November 16, 2012
Historic trades poured the barrel of a light three-pounder October 25. The resulting casting shown here is still covered with mold material and flash and is actually prettier than it looks. Next, the barrel will be drilled and polished.
November 14, 2012
The next morning, Friday the 26th, members of the crew as well as a handful of onlookers gathered at the furnace. They excavated the mold, hoisted it from the pit, and went at it with a sledgehammer to begin breaking the mold material away from the casting. Gradually the deadhead and the barrel itself began to emerge. Within half an hour, there were trunnions, a cascabel, a nicely shaped muzzle, and everything in between. With a great collective sigh of satisfaction, the experts pronounced that it looked good and sounded good, ringing like a bell.
The proof will come when we start to clean up the outside and drill the bore—but so far, so good. It was a great crew. The efforts of many, and the coordination of it all was, once more, a joy to watch. More to come, but for now, a big thanks to all!
June 6, 2012
Thursday’s pour was one of those half-full, half-empty glass days. But, in the end, I am certain that the half-full was way more important than the half-empty.
We had a great crew at the furnace all day. As you can see in the video, there was a much greater mix of modern and period clothing than in the past. In addition to Stephen Williams, foundry metallurgist at Newport News Shipbuilding, two apprentices from NNS also were there: Sean Massey and Jonathan Johnson as well as a member of the foundry’s melt crew, Andrew Piskorski. Phillip E. Harrison, industrial designer and operator of Penumbra Design Studio, who also is involved in historical foundry work, came along at Stephen’s request, and Nick White, of Mendip Fireplaces in England, just happened to be in town. Enthusiastic supporters Billy and Nancy Stark were there, along with some other volunteers.
So, there were a variety of other sets of knowledge and experience to add to that of our Historic Trades founders, Suzie and Mike, and others from the Department. All-in-all, it was a day packed with high energy, hard work, free flowing questions, answers, and discussions, and a lot of congenial camaraderie.
The Shipbuilding crew had previously washed the interior of the mold parts with a refractory coating, and the day started out with setting the mold in the casting pit, tilting its top about 10° toward the furnace so that the bronze would run down along its side rather than straight down the middle—should be like pouring a good beer, one of the guys informed us.
As that was being done, we began to ramp up the heat in the furnace, taking its temperature with one of several pyrometers along the way and methodically recording time intervals of fueling, amount of fuel added, and the resulting effect. As this process went along, we learned a lot more about how the furnace was working and just what we needed to do to keep its temperature rising in a gradual curve. We also added a fire in the furnace archway under the melting area to make certain the melting floor was raised to a temperature that would preclude any bronze freezing to it.
In addition to the temperature-measuring equipment, the Shipbuilding folks and Phillip also added a couple other high-tech ingredients. One that proved very helpful was a ceramic cloth insulator donated by Specialty Foundry Supply that allowed us to open and close the fuel feeding opening more readily and also insert behind the feeding door to more precisely control the air intake there. The second was the use of FOSECO insulating sleeve tube, cut in half longitudinally to use as the pouring trough. It is such a good insulator that it doesn’t pull heat from the bronze as it runs, and it is much more reliable and cleaner than the heated clay troughs we have used in the past.
All of these modern bits significantly reduced the variables with which we were contending and let us concentrate on the basic furnace operation.
Morning fueling of “10 at 10”—ten sticks of oak kindling at ten minute intervals—soon changed to varying amounts of wood at experimental intervals. When things really got rolling, it was “10 at 4”.
A couple of times, the furnace temperature seemed to plateau out, but a bit of experimentation got things moving again. A couple of times it dropped, but experimenting with the amount of air drawn through the ash pit, allowing air to enter via the charging door, and the setting of the chimney dampers again led to everything moving nicely along.
This Tin Bronze (90% copper & 10% tin) begins to liquefy at 1550 degrees and then reaches its liquidus at 1850 where it is completely liquid. Stephen and Phillip decided that the best time to pour would be after the metal reached and stabilized between 1900 and 2000 degrees F. We had hoped to do that about 1:00, but given temperature stalls and ups and downs, it actually was approaching 7:00 pm before we decided to go. The last couple of temperature checks using a pyrometer with a probe to dip into the metal gave the desired results, but something was wrong. Stephen and Phillip noticed a difference in how the inside of the melting pan looked.
Just as we were about to pour, they realized that the level of metal was lower than before and dropping ever more rapidly. The melting chamber had developed a leak. We decided we had to pour right then. As seen in the video, the bronze came rushing out of the tap hole, stalled for a while when the iron plug inside blocked the flow, but resumed again when Stephen raked it out of the way. It was a beautiful pour—just what we had hoped for—except that we had only about half, maybe even less, of the bronze needed to fill the mold.
Everyone was disappointed—such a last minute unforeseen—but encouraged nonetheless. On Friday morning, we dug up the mold, broke it away, and found we have what looks like a really nice back end of a light three pounder, from cascabel to about where the trunnions begin. The surface looks good and the casting rings solid. We’ll know more when we cut into it.
In the meantime, though, we are realizing we are way ahead of where we were when we began this pour. We know much more about how to heat the furnace and its idiosyncrasies. We have a better loam mixture for the molds, and using the modern mold wash resulted in a good cast surface. The poling process to burn off impurities worked well, and the mechanics of tap hole, plug, and pouring trough worked extremely well.
