Author Topic: Oil fired crucible furnace  (Read 49755 times)

MetalCaster

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Re: Oil fired crucible furnace
« Reply #25 on: July 19, 2013, 02:45:09 PM »
You have seen my work, nothing new to show there.

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Re: Oil fired crucible furnace
« Reply #26 on: July 19, 2013, 03:12:21 PM »
Doubly unfair!

Apologies.
I love it when a Plan B comes together!
Steve
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MetalCaster

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Re: Oil fired crucible furnace
« Reply #27 on: July 19, 2013, 04:34:08 PM »
No apologies due or required.

Pat J here.

Offline doubleboost

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Re: Oil fired crucible furnace
« Reply #28 on: July 19, 2013, 04:53:04 PM »
Steve

I used to sprinkle something on the plinth brick to stop it sticking to the crucible but for the life of me I cannot remember what. Can't have been sand as that would fuse at those temperatures

Beer mats work well
John

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Re: Oil fired crucible furnace
« Reply #29 on: July 19, 2013, 05:00:34 PM »
Do they need a dousing in Newcastle Brown Ale first ? 

 :lol:
Andrew Mawson
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Offline dsquire

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Re: Oil fired crucible furnace
« Reply #30 on: July 19, 2013, 05:05:58 PM »
You have seen my work, nothing new to show there.

MetalCaster

I have checked all of your previous posts and can find no pictures of your work. It would be nice to see your work as you sound like you have a lot of skill and experience.  :)


Perhaps you could go to http://madmodder.net/index.php/board,3.0.html and make an introductry post to help the members get to know you.  :D


Cheers  :beer:

Don
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Never let it rest,
'til your good is better,
and your better best

Offline tekfab

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Re: Oil fired crucible furnace
« Reply #31 on: July 19, 2013, 05:07:11 PM »
I'm guessing he was here previously under a different guise ?

Mike

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Re: Oil fired crucible furnace
« Reply #32 on: July 19, 2013, 05:15:13 PM »
Steve

I used to sprinkle something on the plinth brick to stop it sticking to the crucible but for the life of me I cannot remember what. Can't have been sand as that would fuse at those temperatures

Beer mats work well
John

Damn, I should have saved up back when I remembered where they came from!
I love it when a Plan B comes together!
Steve
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Re: Oil fired crucible furnace
« Reply #33 on: July 19, 2013, 07:39:47 PM »
Today I increased the size of the exhaust port in the furnace lid to 4". Don't know if that will help or hinder melting. I think it will probably allow more air through, by reducing back pressure, which means I can open the fuel up all the way.

I couldn't do that before without the furnace smoking. The main reason I did it though, was to allow dropping additional metal more easily into the crucible, and also observing the melt.

I also tried out making some cores using Ironman's Portland cement and sand mix method. I used 1" PVC pipe as the core boxes. I slit them ahead of time. I used a very fine grade of sand I had on hand.

I was worried they would dry out before curing (in 3 days) so I put them inside a ziplock plastic bag, and also put a crumpled up wet paper towel in with them. Since humidity would then be 100% inside the bag, I didn't see any reason not put the whole thing out in the sun -- since that would speed up cure. Concrete blocks are rapid cured when cast by exposure to steam, so I though this might work in a similar way.

It's been very hot here the last week, but sunny at last. Temperatures have been up in the mid 90's F (34 C). So I'm sure the temperature was high in that bag today. Condensation showed the humidity was in there. I'll probably still go 3 days and then dry the cores as well after. But this was just an expeiment.
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Offline ironman

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Re: Oil fired crucible furnace
« Reply #34 on: July 19, 2013, 08:21:15 PM »
vtsteam

What you can do is before you add water to your sand is weigh the sand dry and then put in 4% water. For future mixes you may have to adjust the moisture level. For thick castings ram the sand more gently so it has more porosity.

 I see that you noticed I don't put in vents in the middle of the core. When molten iron touches the core/mold surface gases have to travel through the sand to reach the vent. If the sand has no porosity it will bubble through the metal. It will always take the path of lest resistance. Can you see why I don't bother with vents?

