put me off!!!, I'll stick to my rotary annealer I got from Lubo on TSD :)

[Dahonis]

I have a PID and an old Lee Pot to use as a vestibule. Its the high temperature and the risk of an explosion puts me off

[FredB]

I use a blow torch and a four inch nail in the chuck of a rechargeable drill. Some people, especially in the shooting game will do anything to make life more complicated.
Fred

[The Gun Pimp]

I call a blow-torch and a four inch nail in a drill complicated - can't get simpler than an AMP annealer.

[dromia]

£1300 sounds complicated to me.