first cast with Cast iron mould

[mdevlin53]

I recently bought a 43-370-FN RCBS mold here on the swapping site. nice mold in great shape (Thanks Paul) I cast up a half a hundred over the week end and for the most part they were real nice drops. Today while lubing some up i noticed that some of them looked a little weird, while most of the boolit was nice aand shiney there was a small area on the nose just above the top band that was frosty and just a bit sunken in, it just went a quarter of the way around. Frosty usualy means too hot but why in just a small area. About a dozen were this way. Anybody ever see this and what do you think i need to change to prevent it. Alloy was 20-1
Michael

[Mk42gunner]

I have wanted to try that mold, but I have two others to try in my Rolling Block first.

It sounds to me like there may be a hot spot inside your mold cavity, causing localized frosting. How are you filling the mold?

Good Luck,

Robert

[stubshaft]

Pics would help.

[KYCaster]

Happens to me when I let the mold get too hot.

Usually large diameter and/or heavy boolits. That shrunken area is always where the cavities are closest together. There's not enough metal between the cavities to conduct the heat away.

The mold radiates heat from the surfaces. Heat has to be conducted to the surface so the core is the last to cool.

Slow down your casting cadence a bit or hold the mold open a couple of seconds after dumping the boolits.

Could also be a venting problem which can be aggravated by a too hot mold (see above). I had a six cav Lee mold that wouldn't cooperate till I cut a vertical vent line between the cavities.

If it is a vent problem then "swirl casting" may help. Tilt the mold slightly and direct the lead stream to the side of the sprue hole (the gate) so the lead swirls into the mold like water down the bath tub drain.

Jerry

[runfiverun]

it was from a hot spot in the mold most likely caused from the alloy hitting that same spot when filling the cavity.

[HARRYMPOPE]

A few molds i have do this and others dont.Like other said try pouring a different way or alter your pace(fast or slow).I get this problem more with scrounged alloy or particularly wheel weight rather than say Linotype or 1-20 myself.Each mold is to its own and there is no hard answer to it only suggestions.

George

[mdevlin53]

probably wont get back to casting for a couple weeks so i will have to keep tis info in mind for then. weird thing is it wasn't til i looked real close that i noticed it. the frosting is very light and the reduced area is .010 or less so it was not really noticable when they dropped onto the towel. Next time i will pay closer attention and see if i can figure out what is going on at the time it starts. Like i said most of the drops were perfect.
thanks
Michael

[Alchemist]

I've encountered the same thing with an aluminum mold and 20/1 alloy. Casting tempo with an unfamiliar (to you) mould material involves a learning curve, just like when you started casting to begin with. As you stated above, the reduced area is slight; so I didn't notice it until I was culling rejects, which ended up being most of 'em.

So it goes sometimes....

[mdevlin53]

I snapped a few pic today after fishing this off the top of the melting pot,http://castboolits.gunloads.com/imagehosting/thum_237435065fb3d24055.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=6828)http://castboolits.gunloads.com/imagehosting/thum_237435065fb497f1f0.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=6829)
As you can see I hope, the reduced area is really localized I took the molds off the handles and cleaned them and inspected them. there were a few spots on the faces where there was some flash but i would have thought anthing between the mould halves would make for a bigger boolit not a smaller area.