• Journal of the Korean Ceramic Society
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• v.13 no.1
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• pp.20-24
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• 1976

These are many kinds of self-hardening methods for sand mold using sodium silicate. When sodium silicate solution is mixed with calcium-orthosilicate powder hardening reaction occurs, which is based for self-hardening method at high temperature. The high temperature strength and resicual strength of mold are related to the mole ratio of sodium silicate and the contents of calcium-orthosilicate powder. The results obtained in this study were as follows: 1) The high temperature strength of mold was maximum at about $600^{\circ}C$, and at higher temperature showed lower value on the contrary. 2) The high temperature strength of mold was increased by increasing the amount of sodium silicate having lower mole ratio and high concentration. 3) The residual strength of mold was reduced by increasing the mole ratio of sodium silicate and increasing the concentration of calcium-orthosilicate.

• Architectural research
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• v.14 no.4
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• pp.153-161
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• 2012

This paper presents an integrated procedure to predict the temperature and moisture distributions in hardening concrete considering the effects of temperature and aging. The degree of hydration is employed as a fundamental parameter to evaluate hydro-thermal-mechanical properties of hardening concrete. The temperature history and temperature distribution in hardening concrete is evaluated by combining cement hydration model with three-dimensional finite element thermal analysis. On the other hand, the influences of both self-desiccation and moisture diffusion on variation of relative humidity are considered. The self-desiccation is evaluated by using a semi-empirical expression with desorption isotherm and degree of hydration. The moisture diffusivity is expressed as a function of degree of hydration and current relative humidity. The proposed procedure is verified with experimental results and can be used to evaluate the early-age crack of hardening concrete.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.78-84
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• 2007

Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.

• Journal of Korea Foundry Society
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• v.4 no.2
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• pp.102-107
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• 1984

The variations of the mold compression strength were studied by varing the contents of the silicon powder and water glass, silion purities, and molecule rates of the water glass, when domestic JA EUN DO sand is mixed with water glass (sodium silicate) and metallic silicon or ferro - silicon powder by the self - hardening N - PROCESS method. The results obtained from this experiment are as follows; 1) The compression strength of the mold used with metalic powder was higher and more stable than to be used ferro - silicon powder. 2) 6% water glass of 2.8 molecule rate and 1.5% of ferro - silicon of 75% purity for the N - PROCESS used with JA EUN DO sand was suitable mixing rate. 3) The compression strength increased with self - hardening time, and the PH values of the mixture of silicon powder and water glass did not change after 2 hours, but the compression strength increased steadily due to the reaction of remained silicon. 4) It is recommended to take 24 hours for self - hardening time at least.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.04a
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• pp.207.2-207
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• 2003

• Transactions of Materials Processing
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• v.28 no.1
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• pp.27-33
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• 2019

The effect of hardening methods and process parameters on surface hardening of a Ti-6Al-4V Alloy has been investigated in this study. To characterize the effectiveness of the respective surface hardening methods, samples of a Ti-6Al-4V alloy were self-quenched, laser-nitrided, laser-carburized, laser-carbonitrided at the same laser irradiation conditions. This experimental procedure was followed by comparing the microstructural evolutions and mechanical properties of the respective samples after the laser surface hardenings. The hardening characteristics of the respective laser surface hardenings were well defined in this study, and the hardness was significantly influenced by the reaction compounds and laser energy density.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1048-1054
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• 2011

Laser surface hardening process is the method of hardening surface by inducing rapid self quenching of laser injected area through transfer of surface heat to inside after rapid heating of laser injected area only by high density energy heat source. This surface treatment method does not involve virtually any thermal deformation by heat treatment nor accompanies any other process after surface hardening treatment. In addition, allowing local machining, this method is a surface treatment method suitable for die with complicated shape. In this study, die material cast iron was surface-treated by using high power diode laser with beam profile suitable for heat treatment. Since the shapes of die differ by press die process, specimens were heat-treated separately on plane and corner depending on the applied parts. At this time, corner heat treatment was done with optic head inclined at $10^{\circ}$. As a result, corner heat treatment easily involves concentration of heat input due to limitation of heat transfer route by the shapes compared with plane part, so the treatment accomplished hardening at faster conveying speed than plane heat treatment.

• Laser Solutions
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• v.2 no.2
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• pp.42-51
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• 1999

This study has been performed to investigate into some effects of the output power and traverse speed of laser beam on the microstructures, hardness and fatigue resistance of the ductile iron surface-hardened by $CO_2$ laser defocussed beam. Optical micrographs have shown that with increasing the output power and decreasing the traverse speed, the martensite was coarsened and some retained austenite were appeared in ductile iron. The microstructures of hardening zone were composed of bull's eye and some nodular graphite dissolved structures by the effect of self quenching. Fatigue fracture characteristics of ductile iron have appeared in the high stress and low stress ranges. The fracture initiated at nodular graphites in the surface hardened layer due to the stress concentration caused by a notch effect. The interior graphite nodules were broken away or popped out during crack propagation. Fatigue test has shown that values of fatigue strength considerably increased with increasing output power at a given traverse speed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.246-251
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• 2005

Laser surface hardening is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power $CO_2$ lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching to occur and the formation of martensitic structure. In this investigation, the microstructure features occurring in Nd:YAG laser hardening SM45C steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimism of the processing parameters for maximum hardened depth of SM45C steel specimens of 3mm thickness by using CW Nd:YAG laser. Travel speed was varied from 0.6m/min to 1.0m/min. The maximum hardness and case depth fo SM45C steel are 780Hv and 0.4mm by laser hardening.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.449-452
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• 2008

This study is to manufacture HSCC (High flowing Self-Compacting Concrete) be able to construction without vibration & hardening, and it is stable according to the change of the surface number of aggregate and to examine the factor of reduction occurred before after hardening through the indoor experiment. It is essential to use of the thickener to increase the viscosity in the combined HSCC. In this result, it make more bubbles than HSCC of pulverulent body. The result of study has shown, through the surface air bubble by not passed air bubbles within concrete after hardening, It has bad effect in not only appearance of structures but strength & duration. It is the experiment for air bubble of concrete according to the types of aggregate (fine aggregate), mixing time of concrete, exfoliation, material of model form and so that reduce the air bubble of combined HSCC. Experiments have shown, the effect of exfoliation was bigger than the effect of form for the performance of surface finishing of combined HSCC after hardening according to the exfoliation or material of model form and the opaque guris has good condition of finishing.