ON THE INFLUENCE OF THE SIZE OF FLAKE GRAPHITE INCLUSIONS AND ITS VOLUME CONTENT ON THE ACOUSTIC PARAMETERS OF CAST IRON AND THE CHARACTERISTICS OF ULTRASONIC LONGITUDINAL WAVE SIGNALS

2021 ◽  
pp. 4-15
Author(s):  
V. N. Danilov ◽  
L. V. Voronkova
Keyword(s):  
Computer Simulation ◽  
Cast Iron ◽  
Longitudinal Wave ◽  
Attenuation Coefficient ◽  
Volume Content ◽  
Phased Array ◽  
Flake Graphite ◽  
Layered Model ◽  
Linear Probe ◽  
Graphite Inclusions

Algorithms have been presented for calculating the velocity (in the approximation of a fine-layered model) and the attenuation coefficient of a longitudinal ultrasonic wave in cast iron, depending on the average size of graphite elements and its volume content, the calculation results for which are qualitatively confirmed experimentally. The calculation was performed using a fine-layered model of the structure, the graphite inclusions were described in the form of plane-parallel layers placed in an isotropic elastic medium (metal base). Computer simulation of acoustic paths for a mediumcast iron with flake graphite for standard direct converters is carried out in order to study the influence of such a medium on the characteristics of transmitted and received signals during ultrasonic testing. In the course of the research, a previously developed model was used to calculate the attenuation coefficient of longitudinal waves in cast iron with flake graphite due to their Rayleigh and phase scattering on graphite inclusions. Computer simulation of the acoustic characteristics of the signals of a direct linear probe with a phased array in cast iron with flake graphite was carried out, during which the shape of the acoustic pulses of the longitudinal wave was calculated, depending on the distance traveled by the wave and the value of the attenuation coefficient for various models of cast iron. The main modeled characteristics of the transducer include the directivity characteristic and the change in the signal amplitude along the acoustic axis. It is shown that for cast iron with flake graphite, there are cases when the directivity of the probe with a phased array transmitted into the cast iron is practically absent.

SOME FEATURES OF ULTRASONIC TESTING OF CAST IRON OBJECTS WITH FLAKE AND GLOBULAR GRAPHITE USING NORMAL LINEAR PROBES WITH PHASED ARRAYS

2020 ◽  
pp. 4-19
Author(s):  
V. N. Danilov ◽  
L. V. Voronkova
Keyword(s):  
Cast Iron ◽  
Longitudinal Wave ◽  
Attenuation Coefficient ◽  
Computer Modelling ◽  
Signal Spectrum ◽  
Flake Graphite ◽  
Longitudinal Waves ◽  
Globular Graphite ◽  
The Difference ◽  
Directivity Characteristics

Computer modelling of the acoustic characteristics of signals of direct normal probe with phased array (PFR) in the cast iron with flake and globular graphite was performed. As a result the form of acoustic pulses of a longitudinal wave, depending on the passed by wave distance and the values of attenuation coefficient for different models of cast iron was calculated. The main modeled characteristics of the probe include the directivity characteristic and the change in the amplitude of the signal along the acoustic axis. It is shown that the difference in the PFR directivity characteristics for cast iron with flake graphite of different models and steel is due to two factors – significantly lower longitudinal wave velocities in cast iron compared to steel and a decrease in its operating frequency due to attenuation. In this case, for cast iron with globular graphite, a small change in the width of the diagrams is due only to the lower speed of longitudinal waves in cast iron compared to steel. For cast iron with flake graphite model 3, the phenomenon of nonlinear attenuation due to a decrease in the frequency of the maximum of the signal spectrum during the propagation of a longitudinal wave in cast iron with a corresponding decrease in the frequency – dependent attenuation coefficient is established. Evaluation of the nonlinearity of attenuation for cast iron with globular graphite showed that it is very small. The influence of calculation of initial signal delays on the velocity of longitudinal waves in steel on the directivity characteristics in cast iron, decreasing with increasing focus distance, is established. It is shown that for cast iron with flake graphite there are cases when the direction of transmitting of PFR in cast iron is practically absent.

INVESTIGATION OF THE EFFECT OF ATTENUATION OF ELASTIC LONGITUDINAL WAVES IN CAST IRON WITH FLAKE GRAPHITE ON THE CHARACTERISTICS OF SIGNALS DURING ULTRASONIC TESTING

2019 ◽  
pp. 18-33 ◽  
Author(s):  
V. N. Danilov ◽  
L. V. Voronkova
Keyword(s):  
Cast Iron ◽  
Mean Value ◽  
Flake Graphite ◽  
Metal Base ◽  
Longitudinal Waves ◽  
The Mean ◽  
Average Size ◽  
Graphite Inclusions ◽  
Bulk Elasticity ◽  
Directivity Characteristics

