Information on metallurgy, casting and foundry work

[ken572]

Hi-cycle or frequency induction furnaces are prefered now because of the properties and 'activating' the metal in the vessel by the magnetic currents imposed. (self stiring)

Anyone got a picture of the above furnaces? Or a free sample ;-}

Bob,

This should give you a start

http://www.chaski.org/homemachinist/vie ... 44&t=96630

Ken.

[Pipescs]

The order from petrobodforsale.com was sitting on my back porch when I came in today. Order was placed on line the 19th of the month.

I came in USPS boxes at around 35 pounds each. Much easer to handle than the hundred pound box I received years ago from Budget Casting Supply.

Took Fenders lead and stored this batch in 3.00 buckets from Lowes. One change I made is to not put fifty pounds on a five gallon can. It is now 35 pounds per can. Much easier on the back.

This gives me two hundred pounds total to work with now.

Cost was 149.00 for 105 pounds. No shipping charge.

[Harold_V]

Hi-cycle or frequency induction furnaces are prefered now because of the properties and 'activating' the metal in the vessel by the magnetic currents imposed. (self stiring)

Anyone got a picture of the above furnaces? Or a free sample ;-}

There's not really much to see. The power supply can be huge (mine weighs 6,000 pounds, and is a motor/generator unit). Such units are considered to be second generation furnaces. First generation were large transformers and a spark gap (usually mercury). Third generation induction furnaces are solid state, and weigh much less.

In so far as the actual furnace is concerned, not much to see. The (copper) coil (which is water cooled) is embedded within the refractory material that surrounds the melting chamber. Typically, melting is accomplished directly in the furnace, sans a crucible, although there are crucible type furnaces in existence. Water cooled leads connect the power supply to the furnace.

Envision a somewhat square box with a pour spout on the top, with trunnions that permit the furnace to be tipped and you pretty much have the full picture. The pivot point of the trunnions is such that the spout remains stationary (aside from rotating with the box) as the box is tilted, so the stream of molten metal can be properly directed.

They operate virtually silently, although you may hear a high frequency squeal, which I've experienced when seeing them operate.

Harold

[RCW]

Ok. You got my curiosity up. Found a picture on-line. Don't know if a Chinese import is a good idea, but sure would like to have something in my shop that looks like this picture (exactly as Harold described!)
http://ae-bds.en.made-in-china.com/prod ... ABDS-.html

[Harold_V]

One must know a little before jumping in. Size of furnace is frequency reliant, for example. If you were to apply a 1,000 Hz machine to a small furnace (say a 10 pound capacity), it wouldn't melt, although it might create some heat. They operate through a reasonable range, but achieve maximum efficiency at the proper frequency for the furnace size. In addition, how the furnace is charged makes a difference, as it affects heat generation. If miniscule particles are to be melted, without a heel to be heated, you'd need a much higher frequency power supply in order to induce the necessary heat.

To my knowledge, the modern induction furnace pretty much runs without intervention from the operator, but that's not true of the first and second generation machines. Because reactance changes as the charge melts, power factor correction is required constantly, and is accomplished by switching in or out a series of capacitors.

I'd be cautious about investing the kind of money an induction furnace costs if it was made in China. My chief concern would be the availability of replacement parts. While their units are not cheap, they are far less expensive than American built furnaces of the third generation.

Another consideration. Unless I didn't explore deeply enough, I took note that they were discussing a 380 primary voltage. That could prove troublesome for US individuals, as that isn't a common voltage for us. I was somewhat further alarmed to read of the limited melting capacity of the units offered. My 50 kw unit should be capable of melting 200 pounds of steel, although an ideal charge would be 100 pounds (determined by the coil and furnace). As the volume of the charge increases, so, too, does melting time. I would expect that a 50 kw unit would be recommended for melting 100 pounds of ferrous materials. If I'm wrong, please feel free to correct me.

First generation units (transformer and spark gap) were reputed to operate @ 25% efficiency, with the second generation machines (motor/generator) operating @ 50% efficiency. Third generation machines approach 100% efficiency, which is what troubles me about the limited melting capacity of the Chinese unit. It must be very light duty, or well under rated. I have no clue which would be true.

