• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2468-2479
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• 1996

An upper bound solution is obtained to perform the process analysis of hot strip rolling process. The material flows within the roll bite at various geometries and frictional conditions are obtained from finite element analysis and the typical flow pattern which is necessary to determine the kinematically admissible velocity field is assumed. From the kinematically admissible velocity field, the upper bound energy is calculated and the rolling load, angle of neutral point and forward slip ratio at various operational conditions are obtained from upper bound energy. The process analysis of above mentioned parameters at various operational conditions have provided valuable information which is hard to obtain during rolling operation and the predicted ranges of quantitive values from these analyses lie whthin the bound of actual operational data.

• Journal of the Korean Society of Safety
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• v.32 no.1
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• pp.15-20
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• 2017

A large amount of research has been performed on the rolling contact fatigue(RCF) life of bearings, since it directly affects the safety and reliability of mechanical systems. It is well known that rolling contact fatigue life is influenced by several parameters including contact pressure, oil contamination by water or metal particles, and the surface conditions of bearings. However, the detailed damage mechanisms involved in rolling contact fatigue have not been clearly identified yet. In this paper the effects of water contamination of the lubricant and surface roughness of bearing steel on the rolling contact fatigue life were investigated. Two types of specimens with different surface roughness values were prepared through turning and lapping operations. They were tested under two different lubrication conditions, i.e. oil lubricant with 100% of oil and the water contaminated condition with 80% of oil and 20% of water using the rolling contact fatigue testing machine. The surface damage induced by the rolling contact fatigue was observed by using atomic force microscope(AFM). Experimental results show that the rolling contact fatigue life, $L_{10}$ was reduced by 24 to 33% depending on the lubrication condition. The reduction of fatigue life in the range of 53 to 57% was also observed at different surface roughness conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.319-324
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• 2004

Cross wedge rolling process is utilized to manufacture multi-stepped axis symmetrical parts. This process is generally performed under high temperature conditions in order to induce serious deformation. But cold cross wedge rolling process has been rarely studied due to the limits of deformation. Recently, the cold cross wedge rolling process has been utilized to enhance the material strength in specified parts of manufactured products. In this paper, experimental researches were carried out with various forming conditions of cold cross wedge rolling process in order to suggest the design guidance to make preform for cold cross wedge rolling. The tensile strength and the surface hardness of specified region were compared to that of initial material with the variation of the area reduction and the rotational speed of rolling die. With respect to the area reduction, the maximum tensile strength was linearly increased and the surface hardness was rapidly increased within lower percent of area reduction. The surface hardness was saturated over the rotational die speed of 0.8 RPM.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.242-251
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• 1999

The temperature distribution over the work roll length was estimated by solving a 2-dimensional heat transfer equation based on the rolling conditions and the thermal boundary conditions. In order to solve the governing equation, a finite volume method was employed. In the rolling conditions, the strip temperature, the contact time between roll and strip, the roll speed, the strip thickness, the rolling force and the rolling and idling time were used as input data. In order to verify the accuracy of temperature estimation, roll surface temperatures were measured in the roll shop. The measured temperatures showed a good correlation with the calculated ones.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.200-207
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• 1999

To increase dimensional accuracy of strip width, model to compensate width spread during roughing mill has been developed. To measure the amount of width spread during the production rolling more precisely, special roughing rolling procedures for the horizontal rolling and dog-bone rolling were designed in the actual production mill. From the operational data analysis, it is known that the prime factors influencing on the width spread were strip width, strip thickness, edging amount, number of pass and type of edger roll etc., Based upon the statistical analysis of rolling data, new models which can predict width spread during horizontal rolling and dog-bone rolling were developed and tested on the actual processing conditions for the reliability. The application test showed that newly developed model gave fairly accurate predictions on the width spread during roughing passes.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.105-113
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• 2001

The effect of silver particle introduction on the rolling friction of AISI 52100 steel pairs has been investigated. Experiments were performed in dry conditions using a thrust bearing-type rolling test rig at a load range of 12 - 960 N and a sliding velocity range of 8 - 785 mm/sec with pure(99.99%) silver particles. Results showed that the introduced silver particles formed transfer layer, which protected virgin bearing surfaces and resulted in low rolling friction. By changing the quantity of silver particles, transitions in the rolling friction wear found. Results also showed that the variations in normal load and rolling speed also affected the rolling friction behavior. Analyses using SEM and EPMA showed that tile formation of transfer layer was mainly governed by the silver particle quantity, normal load and rolling speed, and this resulted in the different behavior of rolling friction. In this study, it was found that the low and stable rolling friction was resulted from the shakedown phenomena occurred at the silver transfer layer.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.202-205
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• 2000

The effect of two step cold rolling and intermediate annealing conditions on the microstructure and texture evolution in type 430 stainless steel has been investigated tin order to improve ridging characteristic and deep drawability. The rolling and recrystallization textures were examined by orientation distributionfunction(ODF) and electron backscattered diffraction(EBSD). The observation showed that the intensity of ${\gamma}$-fiber was increased with two-step cold rolling process and so ridging characteristic and deep drawability were considerably improved. The relation between these properties an texture evolution has been discussed.

• Tribology and Lubricants
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• v.29 no.4
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• pp.218-222
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• 2013

Water-lubricated ball bearings consist of rolling elements, an inner raceway, an outer raceway, a retainer, and an operating lubricant. In the water environment, ball bearings are required to sustain high loads at high speeds under poorly lubricated conditions. For the analysis of bearing behavior, friction torque is considered as the main factor at various flow rates, rotating speeds, and roughnesses between the rolling element and raceways. When the bearing operates at high rotating speeds, the friction torque between the raceway and rolling elements increases considerably. This frictional torque is an important factor affecting bearing reliability and life cycle duration. For understanding the flow conditions in the inner part of the bearing, this study focuses on the flow around the rotating and revolving rolling elements. A simple model of fluid flow inside the ball bearing is designed using the commercial CFD program ANSYS.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.163-172
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• 2004

A fast, accurate model for calculating roll gap variables are critical to the implementation of computer based automation systems for cold rolling mills. Based on the work of Fleck and Johnson, rollgap simulator with non-circular arc model was developed using the influence function. This developed model is capable of predicting values of force, torque and slip which can be applied over the wide range of rolling conditions including cold rolling/DR/temper mill with high execution speed. Friction coefficient was obtained as a function of operation conditions through analyzing measured data. After combination of rollgap simulator with production strategy, draft schedule for No.3 RCM (Reversible Cold Rolling Mill) in Incheon works of Dongbu Steel was developed. This draft schedule will be installed in the setup computer of No.3 RCM replacing old Hitachi model.

• Tribology and Lubricants
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• v.15 no.2
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• pp.150-155
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$balls were fabricated using different raw materials, sintering aids and sintering conditions. Commercially available Si$_3$N$_4$ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls fer Ball Bearings) with a size of 9.525 mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) microstructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$phase.