Induction furnace

[Warpspeed]

Really good info there Geof. I believe then, that just about any low cost mineral based automotive oil should be up to the job. Synthetic oil may be even better?

The only contaminant I see as being a potential problem for us is water. If the oil system is vented to atmosphere, it will breathe as the system is thermally cycled. Normal humidity in the air, over time, would slowly trap condensation inside the oil system, potentially leading to a very slow buildup of water in the oil. That is no big deal. Automotive brake systems suffer from exactly the same problem. Most brake fluids being very slightly hygroscopic will absorb a small amount water, which could then flash into steam in the brake calipers under extreme use.

The solution is rather simple. The oil top up reservoir just needs a big floppy diaphragm seal under the screw cap. A pin hole in the cap vents to atmospheric pressure, but the diaphragm creates a flexible pressure balancing barrier, that isolates the air inside the oil reservoir with outside air. The system can breathe and allow for expansion of the oil, but no water vapor can enter the system. A standard plastic remote mounted brake fluid reservoir with its special cap and seal should work fine for us. That would be ideal, because the oil top up reservoir needs to be located at the highest point of the system to prevent oil drain back from flooding the reservoir.

Another step in this direction would be to use a normal automotive screw in engine oil filter, and fill it up with some silica gel crystals. That would dry the oil, and the filter element would trap any stray particles. It would also prevent the silica gel from circulating around with the oil.

All this is probably far too much trouble to go to. If an induction heater will work with a 100% water based cooling system, a minute amount water in an oil based cooling system is hardly going to be catastrophic. But I still believe that oil may make a far better cooling medium than water, for both electrical and corrosion reasons.

[jc56au]

Considering the use of refractory around the crucible a fairly key point is efficiency in reducing radiant heat loss. This is proportional to the fourth power of the temperature (Stefan-Boltzmann law). Assuming the aim is to melt metal the losses due to radiant heating are likely to be much more than those due to coupling with thing other than the charge.

Another of the reasons why induction melting doesn't scale down very well.

[Warpspeed]

An interesting point there jc.

All the castable refractory I have seen has been a white colour, which should reflect radiant heat energy fairly well back into the melt, even if the refractory itself does not get that hot. I am guessing it should all still scale down, particularly if a higher operating frequency is selected.

I now have a working oil pump, which is a typical vane type power steering pump running at 950 Rpm. This pumps just under a gallon a minute of automatic transmission fluid (mineral oil), and almost fully loads the 1/2 hp drive motor. The next step in all this will be to assemble all the components of the 15Kw dc power supply, and the oil cooling system onto a large piece of reinforced 3mm aluminium sheet.

[Shawn D]

Well people, I've been traveling around for a while and honestly forgot to check back on this thread for over a month.

Warpspeed - can you give us an update on your progress?
BTW, I would just stick with water or water/glycol mix for the cooling medium. Use a refractory cast coil to keep the molten metal off the coil.
Just my humble opinion.

97T - so, you've peaked my curiosity. We've met a couple of times, the induction industry is like living in a small town, everyone knows, or knows of everyone else. Drop me a pm.

[Warpspeed]

Shawn, progress has been slowed by having to repair some major car engine problems, and various other annoying little distractions. But I am now firmly back on track.

Before I could really begin assembling anything, I needed to get and test all the larger and more important parts to figure out how it was all going to go together. That stage has only now been reached, and just yesterday I welded up a steel angle frame.

Here are the major parts. A 15Kva transformer, one gallon per minute oil pump, fan coil unit, and the all important 20Khz tank components. The steel frame has just been painted with zinc chromate primer only hours ago, and is not yet properly dry.

[FPV_GTp]

Hi

I will give you credit guys , some very impressive ideas and working induction furnaces.

Dammmmmmmmmm i need more hours in a day and a extra set of hands .

Seems i have to stick to my LPgas fired furnace for now

keep up the good work guys

cheers

[Warpspeed]

O/k guys, further update on progress.

I now have all the heavy low tech and not very interesting "life support system" components mounted into the main frame, and on wheels.



The electrical system comprises a three phase auto transformer, 240v 20Amps per phase in, 175v 27 Amps per phase out continuously rated. It has a 100 ohm 225 watt soft starting resistor in one phase only, operated from a 0-5sec time delay relay and contactor.

I still have to provide a 20Amp three phase circuit breaker and an ac ammeter. These will be mounted on the outer sheet metal covers that will probably be about the last thing to be done.



The oil cooling system part of it is now complete. It consists of the tall grey neck, which is an air separator and reservoir for the hot return oil. It holds one litre when half full. This feeds the Toyota power steering pump driven at 950 rpm with a half horse motor. The oil then flows through the fan coil unit fitted with a 1,200 cfm fan. Actual measured airflow is around 850 cfm. Oil from the fan coil unit then goes through a small automotive oil filter.

All of the more interesting stuff will be mounted onto a single large flat 3mm aluminium plate. This plate will bolt on top of the frame with the six mounting holes visible in the picture. This plate will be readily removable from the top of the main frame for convenience. Oil and power connections to the main electronics will be arranged to be very easily and quickly disconnected.

Now all the big heavy stuff is completed, I can concentrate on the more interesting electronics fitted onto this aluminium top plate. The next thing to do, will be building the rectifiers and dc power supplies.

