Jason's " Rogue " casting thread.

[Alyn Foundry]

Hello Jason.

Your last two photos aren't sand inclusion IMO. They appear to be " Slag inclusion " this is caused by a turbulent metal entry into the mould oxidising the lower melting point material that's alloyed with the Copper.

Kind regards, Graham.

[Jasonb]

So the white gritty stuff in the holes was slag and not sand?

[Alyn Foundry]

So the white gritty stuff in the holes was slag and not sand?

Hello Jason.

Possibly, a lot would depend on the Alloy which is of course is unknown.

Kind regards, Graham.

[KWIL80]

When I have iron castings made for me I always specify "leave the castings in the sand untill all is cool".
No kicking them out of the  sand mould while still red!! Certainly avoids the chilling.

Minimum fettling as well, this avoids having wanted metal ground off.

[Jasonb]

I picked up another casting the other week which deserves a place here, being teh last of the three to pick up the castings I got the scabby one

This is a pic of the cast surface - almost flaky, infact a dig with a screwdriver and pieces could be prized off in flakes. Looks like this was probably the upper surface of the casting which was also cored



And this is what was under his skin after the first cut, this continued for 5mm depth with bits flaking off to leave craters upto 3mm deep.



Anyone got any ideas on the cause?

[Alyn Foundry]

Hi Jason.

That's an easy one!!

The core used didn't have sufficient venting causing the casting to " blow "....

There are many ways to prevent this, the simplest is to drill the core after curing.

Kind regards, Graham.

[Jasonb]

Thanks Graham, it was quiet a long core at 14" x 1 1/4"

To give the Foundry their due they did offer to cast another if it could not be used.

[mnay]

Just read through the entire thread.  Very good information.

[Casting Iron]

From post #34, it appears the gate is on the large part of the casting.
I see a lot of folks with a runner directly from the bottom of the sprue to the gate, and when you do it this way, then the air that can be entrained in the sprue while it is filling can travel straight into the mold cavity, along with any loose sand and slag.

If you let the runner travel past the gate, and have the gate on top of the runner, then the runner fills first, and then the gate tends to skim off slag when it passes through the gate.

If you use a spin trap at the end of the runner, then initial flow of metal with entrained air/slag/sand passes down the runner into the spin trap, and when the runner finally gets full, you have a flow of clean metal that enters the gate.

I never see hobby folks using spin traps, and not many commercial foundries using them either, but they seem to be very effective.
I use spin traps religiously, and they work well.

.

[Jasonb]

Pat it was nothing to do with entrapped air. As stated it was due to a long unvented core. I am not sure where you are getting the position of th egate from as it cannot be seen in any of those photos of the casting

The Foundry did recast another from the batch of three with a vented core and that was fine. Turns out the Foundry owner left the initial job to someone with less experience and he did not vent the casting. When the owner did it himself with the vented casting it was fine.

[Casting Iron]