Casting Shibuichi

[Nicholas G]

    Hi, I’m trying my hand at making knife and sword hardware out of Shibuichi.  Melting the metals together without oxidizing the alloy is fine, but every time I try to pour into the mold, it cools too quickly and clogs the top.

    I’ve been using steel to make my molds.  The first mold was 3”x3”x1/8”.  I’ve seen videos of people making it and their molds don’t seem much different.

    What am I doing wrong?  Do I need to preheat the mold?  Use a different material?

[George N. M.]

Welcome aboard from 7500' in SE Wyoming.  Glad to have you.

If you put your general location in your profile we can give you better aswers.  We don't know where you are in the world, Tasmania, Lapland, or Nebraska.

Is sounds to me that your problem is almost certainly a cold mold.  The mold is a heat sink that is dropping the temperature of the molten metal below the temperature where it is a liquid.  I would try to preheat the mold before the pour so that this does not happen.  You could do it with a torch or in whatever you are using to melt your metal.  I'd try heating it to "black heat" where it is very hot but does not show any color.  If there is atill a problem try taking it up to barely red.

Also, I don't know if this is an open mold or a closed mold.  If the latter make sure the channels to the shape are large enough and that you have air escape channels from the shape. 

"By hammer and hand all arts do stand."

[Nicholas G]

I’m in Washington state.

   I tried to preheat on my third attempt, but I don’t think I got it as hot as you’re suggesting…  As far as mould type, I’m trying to leave the top open, so it’s basically a narrow slit that’s about 1/8” wide, 3” long, and 3” deep.

    Would there be a danger of the copper alloy fusing to the steel mould if I preheat like that?

[George N. M.]

I'm not terribly experienced as a caster but I have done a bit.  You can experiment by heating a piece of steel and them pouring a bit (drops) on it let it cool and see how it adhere or doesn't stick to the steel.  You might also polish your mold anywhere it comes in contact with the copper.  Also, there are mold releasers you can apply (think high temperature Pam), you could coat the inside of the mold with graphite.  It may stick to the cast form but you are probably going to polish or grind the surface anyway.

Finally, I hape you have some casting experience and are aware of the safety hazards and have addressed them.  High temperature molten metal, like copper, can be exteremley dangerous and can result in an accident that can be life altering, and not in a good way, or even life ending.  I hope you have proper PPE, proper crucibles and tongs, rehearse the movements of the pour, and are always aware of the potential dangers.

GNM

[Nicholas G]

    I’ve got plenty of experience with molten metals through work, as well as forging experience.  Safety isn’t really the issue, just knowledge.  Usually when I’m dealing with molten metals I’m attempting to be careful not to over heat and I want it to cool as quickly as possible.  This seems to be the opposite spectrum and it sure is giving me a run for my money.

[George N. M.]

In a commercial situation you want the casting to cool as quickly as possible, break the mold and move on and do it again.  Often with small scale "art" casting heat and ad time are your friend and there is nothing wrong with doing a pour and then going away to let everything cool over night.  That said, sometimes quenching a hot mold can help break loose the casting inside it because of differing coefficints of expansion.

"By hammer and hand all arts do stand."

 

[Nicholas G]

    Preheating my mould and crucible helped a ton.  Thank you.  I pulled out my infrared thermometer and got both to about 1,500F before starting this time and it worked like a charm.  I was even able to forge out a small piece from 1/8”x3” to 1/16”x3-1/2”.  It’s a little small for what I had in mind, but at least I was successful.

[George N. M.]

Excellent!  What ratio of silver to copper are you using?