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Problems with the Foundry

Rick Rowlands

Titanium
Joined
Jan 8, 2005
Location
Youngstown, Ohio
Well I screwed up, big time! Saturday was the first heat and everything was going well and the metal was melting fine until we seemed to lose power. What I didn't know at the time but I was burning up the generator windings beause of insufficient cooling. The genset is water cooled and the temporary cooling arrangement I had set up wasn't handling the job.

We went to troubleshoot the problems yesterday and after ruling out the field rectifier I tried to get a voltage reading off the generator. It should have been around 400 volts but the most I'm getting out is 130 with practically no amps.

Fortunately there is another generator that I can borrow to replace the burned up one. I'll find out what I have to change to get it to fit into my system today and possibly have it moved to the foundry later this week.

However I am going to be putting in a proper cooling system so that I don't encounter this problem again. I'm going to head to Cleveland today to look for a cooling tower and when I get back I'm going to start construction of a proper closed type cooling system. Fortunately I found a three ring binder with cooling system specifications and designs with some other documents I obtained from a former foundry. This system calls for ethylene glycol as antifreeze. (This answers the question I had a while back about what to use in my cooling system).

I'm so pissed off about this. I was rushing to get things running and I just didn't put any time into designing a cooling system. So instead of melting metal today I'm back to square one redoing much of the work I've already done. Its quite an expensive learning curve to be sure.

Hopefully by this weekend I'll be able to give this another try. If anyone has a larger water cooing tower or huge radiator or an air seperator that you're willing to sell let me know. I think I found a unit at HGR but until I get up and look at it I don't know if it will work.
 
Just recall that

heat transfer rate = m (dot) * c * delta T

m (dot) is a mass flow rate
c is a specific heat value
delta T is the diff in temps between the media in question

So...a good mass flow rate helps...get a good strong pump to keep things circulating. The c factor you can't do so much about, and a better/larger radiator will help maximize the heat rejection...

You can use a larger reservoir...that is somewhat of a thermal resistor...helps to mitigate temp rise on the water side by virtue of more mass.

You can force-convect the radiator...with a fan...helps increase the mass flow rate of the air. But it all goes back to that useful little formula.

Also, keep in mind you want to oversize slightly if you intend to run in the dead of summer.

I hope the repairs to your genset are not expensive.

-Matt
 
Hi Rick, followed your foundry progress.
About your cooling requirements, have you decided on forced convection or natural draft cooling? Natural draft towers need considerably more surface area Also to consider is tube scale buildup in your primary heat exchanger, usually requiring some sort of chemical injection such as sodium sulfite. You'll probably want 2 primary heat exchangers so as to swap service while one is cleaned, and a tower bypass for cold weather operation.
A simpler solution might be a large chiller unit, except you have to watch for condensation in your generator(BAD). What are your heat transfer requirements in terms of BTU's/hour?
 
Rick, sorry to hear about the setback...been there, I feel your pain. Forced draft is probably preferable to natural convection. I don't know if it would be workable nor not, but have you thought about the radiator off of a large CAT genny? They are pretty large relatively speaking....

In addition to lowering the freezing point, the antifreeze will also help you to raise the upper boiling point of the coolant.

Something you might want to consider is a thermometer at the outlet of the genset with a flashing warning light. This, at least, will let you know if you're getting near the danger zone with your genny.

Good luck!

Nick :cool:
 
I was thinking, on the subject of instrumentation...that a cheap and easy setup might be automotive temp gages, auto parts stores or on ebay.

Some are mechanical, others are electrical and could be run with a 12v power supply.

Of course you could get more radical with thermocouples...used to do that...but it gets more expensive.

-Matt
 
You might consider installing adjustable Murphy switch gauges that would kill the ginny in the event of overtemp or oil pressure failure. Provided you have electric shutoff rather than manual. They're spendy but a lot cheaper that another genny and can be wired to an alarm or 12 volt light as well.

http://www.baileymotorequip.com/murphy.html#Temp

I have no association with this company.
 
"heat transfer rate = m (dot) * c * delta T

m (dot) is a mass flow rate
c is a specific heat value
delta T is the diff in temps between the media in question"

that's almost correct-- delta T is (Tout-Tin) of your coolant. In some cases (Tout-Tin) might equal the temperature difference between the two media, but it doesn't always.

-Justin
 
Good catch there Justin. If you want a project which will cause you to tear your hair out setup a simple heat exchanger...like oil to water and try to quantify the heat transferred with instrumentation.

Get your temps in and out...get your flow rates from flowmeters on both sides.

Getting the result to come out right is quite difficult...even resorting to RTDs for temp instrumentation was ineffective.

Even switching all instrumentation from one side to the other was proving that I had invented a heat generating device. :D This despite the obvious losses to natural air convection...heat exchanger was so hot on the exterior that one couldn't touch it.

There's some subtlety that I missed when doing that job...I don't know if it was mixing the fluid streams appropriately to try to get a homogeneous temp distribution or someone more knowledgeable was playing a practical joke.

