Laser cladding methylamine pump inlet valve parts sealing surface
Abstract: The sealing surface of methylamine pump inlet and outlet valve in urea production line is strengthened by laser cladding technology. A 5kW cross-flow CO2 laser was used to scan the Co-based self-fluxing alloy powder on the sealing surface of valve bonnet parts with the base material of Cr18Ni12Mo2Ti stainless steel. The surface of the laser melting layer was smooth with a thickness of 2mm. . Laser cladding eliminates pores, cracks, inclusions and other defects, the organization of dense, fine grain size, higher hardness and toughness. Melt layer and the substrate to achieve a metallurgical bond. Keywords: laser cladding; into the drain valve; surface enhancement 1 Introduction Methylamine solution on the urea production line has a very strong corrosive, the corrosive liquid through the main equipment pipelines and control components of the internal parts are mostly used Acid-resistant stainless steel manufacturing. It is of great significance to strengthen such components or their working surfaces to improve their working performance and service life, and to enhance the reliability and safety of the system. In this paper, high-power laser, the methylamine pump into the drain valve sealing surface enhanced laser cladding test, and the detection analysis and the use of verification. 2 methylamine pump inlet and outlet valve structure and working conditions Methylamine pump inlet and outlet valves operating conditions are: working medium is ammonium carbamate, the pressure range of 1.7 ~ 20MPa (17 ~ 200kgf / cm2), the medium temperature of 188 ~ 200 ℃, valve bonnet seal surface impact 20MPa, impact frequency 50 ~ 70r / min. From the structural point of view, the valve body is more complex than the valve cover, there are dozens of through holes or blind holes on the cylindrical valve body. There are two narrow concentric annular sealing faces between the two faces of the valve body, respectively, φ132 × 2.5) mm + (φ95 × 3.5) mm and (φ83 × 4.5) mm + (φ50 × 4.5) mm. Body and bonnet materials are Cr18Ni12Mo2Ti. The use of flame, arc surfacing, plasma spray welding and other processes to strengthen such a narrow sealing surface has welding difficulties, thermal effects, easy to make the workpiece deformation and internal stress. Therefore, the sealing surface has not been any intensive treatment. Due to the impact of the sealing surface wear, pad damage and corrosion caused by valve deformation and other short life, thus stopping the number of workers with high labor intensity, raw material consumption. 3 laser cladding test Sealing surface coating using commercially available Co-based powder, the use of 2123 phenolic resin as a binder, reconcile with alcohol and pre-placed on the processing surface, the thickness of the pre-coating 2mm, the test first in the same material The test block or simulation on the last part to do. Processing machine for the HGL-90 type 5kW cross-flow CO2 laser, the output beam wavelength of 10.6μm, the light guide system consists of shutter, mirror and GaAs crystal lens. After the focused laser beam pre-coating on the toroidal surface of the specimen, a single laser scanning is performed. The process parameters are: laser power P = 2-3kW, scanning speed V = 6-10mm / s, spot size φ = 6mm. The energy distribution of the laser beam is in the form of "Gaussian distribution" with no shielding gas. The specimen is driven by CNC MNC801 rotary table. Generally smaller or simpler parts do not need to be preheated and post-processed, and the larger body parts need to be pre-heated and cladding annealed to prevent cracking and stress relief. 4 Test results and analysis 4.1 Microstructure of cladding layer Fig.1 shows the microstructure of laser cladding layer near the bonding surface. It can be divided into the melting zone, the mutual fusion zone and the matrix 3 areas. From the mutual fusion zone, as shown in Figure 1 between the laser melt layer and the substrate is a narrow band, the bandwidth of about 10 ~ 30μm. Such as controlling the energy density and scanning speed, the melting layer can not only firmly bonded with the substrate, the mutual melting zone is small, and thermal effects on the substrate is small. Figure 2 shows the morphology of the upper microstructure in the laser-treated melt layer. The dendritic microstructure of the laser melt layer is dominant. The microstructure