Abstract This paper introduces the laser cladding repairing technology of the valves of Tangshan Power Plant so that the valve sealing surface can achieve the purpose of abrasion resistance, corrosion resistance, high temperature resistance and impact resistance. At the same time, the characteristics and application effects of laser cladding are described.
Key words laser cladding; valve; wear resistance; corrosion resistance; high temperature; impact resistance Preface There are a large number of valve wear in the industrial field waiting to be repaired, such as high temperature and high pressure power station valves, nuclear industrial valves, long-distance pipeline valves, Chemical valves, etc., its working conditions are very poor, and some working pressure up to 42.0Mpa, and some working temperatures up to 540 ℃ above, and some require the opening of 100,000 sealing surface is not damaged, and some valves require 30-year sealing surface does not leak , So harsh requirements, not ordinary materials and general process can be solved. Therefore, some industrial countries in the valve sealing surface of the surfacing materials, welding technology, welding equipment, a large number of experimental studies, part of the valve sealing surface space constraints traditional repair there is a great difficulty, semiconductor laser cladding can overcome the space Limit, to complete the valve sealing surface repair. And the laser cladding compared with the traditional welding: ①eliminate the traditional welding caused by stress concentration is easy to crack; ② to avoid welding holes generated by slag inclusions and other secondary defects; ③ cladding repair deformation of small pieces . ④ The use of special alloy materials and sealing surface to achieve complete metallurgical combination greatly enhance the valve life.
1 laser cladding repair valve process 1.1 valve repair state Tang Steel Power Plant gas control valve due to the frequent use of the valve sealing surface and valve seat wear and tear with lax, resulting in gate valve leakage in the closure, there is a great security risk. So the power plant decided to close the valve upstream to replace the valve. Also check the other line control valve if the doors there is a similar situation, a similar situation was found replaced together. After inspection found that a large number of control valves need to be replaced, taking into account the large quantities of new products to buy a one-time cost more investment, the final decision to re-use after repair.
1.2 Dismantling, testing First of all to be repaired valve dismantling test, the test found that the valve sealing surface wear 0.4 ~ 0.6mm, seat wear 0.8 ~ 1.1mm. The reason for the failure is the valve sealing surface and the seat wear, resulting in the closure of the valve seat and valve sealing surface with lax.
1.3 laser cladding recovery size shown in Figure 1 The valve flange bore diameter ∮ 100, and the valve sealing surface depth of 200mm. Due to space constraints can not be repaired by hand, if the use of laser cladding repair coaxial delivery powder or bypass powder can not be successfully repaired. Finally, the study decided to use internal pre-powder laser cladding.
As the valve is made of cast iron, the surface of the repaired place is polished and derusting before the repairing work. At the same time, we conducted an in-depth study on the powder and the machining process. Using a Dilas 3KW semiconductor laser as the light source, the spot size is 3 × 3mm and the ABB six-axis robot is in charge of running the program. Using Co2F model powder, particle size of 200-300 mesh, ductile iron as a substrate. In order to ensure sufficient allowance, it is decided that the lapping ratio of the cladding layer is 1/2, the scanning speed is 20mm / s and the output power is 2200W. In addition, due to the control valve body is small, the temperature gradient in the cladding process will have a greater change, in order to avoid the breeding of cracks, the control valve preheating, insulation and slow cooling. Finally, there is no obvious cracks on the surface of the cladding layer and the formation of holes, the overall uniform and smooth, bright color. The thickness of the cladding was measured to be 1.1 mm. As shown in Figure 3.
At the same time, the valve seat adopts coaxial powder feeding method for laser cladding, the output power is 1800W, the spot size is 3 × 3mm, the cladding speed is 10mm / s and the feeding powder quantity is 40mg / m. As the sealing surface wear larger, and there is a partial scratch, as shown in Figure 2. So on the first seat sealing surface grinding rust treatment, and then use iron-based powder 316L partial filling and the base transition process. Transition layer using 1/3 of the lap rate, cladding thickness 0.5mm, Co2F surface coating type cladding layer 1/2 lap rate, cladding thickness 1.1mm. Due to the small size of the control valve seat, the temperature gradient in the cladding process will be greatly changed. In order to avoid the crack propagation, the control valve seat is preheated, insulated and slowly cooled. Finally, there is no obvious cracks on the surface of the cladding layer and the formation of holes, the overall uniform and smooth, bright color. The thickness of the cladding was measured to be 1.6 mm. As shown in Figure 4.
1.4 sealing surface processing, grinding dimensions in accordance with the drawings using the milling machine sealing surface, the processing surface roughness of 1.6μm. After penetrant inspection no cracks, pores, slag and other defects. After the surface inspection of the sealing surface grinding treatment, respectively, using 6000 #, 8000 #, 10000 #, 14000 # grinding paste from coarse to fine grinding. After grinding, respectively, with water and compressed air pressure test, the test pressure of 6MP. After several tests to confirm the seal after the site trial. Use gas alarm during the regular testing.