If you're interested in induction melting, it wouldn't hurt to keep an eye open for a used second generation unit, similar to mine. They appear on the market occasionally, and have been known to be procured for as little as a few hundred dollars. There are a few makers, one of which is Inductotherm, who marketed smaller units. I am aware of both 20 and 30 kw units. Ajax Magnethermic, too, made smaller units, although they don't appear to be as common as the Inductotherm. The problem is, they (all) require 3 phase service, so you may be limited in options. If you were to get a small enough unit, it most likely would operate on single phase, but it would also be quite limited in its capability, so you couldn't cast large items.

I was discussing frequency. My unit has an output of 3,000 Hz. (@ 400 volts) They (Ajax Magnethermic) built the identical unit that operated @ 10,000 Hz, What it would be used for would determine the required frequency, along with furnace capacity. If one intended to melt chips, for example, the 10,000 Hz machine would be a better choice than the 3,000 Hz machine.

As size of the furnace increases, the frequency demand is lowered. There are line frequency induction furnaces, but they are huge--far beyond anything a home shop would even consider (50 ton capacity, for example).

Hope some of this helps.

Harold

[ken572]

One must know a little before jumping in. Size of furnace is frequency reliant, for example. If you were to apply a 1,000 Hz machine to a small furnace (say a 10 pound capacity), it wouldn't melt, although it might create some heat. They operate through a reasonable range, but achieve maximum efficiency at the proper frequency for the furnace size. In addition, how the furnace is charged makes a difference, as it affects heat generation. If miniscule particles are to be melted, without a heel to be heated, you'd need a much higher frequency power supply in order to induce the necessary heat.

To my knowledge, the modern induction furnace pretty much runs without intervention from the operator, but that's not true of the first and second generation machines. Because reactance changes as the charge melts, power factor correction is required constantly, and is accomplished by switching in or out a series of capacitors.

I'd be cautious about investing the kind of money an induction furnace costs if it was made in China. My chief concern would be the availability of replacement parts. While their units are not cheap, they are far less expensive than American built furnaces of the third generation.

Another consideration. Unless I didn't explore deeply enough, I took note that they were discussing a 380 primary voltage. That could prove troublesome for US individuals, as that isn't a common voltage for us. I was somewhat further alarmed to read of the limited melting capacity of the units offered. My 50 kw unit should be capable of melting 200 pounds of steel, although an ideal charge would be 100 pounds (determined by the coil and furnace). As the volume of the charge increases, so, too, does melting time. I would expect that a 50 kw unit would be recommended for melting 100 pounds of ferrous materials. If I'm wrong, please feel free to correct me.

First generation units (transformer and spark gap) were reputed to operate @ 25% efficiency, with the second generation machines (motor/generator) operating @ 50% efficiency. Third generation machines approach 100% efficiency, which is what troubles me about the limited melting capacity of the Chinese unit. It must be very light duty, or well under rated. I have no clue which would be true.

If you're interested in induction melting, it wouldn't hurt to keep an eye open for a used second generation unit, similar to mine. They appear on the market occasionally, and have been known to be procured for as little as a few hundred dollars. There are a few makers, one of which is Inductotherm, who marketed smaller units. I am aware of both 20 and 30 kw units. Ajax Magnethermic, too, made smaller units, although they don't appear to be as common as the Inductotherm. The problem is, they (all) require 3 phase service, so you may be limited in options. If you were to get a small enough unit, it most likely would operate on single phase, but it would also be quite limited in its capability, so you couldn't cast large items.

I was discussing frequency. My unit has an output of 3,000 Hz. (@ 400 volts) They (Ajax Magnethermic) built the identical unit that operated @ 10,000 Hz, What it would be used for would determine the required frequency, along with furnace capacity. If one intended to melt chips, for example, the 10,000 Hz machine would be a better choice than the 3,000 Hz machine.

As size of the furnace increases, the frequency demand is lowered. There are line frequency induction furnaces, but they are huge--far beyond anything a hope shop would even consider (50 ton capacity, for example).

Hope some of this helps.

Harold

Harold,

Thanks for the great write up.

Very informative.

Ken.

[RCW]

Let me echo Ken's "Thanks!"

And follow it up with a dumb question. Are induction units only for ferrous metals?

[Harold_V]

Are induction units only for ferrous metals?

No. Virtually any substance can be heated (think of a microwave oven, which operates in similar manner). Again, frequency is critical. For non-conductive things to be heated, frequency must be exceedingly high.

I'm not an electrician, nor an EE, but as I understand the operation, eddy currents are induced in the chamber, which is considered to be a shorted secondary. These eddy currents do the melting, and the stirring as well. The stirring action borders on being violent, so the charge tends to be quite homogenous.

