Laser cladding is an important application of laser processing technology. During the cladding process, a thin layer of matrix material is irradiated by a high-energy density (generally 10 2 ~10 4 W/mm 2 ) laser beam to melt, mix with the same melted filler material, and generate a heat-affected zone of a certain thickness, forming a metallurgically bonded cladding layer on the surface of the substrate to achieve surface modification and additive manufacturing. The following figure shows the principle of laser cladding.
In recent years, laser remanufacturing repair technology has been tried to eliminate rotor shaft wear. The rotor is a steam turbine's core component and must withstand severe working conditions such as high temperature, high pressure, high speed, and high stress. However, due to lubricating oil quality, impurities, and other unfavorable operating factors, the rotor journal is sometimes worn, seriously affecting the steam turbine unit's safe and stable operation.
Compared with traditional electroplating, chemical crossing, thermal spraying, arc welding, and other traditional techniques, laser cladding technology has the advantages of high bonding strength, small heat-affected zone, low dilution rate, small deformation, small subsequent processing allowance, strong area selection, and high automation.
After 8 years of operation of a steam turbine in service in a power plant, the journal of the low-pressure rotor suffered multiple abrasions, which seriously affected the safe operation of the unit. As a remanufacturing method with low heat input, laser cladding has shown its adaptability to the additive repair of low-pressure rotors with high dimensional accuracy requirements and difficult welding of body materials. Due to the high energy density of laser cladding, it can complete the repair of the rotor journal with less welding heat impact.
The equipment undertaking the repair work is a movable laser cladding workstation, which can be easily transported to a designated station in a power plant or factory for laser cladding work, and is suitable for repairing various parts. The workstation mainly comprises a high-power laser, a six-axis robot, a powder feeder, a coaxial powder feeding cladding head, and auxiliary systems such as power supply and cooling that support the system's operation.
The state of the rotor journal before repair: the wear area of the rotor was measured before the repair. The journal of the bearing bush has been worn in many places, and the most serious part has worn out a groove with a depth of 1.3mm. The surface condition of the rotor can no longer meet the safe operation of the unit.
After repairing with special cladding powder, use a Leeb hardness tester to randomly test the hardness on the journal, and the hardness of the entire area to be clad is consistent with that of the rotor base. The test results show that the damaged part of the journal has been completely removed, and the dimensional tolerance and surface roughness of the journal after repair has been fully restored to the original design requirements, which can meet the matchingrequirements between the bearing bush and the journal. Penetrant testing was carried out on the shaft journal according to the factory standard of new rotor products. The penetrant testing results showed that the cladding layer had no defects such as slag inclusions, incomplete penetration, cracks, and pores, and the quality of the cladding layer met the standard requirements. The journal repair of the rotor achieved accurate partial repair and did not have adverse effects on other parts of the rotor. According to the feedback from the power plant, the low-pressure rotor was repaired and put into operation. The lubricating oil temperature, bearing bush temperature, and shaft vibration of the unit all met the requirements, and the operation was in good condition.
requirements between the bearing bush and the journal. Penetrant testing was carried out on the shaft journal according to the factory standard of new rotor products. The penetrant testing results showed that the cladding layer had no defects such as slag inclusions, incomplete penetration, cracks, and pores, and the quality of the cladding layer met the standard requirements. The journal repair of the rotor achieved accurate partial repair and did not have adverse effects on other parts of the rotor. According to the feedback from the power plant, the low-pressure rotor was repaired and put into operation. The lubricating oil temperature, bearing bush temperature, and shaft vibration of the unit all met the requirements, and the operation was in good condition.