Designing Induction Coils Parallel

[dvontedlores]

Hello everyone, so this topic might get a bit complicated. I am currently designing/building/redesigning a system to cast palladium via induction for jewelry. To spare the details, I will try to summarize. This will have an argon atmosphere above the melt, a vacuum below the mold, and 15kw (7.5kw in reality) chinese induction heater. Currently attempting to melt a tiny 1g palladium ingot I bought online. At least in my current quantities I am not getting it hot enough. During one experiment I had a graphite crucible sitting on a concrete block and I managed to melt the concrete, but not the palladium. I have not found an affordable infrared thermometer that can reach above 3000°f and my current one only goes to 800. Concrete is supposed to melt at 2300ish F, and palladium 2800, so I know I am getting close lol. Since then, I have made lots of design changes. My graphite crucible (it will be lined eventually) slides down into a vacuum chamber which is insulated with ceramic insulation. The induction coil is inside the chamber.
The induction coil is causing issues. Too many loops and the machine cannot run it. Too few loops and it doesnt get hot enough. I have heard that the crucible can be slowly inserted and it will work because there is less resistance as it heats up, but due to the nature of this design, I dont think I can do that and it seems janky. I have seen references to parallel coil systems, but I have not found anyone that has done this. Essentially there is still two main lines in and out of the induction heater, but just before the coil, it splits into two lines per side. These run to top positive and bottom positive for one line and top negative and bottom negative for the other line. I know this terminology is incorrect but you get the idea. I fail to understand how this would benefit more than just a long coil, but I read that if you make your coil length too long for one coil, you need to split it up into two coils in parallel. Any thoughts? Has anyone successfully done this?

 

[Yggdrasil]

Hello everyone, so this topic might get a bit complicated. I am currently designing/building/redesigning a system to cast palladium via induction for jewelry. To spare the details, I will try to summarize. This will have an argon atmosphere above the melt, a vacuum below the mold, and 15kw (7.5kw in reality) chinese induction heater. Currently attempting to melt a tiny 1g palladium ingot I bought online. At least in my current quantities I am not getting it hot enough. During one experiment I had a graphite crucible sitting on a concrete block and I managed to melt the concrete, but not the palladium. I have not found an affordable infrared thermometer that can reach above 3000°f and my current one only goes to 800. Concrete is supposed to melt at 2300ish F, and palladium 2800, so I know I am getting close lol. Since then, I have made lots of design changes. My graphite crucible (it will be lined eventually) slides down into a vacuum chamber which is insulated with ceramic insulation. The induction coil is inside the chamber.
The induction coil is causing issues. Too many loops and the machine cannot run it. Too few loops and it doesnt get hot enough. I have heard that the crucible can be slowly inserted and it will work because there is less resistance as it heats up, but due to the nature of this design, I dont think I can do that and it seems janky. I have seen references to parallel coil systems, but I have not found anyone that has done this. Essentially there is still two main lines in and out of the induction heater, but just before the coil, it splits into two lines per side. These run to top positive and bottom positive for one line and top negative and bottom negative for the other line. I know this terminology is incorrect but you get the idea. I fail to understand how this would benefit more than just a long coil, but I read that if you make your coil length too long for one coil, you need to split it up into two coils in parallel. Any thoughts? Has anyone successfully done this?

What are you going to use the ingot for when you have it melted?

You risk Carbon imbrittlement if you melt it in a Graphite crucible.
The way they do it, if the metal is in powder or to small pieces is either have a proper crucible inside a Graphite crucible,
or create a heel (Compress the powder to a solid or have a small piece of solid metal) to start the heating.

Can you get your ingot to "take"?
Streamlining the coils is a massive subject and there are literally written books on that.

What material are you using for your chamber?

 

[dvontedlores]

What are you going to use the ingot for when you have it melted?

