Type of Steel Needed for Design? 2

[BryceKohler]

I am designing an overflow tub for an aluminum melter. It has a fairly high capacity of volume at about 7000 lbs. Currently we use a cast steel structure. We are unable to repair these after some use tho because of the thermal fractures.

Hence I am making a welded contstruction design, but I have not found an answer as to what type of steel to use for this? It will be subjected to molten aluminum of about 1500F. Any help would be great.

 

[unclesyd]

Are you sure that the existing tub is cast steel not Cast Iron?

The two pots that I've seen in similar operations were cast iron and as you say were not easily repairable. These pots didn't run much over 1250F. Cast steel should be more easily repaired than CI but not impossible .

 

[BryceKohler]

I am positive they are cast steel. From the research I have done lately a SST 436 would have the least coefficient of expansion, but the welds are what I am worried about holding up. Any thoughts?

 

[TVP]

For a fabrication like this it is very important to eliminate, or at least minimize, the residual stresses from welding. Normalizing or some type of annealing would be typical for carbon/alloy steels. Not sure what Type 436 stainless steel would require.

 

[metengr]

I don't believe a welded 436 ss tub is a good option here because of concerns related to filler metal choices. I believe unclesyd's mention of a cast iron tub would be a wiser material choice for this application.

 

[BryceKohler]

I agree with all of you! However my project is to make a tub with a welded construction type to try out.
So, with that in mind (dumb as it may be , what sort of steel do you recommend?

 

[arunmrao]

Cast iron pots will be more suitable for such applications.However,I have come across cast steel pots too being recommended.

The steel grades I recall is plain carbon steel,with little Ni and Mo(less than 1%)

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[metengr]

BryceKohler;
I did some checking on this and the problem you are going to have with this current set-up is wastage (dissolution) of the steel or stainless steel (iron will dissolve in molten aluminum) with exposure to molten aluminum for any appreciable length of time.

I would suggest if you intend to fabricate the tub, I would use 2.25% Cr-1% Mo steel plate (A 387 Grade 22) which is suited for elevated temperature service. The material is readily weldable and easy to fabricate into a tub geometry.

Now, what I would suggest is to line this tub with a suitable refractory to protect the steel from dissolution with molten aluminum at 1250 deg F or higher. This will also keep the aluminum relatively clean - no iron contamination.

 

[arunmrao]

The drawings that I had access to,did not indicate any refractory linings.This was for a fairly large aluminium plant in Middle East. I had always this nagging fear of iron contamination,but for some reason was not considered by the company. They were insistent on buying the lowest(read cheapest) grade of cast steel as they had doubts of cast iron pots cracking during handling.

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[EdStainless]

I would suggest the 2Cr or 5Cr grades. you also want to look at the design for resistance to thermal shock. Do not make it too rigid, allow it to deform. this will minimize one of the major issues.

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Plymouth Tube

 

[MJCronin]

I would expect to see refractory incorporated into a design subject to quick thermal shock.

Refractory must, of course, be periodically inspected and replaced

Cast iron with refractory lining is tough to beat..

-MJC