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With the rapid development of China's subway construction, shield method tunnel construction technology is widely used in the development of urban underground space. However, with the rapid development of subway tunneling construction, the shield machine has gradually exposed some problems, mainly manifested as:

Slow construction speed, rapid wear and tear of shield machine tools, high maintenance costs, low boring efficiency, etc. At present, the domestic shield construction technology level continues to improve, shield machine is also in the direction of the development of larger diameter, but the shield machine used at present are basically imported from abroad.

In order to solve the problems faced by China's subway construction, save project cost and accelerate urban development, all major cities in China have adopted the shield method of construction. However, due to the late start of China's subway construction, the technical level is relatively low, so the subway construction mainly relies on imported shield cutting tools.

Foreign shield tool manufacturers in the shield tool has a high technical content, the production of tools generally have high wear resistance, corrosion resistance, high strength, high toughness and so on, which makes the foreign shield tool in the domestic subway construction in the service life is longer.

Domestic shield tool manufacturers in the technical level of the gap between foreign countries, the domestic shield tool wear resistance is not high, can not adapt to the current rapid development of subway construction needs, such as in the subway tunnel construction process, tool wear fast, frequent replacement, seriously affecting the tunnel construction progress.

With the rapid development of China's economic construction and the accelerated urbanization process, the development of urban underground space has increased, in order to avoid the rapid wear of shield tool and affect the construction progress, there is an urgent need to remanufacture the domestic shield tool.

The basic principle of brazing coated diamonds

The process of brazing coated diamond is to use brazing agent to firmly weld the diamond particles onto the metal substrate. The choice of diamond brazing material is important, it must have good chemical stability, heat resistance and high temperature strength, and good wettability to the base material and the brazed material.

The surface of the diamond particles is covered with a layer of metal oxide with high melting point and good heat resistance as brazing material, and then the diamond particles are brazed to the substrate. In this way, on the one hand, the diamond particles can be prevented from contacting each other in the brazing material to form a strong welding layer; on the other hand, a strong bonding strength can be formed between the diamond and the substrate.

Adding a small amount of cemented carbide powder or graphite powder to the brazing material as a reinforcing agent can improve the bonding strength between the diamond and the substrate, thus enabling the diamond particles to be more firmly welded to the substrate.

The type of brazing agent and the method of use are also very important, different kinds of brazing agent, the wettability of diamond is different, add an appropriate amount of binder in the brazing material can improve the wettability between the diamond and the substrate, so as to make the diamond better combined with the substrate.

Due to the very harsh environment of shield tool use, often in the process of tool use will produce a lot of wear or breakage, resulting in the tool can not work normally. The use of brazing coating method for shield tool repair can not only save a lot of production costs, but also effectively improve the service life of shield tool. On this basis, this paper further studies and analyzes the brazing coating technology.

Brazing coating technology refers to the method of firmly brazing diamond particles onto a metal substrate. Since the wettability between brazing material and diamond is different, the brazing agent must meet certain wetting conditions.