It is extremely rare for me to get blowholes in my castings so I must be doing something right. Have a look at my video " How to change steel to cast iron using a waste oil furnace" to see how I solved the shrinkage problem on the pulley casting. You will notice how shallow the copes are on my molds.

Just increasing the head pressure will not fix the shrinkage problem, making large enough risers so they will freeze last instead of the casting feeding the riser. 

When I saw the photo of how distorted your crucible was it would have been scary to lift out the crucible. Years ago I used to ask the foundry supplier is the crucible rated for iron? His answer was the crucible was rated for 1400C. Since then I never ask if the crucible is rated for iron and use them for iron. I have used a lot of crucibles over the years and never had one deform like yours.

 I have seen photos in other forums of crucibles with bad faults and are unusable after two melts. It is sad to say but I have come to the conclusion that the U.S.A. makes really bad crucibles. The ones I use are imported from Mexico, India, scotland and Brazil and never had a problem with them. I find some brands will last longer than others.

I have destroyed two crucibles through misuse, so making mistakes is part of the learning process. I never use flux with cast iron. Soda ash is the second worst flux to use in a crucible, the worst is borax. They will dissolve your crucible very quickly. If you insist on use fluxes your crucible, it will have a very short life.

vtsteam as a beginner there is no way your furnace will reach 1650C (3000F) I have a pyrometer that will measure to 1770C (3218) and in a typical iron melt the furnace is struggling to get over 1570C (2858F). I have never used a silicon carbide crucible for iron. I was hoping someone would buy one and see how much longer they last compared to a clay graphite crucible.

 Over the years many hobbicasters have visited my home foundry and everyone has said I do everything differently from what is written in books or the way they think it should be done. But when they leave I find out a few weeks later they have copied nearly every method I use. 

Metalcaster welcome to the forum. I'm sure everyone would like to know what sort of casting you have done.

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Re: Oil fired crucible furnace
« Reply #35 on: July 19, 2013, 10:08:41 PM »
Thanks greatly Ironman!!

Crucible life:

I will definitely drop using the sodium carbonate. I also put a few charcoal pieces in, but I would guess you wouldn't think that hurt anything this last time.

Risers:

I did watch all of your casting videos last night looking for clues and tips about my shrinkage and bubbles problem, so I definitely noticed the two big risers on that pulley.

But I also noticed lots of castings where you had no risers, and much smaller sprues, and different shapes and sizes for gates than I used -- so I would like to try to get closer to what you do there first, to see what happens, before adding a riser. My sprue was 1.25" diameter. And I couldn't pour fast enough to fill it -- I think my 2 gates were too big in cross section, too.

Actually, I probably can't add a riser because of lack of crucible capacity. Although smaller sprue might help that quantity problem. Everything is interrelated.

Crucible distortion:

That happened in the last melt -- it didn't do that in the earlier ones. But I really cranked the furnace in the last 20 minutes this time -- and there was more flux.

Or maybe as you say, I should try a different make of crucible. Can you recommend a brand to look for? Is there any particular one you like?

I have one more new one, and I will try to see how it lasts without flux, a little gentler temp ramp up, etc. Maybe there will be a difference in lifespan. I will be very cautious about any leathery "feel".

I'm very happy copying what you do in preference to books where they differ, and grateful for your experience.



I love it when a Plan B comes together!
Steve
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Re: Oil fired crucible furnace
« Reply #36 on: July 19, 2013, 10:17:44 PM »
One more thing I noticed in the video -- if a video can show such a thing -- I don't think you ram as hard. I'm guessing that would affect blow holes if your sand is more permeable because of lighter ramming.
I love it when a Plan B comes together!
Steve
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Re: Oil fired crucible furnace
« Reply #37 on: July 19, 2013, 11:18:54 PM »
Sorry to make multiple posts, but I just also re-read your post and  you mentioned your shallow cope height. I definitely noticed that!

