Sweep Yuan

Chapter 149 First, Solve the Difficult Problems in Casting Heavy Machinery

With Chuzhou now captured, the Red Flag Battalion has revealed its true strength and can no longer afford to hide its power. This will inevitably invite a stronger counterattack from the Yuan court.

However, there's no need to worry too much.

In terms of current prominence, the Red Flag Battalion is far less prominent than the Xu Song regime, which is currently expanding rapidly in Jiangnan.

Sesame Plum and Stone Mountain merely blocked the Yellow River and Huai River waterway, disrupting the Yuan court's grain transport from the south to the north, thus incurring the Yuan court's wrath.

However, river transport was only one of the lifelines of the Yuan Dynasty's grain transport. If river transport was blocked, sea transport could still be used as an emergency measure.

If the Xu Song regime continues its rapid advance until the situation in Jiangnan completely collapses, the southern grain supplies that the Yuan court relies on to survive will be cut off.

At that time, no matter if war breaks out in Henan and Jiangbei, the Yuan court will first mobilize a large army to suppress the Xu Song dynasty.

The rebel leaders, such as Sesame Li, Shishan, and Liu Futong, will all benefit from this and gain a valuable respite.

But no one knows when the Yuan court will march south, or how long the Xu Song regime can withstand the Yuan court's counterattack.

Shi Shan would never entrust his life to others; he would always need more means to protect himself.

The seat of Chuzhou was located in Qingliu County, at the Shishan Military Headquarters.

The bell-casting craftsman Ma Hua respectfully presented two blueprints to Marshal Shi with both hands.

"Based on the drawing provided by the Marshal, I have made some minor modifications to the parameters. I humbly request the Marshal to take a look."

The Battle of Qingliu proved that the bowl-shaped cannon was not capable of siege warfare. After the city was breached, Shishan drew a sketch of the cannon and handed it to Ma Hua, explicitly asking the latter to modify and improve the drawing by referring to existing casting techniques.

The old craftsman was very cautious, and after two days of careful consideration, he finally submitted the revised drawings to Shishan today.

There are two drawings. The first one was drawn by Shishan and has only some dirt on it.

Ma Hua didn't dare to modify the drawings directly, so he drew a second one. The overall structure of the cannon didn't change much; he only adjusted the dimensions of some castings and noted the reasons for the modifications and the specific parameters after the modifications.

Shishan didn't understand the technical details, but he was well aware of the principle of trusting people and believed in the professional opinions of Ma Hua and others. He only cared about the specific process and time required for casting cannons.

"What are the steps involved in casting such a bronze cannon, and how long does it typically take?"

Four years ago, Bi Si and others from Jiqing Road launched an uprising. Zhennan King Boluobuhua led an army of 100,000 to surround the rebel army, but failed to conquer it after a long siege. He even forcibly conscripted craftsmen such as Ma Hua to cast a "bronze general".

The Tartars, in their relentless pressure to meet the deadline, nearly drove the craftsmen insane.

Ma Hua didn't understand Shi Shan's temperament and worried that Marshal Shi was as eager for quick success as the Tartars, so he didn't dare to speak too confidently.

"At the fastest... it will take about six months."

Shishan knew that casting cannons was very time-consuming, but he did not expect it to be so long. He searched his memory to see if there was any way to shorten the casting cycle.

Seeing Shi Shan frown and remain silent, Ma Hua's heart tightened, fearing the marshal's displeasure, and he quickly explained:
"When casting bronze swords, even apprentices can forge swords up to two feet in length. But if they exceed three feet, even skilled master craftsmen dare not guarantee that they can forge them well. The cannon designed by the Marshal weighs dozens of times more than a bowl-shaped cannon, and the difficulty is simply too great. I dare not guarantee that I can forge it well on the first try."

The logic is simple: Shishan wouldn't assume that future generations could cast it well, and therefore force contemporary craftsmen to do so as well. He said:

“I understand that principle. Just tell me exactly what makes the cannon-casting process so difficult, and we can figure it out together and see if we can improve the process.”

Ma Hua was diligent and eager to learn from a young age. He studied under many master craftsmen and had been casting bells for decades. He was extremely experienced and did not believe that Shi Shan could provide guidance in his professional field. However, he did not dare to reprimand Marshal Shi and could only try his best to explain the difficulty of the process.

"When casting large objects, the first priority is to make molds. For small objects, one must first ask a skilled carpenter to carve wooden molds of the cannon body, cannon ears, and cannon hoops from cedar wood. Then, sand and mud are mixed with wool to make soft clay, which is then brushed onto the wooden molds layer by layer."

This step is the most time-consuming; each layer of sand and mud must be allowed to dry completely in a cool, shady place before the next layer can be applied.

