1/4 oz Graphite Ingot Mold

[DNIndustry]

I appreciate the info and my bad for not adding this. Originally I was using Coors crucibles. the ones I had were too tall and always cracked.
The max temp is 1150. i prepared the dishes as per the tutorial but maybe im torch happy.

I moved to graphite crucibles and molds. The molds are top notch. Crucibles=Ass

Frustrated I spoke with my Jeweler friend and he had a heavy duty ceramic unit that looked like a cradle. It works wonderfull. More of a porous feel like cement. He uses "Boric Acid". The stuff melts wonderfully. I have 20 Mule & Actual sodium borate but his stuff blows them out of the water. It doesnt smell as nice as the 20 mule though

 

[qst42know]

Harold.

I'll never get tired of that photo :wink: :lol:

 

[Harold_V]

I appreciate the info and my bad for not adding this. Originally I was using Coors crucibles. the ones I had were too tall and always cracked.
The max temp is 1150. i prepared the dishes as per the tutorial but maybe im torch happy.

No, you're not torch happy, you just didn't heed advice that was given early on, assuming I gave it.

If I didn't comment on the Coors crucibles early on, my bad. They are NOT acceptable for melting gold. Full stop.

You must use vessels that are not overly sensitive to thermal shock. Coors is just the opposite.

I moved to graphite crucibles and molds. The molds are top notch.

Yes, for now. My choice would not be graphite for a mold, but then I had options open to me that you may not. You will do what you can, even if it may not be the most desirable choice.

Graphite molds are not constant. They degrade with every pour, and degrade all the faster if one attempts to melt with them. That's the problem with using graphite.

By contrast, an iron mold (ductile being the best choice) can be used endlessly with no deterioration, assuming it is treated with respect. That would include preheating to eliminate surface moisture, and proper blackening before pouring an ingot. For large ingots, it would also include moving the location of the pour as the metal is introduced, to eliminate any chance of burning through the blackened surface, yielding soldering of the ingot to the mold.

Crucibles=Ass

I'm afraid you lost me here.

Frustrated I spoke with my Jeweler friend and he had a heavy duty ceramic unit that looked like a cradle. It works wonderfull.

Yes, a crucible for a centrifuge. Not necessary, and too expensive. You can achieve perfect results with inexpensive melting dishes, and they'll last a long time. Best of all, they are available in sizes, so you can purchase one that suits your needs.

If my assessment of your choice is correct (crucible for a centrifuge), unless it is for a large, motor driven centrifuge, it has very limited capacity. That can be a problem, assuming you are dealing with lots larger than a couple ounces.

He uses "Boric Acid"

You shouldn't. Boric acid is not the same as borax. Boric acid reduces oxides, much the same as soda ash. That's not what you want to do unless you're working with alloys. If your objective is pure gold, you should use NOTHING but a trace of borax, and that should do nothing more than wet the surface of your melting vessel to allow the gold to flow freely, without sticking. If it can pour off with the values, you've used WAY too much. Do not, under any circumstance, get flux involved in your molds when casting ingots. The area in which the flux makes contact may wash clean and free of blackening, and solder your values to the mold. If that isn't a problem, where the flux collects will be. It deforms the surface of the ingot, defining exactly where the flux cooled.

Harold

 

[Oz]

By contrast, an iron mold (ductile being the best choice) can be used endlessly with no deterioration, assuming it is treated with respect.

I'm curious that you mention ductile being the best as I hear frequent references to cast iron being the best. I do understand there are in betweens but usually ductile iron is considered mild steel while cast is anything but ductile due to carbon content. As a machinist I’m sure you can clarify my possible misunderstanding. I have access to a lathe but it is hard to find a piece of cast iron of the proper thickness, mild steel does not present this problem.

Speaking of you being a machinist have you considered making molds for sale?

I know you regretfully let your steam engine go with your move but I would think you saved a milling machine or lathe.

 

[Harold_V]

I'm curious that you mention ductile being the best as I hear frequent references to cast iron being the best. I do understand there are in betweens but usually ductile iron is considered mild steel while cast is anything but ductile due to carbon content. As a machinist I’m sure you can clarify my possible misunderstanding.

With pleasure.
Ductile iron is cast iron. It is not mild steel, but it is often compared with mild steel because it closely resembles it in that it has similar tensile strength, and can be welded much easier than can gray iron, which we commonly call cast iron.

The only differences between cast iron (gray iron) and ductile iron are very small, at least as far as composition is concerned. Ductile iron starts life as gray iron. It is either made from low sulfur material, or the sulfur content is reduced, which allows the conversion from gray iron to ductile iron. The process involves the introduction of magnesium to cast iron, which causes the free carbon (graphite) to form spheres instead of flakes. The conversion is temporary in that if the material is not cast and cooled within a narrow time frame (a few minutes), the magnesium is lost and the iron reverts back to gray iron.