In addition, we have been fortunate to form an awesome team to continue the project. All are ready to get the furnace repaired (which looks like it may not be all that difficult) and making another set of molds to try it again this fall. Being out there on the site all day, feeling the anticipation and curiosity, listening to the exchange of ideas, knowing that we were approaching things with much more insight than in the past, and, despite the hard work, seeing people enjoying themselves, each other, and the project is a great example of what the preservation aspect of Historic Trades is all about.
May 24, 2012
Turns out that we do not have the connectivity to set up a webcam out at the furnace, but we will try to post pictures as they are available.
In the meantime, we began preheating the furnace on Monday and have been heating it slowly since with a fire at ground level in the furnace ash pit. This morning the interior reached about 1000⁰ F. The folks from Newport News Shipbuilding have been monitoring the temperature with a “point and shoot” pyrometer and have been providing us with some other high-tech assistance. We’ll fill everyone in on details later.
At this point, we want to hold a temperature somewhat below the melting point to heat up the entire mass of the furnace, and, as we get closer to pouring, we will build a fire in the archway under the melting floor to ensure it is heated and the bronze doesn’t freeze to it. We also are playing with chimney dampers and an iron door covering the upper ash pit opening. When it is decided to start ramping up the temperature for the melt, we will move the fire up to the fire grating higher in the furnace. Don’t know yet exactly when it all will take place. We’ll wait until it is ready, whenever that is.
May 11, 2012
Our apologies for the absence of recent posts to the cannon blog. Historic Trades’ attention has been focused on the Armoury project and a host of smaller undertakings around town, but a group of folks has been working diligently behind the scenes to get ready for another pour.
After our failed pour of June 2010, the Historic Trades brickmasons removed the entire superstructure of the furnace down to the melting pan. Examining the mass of bronze there did not reveal anything conclusive about the failure, but reinforced the probability that the metal simply was not hot enough when we tapped the furnace. Based on that, the founders, gunsmiths, and masons made some changes in the furnace design, and beginning last autumn, the masons rebuilt the furnace accordingly. The new design also incorporates a wooden shed, built by the Historic Trades carpenters. This shed will cover the kiln to protect it from the weather on an everyday basis, provide some protection for the furnace should it rain during the firing process, and t better support the hoisting gear with which the molds and castings are handled.
Cutting up the hunk of bronze left in the furnace so that we could reuse it was more difficult than expected. After a couple unsuccessful attempts, rescue came in the form of Newport News Shipbuilding. Several of their employees picked up the mass, hauled it to Newport News, used some of their specialized equipment to cut it up, and returned it to us in pieces that we can set directly into the furnace.
While all this was going on, the founders and gunsmiths completed another set of light three-pounder molds. Their experiments with new loam mixtures led to much more satisfactory results than in the past. When they removed the core and burned out the wax, they ended up with sharp, clean interiors, and the molds seem to be more sturdy than earlier ones. They will take the molds over to the College of William and Mary on May 7, where Professor Mike Jabbur will fire them to a “redware” hardness and ensure that they are completely dry.
So, we are ready to try again. With some extremely helpful advice and hands-on assistance from Andrew Eshelman and Stephan Williams of Newport News Shipbuilding, we are planning to pour on Thursday, May 24. We will be preheating the furnace much longer than in the past, and will be using a modern pyrometer to monitor heating more accurately and better understand how the furnace is operating.
The proposed schedule — all weather dependent, of course — from now until then is:
May 7: Load molds in ceramic kiln at the College of William and Mary
May 9: Pick up molds
May 14: Test fire furnace
May 21: Load bronze in furnace and start preheating
May 22: Continue to raise furnace temperature
May 23: Continue firing. Bury mold
May 24: Build tapping channel. Bring bronze to pouring temperature. Pour.
May 25: Excavate mold and open
From May 21 until pouring, this will be a round-the-clock operation. As before, it all will be happening adjacent to the parking lot across from the Visitor Center and adjacent to Great Hopes Plantation.
November 4, 2010
This June’s attempt to pour the light three ended in disappointment. It is pretty obvious that the bronze “froze” at the inside end of the tap hole as it started to flow. It wasn’t hot enough to run—that was one problem at least. There might be others we have not yet uncovered.
We have begun to disassemble the furnace to see if we can determine what happened and what we need to do to correct the problem. So far, we have removed masonry down to the tap hole and sectioned the tap hole itself.
Over the next few weeks, we will be getting further into the furnace structure to see what else might be revealed and to figure out how to remove the 500-pound mass of bronze that remains in there.
We have not yet removed the molds from the ground—something we will have to do to prepare for the next pour. The molds were almost certainly damaged by an afternoon downpour the day of the pour, and we are not going to re-use them.
The founders are in the process of making a whole new set of molds while the weather remains good this fall. Much of this is an outdoor activity, and we want them to be complete and ready to use when we are set to make another attempt early next spring.
Over the winter, with new information in hand, the masons and founders will determine what modifications should be made to the furnace to increase its heating capability and any other problems associated with it. They will rebuild/modify the furnace next spring when weather and time permit, and another pour will follow shortly.
This project is possible through a generous gift by the Ambrose and Ida Fredrickson Foundation. Research assistance was provided by Firepower: The Royal Artillery Museum, and the National Park Service. We are grateful to the Museum Restoration Service and The Royal Artillery Historical Trust for the use of their images.