At long last on Thursday last week, we got to open the mold! We cut some welds off of the side and began digging! We'll just get right too it, shall we? The first few of these pictures were taken by Helena Jonsson who is the managing director at Tierp.
Success! There is a cannon in the mold! The details look great. However, there was one problem in that the bronze permeated the sand in places in the mold, creating a mixture of sand and bronze that was an exact mold of the surface. This was a little unexpected and something I'd never seen, but apparently with the right heat and pressure, you can force molten bronze in between the air space and grains of sand! Crazy physics, but very annoying to remove.
In places where this was thin, a simple hammer and chisel could be used to remove it, thicker section took a torch and a jackhammer, leading to some errant blows that will need to be repaired. However, all and all, the cannon looks great, the core seems to be able to be removed, and it looks solid. Heres a bunch of pictures of the 30 hours I spent with a jackhammer and one of the biggest air fueled torches I've had the pleasure of using!
When you run a grinder over the surface, it is mostly bronze.
Ladle warming torches are the coolest.
It took me the better part of 30 hours to get to this point. Ooof.
The final pieces of decoration, including the Coat of Arms. It was amazing that that stuff wasn't adhered to the surface, I can thank the graphite coating for that!
Also, we needed to remove the gunhead, the extra material at the end of the gun that helps feed the gun as it cools! After that, they began drawing the core rod with a 100 ton jack, they had moved it about 15 cm before I needed to leave.
With a little bit of luck, they'll pull the core and ship the cannon down to the museum tomorrow or Monday, and I can treat you guys to some nice photos of it before I head back home to the United States for the time being!
Also, a few exterior links from the media and video stuff!
Applogizing for the late update! But we we're asked to wait for the media to publish first! We poured the cannon on friday, first and foremost. We had members of the media and other employees from Vasamuseet present for the event, as well as no less than three crews filming! All of these photos were taken by Evelyn Ansel, current Fulbright Researcher, as I am the former Fulbright Researcher.
Martin Wildman and his camera man from Deep Sea Productions!
Monica and Håkan, you may know them from Vasa's regular blog, they're some of the ship's carpenters!
Thomas Carlsson, the foundry master and Bertil Bjorkman, the head of the Friends of Vasa.
Dr. Fred Hocker and I!
Our materials for the day had to be made, Bronze is a copper alloy and we needed to produce our own. We used pure copper that has been reclaimed from wiring and electronics by the foundry's parent company Lantz Metal, which specializes in this. Then since the alloy we were aiming for requires about 5% tin, 1% lead and 1% zinc, we loaded the crucibile with additional bronze and brass scrap, as well as 90kg of old pewter commemorative plates, some of which even came from our own museum shop in years past!
After a bit of melting, mixing and checking, we arrived at about what we needed. We poured the metal out at a crispy 1200C into the ladle to warm the ladle up, then we pour the metal back into the furnace. We did this process again and while we had the metal out, we poured the lifting dolphins.
At this point, we were ready to pour. We had set up the mold the day before so we could concentrate on getting the metal mixture right, so all we had to do was dump the mold back into the ladle for the 3rd time. This time, however, we ramped the furnace up to 1300C so while we transfered the metal into the room with the mold, it would not drop below our optimal pouring temperature of 1150C! The ladle was skimmed and poured! It went off without a hitch!
After we poured the metal we had a good round of congradualtions, photography and interviews! Then we got to have a mini christmas in opening up the molds for the lifting dolphins! We were a little worried that one of them may not have cast due to a leak in the mold, but they came out beautifully. Johan, one of the owners of Lantz and Tierp was also able to check the alloy with this cool hand held x-ray spectrometer that we suspect could also turn you into the Incredible Hulk, and that was spot on as well!
The failed casting.
The good casting!
Now, Thursday we should be able to open up the mold and see how we did, if the actual pour day is any indication, we should have done very well, but you never know what surprises are in the mold! But knock on wood and hopefully there a beautiful bronze Vasa 24 sitting inside our 7 ton Christmas present on Thursday!
Well here it goes, we've started on the real deal which we plan to cast this Friday! Which means a cannon with pretty ornamentation and everything! However, over the last few months the plastic parts I had previously cast had broken. So I had to go back to the old molds and recast all of the plastic details. What I could do with some of the details that were broken was to see if my theory on the mold release of the plastic parts would work. And amazingly, it works easily and crisply for making details on a round surface! During this I was also able to make molds of the dolphins to be attached to the top of the cannon!
After recasting the plastic, we could go back to mold making! And it went very well again, we were able to pull all of the details with incredibly little damage to the mold, just a few of the deeper details in some of the ornamentation broke, but it can all be fixed in the metal. So they're just attached to the mold with double sided tape, its a really simple set up. I had to sand the silver paint off of the model so the tape would stick, but other than that, very straight forward.
Once I set all of the ornamentation we made the mold! Next day, we were able to pull the mold and see the results!
One of the other things we needed to handle this week was re-lining a furnace and a ladle. This is because you can't melt more than one type of metal in a furnace or ladle without risking contamination. The ladle is made of a heat reflective cement called refractory cement. And the process of doing this is pretty straight forward. a fiberglass matting is applied to the inside of the new ladle, this keeps the cement from actually adhering to the ladle's body for easy removal later. Then they put some cement on the bottom of the mold, and place a mold form over that which just takes up the bucket and spout shapes on the inside of the form. Then once it has solidified, it needs to be cured with heat, which mounts to just starting a wonderful pallet fire inside it! As far as the furnace goes, I didn't get to watch that because I didn't know it was happening. However I know that the second furnace is functional and clean!
And now to wait until Friday!
A successful test! Not perfect, but certainly was a good attempt. The mold held together, and poured wonderfully well. When I came back to Tierp on Monday, the flask had been put outside and we went to open it up! A few things went really well, and a few things could be improved. The mold registered really well in the round, about 1mm off of being perfect, and not as well front to back, about 3-4 mm off of lining up all of the details. The rod holding the core in place is seemingly stuck, but we can't really see what is holding it. So to fix these on the next round of mold making I've made some adjustments and figured out a new way of centering the core in the back of the mold. The surface of the casting was fantastic, though!
Also, for terms of this casting we learned that this mold contains so much thermal mass the the molten iron can fuse the silica sand used in the mold. While its not cemented to casting itself, it creates an incredibly tough cementlike casing around the entire mold. We don't think this will be a problem in the bronze though, as the bronze is much cooler to cast.
And another update to come!