One of the advantages of ductile as opposed to common gray iron is that it has greater shock resistance. Cast iron is easy to crack simply by heating. Because the spheres of graphite do not interrupt the slip plain of iron the same way flakes of graphite do, it is far more resistant to fracturing. That accounts for its greater tensile strength. It machines very much like gray iron, but has a tendency to produce a chip instead of powdery flakes that are so common to gray iron. Both are messy in that copious amounts of free carbon are liberated in machining.

The presence of excess sulfur prevents the transformation, so iron that is melted in a cupola is generally desulfurized in the collection ladle by the addition of small amounts of calcium carbide, which combines with sulfur and is then skimmed from the surface. The introduction of the magnesium (via a product known as Glomag) is in the ladle, just prior to casting.

I have access to a lathe but it is hard to find a piece of cast iron of the proper thickness, mild steel does not present this problem.

Unfortunately, mild steel presents a whole different set of problems, one of which is deformation. Another is scaling. It would not be a choice I'd entertain.

Speaking of you being a machinist have you considered making molds for sale?

That's a difficult question. One of my qualities of which I am very proud is the fact that I share my knowledge with readers with no strings attached. I have no ulterior motives in posting, certainly not one of capitalizing on readers to make a dime. However, there's more to my reply, below.

I know you regretfully let your steam engine go with your move but I would think you saved a milling machine or lathe.

I not only saved my machines, but I have been adding to my stable. My long term goal is to build a functioning scale model (1.6"=12") of a UP Northern. As a result, I recently purchased a fairly new CNC mill, fully capable of 3 D machining. It is not a table top machine, and is, in fact, a HAAS TM-1, a toolmaker's mill. It would be excellent for making molds, which I may do when I am finished with my house building project. I also have the capability (an induction furnace) to make ductile iron (or gray iron), so procuring the needed metal would not be such a tough objective.

In answer to your question, yes, it's possible I would make molds, but that won't be in the immediate future. If I find there is a large enough demand for me to dedicate the kind of time that would be required, I would make molds very similar to those I have shown in the past. Those were all made on a manual milling machine, and worked exceedingly well for the intended purpose. I expect I would make molds that poured ingots sized in ½, 1, 2, 5 and ten ounces. That is a size spread that would be adequate for almost all small time refiners. I would entertain special sizes, but I would not encourage them.

One is not free to make a mold any size they wish. Gold does not spread well, so small weight ingots must also be small in physical size, otherwise the ingot does not fill the mold. That would not be true of ingots that are die struck, but that is beyond the scope of my purpose.

Harold

 

[bmgold]

That's some nice pictures of your ingots Harold. 50 ounces times 800+ makes that bunch of ingots pretty valuable.

I recently purchased a fairly new CNC mill, fully capable of 3 D machining.

I work with CNC tools and once you get the hang of programming them, they can do amazing work that would be difficult if not impossible to do manually. A CAD/CAM program helps a lot and would probably be necessary for 3D work unless you really know your programming and have a lot of time.

In answer to your question, yes, it's possible I would make molds, but that won't be in the immediate future.

I can see the CNC being a great help for this job also especially with a CAD program. We used the CNC mill at work (A Mazak machine) to do some engraving or lettering on some jobs. With a little programming work I could see you making molds with some custom engraved design in them (like your personal stamp in the pictures of your gold ingots) or even just a lable on the outer surface of the mold to designate the size of the mold or your Made by Harold logo or ???? I really like the CNC tools for the production and speed they allow as well as the incredible accuracy they make easy.

If I find there is a large enough demand for me to dedicate the kind of time that would be required, I would make molds very similar to those I have shown in the past.

I'll bet there would be a demand for your molds if for no other reason than:

One of my qualities of which I am very proud is the fact that I share my knowledge with readers with no strings attached. I have no ulterior motives in posting, certainly not one of capitalizing on readers to make a dime.

Something made by you might just have some collectors value at least to the members of this forum who have been helped out and learned SO MUCH from your freely shared knowledge and advice. :wink: Just something to think about.

 

[Noxx]

Bmgold,
Do you have experience in CAD programming ? I'm asking because it's one of my projects to make 10 grams gold bars. I have access to a 100 tons press and I already have a block of D2 tool steel, but what I need now is a CAM programmer. I also have access to a CNC Mill and a friend of mine is able to operate this machine.

If you're interested, please let me know.

Thanks in advance.

 

[Harold_V]

I work with CNC tools and once you get the hang of programming them, they can do amazing work that would be difficult if not impossible to do manually. A CAD/CAM program helps a lot and would probably be necessary for 3D work unless you really know your programming and have a lot of time.

