Salt quench bath boil over - cause?

[twistedneck]

Tonight i had a big boil over in my salt pot. I think it soaked up the dampness over the summer in my basement - i left the cap off for at least two months. dumb i know.

Can i boil the water off by holding at the boiling temp for a while? heck, it started boiling at only 550F!! It was like a pepsi opening, ran over the side, shorted out both burners ($$$).. I need a splash guard for sure.

 

[unclesyd]

Nearly all heating salts are hygroscopic so the scenario as you describe is quite possible. One other thing is that you might have had too high a heating rate a the start.

Depending on your bath composition you may have irreversibly damaged it. Some hydrated salts have to taken to pretty high temperature to become anhydrous.

I would get with your bath supplier and discuss the ways and means to rectify you salt bath if possible.

 

[twistedneck]

unclesyd, some of my guys on the sword forum said the same thing

http://forums.swordforum.com/showthread.php?s=&postid=836484#post836484

I'm going to Contact Glen at Hubbard Hall and see if i can boil it out slowly.

Heating rate did not change, that's why i was so surprised initially.. i have it low and slow like a bbq.

When you say damaged i think what that means.. is it just elevated boiling point? or is the salt haet transfer now slowed down?

 

[unclesyd]

What happens is that you essentially hydrate the various chemical components. Some salts will give up this water very easily while others require high heat to give up the water. You want your bath to as anhydrous as possible to prevent water being liberated during operation which can cause problems with corrosion. Degrading can cause several things to happen and all are bad. The heat transfer rate will change. The heat capacity of the bath will change. There are operational problems as you have seen.
I think the biggest problem in your case there is a possibility that the bath will superheat and erupt when anything is put into it.

You might try to slowly heat the bath to bubble point and hold it there for several hours and they very slowly increment the temperature a few degerees a at time. After each rise in temperature hold for a few minutes and see what happens. I Still would get with your supplier concerning remediation.

Until you change out the bath or successfully rectify it I would put something between the bath and any personnel. There is a still the possibility that the bath will erupt.

Do not cover with a tight fitting cover unless cold.

I would not attempt to agitate the bath.

Again I recommend getting with your supplier about rectifying the salt bath or better yet if the salt bath is relatively small dump it and start over.

 

[twistedneck]

Agreed unclesyd, i'm going to just replace the cylinder (relatively cheap) and the salt. The difficult part is the controls and supply energy anyhow..

Excellent call on the bath looking 'fixed' but still erupting when parts are added.

I'll try to salvage the cylinder.. Especially since the stirring prop and thermocouple are burried inside!

The two electric burners are toast.. along with both SSR's.. Learned a lesson there two, larger surface area burners mean even contact upon initial heating, less hot spots (that was an issue also).

I think we got this one solved, i'll let you know what Glen from Hubbard Hall says.

These lessons dont come easy.