One man's insanity---the story of an induction furnace

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rrnut-2
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Re: One man's insanity---the story of an induction furnace

Post by rrnut-2 » Tue Feb 06, 2018 5:40 pm

We used phenolic for the insulators. Most of our furnace parts were made of aluminum, but parts still get hot.
I gave Liz a hug for you. Give Susan our best.

We are hoping to make Train Mountain this year, but see my PM

Jim B

rrnut-2
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Re: One man's insanity---the story of an induction furnace

Post by rrnut-2 » Tue Feb 06, 2018 5:58 pm

Just watched your video...WOW...that brings back memorys. Looking good!

Jim B

John Hasler
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Re: One man's insanity---the story of an induction furnace

Post by John Hasler » Tue Feb 06, 2018 10:48 pm

Asbestos is just about ideal for this application. It's quite safe to machine it as long as you keep it wet.

Treasure your asbestos supply. There will never be any more.

Harold_V
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Re: One man's insanity---the story of an induction furnace

Post by Harold_V » Wed Feb 07, 2018 2:35 am

John Hasler wrote:
Tue Feb 06, 2018 10:48 pm
Asbestos is just about ideal for this application. It's quite safe to machine it as long as you keep it wet.

Treasure your asbestos supply. There will never be any more.
I was gifted a large stack of one type, light brown in color, many, many years ago, while it was still available. I put some of it to good use in building the custom filtered fume hood I needed when I was actively refining gold and other precious metals. I still have a large supply, which is in 1¼" thick sheet, about 18" wide and 8' long. I also have a small amount of what was known as Colorlith, and some Transite. I have no clue what the thick stuff was called, but it appears to be bonded with some type of plastic. The remnants I received were leftovers from making countertops. This all occurred right when action was being taken against the use of asbestos, and it was still available, although already tainted by its reputation.

I wear a good respirator when I machine this stuff, and run a vacuum cleaner (built in, twin motors) that discharges fine particulate matter out of doors. The vacuum cleaner has a cyclonic separator, with no filter to clog. As we live in a remote area, on 5½ acres, I feel reasonably safe in doing so.

On the subject of machining wet. I had to make some spacers for the coil (a long story which I will detail in the near future). The piece of Transite I used was outside in the rain. I found it machined wonderfully while wet, which I had never tried before.

H
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Re: One man's insanity---the story of an induction furnace

Post by neanderman » Wed Feb 14, 2018 1:56 am

I am humbled in your collective presence.
Ed

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Harold_V
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Re: One man's insanity---the story of an induction furnace

Post by Harold_V » Sun Feb 25, 2018 2:53 am

Ok! I got the covers painted, then I turned my attention to the electrical portion of the power supply. I began by reinstalling all of the indicator lights and switches that were removed for painting. The process was relatively uneventful, although one of the contacts for an indicator light broke. It was soldered originally, and under spring pressure, but a little shimming allowed me to extend the terminal so it could be re-soldered.

I had a bit of trouble following some of the wires when reattaching, although in the end all was well. While the wires are all identified with tags, some of the tags were buried in the loom.

I had previously removed the switch used for switching the capacitors. It had been rusted to the point where it would not function. A simple device, a series of cams which active a serious of microswitches, which, in turn, activate numerous contactors. The shaft was polished, along with related components, with contacts cleaned, then it was re-assembled, and had been placed in storage until needed. It was retrieved and installed. I now regret I took no pictures of that operation. I also dismantled the switch used for switching the furnace voltage, and didn't get pictures of that, either. There's a high frequency transformer included with the machine, with eight positions. Voltage is selected so full power can be achieved, plus the capacitor switch allows for power factor correction, so the unit operates at unity. The contacts were burnished and the switch cleaned up and lubricated, then reassembled.

It is important to understand that power factor is ever changing with an induction furnace, as it relates to the state and size of the charge. As it melts, unity shifts, so it requires constant attention. The third generation of induction furnaces are solid state, with power factor adjusted without intervention. My dinosaur unit (motor generator) lacks that nice feature, but I'm happy to have the unit, as a solid state induction furnace is well beyond my finances.

In order for the generator to not be able to run wild, there's a detector (a lightning arrestor is used) to instantly kill the power that excites the generator. A disruption of power to the furnace can give cause for an almost instant high voltage spike of the generator, so this unit is intended to prevent such a situation, which destroys the generator. There is no simple test to determine if the arrestor was good, or not, so I perused ebay to see if I could find a new one. Turns out the one in the machine is obsolete, but the replacement, which mounts slightly differently, would suffice. I found an offer to buy them, new, for $20 each, so I purchased a pair, one as a backup, should it be needed. I had to modify the mounting ever so slightly, but it installed without issue. That circuit is activated ONLY upon failure, at which time the far left red light on the control panel is lighted. It is never lighted otherwise, not even upon starting the unit. All of the others show red until they are reset, which then permits the motor starter to engage.