is fine and uniform with the grain size of 10-12. From Figure 1 and 2, it can be seen that the melt layer is much more dense than the matrix, and the fine structure can improve the grain boundary binding force and corrosion resistance and increase the toughness of the cladding layer. Fig.1 The vicinity of heat affected zone of laser fusion layer × 320Fig.2 The microstructure of the upper part of laser cladding layer × 320 4.2 The thickness and quality of the melt layer In this experiment, the thickness of the laser cladding layer can reach 2mm and the surface of the melt layer is smooth and flat. The flatness of the annular sealing surface can be controlled below 0.4mm. Melting layer surface roughness Ra6.3μm, with X2005 X-ray laser welding parts melting test, found no defects, the yield can be greater than 95%. Figure 3 shows the valve cover after laser cladding. Figure 3 valve body after laser cladding valve 4.3 composition and hardness of the laser cladding laser cladding process due to the rapid role of high-energy heat source, the melting alloy melt and solidified in an instant, the thermal effect on the substrate is small, melting and matrix elements each other diffusion Small, effectively ensure that the design of the melt layer less matrix diluted and diffused to the matrix. Large degree of undercooling greatly increased the hardness of the melt layer, the sealing surface hardness also depends on the powder composition, cladding method and process parameters can be controlled and adjusted as needed. The test valve cover sealing surface hardness of 40 ~ 48HRC. 4.4 Melting layer wear-resistant corrosion resistance In the MM200-type wear tester on the cladding and the valve were sampled for wear resistance comparison test. The test conditions are: two samples of each system to take 6, 3 for a group. The laser or plasma sample is stationary. Grinding parts speed 400r / min, hardness 56HRC, load 294N (30kgf), wear time 4h. With one hundred thousandths of balance, before and after each group of test strips were weighed, averaged, measured with a one-thousandth microscopic measurement of the width of the wear scar, taking the average of each group. Results The laser cladding is more than ten times more wear resistant than the matrix. Corrosion tests conducted in different solutions also show that the corrosion resistance of the laser cladding strengthened layer is not lower than that of the matrix. 5 Conclusion The use of high-power laser cladding process can methylamine pump inlet and outlet valve parts sealing surface to be strengthened, laser-enhanced melt layer surface finishing, melt layer and the substrate to achieve a reliable metallurgical bond, the substrate is less affected by heat, the basic no Deformation. Melt layer composition dilution and diffusion rate of the smallest, can effectively maintain and play the role of alloying components. Laser cladding dense, fine grain, higher hardness and toughness. Installed operating instructions, the laser cladding enhanced methylamine pump into the drain valve sealing surface in the strong corrosion, frequent impact, high temperature and high pressure conditions, the service life of the original without laser cladding enhanced 2 ~ 3 times, improve system reliability and security. Due to the laser beam energy is high and concentrated on the non-reinforced parts and the environmental thermal effects of small, easy operation and control; also due to laser parallelism and non-contact flexible processing methods and other advantages, so for many important parts of the surface, especially the traditional process can not or Inconvenient processing of the surface, laser-enhanced process has obvious advantages. References: [1] Fu Ge Yan. Methylamine pump system reliability analysis and reliability growth [J]. Mechanical Science and Technology, 1999 (5): 805 ~ 807. [2] Yan Yu Wo. High-power laser processing and its application [M]. Tianjin: Tianjin Science and Technology Press, 1994: 112 ~ 167. [3] Shi Shihong and so on. Laser cladding valve parts research and application [J]. China Mechanical Engineering, 1999 (5): 586 ~ 588. [4] Weerasinghe VM et al. Proc. Conf, Laser in Material Processing [C]. : Los Angeles, 1983. [5] Macintyire RM. Laser in Manufacing. Proc. Conf. [C]. 1983. [6] Wang Jiajin. Laser processing technology [M]. Beijing: China Metrology Press, 1992: 274 ~ 279.
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