I have been thinking of making some of your style aluminum flasks. My eyeball estimate from the video is something like 1.75" flask height by 9" by 12". Is that right?

And about 3/8" thickness with small triangular corner gussets with tapped holes for screwing frames together, and positioning pins and holes mid frame(1/4" diameter?) Probably offset in position some so they can't be put together the wrong way.....
I love it when a Plan B comes together!
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MetalCaster

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Re: Oil fired crucible furnace
« Reply #38 on: July 19, 2013, 11:30:52 PM »
Use one 1/4" and one 5/16" pin so you can't reverse the cope and drag.
The Alloy Avenue guy mentions that carriage bolts with the head sawn off make good pins, and I can vouch for that.

Ironman- You are familiar with my work too.  PatJ from you-know-where.

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Re: Oil fired crucible furnace
« Reply #39 on: July 20, 2013, 08:32:50 AM »
Pat, this is what I'm talking about wanting to make:

I love it when a Plan B comes together!
Steve
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MetalCaster

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Re: Oil fired crucible furnace
« Reply #40 on: July 20, 2013, 12:39:26 PM »
Ironman makes it look easy.
Not only has he mastered iron, he has mastered green sand.
My sand too often is to wet, or too dry (I use oil-based sand), or something else goes wrong with the sand, and just about time I get the mould done and all the gates and risers cut, it all falls out of the flask half.

Some put a groove or two in the walls of the flask, but if your sand is right, you probably can use a bare inner wall.

Here are a few made locally.
I would try and make the tabs on either end cast integral to the unit (I think in the photos below they are screwed on).
I will have to review Ironman's tabs to see if they are cast on.

And the pins seem abnormally large in the photos below, but the flasks I have which use 1/4" carriage bolts on one side are prone to getting out of alignment.
In the future I will use 5/16" and larger bolts for the pins (different size either side).

I only have wood flasks at this point, but hope to make some metal flasks one day.
Metal ones last a lot longer than the wood ones.

Edit:  Yep, ironman uses an integrally cast handle, as I suspected he would.

Offline ironman

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Re: Oil fired crucible furnace
« Reply #41 on: July 21, 2013, 04:21:59 AM »
vtsteam

For many years I used Morgan crucibles made in Australia and they were terrible! I used to call them candle wax crucibles because they would melt every time they were used. A friend told me about Vesuvius crucibles, so I bought one and it lasted four times longer melting iron than the morgan crucible. I got really lucky there and when I saw the morgan rep I said I would never buy his crucibles ever again. That being said I still have to buy the crucible pedestals from morgan because Vesuvius don't have small pedestals.

When I started to melt iron I used soft fire bricks as a pedestal and the same thing happened, it leaned over and touched the furnace wall. I then used hard fire brick and they cracked because of the weight of the iron in the crucible. I gave up on fire bricks and got the pedestals from morgan. They last as long as the crucible.

The top of the crucible to the exhaust vent is the hotest part of my furnace, so that is where the most wear and tear happens. Over time my crucibles get shorter because of this.
 
You must have micrometers in your eyes, every dimention with the molding box is correct except for the height (50 mm).

It is very hard to put into words how to gate castings because each one is different. I have a lot of experience and know what to do. Reading books without experience can lead to errors, you just have to make mistakes to learn. Good judgement comes doing as well as reading.

Pat

My early boxes had screw in handles but thought that cast in handles were less trouble to make.


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Re: Oil fired crucible furnace
« Reply #42 on: July 21, 2013, 07:09:31 AM »
Thank you again Ironman for your advice and experience.

Putting two and two together, if you use less ramming force than I have, and use a cope of 1/2 the depth I have, the gas permeability of your cope must be a fraction of what mine is. I think I can see why you don't get blow holes, and don't need to vent cores.

You are (I think) using finer sand -- probably finer than I could have used without getting a lot of gas entrapment. Years in the past with aluminum, I tried very fine sand -- 140 mesh, but had blow hole problems that way. So I just used that fine stuff for facing sand. That's the reason I asked about the mesh of your facing sand.

