I read a thread once describing cannonballs, and how some had hollows in the center in which gunpowder was stuffed, to make them explosive. I thought about it for a moment, and, in my ignorance of the art of metalcasting, couldn’t figure out a way to make a cannonball with a hollow in the center. How did they do it? The only ways I could figure were casting the ball in two halves, half-hollow included, and soldering/welding them together, and casting the ball, and work the hollow in while the metal was still pliable.
Or have I missed the mark entirely? How did they cast hollow cannonballs?
How about this?: making a clay ball and supporting it on a little pillar inside a slightly larger hollow clay sphere; pour in the molten metal and when it cools, you have a hollow metal sphere, erm, well, not quite, it’s full of clay (that has now been baked hard by the heat, but using a long metal spike (inserted through the hole where that little pillar was) you can break up the clay into pieces and shake it out. Time consuming, yes, but labour is cheap.
(FTR this is speculation, it’s how I’d do it, but I don’t know if it’s how they did it).
My guess would be they Slag Cast it. (At least that’s what I think it’s called) Basically they don’t pour enough molten metal into the mold to form a solid ball. While the metal is still liquid they shake the mold and when it hits the sides it cools quickly and hardens there. I know this can be done but I’m not sure if it works on something as large as a cannonball. I’ll be meeting with some people soon that have much more knowledge in this area then I do. I’ll ask them and let you know if a satisfactory answer does not surface soon.
Hello all,
No disrespect, but casting in clay would be very dangerous as the water was driven off as steam under your still molten 2800 F iron. Dry compacted sand was used instead…
The easiest way is to mould the two hemispheres in a sand cast( negative mould of each with a ‘lump’ the size of the intended hollow and the void space equal to the wall thickness) and then weld the halves together in the forge. The sand is then hammered free.
You could ‘pig’* several of these half moulds together and make five or six easily with each pour.
*Some laignappe- The term Pig Iron comes from the large castings used to make iron billets, these had a central line and many smaller feeder lines that lead to each billet. When these cooled and were removed from the sand to have each sprue removed they looked like a sow with her piglets.
-BMoK
The same technique was used to make many items back then- as in, around the advent of the Bronze Age and up.
Cannonballs needed to be, first and foremost, cheap. Welding or brazing halves was expensive (forges needed coal and coke, only skilled blacksmiths could do it, etc) for something that was going to be fired in large quantities during a siege. For that matter, iron itself was terribly expensive, being literally hand-wrought from iron ore. Many of the “explosive” shells were in fact wooden spheres, usually banded with iron strips, and occasionally wrapped with leather.
The later hollow cannon shells (not really just a ball anymore) were indeed cast around a hollow core. There wasn’t a problem with wet clay, since the cores were baked dry beforehand.
Once the ball was cast, some flunky with an iron rod and a mallet pounded out the clay through the support strut, which then became the fuse hole.
I worked in a steel foundry once (long ago) and casting iron and steel parts with interior hollows was routine. The trick was to put molded sand inserts where you wanted the hollows to be.
You probably already know most of this but – each mold consisted of two halves of a positive image, usually made of wood. A metal casing was placed around each half, which was then filled with sand. The sand wasn’t dry – it had a special binder mixed in to help it hold its shape. The sand was compressed (hydraulically) and then the positive image was withdrawn, leaving a negative to be filled by the cast. At this point the skilled mold operators would inspect the negative, removing any inclusions, filling any gaps, etc. This is also the point where they would add any interior inserts. These were also made of sand but they used a stiffer binder and were baked to allow them to be handled without falling apart. Part of the mold design was to provide slots that would support the inserts. If the design called for an insert was cantilevered out too far it was supported by what were essentially toothpicks, which would provide support until the metal was poured and then they would burn away.
There are limits, of course, to how big these inserts could be. You couldn’t have a great big insert supported on a tiny little neck, which is what you want for a thin-walled hollow cannonball. There would be some limit to just how hollow the cannonball could be and still be cast in one piece.
