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Discussion Starter · #1 ·
I was thinking of having a Dahlgren 3.4 inch rifled howitzer carriage made by a carriage maker who has a good rep. The only material he will consider using for the trail and axle is ductile iron. If memory serves, the Dahlgren boat howitzer carriages were originally made of either wrought iron or steel. I'm not familiar with ductile iron and I certainly don't want an expensive carriage to break during firing. I have no idea how ductile iron compares to anything else as far as ability to resist bending and breaking under shock loading from the cannon firing. There must be a very considerable downward shock exerted through the elevating screw on the Dahlgren boat howitzers and rifles due to the distance the pivot point is below the bore (pivot point is in center of trunnion loop which is many inches below centerline of bore, creating a "moment" of force times distance.)

Anyway, here's a reminder of what the heavy Dahlgren carriage looks like. This particular gun is registry no. 298, and is one of the few cast steel muzzle-loading Dahlgren 3.4 inch rifles ever made. They were experimental and were not issued to ships as far as we know. The bronze versions were all issued to ships.

Is ductile iron good enough for this application or questionable?

http://s17.photobucket.com/albums/b...tc/forums35/?action=view&current=0fc710df.pbw
 

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Discussion Starter · #3 ·
Is he casting the axle and mounting points or machining them ?
My understanding is that he will make patterns and have the ductile iron cast to pattern. Typically some machining would be done afterwards in areas such the ends of the axle. But basically anything he can cast, he will make a pattern and cast it.

The whole issue with me is having large parts like axle and carriage trail, cast from what is a form of cast iron. I'm always worried about brittleness, cracking etc. when I think about any kind of cast iron.

The links above are for prefab shapes of ductile iron, which is a bit different from cast-to-pattern stuff, in that the shapes can be made in very controlled conditions. What will happen when he casts my carriage parts is that he'll go to whatever small foundry and tell them to cast to his patterns using ductile iron. There will not be much process control compared to the prefab shapes situation. I'm a bit worried about the ferrites and stuff that form like crystals in cast iron, and you really don't know how much of that stuff you are going to get until you are done casting and have the product, for better or worse. But I only know enough about iron foundries to be dangerous. I know a few buzzwords but not much about how it all works.
 

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Our experience with ductile iron has been entirely in it's use as a projectile material and in that capacity it has proved to be incredibly tough. We have never seen any cracks, fissures, large dents or gouges in any that we have fired. A large number of these ductile iron projectiles were fired at the 10th Mountain Division WWII training area near Leadville, Colorado called Camp Hale on the old infantry weapons range. The backstop is solid granite boulders and many puffs of broken granite dust and shards were observed as our larger 9 lb. solid shot impacted this backstop at approx. 200 yards. Scratches and very small gouges easily cleaned up with a few licks of a file were the extent of the damage we observed.

Talk about a high shock application, this is it! Sphericity was not affected negatively as the balls still rolled through the gage with no difficulty. We are very impressed with ductile iron based on these experiences.

FYI,

Mike and Tracy
 

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Discussion Starter · #5 ·
Thanks M&T. This is probably a stupid question but did you machine your projectiles from prefab shapes of ductile iron you got from a metal supplier, or did you have the projectiles cast in chills or sand-cast?
 

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John, all of our projectiles were sand-cast at LaPan's Foundry in Glens Falls, NY and at Slack Horner Foundry in Longmont, CO. They were all spherical within 1/32" before and after being fired. Good luck with this project; that is a great looking carriage in any scale, but, in this case, bigger is better in our view.

Tracy and Mike
 

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Here is a site that is all about castings with ductile iron looks like it has taken over as far as
many industries are concerned replacing steel forgings welded steel forms in automotive structures
as an economical material which has good machining qualities and tensile strength.
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http://www.ductile.org/didata/Section3/3part1.htm
 

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When I was involved in the drag race car fabrication industry, we used nodular iron rear center sections that were good for 2500+ horsepower. I'm not sure if or what the difference is between ductile or nodular iron if there is any, but I was told the nodular iron is stronger. There is a tremendous amount of stress placed on some thin sections of iron there and it held up very well.
 

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Discussion Starter · #9 ·
The link Allen posted has an article about ductile iron. When you cast it for a certain application, you do things to make it fit that application better, then after it cools you can do more things including heat treating.

The circumstances under which this thing will be cast, I'm sure will not include any of those tailoring kind of treatments, so I guess I will have to assume the worst case, or how weak and/or brittle can ductile iron get if you do everything wrong when you cast it. If it is still adequately ductile, strong, etc. in that condition, I guess it would be OK.
 

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I use ductile iron drifts in blacksmithing, one of which is a tomahawk drift, (to shape for the haft), that has been driven through hot steel hundreds of times. I use a heavy bronze hammer for this, and the hammer is taking much more of a beating than the drift. IMO this is pretty tuff stuff, it's certainly not sand cast junk.
 

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It might be a good idea to ask your supplier what processes will be involved in the making of your carriage.  Then you will have some data from which you can make an assessment.

He could also cheat on the section (making it thicker) which would give more strength.
 

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Is this going to be the carriage that you intend on mounting the 'Moffatt 3.4-inch BL Rifled Howitzer' on?
 

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Discussion Starter · #13 ·
Is this going to be the carriage that you intend on mounting the 'Moffatt 3.4-inch BL Rifled Howitzer' on?
Yes. I have an original 12-lbr. Heavy Boat Howitzer carriage which either of the two Moffatt breechloaders would fit, but I really don't want to take that out and drag it around in the field and bang it up. It has a nice bronze tube on it and I'd just like to leave that one alone.
 

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You might ask your carriage builder if he will use a foundry that can produce Meehanite (or equivalent) castings for your project...

http://www.globalspec.com/Supplier/Profile/MeehaniteMetal

The Meehanite process has been a standard for cast iron machinery components since it was developed.
 

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Discussion Starter · #15 ·
You might ask your carriage builder if he will use a foundry that can produce Meehanite (or equivalent) castings for your project...
Thanks, under other circumstances that would be a good idea. some of these guys will discuss things like that and some will not. I'm getting the impression that this one is in the latter category, which isn't necessarily an intolerable situation.

I may just change tactics, like requesting a guarantee that carriage axle and trail won't break due to firiing, or they will be replaced for free. That's easier for everyone-he seems certain of the material and the process, whatever that is, so it would be easier to use what in gov't we called a "performance specification" rather than a "process specification" or "build to print."
 

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I doubt that any foundry will provide you with a performance spec for a one-off, especially considering castings made from a pattern by someone off the street.

A process spec for the casting method/material is probably the best you can hope for. If you decide to go with that, be sure that the industry standard spec# or Mil spec# is listed on the purchase order from the foundry (not just from your carriage builder).

IMO, if you can't get that squared away it wouldn't be prudent to continue.
 
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