20 March 2017, Volume 41 Issue 3

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  • ZENG Zhao-feng
    Materials For Mechanical Engineering. 2017, 41(3): 1-6. https://doi.org/10.11973/jxgccl201703001
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    The paper briefly describes the most common preparation methods of Al2O3/Cu composite and their respective advantages and disadvantages. The factors of affecting the properties of the composite are analyzed from amounts, size and shape of Al2O3 particle and surface activity, substrate metals and follow-up treatment, and so on. At last, this paper also puts forward the research development direction of Al2O3/Cu composite.
  • SONG Wei, WEI Bo, XIAO Hong-jun, LIU Zheng, JIANG Zhuo-jun
    Materials For Mechanical Engineering. 2017, 41(3): 7-12. https://doi.org/10.11973/jxgccl201703002
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    Butt welding was carried out on 15Ni3CrMoV steel and 10Ni5CrMoV steel by TIG(tungsten inert gas) welding and manual arc welding, the microstructure, tensile property, impact property and hardness of the butt joint were studied. The results show that typical dendrite microstructure was found in the weld seam of dissimilar steels butt joint, the grains in weld seam of manual arc welding butt joint exhibit the characteristic of vertical growth, while the grains in weld seam of pulse TIG welding butt joint exhibit the characteristic of horizontal growth. Tensile fracture position of the butt joint at room temperature located in weld seam zone, and the hardness of heat-affected zone is highest. Compared with manual arc welding butt joint, the pulse TIG welding butt joint has higher tensile strength and impact toughness.
  • LU Jia-rui, ZHU Peng-cheng, SHEN Yin-zhong
    Materials For Mechanical Engineering. 2017, 41(3): 13-18. https://doi.org/10.11973/jxgccl201703003
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    Tensile test was carried out on 11Cr3W3Co steel in standard heat treatment state at different strain rates (5×10-5-2×10-4 s-1) and different temperatures(25-700℃), and the serrated flow behavior at different temperature of the steel was analyzed. The results indicate that the normal Portevin Le Chatelier (PLC) effect with sawtooth formation activation energy of 124 kJ·mol-1 occurred at intermediate temperature of 285-325℃, serrated flow behavior was mainly caused by the interaction between substitutional solute chromium atoms and moving dislocations; regarding the abnormal PLC effect appeared at temperatures of 325-365℃, one possible reason is that the diffusion ability of solute atoms was strong with the increase of tensile temperature so that solute atmosphere was unstable to be present, resulting in a weaken of dynamic strain aging (DSA), another possible reason is that precipitates become sink positions due to the increase of temperature, resulting in a disappearance of serrated flow; at high temperature, rapid reduce in strength and rapid increase in plasticity imply that dynamic recovery plays a major role during the plastic deformation.
  • ZHANG Liang, YONG Qi-long, LIANG Jian-xiong, WANG Chang-jun, YANG Zhi-yong
    Materials For Mechanical Engineering. 2017, 41(3): 19-23,28. https://doi.org/10.11973/jxgccl201703004
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    Solid-solution treatment was carried out on PH13-8Mo high strength stainless steel at 925℃, and then aging treatment was carried out at 510,540,550,565℃and 595℃ to study the type and content of precipitated phases and the effect of precipitated phase on mechanical properties of the tested steel. The results show that the precipitated phase in the tested steel mainly is M2C after aging at lower temperature, the precipitated phases are M2C, M23C6, Ni3Al and NiAl after aging at intermediate temperature, and the main precipitated phases are NiAl and M23C6 after high temperature aging.With the increase of aging temperature, the precipitated phase's content increases, and tensile strength and yield strength of the tested steel gradually decrease, while ductility and toughness continuously improve. The precipitated second particles during aging can impede dislocation movement, and thus increase strength of the tested steel.The optimum comprehensive properties can be obtained for the tested steel after quenching at 925℃ and then aging at 540℃.