Simple molds would be easy. Instead of straight cutters, tapered end mills are used, so the desired configuration is a function of simple milling. That keeps machining time to a minimum. I could actually produce them easily on my manual mill, which is how they were made when I was actively refining. The CNC, however, will make them affordable for others because of the much shorter milling time.

I can see the CNC being a great help for this job also especially with a CAD program.

Indications are I will have access to MasterCAM for programming, which should be quite helpful.

I am not a CNC machinist. I prided myself in machining with manual machines, and did so up to the day I closed the doors on my machine shop. The nature of the work I produced made it easy to avoid their use, plus they were not nearly as well advanced then as they are now. At the time, they were not overly popular, but were gaining quickly.

I avoided CNC on purpose, but I now regret having made that decision. It would have been much easier for me to have grown with the machines instead of breaking in at my advanced age. Luckily, I have a friend that is well experienced and is willing to share his time bringing me along. I don't fear the machining, only the numerical control part.

I've used the CNC mill at work (A Mazak machine) to do some engraving or lettering on some jobs. With a little programming work I could see you making molds with some custom engraved design in them (like your personal stamp in the pictures of your gold ingots) or even just a lable on the outer surface of the mold to designate the size of the mold or your Made by Harold logo or ???? I really like the CNC tools for the production and speed they allow as well as the incredible accuracy they make easy.

Engraving is one of the chief reasons I purchased the machine. My original plan was to go with a 3D pantograph, but the mill will make many of my intended projects easier, including making molds for investment casting of components for models. Fact is, I would also be able to make stamps of various types, such as the one I used on my ingots. I had that one made professionally, due to not having the proper equipment at my disposal, but that is no longer the case. I have heat treat and grinding capabilities now, so I can do all of the necessary steps in-house.

Something made by you might just have some collectors value at least to the members of this forum who have been helped out and learned SO MUCH from your freely shared knowledge and advice. :wink: Just something to think about.

That's a nice thought. I'd like readers to have something by which I will be remembered. I'll keep that thought in mind when I am finally able to pursue the making of molds.

Harold

 

[Oz]

Harold,

Sorry it took so long for me to reply to this. You have once again added to my level of understanding. What I take from this is that finding an appropriately sized piece of cast iron (grey) and machining a mold from it may be a bad idea. The only thing that makes me question that is that I believe most cast iron skillets are grey cast iron and can be taken to a rather red heat and air cooled without typically breaking. Since I agree entirely with the problems associated with mild steel, do you feel that grey iron would be a waste of time trying?

I would be making a mold that would not exceed 10 ounces troy and would think if I had preheated it properly and slow cooled in pearlight after pouring that would give me the best chance for success. It may also help to have mold walls of ¾-1 inch thick to absorb the excess heat from the molten metal.

For what it is worth, I for one would far rather buy a mold made by you than from elsewhere. It would certainly be of superior quality and have extra value being crafted by someone I have learned so much from in refining.

Thank you

 

[Harold_V]

What I take from this is that finding an appropriately sized piece of cast iron (grey) and machining a mold from it may be a bad idea.

Then I have failed in my comments. I'm sorry for that.
All of my molds were made exactly as you proposed. In fact, some were made from sprues or risers, which often are just kish. You must be very selective if you pick them to machine. I mentioned ductile iron only because it offers all of the properties of gray iron, with the increased tensile strength and thermal stability. Understand that cast iron will tolerate considerable heat, but it must be uniform and not a rapid change. Arc welding on cast iron is a source of cracking for that reason. Well experienced workmen can weld it with success, but the novice is inclined to do more damage than the damage that is repaired.

It may also help to have mold walls of ¾-1 inch thick to absorb the excess heat from the molten metal.

That's exactly what you should do. Also, always preheat the mold to well above the boiling point of water. What you don't want to experience is a steam explosion when pouring molten gold or silver.

For what it is worth, I for one would far rather buy a mold made by you than from elsewhere. It would certainly be of superior quality and have extra value being crafted by someone I have learned so much from in refining.

I thank you for the kind comments, and I appreciate the sentiment. I value highly objects that have come to me from people I cherish. I think I understand.

As far as mold quality goes---I'm of the opinion that anyone that has access to a CNC can turn out a very functional mold. Doing one manually requires a little skill and knowledge to avoid undercuts in corners and other minor anomalies, but a CNC takes care of all of those issues, even when the operator may know very little about machining. They truly are the great equalizer. However, nothing would please me more than to have some of my work out in the field, acting as a constant reminder of my few contributions. I look at Hoke that way, as you may have noticed.

Harold

 

[Oz]

Harold,

You have not failed in your comments, I could have failed in my interpretation.

No matter, that is what is great about this living document we call a forum. It allows for opinion and clarification with few absolutes.

