Salt mixture for salt bath annealing

[CUBUFF89]

So like many on the SH forum I started salt bath annealing using a kit from Ballistic Recreations. It has worked well so far except that I only ordered one container of his salt mixture and now I don't have enough to fill the pot to the desired level.

So in search of replacement salts I read some of the threads on this forum and most people reported using a mixture of Sodium Nitrate and Potassium Nitrate which I ordered from Duda Energy. After my order arrived I looked more closely at the little container from BR and Gary actually uses Sodium Nitrite and Potassium Nitrate.

Now I don't remember much from high school chemistry so I started looking on the web. BR says the mixture attempts to match MIL-Std-10699 Type 1. I found the MIL-Std-10699 doc on everyspec.com and sure enough Class 1 uses a mixture of Sodium Nitrite, Potassium Nitrate and (optionally) Sodium Nitrate. It lists a working temperature of 163-593 degrees Celsius. The mixture for Class 2 has a working temperature of 288-593 degrees Celsius and is a 50/50 mixture of Sodium Nitrate and Potassium Nitrate.

My question to anyone who is more knowledgeable than I is: does it matter, Class 1 or 2? If the BR salts I've been using are Class 1, is it ok now to add Class 2 mixture of NaNO3 and KNO3? Seems like the main difference is the lower end working temperature. I monitor my salt temperature and keep it well below 550 degrees C as BR recommends.

BTW, MIL-Std-10699 actually has a very stern warning in Sec 6.3 about the use of Nitrate salt baths. The warning cautions against overheating above 593 degrees C and against the accidental immersion of any aluminum alloys as an explosion hazard. Worth a read.

Would like to hear what someone who is more of an expert has to say.

 

[CUBUFF89]

Anyone?

Where are the salt bath annealers out there? Surely someone else has researched the chemistry of the salts.

 

[TheOfficeT-Rex]

That's a question with a pretty specific and advanced knowledge requirement to answer correctly.

Why do you want to mix the salts, instead of using only the new stuff you bought? There are reports of people using different salt mixtures from the BR kit and don't report any change in practical use.

 

[jimdog708]

It looks to me that there are several mixtures that will work. (See attatched chart)

Salt bath heat treatment [SubsTech]

www.substech.com

 

[CUBUFF89]

It looks to me that there are several mixtures that will work. (See attatched chart)

Salt bath heat treatment [SubsTech]

www.substech.com

Thanks for the link. It looks like from that table that Ballistic Recreation supplies salt composition #4 and what people on the hide report using is composition #6. I think that satisfactory results can be achieved with either.

My purchase of salts from Duda will enable me to replicate #6 and I'll go from there.

 

[HandsOff]

I just started salt bath annealing with the BR kit, so I'm no expert on the subject, but I just came across this article on salt bath annealing that gives the Ballistic Recreations salt formula and thought it might help.

SALT-BATH ANNEALING BY PAUL PARKINSON

We’ve covered annealing of brass cartridge cases before but to recap – annealing is a heat treatment process that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above...

www.targetshooter.co.uk

 

[J McGriddle]

High Temperature Tools & Refractory | Salt Tubes for Heat Treating Applications

High Temperature Tools & Refractory is your source for refractory and other knifemaking supplies. We specialize in high temperature tools and refractory for forges, kilns, and heat treating applications. We have been serving the needs of industry, small business, and the individual craftsman...

www.hightemptools.com

 

[clcustom1911]

60% sodium nitrate 40% potassium nitrate

Have at it. I do 950-960 degrees for 8 seconds for 6.5 Creedmoor brass and 13 seconds for my 7mm RemMag brass.

I started with the 5 second thing initially, but then began experimenting longer times. Wear leather gloves that brass is gonna be really hot when you pull it from the shell holder.