  • LIAO Hui-min, HE Hong-yan, YANG Yang, ZENG Ming
    Materials For Mechanical Engineering. 2017, 41(3): 24-28. https://doi.org/10.11973/jxgccl201703005
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    Butt welding test was carried out on hot-rolled AZ31 magnesium alloy sheets with thickness of 2 mm by TIG (tungsten inert gas) welding at different welding heat inputs. Microstructure and mechanical properties of welded joints were analyzed by using microscope, micro-hardness tester, tensile testing machine and so on. The results show that the microstructure of the base metal is single-phase α-Mg solid solution, and the microstructures of heat affected zone and weld zone are all single-phase α-Mg solid solution and dispersively distributed β-Mg17Al12. With the increase of the heat input, the grain size in weld zone grows and the amount of β-Mg17Al12 increases. The micro-hardness from large to small is weld zone, base metal zone and the heat affected zone. The tensile strength of welded joints increases firstly, and then decreases with the increase of the heat input. The welded joints owned the best tensile strength of 223 MPa at welding current of 90 A, the value was about 89.2% of the base metal, meanwhile, the elongation was 10.0%.It is founded that the fracture mainly occurres in HAZ and the fracture mode is quasi-cleavage fracture.
  • FENG Bo, LI Yu-jia, MEI Lin-bo, XUAN Fu-zhen
    Materials For Mechanical Engineering. 2017, 41(3): 29-32,38. https://doi.org/10.11973/jxgccl201703006
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    In the saturated steam with oxygen content less than 1 mg·L-1 at 100℃, axial constant-amplitude force controlled fatigue tests were conducted on the precipitation hardening stainless steel Custom 450 with three stress ratios (-1, -0.6, 0.1). The fatigue fracture morphology was observed, and the ultra-high cycle fatigue fracture mechanism was investigated. The results show that the S-N curves of the tested steel presented a continuous decline shape without a horizontal asymptote, indicating that the tested steel had no fatigue limit. Three crack initiation patterns, namely forming crack sources at surface defects, internal inclusions and internal defects, were observed on the fracture surfaces. With the increase of stress ratio, the probability of the surface crack initiation increased while that of the internal crack initiation decreased.
  • TAO Da-wei, DAI Meng-jia, CAO Yu-jie, WANG Wen-fang, LIU Jia-qin
    Materials For Mechanical Engineering. 2017, 41(3): 33-38. https://doi.org/10.11973/jxgccl201703007
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    Long PAN-based carbon fiber was surface-modified by pyrophosphate copper plating with self-made equipment. The influences of bath composition, current density, plating temperature and pH value of bath on quality of coating were systematically analyzed to optimize the continuous copper electroplating process parameters, and C/Cu composite fiber with better properties was prepared. The results indicate that the problem of black core and agglomeration were well solved by electroplating in a bath with content (mole fraction) ratio 7.0 of P2O74- to Cu2+ and 25 g·L-1 ammonium citrate as the additive under the conditions of current density of 2.0-2.5 A·dm-2, bath temperature of 40℃, and bath's pH of 8.2-8.8. The obtained coating is complete, uniform and compact, it also owns high bonding strength, and the C/Cu composite fiber obtains significantly enhanced conductivity.
  • XU Jin-peng, ZHANG Xiu-qing, XU Jin-fu, PU Hai-zhou, GU Liang-nan, XUE Ling-hua
    Materials For Mechanical Engineering. 2017, 41(3): 39-42,48. https://doi.org/10.11973/jxgccl201703008
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    AlN/Zr-Cu composites were prepared with raw materials of Cu powder, Zr powder and AlN powder by the spark plasma sintering method. The effects of AlN mass fraction (1%-20%) on the micromorphology, mechanical properties, friction and wear property of the composite were studied, and the wear mechanism was analyzed. The results show that fine AlN particles dispersively distributed in the copper alloy matrix. With the AlN mass fractions of 1% to 15%, the composites were relatively dense while the microstructure was loose with the AlN mass fraction of 20%. With the increase of AlN content, the micro-hardness and compressive strength of the composites presented a trend of first increasing then decreasing, while the friction coefficient and abrasion loss first decreased then increased. The wear mechanism changed in the order of adhesive wear, abrasive wear and spalling wear.
