Chapter 146: Casting Cannons (Part 3)

The Artillery Group now faced a crossroads: should they pursue solid-casting with deep-drilling for their barrels, or continue refining their hollow-casting technique?

"Why not try the drilling method next?" suggested the Mechanical Group members, their enthusiasm undimmed. "Though we'll need to build a drilling machine first."

Lin Shenhe shook his head. "Drilling is finicky work, and the efficiency leaves much to be desired. I'd recommend we attempt Rodman Casting instead."

"Center-cooling casting?" Wang Luobin asked.

Lin Shenhe raised an eyebrow. "You've heard of it? I didn't think many people in China knew about the technique."

"Personal hobby," Wang Luobin replied with a slight shrug. "Purely a personal hobby." What he kept to himself was the thought: If I hadn't been stuck in a nation where such things were frowned upon—not free like you in decadent America—I'd have cast my own cannons long ago.

The Rodman method, properly called internal-mold water-cooling, operated on an elegantly simple principle. The rate at which pig iron cooled during casting directly affected its mechanical properties—faster cooling produced harder material. Ideally, a cannon should be hardest at its center, around the bore where the greatest stresses occurred. But conventional casting produced exactly the opposite result. The bore cooled slowest for two inescapable reasons: first, the outer layers enclosed the inner ones, preventing the exterior from cooling before the interior; second, the outer surface area far exceeded the inner, and whether through radiation or convection, cooling rate remained proportional to surface area. The result was that the outside hardened first, leaving the barrel's density distribution far from optimal and dramatically reducing its service life.

What cooled first also shrank first. When the outer layer hardened while the inner remained molten, the exterior became harder than the interior. The inner bore might warp, or cracks could propagate as the center finally cooled. This phenomenon drove up rejection rates, shortened barrel lifespans, and sometimes compromised firing performance entirely.

During the 1860s American Civil War, U.S. Army Major Thomas Jackson Rodman devised an ingenious solution: a hollow-casting process that placed water-cooled cores at the center of the mold. This forced the bore interior to harden first. As the outer metal subsequently cooled and contracted, it pressed inward against the already-hardened inner layers, placing them under compression. When propellant detonated, the explosive force would be absorbed by the entire thickness of metal surrounding the bore rather than expanding outward layer by layer. Throughout the Civil War and the two decades that followed, this method produced most of the U.S. Navy's heavy cast-iron artillery. Its greatest virtue was the dramatic reduction in casting rejections, particularly for the largest cannons.

From a cost perspective, the advantages compounded. Fewer rejected castings meant lower production costs. Extended barrel lifespan meant reduced operating expenses over time.

The travelers faced enemies and potential enemies who commanded far greater manpower and resources. To prevail against such odds, the transmigrators needed to control every cost they could.

"This method is worth pursuing," Ji Wusheng said, working through the casting implications. "But we'll need a hard core capable of containing water—clay molds won't do."

"Iron-mold casting, then," someone suggested. "Apparently the Chinese invented that technique first."

"Correct—Gong Zhenlin developed it. The man was something of a genius."

Gong Zhenlin had served as deputy magistrate of Jiaxing County in Zhejiang, a position that would seem to have nothing to do with munitions. Yet his reputation for being "naturally clever" preceded him, and during the Opium War, Governor-General Yu Qian transferred him to the Ningbo military camp specifically to oversee cannon production.

At that time, Chinese cannon-casting remained extraordinarily primitive. The traditional method involved mixing clay with water to form molds, then casting molten metal layer by layer into pattern joints. These clay molds had to be completely dried before use—if the exterior appeared dry while moisture lingered within, contact with molten metal would flash that moisture into steam. The resulting cannons would be riddled with honeycomb voids; firing them risked bursting the barrel and killing the crew. Drying a clay mold often took a full month, and during rainy, snowy, or cold weather, the process stretched to two or three months. Worse still, each mold produced only a single cannon before being discarded. None were reusable.

From these accounts, it was clear that the techniques employed by Chinese cannon smiths in the 1840s matched the pre-1713 European methods the transmigrators had experimentally replicated. Yet simple refinements that European smiths had adopted a century and a half earlier—mold reinforcement ribs, kiln-firing the molds, post-casting bore polishing—remained completely unknown.

The craftsmen worked without standardized mold-making procedures; dimensions and techniques existed only in their memories. Proper cannon proportions received little attention. These already-obsolete methods constituted the artisans' livelihoods and were jealously guarded as "secret techniques." No technical exchange occurred; no improvements emerged. The craft existed in complete isolation from the era, yet paradoxically fragmented into multiple closed schools, each keeping its methods hidden from the others. The predictable result: the cannons produced were inferior even to Ming-dynasty copies of the Red Barbarian Cannon.