The model of estimation of damping coefficient of elastic longitudinal waves in cast iron with flake graphite due to their Rayleigh and phase scattering on graphite inclusions, considering the deviation of the modulus of bulk elasticity of the phases of cast iron (metal base and graphite) from the mean value, is developed according to the theory of Mason. At the same time, the characteristics of cast iron used for calculations include the value of the longitudinal wave velocity, the mass content of graphite inclusions and their average size. In the process of studying the effect of attenuation of elastic longitudinal waves in cast iron with flake graphite on the characteristics of signals with narrow, medium width and wide spectra, a difference in the nature of the spectra changes due to frequency-dependent attenuation depending on the nominal pulse frequencies, cast iron models and the distance traveled by the ultrasonic wave is established. It is shown that the shorter the pulse, the greater the shift of the spectrum maximum in the frequency range less than the nominal. The effect of attenuation of longitudinal waves in cast iron with flake graphite on the impulse directivity characteristic of the round piezoplate depending on the cast iron model and pulse spatial length is established. The expansion of pulse directivity characteristics with increasing of the distance traveled by the wave in cast iron is shown, the greater the wider the pulse spectrum.

Analysis of the Common Causes of Papermaking Cast Iron Dryer's Defects and the Study of Test On-Line

2014 ◽  
Vol 936 ◽  
pp. 1851-1856
Author(s):  
Wen Wei Li ◽  
Qing Du ◽  
Wei Zhong Li
Keyword(s):  
Cast Iron ◽  
Longitudinal Wave ◽  
Transition Zone ◽  
Safety Assessment ◽  
Large Angle ◽  
Online Testing ◽  
Destructive Testing ◽  
Double Crystal ◽  
Testing Technology ◽  
Shrinkage Cavities

The existing researches only put forward the stress concentration portion and design improvements from the perspective of stress analysis, or conducts safety assessment on dryers with the methodology of fracture mechanics, without non-destructive testing methods. Based on over 3,400 tests on cast iron dryers in Hangzhou, an ultrasonic testing technology with longitudinal wave double crystal probe is developed in the present investigation. This study illustrates how to identify the volume defects through testing on the air holes, shrinkage cavities and inclusions in the dryer cylinder and small R transition zone with longitudinal wave double crystal probe at a small angle (5°), as well as plane defects with deep cracks through testing on the dryer cylinder and small R transition zone with longitudinal wave double crystal probe at a large angle (42°). It addresses the issues of how to measure the thickness in regular online testing for cast iron dryers, to calculate the intensity or compare with the design value, to identify low hardness value, to determine the key parts in online testing, and how to conduct safety assessment on the cast iron dryers with small cracks. This technique may resolve various problems in cast iron dryer testing.

On a possibility of replacing grey cast iron for manufacturing cast elements of electrolyzer gas collecting bell

2021 ◽  
Vol 77 (9) ◽  
pp. 1063-1070
Author(s):  
A. A. Usol’tsev ◽  
N. A. Kozyrev ◽  
S. V. Knyazev ◽  
A. I. Kutsenko ◽  
A. R. Mikhno
Keyword(s):  
Corrosion Resistance ◽  
Cast Iron ◽  
Heat Resistance ◽  
High Strength ◽  
Grey Cast Iron ◽  
Simultaneous Formation ◽  
Metal Base ◽  
Spherical Graphite ◽  
Grey Cast ◽  
Graphite Inclusions

The main process leading to the destruction of the cast elements of gas-collection bell of electrolyzer, made of grey cast iron, is the oxidation of iron by oxygen, SO2 gas and sulfur vapors to form magnetite, hematite and pyrrhotin. The simultaneous formation of iron oxides and sulfides does not prevent further corrosion, since scale is formed with a loose structure that does not have protective properties. Reducing the length of the interfacial boundaries inside the material of the cast enables to reduce the rate of corrosion destruction, which can be achieved by modifying the cast iron to change the shape of graphite inclusions, i.e. obtaining high-strength cast iron with a spherical shape of graphite inclusions. However, the obtaining spherical graphite in cast iron using magnesium modification does not exclude the access of aggressive gases to the surface of the products and the possibility of their diffusion along the grain boundaries. It was shown that alloying can be an alternative, which leads not only to the exclusion of lamellar secretions of graphite in the structure of cast iron, but also to the formation of surface oxide layers based on the alloying element preventing the corrosion. Alloying with chromium gives cast iron high abrasive resistance due to the presence of a carbide component in the structure, as well as corrosion resistance due to the alloying of the metal base, heat resistance due to increasing the electrochemical potential of the metal base and creating a strong neutral oxide film on the surface of the castings, heat resistance, etc. An experimental comparative analysis of the corrosion resistance of cast iron used for manufacturing of gas collecting bell of electrolyzers showed that chromic cast iron ЧХ3 has a higher corrosion resistance than high-strength cast iron with spherical graphite ВЧ50 and much higher than grey cast iron with lamellar graphite. However, chromic cast iron ЧХ3 has low casting properties, is very sensitive to the cooling rate and has a large heterogeneity in structure, which makes it difficult to use it for the manufacture of gas collecting bell of electrolyzers.

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