Trouble with LG2 green sand castings.

[Rex9]

Hey everyone,

I work for a small foundry and we're having some problems with LG2 castings, all moulds are made with green sand in steel boxes.

The issue we're having is small air bubbles just under the surface of the castings, now this isn't everytime and is kind of hit and miss when it happens. This is becoming a major issue and we can't figure it out. We never had this problem in the past. The metal is poured into 90mm pouring cups as the entry point and the bubbles even appear in the runner when removed.

Does anyone have any ideas on how to prevent this?

1st picture is bisection of a casting, as in cut in half and the second is of the runner.

[ThomasPowers]

How are you degassing the melt before pouring and are you controlling your overheat well?  I'm an amateur caster and those are the two areas that come to mind in my work.

[Frosty]

Welcome aboard Rex, glad to have you. Where are you located generally? 

LG2? I'm not familiar with the term and can think of a few that might apply.

Are the castings bronze or something else?

Frosty The Lucky.

[Irondragon Forge ClayWorks]

I think LG2 is what they call leaded gunmetal bronze.

[Frosty]

Hmmm, don't know anything about that stuff, guess I'll do some reading. 

Frosty The Lucky.

[Frosty]

There a number of manufacturers of "leaded gun metal" bronze, LG2 being a brand designation. Analysis shows them to be easy machining and containing 4%-5% lead. How safe is that to cast? Claims are it's low porosity but that's from the maker, not one word about casting for the end user. 

I may be wrong but I think there are a number of better choices for the home caster than leaded or phosphor bronzes.

Frosty The Lucky.

[Scott NC]

On 12/16/2021 at 5:35 AM, Rex9 said:

 We never had this problem in the past.

  I would ask myself, "What has changed?".  Different material, technique, new employee or equipment, etc...  

[Rex9]

On 12/17/2021 at 6:30 PM, ThomasPowers said:

How are you degassing the melt before pouring and are you controlling your overheat well?  I'm an amateur caster and those are the two areas that come to mind in my work.

We degas with regular bronze degassing tablets, can't remember the name of them. Not sure on the overheat really, I'm just an employee there and have kinda taken making this post upon myself because im tired of making the same casting twice, my boss has been doing it for a long long time and just seems to know when the temps right.

On 12/18/2021 at 5:15 PM, Frosty said:

There a number of manufacturers of "leaded gun metal" bronze, LG2 being a brand designation. Analysis shows them to be easy machining and containing 4%-5% lead. How safe is that to cast? Claims are it's low porosity but that's from the maker, not one word about casting for the end user. 

I may be wrong but I think there are a number of better choices for the home caster than leaded or phosphor bronzes.

Frosty The Lucky.

Hey Frosty,

Thanks for the welcome, yes LG2 is what we refer to as gun metal here.

I'd say it's as safe as any other metal haha, we get requests specifically to use gun metal as its self lubricating and often used on gears and things like that.

We're in the UK and yes they're gun metal bronze.

 

[Frosty]

Nice to meet you Rex, hope you'll stick around. Telling us where you are once won't stick in anybody's memory once we open a different post. If you put it in the header it'll be there every time you post a message. Lots of info is location specific for example just what LG2 is. Make sense?

Seeing as this is an issue for a commercial foundry with a long term material and process, I have to suggest you look for changes. Yes, Ditto Nodebt. Seeing as the master founder has been doing this so long and does much by eye I can imagine something new in the alloy behaving differently, so that'd be my first guess and I'd order independent analysis. My #2, suspect is the degassing pellets, perhaps the supplier has a new supplier. Maybe worth analyzing. A contaminant or change in blend in the fuel: gas, oil, used sweat sock charcoal, etc. Lastly of the obvious (to a guy who hasn't done any casting since high school) a contaminant in the: green sand, perhaps residue from previous use, perhaps something in the water, or maybe a change in the clay used as binder in the green sand. 

Frosty The Lucky.