Gong Zhenlin faced a crisis. With warfare raging, cannon losses mounting, and demand insatiable, he could not afford to wait a month for each batch. Through determined experimentation, he finally invented iron-mold cannon casting.

The process used iron to create rigid, reusable molds. Before casting, workers brushed two layers of slurry inside each mold segment. The first layer consisted of fine rice-hull ash mixed with sand-clay; the second, high-quality fine kiln coal suspended in water. The segments were then assembled and clamped together with iron hoops, heated thoroughly, connected end-to-end, and finally filled with molten metal. Once the liquid had set and cooled sufficiently, the iron-mold segments were removed like peeling bamboo shoots—gradually exposing the barrel. The internal clay core was extracted last, leaving a bore interior that emerged naturally smooth.

Compared to traditional clay-mold casting, the advantages were transformative. The barrels produced were high-quality with smooth interiors and exteriors, free from the air bubbles that plagued clay molds. The laborious preparation and interminable drying periods vanished—production became fast and weather-independent. Reusable molds enabled rapid output, high volume, and low cost. But the greatest significance lay in standardization. For the first time, manufacturing could produce batches of cannons with nearly identical external appearance and performance—a consideration of paramount importance for artillery.

Colleagues praised the innovation extravagantly: "The method is extremely simple; its application extremely convenient. One worker achieves the benefit of a hundred; one cannon saves tenfold the cost. Casting produces immediately, without delays. Flawless and naturally smooth. Half the effort, double the results, with endless utility. He has pioneered untrodden paths and opened methods for a thousand years. How could such military benefit to the nation be called trivial!"

Gong Zhenlin's iron-mold casting preceded comparable Western techniques by thirty years—one of China's rare modern-era achievements in world-leading technology.

The Artillery Group returned to pester the Lumber Factory, first producing wooden positive-molds. Then Ji Wusheng and Zhan Wuya collaborated on sand-casting to create iron negative-molds for the actual cannon casting. The cores were also iron—hollow inside—with water inlet and outlet pipes fitted at either end.

When molten metal filled the molds, it began its slow cooling. Then the water circulating through the inner core came into play—the metal nearest the core cooled first, solidifying into steel, while the outer portions cooled more gradually. Due to thermal expansion and contraction, by the time the entire casting had cooled, the slower-cooling outer portions had constricted tightly around the earlier-cooled inner portions. This generated an inward clamping force that enabled the barrels to withstand far greater chamber pressures—the controlled cooling of the internal mold achieving what was known as the "barrel self-stressing" effect.

Self-stressed barrels enjoyed dramatically extended service lives. They also permitted substantially reduced barrel thickness, cutting weight and improving mobility.

The Rodman Casting process itself was surprisingly straightforward. With the molds prepared, the Artillery Group quickly produced their first finished cannon. This piece was far superior to any clay-mold version—most notably, it required no bore polishing. The smoothness of the bore had improved markedly. Some polishing remained necessary, but tool consumption dropped considerably.

To verify that the cast cannons met their technical parameters, the Artillery Group scheduled test-firing at Bopu. The shells were solid shot of cast iron, with bore-gap tolerances carefully controlled during casting. The Mechanical Group constructed two-wheeled carriages for both cannons and built ammunition limbers to accompany them. The assembled pieces looked quite professional. Wang Luobin visited the farm and managed to borrow four horses. But on-site, a problem emerged: no one had suitable multi-horse harnesses. The two-wheeled carts used for road transport employed single horses, and harnesses for those had simply been purchased from the original timespace. Nobody knew how to make harnesses for multiple-horse teams. In the end, they had to consult the resource library yet again, finally finding the answer in a photograph.

Before the harnesses could be completed, the impatient Navy got word that the cannons were finished and immediately dispatched a rowboat. The two six-pounders and their carriages were lashed to rafts made from empty oil drums and towed by the rowboat to Bopu Harbor.

The cannons were set up on open ground beside the Bopu shipyard. Spectators streamed past in an endless parade—the Navy men especially, nearly all of them finding excuses to fondle the two black-iron guns. Beautiful from every angle, they agreed. One sailor named Li Haiping proposed mounting them on ships immediately.

"Mount them on ships?" Zhang Bailin bristled the moment he heard, leaping to object. "Look clearly—these are towed six-pounder field cannons. Genuine Army guns."

Li Haiping looked thoroughly unimpressed. "Forget 'towed'—you got self-propelled artillery? These little popguns? The Navy doesn't even want them."

"What did you just say?!" Zhang Bailin's hackles rose; he looked ready to throw a punch and demonstrate Army strength firsthand.

"What's there to argue about?" Wang Luobin hurried over to mediate. "Whether these cannons can even fire remains to be seen. Why bicker before we know?"

(End of Chapter)