[chistyakov1971]

I recommend the sizes (approximately, very difficult and not linear dependence)

For small furnaces height of liquid metal / diameter of liquid metal = 0,5
For the big furnaces from 0,5 to 1

The coil
Internal diameter / height = 1 - 1,2 (approximately, depends on thermal losses)

Coil height / height of liquid metal 0,9-1.3 (depends on thermal losses)

In small furnaces - small EFFICIENCY, the basic problem thermal losses.

I have specified factor of transformation 1/10 - 1/20 for connected one after another (not parallel) the coil and the condenser, a resonance on a secondary coil (low voltage)
For an input in the inverter of 220 volt of 50 Hz

The thermal protection for your furnace the coil/ crucible, is enough 2-2.5 sm

Thickness of a crucible not less than 5 mm (I am not assured, there is no operational experience with stainless steel
For an ordinary steel of 10 mm 17 000 Hz), desirable frequency of 66 000 Hz. It will allow to apply and a crucible from graphite

If you do not have electric leaks, it is possible to manage and without coil isolation.
I do isolation by special fiber glass fabric by the impregnated pitch
Two layers a thickness of a layer of 0,2 mm. I wind a copper tube on all length, a photo I will show after. Water in the coil cools isolation.
For industrial big coils, isolation multilayered, difficult

"Should I protect the inner wall of the crucible with some "stuff"?"
It is desirable, aluminium reacts with iron, but it is very difficult. I the reference to manufacturers of crucibles.
For a house, fusion admit also a steel crucible, OK
======
Photo of furnaces for jewellers
http://www.mexel.narod.ru/Foto.html

The sizes of graphite crucibles for fusion of gold, silver, copper, FOR independent manufacturing
http://www.mexel.narod.ru/Tigel.html

Designs of furnaces
http://www.mexel.narod.ru/Draiv2.html

Thermal protection of crucibles, the sizes
http://www.mexel.narod.ru/Draiv1.html

http://www.mexel.ru/

Site in Russian
======

[T3sl4]

The choice of coil size also depends on required coupling. A resonant coupled system (series or LLC network) will deliver maximum power output at only one load level. If loaded lightly, current limiting restricts power output. If loaded heavily, Q drops and "Q multiplication" no longer provides enough voltage or current gain; the limiting case is a short circuit, where the system is no longer resonant at all. (On the plus side, this type of system is short-proof.) If current is not limited (by reducing voltage or changing frequency), then maximum power is delivered when unloaded (dissipated as resistive loss in the work coil and dielectric loss in the tank capacitor).

A constant voltage tank will deliver more current into a heavier load, acting much like an ordinary transformer. One example is a self-excited class C oscillator, like this,

from which I got about 100W when scaled up:



Downsides include low efficiency, the danger of quenching oscillation (resulting in sudden large power dissipation) and an inconvienient 'feedback' winding around the work coil. Generally, operation is with the transistor as a saturated switch, so the peak amplitude will always be slightly less than the supply voltage. If saturation slips, then amplitude drops, resulting in less feedback, and pretty soon oscillation stops and the transistor is dissipating full bias current.

Variations on this, with a traditional switching approach (e.g., full bridge output stage), can be imagined. (Yes, driving a parallel resonant tank with a full bridge, no series inductor. A constant current supply is required, however.) Stability then becomes a matter of control circuitry.

The nice thing about driving the tank parallel is you can drive as hard as you want. This is very important when, for instance, heating cold steel with a tight-fitting coil, which might have a Q of 2 or less in resonant terms. It stops looking like a resonant tank and more like a transformer with power factor correction!

As for microcontrollers (mentioned earlier), if you have lots of experience, go right ahead and do it. If you don't, you'll probably end up writing a buggy program and neglect possible startup and shutdown conditions. The microcontroller doesn't give a damn if its outputs end up high at the same time... an SG3524 does!

FYI, I may write a program to replace the moderately sized control board in my kit, with the added bonus of LCD display, menu driven control and timer functions. When used properly, microcontrollers can deliver the required signals safely, greatly simplifying the circuit, while adding complex and precise features. I'm worried that interfacing the signals will take as much analog circuitry as building it all in analog in the first place

Tim

[siamon99]

CD4046 -Smooth adjustment for frequency,good PLL
The microcontroller provides the big step of step-type behaviour of frequency and cannot be good PLL, Small speed PLL

Dear chistyakov1971,
Hi, I am siamon99 and member of cnc zone not long enough, I had seen your posts on melting and casting forum, Iam a mechenicat engineer and involve in techenical jobs regarding melting and casting of copper and copper alloys. I think that melting coppor in an induction melting furnace is benifical due to short melting time required in induction melting furnace. What is your observation. Seacondly i am intrusted in building induction melting furnace 25 KW running on 440v 3phase 60Hz if you have any circut diagram of it electrical power supply unit i am willing to pay its price. Kindly let me know if you are intrusted in this deal, and the price the out put frequency should be 30KHz with power out put of 25 KW.