  • WEN Ning-hua, LUO She-ji, WANG Rong
    Materials For Mechanical Engineering. 2017, 41(3): 43-48. https://doi.org/10.11973/jxgccl201703009
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    In order to understand the effect of alloying elements of Cr and Al on electrochemical corrosion behavior of J55 steel, the steel's electrochemical corrosion behavior in 3.5wt% NaCl solution was investigated by electrochemical measuring and immersion testing. The results show that, after adding 1.49wt% Cr, 1.47wt% Al and 1.98wt% Cr, 1.95wt% Al into J55 steel, open corrosion potention (Eocp) or self-corrosion potential of the alloyed J55 steel moved to the positive direction, this indicating the reduction of corrosion activity. The alloyed steels exhibited higher corrosion resistance, lower corrosion current density and lower corrosion rate. After the alloyed steels were immersed in NaCl solution for 200 d, protective corrosion product with Cr- and Al-rich was found on the surface of the steels, the corrosion resistance of the steel was increased by the corrosion product.
  • LIU Jun, YANG Li-ming, XIE Shu-gang, WU Hao, ZHANG Sai, HUANG Ya-feng, CHENG Guo-yang, MENG Xian-ming
    Materials For Mechanical Engineering. 2017, 41(3): 49-53. https://doi.org/10.11973/jxgccl201703010
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    The dynamic tensile properties of 6061 aluminum alloy was studied by the uniaxial tensile experiment at strain rates of 0.08,35,110,210,550 s-1. The trure stress-ture strain curves were obtained at different strain rates. A plastic deformation constitutive model of the aluminum alloy was established based on the Johnson-Cook model, and the model was verified. The results show that, with the increase of strain rate, yield strength of 6061 aluminum alloy increased and elongation after fracuture decreased, but its fracture strength had not obvious changes. The constitutive model can describe well the change of flow stress of 6061 aluminum alloy during plastic deformation.
  • LIU Xiang-ru, ZHOU Xu-dong, LI Jun, WANG Jian
    Materials For Mechanical Engineering. 2017, 41(3): 54-57. https://doi.org/10.11973/jxgccl201703011
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    With the help of Gleeble-1500D thermomechanical simulator, the effects of heat treatment temperature and cooling rate on bake-hardening properties of DP980 steel were studied. The steel was treated at different temperature (750℃, 850℃ and 950℃) for 2 min, and followed by cooling with cooling rates of 10, 20, 50℃·s-1; after that, pre-strains were carried out at deformation amounts of 0.2% and 2%, at last the bake-hardening aging process was completed at 170℃ for 20 min. The results show that, DP980 steel has higher bake-hardening property because there are a lot of precipitates with size of 10-20 nm in ferrite after bake-hardening treatment; when heat treatment temperature was 750℃ and 850℃, the bake-hardening value firstly decreased and then increased as the cooling rate increased. But When the heat treatment temperature was 950℃, the bake-hardening value exhibited the contrary trend. At the same cooling rate, the bake-hardening value is greatly affected by the heat treatment temperature, and the influence on the bake-hardening value would be greater when the cooling rate more faster. When the heat treatment temperature was 850℃ and the cooling rate was 50℃·s-1, the highest bake-hardening could be obtained, and the microstructure of the steel was fine martensite laths and ferrite.