As he spoke, Ma Hua glanced at Marshal Shi's expression. Seeing that he was listening attentively and showed no impatience, he breathed a slight sigh of relief and continued:

"To prevent the heavy gun barrel from damaging the clay mold during casting, each layer of clay mold needs to be reinforced with iron wire, and the outer layer needs to be reinforced with iron strips and hoops. The thickness of the clay mold after it is formed is about 1.6 to 1.7 times the inner diameter of the gun barrel."

After a brief pause to allow Shishan to process this step of the explanation, Ma Hua continued:

"In addition to the outer clay mold, an inner core mold also needs to be made. After the surface of the core mold is brushed with coal ash slurry, it also needs to be placed in a shady place to dry. If it is a bowl-shaped cannon, the inner and outer clay molds can be dried in about half a month; but the cannons needed by the marshal are too big, and it may take three months for the clay mold and core mold to dry completely."

Meanwhile, materials were prepared and the furnace was started. Once the clay mold was completely dry, the wooden mold was removed before molten bronze could be poured in. After pouring, the cannon body cooled and solidified, which took another five to eight days.

"After that, opening the fire gate and setting off the firebox didn't take more than a few days."

Ma Hua then changed the subject, looking troubled, and said:

"But the Marshal required that the bore be smooth and round, and that the inner diameter be the same from front to back, which is an extremely delicate and slow process. It requires a skilled craftsman to slowly grind it with a whetstone. When I cast the bowl-shaped cannon, I did not have this process, so it is really hard to estimate how long it would take."

Ma Hua truly deserves his reputation as a master craftsman; he explains complex concepts in a simple and easy-to-understand way.

Shishan had already understood the process of casting cannons and knew that the most time-consuming parts were the mold making and the grinding of the barrel.

Suddenly, a thought flashed through my mind: the inner bore of cannons in later generations was mostly milled by milling machines. I wonder if it would be feasible to cut bronze with refined steel as the milling cutter. I'll have to verify it later.

If successful, the milling machine can be converted to hydraulic drive, which will save even more time and effort.

As for the most time-consuming part, making the clay mold, Shishan had at least seen some casting videos and knew that this outdated technique had been phased out in later generations, so he immediately raised his doubts.

"Master Ma, why must we use a mixture of sand, mud, and wool for making the mold? Wouldn't it be better to use finer clay instead?"

This is a question usually asked by apprentices, yet Marshal Shi humbly inquired about it. Ma Hua was very pleased and patiently explained:
"If the mud contains moisture and air, it will cause air holes all over the cannon body during casting, or even cause the mold to explode and injure people. The sand and mud mixed with wool is for ventilation. Layering the mud is also to make the moisture dissipate faster. Even so, it cannot be guaranteed that every mold will be able to become a cannon."

Ma Hua hesitated for a moment, then decided to speak frankly to avoid being punished by Shi Shan if the cannons failed to be cast. He said:

"Old man, when casting the bowl-shaped cannon, always keep double the amount of clay molds on hand, in case of discarded cannons need to be recast. The clay molds used for cannons are many times thicker, making it even harder for moisture to escape. And since this is my first attempt, I'm afraid only one in ten will survive. It would be safer to have at least ten times the amount of clay molds on hand." Shi Shan had calculated that the bronze cannon he designed would weigh over 700 jin, and he planned to cast six at once. Because he had only collected this much copper material, even if Ma Hua made sixty clay molds, he could only cast a maximum of six cannons at a time.

Only after it has completely cooled down can you first check for air pockets, and then gradually increase the charge from 50% to test whether it can reach the designed chamber pressure.

If we calculate based on a 10% success rate, and if we're unlucky, it would be difficult to cast six cannons within six months, let alone a year.

But Ma Hua's explanation still cleared up Shi Shan's doubts.

Sand and mud have poor air permeability. Even if wool is added, it only changes the local air permeability. Sand and mud are still mud, and the overall air permeability is still very poor.

Just look at the tiny pores on the breech-loading cannon and the iron bullets to see how difficult it is to expel water vapor.

It's no wonder that such an inefficient technology was eventually phased out by the times.

Shishan thought of the upgraded techniques of later generations and said:
"Since moisture is difficult to expel, why not just use finer sand with better air permeability for mold making?"

Ma Hua immediately shook his head and said:

"Fine sand has no binding properties and cannot be shaped, so how can it be—"

He froze halfway through his sentence.

Sand and mud, muddy sand?
If there is more mud than sand, it is called muddy sand; if there is more sand than mud, it is called sandy mud.

The technique passed down from our ancestors is to mix sand and wool into the mud to enhance its breathability. Why can't we do the opposite and mix a little mud into the sand to enhance its stickiness, so that it can both be breathable and shaped?

Ma Hua was only excited for a moment before rejecting his own idea.

