Zhang Baigui was also excited when he learned that Liu Juntao was ready to start casting cannons, after all, the matter of casting cannons had been delayed for a long time, and now he was finally ready to start the implementation.

So, Zhang Baigui hurried back to the Yushan Military Bureau, while directing his craftsmen to hurry up to build military equipment, and at the same time carefully selected twenty craftsmen from his subordinates as the main personnel for casting artillery.

Then, Zhang Baigui urgently mobilized high-quality pig iron and specially opened up a site in the Yushan Town Military Bureau, which was specially used as an artillery workshop and a warehouse for casting cannons.

A few days later, Zhang Baigui had already made preparations for casting cannons, and Liu Juntao arrived with a team of personal guards.

Since the end of the New Year, Liu Juntao has not taken a day off, and even with his wife Guo Muying, they have been busy with all aspects of things.

After rushing to the Yushan Town Military Bureau on this day, Liu Juntao came to the newly established artillery workshop under the guidance of Zhang Baigui.

"Zong Zhen, these are the craftsmen I selected, and they are all good hands in the War Bureau!"

Liu Juntao looked at the twenty craftsmen, and saw that all of them had black and red faces, and their hands were full of calluses.

At this time, Zhang Baigui said with a smile: "Zongzhen, should we start casting cannons?" ”

Liu Juntao saw that Zhang Baigui was anxious, and said with a smile: "Then Zhang Sicheng will talk about it, the doorway of this cannon." ”

Zhang Baigui saw that Liu Juntao wanted to test himself, so he smiled, but he had done enough homework before, so he said: "It is best to use copper for this cast cannon, so that the life of the cannon will be much longer than that of pig iron cast cannons; If it is a pig iron cast gun, the cost will be much lower, and the pig iron contains less sulfur, which is very suitable for casting guns. That's why I suggest we use cast iron cannons,"

Liu Juntao listened to Zhang Baigui's words, and recalled some information in his mind: in history, the pig iron produced in the Fujian and Guangdong regions of the Ming Dynasty was known for its superior quality, and the ironmaking workshops in this area were much lower than the pig iron smelted from coal in the north because they used charcoal as fuel to make iron. Sulfur is a major factor in making pig iron brittle and deteriorating in quality. The people of the Ming Dynasty could not understand this reason, but it became a consensus at that time that the artillery cast in the south was stronger than that in the north, so that by the end of the Ming Dynasty, the large-scale cannon casting in the imperial court was carried out in Guangdong.

Later, in the 47th year of Wanli, when Xu Guangqi was ordered to train troops to defend the capital, he suggested that the imperial court recruit craftsmen from Fujian and Guangdong to cast cannons in Beijing. In the third year of Chongzhen, he invited himself to go to Guangzhou to cast cannons, the reason is: "there are many craftsmen, the iron material is particularly fine, and the price can also be saved by one-third ......" and in the early years of Chongzhen, Wang Zunde, the governor of Liangguang, cast 200 cannons at one time.

Of course, these are the conditions of the late Ming Dynasty, but at this time during the Jingtai period, the casting skills and numbers of cannons in the south of the Ming Dynasty have begun to surpass the northern provinces.

However, at this time, the Daming artillery had some defects, that is, the charge was small, the firing range was short, there was no crosshair, and it was impossible to carry out accurate aiming, the outer mouth of the gun chamber was wide, and the interior was small, which could not effectively gather gunpowder gas, and the inside of the gun chamber could not be qualified to be round, and the gun chamber was not boring. The shells are as big as you want and even in any shape. The projectile clearance is too large.

In addition, the cannon has no lugs, and it is top-heavy, and if the charge is too dense, it will explode upside down and itself when the gun is fired.

Therefore, before coming to the Yushan Town War Bureau, Liu Juntao had already made up his mind to improve these shortcomings of the existing artillery of the Ming Dynasty.

After all, Liu Juntao studied science and engineering before the crossing, and he could use his theoretical knowledge to thicken the wall of the artillery, increase the diameter of the artillery, and at the same time thicken the gun body from front to back.

In this way, the artillery cast by the Yushan Town War Bureau will have many advantages in terms of range, lethality and safety.

At the same time, Liu Juntao also prepared to add a crosshair and a light door to the new artillery cast by the Yushan Town Military Bureau to increase the accuracy of the artillery; The addition of lugs to the gun body makes it easy to mount the gun on the gun carriage, as well as to adjust the firing angle and facilitate movement.

Before coming to the Yushan Town War Bureau, Liu Juntao had already drawn a sketch of the new artillery, and the artillery to be manufactured this time was a smoothbore cannon, which could be regarded as an imitation of the Hongyi cannon, but the blueprint was slightly more advanced.

