Application background

Coal mining is an important energy industry in our country, but the coal mining industry faces many difficulties and challenges. One of the important problems is the damage and short service life of coal machine parts. During the coal mining process, coal machine parts are often exposed to harsh environments such as high temperature, high pressure, moisture, and corrosion, which places higher requirements on technical indicators such as surface hardness, wear resistance, corrosion resistance, and fatigue life.

Relevant environmental protection policies of national and local governments

In recent years, our country has successively issued the “14th Five-Year Plan for Ecological and Environmental Protection”, “Opinions on Comprehensively Strengthening Ecological Environmental Protection and Resolutely Fighting the Fight against Pollution”, and “Effectiveness Assessment Measures for Provincial (Autonomous Regions, Municipalities) Pollution Prevention and Control” and other important policy documents, encourage the development of new business forms and model innovation and comprehensively promote clean production transformation or clean transformation in industries such as energy, metallurgy, building materials, non-ferrous metals, chemicals, electroplating, papermaking, printing and dyeing, agricultural and sideline food processing.

The following are relevant environmental protection policies issued by several major coal provinces in my country:

Henan Province – In 2019, the “Regulations on Environmental Protection Management of Construction Projects in Henan Province” was revised, and in 2023, the “Henan Province’s Several Measures for Implementing the “Opinions on Promoting Functional Departments to Do a Good Job in Ecological Environmental Protection” were issued.

Inner Mongolia – 2018, the “Three-Year Plan for Soil Pollution Prevention and Control in the Inner Mongolia Autonomous Region” was issued in 2018, and in 2023, the “Implementation Opinions of the General Office of the People’s Government of the Inner Mongolia Autonomous Region on Further Improving Social Capital’s Participation in Ecological Protection and Restoration Work” was proposed.

Shanxi Province – In 2023, the “Notice of the General Office of the People’s Government of Shanxi Province on Issuing the Interim Measures for the Management of Construction Projects in the Coal Washing Industry in Shanxi Province” and in 2023 the “Implementation Opinions on Comprehensively Strengthening Ecological Environmental Protection and Resolutely Fighting the Fight against Pollution” will be implemented in 2023 》.

Shaanxi Province – The “13th Five-Year Plan for Environmental Protection of Shaanxi Province” was issued in 2017, and the “Shaanxi Province Carbon Emission Data Quality Management Measures (Trial)” was issued in 2023.

At present, the domestic solution for replacing electroplating technology is mainly laser reprocessing technology, which has gradually become a new industry development direction. The core of this technology is to use laser cladding technology to replace hard chromium plating, use laser quenching to replace high-frequency quenching and medium-frequency quenching, and use laser technology for nitriding surface treatment, which not only effectively controls the pollution problem of electroplating, but also greatly saves production costs. , the entire repair process is not affected by the operating environment.

Advantages of laser cladding technology compared to traditional processes

1. Improve service life
Laser cladding technology uses a laser to coat high-performance metal materials on the surface of the part base. Due to the extremely high energy of the laser beam, the cladding material and the base material are melted at the same time. After rapid cooling, a perfect metallurgical bonding coating is formed, thereby significantly improving the surface of the part. Wear resistance, corrosion resistance, high-temperature resistance, oxidation resistance and other properties.

2. Save production costs
Ultra-high-speed cladding technology uses a cladding speed that is two orders of magnitude faster than traditional laser cladding technology (up to several meters per second) to provide high-efficiency coating cladding on the surface of the substrate. High-efficiency coatings of more than 0.5 square meters/hour can reduce the cost of laser cladding to the same cost as hard chrome plating.

3. Excellent molding effect
The electroplating coating is a physical combination, and the thickness of the coating is generally 20-60μm. The ultra-high-speed cladding coating thickness reaches at least 120 μm and can reach up to 1000 μm. The combination of the laser coating and the substrate is a metallurgical bond, and there will be no coating peeling or delamination. The coating hardness, toughness, corrosion resistance, and other properties are better than the traditional chrome plating process.

4. Green manufacturing process
Compared with the traditional chrome plating process, laser cladding is a green manufacturing process. The production process is simpler and the energy consumption is lower. No waste water, exhaust gas and other pollutants are produced during the production process, which greatly saves the cost of waste disposal.

Hydraulic support column repair case

Hydraulic columns have been corroded by acid and alkaline media for a long time and operate in harsh, heavy-load, vibration, impact, and other environments. Their surfaces are easily prone to failure due to severe wear, corrosion, and other factors. Laser cladding of failed columns can restore their size and function, which can effectively extend their service life.

skills requirement

1. The cladding layer and the base material are metallurgically bonded, and the cladding layer has no defects such as cracks, pores, or lack of fusion;
2. The thickness of the cladding layer reaches 0.6MM;
3. The cladding efficiency is not less than 0.4 square meters/hour;
4. The corrosion resistance and wear resistance of the cladding material meet the requirements for column use in the coal mining industry.

Technical plan for laser repair of column outer surface

a) Technical requirements for laser cladding of outer circumference of columns:

1. There are no visible cracks, slag inclusions, pores and other defects;
2. The pore diameter on the surface of the cladding layer is not greater than 0.2mm, and the pores are ≤ 5 points/dm²;
3. Dimensional inspection: Surface hardness HRC: 50~55, surface roughness ≤ 0.4μm, straightness ≤ 2‰, cylindricity ≤ 0.02mm;
4. Non-destructive testing:

100% MT testing, implementing standard ISO17638-2003

100% UT testing, implementing standard ISO11666-2010

The technical solution for laser repair of column outer surface:

The laser cladding process is used to repair the corrosion on the outer surface of the column. Two laser claddings are used: 1. Cladding of the base layer (depending on the corrosion of the column); 2. Cladding of the corrosion-resistant and wear-resistant layer (the column is corrosion-resistant). Wear-resistant laser cladding special powder).

Internal hole cladding column

b) Technical requirements for inner hole repair:

1. The cladding layer has no defects such as pores, slag inclusions, cracks, and lack of flesh;
2. Dimensions must meet the requirements of the original design tolerance level ΦDH9, as required by the drawings;
3. The inner hole chamfer has a smooth transition and the chamfer is 6×20°;
4. Coaxiality with the inner hole ≤ 0.05mm;
5. Inner hole surface roughness ≤ Ra0.4;
6. Detect the hardness of the inner hole cladding layer HB180 ~220.

Metallographic test

After cladding, use wire cutting to cut along the direction perpendicular to the laser scanning, cut into metallographic specimens, grind and polish, corrode with picric acid, then rinse with alcohol and blow dry. Use a metallographic microscope to observe the metallographic structure.