• Journal of the Korean Society for Precision Engineering
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• v.18 no.7
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• pp.127-133
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• 2001

The effects of triangular and rectangular discharge current waveforms on anode erosion in wire electric discharge machining is investigated based on heat transfer analysis of half-space subject to time and space-dependent heat flux. The thermal load on the anode is simulated by a hear flux that is calculated from time-dependent discharge channel radius and energy. Evolution of the melting front during discharge, the molten volume at the experimental result for qualitative verification of the analysis. It is demonstrated that the triangular current waveform is more efficient in eroding the anode than the rectangular one.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.255.2-255.2
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• 2014

Electrode erosion is indispensable for atmospheric plasma systems, as well as for switching devices, due to the high heat flux transferred from arc plasmas to contacts, but experimental and theoretical works have not identified the characteristic phenomena because of the complex physical processes. Our investigation is concerned with argon free-burning arcs with anode erosion at atmospheric pressure by computational fluid dynamics (CFD) analysis. We are also interested in the energy flux and temperature transferring to the anode with a simplified unified model of arcs and their electrodes. In order to determine two thermodynamic quantities such as temperature and pressure and flow characteristics we have modified Navier-Stokes equations to take into account radiation transport, electrical power input and the electromagnetic driving forces with the relevant Maxwell equations. From the simplified self-consistent solution the energy flux to the anode can be derived.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.2
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• pp.56-66
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• 1995

Recently, with theraped advancement in th oceanology such an ocean-going vessel and oceanic structures, there is a need to study the cavitation erosion-corrosion control of pump impeller, the partial element of ocean machinery, for more effective operation. Especially, the cathodic protection (impressed current method & Al-sacrificial anode method) was applied to sea water, and Cu-alloy material mixed Zn & Al was used as a control method of cavitation erosion-corrosion. In this study, used the piezoelectric vibrator with 20KHz, 24.mu.m to cavity generation apparatus, and investigated the weight loss, weight loss rate, electrode potential & current density etc. under this condition. According to test result, thos describes how to indentify an influence of the cathodic protection and Al & Zn addition in material development for the control of cavitation erosion-corrosion, and those will serve as fundamental data on the cavitation erosion-corrosion control of oceanic centrifugal pump.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.972-974
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• 2005

The present work deals with the theoretical study of the effects of copper vapours resulting from the erosion of the electrodes on the properties of a SF6 arc in a Laval nozzle. Computations have been done for a DC arc of 1000A with upstream gas pressure of 3.75MPa. The arc plasma is assumed to be in local thermodynamic equilibrium(LTE). The sheath and non-equilibrium region around the electrodes are not considered in this model. However, its effects on the energy flux into the electrodes are estimated from some experimental and theoretical data. The turbulence effects are calculated using the Prandtl mixing length model. A conservation equation for the copper vapour concentration is solved together with the governing equations for mass, momentum and energy of the gas mixture. Comparisons were made between the results with and without electrodes erosion. It has been found that the presence of copper vapours cools down the arc temperature due to the combined effects of increased radiation and increased electrical conductivity. The copper vapour distribution is very sensitive to the turbulent parameter. The erosion of upstream electrode(cathode) has larger effects on the arc compared to the downstream electrode(anode) as the copper vapour eroded from the anode cannot diffuse against the high-speed axial flow.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.106-111
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• 2000

Recently it was reported that the life of Al Sacrifical anode is being used in port piers has been significantly shortened compared with the original design life (e.g. average life shortened from 20 years to 13-15 year) Those factors involving these problems mentioned above were seemed to be a quality of anode material and diverse environmental factors such as pH flow rate temperature Dissolved oxygen Chemical oxygen demand and resistivity etcm In this study flow rate and contamination degree(pH) of sea water affecting to sacrificial anode life hve been investigated in terms of electrochemical characteristics of Al alloy sacrificial anode It was known that the lifetime of Al alloy anode was shortened not only by increasing of self-corrosion quantity by varying flow rate of sea water but also by increasing corrosion current density due to the potential difference increment between Al anode and steel structure cathode by varying contamination degree of sea water. Especially when anode current density is from 1mA/cm2 to 3mA/cm2 and flow rate of sea water is under 2m/s anode current efficiency is 90% above However flow rate is over 2m/s anode current efficiency fell down sharply due to erosion corrosion as well as galvanic corrosion.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.8
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• pp.968-973
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• 2014