Liu Juntao copied the 12-pounder cannon of the French army in the early 19th century, and improved it according to what Liu Juntao had learned, lengthening the barrel and thickening the barrel.

According to the design, the effective firing range of this gun is two miles, the maximum firing range is three miles, and the weight of the gun body is about 1,200 catties.

After Zhang Baigui finished speaking, Liu Juntao also came back from his thoughts and handed over the drawings he had drawn.

Zhang Baigui hurriedly took it with both hands and looked at it carefully, and the twenty craftsmen next to him also gathered around, and everyone whispered from time to time, and even discussed.

Liu Juntao asked with a smile: "What method are you going to use to cast the cannon?" ”

A craftsman immediately said: "Back to the main town, of course, I made a clay mold first!" ”

Zhang Baigui and the rest of the craftsmen also echoed one after another.

Liu Juntao was not very satisfied, and immediately rejected everyone's proposal.

The method of casting cannons proposed by Zhang Baigui and others was also the mainstream method in China and the West at this time.

In this regard, Liu Juntao asked: "You use clay molds to cast cannons, what will happen to the water vapor in the soil after it encounters high temperatures?" As soon as the molten iron at a high temperature is poured into it, as long as there is a trace of water in the mud mold, it will immediately evaporate in the iron cannon to form bubbles. This bubble is a big hazard of artillery, and it can easily lead to the fragility of the cannon wall and the danger of exploding! ”

Liu Juntao is very familiar with the casting technology of this era, so the questions asked are also very professional and tricky, and those craftsmen know that Liu Juntao is an insider when they hear it.

Zhang Baigui and the craftsmen were stunned when they heard this, they didn't expect that Liu Juntao, who was the chief military officer, would still understand such a professional problem, and they glanced at each other, but Zhang Baigui replied: "The head town is high!" This clay mold is indeed easy to hide water, so we have to air dry it for a month before using it. However, even so, it is inevitable that some slight moisture will make the copper cannon form a hornet's nest, and under normal circumstances, only one cannon can be used if an average of ten cannons are cast. ”

"A 1 in 10 success rate?"

Hearing this probability, Liu Juntao also frowned, obviously very dissatisfied.

So, Liu Juntao directly overturned everyone's suggestion and said: "What if you don't use clay molds, but use cast iron to make casting molds?" There is no moisture in the cast iron, and no bubbles will be formed, so the yield will be greatly improved, right? Moreover, the inner and outer walls of the cannon produced by casting iron casting molds will be relatively smooth, which can also reduce the workload of surface cleaning and internal cleaning! ”

Hearing Liu Juntao's words, Zhang Baigui and all the craftsmen were dumbfounded, when they were apprentices, they used clay molds to cast cannons, and they have been using the craftsmanship passed down by their masters to make cannons for many years, but they never thought of using cast iron to make casting molds.

However, after all, these craftsmen also have rich experience, and after Liu Juntao's little stroke, they immediately had a flash of inspiration, and they all felt that it was indeed a good way to use cast iron to make casting molds.

Without the bubbles in the casting process, wouldn't every cast gun be usable? There will never be so many defective products again!

However, at this time, Zhang Baigui also thought of a specific question, so he asked with a smile: "This idea of the general town is very good, but if cast iron is used to make a casting mold, how will this casting mold and artillery be separated at that time?" ”

Liu Juntao actually guessed that someone would ask this question, so he said: "When casting artillery with an iron mold, first brush the inner surface of the mold with a paint synthesized with fine rice husk ash and fine sand mud and water, and then paint the second layer of paint prepared by extremely fine coal powder, and then clamp the iron mold, while the gun god is still red-hot, clear burrs, and you can get the finished product." However, the specific proportion of this paint still needs to be considered by yourself. ”

The method Liu Juntao said was actually recorded in Zhao Shizhen's "Artifact Spectrum" at the end of the Ming Dynasty, and Liu Juntao had also read it in detail before crossing over, so it was naturally easy to pinch it.

Hearing Liu Juntao's words, Zhang Baigui and the twenty craftsmen fell silent again, and they silently thought about the method that Liu Juntao had just said.

In fact, China is also the first country in the world to use metal model casting tools, as early as the Warring States Period, began to use iron fan to cast pig iron farm tools and tools in batches. The double-layer coating used in iron mold casting mentioned in it is actually the evolution of traditional Chinese casting technology, and it is not even the first one created by Zhao Shizhen, which Liu Juntao still remembers vividly.