The increase in steel production has allowed Meicheng to have more options in terms of urban construction, and new buildings have become more stable than before.

Because of the large amount of steel, it was possible to mint a large number of coins. Mei Xiaohan loved to collect coins when she was a child, so she had a special preference for various styles of coins.

However, in order to mint coins of the same size and size, a mold is required. The widespread minting and use of metal currency began during the Spring and Autumn Period and the Warring States Period. After the Qin and Han dynasties, a unified currency was minted.

Linzi, the ancient capital of Qi State, unearthed a "Qi to (French) (goods)" copper fan box, rectangular, flat back, surrounded by edges, two Yangwen Qi knife coins in the inner bottom, the straight gate is in the center, the inner gate is connected with the back of the knife and the handle, and the two sides are provided with the positioning of the child and mother tenon.

The clay models it reproduces have a uniform specification and can be minted with knife coins of equal size and weight. A number of slabs are layered on top of each other, wrapped in grass and mud on the outside, and baked to form a set of stacked slabs, which can be minted into multiple coins at once using a vertical sprue in the center. It can be used to directly cast money Yin Wen copper fan, with the child and mother tenon for the model, the center of the fan is set up with a straight sprue, and the inner gate on both sides is set up to communicate with each money cavity, and the money cavity is symmetrically arranged, with two rows, four rows, six rows, and eight rows.

The Western Han Dynasty has made new developments in mold design, molding material selection and casting system arrangement. There are three types of shapes: rectangular, oval and round, among which the round model is the most. In the Eastern Han Dynasty, there was a stone fan cast at both ends, it was rectangular, divided into two fans, each fan carved four "five hundred knives" money cavity, the two ends were not connected, each opened a gate, after the fan was cast one end first, and then the other end was cast in turn. This coin is long, it is easy to hold the breath when casting, and the air hole is opened in the handle of the knife coin to ensure the quality of the coin.

The Tang Dynasty began to mold models with money.

According to the record of "Tang Hui Yao": Wax models have been used when casting Kaiyuan Tongbao. In the Ming Dynasty, the "mother money" (money mold) was carved with tin, and it was spread on a special frame, and more than ten frames of money were repeatedly made, and they were tied together with ropes for casting. This craft was handed down until the end of the Qing Dynasty.

Because metal coins have the advantages of easy use, wear resistance, and long circulation life. In addition to its own monetary function, it also has a high art appreciation and collection value preservation function. But how are coins formed? The entire coin manufacturing process can be summarized into three basic elements: material selection and cake processing, design and molding, and stamping.

1. The more common and relatively inexpensive metals are used to mint low-denomination coins, usually using metals such as copper, zinc, aluminum, etc.

2. The selected metal is placed in a furnace to be melted into a liquid alloy.

3. Poured into the trough, cooled and pressed into strips (thicker).

4. In the hydraulic workshop, the thicker strips are rolled several times to make them become strips whose thickness meets the requirements of the blank cake.

5. The strips are stamped into semi-finished blanks and wait for further processing.

6. The coin is embossed by the blank cake, so the quality of the blank cake directly affects the quality of the finished product, so the processing of the blank cake is very critical.

7. The blank cake stamped off the alloy strip is very rough and not smooth, and further finishing is required.

8. Design the design on both sides of the coin. 9. Design and mold, and the selected pattern will be hand-carved by the engraver.

1 0. Embossed coins, there is no problem can basically be put into the market circulation.

However, the material of each coin is different.

ZG Fourth Set of RMB Coins:

1 dime aluminum-magnesium alloy (1999)

1 Dime Stainless Steel (2005)

5 Jiao Coin Steel Core Copper Plated Alloy (2002)

1 Yuan Coin Steel Core Nickel Plated (1999)

The steel core is nickel-plated with ferromagnetic metallic elements, which are highly polished and resistant to corrosion. It is mainly used in alloys (such as nickel steel and nickel silver) and as a catalyst (such as Lane nickel, especially as a catalyst for hydrogenation), which can be used to make currency, etc., and plating on other metals to prevent rust.

The 1 yuan steel core is nickel-plated, the 5-angle steel core is copper-plated, and the 1 corner is stainless steel from 05 years, and the previous 1 corner is aluminum-zinc alloy.

The chemical properties can be viewed separately, and the metal plated on the outer layer does not change the properties of the inner alloy (steel).

Definition of steel: with iron as the main element, the carbon content is generally below 2.0% and contains other elements of the metal material, there are many differences in the alloy properties of steel and different elements, usually for different purposes and synthesis, in general, the higher the quality of the steel contains less impurities.

Steel with a chromium content of more than 13% is stainless steel, which has strong corrosion resistance and wear resistance.

Nickel plating on other metals can prevent rust, has magnetism and good plasticity; It is not oxidized in the air and dissolves in nitric acid.

Copper has very good ductility. Good thermal and electrical conductivity. Copper and some of its alloys have good corrosion resistance and are very stable in dry air. However, in the humid air, a layer of green basic copper carbonate Cu2(OH)2CO3 can be generated on its surface, which is called patina.

When choosing a minting material, factors to consider include the hardness of the metal, the corrosion resistance of the metal, and the matching price of the metal with the face value of the coin.

According to the circulation characteristics of coins, it can be seen that the coins minted should have strong corrosion resistance, large hardness, and the metal value used to make the coins should be close to the face value of the coins.

All things considered, the one-yuan coin is a nickel-plated alloy with a steel core, and the five-dollar coin is a copper-plated alloy with a steel core.

Nickel is a silvery-white metal that was first isolated in 1751 by the Swedish mineralogist A. dt. Because it has good mechanical strength and ductility, refractory high temperature resistance, and has high chemical stability, no oxidation in the air and other characteristics, it is a very important non-ferrous metal raw material, which is used to make stainless steel, high nickel alloy steel and alloy structural steel, and is widely used in various military manufacturing industries such as aircraft, radar, missiles, tanks, ships, spaceships, atomic reactors, etc.

In the civil industry, nickel is often made into structural steel, acid-resistant steel, heat-resistant steel, etc., which is widely used in various machinery manufacturing industries. Nickel can also be used as ceramic pigments and anti-corrosion coatings, nickel-cobalt alloy is a permanent magnet material, widely used in electronic remote control, atomic energy industry and ultrasonic process and other fields, in the chemical industry, nickel is often used as a hydrogenation catalyst.

The old experts are particularly familiar with the distribution of various minerals, but there are great difficulties in mining. Without large-scale modern equipment, it is difficult to mine minerals.

Therefore, most of the first coins, especially those that could be widely circulated, were made of steel or stainless steel, and the biggest advantage of using these materials was that they were easy to circulate and difficult to counterfeit. After all, the ancients did not have as much expertise as the modern people, and it was very difficult for them to counterfeit currency made with modern technology.