Can I do this at home? Induction forge ?

[vicegrip]

http://www.youtube.com/watch?v=MQJna...FC6B&index=170

Wow easy to construct ??
http://www.youtube.com/watch?v=I_gFJ...FC6B&index=174

Any health risks?
http://www.youtube.com/watch?v=y_-Iv...FC6B&index=173

VG

[usmcpop]

Yeah, you could. It's rather violent for decent alloy steels, methinks.

[ptsideshow]

You may want to be careful with some of the stuff on the you tube/stupid .com As a lot are not what they seem or they leave important things out, like building it safely. As in the plasma cutter that has 220 across the ground, and table and nozzle with no breakers or safety. The guy's warning was don't touch it in use. So many with out a clue where answering and commenting on building it he stopped answering the questions in the comments. But when somebody gets fried their family should have an easy win with the lawsuit.

When Dentists, made the crowns and other teeth caps and bridges in house they used inductions melters, some jewelers still use them.

Here is a picture of an old induction melter centrifugal caster unit made in Italy from the 50's and 60's

The workings inside

The crucible and induction coil,

This is a type for melting metal,
You can also build one for just heating up for forging, or heat treating.
Here is a link to a good site with great info, and clear pictures.
http://www.richieburnett.co.uk/indheat.html
Also do a google search you will turn up a bunch some good, a lot bad to dangerous.
Check out the blacksmiths sites as some have had a number of threads on the induction heating forge furnaces. They do spin the meter

[ptsideshow]

Another don't do this at home vid

Here is one of the reasons why you shouldn't want to copy everything you see on Stupid tube
http://www.youtube.com/watch?v=KAplLEjTriE

As you can see at the end he isn't wearing a shield and he probably borrowed the US Navy coveralls from his sisters current boyfriend. safety job one!

[vicegrip]

When Dentists, made the crowns and other teeth caps and bridges in house they used inductions melters, some jewelers still use them.
The crucible and induction coil,

This is a type for melting metal,
You can also build one for just heating up for forging, or heat treating.
Here is a link to a good site with great info, and clear pictures.
http://www.richieburnett.co.uk/indheat.html
Also do a google search you will turn up a bunch some good, a lot bad to dangerous.
Check out the blacksmiths sites as some have had a number of threads on the induction heating forge furnaces. They do spin the meter

Thanks for putting up the info!!
I worked with a tech from Pillar for a while in the 80's.
But we parted before I could obsorb much of what he was talking about.
Been courious ever since.

VG

[usmcpop]

These folks make induction heating stuff up to 16,000 kW.

http://www.ajaxtocco.com/default.asp?ID=2

[usmcpop]

May I suggest you read through this, which may be a good intro to the whole thing:

http://www.richieburnett.co.uk/indheat.html

[ptsideshow]

The coils, in the dental caster I pictured are copper tubing with water flowing thru the inside and the electrics flowing thru copper to heat the crucible to melt the metal. There are all sizes and types and configurations of induction heaters used in the manufacturing of all type of products from the soldering of eyeglass frames by the clamps holding the parts induction heating. To all most any thing you are willing to pay for. There are heating and large industrial induction melting furnaces to heat treating systems. After reading the site in the UK that I and POP listed as it is the best one with no BS on it. Doing some searches and a look through Thomas Register for companies that build the various units. You probably will still need to do some serious study playing with 480/3Ø power.

[enlpck]

Long response (due to too much coffee today?)

The magnetic field from the coil is what transfers energy to the work piece. It is strongest in the center of the coil, but the field extends out of the coil and around it, as well. The coil design influences how efficiently energy can be transferred to a workpiece in a given position (inside the coil, out side the coil in line with the coil axis, outside the coil to the side, etc) Generally, a workpiece inside the coil will heat fastest, as the magnetic field is strongest there.

Pretty much any induction heater is going to need conductors that have integral cooling. This means that the primary coil will be tube. The current is carried by the tube material.

The coil material itself has little to do with how fast heating takes place or what the final temperature is, other than due to the ability to keep it cool. It carries a high current (as it few turns and must provide a high power), so copper or silver are pretty much the only practical materials, both due to the electrical conductance adn the thermal conductance (which go together). Aluminum could be used, but the losses would be higher and cooling would be tougher, at a given power level.