Nice thing with an induction furnace is that the charge isn't altered by the melting action. For example, if one introduces steel to an induction furnace, it yields steel in return. If steel is introduced to a cupola, the end product is cast iron. Further, they are, more or less, unlimited in their ability to heat to high temperatures, although one is limited by the refractory choice. As a result, metals such as platinum, which melts at 3,215° F, can be melted with ease.

Harold

[Pipescs]

New Question.

Will adding zinc to a questionable mix make it brighter?

[RCW]

I'd be cautious about investing the kind of money an induction furnace costs if it was made in China.

"Cautious" is a kinder word than I would have used. I was only looking for a picture.

Another consideration. Unless I didn't explore deeply enough, I took note that they were discussing a 380 primary voltage. That could prove troublesome for US individuals, as that isn't a common voltage for us. I was somewhat further alarmed to read of the limited melting capacity of the units offered. My 50 kw unit should be capable of melting 200 pounds of steel, although an ideal charge would be 100 pounds (determined by the coil and furnace). As the volume of the charge increases, so, too, does melting time. I would expect that a 50 kw unit would be recommended for melting 100 pounds of ferrous materials. If I'm wrong, please feel free to correct me.

You're seldom wrong unless you are writing in the thread on "Cats."

If you're interested in induction melting, it wouldn't hurt to keep an eye open for a used second generation unit, similar to mine. They appear on the market occasionally, and have been known to be procured for as little as a few hundred dollars. There are a few makers, one of which is Inductotherm, who marketed smaller units. I am aware of both 20 and 30 kw units. Ajax Magnethermic, too, made smaller units, although they don't appear to be as common as the Inductotherm. The problem is, they (all) require 3 phase service, so you may be limited in options. If you were to get a small enough unit, it most likely would operate on single phase, but it would also be quite limited in its capability, so you couldn't cast large items.

Big problem. Many of us are on electric co-ops and only have single-phase 220. You mention "motor/generator units." Goofy idea, but could one substitute an internal combustion prime mover for the motor, without having to re-invent the wheel? It's not like hobbyists will be running it 16 hours a day, six days per wek.

Hope some of this helps.

Harold

You almost always help. That's one reason I'm addicted to this forum.

[Harold_V]

Big problem. Many of us are on electric co-ops and only have single-phase 220. You mention "motor/generator units." Goofy idea, but could one substitute an internal combustion prime mover for the motor, without having to re-invent the wheel? It's not like hobbyists will be running it 16 hours a day, six days per wek.

In lieu of that option, it would most likely make more sense to simply purchase a surplus generator. I gave that option some thought before investing in my 3 phase service, but was turned off immediately when I considered that I'd need about 150 kw of generator to operate the 50 kw induction furnace. Might have even gotten by with one somewhat smaller, as the large units tend to be equipped with soft start. However, that didn't solve the problem for the balance of my equipment, and the fact that the size genset required would consume about 9 gallons/hr fuel, it made it easy to commit to having three phase installed. With fuel now at nearly $4/gallon, it makes all the more sense.

The sole problem, as I see it, is that the motor and generator are on a common shaft, so you can't really eliminate the motor portion. To complicate things a little for my unit, it's a vertical motor/generator. Why, I do not know. I've seen a 100 kw Ajax Magnethermic and it is not.

I have had three phase service at three different addresses. The third one is the only one that cost me anything. I also learned that most of the power supply entities love telling the consumer that they can't have three phase power. They tried that with me when I applied for my second service, at the castle. I stood my ground and told the rep to get his superior, as I came to get hooked up with three phase power and would settle for nothing less. If they failed to cooperate, I'd involve the public services commission, as they had a monopoly and were required to provide the needs of the customer. The tone of the rep changed immediately. His comments of it would be too expensive and not available, anyway, changed to one of total cooperation. I ended up signing a guarantee of consumption and got my service free of charge. They had to set poles and transformers, so it was not a simple matter.

Harold

[rrnut-2]

Harold,

Excellent description of induction melting. One way of thinking about how the systems works is this; picture a transformer with the secondary shorted. It will get hot and melt.

All of our old motor/generator units were horizontal shaft. Yours was the first vertical that I have seen.

I did buy a 175kw Inductotherm solid state unit about 10 years ago, and resold it to a small foundry here in NH. He powered it with a diesel generator. Three phase power
was miles away and he didn't want to pay for it to be installed.

Jim B