Also, if you are using smaller diameter sprues and copes of 1/2 the depth compared to those I have used, then the amount of material tied up in sprues is possibly 1/3 what I have.  This means, with a limited size crucible, that I would have more capacity to add a riser, possibly.

Speaking of crucible capacity, I have what were advertised as A-6 crucibles. I checked their capacity by weighing the amount of water they held on a gram scale, and it turns out they are A-4 crucibles of about .75 liter.  Their designation is A for shape and the 6 is the number of kilograms of brass it will hold. Thus an A-6 will hold 13.2 pounds of brass in our weight system.

The Morgan crucibles, on the other hand, designate the A as shape, again, but the 6 designates the number of pounds of aluminum it holds. Since brass is about 3 times as dense as aluminum, that would translate to about 18 pounds of brass -- 1.2 liter -- or a substantial difference.

After carefully measuring my furnace and tongs, it looked like I could fit a true A-6 rather than the smaller A-6's I have and get nearly 50% more capacity. Unfortunately I hadn't seen your reply yet last night, so I ordered a Morgan Salamander A-6.

Oh well!  I guess when all of these crucibles give up the ghost, (which may not be very long in the future) I'll finally get the right size and right brand.

A question about crucible treatment, Ironman:

Do you replace the crucible in the furnace after a pour to let it cool down slowly, or do you leave it in air to cool?

I love it when a Plan B comes together!
Steve
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MetalCaster

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Re: Oil fired crucible furnace
« Reply #43 on: July 21, 2013, 11:16:54 AM »
I have not had any problems with the Morgans, but there are different grades even within one manufacturer such as Morgan.

The rep told me that for non-ferrous work, the Morgan "Hi-Melt" was the most long-lasting, and this is a silicon carbide crucible.
The "Hi-melt" is rated 1000-1400 C (1830-2550 F).

For ferrous work, he recommended the "Salamander Super" which is rated 850-1600 C (1562-2912 F), and these are clay-graphite.
The brochure mentions that they can also be used for non-ferrous work.

Note in the photo below that both are labeled "Slamander", which is very misleading given the fact that one is only rated for 2550 F and non-ferrous work.

I think you would get good service from either of these two units if used with the respectively rated metals.

I have also heard reports of crucibles cracking if not placed back into the furnace to cool slowly.
I put mine back in the furnace just to keep them clean, dry and protected until they are cool and can be stored sealed in a plastic bag.

Morgan mentions many things that will damage a crucible such as heating them too fast when they are cold, causing uneven thermal expansion and cracking, improper loading, lifting and supporting from the wrong position, not keeping them dry, etc.
I think the silicon carbide units have to be fired at least once to seal the glaze before they are used to melt metal.
Morgan also mentions not letting the flames impinge directly onto the curcible.

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Re: Oil fired crucible furnace
« Reply #44 on: July 21, 2013, 01:03:31 PM »
Thanks Pat, I had already looked at Morgan manufacturer's literature before ordering the crucible, a Super.

I would like to hear what Ironman does in his own shop, re. crucible care, since that is genuine long time practical experience that I trust.
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Steve
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MetalCaster

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Re: Oil fired crucible furnace
« Reply #45 on: July 21, 2013, 01:22:08 PM »
Ironman has 20 years experience with pouring iron using both crucibles and cupolets (if I understood him correctly), and more importantly a lot of experience with making green sand.
Both are really critical since no matter how good you are at melting and pouring iron, if your mould fails, then you have nothing.

Edit:
Someone corrected me on the word "cupola", and said that the small units that are top-fed are "cupolets", not "cupolas".


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Re: Oil fired crucible furnace
« Reply #46 on: July 21, 2013, 08:17:25 PM »
I made several changes and cast iron today.

