Need help melting on gas turbine generator copper

[Bearded Familyman]

I work  at a combined cycle power plant and we had a gas turbine generator winding failure. We want to melt down some of the old damaged copper to make challenge coins on my CNC for all the employees and the GE generator overhaul techs. If someone can melt down what I need for the coins you can have the rest of the copper as payment. It’s EXTREMELY heavy. It took me almost 4 hours to break one of these so hopefully someone will have a better option for me. 

[Brian Hibbert]

 

Welcome aboard!  I don't do melting, but there are many on this forum who do.  BUT, this is a world wide forum.

It would be helpful to know where you are for a question like this.  Please edit your profile and put the general location in it.

 

[George N. M.]

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

First, we need to know where you are located.  This is a world wide forum and we don't know if you are in Lapland, Tasmania or Kansas.  Knowing your general location will help with answers.  Add it to your profile and read the "Read this first" tab.

OK, so many issue with making coins from chunks of copper.  First, you can do this hot by casting or semi-cold (heating to anneal but not melting the metal).  The semi hot method would involve making a steel die with the lettering and design cut into it in reverse.  To prepare the copper you need to reduce it to pieces about as thick as you want the coins,  either by slicing or sawing or shearing or forging it out to a thin sheet and then cutting it up into disks or rectangles or whatever shape you want the coins to be.  This will be easier if you anneal the copper first. which involves heating it and then quenching it to soften it.  The metal reacts the opposite of medium to high carbon steel in that the quenching makes it soft instead of hard.  Copper work hardens when hit cold and becomes harder and brittle.

The second way to do this involves making a mold out of some reusable material which is heat resstant (my first thought is soapstone).  Agan with the design reversed. and pouring molten copper into the mold to make the coins one at a time.  If you want designs on both sides you will have to make a 2 sided mold. 

Casting, particularly with a heavy and high temperature metal like copper can be exceedingly dangerous, even more so if you don't not have the knowledge and experience to do it safely.  And this is dangerous in the sense of it can kill or disable or disfigure you in a way that will hurt a LOT.  Molten netal is very unforgiving and contains a LOT of energy.  Contact with even a small amount of water can cause an amazingly large steam explosion that can throw molten metal around fast and far.  To avoid this you need specialized PPE including face protection, apron, pants, and shoes.  You also need specialized tongs to handle the crucible holding the molten metal.  And you have to rehearse the moves you will make to move the crucible to the mold with everything cold.  Think of the care with which bomb disposal experts (EOD) do all their movements and the preparation they do.

The safer way is to do the semi cold way.  To make a die you can strike in letters that are symmetrical (A, M, V, X, etc.) with a letter stamp set.  Asymmetrical letters will have to be done with small chisels.  Always remember that the die is done in reverse.  The design, e.g. a profile of your power plant, can be done with chisels or a rotary tool with diamond or carbide tips or a combination of techniques.  Then grind the face of the die flat to eliminate the little ridges on either side of anything you have struck into the die and polish the die face.  Then, put a piece of copper, either cold and annealled or hot and soft, on an anvil or something similar, and put the die on top of it and hit the die hard.  It will take a surprising amount of force.  If you have access to a hydraulic or screw press you can use that.  If you want a design on both sides you will have to make two dies and strike the blank between them.

Either method takes a lot of time and work.  If it were me, I'd contact a company that makes challenge coins and send them the copper.  This can be done at a reasonable cost.  My Vietnam War unit veterans' organization had challenge coins made.  Cost will depend on how many you want made.  Most of the power plants I know of have a few dozen employees. 

I suggest that if you have little or no experience with these processes that you experiment with small examples first before going into full on production.

Others may have more suggestions.  Good luck and let us know how it goes and post photos.  We LOVE pictures.

"By hammer and hand all arts do stand."

[Frosty]

Welcome aboard Bearded guy, glad to have you. If you put your general location in the header you'll have a chance of meeting up with Iforge members living within visiting distance.

As already said and well, casting metals, especially high temp melts like copper is no trivial pursuit and requires good PPE. AFTER you've acquired the necessary knowledge to do so safely.

Were I to undertake this my first choice would be to remove the copper and take it to a friend of mine, a professional caster. Copper isn't his usual media but it's close enough he wouldn't need to crack a book for the particulars.

If (shudder) I had to do it myself I'd build a cupola that when tapped drained directly into a vertical tube mold that had a sizable pour cup to provide metal and weight to account for shrinkage.

Could I do this? You bet, I've been doing casual casting since jr. high school in the mid 60s. Would I? Hah, I'd sell it as scrap and buy an appropriate diameter copper bar and slice "blanks" for the coining die. I'd contact another local club member who coins and milk him for info. Making a closed die coin die is pretty straight forward as George lays out above but I'd probably make a spring die to use under my 50lb. Little Giant power hammer or shanghi a striker at the next club meeting to swing my 22lb. stone mason's hammer. I'd have to experiment to see if I'd have to smooth out the saw marks. If so I'm probably make a polished smooth die and hit blanks twice. First try would tell me if I needed to anneal between stamping or do it hot. Hot get's my vote, if I have to heat it up anyway, why not just hit them hot. Hmmmm?

I agree with contacting someone who strikes coins, I recall there being a forum of folks who do so I imagine a little web searching would come up with folks who do this sort of thing.

Frosty The Lucky.

[Steve Sells]

I second Frosty statement of scrap it, and use the money to buy appropriate gauge stock to stamp out coinage from, you will get a guaranteed quality that way as well

[George N. M.]

Here is a link to a video about the mini mint at the American Numistmatic Association at the Money Museum in Colorado Springs, CO.  It uses late 18th and early 19th century techmology.  Of course, coins were hand struck going back to the Ancient Greeks using dies and hand hammers and, sometimes, casting.  It is possible that some Roman coins were struck using water powered trip hammers.  The video will give you an idea of the processes used for striking coins.

 

[Will Brouwers]

It sounds like this guy just wants someone who can get stuff hot enough to melt copper into blanks, and then he will do the rest with his CNC machine.

But, Bearded Family Man, we don't know how far away you are, and therefore if any of us can help, if yo don't give us your location.