Inconel in molten aluminium

I wouldn't have thought molten aluminium was an aggressive media, in the way you or he describes...?

I will be interested in what others have to say... John.

Aluminium is very chemicaly reactive, it can spontaniously ignite and will react with many other metals. Temperature is not a real problem plenty of other metals have a higher melting point. Yes ceramic is the best material to use here. Heed your elderly gent he knows best.

Problem is that we can't use ceramic as it's a fairly rough enviroment and it will get broken. My thermocouple supplier suggested 601 Inconel or ideally Sialon as materials they have supplied for use with aluminium previously.

I have no problem heeding my elderly gent except that he has been anti every improvement we have made and has got it wrong more times than he has got it right. On the other hand he's been working with molten metals for more years than I've been alive so should know what he is taking about. Equally so, so should my thermocouple provider!!

Who to believe?!

here you go.

http://nanmac.com/handbook/a38.htm

milo

Ah-ha, that sounds promising. Sintered ceramic. I'll get busy on local availability. Thank you.

you're welcome.

Milo

Further to the above post. I just received an apologetic phone call from my thermocouple supplier informing me that they made an error in recommending Inconel for my application. I'm now engaged in scraping egg off my face and am not very impressed!!

Well you learn something new every day...

My field is electronics / electrical but I'd have thought molten metal was just hot and not corrosive etc...

John.

Yeh, I thought the same. I'm now doing what the prudent person does when presented with something he knows bugger all about; make it the customers problem! I'm submitting a revised quote specifically stating that supply of appropriate thermocouples is the clients responsibility.

There's no problem so big that it can't be run away from!

I used to work as an industrial electrican at a local aluminum extrusion plant that had a remelt plant. We made are own billets and we only used ceramic thermowells at the holder for the drop. I'm sorry I don't remember where we got them from, but you'll be alot safer with the ceramic than anything else.

OK. So why not use Infra Red registering temperature probes that measure the temperature indirectly!

Been there, looked at that. Problem is the emissivity of aluminium throws up a whole raft of problems. Other issue is that these thermocouples are intended to supervise an unattended furnace and I just can't take any chances on bogus readings. In the metal is in the metal, no ifs and buts. Thanks for the thought though but I've already soul searched over that one!

I'm not an expert but you might look into platinum as a sheath material for your thermocouple. It is very expensive, but you don't need much and I believe it stands up to molten glass, which is also very agressive at dissolving other materials, even ceramics. Platinum is commonly used today as spark plug electrodes to extend their life.

Can not a thermo-well work?

Thermo well may isolate thermocouple from reactive melt...

A thermowell is essential for maintenance reasons, but it still has to be made out of something doesn't it?

John.

Just an update on the current state of play with this project.

The customer has ordered a couple of Sialon sheaths for the thermocouples. There is much debate as to whether this ceramic based material will withstand the rigours of life in these pots. I have suggested that if it does not I can build a "no temperature" time into the PLC. The idea being that they load their pot (sans thermocouple) at night and go home. In the early hours the burner fires but does not look for a temperature for a set period of time. Within that time period the operators arrive to a nearly fully molten pot and insert the thermocouple. If they do not, the control system will look for a minimum temperature from the thermocouple and if it's not there, shut down.

Anyway the first step is to trial the Sialon sheaths. If they're tough enough, it keeps things simple. I'll post the outcome of all this but it may not be for several weeks (or more) as the sheaths have to be ordered from afar! Thanks for all the contributions.