  • JIN Shi-lei, LI Xiao-hui, SHAN Yang, MA Chao, MA Feng-ling, YU Guang-yi
    Materials For Mechanical Engineering. 2017, 41(3): 58-62. https://doi.org/10.11973/jxgccl201703012
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    Friction pairs were composed of carbon fiber reinforced polytetrafluoroethylene (PTFE) composites and 4032 aluminum alloy or anodized 4032 aluminum alloy. Coefficient of friction, scar width and wear morphology were studied by friction and wear test under the conditions of dry friction and oil lubrication. The results show that, under dry friction condition, the serious abrasive wear emerged during the wear process of composites against aluminum alloy, and the scar width is larger. The adhesive wear acted the major role during the wear process of composites against anodized aluminum alloy, and the wear process accompanied by slight abrasive wear. Under oil lubrication condition, with the increase of carbon fiber content, the scar widths of the composite against aluminum alloy or anodized aluminum alloy were decreased, the abrasive wear was not emerged during the wear process.
  • DING Kai-yong, LI Lei, JI Guo-liang, LI Qiang
    Materials For Mechanical Engineering. 2017, 41(3): 63-66,72. https://doi.org/10.11973/jxgccl201703013
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    Effects of deformation temperature, deformation amount and strain rate on dynamic recrystallization (DRX) behavior of M50NiL steel were investigated based on thermal compression simulation experiments. Results show that no DRX occurs if the deformation temperature is below 900℃. When the deformation temperature increases to 1 000℃, DRX is not enough and mixed grains microstructure is formed. When the deformation temperature increases to 1 100℃, DRX is fully completed, and the uniform fine equiaxed grains are obtained. However, if the deformation temperature reaches to 1 200℃, the grain tends to coarsen up. DRX nucleation rate increases with the increase of deformation amount under the conditions of deformation temperature of 1 100℃ and strain rate of 10 s-1; DRX is finished when the deformation amount is up to 60%. DRX nucleation increases with the increase of the strain rate when the deformation temperature and deformation amount are 1 100℃ and 60%, respectively; furthermore, when the strain rate increases to 20 s-1, DRX is fully completed, and fine and uniformly distributed equiaxed grains are obtained.
  • ZHANG Cheng-xing, LI Yan, YANG Ming-shun, YAO Zi-meng, ZHANG Jing-chong
    Materials For Mechanical Engineering. 2017, 41(3): 67-72. https://doi.org/10.11973/jxgccl201703014
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    Some parameters, such as damage strain, triaxial stress and strain ratio, were considered as a ductile damage standard of Q235 steel sheet, taking forming conical part as an example, using ABAQUS finite element software to simulate ductile damage of Q235 steel sheet during single point incremental forming, and the related experiments were carried out. The results show that on the forming region of Q235 steel sheet, the thickness of the sheet metal is uneven. The change rates of thickness at the bottom and top of the conical parts are symmetrical, the middle area of the conical part is the thinnest, where the ductile damage appears easily. The results of simulation can predict accurately the ductile damage position of Q235 steel sheet, the experimental results also prove the correctness of finite element model.
  • WENG Wen-ping, QU Tian-peng, SHENG Min-qi, JI-fang, ZHOU Wei, WANG Jing
    Materials For Mechanical Engineering. 2017, 41(3): 73-78. https://doi.org/10.11973/jxgccl201703015
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    The microstructure and micro-area chemical composition of central-line segregation in magnesium alloy cast-rolled strip were investigated by optical microscopy, scanning electron microscopy, etc. The heat transfer in solidification process and flow process were analyzed by finite difference method. Based on the above, the forming reasons and control method of central-line segregation in magnesium alloy cast-rolled strip were analyzed. The results indicate that solute elements of Al and Zn were enriched and Mn was diluted in the central-line segregation area. The area's microstructure was composed of equiaxed grains with fine size. During the casting and rolling process, magnesium alloy melt nucleated on the roll surface and formed developed columnar crystals along the heat transfer direction. Solute redistribution occurred at the solidification interface. The solute was enriched at the solidification front, particularly at the freezing point. Central-line segregation was formed during the subsequent rolling deformation process. The casting and rolling speed markedly affected the heat transfer and flow in solidification process. The central-line segregation could be controlled by adjusting casting and rolling speed to control the freezing point in a proper location because the overheated melts supplied by feed tip could caused the re-melt of the solidification front and the forced convection, and thus improved the diffusion condition of solute elements during the casting and rolling process.