2 laser cladding characteristics This shows that the laser cladding technology in the control of valve sealing surface has great potential for strengthening, in this area if the formation of strengthening or repair technology standards, the valve and laser cladding technology are Is of great significance. By laser cladding method to strengthen or repair the surface of the face of different parts, according to the needs of the working conditions, the cladding process affected by the more complex factors, in addition to the main parameters of laser power, scanning speed , The lap-over rate, and the powder feeding rate, the formation of the cladding layer and the use of the powder due to the positional relationship between the focal point of the powder and the light spot, due to the two kinds of cladding methods of the pre-powder and the coaxial powder- The rate also has a certain impact, followed by the use of the powder and the substrate intermiscibility ratio, the particle size of the powder, the substrate surface processing conditions, the entire process of interaction between various factors, the relationship between the entire cladding Layer forming quality.
In addition, laser cladding technology is the use of laser irradiation to the matrix and the filler material melting, and rapid solidification to form a very low dilution and metallurgical bonding with the substrate surface coating. Laser cladding repair parts deformation is small; substrate and cladding material for metallurgical bonding, high bonding strength; cladding can reach no porosity, porosity, inclusions, cracks and other defects; according to parts conditions, the design configuration Special materials with specific properties, with great flexibility; can save a lot of precious metal materials because the key parts of the parts can be repaired by cladding. Thereby significantly improving the wear resistance of the substrate surface, corrosion resistance, heat resistance, oxidation resistance and other characteristics.
3 Application Results We have used the tracked control valve on site. The statistical analysis of the data found that the control valve after laser cladding repair life than untreated valve life increased by 4 to 5 times. The repair cost is low, only 30% of the valve price, and the repair efficiency is high, only the key parts of the local strengthening, not only save the cost of repair, but also improve the service life of the product. Through the stable use effect and long service life, the repair plan has been approved by users.
4 Conclusion At present, we are on the laser cladding repair valve technology to continuously improve and perfect. At the same time, different environments using the valve to develop the corresponding set of repair process. Compared with surfacing, spray coating and electroplating, laser cladding has the characteristics of small dilution, dense structure, higher hardness, abrasion and corrosion resistance, impact resistance. Therefore, laser cladding technology in the field of valve repair and remanufacturing prospects are very broad.
Key words laser cladding; valve; wear resistance; corrosion resistance; high temperature; impact resistance Preface There are a large number of valve wear in the industrial field waiting to be repaired, such as high temperature and high pressure power station valves, nuclear industrial valves, long-distance pipeline valves, Chemical valves, etc., its working conditions are very poor, and some working pressure up to 42.0Mpa, and some working temperatures up to 540 ℃ above, and some require the opening of 100,000 sealing surface is not damaged, and some valves require 30-year sealing surface does not leak , So harsh requirements, not ordinary materials and general process can be solved. Therefore, some industrial countries in the valve sealing surface of the surfacing materials, welding technology, welding equipment, a large number of experimental studies, part of the valve sealing surface space constraints traditional repair there is a great difficulty, semiconductor laser cladding can overcome the space Limit, to complete the valve sealing surface repair. And the laser cladding compared with the traditional welding: ①eliminate the traditional welding caused by stress concentration is easy to crack; ② to avoid welding holes generated by slag inclusions and other secondary defects; ③ cladding repair deformation of small pieces . ④ The use of special alloy materials and sealing surface to achieve complete metallurgical combination greatly enhance the valve life.
1 laser cladding repair valve process 1.1 valve repair state Tang Steel Power Plant gas control valve due to the frequent use of the valve sealing surface and valve seat wear and tear with lax, resulting in gate valve leakage in the closure, there is a great security risk. So the power plant decided to close the valve upstream to replace the valve. Also check the other line control valve if the doors there is a similar situation, a similar situation was found replaced together. After inspection found that a large number of control valves need to be replaced, taking into account the large quantities of new products to buy a one-time cost more investment, the final decision to re-use after repair.
1.2 Dismantling, testing First of all to be repaired valve dismantling test, the test found that the valve sealing surface wear 0.4 ~ 0.6mm, seat wear 0.8 ~ 1.1mm. The reason for the failure is the valve sealing surface and the seat wear, resulting in the closure of the valve seat and valve sealing surface with lax.
1.3 laser cladding recovery size shown in Figure 1 The valve flange bore diameter ∮ 100, and the valve sealing surface depth of 200mm. Due to space constraints can not be repaired by hand, if the use of laser cladding repair coaxial delivery powder or bypass powder can not be successfully repaired. Finally, the study decided to use internal pre-powder laser cladding.