[Geof]

You do realise that real backyard boffin would have tacked everything together with baling wire and sellotape. That looks far too professional .

[Shawn D]

Originally Posted by Geof You do realise that real backyard boffin would have tacked everything together with baling wire and sellotape. That looks far too professional .

I agree. I don't think I've ever assembled anything at home that looks as nice as your project Warpspeed. Good work.

[Warpspeed]

Rectifiers and filter capacitors have been fitted to the top deck plate, easy and there is not much really to show. The common mode choke for the three phase rectifier, is also now complete and bolted down.


Next job on the list is the 4mH 35 amp high frequency inductor for the buck regulator, mainly because it will be so large that other components will need to fit in around it. Planning this has been a fairly frustrating exercise.

My first approach was to use four great slabs of powdered iron arranged in a rectangle, and the ideal material to use would be the Fluxtrol flux concentrating material sometimes used with induction heaters. That idea rapidly died when I received a quote of $1,800 dollars for four pieces considerably smaller than I required.

Attempt number two was a redesign using a stack of the largest powdered iron toroids available. Something around five inches in diameter and six inches tall would have been about right, requiring around 250 turns. The only cores available ex stock were of a completely unsuitable material. Being toroids there is no air gap to adjust. What you buy is what you get and impossible to do anything with if it does not work out as expected. I was quoted FOUR MONTHS delivery on suitable cores. So that idea was shelved.

The other problem with toroids is the difficulty of winding, especially something on this large a scale, so I went back to the patient and long suffering powdered iron core sales rep, and inquired about the largest available powdered iron E cores. He never even bothered to get back to me.

That left ferrite cores as a possibility. Ferrite is less desirable because it saturates at only around a quarter of the flux density of powdered iron, and it is far more expensive. Anyhow I scrounged eight sets of large UI cores that will do the job, and as they were free, the price was right. Just as well because new ones would have cost me $480.

The C coress shown in the lower right of the picture were what I intended to use originally when I was thinking in terms of 5KW maximum power. This whole project has now morphed into 15+ KW thinking, so the eight sets of UI cores will be what I will be usinge. There is 9Kg of ferrite there !

[FPV_GTp]

hi Warpspeed

I must commend you on a very professional undertaking in a electric furnace . Ideal one just flicks a ON/OFF switch and away you melt.

Very expensive to man this electric furnace and probably beyond the average backyard hobbyist.

That's why i chose my trust LPgas fired furnace , i experiment with a few different size LPgas torches and wooooooooooo some of the heat i can put out is enormous. It is clean burning and works great to and cheap to make and run also.

The main reasons i built a LPgas fired furnace is cause i get old discarded LPgas tanks form fitters around my area for nothing and generally there well over hal full of LPgas. Scrap metal yards will not take LPgas tanks for scrap unless there completely empty and all the valving removed . Otherwise there is a dangerous element that they could have a LPGas explosions in there scrap metal facility while processing the scrap metal.

Here in Australia the LPgas units fitted to vehicles and machinery have to be inspected every ten years the gas storage tanks. Some gas tanks are not re-used as to have a inspection done and the tank brought upto todays standards exceeds the cost of a new tank , so alot of old tanks are just pulled out and thrown away.

My LPgas torches , some times i use to 2 inch torches to melt large sums of metal quickly and when i have both or even one running on over 30psi LPgas pressure they sound like jet fighter planes flying over my workshop. When i run them on around 5 psi Lpgas pressure they just sound nice .

I modelled my torch of this website

http://members.optusnet.com.au/terrybrown/welcome.html
http://members.optusnet.com.au/terry...PGasTorch.html

http://home.earthlink.net/~jschwytze...e_furnace.html

http://www.nhsouth.com/crafts/workbench/lptorch.htm

http://www.backyardmetalcasting.com/refractories.html

The flame is over a meter long and about 15 to 20 cm wide in a section , looks awesome at night starts.

It took me a while to get the jetting right for the correct burn ratio of the flame , it is colorless and odorless the burning flame. No external fans required to aid in additional air for the flame.

Like i said it sounds awesome when one cranks up the gas pressure
I melt 10 to 20 kilos of aluminum in anyone pour a very quick time once i have heated up the furnace.

I am in the process of gathering materials for a bigger furnace build so i can melt larger quantities of metal. one 25 kg Blast Furnace Refractory cement is $55 per bag and i need 30 bags

This is a awesome build can't wait to see it in action though.

Warpspeed , keep up the good work.

[Warpspeed]

Propane works very well for melting aluminium, and with a well designed burner and furnace, copper and bronze too. But melting iron or steel is just not going to happen with a basic propane fired furnace.

Even with a flame a hundred feet long, the temperature is just not there. Gas welding steel with a propane/air burner is just not possible.

Natural gas is just as good as propane, and only a fraction of the cost, at least in Australia it is. To tune your burner, try hooking up an automotive exhaust oxygen sensor. It will give a very sensitive indication of correct stoichiometric air/gas ratio and maximum peak flame temperature.

A decent sized induction furnace is certainly not a low cost beginners project, that's for sure. I don't even know if this is going to work. The internet is littered with failed induction furnace projects where people have given up trying to reach decent power levels. But I am willing to give this a try, no matter how it eventually turns out.