It still doesn't work!

As the saying goes, a pile of loose sand is still a pile of loose sand even if you add a little mud.

However, to save face for Marshal Shi, he spoke rather tactfully, saying:

"Adding a little mud to sand should allow you to make a mold. But a sand mold can only barely take shape; if you add too little mud, it will easily fall apart. If you add too much mud, it will become a mud mold."

Seeing that Ma Hua was imagining sand mold making using clay mold techniques, Shi Shan knew he had fallen into a misconception. He smiled and gestured:
"Why use mud? Just mix a small amount of clay into fine sand, and then make two wooden boxes of the same size. First, lay the bottom with fine sand, then place the wooden mold on top, pour in more sand, and then put the two boxes together and press them down firmly. Wouldn't that fix the mold in place?"

Ma Hua: !
Many groundbreaking technological breakthroughs are just a matter of a thin layer of paper!

Ma Hua, a master forger, possesses unparalleled skills, but due to being bound by conventions, he finds himself in a dead end.

At that moment, Shi Shan's words enlightened him, and he instantly understood the sand casting process.

At the same time, the many advantages of sand casting were also ingrained in my mind.

This method not only effectively solves the problem of air permeability of the mold, but also directly uses clay instead of mud, greatly shortening the time required for drying the mold. More importantly, the mold can be reused for casting small parts such as cannon ears and cannon hoops.

Brilliant! Absolutely brilliant!!!

Ma Hua was so excited that he couldn't sit still. His mind was filled with sand molds, and he wished he could immediately start a furnace to melt copper and verify the method!
Seeing the gleam in Ma Hua's eyes, Shi Shan knew the time was right and continued:
"Furthermore, could the core be made directly from iron, or fired from kaolin clay? This would allow for repeated use and ensure a tight seal between the inner diameters of all the gun barrels!"

Ma Hua: !!!
"Master Ma, is this method feasible?"

"It's feasible! It's definitely feasible!"

Ma Hua's voice trembled with excitement.

……

There are iron mines near Chuzhou with good quality and less difficulty in mining than in Huaiyuan. It is said that during the Northern Song Dynasty, an official ironworks was set up here, with nearly a thousand miners and smelters. The iron produced could not only meet the needs of the military and civilians of Chuzhou, but also supply the surrounding prefectures.

Unfortunately, this large ironworks was destroyed in the protracted war between the Song and Jin dynasties.

After the Yuan Dynasty unified the country, fearing that the people under its rule would rebel, it restricted the use of many iron products. As a result, the production of pig iron was much lower than during the Song and Jin Dynasties. The official ironworks in Chuzhou, which had been abolished, were never rebuilt. However, there were still some iron smelting furnaces in the private sector, and the smelting infrastructure was incomparable to that of Huaiyuan County.

—This information was obtained by Shishan from the registers of the prefectural government after the Red Flag Battalion captured Chuzhou.

Time waits for no one. The iron ore mine in Huaiyuan, as a "strategic backup" and supplement to production capacity, should continue to be developed.

Chuzhou was to serve as the main smelting base, recruiting craftsmen, sending miners, building blast furnaces, and simultaneously casting cannons and smelting iron.

Two days ago, Shishan sent Fu Youde and Hu Dahai, each with two thousand troops, to attack Quanjiao County and Lai'an County respectively, to clear the outskirts of Chuzhou. He also sent Guo Xing with Dingyuan cavalry and Guo Zixing's troops to Liuhe County.

Two days later, Guo Xingfei reported on horseback: Liuhe County was heavily fortified, and the garrison, fearing an attack from the Red Flag Battalion, had already demolished the messy buildings outside the city.

Liuhe is a county under the jurisdiction of Zhenzhou, which is located next to the Yangtze River. If Shishan continues to advance eastward and takes Zhenzhou, he will face a joint attack from the three major river defense towns of Yangzhou Road, Jiqing Road and Zhenjiang Road.

The Red Flag Battalion currently lacks a navy and is therefore unable to establish a foothold in Zhenzhou.

Shishan's original plan was to take advantage of the chaos caused by Chelibuhua's retreat to launch a surprise attack and seize Liuhe, thus creating a barrier for Chuzhou and restricting the westward advance of the Zhenzhou garrison.

Since the garrison at Liuhe has been mobilized and a surprise attack is hopeless, we should temporarily abandon the idea of ​​advancing eastward.

However, when Zhou Wendao left Dangtu, he personally witnessed the Jiangzhe Province Pingzhang Jiaohua leading a large army back to Jiangnan.

During this period, the Yuan army's forces in Luzhou Road were weak. If Shishan did not take advantage of this great opportunity to extend his reach into Luzhou Road, it would be a great waste of such a heaven-sent opportunity.

(End of this chapter)