As the valve is made of cast iron, the surface of the repaired place is polished and derusting before the repairing work. At the same time, we conducted an in-depth study on the powder and the machining process. Using a Dilas 3KW semiconductor laser as the light source, the spot size is 3 × 3mm and the ABB six-axis robot is in charge of running the program. Using Co2F model powder, particle size of 200-300 mesh, ductile iron as a substrate. In order to ensure sufficient allowance, it is decided that the lapping ratio of the cladding layer is 1/2, the scanning speed is 20mm / s and the output power is 2200W. In addition, due to the control valve body is small, the temperature gradient in the cladding process will have a greater change, in order to avoid the breeding of cracks, the control valve preheating, insulation and slow cooling. Finally, there is no obvious cracks on the surface of the cladding layer and the formation of holes, the overall uniform and smooth, bright color. The thickness of the cladding was measured to be 1.1 mm. As shown in Figure 3.
At the same time, the valve seat adopts coaxial powder feeding method for laser cladding, the output power is 1800W, the spot size is 3 × 3mm, the cladding speed is 10mm / s and the feeding powder quantity is 40mg / m. As the sealing surface wear larger, and there is a partial scratch, as shown in Figure 2. So on the first seat sealing surface grinding rust treatment, and then use iron-based powder 316L partial filling and the base transition process. Transition layer using 1/3 of the lap rate, cladding thickness 0.5mm, Co2F surface coating type cladding layer 1/2 lap rate, cladding thickness 1.1mm. Due to the small size of the control valve seat, the temperature gradient in the cladding process will be greatly changed. In order to avoid the crack propagation, the control valve seat is preheated, insulated and slowly cooled. Finally, there is no obvious cracks on the surface of the cladding layer and the formation of holes, the overall uniform and smooth, bright color. The thickness of the cladding was measured to be 1.6 mm. As shown in Figure 4.
1.4 sealing surface processing, grinding dimensions in accordance with the drawings using the milling machine sealing surface, the processing surface roughness of 1.6μm. After penetrant inspection no cracks, pores, slag and other defects. After the surface inspection of the sealing surface grinding treatment, respectively, using 6000 #, 8000 #, 10000 #, 14000 # grinding paste from coarse to fine grinding. After grinding, respectively, with water and compressed air pressure test, the test pressure of 6MP. After several tests to confirm the seal after the site trial. Use gas alarm during the regular testing.
2 laser cladding characteristics This shows that the laser cladding technology in the control of valve sealing surface has great potential for strengthening, in this area if the formation of strengthening or repair technology standards, the valve and laser cladding technology are Is of great significance. By laser cladding method to strengthen or repair the surface of the face of different parts, according to the needs of the working conditions, the cladding process affected by the more complex factors, in addition to the main parameters of laser power, scanning speed , The lap-over rate, and the powder feeding rate, the formation of the cladding layer and the use of the powder due to the positional relationship between the focal point of the powder and the light spot, due to the two kinds of cladding methods of the pre-powder and the coaxial powder- The rate also has a certain impact, followed by the use of the powder and the substrate intermiscibility ratio, the particle size of the powder, the substrate surface processing conditions, the entire process of interaction between various factors, the relationship between the entire cladding Layer forming quality.
In addition, laser cladding technology is the use of laser irradiation to the matrix and the filler material melting, and rapid solidification to form a very low dilution and metallurgical bonding with the substrate surface coating. Laser cladding repair parts deformation is small; substrate and cladding material for metallurgical bonding, high bonding strength; cladding can reach no porosity, porosity, inclusions, cracks and other defects; according to parts conditions, the design configuration Special materials with specific properties, with great flexibility; can save a lot of precious metal materials because the key parts of the parts can be repaired by cladding. Thereby significantly improving the wear resistance of the substrate surface, corrosion resistance, heat resistance, oxidation resistance and other characteristics.
3 Application Results We have used the tracked control valve on site. The statistical analysis of the data found that the control valve after laser cladding repair life than untreated valve life increased by 4 to 5 times. The repair cost is low, only 30% of the valve price, and the repair efficiency is high, only the key parts of the local strengthening, not only save the cost of repair, but also improve the service life of the product. Through the stable use effect and long service life, the repair plan has been approved by users.
4 Conclusion At present, we are on the laser cladding repair valve technology to continuously improve and perfect. At the same time, different environments using the valve to develop the corresponding set of repair process. Compared with surfacing, spray coating and electroplating, laser cladding has the characteristics of small dilution, dense structure, higher hardness, abrasion and corrosion resistance, impact resistance. Therefore, laser cladding technology in the field of valve repair and remanufacturing prospects are very broad.
JIANGSU LINHAI POWER MACHINERY GROUP CO., LTD. , https://www.atv-linhai.com