-Matt
 
I would try salvage yards for semi tractors for used semi radiators if you want water to air cooling. A large 4 core should be good for 750,000 btu with about 60 degree delta T. It will take at least a 25 hp fan to move enough air for that performance. That is also with antifreeze, add 20 percent performance for pure water.

What is your price of water? Some places it is cheaper to pump water for cooling than any other method.
 
My trip to HGR was a successful one. I brought back a condenser unit, basically a 6' wide x 8' long horizontal radiator on legs with two 1 horsepower fans to provide forced cooling. The total cost was $450 and aside from repairing the inevitable forklift damage which everything at HGR seems to be inflicted with I should have a good unit.

Also on the way back I stopped and picked up another 50kw motor generator set. The only difference is that the frequency is 9600 cycles instead of 3000 on my unit. My friend assures me that the higher frequency won't matter and that it will still work with my equipment.

Starting tommorrow I'll be installing the new cooling system. The condenser will go outside and I will run plastic pipe into the building. Both lines will have thermometers just inside the building so I'll be able to keep tabs on the temps of the water before and after its trip to the unit. The manufacturer specifies that the inlet water should be no hotter than 95 degrees.

Once the basic cooling system is installed and running I will expand the system to add an additional backup pump and possibly a second cooling apparatus. I'll find out how good it cools once summer rolls around and I try to melt on a 90 degree day.

I got pretty lucky on this one. This is just going to set me back a week. It could havbe been worse.

As for the old MG set I am going to take it apart when I have time and determine the cause of the problem. At the worse it would need rewould. Does anyone here have experience rewinding motors?
 
Rick, CPVC may be the best choice since the water is going to be hot.

Personally, I would run copper, despite the higher cost. It is quite bulletproof to the normal shop bumps and scrapes, reasonably easy to reconfigure and there will be some heat extraction from the metal pipe itself. I would join with Stay Brite #8 solder as it won't creep under the temps and easily applied with a propane torch. It wicks like the old leaded solder. Again, higher price but premium performance.

-Matt
 
Wait, wait...I just remembered....we run thousands of gallons of 50/50 mix every day at room temperature. All the CPVC piping...grey Schedule 80, mind you, has now been changed over to copper.

Reason being...it had a nasty habit of breaking the output (mixed) side on the weekend and the 3pc - 500 gallon mix tanks making a lake in the plant if the pumps were left on.
let_it_all_out.gif


The glycol somehow crazes or embrittles the CPVC.

One run was over 1000 feet, and we soldered copper pipe for several days making up that run again.

I had forgotten about those days of pain now that the system is so troublefree. :D

The radiant heating guys may tell you that PEX or some such is even better...I have no experience with this though.

-Matt
 
If it's a solid system, and it sounds like it is, CPVC can easily shatter from water hammer, like starting a pump with the discharge valve open. For copper pipe, it needs to be wrapped with brass at contact points to steel hangars or mounts to prevent galvanic corrosion. Even though more expensive, I gotta agree copper would be the ideal end result.
 
Hmmm, 1 1/4" copper tubing is gonna be expensive, but I suppose its worth it if it gives me trouble free performance. The additional cooling surface from the runs will help too. I'll be checking prices tommorrow.
 
Rick does the coolant carry electricity to the melter ? If so you may want to look at propylene glycol (RV antifreeze) as that carries juice much better than ethylene glycol.

Inductotherm 100kw & Ajax 500kW on propylene w/ copper all the way.
 
rick u could use black iron pipe, cheeper the only problem u would have to run a rust inhibiter
but if u use antifreeze it has a inhibiter in it allready
on electric trains (10,000 horse) they use oil to cool the transformer
 
Hello Rick.
I had a foundry for many years and we ran two old tilt induction furnaces that used a motor generator to power them. We had fun with our cooling system occasionally failing for one reason or another so we installed a direct connection to the water supply such that if the water flow from the cooling tower failed, a solenoid opened and just pumped cool water directly from the water supply through the generator and induction coils to stop them from cooking. Ours were used units from the Mint in Perth. Man did we create some problems for the locals around us when we installed those old buggers. We eventually installed an Inductertherm pop-up unit. That was a few years ago now but I seem to remember something about different cycles for different metals. When we melted Aluminium in our furnace it would suspend the molten metal in mid air with no conact with the crucible at all. It was always a great show piece to show visitors to the factory. I will follow your foundry as I miss the old days of Brass and Aluminium (Aluminum) being splashed around my feet.
Good luck with it.
Danny
 
It's interesting to hear of cooling problems, and the solutions. I have a property fed by a spring, that puts out 30 gallons per minute in the dead of summer, jumping up to at least 100 gallons per minute in the winter. The spring feeds into about a quarter acre pond. I use it for irrigation, but it's also able to be run through a 8 foot by four foot radiator in my shop, that has a rather larger blower behind it. I use a three horsepower Berkeley Jet pump to pump the water for irrigation. So I can have my shop cooled in the summer at the same time I irrigate, or just run the water back down into the creek.

Guess I should put in my own foundry so I can take advantage of this cooling capacity! Maybe I could reverse this proccess and use the foundry heat to keep warm.
 
Ethylene glycol has a lower electrical conductivity than plain water and that is better in a melting system since you don't want the water carrying any current.
 








 
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