  • ZHOU Xu-dong, LIU Xiang-ru, LI Jun, WANG Jian
    Materials For Mechanical Engineering. 2017, 41(3): 79-83. https://doi.org/10.11973/jxgccl201703016
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    Isothermal annealing heat treatment experiment of C-Mn cold-rolled sheet with carbon content 0.159 1wt% was carried out by using thermomechanical simulation testing machine at different temperatures and holding time, and then the steel's tensile properties was tested. A segmented tensile properties mathematical model based on the weighting method was built and verified. The results show yield strength of the tested steel decreases with the increase of isothermal temperature and holding time. The change rules of tensile strength with isothermal temperature and holding time are relatively complex; from a general view, the tensile strength decreases with the increase of isothermal temperature and the holding time. The change trend of elongation is opposite to that of the strengths. The segmented mathmatical model has good accuracy, the relative errors of yield strength, tensile strength and elongation from calculation and experiment are 3.93%, 3.21% and 19.91%, respectively.
  • YE Sheng-ping, CHEN Kang-hua, CHEN Song-yi, ZHU Chang-jun, LOU Jing
    Materials For Mechanical Engineering. 2017, 41(3): 84-88. https://doi.org/10.11973/jxgccl201703017
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    The quenching factor analysis(QFA) method based on precipitation kinetics of aluminum alloy is combined with the finite element analysis method (FEM) to calculate the quenching sensitivity factor for the spray quenching process of 7050 aluminum alloy thick plate; and then the hardness of end-quenched sample was simulated, the effects of the plate thickness and the spray pressure on quenched hardness were analyzed. At last, the simulation results are verified by end quenching experiment. The results show that the decrease of spray pressure will cause loss of hardness, and the influence of water pressure decreases with the increase of plate thickness. The quenching effect of thin plate(thickness of 50 mm) is closely related to the spray pressure, when the spray pressure reduced from 500 kPa to 10 kPa, the core hardness decreased by 1.8%. The quenching effect of thick plate with thickness more than 100 mm is limited related to the spray pressure, when the spray pressure reduced from 500 kPa to 10 kPa, the decrease of core hardness was lower than 0.5%.
  • WANG Tong-bo, LI Bo-long, YUAN Jie
    Materials For Mechanical Engineering. 2017, 41(3): 89-92,97. https://doi.org/10.11973/jxgccl201703018
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    Low-cost titanium alloys (Ti-xFe-3Al) with super high strength were prepared by using low-cost alloying elements, iron and carbon, instead of higher cost vanadium element. The alloy's thermal deformation behavior was studied by using Gleeble-3500 thermal simulation tester, and forging processes of the alloys were determined. The results show that the stress-plat in stress-strain curve was more stable when deformation temperature of the alloys was 850℃ and strain rate was 10 s-1, and the flow stress was under 400 MPa. It was suitable for the forging process. Based on that, the better forging temperature of the alloys was (850±20)℃. Shearing band did not find in the as-forged alloys, and the alloy's tensile strength was over 1 200 MPa.
  • YANG Qin-zheng, LI Xiao-yan, ZHANG Liang
    Materials For Mechanical Engineering. 2017, 41(3): 93-97. https://doi.org/10.11973/jxgccl201703019
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    The welding residual stress in welded joint of thick-walled 316LN stainless steel pipes was studied by finite element modeling, and the influence of lumped pass on simulation results was analyzed. At last, simulated results were verified by X-ray diffraction stress measurement. The results show that the simulated results were corresponded with measured results if initial stress of pipes was considered. The axial residual tensile stress is found near the cosmic weld beads and located at the region that below the last weld bead. The value of tensile residual stress is higher and its distribution region is larger. The lumped pass method had a great influence on the distribution and value of residual compressive stress rather than the residual tensile stress that distributed across the cosmic welds. Reasonable lumped pass model is suitable for welding residual stress simulation of large-scale welding structure for its efficiency and reliable accuracy.