Moving on… since I live in farm country I would probably scout the old farm equipment for a suitable piece of cast iron. Speaking of pre-heat as I am low budget/low tech I would use a toaster oven at 350-400 degrees F to avoid burning off my carbon soot prep., I have witnessed steam explosions with molten metal and have no desire to be close to them (water expands in volume by a factor of 40,000 if I remember correctly).

I thank you for the kind comments, and I appreciate the sentiment. I value highly objects that have come to me from people I cherish. I think I understand

I believe you do. A side note to that, it would be nice seeing a signature on the outside as a hallmark either CNC or acid etched to set them apart. And as to your comment “However, nothing would please me more than to have some of my work out in the field, acting as a constant reminder of my few contributions. I look at Hoke that way, as you may have noticed” you and a few other refiners on this forum that could well rest on your laurels but instead enjoy sharing your experiences are like living Hokes, at least to me. Unfortunately one can not get one on one from a book, no matter its quality.

Mold quality… How many degrees of relief would you recommend in a mold for silver and would you change it for gold? I imagine it may have confused some when I spoke of a lathe before to make a mold but I’m sure you got it Harold. For others one does this by mounting the piece to be milled in the tool rest and the cutting mill in the chuck. On most lathes you would have to shim the piece to get the breadth of cut needed. The hard way to be sure but it works when you have a lathe and no milling machine.

 

[Harold_V]

Mold quality… How many degrees of relief would you recommend in a mold for silver and would you change it for gold?

The amount of angle (draft) is rather optional, but it stands to reason that if you can machine a mold without anomalies, very little is required. This can be a matter of personal choice. Too much angle makes a strange looking ingot.

I just searched my tool cabinet and found one of the end mills I used. It was the one used for the larger molds, and has a 10° included angle. You could get by with slightly less, perhaps as low as 6°. Again, it's up to personal taste. There is no need to use different angles for silver and gold. I used the same molds for both metals with equal results. What ever pleases you is what matters.

Because a mold is (or should be) properly blackened, the metal does not bind in the form. Ingots dump out without effort, assuming they do not solder to the mold. That is a bad situation that can be avoided by not super heating the metal, and by moving around as the mold is filled. It's a non-issue for small ingots, which give up their heat rapidly, but larger ingots, above five ounces, can be troublesome, particularly with gold. It should go without saying that the mold should be generously blackened, not just a light coat. All of this will require a little fiddling until you achieve a working combination. Don't be discouraged if your first attempt or two doesn't work out as well as you might desire. Casting ingots is an art, one that is not easily mastered. I was never satisfied with the results I achieved.

If you are familiar with machining cast iron, you won't need this information, but for those that are not, it is important to understand the nature of the material. Cast iron generally is difficult to machine on the surface, the result of minute bits of sand being included in the iron, plus it can be chilled from too rapid cooling. Chilled iron does not machine well, if at all. It all depends on how quickly the iron was chilled, and how deep the hardening.

It is highly recommend that cast iron be machined no less than 1/8" deep for a full pass, with the entire surface being removed. That should get you down to clean metal, which will minimize the chance of ruining a special end mill. It is also a good idea to rough a mold with a straight end mill, staying well away from the finished size, so the tapered end mill is used only for finish cuts. That will prolong its useful life. If you have access to tungsten carbide tools, use a C2 grade of carbide for cast iron. Higher grades (C5, for example) will fail quickly if the material is chilled slightly, or it has small amounts of sand included. Some cast iron is dead clean and soft, so this may or may not be important.

Tapered end mills are generally available with sharp corners. It's a real good idea to grind a radius on the corners of the teeth, so the ingot has a radius instead of a sharp corner. If you have not sharpened cutters before, this may be a daunting task. If you are familiar with relief angles and are comfortable with off-hand grinding, it's not a hard job. Use a radius gauge to keep the radius uniform in size from tooth to tooth. The end result will be an average of the highs of all the teeth.

Be mindful of the diameter of the end mill at the small end. That will determine the size of the end corner radius of your ingots. A large end mill will make a goofy looking ingot.

Hope some of this helps.

Harold

 

[Oz]

Yes it does, in particular in the choice in grade of end mill.

Thank you

 

[qst42know]

Casting ingots is an art, one that is not easily mastered. I was never satisfied with the results I achieved.
Harold

Harold.

I've seen your ingots.

I think you are the only one who would be unsatisfied with your results.

 

[Harold_V]

Thanks for the kind words. I realize they were acceptable, but I wanted something that looked more like jewelry.

Noxx had a picture of some ingots as his avatar some time ago. They resemble what I would have desired.

I'm a realist----I realize I would have to die strike to achieve my desired goal. I worked very hard at producing acceptable ingots----I know how hard it is. It's much easier to refine the gold than it is to cast ingots.

Harold

 

[Anonymous]

if anyone is interested i am a programming , by way of mastercam , cnc machinist . i will write cnc programs for making and engraving molds.