You risk Carbon imbrittlement if you melt it in a Graphite crucible.
The way they do it, if the metal is in powder or to small pieces is either have a proper crucible inside a Graphite crucible,
or create a heel (Compress the powder to a solid or have a small piece of solid metal) to start the heating.

Can you get your ingot to "take"?
Streamlining the coils is a massive subject and there are literally written books on that.

What material are you using for your chamber?

So like I mentioned, the graphite crucible will have a proper liner eventually. My current concern is just getting it to even melt in graphite. Once I am sure I can melt it, I will then try adding a liner and melting larger amounts more purely. The amount I have right now is simply a test amount. (I don't want to buy several thousands of dollars of palladium that I can't even melt.) But I realize to an extent melting will be easier with larger amounts. Really I was just hoping to find someone who has made a parallel coil. Maybe I will purchase one of those books. Everything I have found online seems to be in reference to parallel coils in more of an electrical engineering theory standpoint and it doesnt seem to actually be referring to induction coils used for induction heaters, but maybe transformers or something? I can't make much of that content because it doesn't seem to apply to induction heating.

Not sure what you mean by getting it to "take". The palladium turns bright red hot, but does not melt.

I may buy more palladium but each time I shop I get overwhelmed. I can't decide which form is best, powder, sponge, or tiny little ingots. Either way it is expensive, but since I dont know how much powder it takes to make a gram of solid palladium, I really have no idea which is more expensive. It seems solid palladium avoids lots of problems when it comes to melting. Powder tends to fly around if not made into a perfect heel, which apparently is quite hard to do. I also dont want powder flying around if it is as incredibly toxic and horrible as everyone says. Any help is appreciated. I am becoming quite irritated at this project because I feel I have made little progress after multiple massive prototypes and endless amounts of time. And yes, I am aware that a few companies sell palladium casting machines, but the prices are quite unreasonable and I have already invested so much here.

 

[Yggdrasil]

So like I mentioned, the graphite crucible will have a proper liner eventually. My current concern is just getting it to even melt in graphite. Once I am sure I can melt it, I will then try adding a liner and melting larger amounts more purely. The amount I have right now is simply a test amount. (I don't want to buy several thousands of dollars of palladium that I can't even melt.) But I realize to an extent melting will be easier with larger amounts. Really I was just hoping to find someone who has made a parallel coil. Maybe I will purchase one of those books. Everything I have found online seems to be in reference to parallel coils in more of an electrical engineering theory standpoint and it doesnt seem to actually be referring to induction coils used for induction heaters, but maybe transformers or something? I can't make much of that content because it doesn't seem to apply to induction heating.

Not sure what you mean by getting it to "take". The palladium turns bright red hot, but does not melt.

I may buy more palladium but each time I shop I get overwhelmed. I can't decide which form is best, powder, sponge, or tiny little ingots. Either way it is expensive, but since I dont know how much powder it takes to make a gram of solid palladium, I really have no idea which is more expensive. It seems solid palladium avoids lots of problems when it comes to melting. Powder tends to fly around if not made into a perfect heel, which apparently is quite hard to do. I also dont want powder flying around if it is as incredibly toxic and horrible as everyone says. Any help is appreciated. I am becoming quite irritated at this project because I feel I have made little progress after multiple massive prototypes and endless amounts of time. And yes, I am aware that a few companies sell palladium casting machines, but the prices are quite unreasonable and I have already invested so much here.

What is the reason you want to melt the Palladium?
In the form of Ingots with stamps and all, it has a significant certified value, the moment you melt it it is much less valuable.
It is no longer certified.
Does the bar get hotter than the Graphite?

If you search for "Induction coil design" you will amongst other find this link.
Complete Guide to Induction Coil Design which has a free Pdf for down load

 

[Golddigger76]

I have seen a video of a person melting platinum with a small induction machine, once the platinum was red hot he finished heating it with a torch and it definitely melted.

 

[snoman701]

Larger coil with the right number of coils. I can't remember if it's 5 or 6. I'll look next time I go to the shop. But with only 15 Chinese kilowatts, you have a lot less room to err from the optimum coupling diameter.