Kind Regards
Siamon99

[siamon99]

My power module for the inverter of 30-40 kw

Control system, the driver - are already made and adjusted.
There was an assemblage in the case.
I will be engaged in assemblage after start of the module for fusion of a steel of 1.5 kg.

Is your power module based on IGBT or you have any designe for a 25 KW induction furnace i am intrusted in it.

siammon 99

[chistyakov1971]

siamon99
Look mail

I have this scheme for industrial use, serial release of inverters, for induction heating and an induction melting furnace
I have possibility to develop the scheme for your conditions, at professional level
Has 10 channels of protection
Drives on the ACPL-333
look post 234

[elifarley]

Have you guys seen this project from Open Source Ecology?

They're offering from US$ 1k to 3k to the best induction furnace project submitted.

The project should include:

1. Design of an induction furnace circuit scalable up to 50 kW in units of 1 or 5 kW
2. Design allows for power and frequency selection
3. Power source may be either 1 or 3 phase electrical power.
4. Specifications of a cooling or heat dissipation system
5. Adaptable design specifications for primary coil windings
6. Geometrical design of melt chamber and basic power transfer calculations
7. Melt chamber includes provisions for loading and pouring.
8. Complete bill of materials
9. Fabrication files for circuit and other components
10. Sourcing information for components
11. System design and process flow drawings

You can learn more at their page.

[chistyakov1971]

Thanks for the reference.
I have all.
Only there is no desire to participate. My opinion: competitions it is swindle on gathering of schemes
Induction heating is very old theme for inventions.
To think up something new it is very difficult and it is unreal

[T3sl4]

That furnace looks good. The next step is lining with refractory?

What is the board material on top?

Do you have a problem with the steel parts heating up from the magnetic field? I would use heavy aluminum near the coil.

Tim

[chistyakov1971]

The following step crucible creation, material Finmix 0.5
The technology is debugged and applied in industrial induction furnaces.
Furnace top: assemblage of the asbesto-cement plates, special, heat-resistant.
I envy you, you can apply plates for example: Fiberfrax
Problems with a steel skeleton are not present. A steel: corrosion-proof, not the magnetic.
Approximate your analogue 18/10.
The furnace design corresponds to norms for industrial furnaces.
Aluminium can apply, look sites on manufacture of induction furnaces in China. There it is a lot of photos
Attention! The no closed horizontal contours

[Hernangonzalez]

great work chistyakov1971! I want to build one
I want to see the first steel casting .

[chistyakov1971]

The induction furnace is constructed and handed over the customer.
Works in laboratory.
Unfortunately I have no access to laboratories, a private property and other organisation

Now I work over installation of induction heating for volume hot punching

[siamon99]

siamon99
Look mail

I have this scheme for industrial use, serial release of inverters, for induction heating and an induction melting furnace
I have possibility to develop the scheme for your conditions, at professional level
Has 10 channels of protection
Drives on the ACPL-333
look post 234

Dear chistyokov1977
Iwant to use induction furnace for melting coppor
Cruicable material graphite
In put supply 3 phase 440 volts 50 HZ
Out put 20 KW 500 volts 30 KHZ
Material melted in one charge 15 KG
IGBT based circut.
Charges will be paid by me to be agreed in advance
siamon99

[chistyakov1971]

Look the mail

[rustyolddo]

If anyone is interested I have a copy of the schematics that were originally posted on the hvguy aka Aron Koscho & Justin Hays website (the current website is infected with a virus). They were for a 2.5kW unit. If someone has a way to host them, shoot me an email and I'll email you the whole nine yards, I saved the web page a long time ago for off line viewing. If someone takes the initiative to produce boards for the design, let me know as I'd like to build the unit for heat treating use.

[chistyakov1971]

New works :
2 KW, 66 kHz, for melting Cu, Ag, Au


and 30KW



without the commentaries
===================

Old photo, adjustment

[garettc]

I have been interested in induction heating for the better part of a decade, and have given in and bought several commercial units. The gist of it is, if it's good, it's expensive (like the Magneforce 1500R I bought), and if they are cheap they usually don't work well or don't last long.

I don;t know what the linking rules are here, but if you do a search for Neon John Induction Heater you'll find a very cool page. Unlike all the other blog pages, here you can actually find plans, pcb layouts and ExpressPCB files, and loads of USEFUL information.

If you are on a budget, this is a great place to get some traction on your project....

FYI

G

[chistyakov1971]

Old photos,
The sample for debugging, 66 кГц, 2 kw
The first melting, 13 minutes (cold start)
The subsequent meltings approximately 4 minutes




Defect of casting from for the cold molds
The experiment purpose not copper fusion.
The experiment purpose: research of characteristics of the furnace

[T3sl4]

I've got my improved version cooking:

[nomedia="http://www.youtube.com/watch?v=fE8_-i931zw"]YouTube- Big Induction Heater[/nomedia]

[asuratman]

chistyakov1971,
Is it possible to make 5" long tubing/pipe 3-1/2" OD with .25" thichness to become red hot with 2000 w induction furnace. I plan to expand end of tubing about 4"-5" long. Thanks.

[chistyakov1971]

Now I work over the similar furnace.
I can not give consultation