First change was the enlarged exhaust hole in the furnace lid.
Second change was reducing the size of the sprue from 1.25" to 1" in order to keep it choked with metal.
Third change was to add some of my 140 mesh sand to the 60 mesh greensand I have used recently. About 15% was added.
Fourth change was to ram somewhat lighter
Fifth change was to use no sodium carbonate as flux
Sixth change was to preheat the new crucible to red heat at moderate burner throttle before adding metal.
Seventh change was to alter the pattern to include a semicircular groove to form a greensand core. This piece willl later be bored out, and the cored channel will make this easier. It also reduces the the mass of metal poured..

First Try:

I'd like to say everything worked out, but unfortunately I poured short. The much larger amount of slag of a very pasty consistency fooled me into thinking there was more metal in the crucible than there was -- and that it was hotter than it was when i dipped in a poker and it came out clean. Also the gates were a little shallow, so basically I ended up with a nice bar ingot of about 3/4" thick, but not a part.

Second Try:

I could tell the pour was short, so I didn't wait very long to unmold. I decided to use the residual heat in the furnace to attempt another melt. So I quickly broke up more scrap, and fired up the furnace. While it was heating I rammed up a new mold. I decided that I'd try a riser in this one as an additional change, but make sure the crucible was full of metal, not just 1/3 slag. I figured my smaller sprue, and the new core groove would give me enough additional metal in a full crucible to afford an 1.25" riser. Also I'd put in slightly deeper gates, and be absolutely sure the metal under the slag was fluid.

I pulled the crucible out when I thought it was ready, and scraped the very thick sluggish slag out of the way where I would pour -- I couldn't scoop it all off easily, as I had when I used Sodium Carbonate -- that stuff really liquifies the slag.

I poured and watched the riser fill to the brim, and had enough metal left over to pour an ingot as well. Good!

In a couple minutes the riser started to shrink down -- which I took as a good sign! Both the sprue and riser dropped quite a bit. Here's a pic:



« Last Edit: January 14, 2018, 10:40:34 AM by vtsteam »
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Re: Oil fired crucible furnace
« Reply #47 on: July 21, 2013, 08:43:42 PM »
The part came out well!  The surface wasn't smooth I still don't have seacoal for a facing sand, but the added 140 mesh sand seems to have made for a finer surface grain than before. The lighter ramming doesn't seem to have caused any irregularity or coarse patterns, and the corners look good.


Bottom of the part:


« Last Edit: January 14, 2018, 10:41:08 AM by vtsteam »
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Re: Oil fired crucible furnace
« Reply #48 on: July 21, 2013, 08:57:24 PM »
The top surface shows a big improvement over the last pour of this part. There are only 3 small shallow blow holes -- these will be easily removed with the machining allowance, and when the part is bored -- unless there are some hidden holes. I have a feeling that's all there are.

I believe the reduction in ramming pressure and smaller sprue (which I kept choked while pouring) helped trap less gas, and relieve it where present, creating fewer and smaller pockets. If I go to a shallower cope, it's possible venting and permeability will improve even further.

The greatest improvement was the elimination of the shrink depression. This was probably due to the addition of the riser. The greensand core that formed the channel might have helped as well by reducing the thickness in the center of the casting. Less thickess, less retained  heat at the center. Since the channel also makes machining easier, it was definitely worthwhile adding it to the pattern.

I'm very happy with the results and  feel I'm on the right track. Plus I have a good part!

Here's the top  (dark areas are dampness from a rinse):







« Last Edit: January 14, 2018, 10:41:55 AM by vtsteam »
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Re: Oil fired crucible furnace
« Reply #49 on: July 21, 2013, 09:08:18 PM »
And as a follow-up for furnace operation, the furnace consumed 2.5 gallons of diesel fuel total over the two melting sessions during a 4 hour period.

Actual time to melt for the first pour was 1 hour 5 minutes from lighting, and after a 45 minute cool down, the furnace ran for an additional hour to achieve the second melt -- which had more metal.

The crucible looked in good condition, though I couldn't remove a fair amount of pasty slag this time because without flux it was tough stuff  to try to scrape out. I put the crucible back in the hot furnace to cool slowly, so I'll get a better look at it tomorrow. I think it is retaining wall thickness better than the first one had. It felt solid, not leathery during the pours.
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