You can buy 5/16" copper tubing from mcmaster which will interface with that so you can wind your own.

To my knowledge, they don't make an inexpensive IR thermocouple that can measure high temperature, if you find one, please post it here.

You will want to use pellets if you can, again it's the coupling issue as well as the general nature of palladium.

Got pictures? Good project.

I don't have any knowledge of the parallel coil, but I like the idea.

 

[Muratthechemist]

I have seen a video of a person melting platinum with a small induction machine, once the platinum was red hot he finished heating it with a torch and it definitely melted.

Yes i also see that in my eyes, i also took video and try it in our side. Definitely melt and can reshape. That means over heated to shape again.
Torch is not an option for your ddesign. In vacuum induction furnaces, there must be inert gas such as argon feed. also its closed systems. That argon is also cool gas so its not helping to melt palladium.
I read your problem but on this induction furnace, quite impossible to melt palladium. You can create sponge only from the palladium amino powder.
What i see also different companies, all of them uses circle design induction furnaces. Even 0.5kg capacity works perfect.
Paralel ones uses very big graphite crucibles. Graphite crucible helps to get higher temps. Its using it conductivity.

What i suggest, you can make circle copper pipe design, and cover it with heat isolated cement. Only option looks to me. But you need to know how circle you should make inside of that chamber. I hope you can solve it. Shape will be brilliant.

 

[Joseph Pramudito]

am not getting it hot enough. During one experiment I had a graphite crucible sitting on a concrete block and I managed to melt the concrete, but not the palladium.

The temperature will depend on joule gain - joule loss of the object. The gain is delivered by induction (7.5kW times the coupling factor), while the loss is mainly due to convection and at higher temp it's due to radiation too (to the power of four of temp).

It's not an easy task to keep the effect of radiation to minimum at melting temp. It's not uncommon for industrial melting furnace to have aluminium lining, specially build to reflect some part of heat radiation back to the melting object. There are several other applicable techniques as well for this radiation management.

To manage convection, a good vacuum will help. Just pump to something like 10e-5 Torr (this requires special pump).

Your other option is go with bigger induction equipment to overpower convection and radiation on top of powering the energy needed for heating and melting of the object. You may as well keep the hot surface smaller (do smaller batch and crucible) limiting the radiation and convection.

 

[Yggdrasil]

So like I mentioned, the graphite crucible will have a proper liner eventually. My current concern is just getting it to even melt in graphite. Once I am sure I can melt it, I will then try adding a liner and melting larger amounts more purely. The amount I have right now is simply a test amount. (I don't want to buy several thousands of dollars of palladium that I can't even melt.) But I realize to an extent melting will be easier with larger amounts. Really I was just hoping to find someone who has made a parallel coil. Maybe I will purchase one of those books. Everything I have found online seems to be in reference to parallel coils in more of an electrical engineering theory standpoint and it doesnt seem to actually be referring to induction coils used for induction heaters, but maybe transformers or something? I can't make much of that content because it doesn't seem to apply to induction heating.

Not sure what you mean by getting it to "take". The palladium turns bright red hot, but does not melt.

I may buy more palladium but each time I shop I get overwhelmed. I can't decide which form is best, powder, sponge, or tiny little ingots. Either way it is expensive, but since I dont know how much powder it takes to make a gram of solid palladium, I really have no idea which is more expensive. It seems solid palladium avoids lots of problems when it comes to melting. Powder tends to fly around if not made into a perfect heel, which apparently is quite hard to do. I also dont want powder flying around if it is as incredibly toxic and horrible as everyone says. Any help is appreciated. I am becoming quite irritated at this project because I feel I have made little progress after multiple massive prototypes and endless amounts of time. And yes, I am aware that a few companies sell palladium casting machines, but the prices are quite unreasonable and I have already invested so much here.

Can you share a bit more on your design and use of materials?