  • CHENG Xiao-nong, ZHU Jing-jing, LUO Rui, ZHENG Qi, HAN Bing-lin
    Materials For Mechanical Engineering. 2017, 41(3): 98-102. https://doi.org/10.11973/jxgccl201703020
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    Hot deformation behavior of new-typed CHDG-A06 austenitic stainless steel in temperature range of 950-1 100℃ and strain rate range of 0.01-1 s-1 was studied by single-pass compression test on a Gleeble-3500 thermal-mechanical simulator, and the steel's microstructure was observed. Based on stress and strain curves of the steel, high-temperature thermal deformation constitutive model was constructed through linear regression method. The results reveal that flow stress was sensitive to deformation temperature and strain rate during thermal deformation. The flow stress decreased with the increase of deformation temperature or the decrease of strain rate. The dynamic recrystallization was likely to occur at comparably lower strain rates(≤ 0.1 s-1) or higher deformation temperatures(≥ 1 050℃). The peak stress was used to attain the hyperbolic sine constitutive equation, and hot deformation activation energy of the steel was calculated to be 453.674 4 kJ·mol-1.
  • XU Jun-yan, BU Jian-rong, ZHU Nan
    Materials For Mechanical Engineering. 2017, 41(3): 103-106. https://doi.org/10.11973/jxgccl201703021
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    In order to solve the not enough filling problem of the gear blank with ribbed plate under the original closed hot precision forging process scheme, the metal flow was simulated with the help of Deform-3D software, and the reason of not enough filling were found in the original process. On this basis, the process was improved and verified by experiment. Results show that the deformation of original process is too large, the hitting energy consumption is too fast and the hitting power is insufficient in final forming stage, these lead to the dissatisfaction of the mold filling. A modified closed hot precision forging process with pre-forging operation is proposed. The numerical simulation results of the modified process show that the filling of the forge piece is full and no defects are found. Experimental results are in accordance with the simulated ones.
  • MA Xiao-ming, ZHOU Yang
    Materials For Mechanical Engineering. 2017, 41(3): 107-111. https://doi.org/10.11973/jxgccl201703022
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    A fracture accident of screw shaft of a twin-screw extruder occurred during operation. In order to find the fracture reasons, the failure analysis was carried out by means of macroscopic fracture observation, scanning electron microscope observation, chemical composition analysis,microstructure observation,mechanical property testing and finite element simulation. The results show that torsional fatigue was the cause of the fracture, and the cracks originated from the tooth root, with several fatigue crack sources. Stress concentration at root of the tooth; poor thermal treatment process leads to microporous aggregation and uneven microstructure, these factors were the reasons together caused the screw shaft fracture in the early service life.
  • WANG Ruo-ming, ZHAN Ma-ji, JI Kun, YAN Bo, WANG Fu-cheng, DU Xiao-dong
    Materials For Mechanical Engineering. 2017, 41(3): 112-116. https://doi.org/10.11973/jxgccl201703023
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    The corrosion failure reason of a tension clamp was investigated by the analysis of the macro-morphology, chemical composition and corrosion products of the tension clamp for high voltage electricity transmission and the holding conductor. The results show that some aluminium strands broke during the pressure connecting process of the clamp, which made acidic rainwater easily run into the inside of the pressure connecting pipe during service. So that the joint surface between clamp and aluminium conductor steel reinforced wires corroded and produced corrosion products, resulting in the increased resistance of the tension clamp. With the corrosion continuing, the resistance of the clamp increased, followed by the increase of the temperature. When the clamp temperature increased over the critical temperature, the thermal equilibrium state was broken, finally the clamp was overheated, resulting in the high-temperature combustion failure. The on-line infrared monitoring of temperatures of the clamp pressure connecting pipe should be strengthened, and the pressure connecting pipe with abnormal temperatures should be replaced in time.