Chapter 104: Casting Cannons (III)

Now the artillery team faced another choice: whether to adopt the solid casting plus deep drilling process to manufacture the barrel, or to continue using the hollow casting method.

“Let’s try the drilling method next, shall we? But we have to build a drilling machine first.” The few people in the machinery group were all enthusiastic.

“The drilling method is a bit difficult,” Lin Shenhe thought for a moment, “and the efficiency is a bit low. I think we can try Rodman Casting.”

“Center cooling casting?” Wang Luobin asked.

“You know about it?” Lin Shenhe was a little surprised. “I thought not many people in the country knew about this.”

“Personal hobby, purely personal hobby.” Wang Luobin thought to himself, if I weren’t in a major aquatic products country and not as free to do whatever I want as you are in the decadent American empire, I would have cast cannons long ago.

The so-called Rodman Casting method is the inner mold water cooling method.

Its principle is very simple: the cooling rate of cast iron during casting will affect its mechanical properties. Theoretically, the higher the cooling rate, the harder the texture. The ideal cannon is the hardest in the middle (the bore), but the reality is the opposite. When casting a cannon, the middle cools the slowest. Because the first outer layer wraps the inner layer, the inside cannot cool down if the outside does not cool down. Secondly, the surface area of the outer tube is also larger than that of the inner tube. Whether it is radiation or convection heat conduction, the heat dissipation speed is equal to the surface area, so the outside will cool first. This makes the distribution of the barrel density not ideal, and the life of the barrel is greatly reduced.

The one that cools first shrinks first. After the outer layer cools and hardens, if the inner layer has not yet cooled, it will cause the outer layer to be harder than the inner layer, and the inner tube of the inner layer may deform, or cracks may occur when the inner layer cools. This leads to an increase in the scrap rate during cannon casting, shortens the life of the barrel, and sometimes affects the firing performance of the cannon.

During the American Civil War in 1860, US Army Major Thomas J. Rodman invented this hollow casting process, casting cannons around a core, and cooling the inside of the core with running water. This is a method that allows the inside of the bore to harden first. This is the so-called Rodman Casting method. This process was a logical development of earlier sleeve cannon experiments. When the outer metal cools, it shrinks inward and continues to press on the already hardened inner layer. In this way, the explosive force of the propellant is absorbed by the entire thick metal layer around the bore, instead of expanding outward layer by layer. Most of the heavy cast iron cannons of the US Navy were manufactured using this method during the Civil War and for the next 20 years. The greatest significance of the Rodman Casting method is that it greatly reduces the scrap rate of cannon barrels during casting, especially when casting heavy cannons.

From a cost perspective, the Rodman Casting method greatly reduced the scrap rate and the casting cost of cannons. Secondly, this process greatly increased the service life of the cannon barrel and reduced the cost of use.

The enemies and potential enemies that the transmigrators faced were far greater than the transmigrators in terms of both manpower and material resources. To defeat them, the transmigrators had to control their various costs.

“This method can be tried, but in this case we have to make a hard inner mold that can hold water, so we can’t use the clay mold just now.” Ji Wusheng considered the casting problem.

“Let’s use the iron mold casting method. It seems that the Chinese were the first to use it.”

“That’s right, it was invented by Gong Zhenlin. He was a genius.”

Gong Zhenlin was the county magistrate of Jiaxing County, Zhejiang Province. He had nothing to do with the arms industry, but he had a reputation for being “ingenious.” During the Opium War, he was transferred to the Ningbo military camp by the governor of Liangjiang, Yuqian, to be specifically responsible for casting cannons.

At that time, China’s cannon casting technology was very backward. The method was:

Mix water and mud to make a mold, then cast it in layers. The mud mold must be thoroughly dried, otherwise, although the surface is dry, the inside is wet. When it encounters molten metal, moisture will be generated, and the cast cannon will have honeycombs. When fired, the barrel is easy to burst and injure people. It often took a month to dry a mud mold, and if it encountered rainy, snowy, or cold weather, it would take two or three months. Moreover, a mud mold could only cast one cannon and was then discarded and could not be reused.

From these descriptions, the technology used by Chinese cannon makers in 1840 was roughly the same as the European casting technology used experimentally by the transmigrators before 1713. However, some very simple processing methods used by European cannon makers 150 years ago, such as reinforcing ribs for mud molds, firing of mud molds, and boring of iron cannons after casting, were completely unknown.

The craftsmen had no standards for making mud molds. The dimensions and techniques were all in their minds, and they didn’t pay much attention to the proportions and dimensions of the cannons. These technologies, which were already far behind the times, were the craftsmen’s livelihood and were regarded as “secret methods.” There was no technical exchange or improvement. In this way, under the out-of-date cannon casting level, there were still multiple completely closed and mutually secret “schools.” The result was that the cannons produced were not even as good as the imitation Hongyi cannons of the Ming Dynasty.

Gong Zhenlin, because of the urgency of the war, the heavy loss of cannons on the front line, and the huge demand, if it took a month to produce a batch of cannons, the various forts in Humen, which had been dismantled by the British, would not be replenished for many years. After several experiments, he finally invented the iron mold casting method.