At the operating frequency, the current is carried primarily near the surface of the conductor. The thickness is determined by the skin depth, and for reasonable efficiency a tubular conductor should be AT LEAST two skin depths thick, preferably five or more. Not diameter, wall thickness. At five depths, you have about 99% of the conductance of a solid conductor of the same diameter. The current drops off as an inverse exponential function of thickness. The skin depth is where the current is e^-1 of the surface current.. this is about 0.37. Is the conductor isn't significantly larger in diameter than the skin depth, then the current distribution won't follow this rule exactly, and if the conductor is of the same scale as the skin depth (wall thickness for tubular conductors, diameter for solid conductors), the current will be roughly uniform throughout the thickness. At high frequencies, where skin depth is small, this is very important to consider. For an efficient induction heater, the frequency is high enough for this to be considered. At lower frequencies, like the 60Hz use for power distribution, the skin depth is great enough that it isn't important for most practical conductors, and the current density is nearly uniform throughout.

At 100KHz, skin depth for copper is about 200 microns (8 thousandths of an inch), so pretty much any copper tubing is fine. For aluminum, the skin depth is about 260micron, but the resistivity is nearly twice that of copper.

For reference, at 60Hz, the skin depth is about 1/2" in copper, so nonuniform current density has little effect on a conductor less than about an inch in diameter, and only becomes significant at about 2" diameter. At about a 4" diameter, more copper doesn't buy much at 60HZ. (for smaller wires, with radius one skin depth or less, give or take, current density is uniform throughout the conductor, and since doubling the diameter gives four times the cross sectional area, the current capacity goes up by a factor of a bit more than three, limited by the heat dissipation ability going up with surface area. Once diameter is much larger than about 10 or so skin depths, the current capacity goes up directly with diameter, doubling for a doubling in diameter, and any material in the middle does nothing for current carrying ability)

Since the operating frequency needs to be up fairly high for efficient induction heating, a substantial power supply is needed, either a switching supply or a resonant supply. The only thing about the feed to the supply that really matters is how much power can be delivered. Whether it is one phase or three phase only determines a few details of design.



All of this said, design of an induction heating system that will be functional and safe is not a simple task. There are a lot of factors that arn't obvious and are not easy to analyse. It is not an area where you will be successful without a lot of background study. A good knowledge of circuit analysis is critical (If Laplace Transform and differential equations don't ring a bell, you are at a disadvantage) as well as the physics of magnetic fields and materials, at a minimum. This is not the type of project most people will get into as a weekend quickie.

Looked at a few of these links and videos on youtube, also recalling some past experience watching a guy at a salvage yard remove glass with one and I have a couple questions that maybe someone here can answer? I am still having a bit of difficulty wrapping my head around how it actually works but...

First is, it seems that an object placed within the work coil heats up rather quickly (obviously this has to be a function of the frequency, voltage and amperage fed to the work coil) but it seems to me that many inductive heaters (such as this one: http://www.theinductor.com/) advertise their ability to heat up obects near but outside of the work coil, such as I've seen at a wrecking yard as used to remove glass from a wrecked car. Does this work outside of the work coil at a slower rate just due to the proximity to magnetic field? Then is a work coil designed differently if its primary usage is to heat objects not contained within the wrappings of the coil?

Second is, I'm intriqued by this concept and interested in building one of my own based on some websites I've visited that make this seem not terribly hard - I do already have a lot of electronics tools and some experience to make it happen (Oscope, DMM, soldering iron, wire tools etc) and, since I would use this mostly if not entirely at work if I wanted to make a BIG one I have access to 220/1ph and 480/3ph power. I am curious about a couple of design considerations:
1) for a larger one (not thinking about making a big one right away just curious) would it be suitable to make the work coil out of copper tubing to watercool, or are the watercooled ones using copper tubing wrapped around a core wire of some sort?
2) I have not yet grasped what effect the material the work coil is made of has on its abilities to heat an object up/time to a given temperature? What effect would it make to create a work coil out of steel wire? Aluminum? All the projects I've seen online have used copper wire
3) How is the thickness of the work coil material determined? Overall length? Number of coils? What effect would it have to space the work coil a longer distance away from the power supply?

Hope someone can answer these for me if not I guess I'm going to spend some serious hours studying a few high voltage project forums...

[vicegrip]

Long response (due to too much coffee today?)

(If Laplace Transform and differential equations don't ring a bell, you are at a disadvantage) as well as the physics of magnetic fields and materials, at a minimum. This is not the type of project most people will get into as a weekend quickie.

Sorta counts me out.

"Spendifforace" is about my upper limit.
Thanks for the usual definitive brakedown.
Cheers
VG

[uncrichie]

I don't know about being that close to all that RF energy? I suppose the risk is dependant on the design. Making a homemade one a real crap shoot! But I have to admit, "that is really neato cool". It sure would be handy to heat up small items before hammering instead of firing up the oxy/acet torch all the time. Uncrichie.