An Update On The Troll

[bmac2]

Hi all
Thought I’d throw out an update on the Troll (coffee can) furnace. As it turns out I was correct in my thinking that the physical act of melting aluminum is easy. If you gave 100 monkeys 100 matches and 100 pop cans eventually one of them is going to melt some aluminum. Getting a metal casting that actually looks like the part you had in mind . . . . whole different story.
I don’t think I’ve done this much reading since school. For every hour I spend doing something hands on I probably do 6+ hours of reading. Between working to get green sand I can live with, practising pattern making, and understanding the differences in how alloys behave, gates, spurs, runners and venting, don’t forget to vent, I just don’t spend much time actually melting metal.
My two must reads for anyone thinking of getting into casting are the US Navy Foundry Manual (http://www.hnsa.org/resources/manuals-documents/single-topic/foundry-manual/) and Wood pattern-making by Horace Traiton Purfield (https://archive.org/details/woodpatternmakin00purfiala). These are both free downloads.
With my first crack at casting was going to be with a straight cylinder and a “T” that I’d made up. Both required cores. A bit ambitious for a first try but I’d have to go there sometime. I had picked up some sodium silicate to make the cores and did 2 cores for each pattern one in course sand and one in fine. I’d been mixing green sand in small batches and realised I didn’t have enough of the sand I wanted to use to fill two flasks so I could only do one pour. Go big or go home time. I decided on the “T” pattern with the fine sand core.

 

[bmac2]

Fresh out of the sand it wasn’t great with a lot on sand inclusions and my sand was too wet but I was ecstatic that I’d actually got something. I could even almost read the dymo tape date I put on. Cleaned it up and it now holds special spot on the shelf.

 

[bmac2]

I still had the other 2 cores so after some more reading and working on the sand my second cast was going to be both of the patterns at the same time. I’d been reading up on gates and runners and wanted to try something.

 

[bmac2]

The casting was . . . . . well no improvement on the first. Scabs, inclusions, pin-holing you name it I got it. Back to the books and more work on the sand. But these where cored casting and only my second attempt.

 

[bmac2]

The next couple of weeks was spent basically reading, adjusting my sand, ramming the patterns, adjusting my sand and more reading, casting, analyzing and repeat. I finaly got tired of pouring things that looked like something I could pick up at Home Depot for $1.00 and dusted off my scroll saw. I was feeling pretty confident in my sand by this point and wanted to try something fun for a change. The gecko was born. Sanded it down to get something resembling draft and after some paint it went into the sand.

 

[bmac2]

This was way more fun than casting pipe fittings. Despite the little toes and some very tight angles I was very happy with the little lizard as soon as I got it out of the sand. Cleaned up I think it turned out great.

 

[bmac2]

I have been keeping an eye open for a damaged alloy rim to break down so I would have some better quality stuff on hand for the day I get a real project going. The other day a friend of mine that works in the auto industry called me up and said he had aluminum for me. When I got over I was not expecting a complete Nissan 4L V6. Holy crap how was I going to break this down!

 

[bmac2]

Between the 4x6, the sawzall and a very big hammer I got a good start on it. That’s a 64L tub half full of crucible size (3”x6”) pieces. I’m still working on the heads and block.

 

[bmac2]

Yesterday I fired up the Troll and started pouring ingots. Melted 28 lbs of engine scrap that yielded 60 ingots for 21 lbs of the shiny stuff in just over 2 hours.

 

[bmac2]

I weighed the propane tank before I started and I only used 4 pounds of propane. After the last pour I was giving the crucible a bit of a cleanout and noticed a small amount of aluminum on the outside. When I went to clean it off my pliers went right through the side. If it’s going to fail, and it fails empty outside the furnace I’ll take that any day. It was my first kick at making a crucible and I got 30+ melts out of it so it’s earned a decent burial. Good thing I made a spare.

 

[bmac2]

So if you know anyone that doesn’t like the maintenance schedule on their vehicle. You tell them there right and it’s just the man trying to stick it to them and I’ll get them my phone number Thm:. I need a bigger furnace. . . .

 

[charlesfitton]

Really enjoyed this - what are you using to control temperature?

f

 

[TorontoBuilder]

Hi Bob,

Those are some nice looking ingots... too bad they're not your end product eh?

Regarding your crucible, did it fail at the location of your burner inlet to your furnace? It looks like that may be the case. Perhaps rotating the crucible each time you fire may extend the life of it?

 

[bmac2]

Really enjoyed this - what are you using to control temperature?

f

Hi. Thank you, I'm glad you liked it. It's been a lot of fun.
To control the temperature of the furnace I use a 0 – 30 psi adjustable regulator. In affect it’s the same as using the knob on a gas BBQ except that low is low and high is Scary! When I first started I had the regulator set to around 2 lbs and it probably would have melted the load eventually but it would be like boiling a pot of water on low. By slowly increasing the pressure I found what I feel is a happy medium at around 6 lbs. This will melt a full crucible (3-4lbs) of aluminum in about 15-20 minutes from a cold start. I have run the burner up to 20 lbs and at that setting it will melt the load about as fast as you can feed it but it’s a bit ridicules on a furnace this small (http://www.homemodelenginemachinist.com/showthread.php?t=23743&page=2). The up side of the Troll is that when I’m not using it the whole setup, furnace, propane, sand, flanks and a bunch of miscellaneous stuff all sit on a 4ft shelf in my garage. I am thinking of making something bigger but I’m not sure how much of that is “need” and how much is testosterone. Having one individual aluminum casting in a model engine weighing 3 or 4 pounds is pretty big considering that the flywheels generally aren’t aluminum.