Getting the sand out after casting is not a problem. The heat of the cast destroys the binder and the sand falls out. In our foundry there was a big shaker table at the end of the casting row to shake out the loose sand.
I’m sure there have been advances in chemistry to make better, more reliable binders, etc., but metalcasting is an ancient art and I doubt they did it much differently back in the cannonball days. (Which were, for the record, before my time.)
The earliest refernces to shells I can find refer to 15th century models made out of two iron halves filled with powder and joined together with an iron band. By the 17th century there are references to hollow iron frames wrapped in leather. these were used up until the 19th century.
Some mid-18th century balls still in museums were made of strips of metal ,commonly bronze, coiled into a spherical shape like an apple peeling. These had the advantage of allowing the gaps to be filled with the match fuse.
So the answer to the question seems to be that there were any number of techniques used.
I’ve done a little bit of metalcasting in various sculpture classes. The “lost wax” technique was, I believe, developed by the romans and is still used sometimes today.First you would make a positive mold of your object (cannonball) but you would make it in wax. In wax it would be much easier to stick two empty halves of a ball together. Leave a hole in the ball that leads to the hollow cavity and fill it with a plaster and sand mixture. Attach wax rods to the outside of the ball (plumbing for the metal to get in). Than encase the mold in more of your plaster/sand. Stick the entire mold in a burnout kiln upside down for a time and the wax will melt and drip out leaving a hollow cavity in the mold which can then be filled with molten metal. Chip away the plaster from the outside and the inside and you have a hollow metal ball which you could fill with gunpowder plug up the hole and send it as flaming death at your enemies.
I realize this is rather time consuming and complicated for cannonballs that need to be produced by the dozens so they probably found a better way of doing it, but this is the traditional method of pouring metals. So I guess this was all just an excuse to talk about metalcasting because its so very cool. Its extremely intense to be decked out in flame retardent clothing and welding leathers and to be pouring molten bronze. It blows your mind. Art never looked as good as it does when its still a 2100 degree liquid. lol
I had always thought that this was a Hollywood myth, that cannonballs were solid and did their damage through brute kinetic energy, best used against stone walls and such. Even in the American Civil War, circa 1865, cannons were using solid ammo. When attacking infantry instead of fortifications, scattershot was used in the cannons.
I would expect that a powder-filled cannonball would be just as liable to explode on firing as it would on impact. I would think that until fusing mechanisms were developed (late 1800’s) a hollow powdered cannonball would be impractical. The only thing I could think of is a cannonball that has it’s own lit fuse that later explodes after impact, which would require pre-igniting the cannonball itself before firing it.
Exploding shells were set off by a fuse carried along with the shell. They were commonly fired at a high angle to drop inside a fortification, with the fuse trimmed to a length that would detonate the shell just before impact. The British Navy used such weapons during the Napoleonic Wars.
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On lost-wax casting: Shortly before the movie Excalibur was released, I saw a TV interview with the [writer/producer/director?] talking about the origin of the word: ‘ex’ - Latin ‘out of’ and ‘calibur’ - Arabic ‘mould’. He said that lost-wax casting was used to attach the handle and hilts securely to a sword blade. Carve it in wax, cover with clay, fire it to get rid of the wax, and pour molten metal in place around the blade. I don’t recall him mentioning it, but I sould speculate that since we call fired-clay dishes ‘stoneware’, that would give us the ‘Sword in the Stone’.
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Yeah, you’re completely wrong, but you’re also beyond help.
Seriously though, like I said above shells have been around since the 15th century and of course fuses just as long. The first fuses were just metal tubes filled with powder and attached to the shell. The detonation form firing lit the fuse. Not real reliable. Later wooden fuses were marked for length of burn and could be cut to order. By the mid 17th century they had fully functional match fuses that were lit prior to the cannon being fired. Like RJK said they could be timed fairly precisely to detonate just above the ground.