The iron mold casting method uses iron to make a hard mold. When casting a cannon, first brush two layers of slurry on the inside of each half of the iron mold. The first layer of slurry is made of fine rice husk ash and fine sandy mud; the second layer of slurry is made of top-grade fine kiln coal mixed with water. Then, the two halves are joined, clamped with iron hoops, heated, and connected section by section. Finally, the molten metal is poured. After the molten metal is poured and cooled to form, the iron mold is immediately peeled off in the order of the mold halves, like peeling off a bamboo shoot shell, gradually revealing the cannon body. Then, the mud embryo in the core of the cannon is removed, and the inside of the bore is naturally smooth.

Compared with traditional mud mold casting, the superiority of iron mold casting is that the quality of the cast cannon body is good, and the inner and outer surfaces are smooth, unlike mud molds that will cause bubbles in the cannon body. In addition, because it does not require the laborious application of mud molds to dry, the manufacturing speed is fast and is not affected by the climate. Because the mold can be reused, the production speed is fast, the output is large, the cost can be kept very low, and the greater significance lies in standardized manufacturing. Standardized manufacturing can mass-produce products with almost exactly the same appearance and performance, which is crucial for artillery.

His colleagues praised him, saying: “His method is the simplest, and its use is the most convenient. One worker can achieve the benefit of hundreds of workers, and one cannon can save dozens of times the cost. And it can be cast and produced in a short time, without delay, without flaws, naturally smooth, with half the effort and twice the result, and its use is endless. It is a guide for all discussions and opens a door for thousands of years. Its benefit to the country’s military preparedness is by no means small!”

Gong Zhenlin’s invention of mold casting for cannons was 30 years ahead of the West. This was a rare scientific and technological achievement in modern China that led the world.

The artillery team continued to harass the wood processing factory, asking them to first make a male mold out of wood. Then Ji Wusheng and Zhan Wuya worked together to carry out sand casting to cast an iron female mold, which could then be used to cast cannons. The core was also made of iron, hollow inside, with pipes at both ends for water inlet and outlet.

When the molten metal was poured into the mold, the molten metal began to cool slowly. At this time, the water in the inner mold came into play. The molten metal near the inner mold was the first to cool and solidify into steel under the action of water, while the molten metal in the outer layer cooled more slowly. Because of the principle of thermal expansion and contraction, when the entire casting was cooled, the later cooled part of the outer layer would tightly hoop the first cooled part of the inner layer. In this way, the entire casting would produce an inward hooping force. It was with this force that the barrel could withstand a greater chamber pressure. This method of controlling cooling with an inner mold can have the effect of “barrel self-tightening.”

The service life of the barrel processed by the barrel self-tightening process is greatly extended, and the thickness of the barrel can be greatly reduced, reducing the weight and increasing the mobility of the artillery.

The process of Rodman Casting was very simple. After having the mold, the artillery team quickly produced the first finished product. This cannon was much better than the one made with a clay mold. In particular, the cannon body no longer needed any polishing, and the smoothness of the bore was also greatly improved. Although the boring process was still needed, the consumption of cutters was much smaller.

In order to test whether the cast cannon met various technical parameters, the artillery team decided to conduct a test firing at Bopu. The cannonballs were solid balls made of cast iron. During casting, the clearance accuracy was controlled as much as possible to prevent it from being too large. The machinery group manufactured two-wheeled gun carriages for these two cannons, and also brought a limber, which looked very much like the real thing. Wang Luobin went to the farm once and borrowed 4 horses from the farm. But when the horses arrived at the scene, a problem was discovered: there was no suitable harness for multi-horse traction—the two-wheeled carts running on the highway were all single-horse traction, and the harnesses were also directly bought from the original time and space. Although the harness is not a profound knowledge, no one knew how to make it. In the end, they had to continue to use the database and found the answer from a photo.

Before the harness could be made, the impatient navy heard that the cannons had been cast and immediately sent a boat to transport the cannons. The two 6-pounder cannons and their carriages were tied to a raft of empty oil drums and towed to Bopu Port by a boat.

The cannons were placed on the open ground next to the shipyard in Bopu. There was an endless stream of people coming to watch the excitement, especially the navy personnel. Almost everyone was fond of these two black iron cannons. No matter how they looked at them, they were lovely. A navy man named Li Haiping simply proposed to install the cannons on the ship just like that.

“Install them on the ship? Look clearly, this is a towed 6-pounder cannon, a genuine army artillery piece.” Zhang Bolin saw that his beloved cannon was about to be taken by the navy and immediately jumped out to stop it.

“Come on, it’s still towed. Can you give me a self-propelled one?” Li Haiping looked disdainful. “The navy doesn’t even care about this little broken cannon.”

“What did you say?!” Zhang Bolin was furious and wanted to rush up and punch him to show him the power of the army.

“What are you arguing about?” Wang Luobin hurried over to smooth things over. “It’s still unknown whether this cannon can be fired. What are you arguing about!”