While the 400 amp disconnect had power, I had not yet run leads to the supply, but I wanted to determine if the control circuits were operational. In studying the prints (provided to me years ago by Ajax), I determined that the entire control system operated on 120 volts, so I removed the secondary leads from the transformer in the power supply and connected the two leads directly to 120 volts. By shunting the water pressure switch, I was then able to try each of the controls. I was not pleased, as the exposure to weather, coupled with the many years the unit sat out of service, the control relays were not reliable, and the relays that switch the capacitors, as well as the contactors for the motor starter and the furnace power were extremely noisy.

When the button was pushed to reset the relays, a necessity in order to start the motor/generator, some of the control relays would, some would not, and it wasn't always the same units that failed to work. Here's a picture of the relays, which are the seven square items in the second row of components.
Original relays.jpg
Failure of the relays to reset was random. That would make the startup of the unit questionable, so I tried to find new relays, only to discover that they were obsolete, thus, no longer available. It was virtually impossible to access the contacts so they could be cleaned, as the assemblies were staked together, and the lower set of contacts were not accessible even when they were opened. I decided that new relays would be required, so I perused ebay until I found a deal on several, which were purchased. They were easily changed to function as needed, so I decided to mount them at the bottom of the panel, where there was just enough room to do so without interfering with other details inside the cabinet. I also concluded that using the original relay bases would simplify wiring, so each relay was gutted, and a grommet installed in the left side of the housing so wiring could be introduced through the housing. A proper sized grommet was fitted to protect the wires from the sharp edges of the thin sheet metal covers. By removing the original contacts, I could solder the wiring to the holes where they were mounted. That required bending them, so the lower contact could be removed, which was to my benefit, as it allowed for much easier soldering. You can see the added relays in the picture, below, along with the wiring leading to the original relay housings. There was adequate room to mount the new relays under the existing electrical devices, so I made a rack and did so.
New relays.jpg


The circuit discussed above, the one with the lightning arrestor, triggers a DC circuit. It required a different relay, which you can see is clearly different from the AC relays. It's the one on the right. Interestingly, this power supply is old enough that rectification for the various DC circuits is accomplished by various selenium rectifiers. I was really showing my age when Patio and I discussed them. He is a modern day electrician and had never experienced one.

I addressed each of the contactors by burnishing the contacts, and hand cleaning the rust on the armatures that was preventing each from making intimate contact. That eliminated the vast majority of the noise each was making, although they all have the characteristic hum of such items. I figured the limited noise wouldn't be much of an issue when the unit was in operation, so I considered my efforts to be a success. They all worked, and I could move on with other issues.

Out of time for now, but I'll add to this in the near future. Thanks for looking.

H
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NP317
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Re: One man's insanity---the story of an induction furnace

Post by NP317 » Sun Feb 25, 2018 11:15 am

Wow! You are working like an obsessed person on that project! (compliment.)
Classy rewiring for the new relays!

I recognized the selenium rectifier with the cooling fins. My experience with those is that they exhibit increasing leakage with age.
If you haven't already done so, check them out for proper operation. I've replaced my share of those with modern diode rectifiers.

When I taught at the University of Washington (Seattle) Mechanical Engineering College (1997 - 2008), I was responsible for restoring to modern standards a student "Learning Facility" with 36 ancient machines including a more modern Ajax solid state induction furnace, running on 440 Vac, 3-phase. Two of the Power Supply's giant water-cooled diodes failed, which I diagnosed, acquired, and replaced. After I left that UW position, the furnace power supply failed again. My "replacement" chose to surplus that entire system. No more induction furnace casting has been taught since then. 3D printing is the modern replacement now taught in place of the casting.
I've often wondered if someone purchased the surplussed Ajax system and got it back into operation.

Nice to read of your progress.
~RussN

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Re: One man's insanity---the story of an induction furnace

Post by John Hasler » Sun Feb 25, 2018 12:44 pm

If you do replace the selenium rectifiers with silicon ones check the output voltage to be sure it is not out of spec. Seleniums have a lot of internal resistance. You may need to add a resistor or move a transformer tap.

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Re: One man's insanity---the story of an induction furnace

Post by Harold_V » Sun Feb 25, 2018 4:41 pm

Thanks for the comments on the selenium rectifiers. As best I was able, I checked them to determine if they were still functional, and assume they are. It's not clear on the two that are housed on the panel in the picture, as they are the ones that are fired ONLY if there is a spike in voltage.