 

[bmac2]

Hi Bob,

Those are some nice looking ingots... too bad they're not your end product eh?

Regarding your crucible, did it fail at the location of your burner inlet to your furnace? It looks like that may be the case. Perhaps rotating the crucible each time you fire may extend the life of it?

John. yep that’s part of it, classic case of direct flame impingementThm:. I always give the crucible a light rap all over with a screwdriver before I start a melt and with the volume I had run that’s what I was doing when I found the failure. When I first built the troll I’d made up a plinth that was overly complicated and as it turned out fragile and it broke early in the game. I’d replaced it with a chunk of broken fire brick that was too short and set the weld line of the crucible below the center of the tuyere.
Between the flame location and the general nastiness (http://www.brunel.ac.uk/__data/assets/pdf_file/0011/295193/Durability-of-materials.pdf) of molten aluminum getting 30 something melts out of a homemade steel crucible isn’t all that bad and it had been abused (see running at 20psi, above). On the myfordboy blog he use to use stainless steel containers and said he would normally get 10 melts out of them. I’ve read a few articles and postings on coating the inside of the crucible to extend the life but the pipe I used for the two I have only cost $4.50 so I haven’t tried anything yet.
I’ve started work on the patterns for my first real project but that all got put on hold when I got this engine. Breaking it down into nice clean ingots has to take priority for now. I live in suburbia with a small lot (58’ x 115’) and I don’t want to be the guy with a bunch of car parts in the yard.:fan:

 

[Cogsy]

I am thinking of making something bigger but I’m not sure how much of that is “need” and how much is testosterone.

A while back in your Mako Burner thread I mentioned I was thinking of cutting a used 20lb propane cylinder apart. I'm happy to say it was an easy job and there was no explosion or fire at all, in fact it seemed fairly safe. I unscrewed the valve out of the top (that's the tough bit as it has some heavy duty sealant on it) then flushed it with water a couple of times and left it upside down to drain overnight. Next morning I flashed a blow torch over the hole and there was no reaction so I cut it apart with an angle grinder. Simple!

It's now turned into a furnace and while I am happy with the size, I'll need to make a cart for it as it's a little heavy to lug around easily.

 

[bmac2]

Hi Al
Any build on your furnace?
Pictures?

I’ve got an old tank sitting and just waiting for me to start on it. A 20 pounders not testosterone. A 50 gallon drum or a tilting wreaking furnace, that’s testosterone .
I’m actually surprised how the Troll has held up. I started to get a few cracks on the inside so I gave it a quick coat with some furnace cement I had left over. I degased a melt for the first time the other day and was glad the crucible was just over half full. Lots of big bubbles and I thought it was going to boil over.
I have only made two small flasks (6x6 and 7x9) and that’s about all I can pour. With some of the engines I’m thinking about and the one I’ve started some of the pattern work on it would be nice to pour two of each of the major parts. That way if I mess one up I’d have a spare, if by some miracle I don’t screw up the second casting I can just melt it down again. Then there’s the stuff my wife has started asking about and some of them could be well over my 4 lb limit.

 

[charlesfitton]

Hi. Thank you, I'm glad you liked it. It's been a lot of fun.
To control the temperature of the furnace I use a 0 – 30 psi adjustable

Yep- but how do you control the temperature?

f

 

[Cogsy]

Here's a couple of pics I have so far.

This is the shell freshly cut with a 1mm grinding disc.

The just-set refractory lining. I used a castable commercial product which is rated for 1450 Celsius - might not be the best but was all I could get at the time and should last a reasonable amount of time. The form for the centre was 2 paint tins stacked on top of each other and wrapped in thick cardboard to bring it up to approx. 8" dia. (The cardboard is why the hole isn't round but has flats in it)

And finally an action shot while curing the refractory. Once I got to the point in the process where I had to bring it up to max temp I decided to bang a crucible in there and melt some aluminium at the same time. I never noticed the aluminium itself glowing red til I looked at this picture. The crucible is a little undersize at only 3-1/2" dia. I'm looking for a suitable replacement now but it's vitally important that it be cheap so the search is taking a while!

 

[bmac2]

Al your furnace is looking good and you got it done in time for what must be the Australian casting season. Ahhh. Now I have Furnace Envy. Looks like I’m going to have to start one more spring project:wall:. With your picture of the crucible in the furnace I’ve noticed the same thing. Looking at it in the real world it’s either light gray with dross of very shiny but in the pictures or even on videos the camera sees it as the red hot that it is.