Advise on Smooth Bars

Hi Experts

My 2 Kg ish Brass bars are coming out with a varied amount of pitting and very rough top/bottom ,meaning endless grinding before i can polish.
Im planning to move to Silver soon and i want to avoid this.
I have tried picking up the hot mould after pouring and banging it on the work top using grips but it doesn't seem to work.
is there another way??
Perhaps with air pressure or coating the inner mould with something???
My mould is good quality.
Any Advise??

 

Do you preheat your mold? That could help. How about degassing? Do you do that? Molten brass tends to get more bubbly the more you stir it.

Does that mean you are using a pressurized mold? You could coat the mold with powdered graphite. That will sometimes help the surface finish.
Patrick

 

No pressurized mould. Its just a £30 mould that i pour the moultern brass into.
What is a pressurized mould??

 

I do preheat the mould for a few mins.
I dont know about degassing.
When the brass is melting i do stir it a bit and i suppose when i skim off the top it does to...

 

Would the graphite help??
Do you mean the dry lube for locks etc??

 

A pressurized mold is a mold that is air pressurized, so that it fits to the mold. It is used in the die casting industry.

 

pressurized mould sounds good. can you send a link so i know what im looking for

 

Yes I mean that stuff. I use it all the time and it helps get a smother finish.
Patrick

 

I will look, they are not easy to find. I will send you a link when I get the chance.
Patrick

 

Here is a link to an article about how they work. https://thelibraryofmanufacturing.com/pressure_casting.html
Patrick

 

I'm guessing what you are referring to as bars we might call ingots?

What are you fluxing your brass with?

If you're pouring clean brass into steel molds you should be getting a pretty good finish.

 

Yes Ingots. About 2kg a time.
Im not fluxing.
I just melt with an electric furnace electrical/plumbing brass or Objet d'art brass and pour into a mould.

 

I melt scrap brass regularly and if I don't put some flux in it I get lots of slag. I use brass flux from Budget Casting Supply. It works well. I don't know about the UK.

 

OK. Can you send me a link please so i know what to look for...

 

This is flux that Andy was referring to: https://www.budgetfoundrysupply.com/brass-bronze-copper-flux
In the U.K. check with https://www.artisanfoundry.co.uk/. They have a couple of different fluxes for copper based alloys, maybe contact them to see what they recommend.

 

Sounds like open face casting to me. What's the mould made of?