Selenium rectifiers are actually still available, but hold on to your hat if you need one. I priced a replacement (new built) for the large one in the picture and was quoted right at $700. Yikes!

I have on hand several large solid state bridge rectifiers, but the output voltage would likely be too high if they are substituted, so I have, thus far, resisted the change. The control panel for the generator exciter has two more, much, much larger in size, and they are the ones that are of serious concern, as I have been unsuccessful in determining the actual voltage that is produced (because of the internal resistance). They have not been tested in use, as I do not have an operational furnace to which I could send the resulting output of the generator, and that, alone, would likely trigger a spike, possibly destroying the generator.

Several years ago, a guy in Olympia purchased an induction furnace, which he then liquidated. I wonder if, maybe, it was the unit mentioned by Russ. I think it was. We communicated briefly, but I have now lost the contact information and do not recall who it was.

H
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Re: One man's insanity---the story of an induction furnace

Post by John Hasler » Sun Feb 25, 2018 5:03 pm

Your seleniums are probably ok. When they fail they don't tend to be secretive about it. Determining the correct way to replace the large ones would require a bit of engineering since their characteristics have probably been designed in.

Do you have part numbers for the large ones? High power silicon rectifiers are quite inexpensive these days. It might be possible to build a plug-in replacement for modest cost.

BTW each cell of a selenium rectifier is good for a maximum of about 25 volts so you can use that to estimate the voltage rating.

Googling selenium+rectifier+characteristic gets lots of hits. To test and reform your seleniums take them out of the circuit and use a variac, a load resistor, and an oscilloscope (or a multimeter if that's all you have).

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Re: One man's insanity---the story of an induction furnace

Post by Harold_V » Mon Feb 26, 2018 4:16 am

John Hasler wrote:
Sun Feb 25, 2018 5:03 pm
Your seleniums are probably ok. When they fail they don't tend to be secretive about it.
I recall one failing in my Graziano, many years ago. It was replaced by a solid state device by an electrician. Yeah, it smelled just like selenium (garlic) in the shop afterwards. :wink:
Do you have part numbers for the large ones? High power silicon rectifiers are quite inexpensive these days. It might be possible to build a plug-in replacement for modest cost.
If memory serves, there's four selenium devices in the power supply, each with a number attached. I don't know that that information does me much good though. Are you alluding that, armed with the number, one might be able to come up with an equivalent solid state device? If so, I may have one that would work, assuming voltage isn't a problem. The type I have is rated @ 50 amps, which is far greater than the demand of the circuits involved. I'm tripping over voltage, alone.
BTW each cell of a selenium rectifier is good for a maximum of about 25 volts so you can use that to estimate the voltage rating.

Googling selenium+rectifier+characteristic gets lots of hits. To test and reform your seleniums take them out of the circuit and use a variac, a load resistor, and an oscilloscope (or a multimeter if that's all you have).
Thanks for that. What I did was disconnect each one, then determine if it had shorted. None appear to be damaged, and the multimeter I have (a Triplett) indicated they functioned as expected. I am not well versed in electronics, but understand basic electricity to some degree. No oscilloscope, for sure, aside from the MPI-4 McIntosh that is a part of my stereo system.

Thanks for your comments. Everything helps in the scheme of things. :wink:

H
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rrnut-2
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Re: One man's insanity---the story of an induction furnace

Post by rrnut-2 » Mon Sep 24, 2018 1:01 pm

Harold, I finally got a chance to sit down to Solidworks and throw together what we had as water savers for our induction units.

The operation of these is fairly simple. The water from the power supply and one furnace at a time drains back into the this tank. A temperature switch in the pump discharge line adds Make Up (cold) water to cool the tank down. This switch has to be set above dew point of the ambient air temperature. If it isn't, you will have a rain storm inside of your power supply; complete with Lightning!

There is a level switch that keeps the water level from getting too low. That switch also turns on the Make Up water solenoid. Excess water goes out the drain.

This water saver was supplied cooling water from our well which ran about 450 gallons a minute.

I said one furnace at a time, because our units where hard pressed to supply two furnaces at once. The power supply could only power one furnace at a time, but it was not unusual to cast with one alloy in "A" furnace and then switch to "B" furnace to cast a different alloy. The Inductotherm Dual-Tracs could run two furnaces at a time, but those had cooling towers and have 2k lbs furnaces. Cooling requiresments are alot different, and disposal of the cooling water is controlled by big brother.

Jim B
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