Ingot results - why the differences?

In the molten state Aluminum will absorb H2 from the atmosphere. This is mitigated but running the furnace slightly lean. but with hydrocarbon combustion (Oil, NG, Propane) you're creating more H2 than is in the air normally, charcoal, wood, induction, electric furnace etc doesn't have this problem. Overheating and long hold times increase the H that gets into the melt. If you are keeping your melts as cool as you can to get a good cast and not leaving them sit in the furnace molten for a long time. This will give you the best chance to keep the H out. If you are doing that but are still having issues with gas bubbles in your casting. That comes from dirty scrap. Oils, paint etc, can increase the H in you molten Aluminum. Clean off your scrap as best as you can, but if you are having issues you may need to look into a method to degas your melt. Commercial degassing tabs, An argon lance (look up Kelly's for a good Start), or a home remedy (pool shock tabs, etc) are common. Dirty scrap can also cause inclusions in the melt little bits of dross get mixed in and cause pinholes that are similar to gas bubbles. This is the stuff that the salt fluxes help clean out. Again there are also commercial fluxes that you can get to help with this. Or you can just buy everything in ingot form to be sure it's clean and gas free to start with (if you buy from a reputable supplier). There is always going to be dissolved H in our melts at home. Unless you are running a vacuum furnace, then that's a whole other set of issues. The goal is to keep the bubbles microscopic so they don't impact the overall strength of the part.

CBB

 

Jeff those methods came from C.W. Ammens book called casting in aluminium, he said salt could be used to degas aluminium and potassium salt. To degas the correct material has to give of a gas and plunged to the bottom of a melt. He said that fluxes could degas aluminium.

 

Personally I don't give a flux.. Never used it with my bronze.

You know I just had to go there.

 

I have observed that no matter where my eye turns there are lifetimes of study, experimentation, trial and error, and new ideas in every area. Constantly amazes me how much is possible with the barest of understandings, while simultaneously such extreme depth is required to move from apprentice to master.

 

My dilemma precisely. I have too many interests to develop a good level in any one of them. However I have come to appreciate greatly the time tested methods and designs of those who have gone before us. One shortcoming of the novice is thinking they can easily improve on old methods. Seldom does that actually happen, you can't improve a basic ball pein hammer, for instance: size, relative dimensions, etc. I've learned this in blacksmithing, broom making, and many things in between. It is really hard to make improvements in tools and methods until you truly master the old tools and methods. And by the time you've mastered them you appreciate them and see little reason to change. Strange attitude for an engineer in the modern day.

 

I've literally made my career foundation 'standing on the shoulders of giants'. There is only so much time and so much value to be had in re-inventing the wheel and/or perfecting craft, especially when it seems commonplace these days to expect everyone to be able to do everything. There are others who have a very very narrow focus, and this is good, we need folks like that, too. But I'm just a normal guy. For example, when we have these discussions on reading material and whatnot, it's always a goal of mine to have the necessary/fundamental stuff highlighted and separate, so that you can hit your 70-80% relatively easily (and KNOW your limitations), and leave the last 20% to those who have a focused passion (or do it as a job).

So to tie that back into this thread, lol, I ask 'why the difference' only because it could be something simple I'm doing wrong, and perhaps others in future could learn the same lesson without having to invest the effort.

However, sounds like I'm getting close to that 80% wall. I really need to make me some greensand and get to doing actual parts...

 

Those who don't think they are standing on the shoulders of giants are quite mistaken. I'm continually astounded by what was done in antiquity.

For me it is important to focus on what I'm wanting to do. (Past melting and pouring metal)

Nothing quite like getting your feet wet. I bought my first greensand to limit the unknowns and am very glad I did. Consistent proper grain size (not a lot of fines) already mulled properly gives you a real leg up on avoiding problems with sand casting. I finally used my bentonite for other stuff.

Of course plain sand and foam makes some pretty good parts too. But I really want to sand cast, so I'm making parts with lost foam while I practice at sand casting. Often I pour a sand mold and a foam pattern from the same crucible melt.

 

Jeff it seemed very silly to me that a flux could be used to degas aluminium.

 

The difference between fluxing and degassing (and that they are two distinct activities/processes), something I confused - and presumably others have as well.

 

Is ferrosilicon considered a flux for cast iron.
I am sure I have read that somewhere, but can't recall if that is true or not.
It seems to make the molten cast iron significantly more fluid.

Edit:
I recall now that ferrosilicon is added to iron to accelerate graphitization; ie: it prevents the hard spots that are sometimes called "chills" that are difficult or impossible to machine.
I guess making the iron more fluid is just a side effect?

Lime or limestone is used as an iron flux, and I recall now that I bought some crushed limestone last year to try with iron.

Here is a paper on flux.
https://www.911metallurgist.com/blog/wp-content/uploads/2016/03/FLUXES-FOR-METALLURGY.pdf

I need to get back to casting before I forget everything I ever learned.

 

Silicon carbide can be used to improve cast iron especially when adding scrap steel to the melt. The conclusion of this article comparing silicon carbide to ferrosilicon found silicon carbide was superior in certain instances such as using scrap steel in the melt. If you skip ahead to page 96 in the document, the last paragraph has the conclusion of substituting silicon carbide for ferrosilicon and increasing the scrap steel content of the melt to end up with an iron with improved mechanical properties.

http://www.afe.polsl.pl/index.php/e...properties-of-synthetic-nodular-cast-iron.pdf