Aluminum anode of marine growth prevention system for ship is installed in seachest or sea water strainer. The Al anode is connected to a control panel that feeds a current to the anode. The dissolved ions produced by the anode are transferred in sea water, spreads through the sea water pipe system and creates a protective film in the pipelines. Thereby, corrosion in pipeline system significantly is reduced. In application on condition as a steel ship, the big accident can be caused by the corrosion. Accordingly, in this research, we evaluated influence of applied current and flow velocity on electrochemical characteristics of Al anode for marine growth prevention system (MGPS). Based on the results of the erosion-cavitation experiments, cavitation rate increased greatly until 120 min. of the experimental time and decreased a little at the point of 180 min. where pit grew and merging occurred but showed a tendency of steadily increasing consumption rates. Based on the results of the Tafel analysis, compared to static states, corrosion current densities show a rapidly increasing tendency when flow occurred.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.632-635
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• 2004

The purpose of this paper is to investigate the effect of arc current and contact velocity on the erosion of silver-based contact materials to be used in low voltage circuit breakers. The opening velocity during breaking, which is constant, ranges between 2m/s to 6m/s in the 415V $25kA_{rms}$. Contact erosion is evaluated by measuring the mass change of the cathode and anode. The results show that the increase in opening velocity from 2m/s to 6m/s leads to a decrease in the contact erosion. It is shown that the material transfer from one electrode to another depends on the transfer charge and the opening velocity of the contacts. The contact pairs of AgWC/AgCdO are superior to $AgWC/AgSnO_2In_2O_3$ or AgWC/AgC contact pairs in the contact erosion.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.517-520
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• 2003

The purpose of this paper is to investigate the effect of arc current and contact velocity on the erosion of silver contact to be used in low voltage circuit breakers. The arc current range from $2kA_{rms}$ to $20kA_{rms}$. A test system allows the control of the opening velocity profiles with contact velocities up to 10m/s and also enables the synchronization of the contact opening with a point on the arc current waveform. Contact erosion is evaluated by measuring the mass change of the cathode and anode. The results show that increase the opening velocity from 2m/s to 6m/s leads to an decrease in the contact erosion. The material transfer from one electrode to another is shown to depend on the transfer charge and the opening velocity of the contacts.

• Corrosion Science and Technology
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• v.6 no.6
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• pp.291-296
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• 2007

The corrosion of metals and alloys in flowing liquids can be classified into uniform corrosion and localized corrosion which may be categorized as follows. (1) Localized corrosion of the erosion-corrosion type: the protective oxide layer is assumed to be removed from the metal surface by shear stress or turbulence of the fluid flow. A macro-cell may be defined as a situation in which the bare surface is the macro-anode and the other surface covered with the oxide layer is the macro-cathode. (2) Localized corrosion of the differential flow-velocity corrosion type: at a location of lower fluid velocity, a thin and coarse oxide layer with poor protective qualities may be produced because of an insufficient supply of oxygen. A macro-cell may be defined as a situation in which this surface is the macro-anode and the other surface covered with a dense and stable oxide layer is the macro-cathode. (3) Localized corrosion of the active/passive-cell type: on a metal surface a macro-cell may be defined as a situation in which a part of it is in a passivation state and another in an active dissolution state. This situation may arise from differences in temperature as well as in the supply of the dissolved oxygen. Compared to uniform corrosion, localized corrosion tends to involve a higher wall thinning rate (corrosion rate) due to the macro-cell current as well as to the ratio of the surface area of the macro-anode to that of the macro-cathode, which may be rationalized using potential vs. current density diagrams. The three types of localized corrosion described above can be reproduced in a Jet-in-slit test by changing the flow direction of the test liquid and arranging environmental conditions in an appropriate manner.

• Journal of the Korean institute of surface engineering
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• v.44 no.3
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• pp.105-116
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• 2011

Ships and offshore structures are exposed to harsh marine environments, and maintenance and repair are becoming increasingly important to the industry and the economy. The major corrosion phenomenons of metals and alloys in marine environment are pitting corrosion, stress corrosion cracking, crevice corrosion, fatigue corrosion, cavitation-erosion and etc. due to the effect of chloride ions and is quite serious. Methods of protection against corrosion can generally be divided into two groups: anodic protection and cathodic protection. Anodic protection is limited to the passivity characteristics of a material in its environment, while cathodic protection can apply methods such as sacrificial anode cathodic protection and impressed current cathodic protection. Sacrificial anode methods using Al and Zn alloys are widely used for marine structures and vessels intended for use in seawater. Impressed current cathodic protection methods are also widely used in marine environments, but tend to generate problems related to hydrogen embrittlement caused by hydrogen gas generation. Therefore, it is important to the proper maintenance and operation of the various corrosion protection systems for ship in the harsh marine environment.