In ancient times, making cannons was technically easier than making guns.
The reason is that the artillery can be made of thick copper, and the iron pile makes it less likely to explode the chamber. The musket needs to be carried by a single soldier, so it needs to be light in weight. This determines that the barrel cannot be too thick, so the chamber explosion is a common occurrence.
So much so that when making a gun, you have to cast a whole iron rod first and then slowly drill it with a steel drill. It often takes a worker several months to drill a qualified gun barrel.
Artillery is not so troublesome.
The most primitive artillery is to directly make a gun mold embryo out of soil, then pour copper water into it, take out the metal tube after cooling, and then use copper hoops or iron hoops to hoop around the gun barrel and medicine chamber.
Of course, the artillery Shen Bing wants to make will not be so primitive...
This primitive artillery also has the problem of exploding the chamber.
Shen Bing asked the blacksmith to cast the cannon into two layers. The inner layer was made of iron and used new iron.
At present, there is no new iron in Shazhou, but this is not a big problem. Shen Bing directly transferred several Yuezhi iron smelting workshops to the Qin army, including the craftsmen in the workshops.
Then the blast furnace was knocked down and a waterwheel was built.
As for coal, it is not necessary.
In fact, using coal to make iron cannot improve the quality of iron, but can reduce costs through mass production.
At this time, Shen Bing did not use much iron to make cannons, and could completely solve the problem with carbon.
The person in charge of these iron smelting workshops was a Qin man named Ming.
In fact, I don’t know if he is from Qin or not.
Like Liqing in the past, he was captured by the Yuezhi in his parents' generation, so he grew up in the Yuezhi since childhood, and his living habits are the same as those of the Yuezhi people.
Because Ming could speak the Central Plains dialect, King Yuezhi put him in charge of the blacksmiths from the Central Plains.
Ming immediately got close to Shen Bingtao:
"I wonder who the general is from?"
"My parents are from Xianyang. They were robbed while doing business with the Yuezhi, so they ended up living here."
"My subordinates yearn for the Qin Kingdom but cannot escape. Now that the general has come, I can give my subordinates what they hoped for!"
Shen Bing was unconvinced.
Because he knew that if this Ming Zai Yuezhi could get into the position of being responsible for the Yuezhi's iron smelting, he would be deeply trusted by the Yuezhi.
If he is deeply trusted by the Yuezhi, he must have expressed his loyalty to the Yuezhi King in various forms. At this time, it is not very credible for him to say that he yearns for the Qin Dynasty...
But Shen Bing didn't care about this.
Because Shen Bing had already told Wang Ben, all the blacksmiths and their families who had been brought under the control of the Qin army had also moved in and were under the strict supervision of the Qin army and were not allowed to leave the camp.
Shen Bing doesn't dare to be careless about this, because just the new iron technology is a big deal, plus the artillery technology, how about it?
Now that Ming has been spotted, Shen Bing doesn't care whether what he said "wholeheartedly yearns for Da Qin" is true or false.
Shen Bing handed the sketch of the artillery to Ming and said:
"Is there any difficulty in casting this kind of bronze cannon?"
Ming took a look and replied confidently:
"It's not difficult, it's not difficult! I will make it for the general right away!"
It's really not difficult. In the final analysis, it's just a copper pipe.
To be precise, it is an outer copper pipe and an inner iron pipe. It just needs to leave a fire door in the medicine room for ignition.
Shen Bing asked:
"How long does it take to make it?"
Ming calculated it and replied:
"If you want to cast new iron in a new furnace, I'm afraid it will take a month to make it!"
Shen Bing nodded:
"Make twenty of them, and use new iron to make projectiles!"
Ming responded and retreated.
This iron-core copper cannon is something only found in the Qing Dynasty.
It's just that in the Qing Dynasty, the cannon was made by drilling out the barrel of the cannon from an entire iron pillar, just like making a gun.
The cannon created in this way is stronger and more accurate, but the disadvantage is that it takes a very long time.
Shen Bing didn't need such precision and longevity at this time, so he used casting methods to quickly prototype it.
The disadvantage of casting is that it is easy to explode the barrel, and the iron core copper coating can reduce the risk of the chamber explosion to a considerable extent... When the two are combined, you will get a cannon that can be quickly produced and has good performance.
The reason why the iron core copper coating can reduce the risk of explosion is related to the thermal expansion of the artillery when it is used.
If the gun body is entirely made of copper or iron, there will be a problem: the barrel will be heated unevenly, and the heat will always spread from the inside out after firing.
If the gun barrel is divided into an inner wall and an outer wall, the inner wall will always receive more heat than the outer wall.
As a result, the inner wall expands even more due to heat, forming a tension that forcefully stretches the outer wall open.
If we want to analyze it carefully, there is also the problem of different arc lengths at the same angle between the inner and outer walls:
The inner wall is close to the center of the circle. As long as it expands by a small amount due to a little heat, the outer wall needs to expand several times in length to adapt to it.
The result is that after firing a few cannonballs, many cracks that cannot be seen by the naked eye will appear on the outer wall. If there are not many cracks, it will be fine, but as the number increases and they are eventually connected...then firing more cannonballs will cause "bombing". "It exploded with a sound.
This cannot be solved by simply stacking copper and iron. Even if more copper and iron are piled to make the barrel thicker, the uneven stress on the inner and outer walls will become more serious.
The modern solution to this problem is to use "single wall self-tightening" technology.
To put it simply, the inner wall is in a more compact and dense state than the outer wall as soon as it is produced, and its thermal expansion is just in line with the expansion of the outer wall, so it is not easy to explode.
This technology sounds simple, but in modern times, few countries in the world can master it. Because Japan does not have this technology, tank barrels have to be imported from Germany.
Even so, Japan can still boast that every time it produces a tank, it calls it "Asia's No. 1"...
The reason why iron-core copper cannons are not easy to explode:
One is because the characteristics of iron itself are that it has better toughness and tension, and is not as brittle and easy to break as bronze.
More importantly, the expansion systems of iron and copper are different.
The thermal expansion coefficient of iron is 12.2, while the thermal expansion coefficient of copper is 17.5.
Therefore, with this special structure of inner iron and outer copper, although the thermal expansion of the gun barrel cannot be adapted to the "single wall self-tightening", it can reduce the risk of explosion in a series.
Shen Bing left this matter to Wang Ben for supervision.
Wang Ben was from a Legalist background. Not only was he ruthless, but he was also very strict in his work. Shen Bing could rest assured.
However, Wang Ben had some criticisms about the production of artillery:
"General, we are trying to figure out how to march into the Western Regions. What is the use of making these iron pipes?"
"Could it help me defeat the Xiongnu?"
Shen Bing replied with a smile:
"But the captain guessed that this iron pipe was used to defeat the Huns!"
Wang Ben had disbelief written all over his face:
"This iron pipe...can break the Huns?"
"General, don't say it's a joke!"
Shen Bing just smiled and didn't explain much.
There are many things that I can't explain even if I want to.
For example, if he told Wang Ben that this iron pipe could shoot a solid iron bullet hundreds of steps away... that would be beyond his imagination.